A cleaning device, a lithographic apparatus and a lithographic apparatus cleaning method

A CLEANING DEVICE, A LITHOGRAPHIC APPARATUS AND A LITHOGRAPHIC APPARATUS CLEANING METHOD

<p>The present invention relates to a lithographic apparatus and a method for cleaning a lithographic apparatus.</p><p>This application claims priority to U.S. Provisional Patent Application No. 60/924,244 filed on May 4, 2007 with the title "Lithographic Apparatus and Lithographic Apparatus Cleaning Method" as the title of the invention, and the content of this patent application is within this specification It is used as reference material.</p>

<p>A lithographic apparatus is an apparatus that imparts a desired pattern onto a substrate, typically on a target area of the substrate. The lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, referred to as a mask or reticle, may be used to create a circuit pattern to be formed on each layer of the integrated circuit. This pattern may be transferred onto a target area (eg, comprising a portion of a die, a single die, or multiple dies) on a substrate (eg, a silicon wafer). Transfer of the pattern is typically accomplished via imaging onto a layer of radiation-sensitive material (resist) provided on a substrate. In general, a single substrate will contain a network of adjacent target regions that are successively patterned. The known lithographic apparatus is a so-called stepper, in which each target area is irradiated by exposing the entire pattern onto the target area at once, and scanning the pattern in a given direction ("scanning"-direction) through a beam of radiation. On the other hand, it includes a so-called scanner in which each target area is irradiated by simultaneously scanning the substrate in a direction parallel to this direction (a direction parallel to the same direction) or an anti-parallel direction (a direction parallel to the opposite direction). It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern on the substrate.</p><p>It has been proposed to immerse a substrate in a lithographic projection apparatus in a liquid having a relatively high refractive index, such as water, to fill the space between the final element of the projection system and the substrate. The gist of doing this is to enable imaging of smaller features, since the exposure radiation will have a shorter wavelength in the liquid (the effect of the liquid increases the effective NA of the system and also increases the focal length as will be considered). Other immersion liquids including water in which solid particles (eg, quartz) are present in a suspended state have also been proposed.</p><p>However, immersing the substrate or substrate table in a bath of liquid (see, eg, US Pat. No. 4,509,852) means that a significant volume of liquid must be accelerated during scanning exposure. Doing so would require adding a motor or using a more powerful motor, and fluctuations in the liquid would cause undesirable and unpredictable effects.</p><p>In one of the solutions proposed to this, the liquid supply system causes the liquid supply system to provide liquid using a liquid confinement system only to a local area of the substrate and between the final element of the projection system and the substrate (the substrate is usually have a larger surface area than the final element of the projection system). One of the proposed ways to achieve this is disclosed in the PCT Patent Application Publication No. WO 99/49504. 2 and 3 , the liquid is preferably provided on the substrate by at least one inlet IN along the direction of movement of the substrate relative to the final element, and after passing under the projection system at least one is removed by the OUT of the That is, when the substrate is scanned in the -X direction under the final element, liquid is provided on the +X side of the final element and absorbed at the -X side. 2 schematically shows a configuration in which liquid is provided via an inlet IN and absorbed on the other side of the final element by an outlet OUT which is connected to a low pressure source. In the example of FIG. 2 , the liquid is provided along the direction of movement of the substrate relative to the final element, although this need not be the case. Various orientations and numbers of inlets and outlets located around the final element may be used. As an example thereof, FIG. 3 shows an example in which four sets of inlets and outlets located on either side are provided in a regular pattern around the final element.</p><p>Another immersion lithography solution using a local liquid supply system is shown in FIG. 4 . The liquid is supplied by two grooved inlets IN on both sides of the projection system PL, and is removed by a plurality of discontinuous outlets OUT radially arranged outside the inlets IN. An inlet IN and an outlet OUT are arranged in a plate having a hole formed in the center, through which a projection beam is projected. Liquid is supplied by a single grooved inlet IN on one side of the projection system PL and is removed by a plurality of discontinuous outlets OUT on the other side of the projection system PL so that the projection system PL and A thin liquid film flows between the substrates (W). The choice of which combination of inlet IN and outlet OUT to use will depend on the direction of movement of the substrate W (other combinations of inlet IN and outlet OUT will be inactive).</p><p>In European Patent Application Publication EP 1420300 and US Patent Application Publication US 2004-0136494, the entire contents of which are incorporated herein by reference, the concept of a dual or dual stage immersion lithographic apparatus is disclosed. This apparatus is provided with two tables for supporting the substrate. A leveling measurement is performed on the table in the first position without immersion liquid, and exposure is performed on the table in the second position with immersion liquid. Alternatively, the device may have only one table.</p><p>The immersion liquid lifts debris or particles (eg, left over from the manufacturing process) from portions of the lithographic apparatus and/or substrate or erodes the components to cause particles. Such debris may remain on the substrate after imaging, or interfere with imaging while suspended in liquid between the projection system and the substrate. Therefore, in the immersion lithography apparatus, matters concerning contamination must be resolved.</p>

<solutionproblem><p>For example, it would be desirable to provide a lithographic apparatus that can be cleaned easily and efficiently, and also to provide a method for efficiently cleaning an immersion lithographic apparatus.</p></solutionproblem><meansproblemsolution><p>According to a feature of the present invention, there is provided an apparatus for cleaning an immersion lithographic projection apparatus, the apparatus comprising: a megasonic transducer configured to clean a surface of the immersion lithographic apparatus; cleaning with the megasonic transducer a liquid supply system configured and arranged to supply a liquid between the surfaces to be formed, and a cleaning liquid outlet configured to allow an outflow of the cleaning liquid.</p><p>According to a feature of the present invention, an immersion lithographic projection apparatus is provided, the apparatus comprising: a substrate table configured and arranged to hold a substrate; a projection system configured to project a patterned radiation beam onto the substrate; a megasonic transducer, a liquid supply system configured and arranged to supply liquid between the megasonic transducer and the surface to be cleaned, and a cleaning liquid outlet configured to allow an outflow of the cleaning liquid.</p><p>According to a feature of the present invention, there is provided a method for cleaning a surface of an immersion lithographic projection apparatus using a megasonic wave emitted from a megasonic transducer, the method comprising: a surface to be cleaned and the megasonic transducer covering the surface of the deductor with a liquid, introducing the megasonic waves into the liquid, and extracting the liquid through a liquid outlet adjacent the surface to be cleaned.</p><p>According to a feature of the present invention, there is provided a cleaning apparatus for cleaning a surface of a component of a lithographic projection apparatus, the cleaning apparatus comprising: a liquid flow generating apparatus configured to generate a flow of liquid adjacent the surface; and the liquid and a sonic transducer configured to emit a sonic wave on the surface through</p><p>According to a feature of the present invention, there is provided a lithographic projection apparatus comprising: a substrate table configured and arranged to hold a substrate, a projection system configured to project a patterned radiation beam onto the substrate, configuration of the lithographic projection apparatus A cleaning device configured to clean a surface of an element, the cleaning device comprising: a liquid flow generating device configured to create a flow of liquid adjacent the surface; and a sonic configured to emit sound waves through the liquid and onto the surface. including transducers.</p><p>According to a feature of the present invention, there is provided a method of cleaning a surface of a component of a lithographic projection apparatus, the method comprising the steps of providing a liquid on the surface, generating a flow in the liquid, and dispensing the liquid and providing a sound wave therethrough.</p><p>According to a feature of the present invention, there is provided a method of cleaning a surface of an object of a lithographic apparatus, the method comprising: providing a liquid comprising a first additive between a sonic transducer and the surface to be cleaned; emitting sound waves from a sonic transducer onto the surface, providing a liquid between the surface to be cleaned and the sonic transducer comprising a second additive different from the first additive, and from the sonic transducer and emitting a sound wave of</p><p>According to a feature of the present invention, there is provided a lithographic projection apparatus, the apparatus comprising: a sonic transducer having, in use, a side facing a surface to be cleaned, configured to provide a liquid between the sonic transducer and the surface to be cleaned a liquid supply system and an extractor configured to remove the liquid from between the sonic transducer and the surface, the inlet of the extractor, in use, substantially centered on the face of the sonic transducer; positioned to form a radially inward flow of the liquid between the surface and the sonic transducer facing.</p></meansproblemsolution>

<p>DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention, for purposes of illustration only, will be described below with reference to the accompanying schematic drawings in which corresponding reference numerals are assigned to corresponding parts.</p><p>1 schematically shows a lithographic apparatus according to an embodiment of the present invention. This lithographic apparatus includes:</p><p>- an illumination system (illuminator, IL) configured to condition a radiation beam (B, eg UV radiation or DUV radiation);</p><p>- a support structure (eg mask table) MT configured to support a patterning device (eg mask) MA and connected to a first positioner PM configured to precisely position the patterning device according to predetermined parameters );</p><p>- a substrate table (eg wafer table) configured to hold a substrate (eg resist coated wafer) W and connected to a second positioner PW configured to precisely position the substrate according to predetermined parameters (WT); and</p><p>- a projection system (eg refractive projection lens system) configured to project a pattern imparted to the radiation beam by the patterning device MA onto a target area C (eg comprising one or more dies) of the substrate W (PS).</p><p>An illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, to direct, shape, or control radiation. have.</p><p>The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions such as, for example, whether the patterning device is maintained in a vacuum atmosphere. The support structure may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or table that is fixed or movable as required. The support structure may allow the patterning device to be in a desired position with respect to the projection system, for example. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device".</p><p>As used herein, the term "patterning device" should be broadly interpreted to include any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target area of a substrate. It should be noted that the pattern imparted to the radiation beam may not exactly match the desired pattern in the target area of the substrate, for example if it contains phase shifting features or so-called assist features. In general, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device to be created in the target area, such as an integrated circuit.</p><p>The patterning device may be either a transmissive type or a reflective type. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in the lithography art, and include mask types such as binary, alternating phase inversion, and attenuated phase inversion, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.</p><p>As used herein, the term "projection system" refers to refractive, reflective, catadioptric, magnetic, as appropriate with respect to the exposure radiation used, or with respect to other factors such as the use of an immersion liquid or the use of a vacuum. It should be broadly interpreted as including any type of projection system, including , electromagnetic, and electrostatic optical systems, or any combination thereof. As used herein, the term "projection lens" may be considered a synonym for the more general term "projection system".</p><p>As described herein, the device is of the transmissive type (eg employing a transmissive mask). Alternatively, the device may be of a reflective type (eg employing a programmable mirror array of a type as described above, or employing a reflective mask).</p><p>The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more support structures). In such "multiple stage" machines, additional tables and/or support structures may be used in parallel, or preparatory work steps on one or more tables and/or support structures while one or more tables and/or support structures are being used for exposure. may be performed.</p><p>Referring to FIG. 1 , an illuminator IL receives a radiation beam from a radiation source SO. For example, if the radiation source is an excimer laser, the radiation source and the lithographic apparatus may be separate entities. In this case, the radiation source is not considered to form part of the lithographic apparatus, the radiation beam being, for example, with the aid of a beam delivery system BD comprising suitable directing mirrors and/or beam expanders, the radiation source from SO to the illuminator IL. In other cases, for example, if the radiation source is a mercury lamp, this radiation source may be an integral part of the lithographic apparatus. The radiation source SO and the illuminator IL may optionally be referred to as a radiation system together with the beam delivery system BD.</p><p>The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. In general, at least the outer and/or inner radial magnitudes (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator (IN) and a condenser (CO). An illuminator may be used to condition the radiation beam to have the required uniformity and intensity distribution in its cross-section.</p><p>The radiation beam B is incident on a patterning device (eg mask) MA held on a support structure (eg mask table) MT and is patterned by the patterning device. Across the patterning device MA, the radiation beam B passes through the projection system PS and is focused on the target area C of the substrate W. With the support of a second positioner PW and a position sensor IF (such as an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can, for example, be positioned in a different target area eg in the path of the radiation beam B. C) can be precisely moved to position it. Likewise, the first positioner PM and the other position sensors (not explicitly shown in FIG. 1 ) are in the path of the radiation beam B, for example after mechanical withdrawal from a mask library or during scanning. can be used to accurately position the patterning device MA with respect to . In general, the movement of the support structure MT is performed by a long-stroke module (coarse positioning) and a short-stroke module forming part of the first positioner PM; It will be realized with the help of fine positioning). Likewise, the movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module which form part of the second positioner PW. In the case of a stepper (unlike a scanner), the support structure MT may only be connected to a short-stroke actuator, otherwise it will be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1 , M2 and substrate alignment marks P1 , P2 . Although the substrate alignment marks occupy designated target areas as shown, these marks may be located within the space between the target areas (these are known as scribe-lane alignment marks). Likewise, in situations where more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.</p><p>The device shown can be used in one or more of the following modes:</p><p>One. In the step mode, the support structure MT and the substrate table WT are held essentially stationary, while the entire pattern imparted to the radiation beam is projected onto the target area C at one time (ie a single static exposure). . Thereafter, the substrate table WT is moved in the X direction and/or the Y direction so that different target areas C can be exposed. In step mode, the exposure field of maximum magnitude limits the size of the imaged target area C in a single static exposure.</p><p>2. In the scan mode, the support structure MT and the substrate table WT are scanned simultaneously while the pattern imparted to the radiation beam is projected onto the target area C (ie, a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure MT may be determined by the enlargement (reduction) and image reversal characteristics of the projection system PS. In scan mode, the exposure field of maximum magnitude limits the width of the target area (the width in the non-scanning direction) in a single dynamic exposure, while the length of the scanning operation determines the height of the target area (the height in the scanning direction). decide</p><p>3. In another mode, the support structure MT is held essentially stationary with the programmable patterning device, while the pattern imparted to the radiation beam is projected onto the target area C, while the substrate table WT is moved or scanned. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography using a programmable patterning device such as a programmable mirror array of a type as mentioned above.</p><p>Also, combinations and/or variations of the above-described modes of use, or entirely different modes of use, may be employed.</p><p>Another immersion lithography solution (IH) using a topical liquid supply system proposed for this is, in the liquid supply system, a barrier member extending along at least a portion of the boundary of the space between the final element of the projection system and the substrate table. ) to install. Such a solution is illustrated in FIG. 5 . The barrier member is substantially stationary in the XY plane, although there may be some relative movement in the Z direction (optical axis direction) with respect to the projection system. In this embodiment, a sealing portion is formed between the barrier member and the surface of the substrate, and a non-contact sealing portion such as a glass sealing portion is possible as this sealing portion.</p><p>The barrier member 12 contains liquid at least partially in the space 11 between the final element of the projection system PS and the substrate W. A non-contact seal 16 to the substrate W is formed around the image field of the projection system so that liquid will be confined in the space between the substrate surface and the final element of the projection system. This space is at least partially delimited or defined by a barrier member 12 located below and surrounding the final element of the projection system PS. Liquid will enter the space below the projection system and within the barrier member 12 by a liquid inlet 13 and will be removed by a liquid outlet 13 . The barrier member 12 extends slightly above the final element of the projection system, and the liquid level rises above the final element to provide a buffer of liquid. In one embodiment, the upper portion of the inner perimeter of the barrier member 12 will closely conform to the shape of the projection system or final element of the projection system, eg, rounded. The bottom of the inner periphery need not be case-shaped, but closely conforms to the shape of the image field, for example a rectangular shape.</p><p>The liquid is confined in the space 11 by a gas seal 16 formed between the bottom of the barrier member 12 and the surface of the substrate W during use. The gas seal is formed, for example, by air or synthetic air, but in this embodiment N is provided in the gap between the barrier member 12 and the substrate through the inlet 15 under pressure and is extracted through the outlet 14 .<sb>2</sb> or other inert gases. The excessive pressure on the gas inlet 15 , the vacuum level on the outlet 14 , and the geometry of the gap are determined and placed so that a high velocity gas flow that confines the liquid is created inside. These inlets/outlets will be annular grooves surrounding the space 11 , and the flow of gas 16 is effective to confine the liquid within the space 11 . Such a system is disclosed in US Patent Application Publication US 2004-0207824.</p><p>As mentioned above, an immersion lithographic apparatus is an apparatus in which a substrate is imaged through a liquid. That is, an immersion liquid is provided between the final element of the projection system PS and the substrate. This configuration poses one or more particular problems. Specifically, the liquid should be confined within the device, and the liquid should preferably be free from particles of foreign objects that could cause defects by creating defects during imaging and/or remaining on the substrate surface after imaging and prior to downstream processing. will have to be maintained Occasionally, the immersion liquid intentionally contains particles in a suspended state.</p><p>One way to address the problem of foreign object particles is to apply a cleaning liquid to the surface to be cleaned and/or inject sound waves (ultrasonic or megasonic waves) into the liquid to clean the surface. The cleaning liquid may or may not be the same as the immersion liquid. For example, extremely pure water is possible as the cleaning liquid.</p><p>Compared to sound waves, megasonic waves generate cavitation bubbles (implosion or vibrating bubbles), which are very small and will adhere to the surface to be cleaned. However, there is a limit to the amount of energy that can be provided in a liquid using megasonic. In general, ultrasonic energy can be provided anywhere in a liquid and can be distributed throughout the liquid, whereas megasonic energy is only locally focused and must be directed in a straight line to the surface to be cleaned. That is, there must be a direct path (line of sight/straight line) between the transducer providing the megasonic wave and the surface to be cleaned. The entire length of the path must be filled with liquid.</p><p>Megasonic frequencies are generally considered to be in the range of 750 kHz to 3 MHz. For the purposes of the present invention, frequencies of about 750 kHz or higher, 1 MHz or higher, or 1.5 MHz or higher are used.</p><p>The stagnant boundary layer in the cleaning liquid near the surface of the object to be cleaned becomes thinner as the frequency of the sonic energy provided is increased. At megasonic frequencies, cleaning is achieved, in part, by megasonic pulsing and acoustic streaming with high velocity pressure waves in the cleaning liquid as well as bubble oscillations and to a lesser extent cavitation and bursting of bubbles.</p><p>At megasonic frequencies, particles with a diameter of less than 0.5 μm will be removed without damage to the surface to be cleaned. As mentioned above, there must be a cleaning path (line of sight) from the transducer to the surface to be cleaned. To further increase the cleaning efficiency, the gas will dissolve in the liquid to promote cavitation (bubble formation). Suitable gases include nitrogen, carbon dioxide, oxygen, and mixtures of these gases (including air), although other gases such as ozone or hydrogen (including water) will also be suitable. For example, solvents such as liquid surfactants (detergent, soap, etc.), acidic liquids, alkaline liquids, non-polar organic solvents or polar organic solvents, H<sb>2</sb>O<sb>2</sb> The use of a solution, or any other suitable chemistry, in the lithographic apparatus may further improve cleaning efficiency. Use detergent or solvent in the cleaning solution, or<sb>2</sb>O<sb>2</sb> Adding the solution can improve the oxidizing nature of the fluid, which will help remove organic contaminants. Another example is hypochlorite.</p><p>The polarity of the cleaning solution can be changed, for example, by adding a liquid-miscible solvent (e.g., a water-miscible solvent) having a lower polarity than the liquid (e.g., water), such as alcohol, ketones, organic acids, and amines. Examples of alcohols include diethylene glycol monobutyl ether and/or ethoxylated secondary C12-14-alcohols such as aldyloxypolyethyleneoxyethanol. One problem that may arise with the addition of such additives is that the flash point of the resulting cleaning solution is lowered. Therefore, it is desirable to add an organic-based additive having a high flash point in order to change the cleaning liquid properties without causing a risk of flammability. Such additives include N-methylpyrrolidone (NMP) and glycol ethers. Of course, other additives may be added to the cleaning solution. For example, it may be desirable to add a chemical that has a specific chemical attack on one or more specific contaminants to be removed. For example, the resist particles may be removed with chemicals such as methyl ethyl ketone, ethyl acetate and/or acetone. In this embodiment, as the cleaning liquid, water, diethylene glycol monobutyl ether, and "alcohol, C12" such as "TLDR-A001" or "TLDR-A001-C4" manufactured by "Tokyo Ohko Kogyo Co., Ltd." -14-secondary, ethoxyoxidation" mixtures are possible.</p><p>In one embodiment of the invention, the cleaning of the surface is performed in a plurality of steps, so that different contaminants are removed during different steps. Therefore, in the first step, a cleaning liquid with a specific first additive is used to remove the first contaminant. The sonic wave is then used to clean the surface through a cleaning solution having a specific first additive. In the second step, a liquid with a second additive different from the first additive designed to attack different contaminants between the sonic transducer and the surface to be cleaned is used. These steps may be performed multiple times and may or may not require rinsing of the surface between use of the cleaning solution with different additives (eg, with different first additives and different the second additive may not be compatible). This sequential cleaning scheme may result in an increase in overall particle removal performance.</p><p>Objects requiring cleaning in an immersion lithographic apparatus include one or more portions of the substrate table WT (the top surface thereof) supporting the substrate W, the final elements of the projection system PS being immersed in the immersion liquid during imaging; and/or a liquid confinement system (eg, the liquid confinement system illustrated in FIGS. 2-5 ) that provides liquid between the final element of the projection system PS and the substrate W during imaging. does not Although the following embodiments of the present invention will be described in relation to cleaning the barrier member and the top surface of the substrate table, the present invention is not limited to cleaning the substrate table and the barrier member.</p><p>In one embodiment, the liquid supply system provides liquid between the sonic transducer and the surface to be cleaned. In this embodiment, the liquid supply system provides a flow of liquid from which the liquid is removed such that particles removed from the surface are transported when the surface is cleaned. One suitable liquid is water in its extremely pure form. However, other types of liquids may be suitable. Moreover, additives to liquids, such as surfactants as described above, may also have advantages. Other cleaning solutions are, for example, water/hydrogen peroxide, water/ethanol, water/iso-propyl alcohol (IPA), water/aluminum or water/acetone mixtures. Other chemicals useful as additives include tetramethylammonium hydroxide (TMAH) and SC-1 or SC-2.</p><p>One reason for injecting a gas (or some solvent) into a liquid is that doing so promotes stable cavitation. As a result, stable bubbles are formed in the liquid. These bubbles are then vibrated by megasonic waves to produce a cleaning that is less likely to damage the surface to be cleaned than so-called transient cavitation, which implodes or collapses after the solvent evaporates into the bubbles. Occurs. Such intense implosion will cause damage to the surface and will normally occur at ultrasonic frequencies, but not significantly at megasonic frequencies, producing bubbles smaller than those produced at ultrasonic frequencies. However, as mentioned above, the megasonic wave must be supplied to the crosshair of the surface to be cleaned by the megasonic wave.</p><p>Treatment times of up to 100 seconds will result in particle removal efficiencies of up to 100% at frequencies of about 1 MHz. If the acoustic frequency is well above 3 MHz, the particle removal efficiency will decrease sharply compared to frequencies slightly higher than 1 MHz. By injecting the gas into the liquid, it has a significant effect on the particle removal efficiency. When oxygen is injected into the liquid at a level of 20 ppm, SiO with a diameter of 34 nm<sb>2</sb> The particle removal efficiency will increase from 0% to 30%. Therefore, gas concentrations of approximately 5 ppm or higher may be used.</p><p>Temperature is also an important factor, and the temperature should be appropriately chosen so that they are balanced, taking into account that higher temperatures (eg 55° C.) allow for faster reaction times but less gas dissolved.</p><p>There is also an effect of the pH of the liquid. At low pH, a large number of Hs in the liquid<sp>+</sp> The presence of ions creates a positive surface charge, but at high pH, a large number of OH in the liquid<sp>-</sp> The presence of ions creates a negative surface charge. Thus, by moving the pH of the liquid away from pH 7, the likelihood that these particles will not re-deposit after removing the particles is increased. Moreover, when the particle and the surface are equally charged (either positively or negatively), the electrostatic repulsive force between the particle and the surface helps to lift the particle from the surface.</p><p>The transducer power is preferably 0.2 to 5 W/cm 2 , the irradiation distance is 5 to 20 mm, and the cleaning time is preferably 10 to 90 seconds. For an acoustic wave from a megasonic transducer that travels a direct path from the megasonic transducer to the surface to be cleaned, several designs have been proposed for cleaning different parts of the immersion lithographic apparatus.</p><p>Megasonic scrubbers are well suited for removing particles from surfaces.</p><p>6 illustrates an apparatus used to clean a top surface of a substrate table WT including, for example, a retractable barrier 80 extending over and around the top surface of the substrate table WT to be cleaned when in a cleaning position. are doing When the barrier 80 protrudes into the cleaning position of the barrier, liquid can be provided on the surface to be cleaned, and the megasonic transducer 20 is moved over the surface of the substrate table WT (in arrow direction "25") ) (the bottom surface of the transducer 20 is covered by the liquid) and/or the substrate table WT can be moved under the transducer 20, whereby the top surface of the substrate table WT is cleaned . Of course, similar configurations are possible in which the barrier 80 is not retractable, is permanently fixed to the substrate table WT, or in which the barrier 80 is a removable part. The transducer 20 may be stationary or movable (specifically in the Z direction) and/or movable in the X/Y axis during the cleaning operation.</p><p>When the top surface of the substrate table WT is cleaned, it is also possible to clean one or more sensors installed on the top surface of the substrate table WT at the same time. Examples of this type of sensor are transmission image sensors, lens interferometers and/or spot sensors, and the like.</p><p>It would be desirable to have the acoustic wave generated by the transducer impinge at 90° on the surface to be cleaned. To this end, a micrometer will be provided for adjusting the inclination of the transducer 20 with respect to the surface to be cleaned. In one of the designs for the device, it would be advantageous to provide a transducer that is inclined relative to the surface, which can also be adjusted using a micrometer. The micrometer can also be used to adjust the distance from the transducer to the surface to be cleaned.</p><p>The problem of contamination in immersion lithographic apparatus is addressed in US Patent Application Serial No. 11/437,876, filed May 22, 2006. In this patent application, a lithographic apparatus includes a megasonic transducer configured to easily and efficiently clean a surface. Megasonic transducers are well suited for removing particles from surfaces. However, there are cases where the particles are re-deposited on the cleaned surface and re-adhered. Re-deposition readily occurs when fluid flow is not precisely controlled, which typically occurs at one or more locations where the flow velocity is zero (regions without flow) or at the interface of a fluid and gas (eg, air). Accordingly, it is desirable to provide a flow of liquid between the megasonic transducer and the substrate being cleaned. Specifically, it is desirable to design the device so that a point of zero flow rate (region without flow) occurs.</p><p>For example, it would be desirable to alleviate the aforementioned problem of re-depositing the particles themselves by providing a lithographic apparatus in which the flow of the cleaning liquid is efficiently controlled to minimize re-deposition of contaminant particles on the surface being cleaned. It is also desirable to provide a flow of liquid between the megasonic transducer and the surface being cleaned, so that the liquid in which the particles are suspended is moved out quickly. Therefore, the number of points where the flow velocity is zero (regions without flow) is reduced, and re-deposition is prevented.</p><p>According to a feature of the present invention, there is provided an apparatus for cleaning an immersion lithographic projection apparatus, the cleaning apparatus comprising: a megasonic transducer configured to clean a surface of an immersion lithographic apparatus, a liquid between the megasonic transducer and the surface to be cleaned and a liquid supply system configured and arranged to supply the liquid, and a cleaning liquid outlet configured to discharge the cleaning liquid. The cleaning liquid outlet is adjacent the surface to be cleaned. The surface of the megasonic transducer and the surface to be cleaned are immersed in a cleaning solution for cleaning.</p><p>According to a feature of the present invention, an immersion lithographic projection apparatus is provided, the apparatus comprising: a substrate table configured and arranged to hold a substrate; a projection system configured to project a patterned beam of radiation onto the substrate; a megasonic transducer, a liquid supply system configured and arranged to supply a liquid between the megasonic transducer and a surface to be cleaned, and a cleaning liquid outlet configured to allow an outflow of the cleaning liquid. The surface of the megasonic transducer and the surface to be cleaned are immersed in the cleaning liquid during cleaning.</p><p>According to a feature of the present invention, there is provided a method for cleaning a surface of an immersion lithographic projection apparatus using a megasonic wave emitted from a megasonic transducer, the method comprising: a surface to be cleaned and a surface of the megasonic transducer covering with a liquid, injecting the megasonic wave into the liquid, and discharging the liquid through a liquid outlet adjacent the surface to be cleaned.</p><p>In a variant of the device shown in FIG. 6 , a cleaning liquid 30 flows between the transducer 20 and the surface to be cleaned. 7 shows one design in which a megasonic transducer 20 is held over a portion (eg, a mirror block) of a top surface of a substrate table WT, forming an area A to be cleaned. The lower surface of the megasonic transducer is immersed in a cleaning solution 30 held in a reservoir. The cleaning solution 30 is discharged away from the megasonic transducer 20 toward the side of the reservoir through one or more outlets 10 located on the surface of the reservoir. When the megasonic transducer 20 is smaller than the substrate table WT to be cleaned, the transducer and/or the substrate table must move around.</p><p>Gas/liquid (eg air/water) interfaces are particularly susceptible to particle re-deposition. As the megasonic transducer 20 moves across the surface of the substrate table WT (and/or vice versa), a gas/liquid interface passes over the critical cleaned area. Contaminants, portions of which have been removed from the substrate table WT, may deposit on the substrate table WT below the gas/liquid interface, between the surface being cleaned and the one or more outlets.</p><p>8 shows an apparatus in which the surface of the megasonic transducer facing the substrate table is immersed in a cleaning solution such that there is no gas (ie, air)/liquid interface between the megasonic transducer 20 and the substrate table WT. is showing In this arrangement, a sonic transducer 20 is provided in which a megasonic transducer may be used. A cleaning solution 30 is provided on the upper surface of the substrate table WT. In the illustrated apparatus, a barrier 80 provided on the substrate table (which may also be removable or retractable) prevents the cleaning solution 30 from escaping. The liquid is provided radially outward of the sonic transducer 20 , and may be provided, for example, at a point in close contact with the barrier 80 .</p><p>It is advantageous to have a flow 35 of liquid between the sonic transducer 20 and the substrate being cleaned. Specifically, it is preferable that the movement of the cleaning liquid 30 is directed toward a region having a higher concentration of particles and a region still irradiated with sound waves. This configuration is particularly desirable in situations where a liquid/air interface is present. This is because contaminant particles removed from the surface do not migrate towards the liquid/air interface, which improves cleaning. This is accomplished, in the embodiment of FIG. 8 , by extracting the liquid through a tube or pipe 100 that passes substantially through the center of (or at least surrounded by) the sonic transducer 20 . While the sonic transducer 20 is illustrated as being a single transducer, a plurality of sonic transducers are positioned adjacent to each other about a central axis that is orthogonal to the surface to be cleaned and is coaxial with the tube 100 illustrated in FIG. 8 . It is obvious that it may be provided as Of course, the tube 100 may deviate from the central axis.</p><p>The transducer 20 has a substantially centrally located extraction pipe 100 having an outlet 10 formed thereon. The outlet 10 is located adjacent to, adjacent to, or juxtaposed to the area A to be cleaned. The other end of the pipe 100 is connected to, for example, a wet vacuum machine, that is, an extractor. The liquid is drawn upward through the outlet 10 , causing the cleaning liquid to flow from below the transducer 20 towards the center of the megasonic transducer 20 . Therefore, the contaminants separated from the surface of the substrate table WT are removed by the flow of the cleaning liquid 30 before being re-deposited on the surface of the upper surface of the substrate table WT being cleaned.</p><p>Because megasonic waves are directional, the cleaning is preferably localized or compartmentalized with respect to the surface of the substrate table in a straight line in the path of the megasonic wave. In the device shown in FIG. 8 , the surface to be cleaned is directly under the transducer 20 . Thus, the particle concentration in the cleaning solution below the transducer 20 is high, while the particle concentration in the cleaning solution next to the transducer is low. Under the influence of the radial flow 35 , a bulk flow of fluid is directed towards the most polluted area within the area of the extraction pipe outlet 10 . The cleaning liquid 30 flowing under the transducer may exhibit a radial flow.</p><p>In the configuration shown in FIG. 8 , there is no gas (eg air)/liquid interface between the area of the substrate table WT being cleaned and from the area of the substrate table being cleaned to the outlet 10 of the extraction pipe 100 . It is beneficial not to The apparatus may be implemented in an off-line cleaning apparatus. To use the off-line cleaning apparatus, the cleaning apparatus is fixed to the substrate table WT. The substrate table WT may be removed from the lithographic apparatus during cleaning. A variant of the device may be implemented in an in-line configuration.</p><p>In the apparatus of FIG. 8 , the extraction pipe 100 is connected to an under pressure source (wet vacuum), thereby generating a radially inward flow of liquid towards a central axis coaxial with the tube 100 . . However, other types of flow may occur, such as vortex flow, in which the liquid flows inward (as a component) toward an axis coaxial with the tube 100 , but is not exactly radial.</p><p>Although the pipe 100 is illustrated as being positioned toward the center of the sonic transducer 20 in FIG. 8 , other configurations are also possible. For example, the liquid may be extracted through the surface itself being cleaned. However, such an arrangement is more suitable if the position of the sonic transducer 20 is fixed relative to the surface A to be cleaned. When cleaning the top surface of the substrate table WT with a sonic transducer 20 that is planarly smaller than the top surface of the substrate table, the sonic transducer 20 moves relative to the substrate table WT as illustrated by arrow 25 . Thus, the entire upper surface of the substrate table WT will be able to be cleaned.</p><p>Preferably, an inward flow 35 of the liquid occurs from a region with a low concentration of pollutant particles toward a region with a high concentration of pollutant particles. Regions with a low concentration of particles include regions radially outward from the central axis of the sonic transducer 20, in which the sound waves do not detach the particles from the surface A being cleaned. Areas with a high concentration of particles include areas such as between the sonic transducer 20 and the surface A to be cleaned. In this way, the cleaning liquid replenishes the contaminated liquid without flowing through another passage. Moreover, particles removed from the surface to be cleaned will reattach themselves to each other. With radial inward flow, these particles will reattach themselves to one another at a location radially inward of where they were originally attached. Thus, geometrically, the location of the reattachment should be below the transducer 20 , ie the area where particles can be removed again by sound waves from the sonic transducer 20 .</p><p>Creating an inward flow is an important factor, but how to achieve it is not. Although one or more specific embodiments have been described, other configurations are possible, and the tube 100 must be aligned with the center of the plurality of megasonic transducers forming the megasonic transducer 20 or the entire transducer 20 in a straight line. It will be appreciated by those skilled in the art that there is no need to go through. For example, the tube only needs to be capable of generating an inward flow through the cleaning liquid 30 to the location required to extract the liquid.</p><p>FIG. 9 illustrates an embodiment more suitable for use in-line (ie within an immersion lithographic apparatus) than the embodiment of FIG. 8 , by removing the barrier 80 of the embodiment of FIG. 8 . In this embodiment, the sonic transducer 20 is similar to that illustrated in FIG. 8 (except that it has a smaller area in plan). The sonic transducer 20 is surrounded by the barrier member 12 described with respect to FIG. 5 . This barrier member 12 may be moved in the XY plane relative to the top surface of the substrate table WT while liquid is provided between the sonic transducer 20 and the surface to be cleaned (and vice versa). In this embodiment, likewise, liquid is extracted through tube 100 to provide the desired inner flow of liquid. Thus, a higher flow rate of liquid will be required than during imaging as described with respect to FIG. 5 .</p><p>The substrate table WT and/or the transducer 20 are moved relative to each other so that all of the top surface of the substrate table WT can be cleaned. Cleaning may occur in an automated manner within the lithographic apparatus, or may be performed manually by moving the transducer 20 relative to the top surface of the substrate table WT by hand or some tool.</p><p>Once the cleaning process is automated, one way to automate the cleaning process is to enable the transducer 20 to be moved from a stationary storage position to a cleaning position (also stationary), and the transducer 20 to the cleaning position ( moving the substrate table WT relative to the transducer 20 when in a stationary state). The substrate table WT will need to be moved in the Z axis prior to operation of the liquid supply system of the cleaning apparatus. After the gas flow 16 is created, liquid is provided to the barrier member 12 and the substrate table WT is moved in the XY plane so that the surface required to be cleaned can be cleaned.</p><p>A flow of liquid across the gap between the transducer and the surface to be cleaned is preferred, but not essential.</p><p>Another method for preventing or at least reducing the re-adhesion of particles to a surface is by altering one or more properties of the liquid between the transducer and the substrate by the zeta potential of the particle and the zeta potential of the surface, It is such that the particles are not attracted to the surface, or preferably, the particles are pushed away from the surface.</p><p>The zeta potential is the potential of a surface in a liquid. The zeta potential generally decreases with distance from the surface. Certain types of materials have a certain zeta potential for certain types of liquids. One method of changing the zeta potential of a surface is a method of changing the concentration of an electrolyte in a liquid, and another or additional method of changing the zeta potential is a method of changing the pH of the liquid. By careful selection of the concentration of the electrolyte (eg, salt) in the liquid and/or the pH of the liquid, (i) the zeta potential of the surface from which particles are removed (and/or any other surface where adhesion is to be prevented), and (ii) The zeta potential of the particle can be selected. These two zeta potentials are preferably selected so that they have the same polarity, so that one of the objects with each zeta potential is repelled from the other.</p><p>Knowing the materials from which the surface being cleaned is known, and the types of materials likely to produce particles, the pH of the liquid and/or the concentration of the electrolyte can be selected. When these materials are the same, it becomes easy to select a pH and/or electrolyte concentration at which the zeta potential does not become zero for both the surface and the particle. In such an environment, the dislocation will be either a positive potential or a negative potential for both the surface and the particle, which will repel each other, making it difficult for the particle to reattach to the surface. If the materials are different, the choice of pH and/or electrolyte concentration may be more difficult, but there will be at least one pH and/or electrolyte concentration such that the zeta potential has the same polarity for both materials.</p><p>Changing the pH of a liquid can negatively affect the solubility of the material, which itself can lead to contamination or loss of material integrity. If this is a problem, it may be desirable to change the electrolyte concentration rather than the pH. If the change in the electrolyte concentration is made by adding a well-selected salt (eg NaCl), it will not significantly affect the pH of the liquid (ie the liquid remains neutral).</p><p>It would be best to use a combination of two or more of the above techniques (especially altering the pH and/or electrolyte concentration to alter the zeta potential, and using a surfactant) in combination.</p><p>A problem that occurs when cleaning a liquid confinement system (LCS), such as an immersion hood (see FIG. 5), is that when the cleaning occurs in-situ, the megasonic wave The point is that the optical element (the final optical element) of the projection system will be heated from below. The reason is that the opening 200 is configured through the liquid confinement system LCS so that a portion of the projection system PS is exposed from below. The opening 200 is filled with liquid during imaging of the substrate, and the projection beam PB is directed through the opening 200 to the substrate W. Accordingly, it is desirable to clean the surface of a liquid confinement system (LCS) without dissipating energy within the optical element while ensuring that the optical element, typically a "WELLE" lens, is not heated. As shown in U.S. Patent Application Serial No. 11/802,082, filed May 18, 2007, which claims priority to U.S. Patent Application Serial No. 11/437,876, a gas (e.g., air ) gap will be used. However, under certain conditions, liquid may enter the gap.</p><p>In this embodiment, a shield, preferably comprising a plate, will be used to shield the final element of the projection system from megasonic waves and/or liquid. Preferably, the shield is a solid barrier 310 between the transducer 20 and the portion of the projection system PS exposed through the opening 200 . In this embodiment, the physical presence (barrier) in every straight path from the transducer 20 to the opening 200 is the shield. The barrier and/or gas gap 75 (the barrier assists in maintaining the gap) is effective to reflect sonic vibrations from the transducer 20 away from the opening 200 . In this embodiment, barrier 310 also shields opening 200 to prevent liquid from entering opening 200 . Thereby, the gas gap remains intact, and the liquid does not come into contact with the surface of the optical element.</p><p>10 and 11 show a cleaning tool that may be secured to the underside of a liquid confinement system (LCS). Referring first to the embodiment of Fig. 10, although the apparatus shown in Fig. 10 is generally circular in plan view, embodiments of the present invention will work with any type of liquid confinement system that is not circular. The cleaning tool is secured to the liquid confinement system LCS by an outer seal 400 that seals the cleaning tool body 300 against the underside of the liquid confinement system LCS. The outer seal 400 is typically an O-ring. The outer seal defines the maximum surface of the underside of the liquid confinement system (LCS) to be cleaned. Within the cleaning tool body 300 is a megasonic transducer 20 positioned to direct a megasonic wave at the underside of the liquid confinement system LCS. A cleaning liquid is filled between the cleaning tool body 300 and the lower surface of the liquid confinement system LCS to form a reservoir.</p><p>The cleaning apparatus comprises, in addition to the gas gap 75 between the optical element and the upper surface of the reservoir, a barrier 310 forming a solid separator between the transducer 20 and the gas gap 75 . have a shield Barrier 310 improves the effectiveness of the shield by reflecting megasonic waves away from the optical element. Barrier 310 is functionally shaped to act as an umbrella for the optical element, ie to shield the optical element from liquid. The guard covers the opening 200 formed by an inner rim 318 formed in the liquid confinement system (LCS) in the vicinity of the opening 200 , the barrier 310 (the guard) and the liquid confinement system (LCS). ) is secured to the liquid confinement system (LCS) by an inner seal 500 , typically an O-ring. The inner seal 500 prevents the cleaning liquid from entering the gas gap 75 threatening the performance of the gas gap 75 .</p><p>The cleaning tool also includes a tube 320 that is attached to the barrier 310 , which passes through the cleaning tool body 300 and has an inlet 330 for supplying cleaning liquid to the reservoir. The inlet is located near or adjacent to the upper end of the rinse liquid reservoir, near the inner rim 318 formed in the liquid confinement system (LCS). The inlet 330 may be provided as a single slit, or as a plurality of discrete apertures around the outer edge of the barrier 310 such that a flow of liquid is provided in all radial directions. On the underside of the liquid confinement system (LCS) is formed an outlet 10 connected to a low pressure source (eg, a wet vacuum) for removing the cleaning liquid. The outlet 10 is located adjacent or parallel to the surface of the liquid confinement system (LCS) to be cleaned and has a shape already provided in conventional liquid confinement systems (e.g., the outlet OUT in FIGS. 2-4 and /or outlet 14 in FIG. 5). Therefore, in use, cleaning liquid flows towards the outlet between the cleaning tool body and the liquid confinement system LCS. Therefore, this embodiment provides for a flow of liquid past the surface being cleaned. The flow of the liquid is radial, but generally directed outward in this embodiment. However, since the transducer 20 does not move relative to the surface to be cleaned, this is not critical in this embodiment.</p><p>The cleaning tool may be implemented in an in-line or off-line configuration. When implemented in an off-line configuration, the liquid confinement system (LCS) may be removed from the lithographic apparatus for provision for a cleaning tool.</p><p>The apparatus shown in FIG. 10 may face one or more problems. A source of potential instability is the low pressure section in the cleaning tool, ie the connection of the outlet 10 to the low pressure section. The suction force may vary, and control becomes difficult due to bubble formation and pressure fluctuations. If the degree of low pressure is too great, bubbles are formed in the washing water bath. These bubbles threaten the performance of the megasonic transducer 20 . When surfactants and/or detergents are used in the liquid, foaming occurs, as described below. If the degree of low pressure is too small, the pressure rises within the device, causing the cleaning liquid to flow through the exhaust passage in the liquid confinement system (LCS) and enter the gas gap 75 .</p><p>The seal 500 between the cleaning tool and the liquid confinement system (LCS) may deteriorate, causing liquid to leak into the gas gap 75 . After the cleaning liquid contacts the optical element, the optical element may absorb the megasonic waves and heat. Mechanical damage caused by megasonic energy can also be a problem. For this reason, the performance of the gas gap as an insulating shield of temperature and megasonic waves may be compromised.</p><p>A further or other problem with the inner seal 500 is that the design of the cleaning tool is dictated by the size of the barrier 310 (protection) required for the inner seal 500 to function. The cleaning tools may not be of a generic type, and thus different designs of cleaning tools may be required for different designs of liquid confinement systems (LCS). Also, there may be one or more openings in the liquid confinement system (LCS) that open to the bottom of the liquid confinement system (LCS) and are in fluid communication with the openings (200). It is possible to migrate liquid through the liquid confinement system (LCS) and into the gas gap 75 through one or more openings. If this happens, there may be no way to remove the liquid in the embodiment of FIG. 10 .</p><p>While adding additives (eg, surfactants and/or detergents) to cleaning solutions such as very pure water may improve cleaning, additives may also cause problems. In wet vacuum systems, the cleaning liquid may be agitated, causing the cleaning liquid to foam. Bubbles are a problem, as certain parts of the lithographic apparatus, such as sensors, can be damaged upon contact with the bubbles. Bubbles will cause the lithographic apparatus to fail or create additional problems for the manufacturing environment. This problem may be magnified by the use of a re-cycling loop in wet vacuum generators. If a pressure lower than that provided by the wet vacuum is used, the pressure in the reservoir will rise, making it more prone to leakage of liquid through the one or more openings into the gas gap 75 described above.</p><p>11 and 12 show another embodiment of a cleaning tool secured to the underside of a liquid confinement system (LCS). This embodiment has some features identical to the cleaning tool shown in FIG. 10 except for the following differences. The cleaning solution 30 flows in opposite directions through the reservoir and barrier 310 , such that an open opening in the barrier 310 acts as an outlet 10 . The rim 317 of the open opening of the barrier 310 is positioned adjacent or parallel to the underside of the liquid confinement system LCS to be cleaned. Between the barrier 310 and the inner rim 318 of the liquid confinement system (LCS) there is a gap sufficient to allow the cleaning liquid 30 to flow from the cleaning reservoir into the outlet 10 defined by the open opening of the barrier 310 . have.</p><p>Barrier 310 functions as a protection and has a funnel shape (ie, a truncated cone shape within the reservoir). This shape, along with other features of the cleaning tool, will improve the effectiveness of the insulating shield in that in use it reflects megasonic waves away from the optical element at an angle different from the angle at which they impinge upon the shield. The cleaning liquid 30 overflows the rim 317 of the barrier 310 and flows into the outlet 10 and outlet tube 320 under the influence of gravity. The barrier 310 therefore provides an outlet 10 through which the liquid exits the reservoir by gravity. Thus, the system can be viewed as an open system (compared to the embodiment of FIG. 10 which may also be viewed as a closed system). Also, the funnel shape of the outlet 10 and the outlet tube 320 causes a gentle flow of liquid out of the reservoir. The reason is, specifically, because of the opening and the funnel shape of the discharge tube 320 , the liquid flows along the inclined surface of the opening to the starting point of the tubular part of the discharge port. This reduces the likelihood of foam formation even when only slight force is applied to the liquid. By extracting the liquid from the center of the reservoir, a radially inwardly directed radial flow is generated, as in the embodiment of FIGS. 8 and 9 . A liquid inlet is provided and may be installed on the surface of the cleaning tool body 300 and/or the liquid confinement system (LCS).</p><p>Rim 317 is provided with a cross-sectional deformation or shaping to complement the inner rim 318 of the liquid confinement system (LCS), such that the flow path of the cleaning liquid 30 outside the reservoir is curved, or It is possible to change direction (ie, not form a straight line) as it passes through the space separating the rim 317 and inner rim 318 . Please refer to FIG. 12 for this. Accordingly, it may be possible to prevent megasonic waves from entering the opening 200 . Alternatively or in addition, such cross-sectional deformation or shaping may be provided on the inner rim 318 of the liquid confinement system (LCS) to complement the shape of the rim 317 . The height of the upper end of the rim 317 and the hydrostatic pressure in the reservoir determine the size of the gas gap 75 .</p><p>The flow of liquid may be supported by a "slow speed" pump 325 (connected to outlet 10) that provides some low pressure to prevent the formation of air bubbles in the cleaning liquid. A typical flow rate is 0.5 to 3 l/min. In this embodiment, the cleaning liquid flow does not pass through the wet vacuum. A restriction 328 (ie, a flow restrictor) may be present between the funnel-shaped barrier 310 and the low speed pump, preferably in the discharge tube 320 . The restriction helps to minimize the formation of bubbles.</p><p>In this embodiment, the pressure used to force the cleaning liquid to flow through the cleaning tool is always the same. This pressure is determined by the difference in height between the rim 317 of the funnel-shaped barrier 310 and the inlet for supplying the cleaning solution into the reservoir. In this embodiment, the cleaning apparatus is a stable system because the pressure required to operate the cleaning apparatus is automatically controlled. Therefore, the risk of overflowing the gas gap 75 is reduced, making the gas gap 75 more stable. The cleaning tool will provide effective insulating shielding of the optical element from temperature fluctuations and/or megasonic waves.</p><p>A tube 340 installed parallel to the funnel-shaped barrier 310 and in fluid communication with the reservoir, which may be used as an indicator, provides improved stability and additional control. Since the level of cleaning liquid in tube 340 is equal to the level of cleaning liquid in the reservoir, a determination can be made as to whether gas gap 75 is large enough. The indicator may indicate if there is a blockage in the tube of the barrier 310 that may cause the gas gap 75 to overflow with the cleaning solution 30 .</p><p> An advantage of constant pressure in the cleaning tool is that it can reduce the amount of air bubbles formed in the reservoir. As a result, the efficiency of the megasonic transducer will increase.</p><p>When the cleaning liquid flows smoothly through the cleaning tool, less gas/cleaning liquid contact will occur than in known wet vacuum systems. Thus, foam formation in the cleaning tool will be reduced. This makes it possible to add additives (surfactants and/or detergents) to the cleaning solution, which are usually limited in their use due to excessive foaming. Such additives include surfactants such as soap. The additive may be in a formulation, such as a soap formulation, including an agent to control the lathering properties of the additive. If the formulation does not include such agents, antifoam additives may be added to the cleaning solution to reduce and control foam formation. Examples of antifoam additives include, but are not limited to, compounds based on silicones such as paraffin, polyglycol or polydimethylsiloxane.</p><p>Note that in this embodiment, the system is an open type, not a closed type. Thus, it provides the advantage that an inner seal is not required (the outer seal is still present). In the elongate device shown in FIG. 10 , the guard 310 is dimensioned to be secured to an opening 200 formed in the liquid confinement system (LCS). Thus, for different types of liquid confinement systems (LCS), slightly different designs of cleaning tools and completely different process setups may be required. The cleaning apparatus of FIGS. 11 and 12 can be used with many types of liquid confinement systems (LCS) using fixed process setups.</p><p>The cleaning tool shown in FIGS. 10-12 may be modified such that the cleaning liquid 30 exhibits a radial flow.</p><p>Also, the concept of sucking the cleaning liquid from the reservoir in the cleaning tool by gravity to prevent foaming can be used with any type of cleaning tool, not just the type illustrated in FIGS. 11 and 12 . Specifically, this concept (that is, the concept of installing an outlet configured and arranged to discharge the cleaning solution by gravity) can also be applied to the apparatus illustrated in FIGS. 6 to 8 . In this case, however, the radial flow characteristics of the apparatus illustrated in FIGS. 6 to 8 may be sacrificed (but not necessarily).</p><p>By attaching the megasonic cleaning tool to a liquid confinement system (LCS) and actuating the transducer 20, it will generate vibrations in the part to be cleaned (eg, in the MHz range). Vibrations in this range will cause bubble cavitation, megasonic pulsing, and acoustic streaming, which together will become the basis for megasonic cleaning. The supply of the cleaning liquid 30 is made in such a way that the optical element is protected against megasonic energy, the cleaning liquid being in such a way that negative influences within the cleaning device (such as air bubbles, particle re-deposition, and/or foam formation) are avoided. is provided</p><p>The illustrated cleaning solution supply configuration will improve yield by, for example, improving the cleanliness of the lithographic apparatus, thereby contributing to the reduction of defectivity levels.</p><p>All of the illustrated embodiments may be practiced off-line. An on-line implementation of the embodiment is also possible.</p><p>Although reference has been made herein to specific examples of use of lithographic apparatus in the manufacture of integrated circuits (ICs), the lithographic apparatus described herein includes integrated optical systems, guidance and detection patterns for magnetic domain memories, It should be understood that it may have other applications such as flat panel displays, liquid crystal displays (LCDs), and fabrication of thin film magnetic heads. One of ordinary skill in the art, with respect to these other applications, any use of any term such as "wafer" or "die" as used herein may be considered synonymous with the more general term "substrate" or "target area", respectively. will understand that The substrates referred to herein may be processed before or after exposure, such as in a track (an apparatus that typically applies a layer of resist to a substrate and develops the exposed resist), or metrology equipment, or inspection apparatus. To the extent applicable, the disclosure of the present specification may be applied to the substrate processing apparatus and other substrate processing apparatuses. Also, since the substrate may be processed multiple times, for example to create a multilayer integrated circuit, the term substrate as used herein may also refer to a substrate comprising layers that have already been processed multiple times.</p><p>As used herein, the terms "radiation" and "beam" encompass all forms of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having a wavelength of 365, 248, 193, 157, or 126 nm). .</p><p>The term "lens" contemplated herein may refer to any one or combination of various types of optical elements, including refractive and reflective optical elements.</p><p>Although specific embodiments of the present invention have been described above, it will be understood that the present invention may be practiced otherwise than as described. For example, the present invention relates to a computer program comprising one or more sequences of machine readable instructions describing a method as disclosed above, or a data storage medium (eg, semiconductor memory, magnetic disk or optical disk) in which the computer program is stored. may take the form. The present invention may be carried out under the control of a controller which may be programmed by the aforementioned computer program.</p><p>One or more embodiments of the present invention may be applicable to any immersion lithographic apparatus, including the types described above, whether the immersion liquid is provided in the form of a water bath or only on a local surface area of a substrate. A liquid supply system as contemplated herein is to be construed broadly. In some embodiments, the liquid supply system may be a mechanism or combination of structures that provides liquid to the space between the projection system and the substrate and/or substrate table. The liquid supply system may include a combination of one or more structures that provide liquid to the space, one or more liquid inlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outlets. In one embodiment, the surface of the space may be part of the substrate and/or substrate table, or the space may enclose the substrate and/or substrate table. The liquid supply system may optionally further include one or more elements for controlling the position, quantity, quality, shape, flow rate or other characteristic of the liquid.</p><p>The immersion liquid used in the apparatus of the present invention may have a different composition depending on the desired nature and wavelength of the exposure radiation used. For exposure wavelengths of 193 nm, extremely pure water or water-based compositions can be used, for this reason the immersion liquid is sometimes also referred to as water, and water related terms such as hydrophilicity, hydrophobicity, moisture, etc. may be used. .</p><p>The foregoing is for illustrative purposes only and is not intended to limit the present invention. Accordingly, it will be understood by those skilled in the art that modifications may be made to the present invention described above without departing from the scope of the following claims.</p>