Electron beam exposure system

Several types of electron beam exposure systems are known in the art. Most of these systems are provided to transfer very accurate patterns to the exposed surface of the substrate. Since lithographic features are driven to become smaller and smaller according to Moore's Law, the high resolution of electron beams could also be used to continue the motivation for even smaller features than today.

Conventional electron beam exposure equipment has a throughput of about 100 wafers per hour. However, for lithographic purposes, at least the hourly electron beam exposure apparatus needs a commercially acceptable throughput of wafers. Several ideas have been proposed to increase the throughput of electron beam exposure equipment.

For example, U.S. Patent Application Publication No. 5,760,410 and U.S. Patent Application Publication No. 6,313,476 disclose a lithography system that uses an electron beam and has a cross section that is modified during pattern transfer to the exposed surface of the target. .. The particular cross section or shape of the beam is established during operation by moving the radiated beam inside the device by using electrostatic deflection. The selected aperture blanks partially, thereby forming an electron beam. The target exposed surface moves under the beam to renew the surface. The pattern is written in this way. The throughput of this system is still limited.

U.S. Patent Application Publication No. 20010028042, U.S. Patent Application Publication No. 20010028043, and U.S. Patent Application Publication No. 20010028044 use multiple sustained-wave (CW) emitters to generate multiple electron beamlets. An electron beam lithography system using the electron beam of the above is disclosed. Each beamlet is then individually shaped and blanked to create a pattern on the underlying substrate, producing a pattern on the underlying substrate. Beamlet homogeneity is a problem because all these emitters have slightly different emission characteristics. This was corrected by homogenizing every individual beam current to the reference current. The correlation value of the discrepancy is extremely difficult to calculate, requires a considerable amount of time, and reduces system throughput.

Journal of Vacuum Science and Technology B18 (6) pp. 3061-3066 to generate one electron beam that is continuously magnified, parallelized and split into multiple beamlets. One LaB₆Systems that use the source are disclosed. The target exposed surface is mechanically moved with respect to the plurality of beamlets in the first direction, and the beamlets are switched on and off using a blanking electrostatic deflector, and at the same time scan deflection. The vessel wipes out the beamlet through the blanker array over the target exposed surface in a direction perpendicular to the first direction, thus creating an image each time. In this known system, an electrostatic lens and / or a magnetic lens is used to reduce the image before it is projected onto the target exposed surface. The reduction process creates at least one complete intermediate image that is smaller than the previous image. The entire image is projected onto the target exposed surface when it has the desired dimensions. The main disadvantage of this approach is that the plurality of electron beamlets together pass through at least one complete crossover. In this crossover, Coulomb interactions between electrons in different beamlets disturb the image, thus reducing resolution. Further, due to the strong reduction of the image, the area exposed once is quite small and therefore requires multiple wafer scans to expose the mold. That is, 16 scans are required to expose a single mold, and very high speeds are required to reach commercially acceptable throughput.

UK Patent Application Publication No. 2,340,991 discloses a multi-beam particle lithography system with an illumination system that generates multiple ion subbeams. The lighting system uses either a single ion source with an aperture plate to split one beam in the subbeam, or multiple sources. In systems using a single ion source, the aperture plate is projected (reduced) onto the substrate using a multi-beam light system. The system further uses a deflector of an electrostatic multiples magnetic field system placed after the multi-beam optical system to correct the individual imaging aberrations of the sub-beams and position the sub-beams during writing. This publication does not disclose how each subbeam is modulated. In addition, controlling individual subbeams is a problem and maintains inter-subbeam uniformity.

Japan, Japan Applied Physics (J.Appl.Phys.) Vol. 34, (1995) 6689-6695, multi-electrons with a special ZrO / W-TFE thermal radiation source whose emitter tip is immersed in a magnetic field A beam (probe) lithography system is disclosed. The disadvantage of such sources is the limited output of this. In addition, this source requires a crossover. The mutual homogeneity of the "probe" is not further explained. In addition, the strength of the source is an issue.

The article also refers to a writing strategy in which the steps are generally moved in one direction and the deflector moves the "probe" at the same distance perpendicular to the direction of the step movement at the same time. An additional issue not recognized in this publication is the correction of deflection of electron beamlets from their intended position.

It is an object of the present invention to improve the performance of known electron beam exposure devices.

Another purpose is to improve the resolution of known electron beam exposure equipment.

It is yet another object of the present invention to improve the throughput of known electron beam exposure devices.

Yet another object of the present invention is to overcome problems related to Coulomb interactions and reduction methods in the prior art.

Another object of the present invention is to make it easy to control the uniformity of the beamlet, especially during writing.

The present invention A beamlet generator for generating multiple electron beamlets, A modulation array including a plurality of modulators for receiving the plurality of electron beamlets and modulating the intensity of the electron beamlets. A controller that is operationally connected to the modulation array and uses control signals to individually control the modulator. A regulator that is operationally connected to each modulator and individually adjusts the control signal of each modulator, A convergent electron light system, each comprising an array of electrostatic lenses that converge the corresponding individual beamlets transmitted by the modulation array to a cross section smaller than 300 nm. A target holder for holding a target with an exposed surface thereof, wherein the pattern is transferred on the first convergent surface of the convergent electron light system. The present invention relates to an electron beam exposure apparatus for transferring a pattern onto the surface of a target.

With this device, electronic crossover could be avoided because it does not shrink the complete image (part). In this way, the resolution and writing speed are increased. Moreover, it avoids the need to control the current within each individual beamlet. The device is less complex as it integrates position correction and modulation.

In an embodiment of an electron beam exposure apparatus according to the present invention, the modulation array is A beamlet blanker array with multiple beamlet blankers for deflection of passing electron beamlets, A beamlet stop array having a plurality of openings aligned with the beamlet blanker of the beamlet blanker array. To be equipped.

In this way, it is possible to avoid electron beamlet crossover at one single focus and enable fast modulation. In one embodiment, virtually every beamlet blanker is aligned with the electron beamlet to allow individually modulation of every beamlet. In addition, the beamlet stop array comprises at least one plane of aperture, with virtually any aperture aligned with one beamlet, preferably with an aperture centered with respect to the beamlet. In this way, the beamlet passes through the aperture when the electron beamlet is not deflected, and the beamlet is blocked or stopped when the beamlet is deflected. In this modulation array embodiment, the controller is operatively connected to the beamlet blanker.

In one embodiment, the electron beam exposure apparatus further comprises measuring means for measuring at least one actual position of the beamlet, and the controller is a memory means for storing the actual position and the desired position. And a comparator for comparing the desired position of the beamlet with the actual position, the regulator was measured between the desired position of the electron beamlet and the actual position. It is operationally connected to a controller for receiving instructions to adjust the control signal issued to the modulator to compensate for the difference. By adjusting the control signal in this way, the positioning of the beamlet can be easily corrected. Actual position measurements can be made, for example, as described in US Patent Application Publication No. 5,929,454.

In one embodiment, the controller is operatively connected to the beamlet blanker in one embodiment via a regulator.

In one embodiment, the regulator is operationally connected to the controller to receive an instruction indicating the amount of adjustment. The amount of adjustment can be determined based on the values that result from the comparators described above.

In additional embodiments, the regulator is adapted to individually adjust the timing of each control signal. The correction can be achieved in this very simple way.

In one embodiment of the electron beam exposure apparatus according to the present invention, the beamlet generating means is With a source for emitting at least one electron beam, With at least one beam splitter for splitting the at least one ejected electron beam into the plurality of electron beamlets. To be equipped. In this way, uniform intensity distribution between beamlets is easily achieved if the source ejects uniformly in all relevant directions. In one embodiment, the electron beam exposure apparatus further comprises a second electrostatic lens array located between the beam dividing means and the beamlet blanker array in order to converge the plurality of electron beamlets. In this embodiment, virtually all electrostatic lenses are aligned to allow one electron beamlet to converge. In this additional embodiment, the beamlet blanker array is located on the converging surface of the second electrostatic lens array.

In one embodiment of the electron beam exposure apparatus of the present invention with a beam splitter, the beam splitter comprises a spatial filter, preferably an aperture array. In this way, one source with one beam, or when the source intensity is inadequate, or the intensity varies across the beam, the multiple sources are easily split into multiple beamlets.

When the source intensity is high, the splitting means may include a plurality of contiguous aperture arrays along the path of the electron beam or a plurality of beamlets, the aperture array having openings that are manually aligned, respectively. The next aperture array follows the path from the source or to a target with an aperture smaller than the aperture of this aperture array. This reduces heat loss.

In one embodiment of the aperture array, the apertures of each aperture array are arranged in a six-sided structure, allowing close integration to be obtained.

In an additional embodiment of said electron beam exposure apparatus with a splitting means comprising an aperture array, each aperture of the aperture array has an area inversely proportional to the current density based on the beamlet transmitted through this same aperture.

In an additional embodiment of an electron beam exposure apparatus with a beam splitter, the beam splitter comprises an aperture array, where the aperture size of the aperture array is adapted to produce a discrete set of predetermined beamlet currents.

These embodiments improve the uniformity of the electron beamlet.

In a further embodiment of an electron beam exposure apparatus with a beam splitter, the beam splitter comprises an electrostatic quadrupole lens array.

In one embodiment, the electron beam exposure apparatus according to the present invention comprises a thermal ion source. In one embodiment, the thermal ion source is adapted to operate in a space charge limiting regime. Which is advantageous in this particular application, the space charge is homogenized estuary was found to have a fruit. Further, at certain settings, the spatial electrification may have a negative lens effect.

In additional embodiments using a thermal ion source, the thermal ion electron source has a spherical cathode surface. In embodiments, the thermal ion source comprises at least one extraction electrode. In another embodiment, the extraction electrode is a planar extraction electrode. In this embodiment, the extractor is located after the space charge region and is given a positive voltage to give a negative lens effect. The voltage can be set at a predetermined value to cause a negative lens effect on the emitted electron beam.

In an alternative embodiment, the extraction electrode has a spherical surface with through holes. All these embodiments serve to create a negative lens effect on the electron beam, thus avoiding crossovers in the electron beam.

In another embodiment of the electron beam exposure apparatus of the present invention, the apparatus further comprises a lighting system that converts an electron beam emitted by the source into a parallel electron beam before it reaches the dividing means.

In yet another embodiment of the electron beam exposure apparatus, the beamlet generator comprises an array of sources in which each source is responsible for generating the electron beamlets. In this additional embodiment, the electron beam exposure apparatus comprises a second electrostatic lens array located between the source array and the beamlet blanker array to converge the plurality of electron beamlets.

In one embodiment of an electron beam exposure apparatus with beamlet blanking means, the beamlet blanker comprises an electrostatic deflector.

In yet another embodiment of the electron beam exposure apparatus according to the present invention, it further comprises between the modulation array and a convergent convergent electron light system for deflecting the electron beamlet to scan the target exposed surface. The scanning deflection means provided in the above is provided. In this embodiment, the scanning changing means includes an electrostatic scanning deflector. In this additional embodiment, the electron beam exposure apparatus is transferred with an actuating means for moving the electrostatic scanning deflector in a direction different from the direction of deflection performed by the electrostatic scanning deflector. Further provided with said means for holding the targets relative to each other in the plane of the surface.

In one embodiment, the regulator or time shifter is configured to shift the timing bases of the scanning deflection means and the actuator to each other. In this embodiment, the modulator control signal has a timing base, the target holder actuator has a second timing base, and the timing bases can shift from each other. This can be used, for example, to have a critical component between two beamlets that must be written to the target surface and are written using only one beamlet.

In this additional embodiment, the electron beam exposure apparatus further comprises an additional aperture plate between the modulation array and the convergent electron light system, with the additional aperture plate directed towards the exposed surface of the target and substantially parallel1. The electrostatic scanning deflector has two surfaces and is placed on the side surface of an additional aperture plate facing the exposed surface of the target located between the blanker array and the electrostatic lens array of the convergent electron light system. It is a sex strip. In this other embodiment, the electrostatic scanning deflector is a conductive strip placed on the target exposed surface of any of the lens plates present in the convergent electron light system. In this embodiment, the conductive strips alternately have positive or negative potentials.

In an embodiment of an electron beam exposure apparatus with a blanking electrostatic deflector, these deflectors deflect the electron beamlet such that a predetermined section of the beamlet is stopped by the beamlet stop array.

In an additional embodiment of the electron beam exposure apparatus according to the present invention, it is further between the electrostatic lens array of the convergent electron light system and the protective means to accelerate the electrons in the plurality of transmitted electron beamlets. Equipped with a post-reduction acceleration stage located.

In one embodiment of the controller, it is Comparing the theoretical position of the beamlet with the actual position Adjusting the control signal to compensate for the measured difference between the theoretical position of the electron beamlet and the actual position. Further, a correction means for compensating for the misalignment of the electron beamlet on the target exposed surface is provided.

In one embodiment of the electron beam exposure apparatus according to the present invention, it is further preferably located between the electrostatic lens array of the convergent electron light system and the exposed surface of the target, preferably having an aperture smaller than 20 μm in size. It comprises protective measures to prevent particles released by being collided with electrons to reach any one of an aperture array, a lens array or a blanker array, including an aperture array.

In one embodiment of the electron beam exposure apparatus according to the present invention, all lens arrays, aperture arrays and blanker arrays clean the plates when gas is allowed into the system and all contaminants. Is connected to a power source that produces plasma to remove.

In an additional embodiment, the electron beam exposure apparatus according to the present invention is operated at a high temperature of about 200 ° C. to 600 ° C. for the system to keep the apparatus clean.

The present invention further A beamlet generator for generating multiple electron beamlets, A modulation array including a plurality of modulators for modulating the intensity of the electron beamlets for receiving the plurality of electron beamlets, and a modulation array. A controller that is operationally connected to a modulation array to control the modulator individually using control signals, and A convergent electron light system with an array of electrostatic lenses, each lens focusing on a corresponding individual beamlet, transmitted by the modulation array in a cross section narrower than 300 nm. A target holder for holding the target on this exposed surface, where the pattern is transferred on the first convergent surface of the convergent electron light system, With respect to an electron beam exposure device for transferring a pattern onto the surface of a target comprising There, the beamlet generator comprises at least one thermal ion source, said source comprising at least one extraction electrode adapted to be operated in a space charge limiting region, said source generating an electron beam. The beamlet generator further comprises a beam splitter for splitting the electron beam into a plurality of electron beamlets.

The use of such a particular beamlet generator provides a uniform beamlet with sufficient current to provide high throughput.

In this embodiment, the extraction electrode is located after the space charge region and is given a positive voltage to produce a negative lens effect on the electron beam.

The present invention further relates to an electron beam generator for generating a plurality of electron beamlets, wherein the beamlet generator comprises at least one thermal ion source, the source being operated within a space charge limiting region. The source is configured to generate an electron beam, the beamlet generator further comprises a beam splitter for splitting the electron beam into a plurality of electron beamlets. To be equipped with.

The present invention further provides each modulator with a beamlet generator for generating a plurality of electron beamlets, a plurality of modulators for modulating each electron beamlet, and a control signal having a timing base. With respect to an electron beam exposure apparatus for transferring a pattern onto the surface of a target comprising the controller, wherein the controller is adapted to individually adjust the timing base of the control signal with respect to other control signals.

In this device, the problem of positioning and modulation is solved in a very simple and precise way, reducing the number of components and providing a robust device.

The present invention further relates to a method for transferring a pattern onto a target exposed surface using an electron beam using the electron beam exposure apparatus described above, and a wafer processed using the apparatus of the present invention. Regarding. The device can also be used for the production of masks, such as those used in state-of-the-art optical lithography systems.

<figref num="1">It is a figure which shows the apparatus according to this invention.</figref><figref num="2A">It is a figure which shows the detail of the known electron beam exposure apparatus.</figref><figref num="2B">It is a figure which shows the detail of an electron beam exposure apparatus.</figref><figref num="3">It is a figure which shows the electron source with a spherical outer surface.</figref><figref num="3A">It is a figure which shows the source which has a space charge region.</figref><figref num="4">It is a figure which shows the embodiment of the electron beam exposure apparatus which starts from a beamlet.</figref><figref num="5A">It is a figure which shows the embodiment of the scan deflection array of this invention.</figref><figref num="5B">It is a figure which shows the embodiment of the scan deflection array of this invention.</figref><figref num="6A">It is a figure which shows the scanning locus of this invention.</figref><figref num="6B">It is a figure which shows the scanning locus of this invention.</figref><figref num="7A">(A) and (B) are diagrams showing the adjustment of the modulation timing.</figref><figref num="7B">(C) and (D) are diagrams showing the adjustment of the modulation timing.</figref><figref num="8A">It is a figure which shows the influence of the adjustment of a modulation timing.</figref><figref num="8B">It is a figure which shows the influence of the adjustment of a modulation timing.</figref>

The present invention will be further described in the following embodiments of the electron beam exposure apparatus according to the present invention.

Embodiments of the present invention are schematically shown in FIG. Electrons are emitted from a single stable electron source 1. The lighting system converges and parallelizes the emitted electron beam 5 to uniformly illuminate the desired area on the aperture plate 6. This can be established, for example, by using lenses 3 and 4. Due to the aperture plate 6, the electron beam 5 is divided into a plurality of electron beamlets (small electron beams), of which two electron beamlets 5a and 5b are shown. An alternative method for producing multiple electron beamlets is to use an array of electron sources. Each electron source produces an electron beamlet that is modulated in the same way as that produced using a single source and a combination of dividing means. Single source 1 with beam splitter 6 is preferred because the emission characteristics of each source are slightly different. The array of electrostatic lenses 7 converges each beamlet to the desired diameter. The beamlet blanker array 8 is arranged so that each individual beamlet coincides with the opening in the plate of the beamlet blanker array 8. The beamlet blanker array 8 includes a beamlet blanker such as a blanking electrostatic deflector. When a voltage is applied to the blanking deflector, an electric field across the corresponding aperture is established. The passing electron beamlet, for example the beamlet 9, deflects the beamlet stop array 10 located behind the beamlet blanker array 8 that follows the trajectory of the electron beamlet and stops at the beamlet stop array 10. In the absence of voltage applied to the blanking deflector, the electron beamlet passes through the beamlet stop array 10 to reach a convergent electron light system with an array 13 of electrostatic lenses. The array 13 individually converges each of the transmitted beamlets 12 on the target exposed surface 14. Finally, scanning deflection means, which are mostly electrostatic scanning deflectors, move the beamlets together in one direction on the target exposed surface 14. Implementation shown in Figure 1 In the embodiment, the scan deflector is located on the target exposed surface side surface 11a of the beamlet stop array 10 and thus forms an additional scan deflection array 11. However, other locations are possible. During scanning, the target exposed surface 14 and the scanning deflector move relative to each other in a direction different from the scanning deflection direction. Usually, the target is a mask covered with a wafer or resist layer.

A notable aspect of the configuration shown in FIG. 1 is that the entire image produced by the combination of the beamlet blanker array 8 and the beamlet stop array 10 is not reduced as a whole. Instead, each individual beamlet converges individually to the target exposed surface 14 by the convergent electron light system 13. The differences between these two methods are shown in Figures 2A and 2B. In FIG. 2A, the entire image with the two electron beamlets 5a, 5b is reduced to obtain the desired resolution. Shrinking an image requires at least one intersection X. At this intersection, all electrons pass through a small area. Coulomb interaction exacerbates the resolution at this intersection X.

In the present invention, the method shown in FIG. 2B is used. Consider two adjacent beamlets 5a and 5b projected onto the target exposed surface 14. When the reduction technique is used, the distance between the two beamlets is reduced. However, the convergence method of the present invention does not change this distance between the two beamlets. Only the cross section of each beamlet is reduced.

The electron source 1 in Figure 1 typically has an area of about 30 to 300 square microns to 100 A / cm.²To transmit. In one embodiment, a thermal ion source is used. Electrons are emitted in a space charge limiting emission regime, preferably to benefit from the effects of space charge homogenization. An example of such a source is LaB₆A dispenser sauce with crystals, barium oxide, or a layer of barium or tungsten covered with scandium oxide.

The extraction electrode 2 usually, but not necessarily, converges the beam. Illumination lenses 3 and 4 generate a parallel electron beam 5 on the aperture array 6. Lenses 3 and 4 are optimized to limit beam energy diffusion as a result of Coulomb interaction. That is, the aperture angle of the beam is made as large as possible. In addition, lenses 3 and 4 are optimized to limit the blurring of the beam caused by the effects of chromatic aberration and spherical aberration. In the latter case, it may be advantageous to use the aperture array 6 as the lens electrode because it causes negative chromatic aberration and spherical aberration, which results in compensation for the aberrations of the lenses 3 and 4. In addition, it is also possible to use the lens 4 by slightly focusing (focusing) or shifting it (defocasing) for magnifying the pattern.

However, in such an embodiment, the electron beam emanating from a single emitter is focused in a small crossover x before being magnified. Within this crossover x, there is a large energy diffusion due to the electron-electron interaction at this crossover x. Eventually, the crossover x is imaged and reduced at the target exposed surface. Due to Coulomb interaction, the desired resolution is not achieved. Therefore, a method for magnifying and parallelizing the magnified beam without crossover is desirable.

In the first embodiment illustrated in FIG. 3, the crossover in the illuminated electron optics system is avoided by using the electron source 1 on the spherical or hemispherical outer surface 15. In this configuration, a large aperture angle α is formed, reducing haze due to electron-electron interactions within the ejected electron beam 5. In addition, the electron beam forms a spherical wave surface, creating a virtual crossover 16 located in the center of the source. There are no electrons present in the virtual crossover, so there are no disturbing electron-electron interactions.

Electrons can be extracted using a spherical extractor with large holes. The main advantage of the spherical shape of the extractor is the more homogeneous field created.

In the alternative embodiment illustrated in FIG. 3A, crossover is avoided by extracting electrons from the source / cathode 1 at voltage V and having a distant planar extractor 11. The planar extractor has a positive voltage + V with respect to source 1.₁Have. Here, the combination of the source and the extraction device functions as a negative lens. Extractor 1₁The extracted electrons passing through the are expanded due to the branching electric field. Again, virtual crossover occurs, reducing a significant range of resolution losses due to Coulomb interaction. Source 1 and extractor 1 as shown in Figure 3.₁There is a space charge region S between them. The presence of this space charge improves the negative lens effect caused by the source-extractor combination.

V₁It is possible to operate Source 1 in this space charge limited emission mode by adjusting. The main advantage of this emission mode is the significant increase in emission homogeneity. The increase in total current can be limited by selecting a source in a limited emission area.

The aperture array 6 has a plurality of openings with a diameter of 5 to 150 μm, typically with a pitch of about 50 to 500 μm. These openings are preferably arranged in a hexagonal pattern. The aperture array 6 typically splits the incident parallel electron beam 5 into multiple electron beamlets on the order of about 5,000 to 30,000. The size of these apertures is adjusted to compensate for the non-uniform current density of the illumination. Each aperture has an area that is inversely proportional to the current density based on the individual beamlets transmitted through this same aperture. As a result, the current in each individual beamlet is the same. If the heat load on the aperture plate becomes too great, the aperture arrays will be arranged in succession and the aperture diameter will decrease along the path of the electron beam or electron beamlets. These aperture arrays have apertures that are aligned with each other.

Another possible way to split the electron beam 5 collimated into multiple electron beamlets is to use a quadrupole lens array. A possible configuration of such an array is disclosed in US No. 6,333,508 referred to herein as if this document were fully stated.

FIG. 4 shows a detailed, closer image of the lithography system in one of the embodiments of the invention starting with multiple beamlets. The condenser lens array 7 converges each beamlet to a diameter of approximately 0.1 to 1 μm. It has two plates aligned with the holes. The thickness of the plate is usually 10 to 500 μm. These holes are typically 50-500 μm pitched and about 50-200 μm in diameter. Insulators (not shown) shielded from the beamlets support the plates at a typical distance of 1 to 10 millimeters from each other.

The modulation array includes a beamlet blanker array 8 and a beamlet stop array 10. In this beamlet blanker array 8, the typical transverse energy is about 1 to 20 meV, while the typical beam diameter is 0.1 to 5 μm. Beamlet blanking means 17 is used to turn the electron beamlet on and off. They have a blanking electrostatic deflector with a plurality of electrodes. Preferably, at least one electrode is grounded. Another electrode is connected to the circuit. Through this circuit, control data is transmitted towards the blanking electrostatic deflector. In this way, each blanking deflector can be controlled individually. When the beamlet blanking means 17 is not used, the electron beamlet passes through the beamlet stop array 10 through the aperture. When a voltage is applied to the blanking electrostatic deflector electrode in the beamlet blanker array 8, the corresponding electron beamlet is deflected into the beamlet stop array 10.

In one embodiment, the beamlet blanker array 8 is located on the electrostatic convergence surface of the electron beamlet. With the blanker array in this position, the system is less sensitive to distortion. In this embodiment, the beamlet stop array is located outside the convergence plane of the electron beamlet.

The transmitted beamlet is here converged on the target exposed surface 14. This is done by a convergent electron light system 13 with at least one array with electrostatic lenses. The individually transmitted electron beamlets are converged on the target exposed surface by the corresponding electrostatic lens. The lens array comprises two or more plates 13a, 13b, both having an aperture of about 10-500 μm and an aperture 13c with a diameter of about 50-250 μm. The distance between two continuous plates is somewhere between 50 μm and 800 μm and can vary from plate to plate. If desired, the convergent electron light system may also include a magnetic lens array. As a result, it is located between the beamlet stop array 10 and the electrostatic objective lens array 13 to further enhance the convergence characteristics of the electron light system.

A major problem in all electron beam lithography systems that pattern wafers or masks is contamination. It significantly reduces the performance of the lithography system due to the interaction between the electrons and particles in the resist layer, and the resist deteriorates. In polymerized resists, the molecules are released due to cracks. The released resist particles move through a vacuum and can be absorbed by any of the structures present in the system.

To address the pollution problem, in certain embodiments, the protective means is located close to the target exposed surface, i.e. between the target exposed surface and the convergent electron light system. The protective means may be a foil or a plate. Both of these options have openings with diameters smaller than 20 μm. The protective means also absorbs the released resist particles before they reach any of the sensitive elements in the lithography system. In some cases, it is necessary to renew the protective measures after a predetermined period of time, for example after any processed wafer or mask. In the case of a protective plate, the entire plate can be replaced. In certain embodiments, the foil is wound around a coil winding machine. A small portion of the foil is tightened just above the entire target exposed surface 14. This area is exposed to contaminants. After a period of time, the protective capacity of the foil deteriorates rapidly due to the absorbed particles. The exposed foil portion needs to be replaced next. To do this, the foil is transported from one coil winding machine to the other coil winding machine, thus exposing new foil portions to contaminated particles.

The entire system described above operates at relatively low voltages. For operations that require high energy electrons, an additional acceleration stage is placed between the electrostatic lens array of the convergent electron light system 13 and the protective means. This acceleration stage adds energy to the passing electrons. The beam may be accelerated by an additional tens of kiloelectronvolts, eg 50 keV.

As described above in FIG. 1, the beamlet 12 that has successfully passed through the beamlet stop array 10 is directed to a desired position on the target exposed surface 14 by two means. The first of all actuating means moves towards the target exposed surface 14 and the rest of the system in a particular machine scanning direction. Second, the scanning deflection means scans the electrostatically transmitted beamlet 12 in a direction different from the mechanical scanning direction. The scan deflection means includes an electrostatic scan deflector 18. In FIGS. 1 and 3, these scan deflectors 18 are located on an additional aperture array 11 and are depicted in FIG.

In one embodiment, the electrostatic scanning deflector 18 is placed on the target exposed surface side of one of the plates of the objective electrostatic lens array 13, so that the deflection is inherently generated at the front converging surface of the objective lens. The desired result is that the deflected beamlet collides perpendicularly with the target surface.

In another embodiment, there are two deflector arrays, one deflecting in the first direction and the other deflecting in the second opposite direction. The combination of the deflections results in a dislocation of the beamlet at the target plane position without changing the vertical axis of the beamlet with respect to the target plane.

In the second embodiment, the electrostatic scanning deflector 18 is located in the positive means.

The electrostatic scanning deflector 18 comprises scanning deflection electrodes that are configured to deflect the assembly of electron beamlets in the same direction. The scanning deflection electrode may be placed in the form of a strip 19 on a suitable plate 20 on the side of the target exposed surface, as illustrated in FIG. 5A. This causes d when strip 19 is placed near the beamlet and thus near opening 21._b-sdIs reduced, so the highest yield can be established. Further, it is preferable to arrange the scanning deflection electrodes outside the individual beamlet crossover planes.

In one embodiment, by applying an AC voltage over the continuous strip 19 as illustrated in FIG. 5B, the next assembly is scanned in the opposite direction, while the first assembly is scanned in one direction. The first strip has a positive potential, for example, the second strip has a negative potential, the next strip has a positive potential, and so on. For example, the scanning direction is indicated by y. As a result, at the same time, the next line is directed to + y, but one line of the transmitted electron beamlet is scanned in the y direction.

As already mentioned, there are two scanning directions, the mechanical scanning direction M and the deflection scanning direction S, both shown in FIGS. 6A and 6B. Mechanical scanning can be performed in three ways. That is, the target exposed surface moves, the rest of the system moves, or both move in different directions. Deflection scans are performed in a different direction than mechanical scans. This is because the deflection scanning angle α with the same scanning deflection length Δx_sdIn the case of, it is preferable that it is perpendicular to or substantially perpendicular to the mechanical scanning direction because it becomes larger. For clarity, there are two preferred scan trajectories, both illustrated in FIG. The first scanning locus is a triangular scanning locus (FIG. 6A), and the second locus is a sawtooth-shaped scanning locus (FIG. 6B).

When mechanical scan length is a throughput limiting factor, the assembly of electron beam exposure equipment as described above is used to simultaneously expose the entire wafer.

It is assumed that an ideal grid exists on the wafer and the electron beamlets can be accurately positioned on the grid coordinates. For example, the correct pattern is created when the electron beamlet can be placed within 1 / 30th of the minimum feature size. Then to write one pixel, 30 scan lines, and therefore 30^*30 = 900 grid points are required. For 45 mm mode, positioning must be adjustable within the range of 1.5 nm. Therefore, the data path must be able to handle huge amounts of data.

The write strategy described above is based on the assumption that the beamlet can be turned on or off. Reducing the amount of data with fewer grid lines and therefore fewer grid cells is considered a logical approach. However, the control of the desired pattern dimensions is significantly worse. A technique to avoid this problem is to pattern the target exposed surface 14 using individual dose management. Again, the pattern is divided according to the rectangular grid. However, the number of grid lines is much smaller, for example 2 to 5 per dimension, resulting in a grid point number of about 4 to 25. The strength of each grid cell is variable in order to obtain the same pattern reliability as for finer grids. Intensity is represented by the so-called grayscale value. In the case of 3-bit gray value representation, the values are 0, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7 and 1 x maximum dose. Each cell is further represented with multiple pieces of information due to controlled dose changes, but the number of data required for the location of the beamlet is reduced.

In the present invention, grayscale writing can be introduced in a plurality of ways. A portion of the beam continues to move towards the target exposed surface 14, but the first of all deflections of the beam may be controlled so that the portion of the beam passes through the beamlet stop array 10. In this way, for example, 1/3 or 2/3 of the beam can be stopped, resulting in 4 doses on the target exposed surface, ie 0, 1/3, corresponding to the 2-bit gray value representation. Produces 2/3 and 1 × maximum dose.

Another way to produce gray levels is to deflect the beamlets so that they do not move relative to the target surface for a given time T, which time T is the minimum on / of blanker. Longer than off time. During time T, the modulator can now place 1, 2, 3 etc. shots in one position, thus creating gray levels.

Another way to create these four so-called gray values is to change the aperture size of the aperture array 6. For example, if there are three aperture sizes, the original size, a size that allows half of the original current to pass, and an area that allows only a quarter of the original current to pass, as described above. The same individual dose values as were created are created. The desired dose can be adhered to the target exposed surface 14 by switching the beamlet on and off using the deflection electrode 17 of the beamlet blanker array 8. The disadvantage of the latter method is the fact that more beamlets are needed to write a single pixel. Most, including the methods described above for individual dose control, can also be used to create more than four gray values, eg S, 16, 32 or 64.

The position of the beamlet on the target exposed surface does not correspond exactly to the desired position in most cases. This is, for example, for the alignment of various arrays with respect to each other. In addition, manufacturing errors may also contribute to the deviation of individual beamlets. Corrections must be made to transfer the correct pattern from the controller to the exposed surface of the target. For this purpose, in certain embodiments, firstly, the positions of all beamlets are measured and stored. Each position is then compared to the position that the beamlet will do. These positional differences are then integrated into the pattern information transmitted to the modulation means.

Since it takes a considerable amount of time to change the signal sequence transmitted towards the modulation means, the measured difference in position is included in the pattern information by transforming it into the corresponding difference in timing in beamlet modulation control. Will be integrated. 7A and 7B and 8A and 8B illustrate how adjustments are achieved. As already mentioned, beamlet scanning is performed by combining two scanning mechanisms: mechanical scanning and deflection scanning. All pattern data transmitted to each beamlet is applied for each deflection scan line. Desired deflection scan width W of the exposed surface of the patterned target_scanIs a deflection scan width W that can be processed by the device, as illustrated in FIGS. 7A (A) and (B)._overscanSmaller. The overscan capability allows correction in the deflected scanning direction. In (A) of FIG. 7A, the beamlets are placed correctly. However, in FIG. 7A (B), the beamlet has moved to the right. The deviation can be compensated by adjusting the timing so that the pattern data is applied when the beamlet enters the desired region. The mechanical scan direction adjustment is less accurate than shown in FIG. 7A (B). Since pattern data is written for each scan line, only discrete-time delay is possible. That is, pattern generation can be postponed or accelerated for each scan line. Random time delays will give rise to completely new control data sequences. Calculation of such a new sequence takes a considerable amount of time and is not desirable. (C) and (D) of FIG. 7B show what the result will be. In FIG. 7B (C), again, the desired position of the beamlet is shown with its first five corresponding scan lines. FIG. 7B (D) shows the actual position of the beamlet and its trajectory. For clarity, the desired beamlets and scan lines are also drawn using empty circles and dashed lines, respectively. It can be seen that the first scan line in the desired situation does not cover the area that needs to be patterned by the beamlet. Therefore, the beamlet begins patterning in the middle of the second scan line. In effect, the delay in information takes the time required to scan a single deflected scan line.

Figures 8A and 8B show examples of how timing changes are not ideal and correct for early mispositions of structures written by positioned beamlets. Figure 8A depicts a situation where timing correction is not performed. The filled points represent the actual position of the beamlet, while the empty points represent the beamlet in the correct position. The beamlet is scanned along the lines drawn to write the pattern. The line is a dashed line in the ideal case, but a solid line in the real case. In this example, the written structure is a single line. Consider the black and white writing strategy, that is, the beamlet is "on" or "off". The pattern is written when the "on" signal is transmitted towards the modulation means. To write a single line, a particular signal sequence, such as the sequence shown in the upper curve, is transmitted towards the modulation means. When the same signal sequence is actually transmitted, the lines are written at different positions than desired. The deviation of the beamlet leads to the deviation of the structure to be written.

FIG. 8B shows the situation where the timing correction is applied. Again, theoretical and real points and trajectories are drawn using dashed lines and practices and points, respectively. The signal sequence in the real situation is theoretically transmitted in the fact that the signal sequence in the real situation (lower curve) is transmitted at a different time than the same sequence is transmitted in the ideal configuration (upper curve). It is different from the pattern information of. As a result, a single line is now written in the correct location in the deflection scan direction. In addition, patterning starts one scan line faster, resulting in even better positioning of a single line in the mechanical scan direction. This is due to the slight deviation between the scan line in the ideal situation and the scan line in the real situation.

Therefore, current electron beam exposure systems can dynamically adjust the position of scanned lines using timing correction. This allows the critical components in the pattern to be written to one scan line instead of using two halves of the two scan lines that would spread the critical components on the two scan lines. .. This correction can also be made locally. That is, the timing can be corrected in a small time window. Therefore, the controller needs to identify the critical components that are normally diffused by the two scan lines. After that, the controller needs to calculate the corrected timing window and apply the corrected timing window to the timing base used to scan the electron beamlet. (D) in Figure 7B shows the adjustment principles that could be used for this purpose.

All lens plates, aperture plates and blanker plates can be connected to a power source that produces plasma as the gas enters the system. The plasma cleans the plate and removes all contamination. If one plasma does not clean enough, two gases may be introduced into the system in succession. For example, oxygen may be added first to remove all hydrocarbons remaining in the system. After removal of the oxygen plasma, a second plasma, for example with HF, is created to remove all existing oxides.

Another possibility of reducing pollution is to perform all operations at high temperatures, that is, at 150-400 ° C. Pretreatment at 1000 ° C to 1500 ° C may be required. At these temperatures, hydrocarbons do not have a probability of condensing with any of the elements in the system. A small amount of oxygen can get into the system to further improve the cleaning process.

It should be understood that the description is included to illustrate the operation of preferred embodiments and is not intended to limit the scope of the invention. The scope of the invention should be limited only by the following claims. From the above description, many modifications that will be embraced by the spirit and scope of the present invention will be apparent to those skilled in the art.

1 ... Source, 2 ... Extraction Electrode, 3 ... Lens, 4 ... Lens, 5 ... Electron Beam, 5 ... Parallel Electron Beam, 5a ... Beamlet, 5b .. .Beamlet, 6 ... Aperture Array, 8 ... Beamlet Blanker Array, 9 ... Beamlet, 10 ... Beamlet Stop Array, 11 ... Aperture Array, 12 ... Beamlet, 13 ... Convergent Electron Optical System, 13a ... Plate, 13b ... Plate, 13c ... Aperture, 14 ... Target Exposed Surface, 15 ... Outer Surface, 16 ... Virtual Crossover, 17 ... deflection electrodes, 18 ... scanning deflectors, 19 ... strips, 20 ... plates, 21 ... openings.