Ceramic showerhead with embedded rf electrode for capacitively coupled plasma reactor and substrate processing system using the same

[Cross-reference to related applications]

The present application claims the benefit under US Provisional Patent Application No. 61 / 770,894 filed February 28, 2013, in which the entire disclosure of the application is incorporated herein by reference.

The present disclosure relates to substrate processing systems, in particular to showerheads for substrate processing systems.

The description of the background art provided herein is for the purpose of schematically presenting the background of the present disclosure. The work of the inventor named herein, to the extent described in this background art, with respect to the present disclosure, both expressly and implicitly, with aspects described that would not normally be considered as prior art at the time of filing. Not recognized as a prior art.

Substrate processing systems typically include a processing chamber with one or more reaction spaces. The platform is usually placed in the reaction space. Substrates such as semiconductor wafers are placed on a mounting table. One or more processing gases can be fed into the reaction space using a shower head and the plasma can be ignited in the reaction space. A thin film such as a dielectric layer is formed on the substrate.

Shower heads can be utilized in capacitively coupled plasma (CCP) reactors. The shower head drives the plasma by acting as a radio frequency (RF) electrode while distributing the processing gas throughout the substrate. Shower heads are usually made from metallic materials. The metal electrodes substantially reduce or eliminate the electric field in the gas plenum of the shower head, preventing plasma formation and premature activation of the gas in the shower head.

Shower heads for CCP reactors are usually made of aluminum and have a face plate welded to the body. The showerhead faceplate typically has a plurality of spaced gas holes to provide uniform gas distribution over the exposed surface of the substrate. RF voltage can be applied to the shower head, another electrode (such as a mount), or both.

Aluminum shower heads are compatible with many treatment agents (or gas compositions). However, aluminum is incompatible with processing gases that leach elements from metal surfaces. In particular, chlorine-based chemicals tend to leach aluminum at operating temperatures above 300 ° C. As a result of chemical erosion of the shower head on the metal surface by the chlorine-containing gas, the metal material can be deposited on the substrate as a thin film. This is often detrimental to device processing on the substrate. For example, in some examples, the metallic material is a dopant that can impair the operation of the integrated device.

Unwanted metal contamination can also occur during cleaning of the processing chamber. Since fluorine atoms are commonly used for cleaning, the faceplate (the hottest region of the showerhead) reacts with fluorine to form aluminum fluoride. As the thickness of aluminum fluoride increases over time, the properties of the showerhead surface (eg, roughness, conductivity, and emissivity) change. As a result, the risk of particle contamination increases due to the variation in the vapor deposition process.

Also, the structure (design) of the shower head does not allow cleaning of the inside of the (welded) shower head when the shower head is installed in the processing chamber. In extreme cases, fluorination of the aluminum surface in the gas holes of the faceplate can change the diameter of the holes and change the uniformity of the gas flow.

Some metal materials, such as aluminum, soften at high temperatures (400 ° C and above), which can cause the showerhead faceplate to begin to hang down. This can change the gas flow and plasma density distribution.

The showerhead assembly for the substrate processing system includes a back plate that is coupled to the gas flow path. The front plate is joined adjacent to the first surface of the back plate and has a gas diffusion surface. Electrodes are located in one of the back and front plates and are connected to one or more conductors. A gas plenum is defined between the back plate and the front plate and communicates with the gas flow path. The back plate and front plate are made of non-metallic material.

In another feature, the stem is coupled to the back plate, defining the gas flow path. One or more conductors penetrate the stem.

In another feature, the gas diffusing surface of the front plate is provided with spaced holes, the gas diffusing surface of the front plate is provided with perforations, or the gas diffusing surface of the front plate is porous.

In another feature, the plasma suppression structure is located adjacent to the second surface of the back plate. The first surface of the back plate is the opposite surface of the second surface of the back plate.

In another feature, the plasma suppression structure comprises N plates that are spaced apart and arranged parallel to each other. N is an integer greater than or equal to 2, and the N plates are made of a dielectric material.

In another feature, the plasma suppression structure comprises a collar extending from one of the N plates towards the top surface of the processing chamber of the substrate processing system. The collar consists of a dielectric material.

In other features, N is greater than or equal to 3 and the N plates are evenly spaced. N is greater than or equal to 3, and at least part of the N plates is unevenly spaced. At least one of the N plates has multiple perforations. At least one of the N plates has a serrated surface. The stem, back plate, and front plate are made of ceramic material. The stem, back plate, and front plate consist of at least one of aluminum nitride and aluminum oxide.

In another feature, the front plate is coupled to the back plate so as to maintain a seal between the front plate and the back plate while allowing lateral movement of the front plate with respect to the back plate.

In another feature, the baffle is located between the gas flow path and the gas plenum. The collar couples the stem to the top surface of the substrate processing chamber. The back plate is attached to the front plate using fasteners. The height dimension of the gas plenum is less than twice the expected plasma sheath thickness. The first dimension between the electrode and the first surface of the back plate is smaller than the second dimension between the electrode and the second surface of the back plate. The first surface of the back plate is the opposite surface of the second surface of the back plate. The electrodes are disk-shaped.

In another feature, the substrate processing system comprises a processing chamber that includes a reaction space. The shower head assembly is placed in the reaction space. A mounting table is arranged adjacent to the faceplate in the reaction space.

In another feature, a radio frequency (RF) circuit is configured to feed an RF signal with a frequency greater than 1 MHz to one or more conductors. The controller is configured to control the processing gas flowing through the gas flow path and the operation of the RF circuit.

In another feature, one or more conductors include a cylindrical conductor that surrounds the gas flow path.

The detailed description, claims, and drawings reveal additional areas to which this disclosure can be applied. The detailed description and specific examples are for illustration purposes only and are not intended to limit the scope of the present disclosure.

The present disclosure can be more fully understood from the detailed description and the accompanying drawings described below.

<figref num="1A">A functional block diagram and a schematic cross-sectional view showing an example of a substrate processing system according to the present disclosure.</figref><figref num="1B">A functional block diagram and a schematic cross-sectional view showing an example of a substrate processing system according to the present disclosure.</figref>

<figref num="2A">Partial sectional view showing a part of an example of a shower head according to the present disclosure.</figref><figref num="2B">Partial sectional view showing a part of an example of a shower head according to the present disclosure.</figref>

<figref num="3">The figure which shows an example of the non-uniform spacing between plates of a plasma suppression structure.</figref>

<figref num="4">The figure which shows an example of the wavy surface in the plate of the plasma suppression structure.</figref>

<figref num="5">The figure which shows an example of the perforated plate of the plasma suppression structure.</figref>

The same reference numerals may be used in the drawings to identify similar and / or identical elements.

1A, 1B, 2A, and 2B show examples of shower heads 10 according to the present disclosure. In FIG. 1A, the shower head 10 includes a back plate 20, a stem 24, and a front plate 30. In some examples, the back plate 20, stem 24, and front plate 30 of the shower head 10 are made of a non-metallic material such as a ceramic material (manufactured using, made of a non-metallic material). Although the stem 24 is shown, the stem 24 may be omitted and the back plate can be placed, adjacent, and / or fitted on the surface of the processing chamber (FIG. 1B). In some examples, the ceramic material is aluminum nitride (AlN), aluminum oxide (Al).₂O₃), Or other suitable ceramic materials.

In some examples, the back plate 20 comprises a substantially flat disc. The stem 24 is coupled to the back plate 20. In some examples, the stem 24 is cylindrical and the axis of the stem 24 is joined perpendicular to the plane containing the back plate 20. For example, the stem 24 and the back plate 20 may be fixed and joined using diffusion bonding or brazing. Alternatively, the stem 24 and the back plate 20 may be detachably joined by fasteners, male and female connectors, or otherwise.

The stem 24 defines a gas flow path 34 that extends axially through the stem 24. Gas flows through the gas flow path 34 onto a baffle 38 optionally provided and into a gas plenum 32 defined between the back plate 20 and the front plate 30. One or both of the back plate 20 and the front plate 30 may include a recess 36 for defining the height of the gas plenum 32.

The faceplate 30 defines a gas diffusion surface 41 that acts as a gas diffuser between the gas plenum 32 and the reaction space 44. The gas diffusion surface 41 may be perforated, have holes, be porous, and the like. For example, in FIG. 1A, the processing gas in the gas plenum 32 can flow into the reaction space 44 through the spaced holes 42 of the front plate 30. The separated holes 42 distribute the processing gas relatively uniformly over the exposed surface of the substrate 46 arranged on the mounting table 48.

The radio frequency (RF) electrode 50 is embedded in either the back plate 20 (FIGS. 1 and 2A) or the front plate 30 (FIG. 2B). One or more conductors or rods 54 penetrate a portion of the stem 24 and the back plate 20. The conductor 54 is in electrical contact with the RF electrode 50. In some examples, four conductors 54 are used, but more or less conductors 54 may be used. The electric field along the gas flow path 34 decreases as the number of rods increases. In some examples, the conductor 54 is cylindrical and surrounds the gas flow path 34. One or more conductors 54 may be connected to an RF voltage or may be connected to a reference potential (such as ground) when the showerhead 10 is configured as a ground electrode.

The shower head 10 includes a plasma suppression structure 60 disposed between the top surface of the back plate 20 and the top surface of the processing chamber to reduce or eliminate parasitic discharges driven through the back plate 20. In some examples, the plasma suppression structure 60 may be manufactured in accordance with US Patent Application No. 13 / 303,386 "MECHANICAL SUPPRESSION OF PARASITIC PLASMA IN SUBSTRATE PROCESSING CHAMBER" filed November 23, 2011 by the same applicant. The application is incorporated herein by reference in its entirety.

The stem 24 may be attached to the collar 80. The collar 80 may then be attached to the top surface of the processing chamber. The collar 80 may include a stem 85 and a flange 86 that extends radially outward from the stem 85 adjacent to the top of the collar 80. The collar 80 may be made of a dielectric (insulating) material and may have dimensions (ie, thickness or height) that minimize capacitive coupling to ground. A valve 90 and a pump 92 may be used to evacuate the reaction space 44.

The front plate 30 is attached to the back plate 20 to provide a gas seal while allowing some relative lateral movement to and from the back plate 20 due to differences in thermal expansion. As used herein, lateral motion is motion parallel to the plane containing the faceplate. In other words, the front plate 30 is attached to the back plate 20 so that it can thermally expand without transmitting stress to the back plate 20 and at the same time seal the gas / vapor in the gas plenum 32.

As best seen in FIG. 2A, in some examples, the edges of the back plate 20 and front plate 30 are joined using fasteners 64. In some examples, the fastener 64 comprises a screw 66 pre-loaded with a washer 67. The screw 66 may be rotated until a predetermined torque is applied to maintain contact between the front plate 30 and the back plate 20. In some examples, the fastener 64 may be a stepped screw and the washer 67 may be a spring washer. The stepped screw applies a given pressure to the spring washer to create a given load. In some examples, the front plate 30 of the shower head 10 can be replaced by removing the fastener 64, installing a new front plate, and reattaching the fastener 64.

In some examples, the spaced holes 42 of the faceplate 30 have a diameter in the range of 0.02 inches to 0.06 inches to prevent plasma ignition inside the separated holes 42. The spaced holes 42 of the faceplate 30 can be arranged in various patterns to optimize the properties of the thin film on the wafer. The number of spaced holes 42 may range from 50 to 6000, but more or less holes may be used. The diameters of the spaced holes 42 may be the same for a given face plate, or two or more different sizes may be used for a given face plate.

In some examples, the RF electrode 50 embedded in the back plate 20 is disc-shaped and has a first CTE comparable to the second coefficient of thermal expansion (CTE) of the material used for the shower head 10. It consists of a metal that has. As can be seen from FIG. 2B, the electrode 50 can be located within the faceplate 30. As can be seen, the electrodes 50 are patterned to correspond to the pattern of the spaced holes 42. The RF electrode 50 in the back plate 20 or front plate 30 allows the high frequency RF to pass through the gas plenum 32 of the shower head 10 without ignition.

As can be seen from FIG. 2A, in some examples, the RF electrode 50 is placed as close as possible to the underside of the back plate 20 facing the substrate to improve power coupling (dimension d in FIG. 2A).₂). In some examples, dimension d₁Is the dimension d₂Greater than The conductor 54 is embedded in the wall of the stem 24 to connect the RF electrode 50 to the RF circuit 70. In some examples, the conductor 54 is configured to minimize the electric field along the flow path for introducing the gas. The face plate 30 has any suitable thickness (dimension d)₄) May have.

If the RF electrode 50 is embedded in the back plate 20, the electric field driving the discharge must pass through the gas plenum 32 and the front plate 30. In some examples, the height of the gas plenum (dimension d in Figure 2A)₃) Is less than twice the expected plasma sheath thickness. By using this approach, the parasitic plasma discharge cannot be reliably maintained. In some examples, dimension d₃Is less than 1/8 inch (3.175 mm) to avoid the condition of maintaining parasitic plasma inside the gas plenum 32 and to minimize the voltage drop across the gas plenum 32.

As best seen in FIG. 1A, suppression of parasitic discharges on the back or top of the shower head 10 may be performed using the plasma suppression structure 60 when the RF electrode 50 is embedded within the back plate 20. In some examples, the plasma suppression structure 60 comprises two or more spaced plates 100-1, 100-2, ..., And 100-N (collectively plate 100), where. N is an integer greater than or equal to 2. In some examples, N is equal to 5, but more or less plate 100 may be used. In some examples, the plate 100 consists of a ceramic material or any other suitable dielectric material. The spacing between the plates 100 is optimized to prevent spontaneous discharge between the plates 100 and to significantly reduce the voltage within the plasma suppression structure 60 so that parasitic discharges cannot be maintained behind the plasma suppression structure 60. Will be done. One or more spacers 102 may be provided to define the spacing of the plates 100 of the plasma suppression structure 60. Also, the collar 110 may be provided above the top plate 100 (100-5 in the example of FIG. 1A) and around the stem 85 of the collar 80. The collar 110 may be made of a dielectric material.

The controller 120 may be connected to one or more sensors 124, which may be located both inside and outside the processing chamber. Sensor 124 detects system operating conditions and may include pressure sensors, temperature sensors, and / or other sensors. The controller 120 selectively supplies the processing gas from the gas source 126 to the gas flow path 34 using one or more mass flow controllers (MFC) 128 and a valve 130.

In some examples, the RF electrode 50 is connected to the RF circuit 70, which provides high frequency excitation. In some examples, the high frequency excitation is above 1 MHz. A laminate of ceramic materials and gas plenum 32 form a capacitive structure that increases the discharge impedance. As the excitation frequency increases, the impedance decreases. In order to provide efficient operation of the shower head 10, it is preferable that most of the supplied power is consumed by the discharge above the substrate. The plasma behind the shower head 10 is considered to be parasitic plasma. To maximize power consumption on the substrate, the impedance of the front plate 30 is less than the impedance of the back plate 20 (otherwise the plasma on the back can consume a significant portion of the power supplied). If the shower head 10 includes an RF electrode 50 embedded in the back plate 20, more power tends to be coupled through the back plate 20. This behavior can be reduced by using the plasma suppression structure 60.

The power coupling can be analyzed by an impedance model. Impedance Z for plasma discharge occurring in front of the faceplate (ie above the wafer)_faceIs estimated as:<maths num="1"><img file="JP6552155B2_D0001.tif" /></maths>Where C_iIs the capacitance of layer i, A is the area, f is the frequency, d_iIs the thickness of layer i, ε₀Is the permittivity, ε₂= ε₄= 9 (AlN or Al₂O₃Dielectric constant), ε₃= 1 (vacuum permittivity).

AlN and Al₂O₃Because of the dielectric constant of about 9, the plate contributes significantly less to impedance than a vacuum gap of comparable thickness. For plasma discharge (parasitic plasma) generated above the back of the shower head, the impedance without the plasma suppression structure 60 is Z._back= (1 / 2πfAε₀) . (D₁Calculated by / 9). For shower heads that do not have the plasma suppression structure 60, Z due to the high impedance (= 1) of the gas plenum._face&gt; Z_backIs. To counter this, a large impedance Z_suppWhen the plasma suppression structure 60 with is installed on the back plate 20, Z_face&lt;&lt; Z_back+ Z_suppIs guaranteed.

The impedance of the plasma suppression structure 60 is largely determined by the vacuum gap between the plates 100. However, if the gap is too wide, capacitive parasitic discharges can occur between the plates 100.

The impedance model used above assumes a parallel plate capacitor and a uniform electric field. In reality, a fringe electric field is generated, which is different from the above result, but this effect is expected to be small.<u style="single">Fringe electric field</u>Is the largest in the immediate vicinity of the RF electrode 50. As a result, the first gap (the gap between the back plate 20 and the first plate 100-1 of the plasma suppression structure 60) is most likely to ignite the parasitic discharge.

In some examples, the interplate gap is uniform. In another example, the interplate gap is not uniform. For example, in FIG. 3, some or all of the plate-to-plate gaps 200-1, 200-2, 200-3, 200-4, and 200-5 (collectively plate-to-plate gaps 200) are from the back plate 20. May increase with distance. For example, the inter-plate gap 200 may increase in the order 40-60-100-150-200 (mill), but other values may be used. Plate for understanding<u style="single">100</u>The ends of the may be closed, for example, with one or more plugs (not shown).

Preventing interplate parasitic discharge between the plates 100 of the plasma suppression structure 60 depends on the relationship between gap width and plasma sheath thickness. For example, in FIG. 4, for undesired ignition by plates 220-1, 220-2, 220-3, and 220-4 (collectively plate 220) containing one or more serrated or wavy surfaces 230. Protection can be improved. For each of the plates 220, only one side is shown to be a wavy surface 230, but both sides of each plate 220 may be wavy. The large surface area provides more sites for recombination of ions and electrons, increasing their loss rate and making them less prone to spontaneous parasitic discharges. As can be seen, the ends of the plate 220 may be closed, for example, with one or more plugs (not shown).

For example, in FIG. 5, plates 250-1, 250-2, and 250-3 (collectively plate 250), each containing one or more perforations 260, may improve protection against unwanted ignition. The large surface area provides more sites for recombination of ions and electrons, increasing their loss rate and making them less prone to spontaneous parasitic discharges. As can be understood, the ends of the plate 250 may be closed, for example, with one or more plugs (not shown).

As will be appreciated, the plasma suppression structure 60 for the substrate processing chamber may include variations of the above characteristics such as uniform and non-uniform spacing, one or more wavy surfaces, and / or perforations.

The above description is merely exemplary and is not intended to limit this disclosure, application, or usage. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure is such that the drawings, the specification, and the following claims reveal other variations. The example is not limited to. As used herein, the expression "at least one of A, B, and C" is meant to mean logic (A or B or C) using a non-exclusive OR. Should be interpreted. It should be understood that one or more steps included in the method may be performed in different order (or at the same time) without altering the principles of the present disclosure.

In the present application, the term controller is interchangeable with the term circuit, including the following definitions. The term controller is an application specific integrated circuit (ASIC), digital, analog, or analog / digital mixed discrete circuit, digital, analog, or analog / digital mixed integrated circuit, combined logic circuit, field programmable gate array (FPGA). ), A processor that executes code (shared, dedicated, or group), a memory that stores the code executed by the processor (shared, dedicated, or group), and other suitable hardware that provides the written functionality. It may be part of, or may include, a component, or a combination of some or all of the above, such as a system-on-chip.

The term code may include software, firmware, and / or microcode, as used above, and may refer to programs, routines, functions, classes, and / or objects. The term shared processor includes a single processor that executes some or all of the code from multiple controllers. The term group processor, along with additional processors, includes processors that execute some or all of the code from one or more controllers. The term shared memory includes a single memory that stores some or all of the code from multiple controllers. The term group memory includes additional memory as well as memory that stores some or all of the code from one or more controllers. The term memory can be a subset of the term computer-readable medium. The term computer-readable medium does not include transient electrical and electromagnetic signals propagating through the medium and can therefore be considered tangible and persistent. Examples of persistent tangible computer readable media include, but are not limited to, non-volatile memory, volatile memory, magnetic storage, and optical storage.

The devices and methods described herein may be partially or completely implemented by one or more computer programs executed by one or more processors. A computer program contains processor executable instructions stored on at least one persistent tangible computer readable medium. Computer programs may also contain and / or depend on stored data.<u style="single"> Application Example 1: A showerhead assembly for a substrate processing system that comprises a back plate coupled to a gas flow path and a gas diffusion surface coupled adjacent to a first surface of the back plate. A gas plenum comprises a front plate, one or more conductors, and an electrode located on one of the back plate and the front plate and connected to the one or more conductors. A showerhead assembly defined between a front plate and fluid communication with the gas flow path, wherein the back plate and the front plate are made of non-metallic material.</u><u style="single"> Application Example 2: The showerhead assembly according to Application Example 1, further comprising a stem coupled to the back plate and defining the gas flow path, the stem being made of a non-metallic material, said 1 or A shower head assembly in which the plurality of conductors penetrate the stem.</u><u style="single"> Application Example 3: The showerhead assembly according to Application Example 1, wherein the gas diffusion surface of the front plate is provided with a spaced hole, or the gas diffusion surface of the front plate is provided with a perforation. , The gas diffusing surface of the front plate is porous, the shower head assembly.</u><u style="single"> Application Example 4: The shower head assembly according to Application Example 2, further comprising a plasma suppression structure disposed adjacent to a second surface of the back plate, the first surface of the back plate. Is the opposite surface of the second surface of the back plate, the shower head assembly.</u><u style="single"> Application Example 5: In the showerhead assembly according to Application Example 4, the plasma suppression structure comprises N plates arranged in parallel with each other at intervals, where N is an integer of 2 or more and said N. The plates are a shower head assembly made of dielectric material.</u><u style="single"> Application Example 6: The showerhead assembly according to Application Example 5, wherein the plasma suppression structure comprises a collar extending from one of the N plates toward the top surface of the processing chamber of the substrate processing system. The collar is a shower head assembly made of dielectric material.</u><u style="single"> Application Example 7: The shower head assembly according to Application Example 5, wherein N is 3 or more, and the N plates are uniformly separated.</u><u style="single"> Application Example 8: The shower head assembly according to Application Example 5, wherein N is 3 or more, and at least a part of the N plates is unevenly separated.</u><u style="single"> Application Example 9: The shower head assembly according to Application Example 5, wherein at least one of the N plates comprises a plurality of perforations.</u><u style="single"> Application Example 10: The shower head assembly according to Application Example 5, wherein at least one of the N plates has a serrated surface.</u><u style="single"> Application Example 11: The shower head assembly according to Application Example 2, wherein the stem, the back plate, and the front plate are made of a ceramic material.</u><u style="single"> Application Example 12: The shower head assembly according to Application Example 2, wherein the stem, the back plate, and the front plate are made of at least one of aluminum nitride and aluminum oxide.</u><u style="single"> Application Example 13: A shower head assembly according to Application Example 1, further comprising a baffle disposed between the gas flow path and the gas plenum.</u><u style="single"> Application Example 14: A shower head assembly according to Application Example 2, further comprising a collar that couples the stem to the top surface of a substrate processing chamber.</u><u style="single"> Application Example 15: In the showerhead assembly according to Application Example 1, the front plate is a seal between the front plate and the back plate while allowing lateral movement of the front plate with respect to the back plate. A shower head assembly that is attached to the back plate to maintain.</u><u style="single"> Application Example 16: A shower head assembly according to Application Example 1, wherein the height dimension of the gas plenum is less than twice the expected plasma sheath thickness.</u><u style="single"> Application Example 17: In the showerhead assembly according to Application Example 1, the first dimension between the electrode and the first surface of the back plate is the second surface of the electrode and the back plate. A shower head assembly that is smaller than the second dimension between the back plate and the first surface of the back plate is the opposite surface of the second surface of the back plate.</u><u style="single"> Application Example 18: A shower head assembly according to Application Example 1, wherein the electrodes are disk-shaped.</u><u style="single"> Application Example 19: A shower head assembly according to Application Example 2, wherein the one or more conductors include a cylindrical conductor surrounding the gas flow path.</u><u style="single"> Application Example 20: A substrate processing system in which a processing chamber including a reaction space, a shower head assembly of claim 1 arranged in the reaction space, and an arrangement adjacent to the front plate in the reaction space. A board processing system that includes a mounting table that is equipped with a mounting table.</u><u style="single"> Application 21: The radio frequency (RF) circuit according to Application Example 20, further configured to supply an RF signal having a frequency greater than 1 MHz to the one or more conductors, and the radio frequency (RF) circuit. A substrate processing system including a controller configured to control the processing gas flowing through the gas flow path and to control the operation of the RF circuit.</u><u style="single"> Application 22: The substrate processing system according to Application 21, wherein the back plate is directly coupled to the wall of the processing chamber.</u>