Patent Application
20190338408
The subject invention relates to plasma processing chambers and, in particular, to chamber arrangements using coating for internal chamber parts, which enhance the performance of the plasma chamber.
In plasma processing chambers, a showerhead is often used to inject the process gas. In certain plasma chambers, such as capacitively-coupled plasma chambers, the showerhead may also function as an electrode, coupled to either ground or RF potential. However, during processing the showerhead is exposed to the plasma and is attacked by the active species within the plasma, such as halogen plasma of CF4, Cl2, etc. This phenomenon is especially troublesome for showerheads having a chemical vapor deposited silicon carbide coating (CVD SiC).
Plasma chambers also utilize an electrostatic chuck, attached to a pedestal, to hold the substrate during processing. Generally, the diameter of the chuck and/or pedestal is larger than that of the substrate. Therefore, various additional elements are required to protect the chuck and/or pedestal from the active species in the plasma, and also to control the RF power coupling so as to sustain uniform plasma over the substrate. Such elements may include a focus ring, a cover ring, flow equivalent ion shied, and a plasma confinement ring, etc.
The substrate 130 is held in place by chuck 135, which is attached to a pedestal 140. RF power is delivered to an electrode that may be embedded in the chuck 135 or may be part of the pedestal 140. A focus ring 140 is provided around the substrate and helps to control plasma uniformity. A cover ring 145 is provided around the focus ring and serves mainly for erosion protection from active plasma species. A plasma confinement ring 150 prevents plasma from igniting and/or sustaining below the plasma confinement ring 150, such that the plasma is confined to the processing zone of the vacuum enclosure.
As is known, during processing the plasma may be rather corrosive to the various elements of the chamber, especially the showerhead, since it forms a part of the capacitive RF power circuit. Therefore, various coatings have been proposed and tested in the prior art for protecting the showerhead from plasma erosion. Yttria (Y2O3) coating is believed to be promising; however, it has been very difficult to find a process that results in good coating, especially one that does not crack or generate particles. For example, there have been proposals to use plasma spray (PS) to coat a showerhead made of metal, alloy or ceramic. However, conventional PS Y2O3 coating is formed by the sprayed Y2O3 particles, and generally results in a coating having high surface roughness (Ra of 4 micron or more) and relatively high porosity (volume fraction is above 3%). The high surface roughness and porous structure makes the coating susceptible to generation of particles, which may contaminate the wafer being processed. In addition, the particle will come out from the gas holes and dropped on the wafer when the as-coated shower head is used in the plasma process, as the plasma sprayed coating inside the gas hole is very rough and has poor adhesion to the substrate.
Other proposals for forming Yttria coating involve using chemical vapor deposition (CVD), physical vapor deposition (PVD), ion assisted deposition (IAD), active reactive evaporation (ARE), ionized metal plasma (IMP), sputtering deposition and plasma immersion ion process (PIIP). However, all these deposition processes have some technical limitations such that they have not been actually used to scale up for the deposition of thick coating on the chamber parts for the plasma attack protections. For instance, CVD of Y2O3 can not be carried out on substrates that cannot sustain temperatures above 600° C., which excludes the deposition of plasma resistant coating on chamber parts that are made of aluminum alloys. PVD process, such as evaporation, can not deposit dense and thick ceramic coating because of their poor adhesion to substrate. Other deposition processes can not deposit thick coating either due to the high stress and poor adhesion (such as sputtering deposition, ARE and IAD) or the very low deposition rate (such as sputtering deposition, IMP and PIIP). Therefore, so far no satisfactory coating has been produced, that would have good erosion resistance, while generating low or no particles and can be made thick without cracking or delamination.
Moreover, when the showerhead assembly, e.g., showerhead and ground ring, is coated or replaced by a one piece Y2O3 coated SiC showerhead, the RF coupling between the upper electrode and the bottom electrode is maintained between Y2O3 and silicon surfaces (i.e., wafer) or between Y2O3 showerhead and silicon wafer and SiC focus ring surface. Consequently, the RF induced plasma distribution on the wafer is quite different from the plasma distribution on wafer when uncoated SiC showerhead is used.
In view of the above-described problems in the art, a solution is needed for a showerhead coating that resists plasma species attack and does not generate particle or cracks. The coating should have acceptable roughness and porosity values, so that it could provide long service life. Additionally, the solution should maintain ER uniformity over the wafer. The process for fabricating the coating should allow thick coating without being susceptible to cracking or delamination.
The following summary of the invention is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.
According to an aspect of the invention, methods are provided for the formation of advanced plasma resistant coatings on showerheads. According to various embodiments, the process of the coating the showerhead surface is provided so that the service performance of the coated showerhead is improved. Other embodiments involve the modification and installation of the coated showerhead into the plasma chamber, so as to improve the plasma process quality.
According to various embodiments, etch uniformity is maintained, while the showerhead is protected by an effective Y2O3 coating. In one example, a hardware configuration of a capacitively coupled plasma (CCP) chamber is provided where at least the perforated plate of the showerhead is coated with Y2O3, while at least one opposing conductive surface of the CCP is also coated with Y2O3. The opposing surface may be any one or a combination of focus ring, cover ring, flow equivalent ion shied, and/or plasma confinement ring. In one embodiment, the perforated plate and ground ring are replaced by a one-piece equivalent plate, which is made of conductive material, e.g., SiC or Al alloy, and has a protective coating, e.g., Yttrium-based coating, such as Y2O3. To maintain good plasma uniformity, the opposing surface is also coated. For example, the focus ring and cover ring are coated using the same coating as the showerhead. In some examples, the focus ring and cover ring are combined into a single equivalent ring which is coated. Also, if either is used, the plasma confinement ring or the flow equivalent ion shield can be coated.
In an exemplary process, an advanced Yttria coating, e.g., Y2O3 or YF3 based coatings, with fine/compact grain structure and random crystal orientation is created by a plasma enhanced physical vapor deposition (PEPVD) process, in which (1) the deposition is carried out in a low pressure or vacuum chamber environment; (2) at least one deposition element or component is evaporated or sputtered out off a material source and the evaporated or sputtered material condenses on the substrate surface (this part of the process is a physical process and is referred to herein as the physical vapor deposition or PVD part); (3) meanwhile, a plasma source (or sources) is (are) used to emit out ions and to generate plasma that surrounds the showerhead surface and at least one deposition element or component is ionized and reacted with the evaporated or sputtered elements or components in plasma or on the surface of the showerhead; and (4) the showerhead is coupled to a negative voltage, such that it is bombarded by the ionized atoms or ions during the deposition process. The actions from (3) and (4) are referred to as the “plasma enhanced (PE)” function of the PEPVD.
It should be mentioned that the plasma source(s) could be used either (1) to ionize, decompose, and activate the reactive gases so that the deposition process can be performed in a low substrate temperature and with a high coating growth rate as more ions and radicals are generated by plasma, or (2) to generate the energetic ions aimed at the showerhead so that the ion impinges on the surface of the shower head and helps to form the thick and dense coatings thereon. More perfectly, the plasma sources will be used as the alternative or the combinations of functions (1) and (2), to lead the formation of the coating on the shower head. Such a coating synthesized with the enough thickness and the dense structure is generally referred to herein as “advanced coating” (referred to A-coating herein), for instance, such as A-Y2O3, A-YF3, or A-Al2O3 based coatings.
In order to improve the coating formation, the deposition of A-coating is performed on a roughened surface of the substrates or showerhead, to improve the adhesion of the coating to substrate and to increase the deposition thickness. This is because the increase of surface roughness of the material increases the contact area in the interfacial region between the coating and substrate surface, and changes of the coating contact area from more 2-dimensional fraction to more 3-dimensional fraction. The deposition on the rough surface induces the formation of coating with random crystal orientation and results in the release of the interfacial stress between the A-coating and the substrates, which enhances the coating adhesion to the substrate and promotes the formation of thick and dense coating thereon. It has been expected that the improved stability of A-coating on materials surface can be reached if the coating is deposited on materials with the surface roughness at least above 4 um.
In order to reduce the production cost, another embodiment involves the formation of double layered coating combinations in which the first layer or coating is formed on the showerhead base as the anodization, the plasma spray Y2O3, or other plasma resistant coatings, with a certain thickness designed to maintain the required electrical properties of the formed showerhead and the first layer has the surface roughness above 4 um. A second layer or coating is formed over the first layer that is at least 4 um in roughness and the second layer or coating thus has a top surface facing to plasma in the plasma processes. The second coating can be formed as the A-coating (e.g. A-Y2O3, A-YF3, etc.), and the formed coatings have the specified roughness (surface roughness Ra≤1.0 um) and dense structure with random crystal orientation and with a porosity less than 1% or without porous defects. Consequently, particle contamination, which is usually induced by plasma spray coating due to the rough surface and porous structure, can be reduced, while A-coating is used as the showerhead exterior surface. In addition, due to the dense crystal structure, the second coating has reduced plasma erosion rate, which could further reduce metal contamination in the plasma processes. The thicknesses of either the first coating or the second coating can be adjusted according to the performance requirement on the showerhead.
In another embodiment, the showerhead surface is coated by double layered coating combinations, in which the first layer or coating is formed on the showerhead base by anodization, by plasma spray, or by other technologies, and with enough thickness to provide the desired process functions of the showerhead in the plasma processes (such as required electrical conductivity, thermal conductivity or thermal barrier function, and other functions). The second layer or coating is formed on the first layer or coating to form a top surface facing the plasma in the plasma etch processes. The first layer or coating could be either plasma resistant or other function coatings with or without uniform distribution in thickness and/or composition on the showerhead base surface. The second coating is the A-coatings, such as A-Y2O3 coating. Since the A-coating has the specified roughness (Ra≤1.0 um) and dense structure with random crystal orientation and with a porosity less than 1% or without porous defects, the A-coating has plasma erosion rate much lower than the first coating, which would not create particles and should have reduced metal contamination in the plasma processes. The thicknesses and the roughness of either the first coating or the second coating can be adjusted according to the performance requirement on the showerhead.
In another embodiment, the multi-layered coatings are deposited on the showerhead, such that the coated showerhead has an increased coating thickness, a stable surface facing the plasma chemistry, and the desired functions to improve the process performance of the plasma chamber. As different from the coating that is deposited as a single layered structure, the same material with the multilayered structure can be deposited to reach an increased thickness with a reduced risk of crack formation, as the increased interfacial areas due to the multi-layers can release the coating stress that is usually increased with the increase of the layer or coating thickness. The multilayered coating is composed by either the multilayered A-coatings or the combination of the multi-layered functions coating with the multi-layered A-coatings whose top layer faces the plasma, for instance, when the coatings are deposited on the showerhead. It has been confirmed that the multi-layered A-coating with random crystal orientation can be deposited on the showerhead to thicknesses above 50 um without cracking and delamination if the showerhead has a surface roughness above 4 um.
In another embodiment, in order further to improve the performance of the coating packaged showerhead, surface processes are applied on the as-coated showerhead, which includes, but not limited to, surface smoothening or roughening to reduce the particles, surface modification to enhance the surface density and stability of the coatings, and surface chemical cleaning to remove the particles and contamination that are formed on the coated showerhead either due to the coating deposition process or due to the plasma etching process.
According to one aspect, the surface roughness of the A-coating is controlled, since if the surface is too smooth, polymer deposition during etching will not adhere well to the surface, and thus induce particles. On the other hand, too rough surface will directly create particles due to the plasma etching. The recommended surface roughness is at least 1 um or above for the A-coatings, which can be reached by the adjustment of the substrate roughness, by the deposition process, or by lapping, polishing and other post surface treatment on the deposited coatings.
According to another aspect, the energetic ion bombardment or plasma etching in the PEPVD is used to smooth/rough and densify the surface of A-coating coated showerhead. The coated showerhead surface can be cleaned by wet solution cleaning in which the erosive solution or slurry or aerosol is used to blast away the surface particles and to control the surface roughness of the coating either on the flat plate or inside the gas holes. The dense coating with the specified roughness could have the fine and compact grain structure with reduced porous volume defects, and thus reduce the plasma erosion rate and maintain clean environment during the plasma etch processes.
To reach performance improved etch processes, the coated showerhead can be formed with modification or combination of the gas distribution plate, showerhead aluminum base and the upper ground ring into one piece of coated showerhead, or the one piece of showerhead with the build-in heater, so that the formation of the new coated showerhead can reduce the production cost and the coated showerhead is easy to be refurbished once it is used for a certain service cycles. In essence, the various parts of the showerhead can be coated so as to be “packaged” by or inside the A-coating layer.
The base or intermediate coating could be of metals, alloys, or ceramics (such as Y2O3, YF3, ErO2, SiC, Si3N4, ZrO2, Al2O3 and their combinations or combination of them with other elements). The second or the top coating with the surface facing the plasma could be A-coating of Y2O3, YF3, ErO2, SiC, Al2O3 and their combinations or combination of them with other materials. As quite different from the prior art, it is suggested that the A-coating is deposited on the substrate materials that may have the element(s) and/or component(s) which are also contained in the A-coating, such as the deposition of A-Y2O3 on anodized surface, Y2O3 surface, or Al2O3 surface. Since the same elements or components occurred in both the coating and the substrate will result in the formation of the atomic bondings from the same elements or components in the interfacial region between the A-coating and the substrates, which promotes the formation of A-coating with the increased thickness and the improve adhesion to the substrates or showerhead.
Various methods are disclosed for deposition of A-coating with random crystal orientation and thickness of 50 microns or more, without cracks or delamination. In one embodiment, the surface of the part to be coated is roughened to Ra of 4 microns or more prior to the coating. It was shown that the roughness of 4 micron is critical for reduction of cracks and delamination. Additionally, rather than depositing a single-layer coating to the desired thickness, a series of thinner coatings are deposited, that add up to the desired thickness. For example, if a 50 micron coating of A-Y2O3 is desired, rather than depositing a single layer, several layers, e.g., five layers of ten microns each are deposited sequentially. Normally, as the thickness of the coating increases, the stress within the coating also increases. However, depositing the coating as a multi-layer structure releases the stress, thus reducing the risk of cracks and delamination.
The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale.
Various embodiments will now be described, providing improved coatings for showerheads, which improve erosion and particle performance of the showerhead, together with coated cathode assembly for enhancing etch rate and plasma uniformity.
For example, in one embodiment the upper electrode is fabricated as a combined showerhead and grounding ring, while the bottom electrode is the combination of the chuck electrode—coupling the power via the silicon wafer, plus an extended electrode that is formed by the coated focus ring, the coated cover ring, and the coated FEIS ring. In this embodiment, the upper electrode is fabricated from SiC or Al alloy, and is coated with Y2O3. The coating has fine/compact grain structure and random crystal orientation, as will be described in more details below. The extended electrode may be made of conductive material and also has the Y2O3 coating.
Also shown in
In the embodiment of
According to another embodiment, illustrated in
According to one specific another embodiment, the composite cover ring 749 is made by the deposition of Y2O3 coatings onto Al2O3 substrate. Comparing the properties of other materials list in Table 2, Al2O3 has coefficient of thermal expansion (CTE) that is almost the same as that of Y2O3. This property ensures that thick Y2O3 coating can be synthesized on the Al2O3 surface, with a stable structure and the good adhesion. The combination can also withstand operating in high service temperatures. Additionally, the Al2O3 based composite cover ring (CCR) will have enhanced service function in various plasma environments, as Al2O3 substrate has good thermal conductivity, comparing to solid Y2O3 CCR.
As can be understood from the embodiments disclosed above, when providing Y2O3 coated FR, Y2O3 coated CR, and/or Y2O3 coated FEIS ring, which aren't grounded, i.e., being floating or RF biased, they function as an extended bottom electrode. When the plasma is ignited and maintained between bottom electrode, i.e., the combined electrostatic chuck and wafer, and upper electrode Y2O3 coated SH, the plasma is also simultaneously ignited and maintained between the upper electrode Y2O3 coated SH and the extended bottom electrode, i.e., the Y2O3 coated FR, the Y2O3 coated CR, and the Y2O3 coated FEIS ring. Since the upper electrode and the extended bottom electrode have the Y2O3 surfaces, it helps to stable the RF coupling and maintain uniform plasma distribution between the CCP electrodes and thus promote the uniform plasma etch on the wafer's surface. It is noted that in the embodiment of
The description now turns to the apparatus and method for forming the coating, which may be used to coat the showerhead and the extended bottom electrode described above.
Unlike conventional plasma spray, in which the coating is deposited in atmospheric environment, the advanced coating disclosed herein is deposited in low pressure or vacuum environment. Also, while in plasma spray the coating is deposited using small powdery particles, the advanced coating is deposited by the condensation of atoms, radicals, or molecules on the materials surfaces. Consequently, the characteristics of the resulting coating layer is different from the prior art coating, even when the same material composition is used. For example, it was found that a Y2O3 coating deposited according to embodiment of the invention has practically no porosity, specified surface roughness above 1 um, and has a much higher etch resistance than the conventional PS Y2O3 coating.
The embodiments of the invention will now be described in detail with reference to the Figures. First, the equipment and method for depositing the advanced coating will be described.
In
A source material 820 containing species to be deposited is provided, generally in a solid form. For example, if the film to be deposited is Y2O3 or YF3 based, source material 820 would include yttrium (or fluorine)—possibly with other materials, such as oxygen, fluorine (or yttrium) etc. To form the physical deposition, the source material is evaporated or sputtered. In the example of
The plasma enhanced part is composed of a gas injector 835, which injects into chamber 800 reactive and non-reactive source gases, such as argon, oxygen, fluorine containing gas, etc., as illustrated by the dotted lines. Plasma 840 is sustained in front of part 810, using plasma sources, e.g., RF, microwave, etc., one of which in this example is shown by coil 845 coupled to RF source 850. Without being bound by theory, it is believed that several processes take place in the PE part. First, non-reactive ionized gas species, such as argon, impinging the part 810, so as to condense the film as it is being “built up.” The effects of ion impinging may result from the negative bias on part 810 and part holder 805, or from the ions emitted out from the plasma sources and aimed at part 805. Second, reactive gas species or radicals, such as oxygen or fluorine, react with the evaporated or sputtered source material, either inside the chamber or on the surface of the part 810. For example, the source Yttrium reacts with the oxygen gas to result in Y containing coating, such as Y2O3 or YF3. Thus, the resulting process has both a physical (impingement and condensation) component and a chemical component (e.g. oxidation and ionization).
While according to above embodiment the surface of the coated perforated gas plate is characterized with the specified surface roughness (surface roughness is controlled equal to or larger than Ra 1.0 um), according to one embodiment the surface is roughened in order to promote polymer adhesion during plasma processing. That is, according to one aspect, the surface roughness of the A-coating is controlled, since if the surface is too smooth, polymer deposition during etching will not adhere well to the surface, and thus induce particles. On the other hand, too rough surface will directly create particles due to the plasma etching. Therefore, according to this embodiment the recommended surface roughness Ra is equal to or above 1 um. Perfectly, the recommended surface roughness Ra is above 1 um, but below 10 um (1 um<Ra<10 um). It has been found that in this range the particle generation is minimized, while polymer adhesion is controlled. That is, the noted range is critical because using higher roughness leads to particle generation, while using smoother coating diminishes adhesion of the polymers during plasma processing. In all cases, the A-coating with either single or multilayered structure has the dense structure with random crystal orientation and porosity less than 1% and has no any crack or delamination.
According to one embodiment this roughness is achieved by the as-deposited coating, or by lapping, polishing or other post PEPVD surface treatment on the as-deposited coatings. On the other hand, according to one embodiment the surface of the perforated gas plate is first roughened to the desired roughness (Ra>4 um), and then the coating is deposited. Since the coating is done using PEPVD, the resulting coating may have the same or different roughness as the surface prior to the coating, according to the thickness of the coating and the deposition process.
According to one example, the perforated gas plate is the anodized plate where the surface and inside gas holes are all protected by the anodization, such as the hard anodization. Then, the deposition of A-coatings, such as A-Y2O3 is performed either on the surfaces of perforate gas plate (expect the back side surface contact to the conductive plate 905 and back plate 910) as showing in
According to various embodiments, the intermediate layer or coating could be of metals, alloys, or ceramics (such as Y2O3, YF3, ErO2, SiC, Si3N4, ZrO2, Al2O3, AlN and their combinations or combination of them with other elements). The second or the top coating with the surface facing to plasma is the A-coating of Y2O3, YF3, ErO2, SiC, Al2O3 and their combinations or combination of them with other materials.
As quite different from the prior art, according to some embodiments the A-coating is proposed to be deposited on the substrate materials that could have at least one element or component which is also contained in the A-coating, such as the deposition of A-Y2O3 on anodized surface, Al2O3 or Y2O3 surface. Since the same elements or components occurred in both the coating and the substrate will result in the formation of the atomic bonding from the same elements or components in the interfacial region between the A-coating and the substrates, which promotes the formation of A-coating with the increased thickness and the improve adhesion to the substrates or showerhead.
It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations will be suitable for practicing the present invention.
Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201210421964.4 | Oct 2012 | CN | national |
This application is a divisional of U.S. patent application Ser. No. 14/065,323, filed on Oct. 28, 2013, which claims the priority to Chinese Patent Application No. 201210421964.4, filed on Oct. 29, 2012, which are incorporated by reference in their entireties herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14065323 | Oct 2013 | US |
| Child | 16517491 | US |
