COATING FOR PERFORMANCE ENHANCEMENT OF SEMICONDUCTOR APPARATUS

Abstract

A plasma processing chamber having advanced coating for the showerhead and for an extended bottom electrode. The extended bottom electrode can be formed by one or more of the focus ring, cover ring, and plasma confinement ring. The extended electrode can be formed using a one-piece composite cover ring. The composite cover ring may be made of Al.sub.2O.sub.3 and include a Y.sub.2O.sub.3 plasma resistant coating. The plasma confinement ring may include a flow equalization ion shield that may also be provided with the plasma resistant coating. The plasma resistant coating of the extended electrode may have elements matching that of the showerhead.

Claims

1. A method for fabricating a showerhead for a plasma processing chamber, comprising: fabricating a showerhead assembly, the showerhead assembly comprising a perforated plate; placing a source material containing Yttrium in a vacuum chamber; placing the perforated plate in the vacuum chamber; evaporating or sputtering the source material to perform physical vapor deposition of the source material on the perforated plate; injecting into the vacuum chamber source gas; igniting plasma inside the vacuum chamber in front of the perforated plate; thereby forming a protective coating containing Yttrium on the perforated plate.

2. The method of claim 1, wherein fabricating the showerhead assembly comprises fabricating the perforated plate from SiC.

3. The method of claim 1, wherein fabricating the showerhead assembly comprises fabricating the perforated plate from Al alloy.

4. The method of claim 1, wherein fabricating the showerhead assembly comprises fabricating an integrated perforated plate and grounding ring.

5. The method of claim 1, further comprising anodizing the perforated plate prior to placing the perforated plate in the vacuum chamber.

6. The method of claim 1, wherein injecting source gas comprises injecting at least one of argon, oxygen, and fluorine.

7. The method of claim 1, further comprising coupling the perforated plate to a negative voltage when the perforated plate is in the vacuum chamber.

8. The method of claim 1, wherein fabricating a showerhead assembly further comprises: fabricating a back plate, a support ring and a conductive ring; assembling the perforated plate, the back plate, the support ring, and the conductive ring to form the showerhead assembly; and wherein placing the perforated plate in the vacuum chamber comprises placing the perforated plate assembled into the showerhead assembly, such that forming the protective coating packages the assembled showerhead assembly.

9. The method of claim 1, wherein the source gas comprises oxygen containing gas, thereby forming the protective coating of Yttria.

10. The method of claim 1, wherein the source gas comprises fluorine containing gas, thereby forming the protective coating of YF.sub.3.

11. The method of claim 1, wherein injecting source gas comprises injecting argon and a reactive gas selected from oxygen and fluorine.

12. The method of claim 1, further comprising forming an intermediate coating on the perforated plate prior to placing the perforated plate in the vacuum chamber, wherein the intermediate coating contains aluminum or yttrium.

13. The method of claim 12, wherein the intermediate coating comprises plasma sprayed Y.sub.2O.sub.3 coating.

14. The method of claim 1, further comprising: fabricating a focus ring, a cover ring, and a plasma confinement ring; placing at least one of the focus ring, the cover ring, and the plasma confinement ring in the vacuum chamber; evaporating or sputtering the source material to perform physical vapor deposition of the source material on the at least one of the focus ring, the cover ring, and the plasma confinement ring; injecting into the vacuum chamber source gas; igniting plasma inside the vacuum chamber in front of the at least one of the focus ring, the cover ring, and the plasma confinement ring; thereby forming a protective coating containing Yttrium on the at least one of the focus ring, the cover ring, and the plasma confinement ring.

15. The method of claim 14, wherein fabricating the focus ring and the cover ring comprises fabricating a single-piece composite cover ring.

16. The method of claim 15, wherein fabricating the composite cover ring comprises fabricating the composite cover ring from Al.sub.2O.sub.3.

17. The method of claim 16, further comprising coupling the composite cover ring to RF power supplier to form an extended electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] FIG. 1 is a schematic of a prior art capacitively coupled plasma chamber;

[0029] FIG. 2 is a plot illustrating etch rate distribution for SiC showerhead and coated showerhead;

[0030] FIG. 3 is a schematic illustrating capacitive coupling of RF power between the showerhead assembly and the bottom electrode assembly;

[0031] FIG. 4 illustrates a plasma chamber according to one embodiment;

[0032] FIG. 5 is a plot demonstrating the effects of having Y.sub.2O.sub.3 coated showerhead as upper electrode and Y.sub.2O.sub.3 coated focus ring and cover ring as extended lower electrode;

[0033] FIG. 6 illustrates the results obtained with the same hardware set-up, but using Recipe 2 in Table 1;

[0034] FIG. 7 illustrates a plasma chamber according to another embodiment;

[0035] FIG. 8 illustrates an apparatus for depositing advanced coating in accordance with one embodiment of the invention;

[0036] FIG. 9A illustrates a conventional showerhead and electrode assembly for a plasma chamber;

[0037] FIG. 9B illustrates a showerhead having generally the same structure as that of FIG. 9A, except that it includes the advance coating according to an embodiment of the invention;

[0038] FIG. 9C illustrates another embodiment, wherein the showerhead assembly has one piece gas distribution plate that is packaged in the A-coating;

[0039] FIG. 9D illustrates another embodiment, wherein the perforated gas plate, conductive ring, and support ring are fabricated as one piece perforated gas distribution plate (or GDP);

[0040] FIG. 9E illustrates another embodiment, wherein the showerhead assembly with one piece gas distribution plate is packaged in the A-coating; and

[0041] FIG. 9F illustrates another embodiment, wherein the showerhead assembly with one piece gas distribution plate is coated with an intermediate coating and then with the A-coating.

DETAILED DESCRIPTION

[0042] 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. FIG. 3 is a schematic illustrating the arrangement for a capacitively coupled plasma chamber. In this embodiment, the top electrode 322 is grounded and the RF power is applied to the bottom electrode, which in this example is composed of electrode 362 and extension 342. The top electrode 322 may be composed of the perforated plate, or a combination of perforated plate and grounding ring. The bottom electrode 362 may be embedded in the chuck, or be part of the pedestal supporting the chuck. The extension 342 may be composed of one or a combination of focus ring, cover ring, flow equivalent ion shied, and/or plasma confinement ring. By proper selection of the elements comprising the upper and lower electrodes, and proper coating of these elements, etch rate can be enhanced without deteriorating etch uniformity. Moreover, coated parts are better protected from plasma corrosion.

[0043] 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 electrodecoupling 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 Y.sub.2O.sub.3. 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 Y.sub.2O.sub.3 coating.

[0044] FIG. 4 illustrates an embodiment where the upper electrode is a combined showerhead and grounding ring, illustrated as shower-plate 430. In this embodiment the shower-plate 430 is made of either SiC or Al alloy, and has a protective coating 434. Also, in this embodiment the coating is yttrium-based, such as, e.g., Y.sub.2O.sub.3, Y.sub.2F.sub.3, etc. For enhanced plasma-corrosion resistance, it is best to coat the showerhead with the advanced coating, as described more fully below.

[0045] Also shown in FIG. 4 are focus ring 440, cover ring 445, and plasma confinement ring 450. The plasma confinement ring may include flow equalization ion shied (FEIS) ring 447. The FEIS ring 447 functions to create equivalent flow to the vacuum pump and block ions from flowing into the exhaust path to the vacuum pump. In the embodiment of FIG. 4, at least one of the focus ring 440, cover ring 445, plasma confinement ring 450 and/or flow equivalent ion shied (FEIS) ring 447 is coated with the same coating as the shower-plate 430.

[0046] FIG. 5 is a plot demonstrating the effects of having Y.sub.2O.sub.3 coated showerhead as upper electrode and Y.sub.2O.sub.3 coated focus ring and cover ring as extended lower electrode. Notably, the etch rate is high as for the case where only the showerhead was coated. However, uniformity has improved dramatically to 2.66%. In fact, the uniformity is even better than what it was prior to coating the showerhead. This result was obtained by using the etch recipe indicated as Recipe 1 in Table 1. FIG. 6, on the other hand, illustrates the results obtained with the same hardware set-up, but using Recipe 2 in Table 1. As can be seen by comparing the two plots of FIG. 5 and FIG. 6, the etch rate remains the same, but the etch uniformity can be changed by changing recipe parameters. Note that the uniformity for Recipe 2 is 2.88%, which is better than that uniformity achieved without the coating.

TABLE-US-00001 TABLE 1 60 MHz 2 MHz Pressure Power Power CF.sub.4 C.sub.4F.sub.8 Ar N.sub.2 O.sub.2 Recipe mT W W sccm No 1 90-110 1300-1700 1600-2000 450-500 200-250 75-100 No 2 70-90 1300-1700 2300-2700 50-70 40-60 500-700 100-200 50-75

[0047] In the embodiment of FIG. 4, leading to the results plotted in FIGS. 5 and 6, the focus ring was made of SiC or quartz and the cover ring was made of quartz, both of which were coated with Y.sub.2O.sub.3. However, according to another embodiment, the both focus ring and cover ring are made using solid Y.sub.2O.sub.3. According to this embodiment, the ER uniformity can be improved and the service life of cover ring (CR) and focus ring (FR) can be prolonged.

[0048] According to another embodiment, illustrated in FIG. 7, the quartz cover ring (CR) and SiC focus ring (FR) are replaced by a one piece composite cover ring 749, that is actually the combination of the original quartz CR and SiC FR. The composite cover ring (CCR) 749 can be made of solid Y.sub.2O.sub.3, or other materials, such as but not limited to, Si, SiC, Quartz, Al.sub.2O.sub.3 or other plasma resistant ceramics. On the other hand, the one-piece composite cover ring 749 can be made of materials, such as, but not limited to, Si, SiC, Y.sub.2O.sub.3, Quartz, Al.sub.2O.sub.3 and other ceramics, and include a plasma resistant coating. The plasma resistant coatings can be, such as, but not limited to, Y.sub.2O.sub.3, YF.sub.3, ErO.sub.2, SiC, Si.sub.3N.sub.4, ZrO.sub.2, Al.sub.2O.sub.3 and their combinations, or a combination of them with other elements. The selection and deposition of different coatings on the composite cover ring highly depends on the combinations of the materials that are used to form the upper electrode and the bottom electrode. The use of such one-piece cover ring 749 reduces the production cost, but keeps the benefits of etch rate and etch uniformity.

[0049] According to one specific another embodiment, the composite cover ring 749 is made by the deposition of Y.sub.2O.sub.3 coatings onto Al.sub.2O.sub.3 substrate. Comparing the properties of other materials list in Table 2, Al.sub.2O.sub.3 has coefficient of thermal expansion (CTE) that is almost the same as that of Y.sub.2O.sub.3. This property ensures that thick Y.sub.2O.sub.3 coating can be synthesized on the Al.sub.2O.sub.3 surface, with a stable structure and the good adhesion. The combination can also withstand operating in high service temperatures. Additionally, the Al.sub.2O.sub.3 based composite cover ring (CCR) will have enhanced service function in various plasma environments, as Al.sub.2O.sub.3 substrate has good thermal conductivity, comparing to solid Y.sub.2O.sub.3 CCR.

TABLE-US-00002 TABLE 2 Materials PS Y.sub.2O.sub.3 Si SiC Al.sub.2O.sub.3 Al CTE, 106 .Math. K1 5.9 2.6-3.2 2.9-3.2 5.4 20 Thermal conductivity, 3.8 149 150 30 125 W .Math. m1 .Math. K1

[0050] As can be understood from the embodiments disclosed above, when providing Y.sub.2O.sub.3 coated FR, Y.sub.2O.sub.3 coated CR, and/or Y.sub.2O.sub.3 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 Y.sub.2O.sub.3 coated SH, the plasma is also simultaneously ignited and maintained between the upper electrode Y.sub.2O.sub.3 coated SH and the extended bottom electrode, i.e., the Y.sub.2O.sub.3 coated FR, the Y.sub.2O.sub.3 coated CR, and the Y.sub.2O.sub.3 coated FEIS ring. Since the upper electrode and the extended bottom electrode have the Y.sub.2O.sub.3 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 FIG. 3, the diameter of the extended bottom electrode is larger than the diameter of the showerhead.

[0051] 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.

[0052] 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 Y.sub.2O.sub.3 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 Y.sub.2O.sub.3 coating.

[0053] 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. FIG. 8 illustrates an apparatus for depositing advanced coating in accordance with one embodiment of the invention. This apparatus is used for depositing the advanced coating using the process referred to herein as PEPVD, where the PE and PVD components are highlighted by the broken-line callouts in FIG. 8. Traditionally, chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD) refer to a chemical process where a thin film is formed on the substrate's surface by exposing the substrate to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposited film. PVD, on the other hand, refers to a coating method which involves purely physical processes, where thin films are deposited on the surface of the substrate by the condensation of a vaporized or sputtered form of the desired film materials that can be usually the solid source materials. Therefore, one may characterize PEPVD as somewhat of a hybrid of these two processes. That is, the disclosed PEPVD involves both physical process of atom, radicals, or molecular condensation (the PVD part) and plasma induced chemical reaction in the chamber and on the substrate's surface (the PE part).

[0054] In FIG. 8, chamber 800 is evacuated by vacuum pump 815. The part 810 to be coated, in this example the showerhead, focus ring, cover ring, confinement ring, etc., is attached to a holder 805. Also, a negative bias is applied to the part 810, via holder 805.

[0055] 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 Y.sub.2O.sub.3 or YF.sub.3 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 FIG. 8, the evaporation is achieved using electron gun 825, directing electron beam 830 onto the source material 820. As the source material is evaporated, atoms and molecules drift towards and condense on the part 810 to be coated, as illustrated by the broken-line arrows.

[0056] 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 Y.sub.2O.sub.3 or YF.sub.3. Thus, the resulting process has both a physical (impingement and condensation) component and a chemical component (e.g. oxidation and ionization).

[0057] FIG. 9A illustrates a conventional showerhead and electrode assembly for a plasma chamber. Conductive plate 905, sometimes, can be converted as the heater to control the temperature of the showerhead, is sandwiched between back plate 910 and perforated gas plate 915. Conductive ring 920 surrounds the perforated gas plate 915 and can work as the extended upper electrode or as a grounding ring. Support ring 925 surrounds conductive plate 905 and is also sandwiched between conductive ring 920 and back plate 910. Perforated gas plate 915, actually working as a gas distribution plate (or GDP), may be made of ceramic, quartz, etc., for example, it may be made of silicon carbide, and may be assembled to the lower surface of conductive plate 905. Conductive ring 920 may be made of ceramic, quartz, etc., for example, it may be made of silicon carbide, and may be assembled to the lower surface of support ring 925. The support ring 925, the conductive plate 905 and the back plate 910 may be made of metal and alloy, e.g., aluminum, stainless steel, etc. The showerhead is affixed to the ceiling of the plasma chamber, in a well-known manner.

[0058] FIG. 9B illustrates a showerhead having generally the same structure as that of FIG. 9A, except that it includes the advance coating according to an embodiment of the invention. In FIG. 9B the advanced coating 935 (for example, A-Y.sub.2O.sub.3) is provided on the bottom surface of the perforated gas plate 915, i.e., the surface that faces the plasma during substrate processing. The advanced coating 935 may be the single layer or the multilayered coatings. In this embodiment, the perforated gas plate is fabricated according to standard procedures, including formation of gas injection holes/perforations. Then, the plate is inserted into a PEPVD chamber and the bottom surface is coated with advanced coating. Since the PEPVD coating uses atoms or molecules for buildup of the coating, the interior of the gas injection holes is also coated. However, unlike prior art coating, the advance coating is formed by the condensation of atoms and molecules, and results in a dense and uniform A-coating with the good adhesion to the interior surface of the gas holes, thereby providing smooth gas flow and avoiding any particle generation.

[0059] 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.

[0060] 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.

[0061] FIG. 9C illustrates another embodiment, where the showerhead assembly is packaged in the A-coating. That is, as shown in FIG. 9C, the lower surface of the entire showerhead assembly is coated with the A-coating 935 (for example A-Y.sub.2O.sub.3). In this example, various parts forming the showerhead are first assembled, and then are positioned inside the PEPVD chamber to form the advanced coating over the lower surface of the entire assembly. In this manner, the showerhead assembly is packaged by the advanced coating and is fully protected from plasma erosion. As discussed with reference to FIG. 9B, the surfaces may remain smooth, or may be roughened so as to promote polymer adhesion. In all cases, however, the coating thickness is above 50 um.

[0062] FIG. 9D illustrates another embodiment, where the perforated gas plate 915, conductive ring 920 and support ring 925 in former embodiments are united as one piece perforated gas plate (or GDP) 915 in this embodiment. As quite different from the prior art, the one piece perforated gas plate 915 can be made of metals, for instance, Al alloy, and the surface can be protected by the deposition of A-coatings 935, such as A-Y.sub.2O.sub.3. As comparing to the prior art, the formation of showerhead by A-Y.sub.2O.sub.3 coating 935 over the perforated gas plate 915 can reduce the product cost, simplifies the assembly and manufacture procedure of shower head, and increase the work life time. Another advantage is that it provides the possibility to refurbish the used showerhead simply by the re-deposition of A-coating 935 over the one piece perforate gas plate 915. In addition, it is more easy to form the A-coating packaged showerhead, as again another embodiment showing in FIG. 9E, since the deposition of A-coating is carried out on the showerhead that formed only by the assembly of the one piece perforated gas plate 915 to the conductive plate 905 and back plate 910.

[0063] FIG. 9F illustrates yet another embodiment of the invention. FIG. 9F is drawn as a callout from FIG. 9E to indicate that it depicts an enlarge section of a showerhead similar to that shown in FIG. 9E, except that it has a different coating scheme. In the embodiment of FIG. 9F, the perforated gas plate 915 has an intermediate layer or coating 913. The intermediate layer is formed on the roughened surface of the perforate gas plate 915, and the surface of the intermediate layer where the A-coating is deposited thereon also has a roughened surface. The intermediate layer may be, for example, an anodized layer or a plasma sprayed Y.sub.2O.sub.3 coating. Then an advanced coating 935, according to any of the embodiments described herein, is deposited as a single layer or multi-layered structure over the intermediate layer or coating 913. Moreover, each of the A-coating 935 and the intermediate layer 913 can be formed as the multi-layered coatings, so that the thickness of the coating can be increased and the structure stability of the deposited coatings can be improved.

[0064] 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-Y.sub.2O.sub.3 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 FIG. 9D or on the surface of the assembled showerhead as showing in FIG. 9E. Since the deposition of A-coating is directly on the anodized surface, there is no interfacial issue between A-coating and anodization, which usually exists between the PS Y.sub.2O.sub.3 coating and the anodized surface as the PS Y.sub.2O.sub.3 is normally deposited on the bare Al alloy, to reach a good adhesion of PS Y.sub.2O.sub.3 coating to the chamber parts.

[0065] According to various embodiments, the intermediate layer or coating could be of metals, alloys, or ceramics (such as Y.sub.2O.sub.3, YF.sub.3, ErO.sub.2, SiC, Si.sub.3N.sub.4, ZrO.sub.2, Al.sub.2O.sub.3, 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 Y.sub.2O.sub.3, YF.sub.3, ErO.sub.2, SiC, Al.sub.2O.sub.3 and their combinations or combination of them with other materials.

[0066] 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-Y.sub.2O.sub.3 on anodized surface, Al.sub.2O.sub.3 or Y.sub.2O.sub.3 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.

[0067] 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.

[0068] 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.