Forming aluminum nitride coating on aluminum-containing metal

Abstract

One example provides a method of forming a grown aluminum nitride coating on a component comprising aluminum-containing metal. The method comprises placing the component into a controlled atmosphere environment, heating the component to an aluminum nitride growth temperature, introducing a vapor of an aluminum oxide removal agent into the controlled atmosphere environment upstream of the component, and introducing a flow of a nitrogen-containing gas into the controlled atmosphere environment while heating the component and while introducing the vapor of the aluminum oxide removal agent to grow the grown aluminum nitride coating.

Description

FORMING ALUMINUM NITRIDE COATING ON ALUMINUM-CONTAINING METALBACKGROUND

[0001] Semiconductor device fabrication processes can involve many steps of material deposition, patterning, and removal to form integrated circuits on substrates. Many processing tools used to make integrated circuits utilize processing chambers in which a substrate is exposed to a controlled chemical environment. Over a number of processing cycles, processing residues can form on surfaces within a processing chamber. Thus, to prevent such residues from contaminating substrates during processing, the processing chamber can be periodically cleaned. Cleaning can involve, for example, forming a plasma using a fluorine-containing compound. Reactive fluorine-containing species formed in the plasma can react with residues in the processing chamber to form volatile products that can be removed from the processing chamber.SUMMARY

[0002] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

[0003] One example provides a method of forming a grown aluminum nitride coating on a component comprising aluminum-containing metal. The method comprises placing the component into a controlled atmosphere environment, heating the component to an aluminum nitride growth temperature, introducing a vapor of an aluminum oxide removal agent into the controlled atmosphere environment upstream of the component, and introducing a flow of a nitrogen-containing gas into the controlled atmosphere environment while heating the component and while introducing the vapor of the aluminum oxide removal agent to grow the grown aluminum nitride coating.

[0004] In some such examples, the nitrogen-containing gas comprises molecular nitrogen.

[0005] Alternatively or additionally, in some such examples, the nitrogencontaining gas omits hydrogen.

[0006] Alternatively or additionally, in some such examples, introducing the vapor of the aluminum oxide removal agent comprises introducing magnesium vapor into the controlled atmosphere environment.

[0007] Alternatively or additionally, in some such examples, introducing magnesium vapor into the controlled atmosphere environment comprises heating a magnesium powder that comprises a multi-modal particle size distribution.

[0008] Alternatively or additionally, in some such examples, the method further comprises, prior to introducing the vapor of the aluminum oxide removal agent and the nitrogen-containing gas, introducing a flow of an inert gas into the controlled atmosphere environment while heating the component up to the aluminum nitride growth temperature.

[0009] Alternatively or additionally, in some such examples, heating the component comprises heating the component to a temperature of 550 °C or lower.

[0010] Alternatively or additionally, in some such examples, the component comprises a showerhead, and wherein growing the grown aluminum nitride coating comprises growing the grown aluminum nitride coating on the interior surfaces of outlet holes of the showerhead and on an exterior surface of the showerhead.

[0011] Alternatively or additionally, in some such examples, introducing the vapor of the aluminum oxide removal agent comprises volatilizing the aluminum oxide removal agent using a different heater than a heater used to heat the component.

[0012] Alternatively or additionally, in some such examples, introducing the vapor of the aluminum oxide removal agent comprises volatilizing the aluminum oxide removal agent using a same heater as a heater used to heat the component.

[0013] Alternatively or additionally, in some such examples, growing the aluminum nitride coating comprises growing the aluminum nitride coating to a thickness of 1 micron or greater.

[0014] Another example provides a component for a substrate processing tool, the component comprising an aluminum-containing metal, and a grown aluminum nitride coating disposed on a processing chemical-exposed surface of the aluminum- containing metal.

[0015] In some such examples, the grown aluminum nitride coating has a thickness of 1 micron or greater.

[0016] Alternatively or additionally, in some such examples, the aluminum- containing metal is an AL-6061 aluminum alloy.

[0017] Alternatively or additionally, in some such examples, the component comprises a showerhead comprising outlet holes with interior surfaces, and wherein the aluminum nitride coating is on the interior surfaces of the outlet holes and on showerhead surfaces outside of the outlet holes.

[0018] Alternatively or additionally, in some such examples, the component comprises a pedestal configured to hold a substrate.

[0019] Alternatively or additionally, in some such examples, the component is a processing chamber, and the grown aluminum nitride coating is on an interior surface of the processing chamber.

[0020] Another example provides a method of growing an aluminum nitride coating on a component comprising aluminum-containing metal. The method comprises placing component into a controlled atmosphere environment, heating the component in the presence of an inert gas to an aluminum nitride growth temperature, introducing magnesium vapor into the controlled atmosphere environment upstream of the component, and upon reaching the aluminum nitride growth temperature, introducing a flow of molecular nitrogen into the controlled atmosphere environment while introducing the magnesium vapor to grow the grown aluminum nitride coating.

[0021] In some such examples, growing the grown aluminum nitride coating comprises growing the grown aluminum nitride coating on the interior surfaces of the outlet holes.

[0022] Alternatively or additionally, in some such examples, growing the aluminum nitride coating comprises growing the aluminum nitride coating to a thickness of 1 micron or greater.

[0023] Alternatively or additionally, in some such examples, introducing magnesium vapor into the controlled atmosphere environment comprises heating a magnesium powder comprises a multi-modal particle size distribution.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows an example Al-6061 alloy coupon used in aluminum nitride coating growth experiments.

[0025] FIG. 2 shows an example process flow for forming an aluminum nitride coating on the coupon of FIG. 1.

[0026] FIG. 3 shows an example placement of the coupon of FIG. 1 and powdered magnesium in an example controlled atmosphere environment comprising a tube furnace.

[0027] FIG. 4 shows an example temperature versus time profile for growth of a grown aluminum nitride film on the coupon of FIG. 1 using the process flow of FIG. 2.

[0028] FIG. 5 shows a graph of the Gibbs free energy versus energy for the reaction of aluminum metal and nitrogen.

[0029] FIG. 6 shows a graph of equilibrium partial pressures of oxygen and nitrogen for the oxidation and nitridation of aluminum.

[0030] FIG. 7 shows a graph of the Gibbs free energy versus temperatures for reactions of aluminum and magnesium with unit moles of oxygen and moisture.

[0031] FIG. 8 shows a 0-20 XRD scan of an example Al-6061 alloy sample after being subjected to a furnace temperature of 550 °C for 18 hours in a continuous flow of nitrogen gas without any magnesium powder present in the system.

[0032] FIG. 9 shows an example Al-6061 coupon, and example magnesium powder, before and after performing an example of the process flow of FIG. 2.

[0033] FIG. 10 shows (a) an x-ray diffraction pattern of the coupon of FIG. 9(d) after aluminum nitride coating growth, and (b) locations of peaks of wurtzitic aluminum nitride.

[0034] FIG. 11 shows (a) an x-ray diffraction pattern of the magnesium powder of FIG. 9 after aluminum nitride coating growth (FIG. 9(b)), and (b) Miller indices and locations of peaks of cubic magnesium nitride.

[0035] FIG. 12 shows SEM micrographs of the aluminum nitride coating on a coupon at different magnifications.

[0036] FIG. 13 shows cross-sectional images of an example aluminum nitride coating on a coupon.

[0037] FIG. 14 shows aluminum, nitrogen, magnesium and oxygen EDX (energy-dispersive x-ray spectroscopy) elemental dot-maps for the coupon of FIG. 9.

[0038] FIG. 15 shows (a) a low magnification TEM (transmission electron microscopy) micrograph of a coating cross-section near a coating / alloy interface; b) ahigher magnification TEM micrograph of the coating / substrate interface, with EDX spot scans from c) a ribbon-like dendrite, and d) a grain between the dendrites; e) a higher magnification TEM micrograph of dense dendritic structure further into the coating, with f) an EDX spot scan from a dendrite in this region.

[0039] FIG. 16 shows a plot of average thickness of aluminum nitride coatings as a function of the duration of nitrogen exposure at plateau temperature for coupons processed according to the example process flow of FIG. 2.

[0040] FIGS. 17a-f show optical micrographs of an example aluminum nitride- coated sample (FIG. 17a), a polished cross section of the sample (FIG.17b), an SEM micrograph of the coating cross section in the smaller hole (FIG. 17c) with the coating highlighted by the N (nitrogen) EDX elemental dot map (FIG. 17d), and an SEM micrograph of the surface coating cross-section (FIG. 17e) with the coating highlighted by the N EDX elemental dot map (FIG. 17f).

[0041] FIG. 18 shows a sample coupon comprising a grown aluminum nitride coating after being subjected to six thermal cycles to a temperature of 400 °C.

[0042] FIG. 19 shows an example processing tool.

[0043] FIG. 20 shows an example showerhead for a processing tool.

[0044] FIG. 21 shows a sectional view of an example showerhead for a processing tool.DETAILED DESCRIPTION

[0045] As described above, a processing chamber of a processing tool can be periodically cleaned to remove residues from substrate processing. Cleaning can involve, for example, forming a plasma using a fluorine-containing molecule, such as molecular fluorine, hydrogen fluoride, or a fluorocarbon. Reactive fluorine-containing species formed in the plasma can react with residues in the processing chamber to form volatile products (e.g. silicon tetrafluoride where a silicon oxide deposition chamber is being cleaned) that can be removed from the processing chamber.

[0046] Fluorine from such cleaning processes also can react with the materials used to make processing tool components. For example, various components in some deposition and etching chambers can be made from aluminum alloys, such as Al-6061. One example of such a component is a showerhead. Showerheads are processing chemical outlets for dispersing processing gases across an area of a substrate. Such a showerhead also can be used as an electrode to form a capacitively coupled plasma forplasma-enhanced substrate processing. Other components that can be made from aluminum alloys include processing chamber walls and substrate holders (e.g. pedestals). Al-6061 contains magnesium (e.g. 0.8 - 1.2 weight percent). Aluminum and magnesium can react with fluorine in a fluorine-based cleaning process to form surface fluoride compounds. A magnesium fluoride layer formed when Al-6061 is exposed to fluorine can act as a protective layer that resists halogen diffusion. However, aluminum fluoride formed along with the magnesium fluoride can flake off over time. This poses a risk of contaminating substrates in the processing chamber. Further, metal fluoride coatings, such as magnesium fluoride, that form from exposure of the aluminum alloy to fluorine can be discontinuous, providing more surface area for forming aluminum fluoride. Also, over time, aluminum fluoride can form even in the presence of a magnesium fluoride surface layer.

[0047] To avoid risks posed by the use of uncoated aluminum-containing metal components in a processing chamber that is subjected to fluorine-based cleaning processes, aluminum-containing metal components can be coated with a protective coating. However, forming protective coatings on aluminum alloy processing chamber components can pose challenges. For example, reentrant geometries found on some parts such as showerheads can be difficult to completely coat using electroless nickel plating (ENi) and aluminum anodization. Silicon oxide / silicon nitride coatings can be conveniently applied in a processing chamber, but etch in fluorine cleans. As such, these coatings require replenishment after fluorine-based cleanings. This results in tool down-time.

[0048] One possible material that may resist damage from fluorine-based cleaning processes is aluminum nitride. Aluminum nitride is corrosion resistant when exposed to fluorine-based cleaning chemistries. Aluminum nitride also can withstand damage from chlorine-containing environments, such as chlorine etch chemistries used in dry etching processes. As such, a relatively thin, conformal coating of aluminum nitride may provide for an effective protective coating for aluminum-containing metal parts in a processing chamber.

[0049] Some potential methods for forming aluminum nitride coatings on aluminum-containing metal components include vapor deposition techniques. Example vapor deposition techniques include physical vapor deposition methods (e.g. sputtering), chemical vapor deposition, and atomic layer deposition. However, each of these can pose challenges. For example, sputtering is line-of-sight, in that the coatingbeing deposited grows at a much higher rate on surfaces facing the material source (e.g. a sputtering target) than on surfaces facing in other directions. As such, it can be difficult to coat inside surfaces of showerhead outlet holes using sputtering. Chemical vapor deposition tends to form non-conformal films. Further, current chemical vapor deposition techniques for forming aluminum nitride may be performed at temperatures that exceed the melting temperature of many aluminum alloys. One such method uses trimethylaluminum and ammonia respectively as the aluminum-containing precursor and reactant. However, such a method is performed at temperatures on the order of 1000 °C, whereas aluminum alloys can start melting at temperatures as low as 600 °C. Atomic layer deposition can form highly conformal films, but suffers from low growth rates, which increase the time and expense of forming the protective coatings.

[0050] Further, such deposited coatings may risk cracking and / or delamination when subjected to thermal cycling. At room temperature, aluminum has a face centered cubic (FCC) crystal structure. AIN assumes a hexagonal arrangement of atoms in the wurtzitic crystal structure, which resembles the zinc oxide structure. An important factor to consider is the difference in the coefficients of thermal expansion (CTE) of Al and AIN. Dissimilar CTE values between two conjoined materials can affect the adhesion negatively due to high thermal stresses during thermal cycling. This also becomes significant when dealing with AI-AIF3 systems.

[0051] A grown aluminum nitride coating, rather than a deposited aluminum nitride coating, may be more robust than a deposited coating as a protective coating on an aluminum-containing metal component. The term “grown aluminum nitride coating” as used herein refers to an aluminum nitride layer grown on aluminum that uses the underlying aluminum-containing metal substrate (e.g. an aluminum alloy component) as the aluminum source for the aluminum nitride film. In contrast, a deposited film utilizes a vapor phase aluminum-containing precursor that reacts with a nitrogen-containing reactant (e.g. ammonia, hydrazine, molecular nitrogen, etc.), or aluminum ions from a sputtering target, to form the aluminum nitride film. A grown aluminum nitride coating may adhere more strongly to the underlying aluminum- containing metal substrate than a deposited aluminum nitride coating. As such, a grown aluminum nitride coating may be less prone to damage from thermal cycling than a deposited aluminum nitride coating.

[0052] However, forming a grown aluminum nitride coating on an aluminum- containing metal substrate, such as a processing chamber component, poses challenges.Conventionally, aluminum nitride synthesis in bulk usually involves reduction of aluminum oxide (AI2O3) (alumina) in powder form by nitrogenous compounds such as ammonia or nitrogen-containing organic compounds. However, such methods are not feasible for growing surface coatings on aluminum-containing metal components. Nitrogen alone cannot be reacted directly with aluminum to create aluminum nitride, as the aluminum alloy is covered with protective aluminum oxide layer. Further, such methods are often performed at temperatures exceeding 1400 °C.

[0053] One approach in synthesizing aluminum nitride coatings on aluminum- containing metal substrate is to use a nitrogen carrier species. The nitrogen carrier species is selected to give either nascent nitrogen or a derivative which reduces the oxide layer and reacts with aluminum to form aluminum nitride. However, this process requires high temperatures, often exceeding the melting point of aluminum. Another approach is to ball mill the aluminum-containing metal components with coarse alumina powder in a nitrogen environment. The friction wears the protective oxide layer, and the milling energy facilitates nitrogen impregnation and dissociation on the alloy surface. However, this method is limited to small parts. Further, the ball milling disturbs the precise dimensions of the part. This makes the ball milling process unsuitable for fabrication of aluminum nitride coated processing tool components.

[0054] Yet another method to form a grown aluminum nitride coating is to heat the aluminum in nitrogen environment with magnesium powder in the vicinity. This facilitates alumina reduction as well as aluminum nitride nucleation. There have been several studies on this methodology, but none have been able to achieve full coverage of aluminum-containing metal parts.

[0055] Accordingly, examples are disclosed that relate to the nitridation of an aluminum-containing metal component in a manner that overcomes the difficulties described above. One example provides a method of forming a grown aluminum nitride coating on a component comprising an aluminum-containing metal. The method comprises placing the component into a controlled atmosphere environment, and heating the component to an aluminum nitride growth temperature. The method further comprises introducing a vapor of an aluminum oxide removal agent into the controlled atmosphere environment upstream of the component, and introducing a flow of a nitrogen-containing gas into the controlled atmosphere environment while heating the component and while introducing the vapor of the aluminum oxide removal agent to grow the grown aluminum nitride coating. In some examples, the aluminum oxideremoval agent comprises magnesium vapor. Further, in some examples, the nitrogencontaining gas comprises molecular nitrogen. As explained in more detail below, magnesium vapor can react with molecular nitrogen to form magnesium nitride. Magnesium nitride is strongly hygroscopic, and thus can help to remove water vapor from the controlled atmosphere environment. Further, magnesium metal also is an effective oxygen getter, and thus can help to remove oxygen from the controlled atmosphere environment that could otherwise react with aluminum to form aluminum oxide. This can allow the omission of hydrogen gas and / or other oxygen scavengers from the controlled atmosphere environment.

[0056] Without wishing to be bound by theory, when the magnesium is heated to a volatilization temperature (e.g. greater than 500 °C), the flow of nitrogencontaining gas carries the magnesium vapor downstream. The magnesium vapor can, in some examples, take the form of a burst of supersaturated magnesium vapor caused at least partially by the exothermal nitridation (combustion) of the magnesium powders. Magnesium reaching the aluminum-containing metal component can react with the nitrogen gas to form magnesium nitride. Thus, magnesium nitride can form all over the exposed surface of the aluminum metal-containing component. Magnesium nitride is less thermodynamically stable than aluminum nitride. Further, magnesium oxide is more thermodynamically stable than aluminum oxide. Thus, the magnesium nitride can react with aluminum oxide to remove a native aluminum oxide layer on the aluminum metal-containing component, forming magnesium oxide. Additionally, the magnesium nitride also can provide nitrogen to react with the aluminum to form the aluminum nitride. In other examples, other suitable materials than magnesium can be used to facilitate the growth of a grown aluminum nitride film on an aluminum- containing metal substrate. Suitable materials include other metals that can be volatilized, that form less thermodynamically stable nitrides than aluminum, and that form more thermodynamically stable oxides than aluminum. Examples of such materials can include calcium, barium and silicon. Each of these can form a more stable oxide than aluminum oxide, and a less stable nitride than aluminum nitride. However, these materials also may have lower vapor pressures than magnesium at coating growth temperatures. In yet further examples, different materials can be used to remove the native aluminum oxide layer and form the aluminum nitride coating. Additionally, in some examples, different material(s) can be used as oxygen getters and / or water vapor getters than magnesium / magnesium nitride.

[0057] As described in more detail below, additional aluminum nitride growth can be achieved by continuing the flow of nitrogen and the introduction of the magnesium vapor (or other aluminum oxide removal agent) while heating the component. In this manner, grown aluminum nitride coatings with continuous coverage on the component and having thicknesses in a range of 1 micron to 12 microns or greater can be formed by allowing the reaction to continue, for example, for between one to twenty hours. In other examples, depending upon reaction conditions, different growth rates can be achieved. In addition to outward growth by diffusion of aluminum through the grown aluminum nitride coating, some inward growth can occur as well.

[0058] In the specific example of Al-606 aluminum alloy, the magnesium present in the alloy can be insufficient for carrying out the process described above. Without wishing to be bound by theory, the magnesium in the aluminum alloy preferentially forms oxide over nitride at the surface of the alloy. This prevents nitridation from occurring, and thereby prevents growth of the grown aluminum nitride coating. Likewise, even after some thickness of aluminum nitride has been formed, additional growth can be poisoned where the controlled atmosphere environment has insufficient magnesium vapor. The magnesium deficiency, and / or the resulting magnesium nitride deficiency at the growth surface of the grown aluminum nitride coating, can lead to elevated layers of magnesium oxide at the growth surface, which can poison further growth.

[0059] More particularly, excessive oxygen concentrations in the flow of nitrogen can lead to excessive magnesium oxide formation on the aluminum nitride coating surface, particularly during the sample cooldown phase. Excessive magnesium oxide formation on the aluminum nitride surface coating is termed as ‘magnesium oxide poisoning’ since it inhibits further aluminum nitride coating growth. Residual magnesium and magnesium nitride in the powder bed getter the oxygen and moisture in the reaction chamber, respectively, thereby keeping the oxygen content sufficiently low to avoid magnesium oxide poisoning, provided the hermetic integrity of the chamber is maintained. Although the MgO is well integrated onto the sample surface (i.e., it does not come off by the force of compressed air), it is undesirable to have a large Mg concentration on the coating surface due to its deleterious effects on fluorine attack. Furthermore, it has been found that if an aluminum nitride coating with a relatively higher concentration of magnesium oxide (‘dark-colored’ coatings) was cooled down to room temperature and was then subjected to a second nitridation cyclein the presence of magnesium powders, the coating did not grow during the second cycle. This is in contrast with ‘beige-colored’ characteristic of less surface contamination, that would continue to grow during the second cycle. The “beigecolored” coatings were confirmed to be wurtzitic aluminum nitride by x-ray diffraction. Thus, a magnesium oxide poisoned region of a coating can be discerned by dark coloration, as opposed to a beige coloration. Magnesium oxide-poisoned surfaces also show a change in surface morphology. The presence of elevated Mg and O signals in the EDX scan of the surface also can be used to indicate magnesium oxide poisoning.

[0060] To ensure continued growth of an aluminum nitride coating being grown, sufficient levels of magnesium or other suitable oxygen getter should be maintained. On the other hand, the use of too much magnesium also can lead to issues with aluminum nitride coating growth. For example, too much magnesium powder can generate excess magnesium nitride. This can lead to contamination by magnesium nitride dust. It has been found that a particle size of magnesium particles can affect these conditions. For example, smaller particle sizes provide for a larger surface area than larger particle sized. Thus, when heated, smaller particle sizes can provide for higher magnesium vapor concentrations than larger particle sizes. As such, a concentration of magnesium vapor in the controlled atmosphere environment during growth of a grown aluminum nitride coating can be varied (with other variables remaining constant) by controlling a particle size distribution of magnesium particles that are heated. In some examples a multi-modal particle distribution can be used. As a more specific example, a bi-modal distribution can be used, with a first distribution centered around a smaller particle size and a second distribution centered around a larger particle size. Varying the relative amounts of the smaller and the larger particle size distributions can allow the magnesium vapor concentration to be controlled, in combination with control of temperature, gas flow rates, and other process variables. This can help avoid issues with both magnesium oxide poisoning and poor coverage at a leading edge of the part being coated (which can be referred to as the ‘front edge anomaly’).

[0061] More particularly, the effect of magnesium particle size on sample Al- 6061 substrates coated with a grown aluminum nitride film using a furnace setpoint of 560 °C for 18 hours of nitridation time was investigated. When only 65 pm diameter (coarse) powders were used, the conversion of magnesium to magnesium nitride (the ‘combustion’ process) appeared not to be homogeneous through the powder bed. Theresulting coating exhibited significant magnesium oxide poisoning. Conversely, when only 40 pm diameter (fine) powders were used, nitridation of the magnesium appeared to be uniform, but there was a significant front edge anomaly in this sample. When a mixture of 1g of coarse powder and 0.3g of fine powders was used, uniform nitridation of the powder mixture was seen, and the sample did not show a front edge anomaly.

[0062] In some examples that utilize magnesium vapor as an aluminum oxide removal agent, the magnesium can be volatilized by a same heat source that is used to heat the component. In some such examples, the magnesium powder and the component comprising the aluminum-containing metal can be placed in a same tube furnace. In such examples, the furnace can be heated to a temperature sufficient to volatilize the magnesium and to form magnesium nitride in sufficient quantity to avoid poisoning from magnesium oxide. It can be desirable to maintain a component temperature of 550 °C or lower, as aluminum alloys can begin to melt at temperatures of approximately 600 °C. However, a temperature of 550 °C or higher can be beneficial to produce a desirable concentration of magnesium vapor. Where a same furnace is used to heat the magnesium powder and the component, the magnesium powder can be placed in the hottest zone of the furnace, and the component can be placed downstream of the magnesium powder and in a somewhat cooler zone of the furnace. In other examples, the magnesium vapor can be produced using a different heater than that used to heat the component. In such examples, the magnesium powder used to produce the magnesium vapor can be heated to a temperature of 550 °C or greater, and the aluminum metal-containing component can be heated to a temperature of 550 °C or lower, but sufficiently high to drive the reactions disclosed herein.

[0063] It has been found that temperatures for the aluminum metal-containing component that are insufficiently high can result in magnesium oxide poisoning. When maintained within a temperature range of 455-499 °C, an aluminum nitride coating failed to grow on an Al-6061 substrate. Instead, magnesium oxide poisoning of the surface of the substate was observed. This suggests a possible temperature threshold below which the Al-alloy will not form AIN regardless of Mg vapor concentration in the vicinity. When an Al-6061 substrate was maintained in a temperature range of 499- 524 °C, an AIN coating did form on the surface, but there was significant magnesium oxide poisoning on the coating surface. When an Al-6061 substrate was maintained within a 524-549 °C range during aluminum nitride film grown, the desired aluminum nitride film was grown. Similarly, lower temperatures of the magnesium powder bed(below furnace setpoints of 530 °C) also lead to magnesium oxide poisoning, while the use of a setpoint of 560 °C (leading to the magnesium powder to be in a range of 570- 583 °C) lead to the desired aluminum nitride film growth.

[0064] It further has been found that magnesium oxide poisoning can occur during cool-down. Oxidation of magnesium is thermodynamically preferred to nitridation of magnesium, particularly at low temperatures. Thus, to avoid magnesium oxide formation during cool-down, efficient gettering of oxygen should be maintained. Efficient gettering can be maintained by maintaining a sufficiently high temperature for the magnesium powder during cool-down of the aluminum metal-containing part, based upon a particulate size and total mass of magnesium powder used.

[0065] The above-mentioned front-edge anomaly may arise due to coverage of the leading edge of the aluminum-containing part with loose magnesium nitride particulates. The particulates can provide a physical barrier for the magnesium and nitrogen gas flow, thereby hindering growth of the magnesium nitride coating. The front-edge anomaly is observed when a higher concentration of smaller magnesium particles is used, which can lead to a higher concentration of magnesium vapor at the “burst” when combustion begins. As such, magnesium particle size distribution can be tailored to avoid the front edge anomaly.

[0066] Further, the effect of nitridation time on the surface morphology of an AIN coating on an Al-6061 substrate was investigated. In this context, nitridation time is defined as the duration for which a plateau temperature is held before shutting off the furnace. Once shut off, it took roughly two hours for the furnace to cool down to room temperature in continuously flowing nitrogen gas. When nitridation time was 30 minutes, island regions bearing characteristic AIN crisscross morphology were observed on the Al-6061 substrate. When nitridation time was 1 hour, AIN formation covered the entire surface of the Al-6061 substrate. As time increased, more AIN was seen, while the original grains grew as columnar dendrites that spread in all directions. When nitridation time was 7 hours, larger cauliflower features emerged, which appeared columnar with gaps between them. When the nitridation time was 12 hours, the intercolumnar gaps seemed to get filled up. When the nitridation time was 18 hours, the lateral growth of the columns densified the surface of the coating, and a dense coating layer with reduced surface roughness was formed. The surface of the coating after 18 hours was found to have a distinct cauliflower-like surface morphology. Thus, 18 hours of nitridation time was taken as the standard.

[0067] As explained by example in the experimental results discussed below, the disclosed example methods can be used to form grown aluminum nitride coatings on parts with complex geometries, such as showerheads, that cannot be coated using line-of-sight physical vapor deposition methods. In particular, the disclosed examples can be used to form aluminum nitride coatings both on major surfaces of a showerhead (e.g. a substrate-facing surface of the showerhead), as well as on interior surfaces of outlet holes of the showerhead. Further, the grown aluminum nitride coatings were found to be stable and intact after undergoing several heating cycles between room temperature and 400 °C. Also, in some examples, the grown aluminum nitride films can be formed using molecular nitrogen, without using ammonia or other nitrogencontaining compounds. In some examples, the grown aluminum nitride films may be grown by passing the nitrogen-containing gas and aluminum oxide removal agent through the showerhead itself as part of a flow path. Additionally, the disclosed examples allow the omission of hydrogen gas as an oxygen getter.EXPERIMENTAL1. Materials and experimental methods1.1. Materials

[0068] FIG. 1 shows an illustration of an example Al-6061 alloy coupon used in the experiments. Aluminum alloy Al-6061 samples were procured in the form of cold rolled sheets comprising a thickness 102 between 3 / 16” - 1 / 4” (4.76 mm - 6.35 mm). Electrical discharge machining (EDM) was used to cut the sheet into square blocks of dimensions 104 0.6” x 0.6” (15.1 mm x 15.1 mm). A drill-press was used to punch two pairs of holes in each aluminum ‘coupon’, one pair 106 with a 1.8 mm diameter 108, and the other pair 110 with a 0.8 mm diameter 112. The coupons were then ground using silicon carbide emery papers of increasing grit (decreasing roughness) until desired surface finish was reached (usually 600 grit). The sample was cleaned by ultrasonication in deionized water. Table 1 below shows Al-6061 alloy composition by weight % of alloying constituents.Table 1

[0069] Magnesium in powder form was procured from Sigma Aldrich chemicals (230 mesh size or 0.40 pm median size of powder particles). 316 stainlesssteel (S.S.) wire mesh is used to contain the magnesium powder within the chamber. The mesh is rated as 200 x 600 mesh size, which corresponds to 200 openings per inch in one direction, and 600 openings in the perpendicular direction. 316 stainless steel sheets (thickness 1 / 32” or 0.79 mm) were used to make holder fixtures for the alloy coupon and magnesium powder. High temperature mica sheets (0.016” or 0.4 mm) were used to create partitions within the holder fixtures to direct gas flow. Ultra-high purity nitrogen (99.999% purity) and argon (99.9999% purity) gases were used.1.2. Experimental methods

[0070] FIGS. 2 and 3 show the experimental method detailed herein. FIG. 2 shows a flow diagram of the method. First, as shown in FIG. 2, an Al-6061 coupon 204 and Mg powder 202 are placed in a furnace at 206. These steps 204 and 202 are schematically shown in FIG. 3. FIG. 3 shows the schematic of the placement of the aluminum alloy and magnesium powder inside the furnace. Fixed amounts (for example, 0.5 g - 1.5 g) of Mg powders 302 were taken in a boat made of stainless steel wire mesh 304 and placed on the stainless steel holder 306 with support of mica paper cutouts 308. Similarly, an Al-6061 coupon 310 was hung on to another stainless steel holder 312 using stainless steel wires 314. The two holders 306 and 312 were then placed in a 45 mm inner diameter alumina tube 316 in a single-zone tube furnace, set at 560 °C. Referring back to FIG. 2, the alumina tube was then hermetically sealed shut to limit oxygen inlet, and a continuous argon flow was introduced at 208B, effusing out to a bubbler. Once the tube was sealed, air was evacuated by a roughing pump for a set amount of time. Any leakages or imperfect seals were revealed at this stage. The furnace was then turned on and the temperature was ramped up at 208 A, at a constant 10 °C / min, and the temperature was allowed to plateau at 210A. Once temperature plateau was reached, the argon gas was turned off, and the nitrogen gas flow was introduced at 210B.

[0071] Heating the sample in the presence of argon can allow the peak temperature of the furnace to be reached before conversion of magnesium into magnesium nitride begins. In contrast, heating the sample in the presence of nitrogen can allow magnesium nitride to form before the furnace has reached the peak temperature. The temperature spike caused by the commencement of magnesium nitride formation can be larger when magnesium nitride formation starts at a higher temperature. Thus, heating under argon and then introducing nitrogen once peakfurnace temperature has been reached can help to send a larger concentration of vapor phase magnesium to the coupon (or other aluminum parts, such as a showerhead or other processing chamber component) initially than heating under nitrogen. It has been found that the surfaces of the AIN coatings for samples with nitrogen flow during heatup tend to show a significantly larger propensity for magnesium oxide poisoning while coatings formed with heat-up in argon gas were much less likely to develop magnesium oxide on the surface.

[0072] The nitrogen flow continued at the set temperature for the desired duration, after which the furnace was turned off, and nitrogen flow continued until the furnace was cooled down to room temperature, at 212A and 212B. The method results in an AIN coated coupon 214, and in MgsN? sintered powder 216.

[0073] After deposition, the coating phase was characterized by x-ray diffraction (XRD) using 0-20 scans. The coating surface was characterized using scanning electron microscope (SEM). Furthermore, the samples were mounted in epoxy to examine in cross-section. The polished cross-sections were characterized in the SEM by secondary electron imaging, and energy dispersive x-ray spectroscopy (EDX).

[0074] Fluorination operations in a processing chamber of a processing tool can involve temperatures as high as 350 °C. The aluminum nitride coating grown on the aluminum alloy must thus withstand several thermal cycles. Aluminum nitride coated Al-6061 alloy samples were subjected six thermal cycles at 400 °C. FIG. 4 shows a schematic temperature versus time set up for the thermal cycles. Each cycle comprised a 1 hour of ramp-up period starting from room temperature, as shown at 402, then 45 minutes of dwell time at 400 °C, as shown at 404, and finally 2 hours of furnace cooldown to room temperature, as shown at 406. Weight change and visual inspection (color and appearance) were used to track changes, if any.2. Reaction thermodynamics2.1. Feasibility of nitridation of aluminum

[0075] The process to grow aluminum nitride on Al-6061 alloy requires nitrogen incorporation on the surface of the alloy to synthesize aluminum nitride directly on the surface. The reaction of aluminum and nitrogen forming aluminumnitride is thermodynamically favorable, as reflected in the Gibbs free energy versus temperature plot in FIG. 5. The large negative values of the Gibbs free energy of the reaction implies that the reaction is energetically favorable. However, this reaction is kinetically inhibited by the presence of the passivating aluminum oxide layer on the alloy, as seen below. This necessitates the removal or reduction of oxygen layer over the alloy surface.2.2. Inhibiting processes

[0076] FIG. 6 shows the equilibrium partial pressures 602, 604, 606, and 608 of oxygen and nitrogen for the oxidation and nitridation reactions shown in box 610, with unit activities of aluminum and magnesium, respectively. The miniscule values of the equilibrium partial pressures of oxygen and nitrogen suggest very high extent of conversion into respective oxide and nitride phases, reinforcing the high energetic favorability of the reactions. If the differences in partial pressures of oxidation against nitridation are compared for the respective metals, two things stand out. First, at unit activities of aluminum and magnesium, magnesium has a higher propensity for oxygen, while aluminum has a higher propensity for nitrogen. This implies that magnesium can reduce aluminum oxide. Secondly, it can be seen that oxygen equilibrium partial pressure is several orders less than nitrogen partial pressures in each case. Thus, oxidation in both cases has comparatively higher favorability. A miniscule amount of oxygen is sufficient to supersede nitridation reaction in favor of oxidation. Hence, not only does the oxide layer need to be removed from the alloy surface, but a sufficiently low level of oxygen must be maintained throughout the process. Moreover, it takes only a few seconds to grow the few nanometers thick aluminum oxide layer. Thus, the use of an oxygen getter is highly beneficial in the process.

[0077] Moisture can also be a source of oxygen. FIG. 7 shows the plot of Gibbs free energy versus temperatures plots for reactions 702, 704, 706, and 708 of Al and Mg with unit moles of oxygen and moisture. The plots imply that oxidation reactions are much more energetically favorable with oxygen as compared to moisture. Nonetheless, the Gibbs free energy of all the reactions have large negative values in hundreds of kilojoules. Thus, presence of moisture in the gas phase can provide oxygen that can also interfere in the nitridation process. As mentioned above, and as discussed in the next section, the magnesium powders get converted to magnesium nitride (Mg3N2), which is an excellent moisture getter.3. Results and discussion3.1. Nitriding without Mg powder

[0078] FIG. 8 shows a 0-20 XRD scan of an Al-6061 alloy sample after being subjected to a furnace temperature of 550 °C for 18 hours in a continuous flow of nitrogen gas without any magnesium powder present in the system. Apart from the labeled aluminum peaks 802, 804, 806, and 810 in the scan, no other discernible peaks can be seen. This clearly indicates that a flowing nitrogen atmosphere at high temperature is insufficient to synthesize surface aluminum nitride on an Al-6061 sample. This highlights the importance of removing the aluminum oxidelayer from the aluminum alloy, as even the energetically favorable nitridation reaction cannot commence without it.3.2. Nitridation with Mg powder

[0079] When an Al-6061 sample is subjected to high temperature with magnesium powder in the vicinity in a continuous nitrogen flow, it develops a graybrown coating over the entirety of its surface. At the same time, magnesium powder residue turns bright yellow in color, which is characteristic identifier of magnesium nitride. FIGS. 9A-9B show the magnesium powder, and FIGS. 9C-9D show the Al- 6061 coupon before and after subjecting them to the process.3.3. Crystal structure characterization

[0080] FIG. 10 shows (a) the X-ray diffraction (XRD) analysis of the sample after growing the aluminum nitride coating. Apart from the aluminum peaks 1002, several new peaks can be seen. All these peaks whose locations are marked by dashed vertical lines can be attributed to aluminum nitride in its wurtzitic form 1004. This result clearly demonstrates that the gray -brown appearance of the sample after the nitridation treatment (FIG. 9D) is due to the formation of a surface aluminum nitride coating layer.

[0081] FIG. 11 shows the X-ray diffraction peaks of the yellow residue obtained from the magnesium powder after the nitridation cycle. The peaks marked by the dashed vertical lines correspond to cubic magnesium nitride 1102. This is a clear indication that a significant portion of the magnesium powder gets converted to magnesiumnitride. Additionally, magnesium oxide 1104 and magnesium 1106 peaks are also observed, highlighted by the dotted vertical lines and dotted and dashed vertical lines, respectively. Recording the mass gain of the magnesium powder after nitridation gives a rough estimate of the conversion extent (measured on the scale 0-100% conversion, where 100% is when all the Mg is converted to magnesium nitride). The conversion extent is routinely above 80%.3.4. Microstructural analysis of aluminum nitride coating

[0082] FIG. 12 shows SEM micrographs of the aluminum nitride coating surface at different magnifications. At 500x magnification, in FIG. 12(a), we see that the surface is covered by ball-like, or ‘cauliflower-like’, grains of aluminum nitride. A closer examination at 5000x reveals a secondary morphology which resembles dendritic growth (FIG. 12(b)). It is noteworthy that the grain size in recrystallized Al- 6061 (~ 100 pm) is significantly larger than cauliflower size (~ few pm), thus there is no correlation between the two.

[0083] The aluminum nitride coated Al-6061 samples were sectioned using a precision saw and mounted in epoxy. Once the epoxy set in, the epoxy-clad samples were ground and polished to examine the cross-section of the aluminum nitride coating. FIGS. 13(a) and 13(b) show the cross-section of the aluminum nitride coating. The coating width is observed to be roughly 20 pm. The coating covers the entire substrate region visible in FIG. 13(a). In the magnified image 13(b), it can further be seen that the coating is dense, and the interface is free of pores or irregularities. The non-planarity apparent at the coating outer surface can be attributed to the cauliflower topography of aluminum nitride coating. Despite that, there is good uniformity of coating throughout the substrate. In FIGS. 13(a)-(b), the alloying precipitates are visible in the cross-section SEM image, some of which are indicated by arrows. These precipitates comprise primarily iron (Fe), silicon (Si), magnesium (Mg), chromium (Cr), manganese (Mn), and zinc (Zn). These precipitates also act as markers in the deposition process. The precipitates are never observed in the coating but always in the substrate. If the coating grew by inward diffusion of nitrogen through the growing aluminum nitride coating, then it may be expected to see some of these precipitates in the coating. The absence of the precipitates supports an outward diffusion of aluminum through the growing aluminum nitride coating as the coating growth mechanism.

[0084] FIG. 14 shows Al, N, Mg and O EDX elemental dot-maps of the coating and alloy at a lower magnification. The leftmost EDX dot-map shows a composite of the Al, N, Mg, and O EDX dot-maps. The nitrogen map highlights the coating region clearly and confirms that the distinct layer comprises primarily AIN. At the coating / alloy interface, Mg and O are highlighted slightly. This may show that Mg can help remove the protective aluminum oxide at the interface by replacing it with magnesium oxide. The removal of the native aluminum oxide on the sample surface facilitates the formation of the aluminum nitride coating.

[0085] FIG. 15(a) shows a TEM micrograph of a coating near the coating / alloy interface. The figure shows dendritic structures in the coating, with the spatial density of dendrites increasing from the coating / substrate interface towards the coating surface. FIG. 15(b) shows a higher magnification micrograph of the interface. FIG. 15(c) is an EDX spot scan from a ribbon like dendrite close to the interface, showing it to be an aluminum nitride grain with additional magnesium, silicon, and oxygen peaks. FIG. 15(d), taken from a grain between two aluminum nitride dendrites, shows that that aluminum grains are located between aluminum nitride dendrites, close to the interface. The regions between the dendrite appear to have a higher Al concentration, while the dendrites appear to be richer in N. Although Al appears to have a higher concentration between the dendrites, they also exist at a lower concentration in the dendrites. This suggests that the AIN coating is actually two phase, with an AIN dendritic network, with Al grains between the AIN dendrites. Further, this suggests that the nucleation density of aluminum nitride on the coating surface is sparse, and aluminum grains are formed between the laterally spreading dendrites in a growing coating, till the dendrites coalesce around the center of FIG 15(a). FIG. 15(e) shows dense packing of dendrites from this region at a higher magnification. An EDX spot scan from a dendrite from this region (FIG. 15(f)) shows that the grain is essentially aluminum nitride with virtually no magnesium, silicon or oxygen signals seen in aluminum nitride grains close to the interface. FIGS. 15(a)-(f) show that the coating starts out as a two-phase mixture of aluminum nitride and aluminum, with the aluminum nitride content increasing away from the interface till a dense packing of aluminum nitride dendrites is achieved. This initial two-phase mixture near the coating substrate interface has been previously observed in diffusion coatings formed on nickel-chromium alloys by hot-dip aluminizing. The presence of magnesium and oxygen signals from the aluminum nitride grain near the interface is consistent with the presence of magnesium oxide (formed byremoval of the native aluminum oxide layer), although individual grains were not found with only magnesium or oxygen signal. This could be either because the magnesium oxide grains are smaller than the thickness of the TEM sample / beam size, or that magnesium and oxygen are incorporated as dopants in the initially growing aluminum nitride at the interface. The presence of Si in the aluminum nitride whisker near the interface is likely from the silicon in the alloy. The fact that silicon is not present in the aluminum nitride grains away from the interface corroborates this hypothesis. Again, no individual grains near the interface with only silicon, nitrogen and / or oxygen signals were found.3.5. Coating growth trend

[0086] Coatings were grown for different growth times using the same overall procedure described in the experimental section. The coatings were polished in crosssection and SEM images of the coating cross-sections were taken. The average thicknesses of the coatings were measured by image analysis using ImageJ software (developed by National Institutes of Health and the Laboratory for Optical and Computational Instrumentation (LOCI, University of Wisconsin)). FIG. 16(a) shows a plot of average thickness of coatings as a function of the duration of nitrogen exposure at plateau temperature. The thickness versus time plot roughly follows a parabolic curve. The thickness squared shown in FIG. 16(b) consequently shows a reasonable linear fit with time. This implies that that the coating growth kinetics is controlled by outward Fickian Al diffusion through the growing aluminum nitride coating.

[0087] FIGS. 17(a)-(f) show optical micrographs of the coated sample (Fig. 17(a)), and a polished cross section of the sample (Fig.17(b)). Figure 17(c) shows an SEM micrograph of the coating cross section in the smaller hole, with the coating highlighted by the N (nitrogen) EDX elemental dot map shown in Figure 17(d). Figure 17(e) shows an SEM micrograph of the surface coating cross-section with the coating highlighted by the N EDX elemental dot map shown in Figure 17(f). As seen in FIGS. 17(a)-(f), both the planar surfaces and hole surfaces are completely covered by aluminum nitride coating, that are relatively uniform in their specific locations. However, the aluminum nitride coating on the planar surface is roughly twice as thick as and has a higher surface roughness compared to the coating in the hole.

[0088] There may be many reasons for this thickness difference at the two locations. These include differences in surface treatment and the gas-flow dynamicspast these surfaces. The planar surface was subjected to surface preparation (grinding, polishing, etc.). However, the holes did not receive the same surface treatment. The planar surface experiences direct flow of nitrogen and other gaseous precursors, while the hole surface is obstructed from direct gas flow. These differences between the surface pre-treatment and gas flow dynamics are expected to influence the nucleation and growth characteristics. Nevertheless, this process successfully grows an aluminum nitride coating on all surfaces of the sample, including restricted features such as holes indicating process robustness even with differences in the surface treatments.3. 7. Thermal cycling performance of aluminum nitride coating

[0089] FIG. 18(a) shows a sample before thermal cycling. FIG. 18(b) shows a sample subjected to 6 cycles, each of 45 minutes dwell time at 400 °C. No weight change was observed after thermal cycling, and visually no coating delamination and no changes in the sample color and texture were observed. This implies that the coating is stable under thermal cycling conditions found in the fluorination process.

[0090] As mentioned above, TEM examination of the coating revealed that the coating is a composite of AIN dendrites in an Al matrix. This unique microstructure can help give the coating increased thermal fatigue resistance and the coating can stay adherent to the substrate after several thermal cycles despite a fivefold difference in coefficients of thermal expansions of Al and AIN.

[0091] Further, the factor of 5 difference in CTE value could lead to high interfacial stresses if the coating was indeed pure AIN, and could potentially lead to coating spallation. However, it is expected that the A1N / A1 composite would have a lower overall CTE value that is closer to Al-6061 than AIN alone. This may be a reason why the interfacial stresses are reduced, and the coatings exhibit excellent adhesion on thermal cycling.3.8. Mechanism of coating formation

[0092] Despite being favorable energetically, the nitridation of aluminum alloy does not commence with nitrogen alone due to the protective aluminum oxide layer on alloy surface. The primary role of magnesium powder is to assist in the removal of the aluminum oxide layer. At temperatures exceeding 550 °C, magnesium evaporates due to its low vapor pressure. When the magnesium vapor comes in contact with the native aluminum oxide on the surface of the sample, the aluminum oxide is reduced, andmagnesium oxide forms. The outward growth of the coating ensures that the magnesium oxide remains at the coating / alloy interface (FIG. 14). The second role of the magnesium is to getter trace oxygen in the nitrogen by forming magnesium oxide on the surface of the magnesium powders. However, magnesium oxide is not protective or self-passivating, and when nitrogen is introduced, magnesium is rapidly converted to magnesium nitride. Additionally, magnesium nitride is an excellent moisture absorber, thereby contributing to the removal of the additional source of oxygen in the input gases. Removal of both oxygen sources is desired as oxygen preferentially reacts with aluminum and magnesium even at very low concentrations and can hinder the nitridation process, as seen in the thermodynamic calculations (FIGS. 5 and 6). Moisture can also potentially break down the aluminum nitride, releasing ammonia. It is believed that magnesium and magnesium nitride in this process actively getter trace oxygen and moisture.5. Conclusions

[0093] In summary, a process to grow aluminum nitride coatings over Al-6061 aluminum alloy has been successfully developed. In some examples, the process uses only gaseous nitrogen as the nitrogen carrier. Further, in some examples, the process also uses magnesium powder, which helps in removal of the native protective aluminum oxide surface layer on the alloy surface and getters any trace oxygen in the nitrogen (and argon) gas. The removal of the aluminum oxide layer exposes the surface of the alloy to nitrogen, and the aluminum nitride coating grow by outward diffusion of aluminum through the growing aluminum nitride coating. The magnesium powder also gets nitride to magnesium nitride which, as an excellent moisture getter, also removes an additional oxygen source in the reaction chamber. The coatings formed are dense and uniform and cover the entire surface of the alloy samples. This process also serves to uniformly coat features with large aspect ratios, demonstrated by coverage on the surface of narrow holes in the Al-6061 alloy samples. The coatings were stable when subjected to several 400 °C thermal cycles.EXAMPLE PROCESSING TOOLS AND COMPONENTS

[0094] FIG. 19 shows an example processing tool 1900 for processing a substrate. The processing tool 1900 can be configured for thermal or plasma-enhancedchemical vapor deposition (CVD), thermal or plasma-enhanced atomic layer deposition(ALD), etching processes such as reactive ion etching (RIE), atomic layer etching(ALE), cryoetching, and / or other substrate processes. The processing tool 1900 comprises a processing chamber 1902 including a showerhead 1904. The showerhead 1904 comprises a stem 1906 connected to the processing chamber. The showerhead 1904 also includes a lower portion 1910 that extends radially outwardly from a bottom of the stem 1906. As described in more detail below, the showerhead 1904 includes a plurality of outlet holes formed in a major plane of the showerhead.

[0095] The processing tool 1900 further includes a pedestal 1914. The depicted pedestal 1914 is configured as an electrostatic chuck pedestal. During operation, a substrate 1916 is arranged on the pedestal 1914. Electrodes 1918 electrostatically attract the substrate 1916 during processing to hold the substrate securely. In other examples, other types of pedestals can be used.

[0096] The processing tool 1900 is configured to perform plasma-enhanced substrate processing. Thus, the processing tool 1900 includes an RF generating system 1920 to generate and output RF power. In this example, the pedestal 1914 is configured as a powered electrode, and the showerhead 1904 is grounded. In other examples, the showerhead 1904 can receive power from the RF generating system 1920, and the pedestal 1914 can be grounded. The RF generating system 1920 includes an RF generator 1922 that generates the RF power. The RF generating system 1920 further includes a matching and distribution network 1924. The substate processing tool further includes an actuator 1926 and a lift pin assembly 1928. The lift pin assembly includes P lift pins 1928, where P is an integer greater than 2. The actuator 1926 and the lift pin assembly 1928 are used during loading and unloading of the substrate 1916 from the chamber.

[0097] The processing tool 1900 further comprises a gas delivery system 1930. The gas delivery system 1930 includes one or more gas sources 1932-1, 1932-2, ... , and 1932-N (collectively gas sources 1932), where N is an integer greater than zero. The gas sources 1932 supply one or more processing gases such as deposition precursors, purge gas, etch gas, etc. In some examples, vaporized precursors may also be used (not shown). The gas sources 1932 are connected by valves 1934-1, 1934-2, ... , and 1934-N (collectively valves 1934), mass flow controllers 1936-1, 1936-2, ... , and 1936-N (collectively mass flow controllers 1936), and valves 1938-1, 1938-2, ... , and 1938-N (collectively valves 1938) to a manifold 1940. An output of the manifold 1940is fed by the gas delivery system 1930 to the processing chamber 1902. For example, the output of the manifold 1940 is fed to the showerhead 1904.

[0098] A heater controller 1942 (“HC”) is connected to resistive heaters arranged in the pedestal 1914. The heater controller 1942 can be used to control a temperature of the pedestal 1914. In addition, the pedestal 1914 can include internal channels (not shown) to flow a fluid from a fluid source (not shown) to provide further control of the pedestal and substrate temperatures.

[0099] A valve 1950 and pumping system 1952 can be used to evacuate reactants and products from the processing chamber 1902 and / or to control pressure in the processing chamber. A controller 1960 can be used to control the various components of the processing tool 1900 described herein. For example, the controller 1960 can cause a robot arm 1970 to load the substrate 1916 onto the pedestal 1914, and unload the substrate 1916 from the pedestal 1914. The controller 1960 communicates with the gas delivery system 1930 to control supply of process, purge and / or inert gases. The controller communicates with the valve 1950 and pump 1952 to control pressure within the processing chamber and / or evacuation of reactants. The controller 1960 also causes a voltage source 1972 to output voltage to the electrodes 1918 to clamp and unclamp the substrate.

[0100] FIG. 20 shows an example showerhead 2002 for a processing tool, and FIG. 21 shows a sectional view of the example showerhead 2002 for a processing tool. The example showerhead 2002 of FIGS. 20 and 21 can be used as showerhead 1904 in processing tool 1900, for example. As can be seen in FIG. 20, the showerhead has a substrate-facing surface 2004 in which a plurality of outlet holes such as outlet hole 2006 are formed. As can be seen in FIG. 21, the plurality of outlet holes such as outlet hole 2006 lead from a plenum 2102 within the showerhead to the outside of the showerhead. Processing gases can pass through the outlet holes from the plenum 2102 to a substrate being processed, as indicated schematically in FIG. 21 by diverging plumes 2104 extending downwardly from outlet holes. The showerhead 2002 of FIGS. 20 and 21 can be formed from an aluminum-containing metal, such as an aluminum alloy. Example aluminum alloys include Al-6061. As described above, the example methods disclosed herein of forming grown aluminum nitride coatings can be used to coat the showerheads of FIGS. 20 and 21. Because the disclosed examples do not use line-of-sight techniques such as sputtering, aluminum nitride coatings can be formed on the substrate-facing surface and other outer surfaces of the showerheads, as well ason interior surfaces within the outlet holes, and potentially other interior surfaces that the aluminum oxide removal agent (e.g. magnesium vapor / magnesium nitride) and nitrogen gas can reach during a treatment process. Further, in some examples, a grown aluminum nitride coating can be formed on other components within a processing tool than a showerhead. Examples include pedestals (e.g. pedestal 1914 of FIG. 19) and interior processing chamber walls (e.g. interior walls of processing chamber 1902), among other components.

[0101] The subject matter of the present disclosure includes all novel and non- obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and / or properties disclosed herein, as well as any and all equivalents thereof.

Claims

CLAIMS:

1. A method of forming a grown aluminum nitride coating on a component comprising aluminum-containing metal, the method comprising: placing the component into a controlled atmosphere environment; heating the component to an aluminum nitride growth temperature; introducing a vapor of an aluminum oxide removal agent into the controlled atmosphere environment upstream of the component; and introducing a flow of a nitrogen-containing gas into the controlled atmosphere environment while heating the component and while introducing the vapor of the aluminum oxide removal agent to grow the grown aluminum nitride coating.

2. The method of claim 1, wherein the nitrogen-containing gas comprises molecular nitrogen.

3. The method of claim 1, wherein the nitrogen-containing gas omits hydrogen.

4. The method of claim 1 wherein introducing the vapor of the aluminum oxide removal agent comprises introducing magnesium vapor into the controlled atmosphere environment.

5. The method of claim 1, wherein introducing magnesium vapor into the controlled atmosphere environment comprises heating a magnesium powder that comprises a multi-modal particle size distribution.

6. The method of claim 1, further comprising, prior to introducing the vapor of the aluminum oxide removal agent and the nitrogen-containing gas, introducing a flow of an inert gas into the controlled atmosphere environment while heating the component up to the aluminum nitride growth temperature.

7. The method of claim 1, wherein heating the component comprises heating the component to a temperature of 550 °C or lower.

8. The method of claim 1, wherein the component comprises a showerhead with outlet holes having interior surfaces, and wherein growing the grown aluminum nitride coating comprises growing the grown aluminum nitride coating on the interior surfaces of the outlet holes and on an exterior surface of the showerhead.

9. The method of claim 1, wherein introducing the vapor of the aluminum oxide removal agent comprises volatilizing the aluminum oxide removal agent using a different heater than a heater used to heat the component.

10. The method of claim 1, wherein introducing the vapor of the aluminum oxide removal agent comprises volatilizing the aluminum oxide removal agent using a same heater as a heater used to heat the component.

11. The method of claim 1, wherein growing the aluminum nitride coating comprises growing the aluminum nitride coating to a thickness of 1 micron or greater.

12. A component for a substrate processing tool, the component comprising: an aluminum-containing metal; and a grown aluminum nitride coating disposed on a processing chemical-exposed surface of the aluminum-containing metal.

13. The component of claim 12, wherein the grown aluminum nitride coating has a thickness of 1 micron or greater.

14. The component of claim 12, wherein the aluminum-containing metal is an AL- 6061 aluminum alloy.

15. The component of claim 12, wherein the component comprises a showerhead comprising outlet holes with interior surfaces, and wherein the aluminum nitride coating is on the interior surfaces of the outlet holes and on showerhead surfaces outside of the outlet holes.

16. The component of claim 12, wherein the component comprises a pedestal configured to hold a substrate.

17. The component of claim 12, wherein the component is a processing chamber, and wherein the grown aluminum nitride coating is on an interior surface of the processing chamber.

18. A method of growing an aluminum nitride coating on a component comprising aluminum-containing metal, the method comprising: placing component into a controlled atmosphere environment; heating the component in the presence of an inert gas to an aluminum nitride growth temperature; introducing magnesium vapor into the controlled atmosphere environment upstream of the component; and upon reaching the aluminum nitride growth temperature, introducing a flow of molecular nitrogen into the controlled atmosphere environment while introducing the magnesium vapor to grow the grown aluminum nitride coating.

19. The method of claim 18, wherein growing the grown aluminum nitride coating comprises growing the grown aluminum nitride coating on the interior surfaces of the outlet holes and on an exterior surface of the showerhead.

20. The method of claim 18, wherein introducing magnesium vapor into the controlled atmosphere environment comprises heating a magnesium powder comprises a multi-modal particle size distribution.

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