PLASMA RESISTANT SEMICONDUCTOR PROCESSING CHAMBER COMPONENTS

Abstract

Described herein are components of a semiconductor processing apparatus, where at least one surface of the component is resistant to a halogen-containing reactive plasma. The component includes a solid structure having a composition containing crystal grains of yttrium oxide, yttrium fluoride or yttrium oxyfluoride and at least one additional compound selected from an oxide, fluoride, or oxyfluoride of neodymium, cerium, samarium, erbium, aluminum, scandium, lanthanum, hafnium, niobium, zirconium, ytterbium, hafnium, and combinations thereof.

Claims

1. A component of a semiconductor processing apparatus, wherein a surface of the component is resistant to a halogen-comprising reactive plasma, the component comprising: a solid structure having an overall uniform composition, wherein the composition comprises: crystal grains selected from a group consisting of yttrium oxide, yttrium fluoride and yttrium oxyfluoride, and at least one additional compound selected from a group consisting of an oxide, fluoride, or oxyfluoride of neodymium, cerium, samarium, erbium, aluminum, scandium, lanthanum, hafnium, niobium, zirconium, ytterbium and combinations of an oxide, fluoride or oxyfluoride of at least one of these elements.

2. The component of claim 1, wherein the composition further comprises an amorphous phase comprising yttrium and fluorine.

3. The component of claim 1, wherein the composition comprises a yttrium aluminum oxyfluoride (YAlOF) amorphous phase.

4. The component of claim 1, wherein the composition comprises a yttrium oxide.

5. The component of claim 1, wherein in the composition comprises a yttrium fluoride.

6. The component of claim 1, wherein the composition comprises a yttrium oxyfluoride.

7. The component of claim 1, wherein the at least one additional compound comprises aluminum oxide, aluminum fluoride or aluminum oxyfluoride.

8. The component of claim 1, wherein the at least one additional compound comprises zirconium oxide, zirconium fluoride or zirconium oxyfluoride.

9. The component of claim 1, wherein the at least one additional compound comprises an oxide, fluoride or oxyfluoride of neodymium, cerium, samarium, erbium, scandium, lanthanum, hafnium, niobium, ytterbium or hafnium.

10. The component in accordance with claim 1, wherein the component is selected from a group consisting of a shower head for gas distribution, a process chamber lid interior, a process chamber liner and an electrostatic chuck.

11. A component of a processing apparatus, comprising: a solid structure having a surface resistant to a halogen-comprising reactive plasma, wherein the composition comprises: crystal grains selected from a group consisting of yttrium oxide, yttrium fluoride, and yttrium oxyfluoride, and at least one additional compound selected from a group consisting of erbium oxide, erbium fluoride, erbium oxyfluoride, aluminum oxide, aluminum fluoride, aluminum oxyfluoride, hafnium oxide, hafnium fluoride, hafnium oxyfluoride, zirconium oxide, zirconium fluoride, zirconium oxyfluoride, and combinations thereof.

12. The component of claim 11, wherein the composition further comprises an amorphous phase comprising yttrium and fluorine.

13. The component of claim 11, wherein the composition comprises a yttrium aluminum oxyfluoride (YAlOF) amorphous phase.

14. The component of claim 11, wherein the composition comprises a yttrium oxide.

15. The component of claim 11, wherein in the composition comprises a yttrium fluoride.

16. The component of claim 11, wherein the composition comprises a yttrium oxyfluoride.

17. The component of claim 11, wherein the at least one additional compound comprises aluminum oxide, aluminum fluoride or aluminum oxyfluoride.

18. The component of claim 11, wherein the at least one additional compound comprises zirconium oxide, zirconium fluoride or zirconium oxyfluoride.

19. The component in accordance with claim 11, wherein the component is selected from a group consisting of a shower head for gas distribution, a process chamber lid interior, a process chamber liner and an electrostatic chuck.

20. The component in accordance with claim 11, wherein the composition comprises about 22 molar % YAlOF amorphous phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the exemplary embodiments of the present invention are attained is clear and can be understood in detail, with reference to the particular description provided above, and with reference to the detailed description of exemplary embodiments, applicants have provided illustrating drawings. It is to be appreciated that drawings are provided only when necessary to understand exemplary embodiments of the invention and that certain well known processes and apparatus are not illustrated herein in order not to obscure the inventive nature of the subject matter of the disclosure.

[0013] FIG. 1 is a schematic 100 representative of the use of a glaze/glass ceramic as a coating layer over a ceramic substrate such as aluminum oxide or aluminum nitride.

[0014] FIG. 2A shows a photomicrograph 200 illustrating the crystal structure of an aluminum substrate 202 directly adjacent a transition area 204, which is directly adjacent a yttrium fluoride glass ceramic 206.

[0015] FIG. 2B shows a photomicrograph 220 illustrating the crystal structure of the yttrium fluoride glass ceramic 206 at a magnification which is two times that shown in FIG. 2A.

[0016] FIG. 3A shows a photomicrograph 300 of the crystalline structure of an aluminum oxide substrate 302 directly adjacent a transition area 304, which is directly adjacent a yttrium fluoride glass ceramic doped with neodium fluoride 306.

[0017] FIG. 3B shows a photomicrograph 320 of the crystalline structure of the neodium fluoride-doped yttrium fluoride glass ceramic 306 at a magnification which is five times that shown in FIG. 3A.

[0018] FIG. 4 shows a bar graph 400 which illustrates the relative normalized erosion rates of various solid substrates including aluminum nitride 402, aluminum oxide 404, a series of three yttrium oxides (404, 408, 410, and 412) available from different vendors, and a yttrium oxyfluoride glass ceramic 414.

[0019] FIG. 5 shows a photomicrograph 500 which illustrates a transition layer 502 directly adjacent an aluminum oxide substrate (not shown on the left), which is directly adjacent a yttrium oxyfluoride glass ceramic 504. A crack 506 passing through transition area 502 stops at the yttrium oxyfluoride glass ceramic coating.

[0020] FIG. 6 shows a sintering profile 600 for a coating of yttrium oxyfluoride glass ceramic applied over an aluminum oxide substrate. The sintering time is shown in minutes on axis 602 and the temperature is shown on axis 604.

[0021] FIG. 7 shows a sintering profile 700 for a coating of neodium fluoride doped yttrium oxyfluoride glass ceramic applied over an aluminum oxide substrate. The sintering time is shown in minutes on axis 702 and the temperature is shown on axis 704.

DETAILED DESCRIPTION

[0022] As a preface to the detailed description, it should be noted that, as used in this specification and the appended claims, the singular forms a, an, and the include plural referents, unless the context clearly dictates otherwise.

[0023] When the word about is used herein, this is intended to mean that the nominal value presented is precise within 10%.

[0024] The materials and methods described herein are useful in designing and in fabrication of component apparatus parts for semiconductor and MEMS processing equipment. In particular, the materials and methods of fabricating components produce component apparatus which is resistant to halogen plasmas in general and to the fluorine-containing plasmas which are so problematic in terms of reaction with and erosion of surfaces of the components. Example component parts of the kind which particularly benefit from the materials and methods described herein include plasma processing chamber apparatus such as shower heads for gas distribution, process chamber lid interiors, process chamber liners, and electrostatic chuck surfaces, by way of example and not by way of limitation. Use of the materials described herein and the method of fabricating parts from these materials will decrease the amount of particles formed and metal contamination which occurs during the performance lifetime of the component part, and extend the lifetime of the component part as well.

[0025] A protective coating composition of the kind described herein is useful over a surface of an aluminum oxide, aluminum nitride, quartz, silicon carbide, silicon nitride, and other ceramic or glass substrates with a melting point higher than about 1600 C. The protective coating is a sintered composition including a yttrium-based fluoride crystal, or a yttrium-based oxyfluoride crystal, or an oxyfluoride amorphous phase, or a combination thereof. The materials which are selected for formation of the coating depend on the plasma resistance and mechanical, thermal, and electrical properties required for a given component. The starting materials typically comprise compound powders, a suspension medium, and a binder. A majority % of the compound powders (typically about 30% by weight or greater) is a yttrium compound, which may be an oxyfluoride, a fluoride, or combinations of these. This majority compound may be doped with a minority component powder, for example, an oxide, fluoride, or oxyfluoride of: neodymium, cerium, samarium, erbium, aluminum, scandium, lanthanum, hafnium, niobium, zirconium, ytterbium, hafnium, and combinations thereof. Properties such as thermal conductivity, thermal expansion coefficient, hardness, toughness, dielectric strength, dielectric constant, loss tangent, electrical resistivity, and erosion resistance will be determined in large part by the compounds selected for combination in forming a sintered coating.

[0026] The suspension medium may be selected from water or organic chemicals, including but not limited to methanol and ethanol, and combinations thereof, by way of example. Typically, when the suspension medium is methanol or ethanol, the concentration of this suspension medium in the suspension ranges from about 30 weight % to about 90 weight %. The binder may be selected from polyvinyl alcohol (PVA) and polymeric cellulose ether, or combinations thereof, by way of example and not by way of limitation.

[0027] Once the materials have been selected, there are a number of other variables which must be determined. These include the relative weight or volume percentages (or ratios) of the powdered materials, and the size of the starting powdered materials; the relative weight percentage of suspension medium; and the relative weight % of binder. Determination of these variables will affect the properties of the suspension such as the viscosity and the manner in which the suspension may be applied over a substrate surface. All of these variables affect the properties including thickness of the coating on the substrate prior to sintering, and ultimately affect the properties including thickness of the sintered coating. The sintering time and temperature profile determines the composition which is formed and the final crystalline structure of the sintered coating. As was discussed initially, when the cooling rate is fast, a glaze is formed, and when the cooling rate is slow, a glass-ceramic is formed. In addition, the ambient environment (atmosphere) in which the sintering takes place may introduce additional elements into the coating surface. For example, when oxygen is present in the sintering atmosphere, oxygen will be introduced into the sintered body. The time and temperature profile of the sintering will affect the depth to which the oxygen penetrates into the coating and the compounds which are formed. Initially, a large amount of empirical work was required to establish the guidelines from which satisfactory products of the present invention were produced.

[0028] The thickness of the sintered coating may be adjusted by changing the slurry viscosity, which depends on the variables discussed above and also on the final pH of the slurry, which may be adjusted by adding an acid or a base.

[0029] A glass-ceramic structured coating makes possible adjustment of the coefficient of expansion, so that the difference between the substrate and the coating approaches zero. However, in cases where other desired properties would be sacrificed in an attempt to reduce the coefficient of expansion difference, we have discovered that by controlling the variables discussed above, it is possible to produce, in-situ, a transition area between the substrate and the coating. The transition area may be used to dissipate the stress due to differential in thermal expansion between the substrate and the coating. In addition, the transition area may be used to provide a stronger bond between the substrate and the coating.

[0030] According to certain embodiments, described herein is a substrate that may be protected by a coating which is resistant to a halogen-comprising plasma. The coated substrate may include a sintered composition including a yttrium-based fluoride (e.g., having a crystal phase), or a yttrium-based oxyfluoride (e.g., having a crystal), or an oxyfluoride phase (e.g., amorphous), or a combination thereof, wherein the coating is present over a surface of the substrate which has a melting point higher than about 1600 C. In some embodiments, a portion of the yttrium-based oxyfluoride or the yttrium-based fluoride is present as a crystalline phase and the oxyfluoride phase is present as an amorphous phase. In certain embodiments, additional crystalline phase compounds are present in the coated substrate and are formed during sintering of the composition due to the presence of a dopant selected from an oxide, or fluoride, or oxyfluoride of neodymium, cerium, samarium, erbium, aluminum, scandium, lanthanum, hafnium, niobium, zirconium, ytterbium, and combinations of an oxide, or fluoride or oxyfluoride of at least one of these elements. In some embodiments, the crystalline portion of the coating composition ranges from about 70% by weight to about 100% by weight.

[0031] According to certain embodiments, described herein is a component of a semiconductor processing apparatus, wherein a surface of the apparatus is exposed to a halogen-containing reactive plasma, the component structure includes a solid structure having an overall uniform composition. The composition includes crystal grains selected from yttrium oxide, yttrium fluoride and yttrium oxyfluoride, and at least one additional compound selected from an oxide, fluoride, or oxyfluoride of a rare earth metal (e.g., neodymium, cerium, samarium, erbium, scandium, lanthanum, hafnium, niobium, ytterbium, hafnium), aluminum, zirconium, and combinations thereof.

Exemplary Slurry Compositions and Methods of Applying a Coating of Glass/Glass-Ceramic Over a Ceramic Substrate

[0032] To establish the boundaries of variables which should be adjusted, two systems were selected for illustration in examples. The first system is a pure YF.sub.3 powder system. The second system is a YF.sub.3NdF.sub.3 doped powder system. The suspension media used was ethanol. There was no binder used during sintering of the powder compositions which were sintered in the embodiment examples described herein. As an alternative to the described embodiments, the suspension media could be water, used in combination with a polyvinyl alcohol (PVC) binding agent, for example and not by way of limitation.

Example One

[0033] FIG. 1 is a schematic 100 representative of the use of a glaze/glass ceramic as a coating layer over a ceramic substrate such as aluminum oxide or aluminum nitride. FIG. 1 shows the coating 106 overlying a transition layer (transition area) 104, which overlies the substrate 102. In Example One, the substrate was aluminum oxide, Al.sub.2O.sub.3, but one of skill in the art will recognize that the substrate could be AlN. The powder used to form the glaze/glass-ceramic coating layer 106 was pure YF.sub.3. We discovered that a different sintering time and temperature profile led to different phase compositions for the sintered coating. The sintering was carried out in flowing argon protective gas at atmospheric pressure. The glass ceramic coating described in this example was sintered from pure YF.sub.3 powder having an average powder size of about 100 nm. Powder having an average particle size within the range of about 30 nm up to about 1 m may be used. The YF.sub.3 powder was suspended in an ethanol suspension media, where the weight % YF.sub.3 powder was about 30%, and the weight % ethanol in the suspension was about 70%. As previously mentioned, as an alternative, the suspension media may be water where a binder is used. A binder such as PVA works well. The coating was applied over an aluminum oxide substrate using a dipping technique of the kind known in the art. The substrate can be dipped in the suspension a number of times to achieve a desired coating thickness. In the present instance, the coating thickness prior to sintering was about 100 m.

[0034] The sintering process was carried out in flowing argon protective gas at atmospheric pressure. The sintering time/temperature profile for the coating present over an aluminum oxide substrate having a thickness of about 25 m is shown in FIG. 6. The graph 600 shows the time period in minutes on axis 602 and the temperature in C. on axis 604. As indicated, the substrate with coating applied was rapidly increased in temperature at a linear rate from room temperature to 1000 C. over a time period of about 60 minutes as illustrated in area 606. The heating rate was then slowed, as indicated by region 608 of the curve, during which the temperature was increased from 1000 C. to 1410 C. over a time period of about 140 minutes. The sintering was then held at a constant temperature of 1410 C. as illustrated in area 610 of the curve for a time period of about 180 minutes. Finally, the coated substrate was cooled at a linear rate from 1410 C. to room temperature over a time period of about 275 minutes, as indicated by region 612 of the curve. The thickness of the sintered coating produced was about 25 m.

[0035] Four crystal phases were found in the x-ray diffraction of the glass-ceramic coating structure which was sintered at 1410 C. The coating layer composition near and at the coating surface included YOF and Y.sub.2O.sub.3. There was a transition area between the coating and the aluminum oxide substrate which was AlF.sub.3, followed by Al.sub.2O.sub.3 adjacent to and in contact with the substrate. There is about 22 molar % of YAlOF amorphous phase distributed between crystal grains in the surface layer and the transition layer. The Composition of Phases, Phase Composition %, and Grain Size for the coating structure are shown below in Table One.

TABLE-US-00001 TABLE ONE Composition Phase Composition molar % Grain Size (nm) Amorphous 22.04 YAlOF Y.sub.2O.sub.3 3.79 18.6 YOF 41.58 46 AlF.sub.3 3.89 2.9 Al.sub.2O.sub.3 28.7 >100

Example Two

[0036] The composition of the starting suspension was the same for Example Two as described for Example One. The thickness of the unsintered coating on the substrate was about 100 m. The sintering was carried out in flowing argon protective gas at atmospheric pressure. The sintering time/temperature profile is shown in FIG. 7. The graph 700 shows the time period in minutes on axis 702 and the temperature in .degree. C. on axis 704. As indicated, the substrate with coating applied was rapidly increased in temperature at a linear rate from room temperature to 1000 C. over a time period of about 58 minutes as illustrated in area 706. The heating rate was then slowed, as indicated by region 708 of the curve, during which the temperature was increased from 1000 C. to 1430 C. over a time period of about 145 minutes. The sintering was then held at a constant temperature of 1430 C. as illustrated in area 610 of the curve for a time period of about 120 minutes. Finally, the coated substrate was cooled at a linear rate from 1430 C. to room temperature over a time period of about 265 minutes, as indicated by region 712 of the curve. The thickness of the sintered coating produced was about 25 m.

[0037] Five crystal phases were found in the x-ray diffraction of the glass-ceramic coating structure. The coating layer included YOF, Y.sub.2O.sub.3, and crystalline YF.sub.3. There was a transition area between the coating and the aluminum oxide substrate which was AlF.sub.3, followed by Al.sub.2O.sub.3 adjacent to the substrate. X-ray diffraction was unable to detect an amorphous phase in this glass ceramic, indicating that the amorphous phase content is lower than 1% by weight. The Phase Composition and Grain Size analyzed by XRD for the coating structure are shown below in Table Two.

TABLE-US-00002 TABLE TWO Composition Phase Composition molar % Grain Size (nm) Amorphous 0.0 YAlOF Y.sub.2O.sub.3 11.46 17.5 YOF 37.43 >100 YF.sub.3 18.1 >100 AlF.sub.3 23.88 58.6 Al.sub.2O.sub.3 9.13 59.4

[0038] The sintering profile, including heat up rate and cool down rate were the same as for Example One. However, the sintering temperature increase to 1430 C., and the reduction in dwell time to 2 hours had a very significant and surprising effect on the overall structure of the coating. FIG. 7 shows the sintering conditions, which produced a coating where there is no amorphous material present, and the grain sizes of the various compounds is significantly altered. For example, the grain size of the YOF phase increased from about 46 nm to greater than 100 nm. The YF.sub.3 crystalline phase did not forth in the previous sintering profile where the maximum temperature was 1410 C., but did form when the sintering profile where the maximum temperature was 1430 C. The grain size for YF.sub.3 crystalline phase was greater than 100 nm. The AlF.sub.3 grain size has increased from 2.9 nm to 58.6 nm. While the grain sizes of all of these crystalline components increased, the grain size of the Al.sub.2O.sub.3 crystalline component decreased from greater than 100 nm to about 59.4 nm. The difference in composition of the resulting glass-ceramic coating produced was surprising, in terms of the amount of shifting in phase composition and grain size for the various phases. In addition, the transition area from the substrate to the coating has significantly changed, where the composition of the transition area has become mainly AlF.sub.3 (23.88% AlF.sub.3 and 9.13% Al.sub.2O.sub.3) compared with the transition area of the coating discussed in Example One, where the transition area was mainly Al.sub.2O.sub.3 (28.7% Al.sub.2O.sub.3 and 3.89% AlF.sub.3). This difference in composition led to the different thermal and mechanical properties of the transition layer.

[0039] This change in the transition area determines both the ability of the coating to withstand temperature fluctuations which cause stress due to differences in coefficient of expansion between the substrate. The stresses created can cause cracking of the coating, as will be discussed subsequently.

Example Three

[0040] FIGS. 2A and 2B show photomicrographs which illustrate the fracture surface observation for a coated aluminum oxide substrate which was produced in the manner described in Example One. In FIG. 2A, the structure 200 includes the aluminum oxide substrate 202 which is comprised of crystals which demonstrate obvious porosity potential. The average crystal size of the aluminum oxide is greater than 100 nm. In direct contact with these crystals is transition area 204. Transition area 204 comprises some aluminum oxide adjacent the aluminum oxide substrate 202, but extending away from the substrate is an AlF.sub.3 composition which has a much smaller crystal size, on the average of about 2.9 nm. This smaller crystal is able to provide a more densely packed structure, as shown in the photomicrograph. Moving away from the transition area 204 is the coating layer 206 which includes a combination of Y.sub.2O.sub.3 and YOF. The average crystal size of the Y.sub.2O.sub.3 is about 18.6 nm and the average crystal size of the YOF is about 46 nm. The presence of the amorphous YAlOF phase, which acts as a matrix to surround the Y.sub.2O.sub.3 and YOF crystals provides an impervious coating. FIG. 2B shows a photomicrograph of structure 220, where the coating 202 is the Y.sub.2O.sub.3 and YOF crystal grains interspersed with amorphous YAlOF phase, shown at a magnification of 2 the magnification shown for area 206 in FIG. 2A. The finished coating surface (not shown) is dense and free from loose particulates, as would be expected looking at the non-fractured area 206 toward the right of structure 220.

[0041] The oxygen present in the Y.sub.2O.sub.3 and YOF crystalline portion of the coating matrix was generally supplied from the oxide substrate. During the sintering process, flowing argon was circulated through the sintering furnace. The AlF.sub.3 transition layer was formed according to the following mechanism: The 1410 C. to 1430 C. sintering temperature is higher than the melting temperature of YF.sub.3. A YAlOF melt is formed. However, the melt composition is not homogeneous and, in the area close to the Al.sub.2O.sub.3 substrate, there is a higher Al content. During cooling of the melt, the nucleation of AlF.sub.3 (heterogeneous) starts in the location of the boundary between the Al.sub.2O.sub.3 substrate and the melt, and the growth continues during cooling, to produce the AlF.sub.3 crystal grains.

Example Four

[0042] In Example Four, the substrate was also Al.sub.2O.sub.3, but one of skill in the art will recognize that the substrate could be aluminum oxide or aluminum nitride. The ceramic powder used to produce the coating was a mixture of 80% by weight YF.sub.3 and 20% by weight NdF.sub.3. Again, we determined that a different sintering time/temperature profile led to different phase compositions for the sintered ceramic coating. The sintering was carried out in flowing argon protective gas at atmospheric pressure. The glass-ceramic coatings sintered from the 80% by weight YF.sub.3 and 20% by weight NdF.sub.3 mixture were first sintered using the sintering profile described with respect to Example One and illustrated in FIG. 6. The YF.sub.3 powder had an average powder size of about 100 nm. The NdF.sub.3 powder had an average powder size of about 100 nm. The powders were suspended in an ethanol suspension media, where the weight % of the powder mixture was about 30%, and the ethanol in the suspension was about 70 weight %. The coating was applied over an aluminum oxide substrate using a dipping technique, to produce a resulting unsintered coating thickness over the substrate of about 100 m.

[0043] As previously mentioned, the sintering time/temperature profile for the coating present over an aluminum oxide substrate having a thickness of about 25 m is shown in FIG. 6.

[0044] Five crystal phases were found in the x-ray diffraction of the glass-ceramic coating structure. The coating layer included YOF, Nd.sub.6O.sub.11, Nd.sub.4Al.sub.2O.sub.9, NdAlO.sub.3, and Al.sub.2O.sub.3. There is about 20 molar % of amorphous YNdAlOF phase distributed between the crystal grains. The YOF and Nd.sub.6O.sub.11 were from the upper portion of the coating, nearer the surface of the coating. The NdAlO.sub.3 and Nd.sub.4Al.sub.2O.sub.9 were from the transition layer, and the Al.sub.2O.sub.3 was adjacent the Al.sub.2O.sub.3 substrate surface. Amorphous YNdAlOF phase was present throughout the upper portion and the transition area of the coating. The Phase Composition and Grain Size analyzed by XRD for the coating structure are shown below in Table three.

TABLE-US-00003 TABLE THREE Composition Phase Composition molar % Grain Size (nm) Amorphous 20.26 YNdAlOF YOF 23.92 5.9 Nd.sub.6O.sub.11 36.27 22.2 NdAlO.sub.3 1.48 16.5 Nd.sub.4Al.sub.2O.sub.9 16.72 >100 Al.sub.2O.sub.3 1.35 60.9

Example Five

[0045] The composition of the starting materials were the same for Example Four. The sintering time/temperature profile is shown in FIG. 7, where the coating was sintered at 1430 C. for 120 minutes (2 hours).

[0046] Five crystal phases were found in the x-ray diffraction of the glass-ceramic coating structure. The coating layer included YOF and Nd.sub.2O.sub.3. There was a transition area between the coating and the aluminum oxide substrate which was Nd5Y.sub.25Al.sub.3O.sub.12, Nd.sub.4Al.sub.2O.sub.9, and AlF.sub.3, followed by Al.sub.2O.sub.3 adjacent to the substrate. There was no amorphous phase indicated. This means that the amorphous phase content is lower than 1% by weight and X-ray diffraction cannot detect a presence. The presence of one NdAlO phase (Nd.sub.4Al.sub.2O.sub.9) with one NdYAlO phase (Nd.sub.25Y.sub.25Al.sub.3O.sub.12) and one AlF.sub.3 phase in the transition area between the glass-ceramic coating and the substrate provided particularly strong binding between the coating and the substrate. The surface of the coating remains impervious to erosion despite the fact that X-ray diffraction cannot detect an amorphous phase, as there is still a low content of amorphous phase which makes up the grain boundaries between crystals.

Example Six

[0047] In Example Six, the substrate was also Al.sub.2O.sub.3, but one of skill in the art will recognize that the substrate could be either aluminum oxide or aluminum nitride. The ceramic powder used to produce the coating was a mixture of 90% by weight YF.sub.3 and 10% by weight NdF.sub.3. The YF.sub.3 powder had an average powder size of about 100 nm. The NdF.sub.3 powder had an average powder size of about 100 nm. The powders were suspended in an ethanol suspension media, where the weight % of the powder mixture was about 30%, and the ethanol in the suspension was about 70 weight %. The coating was applied over an aluminum oxide substrate using a dipping technique, to produce an unsintered coating thickness over the substrate of about 100 m. The sintering process was carried out in flowing argon protective gas at atmospheric pressure using a sintering profile as shown in FIG. 7, where the sintering temperature was 1430 C. for a time period of 120 minutes.

[0048] Six crystal phases were found in the x-ray diffraction of the glass-ceramic coating structure. The upper portion of the coating is YOF and Nd2O3 (or Nd.sub.6O.sub.11). The transition layer is composed of Nd5Y.sub.25Al.sub.3O.sub.12, Nd.sub.4Al.sub.2O.sub.9, and AlF.sub.3, with an Al.sub.2O.sub.3 phase being present near the surface of the Al.sub.2O.sub.3 substrate. There is about 4 molar % of amorphous YNdAlOF phase distributed between crystal grains. The presence of one NaAlO phase (Nd.sub.4Al.sub.2O.sub.9) with one NdYAlO phase (Nd.sub.25Y.sub.25Al.sub.3O.sub.12) and one AlF.sub.3 phase in the transition area between the glass-ceramic coating and the substrate provides particularly strong binding between the coating and the substrate. The Phase Composition and Grain Size analyzed by XRD for the coating structure are shown below in Table Four.

TABLE-US-00004 TABLE FOUR Composition Phase Composition molar % Grain Size (nm) Amorphous 4.48 YNdAlOF YOF 11.14 7.1 Nd.sub.25Y.sub.25Al.sub.3O.sub.12 14.64 >100 Nd.sub.4Al.sub.2O.sub.9 10.49 77.1 Nd.sub.2O.sub.3 49.58 2.4 AlF.sub.3 4.47 47 Al.sub.2O.sub.3 5.2 >100

[0049] The upper portion of the coating was YOF and Nd.sub.2O.sub.3 (or Nd.sub.6O.sub.11) and amorphous YNdAlOF phase. The transition layer was Nd.sub.25Y.sub.25Al.sub.3O.sub.12, Nd.sub.4Al.sub.2O.sub.9, AlF.sub.3, and amorphous YNdAlOF phase, with an Al.sub.2O.sub.3 phase being present near the surface of the Al.sub.2O.sub.3 substrate.

Example Seven

[0050] FIGS. 3A and 3B illustrate the coating structure obtained for a coating of the kind produced as described in Example Six. FIG. 3A shows a photomicrograph of the structure 300, with the Al.sub.2O.sub.3 substrate 302, the transition area 304, and the coating 306 having phases of crystalline YOF and Nd.sub.2O.sub.3, in combination with amorphous YMdAlOF phase. FIG. 3B shows an enlargement of the coating 306 including the three phases where the magnification is 5.times. that shown in FIG. 3A.

[0051] FIG. 5 shows the lower portion of the photomicrograph from FIG. 3A near the area marked with the scale of dimension in .mu.m. The magnification has been increased 2 from that in FIG. 3A, to show a crack which has progressed through the transition layer and stopped at the upper portion of the coating layer which is the glass-ceramic matrix. The structure 500 illustrated shows the transition area 502, a crack 506 progressing through the transition area 502 and the end of the crack 508 at the point the crack would progress into the glass-ceramic coating 504. This photomicrograph illustrates the ability of the glass-ceramic structure to provide integrity for the coating even when the coating is put under extreme stress, such as when the structure is fractured to provide a photomicrograph sample.

[0052] FIG. 4 shows a bar graph 400 which illustrates the relative normalized erosion rates of various solid substrates including aluminum nitride 402, aluminum oxide 404, a series of three yttrium oxides (404, 408, 410, and 412) available from different vendors, and yttrium oxyfluoride glass ceramic 414. The yttrium oxyfluoride glass-ceramic test specimen was an aluminum oxide substrate protected by a coating of the kind described in Example One, above. The test specimens were processed in an etchant plasma created from a CF.sub.4/CHF.sub.3 plasma source gas. The etch processing was of the kind typically used during plasma etching of a silicon substrate. The erosion rate of the yttrium oxyfluoride glass ceramic coating provides better than a 25% improvement over the erosion rate of solid Y.sub.2O.sub.3 substrates, better than a 600% improvement over the erosion rate of an Al.sub.2O.sub.3 substrate, and better than an 800% improvement over an A/N substrate. This improved erosion rate, combined with the improved mechanical, thermal, and electrical properties described above, and the resistance to cracking under stress illustrated in FIG. 5, supports the inventors' assertion that the materials they have developed provide a surprising improvement over competitive materials previously known in the art.

[0053] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised in view of the present disclosure, without departing from the basic scope of the invention, and the scope thereof is determined by the claims which follow.