Patent Application
20190256405
The present invention relates to coated ceramics for use in environments where exposure to plasma is to be expected; and is particularly, although not exclusively, related to coatings of ceramic components used in semiconductor manufacture.
Semiconductor manufacture involves exposure to aggressive environments including, for example, exposure to fluorine or chlorine containing plasmas.
Ceramics, for example alumina and aluminum nitride, are common materials used in semiconductor chamber components such as lids, nozzles and electrostatic chucks. However, due to their high reactivity with halide (typically fluorine or chlorine) based plasma, it is known to provide protective coatings of yttrium aluminum garnet (YAG) or yttria (Y2O3) to ceramics used in such environments.
Dense and smooth coatings with high plasma erosion resistance are ideal for reduced particle defect on semiconductor processing; however, current coating methods for YAG and like coatings are insufficient to produce smooth coatings on all substrates.
Plasma sprayed coatings are porous and rough whatever the substrate.
Thin film deposition methods such as e-beam deposition, atomic layer deposition (ALD), chemical vapor deposition (CVD) and sputtering may generate dense and smooth coatings, but to do so require a dense and smooth substrate. This is because the thin coatings tend to duplicate the substrate surface, and any defects on the substrate materials such as grain pull-out, damage or scratches, will be transferred to the coating surface and so has the potential for defects on the coating.
Therefore, there is a need for articles having a dense and smooth coating with good erosion resistance.
In a first aspect of the present invention, there is provided a rare earth coating comprising;
20 to 90 mol % SiO2
0 to 60 mol % Al2O3
10 to 80 mol % rare earth oxides and or rare earth fluorides (REX), wherein SiO2+Al2O3+REX≥60 mol %.
Optionally, the amount of rare earth elements in mol % is greater than the amount of Al in mol %.
The present invention, in particularly, addresses this need to develop plasma resistant coatings over ceramics such as alumina and AlN by providing a glaze coating.
The coating is preferably resistant to halide (e.g. fluorine or chlorine) based plasma.
Preferably, the molar % of SiO2 is greater than the molar % of Al2O3.
In some embodiments, the rare earth coating comprises:
In alternative embodiments, the rare earth coating comprises:
Preferably, the ratio of rare earth oxides to rare earth fluorides is between 1:10 and 10:1 and more preferably between 5:10 and 10:5.
In a preferred embodiment, REX comprises yttrium oxide and/or yttrium fluoride.
Preferably, the coating comprises at least 5 mol % rare earth fluorides, as the fluorides increase the glass formation range of the REX glass, as well as also increasing the coefficient of thermal expansion (CTE) of the glass to have a better match with the substrate, such as alumina. The rare earth fluorides may be present in amounts up to 50 mol %, or even more, but typically can be present in amounts up to 40 mol %, or up to 30 mol %.
The coating may further comprise fluorides of one or more of Y, La, Zr, Sc, Nd, Ce and Al.
The coating is preferably a glassy coating or a glass ceramic coating.
The surface roughness Ra of the coating is preferably less than 20 μm, more preferably less than 2 μm; even more preferably less than 1.5 μm and yet even more preferably less than 1.0 μm. In glass ceramic embodiments, which may comprises crystalline surface particles, the Ra of the coating is preferably less than 50 μm and more preferably less than 30 μm.
The open porosity of the coating is preferably less than 5.0%, more preferably less than 3.0% or less than 2.8% or less than 2.0% and even more preferably less than 1%.
In a second aspect of the present invention, there is provided a glaze precursor mixture comprising a composition to produce a coating of the first aspect of the present invention.
In a third aspect of the present invention, there is provided a coated article comprising a coating as defined in the first aspect of the present invention.
The article is preferably a ceramic article and more preferably comprises alumina or aluminum nitride.
There may be two or more coatings applied to the article of the same or different composition.
In a preferred embodiment, the article is an article for use in semiconductor manufacture.
In a fourth aspect of the present invention, there is provided a method for protecting an article against halide plasma, the method comprising applying a rare earth-containing glaze to the surface of the article.
Preferably, glaze precursors are applied to the surface of the article and the article and glaze precursors are fired to a temperature sufficient to convert the glaze precursors into a glaze.
The glaze precursors are preferably in the form of a slurry comprising glaze precursors in a carrier. The slurry is then applied to the surface of the article; and the article and glaze precursors are fired to a temperature sufficient to convert the glaze precursors into a glaze.
In a preferred embodiment, the glaze precursors comprise a glassy frit.
The glaze precursors preferably comprises the component to form the coatings as defined within the first aspect of the present invention.
Rare earth elements include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu),gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd),praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb),thulium (Tm), ytterbium (Yb) and yttrium (Y). As stated above, yttria is used in the form of yttrium aluminum garnet to provide plasma resistant coatings, and the applicants believe that other rare earth elements can also provide such resistance. Known plasma resistant coatings comprise sintered ceramics such as yttrium aluminum garnet.
By “glaze” is meant a coating, that may be applied in liquid form, which solidifies to form the coating, and the coating is either a glass, a partially crystallized glass, or a glass-ceramic.
Application as a glaze means that when liquid the glass at least partially fills any defects in the substrate, and surface tension in the liquid results in a glazed surface that is as smooth or smoother than the substrate to which the glaze is applied.
As an example, yttria containing glaze, for example an yttrium aluminum silicate (YAS) glaze has good erosion resistance and it can serve as substrate materials for other coatings such as physical vapor deposited (PVD) YF3, Y2O3 etc.
In addition, a silica based surface is the preferred material for ALD process chamber due to its low surface recombination with radicals. Chamber surfaces with low recombination of radicals are critical for ALD processing for enhanced deposition rate and lower preventative maintenance (PM) cycle for processing chambers.
The working of the invention is detailed through the following non-limitative examples:
Samples were sintered at 1550 C for 15 minutes in an air furnace. Optical micrograph and SEM-EDS analysis of the coating after firing is shown in
Samples were sintered at 1550 C for 15 minutes in a N2 furnace. Optical micrograph and cross-sectional view of the coating after firing is shown in
Same coating composition as described on example 1 was applied over alumina based substrates. Samples were dried at 80 C for one hour followed by sintering in an air furnace to 1650 C for 2 hours. The surface morphology and SEM-EDS analysis of the coating is shown on
Samples were sintered at 1500 C for 15 minutes in a N2 furnace. SEM-EDS analysis of the coating after firing is shown in
It is believed that the addition of YF3 significantly increased the glass formation range of the YAS glass, it also increase the coefficient of thermal expansion (CTE) of the glass to have a better match with the alumina substrate.
The CTE of YAS glass shown in example 1 has CTE 5 ppm/K slightly lower than the alumina substrate (CTE 7 ppm/K), therefore a thick coating may resulted in cracking. The addition of fluoride into the YAS glass increased the CTE of glass (CTE of YF3 and Y2O3 are 13 ppm/K and 7 ppm/K; respectively).
In addition, under fluorine attack one mole of Y2O3 would lead to two moles of YF3. The molecular weight of Y2O3 is 225.81 g/mol and its density is 5.01 g/cm3 so the molar volume is 45.1 cm3/mol. The molecular weight of YF3 is 145.9 g/mol and its density is 4.01 g/cm3 so the molar volume is ˜36.4 cm3/mol. This means that fluorinating a mole of Y2O3 completely to YF3 would lead to an increase in molar volume from 45.1 cm3/mol to ˜72.8 cm3/mol. By incorporating YF3 into the material, the volume change consequent on fluorine attack will be reduced. This, in combination with the closer matching of CTE to alumina, leads to a lessened propensity to crack after fluorine attack.
Table 1 shows further materials used as coatings and particularly to coat alumina and aluminum nitride substrates.
These materials had different attributes.
As mentioned with respect to Example 4, the presence of fluorine (YASF) leads to a lessened propensity to crack after fluorine attack.
Zirconia addition (YASZ) and MgO addition (YASM) also provides better crack resistance, in part through the ability to tailor CTE with substrates.
In addition, both zirconia and MgO lower viscosity permitting good flow of the coating.
Zirconia may be present in amounts up to 20 mol %, or up to 15 mol %, or up to 10 mol %, or up to 5 mol %.
MgO may be present in amounts up to 20 mol %, or up to 15 mol %, or up to 10 mol %, or up to 6 mol %.
Coatings within some embodiments may comprise:
In contrast YASH had a higher viscosity, enabling selected areas of substrate to be coated, but importantly also showed a very low etch rate. In particular, the YASH coating displayed a significantly lower etch rate when compared to the YAS sample, when assessed using comparable methodology to that described in US2009/0214825 (table one;
In the examples a lacquer forming carrier was used, but this is not essential. Other carriers (for example terpineol oil, isopropyl alcohol, acetone, or inks) may be used to deliver the glaze precursors to the surface of the article.
Components other than SiO2, Al2O3, and rare earth oxides and fluorides may be present. The amount of such other components may be as much as 40 mol % or less than 30 mol %, less than 20 mol %, less than 10mol % or less than 5mol %. SiO2+Al2O3+REX may be ≥60 mol %, ≥70 mol %, ≥80 mol %, ≥85 mol %, ≥90 mol %, or ≥95 mol %.
In addition to the claimed ranges, the coatings may comprise
or
For use in semiconductor manufacture it is preferable (although not essential) that the alkali metal content (if present) be kept low, for example, expressed as oxide, at less than 0.5 mol %, less than 0.1mol % or even lower.
To facilitate glass formation it is preferable (although not essential) that any transition metals (if present) be kept low, for example, expressed as oxide, at less than 10mol %, less than 5mol %, less than lmol % or even lower.
In contrast to the coating of the present invention, conventional plasma sprayed Y2O3 coating has a relatively rough surface, but after polishing the surface roughness reduces to about 8 microinches (0.2 μm). The polished surface typically has about 3% open porosity within the coating with the surface comprising small pores and residual particles that affect performance.
The presently disclosed coatings not only provide a halogen-plasma resistant coating, they also provide a dense and smooth surface leading to low particle contamination and easy cleaning.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/078048 | 11/2/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62416369 | Nov 2016 | US |
