Lanthanoid enhanced corrosion resistance

Abstract

A sintered ceramic having corrosion resistance to a halogen containing corrosive gas or plasma, the sintered ceramic is disclosed. The sintered ceramic is a mixed lanthanoid garnet phase aluminum oxide having a formula of (YpLnq)3Al5O12) wherein p plus q are less than or equal to 100 mole percent wherein p is greater than or equal to 25 mole percent and less than or equal to 75 mole percent and wherein is greater than or equal to 25 mole percent and less than or equal to 75 mole percent wherein Y is yttrium and Ln is a lanthanoid, such as erbium, ytterbium, lutetium and combinations thereof.

Description

LANTHANOID ENHANCED CORROSION RESISTANCE[1] TECHNICAL FIELD[2] This invention relates to a method of producing lanthanoid enhanced corrosion-resistant, sintered ceramics and components formed therefrom.[3] BACKGROUND[4] Semiconductor processing requires the use of halogen-based gases in combination with high electric and magnetic fields to create a plasma environment. This plasma environment is made within vacuum chambers for etching or depositing materials on semiconductor substrates. These vacuum chambers typically include ceramic component parts such as disks or windows, liners, injectors, rings, and cylinders. During semiconductor plasma processing, the substrates are typically supported within the vacuum chamber by substrate holders, as disclosed, for example, in US 5,262,029 and US 5,838,529. Process gas for creation of the plasma processing environment can be supplied to the chamber by various gas supply systems. Some processes involve use of a radio frequency (RF) field and process gases are introduced into the processing chamber while the RF field is applied to the process gases to generate a plasma of the process gases. Ceramic materials used within these systems, in particular for RF applications, are required to have low dielectric loss tangents, on the order of 1 x 10'3and less when tested in the MHz or GHz frequency range. Dielectric losses higher than this cause overheating and hot spots within the components during use, leading to failed components, process variability and yield loss. Components fabricated from highly pure starting powders and use of manufacturing processes retaining initial purity will provide sintered ceramics to meet these low loss requirements. The harsh plasma processingenvironment necessitates the use of highly corrosion and erosion resistant materials for chamber components. These components have been formed from materials that provide resistance to corrosion and erosion in plasma environments and have been described, for example, in US 5,798,016, US 5,911 ,852, US 6, 123,791 and US 6,352,611 . Moreover, plasma processing chambers have been designed to include parts such as disks, rings, and cylinders that confine the plasma over the wafer being processed. However, these parts used in plasma processing chambers are continuously attacked by the plasma and consequently, ultimately corrode, erode, or accumulate contaminants and polymer buildup. The plasma etch and deposition conditions cause erosion and roughening of the surfaces of the chamber parts that are exposed to the plasma. This corrosion contributes to wafer level contamination through the release of particles from the component surface into the chamber, resulting in semiconductor device yield loss.[5] To address this, oftentimes chamber components that cannot be made directly from etch resistance materials are fabricated from a ceramic such as aluminum oxide, then have a surface coating layer which is resistant to corrosion and erosion upon exposure to the process gases. The surface layer is formed atop a base or substrate which may have superior mechanical, electrical or other preferred properties. Corrosion resistant films or coatings of, for example, yttrium oxide have been known to be deposited atop a base or substrate formed of a different material, such as alumina, which are lower cost and have increased mechanical properties compared to most corrosion resistant materials. Such films or coatings have been made through several methods known in the art, including but not limited to, plasma spray, aerosol deposition, physical vapor deposition, chemical vapor deposition and atomic layer deposition. Each method haslimitations with coating thickness, uniformity, process time, coating density, adhesion and material compatibility.[6] Commercially available methods for film deposition onto sintered substrates limit film thicknesses to less than about 0.45 mm and less. Such film thicknesses often have holes resulting from non-uniform ities in the underlying substrate, and the presence of holes and limited film thickness makes the film surface layer prone to cracking, exposing the underlying substrate to corrosive process gases and particle generation during processing.[7] Other approaches to form a corrosion resistant, high strength sintered bodies and / or components involve laminating pre-cast films, applying pressure to the films to form a laminate, followed by co-sintering of the laminate. These methods typically use pressureless sintering and the flatness of the sintered laminate is dependent upon closely matching the sintering rates of the respective films. For example, if the sintering rate of the top film is greater than that of the bottom layer, the sintered ceramic laminate will have a concave curvature, whereas if the sintering rate of the bottom film is greater than that of the top film, the sintered ceramic laminate will have a convex curvature (both as configured with the top film facing upwardly). Variances in sintering rates create residual stress in the sintered laminate, making it prone to breakage and cracking, in particular at large dimensions. Thus, materials selected for co-sintering are limited to those having the same or very similar sintering profiles of time, temperature and duration as known to those skilled in the art.[8] Additionally, these sintered laminates often exhibit poor interfacial adhesion between layers, resulting in peeling and spalling of the top layer, combined with low densities, making them prone to breakage, delamination, and cracking.[9] As dimensions of semiconductor substrates increase, there is a need for corrosion resistant, high strength sintered ceramic bodies, and in particular those of large dimension (greater than 100 mm, such as, for example, from 100 mm to 625 mm), to enable fabrication of semiconductor devices at a large scale.

[0010] As a result, there is a need in the art for a sintered ceramic body having the combined properties of corrosion and erosion resistance for use in plasma processing chambers. Indeed, rare earth oxides, and in particular YAG (Yttria-Alum ina-Garnet namely, Y3AI5O12 garnet phase) and the family of yttrium aluminum oxides, such as YAG, YAP and YAM are known to have a wide range of technological and industrial applications as are known from US Patent Publication no. 2022 / 0388909 A1 which is incorporated by reference in its entirety as if fully set forth herein (see appendix A)

[0011] Other rare earth oxides having garnet structure containing lanthanoids, for example, erbium, thulium, ytterbium, and lutetium (herein referred to “Ln” and having a formula LnsAlsO^ garnet phase) but not containing yttrium have been shown to have corrosion resistance; for example, in US Pat. No. 6,326,076 B1 . By way of reference. Ln is a rare earth element or a combination of rare earth elements which may be selected from the group consisting of dysprosium, holmium, erbium, thulium, ytterbium, and lutetium or, preferably, from the group consisting of erbium, thulium, ytterbium, and lutetium. However, these lanthanoid (Ln) based oxides present additional problems, such as cost, difficulties in fabrication and the physical properties may limit use within theplasma chambers as monolithic ceramic components, such as those typically made from aluminum oxide or yttrium oxide.

[0012] It is theorized that YAG sintered ceramic bodies and / or components could be combined with lanthanoids possible enhancements corrosion / erosion resistant to halogen corrosive gases and plasmas used in plasma reaction chambers could be achieved.

[0013] Methods to create a sintered ceramic body with lanthanoids are known, such as are found in the following background patents, patent publications and non-patent literature (if any), which are found in the appendices and incorporated by reference in their entireties, are disclosed merely for background purposes and relevant to the state of the art, but do not contain one or more of the elements of the present invention: US Pat. No. 6,326,076 B1 (appendix B) and US Pat. Publ. no, 2008 / 0169183 A1 (appendix C).

[0014] SUMMARY

[0015] To meet these and other needs, and in view of its purposes, the disclosure relates to an improved ceramic that when sintered has an enhanced corrosion resistance to a halogen containing corrosive gas or plasma thereof.

[0016] A sintered ceramic may also be called a sintered ceramic body or bodies, such that a single body (corresponding to one layer without additional layers) or may be multi-layer sintered ceramic bodies. These sintered ceramics provide high corrosion resistance to chlorine and fluorine-based process gases, low dielectric loss tangents (tan 8), high thermal conductivity and high mechanical strength, and are thus desirable for use as components in semiconductor plasma processing chambers utilizing halogen-basedprocess gases. The sintered ceramics are particularly suited for use as large chamber components of dimension 100 mm and greater.

[0017] A preferred embodiment includes a sintered ceramic having corrosion resistance to a halogen containing corrosive gas or plasma, the sintered ceramic comprising a garnet phase aluminum oxide having a formula of (YpLnq)3AlsOi2) wherein p plus q are less than or equal to 100 mole percent wherein p is greater than or equal to 25 mole percent and less than or equal to 75 mole percent and wherein is greater than or equal to 25 mole percent and less than or equal to 75 mole percent and wherein Y is yttrium and Ln is a lanthanoid. More preferably, the lanthanoid, Ln, is selected from the group consisting of erbium, ytterbium, lutetium, and combinations thereof. Most preferably, the lanthanoid, Ln, is ytterbium.

[0018] Also preferably, the sintered ceramic has wherein p is greater than or equal to 40 mole percent and less than or equal to 60 mole percent and wherein q is greater than or equal to 40 mole percent and less than or equal to 60 mole percent. More preferably, p is 50 mole percent and wherein q is 50 mole percent, and most preferably, p plus q is equal to 100 mole percent.

[0019] Other preferred embodiments of the sintered ceramic include where the sintered ceramic has a surface roughness (Sa) not exceeding 25 nm (nanometers) Sa and wherein the sintered ceramic has a porosity not exceeding 1 percent; where the sintered ceramic prior to sintering is composed of particles having a grain size not exceeding 10 micrometers; and where the sintered ceramic is a layer that is at least 2 mm in thickness.

[0020] The structure, overall operation and technical characteristics of the present invention will become apparent with the detailed description of preferred embodiments and the illustration of the related drawings herein.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a graph of temperature and pressure versus time of heat and pressure applied to samples in a direct current sintering furnace; and

[0023] Figure 2 illustrates a sample holder with masked etched samples.

[0024] DETAILED DESCRIPTION

[0025] Preparation of the sintered ceramic may be achieved by use of pressure assisted sintering, such as for example Spark Plasma Sintering (SPS), also known as Field Assisted Sintering Technology (FAST), or Direct Current Sintering (DCS). These direct current sintering assisted, and related techniques employ a direct current to heat up an electrically conductive die configuration or tool set, and thereby a material to be sintered. This manner of heating allows the application of very high heating and cooling rates, enhancing densification mechanisms over grain growth promoting diffusion mechanisms, which may facilitate preparation of ceramic sintered bodies of very fine grain size, and allowing materials to be made with properties approaching their theoretical values for dense sintered components. The pressure and current assisted methods as disclosed herein utilize a preferably unpulsed, continuous direct current to heat the tool set as disclosed herein.

[0026] Preparation of the sintered ceramic bodies as disclosed herein may also be achieved through use of pressure assisted sintering methods such as Uniaxial HotPressing whereby the die configuration or tool set is heated by way of an externally applied heat source such as induction heating or traditional heating elements.

[0027] The above-mentioned characteristics of the corrosion resistant sintered ceramic according to an embodiment are achieved in part by adapting the purity and specific surface area (SSA) of the first and second powder mixtures, the pressure to the first and second powder mixtures, the temperature of the first and second powder mixtures, the duration of sintering of the first and second powder mixtures, the temperature of the multilayer sintered ceramic during the optional annealing step, and the duration of the annealing step.

[0028] Sintered ceramics of yttrium aluminum garnet Y3AI5O12, ytterbium aluminum garnet YbaAlsOi , lutetium aluminum garnet LU3AI5O12 and erbium aluminum garnet Er3AlsOi2 and ( YPLuq)3AlsOi2 and ( YPYbq)3AlsOi2 where p was either 25, 50 or 75 mole percent and q was 75, 50 or 25 mole percent, respectively, were prepared by sintering powder compacts of the respective composite oxide powders. Commercially available high purity powders were used, in particular 99.999% purity alumina (AI2O3) and 99.999% purity yttria (Y2O3) powders were used as raw materials to synthesize yttrium aluminum garnet (Y3AI5O12), frequently abbreviated as YAG. To synthesize alternative lanthanoid aluminates, Y2O3 was replaced with Er20s and LU2O3 (>99.99% purity) respectively. The purity was confirmed using inductively coupled plasma (ICP) mass spectrometry (ICP- MS), with an instrument commercially available from Agilent Technologies, Inc. of Santa Clara, California, USA (instrument model 7900 ICP-MS).

[0029] The raw materials were weighed according to stoichiometry to create batches of 250g of each powder. The same amount of alumina grinding balls (0 10 mm)and 0.4 liters of ethanol were added to form a slurry. After homogenization for 24h on a roller bench, the slurry was dried using a rotary evaporator. After a subsequent sieving step (90 pm mesh), the powder was calcined for 3.5h at 1000°C, followed by another sieving step (90 pm mesh).

[0030] Reactive spark plasma sintering (FAST / SPS) was used to produce highly dense polycrystalline ceramics with garnet structure in a single sintering step. An SPS press model DCS 50 direct current sintering furnace from Thermal Technology LLC, of Minden, Nevada, USA SPS was used to press 40 mm disks in a graphite die. Following a pre-compaction step with 20 MPa, the powders were heated with a heating rate of 25 K / min to 1000°C and then with a heating rate of 10 K / min to 1625°C. Uniaxial pressure of 5 MPa and 25 MPa was applied during the respective heating steps. Heating was followed by a 30 min dwell at 1625°C with 25 MPa pressure. Afterwards, the sintering furnace was switched to active cooling mode. Data for the applied sintering and heating and pressure is shown in Figure 1.

[0031] The powders were heated in the sintering furnace under vacuum conditions with an applied temperature and uniaxial compression force of 15 MPa and held at that temperature and pressure for 60 minutes, which resulted in a sintered disk approximately 7.5 mm thick and four inches in diameter (101 ,6mm). Additional samples were produced under the same conditions but held at the foregoing temperature and pressure for only 30 minutes, instead of 60 minutes. The samples held for 30 minutes were not transparent, which was attributed to greater porosity in which pores scattered light rays and prevented the appearance of transparency. Thus, the samples held for 30 minutes at the target pressure and temperature were concluded to not be successful. The other samples wereconcluded to be successful and the porosity of each sample was determined in accordance with ASTM B311 -17. Each successful sample was determined to have a porosity not exceeding 1 percent using the procedure described in ASTM B311-17 (test method based on water displacement).

[0032] These sintered and surface-polished composite oxide samples were exposed to a plasma atmosphere of carbon tetrafluoride gas mixture in accord with Kindelmann, M, et al. J. Am. Ceram. Soc. 2021 , 104: 1465-1474 (see appendix D which is incorporated herein in its entirety as if fully set forth herein), as follows:Plasma parameters:PICP[W] etch Im*n] P [mbar] UB[V] CF4[seem] Ar [seem] O2[scorn]600 120 0.02 -150 1.0 5.0 0.3

[0033] For plasma etching, the samples were cut in squares (side length 10 mm) and the thickness was reduced below 1 mm by grinding and polishing. The arithmetical mean height (Sa) of the polished surface of each sample was measured using a scanning electron microscope. The Sa of the polished surface for each sample was measured using a Keyence confocal laser microscope, commercially available from Keyence International NV / SA (Belgium). For each sample, the polished ceramic surface had a surface roughness not exceeding 25 nm Sa. Before the plasma exposure, all samples were masked with plasma-resistant polyimide tape (commercially available under the tradename KAPTON from DuPont de Nemours, Inc. of Wilmington, Delaware) to induce etch steps and observe the etch rate. The sample holder 10 and masked samples 12 areshown in Figure 2. A quartz glass (SiO2) reference sample was etched in each run to keep track of process drifts and ease comparability of the different runs.

[0034] The etch experiments were conducted in an inductively coupled plasma (ICP) plasma reactor using CF4, Ar and 02 as plasma gases. The samples were mounted to the ceiling of the etching chamber, to prevent particle contamination. In the beginning of each run the etching chamber was evacuated and the gas flow was adjusted according to the desired etching parameters set forth previously. Thereafter, the plasma was ignited and maintained by the ICP generator. The continuous gas flow grants a stable gas pressure and composition throughout the experiment.

[0035] After the plasma treatment, different characterization techniques were combined to characterize the surface and the reaction layer. Atomic force microscopy (AFM, Bruker Dimension Icon, USA) was used to investigate the surface topography using a model Dimension Icon atomic force microscope from Bruker Corporation of Billerica, Massachusetts, USA. Tapping mode was used for the measurements and the results were evaluated using an opensource software package called Gwyddion, downloadable from the universal resource locater (URL) of qwddion.net. Measurement artifacts such as scars and strokes were removed and suitable background functions were used to achieve comparable results.

[0036] The plasma treatment induced a chemical gradient that was analyzed by means of time-of-flight secondary ion mass spectrometry instrument, Model ToF-SIMS 5 NCS, available from IONTOF GmbH of Muenster, Germany. A Bi+ liquid metal ion gun (Energy: 30keV) was used as the primary ion source and Cs+ (Energy: 1 keV) ions were used as sputter ions.

[0037] Transmission electron microscopy with a transmission electron microscope (TEM), model JEM-F200, available from JEOL Ltd., of Tokyo, Japan, was used to resolve the reaction layer. High-resolution TEM (HRTEM) was used to depict the crystal structure and potential damage due to Ar+ sputtering. Scanning TEM (STEM) enables the characterization of the induced chemical gradient. The lamellae were extracted from a representative surface area using focused ion beam technology with a model Strata 400 STEM instrument available from the FEI Company of Hillsboro, Oregon, USA.

[0038] The etching rate normalized to a SiO2 reference in nm was calculated to give the results shown in Table 1 :TABLE 1

[0039] In the first column of Table 1 , the numeral proceeding the chemical symbol indicates the percentage of atoms of that element replacing yttrium in yttrium aluminum garnet (Y3AI5O12) for that particular sample. For example, 25Yb indicates that 25% of the yttrium atoms in yttrium aluminum garnet were replaced with ytterbium atoms. Surprisingly, it has been observed that a garnet phase having a formula (Yo.5Ybo.5)3Al50i2 provided a significantly enhanced corrosion resistance. It is hypothesized that other combinations of yttrium with lanthanoids may also enhance corrosion resistance.

Claims

CLAIMSWhat is claimed is:1 . A sintered ceramic having corrosion resistance to a halogen containing corrosive gas or plasma, the sintered ceramic comprising: a garnet phase aluminum oxide having a formula of (YpLnq)3AlsOi2) wherein p plus q is less than or equal to 100 mole percent and wherein p is greater than or equal to 25 mole percent and less than or equal to 75 mole percent and wherein is greater than or equal to 25 mole percent and less than or equal to 75 mole percent and wherein Y is yttrium and Ln is a lanthanoid.

2. The sintered ceramic of claim 1 wherein the lanthanoid, Ln, is selected from the group consisting of erbium, ytterbium, lutetium, and combinations thereof.

3. The sintered ceramic of claim 1 or 2 further wherein the lanthanoid is ytterbium.

4. The sintered ceramic of claim 1 or 2, wherein p is greater than or equal to 40 mole percent and less than or equal to 60 mole percent and wherein q is greater than or equal to 40 mole percent and less than or equal to 60 mole percent.

5. The sintered ceramic of claim 1 or 2, wherein p is 50 mole percent and wherein q is 50 mole percent.

6. The sintered ceramic of claim 1 or 2, wherein p plus q is equal to 100 mole percent.

7. The sintered ceramic of claim 1 or 2, wherein p plus q is equal to 100 mole percent.

8. The sintered ceramic of claim 1 or 2, wherein the polished ceramic has a surface roughness not exceeding 25 nm Sa and wherein the sintered ceramic has a porosity not exceeding 1 percent.

9. The sintered ceramic of claim 1 or 2, wherein the sintered ceramic prior to sintering is composed of particles having a grain size not exceeding 10 micrometers.

10. The sintered ceramic of claim 1 or 2, wherein the sintered ceramic is a layer that is at least 7 mm in thickness.

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