JP2000302537A - Corrosion resistant alumina sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve plasma resistance by adjusting Si/Al atomic ratio of alumina ceramic intercrystalline domain to below the specified value. SOLUTION: The Si/Al atomic ratio of alumina ceramic intercrystalline domain is adjusted to below 0.2 and the width of the intercrystalline domain is preferably made less than 10 Angstroms. A silica glass phase existing in the intercrystalline domain is corroded by fluorine plasma having high chemical activity and subsequently the formed pit-shaped corrosion holes physically damage the alumina ceramic as the starting points. Therefore the improvement of the chemical corrosion property is indispensable for improving the fluorine plasma resistance of the alumina ceramic. It is necessary that the state of the silica glass phase existing in the intercrystalline domain is changed so that the phase is hardly volatile and corroded chemically even when irradiated by fluorine plasma. The Si/Al atomic ratio of the intercrystalline domain can be changed by adjusting the particle size, the purity, etc., of alumina powder of the raw material. When the Si/Al atomic ratio is low, the plasma resistance is improved. This sintered compact is obtained by sintering under a nitrogen atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion-resistant alumina sintered body, and more particularly to a constituent material such as a part used in an environment exposed to highly corrosive plasma such as fluorine in a semiconductor manufacturing apparatus or a liquid crystal display manufacturing apparatus. The present invention relates to a corrosion-resistant alumina sintered body that is suitable as a material.

[0002]

2. Description of the Related Art In recent semiconductor manufacturing processes and liquid crystal display manufacturing processes, corrosive gases and high-density plasma are frequently used. In particular, since highly corrosive plasma such as fluorine is used in the etching apparatus, high corrosion resistance is required for each part in the etching apparatus. For this reason, many techniques (for example, Japanese Patent Application Laid-Open No. 7-183277) have been proposed in which a ceramic material such as Al ₂ O ₃ , AlN, or SiC is used as a component. The plasma properties are not sufficient, and especially fluorine-based plasma has a high ion density under a very low pressure and low energy state, and thus has no sufficient resistance to fluorine-based plasma.

[0003] Japanese Patent Application Laid-Open No. Hei 8-231266 discloses a technique for controlling the particle size distribution of alumina ceramics to improve the plasma resistance against the fluorine-based plasma. However, although this method slightly reduces the initial etching rate as compared with the conventional example, it contains about 0.2 to 0.5 wt% of a mixture of SiO ₂ , CaO, and MgO as a sintering aid in addition to alumina. It is not suitable for a process such as a semiconductor manufacturing process which rejects contamination of foreign matter. Japanese Patent Application Laid-Open No. Hei 10-279349 discloses an alumina ceramic having a plasma resistance of 99.99% or more in purity. According to this method, the contamination of the foreign matter as described above can be prevented, and it shows sufficient corrosion resistance to CF-based plasma, but contains a grain boundary having a width of several tens of mm including a silica glass phase. Therefore, the corrosion resistance to higher energy, for example, NF-based plasma was not sufficient. As a material having excellent plasma resistance, single crystal alumina is known (Japanese Patent Application Laid-Open No. 7-29959).
In order to obtain single-crystal alumina, there is a problem that a long-term production step called a single crystal pulling method from a melt is required, and the productivity is low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can be obtained by a general sintering method instead of a special method such as a single crystal pulling method. It is an object of the present invention to provide an alumina ceramic exhibiting sufficient corrosion resistance to a plasma containing a halogen system such as fluorine.

[0005]

The corrosion-resistant alumina sintered body according to the present invention is characterized in that the grain boundary has an Si / Al atomic ratio of 0.2 or less. At this time, if a grain boundary having a width of less than 10 ° is observed, the plasma corrosion resistance is further improved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Damage mechanisms when plasma is applied to alumina ceramics are roughly classified into physical damage and chemical damage. Physical damage is a damage mechanism in which charged particles in the plasma are accelerated by a bias potential applied to the alumina ceramics part and are sputtered by alumina ceramics. From the starting point, the damage spreads on the crater. In other words, alumina ceramics with low density and pores in the structure are
Damage progresses from the pores on the surface.

On the other hand, chemical damage of alumina ceramics caused by plasma occurs in the alumina ceramic grain boundary phase. For example, when fluorinated plasma having high chemical activity is irradiated on alumina ceramics, the silica glass phase present at the alumina ceramic grain boundaries is corroded, and the silica glass phase is volatilized as a gas component called SiF ₄ ,
Pit-shaped corrosion holes are formed at the triple point grain boundaries. When pit-like corrosion holes are formed due to chemical damage in this way,
The physical damage is caused from the corrosion hole as a starting point, and the damage by plasma further progresses. It is considered that such chemical damage occurs not only in the fluorine-based plasma but also in other halogen-based plasmas (for example, chlorine-based) that can corrode the silica glass phase at the grain boundary by the same mechanism. .

Accordingly, the present inventors have worked on improvement of chemical damage with the aim of improving the corrosion resistance of fluorine-based plasma.
As described above, the silica glass phase exists at the ceramic grain boundaries, and is corroded by fluorine-based plasma having high chemical activity. As a result, severe physical damage is caused from the formed pit-shaped corrosion holes. Therefore, it is indispensable to improve the chemical corrosion property in order to dramatically improve the fluorine plasma resistance of alumina ceramics.

In order to improve the chemical corrosivity, it is necessary to change the state of the silica glass phase present at the grain boundaries to a property that does not undergo volatilization and chemical corrosion even when irradiated with fluorine-based plasma. For this purpose, a method in which an element that does not volatilize even when fluorinated is dissolved in the silica glass phase can be considered. For example, if a metal element such as an alkali (earth) metal such as Na or Ca or a heavy metal is dissolved in silica glass or the like in advance, even if the silica glass is fluorinated, it does not become a gas but remains as a solid, so that pits are formed. It will not be done. However, due to the need for high purity semiconductor processes,
The addition of the metal element is inappropriate.

Therefore, the present inventors presuppose that the composition is made of an element which does not cause a problem in the semiconductor process, and as a result of repeated experiments, the atmosphere during sintering (mainly nitrogen partial pressure), the particle size of the raw alumina powder Further, the inventors have found that the Si / Al atomic ratio of the grain boundary changes due to the change in the purity and that the plasma resistance is improved when the Si / Al atomic ratio is low. In the present invention, the atomic ratio of Si / Al is specified to be 0.2 or less (preferably 0.1 or less). Alumina ceramics having a grain boundary having a Si / Al atomic ratio of 0.2 or less can be obtained by performing sintering in an atmosphere containing nitrogen, as shown in Examples described later.

Here, the action of nitrogen is considered as follows. Silicon silica glass (Si-O) phase constituting the grain boundary (Si) is expected to cause the following reactions during sintering and nitrogen (N _2). Si + 1 / 2N ₂ (g) → SiN (gas) ↑... (1) In addition, other components such as Na and Ca contained in the grain boundary are also removed from the grain boundary in the same manner as Si by reaction with nitrogen. Can be. The reaction of the above (1) is different from the reaction of the following (2) that occurs during sintering under an inert atmosphere such as argon, and removes Si by a chemical reaction, so that impurities such as silicon in grain boundaries can be significantly efficiently removed. Suitable for removal. Si + (Ar) → Si (gas) ↑ ・ ・ ・ ・ (2)

When the above reaction (1) is used, the silicon constituting the silica glass phase at the grain boundaries of alumina ceramics is reduced as a first step, so that the pits are exposed even when irradiated with fluorine-based plasma having high chemical activity. Are not easily formed, severe physical damage starting from the pit portion is prevented, and the plasma resistance is improved. Then, by increasing the nitrogen partial pressure during sintering or reducing the particle size of the raw material alumina powder, the grain boundary width is reduced, and when the grain boundary having a grain boundary width of less than 10 ° occupies all or most of the grain boundaries, furthermore, Plasma corrosion resistance is improved.

[0013]

Example: Alumina powder A (purity 99.99%; average particle size)
Diameter 0.15 μm) and alumina powder B (purity 99.8)
%; Average particle size of 0.6 μm).
After that, degreasing and sintering were performed under the conditions shown in Table 1 and below.
Alumina ceramic sintered body with relative density of 98% or more
No. 1 to No. 12 was obtained. Manufacturing conditions Degreasing conditions: 500 ° C x 2 hours Sintering conditions: Sintering under 10 atm or less degreases both powders A and B
The body is sintered under the following conditions and exceeds 10 atmospheres (100
Pressure, 1500 atm).
Pre-sintering at 0 ° C (powder A) and 1650 ° C (powder B)
(Under the following conditions)
And sintered under the following conditions. -Heating rate: 600 ° C / hr-Sintering time-2 hours-Cooling rate-Cooling in furnace The relative density of the above alumina ceramic is theoretically high
3.98 g / cm ³Archimede using pure water
The actual density is measured by the following method and found by the following equation (3).
Was. ρr = ρm / ρt × 100 (3) ρr: relative density (%) ρm: measured density (g / cm)³) Ρt: theoretical density (g / cm³)

[0014]

[Table 1]

The grain boundary width and the Si / Al atomic ratio of the alumina ceramic grain boundary were determined by the TEM image (apparatus: HF2000, manufactured by Hitachi, Ltd.) and X-ray microanalysis (energy dispersive type, apparatus: SIGMA, manufactured by Quebex Corporation). Identification was performed in the same manner, and the results are shown in Table 1.・ Grain boundary width: A TEM photograph (1,000,000 times) was prepared by preparing a thin sample from the above alumina ceramic, adjusting the sample angle with an acceleration voltage of 200 kV and an objective aperture of 80 μm so that the electron beam was parallel to the grain boundary. The film was taken, stretched 1.5 times, and the grain boundary width was measured. In Table 1, the grain boundary width 1
Less than 0 ° is a sample in which a grain boundary having a grain width of less than 1.5 mm was observed in the photograph stretched to 1.5 times. In the sample No. 1, a grain boundary in which the width of the grain boundary could not be measured as the width as shown in FIG. 1 (No. 1) was observed.・ S
i / Al atomic ratio: A sample was prepared from the above alumina ceramics, and a predetermined amount was analyzed using X-ray microanalysis with a spot diameter of 1.5 nm so that the center of the spot was located at the center of the grain boundary. Averaged. Note that Si
For samples in which no peak was detected, Si
The ratio of (atomic%) / Al (atomic%) was shown as 0 in Table 1.

Subsequently, these alumina ceramics were cut into a plate of 20 × 20 × 1 mm thick, and one side was 3 μm.
polished with a diamond grindstone of m, surface roughness Ra: 0.3
It was finished to a mirror surface of μm. Next, after acetone cleaning, acid cleaning, and alkali cleaning, they were set in a vacuum chamber, and a plasma corrosion test was performed under the following etching conditions. “Etching conditions” Gas: NF ₃ / Ar = 15/40 sccm Gas pressure: 55 Pa Top RF: 1800 W (13.56 MHz) Bias RF: 100 W, Vpp = 1000 V (700 kHz) Susceptor temperature: 27 ° C. Irradiation time: 120 minutes

The degree of damage to the sample was evaluated by the weight loss before and after the corrosion test. The weight of the sample piece was about 1.6 g, and a detailed change in weight was measured to the nearest 0.01 mg with a precision electronic balance (manufactured by Sartorius, model R200D), and the weight loss rate by the corrosion test was determined by the following equation (4). . The results are shown in Table 1. R = {(Wb−Wa) / Wb} / t × 100 (4) R: Weight loss rate (wt% / h) Wb: Weight before corrosion test (g) Wa: Weight after corrosion test (g) T) Irradiation time (h)

FIG. 2 shows a plot of the plasma irradiation test results (weight loss rate) and the Si / Al ratio in Table 1.
From FIG. 2, it can be seen that the alumina ceramic having the Si / Al atomic ratio in the grain boundary of 0.2 or less has good plasma resistance. Table 1 also shows that alumina ceramics having a grain boundary width of less than 10 ° have better plasma resistance.

[0019]

According to the present invention, alumina ceramics exhibiting sufficient corrosion resistance to plasma containing halogen such as fluorine can be obtained by a general sintering method.

[Brief description of the drawings]

FIG. 1 is a diagram (TEM photograph) of an alumina ceramic grain boundary of an example (sample No. 1).

FIG. 2 shows the weight loss rate and Si /
It is the figure which plotted Al ratio.

Continued on the front page (72) Inventor Atsushi Hisamoto 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo F-term in Kobe Steel, Ltd. Kobe Research Institute 4G030 AA36 AA37 BA33 CA05 GA22 GA26 GA27 5F004 AA16 BB29 DA17 DA23 DB00

Claims (2)

[Claims] 1. A corrosion-resistant alumina sintered body characterized in that the grain boundary has an atomic ratio of Si / Al of 0.2 or less. 2. The corrosion-resistant alumina sintered body according to claim 1, wherein a grain boundary having a width of less than 10 ° is observed.