JPH10134956A - Material for high frequency wave introduction window - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide material for a high frequency wave introduction window, which can enhance the reliability of the introduction window to a great extent, and simultaneously can introduce/output microwaves, and millimeter waves at the level of high electric power. SOLUTION: The material for a high frequency wave introduction window is so constituted as to be formed out of the sintered product by the nature of silicon nitride, which is mainly composed of silicon nitride, and contains both the 3a th group element compound in the periodic table, of at least one kind selected out of a group of Y, Dy, Er, Yb, Tm, Lu and Sc, and impurity oxygen, wherein in the sintered product by the nature of silicon nitride, the grain boundaries of silicon nitride crystals are crystalized while silicon nitride is being sintered, the amount of aluminium in the aforesaid sintered product is less than 2% by weight in terms of aluminium oxide, and dielectric loss in 10GHz is less than 1×10<-4> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency introduction window, for example, in a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus, a photosensitive drum manufacturing apparatus, a diamond film forming apparatus, a nuclear fusion apparatus, and the like. The present invention relates to a CVD apparatus for generating plasma using a high frequency such as a millimeter wave or a high frequency introducing window material used for a microwave output device and an oscillator.

[0002]

2. Description of the Related Art In recent years, a microwave plasma processing apparatus has been widely used mainly for CVD, etching, and resist processes in the production of semiconductors, liquid crystals, and thin films. In addition, linear accelerators, high-frequency generators used for nuclear fusion (eg, gyratron)
In U.S. Pat. No. 5,953,867, microwave or millimeter-wave large power exceeding 20 GHz is output and introduced into a fusion reactor to generate high-energy plasma. An introduction window and an output window made of a material having good high-frequency transmissivity are used for a high-frequency introduction section and an output section of the apparatus for generating plasma using high frequencies such as microwaves and millimeter waves.

[0003] Such an introduction window and an output window (hereinafter collectively referred to as an introduction window) have a high-frequency transmissivity (low dielectric constant and low dielectric loss property) as well as a temperature rise and a rapid temperature change. Although heat resistance, thermal shock resistance, and vacuum tightness are required, in recent years, productivity improvement in manufacturing equipment is required, and in order to achieve nuclear fusion, high temperature of plasma, that is, introduction of high frequency High power is required,
Even higher performance and higher reliability are required for introduction windows.

In these introduction windows, quartz glass, alumina ceramics, single-crystal alumina (sapphire), aluminum nitride (AlN), which have been considered to be high-density, low-dielectric-loss, and dense with emphasis on high-frequency transmittance and vacuum tightness. ) And beryllia (BeO) are mainly used.

[0005]

However, when these materials all have poor thermal shock resistance and transmit high power and high frequency, pinholes due to cracks and melting occur in the introduction window due to local temperature rise of the introduction window. There was a problem that it easily occurred. As a result, there is a problem that the vacuum tightness is reduced.

[0006] In order to solve these problems, conventionally, from the viewpoint of preventing a rise in the temperature of the surface of the introduction window, for example, coating the surface of the window with TiN or a film having high thermal conductivity,
Further, from the viewpoint of improving strength, for example, Japanese Patent Application Laid-Open No. 6-345
No. 527, and a window material made of an alumina-zirconia composite material disclosed in JP-A-4-280976 have been proposed. These ceramics have a thermal shock resistance of 200 to 300.
Since the temperature is as low as about ° C., the reliability is insufficient, and cracks and the like are easily generated in the introduction window. Therefore, the mechanical reliability is poor, and it is difficult to increase the power at a high frequency.

That is, it is required that the high-frequency window material has high strength, heat resistance, and thermal shock resistance in addition to low dielectric loss characteristics having excellent microwave transmission properties.
Heretofore, obtaining such materials has been difficult.

On the other hand, silicon nitride (Si ₃ N ₄ ) is known as a ceramic which is remarkably superior in heat resistance, thermal shock resistance and mechanical properties as compared with the above ceramics, but silicon nitride is used for structural parts. Although used, it has not been studied as a high frequency introduction window material.

[0009]

Means for Solving the Problems The inventors of the present invention have proposed a method of selecting a specific element as a group 3a element oxide of the periodic table, which is a sintering aid, and blending the aluminum contained in a silicon nitride sintered body. By controlling the content to a specific amount and further crystallizing the grain boundary phase, the dielectric loss at 10 GHz becomes 1 × 10 ^−4.
It has been found that this can be reduced to the following, and that this is a suitable material for a high-frequency introduction window material, leading to the present invention.

That is, the high-frequency introduction window material of the present invention is mainly composed of silicon nitride, and at least one kind of the third material in the periodic table of the third type selected from the group consisting of Y, Dy, Er, Yb, Tm, Lu and Sc.
a silicon nitride-based sintered body containing a group a element compound and impurity oxygen, wherein the grain boundaries of silicon nitride crystals in the sintered body are crystallized, and the oxide equivalent of aluminum in the sintered body is calculated. The amount is 2% by weight or less, and the dielectric loss at 10 GHz is 1 × 10 ⁻⁴ or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION
It is mainly composed of silicon nitride, and as a component other than silicon nitride, among the elements of Group 3a of the periodic table, Y, Dy, E
It contains at least one selected from the group consisting of r, Yb, Tm, Lu and Sc and impurity oxygen. Here, the impurity oxygen refers to a silicon dioxide (SiO ₂ ) component of the oxygen contained in the silicon nitride sintered body, and the impurity oxygen is an impurity unavoidably contained in the silicon nitride raw material. This is due to oxygen or intentionally added silicon oxide (SiO ₂ ).

The Group 3a element compound of the periodic table is a component added as a sintering aid.
a, Ce, Sm, Dy, Ho, Er, Yb, Lu and Sc. Among them, in the present invention, Y, Dy, Er, Yb having a small ionic radius to reduce the strength and the dielectric loss among them. , Tm, Lu and Sc, it is important to contain at least one of them, and among these, Lu is particularly desirable. These specific periodic table 3a
The group-group element compound is suitably 0.5 to 10 mol%, preferably 0.5 to 3 mol% in terms of oxide. Also,
The amount of the above-mentioned impurity oxygen in terms of SiO _{2 is} calculated according to Periodic Table 3a.
The molar ratio (SiO ₂ / RE ₂ O ₃ ) with respect to the oxide equivalent (RE ₂ O ₃ ) amount of the group element compound is preferably 1.5 to 10, and particularly preferably 1.8 to 3.5.

Further, from the viewpoint of dielectric properties, the amount of Al greatly affects the dielectric loss as a dielectric. It is not clear why the presence of aluminum increases the dielectric loss, but aluminum usually forms a solid solution with silicon nitride to form sialon (Si-Al-O-N), lowering the thermal conductivity and simultaneously reducing the grain boundary. It is known that a low melting point composition is formed and the high temperature strength is also deteriorated. From these facts, it is presumed that Sialon or the low melting point composition greatly affects the dielectric loss characteristics.

From these findings, the content of aluminum (Al) in the window material of the present invention is determined by the oxide (Al ₂ O ₃ )
It is important that the content is 2% by weight or less in terms of conversion.
It is desirable that the content be 5% by weight or less and less than 0.1% by weight. If the Al content exceeds 2% by weight, a low-loss sintered body aimed at by the present invention cannot be obtained.

Further, according to the window material of the present invention, it is also important that the grain boundary phase in the silicon nitride based sintered body is crystallized. Regarding the cause of the influence of the grain boundary phase, when the grain boundary phase is vitrified, the dielectric loss of the grain boundary phase itself is expected to increase. At that time, it is presumed that the smaller the ionic radius, the smaller the dielectric loss of the grain boundary phase itself, and as a result, the smaller the dielectric loss in the sintered body.

Here, the grain boundary phase is a portion existing between silicon nitride crystal grains, mainly containing a Group 3a element of the periodic table added as a sintering aid, and is mainly composed of RE-Si-O-N. A compound or an RE-Si-O compound (RE is a rare earth element). When crystallized, mainly RE ₂ Si ₂
O ₇ , RE ₂ SiO ₅ , RE ₄ Si ₂ N ₂ O ₇ , RE ₂₀
N ₂ Si ₁₂ O _{18 and the} like are deposited, but in order to reduce strength and dielectric loss in particular, RE ₂ Si ₂ O ₇ , RE ₂ SiO ₅
It is preferable to deposit an oxide such as RE ₂ Si ₂ O ₇ .

In particular, it is desirable that the grain boundary phase is substantially completely crystallized. Here, complete crystallization means that, for example, when a crystallization heat treatment or the like at 1000 to 1500 ° C. is performed and the degree of crystallization is examined by X-ray diffraction, the X-ray diffraction result does not change before and after the treatment. It indicates that the processing is saturated.

In addition, the density of the dielectric material of the present invention is not particularly limited as long as it is dense as a sintered body.
%, Particularly preferably 98% or more.

The window material of the present invention is not limited to satisfying the above-mentioned Al content, and as long as it does not affect the dielectric properties, a composite of an alkaline earth metal, molybdenum, a tungsten compound or the like as another component. A small amount of particles may be contained. However, the cationic impurities are not particularly limited as long as aluminum satisfies the above range,
From the viewpoint of strength, a smaller one is preferable. Fe, Ni, Zn
The transition metal is preferably 1% by weight or less, preferably 0.5% by weight or less, in terms of oxide. The amount of fluorine (F) and chlorine (Cl) adsorbed on the silicon nitride raw material is not problematic as long as it is at or below the level of a commercially available silicon nitride powder, that is, 0.1% by weight or less. If the amount of an alkali metal such as Na or K is too large, the dielectric loss may be affected.
It is desirable that the content be 1% by weight or less.

The high frequency introduction window material of the present invention uses, for example, a raw material having a small amount of Al as a silicon nitride raw material, and adds a compound such as an oxide of the specific group 3a element of the periodic table,
In some cases, after adding silicon oxide and mixing it,
After being formed into a desired shape such as a block shape or a sheet shape by a desired forming means, for example, a die press, a cold isostatic press, an extrusion molding, a doctor blade method or the like, it is fired.

It is necessary to perform calcination in nitrogen under conditions capable of suppressing the decomposition of silicon nitride, and a known calcination method such as normal pressure calcination, nitrogen gas pressure calcination, or hot isostatic calcination is used. can do. The firing temperature depends on the composition, but firing is performed so that a density of 90% or more is achieved in a temperature range of 1600 to 2000 ° C. At this time, in order to crystallize the grain boundary phase, the cooling rate is reduced, or
It is easily crystallized by performing a heat treatment for crystallization at 00 to 1500 ° C. for about 10 to 100 hours.

According to the present invention, as the high frequency introduction window material,
It is made of a sintered body containing silicon nitride as a main component, containing a specific Group 3a element of the periodic table, reducing the amount of Al, and crystallizing the grain boundary phase, and having a dielectric loss of 1 × 10 ^{−4 at} 10 GHz.
It is a low-loss high-frequency window material excellent in the following excellent properties, for example, heat resistance, thermal shock resistance, mechanical properties, and vacuum tightness.

The high-frequency window material of the present invention exhibits excellent high-frequency transmittance with a low dielectric loss (tan δ) of 1 × 10 ⁻⁴ or less even at a high frequency of 10 GHz, It has significantly better thermal shock resistance, heat resistance and high strength. Therefore, the high-frequency introduction window material of the present invention has a frequency of several hundred MHz to 300 GHz, such as microwaves, millimeter waves, etc., and more preferably
It is a window material suitable for devices and oscillators for introducing and outputting a high frequency of 00 GHz. By using such a window material, the reliability of the introduction window can be remarkably improved, and at the same time, microwaves and millimeter waves of higher power can be used. Introduction and output are possible, and higher efficiency and higher performance of manufacturing equipment can be achieved.

[0024]

EXAMPLE A high-purity silicon nitride raw material with an α ratio of 95% (transition metal impurity total amount 100 ppm or less, Al content 20 ppm or less; A raw material) produced by an imide decomposition method and an α ratio produced by a direct nitridation method 90% silicon nitride raw material (total transition metal impurity total 1000 ppm or less, Al content 200 ppm or less;
B raw material) and a low-purity silicon nitride raw material (transition metal impurity amount of 10,000 pp) with an α ratio of 70% manufactured by a direct nitriding method.
m, an Al content of 1000 ppm or less; a C raw material (BET specific surface area of at least 8 m 2 / g, average particle size of 2)
５5 μm).

As a sintering aid, Al ₂ O ₃ , SiO ₂ and oxide of a Group 3a element of the periodic table (RE ₂ O ₃ ) having a purity of 99.9% or more were used. Weighed to the indicated composition. Among them, SiO ₂ includes those obtained by converting impurity oxygen in the silicon nitride raw material into SiO ₂ . A predetermined amount of this weighed powder is placed in a polyethylene 500 ml pot, mixed with a urethane ball using a rotary mill for 72 hours using IPA (isopropanol) as an organic solvent, pulverized, a binder is added to the obtained slurry, and spray-dried to granulate. A powder was obtained. Molding was performed with a mold press at a molding pressure of 1 ton / cm2 to a shape of 20 mm in diameter and 10 mm in thickness and a 5 x 6 x 45 mm shape for strength measurement. And

The firing is performed at 1750 ° C. for 5 hours in a nitrogen atmosphere at 1.2 atm (PLS method). After firing by the PLS method, firing is further performed at 1850 ° C. for 5 hours in a nitrogen atmosphere at 9 atm (GPS). The method was adopted. Further, heat treatment was performed in nitrogen at 1000 to 1500 ° C. for 24 hours for crystallization of the grain boundary phase.

After confirming that the sample has been densified to 95% or more, a cylinder and a surface are ground and processed into a sample having a diameter of 15 mm and a thickness of 7 mm for measuring dielectric loss characteristics, and a JIS test for strength and other analysis. Piece shape (3 × 4 × 35m
m) to obtain a sample for evaluation.

The dielectric loss was measured at a resonance frequency of 10 GHz by a cylindrical dielectric resonator measurement method. The center of the sample was cut out after the measurement, the amount of Al was quantified by ICP analysis, converted to alumina (Al ₂ O ₃ ), and crystal phases other than the silicon nitride crystal phase were identified by powder X-ray diffraction. The strength characteristics were measured by a four-point bending test according to JISR1601, and the results are shown in Tables 1 and 2.

In order to confirm the performance of each sample as an introduction window material, each sample was manufactured to have a diameter of 60 mm and a thickness of 1.5 to 2.0 mm (thickness with small reflection calculated from the dielectric constant). The sample was irradiated with a microwave output from a 28 GHz, 10 KW gyrotron with an irradiation diameter of 30 mm to the sample, and the temperature rise at the center was reduced by I
The output was measured with an R camera, and the output at which the temperature rise runs away (thermal runaway), that is, the usage limit output was measured.
Further, the temperature of the sample after irradiation at 10 KW for 1 minute was also measured.
These results are also shown in Tables 1 and 2.

In order to compare the performance as an introduction window material, the present inventors used quartz glass for a microwave introduction window and a high-purity alumina sintered body having a purity of 99% or more as an introduction window. Was done. Quartz glass is made of SiO ₂ 9
9.9 mol%, and the dielectric loss is 1 × 10
^-4 , the room temperature strength is 100 MPa or less. The alumina sintered body contains 0.5 mol% of SiO _2, has a dielectric loss of 1 × 10 ⁻⁴ and a room temperature strength of 400 MPa. As a result of the test, in the case of the sample using quartz glass, about 10
Although the temperature was increased by 00 ° C., a crack occurred at the moment when the output was terminated. Further, in the case of the sample using the alumina sintered body, when this alumina
It exceeded 00 ° C and led to thermal runaway.

[0031]

[Table 1]

[0032]

[Table 2]

According to the results shown in Tables 1 and 2, Samples Nos. 15, 16, 18, and 19 having an Al content of more than 2% by weight,
Samples No. 20, 21, 22, without crystallization treatment
In No. 23, the dielectric loss exceeds 1 × 10 ⁻⁴ , and thermal runaway occurs with power of less than 10 KW.
W, the temperature after 1 minute irradiation also exceeded 200 ° C., and cracks and the like were observed.

From these comparative examples, it can be seen that the dielectric loss can be reduced to 1 × 10 ⁻⁴ or less by reducing the amount of Al and performing heat treatment to crystallize the grain boundaries. In particular, when the Al content is 0.05% by weight or less, when Dy, Er, and Y are selected as Group 3a elements of the periodic table, 0.9 × 10 ⁻⁴ or less, Sc, Yb, When Tm is selected, 0.8 × 10 ⁻⁴ or less is achieved, and when Lu is selected, 0.7 × 10 ⁻⁴ or less is attained. The temperature after irradiation for 1 minute was 200 ° C. or less, showing good characteristics.

[0035]

As described above in detail, the high-frequency window material of the present invention has a dielectric loss (tan δ) even at a high frequency of 10 GHz.
^Has excellent dielectric properties with low loss of 1 × 10 ^-4 or less, and also has much higher thermal shock resistance, heat resistance, and high strength than previously known introduction window materials. It shows good transmission characteristics without thermal runaway even when passing through the lower microwave. Therefore, the high-frequency introduction window material of the present invention has a frequency of several hundred MHz to 300 GHz, particularly 1-2 GHz, such as microwaves and millimeter waves introduced to generate plasma.
It is a window material suitable for devices and oscillators for introducing and outputting a high frequency of 00 GHz. By using such a window material, the reliability of the introduction window can be remarkably improved, and at the same time, microwaves and millimeter waves of higher power can be used. Introduction and output are possible, and higher efficiency and higher performance of manufacturing equipment can be achieved.

Claims (1)

[Claims] 1. The method according to claim 1, wherein the main component is silicon nitride, and Y, Dy, Er, Y
b, Tm, Lu and Sc, at least one element selected from the group 3a element of the periodic table and a silicon nitride-based sintered body containing impurity oxygen, and the silicon nitride crystal in the sintered body And the amount of aluminum oxide in the sintered body is not more than 2% by weight and 10 GH
A high frequency introducing window material, wherein the dielectric loss at z is 1 × 10 ⁻⁴ or less.