JPH08169765A - Production of silicon nitride sintered compact - Google Patents

Abstract

PURPOSE: To obtain a high purity and high strength silicon nitride sintered compact capable of producing an article of a complex shape by compacting a powdery mixture of high purity silicon nitride powder with high purity silicon powder in a prescribed shape and nitriding the silicon in the resultant compact under an elevated pressure of gaseous nitrogen. CONSTITUTION: A mixture is prepd. by mixing 20-80wt.% Si3 N4 powder contg. <=20ppm Fe and <=200ppm, in total, of metallic impurities other than Fe with 20-80wt.% (expressed in terms of Si3 N4 ) Si powder contg. <=20ppm Fe and <=200ppm, in total, of metallic impurities other than Fe. This mixture is compacted and the Si in the resultant compact is nitrided at 1,150-1,400 deg.C under >1atm pressure of gaseous nitrogen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity silicon nitride sintered body applied to various devices used in semiconductor manufacturing, for example, a CVD device, an etching device, a carrying jig, an inspection stand, a heater for heating, etc. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Conventionally, silicon nitride-based ceramics have characteristics such as light weight, high strength and high hardness, as well as creep resistance and
Since it has excellent properties such as heat resistance, corrosion resistance, and thermal shock resistance, it is applied to various fields such as automobile engine parts, gas turbine parts, machine tool parts, and cutting tools.

However, in the applications related to the semiconductor manufacturing equipment as described above, in addition to heat resistance and high temperature strength, there is a great demand for the purity of the material constituting the equipment in order to prevent contamination from the equipment. Strictly, in a conventional silicon nitride sintered body using a sintering aid such as yttria (Y ₂ O ₃ ), alumina (Al ₂ O ₃ ), magnesia (MgO), the sintering aid component is an impurity. To show dynamic behavior,
It has a drawback that it cannot be used as a material for semiconductor manufacturing equipment.

Therefore, in order to realize high purity of a silicon nitride sintered body, for example, in Japanese Patent Laid-Open No. 2-243568, a silicon nitride powder obtained by nitriding a high purity metal silicon powder is used as a sintering aid. A high-purity silicon nitride sintered body suitable for a material for a semiconductor manufacturing apparatus is manufactured by molding and firing without adding an agent, and JP-A-4-77365 discloses a rare earth element oxide. A silicon nitride sintered body for a semiconductor manufacturing apparatus is disclosed in which only sodium (Na) and calcium (Ca) as impurities are reduced while being added as a sintering aid. In addition, Japanese Patent Publication No. 3-21502
The publication discloses that a silicon nitride powder without a sintering aid is hot isostatically fired to densify it to obtain a high-purity silicon nitride sintered body.

[0005]

However, the higher the purity of the silicon nitride sintered body or the silicon nitride sintered body obtained as described above, the lower the strength or the higher the strength. There is a problem that even if high strength can be realized with purity, it is impossible to manufacture a complicated shape product, and it is still possible to manufacture a complicated shape product having high strength in addition to high purity. No manufacturing method has been found.

[0006]

The present invention has been made in view of the above problems, and as a result of repeated studies, a mixed powder composed of high-purity silicon nitride powder and high-purity silicon powder was molded into a predetermined shape,
By nitriding the silicon in the compact in a high-pressure nitrogen gas, or impregnating the nitride with an organosilicon compound, the organosilicon compound is pyrolyzed to further densify it to obtain high purity. The inventors have found that it is possible to manufacture a complex-shaped product made of a silicon nitride sintered body having high strength, and have reached the present invention.

That is, according to the method for producing a silicon nitride sintered body of the present invention, silicon nitride (Si ₃ N ₄ ) containing iron (Fe) of 20 ppm or less and the total amount of other metal impurities of 200 ppm or less.
20 to 80% by weight of powder, and 20 to 80% by weight of silicon (Si) powder in which iron (Fe) is 20 ppm or less and the total amount of other metal impurities is 200 ppm or less is converted into silicon nitride (Si ₃ N ₄ ). % Of the mixed powder is formed into a predetermined shape, and the formed body is fired at a temperature of 1150 to 1400 ° C. under a pressure of nitrogen gas exceeding 1 atm to nitride the silicon (Si). It is a thing.

The silicon nitride (Si ₃ N ₄ ) powder of the present invention is
It is important as a material for a semiconductor manufacturing apparatus that the contained iron (Fe) is 20 ppm or less and the total amount of other metal impurities is 200 ppm or less.

That is, when the amount of these metals is larger than the above amount, when metal impurities are released from the system during semiconductor production, the semiconductor wafer is contaminated and the characteristics thereof are adversely affected. Specific to the range, iron (F
More preferably, the content of e) is 10 ppm or less and the total amount of other metal impurities is 100 ppm or less.

The silicon nitride (Si ₃ N ₄ ) powder may be either α type or β type, but the average particle size is 0.1.
-5 μm is suitable, and powder synthesized by imide thermal decomposition method, gas phase synthesis method or the like is particularly desirable.

The silicon nitride (Si ₃ N ₄ ) powder contains impurity oxygen, but this amount is not particularly limited.

On the other hand, in the silicon (Si) powder, the iron (Fe) content is 20 ppm or less and the total amount of other metal impurities is 200 ppm or less.
For the same reason as in the case of i ₃ N ₄ ), it is important as a material for semiconductor manufacturing equipment, but the amount of iron (Fe) is 1
The total amount of other metallic impurities is 100p at 0ppm or less.
pm or less is preferable, and iron (Fe) is most preferably 2 ppm or less and the total amount of other metal impurities is most preferably 20 ppm or less.

The average particle diameter of the silicon (Si) powder is preferably 1 to 20 μm.
i) It is important to use powders because high-purity powders are easily available as materials for electronic parts.

Next, the mixing ratio of the silicon nitride (Si ₃ N ₄ ) powder and the silicon (Si) powder is
₃ N ₄ ) powder is less than 20% by weight, or silicon (Si)
If the powder content exceeds 80% by weight in terms of silicon nitride (Si ₃ N ₄ ), it becomes difficult to completely nitride silicon (Si), and the residual silicon (Si) causes strength reduction.

On the contrary, if the silicon nitride (Si ₃ N ₄ ) powder exceeds 80% by weight or the silicon (Si) powder becomes less than 20% by weight in terms of silicon nitride (Si ₃ N ₄ ), The density of (Si) after nitriding is low, which causes a decrease in strength.

Therefore, the amount of silicon nitride (Si ₃ N ₄ ) powder is 20 to 80% by weight, and the amount of silicon (Si) powder is 20 to 80% by weight in terms of silicon nitride (Si ₃ N ₄ ). It is limited, and in particular, silicon nitride (Si ₃ N ₄ ) powder is 40-
70% by weight, silicon (Si) powder is silicon nitride (Si ₃
It is preferably 30 to 60% by weight in terms of N ₄ ).

When mixing these, it is important to use a resin pot, a ball or the like in order to avoid mixing of impurities from the grinding media.

The method for molding the mixture is not particularly limited, but may be a desired method such as a press molding method, a cast molding method, an extrusion molding method, an injection molding method, or a cold isostatic molding method. It can be formed into a shape.

In the nitriding step of the present invention, when the nitrogen gas pressure is 1 atm or less, for example, atmospheric pressure, metallic silicon (Si) remains, and when the nitriding temperature is less than 1150 ° C., the nitriding reaction does not proceed and 1400 ° C. When the temperature exceeds 1, the silicon (Si) elutes before nitriding. Therefore, the temperature is specified in the temperature range of 1150 ° C to 1400 ° C under the pressure of nitrogen gas exceeding 1 atm.

Further, in general, the higher the purity of silicon (Si), the slower the nitriding, while 3Si + 2N
_From the reaction of ₂ = Si ₃ N _4, the nitriding reaction proceeds when the nitrogen gas pressure is increased. Therefore, it is effective to increase the nitrogen gas pressure to promote the nitriding reaction in the low temperature range.

Further, the nitriding treatment temperature is from 1150 ° C. to 14
It is more desirable to raise the temperature stepwise to 00 ° C. or to raise the temperature slowly in order to improve the characteristics.

Note that once nitriding is completed, it does not matter if firing is performed at a higher temperature.

In the method for producing a silicon nitride sintered body of the present invention, the nitride obtained in the same manner as above is impregnated with an organosilicon compound containing no metal element other than silicon (Si) after thermal decomposition. Therefore, the organic silicon compound is thermally decomposed at a high temperature to have a high density.

It is important that the organosilicon compound of the present invention does not contain a metal element other than silicon (Si) after thermal decomposition. If the organosilicon compound contains a metal element other than silicon (Si), they are removed from the system during semiconductor production. When released, it contaminates the semiconductor wafer and adversely affects its characteristics as described above.

As the organosilicon compound, polysilazane, polycarbosilane, polycarbosilazane, polysilastyrene, etc. may be mentioned, especially in air or
When treated in argon gas, nitrogen gas, or ammonia gas, silicon dioxide (SiO ₂ ) or silicon oxynitride (Si ₂ N _2
The most desirable is polysilazane which does not deteriorate the original characteristics of the silicon nitride sintered body by changing to ₂ O) or silicon nitride (Si ₃ N ₄ ).

Further, the impregnation of the organosilicon compound and the thermal decomposition may be repeated, and it is also possible to use silicon carbide (SiC) particles, whiskers, fibers, or silicon nitride (Si ₃ N ₄ ). Add an appropriate amount of whiskers and fibers,
Naturally, it is also possible to improve the properties as a composite material.

[0027]

According to the method for producing a silicon nitride sintered body of the present invention,
A mixture of high-purity silicon nitride (Si ₃ N ₄ ) powder and high-purity silicon (Si) powder is molded and nitrided under nitrogen gas pressure exceeding 1 atm, or the obtained nitride is made into high-purity By impregnating an organic silicon compound and thermally decomposing it, a high-purity, high-strength silicon nitride sintered body can be obtained, and it becomes possible to manufacture complicated shaped products, which can be applied as parts for various semiconductor manufacturing equipment. Becomes

[0028]

EXAMPLES The method for producing a silicon nitride sintered body of the present invention will be described in detail below based on examples.

(Example 1) High-purity silicon nitride (Si ₃₎ synthesized by an imide pyrolysis method with an average particle size of 0.7 μm in which the total amount of iron (Fe) and metal impurities other than iron (Fe) was variously set. N ₄ ) powder and iron (Fe) and the total amount of metallic impurities other than iron (Fe) are variously set to have an average particle diameter of 5 μm.
m high-purity silicon (Si) powder was weighed at the ratio shown in Table 1, and this was mixed for 48 hours in a polyethylene pot with methanol as a medium, and then a known binder was added to prepare a slurry. , Diameter of 60m using the slurry
A disc having a thickness of 10 mm and a thickness of 10 mm was cast and molded.

Next, after removing the binder from the molded body, nitriding treatment was performed under the nitriding conditions of nitrogen gas pressure and temperature shown in Table 2.

[0031]

[Table 1]

[0032]

[Table 2]

The density after nitriding was obtained from the test piece cut out from the evaluation sample thus obtained, and the test piece cut out from the center of the evaluation sample was crushed, and the presence or absence of residual silicon was confirmed by powder X-ray diffraction. did.

On the other hand, the cut out test piece is JIS R16.
According to the 01 standard, it was ground to a predetermined size and the 4-point bending strength was measured.

Further, in order to investigate the influence on the semiconductor wafer, the test piece was placed on a single crystal Si wafer having a purity of 99.9999%, and the test piece was placed in a vacuum of 10 ^-3 torr or less for 100.
After performing a heat treatment for 1 hour at a temperature of 0 ° C., a Si wafer
Secondary ion mass spectrometry (SIMS) of the contact surface with the test piece of
It was investigated whether or not a metal other than Si was detected, and the presence or absence of contamination by metal impurities was evaluated.

[0036]

[Table 3]

As is clear from Table 3, silicon nitride (Si
Sample Nos. 1 and 2 in which the amount of ₃ N ₄ ) powder exceeds 80% by weight have low densities and bending strengths of 150 MPa or less, and those in which the amount of silicon (Si) powder exceeds 80% by weight and nitriding conditions. Residual Si was found in sample numbers 7, 8, 9, 12 and 13 where the temperature is less than 1150 ° C or exceeds 1400 ° C
Furthermore, in sample numbers 15, 18, 19 and 20 in which the amount of impurities in the silicon nitride (Si ₃ N ₄ ) powder is outside the range of the present invention, contamination of the Si wafer with metallic impurities is detected.

On the other hand, in the present invention, the density is 2.03.
It was as high as g / cm ³ or more, the bending strength was 210 MPa or more, there was no residual Si, and no diffusion due to metallic impurities in the Si wafer was observed.

(Example 2) Sample N obtained in Example 1
o. Using the same sample as No. 11, various organic silicon compounds shown in Table 4 were impregnated in vacuum, and then the organic silicon compounds were thermally decomposed under the heat treatment conditions shown in Table 4.

[0040]

[Table 4]

The density of the test piece cut out from the thus-obtained evaluation sample was determined, and the cut-out test piece was JIS.
-Four-point bending strength was measured by polishing to a predetermined size according to the R1601 standard.

Further, in order to investigate the influence on the semiconductor wafer, the test piece was placed on a single crystal Si wafer having a purity of 99.9999%, and the test piece was placed in a vacuum of 10 ^-3 torr or less for 100.
After performing a heat treatment for 1 hour at a temperature of 0 ° C., a Si wafer
Secondary ion mass spectrometry (SIMS) of the contact surface with the test piece of
It was investigated whether or not a metal other than Si was detected, and the presence or absence of contamination by metal impurities was evaluated.

[0043]

[Table 5]

As a result, in the sample No. 39 containing Ti as the impurity metal, the diffusion of the impurity metal into the Si wafer was detected, whereas the samples of the present invention were excellent in bending strength and Si. No diffusion of impurity metal into the wafer was observed.

[0045]

As described in detail above, according to the present invention,
It is possible to provide a method for manufacturing a silicon nitride sintered body capable of manufacturing a complex-shaped product having high strength in addition to high purity, and thereby providing a high-purity silicon nitride sintered body for a semiconductor manufacturing apparatus. The application can be expanded as various parts.

Claims (2)

[Claims] 1. Iron (Fe) is 20 ppm or less, iron (Fe)
20-80 wt% of silicon nitride (Si ₃ N ₄ ) powder having a total amount of metal impurities other than 200 ppm or less, and iron (Fe)
Is 20 ppm or less and the total amount of metal impurities other than iron (Fe) is 200 ppm or less, and a step of mixing 20 to 80% by weight in terms of silicon nitride (Si ₃ N ₄ ) and the mixed powder. A method for producing a silicon nitride sintered body, which comprises a step of forming and a step of nitriding the silicon (Si) at a temperature of 1150 to 1400 ° C. under a pressure of nitrogen gas exceeding 1 atm. . 2. Iron (Fe) 20 ppm or less, iron (Fe)
20-80 wt% of silicon nitride (Si ₃ N ₄ ) powder having a total amount of metal impurities other than 200 ppm or less, and iron (Fe)
Is 20 ppm or less and the total amount of metal impurities other than iron (Fe) is 200 ppm or less, and a step of mixing 20 to 80% by weight in terms of silicon nitride (Si ₃ N ₄ ) and the mixed powder. A step of molding, a step of nitriding the silicon (Si) at a temperature of 1150 to 1400 ° C. under a nitrogen gas pressure of more than 1 atm, and a metal other than silicon (Si) after thermal decomposition into the nitride. Manufacture of a silicon nitride sintered body comprising a step of impregnating an organosilicon compound containing no element and a step of heat-treating the impregnated body to thermally decompose the organosilicon compound to densify it. Method.