JP2000154062A - Boron carbide sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a graphite phase in a sintered compact and to produce a dense high strength boron carbide sintered compact. SOLUTION: Boron carbide powder having <=5 μm average particle diameter is mixed with 4-12 wt.% metallic boron powder having <=3 μm average particle diameter, 0.5-5 wt.% (expressed in terms of silicon carbide) metallic silicon powder or powdery metallic silicon-silicon carbide mixture having <=5 μm average particle diameter and 0.5-5 wt.% carbon source such as carbon powder. The resultant mixture is compacted and subjected to purification treatment in vacuum at 1,600-2,100 deg.C until the total amount of alkali metals, alkaline earth metals and transition metals is reduced to <=300 ppm. The purified compact is fired at 1,900-2,250 deg.C to obtain the objective boron carbide sintered compact having >=96% relative density. In X-ray diffraction measurement, the ratio (Ib/Ia) of the peak intensity Ib of the (002) plane of graphite to the peak intensity Ia of the (021) plane of boron carbide in the sintered compact is <=0.01.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity and high-strength boron carbide sintered body used for a jig for a semiconductor manufacturing apparatus, in particular, a precision processing product such as a jig used in a halogen plasma, and its production. About the method.

[0002]

2. Description of the Related Art Hitherto, it has been proposed that a boron carbide sintered body be used for a porous electrode for a dry etching apparatus because of its excellent plasma resistance (Japanese Patent Application Laid-Open No. 01-2001).
59818). This boron carbide sintered body has a purity of 99.
It is prepared by filling a graphite die with 5% boron carbide powder having an average particle diameter of 100 μm and then sintering by hot pressing.

On the other hand, as a technique for producing a dense sintered body, a powdered boron carbide having a particle size distribution of 1 μm or less has a density of 90% or more of the theoretical density obtained by mixing 0.5 to 10% of free carbon. A sintered body has been proposed (Japanese Patent Publication No. 58-
No. 30263).

The inventors of the present invention have proposed a technique for producing a high-density sintered compact of a silicon compound, particularly 0.05 to 5% by weight of a silicon carbide and an organic compound which can be converted to carbon by thermal decomposition. Is added in an amount of 0.5 to 5% by weight in terms of carbon, followed by baking after the purification treatment.

[0005]

However, the above-mentioned boron carbide sintered body containing no additive has an open porosity of 20% or more and the strength of the sintered body itself is not sufficient. Further, the sintered body to which free carbon is added as an auxiliary agent contains a large amount of alkali metals, alkaline earth metals, and transition metals, and these have a problem in using them for semiconductor manufacturing equipment because they stain products. .

The primary material of boron carbide contains a graphite phase as an impurity, and since the graphite phase segregates during the sintering process, it tends to form a heterogeneous structure in the structure of the sintered body. In addition, since the graphite phase has low corrosion resistance to halogen gas plasma, if a sintered body containing a large amount of the graphite phase is used in a halogen plasma such as a highly corrosive one, the etching of the graphite phase as an initial corrosion is performed. And the etching rate is remarkably increased. Therefore, there is a problem in using it as a material for a plasma-resistant member for a semiconductor manufacturing apparatus.

[0007] Accordingly, an object of the present invention is to provide a dense and high-strength boron carbide sintered body which reduces the graphite phase in the sintered body and a method for producing the same.

[0008]

Means for Solving the Problems As a result of repeated studies on the above objects, the present inventors have found that by adding a predetermined amount of metallic boron to boron carbide or adding metallic silicon, It has been found that the graphite phase can be reduced by reacting metallic boron or metallic silicon with excess carbon and converting it to boron carbide or silicon carbide. In this case, when the alkali metal, the alkaline earth metal and the transition metal are reduced and the graphite phase satisfies a specific relationship in peak intensity by X-ray diffraction measurement, excellent strength and durability to halogen plasma are obtained. Have been found, and the present invention has been achieved.

More specifically, the boron carbide sintered body of the present invention contains boron carbide as a main component, and in X-ray diffraction measurement, the peak intensity of a diffraction peak belonging to the (021) plane of boron carbide is Ia, and the peak intensity of graphite is (002). ) When the peak intensity of the diffraction peak attributed to the plane is Ib, the peak intensity ratio represented by Ib / Ia is 0.01 or less, and the total amount of alkali metals, alkaline earth metals and transition metal elements is 300 ppm or less. And a relative density of 96% or more.

Further, another boron carbide sintered body of the present invention comprises:
The main component is boron carbide, and silicon carbide is 0.5 to 5% by weight.
Contained in boron carbide in X-ray diffraction measurement.
1) When the peak intensity of the diffraction peak attributed to the plane is Ia and the peak intensity of the diffraction peak attributed to the (002) plane of graphite is Ib, the peak intensity ratio represented by Ib / Ia is 0.01 or less; The total amount of the alkali metal, alkaline earth metal and transition metal element is 300 ppm or less, and the relative density is 96% or more.

Further, according to the present invention, in producing the above-described sintered body, a metal boron powder having an average particle diameter of 3 μm or less is added to a boron carbide powder having an average particle diameter of 5 μm or less by 4 to 4 μm.
Mixing 12% by weight of carbon powder or an organic compound which can be converted to carbon by pyrolysis at a ratio of 0.5 to 5% by weight in terms of carbon; forming the mixture into a predetermined shape; Heat treatment in a vacuum of 1600 ° C. to 2100 ° C. to purify the alkali metal, alkaline earth metal and transition metal element to a total amount of 300 ppm or less, and baking at a temperature of 1900 to 2250 ° C. after the purification treatment. Densification to a relative density of 96% or more.

Further, as another production method, a boron carbide powder having an average particle diameter of 5 μm or less, a metal silicon powder having an average particle diameter of 5 μm or less, or a silicon carbide powder having an average particle diameter of 1 μm or less with the metal silicon Alternatively, a mixture with an organic compound that can be converted to silicon carbide by thermal decomposition is 0.5 to 5% by weight in terms of silicon carbide, and a carbon powder or an organic compound that can be converted to carbon by thermal decomposition is 0.5 to 5% by weight. And then heat-treating in a vacuum at 1600 ° C. to 2100 ° C. until the total amount of alkali metals, alkaline earth metals and transition metal elements becomes 300 ppm or less. It has been found that by purifying and further firing at a temperature of 1900 to 2250 ° C., it is possible to densify to a relative density of 96% or more.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First of all, a boron carbide sintered body of the present invention comprises an alkali metal such as Li, Na or K, M
g, alkaline earth metals such as Ca and Ba, and Y, rare earth elements, Ti, V, Ta, Mo, W, Mn, Cr, C
Transition metal elements such as o, Fe, and Ni are 300 pp in total.
m or less, especially 150 ppm or less, furthermore 50 ppm or less, in other words, alkali metal, alkaline earth metal, and transition metal are each 100 ppm or less, particularly 50 ppm or less.
It is important that the content be 10 ppm or less. This is because if the amount of the element is more than 300 ppm, when used in a semiconductor manufacturing apparatus, the semiconductor product is contaminated during semiconductor manufacturing, and the characteristics of the semiconductor are deteriorated.

It is important that the boron carbide sintered body of the present invention is a dense body having a relative density of 96% or more, preferably 98% or more. If the relative density is less than 96%, the strength decreases, and the desired strength cannot be obtained. Here, the relative density is expressed as a percentage with respect to the theoretical density.

Further, in the boron carbide sintered body of the present invention, the peak intensity of the diffraction peak belonging to the (021) plane of boron carbide is Ia, and the peak intensity of the diffraction peak belonging to the (002) plane of graphite is Ib. It is important that the peak intensity ratio represented by Ib / Ia is 0.01 or less, particularly 0.002 or less.

If the peak intensity ratio is higher than 0.01, the graphite phase present in the grain boundaries of the sintered body segregates to form a heterogeneous structure, and the corrosion by plasma proceeds from this point as a starting point. This is because the plasma resistance is significantly deteriorated.

According to the present invention, it is possible to contain silicon carbide in a ratio of 0.5 to 5% by weight which has no adverse effect on the production of a semiconductor and is stable from a vacuum to a high temperature. This silicon carbide acts as a sintering aid,
If the amount is less than 0.5% by weight, the effect as a sintering aid cannot be expected, and if it exceeds 5% by weight, boron carbide will grow and the strength of the sintered body will be reduced.

A method for producing such a high-purity and high-strength sintered boron carbide body includes at least the following steps (1) to (4).

(1) First, as starting materials, a) boron carbide powder, b) metal boron powder having an average particle size of 3 μm or less, c) metal silicon powder having an average particle size of 5 μm or less, or A silicon carbide component having a particle size of 1 μm or less and a mixture with a silicon carbide powder or an organic compound that can be converted to silicon carbide by thermal decomposition;
d) b) and / or c) are added and mixed to a) and c) using a carbon source such as carbon powder or an organic compound which can be converted to carbon by thermal decomposition.

In this case, the average particle size of the main component a) boron carbide powder needs to be 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less. If the average particle size exceeds 5 μm, Insufficient densification causes a reduction in strength.

It is desirable that the metallic boron of the above b) is added in a ratio of 4 to 12% by weight, particularly 7 to 9% by weight. If the amount is less than 4% by weight, a graphite phase remains, If it is more than 12% by weight, excess boron inhibits densification.

The silicon carbide component (c) is 0.5 to 5% by weight, preferably 1 to 4% by weight, more preferably 2 to 3% by weight in terms of silicon carbide. If the amount is less than 0.5% by weight, densification is difficult, and if it exceeds 5% by weight, boron carbide causes grain growth and lowers the strength.

According to the present invention, the average particle size is 5 μm.
The following metal silicon is contained as an essential component, and particularly 0.05% by weight or more, preferably 1% by weight in terms of silicon carbide.
Add at the above ratio. This metal silicon reacts with the graphite phase present in the primary material of boron carbide during the purification process described later to generate silicon carbide, and suppresses the carbon source from remaining in the sintered body as the graphite phase. This is because you can do it. If the average particle size of the metal silicon is larger than 5 μm, the reactivity with the graphite phase is reduced, and the unreacted graphite phase tends to remain. Preferably it is 2 μm or less.

The organic compound capable of forming silicon carbide by thermal decomposition includes polycarbosilane and the like.

The d) carbon source is 0.5% in terms of carbon.
５5% by weight, preferably 1-4% by weight. This carbon source reacts with B ₂ O ₃ contained in the boron carbide main raw material or the like during sintering to remove oxygen.
Since B ₂ O ₃ impairs sinterability, B ₂ O ₃ is reductively decomposed to promote sinterability. Therefore, if the carbon content is less than 0.5% by weight, B ₂ O ₃ is not sufficiently reduced and densification is difficult, and if it exceeds 5% by weight, on the contrary, boron carbide particle growth is suppressed and densification is performed. This is because it hinders. Note that examples of the organic compound that can be converted to carbon by thermal decomposition include coal tar pitch, furfuryl alcohol, corn starch, sugars, phenol resins, and the like.

(2) Next, the mixture is formed into an arbitrary shape by a known desired forming means, for example, a die press, a cold isostatic press, an injection molding, an extrusion molding or the like.

(3) Then, the molded body is first
By performing heat treatment in a vacuum of 00 ° C to 2100 ° C,
Purification is performed so that the total amount of alkali metals, alkaline earth metals, and transition metal elements in the molded body is 300 ppm or less. Further, the vacuum pressure at this time is desirably 10 Pa or less, and if it exceeds 10 Pa, it becomes difficult to efficiently remove the above elements.

The temperature of this purification treatment is from 1600 ° C. to 210
The temperature is 0 ° C., preferably 1800 ° C. to 2000 ° C. If the temperature is lower than 1600 ° C., purification treatment cannot be performed and 2100 ° C.
If the temperature exceeds ℃, the added silicon carbide is scattered to inhibit densification and cause a decrease in strength.

(4) After the above purification treatment, 1900 to 225
It is fired at a temperature of 0 ° C. to densify to a relative density of 96% or more. The firing temperature is preferably 1900 ° C. to 2100
C. and preferably fired in a vacuum or in an inert atmosphere, particularly in argon gas. This firing temperature is 225
If the temperature exceeds 0 ° C., boron carbide grows and the strength is reduced. If the temperature is lower than 1900 ° C., it is difficult to make the relative density 96% or more.

The firing method includes normal pressure firing (normal firing) and hot press firing at 200 kg / c.
Firing can also be performed while applying a mechanical pressure of m ² . In the hot press method, after the powder of (1) is filled in a hot press mold and subjected to the above-mentioned (3) purification treatment, while applying a mechanical pressure of 500 kg / cm ² or more, (4) Firing under the above conditions is advantageous in that the (2) forming step can be performed simultaneously with the (4) firing step, and the densification can be performed in a short time.

The sintered body thus obtained is a boron carbide sintered body having a high purity and a high density and a high strength and a high halogen plasma resistance, and is used for a jig or a susceptor for a semiconductor manufacturing apparatus. Also in alkali metals,
This has the effect that the semiconductor is hardly contaminated by the alkaline earth metal and the transition metal.

Moreover, the boron carbide sintered body of the present invention is a high-strength material having conductivity, and is used for electrodes, susceptors, etc. used in a dry etching process or a film forming process in a plasma atmosphere such as a halogen plasma. Jigs and other parts for semiconductor manufacturing equipment, chambers (walls) for semiconductor manufacturing equipment, various jigs and tools for industrial machinery, various wear-resistant parts, and parts for precision machining.

[0033]

EXAMPLES As boron carbide powder, Na, Ca, and Fe were 840 ppm, 120 ppm, and 300 ppm, respectively.
And powder having an average particle size of 0.8 μm (Sample Nos. 1 to 32)
And a powder having an average particle diameter of 20 μm (Sample No. 33).

The metal boron powder has an average particle size of 1
μm was used. Average particle size 4μ for metal Si powder
m. As the silicon carbide powder, α-silicon carbide powder having an average particle diameter of 0.6 μm was used. As a carbon source, a phenol resin having a carbonization ratio of 20% was used by being dissolved in an organic solvent.

Then, the above-mentioned boron carbide powder, metallic boron or silicon carbide source, and carbon source are weighed in combinations and amounts shown in Tables 1 to 3, mixed in an organic solvent using a plastic ball, and then mixed with an evaporator. A dry powder was obtained.

For firing, a hot press firing device (HP) and a normal firing (PLS) device were used. In the case of hot press firing, the mixed powder is put into a carbon mold and subjected to a purification treatment at a temperature shown in Tables 1 to 3 in a vacuum of 5 Pa for 2 hours.
Under the pressure of 00 kg / cm ^{2 and} the firing temperature shown in the table, it was kept in argon for 2 hours and fired. In the case of normal firing, this powder is subjected to hydrostatic pressure treatment at a pressure of 3 t / cm ² to produce a molded body, and purified at a temperature shown in Tables 1 to 3 in a vacuum of 5 Pa for 2 hours. At the firing temperature shown in Tables 1 to 3, it was held and fired in an argon gas for 3 hours.

For comparison, a graphite sintered body was prepared by firing carbon powder at 2500 ° C. for 5 hours in a vacuum atmosphere (Sample No. 34).

A test piece was cut out from the obtained sintered body and polished. Then, the specific gravity was determined based on JISR2205, and the relative density was determined. As the strength value, a room temperature strength was obtained from a four-point bending test based on JISR1601. Further, the sample was pulverized and subjected to X-ray diffraction measurement to determine the peak intensity Ia of the diffraction peak belonging to the (021) plane of the B ₄ C phase and the peak intensity Ib of the diffraction peak belonging to the (002) plane of the graphite phase. , Ib / Ia were determined. In the table, sample No. 3 (product of the present invention) and sample No. 1
The X-ray diffraction measurement results of the (comparative product) are shown in FIGS. Furthermore, the pulverized powder was subjected to ICP emission spectroscopy to measure the amounts of alkali metals, alkaline earth metals, and other transition metals.

The sample was set in a reactive ion etching apparatus, and chlorine gas was introduced into the apparatus to maintain the pressure in the apparatus at 7 to 10 Pa. And 1
Plasma was generated by introducing a high frequency of 3.56 MHz and 1 kW, and the sample was brought into contact with the plasma. The sample temperature was set at room temperature (25 ° C.). After performing the etching treatment under the above conditions for 3 hours, the etching rate was calculated from the weight loss of the sample.

The amount of silicon carbide was calculated from the obtained sintered body. The amount of silicon carbide was determined in terms of silicon carbide from the total amount of silicon in the sintered body, since no metallic silicon was detected in the sintered body.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

According to Tables 1 to 3, all the samples within the scope of the present invention have high purity, high strength of 200 MPa or more, and excellent plasma resistance at an etching rate of 40 ° / min or less. In particular, when silicon carbide was contained in the sintered body, improvement in strength was observed.

On the other hand, the graphite sintered body has a remarkably high etching rate and low plasma resistance. On the other hand, the sample N without addition of metallic boron or metallic silicon
In O. 1 and 19, the peak intensity ratio was higher than 0.01, a heterophase structure in which the graphite phase in the primary raw material segregated was formed, and the plasma resistance was low.

Sample No. 35 using a powder having an average particle size exceeding 5 μm was insufficient in densification, resulting in a decrease in strength.

[0047]

As described above, the boron carbide sintered body of the present invention has excellent bending strength and high purity and excellent plasma resistance. It can be used for precision processing products such as jigs used in plasma.

[Brief description of the drawings]

FIG. 1 shows the X of the boron carbide sintered body of the present invention (sample No. 3).
It is a figure showing a line diffraction chart.

FIG. 2 is a view showing an X-ray diffraction chart of a conventional boron carbide sintered body (sample No. 1).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Takasaka 1-4-4 Yamashita-cho, Kokubu-shi, Kagoshima F-term in Kyocera Research Institute (reference) 4G001 BA22 BA23 BA60 BA62 BA71 BA78 BB22 BB23 BB60 BB71 BC12 BC13 BC31 BC46 BC47 BC52 BD14 BD37 BD38 BE11 BE33

Claims (4)

[Claims] 1. An X-ray diffraction measurement comprising boron carbide as a main component, wherein the peak intensity of a diffraction peak belonging to the (021) plane of boron carbide is Ia, and the peak intensity of a diffraction peak belonging to the (002) plane of graphite. Is Ib, Ib
/ Ia, wherein the peak intensity ratio is 0.01 or less, the total amount of alkali metals, alkaline earth metals and transition metal elements is 300 ppm or less, and the relative density is 96% or more. Sintered body. 2. The method according to claim 1, wherein the main component is boron carbide, and the silicon carbide is 0.1%.
In X-ray diffraction measurement, the peak intensity of the diffraction peak attributed to the (021) plane of boron carbide was Ia, and the peak intensity of the diffraction peak attributed to the (002) plane of graphite was Ib. In this case, the peak intensity ratio represented by Ib / Ia is 0.01 or less, the total amount of alkali metals, alkaline earth metals, and transition metal elements is 300 ppm or less, and the relative density is 96% or more. Boron carbide sintered body. 3. A boron carbide powder having an average particle diameter of 5 μm or less, and a metal boron powder having an average particle diameter of 3 μm or less being 4 to 12 μm.
% By weight, a step of mixing 0.5 to 5% by weight of carbon powder or an organic compound which can be converted to carbon by thermal decomposition, a step of forming the mixture into a predetermined shape, Heat-treating in a vacuum of 1600 ° C. to 2100 ° C. to purify the alkali metal, alkaline earth metal and transition metal element to a total amount of 300 ppm or less; and firing at a temperature of 1900 to 2250 ° C. after the purifying treatment. ,
Densifying to a relative density of 96% or more. 4. A boron carbide powder having an average particle size of 5 μm or less, a metal silicon powder having an average particle size of 5 μm or less, a silicon carbide powder having an average particle size of 1 μm or less, or silicon carbide by thermal decomposition. A mixture with an organic compound that can be converted is mixed at a ratio of 0.5 to 5% by weight in terms of silicon carbide, and a carbon powder or an organic compound that can be converted to carbon by pyrolysis is mixed at a ratio of 0.5 to 5% by weight in terms of carbon. A step of forming the mixture into a predetermined shape; and heat-treating the formed body in a vacuum at 1600 ° C. to 2100 ° C. until the total amount of alkali metals, alkaline earth metals and transition metal elements becomes 300 ppm or less. Purifying, after the purification treatment, firing at a temperature of 1900 to 2250 ° C.,
Densifying to a relative density of 96% or more.