JP2003300777A - High purity calcium fluoride sintered compact and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength, inexpensive, high purity calcium fluoride sintered compact which has improved sintering properties without reducing its purity or rather improving the purity by utilizing the cut scraps of high purity calcium fluoride single crystals for an optical member, or the like, as the raw material, and is suitable as a plasma resistant member used in a semiconductor production process, particularly, a large-sized product or a member having a complicated shape, and to provide a production method therefor. <P>SOLUTION: The high purity calcium fluoride sintered compact having a purity of ≥99.0% and a density of ≥3.17 g/cm<SP>3</SP>is obtained by using a production method wherein powder obtained by pulverizing calcium fluoride single crystal pieces as the raw material is sintered by a hot press. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity calcium fluoride sintered body and a method for manufacturing the same, and more particularly, a high-purity calcium fluoride sintered body suitable for a plasma resistant member used in a semiconductor manufacturing process. The present invention relates to a body and a manufacturing method thereof.

[0002]

2. Description of the Related Art Plasma C is used in a semiconductor manufacturing process.
Various plasma processing apparatuses used for processing performed by generating plasma such as VD, plasma etching, plasma cleaning, and plasma ashing are used.
Since plasma is extremely reactive, a material having excellent plasma resistance is selected and used for the constituent members such as the chamber and the processing jig of the above apparatus.

In semiconductor manufacturing, it is important to avoid contamination by impurity metals and particles and particles. These contaminations lead to a decrease in the yield and performance of semiconductor products such as occurrence of crystal defects in semiconductor product wafers, abnormal growth of crystals, changes in resistance value, changes in breakdown voltage, and the like. Therefore, in the above plasma processing apparatus, in addition to excellent plasma resistance, it is also required to be excellent in pollution control.

By the way, calcium fluoride has a melting point of 14
It is a cubic colorless crystal having a temperature of 18 ° C., a boiling point of 2500 ° C. and a Mohs hardness of 4. For this reason, high-purity single crystals have good transparency, and particularly good ultraviolet and infrared transmittances, and thus have been conventionally used as optical members such as prisms for spectroscopes and photographic lenses. Recently, ArF excimer lasers have been used. As an optical member using an excimer laser as a light source. On the other hand, it is also known that the material is excellent in plasma resistance. For example, in Japanese Patent No. 3017528, a surface of an electrode made of a material containing aluminum or stainless steel exposed to plasma is It is disclosed that by forming a coating film by using ion plating and vacuum deposition together with calcium fluoride, a plasma processing apparatus having excellent plasma resistance and not serving as a source of contamination metal elements and fluorine can be obtained. Has been done.

[0005]

However, for example, a member having a large surface area such as a chamber lining material of a plasma processing apparatus, particularly a member having a complicated shape with many irregularities or a large-sized product is uniformly coated with calcium fluoride. Coating is difficult even by ion plating or the like. Further, even if it is possible to coat, calcium fluoride has a relatively low strength (Mohs hardness of 4),
It has a problem of easy peeling.

Therefore, in order to use calcium fluoride as a plasma resistant member, a high purity calcium fluoride single crystal used for an optical member is directly ground into a plasma resistant member used in a semiconductor manufacturing process. Can also be considered. However, also in this case, since the strength is low as described above, it is easily cracked and is difficult to process, and in particular, it is very difficult to manufacture a member having a large size and a complicated shape. In addition, the high-purity single-crystal calcium fluoride used as a raw material itself is very expensive and has a problem of high cost, so it cannot be said that it is suitable for practical use.

It is also possible to use a sintered body of polycrystalline calcium fluoride powder as the plasma resistant member. Commercially available calcium fluoride powder is roughly classified into a natural product that is naturally produced as fluorite and a synthetic product depending on its raw material. In order to obtain high-purity calcium fluoride, a synthetic product is usually used, and a sol-gel method by hydrofluoric acid hydrolysis of calcium alkoxide,
It is produced by a method in which powder of ammonium hydrogen fluoride is mixed with calcium carbonate subjected to purification treatment such as acid treatment and heated, or an excess of hydrofluoric acid is added for digestion.

[0008] However, the sol-gel method is expensive, and the fine particles of calcium fluoride thus obtained usually have a release agent on the surface of the particles in order to prevent the fine particles from coagulating. It was coated, and during sintering, it was liable to cause inhibition of sintering and generation of unnecessary sintered grain boundaries. Further, purification treatment such as acid treatment requires considerable labor and time, resulting in high cost and, conversely, undesired contamination of impurities, leading to stable high-quality raw materials. It was difficult to get. Furthermore, calcium fluoride is generally difficult to sinter, and even if it is sintered, it has low strength and impurities are easily incorporated into the grain boundary phase. Therefore, an effect commensurate with the cost cannot be obtained, and it has been difficult to use a commercially available sintered body of calcium fluoride powder as a raw material as a plasma resistant member used in a semiconductor manufacturing process.

The present invention has been made in order to solve the above technical problems, and reduces the purity by using, as a raw material, cutting waste of high-purity calcium fluoride single crystal for optical members and the like. Rather than improving the sintering characteristics, the sintering characteristics are improved, and high-strength, low-cost, high-purity fluorine suitable for plasma-resistant members used in semiconductor manufacturing processes, especially large-sized products and members with complex shapes. An object of the present invention is to provide a calcium chloride sintered body and a method for producing the same.

[0010]

The high-purity calcium fluoride sintered body according to the present invention is made of calcium fluoride single crystal pieces as a raw material, and has a purity of 99.0% or more and a density of 3.17 g.
/ Cm ³ or more. By using high-purity single crystal pieces such as calcium fluoride single crystal cutting scraps for optical members as the starting material, the once-single-crystallized raw material is sintered, so that the grain boundary phase can be reduced. You can
A high-purity and high-density calcium fluoride sintered body can be obtained at low cost.

It is preferable that the content of Na element contained in the calcium fluoride single crystal piece is 3 ppm or less. From the viewpoint of making it suitable for the plasma resistant member used in the semiconductor manufacturing process, it is preferable to suppress the content of the impurity metal which becomes a contamination source of the semiconductor as much as possible.

The high-purity calcium fluoride sintered body is preferably used as a member for semiconductor manufacturing equipment. Since the high-purity calcium fluoride sintered body has excellent plasma resistance, high purity and high strength, it can be suitably used also in the semiconductor manufacturing process.

The method for producing a high-purity calcium fluoride sintered body according to the present invention is characterized in that a powder obtained by crushing a calcium fluoride single crystal piece is sintered by hot pressing. According to the above-described manufacturing method, even if a large-sized product such as a chamber lining material of a plasma processing apparatus or a member having a complicated shape is used, it is possible to obtain a high-density and high-strength sintered body without using a sintering aid. Can be obtained at a cost.

The powder obtained by crushing the above-mentioned calcium fluoride single crystal pieces has an average particle size of 0.1 μm or more and 50 μm or less, and particles having a particle size of 10 μm or more and 20 μm or less are 90% by weight or more of the whole. Is preferred. By using the powder raw material having the above particle size distribution, the grain boundary phase in the sintered body can be reduced, the crystallinity of the particles can be improved, and the high purity with excellent homogeneity, denseness, strength characteristics, etc. A calcium fluoride sintered body can be obtained.

The sintering by hot pressing is 8
00 ° C or higher and 1200 ° C or lower, pressure 0.1 ton / cm ²
It is preferably performed at 5 ton / cm ² or less.
The temperature and pressure conditions suitable for forming and sintering a high-purity and high-strength calcium fluoride sintered body into a homogeneous and dense material are defined.

Further, the powder obtained by crushing the above-mentioned calcium fluoride single crystal piece has BaO _{2 of} 1 ppm or more and 10 ppm or less and Al ₂ O _{3 of} 1 ppm or more and 100 pp.
m or less may be added for sintering. These trace amounts of additives can blacken the originally transparent high-purity calcium fluoride sinter, which can reduce the light transmittance and suppress heat, light scattering, and diffusion loss. Therefore, it is particularly suitable for manufacturing a plasma resistant material used in a heat treatment step of semiconductor manufacturing.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. The high-purity calcium fluoride sintered body according to the present invention is characterized by using not a commercially available calcium fluoride powder but a calcium fluoride single crystal piece as a raw material. INDUSTRIAL APPLICABILITY The present invention uses a powder obtained by pulverizing a high-purity single crystal piece having a purity of 99.0% or more, such as cut-out scraps of a calcium fluoride single crystal for an optical member, as a starting material, so that the single crystal is once made Since the above raw materials are sintered, it is possible to manufacture a high-purity calcium fluoride sintered body at low cost.

In the present invention, a piece of calcium fluoride single crystal is used as a raw material. Specifically, for example, an unnecessary cut-out piece produced when the calcium fluoride single crystal is processed into a product such as the above optical member, It is possible to use, as a raw material, a powder obtained by crushing a single crystal processing waste such as cutting waste. By using such a raw material, a high-purity raw material can be obtained at low cost, and a calcium fluoride sintered body can be obtained with a high purity of 99.0% or more.

The density of the high-purity calcium fluoride sintered body is 3.17 g / cm ³ , preferably 3.18 g / cm ³ .
When it is cm ³ or more, the grain boundary phase that causes the incorporation of impurities is small, and a dense and high-strength sintered body having excellent crystallinity can be obtained.

The powder obtained by crushing the calcium fluoride single crystal piece preferably has a Na element content of 3 ppm or less. In particular, when the high-purity calcium fluoride sintered body is used as a member for a semiconductor manufacturing apparatus, it is preferable that the metal impurities are as small as 1000 ppm or less from the viewpoint of preventing contamination of semiconductor products such as wafers by the member. Among these metal impurities, especially Na element is a serious source of contamination of semiconductor products, so the content in the raw material powder is 3 ppm or less, more preferably 2 ppm or less.

The high-purity calcium fluoride sinter according to the present invention has excellent plasma resistance, high purity and high strength, so that it is used as a chamber inner wall material or lining for a plasma processing apparatus used in a semiconductor manufacturing process. It can be suitably used as a member for a semiconductor manufacturing apparatus such as a material.

The high-purity calcium fluoride sintered body as described above is produced by hot pressing a powder obtained by crushing the calcium fluoride single crystal piece according to the manufacturing method of the present invention. Can be obtained by Sintering by hot pressing is a method in which a raw material powder is put in a molding die and pressure-molded and sintered while being heated. In ordinary pressureless sintering, the stress resulting from the surface energy is the driving force for densification, whereas according to the hot pressing, the surface energy during the sintering is increased by the external pressure (usually 1 It is possible to make the density higher by adding (about 50 MPa). Therefore, according to the hot pressing, the densification stress at the time of sintering becomes several times or more the stress due to only the normal particle surface energy, so that it is possible to densify a material that is difficult to sinter. Further, since it can be sintered at a relatively low temperature, it has the advantages that grain growth can be suppressed and that it can be obtained with high dimensional accuracy.
It is possible to obtain a sintered body having a high density close to the theoretical density and high strength.

The surface energy of calcium fluoride (solid) is about 450 × 10 ⁴ erg / m ^2, which is lower than that of alumina (905 × 10 ⁴ erg / m ² ) and the like. Even if a sintering aid is used, it is difficult to obtain a high-density and high-strength sintered body. On the other hand, according to the method of the present invention, the powder obtained by crushing the calcium fluoride single crystal piece can be sintered without using a sintering aid or the like. It is possible to obtain a sintered body while maintaining the high purity.

Sintering by the hot press is performed at 800 ° C. or higher to obtain a high-quality sintered body with high density and high strength.
00 ° C or less, pressure 0.1 ton / cm ² or more, 5 ton /
It is preferable to carry out under conditions of cm ² or less.

In the production method according to the present invention, the powder obtained by crushing the calcium fluoride single crystal pieces has an average particle size of 0.1 μm or more and 50 μm or less and a particle size of 10 μm or more and 20 μm or less. 90 particles below
It is preferable that the crystal powder has a relatively narrow particle size distribution width of not less than wt%. The average particle size is 5 μm or more and 20 μm
The following is more preferable. By using the powder raw material having the above particle size distribution, the grain boundary phase in the sintered body can be reduced and the crystallinity of the particles can be improved.

When the average particle size exceeds 50 μm, it becomes difficult to form a homogeneous compact during sintering by the hot press, and a high density sintered body cannot be obtained. On the other hand, if the average particle size is less than 0.1 μm, it is not preferable from the economical point of view, and the bulk density of the powder becomes small and the volume shrinkage at the time of sintering becomes too large. Molding is difficult.

Further, in the case of a powder having a particle size of 10 μm or more and 20 μm or less and less than 90% by weight of the whole and having a wide particle size distribution width, a crystal grain boundary that causes the incorporation of impurities during sintering. This leads to an increase in phases. In the calcium fluoride sintered body, the grain boundary phase is preferably 4% or less, more preferably 2% or less, from the viewpoint of preventing the incorporation of impurities.

Since the above-mentioned raw material powder is obtained from a single crystal, its crystallinity is very good as compared with the commercially available synthetic powder, and the peak of the absorption intensity in the powder X-ray diffraction method is sharp. , It is recognized that it consists of almost perfect crystalline material. Further, the particles of the raw material powder according to the present invention, because there is no release agent or the like on the particle surface, unlike commercially available synthetic product powder, does not agglomerate when the powder is stirred in water, forming process It is also excellent in sex.

In the manufacturing method according to the present invention, a small amount of barium dioxide (BaO ₂ ) and alumina (Al ₂ O ₃ ) are added to the powder raw material of the calcium fluoride single crystal piece before sintering, and this is added. Alternatively, it may be sintered by hot pressing. This makes it possible to blacken the high-purity calcium fluoride sintered body, which is originally transparent, to reduce the light transmittance,
It is possible to prevent loss due to scattering and diffusion of heat and light. The blackened high-purity calcium fluoride sintered body is particularly suitable for an inner wall material of a chamber of a heat treatment apparatus used in a semiconductor manufacturing process, a plasma resistant material, a heat receiving plate, and the like. The amount of BaO ₂ added is 1 ppm or more and 10 p
pm or less, the addition amount of Al ₂ O ₃ is 1 ppm or more and 100 pp
The range of m or less enables blackening, and
It is preferable from the viewpoint of suppressing the impurity content to the minimum.

[0030]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples. [Example] A single crystal piece of calcium fluoride was crushed using an alumina mortar and a pestle to obtain a powder. The impurity content concentration of this powder was measured by an ICP emission spectrophotometer (lower limit concentration of detection: 1 ppm). Table 1 shows the impurity metal concentrations thus detected. As a result, Na was not detected. Table 1 also shows the results of measuring the particle size distribution of the powder. Furthermore, when this powder was analyzed by a powder X-ray diffraction method, it was confirmed that the powder showed a peak intensity and a peak broadening equivalent to those of a single crystal, and was composed of almost perfect crystalline particles.

Next, the single crystal powder was sintered by hot pressing under the conditions of 1100 ° C. and a pressure of 0.3 ton / cm ² to obtain a plate-shaped sintered body of 50 mm × 50 mm × 6 mm. . The bulk density and three-point bending strength of this plate-shaped sintered body were measured, and the crystallinity was evaluated. The results are shown in Table 1.

[Comparative Example] With respect to commercially available synthetic calcium fluoride powder, the impurity metal concentration and the particle size distribution were measured in the same manner as in the example. The results are shown in Table 1. In this commercially available powder, metal impurities other than Na were almost the same as those in the example, and no significant difference was observed, but Na was detected at 4 ppm. Further, it was confirmed that this commercial powder had a release agent on the surface, and that the powder agglomerated when the powder was stirred in water. Furthermore, when the powder X-ray diffraction method was used to analyze this commercially available powder in the same manner as in the example, the peak intensity was lower than in the case of the example.
It was confirmed that the peak spread was broad and the crystallinity was poor.

Next, a slip was prepared by using a part of this powder, and molding and sintering were attempted in the same manner as in the example, but a dense sintered body as in the example could be obtained. There wasn't.

[0034]

[Table 1]

As shown in Table 1, the case of using calcium fluoride single crystal pieces as a raw material (Example) is better than the case of using commercially available synthetic powder as a raw material (Comparative Example). It was confirmed that a high-purity calcium fluoride sintered body having high crystallinity, high density and high strength was obtained.

[0036]

EFFECT OF THE INVENTION The high-purity calcium fluoride sinter according to the present invention can be used as a raw material by using, as a raw material, cutting scraps of high-purity calcium fluoride single crystals for optical members and the like.
Since it hardly contains an impurity metal element such as, for example, it can be suitably used as an inner wall material of a chamber used in a semiconductor manufacturing process, particularly as a plasma resistant material in a plasma processing apparatus. Further, according to the manufacturing method of the present invention, even in the case of a large-sized product such as a chamber lining material of a plasma processing apparatus or a member having a complicated shape, high density and high strength can be achieved without using a sintering aid. A sintered body can be obtained at low cost.

Claims (7)

[Claims] 1. A raw material is a piece of calcium fluoride single crystal, which has a purity of 99.0% or more and a density of 3.17 g / cm 3.
High-purity calcium fluoride sintered body characterized by being ³ or more. 2. The high-purity calcium fluoride sintered body according to claim 1, wherein the content of the Na element contained in the calcium fluoride single crystal piece is 3 ppm or less. 3. The high-purity calcium fluoride sintered body according to claim 1, which is used as a member for a semiconductor manufacturing apparatus. 4. A method for producing a high-purity calcium fluoride sintered body, which comprises sintering a powder obtained by crushing a piece of calcium fluoride single crystal by hot pressing. 5. The powder obtained by pulverizing the calcium fluoride single crystal pieces has an average particle size of 0.1 μm or more and 50 μm.
The method for producing a high-purity calcium fluoride sintered body according to claim 4, characterized in that the content of particles having a particle size of 10 μm or more and 20 μm or less is 90% by weight or more of the whole. 6. The sintering by hot pressing is 800
° C. or higher 1200 ° C. or less, the pressure 0.1ton / cm ² or more 5 ton / cm ² The method according to claim 4 or claim 5 calcium fluoride sintered body, wherein the carried out that in the following. 7. The powder obtained by pulverizing the calcium fluoride single crystal piece is added with BaO ₂ 1 ppm or more and 10 ppm or less and Al ₂ O ₃ 1 ppm or more and 100 ppm or less and sintered. Item 4 to Item 6
A method for producing a high-purity calcium fluoride sintered body according to any one of 1 to 3 above.