JP5199599B2 - Yttria sintered body and member for plasma process equipment - Google Patents

Description

    The present invention relates to a yttria sintered body suitable for use as a corrosion-resistant member of an apparatus having a plasma process (hereinafter referred to as “plasma process apparatus”) such as a semiconductor manufacturing apparatus.

  A high-purity yttria sintered body has a much higher resistance to halogen-based corrosive gases and plasmas than other general ceramic materials such as alumina, silicon carbide, silicon nitride, and zirconia. It is known and its application is being studied as a corrosion-resistant member for plasma processing apparatuses.

  However, various problems remain when the yttria sintered body is used as a plasma process apparatus member. That is, if the mechanical strength is low, or pores remain in the structural material, the solid phase reaction product with the halogen-based corrosive gas, yttria dust finely separated by impact, etc., are scattered as particles when exposed to plasma. And further contamination of the wafer occurs.

  Patent Document 1 discloses a ceramic sintered body in which a portion exposed to plasma is mainly a compound containing a group 3a element of the periodic table, its surface roughness (Ra) is 1 μm or less, and its porosity is 3% or less. A configured member for a plasma processing apparatus is disclosed. The present invention is said to exhibit excellent corrosion resistance against halogen-based corrosive gases and their plasmas.

  Patent Document 2 discloses a plasma-resistant member composed of an yttria sintered body having Ra: 2.5 μm or less and a porosity of 2% or less. In the present invention, it is said that plasma resistance can be improved and generation of particles can be reduced by hydrogen atmosphere sintering, addition of yttrium aluminate, or the like.

  Patent Document 3 discloses an invention relating to a ceramic member in which the surface of various ceramic substrates such as yttria is eroded in an acidic etching solution to make the surface uneven. In the present invention, particles can be reduced by the anchor effect.

  Patent Document 4 discloses an invention relating to a corrosion-resistant member made of an yttria sintered body obtained by etching an yttria sintered body with an acid such as hydrofluoric acid. According to the present invention, the processing crushed layer can be removed and the generation of particles can be reduced.

  Patent Document 5 discloses an invention relating to a high-purity yttria sintered body fired at 1710 to 1850 ° C. in a hydrogen atmosphere.

  On the other hand, yttria is an expensive material, and there remains a problem as a structural material such as a low strength of the sintered body. A base material is an inexpensive and high-strength material such as metal material or alumina. Corrosion-resistant members in which an yttria sprayed film is formed may be used. However, the sprayed film generally has more pores than a sintered body of the same material, and there is a risk of peeling from the substrate.

  In Patent Document 6, a metal undercoat layer and a composite intermediate layer of alumina or alumina and yttria are provided between the base material and the yttria sprayed coating to improve adhesion to the base material and halogen plasma resistance. A thermal spray member is disclosed.

  Patent Document 7 discloses a corrosion-resistant member that realizes high adhesion, hardness, and low porosity as a sprayed film by spraying yttria after supplying a gas containing oxygen with a double anode type plasma spraying apparatus. It is disclosed.

Japanese Patent No. 3619330 JP 2002-68838 A JP 2002-308683 A JP 2004-244294 A JP 2004-269350 A Japanese Patent No. 3510993 Japanese Patent No. 3649210

  In Patent Document 1, the effect of reducing the etching rate when exposed to a halogen-based plasma is sufficiently studied, but the particle contamination of the processed wafer is hardly studied. Moreover, according to the Example of Cited Document 1, when Ra exceeds 1 μm, the etching rate is high and the plasma resistance is rapidly deteriorated. For this reason, if the member of Cited Document 1 is used, the surface of the member cannot be uneven to prevent particle scattering.

  Also in the invention described in Patent Document 2, when the surface roughness Ra is increased, the plasma resistance is significantly deteriorated. That is, in order to prevent scattering of particles and to achieve a low etching rate, it is necessary to take measures to make it difficult for particles to fall off from the surface layer, such as designing a material that does not cause fine processing marks due to the roughening treatment.

In Patent Document 3, in order to obtain a good roughened shape, a long-time treatment under a pressurized condition is required under heating of a treatment liquid such as sulfuric acid and phosphoric acid. There is a description that the roughening method is insufficient. Further, the confirmation of the anchor effect by cross-sectional SEM observation is verified only with alumina and YAG (yttrium aluminum garnet: Y ₃ Al ₅ O ₁₂ ), and the yttria sintered body is not verified. Therefore, a high corrosion resistance and high purity yttria sintered body that can obtain a good particle scattering prevention effect only by blasting is not disclosed.

  In the invention described in Patent Document 4, Ra is reduced to less than 0.8 μm in order to improve plasma resistance, and since the surface of the product is smoothed, the anchor effect cannot be obtained, and the particle It becomes difficult to prevent scattering of the water.

  As shown in the Examples of Patent Document 5, the bending strength of the yttria sintered body described in this document is as low as 50 to 145 MPa. For this reason, this yttria sintered body is low in reliability as a structural material, and has limitations in grinding processing such as a large product, a complicated shape, and a screwed structure cannot be applied. Therefore, it is difficult to perform additional processing such as roughening, and particle scattering due to plasma processing cannot be prevented.

  In the invention described in Patent Document 6, the porosity of the surface layer directly exposed to plasma is as large as 5 to 9%. The invention described in Patent Document 7 realizes excellent film quality as an yttria sprayed film, with a porosity of about 0.004 cc / g and a cumulative pore volume with a pore diameter of 0.1 to 100 μm. However, it has not reached the level of a dense sintered body.

  When the plasma process is performed in the yttria sprayed member described in Patent Documents 6 and 7, the etching rate of the material increases due to the presence of pores. Further, a large number of particles composed of the gas species constituting the plasma and the reaction product of the corrosion-resistant member or the peeled yttria particles are generated, and the processed material such as a wafer is contaminated.

  The present invention is applicable to a structural member disposed in a plasma process reaction chamber such as a focus ring of a CVD film forming apparatus, an etching apparatus, or a chamber using a halogen-based corrosive gas and its plasma. An object of the present invention is to provide a high-purity yttria sintered body and a member for a plasma processing apparatus that are excellent, have little particle scattering, and have high strength.

  The present inventors conducted various studies from the viewpoint of improving the mechanical strength and plasma resistance of the yttria sintered body and preventing particle scattering.

  Accordingly, the inventors of the present invention have obtained a sintered body obtained from a high-purity yttria raw material that can be used in a semiconductor manufacturing process, with an average crystal grain size of 3 μm or less, a porosity of 1% or less, and a bending strength of 180 MPa. Designed as above. The inventors of the present invention can easily roughen the yttria sintered body by blasting, and even when roughened, the yttria sintered body has almost plasma resistance (plasma etching rate) as compared with a smooth surface (mirror polished product). I found that it does not get worse.

The present invention has such a was made based on the finding, and the gist of the yttria sintered body and plasma process apparatus for member shown in (2) below as shown in the following (1).

(1) Average crystal grain size of 3μm or less, with porosity of 1% or less, and flexural strength than 180 MPa, a surface roughness (Ra) of a yttria sintered body is 0.05 to 5 [mu] m, surface Yttria sintered body having a roughness (Ra) of 1 μm or more, an etching rate E (nm / min) when an arbitrary fluorine-based gas plasma treatment is performed, and an Ra of 0.05 μm A yttria sintered body satisfying the following equation (1) when the etching rate (nm / min) when the fluorine-based gas plasma treatment is performed under the same conditions is E _0:
E ≦ 1.20 × E ₀ (1)

(2) A member used in a plasma process apparatus, wherein at least a portion exposed to a halogen-based corrosive gas or plasma thereof is composed of the yttria sintered body described in (1) above. A member for a plasma processing apparatus.

    The yttria sintered body of the present invention has a bending strength of 180 MPa or more, which is a very high level as a normally sintered yttria sintered body. Under the most suitable conditions, a bending strength of 200 MPa or more can be realized. As a result, the surface roughness of the yttria sintered body used as the corrosion-resistant member can be controlled in a wide range. Furthermore, the yttria sintered body of the present invention has little decrease in the plasma etching rate even if the surface is roughened.

  For this reason, if a part or all of the yttria sintered body of the present invention is roughened and used as a corrosion-resistant member exposed to at least the halogen-based corrosive gas or the plasma in the plasma process apparatus, it has high plasma resistance. However, scattering of particles can also be prevented. Since the yttria sintered body of the present invention is superior in material strength as compared with the conventional yttria sintered body, it is easy to reduce the thickness and can be applied to products with improved heat transfer. Moreover, since it can manufacture also by normal pressure sintering, the product design of a complicated shape with a restriction | limiting and a large sized product is also attained by hot press sintering or hot isostatic pressing (HIP method).

Average crystal grain size: 3 μm or less When the average crystal grain size exceeds 3 μm, the strength of the sintered body decreases, and a bending strength of 180 MPa or more cannot be achieved. Moreover, it becomes easy to detach from a crystal grain boundary part, and it becomes difficult to ensure plasma resistance when roughened. Therefore, the average crystal grain size is set to 3 μm or less.

  The average crystal grain size is preferably as small as possible. However, since crystal grains grow during sintering, it is difficult to make the crystal grain size of the sintered body equal to or smaller than that of the starting raw material powder. Therefore, it is preferable to use a primary raw material powder having an average particle size as small as possible and a small particle size distribution (with a uniform particle size) as long as there is no problem in the manufacturing process.

Porosity: 1% or less Porosity greatly affects the compactness of the sintered body. When the porosity exceeds 1%, the bending strength decreases and the plasma etching rate increases. In addition, the amount of generated particles increases. Therefore, the porosity is set to 1% or less.

Bending strength: 180 MPa or more Since the yttria sintered body of the present invention has a bending strength of 180 MPa or more, it has a high degree of freedom in grinding. For this reason, the surface roughness by the roughening treatment such as blast treatment can be easily adjusted, and the scattering of particles can be prevented without increasing the plasma etching rate. Moreover, since the heat transfer property of the product can be improved by reducing the thickness, reliability in use in a heating environment can be improved. A desirable bending strength is 200 MPa or more.

Surface roughness Ra: 0.05 to 5 μm
When the surface roughness Ra is too low, particles generated during the plasma treatment are not captured by the surface layer of the corrosion-resistant member and are likely to be scattered. Particle scattering becomes significant when the surface roughness is less than 0.05 μm. On the other hand, when the surface roughness Ra exceeds 5 μm, the surface area of the plasma exposed surface becomes too large, the corrosion resistance is lowered, and the particles fall off from the surface layer easily. Therefore, it is desirable to adjust the surface roughness Ra in the range of 0.05 to 5 μm. In order to reduce the amount of scattered particles, Ra is desirably 1 μm or more.

Note that the fact that the plasma etching rate does not increase specifically means that the plasma etching rate E satisfies the relationship of the following expression (1).
E ≦ 1.20 × E ₀ (1)
However, E and E ₀ in the formula (1) are the etching rates (nm / min) when the same conditions of plasma processing are performed on yttria sintered bodies having the same material but different surface roughness. E ₀ means the etching rate (nm / min) of which the surface roughness (Ra) is 0.05 μm.

  The yttria sintered body in which the increase amount of the plasma etching rate exceeds 20% before and after the roughening becomes insufficient in corrosion resistance. In order to obtain a yttria sintered body satisfying the above formula (1), the crystal grain size and the porosity should be adjusted within the range defined by the present invention, and yttria powder having a high purity should be used. Must be selected.

Method for Producing Yttria Sintered Body The yttria sintered body of the present invention is produced by, for example, granulating and forming yttria raw material powder, performing surface finishing treatment, firing, and subjecting the sintered body to surface roughness finishing treatment. can do. In consideration of dimensional shrinkage due to firing, surface roughness finishing may be completed for some or all surfaces of the target product before firing, and surface roughness finishing treatment after firing may be omitted.

<Granulation process>
Granulation of the yttria raw material powder can be performed by, for example, blending a binder or the like with the yttria raw material powder, adjusting the slurry, and then obtaining the yttria granule powder by a technique such as spray drying. Here, yttria raw material powder having an average particle size of 0.5 μm or less is preferably used. In particular, it is preferable to use a high purity product having a purity of 99.9% or more. With such a yttria raw material powder, it is easy to obtain a dense sintered body having a porosity of 1% or less, and even if the grains grow during sintering, the average crystal grain size of the sintered body can be easily controlled to 3 μm or less. It is.

  With such yttria raw material powder, it is desired to be obtained by atmospheric sintering without using a special technique such as hot press sintering or post-sintering HIP (hot isostatic pressing) in the subsequent firing step. It is easy to obtain a material with the performance to do. When the purity of the raw material is low, the semiconductor manufacturing process may be adversely affected, and further, grain boundary segregation of impurity components, non-uniform grain growth, etc. may be caused, leading to a decrease in material strength and plasma resistance. .

  As a binder used for slurry preparation, it can use combining commercial materials, such as polyvinyl alcohol, polyvinyl butyral, polyacrylate, polymethacrylate. Some of these binders are commercially available in the form of copolymers. In addition, plasticizers such as polyethylene glycol and lubricants such as stearate can be used.

  The type and blending amount may be appropriately selected and adjusted in consideration of securing the strength of the molded body, smoothness of the granules, imparting flexibility suitable for pre-firing processing, and the like. When the amount of the binder is small, the binder does not circulate well at the time of molding, and the granules are not crushed cleanly.On the other hand, when the amount is large, a high density of the molded body can be achieved at the time of molding. As a result, it is difficult to increase the final density, which greatly affects the dry processability before firing.

  Slurry can be prepared for both organic and aqueous systems, but an aqueous system is preferred in terms of environment and cost. In that case, in order to improve the dispersibility of the primary particles, it is preferable to use a commercially available brazing material (polymer surfactant or the like). Moreover, you may use an antifoamer and a surface modifier as needed.

<Molding process>
The yttria granule powder obtained as described above is molded by a die press, CIP (cold isostatic pressing) molding, casting molding, or the like, and further molded into a rough shape by dry machining if necessary. Apply processing.

<Surface finishing treatment before firing>
Machining by machining or the like, polishing (hand polishing by paper or mechanical polishing), etc. can be selected. In any case, dry treatment is preferred. In the case where all or part of the baked surface is applied to the product as it is, means such as enclosure and filling may be used in order to reduce contamination by impurities from the furnace atmosphere.

  In the case where the surface roughness finishing treatment after the subsequent firing is not performed, the fired surface can be utilized. In this case, since there is no grinding process trace, it is advantageous for particle suppression.

<Baking process>
Firing is performed at atmospheric pressure 1600-1700 ° C. in an atmospheric furnace. Techniques such as hot press sintering and HIP treatment may be used to shorten the manufacturing process.

<Roughness finishing treatment of fired body>
After firing, after processing to the desired product shape by various grinding processes, surface roughness finishing treatment of the fired body may be performed. When roughening after firing, a simple sand blasting method can be applied. Further, only a specific part of the member can be roughened by masking. For parts necessary for product design, surface smoothing by lapping or the like may be performed.

  High purity yttria powder having an average particle size of 0.1 μm and purity of 99.9%, high purity yttria powder having an average particle size of 1.0 μm and purity of 99.9%, and purity of 99.0% having an average particle size of 1.0 μm % Yttria powder was prepared, each was added with a binder, granulated by a spray drying method, and a compact was obtained by CIP (cold isostatic pressing). The formed body was fired under normal pressure in an atmospheric furnace to obtain a yttria sintered body. Table 1 shows the conditions of the yttria powder, the firing temperature, the porosity of the yttria sintered body, the average crystal grain size, the bending strength, and the etching rate. The porosity and the like were determined by the following method.

<Porosity of yttria sintered body>
The open porosity was calculated according to the method specified in JIS R 1634.

<Crystal grain size>
After the arbitrary cross section of the sintered body is polished until the surface roughness Ra becomes about 0.05 μm, a short-time atmospheric heat treatment is performed at each sintering temperature of −50 ° C. to thermally etch the grain boundary portion. did. The crystal grains of the sintered body were photographed with a digital microscope, the apparent crystal particle diameters from the cross section were totaled, and the average particle diameter was calculated.

<Bending strength>
Based on JIS R 1601, the three-point bending strength at room temperature was measured.

<Plasma etching rate>
A test piece was obtained from a sintered body prepared to have a required surface roughness (Ra) by performing a surface treatment such as mirror polishing. The test piece was masked with a polyimide tape on a part of the surface-treated surface, and then placed in a reactive ion etching (RIE) apparatus treatment chamber. CF ₄ gas was introduced into the processing chamber as a plasma source at a flow rate of 100 ml / min. By applying a high frequency bias (13.56 MHz to 1 kW) under a pressure of 10 Pa in the reaction chamber, plasma was generated in the processing chamber to selectively etch the surface of the test piece masked. After performing the plasma etching treatment for 6 hours, the masking tape of the test piece was peeled off, and after cleaning, the difference in height between the plasma exposed portion and the masking portion was determined by a probe type step gauge. This was divided by the processing time (6 hours) to calculate the etching rate (nm / min).

  Since the plasma etching rate varies depending on the shape of the test piece, the mounting position in the plasma processing apparatus, etc., attention was paid to matching the conditions.

  Note that a weight method for obtaining an etching rate from a weight change before and after the plasma treatment is also applicable. In the material of the present invention, the weight method has a tendency and an etching rate evaluation value almost the same as the step method.

<Surface roughness Ra>
Ra was measured with a stylus type surface roughness tester in accordance with JIS surface / shape measurement items (B 0651, etc.).

<Evaluation of particles>
Various yttria sintered bodies that were processed into a ring shape corresponding to a silicon wafer having a diameter of 300 mm and adjusted to Ra on the plasma exposure surface were incorporated into a plasma CVD apparatus. Using this apparatus, a process including an etching process using fluorine-based plasma was performed on a 300 mm silicon wafer. The processed silicon wafer was placed in a laser light scattering type substrate foreign matter inspection apparatus (particle counter), and particle counting and mapping were performed. The case where the number of particles having a particle diameter of 1 μm or more confirmed on the silicon wafer was less than 5 was evaluated as “good”, and the case of 5 or more particles was evaluated as “bad”.

  As shown in Table 1, in Examples 1 to 3, which satisfy all the conditions of the porosity, average crystal grain size, and bending strength of the yttria sintered body, the etching rate was small and the plasma resistance was high. On the other hand, in Comparative Examples 1 to 4 where the yttria sintered body does not satisfy any of the conditions of porosity 1% or less, average crystal grain size 3 μm or less, and bending strength 180 MPa or more, the etching rate is higher than that of Examples 1 and 2. Large and plasma resistance decreased. Further, in Comparative Example 5, an yttria sintered body was obtained by the same manufacturing method as in Example 2 except that a slightly lower (99.0%) raw material powder was used, but the bending strength was 180 MPa or more. It could not be satisfied and was inferior in plasma resistance. This may be due to the effect of segregation of impurity components derived from the raw material on the grain boundary portion.

Subsequently, for the yttria sintered bodies of Examples 2 and 3 and Comparative Example 3 whose surface roughness was prepared by the method shown in Table 2, plasma treatment was performed, and bending strength and etching rate were measured. In Table 2, “E ₀ ” indicates the etching rate E of Example 2 for Examples 4 to 9, the etching rate E of Example 3 for Examples 10 to 12, and the comparative examples 6 to 8. The etching rate E of Comparative Example 3 is meant.

  For mirror polishing (LAP), many lapping liquids containing various types of abrasive grains and particle sizes and containing rust preventives, dispersions, etc. are commercially available. Also, various materials and surface states can be selected for the LAP board. In the example of Table 2, the finished state (Ra value) was prepared by these selections.

As shown in Table 2, in the examples shown in Examples 5 to 11, even when the surface was roughened and the Ra value was increased, the change in the etching rate was very small. Satisfy the relationship. In Example 4, lapping was performed to obtain a Ra value of 0.01 μm. In this case as well, the change in the etching rate is very small, and the etching rate E satisfies the relationship of the following expression (1). . Therefore, it can be seen that excellent plasma resistance can be maintained in these examples. On the other hand, in Comparative Examples 6 to 8 using Comparative Example 3 out of the ranges of porosity, bulk density, average crystal grain size, and bending strength defined in the present invention, the etching rate increases as Ra increases and the plasma resistance is increased. Was down.
E ≦ 1.20 × E ₀ (1)

  Next, after using the yttria raw material powder used in Example 2 and molding the same in the same manner as in Example 2, the surface preparation treatment shown in Table 3 was performed, and firing was performed under the same conditions as in Example 2. A yttria sintered body was produced. After sintering, no grinding process or the like was performed, and plasma etching was performed on the fired surface. Table 3 shows the surface roughness before and after firing and after the plasma treatment, and the etching rate.

  In Examples 13 to 16, even when the surface is roughened and the Ra value is increased, the etching rate is hardly changed, that is, the relationship of the above expression (1) is satisfied, and excellent plasma resistance can be maintained.

  Next, for Examples 2, 4, 8 and 11 and Comparative Example 7, the amount of particles generated was examined by the method described above. The results are shown in Table 4.

  As shown in Table 4, it was found that if the yttria sintered body of the present invention is used and Ra of the plasma exposure part is 0.05 μm or more, the scattering of particles is suppressed.

  The yttria sintered body of the present invention has a bending strength of 180 MPa or more, which is a very high level as an yttria sintered body, and 200 MPa or more under the most preferable conditions. Moreover, it is difficult for the particles to fall off the surface layer. As a result, the degree of freedom in product design of the yttria sintered body used as the corrosion-resistant member is widened, and the surface roughness can be controlled in a wide range. On the other hand, the yttria sintered body of the present invention has little decrease in etching rate even when the surface is roughened.

  For this reason, if a part or all of the yttria sintered body of the present invention is roughened and used as a corrosion-resistant member exposed to at least the halogen-based corrosive gas or the plasma in the plasma process apparatus, it has high plasma resistance. However, scattering of particles can also be prevented.

Claims (2)

An yttria sintered body having an average crystal grain size of 3 μm or less, a porosity of 1% or less, a bending strength of 180 MPa or more, and a surface roughness (Ra) of 0.05 to 5 μm,
The surface roughness (Ra) is 1 μm or more, and
When the yttria sintered body having the same material with the same etching rate E (nm / min) and Ra of 0.05 μm when the arbitrary fluorine-based gas plasma treatment is performed is subjected to the same conditions as the fluorine-based gas plasma treatment. When the etching rate (nm / min) of E is set to E ₀ , the yttria sintered body satisfies the relationship of the following formula (1)
E ≦ 1.20 × E ₀ (1) A member used in a plasma processing apparatus, wherein at least a portion exposed to a halogen-based corrosive gas or plasma thereof is composed of the yttria sintered body according to claim 1 . Element.