JP4275767B2 - Method for manufacturing silicon carbide dummy wafer - Google Patents

Description

【００３３】
図１に、表１を基に、本発明におけるＳｉＣダミーウェハと、従来法によるＳｉＣダミーウェハ、そしてＳｉダミーウェハと、形成されるＳｉ₃ Ｎ₄ の累積膜厚及びその時のパーティクル数の関係を示す。この図より、本発明によるＳｉＣダミーウェハは従来使用されていたシリコンダミーウェハや従来法により作製されていたＳｉＣダミーウェハに比較し、表面粗さを大きくすることにより、形成される膜との付着性が向上し、パーティクルの発生前までの許容される累積膜厚が大幅に向上することが分かる。
【００３４】
【発明の効果】
以上のように、ダミーウェハの表面粗さを１μｍ以上とすることで、形成される膜の付着力が向上し、パーティクルの発生が抑制できる。即ち、本発明のＳｉＣダミーウェハを使用することにより、ＬＰＣＶＤ処理工程において、ダミーウェハの交換、洗浄までの時間を大幅に延長でき、装置の稼働率が向上し、半導体製造コストの低減が可能となる。
【図面の簡単な説明】
【図１】実施例に係る形成されるＳｉ₃ Ｎ₄ の累積膜厚とパーティクル発生数の関係図。
【図２】実施例に係る各ダミーウェハの評価試験時の縦型ウェハボートの断面該略図。
【図３】半導体製造工程における縦型ＬＰＣＶＤ炉の一例の断面概略図。
【符号の説明】
１０ 炉本体
１１ 円筒状ヒータ
１２ 均熱管
１３ 反応管
１６ シリコンウェハ
１７ 縦型ウェハボート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon carbide dummy wafer used in a process of forming a polysilicon or silicon nitride film on a semiconductor wafer in a semiconductor manufacturing process.
[0002]
[Prior art]
Among the semiconductor manufacturing processes, there is a low pressure CVD process for forming a silicon nitride (Si ₃ N ₄ ) film or a polysilicon film (polycrystalline silicon film) on a silicon wafer. In this process, a vertical low pressure CVD furnace (hereinafter LPCVD) as shown in FIG. 3 is used. In FIG. 3, the furnace body 10 is provided with a cylindrical heater 11 so that the inside of the furnace can be depressurized to 10 Torr or less. A reaction tube 13 is disposed inside the cylindrical heater 11 via a soaking tube 12. A boat receiver 18 is installed at the center of the base 19 covered with the reaction tube 13, and a vertical wafer boat 17 made of quartz or silicon carbide (SiC) is provided on the boat receiver 18. It has been. On the boat 17, objects to be processed 16, which are semiconductor materials such as silicon wafers, are stored and arranged in a state where a large number are set at appropriate intervals. In addition, a protective tube 14 incorporating a thermocouple for temperature measurement and a gas introduction tube 20 are arranged inside the reaction tube 13.
[0003]
Along with the silicon wafer 16 forming the film, 15 to 20 dummy wafers are placed on the vertical wafer boat 17 in order to increase the soaking temperature in the furnace and adjust the gas flow. Conventionally, a silicon wafer, quartz, or the like having the same and same shape as the silicon wafer that is the object to be processed has been used for this dummy wafer.
[0004]
However, a film is formed on these dummy wafers at the same time as the film is formed on the silicon wafer 16 that is the object to be processed. And after several uses, the stress generated from the difference in thermal expansion with this film causes warping or cracking during processing, or the formed film peels off, causing particles and particles to enter the furnace. It becomes a cause of lowering the yield, such as scattering and contaminating the inside of the furnace. For this reason, replacement is necessary before these problems occur. In addition, silicon has insufficient chemical resistance, and the dummy wafer itself is damaged when the formed film is chemically cleaned with hydrofluoric acid, hydrofluoric acid, or the like, so it must be replaced after several uses.
[0005]
Therefore, it is considered that these dummy wafers are required to have the following characteristics.
(1) Good adhesion to Si ₃ N ₄ film and polysilicon film, and difficult to peel off.
(2) The chemical solution can be repeatedly cleaned and used as a dummy wafer many times after cleaning.
(3) High purity.
[0006]
Recently, SiC dummy wafers are often used as a material having the characteristics considered to be necessary for the dummy wafers. In JP-A-10-116757, SiC is coated on a graphite substrate by a CVD method, and the graphite substrate is incinerated to make only SiC, and its surface roughness Ra is adjusted to 0.01 to 0.7 μm. As a result, the adhesion of the formed film is improved, the cumulative film thickness of Si ₃ N ₄ at the time of particle generation is about 3 μm, and the dummy wafer replacement frequency is greatly improved compared to the conventional silicon dummy wafer, A technique for improving the operating rate of the apparatus is disclosed. The surface roughness Ra of the conventional SiC dummy wafer is 0.2 to 0.9 μm.
[0007]
[Problems to be solved by the invention]
However, along with the increase in the diameter of silicon wafers to be processed, there is a demand for further improvement in apparatus operating rate and reduction in manufacturing cost. There is a demand for a SiC dummy wafer that further improves the device operating rate over the SiC dummy wafer disclosed in 116757.
[0008]
An object of the present invention is to provide a silicon carbide dummy wafer capable of suppressing the generation of particles and greatly improving the operation rate of the apparatus and having characteristics considered to be necessary as the dummy wafer.
[0009]
[Means for Solving the Problems]
The present inventors believe that by applying the prior art by the present inventors (Japanese Patent Application No. 8-224212), a silicon carbide dummy wafer that satisfies the characteristics considered necessary for the dummy wafer can be provided. During intensive research, it was discovered that the generation of particles can be suppressed by roughening the surface roughness compared to conventional products, and the film thickness at the time of particle generation is greatly improved, completing the present invention. It came to do.
[0010]
That is, according to the first aspect of the present invention, a silicon carbide dummy wafer is formed by coating a porous silicon carbide surface having a surface roughness of 1 μm to 10 μm by cutting with dense silicon carbide by a CVD method. Is a method for producing a silicon carbide dummy wafer in which the surface roughness of the silicon carbide is 1 μm to 10 μm.
[0011]
The invention according to claim 2 is the production of a silicon carbide dummy wafer according to claim 1, wherein the porous silicon carbide is obtained by converting a graphite base material into silicon carbide by a CVR method. Is the method .
[0012]
The invention according to claim 3 is the method for producing a silicon carbide dummy wafer according to claim 2 , wherein the graphite base material is a graphite material having a bulk density of 1.0 to 1.5 g / cm ³ .
[0013]
4. The silicon carbide dummy wafer according to claim 1 , wherein the porous silicon carbide is purified before coating the dense silicon carbide. It is a manufacturing method.
[0014]
In the present invention, the surface roughness Ra of the SiC dummy wafer is adjusted to 1 μm or more in order to improve the adhesion of the formed film. This improves the adhesion between the film and the dummy wafer, makes it difficult to peel off, and suppresses the generation of particles during processing.
[0015]
The surface roughness of the conventional SiC dummy wafer was Ra of 0.2 to 0.9 μm. This is because it is necessary to adjust the dummy wafer to 0.735 mm, which is the same thickness as the silicon wafer that is another object to be processed, and in order to prevent cracks that occur during machining, SiC, which is a difficult-to-cut material, is used. It is presumed to be due to the cutting conditions such as the cutting speed and the cutting depth during the machining required for adjusting the thickness, improving the yield, and reducing the manufacturing cost. In order to make the surface roughness higher than this, it can be obtained by increasing the above-mentioned cutting speed, the amount of cutting, etc., but increasing the cutting force with dense SiC and thin SiC like a dummy wafer. If processed, cracks will occur and the yield will be very poor. On the other hand, in order to make the surface roughness smoother than this value, it can be obtained by reducing the cutting speed and the cutting depth. However, the processing takes a long time, which causes an increase in the manufacturing cost of the dummy wafer.
[0016]
However, in the SiC dummy wafer according to the present invention, a high-purity graphite substrate of 1.0 to 1.5 g / cm ³ is first processed into a predetermined disk shape, and then CVR treatment is performed to convert it into 100% SiC. SiC is produced. Cutting is performed only in the thickness direction of the porous SiC to adjust the thickness, and the surface roughness is adjusted to 1 μm or more, preferably 2 μm or more, more preferably 5 μm or more. Since SiC at this stage is porous, it is relatively easy to process. Therefore, the restriction on cutting conditions is relaxed, and processing with a rough surface is also possible.
[0017]
After adjusting the thickness and surface roughness, a purification treatment is performed with a halogen gas, and the surface of this porous SiC is subjected to a CVD process, so that the SiC wafer has a thickness of 0.725 mm, which is the same thickness as the silicon wafer to be processed Coating. At this time, the surface roughness is adjusted to 1 μm or more, preferably 2 μm or more, more preferably 5 μm or more by controlling the CVD process conditions.
[0018]
As described above, in the present invention, the porous SiC before the SiC coating by the CVD process is machined and purified, and then the SiC is coated by the CVD to produce the SiC dummy wafer. It becomes a very high purity dummy wafer. In addition, the surface roughness can be adjusted coarsely at the stage of machining, and at the same time, since the SiC is coated on the porous surface by CVD, a rough surface can be formed.
[0019]
Moreover, when the surface roughness Ra is 10 μm or more, the adhesion of the film is improved, and a very thick film can be formed before particles are generated. However, at present, the vacuum chuck method is adopted for automatic transfer of these wafers. Therefore, if the surface roughness Ra is 10 μm or more, the wafer cannot be sucked and automatically transferred by the vacuum chuck. The upper limit of 10 μm. In the future, when this transport technology is improved, it is considered that the surface roughness Ra can be reduced to several tens of micrometers, and further reduction in manufacturing cost can be expected.
[0020]
Since the generation of particles depends on the surface roughness of the dummy wafer, if the rough surface can be processed industrially with the progress of machining technology in the future, the SiC wafer surface is made of SiC by the CVD method. SiC-coated dummy wafers, or the surface of graphite base material coated with CVD-SiC, and then the graphite base material is ashed, and SiC-based dummy wafers made of SiC alone are roughened to generate particles. There is a possibility that it can be suppressed.
[0021]
Examples are given below to illustrate the present invention.
(Example 1)
The graphite substrate of bulk density 1.3 g / cm ^3, and processed into a diameter of 200 mm, a thickness of 3 mm, was converted to 100% SiC performs CVR process to prepare a SiC porous. Next, only the thickness direction was cut and adjusted to a thickness of 0.485 mm. At this time, the surface roughness Ra was adjusted to 1.0 μm. Thereafter, the porous SiC base material is purified with a halogen gas, and then subjected to a CVD process to form SiC on the surface. An 8-inch SiC dummy wafer having a thickness of 0.725 mm and an average roughness Ra of 1.0 μm is obtained. Obtained.
[0022]
(Example 2)
A SiC dummy wafer having a final surface roughness Ra of 2.3 μm was produced by setting the average roughness Ra during cutting to 2.3 μm in the same procedure as in Example 1.
[0023]
(Example 3)
A SiC dummy wafer having a final surface roughness Ra of 5.1 μm was produced by setting the average roughness Ra at the time of cutting to 5.1 μm in the same procedure as in Example 1.
[0024]
(Example 4)
A SiC dummy wafer having a final surface roughness Ra of 10.0 μm was produced by setting the average roughness Ra during cutting to 10.0 μm in the same procedure as in Example 1.
[0025]
( Reference Example 1 )
A SiC dummy wafer having a final surface roughness Ra of 15.2 μm was produced by setting the average roughness Ra during cutting to 15.2 μm in the same procedure as in Example 1.
[0026]
(Example 5 )
Bulk density 1.8 g / cm ³ The graphite base material was processed into a diameter of 200 mm and a thickness of 3 mm, and dense SiC was formed on the surface by CVD treatment. Then, this center is sliced and divided in half, the graphite base on the surface not coated with CVD-SiC is removed by machining, and the surface roughness is adjusted by machining over time. An 8-inch SiC dummy wafer having a surface roughness Ra of 1.6 μm was produced.
[0027]
(Comparative Example 1)
A SiC dummy wafer having a final surface roughness Ra of 0.5 μm was produced by setting the average roughness Ra during cutting to 0.5 μm in the same procedure as in Example 1.
[0028]
(Comparative Example 2)
Using a graphite substrate of the same quality as in Example 6, an 8-inch SiC dummy wafer having a final surface roughness Ra of 0.2 μm was produced in the same procedure.
[0029]
(Comparative Example 3)
An 8-inch silicon wafer of the same quality as the material to be treated and having a surface roughness Ra of 0.002 μm was used as a dummy wafer.
[0030]
Twenty-five dummy wafers having the surface roughness of each of Examples 1 to 5, Reference Example 1 and Comparative Examples 1 to 3 were prepared and placed on a vertical wafer boat as shown in FIG. 2 to generate a Si ₃ N ₄ film. did. Three monitor wafers, one each of 8-inch silicon wafers in the upper, middle, and lower stages, for a total of three, each monitor wafer has 50 or more particles (with a size of 0.2 μm or more) The thickness of the Si ₃ N ₄ film formed on the SiC dummy wafer was measured. At the same time, it was investigated whether automatic conveyance of the vacuum chuck type was possible.
[0031]
Table 1 shows the test results.
[0032]
[Table 1]

[0033]
FIG. 1 shows the relationship between the SiC dummy wafer according to the present invention, the SiC dummy wafer according to the conventional method, the Si dummy wafer, the accumulated film thickness of Si ₃ N ₄ formed, and the number of particles at that time, based on Table 1. From this figure, the SiC dummy wafer according to the present invention is more adherent to the film to be formed by increasing the surface roughness compared to the conventionally used silicon dummy wafer and the SiC dummy wafer produced by the conventional method. It can be seen that the cumulative film thickness allowed before the generation of particles is greatly improved.
[0034]
【The invention's effect】
As described above, by setting the surface roughness of the dummy wafer to 1 μm or more, the adhesion of the formed film can be improved and the generation of particles can be suppressed. That is, by using the SiC dummy wafer of the present invention, the time until replacement and cleaning of the dummy wafer can be greatly extended in the LPCVD process step, the operating rate of the apparatus can be improved, and the semiconductor manufacturing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the cumulative film thickness of Si ₃ N _{4 and} the number of particles generated according to an embodiment.
FIG. 2 is a schematic cross-sectional view of a vertical wafer boat during an evaluation test of each dummy wafer according to an example.
FIG. 3 is a schematic cross-sectional view of an example of a vertical LPCVD furnace in a semiconductor manufacturing process.
[Explanation of symbols]
10 furnace body 11 cylindrical heater 12 soaking tube 13 reaction tube 16 silicon wafer 17 vertical wafer boat

Claims (4)

The surface of the porous silicon carbide surface roughness was 1μm~10μm by cutting, coating the dense silicon carbide by the CVD method, coal surface roughness of the silicon carbide dummy wafer was set to be 1 [mu] m 10 .mu.m A method for manufacturing a silicon nitride dummy wafer . The porous silicon carbide manufacturing method of silicon carbide dummy wafer according to claim 1, wherein the Ru der those converted to silicon carbide by CVR method graphite substrate. The graphite substrate has a bulk density of 1.0 to 1.5 g / cm. ³ The method for producing a silicon carbide dummy wafer according to claim 2, wherein the graphite material is a graphite material. The method for producing a silicon carbide dummy wafer according to any one of claims 1 to 3, wherein the porous silicon carbide is purified before the dense silicon carbide is coated.

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