JPH09139329A - Semiconductor heat treatment dummy wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a semiconductor heat treatment dummy wafer many times and prevent the generation of dust by forming the dummy wafer of glass-type carbon material which has a specific thermal expansion coefficient. SOLUTION: Glass-type carbon material which forms a dummy wafer has an appearance of glass-type highly hard carbon, is abrasion resistant, gas impermeable and is basically manufactured by solid-phase carbonization. The preferable glass carbon material is the material that has a thermal expansion coefficient of 3.0-3.5×10<-6> / deg.C. In the case of forming a film by semiconductor heat treatment, polysilicon is formed on the dummy wafer. The dummy wafer formed of the glass-type carbon material is preferably used by forming fine ruggedness on the surface by sand-scratching to provide the surface roughness Ra at 3-30μm, preferably, 5-20μm. Thus, the film on the dummy wafer is prevented from removing in the film forming heat treatment and the generation of dust is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor heat treatment dummy wafer, and more specifically, it can uniformly process a silicon wafer, which is a semiconductor substrate, in a heat treatment furnace to prevent generation of defective products and to prevent contamination. The present invention relates to a semiconductor heat treatment dummy wafer formed of a glassy carbon material that can be prevented.

[0002]

2. Description of the Related Art Conventionally, a semiconductor substrate such as a silicon wafer has been subjected to various treatments in a furnace core tube. In these processes, generally, a wafer to be processed is set on a mounting device such as a boat, charged into a heated core tube, further heated, and a processing gas is introduced to perform heat treatment. As the heat treatment furnace, either a horizontal furnace in which a plurality of wafers are arranged vertically in a horizontal direction or a vertical furnace in which a plurality of wafers are arranged horizontally in a vertical direction is used depending on processing conditions. In these heat treatment furnaces, conventionally, a plurality of dummy wafers are set at predetermined positions of a boat so that the introduced gas does not directly impinge on the processed wafer to prevent the wafer from being contaminated. Further, the dummy wafer is used to control the gas flow to achieve uniform heating in the furnace.

The dummy wafer used in the above heat treatment furnace is generally a silicon plate, and other materials include an alumina single crystal plate, a quartz plate or a SiC film plate. In recent years, with the high integration of semiconductors. Higher homogeneity is required for the substrate as well, to prevent contamination during processing more than before, to prevent uneven heat in the furnace, and to improve the yield in the heat treatment process. In addition, various improvements of dummy wafers have been proposed. For example, in Japanese Unexamined Patent Publication (Kokai) No. 5-283306, a CVD film made of a predetermined alumina and silica is formed on the surface of a silicon carbide-impregnated silicon carbide base material mainly for the purpose of improving the impermeability of light of a predetermined wavelength required as a dummy wafer. Formed dummy wafers have been proposed. In addition to being opaque, the dummy wafer is generally required to have high cleanliness, high corrosion resistance, heat resistance, high strength, etc. as described in the above publication.

As described above, the first purpose of arranging the dummy wafer is to prevent contamination of the silicon wafer to be processed, and the original purpose cannot be achieved if the dummy wafer itself becomes a contamination source. Therefore, after satisfying high cleanliness,
Further, those satisfying other requirements are preferable. In the heat treatment process, generally, it is important to make various gases flow to form a film on the surface of a silicon wafer, and a film is formed on a dummy wafer in the same manner as a silicon wafer. Therefore, it is needless to say that the contaminant itself is not emitted from the material itself forming the dummy wafer and that the film adhered and formed on the dummy wafer is prevented from peeling and scattering during the processing. In the past, prevention was often performed by using a dummy wafer of SiC-CVD film. However, when the surface is rough, it is easy to trap dust, and when the dust becomes trapped to a certain extent, it tends to diverge, so that the surface of the dummy wafer is usually made smooth.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors have made various studies on the material of the dummy wafer, and the glassy carbon material has heat resistance, corrosion resistance, light opacity, non-gas permeability, and high strength. As a result, the inventors have found that they have excellent characteristics as above, and have studied for the purpose of practical application of a dummy wafer made of a glassy carbon material. As a result, by identifying the surface roughness and the coefficient of thermal expansion of the glassy carbon material, it was found that the glassy carbon material can be used many times and is effective in preventing dust generation, and completed the present invention.

[0006]

According to the present invention, a dummy wafer for semiconductor heat treatment having a thermal expansion coefficient of 3.0.
Provided is a dummy wafer for semiconductor heat treatment, which is formed of a glassy carbon material having a temperature of ˜3.5 × 10 ⁻⁶ / ° C. Further, the present invention is a dummy wafer for semiconductor heat treatment, which is formed of a glassy carbon material and has a surface roughness Ra of at least one surface of 3 to 30 μm.
Provided is a dummy wafer for semiconductor heat treatment, which is formed by: The above-mentioned dummy wafer for semiconductor heat treatment of the present invention can be preferably used particularly in a film formation heat treatment step of a polysilicon film.

The present invention is configured as described above, and a dummy wafer for a semiconductor heat treatment step is formed of a glassy carbon material having a predetermined coefficient of thermal expansion, and is used in a film forming process to prevent generation of dust such as peeling. be able to. In addition, since at least one surface of the surface is formed to have a roughened grain,
The coating film that adheres to the dummy wafer during film formation can be firmly held during the processing step, wafer contamination due to peeling of the coating film can be prevented, and a uniform processed wafer with good yield can be obtained. Further, the glassy carbon material has excellent corrosion resistance and heat resistance, and sufficiently satisfies the requirements as a dummy wafer, and in particular, the coating on the dummy wafer can be removed by washing with hydrofluoric acid or an aqueous solution of hydrofluoric nitric acid to recover and regenerate the surface state. ,
Reusable and extremely practical.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The shape and the like of the dummy wafer of the present invention are not particularly limited. Usually, it is formed in a form substantially similar to the silicon wafer to be processed set in the quartz boat. That is, it has a thickness of about 600 to 800 μm. Further, the number of dummy wafers of the present invention to be set in the boat and the setting position can be appropriately selected according to each processing condition. Usually about 1 each at the top and bottom of the boat
~ 15 sheets are set each.

The glassy carbon material forming the dummy wafer of the present invention is highly hard carbon having a glassy appearance, is abrasion resistant and gas impermeable, and is basically manufactured by solid phase carbonization. is there. In the present invention, a preferable glassy carbon material has a heat resistance temperature of 2000 ° C. or higher, a bulk specific gravity of 1.5 to 1.6 g / cm ³ , a bending strength of 100 MPa or higher, and a thermal conductivity of 5 to 10 W / m · K, and particularly, 3.0
It is preferable to have a coefficient of thermal expansion of ˜3.5 × 10 ⁻⁶ / ° C. (value from room temperature to 450 ° C. by the quartz push-end method). When a film is formed by a semiconductor heat treatment, a film forming composition is also formed on a dummy wafer. According to the inventors, films formed of different materials are strong against compressive stress but tensile stress. Was found to be weak. Therefore, it has been found that when a material having a coefficient of thermal expansion larger than that of the film-forming composition is used, the film formed on the dummy wafer at high temperature has less peeling and warpage during cooling after the film formation. . For example, when depositing polysilicon, the coefficient of thermal expansion of polysilicon is about 2.8 × 10 ⁻⁶ / ° C., which is 3.0 × 10 ^{−6 which} is larger than the coefficient of thermal expansion of that polysilicon.
By using a glassy carbon material having a coefficient of thermal expansion of / ° C. or more, peeling and warpage of the film could be significantly improved. On the other hand, a glassy carbon material exceeding 3.5 × 10 ⁻⁶ / ° C. can withstand many uses, but has problems in oxidation resistance, corrosion resistance, dust generation, etc., and is not suitable as a dummy wafer.

The dummy wafer formed of the glassy carbon material of the present invention is preferably used by graining the surface roughness Ra to 3 to 30 μm, preferably 5 to 20 μm to form fine irregularities on the surface. preferable. The surface roughness (Ra) of the glassy carbon material generally manufactured is usually 1 μm.
However, since the surface of the dummy wafer of the present invention is formed as described above, peeling can be prevented and contamination of the wafer to be processed can be prevented by increasing the number of places where the deposited film forming composition is captured and held. It was discovered that this could be done. When the surface roughness is smaller than 3 μm, for example, 0.01 μm, the adhesion is poor and peeling occurs due to thermal shock or the like because the polysilicon film adhered on the dummy wafer made of glassy carbon material has few attachment points. It was confirmed that dust was generated and the silicon wafer was contaminated. Further, in the case of rough processing exceeding 30 μm, for example, when it is 50 μm or more, the carbon protrusions on the glassy carbon surface become dust,
It was also confirmed that the silicon wafer was contaminated. The method for forming roughness of the surface state, that is, the graining method is not particularly limited, and known grinding and polishing processes can be appropriately applied. It is particularly preferable that the dummy wafer formed of the glassy carbon material of the present invention has the above-mentioned coefficient of thermal expansion and is further grained to the above-mentioned surface roughness.

The glassy carbon material used in the present invention is generally extremely hard and difficult to process. Therefore, the glassy carbon material is formed into a predetermined shape in advance and then carbonized to be manufactured. For example, it is produced by calcining a thermosetting resin such as a furan-based resin, a phenol-based resin, or an epoxy resin at a temperature of about 800 ° C. or more slowly in an atmosphere of an inert gas such as nitrogen or argon for a long time. In particular, as the glassy carbon of the present invention, high-purity carbon produced by the method disclosed in JP-A-3-285086 is preferable.
That is, an organic sulfonic acid was added to a thermosetting resin to polymerize at room temperature to form a fluid polymer, which was poured into a mold in a fluid state and gradually heated to cure to form a molded product. The molded body is gradually heated to 800 to 1200 ° C., calcined and carbonized, and if necessary, surface-treated, and further 2000 to 250.
This is a method of heating to 0 ° C. for purification treatment. The glassy carbon material obtained by this method can be produced without a grain boundary, and can have a minimum maximum pore diameter of 0.1 μm or less and an open porosity of 0.01% or less. It can be applied when there is no risk of scattering carbon fine particles and the like is extremely disliked by contamination.

The dummy wafer of the present invention is made of the above glassy carbon material, has excellent heat resistance and thermal conductivity, and is excellent in cleanliness. Particularly, it is effective in preventing dust generation in the film forming process of polysilicon. There is. Further, the glassy carbon material has high corrosion resistance, can be surface-cleaned with an HNO ₃ -HF aqueous solution, and can easily recover the surface state.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. However, the present invention is not limited by the following examples. Examples 1 to 5 and Comparative Examples 1 to 2 A vertical diffusion furnace was used to perform heat treatment for forming a polysilicon film on the surface of a silicon wafer. First, using a fluid polymer obtained by adding 0.4 parts by weight of p-toluenesulfonic acid to furfuryl alcohol and polymerizing, a diameter of 260 m
m, thickness 1.5 mm, orientation flat width 65 m
It was molded into a disk shape of m and heated to cure. The obtained cured product was heated and baked to 1000 ° C. in a nitrogen atmosphere, further heated to 2300 ° C. and purified to produce a rough dummy wafer made of a glassy carbon material. The produced glass-like carbon material rough dummy wafer has a porosity of 0.1%, a surface roughness (measured by a contact surface roughness meter) of 1 μm, a thermal conductivity of 8 W / m · K, and a thermal expansion coefficient of 3.2. It was × 10 ^-6 / ° C. Then, the obtained rough dummy wafer was subjected to surface treatment using a polishing apparatus, and adjusted to have the surface roughness shown in Table 1,
Each dummy wafer was formed.

Then, CVD-on the surface of the Si-SiC substrate.
Total length 800mm coated with SiC film, 125 grooves
In a vertical boat with a pitch of 6.0 mm and a groove width of 2.5 mm, each of the dummy wafers obtained above was placed on the upper side with two grained surfaces facing downward, and on the lower side with the grained surface facing upward. Three
Each of them was set, and four lots of 200 mm diameter silicon wafers were set in lot units. The set boat is loaded into a vertical core tube, and the temperature in the central part of the furnace is 60
The temperature was adjusted and maintained at 0 ° C. SiH ₄ gas was introduced into the furnace core tube as a processing gas at a flow rate of 0.5 liter / min (standard state) to form a film for 10 minutes.

Each of the glassy carbon dummy wafers used was dipped in an HNO ₃ -HF aqueous solution to wash and remove the polysilicon film adhering to the surface, and then taken out and washed with pure water to remove adhering water at the time of washing. It was dried by hot air so as to be completely removed, and the surface condition was recovered and regenerated. The pass / fail judgment of the surface state of each processed wafer was performed by repeating the film forming process similar to the above 10 times while reusing the glassy carbon material dummy wafer cleaned and regenerated as described above, and obtained 40 lots of silicon. For each wafer, the film formation homogeneity, dust level, and impurity level were measured, and the results showed that the film formation homogeneity was within 5% of the polysilicon film thickness within the silicon wafer surface. Yes, 100 or less on the silicon wafer surface for dust level, F for impurity level
The non-defective rate was calculated on the condition that each of e, Ni, Cr, Mo, Al, Na, K, and Cu is 1 × 10 ¹⁶ atoms / cm ³ or less. The results are shown in Table 1.
Table 1 also shows the temperature inside each furnace.

[0016]

[Table 1]

After the above 40 lots were subjected to the film forming treatment, the dummy wafers made of the glassy carbon material used were further washed and regenerated with the HNO ₃ -HF aqueous solution in the same manner, and were repeatedly used 60 times. No defects occurred on the silicon wafer, and no trouble occurred. In addition, since the dummy wafer which is not grained is also formed of glassy carbon, it has the same durability. In addition, it was confirmed that when the surface roughness was 50 μm, the dust level was remarkably deteriorated due to detachment of protrusions and adhesion of dust.

As is clear from the above examples and comparative examples, when a dummy wafer made of glassy carbon material having a surface roughness of 3 to 30 μm is set, the silicon wafer is contaminated during the polysilicon film forming process. Is significantly reduced, yield is improved with almost no defective products, and
It can be seen that the product can be recycled and reused and the productivity is increased. Especially,
It can also be seen that the dummy wafer made of a glassy carbon material having a surface roughness of 5 to 20 μm has a high yield rate of silicon wafers. On the other hand, when the surface roughness is 0.01 μm and the surface is processed into a smooth surface, or when the surface is roughened to 50 μm or more,
It can be seen that the surface of the silicon wafer is contaminated and the yield is reduced.

[0019]

Industrial Applicability The dummy wafer for semiconductor heat treatment of the present invention is formed of a glassy carbon material having a predetermined coefficient of thermal expansion and / or a grained surface to have a predetermined surface roughness. Therefore, by setting the silicon wafer to be processed together with the silicon wafer to be processed in a boat and arranging it in a heat treatment furnace, there is no peeling of the film on the dummy wafer during the film formation heat treatment having a difference in thermal expansion coefficient from the dummy wafer. It is possible to prevent the generation of dust and prevent the processing yield from decreasing. Moreover, even after cleaning and regeneration treatment, effective characteristics are maintained for a long period of time and excellent durability,
Since it can be reused, the productivity of wafers is significantly improved.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomohiro Nagata 378 Oguni-machi, Oguni-machi, Nishiokitama-gun, Yamagata Pref.

Claims (3)

[Claims] 1. A semiconductor wafer heat treatment dummy wafer, which is formed of a glassy carbon material having a thermal expansion coefficient of 3.0 to 3.5 × 10 ⁻⁶ / ° C. Dummy wafer. 2. A dummy wafer for semiconductor heat treatment, which is formed of a glassy carbon material and has at least one surface roughness Ra of 3 to 30 μm. 3. The dummy wafer for semiconductor heat treatment according to claim 1, wherein the semiconductor heat treatment is a film formation step, and the film formation composition is a polysilicon film.