Coating apparatus – Work holders – or handling devices
Patent
1981-01-11
1983-06-28
Smith, John D.
Coating apparatus
Work holders, or handling devices
118729, 432241, 432246, 104138R, 105365, B61B 1300
Patent
active
043899676
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a boat for carrying semiconductor substrates, which boat is used in an impurity-diffusion process, an oxidation process or an annealing process.
Recently, the size of a semiconductor substrate, for example, a silicon wafer used for producing semiconductor devices, e.g., ICs and LSIs, has become larger than 2 inches in diameter. When a large number of the semiconductor substrates are subjected to a diffusion or oxidation process, the total weight of a boat, which is made of quartz and carries a large number of the large size semiconductor substrates, is heavy. When the heavy boat is put in and out of a quartz tube of a diffusion furnace or an oxidation furnace, finely powdered quartz is generated by friction between the quartz boat and the quartz tube. In the case of a boat made of polycrystalline silicon instead of the quartz, finely powdered quartz and polycrystalline silicon are generated by friction between the polycrystalline silicon boat and the quartz tube. In order to reduce the generation of fine powder to as small an amount as possible, the boat is provided with wheels made of the same material as that of the boat, so as to reduce the friction.
However, since axles and bearings (e.g. plates with through-holes) for the wheels of the above-mentioned quartz boat are made of quartz, the axles seize with the bearings so that the wheels cannot turn, when the quartz boat is heated at temperatures above 1000.degree. C. during the diffusion or oxidation process. Moreover, the quartz wheels seize with the quartz tube. In order to avoid such seizures, generally, the quartz boat is incessantly moved back and forth during the diffusion or oxidation process. However, the movement of the quartz boat causes the generation of the finely powdered quartz from friction surfaces, i.e., contacting surfaces between the axles and the bearings and between the wheels and the quartz tube. When the wheels, axles and bearings of the above-mentioned polycrystalline silicon boat are made of polycrystalline silicon, and the boat is used for heat-treatment in an oxidizing atmosphere such as oxygen or water vapor, the surfaces of the wheels, axles and bearings are converted into silicon dioxide and seizure occurs in the same manner as the above-mentioned case of the quartz boat.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved boat with wheels for carrying semiconductor substrates, which boat does not seize at temperatures above 1000.degree. C. during the diffusion, oxidation or annealing process for the semiconductor substrates.
The above-mentioned object is attained by an improved boat with wheels for carrying semiconductor substrates, in which the improvement comprises that the friction surfaces of the wheel systems are coated with a silicon nitride film.
The body, wheels, axles and bearings of the boat are made of quartz, e.g., fused quartz, or polycrystalline silicon. It is preferable to coat the surfaces of the axles and the bearings that contact with each other and the surfaces of the wheels that contact the quartz tube of a heating furnace with the silicon nitride film having a thickness of 300.about.600 nm by a conventional coating process, e.g., a chemical vapor deposition (CVD) process or a direct surface nitrification process.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view of a boat with wheels, which boat carries semiconductor substrates;
FIG. 2 is a segmental sectional view illustrating a wheel system of a boat with wheels according to the present invention;
FIG. 3a is a schematic sectional view of a plate for the bearings for the wheel;
FIG. 3b is a schematic sectional view of the plate for the bearings, which plate is coated with a silicon nitride film;
FIG. 3c is a schematic sectional view of the bisected plate of FIG. 3b;
FIG. 3d is a schematic sectional view of a wheel and an axle, and
FIG. 3e is a schematic sectional view of the wheel and the axle coated with a silicon nitride film.
REFERENCES:
patent: 3640398 (1972-02-01), Loxley et al.
patent: 3705714 (1972-12-01), Alliegro
patent: 3746569 (1973-07-01), Pammer et al.
patent: 4089735 (1978-05-01), Sussmann
patent: 4089992 (1978-05-01), Doo et al.
Shimoda Haruo
Tanabe Kaoru
Fujitsu Limited
Plantz Bernard F.
Smith John D.
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