JPS6047737B2 - Aluminum diffusion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reacting aluminum and silicon and diffusing aluminum from a regrown layer containing aluminum that is formed during the cooling process.The purpose of this invention is to uniformly form the regrown layer. An object of the present invention is to provide an aluminum diffusion method that can repeatedly keep the concentration and diffusion depth of aluminum in a silicon substrate constant.

Among the diffusion methods that use aluminum as a source of diffusion impurities, aluminum is applied in advance to a silicon substrate by, for example, vacuum evaporation, and then placed in a diffusion tube, and then diffused as appropriate from one end of the diffusion tube. Heating while supplying oxygen gas and nitrogen gas in proportion, aluminum and silicon undergo an alloy reaction, and during the cooling process, a regrowth layer containing a eutectic layer and aluminum is grown on the silicon substrate.
A diffusion method in which the eutectic layer is then removed and aluminum from the regrown layer is used as a diffusion source is a method that can efficiently diffuse aluminum using simple equipment.

Conventionally, this method has had the disadvantage that the formation of the regrown layer is non-uniform, resulting in significant variations in diffusion concentration and diffusion depth. The present invention has experimentally demonstrated that the above-mentioned non-uniformity of the regrown layer occurs when the cooling rate during the cooling process is high and when the temperature at which the silicon substrate is taken out after cooling is higher than the eutectic temperature of aluminum and silicon. Confirmed by
The cooling rate is 5°C or less per minute, and the temperature at which the semiconductor substrate is taken out is 500°C or less, which is lower than the eutectic temperature of aluminum and silicon.

The present invention will be explained below with reference to embodiments shown in the drawings.

As shown in FIG. 1a, on an n-type silicon substrate 1,
A thin aluminum film 2 is formed by vacuum evaporation. Next, in an atmosphere where the ratio of nitrogen and oxygen is, for example, 100:1, it is heated at a temperature higher than the eutectic temperature of aluminum and silicon, for example, 1050°C, for one hour to cause an alloy reaction between aluminum and silicon, and then cooled. As shown in FIG. 1b, on the silicon substrate 1, an aluminum-silicon eutectic alloy layer 4 and a silicon regrowth layer 3 containing aluminum are formed. The eutectic alloy layer 4 is removed using aqua regia, as shown in FIG. 1c. Thereafter, aluminum contained in the regrown layer 3 is diffused as a diffusion source to form an aluminum diffusion layer 5 as shown in FIG. 1d. Aluminum concentration distribution of aluminum diffusion layer 5, diffusion depth is same as regrowth layer 3
It also varies depending on the thickness. The thickness of the regrown layer 3 is controlled by the thickness of the aluminum vapor deposited film 2, the alloy reaction temperature of aluminum and silicon, and the atmosphere at this time. Since the silicon is regrown on the silicon substrate 1, if the cooling rate is too high, a portion of it will remain in the molten phase, resulting in a thickness that is thinner than that determined by the aforementioned control factors and is non-uniform. becomes. Further, even if the cooling rate is appropriately set, the regrown layer 3 will be non-uniform for the same reason if the silicon substrate is rapidly cooled at a temperature above the aluminum-silicon eutectic temperature and taken out from the diffusion tube. Therefore, the temperature reached by slow cooling should be 500'C or lower, which is lower than the silicon eutectic temperature, and the cooling rate should be 5°C per minute based on experimental facts for various thicknesses of the regrowth layer determined by the control factors mentioned above. By doing the following, non-uniformity in the thickness of the regrown layer can be reduced, and the desired aluminum diffusion layer 5 can be made uniform with good reproducibility. As described above, according to the present invention, it is possible to uniformly diffuse aluminum from the regrown layer with good workability and good reproducibility, which has great economic advantages.

[Brief explanation of the drawing]

FIGS. 1a to 1d are process diagrams for explaining one embodiment of the present invention. 1...Silicon substrate, 2...Aluminum vapor deposited film, 3...Silicon regrowth layer containing aluminum, 4...Aluminum●silicon eutectic alloy layer, 5...Aluminum diffusion layer.

Claims (1)

[Claims] 1 In the aluminum diffusion method, which involves alloying aluminum and silicon and diffusing aluminum from the aluminum-containing silicon regrowth layer formed during the cooling process into the silicon substrate, the cooling rate after the alloying reaction is kept within a range of 5 degrees Celsius per minute or less. An aluminum diffusion method characterized by cooling to 500°C or less to make the silicon regrowth layer uniform.