As semiconductor device manufacturing methods, there are various processing methods such as oxidizing processing for oxidizing a silicon surface at a high temperature to obtain an oxide film (an insulating film) on the silicon surface, and diffusing processing for heating a silicon layer formed with an impurity layer on the surface thereof to thermally diffuse the impurities in the silicon layer.
As the heat treatment apparatus used for oxidizing and diffusion processing, a vertical heat treatment apparatus of the batch type is well known in the art. In this heat treatment apparatus, however, in the case where an extremely thin film or a shallow position matching is required as when a capacitor insulating film or a gate oxide film is formed or when the diffusion processing is required for impurity ions, for instance, the film quality, the film thickness, and the diffusion depth are all subjected to serious influence by the thermal budget (thermal history). In the batch type heat treatment apparatus, in particular, there exists a large difference in thermal history between the wafers first carried into a reaction pipe and the wafers carried last into the reaction pipe.
To overcome this problem, a single wafer type heat treatment apparatus has been so far studied, by improving a heat treating furnace of the above-mentioned heat treatment apparatus. In this apparatus, after a wafer has been mounted on a wafer holder member one by one and then carried to a predetermined position in a reaction pipe, the carried wafer is heated quickly. This single wafer type heat treatment apparatus will be explained hereinbelow with reference to FIG. 18. In the drawing, a heat treating region of a vertical reaction pipe 1 is enclosed by a heat insulating body 10. In this reaction pipe, a supply pipe 11 and an exhaust pipe 12 are provided so that a processing gas can flow from the upper portion to the lower portion thereof.
In the reaction pipe 1, in order to secure the throughput, a wafer holder member 13 is disposed so as to be movable up and down at a speed of about 150 to 200 mm/sec, for instance. On the wafer holder member 13, a single wafer W is mounted by use of a wafer carrying member (not shown) disposed in a shift and mount chamber 14 disposed under the reaction pipe 1. Therefore, after having been moved upward to a predetermined position, the wafer W is heated to a predetermined heat treatment temperature by a heating section 15 composed of a resistance heater 15a and a heat uniformalizing body 15b, and further oxidized under atmospheric pressure, for instance by supplying a processing gas into the reaction pipe 1 through the processing gas supply pipe 11.
Further, a shutter 16 which functions as a light shutting valve is movably disposed between the reaction pipe 1 and the shift and mount chamber 14 on the outer circumferential side of the shift and mount chamber 14, in order to cool the processed wafer W and to reduce the influence of the thermal history of the wafer W carried into the shift and mount chamber 14. This is because the thermal history is caused by the direct radiant heat radiated from the heating section 15. Further, the shutter 16 is formed with two semicircular cutout portions 16a and 16b at each end thereof. These cutout portions 16a and 16b are brought into tight contact with an outer circumference of a lift shaft 17 of the wafer holder member 13 when closed. Further, a purge gas supply pipe (not shown) is disposed to purge a region communicating with a lower side (lower than the exhaust pipe 12) in the reaction pipe 1 by use of a purge gas (e.g., inert gas).
In the prior art heat treatment apparatus as described above, however, when the wafer W is moved upward to a predetermined position from the shift and mount chamber 14 by use of the wafer holder member 13, the wafer W is moved upward in the reaction pipe 1 at a high speed of about 150 to 200 mm/sec against the flow of the processing gas. Therefore, when the surface area of the wafer W is large, a large resistance (wind pressure) is applied to the wafer W moving upward, so that a negative pressure is generated at the rearward (reverse surface side) region just under the wafer W. As a result, a difference in pressure is generated between the right surface side and the reverse surface side of the wafer.
Therefore, the gas stream is disturbed in the reaction pipe 1, and thereby the supply of the processing gas onto the wafer surface is not uniform. As a result, the uniformity of the intra-surface thickness of the film formed on the wafer W is degraded. For instance, when a target intra-surface uniformity of the film thickness is 50.+-.0.5 angstrom, the difference in intra-surface thickness is as large as 50 .+-. several angstrom (e.g., 5 angstrom). Here, the above-mentioned single wafer type heat treatment apparatus has been developed in order to form an extremely thin film at a high precision so as to cope with the microminiaturization technique for the semiconductor device. Therefore, the above-mentioned problem causes a serious problem in the heat treatment apparatus from the performance standpoint.
Further, in the case where a negative pressure is generated in the region backward (the reverse side) of the wafer W as described above, when the wafer W is passed in front of the exhaust port, since the gas flows backward from the exhaust pipe 12 to the reaction pipe 1, there exists another problem in that substances adhered onto the inner wall of the exhaust pipe 12 or particles collected by a particle removing device disposed in the exhaust pipe 12 flow in the backward direction into the reaction pipe 1, with the result that the reaction pipe 1 is contaminated.
With these problems in mind, therefore, it is the object of the present invention to provide a heat treatment method and apparatus, which can suppress the pressure fluctuations in the reaction pipe, when a processed body (e.g., substrate) is moved upward or downward, in order to obtain a processed body (substrate) with a high intra-surface uniformity of film thickness.