The use of steam and fluid pressure to grow oxides on semiconductor wafers is well known and has been used extensively in the past. Typical temperatures of steam for this purpose are about 900.degree. to 1,000.degree. C., and fluid pressures are about 10 to 25 atmospheres. At these operating conditions, wafers in a batch can be processed at a moderate rate, such as less than 2 hours, an acceptable time period for profitable yield. Batch processing thus gives a high throughput while providing for acceptable process conditions.
Due to improved vertical holders or towers for semiconductor wafers, batch processing of wafers is being done in an expeditious manner. The reasons for this batch wafer trend includes greater control of the wafers in the tower, the relatively high cost of the wafers, and the relatively large size of the wafers. Moreover, with greater wafer control and when the wafers are in a batch, the possibility of wafer damage or breakage is minimized. Furthermore, the sizes of wafers are increasing. Typically, 6" wafers are now being used, and it is foreseeable that 8" and 12" wafers will be used in the future. Because of the problems associated with conventional techniques of batch processing, a need exists for improvements in the batch processing of semiconductor wafers so that such processing can be more economically feasible. The present invention satisfies this need.
Disclosures relating to the field of the present invention include U.S. Pat. Nos. 4,167,915, 4,268,538, 4,315,479 and 4,599,247. The method and apparatus to be described herein are improvements over the single wafer processing apparatus and method disclosed in U.S. patent application Ser. No. 311,686, filed Feb. 15, 1989.