| 摘要 |
PURPOSE: A high-density ROM is provided to increase the capacity of memory as much as three times in comparison with the capacity of conventional memory by using post transistors shared by three ROM cells. CONSTITUTION: A p type wafer is doped by As ions to form a n+ type semiconductor layer 11 which is served as a source(11). A CVD process or an implanting process is employed to epitaxially fabricate a p type semiconductor layer(12) having a thickness of about 0.5 to 2 micrometers on the n+ type semiconductor layer. After boron ions have been doped in the epitaxial process, the doping density near n+ type semiconductor layer is higher than the doping density of other areas. The doping density is decreased as the epitaxial thickness reached about 0.2 to 0.4 micrometers. P+ type and p- type semiconductor layers are formed on the n+ type semiconductor layer. The p+ type and the p- type semiconductor layers are formed as a substrate(121) and a channel(122) of a ROM cell, respectively.
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