| 摘要 |
PURPOSE:To prevent the occurrence of punch-through in an epitaxial layer by a method wherein a PNP transistor is provided in the n type epitaxial layer of a semiconductor substrate. CONSTITUTION:An n type Si epitaxial layer 4 is formed in a p type Si substrate 1. In the epitaxial layer 4, n type regions 26, 27 having higher impurity concentrations than this layer 4 are formed, and lateral PNP transistor 22 and a vertical PNP transistor 20 are formed in these regions 26, 27, respectively. This construction can reduce the spread of a depletion layer in the collector-base junction to the base side by a factor of higher impurity concentration. Thereby, even in the case of thinning the Si epitaxial layer 4 to an extremity of e.g. 2mum, the collector-emitter withstand voltages VCEO of the lateral PNP transistor 22 and the vertical PNP transistor 20 can be much increased. Accordingly, very high operating frequency fT can be obtained without the occurrence of punch-through.
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