Semiconductor device including a capacitance

摘要

It is an object to obtain a semiconductor device including a capacitance having a great Q-value. In an SOI substrate comprising a support substrate ( 165 ), a buried oxide film ( 166 ) and an SOI layer ( 171 ), an isolating oxide film 167 ( 167 a to 167 c) is selectively formed in an upper layer portion of the SOI layer ( 171 ) with a part of the SOI layer ( 171 ) remaining as a P^- well region ( 169 ). Consequently, an isolation (partial isolation) structure is obtained. An N⁺ diffusion region ( 168 ) is formed in the SOI layer ( 171 ) between the isolating oxide films ( 167 a) and ( 167 b) and a P⁺ diffusion region ( 170 ) is formed in the SOI layer ( 171 ) between the isolating oxide films ( 167 b) and ( 167 c). Consequently, there is obtained a junction type variable capacitance (C 23 ) having a PN junction surface of the P^- well region ( 169 ) provided under the isolating oxide film ( 167 b) and the N⁺ diffusion region ( 168 ).