| 摘要 |
PURPOSE:To make a device fit for amplification of a high frequency such as VHF, by a method wherein a P type layer having impurities in a little higher density than those of a substrate is formed deeper than an N<-> layer of high voltage resistance, on the surface of a P<->Si substrate between a source and a drain, including some parts of first and second gates in a twin-gate type MISFET. CONSTITUTION:N<+> region 2 and 3 serving as a source and a drain respectively are formed on the surface of a low-density P<->Si substrate 1 by the high-density deposit and diffusion of P (phosphorus), for instance. Then, a mask 8 of a photoresist film is formed on the surface of the Si substrate on the drain side. This mask 8 is formed in a position including a part of a portion to serve as a second gate. Next, by the implantation of B ions, a P layer 6 having somewhat higher density than the substrate is formed sufficiently deep (e.g. 1mum) on the surface of the Si substrate whereon the mask 8 is not formed. Then, with an Mo gate and a thick oxide film used as masks, P ions are implanted in low density and in a self-alignment manner (N: 10<18> atoms/cm<3>, approx.), and thereby N<-> layers 5a-5c to serve as high voltage resistance layers are formed on the surface of the Si substrate in the regions between the source and a gate G1, between gates G1 and G2, and between G2 and the drain. |
