| 摘要 |
PURPOSE:To improve a BiCMOS type semiconductor integrated circuit in high frequency characteristics by a method wherein a thick isolating oxide film is formed in a bipolar transistor, and a transistor conventional isolating oxide film is formed in a PMOS or an NMOS transistor taking advantage of the selective oxidation process of a polysilicon layer. CONSTITUTION:A semiconductor substrate 21 where a bipolar transistor element isolating region is provided is removed as thick as required, a bipolar transistor element isolating thick oxide film 28 is formed through a selective oxidation, the element isolating region of a PMOS and an NMOS transistor is selectively oxidized at the same time when a polysilicon layer 30 deposited on a bipolar transistor forming region is selectively oxidized to form an element isolating oxide film 36 used for the element isolation of a PMOS and an NMOS transistor. By this setup, the optimal isolating oxide film can be formed corresponding to the types of transistors, so that a diffusion layer can be prevented from increasing in depth due to the increase of processes and the frequency of thermal treatments.
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