| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem such that in the conventional devices variance in electric characteristic or decrease in yield occurs because the speed of thermal diffusion is too high to stabilize the device after the completion of thermal diffusion, even through impurities are introduced to a polysilicon layer to form a thinner emitter are through thermal diffusion, for the purpose of making a silicon bipolar transistor to operate at high frequency. SOLUTION: A polysilicon is divided into two layers, and an oxidized layer is provided therebetween, so that the thermal diffusion time of impurities is controlled and delayed by using the oxidized layer. Accordingly, a device can be operated in stable condition, so that a semiconductor device having uniform electric characteristics can be provided. In addition, the thermal diffusion time can be controlled by changing the thickness of the oxidized layer, thus contributing to the improvement in productivity.
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