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以浓掺杂的多晶硅做为扩散源用在薄基区晶体管的砷扩散和磷扩散的一种新工艺已经发展起来。它包含用化学气相淀积方法淀积掺杂的多晶硅(掺杂的多晶硅以下称为DOPOS)和在氧化环境中的扩散过程。扩散过程中,在DOPOS表面上形成硅氧化膜,它阻止了杂质的外扩散并导致了杂质在DOPOS层中的凝聚。这样一来,通过1000℃的扩散可以在硅衬底中引起大约2×10~(20)原子/厘米~3的高表面浓度。背面散射分析表明在DOPOS和硅衬底的接触面上没有杂质积累;也就是说没观察到堆积现象。DOPOS工艺在重复性和器件大量生产方面是优越的,尤其作为砷发射极扩散方法更有效。由于在扩散过程以后在发射区上面保留了DOPOS,因此成功地防止了铝电极引起的发射极-基极短路。在单个晶体管情况下(As—DOPOS),f_T达5千兆赫;对电流型逻辑门电路的单片集成电路(P—DOPOS),t_(oa)在35毫瓦/门电路时达0.6毫微秒。
A new process for the diffusion of arsenic and phosphorus into thin base-region transistors using heavily-doped polysilicon as a diffusion source has been developed. It involves the deposition of doped polysilicon (doped polysilicon, hereafter DOPOS) by chemical vapor deposition and the diffusion process in an oxidizing environment. During diffusion, a silicon oxide film is formed on the surface of the DOPOS, which prevents the out-diffusion of impurities and leads to the agglomeration of impurities in the DOPOS layer. As a result, a high surface concentration of about 2 × 10 20 atoms / cm 3 can be induced in the silicon substrate by diffusion at 1000 ° C. Backscattering analysis showed no impurity buildup at the interface between the DOPOS and the silicon substrate; that is, no build-up was observed. The DOPOS process is superior in repeatability and device mass production, especially as arsenic emitter diffusion method. Due to the DOPOS remaining above the emitter after the diffusion process, the emitter-base short circuit caused by the aluminum electrode was successfully prevented. In the case of a single transistor (As-DOPOS), f_T reaches 5 Gigahertz; for a current-mode logic gate monolithic integrated circuit (P-DOPOS), t oa reaches 0.6 nanoseconds at 35 milliwatts / gate second.