In-Situ Doped Emitter-Polysilicon for 0.5 μm Silicon Bipolar Technology

A reduced emitter doping concentration in deep submicron devices is often observed, if an implanted polysilicon is used as diffusion source for the emitter. The resulting enhanced base width leads to a decrease of the cut-off frequency in devices with narrow emitter widths. In addition, two-dimensional effects have to be taken into account for transistors with submicron dimensions. This work demonstrates how to avoid the cut-off frequency decrease for a 0.5 μm technology with an effective emitter width of 0.2 μm. This is realized by the combination of in-situ doped emitter-polysilicon (to avoid a reduced emitter junction depth in narrow devices) with an optimized spacer technique, which reduces the perimeter to area ratio of the active transistor region.