Shallow Doping Profiles for High-Speed Bipolar Transistors

Within the framework of a double polysilicon self-aligned bipolar technology shallow base widths WB for npn transistors were obtained by low-energy implantation of boron into either crystalline Si (WE = 150 nm), preamorphized Si (WE = 125 nm) or by diffusing boron out of polysilicon (WE = 85 nm). Rapid thermal processing was used for the emitter drive-in. A transit frequency of 22 GHz was achieved for WE = 85 nm. Comparison with one-dimensional calculations indicates the potential of further enhancement of intrinsic device speed by optimization of the proposed technological approaches.