The reduction of base dopant outdiffusion in SiGe heterojunction bipolar transistors by carbon doping

In SiGe heterojunction bipolar transistors (HBTs) the outdiffusion of the b ase dopant out of the SiGe region into emitter or collector strongly degrad es device performance. This letter describes an extremely sensitive method to quantitatively determine the amount of this diffusion by electrical char acterization of fabricated HBTs. The method was used to investigate the red uction of boron diffusion by carbon doping as a function of carbon concentr ation and position within the base. It was found that carbon is only effect ive when it is placed within the doped base region. At a carbon level of 2x 10(19) cm(-3) the allowable anneal time may be increased by a factor of 3. (C) 1999 American Institute of Physics. [S0003-6951(99)03235-0].