Dopant Control and Diffusion at the Si/Si1-xGex Interface for High-Speed Heterojunction Bipolar Transistors

Optimum high-frequency performance of Si/Si1-xGex heterojunction bipolar transistors can be obtained only with precise control of doping profiles within the heterostructure. With low-temperature chemical vapor deposition and advanced SIMS depth profiling techniques, we demonstrate the capability to place and measure hyperabrupt boron junctions relative to the Si/Si1-xGex heterointerface with an accuracy of 20 Angstroms. Capacitance-voltage measurements as a function of junction displacement from the heterojunction are also presented. Measurements of boron diffusivity in Si1-xGex strained layers are combined with data on boron segregation in the Si/Si1-xGex system to accurately model dopant motion across the heterointerface.