Characterization of Ge gradients in SiGe HBTs by AES depth profile simulation

We show that AES depth profiling extended by a simple profile simulation technique allows characterization of details in the Ge concentration gradients for SiGe hetero-bipolar transistors (HBTs). Using the mixing-roughness-information depth (MRI) model to simulate the experimental data allows us to reveal concentration steps with a precision of about ±2 at.% and small deviations from linear concentration gradients. The obtainable high lateral resolution of AES facilitates an application for process optimization and control in small microelectronic structures.