High depth resolution Secondary Ion Mass Spectrometry (SIMS) analysis of Si[sub 1−x]Ge[sub x]:C HBT structures

Abstract

Low energy Secondary Ion Mass Spectrometry (SIMS) was employed to study graded-base Si1−xGex:C heterostructure bipolar transistors (HBTs) structural properties. Using an O2+ beam at 500 eV with normal incident angle, Ge profiles can be quantified by minimizing the influence of matrix effect. This is achieved with a correction based on the linearity of the ratio (IGe/ISi) with respect to the ratio (x/1−x). The SIMS results showed an excellent correlation with the graded Auger Ge profile in 5–20% range. Moreover, SIMS analysis revealed an enhanced Ge diffusion with the carbon incorporation, which was used to suppress base boron diffusion during the rapid thermal annealing (RTA) process. Based on the SIMS Ge profile, device simulation can be used to design Ge profile shape in order to optimize process throughput without impact on the device performance. The high depth resolution SIMS data is essential for Si1−xGex:C HBTs structural characterization and process optimization.