Showing papers by "Bernd Tillack published in 1995"

Successful Preparation of High Frequency HBT by Integrated RTCVD Processes

Abstract: Complete epitaxial Si-SiGe-Si- stacks with a defined doping profile for each component have been deposited on Si substrates from the system SiH4, GeH4, H2, B2H6, PH3 by RTCVD. The deposition has been carried out at a temperature of 650°C for Si and of 500°C for SiGe, respectively, both at a pressure of 2 mbar. The developed epitaxial process including an effective H2 in-situ preclean annealing has been integrated in a simple double mesa technology for the preparation of SiGe base heterojunction bipolar transistors (HBT). Despite the simplicity of the technology and the lithographical level allowing emitter dimensions of 2.3×2.5 μm2 only, test devices on 4” wafers reached transit frequencies fT and maximum oscillation frequencies fmax of higher than 60 GHz and 30 GHz, respectively. Besides, a low base current has been measýnl as proof for a good layer quality.

Thermal Generation in Depleted Si/SiGe/Si-Structures, Grown by MBE, APCVD and RTCVD and their Correlation to the Base Currents of Double Mesa HBT's with Corresponding Blanket Epitaxial Layers

Abstract: The base currents of double mesa SiGe-HBT's at V BE =0.75 V as well as the thermal generation currents of deeply depleted MOS-structures, both grown with identical Ge-profiles, have been measured. The epilayers were deposited by MBE, RTCVD, and APCVD to compare the influence of these epitaxial techniques on the electrical parameters of the prepared HBT's. As a preliminary result, the base currents of MBE-HBT's and the generation currents measured at corresponding MOS-structures are found to be significantly higher compared to CVD grown structures. The very simple preparation of MOS-structures favours the used double sweep I(V)-technique for generation current determination as a useful method for optimizing the epitaxial process for HBT-preparations within rapid iteration cycles. First results of such optimizations are reported.