Growth monitoring of GaInP/GaAs heterojunction bipolar transistors by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) was applied as in situ probe during the growth of GaInP/GaAs heterojunction bipolar transistors (HBT) under production conditions, i.e. wafer rotation. The amplitude of the oscillating signal (RAS transients taken at a fixed photon energy) gives the same information on surface anisotropy as obtained on static wafers. In these transients each layer of the HBT structure is represented by a specific signal amplitude. P-GaAs (3 x 10(19) cm(-3)) and n-GaAs layers with different doping levels (10(16)-10(18) cm(-3)) are distinguished. GaInP etch-stop and emitter layers cause pronounced interference structures that allow for the assessment of the emitter thickness on the nanometer scale. Due to its self-normalizing signal, RAS measurements are reproducible and largely not disturbed by wafer wobble, making this technique compatible with production requirements. (C) 1998 Elsevier Science B.V. All rights reserved.