Characterization of Si1−xGex∕Si layers and depth profile of their heterobipolar transistor structures by high-resolution x-ray diffractometry and computer simulations

Abstract

Using high-resolution x-ray diffractometry (HRXRD) and computer simulations, germanium content x, thickness T of pseudomorphic Si1−xGex layers, and Ge depth profile in their advanced heterobipolar transistor (HBT) structures grown on (001)Si substrates have been determined. High-resolution rocking curves (RCs) with well-resolved intensity oscillations have been recorded by using a double-crystal x-ray diffractometer in (+,−) geometry with CuKα1 radiation from a 12-kW rotating anode x-ray generator. The experimental RCs were simulated with the in-house developed computer program based on the semikinematical theory. In addition to the Ge depth profile, the thickness of SiGe layer, Si cap layer, and SiGe plateau layers of the HBT structures have been determined for the best fit of the experimental RCs with the theoretically simulated RCs. Due to the decay of intensity oscillations, in the case of partially relaxed layers, the values of germanium content x and relaxation R were calculated from the perpendicular and parallel (in-plane) lattice constants a⊥ and a‖ obtained by recording a pair of RCs from symmetric and asymmetric lattice planes. The simulation method using HRXRD has been described with the help of typical results obtained from samples of different structures. In this method the maximum error values of x and T are, respectively, ±0.5% and 1%. The error in the value of R is ±2% for partially relaxed samples. In the case of HBT structures, the maximum error in the value of thickness of SiGe and cap layers is ±1% and that of plateau layer is ±5%. The method is very convenient, faster, accurate, and nondestructive in comparison with other methods such as transmission electron microscopy and Secondary-ion-mass spectroscopy.