High Resolution Determination of the Ge Depth Profile in SiGe Heterobipolar Transistor Structures by X-Ray Diffractometry

Abstract

X-ray double crystal diffractometry is used to measure the rocking curve (RC) of SiGe heterobipolar transistor structures using CuKα 400 reflection. The depth profile of the Ge concentration is determined by simulation of RCs with a semi-kinematical theory and fitting the calculated RCs to the experimental one. The problem of achievable accuracy in the determination of the main structural parameters, Si cap layer thickness, total SiGe layer thickness, plateau layer thickness, and the maximum Ge content, is discussed in detail for three different samples by analyzing sets of independent simulations with slightly modified starting conditions. Using only one fitting procedure, it is possible to determine the thickness of the Si cap layer and the total thickness of the SiGe layer with an error of less than ±0.5 nm. The accuracy of the plateau thickness and of the maximum Ge content depends on the total SiGe layer thickness. Errors for the plateau layer thickness of less than ±2 nm and for the maximum Ge content of less than 0.5% are possible.