HIGH-RESOLUTION DETERMINATION OF THE GE DEPTH PROFILE IN SIGE HETEROBIPOLAR TRANSISTOR STRUCTURES BY X-RAY-DIFFRACTOMETRY

X-ray double crystal diffractometry is used to measure the rocking cur ve (RC) of SiGe heterobipolar transistor structures using CuKalpha 400 reflection. The depth profile of the Ge concentration is determined b y simulation of RCs with a semi-kinematical theory and fitting the cal culated RCs to the experimental one. The problem of achievable accurac y in the determination of the main structural parameters, Si cap layer thickness, total SiGe laver thickness, plateau layer thickness, and t he maximum Ge content, is discussed in detail for three different samp les by analyzing sets of independent simulations with slightly modifie d starting conditions. Using only one fitting procedure, it is possibl e to determine the thickness of the Si cap layer and the total thickne ss of the SiGe layer with an error of less than +/- 0.5 nm. The accura cy of the plateau thickness and of the maximum Ge content depends on t he 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.