THICKNESS DETERMINATION OF UNIFORM OVERLAYERS ON ROUGH SUBSTRATES BY ANGLE-DEPENDENT XPS

Angle-dependent XPS thickness determinations of thin overlayers are of ten based on a simple model assuming a perfectly flat substrate. In th is paper we analyze the errors involved in applying this method to uni form overlayers on rough substrates. The analysis is based on an algor ithm for simulation of fractional Brownian motion to model substrate r oughness and on a Monte Carlo method for electron trajectory simulatio n. Calculations for a SiO2/Si and Au/Si system show that the errors st rongly depend on off-axis angle, ranging from -50% to +50% and more. A t similar to 35 degrees, however, the error is remarkably small, and e ven negligible compared to errors caused by neglecting elastic scatter ing. Atomic Force Microscopy and XPS measurements on a roughened silic on wafer confirm these findings.