HIGH-SPEED, HIGH-ACCURACY OPTICAL MEASUREMENTS OF POLYCRYSTALLINE SILICON FOR PROCESS-CONTROL

Highly accurate non-contact polycrystalline silicon (poly-Si) film thi ckness measurements are important for both real-time feedback control and run-to-run control. Both spectroscopic ellipsometry (SE) and norma l-incidence spectral reflectometry (SR) are complicated by poly-Si sur face effects and variable bulk poly-Si refractive indices. In this art icle we will describe an empirical modification of Beckmann/Kirchhoff scattering theory to account for the effects of rough layers in SR. We will present results from in situ monitoring of reactive ion etching of poly-Si/SiO2/Si and ex situ comparisons to TEM and AFM. Preliminary conclusions on the applications of this model to SE analysis of poly- Si will also be presented. (C) 1998 Elsevier Science S.A.