IN-SITU FAST ELLIPSOMETRIC ANALYSIS OF REPETITIVE SURFACE PHENOMENA

We present an ellipsometric technique and ellipsometric analysis of re petitive phenomena, based on the experimental arrangement of conventio nal phase modulated ellipsometers (PME) conceived to study fast surfac e phenomena in repetitive processes such as periodic and triggered exp eriments. Phase modulated ellipsometry is a highly sensitive surface c haracterization technique that is widely used in the real-time study o f several processes such as thin film deposition and etching. However, fast transient phenomena cannot be analyzed with this technique. beca use precision requirements limit the data acquisition rate to about 25 Hz. The presented new ellipsometric method allows the study of fast t ransient phenomena in repetitive processes with a time resolution that is mainly limited by the data acquisition system. As an example, we a pply this new method to the study of surface changes during plasma enh anced chemical vapor deposition of amorphous silicon in a modulated ra dio frequency discharge of SiH4. This study has revealed the evolution of the optical parameters of the film on the millisecond scale during the plasma on and off periods. The presented ellipsometric method ext ends the capabilities of PME arrangements and permits the analysis of fast surface phenomena that conventional PME cannot achieve. (C) 1997 American Institute of Physics.