SPATIALLY-RESOLVED OPTICAL-EMISSION STUDY OF SPUTTERING IN REACTIVE PLASMAS

The study of material sputtering under low-pressure reactive ion etchi ng conditions in various gases (Cl-2, SiCl4, O-2) was performed using optical emission spectroscopy with high spatial resolution. Sputtering -induced secondary photon emission (atomic and molecular) from the pro cessed materials (Si, Al2O3, GaAs) was found to be strongly localized near the target surface. A spatial distribution of atomic line emissio n intensity was shown to be essentially nonmonotonical with distance f rom the surface. This effect was explained by a cascade feeding from t he upper lying atomic levels, which is enhanced in plasma (collisional ) environment. A simplified model accounting for the cascading has bee n developed, and velocities of sputtered excited atoms (in the range o f 2-7 x 10(6) cm/s) and molecules (about 2-5 x 10(5) cm/s) have been e valuated from the emission spatial decay parameters, The excited sputt ered atoms and molecules are produced in different types of collisions . Fast elicited atoms can be produced only in the first few collisions of the incident ion in the surface top layers, whereas excited molecu les are knocked off by secondary (slow) atoms originated from a collis ion cascade inside the solid. Based on this concept of the process, si mple expressions for atomic and molecular excitation yields as functio ns of the incident ion flux and surface coverage were deduced. The tec hnique can he used for in situ surface probing during plasma processin g. (C) 1998 American Vacuum Society.