OBSERVATION OF INVERSE REACTIVE ION ETCHING LAG FOR SILICON DIOXIDE ETCHING IN INDUCTIVELY-COUPLED PLASMAS

The slowdown of the oxide etch rate with width of submicrometer struct ures is known as reactive ion etching (RIE) lag and has been explained by ion shadowing and differential charging of the sidewalls, among ot her effects [R. A. Gottscho and co-workers, J. Vac. Sci, Technol, B 10 , 2133 (1992)]. Here we show for an inductively coupled high density p lasma reactor working in the pressure regime from 6 to 20 mTorr that i nverse RTE lag is primarily observed, i,e., the etch rates increase as the width of the microstructures decrease. Inverse RIE lag, which was first discussed by Vitkavage et al. [Tegal Plasma Proceedings Symposi um, San Francisco, 1991 (unpublished)], may be explained by considerin g the neutral flux distribution at the structure bottom. The neutral f lux has a stronger dependence on the aspect ratio than the ion flux du e to its isotropic velocity distribution, The neutral flux distributio n has been modeled and is consistent with etching profiles observed at high pressure. (C) 1996 American Istitute of Physics.