TETRAETHYLORTHOSILICATE REACTION-RATES ON SIO2 AT 1000 K - ZERO-ORDERDEPENDENCE ON HYDROXYL COVERAGE AND IMPLICATIONS FOR REACTIONS WITH 3-MEMBERED SILOXANE RINGS

We have determined key kinetic parameters for the reaction of tetraeth ylorthosilicate (TEOS) on SiO2. This was accomplished under conditions (20-500 mTorr at 1000 K) that pertain directly to TEOS-based chemical vapor deposition processes. TEOS reactions were carried out using deu terated silanols (SiOD) on the initial SiO2 surface. This allowed Four ier transform infrared spectroscopy measurements to distinguish the co nsumption of SiOD by TEOS from the concurrent formation of SIGH which results from TEOS decomposition at 1000 K. While SiOD consumption did exhibit a first-order dependence on SiOD coverage, TEOS decomposition exhibited a zero-order dependence on the total coverage of hydroxyl gr oups. This suggests that reactions with hydroxyl groups alone cannot a ccount for all of the TEOS decomposition reactions at 1000 K. Since th e low coverage of two-membered siloxane [(Si-O)(2)] rings was consumed during the initial TEOS exposure, siloxane (Si-O-Si) bridges in three -membered siloxane [(Si-O)(3)] rings may be the additional species res ponsible for the constant rate of TEOS decomposition. However, it is n ot conclusive that this type of site-specific mechanism controls the c hemistry. The data may also be explained with a site-independent mecha nism in which intramolecular decomposition of TEOS on the surface prov ides a common rate-determining step for subsequent consumption of hydr oxyls and siloxane bridges on SiO2. Regardless of the specific mechani sm, our results predict that deposition rates will be insensitive to t he relative coverages of siloxane bridges and hydroxyls on SiO2. There fore, a precise knowledge of the coverages of these species on SiO2 is not essential for modeling thermal TEOS decomposition rates. (C) 1996 American Vacuum Society.