Low Pressure Chemical Vapor Deposition of Borophosphosilicate Glass Films Produced by Injection of Miscible DADBS-TMB-TMP Liquid Sources

This study is a follow-up of earlier work in which the concept of injecting miscible liquid precursors into an LPCVD reactor was implemented for the preparation of BPSG films from a mixture of tetraethylorthosilicate (TEOS), trimethylborate (TMB), and trimethylphosphite (TMP). The depletion effects encountered in the use of TMP are circumvented here by the substitution of diacetoxyditertiarybutoxysilane (DADBS) for TEOS. The choice of this less thermally stable SiO₂ precursor allows for a decrease in deposition temperature from approximately 700° down to 500°C. In this lower temperature regime, BPSG deposits are shown to be uniform in terms of both thickness and composition across a wide isothermal zone. Variations in the proportion of the liquid phase indicate that a solution consisting by volume of 44.3% DADBS, 48.2% TMB, and 7.5% TMP yield BPSG films close to the desired composition (i.e., 4 w/o B and 4 w/o P). Typical BPSG films produced by this process are shown to exhibit good compositional uniformity, perfectly conformal step coverage, and desirable flow profiles at temperatures and phosphorus concentrations significantly lower than previously achieved with phosphosilicate glass films.