Role of HCl in CVD reaction mechanisms involving chloridic precursors: the deposition kinetics of SiC from MTS

摘要

The deposition rates of carbides, nitrides and oxides formed from chloridic precursors by CVD are often considerably slowed down by HCl either produced in the process or added to the feed gas. In detail, the deposition rate of β-SiC from methyltrichlorosilane (MTS) as a function of MTS, H_2 and HCl partial pressures was experimentally determined. From the respective reaction orders found, a reaction model for the SiC deposition could be derived consisting of 4 consecutive reaction steps, Step 1: CH_3SiCl_3 → CH_2SiCl_2 + HCl Step 2: CH_2SiCl_2 + H_2 → CH_2SiHCl + HCl Step 3: CH_2SiHCl + H_2 → CH_2SiH_2 + HCl Step 4: CH_2SiH_2 → … → SiC + 2H_2 of which the second step is rate-determining in a temperature range up to 900 °C, and the fourth step above 900 °C. The respective rate equations have been determined and experimentally confirmed to be j_(SiC)(I) = k_I [MTS] [H_2] [HCl]~(-1) (range I ≤ 900 °C) j_(SiC)(II) = k_(II) [MTS] [H_2]~2 [HCl]~(-3) (range II > 900 °C)