The sidewall profile of Si etched in BCl3/Cl2chemistry from a single‐wafer plasma reactor was found to depend on pressure, presence of resist, BCl3flow rate, and the addition of CHCl3. In a RIE type of single‐wafer plasma reactor, higher pressure and higher power density are used to achieve a higher etch rate. In this case features such as corner trenching, sidewall bowing, and tapering occur more frequently. The correlations between these features and the etch parameters are discussed with a particular emphasis on sidewall passivation effect.