Sulfur-containing molecules for high aspect ratio plasma etching processes

An etching method for forming a structure by selectively etching one or more silicon-containing films in a substrate using a patterned mask layer deposited on top of the one or more silicon-containing films, the method comprising:

• mounting the substrate in a reaction chamber;
• introducing an etching gas containing a sulfur-containing gas into the reaction chamber;
• converting the etching gas to a plasma;
• and
• allowing an etching reaction to proceed between the plasma and the one or more silicon-containing films so that the one or more silicon-containing films are selectively etched versus the patterned mask layer to form the structure,
• wherein the sulfur-containing gas contains a —SH thiol group and an aromatic 6 membered carbon ring having the formula
• wherein R1, R2, R3, R4 and R5 are independently selected from F, H, and/or CxFyHz group substituted on the aromatic ring, where x, y and z are integers, at least one of the R1, R2, R3, R4 and R5 contains at least one fluorine atom, and S represents the —SH thiol group.