US Patent 11551938 Alternating etch and passivation process

Tin oxide films are used as spacers and hardmasks in semiconductor device manufacturing. In one method, tin oxide layer (e.g., spacer footing) needs to be selectively etched in a presence of an exposed silicon-containing layer, such as SiOC, SiON, SiONC, amorphous silicon, SiC, or SiN. In order to reduce damage to the silicon-containing layer the process involves passivating the silicon-containing layer towards a tin oxide etch chemistry, etching the tin oxide, and repeating passivation and etch in an alternating fashion. For example, passivation and etch can be each performed between 2-50 times. In one implementation, passivation is performed by treating the substrate with an oxygen-containing reactant, activated in a plasma, and the tin oxide etching is performed by a chlorine-based chemistry, such as using a mixture of Cl