Tin oxide films are used as mandrels in semiconductor device manufacturing. In one implementation the process starts by providing a substrate having a plurality of protruding tin oxide features (mandrels) residing on an exposed etch stop layer. Next, a conformal layer of spacer material is formed both on the horizontal surfaces and on the sidewalls of the mandrels. The spacer material is then removed from the horizontal surfaces exposing the tin oxide material of the mandrels, without fully removing the spacer material residing at the sidewalls of the mandrel (e.g., leaving at least 50%, such as at least 90% of initial height at the sidewall). Next, mandrels are selectively removed (e.g., using hydrogen-based etch chemistry), while leaving the spacer material that resided at the sidewalls of the mandrels. The resulting spacers can be used for patterning the etch stop layer and underlying layers.