Abstract: In described embodiments, methods for selective etching (thermal etching) of metals, especially molybdenum- and tungsten-containing materials, and titanium nitride, using thionyl chloride (SOCl2) as an etching gas at low temperatures and low pressure without a need of plasma, for device manufacturing processes and for process chamber cleanings are disclosed. Methods for cleaning reaction product deposits from interior surface of a reactor chamber or from a substrate within said reaction chamber using thionyl chloride (SOCl2) at low temperatures and low pressure without a need of plasma are also disclosed. An additional co-reactant such as hydrogen may be used in combination with thionyl chloride. The processes are carried out in temperature ranging from approximately 150° C. to approximately 600° C., pressure under<100 Torr without the need of a plasma-activation.