Atomic layer etching of molybdenum

A method of etching a molybdenum layer on a semiconductor substrate, the method comprising:

• pre-coating a process chamber for housing a semiconductor substrate with silicon tetrachloride;
• and
• performing a single etch cycle to controllably remove between about 8 Å to about 15 Å of the molybdenum layer, the single etch cycle comprising:
• (a) exposing the semiconductor substrate to an oxygen-containing reactant to oxidize at least a portion of the molybdenum layer to molybdenum oxide,
• (b) after the molybdenum oxide has formed, exposing the semiconductor substrate to boron trichloride to convert the molybdenum oxide to volatile molybdenum oxychloride while forming boron oxide on the semiconductor substrate, and
• (c) exposing the semiconductor substrate to a fluorine-containing reactant to remove the boron oxide from the semiconductor substrate,
• wherein steps (a)-(c) are performed in an absence of plasma and at a temperature ranging from about 400° C. to about 600° C.