Self-limiting growth

A method comprising:

• providing a substrate including a structure;
• exposing the substrate to a mixture of a silicon-containing gas and a boron-containing gas at a first substrate temperature of no more than 400° C. to form a conformal reducing agent layer on the structure;
• raising the temperature of the substrate to a second substrate temperature of at least 500° C.;
• and
• at the second substrate temperature, exposing the conformal reducing agent layer to a tungsten-containing or molybdenum-containing precursor to convert the reducing agent layer to tungsten or molybdenum.

A method comprising:

• providing a substrate including a structure;
• exposing the substrate to a mixture of a silicon-containing gas and a boron-containing gas to form a conformal reducing agent layer on the structure;
• and
• exposing the conformal reducing agent layer to a molybdenum-containing precursor to convert the reducing agent layer to molybdenum.