Microstructure, growth, resistivity, and stresses in thin tungsten films deposited by rf sputtering

The growth process and the microstructure of very thin W films (80–500 A) deposited by rf sputtering on SiO2 and Si substrates have been observed by transmission electron microscopy (TEM). The resistivity and stress in these films have been related to the film microstructure, composition, and to the deposition conditions (substrate bias and rf deposition power). Thin W films deposited on silicon dioxide substrates under zero or positive bias have been found to grow in two distinct growth stages. Stage I corresponds to the formation of a thin continuous film (80–100 A thick) of β‐W. The β‐W phase has the A‐15 crystal structure and has been identified as a faulted W3W compound. A small grain size (50–100 A) is characteristic of the β‐W film. Stage II corresponds to the transformation of the β‐W film into a pure α‐W film with the bcc crystal structure. This thermally activated phase transformation takes place in the temperature range 100–200 °C. It is characterized by the growth of α‐W nuclei until complete ...