Physicochemical properties in tungsten films deposited by radio‐frequency magnetron sputtering

Abstract

The microstructure, reflectivity, resistivity, and oxygen contamination of thin tungsten films (<250 nm) deposited by rf magnetron sputtering on silicon substrates are reported. Three structural stages, depending on the operating conditions, are found to occur during the deposition: (i) In the range of the rf applied power density studied (<6 W cm−2), an amorphous structure is always observed when the film thickness does not exceed ∼80 nm. The resistivity remains at a fairly high level (≂1.3 μΩ m). (ii) Upon further deposition and if the power density is <0.6 W cm−2, the β‐W phase is detected. (iii) A thermally activated transformation of the β‐W phase into pure α–W occurs for a critical temperature ∼150 °C during depositions carried out at higher powers(≥1 W cm−2). The resulting β‐W or α‐W films consist of small grains (5–20 nm) which present a low dislocation density. Resistivity and reflectivity are mainly related to the oxygen content of the films. When the rf deposition power density is low (≤0.6 W c...