New type of plasma reactor for thin film deposition: magnetron plasma process assisted by microwaves to ionise sputtered vapour

A new type of plasma reactor for thin film deposition has been designed: a magnetron-sputtering device assisted by microwave applicators to ionise the sputtered vapour of the magnetron. Ionizing the vapour has several advantages: improvement of the film quality, deposition on substrates with complex shapes, enhancement and control of the reactivity. The reactor consists of a planar rectangular magnetron cathode (22 cm×9 cm) and of two coaxial-type microwave applicators located perpendicularly to the substrate–magnetron axis, on both sides of the sputtered vapour flow. This reactor can operate on a wide pressure range: from 0.2 to 60 Pa. Several in-situ diagnostics have been performed to characterise the process in argon gas with chromium and titanium targets. Electron density of the order of 1011–1012 cm−3 and electron temperature of 1.5–2 eV were measured in the microwave plasma by a cylindrical Langmuir probe; emission of metallic ions (Cr+, Ti+) was clearly identified when the microwave plasma is turned on; concentration of Cr or Ti atoms was measured by absorption spectroscopy, a decrease of this concentration is observed when the microwave power is increased. Characterisation of thin titanium films was performed ex-situ by Rutherford backscattering spectroscopy (RBS) for Ti content and nuclear reaction analysis (NRA) for oxygen contamination. Film density was deduced from RBS and NRA measurements and X-ray reflectometry. Oxygen contamination in the film is clearly decreased when microwave plasma is turned on and with a bias applied to the substrate.