Influence of Pressure and Power on the Composition and Time Evolution of Plasmas in High Power Impulse Magnetron Sputtering

摘要

High power impulse magnetron sputtering (HIPIMS) is a novel physical vapor deposition technique whereby magnetron sputtering is carried out with extreme pulsed power densities in the range of 3000 Wcm~(-2). HIPIMS achieves high ionization fraction of the sputtered metal flux and has been successfully applied for materials synthesis. In this work, spatial and time-resolved electrostatic probe measurements have been used to study the development of the discharge. Results showed that the spatial distribution of plasma is highly homogeneous at distances of 10 cm and greater. Extremely high peak ion saturation current densities (Js) of 20 mAcm~(-2) were found at the position of the substrates some 20 cm from the target. Time-resolved measurements of Js showed that at gas pressures of 0.7 mTorr the main plasma drifts away from the cathode in ensemble at a high rate of > 20 km/s. In contrast, at high pressures of 10 mTorr, the plasma drift occurs in three subsequent groups with an average velocity of approximately 2 km/s. HIPIMS of Cr in Ar atmosphere at a pressure of 3 mTorr was carried out for power densities ranging from 0.5 to 3 kWcm~(-2). Optical emission spectroscopy studies of the plasma composition showed that the intensity of Cr(1+) and Cr(2+) had a similar increasing slope of 2 as a function of power. At the same time, Cr neutrals exhibited a slope of 0.5 and Ar neutrals 0.75. These dependencies are different from those predicted by published models for conventional sputtering. An alternative mechanism of species formation is discussed.