Power conversion and control for pulsed magnetron reactive sputtering

Abstract

The application of reactive sputtering is pervasive in the field of thin film coatings. This dissertation addresses process dynamics during and after arc response shutdown, dual magnetron reactive co-sputtering process control requirements, and pulsed pow er supply requirements for high pow er pulsed magnetron sputtering (HPPM S). In reactive sputtering processes, the flux of target atoms to chamber surfaces is shut off when the power supply output turns off for arc handling. This causes the partial pressure of the reactive gas to rise. It is necessary to respond quickly to an arc in order to keep gas pressure within an acceptable range. The partial pressure variation, target and chamber surface coverage fractions, and deposition rate when process pow er is reestablished, may be estimated with a simple dynamical process simulation model. This can provide guidance for arc detection and response time scale requirements for transition mode operation. A representative large area reactive coating process is simulated to explore arc response time guidelines. Pulsed current source supplies can independently regulate pow er delivered to each magnetron in a dual magnetron sputtering arrangement. This enables reactive co-sputtering of optical films when one target material is different than the other. Modeling shows that reactive gas partial pressure must be regulated, in addition to independent regulation of power to each target, in order to gain control over film composition. This is confirmed by experiment. Optical films having a customized index of refraction were deposited by dual magnetron reactive co-sputtering, with independent regulation of the pow er delivered to each target. Reactive gas partial pressure was regulated by using a mass spectrometer as the partial pressure sensor. HPPM S has created growing interest because of its ability to generate dense plasma with high target material ion content, using essentially conventional magnetron sputtering equipment. However, HPPM S is also capable of delivering large energies to unavoidable process arcs. Unless properly handled, arcs can generate macro-particles and target damage, limiting the usefulness of the technique. However, coatings quite suitable for industrial applications may be applied if the pulsed supply incorporates arc handling. A novel arc handling topology with energy recycling is proposed. Simulation and experiments with representative hardware both confirm operation of the topology. An experimental power supply incorporating this arc handling topology, capable of peak powers up to 3 megawatts and peak currents to 3000 A, at discharge voltages reaching 2 kV, has been designed and constructed. This new power supply technology enables the practical application of a whole new range of sputtering processes. These processes can exploit the flux of ionized target material from essentially conventional magnetron sputtering equipment to deposit dense equi-axed films. The HPPM S power supply performance was experimentally verified by driving large and small magnetron loads. Temporal current and voltage waveforms are shown for normal and arcing operation. In addition, this power supply has been used in collaborative efforts to enable HPPM S deposition of high density (2.7 g/cm3) thin (<200 Å) carbon films and HPPM S reactive sputtering deposition of dielectric films on dielectric substrates.