Bipolar high-power impulse magnetron sputtering

Magnetron sputtering is a thin-film deposition process based on the generation of a cold plasma at low pressure. This technology, already implemented on an industrial scale for several decades, has evolved over time to offer ever finer control over the physical and chemical properties of the deposited films. The most recent of these developments is HiPIMS (High-Power Impulse Magnetron Sputtering) technology in the bipolar regime, which has attracted a great deal of interest because it enables us to control the kinetic energy of the metal ions involved in the formation of the functional film.

In this type of pulsed discharge, a high-power negative voltage pulse is applied to the cathode (target), followed by a positive voltage pulse. As a result of applying a high-voltage negative pulse to the cathode, a large proportion of the sputtered material arrives on the substrate in the form of positive ions, whereas in a conventional DC discharge, the particle stream is essentially composed of neutral atoms. The advantage of this ionized deposition flow is that it can be controlled by electric and magnetic fields. Controlling the flow of charged particles reaching the surface of the growing film, in particular singly or multiply charged ions, is of paramount importance, as these affect film growth and properties.

Consequently, the power supplies used to generate a HiPIMS discharge have recently been modified to provide the cathode with a negative pulse followed by a positive voltage pulse whose value can be set typically from 0 to + 300 V. These pulses are synchronized, and adjustable in voltage and duration, providing new parameters for accelerating ions towards the substrate and further fine-tuning thin film properties (density, hardness, grain size, etc.). The applications of this new sputtering regime are numerous: substrate cleaning and functionalization, deposition of barrier layers, synthesis of hard coatings, modification of film optical properties, etc.

This breakthrough opens up new prospects for the growth of high value-added thin films. In this respect, this paper proposes: (i) introduce the electronic circuit topologies commonly used for high-power pulse generation in the HiPIMS (bipolar) regime; (ii) address the problem of arc management in a conventional HiPIMS process; (iii) shed light on the effect of the cathode's electromagnetic field on plasma properties in the bipolar HiPIMS regime; and (iv) analyze the properties, notably structural, of metallic titanium films deposited on electrically conductive substrates, as well as titanium dioxide films deposited on glass.