Electron-enhanced high power impulse magnetron sputtering with a multilevel high power supply: Application to Ar/Cr plasma discharge

A high-power impulse magnetron sputtering (HiPIMS) power supply, called e-HiPIMS, has been developed and used to deposit chromium thin films within an argon discharge. This power supply comprises three stages; each can deliver a voltage pulse up to 300 V. The advantage of this power supply is the possibility of tailoring a pulse waveform on the cathode with several voltage levels. This e-HiPIMS can operate in the standard HiPIMS mode (s-HiPIMS) and multipulse HiPIMS mode. Each voltage sequence is independently managed regarding the width, delay, and voltage level. They can all be synchronized, giving the s-HiPIMS, or shifted in time and added to each other. Hence, the idea is to favor a specific ion population compared to others, according to the process needs and the targeted application. A beneficial example used a three-pulse sequence with different voltage levels. The influence of the temporal behavior on the plasma parameters, namely, currents and electron energy, has been studied for each pulse sequence. The results show that the discharge current stays within the same order of magnitude as in the standard HiPIMS. The reference current level can be obtained quickly, adding a short over-pulse, even if its voltage level is relatively low. Furthermore, measurements by the Langmuir probe reveal that a maximum electron density is obtained at 0.2 and 0.6 Pa of argon for a configuration that adds two distinguished voltage-pulse sequences, one between 5 and 15 mu s and the other between 20 and 40 mu s. It comes out that this e-HiPIMS sequence significantly increases the electron density.