Time-resolved study and comparison of plasmas in high power pulsed and modulated pulse power magnetron sputtering

Summary form only given. High power pulsed magnetron sputtering (HPPMS) and its derivative, modulated pulse power (MPP) magnetron sputtering were studied in a 36 cm diameter circular planar magnetron, using a Ti target and an Ar atmosphere. The discharge characteristics and time-dependent plasma behaviors were measured to further understand their individual mechanisms and performances. The HPPMS plasma generator allowed a direct change of the pulse voltage to control the pulse current and arcing events. MPP, on the other hand, had an advantage of flexibly adjusting on- and off-time for each pulse, so that a long pulse with desired waveform shapes could be generated. Distinct discharge stages were observed in an MPP pulse. A time-resolved triple Langmuir probe was employed to measure the temporal evolution of the plasma in both magnetrons. A typical average electron density (n_e) of 10¹⁸ m^-3 and an electron temperature (T_e) of 10 eV during the pulse were obtained. For the HPPMS plasma, the pulse voltage strongly affected T_e, while ne increased with the pulse duration before saturated at about 150 μs. For the MPP magnetron sputtering, plasma behaviors were observed to closely depend on the programmed pulse waveforms. Various parameters, including pulse current, pulse frequency, pressure, and distance from the target, also affected the electron density and temperature. The effects of each parameter on the pulsed plasma dynamics are analyzed and attributed to mechanisms such as electron impact ionization, gas heating, and magnetic confinement. Comparisons of the two types of sputtering plasma with a same average power or pulse duration were performed and discussed.