Pulsed magnetron sputtering generally adopts a rectangular wave voltage. This is not only because the existing electronic devices can be easily used to obtain the waveform of rectangular wave voltage by using a switching mode, but also the rectangular wave voltage waveform is favorable for studying the variation of sputtering discharge plasma. Fig. 1 shows a rectangular wave voltage waveform for pulse sputtering. The pulse period is T. The time during which the target is sputtered in each cycle is T-ΔT, and ΔT is the time (width) of the positive pulse applied to the target. V+ and V- are respectively the voltage amplitudes of the negative and positive pulsed that applied to the target. In order to maintain a higher sputtering rate, the duration of the positive pulse ΔT is much smaller than the pulse period T.
In order to fully neutralize the positive charge accumulated on the target surface insulation layer in a shorter ΔT time, the positive voltage V on the target surface cannot be too low, but it is generally not higher than 100V. Since the pulse waveform used is asymmetric, it is named as asymmetric pulsed magnetron sputtering.
Fig. 1 Waveform of rectangular wave voltage for pulsed reactive sputtering
Pulse sputtering is different from intermediate frequency dual target sputtering in that it generally uses only one target. By using pulse reactive magnetron sputtering technology, long-term stable deposition of Al2O3 films was achieved with a deposition rate of 240 nm/min. The thickness of the coated Al2O3 film was up to 50 μm. Due to the successful elimination of target ignition, defects of Al2O3 films are reduced by 3 to 4 orders of magnitudes. Pulse reactive magnetron sputtering shows its superiority in the deposition of Si O2, Ti Ox, Ta Ox, Si Nx, DLC, Al2O3, ITO and other films.
Pulse sputtering is more favorable for the heat dissipation of the target, that is, it is possible to supply power with high power pulses. Therefore, the sputtering process has greater selectivity and flexibility. The emergence of intermediate frequency AC magnetron sputtering technology and asymmetrical pulse sputtering technology laid the foundation for industrialization of chemical reaction sputtering film forming technology.