Equivalent circuit model for large-area ac magnetron sputtering of dielectrics

Abstract

Some important circuit considerations for ac reactive magnetron sputtering of dielectrics are addressed. We start with a simplified circuit model of a discharge appropriate to the ultrasonic frequency range. The model predicts that a power supply with sufficient secondary leakage inductance acts as a constant current source. The model accurately represents the wave form of the current observed in practice. A large spike observed on the rising edge of the voltage waveform is not predicted by the model. Results are presented for reactive sputtering of silicon-dioxide thin films from cylindrical silicon targets employing a dual magnetron rotatable cathode powered with an ac power supply operating at about 30 kHz. Single layer SiO 2 films produced over a period of more than 150 h. The lateral film thickness variation was less than ±3% and refractive index stability was ±0.004 at 545 nm. Samples coated after 150 h of continuous cathode operation exhibited small densities of arc-related film inclusions.