The in situ sputter removal of oxide layers prior to subsequent depositions or growth is increasingly important as device sizes and hence interlayer contact sizes shrink. Electron cyclotron resonance (ECR) plasma sputter removal of oxides has been investigated since it offers the combination of high plasma densities and low ion energy induced substrate damage. In this study, ECR argon discharge sputter removal of SiO2 was investigated using a 9 and 25 cm diam discharge. The uniformity and rate of oxide removal on 3 and 6 in. silicon wafers were investigated with respect to pressure (0.6-2 mTorr), microwave power (200-800 W), radio-frequency induced bias (-30 to -80 V) and downstream position (6.3-11.8 cm) of the wafer. Uniformity and rate results show good correlation to ion density measurements and to an ambipolar plasma diffusion model.