A means has been found to control the rf potential of the substrate during rf sputtering. The application of this technique to the deposition of silica films has been investigated in detail. The technique can be described as the use of an adjustable rf impedance between the substrate holder and ground electrodes, which generates an rf potential by virtue of the flow of rf current through it. Adjustment of the rf potential of the substrate results in a controlled dc bias potential developed at the film surface, which correlates directly with the physical properties of the deposited films. In general, the most desirable film properties are obtained when the dc substrate bias (obtained by adjusting the substrate-holder rf impedance) is at a high negative potential. The effect of substrate bias on etch rate, pinhole breakup thickness, and argon content has been measured.
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