During bias sputter deposition, the accumulation rate is found to vary significantly with impressed substrate bias. In the case of rf bias sputter deposition, the rate may increase or decrease depending on the biasing method. Measurements of the harmonic content of the radiation from a rf sputtering discharge have been made as a function of impressed substrate bias, both dc and rf, and for self bias obtained by tuning of the substrate circuit. These measurements indicate that for rf sputter deposition with dc bias, the target and substrates are non-interacting. For rf self-bias operation, the two circuits interact strongly, modifying the discharge characteristics to allow the dissipation of greater amounts of useful power.