Time-dependent O-2 mass balance change and target surface oxidation duringmode transition in Ti-O-2 reactive sputtering

Time-dependent O-2 mass balance change among the amounts injected into the chamber, pumped out from the chamber, gettered by sputtered Ti metal, resid ing in the chamber, and consumed to oxidize the target surface has been inv estigated as a function of time elapsed after the discharge ignition in Ti- O-2 reactive sputtering. From the mass balance results obtained, target sur face coverage has been estimated. In the period of up to 10 s after dischar ge ignition, the gettering of O-2 by sputtered Ti dominated the process cha nge. In this period, the target surface oxidation rate was low. In the peri od of 20-50 s, the amount of O-2 consumed to target surface oxidation surpa ssed the amount of O-2 gettered by deposited Ti, resulting in a drastic inc rease in the target coverage. After the target surface oxidation was comple ted, the process became stable. In this period, the amount of O-2 pumped ou t without causing any process changes increased and a very small amount of O-2 was consumed to oxidize the target surface. The equilibrium in the bala nce between the formation and sputter etching of the oxide layer on the tar get surface resulted in the stable condition. Calculated target coverage ac hieved more than 250 monolayers at 600 s after the glow discharge ignition. This value equated with the oxide thickness of about 100 nm. It is conclud ed that the nonlinear target surface oxidation process causes a nonlinear p rocess change occurring during the mode transition. (C) 2000 American Insti tute of Physics. [S0021-8979(00)05904-1].