TIN REACTIVE SPUTTER-DEPOSITION STUDIED AS A FUNCTION OF THE PUMPING SPEED

TiN is an extremely important barrier material in present day integrat ed circuits. The most common deposition method is reactive sputter dep osition from a titanium target in a argon-nitrogen gas mixture. In rea ctive sputter deposition of TiN a fraction of the nitrogen feed gas is incorporated in the film. This consumption might lead to non-uniform deposition for large wafersizes and/or low pumping speeds. For relativ ely low pumping speeds, or a large fraction of incorporated nitrogen, it was expected that the film uniformity over the wafer would deterior ate. TiN was deposited at fixed partial pressures of argon and nitroge n. The pumping speed was varied over one order of magnitude. Even at t he lowest pumping speed tested, i.e. at 84% consumption of the supplie d nitrogen, the uniformity did nor deteriorate. The process proved to be insensitive to the pumping speed. We propose that the explanation o f this insensitivity is due to the high reactivity of Ti atoms on the target to N atoms, while the chance for additional nitrogen atoms to b e adsorbed at the nitrided target is very small. The target is operate d in the poisoned mode which means that the target surface consists of TiN. Calculations showed that the number of N atoms striking the targ et is about 80 times larger than the flux of Ti atoms sputtered from t he target. The sticking coefficient of N-2 on Ti is high, therefore th e chance for the target to recover its TiN surface after a nitrogen at om or a TiN fragment is sputtered off is high. On the other hand the s ticking coefficient of nitrogen on TW is very low. An increase in part ial pressure of nitrogen will not result in extra 'adsorbed nitrogen' on the target. Therefore the ratio of titanium to nitrogen atoms remov ed from the target by the ion bombardment is insensitive to the partia l pressure of the nitrogen and hence to the pumping speed. (C) 1998 El sevier Science S.A. All rights reserved.