The surface oxidation of tungsten is a serious issue in plasma processing of advanced integrated-circuit devices where tungsten is being used as a gate electrode. In this article, we study tungsten oxidation in O-2/H-2/N-2 downstream plasma at a temperature <= 300 degrees C. The results show that oxidation occurs rapidly in O-2 downstream plasma to form stable WO3. However, oxidation can be reduced effectively by adding H-2 and totally suppressed when H-2 concentration in the gas feed reaches a certain low level at which the plasma is still oxygen dominant. Tungsten oxidation increases significantly with sample temperature and exposure time in O-2 downstream plasma. However, H-2 addition reduces both temperature and time dependences due to the coexistence and competition of oxidation and reduction processes. When N-2 is also added, the efficiency of H-2 in O-2 downstream plasma in controlling tungsten oxidation is lowered. The findings may provide effective approaches to various applications of selective oxidation over tungsten, such as photoresist stripping and polysilicon oxidation on tungsten gate structures. (c) 2008 American Vacuum Society.