Study of the impact of the time-delay effect on the critical dimension of a tungsten silicide/polysilicon gate after reactive ion etching

The addition of HBr has been used with oxygen and chlorine-based chemistrie s to improve selectivity of polysilicon to gate oxide in gate-stack etching . As a consequence of high selectivity, polymer residues become a major fac tor in critical-dimension (CD) control. It is believed that the presence of HBr in the plasma is responsible for polymer formation. HBr and its polyme r residues may induce surface reactions to form thin oxide layers. Such a p henomenon has been observed if the wafers are not treated with HF vapor imm ediately after reactive ion etching (RIE) of the gate. The magnitude of the oxide film growth is proportional to the delayed time between RIE and HF v apor treatment. The sidewall thickness of the gate is also affected by the time-delay effect. The growth of the oxide film on the sidewalls can eventu ally affect the gate CD, and thus the device performance. A simple reaction model for the growth of the oxide film is proposed to explain the correlat ion between delayed time and CD bias. (C) 2000 American Vacuum Society. [S0 734-2101(00)09304-0].