AVS 46th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuM

Paper PS-TuM3
Microscopic Uniformity in Oxide Etch during Overetch Time in Polysilicon Gate Etching

Tuesday, October 26, 1999, 9:00 am, Room 609

Session: Plasma-Surface Interactions I
Presenter: K. Ono, Kyoto University, Japan
Authors: K. Ono, Kyoto University, Japan
T. Mutumi, Mitsubishi Electric Corporation, Japan
Correspondent: Click to Email
Plasma-surface interactions during polysilicon gate etching have been studied in ECR Cl@sub 2@ and Cl@sub 2@/O@sub 2@ plasmas, with emphasis on a better understanding of competitive mechanisms for microscopic uniformity i n etching of underlying SiO@sub 2@ that occur during overetch time. Experim ents were performed as a function of pressure, O@sub 2@ percentage, and rf b ias power, using samples for etching masked with a photoresist pattern of li nes and spaces (0.35-5 µm). The results of SiO@sub 2@ etching exhibit ed aspect-ratio dependent etch rates similar to those of poly-Si. In pure C l@sub 2@ plasmas, an RIE lag was observed at relatively low pressures (<5 mT orr), and its magnitude was significantly enhanced as the bias power was low ered. In Cl@sub 2@/O@sub 2@ plasmas, a transition from regular to inverse R IE lag was found to occur as the O@sub 2@ percentage was increased, which ga ve microscopically uniform etch rates at low level (10%) O@sub 2@ addition; the magnitude of inverse RIE lag at high O@sub 2@ percentages (>20%) was muc h larger for SiO@sub 2@ than for poly-Si. The inverse RIE lag also occurred at high pressures in pure Cl@sub 2@ plasmas, probably owing to background o xygen. Moreover, microscopically nonuniform thinning and breaking of thin g ate oxides was found to occur during overetch time; the thinning and breakin g occurred preferentially in large open fields in pure Cl@sub 2@ plasmas, wh ile in dense areas at high level O@sub 2@ addition in Cl@sub 2@/O@sub 2@ pla smas. A comparison of the experiments with the predictions of rate model an alysis indicated that the microscopic uniformity of SiO@sub 2@ etch rate pre sently observed in chlorine-containing plasmas is interpreted in terms of tw o competing processes caused by incoming ions and neutrals from the plasma i nto microstructures: carbon-enhanced oxide etching and removal of carbonaceo us materials by oxygen. The carbonaceous materials of interest are attribut able primarily to hydrocarbon fragments from sputtered photoresist, and the background and/or added oxygen is assumed to scavenge such hydrocarbon fragm ents adsorbed on SiO@sub 2@ surfaces before they enhance the oxide etch rate.