Reactor Characterization for an SiO2 Plasma Etchback Process with Response‐Surface Methodology: Effects of Interelectrode Spacing

Abstract

The characteristics of plasmas which are used to etch composite layers of sacrificial photoresist and underlying have been examined with experimental design and modeled empirically by response‐surface methodology using a Lam Research Autoetch 480 single‐wafer system. The effects of variations of process gas flow rates for (150–200 sccm) and (0–50 sccm), reactor pressure (900–2000 mtorr), and interelectrode spacing (4–6 mm) on the etch rates of and photoresist were explored at fixed radio frequency power (500W at 13.56 MHz) at . Variation in spacing shows different effects for these two materials; whereas the etch rates generally increase with increasing spacing as the other parameters are varied, the photoresist etch rates exhibit more complex behavior. At the lower spacing of 4 mm, neither film has a measurable etch rate for low settings of the other variables. The etch rates are virtually constant with increasing flow rate for low, middle, and high settings of the other variables. At low settings of the other variables, the photoresist etch rates are zero over the range of flow rates but increase with increasing flow rates for middle and high settings of the other variables. At a spacing of 4 mm, the etch rates of both films are negligible over the range of flow rates and the range of reactor pressure. At larger spacings the etch rates of photoresist increase with increasing flow rate, while the etch rates of are similar for middle and high settings of the other variables over the range of flow rates. Process optimization using the empirical models to attain suitable etch rates for both films for planarization of a composite layer of photoresist and with high etch uniformity was achieved at 500W of RF power, 1450 mtorr, 150 sccm of , 0 sccm , and a spacing of 5.5 mm. Hence, for a plasma with this reactor adequate planarization is obtained without the use of . The addition of small concentrations of to a plasma resulted in increasingly higher etch rates for photoresist as the process progressed.