Simultaneous etching of polysilicon materials with different doping types by low-damage transformer-coupled plasma technique

The feasibility of simultaneously etching n⁺, p⁺, and undoped polysilicon (poly-Si) materials by a commercial transformer coupled plasma (TCP) reactor has been investigated in this study. Response surface methodology (RSM) was used to optimize process parameters including pressure, TCP source power, bias power, and Cl₂/HBr flow on the main etch step. Quantitative relationships between etching performance and process parameters were established. Our results indicate that there exists a process parameter window that meets the requirements of etching polysilicon with different doping types simultaneously. High etch rate, superior uniformity, good end point detection (EPD) characteristics and profile control can be simultaneously obtained with the optimized recipe, irrespective of the doping types. Furthermore, only minor plasma-induced damage is detected as monitored from antenna transistors' charge-to-breakdown (Q_bd), threshold voltage and charge pumping current.