Enhanced plasma etching using nonlinear parameter evolution

This study explores the development and characterization of plasma etching for sub-micron features using a nonlinear evolution of parameter in a three-step cyclic Bosch process. Comparing this nonlinear approach with traditional linear parameter evolution, we aimed to address issues such as bowing at the top of the features and narrowing at the bottom. Constant parameter etching produced tapered profiles, undercutting, and non-uniform scallops due to particle deflection. Linear parameter evolution partially mitigated these problems by balancing etch and deposition cycles and gradually increasing radio frequency power, achieving high selectivity to the photoresist. One nonlinear exponential evolution method resulted in a higher etch rate but caused slight damage to the top-side wall, while the etch depth was reduced. The other nonlinear method balanced the etch and deposition steps more effectively, achieving a comparable etch rate and selectivity to the linear method. Further optimization of this second method led to improved vertical profiles and controlled scallops, achieving greater depth, smoother sidewalls, and higher etch rates. This optimized technique successfully fabricated high aspect ratio periodic sub-micron structures with excellent uniformity across the wafer, demonstrating its potential for achieving even higher aspect ratios with thicker masks. • Technique Comparison : Linear and nonlinear parameter evolution are compared in cyclic Bosch processes for sub-micron plasma etching. • Optimized Nonlinear Method : This method balances etch and deposition steps, enhancing vertical profiles, scallop control, and high selectivity to the PR mask. • Improved Etch Quality : Linear parameter evolution boosts etch quality, ensuring high selectivity to the PR mask and reducing undercutting and bowing. • Higher Etch Rates : The optimized nonlinear method demonstrates higher etch rates with minimal sidewall damage. • High Aspect Ratio Structures : The technique fabricates high aspect ratio sub-micron structures with outstanding uniformity.