Polymer thickness effects on Bosch etch profiles

Time-multiplexed etching, the Bosch process, is a technique consisting of alternating etch and deposition cycles to produce high aspect-ratio etched features. The Bosch process uses ${\mathrm{SF}}_6$ and ${\mathrm{C}}_4{\mathrm{F}}_8$ as etch and polymer deposition gases, respectively. In these experiments, polymer thickness is controlled by both ${\mathrm{C}}_4{\mathrm{F}}_8$ gas flow rates and by deposition cycle time. The authors show that polymer thickness can be used to control wall angle and curvature at the base of feature walls. Wall angle is found to be independent of trench width under thin-polymer deposition conditions. Experimental results are compared to results obtained by other researchers using the more conventional simultaneous etch/deposition technique.