The effect of the duty cycle on the etching process and on the formation of silicon grass for different etching widths was investigated. As the duty cycle is defined as the chuck power application per second, it determines the etch rate and etching profiles. It was found that decreasing the duty cycle improves the etching profiles of the trench but it may also cause the formation of silicon grass at the bottom when the nominal width is significantly large. Therefore, for a large nominal width, lowering the duty cycle promotes the formation of silicon grass. Moreover, a large duty cycle induces undercut on the sidewall, which is deleterious to the etching profiles. Activation of the chuck power is controlled by the duty cycle and it also accelerates photo resist erosion or a bowing effect. Therefore, when the duty cycle becomes large, the etch rate is drastically enhanced. Finally, we can conclude that a low duty cycle is suitable for a Bosch process in order to prevent undesirable etching side effects, such as undercut or bowing.

Keywords: Duty cycle, etch rate, Bosch process, silicon grass.