Asynchronously Pulsed Plasma for High Aspect Ratio Nanoscale Si Trench Etch Process

Abstract

The fabrication of high aspect ratio Si trenches has been becoming difficult due to the decrease in critical dimension (CD) to deep nanoscale. Especially, aspect ratio dependent etching (ARDE), which decreases the etch rate as the pattern width gets smaller, makes process uniformity get worse. In this study, the effects of bias pulsing parameters during asynchronous pulsing, which alternatively applies the source power and bias power, as well as the effect of additive gas such as CF₄ and C₄F₈ on the nanoscale Si trench etch characteristics during Cl₂/Ar plasma etching were investigated. It was found that the bias pulsing parameters during the asynchronous pulsing, such as bias pulse duty ratio and bias pulse delay time, can affect the etch characteristics such as etch rate, etch selectivity, and ARDE by changing the ion dose and ion energy during the etching. However, the variation of bias pulse parameters during the asynchronous pulsing did not change the etch profile noticeably, and it showed bowed Si trench etch profiles. To improve the etch profile, the addition of fluorocarbon gas such as CF₄ and C₄F₈ was required, and by using C₄F₈ instead of CF₄, more anisotropic Si etch profile without sidewall bowing could be obtained due to the improved sidewall passivation by a fluorocarbon layer even though it degraded etch selectivity and ARDE. Therefore, it is believed that by controlling the bias pulsing parameters with additive gas, nanoscale Si trench etch characteristics can be more easily controlled.