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

The fabrication of high aspect ratio Si trenches hasbeen becomingdifficult due to the decrease in critical dimension (CD) to deep nanoscale.Especially, aspect ratio dependent etching (ARDE), which decreasesthe etch rate as the pattern width gets smaller, makes process uniformityget worse. In this study, the effects of bias pulsing parameters duringasynchronous pulsing, which alternatively applies the source powerand bias power, as well as the effect of additive gas such as CF4 and C4F8 on the nanoscale Si trenchetch characteristics during Cl-2/Ar plasma etching wereinvestigated. It was found that the bias pulsing parameters duringthe asynchronous pulsing, such as bias pulse duty ratio and bias pulsedelay time, can affect the etch characteristics such as etch rate,etch selectivity, and ARDE by changing the ion dose and ion energyduring the etching. However, the variation of bias pulse parametersduring 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 profilewithout sidewall bowing could be obtained due to the improved sidewallpassivation by a fluorocarbon layer even though it degraded etch selectivityand ARDE. Therefore, it is believed that by controlling the bias pulsingparameters with additive gas, nanoscale Si trench etch characteristicscan be more easily controlled.

Automated summary

This study investigated the effects of bias pulsing parameters and additive gases on the nanoscale Si trench etch characteristics during Cl-2/Ar plasma etching. It was found that the bias pulsing parameters during the asynchronous pulsing can affect the etch characteristics, such as etch rate, selectivity, and ARDE. The addition of CF4 and C4F8 gases improved the etch profile, with C4F8 providing a more anisotropic Si etch profile without sidewall bowing but sacrificing etch selectivity and ARDE.