The process performance requirements for shallow trench etch are very unique and depend very much on the specifics of the device (slide 1).
Depending on the mask scheme (resist or hardmask), chlorine or hydrogen bromide based plasmas can be used to etch shallow trenches (slide 2).
For both chemistries, the tapered profile is achieved by the formation of sidewall passivation layers comprised of oxyhalogenides which are the by-products of the etch process. The sidewall passication is typically thicker in the case of HBr processes. There is evidence that direct surface oxidation plays a role in the case of chlorine processes while backsputtering of reaction by-products is the primary mechanism in the case of HBr (slide 3).
These differences in the etch mechanism lead to significantly different profile and etch rate microloading (slide 4).
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