Deep reactive ion etching of sub-micrometer trenches with ultra high aspect ratio

This paper focuses on deep reactive ion etching (DRIE) of sub-micrometer features. Very high aspect ratios up to 160:1 on trenches of 250 nm have been achieved using the Bosch process and up to 120:1 on trenches of 35 nm using a cryogenic process. The proposed etch recipes are specifically optimized for sub-micrometer features, and are not compatible with feature sizes in the tens of micrometer range. Based on analyzing data from our experiments and from literature, we show that a previously reported two-parameter empirical logarithmic law accurately describes the dependency of aspect ratio on trench width over a wide range of widths and etch parameters, including the sub-micrometer regime. We also propose a new figure of merit (FOM) that describes the ultimate aspect ratio achievable for any given etching process. This FOM also allows comparison of different aspect ratio performances, while taking into account in the same time, the dimension of the trench for which this performance is attained.

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