A Study of Sigma-Shaped Silicon Trench Formation

Abstract

The strict shape control of sigma-shaped silicon trench has to leverage the dry etch process coupled with the appropriate post-etch treatment (PET). Here we addressed the strong link between the shape of dry etch based silicon recess and its effect on the definition of final sigma-shaped trench. Experiment results indicate the critical physical parameters of final sigma-shape silicon trench could be predicted by means of geometry analysis and monitoring dry etching related recess in bulk silicon. Besides, we also noticed the effect of pattern-dependent depth loading at dense areas. Organic polymer generated during etch process tends to introduce the trench depth variation. Polymer lean etch process has been proven as one of effective knobs to overcome such loading to some extent. In addition, the oxidation capacity of post-etch treatment can not be ignored. The ultra-thin silicon oxide film on silicon trench sidewall must be completely removed by dilute hydrofluoric acid before PET to avoid the possible trench depth loading.

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“…However, in our experiments, the recessed depth loading is not only correlated to the pitch of gate electrodes but also depends on the different dry etch approaches (Table 1). This is mainly because of the lean etchant gases in the isotropic silicon etch gas resources (6). The trench depth loading between dense and isolated areas was over 3nm but it can be controlled less than 1nm by the addition of the isotropic recess step for the two-step silicon etch approach.…”