Multiscale approach for simulation of silicon etching using SF6/C4F8 Bosch process

This study is dedicated to the development of a multiscale approach for the simulation of silicon etching using the Bosch process. The etching simulator is composed of three modules: plasma kinetic model, sheath model, and surface model. The top down connection of these three modules allows us to track the etch profile evolution through the mask versus the reactor parameters. Complex reaction schemes are used for both SF6 and C4F8 plasmas to quantify the neutral and ion species densities and fluxes. For the SF6 plasma used in the etching cycle and in our pressure and power ranges, the fluorine flux is still preponderant compared to the positive ion flux, indicating that the silicon etching is mainly ensured by the chemical processes. For the C4F8 plasma used in the deposition cycle, the simulation results reveal that CFx species are preponderant in comparison with atomic fluorine, confirming that, in our operating conditions, CFx species promote the deposition of a polymer layer instead of the chemical etching by fluorine F. Plasma parameters in terms of the reactive neutral and ion fluxes and sheath parameters in terms of ion energy distribution functions are used in the surface model to track the etch profile evolution. The duty cycle corresponding to the SF6 to C4F8 plasma pulse ratio is a crucial parameter in controlling the Bosch process performances in terms of the etch rate, anisotropy, and scalloping defect development. A parametric study is performed to show the role of the duty cycle in the etch anisotropy and the scalloping propagation along the sidewall. While the scalloping defect is more important when the duty cycle is higher, the diminution of this parameter may reduce the global etch rate of silicon. (C) 2017 American Vacuum Society.