Undercut in a CF4-Based High-Pressure Poly-Si Plasma Etch

The behaviour of the plasma etching of polycrystalline Si (P-doped and undoped) in a CF4-based high-pressure glow discharge is studied as a function of the power density, of the exposed poly-Si surface area (the so called loading effect), of the flow rate of CF3Cl and of the flow rate of N2O and O2 as additive gases. Partially in contrast with the current results reported in the literature, the experimental data here presented show that P-doped poly-Si is etched slower than undoped poly-Si in the mixture CF4+CF3Cl+N2O as well as in the mixture CF4+CF3Cl+O2, probably as a result of the different interaction mechanisms between substrate and gaseous reactants, which could be established at such high pressure and flowrate as in our experiment. Furthermore, our data reveal that the lateral etch rate (or undercut) is critically determined by the effective concentration of atomic F. Finally, we observed that CF3Cl has a clear anisotropic mechanism of etch.