Regulation of silicon bottom corner flatness through multi-parameter collaborative optimization in deep reactive ion etching

Deep reactive ion etching (Bosch process) is a core technology in silicon microfabrication; however, its performance is still limited by outline defects, such as bottom corner height differences. We systematically investigated the influence mechanism of the aforementioned parameters on the bottom-of-trench etching flatness by solely regulating key process parameters during the passivation layer deposition (C4F8) and etching (SF6) stages. These parameters included gas flow rates, time ratios, and bottom radio frequency power. Throughout the process, no other gases, such as chlorine-based gases, were introduced. Only these two gases were employed for process adjustment. Experimental results indicate that optimal bottom flatness is achieved with a C4F8 flow rate of 150 to 350 sccm, an SF6 flow rate of 500 sccm, a passivation/etching time ratio of 1.12:1, and a bottom radio frequency (RF) power of 100 W. In addition, findings reveal that increasing the C4F8 time significantly enhances bottom height differences; increasing the SF6 flow rate initially decreases height differences before causing them to rise again; and bottom RF power below 80 W induces micro-mask effects, whereas power levels above 120 W exacerbate height differences, with 100 W identified as the equilibrium point. We quantify the critical process window, providing a theoretical foundation and process pathways for achieving high-precision control over silicon etching morphology.