Understanding sidewall passivation composition of single-step non-Bosch processes for deep Si etch using alternative gas mixtures

Bosch processes involving C4F8 and SF6 have been conventionally used for through-silicon via etch. However, given the high global warming potential of C4F8 and the importance of high aspect-ratio deep-Si etch processes for packaging applications in next-generation technology nodes, it is of great interest to explore alternative plasma chemistries focusing on sustainable process development in the future. In our previous work, we reported the feasibility of using CH4 and C4F6 gas mixtures in lieu of C4F8, and BCl3 as an etchant additive along with SF6 in a single-step non-Bosch system. Parametric studies for throughput improvement were conducted, and “transition” discontinuities were observed for which a formation mechanism was proposed. In this work, the role of BCl3 as an additive in CH4-C4F6-BCl3-SF6 gas mixtures is discussed and further characterization on the sidewall composition is presented using time-of-flight secondary-ion mass spectrometry. The addition of BCl3 showed significant reduction in the F:C ratio of the polymer film as measured by x-ray photoelectron spectroscopy, with the effect being more pronounced in the areas subject to ion-bombardment.