The damage mitigation process for Si nanopillar structure using silica nanosphere lithography and metal assisted chemical etching

Abstract

This work focuses on mitigating the damage from nanostructure fabrication using silica nanosphere lithography (SNL) and metal assisted chemical etching (MACE). Metal contamination and plasma damage are the two main factors to limit the Si wafer's minority carrier lifetime. Ni/Au and Ti/Au metal layers on bare Si wafer are compared using lifetime recovery test. Ti/Au shows to be more suitable for the MACE process. Samples deposited with Ni/Au and Ti/Au show lifetimes of $7 \mu \mathrm{s}$ and $1200 \mu \mathrm{s}$, respectively. The silicon surfaceis degraded significantly by the RIE plasma during the nanosphere etching process. SiO2 protective layer was added to the process, mitigating significantly the plasma damage on the siliconsurface. Lifetime measurements shows an improvement over 1 ms when SiO2 protective layer on planar Si wafer is used. Lifetimes of $353 \mu \mathrm{s}$ and implied open circuit voltages of 651mV were accomplished on nanopillar structured wafers using SiOx protective layer and Ti/Au.