Advanced damage-free neutral beam etching technology to texture Si wafer with honeycomb pattern for broadband light trapping in photovoltaics

We introduce a new innovative damage-free neutral beam etching (NBE) technique to transfer a honeycomb resist pattern to silicon (Si) wafer (thickness of 180 mu m). Front-surface texturing of Si helps to reduce surface reflection and increase light absorption for solar cell applications. NBE was performed with Cl-2 and Cl-2/SF6 gases chemistries, and the influence of the etching time on the etching profiles, surface reflection and potential short-circuit densities (p-J(SC)) was studied. The Si etching rate with pure Cl-2 was similar to 5 nm/min and resulted in anisotropic etch profiles and a minimum surface reflection of 15% at 1000 nm, which is too high for practical use. With the introduction of 5% of SF6, the etching rate increased to 30 nm/min, the etching became isotropic (anisotropy of similar to 1), and sloped sidewalls appeared. NBE with Cl-2 (95%)/SF6 (5%) produced a sample with an average surface reflection of 3.7% over the wavelength range 300-1000 nm without any antireflection coating. The minimum surface reflection in this case was similar to 1% at 1030 nm and p-J(SC) was 40.63 mA/cm(2). This type of surface pattern is well suited for low-consumption-material (thin), high-efficiency Si solar cells.

Automated summary

This study introduces a new damage-free neutral beam etching technique for transferring resist patterns to silicon wafers. By introducing SF6 gas, the etching rate and profiles were improved, resulting in a significant reduction in surface reflection to 3.7%.