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 µm). Front-surface texturing of Si helps to reduce surface reflection and increase light absorption for solar cell applications. NBE was performed with Cl₂ and Cl₂/ 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 Cl₂ was ~ 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 ~ 1), and sloped sidewalls appeared. NBE with Cl₂ (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 ~ 1% at 1030 nm and p-J_SC was 40.63 mA/cm². This type of surface pattern is well suited for low-consumption-material (thin), high-efficiency Si solar cells.