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

• Published in: Journal of materials science. Materials in electronics 2021-12, Vol.32 (23), p.27449-27461
• Main Authors: Sekhar, Halubai, Fukuda, Tetsuo, Kubota, Tomohiro, Rahman, Mohammad Maksudur, Takato, Hidetaka, Kondo, Michio, Samukawa, Seiji
• Format: Article
• Language: English
• Subjects: Anisotropy; Antireflection coatings; Broadband; Characterization and Evaluation of Materials; Chemistry and Materials Science; Damage; Electromagnetic absorption; Etching; Light reflection; Materials Science; Neutral beams; Optical and Electronic Materials; Photovoltaic cells; Short circuits; Silicon; Solar cells; Texturing
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-021-07121-9

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 Cl 2 and Cl 2 / SF 6 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 ~ 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 SF 6 , the etching rate increased to 30 nm/min, the etching became isotropic (anisotropy of ~ 1), and sloped sidewalls appeared. NBE with Cl 2 (95%)/SF 6 (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/cm 2 . This type of surface pattern is well suited for low-consumption-material (thin), high-efficiency Si solar cells.