Etching Techniques for Thinning Silicon Wafer for Ultra Thin High Efficiency Interdigitated Back Contact Solar Cells

Iduabo John Afa^1, , Gema López¹ and Pablo Rafael Ortega Villasclaras¹

¹Grup de Recerca en Micro i Nanotecnologies (MNT), Universitat Politècnica de Catalunya (UPC), C. Jordi Girona, Barcelona, Spain

Cite this paper:
Iduabo John Afa, Gema López and Pablo Rafael Ortega Villasclaras. Etching Techniques for Thinning Silicon Wafer for Ultra Thin High Efficiency Interdigitated Back Contact Solar Cells. Journal of Optoelectronics Engineering. 2015; 3(1):7-14. doi: 10.12691/joe-3-1-2

Abstract

High efficiency Interdigitated back contact (IBC) solar cells help reduce the area of solar panels needed to supply sufficient amount of energy for household consumption. We believe that a properly passivated IBC cell with the aid of light trapping schemes can maintain an efficiency of 20% even with thickness under 20 μm. In this work, photolithography and etching techniques are used for deep etching of crystalline Silicon (c-Si) wafer to a thickness less than 20 μm. Tetramethylammoniumhydroxide (TMAH) wet anisotropic etching and plasma based Reactive ion etching (RIE) are used with SPR 220-7.0 and SU-8 photoresists. SiO₂ is used as making layer for TMAH etching. TMAH etch of a 4-inch c-Si wafer is done at a temperature of 80°C for 8 hours. RIE of a quarter of a 4-inch c-Si wafer is done for 3 hours using SF₆ as reactive gas. A baseline photolithography process flow for SU-8 photoresist deposition was developed. The etch rates of TMAH etch techniques fall within the range of 0.3 – 0.45 μm/min and etch rates for RIE fall within the range of 1.2 – 1.8 μm/min. The RIE shows capability of achieving smaller thickness sizes with greater advantages than the TMAH etching technique.

Keywords:
IBC solar cells masked etching photolithography reactive-ion etch and tMAH etching

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