Surface Texturing for Silicon Solar Cell Application Using Icp-pecvd Plasma Technique

This work is focused on plasma-induced texturing using a single chamber inductively coupled plasma – plasma-enhanced chemical vapour deposition (ICP-PECVD) lab-tool. Plasma treatment using pure NF3 under low pressure conditions leads to high etch rates (1.2–1.4 μm/min) enabling fast surface texturing. 6 min plasma treatment on wafers with saw damage decreases the effective reflectivity Reff from 31% to 13.7% without anti-reflection coating (ARC), which is lower than the value for a common alkaline surface texture. For planar (KOH pre-treated) samples Reff can be reduced from 38% to 17.8% after 4 min plasma treatment. Lifetime measurements reveal a postprocess lifetime of 250 μs without any further damage removal etching (DRE). This refers to a low density of plasma-induced defects. Furthermore, it is demonstrated that plasma textured surfaces enable excellent contact formation for screen-printing of Ag/Al pastes on boron emitters leading to low specific contact resistances below 5 mΩcm even for low set peak firing temperatures (TSet < 800°C). These values are much lower than values realized with a common isotropic wet acidic etch and slightly lower than values realized with a common alkaline surface texture, leading to reduced power losses due to lowered series resistance. In addition, the specific contact resistance on POCl3 emitters by screen-printing of commercial available Ag pastes is determined to be below 1 mΩcm, nearly independent of the set peak firing temperature.