Inverted Pyramidal Texturing of Silicon Through Blisters in Silicon Nitride

We have demonstrated a novel process for the fabrication of inverted pyramidal structures on silicon. The proposed technique uses no photolithography step and is instead replaced by a thin-film deposition step and thermal annealing. In this paper, inductively coupled plasma CVD (ICP-CVD) silicon nitride was used as the thin film. Blisters were formed on the silicon nitride film upon annealing at 800°C. The silicon nitride film remaining on the surface of the wafer acts as an etch mask for the texturization process, which is carried out in an alkaline solution. It was observed that only open blisters participated in the etch process, while closed blisters were resistant to the etching solution. It was observed that the gas flow ratio, annealing time, and temperature played an important role in determining the shape, size, and areal density of the blisters. By integrating an argon plasma pretreatment in the silicon nitride deposition process, surface coverage of 51% was obtained for lower annealing temperatures of 550°C. Upon etching the sample in an alkaline solution, a weighted average reflectance of 17.3% was obtained, indicating the potential of this process.