Influence of Silicon Nitride Thickness on the Passivation and Contact Properties of Phosphorus-Doped Poly-Silicon on Oxide Structures

Polysilicon on oxide (poly-Si/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>) passivating contacts are widely used in high efficiency solar cells since they allow excellent surface passivation levels both in metallized and in non-contacted areas. Poly-Si/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> are often capped with hydrogenated silicon nitride (SiN:H) layers providing enhanced passivation and stability upon fast firing steps used during metallization processes. In this work, we study the influence of different SiN:H layers thicknesses on the electrical properties (surface passivation and contact resistivity) of phosphorus-doped poly-Si/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> stacks depending on the fast firing temperature. Reducing the SiN:H thickness from 90 nm to 30 nm leads to more stable passivation properties after firing at high temperatures (above 750°C), but with increased contact resistivity values and metal-induced recombination. An optimum SiN:H thickness of about 60 nm is shown to combine high passivation level and excellent metal contact properties.