In Situ Annealing of Boron-Doped Amorphous Silicon Layers Using APCVD Technology

In this work, we developed an in situ annealing process to crystallize boron-doped amorphous silicon [a-Si(p⁺)] layers deposited by atmospheric pressure chemical vapour deposition (APCVD) to form boron-doped polycrystalline silicon [poly-Si(p⁺)] layers. The influence of the temperature profiles during a-Si(p⁺) inline deposition on structural, electrical, and passivation properties was studied in detail. The results show that a-Si(p⁺) layers can be successfully crystallized by fine-tuning the temperature profiles in the postdeposition zones of the APCVD tool. It was observed that the hydrogenation processes during the fast firing play a significant role in enhancing the passivation quality as well as the electrical properties of the in situ annealed poly-Si(p⁺) layers. The sheet resistance (R_sh) and implied open circuit voltage (iV_oc) of the best in situ annealed poly-Si(p⁺) layers were found to be comparable to the ones that were ex situ annealed in the tube furnace at 950 $^\circ $C for 30 min. The sheet resistance of 200 $\Omega$/$\square$ could be obtained on 150-nm thick poly-Si(p⁺) layers with an (iV_oc) of 718 mV. The use of this novel in situ annealing process to form poly-Si(p⁺) layers opens a new horizon for a lean process sequence without the additional high-temperature annealing step for fabricating solar cells concepts based on passivating contact.