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Journal of Applied Science & Engineering

Dhaka University Journal of Applied Science & Engineering

Issue: Vol. 6, No. 1, January 2021
Title: Formation of N-Type Layer upon Silicon Wafer Using POCl3 Diffusion Process

Keywords: Sheet Resistance; Deposition time; Drive time; Monocrystalline P-type silicon wafer

The application of N-type layers, formed upon P-type layers, has a huge impact on the solar cell industry. The formation process of N-type layers (Emitter) upon both side of monocrystalline P-type silicon wafers (Base) using POCl3 (Phosphorus Oxychloride) diffusion process has been investigated and discussed in this paper. Both side ascut P-type silicon wafers have been used as the substrates. The diffusion procedure has been carried out at 875°C in a POCl3 diffusion furnace using POCl3, N2 and O2 gas. The main goal of this research is to find out a low-cost N-type layer fabrication method with a standard sheet resistance value of 40 Ω/sq - 90 Ω/sq. By experimental trials, attempt has been made to reduce the cost by minimizing the utilization of POCl3. The utilization of POCl3 gas has been minimized by decreasing the deposition time and compensating it with using increased drive time by means of low cost N2 gas. By varying the deposition time, a number of experiments have been done to get the optimum deposition time and drive time. During the diffusion process, the deposition time and drive time variations were 5, 10, 20, 30 min and 10, 15, 25 and 35 min, respectively. Thermal oxidation has been applied after diffusion process. The formation of N-type layer has been confirmed by hot point probe experiment. Furthermore, sheet resistance has been determined experimentally using four-point probe measurement equipment. In addition, electron concentration of the substrate has been calculated. With 5 KeV and 20 KeV accelerating voltage, elements of the fabricated layer have also been analyzed with Energy Dispersive X-ray Spectroscopy (EDS). Remarkably, 65.25 Ω/sq sheet resistance has been obtained with 5 min diffusion and 10 min drive time. Utilization of 5 min diffusion and 10 min drive time recipe can be a low cost procedure for the creation of N-type layer and it is proposed to be used for the solar cell industry

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