Electronic Properties of a-SiO N :H/SiN Stacks for Surface Passivation of P-Type Crystalline Si Wafers

• Published in: IEEE journal of photovoltaics 2016-09, Vol.6 (5), p.1103-1108
• Main Authors: Xuemei Cheng, Haug, Halvard, Di Sabatino, Marisa, Junjie Zhu, Marstein, Erik Stensrud
• Format: Article
• Language: English
• Subjects: Chemicals; Crystal structure; Defect density; Density; Firing; fixed carriers; Mathematical models; Passivation; photovoltaic cells; PL-V; plasma-enhanced chemical vapor deposition (PECVD); Semiconductor device measurement; Silicon; Silicon nitride; silicon oxynitride/silicon nitride stacks; silicon surface passivation; Stacks; Thermal stability; Thickness; Voltage measurement; Wafers
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2016.2581421

The surface passivation quality of plasma-enhanced chemical vapor-deposited silicon oxynitride/silicon nitride (a-SiO x N y :H/SiN x ) stacks has been investigated for p-type float-zone crystalline silicon wafers. The effective lifetime τ eff , density of fixed charge Q f , and density of interface defects D it were measured as a function of the a-SiO x N y :H layer thickness both before and after firing at 800°C for 3 s. Photoluminescence imaging under applied bias has been used to characterize Q f and the surface recombination parameters S 0n and S 0p through fitting τ eff versus voltage curves to an extended Shockley-Read-Hall (SRH) model. The results are in good agreement with values measured using capacitance-conductance-voltage measurements. Good surface passivation has been obtained with a peak effective lifetime of 2.41 ms. For both as-deposited and fired samples, Q f and D it decrease with increasing a-SiO x N y :H layer thickness up to ~18 nm. The results indicate that the field-effect passivation is weakened as the a-SiO x N y :H thickness increases and that chemical passivation from a-SiO x N y :H/SiN x plays a prominent role. Increasing the a-SiO x N y :H/SiN x thickness to 50 nm produces similar results, indicating that an 18-nm interlayer is enough to obtain the desired passivation properties. Compared with as-deposited samples, fired samples exhibit lower D it , indicating that the firing process enhances chemical passivation of the a-SiO x N y :H/SiN x stacks.