5:30 PM - 5:45 PM
▲ [14p-2C-11] Change in optical properties by texturing Si compounds by F2 and NOx gases
Keywords:Chemical dry etching,Texturing,Photovoltaic cell
Reducing light reflection from the surface of photovoltaic cells made of silicon nitride films deposited on the textured single or multi crystalline Si plays a key role to improve the cell efficiency. Recently, chemical dry etching using ClF3 have been intensively studied to texture single and/or multi crystalline Si. In order to reduce the process cost and the process chamber corrosion induced by Cl, we have been investigating the nanoscale Si surface texturing by the reaction of F2 + NOx (X=1, 2) -> F + FNOx. In this study, we evaluated the change in optical properties of various Si compounds by modulating the NO/F2 ratio that would modify the nanoscale surface texturing by controlling the adsorption of F2, NOx, F, and FNOx on the Si surface. The chemical bonding structures, responsible to pattern the Si surface, were predicted by the density functional theory (DFT) using CAM B3LYP 6-311 G+(d,p) in Gaussian 09. The reflectance was reduced by 2/3 to 1/2 when the surface have different sizes of etch pits generated by the chemical adsorption of F2, NOx, F, and FNOx. Based on the reaction model generated by the DFT calculation, F2, F, and FNO promoted the etching while NOx and FNOx acted as etching inhibitor by capping the dangling bond. NOx rich surface generated by the NOx/F2 ratio of ~ 2.2 showed the lowest reflectance due to the presence of NOx rich bond that would act as a nanoscale etch mask to generate the 30-50 nm nanoscale etch pits and the width of the etch pit of ~ 100 nm. The size of the etch pit is close to the width of the previously reported Ag island to improve the photovoltaic efficiency by increasing the scattering efficiency.