Investigation of ablation mechanisms for selective laser ablation of silicon nitride layers

In this work SiNX deposited on silicon was locally ablated using laser irradiation. The focus was set on the investigation of the ablation mechanisms where a picosecond (ps) pulse laser is used with three wavelengths 1064, 532, 355 nm. The ablated areas were characterized by light microscopy and the threshold fluences were determined for various layer thicknesses. Furthermore, four-probe sheet-resistance and SunsVoc measurements were conducted. Light microscopy images were taken and compared to simulated color maps, which were calculated from spectral reflection coefficients.The results of sheet resistance and SunsVoc measurements show an influence on the underlying silicon for all three wavelengths used. However, light microscopy images reveal for the first time a change from indirect ablation (lift-off) to partial lift-off for a thin a-SiNx:H-layer (n ≈ 2.1, t ≈ 75 nm) by using a VIS picosecond laser. Thus, a first step towards selective laser ablation was made of dielectrics.