Non-linear absorption of femtosecond laser pulses in a SiN layer—influence of silicon doping type

Abstract

Abstract In this article, silicon nitride (SiN x ) layers deposited on planar silicon wafers with two different doped areas (emitter: highly phosphorous doped and bulk: lightly boron doped) were locally irradiated by laser pulses. Our investigation is focused on the ablation mechanisms. For that purpose, an ultra-short laser source (pulse duration 0.3–12 ps, wavelength 1025 nm, Gaussian profile) was used. For high pulse durations and low fluences the SiN x layer is removed completely by lift-off. However, for lower pulse durations and higher fluences, the SiN x layer is not completely removed, due to direct ablation. By using an emitter, direct ablation of SiN x layers were observed also for higher pulse durations. Thus, the absorption process in the SiN x layer can be described as avalanche ionization with seed electrons from silicon.