Depth Profiling of Phosphorus in Photonic-Grade Silicon Using Laser-Induced Breakdown Spectrometry

Abstract

Laser-induced breakdown spectrometry (LIBS) has been evaluated for depth profiling of phosphorus doping in silicon. Laser plasmas were formed by focusing a Nd:YAG laser (operating in the second harmonic, 532 nm) on the sample surface. Plasma emission was collected, dispersed, and detected with the use of a charge-coupled device (CCD). Experimental parameters, such as delay time and sample position relative to the laser focal point, were optimized to improve the signal-to-background ratio of phosphorus line emission. Diffusion profiles by LIBS of samples with different phosphorus diffusion steps are shown. Crater depth per pulse and ablated mass per pulse were measured to be 1.2 μm pulse⁻¹ and 50 ng pulse⁻¹, respectively. The knowledge of depth per pulse permitted the estimation of thickness of the P diffusion layer.