Laser ablation ICP-MS to determine Cu on a Si wafer prepared by ion sputtering

Abstract

This work describes an analytical method using laser ablation (LA)-ICP-MS to determine the Cu metal deposited on a silicon wafer by ion sputtering, which can be applied to control the manufacturing process of semiconductors and silicon-based solar cells. The number of Cu atoms on a layer with thickness of 1.0 µm was determined to be 1.1 × 10¹³ (±2%) atoms per cm² by ICP-MS with chemical vapour deposition followed by radial scanning. Since LA-ICP-MS lacks proper standards for silicon wafer analysis, a glass NIST SRM 616 was used as a reference material. For the calculation of Cu level, the concentration ratio of Cu on the silicon wafer to the glass SRM was determined by a non-matrix matched standard addition using a desolvation nebulizer. Due to the internal standard effect of the nebulized aerosols, this method minimized experimental errors caused by possible fluctuations in particle generation, transportation and ionization. In order to quantify the Cu on a silicon wafer, the weight of particles transported to the plasma was estimated to be approximately 15 ng per single laser shot. The number of Cu atoms on the wafer was determined to be 9.3 × 10¹¹ (±28.7%) atoms per cm². The most significant error occurred during the ablation process resulted from the interaction of the laser beam with the surface material, which produced irregular craters and particles due to their unique physical properties of reflective index and hardness.