A Novel Method for Measuring Thickness of Silicon Epitaxial Layer on Silicon Substrate

Currently the thickness of the silicon epitaxial (Epi) layer on the silicon substrate is measured and monitored using infrared spectroscopy (FTIR) or spreading resistance profiling (SRP). However, using these traditional failure analysis methods, the problems faced are with long analysis time and high analysis cost. In this paper, we proposed a novel method to measure the thickness of a silicon epitaxial (Epi) layer on a silicon substrate, by preparing a cross-section of a wafer sample and using a chemical staining technique to distinguish the silicon epitaxial layer from its silicon substrate successfully. The chemical staining solution is prepared from nitric acid with a mass concentration of 69% and hydrofluoric acid with a mass concentration of 49% in a volume ratio of 20:1, and DI water is used as a diluent. The final chemical staining recipe is H2O:HNO3:HF = 15:20:1 for 5 secs at room temperature 25°C. The method for measuring the thickness of the silicon epitaxial (Epi) layer on the silicon substrate proposed in this paper had been applied in process qualification, monitoring and failure analysis.