Understanding damage caused by mechanical grinding is required for wafer thinning processes, because such damage significantly affects device performance in large-scale integrated circuits. Herein, in-depth analysis of damage caused by mechanical grinding was conducted by measuring minority carrier lifetime and by the photoacoustic displacement (PAD) technique, which are highly sensitive and quantitative methods for measuring damage. Previous low-sensitivity damage measurements indicate that grinding damage is distributed within a 5-μm-thick surface layer. However, although a 10-μm-thick surface layer is removed by chemical spin etching (CSE), the minority carrier lifetime remains low. This result suggests that significant damage still exists in layers deeper than 10 μm. After etching a 200-μm-thick layer, PAD measurements show that displacement at the surface recovers to 20 pm, which is the level of undamaged silicon. While minority carrier lifetime gradually increases with increased etching, this lifetime remains low after removing a 100-μm-thick strain layer. The minority carrier lifetime reaches that of defect-free silicon after removing a 300-μm-thick layer. These results clearly indicate that deep damage (i.e., depth of 200 μm) is caused at the silicon surface by conventional mechanical grinding. Additionally, we conclude that the CSE process is useful for thinning silicon wafers without inducing damage or strain.