A method for detecting defects in deep features like channel holes, via holes or trenches based on laser-enhanced electron tunneling effect. A substrate having thereon a film stack is provided. First and second deep features are formed in the film stack. The first deep feature has a sacrificial oxide layer disposed at its bottom. The second deep feature comprises an under-etch defect. The sacrificial oxide layer has a thickness of less than 50 angstroms. The substrate is subjected to a laser-enhanced electron beam inspection process. The substrate is scanned by an electron beam and illuminated by a laser beam. The laser beam induces electron tunneling across the sacrificial protection layer, thereby capturing a bright voltage contrast (BVC) signal corresponding to the first deep feature, and detecting a dark voltage contrast (DVC) signal corresponding to the second deep feature.