US Patent 7481944 Etch amount detection method, etching method, and etching system

This invention accurately detects an etch amount of an etching target layer irrespective of a type of a mask layer. A light La is reflected by an upper surface of a photoresist mask layer 316 and a bottom of a hole H. Thereby a reflected light La1 and a reflected light La2 are obtained. The reflected lights La1 and La2 interfere with each other, thereby generating an interference light Lai. A light Lb is reflected by an interface between the photoresist mask layer 316 and a polysilicon film 304, and the upper surface of the photoresist mask layer 316. Thereby a reflected light Lb1 and a reflected light Lb2 are obtained. The reflected lights Lb1 and Lb2 interfere with each other, thereby generating an interference light Lb1. Using the interference lights Lai and Lbi, an etch amount of the polysilicon film 304 is calculated.