Patent ID: 7481944

Claim:
An etch amount detection method for detecting an etch amount of an etching target layer when an etching process is carried out to the etching target layer on an object to be processed while using a patterned mask layer as a mask, the method comprising steps of: irradiating a first light having a first wavelength, which does not propagate the mask layer, and a second light having a second wavelength, which is different from said first wavelength and propagates the mask layer, onto said object to be processed; detecting a first interference light generated by interference of a first reflected light obtained when said first light is reflected by a surface of said mask layer with a second reflected light obtained when said first light is reflected by a bottom of an etching target portion etched of said etching target layer; detecting a second interference light generated by interference of a third reflected light obtained when said second light is reflected by the surface of said mask layer with a fourth reflected light obtained when said second light is reflected by an interface between said mask layer and said etching target layer; and calculating an etch amount of said etching target portion based on said first interference light and said second interference light.