Abstract: A method for measuring the depth of a subject trench includes the steps of forming on a substrate a plurality of measurement trenches having different widths aj (ai<aj+1, i=1, 2, . . . , n) and a depth equal to the depth d0 of the subject trench, irradiating the measurement trenches with a parallel ray at an incidence angle of &thgr; with respect to the substrate surface while detecting the reflected ray from the substrate, separating the measurement trenches into a first group providing dark images and a second group providing bright images, and calculating a range for the depth d0 by using a largest width ak of the measurement trenches in the first group and a smallest width ak+1 of the measurement trenches in the second group based on the following relationship: (ak/2)tan &thgr;<d0≦(ak+1/2)tan &thgr;.

Abstract: A method for measuring the depth of a subject trench includes the steps of forming on a substrate a plurality of measurement trenches having different widths aj (aj<aj+1, i=1, 2, . . .