Method and apparatus for measuring depth of holes formed on a specimen

A method of measuring an amount of over-etching of a hole on a sample, comprising the steps of:

• acquiring height profile information of the sample, having hole patterns formed in an insulator layer thereof, on a plurality of hole patterns by scanning with a sytlus on the surface of the sample in which the hole patterns are formed by etching:
• and
• measuring the depths of said hole patterns on the bottom faces of hole patterns and in the respective vicinities of said hole patterns on the basis of said height profile information;
• wherein said hole patterns include a regular hole formed in the insulator layer located on a stopper layer having smaller etching rate compared to said insulator layer and a dummy hole formed in the insulator layer adjoining said regular hole where there is no stopper layer and both said regular hole and said dummy hole are formed together in an etching process further comprising a step of calculating an over-etching amount of said regular hole using measured depths both of said regular hole and said dummy hole and etching rates both of said insulator layer and said stopper layer.