Patent ID: 7115426

Claim:
A method for, during formation of a trench a portion of the way through a semiconductor substrate sample from a first substrate surface to a second substrate surface, said trench having a trench floor, said trench floor having a thickness profile relative to said second substrate surface, determining the uniformity of said thickness profile, comprising the steps of: a) optically observing thickness non-uniformity-related interference fringes at said trench floor during trench formation; b) determining and quantifying the thickness non-uniformity across said trench floor from said observation of said interference fringes, by at least one of 1) determining thicknesses at multiple points, and 2) guanatitatively determining the slope of said trench floor at at least one location: c) forming a map of the thickness profile across the trench floor: thereby enabling compensating for said thickness non-uniformity.