Patent ID: 9568304
Date: 2017-02-14
CPC Classifications: G01B,G02B

Claim:
1. A method for determining the height of a plurality of spatial positions on a surface of a specimen, the method comprising: projecting a light beam on the surface of the specimen, the light beam having a spatial pattern which is periodic in at least two directions perpendicular to an optical axis of the light beam; moving the spatial pattern to different spatial pattern positions; scanning the surface along the optical axis in different scanning positions, wherein there is a fixed relationship between a moving distance between subsequent spatial pattern positions, and a scanning distance between subsequent scanning positions; detecting the light reflected by the surface in scanning positions with the spatial pattern having corresponding spatial pattern positions; determining, from the detected light for each spatial position of the surface, an envelope curve of intensity values corresponding to scanning positions; and selecting a maximum of the envelope curve and its corresponding scanning position being representative of the height of the spatial position of the surface, wherein the spatial pattern is a sinusoidal pattern having a pattern wavelength in the at least two directions, the spatial pattern being moved in a sequence of 2n steps (n>2), the spatial pattern being moved by n times repeating the following steps (a)-(c) involving a starting spatial pattern position, and a next spatial pattern position: (a) moving the spatial pattern relative to the starting spatial pattern position in a first spatial direction over a first moving distance of ¼ pattern wavelength; (b) moving the spatial pattern relative to the starting spatial pattern position in a second spatial direction over a second moving distance of 1/n pattern wavelength to the next spatial pattern position; and (c) making this next position the starting spatial pattern position.