Patent ID: 8351024

Claim:
A level sensor configured to determine a height level of a substrate, the level sensor comprising: a projection unit to project a measurement beam on the substrate, the projection unit comprising a projection grating arranged to impart the measurement beam with a substantially periodic radiation intensity; a detection unit to receive the measurement beam after reflection on the substrate, the detection unit comprising: a detection grating arranged to receive the reflected measurement beam, the detection grating comprising at least one array of three or more segments together having a length substantially equal to a length of a period of the measurement beam projected on the detection grating, wherein the three or more segments are configured to split the reflected measurement beam in three or more reflected measurement beam parts, and three or more detectors each arranged to receive one of the three or more measurement beam parts; and a processing unit to calculate the height level on the basis of the measurement beam parts received by the three or more detectors.