A level sensor configured to determine a height level of a substrate is disclosed. The level sensor includes a projection unit to project a measurement beam having a substantially periodic radiation intensity on the substrate; a detection unit to receive the measurement beam after reflection on the substrate, the detection unit having 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, and 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 a height level on the basis of the measurement beam parts.