Method for correcting disturbances in a level sensor light path

• Main Authors: VIGUURS MACHIEL JACOBUS J, BLOKLAND HUIBERT, VAN WELL ALEXANDER CHARLES F.A, VAN LOENHOUT ELKE, VAN ASTEN NICOLAAS ANTONIUS ALLEGONDUS J, OUWEHAND LUBERTHUS, BALAN OANA C, CHENG LUN K, BALTUS BAKKER HANS
• Format: Patent
• Language: English
• Published: 07.12.2006
• Subjects: APPARATUS SPECIALLY ADAPTED THEREFOR; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY; MATERIALS THEREFOR; MEASURING; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS; MEASURING LENGTH, THICKNESS OR SIMILAR LINEARDIMENSIONS; ORIGINALS THEREFOR; PHOTOGRAPHY; PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES,e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTORDEVICES; PHYSICS; TESTING

The invention relates to a level sensor for determining a height of a substrate. The level sensor generates one or more measurement beam and directs the measurement beam to a measurement spot on the substrate and produces a reflected measurement beam. The level sensor also generates one or more reference beams. A detector detects both the reflected measurement beam and the reference beam, respectively, and produces a measurement signal and a reference signal, respectively, the measurement signal being indicative for the height at the measurement spot. A processor that receives these signals and corrects the measurement signal based on the reference signal. The level sensor has an optical arrangement in a predetermined area close to where the substrate is to be located. The measurement beam and the reference beam propagate along substantially equal optical paths of propagation in the predetermined area. The optical arrangement deviates the reference beam from the substantially equal optical paths of propagation in the predetermined area such that the at least one reference beam does not hit the substrate.