Autofocus system and method

Abstract

New and useful concepts for an autofocus system and method are provided. A basic concept uses fringe projection in an autofocus system and method. A further aspect provides spatial filtering concepts for the fringe projection concept. In yet another aspect, the fringe projection autofocus system and method is provided with temporal phase shifting using no moving parts. In a still further aspect, the fringe projection autofocus system and method is provided with unambiguous height measurement concepts.

1 . An autofocus system comprising
 a. a fringe detection system configured to detect a fringe projection from a substrate that is movable relative to an imaging location,   b. a fringe projection system that projects fringes onto the substrate, the fringe projection system comprising one or more sources and fringes produced by beams that are directed onto and reflected from the substrate for each source,   c. a fringe relay system that relays beams reflected from the substrate to the fringe detection system in a manner such that the beams interfere at the fringe detection system, and   d. a processing system for processing data from the fringe detection system and producing output related to the orientation of the substrate relative to the imaging location.   
     
     
         2 . The autofocus system of  claim 1 , wherein the fringe projection system produces fringes that comprise two beams associated with each source that are directed onto and reflected by the substrate, and then relayed by the fringe relay system to interfere at the fringe detection system. 
     
     
         3 . The autofocus system of  claim 2 , wherein the fringe projection system comprises a grating that is illuminated by a collimated beam from each source. 
     
     
         4 . The autofocus system of  claim 3 , wherein the grating produces +1 and −1 diffracted order beams for each source, and the fringe projection system is configured to direct only the +1 and −1 diffracted order beams onto the substrate. 
     
     
         5 . The autofocus system of  claim 4 , wherein the fringe projection system comprises one or more non monochromatic sources, each of which produces a collimated beam that illuminates the grating. 
     
     
         6 . The autofocus system of  claim 5 , wherein the fringe relay system is configured to spatially separate projected beams reflected from the substrate in a manner such that projected interfering beams from each source do not overlap projected beams from other sources at the fringe detection system. 
     
     
         7 . The autofocus system of  claim 6 , wherein the fringe detection system comprises an area detector for detecting projected fringes produced by interfering beams from each source. 
     
     
         8 . The autofocus system of  claim 7 , wherein the fringe projection system and the fringe detection system are configured to provide temporal phase shifting in the fringes reflected from the substrate that are relayed to the fringe detection system. 
     
     
         9 . The autofocus system of  claim 8 , wherein the fringe projection system and the fringe detection system are configured to provide temporal phase shifting by synchronizing the rate of capture of the projected fringes by the area detector with the movement of the substrate relative to the imaging location, to enable detection of projected fringes at a predetermined set of phase differences from the same region of the substrate to a different region on the area detector as the substrate moves relative to the imaging location. 
     
     
         10 . The autofocus system of  claim 1 , wherein the fringe detection system comprises an area detector for detecting projected fringes produced by interfering beams from each source. 
     
     
         11 . The autofocus system of  claim 10 , wherein the fringe projection system and the fringe detection system are configured to provide temporal phase shifting in the fringes reflected from the substrate that are relayed to the fringe detection system. 
     
     
         12 . The autofocus system of  claim 11 , wherein the fringe projection system and the fringe detection system are configured to provide temporal phase shifting by synchronizing the rate of capture of the projected fringes by the area detector with the movement of the substrate relative to the imaging location, to enable detection of projected fringes at a predetermined set of phase differences from the same region of the substrate to a different region on the area detector as the substrate moves relative to the imaging location. 
     
     
         13 . The autofocus system of  claim 6 , wherein the fringe projection system, the fringe relay system, the fringe detection system and the processing system are configured to correct for Goos Hanchen errors. 
     
     
         14 . The autofocus system of  claim 13 , wherein the fringe detection system comprises an area detector, wherein the fringe projection system and the fringe relay system are configured to project and relay beams at plural wavelength bands and plural polarization states to the area detector, and wherein the processing system is configured to process the detected fringes with a set of coefficients designed to enable compensation for Goos Hanchen errors. 
     
     
         15 . The autofocus system of  claim 1 , wherein the processing system is configured to correct for geometric errors produced by substrate tilt. 
     
     
         16 . The autofocus system of  claim 1 , wherein the fringe projection system is further configured to project beams from at least one source to a reflector that is separate from the substrate, and beams from the reflector are projected to the detection system for use by the processing system as a reference fringe pattern in the production of the autofocus information. 
     
     
         17 . The autofocus system of  claim 1 , wherein the processing system is configured to spatially filter data from the fringe detection system to remove pattern induced errors outside a predetermined spatial frequency range. 
     
     
         18 . The autofocus system of  claim 1 , wherein the fringe relay system comprises a pupil plane and a spatial filter device located in the pupil plane, and wherein the spatial filter device is configured to suppress scattered light projected from the substrate while passing specularly reflected light from the substrate. 
     
     
         19 . The autofocus system of  claim 6 , wherein the fringe projection system, the fringe relay system, the fringe detection system, and the processing are configured to allow unambiguous autofocus processing. 
     
     
         20 . The autofocus system of  claim 19 , wherein the fringe detection system comprises an area detector, the fringe projection system is configured so that the rate of fringe shift with substrate height is different for the different sources, and the processing system is configured to estimate the unambiguous height of the substrate. 
     
     
         21 . The autofocus system of  claim 5 , wherein the fringe projection system is configured to introduce a delay in one of the two beams associated with each of the one or more sources that is longer than the respective coherence length, and the relay system is configured to introduce a compensating delay in the other of the two beams associated with each of the one or more sources, producing fringes at the detector and not at the substrate and reducing the effect of light scattered by the substrate. 
     
     
         22 . An autofocus method comprising
 a. projecting fringes from each of one or more sources onto a substrate that is moveable relative to an imaging location, where the fringes are produced by beams from each of the one or more sources that are directed onto and reflected by the substrate,   b. relaying reflected beams from the substrate to a fringe detection system in a manner such that the beams interfere at the fringe detection system, and   c. processing data from the fringe detection system to produce output related to the orientation of the substrate relative to the imaging location.   
     
     
         23 . The autofocus method of  claim 22 , wherein the projection of fringes onto the substrate comprises producing two beams associated with each source that are directed onto and reflected by the substrate, and then relayed to interfere at the fringe detection system. 
     
     
         24 . The autofocus method of  claim 23 , wherein projecting fringes onto the substrate comprises illuminating a grating by a collimated beam from each source. 
     
     
         25 . The autofocus method of  claim 24 , wherein the grating produces +1 and −1 diffracted order beams for each source, and projecting the fringes onto the substrate comprises directing only the +1 and −1 diffracted order beams onto the substrate. 
     
     
         26 . The autofocus method of  claim 25 , wherein projecting fringes onto the substrate comprises providing one or more non monochromatic sources, and producing from each non monochromatic sources a collimated beam that illuminates the grating. 
     
     
         27 . The autofocus method of  claim 26 , wherein relaying reflected beams from the substrate comprises spatially separating beams reflected from the substrate in a manner such that projected beams from each source do not overlap projected beams from other sources at the fringe detection system. 
     
     
         28 . The autofocus method of  claim 27 , wherein the fringe detection system comprises an area detector, and relaying reflected beams from the substrate to the fringe detection system comprises relaying the reflected beams in a manner such that the beams interfere at the area detector. 
     
     
         29 . The autofocus method of  claim 28 , including providing temporal phase shifting in the beams reflected from the substrate that are relayed to the fringe detection system. 
     
     
         30 . The autofocus method of  claim 29 , wherein providing temporal phase shifting comprises synchronizing the rate of capture of the projected fringes by the area detector with the movement of the substrate relative to the imaging location, to enable detection of projected fringes at a predetermined set of phase differences from the same region of the substrate to a different region on the area detector as the substrate moves relative to the imaging location. 
     
     
         31 . The autofocus method of  claim 22 , wherein the fringe detection system comprises an area detector, and relaying reflected beams from the substrate to the fringe detection system comprises relaying the reflected beams in a manner such that the beams interfere at the area detector. 
     
     
         32 . The autofocus system of  claim 31 , including providing temporal phase shifting in the beams reflected from the substrate that are relayed to the fringe detection system. 
     
     
         33 . The autofocus method of  claim 32 , wherein providing temporal phase shifting comprises synchronizing the rate of capture of the projected fringes by the area detector with the movement of the substrate relative to the imaging location, to enable detection of projected fringes at a predetermined set of phase differences from the same region of the substrate to a different region on the area detector as the substrate moves relative to the imaging location. 
     
     
         34 . The autofocus method of  claim 27 , including providing correction for Goos Hanchen errors. 
     
     
         35 . The autofocus method of  claim 34 , wherein the fringe detection system comprises an area detector, wherein providing correction for Goos Hanchen errors comprises configuring the projecting of fringes from each of one or more sources onto the substrate and the relaying of reflected beams from the substrate to the fringe detection system comprises projecting and relaying beams at plural wavelength bands and plural polarization states to the area detector, the processing of data from the fringe detection system comprises processing the detected fringes with a set of coefficients designed to enable compensation for Goos Hanchen errors. 
     
     
         36 . The autofocus method of  claim 22 , including processing the data from the fringe detection system in a manner that corrects for geometric errors produced by substrate tilt. 
     
     
         37 . The autofocus method of  claim 22 , including projecting beams from at least one source to a reflector that is separate from the substrate, and projecting beams from the reflector to the fringe detection system for use by the processing system as a reference fringe pattern in the production of the autofocus information. 
     
     
         38 . The autofocus method of  claim 22 , including processing the data from the fringe detection system to spatially filter the data in a manner that removes pattern induced errors outside a predetermined spatial frequency range. 
     
     
         39 . The autofocus method of  claim 22 , wherein relaying reflected beams from the substrate to the fringe detection system comprises suppressing scattered light projected from the substrate while passing specularly reflected light from the substrate to the fringe detection system. 
     
     
         40 . The autofocus method of  claim 27 , wherein configuring the projecting of fringes from each of one or more sources onto the substrate, relaying of reflected beams from the substrate to the fringe detection system, and processing the data from the fringe detection system are configured to allow unambiguous autofocus processing. 
     
     
         41 . The autofocus method of  claim 40 , wherein the fringe detection system comprises an area detector, the projecting of fringes from each of the one or more sources onto the substrate and the relaying of reflected beams from the substrate are configured so that the rate of fringe shift with substrate height is different for the different sources, and the processing of data from the fringe detection system is configured to estimate the unambiguous height of the substrate. 
     
     
         42 . The autofocus method of  claim 26 , wherein the projecting of fringes onto the substrate is configured to introduce a delay in one of the two beams associated with each of the one or more sources that is longer than the respective coherence length, and the relaying of reflected beams from the substrate is configured to introduce a compensating delay in the other of the two beams associated with each of the one or more sources, producing fringes at the detector and not at the substrate and reducing the effect of light scattered by the substrate.