Seamless Stitching of Patterns Formed by Interference Lithography

Abstract

This invention addresses the scalability problem of periodic “nanostructured” surface treatments such as those formed by interference lithography. A novel but simple method is described that achieves seamless stitching of nanostructure surface textures at the pattern exposure level. The described tiling approach will enable scaling up of coherent nanostructured surfaces to arbitrary area sizes. Such a large form factor nanotechnology will be essential for fabricating large aperture, coherent diffractive elements. Other applications include high performance, antiglare/antireflection and smudge resistant Motheye treatments for display products such as PDA's, laptop computers, large screen TV's, cockpit canopies, instrument panels, missile and targeting domes, and, more recently, “negative-index” surfaces. Although ideal for seamless stitching of nanometer scale patterns, the technology is broadly applicable to any situation where an arbitrarily large area needs to be seamlessly tiled with a smaller base pattern that has periodic overlap able boundaries.

1 . A system for pattern stitching alignment using interference lithography comprising:
 (a) a movable stage for holding a substrate;   (b) a plurality of interfering exposure radiation beams configured to project a patterned beam of radiation onto first and second overlapping target portions of the substrate and having attenuation controls for modulating the intensity of the exposure beams;   (c) positioning control for positioning the exposure beams onto at least one surface of the substrate;   (d) means for dithering and stitch alignment fine relative positioning of the substrate;   (e) one or more sensors capable of detecting and measuring exposure beam signal intensities;   (f) a means for reducing electronic and ambient radiation noise; and   (g) a computer controller, having alignment feedback signal processing and automatic tiling and stitch alignment control, configured such that the exposure beams are capable of producing a first pattern during a first exposure period and a second pattern during a second exposure period.   
     
     
         2 . The system according to  claim 1 , wherein the attenuation controls modulate the intensity of the exposure beams from pre-exposure to full exposure intensity conditions. 
     
     
         3 . The system according to  claim 2 , further comprising differential phase controls for modulating a multi-beam interference fringe pattern to align the spatial phase of the fringes. 
     
     
         4 . The system according to  claim 3 , wherein the controller is configured to redistribute the pattern within the overlapping region. 
     
     
         5 . The system according to  claim 4 , wherein the positioning control comprises one or more course positioners for rough stitch tile positioning and one or more fine positioners with resolution suitable to the stitched pattern feature periods and wherein the positioning control is dithered to locate and lock the pre-exposure pattern to the previous exposed pattern in the overlap region. 
     
     
         6 . The system according to  claim 5 , wherein the fine positioning control is a phase control means for adjusting the phase of at least one of the interfering beams to control the interference pattern and thereby adjust the spatial phase of the pattern fringes. 
     
     
         7 . The system according to  claim 4 , wherein the exposure beams are single mode Gaussian beams delivered by collimating optics means. 
     
     
         8 . The system according to  claim 7 , wherein radiation reflection or transmission is measured by one or more photo-detectors. 
     
     
         9 . The system according to  claim 8 , wherein the exposure source radiation comprises collimating optics positioned to achieve cylindrical beam waists at the interference pattern on the substrate surface. 
     
     
         10 . The system according to  claim 9 , wherein a plurality of monochromatic beams is used to create the interference pattern on the substrate recording plane. 
     
     
         11 . The system according to  claim 10 , wherein the image processing for determining stitch alignment error polarity is by reflected image processing using a suitably reflecting or transmitting substrate. 
     
     
         12 . The system according to  claim 11 , wherein the positioning control is capable of differential phase sweep or dithering over at least 180 degrees during the fine positioning. 
     
     
         13 . The system according to  claim 11 , wherein the positioning control is capable of differential phase sweep or dithering over at least 270 degrees during the fine positioning using DC bias offset control level. 
     
     
         14 . The system according to  claim 2 , wherein the interference pattern is a linear grating pattern. 
     
     
         15 . The system according to  claim 14 , wherein the optic sensor comprises an objective lens aligned to image a small circular region of the recording plane within the stitch alignment region of the post exposure pattern and the current pre-exposure pattern. 
     
     
         16 . The system according to  claim 15 , further comprising an optical splitter within the path of the beam of light, wherein the optical splitter splits the beam of light into a plurality of beams of light. 
     
     
         17 . The system according to  claim 16 , wherein the beam splitting device is configured to split off a portion of the imaged intensity profile for high sensitivity analog feedback signal sensing using a photo-detector. 
     
     
         18 . The system according to  claim 17 , wherein the beam splitting device is configured to split off a portion of the imaged intensity profile to fall on an imaging device. 
     
     
         19 . The system according to  claim 18 , wherein the imaging device measures relative intensity while the photo-detector measures the total transmitted optical power. 
     
     
         20 . The system according to  claim 19 , wherein the image information is used to determine the stitch position error signal so as to generate a bipolar servo stitch alignment feedback signal.