Pulsed laser micro-deposition pattern formation

Abstract

A method of forming patterns on transparent substrates using a pulsed laser is disclosed. Various embodiments include an ultrashort pulsed laser, a substrate that is transparent to the laser wavelength, and a target plate. The laser beam is guided through the transparent substrate and focused on the target surface. The target material is ablated by the laser and is deposited on the opposite substrate surface. A pattern, for example a gray scale image, is formed by scanning the laser beam relative to the target. Variations of the laser beam scan speed and scan line density control the material deposition and change the optical properties of the deposited patterns, creating a visual effect of gray scale. In some embodiments patterns may be formed on a portion of a microelectronic device during a fabrication process. In some embodiments high repetition rate picoseconds and nanosecond sources are configured to produce the patterns.

What is claimed is: 
     
         1 . A method of pulsed laser deposition to produce a pattern on a medium, said medium being substantially transparent at a wavelength of said pulsed laser, said method comprising:
 generating pulsed laser beams from a pulsed laser source;   transmitting said pulsed laser beams through said medium;   focusing said pulsed laser beams onto a target, said target producing ejecta in response to an interaction of said pulsed beams and said target;   scanning said laser beams relative to said medium and target;   accumulating at least a portion of said ejecta on said medium to form material deposits on said medium; and   varying at least one of a laser beam scan speed and scan line density for controlling thickness of said material deposits to vary an optical density of a region of said medium, and to form a spatial pattern having varying optical density,   wherein said laser beam scan speed or said scan line density is varied according the gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.   
     
     
         2 . The method of  claim 1 , wherein said interaction causes sufficiently high temperature and pressure to expel ejecta sideways relative to said scan direction and to concentrate ejecta toward the periphery of the path of said laser beams such that the material deposits are formed with central low thickness portions bounded by immediately adjacent, thicker outer portions, and wherein said medium and said target are spaced apart by a gap, or are in direct physical contact, and the thickness of said deposits is controlled with a repetition rate and said scan speed of said laser beams. 
     
     
         3 . The method of  claim 1 , wherein said pulsed laser source provides a repetition rate from about 100 kHz to 1 GHz, a laser pulse having a pulse duration in the range from about 10 femtosecond up to 100 nanosecond, and a laser pulse energy in the range from about 100 nanoJoules (nJ) to about 100 microJoules (μJ). 
     
     
         4 . The method of  claim 1 , wherein said medium comprises glass, quartz, sapphire, or a polymer. 
     
     
         5 . The method of  claim 1 , wherein said target comprises a metal. 
     
     
         6 . The method of  claim 1 , wherein said target comprises a functional material for emitting light, said function comprising one or more of phosphor luminescence and electro-luminescence. 
     
     
         7 . The method of  claim 1 , wherein said target comprises a material for color printing. 
     
     
         8 . The method of  claim 1 , wherein said laser beam scan speed is in the range from about 1 mm/s to about 1 m/s, and utilized to produce accumulated deposition of material. 
     
     
         9 . The method of  claim 1 , wherein said medium is placed in contact with said target, or at a distance up to about 5 millimeters from said target. 
     
     
         10 . The method of  claim 1 , wherein said target has a surface with a roughness greater than an output wavelength of said laser source. 
     
     
         11 . The method of  claim 1 , wherein said pattern comprises a bitmap image or a vector graphic. 
     
     
         12 . The method of  claim 1 , wherein a grey scale image having a discernible feature is obtainable with ambient or controlled illumination of said pattern. 
     
     
         13 . The method of  claim 1 , wherein said medium is disposed between said source and said target, and said ejecta propagates reversely to the laser incidence direction. 
     
     
         14 . The method of  claim 1 , wherein said controlling comprises scanning said pulsed laser beams, and varying said scan speed. 
     
     
         15 . The method of  claim 1 , wherein controlling comprises scanning said pulsed beams and varying the line density of said pulsed beam scan. 
     
     
         16 . The method of  claim 1 , wherein controlling comprises scanning said pulsed beams in one or more of a raster or vector pattern over said target. 
     
     
         17 . A system for pulsed laser deposition to produce a pattern having optical density on a medium, said medium being is substantially transparent at a wavelength of said pulsed laser, said system comprising:
 a high repetition rate laser source for generating pulsed laser beams;   a beam delivery system, comprising: a focusing sub-system to transmit said pulsed laser beams through said medium and to focus said pulsed laser beams onto a target;   said target producing ejecta in response to an interaction of said pulsed beams and said target, accumulations of said ejecta forming material deposits on said medium; and   a controller coupled to said source and said beam delivery system and controlling thickness of said material deposits to form a spatial pattern having varying optical density, by controlling scanning of said laser beams relative to said medium and target such that at least one of a laser beam scan speed and scan line density is varied, and   wherein said laser beam scan speed or said scan line density is varied according to the gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.   
     
     
         18 . The system of  claim 17 , wherein said delivery system comprises a beam deflector, and said focusing sub-system comprises a scan lens. 
     
     
         19 . The system of  claim 17 , wherein said medium and said target are spaced apart by a gap providing separation, and said gap is configured to contain ambient air, flowing dry air or an inert gas. 
     
     
         20 . The system of  claim 17 , wherein said medium and said target are in direct contact. 
     
     
         21 . The system of  claim 17 , wherein the material deposits have central low thickness portions bounded by immediately adjacent, thicker outer portions, and wherein said medium and said target are spaced apart by a gap, or are in direct physical contact, and wherein said controller further controls a repetition rate of said pulsed laser beams and controls thickness of said deposits with said repetition rate and said scan speed of said laser beams. 
     
     
         22 . A method of pulsed laser deposition to produce a pattern on a medium, said medium being substantially transparent at a wavelength of said pulsed laser, said method comprising:
 generating pulsed laser beams from a pulsed laser source;   transmitting said pulsed laser beams through said medium;   focusing said pulsed laser beams onto a target, said target producing ejecta in response to an interaction of said pulsed beams and said target;   scanning said laser beams relative to said medium and target;   accumulating at least a portion of said ejecta on said medium to form material deposits on said medium, said deposits comprising a functional material that is operable to emit radiation in response to a stimulus; and   varying at least one of a laser beam scan speed and scan line density for controlling thickness of said material deposits to vary an optical property of said material deposits, and to form a spatial pattern having varying optical density,   wherein said laser beam scan speed or said scan line density is varied according to a gray scale of the pattern to be printed, the gray scale including at least three gray levels in a digitized image of said pattern.   
     
     
         23 . The method of  claim 22 , wherein an optical property of said functional material comprises one or more of phosphorescence, electro-luminescence, and selective light absorption and emission for visual color effects. 
     
     
         24 . The method of  claim 22 , wherein said stimulus comprises input radiation. 
     
     
         25 . A medium having a pattern formed thereon, said medium comprising material deposits formed, over microscopic region(s), with central low thickness portions bounded by immediately adjacent, thicker outer portions, said material deposits of said pattern providing for discernible images when viewed by the unaided eye or at low magnification. 
     
     
         26 . The medium of  claim 25 , wherein said pattern is viewed with ambient illumination. 
     
     
         27 . The medium of  claim 25 , wherein said pattern is viewed with controlled illumination. 
     
     
         28 . The medium of  claim 25 , wherein said pattern is formed with the pulsed laser deposition method of  claim 1 . 
     
     
         29 . The medium of  claim 25 , wherein said pattern is formed with the pulsed laser deposition method of  claim 22 .