Laser-based method and system for processing targeted surface material and article produced thereby

Abstract

A laser-based method and system for processing targeted surface material and article produced thereby are provided. The system processes the targeted surface material within a region of a workpiece while avoiding undesirable changes to adjacent non-targeted material. The system includes a primary laser subsystem including a primary laser source for generating a pulsed laser output including at least one pulse having a wavelength and a pulse width less than 1 ns. A delivery subsystem irradiates the targeted surface material of the workpiece with the pulsed laser output including the at least one pulse to texture the targeted surface material. The pulsed laser output has sufficient total fluence to initiate ablation within at least a portion of the targeted surface material and the pulse width is short enough such that the region and the non-targeted material surrounding the material are substantially free of slag.

1 . A method for processing targeted surface material within a region of a workpiece while avoiding undesirable changes to adjacent non-targeted material, the method comprising: 
 generating a pulsed laser output including at least one pulse having a wavelength and a pulse width;    irradiating the targeted surface material of the workpiece with the pulsed laser output including the at least one pulse to texture the targeted surface material, the pulsed laser output having sufficient total fluence to initiate ablation within at least a portion of the targeted surface material and the pulse width being short enough such that the region and non-targeted material surrounding the region are substantially free of slag.    
     
     
         2 . The method as claimed in  claim 1 , wherein the textured surface material comprises indicia and wherein the indicia is at least semi-permanent or erasable.  
     
     
         3 . The method as claimed in  claim 1 , wherein the targeted surface material is at least one of a semiconductor substrate, a thin film, a metal layer and a dielectric layer.  
     
     
         4 . The method as claimed in  claim 1 , wherein the workpiece is one of a MEMs device, an optoelectronic device and a biomedical chip.  
     
     
         5 . The method as claimed in  claim 2 , wherein the indicia are machine-readable and wherein the indicia have a font size less than 0.3 mm.  
     
     
         6 . The method as claimed in  claim 1 , further comprising generating a secondary laser output and irradiating the textured surface material with the secondary laser output to process the textured surface material.  
     
     
         7 . The method as claimed in  claim 6 , wherein the textured surface material comprises indicia and wherein the indicia are erased during the step of irradiating with the secondary laser output.  
     
     
         8 . The method as claimed in  claim 1 , wherein the textured surface material comprises a microtextured pattern and wherein the pattern is one of a bar pattern, a matrix pattern, an alphanumeric character string, and a logotype.  
     
     
         9 . The method as claimed in  claim 1 , wherein the pulse width of the at least one pulse is below about 1 ns.  
     
     
         10 . The method as claimed in  claim 9 , wherein the pulse width is about 100 ps or less.  
     
     
         11 . The method as claimed in  claim 1 , wherein the total fluence is measurable over a spatial dimension of a spot of the output.  
     
     
         12 . The method as claimed in  claim 11 , wherein the textured surface material comprises indicia and where the step of irradiating includes the step of directing the laser output in response to at least one control signal that represents a first location of at least a part of the indicia to impinge the region at the first location.  
     
     
         13 . The method as claimed in  claim 1 , wherein the step of irradiating substantially increases surface roughness of the targeted surface material within at least a portion of the region.  
     
     
         14 . The method as claimed in  claim 1 , wherein the non-targeted surface material surrounding the region has a surface with a strong specular reflection component.  
     
     
         15 . The method as claimed in  claim 2 , wherein diffuse reflectance of the indicia is in a range of 0.5% to 5%.  
     
     
         16 . The method as claimed in  claim 1 , wherein the total fluence exceeds about 0.1 J/cm 2 .  
     
     
         17 . The method as claimed in  claim 1 , wherein the wavelength is less than an absorption edge of the targeted surface material.  
     
     
         18 . The method as claimed in  claim 1 , wherein the wavelength is ultraviolet.  
     
     
         19 . The method as claimed in  claim 1 , wherein the targeted surface material is silicon.  
     
     
         20 . The method as claimed in  claim 1 , wherein the targeted surface material is a metal or a dielectric.  
     
     
         21 . The method as claimed in  claim 1 , wherein the targeted surface material is a portion of a dielectric passivation layer and wherein the dielectric of the layer is an inorganic, organic, or a low-k dielectric.  
     
     
         22 . The method as claimed in  claim 1 , wherein the targeted surface material is part of a MEM device.  
     
     
         23 . The method as claimed in  claim 2 , wherein a portion of the indicia has surface variations in a range of about 0.25 microns to about 1 micron.  
     
     
         24 . The method as claimed in  claim 2 , wherein a feature dimension of the indicia is in a range of several microns to tens of microns.  
     
     
         25 . The method as claimed in  claim 2 , wherein a feature dimension of the indicia is a few wavelengths of the at least one pulse.  
     
     
         26 . The method as claimed in  claim 1 , wherein the step of irradiating includes the step of controlling polarization of the pulsed laser output to enhance or control a characterization of the textured surface material.  
     
     
         27 . The method as claimed in  claim 11 , wherein the step of irradiating includes the step of shaping the spot to obtain a shaped spot.  
     
     
         28 . The method as claimed in  claim 27 , wherein the shaped spot has a top-hat irradiance profile.  
     
     
         29 . The method as claimed in  claim 27 , wherein the shaped spot has a depressed center with energy concentrated in a perimeter of the shaped spot.  
     
     
         30 . The method as claimed in  claim 6 , wherein the pulsed laser output finely textures the targeted surface material and the secondary laser output coarsely processes the textured surface material.  
     
     
         31 . The method as claimed in  claim 6 , wherein the pulsed laser output coarsely textures the targeted surface material and the secondary laser output finely processes the textured surface material.  
     
     
         32 . The method as claimed in  claim 6 , wherein the textured surface material comprises indicia and wherein a negative window mark is created during the step of irradiating with the secondary laser output.  
     
     
         33 . The method as claimed in  claim 6 , wherein the textured surface material comprises a pattern and wherein the step of irradiating with the secondary laser output micromachines the pattern.  
     
     
         34 . The method as claimed in  claim 6 , wherein the step of irradiating with the secondary laser output trims an electrical or mechanical parameter of the textured surface material.  
     
     
         35 . The method as claimed in  claim 6 , wherein the secondary laser output includes at least one pulse having a wavelength which is absorbed into the textured surface material.  
     
     
         36 . The method as claimed in  claim 35 , wherein the wavelength of the at least one pulse of the secondary beam is also absorbed into the non-targeted material surrounding the region.  
     
     
         37 . The method as claimed in  claim 35 , wherein the wavelength of the at least one pulse of the secondary beam is not absorbed into the non-targeted material surrounding the region.  
     
     
         38 . A system for processing targeted surface material within a region of a workpiece while avoiding undesirable changes to adjacent non-targeted material, the system comprising: 
 a primary laser subsystem include a primary laser source for generating a pulsed laser output including at least one pulse having a wavelength and a pulse width;    a delivery subsystem for irradiating the targeted surface material of the workpiece with the pulsed laser output including the at least one pulse to texture the targeted surface material, the pulsed laser output having sufficient total fluence to initiate ablation within at least a portion of the targeted surface material and the pulse width being short enough such that the region and the non-targeted material surrounding the material are substantially free of slag.    
     
     
         39 . The system as claimed in  claim 38 , wherein the primary laser source includes an ultrafast laser.  
     
     
         40 . The system as claimed in  claim 38 , wherein the delivery subsystem includes a controller that accepts data that represents a location of the targeted surface material to be textured and produces at least one position control signal.  
     
     
         41 . The system as claimed in  claim 40 , wherein the delivery subsystem includes a positioning subsystem for directing the laser output to the location of the targeted surface material so as to texture the targeted surface material in response to the at least one position control signal.  
     
     
         42 . The system as claimed in  claim 38 , further comprising a secondary laser subsystem including a secondary laser source for generating a secondary laser output which irradiates the textured surface material.  
     
     
         43 . The system as claimed in  claim 42 , wherein the secondary laser output at least erases, micromachines, welds or actuates the region of the textured surface material.  
     
     
         44 . The system as claimed in  claim 42 , wherein the secondary laser source includes one of a pulsed, modulated or CW source.  
     
     
         45 . The system as claimed in  claim 42 , wherein irradiation with the secondary laser output is below the fluence breakdown threshold of the targeted surface material to heat the region.  
     
     
         46 . The system as claimed in  claim 42 , wherein irradiation with the secondary laser output is above the fluence breakdown threshold of the targeted surface material to effect at least one property change of the targeted surface material.  
     
     
         47 . The system as claimed in  claim 42 , wherein the secondary laser output includes at least one pulse having a wavelength near or exceeding the absorption edge of the material of the workpiece.  
     
     
         48 . The system as claimed in  claim 42 , wherein the primary laser source comprises the secondary laser source.  
     
     
         49 . The system as claimed in  claim 42  wherein the primary laser source is separate from the secondary laser source.  
     
     
         50 . The system as claimed in  claim 38 , wherein the delivery subsystem includes a polarization controller for controlling polarization of the laser output.  
     
     
         51 . The system as claimed in  claim 38 , wherein the primary laser source includes a diode-pumped, solid-state UV laser and wherein the pulse width is less than about 20 ns.  
     
     
         52 . The system as claimed in  claim 51 , wherein the pulse width is less than about 1 ns.  
     
     
         53 . The system as claimed in  claim 41 , wherein the positioning subsystem includes at least one translation stage to move the workpiece relative to the laser output.  
     
     
         54 . The system as claimed in  claim 38 , wherein the primary laser source includes a mode-locked oscillator and a diode-pumped, solid-state laser amplifier.  
     
     
         55 . The system as claimed in  claim 38 , wherein the laser output has an average laser output power in the range of 0.01 W-2 W.  
     
     
         56 . The system as claimed in  claim 38 , wherein the textured surface material comprises indicia and wherein the system further comprises a viewing subsystem for reading the indicia, the viewing subsystem including an illuminator and an electronic imaging subsystem.  
     
     
         57 . The system as claimed in  claim 56 , wherein the illuminator is one of a bright-field, a dark-field, and a combination of both bright- and dark-field.  
     
     
         58 . An article of manufacture comprising: 
 at least one surface material having discernible indicia formed thereon during at least one step of manufacturing the article, the indicia being formed by a method of selectively irradiating targeted surface material within a region of a workpiece with a pulsed laser output, the indicia being at least semi-permanent and useable during a subsequent step of manufacturing the article;    the region and non-targeted material surrounding the region are substantially slag-free; and    surface roughness is increased within at least a portion of the region during the at least one step of manufacturing, thereby reducing reflection of energy used for reading the indicia.    
     
     
         59 . The article as claimed in  claim 58 , wherein high reflectance contrast is obtained between the region and a background of the region over a wide range of viewing angles.  
     
     
         60 . The article as claimed in  claim 58 , wherein a surface of the background of the region has a strong specular reflection component.  
     
     
         61 . The article as claimed in  claim 58 , wherein reflectance contrast between the discernible indicia and a background of the region exceeds 30:1 over an angular viewing range of at least 20 degrees.  
     
     
         62 . The article as claimed in  claim 58 , wherein the indicia include an alphanumeric indicium having a font dimension 0.3 mm or finer.  
     
     
         63 . The article as claimed in  claim 58 , wherein the indicia include a two-dimensional matrix code.  
     
     
         64 . The article as claimed in  claim 58 , wherein the indicia are useable for one or more steps of manufacturing the article in addition to identification.  
     
     
         65 . The article as claimed in  claim 58 , wherein the indicia are distinguishable from a background of the region with a roughness measurement obtained by at least one of SEM (scanning electron microscope) data, and AFM (atomic force microscope) data.  
     
     
         66 . The article as claimed in  claim 58 , wherein DIN 4768 roughness measurement standards may be utilized to compare roughness of a portion of the indicia with a background of the region.  
     
     
         67 . The article as claimed in  claim 58 , wherein the indicia are distinguishable from a background of the region with a measurement of image contrast.  
     
     
         68 . The article as claimed in  claim 58 , wherein the indicia are machine readable.  
     
     
         69 . The article as claimed in  claim 58 , wherein the indicia appear as a sequence of non-overlapping dots that form a dot matrix code.  
     
     
         70 . The article as claimed in  claim 58 , wherein the indicia are usable in at least one of traceability, component identification, and sorting.