Laser processing method and processing device

Abstract

Laser beam is irradiated to a surface of a processing target after reforming a cross section of the laser beam with a mask having a pierced hole by concentrating the laser beam passing through the pierced hole by a lens to foreman image of the pierced hole of the mask on the surface of the processing target. The laser beam passing through the lens is scanned to move an irradiating position of the laser beam on the surface of the processing target, and the image of the pierced hole of the mask is formed on the surface of the processing target during the scanning for processing the processing target. A high quality laser process can be carried out.

1 . A laser processing method, comprising the steps of: 
 (a) irradiating laser beam from a laser source through an optical system onto a surface of a processing target; and    (b) scanning said laser beam on the surface of the processing target by the optical system and so controlling at least one parameter among those of said laser source and said optical system that variation of an irradiating condition of the laser beam on the processing target caused by the scanning is suppressed.    
   
   
       2 . The laser processing method according to  claim 1 , wherein 
 said step (a) shapes a cross section of the laser beam with a mask having a pierced hole, and collects light of the laser beam passed through the pierced hole and focuses the pierced hole of the mask on the surface of the processing target by a lens, and    said step (b) controls the optical system so that the pierced hole of the mask is focused on the surface of the processing target during the scanning of the laser beam.    
   
   
       3 . The laser processing method according to  claim 2 , wherein 
 said step (b) controls the optical system so that an optical length between the mask and the lens and an optical length between the lens and the surface of the processing target are fixed.    
   
   
       4 . The laser processing method according to  claim 2 , wherein 
 said step (b) comprises the step of moving the lens along a direction parallel to a direction of the laser beam passing through the lens and moving the mask along a direction parallel to a direction of the laser beam passing through the mask.    
   
   
       5 . The laser processing method according to  claim 2 , wherein 
 said step (a) shapes a beam spot on the surface of the processing target in a shape having a pair of parallel sides, and    said step (b) moves the beam spot along a direction parallel to the pair of parallel sides.    
   
   
       6 . The laser processing method according to  claim 2 , wherein the laser beam on the surface of the processing target has density distribution in which strength in a peripheral area of the beam spot is greater than strength in a central part of the beam spot.  
   
   
       7 . The laser processing method according to  claim 2 , wherein the laser beam is pulsed laser beam, and 
 said step (b) comprises the step of increasing pulse energy of the laser beam when an incident angle of the laser beam to the surface of the processing target becomes large.    
   
   
       8 . The laser processing method according to  claim 2 , wherein 
 said step (b) moves the mask and the lens to decrease a variation in an area of the beam spot on the surface of the processing target when an incident angle of the laser beam on the surface of the processing target is varied.    
   
   
       9 . The laser processing method according to  claim 1 , wherein 
 said step (a) condenses the laser beam by a lens, and    said step (b) controls the optical system so that change in optical length between the lens and the surface of the processing target is suppressed.    
   
   
       10 . The laser processing method according to  claim 9 , wherein said step (b) comprises the step of moving the lens along a direction of the laser beam passing through the lens.  
   
   
       11 . The laser processing method according to  claim 9 , wherein the laser beam irradiating on the lens is collimated beam, and an optical length between the lens and the surface of the processing target is same as a focal length of the lens.  
   
   
       12 . The laser processing method according to  claim 1 , wherein 
 said step (a) condenses the laser beam by a lens, and    said step (b) controls at least one of the laser source and the optical system so that variation in pulse energy density or power density of the laser beam on the surface of the processing target caused by shift of an incident point is suppressed when the incident point of the laser beam on the processing target is moved.    
   
   
       13 . The laser processing method according to  claim 12 , wherein said step (b) comprises the step of moving the lens along a direction of the laser beam passing through the lens.  
   
   
       14 . The laser processing method according to  claim 13 , wherein said step (b) so moves the lens along the direction of the laser beam that a focal point of the laser beam goes away from the incident point on the target when increase in the pulse energy density or power density of the laser beam on the surface of the processing target is suppressed, and so moves the lens along the direction of the laser beam that a focal point of the laser beam comes closer to the incident point on the target when decrease in the pulse energy density or power density of the laser beam on the surface of the processing target is suppressed.  
   
   
       15 . The laser processing method according to  claim 12 , wherein said step (b) adjusts power of the laser beam by using a variable attenuator.  
   
   
       16 . The laser processing method according to  claim 1 , wherein 
 said step (a) condenses the laser beam by a lens, and    said step (b) suppresses a variation in an area of a beam spot of the laser beam on the surface of the processing target caused by motion of an incident point when the incident point of the laser beam on the processing target is moved.    
   
   
       17 . The laser processing method according to  claim 16 , wherein said step (b) comprises the step of moving the lens along a direction of the laser beam passing through the lens.  
   
   
       18 . A laser processing method, comprising the steps of: 
 (c) obtaining a spread angle of laser beam and a distance between proximity mask and a surface of a processing target in accordance with a relationship among a spread angle of the laser beam passing through the proximity mask having a pierced hole, a distance between the proximity mask and the surface of the processing target and precision of transferring the pierced hole of the proximity mask on the surface of the processing target; and    (d) transferring the pierced hole on the surface of the processing target by irradiating the laser beam of which spread angle is adjusted by a value obtained in said step (c) and passing through the pierced hole of the proximity mask of which distance to the surface of the processing target is adjusted by a value obtained in said step (c) onto the surface of the processing target, while sweeping the laser beam.    
   
   
       19 . A laser processing method, comprising the steps of: 
 (e) irradiating continuous-wave laser beam from a laser source through an optical system which can be switched over between a first configuration in which the laser beam is emitted and a second configuration in which the laser beam is not emitted;    (f) projecting the laser beam emitted from the optical system on a mask having a rectangle-shaped pierced hole to shape a cross section, condensing the laser beam by a lens, and focusing an image of the pierced hole on a surface of a processing target; and    (g) moving the image of the pierced hole along a direction parallel to a side of the rectangle image on the surface of the processing target wherein    said step (e) emits the laser beam from the optical system intermittently when discrete dotted pattern is to be formed on the surface of the processing target, and    said step (e) emits the laser beam from the optical system continuously when a linear pattern is to be formed on the surface of the processing target.    
   
   
       20 . The laser processing method according to  claim 19 , further comprising, after the step (g), the steps of: 
 (h) rotating the mask around an axis parallel to a direction of the laser beam so that the image of the pierced hole rotates on the surface of the processing target; and    (i) moving the image of the rotated pierced hole on the surface of the processing target along a direction parallel to a side of the rotated image of the rectangle pierced hole.    
   
   
       21 . A laser processing method, comprising the steps of: 
 (j) emitting pulsed laser beam from a first laser source and continuous-wave laser beam from a second laser source;    (k) preheating a target spot defined on a surface of a processing target having abase layer and a surface layer formed of a material that is harder to be processed by laser irradiation than the base layer, with the continuous-wave laser beam from the second laser source, and thereafter irradiating the pulsed laser beam from the first laser source to the target spot to form a hole in the surface layer of the processing target.    
   
   
       22 . The laser processing method according to  claim 21 , wherein said step (k) preheats the processing, target while keeping a temperature of the base layer not higher than a melting point of the base layer by irradiating the continuous-wave laser beam from the second laser source.  
   
   
       23 . The laser processing method according to  claim 21 , wherein said step (k) scans the continuous-wave laser beam and pulsed laser beam on the surface of the processing target wherein a beam spot of the pulsed laser beam is included inside of a beam spot of the continuous-wave laser beam.  
   
   
       24 . The laser processing method according to  claim 23 , wherein a shape of the beam spot of the continuous-wave laser beam on the surface of the processing target is a circle, and the beam spot of the pulsed laser beam is positioned at a center of the circle.  
   
   
       25 . A laser processing apparatus, comprising: 
 a laser source that emits laser beam;    a holder that holds a processing-target;    an optical system comprising a lens that condenses the laser beam from the laser source, and a beam scanner that sweeps the laser beam passed through the lens, to scan an incident point of the laser beam on a surface of the processing target held by the holder; and    a controller which so controls at least one parameter among those of said laser source and said optical system that variation of an irradiating condition of the laser beam on the processing target caused by scanning is suppressed.    
   
   
       26 . The laser processing apparatus according to  claim 26 , wherein said optical system further comprises 
 a mask disposed on a light path between the laser source is and the lens and having a pierced hole for shaping a cross section of the laser beam,    the lens condenses the laser beam of which cross section is shaped by the mask and forms an image of the pierced hole on the surface of the processing target held by the holder, and    the controller comprises a moving mechanism that moves the mask and the lens, and a synchronizer that synchronizes scanning by the beam scanner with motion of the mask and the lens by the moving mechanism.    
   
   
       27 . The laser processing apparatus according to  claim 26 , wherein the moving mechanism keeps an optical length between the mask and the lens fixed and between the lens and the surface of the processing target fixed, by moving the lens along a direction of the laser beam passing through the lens and moving the mask along a direction of the laser beam passing through the mask.  
   
   
       28 . The laser processing apparatus according to  claim 26 , wherein the moving mechanism moves the mask and the lens to decrease a variation in an area of the image of the pierced hole formed on the surface of the processing target when an incident angle of the laser beam on the surface of the processing target is varied.  
   
   
       29 . The laser processing apparatus according to  claim 26 , wherein the controller further comprises a variable attenuator that adjusts pulse energy of the laser beam irradiated from the laser source wherein an attenuation rate of the pulse energy is decreased when the incident angle of the laser beam on the surface of the processing target becomes large.  
   
   
       30 . The laser processing apparatus according to  claim 26 , wherein said controller further comprises a pulse energy density changer that increases the pulse energy density in a peripheral area of a cross section of the pulsed laser beam compared to a central part.  
   
   
       31 . The laser processing apparatus according to  claim 26 , wherein the pierced hole of the mask has a shape having a pair of sides parallel to each other.  
   
   
       32 . The laser processing apparatus according to  claim 31 , wherein, when an X-direction and a Y-direction which are crossing with each other at a right angle are defined on the surface of the processing target held by the holder, 
 the beam scanner comprises an X-direction scanner for scanning the laser beam along the X-direction and a Y-direction scanner for scanning the laser beam along the Y-direction on the surface of the processing target, and    the lens forms an image of the pair of the parallel sides of the pierced hole on the surface of the processing target in the X-direction.    
   
   
       33 . The laser processing apparatus according to  claim 25  wherein the controller comprises a moving mechanism that moves the lens, and an adjuster so adjusts the moving mechanism that a variation in pulse energy density or power density of the laser beam on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target.  
   
   
       34 . The laser processing apparatus according to  claim 33 , wherein the adjuster adjusts the moving mechanism to so move the lens along the direction of the laser beam that a focal point of the laser beam goes away from the incident point on the target when increase in the pulse energy density or power density of the laser beam on the surface of the processing target is to be suppressed, and so to move the lens along the direction of the laser beam that a focal point of the laser beam comes closer to the incident point on the target when decrease in the pulse energy density or power density of the laser beam on the surface of the processing target is to be suppressed.  
   
   
       35 . The laser processing apparatus according to  claim 25 , wherein the controller comprises a moving mechanism that moves the lens, and an adjuster that adjusts the moving mechanism to so move the lens that variation in an area of a beam spot on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target.  
   
   
       36 . The laser processing apparatus according to  claim 25 , wherein the controller further comprises a variable attenuator that attenuates power of the laser beam at a variable attenuation rate, and an adjuster that so adjusts the variable attenuator that variation in pulse energy density or power density of the laser beam on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target.  
   
   
       37 . A laser processing apparatus, comprising: 
 a laser source that emits laser beam;    a holder that holds a processing target;    a first lens that converges or diverges the laser beam from the laser source;    a second lens that condenses the laser beam passed through the first lens;    a beam scanner that sweeps the laser beam passed through the second lens, to scan an incident point of the laser beam on a surface of the processing target held by the holder;    a moving mechanism that moves the first lens; and    a controller that controls the moving mechanism to so move the first lens that variation in pulse energy density or power density of the laser beam on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target, and wherein    NA 1 /NA 2  is not less than 2 when a numerical aperture of the first lens for the laser beam irradiated on the first lens is NA 1 , and a numerical aperture of the;second lens for the laser beam irradiated on the second lens is NA 2 .    
   
   
       38 . A laser processing apparatus, comprising: 
 a laser source that emits laser beam;    a holder that holds a processing target;    a beam cross section shaper that has a pierced hole through which the laser beam from the laser source passes and can change a length in one direction of a cross section of the laser beam passing through the pierced hole upon reception of an external signal;    a lens that condenses the laser beam from the beam cross section shaper;    a beam scanner that sweeps the laser beam passed through the lens, to scan an incident point of the laser beam on a surface of the processing target held by the holder; and    a controller that so controls the beam cross section shaper that variation in a shape of a beam spot on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target.    
   
   
       39 . The laser processing apparatus according to  claim 38 , wherein said controller inclines said beam cross section shaper from a surface vertical to a direction of the laser beam when the cross section of the laser beam is to be shaped into a shape of which one direction is longer than another.  
   
   
       40 . The laser processing apparatus according to  claim 39 , wherein the beam cross section shaper can rotate the pierced hole around an axis parallel to the direction of the laser beam.  
   
   
       41 . A laser processing apparatus, comprising: 
 a laser source that emits laser beam;    a holder that holds a processing target;    a lens that condenses the laser beam from the laser source;    a beam scanner that sweeps the laser beam passed through the lens, to scan an incident point of the laser beam on a surface of the processing target held by the holder; and    a proximity mask disposed on a path of the laser beam directed to the processing target from the beam scanner and has a pierced hole through which the laser beam is allowed to pass to be irradiated on the processing target.    
   
   
       42 . The laser processing apparatus according to  claim 41 , further comprising: 
 a moving mechanism that moves the lens; and    a controller that controls the moving mechanism to so move the lens that variation in pulse energy density or power density of the laser beam on the surface of the processing target is suppressed when the beam scanner moves an incident position of the laser beam on the surface of the processing target.    
   
   
       43 . A laser processing apparatus, comprising: 
 a laser source that emits continuous-wave laser beam;    a holder that holds a processing target;    an optical system receiving the laser beam from the laser source, which can switched over between a first configuration in which the laser beam is emitted and a second configuration in which the laser beam is not emitted;    a mask that has a rectangle-shaped pierced hole which allows the laser beam from the optical system to pass and be shaped;    a lens that condenses the laser beam from the mask and forms an image of the rectangle-shaped pierced hole on a surface of the processing target held by the holder;    a moving mechanism that moves the holder and can move an incident position of the laser beam from the lens on the surface of the processing target;    a mask rotating mechanism that rotates the mask around an axis parallel to an optical axis of the laser beam passing through the pierced hole of the mask; and    a controller that controls the first or second configuration of the optical system, controls the moving mechanism to move the incident position of the laser beam on the processing target along a first direction and controls the mask rotating mechanism to rotate the mask to make a certain side of the image of the rectangle-shaped pierced hole on the surface of the processing target parallel to the first direction before the moving mechanism moves the incident position of the laser beam on the processing target along the first direction.    
   
   
       44 . A laser processing apparatus, comprising: 
 a holder that holds a processing target;    a first laser source that emits pulsed laser beam;    a second laser source that emits continuous-wave laser beam;    an optical system that transmits the pulsed laser beam from the first laser source and the continuous-wave laser beam from the second laser source on a surface of the processing target held by the holder in such a manner that a beam spot of the pulsed laser beam is included inside a beam spot of the continuous-wave laser beam; and    a moving mechanism that moves the beam spots of the pulsed laser beam and the continuous-wave laser beam on the surface of the processing target.    
   
   
       45 . The laser processing apparatus according to  claim 44 , wherein the optical system joins the pulsed laser beam from the first laser source and the continuous-wave laser beam from the second laser source, and transmits the laser beams on the surface of the processing target along same optical path.