Laser processing

Abstract

The invention provides a system and method for vaporizing a target structure on a substrate. According to the invention, a calculation is performed, as a function of wavelength, of an incident beam energy necessary to deposit unit energy in the target structure. Then, for the incident beam energy, the energy expected to be deposited in the substrate as a function of wavelength is calculated. A wavelength is identified that corresponds to a relatively low value of the energy expected to be deposited in the substrate, the low value being substantially less than a value of the energy expected to be deposited in the substrate at a higher wavelength. A laser system is provided configured to produce a laser output at the wavelength corresponding to the relatively low value of the energy expected to be deposited in the substrate. The laser output is directed at the target structure on the substrate at the wavelength corresponding to the relatively low value of the energy expected to be deposited in the substrate, in order to vaporize the target structure.

1 - 25 . (canceled)  
   
   
       26 . A system for vaporizing a target structure on a silicon substrate, comprising: 
 a laser pumping source;    a laser resonator cavity configured to be pumped by the laser pumping source;    a laser output system configured to produce a pulsed laser output beam from energy stored in the laser resonator cavity and to direct the pulsed laser output beam at the target structure on the silicon substrate in order to vaporize the target structure, at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns, the silicon substrate being positioned beneath the target structure with respect to the laser output, the laser output system being configured to produce the pulsed laser output beam at an incident beam energy;    a computer programmed to generate computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure; and    an optical switch that is controllably switchable based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure and to permit selective reduction of the incident beam energy;    wherein the incident beam energy at which the target structure is vaporized is reduced relative to an incident beam energy necessary to deposit unit energy in the target structure sufficient to vaporize the target structure at a higher wavelength below the absorption edge of the silicon substrate.    
   
   
       27 . The system of  claim 26  wherein the laser output system comprises a wavelength shifter.  
   
   
       28 . The system of  claim 26  wherein the laser resonator cavity produces laser radiation at the wavelength corresponding to the relatively low value of energy expected to be deposited in the substrate.  
   
   
       29 . The system of  claim 26  wherein the target structure comprises a metal having a conductivity greater than that of aluminum.  
   
   
       30 . The system of  claim 29  wherein the metal comprises copper.  
   
   
       31 . The system of  claim 29  wherein the metal comprises gold.  
   
   
       32 . The system of  claim 28  wherein the target structure on the substrate comprises a link of a semiconductor device.  
   
   
       33 . The system of  claim 32  wherein the semiconductor device comprises an integrated circuit.  
   
   
       34 . The system of  claim 32  wherein the semiconductor device comprises a memory device.  
   
   
       35 . The system of  claim 28  wherein the energy expected to be deposited in the substrate is substantially proportional to the incident beam energy necessary to deposit unit energy in the target structure minus the energy deposited in the target structure, multiplied by absorption of the substrate.  
   
   
       36 . The system of  claim 26  wherein the identified wavelength corresponding to a relatively low value of the energy expected to be deposited in the silicon substrate is within a visible region of spectrum.  
   
   
       37 . The system of  claim 36  wherein the identified wavelength corresponding to a relatively low value of the energy expected to be deposited in the silicon substrate is within a green region of spectrum.  
   
   
       38 . The system of  claim 26  wherein the laser output at the incident beam energy comprises short pulses.  
   
   
       39 . The system of  claim 26  wherein the laser resonator cavity is a neodymium vanadate laser resonator cavity.  
   
   
       40 . A system for vaporizing a target structure on a silicon substrate, comprising: 
 a laser pumping source;    a laser resonator cavity configured to be pumped by the laser pumping source;    a laser output system configured to produce a pulsed laser output beam from energy stored in the laser resonator cavity and to direct the pulsed laser output beam at the target structure on the silicon substrate in order to vaporize the target structure, at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns, the silicon substrate being positioned beneath the target structure with respect to the laser output, the laser output system being configured to produce the pulsed laser output beam at an incident beam energy, the laser output comprising short pulses;    a computer programmed to generate computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure;    an optical switch that is controllably switchable based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure; and    an optical system including at least one focusing element for focusing the incident beam energy onto the target structure with a small spot size that is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns.    
   
   
       41 . The system of  claim 40  wherein the laser resonator cavity is a neodymium vanadate laser resonator cavity.  
   
   
       42 . A system for vaporizing a target structure on a silicon substrate, comprising: 
 a laser pumping source;    a laser resonator cavity configured to be pumped by the laser pumping source;    a laser output system configured to produce a pulsed laser output beam from energy stored in the laser resonator cavity and to direct the pulsed laser output beam at the target structure on the silicon substrate in order to vaporize the target structure, at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns, the silicon substrate being positioned beneath the target structure with respect to the laser output, the laser output system being configured to produce the pulsed laser output beam at an incident beam energy;    a computer programmed to generate computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure;    an optical switch that is controllably switchable based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure to permit selective reduction of the incident beam energy; and    an optical system including at least one focusing element for focusing the incident beam energy onto the target structure with a small spot size that is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns;    wherein the incident beam energy at which the target structure is vaporized is reducible relative to an incident beam energy necessary to deposit unit energy in the target structure sufficient to vaporize the target structure at a higher wavelength below the absorption edge of the silicon substrate.    
   
   
       43 . A method of vaporizing a target structure on a silicon substrate, comprising the steps of: 
 providing a laser system configured to produce a pulsed laser output beam at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns; and    directing the pulsed laser output beam at the target structure on the silicon substrate at the wavelength and at an incident beam energy, in order to vaporize the target structure, the silicon substrate being positioned beneath the target structure with respect to the laser output; generating computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure;    focusing the incident beam energy onto the target structure with a small spot size that is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns;    controllably switching an optical switch based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure;    wherein the incident beam energy at which the target structure is vaporized is reduced relative to an incident beam energy necessary to deposit unit energy in the target structure sufficient to vaporize the target structure at the higher wavelength below the absorption edge of the silicon substrate.    
   
   
       44 . The method of  claim 43  wherein the identified wavelength corresponding to a relatively low value of the energy expected to be deposited in the silicon substrate is within a visible region of spectrum.  
   
   
       45 . The method of  claim 44  wherein the identified wavelength corresponding to a relatively low value of the energy expected to be deposited in the silicon substrate is within a green region of spectrum.  
   
   
       46 . The method of  claim 43  wherein the laser output at the incident beam energy comprises short pulses.  
   
   
       47 . The method of  claim 43  wherein the laser system comprises a neodymium vanadate laser.  
   
   
       48 . A method of vaporizing a target structure on a silicon substrate, comprising the steps of: 
 providing a laser system configured to produce a laser output at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns; and    directing the laser output at the target structure on the silicon substrate at the wavelength and at an incident beam energy, in order to vaporize the target structure, the silicon substrate being positioned beneath the target structure with respect to the laser output, wherein the laser output at the incident beam energy comprises short pulses;    generating computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure; and    controllably switching an optical switch based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure to permit selective reduction of the incident beam energy.    
   
   
       49 . The method of  claim 38  wherein the laser system comprises a neodymium vanadate laser.  
   
   
       50 . A method of vaporizing a target structure on a silicon substrate, comprising the steps of: 
 providing a laser system configured to produce a laser output at a wavelength below an absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns;    directing the laser output at the target structure on the silicon substrate at the wavelength and at an incident beam energy, in order to vaporize the target structure, the silicon substrate being positioned beneath the target structure with respect to the laser output; generating computer-controlled timing signals synchronized with the position of the pulsed laser beam relative to the target structure;    focusing the incident beam energy onto the target structure with a small spot size that is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns; and    controllably switching an optical switch based on the timing signals so as to cause output pulses of the pulsed laser beam to be transmitted to the target structure and to permit selective reduction of the incident beam energy;    wherein the incident beam energy at which the target structure is vaporized is reducible relative to an incident beam energy necessary to deposit unit energy in the target structure sufficient to vaporize the target structure at a higher wavelength below the absorption edge of the silicon substrate below the absorption edge of the silicon substrate.    
   
   
       51 . The system of  claim 26 , wherein the optical switch permits selective reduction of the incident beam energy to about 10% of a gross laser output  52 . The system of  claim 26  wherein, at the wavelength below the absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns, a spot size of the laser output at the target structure is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns.  
   
   
       53 . The system of  claim 40 , wherein the optical switch permits selective reduction of the incident beam energy.  
   
   
       54 . The method as claimed in  claim 43 , wherein said step of controllably switching the optical switch permits selective reduction of the incident beam energy.  
   
   
       55 . The method as claimed in  claim 48 , wherein at the wavelength below the absorption edge of the silicon substrate and between about 0.30 microns and about 0.55 microns, a spot size of the laser output at the target structure is proportionally smaller according to wavelength than a larger spot size that would be focused onto the target structure by an optical system having an ƒ number at a wavelength of at least about 1.047 microns.