Laser-based method and system for memory link processing with picosecond lasers

Abstract

A laser-based method of removing a target link structure of a circuit fabricated on a substrate includes generating a pulsed laser output at a pre-determined wavelength less than an absorption edge of the substrate. The laser output includes at least one pulse having a pulse duration in the range of about 10 picoseconds to less than 1 nanosecond, the pulse duration being within a thermal laser processing range. The method also includes delivering and focusing the laser output onto the target link structure. The focused laser output has sufficient power density at a location within the target structure to reduce the reflectivity of the target structure and efficiently couple the focused laser output into the target structure to remove the link without damaging the substrate.

1 - 61 . (canceled)  
     
     
         62 . A system for removing target material associated with electrically conductive links positioned between respective pairs of electrically conductive contacts in a circuit fabricated on a substrate, said links defining a link width, said system comprising: 
 a laser for generating at least two closely spaced laser output pulses during a first time interval;    an optical switch configured to select processing pulses for focusing onto a spot on the substrate, each of the pulses defining a laser spot size larger than the link width and having energy characteristics which prevent undesirable damage to a passivation layer beneath the link;    a beam positioning system imparting relative movement of a laser spot position over the substrate in response to processing control signals representing one or more locations of electrically conductive links;    a controller for coordinating the optical switch and the beam positioning system such that the relative movement is substantially continuous and the laser output pulses impinge a first electrically conductive link at a first location between first contacts and encompass the link width, the output pulses removing target material without causing undesirable damage to the substrate or passivation material below the link.    
     
     
         63 . The system of  claim 62 , wherein each of the laser output pulses having a pulse duration in the range of several picoseconds to about ten nanoseconds.  
     
     
         64 . The system of  claim 62 , wherein said laser comprises a pumped, mode locked, pulsed laser.  
     
     
         65 . The system of  claim 62 , wherein said laser comprises a seed laser diode and a fiber amplifier.  
     
     
         66 . The system of  claim 63 , wherein said laser comprises a seed laser diode and a fiber amplifier.  
     
     
         67 . The system of  claim 62 , wherein the laser outputs pulses having energy of 0.1 microjoules to 3 microjoules, wherein said optical switch attenuates the laser output pulses from the laser by up to 90% such that the energy of the pulses output from the optical switch and impinging the target material ranges from 10 nanojoules to 3 microjoules.  
     
     
         68 . The system of  claim 62 , wherein said laser comprises a Q-switched, solid state laser and the optical switch is positioned external to the laser.  
     
     
         69 . The system of  claim 62 , further comprising an amplifier for amplifying the laser output pulses.  
     
     
         70 . The system of  claim 62 , wherein the pulses sever the link.  
     
     
         71 . The system of  claim 62 , wherein the link is covered with an overlying passivation layer, and the pulses remove the layer and sever the link.  
     
     
         72 . The system of  claim 62 , wherein said link comprises metal, polysilicide, or polysilicon.  
     
     
         73 . The system of  claim 62 , wherein the underlying layer comprises an underlying layer of SiO 2 .  
     
     
         74 . The system of  claim 62 , wherein links are processed at a rate of at least 1 kHz to somewhat less than about 20 kHz.  
     
     
         75 . The system of  claim 62 , wherein each of the laser pulses has a pulse width in the range of several picoseconds to about ten nanoseconds.  
     
     
         76 . The system of  claim 62 , wherein each of the laser pulses has a pulse width of less than 5 nanoseconds.  
     
     
         77 . The system of  claim 62 , wherein each of the amplified pulses has an energy of 0.1 microjoules up to 3 microjoules of energy.  
     
     
         78 . The system of  claim 62 , wherein each of the pulses produces a focused laser spot having a peak power of at least 10 9  W/cm 2 , a diameter of about 1 to 4 micrometers, and duration of several picoseconds to about 10 nanoseconds.  
     
     
         79 . The system of  claim 78 , wherein said pulses have an energy ranging from about 0.1 nanojoules to about 5 microjoules.  
     
     
         80 . The system of  claim 62 , wherein each of the output pulses have approximately the same energy.  
     
     
         81 . The system of  claim 62 , wherein at least two of the output pulses have different energies.  
     
     
         82 . The system of  claim 62 , wherein the pulses are generated at a wavelength of less than about 2000 nm.  
     
     
         83 . The system of  claim 62 , wherein the beam positioning system causes relative movement at substantially constant speed during processing.  
     
     
         84 . The system of  claim 62 , wherein said laser generates a sequence of short pulses in rapid succession.  
     
     
         85 . The system of  claim 62 , wherein said short pulses have variable width.