Abstract:
Laser singulation of electronic devices from semiconductor substrates including wafers is performed using up to 3 lasers from 2 wavelength ranges. Using up to 3 lasers from 2 wavelength ranges permits laser singulation of wafers held by die attach film while avoiding problems caused by single-wavelength dicing. In particular, using up to 3 lasers from 2 wavelength ranges permits efficient dicing of semiconductor wafers while avoiding debris and thermal problems associated with laser processing die attach tape.

Description:
TECHNICAL FIELD 
       [0001]    The present invention regards aspects of laser singulation of electronic substrates. In particular it regards laser singulation of electronic devices from semiconductor substrates including wafers using up to 3 lasers from two wavelength ranges. In more particular it regards efficient singulation of electronic devices from substrates including wafers held with die attach film while avoiding problems associated with laser processing die attach film. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electronic devices are nearly universally manufactured by constructing multiple copies of the circuit or device on a large substrate in parallel. In particular, devices which rely on semiconducting materials are constructed on wafers made of silicon, germanium, sapphire, gallium arsenide, indium phosphide, diamond or ceramic. These wafers typically need to be singulated into individual devices. Singulation can be performed by first scribing the wafer with a diamond saw or laser followed by cleaving or by dicing. Scribing is defined as creating a modified region on the surface or within the volume of a wafer with a laser or diamond saw which facilitates cracking and thereby the separation of the wafer proximate to the scribe. Dicing is defined as performing through cuts or near through-cuts in the wafer with a laser or diamond saw so that the wafer can be subsequently separated into individual devices with minimal force.  FIG. 1  shows a typical wafer  10  containing multiple devices  12  separated by orthogonal streets  14 ,  16 . Streets are regions of the wafer which are deliberately devoid of active circuitry to permit scribing or dicing in the street region without damaging active circuitry. The wafer  10  is supported by tape  20  attached to a tape frame  18 . Laying out streets in this fashion permits the wafer  10  to be singulated by scribing or dicing linearly along the streets  14 ,  16  thereby separating the individual devices  12 . Using a laser rather than a diamond-coated saw blade also permits scribing or dicing in patterns other than linear. Wafers  10  are often adhesively attached to a die attach film (DAF)(not shown) which is then attached to the tape  20  which is in turn attached to the tape frame  18  during manufacturing to permit handling the wafer  10 . 
         [0003]    The advantages of using lasers to singulate devices constructed on a wafer is known, as shown in U.S. Pat. No. 6,960,813, METHOD AND APPARATUS FOR CUTTING DEVICES FROM SUBSTRATES, inventor Kuo-Ching Liu, issued Nov. 1, 2005. In this patent, a UV pulsed laser is used in cooperation with a porous vacuum chuck to singulate semiconductor wafers. No mention is made of issues which may arise because of the use of DAF. DAF is an engineered adhesive material designed to remain attached to the device following singulation to permit the device to be adhesively attached to other substrates or devices as part of the further packaging process. As such the DAF must maintain its bond to the wafer it is bonded to and remain undamaged and free of debris following laser dicing in order to function properly. Exemplary DAF is manufactured by Al Technology, Inc. Princeton Junction, N.J. 08550. Typically during the dicing process the wafer, the DAF and possibly part of the tape are cut by the laser or the saw. Laser dicing of wafers has many advantages over diamond saw dicing; however, removing the DAF in the desired region associated with the through cut with the same laser that makes the through cut has the disadvantages of low efficiency and increased debris and damage.  FIG. 2  shows a cross-sectional diagram of a wafer  30  with applied layers containing active devices  32 ,  34  and a street  36 . The wafer  30  is attached to DAF  38  supported by tape  40  which is attached to a tape frame  42 . 
         [0004]    The presence of DAF on a wafer can cause problems with laser singulation. Attempting to remove DAF using the same UV laser that is used to through cut the wafer can cause excessive debris and thermal damage to the wafer and DAF.  FIG. 3  is a microphotograph of a portion of the bottom side of a silicon wafer  30  after being diced by a 355 nm UV laser (not shown) having 2.8 W of power at 30 KHz pulse repetition rate a 40 micron wide shaped beam using nanosecond pulse widths showing the exposed DAF  32 ,  34  and the kerf  36  formed by the through cut. The kerf is bordered on both sides by debris and damaged DAF  38  as a result of the laser through cut. In this microphotograph, the through cut is about 50 microns wide. Thermal damage, including delamination of DAF from the wafer and debris including melted or vaporized DAF material redeposited on the sidewalls of the kerf. These types of debris or damage caused by prior art approaches to laser singulation in the presence of DAF can cause problems in subsequent manufacturing steps. For example, delamination or excessive debris could hinder proper placement when DAF is used to pick and position the device for packaging. In addition excessive debris redeposited on the sidewalls of the kerf could hinder further processing such as sidewall etching. 
         [0005]    In U.S. Pat. No. 6,562,698, DUAL LASER CUTTING OF WAFERS, inventor Ran Manor, issued May 13, 2003, discusses singulating wafers with two laser beams at two different wave lengths with the aim of removing a layer of material from the wafer to permit the second wavelength to more efficiently process the wafer. No mention is made of DAF or tape or issues associated with laser singulating wafer in the presence of DAF. U.S. patent application no. 2008/0160724, METHOD OF DICING, inventors Hyun-Jung Song, Kak-Kyoon Byun, Jong-Bo Shim and Min-Ok Na, published Jul. 3, 2008, discussed issues associated with laser dicing in the presence of DAF and propose modifying DAF adhesive formulas and adding steps and material to the process by which DAF is applied to the wafer during manufacturing. Both of these approaches have drawbacks that make them less than desirable solutions. U.S. Pat. No. 6,992,026, LASER PROCESSING METHOD AND LASER PROCESSING APPARATUS, inventors Fumitsugo Fukuyo, Kenshi Fukumitsu, Naoki Uchiyama, Toshimitsu Wakuda, issued Jan. 31, 2006 proposes the singulation of the wafer by focusing the laser inside the bulk wafer material to create cracks along the scribing streets to guide subsequent cleaving. The devices are separated by stretching the tape and therefore the wafer before through cutting the DAF with a laser through the so formed openings between devices. The disadvantage of this approach is the difficulty in performing positional alignment of the laser beam with respect to the opening for the cut due to the nonlinear and irregular expansion of devices on DAF and tape. Re-aligning the wafer following separation of the devices on DAF also takes time, thereby slowing throughput undesirably. 
         [0006]    What these approaches have in common is a desire to singulate wafers in the presence of DAF efficiently without undesirable damage or debris. What is required then and has not been disclosed by the prior art is a method for efficiently laser singulating electronic devices from electronic substrates such as wafers while avoiding problems associated with laser processing die attach film. 
       SUMMARY OF THE INVENTION 
       [0007]    Aspects of this invention represent an improved method for singulation of wafers mounted on die attach film (DAF) with a laser processing system. The wafer has predefined streets and a layer of material on the surface opposite the DAF. The laser processing system has first, second, and third lasers having first, second and third laser parameters including wavelengths in the visible or ultraviolet (UV), infrared (IR), and visible or ultraviolet (UV) respectively. A maximum surface texture of the wafer is determined that permits backside removal of the DAF with the second laser using predetermined second laser parameters. First laser parameters are determined that permit the first laser to remove portions of the layer of material from the wafer in a desired region so that substantially all of the layer of material is removed from the desired region and the surface texture of the resulting surface within the desired region is less than said determined maximum surface texture. The first laser is then directed to remove the layer of material from the wafer within a desired area substantially within the streets using the said laser parameters. Following this the second laser is directed to perform backside removal of portions of the die attach film using the predetermined second laser parameters in regions aligned with the streets. Then the third laser is directed to perform through cuts in the wafer with the predetermined third laser parameters substantially within the streets thereby singulating the wafer. 
         [0008]    Aspects of this invention also singulate devices on wafers by forming a deteriorated region in the DAF by backside illumination. A layer or layers of materials are removed from the surface of the wafer with a visible or UV laser leaving the surface roughness less than 10% of the wavelength of the IR laser to be used to form a deteriorated region in the DAF. Following through cutting of the wafer with a visible or UV wavelength laser the tape is stretched to separate the devices and since the DAF has a deteriorated region aligned with the streets where most of the tension will be applied to the DAF by the stretching tape, the DAF separates where desired. Forming deteriorated regions can require less energy and create less debris following separation than removal of DAF in desired regions. 
         [0009]    Backside DAF removal refers to removing or deteriorating DAF by directing laser pulses to the DAF through the wafer by selecting laser wavelengths that are preferentially absorbed by the DAF and are substantially transparent to the wafer. Lasers with wavelengths in the IR regions are substantially transparent to many wafer materials including silicon and germanium but are readily absorbed by DAF, thereby permitting the laser processing system to focus the laser pulses onto the DAF through the wafer. Aspects of the current invention remove material in a layer or layers on the front or top surface of the wafer with a visible or UV laser to expose the surface of the wafer in order to permit backside removal of DAF by directing IR laser radiation through the wafer. In order to efficiently transmit laser power through the surface of the wafer to the DAF, the newly exposed surface of the wafer must be smooth enough to transmit laser energy without excessive scatter or diffusion. The surface roughness of the exposed wafer surface as measured by RMS average height distribution measured in microns along an approximately 75 micron long line should be less than 10% of the length of the wavelength of laser radiation to be used. In this case, using a 10.6 micron CO2 laser would require that the RMS surface roughness measure less than 1.06 microns. Backside removal of DAF with a CO2 gas laser operating at 10.6 microns through a silicon wafer with surface roughness of less than 10% of the laser wavelength following removal of a surface layer according to aspects of this invention quickly and cleanly removes DAF from the desired region while avoiding excessive debris or thermal damage to the wafer. 
         [0010]    An ESI model 9900 Ultra-thin Wafer Dicing System is an exemplary laser processing system that can be adapted to implement aspects of this invention. This laser processing system is manufactured by Electro Scientific Industries, Inc., Portland Oreg. 97239. This system may be adapted by using three lasers and three sets of laser optics to dice wafers; a visible or UV wavelength laser and optics to remove surface layers, an IR laser and optics to perform backside removal or deterioration of DAF and a visible or UV wavelength laser and optics to through cut the wafer. Alternatively the laser processing system may be adapted by using two laser and two sets of laser optics; a visible or UV laser and optics to remove surface layers and through cut the wafer and an IR laser and optics to perform backside removal or deterioration of DAF. The laser processing system may also be adapted by using single laser which can switch or be switched between IR and visible or UV wavelengths, optics to handle both wavelengths and has sufficient power to be able to process wafers efficiently. 
         [0011]    Singulation of electronic devices from a wafer in this manner is efficient since the wafer does not have to be moved or re-aligned during the process as is required by other approaches to solving the problems associated with singulation of wafers on DAF. Aspects of this invention also provide a substantially debris-free and undamaged wafer following singulation due to the limited amount of debris and thermal damage caused by removal of the DAF by laser. In addition the DAF which remains attached to the electronic device by design is substantially debris-free and is trimmed accurately to the device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1 . Prior art wafer 
           [0013]      FIG. 2 . Prior art Cross-section of wafer on DAF and tape 
           [0014]      FIG. 3 . Prior art through cut wafer with DAF 
           [0015]      FIG. 4 . % Absorption vs. wavelength for silicon 
           [0016]      FIGS. 5   a - f . Laser dicing with DAF 
           [0017]      FIG. 6   a - g . Surface roughness measure of wafer following removal of layer 
           [0018]      FIG. 7 . DAF after singulation by CO 2  laser 
           [0019]      FIG. 8 . Silicon wafer with attached DAF following singulation 
           [0020]      FIG. 9 . Laser dicing with DAF 
           [0021]      FIG. 10  Laser processing system using three lasers 
           [0022]      FIG. 11  Laser processing system using two lasers 
           [0023]      FIG. 12  Laser processing system using one laser 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    Embodiments of this invention represent an improved method for singulation of wafers mounted on die attach film (DAF) with a laser processing system. The wafer has predefined streets and a layer of material on the surface opposite the DAF. The laser processing system has first, second, and third lasers having first, second and third laser parameters. A maximum surface texture of the wafer is determined that permits backside removal of the DAF with the second laser using predetermined second laser parameters. First laser parameters are determined that permit the first laser to remove portions of the layer of material from the wafer in a desired region so that substantially all of the layer of material is removed from the desired region and the surface texture of the resulting surface within the desired region is less than said determined maximum surface texture. The first laser is then directed to remove the layer of material from the wafer within a desired area substantially within the streets using the said laser parameters. Following this the second laser is directed to perform backside removal of portions of the die attach film using the predetermined second laser parameters in regions aligned with the streets. Then the third laser is directed to perform through cuts in the wafer with the predetermined third laser parameters substantially within the streets thereby singulating the wafer. 
         [0025]    Backside DAF removal refers to removing DAF by directing laser pulses to the DAF through the wafer by selecting laser wavelengths that are preferentially absorbed by the DAF and are substantially transparent to the wafer. Lasers with wavelengths in the IR regions are substantially transparent to many wafer materials including silicon and germanium but are readily absorbed by DAF, thereby permitting the laser processing system to focus the laser pulses onto the DAF through the wafer.  FIG. 4  is a graph plotting percent absorption vs. wavenumber measured in inverse centimeters for silicon. The arrows A and B represent the principle wavelengths emitted by a CO2 laser (10.6 and 9.4 microns) and show that silicon has very low absorption and hence very high transmission of laser wavelengths in this range. 
         [0026]    Embodiments of the current invention remove material in a layer or layers on the front or top surface of the wafer with a visible or UV laser to expose the surface of the wafer itself in order to permit backside removal of DAF by directing IR laser radiation through the wafer.  FIGS. 5   a  through  5   f  illustrate this process by showing a cross-sectional view of a wafer  50  on DAF  56  supported by tape  58 . In  FIG. 5   a  a wafer  50  on DAF  56  supported by tape  58  has a surface layer  52  containing active circuitry with a street  54  indicated. First laser pulses  60  are directed to the street area  54  to remove material  52  and expose the surface of the wafer  50 .  FIG. 5   b  shows the wafer  50  after partial removal of the surface layer  52 , which exposes the surface of the wafer  62 . Also shown are regions of the street  63  which remain following material removal.  FIG. 5   c  shows second laser pulses  64  being focused through the exposed surface of the wafer  62  onto the surface of the DAF  56 . As shown in  FIG. 5   d , the second laser pulses  64  have removed or caused deterioration in a region of the DAF  66  aligned with the exposed region of wafer  62 . In  FIG. 5   e , third laser pulses  68  are directed to the exposed surface of the wafer  62 . In  FIG. 5   f  the third laser pulses  68  have formed a through cut  70  in the wafer  50  in alignment with the removed or deteriorated DAF  66  to thereby singulating the wafer  50 . 
         [0027]    Embodiments of this invention also singulate devices on wafers by forming a deteriorated region in the DAF by backside illumination.  FIGS. 6   a  through  6   f  illustrate this process. In  FIG. 6   a , a wafer  80  with a topside layer  82  having a street  84  on DAF  86  and tape  88  is illuminated by a visible or UV laser  90 .  FIG. 6   b  shows the topside layer  82  with the surface of the wafer exposed  92 . Note that portions of the street  93  may remain adjacent to the exposed wafer  92 . This layer or layers of material is removed from the surface of the wafer with a visible or UV laser leaving the surface roughness less than 10% of the wavelength of the IR laser to be used to form a deteriorated region in the DAF.  FIG. 6   c  shows the IR laser pulses  94  being directed to the DAF  86  through the exposed surface of the wafer  92 .  FIG. 6   d  shows the deteriorated region  96  created in the DAF  86 .  FIG. 6   e  shows visible or UV laser pulses  98  being directed to the wafer  80  to form a through cut.  FIG. 6   f  shows the through cut  100  in wafer  80  which stops at the deteriorated region  96  of DAF  86 . FIG.  6   g  shows the tape  88  stretched in the directions of the arrows to separate the wafer  80 . Since the DAF  86  has a deteriorated region  96  aligned with the though cut  100  tension will be applied to the deteriorated region  96  by the stretching tape  88 , thereby forming a separation  102  in the deteriorated region  96 , causing the DAF to separate where desired. Forming deteriorated regions can require less energy and create less debris following separation than complete removal of DAF. 
         [0028]    Embodiments of this invention focus laser pulses at or within the DAF on the bottom side of the wafer to remove or alter the DAF while the wafer is fixtured and aligned on the laser processing system. Backside removal of DAF depends upon starting the removal process at an edge of the wafer and proceeding towards the interior in order to provide a path for the vaporized DAF material to escape without cooling and redepositing material. High pressure gas created by the laser pulses ejects the vaporized or melted DAF material away from the laser machining site and thereby keeps the debris from forming. Embodiments of this invention also singulate devices on wafers by forming a deteriorated region in the DAF by backside laser processing. In this case the laser energy used is not sufficient to ablate or vaporize the DAF but rather causes a deteriorated region in the DAF which permits the DAF to separate cleanly and easily in desired locations when subjected to tension caused by stretching the tape to separate the devices. 
         [0029]    Embodiments of this invention remove a layer or layers of material from the surface of a wafer to permit a second laser to remove or deteriorate DAF through the wafer. In order to efficiently transmit laser power through the surface of the wafer to the DAF, the newly exposed surface of the wafer must be smooth enough to transmit laser energy without excessive scatter or diffusion. The surface roughness of the exposed wafer surface as measured by the maximum height difference in microns of points measured along an approximately 75 micron-long line should be less than 10% of the length of the wavelength of laser radiation to be used. For example, using a 10.6 micron CO2 laser would require that the surface roughness measure less than 1.06 microns. Backside removal of DAF with a CO2 gas laser operating at 10.6 microns through a silicon wafer with surface roughness of less than 10% of the laser wavelength following removal of a surface layer according to embodiments of this invention quickly and cleanly removes DAF from the desired region while avoiding excessive debris or thermal damage to the wafer. 
         [0030]      FIG. 7  shows a microphotograph of a wafer  110  having a surface layer of material  112 ,  113  which has been removed to expose the surface of the wafer  114 . The material was removed using a 16 W UV laser (not shown) emitting pulses with pulse duration between 10 and 1000 picoseconds and pulse energy of less than 200 uJ at 355 nm using a 45 micron spot square-shaped (top hat) beam focused at the surface layer  112 ,  113 . Shown in this microphotograph are three line segments  116 ,  118 ,  120  along which samples of the height of the surface were measured and averaged. As can be seen, the maximum height difference for all samples averaged is 0.568 which is less than the desired maximum value of 1.06. The data from these measurements is shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Profile 
                 Horizontal  
                 Height  
                 Height  
               
               
                   
                 # 
                 distance 
                 Difference 
                 Average 
               
               
                   
                   
               
             
             
               
                   
                 All 
                 251.712 μm 
                 0.568 μm 
                 3.093 μm 
               
               
                   
                 Seg. 1 
                  75.275 μm 
                 0.317 μm 
                 3.755 μm 
               
               
                   
                 Seg. 2 
                  72.891 μm 
                 0.521 μm 
                 2.511 μm 
               
               
                   
                 Seg. 3 
                  74.594 μm 
                 0.780 μm 
                 3.051 μm 
               
               
                   
                   
               
             
          
         
       
     
         [0031]      FIG. 8  is a microphotograph showing tape  130  with overlaying DAF  132 ,  133  following processing according to embodiments of this invention. The wafer (not shown) has been removed to show the debris-free and smooth edges  136  of the kerf  134  formed in the DAF  132 ,  133 , a desired result. The kerf  134  was formed in the DAF  132 ,  133  using a 200 W CO2 laser (not shown) operating at 10.6 microns using a clipped Gaussian beam focused at the DAF through the wafer (not shown). Clipping a Gaussian beam refers to passing the laser pulse through an aperture which can be circular or otherwise shaped to pass only the central part of the laser pulse and block transmission of the outermost laser energy.  FIG. 9  shows a microphotograph of a portion of a silicon wafer  140  which has been singulated along with the underlying DAF  142  to form a singulated electronic device according to an embodiment of this invention. The surface layer (not shown) was removed with a 16 W UV laser (not shown) operating at 355 nm with a square shaped beam focused to a 10 micron focal spot at the surface layer. The DAF  142  was then processed with a 200 W CO2 IR laser (not shown) operating at 9.4 micros with a square shaped beam focused to a 50 micron spot at the DAF  142 . Following this the wafer  140  was through cut with a 16 W UV laser (not shown) operating at 355 nm with a square shaped beam focused to a 10 micron focal spot at the wafer  140 . Note that the DAF  142  is continuously attached to the silicon wafer  140  and is well within acceptable size and debris limits, a desired result. 
         [0032]    An ESI model 9900 Ultra-thin Wafer Dicing System is an exemplary laser processing system that can be adapted to implement aspects of this invention. This laser processing system is manufactured by Electro Scientific Industries, Inc., Portland Oreg. 97239. This system is described in publication “Model 9900 Site Requirements and Installation Guide”, ESI part no. 187054a and is included herein in its entirety by reference. In an embodiment of this invention this system is adapted by using three lasers and three sets of laser optics to dice wafers as shown in  FIG. 10 . Firstly, a visible or UV wavelength laser  150  produces visible or UV laser pulses  152  which are directed by visible or UV laser optics  154  to remove surface layer  182  within street  188  on wafer  180  held on DAF  184  attached to tape  186 . Secondly, an IR laser  160  produces IR laser pulses  162  which are directed by IR laser optics  164  to perform backside removal or deterioration of DAF  184  through wafer  180  following removal of surface layer  182  in street  188 . Thirdly, a visible or UV wavelength laser  170  produces visible or UV laser pulses  172  which are directed by visible or UV optics  174  to through cut wafer  180 . 
         [0033]    A laser which may be used as the first  150  and third  170  visible or UV laser is the Coherent Avia, manufactured by Coherent Inc., Santa Clara, Calif. 95054. This laser is a Q-switched Nd:YVO4 conventional solid state diode-pumped laser which operates at 355 nm wavelength at a pulse repetition rates of up to 100 kHz and average power of 16 W. The visible or UV laser optics  154 ,  174  can include temporal pulse shaping optics such as an AOM or EOM, spatial pulse shaping optics such as diffractive beam shaping optics or collimators, beam steering optics such as AOMs or galvanometers and field optics to direct the shaped, steered laser pulses to the workpiece. The IR laser  160  may be a Coherent Diamond K-Series CO2 laser manufactured by Coherent Inc., Santa Clara, Calif. 95054 which operates at 9.6 micron wavelength at pulse repetition rates of up to 100 KHz and average power of over 200 W. The IR optics  164  contain the same elements as the visible or UV laser optics  154 ,  174  and perform the same basic functions except that the IR optics  164  are optimized to process IR wavelengths. 
         [0034]    Alternatively, embodiments of this system adapt the laser processing system by using two laser and two sets of laser optics as shown in  FIG. 11 . Firstly, a visible or UV laser  190  produces visible or UV laser pulses  192  which are directed by visible or UV laser optics  194  to first remove surface layer  212  within street  218  and then through cut the wafer  210  following removal or deterioration of DAF  214  on tape  216  by IR laser pulses  198 . Secondly, an IR laser  196  produces IR laser pulses  198  which are directed by IR laser optics  200  to perform backside removal or deterioration of DAF  214 . The visible or UV laser  194  can be a Coherent Avia operating at 355 nm and the IR laser  196  can be a Coherent Diamond K-series CO2 laser operating at 9.6 microns. Visible and UV laser optics  194  are the same as the visible and UV laser optics  154 ,  174  and IR laser optics  200  are the same as IR optics  164 . 
         [0035]      FIG. 12  shows the laser processing system adapted by using a single laser. The laser processing system is adapted by using single laser  240  which produces laser pulses  242  which can switch or be switched between IR pulses  248  and visible or UV pulses  246  by the optical switch  244 . The system is further adapted by adding IR laser optics  252  and visible and UV laser optics  250  direct the visible or UV laser pulses  246  to first remove the surface layer  262  from within the street region  268  to expose the surface of the wafer  260 , then to use IR laser optics  252  to direct the IR laser pulses  248  to perform backside removal or deterioration of the DAF  264  on tape  266  through the wafer  260 , followed by using the visible or UV laser optics  250  to direct visible or UV laser pulses  246  to through cut the wafer. 
         [0036]    In an embodiment of this invention the laser  240  is a member of the solid state laser family which includes both conventional solid-state diode pumped such as those employing Nd:VO4 crystals, fiber lasers which employ Nd-doped glass fibers and various combinations of conventional and fiber solid state lasers arranged as light pumps, resonators and amplifiers. The laser  240  could possibly include harmonic generating crystals such as monopotassium phosphate (KDP), lithium triborate (LBO) or B-barium borate (BBO) which convert IR radiation in the 1064 nm wavelength range to shorter wavelengths such as 532 nm (visible) or 355 nm (UV). This harmonic generating capability may be internal to the laser  240  or external as part of the optical switch  244  and arranged to permit the system to emit either IR pulses  248  or visible or UV pulses  246 . The laser  240  or optical switch  244  may also include an optical parametric oscillator (OPO) which converts 1064 nm IR wavelengths to wavelengths longer than 1300 microns to improve transmission of laser radiation through the wafer  260 . These pulses  246 ,  248  are directed to the street  268 , wafer  260  or DAF  264  by the IR laser optics  252  or visible or UV optics  250  respectively. The IR optics  246  and visible or UV optics  250  are constructed similarly to their counterparts in  FIGS. 10 and 11 . In this case the laser processing system (not shown) must switch the laser power between low power, or about 10 to 20 W of power while removing material from the streets and through cutting to higher power, or more than 200 W of power while removing or deteriorating DAF by controlling the laser  240 , the optical switch  244 , the IR laser optics  252  or the visible or UV optics  250 . 
         [0037]    Laser pulse parameters for removing a layer or layers of material  182  to expose the wafer surface  180  include a wavelength between about 255 nm and 532 nm, a pulse width between 10 ps and 100 ns, pulse energy of between about 0.1 μJ and 1.0 mJ per pulse, pulse repetition rate of greater than 100 kHz and pulse shapes which include Gaussian, top hat (circular) or top hat (square). Laser parameters for backside removal of DAF  214  include a wavelength between about 1.064 microns and 10.6 microns, either pulsed or shuttered continuous wave (CW) operation, either pulse energy of greater than 10 μJ for pulsed operation or laser power of greater than 200 W in the case of CW operation, and pulse shapes which include Gaussian, top hat (circular) or top hat (square). Laser parameters for through cutting the wafer  180  include a wavelength between about 255 nm and 532 nm, a pulse width between 10 ps and 500 ns, pulse energy of between about 0.1 μJ and 10.0 μJ per pulse, pulse repetition rate of greater than 100 kHz and pulse shapes which include Gaussian, top hat (circular) or top hat (square). 
         [0038]    Singulation of electronic devices from a wafer in this manner is efficient since the wafer does not have to be moved or re-aligned during the process as is required by other approaches to solving the problems associated with singulation of wafers on DAF. Embodiments of this invention also provide a substantially debris-free and undamaged wafer following singulation due to the limited amount of debris and thermal damage caused by removal of the DAF by infrared (IR) laser. In addition the DAF which remains attached to the electronic device by design is substantially debris-free and is trimmed accurately to the device. Advantages of using three lasers to process wafers in this fashion include greater throughput although at a greater system cost. Using two lasers can increase throughput to a lesser extent than using three lasers but at a lower incremental system cost. The solution using one laser may have the lowest system cost but correspondingly lower system throughput. 
         [0039]    It will be apparent to those of ordinary skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.