Patent Publication Number: US-2015072515-A1

Title: Laser ablation method and recipe for sacrificial material patterning and removal

Description:
FIELD 
     Integrated circuit packaging. 
     BACKGROUND 
     One method of connecting a semiconductor die to a substrate such as a package substrate is through a soldered connection between a contact pad of the die and a contact pad of the substrate (e.g., a package substrate). An underfill material of, for example, an epoxy resin may be disposed around the soldered connection to improve, among other things, temperature cycling capability. One technique for introducing an underfill material is to introducing it to the die at the wafer level (i.e., before dicing of the wafer into individual dice). A typical process includes applying an underfill material as a blanket over a wafer surface including the over contacts. The underfill material is then baked/cured and then planarized to a plane of the contact pads to expose the contact pads. A photoresist is then introduced and patterned leaving the contact pads exposed. This is followed by the application of a soldered paste to the contact pads and reflow to establish the solder connection to the individual contact pads. The photoresist material is then removed leaving the solder on the contact pads and the underfill material surrounding the contact pads. 
     To expose the contact pads through underfill material, current methods involve grinding, chemical mechanical polish or fly cut techniques. These methods produce residues that can embed in the underfill material between pads and potentially damaged fragile dielectric materials on the die. In addition, the current techniques to remove photoresist material from the wafer after solder reflow use wet (aqueous or organic) strippers. These strippers have a tendency to etch the backside of the wafer, solder and other film material. Photoresist materials are difficult to remove using conventional strippers because they generally have a high density of cross-linking to withstand a solder reflow temperature (e.g., 260° C.) and be compatible with a solder paste material and other processing materials. The more cured the photoresist material, the more cross-linking and the more difficult it is to remove without damaging other materials on the wafer. The temperature associated with solder reflow often contributes to the curing of the photoresist material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a portion of a wafer including a contact pad on a surface and a passivation material on the surface and over the contact pad. 
         FIG. 2  shows the structure of  FIG. 1  following the removal of passivation material to expose the contact pad. 
         FIG. 3  shows the structure of  FIG. 2  following the introduction of sacrificial material to a thickness suitable for solder introduction on the contact pads. 
         FIG. 4  shows the structure of  FIG. 3  following the formation of an opening in the sacrificial material to the contact pad. 
         FIG. 5  shows the structure of  FIG. 4  following the introduction of solder material. 
         FIG. 6  shows the structure of  FIG. 5  following the formation of a solder bump. 
         FIG. 7  shows the structure of  FIG. 6  following the removal of the sacrificial material. 
         FIG. 8  shows a side view portion of a silicon wafer including a contact pad on a surface and a passivation material on the surface and over the contact pad according to a second embodiment. 
         FIG. 9  shows the structure of  FIG. 8  following planarization or ablating of the passivation material to expose the contact pad and bring the blanket layer of the underfill material to a plane of the contact pad. 
         FIG. 10  shows the structure of  FIG. 9  following the introduction and patterning of sacrificial material on the passivation material with an opening to the contact pad and a solder material formed in the opening. 
         FIG. 11  shows the structure of  FIG. 10  following the formation of a solder bump. 
         FIG. 12  shows the structure of  FIG. 11  following the removal of the sacrificial material. 
         FIG. 13  shows a perspective top, side view of a laser ablation system including a pulsed-wave ultraviolet laser. 
         FIG. 14  shows a perspective top, side view of a laser ablation system including a constant wave excimer projection ultraviolet laser. 
         FIG. 15  illustrates a schematic illustration of a computing device. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-7  describe an embodiment of a process of introducing a passivation material on a wafer, patterning a sacrificial material on the passivation material to expose contact pads on the wafer, introducing solder and removing the sacrificial material after solder reflow.  FIG. 1  shows structure  100  that is, for example, a side view of a portion of a wafer. Wafer  110  is, for example, a silicon wafer with many integrated circuit dice formed therein. Each die has a number of contact pads on a surface to connect the die to, for example, a substrate package after dicing.  FIG. 1  shows one contact pad, contact pad  120  on a surface of wafer  110 . Contact pad  120  is, for example, a copper pad. 
     Overlying contact pad  120  as a blanket over, for example, a surface of wafer  110  is passivation material  130 . Passivation material  130  is, for example, any fabrication passivation such as inorganic passivation (such as silicon nitride or silicon oxinitride), or organic passivation (such as polyimide). In another embodiment, passivation material is an underfill material of, for example, an epoxy material. Representative epoxy material includes an amine epoxy, imidizole epoxy, a phenolic epoxy or an anhydride epoxy. Other examples of underfill material include a bismalleimide type underfill, a polybenzoxazine (PBO) underfill, or a polynorborene underfill. Additionally, the passivation material  130  may include a filler material such as silica. 
     Following the introduction of passivation material  130  on wafer  110 , where necessary, the passivation material is cured. One technique for curing an epoxy-based underfill material as passivation material  130  is by heating structure  100 . 
       FIG. 2  shows the structure of  FIG. 1  following the removal of passivation material  130  to expose contact pad  220  and bring the blanket layer of underfill material to a plane of the contact pad (e.g., contact pad  220 ).  FIG. 2  shows the structure with passivation material  130  surrounding contact pad  120 . In one embodiment, passivation material  130  is ablated using temporally coherent electromagnetic radiation. For example, a pulsed-wave UV laser ablation technique, in one embodiment, uses a raster-based system that sequentially ablates passiavtion material  130  on wafer  110 . The raster-based system sequentially ablates passivation material across wafer  110  until contact pads (e.g., contact pad  120 ) are exposed. A second laser ablation recipe may then optionally be used to clean the contact pads of any debris or oxide. A DXF file of a contact pad pattern on a specific device may be imported into a laser milling tool and a galvo system used to direct the laser energy only to the contact pad region. 
     Where a constant wave excimer laser is used, in one embodiment, such system uses a projection-based system where large areas of passivation material can be ablated sequentially until contact pads (e.g., contact pad  120 ) are exposed. In addition, once the contact pads are exposed, the pads may be cleaned of any residual debris or oxide using a second laser ablation recipe. A photomask of the contact pad pattern may be used or such second ablation to protect the underfill material around the exposed contact pads. 
     A pulsed-wave UV laser ablation recipe for removal of passivation material is shown in Table 1: 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 2.5 to 3.7 mJ 
               
               
                   
                 Frequency (rep rate): 55 kHz 
               
               
                   
                 Galvo speed: 500 mm/s 
               
               
                   
                 Beam expansion: 10X (beam diameter ~40 μm) 
               
               
                   
                 Number of passes depends on thickness of underfill material over 
               
               
                   
                 contact pads that need to be removed 
               
               
                   
                   
               
            
           
         
       
     
     A pulsed-wave UV laser ablation recipe for cleaning copper contact pads is shown in Table 2: 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 218 mJ 
               
               
                   
                 Frequency (rep rate): 32 kHz 
               
               
                   
                 Galvo speed: 210 mm/s 
               
               
                   
                 Laser spot size: 8 microns 
               
               
                   
                 Beam expansion: 10X (beam diameter ~40 μm) 
               
               
                   
                 A DXF file of the contact pad pattern is imported to the system and 
               
               
                   
                 galvo directs the laser beam to ablate only the copper contact pad 
               
               
                   
                 regions 
               
               
                   
                   
               
            
           
         
       
     
     Once passivation material  130  is brought to a plane of a surface of contact pad  120  or a desired level above the plane, a sacrificial material may be introduced and patterned to form openings to contact pads (e.g., contact pad  120 ) on wafer.  FIG. 3  shows the structure of  FIG. 2  following the introduction of sacrificial material  140  to a thickness suitable for solder introduction on the contact pads. In one embodiment, sacrificial material  140  is a linear material. A linear material as used herein is a material that does not include cross-linking agents or fillers that cross-link polymers of the material together when exposed to a photo (light) source. In this sense, linear materials include polymerizable materials including, but not limited to, materials that are susceptible to polymerization of monomers in the presence of light (e.g., UV light) without cross-linking agents or fillers. Examples of linear materials include organic materials such as acrylics, epoxies and polyimides. In another embodiment, sacrificial material  140  of a linear material may be introduced as a liquid in, for example, a spinning process and allowed to cure. In one embodiment, sacrificial material  140  is a non-linear material such as a photoresist material or dry film resist material. An example of such material is Riston™ commercially available from E.I. DuPont de Nemours and Company of Wilmington, Del. that may be introduced, for example, by a spinning process. 
       FIG. 4  shows the structure of  FIG. 3  following the patterning of openings in sacrificial material  140  on wafer  110  to expose desired contact pads such as opening  145  to contact pad  120 . Where sacrificial material  140  is a non-linear material such as a photoresist material, conventional photolithography techniques may be used to pattern sacrificial material  140 . Such techniques include introducing the material by spin coating using light to transfer a pattern from a photomask to the light sensitive photoresist and then a developer to remove the unwanted material. 
     In an embodiment where sacrificial material  140  is a linear material, openings such as opening  145  to desired contact pacts (contact pad  120 ) on wafer  110  may be formed by ablation using temporally coherent electromagnetic radiation. Representatively, such temporally coherent electromagnetic radiation may be in the form of a pulsed-wave UV laser or a constant wave excimer laser radiation. The energy level associated with the laser is tailored to be lower than the laser damage threshold energies for copper and solder to allow sacrificial material  140  to be removed without damage to the contact pad. 
     A laser or photoablation process allows selective removal of polymeric materials through photochemical versus thermal ablation. An advantage of a photoablation process is depth control in the organic material and clean removal of the organic material. The “cold” photoablation process would require assist of photon energy in with UV spectrum, with photon energy above hydro-carbon bond breakage. From the literature, C—C bond breakage requires a photon energy of 3.6 electron-volts (eV) which suits UV 355 nm laser radiation (third harmonic of YAG laser), and for C—H bond 4.3 eV which suits deep UV 266 nm laser radiation (fourth harmonic of YAG laser). The “hot” or “thermal” ablation process required excitation of vibrational energy modes in lattice of hydro-carbonic molecule, where IR-UV lasers are all suited. An advantage of deep UV lasers is obvious since ablation will promote clean and residue-free ablation of hydro-carbonic material by means of all ablation mechanisms. 
     A pulsed-wave UV laser ablation recipe for selective removal of a sacrificial material of RISTON™ photoresist is shown in Table 3. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 15.5 to 16.0 mJ 
               
               
                   
                 Frequency (rep rate): 44 kHz 
               
               
                   
                 Galvo speed: 440 mm/s 
               
               
                   
                 Laser spot size: 32 microns 
               
               
                   
                 Number of passes depends on thickness of sacrificial material to be 
               
               
                   
                 removed. 
               
               
                   
                   
               
            
           
         
       
     
     Utilizing a process flow and mechanism involving a linear sacrificial material opens up options for materials that can be considered making it easier to meet the process requirements. This also simplifies the processing of the materials since only application and cure are required. 
     Using a sacrificial material that is a linear material of an organic material without cross-linking agents or fillers further allows for finer features to be defined in laser processing then with filled materials where the cross-linking agents or fillers can attenuate the light resulting in poorer definition particularly for thick films. 
     The ability to use fully cured sacrificial materials with laser ablation techniques still further allows for better process stability to thermal and chemical processing. Alternative cure processes can be utilized to minimize wafer warpage. For example, a UV cure polyimide could be used that would minimize the thermal processing used since the only thermal processing required will be reflow of the bump in the solder formation process. 
     A wider range of material can be considered since there are no requirements for photo sensitivity. This could allow for specific selection of polymeric materials that can be removed without damaging underlying organic materials such as underfill material and passivation stress buffer material which are typically filled in the case of underfill material. 
       FIG. 5  shows sacrificial material  140  having opening  145  to contact pad  120 .  FIG. 5  also shows solder material  150  introduced into opening  145 . Solder material  150  includes, but is not limited to, solder paste material, solder balls or plated solder. 
       FIG. 6  shows the structure of  FIG. 5  following the formation of solder bump  160 . One way solder bump  160  is formed is through heating structure  100  (solder reflow). Once solder bump  160  is formed, sacrificial material  140  may be removed by, for example, an aqueous or organic stripper or temporally coherent electromagnetic radiation such as a pulsed-wave UV or constant wave excimer laser operated as described above and at an energy below damage threshold energies for a material of the contact pads and a material of the solder. 
       FIG. 7  shows the structure of  FIG. 6  following the removal of sacrificial material  140 . Where the process described in  FIGS. 1-7  is done at the wafer level, the wafer may now be diced into individual dice having contact pads including solder bumps (e.g., solder bump  160 ). An individual die may then be assembled into a package substrate. 
       FIGS. 8-10  describe a second embodiment of introducing a passivation material on a wafer and using a laser ablation method to expose contact pads and planarize the passivation material.  FIG. 8  shows structure  200  that is, for example, a side view portion of a wafer (e.g., a silicon wafer).  FIG. 8  shows contact pad  220  on a surface of wafer  210 . It is appreciated that wafer  210  may have thousands of similar contact pads across its surface. Contact pad  220  is, for example, a copper pad. Overlying contact pad  220  as a blanket over, for example, a surface of wafer  210  is passivation material  230 . Passivation material  230  may be any of the passivation materials referenced above including an underfill material of, for example, an epoxy material or other materials noted above. In one embodiment, passivation material  230  of underfill material is introduced on the surface of wafer  210  and then cured with, for example, by heating structure  200 . 
       FIG. 9  shows the structure of  FIG. 8  following the removal of passivation material  230  to expose contact pad  220 . In this embodiment, the removal involves a planarization of a surface of the structure to expose contact pad  220  and bring the blanket layer of passivation material  230  to a plane of the contact pad (e.g., contact pad  220 ). In one embodiment, removal of passivation material  230  involves ablation using temporally coherent electromagnetic radiation in a process such as described above. For example, a pulsed-wave UV laser ablation technique, in one embodiment, uses a raster-based system that sequentially ablates passivation material  230  on wafer  210 . The raster-based system sequentially ablates passivation material across wafer  210  until contact pads (e.g., contact pad  220 ) are exposed. A second laser ablation recipe may then optionally be used to clean the contact pads of any debris or oxide. A DXF file of a contact pad pattern on a specific device may be imported into a laser milling tool and a galvo system used to direct the laser energy only to the contact pad region. 
     Where a constant wave excimer laser is used, in one embodiment, such system uses a projection-based system where large areas of passivation material can be ablated sequentially until contact pads (e.g., contact pad  220 ) are exposed. In addition, once the contact pads are exposed, the pads may actually be cleaned of any residual debris or oxide using a second laser ablation recipe. A photomask of the contact pad pattern may be used or such second ablation to protect the passivation material around the exposed contact pads. 
     A pulsed-wave UV laser ablation recipe for removal of an amine epoxy underfill material as a passivation material is shown in Table 4: 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 2.5 to 3.7 mJ 
               
               
                   
                 Frequency (rep rate): 55 kHz 
               
               
                   
                 Galvo speed: 500 mm/s 
               
               
                   
                 Spot size: 8 microns 
               
               
                   
                 Beam expansion: 10X (beam diameter ~40 μm) 
               
               
                   
                 Number of passes depends on thickness of underfill material over 
               
               
                   
                 contact pads that need to be removed 
               
               
                   
                   
               
            
           
         
       
     
     A pulsed-wave UV laser ablation recipe for cleaning copper contact pads is shown in Table 5: 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 218 mJ 
               
               
                   
                 Frequency (rep rate): 32 kHz 
               
               
                   
                 Galvo speed: 210 mm/s 
               
               
                   
                 Laser spot size: 8 microns 
               
               
                   
                 Beam expansion: 10X (beam diameter ~40 μm) 
               
               
                   
                 A DXF file of the contact pad pattern is imported to the system 
               
               
                   
                 and galvo directs the laser beam to ablate only the copper 
               
               
                   
                 contact pad regions 
               
               
                   
                   
               
            
           
         
       
     
     Once passivation material  230  is brought to a plane of a surface of contact pad  220  or a desired level above the plane, a sacrificial material may be introduced and patterned to form openings to contact pads (e.g., contact pad  220 ) on wafer. A representative sacrificial material is a photoresist material.  FIG. 10  shows sacrificial material  245  introduced and patterned on underfill material  230  of wafer  210 . Sacrificial material  245  is patterned to have opening to desired contact pads.  FIG. 10  shows sacrificial material  245  having opening  240  to contact pad  220 . Following the introduction and patterning of sacrificial material  245 , solder material  250  is introduced into opening  240 . 
       FIG. 11  shows the structure of  FIG. 10  following the formation of solder bump  260 . One way solder bump  260  is formed is through heating structure  200  (solder reflow). Once solder bump  260  is formed, sacrificial material  245  may be removed by, for example, an aqueous or organic stripper or temporally coherent electromagnetic radiation such as a pulsed-wave UV or excimer laser operated as described above and at an energy below damage threshold energies for a material of the contact pads and a material of the solder. 
     A pulsed-wave UV laser ablation recipe for selective removal of RISTON™ photoresist material (commercially available from E.I. DuPont de Nemours and Company of Wilmington, Del.) is shown in Table 6. 
     
       
         
           
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
             
            
               
                   
                 Laser wavelength: 355 nm 
               
               
                   
                 Power: 15.5 to 16.0 mJ 
               
               
                   
                 Frequency (rep rate): 44 kHz 
               
               
                   
                 Galvo speed: 440 mm/s 
               
               
                   
                 Laser spot size: 32 microns 
               
               
                   
                 Number of passes depends on thickness of sacrificial material 
               
               
                   
                 to be removed. 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 12  shows the structure of  FIG. 11  following the removal of photoresist material  245 . Where the process described in  FIGS. 8-12  is done at the wafer level, the wafer may now be diced into individual dice having contact pads including solder bumps (e.g., solder bump  260 ). An individual die may then be assembled into a package substrate. 
     In the above embodiments, methods for removing or ablating materials (e.g., passivation material, sacrificial material) included ablation using temporally coherent radiation was described. Specific examples of providing such temporally coherent radiation included through a pulsed-wave UV laser ablation process and a constant wave excimer projection laser process.  FIG. 13  shows a schematic, perspective top, side view of a system for conducting a pulsed-wave UV laser ablation process. Referring to  FIG. 13 , system  300  includes pulsed-wave UV laser  310  connected to servomechanism  320  that controls a mechanical position in at least an XZ direction of laser  310 . Laser  310  directs electromagnetic radiation in the form of a beam to galvanometer  330  that steers the beam toward stage  350 . Mirror  340  may be disposed between galvanometer  330  and stage  350  to, for example, collimate the radiation. A DXF file of a pad pattern for structure  100  is transferred from computer  360  to system  300  and non-transitory machine readable instructions stored in computer  360  may be executed to direct a laser ablation process of material on wafer  370  on stage  350  of the system. 
       FIG. 14  shows a schematic perspective top, side view of a system employing a constant wave excimer projection laser. Referring to  FIG. 14 , system  400  includes laser  410  with an output disposed above wafer  470  (e.g., wafer) on stage  450 . Disposed between laser  410  and wafer  470  is photomask  440 . Photomask  440 , in one embodiment, includes a contact pad pattern to protect the material around contact pads of wafer from ablation and expose areas of material over contact pads. The ablation of the underfill material by way of a constant wave excimer laser may be directed by computer  460  that contains non-transitory executable machine-readable instructions to direct laser  410 . 
       FIG. 15  illustrates a computing device  500  in accordance with one implementation. Computing device  500  houses board  502 . Board  502  may include a number of components, including but not limited to processor  504  and at least one communication chip  506 . Processor  504  is physically and electrically connected to board  502  through, for example, a package substrate. Processor  504  is a die including solder bumps on contact pads, formed as described above, to connect to the package substrate. In some implementations the at least one communication chip  506  is also physically and electrically coupled to board  502 . In further implementations, communication chip  506  is part of processor  504 . 
     Depending on its applications, computing device  500  may include other components that may or may not be physically and electrically coupled to board  502 . These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth). 
     Communication chip  506  enables wireless communications for the transfer of data to and from computing device  500 . The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. Communication chip  506  may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. Computing device  500  may include a plurality of communication chips  506 . For instance, a first communication chip  506  may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip  506  may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. 
     In various implementations, computing device  500  may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, computing device  500  may be any other electronic device that processes data. 
     EXAMPLES 
     The following examples pertain to embodiments. 
     Example 1 is a method including introducing a passivation material over contact pads on a surface of an integrated circuit substrate; patterning a sacrificial material on the passivation material to define openings in the sacrificial material to the contact pads; introducing solder to the contact pads; and after introducing the solder, removing the sacrificial material with the proviso that, where the sacrificial material is a non-linear material, removing includes using temporally coherent electromagnetic radiation. 
     In Example 2, the sacrificial material in the method of Example 1 is a linear material and patterning the sacrificial material to define openings to the contact pads includes ablating with temporally coherent electromagnetic radiation. 
     In Example 3, the sacrificial material in the method of Example 1 is a linear material and removing the sacrificial material includes using temporally coherent electromagnetic radiation. 
     In Example 4, the sacrificial material in the method of Example 1 is a non-linear material. 
     In Example 5, the temporally coherent electromagnetic radiation in the method of Example 1 is provided by a pulsed wave ultraviolet laser. 
     In Example 6, the temporally coherent electromagnetic radiation in the method of Example 1 is provided by a constant wave excimer projection laser. 
     In Example 7, introducing the solder in the method of Example 1 includes introducing a solder paste or solder ball and reflowing. 
     In Example 8, prior to patterning the sacrificial material on the passivation material in the method of Example 1, the method includes ablating the passivation material to a thickness of the contact pads using temporally coherent electromagnetic radiation. 
     In Example 9, any of the methods of Examples 1-8 are used in the formation of an integrated circuit substrate such as a microprocessor including contact pads for connection to a package. 
     Example 10 is a method including introducing a passivation material over contact pads on a surface of an integrated circuit substrate; exposing the contact pads; patterning a non-linear material on the passivation material to define openings in the photosensitive material to the exposed contact pads; introducing solder to the contact pads; and after introducing the solder, removing the non-linear material using temporally coherent electromagnetic radiation. 
     In Example 11, the temporally coherent electromagnetic radiation in the method of Example 10 is provided by a pulsed wave ultraviolet laser. 
     In Example 12, the temporally coherent electromagnetic radiation in the method of Example 10 is provided by a constant wave excimer projection laser. 
     In Example 13, the temporally coherent electromagnetic radiation in the method of Example 10 is administered at an energy level lower than the damage threshold energy for solder and the contact pads. 
     In Example 14, exposing the contact pads in the method of Example 10 includes ablating the passivation material to a thickness of the contact pads using temporally coherent electromagnetic radiation. 
     In Example 15, any of the methods of Examples 10-14 are used in the formation of an integrated circuit substrate such as a microprocessor including contact pads for connection to a package. 
     Example 16 is a method including introducing a passivation material over contact pads on a surface of an integrated circuit substrate; exposing the contact pads; patterning a linear material on the passivation material to define openings in the linear material to the exposed contact pads; introducing solder to the contact pads; and after introducing the solder, removing the linear material. 
     In Example 17, removing the linear material in the method of Example 16 includes removing using temporally coherent electromagnetic radiation. 
     In Example 18, the temporally coherent electromagnetic radiation in the method of Example 16 is provided by a pulsed wave ultraviolet laser. 
     In Example 19, the temporally coherent electromagnetic radiation in the method of Example 16 is provided by a constant wave excimer projection laser. 
     In Example 20, the temporally coherent electromagnetic radiation in the method of Example 16 is administered at an energy level lower than the damage threshold energy for solder and the contact pads. 
     In Example 21, exposing the contact pads in the method of Example 16 includes ablating the passivation material to a thickness of the contact pads using temporally coherent electromagnetic radiation. 
     In Example 22, any of the methods of Examples 16-21 are used in the formation of an integrated circuit substrate such as a microprocessor including contact pads for connection to a package. 
     In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
     It should also be appreciated that reference throughout this specification to “one embodiment”, “an embodiment”, “one or more embodiments”, or “different embodiments”, for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.