Abstract:
Economical production of configured, laser-drilled, high-precision, ultra-miniature multiple-via-hole patterns is accomplished by multiplexing the homogenized, shaped, nearly-collimated output of one or more high-power excimer lasers into a set of beamlines, differently configured at different depths through the thickness of the substrate. A substrate delivery subsystem provides a continuous supply of film substrate strips or segments, which may be blanks or intermediates. Various stencils in a mask provide a cup-shaped partial hole, which is subsequently provided with a mating stem hole. Each stem portion of each hole is laser-drilled into the bottom of the cup portion from either above or below to form a via-hole with a desired configuration, such as stem-glass (or cup/funnel), as desired for multi-micro-via-hole arrays for filtering or for forming clog-resistant aerosol nozzles. Parameter changes of one or both of duration and focus may substitute for changes of mask to effect the changes in cup configuration as contrasted to stem configuration.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This is a Continuation-in-Part to U.S. patent application Ser. No. 08/794,217, filed Jan. 27, 1997, to be issued Mar. 21, 2000, as U.S. Pat. No. 6,040,552, HIGH SPEED DRILLING SYSTEM FOR MICRO-VIA PATTERN FORMATION, AND RESULTING STRUCTURE, Jain, Dunn, Farmiga, Weisbecker &amp; Kling. This is a division of U.S. patent application Ser. No. 09,1531,629, filed Mar. 21, 2000, CONFIGURED-HOLE HIGH-SPEED DRILLING SYSTEM FOR MICRO-VIA PATTERN FORMATION, AND RESULTING STRUCTURE, Kling. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a via-drilling system and, more particularly, this invention relates to a low-cost, high-throughput drilling system for multi-micro-via-hole arrays, wherein each micro-via-hole is configured as a result of plural controlled applications of energy from sources including at least one patterned high-energy laser beam, resulting in an array of configured micro-via-holes.  
           [0004]    2. Description of Related Art  
           [0005]    The desire for multi-hole patterns of ultra-miniature via holes, are precisely located and of precise dimensions (multi-micro-via-hole patterns), is recognized in the fields of ink-jet print heads, aerosol generation and micro-filtering. Other, similar desires are expected as well, as other fields become more miniaturized. Miniaturization has far exceeded the capability of the metal drill bit, at least for high-precision via-drilling in tough substrates, because of bit breakage and bending, which not only destroys the drill bit but also destroys the symmetry and precision of the via-hole. Laser drilling is becoming the art of choice for drilling micro-via-holes. However, laser drilling is quite costly, and prior art technologies typically produce via-holes with low aspect ratios (hole depth: hole diameter of≦1: 1), or produce imprecise via-hole dimensions. Such laser drilling has exhibited low yields of acceptable multi-micro-via-hole patterns. As miniaturization continues, laser output beams take on the characteristics of shotgun patterns, making an untreated laser beam unsuitable for multi-micro-via-hole-array drilling. A previous patent application, Ser. No. 08/794,217, filed Jan. 29, 1997, HIGH SPEED DRILLING SYSTEM FOR MICRO-VIA PATTERN FORMATION, AND RESULTING STRUCTURE, K. Jain, T. J. Dunn, N. O. Farmiga, C. S. Weisbecker &amp; C. C. Kling, by a set of inventors which includes the inventor in this application, solves the shotgun pattern effect problem and many other problems with a technique involving a laser beam treated by homogenizer and projection optics to achieve an intense, self-luminous small-field image which is configured as a polygon. The substrate is scanned by complementary polygonal scans, through a mask, to ablate the desired via-hole pattern in a plastic ribbon. The previous patent application results in a via hole with entry aperture only somewhat larger than the exit aperture; the via hole is conical in configuration. A separate patent application, Ser. No. 08/889,307, filed Jul. 7, 1997, SIMULTANEOUS, TWO-SIDED PROJECTION LITHOGRAPHY SYSTEM, K. Jain, an inventor of the above patent application, has a technique for laser-imaging both sides of a substrate simultaneously, with registration of topside and bottom patterns. The technologies of these two prior art patent applicationss is useful in implementing this invention, but do not supply the control of configuration of micro-via-holes which is the subject matter of this invention.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    The object of the invention is to control the configuration of micro-via-holes in tough, thin substrates, by controlling partial drilling of micro-via-holes in a first step, and in a subsequent step by controlling patterned, homogenized laser ablation of the finished micro-via-holes within partially drilled holes produced during said first step.  
           [0007]    Another object of the invention is to provide a novel laser micro-via-hole drilling system which can contemporaneously drill a large number of configured high-quality via-holes in a selected micro-via-hole array pattern, with exceptional precision, speed and economy.  
           [0008]    A feature of the invention is the provision of a beam divider for efficiently separating the laser beam into a number of separate sub-beams for delivery of drilling pulses to top and bottom surfaces of pattern drilling beamlines simultaneously, registered so that the micro-via-hole is not only configured with a selected configuration but passes through the substrate in the selected alignment.  
           [0009]    An advantage of the invention is that configured micro-via-holes may be made resistant to blockage by having the exit hole larger than the entry hole.  
           [0010]    Another advantage of the invention is that the configuration of micro-via-holes is easily changed, allowing the same “soft tooling” equipment to serve in the laboratory by making prototypes, to serve as a pilot system to prove out techniques and product, and then to serve as an easily changed mass production tool —without the cost and risk of investing in special purpose “hard tooling.” 
           [0011]    Still another advantage of the invention is that the precision resulting from the use of masked projection lithography is combined with high-repetition presentation of the substrate for very high-speed, very-high-precision micro-via-pattern drilling at low cost for high production volumes.  
           [0012]    Yet another advantage of the invention is that the flow resistance of a micro-nozzle array can be dissociated from the thickness of the substrate by adjusting the relative depths of the cups and of the stems of cup/funnel-configured via holes in the array. 
       
    
    
       [0013]    Other objects, features and advantages of the invention will be apparent from the following written description, claims, abstract and the annexed drawings.  
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0014]    [0014]FIG. 1 is a semi-schematic view of a preferred embodiment, shown as in use to carry out the initial partial drilling of an array of micro-via-holes by dimpling.  
         [0015]    [0015]FIG. 2 is a semi-schematic view of a simplified version of an individual dimpler of the preferred embodiment shown in FIG. 1.  
         [0016]    [0016]FIG. 3 is a side elevation view of a two-stage laser system for drilling configured micro-via-holes, shown semi-schematically in use.  
         [0017]    [0017]FIG. 4 is a side elevation cutaway view of a thin plastic ribbon substrate with three differently configured micro-via-holes.  
         [0018]    [0018]FIG. 5 is a side elevation cutaway view of a thin plastic ribbon substrate with stem/cup configured micro-via-holes.  
         [0019]    [0019]FIG. 6 is a side elevation cutaway view of a thin plastic ribbon substrate with micro-via-holes configured as canted cup/funnels.  
         [0020]    [0020]FIG. 7 is a side elevation cutaway view of a thin plastic ribbon substrate with micro-via-holes configured as cone-stem cups.  
         [0021]    [0021]FIG. 8 is a side elevation schematic view of two-stage laser drilling equipment for micro-via-holes configured as canted cup/funnels in a thin plastic ribbon substrate.  
         [0022]    [0022]FIG. 9 is a side elevation schematic view of a dimpler for first-stage forming of cups for micro-via-holes configured as canted cup/funnels in a thin plastic ribbon substrate.  
         [0023]    [0023]FIG. 10 is a side elevation schematic view of first-stage drilling technique in which a photoresist is patterned for etching or ablation of first-stage cups for micro-via-holes.  
         [0024]    [0024]FIG. 11 is a side elevation schematic view of equipment for first-stage and coordinated top and bottom registered drilling, in which each micro-via-hole is configured with a cup and a pinch-waist stem.  
         [0025]    [0025]FIG. 12 is a simplified plan view of a mask for laser drilling of configured holes in two stages.  
         [0026]    [0026]FIG. 13 is a simplified plan view of an aerosol nozzle with cup/funnel via holes configured by the coordinated top/bottom equipment of FIG. 11 according to the mask of FIG. 12.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Pilot System  
         [0028]    [0028]FIGS. 1 and 2, which should be considered together, function to provide a pattern of dimples to serve as the cups of configured micro-via-holes in ribbon substrate  1 . Feed rollers  2  provide ribbon substrate  1  to dimpling roller  3  which presses dimplers  4  into ribbon substrate  1 , which is resting on anvil roller  5 . The result is that ribbon substrate  1  has a number of dimples  6  pressed into it. Dimplers  4 , and dimpling roller  3  as required, are preferably heated to cause plastic flow out of the dimples  6 .  
         [0029]    [0029]FIG. 1 and FIG. 2 are useful in a pilot system to make cup dimples in the surface of the substrate  1 . Dimpler wheel  3  has dimplers  4  which press into substrate  1  as it passes over anvil roller  5 . The substrate  1  dimples  6  act as cups, preferably at the exit side of each via-hole in the substrate  1  After dimpling, each via-hole is completed by a mating laser-drilled hole through from the cup dimple  6  to the opposite surface.  
         [0030]    Production System  
         [0031]    FIGS.  3 - 12  illustrate a preferred production system.  
         [0032]    Single-surface Production Illumination  
         [0033]    [0033]FIG. 3 shows, greatly simplified, a system using two lasers  7  and  8  to drill the cups and the stems, respectively, of cup/funnel via holes, in a single pass of the substrate  1  past the drilling station. Laser  7  produces wide beam  9 ; laser  8  produces narrow beam  10 . Wide beam  9  drills cups  11 - 16  halfway through the substrate  1 . Narrow beam  10  drills stem holes  17 - 20  respectively from cups  13 - 16  to the opposite surface of substrate  1 , connecting via holes  17 - 20  respectively with cups  13 - 16 .  
         [0034]    Note that FIG. 3 is shown simplified. In production, it is advisable to use the overlapping complementary polygonal scanning technique, with mask and substrate mounted on a common stage, described in the Jain et al. U.S. patent applications listed in the Prior Art section. Note that, depending upon the power of the laser, the configuration of the via-holes and the characteristics of the substrate, it is possible for one laser to drill an entire array pattern of via holes without changing the substrate position on the stage. Beam  9 , for example, if properly masked, may be drilling a pattern of a thousand cup-holes in the position shown as cup  11 , with beam  9  actually being a single beam scanning a thousand holes in a mask. Each micro-via-hole pattern thus may include a multiplicity of via-holes. Similarly, laser  8  provides drilling beam  10 , which is narrower than drilling beam  9 , or which has more narrowly constricted sub-beams, to perform the drilling of the narrow stems. Cup  11  is in the process of being drilled; completed cup portions  12 - 16  are shown. Stem portion  17  is in the process of being drilled; completed stem portions  18 - 20  are shown. Care must be taken in aligning the stem portions with the cup portions for each array. Much of the alignment, once achieved, is retained so long as the substrate is not moved. Alignment techniques used in semiconductor patterning are effective here.  
         [0035]    FIGS.  4 - 7  illustrate three differing micro-via-hole configurations, with three differing cup/funnels  14 ,  23  and  25  in one substrate strip in FIG. 4; straight-stem cup/funnels  21 - 22  in FIG. 5; canted-stem cup/funnels  23 - 24  in FIG. 6; and cone-base cup/funnel  25 - 26  in FIG. 7.  
         [0036]    Note that while it is preferred to use two different lasers for cup and stem, respectively, it is also possible to use a single laser, but to alter the focus and the effective drilling time to drill different sizes of cup/funnel and cone/stem-base. Focus alterations can be done by various means, such as by a vertical shift of the substrate with respect to the mask.  
         [0037]    Configurations of Via Holes  
         [0038]    [0038]FIG. 8 shows a two-stage laser drilling apparatus for configuring canted cup/funnel via holes. The ribbon substrate is fed right-to-left. Laser  7  provides a wide beam  9  which drills a standard cup  11  into the surface of substrate  1 . Laser  7  has already drilled the cup portions of cup/funnels  12 - 13  and  14 ′- 16 ′. Cup funnel  14 ′, for example, already has been completed with cup portion  23  and stem portion  24 . The stem portion of cup/funnel  13  is being drilled by laser beam  10  of laser  8 ′, which is arranged non-perpendicularly, at an angle to provide a narrow laser beam  10 , with the desired cant, to the canted-stem cup/funnel configurations being drilled.  
         [0039]    [0039]FIG. 9 shows a cylindrical dimpler roller  4  in greater detail than in FIG. 1. The cup dimpler  4  provides configured pressure to cause flow in the substrate material; heat may be applied as required.  
         [0040]    [0040]FIG. 10 shows a photoresist technique for providing an intermediate substrate for self-masked laser ablation of the cup portions of the cup/funnels. Photoresist layer  27  is exposed and developed to provide a pathway through its protective layer in which etching or other ablation may take place. The cups are then prepared and further configurations are made as before. It is possible to use the laser as the ablating mechanism, by overplating photoresist layer  27  with a mirror layer  28  which reflects the laser beam away. The laser beam then can serve in two phases to ablate first the cup and then, after refocusing or remasking, to ablate the stem. The substrate intermediate, for use in making micro-via arrays of configured via-holes, is made by the following process, comprising:  
         [0041]    step a) coating the substrate with a and protective metallic layer  27  for passivation against subsequent laser drilling:  
         [0042]    step b) coating the metallic-layer-coated substrate with a protective phiotoresist layer  28  for passivation against subsequent chemical etching:  
         [0043]    step c) exposing the twice-coated substrate with an array pattern for defining cup portions of the array to be made;  
         [0044]    step d) removing photoresist from the exposed pattern;  
         [0045]    step e) chemically etching away the metallic layer in the exposed pattern;  
         [0046]    step f) removing the remnants of the photoresist layer.  
         [0047]    The intermediate is thus patterned for self-masked laser ablation of the cup portions of the micro-via hole array.  
         [0048]    [0048]FIG. 11 shows how a complex configuration may be provided to the configured micro-via-holes in the array. A first laser  31  drills the cups. A second laser  32  drills the top portions of the stems. Note that, while individual micro-via-holes are shown, in practice the laser beam is patterned to ablate an entire array of holes simultaneously. The beam from the second laser  32  passes partially through a beam splitter  33 , and is partially reflected along a path of beam-directing mirrors  34  so as to drill the bottom portions of the stems directly in line with the top portions. As shown, this results in an array of configured micro-via-holes, each in the configuration of a cup/funnel with a pinch-waist stem. The configuration can be adjusted by adjusting the sub-beam diameters, sub-beam configurations, beam strength or beam duration of the various laser beams. FIG. 12, greatly simplified, shows a representative array mask  37 , with cup stencils  40  and stem stencils  41  set up for use in the coordinated top/bottom laser drilling equipment of FIG. 11.  
         [0049]    High-throughput Via-drilling Production System  
         [0050]    The production embodiment of the invention for a high-throughput via-drilling production system is similar to the design of the pilot system except that it utilizes an industrialized, high-powered excimer laser such as the LP 3308 from Lambda Physik. This excimer laser is a 3000 series industrialized system with output wavelength at 308 nm. It can produce 150 W of output power at 300 Hz repetition rate. The laser system is controlled via a LAN fiber optic data ring and PC controller which maintains a history and logbook file. The system also has control capability using RS-232 interfacing and modem support.  
         [0051]    The laser pulse energy is 500 mJ during stabilized operation at 300 Hz. This makes it possible to simultaneously feed up to 15 beamlines and generate up to 20 nozzle array patterns simultaneously in an exposure time as short as 2 seconds. This translates to a throughput of approximately 10 multi-via strips per second, depending primarily upon substrate delivery time.  
         [0052]    Two-surface Illumination  
         [0053]    [0053]FIG. 11 shows an illumination system comprising a stage  30 , two lasers  31  and  32 , and a semi-reflective mirror beam divider  33  feeding the beam from laser  32  to both sides of the substrate simultaneously as directed by mirrors  34 . All lasers and mirrors, as well as substrate  1 , are shown schematically as being supported by bridge  35 . In practice, it is usually advantageous to mount the lasers and bridge separately to a common structure, to use standardized beam-directing mirrors to direct the beam appropriately, and to mount the stage  30  separately to move the substrate  1  and any required mask  37 . The mask  37  is held in mask holder  38  which is mounted to the stage  30  by mask bridge  39 . The optics remain fixed; the substrate  1  and mask  37  are moved in exact synchronism by stage  30 .  
         [0054]    [0054]FIG. 12 shows, greatly simplified, detail of mask  37 . Cup-stencil holes  40  and stem-stencil holes  41  are arranged to operate with the coordinated to-bottom scanning equipment shown in FIG. 11. This accounts for the double set of stem-stencil holes  41 , positioned so that the stem is drilled from two sides to meet within the bulk of the substrate  1 .  
         [0055]    [0055]FIG. 13 shows, also greatly simplified, the completed array  42 , which is a section cut from a substrate  1 , having three holes shown as straight cup/funnels  43 .  
         [0056]    Process and Product-by-process  
         [0057]    FIGS.  4 - 7  show representative multi-hole via-patterns in a nozzle structure for aerosols, as produced by the process. The process results in an economical, high-quality via-patterned nozzle blank, having a via-pattern as required, cut from the substrate  1 . Note the representative via-holes  21 - 26  are shown enlarged, but not exactly to scale. Each entry hole and the related exit hole, of the individual via-holes produced by the process, conforms to its own assigned configuration criterion. The nozzle structure, produced by the process of drilling micro-vias in a substrate according to a set of related masks, is characterized by the following steps:  
         [0058]    (Step 1) Providing laser means to provide a beam having sufficient power to perform simultaneous via-hole-drilling of a large number of via-holes;  
         [0059]    (Step 2) Arranging beam processing to accept the beam output of said laser means and forward a shaped beam with a selected numerical aperture;  
         [0060]    (Step 3) Arranging homogenizer recollimator means to accept the beam Output of said beam processing means and forward a shaped, nearly collimated beam; and  
         [0061]    (Step 4) Arranging masking means to reconfigure the beam output into a set of sub-beams in an operational pattern, individual sub-beams differing in at least one parameter so as to configure a via hole differently at differing depths.  
         [0062]    Summary  
         [0063]    Laser drilling of micro-via-holes not only “drills” an array of a great number of very tiny via-holes through a ribbon substrate, but can also configure the individual micro-via-holes for optimums of flow with cleanability. Generally, such optimums of flow are found where a reversed wineglass-shaped funnel configuration is used. This permits the ribbon substrate to be reliably strong, with individual via-holes being of small diameter at the entrance to resist clogging by particles, and larger at the exit to permit greater flow. Where clogging is not a major consideration, however, it may be advisable to have conical or cylindrical hole configurations, hourglass configurations, upright wineglass configurations, or canted configurations.  
         [0064]    While the invention has been shown and described in terms of a number of embodiments, with a number of suggested modifications for special needs, for a number of uses, it will be clear that further modifications and additional uses are possible.