Abstract:
Selective area stamping of optical elements may be performed to make multiple micro-optic components on one or two sides of a substrate may be fabricated using a batch process. The presence of molding material may be controlled on the substrate through the use of gaps.

Description:
BACKGROUND  
       [0001]     Micro-optic components are typically used in imaging or optical interconnect applications. Conventionally, such optical components are manufactured by directly etching the desired shape into a suitable substrate using standard lithography and semiconductor processing techniques or by building a mold to allow injection molding of a thermoplastic to create the optical component. The first method creates an environmentally stable optical component but is typically slow and expensive. The second method rapidly creates parts but is limited to thermoplastics that are unstable at elevated temperatures.  
       BRIEF SUMMARY OF THE INVENTION  
       [0002]     In accordance with the invention, multiple micro-optic components on one or two sides of a substrate may be fabricated using a batch process. The substrate may then be diced into individual lens assemblies. A large number of optical lenses may be molded from an optically curable polymer on a suitable substrate. Alternatively, a thermally curable polymer may be substituted for the optically curable polymer. The substrate may be then diced into individual lens assemblies. This typically allows finished lens assemblies to have the mechanical properties of the substrate. Metal alignment marks and optical elements may be patterned onto the substrate prior to optical lens fabrication.  
         [0003]     Typically, selective area stamping of optical lenses allows various optical elements to be combined on a substrate by using multiple simple molds and processes optimized for element function, mold shape and size. Different materials optimized for different optical elements may be used. If lenses are molded from a continuous layer of polymer as opposed to selective area stamping in accordance with the invention, all optical elements would typically be formed at the same time, from the same material and by the same process. Selective area stamping allows easy singulation in accordance with the invention. In selective area stamping, the optically curable polymer is not contiguous over the substrate which decreases breakage during singulation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIGS. 1   a - 1   e  show molding of micro-optic components from an optically curable polymer material in accordance with the invention.  
         [0005]      FIGS. 2   a - 2   d  show molding of a stamper from an optically curable polymer material using a master in accordance with the invention.  
         [0006]      FIG. 2   e  shows an alternative to  FIG. 2   a  in accordance with the invention.  
         [0007]      FIGS. 3   a - 3   b  show another method for molding of a stamper from an optically curable polymer material using a master in accordance with the invention.  
         [0008]      FIGS. 4   a - 4   c  show molding a stamper from an optically curable polymer material where optical elements are formed at the bottom of a cavity in accordance with the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]      FIGS. 1   a - e  show an embodiment in accordance with the invention.  FIG. 1   a  shows stampers  110  which may be molded from a master or stampers  110  may be directly fabricated as the inverse of the desired lens profile. Molding stampers  110  from a master is described further below.  
         [0010]     Substrate  120  typically has metal alignment mark  140  to provide for alignment of stampers  110  with substrate  120 . Molds  145  for the optics in stampers  110  may be made larger than the desired optics to allow for the shrinkage in optically curable polymer  115  (see  FIG. 1   b ) when cured. The use of molded polymer optics is typically less expensive than molding or etching lenses from inorganic materials such as glass. Optically curable polymer  115  may be a UV curable polymer such as J91® or SK-9® available from Summers Labs or Norland 61® available from Norland. Use of green initiators such as titanocene dichloride or blue initiators such as camphotoquinone, for example, allow curing under green or blue light conditions. With the use of the appropriate initiators curing can be shifted to different parts of the optical spectrum as desired.  
         [0011]     In accordance with an embodiment of the invention, stampers  110  are typically coated with release layer  117  as shown in  FIG. 1   b.  Providing release layer  117  on stampers  110  prevents molded optics  159  from sticking to molds  145  instead of substrate  120 . Release layers, such as release layer  117  are typically made from polytetrafluoroethylene (e.g. fluorinated carbon ) non-stick type materials. Optically curable polymer  115  is locally dispensed onto stamper  110 . For example, optically curable polymer  115  may be mechanically dispensed. In an embodiment, optically curable polymer  115  may be forced through a needle or other suitable orifice using mechanical pressure or gas or liquid pressure. In another embodiment, screen printing that forces optically curable polymer through holes in a suitable defined mask may be used.  
         [0012]     In another embodiment, optically curable polymer  115  may be transferred to the surface of stampers  110  by contacting molds  145  of stampers  110  with a reservoir, such as a pool of optically curable polymer  115  or a porous material saturated with optically curable polymer  115  in a manner analogous to a stamping pad saturated with ink. Typically, care should be taken to control the amount of optically curable polymer  115  dispensed onto stampers  110  to ensure that coverage of optically curable polymer  115  is limited on substrate  120  once curing has occurred. Optionally, stampers  110  with optically curable polymer  115  as shown in  FIG. 1   b  may be placed into a vacuum chamber in a degassing step to remove any trapped air pockets.  
         [0013]      FIG. 1   c  shows the step of bringing locally optically curable polymer  115  coated stampers  110  into contact with substrate  120 . Substrate  120  is typically a flat piece of material that serves a mechanical support function as well as an optical function. For example, substrate  120  may be substantially transparent in applications where light passes through the optical elements or reflective for optical elements that require reflection from the interface between substrate  120  and the optical elements. Substrate  120  may also be an active element such as a laser or detector. The surface of substrate  120  may be prepared prior to contact with locally optically curable polymer  115  coated stampers  110  to enhance adhesion of optically curable polymer  115  when cured.  
         [0014]     The separation distance d between substrate  120  and molds  145 , when optically curable polymer  115  begins to flow as substrate  120  and molds  145  are brought into contact with each other, typically determines the dimensions needed for gap  191  to function in accordance with the invention. The separation distance d sets the approximate height and area dimensions needed for the size of gap  191  so that excess optically curable polymer  115  will collect in gap  191  instead of forming a thick film over substrate  120 . If gap  191  has the appropriate dimensions as determined from the separation distance d, optically curable polymer  115  will tend to move vertically up the sides of gap  191  as molds  145  and substrate  120  are brought together, reducing the thickness of the film formed on the surface of substrate  120 . Use of release layer  117  enhances this effect. Gap  191  may be made larger than the dimensions described above to keep areas in and around elements such as semiconductor lasers on substrate  120  free from optically curable polymer  115 .  
         [0015]     Metal alignment mark  140  may be patterned on substrate  120  for alignment purposes and thin metal elements may be patterned on substrate  140  for optical functions such as, for example, a diffraction grating. Stampers  110  may be aligned to features present on substrate  120  prior to bringing stampers  110  into contact with substrate  120 . Parallelism of stampers  110  and substrate  120  is typically controlled using the bonding equipment. Stampers  110  and substrate  120  in  FIG. 1   c  may be held together through the use of an applied force or by the weight of substrate  120 . Once substrate  120  and locally optically curable polymer  115  coated stampers  110  are in contact as shown in  FIG. 1   c,  stamper  110 , optically curable polymer  115  and substrate  120  are exposed to light to cure optically curable polymer  115 . For creation of single sided optical elements, stampers  110  and substrate  120  are separated leaving molded optical element  190  on substrate  120  (e.g., see  FIG. 1   e ).  
         [0016]      FIG. 1   d  shows the configuration for making optical elements on both sides of substrate  120  in accordance with the invention. The process described above is repeated with bonded stamper  110  and substrate  120  serving as a substrate to make additional optical elements.  
         [0017]      FIG. 1   e  shows that multiple local stampings of optical elements  190  may be made on a side of substrate  120 . Stamper  112  is removed and the process is repeated as many times as necessary. Each separate stamping of optical elements  190  may use different polymer materials, different stamping molds and different curing conditions to optimize the process. This procedure may be performed in parallel where an array of stampers  112  is used with different molds and different polymer materials  
         [0018]     Molded optical elements  190  may be coated with anti-reflective coatings or reflective coatings, if desired, and substrate  120  with molded elements  190  is then typically singulated as required.  
         [0019]     Some polymers used in accordance with the invention will not cure in the presence of air. Stamper  110  is designed such that excess optically curable polymer  115  is squeezed into areas where optically curable polymer  115  is exposed to air during the curing process. Following curing and separation of stamper  110  from substrate  120 , excess uncured optically curable polymer  115  may be removed from substrate  120 . For example, a solvent that preferentially dissolves uncured polymer such as acetone may be used. Hence, the remaining optical elements  190  have very little excess material allowing easy singulation and the requirements for precise volume control discussed above are relaxed.  
         [0020]     For local stamping of optical elements, it is typically useful to have a specific shape characteristic for stampers  110 . The desired shape in accordance with the invention has the molds for optical elements  190  (see  FIG. 1   e ) contained within plateau areas  157  of polymer material. This typically allows more force to be applied to the local areas where the molding is taking place. Hence, when a fixed force is applied during the molding process (see above), the force is concentrated on plateau areas  157  where the molding is taking place instead of having the force being uniformly distributed if stampers  110  had a more planar design where gaps  191  would be missing in  FIG. 1   e . This results in thin field regions, typically on the order of 1 μm to 2 μm where optically curable polymer  115  is squeezed between stampers  110  and substrate  120 . Excess amounts of optically curable polymer  115  forced from between stampers  110  and substrate  120  accumulate in gaps  191  at the edge of plateau areas  157  instead of being distributed as a field film over substrate  120 . Also, if local dispensing of optically curable polymer  115  is used with a planar stamper having no gaps  191 , excess optically curable polymer  115  will typically spread out as a large thick film over substrate  120  which is undesirable.  
         [0021]      FIGS. 2   a - 2   d  show stamper fabrication in accordance with the invention.  FIG. 2   a  shows stamper blank  210 . Stamper blank  210  is a flat substrate which provides mechanical support for molding polymer  215 . In accordance with the invention, stamper blank  210  is typically made of a material transparent to light.  
         [0022]     Stamper blank  215  may be patterned with dicing marks  230 . In this embodiment, locally dispensed optically curable polymer  215  will tend to pool between dicing marks  230  on the surface of stamper blank  210  as shown in  FIG. 2   a.  Another method of patterning stamper blank  210  in accordance with the invention involves scribing the surface.  
         [0023]     Stamper blank  210  may also be patterned so that optically curable polymer  215  will wet only specific areas. For example, as shown in  FIG. 2   e,  release layer  218  may be patterned by a photolithographic process to allow wetting of only specific areas. Alternatively, a shadow mask may be used to pattern release layer  218 . Optically curable polymer  215  is then typically dispensed locally as described above.  
         [0024]      FIG. 2   b  shows master  250  typically coated with release layer  217  to prevent optically curable polymer  215  from sticking to master  250  and alignment of master  250  with the local areas of optically curable polymer  215  on stamper blank  210 . Because master  250  does not provide an optical function, master  250  may typically be made from a wide variety of materials such as, for example, silicon, metal, glass or plastic and may be fabricated by many different methods. The features of master  250  may be made larger than the desired final features of the optical elements to accommodate shrinkage of optically curable polymer  215  during curing. Master  250  may have optional alignment features such as relief  291  that are transferred to mold  245  at the same time as the optical elements (see  FIG. 2   d ).  
         [0025]     Parallelism of stamper blank  210  and of master  250  is adjusted accordingly in  FIG. 2   b  Then, stamper blank  210  and master  250  are brought into contact as shown in  FIG. 2   c.  External force may be provided to hold stamper blank  210  and master  250  in contact. Light is applied to cure optically curable polymer  215 .  FIG. 2   d  shows resulting stamper  211  with mold  245  separated from master  250  including optional alignment feature  292  transferred to mold  245  through use of relief  291 .  
         [0026]      FIGS. 3   a - 3   b  show stamper fabrication in accordance with the invention. With reference to  FIG. 3   a,  stamper blank  310  is coated with a blanket layer of optically curable polymer  315  using dip coating, spray coating or other suitable coating methods. Master  350  is coated with release layer  317  to prevent optically curable polymer  315  from sticking to master  350 . Stamper blank  310  is brought into contact with master  350  while parallelism of stamper blank  310  and master  350  is maintained. Light is used to cure optically curable polymer  315 .  FIG. 3   b  shows resulting mold  345  and stamper  311 . Stamper blank  310  and master  350  are separated after optically curable polymer  315  is cured. Regions  375  are removed either mechanically by dicing or milling or chemically by etching to provide stamper  311 . The process may remove just the excess portion of optically curable polymer  315  or also part of stamper blank  310 .  
         [0027]      FIGS. 4   a - 4   c  show stamper fabrication in accordance with the invention. Master  450  has optical element shapes  435  formed at the bottom of cavity  495 . Master  450 , including optical element shapes  435  are typically coated with release layer  417 . Optically curable polymer  415  is locally dispensed on master  450  to fill cavity  495  as shown in  FIG. 4   a.  In practice, there typically are a number of cavities  495  with optical element shapes  435  on master  450  to allow creation of stampers  411  in parallel.  
         [0028]      FIG. 4   b  shows master  450  with dispensed optically curable polymer  415  and stamper blank  410  being brought into contact with one another. Light is then used to cure optically curable polymer  415 . Finally, master  450  and stamper blank  410  are separated leaving stamper  411  with cured mold  445 .  
         [0029]     While the invention has been described in conjunction with specific embodiments, it is evident to those skilled in the art that many alternatives, modifications, and variations will be apparent in light of the foregoing description. Accordingly, the invention is intended to embrace all other such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.