Abstract:
A structure having an optical element thereon has a portion of the structure extending beyond a region having the optical element in at least one direction. The structure may include an active optical element, with the different dimensions of the substrates forming the structure allowing access for the electrical interconnections for the active optical elements. Different dicing techniques may be used to realize the uneven structures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/273,321 entitled “Separating of Electro-Optical Integrated Modules and Structures Formed Thereby” filed Mar. 3, 2001, the entire contents of which are hereby incorporated by reference in their entirety for all purposes. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention is directed to techniques for separating modules on a wafer, particularly for use in creating wafer level assembly of electro-optical modules with manageable electrical input-output, and the structures formed thereby. The present invention is further directed to providing a mechanical support ledge for integrating an optical module with another structure, e.g., a circuit board.  
         BACKGROUND OF THE INVENTION  
         [0003]    One obstacle encountered in integrating electrical devices with optical components on a wafer level is how to manage the electrical connections. Typical wafer assembly and separating can yield an excellent optical assembly, but with no feasible location for electrical connections, as shown n FIG. 1. In FIG. 1, the module includes an active element  10  mounted on a submount  20  and an optics block  30  with an optical element  40  thereon. Interconnection lines  22  are formed on the submount  20  to provide electrical signals to and/or from the active element  10 . The active element  10 , e.g., a vertical cavity surface emitting laser (VCSEL), can bonded to the submount  20  at the wafer level, optics and any spacers aligned thereto and integrated therewith. When the individual modules are separated, the electrical connections  22  to the active element  10  are difficult to access.  
           [0004]    Another problem arises when attempting to integrate optical element elements formed on a wafer level with planar systems, such as a printed circuit board, or any system which is not to continue the stacked structure of the wafer level constructions. Support and alignment are both issues in this integration.  
           [0005]    One potential solution is to assemble the optics and spacers at the wafer level, then separate and bond to the individual submounts. However, this does not take fill advantage of wafer level assembly.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is therefore directed to methods and structures of providing interconnections to electro-optical elements in an electro-optical module formed on a wafer level which overcome at least one of the above disadvantages.  
           [0007]    The present invention is also directed to methods and structures of providing alignment and support for wafer based integrated optical subassemblies with non-stacked systems that overcome at least one of the above disadvantages.  
           [0008]    At least one of the above and other objects may be realized by providing a method of creating an electro-optic module including providing an active element wafer having a plurality of active elements thereon; aligning a feature wafer having features thereon to the active element wafer, providing an electrical bonding pad on at least one of the active element wafer and the feature wafer, attaching the feature wafer and the active element wafer to form an integrated wafer, and separating dies from the integrated wafer, at least one die including at least one active element and a feature, said separating including separating along different vertical paths through the integrated wafer such that at least a portion of the wafer having the electrical bonding pad extends beyond the other wafer.  
           [0009]    At least one of the above and other objects may be realized by providing an integrated electro-optical module including an active element on a first substrate, a feature on a second substrate, a bonding pad on one of the first and second substrates, the first substrate and the second substrate being attached in a vertical direction to one another, a portion of the first and second substrates having the bonding pad thereon extending further in at least one direction than the other substrate.  
           [0010]    At least one of the above and other objects may be realized by providing an apparatus including a planar structure having a hole therein, an optical element formed on a surface of a substrate, the surface having the optical element thereon extending through the hole of the planar structure, a mounting surface, integrated with the substrate having the optical element, the mounting surface extending in at least one direction beyond the substrate; and an attachment mechanism securing the optical element to the planar structure via the mounting surface.  
           [0011]    These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The foregoing and other objects, aspects and advantages will be described with reference to the drawings, in which:  
         [0013]    [0013]FIG. 1 is a schematic perspective view of an electro-optic module which has been formed at the wafer level and separated in a conventional manner;  
         [0014]    [0014]FIG. 2A is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0015]    [0015]FIG. 2B is a schematic side view of a plurality of electro-optic modules of FIG. 2A after being separated in accordance with the present invention;  
         [0016]    [0016]FIG. 3A is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0017]    [0017]FIG. 3B is a schematic side view of a plurality of electro-optic modules of FIG. 3A after being separated in accordance with the present invention;  
         [0018]    [0018]FIG. 4A is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0019]    [0019]FIG. 4B is a schematic side view of a plurality of electro-optic modules of FIG. 4A after being separated in accordance with the present invention;  
         [0020]    [0020]FIG. 5 is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0021]    [0021]FIG. 6A is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0022]    [0022]FIG. 6B is a schematic side view of a plurality of electro-optic modules of FIG. 6A after being separated in accordance with the present invention;  
         [0023]    [0023]FIG. 7A is a schematic side view of a plurality of electro-optic modules before being separated in accordance with the present invention;  
         [0024]    [0024]FIG. 7B is a schematic side view of a plurality of electro-optic modules of FIG. 7A after being separated in accordance with the present invention;  
         [0025]    [0025]FIG. 8 is a top view of the connection of an electro-optic module shown in FIG. 2B with a flexible printed circuit board in accordance with the present invention; and  
         [0026]    [0026]FIG. 9 is a schematic top view of the mounting of an optical subassembly with a circuit board in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0027]    In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices and methods are omitted so as not to obscure the description of the present invention with unnecessary details. As used herein, the term “wafer” is to mean any substrate on which a plurality of components are formed which are to be separated prior to final use.  
         [0028]    [0028]FIG. 2A is an exploded side view of the wafer level assembly of a plurality of integrated electro-optical modules. As in FIG. 1, the submount wafer  20  has an electro-optical element  10  thereon with interconnection tracks  22 . An optics wafer  30  having corresponding optical elements  40  formed thereon is also provided. A spacer wafer  50  separates the optics wafer  30  and the submount wafer  20 . The spacer wafer includes passages  52  therein which allow light to pass between the optical element  40  and the active element  10 . As shown in FIG. 2A, these passages  52  may be formed by etching when the spacer wafer  50  is silicon.  
         [0029]    In FIG. 2A, the spacer wafer  50  also includes indentations  54 , here also formed by etching, These indentations  54  are provided over the bond site  24  so that upon separating along lines  62 ,  64 , the bond site  24  will be accessible in the separated module, as seen in FIG. 2B. This facilitates electrical connections required to the electro-optical element  10 . The separating may include dicing the optics wafer  30  and the spacer wafer  50  along line  62  and dicing through all three wafers along line  64 . Alternatively, a wide blade may be used to dice the entire width between lines  62 ,  64  through the optics wafer  30  and the spacer wafer  50 , and then using a thin blade to dice only the submount wafer  20 . The attached structure may be flipped to facilitate dicing of only the submount wafer  20 .  
         [0030]    An alternative configuration is shown in FIGS. 3A and 3B, in which the spacer wafer includes holes  56  therein over the bond site  24 , rather than the indentations  54 . The separating lines  65 ,  64  remain the same and may be realized in either process noted above. However, the resulting structure will not have even edges of the optics wafer  30  and the spacer wafer  50 .  
         [0031]    Another configuration is shown in FIGS. 4A and 4B. Here, rather than forming the same active element  10 —bonding site  24  pairs on the submount wafer  20 , adjacent structures will be mirror images of one another. This allows large indentations  58  to be placed over two bonding site  24 ,  24 ′. The separating along separating line  76  may be performed in a conventional manner. Separating along separating lines  70 ,  72  is only through the optics wafer  30  and the spacer wafer  50 , and may be realized either by dicing along either line or with a thick dicing blade covering the width of the gap between separating lines  70 ,  72 . The submount wafer  20  is then separated along separating line  74 , preferably using a thin blade.  
         [0032]    [0032]FIG. 5 illustrates another configuration, requiring less separating. Here, the spacer wafer again includes the holes  56 . The optics wafer  30  also includes holes  36 , here etched in the optics wafer  30 , isolating the different optics needed for each module. Also as shown herein, the submount  20  includes two electro-optical elements  10 ,  12  requiring interconnection. Here the electro-optical elements are different from one another, with the electro-optical element  12  being monolithically integrated with the submount wafer  20 . Additional optical elements  42  are provided on the optical wafer  30  for the electro-optical element  12 . Here, only separation of the submount wafer  20  along separating line  80  is required to realize the individual modules.  
         [0033]    Another alternative is shown in FIGS.  6 A- 6 B. Here, a bonding pad  124  is provided on the optics wafer  30 . An interconnection line  122  connecting the active element  10  and the bonding pad  124  would be on both the mount wafer  20  and the optics wafer  30 . As shown on FIGS. 6A and 6B, the bonding between the mount wafer  20  and the optics wafer  30  is via an electrically conductive material, here shown as solder balls  90 . Alternatively, the spacer used in the previous configurations could be coated with metal where needed to provide the lead from the active element  10  to the bonding pad  24  on the optics wafer  30 . Now the separating lines  92 ,  94 ,  96  lead to a separation of the module that results in the optics wafer  30  extending beyond the mount wafer  20  in at least one direction, i.e., so that the bonding pad  124  is easily accessible.  
         [0034]    Another alternative is shown in FIGS.  7 A- 7 B. Here, one bonding pad  124  is provided on the optics wafer  30  while another bonding pad  24  is provided on the mount wafer  20 . A spacer wafer  50  is also provided in this configuration. The interconnection line  122  connecting the bonding pad  124  and the active element  10  would be on the mount wafer  20 , the spacer wafer  50  and the optics wafer  30 . As shown on FIGS. 7A and 7B, the interconnection line  122  follows the spacer wafer  50  between the mount wafer  20  and the optics wafer  30 . Alternatively, a metal or other electrically conductive material may be patterned on the wafer, and the interconnection line  122  being only on the mount wafer  20  and the spacer wafer  30 , with the electrically conductive material on the spacer wafer  50  providing connection therebetween. Now separating lines  93 ,  95 ,  97 ,  99  lead to a separation of the module that results in the optics wafer  30  extending beyond the mount wafer  20  in at least one direction, i.e., so that the bonding pad  124  is easily accessible, and the mount wafer  20  extending beyond the optics wafer  30  in at least one direction, i.e., so that the bonding pad  24  is easily accessible.  
         [0035]    As shown in FIG. 8, a flexible printed circuit board (PCB)  100  may be directly attached to the modules formed by any of the above configurations. While the above configurations show a cross-section of the modules, it is to be understood that any of the electro-optical element—bonding site pairs may be an array thereof, as shown in module  110  of FIG. 8. Due to the separating discussed above, a step  26  formed by the extension of the wafer having the bonding sites  24  thereon readily provides electrical connection to another device, here a PCB  100 . Further, the module  110  may be separated to provide steps  28  in the wafer having the bonding pads  24  thereon, here shown as the mount wafer  20 , on either side of the other wafer, here shown as the optics wafer  30 , to facilitate mechanical strain relief for the flex lead of the PCB. The steps  28  may extend around the whole perimeter.  
         [0036]    Even if electrical interconnections are not to be provided on the steps  28 , when integrating an optical subassembly formed on a wafer level with a system which is not t be stacked as the rest of the wafer assembly, these steps  28  may be used to provide support and/or alignment features. For example, as shown in FIG. 9, an optical subassembly  130  to be mounted in a circuit board  120  having a hole  125  therein for receiving the optical subassembly  130  may include steps  128  to provide mechanical support and/or alignment to the circuit board. The steps  128  may extend around the entire perimeter of the optical subassembly  130 . The optical subassembly  130  and the steps  128  may be formed on a wafer level. The steps  128  may include alignment features for facilitating alignment of the circuit board  120  and the optical subassembly  130 . The steps  128  may provide mechanical mounting surface for mounting the optical subassembly  130  to the circuit board  120 . The use of the steps  128  for attachment also allows the bonding material to be kept out of the optical plane.  
         [0037]    It will be obvious that the invention may be varied in a plurality of ways, such as the use of different bonding materials, extension in one or more directions, and different, or no, spacer configurations. Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the appended claims.