Abstract:
Optical components may be precisely positioned in three dimensions with respect to one another. A bonder which has the ability to precisely position the components in two dimensions can be utilized. The components may be equipped with contacts at different heights so that as the components come together in a third dimension, their relative positions can be sensed. This information may be fed back to the bonder to control the precise alignment in the third dimension.

Description:
BACKGROUND  
         [0001]    This invention relates generally to the assembly of components for optical communication networks.  
           [0002]    In optical networks, a number of components may be placed on a structure, such as an optical bench or a planar lightwave circuit. It is advantageous to precisely position these structures using high precision flip chip bonders. However, such bonders are only able to provide alignment in the X and Z coordinates, which basically exist in a plane corresponding to the plane of the optical bench or the planar lightwave circuit.  
           [0003]    These bonders do not control the positioning in the transverse or Y direction normal to the surface of the bench or circuit. Unfortunately, optical coupling efficiency between components is also highly dependent on the Y-height placement. However, the present inventors know of no methodology or tooling to address the Y-height placement aspect.  
           [0004]    Thus, there is a need for better ways to provide alignment operations for building passive optical devices.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is an enlarged, cross-sectional view of one embodiment of the present invention;  
         [0006]    [0006]FIG. 2 is a schematic depiction of the embodiment shown in FIG. 1;  
         [0007]    [0007]FIG. 3 is an enlarged, cross-sectional depiction of another embodiment of the present invention;  
         [0008]    [0008]FIG. 4 is a schematic depiction of the embodiment shown in FIG. 3;  
         [0009]    [0009]FIG. 5 is an enlarged, cross-sectional view of still another embodiment of the present invention;  
         [0010]    [0010]FIG. 6 is a schematic depiction of the embodiment shown in FIG. 5; and  
         [0011]    [0011]FIG. 7 is a schematic depiction of another embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring to FIG. 1, an optical amplifier  14  may be positioned on a silicon optical bench or planar lightwave circuit  12  in one embodiment of the present invention. The bench  12  may be L-shaped in cross section in one embodiment of the present invention. The bench  12  and the optical amplifier  14  may each have a part  16   a ,  16   b  of a waveguide  16  that ultimately needs to be aligned. Thus, it is desirable to use a high precision flip chip bonder or other chip placement tool to position the amplifier  14  precisely on the bench  12  so that the portion  16   a  of the waveguide lines up with the portion  16   b  of the waveguide on the separate bench  12  and amplifier  14 .  
         [0013]    Though the present description speaks of amplifiers and benches, the present invention is applicable to aligning and positioning any optical component with respect to any other optical component. Thus, the discussion of optical amplifiers and benches is merely meant as an illustrative example.  
         [0014]    The amplifier  14  may have a bonding pad  18  including a plurality of portions  18   a - 18   d . Each of the portions  18   a - 18   d  may be a distinct portion that extends downwardly from the amplifier  14  and is separated from adjacent portions in one embodiment.  
         [0015]    Conversely, on the bench  12 ; a plurality of bonding pads  20   a - 20   d  may be provided which extend upwardly and which are distinct and separate from their respective neighbors in one embodiment. In one embodiment, the bonding pads  20  and the bonding pads  18  are made of the same material, such as gold. However, the bonding pads  20   a - 20   d  have a stepped configuration such that the height of the pads  20   a  is higher than the pads  20   b , which is higher than the pads  20   c , which is higher than the pads  20   d.    
         [0016]    Thus, when the amplifier  14  is lowered onto the bench  12 , one or more of the pads  18  makes physical contact with one or more of the pads  20 . However, as shown in FIG. 1, there is no contact between any of the pads  18  or any of the pads  20  since the amplifier  14  and bench  12  are being positioned in the Y direction. The physical contact between particular pads  18  and  20  may also close an electrical switch  21  whose contacts are formed by the pads  18  and  20 .  
         [0017]    Thus, referring to FIG. 2, the pads  18  and  20  form a plurality of switches  21  (which are closed when the pads  18  make contact with their aligned pads  20 ). The switches  21  are shown in their open position because no contact has been established between pads  18  and  20  in FIG. 1. The switches  21   a - 21   d  in FIG. 2 are coupled to a contact  22   a - 22   d . The contact  22  may be probed by a probing tool or other device to determine whether or not the switches  21  are open or closed.  
         [0018]    Depending on which switches  21  are closed, the precise Y dimension orientation of the amplifier  14  and the bench  12 , relative to one another, can be determined. In particular, since each pad  20  may have a different height in one embodiment, closure of any switch  21  indicates a relative spacing between the amplifier  14  and bench  12 .  
         [0019]    For example, referring to FIG. 3, the pad  18   a  has now made contact with the pad  20   a , as indicated at B. Thus, referring to FIG. 4, the switch  21   a  is closed, but the other switches  21  remain open. As indicated at A′, the waveguide portions  16   a  and  16   b  are still not precisely aligned.  
         [0020]    Referring to FIG. 5, after further displacement in the Y dimension, the pad  18   b  now also contacts the pad  20   b , as shown in B′. To achieve this result, the pad  18   a  may be deformed in one embodiment. In this position, the waveguide portions  16   a  and  16   b  are precisely aligned as shown at A″. Here, the switches  21   b  and  21   a  are both closed and the switches  21   c  and  21   d  are both open as shown in FIG. 6. Thus, the precise relative positions in the Y dimension can be determined to any desired granularity. More or fewer switches  21  may be provided to achieve the desired results, with variations in their heights in units of 0.2 nm, for example, or any other value such as 0.05 nm or 0.5 nm as desired for the particular application.  
         [0021]    The flip chip bonder has precise alignment in the X and Z coordinates. Through the provision of the switches  21 , precise alignment can be obtained in the Y direction. Therefore, the precise positioning of the parts is possible on a real time basis in some embodiments of the present invention. Rapid, nondestructive screening and sorting may also be accomplished using for example a prober to determine the resistance of the switches after the bonding step has been completed.  
         [0022]    In some embodiments, the switches  21  may be fabricated during wafer processing using combinations of masking and etching, dry or wet, and the same process steps as deposition, via etch, and the like. Resolution of the switches  21  may be defined by the thicknesses of the respective pads  18 ,  20 . Since the pads  18  and  20  define the switches  21 , a material to facilitate electrical contact (such as gold) may be provided on the facing surfaces of the pads  18  and  20 .  
         [0023]    During the bonding process, a metal on the amplifier  14  side may deform or shrink to enable bond establishment between the amplifier  14  and bench  12 . The deformation stops when the bonding force is withdrawn. This action facilitates the connection of the bond pad  18  on the amplifier  14 , connecting or shorting the switches  21  at different step heights. Depending on the degree of deformation or transformation of the pads  18  on the amplifier  14 , more or fewer contacts may be closed. By measuring the resistance of the switches  21  after bonding, one can determine the distance (and/or deformation) in the Y dimension of the amplifier  14  relative to the bench  12 .  
         [0024]    The construction of the switches  21  can be reversed depending on the overall process sequence. Pads of different heights may be fabricated on the amplifier  14  and the mating pads may be provided on the bench  12  in another embodiment. The concept of the switches  21  can be extended to checking other critical bonding factors which determine coupling efficiency, such as bonding integrity, tilt angle, and rotation angle.  
         [0025]    The Y-height can be determined immediately after bonding by checking the switches  21  using wafer probing. In cases where the bench is a wafer and multiple components are aligned using this method, the prober may provide a wafer map for sorting and the wafer map may reduce the cost of testing for bad bench/amplifier combinations  10 , translating to lower cost of the overall product in some embodiments. With a continuity meter or prober communicating with the bonder, besides the X and Z coordinates, the real time Y-height bonding data can be fed back to the bonder for real time control. The feedback may facilitate the optical passive alignment and high volume production and, therefore, may further reduce manufacturing costs.  
         [0026]    Referring to FIG. 7, the amplifier  14  and bench  12  may be represented by integrated switches  21 . Those switches  21  sense the distance between the amplifier  14  and the bench  12 . That information may be read out by a wafer prober or continuity tester  26  using the contacts  22 . The information about what switches  21  are open and closed may then be converted into a relative position in the Y direction. That information may then be provided by the prober  26  back to the bonder  24 . The bonder  24  may then appropriately position the amplifier  14  and bench  12  based on the desired orientation.  
         [0027]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.