Abstract:
A system and method for optimizing the output of a semiconductor die is described. A lid for a semiconductor package includes a radio frequency resonance dampening material which can be repatterned in real time to minimize resonance reflection within the package. The patterning may take the form of structures within the material or different sections of the material having differing resistivities to resonance reflection. Upon determing that acceptable resonance reflection has been achieved, the material is cured.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention generally relates to the suppression of radio frequency resonance in the packaging of semiconductor dies or chips.  
         BACKGROUND  
         [0002]    The packaging of semiconductor dies is well known. High speed dies used in optoelectric applications are typically coupled electrically and physically to a thermoelectric cooling (TEC) device. Specifically, high speed dies are typically attached to a submount, which in turn is physically coupled to the TEC device. A high speed connector, which is electrically connected with the die, leads from the submount to connect the die with a semiconductor device.  
           [0003]    It is standard practice to house the die, submount and TEC device within a package. The package provides physical protection to the die, submount, TEC device and attendant connectors. The electrical current that flows into the die, however, can create a radio frequency (RF) resonance. The RF resonance may degrade the performance of the die, and hence the overall performance of the semiconductor device.  
           [0004]    The side walls of some known packages have been coated with an RF resonance dampening material, such as a carbon-filled epoxy. One disadvantage to this is that after coating the side walls, curing the coating, and attaching the TEC device to a floor of the package, it may be determined that the RF resonance dampening material may not affect, or may insufficiently affect, the deleterious effects of the RF resonance. However, with known packages, the die, submount and TEC device must be removed from the package and either a new RF resonance dampening material must be added to the side walls of the package, a new pattern must be put in the material already on the side walls, or a new package must be used. However, there is no guarantee that the alteration of the RF resonance dampening material, or the new package, will be sufficiently effective to suppress the RF resonance to acceptably low levels. If the alteration is not sufficiently effective, the die, submount, and TEC device must again be removed from the package. Removal of the die, submount, and TEC device is time consuming and increases the costs of semiconductor packaging.  
         SUMMARY  
         [0005]    The invention provides a semiconductor package that includes a package body having a cavity, a die being located within the cavity, and a package lid for closing the cavity. The lid has a radio frequency resonance dampening material applied to an undersurface thereof.  
           [0006]    In one aspect of the invention, the semiconductor package includes a submount and a die mounted on the submount. The die and submount are located within the cavity. The lid allows for easy access to the packaged devices and quick and easy replacement and/or modification of the dampening material.  
           [0007]    These and other advantages and features of the invention will be more readily understood from the following detailed description which is provided in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a top view of a semiconductor package constructed in accordance with an embodiment of the invention.  
         [0009]    [0009]FIG. 2 is a cross-sectional view taken along line II-II of the semiconductor package of FIG. 1.  
         [0010]    [0010]FIG. 3 is a bottom view of a package lid constructed in accordance with another embodiment of the invention.  
         [0011]    [0011]FIG. 4 is a cross-sectional view taken along line IV-IV of the package lid of FIG. 3.  
         [0012]    [0012]FIG. 5 is a bottom view of a package lid constructed in accordance with another embodiment of the invention.  
         [0013]    [0013]FIG. 6 is a bottom view of a package lid constructed in accordance with another embodiment of the invention.  
         [0014]    [0014]FIG. 7 is a cross-sectional view taken along line VII-VII of the package lid of FIG. 6  
         [0015]    [0015]FIG. 8 is an alternative cross-sectional view taken along line VII-VII illustrating a package lid constructed in accordance with another embodiment of the invention.  
         [0016]    [0016]FIG. 9 illustrates process steps for fabricating a packaged semiconductor in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    Referring now to FIGS.  1 - 2 , there is illustrated a semiconductor package  10  which includes a package body  12 , a removable package lid  16 , a semiconductor chip or die  24 , a submount  26 , a TEC device  28  (shown schematically), a high speed connector  18 , and a conduit  22 . The conduit  22  is positioned on an external surface of the package body  12 .  
         [0018]    The TEC device  28 , submount  26 , and die  24  are positioned within a cavity  14  of the package body  12 . Specifically, the TEC device  28  is anchored to a lower wall  15  of the cavity  14 . The submount  26  is physically coupled to an upper portion of the TEC device  28 . The die  24  is physically coupled to an upper portion  25  of the submount  26 . Further, the die  24  is electrically coupled, by way of a connector  30 , to a coplanar waveguide (not shown) on an upper portion  25  of the submount  26 . The high speed connector  18  extends from the coplanar waveguide out of the cavity  14  through a channel  20  of the conduit  22 .  
         [0019]    The submount is preferably formed of a thermally conductive electrically insulating material, such as, for example, beryllium oxide. The TEC device  28  is a thermoelectric cooler which actively provides sufficient cooling based upon the dynamic characteristics of the die  24 . As an example, the optical performance output of an optoelectric die, such as the die  24 , changes over time and with temperature variations. As an output signal of the die  24  changes with time and temperature, the TEC device  28  is able to alter its cooling characteristics to provide optimum cooling to place the output signal within desired specifications.  
         [0020]    The lower wall  15  and interior side walls  17  of the cavity  14  may be coated with an RF resonance dampening material. The RF resonance dampening material may be applied as a viscous liquid, such as an epoxy, which creates ease of application to the interior side walls  17  and the lower wall  15 .  
         [0021]    The lid  16 , which is removable from the package body  12 , includes an undersurface  32 . An RF resonance suppressing material  34  is attached to the undersurface  32 . By attaching the material  34  to a removable structure, e.g. the lid  16 , the RF performance of the semiconductor package  10  can be measured with the lid  16  in place and the material  34  can be easily altered prior to its curing and without removing the die  24 , submount  26 , and TEC device  28 . Measurement of the RF performance may be accomplished by electrically biasing the die  14  and analyzing the output of the die  14  to determine its speed and/or other desired operating characteristics. An analyzer  60  (FIG. 2), including a display device  62 , is used to analyze the output and show the effectiveness of resonance dampening. Thus, the display device  62  indicates acceptable dampening or a need to alter the material  34 .  
         [0022]    Alteration of the material  34  may be accomplished in various ways. For example, alteration of the material  34  may be accomplished by removing the lid  16  and replacing it with another lid  16 . Alternatively, the lid  16  may be removed and the material  34  may be altered right on the lid or removed and replaced by a second material  34 . The various changes that may be exacted on the material  34  will be further discussed below. By altering the material  34  in this way, the RF performance of the semiconductor package  10  can be retested in real time, thus allowing an optional RF resonance suppression system to be put in place around the package  10  in real time. Once an acceptable RF resonance suppression is obtained, the material  34  is cured and the lid  16  is sealed.  
         [0023]    The material  34  is preferably a material which is easily applied to the lid  16  and which is readily formable and repatternable thereon, such as a viscous epoxy. While the material  34  has been illustrated as patternless, the material may be patterned, as will now be discussed.  
         [0024]    FIGS.  3 - 4  illustrate a material  134  which has been three-dimensionally patterned. The pattern includes an inclined surface  136  and a ledge  137  which form a saw-tooth profile. The material  134  is similar to the material  34 , with the exception that the material  134  includes the three-dimensional pattern. Each inclined surface  136  is shown extending the width W of the material  134 , although the inclined surfaces may not all extend the full width W.  
         [0025]    [0025]FIG. 5 illustrates a material  234 , which is similar to the material  134 , except that the material  234  has a two-dimensional sinuous pattern  236  instead of the three-dimensional saw-tooth pattern. The sinuous pattern  236  may extend the length L of the material  234 . The sinuous pattern  236  may be obtained by applying the material  234  to the lid  16  in alternating sections  237 ,  239 . Further, the material  234  may be formulated with various different dopants used in various sections of on the undersurface  32  of the lid  16 . For example, a carbon-doped material  234  may be used in the sections  237  and a silicon-doped material  234  may be used in the sections  239 . The carbon-doped and silicon-doped sections  237 ,  239  may be doped to provide different degrees of resonance reflection suppression.  
         [0026]    FIGS.  6 - 8  illustrate various other patterns of RF resonance dampening material which can be used. Specifically, a material  334  may be coated onto the lid  16  and patterned into cones  336  (FIG. 7). Alternatively, a material  434  may be coated onto the lid  16  and patterned into bumps  436 . In addition, both cones  336  and bumps  436  may be patterned in the material in alternating arrangement.  
         [0027]    Next will be described, with reference to FIG. 9, a method for optimizing the output of a semiconductor die, such as the die  24 . At step  500 , the semiconductor package body  12  is provided with a lid  16  including an RF resonance dampening material, such as the material  34 . The output of the die  24  is analyzed by the analyzer  60  at step  502 . A decisional step occurs at step  504 , namely whether the tested output is acceptable or not acceptable. If it is acceptable, then the material  34  can be cured (step  512 ). If instead the display device  62  indicates an unacceptable level of performance output of the die  24 , the material  34  can be altered at step  506 . The alteration may come in several forms. The lid  16  can be replaced by a second lid  16  having a material which has a different resistivity to resonance reflection, or the lid  16  can be removed and the material  34  thereon can be altered. The alteration can take the form of the addition of structures within the material, such as the inclined surfaces  136  and ledges  137  forming a saw-tooth profile, the two-dimensional sinuous pattern  236 , the cones  336 , the bumps  436 , or other suitable structures. At step  508 , the output of the die is retested. A decisional step occurs at step  510 , namely whether the retested output is still unacceptable. If it is, step  506  can be repeated as necessary. If an acceptable output has been achieved, the RF resonance suppression material is then cured at step  512 .  
         [0028]    While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, although waves, cones and bumps have been illustrated, any suitable structure may be patterned in the material  34 - 434 , such as, for example, cubes, pyramids, or amorphous undefined structures. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.