Abstract:
In one embodiment, wafer-scale antenna module is provided that includes: a substrate having a first surface and an opposing second surface; a plurality of conductive contact regions extending from the first surface into the substrate towards the second surface; active circuitry formed in the substrate adjacent the second surface, the active circuitry electrically coupled to the conductive contact regions; an insulating layer adjacent the first surface, the insulating layer forming a plurality of vias arranged corresponding to the plurality of conductive contact regions, each via forming an opening at the corresponding conductive contact region; and a plurality of antennas formed on the insulating layer corresponding to the plurality of vias; wherein each via contains an electrical conductor to electrically couple the corresponding contact region to the antenna corresponding to the via, whereby a resulting separation between the driving circuitry and the antennas aids an electrical isolation of the driving circuitry from the antennas.

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. application Ser. No. 10/891,352, filed Jul. 14, 2004, now U.S. Pat. No. 7,042,388, which in turn claims the benefit of U.S. Provisional Application No. 60/487,418, filed Jul. 15, 2003, the contents of both of which are incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates generally to beam forming antenna systems, and more particularly to a beam forming wafer scale antenna module with backside connectivity. 
   BACKGROUND 
   Conventional beam forming systems are often cumbersome to manufacture. In particular, conventional beam forming antenna arrays require complicated feed structures and phase-shifters that are impractical to be implemented in a semiconductor-based design due to its cost, power consumption and deficiency in electrical characteristics such as insertion loss and quantization noise levels. In addition, such beam forming arrays make digital signal processing techniques cumbersome as the operating frequency is increased. In addition, at the higher data rates enabled by high frequency operation, multipath fading and cross-interference becomes a serious issue. Adaptive beam forming techniques are known to combat these problems. But adaptive beam forming for transmission at 10 GHz or higher frequencies requires massively parallel utilization of A/D and D/A converters. 
   To avoid the problems in the prior art, U.S. Pat. No. 6,885,344 discloses a beam forming antenna system that is compatible with semiconductor processing techniques. For example,  FIG. 1  illustrates a beam forming antenna system  100 . For illustration clarity, only a single antenna  160  is illustrated. Any suitable topology may be used for the antennas, such as patches, dipoles, or monopoles. For example, antenna  160  may comprise a T-shaped dipole antenna formed using conventional semiconductor processing techniques. Antenna  160  is excited using vias  110  that extend through insulating layers  105  and through a ground plane  120  to driving transistors formed on an active layer  130  separated from a substrate  150  by insulating layer  105 . Two elements  101  may be excited by switching layer  130  to form a T-shaped dipole pair  160 . To provide polarization diversity, two dipole pairs  160  may be arranged such that the transverse arms in a given dipole pair are orthogonally arranged with respect to the transverse arms in the remaining dipole pair. 
   Depending upon the desired operating frequencies, each dipole pair  160  may have multiple transverse arms. The length of each transverse arm is approximately one-fourth of the wavelength for the desired operating frequency. For example, a 2.5 GHz signal has a quarter wavelength of approximately 30 mm, whereas a 10 GHz signal has a quarter wavelength of approximately 7.5 mm. Similarly, a 40 GHz signal has a free-space quarter wavelength of 2.1 mm. Thus, a T-shaped dipole  160  configured for operation at these frequencies would have three transverse arms having fractions of lengths of approximately 30 mm, 7.5 mm and 2.1 mm, respectively. The longitudinal arm of each T-shaped element may be varied in length from 0.01 to 0.99 of the operating frequency wavelength depending upon the desired performance of the resulting antenna. For example, for an operating frequency of 105 GHz, a longitudinal arm may be 500 micrometers in length and a transverse arm may be 900 micrometers in length using a standard semiconductor process. In addition, the length of each longitudinal arm within a dipole pair may be varied with respect to each other. The width of a longitudinal arm may be tapered across its length to lower the input impedance. For example, it may range from 10 micrometers in width at the via end to hundreds of micrometers at the opposite end. The resulting input impedance reduction may range from 800 ohms to less than 50 ohms. 
   Advantageously, each antenna element  101  is formed using an available metal layer provided by the semiconductor manufacturing process. Each metal layer forming an antenna element may be copper, aluminum, gold, or other suitable metal. To suppress surface waves and block the radiation vertically, insulating layer  105  between adjacent antenna elements within a dipole pair may have a relatively low dielectric constant such as ε=3.9 for silicon dioxide. The dielectric constant of the insulating material beneath the antenna elements forming the remainder of the layers may be relatively high such as ε=7.1 for silicon nitride, ε=11.5 for Ta 2 O 5 , or ε=11.7 for silicon. Similarly, the dielectric constant for the insulating layer  105  above ground plane  120  should also be very low (such as ε=3.9 for silicon dioxide, ε=2.2 for Teflon, or 1.0 for air should the insulating layer comprise a honeycombed structure). 
   The quarter wavelength discussion with respect to each antenna element may be generally applied to other antenna topologies such as patch antennas. However, note that it is only at relatively high frequencies such as the upper bands within the W band of frequencies that the quarter wavelength of a carrier signal in free space is comparable or less than the thickness of substrate  150 . Accordingly, at lower frequencies, integrated antennas should be elevated away from the substrate by using an interim dielectric layer. An exemplary beam forming system  200  having such an interim dielectric layer is shown in  FIG. 2 . Several T-shaped dipole antennas  201  are shown in  FIG. 2 . A semiconductor substrate  250  includes RF driving circuitry  230  that drives each T-shaped dipole antenna  201  through vias  210  analogously as discussed with respect to beam forming system  100 . However, a grounded shield  120  is separated from the T-shaped dipole antennas  201  by a relatively thick dielectric layer  240 . For example, dielectric layer  240  may be 1 to 2 mm or more in thickness. In this fashion, lower frequency performance is enhanced. In addition, dielectric layers  240  and an inter-layer dielectric layer  270  may be constructed from flexible materials for a conformal application. Layers  240  and  270  may be separated by an additional ground plane  225 . 
   Although the beam forming systems of  FIGS. 1 and 2  advantageously may be integrated onto a semiconductor wafer, the driving transistors are formed on a substrate surface that faces the antennas. As the number of antennas within the array is increased, the coupling of signals to the antenna&#39;s driving circuitry becomes cumbersome, particularly for a wafer-scale design. 
   Accordingly, there is a need in the art for improved wafer scale beam forming antenna systems. 
   SUMMARY 
   In accordance with another aspect of the invention, a wafer-scale antenna module is provided that includes: a substrate having a first surface and an opposing second surface; a plurality of conductive contact regions extending from the first surface into the substrate towards the second surface; active circuitry formed in the substrate adjacent the second surface, the active circuitry electrically coupled to the conductive contact regions; an insulating layer adjacent the first surface, the insulating layer forming a plurality of vias arranged corresponding to the plurality of conductive contact regions, each via forming an opening at the corresponding conductive contact region; and a plurality of antennas formed on the insulating layer corresponding to the plurality of vias; wherein each via contains an electrical conductor to electrically couple the corresponding contact region to the antenna corresponding to the via, whereby a resulting separation between the driving circuitry and the antennas aids an electrical isolation of the driving circuitry from the antennas. 
   In accordance with another aspect of the invention, a method is provided that includes: forming conductive contact regions in a substrate extending from a first surface of the substrate towards an opposing second surface of the substrate; forming active circuitry in the substrate adjacent the second surface, the active circuitry coupling to the conductive contact regions; and forming a plurality of antennas adjacent the first surface of the substrate. 
   The invention will be more fully understood upon consideration of the following detailed description, taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a wafer-scale beam forming system having T-shaped dipole antennas formed using semiconductor process metal layers; 
       FIG. 2  is a cross-sectional view of a wafer-scale beam forming system having T-shaped dipole antennas separated from the semiconductor substrate by a passivation layer; 
       FIG. 3  is a cross-sectional view of a wafer-scale beam forming antenna module in which the active circuitry is formed on a backside of the substrate in accordance with an embodiment of the invention; 
       FIG. 4  is a cross-sectional view of a substrate masked with photoresist during the manufacture of a wafer-scale beam forming antenna module in accordance with an embodiment of the invention; 
       FIG. 5  is a cross-sectional view of the substrate of  FIG. 4  with the trenches through windows in the photoresist layer; 
       FIG. 6  is a cross-sectional view of the substrate of  FIG. 5  with the trenches lined with an oxide layer; 
       FIG. 7  is a cross-sectional view of the substrate of  FIG. 6  with the lined trenches filled with conductive material; 
       FIG. 8  is a cross-sectional view of the substrate of  FIG. 7  with active circuitry formed on the backside; 
       FIG. 9  is a cross-sectional view of the substrate of  FIG. 8  with the active circuitry passivated; 
       FIG. 10  is a cross-sectional view of the substrate of  FIG. 9  with the passivation layer covered with a shield layer; 
       FIG. 11  is a cross-sectional view of the substrate of  FIG. 10  after being flipped and thinned; 
       FIG. 12  is a cross-sectional view of the substrate of  FIG. 11  with the front surface of the substrate covered with a patterned shielding layer; 
       FIG. 13  is a cross-sectional view of the substrate of  FIG. 12  with a via-containing insulating layer on the front surface; and 
       FIG. 14  is a cross-sectional view of the completed wafer-scale antenna module in accordance with an embodiment of the invention. 
   

   Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
   DETAILED DESCRIPTION 
   Reference will now be made in detail to one or more embodiments of the invention. While the invention will be described with respect to these embodiments, it should be understood that the invention is not limited to any particular embodiment. On the contrary, the invention includes alternatives, modifications, and equivalents as may come within the spirit and scope of the appended claims. Furthermore, in the following description, numerous specific details are set forth to provide a thorough understanding of the invention. The invention may be practiced without some or all of these specific details. In other instances, well-known structures and principles of operation have not been described in detail to avoid obscuring the invention. 
   The present invention provides a wafer scale antenna module having improved connectivity properties. In this improved wafer scale antenna module, the antennas are adjacent a first side of the semiconductor wafer whereas the driving circuitry is formed on an opposing second side of the wafer. In this fashion, connectivity to the driving circuitry for control and power purposes is not hampered by the necessary coupling between the driving circuitry and the antennas. An exemplary embodiment for such a “backside” wafer-scale antenna module  300  is shown in  FIG. 3 . In this embodiment, the antennas elements comprise patch antenna elements  370 . As discussed with regard to  FIG. 2 , wafer-scale antenna module  300  includes a relatively thick dielectric layer  350  such that patch antenna elements  370  are separated from a substrate  305  by the relatively thick dielectric layer. To allow the formation of active circuitry on one side of the substrate and the patch antennas on the opposing side of substrate, heavily doped (which may be either n+ or p+ depending upon design considerations) contact areas  310  are diffused through the substrate to serve as feed structures for the patch antennas. Active circuitry  315  to drive the antennas may then be formed on a back surface  311  of the substrate. The active circuitry may next be passivated through the deposition of a passivation layer  320  on surface  311 . For example, layer  320  may comprise a low temperature porous SiOx layer and a thin layer of Nitride (Si x O y N z ) such that passivation layer  320  is a fraction to a few microns in thickness. Passivation layer  320  may then be coated with an electrically and thermally conductive material  325  and taped to a plastic adhesive holder so that the substrate may be flipped to expose an as yet-unprocessed side  330  of the substrate/wafer. 
   To ensure that contact areas  310  electrically couple through the substrate, side  330  may be back-grinded such that the substrate has a thickness of a few tens or fractions of tens of micrometers. An optional metallization layer  340  may then be sputtered or alternatively coated using conductive paints onto surface  330 . Layer  340  acts as an electromagnetic shield as well as a reflective plane between the antennas and the active circuitry. To assist electrical coupling to the antennas, metal layer  340  may be patterned to form metal lumps on top of contacts  310 . The relatively thick dielectric layer  350  of porous low dielectric material or honeycomb structure may then be deposited or placed onto metal layer  340 . Layer  350  may also be formed of flexible material for conformal designs. Target alignment patterns that were etched during conventional manufacturing of the substrate may then be used to guide the location of vias  355 , which may be bored using micro-machining techniques through layer  350 . Alternatively, a conventional infra-red alignment scheme may be used to locate vias  355 . Precision rods  360  are then inserted through vias  355  to allow electrical coupling between the active circuitry and the antennas. Alternatively, a conductive material may be deposited into vias  355 . Advantageously, the formation of metal bumps as described previously in metal layer  340  eases the formation of ohmic contacts between contacts  310  and rods  360 . Without these bumps, inserting rods into metal layer  340  would involve an increased risk of cracking substrate  305 . Antennas plates  370  may then be formed using conventional photolithographic techniques and protected by a passivation layer  375 , which also provides impedance matching to the outside environment. It will be appreciated that other types of antennas such as the T-shaped dipoles described previously may also be formed using the technique discussed with respect to  FIG. 3 . Moreover, contacts  310  may be formed from the back side  330  of the substrate such that the active circuitry could cover overlay the heavily-doped contact areas. In such an embodiment, the contact areas need not extend all the way through the substrate but just reach to the level where the active circuitry is formed. Regardless of how the contact areas are formed, it will be appreciated that electrical isolation between the active circuitry and the antenna elements is enhanced by such a design. In addition, the ease of coupling to the active circuitry using, for example, intra-chip metal lines  380  and inter-chip metal lines  385  is greatly enhanced. Moreover, such a design allows the application of thermally conductive material  325  on the same side of the substrate where the active circuitry is formed. Should the active circuitry be formed on the same side of the substrate in common with the antenna elements as seen in  FIGS. 1 and 2 , a thermally conductive material would have to be placed on the opposite side of the substrate, thereby reducing its effectiveness. 
   The manufacture of a backside wafer-scale antenna module will now be discussed in greater detail. Turning now to  FIG. 4 , back surface  311  of substrate  305  is masked using, e.g., a photoresist layer  400 . A plurality of windows  405  in the photoresist layer correspond to the locations of future heavily doped contact areas  310  of  FIG. 3 . Should contact areas  310  be formed using a deep diffusion process, the masked substrate would be subjected to the appropriate diffusion at this time. 
   Alternatively, the contact areas may be formed using an etching process as seen in  FIG. 5 . For example, a reactive ion etch may be used to begin the etching within each window in the photoresist layer, followed by an isotropic chemical etching process. In this fashion, trenches  500  are formed that taper towards surface  330  of the substrate. Advantageously, this taper increases the spacing between ends  505  of the trenches. In this fashion, increased area is provided for the formation of active circuitry on surface  330 . 
   To complete the contact areas, the photoresist layer may be removed and the trenches lined with an oxide layer  600  as seen in  FIG. 6 . A conductive material such as doped polysilicon may fill the trenches to complete contact areas  310  as seen in  FIG. 7 . To prevent electrical isolation between the doped polysilicon and the trench ends  505 , the trenches may be subjected to an appropriate etching such as a reactive ion etch after deposition or growth of oxide layer  600  to remove any oxide from ends  505 . Turning now to  FIG. 8 , active circuitry  315  for beam forming transmission and reception (Tx/Rx) may then be formed on back surface  330  of the substrate. The active circuitry would couple to a diffusion region (not illustrated) that would be located adjacent ends  505  of the contact areas  310  to electrically couple the structures. To complete the backside structure, the active circuitry may be passivated with an insulating layer  320  such as a low-temperature-deposited porous silicon oxide having a final thin layer of nitridized oxide (Si x O y N z ). The insulating layer may include intra-chip metal lines  380  and inter-chip metal lines  385  as shown in  FIG. 9 . A set of external contacts  900  may then be patterned. An electrically-conductive and also thermally-conductive layer  325  completes the backside of the wafer as seen in  FIG. 10 . The wafer backside may then be taped to an adhesive holder and flipped to expose an unprocessed surface  311  of the substrate. The wafer may then be chemically ground or polished to reduce the substrate thickness to range between a few and tens of microns as seen in  FIG. 11 . 
   Surface  330  may then be coated with an electric shield  340  using as seen in  FIG. 12 . Shield  340  may be evaporated onto the surface, sputtered, or formed using conductive paints. Regardless of how shield  340  is formed, it functions to form a reflective plane for the antennas and shields the antennas from the active circuitry. In addition, shield  340  may function to form ohmic contacts as will be described later. Thus, shield  340  may be patterned to form bumps  1200  at surface of contacts  310 . Turning now to  FIG. 13 , a porous low dielectric material of Teflon or other suitable material is deposited as an insulating layer  350  on shield  340 . Alternatively, a honeycomb material may be deposited to form insulating layer  350 . To assist in the formation of vias  355  in insulating layer  350 , a target alignment pattern (not illustrated) used during conventional manufacture of the wafer may be used. Alternatively, an infrared alignment scheme may be used for positioning of the vias. The vias may be then be opened in insulating layer  350  using a variety of methods such as milling, mechanical drilling, ion drilling, or chemical etching. As seen in  FIG. 14 , precision metallic rods (not illustrated) may then be inserted into the vias to provide an electrical contacts to patch antennas  370 . To suppress surface waves, antennas  370  may be separated from insulation layer  350  by thin plates (not illustrated) of a high dielectric material such as Ta 2 O 5 . A final passivation layer  375  protects the antennas and also matches their impedance to free space. To provide electrical isolation, the substrate may be laser scribed to form isolation walls  1400 . In an alternative embodiment (not illustrated), the walls may extend through isolation layer  350 . In yet another alternative, the walls may be filled with a low-dielectric material that adds mechanical strength and rigidity. 
   In an alternative embodiment, the antenna layer consisting of insulating layer  350  and its associated structures may be formed separated from the substrate and then attached to the substrate using an adhesive or glass fusion process. It will thus be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects. The appended claims encompass all such changes and modifications as fall within the true spirit and scope of this invention.