Abstract:
A semiconductor structure for providing isolations for on-chip inductors comprises a semiconductor substrate, one or more on-chip inductors formed above the first semiconductor substrate, a plurality of through-silicon-vias formed through the first semiconductor substrate in a vicinity of the one or more on-chip inductors, and one or more conductors coupling at least one of the plurality of through-silicon-vias to a ground, wherein the plurality of through-silicon-vias provide isolations for the one or more on-chip inductors.

Description:
BACKGROUND 
     The present invention relates generally to semiconductor device structures, and, more particularly, to on-chip inductor&#39;s shielding structures. 
     Modern analog circuits increasingly embed inductors on the chip.  FIG. 1A  illustrates an on-chip spiral inductor  100 , which is formed by a spiral metal line  106 . A first terminal  102  of the inductor  100  is on the same metal layer of the spiral metal line  106 . A second terminal  104  is connected to an end of the spiral metal line  106  through vias  120  and a metal line  110  on another metal layer.  FIG. 1B  is a cross-sectional view of the on-chip spiral inductor  100  at a location A-A′. The inductor  100  is formed inside a dielectric material  130  on top of a semiconductor substrate  140 . 
     Performance of these analog circuits depends heavily on the quality of the inductor, where poor inductor quality factor (Q) of silicon processes leads to degradation in circuit efficacy, especially at radio frequency (RF) and microwave frequencies. The inductor quality factor (Q) is defined as: 
                   Q   =     2   ⁢           ⁢     π   ·       energy   -   stored       energy   -   loss   -   in   -   one   -   oscillation   -   circle                   (   1   )               
The inductor Q degrades at high frequencies due to energy dissipation in the semiconductor substrate. Noise coupling via the substrate at gigahertz frequencies has also been reported. As inductors occupy substantial chip area, they can potentially be the source and receptor of detrimental noise coupling. Therefore, decoupling the inductor from the surrounding materials, including the substrate, can enhance the overall performance of the inductor: increase Q, improve isolation, and simplify modeling.
 
       FIG. 2  is a cross-sectional view of a patterned-ground-shielding (PGS)  203  traditionally used to provide the decoupling of the inductor  100  from the semiconductor substrate  140 . The PGS  203  is commonly inserted between the inductor  100  and the substrate  140 , and formed by either a polysilicon layer or a metal layer. However, it is often difficult to find optimized widths and spacings for the PGS  203  to achieve maximum Q improvement. The fact that the PGS  203  is formed inside the dielectric layer  130  also limits its effectiveness in improving the Q of the inductor  100 . 
     As such, what is desired are alternative shielding structures for on-chip inductors that may benefit from new semiconductor processes, and these alternative shielding structures are often augmentative to traditional shielding structures. 
     SUMMARY 
     In view of the foregoing, the present invention provides a semiconductor structure for providing isolations for on-chip inductors. According to one aspect of the present invention, the semiconductor structure comprises a semiconductor substrate, one or more on-chip inductors formed above the first semiconductor substrate, a plurality of through-silicon-vias formed through the first semiconductor substrate in a vicinity of the one or more on-chip inductors, and one or more conductors coupling at least one of the plurality of through-silicon-vias to a ground, wherein the plurality of through-silicon-vias provide isolations for the one or more on-chip inductors. 
     According to another aspect of the present invention, the one or more conductors that couple at least one through-silicon-via of the plurality of through-silicon-vias to a ground are formed by a metallized backside of the semiconductor substrate. 
     Additionally, traditional patterned-ground-shielding structure can be combined with the semiconductor structure of the present invention by extending the plurality of through-silicon-vias into making contact with the patterned-ground-shielding conductors. Besides, in stacked chip application, both top and bottom chips may have through-silicon-vias in the vicinity of the on-chip inductors. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate an on-chip spiral inductor. 
         FIG. 2  illustrates a traditional patterned-ground-shielding for the on-chip spiral inductor. 
         FIGS. 3A and 3B  illustrate a first inductor shielding structure formed by through-silicon-vias and a metallized backside according to a first embodiment of the present invention. 
         FIGS. 4A and 4B  illustrates a second inductor shielding structure combining the through-silicon-vias with the traditional patterned-ground-shielding according to a second embodiment of the present invention. 
         FIG. 5  illustrates the through-silicon-vias shielding structure is applied in a face-to-face stacked chip according to a third embodiment of the present invention. 
         FIG. 6  illustrates the combination of through-silicon-via and traditional patterned-ground-shielding being applied to the face-to-face stacked chip according to a fourth embodiment of the present invention. 
         FIG. 7  illustrates a face-to-back stacked chip employing the through-silicon-vias according to a fifth embodiment of the present invention. 
         FIG. 8  illustrates a face-to-back stacked chip employing a combination of the through-silicon-vias and the traditional patterned-ground-shielding according to a sixth embodiment of the present invention. 
         FIGS. 9A and 9B  illustrate an inductor shielding structure formed by patterned metallized backside and the through-silicon-vias according to a seventh embodiment of the present invention. 
     
    
    
     The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer conception of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. 
     DESCRIPTION 
     The following will provide a detailed description of a through-silicon-via (TSV) based shielding structure for improving the quality factor (Q) of on-chip inductors. 
     The TSV is a technology of forming via holes through a semiconductor substrate, which may be made of silicon or other materials. Therefore, the term, through-silicon, may also be called “through-wafer”. The TSV technology is developed to shorten interconnect lengths and to achieve 3 dimensional structure. Operations in the 3-D integration process include through-wafer via formation, deep via etching, laser-drilled vias, deep trench capacitor technology, via filling, deposition of diffusion barrier and adhesion layers, metallization, and wafer thinning, dicing, alignment and bonding. There are currently three process sequences available for the formation of through-wafer vias for wafer-level 3-D devices. In a front-end process sequence, vias can be fabricated using deep trench capacitor technology at any fab capable of embedded DRAM technology, before transistors and interconnect are processed on the chips. Such chips would subsequently go to semiconductor packaging houses where backside thinning would expose the bottom of the vias and allow backside interconnect formation. This sequence places the burden of via formation in the hands of the fab and eliminates the need to leave room within or between cells for post-fab via creation. 
     The second process sequence also requires chips to be specifically designed for 3-D stacking. Specific areas on the silicon, in the interconnect layers, and on the top pad surface are set aside as exclusion zones. Through-wafer connection is subsequently created in the completed chips by etching vias through these exclusion zones and filling them with insulators and conductive metals. 
     The third process sequence is used when chips not specifically designed for 3-D integration are stacked. In this sequence, the connecting vias are formed by redistributing pads into the area between the peripheral pads and via streets. Vias are then etched and filled in these natural exclusion zones. 
       FIGS. 3A and 3B  illustrate a first inductor shielding structure formed by a plurality of TSVs  302  and a metallized backside (MB)  310  according to a first embodiment of the present invention.  FIGS. 3A and 3B  are a cross-sectional view and a layout view, respectively, of the first inductor shielding structure. Referring to  FIG. 3A , the TSVs  302  is formed through the substrate  140 . The MB  310  has contacts with the TSVs  302  to provide a ground connection to the TSVs  302 . Referring to  FIG. 3B , a plurality of TSVs  302  is placed around the on-chip inductor  100 , forming a grounded shielding fence for isolating the inductor  100 . With the shielding fence formed by the TSVs  302  surrounding and under the inductor  100 , Eddy current distributions in the substrate  140  will be stopped. Therefore, the Q factor of the inductor  100  will be improved. Besides, with better grounding of the MB  310  and better isolation of the TSVs  302 , the unwanted or high-order mode will also be suppressed. 
     Minimum cross-sectional widths and lengths of the TSVs  302  and minimum spacings between adjacent TSVs are determined by a process technology being employed to form the TSVs  302 . But other width, length and spacing may also be used to achieve an optimized Q improvement. 
     Although a rectangularly arranged TSV fence is illustrated in  FIG. 3B . A skilled artisan may realize that it is the enclosing nature of the TSV fence provides the isolation to the on-chip inductor  100 , therefore, other shapes of TSV arrangements, such as a U-shape, a circle or even a double circle, may provide equally well Q improvement to the inductor  100 . 
     Although only the TSVs  302  surrounding the on-chip inductor  100  is illustrated in  FIG. 3A , a skilled artisan will realize that TSVs under the on-chip inductor  100  can also provide isolation and Q improvement to the on-chip inductor  100 . An on-chip inductor may have guard-ring of its own, and such guard-ring may be connected to the TSV fence. 
       FIGS. 4A and 4B  illustrates a second inductor shielding structure combining the TSVs  402  with the traditional patterned-ground-shielding (PGS)  420  according to a second embodiment of the present invention.  FIG. 4A  is a cross-sectional view, while  FIG. 4B  is a layout view of the second inductor shielding structure. The PGS  420  is formed in a metal or polysilicon layer in the dielectric material  130 . In forming the TSVs  420 , an etching process, via holes are etched not only through the semiconductor substrate  140 , but also through part of the dielectric material  130  and stopped by the PGS layer  420 . Grounding to both the TVSs  402  and the PGS  420  are provided by the MB  310 . Both the TSVs  402  and PGS  420  provide isolation to the on-chip inductor  100 , and better Q improvement thereof. 
       FIG. 5  illustrates the TSV shielding structure is applied in a face-to-face stacked chip according to a third embodiment of the present invention. A top chip is identical to the inductor structure shown in  FIG. 3A , which includes the semiconductor substrate  140  and the dielectric layer  130 . The on-chip inductor  100  is formed in the dielectric layer  130 . The TSVs  302  are formed through the substrate  140 . The MB  310  provides the ground connection to the TSVs  302 . A second chip is stacked face-to-face on the first chip. The so called face-to-face refers to dielectric layers  130  and  530  of the first and second chip, respectively, come into contact with each other. The second chip includes a second semiconductor substrate  540  and a second dielectric layer  530 . Another plurality of TSVs  502  is formed through the second substrate  540 . Another MB  510  provides the ground connection to the plurality of TSVs  502 . Both the TSVs  302  and the pluralities of TSVs  502  are placed around the on-chip inductor  100  and provide isolations thereto. 
       FIG. 6  illustrates the combination of TSV and traditional PGS being applied to the face-to-face stacked chip according to a fourth embodiment of the present invention. The chip on top is the combination of TSV and traditional PGS structure shown in  FIG. 4A . The chip on bottom is the same as the second chip shown in  FIG. 5 . The traditional PGS adds another layer of isolation to the on-chip inductor  100  of the face-to-face stacked chip. 
       FIG. 7  illustrates a face-to-back stacked chip employing the TSVs according to a fifth embodiment of the present invention. A top chip here is the same as the top chip shown in  FIG. 5 , which is stacked on a bottom chip in a face-to-back fashion, i.e., the dielectric layer  130  of the top chip comes into contact with a substrate  540  of the bottom chip. The bottom chip includes a dielectric layer  530 . As shown in  FIG. 7 , TSVs  702  of the bottom chip make contacts to a metal layer  710  inside the dielectric layer  530 . The metal layer  710  provides the ground connection to the TSVs  702 . A skilled artisan may realize that other conduction layer, such as polysilicon, may be used in place of the metal layer  710 . 
       FIG. 8  illustrates a face-to-back stacked chip employing a combination of the TSVs and the traditional PSG according to a sixth embodiment of the present invention. Here a top chip is the same as the top chip shown in  FIG. 6 , and a bottom chip is the same as the bottom chip shown in  FIG. 7 . The top and bottom chip are stacked in a face-to-back fashion, i.e., the dielectric layer  130  of the top chip comes into contact with the substrate  540  of the bottom layer. 
     Referring to  FIGS. 5 through 8 , the way two chips are stacked, either face-to-face or face-to-back, is determined by various design needs of the stacked chip. The examples shown here in  FIGS. 5 through 8 , illustrate that TSV technologies can equally applied to both face-to-face and face-to-back cases for providing isolations to the on-chip inductor  100 . Variations available to the non-stacked chips shown in  FIGS. 3A and 4A  are also applicable to the stacked chips shown in  FIGS. 5 through 8 . 
       FIGS. 9A and 9B  illustrate an inductor shielding structure formed by patterned metallized backside (MB) and the TSVs according to a seventh embodiment of the present invention.  FIG. 9A  is a cross-section made at location B-B′ shown in  FIG. 9B . The inductor shielding structure shown in  FIGS. 9A and 9B  is the same as the one shown in  FIGS. 3A and 3B , except that the MB  910  shown in  FIGS. 9A and 9B  is patterned. Referring to  FIG. 9A , the MB  910  still makes contacts to the TSVs  402 .  FIG. 9B  shows an exemplary mesh pattern etched on the MB  910 . Apparently the patterned MB can also be applied to the stacked chips shown in  FIGS. 5 through 8 . 
     The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
     Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.