Patent Publication Number: US-10770404-B2

Title: Shielding for through-silicon-via noise coupling

Description:
REFERENCE TO RELATED APPLICATIONS 
     This Application is a Continuation of U.S. application Ser. No. 14/944,907, filed on Nov. 18, 2015, which is a Continuation of U.S. application Ser. No. 13/795,035, filed on Mar. 12, 2013 (now U.S. Pat. No. 9,219,038, issued on Dec. 22, 2015). The contents of the above-referenced Patent Applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates generally to integrated circuit devices and more particularly to shielding for through-silicon-vias. 
     BACKGROUND 
     Since the invention of the integrated circuit, the semiconductor industry has continuously sought to improve the density of integrated circuit components (transistors, diodes, resistors, capacitors, etc.). For the most part, improvements in density have come from reductions in feature size, allowing more components to be formed within a given area. These improvements have been made while components remain in an essentially two-dimensional layout. Although dramatic increases in density have been realized within the limits of a two-dimensional layout, further improvements are difficult to achieve. 
     Three-dimensional integrated circuits (3D ICs) have been created to overcome these limitations. In a 3D IC, two or more semiconductor bodies, each including an integrated circuit, are formed, aligned vertically, and bonded together. Circuits on different semiconductor bodies are connected at least in part through conductive vias penetrating the full thickness of at least one of the semiconductor bodies. These are described as through-silicon-vias (TSV) regardless of whether the semiconductor body is silicon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example embodiment of a 3D-IC according to the present disclosure viewed in cross-section. 
         FIG. 2  is a schematic illustration of the embodiment of  FIG. 1  in plan view. 
         FIG. 3  is a schematic illustration of another example embodiment of a 3D-IC according to the present disclosure viewed in cross-section. 
         FIG. 4  is a schematic illustration of the embodiment of  FIG. 3  in plan view. 
         FIG. 5  is a schematic illustration of another example embodiment of a 3D-IC according to the present disclosure viewed in cross-section. 
         FIG. 6  is a schematic illustration of the embodiment of  FIG. 5  in plan view. 
         FIG. 7  is a chart showing the reduction in noise coupling coefficient provided by an embodiment of the present disclosure for various TSV to DUT distances. 
         FIG. 8  is a chart showing the reduction in noise coupling coefficient provided by an embodiment of the present disclosure for various guard ring widths. 
         FIG. 9  is a flow chart illustrating a method of shielding to prevent signals carried by a through silicon via from causing noise in an active area of an integrated circuit provided by an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Signals carried by the TSVs can cause noise in adjacent active circuits. Shielding has been provided to reduce this noise. One type of shielding is a guard ring of doped semiconductor formed around the TSVs. The doping can be of the p+ type or of the deep n-well (DNW) type. A difficulty with this approach is that the shielding exists only near the surface of the semiconductor body. The TSV signal noise may remain coupled to the active circuit through the deeper parts of the semiconductor body. This type of shielding is largely ineffective against high frequency noise. Another approach is to form one or more shielding TSVs between the signal TSV and the active circuit. This approach is more effective than guard rings around the TSVs, although still less effective than the approach provided by the present disclosure. 
     The present disclosure, in some embodiments, provides 3D integrated circuit devices including first and second semiconductor bodies. The first semiconductor body has an active area, a through-silicon-via outside the active area, and two or more disjoint guard rings. The guard rings are contiguous regions of p+ doped semiconductor. In most embodiments, p+ means having p-type dopants at a concentration greater than a p type region, and in one embodiment may comprise a concentration of at least 5.0×10 18  atoms/cm 3 . The first guard ring encircles the via. The second guard ring encircles the active area, but not the via. In some embodiments, the guard rings reduce the noise coupling coefficient between the via and the active area to −60 dB or less at 3 GHz and 50 μm spacing. 
     In an embodiment, the first guard ring also encircles the second guard ring. In another embodiment the first guard ring encircles the second guard ring and includes an extension that divides the space between the via and the active area. In another embodiment, a portion of the first guard ring divides the space between the via and the active area and is thicker between the via and the active area. 
     The present disclosure, in some embodiments, provides a method of shielding to prevent signals carried by a through-silicon-via from causing undesirably high noise in an active area of an integrated circuit. The method includes forming a first p+ guard ring around the through-silicon-via and forming a second p+ guard ring around the active area. The first and second guard rings are grounded in an embodiment. 
       FIG. 1  is an example embodiment of a 3-D IC device  100  provided by the present disclosure.  FIG. 2  is a plan view of the same device  100 . Only a portion of the device  100  is illustrated in the figures. The device  100  includes a semiconductor body  101 . A through-silicon-via (TSV)  103  penetrates the semiconductor body  101 . An active area  105  is formed on the surface  107  of the semiconductor body  101  and includes an n-well  106 . In some embodiments, the n-well  106  is included. In other embodiments, the n-well  106  is not included. The TSV  103  is outside the active area  105 . The distance  108  between the TSV  103  and the active area  105  is generally in the range from 10 μm to 50 μm. Some separation is used to keep noise coupling within acceptable limits regardless of what shielding is used. On the other hand, it is desirable to limit the amount of separation in order to avoid wasting chip area. In some other approaches, using shielding, a minimum separation of 50 μm was generally required. In some embodiments of the present disclosure, the distance  108  is 35 μm or less. In some other embodiments, the distance  108  is 20 μm or less. 
     As shown in  FIG. 2 , a first guard ring  109  encircles the TSV  103 . A second guard ring  111  encircles the active area  105 . Guard rings  109  and  111  are generally formed by ion implantation and exist in a zone of the semiconductor body  101  proximate the surface  107 . Encircling is used in the sense of surrounding. To encircle means to form a boundary on all sides of an element of interest in at least one plane parallel the surface  107 . While a rectangle is shown in  FIG. 2 , other shapes that surround the TSV  103  or the active area  105  may be employed in various other embodiments. 
     The semiconductor body  101  includes a semiconductor. The semiconductor can be in crystal or polycrystalline form. The semiconductor can be an elementary semiconductor such as silicon or germanium, or a compound semiconductor such as SiGe, GaAs, or InP. The semiconductor composition can vary with position as in a continuously varying ratio of Si to Ge in a SiGe semiconductor. The semiconductor can have a multilayer structure. The semiconductor can be lightly doped. 
     The active area  105  includes one or more active or passive devices. In some embodiments, the active area  105  includes one or more devices such as resistors, capacitors, inductors, diodes, metal-oxide-semiconductor field effect transistors (MOSFETs), complementary MOS (CMOS) transistors, bipolar junction transistors (BJTs), laterally diffused MOS (LDMOS) transistors, high power MOS transistors, FinFET transistors, and/or other types of transistors. In some embodiments, the active area  105  includes passive microelectronic devices. The active area  105  generally includes a plurality of devices and is generally at least 100 μm 2  and is typically at least 500 μm 2  in some embodiments, but may vary in other embodiments. 
     Guard rings  109  and  111  are heavily doped regions of the semiconductor body  101 , contiguous within themselves but disjoint from one-another. The first guard ring  109  reduces noise coupling between the via  103  and the active area  105 , particularly at low frequencies, for example, frequencies below 1 GHz. However, most of the reduction in noise coupling for high frequencies (e.g., frequencies greater than 1 GHz, and more particularly frequencies greater than 2 GHz) is due to the guard ring  111 . This is in part because while the guard rings  109  and  111  have depths generally in the range from 0.1 μm to 5 μm, and typically in the range from 0.2 μm to 1.0 μm, e.g., 0.5 μm. TSV  103 , on the other hand, generally has a height that is at least 10 times greater. The height of TSV  103  is generally in the range from 20 μm to 100 μm, and is typically in the range from 30 μm to 70 μm. The second guard ring  111 , the one surrounding the active area  105 , compliments the first guard ring  109  by significantly reducing the noise coupling from via  103  that can otherwise occur from the via  103  through deeper in the semiconductor body  101 . 
     Noise coupling through deeper portions of the semiconductor body  101  is further reduced in some embodiments by having the first guard ring  109  extend to surround the second guard ring  111  and therefore the active area  105 . The device  200  illustrated by  FIGS. 3-4  provides an example of such embodiments. 
     Noise coupling is a function of the distance  108  between the via  103  and the active area  105 . Noise coupling in the device  100  can be reduced by widening either the first guard ring  109  or the second guard ring  111  in the space between the via  103  and the active area  105 . In some embodiments, the first guard ring  109  is the one widened. 
     The device  200  of  FIGS. 3 and 4  differs from the device  100  of  FIGS. 1 and 2  in that the first guard ring  109  does not include a portion  109  extending through the space between the via  103  and the active area  105 . The shielding in device  200  can be improved by adding to the first guard ring  109  an extension  113  that divides the space between the via  103  and the active area  105 . The 3D IC device  300  illustrated by  FIGS. 5-6  is an example of embodiments employing this feature. The extension  113 , as illustrated in  FIGS. 5 and 6 , can be wider than other portions of the guard ring  109 . 
     In  FIGS. 3-6 , the width  115  of the guard ring  109  and the width  121  of the guard ring  111  are each generally from 0.10 μm to 0.25 μm. In some embodiments, at least one of the guard rings  109  and  111  is wider where it lies between the via  103  and the active area  105  as shown for the example 3D IC device  300  in  FIGS. 5 and 6 . In some embodiments, for example, as illustrated in  FIGS. 5-6 , the sum of the widths  119  and  121  of the guard rings  109  and  111  between the via  103  and the active area  105  is at least 0.25 μm. In some embodiments, the width  119  of the guard ring  109  alone is at least 0.25 μm where it runs between the via  103  and the active area  105 . In some embodiments, the width  119  of the guard ring  109  where it lies between the via  103  and the active area  105  is at least 50% wider than the width  115  of the guard ring  109  elsewhere. In some embodiments, for example, as illustrated in  FIGS. 5-6 , the guard ring  109  includes an extension  113  that is wider than other portions of the guard ring  109  as shown in  FIGS. 5 and 6 . In some embodiments, the width  119  of the guard ring extension  113  of the guard ring  109  is at least 0.25 μmwide. 
     The guard rings  109  and  111  are both grounded in an embodiment. In some embodiments, each of the guard rings  109  and  111  is coupled to distinct ground pads. In some other embodiments, the guard rings  109  and  111  are coupled to a common ground pad. In operation, the guard ring  109  registers noise as a result of signals through the via  103 . Noise within the guard ring  109  generally does not propagate significantly to the guard ring  111 . The guard ring  111  also registers noise as a result of signals through the via  103 , but to a lesser extent than the guard ring  109 . The guard ring  111  therefore generally remains closer to the ground voltage as compared to the guard ring  109 . The guard ring  109  thus operates as a first ground whereas the guard ring  111  is a second ground, wherein the second ground exhibits less noise than the first ground. 
     A guard ring around the via  103  by itself in other approaches provides comparatively little reduction in high frequency noise coupling. The noise coupling coefficients between the via  103  and the active area  105  in other approaches are −50 dB or greater at 3 GHz circuit operating frequency absent the shielding provided by the present disclosure. Unless otherwise stated, these and other noise coupling coefficients reported in this disclosure are for TSVs 10 μm in diameter including an 0.5 μm isolation layer, a TSV height of 50 μm, and a spacing of 40 μm.  FIGS. 7 and 8  show that the noise coupling coefficients at 3 GHz can be reduced to −60 GHz or less using the structures provided by the present disclosure.  FIG. 7  compares the noise coupling coefficient at 3 GHz circuit operating frequency without shielding (light bars)  302  to the noise coupling coefficient at 3 GHz circuit operating frequency with shielding (i.e., p+ guard ring)  304  according to the present disclosure. In an embodiment, the 3 GHz circuit operating frequency corresponds to a frequency of signals passing through the through silicon via (TSV)  103 , however, it may also correspond to a frequency of circuitry within the active area  105 . Results are shown for three different distances (20 μm, 30 μm, and 50 μm)  108  between the TSV  103  and the active area  105 . Without shielding  302 , the noise coupling coefficient is greater than −60 dB for all cases and is greater than −50 db if the distance  108  is less than 50 μm. With shielding  304  according to the present disclosure, the noise coupling coefficient is less than −60 db even if the distance  108  is as small as 20 μm (see  FIG. 5 ).  FIG. 8  compares the noise coupling coefficient for various widths  119  of the guard ring  109  (see  FIG. 6 ) between the TSV  103  and the active area  105 . For the case in which the width is zero at  306 , there is no shielding (no p+ guard ring). For the widths of 0.25 μm and 0.75 μm, the shielding ( 111  ( FIG. 3-4 ) or  109 / 111  ( FIGS. 5-6 )) is provided as described in the present disclosure. The data shows that a 0.25 μm width at  308  is sufficient to reduce the noise coupling to below −60 dB. 
     A method of shielding to prevent signals carried by a through silicon via from causing noise in an active area of an integrated circuit is illustrated in  FIG. 9 , as designated at reference numeral  400 . The method  400  comprises forming a first guard ring, for example, a heavily doped p+ guard ring around a silicon through via at  402 , and forming a second guard ring, for example, a heavily doped p+ guard ring around an active area containing circuitry therein at  404 . The first and second guard rings are then grounded by electrically coupling such guard rings to a ground potential node at  406 . In an embodiment the first guard ring operates as a first ground having a first noise characteristic, and the second guard ring operates as a second ground having a second noise characteristic, wherein the first noise characteristic is larger than the second noise characteristic. Nevertheless, the guard rings operate to reduce the noise coupling coefficient between the silicon through via and the active area, for example, to −60 dB or less in an embodiment. 
     The following claims are directed to 3D integrated circuit devices and related methods. The devices include a semiconductor having an active area and a through silicon via. A first guard ring surrounds the TSV and a second guard ring surrounds the active area. In some embodiments, the first guard ring also encircles or otherwise surround the second guard ring. In some embodiments, the first guard ring includes an extension that divides the space between the via and the active area. In some embodiments, this extension is thicker than other portions of the guard ring. The claims are also directed to methods of shielding TSVs using any of these structures. 
     In some embodiments, an integrated circuit device includes a semiconductor substrate. An active area is disposed in the semiconductor substrate. A first guard ring is disposed in the semiconductor substrate and entirely surrounds the active area. The first guard ring has a first conductivity type. A via penetrates through the semiconductor substrate and is spaced apart from the active area such that the via is disposed outside of the first guard ring. A second guard ring is disposed in the semiconductor substrate and entirely surrounds the via and the first guard ring. The second guard ring has the first conductivity type and is disjoint from the first guard ring. 
     Other embodiments relate to a 3D integrated circuit device which includes first and second semiconductor substrates. An active area is disposed in the first semiconductor substrate. A first guard ring is disposed in the first semiconductor substrate and entirely surrounds the active area. A via penetrates through the first semiconductor substrate and is spaced apart from the active area such that the via is disposed outside of the first guard ring. The via forms a connection with a circuit disposed in or on the second substrate. A second guard ring is disposed in the first semiconductor substrate. The second guard ring surrounds the via and is disjoint from the first guard ring. The second guard ring entirely surrounds the first guard ring. 
     Still other embodiments relate to an integrated circuit device which includes a semiconductor substrate and a through substrate via extending through the semiconductor substrate. A first guard ring surrounds the through substrate via and has a first conductivity type. An active area is disposed within the semiconductor substrate and is spaced and apart from both the first guard ring and the through substrate via. A second guard ring surrounds the active area and has the first conductivity type. The second guard ring is disjoint from the first guard ring and is entirely surrounded by the first guard ring. 
     The components and features of the present disclosure have been shown and/or described in terms of certain embodiments and examples. While a particular component or feature, or a broad or narrow formulation of that component or feature, may have been described in relation to only one embodiment or one example, all components and features in either their broad or narrow formulations may be combined with other components or features to the extent such combinations would be recognized as logical by one of ordinary skill in the art.