Abstract:
Disclosed are systems, methods, and computer program products for electronic systems with through-substrate interconnects and mems device. An interconnect formed in a substrate having a first surface and a second surface, the interconnect includes: a bulk region; a via extending from the first surface to the second surface; an insulating structure extending through the first surface into the substrate and defining a closed loop around the via, wherein the insulating structure comprises a seam portion separated by at least one solid portion; and an insulating region extending from the insulating structure toward the second surface, the insulating region separating the via from the bulk region, wherein the insulating structure and insulating region collectively provide electrical isolation between the via and the bulk region.

Description:
BACKGROUND 
       [0001]    Field of the Invention 
         [0002]    The present invention generally relates to electronic systems, and more particularly to electronic systems with interconnects. 
         [0003]    Background 
         [0004]    A through-silicon via (TSV), also known as a through-substrate via, is an interconnect structure formed in a substrate that provides a vertical electrical connection passing completely through the substrate. 
         [0005]    There are multiple ways to categorize a TSV architecture. One categorization is based on when TSV fabrication process is performed in relation to a CMOS or a MEMS device fabrication process. For example, in a TSV-first architecture, TSVs are completely formed in a substrate prior to forming CMOS or MEMS devices in the same substrate. In a TSV-middle architecture, TSVs are partially formed first and then completed after forming, or partially forming, CMOS or MEMS devices. 
         [0006]    Another categorization is based on the conducting material that is used for the through-substrate conduction. In an example, holes are etched in a substrate and lined with a dielectric. The hole is filled with a conducting material, such as copper. In subsequent fabrication steps, electrical contacts are made to the top and bottom of the filled conducting TSV plug. In another example, a continuous trench is etched partially through the substrate in a closed pattern, such as an annulus. The trench is then partially filled with a dielectric material. Electrical connection is made to the surrounded silicon using a metal trace and a via opening. In subsequent fabrication steps, the substrate is flipped over; an electrical connection, such as a bond pad or solder bump, is made; and, a second trench that intersects with the continuous trench is etched, thereby removing the only remaining electrical connection between the surrounding substrate and the silicon plug inside the closed contour filled with a dielectric material. A similar process is described in U.S. Pat. No. 6,815,827. 
         [0007]    In an alternative process, the silicon plug is doped to create a resistivity within the plug that is lower than that of the surrounding substrate. A similar process is described in U.S. Pat. Nos. 7,227,213 and 6,838,362. 
         [0008]    TSV is commonly used for 3D/2.5D integration of integrated circuits because of its ability to electrically couple two or more substrates that are stacked on top of each other and because of its superior performance compared to conventional interconnects. However, despite these benefits, it is not widely used in the field because it is currently too expensive to fabricate. Therefore, there is a need for a new TSV structure that has a lower fabrication cost than a conventional TSV structure. 
       SUMMARY 
       [0009]    According to an embodiment, an interconnect formed in a substrate having a first surface and a second surface includes a bulk region. A via extends from the first surface to the second surface. An insulating structure extends through the first surface into the substrate and defines a closed loop around the via, wherein the insulating structure comprises a seam portion separated by at least one solid portion. And, an insulating region extends from the insulating structure toward the second surface. The insulating region separates the via from the bulk region, wherein the insulating structure and insulating region collectively provide electrical isolation between the via and the bulk region. 
         [0010]    According to another embodiment, an electronic component includes a substrate having a first surface and a second surface, and the substrate includes an interconnect formed in the substrate. The interconnect includes a bulk region. A via extends from the first surface to the second surface. An insulating structure extends through the first surface into the substrate and defines a closed loop around the via, wherein the insulating structure comprises a seam portion separated by at least one solid portion. And, an insulating region extends from the insulating structure toward the second surface. The insulating region separates the via from the bulk region, wherein the insulating structure and insulating region collectively provide electrical isolation between the via and the bulk region. 
         [0011]    According to another embodiment, a method of forming an interconnect in a substrate having a first surface and a second surface is provided. The method includes forming an insulating structure abutting the first surface and defining a closed loop around a via in the substrate and forming an insulating region abutting the second surface such that the insulating region contacts the insulating structure and separates the via from a bulk region of the substrate. The forming of the insulating structure includes etching the substrate beginning from the first surface to form a trench; filling the trench to form a seam portion; and converting a portion of the substrate to a solid portion to form the closed loop. 
         [0012]    Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
         [0013]    The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention. 
           [0014]      FIG. 1A  illustrates an electronic system, according to an embodiment. 
           [0015]      FIG. 1B  illustrates an electronic component, according to an embodiment. 
           [0016]      FIG. 1C  illustrates a microchip, according to an embodiment. 
           [0017]      FIG. 1D  illustrates a microchip, according to another embodiment 
           [0018]      FIG. 1E  illustrates an electronic component, according to another embodiment. 
           [0019]      FIG. 2A  illustrates a top view of a TSV formed in a substrate, according to an embodiment. 
           [0020]      FIG. 2B  illustrates an isolated top view of a seam portion, according to an embodiment. 
           [0021]      FIG. 2C  illustrates the TSV of  FIG. 2A  with a different set of labels. 
           [0022]      FIG. 2D  illustrates a cross-sectional view of the TSV in  FIG. 2A  taken along line D′, according to an embodiment. 
           [0023]      FIG. 2E  illustrates a cross-sectional view of the insulating structure in  FIG. 2D , according to an embodiment. 
           [0024]      FIG. 2F  illustrates a cross-sectional view of the TSV in  FIG. 2A  taken along line E′, according to an embodiment. 
           [0025]      FIG. 3A  illustrates an isolated view of the insulating structure in  FIGS. 2A-2E . 
           [0026]      FIG. 3B  illustrates an isolated view of an insulating structure, according to another embodiment. 
           [0027]      FIG. 3C  illustrates an isolated view of an insulating structure, according to another embodiment. 
           [0028]      FIG. 3D  illustrates an isolated view of an insulating structure, according to another embodiment. 
           [0029]      FIG. 4  illustrates a cross-sectional view of a TSV, according to another embodiment. 
           [0030]      FIG. 5  illustrates a cross-sectional view of a TSV, according to another embodiment. 
           [0031]      FIG. 6A  illustrates a cross-sectional view of a microchip including a TSV and a MEMS device, according to an embodiment. 
           [0032]      FIG. 6B  illustrates a cross-sectional view of a microchip including a TSV and a MEMS device, according to another embodiment. 
           [0033]      FIGS. 7A-7C  illustrate a partially fabricated TSV after forming a trench, according to an embodiment. 
           [0034]      FIGS. 8A-8C  illustrate a partially fabricated TSV after forming an insulating structure, according to an embodiment 
           [0035]      FIGS. 9A-9C  illustrate TSV  200  after forming an insulating region, according to an embodiment. 
           [0036]      FIG. 10  is a flow chart illustrating a method of fabricating the TSV in  FIGS. 2A-2E , according to an embodiment. 
           [0037]      FIGS. 11A-11H  illustrate a fabrication process for forming a TSV and a MEMS device in a substrate, according to an embodiment. 
           [0038]      FIG. 12  shows a 3D rendering of a cross section of a microchip with a TSV and MEMS device, according to an embodiment. 
       
    
    
       [0039]    The present disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
       DETAILED DESCRIPTION 
     I. Overview 
       [0040]    Embodiments of the invention lower the cost and improve the strength of the resulting TSV structure. Embodiments break a single seam portion of an insulating structure into multiple segments using one or more solid portions to enhance the resulting strength of the TSV structures. Embodiments may also share a process step with a MEMS device fabrication process to further reduce the cost and may not require additional process steps to form a TSV and a MEMS device in the same substrate. 
         [0041]    The following Detailed Description refers to accompanying drawings to illustrate embodiments consistent with the disclosure. The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
         [0042]    The embodiments described herein are provided for illustrative purposes, and are not limiting. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the disclosure. Therefore, the Detailed Description is not meant to limit the present disclosure. Rather, the scope of the present disclosure is defined only in accordance with the following claims and their equivalents. 
         [0043]    The following Detailed Description of the embodiments will so fully reveal the general nature of the present disclosure that others can, by applying knowledge of those skilled in relevant art(s), readily modify and/or adapt for various applications such exemplary embodiments, without undue experimentation, without departing from the spirit and scope of the disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and plurality of equivalents of the exemplary embodiments based upon the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein. 
         [0044]    Those skilled in the relevant art(s) will recognize that this description may be applicable to many various semiconductor devices, and should not be limited to any particular type of semiconductor devices. Before describing the various embodiments in more detail, further explanation shall be given regarding certain terms that may be used throughout the descriptions. 
       II. Terminology 
       [0045]    The terms metal line, trace, wire, interconnect, conductor, signal path and signaling medium are all related. The related terms listed above, are generally interchangeable, and appear in order from specific to general. In this field, metal lines are sometimes referred to as traces, wires, lines, interconnect or simply metal. Metal lines, such as, but not limited to, aluminum (Al), copper (Cu), an alloy of Al and Cu, an alloy of Al, Cu and silicon (Si), tungsten (W), nickel (Ni), titanium nitride (TiN), and tantalum nitride (TaN) are conductors that provide signal paths for interconnecting electrical circuitry. Other conductors, both metal and non-metal are available in microelectronic devices. Materials such as doped polysilicon, doped single-crystal silicon (often referred to simply as diffusion, regardless of whether such doping is achieved by thermal diffusion or ion implantation), titanium (Ti), cobalt (Co), molybdenum (Mo), and refractory metal silicides are examples of other conductors. 
         [0046]    FET, as used herein, refers to a metal-oxide-semiconductor field effect transistor (MOSFET). An n-channel FET is referred to herein as an NFET. A p-channel FET is referred to herein as a PFET. FETs that are formed in a bulk substrate, such as a silicon wafer, have four terminals, namely gate, drain, source and body. 
         [0047]    Substrate, as used herein, refers to the physical object that is the basic workpiece transformed by various process operations into the desired microelectronic configuration. A typical substrate used for the manufacture of integrated circuits is a wafer. Wafers, may be made of semiconducting (e.g., bulk silicon), non-semiconducting (e.g., glass), or combinations of semiconducting and non-semiconducting materials (e.g., silicon-on-insulator (SOI)). In the semiconductor industry, a bulk silicon wafer is a very commonly used substrate for the manufacture of integrated circuits and MEMS. 
         [0048]    The term vertical, as used herein, means substantially perpendicular to the surface of a substrate. 
         [0049]    The term “etch” or “etching” or “etch-back” generally describes a fabrication process of patterning a material, such that at least a portion of the material remains after the etch is completed. For example, generally the process of etching a semiconductor material involves the steps of patterning a masking layer (e.g., photoresist or a hard mask) over the semiconductor material, subsequently removing areas of the semiconductor material that are no longer protected by the mask layer, and optionally removing remaining portions of the mask layer. Generally, the removing step is conducted using an “etchant” that has a “selectivity” that is higher to the semiconductor material than to the mask layer. As such, the areas of semiconductor material protected by the mask would remain after the etch process is complete. However, the above is provided for purposes of illustration, and is not limiting. In another example, etching may also refer to a process that does not use a mask, but still leaves behind at least a portion of the material after the etch process is complete. 
         [0050]    The terms “deposit” or “dispose” describe the act of applying a layer of material to the substrate. Such terms are meant to describe any possible layer-forming technique including, but not limited to, thermal growth, sputtering, evaporation, chemical vapor deposition, epitaxial growth, atomic layer deposition, electroplating, etc. 
         [0051]    In an embodiment, devices fabricated in and/or on the substrate may be in several regions of the substrate, and these regions may not be mutually exclusive. That is, in some embodiments, portions of one or more regions may overlap. 
       III. An Example Electronic System 
       [0052]      FIG. 1A  illustrates an electronic system  100 , according to an embodiment. Electronic system  100  includes a printed wiring board (PWB)  101  and an electronic component  102 . Electronic system  100  as shown in  FIG. 1A  includes only one PWB  101  and one electronic component  102  for the sake of simplicity. However, as would be understood by a person skilled in the art based on the description herein, electronic system  100  may include any number of PWBs and any number of electronic components. Electronic component  102  may be electrically coupled to PWB  101 , and in embodiments where there are more than one electronic components, PWB  101  may further include a set of interconnects to electrically couple one component to another. 
         [0053]    A. An Example Electronic Component 
         [0054]      FIG. 1B  illustrates an electronic component  102 A, according to an embodiment. Electronic component  102 A includes a microchip  104  and may further include a package substrate  103 . Electronic component  102 A as shown in  FIG. 1B  includes only one package substrate  103  and one microchip  104 . However, as would be understood by a person skilled in the art based on the description herein, electronic component  102 A may include any number of package substrates and any number of microchips. Although microchip  104  is shown in  FIG. 1B  to be disposed over package substrate  103 , in alternative embodiments, microchip  104  may be entirely in or partially in package substrate  103 . 
         [0055]    Still referring to  FIG. 1B , package substrate  103  may be, but not limited to, a land-grid array (LGA) package with a laminate substrate, an FR4 substrate, ceramic, silicon, or glass substrate, and Microchip  104  may be, but not limited to, an integrated circuit (IC), a MEMS-only chip, or an integrated MEMS chip. 
         [0056]    According to another embodiment, electronic component  102 A may further include a second microchip disposed over, entirely in, or partially in package substrate  103 . The second microchip may be, for example, an application-specific integrated circuits (ASIC). Microchip  104  may be electrically coupled to the second microchip using at least one interconnect structure. The interconnect structure may be, for example, a wire bond with a first end interfacing with microchip  104  and a second end interfacing with the second microchip. Alternatively, microchip  104  may be electrically coupled to the second microchip through the package substrate  103 , according to an embodiment. For example, microchip  104  may be electrically coupled to package substrate  103  using a first array of solder balls, and package substrate  103  may be electrically coupled to the second microchip using a second array of solder balls. 
         [0057]    B. Example Microchips 
         [0058]      FIG. 1C  illustrates a microchip  104 A, according to an embodiment. Microchip  104 A includes a substrate  106  having a backside  106   a  and a through-substrate via (TSV)  200 , and microchip  104 A may further include a micro-fabricated device  105 . TSV  200  includes an electrically conductive structure and an insulating structure. The insulating structure electrically insulates substrate  106  from the conductive structure. Furthermore, TSV  200  may be electrically coupled to micro-fabricated device  105 , and TSV  200  may also be electrically coupled to package substrate  103  of  FIG. 1B  or to devices that may be present on backside  106   a  of microchip  104 A. 
         [0059]    Still referring to  FIG. 1C , micro-fabricated device  105  may be formed entirely in the substrate, entirely over the substrate, or partially in the substrate. Micro-fabricated device  105  may be, but not limited to, a field-effect transistor (FET) or a micro-electro-mechanical systems (MEMS) device. A MEMS device may be, but not limited to, a MEMS accelerometer or a MEMS gyroscope. 
         [0060]      FIG. 1D  illustrates a microchip  104 B, according to another embodiment. Microchip  104 B includes microchip  104 A of  FIG. 1C  and further includes a cap  108 . Cap  108  may provide hermetic sealing, according to an embodiment. Cap  108  may also include a recess  110  having a depth  110   a.  Such recess prevents cap  108  from contacting micro-fabricated device  105 . In an example where micro-fabricated device  105  is a MEMS device, which may have moving parts, depth  110   a  may be increased to provide additional operating space. 
         [0061]    Still referring to  FIG. 1D , the presence of cap  108  may prevent physical access to micro-fabricated device  105  from the top. However, by electrically coupling micro-fabricated device  105  to TSV  200 , micro-fabricated device  105  may be electrically coupled to through TSV  200  from the backside  106   a  of microchip  104 A. 
         [0062]    Still referring to  FIG. 1D , microchip  104 B may further include a bonding structure  112 , which is used to bond cap  108  to microchip  104 A. Microchip  104 B may also include a first adhesion layer  109   a  and a second adhesion layer  109   b.  In such instances, first adhesion layer  109   a  may be disposed between bonding structure  112  and cap  108 , and second adhesion layer  110  may be disposed between bonding structure  112  and microchip  104 A. The presence of adhesion layers  109   a  and  109   b  may improve adhesion strength between cap  108  and microchip  104 A. 
         [0063]    In an example, bonding structure  112  may be glass frit, and first adhesion layer  109   a  and second adhesion layer  109   b  may be a metal layer such as, but not limited to, aluminum. Alternatively, bonding structure  112  may be made of aluminum-germanium eutectic, and first and second adhesion layers  109   a  and  109   b  may be made of titanium nitride. According to another embodiment, first and second adhesion layers  109   a  and  109   b  may each include a plurality of layers. 
         [0064]    According to an embodiment, microchip  104 B may be oriented relative to a package substrate (e.g., package substrate  103  of  FIG. 1B ) such that cap  108  is positioned between microchip  104 A and the package substrate. Moreover, TSV  200  may be electrically coupled to the package substrate or to another chip on the same package substrate (e.g., the second microchip of electronic component  102 A) using, for example, wire bonds. Alternatively, microchip  104 B may be oriented relative to a package substrate such that microchip  104 A is positioned between cap  108  and the package substrate, and TSV  200  may be electrically coupled to the package substrate using, for example, an array of solder balls. 
         [0065]    C. An Example Electronic Component 
         [0066]      FIG. 1E  illustrates an electronic component  102 B, according to another embodiment. Electronic component  102 B includes electronic component  102 A of  FIG. 1B  and further includes an interposer  107 . Interposer  107  includes a TSV  200  and may be disposed between package substrate  103  and microchip  104 . Package substrate  103  and microchip  104  may be electrically coupled through TSV  200  of interposer  107 . Interposer  107  may be made of, but not limited to, silicon or glass. 
       IV. An Example TSV 
       [0067]      FIG. 2A  illustrates a top view of a TSV  200  formed in substrate  207 , according to an embodiment. TSV  200  includes a via  201 , a bulk region  202 , and an isolating structure  206  having a first width  206   a.  Isolating structure  206  includes a solid portion  204  and a seam portion  205 . Seam portion  205  includes an outer insulator  205   a,  a seam  205   b,  and an inner insulator  205   c,  where seam  205   b  is positioned between outer insulator  205   a  and inner insulator  205   c.  Seam portion  205  and solid portion  204  collectively form a closed loop surrounding via  201 . 
         [0068]    Solid portion  204 , outer insulator  205   a,  and inner insulator  205   c  may be made of one or more insulating dielectric material, for example, silicon dioxide. Via  201  may be made of a conductor or a semiconductor material, for example, silicon or doped silicon. 
         [0069]      FIG. 2B  illustrates an isolated view of seam portion  205  of  FIG. 2A . Seam portion  205  has a first end  205   d  and a second end  205   e,  and both ends are in contact with seam  205   b.    
         [0070]      FIG. 2C  illustrates a top view of TSV  200  as shown in  FIG. 2A .  FIGS. 2D-2E  illustrate cross-sectional views of TSV  200  taken along lines D′ and F′, respectively. 
         [0071]      FIGS. 2D and 2E  illustrate cross-sectional views of TSV  200  taken along line D′ of  FIG. 2C . TSV  200  further includes an insulating region  208  having a width  208   a  and a depth  208   b.  Seam portion  205  of insulating structure has a depth  206   b.  Via  201  has a first surface  201   a  and a second surface  201   b,  and substrate  207  has a first surface  207   a  and a second surface  207   b.  Seam portion  205  further includes a bottom insulator  205   g  having a thickness  205   h.  In another embodiment, seam portion  205  may further include a void  205   f.  Insulating region  208  extends through a second surface  207   b  of substrate  207  into substrate  207  to contact bottom insulator  205   g  of seam portion  205 . In another embodiment, insulating region  208  may extend beyond bottom insulator  205   g  of seam portion  205  such that a bottom insulator  205   g  extrudes into insulating region  208 . 
         [0072]    Still referring to  FIGS. 2D and 2E , width  208   a  of insulating region  208  is shown to be greater than width  206   a  of insulating structure  206 , and depth  208   b  of insulating region  208  is shown to be greater than depth  206   b  of insulating structure  206 . However, in alternative embodiments, depth  208   b  of insulating region  208  may be equal or less than depth  206   b  of insulating structure  206  and width  208   a  of insulating region  208  may be equal or less than width  206   a  of insulating structure  206 . 
         [0073]    Void  205   f  is positioned between seam  205   b  and bottom insulator  205   g  and is defined as the volume enclosed by outer insulator  205   a,  inner insulator  205   c,  and bottom insulator  205   g.  Seam  205   b  is an interface between outer insulator  205   a  and inner insulator  205   c  that is not mechanically fused, but merely in contact. Bottom insulator  205   g  of seam portion  205  is mechanically fused to both outer insulator  205   a  and inner insulator  205   c.    
         [0074]    Insulating region  208  may be made of a gaseous material such as, but not limited to, air, nitrogen, argon, or oxygen. Bottom insulator  205   g  may be made of one or more insulating dielectric material, for example, silicon dioxide, and solid portion  204 , outer insulator  205   a,  inner insulator  205   c,  and bottom insulator  205   g  may all be made of the same insulating dielectric material. In another embodiment, solid portion  204 , outer insulator  205   a,  inner insulator  205   c,  and bottom insulator  205   g  may each be made of a plurality of materials where at least one material is an insulating dielectric material. 
         [0075]      FIG. 2F  illustrates a cross-sectional view of TSV  200  taken along line F′ of  FIG. 2C . The figure illustrates, as noted above, that seam  205   b  is an interface between outer insulator  205   a  and inner insulator  205   c  that is not mechanically fused, but merely in contact, and void  205   f  is defined as the volume enclosed by outer insulator  205   a,  inner insulator  205   c,  and bottom insulator  205   g.    
         [0076]    Therefore, despite via  201  and bulk region  202  being held together by the entire insulating structure  206 , it is only bottom insulator  205   g  and solid portion  204  of insulating structure  206  that mechanically connects via  201  to bulk region  202 . As a result, mechanical reliability may be improved by increasing thickness  205   h  of bottom insulator  205   g,  by increasing width  204   a  of solid portion  204 , or by increasing the number of solid portions. 
       V. Example Insulating Structures 
       [0077]      FIG. 3A  illustrates an isolated view of insulating structure  206  of  FIGS. 2A-2E , which includes seam portion  205  separated by a single solid portion  204 . As noted above, seam portion  205  has a first end  205   d  and a second end  205   e,  and first end  205   d  and second end  205   e  are both in contact with seam  205   b.  Solid portion  204  forms a closed loop with seam portion  205  and is in contact with first end  205   d  and second end  205   e  of seam portion  205 . Insulating structure  206  may have a square shape. In another embodiment, insulating structure  206  may have a rectangular, a circular, or an ellipse shape. 
         [0078]      FIG. 3B  illustrates insulating structure  302 , according to another embodiment. Insulating structure  302  is similar to insulating structure  206  as described above. Therefore, only differences between insulating structures  302  and  206  are described herein. Insulating structure  302  includes a seam portion  303  and four solid portions  306   a - d.  Seam portion  303  is separated into four segments by four solid portions  306   a - d,  and seam portion  303  and four solid portions  306   a - d  collectively form a closed loop. 
         [0079]    As noted above, mechanical reliability may be improved by increasing the number of solid portions. Thus, insulating structure  302  may have improved mechanical reliability compared to insulating structure  206 . 
         [0080]      FIG. 3C  illustrates insulating structure  332 , according to another embodiment. Insulating structure  332  is similar to insulating structure  206  as described above. Therefore, only differences between insulating structures  332  and  206  are described herein. Insulating structure  332  includes an inner region  338 , a solid portion  336 , and a seam portion  333  having a first end  333   a,  a second end  333   b,  a first side  333   c,  and a second side  333   d.  Solid portion  336  and seam portion  332  collectively form a closed loop surrounding inner region  338 . First end  333   a  and second end  333   b  are curved inward toward inner region  338 . In an alternative embodiment, first and second ends  333   a  and  333   b  may be curved away from inner region  338 . Solid portion  336  is in contact with first and second ends  333   a  and  333   b  of seam portion  333 . First and second sides  333   c  and  333   d  may be substantially parallel to each other. 
         [0081]    Curved ends  333   a  and  333   b  of seam portions  333  may provide an advantage over straight ends  205   d  and  205   e  of seam portion  205  during the fabrication of insulating structures. For example, due to optical proximity correction (OPC) techniques used by modern photolithographic processes, two ends  205   d  and  205   e  may be difficult to pattern accurately and may be different from the intended design. In such instances, solid portion  204  may be difficult to form. However, curved ends  333   c  and  333   d  may resolve this issue because the two sides  333   c  and  333   d  of seam portion  333  can be patterned more accurately compared to ends  333   a  and  333   b.    
         [0082]      FIG. 3D  illustrates insulating structure  342 , according to another embodiment. Insulating structure  342  is similar to insulating structure  332  as described above. Therefore, only differences between insulating structures  342  and  332  are described herein. Insulating structure  342  includes a seam portion  343  and four solid portions  346   a - d,  and seam portion  343  is separated into four parts by four solid portions  346   a - d.  Thus, seam portion  343  has eight ends  346   a - h.  Each end is curved inward toward inner region  348 . In an alternative embodiment, each end may be curved away from inner region  348 . Solid portions  346   a - d  are in contact with their respective two ends of seam portion  343 . Solid portion  346  and four seam portions  342   a - d  collectively form a closed loop surrounding inner region  348 . 
         [0083]    Insulating structures  206 ,  302 ,  332 , and  342  of  FIGS. 3A-3D  include one or four solid portions as illustrative examples. However, as would be understood by a person of skilled in the art based on the description herein, an insulating structure may have any number of solid portions. 
       VI. Example TSVs 
       [0084]      FIG. 4  illustrates a cross-sectional view of TSV  400 , according to another embodiment. TSV  400  is similar to TSV  200  as described above. Therefore, only differences between TSV  200  and  400  are described herein. TSV  400  includes a via  401  having a first surface  401   a  and a second surface  401   b,  a bulk region  402 , a first wire  403 , a via pad  404  having a width  404   a,  an insulating structure  406 , and an insulating region  408 . 
         [0085]    Insulating structure  406  may extend over bulk region  402  to electrically insulate first wire  403  from bulk region  402 . First wire  403  is electrically coupled to via  401  through first surface  401   a.  Via pad  404  is disposed over second surface  401   b  and may cover entire second surface  401   b.  Alternatively, via pad  404  may cover a portion of second surface  401   b.  In an example where insulating region  408  is made of a gaseous material, via pad  404  may not extend beyond second surface  401   b.    
         [0086]    First wire  403  may be made of a conductive material. For example, first wire  403  may be made of metal such as, but not limited to, copper or aluminum. Via pad  404  may be made of a conductive material. For example, via pad may be made of metal such as, but not limited to copper or aluminum. In another embodiment, via pad  404  may be made of a plurality of materials. For example, via pad  404  may be a multi-layer under-bump metallization (UBM). 
         [0087]      FIG. 5  illustrates a cross-sectional view of TSV  500 , according to another embodiment. TSV  500  is similar to TSV  400  as described above. Therefore, only differences between TSV  500  and  400  are described herein. TSV  500  includes a via  501  having a width  501   a,  a via pad  504  having a width  504   a,  and insulating region  408  having an upper portion  408   a  and a lower portion  408   b.  Lower portion  408   b  may be made of a solid insulating material, and upper portion  408   a  may be made of a gaseous material. 
         [0088]    Lower portion  408   b  may extend over bulk region  402 . According to an embodiment, lower portion  408   b  may be disposed over a portion of via  501 . Via pad  504  is disposed over portions of bulk region  402 , insulating region  408 , and via  501 . Width  504   a  of via pad  504  may be larger than width  501   a  of via  501 . Via pad  504  is electrically coupled to via  501  and electrically insulated from bulk region  402  by lower portion  408   b.    
         [0089]    Some packaging technologies have requirements on dimensions of pads. And, since TSV  400  of  FIG. 4  may not have width  401   a  of via  401  that is smaller than width  404   a  of via pad  404 , the packaging requirements may imposes a minimum width for via  401 . On the other hand, TSV  500  of  FIG. 5  may have width  504   a  of via pad  504  that is larger than width  501   a  of via  501 , as noted above. Thus, size of TSV  500  may be reduced without being limited by packaging requirements. 
       VII. Example Microchips 
       [0090]      FIG. 6A  illustrates a cross-sectional view of a microchip  600 , according to an embodiment. Microchip  600  includes a wire  603 , a TSV  601  and a MEMS device  602 . TSV  601  is similar to TSV  500  as described above. Therefore, only differences between TSV  601  and  500  are described herein. Insulating structure  606  of TSV  601  further includes an isolation joint portion  606   a,  and MEMS device  602  includes a first portion  602   a  and a second portion  602   b.  In an example, MEMS device  602  requires that first portion  602   a  and second portion  602   b  are electrically insulated from each other. Isolation joint portion  606   a  of insulating structure  606  provide such electrical insulation. 
         [0091]    Still referring to  FIG. 6A , isolation joint portion  606   a  extends through first surface  607   a  of substrate  607  into substrate  607  and is positioned between first portion  602   a  and second portion  602   b  of MEMS device  602 . Isolation joint portion  606   a  may be disposed over first portion  602   a.  Furthermore, isolation joint portion  606   a  may be formed at the same time as insulating structure  606  to reduce fabrication cost. 
         [0092]    Still referring to  FIG. 6A , wire  603  is electrically coupled to via  601  and to second portion  602   b,  but insulating structure  606  electrically insulates wire  603  from first portion  602   a.  According to another embodiment, wire  603  may be disposed over insulating structure  606 , via  601 , first portion  602   a,  or second portion  602   b.    
         [0093]    According to an embodiment, MEMS  602  may be formed after the formation of insulating structure  606  including isolation joint portion  606   a  but before the formation of insulating region  608 . In some embodiments, MEMS  602  may be formed after the formation of wire  603  but before the formation of insulating region  608 . An example of MEMS  602  may be a MEMS device disclosed by U.S. Pat. No. 8,664,731, which is hereby incorporated by reference in its entirety. According to an embodiment, microchip  600  may further include a cap, as illustrated in  FIG. 1D . In such embodiments, microchip  600  may further include a bonding structure and adhesion layers to bond the cap to substrate  607 . 
         [0094]      FIG. 6B  illustrates a cross-sectional view of a microchip  610 , according to an embodiment. Microchip  610  is similar to microchip  600  as described above except that microchip  610  further includes a side trench  611  having a width  611   a.  The presence of side trench  611  may reduce chipping of silicon region  612 . 
         [0095]    Width  611   a  of side trench  611  is smaller than width  608   a  of insulating region  608 , and depth  611   a  may be less than the depth of insulating region  608  thereby leaving some silicon above side trench  611 . In some embodiments, this may be due to etch lag effects that occur when side trench  601  and insulating region  608  are etched at the same time. The presence of silicon above side trench  611  may prevent cracks, formed during a substrate dicing process, from propagating into insulating region  608 . 
       VIII. An Example Fabrication Process for TSV 
       [0096]      FIGS. 7A-7C  illustrate a partially fabricated TSV  200  after formation of a trench  701  having a width  701   a  in substrate  207 , according to an embodiment. Trench  701  and substrate portion  702  collectively form a closed loop surrounding inner region  703 .  FIG. 7A  illustrates a top view, and  FIGS. 7B and 7C  illustrate cross-sectional views taken along lines B′ and C′ of  FIG. 7A , respectively. 
         [0097]    Trench  701  has a width  701   a,  an inner sidewall  701   b,  and an outer sidewall  701   c.  Trench  701  may be formed by any conventional etching methods suitable for etching the material of substrate  207 . For example, a dry etch process such as, but not limited to, reactive ion etching (RIE) or Bosch process may be performed to remove the material of substrate  207  for the formation of trench  301 . 
         [0098]      FIGS. 8A-8C  illustrate a partially fabricated TSV  200  after forming insulating structure  206  by filling trench  701  to form seam portion  205  and by converting substrate portion  702  into a solid portion  204 , according to an embodiment.  FIG. 8A  illustrates a top view, and  FIGS. 8B and 8C  illustrate cross-sectional views taken along lines B′ and C′ of  FIG. 8A , respectively. 
         [0099]    Trench  701  can be filled with an insulating dielectric material to form a seam portion  205 . As noted above, the insulating dielectric material may be, for example, silicon dioxide or other suitable insulating dielectric materials. In an example where the insulating dielectric material is silicon dioxide, an oxidation process may be performed to fill trench  701 . This oxidation process consumes silicon surfaces of the substrate to form silicon dioxide. The resulting volumetric expansion from this process causes the sidewalls  701   b  and  701   c  of trench  701  to encroach upon each other, eventually closing the trench. Since some of silicon is consumed, width  206   a  of insulating structure  206  may be greater than width  701   a  of trench  701 . During this process, trench  701  may be incompletely filled, forming a seam  205   b  and a void  205   f  in seam portion  205 , according to an embodiment. Although a void  205   f  is illustrated in  FIG. 8B , alternative embodiments may not have any void in seam portion  205 . During the same process or in a separate process, substrate portion  702  is also consumed completely and converted to a solid portion  204 , for example, using the same oxidation process as described above for filling trench  701 . 
         [0100]      FIGS. 9A-9C  illustrate TSV  200  after forming insulating region  208 , according to an embodiment.  FIG. 9A  illustrates a bottom view, and  FIGS. 9B and 9C  illustrate cross-sectional views taken along lines B′ and C′ of  FIG. 9A , respectively. 
         [0101]    Insulating region  208 , having a depth  208   b,  may be formed by any conventional etching methods suitable for etching the material of substrate  207 . For example, a dry etch process such as, but not limited to, reactive ion etching (RIE) or Bosch process may be performed to remove the material of substrate  207  for the formation of insulating region  208 . 
         [0102]    In another embodiment, the etch process used to form insulating region  208  may not remove the material of bottom insulator  205   g.  Therefore, as noted above, insulating region  208  may extend beyond bottom insulator  205   g  of seam portion  205  such that bottom insulator  205   g  extrudes into insulating region  208 . 
         [0103]    In another embodiment, substrate  207  may be thinned by removing a portion of substrate  207  from second surface  207   b.  Thinning of substrate  207  may be performed by, for example, a physical grinding, a chemical etching, or a chemical mechanical planarization (CMP) process. This thinning process may be performed prior to formation of insulating region  208 , in an embodiment. Since some etch processes limit the aspect-ratio of etched features, prior thinning of substrate  207  may enable insulating region  208  with a smaller depth  206   b  and width  208   a.  Thus, in some embodiments, depth  208   b  of insulating region  208  may be equal or less than depth  206   b  of insulating structure  206 , and width  208   a  of insulating region  208  may be equal or less than width  206   a  of insulating structure  206 . 
         [0104]      FIG. 10  is a flow chart illustrating a method of fabricating TSV  200  shown in  FIGS. 2A-2E , according to an embodiment. Solely for illustrative purposes, the steps illustrated in  FIG. 10  will be described with reference to example fabrication process illustrated in  FIGS. 7A-7C, 8A-8C, and 9A-9C . 
         [0105]    In step  1010 , trench  701  is formed in first surface  207   a  of substrate  207 , as shown in  FIGS. 7A-7C , by an etch process. The etch process may be, but not limited to, reactive ion etching (RIE) to remove the material of substrate  207 , according to an embodiment. 
         [0106]    In step  1020 , trench  701  is filled to form a seam portion  205  and to convert substrate portion  702  to solid portion  204 , as shown in  FIGS. 8A-8C . Filling of trench  701  may be performed by, for example, growing a thermal oxide such as silicon dioxide directly from substrate  207  using thermal oxidation. Converting of substrate portion  702  to solid portion  204  may be performed by, for example, growing a thermal oxide such as silicon dioxide directly from substrate  207  using thermal oxidation. The thermal oxidation process completely consumes the substrate portion  702  to form silicon dioxide. 
         [0107]    In step  1030 , insulating region  208  is formed surface  207   b  of substrate  207 , as shown in  FIGS. 9A-9C , by an etch process. The etch process may be, but not limited to, reactive ion etching (RIE) to remove the material of substrate  207 , according to an embodiment. 
       IX. An Example Fabrication Process for TSV and MEMS 
       [0108]    Another example fabrication process for forming both a TSV and a MEMS device is described. 
         [0109]    The process starts with the wafer pattern as shown in  FIG. 11A .  FIG. 11A  shows an example TSV trench opening pattern with segmented trenches  1111  that mostly surrounds silicon  1112 . Eventually, the process separates silicon  1112  from surrounding silicon  1113 . 
         [0110]      FIG. 11A  also illustrates an opening for a short isolation segment pair  1116 . Typical dimensions are on the order of 4 μm long, 1.2 μm wide, and separated by 1 μm. Isolation segment pair  1116  is intended to eventually isolate a freestanding MEMS structure from surrounding silicon  1113 . Cross sectional views taken along line B′ are illustrated in  FIGS. 11B-11G  to detail the fabrication process. As noted above, the narrow silicon spaces, generally indicated by  1115  and  1117 , eventually form bridge portions that enhance the structural strength of the insulating structure and the isolation joint. 
         [0111]    When pattern  1111  of  FIG. 11A  is transferred into the silicon using a Bosch silicon etch, trenches  1131  and  1137  are formed, as shown in  FIG. 11B . Mostly surrounded silicon  1112  of  FIG. 11A  is shown as silicon  1135  in  FIG. 11B . Trench opening  1137  of  FIG. 11B  shows where one of the segmented isolation joints will be formed in order to isolate a freestanding MEMS structure. 
         [0112]    In a subsequent step, silicon dioxide is grown until trenches  1131  of  FIG. 11B  close off due to the two oxidation fronts merging from each pair of adjacent trench walls, as shown in  FIG. 11C . At this merger of oxidation fronts, a seam  1158  is formed. The seam  1158  may be weaker than the bulk silicon dioxide material.  FIG. 11C  shows the seam  1158  as being unfilled through the cross section because the two opposing oxidation fronts are not mechanically fused. After an oxidation process, narrow silicon portion  1132  of  FIG. 11B  fully oxidizes and forms a bridge portion  1152 , as shown in  FIG. 11C . 
         [0113]    In a subsequent step, as illustrated in  FIG. 11D , via openings  1171  and  1173  are opened in top oxide  1153 . Metal trace  1172  connects to the TSV structure through via opening  1171 . The eventual freestanding MEMS structure location is generally shown by location  1174 . 
         [0114]    In a subsequent step, as illustrated in  FIG. 11E , a second interlayer dielectric  1181  is deposited and patterned. Additionally, metal layer  1182  is also deposited and patterned in order to provide a bonding interface. A freestanding MEMS structure  1191  is created using a series of processing steps described in, for example, U.S. Pat. No. 8,319,254, the entirety of which is incorporated by reference herein. 
         [0115]    In a subsequent step, as illustrated in  FIG. 11F , a lid  1200  is bonded to substrate  1206  using glass frit  1202 . Metal layers  1201  and  1182  form interface layers to promote adhesion. Alternative materials such as aluminum-germanium eutectics could be used to bond lid  1200  to substrate  1206 . Silicon recess  1203  is used to allow the freestanding MEMS structure  1191  to move through its necessary operational range before hitting silicon stop  1204 . 
         [0116]    Once bonded together, the substrate can be ground on surface  1205  for two reasons. First, the total MEMS stack thickness needs to be reduced to fit into the ever shrinking consumer electronics products. Second, by grinding surface  1205 , the silicon thickness that needs to be etched to form an insulating region is reduced. 
         [0117]      FIG. 11G  illustrate a step to complete the TSV structure. First, metal bond pad  1221  is formed on the end of the TSV structure  1224 . Second, isolation region  1222  is etched into the silicon until the bottoms of the isolation structure  1225  are exposed. At this point in the process, TSV  1224  is electrically isolated from the surrounding silicon  1113 . And, TSV structure  1224  is strengthened by the segmentation of the insulating structure using solid portions  1152 . TSV structure  1224  is electrically connected to freestanding MEMS  1191  through via opening  1171 , metal trace  1172 , and via opening  1173 . Freestanding MEMS  1191  is isolated from surrounding silicon  1113  by the segmented isolation joint  1126 . 
         [0118]    In order to reduce chipping of the silicon adjacent to TSV structure  1224 , trench  1223  is etched with a width smaller than the width of insulating region  1222 . By using a smaller trench width, the resulting trench depth is not as great due to etch lag effects. End point detection is an important part of this process to make sure that the insulating structure  1225  is exposed, but that not all of the remaining silicon  1227  is etched prior to hitting top oxide  1153 . Leaving remaining silicon  1227  is helpful in increasing the strength of the resulting TSV structure  1224 . 
         [0119]      FIG. 11H  illustrates an optional fabrication process step that would allow the dimensions of TSV structure  1224  to be shrunk and therefore lower the total system cost. In  FIG. 11G , the size of bond pad  1221  is determined by the minimum size required by the packaging vendor to place a bond wire on the surface of pad  1221 . If an insulating layer  1333  is deposited on the etched backside of substrate  1206 , via opening  1330  could be opened in insulating layer  1333  and metal  1331  could be deposited and patterned to form a bond pad generally indicated in location  1332 . This optional processing step may reduce the size of TSV structures  1224  and the total system cost. Additionally, wire bonding could take place in location  1332 . 
         [0120]      FIG. 12  illustrates a 3D rendering of a microchip cross-section with a TSV  1224  and a MEMS device  1191 , according to an embodiment. The lid  1200  and device substrate  1206  are bonded together. The cross-sectional view shows the TSV structure  1224  and the adjacent freestanding MEMS device  1191 . 
       X. Conclusion 
       [0121]    It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way. 
         [0122]    The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. 
         [0123]    The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
         [0124]    The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.