Patent Publication Number: US-9431510-B2

Title: Metal-semiconductor wafer bonding for high-Q devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 13/293,075, entitled “Metal-Semiconductor Wafer Bonding for High-Q Devices,” filed on Nov. 9, 2011, which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF DISCLOSURE 
     This disclosure relates generally to electronics, and more specifically, but not exclusively, to apparatus and methods for metal-semiconductor wafer bonding for high-quality devices. 
     BACKGROUND 
     Conventional Metal-Insulator-Metal (MIM) devices, such as MIM semiconductor capacitors, have quality factor (Q) limits due to resistance of thick metal plates with which the conventional MIM devices are fabricated. The thick metal plates resist current flow, which increases the MIM devices&#39; equivalent series resistance (ESR). The high ESR in turn lowers the MIM devices&#39; Q. When the conventional MIM devices are used in radio frequency (RF) circuits, the conventional MIM devices&#39; low-Q restrains performance of the RF circuits and increases the RF circuits&#39; power consumption. 
     Accordingly, there are long-felt industry needs for device fabrication methods and apparatus that mitigate the problems of the conventional methods and the conventional devices. 
     SUMMARY 
     This summary provides a basic understanding of some aspects of the present teachings. This summary is not exhaustive in detail, and is neither intended to identify all critical features, nor intended to limit the scope of the claims. 
     In an example, methods and apparatus for fabricating a capacitor are provided. A first plate is formed on a glass substrate. The first plate can be formed directly on the glass substrate without using an organic bonding agent. A dielectric layer is formed on a silicon substrate. The dielectric layer can be an intrinsic semiconductor. The first plate is bonded to the dielectric layer with an intermetallic layer using thermo compression. The silicon substrate is doped to form an extrinsic semiconductor layer. A second plate is formed on the extrinsic semiconductor layer. At least a portion of a surface of at least one of the intermetallic layer, the dielectric layer, the extrinsic semiconductor layer, and the second plate can be passivated. The capacitor can be coupled as a high-quality factor capacitor in a circuit. The capacitor can be coupled as a varactor in a circuit. The capacitor can be integrated with at least a part of a mobile device. 
     In a further example, provided is a non-transitory computer-readable medium, comprising instructions stored thereon that, if executed by a processor, cause a lithographic device to execute at least a part of the aforementioned method. 
     In an example, provided is a capacitor. The capacitor includes a first plate formed on a glass substrate. In an example, there is no organic bonding agent between the first plate and the glass substrate. The capacitor includes a second plate and a dielectric layer. The dielectric layer can be an intrinsic semiconductor. The capacitor also includes an extrinsic semiconductor layer that is highly-conductive, heavily doped, and adjacent to the dielectric layer. The dielectric layer and the extrinsic semiconductor layer are sandwiched between the first and second plates. An intermetallic layer is formed between the first plate and the dielectric layer. The intermetallic layer is thermo compression bonded to the first plate and the dielectric layer. The capacitor can be coupled in a circuit as a high-quality factor capacitor. The capacitor can be coupled in a circuit as a varactor. The capacitor can be integrated with at least a part of a mobile device. 
     The capacitor can be integrated in a semiconductor die, and can be integrated into a device, selected from the group consisting of a set top box, music player, video player, entertainment unit, navigation device, communications device, personal digital assistant (PDA), fixed location data unit, and a computer. In a further example, provided is a non-transitory computer-readable medium, comprising instructions stored thereon that, if executed by a lithographic device, cause the lithographic device to fabricate at least a part of the apparatus. 
     The foregoing has broadly outlined some of the features and technical advantages of the present teachings in order that the detailed description can be better understood. Additional features and advantages are also described in the detailed description. The conception and disclosed embodiments can be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present teachings. Such equivalent constructions do not depart from the technology of the teachings as set forth in the claims. The novel features that are characteristic of the teachings, together with further objects and advantages, are better understood from the detailed description and the accompanying figures. Each of the figures is provided for the purpose of illustration and description only, and does not limit the present teachings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are presented to describe examples of the present teachings, and are not provided as limitations. 
         FIG. 1  depicts an exemplary communication system in which an embodiment of the disclosure may be advantageously employed. 
         FIG. 2  depicts an exemplary electronic device including a capacitor having a metal-semiconductor wafer bond. 
         FIG. 3  depicts an exemplary cross-sectional view of a capacitor having a metal-semiconductor wafer bond. 
         FIGS. 4A-4E  depict an exemplary fabrication process for fabricating a capacitor having a metal-semiconductor wafer bond. 
         FIG. 5  depicts an exemplary flowchart of a method for fabricating a capacitor having a metal-semiconductor wafer bond. 
     
    
    
     In accordance with common practice, the features depicted by the drawings may not be drawn to scale. Accordingly, the dimensions of the depicted features may be arbitrarily expanded or reduced for clarity. In accordance with common practice, some of the drawings are simplified for clarity. Thus, the drawings may not depict all components of a particular apparatus or method. Further, like reference numerals denote like features throughout the specification and figures. 
     DETAILED DESCRIPTION 
     Examples of the current teachings are disclosed in this application&#39;s text and drawings. The examples advantageously address the long-felt industry needs, as well as other previously unidentified needs, and mitigate shortcomings of the conventional methods and apparatus. Alternate embodiments can be devised without departing from the scope of the invention. Additionally, conventional elements of the current teachings may not be described in detail, or may be omitted, to avoid obscuring aspects of the current teachings. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiments of the invention” does not require that all embodiments of the invention include the discussed feature, advantage, or mode of operation. Use of the terms “in one example,” “an example,” “in one feature,” and/or “a feature” in this specification does not necessarily refer to the same feature and/or example. Furthermore, a particular feature and/or structure can be combined with one or more other features and/or structures. 
     It should be noted that the terms “connected,” “coupled,” or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and can encompass the presence of one or more intermediate elements between two elements that are “connected” or “coupled” together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements can be considered to be “connected” or “coupled” together by the use of one or more wires, cables, and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and/or the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples. 
     It should be understood that the term “signal” can include any signal such as a data signal, audio signal, video signal, multimedia signal. Information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, process step, commands, information, signals, bits, symbols, and chips that can be referenced throughout this description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, and/or any combination thereof. 
     It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations can be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must necessarily precede the second element. Also, unless stated otherwise, a set of elements can comprise one or more elements. In addition, terminology of the form “at least one of: A, B, or C” used in the description or the claims means “A or B or C or any combination of these elements.” 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In the following description, certain terminology is used to describe certain features. The term “mobile device” includes, but is not limited to, a mobile phone, a mobile communication device, personal digital assistant, mobile palm-held computer, a wireless device, and/or other types of portable electronic devices typically carried by a person and/or having some form of communication capabilities (e.g., wireless, infrared, short-range radio, etc.). 
     INTRODUCTION 
     Methods and apparatus for metal-semiconductor wafer bonding are provided. In an example, a capacitor includes a CMOS-compatible intermetallic bonding layer that advantageously has a lower resistance than bonding layers found in conventional devices. The lower resistance provides the capacitor with a higher quality factor (Q) than conventional devices, even when the capacitor has metal conductors that are thicker than conventional conductors, thus improving performance and lowering power consumption. The intermetallic bonding layer in the capacitor is non-organic, does not outgas, and does not degrade as quickly as conventional organic adhesives. The intermetallic bonding layer is also more reliable, easier to fabricate, and has better thickness uniformity than the conventional organic adhesives. In examples, some of the exemplary apparatus disclosed herein have a crystalline semiconductor as the capacitor&#39;s dielectric, so that the capacitor can be used as a varactor. 
     DESCRIPTION OF THE FIGURES 
       FIG. 1  depicts an exemplary communication system  100  in which an embodiment of the disclosure may be advantageously employed. For purposes of illustration,  FIG. 1  shows three remote units  120 ,  130 , and  150  and two base stations  140 . The wireless communication system  100  can have many more remote units and more base stations. The remote units  120 ,  130 , and  150  include at least a part of an embodiment  125 A-C of the disclosure as discussed further herein.  FIG. 1  also shows forward link signals  180  from the base stations  140  and the remote units  120 ,  130 , and  150 , as well as reverse link signals  190  from the remote units  120 ,  130 , and  150  to the base stations  140 . 
     In  FIG. 1 , the remote unit  120  is shown as a mobile telephone, the remote unit  130  is shown as a portable computer, and the remote unit  150  is shown as a fixed location remote unit in a wireless local loop system. In examples, the remote units  130  may be a mobile phone, a hand-held personal communication systems (PCS) unit, a portable data unit such as a personal data assistants, a GPS-enabled device, a navigation device, a settop box, a music player, a mobile device, a video player, an entertainment units, or any other device that stores or retrieves data or computer instructions, or any combination thereof. Although  FIG. 1  illustrates remote units according to the teachings of the disclosure, the disclosure is not limited to these exemplary illustrated units. Embodiments of the disclosure may be suitably employed in any device which includes active integrated circuitry including memory and on-chip circuitry for test and characterization. 
       FIG. 2  depicts an exemplary electronic device  200  in which an embodiment of the disclosure can be advantageously employed. The electronic device  200  can be a mobile device, at least one of the three remote units  120 ,  130 , and  150 , and/or at least one of the two base stations  140 . The electronic device  200  includes a circuit  205  coupled to a capacitor  210  having a metal-semiconductor wafer bond. The capacitors described herein, such as the capacitor  210  can be coupled in a circuit as a high-Q capacitor and/or a varactor having a Q that is improved over conventional Metal-Insulator-Metal (MIM) devices. When coupled to a tuned circuit, the high-Q capacitor and/or the high-Q varactor enables the tuned circuit to have a higher Q, when compared to a conventional tuned circuit. The higher Q in turn reduces phase noise produced by the tuned circuit. For example, when the tuned circuit is a filter, the higher Q varactor provides the filter with greater selectivity than a conventional filter. Further, when the tuned circuit is an oscillator, the higher Q provides lower and slower energy loss than a conventional oscillator, thus saving energy. Thus, if used in a battery-powered device, using the capacitor can advantageously increase battery life. 
     The circuit  205  to which the capacitor  210  can be coupled and/or integrated with can include, and is not limited to: a radio frequency circuit (e.g., a radio frequency front-end circuit), an audio frequency circuit, a filter (e.g., a tracking filter), a tuner, an oscillator (e.g., a voltage-controlled oscillator), an impedance matching device, a lumped element circuit, a DC blocking circuit, a bypass circuit, a phase-locked loop, a frequency synthesizer, an amplifier, a circuit in a mobile device, a circuit requiring a voltage-controlled variable capacitance, and a coupling circuit. 
       FIG. 3  depicts an exemplary cross-sectional view  300  of the capacitor  210  having a metal-semiconductor wafer bond and a high-Q. The capacitor  210  can also be used as a varactor having a high-Q. 
     The capacitor  210  is fabricated on a substrate  305 , such as a glass plate. The substrate  305  can be fabricated of semiconducting crystalline materials such as silicon, germanium, silicon germanium, gallium arsenide, aluminum gallium arsenide, gallium nitride, indium phosphide, and/or another suitable material suitable for carrying the capacitor. 
     A first plate  310  is located on the substrate  305 . In an example, the first plate  310  is in direct contact with the substrate  305 , and no organic bonding agent is used between the first plate  301  and the substrate  305 . The first plate  310  can be fabricated of a conductor, such as aluminum, nickel, silver, gold, chromium, molybdenum, tungsten, titanium, platinum, another suitable material, and/or an alloy thereof. 
     The capacitor  210  includes a dielectric layer  315 . The dielectric layer  315  is fabricated of an insulator, such as an intrinsic semiconductor (e.g., epitaxial germanium or silicon). The first plate  310  is thermo compression bonded to the dielectric layer  315  with an intermetallic bonding layer  320 . The intermetallic bonding layer  320  reduces the equivalent series resistance (ESR) of the capacitor  210 , as compared to conventional devices. The intermetallic bonding layer  320  is an alloy that transitions from a high concentration of the material of the first plate  310  and low concentration of the dielectric material at the first plate  310  to a low concentration of the material of the first plate  310  and high concentration of the dielectric material at the dielectric layer  315 . The alloy of the intermetallic bonding layer  320  can include AlGe, AlSi, NiGe 2 , and/or NiSi 2 . 
     An extrinsic semiconductor layer  325  is on the dielectric layer  315 . The extrinsic semiconductor layer  325  provides charge carriers that lower the ESR of the capacitor  210 . The extrinsic semiconductor layer  325  can be a highly-doped, highly-conductive n+ region. In an example, the dopant is phosphorus. 
     A second plate  330  of the capacitor  210  is on the extrinsic semiconductor layer  325 . The second plate  330  can be fabricated of a conductor, such as aluminum, nickel, silver, gold, chromium, molybdenum, tungsten, titanium, platinum, another suitable material, and/or an alloy thereof. 
     An optional via  335  contacts the first plate  310  and can be coupled to a wire on a layer other than that of the first plate  310 . The via  335  can be fabricated of a conductor, such as aluminum, nickel, silver, gold, chromium, molybdenum, tungsten, titanium, platinum, another suitable material, and/or an alloy thereof. 
     An optional passivation layer  340  passivizes the first plate  310 , the intermetallic bonding layer  320 , the dielectric layer  315 , the extrinsic semiconductor layer  325 , and the second plate  330 . 
       FIGS. 4A-4E  depict an exemplary fabrication process  400  for fabricating the capacitor  210  having a metal-semiconductor wafer bond. 
       FIG. 4A  depicts forming the first plate  310  on a glass substrate  405 . The first plate  310  can be formed directly on the glass substrate  405  without using an organic bonding agent.  FIG. 3A  also depicts forming the dielectric layer  315  on a silicon substrate  410 . The dielectric layer  315  can be an intrinsic semiconductor, such as epitaxial germanium or silicon. The first plate  310  and the dielectric layer  315  can be fabricated using photolithography or any other appropriate technique. 
       FIG. 4B  depicts thermo compression bonding the first plate  310  to the dielectric layer  315 , which forms the intermetallic bonding layer  320 . Thermo compression bonding includes applying heat while applying mechanical force to hold the first plate  310  to the dielectric layer  315 . The heat and mechanical force cause the first plate material and the dielectric material to alloy, thus forming both an electrical bond and a eutectic mechanical bond between the first plate  310  and the dielectric layer  315 . The electrical bond forms an interlayer electrical connection. A bonding chamber or any other appropriate device can be used to perform the thermo compression bonding process. 
       FIG. 4C  depicts optional removing of material from the silicon substrate  410  with a removal process. For example, the silicon substrate  410  can be shaped by thinning, milling, grinding, and/or etching. 
       FIG. 4D  depicts doping the silicon substrate  410  with a dopant to convert the silicon substrate  410  to an extrinsic semiconductor layer  325 . For example, the doping can convert the silicon substrate  410  to an n+ layer. In an example, after doping, the charge carrier concentration is in a range of substantially 10 17  cm −3  to substantially 10 18  cm −3 . The extrinsic semiconductor layer  325  can be fabricated using photolithography, or any other appropriate technique. 
       FIG. 4E  depicts depositing the second plate  330 , depositing the optional via  335 , and optionally passivizing the intermetallic bonding layer  320 , the dielectric layer  315 , the extrinsic semiconductor layer  325 , and the second plate  330  with the passivation layer  340 . The via  335  provides an electrical feedthrough to couple the first plate  310  to a layer other than that of the first plate  310 , and can be fabricated using photolithography or any other appropriate technique. The first plate  310  and the second plate  330  can be electrically coupled to a circuit, such as the circuit  205 . 
     The depositing of materials during the exemplary fabrication process  400  can be performed using, for example, physical vapor deposition, sputtering, chemical vapor deposition, electrochemical deposition, molecular beam epitaxy, atomic layer deposition, and/or another appropriate method. 
       FIG. 5  depicts an exemplary flowchart  500  of a method for fabricating a capacitor having a metal-semiconductor wafer bond, such as the capacitor  210 . The method can be performed, at least in part, by a lithographic apparatus. 
     In step  505 , a first plate is formed on a glass substrate. The first plate can be formed directly on the glass substrate without using an organic bonding agent. 
     In step  510 , a dielectric layer is formed on a silicon substrate. The dielectric layer can be an intrinsic semiconductor. 
     In step  515 , the first plate is bonded to the dielectric layer with an intermetallic layer using thermo compression bonding. 
     In step  520 , the silicon substrate is doped to form an extrinsic semiconductor layer. 
     In step  525 , a second plate is formed on the extrinsic semiconductor layer. 
     In optional step  530 , at least a portion of a surface of at least one of the intermetallic layer, the dielectric layer, the extrinsic semiconductor layer, and the second plate is passivated. 
     In optional step  535 , the capacitor can be coupled as a high-quality factor capacitor and/or a varactor in a circuit. 
     In optional step  540 , the capacitor can be integrated with at least a part of a mobile device. 
     CONCLUSION 
     Those having skill in the relevant art will appreciate that information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, process steps, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     In some aspects, the teachings herein can be employed in a multiple-access system capable of supporting communication with multiple users by sharing the available system resources (e.g., by specifying one or more of bandwidth, transmit power, coding, interleaving, and so on). For example, the teachings herein can be applied to any one or combinations of the following technologies: Code Division Multiple Access (CDMA) systems, Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-Speed Packet Access (HSPA, HSPA+) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, or other multiple access techniques. A wireless communication system employing the teachings herein can be designed to implement one or more standards, such as IS-95, cdma2000, IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network can implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and Low Chip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 and IS-856 standards. A TDMA network can implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network can implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM.®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). The teachings herein can be implemented in a 3GPP Long Term Evolution (LTE) system, an Ultra-Mobile Broadband (UMB) system, and other types of systems. LTE is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP), while cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). Although certain aspects of the disclosure can be described using 3GPP terminology, it is to be understood that the teachings herein can be applied to 3GPP (e.g., Re199, Re15, Re16, Re17) technology, as well as 3GPP2 (e.g., 1xRTT, 1xEV-DO Re10, RevA, RevB) technology and other technologies. The techniques can be used in emerging and future networks and interfaces, including Long Term Evolution (LTE) compatible devices. 
     The methods, sequences and/or algorithms described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module (including instructions) executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. 
     Further, many embodiments are described in terms of sequences of actions to be performed by, for example, elements of a computing device. It will be recognized that various actions described herein can be performed by specific circuits (e.g., application specific integrated circuits (ASICs)), by program instructions being executed by one or more processors, or by a combination of both. Additionally, these sequence of actions described herein can be considered to be embodied entirely within any form of computer readable storage medium having stored thereon a corresponding set of computer instructions, that upon execution would cause an associated processor to perform the functionality described herein. Thus, the various aspects of the invention can be embodied in a number of different forms, all of which have been contemplated to be within the scope of the claimed subject matter. In addition, for each of the embodiments described herein, the corresponding form of any such embodiments can be described herein as, for example, “logic configured to” perform the described action. An embodiment of the invention can include a computer readable media embodying a method described herein. Accordingly, the invention is not limited to illustrated examples and any means for performing the functionality described herein are included in embodiments of the invention. 
     The disclosed devices and methods can be designed and configured into GDSII and GERBER computer files that are stored on a computer readable media. These files are in turn provided to fabrication handlers who fabricate devices, based on these files, with a lithographic device. The resulting products are semiconductor wafers that are then cut into semiconductor dice, which are packaged into a respective semiconductor chip. The chip is are then employed in a device, such as a mobile device. 
     Spatial descriptions (e.g., “top,” “middle,” “bottom,” “left,” “center,” “right,” “up,” “down,” “vertical,” “horizontal,” etc.) used herein are for illustrative purposes only, and are not limiting descriptors. Practical implementations of the structures described hereby can be spatially arranged in any orientation providing the functions described hereby. In addition, in using the term “adjacent” herein to describe a spatial relationship between integrated circuit elements, the adjacent integrated circuit elements need not be in direct physical contact, and other integrated circuit elements can be located between the adjacent integrated circuit elements. 
     Nothing that has been stated or illustrated is intended to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is recited in the claims. While this disclosure shows exemplary embodiments of the invention, it should be noted that various changes and modifications could be made herein without departing from the scope of the invention as defined by the appended claims. The functions, steps and/or actions of the method claims in accordance with the embodiments of the invention described herein need not be performed in any particular order.