Abstract:
A method of forming an integrated circuit including a Schottky diode includes providing a substrate of a first conductivity type, defining a region of a second conductivity type relative to the substrate and forming an insulator over the second conductivity type region. The method also includes removing an area of the insulator for definition of a contact hole, and removing an area encircling the contact hole and forming highly doped regions of the second conductivity type in second conductivity type regions encircling the contact hole. The method further includes depositing a Schottky metal in the contact hole and annealing the metal to form a suicide interface to the second conductivity type region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a Division of U.S. application Ser. No. 08/705,043, filed Aug. 29, 1996, now U.S. Pat. No. 6,130,602 (incorporated herein by reference), which claims priority from U.S. Provisional Application 60/017,900, filed May 13, 1996, titled “Radio Frequency Data Communication Device.” 
    
    
     COPYRIGHT AUTHORIZATION 
     A portion of the disclosure of this patent document, including the appended microfiche, contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     REFERENCE TO MICROFICHE 
     Appended hereto is a microfiche copy of a software guide entitled “Micron RFID Systems Developer&#39;s Guide,” May 2, 1996. This appendix has 5 microfiche providing 266 total frames. 
     TECHNICAL FIELD 
     This invention relates to radio frequency communication devices. More particularly, the invention relates to radio frequency identification devices for inventory control, object monitoring, or for determining the existence, location or movement of objects. In a more specific aspect, this invention relates to method for forming Schottky diodes finding application in such radio frequency identification devices. 
     BACKGROUND OF THE INVENTION 
     As large numbers of objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and flow of objects. Additionally, there is a continuing goal to interrogate the location of objects in an inexpensive and streamlined manner. Furthermore, there is a need for tag devices suitably configured to mount to a variety of objects including goods, items, persons, or animals, or substantially any moving or stationary and animate or inanimate object. One way of tracking objects is with an electronic identification system. 
     One presently available electronic identification system utilizes a magnetic field modulation system to monitor tag devices. An interrogator creates a magnetic field that becomes detuned when the tag device is passed through the magnetic field. In some cases, the tag device may be provided with a unique identification code in order to distinguish between a number of different tags. Typically, the tag devices are entirely passive (have no power supply), which results in a small and portable package. However, this identification system is only capable of distinguishing a limited number of tag devices, over a relatively short range, limited by the size of a magnetic field used to supply power to the tags and to communicate with the tags. 
     Another electronic identification system utilizes an RF transponder device affixed to an object to be monitored, in which an interrogator transmits an interrogation signal to the device. The device receives the signal, then generates and transmits a responsive signal. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter circuit. Since RF signals can be transmitted over greater distances than magnetic fields, RF-based transponder devices tend to be more suitable for applications requiring tracking of a tagged device that may not be in close proximity to an interrogator. For example, RF-based transponder devices tend to be more suitable for inventory control or tracking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. Like names for circuit blocks indicate like components. Where there are a plurality of identical circuit blocks, detailed drawings are provided for one such circuit block. Some circuit schematics have been numbered in a hierarchial manner to reflect the hierarchial nature of these drawings. Notwithstanding the order in which the figures are numbered, note that some detailed drawings provide details to blocks included in more than one higher level drawing. Some circuit schematics have been broken up into many portions due to size requirements for patent drawings. 
     FIG. 1 is a high level circuit schematic showing a circuit embodying the invention. 
     FIG. 2 is a front view of an employee badge according to but one embodiment the invention. 
     FIG. 3 is a front view of a radio frequency identification tag according to another embodiment of the invention. 
     FIG. 4 is a block diagram of an electronic identification system according to the invention and including an interrogator and the tag of FIG.  3 . 
     FIG. 5 is a high level circuit schematic of a monolithic semiconductor integrated circuit utilized in the devices of FIGS. 1-4. 
     FIG. 6 is a circuit schematic illustrating a Schottky diode detector in accordance with one embodiment of the invention. 
     FIG. 7 is a cross-sectional view illustrating a step of a process of manufacturing a Schottky diode. 
     FIG. 8 is a cross-sectional view illustrating a step subsequent to the step of FIG.  7 . 
     FIG. 9 is a cross-sectional view illustrating a step subsequent to the step of FIG.  8 . 
     FIG. 10 is a cross-sectional view illustrating a step subsequent to the step of FIG. 9, and 
     FIG. 11 is an exemplary top plan view of one embodiment of the Schottky diode of FIG.  9 . 
     FIG. 12 is a top view illustrating a step subsequent to the step of FIG.  10  and showing parallel connection of some Schottky diodes of a plurality of Schottky diodes. 
     FIG. 13 is a top view illustrating a step subsequent to the step of FIG. 10 in accordance with an alternative embodiment of the invention and showing parallel connection of all Schottky diodes of a plurality of Schottky diodes. 
     FIG. 14 is a cross-sectional view illustrating a step of an alternative process of manufacturing a Schottky diode. 
     FIG. 15 is a cross-sectional view illustrating a step subsequent to the step of FIG.  14 . 
     FIG. 16 is a cross-sectional view illustrating a step subsequent to the step of FIG.  15 . 
     FIG. 17 is a cross-sectional view illustrating a step subsequent to the step of FIG.  16 . 
    
    
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a p-type substrate; defining an n-type region relative to the substrate; forming an insulator over the n-type region; removing an area of the insulator for definition of a contact hole, and removing an area encircling the contact hole; forming n+regions in the n-type regions encircling the contact hole; depositing a Schottky metal in the contact hole; and annealing the metal to form a silicide interface to the n-type region. 
     Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a substrate; defining a p-type region relative to the substrate; forming an insulator over the p-type region; removing an area of the insulator for definition of a contact hole, and removing an area encircling the contact hole; forming p+regions in the p-type regions encircling the contact hole; depositing a Schottky metal in the contact hole; and annealing the Schottky metal to form a silicide interface to the p-type region. 
     Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing a p-type substrate; defining an n-well region relative to the substrate; forming a BPSG insulator over the n-well region; etching away an area of the BPSG for definition of a contact hole, and etching an area encircling the contact hole; forming n+ regions in the n-well regions encircling the contact hole; depositing titanium in the contact hole; and annealing the titanium to form a silicide interface to the n-well region. 
     Another aspect of the invention provides a method of forming an integrated circuit including a Schottky diode, the method comprising: providing an n-type substrate; defining a p-well region relative to the substrate; forming a BPSG insulator over the p-well region; etching away an area of the BPSG for definition of a contact hole, and etching an area encircling the contact hole; forming p+ regions in the p-well regions encircling the contact hole; depositing titanium in the contact hole; and annealing the titanium to form a silicide interface to the p-well region. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
     Overview of Device 
     FIG. 1 illustrates a radio frequency data communication device  12  embodying the invention. The radio frequency data communication device  12  includes an integrated circuit  16 , a power source  18  connected to the integrated circuit  16  to supply power to the integrated circuit  16 , and at least one antenna  14  connected to the integrated circuit  16  for radio frequency transmission and reception by the integrated circuit  16 . For purposes of this disclosure, including the appended claims, the term “integrated circuit” shall be defined as a combination of interconnected circuit elements inseparably associated on or within a continuous substrate. For purposes of this disclosure, including the appended claims, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). For purposes of this disclosure, including the appended claims, the term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. In the illustrated embodiment, the integrated circuit  16  is a monolithic integrated circuit. For purposes of this disclosure, including the appended claims, the term “monolithic integrated circuit” shall be defined as an integrated circuit wherein all circuit components are manufactured into or on top of a single chip of silicon. The integrated circuit  16  will be described in greater detail below. The power source  18  is a battery or other suitable power source. 
     Housing 
     The radio frequency data communication device  12  can be included in any appropriate housing or packaging. 
     FIG. 2 shows but one example in the form of an employee identification badge  10  including the radio frequency data communication device  12 , and a card  11  made of plastic or other suitable material. In one embodiment, the radio frequency data communication device  12  is laminated to the back face of the plastic card  11 , and the card forms the visible portion of the badge. In another embodiment, the radio frequency data communication device  12  is bonded to the back face of the card by embedding it within a thin bond line of epoxy-based material. Alternatively, the radio frequency data communication device  12  is embedded into the plastic card  11 . In one embodiment, the front face of the badge  10  has visual identification features including an employee photograph as well as identifying text. 
     FIG. 3 illustrates but one alternative housing supporting the device  12 . More particularly, FIG. 3 shows a miniature housing  20  encasing the device  12  to define a tag which can be supported by an object (e.g., hung from an object, affixed to an object, etc.). The housing  20  preferably has the general shape and size, in plan view, of a postage stamp. The embodiment of FIG. 3 also includes a card  21  supporting the device  12  in the housing  20 . The card  21  is formed of plastic or other suitable material having a thickness of about 0.040 inches, a width of about 1.25 inches, and a height of about 1.25 inches. In one embodiment, the device  12  is bonded to a back face of the card  21  with a thin layer of non-conductive epoxy material that cooperates with the card to define the housing  20 . 
     Although two particular types of housings have been disclosed, the device  12  can be included in any appropriate housing. The device  12  is of a small size that lends itself to applications employing small housings, such as cards, miniature tags, etc. Larger housings can also be employed. The device  12 , housed in any appropriate housing, can be supported from or attached to an object in any desired manner; for example using double sided tape, glue, lanyards, leash, nails, staples, rivets, or any other fastener. The housing can be sewn on to an object, hung from an object, implanted in an object (hidden), etc. 
     Antenna 
     Various configurations are possible for the antenna  14 . The integrated circuit  16  includes a receiver  30  and a transmitter  32  (FIG.  5 ). In one embodiment, separate antennas  44  and  46  are provided for receiver and transmitter of the integrated circuit  16 . In another embodiment (FIG.  1 ), a single antenna is shared by the receiver and transmitter sections. In one embodiment, the antenna is defined by conductive epoxy screened onto a card or housing. In the illustrated embodiment, the antenna is conductively bonded to the integrated circuit via bonding pads. 
     In an embodiment where a single antenna is employed, that single antenna preferably comprises a folded dipole antenna defining a continuous conductive path, or loop, of microstrip. Alternatively, the antenna can be constructed as a continuous loop antenna. 
     Battery 
     If the power source  18  is a battery, the battery can take any suitable form. Preferably, the battery type will be selected depending on weight, size, and life requirements for a particular application. In one embodiment, the battery  18  is a thin profile button-type cell forming a small, thin energy cell more commonly utilized in watches and small electronic devices requiring a thin profile. A conventional button-type cell has a pair of electrodes, an anode formed by one face and a cathode formed by an opposite face. Exemplary button-type cells are disclosed in several pending U.S. patent applications including U.S. patent application Ser. No. 08/205,957, “ButtonType Battery Having Bendable Construction and Angled Button-Type Battery,” listing Mark E. Tuttle and Peter M. Blonsky as inventors, now U.S. Pat. No. 5,432,027; U.S. patent application Ser. No. 08/321,251, “Button-Type Batteries and Method of Forming Button-Type Batteries,” listing Mark E. Tuttle as inventor, now U.S. Pat. No. 5,494,495; and U.S. patent application Ser. No. 08/348,543, “Method of Forming Button-Type Batteries and a Button-Type Battery Insulating and Sealing Gasket,” listing Mark E. Tuttle as inventor, now U.S. Pat. No. 5,662,718. These patent applications and resulting patents are hereby incorporated by reference. In an alternative embodiment, the battery  18  comprises a series connected pair of button type cells. Instead of using a battery, any suitable power source can be employed. 
     Overview of Communication System 
     FIG. 4 illustrates a radio frequency communication system  24  including the device  12  and a radio frequency interrogator unit (hereinafter “interrogator”)  26 . The device  12  transmits and receives radio frequency communications to and from the interrogator  26 . Preferably, the interrogator unit  26  includes an antenna  28 , as well as dedicated transmitting and receiving circuitry, similar to that implemented on the integrated circuit  16 . The system  24  further includes a host computer  48  in communication with the interrogator  26 . The host computer  48  acts as a master in a master-slave relationship with the interrogator  26 . The host computer  48  includes an applications program for controlling the interrogator  26  and interpreting responses, and a library (“MRL”) of radio frequency identification device applications or functions. Most of the functions communicate with the interrogator  26 . These functions effect radio frequency communication between the interrogator  26  and the device  12 . These functions are described below in a section titled “Protocol.” 
     One example of an interrogator implemented in combination with a transponder unit is disclosed in U.S. Pat. No. 4,857,893, hereby incorporated by reference. Generally, the interrogator  26  includes an antenna  28 , and transmits an interrogation signal or command  27  (“forward link”) via the antenna  28 . The device  12  receives the incoming interrogation signal via its antenna  14 . Upon receiving the signal  27 , the device  12  responds by generating and transmitting a responsive signal or reply  29  (“return link”). Preferably, the responsive signal  29  is encoded with information that uniquely identifies, or labels the particular device  12  that is transmitting, so as to identify any object or person with which the device  12  is associated. 
     In the illustrated embodiment in FIG. 4, there is no communication between devices  12 . Instead, the devices  12  communicate with the interrogator  26 . FIG. 4 illustrates the device  12  as being in the housing  20  of FIG.  3 . The system  24  would operate in a similar manner if the device  12  is provided in a housing such as the housing  10  of FIG. 2, or any other appropriate housing. Multiple devices  12  can be used in the same field of an interrogator  26  (i.e., within communications range of an interrogator  26 ). Similarly, multiple interrogators  26  can be in proximity to one or more of the devices  12 . 
     Various U.S. patent applications, which are incorporated herein by reference, disclose features that are employed in various alternative embodiments of the invention: Ser. No. 08/092,147, filed Jul. 15, 1993, “Wake Up Device for a Communications System”, now abandoned, and continuation application Ser. No. 08/424,827, filed Apr. 19, 1995, “Wake Up Device for a Communications System”, now U.S. Pat. No. 5,790,946; Ser. No. 08/281,384, filed Jul. 27, 1994, “Communication System Having Transmitter Frequency Control”, now U.S. Pat. No. 5,568,512; Ser. No. 07/990,918, filed Dec. 15, 1992, now U.S. Pat. No. 5,365,551, “Data Communication Transceiver Using Identification Protocol”; Ser. No. 07/899,777, filed Jun. 17, 1992, “Radio Frequency Identification Device (RFID) and Method of Manufacture, Including an Electrical Operating System and Method,” now abandoned; Ser. No. 07/921,037, filed Jul. 24, 1992, “Anti-Theft Method for Detecting The Unauthorized Opening of Containers and Baggage,” now abandoned; Ser. No. 07/928,899, filed Aug. 12, 1992, “Electrically Powered Postage Stamp or Mailing or Shipping Label Operative with Radio Frequency (RF) Communications,” now abandoned; and Ser. No. 08/032,384, filed on Mar. 17, 1993, “Modulated Spread Spectrum in RF Identification Systems Method,” now U.S. Pat. No. 5,539,775. 
     The above described system  24  is advantageous over prior art devices that utilize magnetic field effect systems because, with the system  24 , a greater range can be achieved, and more information can be obtained (instead of just an identification number). 
     As a result, such a system  24  can be used, for example, to monitor large warehouse inventories having many unique products needing individual discrimination to determine the presence of particular items within a large lot of tagged products. The system can also be used to counteract terrorism to monitor luggage entering a plane to ensure that each item of luggage that enters the plane is owned by a passenger who actually boards the plane. Such a technique assumes that a terrorist will not board a plane that he or she is planning to bomb. The system  24  is useful whenever RF transmission over a large range is desirable, such as for inventory control. In one embodiment, the sensitivity of the devices  12  is adjustable so that only devices within a certain range of the interrogator  26  will respond. In another embodiment, the power of the interrogator  26  is adjustable so that only devices within a certain range of the interrogator  26  will respond. 
     However, a power conservation problem is posed by such implementations where batteries are used to supply power to the integrated circuits  16 . If the integrated circuit  16  operates continuously at full power, battery life will be short, and device  12  will have to be frequently replaced. If the battery  18  is permanently sealed in a housing, replacement of the battery will be difficult or impossible. For example, one reason for sealing the battery with the integrated circuit  16  and antenna  14  in a housing is to simplify the design and construction, to reduce the cost of production, and protect the electrical interconnections between devices. Another reason is protection of the battery and integrated circuit  16  from moisture and contaminants. A third reason is to enhance the cosmetic appeal of the device  12  by eliminating the need for an access port or door otherwise necessary to insert and remove the battery. When the battery is discharged, the entire badge or stamp is then discarded. It is therefore desirable in this and other applications to incorporate power conservation techniques into the integrated circuit  16  in order to extend useful life. 
     In one embodiment, the devices  12  switch between a “sleep” mode of operation, and higher power modes to conserve energy and extend battery life during periods of time where no interrogation signal  27  is received by the device  12 . These power conservation techniques are described in greater detail below. 
     In one embodiment of the invention, in order to further extend the life of the battery  18 , the receiver sensitivity of the device  12  is tuned over a range of tuned and detuned states in order to modify the ability of the device to detect signal  27 , and therefore adjust the tendency for the device to wake up. One way to adjust the receiver sensitivity is by adjusting the sensitivity, or impedance of the antenna. Another way is by controlling the gain of amplifiers included in the receiver. Another way is to adjust or switch in different circuit elements in the device  12 , thereby realizing different circuit configurations. Additionally, the transmitting sensitivity for the device  12  can be adjusted. For example, transmitting range can be adjusted by controlling interrogator continuous wave power if the transmitter is operating in backscatter mode, and by controlling output power if the transmitter is in active mode. 
     Overview of Integrated Circuit 
     FIG. 5 is a high level circuit schematic of the integrated circuit  16  utilized in the devices of FIGS. 1-4. In the embodiment shown in FIG. 5, the integrated circuit  16  is a monolithic integrated circuit. More particularly, in the illustrated embodiment, the integrated circuit  16  comprises a single die, having a size of 209×116 mils 2 , including the receiver  30 , the transmitter  32 , a micro controller or microprocessor  34 , a wake up timer and logic circuit  36 , a clock recovery and data recovery circuit  38 , and a bias voltage and current generator  42 . 
     In one embodiment, a spread spectrum processing circuit  40  is also included in the integrated circuit  16  and formed relative to the single die. In this embodiment, signals received by the receiver  30  are modulated spread spectrum signals. Spread spectrum modulation is described below. In the illustrated embodiment, the modulation scheme for replies sent by the transmitter  32  is selectable. One of the available selections for replies sent by the transmitter  32  is modulated spread spectrum. 
     CMOS Process 
     The integrated circuit  16  is formed according to semiconductor wafer processing steps, such as CMOS semiconductor wafer processing steps used to form static random access memories. In the preferred embodiment, the integrated circuit  16  is a single metal integrated circuit. In other words, the integrated circuit  16  is formed using a single metal layer processing method. More particularly, only one layer of metal (e.g., aluminum) is employed. This is advantageous in that it results in a lower cost of production. 
     In this processing method, a p-type wafer is employed. The processing method employed provides n-well areas used to define p-channel transistors; an active area which is used to define p+ and n+ diffused regions inside the p-type wafer or inside the n-well areas. Next, a layer is provided that helps prevent leakage between adjacent devices. Then, transistor are defined by forming n-type and p-type polysilicon. Then, a contact layer is defined for connecting desired intersections of polysilicon with metal (aluminum) that is subsequently formed. The contact layer is also used, in some instances, for connecting desired intersections of the metal that is subsequently formed with active area. Then the metal layer is formed. The contact layer provides a means for connecting metal with layers below the metal. Then, a passivation step is performed. Passivation means that the die is covered with a protective layer and holes are cut around the edge of the die so that electrical connection can be made to the bond pads. 
     In some processing, after the metal layer is formed, an insulating layer is provided, and another layer of aluminum is formed above the insulating layer. Holes are provided at selected locations to interconnect the top layer of aluminum with lower layers. An advantage of using multiple layers of metal is that it provides greater flexibility in how functional blocks are laid out and in how power is bused to various areas. However, multiple metal layers add processing steps. This results in added cost and complexity. 
     The process of the preferred embodiment employs only one layer of metal, and is therefore a relatively simple, inexpensive process. 
     The following U.S. patents, which are incorporated herein by reference, disclose CMOS processing techniques that are employed in various alternative embodiments of the invention: U.S. Pat. No. 5,489,546 to Ahmad et al.; U.S. Pat. No. 5,272,367 to Dennison et al.; and U.S. Pat. No. 5,134,085 to Gilgen et al. 
     Various other processing methods can be employed in alternative embodiments. 
     Transmitter and Receiver 
     The receiver  30  is a radio frequency receiver included in the integrated circuit  16 , and the transmitter  32  is a radio frequency transmitter included in the integrated circuit  16 . In one embodiment, the receiver  30  includes a Schottky diode detector. Various forms of Schottky diode detectors are described in a paper titled “Designing Detectors for RF/ID Tags,” by Raymond W. Waugh of Hewlett-Packard Company, submitted for presentation at the RF Expo, San Diego, Feb. 1, 1995, and incorporated herein by reference. 
     The receiver  30  of the illustrated embodiment makes use of the rate or frequency of data included in incoming signals, but does not make use of the carrier frequency of the incoming signal. In other words, operation of the receiver  30  is independent of the frequency of the carrier of the incoming signal over a wide range of carrier frequencies. 
     Therefore, the device  12  can operate over a wide range of carrier frequencies. For example, the device  12  can operate with carriers of 915-5800 MHZ. In a more particular embodiment, the device  12  can operate with carrier frequencies in the 915, 2450, or 5800 MHZ bands. In the illustrated embodiment, the antennas are half wave antennas, and frequency selectivity of the device  12  is achieved based on selection of the antenna external to the integrated circuit  16 . Capacitors employed in the Schottky diode detector are also selected based on the carrier frequency that will be employed. 
     Schottky Diode RFID Detector 
     Overview 
     For purposes of realizing a cost effective and low power radio frequency receiver on an RFID tag, a simple Schottky diode receiver is utilized. The receiver is formed from a Schottky diode detector, an amplifier, and the receiving antenna[“rxantenna”]. With the implementation of a single integrated circuit  16  RFID tag, an easy and low cost technique for configuring the frequency of operation on a tag is needed. Receiver frequency characteristics can be tailored by selecting an appropriately sized antenna to be coupled to the integrated circuit  16  that supports the Schottky diode detector. Furthermore, adjustment of bias current across the Schottky diode can be used to realize a desired resistance there across, enabling tuning or detuning of the receiver. 
     For purposes of enabling simplified representation, FIG. 6 illustrates a simplified circuit schematic for one embodiment of a receiver  80  having a Schottky diode detector  84  and antenna  44 . 
     The detector  84  includes a Schottky diode  86  having an anode connected to the antenna  44  and having a cathode. 
     The exemplary antenna  44  is formed from a loop or folded dipole construction. The antenna  44  performs band pass filtering. 
     The detector  84  further includes an ideal current source  88  connected to the cathode of the Schottky diode  86  and driving current through the antenna and Schottky diode  86  in the direction from the anode to the cathode. The current source  88  is an ideal current source, and is configured to forward bias the Schottky diode  86 , realizing a desired resistance (or impedance) in the process. 
     The detector  84  further includes a capacitor  90  connected between the cathode of the Schottky diode  86  and ground. The capacitor  90  provides a radio frequency short to ground so that all radio frequency voltage appears across the Schottky diode  86 . This maximizes a base band signal produced by the Schottky diode  86 . 
     The detector  84  further includes a capacitor  92  having a first terminal connected to the cathode and having a second terminal defining an output of the detector  84 . The capacitor  92  provides an AC short to video frequency, and defines the output of the detector  84 . The capacitor  92  allows different bias levels in the detector and at the input of a video amplifier connected to the output of the detector  84 . 
     Integrated Circuit Implementation 
     A Schottky diode detector is configured within a receiver to receive radio frequency signals via a receiving antenna. In operation, the Schottky diode detector and the receiving antenna cooperate to form a tunable receiving circuit. Signals detected by the Schottky diode detector are input to a five stage amplifier, then a comparator, for further signal conditioning. The output of the comparator is a digital representation of the received baseband signal. 
     Each Schottky diode is formed from an array of Schottky diodes. In order to use standard contact hole sizes, each Schottky diode is formed from an array of Schottky diodes connected together in parallel to act as a single Schottky diode. 
     Details of Method of Forming an IC Schottky Structure 
     A method of forming a Schottky structure that can be employed to manufacture the Schottky diode detector will now be described. A Schottky diode is a diode in which a metal and a semiconductor form a pn junction. Electrons injected into the metal have a higher energy level than the charge carriers in a semiconductor, and energy storage at the junction is low because current flow is not accompanied by hole movement. 
     One embodiment of the invention comprises a Schottky diode  220  including an n+ region  222  generally encircling or surrounding an n-well region  224  (FIG.  11 ). In the illustrated embodiment, the n+ region  222  is heavily doped; e.g., 1×10 18  atoms/cm 3  or greater of n-type material, and the n-well region  224  is lightly doped; e.g., 1×10 17  atoms/cm 3  or lower of n-type material. The n-well region  224  defines a contact area  226 , and the n+ region  222  provides a low resistance interconnect to the Schottky diode  220 . The n+ region  222  has a diffused edge  228 , and the n-well region has a contact edge  230 . The distance from the n+ region diffused edge  228  to the n-well region contact edge  230  is minimized. In one embodiment, the distance from the n+ region diffused edge  228  to the n-well region contact edge  230  is less than twenty micrometers. In a more preferred embodiment, the distance from the n+ region diffused edge  228  to the n-well region contact edge  230  is about two micrometers. More particularly, the integrated circuit  16  includes a grid pattern of n+ regions  222 . Each region  222  generally encircles or surrounds isolated n-well regions  224  of a large common n-well region  232  under the n+ regions  222  (FIGS.  11  and  12 ). This provides for parallel connection of a selectable number of Schottky diodes  220 . As described elsewhere, the parallel connection of Schottky diodes  220  acts a single Schottky diode, and allows use of standard sized contact holes. The number of Schottky diodes  220  connected together is selectable to tailor resistance, parasitic capacitance, and electrostatic discharge sensitivity for a specific application. 
     To form the grid of Schottky diodes  220 , the following process steps are performed. 
     First, a p-substrate  234  is provided (FIG.  7 ). Next, n-well region  232  is defined relative the substrate  234 . Next, an insulator  236  is formed over the n-well region. In one embodiment, the insulator  236  is borophosphosilicate glass (BPSG). 
     Next, a removal or etching step is performed to remove areas of the insulator  236  for definition of contact holes  238 , and areas  240  generally encircling or surrounding the contact holes  238  (FIG.  8 ). The contact holes  238  are not necessarily circular in cross-section; any cross-sectional shape is possible. Similarly, any cross-sectional shape is possible for the areas  240  surrounding the contact holes  238 . In a preferred embodiment, the contact holes  238  all have the same diameter (or peripheral extent) to facilitate subsequent filling of the contact holes  238  (described below in greater detail). In an alternative embodiment, different contact holes  238  have different sizes. In the process of the illustrated embodiment, the contact holes  238  do not need to be completely filled with a conductor, and all contact holes therefore do not need to be the same size. 
     In the illustrated embodiment, the n+ regions  222  are formed in the n-well region  232  by diffusion after the etching has been performed, via the openings  240  surrounding the contact holes  238 . The n+ regions  222  can be formed by other processes or in other sequences. For example, the n+ regions  222  can be formed before the insulator  236  is formed over the n-well region  232 . 
     Next, a Schottky forming metal  242  such as titanium is formed in the contact hole openings. In the illustrated embodiment, the Schottky forming metal is deposited on the surface of n-well regions  224  via the contact hole openings  238 . In one embodiment, the thickness of the deposited metal is about 200 Å. The metal is annealed to form a stable silicide interface to the n-well silicon. 
     If it is desired to fill the contact holes, a material such as tungsten  246  may be deposited into the contact holes (FIG.  9 ). The tungsten is then planarized to form final contact structures (FIG.  10 ). 
     Then, an interconnect metallization step is performed (FIG.  12 ). For example, copper doped aluminum  248  is deposited (e.g. sputtered) over the wafer, then the wafer is masked and etched to remove unwanted areas. The mask defines a pattern to interconnect the contacts as desired. 
     A variable number of Schottky diodes may be connected in parallel by simply changing the metal masks and interconnecting only the number of Schottky diodes required by a particular circuit application. In one illustrated embodiment, an array of twelve by twelve Schottky diodes ( 144  total Schottky diodes) is provided (FIG.  13 ). In another embodiment (FIG.  12 ), less than all available Schottky diodes are connected together. In one embodiment, only a six by six array ( 36  Schottky diodes) is connected together in parallel. 
     In one alternative embodiment, aluminum is employed instead of tungsten and silicide. In another alternative embodiment, tungsten is employed instead of aluminum to interconnect contacts, and the step of forming tungsten plugs is omitted. 
     In an alternative embodiment (FIG.  17 ), each Schottky diode includes a p+ region  252  encircling a “p-” p-well region  254  and is formed by a method substantially identical to the method described above except with p-type material substituted for n-type material and vice versa. More particularly, in this alternative embodiment, the following steps are performed. 
     First, an n-type substrate  256  is provided (FIG.  14 . Next, a common p-well region  258  is defined relative the substrate  256 . The common p-well region  258  defines the p-well regions  254  for each of the Schottky diodes. Next, an insulator  260  such as borophosphosilicate glass (BPSG) is formed over the p-well region  258 . Next, an etching step is performed to etch away regions of the insulator for definition of contact holes, and areas  264  generally encircling or surrounding the contact holes (FIG.  15 ). In a preferred embodiment, the contact holes  262  all have the same diameter (or peripheral extent) to facilitate subsequent filling of the contact holes  262  with Tungsten or another conductor. In an alternative embodiment, different contact holes  262  have d different diameters. In the process of the illustrated embodiment, the contact holes do not need to be completely filled, and all contact holes therefore do not need to be the same size. 
     In the illustrated embodiment, the p+ regions  252  are formed in the p-well regions by diffusion after the etching has been performed, via the openings  264  encircling the contact holes. The p+ regions  252  can be formed by other processes or at other times. For example, the p+ regions  252  can be formed before the insulator is formed over the p-well regio n  258 . 
     Next, a Schottky forming metal  266  such as Titanium is formed in the contact hole openings  262 . In the illustrated embodiment, the Schottky forming metal  266  is deposited on the surface of the p-well region  258  via the contact hole openings  262 . In one embodiment, the thickness of the deposited metal is about 200 Å. The metal  266  is annealed to form a stable silicide interface  268  to the p-well region  258 . 
     If it is desired to fill the contact holes  262 , a metal such as tungsten  270  is deposited into the contact holes (FIG.  16 ). The tungsten  270  is then planarized to form final contact structures. 
     Then, an interconnect metallization step is performed (FIG.  17 ). For example, copper doped aluminum  272  is deposited (e.g. sputtered) over the wafer, then the wafer is masked and etched to remove unwanted areas. The mask defines a pattern to interconnect the contacts as desired. 
     The above described processes for forming a Schottky diode are preferred d over a process wherein, after the contact holes a etched, ion implantation of phosphorus into the holes is performed. In such a process, the implant would be a two step process, with a low energy implant (e.g., 35 keV of 4×10 12  ions/cm 2)  followed by a high energy implant (e.g., 120 keV of 4×10 12  ions/cm 2 ). Such implants cause a high doping level at the bottom of the contact hole, which prevents formation of a low leakage Schottky diode. The preferred processes described above eliminates these two contact implants, and allows for formation of a good quality Schottky diode. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.