Patent Publication Number: US-2011074341-A1

Title: Non-contact interface system

Description:
BACKGROUND OF INVENTION 
     Sensor wafers are used to obtain non-invasive, in-situ measurements of actual physical and electrical properties of plasma within an operational plasma processing environment. These sensor wafers are configured to collect, process, and store data received during measurement of the plasma. These sensor wafers may include devices to measure thermal, optical, and electromagnetic properties of the process environment. During the measurement process, these sensor wafers may be exposed to harsh conditions such as excessive heat, corrosive chemicals, and bombardment by high energy ions, and high levels of electromagnetic and other radiative noise. It is important for the sensor wafer to remain resilient in the harsh environment associated with in-situ measurement of plasma. 
     Sensor wafers are currently housed and stored in a front operating universal pod (FOUP) during the in-situ process survey. A FOUP is a specialized plastic enclosure designed to hold wafers securely and safely in a controlled environment, and configured to allow the wafers to be removed for processing or measurement by tools equipped with appropriate load ports and robotic handling systems. A FOUP may be used to communicate with a sensing wafer and recharge the sensing wafer&#39;s batteries during the process survey. Existing communication between a FOUP and sensor wafer is based on operation with a pair of coupled inductors. These coupled inductors are equivalent to an air-core transformer. The physical implementation of these inductors is accomplished by having one coil, the secondary, embedded in the sensor wafer and a second coil, the primary, on a substrate in close proximity. The coupling coefficient, k, is heavily reduced as the distance between the primary and secondary coils grows. Hence, the induced current in the secondary coil and the back reflected impedance of the secondary coil rapidly decrease as a function of distance. In order to obtain an optimal transfer of power and data between the primary and secondary coils, the primary coil must be in close proximity with the secondary coil in the sensor wafer. 
     The forward power transfer between the primary coil and the secondary coil provides power for the re-charging of the sensor wafer batteries. On-Off-Key (OOK) modulation is used to encode the carrier frequency (RF) from the primary coil to the secondary coil with a data stream that can be detected by the sensor wafer as a command. Communication from the wafer/secondary coil to the FOUP/primary coil may be accomplished by altering the load (e.g., impedance) of the secondary coil such that reflection from the secondary coil to the primary coil may be detected by the FOUP as an AM modulated bit stream. 
     The current trend amongst wafer sensors and FOUPs is to scale down the size of primary and secondary coils, thus reducing the resistance associated with the size of the coil. However, the close proximity between the primary coil and the sensor wafer necessitated by reduced coil diameter, as well as the moving parts and exposed electronics within the enclosed FOUP all contribute to particle generation. Particle generation affects the accuracy of the survey process and creates a barrier for entry into particle sensitive applications. 
     It is within this context that embodiments of the present invention arise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a top view schematic diagram illustrating the structure of a sensor wafer that may be used in conjunction with embodiments of the present invention 
         FIG. 1B  is a cross-sectional view schematic diagram illustrating the structure of the sensor wafer of  FIG. 1A . 
         FIG. 1C  is a bottom view schematic diagram illustrating the structure of the sensor wafer of  FIGS. 1A-1B . 
         FIG. 2A  is cross-sectional schematic diagram of an interface system for measuring process parameters according to an embodiment of the present invention. 
         FIG. 2B  is a three-dimensional view schematic diagram of an interface system for measuring process parameters according to an embodiment of the present invention. 
         FIG. 2C  is a side cross-sectional schematic diagram of an alternative interface system for measuring process parameters according to an embodiment of the present invention 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     Embodiments of the present invention overcome the disadvantages associated with the prior art by increasing the diameters of the primary and secondary coils used to charge and/or communicate with a sensor wafer. As a result of the increased coil size, a large inter-coil spacing may be used. 
       FIGS. 1A-1C  illustrate an example of a sensor wafer  100  configured to measure process parameters in a system for processing wafers during semiconductor fabrication. The sensor wafer  100  may include a substrate  101 , with an energy storage device  103  and measurement electronics  105  mounted to the substrate  101 . By way of example, and not by way of limitation, the measurement electronics  105  of the sensor wafer  100  may be implemented with a processor module  107 , a main memory  109 , a transceiver  111 , and one or more sensors  113 ,  115 ,  117 . The substrate  101  may have the same dimensions as a production substrate that is processed by a semiconductor device fabrication system, e.g., 150 mm, 200 mm, or 300 mm. 
     The energy storage device  103  preferably supplies electrical energy at an operating voltage, current handling and has an energy storage capacity that is sufficient to power the electronics  105  on the sensor wafer  100  over a period of time for which the sensor wafer is expected to operate. Furthermore, it is often desirable for the energy storage device  103  thin enough to fit within a recess in the substrate  101  and have a sufficiently small footprint to allow room for the measurement electronics, memory, transceiver and sensors. It is further desirable for the energy storage device  103  to be made of materials suitable for use in the environment of a semiconductor wafer processing tool in which the sensor wafer  100  is to be used. By way of example, and not by way of limitation, the energy storage device  103  may be a rechargeable battery, such as a lithium ion battery. Other suppliers of suitable batteries include Front Edge Technology, Inc. of Baldwin Park, Calif., Infinite Power Solutions of Littleton, Colorado and Cymbet Corporation of Elk River, Minn. One example of a Lithium ion battery is a 4.2 LiPON solid state lithium ion battery from Infinite Power Solutions of Littleton, Colo. The energy storage device  103  may be supplemented with an energy harvesting device, again by way of example, and not by way of limitation, a thermopile generator or photovoltaic cell. 
     The processor module  107  may be configured to execute instructions stored in the main memory  109  in order for the sensor wafer  100  to properly measure process parameters. The main memory  109  may be in the form of an integrated circuit, e.g., RAM, DRAM, ROM and the like. The transceiver  111  allows the sensor wafer  100  to communicate data stored in the memory  109  to an external processing system or to receive data from an external system for storage in the memory  109  or processing by the processor module  107 . The energy storage device  103  provides power for operating the measurement electronics  105  and sensors  113 ,  115 ,  117 . The sensors may include an electromagnetic sensor  113  to measure electromagnetic properties of a given plasma, a thermal sensor  115  to measure thermal properties of a given plasma, and an optical sensor  117  to measure optical properties of a given plasma. 
     As seen in  FIG. 1B  and  FIG. 1C  a secondary inductive coil  121  may be mounted to a bottom of the substrate  101 . The secondary coil includes a plurality of spiral windings of electrically conductive (e.g., copper) wire that are electrically insulated from each other to prevent shorting. The secondary inductive coil  121  may communicate through induction with another primary inductive coil connected to a charging station on a substrate carrier such as a front opening universal pod (FOUP). For convenience, the secondary inductive coil  121  coupled to the sensor wafer  100  will be referred to as the wafer coil  121  and the primary inductive coil coupled to the FOUP will be referred to as the FOUP coil. 
     Existing sensor wafers have been configured such that the wafer coil  121  is scaled down in size to reduce the resistance associated with the coil. In such a configuration, obtaining optimal signal strength to facilitate communication between the FOUP coil and the wafer coil  121  often results in the FOUP coil coming into contact with the sensor wafer  100 . This can introduce particle contamination into the measurement process, which may result in inaccuracies in the result. The wafer coil  121  generally includes one or more conductive (e.g., copper) windings in the form of a flat spiral coil having an inner diameter D 1  and an outer diameter D. In order to overcome particle contamination, the wafer coil  121  according to an embodiment of the present invention may be configured to have a much larger outer diameter D (e.g., at least 50 mm) in order to allow for a greater distance between the FOUP coil and the wafer coil  121  during communication and power transfer. This greatly reduces the particle contamination involved with the measurement process and allows for the sensor wafer to be more widely used with particle sensitive applications. In order to assist with the non-contact transfer of information, the wafer coil  121  may include a transformer core so that the wafer coil  121  may be kept at a larger distance from the FOUP coil during power transfer and communication. In  FIGS. 1B and 2A , (x) represents a coil coming out of the page, and ( . ) represents a coil going into the page. To facilitate inductive coupling, the wafer coil  121  may be wound around an optional ferrite core.  119   
     The FOUP coil may transfer power to the wafer coil  121  through induction, and may also transmit data to the wafer coil  121  through modulation of a carrier frequency. The wafer coil  121  is coupled to both the energy storage device  103  and the measurement electronics  105 . The power transferred from the FOUP coil to the wafer coil  121  is further transferred to the energy storage device  103  so that the sensor wafer  100  as a whole may be charged. 
     By way of example, and not by way of limitation, the wafer coil  121  may have an outside diameter between about 50 mm and the diameter of the substrate  101 . By way of example, the outside diameter may be about 50 mm when the wafer coil  121  is operated at a distance of about 11 mm from the FOUP coil. The wafer coil  121  may be formed as a thin film circuit directly on the substrate  101 . Alternatively, the wafer coil  121  may be a sub-assembly attached within a cavity or depression in the surface of the substrate  101  to maintain a low profile. The wafer coil  121  may have the same number of turns as the FOUP coil. By way of example, the wafer coil  121  may have about 5 to 20 turns. 
       FIG. 2A-2B  illustrate a cross-sectional diagram and a perspective view of an interface system for exchanging power and/or data with a sensor wafer of the type shown in  FIGS. 1A-1C . The system includes a wafer carrier, such as a FOUP  201  that has a plurality of slots  203  configured such that a sensor wafer  100  or a similarly sized and shaped semiconductor wafer  205  may rest comfortably in a slot  203 . An example of a commercially-available FOUP is a type A300 FOUP available from Entegris, Inc. of Chaska, Minnesota. In the example shown in  FIG. 1A , the sensor wafer  100  rests in the second to last slot of the FOUP  201  and another semiconductor wafer  205  rests in separate slot  203  above the sensor wafer  100 . The sensor wafer  100  is configured to exchange data and receive power via a FOUP coil  215  that is mounted in an adjacent FOUP slot  203 . 
     By way of example, the FOUP coil  215  includes one or more turns of electrically conductive (e.g., copper) wire that wind around a hat shaped ferrite core  213 . In the example depicted in  FIG. 2A , the FOUP coil  215  is situated on a disk-shaped support  211  installed in a slot next to the sensing wafer slot. The disk  211  may be made from a material that is compatible with a semiconductor processing environment, such as acrylic. The FOUP coil  215  may similarly be situated on a cantilevered strip  226  made of a high modulus material that extends from the back wall  227  of the FOUP  201  as shown in  FIG. 2B . The FOUP coil  215  may transfer power to the wafer coil  121  through induction, and may also transmit data to the wafer coil  121  through the modulation of a carrier frequency. The wafer coil  121  is coupled to the sensor wafer&#39;s energy storage device  103  and measurement electronics  105 , and may further transmit power and data from the FOUP coil  215  to the sensor wafer&#39;s energy storage device and measurement electronics respectively. Likewise, the wafer coil  121  may communicate with the FOUP coil  215  by altering its load such that data is transmitted during reflection from the wafer coil  121  to the FOUP coil  215 . The FOUP coil  215  may include N′ of turns of wire wound around an optional ferrite core  213 . The FOUP coil  215  may have an outer diameter D′ equal to the diameter D of the wafer coil  121 . The diameter and number of windings in the FOUP coil  215  are preferably the same as the diameter and number of windings of the wafer coil  121 . 
     The FOUP coil  215  may be coupled to an electronics module  216 , referred to herein as FOUP electronics. The FOUP electronics  216  may provide power to the FOUP coil  215  for charging the energy storage device  103  on the sensor wafer  100 . In addition, the FOUP electronics  216  may include processor logic and/or a memory and transceiver to facilitate exchange of data between the FOUP electronics  216  and the electronics module  105  on the sensor wafer  100 . 
     The FOUP coil  215  is preferably situated and oriented in the FOUP such that it is concentric with the wafer coil  121  when the sensor wafer  100  is positioned in a slot  203  on the FOUP  201 . To determine the distance d between the wafer coil  121  and the FOUP coil  215  necessary to facilitate optimal data and power transmission, a ratio between the wafer coil diameter and the distance d may be determined experimentally. In the example shown, by increasing the diameter of the wafer coil  121  to a diameter greater than 50 mm, the distance d between the wafer coil  121  and the FOUP coil  215  may be increased to 20 mm or greater. Preferably, however, wafer coil  121  is at least 8 mm, e.g., between 8 mm and 12 mm, from the FOUP coil  215  when the sensor wafer  100  is in its slot  203  in the FOUP  201 . Generally, the frequency of the voltage signal applied to the FOUP coil  215  is in the range of 1 to 3 Megahertz and the amplitude of the signal is sufficient to supply an RMS current of about 100 to 200 milliamps to the FOUP coil. 
     It was initially believed, even by the inventors themselves, that such a spacing was simply too large and the coil resistance too great to allow for effective inductive coupling between the FOUP coil  215  and the wafer coil  121 . However, a system having a wafer coil and FOUP coil with the following dimensions was found to work effectively. 
     As proof of concept, a FOUP coil and wafer coil were built. Each coil had an outside diameter of 50 mm and included 10 turns. The coils were separated from each other by a distance of about 11 mm. The FOUP coil was operated as a series LC (tuned trap) circuit at a frequency of about 2 MHz. 
     In an alternative embodiment illustrated in  FIG. 2B , However, when the FOUP coil  215  is situated on the cantilevered strip of high modulus material extending from the back wall  227  of the FOUP  201 , as described above, the distance between the wafer coil and the FOUP coil is reduced because the cantilevered high modulus strip needs to be in closer proximity to the sensor wafer  100  in order to optimally transmit data and transfer power. Creating distance between the FOUP coil  215  and the sensor wafer  100  eliminates the particle contamination introduced when the FOUP coil  215  is in contact with the sensor wafer  100 . 
     This interface system may optionally have an optical detector  223  and a network interface  225 . The network interface  225  is configured to allow for bi-directional communication between the FOUP electronics  216  and any computers within a network. In the example shown, the optical detector  223  is configured to detect the presence of a sensor wafer  100  through the side of the FOUP  201 . An optical beam  219  initially passes from a source  217  through the transparent sidewall of the FOUP  201 . The optical light guides  221 ,  221 ′ may be index matched with the wall of the FOUP  201  such that no reflection or refraction of the optical beam  219  occurs at the interface between the light guides  221 ,  221 ′ and the side wall of the FOUP  201 . Optical coupling through the wall of the FOUP  201  avoids having to drill a hole through the wall. The optical beam  219  then travels via a first transparent light guide  221  and is reflected at a beveled end of the light guide  221  through a short gap to a second light guide  221 ′, which is oriented in a mirror image configuration with respect to the first light guide  221 . The second light guide  221 ′ guides the optical beam  219  back towards the wall of the FOUP  201  and into a detector  223 , which may be coupled to the FOUP electronics  216 . When a sensor wafer  100  is situated in the beam path, the wafer interrupts the optical beam  219  and a signal produced by the detector  223  changes as a result. The signal from the detector  223  may be coupled to the FOUP electronics  216  so that the FOUP electronics  216  are notified of the presence of the wafer. It is important to note that the optical source  217 , optical detector  223 , light guides  221 ,  221 ′ and optical beam  219  may be configured to detect the presence of a sensor wafer through the transparent back wall  227  of a FOUP  201  rather than the transparent sidewall. 
     By way of example, the FOUP coil  215  may be formed on a printed circuit board (PCB) in a single layer of spiral turns with an outer diameter of about 50 mm. The wafer coil may have a dual layer of spiral turns with an outer diameter of about 50 mm formed on a backside of the substrate  101 . One or more of the light guides  221  for the wafer presence detector may also be implemented in the PCB. In some embodiments a tertiary coil may be formed on the support  211  on a side opposite the secondary coil and used in conjunction with the primary coil. This forms a multiple tuned transformer coupling. 
       FIG. 2C  illustrates an embodiment in which the FOUP electronics may be located entirely outside the FOUP  201  and penetration of the FOUP wall may be avoided. In this example, the FOUP electronics are coupled to a primary induction coil  227  mounted to a wall of the FOUP  201 . In the example illustrated, the primary induction coil  227  is mounted to a back wall of the FOUP. A secondary induction coil  228  is located inside the FOUP  201  proximate the primary induction coil  227  on the opposite side of the wall. The wall is preferably made of a material that is sufficiently electromagnetically transparent that the primary and secondary coils  227 ,  228  may be inductively coupled to each other. The secondary induction coil  227  is electrically coupled to the FOUP coil  215 , which is mounted to the cantilevered strip  226  in this example. Electrical power and/or control signals from the FOUP electronics  216  may be transferred to the FOUP coil  215 , via inductive coupling between the primary and secondary induction coils  227 , 228 . Data may be transferred from the sensor wafer  100  via the wafer coil  121 , FOUP coil  215  and induction coils  227 ,  228 . Use of inductive coupling as shown in  FIG. 2C  allows the FOUP electronics  216  to be located outside the FOUP  201  without having to pierce the wall of the FOUP  201  in order to couple the FOUP electronics to the FOUP coil  215 . The primary and secondary inductive coils may be mounted to the inside and outside of the wall of the FOUP in a non-penetrating manner, e.g., with suitable adhesives. 
     While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A”, or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”