Patent Publication Number: US-2007113652-A1

Title: Wireless Position Sensing Wafer

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This non-provisional application claims the benefit of provisional application no. 60/724,712, filed Oct. 7, 2005, which application is incorporated herein in its entirety by this reference. 
    
    
     BACKGROUND  
      This application relates to devices for measuring process conditions. In particular, this application relates to devices that can determine location within a process environment.  
      In various industries, substrates are processed by automated equipment that moves the substrates from one location to another with little or no human intervention. In order to setup and maintain such equipment, it is desirable to track the movement of an individual substrate to determine its precise path and to learn what mechanical experiences it undergoes. For example, it may be desirable to know if any mechanical shock or vibration is experienced. It may also be desirable to know the orientation of the substrate as it progresses along its path. Examples of substrates that are processed by automated equipment include semiconductor wafers and flat panel display substrates. Determining the exact position of a substrate or measuring mechanical variables experienced by the substrate may be difficult because of the environment in which the substrate is handled. For example, the substrate may be enclosed in a chamber having chamber walls that prevent easy access for measuring. The chamber may have a controlled environment, for example it may be under vacuum, under pressure or at a controlled (high or low) temperature, making access difficult without disturbing the environment.  
     SUMMARY  
      In one example, a wireless position sensing wafer includes at least one accelerometer that measures acceleration in one direction. Displacement along the direction from a starting point can be derived from readings from the accelerometer. Using two or three such accelerometers, displacement in two or three dimensions may be obtained. Accelerometers may also provide information regarding vibration or shock.  
      A wireless position sensing wafer may include one or more gyroscopes to determine orientation. Using three such gyroscopes, tilt and yaw of a wafer may be measured. Where a wireless position sensing wafer includes both accelerometers and gyroscopes, both position and orientation may be determined at any time.  
      In one embodiment, an external magnetic field is provided so that orientation of a wafer may be determined with respect to the field by a magnetic sensor. Two or more fields may be provided with different orientations. Time-varying magnetic fields may be used so that different fields are distinguishable.  
      In another embodiment, a position sensing wafer uses triangulation to establish its position with respect to transmitters having fixed locations.  
      A position sensing wafer may be considered a Process Condition Measuring Device (PCMD) and may include additional sensors to measure process conditions including: temperature, pressure and gas flow rates. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a position sensing wafer including position sensing circuits according to an embodiment of the present invention.  
       FIG. 2  shows a semiconductor processing tool from above.  
       FIG. 3  shows the semiconductor processing tool of  FIG. 2  from one side.  
       FIG. 4  shows position sensing circuits of  FIG. 1  in more detail.  
       FIG. 5  shows alternative positioning sensing circuits.  
       FIG. 6  shows a sensing wafer in an artificially generated magnetic field.  
       FIG. 7  shows a position sensing wafer that determines position from fixed transmitters. 
    
    
     DETAILED DESCRIPTION  
      A Process Condition Measuring Device (PCMD) that is similar in size and shape to a substrate, and that measures environmental variables experienced by the PCMD as it is handled by automated equipment is described in US Patent Application Publication No. 20040225462, entitled “Integrated Process Condition Sensing Wafer and Data Analysis System,” which patent application is hereby incorporated by reference in its entirety for all purposes. Circuitry on a PCMD may allow collected data from one or more sensors to be stored on the PCMD, or to be transmitted from the PCMD to another location.  
       FIG. 1  shows a position sensing wafer  101 . In this example, position sensing wafer  101  is similar in size and shape to a silicon wafer used to manufacture integrated circuits (e.g. 300 mm diameter). In other examples, other substrates may be used including different sized wafers and other substrates. Position sensing wafer  101  includes a power source  103 , position sensing circuits  105  and data storage and/or transmission circuits  107 . Position sensing wafer  101  may be formed in a similar manner and may contain many of the same components as a PCMD as described in US Patent Application Publication No. 20040225462.  
      Power source  103  may be any suitable source of electrical power to run electronic circuits. Power source  103  may be a battery that is rechargeable or replaceable. In some examples, RF induction circuits are provided so that power can be transmitted wirelessly to a power source to enable wireless recharging of a battery. Alternatively, probes may be used to form electrical connections to pads on a position sensing wafer to supply electrical current to recharge a battery.  
      Position sensing circuits  105  may be any circuits that allow a determination of position to be made. In many cases, this means that the position is determined in three dimensions. However, in some cases, position in one or more dimension is known or unnecessary so that position in only one or two dimensions is needed. Position may be established from some starting point or with respect to some frame of reference that does not require a particular starting point. In some cases, a frame of reference is established by additional apparatus provided for that purpose. Various position sensing circuits are described further below. Positional data from position sensing circuits  105  is sent to data storage and/or transmission circuits  107 . This data may be sent periodically or according to some algorithm that varies the sampling frequency. In addition to positional information, some sensing circuits provide data regarding the orientation of a position sensing wafer. Thus, the tilt and yaw of a position sensing wafer may be measured by position sensing wafer. Tilt occurs when the plane of the wafer is rotated from a horizontal plane, e.g. rotated about the X-axis or Y-axis. Yaw is a condition where the wafer is rotated about a vertical axis, i.e. rotated in a horizontal plane. In addition, position sensing circuits  105  may measure vibration and shock and provide data regarding these parameters.  
      Data storage and/or transmission circuits  107  receive position, orientation or other data from position sensing circuits  105 . Circuits  107  then store this data for later retrieval in some cases, for example in a non-volatile memory. In other examples, circuits  107  transmit data to a remote location as the data are received. Transmission may be wireless in some examples, though wires may also be used in some examples. Data may also be stored for some time before the data are transmitted. At the remote location where the data are retrieved or received, the data may be used to make determinations regarding the equipment.  
       FIG. 2  shows cut-away view of a semiconductor processing tool  260  from above. A robot  261  is located in processing tool  260 . Robot  261  has arms  262  that extend a blade  263  that is used to pick up a wafer  264  from a cassette  265 . After wafer  264  is picked up from cassette  265  it is moved to processing chamber  269  where it undergoes a process such as deposition of a material or etching. The view in  FIG. 2  shows the tool from above, i.e. extending in a horizontal plane shown by the X-axis and Y-axis indicators.  
       FIG. 3  shows a cut-away view of semiconductor processing tool  260  from one side. The Y-axis and Z-axis are indicated accordingly. Clearly, a wafer in semiconductor processing tool  260  moves along the X and Y-axis as it is transferred from cassette  265  to processing chamber  269 . In addition, a wafer may move along the Z-axis as it is moved, for example when being lifted out of cassette  265  or being “dropped” in processing chamber  269 . During initial calibration, it is useful to gather data on the path of a wafer moving through a tool such as semiconductor processing tool  260  so that robot  261  may be calibrated. Other mechanical components may also be calibrated in this way including any mechanism for moving wafers while in cassette  265  or in processing chamber  269 . In addition, it may be useful to gather data on the movement of a wafer for troubleshooting purposes after installation. For example, delays at various points along a wafers path may cause temperature changes. Variation in handling from one wafer to another may cause variation in the devices obtained which may lead to yield loss.  
       FIG. 4  shows a first example of position sensing circuits  410  that may be used as position sensing circuits  105  in position sensing wafer  101 . Position sensing circuits  410  include a processor  412  connected to sensors  414 ,  416 ,  418 . Sensors  414 ,  416 ,  418  provide data regarding parameters such as position, orientation, and acceleration. Sensors  414 ,  416 ,  418  may be formed by Micro-Electro-Mechanical-Systems (MEMS) technology. Such MEMS sensors are widely used, for example in the automobile industry. MEMS sensors include accelerometers and gyroscopes.  
      In one example, sensor  414  is an accelerometer aligned to measure acceleration along the X-axis, sensor  416  is an accelerometer aligned to measure acceleration along the Y-axis and sensor  418  is an accelerometer aligned to measure acceleration along the Z-axis. Sensors  414 ,  416 ,  418  send acceleration data to processor  412  where it is used to calculate displacement from a starting point. The starting point is generally some point where position is precisely established. The wafer is placed at the starting point and sensing by sensors  414 ,  416 ,  418  begins with the wafer at rest so that both velocity and acceleration are at zero. Any acceleration (change in velocity) is measured so that the velocity can be derived at any time. Because velocity is known at any time, displacement from the starting point can also be derived by processor  412 . Thus, sensors  414 ,  416 ,  418  allow the displacement of a substrate from a starting point to be determined as it is moved along its path. In some cases, one or two sensors could be used to determine displacement in one or two dimensions in a similar manner. In addition to measuring acceleration, sensors  414 ,  416 ,  418  or other additional sensors may sense vibration or shock. Data from sensors  414 ,  416 ,  418  may be processed and used to derive data that is sent to output  420 . Alternatively, raw data from sensors  414 ,  416 ,  418  may be sent directly to output  420 . Output  420  connects to data storage and/or transmission circuits.  
      In another example, sensors  414 ,  416 ,  418  are gyroscopes that measure angular change. Thus, sensors  414 ,  416 ,  418  may give data regarding the orientation of the wafer about three axes (both tilt and yaw). In some examples, such gyroscopes are combined with other sensors, such as accelerometers or other sensors to provide additional data. Examples of both MEMS accelerometers and gyroscopes that may be used as sensors  414 ,  416 ,  418  include various MEMS products made by Analog Devices such as iMEMS accelerometers and iMEMS gyroscopes.  
       FIG. 5  shows alternative position sensing circuits  530  that may be used as position sensing circuits  105  in position sensing wafer  101 . Position sensing circuits  530  include a processor  532  connected to a magnetic sensor  534 . Magnetic sensor  534  may simply detect the direction of the magnetic field at the location of magnetic sensor  534 , i.e. magnetic sensor  534  may be a compass. In other examples, magnetic sensor  534  measures magnetic field strength. Using the earth&#39;s magnetic field alone, position sensing circuits may be able to determine the orientation of a wafer by acting as a compass. However, the earth&#39;s magnetic field may be distorted by nearby electrical currents or ferromagnetic components so that the earth&#39;s magnetic field alone may not be reliable.  
      In one embodiment, shown in  FIG. 6 , a magnetic field (H-field)  640  is artificially created by magnetic field generators  642 ,  644  in the area in which a sensing wafer  646  is used so that sensing wafer  646  does not have to rely on the earth&#39;s magnetic field. A magnetic field may be created using permanent magnets or electromagnets. In one example, an artificial magnetic field is a time-varying magnetic field created by electromagnets. For example, the magnetic field may have a periodic variation or may be pulsed. In some examples, multiple magnetic fields may be created in the same area having different frequencies and different orientations. In this way, data regarding the magnetic field measured by a sensor may be filtered according to frequency so that any background magnetic field is separated from an artificially generated periodic field, and different artificially generated fields may be distinguished.  
       FIG. 7  shows another example of apparatus for determining position of a wafer. Position sensing wafer  701  has position sensing circuits  705  that determine the position of wafer  701  with respect to transmitters  750 ,  752 ,  754  by triangulation. Transmitters  750 ,  752 ,  754  may be Ultra Wideband (UWB) transmitters for example. UWB transmitters generally send a pulsed signal over a wide bandwidth. The signals from transmitters  750 ,  752 ,  754  are received by position sensing circuits  705  and used to determine the distances d 1 , d 2  and d 3  from transmitters  750 ,  752  and  754  respectively. The system works similarly to the Global Positioning System (GPS) that uses satellites to accurately determine geographical position using signals from geostationary satellites. Here, instead of geostationary satellites, transmitters  750 ,  752 ,  754  are placed at known, fixed locations so that knowing distances d 1 , d 2 , d 3 , the position of wafer  701  is known. Other transmitters may also be used as transmitters  750 ,  752 ,  754 . For example transmitters using Wi-Fi or some other wireless protocol may be used. Optical or acoustic transmitters could be similarly used. In some cases, more than three transmitters may be used to give greater positional accuracy or to extend the range over which wafer  701  may be moved while determining its position.