Patent Abstract:
A mechanism for mapping the contents of a cassette which is used for delivering substrates to a system for processing semiconductor and similar materials which is independent of load port or loading robot movement. The mapping mechanism includes a U-shaped probe having a photo emitter/receptor mounted on opposing surfaces of its legs. The U-shaped probe is mounted on a carriage for rotation about its longitudinal axis. The carriage is, in turn, mounted on a track for movement over the height of the cassette. The mapping mechanism is mounted on the loading port frame of the processing system adjacent to the load port and is moved into and out of it sensing position by interaction with a cam.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to substrate cassettes which provide a supply of substrates to a processing system and more particularly to a mechanism for sensing the presence or absence of substrates in the slots of the cassettes 
   2. Brief Description of Related Developments 
   In semiconductor and similar materials processing it is well known to mount multiple substrates in slots constructed in an enclosure, such as a cassette. The cassette is mounted in relation to the loading door of a processing system for access by a loading robot. The loading robot extracts a substrate from the cassettes and delivers the substrate to a processing chamber. In order to expedite the loading process it is advantageous to identify the slots of the cassette that contain substrates. This mapping process is needed to avoid unnecessary movement of the loading robot. 
   Cassette mapping has been accomplished in the past by several different methods, such as reflective and through beam sensing. These sensors may be fixed or moveable. They are sometimes mounted on the loading port door or on the loading robot. Fixed reflective sensors must rely on obtaining an accurate reflection and require an array of emitter/receptor pairs. Such systems have been found to be expensive and result in false readings which hinder their reliability. In another solution of the prior art, sensors have been mounted on the load port door and rely on controlled door movement to insure proper scanning of the cassette bay. In this instance door movement has to be controlled to allow access by the sensors to the cassette bay without interfering with the loading process. This has been found to be a relatively slow. 
   It is a purpose of this invention to construct a mapping system which provides an efficient mapping of a cassette independent of load port door movement or loading robot movement. It is a further purpose of this invention to use through beam sensors mounted on the load port frame. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a system for mapping the slots of a cassette to determine the presence of substrates for processing. In the system of this invention, a mapping mechanism is mounted for controlled movement on the frame of the load port. The mapping mechanism includes a sensor assembly, which comprises a lever arm having a pair of parallel projections extending transverse to its longitudinal axis to form a generally U-shaped probe. The parallel projections have opposing surfaces on which are mounted a sensor beam emitter and receptor pair. The sensor is mounted to generate a beam that extends across the opening formed by the distal ends of the projections, i.e., the opening of the U-shaped probe. The lever and arm assembly together form a sensing plane. 
   The sensor assembly is mounted on a carriage which is mounted for movement up and down the substrate stack within the cassette. To accomplish this, the carriage is mounted on a rail and is driven along the rail by appropriate motors, such as stepping motors. To allow the sensor assembly to engage the cassette stack and to avoid interference with the loading process, the sensor assembly is mounted on the carriage for rotation about the longitudinal axis of the lever arm. Rotation of the lever arm is controlled by the interaction of a bias spring, which tends to rotate the lever arm to a position in which the sensing plane of the sensor assembly is parallel to the plane of the substrates in the cassette stack. In addition a cam track is mounted adjacent the sensor movement rail. A cam follower is fixed to the lever arm and extends into engagement with the cam track. The cam track is constructed to rotate the lever arm into its retracted position at one end of the sensor assembly movement. 
   In this manner a sensor assembly is provided which is independent of load port door movement or the movement of the loading robot. It effectively flips into and out of sensing engagement with the substrate stack within the cassette. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail below with reference to the attached drawing in which: 
       FIG. 1  is a perspective view of a substrate processing system; 
       FIG. 2  is a perspective view of a load port of a substrate processing system; 
       FIG. 3   a  is a front view of the sensor assembly of this invention; 
       FIG. 3   b  is a top view of the sensor assembly in the mapping position, extended into substate cassette; 
       FIG. 4  is a side view of the sensor assembly shown in  FIG. 3   a ; and 
       FIG. 5  is a view of the interior side of a load port with the sensor assembly installed. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A system  1  for processing substrates  2  is shown in  FIG. 1  and is constructed with a series of processing chambers  3  communicating with a vacuum chamber  4 . A loading module  5  is connected to the vacuum chamber  4 . Substrates  2  are stacked for processing in cassettes  7  and  8 , as shown in  FIG. 2 . Cassettes  7  and  8  are connected to the loading module through loading ports  9  and  10 . The substrates  2  are moved from a slot in a cassette into loading module  5  by a loading robot (not shown) which forms part of loading module  5 . The substrates  2  are then moved into vacuum chamber  4  either by the loading robot or a processing robot (not shown) positioned in vacuum chamber  4 . Processing is performed when the substrates are placed in one of the processing chamber&#39;s  3 . There are many different configurations of substrate processing systems which may utilize a cassette based delivery system. The system shown in  FIGS. 1 and 2  are for illustration only and do not constitute a significant part of this invention. System  1  will be used as a context for further description of the invention. In addition the system is not limited for use with any particular size substrate. In  FIG. 2 , cassette  8  is shown mounted to load port  10 . Stacked slots  6  of cassette  8  are constructed to receive and store a series of substrates  2 . In order to provide data with respect to the location of slots which contain substrates, a system  11  for mapping the slots  6  of cassette  8  is provided, as shown in  FIGS. 3 through 5 . System  11  includes sensor assembly  12 , mounting carriage  13  and movement control tracks  14  and  28 . System  11  is secured to the loading port frame  31  adjacent to the loading port, as shown in  FIG. 5 . As shown in  FIG. 5 , preferably system  11  is mounted inside the load module  5  for operation through the load port. 
   Sensor assembly  12  is constructed having a lever arm  15  and a pair of parallel projections  16  and  17  extending transverse to the longitudinal axis x-x of lever arm  15  to form a generally U-shaped probe  18 . The lever arm  15  extends longitudinally across an edge of a load port opening through which substrates in the cassette are accessed. The parallel projections  16  and  17  have opposing surfaces  19  and  20  on which are mounted a sensor beam transmitter and receptor pair  21  and  22  respectively. The sensor pair  21 / 22  is mounted with its optical beam  23  extending across the opening formed by the distal ends of the projections  16  and  17 , i.e., the opening of the U-shaped probe  18 . U-shaped probe  18  is formed with a gap having a width w that is determined by the range in size of the substrates that are intended to be processed. The lever arm  15  and sensor probe  18  assembly, together, form a sensing plane  30  as shown in  FIG. 3   b , extending transverse to axis x-x of lever arm  15 . 
   The sensor assembly  12  is mounted on carriage  13  for rotation about its axis x-x, as shown by arrow  24  in  FIG. 3   a . An extension bar  25  projects through carriage  13  from lever arm  15 . A cam arm  26  is attached to the distal end of bar  25  and extends transverse to the longitudinal axis x-x. A cam follower  29  is mounted on the arm  26  for engagement with the cam surface  27  of cam track  14 . Carriage  13  contains a bias spring (not shown) which exerts a force on the lever arm  15  tending to rotate the sensor plane into a parallel relationship with the plane of the stacked substrates  2 . Carriage  13  is mounted for movement on rail  28  and is driven along the rail by appropriate motors  42 , such as stepping motors. The drive motors may be operatively connected to the carriage  13  by an appropriate transmission mechanism such as a belt  44  or rack and pinion arrangement. Track  28  is designed to provide a range of movement h, as shown in  FIGS. 3   a  and  4 . The drive signals for motor  42  provides a convenient indication of the position of the carriage  13  on rail  28 . This is correlated with probe signals to provide a substrate position reading which can be saved in memory for use in process loading. 
   A cam track  14  is provided adjacent track  28  for engagement with cam follower  29 . Cam surface  27  of track  14  is shaped to provide a force on cam lever  26  which tends to rotate the probe  18  against the force of its bias spring. At one extremity of movement, i.e. the upper end as shown in  FIG. 3   a , the sensor plane  30  is allowed to rotate 90° into a position, as shown in  FIG. 4 , in which it is parallel to the load port door and out of the way of load robot movement. 
   In operation sensor probe  18  is lowered, by movement of carriage  13  on rail  28 , to a position on cam surface  27  which allows the lever arm  15  to twist about its axis approximately 90° towards the stack of substrates  2  in cassette  8  (see  FIG. 3   b ). At this point, sensing plane  30  swings into a parallel relation to the substrates  2 . When mounted in the inside of loading module  5 , sensor probe  18  projects through the load port  10  into alignment with the stacked substrates  2 . This is of course accomplished after the load port is opened. Carriage  13 , with sensor probe  18 , is lowered further until a substrate  2  interrupts beam  23 , as shown in  FIG. 3   b.    
   The interruption of beam  23  generates a signal in a well known manner for transmission to microprocessor  40 , as shown in  FIG. 4 . Microprocessor  40  may be a dedicated ASIC which is operatively connected to process control system  50  for processing system  1 . The position of sensor probe  18 , within its range of movement h, on rail  28  is monitored by microprocessor  40 . The interrupt signal is correlated to a carriage position reading to establish the location of a substrate  2  in cassette  8  which is ready for delivery into the processing system  1 . The position of carriage  13  may be monitored in several ways for example by registering drive signals to motor  42  or by actually sensing position along rail  28 . A simple look up table may be established based on the known physical relationship of the components to provide a correlation with a substrate slot. 
   All of the slots  6  of cassette  8  are scanned and a map of its contents is stored in the control system of the processing system. When the scan is complete the control system initiates movement of the probe  18 . The probe  18  is moved back to its start position on travel rail  28  in which engagement of the cam surface  27  by follower  29  will twist lever arm  25  to its stored position. The delivery of substrates to the process system  1  proceeds in an efficient manner. Mapping is accomplished by system  11  independent of the movement of either load port door  10  or a loading robot (not shown). 
   As shown schematically in  FIG. 4 , the sensor interrupt signal is fed to mapper processor  40  through link  41 . Mapper processor  40  generates signals to activate drive motor  42  in response to a mapping command from process controller  50 . The drive signals are monitored to maintain a continuous position reading of carriage  13  on rail  28 . When an interrupt signal is received, the position is registered and stored in memory  43  for use by controller  50  in the substrate loading process. It should be noted that the implementation of the components of the mapping function may be accomplished in many different ways and could be incorporated into process controller  50 . It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

Technology Classification (CPC): 7