Abstract:
The invention relates to a monitoring system for a conveying device for flat articles, especially wafers, which conveying device is provided with a carriage ( 28 ) that is movable along a predetermined path next to a flat article ( 10 ) that is located at a predetermined removal location, the carriage having a receiving device for the accommodation of the flat article ( 10 ), which monitoring system contains a light source ( 50 ) having a light-exit window and a light receiver ( 52 ) having a light-admission window, whereby the light-exit window and the light-admission window are positioned in such a way that a light beam ( 60 ) directed form the light-exit window to the light-admission window is partially covered by the carriage ( 28 ) during its movement through the light beam, and an evaluation unit that is connected to the light receiver and that compares a target signal derived from its movement of the carriage along a target path with an actual signal derived from an actual movement of the carriage, and indicates a deviation.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a monitoring system for a conveying device for flat articles, especially wafers. 
     Wafers are thin disks of silicon, as they are used for the manufacture of integrated circuits, solar cells, etc. Such wafers must be handled extremely carefully in clean rooms, as they are transported, during the course of the manufacture of the integrated circuit, the solar cell, etc., from one processing step to a further processing step. 
     FIG. 3 shows a schematic view of an apparatus for carrying out various processing steps of a wafer. 
     Two racks  4 , 6  are disposed in a housing  2  that forms a supply or storage chamber; the racks have receptacles  8  (FIG. 5) that are disposed one above the other and in which can be accommodated disks  10 . 
     Via a motor  11  and by means of a device that is not illustrated in detail, the housing  2  can be displaced back and forth on a stationary rail  12  in the direction of the double arrow  14 , so that in one selected position, the one rack  4 , and in the other selected position, the other rack  6 , is located across from an opening  16  of a housing  18  that has further openings  20  to which the working chambers  22  are connected. 
     Disposed in a housing  18  is a robot  24  (FIG. 4) that is provided with a supporting arm  26  on which is disposed a carriage  28 . The carriage  28  has an indentation  30 , the base  32  of which is provided with vacuum slots  34  as well as capacitive proximity sensors  36 . 
     To move the supporting arm  26 , motors  38  and  40  are provided via which the supporting arm  26  is pivoted in a plane of movement that is perpendicular to a central axis of rotation of the robot  24 , and via which the spacing of the supporting arm from the axis of rotation can be altered. The carriage  28  can be rigidly connected to the supporting arm  26 , or can be displaceable on the carrying arm  26  via a non-illustrated further drive means. 
     FIG. 5 shows a perspective front view of the partially cut away or basically open toward the front housing  2 , whereby two chambers are visible, of which only the left one is provided with the rack  4 . The motor  10  serves for the back and forth movement of the housing  2  upon the rail  12 . As can be seen, the housing  2  is not directly displaceable on the rail  12 , but rather is disposed upon a frame element  42  that together with the housing  2  is displaceable along the rail  12 . The housing  2  can be displaced in height relative to the frame element  42  via a servo-motor  44 , in the direction of the double arrow  46 , so that the individual receptacles  8 , with the wafers  10  accommodated therein, though not illustrated in FIG. 5, can be positioned one after the other at the same height. 
     The construction and function of the previously described apparatus, various embodiments of which are offered in commerce by various firms, are known and will therefore not be described in detail. 
     The basic function is such that pursuant to FIG. 3, the robot  24 , in a one time lined-up, horizontal plane, introduces the carriage  28  out of the opening  16  and into an oppositely disposed receptacle of the rack  4 . With the aid of the servo motor  44 , the rack  4  is then lowered slightly vertically until the proximity sensors  36  register the approach of a wafer  10  that is disposed upon a base of a receptacle  8 . With a further lowering of the rack  4 , the wafer  10  comes to rest upon the base  32  of the indentation  30 , where it is held in place upon activation of the vacuum slots  34 . The carriage  28  subsequently moves out of the rack  4  into the interior of the housing  18  and through a first one of the openings  20  into a first one of the working chambers  22 , where it is deposited and processed. The wafer  10  is subsequently picked up by the carriage  28  and introduced into a next one of the working chambers, etc. until, after passing through the processing steps in the individual working chambers  22 , the wafer is deposited by the carriage  28  in the right rack  6  of FIG. 3, whereby pursuant to FIG. 3 the housing  2  is moved toward the left. The carriage  28  is subsequently moved out of the rack  6 , the housing is moved toward the right and the next wafer is picked up from the rack  4  by first lowering the rack by the height of one receptacle, so that after the carriage  28  has been introduced into the next receptacle, and after a subsequent further lowering of the rack  4 , the next wafer  10  comes to rest on the carriage  28 . 
     The individual openings  16  and  20  of the housing  18  can be sealed off via vacuum-type slides, so that on the whole it is possible to operate under vacuum. 
     A problem that arises when processing with the described apparatus is that the carriage  28  that is moved by the robot  24  alters its horizontal plane of movement, either due to wear or due to high thermal stresses as it is introduced into the working chambers  22 , which are in part under high temperature. The vertical distance between the individual receptacles  18  in the racks  4  and  6  is relatively small, so that already a slight deformation or deflection of the carriage out of its targeted path of movement brings with it the danger that already upon its introduction into the rack  4  the carriage contacts a wafer and damages it, or that the wafer is then no longer satisfactorily deposited upon the carriage. 
     It is an object of the invention to provide a remedy for the aforementioned problem. 
     SUMMARY OF THE INVENTION 
     This object is realized by a monitoring system pursuant to the main claim. 
     The inventive monitoring system ensures that already slight deviations of the carriage movement from the targeted path of the carriage are detected and can be indicated. In this way, expensive damage to the wafers can be avoided. 
     It is to be understood that the inventive monitoring system for conveying devices pursuant to the main claim is suitable for many different types of flat articles, such as fragile, thin mica plates, thin ceramic plates, loaded printed circuit boards, etc. The inventive monitoring system is particularly well suited for conveying devices for wafers, the handling of which is subjected to particularly high requirements. 
     The dependent claims are directed to advantageous embodiments and further developments of the inventive monitoring system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The inventive monitoring system is explained subsequently with the aid of schematic drawings by way of example and with further details. 
     The drawings represent: 
     FIG. 1 a block diagram of the monitoring system, 
     FIG. 2 curves to explain the functioning of the monitoring system, 
     FIG. 3 the already described view of a processing apparatus for wafers, 
     FIG. 4 a perspective view of a robot used in the apparatus of FIG. 3, 
     FIG. 5 a perspective front view of the apparatus of FIG. 3, 
     FIG. 6 a perspective view of a modified embodiment of a wafer-processing apparatus, and 
     FIG. 7 a cross-sectional view through a preparation chamber of the apparatus of FIG.  5 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The inventive monitoring system contains a light source  50  and a light receiver  52  that is spaced from the light source  50  and is connected with a control device  54  to which is connected an indicator  56 . 
     The light source  50  advantageously contains a laser light source, the light of which is influenced by an optical system in such a way that a parallel light beam  60  (indicated by dashed lines) exits from an exit window  58  that is embodied in the form of a vertical slot. The light beam  60  enters an admission window  62 , of the light receiver  52 , that is disposed across from the exit window  58  and is advantageously embodied in conformity with the exit slot. The light that enters the admission window  62  is focused on a photo diode, the output signal of which is supplied to the control device  54 . 
     In a manner known per se, the control device  54  contains a microprocessor and an evaluation unit  64 , the function of which will be explained in detail subsequently. 
     As can be seen from FIG. 3, the light source  50  is mounted on the stationary housing  18  on one side of the opening  16 , and the light receiver  52  is mounted on the other side of the opening  16 . 
     FIG. 1 illustrates how movement of the carriage  28 , which is movable essentially perpendicular to the plane of the drawing sheet, intersects or covers the light beam  60 . The target plane of movement, in which the carriage  28  moves during its movement into the rack  4  and out of the rack  4 , is such that the underside  66  of the carriage  28  intersects the light beam  60  at a prescribed height, so that a corresponding prescribed height of the admission window  62  is shaded, and the output signal of the light receiver  52  is correspondingly reduced. 
     In FIG. 2, the curve K represents a measurement curve that represents the exit signal of the light receiver  52 . In the region A there is no object between the light source  50  and the light receiver  52 , so that the latter receives the full light intensity, which in the evaluation unit  64  is set to one hundred. If the carriage  28  is moved into the light beam  60 , the intensity of the light falling upon the light receiver  52  drops suddenly, depending upon the contour of the carriage, which is recognized by the evaluation unit  64  and sets a counting or time signal to zero. Depending upon the contour of the carriage  28 , the curve K, as the carriage  28  moves through the light beam  60 , assumes a characteristic path (the brief deviation from the horizontal path in the form of the drop M indicates, for example, a screw that projects from the underside  66  of the carriage  28 ), in order then, depending upon the contour of the carriage, to again increase until the carriage has moved completely through the light beam  60  and in the region A the output signal again assumes its original value. 
     Depending upon the design of the control device  54 , the curve K can be recorded at various cycle frequencies and can be evaluated in various ways. In the case of FIG. 2, the region I between the dashed lines represents a very narrow precision range within which must lie an average value of the output signal that is formed, for example, between the metering positions t 1  and t 2 , so that the movement of the carriage is recognized as being in order to a high degree. As long as the measured value lies between the dot-dashed curves II, the movement of the carriage is seen as being still tolerable. Beyond the range II, the movement is seen as not being tolerable, and leads to an indication of error or malfunction. 
     In the indicator  56 , the indication can be effected directly upon a screen, in a manner similar to what is shown in FIG. 2, and/or the indication can be effected via diodes, with green diodes indicating “in order”, yellow diodes indicating “still tolerable”, and red diodes indicating an insufficient precision of movement that requires a readjustment or the like of the carriage. 
     It is to be understood that a number of other evaluation possibilities exist, and that the monitoring apparatus can be installed as an independent system, or can be integrated into the control system of the motors or the robot and the drive of the housing  2  in a horizontal and vertical direction by supplying, for example, appropriate time markers from the control device of the electric motors to the control device  54 , etcetera. 
     It is also to be understood that a drift of the measurement result can be detected, so that systematic variations can be observed and extrapolated, as a result of which errors can be predicted. Furthermore, it is possible to dispose behind the admission window  62  a diode strip, so that the absolute value of the level of the underside  66  below the light beam  60  can be detected directly. 
     Furthermore, the arrangement can also be embodied in such a way that the upper side of the carriage  28  is scanned, so that initially the upper side of the carriage is detected beyond the indentation  30 , and then a wafer disposed in the indentation  30  is detected, so that with the monitoring of the satisfactory movement of the carriage the satisfactory position of the disk and even the satisfactory quality of the disk itself can be monitored. 
     By calibrating the output signal, with the admission window  62  not covered, respectively to one hundred, there results an extensive insensibility to variations of the light intensity of the light source  50  and to contaminations. 
     FIG. 6 shows a modified embodiment of a wafer-processing apparatus, whereby for functionally similar components the same reference numerals are used as in FIGS. 3 to  5 . With regard to the direction of viewing, the view of FIG. 6 corresponds to a view of the arrangement of FIG. 5 at an angle from behind. The housing  2 , which accommodates a non-illustrated rack  4  and  6 , contains two hermetically sealable housing components  2   a  and  2   b , which contain vacuum chambers in which are accommodated support means  67  for the magazines or racks  4  and  6  (FIGS.  3  and  5 ). The support means  67  are movable vertically by means of servo-motors  68 . The overall housing  2  is rigidly secured on a frame (not illustrated). In contrast to the embodiment of FIG. 3, where the light source  50  and the light receiver  52  are disposed on the housing  18  that accommodates the robot, with the embodiment of FIG. 6 there is disposed within each housing portion  2   a  and  2   b  a light source  50  and a light receiver  52  that are connected via cables  70  to the control device  54  (FIG.  1 ). 
     The receiving chambers formed in the housing portions  2   a  and  2   b  are open in FIG. 6, and can be closed in an airtight manner via slides  72   a  and  72   b . With the slides  72   a  and  72   b  open, racks that are supplied with wafers can be inserted or removed at the support means  67 . 
     The geometrical arrangement can be seen from FIG. 7, which represents a horizontal cross-section through the housing portion  2   a . Visible are the light source  50 , the light receiver  52 , the carriage  28 , the rack  6  and a wafer  10 . The arrangement of the light source  50  and of the light receiver  52 , and the dimensions, are such that the light beam  60  (FIG. 1) freely passes through a gap between two receptacles or compartments that are provided with wafers  10  when the carriage  8  is not disposed within the rack  6  and the rack is in a predetermined step position. The functional sequence of the monitoring system when using the embodiment of FIGS. 6 and 7 is as follows: 
     With the carriage  28  located outside of the housing  2  or one of the housing portions  2 , by actuating the stepping motors  68  the magazines are respectively in a position in which the light beam passes through the gap between two receptacles without being covered, i.e. in the graph of FIG. 2 there results a signal value in the region A, in other words a maximum value of the output signal of the light receiver or receivers  52 . In the following, the function is described for only one of the magazines, for example the non-illustrated magazine that in FIG. 6 is located in the right housing portion  2   b . If in the position of the carriage  28  located outside of the housing portion  2   b  the maximum value of the light intensity is not measured, this indicates an error of the pertaining stepping motor  68  or of its control. The monitoring system can be used to control the actuation of the stepping motor  68  by actuating this motor for such a length of time until the maximum light intensity is achieved. This can occur by trials for an overall, newly inserted magazine that may be loaded with wafers, so that the magazine imprecisions can be compensated for by always actuating the stepping motor  68  in such a way that the gap between two receptacle bases is arranged in such a way that the light beam  60  passes completely there through. It is to be understood that it is advantageous for the height dimension of the light beam  60  to be slightly less than the spacing between two receptacle bases so that the maximum output signal is ensured. 
     In the predetermined position of the magazine, which is controlled with the aid of the light beam, the transport arm  26  is now moved into the housing portion  2   b  into the gap between two receptacle bases, i.e. two disks, the rims of which are accommodated by the receptacle bases, whereby this movement is monitored pursuant to FIG.  2 . The monitoring differs somewhat from the illustration of FIG. 2 in that the carriage is moved out of the left region A only in the region B, and not completely through the light beam. The rack is subsequently lowered, whereby the lowering is effected by only a certain amount, or, if the proximity sensors  36  (FIG. 4) are provided, the lowering is controlled via the proximity sensors  36 . The wafer that rests upon the carriage is then held securely in place with the aid of a supply of vacuum to the vacuum slots  34 , and is moved out of the housing portion  2   a.    
     The deposit of the finish-processed wafer in the rack accommodated in the other housing portion  2   a  is effected in a manner analogous to that explained in conjunction with FIGS. 3 to  5 , whereby the height position of the rack can, as described, be additionally monitored. 
     Thus, on the whole, with the inventive monitoring system described by way of example, in the production apparatus a targeted monitoring is possible at extremely low equipment expense (light emitter and light receiver), whereby the monitoring of the vertical movement of the rack, which is provided with the receptacles for accommodating the wafers, and the movement of the carriage that transports the wafers, utilizes only one light receiver and light emitter, whereby the light receiver generates merely a simple output signal that corresponds to an overall irradiation intensity. 
     The specification incorporates by reference the disclosure of German priority document 19958 082.0 filed Dec. 2, 1999 and International priority document PCT/EP00/12103 filed Dec. 1, 2000. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.