Abstract:
An elevator system automatically adjusts the inclination of a wafer boat during the manufacturing of semiconductor devices so that the wafers in the boat are maintained horizontal during their processing. The elevator system includes the wafer boat, a base on which the boat is supported, an elevator for loading the boat into a processing chamber and removing it from the chamber, a sensing unit for detecting the inclination of the boat relative to the horizontal, a horizontal control unit which is interposed between the base and the elevator and is drivable to maintain the boat in such a position that the wafers in the boat lie in horizontal planes, and a control unit for receiving information from the sensing unit and, based on the information, outputting a control signal to the horizontal control unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an elevator system for transferring a boat during the manufacture of semiconductor devices. More particularly, the present invention relates to an elevator system for transferring a wafer boat such that the wafers in the a boat are maintained horizontal. 
     2. Description of the Related Art 
     In general, the fabrication of a semiconductor device involves the execution of a plurality of processes. Therefore, various kinds of equipment and auxiliary devices are used to fabricate a semiconductor device. 
     These processes include a diffusion process in which a semiconductor device is provided with certain electrical characteristics. The process of diffusion includes a step of forming an oxide film on a wafer, and an annealing step in which the surface of the wafer is exposed to a solid or gas containing boron, phosphorus or the like under a high temperature. 
     A prior art furnace (FIG. 1) in which the diffusion process takes place comprises a quartz tube  19  and a heating chamber  18  for heating the quartz tube. The quartz tube  19  isolates the wafers  10  from the environment while the diffusion process is being carried out. 
     The auxiliary devices include an elevator  17  for loading/unloading a boat  14  of wafers  10  into/from the furnace, a wafer transfer device  13  for transferring the wafers  10  into and out of the boat  14 , a cassette transfer device  12  for transferring a cassette  11  containing a plurality of the wafers  10  to the wafer transfer device  13 , a control unit (not shown) for controlling the above-mentioned devices, and a gas supply unit for injecting refined gas into the heating chamber  18 . 
     In addition to the boat  14 , the conventional elevator system comprises a base  15  disposed under and supporting the boat  14 , an elevator  17  for moving up and down, and a horizontal control plate  16  interposed between an upper plate of the elevator  17  and the base  15 . The horizontal control plate  16  is manually adjustable to control the horizontal attitude of the base  15 . 
     More specifically, as shown in FIG. 2, four hex head bolts  20  extend through the horizontal control plate  16  and into the base  15 . The bolts  20  are arrayed along a pair of X and Y axes. The attitude of the wafers  10  with respect to the horizontal is controlled by rotating the hex head bolts  20  clockwise or counterclockwise and thereby adjusting the angle between the base  15  and the horizontal control plate  16 . A respective pair of wing nuts  21  are provided at opposite sides of each hex head bolt  20  to fasten the bolt  20  and prevent the bolt  20  from becoming loose. 
     The boat  14  should extend vertically from and at a right angle to the base  15 . However, the boat can become inclined when overloaded or due to pressure from the exterior environment. If such a situation were not attended to, the wafers would not be processed properly, and the equipment could be damaged. Accordingly, the operator periodically loosens the wing nuts  21  and rotates the hex head bolts  20  to manually adjust the base  15  by eye. Once the base  15  is adjusted and the boat is perceived by the operator to extend perfectly vertically, the operator tightens the wing nuts  21  to lock the bolts  20  in place. 
     However, the task of adjusting the base  15  is onerous because the operator must rotate the hex head bolts one or more times depending on his visual acuity, and the work of adjusting the hex head bolts and of loosening and tightening the eight wing nuts is very time-consuming. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to overcome one or more of the problems, disadvantages and limitations of the related art. 
     More specifically, one object of the present invention is to provide an elevator system for transferring a wafer boat, wherein the wafers in the boat are automatically oriented so as to lie horizontally. 
     Another object of the present invention is to provide an elevator system for transferring a wafer boat, wherein any deviation from the horizontal of the attitude of the wafers in the boat is corrected without operator intervention. 
     To achieve these and other advantages, the elevator system of the present invention includes the wafer boat, a base on which the boat is supported, an elevator for elevating the boat into a processing chamber and lowering it out of the chamber, a sensing unit for detecting the inclination of the boat relative to the horizontal, a horizontal control unit which is interposed between the base and the elevator and is drivable to maintain the boat in such a position that the wafers in the boat lie in horizontal planes, and a control unit for receiving information from the sensing unit and, based on the information, outputting a control signal to the horizontal control unit. 
     The horizontal control unit comprises a horizontal control plate fixed to the elevator, and a plurality of horizontal control driving units interposed between the base and the horizontal control plate. Each of the horizontal control driving units is movable up and down between the base and the horizontal control plate. The horizontal control unit also comprises a driving force generating unit for driving the horizontal control driving units so that the base can be tilted and hence, the inclination of the wafers relative to the horizontal can be adjusted. 
     The sensing unit can comprise sensors which either detect the actual inclination of the base and/or wafers relative to the horizontal or which provide feedback to indicate that the base and/or wafers are out of alignment with respect to a horizontal plane. For instance, the sensing unit may essentially consist of a level gauge, a pendulum, or two pairs of photo-sensors and light-emitting sensors. In the latter case, the photo-sensors and light-emitting sensors are arrayed such that the incident rays of light from the light-emitting sensors are directed to intersect each other perpendicularly. Receipt or non-receipt of these rays by the photo-sensors is indicative of the axis about which the horizontal control plate must be tilted to bring the wafers back to the horizontal. 
     The elevator system may also include a display unit connected to the control unit and displaying the information received from the sensing unit. Based on the information displayed, an operator can issue an order to the control unit to effect an alignment of the wafers with the horizontal. In this case, an input unit is connected to the control unit, receives the order keyed into the system by the operator, codes the order, and sends the coded order to the control unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof made with reference to the accompanying drawings, of which: 
     FIG. 1 is a schematic diagram of a conventional elevator system for transferring a wafer boat; 
     FIG. 2 is a bottom view of the elevator of the conventional elevator system shown in FIG. 1; 
     FIG. 3 is a schematic diagram of one embodiment of an elevator system for transferring a wafer boat according to the present invention; 
     FIG. 4 is an enlarged view of a portion of the elevator system according to the present invention; 
     FIG. 5 is a bottom view of the elevator illustrating the horizontal control unit; 
     FIG. 6A is a schematic diagram of a portion of the elevator system and showing a horizontal driving unit in the form of a screw jack; 
     FIG. 6B is a schematic diagram of the same portion of the elevator system but showing another form of a screw jack; 
     FIG. 7A is a schematic diagram of one portion of the elevator system and showing a gear transmission of the system, which transfers the force from a driving force generating mechanism to the horizontal driving unit; 
     FIG. 7B is a schematic diagram of the same portion of the elevator system but showing a belt and pulley transmission; 
     FIG. 7C is a schematic diagram of the same portion of the elevator system but showing a chain and sprocket transmission; 
     FIG. 7D is a schematic diagram of the same portion of the elevator system but showing a wire and pulley transmission; 
     FIG. 8A is a schematic diagram of a control portion of the elevator system according to the present invention, and in which the driving force generating mechanism is a DC motor; 
     FIG. 8B is a schematic diagram of another form of the control portion of the elevator system according to the present invention, and in which the driving force generating mechanism is an AC motor; 
     FIG. 8C is a schematic diagram of another form of the control portion of the elevator system according to the present invention, and in which the driving force generating mechanism is a gear reduction motor; 
     FIG. 8D is a schematic diagram of another form of the control portion of the elevator system according to the present invention, and in which the driving force generating mechanism is a stepper motor; 
     FIG. 9 is a schematic diagram of one portion of the elevator system according to the present invention and in which the horizontal control driving unit is in the form of a hydraulic or pneumatic cylinder; 
     FIG. 10A is a schematic diagram of one portion of the elevator system according to the present invention and in which the horizontal control driving unit is in the form of an inflatable tube; 
     FIG. 10B is a diagram similar to that of FIG.  1 OA but showing the tube in an inflated state; 
     FIG. 11 is a schematic diagram of the elevator system according to the present invention with the elevator omitted for the sake of clarity, and showing the form of the driving force generating mechanism when the horizontal control driving units are of the type requiring fluid under pressure; 
     FIG. 12A is a schematic diagram of one form of the sensor unit of the elevator system according to the present invention; 
     FIG. 12B is a schematic diagram of another form of the sensor unit of the elevator system according to the present invention; 
     FIG. 12C is a schematic diagram of still another form of the sensor unit of the elevator system according to the present invention; 
     FIG. 12D is a schematic diagram of yet another form of the sensor unit of the elevator system according to the present invention; and 
     FIG. 13 is another schematic diagram of the control portion of the elevator system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail referring to the accompanying drawings. 
     Referring to FIG.  3  and FIG. 4, a vertically oriented boat  34  made of quartz transfers a plurality of wafers  10  into a processing chamber  18  while supporting the wafers  10  horizontally. A disk-shaped base  35  supports the boat  34 . The base  35 , in turn, is supported by a vertically moving elevator  37 , and a horizontal control plate  36  fixed to the elevator  37 . 
     A plurality of horizontal control driving units  40  support the boat  34  and the base  35 . Each unit  40  is movable up and down between the bottom of the base  35  and the top of the horizontal control plate  36  so as to adjust the distance between the two. Accordingly, the horizontal control driving units  40  control the horizontal attitude of the base  35 . 
     Driving force generating mechanisms  41  are operatively connected to the horizontal control driving units  40  for driving the horizontal control driving units  40  up and down. 
     A control unit  44  receives information indicative of the attitude of the wafers from a sensor unit  43 . Based on this information, the control unit  44  controls the operation of the horizontal control driving units  40 . 
     The horizontal control driving units  40  may consist of an X-axis horizontal control driving unit  40   a  and a Y-axis horizontal control driving unit  40   b (FIG.  5 ). The X-axis horizontal control driving unit  40   a  is located beneath the base  35  and to one side of the origin of X and Y axes along the X-axis. The X-axis horizontal control driving unit  40   a  controls the inclination of the base  35  about the Y-axis. The Y-axis horizontal control driving unit  40   b  is located beneath the base  35  to one side of the origin along the Y-axis. The Y-axis horizontal control driving unit  40   b  controls the inclination of the base  35  about the X axis. 
     The horizontal control driving units  40  can comprise various types of devices such as hydraulic or pneumatic cylinders (FIG.  9 ), or mere tubes (FIGS. 10A and 10B) which can expand or contract in one or both directions upon receipt of hydraulic or pneumatic pressure from the driving force generating mechanisms  41 . 
     When the horizontal control driving units  40  are of the type requiring pneumatic or hydraulic pressure, the driving force generating mechanisms  41  each comprise a pump, and a fluid transfer pipe  41 ′ for transferring the hydraulic or the pneumatic fluid from the pump to the respective horizontal control driving unit  40  associated therewith. In this case, the pumps are controlled by the control unit  44 . 
     In addition, valves  60 , such as solenoid operated flow control valves, are provided in the fluid transfer pipes  41 ′ so that the pipes can be selectively opened and closed to control the operation of the horizontal control driving units  40  (FlGS.  10 A,  10 B and  11 ). The opening and closing of such valves  60  is also controlled by the control unit  44 . 
     However, each horizontal control driving unit  40  preferably is a screw jack (FIG. 6A) comprising a set of female threads  50  integral with the base  35 , a screw member  51  rotatably supported by the horizontal control plate  36  and having male threads engaged with the female threads  50 , and a transmission  42  for transmitting the force received from the driving force generating mechanism  41  as torque for rotating the screw member  51 . 
     FIG. 6B shows an alternative form of the screw jack in which the screw member  51  is keyed to the transmission  42  so as to be capable of moving vertically when rotated by the transmission  42 . 
     The transmission  42  can comprise at least one transmission gear (FIG.  7 A), a belt and pulley (FIG.  7 B), a chain and sprocket (FIG.  7 C), or a wire and pulley (FIG.  7 D). Preferably the transmission  42  comprises a plurality of gears. 
     In addition, the driving force generating mechanism  41  preferably comprises a motor as shown in these figures. The motor may be a DC motor (Direct Current motor) for generating a rotational driving force upon receipt of DC power from the control unit  44  (FIG.  8 A), an AC motor (Alternating Current motor) for generating a rotational driving force upon receipt of AC power from the control unit  44  (FIG.  8 B), a reduction motor comprising gears connected to an output shaft which rotates at a given number of rpms (FIG.  8 C), or a stepper motor having a pulse generator and capable of precise outputs (FIG.  8 D). In the present invention, the stepper motor is preferable due to the precision by which its output can be controlled. 
     The control unit  44  (FIGS.  8 A- 8 D)for controlling the motors  41   a  and  41   b  has an input section which receives the information indicative of the orientation of the boat  34  from the sensor  43 , and a comparator which compares the information with data stored in the memory of the control unit  44 . The control unit  44  controls the motors based on the comparison of the sensed information with the store data. When the motors are AC motors or DC motors (FIGS.  8 A and  8 B), the control unit  44  regulates the voltage or the current supplied to the motor(s). When the motors are stepper motors (FIG.  8 D), the control unit  44  has a waveform regulator (shaper) which converts the power into positive or negative wave pulses which are issued to the stepper motor(s). 
     The sensor unit  43  may comprise two pairs of photo-sensors (PS) and light-emitting sensors (LES) positioned adjacent the base  35  or the wafers  10  so that light emitted from one of the light-emitting sensors towards the photo-sensor associated therewith propagates perpendicularly to the light emitted from the other light-emitting sensor (FIG.  12 A). The degree to which the photo-sensors receive the rays of light from the light-emitting sensors, respectively, indicates the angle at which the base  35  or the wafers  10  is inclined relative to the horizontal. 
     Alternatively, the sensor unit  43  may comprise a plurality of pressure transducers (PT) disposed beneath the base  35  for detecting the load on the base  35  (FIG.  12 B). 
     In another embodiment (FIG.  12 C), the sensor unit  43  comprises a pendulum  43   a  hanging from a stand fixed to the base  35 , and contact sensors or pressure transducers  43   b  located adjacent the pendulum  43   a  for sensing the same. Because the pendulum  43   a  remains vertical under the force of gravity as the base  35  becomes inclined relative to the horizontal, the contact sensors or pressure transducers  43   b  can detect the degree to which the base  35  has tilted relative to the pendulum  43   a  and hence, the inclination of the base  35  relative to the horizontal. 
     Still further, the sensor unit may comprise a level(s)  43 ′ integral with the base  35 , and a suitable device, such as an optical sensor OS, for reading the gauge of the level(s)  43 ′ (FIG.  12 D). 
     Next, referring to FIG. 13, a display unit  99  is connected to the sensor unit  43  and the control unit  44 . The display unit  99  receives the information regarding the attitude of the base  35  or of the wafers  10  from the sensor unit  43  and displays the information to an operator. An input unit  100  is connected to the control unit  44 . When the input unit  100  receives a horizontal alignment operation order, it converts the order into code, and transfers the code to the control unit  44 . 
     During operation, an operator checks the display unit  99  to find out whether the base  35  or the wafers  10  is/are inclined relative to the horizontal. If the base  35  or the wafer  10  is/are inclined relative to the horizontal, the operator inputs an order to the control unit  44  via the input unit  100 . Upon receipt of this order, the control unit  44  analyzes the information produced by the sensor unit  43 , and controls appropriate ones of the driving force generating mechanism(s) to drive the transmission(s)  42  connected to the horizontal control driving unit(s)  40  or to pump fluid thereto, as the case may be. 
     This operation is executed periodically according to a program stored in the control unit  44 . This program is accessed upon order of the operator. 
     As has been described above, the elevator system of the present invention periodically detects the orientation of the wafers in the boat, and based on such detections automatically makes any adjustments needed to maintain the wafers horizontal. The automatic adjusting of the orientation of the wafers saves much time over making the same adjustments manually. Furthermore, the periodic detection of the orientation of the wafers ensures that the wafers will be horizontal as they are moved by the elevator into a processing chamber, for example. Therefore, the present invention ensures that products of high quality will be made by the processing of the wafers. 
     Although the present invention has been described in detail above with respect to the preferred embodiments thereto, various changes, substitutions and alterations thereof will become apparent to those of ordinary skill in the art. All such changes, substitutions and alterations are thus seen to be within the true spirit and scope of the invention as defined by the appended claims.