A METHOD OF TRANSLATING AND ORIENTING FLAT OBJECTS SUCH AS SEMICONDUCTOR WAFERS AND AN APPARATUS FOR TRANSPORTING SUCH OBJECTS

Abstract: An apparatus and method are described for transport­ ing flat objects such as semiconductor wafers between a first carrier and a second carrier, for example plastics and quartz storage boats. The apparatus has means for supporting the first and second carriers and pickup means for picking up the objects and transporting them between the first carrier and the second carrier. An intermediate station receives the ob­ jects from the pickup means with the faces in a first orienta­ tion and the orientation of the faces changes before the ob­ jects are removed by the pickup means.

Description: This invention relates to the transport of flat objects, e.g., placing semiconductor wafers in carriers or boats. It is desirable to rapidly and automatically transfer semiconductor wafers from plastics storage boats to quartz processing boats (in which they are introduced into a diffusion furnace), and vice versa, without introducing contamination on to the surfaces of the wafers. Such contamination often results during wafer placement in the quartz boats, from the wafers scraping against the slots into which they are placed. Contamination can also arise from scraping and sliding of parts within the apparatus being used to accomplish the transfer. Our International Patent Application No: PCT/US83/00783 (Publication No: WO83/04240), the disclosure of which is hereby incorporated by reference, describes prior wafer transfer handling apparatus having two trolleys (one for a quartz boat and one for plastics boats) movable along parallel directions, and a vacuum pickup arm that moves in a transverse direction and engages different wafers in different slots in the boats as the trolleys move the slots into position. In using such apparatus, the fronts and backs of the wafers are typically in the same orientation in the plastics and quartz boats. If it is desired to change the orientation of the faces of semiconductor wafers between their removal from plastics storage boats and their deposit in quartz boats, for example to place wafers back-to-back to effect wafer treatment, the wafers have to be transferred either by hand or by rotating a carrier, e.g., in a mass transfer system, something that can result in contamination of and damage to the wafers. US Patent 3,503,527 discloses use of a vertical spindle to transport individual articles. The spindle incorporates a depending article holder which holds a single flat article in a horizontal plane. To invert the article the holder releases the article, which drops onto a support plate in the form of a shallow triangular pan. A lid then closes and the pan and lid are turned upside down (ie are rotated through 180 degrees about a horizontal axis). With the article resting on the lid, the pan itself is raised, and the article seized by the depending article holder, for its onward journey to the receiving point. In a first aspect thereof, the present invention provides apparatus for transporting flat objects having first and second faces between a first carrier and a second carrier, the apparatus comprising; support means adapted to support said first and second carriers; pickup means adapted to pick up said objects and to transport said objects between said first carrier and said second carrier; and intermediate station means adapted to receive said objects from said pickup means with said faces in a first orientation and to change the orientation of said faces before said objects are removed by said pickup means; and being characterised in that said intermediate station comprises: cradle means provided with a plurality of slots each adapted to receive a section of the perimeter of a said object, said plurality of slots being adapted to support said object with said first and second faces oriented generally in vertical planes in operation; and rotation means adapted to rotate said cradle means about an axis parallel to a said face with said object positioned in said plurality of slots in the said cradle; and in that said objects are oriented vertically throughout transportation by the said apparatus. In preferred embodiments, a vacuum actuator is used to drive the cradle; the actuator is connected to a drive shaft for the cradle via a cable that engages a pulley on the drive shaft; the vacuum actuator rotates the cradle in one direction, and there is a second vacuum actuator that rotates the cradle in the other direction; there are valves for alternately connecting the vacuum actuators to a vacuum source, so that the actuator that is not connected controls the speed with which the vacuum actuator that is connected rotates the cradle; there is a stop mechanism for preventing rotation of the cradle beyond a predetermined position at which the object is in a position to be removed by the pickup means; the stop mechanism comprises a disk mounted for rotation with the cradle, a stop bar mounted on the disk, and a corresponding stop member encountered by the stop bar once the cradle has rotated to the wafer pickup position; the disk has an opening through it, and there is an energy-beam source and sensor to detect the opening; the pickup means has a flat pickup paddle adapted to engage wafers on opposite paddle surfaces, and the cradle has two sets of slots for receiving two wafers at one time; the carriers are supported by trolleys which are slidably mounted for movement along parallel directions, and the pickup means comprises an arm movable in a transverse direction; and the intermediate station is mounted for movement on a trolley. The invention provides in a second and alternative aspect thereof a method of translating and orienting flat objects having first and second faces, the method comprising the steps of: picking up an object from a first carrier and transporting said object to a second carrier while maintaining said object generally in a vertical orientation; and changing the orientation of the said faces of the object in the course of its travel between said first and second carriers by placing said object in a plurality of slot in a cradle means so that said object is supported with said first and second faces oriented generally vertically, and rotating said cradle means about an axis parallel to a said face. Other features and advantages of the invention will be apparent from the following description of the preferred embodiment, and from the claims. We first briefly describe the drawings. Fig. 1 is a diagrammatic perspective view of wafer handling apparatus according to the invention. Fig. 2 is a perspective view, diagrammatic and partially broken away, of an intermediate station of the apparatus of Fig. 1. Fig. 3 is a sectional view, taken at 3-3 of Fig. 2, of a portion of a component of the Fig. 2 station. Fig. 4 is a vertical sectional view, taken at 4-4 of Fig. 1, of the Fig. 2 station with its cradle in a position rotated from that shown in Fig. 2. Figs. 5 and 6 are diagrams of the vacuum activated drive system of the Fig. 2 station. Referring to Fig. 1, there is shown wafer handling apparatus 10, having arm 12 for moving wafers 13 from slots in plastics storage boats 14 into slots in quartz processing boat 16. Pickup paddle 11 is located at the end of arm 12 and has openings 15 connected to a vacuum source on its front and back faces to permit it to pick up and retain one or two wafers at one time. Arm 12 is horizontally and vertically movable in the Y-Z directions. Plastics boats 14 and quartz boat 16 are movable in the X direction by trolleys 17, 19, described in detail in the above-mentioned patent application. Intermediate station 18, which provides for reversing the orientation of the front and back faces of a wafer 13 between its removal from one of plastics boats 14 and its deposit in quartz boat 16 if desired, is attached to trolley 17 for movement in the X direction with plastics boats 14. Referring to Figs. 2-4, intermediate station 18 is shown to include cradle 20 for receiving wafers 13. Cradle 20 is mounted on horizontal support bar 22, which in turn is affixed to the top of vertical drive shaft 24. Drive shaft 24 in turn has drive pulley 26 (0.768"/1.95cm diameter) affixed at its lower end. Drive cable 28 engages drive pulley 26 as well as idler pulleys 30 and 32 (0.8"/2.03 cm diameters), and is connected at its end to vacuum actuators 34 and 36 (Airpot S160P150Y). Disk 38 is mounted above pulley 26 on drive shaft 24, and bears stop bar 40 on its upper surface. Stop bar 40 comes up against either adjustable stop screw 42 or adjustable stop screw 44 as disk 38 rotates, thus stopping the rotation of disk 38 and, in turn, drive shaft 24 and cradle 20. Disk 38 also has slots 46 and 48, which allow for a determination of the position of disk 38 when one of them becomes positioned between its respective infrared source/sensor device 50 or 52, the sources and sensors of which are located above and below disk 38. Adjustable stop screws 42 and 44 and infrared source/sensor devices 50 and 52 are mounted on intermediate support plate 54. The entire drive mechanism for the cradle is encased in housing 56 to protect wafers from contamination caused therein. Bearings 58 and 60 for drive shaft 24 are mounted in the top plate of housing 56 and in support plate 54, respectively. Seal 62 is located on drive shaft 24 between the upper plate of housing 56 and support bar 22. Fig. 3 shows two sets of slots 66, 68, 0.065 inches (0.165 cm) deep, in cradle 20 at four portions 69 (Fig. 4) for receiving two wafers therein. The positions of portions 69 are selected to ensure that only certain sections of the perimeter of a wafer contact the cradle and to accommodate small variations in diameters of wafers having the same nominal diameter. Figs. 5 and 6 illustrate the drive mechanism for intermediate station 18. Vacuum actuators 34 and 36 are connected to solenoid control valves 70 and 72, respectively. Solenoid valve 70 selectively connects the chamber of actuator 34 to either vacuum source 74 or flow restrictor 76. Solenoid valve 72 similarly selectively connects the chamber of actuator 36 to either vacuum source 74 or flow restrictor 78. Piston 79 of vacuum actuator 34 and piston 80 of vacuum actuator 36 are connected to the ends of drive cable 28 by links 82, 84. The overall operation of wafer handling apparatus 10 is described in detail in the above-mentioned patent applications. The standard transfer process involves picking up wafers from plastics boats 14 by arm 12 on paddle 11 and placing the wafers directly in quartz boat 16, the front and back faces of the wafers placed in quartz boat 16 retaining the same orientation they had in plastics boats 14. If one desires to reverse the orientation of the faces of selected wafers before placing them in quartz boat 16, this is accomplished by removing a wafer from a plastics boat 14 and depositing it in cradle 20 using arm 12, rotating cradle 20 180° to reverse the orientation of the faces of the wafer, retrieving the wafer from cradle 20 and placing it in quartz boat 16. Because the wafers are rotated mechanically by intermediate station 18, rather than manually, they are rotated simply and efficiently, and protected from damage and contamination. To rotate cradle 20 clockwise 180° from the initial position shown in Fig. 2, solenoid valves 70, 72 are placed in the control positions shown in Fig. 5 upon receiving control signals from a microprocessor controller (not shown), solenoid valve 70 being connected to vacuum source 74, and solenoid valve 72 being connected to flow restrictor 78. This causes piston 79 in vacuum actuator 34 to move away from idler pulley 32, drawing drive cable 28 with it. The speed with which the cable is drawn is determined by how much resistance is exerted on piston 80 by flow restrictor 78. Movement of drive cable 28 toward actuator 34 causes drive pulley 26 (upon which drive cable 28 is wound several times to prevent slippage) to rotate clockwise in turn causing drive shaft 24 and cradle 20 to correspondingly rotate. The extent of the rotation of cradle 20 is limited to 180° by means of disk 38 attached to drive shaft 24, the rotation of said disk being limited to 180° by virtue of stop bar 40 mounted thereon coming up against stop screw 42. In this position slot 46 is aligned with infrared source/sensor 52, providing a signal to the controller that cradle 20 is in this position. Flow restrictor 78 provides a slow five-second rotation of drive shaft 24 and cradle 20. This slow rotation minimizes jarring of the wafer contained in cradle 20, and so helps to minimize the possibility of wafer damage. To rotate cradle 20 counterclockwise back to the position shown in Fig. 2, solenoid valves 70, 72 are placed in the control positions shown in Fig. 6, solenoid valve 72 being connected to vacuum source 74, and solenoid valve 70 being connected to flow restrictor 76, causing cable 28 to move in the opposite direction. Cradle 20 moves 180° in the corresponding direction until stop bar 40 comes up against stop screw 44, thus returning to its original position, at which slot 48 is aligned with infrared source/sensor 50. Intermediate station 18 can be used to reverse the orientation of the faces of one or more wafers between pickup from plastics boats 14 and deposit in quartz boat 16. For example, alternate wafers can be reversed so that they are placed back-to-back in close proximity (i.e., the width of paddle 11) in the following manner. Arm 12 picks up a wafer 13 on paddle 11 from a plastics boat 14 and places it in cradle 20 for reversal. While that wafer is being reversed, arm 12 picks up another wafer from a plastics boat 14 on paddle 13. Still holding the second unreversed wafer on one side, paddle 13 picks up the reversed wafer from cradle 20 on its other side, the unreversed wafer being accommodated by the second set of slots in cradle 20 (Fig. 3) during pickup of the reversed wafer from cradle 20. These two wafers are then deposited in quartz boat 16. One advantage of using the vacuum actuator/flow restriction mechanism is that using a vacuum, as opposed to positive pressure, helps to prevent contamination by sucking away potential contaminants. A further advantage is its very simplicity; very few electrical connections and controls are required for its operation. Other embodiments are possible within the scope of this invention. For example, instead of providing flow restrictors 76, 78, their connections to solenoid valves 70, 72 could be closed, and one could rely on the small leakage in vacuum actuators 34, 36 to provide the flow restrictions. Also, in place of cable 28 and pulleys 26, 30, 32, one could use a chain and sprocket mechanism or other mechanical linkage mechanism. Also, cradle 20 could be made of a vertical plate having four (or a different number) of polytetrafluoroethylene horizontal members with slots for receiving wafers; an advantage to this structure is that the shapes of the slots and positions of horizontal members can be changed.

Claims: Apparatus for transporting flat objects having first and second faces between a first carrier and a second carrier, the apparatus comprising; support means adapted to support said first and second carriers; pickup means adapted to pick up said objects and to transport said objects between said first carrier and said second carrier; and intermediate station means adapted to receive said objects from said pickup means with said faces in a first orientation and to change the orientation of said faces before said objects are removed by said pickup means; and being characterised in that said intermediate station comprises: cradle means provided with a plurality of slots each adapted to receive a section of the perimeter of a said object, said plurality of slots being adapted to support said object with said first and second faces oriented generally in vertical planes in operation; and rotation means adapted to rotate said cradle means about an axis parallel to a said face with said object positioned in said plurality of slots in the said cradle; and in that said objects are orientated vertically throughout transportation by the said apparatus. Apparatus according to Claim 1, further characterised in that said rotation means comprises a first vacuum actuator connected to drive said cradle means. Apparatus according to Claim 2, further characterised in that said actuator is connected to a drive shaft connected to said cradle means, said actuator being connected to said drive shaft via cable means that engages a drive pulley on said drive shaft. Apparatus according to Claim 2 or Claim 3, further characterised in that said first vacuum actuator is adapted to rotate said cradle means in one direction, and in that said rotation means further comprises a second vacuum actuator adapted to rotate said cradle means in the other direction. Apparatus according to Claim 4, further characterised in that valves are provided adapted operatively alternately to connect said vacuum actuators to a vacuum source, so that the actuator that is not connected controls the speed with which the vacuum actuator that is connected rotates said cradle means. Apparatus according to any of Claims 2 to 5, further characterised in that said rotation means comprises stop means adapted to prevent rotation of said cradle means beyond a predetermined position at which a said object is in a position to be removed by said pickup means. Apparatus according to Claim 6, further characterised in that said stop means comprises a disk mounted for rotation with said cradle means, a stop bar mounted on said disk, and a corresponding stop member mounted apart from said disk in such a position that the stop bar mounted on said disk encounters said corresponding stop member once the cradle means has rotated to said predetermined position. Apparatus according to any preceding Claim further characterised in that said station includes sensing means adapted to determine the position of said cradle means. Apparatus according to Claim 8, further characterised in that said sensing means includes a disk mounted for rotation with said cradle means and having an opening through it, and an energy-beam source adapted and positioned to direct an energy beam along a path that intersects said opening in said disk when said support member and opening are aligned. Apparatus according to any preceding Claim wherein said flat objects are wafers. Apparatus according to Claim 10, wherein said pickup means has a flat pickup paddle adapted to engage said wafers on opposite paddle surfaces, and said cradle means has two sets of slots for receiving two wafers at one time. Apparatus according to any preceding Claim, further characterised in that said support means comprises first and second trolleys slidably mounted for movement along parallel directions, in that said pickup means comprises an arm movable in a transverse direction, and in that said intermediate station is mounted for movement with a said trolley. Apparatus according to Claim 12, further characterised in comprising: means adapted to move said first carrier into position under said pickup arm for pickup of a first object therefrom, means adapted thereafter to move said intermediate station under said pickup arm for receiving said first object, and means adapted to move said second carrier into position under said pickup arm after said pickup arm has removed said first object from said intermediate station in a changed orientation. Apparatus according to Claim 13 as appendant to Claim 11, further characterised in that said first carrier is arranged to be moved into position under said pickup arm for pickup of a second wafer on one face prior to picking up the wafer deposited at the cradle means on the other face. A method of translating and orienting flat objects having first and second faces, the method comprising the steps of: picking up an object from a first carrier and transporting said object to a second carrier while maintaining said object generally in a vertical orientation; and changing the orientation of the said faces of the object in the course of its travel between said first and second carriers by placing said object in a plurality of slots in a cradle means so that said object is supported with said first and second faces oriented generally vertically, and rotating said cradle means about an axis parallel to a said face.

Inventors: FOULKE, RICHARD F.
Applicants: PROCONICS INTERNATIONAL INC.
Application year: 1985
Main classification: H05K13
IPC codes: H01L21, B65G47