WO2003050022A1

WO2003050022A1 - Monorail semiconductor wafer cassette transport system

Info

Publication number: WO2003050022A1
Application number: PCT/US2002/038796
Authority: WO
Inventors: Paul S. Whalen
Original assignee: Intrabay Automation, Inc.
Priority date: 2001-12-11
Filing date: 2002-12-05
Publication date: 2003-06-19
Also published as: AU2002359603A1

Abstract

This invention relates to semiconductor wafer processing systems and more particularly relates to a system for efficiently and automatically transporting semiconductor wafer cassettes throughout a processing plant. The system is comprised of a monorail (12) and a train (10) formed of a plurality of cars (14) riding on the monorail (12). The train (10) is driven by a plurality of stepper motors (20) equally spaced at distances along the monorail (12) sufficient to keep the train (10) moving. Each drive system is comprised of a stepper motor (20) and four Thrombil wheels that provide very low particle generation. The stepper motor (20) operates on a low duty cycle because it only operates when needed which is when a train (10) is passing over the stepper motor (20) and drive wheels. At other times, the motor is off lenghthening the life of the system.

Description

SPECIFICATION TITLE; MONORAIL SEMICONDUCTOR WAFER CASSETTE TRANSPORT SYSTEM BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to storage, retrieval, transfer, and transport of semiconductor wafer cassettes or containers in an automated wafer processing system and more particularly relates to a monorail semiconductor wafer cassette transport system comprised of a plurality of carriers for intra-stocker transportation of semiconductor wafer cassettes.

2. Background Information

The present semiconductor wafer carrier cassette transport systems for storing, retrieval, transferring, and transporting cassettes from stocker to stocker and from one process station to another are both complex and expensive. One such system has a monorail and single cassette carriers inductively powered and remotely controlled. Each carrier must have a complex drive and control system making the system expensive and complex to build and operate.

Integrated circuit (IC) manufacturing from semiconductor wafers involves hundreds of processors spread out over a wide area requiring the transfer of the semiconductor wafers from one processing location to another. Throughout the fabrication process, semiconductor wafers are transferred in sealed cassettes. The semiconductor wafers must be kept in a Class 1, substantially contaminant-free environment, throughout the fabrication process.

While awaiting processing, the sealed cassettes for the .semiconductor wafers are stored in an enclosure known as stockers. Each container may have up to 75-300 mm (12 inch) semiconductor wafers. The cassettes are manually or by complicated automatic transfer and transport systems moved out of the stockers to a port or window to a processing station. After each process is complete, the semiconductor wafers are returned to the cassettes and then usually delivered back to a stocker to await further processing or to another stocker at the next processing step. There will be many stockers strategically placed at intervals along the production line for easy access by personnel performing the processing.

Stockers generally have a plurality of shelves inside a substantially rectangular enclosure. Semiconductor wafer cassettes are returned and retrieved through a port or window in the stocker. After a particular process is complete, the semiconductor wafer cassettes is manually or by automatic transport system returned to a shelf at the in/out window or port. An automatic pick-up and transfer apparatus picks up the semiconductor wafer cassette and places it on an empty shelf in the stocker to await the next processing step.

Cassettes are moved from stocker to stocker or from stocker to a processing station by an inter-stocker transport system such as that shown in U.S. Patent No. 6,129,496 of J. Iwasaki et al issued October 10, 2000. This patent discloses a system including a monorail and having carriages for transporting up to two cassettes throughout a processing plant. The patent disclosed and describes an inter-stocker transportation device that includes a circulating rail. The carriage drive system is not described but is probably an indirect system using the rail. The circulating rail, described as conventional, is comprised of a travel rail forming a loop having carriages for moving up to two cassettes at a time on the carriage.

Another patent that describes a transport system is shown in U.S. Patent No. 5,570,990 of Bonora et al. This patent discloses and describes a mobile loader stocker as part of an overhead transport automated system. The system includes an overhead, horizontal shuttle that is described as standard conveyor belt or roller conveyors known in the art.

Another patent showing a wafer conveying system is disclosed and described in U.S. Patent No. 5,443,346 of Murata et al issued August 22, 1995. This patent discloses a wafer conveying system in a clean room and includes a conveying rail and a platform or conveying equipment that moves on the conveying rail by a linear, motor-driven conveying equipment such as magnetic levitation type. The wafer conveying platform includes a wafer placing unit for placing wafer cassettes on the carriage. This device is complicated to operate and expensive to build.

It is, therefore, one object of the present invention to provide a semiconductor wafer cassette automatic monorail transport system.

Still another object of the present invention is to provide a semiconductor wafer cassette automatic monorail transport system which is simple in construction and relatively easy to operate.

Yet another object of the present invention is to provide a semiconductor wafer cassette automatic transport system comprised of a monorail and a train having a plurality of carriers for transporting a substantial number of wafer cassettes per hour.

Yet another object of the present invention is to provide a semiconductor wafer cassette automatic monorail transport system that is capable of transporting several hundred semiconductor wafer cassettes per hour.

Still another object of the present invention is to provide a semiconductor wafer transport system that is constructed to pass through wafer cassette stockers and transport the cassettes from one stocker to another during the processing of the wafers.

Still another object of the present invention is to provide a semiconductor wafer cassette automated system that is integrated into a complete automated storage, tracking, and retrieval system.

Yet another object of the present invention is to provide a semiconductor wafer cassette automated transport system that includes a plurality of carriers on a monorail track that is operated in a completely closed system.

Still another object of the present invention is to provide a semiconductor wafer cassette automated transport system having a monorail track system that is low in cost and permits the use of redundant tracks. This allows product or wafer cassettes to be delivered close to where they are needed for processing.

Still another object of the present invention is to provide a semiconductor wafer automated transport system including a monorail and a train that is simple in construction and has no electronics.

Yet another object of the present invention is to provide a semiconductor wafer cassette transport system automated transport system that has electrically operated stepper motors on the track that are simple to remove and replace and reliable in operation.

Yet another object of the present invention is to provide an automated transport system for semiconductor wafer cassettes that utilizes stepper motors providing a very low duty cycle since the motors only turn on just before train arrival.

Yet another object of the present invention is to provide an automated transport system for semiconductor wafer cassettes that is low in particle generation to prevent and minimize contamination of the semiconductor wafer processing area.

Still another object of the present invention is to provide an automated transport monorail train system that can have up to six cars for transporting six semiconductor wafer cassettes simultaneously and that has no consumables and is operated on very simple logic. BRIEF DESCRIPTION OF THE INVENTION

The purpose of the present invention is to provide an automated transport system for transporting semiconductor wafer cassettes that is simple in construction, reliable in operation, and can transport hundreds of cassettes per hour.

The semiconductor wafer cassette automatic transport system is comprised of a train having a plurality of cars that travel along a monorail throughout the processing plant. The monorail is a flat suspension plate having an edge forming a track that traverses a path throughout the processing plant to deliver semiconductor wafer cassettes to stockers at each processing station.

The semiconductor wafer cassette train is preferably comprised of up to six cars linked by couplings that travel on the monorail. Each car is identical and is linked to an adjacent car by a cylindrical steel shaft engaging a coupling having shielded miniature ball bearings and mating surfaces that minimize particle generation to prevent contamination. The forward end of the train is a bare truck comprised of a support frame having a channel or slot for engaging the monorail with a wheel formed of a material that minimizes particles generation in the channel. The upper traveling edge of the monorail is coated with a black anodized hard coated process to also minimize particle generation. The base truck or support frame establishes a trajectory for the semiconductor wafer transport train.

Each car of the train has a truck comprised of a swiveling carriage having a horseshoe shaped frame with a channel or slot fitting over the monorail. A traversing wheel in the channel slot rests on the monorail anodized surface. Each truck frame has flanges on either side of the monorail slot with wheel bases attached to the flanges for mounting guide wheels to keep the truck centered on the monorail. A pedestal having a bearing and a disk-shaped mounting plate for swivelly supporting a semiconductor wafer cassette support plate is mounted on top of the truck frame. The semiconductor wafer cassette support plates are bolted to the circular mounting plate on the truck frame. The semiconductor wafer cassette automatic transport system of the present invention preferably has six cars that can transport up to six cassettes from stocker to stocker. This is in contrast to present complicated systems which can transport a maximum of only two cassettes. Also the transport system is operated by a friction drive stepper motors positioned at various spaced apart points around the monorail to drive the train by a drive bar or ski. The stepper motors drive a plurality of Thrombil rollers to minimize particle generation. The Thrombil rollers engage the drive bar or ski attached to each car of the train. Each stepper motor is positioned a distance from the adjacent stepper motor such that a drive bar or ski attached to each car on the train is always in contact with a stepper motor.

A photodetector at each stepper motor detects when a car has arrived or is leaving a stepper motor to activate or shut off the drive motor. Thus, the stepper motors operate on a very low duty cycle and turn on only when needed. Preferably a spacing of approximately six feet per each stepper motor attached to the bottom of the monorail by quick release clips make the system modular allowing for the removal and replacement of a stepper motor rapidly should a malfunction occur.

Each car of the train is connected to the adjacent car by a cylindrical steel shaft having a coupling comprised of a pin engaging a shielded miniature ball bearing. The coupling is attached to the frame or yoke forming the truck for each car of the train. The frame has a channel or recess that fits around the upper edge of the monorail and a wheel mounted in the channel that rests on the monorail black, hard anodized coated edge to minimize particle generation. Flanges on the ends of the truck frame provide mounting holes for a wheel base for mounting guide wheels that engage the flat, opposite sides of the monorail to keep each car of the train centered on the monorail.

Train cassette support platforms are attached to a cylindrical disk mounted on a pedestal. The pedestal is swivelly attached to the upper end of the truck frame to allow the cassette support platform to swivel when the trucks of each car are traversing a bend in the monorail.

Each semiconductor wafer cassette platform is substantially rectangular in shape with centering pins and retaining pins at each corner of the rectangular support platform. A recess in the loading side of the support platform provides clearance for the linear arm of a semiconductor wafer cassette retrieval and transfer system that loads cassettes on the train.

Another unique aspect of the invention is that the train and monorail are constructed to pass through the stockers allowing efficient, quick transfer of semiconductor wafer cassettes to the support platform. A stepper motor and photodetector attached to the monorail inside the stocker stop each car at a position for loading a semiconductor wafer cassette by the retrieval and transfer system linear arm. A bar code reader on the linear retrieval and transfer linear arm reads the bar code of a semiconductor wafer cassette, picks it up, and then places it on the car stopped at the station inside the stocker. Once loaded, the train will move forward to the next car or will automatically go to the next stocker if the train is full or there are no more cassettes to load.

Another unique aspect of the invention is that the semiconductor wafer transport system is comprised of a train that require very little control and can be operated by a single bit of a program. The program detects movements of the train to turn it off, to move it to the next station or stocker and to stop it adjacent to or inside a stocker for retrieving or storing semiconductor wafers cassette.

All parts of the semiconductor wafer cassette automatic transport train are constructed of materials to minimize particle generation. For example, each of the four wheels on the stepper motor drive system are constructed of a low particle generation Thrombil to minimize particle generation when the drive bar or ski engages the wheels. Likewise, the truck centering wheels mounted on the wheel base attached to the truck horseshoe shaped frame are made of similar low particle generation material. The same applies to the wheel in the channel recess that straddles the monorail and rests on the anodized upper edge. Likewise, the shielded miniature ball bearings in the truck coupling for attaching the end of the cylindrical steel pivoting links are made of materials that minimize particle generation.

The above and other novel features of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a semiconductor wafer cassette automatic transport system constructed according to the invention.

Figure 2 is an enlarged partial section of a single car of the semiconductor wafer cassette automatic transport system.

Figure 3 is a sectional view of one car of the train taken at 3-3 of Figure 1.

Figure 4 is a sectional view taken at 4-4 of Figure 3.

Figure 5 is a sectional view taken at 5-5 of Figure 3.

Figure 6 is a top view of the transportation system passing through a stocker to pick up and transport semiconductor wafer cassettes.

Figure 7 is a sectional view through a rectangular stocker illustrating the retrieval and transfer of a semiconductor wafer cassette to the automated transport system constructed according to the invention.

Figure 8 is a top view of the automated transport system passing through a kiosk-type stocker. DETAILED DESCRIPTION OF THE INVENTION

An automatic semiconductor wafer cassette transport system that can transport hundreds of cassettes per hour throughout a processing plant as illustrated in Figure 1. The transport system is in the form of a train 10 that travels on a monorail 12 that circulates throughout the processing plant. In some cases the monorail may be a mile or more long traveling throughout the processing plant and even from one building to another. Wafer cassette train 10 is preferably comprised of up to six cars 14 mounted on truck frames 16 that straddle monorail 12 constructed of a flat metal plate having an edge 28 forming a track. Each car 14 in train 10 has a drive bar or ski 18 for advancing the train on monorail 12.

The unique aspect of this system is the use of a stepper motor drive system 20 spaced at intervals along monorail 12 to engage drive bar or ski 18 to continuously move train 10 throughout the processing plant. Stepper motors 20 drive rollers 22 that frictionally engage drive bar or ski 18 to advance the train. Stepper motors operate on a low duty cycle and only operate when needed. That is, the motor is not activated until a train approaches stepper motor 20. A photocell or detector 24 in the housing of each stepper motor 20 detects the approaching train and starts rotation of roller 22 to advance the train. Stepper motors 20 are spaced at intervals such that at least one drive bar or ski 18 on train 10 is in engagement with a set of drive rollers 22.

Figure 2 is a partial sectional view of a single car 14. Car 14 is comprised of a frame 16 straddling monorail 12 having wheel 26 resting on a black anodized edge surface 28 forming a track of monorail 12 to minimize particle generation. All parts of the monorail and the train cars 14 are constructed in a manner and of materials that minimize particle generation. Guide wheels 30 are mounted on wheel bases 32 attached to truck frame 16 to keep car 14 centered on monorail 12. Cassette support plate or platform 34 is mounted on a pedestal 36 (Fig. 3) for supporting a cassette 36 as will be described in greater detail hereinafter. Each corner of cassette support platform 34 has a centering pin 38 and a pair of retaining pins 40 positioned to engage the corners of semiconductor wafer cassette 36. The details of the construction and mounting of the cars of train 10 are shown in greater detail in Figures 3 through 5. Each car 14 has a swiveling carriage 16 with a recess 42 for receiving riding wheel 26 that straddles monorail 12. Flanges 44 on either side of recess 42 on swiveling carriage 16 support wheel bases 32 for mounting guide or wheels 30 that keep truck frame or carriage 16 centered on the vertical plate monorail 12.

Wafter cassette support plate 34 is mounted on disk 46 formed on swivel mounted pedestal 36. Pedestal 36 is pivotally attached to the top of truck frame 16. Drive bar or ski 18 is attached to pedestal 36 by support 19 secured to one side of the pedestal.

The train is driven by stepper motors 20 spaced at intervals along the bottom edge of monorail 18 which are secured by quick release clamps 21 at either end of stepper motor housing 20. It is an object of this invention to keep the automated transport system as simple as possible and modular in construction so that maintenance and replacement of parts can be achieved economically and quickly. For example, stepper motors 20 secured to the bottom of monorail 12 by quick release clamps 21 allows rapid replacement should one of the motors fail. However, due to the low duty cycle of these motors, it is expected that such failures will be at a minimum. The stepper motors only turn on when needed. That is, detector or photocell 24 detects an approaching drive bar or ski 18 and turns on stepper motor 20 to advance the train. Once the train has passed a particular stepper motor, the motor turns off to await the next train. Each car 14 in train 10 is attached to the next train by a cylindrical steel shaft 48 securely attached to pedestal 36 at one end and pivotally attached to coupling 50 at the other end as illustrated in Figure 4. Cylindrical steel shaft 48 has a pivot pin 52 engaging a socket 56 in coupling 50. Coupling 50 is bolted to the upper end of truck frame 16. Thus, each car 14 of train 10 can be quickly removed by removing pivot pin 52 from coupling 50 from the car ahead as well as the pivot pin in cylindrical shaft 48 from the car behind. The complete car assembly can then be easily lifted off the monorail 12 for repair or replacement.

Steel shaft 38 connecting one car to another is mounted in a socket on coupling 50 having a bearing and seated with pin 52. The bearing and socket are constructed to allow steel shaft to swivel side to side for traversing bends or corners in monorail 12 while allowing cars to be easily separated from the train for repair or replacement.

Stepper motor provides power to drive wheels 22 that engage ski 18 attached to bearing and mounting housing 36 forming a pedestal on top of truck frame or carriage 16. Stepper motor and housing 20 is secured on monorail 12 by quick release clamps 21 at each end of the housing. This allows the stepper motor electronics to be easily removed and replaced if a malfunction occurs.

The operation of the automatic transport system for transporting semiconductor wafer cassettes throughout the processing plant is illustrated in Figures 6 through 8. In one embodiment, train 10 passes through a rectangular semiconductor wafer stocker 54. Stocker 54 has a plurality of shelves 56 for storing a plurality of semiconductor wafer cassettes in between processing steps. Stocker 56 has a retrieval and transfer system 58 having a linear arm 60 for retrieving and transferring cassettes to train 10. Stocker 54 is similar to that shown and described in U.S. Patent Application Serial No. 09/845,538 filed April 30, 2001 by the same inventor herein.

In this embodiment, monorail 12 passes through opening 58 into the interior of stocker 54. A stepper motor beneath semiconductor wafer cassette platform 14 * includes a photocell circuit that starts each car inside the stocker to receive a wafer cassette. Once car 14' is stopped, linear arm 60 on retrieval and transfer system 58 picks up the appropriate cassette by reading the bar code and deposits it on the cassette storage platform with centering pins 38 engaging sockets in the corners of the semiconductor wafer cassette and retaining pins 40 retaining the cassette on the platform of car 14 ' . When a cassette has been replaced or removed from car 14', a command is then automatically given to advance the train to the next car that is empty. In some cases, a car may have a cassette from an earlier stocker that is going to a different position and will automatically be bypassed when the bar code is read.

The forward end of train 10 has a base support frame 16* without the mounting plate or pedestal that establishes a trajectory for the train around the path of monorail track 12.

In operation, train enters stocker 54 through opening port 58 and traverses through the inside of the stocker. A photodetector on the stepper motor detects the position of each car and stops the empty car for receiving a cassette to be transported. Retrieval and transport system 58 reads the bar codes on the cassettes in the container and determines the correct container to retrieve, picks the container up, and deposits it on car 14'. After a wafer cassette container 36 is loaded on car 14 ' , the train 10 advances to the next position and is its position is detected by the photodetector and stops for receiving another cassette. In the meantime retrieval and transfer system 58 linear arm 60 picks up another cassette after reading the bar code to check that it is the correct cassette and places it on the next cassette support platform. Thus up to six cassettes can be rapidly retrieved and placed on cassette train 10 and then transported to the next processing area or stocker.

Figure 8 shows another embodiment of the invention in which automatic transport train 10 travels on monorail track 12 through a kiosk type stocker such as that disclosed and described in U.S. Patent Application Serial No. 09/873,779 filed June 4, 2001 by the same inventor as the inventor herein. Kiosk stocker 70 is somewhat semi-circular in construction and carries up to 20 cassettes with some being inside and some being outside stocker 70. The operation of the kiosk stocker is described in the above-identified patent application. Automatic transport system in the form of train 10 enters kiosk stocker 70 through opening 72 and travels along the curvature of monorail 12. A retrieval and transfer system 58 identical with that used in the embodiment of Figures 6 and 7 retrieves wafer cassettes from shelves inside the kiosk stocker and places them on cars 14 on the train. Centering pins 38 and retaining pins 40 securely hold wafer cassette on platform 14.

In one embodiment, the wafer cassette transport train 10 will be on one level of the building with kiosk stockers 70 being on multiple levels. Retrieval and transfer system 58 will retrieve and transfer wafer cassettes either from the lower level or the upper level to wafer transport train for delivery to another stocker or a processing station.

The kiosk stocker is unique because it has storage positions both inside and outside stocker 70. The outside position or shelves 74 allow placement of wafer cassettes manually to quickly and rapidly replace wafer cassettes that have been retrieved from inside kiosk stocker 70. When retrieval and transfer system 58 picks up a cassette and places it on the support platform of car 14 , it leaves an empty position inside kiosk stocker 70. Each shelf 74 has an automatic system that advances the cassette on that shelf forward to the inside of the stocker to await retrieval by the pick up and transfer system in the next pass.

Various configurations are possible. Transport automatic semiconductor wafer cassette transport train 10 may have up to six cars or as little as four cars. Thus there has been disclosed a novel, automatic semiconductor wafer cassette and transport system that can retrieve and transfer hundreds of cassettes efficiently in a relatively short period of time. The system is simple in construction and easy to operate. The system uses a unique drive system of spaced apart stepper motors that are only in operation at certain time resulting in a very low duty cycle and increasing reliability. The semiconductor wafer cassette train is comprised of a plurality of cars having a support platform mounted on a swiveling pedestal having a disk that is also mounted on top of the truck frame or carriage. The truck frame or carriage has a recess with a wheel that straddles the monorail and a wheel base mounted on flanges at the end of the frame that engage the flat sides of the monorail to maintain the cars centered on the monorail.

In addition, all the parts are constructed in a fashion to be modular for easy maintenance and repair. For example, stepper motor is mounted on the bottom edge of the monorail by quick release clamps that allows a defective stepper motor to be quickly removed and replaced. However, the stepper motors have an extremely low duty cycle since they are only on when needed minimizing their replacement. In another aspect of the invention, the transport system provides a monorail that passes through the stockers to retrieve or replace semiconductor wafer cassettes on the stocker. The stocker includes a retrieval and transfer system having a linear arm that detects the stocker to be removed by a bar code, picks it up, and places it on a car on the train. The system automatically then advances the train to the next car to determine whether a replacement is needed. The system operates with either a rectangular stocker having open sides or a kiosk stocker in which it passes completely through the stocker. It also operates with multiple level kiosk stocker.

Obviously many modifications and variations of the invention are possible in light of the above teachings and it is therefore, to be understood, that the full scope of the invention is not limited to the details disclosed herein, but only by the claims appended hereto, and may be practiced otherwise and as specifically described.

Claims

WHAT IS CLAIMED IS :

1. An automatic semiconductor wafer cassette transport system comprising; a monorail; a train having a plurality of cars constructed to travel on said monorail; a drive system for driving said train, said drive system comprising; a plurality of stepper motors attached at spaced apart intervals to said monorail; said stepper motor constructed and arranged to drive said train; whereby said train an transport a plurality of semiconductor wafer cassettes quickly and efficiently throughout a processing plant.

2. The system according to Claim 1 in which; said stepper motors each drive a plurality of rollers; said rollers positioned to engage a drive mechanism attached to said train.

3. The system according to Claim 2 in which said drive mechanism comprises one or more drive bars attached to said train.

4. The system according to Claim 3 in which each car of said plurality of cars has a drive bar, said drive bar positioned to frictionally engage said rollers when said train passes over a stepper motor.

5. The system according to Claim 4 in which said stepper motor is attached at equally spaced intervals to the bottom edge of said monorail.

6. The system according to Claim 5 in which said plurality of stepper motors are attached to the bottom edge of said monorail by quick release clamps whereby a defective stepper motor may be quickly released for repair or replacement.

7. The system according to Claim 1 in which said monorail is constructed to pass through semiconductor wafer casette stockers for storing said cassettes whereby said automatic semiconductor wafer transport train enters said stocker for receiving or depositing semiconductor wafer cassettes.

8. The system according to Claim 7 in which said semiconductor wafer cassette stocker is a semi-circular kiosk type stocker; said automatic semiconductor wafer cassette transport train and monorail traversing a semi-circular path through said stocker for depositing or retrieving semiconductor wafer cassettes.

9. The system according to Claim 7 in which said semiconductor wafer cassette stocker is a rectangular stocker, said automatic semiconductor wafer transport train and monorail traversing a linear path through one side of said rectangular stocker and out the opposite side.

10. The system according to Claim 9 including a detector for detecting when said automatic semiconductor wafer transport train is passing through said stocker; said detector stopping said automatic transport train at a position for receiving or removing a semiconductor wafer cassettte from a car of said train.

11. The system according to Claim 10 in which said detector is a photodetector.

12. The system according to Claim 11 in which said photodetector stops said automatic semiconductor wafer cassette transport train on command to incrementally move from car to car of said train for filling empty cars on said train.

13. The system according to Claim 1 in which said cars comprise; a U-shaped frame having a channel straddling said monorail; a roller mounted in said channel resting on an upper edge of said monorail; a semiconductor wafer cassette platform mounted on top of said U-shaped frame.

14. The system according to Claim 13 in which said platform is pivotally mounted on top of said frame.

15. The system according to Claim 14 in which a pedestal is pivotally mounted on said U-shaped frame; said cassette platform being mounted on said pivotally mounted pedestal.

16. The system according to Claim 15 including a drive bar attached to each car of said train for engaging said rollers on said stepper motor.

17. The system according to Claim 16 in which said drive bar has a length sufficient to span the rollers on said stepper motors.

18. The system according to Claim 17 in which said drive bar is supported by said pedestal on top of said U-shaped frame.

19. The system according to Claim 18 in which each car has a coupling mounted on a rear surface of said U-shaped frame; each car being coupled to the next car by an elongate shaft and pin engaging said coupling.

20. The system according to Claim 19 including a bare frame at the front of said train coupled to a first car of said train; said bare frame establishing a trajectory for said automated semiconductor cassette transport train.