Material or article handling – Device for emptying portable receptacle – Nongravity type
Reexamination Certificate
1997-08-29
2001-02-06
Werner, Frank E. (Department: 3652)
Material or article handling
Device for emptying portable receptacle
Nongravity type
C414S937000, C414S940000, C414S749100, C414S222010
Reexamination Certificate
active
06183186
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductor wafer manufacturing and, more specifically, to a wafer handling system and method for transporting wafers during wafer processing.
During semiconductor fabrication, ingots are formed and sliced into wafers. The wafers are processed in many steps that require the wafers to be temporarily stored, transported and positioned. Wafer cassettes are often used for temporary storage and transportation of wafers. Cassettes are typically slotted containers which are open at the top and which have four sidewalls and a bottom. Inner surfaces of two opposing sidewalls are fluted to create slots. Individual wafers are each positioned within a respective slot and are held therein, separated from adjacent wafers. When a cassette is fully loaded, the wafers are located in respective slots and spaced apart from one another so that wafers do not abut.
Wafer containing cassettes are typically delivered to a wafer loading station. At such a station, wafers from the cassettes are loaded, for example onto a conveyor. The conveyor transports the individual wafers to a processing station where a manufacturing step takes place. Following the processing step or steps, the wafers are unloaded from the conveyor and delivered into a cassette at a wafer unloading station.
The loading station typically includes a mechanism for removing individual wafers from the cassette and transferring them to the conveyor. The unloading station also typically includes an unloader for returning the individual wafers to cassettes.
In one known approach, wafers are transferred from a conveyor to waiting cassettes utilizing a water slide unloader which, during operation, provides a continuous sheet of water across the entire slide, regardless of whether a wafer is present on the slide. The slide is tilted downwardly at an angle relative to horizontal so that water will flow down the slide. The water slide of this known construction has a uniformly flat planar bottom surface. As a wafer enters the top of the slide, it is supported entirely from below by the water sheet. Therefore, the undersurface of the wafer, adjacent to the upper surface of the slide, does not come into contact with the slide. Any such contact could scratch or otherwise damage the partially processed wafer. As the wafer travels down the slide, it in effect surfs on the sheet of water. That is, the leading (downwardmost) edge of the wafer is elevated relative to the trailing edge by the water as it travels down the slide. In water slides of this type known to the inventors, substantial quantities of water are caused to flow down the water slide. For example, it is not unusual for these known water slide systems to use one hundred gallons of water per hour or more.
These water intensive systems are disadvantageous because relatively expensive distilled water is typically used in these applications. Moreover, water is becoming a scarcer and more costly resource.
Among the known loaders which remove wafers from the cassette are mechanisms described in U.S. Pat. No. 5,299,901. This latter patent specifically describes mechanisms for removing wafers from cassettes and transferring them to a wafer “boat”. Early mechanisms used mechanical tweezers or vacuum tweezers to grip individual wafers and remove them from the cassette and move them. However, these gripper mechanisms could damage some of the wafers. A later transfer mechanism used a “pusher” to push individual wafers up and out of a cassette. A pair of clamps would then grip the wafer and remove it.
In the wafer loader described in the '901 patent, a cassette is attached to a platform and inverted. A wafer boat is located below the inverted cassette. A “lifter” is raised into position below a wafer so that the wafer comes to rest on the lifter. The lifter is then lowered and the wafer, resting on the lifter, descends into the awaiting boat. The wafer is thus loaded from the cassette to the boat.
The wafer transfer mechanism described in U.S. Pat. No. 5,299,901 thereby transfers wafers between devices that can be moved and located vertically atop one another. It does not appear capable of transferring a wafer to another device that is located in a horizontal plane; nor does the transfer mechanism of this patent appear capable of placing a wafer on a horizontal surface. These are some of the limitations that prevent this prior art transfer mechanism from efficiently transferring wafers to some types of work stations and horizontal conveyors.
Another known wafer loader has an elongated arm which is inserted beneath a wafer in a cassette. The arm is removed from the cassette with a wafer coupled to the arm using a vacuum. The arm is then rotated about its longitudinal axis to turn the wafer over for delivery to a second location.
U.S. Pat. No. 5,525,024 discloses yet another form of cassette loader.
Although these prior art wafer handling and transfer mechanisms exist, a need nevertheless remains for an improved wafer handling system and method.
SUMMARY OF THE INVENTION
The present invention provides a wafer handling system and method which loads individual wafers from a wafer cassette onto a conveyor, work table or other location for wafer processing and subsequently unloads individual wafers following processing into wafer receiving cassettes.
Wafer containing cassettes are loaded into a cassette holder of a cassette positioner of a loading station. The cassette positioner shifts the cassettes to position individual wafers in the cassettes into position for extraction by a loader which then places the wafers onto the conveyor or other destination location. Following processing, an unloader retrieves the individual wafers and loads them into cassettes held by a cassette holder of a cassette positioner of an unloading station. The cassette positioner of the unloading station positions the cassettes for receiving the individual wafers from the unloader. The cassettes, after they have been filled with wafers, are removed from the unloading station.
In the preferred arrangement, the cassettes are loaded onto the cassette holder from the rear of the loading station and the loader places the individual wafers onto a conveyor at the front of the loading station. Empty cassettes are also removed from the rear of the loading station. Also, in this construction the unloader retrieves processed wafers from the front of the unloading station with the filled cassettes being removed from the rear of the unloading station. Empty cassettes are also placed onto the cassette holder of the unloading station from the rear of the unloading station. Consequently, in this specific form of the invention, the wafers proceed in one direction through the loading station, the wafer processing stage, and the unloading station.
In a preferred construction of the present invention, the cassette holders and cassette positioners of the loading and unloading stations have interchangeable components to simplify the repair of these subsystems in the event this becomes necessary.
In the wafer handling system of the present invention, the wafer cassette positioners support and shift wafer cassettes having a plurality of wafer holding slots to successively position the respective wafer holding slots at a wafer transfer location. The preferred form of wafer cassette positioner comprises a frame with first and second spaced apart cassette holders coupled to the frame. The first and second cassette holders are each configured to hold at least one wafer cassette with the wafer holding slots of the wafer cassette being generally horizontal. The first cassette holder is coupled to the frame so as to be movable, and most preferably slidable, from a first position to a second position. When in the first position, the at least one wafer cassette supported by the first cassette holder is in a wafer transfer zone. When in the second position, the at least one wafer cassette supported by the first cassette holder is at a second location or cassette transfer zone spaced from the wafer
Gorman Andrew P.
Howells John
Peltola Randall W.
Daitron Inc.
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Werner Frank E.
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