Conveyors: power-driven – Conveyor section – Reciprocating conveying surface
Reexamination Certificate
2002-04-01
2004-03-16
Ridley, Richard (Department: 3651)
Conveyors: power-driven
Conveyor section
Reciprocating conveying surface
C198S775000
Reexamination Certificate
active
06705457
ABSTRACT:
TECHNICAL FIELD OF APPLICATION
The present invention relates to a transport device and a method of transporting to-be-processed elements, in particular, substrates or wafers, through a high-temperature zone, such as they have to pass through, for example, in processing solar cells.
Transport devices are known for all kinds of objects in many fields of technology. Particularly, in the field of semiconductor production, a transport system for the to-be-processed elements has to fulfill special requirements, because neither the elements themselves nor the individual process stations should be contaminated by the transport systems.
STATE OF THE ART
In order to avoid impurities, it is known in the art, to operate the individual process stations, in particular, the high-temperature zones or furnaces, in charges. In the field of semiconductor technology, such a type of furnace usually consists of a high-temperature resistant process tube composed of high-purity quartz glass or silicon carbide. A heating means surrounding this process tube heats the interior, the processing zone, formed by the process tube to the process temperature. Prior to introduction into the furnace, a plurality of the to-be-processed elements are first placed on quartz glass or silicon carbide substrate carriers, which are only used especially for the high-temperature zones. Then, the carrier with the elements is conveyed into the process tube in order to conduct the high-temperature processing. After processing, the carrier with the elements processed in this manner is conveyed out of the furnace and the elements are transferred into other transporting carriers after cooling to approximately room temperature. Transporting into and out of the furnace occurs by means of a paddle, made of silicon or quartz glass, which engages the carrier.
This charge operation has, on the one hand, the advantage of high purity, because all the carriers and drive elements are made of high-purity materials such as quartz glass or silicon carbide. On the other hand, in some cases charge operation, however, leads to undesirable intermittent production flow.
Numerous processes, in which the purity requirements during processing are not as high, also use transport systems for continuous in-line transport through the processing zone. Thus, for example, in silicon solar cell production, in which the-to-be processed silicon wafer is subjected to several high-temperature steps, it is known in the art to utilize circulating conveyor belts to transport the silicon wafers through the high-temperature zones. The silicon wafers are placed on the conveyor belts, which usually are designed as so-called carrying-chain conveyors.
FIG. 1
shows a diagram of an example of such a type of transport system. The circulating chain belt
1
runs through the processing zone
3
over a plurality of deflection rollers and a drive shaft
2
. The to-be-processed silicon wafers
4
are placed flat on the chain belt
1
and transported by it into and out of the processing zone
3
. The belts designed as braided chains of these prior art transport systems usually are composed of nickel chrome compounds. However, the high temperatures occurring particularly in processing zones result in diffusion of metal ions from the conveyor belt into the to-be-processed elements located thereon. As, silicon solar cells, in particular, react to even the smallest metallic impurities, these metal atoms which diffuse into the solar cell diminish the performance of the solar cells. Moreover, the uninterrupted transport of the belt into the processing zone may continuously carry in further impurities from the outside.
To decrease the first-mentioned problem of diffusion of metal ions, the conveyor belt can be coated with a ceramic material. However, the use of such a type of transport system displays other disadvantages especially when utilized in high temperature zones. Thus considerable amounts of energy have to be employed to heat the conveyor belt at the inlet of the furnace and to cool it again at the outlet of the furnace during operation of the system. The conveyor belt enters the furnace at about room temperature, has to be heated in it to 1000° C. and should leave the furnace again at about room temperature. The great thermal mass of the metal belt leads to undesired energy losses and also limits the flexibility of conducting the process so that, for example, no rapid heating can occur in the form of a so-called temperature jump.
Another prior art device for contamination-free transport of substrates or wafers through a treatment path is known from DE 198 57 142 A1. This device utilizes the principle of air-cushion transport, in which, for transport, a gas flow is impinged onto the substrates or wafers. In this device, the transport track is provided with lateral guide guards and numerous gas jets disposed on its bottom. With such a type of air-cushion transport, however, the processing atmosphere may be influenced by the transport gases flowing in.
From EP 486 756 A12 is known a conveyor device for an in-line furnace in which the transport of boards, in particular printed circuit boards or glass-mat-reinforced thermoplastics, occurs via in-parallel-running continuous steel transport cables stretched over deflection rollers located outside the in-line furnace. The drive for these transport cables is provided with a device for reversing the movement in order to always lead the same length of each transport cable through the in-line furnace, thereby preventing splicing for connecting the two ends of the continuous transport cable from entering the in-line furnace and unraveling due to the temperature stress. The conveyor device consists of, in addition, other carrier elements with a lift-and-lower mechanism, which pick up the boards transported through the continuos flow furnace on the return movement of the transport cables. In order to minimize the bearing surface of the to-be-transported boards, the carrier elements of the lift arrangement is also formed of tightly stretched carrier cables.
DE 28 30 589 C2 discloses an in-line furnace for processing small semiconductor boards utilizing walking beam transport technology. In this transport device, for example polysilicon is employed as the material for these walking beams to avoid contamination of the semiconductor material by metallic substances.
The object of the present invention is to provide a transport device and a method of transporting to-be-processed elements through a high temperature zone without the above-mentioned drawbacks. The device and the method should, on the one hand, permit low-contamination transport through the high temperature zone and, on the other hand, permit better energy exploitation during processing and the use of rapid temperature change in the high temperature zone.
DESCRIPTION OF THE INVENTION
The object is solved with the transport device and the method of the claims. Advantageous embodiments of the device and of the method are the subject matter of the subclaims.
The invented transport device for transporting to-be-processed elements through a high temperature zone consists, at least, of a first pair of elongated carrier elements running in parallel and at least one drive mechanism for the carrier elements. The drive mechanism drives the carrier elements to a recurrent lift-and-forward movement on a closed track. The drive mechanism is designed in such a manner that the carrier elements execute a forward movement on an upper half of the track and return on a lower half of the track into a starting position. The transport device is distinguished, in particular, by the elongated carrier elements being composed of a flexible material which is maintained under tensile stress along the longitudinal axes of the carrier elements, which allows using very thin carrier elements, because there is no fracture risk.
The transport kinematics of such a type of device is basically known under the term walking beam principle. This walking beam principle is utilized in other fields of technology for transp
Biro Daniel
Lenz Reinhard
Völk Peter
Wandel Gernot
Breiner & Breiner L.L.C.
Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung
Ridley Richard
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