Process and arrangement for continuous treatment of objects

Details Process and arrangement for continuous treatment of objects Process and arrangement for continuous treatment of objects

2000-02-22

2002-07-23

Ellis, Christopher P. (Department: 3651)

Material or article handling

Apparatus for moving material between zones having different...

C198S741000, C198S747000, C198S468010, C414S191000, C414S225010

Reexamination Certificate

active

06422798

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a process for continuous treatment of objects in a processing unit, in particular for surface treatment of wafer-like objects such as semiconductor elements, preferably silicon wafers where the objects are moved along a conveyor track passing through the processing unit by a first linear-action conveyor device performing a back-and-forward movement and where the objects are supplied to/removed from the conveyor track by a transfer device. The invention further relates to an arrangement for continuous treatment such as surface treatment of objects arranged on supports, in particular wafer-like objects such as semiconductor elements, preferably silicon wafers, comprising a conveyor track passing through a processing unit and transfer devices for supplying/removing the supports to/from the conveyor track.
The surface treatment of objects is indispensable for the manufacture of a wide range of products in many fields of industry. The coating of objects with thin surface layers is particularly widespread, for preserving desirable product characteristics or ensuring them in the long term. Examples here are the coating of steel tools with thin abrasion-proof layers for reducing wear, or the coating of spectacle lenses with thin and optically active layers for reducing reflection. In the photovoltaics industry, solar cells are provided with thin surface coatings having a thickness of, for example, 80 nm, as a result of which their energy efficiency can be increased by up to 30% thanks to a number of physical effects.
Coating processes take place in some cases at atmospheric pressure, but frequently at low pressure. Low pressure is for example necessary to achieve sufficient homogeneity of the coating over the surface of the object. Also, it is frequently the case that certain deposition techniques are only possible at low pressure. A known coating process is low-pressure chemical vapor deposition. Here the surface coating grows from a reaction of one or more gases that are activated thermally or electrically in the form of plasma excitation.
The continuous coating on moving objects is used for improving the surface homogeneity of the coating. It is sufficient here for the coating device to be deposited homogeneously in one dimension, in particular in the direction transverse to the transport direction of the objects, By contrast, a two-dimensionally homogeneous deposition is required for coating on stationary objects, i.e. over the entire surface of the object. This leads to high extra expenditure from the technological viewpoint.
The steady movement of the objects relative to the coating source, necessary for a continuous coating, is achieved by a transport mechanism. The latter moves either the objects to be coated directly, or workpiece supports that receive those objects.
Workpiece supports for receiving the objects to be coated are used if the objects are not two-dimensional and/or the objects are fragile and/or the objects are not permitted to come into contact with the materials of the transport mechanism and/or the workpiece supports must perform a sealing function between the atmosphere and the low-pressure area. The workpiece supports used are as a rule plates made of steel, glass, graphite or ceramics and having recesses for receiving the objects.
Roller, chain and pusher drives can be used as the transport mechanism. In the case of the roller drive the preferably wafer-like objects or the workpiece supports run on a system of rollers that are actively driven.
In a chain drive, the objects are moved on a transport chain by drivers. Lightweight objects/workpiece supports can run directly on the chain. Above a certain weight, additional passively rotating rollers are used to take up the load.
In a pusher drive, the objects or workpiece supports are pushed through the treatment facility in a gap-free and endless line. Only the rearmost object/workpiece support is pushed in each case, and its movement is transmitted to all those in front of it. The pusher drive means that a continuous movement is not possible, since during the rearward movement of the pusher element the complete line of objects/workpiece supports stops. However, pusher drives are impervious to parasitic deposition and high temperatures.
With roller or chain drives, the transition from a timed to a continuous movement is achieved by operating the various roller to chain segments at differing speeds. This permits the use of these systems in low-pressure facilities which can insert and remove the objects/workpiece supports only in timed fashion via airlocks.
The roller or chain drive systems suitable for continuous transport present problems due to parasitic deposition and applications at high temperatures. Parasitic deposition occurs for example with plasma-supported low-pressure chemical vapor deposition. Only a disproportionately high expenditure can here prevent the roller bearings and/or chain links from also being coated and hence becoming hard to move in a very short time. If high temperatures are applied during processing of the objects, actively driven rollers or chains must be adequately protected from overheating. This too entails expensive measures.
The currently available workpiece supports present problems in facilities operating at high temperatures and high throughputs. To attain high resistance to warping at high temperatures, the workpiece supports must be of solid design. This gives them a high thermal capacity that leads to high energy losses when the supports are heated up and then have to be cooled down again outside the coating zone in quick succession. To achieve high throughputs in low-pressure facilities, the airlock chambers in which the supports are located must be evacuated as quickly as possible. This is critical if the airlock chambers have only one evacuation opening, for example due to technical reasons. In this case the air flowing out must flow around the support, thus slowing down the evacuation process. The provision of air flow apertures is only possible to a limited degree for stability reasons. In the case of wafer-like objects, the distance between the individual objects would also have to be increased. This is however undesirable for throughput rate reasons alone.
DE 43 03 462 C2 describes a multi-chamber coating facility in which substrates such as flat glass are treated. The substrates are here arranged spaced on supports and conveyed through the coating facility. To that end, slide elements such as rollers are provided that permit transportation at constant speed through the coating chambers.
U.S. Pat. No. 3,973,665 relates to a conveyor device for treatment of semiconductor substrates, for example by sputtering. To convey the objects, they are accommodated on supports that are conveyed at a distance from one another and in timed fashion. To that end, a conveying beam is provided for conveying the supports from one processing station to the next. It is furthermore necessary that the supports be gripped by further litters movable vertically to the movement of the lifting beam, so that the supports are disengaged from this beam when it moves back. Transport through airlocks is not possible.
GB 2 143 910 A relates to a system of supports that can be lined up to receive objects that are to be treated in a vacuum chamber. The supports themselves have geometrically adapted and interlocking edges that perform a sealing function during insertion into the vacuum chamber. Since the seals of the supports are not sufficiently high-temperature-proof, this system is unsuitable for high temperatures.
A conveying device is known from JP 10067429 A for substrates arrangable on a support that in turn is movable along rails by a spindle. A spindle drive for transporting wafers to be treated is also described in U.S. Pat. No. 4,947,784. The slides receiving the supports are passed through by the spindle. A transport device is known from DE 197 45 646 A1 that comprises shuttle conveyors and support lifting mechanisms for passing semicond

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