WO2004009864A1

WO2004009864A1 - Pellet feeder

Info

Publication number: WO2004009864A1
Application number: PCT/GB2003/002925
Authority: WO
Inventors: Ashley Larthwell; Gary Metcalfe
Original assignee: Cambridge Display Technology Limited
Priority date: 2002-07-22
Filing date: 2003-07-08
Publication date: 2004-01-29
Also published as: GB2406562A; GB0501172D0; GB2406562B; GB0216992D0; AU2003244848A1

Abstract

Provided is a pellet feeder for supplying pellets of a vaporisable material to a vaporisation site in a vacuum chamber, which pellet feeder comprises a pellet holder (1), a gating means (2), a lateral displacement means (3) and a retractable pellet dispenser (4); wherein the pellet holder comprises an exit (5) through which pellets may be delivered, the gating means is located proximal to the exit of the pellet holder, and the gating means is capable of regulating delivery of pellets from the pellet holder to the lateral displacement means such that a single pellet is delivered to the lateral displacement means at any one time; wherein the lateral displacement means is capable of delivering a single pellet at any one time to the retractable pellet dispenser; and wherein the retractable pellet dispenser is adapted to receive a single pellet from the lateral displacement means at a receiving position, and the retractable pellet dispenser is capable of being displaced to a dispensing position proximal to the vaporisation site in the vacuum chamber, dispensing the pellet to the vaporisation site, and retracting to the receiving position.

Description

PELLET FEEDER

The present invention relates to the field of methods and apparatus for vapour deposition in a vacuum chamber. More particularly, the present invention relates to the field of devices and apparatus for introducing pellets of a vaporisable material into vacuum chambers.

Vapour deposition is used in a variety of methods of manufacture. A vaporisable material is typically vaporised in a vacuum chamber and then allowed to deposit onto a substrate in the vacuum chamber. Such a method may be used in order to produce a film, coating, plating or deposition layer of the vaporisable material on the substrate.

The. vaporisable material may be loaded into a crucible in the vacuum chamber, the chamber sealed and the material vaporised. However, such a method requires that the chamber is opened and the vacuum released each time a load of vaporisable material is introduced into the crucible. This is not an efficient method of operation for an industrial- scale production line. A number of methods described in the prior art have attempted to provide a continuous deposition system that does not require release of the vacuum in order to replenish the vaporisable material in the crucible. This is typically done by providing a system for continuous delivery of pellets of the vaporisable material to the crucible.

JP 06173004 A discloses a raw material feeder for continuous vacuum-deposition plating. A granular plating material feeder is arranged outside a vacuum deposition plating chamber. A fixed conveyor and movable charger connects the feeder to the chamber.

IP 05171420 A discloses an apparatus for feeding pellets of a raw material to a crucible below a vapour chamber. The apparatus has a vertical feed pipe, a sluice valve and a horizontal transferring tube. JP 02118071 A discloses a continuous vacuum deposition device constituted of a plurality of differential pressure chambers compartmented with partitions and a vapour deposition chamber. Pellets of raw material are supplied into a crucible via a guide pipe by rotary feeders fitted to the partitions.

US 5,195,651 discloses a ball feeder which delivers balls of a raw material one by one by gravity to an outlet. The ball feeder comprises a container for holding balls, an elongated passageway means, a connecting means, a metering valve, a pass signal generating means and a gate means.

US 5,107,791 discloses an apparatus for manufacturing a deposition film of silicon oxide which includes a means for continuously supplying a shaped deposition material to a heat evaporation member.

A number of problems are associated with the above prior art methods. A first problem is that the presence of components of the feed mechanism in the vacuum chamber above the crucible may cause "shadowing". This means that areas of the substrate are unevenly covered with a deposition film. Furthermore, if components of the feed mechanism are permanently exposed to vapour in the chamber, this may impair their operation over time. This often requires time-consuming cleaning procedures and a shut-down of the production line. A further problem is that the forces exerted on pellets during their movement through the feeder can lead to their deformation and cohesion. This often leads to blockages in the feeder, particularly where soft materials are used.

The present invention aims to overcome the problems associated with the prior art. In particular, the present invention aims to provide a pellet feeder which does not suffer from problems of shadowing and adhesion of pellets.

Accordingly, the present invention provides A pellet feeder for supplying pellets of a vaporisable material to a vaporisation site in a vacuum chamber, which pellet feeder comprises a pellet holder, a gating means, a lateral displacement means and a retractable pellet dispenser;

wherein the pellet holder comprises an exit through which pellets may be delivered, the gating means is located proximal to the exit of the pellet holder, and the gating means is capable of regulating delivery of pellets from the pellet holder to the lateral displacement means such that a single pellet is delivered to the lateral displacement means at any one time;

wherein the lateral displacement means is capable of delivering a single pellet at any one time to the retractable pellet dispenser; and

wherein the retractable pellet dispenser is adapted to receive a single pellet from the lateral displacement means at a receiving position, and the retractable pellet dispenser is capable of being displaced to a dispensing position proximal to the vaporisation site in the vacuum chamber, dispensing the pellet to the vaporisation site, and retracting to the receiving position.

Thus, the present pellet feeder achieves advantages which were not possible using known apparatus, by ensuring controlled delivery of single pellets fed from a pellet reservoir (the pellet holder) through to the vaporisation site (usually a crucible). This controlled delivery of a single pellet at a time prevents pellets rubbing against one another, or being crushed against one another by the dispensing mechanism. The present mechanism also prevents the pellets falling too far or being moved in a poorly directed mamier (these are also factors which can lead to crushing, or can damage the mechanism) by introducing the lateral displacement means in conjunction with the retractable pellet dispenser. This design has the further advantage of removing the feeder from the immediate volume surrounding the vaporisation site, allowing the vast majority of the apparatus to be shielded from the vaporisation site Further advantages of the. present pellet feeder is that it can be easily fitted to existing vacuum chambers, for example by attaching the apparatus to a door of a vacuum chamber. Thus, existing apparatus can be improved at a modest cost. Additionally, when the feeder is fitted with detectors (for detecting the presence or absence of pellets at various key points in the apparatus) it becomes simple to detect a problem with the feeding of pellets, before pellets become crushed together, blocking the apparatus. This is particularly advantageous if, for example, the power is turned off. When the power is restored, the apparatus can determine the location of pellets in the system and ensure particular areas are freed of pellets before further pellets are introduced.

In a further aspect, the present invention provides a vapour deposition apparatus for depositing a vaporisable material onto a substrate, comprising a vacuum chamber and a pellet feeder as defined above.

In a still further aspect, the present invention provides a method for producing a display device, comprising supplying a vaporisable material to a vaporisation site in a vacuum chamber by means of a pellet feeder as defined above, vaporising the material at the vaporisation site, and depositing the material onto a substrate.

In a yet further aspect, the present invention provides a display device obtained by a method as defined above.

The present invention will now be described in further detail, by way of example only, with reference to the Figures, in which:

Figure 1 depicts a schematic representation of a pellet feeder of the present invention; and

The present invention will now be described in more detail. In one preferred embodiment of the present invention, the pellet holder, gating means and/or lateral displacement means are shielded from the vaporisation site. This is possible, since these portions of the device may be located at a distance from the vaporisation site, due to the lateral displacement means. The shielding material is not especially limited, provided that it is capable of shielding the components from the particular material constituting the pellets. Preferably the shield is a metal shield, such as iron, steel, aluminium, bronze or an aluminium/bronze alloy. It is also preferred that in the receiving position the retractable pellet dispenser is shielded from the vaporisation site.

Generally, the pellet holder contains a plurality of pellets of a vaporisable material. The lateral displacement means accepts a single pellet at a time from the pellet holder, but whilst doing this it may either be in the process of transferring a plurality of pellets (e.g. in a conveyor belt fashion) or alternatively may only transfer one pellet at a time. It is particularly preferred that the lateral displacement means handles a single pellet at any one time, such that the lateral displacement means is adapted to receive a single pellet from the pellet holder, and deliver the single pellet to the retractable pellet dispenser, before receiving a further pellet from the pellet holder. The lateral displacement means may operate in a number of different ways, provided that it is capable of transferring pellets to the pellet dispenser one at a time. Thus, it may comprise a moving band or track in the manner of a conveyor, or a moving arm for pushing pellets in the required lateral direction.

The form and dimensions of the pellet holder are not especially limited, provided that crushing and sticking of the pellets to each other, and to the apparatus, is avoided. Preferably, the pellet holder comprises a tube of a diameter such that when pellets are added to the tube, the tube contains a single row or column of pellets one behind another.

The dimensions and form of the gating means are not especially limited, provided that the gating means is capable of regulation the movement of pellets from the pellet holder to the lateral displacement means such that pellets are delivered one at a time. Typically, the gating means comprises a retractable gating member which in a non-retracted position prevents delivery of pellets from the pellet holder to the lateral displacement means, and the retractable gating member is capable of being transiently retracted in a direction substantially orthogonal to a longitudinal axis of the pellet holder to a retracted position, thereby allowing a single pellet to be delivered to the lateral displacement means. Preferably the retractable gating member comprises a pin which may engage the pellet which is due to be transferred to the lateral displacement means. The pin may be positioned below the pellet preventing it from falling, or may engage the pellet directly, holding it in place from the side.

As mentioned above, it is preferred that the pellet feeder further comprises one or more monitoring means capable of detecting the presence (or absence) of a pellet at one or more detection positions in the pellet feeder. This is particularly preferable for avoiding blockages when starting the apparatus up after an unplanned shutdown (e.g. in the event of a power failure). Monitoring means preferably comprises one or more pins capable of detecting the presence or absence of pellets at key positions, by detection of the presence or absence of resistance to the movement of the pins.

Typically, the retractable pellet dispenser comprises a rotatable pellet receptacle capable of receiving a pellet at the receiving position in a first orientation, rotating to a second orientation at the dispensing position, releasing the pellet and rotating to return to the first orientation. Preferably, the rotatable pellet receptacle comprises a retaining member which acts to prevent release of the pellet until the rotatable pellet receptacle has rotated to the second orientation. The retaining member preferably comprises a pin for holding the pellet in place so that it is not transferred prematurely. The pin may be positioned below the pellet preventing it from falling, or may engage the pellet directly, holding it in place from the side.

The apparatus of the present invention may be employed to deposit any vaporisable material on a substrate. Preferably, the vaporisable material is aluminium, gold, silver, lithium, magnesium, sodium, calcium or an alloy thereof, or barium fluoride, lithium fluoride or sodium fluoride.

As mentioned above, the vapour deposition apparatus for depositing a vaporisable material onto a substrate of the present invention comprises a vacuum chamber and a pellet feeder as defined above. In a preferred embodiment, the vapour deposition apparatus further comprises a crucible, the vaporisation site being located in the crucible, wherein the crucible is positioned below the dispensing position of the retractable pellet dispenser, such that the retractable pellet dispenser is capable of releasing a pellet into the crucible.

It is especially preferred that the pellet feeder is fitted on the inside of a door of the vacuum chamber. This has the advantage of being simple to fit to existing vacuum chambers (simple retrofitting). Whether in this configuration or some other configuration, the pellet feeder is generally covered by a sheet of material to shield it from the vaporisation site, wherein the sheet of material leaves the retractable pellet dispenser sufficiently uncovered to allow it to move outside of the protective cover of the sheet when in the dispensing position, to dispense a pellet. Preferably the shield is a metal shield, such as iron, steel, aluminium, bronze or an aluminium/bronze alloy. The other components of the pellet feeder may also be comprised of one or more of these materials.

It is preferred that the equipment for operating the pellet feeder is located outside of the vacuum chamber and communicates with the pellet feeder through one or more vacuum seals. Generally, the equipment for operating the pellet feeder is hydraulic equipment.

The present apparatus are particularly suited to for use in a method for producing a display device. Typically, such a method comprises supplying a vaporisable material to a vaporisation site in a vacuum chamber by means of a pellet feeder as defined above, vaporising the material at the vaporisation site, and depositing the material onto a substrate. The present invention also provides display devices obtained by these methods. The present invention will now be described, by way of example only, with reference to the following specific embodiment.

EXAMPLE

A schematic of a pellet feeder of the present invention is depicted in Figure 1.

The pellet holder (1) in the apparatus depicted in Figure 1 has a preferred tubular form, being adapted to hold a row or column of pellets situated one after the other in single file. This is a preferred arrangement, since it aids in the dispensing of a single pellet at a time. Pellets are held in check by the gating means (2), which in the Figure is comprised of a retractable pin for holding the pellets from below. The pin moves in or out in a direction orthogonal to the plane of the paper. Pellets are transferred through exit (5) to the lateral displacement means (3) one at a time by an appropriate movement of the gating means (2). In this preferred arrangement, the lateral displacement means moves a single pellet at a time and deposits it in the retractable pellet dispenser (4), which has an appropriate indentation for accepting a pellet. The retractable pellet dispenser holds the pellet in place with pin (6). The dispenser moves out of the plane of the paper from its receiving position to its dispensing position. In this position, the pellet is held in the indentation. The dispenser then rotates to a second orientation wherein the pellet drops from the indentation into the vaporisation site. The pellet does not drop until the rotation to the second orientation is complete, since it is held in place by pin (6). When the rotation is complete, pin (6) retracts and the pellet is allowed to fall in a controlled fashion. The retractable dispenser then rotates back to its original orientation and retracts to its receiving position, ready to receive another pellet.

The whole apparatus of Figure 1 is shielded from the vaporisation site by shield (7). The shield has an aperture which allows the retractable pellet dispenser to move from the protection of the shield for a short time to allow a pellet to be dispensed.

Claims

CLAIMS:

1. A pellet feeder for supplying pellets of a vaporisable material to a vaporisation site in a vacuum chamber, which pellet feeder comprises a pellet holder, a gating means, a lateral displacement means and a retractable pellet dispenser;

2. A pellet feeder according to claim 1, wherein the pellet holder, gating means and/or lateral displacement means are shielded from the vaporisation site.

3. A pellet feeder according to claim 1 or claim 2, wherein in the receiving position the retractable pellet dispenser is shielded from the vaporisation site.

4. A pellet feeder according to any preceding claim, wherein the lateral displacement means is adapted to handle a single pellet at any one time, such that the lateral displacement means is adapted to receive a single pellet from the pellet holder, and deliver the single pellet to the retractable pellet dispenser, before receiving a further pellet from the pellet holder.

5. A pellet feeder according to any preceding claim, wherein the pellet holder comprises a tube of a diameter such that when pellets are added to the tube, the tube contains a single row or column of pellets one behind another.

6. A pellet feeder according to any preceding claim, wherein the gating means comprises a retractable gating member which in a non-retracted position prevents delivery of pellets from the pellet holder to the lateral displacement means, and the retractable gating member is capable of being transiently retracted in a direction substantially orthogonal to a longitudinal axis of the pellet holder to a retracted position, thereby allowing a single pellet to be delivered to the lateral displacement means.

7. A pellet feeder according to any preceding claim, which further comprises one or more monitoring means capable of detecting the presence of a pellet at one or more detection positions in the pellet feeder.

8. A pellet feeder according to any preceding claim, wherein the retractable pellet dispenser comprises a rotatable pellet receptacle capable of receiving a pellet at the receiving position in a first orientation, rotating to a second orientation at the dispensing position, releasing the pellet and rotating to return to the first orientation.

9. A pellet feeder according to claim 8, wherein the rotatable pellet receptacle comprises a retaining member which acts to prevent release of the pellet until the rotatable pellet receptacle has rotated to the second orientation.

10. A pellet feeder according to any preceding claim, wherein the pellet holder contains a plurality of pellets of a vaporisable material.

11. A pellet feeder according to claim 10, wherein the vaporisable material comprises aluminium, gold, silver, lithium, magnesium, sodium, calcium or an alloy thereof, or barium fluoride, lithium fluoride or sodium fluoride.

12. A vapour deposition apparatus for depositing a vaporisable material onto a substrate, comprising a vacuum chamber and a pellet feeder as defined in any preceding claim.

13. A vapour deposition apparatus according to claim 12, which further comprises a crucible, the vaporisation site being located in the crucible, wherein the crucible is positioned below the dispensing position of the retractable pellet dispenser, such that the retractable pellet dispenser is capable of releasing a pellet into the crucible.

14. A vapour deposition apparatus according to claim 12 or claim 13, in which the pellet feeder is fitted on the inside of a door of the vacuum chamber.

15. A vapour deposition apparatus according to any of claims 12-14, wherein the pellet feeder is covered by material to shield it from the vaporisation site, and wherein the material leaves the retractable pellet dispenser sufficiently uncovered to allow it to move outside of the protective cover of the sheet in the dispensing position, to dispense a pellet.

16. A vapour deposition apparatus according to any of claims 12-15, wherein equipment for operating the pellet feeder is located outside of the vacuum chamber and communicates with the pellet feeder through one or more vacuum seals.

17. A vapour deposition apparatus according to claim 16, wherein the equipment for operating the pellet feeder is hydraulic equipment.

18. A method for producing a display device, comprising supplying a vaporisable material to a vaporisation site in a vacuum chamber by means of a pellet feeder as defined in any of claims 1 to 11, vaporising the material at the vaporisation site, and depositing the material onto a substrate.

19. A display device obtained by a method as defined in claim 18.