Vacuum Coating Apparatus

Abstract

Vacuum coating apparatus is described wherein substrates to be coated supported on a substrate holder are moved into and from a coating chamber through ingress and egress vacuum locks, and wherein the coating chamber is maintained under continuous vacuum. A substrate holder support carriage is disposed in each of the respective vacuum locks, means reciprocate each carriage between its associated vacuum lock and the coating chamber and further means is operable to remove or deliver a substrate holder with respect to said carriages.

Description

This invention relates to vacuum coating apparatus and, more particularly, to vacuum coating apparatus capable of meeting the need for high production rates for a wide variety of substrates and coatings.

The coating of substrates within a high vacuum has been recognized for some time as being a highly advantageous one in many applications. For example, vacuum coating may be used to provide non-metallic coatings for the control of optical properties of lenses, zinc or aluminum coated papers and plastics for electrical capacitors and decorative applications, refined high pressure metals, the production of metallic foils, and various other applications where high purity or unusual alloy compositions are desirable.

A typical vacuum coating system includes a vacuum tight enclosure in which a vapor source or sputtering cathode is positioned. The vapor source may comprise a crucible or boat in which molten metal is contained and wherein the molten metal is heated by a resistance heated filament. Where longer production runs, high evaporation rates, or high purity is desired, electron beam evaporation may be employed. Typically, in electron beam evaporation, the evaporant is contained within a cooled crucible so that the material to be evaporated is insulated from the crucible by a solid skull of its own composition. The material in the crucible is heated by directing an electron beam or a plurality of electron beams at the surface of the material.

In addition to the vapor source or sputtering cathode, the substrate to be coated is also positioned within the vacuum enclosure. Frequently it is desirable to rotate or otherwise move the substrate with respect to the vapor source or sputtering cathode in order to ensure uniformity of deposition over the entire surface of the substrate, or with respect to other adjacent substrates. In many cases, the substrate or several substrates may be suitably mounted to a device for supporting and moving the substrate or substrates in the vapor or sputter ion flow prior to the time the vacuum enclosure is evacuated. Such arrangements, most often comprising the well known bell jar type of vacuum enclosure, are usually unsatisfactory for high production rates. This is because the vacuum enclosure must be pumped down for each new substrate or batch of substrates which are to be coated.

Accordingly, it is an object of the present invention to provide improved vacuum coating apparatus.

Another object of the invention is to provide vacuum coating apparatus capable of very high production rates.

Another object of the invention is to provide vacuum coating apparatus in which it is unnecessary to pump down the vacuum coating chamber for each new substrate or batch of substrates which are to be coated.

Other objects of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic full section view of vacuum coating apparatus constructed in accordance with the invention; and

FIGS. 2, 3 and 4 are views similar to FIG. 1 illustrating the sequence of operation of the apparatus of FIG. 1.

Very, generally, the apparatus of the invention comprises a coating chamber 11 and a support device 12 within the coating chamber for supporting at least one substrate holder 13 therein at a position for coating a substrate or substrates (not shown) held thereon. A vapor or ion source 15 is provided within the coating chamber and means 16 are provided for maintaining the coating chamber under a continuous vacuum. A pair of vacuum locks 17 and 18 communicate with the coating chamber through the sides thereof. Transfer means 19 and 21 are provided for moving substrate holders between each of the vacuum locks and the coating chamber to a position in the coating chamber to be engaged by the support device.

Referring now more particularly to FIG. 1, the vacuum coating system illustrated schematically therein includes a vacuum tight enclosure 20 defining the coating chamber 11 in which the vacuum coating operation takes place. The chamber 11 is evacuated through a duct 25 in the lower wall of the enclosure 20 by the vacuum maintaining means 16 which comprise a suitable vacuum pump. An opening 29 is provided in the top wall of the enclosure 20 for accommodating the support device 12, explained more fully below.

The source 15 in the illustrated embodiment comprises a vapor source although it is to be understood that a source of sputter ions such as a sputtering cathode could also be used. A water cooled copper crucible 31 has a plurality of coolant passages 32 therein through which coolant is circulated by suitable means, not shown. As a result of the cooling, a skull 35 of solidified evaporant material forms between the cooled crucible 31 and a molten pool 37 from which the vapor for coating is produced. The molten pool is heated by an electron beam 39 produced by an electron beam gun 41. The electron beam gun may be of the type shown in U.S. Pat. No. 3,177,535 assigned to the assignee of the present invention. Means, not shown, are provided for establishing transverse magnetic fields in order to deflect the beam 39 through the curving path illustrated to impinge upon the top of the molten pool 37. By positioning the electron beam gun 41 beneath the crucible, the gun is less susceptible to impingement of vapor particles thereon which would deleteriously affect its operation.

Ingress and egress to and from the chamber 11 are provided by a pair of vacuum valves 43 and 45. The vacuum valve 43 includes a pair of walls 47 and 49 forming a valve chamber 51. Openings 53 and 55 are provided in the walls 47 and 49, respectively, thereby forming a port through which objects may pass into the chamber 11. A valve plate 57 is movable in the chamber 51 in a sealed relationship with the walls 47 and 49 by means of a pneumatic actuator 59 having an extensible actuator rod 61 attached to the valve plate 57. The valve plate 57 is shown in its closed position in FIG. 1, thereby maintaining the valve 43 in the closed condition. The valve 45 is identical to the valve 43 and is illustrated in FIG. 1 in the closed condition.

In order to pass objects through the vacuum valve 43 into the chamber 11 without having to bring the chamber 11 up to atmospheric pressure, the vacuum lock 17 is provided. Similarly, in order to remove objects from the chamber 11 without having to bring the chamber 11 up to atmospheric pressure, the vacuum lock 18 is provided. The vacuum lock 17 communicates with the chamber 11 through the valve 43 and the vacuum lock 18 communicates with the chamber 11 through the valve 45.

The vacuum lock 17 includes an evacuated chamber 67 which is evacuated through a port 69 in the lower wall of the chamber 67 by a suitable vacuum pump 71. The vacuum lock 18 includes a vacuum tight chamber 73 which is evacuated through a port 75 in the lower wall thereof by a vacuum pump 77. A vacuum valve 79 identical with the vacuum valve 43 is disposed at the opposite end of the vacuum lock 17 from the valve 43. A similar vacuum valve 81 closes the end of the vacuum lock 18 opposite the vacuum valve 45. Thus, the locks 17 and 18 may be opened to the atmosphere without loss of vacuum in the chamber 11 provided that the valves 43 and 45 are closed at appropriate times. Flow of materials into and out of the chamber 11 may be on a straight line basis for production efficiency and the use of the vacuum locks enables loading and unloading of substrates while at the same time other substrates are being coated in the chamber 11.

In order to support a substrate or substrates for coating, one or more substrate holders 13 are provided. One of the substrate holders 13 is illustrated in FIG. 1 and is dome shaped and the substrates, not shown, are attached to the concave side of the substrate holder. The illustrated transfer means 19 is a cart having a plurality of wheels 87. The wheels 87 are guided on a track 89 which extends through the vacuum lock 17, the chamber 11, and the vacuum lock 18 to facilitate the straight line throughput arrangement for moving the substrates through the vacuum system. The substrate holder 13 is at least partially ferromagnetic for reasons which will be explained below. In the particular design of the substrate holder illustrated in FIG. 1, a ferromagnetic plate 95 is secured to the top of the holder and constitutes the ferromagnetic part of the substrate holder.

In operating the apparatus of the invention, the chamber 67 is evacuated and the cart 19 is moved through the open valve 43 into the chamber 11 with a substrate holder 13 supported on the cart, as shown in FIG. 2. The support device 12 is employed to support the substrate holder 13 within the chamber 11 independently of the cart 19. In this manner, the cart may be removed from the chamber 11 prior to beginning the vacuum coating operation. During many vacuum coating operations, it is desirable to rotate or otherwise move the substrates being coated within the vapor flow in order to assure uniformity of deposit. This is because the amount of vapor and hence the amount of condensation of the vapor on the substrates in different regions of the chamber may vary. Pseudo random exposure of the substrates to all regions of the vapor will aid in achieving uniform coating thicknesses and quality. In order to provide for picking up the substrate holders and for rotating them within the chamber during coating, the support device 12 is provided with an armature 96 which depends from an actuator 97 into the chamber and which is axially as well as rotatably movable by suitable means in the actuator 97. An electromagnet 98 is attached to the armature 96. Suitable energization of the electromagnet 98 causes the magnet to magnetically engage and secure to the metallic plate 95 on the substrate holder 19. The armature may then be raised axially to raise the substrate holder off of the carriage and to rotate it within the chamber once the carriage is removed. This is shown in FIG. 3. A support device suitable for use as the support device 12 is shown and described in co-pending application Ser. No. 21,837, assigned to the present assignee.

In operating the apparatus of the invention, the substrate holder is first brought into the coating chamber on the cart 19. The electromagnet 98 is in the raised position by appropriately actuating the support device 12 as previously explained. Once the substrate holder 19 is centered in the vacuum chamber 11, with the ferromagnetic plate 95 directly underneath the electromagnet 98, the electromagnet is moved down into position immediately adjacent the plate 95. The electromagnet 98 is then energized and the substrate holder is picked up. In order to provide ample clearance, the electromagnet with the substrate holder attached thereto is raised again and the cart 19 is removed from the vacuum chamber 23. The motor 97 is then energized and rotary motion is transmitted to the shaft 96 for rotating the electromagnet and the substrate holder thereon.

Operation and construction of the support device 12 is not described in greater detail herein. The device 12 may be of any suitable construction, but is preferably the construction shown and described in detail in the aforementioned co-pending application.

In order to prevent vapor from the source from coating up the carts or carriages 19 and 21 while the substrate holders are moved to the coating position, a shutter 101 is provided between the vapor source and the coating position. With the shutter positioned as shown in FIGS. 1, 2 and 4, the vapor from the vapor source is blocked off when the substrates are being moved to and from the coating position. As shown in FIG. 3, the shutter is moved out of the way on a pivot shaft 102 during the coating operation to allow the vapor to reach the substrates.

Once coating of the substrates is completed, the valve 45 is opened and the cart 21 is moved from the chamber 73 into the chamber 11 beneath the substrate holder 12. Prior to opening the valve 45, of course, the chamber 73 is evacuated. The support device 12 is then operated to lower the substrate holder 13 onto the cart 12 and the substrate holder is released from the support device by de-energizing the electromagnet 98. This is shown in FIG. 4.

The cart 21 is then moved back through the open valve 45 into the chamber 73 and the valve 45 is closed. Once the substrates have cooled sufficiently, the chamber 73 is brought to atmosphere, the valve 81 is opened, and the substrate holder is removed from the chamber 73. At the same time, a new substrate holder with substrates thereon may be placed on the cart 19 in the chamber 67 to repeat the sequence of operation as shown in FIG. 1.

The means for moving the carts 19 and 21 between their respective positions may be any suitable mechanism, such as a hydraulic or pneumatic or mechanical linkage. In the drawings, such means comprise crank arms 103 and 104, which are turned by actuators 105 and 106, respectively, to move the carts on their tracks.

The coating chamber 11 is under vacuum at all times. This continuously outgasses the sources, prevents contamination, permits high evaporation rates, and yields products superior to those produced in bell jar systems, which must be pumped down for each load. The load and unload locks, being isolated from the coating chamber 11 by the gate valve, may be provided with heaters 107 and a cooling system 108, respectively, so that the substrates may be heated prior to coating and may be cooled prior to removal. In this manner maximum utilization of the coating chamber can be achieved. By placing the vacuum locks in alignment with each other on opposite sides of the coating chamber, straight through operation may be undertaken for greater efficiency. If desired, vapor sources additional to the single source shown may be provided for simultaneous, sequential, or graded operation.

In order to permit ready repair or replacement of the various elements of the vapor source 15, all vapor sources and associated elements and mechanisms are mounted on a single plate 99. The plate is removably secured in the lower portion of the coating chamber 11 and, once the associated water and electrical leads (not shown) are disconnected, the plate can be removed through a suitable access port, not shown, to remove all the elements mounted on the plate. In this manner, a complete second unit may be kept for immediate placement in the coating chamber and the unit therein removed in the event any repair or replacement becomes necessary. Accordingly, the down time of the vacuum coating apparatus of the invention is minimized.

Operation of the apparatus of the invention may be completely automated. Suitable controls may be provided for each of the elements operating in the sequence of operation to thereby render the apparatus unaffected by human inconsistency. Suitable interlocks may be used to assure that each phase is completed before the subsequent one in the cycle is initiated.

It may therefore be seen that the apparatus of the invention affords a substantial improvement over known prior art devices. The apparatus of the invention is capable of operation at high production rates and produces a superior quality evaporated coating on the substrates.

Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall description the scope of the appended claims.

Claims

What is claimed is:

1. Vacuum coating apparatus comprising, a coating chamber, a support device within said coating chamber for engaging and supporting at least one substrate holder therein at a position for coating substrates held thereon, a vapor or ion source within said coating chamber, means for maintaining said coating chamber under continuous vacuum, a pair of vacuum locks operable to communicate with said coating chamber and with regions outside said coating chamber, a pair of carriages for supporting substrate holders thereon at a position to be engaged by said support device when one of said carriages is in said coating chamber, and means located entirely within each of said vacuum locks and structurally connected to respective ones of said carriages for reciprocally moving each of said carriages between a respective one of said vacuum locks and said coating chamber to transfer substrate holders into and out of said coating chamber said support device being operable to remove said substrate holders from respective ones of said carriages.

2. Apparatus according to claim 1 wherein said means for reciprocally moving said carriages comprise a pair of crank arm mechanisms.

3. Apparatus according to claim 1 including a shutter positioned between said vapor or ion source and the coating position for blocking off vapor or ions when substrates are being moved to and from the coating position.

4. Apparatus according to claim 1 including heating means in at least one of said vacuum locks for heating substrates prior to coating.

5. Apparatus according to claim 1 including cooling means in at least one of said vacuum locks for cooling substrates subsequent to coating.

6. Apparatus according to claim 1 wherein said vapor or ion source is mounted on a plate, and wherein said plate is removable from said coating chamber to facilitate replacement of said source.

7. Apparatus according to claim 1 wherein said support device includes magnetic means for engaging and disengaging the substrate holders.