Abstract:
The invention relates to a magnetic latch for securing substrates on a planetary rotating platform suspended above a coating source in a vacuum chamber of a vapor deposition system, e.g. a chemical vapor deposition (CVD) system or a physical vapor deposition (PVD) system. The magnetic latch includes a permanent magnetic, which is moveable between a latching position, in which the permanent magnet magnetizes the latch for attracting a substrate holder, and an unlatching position, in which the permanent magnet is connected in a bypass circuit, thereby demagnetizing the latch for releasing the substrate holder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present invention does not claim priority. 
   TECHNICAL FIELD 
   The present invention relates to a magnetic latch for use in a vapor deposition system, and in particular to a soft engaging magnetic latch for suspending a substrate holder in a vacuum chamber of a physical vapor deposition (PVD) system or a chemical vapor deposition (CVD) system. 
   BACKGROUND OF THE INVENTION 
   The coating flux from a source in a PVD or a CVD system are relatively stable; however, they have a spatial distribution that can lead to deposited films with non-uniform thickness, if the substrates remain stationary. To improve uniformity, the geometrical relationship between the source and substrate must be selected appropriately. Good results have been observed when the substrate is rotated about an axis perpendicular to the plane of the surface to be coated, and in particular when multiple substrates have been mounted on multiple spindles in a planetary configuration. 
   Conventional planetary gear coating systems, such as the one disclosed in U.S. Pat. No. 5,106,346, issued Apr. 21, 1992 to Stefan Locher et al, includes a large rotating platform with several individual spindles (planets) rotatable thereon disposed within a sealed vacuum chamber. Unfortunately, each substrate holder must be connected to a mounting flange on each spindle using mechanical fasteners, e.g. bolts, requiring manual replacement. Not only do these mechanical systems require extra manual labor, they are more susceptible to misalignment caused by changes in temperature and pressure. 
   In order to isolate as much of the bearing and gear structure as possible from the vacuum chamber, Hurwitt et al disclosed a planetary gear coating system in U.S. Pat. No. 5,795,448 issued Aug. 18, 1998, which includes a magnetic link in the shaft of each spindle. The substrate holders are not suspended over the cathodes, and still require mechanical fasteners for attachment to the mounting flanges of the spindles. 
   The coating system, disclosed in U.S. Pat. No. 6,464,825 issued Oct. 15, 2002 to Shinozaki, includes a robotic arm traveling between a pressurized loading/unloading chamber and the main vacuum chamber to minimize the amount dust entering the main vacuum chamber. The Shinozaki system also includes a magnetic rotational drive and a magnetic levitating member to minimize particulate generation caused by interacting mechanical elements. However, Shinozaki discloses a single rotating platform with a complicated levitating platform and electro-magnets that totally surround the substrate holder. Unfortunately, this approach would be impossible to implement in a planetary gear coating system, as it is very difficult to deliver power separately to individual rotating substrate holders in a planetary system, while operating in a vacuum and at elevated temperatures. 
   An object of the present invention is to overcome the shortcomings of the prior art by providing a magnetic latch for attaching a substrate holder to a spindle suspended over a cathode in a planetary coating system without shock to the substrate and without generation of particulate matter. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention relates to a planetary substrate support of the type for mounting in a process chamber of a coating system, which is for coating substrates mounted on substrate holders, comprising: 
   a main support rotatable about a first axis; 
   a plurality of spindles extending from the main support rotatable about respective spindle axes; and 
   a magnetic latch on an end of each spindle including a permanent magnet, and a mounting surface for receiving a substrate holder; 
   wherein each magnetic latch includes a first section, and a second section movable relative to the first section between a first position in which the permanent magnet magnetizes the mounting surface for attracting a substrate holder, and a second position in which the mounting surface is non-magnetic. 
   Another aspect of the invention relates to a coating system for coating substrates mounted on substrate holders comprising: 
   a process chamber; 
   a coating source disposed in the process chamber for depositing a coating on the substrate; and 
   a planetary substrate support mounted in the process chamber. 
   The planetary substrate support including: 
   a main support rotatable about a first axis; 
   at least one spindle extending from the main support rotatable about respective spindle axes; and 
   a magnetic latch on each spindle for receiving the substrate holder; 
   Each magnetic latch comprising: 
   a first section including a mounting surface for receiving the substrate holder, and 
   a second section including a permanent magnet, one of the first or the second sections movable relative to the other section between a first position in which the mounting surface forms a temporary magnet for attracting a substrate holder, and a second position in which the mounting surface is non-magnetic. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
       FIG. 1  is an isometric view of the coating system according to the present invention; 
       FIG. 2  is an isometric view of the coating system of  FIG. 1  with some outer wall removed; 
       FIG. 3  is a schematic illustration of a planetary substrate holder with a magnetic latch according to the present invention; 
       FIGS. 4   a  to  4   c  are schematic illustrations of the basic principle of the magnetic latch according to the present invention; 
       FIG. 5  is an isometric view of a magnetic latch according to the present invention; 
       FIG. 6   a  is a top view of a stator of the magnetic latch of  FIG. 5 ; 
       FIG. 6   b  is a cross sectional view of the stator of  FIG. 6   a;    
       FIG. 7  is a top view of the magnetic latch of  FIG. 5  in the unlatched position; and 
       FIGS. 8   a  to  8   d  are schematic illustrations of substrate holders according to the present invention. 
   

   DETAILED DESCRIPTION 
   With reference to  FIGS. 1 to 3 , the vapor deposition vacuum system, e.g. Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD), according to the present invention includes a load lock chamber, generally indicated at  1 , and a process chamber  2  with a gate valve  3  therebetween. The gate valve  3  enables the pressure in the load lock chamber  1  to be brought to atmospheric pressure for loading and unloading of substrates or to be re-established to the pressure of the process chamber  2  for substrate transfer, independently of the pressure in the process chamber  2 . The load lock chamber  1  includes a loading container  4  with a cassette elevator  5  therein, and a transfer channel  6  with a robotic arm  7  therein. The control mechanism for the robotic arm  7  is mounted in the cylindrical canister  8  extending from the transfer channel  6 . 
   A cathode  12 , and a planetary substrate support  14  are mounted within the process chamber  2 . The planetary substrate support  14  comprises a main cylindrical platform  16  rotatable about a first axis, with a plurality of, e.g. six, spindles  17  extending therefrom, each spindle  17  rotatable about its own axis, which are preferably parallel to the first axis, but may be at some other angle. In use, as the main platform  16  is rotated, each individual spindle  17  is also rotated to ensure even coating over all portions of each substrate. Each spindle  17  includes a magnetic latch  18  at the outer free end thereof for suspending a substrate over the cathode  12 , which will be further described hereinafter 
   At least one cathode  12 , preferably low arcing cathodes, are mounted inside the process chamber  2 . Extra cathodes  12  may be provided for backup in case of failure or in case the coating supply in one cathode  12  becomes exhausted. Alternatively, several different cathodes  12  can be provided to enable the deposition of different coatings consecutively without opening up the process chamber  2  to the atmosphere. Preferably, minor adjustments can be made to the position of the cathode  12  by movement a mounting platform (not shown), manually or by remote control. 
   The process chamber  2  is evacuated through pumping port  22 , while process gases are supplied to the process chamber  2  via mass flow controllers (not shown). 
   While sputter deposition vacuum systems have been described herein, the planetary substrate support according to the present invention can be utilized with any other suitable coating system such as evaporative systems or CVD systems. The coating process can be enhanced by additional equipment such as shutters, masks, ion bombardment devices, advanced anode concepts, or plasma activation systems. 
   While the coating system is shown in a sputter up configuration herein, magnetic latch according to the present invention can be utilized in other orientations such as coating down and coating sideways. 
   Uncoated substrates mounted in substrate holders  23  are loaded onto the cassette elevator  5  with the gate valve  3  closed, thereby maintaining the pressure in the process chamber  2 . When the load lock chamber  1  is evacuated, the gate valve to the process chamber  2  opens and the robotic arm  7  transfers each substrate holder  23  through the transfer channel  6  and the open valve gate  3  to the process chamber  2  for mounting onto the spindles  17  with the help of the magnetic latches  18 . 
   The basic principle behind the magnetic latch  18  is illustrated in  FIG. 4   a  to  4   c , in which a permanent magnet  31  is disposed in an unlatched position ( FIGS. 4   a  and  4   b ) or a latched position ( FIG. 4   c ). In  FIG. 4   a , a magnetic circuit, indicated by arrow  32 , is completed through a bypass section  33  leaving poles  34   a  and  34   b  non-magnetized. In  FIG. 4   b , the substrate holder  23  is brought in contact with the poles  34   a  and  34   b  providing an alternative magnetic circuit. To complete the alternative magnetic circuit, indicated by arrow  36  in  FIG. 4   c , the permanent magnet  31  is rotated into alignment with the poles  34   a  and  34   b , thereby ensuring that the substrate holder  23  is magnetically attracted by the poles  34   a  and  34   b . Alternatively, the permanent magnet  31  can remain fixed, while the bypass section  33  and the poles  34   a  and  34   b  are moved into and out of alignment therewith. 
   A preferred embodiment of the magnetic latch  18 , illustrated in  FIGS. 5 ,  6   a ,  6   b  and  7 , includes a cylindrical stator  41 , with a cylindrical rotor  42  rotatable thereon. The stator  41  includes three sets of stator poles  43   a  and  43   b  fixed to a base  44  by a plurality of mechanical fasteners, e.g. hex bolts  46 , ensuring good contact. The rotor  42  includes three radially extending permanent magnets  47  sandwiched between rotor poles  48   a  and  48   b . The north and south poles of the permanent magnets extend along the long sides thereof adjacent to the rotor poles  48   a  and  48   b , respectively. Each magnetic latch  18  includes an elongated actuator  49  extending down through the main platform  16  and each spindle  17  for rotating the rotors  42  between the latched position ( FIG. 5 ) and the unlatched position ( FIG. 7 ) from outside of the process chamber  2 . The actuator  49  includes a tongue or other engageable feature on the upper end thereof for engagement by another mechanical device, e.g. a shaft  50  ( FIG. 3 ), above the planetary substrate support. In the unlatched position both of the rotor poles  48   a  and  48   b  are rotated adjacent to one of the stator poles  43   b , thereby shorting the permanent magnet  47 , breaking the magnetic circuit through the stator  41 , and releasing the substrate holder  23 . 
   To facilitate alignment of the substrate holder  23  with the stator  41 , a tapered pin  51  is provided extending from the center of the base  44 . A single tapered pin  51  in the center of the base  44  provides an alignment feature, which ensures the proper alignment of the substrate holder  23  without dictating the exact angular orientation thereof. Tapered pins can be positioned at other positions around the circumference of the stator or other radial positions. 
   Examples of substrate holders  23  are illustrated in  FIGS. 8   a  to  8   d . The substrate holder  23   a , in  FIG. 8   a , includes a base  53  fastened to an annular cover  54 , which includes an annular shoulder  56  for supporting a single substrate  57 . A cylindrical recess  55  is provided in the base  53  for receiving the tapered pin  51 , thereby providing a mating alignment feature therefor. The base  53  if formed entirely or at least partially of a material that is attracted by the magnetic latch  18 , e.g. a ferromagnetic material including one or more of iron, cobalt and nickel. The base  53  also provides a protective cover for the uncoated side of the substrate  57 , thereby preventing unintentional and unwanted back coating. Substrate holder  23   b  ( FIG. 8   b ) includes a multi-disk annular cover  58  fastened to the base  53 . The multi-disk cover  58  includes a plurality of annular shoulders  59  for supporting a plurality of smaller substrates  61 . For odd shaped substrates, such as prisms  62 , a multi-prism cover  63  is provided for mounting to the base  53 , see  FIG. 8   c.    
   As an alternative to the base  53 , a ferromagnetic ring  71 , for attraction to the stator  41 , surrounds a substrate  72  ( FIG. 8   d ). An advantage to the ring  71  is the ability to coat the substrate  72  with the same or different coatings on opposite sides thereof without removing it from the ring  71 . Moreover, the substrate  72  and ring  71  need not be removed from the process chamber  1 , between coatings, e.g. simply flipped over by the robotic arm  7 . 
   A typical substrate would be a glass wafer 200 mm in diameter and 0.7 mm to 1.4 mm thick; however, other substrate forms are possible, e.g. up to 32 mm in thickness and a mass of up to 2 kg.