Patent Publication Number: US-2006016398-A1

Title: Supporting and lifting device for substrates in vacuum

Description:
BACKGROUND OF THE INVENTION  
      The invention addresses pin systems that are used in vacuum chambers in general and in plasma enhanced chemical vapor deposition (PECVD) reactors in particular. These pins are used for lifting and supporting substrates in a reactor. When the reactor is open, the pins are elevated to receive the substrate, which is introduced by a robot fork. After the substrate has been placed on the pins, they are lowered until the substrate reaches the position in which the substrate is to be treated. There are also systems known in the art, where the reactor bottom is elevated relatively to the pins. The pins run in a guidance hole that is machined into the reactor bottom. Typically, the upper end of the guidance hole that disembogue to the reactor&#39;s interior is countersunk. Additionally, the pin head is flared to prevent the pins from falling through the guidance hole. The two latter characteristics of the pin system allow the pin head to be positioned close to flush with the reactor bottom. Usually, an elevator system consisting of a lift-arm and an elevator mechanism lifts the pin in the desired position.  
      The current pin design, both geometry and materials, suffer from frequent pin self-locking and pin breakage. Both issues result in inhomogeneous deposition rates, substrate fracture and can even lead to a reactor shut-down.  
      The pin self-locking is due to lateral forces that are applied on the pin. These lateral forces can be induced by the thermal expansion of the substrate when entering the heated chamber and the pin elevation system that pushes the pin not exactly in the guidance hole axis. High friction at the pin-substrate, pin-elevator and pin-guidance interfaces combined with insufficient guidance (poor pin to guide length ratio) amplify the pin-locking issue. The pin breakage can happen when the elevator pushes on a self-locked pin.  
     DESCRIPTION OF RELATED ART  
      US 2004/0045509 teach how to reduce the friction between the pin and its guidance hole. The solution is based on a pin design, where the pin has at least one larger diameter shoulder that reduces the contact area between the pin and its guidance hole, thereby reducing pin scratching, particle generation and component wear.  
      Another attempt to reducing the lateral forces that act on the pin is described in U.S. application 2003/0205329. Herein, a pin design is presented that decouples the lateral forces that are induced by a lift-arm. The pin system consists mainly of three parts; a lifting pin, an actuator pin and a lift arm. The lifting pin and the actuator pin are each guided in two bushings. The two pins are coaxial positioned in such a way that the actuator pin is used to move the lifting pin in the upper and lower end positions. A connector acts as an interface between the said pins. This connector allows for lateral clearance between the actuator pin and the lift pin. The actuator pin itself is moved by a lift-arm assembly that houses wear pads. The actuator pins are disposed on these wear pads that are larger in diameter as the actuator pin. The actuator pins may float laterally across the wear pads.  
      The solutions presented in US 2004/0045509 and 2003/0205329 only partially solve the aforementioned technical problems. The first is designed to reduce the friction in the pin movement direction and the second is designed to reduce lateral forces on the pin systems that are induced by the elevator system.  
      Prior art does not provide a solution that reduces the friction between the pin system and its guidance hole and the lateral forces that are induced by the elevator at the same time. Additionally, there is no known solution that decouples the lateral forces that are induced by the substrate.  
     SUMMARY OF THE INVENTION  
      The present invention aims at reducing the lateral forces that are acting on the pin and the guidance friction during the elevation movement. Lateral forces can be induced by the lift-arm and the substrate. The elevator system consists of an lift-arm and a sole plate that is attached to the arm. The pin stands loose on the sole plate and resides in a bushing that is mounted on the reactor bottom. Therefore, the contact areas pin/substrate, pin/sole plate and pin/bushing are of primary interest.  
      An inventive pin assembly for lifting and supporting substrates therefore comprises a lift pin ( 1 ) having a top and a bottom end; the top end being construed to receive and support a substrate ( 4 ); the bottom end being construed to be actuated by an elevator system ( 3   a ); the lift pin being movably sustained by a guide, wherein said guide comprises a roller glide to reduce the friction of the pin movement in a vertical axis. In further embodiments the roller glide comprises six rollers, arranged in a bushing and is being mounted on the reactor bottom. Further on the bottom end of the lift pin ( 1 ) is, at least during the lifting operation, in contact with the the elevator system via a sole plate, comprising a top plate ( 7 ) being laterally movable relative to said elevator system. The sole plate further comprises a ball holding plate ( 8 ) with balls ( 9 ) being arranged beyond the top plate ( 7 ), which again may be laterally movable relative to said elevator system. In a further aspect of the invention the top end of the lift pin ( 1 ) further comprises a clearance being construed to hold a rolling ball ( 14 ) being supported by a ball bearing ( 13 ) and secured by a retaining ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1   a ) shows an inventive support and lifting device employing three aspects of the invention.  
       FIG. 1   b ) shows a substrate on said inventive device in a bottom position.  
       FIG. 1   c ) shows a substrate on said inventive device in a top position.  
       FIG. 2  shows a cross section through and a top view on a roller bearing bushing according to one aspect of the invention.  
       FIG. 3  shows ball bearing sole plate according to a further aspect of the invention.  
       FIG. 4  shows a ball bearing head according to a further aspect of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1   a  shows the assembly of a pin system: A pin  1  is guided by the roller glide  2  and is actuated by the sole plate  3 , which is mounted to a lift-arm  3   a.  At least three of these pin systems are applied for supporting and lifting a substrate  4 . The pins are supposed to receive the substrate  4  from a robot fork (not shown in  FIG. 1 ) that places the substrate on the elevating pins. Then, the pins pose the substrate  4  on the reactor bottom  2   a  ( FIG. 1   b ). This is the substrate&#39;s final position before the coating process starts. After the coating process has ended, the pins lift the substrate in the elevated position ( FIG. 1   c ) before a robot fork removes the substrate from the coating chamber.  
      The inventive pin system comprises three elements: a roller glide, a ball bearing sole plate and a ball-bearing head pin.  
      The first of the presented elements is the roller glide  2 . This roller glide is designed for reducing the friction of the pin movement in a vertical axis. The roller glide is mounted on the reactor bottom  2   a  and guides the pin. The glide (see  FIG. 2 ) consists of e.g. six rollers  6 ,  6   a, b, c  that are made out of a material allowing low friction and low wear with the axis and bushing, chemically resistant against the process gases, and which keeps its properties at the process temperature. The rollers itself are held by bushing ( 5 ) made of such a material.  
      A second element defines the interface between the pin and the elevator (see  FIG. 3 ): A ball bearing sole plate. This sole plate minimizes the lateral forces that could act on the pin. The lateral forces are induced by the lift-arm due to its lifting movement that does not match perfectly the pin&#39;s vertical movement axis. The sole plate comprises four main elements: the top plate  7  and the ball holding plate  8  that are elastically borne on the bottom plate  10 . Balls  9  improve the top plate&#39;s lateral freedom of movement and hence minimize the lateral forces that act on the pin. The elastic bearing  7   a,    8   a  of the top plate  7  and the ball holding plate  8  is needed for re-centering said two plates after one pin moving cycle. The restoring force of the elastic bearing, e.g. a spring is a limiting factor for the lateral force that can be transmitted on the pin. Therefore, the spring constant should be relatively low to permit the floating movement of the top plate  7 .  
      The third element according to the invention is a pin ball-bearing head. ( FIG. 4 ) The function of this modified pin head is to reduce the lateral forces that act on the pin. These forces may be introduced by the substrate. The pin head consists of a pin end  11  with a hemispherical clearance and a retaining ring  12 , which holds a ball bearing  13  and a rolling ball  14 . The rotational freedom of movement of the rolling ball  14  is enhanced by the ball bearing  13 . Thereby, the lateral forces that can be induced by the substrate are minimized. The retaining ring ( 12 ) is slightly thicker than the pin shaft in order to prevent the pin from falling through the roller glide.  
     ADVANTAGES OF THE INVENTION  
      The inventive pin design lowers the risk of self-locking considerably. The features of the new solution, less guiding friction paired with decoupling of lateral forces, lead to a higher yield ratio and less downtime of the coating device. Additional positive effects are the reduction of particles in the reactor and the reduction of the risk to scratch the substrate. Thanks to the reduced friction of the pins, the abrasive forces between the pins and its guidance, as well as between the pins and the substrate are minimized. Particle contamination and the risk to scratch the substrate of the reactor are lowered.  
      All these new characteristics increase the productivity and the quality of the coating process and hence increase the economic value to the user of such devices.  
     LIST OF NUMERALS  
     
         
           1  pin, lift pin  
           2  roller glide  
           2   a  reactor bottom  
           3  plate  
           3   a  lift arm, elevator system  
           4  substrate  
           5  bushing  
           6  roller  
           6   a, b, c  roller  
           7  top plate  
           7   a  elastic bearing  
           8  ball holding plate  
           8   a  elastic bearing  
           9  ball(s)  
           10  bottom plate  
           11  pin end  
           12  retaining ring  
           13  ball bearing  
           14  rolling ball