Transport mechanism for disk-shaped workpieces

Abstract

A transport mechanism for disk-shaped workpieces has a horizontally movable transport arm with two elongated carrying elements at one end, for receiving the workpiece. A cassette which includes a comb structure at each side for receiving several workpieces, is inserted free of contact between two adjacent combs with workpieces therein for vertically lifting a workpiece. The carrying elements are disposed such that during a cassette engagement they are each positioned substantially adjacent and parallel to the comb structure along a comb, and that in this region along and between two adjacent comb planes on one side of the cassette, a scanning beam is provided for workpiece acquisition, and that the scanning beam is relatively height-positionable with respect to the cassette. The scanning beam is tilted about a small angle with respect to the horizontal workpiece plane.

1 . Transport mechanism for disk-shaped workpieces ( 2 ,  3 ,  4 ,  5 ,  7 ), in particular for semiconductor wafers, with a controlled, horizontally movable transport arm at whose one end two spaced-apart, elongated carrying elements ( 26 ,  27 ) are disposed for the substantially horizontal reception of the workpiece and that a cassette ( 20 ) is provided, which at two opposite sides includes a comb structure ( 18 ) for the substantially horizontal reception of several workpieces ( 7 ), the carrying elements ( 26 ,  27 ) and the comb structure ( 18 ) being implemented such that these elements can be introduced between two adjacent, spaced-apart combs ( 19 ) of the comb structure ( 18 ) free of contact with the workpieces potentially deposited therein, for lifting or depositing a workpiece ( 7 ) with the aid of an additional vertical movement relative with respect to the cassette ( 20 ) and the transport arm, characterized in that the carrying elements ( 26 ,  27 ) are disposed such that during the cassette engagement these are essentially each positioned ( 18 ) adjacent parallel to the comb structure along a comb and that in this region along and between two adjacent comb planes on one side of the cassette ( 20 ) a scanning beam ( 35 ) is provided for detecting a workpiece ( 7 ) and its position and that the scanning beam ( 35 ) is height-positionable relative with respect to the cassette ( 20 ), the scanning beam ( 35 ) being guided tilted by a small angle ( 34 ) with respect to the horizontal workpiece plane.  
   
   
       2 . Transport mechanism as claimed in  claim 1 , characterized in that for the transport mechanism with transport arm and cassette ( 20 ) are defined handling zones ( 12 ,  13 ) within which the carrying elements ( 26 ,  27 ) interact with the surface of the workpiece ( 7 ), wherein these elements with respect to the workpiece are determined as two spaced-apart parallel opposing strip-shaped areas, which are oriented substantially parallel to the comb structure ( 18 ) when the workpiece is inserted into the cassette ( 20 ).  
   
   
       3 . Transport mechanism as claimed in  claim 2 , characterized in that the width ( 11 ) of the handling zones ( 12 ,  13 ) is determined by the sum of the vertical system tolerances ( 8 ) of the transport mechanism in combination with the maximal upward and downward bending attained by the workpiece when supported on a line-form support ( 1 ) with its bending angles ( 9 ,  10 ) and where these angles intersect with the horizontal planes of the maximum vertical system tolerances.  
   
   
       4 . Transport mechanism as claimed in  claim 2 , characterized in that the workpiece ( 7 ) is a semiconductor wafer and the width of the handling zones is 10 to 20 mm.  
   
   
       5 . Transport mechanism as claimed in  claim 1 , characterized in that the angle of tilt ( 34 ) of the scanning beam ( 35 ) is defined such that the beam guided along two adjacent parallel combs ( 18 ) the comb distance ( 19 ) is not exceeded.  
   
   
       6 . Transport mechanism as claimed in  claim 1 , characterized in that for the positioning of a workpiece ( 7 ) with respect to the cassette ( 20 ) a mechanism is provided for the vertical movement of the cassette ( 20 ).  
   
   
       7 . Transport mechanism as claimed in  claim 1 , characterized in that at the one end of the horizontally disposed comb structure ( 18 ) at least one stop means ( 16 ,  17 ) is provided for delimiting the end position of the workpiece in the cassette ( 20 ), this stop means being disposed outside of the optical path of the scanning beam ( 35 ).  
   
   
       8 . Transport mechanism as claimed in  claim 1 , characterized in that the carrying elements ( 26 ,  27 ) are implemented in the form of rods.  
   
   
       9 . Transport mechanism as claimed in  claim 1 , characterized in that a second permissible handling zone width ( 24 ,  25 ) is determined, which is smaller than the width of the first handling zone ( 12 ,  13 ) and which is located within this first handling zone determined by the system tolerances, and that this second handling zone width ( 24 ,  25 ) is determined by the cross section dimension ( 21 ) of the carrying elements ( 26 ,  27 ) and of the cassette gap width ( 23 ) still free at maximally possible resulting deflections of the workpiece ( 7 ).  
   
   
       10 . Transport mechanism as claimed in  claim 1 , characterized in that a further, tilted scanning beam ( 35 ′) is provided on the opposite side of the first scanning beam ( 35 ) in the proximity of the opposing other comb structure ( 18 ) of the cassette ( 20 ).  
   
   
       11 . Transport mechanism as claimed in  claim 1 , characterized in that it comprises at least two transport robots rotatable about the axes ( 66 ,  67 ) with one transport arm ( 60 ,  61 ) each and a rotating mechanism ( 62 ) for orienting ( 65 ) the handling zones ( 12 ,  13 ) with respect to the transport direction of the transport arms ( 60 ,  61 ) if the transfer position of the workpiece does not lie on the line connecting the two axes ( 66 ,  67 ) of the transport robots.