Charged particle beam source, surface processing apparatus and surface processing method

Abstract

A charged particle beam source for a surface processing apparatus is disclosed. The charged particle beam source comprises: a plasma chamber; a plasma generation unit adapted to convert an input gas within the plasma chamber into a plasma containing charged particles; and a grid assembly adjacent an opening of the plasma chamber. The grid assembly comprises one or more grids each having a plurality of apertures therethrough, the one or more grids being electrically biased in use so as to accelerate charged particles from the plasma through the grid(s) to thereby output a charged particle beam, the major axis of which is substantially perpendicular to the plane of the grid assembly. The transmissivity of the or each grid to the charged particles is defined by the relative proportion of aperture area to non-aperture area, and at least one of the grids has a transmissivity which varies across the grid along a first direction, the transmissivity being lower adjacent a first extremity of the grid than adjacent a second extremity of the grid opposite the first extremity, the first direction lying parallel to the plane of the grid assembly, such that in use the charged particle beam output by the source has a non-uniform charged particle current density profile in a plane parallel to the plane of the grid assembly which varies along the first direction, the charged particle current density being lower adjacent a first edge of the beam than adjacent a second edge of the beam opposite the first edge.

1 . A charged particle beam source for a surface processing apparatus, the charged particle beam source comprising:
 a plasma chamber;   a plasma generation unit adapted to convert an input gas within the plasma chamber into a plasma containing charged particles;   a grid assembly adjacent an opening of the plasma chamber, the grid assembly comprising one or more grids each having a plurality of apertures therethrough, the one or more grids being electrically biased in use so as to accelerate charged particles from the plasma through the grid(s) to thereby output a charged particle beam, the major axis of which is substantially perpendicular to the plane of the grid assembly;   wherein the transmissivity of the or each grid to the charged particles is defined by the relative proportion of aperture area to non-aperture area, and at least one of the grids has a transmissivity which varies across the grid along a first direction, the transmissivity being lower adjacent a first extremity of the grid than adjacent a second extremity of the grid opposite the first extremity, the first direction lying parallel to the plane of the grid assembly, such that in use the charged particle beam output by the source has a non-uniform charged particle current density profile in a plane parallel to the plane of the grid assembly which varies along the first direction, the charged particle current density being lower adjacent a first edge of the beam than adjacent a second edge of the beam opposite the first edge.   
     
     
         2 . A charged particle beam source according to  claim 1 , wherein in use the charged particle beam output by the source has a non-uniform charged particle current density profile in a plane parallel to the plane of the grid assembly which increases monotonically along the first direction, from the first edge of the beam to the a second edge of the beam, at least at a range of distances from the grid assembly. 
     
     
         3 . A charged particle beam source according to  claim 1 , wherein the transmissivity of the at least one of the grids increases monotonically across the grid along the first direction. 
     
     
         4 . A charged particle beam source according to  claim 1 , wherein the transmissivity varies across the grid along the first direction from a minimum transmissivity value adjacent the first extremity of the grid to a maximum transmissivity value adjacent the second extremity of the grid. 
     
     
         5 . A charged particle beam source according to  claim 1 , wherein the transmissivity of the at least one of the grids varies continuously or in discrete steps along the first direction. 
     
     
         6 . A charged particle beam source according to  claim 1 , wherein the transmissivity of the at least one of the grids has an additional radial variation so as to compensate for a radial non-uniformity of the plasma and/or beam. 
     
     
         7 . A charged particle beam source according to  claim 1 , wherein the transmissivity of the at least one grid is varied by locally varying one or more of the size, shape, number or spacing of the apertures through the grid. 
     
     
         8 . A charged particle beam source according to  claim 1 , wherein the transmissivity of each of the grids of the grid assembly varies across the respective grid along the first direction, the transmissivity being lower adjacent a first extremity of the grid than adjacent a second extremity of the grid opposite the first extremity. 
     
     
         9 . A charged particle beam source according to  claim 1 , wherein the transmissivity of each of the grids of the grid assembly varies across the respective grid in substantially the same manner. 
     
     
         10 . A charged particle beam source according to  claim 1 , wherein the apertures of the respective grids are substantially aligned with one another along a direction perpendicular to the plane of the grid assembly. 
     
     
         11 . A charged particle beam source according to  claim 1 , wherein the grid assembly comprises at least two grids which are oppositely biased in use to accelerate charged particles therebetween, and preferably further comprises a third grid which is grounded. 
     
     
         12 - 14 . (canceled) 
     
     
         15 . A surface processing apparatus, comprising:
 a processing chamber;   a substrate holder inside the processing chamber; and   a charged particle beam source in accordance with  claim 1  arranged to output the charged particle beam towards the substrate holder in use;   wherein the substrate holder is configured to hold a substrate, in use, such that the plane of the substrate is non-orthogonal to the major axis of the charged particle beam, the substrate being tilted relative to the charged particle beam source in the first direction such that a first extremity of the substrate is located closer to the charged particle beam source than a second extremity of the substrate, opposite the first, the first extremity of the substrate being located on the same side of the charged particle beam as the first extremity of the at least one grid and the second extremity of the substrate being located on the same side of the charged particle beam as the second extremity of the at least one grid.   
     
     
         16 . A surface processing apparatus according to  claim 15 , wherein the transmissivity of the at least one grid in the first direction varies in a manner dependent on the magnitude of the angle of tilt of the substrate in the first direction such that, in use, the charged particle current density of the charged particle beam incident on the substrate is substantially uniform across the substrate. 
     
     
         17 . A surface processing apparatus according to  claim 15 , wherein in use the charged particle beam output by the source has a non-uniform charged particle current density profile in a plane parallel to the plane of the grid assembly which increases monotonically along the first direction, from the first edge of the beam to the a second edge of the beam, at least at a range of distances from the grid assembly, which range includes the location of the substrate. 
     
     
         18 . A surface processing apparatus according to  claim 15 , wherein the substrate holder is configured to hold the substrate in a fixed, rotationally static position in use. 
     
     
         19 - 20 . (canceled) 
     
     
         21 . A method of surface processing, comprising:
 providing a surface processing apparatus in accordance with  claim 15 ;   mounting a substrate on the substrate holder in the processing chamber of the surface processing apparatus, such that the plane of the substrate is non-orthogonal to the major axis of the charged particle beam, the substrate being tilted relative to the charged particle beam source in the first direction such that a first extremity of the substrate is located closer to the charged particle beam source than a second extremity of the substrate, opposite the first, the first extremity of the substrate being located on the same side of the charged particle beam as the first extremity of the at least one grid and the second extremity of the substrate being located on the same side of the charged particle beam as the second extremity of the at least one grid; and   activating the charged particle beam source to thereby treat the surface of the substrate using the charged particle beam.   
     
     
         22 . A method according to  claim 21 , wherein the charged particle beam output by the source has a non-uniform charged particle current density profile in a plane parallel to the plane of the grid assembly which increases monotonically along the first direction, from the first edge of the beam to the a second edge of the beam, at least at a range of distances from the grid assembly, which range includes the location of the substrate. 
     
     
         23 . A method according to  claim 21 , wherein the transmissivity of the at least one grid in the first direction is configured to vary in a manner dependent on the magnitude of the angle of tilt of the substrate in the first direction such that the charged particle current density of the charged particle beam incident on the substrate is substantially uniform across the substrate. 
     
     
         24 . A method according to  claim 21 , wherein the substrate is fixed in a static rotational position for the duration of the treatment using the charged particle beam. 
     
     
         25 - 27 . (canceled) 
     
     
         28 . A method of manufacturing a grid assembly for a charged particle beam source, comprising:
 (a) selecting a tilt angle at which a substrate is to be positioned relative to the major axis of the charged particle beam output by the charged particle beam source in a first direction;   (b) for the selected tilt angle, determining the non-uniformity in charged particle current density of the charged particle beam output by the charged particle beam source using an arbitrary grid assembly along the first direction at the intersection with the substrate;   (c) based on the determined non-uniformity and the arbitrary grid assembly, designing a grid template in which the transmissivity of the grid varies in the first direction so as to compensate for the determined non-uniformity in charged particle current density; and   (d) making a grid assembly in which at least one of the grids is in accordance with the designed grid template.   
     
     
         29 . (canceled)