Plasma processing apparatus and method of designing the same

Abstract

Disclosed is a plasma processing apparatus having a plasma producing portion and a porous plate provided between the plasma producing portion and an object to be processed, wherein the porous plate has a plurality of holes which are made non-uniform with respect to at least one of shape, size and disposition. Specifically, the shape, the size or the disposition of the holes is determined on the basis of an active species distribution at the plasma producing portion and of diffusion calculation, so that plasma active species adjacent the object to be processed has desired concentration and distribution. This assures uniform plasma distribution adjacent the object while a decrease of plasma density can be well suppressed.

1 . A plasma processing apparatus, comprising: 
 a plasma producing portion; and    a porous plate provided between said plasma producing portion and an object to be processed,    wherein said porous plate has a plurality of holes which are made non-uniform with respect to at least one of shape, size and disposition.    
   
   
       2 . An apparatus according to  claim 1 , the shape, the size or the disposition of the holes is determined on the basis of an active species distribution at said plasma producing portion and of diffusion calculation, so that plasma active species adjacent the object to be processed has desired concentration and distribution.  
   
   
       3 . A plasma processing apparatus, comprising: 
 a plasma producing portion; and    a porous plate provided between said plasma producing portion and an object to be processed,    wherein said porous plate has a plurality of holes being shaped and disposed as determined on the basis of an active species distribution at said plasma producing portion and of diffusion calculation, so that plasma active species adjacent the object to be processed has desired concentration and distribution.    
   
   
       4 . An apparatus according to  claim 1  or  3 , wherein a portion around a hole having a relatively large sectional area is smaller in thickness as compared with other regions.  
   
   
       5 . An apparatus according to  claim 1  or  3 , wherein said porous plate has a thermal expansion coefficient smaller than 1×10 −5 .  
   
   
       6 . An apparatus according to  claim 1  or  3 , wherein said porous plate consists of a material that contains at least silicon.  
   
   
       7 . An apparatus according to  claim 1  or  3 , wherein centers of the holes of said porous plate are distributed on approximately concentric circles and wherein those holes disposed approximately along the same circle have approximately the same sectional area.  
   
   
       8 . An apparatus according to  claim 1  or  3 , wherein centers of the holes of said porous plate are distributed approximately equidistantly.  
   
   
       9 . An apparatus according to  claim 1  or  3 , wherein the active species adjacent the object to be processed is ions.  
   
   
       10 . An apparatus according to  claim 1  or  3 , wherein the active species adjacent the object to be processed is mainly neutral radical.  
   
   
       11 . An apparatus according to  claim 1 , further comprising a plasma processing chamber having a dielectric member for substantially transmitting microwaves, introducing means for introducing microwaves into said plasma processing chamber, and a stage provided inside said plasma processing chamber, wherein said porous plate is provided between the object to be processed, being placed on said stage, and said dielectric member, and wherein surface wave plasma is produced on the basis of the introduce microwaves.  
   
   
       12 . An apparatus according to  claim 11 , wherein said introducing means for introducing microwaves into said plasma processing chamber comprises an endless circular waveguide with a slot.  
   
   
       13 . A method of designing a plasma processing apparatus having a plasma producing portion and a porous plate provided between said plasma producing portion and an object to be processed, comprising: 
 determining a shape and disposition of holes of the porous plate on the basis of active species distribution at the plasma producing portion and of diffusion calculation, so that plasma active species adjacent the object has desired concentration and distribution.    
   
   
       14 . A method according to  claim 13 , wherein sectional areas of all the holes of the porous plate are enlarged or contracted approximately at the same ratio, whereby the concentration of the active species adjacent the object is changed without changing the distribution thereof.