Plasma doping method and plasma doping apparatus

Abstract

Disclosed is a plasma doping method that, even though a plasma doping treatment is repeated, can make a dose from a film to a silicon substrate uniform for each time. According to an embodiment of the invention, there is provided a plasma doping method that places a sample on a sample electrode in a vacuum chamber, generates plasma in the vacuum chamber, and causes impurity ions in the plasma to collide against a surface of the sample so as to form an impurity doped layer in the surface of the sample. The plasma doping method includes a maintenance step of preparing the vacuum chamber having a film containing an impurity formed on an inner wall thereof such that, when the film containing the impurity fixed to the inner wall of the vacuum chamber is attacked by ions in the plasma, the amount of an impurity to be doped into the surface of the sample by sputtering is not changed even though the plasma containing the impurity ions is repeatedly generated in the vacuum chamber, a step of placing the sample on the sample electrode, and a step of irradiating the plasma containing the impurity ions so as to implant the impurity ions into the sample, and doping the impurity into the sample by sputtering from the film containing the impurity fixed to the inner wall of the vacuum chamber.

1 . A plasma doping method for forming an impurity doped layer in a substrate to be processed, the plasma doping method comprising: 
 a step (a) of preparing a vacuum chamber having an inner wall on which a film containing a first impurity is formed;    a step (b) of, after the step (a), placing the substrate to be processed on a sample table; and    a step (c) of, after the step (b), generating plasma including a second impurity in the vacuum chamber and supplying high-frequency power to an electrode having the sample table so as to dope the first impurity and the second impurity into the substrate to be processed and to form the impurity doped layer.    
   
   
       2 . The plasma doping method according to  claim 1 , wherein the inner wall surrounds the sample table on which the substrate to be processed is placed.  
   
   
       3 . The plasma doping method according to  claim 1 , wherein, in the step (c), a dose of the first impurity to be doped into the impurity doped layer is larger than a dose of the second impurity.  
   
   
       4 . The plasma doping method according to  claim 1 , wherein, in the step (c), the second impurity is doped into the substrate to be processed by irradiating the plasma containing the second impurity, and the first impurity to be sputtered and emitted when the film containing the first impurity is exposed to the plasma is doped into the substrate to be processed.  
   
   
       5 . The plasma doping method according to  claim 1 , wherein the first impurity and the second impurity are the same impurity.  
   
   
       6 . The plasma doping method according to  claim 1 , 
 wherein the substrate is a semiconductor substrate; and    in the step (a), the film containing the first impurity is set such that the total distribution of the distribution of the second impurity to be doped from the plasma containing the second impurity and the distribution of the first impurity to be doped from the film containing the first impurity is made uniform in a surface of the semiconductor substrate.    
   
   
       7 . The plasma doping method according to  claim 1 , 
 wherein the inner wall is an inner wall of the vacuum chamber.    
   
   
       8 . The plasma doping method according to  claim 1 , 
 wherein the formation of the impurity doped layer is performed using a plasma doping apparatus having the sample table, and    the step (a) includes a substep of providing the vacuum chamber, from which the film containing the first impurity is removed, in the plasma doping apparatus and then generating plasma containing the first impurity in the vacuum chamber so as to form the film containing the first impurity on the inner wall of the vacuum chamber.    
   
   
       9 . The plasma doping method according to  claim 1 , 
 wherein the formation of the impurity doped layer is performed using a plasma doping apparatus having the sample table, and    the step (a) includes:    a step (a1) of providing the vacuum chamber, from which the film containing the first impurity is removed, in a plasma doping apparatus different from the plasma doping apparatus and then generating plasma containing the first impurity ions in the vacuum chamber so as to form the film containing the first impurity on the inner wall of the vacuum chamber; and    a step (a2) of, after the step (a1), providing the vacuum chamber having the film containing the first impurity on the inner wall in the plasma doping apparatus.    
   
   
       10 . The plasma doping method according to  claim 1 , 
 wherein the inner wall is an inner wall of an inner chamber provided in the vacuum chamber.    
   
   
       11 . The plasma doping method according to  claim 1 , 
 wherein the formation of the impurity doped layer is performed using a plasma doping apparatus that is provided with a head plate having a plurality of gas outlet ports at a position facing the substrate to be processed placed on the sample table.    
   
   
       12 . The plasma doping method according to  claim 1 , 
 wherein the plasma containing the second impurity is plasma of gas containing boron.    
   
   
       13 . The plasma doping method according to  claim 12 , 
 wherein the gas containing boron is gas having boron and hydrogen molecules.    
   
   
       14 . The plasma doping method according to  claim 12 , 
 wherein the gas containing boron is diborane (B 2 H 6 ).    
   
   
       15 . The plasma doping method according to  claim 1 , 
 wherein the plasma containing the second impurity is plasma of gas that is obtained by diluting gas having boron and hydrogen molecules with rare gas.    
   
   
       16 . The plasma doping method according to  claim 15 , 
 wherein the rare gas is an atom having an atomic weight equal to or less than neon.    
   
   
       17 . The plasma doping method according to  claim 15 , 
 wherein the rare gas is helium.    
   
   
       18 . The plasma doping method according to  claim 1 , 
 wherein the plasma containing the second impurity is plasma of gas that is obtained by diluting diborane (B 2 H 6 ) with helium.    
   
   
       19 . The plasma doping method according to  claim 12 , 
 wherein an implantation depth of boron is in a range of 7.5 nm to 15.5 nm.    
   
   
       20 . The plasma doping method according to  claim 1 , 
 wherein, in the step (c), a temperature of the inner wall of the vacuum chamber is set to a desired temperature in a range of 40° C. to 90° C.    
   
   
       21 . A semiconductor device that has an impurity doped layer formed by a plasma doping method, 
 wherein a profile of boron in the impurity doped layer has a depth ranging 7 nm to 15.5 nm with a boron concentration of 5×10 18  cm −3 , abruptness of the depth profile of boron is in a range of 1.5 nm/dec to 3 nm/dec upon evaluation at a distance where the boron concentration is lowered from 1×10 19  cm −3  to 1×10 18  cm −3 .    
   
   
       22 . The semiconductor device according to  claim 21 , 
 wherein the impurity doped layer is an extension region in a MOSFET.