Removal of surface dopants from a substrate

Abstract

A method and apparatus for removing excess dopant from a doped substrate is provided. In one embodiment, a substrate is doped by surfaced deposition of dopant followed by formation of a capping layer and thermal diffusion drive-in. A reactive etchant mixture is provided to the process chamber, with optional plasma, to etch away the capping layer and form volatile compounds by reacting with excess dopant. In another embodiment, a substrate is doped by energetic implantation of dopant. A reactive gas mixture is provided to the process chamber, with optional plasma, to remove excess dopant adsorbed on the surface and high-concentration dopant near the surface by reacting with the dopant to form volatile compounds. The reactive gas mixture may be provided during thermal treatment, or it may be provided before or after at temperatures different from the thermal treatment temperature. The volatile compounds are removed. Substrates so treated do not form toxic compounds when stored or transported outside process equipment.

1 . A method of treating a substrate, comprising:
 disposing the substrate in a processing chamber;   depositing a layer of dopants on a surface of the substrate;   diffusing dopants from the layer of dopants into the substrate;   after diffusing the dopants into the substrate, exposing the substrate to a dopant removal mixture;   forming volatile compounds from dopants on the substrate surface by applying the dopant removal mixture to the substrate surface; and   removing the volatile compounds from the processing chamber.   
     
     
         2 . The method of  claim 1 , wherein the dopants comprise boron (B), arsenic (As), phosphorus (P), or combinations thereof. 
     
     
         3 . The method of  claim 1 , wherein the dopant removal mixture comprises hydrogen (H 2 ), nitrogen (N 2 ), oxygen (O 2 ), ammonia (NH 3 ), nitrogen trifluoride (NF 3 ), silicon tetrafluoride (SiF 4 ), or air. 
     
     
         4 . The method of  claim 1 , wherein the volatile compounds comprise arsine (AsH 3 ), phosphine (PH 3 ), borane (BH 3 ), diborane (B 2 H 6 ), borazine (B 3 H 6 N 3 ), and derivatives thereof. 
     
     
         5 . The method of  claim 1 , wherein the substrate is thermally controlled at a temperatures selected to encourage the volatile compounds to evaporate from the substrate. 
     
     
         6 . The method of  claim 5 , wherein the temperature is at least about 50° C. 
     
     
         7 . A method of processing a substrate, comprising:
 disposing the substrate in a processing chamber;   implanting dopant ions into a surface of the substrate using a plasma immersion process to form a doped substrate;   providing one or more dopant removal mixtures to the chamber;   forming a plasma from the dopant removal mixture;   exposing the doped substrate to the plasma;   producing a volatile compound from the implanted dopants by applying the plasma to the substrate; and   removing the volatile compound from the chamber.   
     
     
         8 . The method of  claim 7 , wherein dopant ions implanted in the substrate comprise boron (B), arsenic (As), phosphorus (P), or combinations thereof. 
     
     
         9 . The method of  claim 7 , wherein the plasma is an inductively coupled plasma. 
     
     
         10 . The method of  claim 7 , further comprising thermally treating the substrate at one or more temperatures selected to cause diffusion and activation of dopants in the substrate. 
     
     
         11 . The method of  claim 7 , wherein the plasma is generated outside the one or more chambers. 
     
     
         12 . The method of  claim 10 , wherein the temperatures comprise a first temperature for producing the one or more volatile compounds and a second temperature for thermally treating the substrate. 
     
     
         13 . The method of  claim 12 , wherein the first temperature is at least about 50° C. 
     
     
         14 . A method of treating a substrate, comprising:
 disposing the substrate in a plasma immersion chamber;   implanting dopants in a surface of the substrate using a plasma immersion processing in the plasma immersion chamber;   exposing the surface region to a gas mixture;   forming volatile compounds by reacting the gas mixture with dopants implanted in the surface region; and   removing the volatile compounds from the substrate.   
     
     
         15 . The method of  claim 14 , wherein the dopants comprise boron (B), arsenic (As), or phosphorus (P). 
     
     
         16 . The method of  claim 14 , wherein the substrate is thermally controlled at a temperature selected to encourage the one or more volatile compounds to evaporate from the surface region of the substrate. 
     
     
         17 . The method of  claim 14 , further comprising forming a plasma from the reactive gas mixture.