Process for forming a thin oxide layer

Abstract

A novel process for forming a robust, sub-100 Å oxide is disclosed. Native oxide growth is tightly controlled by flowing pure nitrogen during wafer push and nitrogen with a small amount of oxygen during temperature ramp and stabilization. First, a dry oxidation is performed in oxygen and 13% trichloroethane. Next, a wet oxidation in pyrogenic steam is performed to produce a total oxide thickness of approximately 80 Å. The oxide layer formed is ideally suited for use as a high integrity gate oxide below 100 Å. The invention is particularly useful in devices with advanced, recessed field isolation where sharp silicon edges are difficult to oxidize. For an oxide layer of more than 100 Å, a composite oxide stack is used which comprises 40-90 Å of pad oxide formed using the above novel process, and 60-200 Å of deposited oxide.

We claim:  
     
       1. A process for forming an oxide layer on a semiconductor substrate comprising the steps of: 
       performing a first oxidation in a first mixture comprising oxygen and a chlorine containing compound, said mixture containing a sufficient amount of said chlorine containing compound such that chlorine exists in said mixture at a volume concentration greater than or equal to 9%; and  
       performing a second oxidation in a second mixture comprising pyrogenic steam to form said oxide layer, said oxide layer being less than 100 Å in thickness.  
     
     
       2. The process as in  claim 1  wherein the thickness of said oxide layer is less than 100 Å and wherein said first oxidation produces approximately 15-50 Å of the thickness of said oxide layer and said second oxidation produces approximately 25-65 Å of the thickness of said oxide layer. 
     
     
       3. The process as defined by  claim 1  wherein said oxide layer is a first oxide layer of a composite oxide stack and wherein said process further comprises the step of depositing a second oxide layer on said first oxide layer by chemical vapor deposition to form said composite oxide stack comprising said first and said second oxide layers. 
     
     
       4. The process as defined by  claim 3  wherein said first oxide layer has a thickness in the range of 40-90 Å and said second oxide layer has a thickness in the range of 60-200 Å. 
     
     
       5. The process as defined by  claim 4  further comprising the step of annealing said composite oxide stack in an annealing ambient. 
     
     
       6. The process as defined by  claim 1  wherein said chlorine containing compound comprises a substance selected from the group consisting of trichloroethane, trichloroethylene, chlorine, hydrogen chloride, or any combination thereof. 
     
     
       7. The process as defined by  claim 1  wherein said first oxidation is performed at a temperature in the range of approximately 750°-900° C. and said second oxidation is performed at a temperature in the range of 750°-900° C. 
     
     
       8. The process as defined by  claim 1  wherein said process is used in the formation of a semiconductor transistor, said semiconductor transistor having a gate oxide comprising said oxide layer. 
     
     
       9. The process as defined by  claim 1  wherein said semiconductor substrate is subjected to a recessed field isolation process. 
     
     
       10. The process as defined by  claim 8  wherein said semiconductor transistor is isolated by a recessed field isolation structure. 
     
     
       11. A process for forming an oxide layer on a semiconductor substrate comprising the steps of: 
       performing an initial oxidation in an initial mixture comprising an inert gas selected from the group consisting of nitrogen, argon, helium, or any combination thereof and approximately 1% oxygen;  
       performing a first oxidation in a first mixture comprising oxygen and a chlorine containing compound, said mixture containing a sufficient amount of said chlorine containing compound such that chlorine exists in said mixture at a volume concentration greater than or equal to 9%; and  
       performing a second oxidation in a second mixture comprising pyrogenic steam to form said oxide layer, said oxide layer being less than 100 Å in thickness.  
     
     
       12. The process as defined by  claim 11  wherein said initial oxidation produces approximately 5-20    5 - 10 Å of the thickness of said oxide layer, said first oxidation produces approximately 15-50 Å of the thickness of said oxide layer and said second oxidation produces approximately 25-65 Å of the thickness of said oxide layer. 
     
     
       13. The process as defined by  claim 11  wherein said chlorine containing compound comprises a substance selected from the group consisting of trichloroethane, trichloroethylene, chlorine, hydrogen chloride, or any combination thereof. 
     
     
       14. The process as defined by  claim 11  wherein said first oxidation is performed at a temperature in the range of approximately 750°-900° C. and said second oxidation is performed at a temperature in the range of 750°-900° C. 
     
     
       15. The process as defined by  claim 11  wherein said process is used in the formation of a semiconductor transistor, said semiconductor transistor having a gate oxide comprising said oxide layer. 
     
     
       16. The process as defined by  claim 11  wherein said semiconductor substrate is subjected to a recessed field isolation process. 
     
     
       17. The process as defined by  claim 15  wherein said semiconductor transistor is isolated by a recessed field isolation structure. 
     
     
       18. A process for forming an oxide layer on a semiconductor substrate comprising the steps of: 
       pushing said substrate into a furnace while flowing a first gas mixture comprising an inert gas selected from the group consisting of nitrogen, argon, helium, or any combination thereof over said substrate;  
       ramping up the temperature of said furnace from a first temperature to a second temperature while flowing a second gas mixture comprising an inert gas selected from the group consisting of nitrogen, argon, helium, or any combination thereof over said substrate;  
       maintaining said second temperature while flowing a third gas mixture comprising an inert gas selected from the group consisting of nitrogen, argon, helium, or any combination thereof and approximately 1% oxygen over said substrate;  
       performing a first oxidation in a third gas mixture comprising oxygen and a chlorine containing compound; and  
       performing a second oxidation in a fifth gas mixture comprising pyrogenic steam to form said oxide layer, said oxide layer being less than 100 Å in thickness.  
     
     
       19. The process as defined by  claim 18  wherein the thickness of said oxide layer is less than 100 Å and wherein said first oxidation produces approximately 15-50 Å of the thickness of said oxide layer and said second oxidation produces approximately 25-65 Å of the thickness of said oxide layer. 
     
     
       20. The process as defined by  claim 18  wherein said chlorine containing compound comprises a substance selected from the group consisting of trichloroethane, trichloroethylene, chlorine, hydrogen chloride, or any combination thereof. 
     
     
       21. The process as defined by  claim 18  wherein said first oxidation is performed at a temperature in the range of approximately 750°-900° C. and said second oxidation is performed at a temperature in the range of 750°-900° C. 
     
     
       22. The process as defined by  claim 18  wherein said process is used in the formation of a semiconductor transistor, said semiconductor transistor having a gate oxide comprising said oxide layer. 
     
     
       23. The process as defined by  claim 18  wherein said semiconductor substrate is subjected to a recessed field isolation process. 
     
     
       24. The process as defined by  claim 22  wherein said semiconductor transistor is isolated by a recessed field isolation structure. 
     
     
       25. The process as defined by  claim 18  wherein the volume concentration of chlorine due to said chlorine containing compound is greater than or equal to 9%. 
     
     
       26. The process as defined by  claim 18  wherein said chlorine containing compound comprises a substance selected from the group consisting of trichloroethane, trichloroethylene, chlorine, hydrogen chloride, or any combination thereof. 
     
     
       27. The process as defined by  claim 18  wherein said second gas mixture further comprises approximately 1% oxygen. 
     
     
       28. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace; and  
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound wherein the volume concentration of    chlorine resulting from said chlorine containing compound is greater than or equal to  9% , said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate has a total oxide thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient.    
     
     
       29. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
         exposing said semiconductor substrate to a first ambient, said first ambient comprising a chlorine containing compound wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   % , said first ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate has a total oxide thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said first ambient;    
       
         exposing said semiconductor substrate to a second ambient after exposing said substrate to said first ambient, said second ambient comprising H 
         2 
         O; and  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.  
       
     
     
       30. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
         exposing said semiconductor substrate to an ambient, said first ambient comprising a chlorine containing compound wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   % , said first ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said first ambient;    
       
         exposing said semiconductor substrate to a second ambient after exposing to said substrate to said first ambient, said second ambient comprising H 
         2 
         O;  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.; and  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature above  750 ° C.  
       
     
     
       31. The process as described in  claim 28  wherein said first ambient is a dry ambient.  
     
     
       32. The process as described in  claim 29  wherein said first ambient is a dry ambient.  
     
     
       33. The process as described in  claim 28  wherein said first ambient comprises trichloroethane.  
     
     
       34. The process as described in  claim 29  wherein said first ambient comprises trichloroethane.  
     
     
       35. The process as described in  claim 31  wherein said first ambient comprises trichloroethane.  
     
     
       36. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient; and  
       
       
         exposing said semiconductor substrate to a second ambient, said second ambient comprising H 
         2 
         O;  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       37. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said ambient comprises trichloroethane; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       38. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.;  
       
       
         wherein said ambient comprises trichloroethane; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       39. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said ambient is a dry ambient;  
       
       
         wherein said ambient comprises trichloroethane; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       40. The process as described in  claim 28  wherein an initial oxide layer is grown on said semiconductor substrate prior to said step of exposing said semiconductor substrate to said ambient.  
     
     
       41. The process as described in  claim 39  wherein said initial oxide layer has a thickness and a range of approximately  5 - 10  Å.  
     
     
       42. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient being a dry ambient, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate comprises an oxide layer of approximately  5 - 10  Å prior to said step of exposing said semiconductor substrate to said ambient; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       43. The method as described in  claim 42  wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.  
     
     
       44. The process as described in  claim 43  wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature above  750 ° C.  
     
     
       45. The method as described in  claim 42  wherein said ambient comprises trichloroethane.  
     
     
       46. The method as described in  claim 43  wherein said ambient comprises trichloroethane.  
     
     
       47. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient being a dry ambient, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate comprises an oxide layer of approximately  5 - 10  Å prior to said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       48. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient being a dry ambient, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate comprises an oxide layer of approximately  5 - 10  Å prior to said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said ambient comprises trichloroethane; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       49. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient being a dry ambient, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said substrate comprises an oxide layer of approximately  5 - 10  Å prior to said step of exposing said semiconductor substrate to said ambient;  
       
       
         wherein said step of exposing said semiconductor substrate to said ambient is performed at a temperature of less than  900 ° C.;  
       
       
         wherein said ambient comprises trichloroethane; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       50. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor substrate in a furnace;  
       
       
         exposing said semiconductor substrate to a first ambient, said first ambient comprising a chlorine containing compound, said ambient oxidizing said semiconductor substrate to form an oxidized layer, wherein said oxidized layer has a thickness of less than or equal to approximately  70  Å after said step of exposing said semiconductor substrate to said ambient;  
       
       
         exposing said semiconductor substrate to a second ambient, said second ambient after exposing said substrate to said first ambient comprising H 
         2 
         O; and  
       
         wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   %.  
     
     
       51. The process of describing  claim 50  wherein said step of exposing said semiconductor substrate to said first ambient is performed at a temperature of less than  900 ° C.  
     
     
       52. The process as described in  claim 51  wherein said step of exposing said semiconductor substrate to said first ambient is performed at a temperature above  750 ° C.  
     
     
       53. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
       
         placing said semiconductor said substrate in a furnace; and  
       
         exposing said semiconductor substrate to an ambient, said ambient comprising a chlorine containing compound, said ambient being a dry ambient, said ambient oxidizing said semiconductor substrate to form an oxidized layer, where is the substrate comprises an oxide layer of approximately  5 - 10  Å prior to said step of exposing said semiconductor substrate to said ambient, and wherein the volume concentration of chlorine resulting from said chlorine containing is greater than or equal to  9   %.  
     
     
       54. A process for treating a semiconductor substrate comprising the steps of: 
       
         providing said semiconductor substrate;  
       
         exposing said semiconductor substrate to a first ambient, said first ambient comprising a chlorine containing compound wherein the volume concentration of chlorine resulting from said chlorine containing compound is greater than or equal to  9   % , said first ambient oxidizing said semiconductor substrate to form a first oxidized layer having chlorine therein, said first oxide layer being less than  100  Å in thickness; and    
       
         exposing said semiconductor substrate to a second ambient after exposing said substrate to said first ambient, wherein said second ambient exposure removes substantially all of said chlorine from said first oxidized layer.