Method for forming gate

Abstract

A method for forming a gate. A gate oxide layer is formed on a substrate having an isolation structure, and a polysilicon layer is formed on the gate oxide layer. A tungsten silicide layer is formed by low pressure chemical vapor deposition with dichlorosilane and tungsten hexafluoride as a gas source on the polysilicon layer. The polysilicon layer and the tungsten silicide layer constitute a polycide layer. A first rapid thermal annealing process is performed in an ammonia atmosphere to form a first protective layer on the tungsten silicide layer. A nitride layer is formed by low pressure chemical vapor deposition on the first protective layer, and then a gate structure is defined. The gate oxide layer, the polysilicon layer, the tungsten silicide layer, the first protective layer and the nitride layer together constitute the gate structure. A second rapid thermal annealing process is performed in an ammonia atmosphere to form a second protective layer on sidewalls of the gate oxide layer, the polysilicon layer and the tungsten silicide layer. A spacer is formed and abuts the sidewalls of the first and second protective layers, and the nitride layer.

What is claimed is:  
     
         1 . A method for forming a gate, comprising the steps of: 
 providing a substrate;    forming a gate oxide layer on the substrate;    forming a polysilicon layer on the gate oxide layer;    forming a tungsten silicide layer on the polysilicon layer;    performing a first rapid thermal annealing process in an ammonia atmosphere to form a first protective layer on the tungsten silicide layer;    forming a nitride layer on the first protective layer;    defining a gate structure, wherein the gate structure includes the gate oxide layer, the polysilicon layer, the tungsten silicide layer, the first protective layer and the nitride layer;    performing a second rapid thermal annealing process in an ammonia atmosphere to form a second protective layer on sidewalls of the polysilicon layer and the tungsten silicide layer; and    forming a spacer to abut against sidewalls of the nitride layer, the first and the second protective layers.    
     
     
         2 . The method of    claim 1   , wherein the first rapid thermal annealing process further comprises: 
 performing a first annealing process for about 25-35 seconds at a temperature of about 750-850° C.; and    performing a second annealing process for about 5-15 seconds at a temperature of about 950-1050° C.    
     
     
         3 . The method of    claim 1   , wherein the first protective layer includes nitride.  
     
     
         4 . The method of    claim 1   . wherein the second rapid thermal annealing process further comprises: 
 performing a first annealing process for about 25-35 seconds at a temperature of about 750-850 ° C.; and    performing a second annealing process for about 5-15 seconds at a temperature of about 950-1050° C.    
     
     
         5 . The method of    claim 1   , wherein the second protective layer includes nitride.  
     
     
         6 . The method of    claim 1   , wherein the step of forming the tungsten silicide layer includes low pressure chemical vapor deposition with SiH 2 Cl 2  and WF 6  as a gas source.  
     
     
         7 . The method of    claim 1   , wherein the step of forming the nitride layer includes low pressure chemical vapor deposition  
     
     
         8 . The method of    claim 1   , wherein a thickness of the nitride layer is about 1400- 1600  Å.  
     
     
         9 . The method of    claim 1   , wherein the polysilicon layer includes doped polysilicon.  
     
     
         10 . A method for maintaining quality of a tungsten silicide layer, which is suitable for a semiconductor process, comprising the steps of: 
 providing a substrate;    forming a tungsten silicide layer on the substrate;    performing a first rapid thermal annealing process in an ammonia atmosphere to form a first protective layer on the tungsten silicide layer;    defining the tungsten silicide layer and the first protective layer to expose sidewalls of the tungsten silicide layer; and    performing a second rapid thermal annealing process in an ammonia atmosphere to form a second protective layer on the sidewalls of the tungsten silicide layer.    
     
     
         11 . The method of    claim 10   , wherein the first rapid thermal annealing process further comprises: 
 performing a first annealing process for about 25-35 seconds at a temperature of about 750-850° C.; and    performing a second annealing process for about 5-15 seconds at a temperature of about 950-1050° C.    
     
     
         12 . The method of    claim 10   , wherein the first protective layer includes nitride.  
     
     
         13 . The method of    claim 10   , wherein the second rapid thermal annealing process further comprises: 
 performing a first annealing process for about 25-35 seconds at a temperature of about 750-850° C.; and    performing a second annealing process for about 5-15 seconds at a temperature of about 950-1050° C.    
     
     
         14 . The method of    claim 10   , wherein the second protective layer includes nitride.  
     
     
         15 . The method of    claim 10   , wherein the step of forming the tungsten silicide layer includes low pressure chemical vapor deposition with SiH 2 Cl 2  and WF 6  as a gas source.