Addition of ballast hydrocarbon gas to doped polysilicon etch masked by resist

Abstract

A chemical composition and method for providing uniform and consistent etching of gate stacks on a semiconductor wafer, whereby the composition includes an etchant and an added ballast gas added. The gate stacks are formed using this combined etchant and ballast gas composition. The ballast gas may either be similar to, or the equivalent of, a gaseous byproduct generated within the processing chamber. The ballast gas is added in either an overload amount, or in an amount sufficient to compensate for varying pattern factor changes across the water. This etchant and added ballast gas form a substantially homogeneous etchant across the entire wafer, thereby accommodating for or compensating for these pattern factor differences. When etching the wafer using this homogeneous etchant, a passivation layer is formed on exposed wafer surfaces. The passivation layer protects the lateral sidewalls of the gate stacks during etch to result in straighter gate stacks.

1 . A method for etching gate stacks on a semiconductor wafer comprising: 
 providing a semiconductor wafer having a gate stack layer within a processing chamber;    flowing an etchant into said processing chamber;    adding an overload amount of a ballast gas within said processing chamber to form a substantially homogeneous etchant across said semiconductor wafer, said substantially homogeneous etchant having a higher concentration of said ballast gas as compared to said etchant;    etching a gate stack in said gate stack layer by contacting said gate stack layer with said substantially homogeneous etchant; and    simultaneously, depositing a passivation layer over all exposed surfaces during said etching using said ballast gas within said substantially homogeneous etchant to provide substantially uniform etching results.    
   
   
       2 . The method of  claim 1  wherein said ballast gas comprises a carbon containing gas having a chemical formula C x H y , wherein x is an integer ranging from 1 to 10, and y is an integer ranging from 2 to 22.  
   
   
       3 . The method of  claim 1  wherein said ballast gas comprises a carbon containing gas having a chemical formula C x H y A, wherein x is an integer ranging from 1 to 10, y is an integer ranging from 0 to 21, and A represents at least one additional substituent selected from the group consisting of O, N, S, P, F, Cl, Br, I, and combinations thereof.  
   
   
       4 . A method for etching gate stacks on a semiconductor wafer comprising: 
 providing a semiconductor wafer within a processing chamber, said semiconductor wafer having a patterned photo resist layer over a gate stack layer;    flowing an etchant into said processing chamber;    contacting said etchant to said semiconductor wafer to generate a reaction by-product that is diffused throughout said etchant at varying concentrations across said semiconductor wafer;    adding a ballast gas within said processing chamber to equilibrate said varying concentrations of said reaction by-product and provide a substantially homogeneous etchant across said semiconductor wafer; and    etching a gate stack in said gate stack layer using said patterned photo resist layer by contacting said gate stack layer with said substantially homogeneous etchant, while simultaneously depositing a passivation layer over all exposed surfaces during said etching to provide substantially uniform etching results.    
   
   
       5 . The method of  claim 4  wherein said gate stack layer is selected from the group consisting of a dual gate stack layer having a pre-doped region and a non-doped region and a uniformly pre-doped region.  
   
   
       6 . The method of  claim 4  wherein said gate stack layer is selected from the group consisting of silicon, doped silicon, polysilicon, doped polysilicon, germanium, silicon germanium, silicon germanium carbon, mixtures thereof, alloys thereof and multilayers thereof.  
   
   
       7 . The method of  claim 4  further including the step of providing a hard mask layer between said photo resist layer and said gate stack layer.  
   
   
       8 . The method of  claim 4  wherein said etchant is selected from the group consisting of a halogen-based plasma in the presence of an oxygen gas, a halogen-based plasma in the presence of a nitrogen gas, and mixtures thereof.  
   
   
       9 . The method of  claim 4  wherein said reaction by-product comprises gaseous by-products desorbed from a surface of said photo resist layer.  
   
   
       10 . The method of  claim 9  wherein said reaction by-product further comprises gaseous particles desorbed from a surface of said gate stack layer.  
   
   
       11 . The method of  claim 4  wherein said ballast gas and said reaction by-product comprise an identical gas.  
   
   
       12 . The method of  claim 4  wherein said ballast gas and said reaction by-product comprise first and second gases, respectively, that are chemically equivalent to each other for depositing said passivation layer.  
   
   
       13 . The method of  claim 4  wherein said ballast gas is added within said processing chamber in an amount that overloads said etchant with said ballast gas such that said ballast gas is a dominating constituent of said etchant.  
   
   
       14 . The method of  claim 4  wherein said ballast gas is added within said processing chamber in an amount that compensates for varying patterns of said patterned photo resist layer residing across said semiconductor wafer, and the varying amounts of said reaction by-product desorbed from said varying patterned photo resist layer and diffused at varying concentrations throughout said etchant.  
   
   
       15 . The method of  claim 4  wherein said patterned photo resist layer comprises a patterned hydrocarbon containing resist layer such that upon contact with said etchant, hydrocarbon containing species are desorbed from said patterned hydrocarbon containing resist layer and diffused throughout said etchant at varying concentrations across said semiconductor wafer, and said ballast gas comprising a carbon containing ballast gas added to said processing chamber to equilibrate said varying concentrations of said hydrocarbon containing species throughout said etchant.  
   
   
       16 . The method of  claim 15  wherein said carbon containing ballast gas has a chemical formula C x H y , wherein x is an integer ranging from 1 to 10, and y is an integer ranging from 2 to 22.  
   
   
       17 . The method of  claim 15  wherein said carbon containing ballast gas has a chemical formula C x H y A, wherein x is an integer ranging from 1 to 10, y is an integer ranging from 0 to 21, and A represents at least one additional substituent selected from the group consisting of O, N, S, P, F, Cl, Br, I, and combinations thereof.  
   
   
       18 . A chemical composition for etching gate stacks on a semiconductor wafer comprising: 
 etchant having desorbed hydrocarbon containing species diffused at varying concentrations throughout said etchant;    carbon containing ballast gas added to said etchant whereby said carbon containing ballast gas equilibrates said varying concentrations of said hydrocarbon containing species throughout said etchant to provide a substantially homogeneous etchant.    
   
   
       19 . The composition of  claim 18  wherein said carbon containing ballast gas has a chemical formula C x H y , wherein x is an integer ranging from 1 to 10, and y is an integer ranging from 2 to 22.  
   
   
       20 . The composition of  claim 18  wherein said carbon containing ballast gas has a chemical formula C x H y A, wherein x is an integer ranging from 1 to 10, y is an integer ranging from 0 to 21, and A represents at least one additional substituent selected from the group consisting of O, N, S, P, F, Cl, Br, I, or combinations thereof.