Method of etching silicon nitride

Abstract

A method of etching an underlying inorganic substrate through a patterned photoresist, including exposing a structure comprising said inorganic substrate and patterned photoresist to a plasma etchant generated from a plasma source gas including at least one fluorine-comprising gas and sulfur dioxide (SO 2 ). The amount of sulfur dioxide present in said plasma source gas may be varied during the etching process. The method is particularly useful when the photoresist is a DUV photoresist. One of the preferred embodiments of the method is the etching of silicon nitride (SiN x ) through a DUV photoresist, where the plasma source gas used to provide the etchant includes at least one fluorine-comprising gas, argon, and sulfur dioxide. Other preferred fluorine-comprising gases include nitrogen trifluoride (NF 3 ), carbon tetrafluoride (CF 4 ), and sulfur hexafluoride (SF 6 ).

What is claimed is:  
     
         1 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of at least one inorganic fluorine-comprising gas and sulfur dioxide (SO 2 ), wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         2 . The method of  claim 1 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         3 . The method of  claim 1 , wherein one of said at least one inorganic fluorine-comprising gases is sulfur hexafluoride (SF 6 ).  
     
     
         4 . The method of  claim 1 , wherein one of said at least one inorganic fluorine-comprising gases is nitrogen trifluoride (NF 3 ).  
     
     
         5 . The method of  claim 1 , wherein said plasma source gas includes two inorganic fluorine-comprising gases.  
     
     
         6 . The method of  claim 1 , wherein a temperature of a substrate which includes said silicon nitride is between about 20° C. and 100° C. during exposure to said plasma etchant.  
     
     
         7 . The method of  claim 6 , wherein said temperature is between about 40° C. and 60° C.  
     
     
         8 . The method of  claim 1 , wherein said silicon nitride etch rate is at least two times said organic DUV photoresist etch rate.  
     
     
         9 . The method of  claim 1 , wherein said patterned organic DUV photoresist has a thickness of less than about 4000 Å.  
     
     
         10 . The method of  claim 1 , wherein said exposing of the structure comprising said silicon nitride and said patterned organic DUV photoresist to said plasma etchant results in an etched inorganic substrate having a feature size less than 2500 Å.  
     
     
         11 . The method of  claim 1 , wherein said selectivity of said silicon nitride relative to said adjacent patterned organic DUV photoresist is greater than 1.5.  
     
     
         12 . The method of  claim 11 , wherein said selectivity is greater than about 2.0.  
     
     
         13 . The method of  claim 1 , wherein said plasma etchant is generated from a high density plasma.  
     
     
         14 . The method of  claim 13 , wherein said plasma density is at least 10 11  e − /cm 3 .  
     
     
         15 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of at least one inorganic fluorine-comprising gas, sulfur dioxide (SO 2 ), and a diluent gas selected from the group consisting of Ar, Kr, Xe, and He, wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         16 . The method of  claim 15 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         17 . The method of  claim 15 , wherein a molecular ratio of said inorganic fluorine-comprising gas to said diluent gas ranges from about 0.1:1 to about 10:1.  
     
     
         18 . The method of  claim 15 , wherein said diluent gas is argon (Ar).  
     
     
         19 . The method of  claim 15 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         20 . The method of  claim 19 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         21 . The method of  claim 15 , wherein said at least one inorganic fluorine-comprising gas amount is about 20%-60% by volume of said plasma source gas.  
     
     
         22 . The method of  claim 21 , wherein said at least one inorganic fluorine-comprising gas amount is about 25%-35% by volume of said plasma source gas.  
     
     
         23 . The method of  claim 18 , wherein said argon amount is about 20%-60% by volume of said plasma source gas.  
     
     
         24 . The method of  claim 23 , wherein said argon amount is about 50%-60% by volume of said plasma source gas.  
     
     
         25 . The method of  claim 15 , wherein one of said at least one inorganic fluorine-comprising gases is sulfur hexafluoride (SF 6 ).  
     
     
         26 . The method of  claim 15 , wherein one of said at least one inorganic fluorine-comprising gases is nitrogen trifluoride (NF 3 ).  
     
     
         27 . The method of  claim 15 , wherein said plasma source gas includes two inorganic fluorine-comprising gases.  
     
     
         28 . The method of  claim 27 , wherein a total amount of said inorganic fluorine-comprising gases is about 20%-60% by volume of the plasma source gas.  
     
     
         29 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of at least one inorganic fluorine-comprising gas, sulfur dioxide (SO 2 ), and hydrogen bromide (HBr), wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         30 . The method of  claim 29 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         31 . The method of  claim 29 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         32 . The method of  claim 31 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         33 . The method of  claim 29 , wherein said at least one inorganic fluorine-comprising gas amount is about 20%-60% by volume of said plasma source gas.  
     
     
         34 . The method of  claim 33 , wherein said at least one inorganic fluorine-comprising gas amount is about 25%-35% by volume of said plasma source gas.  
     
     
         35 . The method of  claim 29 , wherein said hydrogen bromide amount is about 10%-60% by volume of said plasma source gas.  
     
     
         36 . The method of  claim 35 , wherein said hydrogen bromide amount is about 20%-40% by volume of said plasma source gas.  
     
     
         37 . The method of  claim 29 , wherein one of said at least one inorganic fluorine-comprising gases is sulfur hexafluoride (SF 6 ).  
     
     
         38 . The method of  claim 29 , wherein one of said at least one inorganic fluorine-comprising gases is nitrogen trifluoride (NF 3 ).  
     
     
         39 . The method of  claim 29 , wherein said plasma source gas includes two inorganic fluorine-comprising gases.  
     
     
         40 . The method of  claim 39 , wherein a total amount of said inorganic fluorine-comprising gases is about 20%-60% by volume of the plasma source gas.  
     
     
         41 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of at least one inorganic fluorine-comprising gas, sulfur dioxide (SO 2 ), hydrogen bromide (HBr), and a diluent gas selected from the group consisting of Ar, Kr, Xe, and He, wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         42 . The method of  claim 41 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         43 . The method of  claim 41 , wherein a molecular ratio of said inorganic fluorine-comprising gas to said diluent gas ranges from about 0.1:1 to about 10:1.  
     
     
         44 . The method of  claim 41 , wherein said diluent gas is argon (Ar).  
     
     
         45 . The method of  claim 41 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         46 . The method of  claim 45 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         47 . The method of  claim 41 , wherein said at least one inorganic fluorine-comprising gas amount is about 20%-60% by volume of said plasma source gas.  
     
     
         48 . The method of  claim 47 , wherein said at least one inorganic fluorine-comprising gas amount is about 25%-35% by volume of said plasma source gas.  
     
     
         49 . The method of  claim 41 , wherein said hydrogen bromide amount is about 10%-60% by volume of said plasma source gas.  
     
     
         50 . The method of  claim 49 , wherein said hydrogen bromide amount is about 20%-40% by volume of said plasma source gas.  
     
     
         51 . The method of  claim 44 , wherein said argon amount is about 20%-60% by volume of said plasma source gas.  
     
     
         52 . The method of  claim 51 , wherein said argon amount is about 50%-60% by volume of said plasma source gas.  
     
     
         53 . The method of  claim 41 , wherein one of said at least one inorganic fluorine-comprising gases is sulfur hexafluoride (SF 6 ).  
     
     
         54 . The method of  claim 41 , wherein one of said at least one inorganic fluorine-comprising gases is nitrogen trifluoride (NF 3 ).  
     
     
         55 . The method of  claim 41 , wherein said plasma source gas includes two inorganic fluorine-comprising gases.  
     
     
         56 . The method of  claim 55 , wherein a total amount of said inorganic fluorine-comprising gases is about 20%-60% by volume of the plasma source gas.  
     
     
         57 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of sulfur hexafluoride (SF 6 ) and sulfur dioxide (SO 2 ), wherein the molecular ratio of said sulfur hexafluoride to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         58 . The method of  claim 57 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         59 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of sulfur hexafluoride (SF 6 ), sulfur dioxide (SO 2 ), and argon (Ar), wherein the molecular ratio of said sulfur hexafluoride to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         60 . The method of  claim 59 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         61 . The method of  claim 59 , wherein a molecular ratio of said sulfur hexafluoride to said argon ranges from about 0.1:1 to about 10:1.  
     
     
         62 . The method of  claim 59 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         63 . The method of  claim 62 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         64 . The method of  claim 59 , wherein said sulfur hexafluoride amount is about 20%-60% by volume of said plasma source gas.  
     
     
         65 . The method of  claim 64 , wherein said sulfur hexafluoride amount is about 25%-35% by volume of said plasma source gas.  
     
     
         66 . The method of  claim 59 , wherein said argon amount is about 20%-60% by volume of said plasma source gas.  
     
     
         67 . The method of  claim 66 , wherein said argon amount is about 50%-60% by volume of said plasma source gas.  
     
     
         68 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of sulfur hexafluoride (SF 6 ), sulfur dioxide (SO 2 ), and hydrogen bromide (HBr), wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         69 . The method of  claim 68 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         70 . The method of  claim 68 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         71 . The method of  claim 70 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         72 . The method of  claim 68 , wherein said sulfur hexafluoride amount is about 20%-60% by volume of said plasma source gas.  
     
     
         73 . The method of  claim 72 , wherein said sulfur hexafluoride amount is about 25%-35% by volume of said plasma source gas.  
     
     
         74 . The method of  claim 68 , wherein said hydrogen bromide amount is about 10%-60% by volume of said plasma source gas.  
     
     
         75 . The method of  claim 74 , wherein said hydrogen bromide amount is about 20%-40% by volume of said plasma source gas.  
     
     
         76 . A method of improving etch selectivity of silicon nitride relative to an adjacent patterned organic DUV photoresist during plasma etching, comprising: reacting a surface of said patterned organic DUV photoresist with plasma species generated from a plasma source gas consisting essentially of sulfur hexafluoride (SF 6 ), sulfur dioxide (SO 2 ), hydrogen bromide (HBr), and a diluent gas selected from the group consisting of Ar, Kr, Xe, and He, wherein the molecular ratio of said inorganic fluorine-comprising gas to said sulfur dioxide ranges from about 50:1 to about 1:1, to produce a reacted DUV photoresist surface, whereby the etch rate of said organic DUV photoresist is slowed, while said silicon nitride exposed through said patterned organic DUV photoresist is etched.  
     
     
         77 . The method of  claim 76 , wherein the amount of sulfur dioxide (SO 2 ) present in said plasma source gas is varied during said etching of said silicon nitride.  
     
     
         78 . The method of  claim 76 , wherein a molecular ratio of said inorganic fluorine-comprising gas to said diluent gas ranges from about 0.1:1 to about 10:1.  
     
     
         79 . The method of  claim 76 , wherein said diluent gas is argon (Ar).  
     
     
         80 . The method of  claim 76 , wherein said sulfur dioxide amount is about 2%-20% by volume of said plasma source gas.  
     
     
         81 . The method of  claim 80 , wherein said sulfur dioxide amount is about 10%-15% by volume of said plasma source gas.  
     
     
         82 . The method of  claim 76 , wherein said sulfur hexafluoride amount is about 20%-60% by volume of said plasma source gas.  
     
     
         83 . The method of  claim 82 , wherein said sulfur hexafluoride amount is about 25%-35% by volume of said plasma source gas.  
     
     
         84 . The method of  claim 76 , wherein said hydrogen bromide amount is about 10%-60% by volume of said plasma source gas.  
     
     
         85 . The method of  claim 84 , wherein said hydrogen bromide amount is about 20%-40% by volume of said plasma source gas.  
     
     
         86 . The method of  claim 79 , wherein said argon amount is about 20%-60% by volume of said plasma source gas.  
     
     
         87 . The method of  claim 86 , wherein said argon amount is about 50%-60% by volume of said plasma source gas.