Method for etching polysilicon
The invention provides compositions useful in the etching of polysilicon in the presence of silicon oxide and silicon nitride. The compositions comprise choline hydroxide, an oxidizing agent such as periodic acid, and optionally a surfactant, and are useful in the etching of polysilicon in general, and in particular in both the operation of polysilicon trim as well as polysilicon exhume. The utilization of an added oxidizing agent was found to reduce selectivity of silicon etching based on the silicon crystal orientation, which was found to reduce roughness and the presence of residual silicon residues, such as silicon (111) residues after the etching step.
1 . A selective etch composition consisting of:
a. choline hydroxide;
b. water;
c. one or more oxidizing agents;
d. one or more surfactants, including polyethylene glycol p-(1,1,3,3-tetramethylbutyl)phenyl ether; and
e. optionally one or more amines.
2 . The composition of claim 1 , wherein the one or more oxidizing agents are chosen from an iodine-containing oxidizing agent, permangenates, and persulfates.
3 . The composition of claim 2 , wherein the iodine-containing oxidizing agent is chosen from H 5 IO 6 , HIO 4 , or a mixture thereof.
4 . The composition of claim 1 , wherein the one or more surfactants are present and include a non-ionic surfactant.
5 . The composition of claim 1 , wherein the one or more amines are present.
6 . The composition of claim 5 , wherein the one or more amines are chosen from diethylenetriamine, triethylenetetramine, tetramethylenepentaamine, piperazine, and piperidine.
7 . The composition of claim 1 , which comprises about 2 to about 2.4 weight percent choline hydroxide, about 0.04 to about 0.05 weight percent polyethylene glycol p-(1,1,3,3-tetramethylbutyl)phenyl ether, and about 0.03 to about 0.045 weight percent of periodic acid, based on the total weight of the composition.
8 . A selective etch solution consisting essentially of:
a. choline hydroxide;
b. water;
c. one or more oxidizing agents;
d. one or more surfactants, including polyethylene glycol p-(1,1,3,3-tetramethylbutyl)phenyl ether; and
e. optionally one or more amines, wherein the solution selectively etches polysilicon relative to silicon nitride.
9 . The composition of claim 1 , wherein the composition selectively removes polysilicon relative to silicon nitride.