Plating bath and method
View Patent ↗Tin-silver alloy electroplating baths having certain amine-oxide surfactants and methods of electrodepositing a tin-silver-containing layer using these baths are disclosed. Such electroplating baths are useful to provide tin-silver solder deposits having reduced void formation and improved within-die uniformity.
1. An electroplating composition comprising: a water-soluble source of divalent tin ions; a water-soluble source of silver ions; water; acid electrolyte; and an alkoxylated amine oxide surfactant having the formula
wherein R a is selected from a (C 6 -C 22 )alkyl group and a substituted (C 7 -C 22 )aryl group; R b is an alkoxylated unit; m is 0 to 7 and represents the number of moles of R b ; n is 0 or 1; and R c and R d are each at least one alkoxylated unit and the total number of alkoxylated units preresent in R c and R d is from 3 to 30.
2. The composition of in claim 1 wherein the alkoxylated unit is chosen from ethyleneoxy, propyleneoxy, butyleneoxy, and mixtures thereof.
3. The composition of claim 1 wherein R c and R d are each chosen from ethyleneoxy units, propyleneoxy units, and mixtures thereof.
4. The composition of claim 1 wherein m=0.
5. The composition of claim 1 further comprising a mercapto-substituted nitrogen-containing heterocyclic ring compound.
6. The composition of claim 5 wherein the mercapto-substituted nitrogen-containing heterocyclic ring compound comprises a nitrogen-containing heterocyclic ring chosen from: pyridine, pyrrole, imidazole, benzimidazole, purine, thiazoline, tetrazole, triazole, thiadiazole, and pyrimidine.
7. The composition of claim 5 wherein the mercapto-substituted nitrogen-containing heterocyclic ring compound has the following structure (I):
wherein A represents a moiety that forms a 5- to 6-membered heterocyclic ring; each R 1 is independently chosen from (C 1 -C 12 )alkyl, substituted (C 1 -C 12 )alkyl, (C 6 -C 15 )aryl, substituted (C 6 -C 15 )aryl, (C 7 -C 20 )aralkyl, substituted (C 7 -C 20 )aralkyl, NR 2 R 3 , —S—R 4 , hydroxy, (C 1 -C 12 )alkoxy, and COR 5 ; each of R 2 and R 3 is independently chosen from H, (C 1 -C 12 )alkyl, and (C 6 -C 15 )aryl; R 4 is chosen from (C 1 -C 12 )alkyl, substituted (C 1 -C 12 )alkyl, (C 6 -C 15 )aryl, and substituted (C 6 -C 15 )aryl; R 5 is chosen from (CH 2 ) x NR 2 R 3 , R 2 and OR 2 ; m=1-5; n=0 -4; and x=0-6; wherein R 2 and R 3 may be taken together to form a 5- to 6-membered heterocyclic ring; and wherein two or more R 1 groups may be joined to form a fused or spirocyclic 5- to 6-membered ring, which may be saturated, unsaturated or aromatic.
8. The composition of claim 7 wherein A represents a moiety that forms a tetrazole or a triazole ring.
9. A method of depositing a tin-silver layer comprising: contacting a substrate with the composition of claim 1 and; applying a potential for a period of time to deposit a tin-silver-containing layer on the substrate.
10. The method of claim 9 wherein the substrate is a semiconductor substrate.
11. The method of claim 9 wherein the tin-silver-containing layer is an interconnect bump layer.
12. The method of claim 9 wherein tin-silver-containing layer is substantially free of voids.