Electroless deposition of nickel on a masked aluminum surface

Claim 1

A process for pretreating a body prior to electroless deposition of nickel, said body having a surface of aluminum or aluminum alloy patterned with a mask, said aluminum or aluminum alloy having aluminum oxide thereof, said process comprising: (a) cleaning said surface; (b) subjecting said surface to a stop-etchant which removes substantially only said aluminum oxide from said aluminum or aluminum alloy and simultaneously activates said surface for subsequent deposition of nickel thereon; and (c) without rinsing, subjecting said surface to a nickel immersion treatment which further activates said aluminum or aluminum alloy for subsequent deposition of nickel thereon and deactivates said mask against subsequent deposition of nickel thereon.

Claim 8

A method for chemically depositing nickel bonding pads on a semiconductor wafer having an aluminum or aluminum alloy surface, said aluminum or aluminum alloy having aluminum oxide thereon, said method comprising the steps of: (a) applying a suitable mask material on said surface; (b) defining bonding pad areas as apertures in said mask material; (c) cleaning; (d) immersing in a first solution of buffered hydrofluoric acid and a nonaqueous solvent whereby said aluminum oxide is removed and both said aluminum or aluminum alloy and said mask material is activated; (e) immersing in a second solution comprising an aqueous solution of a soluble nickel salt, a complex to give a common ion effect, buffered hydrofluoric acid, and a wetting agent whereby said aluminum or aluminum alloy is further activated and said mask material is deactivated; and (f) chemically depositing nickel on said aluminum or aluminum alloy in an aqueous bath comprising a reducible nickel salt, a hypophosphite reducing agent, an organic acid salt complexing agent, buffered hydrofluoric acid, bath stabilizers, buffers, and wetting agents.

Claim 9

A method for chemically depositing nickel bonding pads on a semiconductor wafer having an aluminum or aluminum alloy surface, said aluminum or aluminum alloy having aluminum oxide thereon, said method comprising the steps of: (a) applying a suitable mask material on said surface; (b) defining bonding pad areas as apertures in said mask material; (c) cleaning; (d) immersing in a first solution of buffered hydrofluoric acid and a nonaqueous solvent whereby said aluminum oxide is removed and both said aluminum or aluminum alloy and said mask material is activated; (e) immersing in a second solution comprising an aqueous solution of a soluble nickel salt, a complex to give a common ion effect, buffered hydrofluoric acid, and a wetting agent whereby said aluminum or aluminum alloy is further activated and said mask material is deactivated; and (f) chemically depositing nickel on said aluminum or aluminum alloy in an aqueous bath comprising a reducible nickel salt, a hypophosphite reducing agent, an organic acid salt complexing agent, buffered hydrofluoric acid, bath stabilizers, buffers, and wetting agents.

Claim 13

A method of chemically depositing metal on a semiconductor wafer having a surface of aluminum or aluminum alloy patterned with a mask, said method comprising: (a) cleaning said surface; (b) subjecting said surface to a first solution of buffered hydrofluoric acid and a nonaqueous solvent; (c) subjecting said surface to a second solution comprising an aqueous solution of a soluble nickel salt, a complex to give a common ion effect, buffered hydrofluoric acid, and a wetting agent; (d) subjecting said surface to an electroless plating bath for the deposition of nickel, said bath comprising: (i) an aqueous solution of a reducible nickel salt; (ii) an organic acid salt complexing agent; (iii) a hypophosphite reducing agent; (iv) buffered hydrofluoric acid; (v) p-toluene sulfonic acid; (vi) formaldehyde; (vii) a low molecular weight alcohol; and (viii) boric acid; said bath being maintained at a pH in the range of about 4.5 to 7 and at a temperature in the range of about 25° C. to 98° C.; (e) cleaning said surface in a solution of buffered hydrfluoric acid and a nonaqueous solvent; and (f) subjecting said surface to a second bath comprising an aqueous solution of a soluble gold cyanide complex, a soluble cyanide salt in an amount sufficient to stabilize said bath, hypophosphite reducing agent, and buffering agents; said second bath being maintained at a pH of about 4.5 to 9 and a temperature of about 18° C. to 98° C.

Claim 14

A method of chemically depositing metal on a semiconductor wafer having a surface of aluminum or aluminum alloy patterned with a mask, said method comprising: (a) cleaning said surface; (b) subjecting said surface to a first solution of buffered hydrofluoric acid and a nonaqueous solvent; (c) subjecting said surface to a second solution comprising an aqueous solution of a soluble nickel salt, a complex to give a common ion effect, buffered hydrofluoric acid, and a wetting agent; (d) subjecting said surface to an electroless plating bath for the deposition of nickel, said bath comprising: (i) an aqueous solution of a reducible nickel salt; (ii) an organic acid salt complexing agent; (iii) a hypophosphite reducing agent; (iv) buffered hydrofluoric acid; (v) p-toluene sulfonic acid; (vi) formaldehyde; (vii) a low molecular weight alcohol; and (viii) boric acid; said bath being maintained at a pH in the range of about 4.5 to 7 and at a temperature in the range of about 25° C. to 98° C.; (e) cleaning said surface in a solution of buffered hydrfluoric acid and a nonaqueous solvent; and (f) subjecting said surface to a second bath comprising an aqueous solution of a soluble gold cyanide complex, a soluble cyanide salt in an amount sufficient to stabilize said bath, hypophosphite reducing agent, and buffering agents; said second bath being maintained at a pH of about 4.5 to 9 and a temperature of about 18° C. to 98° C.