Method of forming semiconductor die
View Patent ↗An embodiment of the disclosure includes a conductive bump on a semiconductor die. A substrate is provided. A bond pad is over the substrate. An under bump metallurgy (UBM) layer is over the bond pad. A copper pillar is over the UBM layer. The copper pillar has a top surface with a first width and sidewalls with a concave shape. A nickel layer having a top surface and a bottom surface is over the top surface of the copper pillar. The bottom surface of the nickel layer has a second width. A ratio of the second width to the first width is between about 0.93 to about 1.07. A solder material is over the top surface of the cap layer.
1. A method of forming a semiconductor die comprising:
providing a substrate;
forming a bond pad over the substrate;
depositing an under bump metallurgy (UBM) layer over the bond pad;
forming a copper pillar over the UBM layer;
depositing a nickel layer over the copper pillar, wherein an interface is defined between the nickel layer and the copper pillar;
depositing a solder material over the nickel layer;
etching the nickel layer and the copper pillar in an aqueous solution comprising 55% to 85% H 3 PO 4 by volume, less than 1% Azole-based compound by volume, and less than 1% Sn by volume; and
etching the UBM layer after the step of etching the nickel layer and the copper pillar.
2. The method of claim 1 , wherein the step of etching in the aqueous solution is performed at a temperature in the range of 30° C. and 70° C.
3. The method of claim 1 , wherein the aqueous solution comprises about 70% H 3 PO 4 by volume.
4. The method of claim 1 , wherein after the two etching steps the etched copper pillar adjacent to the interface has a first width, the etched nickel layer adjacent to the interface has a second width, and a ratio of the second width to the first width is between about 0.93 to about 0.99.
5. The method of claim 1 , wherein the solder material comprises lead free solder.
6. The method of claim 1 , wherein the etching of the UBM layer comprises wet etching, dry etching, or a combination thereof.
7. The method of claim 1 , wherein the conductive pillar has a concave shape.
8. A method of forming a semiconductor die comprising:
providing a substrate;
forming a bond pad over the substrate;
depositing an under bump metallurgy (UBM) layer comprising copper over the bond pad;
depositing a nickel layer over the UBM layer;
depositing a solder material over the nickel layer; and
etching the nickel layer and the UBM layer in an aqueous solution comprising 36% to 42% H 3 PO 4 by volume, 2% to 3% HNO 3 by volume, 44% to 49% CH 3 COOH by volume, and 2% to 3% Sn by volume.
9. The method of claim 8 , wherein the step of etching in the aqueous solution is performed at a temperature in the range of 30° C. and 45° C.
10. The method of claim 8 , wherein the aqueous solution comprises about 40% H 3 PO 4 by volume.
11. The method of claim 8 , further comprising forming a copper pillar over the UBM layer and underlying the nickel layer, thereby forming an interface between the copper pillar and the nickel layer.
12. The method of claim 11 , wherein the copper pillar adjacent to the interface has a first width, the nickel layer adjacent to the interface has a second width, and a ratio of the second width to the first width is between about 0.93 to about 1.07.
13. The method of claim 8 , wherein the UBM layer further comprises titanium.
14. The method of claim 13 , further comprising etching the UBM layer comprising titanium in an aqueous solution comprising less than 1% HF by volume.
15. The method of claim 13 , further comprising etching the UBM layer comprising titanium in a gaseous environment containing Cl2, CFx or CHFx.
16. The method of claim 8 , wherein the solder material comprises lead free solder.