Methods relating to intermetallic testing of bond integrity between bond pads and copper-containing bond wires
View Patent ↗Methods relating to intermetallic compound testing of copper-based wire bonds are provided. For example, a method is generally provided for testing the integrity of wire bonds formed between copper-containing wires and the bond pads of a plurality of microelectronic devices. In one embodiment, the method includes selecting at least one wire bond sample produced in conjunction with the wire bonds formed between the copper-containing wires and the bond pads of the microelectronic devices. One or more copper-containing wires of the wire bond sample are contacted with a liquid copper etchant, which contains a sulfate-based oxidizing agent dissolved in a solvent, to cause separation of the copper-containing wires from the bond pads and exposure of the underlying wire-pad interfaces. Intermetallic compounds formed at the exposed wire-pad interfaces are then measured to assess the integrity of the wire bonds.
1. A method for testing the integrity of wire bonds formed between copper-containing wires and the bond pads of a plurality of microelectronic devices, the bond pads of the plurality of microelectronic devices fabricated from a metallic material different than the copper-containing wires, the method comprising:
selecting at least one wire bond sample produced in conjunction with the wire bonds formed between the copper-containing wires and the bond pads of the plurality of microelectronic devices;
contacting one or more copper-containing wires of the wire bond sample with a liquid copper etchant to cause separation of the copper-containing wires from the bond pads and exposure of the underlying wire-pad interfaces, the liquid copper etchant comprising a sulfate-based oxidizing agent dissolved in a solvent; and
measuring the formation of intermetallic compounds at the exposed wire-pad interfaces to assess the integrity of the wire bonds formed between the copper-containing and the bond pads of the plurality of microelectronic devices.
2. The method of claim 1 wherein the at least one wire bond sample includes at least one of the group consisting of aluminum bond pads, copper bond pads, nickel-palladium bond pads, and gold bond pads.
3. The method of claim 2 wherein the at least one wire bond sample includes aluminum bond pads.
4. The method of claim 1 wherein the at least one wire bond sample includes copper-containing wires comprising at least one of the group consisting of pure copper wires and copper-palladium wires.
5. The method of claim 1 wherein the sulfate-based oxidizing agent comprises at least one of the group consisting of ammonium persulfate, sodium peroxymonosulfate, potassium peroxymonosulfate, and sodium persulfate.
6. The method of claim 5 wherein the sulfate-based oxidizing agent comprises ammonium persulfate.
7. The method of claim 1 wherein the liquid copper etchant further comprises a leaching agent.
8. The method of claim 5 wherein the liquid copper etchant is produced by mixing the sulfate-based oxidizing agent, in powder form, with the leaching agent and the solvent.
9. The method of claim 8 wherein the leaching agent comprises sulfuric acid and wherein the solvent comprises water.
10. The method of claim 9 wherein the liquid copper etchant is formulated to contain about 0.01 gram to about 1.0 gram of the sulfate-based oxidizing agent, in powder form, for every milliliter of water contained therein.
11. The method of claim 10 wherein the liquid copper etchant is formulated to contain about 0.01 milliliter to about 0.25 milliliter sulfuric acid for every milliliter of water contained therein.
12. The method of claim 1 further comprising, prior to contacting the copper-containing wires with the liquid copper etchant and exposing the wire-pad interfaces, baking the at least one bond wire sample at a predetermined elevated temperature for a predetermined time period sufficient to promote the formation of intermetallic compounds at the wire-pad interfaces.
13. The method of claim 12 wherein baking comprises heating the at least sample microelectronic device to a temperature between about 175° C. and about 225° C. for a time period between about 2.5 hours and about 5 hours.
14. The method of claim 1 wherein the liquid copper etchant is free of nitric acid.
15. The method of claim 1 further comprising flooding the exposed wire-pad interfaces with deionized water after contacting the copper-containing wires with the liquid copper etchant and prior to measuring the formation of intermetallic compounds at the exposed wire-pad interfaces.
16. A method, comprising:
ball bonding copper-containing wires to a plurality of bond pads included within a plurality of microelectronic devices, the copper-containing wires comprised of a different material than are the plurality of bond pads;
selecting at least one bond wire sample produced in conjunction with the plurality of microelectronic devices for ball bond integrity testing;
testing the integrity of one or more ball bonds of the at least one bond wire sample, testing comprising:
contacting one or more copper-containing wires of the at least one bond wire sample with a liquid copper etchant to separate the copper-containing wires from the bond pads and expose the wire-pad interfaces, the liquid copper etchant comprising a sulfate-based oxidizing agent, an acid different than the sulfate-based oxidizing agent, and a solvent; and
estimating the percentage of the exposed wire-pad interfaces covered by intermetallic compounds; and
packaging the plurality of microelectronic devices if the percentage of the intermetallic compounds exceeds the predetermined threshold value.
17. The method of claim 16 wherein each of the plurality of microelectronic devices and the at least one wire bond sample comprises a plurality of aluminum bond pads, and wherein the sulfate-based oxidizing agent comprises ammonium persulfate.
18. The method of claim 16 wherein the plurality of microelectronic devices comprise integrated circuits formed on semiconductor die.
19. The method of claim 16 wherein the plurality of microelectronic device comprise microelectromechanical systems devices.
20. A method for testing the integrity of wire bonds formed between copper-containing wires and the bond pads of a plurality of microelectronic devices, the bond pads of the plurality of microelectronic devices fabricated from a metallic material different than the copper-containing wires, the method comprising:
selecting at least one wire bond sample produced in conjunction with the wire bonds formed between the copper-containing wires and the bond pads of the plurality of microelectronic devices;
baking the at least one wire bond sample to promote the formation of intermetallic compounds at the wire-pad interfaces;
applying a sulfate-containing etchant to the at least one wire bond sample at the wire-pad interfaces thereof until the copper-containing wires lift from the bond pads and expose the wire-pad interfaces;
generating at least one image of the exposed wire-pad interfaces; and
analyzing the at least one image to estimate the percentage of the intermetallic compounds present at the exposed wire-pad interfaces and assess the integrity of the wire bonds formed between the copper-containing and the bond pads of the plurality of microelectronic devices.