Copper or copper alloy, bonding wire, method of producing the copper, method of producing the copper alloy, and method of producing the bonding wire
Copper or a copper alloy characterized in having an α-ray emission of 0.001 cph/cm 2 or less. Since recent semiconductor devices are produced to have higher density and higher capacity, there is greater risk of soft errors caused by the influence of α rays emitted from materials positioned near semiconductor chips. In particular, there are strong demands for achieving higher purification of copper and copper alloys which are used near the semiconductor device, such as copper or copper alloy wiring lines, copper or copper alloy bonding wires, and soldering materials, and materials reduced in α-ray emission are also demanded. Thus, the present invention elucidates the phenomenon in which α rays are emitted from copper or copper alloys, and provides copper or copper alloy reduced in α-ray emission which is adaptable to the demanded material, and a bonding wire in which such copper or copper alloy is used as its raw material.
1. A method of producing a copper of low α-ray radiation, comprising the steps of:
preparing an electrolytic cell comprising a copper sulfate solution as a starting electrolytic solution, a positive electrode and a negative electrode, and a diaphragm positioned in the electrolytic cell to partition the electrolytic cell into a positive electrode side containing the positive electrode and a negative electrode side containing the negative electrode;
performing electrolysis with the electrolytic cell equipped with a crude copper raw material as the positive electrode to obtain an anolyte solution formed by anodic dissolution of the crude copper raw material;
extracting and filtering an amount of the anolyte solution to remove lead sulfate precipitates contained in the extracted anolyte solution and to obtain a filtered anolyte solution;
bringing back the filtered anolyte solution to the negative electrode side of the electrolytic cell and performing electrolysis to form an electrodeposited copper on the negative electrode; and
collecting the electrodeposited copper from the negative electrode and melting and casting the electrodeposited and collected copper to form the copper of low α-ray radiation;
wherein the copper of low α-ray radiation has an α-ray count of 0.001 cph/cm 2 or less at a time after a lapse of 30 months from a time of the melting and casting.
2. A method according to claim 1 , wherein the copper sulfate solution has a Cu concentration of 30 to 200 g/L.
3. A method according to claim 2 , wherein the diaphragm is an anion-exchange membrane through which Pb 2+ ions do not pass.
4. A method according to claim 3 , wherein the copper of low α-ray radiation has a Pb content of less than 0.01 wtppm, an U content of less than 5 wtppb, and a Th content of less than 5 wtppb.
5. A method according to claim 4 , wherein the copper of low α-ray radiation has an α-ray count of 0.001 cph/cm 2 or less at each time after a lapse of 1 week, 3 weeks, 1 month, 2 months, 6 months, and 30 months from a time of the melting and casting.
6. A method according to claim 5 , wherein the copper of low α-ray radiation has a purity of 4N (99.99%) or higher.
7. A method of producing a copper alloy of low α-ray radiation, comprising the steps of providing a copper produced by the method according to claim 6 , melting the copper together with one or more of alloying elements to obtain a copper alloy in a molten state, and casting the copper alloy.
8. A method of producing a bonding wire, comprising the step of subjecting the copper alloy produced according to claim 7 to wire drawing processing to form bonding wire.
9. A method according to claim 1 , wherein the diaphragm is an anion-exchange membrane through which Pb 2+ ions do not pass.
10. A method according to claim 1 , wherein the copper of low α-ray radiation has a Pb content of less than 0.01 wtppm, an U content of less than 5 wtppb, and a Th content of less than 5 wtppb.
11. A method according to claim 1 , wherein the copper of low α-ray radiation has an α-ray count of 0.001 cph/cm 2 or less at each time after a lapse of 1 week, 3 weeks, 1 month, 2 months, 6 months, and 30 months from a time of the melting and casting.
12. A method according to claim 1 , wherein the copper of low α-ray radiation has a purity of 4N (99.99%) or higher.
13. A method of producing a copper alloy of low α-ray radiation, comprising the steps of providing a copper produced by the method according to claim 1 , melting the copper together with one or more of alloying elements to obtain a copper alloy in a molten state, and casting the copper alloy.
14. A method of producing a bonding wire, comprising the step of subjecting the copper alloy produced according to claim 13 to wire drawing processing to form bonding wire.