Copper bonding wire

Abstract

There is provided a copper bonding wire that exhibits a favorable bondability even when a scrub at the time of bonding is reduced. The copper bonding wire is characterized in that when a sum of percentages of Cu, Cu.sub.2O, CuO and Cu(OH).sub.2 on a surface of the wire as measured by X-ray Photoelectron Spectroscopy (XPS) is defined as 100%, Cu[II]/Cu[I] which is a ratio of a total percentage of CuO and Cu(OH).sub.2 (Cu[II]) corresponding to bivalent Cu to a percentage of Cu.sub.2O (Cu[I]) corresponding to monovalent Cu falls within a range from 0.8 to 12.

Claims

1. A copper bonding wire a surface of which comprising: Cu, Cu.sub.2O, CuO, and Cu(OH).sub.2, wherein a sum of percentages of Cu, Cu.sub.2O, CuO and Cu(OH).sub.2 on the surface of the copper bonding wire as measured by X-ray Photoelectron Spectroscopy (XPS) is defined as 100%, and wherein a ratio Cu[II]/Cu[I], which is a ratio of a total percentage of CuO and Cu(OH).sub.2 (Cu[II]) corresponding to bivalent Cu to a percentage of Cu.sub.2O (Cu[I]) corresponding to monovalent Cu, falls within a range from 0.8 to 12.

2. The copper bonding wire according to claim 1, wherein a ratio [Cu(OH).sub.2]/[CuO], which is a ratio of a percentage of Cu(OH).sub.2 [Cu(OH).sub.2] to a percentage of CuO [CuO] measured by the X-ray Photoelectron Spectroscopy (XPS), falls within a range from 1 to 5.5.

3. The copper bonding wire according to claim 1, wherein a ratio [CuO]/[Cu.sub.2O], which is a ratio of a percentage of CuO [CuO] to a percentage of Cu.sub.2O [Cu.sub.2O] measured by the X-ray Photoelectron Spectroscopy (XPS), falls within a range from 0.3 to 6.

4. The copper bonding wire according to claim 1, wherein a sum of the Cu[I] and the Cu[II] is 50% or more.

5. The copper bonding wire according to claim 1, containing one or more selected from the group consisting of Pd, Pt, Ag and Rh, and a total concentration thereof is from 100 to 6000 ppm by mass.

6. The copper bonding wire according to claim 1, wherein a diameter of the copper bonding wire is 15 m or more and 100 m or less.

7. The copper bonding wire according to claim 1 which is usable for a semiconductor device.

Description

EXAMPLES

(1) There will be specifically described the present invention with Examples. However, the present invention is not limited to the Examples described below.

(2) (Sample)

(3) First, the method of preparing a sample will be described. For Cu as a raw material of the wire, Cu having a purity of 99.9% by mass or more (3 N) to 99.999% by mass or more (5 N) with the balance composed of inevitable impurities was used. The copper having such a given purity was subjected to continuous casting to manufacture the wire material having a wire diameter of several millimeters. In a case of adding dopants Pd, Pt and Ag, the dopants Pd, Pt and Ag having a purity of 99% by mass or more with the balance being composed of inevitable impurities were used, or alternatively a mother alloy of Cu with a high concentration of the dopants was used. The dopants were added to the copper having the given purity described above so that the content of the dopants therein reaches a desired value, and then the wire material was manufactured by continuous casting so as to have a wire diameter of several millimeters. The resultant wire material was drawn to manufacture the wire having a diameter of 0.3 to 1.4 mm. In the wire drawing, a commercially available lubricant was used, and the wire drawing rate was 30 to 200 m/min. Also, in the wire drawing, the wire drawing process was performed using a plurality of dies having an area reduction ratio of a range from 10 to 26% (at least half of all the dies had an area reduction ratio of 10 to 21%), and the wire was processed to have a final wire diameter. During the wire drawing process, heat treatment was performed 0 to 2 times at 200 to 600 C. for 5 to 15 seconds as needed. The final wire diameter was a diameter of 20 m.

(4) After the wire drawing process, the wire was continuously heated while being swept into a heat treatment furnace. The maximum temperature in the furnace was 400 to 850 C., and the heat treatment was performed under a flow of N.sub.2+5% H.sub.2 gas in the furnace. When the maximum temperature in the furnace is defined as T ( C.), a moving time from the furnace inlet to the maximum temperature region in the furnace is defined as H (second), and a moving time from the maximum temperature region in the furnace to the furnace outlet is defined as C (second), the temporary (apparent) rate of temperature rising is represented as T/H ( C./second), and the temporary cooling rate is represented as T/C ( C./second). In Examples, the temporary rate of temperature rising T/H was set to be within a range from 400 to 1500 C./second, and the temporary cooling rate T/C was set to be within a range from 500 to 2000 C./second. In Comparative Examples, T/H is set to be lower than 400 C./second and T/C is set to be lower than 500 C./second, which is an example of a ordinary condition for manufacturing the copper bonding wire.

(5) (Test and Evaluation Methods)

(6) There will be described test and evaluation methods.

(7) [Measurement and Evaluation of Copper Bonding Wire by XPS]

(8) 1. Preparation of Measurement Sample

(9) The copper bonding wire manufactured in Examples and Comparative Examples was sealed in a bag with nitrogen atmosphere using a commercially available barrier bag, and the bag was opened within one week thereafter. The measurement sample described below was prepared within 2 days after the bag was opened, and the measurement sample was put into a vacuum chamber of the XPS device. The copper bonding wire was wound around a glass plate having a width of 10 mm to prepare the measurement sample. In preparing the measurement sample, the copper bonding wire was wound around the glass plate so that (i) the wire is densely wound multiple times to hide the glass, and (ii) a surface of the obtained measurement sample becomes flat.

(10) 2. Measurement and Evaluation by XPS

(11) XPS measurement was performed on the measurement sample obtained in 1. described above under the following conditions, and spectra of Cu.sub.2p3/2, CuLMM, and O1s were detected. Measurement device: QuanteraII manufactured by ULVAC-PHI, Inc. Ultimate vacuum: about 110.sup.8 Torr X-ray source: monochromatic Al (1486.6 eV) X-ray beam diameter: 100 m (25 W, 15 kV) Detection region: 10000 m.sup.2 Photoelectron extraction angle: 45 degrees

(12) The detected spectra were analyzed by waveform analysis using an analysis software attached to the XPS device, and waveforms were separated for each of the chemical-bonding states of Cu. The percentage for each chemical-bonding state of Cu was calculated in accordance with the following procedures (1) to (3). (1) By using the Cu.sub.2p3/2 spectrum, a total waveform of Cu[0]+Cu[I] is separated from a waveform of Cu[II], and respective percentages thereof are obtained. (2) By using the CuLMM spectrum, a waveform of Cu[0] is separated from a waveform of Cu[I], and respective percentages thereof are obtained. (3) By using the O1s spectrum, a waveform of CuO is separated from a waveform of Cu(OH).sub.2, and respective percentages thereof are obtained. The percentage of 02 components (derived from Cu.sub.2O) of the O1s spectrum is adjusted to be of the percentage of Cu[I].
[Performance Test and Evaluation of Copper Bonding Wire]

(13) With regard to the respective wires manufactured in Examples and Comparative Examples, bonding was performed using a commercially available wire bonder (IConn manufactured by Kulicke and Soffa Industries, Inc.). A Cu alloy lead frame plated with Ag was used as a lead frame, and a chip using Si was used as a semiconductor element. The lead frame plated with Ag described above was used as an electrode. Ball bonding was performed with respect to the semiconductor element, and wedge bonding was performed with respect to the lead frame. Ball formation was performed under a flow of N.sub.2+5% H.sub.2 gas at a flow rate of 0.4 L/min or more and smaller than 0.6 L/min.

(14) <Scrub Evaluation>

(15) In scrub evaluation, the wire was bonded by reducing the number of times of scrubs at the time of wedge bonding to 1 time or 0 (zero) time (without a scrub), which is usually required to be 2 times or more. A bonding temperature was set to be low, specifically, at 150 C., a load condition at the time of bonding was adjusted in a range from 50 to 80 gf, and a setting value of USG Current was adjusted in a range from 15 to 40 as for a condition of ultrasonic vibrations. Regarding the scrub conditions, a scrub amplitude was set to be within a range from 2.5 to 3.5 m, and a scrub frequency was adjusted in a range from 170 to 250 kHz. As a scrub mode, in-line was selected, and a scrub moving direction was parallel with a wire direction. 200 wires were bonded. The number of wires with which a bonding failure, such as a non-bonding that causes detachment at the time of bonding or a stop of the wire bonder, occurs was counted. With regard to the respective wires, the test was performed two times to obtain an average value of the number of wires causing a bonding failure, and evaluation was performed in accordance with the following criteria. Evaluation results are shown in the column of Bondability in Table 1.

(16) Evaluation Criteria:

(17) : 0 : 1 to 3 : 4 to 6 x: 7 or more
<Loop Shape Stability>

(18) For the trapezoid loop having a long span and the loop having a large height difference and a short span, the loop shape stability (reproducibility of a loop profile) was tested and evaluated as follows.

(19) (1) Loop Shape Stability at Time of Forming Trapezoid Loop Having a Long Span

(20) 144 trapezoid loops were connected so as to achieve a wire length of 5 mm and a loop height of 0.4 mm as a severer condition than an ordinary condition of loop formation. A loop portion was observed with an optical microscope. A failure was determined if a bending amount was 0.2 mm or more, and evaluation was performed in accordance with the following criteria. The bending amount was obtained by connecting two bonding parts with a straight line, and obtaining a distance between a maximum bending part and the straight line. Evaluation results are shown in the column of Trapezoid having long span in Loop shape stability in Table 1.

(21) Evaluation Criteria:

(22) : No failure part : 1 to 3 failure parts : 4 to 7 failure parts x: 8 or more failure parts
(2) Loop Shape Stability at Time of Forming Loop Having Large Height Difference and Short Span

(23) 200 loops having a large height difference were connected so that the wire length was 0.6 mm and a height difference between a wedge bonding part and a ball bonding part was 0.5 mm. A loop portion was observed with an optical microscope. A failure was determined if the bending amount was 0.05 mm or more, and evaluation was performed in accordance with the following criteria. Evaluation results are shown in the column of Large height difference and short span in Loop shape stability in Table 1.

(24) Evaluation Criteria:

(25) : No failure part : 1 to 3 failure parts : 4 to 7 failure parts x: 8 or more failure parts
[Capillary Life]

(26) In order to perform a bonding test for accelerating contamination and clogging of the capillary, a capillary having a small hole diameter of 25 m was used, and 50,000 trapezoid loops having a wire length of 1.5 mm were connected under the condition that the bonding temperature was 150 C. and the number of times of scrubs was 2. Subsequently, the capillary was removed from the wire bonder, and the capillary was observed with an optical microscope. The number of capillaries including 3 m or more size of contamination, adhering substances, shavings, and the like at a tip part and an inner part thereof was counted as the number of failures, and evaluation was performed in accordance with the following criteria. Evaluation results are shown in the column of 50,000 bonds in Capillary life in Table 1.

(27) Evaluation Criteria:

(28) : 0 failure : 1 failure : 2 failures x: 3 or more failures

(29) Evaluation was also made with respect to a case of connecting 200,000 trapezoid loops under the same condition as described above. Evaluation results are shown in the column of 200,000 bonds in Capillary life in Table 1.

(30) Evaluation Criteria:

(31) : 0 failure : 1 to 2 failures : 3 to 4 failures x: 5 or more failures

(32) Evaluation results of Examples and Comparative Examples are shown in Table 1.

(33) TABLE-US-00001 TABLE 1 Loop shape stability Bondability Large One 0 Trapezoid height Cu purity Dopant XPS time times having difference Capillary life % ppm Cu[II]/ [Cu(OH).sub.2]/ [CuO]/ of of (no) long and 50,000 200,000 No. by mass by mass Cu[I]*.sup.1 [CuO]*.sup.2 [Cu.sub.2O]*.sup.3 scrub scrub span short span bonds bonds Working 1 99.99 2.05 2.59 0.57 Example 2 99.99 8.71 3.16 2.10 3 99.99 1.31 4.86 0.22 4 99.99 4.47 2.94 1.13 5 99.99 0.93 2.00 0.31 6 99.99 11.72 0.96 5.98 7 99.99 7.00 1.52 2.78 8 99.99 9.69 1.03 4.77 9 99.999 2.19 5.13 0.36 10 99.99 8.76 1.80 3.13 11 99.99 3.94 2.55 1.11 12 99.99 5.75 0.97 2.92 13 99.999 Ag 300 4.47 2.94 1.13 14 99.99 Ag 800 2.19 5.76 0.32 15 99.99 Pd 1000 2.58 3.08 0.63 16 99.99 Pt 6000 6.20 1.58 2.40 Comparative 1 99.99 0.67 1.29 0.29 X X X X X Example 2 99.99 0.44 1.20 0.20 X X X X X 3 99.99 0.56 2.41 0.16 X X X X X 4 99.99 0.56 0.71 0.33 X X X X X X *.sup.1Cu[II]/Cu[I] is the ratio of the total percentage of Cu substances in chemical-bonding state of CuO and Cu(OH).sub.2 (Cu[II]) to the percentage of Cu substances in chemical-bonding state of Cu.sub.2O (Cu[I]), when the sum of percentages of Cu substances in chemical-bonding state of Cu, Cu.sub.2O, CuO and Cu(OH).sub.2 as measured by XPS is defined as 100%. *.sup.2[Cu(OH).sub.2]/[CuO] is the ratio of percentage of Cu substances in chemical-bonding state of Cu(OH).sub.2 [Cu(OH).sub.2] to ther perecentage of Cu substances in chemical-bonding state of CuO [CuO], when the sum of percentages of Cu substances in chemical-bonding state of Cu, Cu.sub.2O, CuO and Cu(OH).sub.2 as measured by XPS is defined as 100%. *.sup.3[CuO]/[Cu.sub.2O] is the ratio of percentage of Cu substances in chemical-bonding state of CuO [CuO] to the percentage of Cu substances in chemical-bonding state of Cu.sub.2O [Cu.sub.2O], when the sum of percentages of Cu substances in chemical-bonding state of Cu, Cu.sub.2O, CuO and Cu(OH).sub.2 as measured by XPS is defined as 100%.

(34) Regarding all of Examples Nos. 1 to 16, the ratio Cu[II]/Cu[I] as measured by XPS falls within the range of the present invention, and it was confirmed that a favorable bondability was exhibited even when the scrub was reduced such that the number of times of scrubs at the time of bonding was 1 or 0. The sum of Cu[I] and Cu[II] as measured by XPS was 50% or more in all of Examples.

(35) Additionally, regarding Examples Nos. 1 to 5, 7 to 11, 13, 15 and 16, the ratio [Cu(OH).sub.2]/[CuO] as measured by XPS falls within the preferred range, and it was confirmed that excellent loop shape stability was achieved even at the time of forming a loop having a long span or at the time of forming a loop having a large height difference and a short span.

(36) Regarding Examples Nos. 1, 2, and 4 to 16, the ratio [CuO]/[Cu.sub.2O] as measured by XPS falls within the preferred range, and it was confirmed that an excellent capillary life was achieved.

(37) On the other hand, regarding Comparative Examples Nos. 1 to 4, the ratio Cu[II]/Cu[I] as measured by XPS was out of the range of the present invention, a bonding failure was caused when the scrub is reduced such that the number of times of scrubs at the time of bonding was 1 or 0, and the loop shape stability and the capillary life were also unfavorable.