JPH0663991B2 - Copper purity evaluation method - Google Patents

Description

The present invention relates to a copper purity evaluation method suitable for evaluating the purity of high-purity copper having a purity of 99.999% by weight (so-called 5 nines) or more.

[Prior Art] In recent years, pure copper materials used in the fields of electronic materials such as bonding wires or copper foils for printed circuit boards, substrates for vapor deposition or sputtering, conductors for acoustics, etc. Along with this, further purification is demanded. As the demand for high purity copper has increased, the complexity of the means for evaluating purity has become a problem.

Conventionally, the purity of so-called about 4 nines is usually analyzed by an emission spectroscopic mass spectrometry method using spark discharge or the like, and the purity can be rapidly analyzed by this method. However, when trying to evaluate the purity of so-called 5-nine high-purity copper with a purity of 99.999% by weight or more, it is necessary to analyze impurity elements with an analysis accuracy of the order of 0.1 ppm or less per element. It is difficult to evaluate the purity by the emission spectroscopic mass spectrometry method using the spark discharge or the like.

Therefore, when measuring the purity of high-purity copper such as 5 nines or more, conventionally, an advanced mass spectrometry method such as inductively coupled plasma atomic spectroscopy mass spectrometry (ICP) or glow discharge mass spectrometry (GDMS) is used. Has been adopted.

[Problems to be Solved by the Invention] However, when the purity is evaluated by these mass spectrometry methods, 24 elements (Na, Mg, Si, P, S, Ca, Al, Cr, Fe, Ni, Z
(n, As, Se, Ag, Cd, Sb, Te, Pb, Bi, Sn, In, B, Cl, O) It is necessary to measure the content of a large amount of elements. Moreover, it is necessary to analyze each element with high accuracy. Therefore, a huge amount of time and cost are required to measure the purity, and the production cost of high-purity copper is further increased due to this purity measurement.

The present invention has been made in view of such problems,
An object of the present invention is to provide a copper purity evaluation method capable of grasping the purity of high-purity copper with high accuracy, quickly and at low cost.

[Means for Solving the Problems] The copper purity evaluation method according to the present invention has a purity of 99.999% by weight.
The calibration curve between the residual resistance ratio and the purity is previously prepared by measuring the known residual resistance ratio of copper,
The residual resistance ratio of copper to be evaluated for purity is measured, and the purity of the copper is evaluated using the calibration curve based on the measurement result.

[Operation] In the present invention, the residual resistance ratio (Residual R
esistivity Ratio (hereinafter referred to as RRR)
Is used as an index of purity. There is a close relationship between the impurity amount and the RRR, and the larger the RRR, the lower the impurity concentration.

The residual resistance ratio RRR will be described below. The electrical resistance ρ (room temperature) of copper at room temperature is calculated according to Matthisen's law (Matt
It is expressed by the following formula (1) according to the Hiessen's Rule).

ρ (room temperature) = ρ (therm) + ρ (chem) + ρ (phys) (1) where ρ (therm) is the resistance due to thermal vibration of the crystal, ρ (che
m) is resistance due to chemical impurities, and ρ (phys) is resistance due to intellectual defects.

Generally, RRR is defined by the following equation (2).

RRR = ρ (room temperature) / ρ _4.2K (2) Here, ρ _4.2K is the electrical resistance at the liquid helium temperature and is represented by the following equation (3).

_{ρ 4.2K ≒ ρ (chem) +} ρ (phys) ... (3) In this case [rho (room temperature) because »ρ is _{4.2 K,} the following (4)
An approximate expression shown in Expression can be obtained.

RRR ≒ [ρ _{(RT) -ρ 4.2K] / ρ 4.2K ≒} ρ (therm) / [ρ (chem) + ρ (phys)] ... (4) Therefore, when the temperature is constant, the residual resistance ratio of the chemical Resistance due to impurities ρ (chem) and resistance due to physical defects ρ (ph
ys) and is inversely proportional to the sum. Therefore, when physical defects such as crystal grain boundaries are eliminated by annealing, the resistance ρ (phys) due to the physical defects becomes approximately zero. As a result, the RRR has a resistance ρ (phe
m), reacts well with the amount of chemical impurities,
It will be a clear indicator.

Therefore, for copper of various purities, the purity is measured by other conventional methods, and the RRR of the copper is measured to prepare a calibration curve between the purities and the RRRs, and the purity is unknown. By measuring the RRR of the target copper, it is possible to grasp the purity of the target copper by using the calibration curve. However, 4 nine-OF that is commercially available
RRR of C (purity of 99.99% by weight or more oxygen-free copper) is 100 to
Since it is as low as 200, the difference in the amount of impurities is unlikely to appear as a difference in RRR, and there is a large variation between the RRR and the amount of impurities, and the correlation between the two is poor, so a calibration curve cannot be created.

However, for high-purity copper with a purity of 5 nines or more, the RRR is large and the correlation between RRR and purity is high. Therefore, if a calibration curve for both is prepared, RRR will be obtained for copper of unknown purity. Therefore, the purity can be grasped with high accuracy. As described above, according to the present invention, it is possible to grasp the purity of high-purity copper having a purity of 5 nines or more extremely quickly and highly accurately without directly analyzing the amount of impurities chemically or physically. .

Example Next, an example of the present invention will be described in comparison with a comparative example with reference to the accompanying drawings.

First, four types of commercially available electrolytic copper plates were melted, respectively, and subjected to wire drawing to manufacture a wire having a wire diameter of 1.5 mm. The respective wires were designated as Comparative Examples 1 to 6.

Next, a copper plate of the same type as the steel plate used in the production of Comparative Example 4 was used as a starting material, and re-electrolytic refining and zone melting refining were performed on the starting material alone or in combination, and this was repeated. By doing so, eight types of high-purity copper were manufactured.

And each of these high-purity copper is drawn to have a diameter of 1.5m.
I made m wires. High-purity wires having different purities were set as Examples 1 to 8, respectively.

GDMS analysis was performed on each of the wires of Examples 1 to 8 and Comparative Examples 1 to 6 described above.

Also, each wire vacuum of 10 ^{- 5} Torr vacuum atmosphere in the
It was annealed by heating at 500 ° C. for 6 hours. After that, the electrical resistance at liquid helium temperature (ρ _{4.2 K} ) and the electrical resistance at room temperature (ρ _{2 9 8 K} ) were measured by the 4-terminal method. Thus, the RRR of each wire of the example and the comparative example
(= Ρ _{2 9 8 K} / ρ _4.2K ) was determined.

The results of these RRR measurements are summarized in Table 1 below.
However, in the GDMS analysis result column in the table, blank items indicate that the element could not be detected. In addition, FIG. 1 shows the relationship between the residual resistance ratio RRR and the total amount of impurities in the wires according to Examples 1 to 8 and Comparative Examples 1 to 6, with the horizontal axis representing RRR and the vertical axis representing total amount of impurities. It is the graph figure which showed.

As shown in Table 1, each wire of Comparative Examples 1 to 6 has a total amount of impurities exceeding 10 ppm and a purity of 4 nines or less. On the other hand, each wire of Examples 1 to 8 has a total amount of impurities of 10 ppm or less and a purity of 5 nines or more.

As is clear from FIG. 1, in the region where the RRR was 400 or more and the total impurity amount was 10 ppm or less, a very high correlation was obtained between the RRR and the total impurity amount. Therefore, for high purity copper with a purity of 5 nines or more,
By measuring the RRR, its purity can be evaluated from the calibration curve shown in FIG. On the other hand, the total amount of impurities is 10
In the case of Comparative Examples 1 to 6 in which the concentration exceeds ppm, the RRR is 250 or less, and thus the correlation between the RRR and the purity is not obtained.

Incidentally, 14 samples of each Example and Comparative Example were annealed to obtain RRR.
It took about 17.5 hours to process the measurement. On the other hand, it took about 112 hours to obtain the total amount of impurities in the 14 samples by the GDMS analysis method. That is, RRR
In the case of measurement, it takes about 1.25 hours per sample,
GDMS analysis required about 8 hours per sample.
Therefore, according to this example, the purity of copper can be measured in an extremely short time as compared with the conventional GDMS analysis method.
Therefore, the cost required for measurement is low.

[Effects of the Invention] As described above, according to the present invention, by utilizing the fact that the purity of copper having a purity of 99.999% by weight or more and its residual resistance ratio show a high correlation, Since the purity of the high-purity copper is evaluated, the purity of the high-purity copper can be grasped with high accuracy, quickly and at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the residual resistance ratio RRR and the total amount of impurities in the wires according to Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] 1. A copper for which purity is to be evaluated by measuring a residual resistance ratio of known copper having a purity of 99.999% by weight or more and preparing a calibration curve between the residual resistance ratio and the purity in advance. Is measured, and the purity of the copper is evaluated by using the calibration curve based on the measurement result.