JP2708573B2 - Bonding wire for semiconductor and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bonding thin wire connecting a semiconductor chip and a lead, particularly to a bonding fine wire containing an alloy element and a method of manufacturing the same.

(Prior art) A bonding thin wire is usually bonded to a semiconductor chip or a lead frame. In this case, characteristics such as strength, ductility, neck (heat-affected zone) strength, loop height, and bondability are required. Is done. Conventionally, these characteristics have been improved by adjusting the components with alloying elements.
For example, JP-B-57-35577, JP-B-57-34659, JP-B-58-26662, and JP-A-63-145729.
In the case of Au wire, Ca, Ge, Be, In
It is disclosed that the addition of the above is effective in improving the characteristics of each.

However, the method of adding these alloying elements is uniformly applied to the material by a melting method.
When it is added, when forming a ball by electric discharge using an electric torch, a true ball cannot be obtained or the composition of the ball becomes finer.
There has been a problem that bonding to the chip cannot be performed or the chip is damaged. Therefore, in general,
Although the addition of alloying elements is limited to the range of several ppm to several tens of ppm, the strength of the heat-affected zone (neck) near the ball is not sufficient, and the semiconductor device is defective due to the breakage of the neck. In many cases, countermeasures are desired.

In addition, when an alloy element is added and the composition of the heat-affected zone is refined to increase the strength, the fine wire tends to be hard and the loop shape tends to be low. If the loop shape is low, the possibility of a short circuit occurring due to contact with a chip or the like increases, and the reliability of the semiconductor device decreases.

In the case of Cu alloy, alloying is also effective for refining the neck structure, but there is a problem that the hardness of the ball portion is too high and the chip is damaged during bonding.

Further, it has been attempted to improve the overall characteristics by adding a plurality of alloying elements in a complex manner, but it is difficult to satisfy all the characteristics, and the conventional method has a limit.

(Problems to be Solved by the Invention) The present invention provides a bonding wire having one or two or more alloying elements at different concentrations to obtain characteristics required for the wire, that is, wire strength, ball neck strength, The main purpose is to improve joint reliability, loop shape, electric conductivity, and the like.

Another object of the present invention is to provide a bonding thin wire having a sufficient tensile strength to make it thin (extremely thin) by drawing.

(Means for Solving the Problems) The gist of the present invention for achieving the above object is as follows.

(1) A bonding thin wire for a semiconductor, comprising an alloy element whose concentration continuously changes from the outer peripheral portion to the central portion of the conductive fine wire.

(2) The bonding thin wire for a semiconductor according to the above (1), wherein the fine wire is 20 μm or less.

(3) The surface of the conductor wire is coated with an alloy element or a high-concentration alloy, and the conductor wire is subjected to a diffusion treatment in which the concentration of the alloy element changes continuously from the outer periphery to the center. Manufacturing method of a semiconductor bonding wire.

(4) An alloy element or a high-concentration alloy is coated on the surface of the conductor wire, and the conductor wire is subjected to a diffusion process in which the concentration of the alloy element continuously changes from the outer peripheral portion to the center portion, and then the wire is drawn. A method for producing a bonding wire for a semiconductor, comprising:

 Hereinafter, the present invention will be described in detail.

As described above, in the present invention, the alloy concentration is continuously changed between the surface layer portion and the central portion of the fine wire in order to improve the overall characteristics of the bonding fine wire.

For each characteristic, for example, in order to increase the loop shape, it is necessary that the thin wire is soft. In this case, the central portion of the thin wire should be broadly and highly pure, or the fine wire should be re-formed. An element that does not raise the crystallization temperature so much may be added. Further, in order to improve the reliability of the neck portion, it is effective to reduce the size of only the recrystallized grains of the fine wire, particularly near the surface. In joining the ball portions, the alloy concentration is made as small as possible so that the balls are easily deformed. Therefore, it is better to limit alloying only to the vicinity of the surface. From this point of view, in order to increase the high loop and ball deformability, most of the central part remains pure, and in order to increase the neck strength, the surface layer is made finer ( Alloying). Therefore, in the thin-wire alloying, it is particularly preferable to change the concentration between the surface layer portion and the central portion in order to satisfy both the characteristic in which the surface layer portion is important and the characteristic in which the central portion is important. In practice, the ratio of the surface concentration (for example, the average concentration in a range of 1/20 of the wire diameter from the surface) to the center concentration (for example, the average concentration of 1/3 of the wire diameter from the center) is 1.2. It is preferably at least 1.5, and most preferably at least 1.5.

When the ratio of the surface concentration to the central concentration (Cs / Co) is 1.2 or less, no remarkable improvement in the loop height and the strength of the neck is not observed. An example when beryllium is alloyed to a gold wire is shown. After uniformly depositing copper-2wt% beryllium alloy on the surface by sputtering 0.5mm gold wire, 40
The concentration ratio between the surface portion and the central portion was adjusted by a diffusion heat treatment at 0 ° C. or higher. After drawing to a wire diameter of 20 μmφ, a finish heat treatment was performed so that the elongation to break of each wire was approximately 4%.

FIG. 1 shows the relationship between the loop height and the ratio (Cs / Co) of the concentration between the surface portion and the center portion of beryllium, and FIG. 2 shows the result of the relationship between the neck portion strength. The loop height is Cs
The ratio of the loop height (H _A ) H _B / H _A when the loop height H _B when _C / Co changes and the Cs / Co is 1.0 (the alloy element concentration is uniform)
Expressed as The neck strength when ball bonding was performed at a span of 2 mm was examined by a pull test. Cs
The ratio F _B / F _A of the strength (F _B ) when / Co was 1.0 or more and the strength (F _A ) when Cs / Co was 1.0 was determined. The concentration when beryllium was diffused uniformly was about 5 ppm.

As is clear from the figure, the effect is effective when Cs / Co is 1.2 or more,
At 1.5 and above, a remarkable effect was observed.

In recent years, with the increase in the number of pins of ICs and LSIs, high-density bonding wiring has been performed. For this reason, ultrafine wires having a diameter of 20 μm or less have been desired. However, when such an ultrafine wire is formed, in the case of ordinary alloying, the strength of the fine wire is insufficient, so that the wire is frequently broken during drawing, and the strength of the neck portion is insufficient. For this purpose, when a high alloy is used, the formation of the ball during bonding is not stable, and the bonding failure often occurs. As will be described later, the present invention uses 20 μm
The following ultra-fine wires can be manufactured without any trouble.
Obtaining an ultrafine line of m or less is also one of the features of the present invention.

The method of forming the concentration change of the alloy element from the outer peripheral portion to the central portion of the thin wire according to the present invention is performed by coating the surface of the fine wire with a high-concentration alloy by means such as vapor deposition and plating, and then performing a diffusion treatment. The vapor deposition method, physical vapor deposition method represented by sputtering, ion putting, vacuum deposition,
A chemical vapor deposition method typified by plasma CVD is used, and plating is usually performed by immersion or electrolytic methods.

Diffusion of the alloy coated in the present invention is performed at a place where the wire diameter is large, and then drawn to obtain a thin wire having a desired diameter. That is, in the present invention, for example, in order to obtain a fine wire having a diameter of 30 μmφ or less, an intermediate material having a diameter of 0.2 mmφ or more is coated with an alloy, subjected to a diffusion treatment, and then drawn. By doing so, the productivity becomes extremely large, and it is possible to prevent coarsening of the grains that occurs when the vapor deposition-diffusion treatment is performed after the thinning.

In addition, the electric conductivity may be lowered depending on the alloy to be added.If the electric conductivity is low, it may cause heat generation and cause a failure of the IC. The thin wire of the present invention is better than the conventional thin wire.

The thin metal wire used in the present invention is Au, Cu, Al, and the alloy element covering it is Au, Cu, Al, Be, Ca, Ge, In, Si,
There are lanthanoids such as Fe, Ga, Zn, Ba, Mg, Ni, Sn and La, Eu, Ce, Nd, etc. One or more of these are used according to the purpose.

A on a fine copper wire (Cu purity 99.999%) with a wire diameter of 150 μmφ
Examples in which u was deposited and then diffusion treatment was performed at different temperatures are shown below.

The diffusion state of the element after the diffusion treatment is shown in FIG.
(B) and (c) show. In these figures, the cross section of the fine wire was polished, and X-ray analysis (EPMA ray analysis) was performed in the diameter direction 2 of the fine wire 1 as shown in FIG. 4. In the heat treatment (c) at 900 ° C. for 4 hours, Although the concentration is slightly reduced at the center, it is almost uniformly diffused in the line, and the concentration gradient of the element is eliminated. On the other hand, under the processing conditions (a) and (b), the density difference between the line surface layer portion and the central portion is apparent. Thereafter, these 150 mmφ Cu wires were drawn to 25 μmφ, and the same X
The line analysis showed that the distribution of elements was almost similar to the case of 150 mmφ.

From the above events, the present inventors considered the diffusion of alloy elements as follows. That is, when an alloy element is diffused into a metal, the diffusion distance (l) of the element is determined by the diffusion temperature (T
゜ K) and the diffusion time (t). This relationship is approximately It is expressed as here, Where D is the diffusion coefficient, it is determined for each temperature, given D ₀ and Q is.

D ₀ and Q are constants specific to each element. For example, “Metal Data Book” edited by the Japan Institute of Metals Science or “C
RC Handbook of Chemistry and Physics ".

 R is a gas constant and T is an absolute temperature.

In order to produce a thin wire having a concentration gradient at the surface portion and the central portion, the alloying element, which is the gist of the present invention, can be estimated by the following equation, where d is the wire diameter when the diffusion process is performed.

Here, K is a constant and is a value substantially between 1 and 10.
And the preferable range as the diffusion condition is And the most preferred range is Becomes

Applying the above calculation using the Au diffusion experiment into the above-mentioned Cu wire as an example, the "CRC Handbook of Chemistry and
According to "Physics", values of D = 0.03 cm ^{2 /} sec and Q = 42.6 kcal are given.
In the heat treatment for less than or equal to the time, the alloy concentration is considered to have changed between the outer peripheral portion and the central portion of the surface. Therefore, when the relationship between d and Kl at that time is obtained, d ≧ 44K, so that K = about 3 to 4. Value, which is within the above range.

Next, the types of elements to be added, the range of the deposition thickness, and the subsequent heat treatment conditions will be described.

As the element, the above-mentioned elements may be used alone or in combination of two or more. Alternatively, only the specific element may be changed in concentration, and the other elements may be uniformly alloyed. The uniform alloying can be performed by a melting method in advance or by subjecting the surface-coated alloy to a high-temperature long-time diffusion treatment.

The deposition, plating thickness, and diffusion treatment conditions of each element differ depending on the atomic size, solid solution amount, and diffusion coefficient of each element in the metal to be deposited. The preferred and preferred thickness for the elements to be deposited on Au and Cu wires are
Examples are shown in Tables and Table 2. Although the wire diameter is 1 mm, when the wire diameter changes, it is necessary to change the deposition amount in proportion to the wire diameter. Further, the selection of the coating thickness has different maximum and minimum values depending on the difference in the effect on the characteristics of each element.
If the amount is too large, the ball formed at the time of joining the fine wires is too hard,
Problems such as damage to the semiconductor chip occur.

(Examples) Examples of the present invention will be described below.

Example 1 An Au wire sample having a diameter of 1 mmφ and a length of 5 m was set on a rotary take-up device having a feed reel and a take-up reel, and this was set in a vacuum chamber of an ion plating device. The wire is transferred from the delivery reel to the take-up reel through the vapor deposition zone while rotating. At this time, in the deposition zone, the alloy element is uniformly deposited on the Au wire surface. The conditions for the vapor deposition are as follows.

Method Ion plating Evaporated substance and thickness As shown in Table 3 (deposition (alloy) elements and film thickness for each sample are shown) Evaporation atmosphere 5 × 10 ^-4 Torr or less Evaporation method Electron beam, 10 kV, 10 to 200 mA High frequency power 0.1kW Coil (line) feed rate 30-100cm / min After the vapor deposition, the wires were subjected to diffusion treatment in two ways, A and B.
The A treatment is a diffusion treatment in which the alloy concentration is made substantially uniform from the wire surface to the central portion. (D is the wire diameter) and the temperature and time were set so that
When the value of the diffusion coefficient D was not found in the literature as data, D was obtained in advance by a diffusion experiment using a rod-shaped sample. The B treatment is a treatment method of the present invention, and the alloy element has a surface portion (range of d / 20 from the surface) of the wire so that the concentration continuously changes between the wire surface portion and the central portion. The temperature and time of the diffusion treatment were set so that the ratio of the average density to the average density at the center (range of 1/3 from the center) was 3 or more. That is, in the above equation Is approximately d / 20. However, K was adopted as 5.

Each of the diffusion-treated samples having a diameter of 1 mm was drawn into a fine line of 25 μmφ. And each sample thin line (No.1
37), the concentration ratio (Cs / Ci) of the diffusion alloy element between the surface part (Cs) and the central part (Ci) was determined by EPMA analysis (see FIG. 2) or chemical analysis. For those with low sensitivity in EPMA analysis, chemical analysis was performed to separate the surface and center of the fine wire sample by acid dissolution. As a result, Cs / Ci of each sample subjected to the treatment A was 1.2 or less, and the diffusion concentration was almost uniform. However, each of the samples subjected to the treatment B was 3 or more. It became clear that the diffusion concentration of the element changed greatly.

Ball bonding and stitch bonding were performed on each of the above-mentioned samples, which had been subjected to a finishing heat treatment so that the elongation after drawing was approximately 4%. The distance between the ball joint side and the stitch joint side was 2 mm. The maximum height of Rupyingu at that time, was determined H _B / H _A mean value of the by A process H _A, the average value of the by B treatment as H _B. Further, the hook breaking strength was measured by a hook test (pulling the hook to a loop formed by joining the ball and the stitch). At this time, the average of the hook strength of the A treatment was F _A , and the B treatment was F _B, and F _B / F _A was obtained. In addition, the average value of 80 measured values was obtained for both the loop height and hook strength.

Table 4 shows the values of H _B / H _A and F _B / F _A in each sample.

From the above results, it is clear that the B-treated material of the present invention is excellent in both the loop height and the hook strength in each sample.

Further, in order to examine the electric conductivity, the increase in electric resistance due to alloying of each sample, that is, the residual resistance (ρ _i ) was measured. The residual resistance is obtained from the ratio of the electric resistance at room temperature (295K) to 4.2K (residual resistance ratio RRR). And what the by A process according to [rho _A, B treatment (invention) and [rho _B, any was determined with [rho _B / [rho _A A is the value 1.2 or more, is excellent due to the invention It was clear.

Example 2 A Cu wire of 0.15 mmφ was subjected to ion plating with the same apparatus and method as in Example 1. Using pure gold (99.999%) as a deposition material, a uniform film of 200 mm was formed on the Cu wire. Thereafter, a diffusion treatment was performed under the conditions of 650 ° C. × 4 hours (B treatment) and 950 ° C. × 4 hours (B treatment, the scope of the present invention), and a thin wire of 25 μmφ was drawn. When the same wire was subjected to the same hook test as in Example 1 for each of the 80 treated materials, and F _B / F _A was obtained, it was all 1.15 or more, indicating that the material according to the present invention exhibited excellent characteristics. It became clear.

Example 3 Au was vapor-deposited on the surface of a 0.15 mmφ Cu wire so as to have a uniform film thickness of 500 ° (using the same ion plating apparatus and method as in Example 1), and then the following diffusion treatment was performed. Was.

650 ° C, 4 hours (Treatment B) 950 ° C, 4 hours (Treatment A) After depositing Cu on the surface of 0.15mmφ Au wire so as to have a uniform film thickness of 7000mm (by the same method as above), The following diffusion process was performed.

950 ° C., 4 hours (A treatment) The following two alloy wires were produced by a melting method, rolled and drawn to a wire diameter of 0.15 mmφ, and then subjected to intermediate annealing.

An alloy wire having the same concentration (0.061 wt% Au) as an alloy wire having the same concentration (0.86 wt% Cu) Each of the above was drawn to a thin wire of 12 μmφ. At this time, the number of disconnections was measured until the wire was formed to a size of 12 mmφ and 1000 mm, and the results are shown in Table 5.

Is a target material of the present invention, and there was no disconnection. However, although the same alloy amount was used, disconnection was observed because of uniform diffusion. Is uniform diffusion as in the case of, but there was no disconnection due to the high alloy concentration. However, when a bonding test with the chip was performed, the chip was found to be damaged.
, Are dissolution methods, inclusions and the like are mixed, and all of them are broken. In particular, the alloy concentration was low, and the number of disconnections was extremely large as compared with. The damage (scratch) at the time of chip bonding was observed as in the case of, although it was small. These results show that the method of the present invention is excellent.

(Effects of the Invention) As described above, the wire rod obtained by the present invention does not contain impurity elements which are found in the melting method or the like due to the addition of alloying elements, the amount of addition can be freely selected, and the soft center portion is obtained. In combination with a surface layer portion having desired characteristics, various characteristics required for a package can be obtained as desired in manufacturing and bonding, and a reliable semiconductor device can be manufactured. , Its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the ratio of the surface concentration and the center concentration of the gold alloy and the loop height, FIG. 2 is a diagram showing the relationship between the ratio of the surface concentration and the center concentration of the gold alloy and the pull strength, FIG. 3 is a diagram showing an EPMA analysis result of each of the wires subjected to the diffusion treatment, and FIG. 4 is a diagram showing an EPME analysis position of the sample (line).

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shunpei Miyajima 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Steel Corporation First Technical Research Institute (56) References JP-A-60-236252 (JP, A) JP-A-1-259541 (JP, A) JP-A-2-52118 (JP, A)

Claims (4)

(57) [Claims] 1. A bonding thin wire for a semiconductor, comprising an alloy element whose concentration continuously changes from the outer peripheral portion to the central portion of the conductive thin wire. 2. The bonding thin wire for a semiconductor according to claim 1, wherein the fine wire is 20 μm or less. 3. The method according to claim 1, wherein the surface of the conductive wire is coated with an alloy element or a high-concentration alloy, and the conductive wire is subjected to a diffusion treatment in which the concentration of the alloy element continuously changes from the outer peripheral portion to the central portion. A method for producing a bonding wire for a semiconductor. 4. A method for coating the surface of a conductive thin wire with an alloy element or a high-concentration alloy, and performing a diffusion process on the conductive thin wire in which the concentration of the alloy element continuously changes from the outer peripheral portion to the central portion. And a method of manufacturing a bonding thin wire for a semiconductor.