JPH05251451A - Solder bump forming material for semiconductor element - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor device having excellent durability in high temperature.high humidity environment by further assuring reliability of connecting an Al electrode on a surface of a chip to a bump formed on the electrode and particularly the reliability in high temperature.high humidity state. CONSTITUTION:A solder bump forming material for a semiconductor element contains 0.001-10wt.% of Zn and 0.001-10wt.% of Sb added to any one essential element of Pb, Sn and In.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder bump forming material for semiconductor devices, more specifically, a wireless bonding method,
In particular, the present invention relates to a solder bump forming material used when a semiconductor element (hereinafter referred to as a chip) is mounted on a substrate by a flip chip bonding method or a tape carrier bonding method.

[0002]

2. Description of the Related Art The applicant of the present application has made a thin alloy wire into a wire, and heat-bonds a ball formed by heating the tip of the wire onto an Al electrode on the surface of a chip and then cutting the ball from the wire to form an Al electrode. A solder bump forming material, which is particularly useful for bump formation using a wire bonding apparatus for forming bumps on the upper surface, was invented and previously filed (Patent application 2
-304509).

[0003]

However, in the semiconductor device in which a bump is formed on the Al electrode of the chip by using the above wire and the chip is mounted on the substrate by the bump, a high temperature and high humidity environment is provided. Under (temperature 85 ℃, humidity 85%)
When a durability test of leaving for 100 hours was conducted, it was found that a local cell reaction occurs at the joint between the bump and the Al electrode, and the Al electrode may be melted due to electrical corrosion of the joint.

The present invention has been made in view of such conventional circumstances, and an object of the present invention is to improve the bonding reliability between the Al electrode on the chip surface and the bump formed on the electrode, especially at high temperature. It is an object of the present invention to provide a solder bump forming material capable of manufacturing a semiconductor device having high reliability in a high humidity state and having excellent durability in a high temperature and high humidity environment.

[0005]

The inventor of the present invention, regarding the above-mentioned local battery reaction, has an Al electrode potential value (-1.66 V),
Pb (+1.5 V), Sn (-0.14 V), In (+0.21)
Paying attention to the large difference between V) and the respective electrode potential values, the potential difference with Al is small and the above-mentioned local battery reaction can be reduced, that is, Zn, which is well known for soldering to Al, is added. Therefore, it is assumed that the above-mentioned purpose can be achieved.

However, it was found that the addition of Zn alone can improve the bonding strength immediately after the bump formation, but the above-mentioned conventional problems cannot be solved under a high temperature and high humidity environment, particularly under a high humidity environment. As a result of earnest research,
It was found that a desired effect can be obtained in a high temperature environment by adding Zn in a predetermined range, and at the same time, a desired effect can be obtained in a high humidity environment by adding Sb in a predetermined range. The present invention has provided a solder bump forming material.

That is, according to the present invention, Z is 0.001 wt% to 10 wt% with respect to any one of the main elements of Pb, Sn and In.
A solder bump forming material for a semiconductor device, characterized in that Sb of n and 0.001 wt% to 10 wt% is added.

[0008]

When the tip of the thin alloy wire produced by using the forming material of the present invention is heated, Zn, which has a strong affinity with oxygen,
Sb is concentrated on the ball surface, and Zn and Sb on the surface side
A pseudo-Zn ball having a high concentration and a high concentration of a main element (one of Pb, Sn, and In) inside the pseudo-Zn ball is formed. Therefore, in the bump formed by this ball, the bonding strength with the Al electrode is improved due to the characteristics of Zn having a wide solid solubility limit with Al and Sb forming an intermetallic compound with Al, and Zn and Sb The rich surface layer reduces the local cell reaction in a high temperature and high humidity environment and obtains a desired effect in improving the bonding strength. Moreover, since the main element concentration is high inside the surface Zn and Sb layers, there is no fear of degrading the bump characteristics that require a predetermined softness.

However, the amount of each of Zn and Sb added is 0.
If it is less than 001 wt%, the above characteristics cannot be obtained. Moreover, if the amount of each of Zn and Sb added exceeds 10 wt%,
When a ball is formed at the tip of the wire, a thick oxide film is formed on the surface of the ball, the shape of the ball becomes distorted, and the bonding strength to the Al electrode decreases, which is not preferable. Therefore, Z
The addition amounts of n and Sb are set within the above range.

[0010]

EXAMPLES Examples of the present invention will be described below. Table 1 is a bump forming material in which various additive elements are mixed with the main element Sn in the amounts described in the table. Sample Nos. 1 to 16 each have a composition (including inevitable impurities) dissolved. It was cast and then drawn to form a wire having a wire diameter of 60 μm.

Samples Nos. 1 and 2 were prepared by adding either Zn or Sb alone, No. 3 was prepared by not adding Zn or Sb, and Nos. 4 and 10 were prepared by Zn or Sb. When the addition amount of one is less than 0.001 wt%, Nos. 9 and 14 are comparative examples showing that the addition amount of one of Zn and Sb exceeds 10 wt%.

Then, each sample was tested for the shear strength immediately after bonding, the shear strength under high temperature and high humidity environment, and the spherical shape of the ball.

The shear strength immediately after bonding is determined by forming a ball at the tip of each sample with a wire bonding device.
It is a value obtained by thermocompression bonding the ball on an Al electrode, cutting it from a wire to form a bump, and immediately after that, measuring the bonding strength between the bump and the Al electrode.

The shear strength under high temperature and high humidity environment is as follows:
The value is the bond strength between the bump and the Al electrode after being left for 100 hours at 85 ° C and 85% humidity.

The spherical shape of the ball has a discharge time of 3 ms.
The discharge current was adjusted so that the diameter of the ball was 2.5 times the wire diameter, the ball was formed, and it was measured whether or not the ball was distorted. As a result of the measurement, the case where there is no distortion is indicated as good, and the case where there is distortion is not indicated, and it is indicated respectively.

[0016]

[Table 1]

According to Table 1 above, when the additive elements Zn and Sb were not added (Sample No. 3), immediately after bonding,
Shear strength in both high temperature and high humidity environment is about 2g,
Sb added alone to this (Sample No. 1), or Zn
It is confirmed that the respective strength values are hardly improved when the addition amount of each is less than 0.001 wt% (Sample No. 4). In addition, Zn alone (Sample No. 2) or S
When the addition amount of b is less than 0.001 wt% (Sample No. 10), the shear strength immediately after bonding is improved, but at high temperature
It is confirmed that there is almost no effect on the shear strength under high humidity environment.

Further, if the addition amount of one of the additional elements Zn or Sb exceeds 10 wt% (Sample Nos. 9 and 14), a thick oxide film is formed on the ball surface, and proper ball formation is impossible. Is confirmed.

Therefore, as is clear from the measurement results of Table 1, the products of the present invention (Sample Nos. 5 to 8, 11 to 13, 15, 16)
According to the above, it was confirmed that predetermined characteristics can be obtained for bump formation of a semiconductor element.

The balls formed by the above bonding method using the wires of Sample Nos. 2, 3, and 7 were subjected to Auger analysis. The results are shown in the graph of FIG. In the graph, (a) is sample No. 3, and (b) is sample No. 2.
(C) represents sample No. 7, respectively.

According to this graph, in graph (a), Z
If n and Sb are not added, Sn on the ball surface
It is shown that the concentration shows some numerical value. In addition, in graphs (b) and (c), addition of Zn alone or Zn
It is shown that by simultaneous addition of Sb and Sb, the Zn concentration and the Sb concentration are high and the Sn concentration is low on the surface of the ball, whereas the Sn concentration is high and the Zn concentration and the Sb concentration are low toward the center of the ball.

As a result, Zn alone is added or Z is added.
It was confirmed that by simultaneous addition of n and Sb, a pseudo-Zn ball having a high Zn and Sb concentration on the surface side and a high concentration of the main element (Sn in this case) on the inside was formed.

Table 2 is a bump forming material obtained by mixing various additive elements with the main element Pb in the amounts described in the table, and Table 3
Indicates the bump forming materials obtained by mixing various additive elements with the main element In in the amounts shown in the table. Each sample No.
17 to 32 and 33 to 48 are made into a wire with a wire diameter of 60 μm by the same method as the above sample Nos. 1 to 16 and then shear strength immediately after bonding, shear strength under high temperature and high humidity environment, and ball The shape was tested for sphericity.

[0024]

[Table 2]

[0025]

[Table 3]

From the measurement results of each sample, the products of the present invention (Sample Nos. 21 to 24, 27 to 29, 31, 32, 37 to 40, 43 to 45, 48,
According to 49), it has been confirmed that the predetermined characteristics can be obtained for forming bumps of a semiconductor element, and thus, even if the main element is Pb or In, the same effect as when the main element is Sn is obtained. I was able to confirm that.

In Table 1, the temperature is 85 ° C and the humidity is 85%.
In the high temperature and high humidity environment, a current of 20 V was passed to perform a test for the presence or absence of Sn whiskers. As a result, when both Zn and Sb were not added, Sn whiskers were generated. It was confirmed that whiskers did not occur when a predetermined amount of either one was added.

It is considered that this is because Zn or Sb is concentrated on the surface of the ball to suppress the generation of Sn whiskers.

[0029]

According to the present invention, when the bumps are formed on the Al electrodes of the chip by using the wire bonding apparatus, the characteristics (ball sphericity, hardness, etc.) are maintained in the same manner as in the prior art, and the bumps are formed. It has become possible to further improve the characteristics of the joint portion with the Al electrode and solve the conventional problem that the Al electrode melts out in a high temperature and high humidity environment.

Therefore, a solder bump forming material which is useful for forming bumps using a wire bonding apparatus and which is particularly excellent in characteristics under high temperature and high humidity environment and which is useful for manufacturing a semiconductor device having high durability and reliability. Could be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the results of Auger analysis of balls formed by using wires made of sample Nos. 2, 3, and 7.

Claims (1)

[Claims] 1. 0.001 wt% to 10 wt% Zn and 0.001 wt% with respect to any one main element of Pb, Sn, and In
A solder bump forming material for a semiconductor element, characterized in that Sb of about 10 wt% is added.