JPH0747791B2 - Bonding wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bonding wire used for electrical connection of a semiconductor device, and more particularly to a bonding wire used for ball bonding.

[Prior Art] Conventionally, aluminum-based or gold-based alloys have been used as bonding wires used for electrical connection of semiconductor devices, and wedge bonding or ball bonding has been used as a bonding method. There is.

Wedge bonding is a method in which a bonding wire is placed on the connection part, pressed from above with a wedge, and pressure-bonded by heating or ultrasonic vibration.
In this method, the tip of the bonding wire is heated by means such as oxyhydrogen flame or arc discharge to form a ball, and the ball is pressure-bonded to the connection portion. Industrially, ball bonding, which has a high work efficiency, is preferably used. As a bonding wire used for this ball bonding, a bonding wire made of a gold-based alloy whose tip is easily spherical due to oxyhydrogen flame or arc discharge is generally used.

However, in such a connection, since the electrode of the semiconductor element to be the connection portion is often aluminum-based,
This is a connection between different metals such as gold and aluminum, and there is a drawback in that an intermetallic compound is generated during heating in a subsequent process and is easily deteriorated. Further, the bonding wire made of a gold alloy has a drawback that the cost is high.

Further, the aluminum-based bonding wire has a problem that it is difficult to form balls and the corrosion resistance is poor.

Therefore, a copper-based bonding wire having excellent ball forming ability and corrosion resistance and low cost has been desired.

[Problems to be solved by the invention]

However, conventional copper-based alloys have poor ball-forming ability,
It was not suitable for ball bonding. In particular, ball bonding using an oxyhydrogen flame could not be performed at all.

Ball bonding by the other arc discharge is a method of forming a ball at the tip of the wire by arc discharge between an electrode provided near the tip of the wire and the wire, but if the energy of the discharge is too large, it is formed. In addition, the root portion of the ball is deteriorated by excessive heat, resulting in a problem that the strength is remarkably reduced or the ball is constricted. Further, there is a problem that a large ball is formed as compared with a wire diameter of 20 to 50 μmφ which is generally used for ball bonding.

Therefore, as a solution to such a problem, it is conceivable to reduce the energy of the arc discharge, but if the energy is reduced, it is easy to cause arc discharge without causing the arc to fly, so it has been attempted to use an argon gas atmosphere. Yes, but not enough.

An object of the present invention is to provide a bonding wire which solves the above-mentioned problems, enables arc discharge with a small energy, and eventually enables ball bonding by arc discharge.

[Means for solving problems]

The bonding wire of the present invention contains 0.01 to 1% by weight of one or more elements having a work function of 3 ev or less, and the balance being copper. Therefore, the purity of copper is preferably 99.99% or more, more preferably 99.997% or more.

[Action and effect]

The bonding wire according to the present invention has a work function of 3 ev.
The following elements, that is, elements that easily emit electrons are 0.01
Since it is contained in an amount of up to 1% by weight, it is possible to perform arc discharge with smaller energy as compared with the conventional bonding wire made of an alloy.

Therefore, since the arc discharge can be performed without giving excessive energy to the ball formed at the tip of the wire, ball bonding can be performed without lowering the strength or constriction at the root portion of the ball.

Further, according to the present invention, since ball bonding with an alloy is possible, the problems of deterioration and high cost due to the formation of intermetallic compounds that occur when using a gold-based alloy are solved, and the reliability of ball bonding is further enhanced. You can

Typical elements having a work function of 3 ev or less used in the present invention include potassium (2.2 ev), cesium (1.9 ev), barium (2.5 ev), and strontium (2.1 e).
v) etc. can be mentioned.

In the present invention, the content of elements having a work function of 3 ev or less is limited to 0.01 to 1% by weight. When the content is less than 0.01% by weight, the characteristic of forming a small uniform ball with a small energy is exhibited. As a result, no improvement in the ball-forming ability is observed, and on the other hand, if it exceeds 1% by weight, wire drawing workability, corrosion resistance and conductivity may be impaired.

〔Example〕

Using 99.99% pure, 99.997% pure copper as a base,
Alloys having the composition shown in Table 1 (% indicates weight%) were melted. After the melting, the billet was continuously cast while removing inclusions of 10 μm or more from the molten metal with a ceramics filter.

After cutting the surface of this billet, it is 10mm by hot extrusion.
After forming the wire of φ, a combination of stripping, wire drawing and heat treatment was performed to produce a bonding wire of 40 μmφ.

With respect to the obtained 40 μmφ bonding wire, ball forming ability and wire drawing workability were evaluated as follows,
The results are shown in Table 1.

(A) Ball bonding ability A bonding wire with a diameter of 40 μm is passed through a sapphire capillary, and the arc is discharged between the electrode provided near the tip of the wire and the wire under argon gas ejection. After being formed, the state of ball formation was evaluated in the following two stages (◯ and ×), and the ball forming ability was defined.

◯: A ball with a surface shape close to a true sphere is formed, and the wire at the base of the ball does not become thin.

X: The ball forming conditions are narrow and the variations are large. Moreover, the surface shape is not excellent. The base of the ball may be constricted.

(B) Wire drawing workability The workability up to wire drawing up to 40 μmφ
The evaluation was made in stages (○ and ×).

◯: No change from conventional one.

X: There is a problem in workability as compared with the conventional one.

As is clear from Table 1, the bonding wire of the present invention has remarkably improved ball forming ability as compared with the conventional one.

Claims (3)

[Claims] 1. Containing 0.01 to 1% by weight of one or more elements (excluding Li) having a work function of 3 ev or less,
The rest is a bonding wire made of copper. 2. The bonding wire according to claim 1, wherein the purity of copper is 99, 99% or more. 3. The bonding wire according to claim 1 or 2, wherein the purity of copper is 99, 997% or more.