JPH0446454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wire bonding method for connecting thin metal wires in the manufacturing process of ICs, transistors, etc., and particularly to a ball bonding method.

[Conventional technology]

In conventional semiconductor devices, gold wires have been used as thin metal wires for bonding, but since this has the drawback of high cost, it is conceivable to use copper wires instead of gold.

Further, in the wire bonding process, ball bonding using a thermocompression bonding method combined with ultrasonic waves is mainly used. FIG. 2 shows a partial front view of the bonding part. In the figure, 1 is a metal wire, 2 is a semiconductor chip, in this case a Si chip, 3 is an aluminum electrode formed on the surface of the chip 2, 4 is a lead, 5 is a ball bond part, and 6 is a stitch bond part. In this method, the spherical part that is formed when the tip of wire 1 is melted and solidified by arc heat input is
It is characterized by being bonded to an aluminum electrode 3 heated to about 200°C.

[Problem that the invention seeks to solve]

Here, from the viewpoint of reducing material costs, we will consider the case where copper is used instead of conventional gold as the metal wire. When a copper wire is used as the metal wire 1, since the hardness and work hardening index of copper are higher than that of gold, in order to obtain the desired bonding strength, in the above-mentioned bonding process, the ultrasonic output, that is, the vibration Although it is necessary to set the amplitude larger than in the case of gold, increasing the vibration amplitude of the ultrasonic wave causes cracks to occur in the Si chip 2.

FIG. 3 is a diagram in which a through hole 7a is opened along the axis of the cylindrical capillary chip 7, and the copper wire 1 is supplied from the through hole 7a, showing the occurrence of cracks during bonding. FIG. 3a shows the copper wire before bonding, and FIG. 3b shows the copper wire after bonding. In the figure, 8 is a spherical portion of the copper wire 1, and 9 is a generated crack. There is a concern that this crack 9 will cause deterioration of the electrical characteristics of semiconductor elements, and even if annealed pure copper wire is used, it will occur with a probability of 5 to 10% when trying to obtain the necessary bonding strength. It is.

This invention was made in order to eliminate the above-mentioned drawbacks, and an object thereof is to provide a wire bonding method that can obtain a sound bonding state between a copper wire and an electrode without causing cracks in a semiconductor chip. It is said that

[Means for solving problems]

In the wire bonding method according to the present invention, a copper wire is bonded to an electrode of a semiconductor chip by using a capillary chip and using ultrasonic vibration, and when bonding the copper wire to the electrode, the tip of the capillary chip and the tip of the copper wire are bonded. Both or one of the balls formed in the ball is heated by laser beam irradiation.

[Effect]

In this invention, during bonding, the ball at the tip of the copper wire is not only heated by heat from the electrode side, but also by the capillary tip heated by laser beam irradiation or by the laser beam. Therefore, the hardness of the ball at the tip of the copper wire is further reduced, and the copper wire can be well connected to the electrode without increasing ultrasonic vibration.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a wire bonding method according to an embodiment of the present invention. In the figure, Figures 2 and 3
The same reference numerals as in the figure indicate the same thing as in the figure, and 10 is
YAG laser or CO ₂ laser laser gun, 11
is a laser beam.

In the method of this embodiment, once the ball 8 is formed at the tip of the copper wire 1 that has passed through the capillary chip 7, a laser beam 11 is irradiated from the laser gun 10 to form the ball 8 at the tip of the capillary chip 7 and the copper wire 1. The ball 8 is heated (see FIG. 1a), and in that state, the ball 8 is bonded to the electrode 3 of the semiconductor chip 2 using a thermocompression bonding method combined with ultrasonic waves (see FIG. 1a).
Immediately after joining, stop laser beam irradiation,
Thereafter, the other end of the copper wire 1 is stitch bonded to the lead 4 (see FIG. 1a).

Here, it is desirable that the tip of the capillary tip 7 and the ball 8 be heated in a temperature range of 100 DEG C. to 150 DEG C. This means ball 8 below 100℃.
The hardness of the copper wire 1 does not decrease sufficiently, and on the other hand, at temperatures above 150°C, the surface oxidation of the copper wire 1 becomes severe, and the coefficient of friction between the inner surface of the capillary tip 7 and the copper wire 1 increases, resulting in a decrease in the strength of the copper wire 1. This is because breakage is more likely to occur synergistically.

In the method of this embodiment as described above, ball bonding is performed with the tip of the capillary chip and the ball heated to reduce the hardness of the ball, so that a healthy sound can be achieved without increasing the ultrasonic output. A good bonding condition is obtained, and almost no cracks occur in the semiconductor chip. As a result, copper wire can be used in place of the gold wire currently used for wire bonding, resulting in a significant reduction in material costs.

In the above embodiment, both the tip ends of the capillary tip and the copper wire are heated, but only one of them may be heated, or a part of the ball may be heated.

〔Effect of the invention〕

As described above, according to the wire bonding method of the present invention, when bonding a copper wire to an electrode, the tip of the capillary chip or the ball formed at the tip of the copper wire is heated by laser beam irradiation. Therefore, during bonding, the ball at the tip of the copper wire is not only heated by heat from the electrode side, but also by the capillary tip heated by laser beam irradiation or by the laser beam. Therefore, the copper wire with high hardness can be well connected to the electrode, and there is an effect that the copper wire can be used in place of the gold wire.

[Brief explanation of the drawing]

1A and 1B are schematic diagrams showing states during and after ball bonding in a wire bonding method according to an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining the wire bonding method, and FIG. Figures a and b are both schematic diagrams for explaining the occurrence of cracks during bonding. 1... Copper wire, 2... Semiconductor chip, 3... Electrode,
4...Lead, 7...Capillary chip, 8...Ball, 11...Inert gas, and the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A wire bonding method in which a copper wire is bonded to an electrode of a semiconductor chip using a capillary chip and using ultrasonic vibration, and when bonding the copper wire to the electrode, a wire bonding method is provided in which a copper wire is formed at the tip of the capillary chip or the tip of the copper wire when bonding the copper wire to the electrode. A wire bonding method characterized in that the ball formed at the tip of the capillary chip and/or the ball formed at the tip of the copper wire is heated by irradiating the ball with a laser beam.