JPH05129382A - Wire bonding method - Google Patents

Abstract

PURPOSE:To enhance the adhesive properties between a bonding ball at the tip of a wire and a pad under a state in which the deformation of the bonding ball is minimum in terms of a bonding process which connects the pad on a semiconductor device to the wire. CONSTITUTION:A contact bonding load produced, when a bonding ball comes into contact with a pad, is adapted to be smaller than the contact bonding load produced when supersonic waves are forced to act on after the contact bonding. The contact bonding load is set to a low load when the ultrasonic waves are oscillated. Then, impact is inflicted upon between the pad and the ball in the oscillation direction of the ultrasonic waves and in the vertical direction when or slightly before the ultrasonic waves are forced to act on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a wire bonding method for electrically connecting an electrode (pad) of a semiconductor element and a lead via a wire.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, there is a wire bonding process for electrically connecting electrodes (pads) of a semiconductor element and leads via wires.

As a wire bonding method, an ultrasonic thermocompression bonding method in which heat and ultrasonic waves are used in combination is widely used. In this ultrasonic thermocompression bonding method, as shown in FIG. 5, a high voltage is applied between the tip of the wire 11 that has passed through the capillary 10 and a discharge electrode (not shown) to cause a discharge phenomenon to cause the tip of the wire to reach a ball. The balls 13 are made to fall, and the capillaries 10 are lowered to press the balls 13 against the pads 12 of the semiconductor element to bond the balls and the pads by the action of ultrasonic waves and heat.

Conventionally, when the ball at the tip of the capillary is pressed against the pad for bonding, the pressure applied to the capillary via the bonding arm is constant as shown in FIG. 6 (a), and the ball is pressed against the pad with this constant load. Then, ultrasonic waves were oscillated for about 15 to 40 ms to bond and fix the ball and the pad with ultrasonic energy and thermal energy.

[0005]

In the wire bonding method using ultrasonic waves, in the initial stage of bonding,
The ball at the tip of the capillary slides on the pad by the vibration of ultrasonic waves, removes dirt and oxide film on the pad, and then the ball and the metal on the pad cause mutual diffusion by ultrasonic energy and thermal energy. To stick to each other.

In order to slide the ball on the pad,
The crimping load is preferably as low as 10 to 40 grams, but if the crimping load is low like this, the ball bounces when the ball hits the pad. Therefore, the movement applied when the ball actually hits the pad. The load will be higher than if it did not bounce. For example, the dynamic load when the crimping load is set to 60 grams and bounce is prevented is about 150 grams, but if the crimping load is set to 30 grams and the ball easily slides on the pad, the dynamic load reaches 250 grams or more. Therefore, the silicon substrate under the pad is cracked.

Therefore, in order to prevent bouncing, it is necessary to increase the pressure-bonding load when the ball comes into contact with the pad to be 45 to 100 gram weight. To increase the pressure-bonding load, the ball slides on the pad. The ultrasonic output of must also be increased. This increases the amount of deformation of the ball after applying ultrasonic waves.

When the deformation amount of the bonding increases, the area to be bonded on the pad increases, so that it is necessary to increase the pad area and the pad spacing.

Further, since the ultrasonic vibration is in a fixed direction, the ball after being pressure-bonded to the pad has an elliptical shape having a large diameter of 2-3 μm when the average pressure-bonding diameter is about 80 μm in the ultrasonic vibration direction. The shortest pad spacing is determined by the length of the long side of this ellipse.

Recently, especially for gate array products, there is a demand for reducing the area of pellets and increasing the number of pads. Therefore, how to reduce the ball diameter without lowering the adhesion strength between the pads and the balls. That is an important issue.

[0011]

According to the wire bonding method of the present invention, a first step of pressing a ball formed at the tip of a capillary against a pad of a semiconductor device with a predetermined crimping load, and after reducing the crimping load, It has a second step of vibrating the capillary or the semiconductor element in a direction perpendicular to the vibration of ultrasonic waves for a predetermined time, and a third step of applying ultrasonic vibration after the start of vibration.

[0012]

The present invention will be described below with reference to the drawings.

FIG. 1A is a characteristic diagram showing the relationship between the bonding pressure applied to the ball and the pad and the bonding time in the first embodiment of the present invention. FIG. 1B shows the ball contacting the pad. 7 is a time chart showing the timing of ultrasonic oscillation during vibration and vibration between the pad and the ball in the direction perpendicular to the ultrasonic wave. 4 is a front view showing the outline of the wire bonding apparatus, and FIG. 5 is a sectional view showing the positional relationship between the semiconductor element, the capillary and the wire when the ball contacts the pad.

The crimping load when the ball 13 contacts the pad 12 is a high load 1, as shown in FIG.
Prevent balls from bouncing on the pad and prevent damage to the silicon substrate under the pad. The load at this time is 4
The weight is 5 to 80 grams, preferably 60 grams, and the speed at which the ball 13 hits the pad 12 is 5
It is desirable to be 10 mm / s. Next, the pressure-bonding load is gradually reduced to a low load 2 of 10 to 40 grams, preferably 23 grams. Fig. 1 (b) between the pad and the ball in the direction perpendicular to the direction of ultrasonic vibration after applying a low load.
Apply vibration as shown in. This vibration is performed by moving the XY table in the Y direction when the vibration direction 6 of the ultrasonic waves is the X direction. The vibration of the XY table is shown in Fig. 2.
When the amplitude and the number of times of the amplitude are expressed as
In μm, the amplitude is performed once or twice. By applying vibration between the ball and the pad in this way, the ball slides on the pad and the oxide film and dirt on the pad are removed. Next, ultrasonic waves are oscillated, and the load at this time is 10 to 4
Since the weight is as low as 0 gram, slippage between the pad and the ball is facilitated, and ultrasonic energy can be reduced. Therefore, the amount of deformation of the ball after pressure bonding can be reduced. Here, the vibration of ultrasonic waves is XY in the X direction.
Since the vibration of the table is in the Y direction, the ball shape after pressure bonding can be closer to a circle than when it is pressure bonded only with ultrasonic waves. Further, since the ball is slid on the pad by the vibration of the XY table to remove the dirt on the pad and the ball and the pad are brought into close contact with each other by ultrasonic waves, the dirt state of the pad and the thickness of the oxide film are Stable adhesion strength can be obtained even if there is some variation.

Further, the vibration between the ball and the pad may be caused not by moving the XY table but by vibrating the bonding stage 5 holding the semiconductor element 9 perpendicularly to the vibration direction of the ultrasonic wave. Since the semiconductor element 9 can be directly vibrated, the vibration can more stably remove the dirt and oxide film on the pad.

FIG. 3 (a) is a characteristic diagram showing the relationship between the bonding pressure applied to the ball and the pad and the bonding time in the second embodiment of the present invention, and FIG. 3 (b) shows the ball acting as the pad. 6 is a time chart showing the timing of ultrasonic oscillation when in contact, ultrasonic vibration, and vertical vibration between a pad and a ball.

In this embodiment, the pressure-bonding load when the ultrasonic wave is oscillated and the pressure-bonding load when the ultrasonic vibration and the vibration between the pad and the ball in the vertical direction are changed at the low load 2a. In this way, the crimping load most effective for removing dirt and oxide film on the pad by vibrating between the pad and the ball and the crimping load most effective for crimping the ball and the pad by ultrasonic waves are set. By setting them separately, more stable bonding becomes possible.

[0018]

As described above, according to the present invention, the crimping load when the ball contacts the pad is made heavier than the crimping load when ultrasonic waves are applied in the state where the ball is then crimped to the pad, and Improving the adhesion between the ball and the pad by applying a vibration between the ball and the pad in the direction perpendicular to the ultrasonic vibration direction at the same time as or slightly before the ultrasonic wave oscillation after the crimping load is reduced. By doing so, it is possible to prevent the balls from coming off the pads after bonding.

Further, since the ball is prevented from bouncing on the pad by increasing the crimping load when the ball comes into contact with the pad with a weight of 45 to 80 grams, the pad is apt to occur when the crimping load is small. The damage of the lower silicon substrate can be prevented. Furthermore, since the compression load between the pad and the ball during vibration and ultrasonic oscillation is as small as 10 to 40 grams, the amount of deformation of the ball after compression can be reduced, and the vibration direction of ultrasonic waves and the vibration direction between the pad and ball can be reduced. Since it is in the vertical direction, the ball shape after crimping can be made closer to a circle by reducing the degree of an ellipse that is long in the vibration direction. Since the amount of ball deformation is small and the ball shape after pressure bonding can be made close to a circle in this way, the area of the pads and the distance between the pads can be reduced while maintaining the adhesion strength, and the integration degree of the semiconductor device can be improved. Can be improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a change over time of a crimping load in a first embodiment of the present invention (FIG. 1A) and a time chart of ultrasonic oscillation during bonding, ultrasonic vibration and vertical vibration ( It is FIG.1 (b)).

FIG. 2 is a diagram showing ultrasonic vibration and vertical vibration.

FIG. 3 is a characteristic diagram (FIG. 3 (a)) showing a temporal change of a crimping load in the second embodiment and a time chart of ultrasonic oscillation during bonding, ultrasonic vibration and vertical vibration (see FIG. b)).

FIG. 4 is a front view showing an outline of a wire bonding device.

FIG. 5 is a cross-sectional view showing a positional relationship between a capillary, a wire and a semiconductor element during bonding.

FIG. 6 is a characteristic diagram (FIG. 6A) showing a time change of a crimping load in a conventional technique and a time chart of ultrasonic oscillation during bonding.

[Explanation of symbols]

 1 High load 2, 2a Low load 3 Bonding head 4 XY table 5 Bonding stage 6 Ultrasonic vibration direction 7 Bonding arm 8 Lead 8a Island 9 Semiconductor element 10 Capillary 11 Wire 12 Pad 13 Ball 14 Ball 14 Contact surface between ball and capillary

Claims (4)

[Claims] 1. A wire bonding method in which ultrasonic waves and thermal energy are commonly used, in which a ball formed at the tip of a capillary is pressed against a pad of a semiconductor element with a predetermined crimping load, and after the crimping load is reduced. A wire bonding method, comprising: a second step of vibrating the capillary or the semiconductor element in a direction perpendicular to an ultrasonic vibration direction for a predetermined time; and a third step of applying ultrasonic vibration in the direction after the vibration is started. 2. The crimping load in the first step is 45 to 80.
The wire bonding method according to claim 1, wherein the crimping load and the vibration amplitude in the second step are 10 to 40 grams and 2 to 6 μm, respectively, and the crimping load in the third step is 10 to 40 grams. 3. The wire bonding method according to claim 1, wherein an XY stage equipped with a bonding head having a capillary is moved to vibrate in a direction perpendicular to a vibration direction of ultrasonic waves. 4. A wire bonding method in which a bonding head holding a semiconductor element is moved to vibrate in a direction perpendicular to a vibration direction of ultrasonic waves.