JP3283548B2 - Electrode for ultrasonic wire bonding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wire bonding electrode joined to a metal wire by ultrasonic bonding, and is suitable for wire bonding between metal wiring on an insulating substrate and metal wiring on a semiconductor substrate. Things.

[0002]

2. Description of the Related Art The wire bonding technique is a technique generally used for electrically connecting metal wirings. In the wire bonding work that connects the aluminum electrode and the lead with a wire in the semiconductor manufacturing process,
Ultrasonic bonding that performs vibration pressure bonding using ultrasonic energy is frequently used.

[0003] In ultrasonic bonding, ultrasonic vibration is applied to an aluminum wire through a tool under a certain load, and the wire is welded by causing a plastic flow similar to that of pressing under high temperature. Since this plastic flow is accompanied by a wave flow caused by ultrasonic waves at the same time as the macroscopic deformation of the wire, the oxide film at the interface between the two metals is destroyed and an atomic bond is formed by contact of the new surface.

[0004]

In the above-described ultrasonic bonding, as shown in FIG. 5, the welding between the aluminum electrode 11 formed on the substrate 10 and the aluminum wire 12 forms the bonding surface 13. The donut is formed not on the entire surface but around the deformed portion, and the central portion is not welded. Therefore, in order to obtain a constant bonding strength, it is necessary to increase each bonding parameter such as weight, ultrasonic output and time. However, as a result, the plastic deformation of the wire 12 increases, and it is difficult to increase the wire bonding pitch.

The reason why the central portion of the bonding surface 13 is not welded and the peripheral portion is welded in a donut shape is apparent from the sectional view at the time of wire bonding shown in FIG. Strongly pressed with
It is considered that the contact pressure (load) at the center increases, no slip occurs between the wire 12 and the aluminum electrode 11 due to the ultrasonic vibration, and no new surface is generated, so that welding does not occur. On the other hand, since the peripheral portion has a low contact pressure, it is considered that slip occurs, a new surface is formed, and welding occurs. FIG. 7 shows the relationship between the distance from the center of the wire and the contact pressure.

Therefore, in the present invention, the area of the non-welded portion generated at the center of the joint surface is reduced, and the area of the welded portion generated at the peripheral portion is increased to reduce the plastic deformation of the wire, thereby reducing the wire bonding pitch. The purpose is to increase the density.

[0007]

Means for Solving the Problems An ultrasonic wa <br/> ear bonding electrode according to the invention forms an electrode made of aluminum thin film on the substrate, the junction surface between the previous SL aluminum thin wire grains Particle size of 0.7 μm or more, film thickness 1 μm
The crystal is grown in a columnar shape as described above and has a surface roughness of 0.05 to 0.3.
The thickness is set to be 0 μm.

[0008]

According to the present invention, the surface roughness of the bonding surface of the aluminum thin film is reduced by the conventional surface roughness (0.03 μm or less).
By making the thickness 0.05 to 0.30 μm, which is coarser than that in the prior art, a portion where the contact pressure is reduced occurs even in the central portion where welding did not occur conventionally, and a new surface is generated by slip and welding occurs. . For this reason, the area of the welded portion generated at the center becomes large, and the conditions of the respective joining parameters such as the weight, the ultrasonic output and the time can be set weaker, and the plastic deformation of the wire is reduced to increase the wire bonding pitch. It can be densified. It is considered that the wire width after plastic deformation is twice as large as the diameter of the wire. When the surface roughness is 0.05 to 0.30 μm, the wire width after plastic deformation is less than twice the diameter. Has been confirmed to be.

[0009]

1 is a schematic view showing a first embodiment of an electrode for ultrasonic wire bonding according to the present invention. FIG. 1 (a) is a plan view, and FIG. 1 (b) is a sectional view taken along line AA. It is. this
In the first reference example , an aluminum electrode 2 is formed on a substrate 1, and a groove 4 and a plane portion 5 are formed on a bonding surface 3 with a wire. Then, the surface roughness of the bonding surface 3 is set to 0.05 to
It is formed to have a thickness of 0.30 μm. In this case, the amplitude of the tip of the bonding tool described above is 1 μm at the maximum at the time of bonding.
Therefore, it is preferable that the width of each of the groove portion 4 and the flat portion 5 is 2 μm or less, and the groove pitch is 4 μm or less.

FIG. 2 is a structural view showing a second embodiment of the present invention, which is a wire bonding electrode in which a large number of fine holes 6 are formed on a joint surface 3 of an aluminum electrode 2. Also in this case, the bonding surface 3 is formed so as to have a surface roughness of 0.05 to 0.30 μm. The pitch of the fine holes 6 is 4 μm.
Preferably, the diameter is half the pitch.

FIG. 3 is a block diagram showing an embodiment of the present invention .
This is an electrode for ultrasonic wire bonding in which an aluminum film 7 having a crystal grain size of 0.7 μm or more is formed on a substrate 1. The aluminum film 7 is grown in a columnar crystal and has a thickness of 1 μm.
m, the surface roughness is 0.05-0.30μ
a m. The conditions for forming the aluminum film 7 are as follows.
For example, it can be achieved by high-temperature low-speed film formation at a substrate temperature of 300 ° C. or more and a film formation rate of 4 [angstrom / sec].

Next, the reason why the surface roughness of the bonding surface 3 is set to 0.05 to 0.30 μm will be described with reference to a characteristic diagram shown in FIG. This characteristic diagram evaluates the bonding when ultrasonic wedge bonding is performed on aluminum electrode surfaces with different surface roughness using aluminum wires with a diameter of 25 μm. Surface roughness and plasticity in the wire breaking mode of the tensile test FIG. 9 is a characteristic diagram illustrating a relationship with a wire width after deformation. In the figure, the horizontal axis represents the surface roughness of the joining surface, and the vertical axis represents the wire width after plastic deformation.

Generally, it is considered that the width of the wire after plastic deformation is twice (2D) the diameter D of the wire. Diameter 25
In the case of a wire of μm, since 2D = 50 μm, a line L is drawn at a position of 2D (= 50 μm) in the drawing. As is clear from this characteristic diagram, the surface roughness is 0.05 to
At 0.30 μm, the wire width after the plastic deformation is 2D or less, which indicates that the wire width is in a range that is advantageous for increasing the wire bonding pitch by miniaturizing the plastic deformation.

[0014]

According to the present invention, the surface roughness of the bonding surface of the aluminum thin film with the wire is reduced to 0.05 to 0.30 μm.
As a result, the surface roughness of the aluminum thin film (0.03 μm or less) is more uneven than that of a general aluminum thin film. A new surface is created and welding occurs.

Further, in the planar shape, even if the oxide film on the surface is broken, there is no place for the oxide film to escape, so that the oxide film hinders the welding of the newly formed surface. Since a part is driven, welding of the new surface becomes easy. By welding at the center in this way, it is possible to set the conditions of the welding parameters such as load, ultrasonic output and time to be weaker, to reduce the plastic deformation of the wire, and to increase the density of the wire bonding pitch. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first reference example of the present invention.

FIG. 2 is a configuration diagram showing a second reference example of the present invention.

FIG. 3 is a configuration diagram showing an embodiment of the present invention .

FIG. 4 is a characteristic diagram showing a relationship between surface roughness and a wire width after plastic deformation.

FIG. 5 is a diagram in which a wire subjected to wire bonding is peeled from a bonding surface.

FIG. 6 is a sectional layout view during wire bonding.

FIG. 7 is a characteristic diagram showing a relationship between a distance from a wire center and a contact pressure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Aluminum electrode 3 Joining surface 4 Groove part 5 Plane part 6 Micro hole 7 Aluminum electrode (columnar grain)

Claims (1)

(57) [Claims] An electrode for ultrasonic wire bonding.
To form an electrode made of an aluminum thin film on the substrate,
Particle bonding surfaces of the wire before Symbol aluminum film grain
Crystals are grown in columns with a diameter of 0.7 μm or more and a film thickness of 1 μm or more.
To the surface roughness 0. An electrode for ultrasonic wire bonding, wherein the electrode has a thickness of 0.5 to 0.30 μm.