TWI553777B - Manufacturing method of semiconductor device - Google Patents

Description

Semiconductor device manufacturing method

Embodiments of the present invention relate to a method of fabricating a semiconductor device.

As a semiconductor wafer in which a circuit including various semiconductor elements is formed on a substrate, the semiconductor wafer is packaged and used in order to protect it from external mechanical, physical, and chemical impact. At this time, it is necessary to electrically extract the circuit of the semiconductor wafer to the outside. As a technique thereof, a method of bonding the electrode pad formed on the semiconductor wafer to the external electrode of the package by a bonding wire is known (wire bonding method).

In the wire bonding method, a gold wire is generally used as a bonding wire. However, in the field of LSI (Large Scale Integration), it is also known to use a copper wire which is easy to obtain in place of a gold wire.

However, since the hardness of copper is higher than that of gold, the electrode pads and the copper wires sometimes have poor connection. In particular, in the case where the unevenness of the probe formed on the surface of the electrode pad is large at the time of inspection of the electrical characteristics of the semiconductor wafer performed before packaging, if the copper having a high hardness is used, the filling cannot be performed. Probe traces are prone to poor connection. That is, the electrode pad of the semiconductor wafer is also used as an electrode for the characteristic inspection. Therefore, the probe will come into contact with its surface every time it is inspected, and depending on the shape of the probe, the contact method, etc., a large unevenness may be generated on the surface.

The problem to be solved by the present invention is to provide a method for reducing the electrical properties of a semiconductor wafer. A method of manufacturing a semiconductor device in which a highly reliable connection between a semiconductor wafer and an external electrode can be realized by a copper wire due to the influence of the unevenness on the surface of the electrode pad due to the probe during inspection.

A method of manufacturing a semiconductor device according to an embodiment includes the steps of: (a) embedding a soft metal having a hardness lower than that of copper into a recess of a semiconductor wafer including an electrode pad having a surface formed by contact of a probe; And the (b) bonding the copper wire to the surface of the electrode pad in which the soft metal is embedded.

10‧‧‧Semiconductor wafer

12‧‧‧Substrate

14‧‧‧Electrical pads

16‧‧‧ Probe traces

18‧‧‧Aluminum wire

20‧‧‧ copper wire

1(a) to 1(c) are schematic cross-sectional views showing the steps of manufacturing a semiconductor device according to an embodiment.

Fig. 2A is a schematic plan view of the electrode pad shown in Fig. 1(a).

Fig. 2B is a schematic plan view of the electrode pad shown in Fig. 1(b).

Fig. 3 is a photograph taken by an optical microscope of a probe trace formed on the surface of an electrode pad.

Fig. 4 is a photograph taken of a probe trace formed on the surface of an electrode pad by a 3D microscope.

Fig. 5 is a graph showing the relationship between the opening area of the probe trace and the bonding strength of the copper wire when the copper wire is bonded to the electrode pad by the method of the comparative example.

Fig. 6 is a graph showing the relationship between the difference in height of the unevenness of the probe trace and the bonding strength of the copper wire when the copper wire is bonded to the electrode pad by the method of the comparative example.

Hereinafter, embodiments will be described with reference to the drawings. Furthermore, the drawings are for illustration only and the invention is not limited by the drawings. In the following description, components having the same or substantially the same functions and configurations are denoted by the same reference numerals, and the description thereof will not be repeated.

1, 2A and 2B are views for explaining a method of manufacturing a semiconductor device according to an embodiment, and Fig. 1 is a schematic cross-sectional view showing a manufacturing step in accordance with a step sequence, and Fig. 2A corresponds to Fig. 1(a). A schematic plan view, and Fig. 2B is a schematic plan view corresponding to Fig. 1(b). Each of these figures only shows the electrode pads formed on the semiconductor wafer and its vicinity.

In the present embodiment, as shown in FIG. 1(a), first, the semiconductor wafer 10 is prepared. The semiconductor wafer 10 is judged to be a good product by the following steps, that is, a step of forming a circuit or various semiconductor elements and circuits on a substrate 12 using a semiconductor material such as germanium, sapphire or GaAs (gallium arsenide) (manufacturing step) And a step of checking the operation of the circuit and the electrical characteristics of the semiconductor element (die sorting step).

On the surface of the semiconductor wafer 10, an electrode pad 14 using an Al alloy such as Al or AlSi for electrically extracting the circuit to the outside is exposed. Since the electrode pad 14 is also used as an electrode in the grain sorting step, irregularities (hereinafter also referred to as probe traces) 16 which are generated by the probe contact at the time of inspection remain on the surface. Fig. 3 is a photograph showing an example of such a probe trace taken by an optical microscope, and it was observed that five contact marks of the probe remained on the surface of the electrode pad. Further, Fig. 4 is a photograph of a probe trace taken by a 3D microscope.

Then, the electrode pad 14 is connected to a bonding wire for electrically extracting a circuit formed on the semiconductor wafer 10 to the outside. Previously, in this step, the probe traces 16 remaining on the surface of the electrode pad 14 were not repaired, and the bonding wires of gold or copper were used for bonding. In this case, when a gold wire having a lower hardness is used as the bonding wire, the gold wire also sufficiently enters the large unevenness of the probe trace 16 to obtain a good bonding strength. In the case of a copper wire, since the hardness is high, it is difficult to obtain the bonding strength with respect to the electrode pad 14 as compared with the case of using a gold wire, and connection failure may occur. In particular, when the opening area of the probe trace (hereinafter, simply referred to as "area") is large and the height difference of the unevenness is large, the decrease in the joint strength is remarkable.

That is, FIG. 5 shows that in order to investigate the method of using a comparative example, a copper wire is bonded to an electrode. A graph showing the experimental results of the relationship between the opening area of the probe trace and the bonding strength (shear strength) of the copper wire in the case of the pad, the horizontal axis represents the probe trace area, and the vertical axis represents the joint strength (shear strength). ). Moreover, FIG. 6 shows the relationship between the height difference of the unevenness of the probe trace and the bonding strength (shear strength) of the copper wire when the copper wire is bonded to the electrode pad by the method of the comparative example. In the graph of the experimental results, the horizontal axis represents the height difference of the unevenness of the probe trace, and the vertical axis represents the joint strength (shear strength). Here, the method of the comparative example refers to a method of connecting by the bonding wires without repairing the probe traces 16 remaining on the surface of the electrode pad 14. The experiments were carried out using three types of probes, and the other conditions such as the outer diameter of the copper wire used for bonding or the bonding conditions were the same. Further, the probe trace area, the height difference of the probe traces, and the joint strength are all expressed as relative values. As is clear from Fig. 5 and Fig. 6, the larger the area of the probe trace, the larger the difference in the unevenness of the probe trace, and the lower the joint strength.

In addition, in recent years, with the increase in the size of semiconductor elements or the miniaturization of circuits, the size of electrode pads has been continuously reduced. In such a miniaturized electrode pad, the ratio of the probe trace area to the surface of the electrode pad is also increased, and the bonding by the copper wire becomes more difficult.

As described above, in the method of the comparative example, the bonding strength of the copper wire to the electrode pad may not be sufficiently obtained, and in recent years, the miniaturization of the electrode pad is progressing. Therefore, in the present embodiment, before the copper wire is connected to the electrode pad, as shown in FIG. 1(b), the aluminum wire 18 is used, and the concave portion is filled and the unevenness is flattened. (stitch bonding) to the probe trace 16. That is, the aluminum wire 18 is pressed against the probe trace 16 while being heated, and is buried in the concave portion. The schematic plan view shown in Fig. 2A shows the surface of the electrode pad 14 before the aluminum wire 18 is stitched to the electrode pad 14, and Fig. 2B shows the surface of the electrode pad 14 after the 18-pin bonding of the aluminum wire.

In this step, as shown in FIG. 2B, the aluminum wire 18 does not need to cover the entire probe trace 16 and, as shown in FIG. 1(b), does not need to be buried in the surface of the recess. As long as the copper will be as follows When the wire is wire bonded, the aluminum wire 18 is buried to such an extent that the desired joint strength can be obtained. As long as the required joint strength is obtained, it may be protruded from the surface of the recess as the case may be. Specifically, it is preferable to embed at least about 1/2 of the probe trace 16 and more preferably at least about 2/3. Further, it is preferably from the surface of the embedded aluminum wire 18 to the surface of the electrode pad 14 within about 100 nm.

From the viewpoint of obtaining a high bonding strength, it is preferable that the surface of the embedded aluminum wire 18 is flat, more preferably the surface is flat, and is buried to substantially the same height as the surface of the electrode pad 14, that is, The surface of the embedded aluminum is embedded in such a manner that the surface of the electrode pad 14 is substantially flush with the surface. The flatness of the embedded aluminum surface can be improved by adjusting the load applied to the aluminum wire 18 at the time of stitch bonding or heating conditions and the like. Further, by adjusting the outer diameter of the aluminum wire to be used, the amount of the aluminum wire 18 can be adjusted so that the surface of the aluminum and the surface of the electrode pad 14 are substantially flush with each other. When the aluminum wire 18 is stitch-bonded, not only the aluminum wire 18 is heated or a load is applied, but also ultrasonic waves can be applied. The flatness of the embedded aluminum surface can also be improved by adjusting the output of the ultrasonic wave.

Further, in the present embodiment, the aluminum is used for the embedding of the probe traces 16 by stitch bonding, but a method such as bump bonding of gold wires may be used. However, from the viewpoints of stability, productivity, cost, and the like of embedding, stitch bonding is preferred.

Further, in the present embodiment, aluminum is used as the material embedded in the probe trace 16. However, if it is a soft metal, that is, the hardness is lower than that of copper and can be easily deformed by heating or the like, it is buried in the probe trace. The metal of 16 is a metal which is less polluting and does not adversely affect the characteristics of the semiconductor wafer, and can be used without particular limitation. From the viewpoint of easiness of embedding or easiness of obtaining, it is preferable to use aluminum, and in the case where the electrode pad 14 contains an Al alloy such as Al or AlSi, aluminum is particularly preferable. When used in this specification, the term "aluminum" includes not only Al but also an alloy mainly composed of Al.

Thereafter, as shown in FIG. 1(c), the copper wire 20 is joined to the surface of the electrode pad 14 in which the aluminum is buried in the probe trace 16 by ball bonding. That is, on the first joint side, by short circuit A ball is formed on the front end of the copper wire, and the ball is heated and applied with a load to be pressed and attached to the electrode pad 14. At this time, ultrasonic waves can also be applied to the electrode pads 14.

In the present embodiment, since aluminum is embedded in the probe trace 16 on the surface of the electrode pad 14, even if the copper wire 20 having a high hardness is not increased in load or increased in application. The output of the ultrasonic wave to the electrode pad 14 can also be joined with a high bonding strength, thereby suppressing occurrence of connection failure. Further, since it is not necessary to increase the load at the time of bonding or increase the output of the ultrasonic wave, peeling of the electrode pad 14 and breakage of the substrate can be prevented, and the reliability of the connection between the copper wire and the electrode pad can be improved.

Further, when the thickness of the semiconductor wafer is as small as, for example, about 40 to 60 μm, peeling of the electrode pad or substrate breakage as described above is particularly likely to occur. In the present embodiment, even in the case of such a thin semiconductor wafer, it is possible to perform connection with high reliability, which is less likely to cause peeling of the electrode pad 14, or breakage of the substrate.

The embodiments of the present invention have been described above, but the embodiments are presented as examples and are not intended to limit the scope of the invention. The present invention can be implemented in various other forms, and various omissions, substitutions and changes can be made without departing from the scope of the invention. The invention and its modifications are intended to be included within the scope and spirit of the invention and are intended to be

10‧‧‧Semiconductor wafer

12‧‧‧Substrate

14‧‧‧Electrical pads

16‧‧‧ Probe traces

18‧‧‧Aluminum wire

Claims (5)

A method of fabricating a semiconductor device, comprising the steps of: (a) embedding a soft metal having a hardness lower than that of copper into a recess of a semiconductor wafer including an electrode pad having a contact with a probe on a surface thereof And forming the recessed portion to include aluminum; and (b) bonding the copper wire to the surface of the electrode pad in which the soft metal is embedded; and in the step (a), embedding the soft metal into the recessed portion Performing a stitch bonding including a line of the soft metal, embedding the soft metal in at least 1/2 of an opening area of the concave portion, and embedding the soft metal surface embedded in the concave portion with the surface of the electrode pad Near the same plane; the soft metal is aluminum. A method of fabricating a semiconductor device, comprising the steps of: (a) embedding a soft metal having a hardness lower than that of copper into a recess of a semiconductor wafer including an electrode pad having a contact with a probe on a surface thereof And forming the recessed portion to include aluminum; and (b) bonding the copper wire to the surface of the electrode pad in which the soft metal is embedded; and the soft metal is aluminum. The method of manufacturing a semiconductor device according to claim 2, wherein in the step (a), the embedding of the soft metal into the concave portion is performed by stitch bonding including a line of the soft metal. The method of manufacturing a semiconductor device according to claim 2 or 3, wherein in the step (a), the soft metal is buried in at least 1/2 of an opening area of the concave portion. The method of manufacturing a semiconductor device according to claim 2 or 3, wherein in the above step (a) In the middle, the surface of the soft metal embedded in the concave portion is close to the same plane as the surface of the electrode pad.