KR101138861B1 - Bonding structure for light emitting device and method of bonding using the same - Google Patents

Abstract

A bonding structure of a light emitting device and a bonding method using the same are disclosed. Here, the present invention provides a bonding structure comprising a sub-mount, a solder bump formed on the sub-mount and an anti-oxidation film formed on the bonding surface of the solder bump, forming a light emitting element, and the light emission Forming a solder bump on the sub-mount to which the device is to be bonded, forming an anti-oxidation film on the bonding surface of the solder bump, and bonding the light emitting device to a bonding surface of the solder bump on which the anti-oxidation film is formed. It provides a bonding method of a light emitting device comprising the step.

Description

Bonding structure for light emitting device and method of bonding using the same}

1 is a cross-sectional view illustrating a case in which a light emitting device is bonded to a sub-mount using flip chip bonding.

FIG. 2 is a photograph showing that the bonding surface of the solder bumps may be oxidized in the bonding of the sub-mount and the light emitting device illustrated in FIG. 1.

3 is a graph showing the amount of heat absorbed by the solder bumps in the process of bonding the light emitting device to the sub-mount as shown in FIG.

4 is a cross-sectional view showing a light emitting device bonding structure according to an embodiment of the present invention, formed in a sub-mount before bonding.

FIG. 5 is a plan view of the light emitting device bonding structure shown in FIG. 4 in a 5-5 'direction.

6 is a cross-sectional view after bonding the light emitting element to the sub-mount via the bonding structure shown in FIG. 4.

FIG. 7 is a photograph showing a bonding surface state of the light emitting device bonding structure in the process of bonding the light emitting device to the sub-mount via the bonding structure shown in FIG. 4.

8 is a graph showing the amount of heat absorbed by the bonding structure in the process of bonding the light emitting device to the sub-mount via the bonding structure shown in FIG.

* Description of the symbols for the main parts of the drawings *

50: submount 52a, 52b: first and second pad layers

54a and 54b: first and second blocking films 56a and 56b: first and second solder bumps

58a, 58b: first and second antioxidant films 60: light emitting elements

62a and 62b: third and fourth pad layers 64a and 64b: first and second conductive films

66: step S1: stack

R1, R2: first and second regions of the light emitting element

The present invention relates to a bonding structure for bonding two structures and a bonding method using the same, and more particularly, to a bonding structure used to bond a light emitting device to a sub-mount and a light emitting device bonding method using the same.

Wire bonding is mainly used to bond light emitting devices such as laser diodes (LDs) and light emitting diodes (LEDs) to a submount. The wire bonding is also a means for applying an operating voltage to the light emitting device, but is also used as a means for removing heat generated in the light emitting device during operation of the light emitting device.

As the degree of integration of the chip including the light emitting device increases, the length of the wire connecting the light emitting device and the sub-mount is felt to be relatively longer than in the past.                         

Since the wire resistance of the wire is proportional to its length, the wire resistance also increases as its length increases. Therefore, when the current is supplied to the light emitting device through a wire, the operating voltage is increased and the heat removal efficiency or heat dissipation efficiency for the light emitting device is lowered.

Accordingly, the need for a new bonding structure that can replace wire bonding has emerged, and interest in flip chip bonding, which directly connects the light emitting device and the sub-mount through the solder bumps, has increased.

1 shows a conventional technology in which a light emitting device is bonded to a sub-mount using such flip chip bonding.

Referring to FIG. 1, two pad layers 12a and 12b are formed on the submount 10. The two pad layers 12a and 12b are spaced apart. A first platinum Pt blocking film 14a is formed on the left pad layer 12a, and a second platinum blocking film 14b is formed on the right pad layer 12b. The first and second platinum blocking layers 14a and 14b may include elements Sn included in the first and second AuSn solder bumps 16a and 16b formed on the first and second platinum blocking layers 14a and 14b, respectively. ) Is prevented from spreading outside.

In FIG. 1, reference numeral S denotes a laminate bonded to the submount via the first and second AuSn solder bumps 16a and 16b. The stack S may include a light emitting device 18, a pad layer 20a facing the first AuSn solder bump 16a, a pad layer 20b facing the second AuSn solder bump 16b, and a pad layer 20a. ) And the second conductive film 22b formed on the surface facing the first AuSn solder bump 16a and the second AuSn solder bump 16b on the pad layer 20b. It is composed of The first and second conductive films 22a and 22b are bonded to the first and first AuSn solder bumps 16a and 16b, respectively. The light emitting device 18 may be divided into a first region R1 having an n-type electrode (not shown) and a second region R2 having a p-type electrode (not shown). The n-type electrode is formed on a surface facing the submount 10 of the first region R1, and the p-type electrode is formed on a surface facing the submount 10 of the second region R2. have. The pad layer 20a facing the first AuSn solder bump 16a is provided to be connected to the n-type electrode. The pad layer 20b facing the second AuSn solder bump 16b is provided to be connected to the p-type electrode.

Meanwhile, bonding of the sub-mount 10 and the light emitting device 18 is performed while the first and second AuSn solder bumps 16a and 16b are melted at about 280 ° C. In this process, the first and second AuSn solder bumps are melted. An oxide layer may be formed on a portion of the bonding surface of 16a and 16b.

Figure 2 is a photograph showing the results of the experiment carried out by the present inventors to show this possibility, reference numeral 30 represents AuSn solder bumps formed on the sub-mount 10, 42 is bonded to the AuSn solder bumps 30 A laminate such as a light emitting device is shown. In the experiment, in order to show that the bonding surface of the AuSn solder bumper 30 may be oxidized in the bonding process, the AuSn solder bumps 30 were formed only on a portion of the bonding surface.

Referring to FIG. 2, it can be seen that the exposed bonding surface of the AuSn solder bump 30 is oxidized in the bonding process to form pits 40 (black portions) on the surface thereof. These results suggest that the bonding surface in contact with the stack 42 of AuSn solder bumps 30 may also be oxidized.                         

 When the bonding surface of the AuSn solder bump 30 is oxidized, an oxide layer is present on the bonding surface. When the oxide layer is present on the bonding surface, even though the temperature becomes the melting point of the AuSn solder bumps 30 during the bonding process, the portion where the oxide layer is present on the bonding surface of the AuSn solder bumps 30 does not melt. Accordingly, the amount of heat absorbed by the AuSn solder bumps 30 at the melting point of the AuSn solder bumps 30 is much lower than when no oxide layer is present on the bonding surface of the AuSn solder bumps 30. Therefore, the presence or absence of an oxide layer on the bonding surface of the AuSn solder bumps 30 may be determined by measuring the amount of heat absorbed by the AuSn solder bumps 30 during the bonding process.

FIG. 3 shows a first graph G1 illustrating a change in absorbed heat amount of the AuSn solder bumps 30 with temperature during bonding of the sub-mount 10 and the stack 42 in the above experiment.

Referring to the first graph G1, it can be seen that the first peak P1 appears at the melting point (about 280.2 ° C.) of the AuSn solder bumps 30. The first peak P1 appears due to the temporary increase in the amount of heat absorbed at the moment when the AuSn solder bumps 30 are melted. However, the height of the first peak P1 is not so high, as described above. The presence of this layer of material, such as an oxide layer, on the bonding surface of means that there is not enough heat absorbed for melting in the AuSn solder bumps 30 at the melting point of the AuSn solder bumps 30.

Through the test results, an oxide layer may also be formed on the bonding surfaces of the first and second AuSn solder bumps 16a and 16b illustrated in FIG. 1, in which case the following problems may occur.                         

That is, since the first and second AuSn solder bumps 16a and 16b are current and heat transfer paths, the bonding surfaces of the first and second AuSn solder bumps 16a and 16b are preferably homogeneous. However, when an oxide layer is present on the bonding surfaces of the first and second AuSn solder bumps 16a and 16b, the oxide layer becomes an obstacle that blocks current and heat transfer, making it difficult to uniformly supply current to the light emitting device. It becomes difficult to quickly remove heat generated in the device. As a result, the light emitted from the light emitting device is cut off or its intensity is not uniform, and the operating voltage is also increased.

The technical problem to be achieved by the present invention is to improve the above-described problems of the prior art, it is possible to implement a light emitting device capable of emitting light without interruption and uniform, and to emit light that can quickly remove heat generated in the light emitting device An object bonding structure is provided.

Another object of the present invention is to provide a bonding method of a light emitting device using the bonding structure.

In order to achieve the above technical problem, the present invention provides a bonding structure comprising a sub-mount, a solder bump formed on the sub-mount and an antioxidant film formed on the bonding surface of the solder bump.

The anti-oxidation film may extend to the exposed front surface of the solder bumps.

In order to achieve the above object, the present invention provides a first step of forming a light emitting device, a second step of forming a solder bump on a sub-mount to which the light emitting device is to be bonded, and a surface to be connected to the light emitting device of the solder bump ( Or a fourth step of forming an anti-oxidation film on the bonding surface) and a fourth step of contacting and bonding the light emitting element to the bonding surface of the solder bump on which the anti-oxidation film is formed. To provide.

The anti-oxidation film may also be formed around the solder bumps.

The anti-oxidation film may be formed of a material film including a noble metal film, a pseudo noble metal film, or a conductive polymer material.

By using the present invention, since the current can be supplied to the light emitting element uniformly, the light emitted from the light emitting element can be prevented from being interrupted, and the intensity of the emitted light can be made uniform. It is also possible to quickly remove heat from the light emitting element.

Hereinafter, a light emitting device bonding structure and a bonding method using the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 4, first and second pad layers 52a and 52b are formed on the submount 50. The first and second pad layers 52a and 52b are spaced apart by a given interval. The first and second pad layers 52a and 52b may be formed of a single layer or multiple layers as the same material layer. When the first and second pad layers 52a and 52b are the same material layer, each of the first and third pad layers 52a and 52b may include first to third metal layers. The first to third metal films are a titanium (Ti) film, a platinum (Pt) film, and a gold (Au) film, respectively. First and second blocking layers 54a and 54b are present on the first and second pad layers 52a and 52b, respectively. The first and second blocking films 54a and 54b prevent the components of the material layers stacked above and below the first and second blocking films 54a and 54b from mutually diffusing. The first and second blocking films 54a and 54b may be, for example, platinum films. First and second solder bumps 56a and 56b are provided on the first and second blocking films 54a and 54b, respectively. The first and second solder bumps 56a and 56b may be AuSn solder bumps, or may be solder bumps made of different materials. Bonding surfaces of the first and second solder bumps 56a and 56b are covered with first and second antioxidant films 58a and 58b, respectively. As shown in FIG. 6, the first and second anti-oxidation layers 58a and 58b are formed by bonding the first and second solders in the process of bonding the stack S1 including the sub-mount 50 and the light emitting device 60. The formation of this material layer, for example, an oxide layer, on the bonding surfaces of the bumps 56a and 56b is prevented. Even if the first and second antioxidant films 58a and 58b exist only in the entire bonding surfaces of the first and second solder bumps 56a and 56b, the desired purpose can be achieved. However, as shown in FIGS. 4 and 5, the first and second anti-oxidation layers 58a and 58b may be provided to cover the exposed front surfaces of the first and second solder bumps 56a and 56b. The first and second antioxidant films 58a and 58b may be a material film having low reactivity with oxygen, for example, a noble metal film such as gold or platinum, a similar noble metal film, or a conductive polymer film.

Meanwhile, in the bonding process, portions formed on the bonding surfaces of the first and second antioxidant films 58a and 58b are dissolved in the first and second solder bumps 56a and 56b. Therefore, after the bonding process is completed, the first and second antioxidant films 58a and 58b do not exist on the bonding surfaces of the first and second solder bumps 56a and 56b. Although the portions formed on the bonding surfaces of the first and second antioxidant films 58a and 58b in the bonding process are dissolved in the first and second solder bumps 56a and 56b, the first and second solder bumps 56a and 56b may be used. It is not good to deteriorate the characteristic of). Therefore, the thicknesses of the first and second antioxidant films 58a and 58b are preferably determined in consideration of the state diagrams of the materials constituting the first and second solder bumps 56a and 56b. For example, when the first and second antioxidant films 58a and 58b are gold films, their thickness may be 300 kPa or less.

Subsequently, referring to FIG. 5, which shows a plane in which FIG. 4 is cut in the 5-5 'direction, the first and second antioxidant films 58a and 58b are formed around the first and second solder bumps 56a and 56b. It can be seen that also formed in. The first and second solder bumps 56a and 56b may have other shapes besides quadrangles, for example, circular shapes.

FIG. 6 is a cross-sectional view of the result of bonding the laminate S1 including the light emitting device 60 to the sub-mount 50 having the first and second solder bumps 56a and 56b formed thereon.

Referring to FIG. 6, it can be seen that the light emitting device 60 is divided into first and second regions R1 and R2. A step 66 exists between the first and second regions R1 and R2. The step 66 is as the second region R2 protrudes.

An n-type electrode (not shown) exists on a surface of the first region R1 facing the sub-mount 50, and is connected to the n-type electrode or provided to cover the n-type electrode. This is present sequentially. The fourth pad layer 62b includes a p-type electrode (not shown) on a surface of the second region R2 facing the sub-mount 50 and is connected to or covers the p-type electrode. ) Are sequentially present. In this case, the p-type electrode may be provided to be connected to the p-type compound semiconductor layer provided in the form of a ridge. The third and fourth pad layers 62a and 62b may be single layers or multiple layers, and may include the same material layer. For example, when the third and fourth pad layers 62a and 62b are formed of the same material layer, the third and fourth pad layers 62a and 62b may be sequentially stacked with the fourth to sixth metal layers. Can include them. The fourth to sixth metal films may be a titanium film, a platinum film, and a gold film, respectively. The first and second conductive films 64a and 64b are stacked on the surfaces of the third and fourth pad layers 62a and 62b facing the submount 50, respectively. The first and second conductive films 64a and 64b may be gold films.

As described above, the inventors conducted experiments for verifying the effect of providing the first and second antioxidant films 58a and 58b on the respective bonding surfaces of the first and second solder bumps 56a and 56b.

In the above experiment, as shown in FIG. 7, the solder bumps 80 were formed on the sub-mount 50, and then the above-described antioxidant film was formed on the solder bumps 80 by electroplating or electroplating. The structure 100 corresponding to the stack S1 of FIG. 6 was formed on a portion of the antioxidant film, and the rest was exposed as it is to observe the change of the antioxidant film during the bonding process. Subsequently, the resultant in which the structure 100 was formed was heated at a temperature at which the solder bumps 80 were melted for a predetermined time.

In FIG. 7, reference numeral 90 shows a portion of the solder bump 80 (hereinafter, referred to as a first portion) in which the exposed portion of the antioxidant film is covered after the bonding process is completed. Comparing FIG. 2 with the first portion 90 of the solder bump 80 in which the exposed portion of the antioxidant film is covered, it can be seen that the antioxidant film is completely melted in the first portion 90, and the surface is flawless. You can see that it is smooth. From this fact, it can be seen that the shading is bonded smoothly with the structure 100 of the solder bump 80.

In other words, it can be seen that the bonding surface of the solder bump 80 is not oxidized in the bonding process, and as a result, this material layer such as an oxide layer is not formed.

As a result, when the light emitting device 60 is bonded to the sub-mount 50 via the bonding structure shown in FIG. 4 as shown in FIG. 6, the first and second solder bumps 56a and 56b are bonded to each other. It is expected that the amount of heat absorbed will increase rapidly at the time of melting.

Referring to FIG. 8, it can be seen that this prediction is valid.

Specifically, FIG. 8 is a measure of the heat of absorption of the solder bumps 80 during the bonding process of the experiment, and reference numeral G2 is a second graph showing the change of heat of absorption according to the bonding temperature.

Referring to the second graph G2, the second peak P2 appears around 280 ° C., and the height of the second peak P2 is much higher than that of the conventional first peak (see FIG. 3). The fact that the height of the second peak P2 is high means that the amount of heat absorbed by the solder bumps 80 rapidly increases as the temperature of the solder bumps 80 reaches the melting point in the bonding process. Thus the prediction is justified.

In addition, one of the conditions for the rapid increase in the heat of absorption at the melting point of the solder bump 80 is that the bonding surface of the solder bump 80 is clean, the material layer does not exist on the bonding surface, the second graph ( The second peak P2 appearing in G2) means that the bonding structure of the present invention satisfies the above condition.                     

Next, a method of bonding a light emitting device such as an LED or an LD to a sub-mount using the bonding structure will be briefly described.

First, a light emitting element for bonding is formed. 6, third and fourth pad layers 62a and 62b are formed on the surface where the n-type electrode and the p-type electrode are formed, respectively, as shown in FIG. First and second conductive films 64a and 64b are formed on the third and fourth pad layers 62a and 62b, respectively. The descriptions of the third and fourth pad layers 62a and 62b and the first and second conductive films 64a and 64b are omitted herein.

As such, after forming the light emitting device and forming the members necessary for bonding to the light emitting device, the first and second pad layers 52a and 52b and the first pad layer are formed on the sub-mount 50 as shown in FIG. 4. And second blocking films 54a and 54b are sequentially formed. The first and second solder bumps 56a and 56b are formed on the first and second blocking films 54a and 54b using a predetermined method, for example, an electroplating method. Subsequently, first and second anti-oxidation films 58a and 58b are formed on the bonding surfaces of the first and second solder bumps 56a and 56b to be bonded to the light emitting devices to have a predetermined thickness using an electroplating method or an electroplating method. . In this case, the first and second antioxidant films 58a and 58b may be formed on the exposed front surfaces of the first and second solder bumps 56a and 56b as well as the respective bonding surfaces. The first and second antioxidant films 58a and 58b may be formed of a material film having low reactivity with oxygen, such as a precious metal film such as gold or platinum, a similar precious metal film, or a film made of a conductive polymer material. The first and second antioxidant films 58a and 58b formed on the bonding surfaces of the first and second solder bumps 56a and 56b are dissolved into the first and second solder bumps 56a and 56b during the bonding process. After the bonding process is completed, it is preferably not present on the bonding surface. Therefore, it is preferable to form the first and second antioxidant films 58a and 58b to an appropriate thickness in consideration of this, and the thickness may vary depending on the material used.

For example, when the first and second antioxidant films 58a and 58b are formed of a noble metal such as gold or platinum, the thicknesses of the first and second antioxidant films 58a and 58b formed on the bonding surface are the bonding temperature. In order to be completely melted with the solder bumps in the Au-Sn state, it is preferable to form the 300 Å or less with reference to the state diagram.

As described above, after the first and second antioxidant films 58a and 58b are formed, the first conductive film 64a formed on the n-type electrode side of the light emitting element 60 and the second conductive film formed on the p-type electrode side The stack S1 and the sub-mount 50 including the light emitting device 60 are aligned so that the film 64b faces the first and second solder bumps 56a and 56b, respectively. When the stack S1 and the sub-mount 50 are brought into contact with each other in this manner, and the predetermined temperature, for example, the first and second solder bumps 56a and 56b is made of AuSn, the predetermined temperature is about 280 ° C. The contacted product is heated for a period of time. In this process, the first and second antioxidant films 58a and 58b formed on the bonding surfaces of the first and second solder bumps 56a and 56b are dissolved in the first and second solder bumps 56a and 56b.

As such, since the anti-oxidation film is present on the bonding surfaces of the first and second solder bumps 956a and 56b during the bonding process, the bonding surface is not oxidized.

While many details are set forth in the foregoing description, they should be construed as illustrative of preferred embodiments, rather than to limit the scope of the invention. For example, a person having ordinary knowledge in the technical field to which the present invention pertains can make the configuration of the first to fourth pad layers different, and bonding the light emitting device by forming an oxide film on the bonding surface and bonding it. In addition, it can be applied to other bonding processes. In addition, the anti-oxidation film formed around the solder bumps after completion of the bonding may be removed. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the technical spirit described in the claims.

As described above, the light emitting device bonding structure of the present invention is covered with a thin antioxidant film, at least the bonding surface of which is dissolved in the solder bumps during the bonding process. Therefore, in the bonding process, this material layer, such as an oxide layer, which poses a problem in the prior art, is not formed on the bonding surface. Accordingly, when the light emitting device is mounted on the sub-mount using the bonding structure of the present invention, the bonding structure, that is, the entire surface of the bonding surface of the solder bumps may be in contact with the light emitting device, so that current supply through the solder bumps is made uniform. Can be. Therefore, the light emitted from the light emitting device can be prevented from being cut off, and the intensity of the emitted light can be kept uniform. In addition, heat can be quickly removed from the light emitting device.

Claims (10)

Submount; A solder bump formed on the sub mount; And An anti-oxidation film formed on the bonding surface of the solder bumps, And a pad layer and a blocking film are sequentially stacked on the sub-mount, the solder bumps are formed on the blocking film, and the pad layer and the blocking film are in direct contact with each other. The bonding structure of claim 1, wherein the anti-oxidation film extends to an exposed front surface of the solder bumps. The bonding structure according to claim 1 or 2, wherein the anti-oxidation film is a film made of a noble metal film, a pseudo noble metal film or a conductive polymer material. The bonding structure according to claim 1, wherein the thickness of the antioxidant film is 300 kPa or less. Forming a light emitting device; Forming a solder bump on a sub-mount to which the light emitting device is to be bonded; Forming an anti-oxidation film on a surface (hereinafter, a bonding surface) to be connected to the light emitting device of the solder bumps; And And bonding the light emitting device to a bonding surface of the solder bump on which the anti-oxidation film is formed, and bonding the light emitting device. The solder bumps are formed on the sub-mount in order to sequentially form a pad layer and a blocking film, and then formed on the blocking film, the pad layer and the blocking film is characterized in that the direct contact between the light emitting device. 6. The method of bonding a light emitting element according to claim 5, wherein the anti-oxidation film is also formed around the solder bumps. 6. The method of claim 5, wherein the anti-oxidation film is formed of a material film containing a noble metal film, a pseudo noble metal film, or a conductive polymer material. 6. The method of claim 5, wherein the anti-oxidation film is formed to a thickness of 300 kPa or less. delete 6. The method of bonding a light emitting element according to claim 5, wherein the anti-oxidation film is formed by an electroplating method or an electroplating method.

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