KR20070094047A - Led having vertical structure - Google Patents

Abstract

A vertical-type light emitting device is provided to minimize crack to be generated in a GaN thin film by absorbing shock and stress generated in a process of separating a substrate through a shock buffer layer. A first electrode(30) is positioned on one side of a semiconductor layer(20), and a second electrode(70) is positioned on the other side of the semiconductor layer. A shock buffer layer(50) is attached to the first electrode, and a metal support(60) is positioned on the shock buffer layer. The shock buffer layer has flexibility higher than that the metal used in the metal support, and is made of at least one selected from a group consisting of In, Sn, Ag, Au, Pt, and Al.

Description

Vertical light emitting device {LED having vertical structure}

1 is a schematic diagram showing a state of separating a substrate in a conventional vertical light emitting device structure.

2 is a photograph showing a surface separated from a substrate in a conventional vertical light emitting device structure.

3 is a cross-sectional view illustrating a state in which a vertical light emitting device is separated by bonding a conventional semiconductor wafer.

4 is a cross-sectional view illustrating a state in which a vertical light emitting device is separated by bonding a conventional metal support plate.

5 is a cross-sectional view showing the manufacturing process of the first embodiment of the vertical light-emitting device of the present invention.

6 is a cross-sectional view showing a first embodiment of the vertical light emitting device of the present invention.

7 is a cross-sectional view showing the manufacturing process of the second embodiment of the vertical light-emitting device of the present invention.

8 is a cross-sectional view showing a second embodiment of the vertical light-emitting device of the present invention.

9 is a cross-sectional view showing the manufacturing process of the third embodiment of the vertical light-emitting device of the present invention.

10 is a cross-sectional view showing a third embodiment of the vertical light-emitting device of the present invention.

11 is a cross-sectional view showing the manufacturing process of the fourth embodiment of the vertical light-emitting device of the present invention.

12 is a cross-sectional view showing a fourth embodiment of the vertical light-emitting device of the present invention.

<Brief description of the main parts of the drawing>

10: substrate 20: semiconductor layer

30: first electrode 40: bonding metal

50: shock absorbing layer 60: metal support

70 second electrode 80 passivation layer

The present invention relates to a vertical light emitting device, and more particularly, to a vertical light emitting device having a structure that can mitigate the impact generated in the process of separating the substrate.

Light Emitting Diodes (LEDs) are well-known semiconductor devices that convert current into light.In 1962, red LEDs using GaAsP compound semiconductors were commercialized. It has been used as a light source for display images of electronic devices.

The wavelength of light emitted by such LEDs depends on the semiconductor material used to make the LEDs. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material, which represents the energy difference between valence band electrons and conduction band electrons.

Gallium Nitride (GaN) semiconductors have received a lot of attention. One reason for this is that GaN can be combined with other elements (indium (In), aluminum (Al), etc.) to produce semiconductor layers that emit green, blue and white light.

In this way, the emission wavelength can be adjusted to match the material's characteristics to specific device characteristics. For example, GaN can be used to create white LEDs that can replace incandescent and blue LEDs that are beneficial for optical recording.

In addition, in the case of the conventional green LED, it was initially implemented as GaP, which was inefficient as an indirect transition type material, and thus practical pure green light emission could not be obtained. However, as InGaN thin film growth succeeded, high brightness green LED could be realized. It became.

Because of these and other benefits, the GaN series LED market is growing rapidly. Therefore, since commercial introduction in 1994, GaN-based optoelectronic device technology has rapidly developed.

Since the efficiency of GaN light emitting diodes outperformed the efficiency of incandescent lamps and is now comparable to that of fluorescent lamps, the GaN LED market is expected to continue to grow rapidly.

Despite the rapid development of GaN device technology as described above, the manufacturing of GaN device has a large cost disadvantage. This is related to the difficulty of growing GaN epitaxial layers and subsequently cutting the finished GaN-based devices.

GaN-based devices are typically fabricated on sapphire (Al ₂ O ₃ ) substrates. This is because sapphire wafers are commercially available in sizes suitable for mass production of GaN-based devices, support relatively high quality GaN thin film growth, and have a wide range of temperature processing capabilities.

In addition, sapphire is chemically and thermally stable, has a high melting point to enable high temperature manufacturing processes, high binding energy (122.4 Kcal / mole) and high dielectric constant. Chemically, sapphire is crystalline aluminum oxide (Al ₂ O ₃ ).

On the other hand, since the sapphire is an insulator, the shape of the LED element available when using the used sapphire substrate (or other insulator substrate) is, in fact, limited to a lateral or vertical structure.

In this horizontal structure, the metal contacts used to inject current into the LED are all located on the top surface (or on the same side of the substrate). In the vertical structure, on the other hand, one metal contact is on the top face and the other contact is located on the bottom face after the sapphire (insulation) substrate is removed.

In addition, a flip chip bonding method in which the chip is attached upside down to a submount such as a silicon wafer or a ceramic substrate having excellent thermal conductivity after the manufacture of the LED chip is also widely used.

However, the above-described horizontal structure or flip chip method is a problem in heat dissipation efficiency because the thermal conductivity of the sapphire substrate is about 27 W / mK and the heat resistance is very large. The flip chip method is a photolithography process of many stages. There was a disadvantage in that the manufacturing process was complicated.

In connection with these problems, the vertical structure of the LED for removing the sapphire substrate has attracted much attention.

In order to solve the above problems of the sapphire substrate in the vertical LED, the sapphire substrate is removed by using a laser lift off (LLO) method to manufacture the device.

In applying the laser lift-off method, the front surface of the sapphire substrate cannot be removed at once because of the size and uniformity of the laser beam. .

In this case, a stress caused by a laser is applied to the GaN thin film when the laser is incident. As shown in FIG. 1, in order to separate the sapphire substrate 1 and the GaN thin film 2, a laser beam having a high energy density is used. It should be used and decomposed into metal Ga and gaseous nitrogen (N ₂ ) by this laser beam.

Since the decomposed nitrogen gas has a great expansion force, not only the GaN thin film 2 but also the support layer and each metal layer for device fabrication have a significant impact, which primarily degrades the adhesion and further impairs the electrical properties.

This result can be observed in FIG. 2, where the GaN thin film after the LLO process may appear to have ripples appearing to have curvature at the edge portion. In addition, during the LLO process, it is possible to observe a lot of the poor adhesion of these thin films.

In addition, this method causes a problem that the back surface of the GaN layer constituting the LED is damaged at overlapping beams, and cracks may be propagated to other parts of the GaN layer, which may occur at some poor quality areas. Done.

In order to prevent such a phenomenon, each of the elements of the GaN layer is etched to separate the elements, and then, as shown in FIG. 3, the semiconductor wafer 5 such as Si, GaAs, or the like is bonded, or Cu, After the metal support 7 is made by plating using a metal such as Au or Ni, a method of separating the sapphire substrate 1 is used.

That is, the characteristic feature of the method of FIG. 3 is a bonding material 4 in which the GaN thin film 2 formed on the substrate 1 is bonded to the electrode 3 with a wafer 5 having a significant difference between the GaN material and the thermal expansion coefficient. As a result of bonding, a large number of voids, which are defects on the bonding interface, can be observed at the same time as the wafer 5 is largely bent after bonding.

At this time, after bonding, air may remain in the empty space of each device and the trench between the devices, and this air is expanded due to the strong thermal energy of the laser, thereby surrounding the GaN thin film 2. This can cause cracks in the product.

On the other hand, as shown in Figure 4, the support substrate manufacturing form by the plating using the metal support 7, such as Cu, Au, Ni, etc., since it does not apply heat compared to the bonding process as shown in Figure 3 has a thermal stability and after the metal support ( The degree of warpage of 7) is also significantly less than that of bonding.

However, even in this plating process, the contact between the GaN thin film 2, the electrode 3, and the bonding metal 6 due to the stress caused by the laser deteriorates, and the metal layer used for fabricating the device using the GaN layer is deteriorated. It also adversely affects the electrical properties of (3, 6), and causes a problem that the electrical properties of the GaN thin film 2 with the ohmic metal, which is an electrical electrode material, deteriorate.

For the above reasons, the necessity of minimizing the impact of the laser when the substrate is separated using the laser is emerging.

The technical problem to be achieved by the present invention is to reduce the impact generated in the process of separating the substrate by performing a laser lift off process to minimize the cracks that may occur in the GaN thin film to secure the stability of the device, and to improve the ohmic characteristics of the electrode It is to provide a vertical light emitting device that can be maintained.

In order to achieve the above technical problem, the present invention, a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; An impact mitigating layer attached to the first electrode; It is preferably configured to include a metal support attached to the impact mitigating layer.

The shock absorbing layer is a metal having a higher ductility than the metal used as the metal support, and is preferably formed using at least one of In, Sn, Ag, Au, Pt, and Al.

A coupling metal may be formed between the first electrode and the shock alleviation layer or between the impact alleviation layer and the metal support to facilitate coupling between metals.

As another aspect for achieving the above technical problem, the present invention, a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; An impact mitigating layer attached to the first electrode; It is preferably configured to include a metal support attached to the impact mitigating layer.

In addition, as another aspect for achieving the above technical problem, a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; An impact mitigating layer attached to the first electrode; A bonding metal covering the impact buffer layer and the passivation layer; It is preferable to include a metal support portion for supporting the plurality of semiconductor layers in a structure covering the bonding metal.

As another aspect for achieving the object of the present invention, a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; A bonding metal covering the first electrode and the passivation layer; An impact mitigating layer disposed on the bonding metal so as to face the first electrode; It is preferable that the structure includes a metal support for supporting the plurality of semiconductor layers in a structure covering the impact alleviating layer and the bonding metal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 5, in manufacturing a vertical light emitting device, first, a plurality of semiconductor layers 20 are grown on a sapphire substrate 10.

The GaN semiconductor layer 20 is composed of an n-type GaN layer formed on the substrate 10, an active layer formed on the n-type GaN layer, and a p-type GaN layer formed on the active layer. A separate buffer layer may be formed between the layer and the substrate 10.

Contrary to the above, a p-type GaN layer may be formed on the substrate 10, and the active layer and the n-type GaN layer may be sequentially disposed thereon.

The active layer 22 may be a GaN-based single quantum well structure (SQW) or a multi quantum well structure (MQW), or a quantum structure such as a supper lattice (SL). It may be.

The quantum structure of the active layer 22 may be formed by combining various GaN-based materials, and for example, AlInGaN, InGaN, or the like may be used.

In this case, the semiconductor layer 20 is divided into unit device regions through etching.

This etching is called trench etching, and is performed until the substrate 10 is exposed.

Subsequently, as shown in FIG. 5, the first electrode 30 is formed on the GaN semiconductor layer 20, and a space that is easily removed by the etching is filled with a material such as an epoxy.

The first electrode 30 may include an ohmic electrode and a reflective electrode, and the ohmic electrode may be a transparent electrode, such as ruthenium / gold (Ru / Au) or nickel / gold (Ni / Au). Or any suitable material, such as indium-tin-oxide (ITO).

The first electrode 30 may be a p-type electrode, but may also be an n-type electrode according to the arrangement of the semiconductor layer 20.

The reflective electrode serves to reflect the light emitted from the semiconductor layer 20 to be effectively emitted, and is formed using silver (Ag) or aluminum (Al) and other materials having high reflectivity.

On the upper side of the first electrode 30, a bonded metal 40 for facilitating the coupling of the metal layers 50 and 60 to be stacked later is stacked.

The bonding metal 40 uses any one of titanium (Ti), platinum (Pt), gold (Au), nickel (Ni), aluminum (Al), or an alloy thereof.

Thereafter, an impact mitigating layer 50 is formed on the bonding metal 40 to mitigate the impact transmitted by the laser lift-off process to be performed later.

As shown in FIG. 7, the impact mitigating layer 50 may be formed in a different order from the bonding metal 40. That is, the impact mitigating layer 50 is formed on the first electrode 30, and the coupling metal 40 may be formed on the first electrode 30.

Referring back to the case of FIG. 5, a metal support 60 is formed on the impact mitigating layer 50 later. The metal support 60 is formed by a method such as electroplating using metals such as Cu, Ni, and Au.

The impact mitigating layer 50 is superior in ductility than the metal used as the metal support 60 to absorb the shock generated in the laser lift-off process, such impact affects the semiconductor layer 20, or the metal layer Prevent damage to the bonds between the liver.

The shock absorbing layer 50 may be made of a metal such as In, Sn, Ag, Au, Pt, Al, or an alloy thereof, and the thickness thereof may be about 1 to 10 μm.

As such, when the light emitting device structure is completed, the substrate 10 is separated through a laser lift-off process.

In this case, as described above, the impact caused by the thermal stress generated in the laser lift-off process, the inflow of nitrogen gas, or the like is absorbed by the impact mitigating layer 50.

Therefore, the impact is prevented from damaging the coupling between the first electrode 30, the bonding metal 40, the metal support 60, and also prevents the impact from being transmitted to the semiconductor layer 20.

As described above, when the substrate 10 is separated, the second electrode 70 is formed on the surface of the semiconductor layer 20 from which the substrate 10 is separated, and is separated into individual elements to form a state as shown in FIG. 6. .

The second electrode 70 may be an n-type electrode, but may also be a p-type electrode according to the arrangement of the semiconductor layer 20.

When such individual elements are packaged, the light emitting element is completed.

In the case of FIG. 7, the shock alleviation layer 50 is coupled to the first electrode 30 as described above. In this case, the impact alleviation layer 50 is the same as the first electrode 30. It can be formed in width.

Other processes are the same as those of FIG. 5, after which the substrate 10 is separated by a laser lift process, and the second electrode 70 is disposed on the surface of the semiconductor layer 20 from which the substrate 10 is separated. And the individual elements are completed as shown in FIG.

In FIG. 9, the semiconductor layer 20 is formed in the board | substrate 10, and after forming the 1st electrode 30, the passivation layer 80 is formed and the state which manufactures an element is shown.

The passivation layer 80 is formed using a dielectric, and protects the semiconductor layer 20, and serves to insulate the semiconductor layer 20 and the bonding metal 40 formed on the outside thereof.

After the first electrode 30 is formed, the impact mitigating layer 50 is formed to cover the side portions of the first electrode 30 and the passivation layer 80, and the impact mitigating layer 50 and the passivation layer ( Bonding metal 40 is stacked to cover 80.

Subsequently, when the metal support part 60 is formed to cover the coupling metal 40, the state as shown in FIG. 9 is obtained.

In this case, the metal support part 60 becomes very large between the semiconductor layers 20. In this case, before the metal support part 60 is formed, a post is formed of a material such as photoresist on the trench-etched portion. (Not shown) may be formed so that the substrate 10 can be separated later and then easily separated when the substrate 10 is separated into individual elements.

When the device is manufactured in this manner, the individual devices are completed in the state as shown in FIG.

On the other hand, as shown in Figure 11, the shock absorbing layer 50 may be formed on the outer side of the bonding metal (40). That is, the impact mitigating layer 50 is located between the bonding metal 40 and the metal support 60, the other structure is the same as the case of FIG.

Subsequently, the substrate 10 is separated using a laser lift-off process as in the above case, and when the second electrode 70 is formed on the separated surface and separated into individual elements, a state as shown in FIG. 12 is obtained. To be.

The above embodiment is an example for explaining the technical idea of the present invention in detail, and the present invention is not limited to the above embodiment, various modifications are possible, and various embodiments of the technical idea are all protected by the present invention. It belongs to the scope.

As described above, the present invention absorbs the instantaneous shock and stress generated in the process of separating the substrate by performing the laser lift-off process in the shock absorbing layer, thereby preventing cracks that may occur in the GaN thin film generated by the shock and stress. By minimizing and improving the contact between the metal layers, it is possible to secure the stability of the device, to maintain the ohmic characteristics of the electrode, and to solve the electrical instability factor between the metal layer and the GaN thin film.

Claims (20)

A plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; An impact mitigating layer attached to the first electrode; And a metal support part positioned on the impact mitigating layer. The vertical light emitting device of claim 1, wherein the impact mitigating layer is made of metal. The vertical light emitting device of claim 1, wherein the impact mitigating layer has a higher ductility than the metal used as the metal support. The vertical light emitting device of claim 1, wherein the impact mitigating layer is formed using at least one of In, Sn, Ag, Au, Pt, and Al. The vertical type light emitting device of claim 1, wherein the impact buffer layer has a thickness of 1 to 10 µm. The vertical light emitting device of claim 1, wherein the first electrode comprises an ohmic electrode and a reflective electrode. The vertical light emitting device of claim 1, wherein the first electrode is formed to cover the semiconductor layer. The method of claim 1, wherein the plurality of semiconductor layers, an n-type semiconductor layer; An active layer adjacent to the n-type semiconductor layer; And a p-type semiconductor layer adjacent to the active layer. The vertical light emitting device of claim 1, wherein the semiconductor layer is made of a GaN-based material. The vertical type light emitting device of claim 1, wherein the metal support part is made of any one of Cu, Ni, and Au. The vertical type light emitting device of claim 1, wherein a coupling metal is formed between the first electrode and the shock absorbing layer to facilitate bonding between the metals. 12. The vertical light emitting device of claim 11, wherein a passivation layer is further provided on a surface where the bonding metal is in contact with the semiconductor layer. The vertical type light emitting device of claim 1, wherein a coupling metal is formed between the shock absorbing layer and the metal support to facilitate coupling between metals. 15. The vertical light emitting device of claim 11 or 14, wherein the bonding metal has a structure surrounding the semiconductor layer. 15. The vertical light emitting device of claim 14, wherein a passivation layer is further provided on a surface where the bonding metal is in contact with the semiconductor layer. A plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; An impact mitigating layer attached to the first electrode; And a metal support positioned on the impact mitigating layer. 17. The vertical light emitting device of claim 16, wherein a bonding metal is provided between the first electrode and the shock absorbing layer, and the bonding metal surrounds the passivation layer. 17. The vertical light emitting device of claim 16, wherein a bonding metal is provided between the shock absorbing layer and the metal support, and the bonding metal surrounds the passivation layer. A plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; An impact mitigating layer attached to the first electrode; A bonding metal covering the impact buffer layer and the passivation layer; And a metal supporter supporting the plurality of semiconductor layers in a structure covering the bonding metal. A plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A second electrode on the other side of the semiconductor layer; A passivation layer positioned on side surfaces of the first electrode and the semiconductor layer; A bonding metal covering the first electrode and the passivation layer; An impact mitigating layer disposed on the bonding metal so as to face the first electrode; And a metal support part supporting the plurality of semiconductor layers in a structure covering the impact alleviating layer and the bonding metal.

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