KR20070018235A - Light emitting diode and method of fabricating the same - Google Patents

Abstract

The present invention relates to a light emitting diode. The light emitting diode according to the present invention includes a bonding metal layer formed on the conductive substrate, a reflective layer formed on the bonding metal layer, and a light emitting structure formed on the reflective layer. A stress absorber capable of absorbing stress is formed in the reflective layer. According to the present invention, the stress difference between the reflective layer and the light emitting structure is minimized by the stress absorber formed in the reflective layer.

Light Emitting Diode, Light Emitting Structure, Reflective Layer, Stress Absorber

Description

LIGHT EMITTING DIODE AND METHOD OF FABRICATING THE SAME

1 is a cross-sectional view of a GaN light emitting diode according to the prior art,

2 is a cross-sectional view of a vertical GaN light emitting diode according to the prior art;

3 is a cross-sectional view of a light emitting diode according to the present invention;

4A to 4E are cross-sectional views illustrating a process of manufacturing a light emitting diode according to the present invention;

5A to 5P are views illustrating some of the patterns that the stress absorber according to the present invention may have.

♧ explanation of the reference numerals for the main parts of the drawing.

111: first substrate 112: second substrate

113: light emitting structure 113n: first cladding layer

113w: active layer 113p: second cladding layer

115: reflective layer 117: stress absorber

118: stress absorbing layer 119a: first bonding metal layer

119b: second bonding metal layer 119: bonding metal layer

120n: first ohmic electrode 120p: second ohmic electrode

The present invention relates to a semiconductor device, and more particularly, to a light emitting diode and a manufacturing method thereof.

In general, a light emitting diode (LED) is a semiconductor device in which electrons and holes emit light based on recombination, and are widely used as light sources of various types in optical communication and electronic devices.

The frequency (or wavelength) of light generated in the light emitting diode is the band gap sum of the semiconductor materials used. In other words, low energy and long wavelength photons are generated in a small band gap, and short wavelength photons are generated in a large band gap. For example, group III nitride semiconductors, in particular gallium nitride (GaN), which are semiconductor materials with relatively large band gaps, produce light having blue or ultraviolet wavelengths. Short wavelength LEDs have the advantage of increasing storage space in optical storage.

GaN generating such short wavelength blue light cannot form a bulk single crystal like other group III nitride semiconductors. Therefore, an appropriate substrate should be used for the growth of GaN crystals. As a substrate for growing such GaN crystals, sapphire, that is, an aluminum oxide (Al ₂ O ₃ ) substrate is typical. However, since the sapphire substrate is insulative, it is severely restricted in forming the structure of the GaN-based light emitting diode.

1 is a cross-sectional view of a GaN light emitting diode according to the prior art.

Referring to FIG. 1, the GaN light emitting diode 10a includes a sapphire substrate 11 and a GaN light emitting structure 13 formed on the sapphire substrate 11. The GaN light emitting structure 13 includes an n-type GaN cladding layer 13n sequentially formed on the sapphire substrate 11 and an active layer 13w having a multi-quantum well (MQW) structure and a p-type GaN cladding layer ( 13p).

A portion of the p-type GaN cladding layer 13p and the active layer 13w is dry-etched to expose a portion of the top surface of the n-type GaN cladding layer 13n. An n-type ohmic electrode 20n and a p-type ohmic electrode 20p are formed on the exposed upper surface of the n-type GaN cladding layer 13n and the upper surface of the p-type cladding layer 13p, respectively. In general, a transparent electrode 25 may be formed between the upper surface of the p-type GaN cladding layer 13p and the p-type ohmic electrode 20p in order to increase the current injection area and not adversely affect luminance.

As described above, since the GaN light emitting diode 10a uses the sapphire substrate 11 as an insulating material, the two ohmic electrodes 20a and 20b may be formed in a substantially horizontal direction. Therefore, when voltage is applied, the current flow from the p-type ohmic electrode 20p toward the n-type ohmic electrode 20n through the active layer is concentrated on the A portion. Due to such a narrow current flow, GaN light emitting diodes have a problem in that the forward voltage increases and current efficiency decreases. Therefore, a vertical GaN light emitting diode has been proposed that can compensate for the disadvantages of the GaN light emitting diode.

2 is a cross-sectional view of a vertical GaN light emitting diode according to the prior art.

Referring to FIG. 2, the GaN light emitting diode 10b includes a conductive substrate 12 and a GaN light emitting structure 13 formed on the conductive substrate 12. The GaN light emitting structure 13 is composed of an n-type GaN cladding layer 13n, an active layer 13w having a multi-quantum well (MQW) structure, and a p-type GaN cladding layer 13p. An n-type ohmic electrode 20n is formed on the n-type GaN cladding layer 13n, and a p-type ohmic electrode 20p is formed under the conductive substrate 12. The reflective layer 15 and the bonding metal layer 19 are interposed between the conductive substrate 12 and the light emitting structure 13.

In general, the reflective layer 15 is formed of a metal such as Ni, Au, Ag, Al, or an alloy thereof, and their thermal expansion coefficient (TEC) is 12.5 × 10 ⁻⁶ / K, 13.9 × 10 ^{−, respectively. 6} / K, 18.9 × 10 ^-6 / K, 23.7 × 10 ^-6 / K. This is largely different from 5.59 × 10 ⁻⁶ / K, which is a thermal expansion coefficient of the p-type GaN cladding layer 13p. This large difference in coefficient of thermal expansion causes separation between the reflective layer 15 and the p-type GaN cladding layer 13p. That is, when the reflective layer 15 is formed on the p-type GaN cladding layer 13p at a temperature of several hundred degrees and then returned to room temperature, the p-type GaN cladding layer 13p and the reflective layer 15 are formed due to the difference in coefficient of thermal expansion. Since the difference in stress is large, the p-type GaN cladding layer 13p and the reflective layer 15 may be separated from each other. In addition, this phenomenon may occur when the sapphire substrate (not shown) is separated by a laser beam or when the bonding metal layer 19 is formed on the reflective layer 15.

The present invention has been proposed in consideration of the above-mentioned situation, and a technical problem to be achieved by the present invention is to provide a light emitting diode and a method of manufacturing the same that can minimize the difference between the stress of the light emitting structure and the reflective layer.

In order to achieve the above technical problem, a light emitting diode according to an aspect of the present invention includes a conductive substrate, a bonding metal layer formed on the conductive substrate, a reflective layer formed on the bonding metal layer, a light emitting structure formed on the reflective layer, and the reflective layer. Formed stress absorbers.

The light emitting structure may be a stacked structure including a first cladding layer, an active layer, and a second cladding layer, wherein the first cladding layer is a p-type GaN layer, and the second cladding layer may be an n-type GaN layer. have.

The stress absorber may be formed of a material selected from the group consisting of W, Cr, Mo, and alloys thereof.

The stress absorber may contact the light emitting structure or the bonding metal layer, and the stress absorber may be formed in a plurality of line patterns or a plurality of island patterns.

The light emitting diode according to the present invention may further include a stress absorbing layer between the reflective layer and the bonding metal layer. In this case, the stress absorbing layer and the stress absorber may be formed of the same material, and the stress absorber may contact the light emitting structure or the stress absorbing layer.

In order to achieve the above technical problem, a method of manufacturing a light emitting diode according to another aspect of the present invention includes forming a second cladding layer, an active layer, and a first cladding layer on a first substrate, and forming a reflective layer on the first cladding layer. And a stress absorber is formed in the reflective layer. Forming a stress absorbing layer covering the reflective layer, adhering and bonding the first substrate having the stress absorbing layer formed thereon and the conductive second substrate having the bonding metal layer formed thereon, and separating the first substrate from the second clad layer; .

The first cladding layer may be formed of p-type GaN, and the second cladding layer may be formed of n-type GaN.

The stress absorber may be formed in a plurality of line patterns or a plurality of island patterns.

Forming the stress absorber may include forming an opening that exposes the first clad layer by etching a portion of the reflective layer, and filling the opening with a stress absorbing material.

The stress absorber and the stress absorbing layer may be formed of the same material, wherein the material may be a material selected from the group consisting of W, Cr, Mo, and alloys thereof.

The method of manufacturing the light emitting diode may further include forming a bonding metal layer on the stress absorbing layer.

The bonding metal layer on the first substrate and the bonding metal layer on the second substrate may be bonded to each other.

In the method of manufacturing a light emitting diode according to the present invention, a second cladding layer, an active layer, and a first cladding layer are formed on a first substrate, a reflective layer is formed on the first cladding layer, and a stress absorber is formed in the reflective layer. . A first bonding metal layer is formed to cover the reflective layer, the first substrate on which the first bonding metal layer is formed, and the conductive second substrate on which the second bonding metal layer is formed are bonded to each other, and the first substrate is formed from the second cladding layer. Separating the.

The first cladding layer may be formed of p-type GaN, and the second cladding layer may be formed of n-type GaN.

The stress absorber may be formed in a plurality of line patterns or a plurality of island patterns.

Forming the stress absorber may include forming an opening that exposes the first clad layer by etching a portion of the reflective layer, and filling the opening with a stress absorbing material.

The stress absorber may be formed of a material selected from the group consisting of W, Cr, Mo, and alloys thereof.

According to the present invention, by forming a stress absorber in the reflective layer, it is possible to minimize the difference between the stress received by the reflective layer and the light emitting structure. This effect can be further enhanced by the stress absorbing layer formed on the reflective layer.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the spirit of the present invention to those skilled in the art will fully convey.

In the embodiments herein, the terms first, second, etc. are only used to distinguish any given layer (film) or region from another layer (film) or region, so that layer (film) or region is such a term. It should not be limited by these.

In the drawings, the thickness of a layer (film) or regions may be exaggerated for clarity. In addition, where it is mentioned that the layer (film) is on or above another layer (film) or substrate, it may be formed directly on the other layer (film) or substrate or between the third layer ( Membrane) may be interposed.

The same reference numerals throughout the specification represent the same components.

3 is a cross-sectional view of a light emitting diode according to the present invention.

Referring to FIG. 3, the light emitting structure 113 is positioned on the conductive substrate 112. As the conductive substrate 112, a Si substrate, a Cu substrate, a GaAs substrate, a Ge substrate, or a Mo substrate may be used. The light emitting structure 113 includes a first cladding layer 113n, an active layer 113w having a multi-quantum well (MQW) structure, and a second cladding layer 113p. The first and second clad layers 113n and 113p may be formed of GaN. The first ohmic electrode 120n is positioned on the first clad layer 113n. The second ohmic electrode 120p is positioned below the conductive substrate 12. The conductive type of the first cladding layer 113n and the first ohmic electrode 120n may be n-type. At this time, the conductivity type of the second clad layer 113p and the second ohmic electrode 120p is p-type.

The reflective layer 115, the stress absorbing layer 118, and the bonding metal layer 119 are positioned between the conductive substrate 112 and the second cladding layer 113p. The reflective layer 115 may be formed of a metal having high reflectance selected from the group consisting of Ni, Au, Ag, Al, ITO, Rh, alloys thereof, and the like. The thermal expansion coefficients of these metals are all 10 × 10 ⁻⁶ / K or more, which is significantly different from 5.59 × 10 ⁻⁶ / K, which is the thermal expansion coefficient of GaN constituting the second clad layer 113p. When the reflective layer 115 is formed on the second cladding layer 113p due to the difference in thermal expansion coefficient, the two layers may be separated from each other due to the difference in stress received by the two layers. In addition, when the bonding metal layer 119 is formed on the reflective layer 115 or when the first substrate (not shown) is separated from the first cladding layer 113n by the laser beam, as described later, the second cladding layer 113p and the reflective layer 115 may be separated from each other by the stress difference between the two layers. However, the stress absorber 117 formed in the reflective layer 115 absorbs the stress generated for various reasons as described above, thereby preventing the second clad layer 113p and the reflective layer 115 from being separated. The stress absorbing layer 118 formed on the reflective layer 115 may further increase this effect. The stress absorbing layer 118 also has a function of protecting the reflective layer 115, but may not be formed. The stress absorber 117 and the stress absorbing layer 118 are materials selected from the group consisting of W, Cr, Mo, alloys thereof, and the like, in which the difference in thermal expansion coefficient is insignificant with respect to GaN constituting the second clad layer 113p. It can be formed as. In this case, the stress absorber 117 and the stress absorbing layer 118 may be formed of the same material.

3 illustrates that the stress absorber 17 is in contact with the second cladding layer 113p, but is not limited thereto. The stress absorber 117 may absorb stress even when the reflective layer 115 is not completely removed between the stress absorber 117 and the second cladding layer 113p.

The stress absorber 117 formed in the reflective layer 115 may have various types of patterns. 5a to 5p are views showing a part of the pattern that the stress absorber according to the present invention can have. 5A to 5P, the stress absorber may be formed of a plurality of line patterns or a plurality of island patterns. However, the stress absorber should not be limited to the pattern shown here, and may have various types of patterns.

4A to 4E are cross-sectional views illustrating a process of manufacturing a light emitting diode according to the present invention.

Referring to FIG. 4A, a light emitting structure 113 is formed on the first substrate 111. The first substrate 111 may be a sapphire substrate. The light emitting structure 113 includes a first cladding layer 113n, an active layer 113w having a multi quantum well structure, and a second cladding layer 113p. The first cladding layer 113n may be formed of n-type GaN, and the second cladding layer 113p may be formed of p-type GaN. When the active layer 113w is GaN-based, various materials and structures may be formed according to emission wavelengths. The light emitting structure 113 may be grown on the sapphire substrate 111 using a deposition process such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). In this case, in order to improve lattice matching with the sapphire substrate 111 before growing the first cladding layer 113n, a buffer layer (not shown) made of AlN / GaN may be formed.

Referring to FIG. 4B, a reflective layer 115 is formed on the second clad layer 113p. The reflective layer 115 may be formed of a metal having high reflectance selected from the group consisting of Ni, Au, Ag, Al, ITO, Rh, alloys thereof, and the like. A portion of the reflective layer 115 is etched to form an opening 115h through which a portion of the upper surface of the second clad layer 113p is exposed. In this case, a portion of the reflective layer 115 to be etched is not completely removed, so that a material constituting the reflective layer 115 may remain on the second clad 113p. Forming the opening 115h is not intended to form a contact for connecting the second clad layer 113p to other components, so it is not necessary to expose the top surface of the second clad layer 113p. .

As will be described later, the stress absorbing material is filled in the opening 115h to form a stress absorber (see FIG. 4C). Accordingly, since the stress absorber has various patterns as shown in FIGS. 5A to 5P, the opening 115h may also be made in various shapes. That is, the pattern of the stress absorber 117 is determined by the shape of the opening 115h.

Referring to FIG. 4C, when a material selected from the group consisting of W, Cr, Mo, an alloy thereof, and the like is filled in an opening (see FIG. 4B), a stress absorber 117 is formed. The stress absorbing layer 118 is formed on the reflective layer 115 and the stress absorber 117. The stress absorbing layer 118 may be formed of the same material as the stress absorber 117. In an embodiment of the present invention, the stress absorbing layer 118 is formed, but the stress absorbing layer 118 is not necessarily formed. The stress absorbing layer 118 assists the stress absorber 117 to prevent the second cladding layer 113p and the reflective layer 115 from being separated from each other, and serves to protect the reflective layer 115. The first bonding metal layer 119a is formed on the stress absorbing layer 118.

4D and 4E, the first bonding metal layer 119a and the second bonding metal layer 119b are bonded to each other to form a new bonding metal layer 119. The first substrate 111 and the second substrate 112 are formed. ) Is merged. At this time, the second substrate 112 is a conductive substrate. As the conductive substrate 112, a Si substrate, a Cu substrate, a GaAs substrate, a Ge substrate, or a Mo substrate may be used. The material constituting the bonding metal layers 119a and 119b may be an alloy that can be used for flip chip bonding, and a material having a low melting point of about 200 ° C. to 300 ° C. and which can be bonded at low temperatures should be used. Such materials may be materials selected from the group consisting of Au-Sn, Sn, In, Au-Ag, and Pb-Sn. Although the bonding metal layers 119a and 119b are formed on both the first substrate 111 and the second substrate 112 in FIG. 4D, the bonding metal layer 119a may not be formed on the first substrate 111. In this case, the stress absorbing layer 118 adheres to the second bonding metal layer 119b formed on the second substrate 112 in place of the bonding metal layer 119a.

Referring to FIG. 4F, when the laser beam is irradiated on the lower surface of the first substrate 111, the first substrate 111 is separated from the first cladding layer 113n. The laser can be a 355nm Nd-YAG laser or a 248nm KrF laser. At this time, stress may occur due to a difference in thermal expansion coefficient between the first substrate 111 and the first cladding layer 113n and lattice mismatch. That is, the thermal expansion coefficient of the sapphire constituting the first substrate 111 is about 7.5 × 10 ⁻⁶ / K, while the thermal expansion coefficient of the first cladding layer 113n is 5.59 × 10 ⁻⁶ / K, and is about between the two layers. Lattice mismatch of 16% occurs. As a result, stresses such as large compressive stress and tensile stress are generated on the contact surfaces of the first substrate 111 and the first cladding layer 113n when the heat is generated by the laser beam. In order to prevent this, the light emitting structure 113 may be cut into individual device units before the first substrate 111 is separated by a laser beam. When the light emitting structure 113 is cut in individual device units, the stress generated at the contact surface between the first substrate 111 and the first cladding layer 113n is sufficiently reduced. Therefore, cracks that may occur on the surface of the first cladding layer 113n when the first substrate 111 is separated are prevented.

Referring to FIG. 4G, the first ohmic electrode 120n is formed on the lower surface of the first cladding layer 113n, and the second ohmic electrode 120p is formed on the second substrate 112. The conductivity type of the first ohmic electrode 120n is the same as the conductivity type of the first cladding layer 113n, and the conductivity type of the second ohmic electrode 120n is the same as the conductivity type of the second cladding layer 113p. Therefore, when the conductivity type of the first cladding layer 113n is n-type and the conductivity type of the second cladding layer 113p is p-type, the conductivity type of the first ohmic electrode 120n is n-type and the second ohmic The conductivity type of the electrode 113p is p-type.

On the other hand, in the detailed description of the present invention has been described with respect to specific embodiments, various modifications are of course possible without departing from the scope of the invention.

Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be defined not only by the claims below but also by the equivalents of the claims of the present invention.

According to the present invention described above, the stress difference between the reflective layer and the light emitting structure is minimized by the stress absorber formed in the reflective layer. The effect can be further increased by the stress absorbing layer formed on the reflective layer. The light emitting diode may have improved reliability, such as low forward voltage and increased brightness. In addition, the light emitting diode is mechanically stabilized.

Claims (19)

Conductive substrates; A bonding metal layer formed on the conductive substrate; A reflective layer formed on the bonding metal layer; A light emitting structure formed on the reflective layer; And A light emitting diode comprising a stress absorber formed in the reflective layer. The method of claim 1, The light emitting structure is a stacked structure including a first cladding layer, an active layer, and a second cladding layer, The first cladding layer is a p-type GaN layer, the second cladding layer is an n-type GaN layer. The method of claim 1, The stress absorber is a light emitting diode formed of a material selected from the group consisting of W, Cr, Mo, and alloys thereof. The method of claim 1, The stress absorber is in contact with the light emitting structure or the bonding metal layer. The method of claim 1, The stress absorber is a light emitting diode formed of a plurality of line patterns or a plurality of island patterns. The method according to any one of claims 1 to 5, The light emitting diode further comprises a stress absorbing layer between the reflective layer and the bonding metal layer. The method of claim 6, The stress absorbing layer and the stress absorber is a light emitting diode formed of the same material. The method of claim 6, The stress absorber is in contact with the light emitting structure or the stress absorbing layer. Forming a second clad layer, an active layer, and a first clad layer on the first substrate, Forming a reflective layer on the first cladding layer, Forming a stress absorber in the reflective layer, Forming a stress absorbing layer covering the reflective layer, Bonding and bonding the first substrate having the stress absorbing layer and the conductive second substrate having the bonding metal layer formed thereon; A method of manufacturing a light emitting diode comprising separating the first substrate from the second cladding layer. The method of claim 9, Wherein the first cladding layer is formed of p-type GaN, and the second cladding layer is formed of n-type GaN. The method of claim 9, The stress absorber is a light emitting diode formed of a plurality of line patterns or a plurality of island patterns. The method of claim 9, Forming the stress absorber, A portion of the reflective layer is etched to form an opening exposing the first clad layer, Method of manufacturing a light emitting diode comprising filling the opening with a stress absorbing material. The method of claim 9, The stress absorber and the stress absorbing layer is formed of the same material, And the material is selected from the group consisting of W, Cr, Mo, and alloys thereof. The method according to any one of claims 9 to 13, Forming a bonding metal layer on the stress absorbing layer; And a bonding metal layer on the first substrate and a bonding metal layer on the second substrate to be bonded to each other. Forming a second clad layer, an active layer, and a first clad layer on the first substrate, Forming a reflective layer on the first cladding layer, Forming a stress absorber in the reflective layer, Forming a first bonding metal layer covering the reflective layer, Bonding and coalescing a first substrate having the first bonding metal layer and a conductive second substrate having the second bonding metal layer formed thereon; A method of manufacturing a light emitting diode comprising separating the first substrate from the second cladding layer.  The method of claim 15, Wherein the first cladding layer is formed of p-type GaN, and the second cladding layer is formed of n-type GaN. The method of claim 15, The stress absorber is a light emitting diode formed of a plurality of line patterns or a plurality of island patterns. The method of claim 15, Forming the stress absorber, A portion of the reflective layer is etched to form an opening exposing the first clad layer, Method of manufacturing a light emitting diode comprising filling the opening with a stress absorbing material. The method of claim 15, The stress absorber is formed of a material selected from the group consisting of W, Cr, Mo, and alloys thereof.

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