KR20170033987A

KR20170033987A - Method for controlling bow of free-standing GaN substrates

Info

Publication number: KR20170033987A
Application number: KR1020150132020A
Authority: KR
Inventors: 전대우; 황종희; 임태영; 이미재; 김진호; 김진원
Original assignee: 한국세라믹기술원
Priority date: 2015-09-18
Filing date: 2015-09-18
Publication date: 2017-03-28

Abstract

The present invention relates to a method of controlling the warping of a free standing gallium nitride substrate by performing one etching or heat treatment during the wet process in accordance with the bending direction of the gallium nitride substrate.
According to the present invention, it is possible to control the bending phenomenon of the freestanding GaN substrate by varying one etching or heat treatment during the wet process according to the bending direction and the stress distribution of the substrate. The free standing GaN substrate with the deflection removed by the method of the present invention exhibits a low dislocation defect density and a self-heating phenomenon, thereby improving the electrical and mechanical characteristics of the device.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of controlling free-standing gallium nitride

The present invention relates to a method of controlling the bending of a free standing gallium nitride substrate (free-standing gallium nitride substrate), and more particularly, to a method of controlling bending of a free standing gallium nitride substrate by performing etching or heat treatment differently according to the bending direction of the gallium nitride substrate. And a method for controlling the same.

GaN is a nitride semiconductor having a Wurzite structure. It has a direct bandgap band gap of 3.4 eV which corresponds to the blue wavelength band of visible light at room temperature. In addition, it can form a solid solution with InN and AlN, And it is most popular as a material for blue display and light emitting device because it exhibits the characteristics of a direct type semiconductor directly within the total composition range of a full scale solid solution.

The GaN single crystal is generally formed on a base substrate made of sapphire (Al 2 O 3), silicon carbide (SiC), or silicon (Si) by Metal Organic Chemical Vapor Deposition (MOCVD) or Hydride Vapor Phase Epitaxy HVPE).

Sapphire is most commonly used as a base substrate used for growth by the above method. Sapphire has a lattice constant difference (about 16%) and a difference in thermal expansion coefficient (about 35%) from that of gallium nitride, A strain is induced and this strain generates lattice defects, warping and cracks in the gallium nitride crystal, making it difficult to grow a high quality gallium nitride film and shortening the lifetime of the device manufactured on the gallium nitride film .

When the stress existing in the sapphire and the gallium nitride is isotropic and the strain generated on the sapphire substrate by the gallium nitride film is less than the yield point, the grown gallium nitride film 12 is grown on the sapphire substrate (11). As the gallium nitride film thickness increases, the curvature radius decreases and the degree of warpage increases. This warp causes a difference in crystallinity between the center portion of the substrate and the peripheral portion on which the gallium nitride thick film is grown. When the light emitting diode device is fabricated using the substrate having the warping, there arises a problem that the light emitting wavelength becomes uneven.

As a method for controlling the warpage, a buffer layer having a similar lattice constant is first formed on the base substrate at a relatively low temperature to relax the lattice strain, and then a GaN single crystal layer is grown on the buffer layer And the like have been proposed. However, the above method requires the use of an expensive base substrate. In addition, when the buffer layer is formed, the production cost is increased by using another growth equipment, and a high dislocation density in the GaN single crystal layer is reduced to a laser diode or a light emitting diode It is not suitable for application.

In recent years, homogeneous epitaxial growth has been carried out using free-standing GaN substrates homogeneous to have low dislocation defect density. However, in order to manufacture a freestanding GaN substrate, it is possible to grow the substrate by a hydride vapor phase epitaxy (HVPE) method on a different substrate, and then remove the dissimilar substrate by laser off or chemical separation.

However, the free standing GaN substrate still has a problem that a bowing phenomenon occurs due to stress existing between sapphire and gallium nitride. The deflection of the freestanding substrate causes a non-uniform distribution of the penetration current and a V _Ga O _N complex defect. Generally, a 2-inch free substrate having a bending radius of 0.6 to 1.5 m exhibits a height difference of 500 to 200 μm at the center and the edge. There is a problem that the GaN layer around the edge region except the central region must be completely removed by the CMP process in order to eliminate such height difference.

SUMMARY OF THE INVENTION The present invention provides a method for controlling the bowing of a freestanding GaN substrate.

The present invention provides a method of controlling the bowing of a free standing GaN substrate in accordance with the bending direction and the stress distribution of the substrate.

The present invention provides a high-performance light emitting diode by eliminating warpage of a free standing GaN substrate.

One aspect of the present invention is

Providing a bowing gallium nitride based substrate; And

And forming a porous region on a surface of the substrate where compressive stress is greater than the upper and lower surfaces of the substrate, thereby planarizing the substrate.

In another aspect,

Providing a bowing gallium nitride based substrate; And

And a step of planarizing the surface of the substrate by applying heat treatment to a surface of the substrate on which the tensile stress is larger than the upper surface and the lower surface of the substrate, thereby controlling the bending of the free standing gallium nitride substrate.

In yet another aspect,

A free standing gallium nitride substrate in which the warping phenomenon is removed by the above method;

And forming a first conductive type semiconductor layer, a photoactive layer, and a second conductive type semiconductor layer on the gallium nitride substrate.

In yet another aspect,

Forming a gallium nitride layer on the substrate;

Separating the substrate and the gallium nitride layer;

Removing the warping of the separated gallium nitride layer by the above method;

And forming a first conductive type semiconductor layer, a photoactive layer, and a second conductive type semiconductor layer on the gallium nitride layer.

The present invention can provide a method for eliminating the warping phenomenon of the free standing GaN substrate according to the bending direction and the stress distribution of the substrate. The free standing GaN substrate with the deflection removed by the method of the present invention exhibits a low dislocation defect density and a self-heating phenomenon, thereby improving the electrical and mechanical characteristics of the device.

Fig. 1 shows a bending deformation phenomenon occurring in a sapphire / GaN laminate.
Fig. 2 shows the relative stress distribution according to the bending type of the substrate.
Figure 3 shows the control of warping through etching.
Figure 4 shows the control of warp through heat treatment.
5 is a diagram showing a schematic configuration of an electrochemical etching apparatus usable in an embodiment according to the present invention.
6 shows a method of manufacturing a light emitting diode according to the present invention.
7 is a SEM photograph of the substrate etched in embodiment 1. Fig.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be achieved by the following description with reference to the accompanying drawings. It is to be understood that the following description is of a preferred embodiment of the present invention and that the present invention is not necessarily limited thereto. In addition, the accompanying drawings may be exaggeratedly expressed relative to the actual layer thickness (or height) or the ratio with respect to other layers in order to facilitate understanding, and the meaning thereof will be properly understood in view of the specific purpose of the related description to be described later .

The lamination structure referred to in the present specification should be understood in an exemplary sense, and the present invention is not limited to such a specific lamination structure.

As used herein, the terms "on" or "on" may be used to refer to the relative position concept, as well as where other elements or layers are directly present in the stated layer, It should be understood that the layer (interlayer) or component may be interposed or present, and also includes the case where the surface of the layer mentioned above (particularly the surface having a three-dimensional shape) is not completely covered, . Therefore, unless otherwise expressly referred to as "directly" is used, it can be understood as a relative concept as described above. Similarly, the expression "underneath", "underneath" or "underneath" may also be understood as a relative concept of the position between a particular layer (element) and another layer (element).

The method of controlling deflection of a free standing gallium nitride substrate of the present invention includes providing a warped gallium nitride based substrate and a planarization step.

Fig. 1 shows a bending deformation phenomenon occurring in a sapphire / GaN laminate. Fig. 2 shows the relative stress distribution according to the bending type of the substrate. Fig. 3 shows controlling the warp through etching, and Fig. 4 shows controlling warp through heat treatment.

Referring to FIGS. 1 and 2, a gallium nitride substrate separated from a base substrate such as a sapphire substrate has a convex shape whose surface is convex due to a stress generated due to a difference in lattice constant and thermal expansion coefficient between sapphire and gallium nitride type or a concave concave shape.

Referring to FIG. 2, compressive stress acts more on N (nitrogen) -face (N-face) than tensile stress on Ga-face It gets bigger. On the other hand, in the concave shape, compressive stress acts more on N (nitrogen) -face (N-face) and tensile stress is larger on Ga-face.

The substrate providing step of the present invention is a step of providing a gallium nitride substrate exhibiting a warping phenomenon during deposition or separation on a base substrate.

The provided gallium nitride substrate may have a thickness ranging from 200 to 300 mu m.

The provided gallium nitride substrate has a predetermined warpage degree. For example, the bow value may range from 20 to +20. The bow value is a numerical value of the degree of bending of the gallium nitride substrate, and is the height difference between the center and the edge of the gallium nitride substrate (wafer). The greater the absolute value of the height difference, the greater the degree of warpage. Further, the degree of bending of the gallium nitride substrate can be expressed by a bow radius. The smaller the radius of curvature, the greater the degree of warpage.

The warping control method of the present invention performs a planarization step according to the stress distribution applied to the substrate.

The " planarization " refers to a change in the stress distribution applied to the substrate to eliminate or reduce deflection. That is, the planarization reduces the absolute value of the bow value to zero or increases the radius of curvature.

The planarizing step forms a porous region on the upper surface and the lower surface of the substrate where the compressive stress is greater.

When the substrate is bent in a convex form, the method etches the N-face of the substrate to form a porous region.

When the substrate is bent in a concave shape, the method etches the Ga-face of the substrate to form a porous region.

Referring to FIG. 3, the planarizing step etches a surface having a greater compressive stress to form a hole-like porous nanostructure 21. The hole-shaped porous nanostructure 21 mitigates the compressive stress, so that the bow value of the bent substrate can be reduced.

The etch may be wet electrochemical etching (EC). The basic principle of the EC etching method will be described with reference to the electrochemical etching apparatus of FIG.

First, a resistive contact is formed on an object to be etched (or a sample), and a platinum (Pt) electrode is used as an opposite electrode to connect the two electrodes. Then, a chemical cell is formed in, for example, oxalic acid, .

By using the electrochemical etching of FIG. 5, the surface of the substrate where the compressive stress is larger than the upper surface and the lower surface is etched to exhibit the porosity. And exhibit porosity characteristics due to a variation in etching rate (i.e., uneven etching).

The voltage range applied to the apparatus is within the range of about 0.1 V to 60 V and the concentration of the electrolyte (e.g., potassium hydroxide, oxalic acid) may be at least about 0.001 M, and in some cases in a molten state (e.g., Molten KOH).

The etching time varies depending on the area of the object or the sample to be etched. The smaller the area, the shorter the required etching time, and the etching time can be set appropriately considering the desired degree of porosity. For example, as the concentration increases or the etching time becomes longer, the higher the applied voltage becomes, the faster the etching speed becomes, and the larger the area where the structure changes to the porous structure becomes.

Since the above-described process conditions (the type and concentration of the electrolyte, the intensity of the light source, the applied voltage, the etching time, etc.) are described for illustrative purposes, the present invention is not necessarily limited to the above-

However, the etching rate tends to increase as the concentration of the electrolyte, the applied voltage, and the etching time are increased. On the other hand, the smaller the etching area, the more uniform the etching pattern.

As used herein, the term "porous" refers to a micro or nano morphology in which a plurality of spaces (or pores) bounded by uneven etching of the surface are formed, and particularly preferably, Quot; nano-porous ", which is understood to be a size (e. G., A size of about 1,000 nm or less).

The average size (or average diameter) of the pores 21 may preferably range from about 30 to 1000 nm

The thickness of the porous region (i.e., the distance to the etched or pored bottom surface) is preferably in the range of about 30 to 3,000 nm, more preferably in the range of about 50 to 300 nm.

Referring to FIG. 4, the method is performed by performing a heat treatment on the upper surface and the lower surface of the substrate where tensile stress is greater.

More specifically, the heat treatment may be performed at 500 to 1100 ° C for 1 minute to 10 hours, but is not limited thereto. If heat treatment is applied to the surface where the tensile stress is larger, the rearrangement effect of the atoms relaxes the tensile stress and the warping can be controlled.

In another aspect, the present invention provides a method of manufacturing a free standing gallium nitride substrate, A photoactive layer, and a second conductive type semiconductor layer formed on the gallium nitride substrate.

The first conductivity type semiconductor, the active layer and the second conductivity type semiconductor may be various semiconductor materials (III-V, II-VI, etc.) known in the art for manufacturing LEDs such as GaN, AlN, InP, InS, ZnS, ZnTe, ZnO, AlxGa1-xN, InxGa1-xN, InxGa1-xAs, ZnxCd1-xS and the like can be used alone or in combination thereof < x < 1).

The first conductivity type semiconductor layer may be formed to a thickness of about 0.5 to 10 mu m, more preferably about 1 to 5 mu m. In addition, the light emitting device of the present invention may optionally include a buffer layer or a buffer layer.

6 shows a method of manufacturing a light emitting diode according to the present invention. Referring to FIG. 6, the method of the present invention includes forming a gallium nitride layer 20 on a substrate 10; Separating the substrate (10) and the gallium nitride layer (20); Removing the warping of the separated gallium nitride layer by the above method; And forming a first conductive semiconductor layer 30, a photoactive layer 40, and a second conductive semiconductor layer 50 on the gallium nitride layer.

The substrate 10 may be, for example, sapphire, silicon carbide (SiC), or silicon (Si) substrate, preferably a sapphire substrate.

The step of forming the gallium nitride layer 20 on the substrate 10 may be performed using a known method to form a gallium nitride layer. The gallium nitride layer may be a GaN, AlGaN, AlN or InGaN layer, and preferably a GaN layer may be formed. More specifically, after the sapphire substrate 10 is loaded in a reactor of a HVPE (Hydride Vapor Phase Epitaxy) apparatus, a GaCl gas and NH 3 gas are supplied as a source together with an N 2 carrier to form a GaN layer 20 on the sapphire substrate 10 to a thickness of about 10 mu m or less. Alternatively, a GaN layer is formed on a sapphire substrate by an MOCVD (Metal-Organic Chemical Vapor Deposition) method.

The step of separating the substrate 10 from the gallium nitride layer 20 can be performed by any known method without limitation. For example, the separation may use a laser lift-off method. Also, the buffer layer may be formed between the substrate and the gallium nitride layer, and then the buffer layer may be removed using a chemical lift-off process to separate the gallium nitride layer.

As shown in FIG. 6, the bending state of the gallium nitride layer bent at the growth or separation step of the gallium nitride layer can be controlled using the above-described method.

The first conductive semiconductor layer 30, the photoactive layer 40, and the second conductive semiconductor layer 50 may be formed on the gallium nitride layer 20 by a known method.

For example, the light emitting device may be formed by a conventional epitaxial layer forming method such as metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE), or hydride vapor phase epitaxy (HVPE) Can be adopted.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following embodiments are provided for the purpose of easier understanding of the present invention, but the present invention is not limited thereto.

Example One ; etching

Using the apparatus of FIG. 5, electrochemical etching was performed on a Convex type GaN substrate. Six samples were etched under the conditions shown in Table 1 below.

First, a magnetic bar was used to homogenize the electrolytes such as oxalic acid and the mixture was stirred on the agitator.

Second, using a power supply such as a power supply, the platinum wire was used as a cathode and the GaN substrate was used as an anode.

Third, the etching thickness and porosity shape were controlled by adjusting voltage, time, and molar concentration.

Table 1 shows voltage, time, surface thickness, and etched surface thickness for six samples, respectively.

Example 2 ; Heat treatment

The concave type GaN substrate (N-face side) was heated at 1000 캜 for 10 minutes.

7 is a SEM photograph of the substrate etched in embodiment 1. Fig. Referring to FIG. 7, it can be confirmed that a nanoporous structure is formed on the substrate of Example 1. FIG. In particular, it can be seen that as the voltage intensity increases from P30V01M to P60V01M, the etched pore size increases.

Table 2 shows the change in the bow value of the substrate etched in Example 1. < tb > < TABLE >

Referring to Table 2, it can be seen that the bow value after etching is reduced by about 4 to 24.

Table 3 shows changes in the bow value of the substrate in which the warp is controlled in the second embodiment.

Referring to Table 3, it can be seen that the bow value was reduced by about 12 ~ 23 before the heat treatment.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

10: sapphire substrate 20: nitride-based substrate
30: first conductivity type semiconductor layer 40: photoactive layer
50: second conductivity type semiconductor layer 21: porous region

Claims

Providing a bowing gallium nitride based substrate; And
And forming a porous region on a surface of the substrate where a compressive stress is more likely to be applied to the upper surface and the lower surface of the substrate, thereby planarizing the surface of the substrate.

2. The method of claim 1, wherein when the substrate is bent in a convex shape, the method comprises etching the N-face of the substrate to form a porous region. Of warpage control.

The method of claim 1, wherein when the substrate is bent in a concave shape, the method comprises etching a Ga-face of the substrate to form a porous region, Of warpage control.

The method of claim 1, wherein the porous region is a wet electrochemical etch.

The method of claim 1, wherein the porous region comprises a plurality of pores.

The method of claim 1, wherein the porous region has a thickness of 30 to 3,000 nm and the pore has a diameter of 30 to 1,000 nm.

[6] The method of claim 5, wherein the electrochemical etching is performed by controlling the concentration of the electrolyte, the applied voltage, or the etching time to control the planarization speed.

Providing a bowing gallium nitride based substrate; And
And performing a heat treatment on a surface of the substrate where the tensile stress is greater than the upper surface and the lower surface, thereby flattening the substrate.

The method according to claim 8, wherein the heat treatment is performed at 500 to 1,000 ° C for 1 minute to 10 hours.

10. The method according to any one of claims 1 to 9, wherein the thickness of the gallium nitride-based substrate ranges from 200 to 400 mu m.

10. The method according to any one of claims 1 to 9, wherein a bow value of the gallium nitride-based substrate is in the range of -20 to +20.

10. A free standing gallium nitride substrate having a warp removed according to any one of claims 1 to 9;
And a first conductivity type semiconductor layer formed on the gallium nitride substrate, a photoactive layer, and a second conductivity type semiconductor layer.

Forming a gallium nitride layer on the substrate;
Separating the substrate and the gallium nitride layer;
Removing the deflection of the separated gallium nitride layer by the method of any one of claims 1 to 9;
And forming a first conductive type semiconductor layer, a photoactive layer, and a second conductive type semiconductor layer on the gallium nitride layer.