WO2009002045A2

WO2009002045A2 - Manufacturing method of vertically structured gan led device

Info

Publication number: WO2009002045A2
Application number: PCT/KR2008/003501
Authority: WO
Inventors: Hyun Chul Ko; Meoung Whan Cho; Pil Guk Jang; Byung Il Cho
Original assignee: Wavesquare Inc.
Priority date: 2007-06-22
Filing date: 2008-06-20
Publication date: 2008-12-31
Also published as: KR100870719B1; WO2009002045A3

Abstract

The present invention relates especially to a manufacturing method of vertically structured GaN-based LED device completely preventing damage to the structure supporting layer using a chemical lift-off process. Manufacturing method of the present invention is comprised of steps including; (a) forming a buffer layer on a sapphire substrate to be removed; (b) growing a GaN-based LED structure having an n-type GaN layer, an active layer, and a p-type GaN layer to form multiple LED devices separately on the buffer layer formed in step (a); (c) forming multiple structure supporting layers on a LED structure formed in step (b) and forming a protection layer to cover the externally exposed areas of multiple structure supporting layers; (d) separating sapphire substrate from the GaN-based LED structure formed in step (b) by removing buffer layer using a CLO process; and (e) removing protection layer covering structure supporting layer.

Description

MANUFACTURING METHOD OF VERTICALLY STRUCTURED GAN LED DEVICE

Technical Field

[1] The present invention relates to a manufacturing method of a vertically structured

GaN-based light emitting diode (LED), especially to a manufacturing method of a vertically structured GaN-based LED device completely preventing damage to the structure supporting layer using a chemical lift-off (CLO) process when performing a separation process of a sapphire substrate. Background Art

[2] In general, a light emitting diode (LED) is a semiconductor device that can realize various colors of light by constructing light emitting sources through changing compound semiconductor materials such as GaAs, AlGaAs, GaN, InGaN, and AlGaInP. Recently, in LED devices, manufacturing of high brightness and high quality products, rather than low brightness conventional products, become possible due to a rapid progress of semiconductor technologies. Moreover, as high quality blue and white diodes are practically realized, the application value of LEDs is expanded to the area such as displays and next generation illumination sources etc. Especially, GaN- based LED devices are getting attention because they have direct transition characteristics to ensure higher lasing probabilities with blue light lasing possibilities.

[3] Figs. 1 and 2 are the cross-sectional views to explain the fabrication methods of the conventional GaN-based LED devices.

[4] According to a conventional fabrication method of a GaN-based LED device, an n- type GaN layer 20, an active layer 30, a p-type GaN layer 40, and a p-type electrode 50 are sequentially stacked on a sapphire substrate 10 as shown in Fig. 1, then the structure is etched as shown in Fig. 2 using predefined patterns for forming of an electrode 70 and separation of each LED device, then an n-type electrode 70 is formed on a n-type GaN layer 20, then individual devices are separated by performing the chip breaking process after scribing or dicing.

[5] In other words, a GaN-based device that is finished using such fabrication method is a planar structured device herein a p-type and an n-type electrode are located in the same direction. Hence, the area of such LED device should be relatively larger to provide a sufficient emission area. Moreover, it is vulnerable to electrostatic discharge (ESD) because a p-type and an n-type electrode are located closely. Most of all, a sapphire substrate is a hard and an electrically non-conductive material having a poor thermal conductivity, hence there has been limitations in size reduction of a GaN- based LED device to reduce the production cost or on improving the optical power output or chip characteristics. Especially it is very important to solve heat dissipation problem of an LED device because a high current must be applied for a high output of an LED device.

[6] As a method to solve such problems of a horizontal structure, there is provided a fabrication method of a vertically structured GaN-based LED device where a sapphire substrate is removed using laser lift-off technique (hereafter referred to as 'LLO') in Korea Patent Publication No. 2007-20840 (hereafter referred to as the 'cited invention').

[7] But, according to the above described cited invention, an expensive laser equipment must be used to remove a sapphire substrate and there are drawbacks like it not only degrades the device characteristics but also lowers the yield and reliability of an LED device due to physical stress applied to the LED device by high-temperature heat generated during an LLO process.

[8] Therefore, to solve above mentioned problems of cited invention, the applicant of the present invention has provided a fabrication method for a vertically structured GaN- based LED device in Korea Patent Application No. 2007-52548 (hereafter referred to as the 'prior invention') wherein a sapphire substrate can be removed more easily and safely from an LED structure without giving physical impact to an LED structure by removing buffer layer using a chemical lift-off (hereafter referred to as the 'CLO') after forming an LED structure having an n-type GaN layer, an active layer, and a p-type GaN layer on a buffer layer formed on a sapphire substrate.

[9] But, according to the prior invention, when a buffer layer is removed using a CLO process, there is a problem that a part of the structure supporting layer is corroded due to a reaction between the structure supporting layer and the relevant solution resulting in ultimate removal of the structure supporting layer. To solve above mentioned problem, the applicant has ended up to this invention. Disclosure of Invention Technical Problem

[10] An objective of the present invention, that has been made to solve the foregoing problems, is to provide a fabrication method for a vertically structured GaN-based LED device wherein a structure supporting layer is protected against penetration of the solution used during a CLO process by removing a buffer layer using a CLO process after forming a layer to protect the structure supporting layer. Technical Solution

[11] To achieve above described objective, a manufacturing method of a vertically structured GaN-based LED device of the present invention is comprised of steps including; (a) forming a buffer layer on a sapphire substrate to be removed; (b) growing a GaN-based LED structure having an n-type GaN layer, an active layer, and a p-type GaN layer to form multiple LED devices separately on the buffer layer formed in the above step (a); (c) forming multiple structure supporting layers on a LED structure formed in the above step (b) and forming a protection layer to cover the externally exposed areas of said multiple structure supporting layers; (d) separating said sapphire substrate from the GaN-based LED structure formed in the above step (b) by removing said buffer layer using a CLO process; and (e) removing said protection layer covering said structure supporting layer.

[12] Also, above described manufacturing method of a vertically structured GaN-based

LED device is preferred to be comprised of steps further including; (pdl) etching a portion of said protection layer while preventing said multiple structure supporting layers from external exposure before to proceed to said step (d); (pd2) separating said GaN-based LED structure into multiple LED devices by etching a portion of said GaN- based LED structure externally exposed as a result of said step (pdl). At this time, said step (d) is to separate multiple LED devices formed in said step (pd2) and said sapphire substrate.

[13] In here, it is recommended that the above step (c) is comprised of steps including;

(cl) forming multiple structure supporting layers on GaN-based structure formed in said step (b); (c2) covering entire surface of said multiple structure supporting layers with surface protection layer; (c3) etching a portion of side area of said multiple structure supporting layer after performing said step (c2); (c4) covering the entire side area of said multiple structure supporting layers with side area protection layer after performing said (c3).

[14] Besides, it is recommended that the above step (cl) is comprised of steps including;

(cl-1) forming a guide pattern, to be used for forming multiple structure supporting layers separately, on a GaN-based LED structure formed in said step (b); (cl-2) removing said guide pattern after forming multiple structure supporting layers on an LED section using said guide pattern.

[15] Also, it is recommended that said steps of (cl-2) and (c3) are performed by a wet etching process, and said steps of (pdl) and (pd2) are performed by a dry etching process.

Advantageous Effects

[16] According to the manufacturing method of vertically structured GaN-based LED device of the present invention, when a buffer layer is removed using a CLO process, penetration of the solution into a structure supporting layer is stopped by a protection layer covering the structure supporting layer so as to bring a damage-free effect on the structure supporting layer.

Brief Description of the Drawings

[17] Figs. 1 and 2 are cross-sectional views to explain a conventional fabrication method for a vertically structured GaN-based LED device; and

[18] Fig. 3 is a flow chart to explain an exemplary embodiment of a manufacturing method of a vertically structured GaN-based LED device of the present invention; and

[19] Figs. 4 to 9 are cross-sectional views at each process step as shown in Fig. 3; and

[20] Fig. 10 is a cross-sectional view of an exemplary modification of a fabrication process shown in Fig. 4.

[21] <Description of Symbols of Main Parts in Drawings>

[22] 110: sapphire substrate 115: buffer layer

[23] 120: n-type GaN layer 125: active layer

[24] 130: p-type GaN layer 135: p-type electrode

[25] 140: reflective layer 145: guide pattern

[26] 150: structure supporting layer 155: surface protection layer

[27] 160: side area protection layer

Best Mode for Carrying Out the Invention

[28] Hereinafter, in accordance with the preferred embodiments of the present invention, a fabrication method of a vertically structured GaN-based LED device will be described in detail with reference to accompanying drawings.

[29] Fig. 3 is a flow chart to explain an exemplary embodiment of a manufacturing method of a vertically structured GaN-based LED device of the present invention, and Figs. 4 to 9 are cross-sectional views at each process step as shown in Fig. 3.

[30] First, the present invention shall be described in accordance with the cross-sectional view shown in Fig. 4. In step Sl 1, a buffer layer 115 is stacked on a sapphire substrate 110. In step S 13, an n-type GaN layer 120, an active layer 125, a p-type GaN layer 130, a p-type electrode 135, and a reflective layer 140 are sequentially stacked on a buffer layer 115 forming an LED section. In step S 15, a guide pattern 120 is formed to guide growth of a structure supporting layer separately on an LED section, that is, a reflective layer 140. In step S 17, structure supporting layers 150 are formed separately on an LED section using such guide patten 120. In step S 19, a surface protection layer 155 is formed on the entire surface of a structure supporting layers 150 and a guide pattern 120.

[31] Here, as a material for a buffer layer 115, later to perform a buffering action preventing an LED section from the stress during the removal process of a sapphire substrate 110, a metal, especially chrome is preferred.

[32] And, after a photoresist is uniformly applied on a surface of a reflective layer 150, a mask having a predetermined grid-like pattern is mounted on this surface, then it is exposed to light to form a guide pattern 120 by developing either a light exposed or an unexposed area.

[33] Besides, it is desirable to form a structure supporting layer 150 at a lower level than a guide pattern 145 as shown in Fig. 4. The reason is to prevent that if structure supporting layers 150 are formed at a higher level than a guide pattern 145, structure supporting layers 150 are not separated from each other but stuck together. Moreover, by separating surface protection layers 150 formed on structure supporting layers 150 and on a guide pattern 145 from each other, it is possible to remove the layer formed on a guide pattern 145 together when a guide pattern 145 is removed later on.

[34] And, it is desirable that a structure supporting layer 150 is made of copper or aluminum or their alloy having good heat radiation characteristics for the heat occurring in an LED section.

[35] Au, Pt, or Ni are desirable as a material for a surface protection layer 155, a layer to protect the surface of a structure supporting layer 150 during partial etching of a side area of a structure supporting layer 150 by removal of a guide pattern 145 later on.

[36] Next, in step S21, a guide pattern 145 is removed using a wet etching process as shown in Fig. 5. At this time, a wet etching solution, not reacting with other structures namely a buffer layer 115, a structure supporting layer 150, and a surface protection layer 155, should be an acetone for example.

[37] Next, in step S23, as shown in Fig. 6, a portion of a side area of a structure supporting layer 150 exposed after removal of a guide pattern 145 is etched using a wet etching process. At this time, a solution to be used should be the one that is not reacting with a buffer layer 115 and a surface protection layer 155.

[38] Next, in step 25, as shown in Fig. 7, a side area protection layer 160 is applied to cover the side area of a structure supporting layer 150 that is externally exposed. At this time, a photoresist can be used to form a side area protection layer 160. In other words, a side area protection layer 160, together with a surface protection layer 155, protects a structure supporting layer 150 from a chemical reactant to be used in a CLO process to remove a sapphire substrate later on.

[39] Next, in step S27, as shown in Fig. 8, an LED structure, comprised of an LED section and a structure supporting layer, is separated into multiple LED devices using a dry etching process. It is important that only a portion of a side area protection layer 160, formed between the structure supporting layers, should be etched during this step. In other words, although step S23 can be omitted to proceed to step S25 from step S21, there is a concern that the side area of a structure supporting layer 150 might be exposed due to a complete removal of a side area protection layer 160 while performing step S27, hence, it is preferred to perform step S23 to prevent this problem. [40] Besides, since the material of a side protection layer 160 is usually a photoresist when the symbol 'A' in Fig. 8, i.e. a side protection layer 160, is partially etched, a development process after light exposure can be used. And, when the symbol 'B', i.e. an LED section and a buffer layer 115, is partially etched, a dry etching process is used.

[41] Next, in step S29, as shown in Fig. 9, a sapphire substrate 110 is separated from LED devices by removing a buffer layer 115 using a CLO process. If we describe this step in more detail, a solution used in a CLO process penetrates to the space, formed when above described step S27 is performed, by the so called "tunneling effect." Therefore, in a buffer layer 115, a chemical reaction occurs in all direction except the junction area between a sapphire substrate 110 and an n-type GaN layer 120 resulting from a CLO process, hence, a sapphire substrate 110 can be stably and easily separated from the individual LED devices. Of course, the solution used for a CLO process might damage a side area protection layer 160, but, since a structure supporting layer 150 is protected by this side area protection layer 160, at least the concern about damage can be diminished than the prior invention.

[42] Next, a residual side area protection layer 160 is removed in step S31, and a surface protection layer 155 is removed in step S33. Later on, an n-type electrode (not shown) on an externally exposed n-type GaN layer 120 is formed as a sapphire substrate 110 and a buffer layer 115 is removed.

[43] As described above, manufacturing method of a vertically structured GaN-based

LED device of the present invention is not limited to those above described exemplary embodiments, but it can be further implemented with various modifications without departing from the technical spirit and scope of the invention. For example, Fig. 10 is a cross-sectional view showing an exemplary modification of a manufacturing process shown in Fig. 4.

[44] In other words, as shown in Fig. 10, after forming a structure supporting layer 150a over entire surface of a reflective layer 140, form a surface protection layer 155 separately, then the portion corresponding to a guide pattern 145 in a structure supporting layer 150a is etched. And, after that time, the process can be performed equally as above described steps between S23 and S33.

Claims

[1] A manufacturing method of a vertically structured GaN-based LED device comprising the steps of:

(a) forming a buffer layer on a sapphire substrate to remove said sapphire substrate;

(b) forming a GaN-based LED structure including an n-type GaN layer, an active layer, and p-type GaN layer on said buffer layer formed in said step (a);

(c) forming multiple structure supporting layers on a GaN-based LED structure formed in said step (b), and forming a protection layer to cover an externally exposed area of said multiple structure supporting layers;

(d) separating said sapphire substrate and said GaN-based LED structure formed in said step (b) by removing said buffer layer using a chemical lift-off process; and

(e) removing said protection layer covering said structure supporting layer.

[2] The manufacturing method of a vertically structured GaN-based LED device of claim 1, further comprising the steps of:

(pdl) etching a portion of said protection layer preventing said multiple structure supporting layers from external exposure before proceeding to said step (d); and

(pd2) separating said GaN-based LED structure into multiple LED devices by partial etching of externally exposed said GaN-based LED structure resulting from said step (pdl), wherein said step (d) separates said multiple LED devices formed in said step (pd2) and said sapphire substrate. [3] The manufacturing method of a vertically structured GaN-based LED device of claim 1, wherein said step (c) comprises:

(cl) forming multiple structure supporting layers on GaN-based LED structure formed in said step (b);

(c2) covering the entire surface of said multiple structure supporting layers with a surface protection layer;

(c3) etching a portion of a side area of said multiple structure supporting layers after said step (c2) is performed; and

(c4) covering the entire side area of said multiple structure supporting layers with a side area protection layer after said step (c3) is performed. [4] The manufacturing method of a vertically structured GaN-based LED device of claim 3, wherein said step (cl) comprises:

(cl-1) forming a guide pattern, used to form multiple structure supporting layers separately, on a GaN-based LED structure formed in said step (b); and (cl-2) removing said guide pattern after forming multiple structure supporting layers on an LED section using said guide pattern. [5] The manufacturing method of a vertically structured GaN-based LED device of claim 4, wherein said steps (cl-2) and (c3) are performed using a wet etching process. [6] The manufacturing method of a vertically structured GaN-based LED device of claim 2, wherein said steps (pdl) and (pd2) are performed using a dry etching process.