WO2008147105A2

WO2008147105A2 - Manufacturing method of vertically structured gan led device

Info

Publication number: WO2008147105A2
Application number: PCT/KR2008/002986
Authority: WO
Inventors: Hyun Chul Ko; Meoung-Whan Cho; Pil Guk Jang; Byung Il Cho
Original assignee: Wavesquare Inc.
Priority date: 2007-05-30
Filing date: 2008-05-28
Publication date: 2008-12-04
Also published as: WO2008147105A3; KR100858322B1

Abstract

The present invention relates to a manufacturing method of a vertically structured GaN-based LED, especially to a manufacturing method of a vertically structured GaN-based LED device having improved yield and device characteristics by minimizing the physical stress applied to an LED device when performing a separation process of a sapphire substrate. And, a manufacturing method of a vertically structured GaN LED of the present invention is comprised of the steps of: (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 an electrode layer and a structure supporting layer sequentially on the multiple LED devices formed in the above step (b); and (d) separating the sapphire substrate from the multiple LED devices formed in the above step (b) by removing the buffer layer using a CLO process.

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 having improved yield and device characteristics by minimizing the physical stress applied to an LED device 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 las ing 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 2Q an active layer 3Q a p-type GaN layer 4Q 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 2Q 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 electrodes 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 electrodes 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] For this reason, as a method to solve above mentioned problems, 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'). Herein major elements of the cited invention are, as described in claim 1, "A manufacturing method of a vertically structured GaN-based LED device comprising the steps of: (a) forming an isolation pattern defining the forming area of a unit LED having pre-determined size on a sapphire substrate; (b) forming a light emitting structure having a sequentially stacked structure of an n-type GaN-based semiconductor layer, an active layer, and a p-type GaN-based semiconductor layer on a sapphire substrate excluding areas where an isolation pattern is formed; (c) separation of a light emitting structure into unit LEDs having pre-determined size by removing the isolation pattern; (d) forming a p-type electrode individually on a separated light emitting structure; (e) forming a structure supporting layer on a p-type electrode; (f) exposing a GaN-based semiconductor layer by removing the substrate; and (g) forming an n-type electrode on each exposed n-type GaN-based semiconductor layer," and especially above described step (f) is performed by an LLO process.

[7] Besides, although it is not mentioned in the detailed description of the cited invention, in general, step (d) is accomplished after applying photoresist on the entire light emitting structure that is separated in step (c), then place a photomask, that is patterned to mask slots formed in-between the light emitting structures in step (c) on the photoresist-coated light emitting structure, then the mask pattern is illuminated for a pre-determined time, and the light-exposed photoresist on the light emitting structure is developed, then a p-type electrode is formed on the developed area through a series of mask pattern process that removes un-exposed photoresist using such as an acetone.

[8] But, according to the above described cited invention, firstly, 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.

[9] Secondly, as described above, a p-type electrode is formed through many complicated steps by a mask pattern process, therefore there is a drawback like a lower productivity due to a generally longer fabrication process. 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 that can remove a sapphire substrate 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.

[11] Yet another objective of the present invention is to provide a fabrication method for a vertically structured GaN-based LED device that can reduce overall production time of an LED device by eliminating another mask pattern process required for forming an electrode layer and a structure supporting layer because the stacking of an electrode layer and a structure supporting layer on an LED structure becomes easy when it is filled with a sacrificial layer formed inside the slots that separates an LED structure into each unit LED devices. Technical Solution

[12] To achieve above described objectives, a manufacturing method of a vertically structured GaN 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 an electrode layer and a structure supporting layer sequentially on the multiple LED devices formed in the above step (b); and (d) separating the sapphire substrate from the multiple LED devices formed in the above step (b) by removing the buffer layer using a CLO process.

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

(cl) forming a sacrificial layer between the multiple LED devices formed in the above step (b); and (c2) stacking an electrode layer and a structure supporting layer on the multiple LED devices formed in the above step (b) and the sacrificial layer formed in step (cl).

[14] Besides, in the above step (d), it is recommended that a sapphire substrate is separated from the multiple LED devices formed in the above step (b) by removing a buffer layer using a CLO process after removing a sacrificial layer formed in the above step (cl).

[15] Also, it is recommended that the above step (b) is comprised of steps including; (bl) forming a guide pattern to be used for isolation of multiple LED devices that is grown on a buffer layer formed in the above step (a); and (b2) forming multiple isolated LED devices from a GaN-based LED structure that includes an n-type GaN layer, an active layer, and a p-type GaN layer on the above buffer layer using a guide pattern formed in the above step (bl).

[16] Moreover, in step (cl), it is recommended that a photoresist is applied between the above multiple LED devices formed in the above step (b) followed by a light exposure process, then the photoresist on the above multiple LED devices is removed through a development process. At this time, it is desirable to add a surfactant in a developer to be used in the above development process.

[17] And, it is recommended to adjust the viscosity of the above photoresist or the speed of the above development process so as to form a step between the multiple LED devices formed in the above step (b) and the buffer layer formed in the above step (cl).

Advantageous Effects

[18] According to the manufacturing method of vertically structured GaN LED device of the present invention, since a sapphire substrate can be removed more quickly and safely from the LED structure without allowing physical impact to the LED structure, the original LED device characteristics can be achieved resulting in enhancement effects in yield and reliability.

[19] Moreover, as it is described above, since an electrode layer and a structure supporting layer can be easily stacked on an LED structure without a complicated multi-step process such as a conventional mask pattern process, a reduction effect on manufacturing time can be obtained. Brief Description of the Drawings

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

[21] Fig. 3 through 9 are cross-sectional views to explain an exemplary embodiment of a fabrication method for a vertically structured GaN-based LED device of the present invention.

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

[23] 110: sapphire substrate 115: buffer layer

[24] 120: guide pattern 125: n-type GaN layer

[25] 130: active layer 135: p-type GaN layer

[26] 140: sacrificial layer 145: p-type electrode

[27] 150: reflective layer 155: structure supporting layer

[28] 165: slot

Best Mode for Carrying Out the Invention

[29] 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.

[30] Fig. 3 through 9 are cross-sectional views of each process step to explain a fabrication method of a vertically structured GaN-based LED device in accordance with an exemplary embodiment of the present invention.

[31] First, a buffer layer 115 is stacked on a sapphire substrate 110 as described in Fig. 3, and then a guide pattern 120 is formed on this buffer layer 115 to guide growth of isolated LED devices. In here, a metal is preferred as a buffer layer 115 material, and later this will perform a buffering action preventing the LED structure, to be described later, from the stress during the removal process of the sapphire substrate 110. Besides, a silicon oxide layer is formed on a buffer layer 115, and a photoresist is uniformly applied on the silicon oxide layer above which a mask having a pre-determined grating-like pattern is positioned, and followed by a light exposure, thereby a guide pattern 120 can be formed by a method that develops area where light is exposed or unexposed. Next, a GaN-based LED structure having an n-type GaN layer 125, an active layer 13Q and a p-type GaN layer 135 is separately grown on the buffer layer 115 by this guide pattern 120.

[32] Meanwhile, a separation process of an LED structure reviewed herein before into each unit LED devices can be accomplished through a pre-determined etching process such as dry etching after a buffer layer 115, an n-type GaN layer 125, an active layer 13Q and a p-type GaN layer 135 are formed sequentially on a sapphire substrate 100 as shown in Fig. 4. But, as disclosed in the cited invention, to minimize the physical stress applied to an LED device by etching process, it is more desirable to grow an LED device separately from the beginning as shown in Fig. 3.

[33] Next, a sacrificial layer 140 is formed using a photoresist in a slot 165 that is formed between the LED devices as shown in Fig. 5. In here, the main function of a sacrificial layer 14Q to be removed before removing a buffer layer 115, is to smoothen the forming of an electrode and a structure supporting layer and a CLO process to be described later.

[34] Besides, a photoresist 140a is completely filled inside of a slot 165 and uniformly applied over a p-type GaN layer 135 followed by an exposure process, and a sacrificial layer 140 can be formed by removing the photoresist on a p-type GaN layer 135 through a development process as shown in Fig. 6. In here, Fig. 7 is a plan view to observe a sacrificial layer 140 to be filled inside of a slot 165 from a different angle, and Fig. 6 is a cross-sectional view taken along the line A-A.

[35] At this moment, it is desirable to have a slight step between a sacrificial layer 140 and a GaN layer 135, to allow such a step, the thickness of a photoresist 140a, that is applied over a p-type GaN layer 135, is important and the development speed of the photoresist should be adjusted properly. Especially, viscosity is the most influential factor for the photoresist thickness, although the photoresist thickness becomes thinner as it becomes less viscous, but the flatness of the sacrificial layer 140 gets worse after a photolithography process. On the other hand, although the flatness becomes better as it becomes more viscous, it will be difficult to remove residual photoresist using a photolithography process due to the thicker photoresist, not to mention the step, to be applied. Meanwhile, it is desirable that a sacrificial layer 140 is made of a polymer- based photoresist which contains a photoactive compound (PAC) having a good photo response or a thermal active compound (TAC) having a good thermal response, besides, it can be made of a silicon dioxide (SiO 2 ), a silicon nitride (SiN) or a benzo- cjclo-butene (BCB). Moreover, it will be more effective in removing a residual photoresist if a surfactant is added to a developer used for a development process.

[36] Next, a p-type electrode 145, a reflective layer 15Q and a structure supporting layer

155 are stacked uniformly on a p-type GaN layer 135 and a sacrificial layer 140 in a sequential manner as shown in Fig. 8, hence a conventional mask pattern process is no longer required. In here, a structure supporting layer 155 is made of a metal and is used perform a device shape maintaining function to protect from the possible damages caused by an external shock during a fabrication and final packaging process of an LED device.

[37] On the other hand, although a structure supporting layer 155 is to be formed all over the reflective layer 150 in Fig. 8, it also can be formed over each LED device individually. In this case, a forming method for a structure supporting layer is as follows: a metal mask that is fabricated using a pre-determined pattern is mounted on a reflective layer 15Q and a solder paste is applied on the mounted metal mask, then the mounted metal mask is removed, and a heat treatment is performed for the solder paste patterned by the metal mask. In other words, after such heat treatment process is finished, a convex-shaped structure supporting layer is completed adhering the reflective layer 150 to the above solder paste while it is solidified from the melt. At this time, as a solder paste to be used for forming a structure supporting layer, solders made of Au-Sn, Sn-Sb, Sn-Ag, Sn-Cu, Bi-Sb, Sn-Cu-Sb, Sn-Bi, Sn-Ag-Cu, Sn- Ag-Cu-Bi, Sn-Ag-Cu-In, Sn-Ag-Bi, Sn-Ag-Bi-In, Sn-Zn-In, Sn-Zn-Bi, Sn-Ag-Cu-Sb, In-Ga, Sn-In-Ga, Sn-Pb, Sn-Pb-Ag, or Sn-Pb-Bi and its alloy can be used.

[38] Besides, for a structure supporting layer using said solder paste having a thickness of less than 10/M, it is difficult to have a shape maintaining function, and a short might happen between the LED structure and other conductive material possibly formed above. On the other hand, if the thickness becomes more than 200/M, the size of the LED device becomes too large. Hence, a desirable thickness of a structure supporting layer 155 is within the range of 10/M to 200/M.

[39] Finally, a vertically structured GaN LED device of present invention is manufactured as shown in Fig. 9, by performing a removal process for a sacrificial layer 14Q a guide pattern 12Q a buffer layer 115, and a sapphire layer 110.

[40] For this process, first, a sacrificial layer 140 is removed using a solution such as an acetone etc. At this time, a guide pattern 12Q not to mention the sacrificial layer 14Q can be easily removed using a buffered oxide etchant (BOE) that reacts with an insulating material because it is an insulating material not a semiconductor material like other parts. As shown in Fig. 7, a sacrificial layer is removed as the solution is soaked into the side of an LED structure.

[41] Next, a sapphire substrate 110 is separated from an LED device by removing a buffer layer 115 using a CLO process, at this time a CLO solution, used for the CLO process, is soaked into the slot 165, a space formed where a sacrificial layer 140 is removed by so-called tunneling effect. Consequently, a chemical reaction by a CLO takes place in a buffer layer 115 all over the direction except the joint area with a sapphire substrate 1 IQ so a sapphire substrate 110 is separated more quickly and stably from an LED structure than a conventional manufacturing method where an LED structure is formed directly on a sapphire substrate 110. Then, an n-type electrode (no drawing) is formed on n-type GaN layer 125, i.e. on each LED device, that is externally exposed through a removal process of a sapphire substrate 110. [42] 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.

Claims

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

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

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

(c) forming an electrode layer and a structure supporting layer sequentially on said multiple LED devices formed in said step (b); and

(d) separation of said sapphire substrate from said multiple LED devices formed in said step (b) by removing said buffer layer using a chemical lift-off (CLO) process.

[2] The manufacturing method of a vertically structured GaN-based LED device of claim 1, wherein said step (c) comprises:

(cl) forming a sacrificial layer between said multiple LED devices formed in said step (b); and

(c2) stacking an electrode layer and a structure supporting layer on said multiple LED devices formed in said step (b) and said sacrificial layer formed in said step (cl).

[3] The manufacturing method of a vertically structured GaN-based LED device of claim 2, wherein said step (d) is (d) separating said sapphire substrate from said multiple LED devices formed in said step (b) by removing said buffer layer using said chemical lift-off process after removing said sacrificial layer formed in said step (cl).

[4] The manufacturing method of a vertically structured GaN-based LED device of claim 3, wherein said step (b) comprises:

(bl) forming a guide pattern used for growing said multiple LED devices separately on said buffer layer formed in said step (a); and (b2) growing said GaN-based LED structure having an n-type GaN layer, an active layer, and a p-type GaN layer to form said multiple LED devices separately on said buffer layer using said guide pattern formed in said step (bl).

[5] The manufacturing method of a vertically structured GaN-based LED device of claim 4, wherein said step (cl) is removing said photoresist from said multiple LED devices through a development process after applying a photoresist between said multiple LED devices formed in said step (b) and performing a light exposure process. [6] The manufacturing method of a vertically structured GaN-based LED device of claim 5, wherein the step of adding a surfactant in a developer to be used in said development process. [7] The manufacturing method of a vertically structured GaN-based LED device of claim § wherein the step of adjusting the viscosity of said photoresist so as to have a step between said multiple LED devices formed in said step (b) and said sacrificial layer formed in said step (cl). [8] The manufacturing method of a vertically structured GaN-based LED device of claim 7, wherein the step of adjusting the speed of said development process so as to have a step between said multiple LED devices formed in said step (b) and said sacrificial layer formed in said step (cl).