KR101553241B1 - Method for Recycling PSS in Sapphire Epi-wafer - Google Patents

Abstract

The present invention relates to a method of regenerating a sapphire substrate (PSS) patterned quickly and economically in an epi wafer determined to be defective before and after an epitaxial growth process in an LED manufacturing process, and more particularly to a method of regenerating a sapphire substrate (PSS) Immersing in a first etching solution containing 40 to 55% (w / w) aqueous solution of KOH as a main component in a volume ratio of 1: 0.5 to 2 by volume at 40 to 60 ° C for 4 to 8 hours; (B) Subsequently, the epi wafer is immersed in a second etching solution containing 40 to 55% (w / w) aqueous KOH solution as a main component at 50 to 70 ° C for 2 to 4 hours to obtain a patterned sapphire substrate (PSS). (C) subsequently cleaning the PSS. ≪ Desc / Clms Page number 2 >

Description

Method for Recycling PSS in Sapphire Epi Wafer {Sapphire Epi-wafer}

The present invention relates to a method for regenerating a patterned sapphire substrate (PSS) quickly and economically in an epi wafer determined to be defective before and after an epitaxial growth process in an LED manufacturing process.

LED (Light-Emitting Diode) is a kind of pn junction diode that uses electroluminescence in which monochromatic light is emitted when voltage is applied in the forward direction. That is, when the forward voltage is applied, electrons in the n-layer and holes in the p-layer are coupled to emit energy corresponding to the height difference (energy gap) between the conduction band and the valance band. Energy is emitted mainly in the form of heat or light, and when emitted in the form of light, it becomes an LED.

The LED manufacturing process is divided into ① substrate manufacturing, ② epitaxy, ③ chip fabrication, ④ packaging and module process, and very different characteristics are needed in each step.

GaAs, sapphire (Al ₂ O ₃ ), SiC, InP, GaN, or the like is used as a component of a substrate for manufacturing LEDs. In the substrate manufacturing process , a large-sized single crystal ingot is produced from these components, Slicing the substrate into a thin plate substrate according to the crystal orientation of the substrate, polishing the substrate by planarizing both sides of the substrate, and the like.

In the epitaxial growth process , an epitaxial wafer is manufactured by growing compound semiconductors on a substrate as a base material by using MOCVD (Metal Organic Chemical Vapor Deposition) equipment or the like. In the epitaxial growth process, for example, a blue LED is described. A first cladding layer (N-GaN), an active layer (InGaN) and a second cladding layer (P-GaN) are sequentially deposited on a sapphire or SiC wafer.

The chip process is a process of manufacturing epi wafers produced through epitaxial growth by precision unit processes such as photolithography, etching, metal electrode metallization, lapping / polishing, and chip scribing / breaking And then separated into individual chips having a size of 0.3 to 1 mm.

The packaging and module process is a step in which chips separated from each other in a chip process are assembled with a driving circuit and an optical device through die bonding, pre-bonding, package sealing, and the like, and are manufactured as modules and systems. At this stage, the chip acts as a protection against mechanical, environmental and electrical hazards, and requires optical design for control of light and efficient heat dissipation.

On the other hand, even if an LED having the same efficiency is fabricated, the ability to emit light to the outside differs depending on the light extraction efficiency. That is, due to the difference in refractive index between the LED and the air, a total loss of light due to total internal reflection occurs, which ultimately provides a decisive factor for reducing the light efficiency of the LED. In order to increase the light extraction efficiency, a flip chip structure, a chip shaping, a surface texturing, a patterned sapphire substrate (PSS), a photonic crystal, an anti- reflection layer) are known. The PSS improves the external quantum efficiency of the LED, and is a method of patterning the pattern on the sapphire substrate surface in a uniform pattern. The PSS significantly improves the light extraction efficiency by using the refractive index of sapphire.

According to the statistics, the cost ratio of the patterned sapphire substrate (PSS) in an LED fabricated with a sapphire substrate is about 30% (sapphire substrate itself 18%, substrate surface patterning cost 12%).

On the other hand, in the epitaxial growth process, the highest value added in the entire LED manufacturing process up to the stage before the rear processing of the chip process (before the physical deformation of the substrate) is high, but the technological difficulty is very high and the defect rate in this process is about 10% It is known. A laser lift-off method, a mechanical-chemical polishing method, a dry etching method, and the like are known as methods for regenerating such a defective epi-wafer (an intermediate product from an epi-growth step to a pre-processing step before the rear surface processing of a chip process).

Laser Lift Off (LLO) is a method originally developed for increasing the efficiency of LED light emission, in which an Eximaer laser is irradiated between a substrate and a GaN layer on the back surface of a sapphire substrate. Since the energy of the laser beam is lower than the band gap of sapphire (about 10.0 eV) and higher than the bandgap of GaN (about 3.3 eV), the laser beam is not absorbed by the sapphire substrate, And the GaN layer are heated and decomposed, thereby separating the substrate from the GaN layer. However, according to this method, expensive LLO equipment is required and high precision is required, so that it is not economical to utilize the substrate for regeneration.

The mechanical-chemical polishing method is a method of polishing and removing an epilayer of an epitaxial wafer with a polishing machine (polishing machine) while applying a polishing slurry to which a predetermined chemical substance is added. According to this method, the epi layer can be removed in a comparatively short time, but since the pattern of the PSS is simultaneously worn during the polishing process, not only the patterning operation but also the thickness of the substrate is thinned and uneven, Is very low.

The dry etching method utilizes RIE (reactive ion etching), which is a dry etching method used for wafer etching in a semiconductor manufacturing process. Plasma is generated in a vacuum container, and plasma ions are vertically incident on the substrate, And removing the layer by etching. However, this method requires a high-priced equipment based on a high-temperature vacuum container, but also causes a change in shape, such as warpage of the wafer due to a high temperature.

Part of the defective epitaxial wafers are recycled as PSS, but most of the defective epi wafers are discarded because the recovery cost is significant and the pattern of the PSS is damaged during the regeneration process.

Therefore, it is an object of the present invention to provide a defective epitaxial wafer regeneration method which does not require expensive equipment and operation costs.

It is another object of the present invention to provide a defective epitaxial wafer regeneration method which does not cause deformation or damage of the PSS substrate itself.

It is another object of the present invention to provide a defective epitaxial wafer regeneration method capable of rapidly regenerating a large number of defective epitaxial wafers.

The present invention provides a method for manufacturing a semiconductor device, comprising the steps of: (A) applying an epitaxial wafer to a first etching solution containing a solution of glycol and 40 to 55% (w / w) KOH aqueous solution in a volume ratio of 1: At a temperature of 60 占 폚 for 4 to 8 hours; (B) Subsequently, the epi wafer is immersed in a second etching solution containing 40 to 55% (w / w) aqueous KOH solution as a main component at 50 to 70 ° C for 2 to 4 hours to obtain a patterned sapphire substrate (PSS). (C) subsequently cleaning the PSS. ≪ Desc / Clms Page number 2 >

As described above, according to the present invention, the epitaxial layer is removed from the defective epitaxial wafer in a large amount by utilizing relatively inexpensive equipment, so that the sapphire substrate that can be utilized in the LED manufacturing process can be regenerated.

This makes it possible to economically recycle the PSS, which accounts for about 30% of the manufacturing cost of the LED, thereby enabling the production of less expensive LEDs.

1 is a conceptual diagram showing that an epi wafer is regenerated as a PSS by a wet process according to the present invention.
2 is a conceptual view showing the effect of forming a scratch on a surface in the course of regeneration of an epi wafer with PSS by the wet process according to the present invention.
3A and 3B are SEM photographs of a surface of an epitaxial wafer before a regeneration treatment and vertical cross-sectional SEM photographs of the present invention.
FIGS. 3c and 3d are a photograph of the surface of the epitaxial wafer, which is an intermediate step in the embodiment of the present invention, and a vertical section SEM photograph.
FIG. 3E is a photograph of the surface of the wafer having been reproduced in the embodiment of the present invention. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the appended drawings illustrate only the contents and scope of technology of the present invention, and the technical scope of the present invention is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention based on these examples.

The present invention relates to a method for regenerating an epitaxial wafer by applying a wet etching method, comprising the steps of (A) preparing an epitaxial wafer by mixing glycol and 40-55% (w / w) aqueous solution of KOH in a volume ratio of 1: 0.5-2 Immersing the first etching solution in a temperature range of 40 to 60 DEG C for 4 to 8 hours; (B) Subsequently, the epi wafer is immersed in a second etching solution containing 40 to 55% (w / w) aqueous KOH solution as a main component at 50 to 70 ° C for 2 to 4 hours to obtain a patterned sapphire substrate (PSS). (C) and then cleaning the PSS (see FIG. 1).

The effect of partially removing the uppermost layer of the epi layer by the first etching liquid treatment occurs.

When the volume ratio of the glycol and the 40-55% (w / w) KOH aqueous solution in the first etching solution was less than 1: 0.5 or more than 1: 2, the etching effect was insignificant. The solution with a KOH concentration exceeding 55% (w / w) was difficult to prepare due to the solubility of KOH, and the etching effect was insignificant when it was lower than 40% (w / w). In addition, the etching effect was insignificant when the temperature of the etching solution and the immersion time were less than the above range. If the temperature was less than the above range, the etching effect was not positively influenced in the second etching solution.

Through the second etchant treatment, the lowermost layer of the epi layer, that is, the GaN layer, is removed by etching to cause the entire epi layer to fall off from the PSS.

When the etching temperature, the immersion time and the concentration of KOH were less than the above range, the etching effect was insignificant. When the etching solution temperature was above the above range, the epilayer was already removed sufficiently.

Of course, cleaning the epi wafer with an organic solvent, alcohol, or purified water before and after step (A) may reduce the reduction in etching effects due to contamination.

A predetermined chemical may be added to the first etchant or the second etchant to increase the treatment efficiency.

In order to remove the GaN layer (the lowest layer of the epi layer) more quickly, a small groove is formed on the surface of the substrate and the substrate is dipped in the etchant, thereby etching the bottom layer N-GaN layer, It is possible to obtain an effect that P-GaN or the like on the difficult N-GaN layer is separated. For this, it is preferable to form fine grooves in the epi layer of the epitaxial wafer not deeper than the epilayer thickness before the step (A) by using a sand blast, a water jet, a laser light source or the like (see FIG.

Meanwhile, in the present invention, the epitaxial wafer immersed in the first etching solution and the second etching solution is chemically reacted at the interface with the etching solution. Therefore, in order to induce an effective chemical reaction, it is preferable to make new etching liquid continuously contact with the surface (interface) of the epi wafer. For this purpose, it is preferable that the epi layer of the epi wafer and the first etchant or the second etchant move relatively in the step (A) or (B). For example, it is preferable that a plurality of epitaxial wafers are vertically or horizontally stacked on a reaction vessel at a predetermined interval, and the first etchant or the second etchant circulates in a vertical or horizontal direction.

Experiments were carried out on 4 - inch epi wafers subjected to epitaxial growth process. A photograph of the surface of the epitaxial wafer before treatment (3400 times magnification) and a SEM photograph of the vertical section were attached to FIGS. 3A and 3B. As shown in the figure, an epi layer of about 6.43 mu m is formed on the sapphire substrate, and the pattern formed on the sapphire substrate through the epi layer is blurred.

The epi wafer was washed with purified water and then immersed in a first etching solution consisting of glycol and a 50% (w / w) KOH aqueous solution at a volume ratio of 1: 1 at 50 ° C for 6 hours, followed by washing with purified water. Subsequently, the epi wafer was immersed in a second etching solution consisting of 50% (w / w) KOH aqueous solution at 60 ° C.

One hour after immersion, one of the epi wafers was taken out and the surface and vertical cross-sections were observed with SEM (see Figs. 3c and 3d, respectively). As shown in the photograph, the GaN layer partially remains on the surface, but most of the sapphire substrate is exposed. In addition, when the cross section of the portion where the epi layer is left appears to be about 1.2 탆 (corresponding to the highest p-GaN layer which is the most problematic in the GaN layer), the epi layer is not removed, but between the epi layer and the sapphire substrate, It can be seen that the epi layer is floating in the air. This shows that not only the surface of the epilayer is removed by the treatment according to the present invention but also the epilayer layer is removed in such a manner that the epilayer layer is separated by forming a gap between the epilayer and the sapphire substrate.

As a result of repeated experiments, it was confirmed that the epilayer can be completely removed by immersing in the second etching solution for 3 hours under the above conditions. A surface photograph (3400 times magnification) of the wafer thus completed is attached to Fig. 3E.

As can be seen from the photograph, only the epi layer on the sapphire substrate PSS patterned by the above process is completely removed, and the pattern of the sapphire substrate is not damaged at all, so that a complete PSS is obtained in which the 'pattern reformation' procedure is not necessary Respectively.

Claims (6)

(A) immersing an epi wafer in a first etching solution consisting of glycol and 40 to 55% (w / w) KOH aqueous solution at a volume ratio of 1: 0.5 to 2 by volume at a temperature of 40 to 60 DEG C for 4 to 8 hours;
(B) Subsequently, the epi wafer is dipped in a 40 to 55% (w / w) aqueous KOH solution at 50 to 70 ° C for 2 to 4 hours to obtain a patterned sapphire substrate (PSS).
(C) subsequently cleaning the PSS;
Gt; PSS < / RTI > in an epi wafer.
The method according to claim 1,
Prior to the step (A)
And forming fine grooves in the epi layer of the epi wafer not deeper than the epi layer thickness.
3. The method of claim 2,
Wherein the fine grooves are formed by a sand blast, a water jet, or a laser light source.
4. The method according to any one of claims 1 to 3,
Before or after the step (A)
Wherein the epi wafer is washed with an organic solvent, alcohol, or purified water.
4. The method according to any one of claims 1 to 3,
Wherein the epi layer of the epi wafer and the first etchant or the second etchant migrate relatively in the step (A) or (B).
6. The method of claim 5,
Characterized in that a plurality of epi wafers are vertically or horizontally stacked in a reaction vessel spaced apart by a predetermined distance and the first etchant or the second etchant circulates in a vertical or horizontal direction. .

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