KR101643342B1

KR101643342B1 - Sapphire substrate and method of fabricating the same

Info

Publication number: KR101643342B1
Application number: KR1020090067181A
Authority: KR
Inventors: 강진기
Original assignee: 한솔테크닉스(주)
Priority date: 2009-07-23
Filing date: 2009-07-23
Publication date: 2016-07-28
Also published as: KR20110009799A

Abstract

A method of manufacturing a high-flatness sapphire substrate by overcoming limitations of flatness by a cross-sectional polishing, and a method of manufacturing such a high-flatness sapphire substrate. A sapphire substrate manufacturing method according to the present invention comprises the steps of: polishing only the front surface of a sapphire substrate with a diamond abrasive; simultaneously polishing the front and back surfaces of the sapphire substrate using a polishing pad and a nanometer-size abrasive; And then sandblasting the back surface of the sapphire substrate, wherein the double-sided polishing step comprises: a primary two-sided polishing step using a polyurethane pad; And a secondary double-sided polishing step using a polytex pad and a pressure less than the primary two-sided polishing step. According to the present invention, by applying the double-side polishing process, it is possible to produce a sapphire substrate having a high flatness, which is difficult to realize in the conventional cross-sectional polishing process. This enables mass production of a sapphire substrate such as PSS required for high- do.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sapphire substrate,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for a semiconductor device and a manufacturing method thereof, and more particularly, to a high flatness sapphire substrate that can be used for manufacturing a high-luminance light emitting diode (LED) and a manufacturing method thereof.

The LED market has grown on the basis of low-brightness LEDs used in portable communication devices such as mobile phones, keypads for small household appliances, and backlight units for liquid crystal displays (LCDs). In recent years, as the need for high brightness and high efficiency light sources used in backlight units of large LCD such as interior lighting, exterior lighting, automobile interior and exterior, traffic lights, and electric signboards has come to the fore, the LED market is also shifting to high brightness products.

The blue or green LED except for the red of the three primary colors is made of nitride semiconducting GaN and the blue LED is able to make the white LED by covering the fluorescent material, to be. A sapphire substrate, which is an aluminum oxide single crystal, is used to grow a GaN light emitting layer of good quality into an epitaxi to manufacture blue and green LEDs. Since the quality of the sapphire substrate surface affects the quality of the LED, which is the final product, in particular, the luminance, the abrasive processing technique of the sapphire substrate is important.

The biggest problem with LEDs is low luminous efficiency. In general, the efficiency of light emission is determined by the efficiency of light generation (internal quantum efficiency), the efficiency of emitting light outside the device (external light extraction efficiency), and the efficiency of light conversion by the phosphor. In order to increase the output of the LED, it is important to improve the active layer characteristics in terms of internal quantum efficiency, but it is very important to increase the external light extraction efficiency of the actually generated light.

The biggest obstacle to emitting light to the outside of the LED is the internal total reflection due to the refractive index difference between the LED layers. Due to the refractive index difference between the LED layers, the light escaping from the interface corresponds to about 20% of the generated light. Moreover, the light that does not pass through the interface is converted into heat when it moves inside the LED, resulting in a low luminous efficiency and an increase in heat generation of the device, thereby shortening the lifetime of the LED.

In order to improve the external light extraction efficiency, a method of increasing the roughness of the p-GaN surface or the n-GaN surface, a method of roughening the surface of the substrate which is the base portion of the device or forming a minute pattern of several microns, Is used. The patterned sapphire substrate is called a patterned sapphire substrate (PSS). By using the PSS, the density of the dislocation, which is a cause of reducing the luminance during the GaN epitaxial growth, is greatly reduced, It was possible.

Such a PSS should be formed by etching a bending pattern on a sapphire substrate. Conventionally, a groove of about 5 microns is formed. If a pattern of such a size is enough, a low-cost mask aligner may be used. Flatness was not a big problem. However, in recent years, it has become necessary to form a groove of about 2 microns by using a stepper in order to form a finer and uniform groove with good reproducibility, as the size of the groove becomes smaller. Flatness, which was not considered in sapphire substrates, has become an important factor. That is, due to the unevenness of the flatness of the conventional sapphire, the problem that the yield rate of the PSS process is lowered is needed.

Most commercially available sapphire substrates are manufactured in the same process sequence as in Fig.

First, a sapphire ingot circularly machined to a diameter of the substrate is cut, or the substrate grown in a plate shape is circularly cut into a diameter size (step s1), and then a double-sided lapping process is performed to reduce the thickness deviation at the time of cutting and to obtain a desired roughness (Step s2). After the edge of the right angle is machined so as not to be sharp (step s3), one side (front side) for epitaxial polishing is polished. First, the wax is melted in the ceramic block to mount the rear surface of the substrate (step s4), and then the front surface is polished with a 2 to 6 micron diamond slurry (step s5) to remove surface roughness and stress caused by the lapping. Then, using a polishing pad and a nano-micron size abrasive, polishing is performed until the roughness Ra of the polished front surface becomes a mirror surface of 1 to 3 angstroms (step s6).

The end face polishing machine 5 shown in Fig. 2 is attached to a rotatable polishing platen 10 and a polishing platen 10, A polishing pad 12 which is rotated in accordance with the rotation of the polishing pad 12 and a polishing pad 12 which is disposed above the polishing pad 12 and fixes the substrate w such that the polishing surface of the sapphire substrate w faces the polishing pad 12, A polishing head 14 of a ceramic block which is pressed and rotated on the pad 12 and a supply portion 16 for supplying an abrasive on the polishing pad 12 during polishing.

In this polishing using the cross-sectional polishing machine 5, only one side of the substrate w is mirror-polished, and the substrate w thus subjected to the cross-section mirror machining is formed by melting the wax attached to the ceramic block and demounting it from the ceramic block Step s7), which is then washed to make the final product. However, even if the sapphire substrate manufactured by such a conventional processing step is mounted on a flat ceramic block, the badness of the back surface is badly transferred to the front surface of the substrate during polishing due to the roughness of the wrapped substrate to improve the quality of the flatness There is a fundamental limitation.

Since only the section polishing is performed, the number of revolutions of the polishing platen 10, the flatness of the polishing platen 10, the flatness of the ceramic block, etc. affect the flatness of the substrate in a complex manner. In the mounting process, factors such as the bonding temperature of the substrate, the wax and the ceramic block, the bonding speed of the substrate, and the bonding pressure affect the flatness. Therefore, it is very difficult to fabricate a substrate having a high trajectory with good reproducibility .

A problem to be solved by the present invention is to provide a method of manufacturing a high flatness sapphire substrate suitable for a PSS process by overcoming limitations of flatness by a cross-sectional polishing, and to provide such a high flatness sapphire substrate.

According to another aspect of the present invention, there is provided a method of manufacturing a sapphire substrate, comprising: polishing a front surface of a sapphire substrate with a diamond abrasive; A double-side polishing step of simultaneously polishing the front and back surfaces of the sapphire substrate using a polishing pad and a nanometer-size polishing agent; And sand blasting the back surface of the sapphire substrate after the double-sided polishing step, wherein the double-sided polishing step comprises: a primary two-sided polishing step using a polyurethane pad; And a secondary double-sided polishing step using a polytex pad with a pressure smaller than that of the primary double-sided polishing step.

According to the above method, according to the present invention, there is provided a high flatness sapphire substrate having a thickness deviation of 5 microns or less.

By applying the double-sided polishing process, it is possible to produce a sapphire substrate having a high flatness, which is difficult to realize in a conventional cross-sectional polishing process. This enables mass production of sapphire substrates such as PSS required for high brightness of LED. In addition, productivity can be maintained by applying a cross-section polished by a diamond abrasive, and a high-flatness substrate can be manufactured by applying double-side polishing using a polishing pad. And the reduction of the roughness of the backside by double-sided polishing can be overcome by introducing the process of sand blasting and heat treatment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. To fully disclose the scope of the invention, and the invention is only defined by the scope of the claims.

Example

3 is a flowchart of a method of manufacturing a substrate according to the present invention.

Referring to FIG. 3, first, a sapphire ingot circularly processed to a diameter of a substrate is cut, or the substrate grown in a plate shape is circularly cut to a diameter size (step s11). In the cutting operation, a blade with a diamond piece is used, or a piano wire called a wire saw is used, so that the surface of the cut wafer has irregularities. Then, a double-sided wrapping process is performed to reduce the thickness deviation at the time of cutting and to obtain a desired roughness (step s12). For example, a double-side wrapping machine is used to perform double-side polishing while introducing GC # 320 abrasive. Next, the corners at right angles are machined so as not to be sharp (step s13), for example, grinding is performed by a diamond wheel with a curvature of 0.3 mm.

Then, the wax is melted in the ceramic block to mount the substrate (step s14), and the step of polishing one surface (front surface) of the substrate with the diamond abrasive is performed. First, a primary diamond abrasive cross-section polishing (step s15) for polishing one side (front side) of the substrate while spraying a 6-micron diamond slurry onto a copper polishing platen on which grooves are formed is performed, Secondary diamond abrasive cross-section polishing (step s16) is performed to spray the diamond 2-micron slurry onto the abrasive platen to polish one side of the substrate in the same manner as the first polishing step (step s16) to remove the roughness and stress of the surface during lapping .

Then, the wax adhered to the ceramic block is melted and the substrate is demounted from the ceramic block (step s17). Thereafter, the two-side polishing, which can be regarded as a process unique to the present invention, is carried out. The front and back surfaces of the substrate are simultaneously processed by the double-sided polishing so that the flatness of the back surface in the cross-section polishing is not transferred to the polished surface. The flatness of the substrate can be greatly improved by such a double-sided polishing process.

The double-side polishing machine 35 shown in FIG. 4 includes a rotatable lower abrasive polishing table 30 and a lower abrasive polishing table 30, A first polishing pad 32 attached on the first polishing pad 32 and rotating in accordance with rotation of the lower polishing table 30, an upper polishing table 34 rotatably disposed above the first polishing pad 32, A second polishing pad 36 which is attached to the first polishing pad 32 so as to face the first polishing pad 32 and rotates in accordance with the rotation of the upper polishing table 34 and a second polishing pad 36 which faces the first polishing pad 32 and the second polishing pad 36 The SUS carrier 38 holds both sides of the sapphire substrate w so as to contact the pads. During the polishing process, the first polishing pad 32 and the second polishing pad 36 rotate in opposite directions to each other, and a nano- or micron-size abrasive is inserted therebetween.

First, a polyurethane polishing pad is used as the first polishing pad 32 and the second polishing pad 36, and the abrasive plates 30 and 32 are rotated in opposite directions using nano- or micron- The first polyurethane pad double-sided polishing is carried out as in step s18 and the polishing pad of the polytex series is used as the first polishing pad 32 and the second polishing pad 36, and a nano- or micron-size polishing agent is used The secondary polishing pad is subjected to double-side polishing as in step s19 of FIG. 3 while the polishing bases 30 and 32 are rotated in the opposite direction, and polished until the roughness Ra becomes a mirror surface of 1 to 3 angstroms. The polishing pressure is very high because the sapphire substrate w is thick (about 0.43 mm), the diameter is small (about 50.8 mm) and very hard (hardness 9). For example, a pressure of 100 kg is applied for the first polyurethane pad double-side polishing, and a pressure of 30 kg for the second polytype pad double-side polishing.

In this way, the mirror-finished substrate is subjected to the simultaneous processing of both sides by the double-sided polishing, so that the flatness of the back surface is not transferred to the polished surface in the single-sided polishing. As a result of the experiment, it was possible to obtain a high flatness sapphire substrate having a thickness deviation of 5 microns or less by this double-sided polishing process.

On the other hand, in the case of double-side polishing, the backside is also polished together to lower the roughness of the backside. If the backside of the product must have a uniform roughness for substrate level optical measurement, etc., The desired roughness can be obtained by using the sand blasting (step s20) process. The sand blasting can be performed by spraying an abrasive such as SiO ₂ , Al ₂ O ₃ , SiC, or B ₄ C onto the back surface of the substrate together with air at 10 atm at 5 atm. In order to release the stress on the sandblasted substrate surface, the substrates may be charged into the electric furnace and further heat treatment may be performed at 900 ° C or higher and 1400 ° C or lower (Step s21). The effect of heat treatment is insignificant at temperatures below 900 ° C and is not required up to temperatures higher than 1400 ° C. As such, sandblasting and subsequent heat treatment are optional steps.

The sapphire substrate has a very high hardness, so that when the two-side polishing is performed without polishing by the diamond abrasive, the polishing time is more than 5 times longer, and the productivity drops sharply. Therefore, in the present invention, the cross-sectional polishing by the diamond abrasive is inevitable, but the polishing using the polishing pad is replaced with the double-side polishing, thereby making it possible to mass-produce a high-flatness substrate. And the reduction of the roughness of the back surface by the double sided polishing was overcome by introducing the process of sandblasting and heat treatment, thereby completing the present invention.

Experimental Example

Comparative Example 1: Conventional level

A sample was prepared according to the flowchart shown in Fig.

First, a sapphire ingot having a diameter of 2 inches (50.8 mm) and a length of 150 mm was cut using a 0.25 mm diameter diamond wire saw so that the substrate having a crystal axis deviating from the C-axis by 0.2 degree in the m-axis direction to 0.550 mm in thickness (Step s31). At this time, the thickness deviation between the substrates was within 15 microns, and the thickness variation within the substrate was within 10 microns. This substrate was processed into a substrate having a thickness of 0.490 mm and a roughness Ra of 0.7 micron by carrying out both-side polishing for about 30 minutes while introducing a GC # 320 abrasive using a double-side wrapping machine (step s32) The deviation was 3 microns. The sharp edges were ground by a diamond wheel with a curvature of 0.3 mm (step s33). Subsequently, the substrates were charged into an electric furnace to heat the lapped substrate surface and annealed at 1200 ° C for 10 hours.

Next, in order to mirror-face one side of the substrate, sixteen substrates are mounted on a ceramic block having a diameter of 360 mm using wax (step s34), and as a primary cross-section polishing, a copper polishing platen Four ceramic blocks were charged to bring the 64 substrate surfaces bonded to the ceramic block into contact with each other. Then, the copper polishing table and the ceramic block were rotated while applying a pressure of 80 kg per ceramic block while spraying a 6-micron diamond slurry, (step s35) to make the thickness of the substrate 0.450 mm. Thereafter, while applying a pressure of 50 kg per ceramic block while spraying a 2-micron slurry of diamond on the tin polishing platen on which grooves are formed, The substrate was polished by 0.01 mm in the same manner as the polish (step s36) to make a 0.440 mm substrate. At this time, microscopic scratches of 2 to 3 microns were observed by a diamond abrasive.

(Step s37) while rotating the polishing platen and the block while applying a pressure of 100 kg per ceramic block while spraying an abrasive of Compol (manufactured by Fujimi) in a cross-sectional polishing machine (see Fig. 2) having a polyurethane polishing pad , A roughness Ra of 3 Å, and then, to complete the mirror surface of 1 to 2 Å, which is the final roughness of the product Ra, a pressure of 30 kg per ceramic block is applied again to the polishing machine with a polishing pad of Polytech series (Step s38), and a sapphire substrate having a thickness of 0.43 mm was made and demounted (step s39).

As a result of examining 64 pieces of 2 inch sapphire completed by this process, it was found that the total thickness variation (difference between the maximum and minimum values of the thickness of the substrate) and the local area divided into 5 mm × 5 mm LTV (max) of the LTV (local thickness variation), which is the TTV of the TTV, is as shown in Table 1 below. (Unit: micron) In the table, the top line represents the TTV and LTV numbers, and the numbers below it represent the number of boards with TTV or LTV corresponding to that number.

0-1 1-2 2-3 3 to 4 4 to 5 5 to 6 6 to 7 7 to 8 8 to 9 9-10 TTV 0 One 4 6 22 19 7 3 One One LTV (max) 5 11 43 3 One One 0 0 0 0

Comparative Example 2: Improvement level

After proceeding to step s37 in the same manner as in the comparative example 1, step s38 was not carried out and the ceramic block was demounted. That is, in Comparative Example 1, only the first polishing was carried out in the same manner during the polishing with the two pads. At this time, the thickness of the substrate was about 0.433.

In this double-side polishing machine (see Fig. 4), the polyurethane pad was attached to the upper polishing platen, the polytex pad was attached to the lower polishing platen, and the mirror surface of the substrate was charged downward, Respectively. At this time, 60 sheets of 64 substrates were charged into 5 SUS carriers, 12 sheets each. At this time, the pressure of the plate was 110 kg, and the thickness of the final substrate after polishing was 0.430.

The flatness of the final substrate obtained by this method was as shown in Table 2. In comparison with Comparative Example 1, both TTV and LTV (max) were slightly improved, but since the polishing amount of the substrate was small, It was difficult. (Unit: micron)

0-1 1-2 2-3 3 to 4 4 to 5 5 to 6 6 to 7 7 to 8 8 to 9 9-10 TTV 0 One 10 21 20 6 2 0 0 0 LTV (max) 6 18 22 13 One 0 0 0 0 0

Experimental Example of the Invention

From the results of the improved Comparative Example 2, it was found that when the amount of polishing was small, the effect of improving the flatness was unsatisfactory. Therefore, the pad polishing twice, that is, both the polyurethane pad polishing and the polytech pad polishing, . That is, the process flow chart as shown in Fig. 3 was followed.

However, in the case of double-side polishing, the lapping thickness was 0.500 mm, the primary diamond polishing was 0.460 mm, and the secondary diamond polishing was 0.450 mm in consideration of the fact that both sides were polished together. Twenty sheets of sixty-four substrates were charged into five SUS carriers, respectively. In the case of the polyurethane polishing, the polishing pressure of the polishing pad was 10 microns while the pressure of 350 kg was applied. In the case of the polishing of the polytex pad, the thickness of the final substrate was 0.435 mm.

Table 3 shows that, as a final result of the present embodiment, both TTV and LTV are significantly improved compared to the conventional method. Particularly, according to the above method, it can be seen that the present invention provides a high flatness sapphire substrate having a thickness deviation of 5 microns or less. Thus, it has been confirmed that the high flatness of the sapphire substrate required for increasing the brightness of the LED can be achieved by the present invention.

In the present invention, the back side is polished together by performing double side polishing. As a method of solving this, a method of rewinding the back surface was tested. However, in order to make the desired back surface roughness uniform, a minimum of 5 microns must be polished on one side, which may cause the flatness to deteriorate again. As shown in the present invention, sand blasting was experimented. The abrasive such as SiO ₂ , Al ₂ O ₃ , SiC and B ₄ C was sprayed on the backside of the substrate together with air of 10 atm at 5 atmospheres, thereby giving a roughness without reduction in thickness.

Such roughness imparts stress to the substrate to warp the substrate by about 70 microns. The warpage of such a substrate is obtained by heat-treating the substrate at a temperature of 900 占 폚 or higher, whereby stress is relieved and the warpage of the substrate is restored to its original state. (Unit: micron)

0-1 1-2 2-3 3 to 4 4 to 5 5 to 6 6 to 7 7 to 8 8 to 9 9-10 TTV 2 15 22 15 6 0 0 0 0 0 LTV (max) 22 23 14 One 0 0 0 0 0 0

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but many variations and modifications can be made by those skilled in the art within the technical scope of the present invention. Is obvious. The embodiments of the present invention are to be considered in all respects as illustrative and not restrictive and cover the scope of the invention as defined by the appended claims rather than the detailed description thereto and the equivalents of the claims and all variations within the means .

1 is a flowchart of a conventional sapphire substrate manufacturing method.

2 is a schematic view of a cross-section polisher used for substrate cross-section polishing.

4 is a schematic view of a polishing apparatus used for substrate-side-surface polishing for practicing the present invention.

5 is a flow chart of a comparative example for comparison with the present invention.

Claims

Polishing the front surface of the sapphire substrate with a diamond abrasive;

A double-side polishing step of simultaneously polishing the front and back surfaces of the sapphire substrate using a polishing pad and a nanometer-size polishing agent; And

Sandblasting the back side of the sapphire substrate after the double-side polishing step,

Wherein the double-

A primary two-sided polishing step using a polyurethane pad; And

And a second double-sided polishing step using a polytex pad with a pressure smaller than that of the primary double-side polishing step.

The method according to claim 1,

Further comprising the step of heat-treating the sapphire substrate at a temperature of 900 ° C or higher and 1400 ° C or lower after the sandblasting.

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