US20110168670A1

US20110168670A1 - Patterned Sapphire Substrate Manufacturing Method

Info

Publication number: US20110168670A1
Application number: US12/687,510
Authority: US
Inventors: Yew-Chung Sermon Wu; Chi-Hao Cheng; Bo-Wen Lin; Wen-Ching Hsu; Szu-Hua Ho
Original assignee: Sino American Silicon Products Inc
Current assignee: Sino American Silicon Products Inc
Priority date: 2010-01-14
Filing date: 2010-01-14
Publication date: 2011-07-14

Abstract

A patterned sapphire substrate manufacturing method uses two-section dip etching procedure to improve the lateral etching rate at each etching position, so as to produce a concave-convex pattern composed of a plurality of triangular pyramid structures protruded from a surface onto an upper surface of a sapphire substrate, such that less planar area of the sapphire substrate surface will remain, and a mixed solution of sulfuric acid and phosphoric acid is used in a first dip etching step, and pure phosphoric acid or a mixed solution of sulfuric acid and phosphoric acid is used in a second dip etching step for etching the sapphire substrate to control the inclination of each triangular pyramid structure precisely, and providing a better light extraction rate for later manufactured light emitting diodes.

Description

BACKGROUND OF THE INVENTION

(a) Field of the Invention
The present invention relates to a method of patternizing a sapphire substrate surface, and more particularly to an etching method of producing concave-convex patterns onto a sapphire substrate surface effectively up to the manufacturing quality.
(b) Description of the Related Art
In general, a light emitting diode comprises a substrate, a first semiconductor layer, an electrode, a light emitting layer, a second semiconductor layer, an ohmic contact layer, and another electrode, wherein the first semiconductor layer, light emitting layer, second semiconductor layer, ohmic contact layer and electrodes are installed sequentially on the substrate, and the light emitting layer is just covered onto a portion of the first semiconductor layer, and the electrodes are installed onto the first semiconductor layer not covered by the light emitting layer.
Sapphire or silicon carbide (SiC) is usually used as a substrate for performing a direct epitaxial growth of a first semiconductor layer on the substrate. Since the epitaxial growing surface of the substrate is in a planar shape, its misalignment defect is extended to quantum wells and the crystalline quality is affected when the epitaxy is performed directly on the plane. Such result only affects the yield rate of the fabricated devices, but also reduces the light emitting efficiency and the electron mobility, and fails to produce light emitting diodes with a higher light emitting efficiency.
Therefore, roughening an epitaxial substrate surface is considered as one of the effective ways of improving the light emitting efficiency of the light emitting diode, and a light emitting device having a surface texturing substrate as disclosed in U.S. Pat. No. 6,091,085 comprises a sapphire substrate, and a rough surface composed of a plurality of protrusions and a plurality of recessions randomly formed on a contact surface of the sapphire substrate with a semiconductor layer by a mechanical polishing method or an ion etching method, so as to improve the light extraction efficiency.
Although the aforementioned method can improve the light extraction efficiency by roughening the sapphire substrate surface, the sapphire substrate surface is damaged easily due to a composition change and a lattice distortion occurred at the sapphire substrate surface and caused by ion bombardments occurred during the roughening process. Furthermore, some mask materials or reacting ions are sputtered and subsided into a certain depth from the substrate surface during the process, so that the quality of epitaxial layer formed at a later stage will be affected. Similarly, the lattice structure of the sapphire substrate surface is damaged in the mechanical polishing process, and thus the quality of semiconductor layer grown at a later stage will be affected, and the internal quantum efficiency will be lowered.
Thereafter, a dry etching method and a wet etching method for producing a concave-convex pattern on a sapphire substrate surface without damaging a lattice structure of the sapphire substrate surface were disclosed. In similar etching methods, a photosensitive material (or photoresist) is coated onto a sapphire substrate surface first, and then a mask is placed onto the sapphire substrate, wherein the mask has a pattern corresponding to the concave-convex pattern, and then an exposure procedure is carried out for performing a selective light sensing to the light sensitive material, such that the pattern on the mask is transferred onto the sapphire substrate. After the exposure procedure is completed, a photolithography is performed, so that the photoresist obtains a same or complementary pattern of the mask pattern, and finally an etching reaction is performed to produce an expected pattern on the sapphire substrate surface.
Although the principle of using an etching reaction to produce an expected concave-convex pattern on a sapphire substrate surface is well known, there are many parameters affecting the quality of the concave-convex pattern finally formed onto the sapphire substrate surface, and these parameters include the photoresist material, mask pattern ratio, exposure time, selection of chemical solution for dipping the sapphire substrate, composition proportion of chemical solution, dipping temperature, dipping time, and even frequency of dipping in the chemical solution, etc.
Therefore, we are unable to predict necessary conditions from a single parameter condition during the process of perceiving the patterned sapphire substrate manufacturing method, but we can do the evaluations indirectly in the complicated manufacturing process to learn the necessary conditions. It is the best measure to explore possible characteristics by continuously and gradually varying the parameter conditions of similar nature.
The inventor of the present invention based on years of experience in the related industry to conduct extensive researches and experiments, and finally invented a patterned sapphire substrate manufacturing method to overcome the shortcomings of the prior art.

SUMMARY OF THE INVENTION

Therefore, it is a primary objective of the present invention to overcome the aforementioned shortcoming and deficiency of the prior art by providing a patterned sapphire substrate manufacturing method for controlling the manufacturing quality of producing a concave-convex pattern onto a sapphire substrate surface effectively.
To achieve the aforementioned objective, the present invention uses a wet etching process to effectively produce a concave-convex pattern on a sapphire substrate surface during a manufacturing process. Since the temperature of the etching process keeps decreasing, and the etching rate tends to become slower to affect the angle, and thus a two-section dip etching procedure is adopted to improve the lateral etching rate at each etching position, so as to produce a concave-convex pattern having a plurality of triangular pyramid structures protruded from the sapphire substrate upper surface, such that a smaller planar area of the sapphire substrate surface will remain, and it helps improving the yield rate of producing devices on the surface of the sapphire substrate at later processes.
A mixed solution of sulfuric acid and phosphoric acid is used in the first dip etching step, and a pure phosphoric acid or a mixed solution of sulfuric acid and phosphoric acid is used in the second dip etching step for etching the sapphire substrate to control the inclination of each triangular pyramid structure precisely, such that the light emitting diode manufactured at a later process can obtain a better light extraction rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a sapphire substrate of the present invention;

FIG. 2 is a cross-sectional view of an etching barrier coated onto an upper surface of a sapphire substrate in accordance with the present invention;

FIG. 3 is a cross-sectional view of a photoresist coated onto an etching barrier together with a mask for performing a yellow light lithography process in accordance with the present invention;

FIG. 4 is a cross-sectional view of a photoresist used for completing a yellow light lithography process in accordance with the present invention;

FIG. 5 is a cross-sectional view of a structure after a photoresist is removed in accordance with the present invention;

FIG. 6 is a cross-sectional view of producing a plurality of triangular pyramid frusta on a sapphire substrate after a first etch takes place in accordance with the present invention; and

FIG. 7 is a cross-sectional view of producing a plurality of whole triangular pyramids on a sapphire substrate after a second etch takes place in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical characteristics of the present invention will become apparent with the detailed description of the preferred embodiments and the illustration of the related drawings as follows.
The present invention provides an etching method with a manufacturing quality capable of enhancing the manufacturing production capability to effectively produce a concave-convex pattern on a sapphire substrate surface and controlling the concave-convex pattern produced on the sapphire substrate surface. A chemical wet etching method is used for etching the sapphire substrate into a specific concave-convex pattern, wherein the specific concave-convex pattern is composed of a plurality of whole triangular pyramid structures protruded from the surface, and a two-section etching procedure is adopted, and the effect of different chemical solutions to different etching rates of each specific crystal face of the sapphire is used for controlling the angle of the triangular pyramid structures of the patterned sapphire substrate.
With reference to FIGS. 1 to 7 for a patterned sapphire substrate manufacturing method in accordance with the present invention, the patterned sapphire substrate manufacturing method comprises the following steps:
(a) Prepare a sapphire substrate 10 as shown in FIG. 1, wherein the sapphire substrate 10 has an upper surface 11 with a crystal orientation (0001). In other words, a C-plane sapphire substrate 10 is prepared first.
(b) Coat an etching barrier 12 as shown in FIG. 2 onto the upper surface 11 of the sapphire substrate 10, wherein the etching barrier 12 is made of silicon oxide, and the etching barrier 12 is formed onto the upper surface 11 of the sapphire substrate 10 by a chemical vapor deposition (CVD) process or a sputtering process in accordance with a preferred embodiment.
(c) Prepare a mask 20 as shown in FIG. 3, wherein the mask 20 has a plurality of square patterns arranged with a predetermined interval apart from each other.
(d) Coat a layer of photoresist 13 as shown in FIG. 3 onto the etching barrier 12, and perform a yellow light lithography process to transfer a pattern of the mask 20 onto the photoresist 13.
(e) Remove the exposed area of the etching barrier 12 which is not covered by the photoresist 13 as shown in FIG. 4, such that the portion not covered by the etching barrier 12 is exposed from the upper surface 11 of the sapphire substrate 10 (which is also the target of the etching process), wherein a buffer oxide etching solution (BOE) is used for removing the exposed etching barrier 12 in the preferred embodiment.
(f) Remove the photoresist on the etching barrier 12 as shown in FIG. 5, wherein the photoresist is removed by dipping the photoresist into an acetone solution.
(g) Perform a first etch, wherein the first etching solution is used for etching an exposed portion of the upper surface 11 of the sapphire substrate 10 which is not covered by the etching barrier 12 as shown in FIG. 6, such that the plurality of triangular pyramid frustum structures 111 are formed onto the upper surface 11 of the sapphire substrate 10, and the etching barrier 12 is coated onto a flat top of each triangular pyramid frustum structures 111.
(h) Perform a second etch, wherein the second etching solution is used for etching an exposed portion of the upper surface 11 of the sapphire substrate 10 which is not covered by the etching barrier 12 as shown in FIG. 7, such that the plurality of triangular pyramid frustum structures are formed into the whole triangular pyramid structure 112, and the etching barrier 12 is removed at the same time, or the etching barrier 12 is removed before the second etch as described in step (h) takes place, such that the whole triangular pyramid structure can be formed.
In a preferred embodiment, the first etching solution used for the first etch is a mixed solution of sulfuric acid and phosphoric acid. In the mixed solution, the ratio of sulfuric acid and phosphoric acid is 3:1. In addition, the first etch is preferably conducted at a temperature of 270° C. The second etching solution used for the second etch is a pure phosphoric acid, and the second etch is preferably conducted at a temperature of 270° C.
In another preferred embodiment, the first etching solution used for the first etch is a mixed solution of sulfuric acid and phosphoric acid, and the ratio of sulfuric acid and phosphoric acid in the mixed solution is 5:1. In addition, the first etch is preferably conducted at a temperature range between 150° C. and 350° C. The second etching solution used for the second etch is a mixed solution of sulfuric acid and phosphoric acid, and the ratio of sulfuric acid and phosphoric acid in the mixed solution is 5:1,and the second etch is preferably conducted at a temperature range between 150° C. and 350° C.
If different parameter conditions of the aforementioned preferred embodiments are used for completing the first etch, there will be some places on the etching barrier 12 not etched by the first etching solution, such that an original C-plane sapphire substrate 10 will remain. Since the etching solution has a slower etching rate on the r-plane of the sapphire substrate 10, therefore there will be three inclined r-planes in three different orientations remained at the periphery of an area covered by the etching barrier 12, after the sapphire substrate (which is also an exposed portion of the upper surface 11) not protected by the etching barrier 12 is etched.
After the etching process by the first etching solution takes place, a plurality of triangular pyramid frustum structures 111 as shown in FIG. 6 will be formed on the upper surface 11 of the sapphire substrate 10, wherein the triangular pyramid frustum structures 111 have a first crystal face with an orientation (1012), a second crystal face with an orientation (0112) and a third crystal face with an orientation (1102), wherein the three crystal faces are the aforementioned three inclined r-planes.
The second etching solution has a slower etching rate on the C-plane of the sapphire substrate 10, and thus the aforementioned triangular pyramid frustum structures 101 will be formed into the whole triangular pyramid structure 112 as shown in FIG. 7 after the etching process by the second etching solution takes place. Here, the “whole triangular pyramid structure” is defined with respect to the triangular pyramid frustum structure. Even there are minor flaws in the triangular pyramid structure formed after the etching process performed by the second etching solution, such triangular pyramid structure is still considered as the whole triangular pyramid structure 112 defined by the present invention.
In the whole triangular pyramid structure formed on the upper surface of the sapphire substrate by the patterned sapphire substrate manufacturing method in accordance with the present invention, the second etching solution is used for the etching and formation, wherein the included angle between the inclined surface and the horizontal surface is equal to 37 degrees. Since the lateral etching rate of the second etching solution is faster, the inclination of the inclined plane of the triangular pyramid gone through etches with different time durations can be controlled. Particularly, optoelectronic semiconductor devices such as light emitting diodes can be manufactured by using the patterned sapphire substrate of the present invention. The patterned sapphire substrate can effectively reduce the density of internal defectives (such as dislocation) occurred during the epitaxial process of the light emitting diode to enhance internal quantum efficiency and light extraction rate of the light emitting diode.
In summation of the description above, the present invention can improve the epitaxial quality of an optoelectronic semiconductor device to enhance the optoelectric properties of the optoelectronic semiconductor device when the patterned sapphire substrate of the present invention is applied for manufacturing the optoelectronic semiconductor device, and the present invention also complies with the patent application requirements, and thus the invention is duly filed for patent application.
While the invention has been described by device of specific embodiments, numerous modifications and variations could be made thereto by those generally skilled in the art without departing from the scope and spirit of the invention set forth in the claims.

Claims

1. A patterned sapphire substrate manufacturing method, and the sapphire substrate having an upper surface with a crystal orientation (0001), and the method comprising the steps of:

(a) selectively forming an etching barrier onto the upper surface of the sapphire substrate, such that a portion of the upper surface is exposed;

(b) using a first etching solution to etch the exposed portion of the upper surface of the sapphire substrate, such that a plurality of triangular pyramid frustum structures are formed onto the upper surface of the sapphire substrate, wherein each triangular pyramid structure of the plurality of triangular pyramid frustum structures has a first crystal face with an orientation (1012), a second crystal face with an orientation (0112), and a third crystal face with an orientation (1102), and the first etching solution is a mixed solution of sulfuric acid and phosphoric acid used for performing a first etch, and the ratio of the sulfuric acid and the phosphoric acid is 3:1;

(c) using the first etching solution to etch the exposed portion on the upper surface of the sapphire substrate, such that the plurality of triangular pyramid frustum structures are formed into the whole triangular pyramid structures, and the second etching solution is pure phosphoric acid.

2. The patterned sapphire substrate manufacturing method of claim 1, wherein the first etch is preferably performed at a temperature of 270° C.

3. The patterned sapphire substrate manufacturing method of claim 1, wherein the second etch is preferably performed at a temperature of 270° C.

4. The patterned sapphire substrate manufacturing method of claim 1, wherein the etching barrier is formed by silicon oxide.

5. The patterned sapphire substrate manufacturing method of claim 1, wherein the etching barrier is formed onto the upper surface of the sapphire substrate by a chemical vapor deposition process or a sputtering process.

6. A patterned sapphire substrate manufacturing method, and the sapphire substrate having an upper surface with a crystal orientation (0001), and the method comprising the steps of:

(b) using a first etching solution to etch the exposed portion of the upper surface of the sapphire substrate, such that a plurality of triangular pyramid frustum structures are formed onto the upper surface of the sapphire substrate, wherein each triangular pyramid structure of the plurality of triangular pyramid frustum structures has a first crystal face with an orientation (1012), a second crystal face with an orientation (0112), and a third crystal face with an orientation (1102), and the first etching solution is a mixed solution of sulfuric acid and phosphoric acid used for performing a first etch, and the ratio of the sulfuric acid and the phosphoric acid is 5:1;

(c) using the first etching solution to etch the exposed portion on the upper surface of the sapphire substrate, such that the plurality of triangular pyramid frustum structures are formed into the whole triangular pyramid structures, and the second etching solution is a mixed solution of sulfuric acid and phosphoric acid, and the ratio of the sulfuric acid and the phosphoric acid is 5:1.

7. The patterned sapphire substrate manufacturing method of claim 6, wherein the etching barrier is made of silicon oxide.

8. The patterned sapphire substrate manufacturing method of claim 6, wherein the etching barrier is formed onto the upper surface of the sapphire substrate by a chemical vapor deposition process or a sputtering process.