Epitaxial layer removal method

Abstract

The present invention provides an epitaxial layer removal method, comprising: providing a substrate on which a gallium nitride epitaxial layer to be processed is formed. Then, the substrate is subjected to high-temperature heat treatment to oxidize the gallium nitride epitaxial layer into a gallium oxide layer, and then the substrate is cleaned with deionized water and ultrasonic oscillation to remove part of the gallium oxide layer. Then, a cleaning agent is used to remove the gallium oxide layer on the substrate.

Description

Technical Field

[0001] The invention relates to a processing technology of an epitaxial substrate, and in particular to a method for removing an epitaxial layer. Background Art

[0002] Epitaxy refers to the technology of growing new crystals on a wafer to form a semiconductor layer. Through the epitaxy process, a gallium nitride epitaxial layer can be grown on a substrate, and then the substrate and epitaxial layer are separated. However, the epitaxial layer will remain on the separated substrate, and a process of removing the epitaxial layer is required. The substrate can be recycled and then the next epitaxial process can be performed.

[0003] In the past, physical grinding was mostly used to remove the epitaxial layer when removing the substrate. However, due to the limitations of existing processing capabilities, it is not possible to grind only 3 microns or less in thickness. If grinding is forced, not only will more parts of the substrate need to be polished, but it is also easy to cause excessive geometric changes in the substrate and cause defects, which will reduce the quality of the epitaxial growth on the substrate and increase the cost of substrate recycling. In addition, the grinding process steps are cumbersome, not only the output is low, but the cost is also high. Summary of the invention

[0004] The present invention is directed to a method for removing an epitaxial layer, which can smoothly remove the epitaxial layer on a substrate without using a grinding process, and also prevents the geometric appearance of the substrate from being seriously damaged and affected. It can effectively remove the gallium nitride layer on the bevel of the substrate periphery, and when corresponding to substrates with special morphologies in the future, it can still maintain a very good geometric appearance.

[0005] According to an embodiment of the present invention, a method for removing an epitaxial layer includes: providing a substrate on which a gallium nitride epitaxial layer to be processed is formed; performing high-temperature heat treatment on the substrate to oxidize the gallium nitride epitaxial layer into a gallium oxide layer; cleaning the substrate with deionized water and ultrasonic oscillation to remove part of the gallium oxide layer; and using a cleaning agent to remove the gallium oxide layer on the substrate.

[0006] In the epitaxial layer removal method according to the embodiment of the present invention, the temperature of the high temperature heat treatment is, for example, 1150° C. to 1400° C., and the time of the high temperature heat treatment is, for example, 0.5 hour to 2 hours.

[0007] In the epitaxial layer removal method according to the embodiment of the present invention, the pressure during the high temperature heat treatment is, for example, above 0.5 atm.

[0008] In the epitaxial layer removal method according to the embodiment of the present invention, the oxygen content during the high temperature heat treatment is, for example, greater than 16%.

[0009] In the epitaxial layer removal method according to an embodiment of the present invention, the frequency / power of the ultrasonic oscillation is, for example, greater than 40 kHz / 1200 W, and the oscillation time of the ultrasonic oscillation is, for example, greater than 20 minutes.

[0010] In the epitaxial layer removal method according to an embodiment of the present invention, the substrate includes a silicon substrate or a silicon carbide substrate.

[0011] In the epitaxial layer removal method according to an embodiment of the present invention, the cleaning agent includes hydrogen fluoride or a mixture of sulfuric acid and hydrogen peroxide (SPM).

[0012] In the epitaxial layer removal method according to an embodiment of the present invention, the ratio of sulfuric acid to hydrogen peroxide in the SPM is, for example, 4:1.

[0013] In the epitaxial layer removal method according to an embodiment of the present invention, after the above-mentioned step of using hydrogen fluoride, it can also include: performing a second deionized water cleaning on the substrate to remove the hydrogen fluoride on the surface of the substrate, then fine-polishing the substrate to make its surface mirror-finished, and then performing RCA cleaning on the substrate.

[0014] In the epitaxial layer removal method according to an embodiment of the present invention, before the step of fine polishing the substrate, the method may further include using an air gun to remove the gallium oxide layer remaining on the outer bevel end of the substrate, wherein the jet pressure of the air gun is, for example, greater than 14.7 psi.

[0015] In the epitaxial layer removal method according to an embodiment of the present invention, the thickness variation of the substrate before the gallium oxide layer is formed and after the gallium oxide layer is removed is, for example, less than 0.1%.

[0016] In the epitaxial layer removal method according to an embodiment of the present invention, at least one of the flatness change, curvature change and warpage change of the substrate before forming the gallium oxide layer and after removing the gallium oxide layer is less than 20%, for example.

[0017] Based on the above, the present invention provides a substrate on which a gallium nitride epitaxial layer to be processed is formed, and the substrate is subjected to high-temperature heat treatment, deionized water cleaning with ultrasonic oscillation, and a cleaning agent is used to remove the gallium oxide layer on the substrate, so as to smoothly remove the epitaxial layer on the substrate and recycle the substrate without seriously damaging or affecting the geometric appearance of the substrate. The gallium nitride layer on the bevel of the outer periphery of the substrate can also be effectively removed, and in the future, when corresponding to substrates with special morphologies, a very good geometric appearance can still be maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a step diagram of a method for removing an epitaxial layer according to an embodiment of the present invention.

[0019] Description of Reference Numerals

[0020] S100, S110, S120, S130, S140, S150, S160, S170: Steps DETAILED DESCRIPTION

[0021] Figure 1 1 is a step diagram of a method for removing an epitaxial layer according to an embodiment of the present invention.

[0022] First, please refer to Figure 1 , step S100 is performed to provide a substrate on which a gallium nitride epitaxial layer to be processed is formed. The thickness of the gallium nitride epitaxial layer is not limited, for example, less than 3 μm. The substrate can be a silicon substrate or a silicon carbide substrate. Since the price of the silicon carbide substrate is expensive, the epitaxial layer removal method of the present invention can effectively improve the recovery rate of the silicon carbide substrate, thereby reducing the cost.

[0023] Then, step S110 is performed to perform high-temperature heat treatment on the substrate to oxidize the gallium nitride epitaxial layer into a gallium oxide layer. At high temperatures, gallium nitride will begin to react to form β-type gallium oxide (β-Ga2O3). Since the lattice matching degree of the β-type gallium oxide (β-Ga2O3) after oxidation changes with the substrate, it is easy to peel off from the substrate. In this embodiment, the peeling phenomenon produced by the above-mentioned substrate is utilized to help the subsequent physical removal of the gallium oxide layer. The temperature and time of the high-temperature heat treatment are deliberately higher than the commonly used annealing parameters to oxidize gallium nitride into β-type gallium oxide (β-Ga2O3). The temperature of the high-temperature heat treatment in this embodiment is, for example, 1150°C to 1400°C, preferably 1175°C to 1225°C, and more preferably 1200°C. And the time of the high-temperature heat treatment is, for example, 0.5 hours to 2 hours, preferably 0.75 hours to 1.25 hours, and more preferably 1 hour. There are no special restrictions on the pressure and oxygen content of the high-temperature heat treatment. However, the silicon carbide substrate will easily volatilize when the pressure is less than 0.5atm, so the pressure is preferably above 0.5atm, preferably 0.75atm to 1.25atm, and more preferably 1atm, which can stabilize the silicon carbide substrate. The oxygen content is preferably greater than 16%, because if the oxygen content is too low, the overall reaction time will be prolonged.

[0024] After the high temperature heat treatment, step S120 is performed to clean the substrate with deionized water and ultrasonic oscillation to remove part of the gallium oxide layer. The frequency / power of the ultrasonic oscillation can be greater than 40kHz / 1200W, and the oscillation time of the ultrasonic oscillation can be greater than 20 minutes. The " / " in the text represents "and". After the deionized water cleaning and ultrasonic oscillation, the aforementioned part of the β-type gallium oxide (β-Ga2O3) can be removed.

[0025] After cleaning with deionized water, some unpeeled gallium oxide layer still remains on the substrate, and there are some protrusions on the appearance of the substrate, so step S130 is performed to use a cleaning agent to remove the gallium oxide layer on the substrate. The cleaning agent in the present invention is not particularly limited, and commonly used chemical agents can be used to remove the gallium oxide layer on the substrate, among which hydrogen fluoride (HF) or a mixture of sulfuric acid and hydrogen peroxide (SPM) is preferably used, and hydrogen fluoride (HF) is more preferably used. In SPM, the ratio of sulfuric acid to hydrogen peroxide is, for example, 4:1. The use of such a cleaning agent can effectively remove the protrusions of the gallium oxide layer on the substrate, and can also effectively remove the gallium oxide layer remaining at the bevel end of the outer periphery of the substrate. This embodiment can effectively enhance the effect of removing the gallium oxide layer due to the combination of ultrasonic oscillation and cleaning agent cleaning steps (steps S120 and S130).

[0026] In the past, it was difficult to remove the GaN epitaxial layer on the outer bevel of the substrate during the polishing process, and it was easy for the GaN epitaxial layer to remain on the edge. This embodiment can effectively remove the GaN layer on the outer bevel of the substrate by chemical methods such as high-temperature heat treatment and cleaning agents. In the future, substrates with special morphologies can still maintain very good geometric appearance.

[0027] After the gallium oxide layer on the substrate is removed by the cleaning agent, step S140 can be optionally performed to perform a second deionized water cleaning on the substrate to remove the chemical agent on the surface of the substrate. Then, after the second deionized water cleaning, a step of removing moisture from the surface of the substrate can be performed. The method is not limited. For example, the moisture remaining on the surface of the substrate can be quickly removed by spinning the substrate.

[0028] Then, step S150 can be performed as required to remove the remaining gallium oxide layer by using an air gun. Specifically, the gallium oxide layer remaining at the outer bevel edge of the substrate can be removed by using an air gun, wherein the jet pressure of the air gun is, for example, greater than 14.7 psi, so that the gallium oxide layer remaining at the outer bevel edge of the substrate can be completely removed.

[0029] Since the aforementioned process may cause slight damage to the substrate, the next step may include performing step S160 to fine-polish the substrate to make its surface mirror-like. The purpose of the fine-polishing process is to remove most of the scratches and damaged layers on the substrate by grinding and improve the surface roughness, and there is no particular limitation on the grinding method, such as grinding on a soft pad material.

[0030] Then, step S170 may be performed to perform RCA cleaning on the substrate after fine polishing, wherein the RCA cleaning process includes using a mixture of water (H2O) / hydrogen peroxide (H2O2) / ammonia (NH4OH) (i.e., standard cleaning solution SC1), using a mixture of water (H2O) / hydrogen peroxide (H2O2) / hydrochloric acid (HCl) (i.e., standard cleaning solution SC2), or using a combination of the above SC1 and SC2. The SC1 solution is used to remove dust particles adsorbed on the surface of the wafer, and can oxidize and remove slight organic pollution and some metal atom pollution. The SC2 solution can dissolve alkali metal ions and aluminum, iron and magnesium hydroxides, because the chloride ions in the hydrochloric acid form complexes with the residual metal ions and dissolve in the aqueous solution. At this point, the epitaxial layer removal method of this embodiment has been completed.

[0031] The epitaxial layer removal method of the present invention is described above based on the embodiments, but the present invention may be implemented in various modified forms without being limited to the described embodiments, such as omitting one or more steps of steps S140, S150, S160 and S170, and other steps that may help remove the epitaxial layer may be added to the above steps.

[0032] The present invention will be described in more detail below with reference to experimental examples and comparative examples, but the present invention is not limited to these examples.

[0033] [Experimental Example 1]

[0034] First, a silicon carbide substrate with a pre-processed gallium nitride epitaxial layer is provided, and then the substrate is placed in a heating furnace and heated for 1 hour at a high temperature of 1200°C, a pressure of 1atm, and an oxygen content of 16%. Then, it is placed in deionized water and ultrasonically oscillated for 20 minutes at a frequency / power of 12kHz / 1200W. The processed silicon carbide substrate is measured for thickness, flatness, curvature, and warpage using a multi-sensor measuring device (FRT company), and the results are shown in Table 1 below.

[0035] [Comparative Example 1]

[0036] In Comparative Example 1, a silicon carbide substrate having a gallium nitride epitaxial layer before treatment is provided, and then the epitaxial layer on the surface is removed by physical polishing to a thickness of 10 μm, and then placed in deionized water and oscillated with ultrasonic waves at a frequency / power of 12 kHz / 1200 W for 20 minutes. The thickness, flatness, curvature and warpage of the treated silicon carbide substrate are measured in the same manner as in Example 1, and the results are shown in Table 1 below.

[0037] [Table 1]

[0038]

[0039] According to the results in Table 1, the high temperature heat treatment method used in Example 1 can make the thickness, flatness, curvature and warpage of the substrate after treatment better than that of the substrate before treatment by the conventional grinding process used in Comparative Example 1. In particular, Example 1 has a relatively small thickness variation, that is, the thickness variation difference ratio is less than 0.1%, and Example 1 also has relatively small flatness, bow and warpage, and the difference ratio of at least one of the three indicators is less than 20%.

[0040] In summary, the embodiments of the present invention can replace the commonly used grinding process in the past, so that the geometric appearance of the substrate with the GaN epitaxial layer will not be seriously damaged and affected after the epitaxial layer is removed, and the GaN layer on the bevel of the substrate can be effectively removed. In the future, for substrates with special morphologies, the geometric appearance can still be kept very good, so as to achieve substrate recycling and effectively reduce losses.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing an epitaxial layer, characterized in that: include: providing a substrate on which a gallium nitride epitaxial layer to be processed is formed; Performing a high-temperature heat treatment on the substrate to oxidize the gallium nitride epitaxial layer into a β-type gallium oxide layer, wherein the temperature of the high-temperature heat treatment is between 1150° C. and 1400° C., and the time of the high-temperature heat treatment is between 0.5 hours and 2 hours; Cleaning the substrate with deionized water and ultrasonic vibration to remove part of the β-type gallium oxide layer; and The β-type gallium oxide layer on the substrate is removed using a cleaning agent.

2. The epitaxial layer removal method according to claim 1, characterized in that: The pressure during the high temperature heat treatment is above 0.5 atm.

3. The epitaxial layer removal method according to claim 1, characterized in that: The oxygen content during the high temperature heat treatment is greater than 16%.

4. The epitaxial layer removal method according to claim 1, characterized in that: The frequency / power of the ultrasonic oscillation is greater than 40kHz / 1200W, and the oscillation time of the ultrasonic oscillation is greater than 20 minutes.

5. The epitaxial layer removal method according to claim 1, characterized in that: The substrate includes a silicon substrate or a silicon carbide substrate.

6. The epitaxial layer removal method according to claim 1, characterized in that: The cleaning agent includes a mixture of hydrogen fluoride or sulfuric acid and hydrogen peroxide.

7. The epitaxial layer removal method according to claim 6, characterized in that: The ratio of sulfuric acid to hydrogen peroxide in the mixture of sulfuric acid and hydrogen peroxide is 4:

1.

8. The epitaxial layer removal method according to claim 6, characterized in that: After using hydrogen fluoride, the method further includes: performing a second deionized water cleaning on the substrate to remove hydrogen fluoride on the surface of the substrate; Fine-polishing the substrate to make its surface mirror-finished; and The substrate is subjected to RCA cleaning.

9. The epitaxial layer removal method according to claim 8, characterized in that: Before fine-polishing the substrate, the method further includes using an air gun to remove the β-type gallium oxide layer remaining on the bevel edge of the outer periphery of the substrate, wherein the jet pressure of the air gun is greater than 14.7 psi.

10. The epitaxial layer removal method according to claim 1, characterized in that: The thickness variation of the substrate before the β-type gallium oxide layer is formed and after the β-type gallium oxide layer is removed is less than 0.1%.

11. The epitaxial layer removal method according to claim 1, characterized in that: At least one of a flatness change, a curvature change, and a warpage change of the substrate before forming the β-type gallium oxide layer and after removing the β-type gallium oxide layer is less than 20%.

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