A surface planarization method for epitaxial group III nitride materials based on stereomask substrates
By using a chemical wet etching process combining molten potassium hydroxide or hot phosphoric acid solution with sodium chloride during GaN epitaxy on a 3D mask substrate, the problem of uneven surface on the epitaxial GaN substrate was solved, achieving low-cost and efficient global planarization and improving the quality and reliability of the epitaxial wafer.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING KAIXIN TECH CO LTD
- Filing Date
- 2023-06-16
- Publication Date
- 2026-05-26
AI Technical Summary
In existing technologies for epitaxial GaN on 3D mask substrates, energy fluctuations during the epitaxial process cause inconsistent GaN heights, resulting in an uneven surface that affects the structure of subsequent epitaxial devices. Furthermore, existing surface planarization methods increase costs and dislocation density.
Chemical wet etching using molten potassium hydroxide or hot phosphoric acid solution combined with sodium chloride is employed. Taking advantage of the anisotropic corrosion characteristics of GaN, the corrosion rate difference is adjusted by adding additives to etch away the a-face and m-face of the protruding part, while retaining the c-face, thus achieving global smoothing.
It achieves low-cost surface planarization without the need for new equipment, improves the flatness and quality of epitaxial wafers, reduces dislocation density, and is suitable for large-scale batch processing.
Smart Images
Figure CN116826523B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, specifically to a surface planarization method based on epitaxial group III nitride materials on a stereomask substrate. Background Technology
[0002] Semiconductor lasers are very important laser electronic devices, especially GaN-based semiconductor lasers. Because doping can enable them to emit light waves covering the ultraviolet to green light bands, GaN-based lasers have significant application value in high-density optical information storage, projection display, laser printing, underwater communication, activation of biochemical reagents, and medicine. Gallium nitride (GaN) is an inorganic compound, a direct bandgap semiconductor, and has been commonly used in light-emitting diodes since 1990. This compound has a structure similar to wurtzite, is very hard, and has a wide bandgap of 3.4 electron volts, making it suitable for high-power, high-speed optoelectronic devices.
[0003] Since the lifetime of GaN-based semiconductor lasers is positively correlated with the crystal density of the material, especially for high-power lasers where much higher voltages and currents are required, defects such as through-dislocations in the crystal material can create leakage paths, increasing heat generation and leading to device burnout. Current research indicates that for a laser lifetime greater than 10,000 hours, the through-dislocation density of the grown material needs to be below 5 × 10⁻⁶. 6 / cm 2 For GaN materials, such high crystal quality requirements are currently difficult to achieve in heteroepitaxial growth (the through-dislocation density of PSS sapphire substrate epitaxy is around 10). 8 / cm 2 The magnitude of the ELOG signal can be reached by 10. 7 / cm 2 (Horizontal). Therefore, a high-quality GaN homogeneous self-supporting substrate is required (the dislocation density of a high-quality GaN homogeneous self-supporting substrate can reach 10). 6 / cm 2 Based on this, the through-dislocation density of epitaxial GaN laser structures can be lower than 5 × 10⁻⁶. 6 / cm 2 Alternatively, the laser structure can be grown on a substrate grown using secondary lateral epitaxy technology.
[0004] Chinese patent CN111653934B discloses a method for fabricating semiconductor lasers based on a 3D mask substrate. This method fabricates a 3D mask layer on a heterogeneous substrate, enabling the production of high-quality substrates for GaN-based laser epitaxy on inexpensive substrates such as sapphire and Si, with a limited number of simple processes and growth steps. However, during GaN epitaxy on the 3D mask substrate, energy fluctuations during the epitaxy process result in inconsistent GaN heights epitaxially emerging from some mask windows. This leads to an uneven surface after merging, which in turn affects the subsequent epitaxial device structure. If the next step of epitaxial growth of high-power devices is required, surface planarization treatment is necessary before proceeding. Meanwhile, existing semiconductor surface planarization methods include reverse etching, glass reflow, spin-coating glass, and chemical mechanical planarization. However, these methods not only require additional equipment and process steps for epitaxial GaN based on 3D mask substrates, but also increase costs, making them unsuitable for epitaxial GaN based on 3D mask substrates. Moreover, during the processing and transportation of the substrate, other chemical impurities, particulate contaminants, and moisture inevitably adhere to the substrate surface. Incomplete removal of these substances will increase the dislocation density of the epitaxial layer, reduce the quality of the epitaxial layer, and shorten the device life. Therefore, this invention proposes a surface planarization method based on epitaxial group III nitride materials on 3D mask substrates to solve the problems mentioned above. Summary of the Invention
[0005] (a) Technical problems to be solved
[0006] To address the shortcomings of existing technologies, this invention provides a surface planarization method for epitaxial group III nitride materials based on a 3D mask substrate. This method offers advantages such as global planarization, no need to introduce new instruments or equipment, and low processing costs. It solves the problem that during GaN epitaxy on a 3D mask substrate, energy fluctuations during the epitaxy process lead to inconsistent GaN heights epitaxial from some mask windows, resulting in an uneven surface after merging, which in turn affects the structure of subsequent epitaxial devices.
[0007] (II) Technical Solution
[0008] This invention reveals that GaN growth in MOCVD occurs at different rates for each crystal plane. Crystal planes with slower growth rates are retained. Therefore, before the GaN epitaxy on the 3D mask substrate is closed, GaN generally retains the a-plane, m-plane, and c-plane. After closure, in GaN regions of the same height, the a-plane and m-plane disappear, leaving only the c-plane. In GaN regions of different heights, the a-plane and m-plane disappear in the lower regions, leaving only the c-plane, while the convex regions still retain the a-plane, m-plane, and c-plane.
[0009] Because GaN materials can be corroded by molten potassium hydroxide (KOH) or hot phosphoric acid (H3PO4) solutions under specific conditions, and because the chemical wet corrosion process of GaN is an anisotropic process with different corrosion rates for different crystal orientations in the solution, generally speaking, the c-plane of GaN materials has a slow corrosion rate, while the a-plane and m-plane have faster corrosion rates than the c-plane.
[0010] In GaN epitaxy using the ELOG method, a large number of through dislocations still exist in the window region of the substrate. After solution etching, these dislocations will form V-shaped pits, affecting subsequent processes and device performance. However, for stacked substrates, which is the stereo mask substrate on which this invention is based, the GaN crystals epitaxially grown on stacked substrates have high quality and very few through dislocations. The c-plane is not easily etched into V-shaped pits by these solutions, and the surface planarization treatment does not affect the subsequent device performance.
[0011] To further reduce the occurrence of V-shaped pits and improve the anisotropic corrosion rate, sodium chloride (NaCl) is added as an additive to the etching solution. When molten potassium hydroxide is used as the etching solution, the added NaCl is partially dissolved and reacts with GaN to form GaCl3. This product coats the surface, providing some protection and preventing the reaction between KOH and GaN, thus reducing the formation of V-shaped pits. Furthermore, due to the different Ga atom densities on the c-plane, a-plane, and m-plane (with the c-plane having the highest Ga atom density, and the a-plane and m-plane having relatively lower Ga atom densities), the resulting GaCl3 coating density varies, with the c-plane having the highest density and the a-plane and m-plane having relatively lower densities. This difference in coating density results in different barrier capabilities against the etching solution. Higher coating density provides better barrier effect but a slower corrosion rate. Therefore, this exacerbates the difference in corrosion rate between the c-plane and the a-plane and m-plane, thereby improving the anisotropic corrosion effect. The same principle applies when using hot phosphoric acid as a solution for corrosion. Adding an appropriate amount of sodium chloride can also produce GaCl3 that adheres to the c, a, and m surfaces of the GaN material, thereby increasing the difference in corrosion rates between the c, a, and m surfaces.
[0012] The epitaxial GaN on the 3D mask substrate is placed in a mixed solution of potassium hydroxide and sodium chloride or a mixed solution of phosphoric acid and sodium chloride under specific conditions for chemical wet etching. The uneven GaN surface is exposed to the etching solution. The solution first etches the a-face and m-face of the GaN exposed in the protruding areas of the surface, thus etching into the GaN from the side of the protrusion. As time increases, the GaN on the a-face and m-face of the protrusion is etched away, so that the entire protrusion disappears, leaving only the c-face, which is the same height as the low-lying area. This makes the thickness of the entire epitaxial wafer the same as the lowest point after folding. Although the etching solution also etches the edges of the epitaxial GaN layer at the top of the 3D mask, it is negligible compared to the top surface of the entire epitaxial GaN on the 3D mask substrate, thus making the surface of the epitaxial wafer smoother.
[0013] To achieve the aforementioned goal of global flattening, the present invention provides the following technical solution:
[0014] A surface planarization method for epitaxial group III nitride materials based on a stereo mask substrate includes using an anisotropic etching rate difference of the c-plane, a-plane, and m-plane of a group III nitride (e.g., GaN) to perform surface planarization treatment on the epitaxially grown group III nitride material layer, wherein the surface planarization treatment is a solution etching treatment.
[0015] Furthermore, the solution corrosion treatment is alkaline solution corrosion or acidic solution corrosion.
[0016] Furthermore, the alkaline solution used for corrosion is a mixed solution of molten potassium hydroxide and sodium chloride, wherein the sodium chloride content is 0-5%, and the acidic solution used for corrosion is a mixed solution of phosphoric acid and sodium chloride, wherein the sodium chloride content is 0-5%. The content of each substance is a mass fraction.
[0017] This invention also provides a method for surface planarization of group III nitride materials epitaxially based on a stereomask substrate, comprising the following steps:
[0018] The substrate surface is treated to remove impurities.
[0019] A stereo mask is fabricated and an epitaxial group III nitride material layer is grown on the side of the substrate away from the bottom surface;
[0020] The epitaxially grown group III nitride material layer was subjected to solution etching treatment;
[0021] After washing and drying, a group III nitride epitaxial wafer with a flat top is obtained.
[0022] Furthermore, the impurity removal process includes alkaline cleaning, acidic cleaning, oxidative cleaning, and ultrapure water cleaning. The cleaning method is immersion cleaning at room temperature. The order of alkaline cleaning, acidic cleaning, and oxidative cleaning can be changed according to needs. Ultrapure water cleaning is necessary and is the final impurity removal cleaning process.
[0023] Furthermore, the alkaline cleaning solution is a sodium hydroxide or ammonium hydroxide solution with a mass concentration of 4%-9%, the acidic cleaning solution is a hydrofluoric acid or hydrochloric acid solution with a mass concentration of 10%-25%, and the oxidative cleaning solution is a solution prepared from concentrated sulfuric acid, hydrogen peroxide, and water with a mass concentration of 85%, and the mass ratio of the solutions is H2SO4:H2O2:H2O = 5:1:1.
[0024] Furthermore, the solution corrosion treatment is achieved using one of the following two methods:
[0025] 1) Alkaline solution etching treatment: Prepare a mixed solution of molten potassium hydroxide and sodium chloride, and then put the epitaxial wafer into the prepared solution. The etching process is set at a temperature of 365-400℃ and an etching time of 30-40min.
[0026] 2) Acidic solution etching treatment: Prepare a mixed solution of phosphoric acid and sodium chloride, and then place the epitaxial wafer into the prepared solution. The etching process is set at a temperature of 250-400℃ and an etching time of 10-20min.
[0027] Furthermore, after the solution corrosion treatment, the temperature is lowered to room temperature, followed by water washing and dehydration drying. The water washing is preferably done with ultrapure water, and the dehydration drying is performed at a temperature of 110-130°C for 3-5 minutes.
[0028] Furthermore, the stereo mask includes a lower mask, an intermediate layer, and an upper mask. The lower mask and the upper mask are made of Si3N4, and the intermediate layer is made of SiO2.
[0029] The present invention also provides a group III nitride material epitaxial wafer with a smooth surface prepared according to the above method.
[0030] (III) Beneficial Effects
[0031] Compared with the prior art, the present invention provides a surface planarization method for epitaxial group III nitride materials based on a stereomask substrate, which has the following beneficial effects:
[0032] This surface planarization method based on epitaxial group III nitride materials (such as GaN) on a 3D mask substrate only requires placing the epitaxial group III nitride material on the 3D mask substrate in a mixed solution of potassium hydroxide and sodium chloride or a mixed solution of phosphoric acid and sodium chloride under specific conditions for chemical wet etching. Sodium chloride can increase the difference in etching rate between the horizontal and vertical surfaces of the uneven epitaxial GaN layer, while potassium hydroxide or phosphoric acid solution will perform lateral etching on the protruding parts of the uneven epitaxial group III nitride material layer surface, making the GaN thickness of the entire epitaxial wafer uniform, thereby achieving the purpose of global planarization.
[0033] This surface planarization method for epitaxial group III nitride materials based on stereomask substrates employs a combination of alkaline cleaning, acidic cleaning, oxidative cleaning, and ultrapure water cleaning when cleaning the substrate surface. Alkaline cleaning removes organic matter and metal ions from the substrate surface, acidic cleaning removes oxides and silica gel impurities, oxidative cleaning removes carbon and metal elements, and ultrapure water cleaning removes tiny particles. This method provides a more thorough cleaning of other chemical impurities, particulate contaminants, and moisture that adhere to the substrate during processing and transportation, thereby improving epitaxial quality.
[0034] This surface planarization method based on epitaxial group III nitride materials using a stereomask substrate is simple to operate and can be prepared using existing technology environments without the need to introduce new instruments and equipment. It has low processing costs and is suitable for large-scale batch processing. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the process steps of a surface planarization method for epitaxial group III nitride materials based on a stereomask substrate according to the present invention.
[0036] Figure 2 This is a schematic diagram of the a, m, and c planes of a GaN crystal, based on a surface planarization method for epitaxial group III nitride materials using a stereomask substrate according to the present invention.
[0037] Figure 3 This is a schematic diagram of the epitaxial wafer structure of a surface planarization method for epitaxial group III nitride materials based on a stereomask substrate according to the present invention.
[0038] Figure 4 This is a schematic diagram of the epitaxial wafer planarization process according to the present invention, which is a surface planarization method for epitaxial group III nitride materials based on a stereomask substrate. Detailed Implementation
[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0040] Example 1:
[0041] A surface planarization method for epitaxial group III nitride materials based on a 3D mask substrate is proposed, using sapphire as the substrate and alkaline solution etching for processing, such as... Figure 1 As shown, it includes the following steps:
[0042] S1 Substrate Cleaning Process: The surface of the sapphire substrate is cleaned by first immersing it in a 7% sodium hydroxide solution for 2 minutes for alkaline cleaning, then removing it and placing it in a 15% hydrochloric acid solution for 2 minutes for acid cleaning, then immersing it in a solution of 85% concentrated sulfuric acid, hydrogen peroxide and water prepared in a ratio of H2SO4:H2O2:H2O = 5:1:1 for 2 minutes for oxidation cleaning, and finally immersing the substrate in ultrapure water for ultrapure water cleaning.
[0043] S2 Stereomask fabrication and epitaxial GaN layer growth process: Stereomask fabrication and epitaxial GaN layer growth are performed on the side of the sapphire substrate away from the bottom surface. The epitaxial GaN layer is as follows: Figure 3 As shown;
[0044] S3 Epitaxial GaN Layer Surface Flattening Process: The entire epitaxial wafer after GaN layer growth is placed in a molten potassium hydroxide and sodium chloride mixed solution with a mass ratio of 0.98:0.02, the temperature is set at 370℃, and the etching time is 35min;
[0045] S4 epitaxial wafer surface cleaning process: After etching, the epitaxial wafer is taken out and cooled to room temperature. The surface of the epitaxial wafer is cleaned with ultrapure water. After taking it out, the temperature is raised to 120℃ and dried for 4 minutes.
[0046] After S5 processing is completed, an epitaxial wafer with a flat top is obtained.
[0047] Figure 2 This is a schematic diagram of the a, m, and c planes of a GaN crystal. In the epitaxial wafer prepared in Example 1, the GaN on the a and m planes of the protruding portion is etched away, the entire protruding portion disappears, and only the c plane, which is the same height as the low-lying region, remains. The GaN thickness of the entire epitaxial wafer is the same as the lowest point after folding, and the surface of the epitaxial GaN layer of the entire epitaxial wafer is smooth, as shown... Figure 4 As shown.
[0048] Example 2:
[0049] A surface planarization method for epitaxial group III nitride materials based on a stereolithography mask substrate, using sapphire as the substrate and acidic solution etching, includes the following steps:
[0050] S1 Substrate Cleaning Process: The surface of the sapphire substrate is cleaned by first immersing it in a 7% sodium hydroxide solution for 2 minutes for alkaline cleaning, then removing it and placing it in a 15% hydrochloric acid solution for 2 minutes for acid cleaning, then immersing it in a solution of 85% concentrated sulfuric acid, hydrogen peroxide and water prepared in a ratio of H2SO4:H2O2:H2O = 5:1:1 for 2 minutes for oxidation cleaning, and finally immersing the substrate in ultrapure water for ultrapure water cleaning.
[0051] S2 Stereomask fabrication and epitaxial GaN layer growth process: Stereomask fabrication and epitaxial GaN layer growth are performed on the side of the sapphire substrate away from the bottom surface;
[0052] S3 Epitaxial GaN Layer Surface Flattening Process: The entire epitaxial wafer after GaN layer growth is placed in a mixed solution of 85% phosphoric acid and sodium chloride with a mass ratio of 0.97:0.03, the temperature is set at 300℃, and the etching time is 15min.
[0053] S4 epitaxial wafer surface cleaning process: After etching, the epitaxial wafer is taken out and cooled to room temperature. The surface of the epitaxial wafer is cleaned with ultrapure water. After taking it out, the temperature is raised to 120℃ and dried for 4 minutes.
[0054] After S5 processing is completed, an epitaxial wafer with a flat top is obtained.
[0055] In the epitaxial wafer prepared in Example 2, the GaN on the a-side and m-side of the protruding portion was etched away, the entire protruding portion disappeared, and only the c-side, which is the same height as the low-lying region, was retained. The GaN thickness of the entire epitaxial wafer is the same as the lowest point after being closed, and the surface of the epitaxial GaN layer of the entire epitaxial wafer is flat.
[0056] Example 3:
[0057] A surface planarization method for epitaxial group III nitride materials based on a stereolithography mask substrate, using silicon as the substrate and alkaline solution etching, includes the following steps:
[0058] S1 Substrate Cleaning Process: The surface of the sapphire substrate is cleaned by first immersing it in a 7% sodium hydroxide solution for 2 minutes for alkaline cleaning, then removing it and placing it in a 15% hydrochloric acid solution for 2 minutes for acid cleaning, then immersing it in a solution of 85% concentrated sulfuric acid, hydrogen peroxide and water prepared in a ratio of H2SO4:H2O2:H2O = 5:1:1 for 2 minutes for oxidation cleaning, and finally immersing the substrate in ultrapure water for ultrapure water cleaning.
[0059] S2 Stereomask fabrication and epitaxial GaN layer growth process: Stereomask fabrication and epitaxial GaN layer growth are performed on the side of the silicon substrate away from the bottom surface;
[0060] S3 Epitaxial GaN Layer Surface Flattening Process: The entire epitaxial wafer after GaN layer growth is placed in a molten potassium hydroxide and sodium chloride mixed solution with a mass ratio of 0.98:0.02, the temperature is set at 370℃, and the etching time is 35min;
[0061] S4 epitaxial wafer surface cleaning process: After etching, the epitaxial wafer is taken out and cooled to room temperature. The surface of the epitaxial wafer is cleaned with ultrapure water. After taking it out, the temperature is raised to 120℃ and dried for 4 minutes.
[0062] After S5 processing is completed, an epitaxial wafer with a flat top is obtained.
[0063] In the epitaxial wafer prepared in Example 3, the GaN on the a-side and m-side of the protruding portion was etched away, the entire protruding portion disappeared, and only the c-side, which is the same height as the low-lying region, was retained. The GaN thickness of the entire epitaxial wafer is the same as the lowest point after being closed, and the surface of the epitaxial GaN layer of the entire epitaxial wafer is flat.
[0064] Example 4:
[0065] A surface planarization method for epitaxial group III nitride materials based on a stereolithography mask substrate, using silicon as the substrate and acidic solution etching, includes the following steps:
[0066] S1 Substrate Cleaning Process: The surface of the sapphire substrate is cleaned by first immersing it in a 7% sodium hydroxide solution for 2 minutes for alkaline cleaning, then removing it and placing it in a 15% hydrochloric acid solution for 2 minutes for acid cleaning, then immersing it in a solution of 85% concentrated sulfuric acid, hydrogen peroxide and water prepared in a ratio of H2SO4:H2O2:H2O = 5:1:1 for 2 minutes for oxidation cleaning, and finally immersing the substrate in ultrapure water for ultrapure water cleaning.
[0067] S2 Stereomask fabrication and epitaxial GaN layer growth process: Stereomask fabrication and epitaxial GaN layer growth are performed on the side of the silicon substrate away from the bottom surface;
[0068] S3 Epitaxial GaN Layer Surface Flattening Process: The entire epitaxial wafer after GaN layer growth is placed in a mixed solution of 85% phosphoric acid and sodium chloride with a mass ratio of 0.97:0.03, the temperature is set at 300℃, and the etching time is 15min.
[0069] S4 epitaxial wafer surface cleaning process: After etching, the epitaxial wafer is taken out and cooled to room temperature. The surface of the epitaxial wafer is cleaned with ultrapure water. After taking it out, the temperature is raised to 120℃ and dried for 4 minutes.
[0070] After S5 processing is completed, an epitaxial wafer with a flat top is obtained.
[0071] In the epitaxial wafer prepared in Example 4, the GaN on the a-side and m-side of the protruding portion was etched away, the entire protruding portion disappeared, and only the c-side, which is the same height as the low-lying region, was retained. The GaN thickness of the entire epitaxial wafer is the same as the lowest point after being closed, and the surface of the epitaxial GaN layer of the entire epitaxial wafer is flat.
[0072] Example 5:
[0073] A surface planarization method for epitaxial group III nitride materials based on a stereolithography mask substrate, using silicon as the substrate and acidic solution etching, includes the following steps:
[0074] S1 Substrate Cleaning Process: The surface of the sapphire substrate is cleaned by first immersing it in a 7% sodium hydroxide solution for 2 minutes for alkaline cleaning, then removing it and placing it in a 15% hydrochloric acid solution for 2 minutes for acid cleaning, then immersing it in a solution of 85% concentrated sulfuric acid, hydrogen peroxide and water prepared in a ratio of H2SO4:H2O2:H2O = 5:1:1 for 2 minutes for oxidation cleaning, and finally immersing the substrate in ultrapure water for ultrapure water cleaning.
[0075] S2 Stereomask fabrication and epitaxial GaN layer growth process: Stereomask fabrication and epitaxial GaN layer growth are performed on the side of the silicon substrate away from the bottom surface;
[0076] S3 Epitaxial GaN Layer Surface Flattening Process: The entire epitaxial wafer after GaN layer growth is placed in an 85% phosphoric acid solution, the temperature is set at 300℃, and the etching time is 12min.
[0077] S4 epitaxial wafer surface cleaning process: After etching, the epitaxial wafer is taken out and cooled to room temperature. The surface of the epitaxial wafer is cleaned with ultrapure water. After taking it out, the temperature is raised to 120℃ and dried for 4 minutes.
[0078] After S5 processing is completed, an epitaxial wafer with a flat top is obtained.
[0079] In the epitaxial wafer prepared in Example 5, the GaN on the a-side and m-side of the protruding portion was etched away, and the entire protruding portion disappeared. A small number of V-shaped pits still existed in the c-side, which was at the same height as the low-lying area.
[0080] The beneficial effects of this invention are:
[0081] This surface planarization method based on epitaxial group III nitride materials (such as GaN) on a 3D mask substrate only requires placing the epitaxial group III nitride material on the 3D mask substrate in a mixed solution of potassium hydroxide and sodium chloride or a mixed solution of phosphoric acid and sodium chloride under specific conditions for chemical wet etching. Sodium chloride can increase the difference in etching rate between the horizontal and vertical surfaces of the uneven epitaxial GaN layer, while potassium hydroxide or phosphoric acid solution will perform lateral etching on the protruding parts of the uneven epitaxial group III nitride material layer surface, making the GaN thickness of the entire epitaxial wafer uniform, thereby achieving the purpose of global planarization.
[0082] This surface planarization method for epitaxial group III nitride materials based on stereomask substrates employs a combination of alkaline cleaning, acidic cleaning, oxidative cleaning, and ultrapure water cleaning when cleaning the substrate surface. Alkaline cleaning removes organic matter and metal ions from the substrate surface, acidic cleaning removes oxides and silica gel impurities, oxidative cleaning removes carbon and metal elements, and ultrapure water cleaning removes tiny particles. This method provides a more thorough cleaning of other chemical impurities, particulate contaminants, and moisture that adhere to the substrate during processing and transportation, thereby improving epitaxial quality.
[0083] This surface planarization method based on epitaxial group III nitride materials using a stereomask substrate is simple to operate and can be prepared using existing technology environments without the need to introduce new instruments and equipment. It has low processing costs and is suitable for large-scale batch processing.
[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for surface planarization of group III nitride materials epitaxially grown on a 3D mask substrate, characterized in that, Includes the following steps: The surface of the substrate is cleaned to remove impurities; A stereo mask is fabricated and an epitaxial group III nitride material layer is grown on the side of the substrate away from the bottom surface. Solution etching treatment was performed on the epitaxially grown group III nitride material layer; After water washing and dehydration drying, a group III nitride material epitaxial wafer with a flat top is obtained; The solution corrosion treatment is achieved using one of the following two methods: 1) Alkaline solution etching treatment: Prepare a mixed solution of molten potassium hydroxide and sodium chloride, and then put the epitaxial wafer into the prepared solution. The etching process is set at a temperature of 365-400℃ and an etching time of 30-40min. 2) Acidic solution etching treatment: Prepare a mixed solution of phosphoric acid and sodium chloride, and then place the epitaxial wafer into the prepared solution. The etching process is set at a temperature of 250-400℃ and an etching time of 10-20min.
2. The surface planarization method for epitaxial group III nitride materials based on a three-dimensional mask substrate according to claim 1, characterized in that, The impurity removal process includes alkaline cleaning, acidic cleaning, oxidative cleaning, and ultrapure water cleaning.
3. The surface planarization method for group III nitride materials epitaxially based on a 3D mask substrate according to claim 2, characterized in that, The alkaline cleaning solution is sodium hydroxide or ammonium hydroxide solution, the acidic cleaning solution is hydrofluoric acid or hydrochloric acid solution, and the oxidative cleaning solution is a solution prepared from concentrated sulfuric acid, hydrogen peroxide and water, with a mass ratio of H2SO4:H2O2:H2O=5:1:
1.
4. The surface planarization method for epitaxial group III nitride materials based on a three-dimensional mask substrate according to claim 1, characterized in that, The stereo mask includes a lower mask, an intermediate layer, and an upper mask. The lower and upper masks are made of Si3N4, and the intermediate layer is made of SiO2.