AlGaN based on porous AlN growth and preparation method thereof

Abstract

The invention relates to AlGaN based on porous AlN growth and a preparation method thereof, and belongs to the technical field of semiconductors. The preparation method comprises the following steps: step 1, providing a sapphire-based AlN substrate; step 2, preparing an alkaline melt solution, completely immersing the substrate into the alkaline melt solution for corrosion, then taking out the substrate, cleaning and drying to obtain a sapphire-based AlN substrate intermediate; corrosion holes are formed in the surface of the AlN layer of the sapphire-based AlN substrate intermediate, and the hole diameter of the corrosion holes is 50-100 nm. 3, after water and oxygen removal treatment is carried out on the sapphire-based AlN substrate intermediate, an AlGaN layer is deposited; the thickness of the AlGaN layer is 1 to 1.5 [mu] m. According to the preparation method, lattice mismatch of AlN and AlGaN is relieved through the lateral epitaxial process in the AlGaN growth process, relaxation stress is achieved, the crystal quality is improved, the surface damage function is reduced, and growth of the thick-film AlGaN with the high quality and the good surface is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductors, and particularly relates to AlGaN grown on porous AlN and a preparation method thereof. BACKGROUND

[0002] III-nitride semiconductors play a key role in the field of electronics and optoelectronics. AlGaN-based light-emitting devices are widely used in water purification, medical treatment, data storage, non-line-of-sight communication and other fields due to their environmental protection, small size, low energy consumption and long service life. AlGaN-based optoelectronic devices with sapphire substrates usually use sapphire / AlN epitaxial transition layers, but there is a certain lattice mismatch between AlN and AlGaN: the continuous accumulation of compressive stress from the AlN substrate in the AlGaN layer leads to deterioration of the epitaxial surface, proliferation of dislocations, and damage to the crystal quality and device performance.

[0003] To address the lattice mismatch between the sapphire-based AlN substrate and the AlGaN epitaxial layer, there are four existing solutions, each with drawbacks: thinning the n-AlGaN layer to less than 500 nm alleviates stress but increases lateral resistance, degrading electrical performance; adjusting the stress design of the bottom AlN layer only achieves 20-30% relaxation improvement, which is insufficient to support high-quality growth; roughening the AlN surface or introducing a mask layer introduces new dislocation defects, exacerbating crystal structure degradation; nano-patterned technology uses lateral epitaxy to suppress dislocation extension, but the difference in atomic mobility between Al and Ga leads to uneven surface atomic distribution, causing roughness and destroying the flatness of the AlGaN layer. Therefore, existing methods either introduce electrical defects and insufficient relaxation or induce new defects and surface degradation, and none of them can effectively solve the mismatch problem while ensuring crystal quality. SUMMARY

[0004] Therefore, the present application provides AlGaN grown on porous AlN and a preparation method thereof. The preparation method uses a method of forming "small patterns" based on substrate edge dislocation corrosion to replace the traditional nano-imprinting large patterns, and through the lateral epitaxy process during AlGaN growth, the lattice mismatch between AlN and AlGaN is relieved, which has the functions of relaxing stress, improving crystal quality and reducing surface damage, and realizes the growth of thick-film AlGaN with high quality and good surface.

[0005] In a first aspect, the application provides a method for preparing AlGaN based on porous AlN growth, comprising the following steps: Step 1, providing a sapphire-based AlN substrate; Step 2, preparing an alkaline molten liquid, immersing the substrate completely into the alkaline molten liquid for etching, then taking out, washing and drying to obtain a sapphire-based AlN substrate intermediate; the AlN layer surface of the sapphire-based AlN substrate intermediate comprises etching holes, and the aperture of the etching holes is 50-100 nm; Step 3, after the sapphire-based AlN substrate intermediate is subjected to water and oxygen removal treatment, depositing an AlGaN layer; the thickness of the AlGaN layer is 1-1.5 μm. The alkaline molten liquid is used to selectively etch the sapphire-based AlN substrate to form etching holes, which act as stress release points in subsequent AlGaN growth, induce lateral epitaxy of the AlGaN layer, promote local stress release mechanism and effectively relieve the lattice mismatch stress between AlN and AlGaN. At the same time, the etching holes can block the dislocation extension path during AlGaN merging, reduce the threading dislocation density and avoid surface cracks and dislocation proliferation caused by stress accumulation in traditional planar growth. On the other hand, the etching holes are essentially the etched morphology of the substrate edge dislocations, and the size of the etching holes is much smaller than that of the traditional nano-imprinting method, which can reduce the spatial distribution difference of Al and Ga atoms in the migration process, thereby inhibiting the atomic aggregation and surface undulation caused by the different atomic migration rates and ensuring the surface flatness and crystal quality of the AlGaN layer.

[0006] In some embodiments, the edge dislocation density of the sapphire-based AlN substrate is 1×10 9 ~3×10 9 cm -2 , and the screw dislocation density is 1×10 7 ~2×10 7 cm -2 . The edge dislocation as the starting point of etching will affect the number distribution of the etching holes formed by subsequent alkaline molten liquid etching: too high density will result in too many etching holes, which is not conducive to the flatness recovery of the surface after etching; too low density cannot provide enough stress release points, which weakens the stress relaxation and dislocation blocking effect. The screw dislocation will cause the etching holes to be too large, so it is necessary to minimize it. Controlling the edge dislocation density and screw dislocation density within the above preferred range can promote local stress release during AlGaN layer growth and reduce the threading dislocation density, while avoiding the problem of large-size etching holes caused by too many screw dislocations, improving the crystal quality and surface flatness of the AlGaN layer.

[0007] In some embodiments, the sapphire-based AlN substrate comprises a sapphire substrate and an AlN layer on at least one side surface of the sapphire substrate; the thickness of the AlN layer is 1000-3000 nm. Controlling the thickness of the AlN layer within the above-mentioned preferred range can ensure that the AlN layer has a sufficient thickness to completely accommodate the etching holes and avoid penetration of the etching to the sapphire substrate, and the AlN layer with an appropriate thickness can provide a stable medium for dislocation etching, ensuring the uniformity of the etching hole morphology and controllability of the depth; on the other hand, during AlGaN epitaxy, the complete AlN layer can effectively isolate the interference of the thermal expansion effect of the sapphire substrate on the growth stress of AlGaN, and the regularly distributed etching hole structure on the surface of the AlN layer can relax the lattice mismatch stress at the AlGaN / AlN interface through lateral epitaxy mechanism, thereby improving the crystal quality of the AlGaN layer and the surface flatness.

[0008] In some embodiments, the alkaline molten liquid comprises NaOH and KOH, and the mass ratio of NaOH to KOH is 1: (3-5). NaOH provides a strong alkaline etching environment, and KOH enhances the stability of the molten state, and this etching liquid system can precisely act on the threading dislocation points of the AlN substrate during the etching process, forming etching holes with controllable depth and size. This ratio range can avoid the problems of unstable etching rate or local intense reaction of a single alkali metal liquid, ensuring the uniformity of the micro-pit morphology and providing consistent stress relaxation points for subsequent lateral growth of AlGaN epitaxy, while reducing surface residual impurities and improving the surface flatness and crystal quality of the epitaxial film.

[0009] In some embodiments, the temperature for immersion is 390-520°C, and the time is 3-5 min. Controlling the temperature and time for immersion within the above-mentioned preferred range can ensure that the alkaline molten liquid selectively etches the threading dislocations of the AlN substrate in a stable state and forms uniform etching holes. Too low temperature leads to increased viscosity of the molten liquid and insufficient ion activity, resulting in too slow etching rate and failure to completely act on the threading dislocation points; too high temperature accelerates the decomposition of the molten liquid or local intense reaction, causing uneven hole diameter or substrate damage; too short immersion time results in too small hole diameter, and too long immersion time results in too large hole diameter.

[0010] In some embodiments, the diameter of the etching hole is 75-90 nm, and the depth of the etching hole is 40-100 nm. Controlling the depth of the etching hole within the above-mentioned preferred range can avoid the problem of out-of-control growth mode caused by depth deviation, ensuring the uniformity of the crystal quality and surface flatness of the AlGaN film and enhancing the stress relaxation efficiency and dislocation blocking effect. Too small depth can easily change the growth process from lateral epitaxy to "filling pits" at non-hole sites.

[0011] In some embodiments, the water and oxygen treatment comprises baking the sapphire-based AlN substrate intermediate in a hydrogen atmosphere. The hydrogen atmosphere can effectively remove water vapor and oxygen residues on the surface of the sapphire-based AlN substrate intermediate, prevent the formation of impurity oxides, avoid the introduction of interface defects or contaminants in subsequent deposition processes, effectively inhibit the lattice distortion or dislocation proliferation problems of the AlGaN layer caused by surface contamination, and ensure the integrity of the epitaxial layer.

[0012] In some embodiments, the baking temperature is 1050-1150℃, and the baking time is 4-6 min. Controlling the baking temperature and time within the above preferred ranges can ensure effective removal of surface contaminants without damaging the micropit morphology, provide a clean growth interface for AlGaN deposition, thereby reducing the dislocation density of the thin film and improving the crystal quality and surface flatness.

[0013] In some embodiments, the deposition of the AlGaN layer comprises: using a MOCVD device to introduce TMAl, TMGa or TEGa and NH3; the pressure of the reaction chamber of the MOCVD device is 50-200 torr, and the reaction temperature is 1050-1150℃; the gas volume flow rate of the TMAl is 60-160 sccm; the gas volume flow rate of the TMGa or TEGa is 4-12 sccm; and the gas volume flow rate of the NH3 is 1000-2000 sccm. Controlling the growth parameters of the AlGaN layer within the above preferred ranges can ensure that the metal organic precursors are fully decomposed and the surface mobility is enhanced without serious desorption of surface atoms, and that a temperature that is too low will result in insufficient atomic surface mobility and poor morphology, and a temperature that is too high will induce gallium desorption or surface roughening; a suitable total flow rate of Al and Ga determines the growth rate, and a suitable NH3 flow rate can enhance the mobility of the metal source, so matching the total flow rate can ensure the step flow growth state of the AlGaN.

[0014] In a second aspect, the application also provides an AlGaN grown on porous AlN, which is prepared by the above method. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A structure diagram of the AlGaN grown on porous AlN provided by the application is shown in the figure; Figure 2 A cross-sectional picture of the sapphire-based AlN substrate intermediate of the application is shown in the figure. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the application more clear, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0017] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the implementation or example are included in at least one implementation or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more implementations or examples in a suitable manner.

[0018] In the prior art, the existence of a certain lattice mismatch between the sapphire-based AlN substrate and the AlGaN epitaxial layer causes the accumulation of compressive stress, which leads to the proliferation of dislocations and surface degradation, and damages the device performance.

[0019] To solve the above problems, the present application provides a preparation method of AlGaN grown on porous AlN, comprising the following steps: Step 1, providing a sapphire-based AlN substrate; Step 2, preparing an alkaline melt, completely immersing the substrate in the alkaline melt for etching, then taking out, washing and drying to obtain a sapphire-based AlN substrate intermediate; the AlN layer surface of the sapphire-based AlN substrate intermediate includes etching holes, and the aperture of the etching holes is 50-100 nm; Step 3, after the sapphire-based AlN substrate intermediate is treated for water and oxygen removal, depositing an AlGaN layer; the thickness of the AlGaN layer is 1-1.5 μm.

[0020] The present application also provides an AlGaN grown on porous AlN, which is prepared by the above preparation method.

[0021] In some embodiments, the etching hole is a reverse hexagonal pyramid pit, and the test of the aperture of the etching hole comprises the following steps: using AFM test to scan a 3 μm×3 μm area at a random position on the sample surface, further reducing the scanning area to 1 μm×1 μm for the etching hole after the etching hole is observed, and determining the aperture and depth by Section function. Specific embodiments Embodiment 1 1) providing a sapphire-based AlN substrate. The thickness of the AlN layer on the sapphire substrate is 2000 nm; the edge dislocation density of the sapphire-based AlN substrate is 2e 9 , and the screw dislocation density is 1e 7 .

[0023] 2) Preparation of the basic molten liquid: NaOH and KOH are mixed in a mass ratio of 1:4, heated at 400°C for 40 min to make them fully molten, and the total amount of the molten liquid can completely immerse the sapphire-based AlN substrate. The sapphire-based AlN substrate is completely immersed in the molten liquid at an immersion temperature of 400°C for an immersion time of 4 min, then taken out, washed and dried to obtain a sapphire-based AlN substrate intermediate; the AlN layer surface of the sapphire-based AlN substrate intermediate includes etching holes with a pore size of 75 nm and a depth of 70 nm.

[0024] 3) Then the sapphire-based AlN substrate intermediate is placed in the MOCVD for growth, first baked at 1130°C in an H2 atmosphere for 5 min to remove surface water oxygen, and then TMAl, TMGa and NH3 are introduced to grow an AlGaN layer. The pressure in the reaction chamber is 60 torr, the reaction temperature is 1070°C; the gas volume flow rate of TMAl is 80 sccm; the gas volume flow rate of TMGa is 6 sccm; the gas volume flow rate of NH3 is 1300 sccm; the thickness of AlGaN is 1.3 μm.

[0025] Example 2 Similar to the preparation method of Example 1, the difference is that the immersion time of the sapphire-based AlN substrate completely immersed in the molten liquid is shortened to 2 min, and the pore size of the etching holes is 50 nm and the depth is 33 nm.

[0026] Example 3 Similar to the preparation method of Example 1, the difference is that: 1) A sapphire-based AlN substrate is provided. The thickness of the AlN layer on the sapphire substrate is 3000 nm; the edge dislocation density of the sapphire-based AlN substrate is 3e 9 , and the screw dislocation density is 2e 7 .

[0027] Example 4 Similar to the preparation method of Example 1, the difference is that: 3) Then the sapphire-based AlN substrate intermediate is placed in the MOCVD for growth, first baked at 1050°C in an H2 atmosphere for 4 min to remove surface water oxygen.

[0028] Example 5 Similar to the preparation method of Example 1, the difference is that: 3) TMAl, TMGa and NH3 are introduced to grow an AlGaN layer. The pressure in the reaction chamber is 200 torr, the reaction temperature is 1150°C; the gas volume flow rate of TMAl is 160 sccm; the gas volume flow rate of TMGa is 12 sccm; the gas volume flow rate of NH3 is 1000 sccm; the thickness of AlGaN is 1 μm.

[0029] Comparative Example 1 Similar to the preparation method of Example 1, except that step 2) was omitted and no etching was performed.

[0030] Comparative Example 2 Similar to the preparation method of Example 1, except that the alkaline molten liquid in step 2) was NaOH molten liquid and the pore size of the etching hole was 40 nm.

[0031] Comparative Example 3 Similar to the preparation method of Example 1, except that the immersion time in step 2) was 7 min and the pore size of the etching hole was 110 nm.

[0032] Performance Test The AlGaN of Examples 1-5 and Comparative Example 1 was subjected to XRD RC AlGaN crystal quality, AFM, and SEM tests. Through AFM, 3 μm x 3 μm of the AlGaN surface was randomly selected, and after scanning, 3 μm x 3 μm RMS could be obtained through software. The surface roughness pit density could be calculated by selecting a random area for 500 μm x 500 μm SEM scanning and counting the surface roughness pits of 5-10 μm in size after Au was sprayed on the AlGaN sample surface. The results are shown in Table 1.

[0033] Table 1

[0034] As can be seen from Table 1, according to the comparison of Examples 1-5 and Comparative Examples 1-3, the AlGaN obtained by the method of the present application has the functions of relaxing stress, improving crystal quality, and reducing surface damage, and can realize the growth of thick-film AlGaN with high quality and good surface. According to the comparison of Example 1 and Comparative Example 1, it can be seen that Comparative Example 1 did not undergo etching treatment, and the surface roughness density was 0, indicating that when there is no etching hole, the stress cannot be relaxed, and the dislocation extension leads to poor crystal quality of the finally grown AlGaN. According to the comparison with Example 3, it can be seen that the surface roughness pit density was 2e 7 cm -2 , indicating that too high edge dislocation and screw dislocation will lead to uneven growth of etching holes.

[0035] As can be seen from Table 1, according to the comparison of Example 1 and Comparative Example 2, although the surface roughness pit density is consistent, since Comparative Example 2 uses a single molten liquid, the etching hole is too small and cannot provide enough space for stress release, resulting in XRD RC (102) values and RMS values that are inferior to those of Example 1, indicating that the mixed alkaline molten liquid ratio can further realize the growth of thick-film AlGaN with high quality and good surface.

[0036] From Table 1, according to the comparison between Example 1 and Comparative Example 3, the RMS value of 0.6 nm indicates that the excessively large hole damages the lateral growth of AlGaN, aggravates the uneven distribution of Al / Ga atoms, and makes the AlGaN surface rough.

[0037] From Table 1, according to the comparison between Example 1 and Example 5, the growth parameters for limiting AlGaN can further relax the stress, improve the crystal quality, and reduce the surface damage, and further realize the growth of thick-film AlGaN with high quality and good surface.

[0038] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing AlGaN grown on porous AlN, characterized in that, Includes the following steps: Step 1: Provide a sapphire-based AlN substrate; Step 2: Prepare an alkaline melt, immerse the substrate completely in the alkaline melt for etching, then remove, clean and dry to obtain a sapphire-based AlN substrate intermediate; the AlN layer surface of the sapphire-based AlN substrate intermediate includes etching holes with a pore size of 50~100nm. Step 3: After dehydrating and deoxygenating the sapphire-based AlN substrate intermediate, an AlGaN layer is deposited; the thickness of the AlGaN layer is 1~1.5μm.

2. The preparation method according to claim 1, characterized in that, The edge dislocation density of the sapphire-based AlN substrate is 1×10⁻⁶. 9 ~3×10 9 cm -2 The screw dislocation density is 1×10 7 ~2×10 7 cm -2 .

3. The preparation method according to claim 1, characterized in that, The sapphire-based AlN substrate includes a sapphire substrate and an AlN layer located on at least one side surface of the sapphire substrate; the thickness of the AlN layer is 1000~3000 nm.

4. The preparation method according to claim 1, characterized in that, The alkaline melt comprises NaOH and KOH, wherein the mass ratio of NaOH to KOH is 1:(3~5).

5. The preparation method according to claim 1, characterized in that, The immersion temperature is 390~520℃, and the immersion time is 3~5 minutes.

6. The preparation method according to claim 1, characterized in that, The diameter of the etched pit is 75~90nm; the depth of the etched pit is 40~100nm.

7. The preparation method according to claim 1, characterized in that, The dehydration and oxygen removal process includes baking the sapphire-based AlN substrate intermediate in a hydrogen atmosphere.

8. The preparation method according to claim 7, characterized in that, The baking temperature is 1050~1150℃, and the baking time is 4~6 minutes.

9. The preparation method according to claim 1, characterized in that, The deposited AlGaN layer comprises: An MOCVD device is used, and TMAl, TMGa or TEGa and NH3 are introduced; the pressure in the reaction chamber of the MOCVD device is 50~200 torr, and the reaction temperature is 1050~1150℃; the gas volumetric flow rate of TMAl is 60~160 sccm; the gas volumetric flow rate of TMGa or TEGa is 4~12 sccm; and the gas volumetric flow rate of NH3 is 1000~2000 sccm.

10. An AlGaN grown on porous AlN, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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