Method for testing dislocation density of aluminum nitride substrate

Abstract

The application discloses a kind of aluminum nitride substrate dislocation density test methods, belong to semiconductor material defect detection technical field, including the following steps: AlN substrate surface organic cleaning;AlN substrate is cleaned after hydrogen in-situ pretreatment to remove surface oxide layer;AlN substrate is immersed in HCl solution after hydrogen in-situ treatment and is treated with low temperature preferential etching to expose dislocation;After etching treatment, washing, drying, microscopic observation and dislocation density statistics.The method of the application overcomes the defects of traditional molten KOH / NaOH etching method, such as high operating temperature (300-400 DEG C is required), difficult to remove alkali residue, and dislocation is missed due to the interference of oxide layer, etc., has the advantages of low operating temperature, no solid residue, and reusable substrate, etc., and can realize the accurate and convenient characterization of AlN substrate dislocation density.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, specifically relating to a method for testing dislocation density on aluminum nitride substrates. Background Technology

[0002] Aluminum nitride (AlN), as a next-generation ultra-wide bandgap semiconductor material, holds significant promise for applications in deep ultraviolet light-emitting devices (DUV-LEDs), high-power electronic devices, and surface acoustic wave (SAW) devices. High-quality AlN single-crystal substrates are fundamental for fabricating these devices, while dislocations in the substrate (including screw dislocations, edge dislocations, and mixed dislocations) are critical defects affecting device performance and reliability. However, AlN wafer growth is still in its early stages, and research on substrate dislocation identification and detection is far from sufficient.

[0003] Currently, the main publicly available method for dislocation characterization of AlN wafers is the molten alkali etching method (KOH / NaOH). This method uses molten KOH or a KOH-NaOH eutectic at high temperatures (approximately 300°C~500°C) to etch the AlN surface. While this method can effectively reveal dislocations, it has the following significant drawbacks: First, it requires operation at temperatures above 300°C, posing a high operational risk and demanding stringent requirements for equipment corrosion resistance. Second, after cooling, the molten alkali solution easily forms difficult-to-remove alkaline residues (such as KAlO2) on the sample surface. These residues not only obscure the observation of the etching pits but can also severely contaminate subsequent device fabrication processes. Due to AlN's sensitivity to water, it is impossible to completely remove the alkali residues by rinsing with large amounts of water. The residual alkaline substances will continue to corrode the wafer surface, affecting the accuracy of subsequent characterization and even damaging the sample. Given the current high cost and scarcity of aluminum nitride substrates, further epitaxy after processing is the optimal choice. Third, the cleaning process for alkaline residues is cumbersome, often requiring multiple acid washes and ultrasonic cleanings, increasing process complexity and time costs. Fourth, after AlN is exposed to air, an oxide passivation layer (mainly Al2O3) quickly forms on its surface, typically 2-5 nm thick. This oxide layer has high chemical stability and acts as a masking layer during corrosion, hindering uniform contact between the etchant and the AlN substrate. This results in some dislocation pits not being effectively displayed or exhibiting uneven pit morphology, leading to an underestimation of dislocation density or measurement errors.

[0004] Therefore, there is an urgent need to develop an AlN dislocation etching method that operates at a low temperature, leaves no alkali residue, and can effectively remove the surface oxygen passivation layer, so as to achieve accurate characterization of the dislocation density of AlN substrates and allow for subsequent epitaxial growth after the process. Summary of the Invention

[0005] In view of the above, the purpose of this invention is to provide a method for testing the dislocation density of aluminum nitride substrates, which is based on a combination of in-situ hydrogen pretreatment and hydrochloric acid preferential etching. It has the characteristics of low operating temperature, no solid residue, and effective removal of surface oxide passivation layer. It can achieve more accurate and convenient characterization of dislocation density of AlN substrates, and the treated aluminum nitride substrates can also be used for subsequent epitaxial growth.

[0006] To achieve the above-mentioned objective, an embodiment provides a method for testing the dislocation density of an aluminum nitride substrate, comprising the following steps: Organic cleaning of the surface of AlN single crystal substrate; After in-situ high-temperature hydrogen pretreatment and cleaning, the AlN substrate is used to remove the surface oxide layer and form a highly active sensitive region at the dislocation outcrop. The AlN substrate, after in-situ hydrogen treatment, was immersed in HCl solution for low-temperature preferential etching to expose dislocations and form etching pits at the dislocation outcrops. After corrosion treatment, the process included cleaning, drying, microscopic observation, and dislocation density statistics.

[0007] In this invention, in-situ hydrogen reduction removes the surface oxide layer and enhances the activity of the aluminum nitride surface. Under high-temperature conditions, hydrogen has strong reducing properties and can react with the native oxide layer (AlOx) on the AlN surface, converting it into volatile H2O and metallic Al, thereby completely removing the oxide layer and exposing a clean intrinsic AlN surface. Taking Al2O3 as an example, the reaction mechanism is: Al2O3 + 3H2 → 2Al + 3H2O↑. The clean AlN surface allows the etching solution to directly and uniformly contact the dislocation outcrop region, ensuring that each dislocation outcrop is fully etched, thus improving the integrity and uniformity of dislocation exposure.

[0008] Preferably, the cleaned AlN substrate is placed in the reaction chamber of an MOCVD device, and a hydrogen etching process is performed on the (0001) orientation plane (Al plane). Hydrogen gas is introduced, and the surface of the AlN substrate is subjected to in-situ hydrogen pretreatment under preset temperature and time conditions. The reducing properties of hydrogen are used to reduce and remove the native oxide layer (AlOx) on the AlN surface, exposing a clean intrinsic AlN surface. More preferably, the temperature of the in-situ hydrogen pretreatment is 1000-1300℃, the treatment time is 5-30 minutes, the hydrogen flow rate is 50-72L, and the pressure is 50-80mbar.

[0009] In this invention, the low-temperature preferred corrosion mechanism of HCl is as follows: In HCl solution, dislocation outcrops possess higher chemical potential and dangling bond density due to lattice distortion, resulting in a significantly higher corrosion rate than dislocation-free, intact lattice regions. The H+ in HCl... + and Cl -Ions can selectively and preferentially attack Al-N bonds at dislocation outcrops, forming characteristic hexagonal corrosion pits at these outcrops. HCl is excellent for removing oxides from AlN surfaces and, after appropriate surface treatment, can serve as an effective preferred etchant.

[0010] Preferably, the AlN substrate, after in-situ hydrogen treatment, is immersed in an HCl solution for selective etching. The HCl solution has a mass concentration of 25-40%, the etching temperature is room temperature to 70°C, and the etching time is 5-15 minutes. The HCl solution selectively and preferentially etches the lattice distortion regions at dislocation outcrops, forming characteristic etching pits.

[0011] In this invention, hydrogen pretreatment and HCl corrosion have a synergistic effect in exposing dislocations: hydrogen pretreatment not only removes the surface oxide layer, but may also form a hydrogen passivation layer on the AlN surface. This hydrogen passivation layer can be selectively desorbed during the subsequent HCl corrosion process, further enhancing the difference in corrosion rate between the dislocation outcrop and the intact lattice region, and improving the contrast and recognizability of the corrosion pits.

[0012] Preferably, the organic cleaning of the AlN substrate surface includes: sequentially placing the AlN single crystal substrate to be tested in anhydrous ethanol for ultrasonic cleaning to remove organic contaminants from the surface, and then drying it with high-purity nitrogen gas.

[0013] Preferably, the post-etching cleaning and drying process includes: after etching, removing the AlN substrate and rinsing it with deionized water, then drying it with high-purity nitrogen gas.

[0014] Preferably, the microscopic observation and dislocation density statistics include: observing the surface of the etched AlN substrate using an optical microscope or a scanning electron microscope (SEM), counting the number of etch pits per unit area, calculating the dislocation density (EPD value), and distinguishing screw dislocations (TSD), edge dislocations (TED), and base plane dislocations (BPD) based on the morphological characteristics of the etch pits.

[0015] Compared with the prior art, the beneficial effects of the present invention include at least the following: (1) Significantly reduced operating temperature: Traditional molten KOH / NaOH methods require high temperatures of 300-500℃. Strong alkali methods not only damage crystals and endanger personnel and the environment, but also have an extremely narrow high-temperature corrosion window, making it difficult to accurately measure misalignment density. The method of this invention safely and controllably performs hydrogen treatment in a closed MOCVD / CVD / RTP chamber, and the hydrochloric acid corrosion step only requires room temperature to 70℃, significantly reducing operational hazards and energy consumption. For steps requiring only corrosion, the use of high-temperature molten alkali is avoided.

[0016] (2) No solid residue pollution: After etching with HCl solution, only deionized water is needed to completely remove the residual acid. It will not produce solid residues that are difficult to dissolve, similar to molten alkali, thus avoiding secondary pollution of the sample surface, ensuring the clarity of subsequent microscopic observation, and facilitating the subsequent epitaxial growth of the sample. Given the current situation of expensive and scarce aluminum nitride substrates, being able to further achieve epitaxy after processing is the optimal choice.

[0017] (3) Effective removal of oxide layer interference: In-situ hydrogen pretreatment can remove the natural oxide layer on the AlN surface, expose the clean AlN intrinsic surface, ensure direct contact between the corrosion liquid and the dislocation outcrop, make the dislocation exposure more complete and uniform, and facilitate the accuracy of dislocation density statistics.

[0018] (4) Good process compatibility: The hydrogen pretreatment step can be completed in standard MOCVD equipment, which is compatible with AlN epitaxial growth equipment and facilitates in-situ integration with epitaxial processes. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for testing dislocation density on an aluminum nitride substrate provided in the embodiments; Figure 2 This is a 1-inch aluminum nitride × 5x optical microscope image obtained by the method of the present invention, with a scale bar of 400 μm, provided in the embodiment. Figure 3 This is a 1-inch aluminum nitride × 100x optical microscope image obtained by the method of the present invention, with a scale bar of 400μm, provided in the embodiment. Figure 4 This is an optical mirror image of the epitaxial gallium nitride after dislocation detection in the example, with a scale bar of 400 μm; Figure 5 This is a topographic image of a 1-inch aluminum nitride sample under a 5x optical microscope, with a scale bar of 400 μm. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0022] like Figure 1As shown, the embodiment provides a method for testing the dislocation density of an aluminum nitride substrate, including the following steps: S1, Organic cleaning of AlN substrate surface; S2, AlN substrate after in-situ hydrogen pretreatment and cleaning to remove surface oxide layer; S3, the AlN substrate after in-situ hydrogen treatment is immersed in HCl solution for low-temperature preferential etching to expose dislocations. S4, after corrosion treatment, cleaning, drying, microscopic observation and dislocation density statistics.

[0023] Based on the above testing methods and steps, the following embodiments and comparative examples are provided to demonstrate that the method of the present invention has the characteristics of low operating temperature, no solid residue, and effective removal of surface oxide passivation layer. Furthermore, it can be used for subsequent epitaxial growth after dislocation characterization, thus achieving a more convenient and economical technical effect for dislocation characterization on AlN substrates.

[0024] Example 1 (1) Take a 1-inch or 1cm*1cm AlN single crystal polishing wafer, place it in anhydrous ethanol for ultrasonic cleaning for 10 minutes each, and then blow it dry with high-purity nitrogen.

[0025] (2) The cleaned AlN substrate was placed in the reaction chamber of the MOCVD equipment, and hydrogen etching was performed on the (0001) orientation plane (Al plane). A mixed gas of H2 (flow rate 62L) was introduced, the temperature was raised to 1300℃, and the temperature was maintained for 5 minutes at a pressure of 60 mbar to perform in-situ hydrogen pretreatment on the AlN surface.

[0026] (3) After the pretreatment is completed, the chamber is cooled to room temperature, the AlN substrate is removed, and immersed in a 37% HCl solution. It is then etched for 15 minutes in a 60°C water bath.

[0027] (4) After etching, remove the AlN substrate, rinse it three times with deionized water, and dry it with high-purity nitrogen.

[0028] (5) The etched AlN surface was observed using an optical microscope. The observation results are as follows: Figure 2 and Figure 3 As shown, the corrosion pits are regular hexagonal with clear boundaries.

[0029] (6) After completing the dislocation criteria, a gallium nitride layer was epitaxially grown on the substrate surface using the MOCVD method. The observation results are as follows: Figure 4 As shown, the surface is smooth and defect-free, and the crystal quality of the epitaxial gallium nitride is shown in Table 1: Table 1 Comparative Example 1 Dislocation etching of adjacent substrates of the same AlN ingot was performed using the traditional molten KOH / NaOH method: KOH and NaOH were mixed in a mass ratio of 1:1, heated to 350°C to melt, and the AlN substrate was immersed in the molten alkali for 5 minutes for etching. After removal and cooling, it was rinsed with deionized water.

[0030] The results showed that there were obvious traces of alkali residue on the surface of the wafer. The strong alkali method not only damages the crystal and endangers personnel and the environment, but also has an extremely narrow high-temperature corrosion window, making it difficult to accurately mark the fault density.

[0031] Comparative Example 2 Without hydrogen treatment, the cleaned AlN substrate was directly immersed in an HCl solution for low-temperature preferential etching according to the parameters in Example 1. The AlN surface was then observed. The observation results are as follows: Figure 5 As shown, no obvious corrosion pits were found.

[0032] Comparative Example 3 The cleaned AlN substrate was treated with hydrogen in MOCVD at a temperature of 600°C according to the parameters in Example 1; then it was immersed in HCl solution for low-temperature preferential etching according to the parameters in the example. The AlN substrate after treatment was observed, and the observation results showed that no obvious corrosion pits were found.

[0033] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing dislocation density on an aluminum nitride substrate, characterized in that, Includes the following steps: Organic cleaning of the surface of AlN single crystal substrate; After in-situ high-temperature hydrogen pretreatment and cleaning, the AlN substrate is used to remove the surface oxide layer and form a highly active sensitive region at the dislocation outcrop. The AlN substrate, after in-situ hydrogen treatment, was immersed in HCl solution for low-temperature preferential etching to expose dislocations and form etching pits at the dislocation outcrops. After corrosion treatment, the process included cleaning, drying, microscopic observation, and dislocation density statistics.

2. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, The in-situ high-temperature hydrogen pretreatment is performed at a temperature of 1000-1300℃, for a time of 5-30 minutes, with a hydrogen flow rate of 50-72L and a pressure of 50-80mbar.

3. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, During the corrosion treatment, the mass concentration of the HCl solution is 25-40%, the corrosion temperature is room temperature to 70℃, and the corrosion time is 5-15 minutes.

4. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, The reaction chamber for in-situ high-temperature hydrogen pretreatment is the reaction chamber of an MOCVD, chemical vapor deposition, or rapid thermal annealing equipment.

5. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, Organic cleaning of AlN substrate surface includes: sequentially placing the AlN single crystal substrate to be tested in anhydrous ethanol for ultrasonic cleaning to remove organic contaminants on the surface, and then drying it with high-purity nitrogen gas.

6. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, After corrosion treatment, the product is rinsed with deionized water and then dried by blowing with high-purity nitrogen.

7. The method for testing dislocation density on an aluminum nitride substrate according to claim 1, characterized in that, Microscopic observation and dislocation density statistics include: observing the surface of the etched AlN substrate, counting the number of etch pits per unit area, calculating the dislocation density, and distinguishing screw dislocations, edge dislocations and base plane dislocations based on the morphological characteristics of the etch pits.

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