A high temperature annealing method for reducing decomposition of an aln surface

Abstract

The application discloses a high-temperature annealing method for reducing surface decomposition of AlN by eliminating surface gap. First, a covering layer material compatible with AlN is completely covered on the surface of an AlN template, and high-purity AlN powder is further inserted when two AlN templates are pasted face to face, so that subsequent high-temperature annealing is carried out in the pasted form. The prepared AlN template has a surface with greatly reduced high-temperature annealing decomposition and a large-area uniform and smooth surface; the process steps adopted by the method are compatible with semiconductor microelectronic technology, and the method is suitable for a process system of high-performance optoelectronic devices related to AlN.

Description

Technical Field

[0001] This invention relates to a high-temperature annealing method for reducing AlN surface decomposition, belonging to the field of semiconductor materials technology. Background Technology

[0002] Ultraviolet (UV) LED technology has numerous applications in disinfection, water treatment, and the medical / biochemical fields. AlGaN-based UV LEDs are widely studied as next-generation UV emitters due to their compactness and durability. AlN templates are the most suitable substrate material for fabricating AlGaN-based UV LEDs because of their low dislocation density, small lattice mismatch, and low coefficient of thermal expansion. However, current techniques for fabricating bulk AlN crystals still have many limitations, leading to significant drawbacks in UV absorption, production costs, and size of the resulting AlN crystal substrates. AlN heteroepitaxial templates grown on heterostructures are widely used for growing AlGaN-based LEDs, with representative methods being metal-organic vapor deposition (MOCVD) and sputtering. MOCVD requires growth temperatures above 1000°C. Sputtering, on the other hand, does not require high temperatures and can even be performed at room temperature. It also does not require expensive raw materials, making it one of the most attractive techniques for reducing epitaxial growth costs. This technique is simple and easy to implement, and it can grow uniform thin films over large areas.

[0003] However, sputtered AlN films suffer from high defect density due to their relatively low growth temperature, necessitating further processing. To improve the crystallinity of sputtered AlN films, the mainstream processing technique is high-temperature annealing (HTA). The crystallinity of HTA-processed AlN films can rival or even surpass that of MOCVD-grown AlN films, and it has already been used to grow high-quality AlGaN-based LEDs on HTA-processed AlN templates. Therefore, HTA-processed sputtered AlN films hold great promise for achieving high-performance AlGaN-based UV LEDs at low cost.

[0004] However, during the high-temperature annealing (HTA) process, the temperature typically reaches around 1700℃. At this high temperature, AlN is prone to surface decomposition in free space, causing Al and N atoms in the crystal to desorb from the surface, resulting in decreased surface smoothness and even film cracking. The current common method is to place two AlN templates face-to-face and then perform high-temperature annealing. While this method compresses the free space on the AlN crystal surface on a macroscopic scale and improves surface decomposition, on a microscopic scale, the two face-to-face AlN surfaces rarely contact each other, leaving numerous voids. This results in observable fine surface decomposition. The reduced uniformity of AlN surface smoothness after HTA affects subsequent material and device fabrication, reducing device yield. Therefore, a method to further suppress AlN surface decomposition is needed during the HTA process.

[0005] Due to the high annealing temperature of AlN, the coating material itself may react with the AlN surface at high temperatures when used in practice. There are reports of coating AlN surfaces with Si3N4 films; however, Si3N4 films also have drawbacks, namely, Si can diffuse into the AlN. The decomposition temperature of silicon nitride crystals is around 1800℃, and typical Si3N4 films are rarely perfect crystals with a Si:N ratio of 3:4; they are mostly excess Si, which makes Si diffusion easier. Therefore, under high-temperature annealing, Si diffusion into AlN is unavoidable. Thus, while protecting the AlN surface, preventing contamination by foreign atoms is also essential. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature annealing method to reduce the decomposition of AlN surface.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A high-temperature annealing method for reducing AlN surface decomposition involves depositing a capping layer on the surface of an AlN template, then placing two AlN templates face-to-face with high-purity AlN powder sandwiched between them, followed by high-temperature annealing of the AlN templates, and finally removing the capping layer after annealing. The capping layer is compatible with the AlN film surface, contains Al or N elements, and can be removed by chemical etching.

[0009] The capping layer is a thin Al metal film with a thickness of 0.5–10 μm. The vacuum-deposited Al metal film uses high-purity Al as the source, with a purity of over 99.999%, and is deposited onto the AlN template surface in a vacuum evaporation apparatus. There are no special requirements for the vacuum evaporation apparatus; conventional high-vacuum metal evaporation equipment can be used, such as electron beam evaporation stages, thermal evaporation stages, sputtering deposition equipment, etc. Since numerous studies have shown that the macroscopic surface undulations on a large area of ​​a semiconductor wafer typically do not exceed 10 micrometers, and can be as low as less than 1 micrometer, and Al films can undergo thickness deformation at stress points when applied face-to-face, this invention's 10-micrometer-thick Al metal film can essentially compensate for macroscopic undulations. Simultaneously, the Al coating on the AlN surface suppresses subsequent Al precipitation from the AlN.

[0010] Preferably, the annealing temperature is 1500–1800°C.

[0011] Preferably, the high-purity AlN powder refers to AlN powder with a purity of 99.99% or higher, an equivalent particle diameter of less than 200 nanometers, and a powder layer thickness of 0.1–1.0 mm. High-purity AlN powder inevitably undergoes partial decomposition during high-temperature annealing, and its products form a high concentration of AlN decomposition products on the AlN template surface, effectively hindering the chemical reaction of the AlN template in the decomposition direction. Furthermore, the AlN powder particles are very small, as small as 50 nanometers, thus filling the gaps remaining after two templates are applied, ensuring the overall consistency of the template surface environment.

[0012] Preferably, the AlN template refers to an AlN film grown on a heterogeneous substrate using MOCVD, HVPE, PVT, MBE or magnetron sputtering methods, and the face-to-face bonding method means that the AlN film of one AlN template faces the AlN film of another AlN template.

[0013] Preferably, the method for removing the coating is to use chemical acid or alkali solutions for corrosion.

[0014] Preferably, the chemical acid solution is one or a mixture of several of phosphoric acid, hydrochloric acid, and sulfuric acid, and the chemical alkali solution is a potassium hydroxide solution.

[0015] The principle of this invention is to eliminate the gaps between face-to-face stacked AlN templates. Its key feature is a two-step surface treatment: first, a capping material compatible with the AlN surface completely covers the AlN crystal surface, preventing direct exposure of the AlN surface; second, high-purity AlN powder is sandwiched between the face-to-face templates during the face-to-face bonding process. After this face-to-face bonding, high-temperature annealing is performed. The "capping material / AlN powder" structure fills the gaps between the face-to-face templates without gaps, improving the high-temperature annealing quality of the crystal. Furthermore, the materials used in this invention contain only Al and N atoms, ensuring no contamination from foreign atoms during the process.

[0016] The beneficial effects of this invention are:

[0017] 1. The high-temperature annealing method of the present invention can obtain an AlN template with a uniform surface and improve the surface flatness of the large surface area, which can be well compatible with subsequent material growth and device fabrication processes.

[0018] 2. The high-temperature annealing method of the present invention is simple, can be implemented in large quantities, and has better stability and consistency of annealing results.

[0019] 3. The high-temperature annealing performed using the method of this invention does not result in diffusion contamination from foreign atoms. Attached Figure Description

[0020] Figure 1This is a schematic diagram of the double-piece template application method of the present invention.

[0021] Figure 2 This is a scanning electron microscope image of the surface of the AlN template sample prepared in Example 1.

[0022] Figure 3 This is a scanning electron microscope image of the surface of the AlN template sample directly applied in Comparative Example 1. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0024] Example 1

[0025] like Figure 1 As shown, this embodiment provides a high-temperature annealing method to reduce AlN surface decomposition, and the surface morphology of the sample is observed and analyzed using a scanning electron microscope. The method includes the following steps:

[0026] Step 1: Place the AlN template in beakers containing acetone, ethanol, and deionized water in sequence for ultrasonic cleaning, then dry it with an air gun and place it in a sample box for later use; the ultrasonic cleaning temperature is preferably room temperature; the ultrasonic cleaning time is preferably 15 minutes; the drying is preferably nitrogen drying.

[0027] Step 2: Fix the cleaned and dried AlN template on the sample tray and place it in a metal thermal evaporation stage. Deposit a high-purity Al film with a purity higher than 99.999% and a thickness of 1 micrometer using a conventional metal evaporation process.

[0028] Step 3: Transfer multiple samples after high-purity Al film deposition into a drying oven for the next step;

[0029] Step 4: In the drying oven, apply AlN powder to the sample surface with the opposite side facing up, with a thickness of 1 mm, then cover it with the sample with the other side facing down and press it firmly.

[0030] Step 5: Apply the sample pair face-to-face (structure as shown) Figure 1 As shown), it is placed horizontally in a high-temperature annealing furnace for high-temperature annealing at 1700℃, and the annealing time can be from 0.5 hours to 5 hours.

[0031] Step 6: After annealing and cooling, place the sample in dilute phosphoric acid to remove all residual coatings on the AlN surface. Finally, ultrasonically clean the sample with deionized water and dry it with nitrogen.

[0032] The scanning electron microscope images of the AlN template surface obtained through the above steps are as follows: Figure 2 As shown.

[0033] Comparative Example 1

[0034] The AlN template was placed in beakers containing acetone, ethanol, and deionized water respectively for ultrasonic cleaning, then dried with an air gun and placed in a sample box for later use. The ultrasonic cleaning temperature was preferably room temperature; the ultrasonic cleaning time was preferably 15 minutes; and the drying was preferably done with nitrogen.

[0035] The AlN template was then placed in a high-temperature annealing furnace for annealing at 1700℃. The resulting scanning electron microscope (SEM) image of the AlN template surface is shown below. Figure 3 As shown. Obviously, Figure 2 The sample prepared by this invention, as demonstrated, has a smoother surface and lacks the characteristics of AlN decomposition. Figure 3 The AlN surface prepared by the traditional high-temperature annealing process exhibits numerous fine grooves, showing the partial decomposition characteristics of the AlN surface.

Claims

1. A high-temperature annealing method for reducing AlN surface decomposition, characterized in that... A capping layer is deposited on the surface of an AlN template. Then, two AlN templates are placed face-to-face, with high-purity AlN powder sandwiched between them. The AlN templates are then subjected to high-temperature annealing. After annealing, the capping layer is removed. The capping layer is a metallic Al thin film with a thickness of 0.5–10 μm. The AlN template refers to a structural material on which an AlN film is grown on a heterogeneous substrate, and the face-to-face bonding method means that the AlN film of one AlN template faces the AlN film of another AlN template.

2. The high-temperature annealing method for reducing AlN surface decomposition according to claim 1, characterized in that: The annealing temperature is 1500~1800℃.

3. The high-temperature annealing method for reducing AlN surface decomposition according to claim 1, characterized in that: The high-purity AlN powder refers to AlN powder with a purity of 99.99% or higher, an equivalent particle diameter of less than 200 nanometers, and a powder layer thickness of 0.1~1.0 mm.

4. The high-temperature annealing method for reducing AlN surface decomposition according to any one of claims 1-3, characterized in that: The AlN template refers to an AlN thin film grown on a heterogeneous substrate using MOCVD, HVPE, PVT, MBE, or magnetron sputtering methods.

5. The high-temperature annealing method for reducing AlN surface decomposition according to claim 4, characterized in that: The method to remove the coating is to use chemical acid or alkali solutions for corrosion.

6. The high-temperature annealing method for reducing AlN surface decomposition according to claim 5, characterized in that: The chemical acid solution is one or a mixture of phosphoric acid, hydrochloric acid, and sulfuric acid, and the chemical alkali solution is a potassium hydroxide solution.

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