Preparation of single crystal diamond self-supporting film and low-damage peeling method

Abstract

This invention relates to a method for preparing a self-supporting single-crystal diamond film and a low-damage peeling process, belonging to the field of semiconductor materials and thin film preparation technology. It aims to achieve high-quality lateral epitaxial growth of diamond and complete peeling of the diamond film through a simple wet etching process. Specifically, the method includes substrate pretreatment, magnetron sputtering, lateral epitaxial growth, and chemical peeling. This invention offers advantages such as high-quality epitaxy, non-destructive peeling, reusable substrate, and wide applicability.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and thin film preparation technology. Specifically, it relates to a method for preparing a diamond self-supporting film, and more particularly to a process for achieving lateral epitaxial growth and low-damage peeling of a diamond film using a silicon dioxide transition layer and a metallic iridium protective layer. Background Technology

[0002] Diamond, due to its unique tetrahedral arrangement of carbon atoms, exhibits outstanding and relatively independent optical, thermal, mechanical, and electrical properties. With its extremely high thermal conductivity, wide bandgap, high carrier mobility, and excellent chemical stability, diamond is hailed as the "ultimate semiconductor material," showing broad application prospects in high-temperature, high-frequency, and high-power electronic devices. Simultaneously, due to its extremely wide spectral transmission range, excellent thermo-optical properties, significant mechanical strength, and unique nonlinear optical characteristics, diamond has also attracted considerable attention in the field of optical windows. However, the high price and limited size of natural diamond restrict its widespread application. Therefore, the preparation of single-crystal diamond using chemical vapor deposition (CVD) has become a current research hotspot. With the continuous expansion of the application range of preparation technology, obtaining high-quality synthetic diamond with low dislocation density, high purity, low residual stress, and low absorption coefficient has become an important goal in this field. Against this backdrop, how to achieve efficient and non-destructive separation of large-area diamond epitaxial layers from their growth substrates has become a key technical challenge that urgently needs to be solved.

[0003] Currently, the most widely used method for separating single-crystal diamond epitaxial layers from the substrate is laser cutting. This method utilizes thermal effects to transform the diamond phase into a graphite phase, forming a thermally damaged layer to achieve separation. Its advantages include non-contact operation and high efficiency; however, cutting losses are proportional to depth, with thickness losses exceeding 0.3 mm in large-size (greater than 10 × 10 mm) processing, and cracking is common. Water-guided laser cutting can reduce losses, but its feasibility for large-size applications is unknown. Ion implantation uses high-energy ions to form a buried sacrificial layer, which is then removed by etching after annealing and graphitization, achieving separation of the epitaxial layer from the substrate. Its advantages include the ability to form films of specific thicknesses; however, it suffers from expensive equipment, complex processes, the need for annealing and diffusion, and residual strain affecting the optical quality of the separated film. The microneedle method involves fabricating micropatterns / needles on a heterogeneous substrate and utilizing the self-fracture effect during cooling to achieve separation. Its advantages include suppressing substrate bending and eliminating stress; however, it suffers from complex growth processes and relatively poor epitaxial layer crystal quality. SiO2 mask method: Selective epitaxy is performed using patterned SiO2 masks. Tensile stress is generated during the cooling process based on the difference in thermal expansion coefficients, which leads to cracking and peeling. The advantage is that self-peeling can be achieved; the disadvantage is that stress control requirements are high.

[0004] The core problem facing existing technologies is that the high bonding strength between the diamond epitaxial layer and the substrate, lattice mismatch, large differences in thermal expansion, and poor etching selectivity lead to difficult peeling, damaged crystal quality, and easy interface damage. Therefore, there is an urgent need to develop a composite substrate structure and preparation method that can ensure high-quality epitaxial growth and achieve non-destructive and efficient peeling. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing and removing a self-supporting diamond film. A SiO2 sacrificial layer and a top Ir film are sequentially deposited on a substrate to form a SiO2 / Ir two-layer mask structure. The top Ir layer provides a surface for diamond epitaxial growth and prevents subsequent plasma etching of the SiO2 layer. Subsequently, a microwave plasma chemical vapor deposition (MPCVD) system is used to achieve epitaxial lateral growth of the diamond film. Finally, the SiO2 sacrificial layer is removed by hydrofluoric acid etching to obtain a self-supporting CVD diamond epitaxial layer.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing and removing a single-crystal diamond self-supporting film with low damage is disclosed, aiming to achieve lateral epitaxial growth of high-quality diamond and complete removal of the diamond film through a simple wet etching process. The method includes the following steps:

[0008] S1: Substrate pretreatment

[0009] Prepare a diamond substrate. To ensure the cleanliness of the diamond substrate used in the experiment, ultrasonically clean the diamond substrate before the experiment to remove any non-diamond phases, dust, and other contaminants that may exist on the surface of the diamond substrate. Use acetone, ethanol, and deionized water to ultrasonically clean for 10 minutes in sequence, and then blow dry for later use.

[0010] S2: Magnetron sputtering process

[0011] The cleaned seed crystal is placed in a magnetron sputtering device, and the sputtering gases are argon gas with a purity of 99.9% and oxygen gas with a purity of 99.9%.

[0012] Deposition of transition layer: The power supply used is radio frequency, and single crystal silicon (high purity Si target) is used as the target material. A silicon dioxide (SiO2) thin film is deposited on the surface of the diamond substrate as a transition layer.

[0013] Deposition of protective layer: The power supply used is DC, and iridium metal is used as the target material to deposit a thin film of iridium metal as a protective layer on the surface of the silicon dioxide transition layer;

[0014] S3: Lateral epitaxial growth

[0015] The composite substrate obtained in step S2 is placed in a microwave plasma chemical vapor deposition (MPCVD) device to perform lateral epitaxial growth of diamond film, forming a diamond epitaxial layer;

[0016] S4: Chemical stripping

[0017] The sample with the diamond epitaxial layer is immersed in a hydrofluoric acid (HF) solution. The intermediate silica transition layer is removed by etching with hydrofluoric acid, thereby achieving mechanical separation between the upper diamond epitaxial layer and the lower diamond substrate, and obtaining a self-supporting diamond film.

[0018] Preferably, in step S2, the process parameters for depositing the silicon dioxide transition layer are: power 100 W, chamber pressure 1.2 Pa, temperature 400°C, argon flow rate 50 sccm, oxygen flow rate 20 sccm, rotation speed 4 RPM, sputtering time 20~100 minutes, and deposition thickness controlled between 400nm and 450nm.

[0019] Preferably, in step S2, when depositing the protective layer, the sputtering gas is argon gas with a purity of 99.9%, the temperature is raised to 500°C, and other process parameters are set as follows: power 120 W, chamber pressure 1.3 Pa, argon gas flow rate 50 sccm, rotation speed 4 RPM, sputtering time 5 minutes; the iridium layer serves as a protective layer, on the one hand to prevent the hydrogen plasma in the subsequent MPCVD growth process from etching the underlying silicon dioxide, and on the other hand as a lattice matching layer for diamond heteroepitaxial growth.

[0020] Preferably, in step S3, the process parameters for the lateral epitaxial growth are set as follows: CH4 / H2 and N2 flow rates and pressures are 8%, 0.01 sccm, and 100~120 Torr, respectively; the growth temperature is set to 880~900°C; and the growth duration is 38 hours. By adjusting the parameters, two-dimensional lateral growth of diamond on the iridium layer is achieved, reducing the extension of longitudinal defects.

[0021] Preferably, in step S4, the hydrofluoric acid solution has a mass concentration of 40%, the immersion time depends on the thickness of the silica layer, and the entire corrosion process takes 10 to 20 hours.

[0022] The principle of this invention is as follows: the silica and Ir introduced by sputtering do not form a dense coating on the diamond surface, and under high-temperature plasma, they easily form a microporous structure, which can serve as a micro / nano mask for subsequent lateral epitaxial growth. During the cooling process, the difference in thermal expansion coefficients between silica and diamond can cause the diamond pillars grown in the micropores to break. Simultaneously, using iridium as a protective layer and epitaxial template ensures high-quality diamond growth during MPCVD, avoiding direct etching of the mask layer by hydrogen plasma. Finally, utilizing the high selectivity of hydrofluoric acid on silica (hydrofluoric acid hardly reacts with diamond and metallic iridium), non-destructive exfoliation is achieved.

[0023] Beneficial effects:

[0024] 1. High-quality epitaxy: The iridium protective layer provides a good lattice matching interface, and combined with MPCVD lateral epitaxy technology, high-quality diamond films with low defect density can be obtained.

[0025] 2. Non-destructive peeling: The silicon oxide mask layer is etched by hydrofluoric acid wet etching, which is simple and inexpensive, and will not cause mechanical or laser damage to the diamond epitaxial layer, thus ensuring the integrity of the self-supporting film.

[0026] 3. Reusable substrate: The surface of the lower diamond substrate after peeling is flat. After simple polishing, it can be used as a "seed" to prepare composite substrates again, realizing reuse and greatly reducing production costs.

[0027] 4. Wide range of applications: This method is not only applicable to homoepitaxial growth, but also provides a feasible solution for preparing large-area single-crystal diamond on heterogeneous substrates. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation and peeling process in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the Raman spectra of the diamond substrate and the release layer. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Example 1

[0032] Using a CVD single-crystal diamond substrate measuring 7 mm × 7 mm and 0.7 mm thick, surface contaminants were removed by sequential ultrasonic cleaning in acetone, ethanol, and deionized water for 15 minutes (40 kHz). Subsequently, a 400 nm thick silicon dioxide film was deposited first, followed by a 50 nm thick iridium layer, using magnetron sputtering as described in step two. The composite substrate was placed in an MPCVD chamber and grown for 38 hours at a microwave power of 2.8 kW, a pressure of 14 kPa, and a temperature of 880–900°C, with a CH4 / H2 gas flow rate ratio of 32 / 400 sccm and an N2 flow rate of 0.01 sccm. The grown sample was then immersed in 40% hydrofluoric acid at room temperature for 10–20 hours to separate the diamond epitaxial layer from the substrate. After removal, it was rinsed with deionized water and dried with nitrogen to obtain a self-supporting diamond film. Raman spectroscopy showed that its diamond characteristic peak was located near 1332 cm⁻¹. Figure 2 As shown, the narrow half-width at half-maximum indicates good crystal quality.

[0033] Example 2

[0034] This embodiment is similar to Example 1, using a CVD single-crystal diamond substrate with dimensions of 7 mm × 7 mm and a thickness of 0.7 mm. Surface contaminants were removed by sequentially ultrasonically cleaning in acetone, ethanol, and deionized water for 15 minutes (40 kHz). Using the magnetron sputtering method described in step two, an iridium thin film with a thickness of approximately 27 nm was first deposited on the substrate. Then, repeating the steps in Example 1, a silicon dioxide layer with a thickness of approximately 400 nm and a metallic iridium layer with a thickness of approximately 39 nm were sequentially deposited on the diamond / iridium composite substrate. The composite substrate was placed in an MPCVD chamber and grown for 38 hours under conditions of microwave power 2.8 kW, pressure 14 kPa, and temperature 880–900°C, with a CH4 / H2 mixed gas flow rate (32 / 400 sccm). The grown sample was then immersed in 40% hydrofluoric acid at room temperature for 10–20 hours to separate the diamond epitaxial layer from the substrate.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing and low-damage peeling of a single-crystal diamond self-supporting film, aiming to achieve lateral epitaxial growth of high-quality diamond and complete peeling of the diamond film through a simple wet etching process, specifically including the following steps: S1: Substrate pretreatment Prepare a diamond substrate. To ensure the cleanliness of the diamond substrate used in the experiment, ultrasonically clean the diamond substrate before the experiment to remove any non-diamond phases, dust, and other contaminants that may exist on the surface of the diamond substrate. Use acetone, ethanol, and deionized water to ultrasonically clean for 10 minutes in sequence, and then blow dry for later use. S2: Magnetron sputtering process The cleaned seed crystal is placed in a magnetron sputtering device, and the sputtering gases are argon gas with a purity of 99.9% and oxygen gas with a purity of 99.9%. Deposition of transition layer: The power supply used is radio frequency, and single crystal silicon is used as the target material. A silicon dioxide thin film is deposited on the surface of the diamond substrate as a transition layer. Deposition of protective layer: The power supply used is DC, and iridium metal is used as the target material to deposit a thin film of iridium metal as a protective layer on the surface of the silicon dioxide transition layer; S3: Lateral epitaxial growth The composite substrate obtained in step S2 is placed in a microwave plasma chemical vapor deposition apparatus to perform lateral epitaxial growth of a diamond film, forming a diamond epitaxial layer. S4: Chemical stripping The sample with the diamond epitaxial layer is immersed in hydrofluoric acid solution. The intermediate silicon dioxide transition layer is removed by hydrofluoric acid etching, thereby achieving mechanical separation between the upper diamond epitaxial layer and the lower diamond substrate, and obtaining a self-supporting diamond film.

2. The method of claim 1, wherein the method further comprises: In step S2, the process parameters for depositing the silicon dioxide transition layer are: power 100 W, chamber pressure 1.2 Pa, temperature 400°C, argon flow rate 50 sccm, oxygen flow rate 20 sccm, rotation speed 4 RPM, sputtering time 20~100 minutes, and deposition thickness controlled between 400nm and 450nm.

3. The method of claim 1, wherein the method further comprises: In step S2, during the deposition of the protective layer, the sputtering gas is argon gas with a purity of 99.9%, the temperature is raised to 500°C, and other process parameters are set as follows: power 120 W, chamber pressure 1.3 Pa, argon gas flow rate 50 sccm, rotation speed 4 RPM, sputtering time 5 minutes; the iridium layer serves as a protective layer, on the one hand to prevent the hydrogen plasma in the subsequent MPCVD growth process from etching the underlying silicon dioxide, and on the other hand as a lattice matching layer for diamond heteroepitaxial growth.

4. The method of claim 1, wherein the method further comprises: In step S3, the process parameters for the lateral epitaxial growth are set as follows: CH4 / H2 and N2 flow rate and pressure are 8%, 0.01 sccm and 100~120 Torr, respectively; the growth temperature is set to 880~900°C; and the growth duration is 38 hours. By adjusting the parameters, two-dimensional lateral growth of diamond on the iridium layer is achieved, reducing the extension of longitudinal defects.

5. The method of claim 1, wherein the method further comprises: In step S4, the hydrofluoric acid solution has a mass concentration of 40%, the immersion time depends on the thickness of the silica layer, and the entire corrosion process takes 10 to 20 hours.

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