CN110172732A - The method for preparing nitride single crystal substrates using transition metal nitride sacrificial layer - Google Patents

Abstract

The invention discloses a method for preparing a nitride single crystal substrate by using a transition metal nitride sacrificial layer. The present invention introduces a β-phase transition metal nitride sacrificial layer with hexagonal crystal structure symmetry between the nitride single crystal thick film and the nitride template, and utilizes the crystal orientation matching between the transition metal nitride sacrificial layer and the nitride single crystal thick film , small lattice mismatch, and the characteristics of selective etching, the selective etching method is used to separate the nitride single crystal thick film from the nitride template, and obtain a large-size, high-quality self-supporting nitride single crystal substrate The present invention is easy to directly nucleate and grow a high-quality nitride single crystal thick film on the transition metal nitride sacrificial layer, without introducing an additional process to assist the nucleation of a nitride single crystal thick film, simplifying the process flow; without using complicated laser lift-off technology , the nitride template can be reused, reducing the difficulty and cost of the stripping process, and improving the yield; the equipment is simple, low energy consumption, easy to operate, and suitable for industrial production.

Description

Method for preparing nitride single crystal substrate by using transition metal nitride sacrificial layer

technical field

The invention relates to the preparation technology of a nitride single crystal substrate, in particular to a method for preparing a nitride single crystal substrate by using a transition metal nitride sacrificial layer.

Background technique

Nitride semiconductor thin film materials with direct bandgap have a continuously adjustable band gap between 0.7-6.2eV, which can realize efficient n-type and p-type doping, good chemical stability, and strong radiation resistance. It is used in optoelectronic devices and electronics Device fields, such as solar cells, visible light LEDs, ultraviolet light sources, high-temperature and high-frequency electronic devices, power electronic devices, extreme environment electronic devices, etc., have great application value. Developed countries represented by the United States and Japan have successively launched development plans for nitride materials and devices as early as the last century, and have achieved a series of results in 5G communications, quantum light sources and other application fields.

Thin film epitaxy is the basis of device fabrication. Due to the scarcity of nitride homogeneous substrates, heteroepitaxy has become the mainstream technology for nitride thin film epitaxy. Although the heteroepitaxy method has the advantages of low cost and wide application, there is a large lattice mismatch and thermal mismatch between the heterogeneous substrate and the nitride film, which makes the prepared nitride film have lower crystal quality and Extremely high dislocation density (>10 ⁹ cm ^-2 ). Crystal defects in nitride epitaxial films will form non-radiative recombination centers in optoelectronic devices, reduce luminous efficiency, and form leakage channels in electronic devices, reduce breakdown field strength and increase reverse leakage, which seriously restricts the use of nitride films in Developments in optoelectronic and electronic device applications. In contrast, homoepitaxial nitride films have atomically flat surface morphology, low dislocation density (~10 ⁵ cm ^-2 ) and high crystal quality, which can significantly improve the performance of nitride optoelectronic devices and electronics. device performance. Therefore, the research and development of low-cost, high-quality nitride single crystal substrates is of great significance.

Currently, methods for preparing nitride single crystal substrates mainly include: high temperature and high pressure method, ammonothermal method, sodium flux method, and hydride vapor-phase epitaxy (HVPE) method, etc. However, the first three methods not only have limited sizes of nitride single crystal substrates, but also require high-temperature and high-pressure equipment or active melt assistance, which consumes a lot of energy and is dangerous. Due to its simple equipment, fast growth speed, and low cost, the HVPE method can grow large-size, high-quality nitride single crystal substrates, and is currently the mainstream preparation technology for nitride single crystal substrates. However, the HVPE method has disadvantages such as immature nitride single crystal thick film and substrate separation technology, and single crystal thick film is easily broken.

Contents of the invention

Aiming at the problems existing in the above prior art, the present invention proposes a method for preparing a nitride single crystal substrate by using a transition metal nitride sacrificial layer, through crystal phase selection and thickness control of the transition metal nitride sacrificial layer, simplifying The nitride single crystal thick film growth and stripping process prepared by the HVPE method reduces the difficulty of stripping the nitride single crystal thick film, thereby obtaining a low-cost, high-quality self-supporting nitride single crystal substrate.

The method for preparing a nitride single crystal substrate using a transition metal nitride sacrificial layer of the present invention comprises the following steps:

1) Select the nitride template with hexagonal crystal structure symmetry as the nitride with hexagonal crystal structure symmetry

Single crystal thick film epitaxial substrates, and chemical cleaning to make the surface clean, nitride templates include heterogeneous substrates and raw materials

A single crystal nitride film grown on it, the single crystal nitride film has a hexagonal crystal structure symmetry;

2) Deposit transition metal nitride on the nitride template by thin film deposition method, and adjust the transition metal nitrogen by controlling the time

The thickness of the compound, and the transition metal nitrogen can be regulated by controlling the temperature and the ratio of transition metal atoms to nitrogen atoms

The crystal orientation and stoichiometric ratio of the compound, thus forming a hexa

The β-phase X ₂ N with square crystal structure symmetry is used as a transition metal nitride sacrificial layer, and X represents a transition metal;

3) Using hydride vapor phase epitaxy (HVPE) technology to grow a nitride single crystal thick film on the transition metal nitride sacrificial layer, through

The thickness of the nitride single crystal thick film is controlled by adjusting the time, and the stress control method is used to reduce the thickness of the nitride single crystal thick film layer.

Stress, thereby forming a crack-free hexagonal crystal layer with a thickness of 50-1000 μm on the transition metal nitride sacrificial layer

Nitride single crystal thick film with bulk structure symmetry;

₄ ) Using xenon difluoride XeF2 dry etching or acid etching technology to selectively etch the transition metal nitride sacrificial layer,

Realize the separation of nitride single crystal thick film and nitride template;

5) Chemically cleaning the nitride single crystal thick film to obtain a self-supporting nitride single crystal substrate.

In step 1), the heterogeneous substrate is sapphire, silicon or silicon carbide with trigonal or hexagonal crystal structure symmetry, with a thickness between 300 and 600 μm; the single crystal nitride film is a single crystal with hexagonal crystal structure symmetry Gallium nitride GaN thin film or single crystal aluminum nitride AlN thin film, the thickness is between 1-5 μm.

In step 2), the film deposition method adopts one of molecular beam epitaxy MBE, ion beam sputtering, magnetron sputtering and pulsed laser deposition PLD. The transition metal is niobium Nb, tantalum Ta or molybdenum Mo, and X ₂ N is an alloy of one or more of niobium nitride Nb ₂ N, tantalum nitride Ta ₂ N and molybdenum nitride Mo ₂ N. Different from sp ² hybridized two-dimensional materials, the transition metal nitride sacrificial layer has sp ³ hybrid structure and has dangling bonds on the entire surface, which is easy to form with a nitride single crystal thick film with the same sp ³ hybrid structure. Nucleation bonding without special activation treatment or insertion of a low-temperature single crystal nitride nucleation layer is conducive to the preparation of nitride single crystal thick films with high crystal quality.

The in-plane lattice mismatch between the transition metal nitride sacrificial layer and the nitride template and nitride single crystal thick film is small. Taking the β-phase niobium nitride Nb ₂ N and gallium nitride GaN as examples, the β-phase The in-plane lattice constant of niobium nitride Nb ₂ N is 0.3056nm, the in-plane lattice constant of gallium nitride GaN is 0.3189nm, and the lattice mismatch Δ=(0.3189-0.3056)/[0.5×(0.3189+0.3056) ] = 4.3%. The small lattice mismatch between the transition metal nitride sacrificial layer and the nitride single crystal thick film will introduce a small mismatch stress in the subsequent nitride single crystal thick film, and suppress the mismatch in the nitride thick film Generation of dislocations. In addition, the growth temperature of the transition metal nitride sacrificial layer is between the conventional working temperature (20-1000°C) of the thin film deposition method, and the prepared thin film crystal quality is good, and the growth temperature of the transition metal nitride sacrificial layer can be controlled only by controlling the deposition time. thickness. Therefore, the thickness of the transition metal nitride sacrificial layer mainly considers the difficulty of selective etching. Therefore, the thickness of the transition metal nitride is adjusted to 50-200 nm by controlling the time.

Considering the consistency of nitride single crystal thick film, transition metal nitride sacrificial layer and nitride template symmetry, choose to prepare the β-phase nitride with hexagonal crystal structure symmetry on the nitride template with hexagonal crystal structure symmetry Niobium Nb ₂ N, tantalum nitride Ta ₂ N, molybdenum nitride Mo ₂ N and their alloys, the deposition temperature range is 780°C to 850°C, and the niobium Nb, tantalum Ta or molybdenum Mo atoms injected per unit time during preparation The ratio of the number of N atoms to the number of active nitrogen N atoms is between 0.5 and 1.2. Deviation from this temperature or ratio range will generate other phase structures without hexagonal crystal structure symmetry, destroying the hexagonal crystal structure symmetry of the transition metal nitride sacrificial layer, Decreases the crystal quality of subsequent epitaxial nitride single crystal thick films.

In step 3), there are two different growth states in HVPE epitaxial growth, ie high-quality growth state and stress release state. The stress control method adopts the function control method to change the epitaxial growth parameters with time according to a specific function. Through the process of gradually changing the growth parameters from the high-quality growth state parameters to the stress-releasing growth state parameters and then gradually changing to the high-quality growth state parameters, the thickness of GaN can be realized. Stress control during HVPE growth of films. Growth parameters such as ammonia NH ₃ flow, hydrogen chloride HCl flow, growth temperature and pressure, etc., ensure the stability of epitaxial material quality and the uniformity of stress release.

In step 4), the nitride template and the nitride single crystal thick film have good chemical stability, acid corrosion resistance, and xenon difluoride XeF ₂ etching resistance. The transition metal nitride sacrificial layer is easy to react with xenon difluoride XeF ₂ or acid mixture, destroying the transition metal nitride sacrificial layer, so that the nitride template and the nitride single crystal thick film are separated. Using xenon difluoride XeF2 dry etching technology, pre _- deposit a metal protective layer on the upper surface of the nitride single crystal thick film, which can protect the flat surface of the gallium nitride thick film and selectively etch the transition metal nitride sacrificial layer, Realize the separation of nitride single crystal thick film and nitride template. The material of the metal protection layer is gold Au, aluminum Al or chromium Cr or the like. The acid etching technology using the acid mixture of hydrochloric acid HCl, nitric acid HNO ₃ and deionized water can selectively corrode the transition metal nitride sacrificial layer and realize the separation of nitride single crystal thick film and nitride template.

In step 5), the chemical cleaning includes acid cleaning and organic cleaning in sequence to remove the remaining metal protection layer on the nitride single crystal thick film and transition metal nitride sacrificial layer residue on the nitride single crystal thick film. Among them, hydrochloric acid solution is used for acid cleaning for ultrasonic treatment; organic cleaning is sequentially used for ultrasonic treatment of trichlorethylene, acetone, alcohol and deionized water. The nitride template is chemically cleaned to remove transition metal nitride sacrificial layer residue on the nitride template to obtain a reusable nitride template.

Advantages of the present invention:

The present invention introduces a β-phase transition metal nitride sacrificial layer with hexagonal crystal structure symmetry between the nitride single crystal thick film and the nitride template, and utilizes the crystal orientation matching between the transition metal nitride sacrificial layer and the nitride single crystal thick film , small lattice mismatch, and the characteristics of selective etching, the selective etching method is used to separate the nitride single crystal thick film from the nitride template, and obtain a large-size, high-quality self-supporting nitride single crystal substrate ; Compared with the two-dimensional crystal transition layer, the transition metal nitride sacrificial layer is simple to prepare, the process is compatible, and the reliability is high; the nitride single crystal thick film and the transition metal nitride sacrificial layer have the same sp ³ hybrid structure, and the lattice loss Small configuration, through the reasonable design of the crystal phase of the transition metal nitride sacrificial layer, it is easy to directly nucleate and grow high-quality nitride single crystal thick film on the transition metal nitride sacrificial layer, without introducing additional processes to assist the nitride single crystal thick film Nucleation to simplify the process flow; compared with the traditional nitride sacrificial layer, through the reasonable design of the thickness of the transition metal nitride sacrificial layer, the transition metal nitride sacrificial layer can be selectively etched without using complicated laser lift-off technology, reducing The difficulty and cost of the stripping process improves the yield; high-quality nitride single crystal template is used, and a small lattice mismatch system is formed between the nitride single crystal template, the transition metal nitride sacrificial layer and the nitride single crystal thick film, which can suppress the mismatch. Cooperate with the generation of stress-induced dislocations to improve the crystal quality of nitride single crystal thick film; realize the separation of epitaxial substrate and nitride single crystal thick film by destroying the transition metal nitride sacrificial layer, without affecting the nitride single crystal thick film The membrane and the nitride template cause damage, and the nitride template can be used repeatedly; the device is simple, low in energy consumption, easy to operate, and low in cost, and is suitable for industrial production.

Description of drawings

Fig. 1 to Fig. 5 are the cross-sectional views of the process flow of the method for preparing a nitride single crystal substrate using a transition metal nitride sacrificial layer according to the present invention in turn;

FIG. 6 is a flow chart of the method for preparing a nitride single crystal substrate using a transition metal nitride sacrificial layer according to the present invention.

Detailed ways

The present invention will be further elaborated below through specific embodiments in conjunction with the accompanying drawings.

Embodiment one

In this embodiment, the nitride template includes c-plane sapphire and 3 μm thick c-plane GaN thin film with hexagonal crystal structure symmetry; transition metal nitride sacrificial layer 3 is β-phase niobium nitride Nb ₂ N, The preparation method is molecular beam epitaxy MBE; the semiconductor single crystal thick film 4 is gallium nitride GaN thick film with hexagonal crystal structure symmetry, the preparation method is hydride vapor phase epitaxy HVPE, and the stripping method is selective etching with acid mixture.

The method for preparing a gallium nitride GaN single crystal substrate using a transition metal nitride sacrificial layer in this embodiment, as shown in FIG. 6, includes the following steps:

1) Select the nitride template for ultrasonic cleaning with trichlorethylene, acetone, ethanol and deionized water to obtain a clean gallium nitride GaN template surface, as shown in Figure 1, the heterogeneous substrate 1 of the nitride template has a thickness of 400 μm The c-plane sapphire, on which the single crystal nitride thin film 2 adopts c-plane, gallium nitride GaN with a thickness of 3 μm and a hexagonal crystal structure symmetry;

2) Put the cleaned nitride template into the molecular beam epitaxy MBE chamber, and use molecular beam epitaxy MBE on the upper surface of the c-plane gallium nitride GaN, the growth rate is 5nm/min, the growth time is 10min, and the growth temperature is 820°C When the ratio of niobium Nb and active nitrogen N atoms is 1.0 during preparation, a 50nm thick transition metal nitride sacrificial layer 3 of Nb ₂ N with β phase with hexagonal crystal structure symmetry is obtained, as shown in Figure 2, in this In the deposition method, nitrogen N ₂ is introduced, and a radio frequency plasma source is used for high-temperature activation treatment to form N atoms, which can be applied to the deposition of transition metal nitride sacrificial layer;

3) Put the nitride template with the transition metal nitride sacrificial layer into the hydride vapor phase epitaxy HVPE reaction chamber for gallium nitride GaN thick film growth to form a nitride single crystal thick film 4: Stress control technology is required during the growth process Prevent cracks in the nitride single crystal thick film while ensuring high crystal quality and surface quality. The thickness of the nitride single crystal thick film is 500 μm, as shown in Figure 3;

4) Acid etching technology is used to selectively etch the transition metal nitride sacrificial layer by utilizing the acid corrosion resistance of the nitride single crystal thick film and the reaction characteristics of the transition metal nitride sacrificial layer and the acid mixture to realize the nitride single crystal thick film Separation from the nitride template, as shown in Figure 4;

5) Perform acid cleaning and organic cleaning on the nitride template and nitride single crystal thick film to remove the transition metal nitride sacrificial layer residue, and obtain a self-supporting nitride single crystal substrate and a reusable nitride template, as shown in Figure 5 shown.

In this embodiment, the transition metal nitride sacrificial layer is made of niobium nitride Nb ₂ N thin film, and the gallium nitride GaN template and the gallium nitride GaN single crystal thick film are separated by selective acid etching, and the available The reusable gallium nitride GaN template and self-supporting gallium nitride GaN single crystal substrate, the test found that the crystal quality and yield of the self-stripping gallium nitride GaN thick film were significantly improved.

Embodiment two

In this embodiment, the nitride template is composed of c-plane silicon carbide (6H-SiC) and 3 μm thick c-plane, aluminum nitride AlN film with hexagonal crystal structure symmetry; transition metal nitride sacrificial layer 3 is β-phase nitrogen Tantalum oxide Ta ₂ N, prepared by magnetron sputtering; nitride single crystal thick film 4 is aluminum nitride AlN thick film, prepared by hydride vapor phase epitaxy HVPE, stripped by xenon difluoride XeF ₂ dry etching erosion technology.

The method for preparing a gallium nitride AlN single crystal substrate using a transition metal nitride sacrificial layer in this embodiment includes the following steps:

1) Select the nitride template for ultrasonic cleaning with trichlorethylene, acetone, ethanol and deionized water to obtain a clean gallium nitride GaN template surface, as shown in Figure 1, the heterogeneous substrate 1 of the nitride template has a thickness of 300 μm The c-plane silicon carbide (6H-SiC), on which the single crystal nitride film 2 adopts a c-plane aluminum nitride AlN film with a thickness of 2 μm and a hexagonal crystal structure symmetry, as shown in Figure 1;

2) Put the cleaned c-plane aluminum nitride AlN template into the magnetron sputtering chamber, and grow β-phase tantalum nitride Ta ₂ N on the upper surface of the nitride template by using magnetron sputtering technology, the growth temperature is 800 °C, the growth rate is 5nm/min, the growth time is 20min, the ratio of nitrogen Ta to active nitrogen N atoms is between 1.0 during preparation, and a transition metal nitride sacrificial layer 2 with a thickness of 100nm is obtained, as shown in Figure 2;

3) Put the nitride template with transition metal nitride sacrificial layer into the hydride vapor phase epitaxy HVPE reaction chamber for aluminum nitride AlN thick film growth to form aluminum nitride AlN thick film layer 4: Stress control is required during the growth process The technology prevents the generation of cracks in aluminum nitride AlN single crystal thick films while ensuring high crystal quality and surface quality. The thickness of aluminum nitride AlN single crystal thick films is 300 μm as nitride single crystal thick films 4, as shown in Figure 3 Show;

4) A metal protective layer is first deposited on the nitride single crystal thick film ₄ , and the nitride single crystal thick film is resistant to xenon difluoride XeF2 etching, and the transition metal nitride sacrificial layer reacts with xenon difluoride _XeF2 , Selectively etch the transition metal nitride sacrificial layer 3 to realize the separation of the nitride single crystal thick film and the nitride template, as shown in FIG. 4 ;

5) Perform acid cleaning and organic cleaning on the nitride template and nitride single crystal thick film to remove transition metal nitride sacrificial layer residue and metal protective layer residue, and obtain a self-supporting nitride single crystal substrate and a reusable nitride template, as shown in Figure 5.

In this embodiment, the transition metal nitride sacrificial layer adopts tantalum nitride Ta ₂ N thin film, and the separation of aluminum nitride AlN template and aluminum nitride AlN thick film is realized by selective xenon difluoride XeF ₂ etching , to obtain reusable aluminum nitride AlN templates and high-quality self-supporting aluminum nitride AlN single crystal substrates, and tests found that the crystal quality and yield of self-stripping aluminum nitride AlN films were significantly improved.

Finally, it should be noted that the purpose of the disclosed embodiments is to help further understand the present invention, but those skilled in the art can understand that various replacements and modifications can be made without departing from the spirit and scope of the present invention and the appended claims. It is possible. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the protection scope of the present invention is subject to the scope defined in the claims.

Claims (8)

1. a kind of method for preparing nitride single crystal substrates using transition metal nitride sacrificial layer, which is characterized in that the side Method the following steps are included:

1) select the nitride template with hexagonal crystallographic texture symmetry as the nitridation with hexagonal crystallographic texture symmetry The epitaxial substrate of object single-crystal thick films, and carry out chemical cleaning and make clean surface, nitride template includes foreign substrate and life Long monocrystalline nitride film on it, monocrystalline nitride film have hexagonal crystallographic texture symmetry；

2) transition metal nitride is deposited using Film forming method on nitride template, by controlling time-controllable transition metal The thickness of nitride, and transition metal nitrogen is regulated and controled by the ratio that is passed through of control temperature and transition metal atoms and nitrogen-atoms The crystal orientation and stoichiometric ratio of compound, so that being formed on the nitride template with hexagonal crystallographic texture symmetry has six sides The X of the β phase of crystal structure symmetry₂N represents transition metal as transition metal nitride sacrificial layer, X；

3) hydride gas-phase epitaxy HVPE technology growing nitride single-crystal thick films on transition metal nitride sacrificial layer are utilized, are led to The thickness of time control nitride single-crystal thick film is overregulated, and answering for nitride single-crystal thick film layers is reduced by stress control method Power, so that being formed on transition metal nitride sacrificial layer has hexagonal knot with a thickness of 50~1000 μm of not crackle The nitride single-crystal thick film of structure symmetry；

4) xenon difluoride XeF is used₂Dry etching or acid etch technology, selective etch transition metal nitride sacrificial layer are real The separation of existing nitride single-crystal thick film and nitride template；

5) chemical cleaning nitride single-crystal thick film obtains self-supporting nitride single crystal substrates.

2. the method as described in claim 1, which is characterized in that in step 1), foreign substrate, which uses, has tripartite or six sides Sapphire, silicon or the silicon carbide of crystal structure symmetry, thickness is between 300~600 μm；Monocrystalline nitride film is with six The mono-crystal gallium nitride GaN film or single-crystal aluminum nitride AlN film of square crystal structural symmetry, thickness is between 1~5 μm.

3. the method as described in claim 1, which is characterized in that in step 2), Film forming method uses molecular beam epitaxy One of MBE, ion beam sputtering, magnetron sputtering and pulse laser deposition PLD.

4. the method as described in claim 1, which is characterized in that in step 2), transition metal uses niobium Nb, tantalum Ta or molybdenum Mo, X₂N is niobium nitride Nb₂N, tantalum nitride Ta₂N and molybdenum nitride Mo₂One of N or a variety of alloys.

5. the method as described in claim 1, which is characterized in that in step 2), the temperature range of deposition is 780 DEG C~850 DEG C, the ratio of the transition metal atoms number and nitrogen N atomicity that are passed through in the unit time is between 0.5~1.2.

6. the method as described in claim 1, which is characterized in that in step 3), stress control method uses function controlling party Method changes epitaxial growth parameters according to specific function at any time, is released by growth parameter(s) in high-quality growth state and stress It frees and changes between long status, realize the Stress Control in growth course.

7. the method as described in claim 1, which is characterized in that use xenon difluoride XeF in step 4)₂Dry etching technology, Coat of metal is previously deposited in the upper surface of nitride single-crystal thick film.

8. the method as described in claim 1, which is characterized in that in step 5), chemical cleaning successively includes acid cleaning and has Machine cleaning.