CN101445956A - Method for epitaxial growth of nitride films - Google Patents

Abstract

The invention provides a method for epitaxial growth of nitride films, comprising the steps as follows: firstly, the temperature of a substrate is directly increased to the growth temperature of the nitride film; subsequently, during the early growth period, the input switch of ammonia gas (NH3) and III-cluster material is controlled by the computer program of growth equipment so that the ammonia gas (NH3) and III-cluster material are alternatively put into to a growth reaction chamber in pulse; during the process, a nucleation layer is formed on the surface of the substrate under the given duration, interval and pulse period; subsequently, the nitride film and device structure thereof with high crystal quality can grow on the nucleation layer. The method can simplify preparation process, reduces growth time, thereby reducing the growth cost and improving the growth efficiency. The method is beneficial for high crystal quality and for the growth of nitride film materials with low dislocation density.

Description

A method for epitaxial growth of nitride thin films

technical field

The invention relates to the technical field of semiconductors, in particular to a method for epitaxial growth of a nitride thin film. The method can be used for the epitaxial growth of low dislocation density, high crystal quality nitride film and device structure material.

Background technique

Nitride (including gallium nitride, aluminum gallium nitride, aluminum nitride, indium gallium nitride, indium nitride, indium aluminum gallium nitride, etc.) is the third generation of direct energy gap wide bandgap semiconductors, and its bandgap width can be Adjustable between 0.7eV-3.39eV-6.28eV, covering the entire mid-infrared, visible and ultraviolet bands. Nitride can be used to make light-emitting devices, photodetection devices and laser devices from ultraviolet light to various colors of visible light and infrared light. At the same time, gallium nitride has high thermal and chemical stability, high electron saturation rate and carrier mobility, high breakdown electric field strength, excellent electronic performance, and can be used in high temperature, high frequency, high power field of microwave devices.

At present, nitride thin film materials are usually heteroepitaxially grown on sapphire, silicon, silicon carbide, gallium arsenide, zinc oxide or homoepitaxially grown on free-standing gallium nitride and other substrates. Because there is usually a large lattice constant mismatch and thermal expansion coefficient difference between nitride and other substrates, the nitride epitaxial layer grown by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) There is a lot of stress and many crystal defects such as dislocations in the material, so the crystal quality of the material is greatly affected, which in turn degrades the performance of the device. People have been exploring various methods to prepare nitride thin film materials with high crystal quality. In 1992, Shuji Nakamura of Japan prepared high-quality gallium nitride thin films by double-flow MOCVD method, which solved the technical problem of low-quality gallium nitride thin films [S.Nakamura et al., Jpn.J.Appl.Phys. 31 (1992) 139], and first prepared into valuable pn junction blue light-emitting diodes, quantum well structure light-emitting diodes, blue lasers, etc. The key process adopts low-temperature buffer layer technology, that is, a 20-30nm thick GaN or AlN nucleation layer is first grown at a low temperature of about 550°C, and then the epitaxy of nitride and required device structure materials is carried out at a high temperature of about 1050°C Growth (Japanese patent: JP2737053). Later, on this basis, people developed methods such as lateral epitaxial growth, hanging and lateral epitaxial growth, and patterned substrates to further reduce the dislocation density of materials. However, for nitride film materials containing Al and In, due to the difference in the surface migration rate of adatoms Al and In on the growth substrate, the combination of component elements in the nitride film containing Al and In is affected, and the crystal of the material Deterioration of quality. For example, during the epitaxial growth process of AlGaN and AlN, the mobility of Al atoms on the surface is low and tends to grow in a three-dimensional island shape, which is easy to form a "mosaic" structure, which greatly affects the crystal quality of the material. Therefore, in order to alleviate the stress caused by the lattice mismatch in the heteroepitaxial growth of the substrate and the nitride film, so that it can be effectively relaxed, it is necessary to develop a new epitaxial growth technology to improve the crystal quality of the nitride film material. of.

Contents of the invention

The object of the present invention is to provide a method for epitaxial growth of a nitride thin film, comprising the steps of:

1) first directly raising the temperature of the substrate 1 to the growth temperature of the nitride thin film 3;

2) In the early stage of growth, the computer program of the epitaxial growth equipment controls the input switch of ammonia gas and group III source materials, so that ammonia gas and group III source materials are pulsed into the growth reaction chamber, and the duration, interval and pulse Periodically, a layer of nucleation layer 2 is formed on the surface of the substrate 1;

3) Epitaxial growth of a nitride thin film 3 on the nucleation layer 2 .

Further, the substrate 1 is sapphire, or silicon, or silicon carbide, or gallium arsenide, or zinc oxide, or self-supporting gallium nitride.

Further, the substrate 1 is a patterned substrate or a planar substrate.

Further, the growth temperature of the nitride thin film 3 is between 600-1300°C.

Further, the feeding duration and interval of the ammonia gas and the Group III source material are both 1-100 seconds, and the pulse period is 1-50 cycles.

Further, the nitride thin film 3 is a layer composed of one or more combinations of gallium nitride, aluminum nitride, indium nitride, aluminum gallium nitride, indium gallium nitride, indium aluminum nitride or indium aluminum gallium nitride Structural materials.

Further, the equipment used for the epitaxial growth of the nitride thin film 3 is one or a combination of metal-organic chemical vapor deposition or molecular beam epitaxy.

The invention can effectively reduce the dislocation density in the nitride thin film, avoid the generation of cracks, improve the crystal quality and uniformity of the epitaxial material, and further improve the performance of the device. At the same time, the method can simplify the preparation process and reduce the growth time, thereby reducing the growth cost and improving the growth efficiency.

Description of drawings

In order to further illustrate content of the present invention, the present invention is described in detail below in conjunction with the example of implementation, wherein:

Fig. 1 is the structural representation of nitride film material;

Fig. 2 is a schematic diagram of the growth of gallium nitride thin films grown by metal-organic chemical vapor deposition epitaxial growth;

Fig. 3 is the growth schematic diagram of metal-organic chemical vapor deposition epitaxial growth aluminum nitride film;

Fig. 4 is a schematic diagram of the growth of InAlGaN thin film epitaxially grown by metalorganic chemical vapor deposition.

specific embodiment

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with three specific embodiments and with reference to the accompanying drawings.

Example 1

This embodiment provides a method for growing a gallium nitride thin film with high crystal quality on a sapphire substrate by using MOCVD equipment. The epitaxial equipment used is a commercial machine produced by VECOO Company of the United States, the model is D150. The V group source used is ammonia (NH3), the group III source material is trimethylgallium (TMG), the carrier gas is N2 and H2, and the flow rates of NH3 and TMG are 10 standard liters per minute (slm) and 100 micromoles, respectively. /min (μmol/m). The pressure of the reaction chamber is 150 Pascals (Pa).

The method for the epitaxial growth of the nitride thin film comprises the following steps:

First, put the 2-inch sapphire substrate into the MOCVD growth equipment.

Then raise the temperature of the sapphire substrate to 1100°C, and heat-treat the substrate for 10 minutes in a flowing H2 atmosphere to form an atomic step structure on the sapphire surface;

Then lower the temperature of the substrate to 1050°C, and keep it constant during the growth process of the GaN film until the end of the growth process. Figure 1 is a schematic diagram of the structure of the nitride film material.

In the early stage of GaN growth, the gas flow of ammonia (NH3) and trimethylgallium (TMG) is alternately pulsed into the growth reaction chamber, which is realized by the operation switch controlled by the computer of the MOCVD equipment system. Figure 2 illustrates the pulse time sequence of Ga source and N source input/off. The alternate feeding time and interval of Ga source and N source are 1s, and there is a 1s time between the time pulses of Ga source and N source as the clearing interval. This interval is chosen to avoid cross-contamination between precursors. The pulse period is 10.

When the reaction gas flow pulse modulation method grows the GaN thin film, there is no common low-temperature buffer layer growth step, which simplifies the process and reduces the growth cost.

Example 2

This embodiment provides a method for growing a high-quality aluminum nitride epitaxial layer on a sapphire substrate by using MOCVD equipment. The epitaxial equipment used is a commercial machine produced by VECOO Company of the United States, the model is D150. The source of group V used is ammonia (NH3), the source material of group III is trimethylaluminum (TMA), the carrier gas is N2 and H2, and the flow rates of NH3 and TMA are 0.5 standard liters per minute (slm) and 33 micromoles, respectively /min (μmol/m). The pressure of the reaction chamber is 75 Pascals (Pa).

The method for the epitaxial growth of the nitride thin film comprises the following steps:

First put the 2-inch sapphire substrate into the MOCVD growth equipment.

Then raise the temperature of the substrate to 1150°C, and heat-treat the substrate for 10 minutes in a flowing H2 atmosphere to form an atomic step structure on the surface;

In the subsequent growth process of the AlN film, the temperature of the substrate is maintained at 1150°C until the end of the growth process. Figure 1 is a schematic diagram of the structure of the nitride film material;

In the early stage of AlN thin film growth, the flow of ammonia gas is pulsed into the growth reaction chamber, which is realized by the computer-controlled switch operated by the MOCVD system. Simultaneously, the flow rate of trimethylaluminum (TMA) is constant, and is always passed into the reaction chamber. Figure 3 shows the pulse time sequence of the N source during the AlN thin film growth process, and its access time and interval are 15s. The pulse period is 8.

Since the mobility of Al atoms on the surface is low and tends to grow in three-dimensional island shape, the gas flow pulse modulation of ammonia gas in the early stage of growth can enhance the mobility of Al atoms on the surface, reduce the side reactions between precursors, and increase the growth rate. The density of the core particles and the two-dimensional growth tendency can effectively relax the stress between the epitaxial layer and the substrate, thereby improving the crystal quality and surface smoothness of the AlN film.

Example 3

This embodiment provides a method for growing a high-quality aluminum gallium indium nitride (AlGaInN) epitaxial layer on a sapphire substrate by using MOCVD equipment. The epitaxial equipment used is a commercial machine produced by VECOO Company of the United States, the model is D150. The V group source used is ammonia (NH3), and the group III source materials are trimethylgallium (TMG), trimethylaluminum (TMA) and trimethylindium (TMI). The carrier gas is N2 and H2, and the pressure of the reaction chamber is 150 Pascal (Pa).

The method for the epitaxial growth of the nitride thin film comprises the following steps:

First, load the MOCVD growth equipment on the 2-inch sapphire substrate.

Then the temperature of the substrate was raised to 1100°C, and the substrate was heat-treated for 10 minutes in a flowing H2 atmosphere to form an atomic step structure on the surface;

Then lower the temperature of the substrate to 800°C, and keep it unchanged during the subsequent growth process of the AlGaInN film until the end of the growth process. Figure 1 is a schematic diagram of the structure of the nitride film material;

In the initial stage of AlGaInN thin film growth, ammonia (NH3) and trimethylgallium (TMG), trimethylaluminum (TMA) and trimethylindium (TMI) gas flows are alternately pulsed into the growth reaction chamber, which is passed through the MOCVD system. Computer-controlled switches to operate the implementation. Figure 3 shows the pulse time series of Al source, Ga source, In source and N source. Every 5s as a pulse duration, TMA, TMI, TMG and NH3 are fed into the MOCVD reaction chamber alternately with the pulse, and after each pulse cycle of the metal-organic source is fed, it is followed by a pulse cycle of NH3. The figure shows Al and N for 3 pulse periods, followed by In and N for 1 pulse period, and then Ga and N for 1 pulse period. The total number of pulses is 5.

When the technology grows the AlInGaN quaternary alloy, it increases the Al composition without hindering the combination of In, so that the various components of the AlGaInN alloy can be modulated more effectively.

In the above embodiments, general MOCVD growth equipment is used, and a computer program is used to control the input/close of V-group source ammonia (NH ₃ ) and corresponding III-group source materials in the early stage of nitride growth, so as to realize pulse modulation of reaction gas flow. This technology can alleviate the stress caused by lattice mismatch during the heteroepitaxial growth process between the substrate and the nitride, and reduce the defect density of the nitride epitaxial layer by improving the mobility of the surface atoms and suppressing the side reactions in the gas phase. The composition of the nitride alloy can be effectively modulated, the generation of cracks can be avoided, the crystal quality can be improved, and then the performance of the device can be improved.

The above is only a specific implementation mode in the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technology can easily think of changes or replacements within the technical scope disclosed in the present invention. All should be covered within the scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (7)

1. A nitride thin film epitaxial growth method, is characterized in that, comprises the steps: 1) first directly raising the temperature of the substrate (1) to the growth temperature of the nitride film (3); 2) In the early stage of growth, the computer program of the epitaxial growth equipment controls the input switch of ammonia gas and group III source materials, so that ammonia gas and group III source materials are pulsed into the growth reaction chamber, and the duration, interval and pulse Periodically, a layer of nucleation layer (2) is formed on the surface of the substrate (1); 3) Epitaxially growing a nitride thin film (3) on the nucleation layer (2). 2. The nitride film epitaxial growth method according to claim 1, characterized in that the substrate (1) is sapphire, or silicon, or silicon carbide, or gallium arsenide, or zinc oxide, Or free-standing gallium nitride. 3. The nitride film epitaxial growth method according to claim 1, characterized in that the substrate (1) is a patterned substrate or a planar substrate. 4. The nitride film epitaxial growth method according to claim 1, characterized in that the growth temperature of the nitride film (3) is between 600-1300°C. 5. The nitride thin film epitaxial growth method according to claim 1, characterized in that, the feeding duration and interval of the ammonia gas and Group III source materials are all 1-100 seconds, and the pulse period is 1-50 seconds. cycle. 6. The nitride thin film epitaxial growth method according to claim 1, characterized in that, the nitride thin film (3) is gallium nitride, aluminum nitride, indium nitride, aluminum gallium nitride, indium gallium nitride , indium aluminum nitride or indium aluminum gallium nitride or a layer structure material composed of one or more combinations. 7. The nitride thin film epitaxial growth method according to claim 1, characterized in that, the equipment used for the nitride thin film (3) epitaxial growth is one or both of metal-organic chemical vapor deposition or molecular beam epitaxy. kind of combination.

Images