CN1713349A - Method for preparing crack-free silicon-based III-nitride thin films with self-adaptive flexible layer - Google Patents

Abstract

A new method for growing large-area crack-free III-nitride thin films on silicon substrates, which is characterized in that one or more layers of III Elementary or quaternary III-nitride self-adaptive flexible layer, this flexible layer can spontaneously adjust its composition with the change of stress during growth, adaptive to the change of large mismatch heteroepitaxial lattice constant or thermal stress, the layer's The main function is to prevent the generation of crack sources at the interface.

Description

Method for preparing crack-free silicon-based III-nitride thin films with self-adaptive flexible layer

technical field

The invention relates to the field of semiconductors, in particular to a method for preparing a crack-free silicon-based Group III nitride thin film with an adaptive flexible layer.

Background technique

Group III nitride semiconductors represented by GaN have very broad application prospects because they can be used in blue LEDs and LDs, high-density optical storage, high-temperature, high-power and high-frequency electronic devices, and ultraviolet detectors.

However, it is difficult to obtain high-quality GaN thin films due to the absence of a homogeneous substrate. Most of the device-grade GaN thin films prepared so far are obtained on sapphire substrates. Because the sapphire substrate is hard, non-conductive, and expensive, it is difficult to produce in large quantities, forcing people to try to grow high-quality GaN on silicon substrates that are cheap, thermally conductive, electrically conductive, large in size, easy to cleave, and easy to optoelectronic integration. To overcome the disadvantages of sapphire substrate.

However, the lattice mismatch between Si and GaN reaches 20%, and the thermal mismatch is as high as 56%. Epitaxial growth of GaN on silicon substrates is very easy to crack, and cracks have become the most important problem for growing device-level high-quality GaN on Si substrates. question.

At present, the main methods to solve cracks in Si-based GaN are as follows:

1. The lateral epitaxy method of masking or direct etching on the silicon substrate. This method artificially splits the continuous surface of silicon and confines GaN epitaxial growth to a small window area, which can effectively relieve the stress in the large plane and prevent the generation of cracks. The disadvantage is that the process is complicated and the crack-free area is small.

2. Insert a low-temperature AlN layer in GaN. Through the low-temperature polycrystalline AlN layer with a certain thickness, the stress caused by thermal mismatch can be partially released, and a crack-free film can be realized.

3. A gradient AlGaN layer is adopted. The lattice constant of AlN is slightly smaller than that of GaN, so that compressive stress appears in the GaN grown on the AlGaN layer, which can partially offset the tensile stress formed during the cooling process and reduce the generation of cracks.

All of the above methods are difficult to grow thicker large-area crack-free GaN films.

On the other hand, research on GaN ternary or quaternary compound semiconductors is also in progress. The main advantage of InAlGaN quaternary compound semiconductor materials is that by adjusting the content of In and Al respectively, a material that matches the lattice of GaN, or InGaN, AlGaN can be obtained, and at the same time, the energy band difference can be adjusted to obtain the potential required for the design. barriers and potential wells. Therefore, InAlGaN is widely used in various superlattice or quantum well structures, and shows high luminous efficiency in the ultraviolet short wavelength region.

At the same time, the study also found that under certain conditions, phase separation will occur in InGaN or InAlGaN: that is, In-rich regions and In-poor regions appear in different regions; or the In content between layers changes during the growth process, that is, the self- Assembled superlattice phenomena. The change of In content during the growth process is mainly related to the stress change in the epitaxial film.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a crack-free silicon-based Group III nitride film from an adaptive flexible layer. Specifically refers to a method of inserting an adaptive flexible layer on a silicon substrate to prepare a crack-free group III nitride film, and the preparation of an InAlGaN or InGaN adaptive flexible layer and inserting a multi-layer InAlGaN adaptive flexible layer into a group III nitride film layer structure to prepare crack-free III-nitride thin films with thicknesses up to 2 μm.

The present invention provides a structure for growing a crack-free group III nitride film on a silicon substrate by using a structure of inserting an adaptive flexible layer. This method has a simple process, and can effectively eliminate cracks in a large-area silicon-based GaN film through the pre-grown composition-adaptive InGaN or InAlGaN flexible layer; by inserting multiple self-adaptive flexible layers, a thickness of about 2 microns can be grown, Crack-free Ill-nitride films for device use. At the same time, the invention has a wider process window and less dependence on equipment conditions, and is a universal method for eliminating silicon-based GaN cracks.

In order to achieve the above object, according to the present invention, a crack-free Group III nitride film is grown on a silicon substrate, and it is characterized in that: after an AlN buffer layer is grown on a silicon substrate by a conventional method, a layer An adaptive flexible layer, the adaptive flexible layer includes InAlGaN or InGaN, and the thickness of the flexible layer is between 50-500nm.

Due to the large lattice mismatch and thermal mismatch between silicon and group III nitrides, when the adaptive flexible layer is epitaxially grown on the silicon surface, a large internal stress will be generated, and the adaptive flexible layer can be controlled according to the internal stress. The size adaptively adjusts the content of In components, so that the lattice constant changes gradually, thereby alleviating the lattice mismatch stress; The -N bond is weak, and the In-rich region can effectively absorb part of the thermal stress and play the role of a flexible layer. Therefore, the present invention names this insertion layer "adaptive flexible layer".

The adaptive flexible layer InGaN or InAlGaN according to the present invention comprises an In component in a proportion of 2% to 20%, an Al component in a proportion of 10% to 90%, and an In, Al and Ga component, or an In and Ga component The proportions add up to 100%.

In the self-adaptive flexible layer InAlGaN, the proportion of the In component is greater than or equal to 10%.

The method for preparing InGaN or InAlGaN self-adaptive flexible layer according to the present invention comprises crystal growth of InGaN or InAlGaN at a growth temperature of 800°C to 950°C, wherein ammonia, trimethylgallium, trimethylindium and trimethylaluminum are used as raw gas.

In the method for preparing InGaN or InAlGaN adaptive flexible layer according to the present invention, the flow rate of ammonia is 4L/min, the flow rate of trimethylgallium is 2umol/min to 20umol/min, and the flow rate of trimethylindium adduct is 20umol/min min to 60umol/min, the flow rate of trimethylaluminum is 1umol/min to 10umol/min.

According to the present invention, a multi-layer inserted self-adaptive flexible layer is prepared, and a crack-free silicon-based group III nitride film with a thickness of 2 microns is grown, and its features include:

On the first self-adaptive flexible layer, grow a group III nitride film with a thickness of about 100-500nm, then grow the second self-adaptive flexible layer, and then grow a group III nitride film on it, so that multiple layers are alternately inserted The structure of the flexible layer.

The growth temperature, layer thickness and composition of In and Al of each self-adaptive flexible layer may be different, but all are within the scope of claim 4 and claim 5.

Description of drawings

The detailed description given below and the accompanying drawings given only by explanation will make the present invention easier to fully understand, but do not limit the present invention thereby, wherein:

Fig. 1 is a structural schematic diagram of a large-area crack-free silicon-based Group III nitride film prepared by an adaptive flexible layer of the present invention;

Fig. 2 is a schematic structural view of preparing a multi-layer insertion (In, Al) GaN flexible layer growth thickness of 2 microns without cracks according to the present invention;

Fig. 3 is a comparison diagram of the surface morphology of the silicon-based GaN epitaxial film with the adaptive flexible layer a inserted and without the adaptive flexible layer b inserted;

Fig. 4 is a comparison diagram of the PL spectrum of the silicon-based GaN epitaxial film with the adaptive flexible layer a inserted and without the adaptive flexible layer b inserted;

In the following, the present invention will be introduced in detail by pre-inserting an adaptive flexible layer InAlGaN structure on a silicon substrate to grow a crack-free Group III nitride film, as well as the method for preparing it, and using a multi-layer inserted InAlGaN adaptive flexible layer structure to An example of growing a crack-free Ill-nitride thin film with a thickness of 2 μm.

Detailed ways:

Taking Metal Organic Chemical Vapor Deposition as an Example

1) As shown in Figure 1, after the Al layer 2 and the 20-30nm high-temperature AlN buffer layer 3 are grown on the surface of the silicon substrate 1 by conventional methods, the temperature is lowered to about 850°C, the carrier gas is replaced with nitrogen, and ammonia is introduced. , trimethylgallium, trimethylindium and trimethylaluminum and other raw material gases to grow InAlGaN or InGaN adaptive flexible layer 4, the thickness of this layer can be adjusted according to the flow rate and temperature of the raw material gas, and can be in the range of 50-500nm change, and finally grow a III-nitride thin film 5 with a certain thickness.

2) As shown in Figure 2, after the Al layer 2 and the 20-30nm high-temperature AlN buffer layer 3 are grown on the surface of the silicon substrate 1 by conventional methods, the temperature is lowered to about 850° C., the carrier gas is replaced with nitrogen, and ammonia is introduced. , trimethylgallium, trimethylindium, trimethylaluminum and other raw material gases, grow InAlGaN adaptive flexible layer 4, and then grow III-nitride thin film 5. The self-adaptive flexible layer 4 and the III-nitride epitaxial layer 5 are grown alternately, which may be two or more layers. The growth temperature of the self-adaptive flexible layer is controlled between 800-900°C, while the growth temperature of the III-nitride epitaxial layer is between 1020-1080°C. The thickness of the two layers must be controlled within 500nm to avoid cracks.

The invention utilizes the inherent characteristics of InGaN and InAlGaN compounds: its components can be adjusted spontaneously according to various internal stresses generated during growth, and the lattice mismatch in self-adaptive large-mismatch heteroepitaxy, while the In-N bond is stronger Weak, In-rich region experiments found that the strain caused by thermal mismatch can be significantly relieved, and the generation and propagation of cracks can be reduced.

Compared with other technologies for growing silicon-based crack-free III-nitride epitaxial films, this technology does not require other auxiliary technologies such as masking and photolithography, and does not need to introduce polycrystalline/single crystal interfaces. The process is simple and can be adjusted spontaneously. Mismatch heteroepitaxy, its principle can be applied to a variety of epitaxy technologies (including MOCVD, MBE and HVPE, etc.) and a variety of material systems, with universal applicability. At the same time, compared with the conventional method, the luminescence performance of GaN grown by the adaptive (In, Al) GaN flexible layer is significantly enhanced (Fig. 4), indicating that the performance of Si-based GaN is significantly improved.

The main method for implementing the present invention includes various semiconductor film preparation methods, such as metal organic chemical vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) and ion sputtering etc., to different semiconductor film preparations system, various growth parameters are adjusted according to specific conditions.

Group III nitrides include: gallium nitride, aluminum gallium nitride, indium gallium nitride, indium aluminum gallium nitride and other thin film materials or structural materials formed by their combination.

Example 1:

Take metal organic chemical vapor deposition (MOCVD) method as an example.

1) Using the single crystal Si (111) surface as the substrate;

2) Raise the temperature to 1000-1100°C, pass through trimethylaluminum TMAl to form a thin Al layer on the silicon surface; then pass through ammonia to form an AlN layer of about 30nm;

3) The temperature is lowered to 800-900° C., and the InAlGaN self-adaptive flexible layer is grown. The raw material gas is ammonia, trimethylgallium, trimethylindium and trimethylaluminum as raw material gas: the flow rate of ammonia is 4L/min, the flow rate of trimethylgallium is 10umol/min, trimethylindium adduct The flow rate of the compound is 30umol/min, and the flow rate of trimethylaluminum is 5umol/min. The thickness of this layer is 300nm;

4) The temperature is raised to a high temperature of 1000-1100° C. to grow a GaN epitaxial film of 700 nm, so that the total thickness of the epitaxial film reaches 1 μm.

Example 2

Using a multi-layer InAlGaN adaptive flexible layer to grow a crack-free III-nitride film with a thickness of 2 microns, the first four steps are the same as in Example 1, except that the thickness of the grown InAlGaN flexible layer and the GaN epitaxial film are both set at 500 nanometers, and the next step is the fifth step:

5) Same as 3) growing a 500nm InAlGaN adaptive flexible layer;

6) Same as 4) to grow 500nm GaN epitaxial film.

Comparing the surface morphology of the 1-micron silicon-based GaN epitaxial film with the adaptive flexible layer inserted and without the adaptive flexible layer, as shown in Figure 3, it was found that the GaN surface grown by the conventional method in Figure 3b has many parallel to each other, criss-cross After a certain process optimization, there can be no cracks in the square range of 10um×10um; while Figure 3a is grown by inserting an adaptive flexible layer of InAlGaN, and the same thickness of GaN is grown by the same process, and the surface cracks The number is greatly reduced, and cracks are rarely found in the observed range shown in Fig. 3a. Because GaN thin films are mainly used in optoelectronic devices, the optical properties of GaN epitaxial films are tested by photoluminescence spectroscopy (PL spectrum), as shown in FIG. 4 . It was found that the luminous intensity of the GaN thin film grown after inserting the InAlGaN adaptive flexible layer in curve a was significantly higher than that of the GaN thin film without the adaptive flexible layer inserted in curve b, and the luminous intensity was increased by about ten times. Therefore, the InAlGaN adaptive flexible layer method was used The luminescent properties of the grown GaN thin films are significantly improved, but the half-width of the PL spectrum is not significantly reduced, indicating that the crystal quality of GaN grown by the InAlGaN adaptive flexible layer method is not significantly reduced.

Compared with the technology in the past, the present invention has the following significance:

1) It is suitable for all kinds of epitaxial growth equipment commonly used at present, such as metal organic chemical vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) and ion sputtering, etc.

2) Utilize the inherent characteristics of InGaN and InAlGaN compounds: their components can be adjusted spontaneously according to various internal stresses generated during growth, and the lattice mismatch in self-adaptive large-mismatch heteroepitaxy, while the In-N bond is stronger Weak, In-rich region experiments found that the strain caused by thermal mismatch can be significantly relieved, and the generation and propagation of cracks can be reduced.

3) It does not require other auxiliary technologies such as mask and photolithography, nor does it need to introduce a polycrystalline/single crystal interface, the process is simple, the cost is low, and it can be completed without adding any new process equipment.

4) Capable of growing crack-free silicon-based gallium nitride films with a thickness of up to 2 microns.

Claims (8)

1. the structure of a self-adapting flexible layer, its structure is as follows: behind silicon substrate 1 superficial growth Al layer 2 and the AlN resilient coating 3, growth InAlGaN or InGaN self-adapting flexible layer 4, the certain thickness III group-III nitride film 5 of growing at last.

2. the generation method of the structure of a self-adapting flexible layer, its step is as follows:

After the high temperature AlN resilient coating 3 of Al layer 2 and 20～30nm has been grown on silicon substrate 1 surface according to a conventional method, be cooled to about 850 ℃, carrier gas is changed to nitrogen, feed ammonia, trimethyl gallium, trimethyl indium and trimethyl aluminium unstripped gas, growth InAlGaN or InGaN self-adapting flexible layer 4, the thickness of this layer is regulated according to the flow velocity and the temperature of unstripped gas, can change in 50～500nm scope, the certain thickness III group-III nitride film 5 of growing at last.

3. according to the structure of the self-adapting flexible layer of claim 1, with the silica-based III group-III nitride of preparation flawless film, its feature comprises:

In the middle of traditional nitride resilient coating and III group-III nitride, insert one deck self-adapting flexible layer, the spontaneous adjusting of various internal stresss that this its component of self-adapting flexible layer can produce according to when growth, lattice mismatch and thermal mismatching in the big mismatch heteroepitaxy of self adaptation, it mainly acts on is generation and the expansion that stops the Interface Crack source.

4. according to the structure of the self-adapting flexible layer of claim 1 or 3, it is characterized in that the self-adapting flexible layer comprises InAlGaN, InGaN comprises:

The Al component of the In component of 2% to 20% ratio, 10% to 90% ratio, and In, Al and Ga component, or the ratio summation of In and Ga component is 100%; The thickness of this self-adapting flexible layer is the 50-500 nanometer.

5. according to the structure of the self-adapting flexible layer of claim 1 or 3, it is characterized in that, self-adapting flexible layer InAlGaN, wherein the ratio of In component is more than or equal to 10%.

6. according to the generation method of the structure of the self-adapting flexible layer of claim 2, it is characterized in that: wherein self-adapting flexible layer InAlGaN or InGaN carry out crystal growth under 800 ℃ to 950 ℃ growth temperature, and wherein ammonia, trimethyl gallium, trimethyl indium and trimethyl aluminium are as unstrpped gas.

7. according to the generation method of the structure of the self-adapting flexible layer of claim 2, it is characterized in that, wherein the flow velocity of ammonia is 4L/min, the flow velocity of trimethyl gallium is 2umol/min to 20umol/min, the flow velocity of trimethyl indium adduct is 20umol/min to 60umol/min, and the flow velocity of trimethyl aluminium is 1umol/min to 10umol/min.

8. a multilayer is alternately inserted the structure of self-adapting flexible layer, and preparation thickness reaches the 2 microns silica-based III group-III nitride of flawless films, and its feature comprises:

Growth one layer thickness is about the III group-III nitride film of 100-500 nanometer on ground floor self-adapting flexible layer, the second layer self-adapting flexible layer of growing then, regrowth III group-III nitride film on it, the structure of alternately inserting multilayer self-adapting flexible layer like this;

The growth temperature of each layer self-adapting flexible layer, bed thickness and In, the component of Al can be inequality, but all within claim 4,5 or 6 scope.

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