A method for producing a nitride thin film

Abstract

The application discloses a preparation method of a nitride film. The method comprises the following steps: sequentially growing a buffer layer and an InGaN / GaN superlattice stack structure on a single crystal substrate; forming a porous structure by decomposing an InGaN sublayer by using a stepwise heating process, so as to construct an InGaN / GaN superlattice porous stress release layer; and continuously growing a high-quality nitride film on the InGaN / GaN superlattice porous stress release layer. After the growth is completed, the nitride film and the porous stress release layer are separated from the original single crystal substrate by using a stripping process, so that the original substrate can be recycled and reused, and the production cost is greatly reduced. The application effectively relieves the lattice mismatch stress between the substrate and the epitaxial layer, and realizes the substrate freedom of the high-quality nitride film by using a stripping and transferring technology, so that a new technical path is provided for the preparation of low-cost, large-size and flexible nitride optoelectronic devices.

Description

Technical Field

[0001] This invention relates to semiconductor thin film technology, and more specifically to a method for preparing nitride thin films. Background Technology

[0002] Gallium nitride (GaN)-based semiconductor materials are ideal for fabricating semiconductor lasers (LDs), light-emitting diodes (LEDs), and high-electron-mobility transistors (HEMTs) in the ultraviolet to red light band, and have broad application prospects in solid-state lighting, laser displays, optical communications, power electronics, and biomedical detection. In particular, the InGaN-based material system, due to its wide tunable bandgap range (covering the near-ultraviolet to red light band), has become a research hotspot for long-wavelength optoelectronic devices. However, existing GaN-based semiconductor device technologies still face the following technical bottlenecks: First, stress accumulation and a high-quality stress-relieving layer are difficult to achieve in heteroepitaxial growth. GaN-based devices are typically heteroepitaxially grown on single-crystal substrates (such as sapphire, SiC, or Si substrates). Due to significant lattice mismatch (approximately 14% mismatch between GaN and sapphire, and approximately 11% mismatch between InN and GaN) and thermal mismatch between the substrate and the epitaxial layer, a high density of through-dislocations (10T) is generated during epitaxial growth. 8 ~10 10 cm -2 Significant residual stress leads to epitaxial wafer warping, cracking, and even fragmentation. Although there are reports of using superlattice structures or compositionally graded layers to relieve stress, these methods have limited effectiveness in stress relief.

[0003] Second, existing lift-off and transfer technologies each have limitations, making it difficult to balance high quality and low cost. Laser lift-off technology typically requires the pre-growth of a laser absorption layer, and the high-energy laser impact can cause thermal and stress damage to the thin film; chemical lift-off technology has stringent requirements for material selection and process control; mechanical lift-off technology struggles to achieve large-area uniform separation. Furthermore, the lift-off thin film often exhibits warping issues, making high-quality transfer to flexible substrates difficult. Simultaneously, GaN-based device fabrication relies on high-quality single-crystal substrates (such as GaN self-supporting substrates), which are expensive. Moreover, in existing technologies, the substrates are often not recyclable after device fabrication, resulting in persistently high manufacturing costs.

[0004] Third, existing technologies utilizing porous structures for assisted lift-off have limited functionality. In existing technologies, the stress relief layer and the lift-off assist layer are designed and fabricated independently, which not only increases the complexity of the epitaxial structure and manufacturing costs but also makes it difficult to achieve simultaneous functionality of the same porous layer in both the growth and lift-off stages. Furthermore, how to achieve compatibility with multiple lift-off methods using a single porous layer while ensuring high-quality epitaxial growth, and how to achieve a complete process loop for substrate recovery and thin film flexibility after lift-off, remain pressing technical challenges in this field. Summary of the Invention

[0005] Objective of the Invention: The main objective of this invention is to provide a method for preparing nitride thin films that combines stress relief and exfoliation assistance functions. By constructing an InGaN / GaN superlattice porous layer with both stress relief and exfoliation assistance functions, high-quality epitaxial growth of nitride thin films is achieved. Furthermore, this method enables the separation of the thin film from the original substrate, transfer to a flexible or arbitrary target substrate, and recycling of the original substrate. Another objective of this invention is to provide a semiconductor device comprising the aforementioned nitride thin film, including but not limited to LED, HEMT, or LD structures.

[0006] Technical solution: The present invention provides a method for preparing a nitride thin film, comprising the following steps: Provide a single-crystal substrate; A buffer layer is grown on the single-crystal substrate; A superlattice stacked structure is formed on the buffer layer. The superlattice stacked structure includes alternating stacked InGaN sublayers and GaN sublayers. The superlattice stacked structure uses GaN sublayers as the starting and ending layers, i.e., its arrangement is GaN / InGaN / GaN / InGaN… / GaN. By using a stepped heating process, GaN sublayers of a certain thickness are grown sequentially in three temperature ranges: 700-800 ℃, 800-900 ℃, and 900-1200 ℃. This causes at least a portion of the InGaN in the InGaN sublayer to thermally decompose and form a porous structure, thereby transforming the superlattice stacked structure into an InGaN / GaN superlattice porous stress-relieving layer containing porous InGaN sublayers. Nitride films are grown on the InGaN / GaN superlattice porous stress-relieving layer.

[0007] Furthermore, the three different temperature conditions are 700-800 °C, 800-900 °C, and 900-1200 °C. The 700-800 °C temperature range is used to grow a low-temperature GaN layer to maintain the quality of InGaN; the 800-900 °C temperature range is used to grow a GaN intermediate layer, causing some InGaN to begin to decompose and form a preliminary porous structure; the 900-1200 °C temperature range is used to grow a high-temperature GaN layer, causing a large amount of InGaN to decompose and form a fully porous structure. The three temperature ranges constitute a gradient porosification process, realizing the gradual release of stress.

[0008] Preferably, the single crystal substrate is selected from any one of GaN substrate, sapphire Al2O3 substrate, or SiO2 / Si composite substrate.

[0009] Preferably, the superlattice stacked structure has 5-20 periods, with the InGaN sublayer having a thickness of 2-5 nm and the GaN sublayer having a thickness of 2-10 nm in each period; the molar fraction of In in the InGaN sublayer is 10%-30%.

[0010] Preferably, the nitride film is at least one of GaN film, AlGaN film, or InGaN film; during or after the growth of the nitride film, any one of the device structures, such as LED structure, HEMT structure, or LD structure, is also grown on the InGaN / GaN superlattice porous stress relief layer.

[0011] Preferably, the method further includes: using a stripping process to separate the nitride film together with the InGaN / GaN superlattice porous stress relief layer from the single crystal substrate.

[0012] Preferably, the peeling process is selected from at least one of laser peeling, chemical peeling, and mechanical peeling; the peeling is performed in a temperature range from room temperature to 200 °C.

[0013] Preferably, the method further includes: transferring the separated nitride film onto the target substrate.

[0014] Furthermore, the single-crystal substrate is recycled after separation and reused for the next epitaxial growth.

[0015] Preferably, the target substrate is selected from flexible substrates or non-flexible substrates; after the nitride film is transferred to the target substrate, it is used for subsequent epitaxial growth of LED structures, HEMT structures or LD structures or device applications.

[0016] The nitride film of the present invention is prepared by the method described herein.

[0017] The semiconductor device of the present invention utilizes the nitride thin film obtained by the method described above and the device structure formed on the nitride thin film.

[0018] Invention Principle: This invention constructs an InGaN / GaN superlattice porous stress-relieving layer. Utilizing the thermal decomposition characteristics of the high-In-content InGaN sublayer during high-temperature GaN growth, a porous structure is formed in situ within the InGaN layer, thereby achieving stress release throughout the entire device growth process. This effectively eliminates residual stress, warpage, and dislocation defects caused by lattice mismatch (approximately 14% mismatch between GaN and sapphire, and approximately 11% mismatch between InN and GaN) and thermal mismatch in heteroepitaxial growth, overcoming the limitation of insufficient stress release in traditional stress-relieving layers. Simultaneously, this porous structure can serve as a lift-off aid layer in the subsequent lift-off process (in... In laser lift-off, it serves as a high-efficiency laser absorption layer; in chemical lift-off, it serves as a selective corrosion-sensitive layer; and in mechanical lift-off, it serves as a stress concentration release layer. This enables low-damage separation of nitride films from the original single-crystal substrate. The peeled single-crystal substrate can be recycled and reused, significantly reducing production costs. Furthermore, the separated nitride films can be transferred to flexible or arbitrary target substrates, overcoming the technical challenge of directly epitaxially growing nitride materials on flexible substrates. Ultimately, this achieves high-quality nitride film preparation and device applications on low-cost, large-size, flexible substrates, opening up a new path for the manufacturing of flexible optoelectronic devices.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Stress release in the epitaxial layer is achieved. This invention constructs an InGaN / GaN superlattice porous stress-relieving layer, utilizing the thermal decomposition characteristics of the high-In composition InGaN sublayer during high-temperature GaN growth to form a porous structure in situ, thus achieving complete release of lattice mismatch stress (approximately 14% mismatch between GaN and sapphire, and approximately 11% mismatch between InN and GaN) and thermal mismatch stress in heteroepitaxial growth. Compared with traditional superlattice or composition-gradient stress-relieving layers, the introduction of the porous structure allows for more complete stress release, significantly reduces epitaxial wafer warpage, and thus significantly improves the crystal quality of the nitride film.

[0020] (2) This invention achieves the first functional integration and synergistic effect of porous stress relief and exfoliation processes. The InGaN / GaN superlattice porous stress relief layer of this invention serves as a stress relief layer during the growth stage to eliminate lattice mismatch stress and ensure high-quality epitaxial growth. During the exfoliation stage, it acts as an exfoliation aid layer, playing a corresponding role depending on the exfoliation method (laser exfoliation, chemical exfoliation, or mechanical exfoliation)—serving as a highly efficient laser absorption layer in laser exfoliation, a selective corrosion-sensitive layer in chemical exfoliation, and a stress concentration relief layer in mechanical exfoliation. This "dual-purpose" design allows the same layer structure to play different roles at different stages. Compared to existing technologies that require separate preparation of stress relief and exfoliation aid layers, this invention significantly simplifies the epitaxial structure design and fabrication process, reducing manufacturing costs. The aforementioned functional integration effect is not a simple superposition of individual technologies, but rather a synergistic technical effect achieved by organically integrating the material properties of the InGaN / GaN superlattice, the in-situ pore-forming process with stepped heating, and the compatibility of multiple exfoliation methods.

[0021] (3) The stepped heating process of the present invention achieves the gradual release of stress. Compared with the thermal decomposition method of single high-temperature holding in the prior art, the three-stage heating of the present invention (700-800 °C, 800-900 °C, 900-1200 °C) corresponds to the quality maintenance, preliminary decomposition and complete decomposition of the InGaN layer, respectively, avoiding epitaxial layer cracking caused by stress abrupt changes, and significantly improving the crystal quality of the nitride film. This mechanism of gradually releasing stress cannot be achieved by a single temperature zone thermal decomposition process.

[0022] (4) The invention enables the lossless recycling and reuse of the original single-crystal substrate. Through a peeling process, the nitride film is separated from the original single-crystal substrate with minimal damage. The peeled GaN substrate, sapphire substrate, or SiO2 / Si composite substrate can be recycled and reused for the next epitaxial growth. Compared with existing peeling technologies, the porous stress-relieving layer of this invention effectively buffers the mechanical stress generated during the transfer process, avoiding damage to the film and substrate, significantly reducing device manufacturing costs, and improving the utilization rate of substrate materials.

[0023] (5) High-quality transfer of nitride thin films to flexible substrates has been achieved. The self-supporting nitride thin films obtained by peeling in this invention can be transferred to flexible substrates (such as polymers, metal foils, etc.) or any target substrate, overcoming the technical difficulty of directly epitaxially growing nitride materials on flexible substrates. This technological breakthrough enables nitride-based optoelectronic devices to be realized on low-cost, large-size, and bendable flexible substrates, providing a key material foundation for emerging application fields such as wearable devices, flexible displays, and biomedicine, and greatly expanding the application scenarios of nitride semiconductor devices.

[0024] (6) Separation of the device structure from the substrate is achieved, improving the heat dissipation performance and light extraction efficiency of the device. For optoelectronic devices such as LEDs or LDs, removing the original light-absorbing or heat-absorbing substrate after stripping can significantly improve the light extraction efficiency and heat dissipation performance of the device. Devices transferred to a high thermal conductivity substrate (such as metal or diamond thin film) have significantly improved thermal management capabilities, which is beneficial for the fabrication of high-power devices and the improvement of reliability.

[0025] (7) Flexible selection of peeling methods and wide applicability. This invention does not limit the specific peeling method and can flexibly select laser peeling, chemical peeling, mechanical peeling or a combination thereof according to actual process conditions and application requirements. Regardless of the peeling method used, the porous stress relief layer can play the dual functions of stress relief and peeling assistance, and has good process compatibility and universality, while the porous peeling layers in the prior art are usually only suitable for a single peeling method.

[0026] (8) The process is simple, low-cost, and easy to scale up. The method of this invention does not require complex equipment or high-cost process steps. It can be achieved using standard MOCVD epitaxial growth and stripping techniques, and has good compatibility with traditional semiconductor manufacturing processes. The formation of the porous stress-relieving layer does not require additional electrochemical etching or photolithography steps. It is completed in situ through a high-temperature growth process, which simplifies the process flow. At the same time, the recycling and reuse of the original single-crystal substrate further reduces production costs and is suitable for large-scale industrial production. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the nitride thin film epitaxial structure in Embodiment 1 of the present invention; Figure 2 The image shown is the XRD pattern of the nitride film in Example 1 of this invention. Figure 3 This is a schematic diagram of the peeling process in Embodiment 2 of the present invention (taking laser peeling as an example).

[0028] Figure reference numerals: 101-single crystal substrate; 102-buffer layer; 103-GaN superlattice layer; 104-InGaN superlattice layer; 105-nitride thin film; 106-flexible substrate. Detailed Implementation

[0029] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0030] Example 1: As Figure 1 As shown, this embodiment provides a method for preparing a nitride thin film. The method first grows a buffer layer 102 and an InGaN / GaN superlattice porous stress relief layer 104 / 103 sequentially on a single crystal substrate 101. Then, a porous stress relief layer is formed by high-temperature treatment, and a nitride thin film 105 is grown on it.

[0031] (1) Single crystal substrate 101: In this embodiment, the single crystal substrate 101 is a sapphire substrate (Al2O3) with a crystal orientation of (0001) and a substrate thickness of 650 μm. Before growth, the substrate is subjected to standard organic cleaning and acid washing treatment to remove surface contaminants.

[0032] (2) Buffer layer 102: A low-temperature GaN buffer layer was grown on a sapphire substrate by metal-organic chemical vapor deposition (MOCVD) at a growth temperature of 550 °C, a thickness of 30 nm, and a V / III ratio of 1200. The temperature was then raised to 1050 °C for high-temperature annealing to recrystallize the buffer layer and provide nucleation centers for subsequent epitaxial growth.

[0033] (3) InGaN / GaN superlattice porous stress relief layer 104 / 103: An InGaN / GaN superlattice stacked structure is grown on the buffer layer 102, with 10 periods. The thickness of the InGaN sublayer in each period is 4 nm, and the In composition is 25% (i.e., In 0.25 Ga 0.75 The InGaN sublayer thickness was 10 nm. InGaN growth was carried out at 780 °C and 300 Torr, using trimethylindium (TMIn), TMGa, and NH3 as precursors and N2 as the carrier gas. The GaN sublayer growth temperature was divided into three stages: 780 °C (2 nm), 900 °C (3 nm), and 1050 °C (5 nm). During the high-temperature GaN growth process, the high-In content InGaN sublayer underwent thermal decomposition, breaking down InGaN into metallic In, a Ga-rich phase, and N2 gas. The escaped N2 gas formed a porous structure in situ. This porous structure exhibited a uniform pore distribution and a porosity of 20%-40%, effectively releasing residual stress caused by lattice mismatch.

[0034] (4) Nitride film 105: A nitride film is further grown on the porous stress-relief layer. The nitride film is a GaN film, grown at a temperature of 1050 °C, a growth pressure of 200 Torr, and a thickness of 2 μm. Due to the presence of the porous stress-relief layer, the lattice mismatch stress in the epitaxial layer has been fully released. The GaN film exhibits a high-quality crystal state with no cracks and low warpage. Its XRD rocking curve full width at half maximum (FWHM) is less than 300 arcsec, and its through-dislocation density is less than 5 × 10⁻⁶. 8 cm -2 (like Figure 2 ).

[0035] Example 2: As a preferred embodiment of the peeling process, this example uses laser peeling technology. For example... Figure 3As shown, this embodiment, based on embodiment 1, further performs laser stripping on the nitride film grown in step (5) to achieve separation from the original single crystal substrate.

[0036] After the nitride film 105 is grown, it is separated from the original single-crystal substrate 101 using laser lift-off technology. Specifically, taking advantage of the high absorption coefficient of InGaN material for a specific wavelength of laser light, laser irradiation is performed from the back side of the single-crystal substrate 101. The lift-off process is carried out at room temperature (approximately 25 °C), or it can be heated to 50-200 °C to assist the lift-off process. The laser wavelength is selected as 248 nm (KrF excimer laser) or 355 nm (third harmonic of Nd:YAG laser), and the laser energy density is 600-800 mJ / cm². 2 The pulse width is 20-50 ns, and the spot size can cover the entire substrate area. When the laser penetrates the sapphire substrate and irradiates the porous stress-relieving layer, the laser energy is efficiently absorbed by the InGaN material and triggers thermal decomposition. InGaN decomposes into metallic In and N2 gas. The pressure of the generated N2 gas causes the nitride film 105, along with the porous stress-relieving layer, to separate from the sapphire substrate 101. Compared with existing technologies using 532 nm lasers, the 248 nm or 355 nm ultraviolet laser used in this invention has higher single-photon energy, enabling more precise peeling control and reducing the thermal impact on surrounding materials.

[0037] After stripping, there are very few residues on the surface of the sapphire substrate 101. After simple cleaning and surface treatment, it can be recycled for the next epitaxial growth, realizing the reuse of the substrate and greatly reducing production costs.

[0038] In other embodiments, the stripping process can also employ chemical stripping (such as selectively etching the InGaN component in the porous layer using hydrofluoric acid or KOH solution to separate the film from the substrate), mechanical stripping (such as separating along the porous layer using ultrasound or mechanical force), or a combination thereof. All of these methods can effectively separate the nitride film from the original single-crystal substrate, and the porous stress-relieving layer can play a dual role of stress relief and stripping assistance in different stripping methods.

[0039] Example 3: In this example, the nitride film obtained after peeling in Example 2 is transferred to a flexible substrate to achieve the flexibility of the nitride film.

[0040] The stripped nitride film 105 (still attached to the porous stress-relieving layer) is transferred to the flexible substrate 106 via van der Waals forces or a polymer adhesion layer (such as BCB, SU-8, etc.). The flexible substrate 106 is selected from any one of polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or metal foil. The integrity and flatness of the film are maintained during the transfer process, and the surface roughness (RMS) of the film after transfer is less than 2 nm.

[0041] The nitride films transferred to the flexible substrate retain their original high-quality crystal properties and can be directly used for the fabrication of subsequent flexible optoelectronic devices (such as flexible LEDs, flexible HEMTs, or flexible LDs), providing a high-quality material basis for emerging applications such as wearable devices and flexible displays.

[0042] Example 4: Based on Example 1, during or after the growth of the nitride film 105, any one of the device structures, such as LED structure, HEMT structure or LD structure, can be grown on the porous stress relief layer. Then, the device structure is separated from the original substrate by the peeling process of Example 2, and the device structure is transferred to a flexible substrate or any target substrate by the transfer method of Example 3, thereby realizing the substrate transfer and flexibility of the complete device.

[0043] Specifically, an n-type contact layer (n-GaN, 2 μm thick, Si-doped 3×10⁻⁶) is sequentially grown on the porous stress relief layer. 18 cm -3 ), multi-quantum well active region (MQW, In) 0.15 Ga 0.85 N / GaN, 3 periods, well thickness 3 nm, barrier thickness 8 nm), electron blocking layer (p-AlGaN, thickness 20 nm, Al composition 0.20), and p-type contact layer (p-GaN, thickness 100 nm, Mg doped 1×10⁻⁶). 19 cm -3 A complete LED epitaxial structure is formed. Then, the LED structure is separated from the sapphire substrate using the lift-off process of Example 2, and then transferred to a flexible substrate using the method of Example 3, ultimately obtaining a flexible LED device. Due to the presence of the porous stress-relieving layer, the stress in the LED epitaxial structure is fully released, and the transferred flexible LED device exhibits excellent luminous performance and mechanical bending stability.

[0044] This invention innovatively integrates the construction of an InGaN / GaN superlattice porous stress-relieving layer with a lift-off technique. By utilizing the thermal decomposition characteristics of high-In-content InGaN at high temperatures to form a porous structure in situ, it achieves the release of heteroepitaxial stress in nitride films. Based on this, the film is separated from the original single-crystal substrate with low damage and the substrate can be recovered through lift-off. At the same time, high-quality nitride films can be transferred to flexible or arbitrary target substrates. This invention completely breaks through the technical bottleneck of traditional nitride devices' dependence on single-crystal substrates and the difficulty of directly epitaxially growing nitride materials on flexible substrates, opening up a new path for the fabrication of low-cost, large-size, flexible nitride optoelectronic devices.

Claims

1. A method for preparing a nitride thin film, characterized in that, Includes the following steps: Provide a single-crystal substrate; A buffer layer is grown on the single-crystal substrate; A superlattice stacked structure is formed on the buffer layer, the superlattice stacked structure comprising alternately stacked InGaN sublayers and GaN sublayers; The superlattice stacked structure uses GaN sublayers as the starting and ending layers. Through a stepped heating process, GaN sublayers of a certain thickness are grown sequentially in three temperature ranges: 700-800 ℃, 800-900 ℃, and 900-1200 ℃. This causes at least a portion of the InGaN in the InGaN sublayer to thermally decompose and form a porous structure, thereby transforming the superlattice stacked structure into an InGaN / GaN superlattice porous stress-relieving layer containing porous InGaN sublayers. Nitride films are grown on the InGaN / GaN superlattice porous stress-relieving layer.

2. The method according to claim 1, characterized in that, The single-crystal substrate is selected from any one of GaN substrate, sapphire Al2O3 substrate, or SiO2 / Si composite substrate.

3. The method according to claim 1, characterized in that, The superlattice stacked structure has 5-20 periods, with the InGaN sublayer having a thickness of 2-5 nm and the GaN sublayer having a thickness of 2-10 nm in each period; the molar fraction of In in the InGaN sublayer is 10%-30%.

4. The method according to claim 1, characterized in that, The nitride film is at least one of GaN film, AlGaN film, or InGaN film; during or after the growth of the nitride film, any one of the following device structures, namely LED structure, HEMT structure, or LD structure, is also grown on the InGaN / GaN superlattice porous stress relief layer.

5. The method according to claim 1, characterized in that, Also includes: A stripping process is used to separate the nitride film, along with the InGaN / GaN superlattice porous stress relief layer, from the single crystal substrate.

6. The method according to claim 5, characterized in that, The peeling process is selected from at least one of laser peeling, chemical peeling, and mechanical peeling; the peeling is carried out in a temperature range from room temperature to 200 °C.

7. The method according to claim 5, characterized in that, Also includes: The separated nitride film was transferred onto the target substrate.

8. The method according to claim 7, characterized in that, The target substrate is selected from flexible substrates or non-flexible substrates; after the nitride film is transferred to the target substrate, it is used for subsequent epitaxial growth of LED structures, HEMT structures or LD structures or device applications.

9. A nitride thin film, characterized in that, It is prepared by any one of claims 1 to 8.

10. A semiconductor device, characterized in that, It includes a nitride thin film prepared by any one of claims 1 to 8 and a device structure formed on the nitride thin film.

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