Large-area Micromechanical Exfoliation Method Based on Graphical GaN-based Epitaxial Layers

Abstract

The present invention discloses a large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer. By covering a two-dimensional material on the surface of an epitaxial substrate to grow a GaN-based epitaxial layer, after epitaxial growth, the GaN-based epitaxial layer is patterned into small patterns on the order of square centimeters. At the same time, the hard mask layer in the patterning process is used as a stress layer to achieve large-area non-destructive peeling of the GaN-based epitaxial layer in a micro-mechanical peeling manner. This method utilizes the weak bonding force between the two-dimensional material and the substrate and the epitaxial layer, or between two-dimensional material layers, and overcomes the problem of uneven stress distribution inside large-size wafers caused by two-dimensional material defects by patterning the GaN-based epitaxial layer into small patterns of a certain area, realizing large-area peeling of the GaN-based epitaxial layer and reusing the epitaxial substrate. Therefore, while realizing high-quality large-area peeling of the GaN-based epitaxial layer, the present invention has the advantages of simple process, good process compatibility, and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology and relates to a method for large-area micro-mechanical peeling based on a patterned GaN-based epitaxial layer. Background Art

[0002] Gallium nitride (GaN)-based wide-bandgap semiconductor materials are particularly suitable for high-frequency, high-power, and high-temperature applications due to their excellent material properties. Their applications in high-frequency, high-power microwave, and millimeter-wave devices have received extensive attention. However, the self-heating effect of the device limits the full play of the high-frequency and high-power performance advantages of GaN-based devices.

[0003] The heat conduction inside the chip determines the operating temperature of the device. Relying on traditional packaging technology cannot effectively solve the heat dissipation problem of high-power devices. Using diamond with ultra-high thermal conductivity as the device substrate can effectively improve the heat dissipation ability of the chip. However, single-crystal diamond is expensive and very small in size. At the same time, the huge lattice mismatch and thermal mismatch between diamond and GaN-based materials further limit the development of high-quality GaN-based materials on diamond substrates. Therefore, peeling the GaN-based epitaxial layer from the native substrate and bonding it to polycrystalline diamond has become an effective solution to the device heat dissipation problem currently.

[0004] In common peeling methods, including chemical peeling, laser peeling, mechanical peeling, and micro-mechanical peeling based on two-dimensional materials: Chemical peeling technology is difficult to achieve because it is difficult to find a sacrificial layer compatible with high-quality nitride epitaxy; Laser peeling technology easily introduces damage in GaN, making the peeled surface roughened (W. Chen et al., Appl. Phys. Lett. 91, 121114, 2007); Mechanical peeling technology relies on a relatively thick stress layer and the peeling interface is very rough (H. Kum et al., Nat. Electron. 2, 439, 2019); Micro-mechanical peeling based on two-dimensional materials realizes the separation of the functional layer and the substrate by means of the van der Waals force between two-dimensional material layers or between two-dimensional materials and the epitaxial layer and the substrate, and the separation interface can reach atomic-level smoothness.

[0005] Whether covering two-dimensional materials on the epitaxial substrate surface by transfer, thermal evaporation, or deposition growth, it is difficult to achieve a complete and uniform covering layer, and there are usually phenomena such as wrinkles, holes, and uneven thickness on the surface of two-dimensional materials. Therefore, the force between the epitaxial layer and the substrate is non-uniformly distributed within the wafer, making it difficult to achieve large-area peeling of the GaN-based epitaxial layer. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer. A GaN-based epitaxial layer is epitaxially grown on an epitaxial substrate / two-dimensional material composite substrate, and then the GaN-based epitaxial layer is etched into small patterns of a specific area, and the GaN-based epitaxial layer is peeled off from the surface of the growth substrate by a micro-mechanical peeling method to achieve large-area non-destructive peeling of the GaN-based epitaxial layer. To solve the deficiencies of the prior art, the present invention provides a large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer. The purpose of the present invention is to achieve large-area non-damaging and high-quality peeling of the GaN-based epitaxial layer by using two-dimensional materials, patterning of the GaN-based epitaxial layer, and micro-peeling method.

[0007] To achieve the above technical objectives and reach the above technical effects, the technical solution of the present invention: A large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer includes the following steps:

[0008] 1) Form a two-dimensional material on the epitaxial substrate;

[0009] 2) Epitaxially grow a GaN-based epitaxial layer on the epitaxial substrate / two-dimensional material composite substrate;

[0010] 3) Etch the GaN-based epitaxial layer into small patterns of a specific area, and the small patterns refer to the order of square centimeters:

[0011] 3a) Coat a photoresist on the surface of the GaN-based epitaxial layer, and expose and develop the photoresist with a photomask to form a pattern;

[0012] 3b) Deposit a hard mask on the surface of the GaN-based epitaxial layer coated with the patterned photoresist, and form a mask pattern through the lift-off technique;

[0013] 3c) Deeply etch the GaN-based epitaxial layer in the maskless area to the surface of the composite substrate;

[0014] 4) Peel off the GaN-based epitaxial layer from the surface of the growth substrate by a micro-mechanical peeling method.

[0015] The epitaxial substrate can be one of the substrates that are crystal symmetry-matched with the GaN-based material: sapphire, SiC, Si(111), single-crystal GaN, single-crystal AlN, single-crystal diamond; the two-dimensional material is single-crystal or polycrystalline graphene, hexagonal boron nitride, or molybdenum disulfide. Preferably, the thickness of the two-dimensional material is 1-3 layers.

[0016] On the other hand, the epitaxial substrate can be one of the substrates that do not have crystal symmetry with the GaN-based material: Si(100), polycrystalline diamond, polycrystalline AlN, silicon oxide, quartz glass; it is required that the two-dimensional material is single-crystal graphene or single-crystal hexagonal boron nitride. Preferably, the thickness of the two-dimensional material is 1-3 layers.

[0017] The growth method of the GaN-based epitaxial layer includes one of metal-organic chemical vapor deposition, molecular beam epitaxy, hydride vapor epitaxy, atomic layer deposition, and chemical vapor deposition.

[0018] In step 3, the GaN-based epitaxial layer is etched into small patterns with a specific area. Preferably, the shape of the small pattern is circular or square, and the area is 0.5 - 2 cm 2 , and the spacing between small patterns is 5 - 500 μm.

[0019] The method for depositing a hard mask on the surface of the GaN-based epitaxial layer can be one of magnetron sputtering, electron beam evaporation, chemical vapor deposition, and atomic layer deposition. The type of the hard mask layer can be one of SiO2, SiN, and metal Ni. Preferably, the thickness of the hard mask layer is 100 - 2000 nm.

[0020] Preferably, the photoresist coated on the surface of the GaN-based epitaxial layer is a negative photoresist, and the pattern of the hard mask layer is formed by the lift-off technique.

[0021] For the etching of the GaN-based epitaxial layer, the etching method is dry etching based on the plasma etching process, the etching gas is a chlorine-based gas, and the etching depth is the overall thickness of the epitaxial layer. Preferably, the etching gas can be one of chlorine gas (Cl2), boron trichloride (BCl3), and silicon tetrachloride (SiCl4), or a mixed gas with hydrogen gas (H2) and argon gas (Ar), and the etching rate is 50 - 500 nm / min.

[0022] In step 4, the GaN-based epitaxial layer is peeled off from the surface of the growth substrate by a micro-mechanical peeling method. The peeling method includes: retaining the hard mask layer on the surface of the GaN-based epitaxial layer, adhering a thermally releasable adhesive or polydimethylsiloxane (PDMS) to the surface of the mask layer, and carrying the GaN-based epitaxial layer to achieve separation from the growth substrate at the two-dimensional material interface.

[0023] Beneficial effects:

[0024] The above technical solutions show that the large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer disclosed by the present invention has the following beneficial effects:

[0025] In the present invention, a GaN-based epitaxial layer is grown by covering a two-dimensional material on the surface of an epitaxial substrate. After epitaxial growth, the GaN-based epitaxial layer is patterned into small patterns on the order of square centimeters. At the same time, the hard mask layer in the patterning process is used as a stress layer, and the large-area non-destructive peeling of the GaN-based epitaxial layer is realized by a micro-mechanical peeling method. In this technical solution, the weak binding force introduced by the two-dimensional material can effectively reduce peeling damage and reduce the roughness of the peeling interface. The prepared high-quality GaN-based epitaxial layer can be bonded to a high thermal conductivity material to improve the heat dissipation capacity of high-power devices, or used in other flexible functional devices. The patterning method can effectively solve the problem of uneven stress distribution in large-size wafers caused by two-dimensional material defects, and can realize single-time large-area peeling of large-size wafers. The hard mask layer serves as both the mask layer in the patterning process and the stress layer in micro-mechanical peeling, and the process is simple and has good compatibility. In addition, this technical solution can recycle the epitaxial substrate and reduce the preparation cost. Description of the Drawings

[0026] Figure 1 It is a flow chart of a large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer shown in an embodiment of the present invention.

[0027] Figure 2 It is a schematic structural diagram of a sample to be peeled after etching the GaN-based epitaxial layer into small patterns in an embodiment of the present invention, where symbol 1 is the epitaxial substrate, 2 is the two-dimensional material, 3 is the GaN-based epitaxial layer, and 4 is the hard mask layer. Detailed Description of the Embodiments

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. The implementation manners not depicted or described in the drawings are forms known to those skilled in the art in the said technical field. This document provides parameter demonstrations including specific values, but the parameters do not necessarily exactly equal the corresponding values, but are approximated to the corresponding values within an acceptable error tolerance or design constraints.

[0029] According to Figure 1 The large-area micro-mechanical peeling method based on a patterned GaN-based epitaxial layer shown in the steps includes:

[0030] 1) Graphene is formed on the SiC substrate by thermal evaporation.

[0031] 2) The SiC / graphene composite substrate is placed in a metalorganic chemical vapor deposition (MOCVD) reaction chamber. After high-temperature baking, an AlN nucleation layer, a GaN high-resistance layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN capping layer are grown in sequence to form a GaN-HEMT epitaxial structure.

[0032] 3) Etch the GaN-based epitaxial layer into small patterns of a specific area

[0033] 3a) Coating a layer of AZ5214 photoresist on the surface of the GaN-based epitaxial layer, converting it into a negative photoresist through flood exposure, and then exposing and developing to transfer the photomask pattern to the photoresist;

[0034] 3b) Depositing metal Ni on the sample surface by magnetron sputtering with a thickness of 100 - 2000 nm, and then immersing the sample in a stripping solution to transfer the pattern to the hard mask - metal Ni layer through the lift-off technique;

[0035] 3c) Introducing a mixed gas of chlorine and argon into an inductively coupled plasma etching machine (ICP) to etch the GaN-based epitaxial layer. The etching depth is controlled by the etching rate, and the etching rate is 50 - 500 nm / min. The structure of the sample after etching is as Figure 2 shown;

[0036] 4) Adhere the thermally released glue or polydimethylsiloxane (PDMS) to the surface of the mask layer, that is, on the surface of the sample with the structure as Figure 2 shown. Here, the hard mask layer serves as a stress layer to assist in micro-mechanical peeling, and the GaN-based epitaxial layer is peeled off by the thermally released glue or PDMS.

[0037] The above specific embodiments further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A large-area micro-mechanical peeling method based on a graphitized GaN-based epitaxial layer, characterized in that, Including: 1) Forming a two-dimensional material on an epitaxial substrate; 2) Epitaxially growing a GaN-based epitaxial layer on the composite substrate of the epitaxial substrate and the two-dimensional material; 3) Etching the GaN-based epitaxial layer into small patterns with a specific area, where the small patterns refer to the order of square centimeters: 3a) Coating a photoresist on the surface of the GaN-based epitaxial layer, and exposing and developing the photoresist with a photomask, to form a pattern; 3b) Depositing a hard mask on the surface of the GaN-based epitaxial layer coated with the patterned photoresist, and forming a mask pattern through the lift-off technique; 3c) Deep etching the GaN-based epitaxial layer in the mask-free area to the surface of the composite substrate; 4) Stripping the GaN-based epitaxial layer from the surface of the growth substrate by a micro-mechanical peeling method; In step 1), when forming the two-dimensional material on the epitaxial substrate, the epitaxial substrate includes one of the following substrates: sapphire, silicon carbide, silicon, gallium nitride, aluminum nitride, diamond, silicon oxide, quartz glass; the two-dimensional material is graphene, hexagonal boron nitride or molybdenum disulfide, and the thickness of the two-dimensional material is 1-3 layers; the formation method of the two-dimensional material on the epitaxial substrate includes transfer, thermal evaporation or deposition growth; In step 2), when epitaxially growing the GaN-based epitaxial layer on the composite substrate of the epitaxial substrate / two-dimensional material, the GaN-based epitaxial layer includes one or several of the following epitaxial layers: AlN nucleation layer, GaN, n-GaN, p-GaN, AlGaN and InGaN; In step 3), the GaN-based epitaxial layer is etched into small patterns with a specific area. The shape of the small patterns is circular or square, and the area is 0.5 - 2 cm 2 , and the spacing between the small patterns is 5 - 500 μm; In step 3), exposing and developing the photoresist with a photomask to form a pattern, and the photoresist is a negative photoresist; In step 4), stripping the GaN-based epitaxial layer from the surface of the growth substrate by a micro-mechanical peeling method, without removing the mask layer, which is used here as a stress layer to assist peeling, adhering a thermal release glue or polydimethylsiloxane to the surface of the mask layer, and carrying the GaN-based epitaxial layer to achieve separation from the growth substrate at the two-dimensional material interface.

2. The large-area micromachining peeling method based on a patterned GaN-based epitaxial layer according to claim 1, wherein In step 3), depositing a hard mask on the surface of the above GaN-based epitaxial layer, and the deposition method includes one of the following methods: magnetron sputtering, electron beam evaporation, chemical vapor deposition, atomic layer deposition; the hard mask includes one of the following masks: SiO2, SiN and metal Ni; the thickness of the hard mask layer is 100-2000 nm.

3. The large-area micro-machining peeling method based on a patterned GaN-based epitaxial layer according to claim 1, wherein In step 3), deep etching the GaN-based epitaxial layer to the surface of the composite substrate, and the etching method used is dry etching based on a plasma etching process, the etching gas is a chlorine-based gas, and the etching depth is the overall thickness of the epitaxial layer.

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