Preparation method of low-dislocation high-efficiency GaN substrate for laser

Abstract

The invention discloses a preparation method of a low-dislocation high-efficiency GaN substrate for a laser. The preparation method comprises the following steps: providing a heterogeneous substrate; a layer of mask is deposited on a heterogeneous substrate, the mask is further subjected to uniform glue etching to be patterned, a GaN single-crystal crystal column is grown on the basis of the patterned mask in a heteroepitaxial mode through an HVPE method, and the GaN single-crystal crystal column is subjected to linear cutting and polishing to form a product. And the GaN crystal column top layer can be used as the original substrate, and is repeatedly used after being subjected to wet etching. The method has the advantages that through mask HVPE epitaxial growth, special treatment of homogeneous epitaxy and wet etching can be utilized, so that lattice mismatch does not exist in homogeneous epitaxy, pits are formed in dislocation positions through wet etching, the epitaxy disappears during regrowth, and in addition, along with continuous increasing of the thickness, the thickness of the epitaxy is gradually increased. Dislocation extending from an original substrate interface layer can be continuously annihilated and disappeared; the top layer of the GaN crystal column generated in each cycle can be repeatedly used; the dislocation density is reduced, so that the polarization effect of the blue-green laser is reduced.

Description

Technical Field

[0001] The invention relates to a gallium nitride single crystal material growth technology, and in particular to a method for preparing a low-dislocation and high-efficiency GaN substrate for a laser. Background Art

[0002] In recent years, gallium nitride and silicon carbide are wide bandgap semiconductor materials, which are called representatives of the third generation of semiconductors. Gallium nitride single crystals have excellent properties such as high breakdown voltage, smaller dielectric constant, higher saturated electron drift rate, better thermal conductivity, wider energy gap (Eg ≥ ​​2.3 eV), and good chemical stability. At present, it is an ideal substrate material for the production of blue-green lasers, radio frequency microwave devices, and power electronic devices. It has broad application prospects in laser display, 5G communication, phased array radar, aerospace, etc.

[0003] Depending on the substrate material, GaN is divided into homoepitaxial growth and heteroepitaxial growth. When epitaxially growing GaN materials on heterogeneous substrates, due to the mismatch in lattice constant and thermal expansion coefficient between the heterogeneous substrate and the newly grown GaN, heteroepitaxial growth will cause strong stress in the epitaxial layer, leading to the appearance of cracks. Recently, taking advantage of the high growth rate and high crystal quality of HVPE, the substrates used are mainly grown on heterogeneous substrates, such as sapphire, silicon carbide, Si, etc. Growing gallium nitride on a substrate (which can be Al2O3, SiC, Si and other materials) is also heteroepitaxial, and there will also be problems of lattice mismatch and thermal mismatch. At present, using HVPE technology combined with mask technology, thermal mismatch, etc., GaN can be directly grown on materials such as Al2O3, SiC, Si, and self-stripping self-supporting GaN single crystal materials can be obtained after cooling.

[0004] Due to the heterogeneous substrate epitaxial growth of mainstream technology, the lattice mismatch causes the dislocations generated on the heterogeneous epitaxial growth interface to extend upward, resulting in the final product body dislocation density of 1.0*10E6cm -2 -1.0*10E7 cm -2 At the same time, heteroepitaxial growth also consumes more Al2O3, SiC, Si and other substrate materials. In terms of thickness, lattice mismatch, excessive stress and warping will cause cracks; due to exhaust emissions from a single furnace and excessive chamber byproducts that need to be cleaned, the thickness of GaN does not exceed 4mm-5mm. No reports have been seen of thicker GaN single crystal products grown in other ways; some people have proposed using GaN homoepitaxial growth as a substrate, but this method is not feasible. First, there are no such large-area GaN single crystal substrates on the market, and second, the price is very expensive. Therefore, large-sized and cheap Al2O3, SiC, Si and other substrate materials are currently used for heteroepitaxial growth.

[0005] For example, China's invention patent publication number CN111607825A discloses a substrate, a self-supporting GaN single crystal based on the substrate, and a preparation method thereof, providing a substrate, including a substrate, the upper surface of which has a nanocolumn layer with uniform distribution and consistent direction and thickness, the height of the nanocolumn layer is 0.2-5um; the interval between any two nanocolumns is equal, the interval is 0.2-5um; the end face of any nanocolumn in the nanocolumn layer is a circular end face or a regular hexagonal end face, and its diameter or diagonal length is 50-1000nm. This patent uses nanocolumns to turn dislocations, but still cannot make the GaN thickness exceed 4mm-5mm. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the thickness of heteroepitaxially grown GaN is limited, there are too many defects and the dislocation density is large. Therefore, a method for preparing a low-dislocation and high-efficiency GaN substrate for a laser is provided.

[0007] The technical solution of the present invention is: a method for preparing a low-dislocation high-efficiency GaN substrate for a laser, comprising the following steps: (1) providing a heterogeneous substrate; (2) making a patterned mask on the heterogeneous substrate; (3) epitaxially growing a GaN single crystal column on the patterned mask using the HVPE technology, wherein the GaN single crystal column and the patterned mask are automatically peeled off during the cooling process to form a GaN crystal column; (4) performing wire cutting on the GaN crystal column in the height direction to obtain multiple or single GaN single crystal product blanks with controllable thickness, wherein the top GaN single crystal product blank is a top GaN material; (5) the top GaN material is used as a homoepitaxial substrate material for the next round of recycling, and is subjected to wet etching to etch out pits, and steps (2), (3) and (4) are repeated, and the cycle is repeated to obtain a GaN single crystal product with a low dislocation density.

[0008] The etching depth of the wet etching in the above scheme is 0.5 μm-1 μm.

[0009] The wet etching solution in the above scheme is one of KOH, H3PO4, and H2O2, the concentration of the etching solution is 50wt%-90wt%, and the temperature of the etching solution is controlled between 80℃-200℃.

[0010] The material of the substrate in the above solution is sapphire, silicon carbide or single crystal silicon.

[0011] The mask described in the above scheme uses PECVD or magnetron sputtering equipment, and the thickness of the deposited mask is 100nm-1000nm. The pattern openings produced can be one of round, square, hexagonal, etc. The side length of the pattern is controlled at 1μm-100μm, and the density of the pattern openings is controlled at 10 5 -107 / cm 2 .

[0012] The HVPE process temperature in the above scheme is 800°C-1200°C, and the chamber pressure is 600torr-900torr.

[0013] The thickness of the GaN crystal column in the above solution is 4mm-5mm.

[0014] The beneficial effects of the present invention are that the epitaxial growth through mask HVPE can utilize the special treatment of homoepitaxial growth and wet etching, so that the homoepitaxial growth has no lattice mismatch, the wet etching forms pits at the dislocations, and the pits disappear during the epitaxial regrowth, and in addition, as the thickness continues to increase, the dislocations extending from the original substrate interface layer will also continue to annihilate and disappear; at the same time, the top layer of the GaN crystal column produced in each cycle can be reused, saving the cost of purchasing original substrates such as sapphire (Al2O3), silicon carbide (SiC), and silicon (Si); the reduction of dislocation density reduces the polarization effect of the blue-green laser, which can further improve the luminous efficiency and reliability of the blue-green laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the method for preparing a low dislocation and high efficiency GaN substrate for lasers of the present invention;

[0016] Figure 2 , Figure 3 Schematic diagram of each step of the gallium nitride substrate manufacturing method of the present invention;

[0017] Figure 4 Actual dislocation distribution diagram of the gallium nitride substrate manufactured by the present invention under CL electron microscope.

[0018] In the figure, 101 is a substrate base, 201 is a patterned mask, 301a is a first layer, 301b is a second layer, 301c is a third layer, 301d is a fourth layer, and 401 is a top layer of GaN material. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0020] The core idea of ​​the present invention is to provide a method for manufacturing gallium nitride substrates, which changes the currently common heteroepitaxial growth in the industry into homoepitaxial growth. Homoepitaxial growth does not produce new dislocations due to lattice mismatch, and as the thickness continues to increase, dislocations will naturally merge and annihilate, thereby achieving the purpose of reducing dislocation density. At the same time, due to recycling, costs are further reduced and quality and efficiency are improved.

[0021] like Figure 1 As shown, a method for preparing a low-dislocation high-efficiency GaN substrate for a laser comprises the following steps: (1) providing an original substrate, i.e., a heterogeneous substrate, which may be sapphire (Al2O3), silicon carbide (SiC), silicon (Si), etc.; (2) making a patterned mask on the heterogeneous substrate, forming a patterned mask layer on the heterogeneous substrate, using the mask layer as a mask, etching on the mask to form a hole array on its surface, and forming a composite substrate with a patterned mask; (3) epitaxially growing a GaN single crystal column on the patterned mask using HVPE technology, and growing a gallium nitride thick film on the composite substrate using hydride vapor phase epitaxy (HVPE), with a growth thickness of 4 mm to 5 mm. The final thickness depends on the surface condition, equipment hardware support, etc. After the growth is completed, the composite substrate and the gallium nitride thick film are self-peeled off, and the gallium nitride thick film forms a GaN crystal column. As the thickness continues to increase, a GaN crystal column is formed from the interface layer of the heterogeneous substrate. The extended dislocations will be continuously annihilated and disappear; (4) The GaN crystal column is wire-cut in the height direction to produce multiple or single pieces of GaN single crystal product blanks with controllable thickness, such as cutting into a first layer 301a, a second layer 301b, a third layer 301c, a fourth layer 301d and a top layer GaN material 401; (5) The top layer GaN material is used as the substrate material for homoepitaxial growth in the next round of recycling, and pits are etched by wet etching, and steps (2), (3) and (4) are repeated, and this cycle is repeated. In the next round of reciprocating cycles, the advantages and characteristics of homoepitaxial growth can be utilized through masked HVPE epitaxial growth, so that the homoepitaxial growth has no lattice mismatch. At the same time, the top layer GaN material produced in each cycle can be reused, saving the cost of purchasing original substrates such as sapphire (Al2O3), silicon carbide (SiC), silicon (Si), etc., and obtaining a GaN single crystal product with a low dislocation density.

[0022] It should be noted that, although there are reports of using substrate sapphire (Al2O3), silicon carbide (SiC), silicon (Si) and the like repeatedly for the purpose of reducing costs, the dislocations of the substrate still extend upwards, and still belong to heteroepitaxial growth, which does not achieve the purpose of reducing dislocations. There are no reports of recycling the top-layer GaN material of one's own product. And even if someone has tried secondary growth, if the accumulated stress on the surface of the top-layer GaN material is not released and eliminated, the stress or dislocation will still continue into the secondary growth, causing cracks and dislocations without reducing other defects. The difference of the present invention is that the top-layer GaN material of the product itself can be used as the substrate for the next round of homoepitaxial growth, and before homoepitaxial growth, special wet etching surface treatment is required to eliminate stress and dislocations, so as to achieve the ultimate goal of gradually reducing dislocations and reducing costs.

[0023] Combine the following Figures 1 to 4 , the gallium nitride substrate manufacturing method of the present invention is described in detail.

[0024] like Figure 2 As shown, a substrate base 101 is provided. The material of the substrate base 101 can be sapphire (Al2O3), silicon carbide (SiC), silicon (Si), etc. The selected material has a lattice mismatch with gallium nitride and has a certain difference in thermal expansion coefficient with gallium nitride.

[0025] On the substrate 101, a deposition method is selected by PECVD or magnetron sputtering to deposit a mask on the substrate 101 material, the mask thickness is 100nm-1000nm, specifically 100nm, 300nm, 600nm or 1000nm; then, a hole pattern is engraved by uniform glue, development, and photolithography, the pattern can be one of circular, square, hexagonal, etc., the side length of the pattern is controlled to be 1μm-100μm, specifically 1μm, 50μm or 100μm, and the density of the pattern opening is controlled to be 10 5 -10 7 / cm 2 , which can be 10 5 / cm 2 or 10 7 / cm 2 At this point, a patterned mask 201 is formed, which is convenient for subsequent HVPE growth.

[0026] After the patterning mask 201 is completed, hydride vapor phase epitaxy (HVPE) is used to epitaxially grow GaN crystal columns 301a, 301b, 301c, 301d and 401 on the patterning mask 201, and the GaN thickness is 4mm or 5mm; the thickness depends on the emission limit of the equipment's tail gas single furnace; on the other hand, depending on the surface condition, confirmation is required after completion to avoid serious surface defects (cracks, deep V-shaped pits, etc.) after completion due to long-term growth, and the growth can be stopped immediately to reduce material waste.

[0027] After the epitaxial GaN crystal column 301a-401 is completed, the crystal column is cut by wire cutting technology to cut out the primary products 301a, 301b, 301c, 301d with a thickness of 300μm, 400μm or 500μm, which become the blanks for subsequent deep processing by grinding and polishing. As the thickness increases, the dislocation density of the primary products 301a, 301b, 301c, 301d decreases, because dislocations will merge or annihilate with the growth of epitaxy.

[0028] The deep processing, grinding and polishing of the initial products 301a, 301b, 301c and 301d are not described in detail here; the top layer GaN material 401 left by the wire cutting is wet-etched to a depth of 0.5 μm, 0.7 μm or 1 μm on the N side or the Ga side to etch out pits, so that dislocations disappear and stress is released, which is convenient for subsequent epitaxial growth. The etching solution can be one of KOH, H3PO4 and H2O2, with a concentration of 50wt%, 70wt% or 90wt%, and the temperature of the etching solution is controlled at 80°C, 100°C, 150°C or 200°C;

[0029] After the top layer of GaN material 401 is wet-etched, a patterned mask 201 and HVPE epitaxially grown crystal columns 301a-401 are repeatedly produced on this basis, and initial products 301a, 301b, 301c, and 301d are cut out by wire cutting, leaving the top layer of GaN material 401. After wet-etching, the patterned mask 201 is repeatedly produced; this cycle is repeated until pits or other defects appear on the surface of the top layer of GaN material 401 and it can no longer be used.

[0030] As the cycle continues, the thickness continues to increase, and the dislocations extending from the original substrate interface layer will continue to disappear. During the wet etching process, the dislocations are corroded into pits. When the cycle continues with epitaxial growth, the dislocations disappear again. Figure 3 As shown; in the different stages of the cycle, Figure 4 This reflects that the dislocation density is also confirmed to be showing a clear downward trend in actual CL measurements.

Claims

1. A method for preparing a low dislocation and high efficiency GaN substrate for lasers, characterized by: The following steps are involved: (1) providing a heterogeneous substrate; (2) fabricating a patterned mask on the foreign substrate; (3) Using HVPE technology to epitaxially grow GaN single crystal columns on the patterned mask, the GaN single crystal columns and the patterned mask will automatically peel off during the cooling process to form GaN crystal columns; (4) The GaN crystal columns are wire-cut in the height direction to produce multiple or single GaN single crystal product blanks with controllable thickness, wherein the top GaN single crystal product blank is the top GaN material; (5) The top GaN material is used as the substrate material for homoepitaxial growth in the next round of recycling, and pits are etched out by wet etching, and steps (2), (3) and (4) are repeated, and this cycle is repeated to obtain a GaN single crystal product with low dislocation density.

2. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The wet etching has a depth of 0.5 μm to 1 μm.

3. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The wet etching solution is one of KOH, H3PO4 and H2O2, the concentration of the etching solution is 50wt%-90wt%, and the temperature of the etching solution is controlled between 80℃-200℃.

4. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The substrate is made of sapphire, silicon carbide or single crystal silicon.

5. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The mask is deposited by PECVD or magnetron sputtering equipment with a thickness of 100nm-1000nm. The pattern openings produced can be circular, square, hexagonal, etc. The side length of the pattern is controlled at 1μm-100μm, and the density of the pattern openings is controlled at 10 5 -10 7 / cm 2 .

6. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The HVPE process temperature is 800° C.-1200° C., and the chamber pressure is 600 torr-900 torr.

7. The method for preparing a low dislocation and high efficiency GaN substrate for laser according to claim 1, characterized in that: The thickness of the GaN crystal column is 4mm-5mm.

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