A double-trench type 3D patterned stack mask substrate structure, a preparation method thereof and an epitaxial growth method

Abstract

The application discloses a double-groove type 3D pattern laminated mask substrate structure and a preparation method and an epitaxial growth method thereof, and belongs to the field of optoelectronic technology. The double-groove type 3D pattern laminated mask substrate structure comprises a substrate, a bottom mask layer and a top mask layer arranged on the substrate in sequence, and the top mask layer is connected with the bottom mask layer through a medium layer; the bottom mask layer is provided with periodically distributed bottom windows, and the top mask layer is provided with periodically distributed top windows; each top window corresponds to two bottom windows, and the two bottom windows are symmetrically distributed on the two sides of the corresponding top window. The application also simultaneously provides a preparation method of the substrate structure and an epitaxial layer growth method based on the structure. The application can eliminate steps formed by adjacent strip merging due to lattice tilting, thereby growing a large-area flat high-quality lateral epitaxial gallium nitride film material, and plays a very key role in a large amount of device epitaxial work subsequently carried out on the basis.

Description

Technical Field

[0001] This invention belongs to the fields of semiconductor material technology and epitaxial growth technology, specifically relating to a dual-groove 3D patterned stacked mask substrate structure and its preparation and epitaxial growth methods. Background Technology

[0002] Due to the high cost of self-supporting substrates for GaN and other group III nitride semiconductor materials, sapphire, silicon, and silicon carbide substrates are often used for heteroepitaxial growth to save costs. Currently, heteroepitaxial growth of GaN and other group III nitride semiconductor materials still faces significant challenges. Developing substrate technology, reducing dislocation density, and improving crystal quality remain persistent goals. To address these goals, many improved technical solutions have been developed, all of which have improved the crystal quality of epitaxial materials to varying degrees.

[0003] Chinese patent CN102492986B discloses a method for fabricating a selected-area heterojunction epitaxial substrate structure and its epitaxial layer growth to improve the crystal quality of epitaxial GaN layers. It employs a 3D patterned stacked mask substrate structure, including a substrate with a bottom mask layer and a top mask layer sequentially disposed thereon. The bottom mask layer has periodically distributed strip-shaped windows, and the top mask layer has periodically distributed cross-shaped windows, with an "I"-shaped top mask region between the cross-shaped windows. The two ends of the "I"-shaped top mask region are connected to the strip-shaped mask regions of the bottom mask layer through discrete dielectric layers. The top cross-shaped windows and the bottom strip-shaped windows are staggered. Combined with its heteroepitaxial growth method, this significantly improves the crystal quality of the epitaxial layer.

[0004] The aforementioned 3D patterned stacked mask substrate structure, as well as other existing 3D patterned stacked mask substrate structures, all have a slot on one side of the bottom mask, i.e., as shown in the figure. Figure 1 As shown, the lower layer window is offset from the upper layer window, with the lower layer window located on one side of the upper layer window. For the technique of single-sided slotting of the bottom mask, the asymmetry of the structure on both sides of the upper layer window during growth leads to asymmetry in the growth process. When the material emerges from the upper layer window during growth, a crystal axis tilt occurs, causing the plane of the material grown on the surface of the top mask layer to be non-parallel to the substrate, exhibiting an angle, such as... Figure 1 As shown. Due to the tilting of a single crystal plane, the thickness of the epitaxial layer is uneven on both sides. Consequently, a height difference occurs during the merging of two adjacent layers. This height difference step results in an uneven surface morphology, such as... Figure 2As shown, this prevents the formation of a large, flat surface, affecting the overall crystal quality of the material and the fabrication of subsequent devices. Even with CMP (Crystal Motion Processing) to flatten the surface, the crystal plane will still deviate from the C-plane, which is detrimental to subsequent epitaxial device growth. Furthermore, due to the different lattice tilt degrees between windows, grain boundaries will inevitably form during the lateral epitaxial fusion of materials from adjacent windows, creating defects. This is also detrimental to improving the overall quality of the material. Summary of the Invention

[0005] The purpose of this invention is to solve the lattice tilting phenomenon caused by growth asymmetry in 3D patterned stacked mask substrate structures.

[0006] The technical solution adopted in this invention is as follows:

[0007] A dual-groove 3D patterned stacked mask substrate structure includes a substrate on which a bottom mask layer and a top mask layer are sequentially disposed. The top mask layer is connected to the bottom mask layer through a dielectric layer. The bottom mask layer has periodically distributed bottom windows, and the top mask layer has periodically distributed top windows. Each top window corresponds to two bottom windows, and the two bottom windows are symmetrically distributed on both sides of its corresponding top window.

[0008] Furthermore, the width of the bottom layer window is less than 5 micrometers; the distance between two bottom layer windows corresponding to one top layer window is 1 to 5 micrometers.

[0009] Furthermore, the width of the top-level window is 1 to 5 micrometers.

[0010] Furthermore, the in-plane symmetry of the top and bottom window patterns is consistent with or a subset of the crystal symmetry of hexagonal group III nitride materials.

[0011] Furthermore, the top-level window and the bottom-level window can be one of the following shapes: bar, equilateral triangle, or regular hexagon.

[0012] Furthermore, the top mask layer and the bottom mask layer are SiN. x The dielectric layer is SiO2.

[0013] A method for fabricating the dual-groove 3D patterned stacked mask substrate structure includes the following steps:

[0014] 1) Deposit the bottom mask layer on the substrate;

[0015] 2) Photolithography is used to spin-coat photoresist onto the bottom mask layer, and then expose and develop to design the bottom window pattern;

[0016] 3) Reactive ion etching is used to create the window of the bottom mask layer;

[0017] 4) Clean and remove the photoresist from the bottom mask layer;

[0018] 5) Deposit a filler layer on the bottom mask layer first, then deposit the top mask layer;

[0019] 6) Using photolithography, photoresist is spin-coated onto the top mask layer, and the top window pattern is designed by exposure and development;

[0020] 7) Reactive ion etching creates the window of the top mask layer;

[0021] 8) Clean and remove the photoresist from the top mask layer;

[0022] 9) Etch the filler layer until the window of the underlying mask layer is exposed, then stop etching.

[0023] Furthermore, a bottom mask layer and a top mask layer are deposited using a CVD method; the filler layer is etched using a BOE solution.

[0024] An epitaxial growth method based on the dual-groove 3D patterned stacked mask substrate structure includes the following steps:

[0025] 1) During the low-temperature nucleation stage, nucleation sites of group III nitride materials are formed on the substrate surface exposed by two symmetrical bottom windows corresponding to a top window, and then island-shaped atomic clusters are formed with the nucleation sites as the center.

[0026] 2) As the temperature increases, the group III nitride materials at the two symmetrical bottom windows grow towards the center at an equal rate, merge and converge in the middle channel, and then grow upward to drill out of the top window.

[0027] 3) After drilling out the top window, the growth continues using lateral epitaxy until the group III nitride material is fused into a flat large plane.

[0028] Furthermore, the group III nitride material is one of the following: GaN, AlN, InN, and ternary or quaternary alloys formed therefrom.

[0029] The beneficial effects of this invention are as follows:

[0030] The key feature of this invention is that the bottom window pattern is a double-groove pattern, and the top mask layer pattern is a single-groove pattern, with the single groove of the top pattern aligned with the parallel midline of the bottom double grooves. This invention features symmetrical grooves on both sides of the bottom mask, ensuring symmetrical growth. The material grower clads with the top window before drilling out, resulting in no significant tilting of the crystal axis of the material grown from the top channel. This ensures that the surface of the material grown on the second mask layer is parallel to the substrate, and no significant height difference occurs during the cladding of adjacent strips, facilitating the formation of a large and flat plane and improving the crystal quality of the cladding area. This invention eliminates the steps formed by the merging of adjacent strips due to lattice tilt, thereby growing a large-area, flat, high-quality lateral epitaxial gallium nitride thin film. This is crucial for subsequent large-scale device epitaxy based on this material. If the surface is uneven or the defect density in the fusion region is too high, it will be difficult to obtain good epitaxial device quality. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a single-groove structure in a 3D patterned stacked mask substrate structure.

[0032] Figure 2 This is a schematic diagram showing the height difference formed on the surface of the grown material due to the tilting of the crystal axis.

[0033] Figure 3 These are scanning electron microscope images showing the actual lattice tilting.

[0034] Figure 4 This is a schematic diagram of the 3D patterned stacked mask substrate structure with a dual-groove structure according to the present invention.

[0035] Figure 5 This is a schematic diagram showing that when the material is grown using the dual-groove structure of the present invention, after nucleation in the two windows at the bottom layer, the material grows towards the middle at an equal rate, and after closing in the middle, it grows upwards to drill out of the top layer window.

[0036] Figure 6 This is a schematic diagram of the flat surface formed when the material is grown using the dual-groove structure of the present invention.

[0037] Figure 7 These are schematic diagrams of window shapes, where (a), (b), and (c) represent a bar, a triangle, and a hexagon, respectively.

[0038] Figure 8 It corresponds Figure 7 Schematic diagrams of three shapes of double-slot windows are shown. (a) is a top view of a strip-shaped double-slot structure, where solid lines represent the top-level window and dashed lines represent the bottom-level window. (b) is a top view of a triangular double-slot structure, where solid lines represent the top-level window and dashed lines represent the bottom-level window. (c) is a top view of a hexagonal double-slot structure, where solid lines represent the top-level window and dashed lines represent the bottom-level window. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0040] Figure 1 This is a schematic diagram of a single-groove structure of an existing 3D patterned multilayer mask substrate structure. The 3D patterned multilayer mask substrate structure includes a substrate 101, a bottom mask 102, a dielectric layer 103, and a top mask 104. 105 in the diagram represents the grown material, such as GaN. The bottom and top masks are made of SiN. x The dielectric layer uses SiO2. A top-level window 1041 is provided on the top-level mask 104, and a bottom-level window 1021 is provided on the bottom-level mask 102. The top-level window 1041 and the bottom-level window 1021 are staggered, meaning the bottom-level window 1021 is located on one side of the top-level window 1041. With this single-groove window structure (i.e., a bottom-level window is only provided on one side of each top-level window), during GaN growth, when the channel is formed, one side of the upper window experiences contact stress, while the other side is free space. This can cause the lattice to tilt, affecting the epitaxial growth process after the channel is formed. During lateral epitaxy, both sides are free space, and there is no mechanism to allow the lattice to tilt back. Therefore, the lateral epitaxy process continues this tilt angle, resulting in an uneven surface morphology of the grown material and the formation of height differences, such as... Figure 2 As shown.

[0041] Figure 3 These are scanning electron microscope (SEM) images showing the actual lattice tilting phenomenon. Actual experiments reveal a significant lattice tilting effect, which has a fatal impact on stripe merging. Therefore, it must be eliminated in practical applications.

[0042] Figure 4 This is a schematic diagram of the dual-groove structure of the present invention. As shown in the figure, it includes a substrate 201, a bottom mask 202, a dielectric layer 203, and a top mask 204. Two bottom windows 2021 are symmetrically distributed on the left and right sides of the top window 2041, i.e., the bottom window has a dual-groove design, with the projections of the two grooves symmetrically distributed on both sides of the top window. During the growth of GaN or other group III nitride semiconductor materials 205, the material source enters from the top window, nucleates in the two bottom windows, and then grows towards the center at an equal rate, merging and converging in the middle channel, and then growing upwards to drill out of the top window, as shown... Figure 5 As shown.

[0043] After the material is drilled out of the trench, i.e., through the top-level window, lateral extension is performed, and the result is as follows: Figure 6As shown, this will produce stripes of uniform height, so that there is no height difference when two adjacent stripes merge, smoothly forming a large, flat plane. The process of the material drilling out of the top window and the subsequent process are structurally symmetrical, thus eliminating the lattice tilt problem.

[0044] The key point of this invention is the design of a symmetrical bottom-layer double slot structure (i.e., two bottom-layer windows corresponding to one top-layer window). The preferred dimensions and spacing of the double slots are described below.

[0045] The width of the double slots in the bottom window is typically less than 5 micrometers. Excessively large slots would increase the suspended area of ​​the top mask, which is prone to deformation, especially during drastic temperature changes in the growth process. Deformation or collapse of the mask layer will negatively impact material growth. Therefore, the slot width should not be too large.

[0046] The spacing between the two channels is typically in the range of 1 to 5 micrometers. Too small a spacing is not conducive to filtering through dislocation defects, while too large a spacing can cause deformation or collapse of the top mask, which is detrimental to material growth. Furthermore, a large spacing increases the channel length, which significantly increases the growth time and is not conducive to efficient production.

[0047] The width of the top-layer window is typically in the range of 1–5 micrometers. A window smaller than 1 micrometer is too narrow, hindering the entry of the gas source into the channel and resulting in a slow growth rate within the channel. A window larger than 5 micrometers is too wide, leading to a decrease in the proportion of high-quality regions in the overall film, which is detrimental to improving the overall performance of the final material.

[0048] The dual-groove 3D patterned stacked mask substrate structure of the present invention can be prepared by the following method:

[0049] 1) Deposit the bottom mask layer on the substrate;

[0050] 2) Photolithography is used to spin-coat photoresist onto the bottom mask layer, and then expose and develop to design the bottom window pattern;

[0051] 3) Reactive ion etching creates a window in the bottom mask layer, i.e., a double-groove structure: suitable etching conditions are required, the sidewalls of the grooves should be as vertical as possible, and the edges of the grooves should be as straight as possible, because fluctuations in the dimensions of the groove edges will cause fluctuations in the groove distance, resulting in inconsistent times when the left and right sides merge and drill out of the grooves during the growth process, which cannot effectively achieve the effect of applying force symmetrically from left to right.

[0052] 4) Clean and remove the photoresist from the bottom mask layer;

[0053] 5) First deposit a filler layer (i.e., a dielectric layer) on the bottom mask layer, and then deposit the top mask layer;

[0054] 6) Using photolithography, photoresist is spin-coated onto the top mask layer, and the top window pattern is designed by exposure and development;

[0055] 7) Reactive ion etching creates the window of the top mask layer;

[0056] 8) Clean and remove the photoresist from the top mask layer;

[0057] 9) Etch the filler layer until the window of the underlying mask layer is exposed, then stop etching.

[0058] In this embodiment, a bottom mask layer and a top mask layer are deposited using a CVD method. The top and bottom mask layers are SiN. x The filling layer is SiO2. The filling layer is etched using BOE solution.

[0059] The top and bottom windows of the 3D patterned stacked mask substrate structure in this invention can have the following shapes: Figure 7 Figures (a) to (c) show one of the following: a strip window, an equilateral triangle, or a regular hexagon. The top-layer window has the same shape as the bottom-layer window. These patterns exhibit in-plane symmetry consistent with or a subset of the crystal symmetry of GaN and other group III nitride materials. Utilizing these patterns with special symmetry enables the fabrication of continuous, flat, high-quality epitaxial GaN and other group III nitride films covering the entire substrate surface, thus ensuring greater compatibility with subsequent device fabrication processes.

[0060] Figure 8 Figures (a) to (c) correspond to Figure 7 Schematic diagrams of three shapes of double-groove windows are shown. (a) is a top view of a strip-shaped double-groove structure, with solid lines representing the top window and dashed lines representing the bottom window. (b) is a top view of a triangular double-groove structure, with solid lines representing the top window and dashed lines representing the bottom window. (c) is a top view of a hexagonal double-groove structure, with solid lines representing the top window and dashed lines representing the bottom window. Each of these shapes can be designed with the bottom double grooves (two bottom windows) symmetrically distributed on both sides of the top groove (top window), i.e., as shown... Figure 4 The structure shown.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention without departing from the principles and scope of the present invention. The protection scope of the present invention should be determined by the claims.

Claims

1. A dual-groove 3D patterned stacked mask substrate structure, characterized in that, The material includes a substrate on which a bottom mask layer and a top mask layer are sequentially disposed. The top mask layer is connected to the bottom mask layer through a dielectric layer. The bottom mask layer has periodically distributed bottom windows, and the top mask layer has periodically distributed top windows. Each top window corresponds to two bottom windows, which are symmetrically distributed on both sides of their corresponding top window. During the growth of a group III nitride semiconductor material, the material source enters from the top window and nucleates on the substrate surface exposed by the two symmetrical bottom windows corresponding to one top window. Then, it grows towards the center at an equal rate, merges and converges in the middle channel, and then grows upward to drill out of the top window. After the material drills out of the top window, it undergoes lateral epitaxy to form a flat large plane and eliminate lattice tilt.

2. The dual-groove 3D patterned stacked mask substrate structure according to claim 1, characterized in that, The width of the bottom layer window is less than 5 micrometers; the distance between two bottom layer windows corresponding to one top layer window is 1 to 5 micrometers.

3. The dual-groove 3D patterned stacked mask substrate structure according to claim 1, characterized in that, The width of the top-level window is 1 to 5 micrometers.

4. The dual-groove 3D patterned stacked mask substrate structure according to claim 1, characterized in that, The in-plane symmetry of the top and bottom window patterns is consistent with or a subset of the crystal symmetry of hexagonal group III nitride materials.

5. The dual-groove 3D patterned stacked mask substrate structure according to claim 4, characterized in that, The top-level and bottom-level windows are graphic shapes of one of the following: bars, equilateral triangles, or regular hexagons.

6. The dual-groove 3D patterned stacked mask substrate structure according to claim 1, characterized in that, The top and bottom mask layers are SiN. x The dielectric layer is SiO2.

7. A method for fabricating the dual-groove 3D patterned stacked mask substrate structure as described in claim 1, characterized in that, Includes the following steps: 1) Deposit the bottom mask layer on the substrate; 2) Photolithography is used to spin-coat photoresist onto the bottom mask layer, and then expose and develop to design the bottom window pattern; 3) Reactive ion etching is used to create the window of the underlying mask layer; 4) Clean and remove the photoresist from the bottom mask layer; 5) Deposit a filler layer on the bottom mask layer first, then deposit the top mask layer; 6) Using photolithography, photoresist is spin-coated onto the top mask layer, and the top window pattern is designed by exposure and development; 7) Reactive ion etching creates the window of the top mask layer; 8) Clean and remove the photoresist from the top mask layer; The filling layer is etched until the window of the underlying mask layer is exposed, at which point the etching stops.

8. The method according to claim 7, characterized in that, A bottom mask layer and a top mask layer were deposited using a CVD method; the filler layer was etched using a BOE solution.

9. An epitaxial growth method based on the dual-groove 3D patterned stacked mask substrate structure of claim 1, characterized in that, Includes the following steps: 1) During the low-temperature nucleation stage, nucleation sites of group III nitride materials are formed on the substrate surface exposed by two symmetrical bottom windows corresponding to a top window, and then island-shaped atomic clusters are formed with the nucleation sites as the center. 2) As the temperature increases, the group III nitride materials at the two symmetrical bottom windows grow towards the center at an equal rate, merge and converge in the middle channel, and then grow upward to drill out of the top window. 3) After drilling out the top window, the growth continues using lateral epitaxy until the group III nitride material is fused into a flat large plane.

10. The method according to claim 9, characterized in that, The group III nitride material is one of the following: GaN, AlN, InN, and ternary or quaternary alloys formed therefrom.

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