A method for separating a sapphire from a gallium nitride substrate

Abstract

The present invention relates to the field of semiconductor production technology, and particularly to a method for peeling a sapphire and a gallium nitride substrate. It mainly aims at the problem that the current mainstream process is to grow a gallium nitride thin film on sapphire, but due to the large lattice mismatch between sapphire and gallium nitride, the quality of the gallium nitride epitaxial layer grown on sapphire is poor, seriously affecting the performance of semiconductor devices; the following technical solutions are proposed: thinning the photoresist, fabricating a layer of aluminum nitride film on the photoresist and silica sapphire composite substrate, and then removing the photoresist. At this time, a part of the aluminum nitride film covers the silica on the silica sapphire composite substrate, and the aluminum nitride film originally covering the photoresist is suspended. Subsequently, a gallium nitride epitaxial layer is grown on the aluminum nitride film, and then the silica layer on the upper part of the substrate is removed using BOE, and finally the epitaxial layer is peeled off from the substrate. By using the peeling method of growing an aluminum nitride layer on the silica sapphire composite substrate and then removing the silica, the present invention greatly reduces the peeling cost, reduces the price of the gallium nitride substrate, expands the application field of the gallium nitride epitaxial layer, and has very good feasibility and application value.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor production, and particularly relates to a method for peeling a sapphire and a gallium nitride substrate. Background Art

[0002] Gallium nitride (GaN), as a typical representative of the third-generation wide-bandgap semiconductors, has excellent physical and chemical properties. Its bandgap width, electron saturation drift velocity, breakdown voltage, and operating temperature are much larger than those of Si and GaAs, making it very suitable for developing high-frequency, high-voltage, and high-power devices and circuits. However, these GaN-based flexible electronic devices usually need to transfer the original GaN functional layer to the final flexible substrate through mechanical, chemical, or laser peeling methods to achieve preparation. Therefore, an efficient and high-quality peeling process directly determines the manufacturing cost and performance of flexible GaN-based electronic devices. The current mainstream peeling technology is the laser lift-off technology (LLO). This process mainly uses an excimer nanosecond pulsed laser to achieve the peeling of GaN devices by inducing the rapid heating and decomposition of the material near the interface between the sapphire and GaN. However, the cost of this method is still relatively high, and industrial production is still relatively difficult.

[0003] Theoretically, the best substrate material for growing gallium nitride epitaxial layers is gallium nitride. However, the production scale of gallium nitride substrates is very small and the price is very high, resulting in a relatively high cost of semiconductor devices. Therefore, currently, the mainstream is to grow gallium nitride thin films on sapphire. However, due to the large lattice mismatch between sapphire and gallium nitride, the quality of the gallium nitride epitaxial layer grown on sapphire is relatively poor, seriously affecting the performance of semiconductor devices. The lattice constants of aluminum nitride (AlN) and GaN are relatively close. Growing an AlN layer on sapphire can reduce the strain caused by the large lattice mismatch between sapphire and GaN, improve the quality of the epitaxial layer, and significantly enhance the performance of the device. Based on the above, we propose a method for peeling a sapphire and a gallium nitride substrate. Using this method, a gallium nitride substrate with very good crystal quality can be prepared at a relatively low cost. Since the peeling cost of this gallium nitride substrate is relatively low and the quality is good, the application range of gallium nitride substrates is greatly expanded. Summary of the Invention

[0004] The object of the present invention is to address the problems existing in the background art, namely, when growing gallium nitride thin films on sapphire at present, due to the large lattice mismatch between sapphire and gallium nitride, the quality of the gallium nitride epitaxial layer grown on sapphire is relatively poor, seriously affecting the performance of semiconductor devices, and the relatively high cost of current gallium nitride peeling. A method for peeling a sapphire and a gallium nitride substrate is proposed.

[0005] Technical solution of the present invention: A method for peeling a sapphire and a gallium nitride substrate. The substrate peeling method mainly involves the following layer compositions: photoresist, alumina, silica, aluminum nitride, gallium nitride epitaxial layer, and buffered oxide etchant. The specific peeling method includes the following steps: S1. Use a conventional process to fabricate CPSS, with silica on the upper part and alumina on the lower part;

[0006] S2. Spin-coat a layer of photoresist on the CPSS prepared in S1 to ensure that the photoresist completely covers the pattern on the CPSS;

[0007] S3. Use oxygen to perform dry etching on the CPSS coated with photoresist until the photoresist thickness remains 0.3 - 1.5 μm and there is no photoresist residue on the upper half of the sidewall of the pattern. To ensure smooth peeling, the remaining height of the photoresist should be higher than the height of the alumina;

[0008] S4. Use a magnetron sputtering device to grow a layer of aluminum nitride film on the CPSS coated with photoresist, so that the film covers the entire CPSS pattern and the photoresist;

[0009] S5. Immerse the substrate wafer covered with the aluminum nitride film and the photoresist in a dissolving liquid for 1 - 100 min to dissolve the photoresist under the aluminum nitride;

[0010] S6. After being processed by S5, obtain the remaining CPSS with the aluminum nitride film;

[0011] S7. Use MOCVD to grow a gallium nitride epitaxial layer on the CPSS with the aluminum nitride film, and the process is the same as the conventional process;

[0012] S8. Immerse the CPSS on which the gallium nitride epitaxial layer has been grown in a buffered oxide etchant for 1 - 100 min to dissolve the upper part of the silica on the CPSS. Since the silica is dissolved, the aluminum nitride and the gallium nitride epitaxial layer are separated;

[0013] Preferably, in S5, QDR is 600 - 1800 s, and the dissolving solution is any one of NMP or acetone.

[0014] Preferably, the size of the CPSS pattern is a bottom width of 0.45 - 9.9 μm and a height of 0.3 - 10 μm.

[0015] Preferably, the morphology of the CPSS pattern can be any one of conical, pyramidal, columnar, or strip-shaped.

[0016] Preferably, the method of removing part of the photoresist in S3 further includes exposing the photoresist using a lithography machine, controlling the exposure energy so that the upper part is exposed through while the lower part is not, and then developing with a developer to remove the photoresist on the upper half of the sidewall of the pattern.

[0017] Preferably, in the dissolution treatment in S8, it is 600 - 1800 s for QDR.

[0018] Preferably, the thickness of the aluminum nitride is 5 nm - 1 μm.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] 1. By growing an aluminum nitride layer on sapphire, the present invention can reduce the strain caused by the large lattice mismatch between sapphire and gallium nitride, improve the quality of the epitaxial layer, and significantly enhance the performance of the device;

[0021] 2. Compared with the substrate obtained by the laser lift-off technology, the manufacturing process of this composite substrate is relatively simple, the manufacturing cost is low, and it has good application prospects; by changing the morphology of the CPSS, the bottom morphology of the composite substrate can be changed to obtain different optical properties, which can be applied in various fields such as sensors, laser generators, and optical devices;

[0022] 3. The method for peeling the sapphire and gallium nitride substrate proposed by the present invention greatly expands the application field of the gallium nitride epitaxial layer, greatly reduces the peeling cost, has high feasibility, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flowchart of a method for peeling a sapphire and gallium nitride substrate;

[0024] Figure 2 is a schematic structural diagram of a gallium nitride epitaxial layer and a buffered oxide etchant.

[0025] Reference numerals: 1, photoresist; 2, aluminum oxide; 3, silicon dioxide; 4, aluminum nitride; 5, gallium nitride epitaxial layer; 6, buffered oxide etchant. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Embodiment

[0027] As Figure 1-2As shown in the figure, a method for peeling sapphire from a gallium nitride substrate proposed by the present invention mainly involves the following layer compositions: photoresist 1, aluminum oxide 2, silicon dioxide 3, aluminum nitride 4, gallium nitride epitaxial layer 5, and buffered oxide etchant 6. The specific peeling method includes the following steps: S1. Use a conventional process to fabricate a CPSS, with silicon dioxide 3 on the upper part and aluminum oxide 2 on the lower part. The size of the CPSS pattern is a bottom width of 0.45 - 9.9 μm and a height of 0.3 - 10 μm. The morphology of the CPSS pattern can be any one of conical, pyramidal, columnar, and strip-shaped;

[0028] S2. Spin-coat a layer of photoresist 1 on the CPSS prepared in S1 to ensure that the photoresist 1 completely covers the pattern on the CPSS;

[0029] S3. Use oxygen to perform dry etching on the CPSS coated with photoresist 1 until the thickness of the photoresist 1 remains 0.3 - 1.5 μm, and there is no photoresist residue on the upper half of the sidewall of the pattern. To ensure smooth peeling, the remaining height of the photoresist 1 should be higher than the height of the aluminum oxide 2. Another way to remove part of the photoresist 1 is to use a lithography machine to expose the photoresist 1, control the exposure energy so that the upper part is exposed through and the lower part is not exposed through, and then develop with a developer to remove the photoresist 1 on the upper half of the sidewall of the pattern;

[0030] S4. Use a magnetron sputtering device to grow a layer of aluminum nitride 4 thin film on the CPSS coated with photoresist 1 so that the thin film covers the entire CPSS pattern and the photoresist. The thickness of the aluminum nitride 4 is 5 nm - 1 μm;

[0031] S5. Immerse the substrate wafer covered with the aluminum nitride 4 thin film and the photoresist 1 in a dissolving liquid for 1 - 100 min to dissolve the photoresist 1 under the aluminum nitride 4, with a QDR of 600 - 1800 s. The dissolving solution can be any one of NMP or acetone;

[0032] S6. After being processed by S5, a CPSS with the remaining aluminum nitride 4 thin film is obtained.

[0033] S7. Use MOCVD to grow a gallium nitride epitaxial layer 5 on the CPSS with the aluminum nitride 4 thin film, and the process is the same as the conventional process;

[0034] S8. Immerse the CPSS on which the gallium nitride epitaxial layer 5 has been grown in the buffered oxide etchant 6 for 1 - 100 min to dissolve the upper part of the silicon dioxide 3 on the CPSS. During the dissolving process, the QDR is 600 - 1800 s. Since the silicon dioxide 3 is dissolved, the aluminum nitride 4 and the gallium nitride epitaxial layer 5 are separated.

[0035] In this embodiment, by thinning the photoresist 1 and fabricating a layer of aluminum nitride 4 film, and then removing the photoresist 1, an overhead layer similar to a "bridge" is formed between the lower part of the pattern and the C surface of the substrate and the aluminum nitride 4 film. Among them, the thickness of the aluminum nitride 4 film is 5 nm - 1 layer of silicon oxide 3 is removed, and finally the epitaxial layer is peeled off from the substrate.

[0036] The above specific embodiments are only the preferred embodiments of the present invention. Based on the technical solution of the present invention and the relevant revelations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for separating a sapphire from a gallium nitride substrate, characterized in that: The substrate peeling method mainly involves the following layer compositions: photoresist (1), aluminum oxide (2), silicon dioxide (3), aluminum nitride (4), gallium nitride epitaxial layer (5), and buffered oxide etchant (6). The specific peeling method includes the following steps: S1. Fabricate a CPSS with silicon dioxide (3) on the upper part and aluminum oxide (2) on the lower part. S2. Spin-coat a layer of photoresist (1) on the CPSS prepared in S1 to ensure that the photoresist (1) completely covers the pattern on the CPSS. S3. Use oxygen to perform dry etching on the CPSS coated with photoresist (1) until the thickness of the photoresist (1) remains 0.3 - 1.5 μm and there is no photoresist residue on the upper half of the sidewall of the pattern. To ensure smooth peeling, the remaining height of the photoresist (1) should be higher than the height of the aluminum oxide (2). S4. Use a magnetron sputtering device to grow a layer of aluminum nitride (4) film on the CPSS coated with photoresist (1) so that the film covers the entire CPSS pattern and the photoresist. S5. Immerse the substrate wafer covered with the aluminum nitride (4) film and photoresist (1) in a dissolving liquid for 1 - 100 min to dissolve the photoresist (1) under the aluminum nitride (4). S6. After the treatment in S5, obtain the CPSS with the aluminum nitride (4) film remaining. S7. Use MOCVD to grow a gallium nitride epitaxial layer (5) on the CPSS with the aluminum nitride (4) film, and the process is the same as the conventional process. S8. Immerse the CPSS with the grown gallium nitride epitaxial layer (5) in the buffered oxide etchant (6) for 1 - 100 min to dissolve the upper part of the silicon dioxide (3) on the CPSS. Since the silicon dioxide (3) is dissolved, the aluminum nitride (4) and the gallium nitride epitaxial layer (5) are separated.

2. The method for separating a sapphire and a gallium nitride substrate according to claim 1, characterized in that In S5, the QDR is 600 - 1800 s, and the dissolving liquid is any one of NMP or acetone.

3. A method for peeling a sapphire from a gallium nitride substrate according to claim 1, characterized in that, The size of the CPSS pattern is a bottom width of 0.45 - 9.9 μm and a height of 0.3 - 10 μm.

4. A method for peeling a sapphire from a gallium nitride substrate according to claim 3, characterized in that, The morphology of the CPSS pattern can be any one of conical, pyramidal, columnar, or strip-shaped.

5. A method for peeling a sapphire from a gallium nitride substrate according to claim 1, characterized in that, In S3, the method of removing part of the photoresist (1) also includes using a lithography machine to expose the photoresist (1), controlling the exposure energy so that the upper part is exposed through and the lower part is not exposed through, and then developing with a developer to remove the photoresist (1) on the upper half of the sidewall of the pattern.

6. A method for peeling a sapphire and a gallium nitride substrate according to claim 1, characterized in that, In S8, the QDR in the dissolving treatment is 600 - 1800 s.

7. A method for separating a sapphire and a gallium nitride substrate according to claim 1, characterized in that, The thickness of the aluminum nitride (4) is 5 nm - 1 μm.

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