A method and system for laser dicing of gallium nitride substrates

Abstract

The application discloses a gallium nitride substrate laser slicing method and system, which comprises the following steps: a pulse laser is incident from the N surface of a gallium nitride substrate without a device layer to the interior of the gallium nitride substrate at a first set energy, is focused to a specific depth of the gallium nitride substrate, and performs first scanning on the gallium nitride substrate to form cavities at each laser focus point in the interior of the gallium nitride substrate; a pulse laser is incident from the N surface of the gallium nitride substrate without the device layer to the interior of the gallium nitride substrate at a second set energy, is focused to the specific depth of the gallium nitride substrate, and performs second scanning on the gallium nitride substrate to make cracks generated around the cavities in the interior of the gallium nitride substrate, and the cracks generated by adjacent cavities are connected to each other to form a modified layer; and the gallium nitride substrate is separated along the modified layer to obtain a gallium nitride substrate laser slice. The gallium nitride substrate laser slicing is quickly and effectively cut.

Description

Technical Field

[0001] This invention relates to the fields of laser manufacturing and semiconductor technology, and in particular to a method and system for laser slicing gallium nitride substrates. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Gallium nitride (GaN) is a typical third-generation semiconductor material with advantages such as high breakdown voltage, fast switching speed, high thermal conductivity, and low on-resistance. It has been widely used in LEDs (lighting and displays), radio frequency communications, and high-frequency power devices. In particular, GaN high-frequency power devices can switch at frequencies up to 10 MHz, with power reaching tens of kilowatts. This switching frequency is 10 times that of silicon carbide (SiC), another third-generation semiconductor, making it crucial for applications in cellular base station power amplifiers, military radar, and satellite communications. Typically, GaN devices are grown on substrates such as SiC, single-crystal silicon, or sapphire. While this method is cost-effective, it results in GaN devices with a dislocation density as high as 10^60^7. 8 / cm 2 This leads to numerous problems such as leakage current, reducing the performance and quality of the device. To obtain high-quality GaN devices, GaN devices need to be epitaxially grown on native GaN substrates, thereby reducing the thread dislocation density by 1 to 2 orders of magnitude. However, native GaN substrates are extremely expensive, about 5 times the price of SiC substrates of the same size and 100 times the price of single-crystal silicon substrates. This results in extremely high costs for high-quality GaN devices produced on these substrates, hindering their commercialization in a wide range of fields.

[0004] Since 2019, several research institutions and companies, including the Ioffe Institute of Physics and Technology in Russia, Nagoya University in Japan, and Toyota Motor Corporation, have reported technologies for slicing commercial GaN substrates using lasers and reusing the substrates. This technology uses a focused laser beam as a "processing tool" to irradiate the interior of the GaN substrate. The GaN substrate absorbs the light energy, locally heats up, melts and vaporizes, decomposing into metallic gallium (Ga) and nitrogen (N2), forming a modified layer inside the substrate. The GaN substrate is then separated along this modified layer through mechanical stretching or other methods. The separated substrate can be repolished and reused, thereby improving the utilization rate of GaN substrates and reducing the manufacturing cost of high-quality GaN devices epitaxially grown from native GaN substrates.

[0005] However, existing GaN substrate laser slicing technologies still have many shortcomings. For example, the LSLO laser slicing method proposed by the Ioffe Institute of Physics and Technology uses a femtosecond laser to penetrate the upper surface (Ga facet) of the GaN substrate and the device layer grown above it, focusing the laser inside the substrate to form a modified layer. The LSLO method requires the device layer to have good light transmittance. Related reports only demonstrate the slicing process of GaN substrates with grown LED devices. This method cannot be used for device layers with poor transmittance, thus having certain limitations. The laser slicing method proposed by Nagoya University, Toyota Motor Corporation, etc. (CN 115966589 A) uses a sub-nanosecond laser to enter from the lower surface (N facet) of the GaN substrate and focus the laser inside the substrate to form a modified layer. In this method, the laser does not need to penetrate the device layer before focusing, eliminating the problem of shading, and it is applicable to slicing GaN substrates with various devices grown on them. However, the main drawback of this method is its low processing efficiency. In order to reduce losses and ensure that the GaN substrate can be effectively separated along the modified layer, a two-stage cutting method is adopted, namely, scanning with a high-energy laser for the first time and then scanning with a low-energy laser for the second time, which results in a long processing time. It takes about 300 minutes to complete a 2-inch GaN substrate slice.

[0006] Therefore, the inventors believe that existing GaN substrate laser slicing technologies cannot achieve rapid and effective cutting of GaN substrate slices. Summary of the Invention

[0007] To address the aforementioned problems, this invention proposes a method and system for laser slicing gallium nitride substrates, achieving rapid and efficient laser slicing of GaN substrates.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: Firstly, a method for laser slicing gallium nitride substrates is proposed, including: A pulsed laser with a first set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate to perform the first scan of the gallium nitride substrate, forming cavities at each laser focus point inside the gallium nitride substrate. A pulsed laser with a second set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate and scanned a second time, causing cracks to be generated around the cavities inside the gallium nitride substrate. The cracks generated in adjacent cavities are connected to each other to form a modified layer. The gallium nitride substrate is separated along the modified layer to obtain a gallium nitride substrate laser slice.

[0009] Secondly, a gallium nitride substrate laser slicing system is proposed, including: a laser output unit, a displacement platform unit, and an electromechanical control unit; The displacement platform unit is used to support the gallium nitride substrate with the N-plane of the gallium nitride substrate facing upwards, and can drive the gallium nitride substrate to move along the X-axis, Y-axis and Z-axis; A laser output unit is used to output pulsed laser light, and the output pulsed laser light can be incident from the N-side of the gallium nitride substrate, reach a specific depth of the gallium nitride substrate and be focused. The electromechanical control unit is used to control the displacement platform unit to move along a specific scanning path and to control the laser output unit to output pulsed laser.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: The method disclosed in the present invention incident a laser on the N-side of a GaN substrate that has not grown any devices. The slicing process is not limited by the growth device, and the laser step length along the m-side (distance between adjacent pulse focal points) is increased by at least 3 times compared with other existing methods. At the same time, the laser parameters do not need to be changed during the entire slicing process. Therefore, the processing efficiency of laser slicing of gallium nitride substrates can be effectively improved, and rapid and efficient cutting of GaN substrates by laser slicing can be achieved.

[0011] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0012] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0013] Figure 1 This is a schematic diagram of a cavity generated inside GaN by pulsed laser irradiation as disclosed in the embodiments; Figure 2 This is the intention of the GaN around the cavity disclosed in the embodiment to be fractured and interconnected; Figure 3 This is a schematic diagram of the pulsed laser scanning path disclosed in the embodiment; Figure 4 This is a schematic diagram of the system architecture disclosed in the embodiment; Figure 5 This is a schematic diagram of pulsed laser forming a modified layer inside a GaN substrate as disclosed in the embodiments; Figure 6 This is a schematic diagram of separating the GaN substrate along the modified layer as disclosed in the embodiment; Figure 7 These are microscope images of the internal cavities of GaN disclosed in the embodiments; Figure 8These are microscope images of GaN without cavities as disclosed in the embodiments; Figure 9 These are photographs of GaN samples after pulsed laser scanning, as disclosed in the embodiments. Figure 10 This is a photograph of the peeled surface of the GaN sample after slicing, as disclosed in the embodiment.

[0014] Among them, 100 is GaN substrate, 110 is device layer, 120 is modified layer, 121 is cavity, 200 is laser output unit, 201 is pulsed laser, 202 is adjustment optical path, 203 is condenser, 204 is pulsed laser, 300 is displacement platform unit, 400 is electromechanical control unit, and 500 is tensile testing machine. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0017] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] Example 1 In this embodiment, a method for laser slicing a gallium nitride substrate is disclosed, comprising: A pulsed laser with a first set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate to perform the first scan of the gallium nitride substrate, forming cavities at each laser focus point inside the gallium nitride substrate. A pulsed laser with a second set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate and scanned a second time, causing cracks to be generated around the cavities inside the gallium nitride substrate. The cracks generated in adjacent cavities are connected to each other to form a modified layer. The gallium nitride substrate is separated along the modified layer to obtain a gallium nitride substrate laser slice.

[0019] like Figure 1As shown, a pulsed laser 204 is incident from the N-side of the GaN substrate 100 where no device layer is grown, and scans at a specific depth to form a modifiable layer 120. By adjusting the energy of the pulsed laser 204, a cavity 121 can be formed inside the modifiable layer. This is because the GaN near the focal point of the pulsed laser absorbs energy and decomposes into metallic gallium and nitrogen gas. Nitrogen gas has a low density, and its expansion causes local deformation. The maximum cavity diameter that only causes deformation but not fragmentation and the pulse energy are set as L0 and E0, respectively. E0 is the first set energy of the pulsed laser used when performing the first scan of the gallium nitride substrate.

[0020] Before performing the first scan on the gallium nitride substrate, it is necessary to first determine the maximum cavity diameter L0 and the pulse energy E0 of the pulsed laser when the laser only causes deformation inside the GaN but does not cause fragmentation. For lasers with different pulse widths and GaN substrates with different properties (such as dislocation density, surface cleanliness, etc.), L0 and E0 may be different. Typically, L0 ranges from 3 to 6 μm and E0 ranges from 0.8 to 2 μJ.

[0021] Figure 1 This is a schematic diagram of a cavity created inside GaN by pulsed laser irradiation. Figure 7 This is a photograph of the internal cavity of GaN under a microscope. Figure 8 These are microscope images of GaN scanned by a low-energy pulsed laser, for comparison. Figure 7 and Figure 8 It can be observed that as the laser pulse energy increases, GaN is decomposed into metallic Ga and nitrogen gas, which expand around the laser focus to form a cavity.

[0022] Measurements showed that when the pulse width of the pulsed laser is greater than or equal to 100 fs and less than or equal to 1 ns, a cavity can be formed inside the gallium nitride substrate. For pulsed lasers with different pulse widths, the maximum cavity diameter L0 and the required pulse energy E0 may differ. Therefore, L0 and E0 need to be remeasured after replacing or adjusting the laser. In addition, other factors affecting L0 and E0 include the material properties of GaN (such as dislocation density), the cleanliness of the N-face treatment, and the size of the pulsed laser spot at the focal point. After measurement, L0 is typically in the range of 3~6 μm, i.e., L0 is greater than or equal to 3 μm and less than or equal to 6 μm, and E0 is in the range of 0.8~2 μJ, i.e., E0 is greater than or equal to 0.8 μJ and less than or equal to 2 μJ.

[0023] Therefore, in this embodiment, when performing the first scan on the gallium nitride substrate, the pulse width of the pulsed laser used is greater than or equal to 100 fs and less than or equal to 1 ns.

[0024] The initial set energy is greater than or equal to 0.8 μJ and less than or equal to 2 μJ; the maximum cavity diameter formed at the focal point is greater than or equal to 3 μm and less than or equal to 6 μm.

[0025] If the characteristics of the pulsed laser used and the material properties of the GaN substrate are fully understood, the values ​​of L0 and E0 can be determined directly without measurement.

[0026] After the first scan of the GaN substrate is completed, the energy of the pulsed laser 204 is increased to perform a second scan. Near the laser focal point, the GaN absorbs energy and decomposes, producing more gallium and nitrogen gas. The stress generated by the expansion of the nitrogen gas exceeds the limiting strength of the GaN crystal, causing the GaN crystal around cavity 121 to fracture. Simultaneously, nitrogen gas fills the cracks in the GaN crystal. By adjusting the energy of the pulsed laser and the spacing between adjacent cavities, the cracks can be interconnected, such as... Figure 2 As shown. It should be noted that: excessively long cavity spacing may prevent the formation of a uniform modified layer, while excessively short cavity spacing will lead to a decrease in efficiency.

[0027] In specific implementation, the energy of the pulsed laser is increased to a second preset energy. The pulsed laser, with the second preset energy, is incident from the N-plane of the gallium nitride substrate (where no device layer is grown) into the interior of the gallium nitride substrate, reaching a specific depth and being focused. A second scan of the gallium nitride substrate is then performed. To ensure that cracks are generated around the cavities inside the gallium nitride substrate during the second scan, and that the cracks generated in adjacent cavities connect to form a modified layer, this embodiment employs the following method... Figure 3 The laser scanning path shown is used to perform the first and second scans on the GaN substrate.

[0028] like Figure 3 As shown, when scanning a gallium nitride substrate, the scanning is performed along edge a of the gallium nitride substrate. Then, the step length is set along edge m, and the scanning is performed along edge a again until the laser can no longer irradiate the gallium nitride substrate after the step length is set along edge m.

[0029] The distance La between adjacent laser irradiation points along side a and the distance Lm between adjacent laser irradiation points along side m are determined based on the cavity diameter L0 and the second set energy.

[0030] The distance Lm between adjacent laser irradiation points along edge m is also the set step length for stepping along edge m.

[0031] Specifically, the second set energy is A times the first set energy E0, where A is greater than or equal to 1.1 and less than or equal to 1.4.

[0032] The distance La between adjacent laser irradiation points along side a is B times the cavity diameter L0, where B is greater than or equal to 0.8 and less than or equal to 1.2.

[0033] The distance Lm between adjacent laser irradiation points along side m is C times the cavity diameter L0, where C is greater than or equal to 3 and less than or equal to 4.

[0034] In order to form a more uniform modified layer, this embodiment performs two scans along edge a of the gallium nitride substrate, one from left to right and the other from right to left, so that two pulsed laser irradiations are performed at the same focal point, thus forming a more uniform modified layer.

[0035] The gallium nitride substrate is then separated along the modified layer using methods such as tensile testing or ultrasonic vibration, which allow the GaN substrate to be separated from the modified layer, to obtain a laser-cut gallium nitride substrate. Selecting an appropriate adhesive or ultrasonic vibration method may help prevent the GaN substrate from fracturing during separation.

[0036] The method disclosed in this embodiment was verified with a laser pulse width of 2.3 ps and a first set energy of 1 μJ.

[0037] A laser with a pulse width of 2.3 ps and a pulse energy of 1 μJ is incident from the N-plane of the gallium nitride substrate into the interior of the gallium nitride substrate to perform the first scan of the gallium nitride substrate. The maximum cavity diameter L0 generated inside the gallium nitride substrate is approximately 5 μm.

[0038] A laser with a pulse width of 2.3 ps and a pulse energy of 1.2 μJ was incident from the N-plane of a gallium nitride (GaN) substrate into the interior of the GaN substrate to perform a second scan. After the scan, a uniform modified layer was formed inside the GaN. The image of the scanned GaN substrate sample is shown below. Figure 9 As shown, the modified layer is black with a metallic luster, which is the color of metallic Ga produced after GaN decomposition.

[0039] During the two scans, La was set to be equal to L0, which is 5 μm; Lm was set to be 3.4 times L0, which is 17 μm.

[0040] The GaN substrate was separated along the modified layer 120 using a tensile testing machine, such as... Figure 6 The upper and middle portions of the GaN substrate without device layers can be polished to remove the modified layer 120 and reused. Figure 10 This is a photograph of the stripped surface of the GaN substrate after separation along the modified layer.

[0041] The test results show that the method disclosed in this embodiment is such that the laser is incident on the N-side of the GaN substrate without any growing device, the slicing process is not limited by the growing device, and the laser step length along the m-side (distance between adjacent pulse focal points) is increased by at least 3 times compared with other existing methods. At the same time, the laser parameters do not need to be changed during the entire slicing process, so the laser slicing time can be reduced by half.

[0042] Example 2 In this embodiment, a gallium nitride substrate laser slicing system is disclosed, such as... Figure 4 As shown, a gallium nitride substrate laser slicing method disclosed in Example 1 can be applied, including: a laser output unit 200, a displacement platform unit 300, and an electromechanical control unit 400; The displacement platform unit 300 is used to support the gallium nitride substrate with the gallium nitride substrate 100N facing upwards, and can drive the gallium nitride substrate to move along the X-axis, Y-axis and Z-axis. The laser output unit 200 is used to output pulsed laser 204, and the output pulsed laser can be incident from the N-side of the gallium nitride substrate, to a specific depth of the gallium nitride substrate and focused. The electromechanical control unit 400 is used to control the displacement platform unit to move along a specific scanning path and to control the laser output unit to output pulsed laser.

[0043] like Figure 5 As shown, the N-plane of the gallium nitride substrate 100 faces upward and serves as the incident surface of the laser. A device layer 110 is grown on the Ga surface of the gallium nitride substrate 100. The device layer 110 faces downward and is fixed on the displacement platform 300 by vacuum suction. The pulsed laser 204 is incident from the N-plane of the GaN substrate and scans at a specific depth within the substrate to form a modified layer 120.

[0044] The laser output unit 200 includes a pulsed laser 201 for outputting pulsed laser; an adjustment optical path 202 for shaping the pulsed laser beam and adjusting the pulsed laser energy; and a concentrator 203 for focusing the pulsed laser after adjustment by the adjustment optical path 202. The focused pulsed laser 204 is precisely focused at a specific depth inside the gallium nitride substrate 100.

[0045] The displacement platform unit 300 includes a vacuum chuck and has at least X, Y, and Z axis adjustment functions.

[0046] The electromechanical control unit 400 is connected to the adjustment optical path 202 to realize laser shaping control and energy control; it is connected to the condenser 203 to realize focus control; and it is connected to the displacement platform 300 to realize the position, movement speed and other control of the displacement platform.

[0047] The system disclosed in this embodiment also includes a tensile testing machine 500 for stretching and separating the GaN substrate along the modified layer 120.

[0048] Preferably, the N-side of the GaN sample and the device layer 110 are fixed to the tensile testing machine 500 using adhesive 501. The GaN sample can be separated along the modified layer by applying a tensile force perpendicular to the modified layer 120. After separation, the sample is removed from the tensile testing machine 500 using a desmearing agent.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for laser slicing gallium nitride substrates, characterized in that, include: A pulsed laser with a first set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate to perform the first scan of the gallium nitride substrate, forming cavities at each laser focus point inside the gallium nitride substrate. A pulsed laser with a second set energy is incident from the N-face of the gallium nitride substrate without a device layer into the interior of the gallium nitride substrate. The laser is focused at a specific depth in the gallium nitride substrate and scanned a second time, causing cracks to be generated around the cavities inside the gallium nitride substrate. The cracks generated in adjacent cavities are connected to each other to form a modified layer. The gallium nitride substrate is separated along the modified layer to obtain a gallium nitride substrate laser slice; The first set energy is greater than or equal to 0.8 μJ and less than or equal to 2 μJ; The diameter of the cavity formed at the focal point is greater than or equal to 3μm and less than or equal to 6μm. At this time, the laser only produces deformation inside gallium nitride but does not break. The second set energy is A times the first set energy, where A is greater than or equal to 1.1 and less than or equal to 1.

4.

2. The method for laser slicing gallium nitride substrates as described in claim 1, characterized in that, The pulse width of a pulsed laser is greater than or equal to 100 fs and less than or equal to 1 ns.

3. The method for laser slicing gallium nitride substrates as described in claim 1, characterized in that, When scanning a gallium nitride substrate, the scan is performed along edge a of the gallium nitride substrate. Then, the step length is set along edge m, and the scan is performed along edge a again until the laser can no longer irradiate the gallium nitride substrate after the step length is set along edge m.

4. The method for laser slicing gallium nitride substrates as described in claim 3, characterized in that, Two scans are performed along edge a of the gallium nitride substrate, one from left to right and the other from right to left, so that two pulsed laser irradiations are performed at the same focal point.

5. The method for laser slicing gallium nitride substrates as described in claim 3, characterized in that, The distances between adjacent laser irradiation points along side a and along side m are determined based on the cavity diameter and the energy of the pulsed laser after the energy is increased.

6. The method for laser slicing a gallium nitride substrate as described in claim 5, characterized in that, The distance between adjacent laser irradiation points along side a is B times the cavity diameter, where B is greater than or equal to 0.8 and less than or equal to 1.

2.

7. The method for laser slicing a gallium nitride substrate as described in claim 5, characterized in that, The distance between adjacent laser irradiation points along side m is C times the cavity diameter, where C is greater than or equal to 3 and less than or equal to 4.

8. A gallium nitride substrate laser slicing system, employing the gallium nitride substrate laser slicing method as described in any one of claims 1-7, characterized in that, include: Laser output unit, displacement platform unit, and electromechanical control unit; The displacement platform unit is used to support the gallium nitride substrate with the N-plane of the gallium nitride substrate facing upwards, and can drive the gallium nitride substrate to move along the X-axis, Y-axis and Z-axis; A laser output unit is used to output pulsed laser light, and the output pulsed laser light can be incident from the N-side of the gallium nitride substrate, reach a specific depth of the gallium nitride substrate and be focused. The electromechanical control unit is used to control the displacement platform unit to move along a specific scanning path and to control the laser output unit to output pulsed laser.

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