A method of laser delaminating gallium oxide

Abstract

The application belongs to the technical field of semiconductor power devices, and particularly discloses a method for laser stripping gallium oxide. The method is characterized in that a super-short pulse laser with a predetermined wavelength is irradiated into the gallium oxide, and a two-photon absorption process occurs when the laser is focused at a position with a specific thickness from the surface. The high temperature generated in the process causes thermal decomposition of the gallium oxide, thereby achieving the purpose of stripping the gallium oxide. Compared with the traditional substrate cutting technology, the stripping method can significantly reduce the cutting consumption of the gallium oxide substrate, and the cut substrate can be reused after polishing, which helps to reduce the manufacturing cost of the gallium oxide device.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor power device technology, and specifically relates to a method for laser stripping gallium oxide. Background Technology

[0002] Gallium oxide (Ga2O3) is a third-generation wide-bandgap semiconductor material with a bandgap of 4.5 eV to 4.9 eV and a theoretical breakdown field strength of 8 MV / cm, far exceeding that of silicon carbide (SiC) (2.5 MV / cm) and gallium nitride (GaN) (3.3 MV / cm). Furthermore, gallium oxide has a Balhican figure of merit (3214) that is 10 times that of SiC and 4 times that of GaN, making it highly suitable for fabricating ultra-high-power devices.

[0003] While gallium oxide (GaO) offers numerous advantages over materials like silicon carbide (SiC) and gallium nitride (GaN), such as a larger bandgap and higher breakdown electric field, making it an ideal material for fabricating ultra-high-power devices, the high cost of GaO substrates currently limits the commercialization of many GaO-based devices. The goal of GaO lift-off technology is to achieve thinner GaO substrate slices with higher yields, minimizing the consumption of expensive GaO substrates. This is a key technology for further advancing the commercialization of GaO-based devices.

[0004] Traditional chemical and mechanical substrate lift-off techniques have many limitations. For example, traditional mechanical lift-off techniques cannot avoid significant cut losses during slicing, and the substrate surface cannot be polished for reuse. In addition, the general process of traditional techniques is to slice first and then carry out subsequent manufacturing. Because the sliced ​​gallium oxide is thin, the chemical and thermal effects that occur during subsequent manufacturing have a wide range of impacts, which can affect the stability of the gallium oxide substrate, increase the possibility of overall device defects, and further increase the manufacturing cost of gallium oxide devices. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a laser-based method for removing gallium oxide, thereby reducing slicing loss, improving substrate utilization, increasing yield, and ultimately reducing the manufacturing cost of gallium oxide devices.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A method for laser stripping of gallium oxide includes the following steps:

[0008] (1) Marking the thermal decomposition plane: Move the gallium oxide substrate along the Z-axis direction so that the focal point of the pulsed laser is located inside the gallium oxide. Then move the gallium oxide substrate at intervals along the X-axis and Y-axis directions so that the focal point of the pulsed laser is exposed point by point inside the gallium oxide substrate. Two-photon absorption occurs at the exposure point inside the gallium oxide substrate to form a series of ablation points, thereby marking the thermal decomposition layer parallel to the surface of the gallium oxide substrate inside the gallium oxide substrate.

[0009] (2) Forming a thermal decomposition plane: The gallium oxide substrate is moved at intervals along the X-axis and Y-axis directions respectively so that the focus of the pulsed laser is exposed point by point inside the gallium oxide substrate. Two-photon absorption occurs at the exposure point inside the gallium oxide substrate to form a series of ablation points, thereby forming a thermal decomposition layer on the marked thermal interface inside the gallium oxide substrate. Then, the upper part and the lower part of the gallium oxide substrate are peeled off from the thermal decomposition layer.

[0010] The distance of the interval movement in step (2) is greater than the distance of the interval movement in step (3).

[0011] The Z-axis of the gallium oxide substrate is perpendicular to the gallium oxide surface, and the X-axis and Y-axis of the gallium oxide substrate are parallel to the gallium oxide surface.

[0012] The specific principle behind this invention is that when a laser irradiates gallium oxide (GaO), GaO converts the absorbed light energy into electron energy, which is then converted into lattice thermal energy through electron-phonon interactions. If the energy of a single photon is greater than the GaO bandgap (4.8 eV), a single photon will be absorbed, causing an electron to be excited from the valence band to the conduction band; this is called single-photon absorption. If the energy of a single photon is less than the GaO bandgap, no electron can be excited. However, when the photon density is sufficiently high, GaO has a certain probability of absorbing two photons simultaneously, causing an electron to transition from the valence band to the conduction band; this is called two-photon absorption. The probability of two-photon absorption is proportional to the square of the light intensity. Two-photon absorption can only occur at the focal point where the photon count is high. During the propagation process before the laser reaches the focal point, due to the relatively low photon density, two-photon absorption will not occur, let alone single-photon absorption. Furthermore, since GaO is a transparent material, photons will not interact with GaO before reaching the focal point, and the overall intensity will not decrease; only the physical and chemical properties of GaO will change at the focal point.

[0013] When an ultrashort pulse (pulse width on the order of femtoseconds to picoseconds) of laser with a specific wavelength is applied to gallium oxide, the power density can reach as high as 10^65 after focusing, because the laser energy is compressed within such a short time interval. 12 W / cm 2A large number of two-photon absorption processes can occur at the focal point, generating high temperatures locally, where gallium oxide is thermally decomposed into metallic gallium and oxygen. Due to the very short pulse duration, heat diffusion to the processing area and its surroundings is greatly reduced, effectively solving the problems of contour, edge, and surface roughness caused by thermal damage during laser processing, thus enabling fine processing of gallium oxide.

[0014] In a preferred embodiment of the present invention, the gallium oxide substrate further includes the following pretreatment process: the surface of the gallium oxide substrate is subjected to physicochemical polishing and cleaning in sequence, so that the root mean square value of its surface roughness is less than 1 nm.

[0015] In a preferred embodiment of the present invention, the distance of the interval movement in step (1) is 4-30 μm.

[0016] As a further preferred embodiment of the present invention, the distance of the interval movement in step (1) is 5 μm.

[0017] In a preferred embodiment of the present invention, the distance of the interval movement in step (2) is 0.1-3 μm.

[0018] As a further preferred embodiment of the present invention, the distance of the interval movement in step (2) is 1 μm.

[0019] In a preferred embodiment of the present invention, in steps (1) and (2), the photon energy of the pulsed laser is 2.756 eV-2.870 eV, the laser pulse width is 10 fs-500 ps, ​​and the peak power density is 1 × 10⁻⁶. 10 W / cm 2 -1×10 13 W / cm 2 .

[0020] In a further preferred embodiment of the present invention, the photon energy of the pulsed laser is 2.870 eV, the laser pulse width is 500 ps, ​​and the peak power density is 2.5 × 10⁻⁶. 11 W / cm 2 .

[0021] In a preferred embodiment of the present invention, the laser energy of the exposure in step (1) is 1-20 μJ.

[0022] As a further preferred embodiment of the present invention, the laser energy of the exposure in step (1) is 2-10 μJ.

[0023] In a preferred embodiment of the present invention, the laser energy of the exposure in step (2) is 0.1-10 μJ.

[0024] As a further preferred embodiment of the present invention, the laser energy of the exposure in step (2) is 0.2 μJ.

[0025] By controlling the focusing distance and the focused light energy, ultrashort pulse lasers can not only process the surface of gallium oxide, but also process its interior at a specific thickness from the surface.

[0026] In a preferred embodiment of the present invention, the thickness of the gallium oxide substrate is greater than 10 μm.

[0027] In a preferred embodiment of the present invention, the thickness of the gallium oxide substrate is 10 μm to 1000 μm.

[0028] In a further preferred embodiment of the present invention, the thickness of the gallium oxide substrate is 500 μm.

[0029] In a further preferred embodiment of the present invention, the distance between the thermal decomposition layer and the surface of the gallium oxide substrate is 250-500 μm.

[0030] In a preferred embodiment of the present invention, the physicochemical polishing includes polishing with a polishing machine and polishing with an SPM mixture, wherein the SPM mixture includes water, concentrated sulfuric acid, and hydrogen peroxide.

[0031] As a preferred embodiment of the present invention, the gallium oxide substrate upper portion and / or gallium oxide submerged portion obtained by the above-mentioned method of laser stripping gallium oxide further includes a cleaning step of hydrochloric acid aqueous solution.

[0032] In a preferred embodiment of the present invention, the gallium oxide substrate further includes gallium oxide epitaxially grown on a heterostructure substrate and gallium oxide substrate containing devices, such as gallium oxide epitaxially grown on a sapphire substrate.

[0033] Compared with existing technologies, this invention has the following advantages: This invention uses laser lift-off for gallium oxide substrate segmentation, which reduces the kerf loss by several times compared to the hundreds of micrometers caused by traditional cutting methods. The kerf loss of this invention can be as low as tens of micrometers or even lower, significantly reducing the consumption of expensive gallium oxide substrates. Furthermore, the cut substrate can be reused after polishing, helping to reduce the manufacturing cost of gallium oxide devices. In addition, traditional substrate cutting methods result in severe damage to the cut surface and residual stress in the substrate, both of which affect device yield in subsequent manufacturing. Laser lift-off, due to its very short pulse duration, greatly reduces heat diffusion to the processing area and its surroundings, effectively solving the problems of contour, edge, and surface roughness caused by thermal damage during laser processing. The defects and other factors affecting subsequent manufacturing are less significant compared to traditional cutting techniques, thus improving yield. Attached Figure Description

[0034] Figure 1 This is a flowchart of laser stripping of gallium oxide in Example 1.

[0035] Figure 2 This is a schematic diagram of the three-dimensional structure of gallium oxide substrate A in Example 1.

[0036] Figure 3 This is a three-dimensional structural diagram of gallium oxide substrate A in Example 1, in the state of marked thermal decomposition plane.

[0037] Figure 4 This is a three-dimensional structural diagram of gallium oxide substrate A in Example 1, in the state of forming a thermal decomposition plane.

[0038] Figure 5 This is a schematic diagram of gallium oxide substrate A after laser lift-off in Example 1. Detailed Implementation

[0039] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific embodiments.

[0040] Please see Figures 1-5 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0041] The gallium oxide substrate described in this invention may include an intrinsic gallium oxide substrate, gallium oxide epitaxially grown on a heterostructure substrate, or a gallium oxide substrate containing devices. As an example, the gallium oxide substrate is an intrinsic gallium oxide substrate (hereinafter referred to as a gallium oxide substrate).

[0042] Specifically, the thickness of the gallium oxide substrate can be selected as needed, such as from 10 μm to 1000 μm. As an example, the thickness of the gallium oxide substrate in Examples 1-3 is selected as 200 μm, 500 μm, and 1000 μm.

[0043] Example 1

[0044] (1) Pretreatment of gallium oxide substrate

[0045] First, refer to Figure 2 The surface of a 500 μm thick gallium oxide substrate A was subjected to standard SPM chemical cleaning to achieve a root mean square roughness of less than 1 nm. Specifically:

[0046] (1a) Polishing the surface of gallium oxide substrate A in a polishing machine;

[0047] (1b) The polished gallium oxide substrate A was immersed in a mixture of concentrated sulfuric acid, hydrogen peroxide and water for 50 seconds, then rinsed with deionized water and placed in a centrifuge to remove water molecules from the surface of the gallium oxide substrate A.

[0048] (2) Mark the thermal decomposition plane (see attached diagram) Figure 3 (As shown)

[0049] Next, the pretreated gallium oxide substrate A is fixed on an electric translation stage with its back side facing upwards, and pulsed laser light is irradiated from the surface inwards. The photon energy of the pulsed laser is 2.870 eV, the pulse width is 500 ps, ​​and the peak power density is 2.5 × 10⁻⁶. 11 W / cm 2 Furthermore, the pulsed laser is split into 6 beams with the same beam diameter and energy by a laser beam splitter, and then focused by a 50x focusing lens. The electric translation stage is adjusted along the Z direction to bring the laser focus to a position 250μm away from the surface.

[0050] Then, the electric translation stage is moved point by point in the X and Y directions at 5 μm intervals. The laser focus is moved point by point inside the gallium oxide substrate A for exposure. Each point is irradiated with 2 μJ of laser energy. Two-photon absorption occurs at the focal point, thereby forming a series of relatively sparse ablation points, thus marking a thermal decomposition layer parallel to the surface of the gallium oxide substrate A inside the gallium oxide substrate A.

[0051] Using a CCD imaging system to observe the processing in real time enables real-time monitoring of the processing.

[0052] (3) Formation of thermal decomposition plane (see attached diagram) Figure 4 (As shown)

[0053] An electrically driven translation stage is moved point-by-point along the X and Y directions at 1 μm intervals. The laser focus moves point-by-point inside the gallium oxide substrate A for exposure, with each point irradiated with 0.2 μJ of laser energy. Two-photon absorption occurs at the focal point, forming a series of relatively dense ablation points, thus creating a complete thermal decomposition layer parallel to the surface of the gallium oxide substrate A. A CCD imaging system is used to observe the processing in real time, enabling real-time monitoring of the process.

[0054] (4) Pull the upper part of gallium oxide substrate A and the lower part of gallium oxide substrate A apart from the thermal interface, as shown in the attached figure. Figure 5 As shown.

[0055] (5) After laser stripping, use a mixed solution with a volume ratio of hydrochloric acid:water = 1:4 to remove the residual Ga on the sample surface.

[0056] Example 2

[0057] (1) Pretreatment of gallium oxide substrate

[0058] The surface of a 200 μm thick gallium oxide substrate A was subjected to standard SPM chemical cleaning to achieve a root mean square surface roughness of less than 1 nm. Specifically:

[0059] (1a) Polishing the surface of gallium oxide substrate A in a polishing machine;

[0060] (1b) The polished gallium oxide substrate A was immersed in a mixture of concentrated sulfuric acid, hydrogen peroxide and water for 50 seconds, then rinsed with deionized water and placed in a centrifuge to remove water molecules from the surface of the gallium oxide substrate A.

[0061] (2) Marking the thermal decomposition plane

[0062] A pretreated gallium oxide substrate A is fixed on an electrically driven translation stage with its back side facing upwards. A pulsed laser is then irradiated from the surface inwards. The photon energy of the pulsed laser is 2.756 eV, the pulse width is 10 ps, ​​and the peak power density is 1.0 × 10⁻⁶. 10 W / cm 2 Furthermore, the pulsed laser is split into two beams with the same beam diameter and energy by a laser beam splitter, and then focused by a 50x focusing lens. The electric translation stage is adjusted along the Z direction to bring the laser focus to a position 100μm away from the surface.

[0063] Then, the electric translation stage is moved point by point in the X and Y directions at 4μm intervals. The laser focus is moved point by point inside the gallium oxide substrate A for exposure. Each point is irradiated with 10μJ of laser energy. Two-photon absorption occurs at the focal point, thereby forming a series of relatively sparse ablation points, thus marking a thermal decomposition layer parallel to the surface of the gallium oxide substrate A inside the gallium oxide substrate A.

[0064] Using a CCD imaging system to observe the processing in real time enables real-time monitoring of the processing.

[0065] (3) Formation of thermal decomposition plane

[0066] An electrically driven translation stage is moved point-by-point along the X and Y directions at 0.1 μm intervals. The laser focus moves point-by-point inside the gallium oxide substrate A for exposure, with each point irradiated with 4 μJ of laser energy. Two-photon absorption occurs at the focal point, forming a series of closely spaced ablation points, thus creating a complete thermal decomposition layer parallel to the surface of gallium oxide substrate A. A CCD imaging system is used to observe the processing in real time, enabling real-time monitoring of the process.

[0067] (4) Pull the upper part of gallium oxide substrate A and the lower part of gallium oxide substrate A apart from the thermal interface.

[0068] (5) After laser stripping, use a mixed solution with a volume ratio of hydrochloric acid:water = 1:4 to remove the residual Ga on the sample surface.

[0069] Example 3

[0070] (1) Pretreatment of gallium oxide substrate

[0071] The surface of a 1000 μm thick gallium oxide substrate A was subjected to standard SPM chemical cleaning to achieve a root mean square (RMS) surface roughness of less than 1 nm. Specifically:

[0072] (1a) Polishing the surface of gallium oxide substrate A in a polishing machine;

[0073] (1b) The polished gallium oxide substrate A was immersed in a mixture of concentrated sulfuric acid, hydrogen peroxide and water for 50 seconds, then rinsed with deionized water and placed in a centrifuge to remove water molecules from the surface of the gallium oxide substrate A.

[0074] (2) Marking the thermal decomposition plane

[0075] A pretreated gallium oxide substrate A is fixed on an electrically driven translation stage with its back side facing upwards. A pulsed laser is then irradiated from the surface inwards. The pulsed laser has a photon energy of 2.870 eV, a pulse width of 500 ps, ​​and a peak power density of 2.5 × 10⁻⁶. 13 W / cm 2 Furthermore, the pulsed laser is split into 10 beams with the same beam diameter and energy by a laser beam splitter, and then focused by a 50x focusing lens. The electric translation stage is adjusted along the Z direction to bring the laser focus to a position 300μm away from the surface.

[0076] Then, the electric translation stage is moved point by point in the X and Y directions at 10 μm intervals. The laser focus is moved point by point inside the gallium oxide substrate A for exposure. Each point is irradiated with 20 μJ of laser energy. Two-photon absorption occurs at the focal point, thereby forming a series of relatively sparse ablation points, thus marking a thermal decomposition layer parallel to the surface of the gallium oxide substrate A inside the gallium oxide substrate A.

[0077] Using a CCD imaging system to observe the processing in real time enables real-time monitoring of the processing.

[0078] (3) Formation of thermal decomposition plane

[0079] An electrically driven translation stage is moved point-by-point along the X and Y directions at 3 μm intervals. The laser focus moves point-by-point inside the gallium oxide substrate A for exposure, with each point irradiated with 8 μJ of laser energy. Two-photon absorption occurs at the focal point, forming a series of relatively dense ablation points, thus creating a complete thermal decomposition layer parallel to the surface of the gallium oxide substrate A. A CCD imaging system is used to observe the processing in real time, thereby achieving real-time monitoring of the processing.

[0080] (4) Pull the upper part of gallium oxide substrate A and the lower part of gallium oxide substrate A apart from the thermal interface.

[0081] (5) After laser stripping, use a mixed solution with a volume ratio of hydrochloric acid:water = 1:4 to remove the residual Ga on the sample surface.

[0082] This invention utilizes laser lift-off for gallium oxide substrate dicing, resulting in a several-fold reduction in kerf loss compared to traditional cutting methods, which incur hundreds of micrometers of kerf. The kerf loss of this invention can be as low as tens of micrometers or even lower, significantly reducing the consumption of expensive gallium oxide substrates. Furthermore, the diced substrate can be reused after polishing, helping to lower the manufacturing cost of gallium oxide devices. In addition, traditional substrate cutting methods result in severe surface damage and residual stress on the substrate, both of which negatively impact device yield in subsequent manufacturing processes. Laser lift-off, with its extremely short pulse duration, greatly reduces heat diffusion to the processing area and its surroundings, effectively solving the problems of contour, edge, and surface roughness caused by thermal damage during laser processing. The resulting defects have fewer impacts on subsequent manufacturing compared to traditional cutting techniques, thus improving yield.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for laser stripping gallium oxide, characterized in that, Includes the following steps: (1) Marking the thermal decomposition plane: Move the gallium oxide substrate along the Z-axis direction so that the focal point of the pulsed laser is located inside the gallium oxide. Then move the gallium oxide substrate at intervals along the X-axis and Y-axis directions so that the focal point of the pulsed laser is exposed point by point inside the gallium oxide substrate. Two-photon absorption occurs at the exposure point inside the gallium oxide substrate to form a series of ablation points, thereby marking a thermal decomposition layer parallel to the surface of the gallium oxide substrate inside the gallium oxide substrate. The laser energy of the exposure is 1-20 μJ; the photon energy of the pulsed laser is 2.756 eV-2.870 eV, the laser pulse width is 10 fs-500 ps, ​​and the peak power density is 1×10 10 W / cm 2 -1×10 13 W / cm 2 ; (2) Forming a thermal decomposition plane: The gallium oxide substrate is moved at intervals along the X-axis and Y-axis directions respectively, so that the focus of the pulsed laser exposes the interior of the gallium oxide substrate point by point. Two-photon absorption occurs at the exposure points inside the gallium oxide substrate, forming a series of ablation points, thereby forming a thermal decomposition layer on the marked thermal interface inside the gallium oxide substrate. Then, the upper part and the lower part of the gallium oxide substrate are peeled off from the thermal decomposition layer. The photon energy of the pulsed laser is 2.756eV-2.870eV, the laser pulse width is 10fs-500ps, and the peak power density is 1×10 10 W / cm 2 -1×10 13 W / cm 2 The laser energy used for the exposure is 0.1-10 μJ. The distance of the interval movement in step (1) is greater than the distance of the interval movement in step (2).

2. The method for laser stripping gallium oxide as described in claim 1, characterized in that, The distance of the interval movement in step (1) is 4-30 μm.

3. The method for laser stripping gallium oxide as described in claim 1, characterized in that, The distance of the interval movement in step (2) is 0.1-3 μm.

4. The method for laser stripping gallium oxide as described in claim 1, characterized in that, In steps (1) and (2), the photon energy of the pulsed laser is 2.870 eV, the laser pulse width is 500 ps, ​​and the peak power density is 2.5 × 10⁻⁶. 11 W / cm 2 .

5. The method for laser stripping gallium oxide as described in claim 1, characterized in that, The laser energy for exposure in step (2) is 4-8 μJ.

6. The method for laser stripping gallium oxide as described in claim 1, characterized in that, The thickness of the gallium oxide substrate is greater than 10 μm.

7. The laser-assisted gallium oxide stripping method according to any one of claims 1-6, characterized in that, The gallium oxide substrate also includes gallium oxide epitaxial on a heterostructure substrate and gallium oxide substrate containing devices.

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