Diamond heterostructure pore formation method

Abstract

The application provides a diamond heterostructure hole forming method, which comprises the following steps: providing a to-be-processed heterostructure, wherein the heterostructure comprises a diamond layer, a semiconductor film layer and a metal layer which are sequentially stacked; coating a photoresist mask on the surface of the diamond layer; focusing a laser beam on the photoresist according to a target hole forming position and size to remove the photoresist by ablation; according to the target hole forming position and size, using a laser beam which has a transmission characteristic for the photoresist to be incident to a reserved height; starting from the reserved height, focusing and irradiating layer by layer according to a preset step height, and changing the crystal structure; removing the area of the diamond layer which is scanned by the laser beam to form a blind hole; using the photoresist layer as a mask, etching the semiconductor film layer and the diamond layer at the reserved height until the metal layer is exposed, then removing the photoresist, and completing the diamond heterostructure hole forming. The application can effectively improve the hole forming efficiency of the diamond heterostructure and avoid thermal damage to the semiconductor film layer and the metal layer.

Description

Technical Field

[0001] This invention relates to the field of diamond processing technology, and in particular to a method for creating holes in heterogeneous diamond structures. Background Technology

[0002] Gallium nitride (GaN), a typical representative of third-generation wide-bandgap semiconductors, possesses high electron saturation velocity and high breakdown field strength, and is widely used in high-frequency, high-power microwave devices. As semiconductor devices evolve towards miniaturization and integration, the self-heating effect under high power density becomes increasingly prominent, making effective thermal management crucial for improving device reliability and stability. Due to its ultra-high thermal conductivity (2000 W / (m•K)), integrating GaN devices with diamond substrates can significantly improve heat dissipation, solving the heat dissipation problem of GaN devices. However, the extremely high hardness of diamond leads to low efficiency and severe damage from traditional mechanical etching methods. Furthermore, diamond's extremely high chemical stability allows it to withstand harsh environments such as acids, alkalis, and high temperatures, making it difficult to etch using conventional wet etching methods. Currently used laser etching methods offer advantages such as high efficiency and strong material applicability, but they are difficult to precisely control the etching depth, easily damaging the device's metal layer. Summary of the Invention

[0003] The method for creating holes in diamond heterostructures provided by this invention can effectively improve the hole-making efficiency of diamond heterostructures and avoid thermal damage to semiconductor films and metal layers.

[0004] This invention provides a method for creating holes in diamond heterostructures, the method comprising:

[0005] A heterostructure to be processed is provided, the heterostructure comprising at least a diamond layer, a semiconductor film layer and a metal layer stacked sequentially;

[0006] A photoresist mask is coated on the surface of a diamond. Based on the target hole location and size, a laser beam is focused on the photoresist to ablate and remove it.

[0007] Based on the target hole location and size, a laser beam with transmittance to photoresist is used to be incident from the surface of the diamond layer away from the semiconductor film layer to the reserved height;

[0008] Starting from the reserved height, the laser beam focuses and scans layer by layer according to the preset step height to change the crystal structure of the diamond layer in the area scanned by the laser beam.

[0009] The area of ​​the diamond layer scanned by the laser beam is removed to form blind holes in the heterostructure;

[0010] Using the photoresist as a mask, the semiconductor film layer and the diamond layer with a reserved height are etched until the metal layer is exposed. Then, the photoresist is removed to complete the diamond heterostructure hole fabrication.

[0011] Optionally, the incident projection from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes:

[0012] A laser beam is formed by selecting a wavelength that is transparent to diamond, and the laser beam is controlled to be incident from the surface of the diamond layer away from the semiconductor film layer to a predetermined height.

[0013] Optionally, the incident projection from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes:

[0014] The laser beam is controlled to be incident from the surface of the diamond layer away from the semiconductor film layer, and focused at a position within the diamond layer at a distance of not less than 50 μm from the interface between the diamond layer and the semiconductor film layer.

[0015] Optionally, the step of focusing and scanning layer by layer from a reserved height according to a preset step height includes:

[0016] The preset step height of the laser focusing position in the height direction is 45±15μm each time. After each step is completed, the laser beam is controlled to scan in the plane.

[0017] Optionally, the step of focusing and scanning layer by layer from a reserved height according to a preset step height includes:

[0018] The laser beam is controlled to focus in a spiral-ascending scanning path within the diamond layer.

[0019] Optionally, the etching of the semiconductor film layer and the diamond layer with reserved height using the photoresist layer as a mask includes:

[0020] The semiconductor film and the diamond layer with reserved height are etched using a plasma dry etching method, with one or a mixture of oxygen, argon, carbon tetrafluoride and sulfur hexafluoride as the gas source.

[0021] Optionally, removing the area of ​​the diamond layer scanned by the laser beam includes:

[0022] The areas of the diamond layer that have been laser-scanned are removed by mechanical drilling or chemical etching.

[0023] Optionally, the step of using a laser beam incident from the surface of the diamond layer away from the semiconductor film layer, and focusing and scanning layer by layer according to a preset step height, includes:

[0024] Based on the preset step height, obtain the hologram required for spherical aberration correction of the laser beam after each step in the height direction by the spatial light modulator;

[0025] Each time the laser beam focusing position is stepped in the height direction, before focusing the laser beam, a hologram corresponding to the current height is loaded onto the spatial light modulator, and the spatial light modulator is used to perform spherical aberration correction on the laser beam.

[0026] Optionally, the step of using a laser beam with transmittance to the photoresist, incident from the surface of the diamond layer away from the semiconductor film layer to the predetermined height, based on the target aperture location and size, includes:

[0027] A laser beam is formed by selecting a nanosecond laser, picosecond laser, or femtosecond laser and incident from the surface of the diamond layer away from the semiconductor film layer.

[0028] Optionally, the step of focusing and scanning layer by layer according to a preset step height, starting from a reserved height, to change the crystal structure of the diamond layer in the area scanned by the laser beam includes:

[0029] A laser beam is incident from the surface of the diamond layer away from the semiconductor film layer, and is focused and scanned layer by layer according to a preset step height, so that the crystal structure of the area of ​​the diamond layer scanned by the laser beam is transformed from the diamond phase to the graphite phase or the amorphous carbon phase.

[0030] In the technical solution provided by this invention, a laser beam is used to focus and irradiate the diamond substrate, causing a change in the crystal structure of the scanned area. After this change, the physical hardness and chemical corrosion resistance of the diamond decrease significantly, thereby reducing the difficulty of machining and chemical etching and improving processing efficiency. Furthermore, compared to simple laser processing, which requires irradiating the processing area to temperatures exceeding 4000°C, or even 5000°C, the technical solution provided by this invention only requires a phase transition in the diamond substrate to reduce its hardness and corrosion resistance, thus only requiring a temperature of 1200°C. Due to the lower phase transition temperature, the laser irradiation time is also reduced, significantly improving processing efficiency. Additionally, in the technical solution provided by this invention, a lower temperature is used to perform phase transition treatment on the diamond, followed by mechanical processing to remove the graphite or amorphous carbon phase regions after the phase transition, and finally, plasma etching of the semiconductor film layer. This avoids significant thermal impact on the semiconductor film layer and metal layer, preventing thermal damage to the semiconductor device and metal layer. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for creating holes in a diamond heterostructure according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the heterostructure to be processed in a diamond heterostructure drilling method according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram illustrating the completion of hole fabrication in a diamond heterostructure fabrication method according to an embodiment of the present invention.

[0034] Figure 4 This is a flowchart of spherical aberration correction in a diamond heterostructure drilling method according to an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram illustrating the principle of spherical aberration formation in a diamond heterostructure drilling method according to an embodiment of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a method for creating holes in heterostructured diamond, such as... Figure 1 As shown, the method includes:

[0038] A heterostructure to be processed is provided, the heterostructure comprising at least a diamond layer, a semiconductor film layer and a metal layer stacked sequentially;

[0039] In some embodiments, such as Figure 2 As shown, the heterogeneous structure to be processed can be, for example, a heterogeneous structure formed of diamond, GaN and a metal layer. In order to avoid thermal damage to the GaN and metal layers, the GaN and metal layers cannot be subjected to high temperatures during the hole-making process. At the same time, the diamond layer has extremely high hardness and is difficult to machine. Therefore, hole-making of such heterogeneous structures is usually difficult to complete efficiently in the existing technology.

[0040] A photoresist mask is coated on the surface of a diamond. Based on the target hole location and size, a laser beam is focused on the photoresist to ablate and remove it.

[0041] In some embodiments, photoresist is typically used to protect the device surface during etching, preventing non-etched areas from being etched away. In this step, photoresist is applied to protect the diamond surface during subsequent etching. Since the flat surface is lost after the blind vias are fabricated, making further photoresist application difficult, photoresist is applied first in this step. After coating, photolithography and development are unnecessary; the photoresist at the via locations is directly removed by laser ablation, simplifying the process and significantly improving efficiency.

[0042] Based on the target hole location and size, a laser beam with photoresist transmittance is used to be incident from the surface of the diamond layer away from the semiconductor film layer to the reserved height.

[0043] In some embodiments, the laser beam used to ablate the photoresist and the laser beam focused inside the diamond can be the same laser beam. Although the laser beam has transmittance characteristics to the photoresist, the extremely high energy density generated when it is focused inside or on the surface of the photoresist can still ablate the photoresist through multiphoton absorption. Since the GaN and metal layers cannot withstand high temperatures, in this step, the laser beam is incident at a predetermined height, rather than starting to focus from the interface between the diamond and the semiconductor film.

[0044] Starting from the reserved height, the laser beam focuses and scans layer by layer according to the preset step height to change the crystal structure of the diamond layer in the area scanned by the laser beam.

[0045] In some embodiments, starting from the reserved height, the diamond layer is scanned layer by layer to graphitize or amorphously carbonize the scanned area, thereby reducing its hardness and corrosion resistance, facilitating subsequent mechanical processing or chemical etching removal.

[0046] The area of ​​the diamond layer scanned by the laser beam is removed to form blind holes in the heterostructure;

[0047] In some embodiments, after the scanned area is graphitized or amorphously carbonized, its hardness and corrosion resistance are greatly reduced, so it can be easily removed by mechanical processing or chemical etching.

[0048] Using the photoresist as a mask, the semiconductor film layer and the diamond layer with a reserved height are etched until the metal layer is exposed. Then, the photoresist is removed to complete the diamond heterostructure hole fabrication.

[0049] In some embodiments, because a portion of the diamond layer with a reserved height is not scanned during the laser scanning process (i.e., it is not graphitized or amorphously carbonized), this portion of the diamond layer needs to be etched before the semiconductor film layer can be etched. To prevent damage to the diamond surface outside the hole-forming area, photoresist is used as a mask for protection. Figure 3 As shown, an exemplary diagram illustrates the structure of a diamond heterostructure after hole drilling is completed.

[0050] In the technical solution provided by this invention, a laser beam is used to focus and irradiate the diamond substrate, causing a change in the crystal structure of the scanned area. After this change, the physical hardness and chemical corrosion resistance of the diamond decrease significantly, thereby reducing the difficulty of machining and chemical etching and improving processing efficiency. Furthermore, compared to simple laser processing, which requires irradiating the processing area to temperatures above 4000°C, or even 5000°C, the technical solution provided by this invention only requires a phase transition in the diamond substrate to reduce its hardness and corrosion resistance, thus only requiring a temperature of 1200°C. Due to the lower phase transition temperature, the laser irradiation time is also reduced, significantly improving processing efficiency. Additionally, in the technical solution provided by this invention, a lower temperature is used to perform phase transition treatment on the diamond, followed by mechanical processing to remove the graphite phase region after the phase transition, and finally, plasma etching of the semiconductor film layer. This avoids significant thermal impact on the semiconductor film layer and metal layer, preventing thermal damage to the semiconductor device and metal layer.

[0051] As an optional implementation, the incident light from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes:

[0052] A laser beam is formed by selecting a wavelength that is transparent to diamond, and the laser beam is controlled to be incident on the surface of the diamond layer away from the semiconductor film layer.

[0053] In some embodiments, the bandgap of single-crystal diamond is 5.5 eV and the cutoff wavelength is 225 nm. Laser wavelengths greater than 225 nm can be selected, such as the commonly used 532 nm and 1064 nm.

[0054] As an optional implementation, the incident light from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes:

[0055] The laser beam is controlled to be incident from the surface of the diamond layer away from the semiconductor film layer, and focused at a position within the diamond layer at a distance of not less than 50 μm from the interface between the diamond layer and the semiconductor film layer.

[0056] As an optional implementation, the step of focusing and scanning layer by layer from a reserved height according to a preset step height includes:

[0057] The preset step height of the laser focusing position in the height direction is 45±15μm each time. After each step is completed, the laser beam is controlled to scan in the plane.

[0058] In some embodiments, the focusing and irradiation of the laser beam within the diamond layer needs to be performed from bottom to top to avoid the influence of already irradiated areas on laser transmission. The lowest focusing position is 50 μm away from the diamond-semiconductor film interface to avoid thermal damage to the semiconductor film and metal layer caused by heat transfer at the lowest focusing position. The spacing between adjacent modified layers is 45 ± 15 μm. In a preferred embodiment, the focusing and irradiation of the laser beam within the diamond layer needs to be performed from bottom to top to avoid the influence of already irradiated areas on laser transmission. The lowest focusing position is 50-100 μm away from the diamond-semiconductor film interface to avoid thermal damage to the semiconductor film and metal layer caused by heat transfer at the lowest focusing position.

[0059] As an optional implementation, the step of focusing and scanning layer by layer from a reserved height according to a preset step height includes:

[0060] The laser beam is controlled to be focused and irradiated from a position 50-100 μm away from the interface between the diamond layer and the semiconductor film layer within the diamond layer, and the focused spot of the laser beam is controlled to scan within the diamond layer in a spiral upward scanning path.

[0061] In some embodiments, spiral scanning can be performed in continuous steps, which can effectively speed up processing efficiency.

[0062] As an optional implementation, the etching of the semiconductor film layer and the diamond layer with a reserved height using the photoresist layer as a mask includes:

[0063] The semiconductor film and the diamond layer with reserved height are etched using a plasma dry etching method, with one or a mixture of oxygen, argon, carbon tetrafluoride and sulfur hexafluoride as the gas source.

[0064] As an optional implementation, removing the area of ​​the diamond layer scanned by the laser beam includes:

[0065] The areas of the diamond layer that have been laser-scanned are removed by mechanical drilling or chemical etching.

[0066] As an optional implementation method, such as Figure 4As shown, the step of focusing and scanning layer by layer from the reserved height according to the preset step height includes:

[0067] Based on the preset step height, obtain the hologram required for spherical aberration correction of the laser beam after each step in the height direction by the spatial light modulator;

[0068] Each time the laser beam focusing position is stepped in the height direction, before focusing the laser beam, a hologram corresponding to the current height is loaded onto the spatial light modulator, and the spatial light modulator is used to perform spherical aberration correction on the laser beam.

[0069] In some embodiments, when focusing a laser beam within the material using a focusing lens, spherical aberration occurs at different depths due to the refractive index mismatch between the diamond material and air. To ensure a focused spot with consistent morphology and energy distribution after each step in the height direction, this embodiment employs a spatial light modulator to correct the spherical aberration of the laser beam after each step in the height direction. During spherical aberration correction, a hologram is loaded into the spatial light modulator to modulate the light at each pixel position. Therefore, it is necessary to pre-obtain the hologram required for spherical aberration correction of the laser beam focused at each height. Each height can correspond to a hologram. Before focusing the laser beam at that height, the laser beam is wavefront modulated using a spatial light modulator loaded with the corresponding hologram to achieve spherical aberration correction, thereby forming a focused spot with consistent morphology and energy distribution at each target layer. During laser focusing, the diamond crystal form in the scanning area is transformed into an easily machinable graphite phase crystal form or amorphous carbon form. Since diamond only needs to be above 1200℃ under normal pressure to transform into the graphite phase or amorphous carbon form, only a temperature above 1200℃ is required in the scanning area. Furthermore, maintaining the scanning area above 1200℃ does not require waiting for all the diamond crystals within the scanning area to transform into the graphite or amorphous carbon form. In the scanning area, only a portion of the diamond crystals need to transform into the graphite or amorphous carbon form, which significantly reduces the difficulty of machining or chemical etching. Figure 5As shown, when focusing a laser beam using a focusing lens, the focused beam refracts at the interface between the diamond and air. Furthermore, due to the different incident angles in different areas covered by the laser beam, the degree of refraction varies, resulting in the spot shape and energy distribution within the diamond being difficult to focus on the target point O'. Instead, the beam is focused at points O, A, and B respectively. The target point O' is the ideal position for focusing the laser beam as it propagates through the air. The deviations of points O, A, and B from the target point O' correspond to the spherical aberration at different positions of the laser beam. When the laser beam is focused at different depths within the diamond, the local incident angle changes, leading to differences in spherical aberration for the same position within the laser beam when focused at different depths. Therefore, spherical aberration compensation is necessary each time the beam is focused at a different depth to avoid a significant reduction in hole quality caused by inconsistent spot shape and energy distribution due to spherical aberration.

[0070] As an optional implementation, the step of using a laser beam with transmittance to the photoresist, incident from the surface of the diamond layer away from the semiconductor film layer to the predetermined height, based on the target aperture location and size, includes:

[0071] A laser beam is formed by selecting a nanosecond laser, picosecond laser, or femtosecond laser and incident from the surface of the diamond layer away from the semiconductor film layer.

[0072] As an optional implementation, the step of focusing and scanning layer by layer according to a preset step height, starting from a reserved height, to change the crystal structure of the diamond layer in the area scanned by the laser beam includes:

[0073] A laser beam is incident from the surface of the diamond layer away from the semiconductor film layer, and is focused and scanned layer by layer according to a preset step height, so that the crystal structure of the diamond layer in the area scanned by the laser beam is transformed from the diamond phase to the graphite phase or the amorphous carbon phase.

[0074] Using the aforementioned implementation methods, high-efficiency deep-hole fabrication of diamond layers is achieved through laser scanning and mechanical drilling. Residual diamond and GaN layers are removed via plasma dry etching, reducing laser damage to the metal layer and improving processing accuracy and quality. Composite drilling enables high-efficiency, high-precision deep-hole back-hole fabrication for diamond heterogeneous integrated devices, promoting the engineering application of gallium nitride-based devices on diamond substrates. Specifically, laser modification induces diamond to undergo transformation into easily machinable graphite phases or a composite of amorphous carbon and cracks, reducing material hardness, simplifying mechanical drilling, minimizing tool wear, and improving drilling efficiency and quality. Finally, plasma dry etching ensures drilling quality, reduces device and metal layer damage, and achieves high-quality, high-efficiency back-hole fabrication for diamond heterogeneous integrated devices.

[0075] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for creating holes in a diamond heterostructure, characterized in that, The method includes: A heterostructure to be processed is provided, the heterostructure comprising at least a diamond layer, a semiconductor film layer and a metal layer stacked sequentially; A photoresist mask is coated on the surface of a diamond. Based on the target hole location and size, a laser beam is focused on the photoresist to ablate and remove it. Based on the target hole location and size, a laser beam with transmittance to photoresist is used to be incident from the surface of the diamond layer away from the semiconductor film layer to the reserved height; Starting from the reserved height, the laser beam focuses and scans layer by layer according to the preset step height to change the crystal structure of the diamond layer in the area scanned by the laser beam. The area of ​​the diamond layer scanned by the laser beam is removed to form blind holes in the heterostructure; Using the photoresist layer as a mask, the semiconductor film layer and the diamond layer with a reserved height are etched until the metal layer is exposed. Then the photoresist is removed to complete the diamond heterostructure hole fabrication. The step of focusing and scanning layer by layer from a reserved height according to a preset step height includes: Based on the preset step height, obtain the hologram required for spherical aberration correction of the laser beam after each step in the height direction by the spatial light modulator; Each time the laser beam focusing position is stepped in the height direction, before focusing the laser beam, a hologram corresponding to the current height is loaded onto the spatial light modulator, and the spatial light modulator is used to perform spherical aberration correction on the laser beam.

2. The method according to claim 1, characterized in that, The incident light from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes: A laser beam is formed by selecting a wavelength that is transparent to diamond, and the laser beam is controlled to be incident from the surface of the diamond layer away from the semiconductor film layer to a predetermined height.

3. The method according to claim 1, characterized in that, The incident light from the surface of the diamond layer away from the semiconductor film layer to the reserved height includes: The laser beam is controlled to be incident from the surface of the diamond layer away from the semiconductor film layer, and focused at a position within the diamond layer at a distance of not less than 50 μm from the interface between the diamond layer and the semiconductor film layer.

4. The method according to claim 1, characterized in that, The process of focusing and scanning layer by layer, starting from a predetermined height and according to a preset step height, includes: The preset step height of the laser focusing position in the height direction is 45±15μm each time. After each step is completed, the laser beam is controlled to scan in the plane.

5. The method according to claim 1, characterized in that, The process of focusing and scanning layer by layer, starting from a predetermined height and according to a preset step height, includes: The laser beam is controlled to focus and scan within the diamond layer in a spiral-ascending scanning path.

6. The method according to claim 1, characterized in that, The etching of the semiconductor film and the diamond layer with a reserved height, using the photoresist layer as a mask, includes: The semiconductor film and the diamond layer with reserved height are etched using a plasma dry etching method, with one or a mixture of oxygen, argon, carbon tetrafluoride and sulfur hexafluoride as the gas source.

7. The method according to claim 1, characterized in that, The removal of the area of ​​the diamond layer scanned by the laser beam includes: The areas of the diamond layer that have been laser-scanned are removed by mechanical drilling or chemical etching.

8. The method according to claim 1, characterized in that, The step of using a laser beam that is transparent to photoresist, incident from the surface of the diamond layer away from the semiconductor film layer to a predetermined height, based on the target hole location and size, includes: A laser beam is formed by selecting a nanosecond laser, picosecond laser, or femtosecond laser and incident from the surface of the diamond layer away from the semiconductor film layer.

9. The method according to claim 1, characterized in that, The process of focusing and scanning layer by layer, starting from a predetermined height and according to a preset step height, to change the crystal structure of the diamond layer in the area scanned by the laser beam includes: A laser beam is incident from the surface of the diamond layer away from the semiconductor film layer, and is focused and scanned layer by layer according to a preset step height, so that the crystal structure of the area of ​​the diamond layer scanned by the laser beam is transformed from the diamond phase to the graphite phase or the amorphous carbon phase.

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