Laser dynamic focusing and in-situ cleaning composite thinning method for semiconductor substrate
By using dynamic focusing and in-situ surface treatment technology, the problems of focus drift and by-product contamination in laser thinning were solved, achieving efficient and low-damage thinning of hard and brittle substrates and obtaining atomically flat surfaces.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-16
- Publication Date
- 2026-04-07
AI Technical Summary
Existing laser thinning techniques for hard and brittle substrates suffer from issues such as focus drift and surface by-product contamination, which affect processing efficiency and quality.
By employing dynamic focusing technology to adjust the laser focus position in real time, and combining it with in-situ surface treatment technology to remove byproducts simultaneously, and then combining it with a final precision polishing step, a highly efficient and low-damage thinning process can be achieved.
It improves processing efficiency and quality, ensures surface cleanliness and consistency, achieves atomic-level surface flatness, and is suitable for a variety of hard and brittle substrate materials.
Smart Images
Figure CN121816031A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of laser-assisted processing technology, specifically relating to a composite thinning method for laser dynamic focusing and in-situ cleaning of hard and brittle substrates. Background Technology
[0002] Hard and brittle substrate materials such as silicon carbide and diamond play a crucial role in power semiconductors, radio frequency communications, LED lighting, and precision optics due to their excellent electrical, thermal, optical, and mechanical properties. In many applications, these substrates must be precisely thinned to reduce device resistance, improve heat dissipation, meet packaging requirements, or achieve specific optical properties. However, these materials generally exhibit extremely high hardness and brittleness, posing significant challenges to traditional mechanical grinding thinning methods, including low efficiency, high cost, and the potential introduction of surface and subsurface damage (such as microcracks and dislocations), severely impacting device performance and yield.
[0003] Laser thinning, as an advanced non-contact processing technology, offers new possibilities for thinning these difficult-to-process materials. However, existing laser thinning methods still face two key technical bottlenecks in practical applications: 1. Focus drift problem: Laser thinning removes material through layer-by-layer ablation. As the substrate thickness decreases, the position of the surface to be processed continuously changes in the Z-direction (vertical direction). If the focal position of the laser system is fixed, the energy density of the laser beam on the actual processing surface will significantly decrease due to defocusing, leading to a sharp reduction in ablation efficiency, processing stagnation, and even deterioration of the surface morphology. This problem severely restricts the efficiency and stability of the laser thinning process; 2. Surface byproduct contamination problem: Under high-energy laser irradiation, the substrate material undergoes complex physicochemical reactions with its surrounding environment (such as air), generating a layer of ablation byproducts on the processing surface. For example, laser ablation of silicon carbide in air generates a silicon dioxide (SiO2) deposition layer; diamond may generate a graphite phase (sp...). 2 (Carbon). The presence of these byproducts can severely interfere with the stable absorption of subsequent laser energy, hindering the direct action of the laser on the target material, and ultimately affecting the rate and quality of thinning.
[0004] In summary, there is an urgent need for an integrated solution that can maintain the optimal focal spot position in real time and simultaneously eliminate surface ablation byproducts during the laser thinning of hard and brittle substrates. Summary of the Invention
[0005] (I) Purpose of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite thinning method for hard and brittle substrates using laser dynamic focusing and in-situ cleaning. This method synergistically couples dynamic focusing technology, in-situ surface treatment technology, and final precision polishing to ensure that the laser focus remains precise throughout the thinning process, while efficiently removing surface ablation byproducts, ultimately obtaining an atomically smooth surface. This achieves high-efficiency, high-quality, and low-damage thinning of hard and brittle substrates.
[0007] (II) Technical Solution
[0008] The present invention is achieved through the following technical solution.
[0009] (1) Place the semiconductor substrate on the work platform, start the laser and set the laser parameters so that the laser scans and ablates the surface of the semiconductor substrate to be processed according to the preset path to achieve layer-by-layer thinning.
[0010] (2) During the scanning ablation process in step (1), a dynamic focusing operation is performed in parallel. The dynamic focusing operation includes: using a position sensing module to monitor the position of the surface to be processed in real time and obtain the position change amount; and according to the position change amount, dynamically adjusting the focal position of the main laser beam through the execution module to compensate for the focal drift caused by the reduction of substrate thickness.
[0011] (3) During the scanning ablation process in step (1), in-situ surface treatment operations are performed synchronously or alternately. The in-situ surface treatment operations are used to remove the oxide layer and other ablation byproducts generated on the surface to be processed during the scanning ablation process.
[0012] (4) Repeat steps (1) to (3) until the thickness of the semiconductor substrate reaches the preset target thickness;
[0013] (5) Perform chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP) on the semiconductor substrate after step (4) to obtain an atomically flat surface.
[0014] Furthermore, the semiconductor substrate in step (1) is either silicon carbide or diamond;
[0015] Further, the laser parameters in step (1) are: laser wavelength 355-1064nm, pulse width 100fs-10ns, single pulse energy 1μJ-200μJ, scanning spacing 5-20μm, scanning speed 50mm / s-500mm / s, and repetition frequency 100kHz-1 MHz.
[0016] Furthermore, in step (2), the position sensing module is at least one of a confocal displacement sensor, a laser interferometer, or a white light interferometer;
[0017] Furthermore, the execution module in step (2) achieves dynamic adjustment of the focus by one of the following methods: moving the Z-axis stage that carries the hard and brittle substrate or moving the Z-axis focusing lens group in the main laser beam optical path;
[0018] Further, the in-situ surface treatment operation in step (3) adopts a vapor phase cleaning method, including: introducing an auxiliary gas into the surface to be processed while laser scanning; the auxiliary gas reacts chemically with the surface modification layer (such as an oxide layer or a graphitized layer) of the surface to be processed under the thermal or photochemical action of the laser, generating volatile products that are then removed; when the semiconductor substrate is silicon carbide, the auxiliary gas is at least one of hydrogen fluoride (HF) vapor, sulfur hexafluoride (SF6), or nitrogen trifluoride (NF3); when the hard and brittle substrate is diamond, the auxiliary gas is oxygen (O2), hydrogen (H2), or a mixture thereof, used to remove the graphitized layer by oxidation or hydrogen etching.
[0019] Furthermore, the in-situ surface treatment operation in step (3) adopts a liquid phase cleaning method, including: precisely spraying chemical cleaning liquid onto the surface to be processed or its adjacent area through a micro-droplet spraying device, and then removing residual liquid through an air blowing and recovery device; the chemical cleaning liquid is at least one of hydrofluoric acid (HF) solution, buffered oxide etching solution (BOE), or standard cleaning solution (SC-1 / SC-2).
[0020] Furthermore, the in-situ surface treatment operation in step (3) is performed synchronously and continuously with the scanning ablation operation in step (1), or alternately after each preset area or preset thickness of scanning ablation is completed.
[0021] (III) Beneficial Effects
[0022] The above-described technical solution of the present invention has the following beneficial technical effects:
[0023] (1) Significantly improves processing efficiency: The dynamic focusing function ensures efficient ablation throughout the process. The in-situ surface treatment function avoids the tedious steps and time consumption of offline cleaning, effectively shortening the total process cycle.
[0024] (2) Significantly improved processing quality and consistency: Stable laser energy density and clean processing surface ensure high repeatability and uniformity of the thinning process, effectively reducing surface defects, thermal damage and morphological deterioration. The final precision polishing step ensures atomic-level surface quality.
[0025] (3) Realize automated and intelligent production: This method integrates key processes such as laser ablation, process monitoring, focus compensation, surface cleaning and final fine polishing into one, forming a complete, closed-loop controlled automated processing flow, which provides key technical support for the intelligent precision manufacturing of hard and brittle substrates.
[0026] (4) Expanded the range of applicable materials: This method is not only applicable to silicon carbide and diamond substrates, but also to other hard and brittle substrates such as sapphire. Attached Figure Description
[0027] Figure 1 This is a schematic diagram of the process flow of the present invention.
[0028] Figure 2 The image shown is an optical microscope image obtained after processing in Example 1. Detailed Implementation
[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention.
[0030] Example 1:
[0031] (1) A 4-inch SiC substrate with an initial thickness of 350 μm was placed and fixed on an XY motion platform for initial focusing. A femtosecond laser was started as the main laser source, and the laser parameters were set as follows: laser wavelength 1030 nm, pulse width 10 ns, single pulse energy 100 μJ, scanning spacing 10 μm, scanning speed 200 mm / s, and repetition frequency 200 kHz. After the laser was started, it began to scan and ablate the substrate surface along a spiral path to perform layer-by-layer thinning.
[0032] (2) During the scanning ablation process in step (1), a confocal displacement sensor continuously measures the Z-axis position of the current processing point and sends the real-time position data to the central control system. The central control system calculates the position change ΔZ of the substrate surface due to ablation based on the data, and immediately instructs the Z-axis motorized focusing mirror integrated in the laser optical path to move by a distance of -ΔZ, so that the laser focus always accurately follows the descending substrate surface, thereby achieving dynamic focusing.
[0033] (3) Simultaneously, during the scanning ablation process in step (1), an in-situ vapor phase cleaning operation is performed concurrently. A vapor phase cleaning device continuously introduces HF vapor into a local atmosphere protective hood covering the processing area at a flow rate of 20 sccm. The SiO2 byproducts generated by laser ablation on the SiC surface react with the HF vapor to generate volatile SiF4 gas, which is then removed by a vacuum pump connected to the protective hood, thereby continuously maintaining the cleanliness of the processed surface.
[0034] (4) Repeat steps (1) to (3) until the integrated online thickness gauge shows that the average thickness of the substrate reaches 100 μm, and the laser thinning process stops.
[0035] (5) The SiC substrate thinned in step (4) is transferred to a chemical mechanical polishing (CMP) device and a polishing slurry containing nanoscale silica abrasive is used for final precision polishing until the surface roughness Ra ≤ 1 nm, and a high-quality flat surface is obtained.
[0036] Example 2:
[0037] (1) A 2-inch diamond substrate with an initial thickness of 300 μm was placed and fixed on a high-precision Z-axis stage for initial focusing. A picosecond laser was started as the main laser source, and the laser parameters were set as follows: laser wavelength 355 nm, pulse width 10 ps, single pulse energy 50 μJ, scanning spacing 15 μm, scanning speed 400 mm / s, and repetition frequency 500 kHz. In this embodiment, an alternating mode was used for processing, with each 5 μm thinning defined as one processing-cleaning cycle. After the laser was started, the substrate surface was scanned along an S-shaped path to perform the first round of ablation thinning.
[0038] (2) During the scanning ablation process in step (1), a laser interferometer monitors the surface position of the diamond substrate in real time and feeds the data back to the central control system. The central control system instructs the high-precision Z-axis stage to make fine adjustments based on the position change to ensure that the laser focus remains stable on the surface of the substrate to be processed.
[0039] (3) When the cumulative thickness reduction reaches 5 μm based on the number of ablation layers, the main laser pauses, and in-situ liquid phase cleaning is performed alternately. The XY platform moves, allowing the recently processed area to pass sequentially through a micro-droplet jet array composed of piezoelectric inkjet heads. The printheads precisely spray standard cleaning solution SC-1 (ammonia-hydrogen peroxide mixture) onto the surface, utilizing its strong oxidizing properties to ablate the graphite phase and other phases generated by the laser ablation on the diamond surface. 2 Carbon byproducts are removed by oxidation. Immediately afterwards, a high-speed nitrogen nozzle blows through the area, carrying the waste liquid and residual droplets into a recovery tank, allowing the surface to dry and become clean quickly.
[0040] (4) Repeat the processing-cleaning alternating cycle from (1) to (3) until the substrate reaches the target thickness of 80 μm.
[0041] (5) The diamond substrate thinned in step (4) is placed in a plasma-assisted polishing (PAP) device and subjected to final precision polishing in a plasma environment containing hydrogen and oxygen to obtain a high-quality flat surface.
[0042] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.
Claims
1. A composite thinning method for semiconductor substrates using laser dynamic focusing and in-situ cleaning, characterized in that... Includes the following steps: (1) Place the semiconductor substrate on the work platform, start the laser and set the laser parameters so that the laser scans and ablates the surface of the semiconductor substrate to be processed according to the preset path to achieve layer-by-layer thinning. (2) During the scanning ablation process in step (1), a dynamic focusing operation is performed in parallel. The dynamic focusing operation includes: using a position sensing module to monitor the position of the surface to be processed in real time and obtain the position change amount; and according to the position change amount, dynamically adjusting the focal position of the main laser beam through the execution module to compensate for the focal drift caused by the reduction of substrate thickness. (3) During the scanning ablation process in step (1), in-situ surface treatment operations are performed synchronously or alternately. The in-situ surface treatment operations are used to remove the oxide layer and other ablation byproducts generated on the surface to be processed during the scanning ablation process. (4) Repeat steps (1) to (3) until the thickness of the semiconductor substrate reaches the preset target thickness; (5) Perform chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP) on the semiconductor substrate after step (4) to obtain an atomically flat surface.
2. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The semiconductor substrate in step (1) is either silicon carbide or diamond.
3. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The laser parameters in step (1) are: laser wavelength 355-1064nm, pulse width 100fs-10ns, single pulse energy 1μJ-200μJ, scanning spacing 5-20μm, scanning speed 50mm / s-500mm / s, and repetition frequency 100kHz-1MHz.
4. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, In step (2), the position sensing module is at least one of a confocal displacement sensor, a laser interferometer, or a white light interferometer.
5. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The execution module in step (2) achieves dynamic adjustment of the focus by one of the following methods: moving the Z-axis stage that carries the hard and brittle substrate or moving the Z-axis focusing lens group in the main laser beam optical path.
6. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The in-situ surface treatment operation in step (3) adopts a gas phase cleaning method, including: while scanning with laser, introducing an auxiliary gas into the surface to be processed; under the thermal or photochemical action of the laser, the auxiliary gas reacts chemically with the surface modification layer (such as an oxide layer or a graphitized layer) of the surface to be processed, generating volatile products that are then removed.
7. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 6, characterized in that, When the semiconductor substrate is silicon carbide, the auxiliary gas is hydrogen fluoride (HF) vapor or sulfur hexafluoride (SF6). + The auxiliary gas is at least one of oxygen (O2), hydrogen (H2), or a mixture thereof, when the hard and brittle substrate is diamond, and is used to remove the graphitized layer by oxidation or hydrogen etching.
8. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The in-situ surface treatment operation in step (3) adopts a liquid phase cleaning method, including: precisely spraying chemical cleaning liquid onto the surface to be processed or its adjacent area through a micro-droplet spraying device, and then removing residual liquid through an air blowing and recovery device.
9. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 8, characterized in that, The chemical cleaning solution is at least one of hydrofluoric acid (HF) solution, buffered oxide etching solution (BOE), or standard cleaning solution (SC-1 / SC-2).
10. The composite thinning method for laser dynamic focusing and in-situ cleaning of semiconductor substrates according to claim 1, characterized in that, The in-situ surface treatment operation in step (3) is performed synchronously and continuously with the scanning ablation operation in step (1), or alternately after each preset area or preset thickness of scanning ablation is completed.