Composite surface finish machining method for hard and brittle semiconductor wafer
By combining reactive plasma pre-modification with femtosecond laser scanning, the problems of low efficiency and high cost in the surface finishing of superhard materials have been solved, achieving efficient and low-cost non-destructive surface processing, which is applicable to silicon carbide and diamond wafers.
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 technologies suffer from low efficiency, high cost, and difficulty in obtaining damage-free surfaces when processing superhard materials such as silicon carbide and diamond. In particular, traditional chemical mechanical polishing processes are inefficient, costly, and prone to introducing new lattice damage.
By combining reactive plasma pre-modification with femtosecond laser scanning, a pre-modified layer is formed. Then, the damaged layer is selectively removed by the cold ablation effect of the femtosecond laser, and an atomically smooth surface is obtained through ultra-fine polishing.
It enables efficient and low-cost finishing of superhard materials, significantly shortens the processing cycle, reduces production costs, and obtains high-quality surfaces free from thermal damage and mechanical stress.
Smart Images
Figure CN121815968A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of laser-assisted processing technology, specifically relating to a composite surface finishing method for hard and brittle semiconductor wafers. Background Technology
[0002] Silicon carbide and diamond, as representative materials of ultra-hard wide-bandgap semiconductors, hold an irreplaceable strategic position in power electronics, radio frequency communications, quantum computing, and extreme environment applications. To maximize their performance, these wafers must achieve atomically flat surfaces free of subsurface damage during fabrication. Standard processing typically relies on a final chemical mechanical polishing (CMP) after fine grinding to achieve this goal.
[0003] However, CMP processes face common and severe challenges when processing these two superhard materials: 1. Efficiency and cost issues: The extremely high hardness of single-crystal silicon carbide and single-crystal diamond results in very low material removal rates in CMP, leading to long processing times and low production efficiency. Simultaneously, it requires large quantities of expensive special polishing fluids and pads, making CMP a major burden on the overall wafer manufacturing cost; 2. Limitations on diamond: Diamond has extremely high chemical inertness, and traditional CMP processes have negligible chemical corrosion effects on it, relying mainly on mechanical grinding. This is not only less efficient but also prone to introducing new lattice damage, making it difficult to obtain ideal surface quality; 3. Process complexity: CMP involves complex process control and wastewater treatment, resulting in a cumbersome process that is environmentally unfriendly.
[0004] Therefore, there is an urgent need in this field for an innovative technology that can efficiently and cost-effectively perform high-quality surface finishing on ultrahard semiconductor wafers in order to break through the technical bottlenecks of traditional CMP. Summary of the Invention
[0005] (I) Purpose of the Invention
[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite surface finishing method for hard and brittle semiconductor wafers, which aims to achieve efficient and precise removal of the damaged layer of ultra-hard wafers after fine grinding, and finally obtain an atomically smooth and damage-free surface, thereby providing a brand-new surface finishing solution for high-end applications of silicon carbide and diamond.
[0007] (II) Technical Solution
[0008] To achieve the above objectives, the present invention provides a composite surface finishing method for hard and brittle semiconductor wafers. This method is used to process hard and brittle semiconductor wafers after fine grinding and includes the following steps performed in sequence:
[0009] (1) Select the appropriate process gas according to the material type of the wafer, and use the reactive plasma generated by the process gas to scan the surface to be processed of the finely ground wafer, and form a pre-modified layer with a loose physical structure and a thickness of micrometers on the surface to be processed.
[0010] (2) Place the pre-modified wafer from step (1) in an inert gas protection or vacuum environment, and set the femtosecond laser parameters so that the laser energy density is higher than the ablation threshold of the pre-modified layer and lower than the ablation threshold of the wafer body material.
[0011] (3) Using a femtosecond laser with the energy density set in step (2), the pre-modified layer is scanned and the pre-modified layer is precisely and selectively removed through the cold ablation effect to obtain a preliminary smooth surface;
[0012] (4) Perform ultra-fine polishing on the wafer after step (3) to remove nanoscale residual undulations and subsurface micro-damage to obtain an atomically smooth surface.
[0013] Further, in step (1), the semiconductor wafer is either silicon carbide or diamond. When the wafer is silicon carbide, the process gas is a mixed gas containing fluorine or chlorine, and the pre-modified layer is a loosely structured layer with silicon depletion and rich in amorphous carbon. When the wafer is diamond, the process gas is oxygen or argon, and the pre-modified layer is a graphite phase (sp). 2 Carbon-modified layer;
[0014] Furthermore, the thickness of the pre-modified layer formed in step (1) is 1-5 micrometers;
[0015] Furthermore, the reactive plasma in step (1) is atmospheric pressure plasma or low vacuum plasma;
[0016] Furthermore, the inert gas protective environment in step (2) is a nitrogen or argon atmosphere;
[0017] Furthermore, the femtosecond laser parameters in step (2) include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning interval, and number of scans, with values set to 200fs-800fs, 532nm-1064nm, 1W-5W, 100KHz-1MHz, 100mm / s-1000mm / s, 20μm-50μm, and 1-5 scans, respectively.
[0018] Furthermore, the ultra-fine polishing process in step (4) is chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP).
[0019] Furthermore, the thickness of the material removed in step (4) is less than 1 micrometer.
[0020] (III) Beneficial Effects
[0021] The above-described technical solution of the present invention has the following beneficial technical effects:
[0022] (1) Strong applicability: This invention successfully applies a process framework to two superhard materials with large differences in properties, silicon carbide and diamond, through a differentiated plasma pre-modification strategy, providing a universal and efficient finishing solution.
[0023] (2) Significant efficiency and cost advantages: The efficient plasma and femtosecond laser steps replace most of the time-consuming and expensive CMP processes, greatly shortening the processing cycle and reducing production costs.
[0024] (3) Excellent surface quality: The “cold processing” and “selective removal” characteristics of femtosecond lasers avoid introducing new thermal damage and mechanical stress when removing the damaged layer, which provides a foundation for obtaining a high-quality surface. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of the process flow of the present invention.
[0026] Figure 2 The image shown is the surface AFM image obtained after processing in Example 1. Detailed Implementation
[0027] 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.
[0028] Example 1: This example describes a method for composite surface finishing of a finely ground 6-inch silicon carbide (SiC) wafer. The initial state of the wafer is: thickness 350 μm, surface roughness Ra of approximately 50 nm, and the depth of its subsurface damage layer is measured to be approximately 1.5 μm.
[0029] (1) Based on the type of wafer material being silicon carbide, a mixed gas of NF3 / He (volume ratio 1:50) was selected as the process gas. The wafer was placed in an atmospheric pressure plasma processing system, and reactive plasma was generated using a dielectric barrier discharge power supply. The plasma was then reciprocated at a speed of 100 mm / s on the wafer surface to form a loose layer on the wafer surface that is depleted of silicon and rich in amorphous carbon, with a thickness of approximately 2 μm, as a pre-modification layer.
[0030] (2) The pre-modified wafer from step (1) is transferred to the processing chamber and filled with nitrogen for protection, forming an inert gas protective environment. The femtosecond laser parameters are set as follows: laser pulse width 300 fs, laser wavelength 532 nm, pulse frequency 100 kHz, scanning speed 800 mm / s, and scanning spacing 30 μm. Through previous experimental calibration, the ablation threshold of this pre-modified layer is approximately 0.2 J / cm. 2 The ablation threshold of SiC bulk is approximately 0.8 J / cm. 2 Based on the set laser parameters, the laser energy density was precisely controlled at 0.5 J / cm². 2 This value is higher than the ablation threshold of the pre-modified layer but lower than the ablation threshold of the SiC wafer body.
[0031] (3) Using a femtosecond laser with the energy density set in step (2), a high-speed galvanometer system is used to perform a comprehensive scan of the entire wafer surface. At this energy density, the loose pre-modified layer is efficiently ablated and removed, while when the laser reaches the underlying SiC substrate, it produces almost no removal effect because the energy is below its ablation threshold, thus achieving precise and selective removal. After this step, the pre-modified layer is completely removed, and the wafer surface roughness is significantly reduced.
[0032] (4) The wafer processed in step (3) is transferred to a standard chemical mechanical polishing (CMP) device for ultra-fine polishing to remove about 0.5 μm of material, and finally obtains the silicon carbide wafer product.
[0033] Example 2: This example describes a method for composite surface finishing of a finely ground 2-inch diamond wafer. The initial damage layer depth of the wafer is approximately 1.0 μm.
[0034] (1) Based on the type of wafer material being diamond, oxygen was selected as the process gas. The wafer was placed in a low-vacuum (10 Pa) plasma processing system, and oxygen plasma was generated using an inductively coupled plasma (ICP) source to treat the wafer surface, forming a graphite phase (sp) layer with a thickness of approximately 1.2 μm on the surface. 2 Carbon-modified layer.
[0035] (2) The pre-modified wafer from step (1) is transferred to a vacuum processing chamber (<1 Pa). The femtosecond laser parameters are set as follows: laser pulse width 400 fs, laser wavelength 1064 nm, pulse frequency 500 kHz, scanning speed 500 mm / s, and scanning spacing 40 μm. Through experimental calibration, the ablation threshold of this graphitized modified layer is approximately 0.1 J / cm. 2 The ablation threshold of the diamond matrix is approximately 1.3 J / cm. 2 Based on the set laser parameters, the laser energy density was precisely controlled at 0.6 J / cm².2 This value also satisfies the condition of being higher than the ablation threshold of the pre-modified layer and lower than the ablation threshold of the diamond wafer body.
[0036] (3) The wafer surface is scanned using a femtosecond laser with the energy density set in step (2). The graphitized modified layer is efficiently and thermally removed, exposing the pure diamond surface underneath.
[0037] (4) The wafer processed in step (3) is transferred to a plasma-assisted polishing (PAP) device for ultra-fine polishing. Final stress-free polishing is performed in a hydrogen plasma environment to remove nanoscale residual undulations. The resulting diamond wafer has no subsurface damage and achieves a high-quality flat surface.
[0038] 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 method for composite surface finishing of hard and brittle semiconductor wafers, characterized in that, This method is used to process hard and brittle semiconductor wafers after fine grinding, and includes the following steps performed in sequence: (1) Select the appropriate process gas according to the material type of the wafer, and use the reactive plasma generated by the process gas to scan the surface to be processed of the finely ground wafer, and form a pre-modified layer with a loose physical structure and a thickness of micrometers on the surface to be processed. (2) Place the pre-modified wafer from step (1) in an inert gas protection or vacuum environment, and set the femtosecond laser parameters so that the laser energy density is higher than the ablation threshold of the pre-modified layer and lower than the ablation threshold of the wafer body material. (3) Using a femtosecond laser with the energy density set in step (2), the pre-modified layer is scanned and the pre-modified layer is precisely and selectively removed through the cold ablation effect to obtain a preliminary smooth surface; (4) Perform ultra-fine polishing on the wafer after step (3) to remove nanoscale residual undulations and subsurface micro-damage to obtain an atomically smooth surface.
2. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, In step (1), the semiconductor wafer is either silicon carbide or diamond. When the wafer is silicon carbide, the process gas is a mixed gas containing fluorine or chlorine, and the pre-modified layer is a loosely structured layer with silicon depletion and rich in amorphous carbon. When the wafer is diamond, the process gas is oxygen or air, and the pre-modified layer is a graphite phase (sp). 2 Carbon-modified layer.
3. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The thickness of the pre-modified layer formed in step (1) is 1-5 micrometers.
4. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The reactive plasma in step (1) is atmospheric pressure plasma or low vacuum plasma.
5. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The inert gas protective environment in step (2) is a nitrogen or argon atmosphere.
6. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The femtosecond laser parameters in step (2) include laser pulse width, laser wavelength, laser power, pulse frequency, scanning speed, scanning interval, and number of scans, which are set to 200fs-800fs, 532nm-1064nm, 1W-5W, 100KHz-1MHz, 100mm / s-1000mm / s, 20μm-50μm, and 1-5 scans, respectively.
7. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The ultra-fine polishing process in step (4) is chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP).
8. The composite surface finishing method for hard and brittle semiconductor wafers according to claim 1, characterized in that, The thickness of the material removed in step (4) is less than 1 micrometer.