A method for rapid maskless processing of silicon microstructures

Abstract

The application discloses a method for rapidly processing silicon microstructure without a mask. The method comprises the following steps: firstly, designing a processing file; secondly, forming an ablation area on the surface of a silicon wafer by laser induction; and thirdly, obtaining a silicon wafer containing microstructure by wet etching after twice acid washing. The method can directly form microchannels / chambers on the surface of a single crystal silicon by combining laser direct writing and wet etching, and does not need mask deposition and photolithography process, thereby reducing the process difficulty, shortening the manufacturing time and enabling the microfluidic chip to meet the design requirements.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic chip fabrication technology, specifically relating to a method for rapid maskless fabrication of silicon microstructures. Background Technology

[0002] Microfluidic chips have wide applications in industries such as chemical engineering, pharmaceuticals, and chemical testing. Common materials for manufacturing microfluidic chips include monocrystalline silicon, glass, and engineering plastics. Among them, silicon, with its advantages of high strength, surface inertness, and strong thermal conductivity, was used earlier in the fabrication of microfluidic chips. The manufacture of silicon-based microfluidic chips involves processing microstructures such as microchannels, microcavities, and micropillars on the surface of monocrystalline silicon to enable fluid flow, mixing, and reactions.

[0003] Traditional methods for fabricating these microstructures on single-crystal silicon surfaces primarily involve photolithography and etching processes, requiring customized photomasks, spin-coating photoresist, and deposition of hard masks, resulting in complex procedures. Therefore, finding a simpler and less technically demanding method is a pressing issue for those skilled in the art. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a maskless, rapid fabrication method for silicon microstructures. This invention combines laser direct writing and wet etching to directly form microchannels / cavities on the surface of single-crystal silicon, eliminating the need for mask deposition and photolithography processes. This reduces process complexity, shortens manufacturing time, and enables the fabrication of microfluidic chips that meet design requirements.

[0005] The technical solution of the present invention is as follows:

[0006] A method for rapid maskless fabrication of silicon microstructures, the method comprising the following steps:

[0007] (1) Design the layout of microstructures and laser processing paths on silicon wafers in a computer program and generate processing files;

[0008] (2) Place the silicon wafer on the processing platform, purge it with nitrogen, turn on the laser processing system, import the processing file, and induce the formation of an ablation area on the surface of the silicon wafer by laser.

[0009] (3) Remove the silicon wafer, purge and clean it with nitrogen, perform acid washing twice, and then clean and purge with nitrogen again;

[0010] (4) After wet etching, cleaning and nitrogen purging, a silicon wafer containing microstructure is obtained.

[0011] Furthermore, the silicon wafer is monocrystalline silicon, and the monocrystalline silicon has a crystal orientation of 100°.

[0012] Furthermore, the microstructure includes microchannels and microcavities; the depth of the microstructure is 0.05-0.5 mm.

[0013] Furthermore, in step (1), the processing path is an S-shaped path.

[0014] Furthermore, in step (2), the power of the laser-induced laser is 3-11.5W, the frequency is 20-80kHz, and the scanning rate is 40-120mm / s.

[0015] Further, in step (3), the first pickling in the two pickling processes involves immersing the silicon wafer in a hydrofluoric acid solution for pickling, and the second pickling involves immersing the silicon wafer in an HPM solution or an SPM solution for pickling.

[0016] Further, the hydrofluoric acid solution is an aqueous solution of hydrogen fluoride with a volume fraction of 5-20%; the HPM solution includes hydrogen chloride and hydrogen peroxide, with the hydrogen chloride having a volume fraction of 5-20% and the hydrogen peroxide having a volume fraction of 5-15%; the SPM solution includes sulfuric acid and hydrogen peroxide, with the sulfuric acid having a volume fraction of 10-30% and the hydrogen peroxide having a volume fraction of 5-15%; the first pickling is performed at room temperature for 1-5 minutes; the second pickling is performed at 20-80°C for 10-60 minutes.

[0017] Further, in step (4), the wet etching solution includes one of potassium hydroxide solution and tetramethylammonium hydroxide solution; the mass fraction of the potassium hydroxide solution is 20-50%, and the mass fraction of the tetramethylammonium hydroxide solution is 10-40%.

[0018] Furthermore, in step (4), the temperature of the wet etching process is 60-100℃ and the time is 20-200min.

[0019] Furthermore, all cleaning processes are ultrasonic cleaning, with a power of 240-360W and a time of 5-15 minutes; the nitrogen purging time is 1-2 minutes.

[0020] The beneficial technical effects of this invention are as follows:

[0021] The method described in this invention utilizes laser to directly induce the formation of ablation regions on the surface of single-crystal silicon, followed by wet etching using an alkaline solution to remove the ablation regions. Because the ablation regions react rapidly with the etching solution, while the unablated regions react more slowly, the etching solution exhibits strong selectivity towards the laser-induced regions. Therefore, this difference in reaction selectivity can be used to form microchannels and microcavities on the silicon surface.

[0022] This invention combines laser direct writing and wet etching to directly fabricate microchannels / cavities on the surface of single-crystal silicon, eliminating the need for mask deposition and photolithography processes, thus shortening manufacturing time. By investigating the effects of different laser parameters on the ablation depth of the silicon wafer, this invention shows that the ablation depth is only related to the laser power and is independent of the laser frequency and scanning speed. Further optimization of the laser power yields a suitable ablation depth. Furthermore, this invention optimizes the cleaning conditions after laser treatment of the silicon wafer, including the type of cleaning solution, cleaning temperature, and cleaning time, reducing the roughness of the single-crystal silicon after laser treatment. This solves problems such as uneven boundaries and silicon particle adhesion after laser ablation that affect subsequent wet etching, thereby improving the quality of the microchannels / cavities. This invention, through optimized laser parameters and post-laser cleaning conditions, combined with wet etching, fabricates microfluidic chips that meet design requirements. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the maskless rapid processing technology for silicon microstructures according to the present invention.

[0024] Figure 2 This is a laser processing path diagram of Embodiment 1 of the present invention.

[0025] Figure 3 The graph shows the relationship between the ablation depth and the laser frequency of the silicon wafers containing microstructures prepared in Examples 1-7 of this invention.

[0026] Figure 4 This is a graph showing the relationship between the ablation depth and the laser scanning speed of the silicon wafers containing microstructures prepared in Examples 1 and 8-11 of this invention.

[0027] Figure 5 The graph shows the relationship between ablation depth and laser power for the silicon wafers containing microstructures prepared in Examples 1, 12-14 and Comparative Examples 1-2 of this invention.

[0028] Figure 6 The images show the cross-sectional morphology of the ablation region of the silicon wafer obtained after step (3) in Examples 1, 12-14 and Comparative Examples 1-2 of the present invention.

[0029] Figure 7 The roughness diagrams of silicon wafers obtained after step (3) in Examples 1 and 15-17 of the present invention are shown.

[0030] Figure 8 The roughness map of the silicon wafer obtained after step (3) of Embodiment 1 and Embodiments 18-22 of the present invention.

[0031] Figure 9 The images show the surface morphology of the ablation zone of the silicon wafer obtained after step (3) of Examples 1 and 18-19 of the present invention.

[0032] Figure 10 Roughness maps of the ablation region of silicon wafers obtained after step (3) in Embodiments 1, 23, and Comparative Example 3 of the present invention.

[0033] Figure 11 The roughness diagrams of the silicon wafers obtained after step (3) in Examples 23-26 of the present invention are shown.

[0034] Figure 12 The roughness diagrams of silicon wafers obtained after step (3) in Examples 23 and 27-31 of the present invention are shown.

[0035] Figure 13 The images show the surface morphology of the ablation zone of the silicon wafer obtained after step (3) of Examples 23 and 28-29 of the present invention.

[0036] Figure 14 The images show the surface morphology of the un-ablated areas of the silicon wafers obtained after step (3) in Examples 1, 23, and Comparative Examples 3-4 of the present invention.

[0037] In the figure: (a) Surface morphology of the un-ablated area of ​​the silicon wafer obtained after step (3) of Comparative Example 4; (b) Surface morphology of the un-ablated area of ​​the silicon wafer obtained after step (3) of Comparative Example 3; (c) Surface morphology of the un-ablated area of ​​the silicon wafer obtained after step (3) of Example 23; (d) Surface morphology of the un-ablated area of ​​the silicon wafer obtained after step (3) of Example 1.

[0038] Figure 15 The roughness diagrams of the un-ablated areas of silicon wafers obtained after step (3) in Embodiments 1, 23, and Comparative Examples 3-4 of the present invention are shown. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] A method for rapid maskless fabrication of silicon microstructures specifically includes the following steps:

[0042] (1) As Figure 2 As shown, an S-shaped laser processing path pattern, including microchannels and square microcavities, is designed in a computer program. The width of the microchannel is 0.3 mm, and the area of ​​the microcavity is 1 mm². 2 Generate processing files;

[0043] (2) Place the silicon wafer (100 single crystal silicon) on the processing platform, purge with nitrogen for 1.5 minutes, turn on the laser processing system, import the processing file, and induce the formation of an ablation area on the surface of the silicon wafer under laser conditions of 6W power, 50kHz frequency and 80mm / s scanning rate.

[0044] (3) Remove the silicon wafer, purge it with nitrogen for 1.5 min, immerse it in deionized water, and ultrasonically clean it for 10 min at 300 W. Then, immerse it in a 10% HF solution and acid wash it at room temperature for 5 min. Next, immerse it in an SPM solution (containing 10% H2SO4 and 10% H2O2) and acid wash it at 60°C for 30 min. Finally, immerse it in deionized water, ultrasonically clean it for 10 min at 300 W, and purge it with nitrogen for 1.5 min.

[0045] (4) Then use a 35% KOH solution to wet etch at 80°C for 30 min; then immerse in deionized water, ultrasonically clean at 300W for 10 min, and then purge with nitrogen for 1.5 min to obtain a silicon wafer containing microstructure.

[0046] Examples 2-7

[0047] The processing methods of Examples 2-7 are basically the same as those of Example 1, except that the laser frequencies of 20kHz, 30kHz, 40kHz, 60kHz, 70kHz and 80kHz are used in Examples 2-7 instead of the 50kHz laser frequency in Example 1, while the rest remain unchanged.

[0048] Examples 8-11

[0049] The processing methods of Examples 8-11 are basically the same as those of Example 1, except that the laser scanning rates of 40mm / s, 60mm / s, 100mm / s, and 120mm / s in Examples 8-11 are used instead of the 80mm / s laser scanning rate in Example 1, while the rest remain unchanged.

[0050] Examples 12-14

[0051] The processing methods of Examples 12-14 are basically the same as those of Example 1, except that the laser scanning power of Example 1 is replaced by 3W, 9W and 11.5W laser power respectively in Examples 12-14, while the rest remain unchanged.

[0052] Examples 15-17

[0053] The processing methods of Examples 15-17 are basically the same as those of Example 1, except that the second pickling in Examples 15-17 uses temperature conditions of 25°C, 40°C, and 80°C respectively instead of the 60°C temperature condition in the second pickling in Example 1, while the rest remain unchanged.

[0054] Examples 18-22

[0055] The processing methods of Examples 18-22 are basically the same as those of Example 1, except that the second pickling in Examples 18-22 uses time conditions of 10 min, 20 min, 40 min, 50 min, and 60 min respectively to replace the 30 min time condition of the second pickling in Example 1, while the rest remain unchanged.

[0056] Example 23

[0057] The processing method of Example 23 is basically the same as that of Example 1, except that the second pickling in Example 23 uses HPM solution (containing 10% HCl and 10% H2O2 by volume) instead of SPM solution in Example 1, and the rest remains unchanged.

[0058] Examples 24-26

[0059] The processing methods of Examples 24-26 are basically the same as those of Example 24, except that the second pickling in Examples 24-26 uses temperature conditions of 25°C, 40°C, and 80°C respectively instead of the 60°C temperature condition in the second pickling in Example 20, while the rest remain unchanged.

[0060] Examples 27-31

[0061] The processing methods of Examples 27-31 are basically the same as those of Example 24, except that the second pickling in Examples 27-31 uses time conditions of 10 min, 20 min, 40 min, 50 min, and 60 min respectively to replace the 30 min time condition of the second pickling in Example 1, while the rest remain unchanged.

[0062] Comparative Examples 1-2

[0063] The processing method of Comparative Example 1 is basically the same as that of Example 1, except that Comparative Examples 1 and 2 use laser power of 0.3W and 12W respectively to replace the laser power of 6W in Example 1, while the rest remain unchanged.

[0064] Comparative Example 3

[0065] The processing method of Comparative Example 3 is basically the same as that of Example 1, except that the second SPM solution acid washing step is omitted in Comparative Example 3, while the rest remains unchanged.

[0066] Comparative Example 4

[0067] The processing method of Comparative Example 4 is basically the same as that of Example 1, except that the two acid washing steps of HF solution and SPM solution in Comparative Example 3 are omitted, while the rest remain the same.

[0068] Comparative Example 5

[0069] The processing method of Comparative Example 5 is basically the same as that of Example 1, except that the second pickling in Comparative Example 4 uses a temperature of 10°C instead of the 60°C temperature in the second pickling in Example 1, while the rest remains unchanged.

[0070] Comparative Example 6

[0071] The processing method of Comparative Example 6 is basically the same as that of Example 23, except that the second pickling of Comparative Example 5 uses a temperature of 10°C instead of the 60°C temperature of the second pickling in Example 23, while the rest remains unchanged.

[0072] Test case

[0073] (1) The effect of laser-induced conditions on the ablation depth of silicon wafers

[0074] The ablation depth of the silicon wafers containing microstructures prepared in Examples 1-7 of this invention was measured using a Keyence shape measurement laser microscope VK-X100K, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the ablation depth range does not fluctuate much within the laser frequency range of 20-80kHz. Therefore, the laser frequency has no significant effect on the depth of microstructures on silicon wafers.

[0075] The ablation depth of the silicon wafers containing microstructures prepared in Examples 1 and 8-11 of this invention was measured using a Keyence shape measurement laser microscope VK-X100K. The results are as follows: Figure 4 As shown. From Figure 4 It can be seen that the ablation depth range does not fluctuate much at laser scanning speeds of 40-120 mm / s. Therefore, the laser scanning speed has no significant effect on the depth of microstructures on silicon wafers.

[0076] The silicon wafers containing microstructures prepared in Examples 1, 12-14 and Comparative Examples 1-2 of this invention were used to detect their ablation depth using a Keyence shape measurement laser microscope VK-X100K. Cross-sectional morphology images of the ablation region of the silicon wafers obtained after step (3) were also taken. The results are as follows: Figure 5 , 6 As shown. From Figure 5It can be seen that as the laser power increases from 3W to 11.5W, the ablation depth of the silicon wafer gradually increases; simultaneously, from Figure 6 It can be seen that low-power conditions (0.3W laser ablation) are insufficient to induce ablation on the silicon surface, making it difficult to form deep regions. When the laser power is too high, reaching 12W, the ablation region on the silicon wafer becomes too deep, easily leading to corrosion penetration and the formation of vias. Therefore, laser power is the main controlling factor for the ablation region depth, and the optimal power range for obtaining the required microchannel depth is 3-11.5W.

[0077] (2) Effect of pickling conditions on the roughness and surface morphology of silicon wafers

[0078] The silicon wafers obtained after step (3) of Examples 1, 15-17, and 23-26 of this invention were subjected to roughness testing using a Keyence shape measurement laser microscope VK-X100K. The results are as follows: Figure 7 , 11 As shown. From Figure 7 , 11 It can be seen that when using HPM or SPM solutions for secondary pickling, the roughness of the silicon wafer gradually decreases as the temperature increases from 25°C to 60°C, reaching its minimum at 60°C, resulting in the best cleaning effect. When the temperature exceeds 60°C, the roughness of the silicon wafer increases again, which may be due to the excessively rapid evaporation of H2O2 in the HPM or SPM solutions caused by excessively high temperatures. In addition, the roughness of the silicon wafers obtained after step (3) of Comparative Examples 5-6 was measured using a Keyence shape measurement laser microscope VK-X100K, and the roughness Ra values ​​were 3.273 and 4.296, respectively. Therefore, the cleaning effect of secondary pickling at excessively low temperatures is poor.

[0079] The silicon wafers obtained after step (3) of Examples 1, 23, and Comparative Example 3 of this invention were tested for roughness of the ablation region using a Keyence shape measurement laser microscope VK-X100K. The results are as follows: Figure 10 As shown. From Figure 10 It can be seen that the roughness of the ablation area treated with HPM solution or SPM solution is lower. The higher roughness of the ablation area is mainly caused by the debris and unstable particle agglomeration generated after laser ablation. This result indicates that HPM solution and SPM solution have a good cleaning effect on debris and particles in the ablation area, with SPM solution having a slightly better cleaning effect.

[0080] The silicon wafers obtained after step (3) of Examples 1, 23, and Comparative Examples 3-4 of this invention were examined using a Keyence shape measurement laser microscope VK-X100K to detect the surface morphology and roughness of the unablated areas. The results are as follows: Figure 14 , 15 As shown. From Figure 14It can be seen that after etching, the sample only washed with water showed some corrosion pits and black spots on its surface. This is because the original natural oxide layer on the sample surface provided some protection to the un-electrode areas. The natural oxide layer was removed after treatment with HF solution alone, which weakened the protective effect on the un-electrode areas, resulting in more corrosion pits and black spots. After treatment with HPM solution or SPM, an oxide layer was formed on the un-electrode surface, providing better protection, with SPM solution treatment showing even better protection. The roughness of the un-electrode areas after etching was characterized. Figure 15 The results also proved this point: the roughness of the un-ablated surface of the silicon wafer treated with HPM solution or SPM solution was significantly reduced compared to water washing and HF solution treatment alone.

[0081] The silicon wafers obtained after step (3) of Examples 1, 18-22, 23, and 27-31 of this invention were subjected to roughness testing using a Keyence shape measurement laser microscope VK-X100K. The results are as follows: Figure 8 , 12 As shown. From Figure 8 It can be seen that when using SPM solution for secondary pickling, the roughness of the silicon wafer gradually decreases as the processing time increases from 10 min to 20 min, but the roughness increases again after the time exceeds 20 min. Figure 12 It can be seen that when using HPM solution for secondary pickling, the roughness of the silicon wafer gradually decreases as the processing time increases from 20 min to 40 min, but the roughness of the silicon wafer increases again after the time exceeds 40 min.

[0082] Meanwhile, the silicon wafers obtained after step (3) of Examples 1, 18-19, 23, and 28-29 of this invention were examined using a Keyence shape measurement laser microscope VK-X100K to obtain surface morphology images of their ablation regions. The results are as follows: Figure 9 , 13 As shown. From Figure 9 It can be seen that after 20 minutes of SPM solution treatment, most of the particle contamination on the surface of the ablated area of ​​the silicon wafer was removed, achieving a good cleaning effect; from Figure 13 It can be seen that when the HPM solution treatment time is less than 40 minutes, there is particulate contamination on the surface of the silicon wafer ablation area, and the cleaning effect is not good. When the HPM solution treatment time is 40 minutes, most of the particulate contamination on the surface of the silicon wafer ablation area is removed, achieving a better cleaning effect.

[0083] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for rapid maskless fabrication of silicon microstructures, characterized in that, The method includes the following steps: (1) Design the layout of microstructures and laser processing paths on silicon wafers in a computer program and generate processing files; (2) Place the silicon wafer on the processing platform, purge it with nitrogen, turn on the laser processing system, import the processing file, and induce the formation of an ablation area on the surface of the silicon wafer by laser. (3) Remove the silicon wafer, purge and clean it with nitrogen, then perform acid washing twice, and then clean and purge with nitrogen again; (4) After wet etching, cleaning and nitrogen purging, a silicon wafer containing microstructure is obtained; The power induced by the laser is 3-11.5 W; In step (3), the first pickling is to immerse the silicon wafer in a hydrofluoric acid solution for pickling, and the second pickling is to immerse the silicon wafer in an HPM solution or an SPM solution for pickling. HPM and SPM solutions have a cleaning effect on debris and particles in the ablation zone. The first pickling time is 1-5 min; the second pickling temperature is 20-80 ℃ and the time is 10-60 min; The hydrofluoric acid solution is an aqueous solution of hydrogen fluoride with a volume fraction of 5-20%; the HPM solution includes hydrogen chloride and hydrogen peroxide, with the hydrogen chloride having a volume fraction of 5-20% and the hydrogen peroxide having a volume fraction of 5-15%; the SPM solution includes sulfuric acid and hydrogen peroxide, with the sulfuric acid having a volume fraction of 10-30% and the hydrogen peroxide having a volume fraction of 5-15%. In step (4), the wet etching solution includes one of potassium hydroxide solution and tetramethylammonium hydroxide solution; the mass fraction of potassium hydroxide solution is 20-50%, and the mass fraction of tetramethylammonium hydroxide solution is 10-40%.

2. The method according to claim 1, characterized in that, The silicon wafer is monocrystalline silicon, and the monocrystalline silicon has a crystal orientation of 100°.

3. The method according to claim 1, characterized in that, The microstructure includes microchannels and microcavities; the depth of the microstructure is 0.05-0.5 mm.

4. The method according to claim 1, characterized in that, In step (1), the processing path is an S-shaped path.

5. The method according to claim 1, characterized in that, In step (2), the frequency is 20-80 kHz and the scan rate is 40-120 mm / s.

6. The method according to claim 1, characterized in that, In step (4), the temperature of the wet etching process is 60-100℃ and the time is 20-200 min.

7. The method according to claim 1, characterized in that, All cleaning processes were performed using ultrasonic cleaning with a power of 240-360W and a time of 5-15 minutes; the nitrogen purging process was performed for 1-2 minutes.

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