A method for dry etching silicon nitride with extremely low power
By employing an ultra-low power dry etching method, combined with composite etching gas and modified substrate, the problems of lattice distortion and high energy consumption caused by high power etching are solved, achieving low-damage, high-selectivity and high-efficiency etching, which is suitable for high-precision processes of semiconductor and MEMS devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEFEI IC VALLEY MICROELECTRONICS CO LTD
- Filing Date
- 2026-03-16
- Publication Date
- 2026-05-26
AI Technical Summary
Existing dry etching technology for silicon nitride suffers from lattice distortion, thermal leakage, contradiction between etching rate and selectivity, high energy consumption, and surface residue and roughness issues at high power, which cannot meet the high precision requirements of semiconductor devices.
The method employs an ultra-low power dry etching process, which utilizes composite etching gas, pulsed RF power supply, and multi-field coupling technology, combined with a modified substrate, to achieve low-damage, high-selectivity, and high-efficiency etching. This includes the synergistic effect of fluorine-containing gas, passivation gas, and activity-enhancing gas, along with temperature and pressure control, and real-time monitoring and feedback adjustment.
It achieves low power consumption, low damage, high speed and high selectivity etching at extremely low power, and is suitable for silicon nitride layers of different thicknesses and types, improving the surface quality and device reliability after etching and reducing equipment maintenance costs.
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Figure CN121843442B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon nitride etching technology, specifically a method for dry etching silicon nitride with extremely low power. Background Technology
[0002] Silicon nitride (SiN) plays a crucial role as a key functional material in semiconductor devices, serving as a gate dielectric, shallow trench isolation (STI), and interconnect passivation. In MEMS, it is used as a structural layer and sacrificial layer, and in optical devices, it acts as a high-reflectivity / anti-reflectivity thin film. Dry etching is the only feasible technique for patterning SiN, but its process window is directly related to device performance.
[0003] Existing technologies often suffer from the following drawbacks:
[0004] High power causes multi-dimensional damage: In traditional processes with power of 50-300W, high-energy ions (energy ≥50eV) in the plasma bombard the silicon nitride lattice, causing surface lattice distortion (distortion rate >5%). At the same time, the wafer temperature rises to 80-150℃, causing thermal leakage in ultra-thin substrates (<5nm) (leakage current increases by 1-2 orders of magnitude), which is particularly fatal to 3nm process GAA (gate all around) devices.
[0005] The contradiction between selectivity and etching rate: To improve selectivity, traditional processes need to increase the proportion of passivation gas, but this will cause the etching rate to drop to 50-80nm / min, which cannot meet the mass production cycle (requiring ≥100nm / min); if the power guarantee rate is increased, the selectivity will drop to 5-8:1, resulting in over-etching of the substrate (etching deviation >10%).
[0006] Energy consumption and equipment wear and tear: High-power operation causes the etching machine to consume 0.8-1.2 kWh of energy per wafer, and the annual energy consumption exceeds 100,000 kWh in large-scale production. In addition, the sputtering erosion rate of plasma on the chamber electrodes reaches 0.5-1 μm / thousand wafers, shortening the electrode replacement cycle to 1-2 months and increasing maintenance costs by more than 30%.
[0007] Surface residue and roughness issues: under high power, fluoropolymers containing carbon are prone to incomplete decomposition, with residual amounts reaching 1-5 at%, and physical sputtering leads to surface roughness Ra>1nm, affecting the adhesion of subsequent atomic layer deposition (ALD) films (adhesion decreases by 20-30%) and device packaging reliability.
[0008] Existing low-power attempts (e.g., 30-50W) have an inherent flaw: simply reducing the power leads to a plasma dissociation efficiency of <30%, F Free radical concentration less than 1×10¹ 5 cm -³, the etching rate is only 30-60 nm / min, and the passivation film is easily broken down by high-energy ions, with a selectivity of <10:1, which cannot meet the needs of industrialization.
[0009] Therefore, it is urgent to construct a synergistic optimization system of "gas system - excitation mode - process parameters" to achieve high-rate, high-selectivity, and low-damage etching at extremely low power. Summary of the Invention
[0010] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for dry etching silicon nitride with extremely low power.
[0011] To achieve the above objectives, the present invention provides the following technical solution:
[0012] A method for dry etching silicon nitride with extremely low power includes the following steps:
[0013] S1. Fix the workpiece to be etched on the chuck of the plasma etching machine, close the chamber and evacuate to the chamber background pressure ≤2mTorr. A silicon nitride layer is formed on the surface of the workpiece to be etched, and a modified substrate is provided below the silicon nitride layer.
[0014] S2. Introduce a composite etching gas into the chamber. The composite gas consists of a main etching gas, a passivation gas, and an activation-enhancing gas, wherein the main etching gas accounts for 40-60 vol%, the passivation gas accounts for 20-40 vol%, and the activation-enhancing gas accounts for 5-20 vol%.
[0015] S3. Start the pulsed radio frequency power supply to excite the composite gas to generate plasma. The radio frequency power should be controlled at 20-30W, the pulse frequency at 10-100kHz, the duty cycle at 30-70%, and the plasma density maintained at 1×10⁻⁶. 10 -5×10 11 cm -3 ;
[0016] S4. The reaction pressure in the control chamber is 120-122 mTorr, the chuck temperature (workpiece temperature) is 20-25℃, the temperature fluctuation is ≤±2℃, and the etching time is set to 60-360s according to the thickness of the silicon nitride layer.
[0017] S5. After etching is complete, stop the etching gas supply, evacuate for 30-60 seconds to remove residual active species, and then purge the chamber with inert helium gas for 20-40 seconds until the chamber pressure returns to atmospheric pressure.
[0018] S6. Introduce a mixed gas of O2 and Ar, with a volume ratio of O2 to Ar of 1-2:1 and a total flow rate of 50-100 sccm. Use 10-20W of radio frequency power to generate plasma and ashing for 10-30s to remove residual carbon-containing fluoropolymers from the surface. After ashing, introduce H2 plasma with a flow rate of 30-50 sccm, a power of 5-10W, and a treatment time of 5-10s to repair dangling bonds on the silicon nitride surface and complete the etching.
[0019] Preferably, the main etching gas is a fluorine-containing gas, selected from one or a combination of two of CF4, SF5, NF3, and C2F6, with a mixing ratio of 1-3:1 when two are combined, and the fluorine-to-carbon ratio (F / C) of the main etching gas is ≥3:1.
[0020] Preferably, the passivation gas is selected from one or more combinations of C4F8, C5F8, CHF3, and C3F6, and the fluorine-to-carbon ratio (F / C) of the passivation gas is ≤2.5:1. It is used to form a dense carbon-containing fluoropolymer passivation film with a thickness of 5-20 nm on the etched sidewalls and substrate surface. The activity-enhancing gas is a binary mixture of a rare gas and a hydrogen-containing gas. The rare gas is selected from Ar, He, and Ne, and the hydrogen-containing gas is selected from H2, NH3, and CH4. The mixing ratio of the two is 5-10:1, and the total flow rate of the activity-enhancing gas is 5-40 sccm.
[0021] Preferably, the coupling method of the radio frequency power supply in step S3 is capacitively coupled plasma (CCP); in CCP mode, only the upper electrode provides power.
[0022] Preferably, in step S4, the chamber pressure is controlled by a mass flow controller and a vacuum valve in coordination, with pressure fluctuations of ±2 mTorr; the chuck uses a chiiller back cooling method to ensure that the workpiece temperature uniformity fluctuations are ±1℃.
[0023] Preferably, the total flow rate of the composite etching gas is 35-240 sccm, of which the main etching gas flow rate is 20-120 sccm, the passivation gas flow rate is 10-80 sccm, the activation enhancement gas flow rate is 5-40 sccm, and the gas flow rate stability fluctuation is ±1 sccm.
[0024] Preferably, F is monitored in real time during the etching process using plasma emission spectroscopy. + CF3 + Si + The emission intensity, of which F + 703.7nm, CF3 + 690.1nm, Si + The wavelength is 288.2 nm. When the intensity fluctuation exceeds ±5%, the main etching gas flow rate is adjusted to ±5 sccm and the RF power duty cycle is ±5%.
[0025] Preferably, the silicon nitride layer of the workpiece to be etched has a thickness of 50-3000 nm, including amorphous silicon nitride, polycrystalline silicon nitride, epitaxial silicon nitride, and doped silicon nitride (P-type or N-type), and the density of the silicon nitride layer is 2.8-3.2 g / cm³. 3 When the silicon nitride layer thickness of the workpiece to be etched is 1000-3000nm, a stepped power control strategy is adopted, with the etching power of 30W for the first 50% thickness and 20W for the last 50% thickness, while the passivation gas ratio is increased by 5-10vol.
[0026] Preferably, the preparation of the modified substrate includes the following steps:
[0027] S11. By mass, immerse 80-100 parts of gallium arsenide into 180-200 parts of etching solution A at a temperature of 23-25°C for 80-90 seconds, and then rinse with deionized water for 25-30 seconds.
[0028] S12. Immerse the gallium arsenide cleaned in step S11 into 180-200 parts of etching solution B at a temperature of 23-25°C for 80-90 seconds. After removing it, rinse it with deionized water for 25-30 seconds and then dry it with nitrogen.
[0029] S13. Immerse the gallium arsenide dried in step S12 into 140-150 parts of a 5% ammonium sulfide aqueous solution, and stir at a speed of 100-200 r / min, at a temperature of 38-40℃ for 20-30 min. After removal, wash with oxygen-free water for 25-30 s and then blow dry with nitrogen. After drying, the modified substrate is obtained.
[0030] Etching solution A consists of concentrated sulfuric acid and a 30% hydrogen peroxide solution in a mass ratio of 5-20:1.
[0031] Etching solution B consists of concentrated hydrochloric acid, 30% hydrogen peroxide solution, and deionized water in a mass ratio of 1:1:5-50.
[0032] Preferably, the chamber wall of the plasma etching machine is coated with an alumina layer to reduce the impact of chamber contamination on etching selectivity; the chamber is pretreated before etching by introducing a CF4 / O2 mixed gas at a flow ratio of 3:1, with a power of 30W, and cleaning for 180s.
[0033] Compared with the prior art, the beneficial effects of the present invention are:
[0034] 1. Extremely low power consumption and low damage: power consumption is only 20-30W, and the power consumption of a single wafer is reduced to 0.15-0.3kWh, which is more than 75% lower than traditional processes; wafer temperature ≤25℃, lattice distortion rate <1%, modified substrate leakage current increase ≤10%, fully compatible with 3nm GAA device process.
[0035] 2. Excellent rate and selectivity: With the help of the modified substrate, the etching rate is 50-150nm / min, which meets the mass production cycle (processing ≥30 wafers per hour); the selectivity of silicon / silicon nitride is ≥18:1, the substrate over-etching deviation is ≤5%, and the sidewall erosion problem of high aspect ratio structure (AR≥10:1) is solved.
[0036] 3. Ultra-high surface quality: after etching, the surface roughness Ra is ≤0.4nm, the polymer residue is <0.5at%, the adhesion of the subsequent ALD film is improved by ≥25%, and the pass rate of the reliability test (1000 hours of high temperature and high humidity) after device packaging is improved to over 99%.
[0037] 4. Full-scene adaptability: It can handle silicon nitride layers of different thicknesses and types (amorphous / polycrystalline / epitaxy / doped) from 50 to 3000 nm without changing equipment or making significant adjustments to the process, and has strong compatibility.
[0038] 5. Low implementation cost: No need to modify the core components of the existing ICP / CCP etching machine, only the gas ratio system and RF pulse control software need to be upgraded, resulting in a significant cost advantage for a single unit. Attached Figure Description
[0039] Figure 1 This is a process flow diagram of the ultra-low power dry etching of silicon nitride according to the present invention;
[0040] Figure 2 This is a flowchart illustrating the fabrication process of the modified substrate of this invention. Detailed Implementation
[0041] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0042] Please see Figure 1-2 The present invention provides a technical solution:
[0043] This invention selects a fluorine-containing gas with a high fluorine-to-carbon ratio (F / C ≥ 3:1) as the main etching gas to ensure the presence of fluorine in the plasma. + F · Active species concentration ≥5×1015 cm -3 It undergoes a highly efficient chemical reaction with silicon nitride: Si3N4 + 12F · →3SiF4↑+2N2↑, the generated SiF4 (boiling point -86℃) and N2 are easily volatile and leave no residue;
[0044] The passivation gas is a fluorocarbon compound with a low fluorine-to-carbon ratio (F / C ≤ 2.5:1), which dissociates in plasma to generate a fluorocarbon-containing polymer (-CF2-). n A dense passivation film is formed on the etched sidewalls and substrate surface, which is effective against F · The free radical diffusion blocking efficiency is ≥90%, and it can withstand ion bombardment at low power (ion energy ≤20eV) to avoid substrate erosion;
[0045] The reactivity enhancement gas selection uses rare gases (Ar / He) to increase the dissociation efficiency of the composite gas from <30% in traditional low-power systems to ≥60% through the Penning ionization effect. Hydrogen-containing gases (H2 / NH3) react with C in the plasma... + The reaction produces CH x + Adjust F · / CF x + Proportion, avoid F · Excessive amounts of NH3 can lead to the decomposition of the passivation film. At the same time, NH3 can provide N atoms, which can inhibit the excessive desorption of N elements in silicon nitride and reduce lattice defects.
[0046] Pulse conduction period (duty cycle 30-70%): Radio frequency power is applied instantaneously, and the plasma rapidly reaches a highly active state (density 1×10⁻⁶). 10 -5×10 11 cm -3 ), F · Free radicals react with silicon nitride in an etching process, achieving efficient material removal;
[0047] Pulse shutdown period: power stops, plasma activity decreases, ion bombardment effect weakens, wafer temperature decreases (≤25℃), and at the same time, passivation gas is fully dissociated, forming a uniform passivation film on the etched surface to repair minor damage during conduction.
[0048] A pulse frequency of 10-100kHz is used to match the etching-passivation reaction cycle (10-100μs) to avoid the passivation film being too thick, which would lead to a decrease in the rate, or too thin, which would lead to a deterioration in selectivity.
[0049] Temperature-pressure coupling: The low temperature environment of 20℃ to 25℃ reduces the desorption rate of the passivation film (the desorption activation energy increases from 80kJ / mol to 120kJ / mol), and the low pressure of 122mTorr prolongs the residence time of active species (from 10μs to 50μs). The two work together to improve etching selectivity.
[0050] Power-bias synergy: In ICP mode, low bias (0-5W) reduces ion bombardment energy (≤20eV), avoids lattice damage, and ensures the directional transport of active species.
[0051] Real-time feedback control: By monitoring the concentration of etching species through OES, the gas flow rate and duty cycle are dynamically adjusted to ensure the stability of the etching process (rate fluctuation ≤ ±3%).
[0052] Example 1
[0053] A method for dry etching silicon nitride with extremely low power:
[0054] The modified substrate is prepared before etching:
[0055] S11. Immerse 80g of gallium arsenide in 180g of etching solution A (etching solution A is composed of concentrated sulfuric acid and 30% hydrogen peroxide solution in a mass ratio of 5:1), at a temperature of 23℃ for 80s, and then rinse with deionized water for 25s.
[0056] S12. Immerse the gallium arsenide cleaned in step S11 into 180g of etching solution B (composed of concentrated hydrochloric acid, 30% hydrogen peroxide solution, and deionized water in a mass ratio of 1:1:5), at a temperature of 23°C for 80s. After removal, rinse with deionized water for 25s and then dry with nitrogen.
[0057] S13. The gallium arsenide dried in step S12 is immersed in 140g of 5% ammonium sulfide aqueous solution. The mixture is stirred at 100r / min, at 38℃ for 20min. After removal, it is washed with oxygen-free water for 25s and then dried with nitrogen. The modified substrate is obtained after drying.
[0058] S1. Fix the workpiece to be etched onto the chuck of the plasma etching machine. After closing the chamber, evacuate to a chamber background pressure of 2 mTorr. A silicon nitride layer is formed on the surface of the workpiece. A modified substrate is placed beneath the silicon nitride layer. The thickness of the silicon nitride layer on the workpiece is 50 nm, and the density of the silicon nitride layer is 2.8 g / cm³. 3 The chamber wall of the plasma etching machine is coated with aluminum oxide. Before etching, the chamber is pretreated by introducing a CF4 / O2 mixed gas at a flow ratio of 3:1, with a power of 30W, and cleaning for 180s.
[0059] S2. Introduce a composite etching gas into the chamber. The composite gas consists of a main etching gas (composed of CF4 and C2F6 in a 1:1 ratio, with a flow rate of 20 sccm), a passivation gas (composed of C4F8 in a 10 sccm flow rate), and an activity-enhancing gas (composed of Ar and H2 in a 5:1 ratio, with a flow rate of 5 sccm). The main etching gas accounts for 40 vol%, the passivation gas for 20 vol%, and the activity-enhancing gas for 20 vol%.
[0060] S3. Start the pulsed radio frequency power supply (coupling method is capacitively coupled plasma) to excite the composite gas to generate plasma. The radio frequency power is controlled at 20W, the pulse frequency is 100kHz, the duty cycle is 30%, and the plasma density is maintained at 1×10⁻⁶. 10 cm -3 ;
[0061] S4. The reaction pressure in the control chamber is set to 120 mTorr, the chuck temperature to 20°C, and the etching time is set to 60 s based on the silicon nitride layer thickness. During the etching process, F is monitored in real-time using plasma emission spectroscopy. + CF3 + Si + The emission intensity, of which F + 703.7nm, CF3 + 690.1nm, Si + It is 288.2nm;
[0062] S5. After etching is complete, stop the etching gas supply, evacuate for 30 seconds to remove residual active species, and then purge the chamber with inert helium gas for 20 seconds until the chamber pressure returns to atmospheric pressure.
[0063] S6. Introduce a mixture of O2 and Ar gas with a volume ratio of 1:1 and a total flow rate of 50 sccm. Use 10W of radio frequency power to generate plasma. After ashing for 10s, introduce H2 plasma with a flow rate of 30 sccm, a power of 5W, and a processing time of 5s. After repairing the dangling bonds on the silicon nitride surface, the etching is completed.
[0064] Example 2
[0065] A method for dry etching silicon nitride with extremely low power:
[0066] The modified substrate is prepared before etching:
[0067] S11. Immerse 100g of gallium arsenide in 200g of etching solution A (etching solution A is composed of concentrated sulfuric acid and 30% hydrogen peroxide solution in a mass ratio of 20:1), at a temperature of 25℃ for 90s, and then rinse with deionized water for 30s.
[0068] S12. Immerse the gallium arsenide cleaned in step S11 into 200g of etching solution B (composed of concentrated hydrochloric acid, 30% hydrogen peroxide solution, and deionized water in a mass ratio of 1:1:50), at a temperature of 25°C for 90s. After removal, rinse with deionized water for 30s and then dry with nitrogen.
[0069] S13. Immerse the gallium arsenide dried in step S12 into 150g of 5% ammonium sulfide aqueous solution, stir at 200r / min, at 40℃ for 30min, remove and wash with oxygen-free water for 30s, then blow dry with nitrogen gas to obtain the modified substrate.
[0070] S1. Fix the workpiece to be etched onto the chuck of the plasma etching machine. After closing the chamber, evacuate to a chamber background pressure of 1 mTorr. A silicon nitride layer is formed on the surface of the workpiece. A modified substrate is placed beneath the silicon nitride layer. The thickness of the silicon nitride layer on the workpiece is 2000 nm, and the density of the silicon nitride layer is 3.2 g / cm³. 3 The chamber wall of the plasma etching machine is coated with aluminum oxide. Before etching, the chamber is pretreated by introducing a CF4 / O2 mixed gas at a flow ratio of 3:1, with a power of 30W, and cleaning for 180s.
[0071] S2. Introduce a composite etching gas into the chamber. The composite gas consists of a main etching gas (composed of SF5 and C2F6 in a 3:1 ratio, with a flow rate of 120 sccm), a passivation gas (composed of C5F8 in a 80 sccm flow rate), and an activity-enhancing gas (He and NH3 in a 10:1 ratio, with a flow rate of 40 sccm). The main etching gas accounts for 45 vol%, the passivation gas for 45 vol%, and the activity-enhancing gas for 10 vol%.
[0072] S3. Start the pulsed radio frequency power supply (coupling method is capacitively coupled plasma) to excite the composite gas to generate plasma. The etching power is 30W for the first 50% thickness of the silicon nitride layer of the workpiece to be etched, and 20W for the last 50% thickness. The pulse frequency is 10kHz, the duty cycle is 40%, and the plasma density is maintained at 5×10⁻⁶. 11 cm -3 ;
[0073] S4. The reaction pressure in the control chamber is set to 121 mTorr, the chuck temperature to 23°C, and the etching time is set to 360 s based on the silicon nitride layer thickness. During the etching process, F is monitored in real-time using plasma emission spectroscopy. + CF3 + Si + The emission intensity, of which F + 703.7nm, CF3 +690.1nm, Si + It is 288.2nm;
[0074] S5. After etching is complete, stop the etching gas supply, evacuate for 60 seconds to remove residual active species, and then purge the chamber with inert helium gas for 40 seconds until the chamber pressure returns to atmospheric pressure.
[0075] S6. Introduce a mixture of O2 and Ar gas with a volume ratio of O2 to Ar of 2:1 and a total flow rate of 100 sccm. Use 20W of radio frequency power to generate plasma. After ashing for 30s, introduce H2 plasma with a flow rate of 50 sccm, a power of 10W, and a processing time of 10s. After repairing the dangling bonds on the silicon nitride surface, the etching is completed.
[0076] Example 3
[0077] A method for dry etching silicon nitride with extremely low power:
[0078] The modified substrate is prepared before etching:
[0079] S11. Immerse 90g of gallium arsenide in 190g of etching solution A (etching solution A is composed of concentrated sulfuric acid and 30% hydrogen peroxide solution in a mass ratio of 10:1), at a temperature of 24℃ for 85s, and then rinse with deionized water for 25-30s.
[0080] S12. Immerse the gallium arsenide cleaned in step S11 into 190g of etching solution B (composed of concentrated hydrochloric acid, 30% hydrogen peroxide solution, and deionized water in a mass ratio of 1:1:30), at a temperature of 24°C for 85s. After removal, rinse with deionized water for 27s and then dry with nitrogen.
[0081] S13. The gallium arsenide dried in step S12 is immersed in 145g of 5% ammonium sulfide aqueous solution. The mixture is stirred at 150r / min, at 39℃ for 25min. After removal, it is washed with oxygen-free water for 27s and then dried with nitrogen. The modified substrate is obtained after drying.
[0082] S1. Fix the workpiece to be etched onto the chuck of the plasma etching machine. After closing the chamber, evacuate to a chamber background pressure of 1.5 mTorr. A silicon nitride layer is formed on the surface of the workpiece to be etched. A modified substrate is placed below the silicon nitride layer. The thickness of the silicon nitride layer on the workpiece to be etched is 800 nm, and the density of the silicon nitride layer is 3 g / cm³. 3 The chamber wall of the plasma etching machine is coated with aluminum oxide. Before etching, the chamber is pretreated by introducing a CF4 / O2 mixed gas at a flow ratio of 3:1, with a power of 30W, and cleaning for 180s.
[0083] S2. Introduce a composite etching gas into the chamber. The composite gas consists of a main etching gas (composed of C2F6, gas flow rate 50 sccm), a passivation gas (composed of C3F6, gas flow rate 50 sccm), and an activity-enhancing gas (a mixture of Ne and CH4 in a 7:1 ratio, gas flow rate 25 sccm). The main etching gas accounts for 50 vol%, the passivation gas accounts for 35 vol%, and the activity-enhancing gas accounts for 15 vol%.
[0084] S3. Start the pulsed radio frequency power supply (coupling method is capacitively coupled plasma) to excite the composite gas to generate plasma. The radio frequency power is controlled at 25W, the pulse frequency is 40kHz, the duty cycle is 70%, and the plasma density is maintained at 3×10⁻⁶. 11 cm -3 ;
[0085] S4. The reaction pressure in the control chamber is set to 122 mTorr, the chuck temperature to 25°C, and the etching time is set to 200 s based on the silicon nitride layer thickness. During the etching process, F is monitored in real-time using plasma emission spectroscopy. + CF3 + Si + The emission intensity, of which F + 703.7nm, CF3 + 690.1nm, Si + It is 288.2nm;
[0086] S5. After etching is complete, stop the etching gas supply, evacuate for 45 seconds to remove residual active species, and then purge the chamber with inert helium gas for 30 seconds until the chamber pressure returns to atmospheric pressure.
[0087] S6. Introduce a mixture of O2 and Ar gas with a volume ratio of O2 to Ar of 1.5:1 and a total flow rate of 70 sccm. Use 15W of radio frequency power to generate plasma. After ashing for 20 seconds, introduce H2 plasma with a flow rate of 40 sccm, a power of 7W, and a processing time of 7 seconds. After repairing the dangling bonds on the silicon nitride surface, the etching is completed.
[0088] Comparative Example 1
[0089] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses conventional high-power etching (100W), and the workpiece to be etched is the same as that in Example 1.
[0090] Comparative Example 2
[0091] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses conventional low-power etching (30W), and the workpiece to be etched is the same as that in Example 1.
[0092] Comparative Example 3
[0093] The only difference between Comparative Example 3 and Example 1 is that the modified substrate in this comparative example is replaced with a conventional gallium arsenide substrate, while the other steps are exactly the same in Comparative Example 3 and Example 1.
[0094] Performance testing:
[0095] This invention utilizes a profilometer to measure the film thickness change before and after etching, and calculates the etching rate using the method of rate = thickness difference / time. AFM scanning (5μm × 5μm area) is used to observe the surface roughness after etching in Examples 1-3 and Comparative Examples 1-2. The data obtained are shown in Table 1 below:
[0096] Table 1 Performance Test Results
[0097]
[0098] As shown in Table 1, the modified substrate of this invention can effectively improve etching efficiency and surface performance. Compared with traditional etching methods, the etching method has a significant improvement in etching rate and surface roughness. It simultaneously meets the requirements of etching rate and surface quality while ensuring low energy consumption. Through the synergistic design of "precise ratio of composite gas system + pulsed radio frequency excitation + multi-field coupling process control", it achieves efficient, highly selective, and low-damage etching of silicon nitride layer at extremely low radio frequency power of 20-30W. It is suitable for scenarios with stringent process compatibility requirements, such as advanced semiconductor processes (3nm and below), MEMS high-precision devices, flexible semiconductors, and optical thin films.
[0099] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for dry etching silicon nitride with extremely low power, characterized in that, Includes the following steps: S1. Fix the workpiece to be etched on the chuck of the plasma etching machine, close the chamber and evacuate until the chamber background pressure is ≤2mTorr. A silicon nitride layer is formed on the surface of the workpiece to be etched, and a modified substrate is provided below the silicon nitride layer. S2. Introduce a composite etching gas into the chamber. The composite gas consists of a main etching gas, a passivation gas, and an activation-enhancing gas, wherein the main etching gas accounts for 40-60 vol%, the passivation gas accounts for 20-40 vol%, and the activation-enhancing gas accounts for 5-20 vol%. S3. Start the pulsed radio frequency power supply to excite the composite gas to generate plasma. The radio frequency power should be controlled at 20-30W, the pulse frequency at 10-100kHz, the duty cycle at 30-70%, and the plasma density maintained at 1×10⁻⁶. 10 -5×10 11 cm -3 ; S4. The reaction pressure in the control chamber is 120-122 mTorr, the chuck temperature is 20-25℃, the temperature fluctuation is ±2℃, and the etching time is set to 60-360s according to the thickness of the silicon nitride layer. S5. After etching is complete, stop the etching gas supply, evacuate for 30-60 seconds to remove residual active species, and then purge the chamber with inert helium gas for 20-40 seconds until the chamber pressure returns to atmospheric pressure. S6. Introduce a mixed gas of O2 and Ar, with a volume ratio of O2 to Ar of 1-2:1 and a total flow rate of 50-100 sccm. Use 10-20W of radio frequency power to generate plasma. After ashing for 10-30s, introduce H2 plasma with a flow rate of 30-50 sccm, a power of 5-10W, and a processing time of 5-10s. After repairing the dangling bonds on the silicon nitride surface, the etching is completed.
2. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The main etching gas is a fluorine-containing gas, selected from one or a combination of two of CF4, SF5, NF3, and C2F6. When two are combined, the mixing ratio is 1-3:1, and the fluorine-to-carbon ratio (F / C) of the main etching gas is ≥3:
1.
3. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The passivating gas is selected from one or more combinations of C4F8, C5F8, CHF3, and C3F6, and the fluorine-to-carbon ratio (F / C) of the passivating gas is ≤2.5:1; the activity-enhancing gas is a binary mixture of a rare gas and a hydrogen-containing gas, wherein the rare gas is selected from one of Ar, He, and Ne, and the hydrogen-containing gas is selected from one of H2, NH3, and CH4, and the mixing ratio of the two is 5-10:
1.
4. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, In step S3, the coupling method of the radio frequency power supply is capacitively coupled plasma.
5. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, In step S4, the chamber pressure is controlled by a mass flow controller and a vacuum valve, with pressure fluctuations of ±2 mTorr; the chuck uses a chiiller back cooling method to ensure that the workpiece temperature uniformity fluctuations are within ±1℃.
6. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The total flow rate of the composite etching gas is 35-240 sccm, of which the main etching gas flow rate is 20-120 sccm, the passivation gas flow rate is 10-80 sccm, the activation enhancement gas flow rate is 5-40 sccm, and the gas flow rate stability fluctuation is ±1 sccm.
7. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, F is monitored in real time during the etching process using plasma emission spectroscopy. + CF3 + Si + The emission intensity, of which F + 703.7nm, CF3 + 690.1nm, Si + The wavelength is 288.2 nm. When the intensity fluctuation exceeds ±5%, the main etching gas flow rate is adjusted to ±5 sccm and the RF power duty cycle is ±5%.
8. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The silicon nitride layer on the workpiece to be etched has a thickness of 50-3000 nm and a density of 2.8-3.2 g / cm³. 3 When the thickness of the silicon nitride layer of the workpiece to be etched is 1000-3000nm, the etching power for the first 50% thickness is 30W, and the etching power for the last 50% thickness is 20W, while the passivation gas ratio is increased by 5-10vol.
9. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The preparation of the modified substrate includes the following steps: S11. By mass, immerse 80-100 parts of gallium arsenide into 180-200 parts of etching solution A at a temperature of 23-25°C for 80-90 seconds, and then rinse with deionized water for 25-30 seconds. S12. Immerse the gallium arsenide cleaned in step S11 into 180-200 parts of etching solution B at a temperature of 23-25°C for 80-90 seconds. After removing it, rinse it with deionized water for 25-30 seconds and then dry it with nitrogen. S13. Immerse the gallium arsenide dried in step S12 into 140-150 parts of a 5% ammonium sulfide aqueous solution, and stir at a speed of 100-200 r / min, at a temperature of 38-40℃ for 20-30 min. After removal, wash with oxygen-free water for 25-30 s and then blow dry with nitrogen. After drying, the modified substrate is obtained. The etching solution A is composed of concentrated sulfuric acid and a 30% hydrogen peroxide solution in a mass ratio of 5-20:
1. The etching solution B is composed of concentrated hydrochloric acid, a 30% hydrogen peroxide solution, and deionized water in a mass ratio of 1:1:5-50.
10. The method for dry etching silicon nitride with extremely low power according to claim 1, characterized in that, The chamber wall of the plasma etching machine is coated with aluminum oxide. Before etching, the chamber is pretreated by introducing a CF4 / O2 mixed gas at a flow ratio of 3:1, with a power of 30W and a cleaning time of 180s.