Carbon-germanium co-sputtered refractive film and method for manufacturing the same

Abstract

The application relates to the technical field of refractive film preparation, and mainly relates to a carbon germanium co-sputtering refractive film and a preparation method thereof. The preparation method of the carbon germanium co-sputtering refractive film comprises the following steps: configuring a substrate for pretreatment; then placing the substrate in a multi-target magnetron sputtering device, vacuumizing, introducing argon, and plasma-activating the substrate; introducing a graphite target and a germanium target, keeping the argon introduced, newly introducing methane and hydrogen, and ion beam reaction co-sputtering the graphite target and the germanium target, and stopping sputtering after depositing the refractive film. The carbon germanium double-target co-sputtering cooperates with the introduction of methane and hydrogen, which not only ensures the stability of carbon germanium atom release through solid-state target material, but also promotes methane dissociation through methane supplementing active carbon groups and hydrogen, so that the carbon germanium atom ratio of the film layer can be preliminarily controlled, which is helpful for adjusting the refractive index control of the deposited film, meanwhile, through the reaction gas of co-sputtering cooperation with methane, the uniformity of the film layer composition and the compactness of the film layer can be ensured, and the refractive performance is improved.

Description

Technical Field

[0001] This application relates to the field of refractive film preparation technology, and mainly to a carbon-germanium co-sputtered refractive film and its preparation method. Background Technology

[0002] Infrared optical devices (such as infrared windows and precision lenses) have stringent requirements for the refractive index accuracy and stability of their refractive films. Current mainstream fabrication processes often use germanium target sputtering combined with methane gas to provide the carbon source, forming germanium carbide refractive films. However, this traditional process has significant drawbacks: Firstly, as a single carbon source, methane's dissociation efficiency is easily affected by environmental factors such as vacuum level and temperature, resulting in large fluctuations in the concentration of active carbon groups. This leads to an uneven carbon-germanium atomic ratio in the film, ultimately causing significant refractive index fluctuations, which cannot meet the requirements of high-precision optics. Secondly, refractive index control relies solely on the methane flow rate. Too low a flow rate results in a germanium-rich film with a high refractive index, while too high a flow rate leads to film embrittlement and decreased adhesion, making adjustment difficult. Therefore, it is necessary to propose a method for fabricating refractive films with easily adjustable refractive indices.

[0003] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a carbon-germanium co-sputtered refractive film and its preparation method, which aims to solve the problem that the refractive index performance is prone to fluctuation when prepared by a single methane carbon source.

[0005] The technical solution of this application is as follows: In a first aspect, this application provides a method for preparing a carbon-germanium co-sputtered refractive film, comprising the following steps: Pre-treatment of the substrate is performed; The substrate is then placed in a multi-target magnetron sputtering apparatus, a vacuum is drawn, argon gas is introduced, and the substrate is activated by plasma. Place a graphite target and a germanium target, keep argon gas flowing through, and then introduce methane and hydrogen gas. Co-sputter the graphite target and the germanium target with an ion beam reaction to deposit a refractive film, and then stop sputtering.

[0006] Furthermore, the vacuum level of the vacuum pump is ≤5×10⁻⁶. -5 Pa; The flow rate of argon is 25-40 sccm, the flow rate of methane is 12-35 sccm, and the flow rate of hydrogen is 3-10 sccm; The volume ratio of the argon, the methane, and the hydrogen is 10:(3-11):(0.8-3).

[0007] Furthermore, the power of the graphite target is 160-240W, the power of the germanium target is 140-280W, and the power ratio of the graphite target to the germanium target is 1:1.2-1:1.6; The ion source voltage of the ion beam is 400-800V and the beam current is 200-260mA.

[0008] Furthermore, a bias voltage of -60 to -200V is applied to the substrate during the sputtering process; The temperature of the substrate is 180-250℃.

[0009] Furthermore, after the sputtering is stopped following the deposition of the refractive film, the process further includes the following steps: The refractive film is annealed.

[0010] Furthermore, the annealing conditions are as follows: Stop introducing methane, and maintain an argon and hydrogen flow rate ratio of 9:1, with a total gas flow rate of 25-40 sccm, ≤5×10 -4 Under a vacuum of Pa, the temperature is increased to 300-350℃ at a rate of 5℃ / min and held for 60-90min. Continue to raise the temperature to 400-450℃ at a rate of 5℃ / min, and hold for 30-60 minutes; Let it cool naturally to room temperature.

[0011] Furthermore, the preprocessing steps include: The sample is ultrasonically cleaned sequentially with deionized water, anhydrous ethanol, and acetone for 10-15 minutes, then immersed in a 5% HF aqueous solution for 30-60 seconds, dried with nitrogen, and finally dried at 120°C for 30-60 minutes.

[0012] Furthermore, the substrate is selected from one of single-crystal germanium, silicon wafer or quartz.

[0013] In a second aspect, this application provides a carbon-germanium co-sputtered refractive film, wherein the refractive film is prepared by carbon-germanium co-sputtering as described in the first aspect.

[0014] Furthermore, the refractive index of the carbon-germanium co-sputtered refractive film is 2.2-3.8.

[0015] Beneficial effects: In this application, a nanoscale rough surface is formed by plasma activation and argon ion bombardment, which enhances the bonding activity between carbon germanium atoms and the substrate and reduces component segregation in the early stage of film formation. The carbon germanium dual-target co-sputtering combined with the introduction of methane and hydrogen not only ensures the stability of carbon germanium atom release with solid target material, but also supplements active carbon groups with methane and promotes methane dissociation with hydrogen, so that the carbon germanium atom ratio of the film can be initially controlled, which helps to adjust the refractive index control of the deposited film. At the same time, the co-sputtering combined with the reaction gas of methane helps to ensure the uniformity of the film composition and improve the density of the film, thus ensuring the refractive performance. Detailed Implementation

[0016] This application provides a carbon-germanium co-sputtered refractive film and its preparation method. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0017] This application provides a method for preparing a carbon-germanium co-sputtered refractive film, comprising the following steps: Pre-treatment of the substrate is performed; The substrate is then placed in a multi-target magnetron sputtering device, a vacuum is drawn, argon gas is introduced, and the substrate is activated by plasma. Place a graphite target and a germanium target, keep argon gas flowing through, and then add methane and hydrogen gas. Co-sputter the graphite target and germanium target with an ion beam reaction to deposit a refractive film, and then stop sputtering.

[0018] In this application, a nanoscale rough surface is formed by plasma activation and argon ion bombardment, which enhances the bonding activity between carbon germanium atoms and the substrate and reduces component segregation in the early stage of film formation. The carbon germanium dual-target co-sputtering combined with the introduction of methane and hydrogen not only ensures the stability of carbon germanium atom release with solid target material, but also supplements the active carbon groups with methane and promotes methane dissociation with hydrogen, so that the carbon germanium atom ratio of the film can be initially controlled, which helps to adjust the refractive index control of the deposited film. At the same time, the co-sputtering combined with the reaction gas of methane helps to ensure the composition uniformity of the film and improve the density of the film, thus ensuring the refractive performance.

[0019] In this application, a multi-target magnetron sputtering equipment is equipped with an ion beam assist device, and a process of magnetron sputtering deposition and ion beam bombardment assistance is used for deposition. High-purity targets with a purity greater than 99.999% can be used for graphite targets and germanium targets. Pre-sputtering can be performed before sputtering to ensure the purity of the preparation.

[0020] Furthermore, the vacuum level achieved during evacuation is ≤5×10⁻⁶. -5 Pa; The flow rate of argon is 25-40 sccm, the flow rate of methane is 12-35 sccm, and the flow rate of hydrogen is 3-10 sccm. The volume ratio of argon, methane and hydrogen is 10:(3-11):(0.8-3).

[0021] In this application, a high vacuum level reduces the interference of impurities on carbon-germanium bonding and avoids abnormal fluctuations in refractive index caused by impurity atoms. By controlling the argon flow rate and the ratio of methane to hydrogen, a stable sputtering atmosphere is maintained with argon, ensuring the bombardment efficiency of the ion beam on the target. The concentration of active carbon groups is controlled by adjusting the methane flow rate gradient; when the methane flow rate increases, the carbon content of the film increases and the refractive index decreases; when the methane flow rate decreases, the film is enriched in germanium and the refractive index increases. By introducing hydrogen co-sputtering, the dissociation efficiency of methane is improved, ensuring the linearity of carbon content control and improving the precision control of refractive index adjustment. Hydrogen can simultaneously treat the film surface during the deposition process, reducing deposition defects and helping to ensure the refractive effect of the deposited film.

[0022] Furthermore, the power of the graphite target is 160-240W, the power of the germanium target is 140-280W, and the power ratio of the graphite target to the germanium target is 1:1.2-1:1.6. The ion source voltage of the ion beam is 400-800V and the beam current is 200-260mA.

[0023] In this application, the carbon source is provided by a graphite carbon target and methane. By controlling the power ratio of the graphite target and the germanium target, the proportion of germanium atoms in the carbon atoms can be controlled to ensure the refractive effect. Appropriate power ensures the formation of stable Ge-C bonds between carbon and germanium atoms, avoiding abrupt changes in refractive index caused by an excess of a single element. High-energy ion bombardment by the ion beam promotes the full diffusion and rearrangement of carbon and germanium atoms, inhibiting columnar crystal growth and improving the film density and hardness.

[0024] Furthermore, a bias voltage of -60 to -200V is applied to the substrate during the sputtering process; The substrate temperature is 180-250℃.

[0025] In this application, since carbon atoms originate from various pathways, applying a substrate bias voltage of -60 to -200V can increase the deposition energy of sputtered particles, enhance film density, and guide the directional deposition of positively charged carbon-germanium particles, helping to reduce component segregation and decrease the refractive index difference between the film edge and center. By controlling the substrate temperature to 180-250℃, appropriate migration energy is provided for atoms, avoiding insufficient atomic migration caused by low temperatures, while preventing scattering caused by substrate deformation or coarse film grains due to high temperatures. Simultaneously, this temperature range promotes the stable formation of Ge-C bonds, improving the structural stability and uniformity of the film.

[0026] Furthermore, after sputtering is stopped following the deposition of the refractive film, the following steps are also included: Anneal the refractive film.

[0027] In this application, the refractive index performance can be further optimized by annealing the refractive film.

[0028] Furthermore, the conditions for annealing are: Stop the introduction of methane, maintain the flow rate ratio of argon and hydrogen at 9:1, the total gas flow rate is 25-40 sccm, and under a vacuum of ≤5×10-4 Pa, heat to 300-350℃ at a rate of 5℃ / min and hold for 60-90min. Continue to raise the temperature to 400-450℃ at a rate of 5℃ / min, and hold for 30-60 minutes; Let it cool naturally to room temperature.

[0029] In this application, after stopping the methane supply, heating and holding the film in an atmosphere of argon and hydrogen removes residual CHx groups, reduces interference from infrared absorption defects on refractive index testing, and ensures refractive accuracy. Holding at 400-450℃ for 30-60 minutes allows for further rearrangement of carbon-germanium atoms, optimizing the Ge-C bond bonding state and reducing internal stress in the film. Natural cooling to room temperature avoids cracking caused by sudden cooling, reduces refractive index fluctuations, and minimizes refractive index drift during use.

[0030] Furthermore, the preprocessing steps include: The sample is ultrasonically cleaned sequentially with deionized water, anhydrous ethanol, and acetone for 10-15 minutes, then immersed in a 5% HF aqueous solution for 30-60 seconds, dried with nitrogen, and finally dried at 120°C for 30-60 minutes.

[0031] In this application, pretreatment removes water-soluble impurities, oil, and organic contaminants from the substrate surface, preventing film formation defects caused by impurity adsorption. Immersion in HF aqueous solution removes the oxide layer on the substrate surface and enhances the bonding activity of carbon and germanium atoms. Drying removes residual moisture from the substrate surface, preventing film porosity caused by water vapor condensation during high-vacuum sputtering. Pretreatment avoids film detachment caused by interfacial impurities and reduces the impact of interfacial scattering on refractive index uniformity.

[0032] Furthermore, the substrate is selected from one of single-crystal germanium, silicon wafer or quartz.

[0033] In this application, the selected substrate has a good lattice arrangement, and the substrate can be selected according to the actual use needs and refractive index requirements.

[0034] This application also provides a carbon-germanium co-sputtered refractive film, wherein the refractive film is prepared by carbon-germanium co-sputtering as described above.

[0035] The preparation method provided in this application can produce a refractive film with an easily adjustable refractive index, which can be adapted to the appropriate refractive index range according to actual needs, thus helping to meet the required refractive index.

[0036] Furthermore, the refractive index of the carbon-germanium co-sputtered refractive film is 2.2-3.8.

[0037] The following specific examples provide further details.

[0038] Example 1 The method for preparing the carbon-germanium co-sputtered refractive film in Example 1 includes the following steps: (1) Select a single-crystal germanium substrate (size 20mm×20mm×1mm), and clean it by ultrasonication for 12min each with deionized water, anhydrous ethanol and acetone; immerse it in 5% HF aqueous solution for 45s; blow it dry with nitrogen and then dry it at 120℃ for 45min.

[0039] (2): Place the substrate in a multi-target magnetron sputtering apparatus and evacuate to 3×10⁻⁶. -5 Pa; Introduce argon gas (flow rate 30 sccm), turn on the plasma source to activate the substrate, and activate for 15 min.

[0040] (3) Place a graphite target (power 200W) and a germanium target (power 240W, power ratio 1:1.2); maintain an argon flow rate of 30 sccm, and add methane (flow rate 25 sccm) and hydrogen (flow rate 6 sccm, argon:methane:hydrogen volume ratio 10:8.3:2); ion source beam voltage 600V, beam current 230mA; apply substrate bias voltage -120V and substrate temperature 220℃ during sputtering; deposition time 90min to obtain a refractive film.

[0041] (4) Stop the flow of methane, maintain an argon:hydrogen ratio of 9:1 (total flow rate 30 sccm), and a vacuum of 3 × 10⁻⁶. -4 Pa; Increase the temperature to 320℃ at a rate of 5℃ / min and hold for 75min; continue to increase the temperature to 420℃ at a rate of 5℃ / min and hold for 45min; allow to cool naturally to room temperature.

[0042] Example 2 The preparation method of the carbon-germanium co-sputtered refractive film in Example 2 is basically the same as that in Example 1, except that the methane flow rate is adjusted to 15 sccm, the hydrogen flow rate is adjusted to 4 sccm (the volume ratio of argon:methane:hydrogen is 10:5:1.3), and the germanium target power is adjusted to 280W (the power ratio of graphite target:germanium target is 1:1.4).

[0043] Example 3 The preparation method of the carbon-germanium co-sputtered refractive film in Example 3 is basically the same as that in Example 1, except that the substrate bias voltage in Example 3 is adjusted to -80V, the substrate temperature is 200℃, the ion source beam voltage is 450V, and the beam current is 200mA.

[0044] Example 4 The preparation method of the carbon-germanium co-sputtered refractive film in Example 4 is basically the same as that in Example 1, except that the methane flow rate in Example 4 is adjusted to 32 sccm and the hydrogen flow rate is adjusted to 9 sccm (argon:methane:hydrogen volume ratio 10:10.7:3).

[0045] Example 5 The preparation method of the carbon-germanium co-sputtered refractive film in Example 5 is basically the same as that in Example 1, except that Example 5 does not undergo an annealing step, and the film is naturally cooled after deposition before being taken out.

[0046] Comparative Example 1 The preparation method of the refractive film in Comparative Example 1 is basically the same as that in Example 1, except that only argon and methane are introduced in the co-sputtering stage of Comparative Example 1, and the methane flow rate is 25 sccm.

[0047] Comparative Example 2 The preparation method of the refractive film in Comparative Example 2 is basically the same as that in Example 1, except that the graphite target power is 160W, the germanium target power is 160W, and the substrate temperature is 150℃ in the co-sputtering stage of Comparative Example 2; no annealing step is performed after sputtering, and the film is naturally cooled after deposition and then taken out.

[0048] The refractive films prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to performance tests. The test items are as follows: (1) Broadband refractive index: Spectroscopic ellipsometry method, using the Cauchy model to fit the optical constants, and calculating the average refractive index of 8-12μm and 400-800nm. (2) Damp heat aging test (temperature 85℃, relative humidity 85%, lasting 1000h), the rate of change of refractive index and the change of adhesion before and after the test (0 grade no peeling, 1 grade a very small amount of peeling, 2 grade obvious peeling at the grid edge). (3) Film internal stress test: Bending method (Stoney formula), curvature meter to test the change of the radius of curvature of the substrate before and after coating, and calculate the film internal stress. Three parallel tests were conducted, and the data fluctuation was ≤±5%.

[0049] The performance test results of Examples 1-5 and Comparative Examples 1-2 are shown in Table 1: Table 1 By comparing the performance test results, it can be found that Example 5 and Comparative Example 1 lacked annealing conditions, resulting in increased refractive index fluctuations. Comparative Example 1 did not use hydrogen, yet its internal stress and fluctuation levels were increased, indicating that introducing hydrogen through co-sputtering can play a certain role in conditioning the film layer.

[0050] The preparation method provided in this application allows for easy adjustment of the refractive index while ensuring stable and good film properties of the resulting refractive film.

[0051] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for preparing a carbon-germanium co-sputtered refractive film, characterized in that, Includes the following steps: Pre-treatment of the substrate is performed; The substrate is then placed in a multi-target magnetron sputtering apparatus, a vacuum is drawn, argon gas is introduced, and the substrate is activated by plasma. Place a graphite target and a germanium target, keep argon gas flowing through, and then add methane and hydrogen gas. Co-sputter the graphite target and the germanium target with an ion beam reaction to deposit a refractive film and then stop sputtering. The vacuum level of the vacuum pump is ≤5×10⁻⁶. -5 Pa; the argon flow rate is 25-40 sccm, the methane flow rate is 12-35 sccm, and the hydrogen flow rate is 3-10 sccm; the volume ratio of argon, methane, and hydrogen is 10:(3-11):(0.8-3); the graphite target power is 160-240 W, the germanium target power is 140-280 W, and the power ratio of the graphite target to the germanium target is 1:1.2-1:1.6; the ion source beam of the ion beam. The voltage is 400-800V, and the beam current is 200-260mA; a bias voltage of -60~-200V is applied to the substrate during sputtering; the substrate temperature is 180-250℃; after the refractive film is deposited and sputtering is stopped, the following step is also included: annealing the refractive film; the annealing conditions are: stopping the introduction of methane, maintaining an argon and hydrogen flow ratio of 9:1, a total gas flow rate of 25-40 sccm, and a temperature ≤5×10 -4 Under a vacuum of Pa, heat to 300-350℃ at a rate of 5℃ / min and hold for 60-90min; continue heating to 400-450℃ at a rate of 5℃ / min and hold for 30-60min; then cool naturally to room temperature.

2. The method for preparing a carbon-germanium co-sputtered refractive film according to claim 1, characterized in that, The preprocessing steps include: The sample is ultrasonically cleaned sequentially with deionized water, anhydrous ethanol, and acetone for 10-15 minutes, then immersed in a 5% HF aqueous solution for 30-60 seconds, dried with nitrogen, and finally dried at 120°C for 30-60 minutes.

3. The method for preparing a carbon-germanium co-sputtered refractive film according to claim 1, characterized in that, The substrate is selected from one of single-crystal germanium, silicon wafer or quartz.

4. A carbon-germanium co-sputtered refractive film, characterized in that, It is prepared by the method for preparing carbon-germanium co-sputtered refractive film as described in any one of claims 1-3.

5. The carbon-germanium co-sputtered refractive film according to claim 4, characterized in that, The refractive index of the carbon-germanium co-sputtered refractive film is 2.2-3.8.

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