High-hardness high-reflectivity hafnium carbide film and preparation method thereof

Abstract

The application provides a hafnium carbide film with high hardness and high reflectivity and a preparation method thereof. The method comprises the following steps: 1) placing a graphite target, a hafnium target and a substrate; 2) pre-treating the surface of the substrate: drying the substrate after ultrasonic cleaning; 3) vacuumizing the chamber and heating the substrate: vacuumizing the chamber to high vacuum and heating the substrate; 4) pre-cleaning the target: introducing inert gas into the chamber and maintaining the working gas pressure, and pre-sputtering cleaning the target; 5) depositing the hafnium carbide film: continuously introducing inert gas into the chamber and maintaining the working gas pressure, the substrate temperature and the substrate self-rotation speed, using a pulse generator to modulate the intermediate frequency pulse waveform applied to the graphite target and the hafnium target, maintaining the current value and carrying out the film plating treatment. The method can prepare a single-phase rock salt structure hafnium carbide film with low carbon vacancy concentration, which has high hardness and wide-band high reflectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of multifunctional thin film preparation, and particularly relates to a hafnium carbide thin film with high hardness and high reflectivity and a preparation method thereof. BACKGROUND

[0002] Multifunctional thin films with high hardness, high melting point and wideband high reflectivity are crucial for protecting optical systems to serve stably in extreme environments. Traditional wideband high reflect films are mainly pure metals such as aluminum, silver, gold and copper. Although such metal thin films have excellent wideband high reflectivity, their hardness and melting point are very low, and they cannot be used in extreme harsh environments with high heat, corrosion and wear. Hafnium carbide ceramic has an ultra-high melting point, high hardness and good thermal and electrical conductivity, and is an excellent high-hard high-reflective thin film candidate material.

[0003] However, amorphous carbon phases are easily precipitated in near-stoichiometric carbides, which significantly affects the performance of the thin film. A small amount of amorphous carbon phase can improve the hardness and wear resistance of the thin film, but it can enhance the shadow effect during thin film deposition, thereby significantly increasing the roughness of the thin film and reducing the reflectivity. More amorphous carbon will simultaneously deteriorate the hardness and reflectivity of the thin film. Reducing the carbon content in the thin film can inhibit the precipitation of amorphous carbon, but it will introduce a large number of carbon vacancies in the thin film, reduce the covalent bond density, and thus result in low hardness of the thin film. Therefore, it is crucial to reduce the carbon vacancies in hafnium carbide as much as possible without precipitating amorphous carbon in order to prepare a hafnium carbide thin film with high hardness and wideband high reflectivity.

[0004] In addition, the hafnium carbide thin films prepared by the existing magnetron sputtering method are prone to precipitate amorphous carbon phases. This is because: on the one hand, the existing magnetron sputtering method usually uses gases such as acetylene and methane as carbon sources, and the active hydrogen atoms will induce the carbon in the thin film to form sp 2 hybrid graphite-like phase. On the other hand, the existing magnetron sputtering method usually uses a constant direct current power supply, which has a high deposition rate, but the working voltage is low, and the energy of the sputtered carbon particles is low, which cannot diffuse into the hafnium carbide lattice sufficiently, thereby forming carbon clusters and further developing into amorphous carbon phases.

[0005] Therefore, how to optimize the existing magnetron sputtering technology to prepare a hafnium carbide thin film with high hardness and wideband high reflectivity is a technical problem that technicians in the field need to solve urgently. SUMMARY

[0006] To solve the above technical problems, the present application provides a method for preparing a hafnium carbide thin film with high hardness and wideband high reflectivity by magnetron co-sputtering, which can prepare a single-phase rock salt structure hafnium carbide thin film with a low carbon vacancy concentration, and the thin film has high hardness and wideband high reflectivity.

[0007] In a first aspect, the present application provides a method for preparing a high-hardness and high-reflectivity hafnium carbide film, comprising the following steps.

[0008] 1) Target position: placing a graphite target, a hafnium target and a substrate.

[0009] 2) Substrate surface pretreatment: drying the substrate after ultrasonic cleaning.

[0010] 3) Chamber vacuum and substrate heating: evacuating the chamber to high vacuum and heating the substrate.

[0011] 4) Target pre-cleaning: introducing inert gas into the chamber and maintaining the working gas pressure, and pre-sputtering cleaning of the target.

[0012] 5) Deposition of hafnium carbide film: continuously introducing inert gas into the chamber and maintaining the working gas pressure, substrate temperature and substrate self-rotation speed, using a pulse generator to modulate the intermediate frequency pulse waveform applied to the graphite target and the hafnium target, maintaining the current value and performing film plating treatment.

[0013] The present application provides a method for preparing a hafnium carbide film with high hardness and wide-band high reflectivity by magnetron co-sputtering, which adopts intermediate frequency pulse direct current magnetron co-sputtering of a graphite target and a hafnium target to prepare a single-phase rock salt structure hafnium carbide film with a lower carbon vacancy concentration, which has high hardness and wide-band high reflectivity. By adjusting the process parameters, a single-phase rock salt structure hafnium carbide film with a stoichiometric ratio of HfC 0.5 ~HfC 0.8 , a hardness greater than 20 GPa, and an average reflectivity of greater than 60% in the 800-2000 nm wavelength band is obtained.

[0014] Preferably, in step 1), the purity of the graphite target and the hafnium target is ≥ 99.95%, the substrate is Si (100), the graphite target is placed horizontally below the substrate at a distance of 8-15 cm from the substrate, and the hafnium target is placed at an angle of 30±2° relative to the graphite target.

[0015] Preferably, in step 2), the substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 5-10 min.

[0016] Further preferably, in step 3), the high vacuum degree is a gas pressure of less than 4×10 -4 Pa, and the substrate heating temperature is 400-600℃.

[0017] Preferably, the chamber is evacuated to a gas pressure of 10 Pa or less, and then evacuated to high vacuum and heated.

[0018] In the present application, the chamber is first vacuumized to an air pressure of 10 Pa or less by a mechanical pump, and then further vacuumized to high vacuum by a turbo molecular pump, while the substrate is heated by a resistance wire to remove the residual gas and volatile matter in the chamber and on the surface of the substrate to the maximum extent, so as to ensure the adhesion of the thin film and the quality of the film layer.

[0019] Preferably, in step 4), the argon flow is 30-50 sccm, and the working air pressure is stabilized at 0.8-1.2 Pa.

[0020] In the present application, preferably, argon is continuously introduced into the chamber, the working air pressure is kept constant by adjusting the molecular pump valve, and then the graphite target and hafnium target are pre-sputtered and cleaned to better remove the oxides and contaminants on the surface of the target, which is beneficial to subsequent processing.

[0021] Further preferably, in step 4), a constant bias voltage of -300 to -350 V and -150 to -200 V is applied to the graphite target and hafnium target respectively, and the pre-sputtering and cleaning time is 5-10 min.

[0022] Preferably, in step 5), the argon flow is 30-50 sccm, the working air pressure is stabilized at 0.5-1.0 Pa, the substrate temperature is stabilized at 400-600℃, the substrate self-rotation speed is kept at 5-20 rpm, the intermediate frequency pulse frequency is 50-150 kHz, the intermediate frequency pulse width is 0.2-0.6 µs, the current applied to the graphite target is 0.3-0.6 A, and the power is 80-180 W, the current applied to the hafnium target is 0.3-0.6 A, and the power is 50-125 W.

[0023] Further preferably, in step 5), the argon flow is 35-45 sccm, the working air pressure is stabilized at 0.7-0.9 Pa, the substrate temperature is stabilized at 450-550℃, the substrate self-rotation speed is kept at 8-12 rpm, the intermediate frequency pulse frequency is 80-120 kHz, the intermediate frequency pulse width is 0.3-0.5 µs, the current applied to the graphite target is 0.3-0.6 A, preferably 0.5 A, and the power is 80-180 W, preferably 150-170 W, the current applied to the hafnium target is 0.4-0.6 A, and the power is 50-125 W, preferably 50-120 W; preferably, the film coating process is performed for 60-180 min.

[0024] Preferably, after step 5), the substrate temperature is lowered to below 100℃, and the substrate is taken out.

[0025] In the present application, after step 5) is completed, the power is turned off, the substrate temperature is lowered to below 100℃, the chamber is opened, and the substrate is taken out, and the thin film on the surface of the substrate is a hafnium carbide thin film with high hardness and wideband high reflectivity.

[0026] In a second aspect, the present application provides a hafnium carbide thin film prepared by the above method, wherein the hafnium carbide thin film is a single-phase rock salt structure, and has a stoichiometric ratio of HfC 0.5 HfC 0.8 , a hardness of ≥20 GPa, and an average reflectivity of ≥60% in a wavelength range of 800-2000 nm.

[0027] The present application has at least the following advantages: 1) The present application uses a graphite target as a carbon source to prepare a hafnium carbide thin film, which can avoid introducing active hydrogen atoms in the thin film, and can reduce the tendency of amorphous carbon phase precipitation in the thin film compared to the prior art technology using acetylene or methane as a carbon source; 2) The present application modulates the pulse DC waveform by a pulse generator, which has a significantly higher sputtering particle energy compared to the constant DC magnetron sputtering technology, and has a significantly higher deposition efficiency compared to the high-power pulse magnetron sputtering technology, and the present application can balance the thin film quality and deposition efficiency; 3) The present application can prepare a single-phase rock salt structure hafnium carbide thin film with low carbon vacancy concentration and without amorphous carbon precipitation, which has high hardness and wideband high reflectivity. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0029] Figure 1 XRD patterns of the single-phase hafnium carbide thin films obtained in Examples 1-3.

[0030] Figure 2 XPS patterns of the single-phase hafnium carbide thin films obtained in Examples 1-3.

[0031] Figure 3 SEM photos of the single-phase hafnium carbide thin films obtained in Examples 1-3.

[0032] Figure 4 TEM photos of the single-phase hafnium carbide thin films obtained in Examples 1-3. DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the following will combine the drawings in the present application to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present application.

[0034] Unless otherwise indicated, the starting materials and reagents used in the following examples are commercially available or can be prepared by known methods. Where specific techniques or conditions are not mentioned, they are not considered critical and are performed according to conventional methods or as described in the literature or as determined by the manufacturer. Where the manufacturer of a reagent or instrument is not mentioned, it is not to be construed as critical.

[0035] Example 1

[0036] The present example provides a method for preparing hafnium carbide thin film with high hardness and wide-band high reflectivity by magnetron co-sputtering, comprising the following steps.

[0037] (1) The purity of the selected graphite target and hafnium target is 99.95%, and the substrate is Si (100). The graphite target is placed horizontally directly below the substrate with a distance of 11 cm, and the hafnium target is placed at an angle of 30° relative to the graphite target.

[0038] (2) The substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 minutes respectively.

[0039] (3) First, the chamber is evacuated to an air pressure of 10 Pa or less by a mechanical pump, and then further evacuated to an air pressure of 4 x 10 -4 Pa by a turbo molecular pump, while the substrate is heated to 500°C by a resistance wire.

[0040] (4) 40 sccm of argon gas is continuously introduced into the chamber, and the working air pressure is kept constant at 0.8 Pa by adjusting the molecular pump valve. The graphite target and hafnium target are pre-sputtered and cleaned for 10 minutes by applying a constant bias voltage of -325 V and -170 V to the graphite target and hafnium target respectively, to remove the oxides and contaminants on the surface of the target materials.

[0041] (5) 40 sccm of argon gas is continuously introduced into the chamber while keeping the working air pressure constant at 0.8 Pa, the substrate temperature at 500°C and the substrate self-rotation speed constant at 10 rpm. The power parameters applied to the graphite target are set as follows: pulse frequency 100 kHz, pulse width 0.4 µs, target current 0.5 A, and target power 162 W; the power parameters applied to the hafnium target are set as follows: pulse frequency 100 kHz, pulse width 0.4 µs, target current 0.4 A, and target power 69 W. The film deposition time is 120 minutes.

[0042] (6) Turn off the power, and when the substrate temperature drops below 100°C, open the chamber and take out the sample.

[0043] Example 2

[0044] The embodiment provides a method for preparing a hafnium carbide film with high hardness and wide-band high reflectivity by magnetron co-sputtering.

[0045] (1) The purity of the selected graphite target and hafnium target is 99.95%, the substrate is Si (100), the graphite target is horizontally placed directly below the substrate at a distance of 11 cm from the substrate, and the hafnium target is placed at an angle of 30° relative to the graphite target.

[0046] (2) The substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 minutes respectively.

[0047] (3) First, the chamber is vacuumed to an air pressure of less than 10 Pa by a mechanical pump, and then further vacuumed to an air pressure of 4x10 -4 Pa by a turbo molecular pump, while the substrate is heated to 500 DEG C by a resistance wire.

[0048] (4) 40 sccm of argon is continuously introduced into the chamber, the working air pressure is kept constant at 0.8 Pa by adjusting the molecular pump valve, and the graphite target and the hafnium target are pre-sputtered and cleaned for 10 minutes by applying a constant bias voltage of-325 V and-170 V to the graphite target and the hafnium target respectively, so as to remove the oxides and contaminants on the surface of the target material.

[0049] (5) 40 sccm of argon is continuously introduced into the chamber while keeping the working air pressure constant at 0.8 Pa, the substrate temperature at 500 DEG C and the substrate self-rotation speed constant at 10 rpm, the power parameters applied to the graphite target are set as follows: pulse frequency is 100 kHz, pulse width is 0.4 µs, target current is 0.5 A, and target power is 165 W; the power parameters applied to the hafnium target are set as follows: pulse frequency is 100 kHz, pulse width is 0.4 µs, target current is 0.5 A, and target power is 94 W. The film plating time is 100 minutes.

[0050] (6) Turn off the power, and when the substrate temperature drops to below 100 DEG C, open the chamber and take out the sample.

[0051] Embodiment 3

[0052] The embodiment provides a method for preparing a hafnium carbide film with high hardness and wide-band high reflectivity by magnetron co-sputtering.

[0053] (1) The purity of the selected graphite target and hafnium target is 99.95%, the substrate is Si (100), the graphite target is horizontally placed directly below the substrate at a distance of 11 cm from the substrate, and the hafnium target is placed at an angle of 30° relative to the graphite target.

[0054] (2) The substrate is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 minutes respectively.

[0055] (3) Firstly, the chamber is vacuumized to an air pressure of 10 Pa or less by a mechanical pump, and then further vacuumized to an air pressure of 4x10 -4 Pa by a turbo molecular pump, while the substrate is heated to 500℃ by a resistance wire.

[0056] (4) 40 sccm of argon is continuously introduced into the chamber, and the working air pressure is kept constant at 0.8 Pa by adjusting the molecular pump valve, and the graphite target and hafnium target are pre-sputtered and cleaned for 10 min by applying a constant bias voltage of -325 V and -170 V to the graphite target and hafnium target respectively, so as to remove the oxides and contaminants on the surface of the target materials.

[0057] (5) 40 sccm of argon is continuously introduced into the chamber, while the working air pressure is kept constant at 0.8 Pa, the substrate temperature is kept constant at 500℃, and the substrate self-rotation speed is kept constant at 10 rpm, the power parameters applied to the graphite target are set as follows: the pulse frequency is 100 kHz, the pulse width is 0.4 µs, the target current is 0.5 A, and the target power is 167 W; the power parameters applied to the hafnium target are set as follows: the pulse frequency is 100 kHz, the pulse width is 0.4 µs, the target current is 0.6 A, and the target power is 120 W. The film deposition time is 90 min.

[0058] (6) The power is turned off, and the substrate temperature is lowered to below 100℃, then the chamber is opened to take out the sample.

[0059] Figures 1-4 The XRD pattern, XPS spectrum, SEM photo and TEM photo of the single-phase hafnium carbide thin film obtained in Example 1-3 are shown in Figures 1-4 respectively. Figures 1-4 It can be seen that the HfC x thin film obtained in Examples 1-3 is of single-phase FCC structure, the thin film is well combined with the substrate, and the surface is flat and dense.

[0060]

[0061] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part of the technical features; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of forming a high hardness, high reflectivity hafnium carbide film, comprising: The method comprises the following steps: 1) target position: placing graphite target, hafnium target and substrate; 2) substrate surface pretreatment: drying the substrate after ultrasonic cleaning; 3) chamber vacuum and substrate heating: vacuumizing the chamber to high vacuum and heating the substrate; 4) target pre-cleaning: introducing inert gas into the chamber and maintaining working pressure, and pre-sputtering cleaning of the target; 5) hafnium carbide film deposition: continuously introducing inert gas into the chamber and maintaining working pressure, substrate temperature and substrate self-rotation speed, and applying a medium frequency pulse waveform generated by a pulse generator on the graphite target and the hafnium target, maintaining the current value and carrying out film plating treatment; the graphite target and the hafnium target are prepared by medium frequency pulse direct current magnetron co-sputtering, the medium frequency pulse frequency is 50-150 kHz, the medium frequency pulse width is 0.2-0.6 μs, the current applied to the graphite target is 0.3-0.6 A, the power is 80-180 W, the current applied to the hafnium target is 0.3-0.6 A, and the power is 50-125 W.

2. The method of claim 1, wherein the method further comprises: In step 1), the purity of the graphite target and the hafnium target is ≥99.95%, the substrate is Si(100), the graphite target is placed horizontally below the substrate at a distance of 8-15 cm from the substrate, and the hafnium target is placed at an angle of 30±2° relative to the graphite target.

3. The method of claim 1, wherein the method further comprises: In step 2), ultrasonic cleaning is carried out in acetone, anhydrous ethanol and deionized water for 5-10 min.

4. The method of claim 1, wherein the method further comprises: In step 3), the high vacuum is less than 4 x 10 -4 Pa, and the substrate heating temperature is 400 to 600°C.

5. The method of claim 1, wherein the method further comprises: In step 4), the argon gas flow is 30-50 sccm, and the working pressure is stabilized at 0.8-1.2 Pa.

6. The method of claim 5, wherein the method further comprises: In step 4), a constant bias voltage of -300 to -350 V and -150 to -200 V is applied to the graphite target and the hafnium target respectively, and the pre-sputtering cleaning time is 5-10 min.

7. The method of claim 1, wherein the method further comprises: In step 5), the argon gas flow is 30-50 sccm, the working pressure is stabilized at 0.5-1.0 Pa, the substrate temperature is stabilized at 400-600°C, and the substrate self-rotation speed is maintained at 5-20 rpm.

8. The method of claim 7, wherein the method further comprises: In step 5), the argon gas flow is 35-45 sccm, the working pressure is stabilized at 0.7-0.9 Pa, the substrate temperature is stabilized at 450-550°C, the substrate self-rotation speed is maintained at 8-12 rpm, the medium frequency pulse frequency is 80-120 kHz, the medium frequency pulse width is 0.3-0.5 μs, the current applied to the graphite target is 0.3-0.6 A, the power is 80-180 W, the current applied to the hafnium target is 0.4-0.6 A, and the power is 50-125 W; the film plating treatment is carried out for 60-180 min.

9. The method of claim 1-8, wherein the method further comprises, After step 5), the substrate temperature is lowered to below 100°C, and the substrate is taken out.

10. The hafnium carbide film obtained by the production method according to any one of claims 1 to 9, characterized in that, The hafnium carbide thin film is single-phase rock salt structure, and the stoichiometric ratio is HfC 0.5 ~ HfC 0.8 The film hardness is greater than or equal to 20 GPa, and the average reflectivity in the 800-2000 nm wave band is greater than or equal to 60%.

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