A method for magnetron sputtering in a slender tube using a DC composite bipolar pulse

Abstract

A method for magnetron sputtering inside a slender tube using a DC composite bipolar pulse belongs to the field of magnetron sputtering coating. It solves the problems of difficult discharge, poor stability, and poor film layer quality inside the existing tube parts. In the present invention, the tube to be coated and the cylindrical target are respectively connected to the positive and negative poles of the power supply, and diode discharge is carried out between the two. The discharge power supply uses a DC composite bipolar pulse power supply, and the discharge mode can be switched among the discharge modes of DC, pulse, bipolar pulse, and DC composite bipolar pulse. The discharge stability and deposition rate are enhanced through the DC part; ionization is enhanced through negative pulse discharge to prepare for the subsequent traction of positive pulses; ions in the plasma are accelerated towards the tube to be coated through positive pulse traction, bombarding and compacting the film layer to improve the film layer quality, and finally realizing the rapid and high-quality preparation of the magnetron sputtering film layer on the inner wall of the slender tube. The present invention is applicable to the field of magnetron sputtering coating on the inner wall of slender tubes.

Description

Technical Field

[0001] The present invention belongs to the field of magnetron sputtering coating, and particularly relates to a method for magnetron sputtering inside a slender tube using a DC composite bipolar pulse. Background Art

[0002] Magnetron sputtering technology is widely used in surface strengthening fields such as medical treatment, petrochemical industry, power engineering, and ocean engineering due to its characteristics of low deposition temperature and good film quality. For example, in the medical field, preparing a DLC film layer on the surface of artificial joints can adjust their hydrophilicity and reduce the friction coefficient, greatly improving the service life of the material; preparing a TiN film layer on the material surface can not only improve the wear resistance of the material, but also obtain various colors by adjusting the film layer composition, improving the aesthetics of the workpiece; preparing film layers such as TiN and TiAlN on the surface of cutting tools can increase their hardness and wear resistance while extending their service life and improving tool performance.

[0003] In the above applications, the film layer is mainly prepared on the outer surface of the material. This does not mean that the demand for film layers on the inner surface of the material is low. On the contrary, in practical applications, thin films have broad application prospects on the inner surface of materials, especially the inner surface of tube parts. For example, in the chemical industry, a large number of pipelines are used for transporting high-temperature corrosive chemical media. Compared with the outer surface, the inner surface of the pipeline becomes the first position where the tube material fails. Preparing a film layer with high temperature and corrosion resistance on its inner surface will greatly improve its service life. However, due to the limited space inside the tube and the large aspect ratio, the research on inner wall protection has progressed slowly. Currently, the main methods for protecting the inner wall of tube materials are adding a liner or using electroplating. The former will form weak points at the welded joints, while the latter has poor film quality and will cause serious environmental pollution. Therefore, it is very meaningful to vigorously develop the application of magnetron sputtering technology for coating the inner wall of tube materials.

[0004] The main difficulties in depositing a film layer on the inner wall of a slender tube part are as follows: 1. The small-diameter tube opening shields the external plasma. The plasma generated by the external plasma source can only enter the inside through the tube opening. As the aspect ratio of the tube part increases, the uniformity of the plasma distribution inside it decreases sharply, making it difficult to effectively and uniformly prepare the film layer. 2. The tube diameter of the tube part limits the generation of plasma inside the tube. For example, for a pipe with an inner diameter of 40 mm, the limit target-substrate distance for internal discharge is usually only a dozen millimeters. The space inside the tube is small, and no additional electrode structure can be applied, so only a diode discharge structure can be used.

[0005] In a conventional DC diode discharge, the particle energy is relatively low. In the bipolar discharge process, the forward pulse uses the tube to be coated as the cathode to attract ions, achieving the bombardment of the film layer and improving the film layer quality. During the narrow-gap discharge process, the plasma dissipation is very fast, the bipolar discharge stability is poor, and it is prone to arcing and extinction. Combining the high deposition rate and high discharge stability of DC with the high ionization rate and high particle energy of bipolar discharge and applying it to film coating inside a slender tube has good application prospects. Summary of the Invention

[0006] The present invention aims at the problems of difficult discharge, poor stability, and poor film layer quality during the film coating process inside an existing slender tube, and provides a method for magnetron sputtering inside a slender tube using a DC composite bipolar pulse.

[0007] A method for magnetron sputtering inside a slender tube using a DC composite bipolar pulse, based on the existing secondary discharge magnetron sputtering method, uses a DC composite bipolar pulse power supply during the magnetron sputtering process. The DC composite bipolar pulse power supply includes three parts: DC power supply, negative pulse power supply, and positive pulse power supply, which can be independently controlled to achieve the on-off of each part. The three parts are controlled by a single-chip microcomputer combined with a semiconductor switch bridge circuit. The negative pulse and the positive pulse together form a bipolar pulse within the same cycle, and the negative pulse and the positive pulse are alternately distributed. There can be N negative pulses and M positive pulses within the same pulse cycle, where N = 0, 1, 2,..., 100; M = 0, 1, 2,..., 100. The DC power supply is turned off during the action of the bipolar pulse and turned on during the pulse interval.

[0008] Furthermore, the current value range of the DC power supply is 0 - 100A, and the supply voltage range is 0 - 2000V.

[0009] Furthermore, the positive and negative pulse widths and voltages of the bipolar pulse can be independently controlled, and the frequency range is 0 - 50kHz.

[0010] Furthermore, the first pulse within the cycle of the bipolar pulse is a negative pulse, and the pulse width ranges of the positive and negative pulses are 0 - 1ms, and the voltage range is 0 - 2000V.

[0011] Furthermore, this method includes the following steps:

[0012] I. Specimen preparation: The tube to be coated is ultrasonically cleaned with acetone and anhydrous ethanol for 5 - 60 minutes each in turn, taken out and dried, and then placed in a vacuum chamber and coaxially installed with a cylindrical target.

[0013] II. Pre-treatment before film coating: The vacuum chamber is evacuated to a pressure below 8×10 -3 Pa and heated and dried for 10 - 60 minutes. Then it is evacuated again to a pressure of 8×10 -3Below Pa, argon is introduced until the air pressure reaches 0.5 - 10 Pa, and then the inner wall of the pipe to be plated is subjected to plasma sputtering cleaning for 5 - 60 min to obtain the pre - treated pipe to be plated;

[0014] III. Sputtering coating: After the plasma cleaning is completed, a mixed gas of working gas and reaction gas is introduced, the power is turned on, the gas parameters and power parameters are set, and magnetron sputtering coating is carried out on the pre - treated pipe to be plated for 10 - 3000 min;

[0015] Further, in step I, the inner diameter of the pipe to be plated is 15 - 2000 mm, the wall thickness is 0.1 - 100 mm, and the material is a magnetic or non - magnetic conductive material;

[0016] Further, in step I, the outer diameter of the target tube of the columnar target is 8 - 100 mm, and the material is a non - magnetic conductive material;

[0017] Further, in step III during the magnetron sputtering coating process, the columnar target is connected to the negative pole of the power supply, and the pre - treated pipe to be plated is connected to the positive pole of the power supply;

[0018] Further, in step III, the working gas is Ar; the reaction gas is one or several of N2, H2, and O2;

[0019] Further, in step III, the gas parameters are: the gas flow rate is 1 - 3000 sccm, and the air pressure is 0.1 - 10 Pa.

[0020] The present invention proposes a method for magnetron sputtering inside a slender tube using a DC composite bipolar pulse, which can effectively solve problems such as difficult discharge, poor stability, and poor film layer quality during the coating process inside an existing slender tube, thereby realizing the rapid and high - quality preparation of a magnetron sputtering film layer on the inner wall of a slender tube.

[0021] The advantages of the present invention are as follows:

[0022] It is very difficult to apply the multi - electrode structure of conventional coating to the inner wall coating of a slender tube. If the conventional DC diode discharge method with the pipe to be plated as the anode and the columnar target as the cathode is used, the particle energy is relatively low, and the film layer cannot be bombarded and compacted, resulting in poor quality. The positive pulse in the bipolar discharge process uses the pipe to be plated as the cathode to attract ions, realizing the bombardment of the film layer and improving the film layer quality. However, due to the small space and narrow target - substrate distance inside the slender tube, the plasma dissipation is very fast during the discharge process, the bipolar discharge stability is poor, and it is easy to generate sparks and extinguish the glow. The present invention combines the high deposition rate and high discharge stability of DC with the high ionization rate and high particle energy of bipolar discharge, thereby realizing the rapid preparation of a high - quality film layer inside a slender tube and promoting the development of the industry.

[0023] A method of magnetron sputtering inside a slender tube using a DC composite bipolar pulse is proposed in the present invention. The discharge mode can be switched among DC, pulse, bipolar pulse, and DC composite bipolar pulse discharge modes, and it is applicable to the field of magnetron sputtering coating on the inner wall of a slender tube. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the discharge waveform that can be realized by the DC composite bipolar pulse power supply in the present invention. Among them, (a) is the waveform diagram when N = 1 and M = 1, (b) is the waveform diagram when N = 2 and M = 1, (c) is the waveform diagram when N = 2 and M = 2, and (d) is the waveform diagram of the symmetric bipolar pulse mode;

[0025] Figure 2 It is a diagram showing the change of the film layer thickness at each position of the DC composite bipolar pulse deposition of TiN film on the inner surface of a stainless steel tube with an inner diameter of Φ50mm in Example 1.

[0026] Figure 3 It is a cross-sectional morphology diagram of depositing Cr film on the inner surface of a carbon steel tube with an inner diameter of Φ40mm in Example 2. Among them, (a) is the result diagram of pure DC deposition, and (b) is the result diagram of DC composite bipolar pulse deposition. Detailed Embodiments

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0028] Detailed Embodiment 1: A method of magnetron sputtering inside a slender tube using a DC composite bipolar pulse. Based on the existing two-stage discharge magnetron sputtering method, a DC composite bipolar pulse power supply is used as the power supply during the magnetron sputtering process. The DC composite bipolar pulse power supply includes three parts: DC power supply, negative pulse power supply, and positive pulse power supply, and the on / off of each part can be controlled separately. The three parts are controlled by a single-chip microcomputer combined with a semiconductor switch bridge circuit. The negative pulse and the positive pulse together form a bipolar pulse within the same cycle, and the negative pulse and the positive pulse are alternately distributed. There can be N negative pulses and M positive pulses within the same pulse cycle, where N = 0, 1, 2,..., 100; M = 0, 1, 2,..., 100. The DC power supply is turned off during the action of the bipolar pulse and turned on during the pulse interval.

[0029] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the current value range of the DC power supply is 0 - 100A, and the power supply voltage range is 0 - 2000V. Others are the same as Specific Embodiment 1.

[0030] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 is that the positive and negative pulse widths and voltages of the bipolar pulse can be controlled separately, and the frequency range is 0 - 50kHz. Others are the same as Specific Embodiment 1.

[0031] Specific Embodiment 4: The difference between this embodiment and Specific Embodiment 1 is that the first pulse in the period of the bipolar pulse is a negative pulse, the pulse width ranges of the positive and negative pulses are 0 - 1ms, and the voltage range is 0 - 2000V. Others are the same as Specific Embodiment 1.

[0032] Specific Embodiment 5: The difference between this embodiment and Specific Embodiment 1 is that the method includes the following steps:

[0033] 1. Specimen preparation: The pipe to be plated is ultrasonically cleaned with acetone and absolute ethanol for 5 - 60 minutes each in sequence, taken out and dried, and then placed in a vacuum chamber and coaxially installed with a cylindrical target;

[0034] 2. Pre - treatment before coating: The vacuum chamber is evacuated to a pressure below 8×10 -3 Pa, heated and dried for 10 - 60 minutes, evacuated again to a pressure below 8×10 -3 Pa, argon is introduced until the pressure is 0.5 - 10Pa, and then the inner wall of the pipe to be plated is subjected to plasma sputtering cleaning for 5 - 60 minutes to obtain the pre - treated pipe to be plated;

[0035] 3. Sputtering coating: After the plasma cleaning is completed, a mixed gas of working gas and reaction gas is introduced, the power supply is turned on, the gas parameters and power supply parameters are set, and magnetron sputtering coating is carried out on the pre - treated pipe to be plated for 10 - 3000 minutes.

[0036] Others are the same as Specific Embodiment 1.

[0037] The power supply mentioned in step 3 of this embodiment is a DC composite bipolar pulse power supply, and its discharge waveform schematic diagram is as Figure 1 shown.

[0038] Specific Embodiment 6: The difference between this embodiment and Specific Embodiment 5 is that in step 1, the inner diameter of the pipe to be plated is 15 - 2000mm, the wall thickness is 0.1 - 100mm, and the material is a magnetic or non - magnetic conductive material. Others are the same as Specific Embodiment 5.

[0039] Embodiment 7: The difference between this embodiment and Embodiment 5 is that in Step 1, the outer diameter of the target tube of the cylindrical target is 8 - 100 mm, and the material is non-magnetic conductive material. Others are the same as Embodiment 5.

[0040] Embodiment 8: The difference between this embodiment and Embodiment 5 is that in Step 3 during the magnetron sputtering coating process, the cylindrical target is connected to the negative pole of the power supply, and the tube to be coated after treatment is connected to the positive pole of the power supply. Others are the same as Embodiment 5.

[0041] Embodiment 9: The difference between this embodiment and Embodiment 5 is that in Step 3, the working gas is Ar; the reaction gas is one or several of N2, H2, and O2. Others are the same as Embodiment 5.

[0042] In this embodiment, when the reaction gas is a mixed gas, each component is mixed in any ratio.

[0043] Embodiment 10: The difference between this embodiment and Embodiment 5 is that in Step 3, the gas parameters are: gas flow rate is 1 - 3000 sccm, and the air pressure is 0.1 - 10 Pa. Others are the same as Embodiment 5.

[0044] The beneficial effects of the present invention are verified through the following examples:

[0045] Example 1:

[0046] I. Specimen preparation: A stainless steel tube with an inner diameter of 50 mm, an outer diameter of 55 mm, and a length of 240 mm is ultrasonically cleaned with acetone and absolute ethanol for 15 minutes each in sequence. After taking it out and drying, it is placed in a vacuum chamber and coaxially installed with a cylindrical Ti target with an outer diameter of 25 mm and a length of 280 mm;

[0047] II. Pretreatment before coating: The vacuum chamber is evacuated to a pressure below 8×10 -3 Pa, and heated and dried for 30 minutes. It is evacuated again to a pressure below 8×10 -3 Pa, and argon is introduced until the pressure is 5 Pa. Then, the inner wall of the stainless steel tube is subjected to plasma sputtering cleaning for 30 minutes to obtain the pretreated stainless steel tube;

[0048] III. Sputtering coating: After the plasma cleaning is completed, a mixed gas of Ar and N2 is introduced, and the flow ratio is 5:1. The power supply is turned on, and the power supply parameters are set as follows: the direct current part current is 0.5 A, the pulse part frequency is 100 Hz, where the number of negative pulses is 1, the voltage is 500 V, the pulse width is 100 μs, the number of positive pulses is 1, the voltage is 50 V, the pulse width is 50 μs, and the deposition time is 20 minutes.

[0049] In this embodiment, a TiN film can be deposited on the inner surface of a stainless steel tube with an inner diameter of Φ50 mm. The film is bright golden yellow, and the thickness of the film layer in the middle 160 mm part is 1.4 - 1.7 μm. The results are as Figure 2 shown.

[0050] Example 2:

[0051] In this embodiment, the film layers prepared by two methods, namely pure DC deposition and DC composite bipolar pulse deposition, are compared.

[0052] The specific process of the coating method is as follows:

[0053] I. Specimen preparation: A carbon steel tube with an inner diameter of 40 mm, an outer diameter of 50 mm, and a length of 240 mm is ultrasonically cleaned with acetone and absolute ethanol for 15 minutes each in turn. After taking it out and drying it, it is placed in a vacuum chamber and coaxially installed with a columnar Cr target with an outer diameter of 25 mm and a length of 280 mm;

[0054] II. Pretreatment before coating: The vacuum chamber is evacuated to a pressure of less than 8×10 -3 Pa, and heated and dried for 30 minutes. Then it is evacuated again to a pressure of less than 8×10 -3 Pa, and argon is introduced until the pressure is 5 Pa. Then the inner wall of the stainless steel tube is subjected to plasma sputtering cleaning for 30 minutes to obtain a pretreated stainless steel tube;

[0055] III. Sputtering coating: After the plasma cleaning is completed, argon is introduced and the power supply is turned on;

[0056] During the pure DC deposition process, the power supply parameters are set as: DC current 1 A, deposition time 120 mm;

[0057] During the DC composite bipolar pulse deposition process, the power supply parameters are set as: DC current 0.6 A, pulse part frequency 100 Hz, where the number of negative pulses is 1, voltage 700 V, pulse width 100 μs, the number of positive pulses is 1, voltage 50 V, pulse width 50 μs, deposition time 120 minutes.

[0058] In this embodiment, a Cr film can be deposited on the inner surface of a carbon steel tube with an inner diameter of Φ40 mm, as Figure 3 shown. Figure 3 (a) is the result of pure DC deposition, Figure 3 (b) is the result of DC composite bipolar pulse deposition. It can be found by comparison that there are no obvious thick columnar crystals in the film layer deposited by DC composite bipolar pulse, and the film layer is denser.

Claims

1. A method for magnetron sputtering in a slender tube using a DC composite bipolar pulse, based on the existing secondary discharge magnetron sputtering method, is characterized in that The power supply in the magnetron sputtering process uses a DC composite bipolar pulse power supply. The DC composite bipolar pulse power supply includes three parts: DC power supply, negative pulse power supply, and positive pulse power supply. Each part can be independently controlled to achieve on / off. The three parts are controlled by a single-chip microcomputer combined with a semiconductor switch bridge circuit. In the same cycle, the negative pulse and the positive pulse together form a bipolar pulse, and the negative pulse and the positive pulse are alternately distributed. There can be N negative pulses and M positive pulses in the same pulse cycle, where N = 1, 2,..., 100; M = 1, 2,..., 100. The DC power supply is turned off during the action of the bipolar pulse and turned on during the pulse interval. The current value range of the DC power supply is 0.5 - 100A, and the supply voltage range is 2000V. The pulse widths and voltages of the positive and negative pulses of the bipolar pulse can be independently controlled, and the frequency range is 100Hz - 50kHz. The first pulse in the cycle of the bipolar pulse is a negative pulse. The pulse width ranges of the positive and negative pulses are 50μs - 1ms, and the voltage range is 50 - 2000V. The method includes the following steps: I. Specimen preparation: The tube to be plated is ultrasonically cleaned with acetone and anhydrous ethanol for 5 - 60 minutes each in turn, taken out and dried, and then placed in a vacuum chamber and coaxially installed with the cylindrical target. II. Pre-treatment before coating: The vacuum chamber is evacuated to a pressure below 8×10 -3 Pa, and heated and dried for 10 - 60 minutes. Then it is evacuated again to a pressure below 8×10 -3 Pa, and argon is introduced until the pressure is 0.5 - 10 Pa. Then the inner wall of the pipe to be coated is subjected to plasma sputtering cleaning for 5 - 60 minutes to obtain the pipe to be coated after pre-treatment; III. Sputtering coating: After the plasma cleaning is completed, a mixed gas of working gas and reaction gas is introduced, the power supply is turned on, the gas parameters and power supply parameters are set, and the pre-treated tube to be plated is subjected to magnetron sputtering coating for 10 - 3000 minutes. Among them, in step I, the inner diameter of the tube to be plated is 15 - 2000mm, the wall thickness is 0.1 - 100mm, and the material is a magnetic or non-magnetic conductive material. In step I, the outer diameter of the target tube of the cylindrical target is 8 - 100mm, and the material is a non-magnetic conductive material. During the magnetron sputtering coating process in step III, the cylindrical target is connected to the negative pole of the power supply, and the pre-treated tube to be plated is connected to the positive pole of the power supply. In step III, the working gas is Ar; the reaction gas is one or several of N2, H2, and O2. In step III, the gas parameters: the gas flow rate is 1 - 3000sccm, and the gas pressure is 0.1 - 10Pa.

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