Method for producing a diamond-like carbon film material

Abstract

A method for producing a diamond-like carbon film material (10) comprising a substrate (12) and a diamond-like carbon film (16) formed on the surface thereof and an intermediate layer (14) arranged therebetween, the method comprising the following steps: Applying a negative bias voltage to the substrate (12) in a plasma to release a metal atom component from the substrate (12) into the plasma, generating a carbon atom from a carbon source, wherein the application of the negative bias voltage to the substrate (12) is continued, Reducing an absolute value of the voltage of the negative bias voltage, whereby the metal atom component from the substrate (12) and the carbon atom are deposited on the surface of the substrate (12) to form the intermediate layer (14) as a composite layer containing the metal atom component from the substrate (12) and a diamond-like carbon, and Reducing the absolute value of the negative bias voltage to zero, whereby only the carbon atom is deposited on the intermediate layer (14) to form the diamond-like carbon film (16).

Description

Background of the invention

[0001] The present invention relates to a method for producing a diamond-like carbon film material comprising a substrate and a diamond-like carbon film formed on the surface thereof and an intermediate layer disposed therebetween.

[0002] It is known that diamond-like carbon (hereinafter also referred to as "DLC") film consists of amorphous carbon, exhibits high hardness and a low friction coefficient, and is therefore used as an abrasion-resistant lubricating film on various substrates. Specifically, DLC film is used as a surface coating on magnetic disk read heads, working tools, and the like. Known methods for forming DLC ​​films include plasma chemical vapor deposition (CVD), sputtering, arc ion plating, and the like.

[0003] The bonding strength between the DLC film and the substrate is not very high, and the DLC film tends to peel off the substrate relatively easily. Therefore, there are various studies on preventing DLC ​​film peeling.

[0004] For example, Japanese Patent Application Laid-Open No. JP H10-203897 A proposes a method for cleaning the surface of a substrate, which includes the steps of irradiating the substrate with hydrogen ions to induce a reduction reaction of the surface, and then applying a sputtering gas to the surface. However, when the substrate is made of a substance that cannot easily be converted into a carbide (such as aluminum, magnesium, silicon, or their alloys), it is difficult to prevent peeling of the DLC film even when using such a cleaned surface.

[0005] Japanese Patent Application Laid-Open No. JP H10-203897 A describes, in section 0023, a method comprising the steps of implanting carbon ions into a substrate to form a carbon-containing layer as an ion-implanted layer, and then forming a DLC film on this layer. However, in this method, the carbon-containing layer is formed within the substrate, so the surface composition of the substrate is unlikely to change significantly due to the ion implantation. Therefore, it is difficult to achieve a satisfactory bonding strength between the DLC film and the surface, thereby preventing peeling of the DLC film.

[0006] Another proposed method for preventing peeling of the DCL film involves forming an intermediate layer between the substrate and the DLC film. For example, Japanese Patent Laid-Open No. JP H10-203896 A describes a method comprising the steps of forming an adhesion layer made of silicon, tungsten, titanium, or aluminum and a DLC pretreatment layer made of silicon carbide, tungsten carbide, titanium carbide, or aluminum carbide in that order on a surface of the substrate, and forming the DLC film on the DLC pretreatment layer.

[0007] Furthermore, Japanese Patent Application Laid-Open No. 2008-024996 A describes a method comprising the steps of forming a metal-containing DLC ​​layer as the intermediate layer on a substrate made of an alloy of aluminum, magnesium, or titanium, and then alternately stacking the DLC film and the metal-containing DLC ​​layer. The metal in the metal-containing DLC ​​layer is tungsten, molybdenum, chromium, or titanium, and the metal content is 5-15 wt%.

[0008] When the intermediate layer is formed in the manner described above, a target and a device for generating a metal for the intermediate layer are required, as described in Fig. 2 of Japanese Patent Application Laid-Open No. JP H10-203896 A and paragraph 0031 of Japanese Patent Application Laid-Open No. JP 2008-024996 A. This results in a complicated, large-scale film production apparatus, which disadvantageously leads to high equipment costs. Summary of the invention

[0009] It is a general object of the present invention to provide a diamond-like carbon film material having a DLC film that does not easily peel off from a substrate.

[0010] An essential object of the present invention is to provide a method for producing a diamond-like carbon film material which can be carried out with a conventional film forming apparatus.

[0011] This object is essentially achieved by the invention by the features of claim 1.

[0012] Advantageous embodiments of the invention are the subject of the subclaims.

[0013] The diamond-like carbon film material includes a substrate and a diamond-like carbon film formed on a surface of the substrate with an intermediate layer formed therebetween. The intermediate layer is a composite layer containing a metal atom component derived from the substrate and a diamond-like carbon. The metal atom component derived from the substrate refers to a metal atom obtained from the substrate as the generation source and does not include a metal atom obtained using a target or the like other than the substrate as the generation source.

[0014] The interlayer containing these components is firmly bonded to the substrate and the DLC film. Because the interlayer contains the metal atom component from the substrate, the interlayer is highly compatible with the substrate. Because the interlayer contains the DLC, the interlayer is also highly compatible with the DLC film.

[0015] Therefore, the interlayer is bonded with sufficient strength to both the substrate and the DLC film. As a result, the DLC film is firmly bonded to the substrate by the intermediate interlayer and cannot peel off.

[0016] Preferred examples of substrate components include aluminum, magnesium, silicon, and alloys containing aluminum, magnesium, and / or silicon. It is known that the DLC film peels off relatively easily from such metals. However, with the present invention, it is possible to form the DLC film so that it does not peel off easily even from these metals.

[0017] The above-mentioned metals are light metals, so the resulting DLC ​​film material can achieve a low weight.

[0018] The composition ratio of the metal atom component in the intermediate layer can be reduced in a direction from the substrate to the diamond-like carbon film. In this case, the intermediate layer can be obtained as a gradient layer whose properties vary depending on the change in the metal and the DLC composition ratios. As a result, even in a case where the substrate and the DLC film have different thermal expansion coefficients, the substrate-side portion of the intermediate layer has a thermal expansion coefficient approximately equal to that of the substrate, and at the same time, the DLC film-side portion of the intermediate layer has a thermal expansion coefficient approximately equal to that of the DLC film.For example, if the DLC film material is used in a high-temperature environment, this can prevent peeling of the DLC film due to a mismatch of the thermal expansion coefficients between the substrate and the DLC film.

[0019] According to the present invention, a method for producing a diamond-like carbon film material comprising a substrate and a diamond-like carbon film formed on the surface thereof, as well as an intermediate layer therebetween, is proposed, the method comprising the following steps: applying a negative bias voltage to the substrate in a plasma to release a metal atom component from the substrate into the plasma, generating a carbon atom from a carbon source while continuing to apply the negative bias voltage to the substrate, reducing an absolute value of the voltage of the negative bias voltage, whereby the metal atom component from the substrate and the carbon atom are deposited on the surface of the substrate to form the intermediate layer as a composite layer comprising the metal atom component from the substrate and a diamond-like carbon,and reducing the absolute value of the negative bias voltage to zero, thereby depositing only the carbon atom on the intermediate layer to form the diamond-like carbon film.

[0020] The intermediate layer containing the substrate-derived metal atom component (the metal atom obtained from the substrate as the generation source) and the DLC film can be easily formed by the steps described above.

[0021] Since the metal atom for the intermediate layer is obtained from the substrate as the generation source, an additional target and equipment for forming the intermediate layer are not required. This simplifies the structure of the film-forming device without increasing the size of the device, resulting in low equipment costs.

[0022] The negative bias voltage originally applied to release the metal atoms from the substrate into the plasma (the initial bias voltage) can be a voltage of -100 to -1,000 V.

[0023] Preferably, the absolute value of the negative bias voltage is gradually or gradually reduced from the initial bias voltage applied to release the metal atoms from the substrate into the plasma to zero to form the diamond-like carbon film. In this case, the intermediate layer can simply be formed such that the metal content decreases and the DLC content increases in the direction from the substrate to the DLC film.

[0024] According to the present invention, the intermediate layer containing the metal atom generated from the substrate and the DLC are formed on the surface of the substrate, and the DLC film is formed thereon. The intermediate layer is highly compatible with both the substrate and the DLC film, thereby firmly bonding them. As a result, the intermediate layer is bonded to both the substrate and the DLC film with satisfactory bonding force. As a result, the DLC film can be firmly bonded to the substrate through the intermediate layer, and peeling of the DLC film is prevented.

[0025] Further developments, advantages, and possible applications of the invention will also become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, individually or in any combination, constitute the subject matter of the invention, regardless of their summary in the claims or their reference back to them. Short description of the drawings Fig. 1 is an enlarged longitudinal section through an essential part of a DLC film material produced according to an embodiment of the present invention; Fig. 2 is a schematic overall view of a film forming apparatus for producing the DLC film material according to Fig. 1; Fig. 3A-3C are enlarged schematic diagrams showing an essential part of the formation of an interlayer and a DLC film; Fig. Figure 4 is a graph showing an example of the change of negative bias voltage over time; Fig. 5 is a graph showing the results of a ball-on-disk friction wear test for samples of an example and a comparative example; Fig. 6 is a 100x scanning electron microscope (SEM) photograph of a wear mark formed by the frictional wear test on the sample of Comparative Example; Fig. 7 is a scanning electron microscope photograph at 1,000x magnification of the wear trace on the sample of Comparative Example; Fig. Fig. 8 is a 100x scanning electron microscope photograph of a wear mark formed by the frictional wear test on the sample according to the invention example, and Fig. 9 is a scanning electron microscope photograph at 1,000x magnification of the wear trace in the sample according to the invention example. Description of the preferred embodiments

[0026] Fig. 1 is an enlarged longitudinal section of an essential part of a DLC film material 10 according to this embodiment. The DLC film material 10 is obtained by forming an intermediate layer 14 and a DLC film 16 in this order on a surface of a substrate 12.

[0027] The substrate 12 is a metallic element. In this embodiment, the substrate 12 preferably contains aluminum, magnesium, silicon, or an alloy containing at least one of these elements. Generally, such metals, especially silicon, cannot be easily converted into a carbide, and it is difficult to prevent the DLC film 16 from peeling off the metal. Nevertheless, in this embodiment, the substrate 12 may be made of the metal.

[0028] The DLC film material 10 may preferably be used in a magnetic disk read head, a working tool, or the like, but is not limited thereto.

[0029] The intermediate layer 14 is a composite layer containing a DLC and a metal atom component derived from the substrate 12 (in this embodiment, aluminum, magnesium, silicon, or the like). The intermediate layer 14 contains the metal atom component from the substrate 12 and is thereby firmly bonded to the substrate 12.

[0030] In the intermediate layer 14, a section closer to the substrate 12 has a higher metal content and a lower DLC content. In contrast, a section farther from the substrate 12 has a lower metal content and a higher DLC content. As a result, the intermediate layer 14 is a gradient layer whose metal and DLC contents vary in the thickness direction.

[0031] A satisfactory and preferred thickness of the intermediate layer 14 is 0.01 to 1.0 µm, although there is no limitation thereto.

[0032] The DLC film 16 formed on the intermediate layer 14 consists solely of DLC. Thus, the DLC film 16 is free of the metal atom component from the substrate 12. In other words, in the DLC film 16, the proportion of the metal atom component from the substrate 12 (the metal contained in the intermediate layer 14) is zero.

[0033] The intermediate layer 14 and the DLC film 16 are formed sequentially by changing the conditions for sputtering the metal atom component onto the substrate 12 to a condition in which no atoms are sputtered. This will be described below. Therefore, the DLC film 16 is highly compatible with the intermediate layer 14 and firmly bonded to it.

[0034] From the above description, it is understood that the intermediate layer 14 is firmly bonded to both the substrate 12 and the DLC film 16 and that peeling off of the DLC film 16 is prevented.

[0035] The thickness of the DLC film 16 can be appropriately selected depending on the desired properties, such as sliding properties. The thickness can be approximately 0.2 to 10 µm, although there is no limitation.

[0036] A method for producing the DLC film material 10 is described below.

[0037] Fig. Figure 2 is a schematic diagram showing the structure of a film forming apparatus 20 (a plasma film forming apparatus) for producing the DLC film material 10. The film forming apparatus 20 includes a vacuum chamber 22 for accommodating the substrate 12, a negative voltage supply 24, such as a high-frequency or direct current supply, and a carbon target 27 electrified by a plasma-generating electrode 26.

[0038] The plasma generating electrode 26 is arranged at the bottom of the vacuum chamber 22, while the substrate 12 is arranged in the opposite position. A plasma generating power supply 28 is electrically connected to the plasma generating electrode 26, while the negative voltage supply 24 is electrically connected to the substrate 12. The voltage generated by the negative voltage supply 24 is controlled by an electrically connected dynamic bias control mechanism 30.

[0039] An inert gas inlet 32 ​​is formed on the vacuum chamber 22. An inert gas is introduced from an inert gas source (not shown) through the inert gas inlet 32 ​​into the vacuum chamber 22 and then used as a plasma source.

[0040] The vacuum chamber 22 is connected to an exhaust gas pump 38 via an exhaust gas passage 36. A baffle plate 42, which is axially rotatably supported by a support shaft 40, is arranged upstream of the exhaust gas pump 38. When the baffle plate 42 moves in the horizontal direction in Fig. 2, the area shielding the exhaust passage 36 is minimized and the amount of exhaust gas is maximized. On the other hand, if the baffle plate 42 extends in the vertical direction in Fig. 2, the shielding area is maximized and the amount of exhaust gas is minimized.

[0041] The DLC film material 10 can be manufactured by using the film forming apparatus 20 having the above-described structure as follows.

[0042] First, the inert gas, for example, argon, is introduced into the vacuum chamber 22 from the inert gas inlet 32, and the exhaust pump 38 is activated. The internal pressure of the vacuum chamber 22 is maintained at, for example, 0.1 to 1 Pa.

[0043] Meanwhile, the plasma generation power source 28 and the negative voltage supply 24 are activated, generating an electric field between the plasma generation electrode 26 and the substrate 12. A plasma is generated in the vacuum chamber 22 by the electric field. A negative bias voltage of -100 to -1,000 V, preferably approximately -600 V, is applied to the substrate 12. The negative bias voltage can be an AC or DC bias voltage.

[0044] The substrate 12 is sputtered by applying the negative voltage (cathode sputtering). Thus, as shown in Fig. As shown in Figure 3A, the metal atoms contained in the substrate 12 (i.e., aluminum, magnesium, or silicon atoms, or the like) are released from the substrate 12 into the plasma. The carbon target 27 is simultaneously sputtered, so that the carbon atoms are released into the plasma.

[0045] The negative bias voltage applied to the substrate 12 is controlled by the dynamic bias control mechanism 30. In detail, as shown in Fig. 4, the absolute value of the negative bias voltage is reduced in a fixed time interval.

[0046] When the negative bias voltage has an excessively high absolute value, the carbon atoms and metal atoms from the substrate 12 are dispersed in the plasma. When the absolute value is reduced, the carbon atoms and metal atoms are attracted from the substrate 12 to the substrate 12. Then, as shown in Fig. 3B, the carbon atoms and the metal atoms from the substrate 12 are deposited onto the substrate 12 to begin the formation of the intermediate layer 14.

[0047] When the negative bias voltage has a larger absolute value, a larger amount of metal atoms is released from the substrate 12. Therefore, a relatively smaller amount of carbon atoms is used in film formation. As a result, a portion of the intermediate layer 14 deposited in the initial phase of film formation has a higher metal content.

[0048] After a predetermined period of time has elapsed, the absolute value of the negative bias voltage applied to the substrate 12 is gradually decreased at a fixed time interval in the manner described above by the dynamic bias control mechanism 30 (see FIG. Fig. 4). Then, the amount of metal atoms and / or carbon atoms released from the substrate 12 is reduced, thereby increasing the relative proportion of carbon atoms in the film. Thus, in the intermediate layer 14, a region deposited after the reduction in the absolute value has a lower metal content and a higher carbon content than a region deposited before the reduction.

[0049] By repeating the negative voltage control, the intermediate layer 14 can be formed as a gradient layer in which the metal content decreases with the thickness and the carbon content increases with the thickness.

[0050] The absolute value of the negative bias voltage is finally reduced to zero. In this stage, no metal atoms are released from the substrate 12, and mainly the carbon atoms are used for film formation. Thus, the formation of the intermediate layer is completed, and the formation of the DLC film 16 begins, as shown in the Fig. 3C and Fig. 4 is shown.

[0051] The formation of the DLC film 16 is completed when the formation is continued for a specified time with the negative bias voltage of zero. This causes the Fig. 1, which has the intermediate layer 14 and the DLC film 16 superimposed in this order on the surface of the substrate 12.

[0052] As described above, the intermediate layer 14 contains the metal atom component from the substrate 12 and the DLC. This increases the bonding strength between the intermediate layer 14 and the substrate 12 and between the intermediate layer 14 and the DLC film 16. The DLC film 16 is firmly bonded to the substrate 12 through the intermediate layer 14 containing the metal atom component from the substrate 12 and the DLC. Conventionally, it is difficult to prevent the DLC film from peeling off from a substance such as aluminum, magnesium, or silicon. In this embodiment, even if the substrate 12 is made of such a substance, peeling off of the DLC film 16 can be effectively prevented or avoided.

[0053] Furthermore, the method according to the embodiment eliminates the need for an additional target and equipment for forming the intermediate layer 14. Therefore, the structure of the film forming apparatus 20 can be kept simple without increasing the size of the apparatus 20, resulting in low equipment costs.

[0054] The DLC film material 10 (i.e., the substrate 12 with the intermediate layer 14 and the DLC film 16) has high abrasion resistance due to the high hardness of the DLC film 16 and exhibits excellent lubricity due to the low friction coefficient. This allows the amount of lubricating oil to be reduced, thereby saving resources and reducing environmental impact.

[0055] Since the DLC film 16 does not peel off easily, a sliding member using the DLC film material 10 can exhibit excellent lubrication properties over a long period of time, resulting in low labor and maintenance costs.

[0056] In addition, aluminum, magnesium, silicon, and their alloys used for the substrate 12 are light metals, so that the resulting DLC ​​film material 10 in this embodiment can achieve a low weight with a low friction coefficient.

[0057] Although the sputtering method using a carbon target was exemplified in the above-described embodiment, the intermediate layer 14 and the DLC film 16 can also be formed by a CVD (chemical vapor deposition) method using a hydrocarbon gas. In this case, the hydrocarbon gas can be, for example, methane gas or acetylene gas.

[0058] In this embodiment, the absolute value of the negative bias applied to the substrate 12 is gradually reduced as shown in Fig. 4. The reduction is not limited to this, and the absolute value can also be continuously (gradually) reduced over time.

[0059] Although aluminum, magnesium, silicon, and alloys containing at least one of these elements have been described as preferred examples of the components of the substrate 12 in the present embodiment, the components are not limited to these. For example, the substrate 12 may also be made of an iron alloy, such as steel. Example 1

[0060] A disc made of A2017 (aluminum alloy according to Japanese Industrial Standard JIS) with a diameter of 24 mm and a thickness of 6 mm was prepared as the substrate 12. In the film forming device 20, which is Fig. 2, the substrate 12 and a graphite target (not shown) were placed in the vacuum chamber 22.

[0061] Then, the internal pressure of the vacuum chamber 22 was reduced to less than 5×10 -4 Pa, and an argon gas was introduced into the vacuum chamber 22 from the inert gas inlet 32. The argon gas was supplied at a flow rate of 4 sccm to control the internal pressure of the vacuum chamber 22 to 1 Pa. The substrate 12 was left in this state for two hours, with a negative voltage of -600 V applied so that a surface of the substrate 12 was cleaned by argon ion etching.

[0062] By applying an electric current, a voltage was applied to the graphite target to generate carbon ions. The beginning of the voltage application was considered the starting point of film formation.

[0063] The absolute value of the negative bias voltage was repeatedly decreased by 100 V at intervals of 5 minutes by the dynamic bias control mechanism 30. As a result, the negative bias voltage was gradually changed to -500, -400, -300, -200, and -100 V. It was found that the negative voltage from -500 to -100 V formed a film on the substrate 12.

[0064] The negative bias voltage was then further changed from -100 V to 0 V, and film formation continued for 5 minutes. A film was also formed under the negative bias voltage of 0 V.

[0065] The films of the resulting sample of the example were examined for their components. It was found that the upper film was a DLC film 16 and the lower film was a metal-containing DLC ​​layer. The metal content of the metal-containing DLC ​​layer increased toward the substrate 12.

[0066] For comparison, the same substrate 12 was subjected to the above-described pretreatment, and then the negative bias voltage was rapidly changed to 0 V to form a DLC film. A sample of a comparative example was thus obtained.

[0067] The samples of the example and the comparative example were subjected to a friction wear test using a ball-on-disk method. This test used a friction material made of SUS304 (a stainless steel according to JIS) with a load of 100 gf, a linear velocity of 0.785 cm / s, a rotational velocity of 0.5 rotations / s, and a rotation radius of 5.0 mm.

[0068] The results are in Fig. 5. As shown in Fig. As shown in Figure 5, in the sample of the comparative example, the DLC film 16 peeled off at about 600 m, corresponding to 40,000 revolutions. In contrast, in the sample of the inventive example, the DLC film 16 did not peel off and maintained the bond even at about 2,000 m, corresponding to 120,000 revolutions.

[0069] Scanning electron microscope photographs of the wear traces obtained by the friction wear test on the sample of the comparative example are shown in the Fig. 6 and Fig. 7, while scanning electron microscope photographs of a wear trace in the sample of the inventive example are shown in the Fig. 8 and Fig. 9. The scanning electron microscope photographs according to the Fig. 6 and Fig. 8 was taken at 100x magnification and those of Fig. 7 and Fig. 9 were taken at 1,000x magnification.

[0070] As in the Fig. As shown in FIGS. 6 to 9, the DLC film 16 in the sample according to the comparative example peeled off, while the DLC film 16 in the sample according to the inventive example merely abraded and retained its bonding to the substrate 12. This demonstrates that peeling of the DLC film 16 can be prevented by forming the intermediate layer 14 containing the metal atom component from the substrate 12.

Claims

[1] A method for producing a diamond-like carbon film material (10) comprising a substrate (12) and a diamond-like carbon film (16) formed on the surface thereof and an intermediate layer (14) disposed therebetween, the method comprising the steps of: Applying a negative bias voltage to the substrate (12) in a plasma to release a metal atom component from the substrate (12) into the plasma, generating a carbon atom from a carbon source, wherein the application of the negative bias voltage to the substrate (12) is continued, Reducing an absolute value of the voltage of the negative bias voltage, whereby the metal atom component from the substrate (12) and the carbon atom are deposited on the surface of the substrate (12) to form the intermediate layer (14) as a composite layer containing the metal atom component from the substrate (12) and a diamond-like carbon, and Reducing the absolute value of the negative bias voltage to zero, whereby only the carbon atom is deposited on the intermediate layer (14) to form the diamond-like carbon film (16). [2] A method according to claim 1, characterized by that an initial bias voltage of -100 to -1,000 V is applied to release the metal atom component from the substrate (12) into the plasma. [3] A method according to claim 1 or 2, characterized bythat the absolute value of the voltage of the negative bias voltage is gradually or gradually reduced from that of an initial bias voltage applied to release the metal atom component from the substrate (12) into the plasma to zero to form the diamond-like carbon film (16). [4] Method according to one of claims 1 to 3, characterized by that the substrate (12) contains aluminum, magnesium, silicon or an alloy comprising aluminum, magnesium and / or silicon. [5] A method according to any one of claims 1 to 4, characterized by that a carbon target (27) is used as the carbon source for generating the carbon atom contained in the intermediate layer (14) and the diamond-like carbon film (16). [6] Method according to one of claims 1 to 4, characterized bythat a hydrocarbon gas is used as the carbon source for generating the carbon atom contained in the intermediate layer (14) and the diamond-like carbon film (16). [7] Method according to one of claims 1 to 6, characterized by that the intermediate layer (14) has a thickness of 0.01 to 1.0 µm. [8] Method according to one of claims 1 to 6, characterized by that the diamond-like carbon film (16) has a thickness of 0.2 to 10 µm.

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