TWI504772B - Copper-manganese alloy film and copper-manganese alloy sputtering target and film formation method of copper-manganese alloy film - Google Patents

Description

Copper-manganese alloy film and copper-manganese alloy sputtering target and copper-manganese alloy film Film formation method

The present invention relates to a copper-manganese (Cu-Mn) alloy film for use in an electrode film or a wiring film for, for example, a flat display element, which requires low reflectance, and a Cu-Mn alloy sputtering target for film formation thereof. A film forming method of a material and a Cu-Mn alloy film.

A liquid crystal display (hereinafter referred to as "LCD (Liquid-crystal Display)"), a plasma display panel (hereinafter referred to as "PDP (Plasma Display Panel)"), an electronic paper, etc., which form a thin film element on a transparent glass substrate or the like. A flat display device (a flat panel display, hereinafter referred to as "FPD (Flat Panel Display)") used in the present invention requires a large screen, high definition, and high-speed response, and accordingly, the wiring film is required to have a low resistance. . Further, in recent years, new products such as a touch panel that adds operability to an FPD or a flexible FPD that uses a resin substrate or an extremely thin glass substrate have been developed.

In addition, while viewing the screen of the FPD, a direct-operating touch surface is provided. The size of the board substrate has also increased, and products for performing touch panel operations on smart phones, tablet PCs, and desktop PCs are also becoming popular. As the position detecting electrode of the touch panel, indium tin oxide (hereinafter referred to as "ITO (Indium Tin Oxide)") as a transparent conductive film is generally used.

In recent years, in the capacitive touch panel capable of multi-point detection, a diamond arrangement in which a quadrangular ITO film is disposed is used, and a metal film is used as a protective film for connecting an electrode film of a tetragonal ITO film or a wiring film. This metal film uses a Mo or Mo alloy which is easy to obtain contact with an ITO film.

In addition, the industry is developing products using flexible FPDs or touch panels using resin film substrates other than glass substrates or ultra-thin glass substrates.

However, it has been clarified that if the metal film of the Mo or Mo alloy is formed into a film in these applications and the substrate is bent, there is a problem in that the Mo film or the Mo alloy film is liable to be formed. In the crack or the like, the adhesion to the substrate cannot be ensured, and the effect of protecting the Cu film of the wiring film cannot be sufficiently maintained. Therefore, as a method of not using Mo or a Mo alloy, the Cu alloy has received the latest attention, and it has been proposed to ensure adhesion to the above-described substrate. (Refer to Patent Document 1 to Patent Document 3)

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2012-211378

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2012-212811

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2013-67857

In order to obtain a wiring film having a low electric resistance value, the Cu alloy film proposed in Patent Document 1 and Patent Document 2 contains Cu selected from the group consisting of Ag, Au, C, W, Ca, Mg, Al, Sn, B, and Ni. The Cu-Mn-X alloy film of at least one element of the group is used as a base film of the Cu film to ensure adhesion to the substrate, the insulating film or the semiconductor film.

Further, in Patent Document 3, it is proposed to form a Cu alloy film containing a Cu-Mn alloy in order to secure barrier properties against a semiconductor film containing indium-gallium-zinc-oxygen (hereinafter referred to as "IGZO film"). In the method, the Cu-Mn alloy contains Mn having a concentration of 8 at% or more and 30 at% or less and inevitable impurities.

On the other hand, in the case of a large 4K-TV having a higher-definition 4x pixel with full hivision in recent years, a method of using lower resistance Cu instead of Al as a main wiring material is being increased. In addition, in the case of a smart phone that operates a display screen at a very close distance of about 10 cm from the eye, the high definition of the full-height display is progressing for a small screen. Along with this high definition, the problem of reflection of the metal film by incident light causes a deterioration in display quality. Therefore, for the metal film, the demand for a new characteristic having a low reflectance (hereinafter sometimes referred to as "low reflection" is rapidly increasing.

Moreover, in the manufacturing steps of the flat display element or the touch panel, the film forming electrode After the film and the wiring film, in the heat treatment step of performing the patterning, the heat treatment at about 230 ° C is performed in an air atmosphere, and therefore it is expected that the film can be obtained at a temperature of 200 ° C or lower as low as possible. Reflective metal film.

Now, an Al film for a wiring film of a flat display element in a flat display device is a metal having a high reflectance of 90% or more in a visible light region. Further, the Cu film which is also used for the wiring film of the flat display element has a reflectance of 70% in the visible light region, and has a high reflectance of 95% or more in the long wavelength region of 600 nm or more. On the other hand, the Mo film or the Mo alloy film laminated to protect the wiring films has a reflectance of about 60%. Since the reflectance of the metal film hardly changes even through the process of the flat display element, the reflection of the metal film is a factor that causes deterioration in display quality in a particularly high-definition display device.

Therefore, in a high-definition display device, an electrode film or a wiring film having a lower reflection of about half of Mo or the like, that is, 30% or less is required.

As described above, various Cu alloy films have been developed so far. However, in these patent documents, attention has been paid to the wiring film or the barrier film, and it is necessary to cope with the new characteristics of the future high-definition display device, that is, the necessary low reflection. No research has been done.

An object of the present invention is to provide a Cu-Mn alloy film which can meet the new requirements for low reflection in an electrode film or a wiring film which is necessary for improving the display quality of a high-definition flat display element, and a Cu-Mn film for film formation. A film forming method of a Cu-Mn alloy sputtering target of an alloy film and a Cu-Mn alloy film.

In view of the above-described problems, the inventors of the present invention have focused on the optimization of additive elements and addition amounts in order to obtain low-reflection characteristics in the manufacturing steps of a flat display element or a touch panel. As a result, it was found that a Cu-Mn alloy film obtained by adding a specific amount of Mn to Cu can obtain low reflection characteristics, thereby completing the present invention.

That is, the present invention is a Cu-Mn alloy film in which, when the total metal component is 100 atom%, the metal component contains 32 atom% to 45 atom% of Mn, and the remainder contains Cu and is inevitable. The impurity has a visible light reflectance of 30% or less.

Further, the Cu-Mn alloy film of the present invention contains a metal component and oxygen, and when the total metal component is 100 atom%, the metal component contains 32 atom% to 45 atom% of Mn, and the balance contains Cu and unavoidable impurities. The ratio of oxygen is 0.3 to 0.6 in terms of atomic ratio with respect to the sum of the metal component and the oxygen.

Further, the Cu-Mn alloy film of the present invention is suitable for an electrode film or a wiring film for a flat display element.

Further, the present invention is a Cu-Mn alloy sputtering target which contains 32 atom% to 45 atom% of Mn, and the remainder contains Cu and unavoidable impurities.

The Cu-Mn alloy sputtering target of the present invention is preferably a structure having a recrystallized structure in a grain boundary of a Cu-Mn alloy powder.

The Cu-Mn alloy film of the present invention can be contained by 32 atom% to 45 original The Cu-Mn alloy film containing Mn of the % and the remaining part containing Cu and unavoidable impurities is obtained by film formation by sputtering in an environment containing 30% by volume to 60% by volume of oxygen.

Further, the Cu-Mn alloy film of the present invention can also be sputtered in an inert gas atmosphere by using a Cu-Mn alloy film containing 32 atom% to 45 atom% of Mn and the remainder containing Cu and unavoidable impurities. Film formation is carried out, and then the Cu-Mn alloy film is heated in an atmosphere of 200 ° C to 225 ° C to obtain.

Since the Cu-Mn alloy film of the present invention can achieve a new characteristic of low reflection which cannot be obtained by the conventional electrode film or wiring film, it is possible to improve display quality such as FPD. Therefore, it is a very useful technique for a next-generation information terminal such as a 4K-TV or a smart phone or a tablet PC, or a flexible FPD using a resin substrate, which is attracting attention as a higher-definition FPD. The reason is that the low reflection of the metal film, especially the metal film, is very important.

Fig. 1 is a photograph of a structure obtained by observing a cross section of a Cu-Mn alloy sputtering target of the present invention by an optical microscope.

An important feature of the present invention resides in the following aspects: as a Cu alloy film suitable for use as an electrode film or a wiring film for, for example, a flat display element, by using Cu A Cu-Mn alloy obtained by adding a specific amount of Mn has found a new characteristic of low reflectance. In the following description, the "reflectance" means an average reflectance in a visible light region, that is, a wavelength range of 360 nm to 740 nm. Hereinafter, the present invention will be described in detail.

In the Cu-Mn alloy film of the present invention, one of the reasons for adding a specific amount of Mn to Cu is to lower the reflectance after the heat treatment step of the photoresist through the patterning. As described above, the Al film which is currently used for the wiring film of the flat display element is a metal having a high reflectance of 90% or more in the visible light region. Further, the Cu film which is also used for the wiring film of the flat display element has a reflectance of 70% in the visible light region, and has a high reflectance of 95% or more in the long wavelength region of 600 nm or more.

On the other hand, the Mo film or the Mo alloy film laminated to protect the wiring films has a reflectance of about 60%. Even if the metal films pass through the process of the display element manufacturing step described above, the reflectance hardly changes.

On the other hand, the Cu-Mn alloy film of the present invention has a low reflectance by using a Cu-Mn alloy obtained by adding a specific amount of Mn to Cu. According to the study of the present inventors, it has been confirmed that the effect of reducing the reflectance is remarkably exhibited when the total amount of Mn added to the metal component is 32 atom% to 45 atom% when the total metal component is 100 atom%. Although the reason is not clear, the Cu-Mn alloy is a completely solid solution alloy, and its melting point is most reduced when the amount of Mn is 38 atom%. Further, when the melting point of the Cu-Mn alloy film is low, it becomes easy to introduce when the heat treatment described above is performed. Recrystallization or atomic migration. Further, when Mn in the Cu-Mn alloy film is heat-treated in the presence of oxygen, Mn easily migrates to the surface of the film through the grain boundary.

In the Cu-Mn alloy film of the present invention, when the total amount of the metal component is 100 atom%, the amount of Mn added to the metal component is 32 atom% to 45 atom%, and the melting point is low. In the composition range, when heat treatment is performed at 200 ° C to 225 ° C in an atmospheric environment, Mn in the Cu-Mn alloy film diffuses to the surface of the film to form an oxide, and the reflectance is lowered.

Further, in order to form a Cu-Mn alloy film having a lower reflectance, when the total amount of the metal component is 100 atom%, the amount of Mn added to the metal component is preferably 32 atom% to 40 atom%, more preferably 32 atom% to 39 atom%.

The Cu-Mn alloy film of the present invention contains a metal component and oxygen. When the total amount of the metal component is 100 atom%, the metal component contains 32 atom% to 45 atom% of Mn, and the remainder contains Cu and unavoidable impurities. With respect to the sum of the metal component and the oxygen, the oxygen ratio is set to 0.3 to 0.6 in atomic ratio, whereby a lower reflectance can be obtained. When the Cu-Mn alloy film is heat-treated in an atmosphere or formed in an atmosphere containing oxygen, the film contains oxygen. In particular, since Mn is more easily combined with oxygen than Cu, the Cu-Mn alloy film containing a specific amount of Mn of the present invention can attain low reflectance by easily absorbing a large amount of oxygen.

In the pure Cu film, oxygen exists in the form of a linear compound on the equilibrium state diagram of Cu ₂ O or CuO. On the other hand, it is considered that the Cu-Mn alloy film contains Mn and becomes a non-equilibrium phase containing MnO or Mn ₃ O ₄ having a wide stable region and Cu, and absorbs oxygen in a wide range of compositions, so that it becomes easy to obtain lower Reflectivity.

In the Cu-Mn alloy film of the present invention, by setting the ratio of oxygen to the total of oxygen in the film to oxygen to be 0.3 or more, reflection with metallic luster can be suppressed, and low reflectance can be achieved. . In addition, the Cu-Mn alloy film of the present invention has a ratio of oxygen to the total of oxygen in the film to an atomic ratio of 0.6 or less, thereby suppressing light transmission and achieving low reflectance. In addition to this, adhesion to a substrate or the like can be improved. Therefore, in the Cu-Mn alloy film of the present invention, the ratio of oxygen contained in the Cu-Mn alloy film is 0.3 to 0.6 in terms of atomic ratio with respect to the total of the oxygen. It is preferably 0.33 to 0.57.

The film thickness of the Cu-Mn alloy film of the present invention is preferably from 20 nm to 200 nm. In the present invention, by setting the film thickness of the Cu-Mn alloy film to 20 nm or more, light transmission is suppressed, and a Cu-Mn alloy film having a low reflectance can be obtained. Further, in the present invention, by setting the film thickness of the Cu-Mn alloy film to 200 nm or less, the time for film formation can be shortened, and the substrate due to film stress after film formation or heat treatment can be suppressed. Warping. In the present invention, in order to stably obtain a Cu-Mn alloy film having a low reflectance with high productivity, it is more preferable to set the film thickness of the Cu-Mn alloy film to 50 nm to 100 nm.

When forming the Cu-Mn alloy film of the present invention, it is preferable to use a sputtering method using a sputtering target. As the sputtering method, a method of forming a film using a Cu-Mn alloy sputtering target having the same composition as that of the Cu-Mn alloy film; or by using, for example, Cu The sputtering target is co-sputtered with a sputtering target of Mn or Mn-Cu alloy to form a film.

Among them, a method of forming a film using a Cu-Mn alloy sputtering target having the same composition as that of the Cu-Mn alloy film is preferably used. Further, in the present invention, the Cu-Mn alloy can be formed simply and stably by using a Cu-Mn alloy sputtering target containing 32 atom% to 45 atom% of Mn and the remainder containing Cu and unavoidable impurities. membrane. Further, as described above, in order to stably obtain a Cu-Mn alloy film having a lower reflectance, it is preferable to use Cu-Mn containing 32 atom% to 40 atom% of Mn, and the balance containing Cu and unavoidable impurities. Alloy sputtering target. The content of Mn in the Cu-Mn alloy sputtering target of the present invention is more preferably in the range of 32 atom% to 39 atom%.

The Cu-Mn alloy sputtering target of the present invention can be produced by melting or casting a raw material formulated into a specific composition, producing an ingot, and manufacturing it by mechanical processing; or atomizing a raw material formulated into a specific composition Or the ingot is pulverized to produce a Cu-Mn alloy powder, which is pressure-sintered by heat equalization (hereinafter referred to as "HIP (hot isostatic pressing)" or the like.

Regarding the method for producing the Cu-Mn alloy sputtering target of the present invention, a method which can be inexpensively and stably produced can be appropriately selected depending on the size or shape of the sputtering target. The Cu-Mn alloy sputtering target of the present invention is preferably produced by using an atomized powder containing a Cu-Mn alloy and optimizing the sintering temperature, thereby forming a grain boundary of the Cu-Mn alloy powder. The tissue that recrystallizes the tissue. By this, the Cu-Mn alloy sputtering target of the present invention can suppress the generation of abnormal particles such as sputtering by stably forming a non-deformed structure of recrystallization, and stably obtain a uniform and high-grade Cu-Mn alloy. membrane.

In the Cu-Mn alloy sputtering target of the present invention, in order to secure a low reflectance, it is preferable that the unavoidable impurities other than Cu account for a small amount of the remainder other than Mn which is an essential element, and the content is not impaired. In the scope of the action of the present invention, unavoidable impurities such as nitrogen, carbon, Fe, and Si may be contained. For example, nitrogen is preferably 1000 ppm by mass or less, carbon is 200 ppm by mass or less, Fe is 500 ppm by mass or less, Si is 100 ppm by mass or less, and the purity of the removed gas component is 99.9% by mass or more.

The Cu-Mn alloy film of the present invention can be obtained by applying a so-called reactive sputtering method, that is, when sputtering is performed using a sputtering target, it is contained in a general sputtering gas, that is, an inert gas, Ar, etc., as reactivity. A sputtering gas made of oxygen from a gas. At this time, the content ratio of oxygen in the sputtering gas is preferably from 30% by volume to 60% by volume.

Further, the Cu-Mn alloy film of the present invention can also be obtained by forming a Cu-Mn alloy film by sputtering in an inert gas atmosphere such as Ar when sputtering is performed using a sputtering target. The Cu-Mn alloy film is then heated in an atmosphere of 200 ° C to 225 ° C.

[Example 1]

First, a sputtering target for forming a Cu-Mn alloy film was produced. The ingot was weighed by using an atomic ratio of 80 atom% of Mn-Cu, and was melted and cast by a vacuum melting furnace to produce an ingot. Thereafter, the ingot was machined to prepare a sputtering target having a diameter of 100 mm and a thickness of 5 mm.

Further, an Al sputtering target for forming an Al film which is a comparative example was prepared by purchasing an Al sputtering target manufactured by Sumitomo Chemical Co., Ltd. Further, the Cu sputtering target for forming a Cu film to be a comparative example was processed by processing an oxygen-free copper (OFC) raw material manufactured by Hitachi Cable Co., Ltd. to prepare a Cu sputtering target. . Further, the Mo sputtering target for forming a Mo film to be a comparative example was a pressure-sintered Mo powder having a purity of 4 N to prepare a Mo sputtering target.

Each of the produced sputtering targets was welded to a copper backing plate and mounted on a sputtering apparatus (Model: CS-200) manufactured by ULVAC. Then, a film of a film thickness as shown in Table 1 was formed on a glass substrate of 25 mm × 50 mm to prepare a sample for evaluation. Further, the film formation of the Cu-Mn alloy film is changed by the co-sputtering method in which the prepared Cu sputtering target and the 80 atom% Mn-Cu sputtering target are simultaneously sputtered, and is applied to each sputtering target. On the electric power, a Cu-Mn alloy film of different composition is formed.

The composition of the formed Cu-Mn alloy film was confirmed using an inductively coupled plasma spectrometer (ICP (Inductively Coupled Plasma) model: ICPV-1017) manufactured by Shimadzu Corporation.

Then, each sample was heat-treated at 150 ° C and 200 ° C for 30 minutes in an air atmosphere to obtain a sample for reflectance measurement. The measurement results of the reflectance of each of the obtained samples are shown in Table 1. Further, the reflectance was measured by a spectrophotometer (model: CM2500d) manufactured by Konica Minolta Co., Ltd. Further, the * mark in Table 1 indicates that it is outside the scope of the present invention.

As shown in Table 1, it is understood that Al or Cu having a low electric resistance value or Mo used for the laminated film hardly lowers the reflectance even when heated at 200 ° C in an atmospheric environment.

On the other hand, it is understood that the reflectance of the Cu-Mn alloy film of the present invention is slightly lowered when heated at 150 ° C, and is further greatly reduced when heated at 200 ° C. In particular, when the amount of Mn added in the Cu-Mn alloy film is in the range of 32 atom% to 43 atom%, it is confirmed that a low reflectance of 30% or less is obtained, and the electrode film is suitable for a flat display element. Or a Cu-Mn alloy film of a wiring film.

[Embodiment 2]

In the sample of Example 1, the samples of Sample No. 1, No. 5, No. 6, and No. 7 were subjected to heat treatment at 225 ° C, 250 ° C, and 300 ° C in an atmosphere. The results of the reflectance of the Cu-Mn alloy film are shown in Table 2. Further, the * mark in Table 2 indicates that it is outside the scope of the present invention.

As shown in Table 2, it was confirmed that the reflectance of the Cu-Mn alloy film was further lowered as compared with 200 °C shown in Table 1 when the heating temperature in the atmosphere was 225 °C. On the other hand, when the heating temperature in the atmospheric environment was confirmed to be 250 ° C, the reflectance of the Cu-Mn alloy film exceeded 30%, which was greatly increased. Therefore, in order to obtain the Cu-Mn alloy film of the present invention, it is confirmed that the heating temperature of the Cu-Mn alloy film in the atmosphere is preferably 200 ° C to 225 ° C.

[Example 3]

In order to produce a sputtering target having an atomic ratio of Cu-34 atom% Mn, an atomized powder having the same composition was prepared, and classification was carried out using a 100-mesh sieve to obtain a Cu-Mn alloy powder having an average particle diameter of 70 μm. As a result of chemical analysis of the Cu-Mn alloy powder, it was confirmed that the purity was 99.9%.

Then, it was filled in a cylindrical steel vessel having an inner diameter of 133 mm × a height of 30 mm and a thickness of 3 mm, and heated at 450 ° C for 5 hours to carry out a degassing treatment. Thereafter, the soft steel container was sealed, and sintered by a HIP apparatus under the conditions of a sintering temperature of 800 ° C, a pressurization pressure of 118 MPa, and a sintering time of 5 hours.

After cooling, it was taken out from the HIP apparatus, and the soft steel container was taken out by mechanical processing to obtain a Cu-Mn alloy sputtering target of the present invention having a diameter of 100 mm and a thickness of 5 mm, and the test piece was cut out from the remaining portion.

The quantitative analysis of the metal elements of the obtained test piece was carried out by an inductively coupled plasma spectrometer (ICP) (Model: ICPV-1017) manufactured by Shimadzu Corporation, and the amount of oxygen was determined by a non-dispersive infrared absorption method. The sum of the analytical values of Cu and Mn was 99.9%, and the oxygen concentration was 560 ppm by mass, and a high-purity Cu-Mn alloy sputtering target was obtained.

The obtained test piece was mirror-polished, and then etched with a nitric acid aqueous solution to observe the structure observed by an optical microscope. As shown in Fig. 1, it was confirmed that the Cu-Mn alloy sputtering target of the present invention has a fine recrystallized structure in the nearly spherical grain boundary of the atomized powder, and no large defects such as segregation or vacancy are observed. A Cu-Mn alloy sputtering target that is preferred for sputter deposition.

Further, after the obtained Cu-Mn alloy sputtering target of the present invention was welded to a copper backing plate, it was mounted on a sputtering apparatus manufactured by Canon Anelva Co., Ltd. (Model: SPF-440HL) On the other hand, sputtering was performed under the conditions of an Ar environment, a pressure of 0.5 Pa, and an electric power of 500 W.

It was confirmed that when the Cu-Mn alloy sputtering target of the present invention is used for sputtering, abnormal discharge does not occur and stable sputtering can be performed.

[Example 4]

The Cu-Mn alloy sputtering target of the present invention prepared in Example 3 was mounted. Sputtering was performed on a sputtering apparatus (model: SBH-2204) manufactured by ULVAC Co., Ltd. using a sputtering gas containing Ar and oxygen at a pressure of 0.8 Pa and an electric power of 300 W.

In the same manner as in Example 1, a glass substrate of 25 mm × 50 mm was used for the substrate, and the amount of oxygen in the sputtering environment shown in Table 3 was adjusted to form a Cu-Mn alloy film at a film thickness of 100 nm. The results obtained by measuring the reflectance of each sample are shown in Table 3. Further, the amount of oxygen in the Cu-Mn alloy film was measured by Electron spectroscopy for chemical analysis (ESCA) (manufactured by KRATOS, model: AXIS-HS). The analysis represents the ratio of oxygen relative to the sum of the metal component and oxygen in atomic ratio. Further, the * mark in Table 3 indicates that it is outside the scope of the present invention.

As shown in Table 3, when the oxygen concentration in the sputtering gas is 30% by volume or more, the reflectance is lowered, and the amount of oxygen in the Cu-Mn alloy film is also increased. On the other hand, it is confirmed that if the Cu-Mn alloy film is combined with oxygen of the metal component and oxygen The ratio of the atomic ratio exceeds 0.6, the transmitted light is increased, and film peeling occurs.

Claims (7)

A copper-manganese alloy film characterized in that, when the total metal component is 100 atom%, the metal component contains 34 atom% to 45 atom% of manganese, and the balance contains copper and unavoidable impurities, and the visible light reflectance is 30% or less. A copper-manganese alloy film comprising a metal component and oxygen, wherein when the metal component is 100 atom% as a whole, the metal component contains 34 atom% to 45 atom% of manganese, and the remainder contains copper and is not Impurities to be avoided; the ratio of oxygen is 0.3 to 0.6 in terms of atomic ratio with respect to the sum of the metal component and the oxygen. The copper-manganese alloy film according to claim 1 or 2, which is an electrode film or a wiring film for a flat display element. A copper-manganese alloy sputtering target characterized by containing 34 atom% to 45 atom% of manganese, and the balance comprising copper and unavoidable impurities. The copper-manganese alloy sputtering target according to claim 4, which has a structure in which a recrystallized structure is contained in a grain boundary of the copper-manganese alloy powder. A method for forming a copper-manganese alloy film, characterized in that a copper-manganese alloy film containing 34 atom% to 45 atom% of manganese and the remainder containing copper and unavoidable impurities is contained in a volume of 30% by volume to 60% In the environment of % oxygen, a film is formed by sputtering. A film forming method of a copper-manganese alloy film, characterized in that: A copper-manganese alloy film containing 34 atom% to 45 atom% of manganese and the remainder containing copper and unavoidable impurities is formed by sputtering in an inert gas atmosphere, followed by an atmosphere at 200 ° C to 225 ° C The copper-manganese alloy film is heated in an environment.