Silver alloy, sputtering target material thereof, and thin film thereof

Abstract

A purpose of the present disclosure is to provide: a silver alloy which can be easily processed, and which satisfies the suppression of a decrease in the reflectance of light of 400 nm even after a heat treatment when formed into a thin film; a sputtering target material thereof; a thin film thereof; and a paste thereof. Another purpose of the present disclosure is to provide a display, a reflective electrode, an electronic component, an optical disk medium, a light component, or an electromagnetic wave shielding film, each of which is obtained using the silver alloy thin film. A silver alloy according to the present disclosure contains 0.20-0.50 atom% of Cu and 0.10-0.40 atom% of Ge, with the balance being made up of Ag and unavoidable impurities, and is characterized in that the total content of Cu and Ge is not less than 0.40 atom% but less than 0.80 atom%.

Description

Silver alloys, their sputtering target materials and thin films

[0001] The present disclosure relates to a silver alloy, a sputtering target material having the silver alloy composition, a silver alloy thin film, and a silver alloy paste. Furthermore, the silver alloy thin film is suitable for applications such as displays, reflective electrodes, electronic components, optical disk media, light components, and electromagnetic wave shielding.

[0002] In the manufacturing of color liquid crystal displays, the reflective electrode film is required to be heat resistant to temperatures up to about 250°C during the heating process used for assembling color filters, etc. Conventionally, aluminum (Al) or alloys containing Al as the main component have been used for the reflective electrode film, but silver alloys are being investigated as a reflective electrode film material in the hope of achieving high reflectivity and low resistivity.

[0003] For example, the present applicant has disclosed an Ag (silver)-Pd (palladium)-Cu (copper) based silver alloy suitable for a reflective electrode film or a reflective wiring electrode film (see, for example, Patent Documents 1 to 3). The silver alloys disclosed in Patent Documents 1 to 3 require palladium as an essential component.

[0004] The present applicant has disclosed an Ag-Pd-Cu-Ge based silver alloy containing germanium (Ge) in a silver alloy with the aim of solving the problems of thermal degradation and sulfurization of the silver alloys disclosed in Patent Documents 1 to 3 (see, for example, Patent Document 4). The silver alloy disclosed in Patent Document 4 also requires palladium as an essential component.

[0005] Furthermore, there is a disclosure of an Ag-based alloy for forming a reflective layer or semitransparent reflective layer for an optical information recording medium with excellent durability, which contains 0.5 atomic % or more of Cu and a total of 0.5 to 3 atomic % of at least one element selected from the group consisting of Nd, Sn, and Ge; and / or 0.1 atomic % or more of at least one rare earth element (see, for example, Patent Document 5). The Ag-based alloy contains Ag and Cu, and may further contain 0.5 atomic % or more of Ge.

[0006] Furthermore, the present applicant has disclosed a silver alloy sputtering target material having a composition of Ag-1.0 wt % Ge-1.0 wt % Cu (see, for example, Patent Document 6, Example 5). When mass % is converted to atomic %, the composition becomes Ag-1.47 at % Ge-1.68 at % Cu.

[0007] Also disclosed is a silver alloy sputtering target material and an Ag alloy thin film having a composition of Ag-0.3Si-0.3Cu-0.1Ge (at %) (see, for example, Patent Document 7, Sample No. 8 in Example 1).

[0008] Japanese Patent Laid-Open No. 2000-109943 Japanese Patent Laid-Open No. 2001-192752 Japanese Patent Laid-Open No. 2001-226765 International Publication No. 2005-031016 Japanese Patent Laid-Open No. 2002-15464 Japanese Patent Laid-Open No. 2006-037169 Japanese Patent Laid-Open No. 2004-149861

[0009] The silver alloy disclosed in Patent Document 4 improves the thermal degradation and sulfidation of the silver alloys disclosed in Patent Documents 1 to 3, but the silver alloy contains palladium. According to the inventors' studies, it was found that when a palladium-containing silver alloy thin film is subjected to a heat resistance test of 300°C in air for one hour, the reflectance at a short wavelength of, for example, 400 nm is likely to decrease. More specifically, it was found that the degree of decrease in reflectance at a short wavelength of 400 nm is greater than the degree of decrease in reflectance at wavelengths of 500 nm and 600 nm, i.e., the degree of decrease in reflectance varies greatly depending on the wavelength band. This decrease in reflectance is due to the formation of PdGe precipitates, which cause particle generation. For example, Example 1 of Patent Document 4 is a 200 nm thick silver alloy thin film produced using a silver alloy sputtering target of 98.7Ag-0.8Pd-0.3Cu-0.2Ge (Ag content: 98.7 wt %, Pd content: 0.8 wt %, Cu content: 0.3 wt %, Ge content: 0.2 wt %), and Example 2 is a sample obtained by heat-treating the silver alloy thin film of Example 1 in air at 250° C. for 1 hour. According to Figure 5, the reflectance at 400 nm, the reflectance at 500 nm, and the reflectance at 600 nm of Example 1 are 89.7%, 93.6%, and 95.2%, respectively, whereas according to Figure 7, the reflectance at 400 nm, the reflectance at 500 nm, and the reflectance at 600 nm of Example 2 are 83.0%, 91.2%, and 94.0%, respectively. Therefore, the reduction in reflectance due to heat treatment is 7.5% at 400 nm, 2.6% at 500 nm, and 1.3% at 600 nm, which shows that the reduction in reflectance at 400 nm is high and there is a large variation in the degree of reduction in reflectance depending on the wavelength band. Here, the "reduction in reflectance due to heat treatment" was calculated according to Equation 1. (Equation 1) Reduction in reflectance due to heat treatment (%) = {(reflectance before heat treatment - reflectance after heat treatment) / reflectance before heat treatment} x 100

[0010] On the other hand, the Ag alloy disclosed in Patent Document 5 does not contain palladium. However, when the Ag alloy disclosed in Patent Document 5, which can contain 0.5 atomic % or more of Ge, is formed into a silver alloy thin film, light absorption occurs due to the inclusion of Ge in Ag, and the light absorption rate increases as the Ge content increases, resulting in a decrease in overall reflectance, with a particular decrease in reflectance at a short wavelength of 400 nm.

[0011] The Ag alloy disclosed in Patent Document 6 does not contain palladium. It is believed that even in a silver alloy thin film having a composition of Ag-1.0 wt % Ge-1.0 wt % Cu (Ag-1.47 at % Ge-1.68 at % Cu), light absorption occurs due to the inclusion of Cu and Ge in Ag, and the light absorption rate increases when the amounts of Cu and Ge are large, resulting in a decrease in reflectance overall, with a particularly large decrease in reflectance at a short wavelength of 400 nm.

[0012] The Ag alloy disclosed in Patent Document 7 contains 0.3 at % of Si. When Si is contained, it becomes difficult to process the sputtering target during production, and SiO ２ Even if a target can be produced, SiO ２ There is concern that this may have adverse effects such as causing variations in film thickness.

[0013] The silver alloy must be (1) easy to process, and (2) when formed into a thin film, the reflectance of 400 nm light must not decrease even after heat treatment in air at 300°C, i.e., the degree of reflectance decrease must vary little depending on the wavelength band.

[0014] The present disclosure aims to provide a silver alloy that is easy to process and that, when formed into a thin film, suppresses a decrease in reflectance at 400 nm even after heat treatment, as well as a sputtering target material thereof, a thin film thereof, and a paste thereof. Furthermore, the present disclosure aims to provide a display, a reflective electrode, an electronic component, an optical disk medium, a light component, or an electromagnetic wave shielding film using the silver alloy thin film.

[0015] The present inventors conducted extensive research to solve the above problems, and discovered that the above problems can be solved by satisfying a specific compositional relationship in an Ag-Cu-Ge alloy that does not intentionally contain Pd, and thus completed the present invention. That is, the silver alloy according to the present invention is a silver alloy containing 0.20 to 0.50 atomic % of Cu, 0.10 to 0.40 atomic % of Ge, and the balance being Ag and unavoidable impurities, and is characterized in that the total content of Cu and Ge is 0.40 atomic % or more and less than 0.80 atomic %.

[0016] The silver alloy sputtering target material according to the present invention is characterized by being formed from the silver alloy according to the present invention.

[0017] The silver alloy thin film according to the present invention is characterized by being formed from the silver alloy according to the present invention.

[0018] The silver alloy thin film according to the present invention preferably has a reflectance of 90% or more at 400 nm after heat treatment in air at 300° C. for 1 hour. The degree of decrease in reflectance at the short wavelength of 400 nm is small.

[0019] In the silver alloy thin film according to the present invention, it is preferable that the arithmetic mean height Sa is 4 nm or less after heat treatment in air at 300° C. for 1 hour. With such an arithmetic mean height Sa, it is possible to maintain reflectance while ensuring sufficient heat resistance.

[0020] The silver alloy thin film according to the present invention preferably has a resistivity of 3 μΩ cm or less after heat treatment in air at 300° C. for 1 hour. Such a resistivity allows the film to be used as an electrode or wiring while ensuring sufficient heat resistance.

[0021] The silver alloy thin film according to the present invention includes forms such as a reflective film, a thin semi-transparent film, or a patterned electrode or wiring.

[0022] The display according to the present invention is characterized by comprising a reflective film according to the present invention and / or a perforated semi-transparent film having light-transmitting holes formed therein for transmitting a portion of incident light to the reflective film according to the present invention.

[0023] The reflective electrode according to the present invention is characterized by comprising the reflective film according to the present invention or a perforated semi-transparent film having light-transmitting holes formed therein for transmitting a part of incident light to the reflective film according to the present invention.

[0024] The electronic component according to the present invention is characterized by comprising the silver alloy thin film according to the present invention.

[0025] The optical disc medium according to the present invention is characterized by comprising at least one of the reflective film and the thin semi-transparent film according to the present invention.

[0026] The light component according to the present invention is characterized by including the reflective film according to the present invention.

[0027] The silver alloy thin film according to the present invention is characterized by being an electromagnetic wave shielding film.

[0028] The silver alloy paste material according to the present invention is characterized by containing silver alloy particles formed from the silver alloy according to the present invention.

[0029] According to the present disclosure, it is possible to provide a silver alloy that is easy to process and that, when formed into a thin film, suppresses a decrease in reflectance at 400 nm even after heat treatment, as well as a sputtering target material thereof, a thin film thereof, and a paste thereof. Furthermore, according to the present disclosure, it is possible to provide a display, a reflective electrode, an electronic component, an optical disk medium, a light component, or an electromagnetic wave shielding film using the silver alloy thin film.

[0030] 1 is a graph showing the reflectance spectrum of a silver alloy thin film having the composition of Test 7, showing (a) the profile before heat treatment and (b) the profile after heat treatment (in air, 300°C, 1 hour). This is a graph comparing the reduction in reflectance (%) due to heat treatment of the silver alloy thin films of Tests 1 to 10, where the heat treatment conditions were in air, 300°C, 1 hour, and the wavelengths were 400 nm, 500 nm, and 600 nm.

[0031] Hereinafter, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications may be made to the embodiments as long as the effects of the present invention are achieved.

[0032] The silver alloy according to this embodiment contains 0.20 to 0.50 atomic percent Cu, 0.10 to 0.40 atomic percent Ge, and the remainder being Ag and unavoidable impurities, with the total content of Cu and Ge being 0.40 atomic percent or more and less than 0.80 atomic percent. The silver alloy according to this embodiment is a ternary alloy of Ag—Cu—Ge. Despite being a ternary alloy, it has good heat resistance and is particularly excellent in maintaining reflectance after heat resistance testing. The silver alloy according to this embodiment does not contain any alloy-constituting elements other than Ag, Cu, and Ge, except for unavoidable impurities that may be contained in trace amounts. The reasons for this are that (1) it is easy to process, and (2) when formed into a thin film, it is unlikely to experience a decrease in reflectance at 400 nm even after heat treatment in air at 300°C, i.e., the degree of reflectance decrease varies little depending on the wavelength band.

[0033] In the silver alloy according to this embodiment, the Cu content is 0.20 to 0.50 atomic percent, preferably 0.25 to 0.45 atomic percent. If the Cu content is less than 0.20 atomic percent, surface roughness due to aggregation and hillocks will develop. On the other hand, if the Cu content exceeds 0.50 atomic percent, light absorption will occur due to the inclusion of Cu in Ag, and the high amount of Cu will increase the light absorption rate and reduce the reflectance.

[0034] In the silver alloy according to this embodiment, the Ge content is 0.10 to 0.40 atomic percent, preferably greater than 0.10 atomic percent but not greater than 0.40 atomic percent, more preferably 0.15 to 0.35 atomic percent, and even more preferably 0.20 to 0.35 atomic percent. If the Ge content is less than 0.10 atomic percent, the effect of suppressing the growth of the microcrystals in the film is small, and heat treatment causes surface roughness due to aggregation, resulting in a decrease in reflectance. On the other hand, if the Ge content exceeds 0.40 atomic percent, light absorption occurs due to the inclusion of Ge in Ag, and the high amount of Ge increases the light absorption rate, resulting in a decrease in reflectance.

[0035] In the silver alloy according to this embodiment, the total content of Cu and Ge is 0.40 atomic % or more and less than 0.80 atomic %, preferably more than 0.40 atomic % and less than 0.80 atomic %, more preferably 0.45 to 0.75 atomic %, and even more preferably 0.50 to 0.70 atomic %. When the total content of Cu and Ge is less than 0.40 atomic %, the effect of suppressing the growth of the microcrystals in the film is small, and the heat treatment causes surface roughness due to aggregation, resulting in a decrease in reflectance. When the total content of Cu and Ge is 0.40 atomic % or more, preferably more than 0.40 atomic %, the decrease in reflectance due to the growth of surface roughness is further suppressed. On the other hand, when the Cu and Ge content is 0.80 atomic % or more, light absorption occurs due to the inclusion of Cu and Ge in Ag, and when the amount of Cu and Ge is large, the light absorption rate increases, resulting in a decrease in reflectance. By including both Cu and Ge in Ag, heat resistance that cannot be obtained by including only Cu or only Ge is obtained. This is achieved by the coexistence of Cu and Ge. Furthermore, since there is almost no precipitation of Cu-Ge intermetallic compounds in Ag-Cu-Ge alloys, they have excellent workability and heat resistance.

[0036] As unavoidable impurities, Pd, Fe, Si, Pb, Bi, Na, Mg, Al, Ca, Cr, Co, Ni, Zn, Cd, In, and K are considered to be the objects of measurement, and mainly Pd, Fe, and K may be detected at a few ppm. The total content of unavoidable impurities is 100 ppm or less, preferably 50 ppm or less.

[0037] In the silver alloy according to this embodiment, Pd may be mixed in as an inevitable impurity, but Pd is not intentionally included. Pure Ag may contain Pd as an inevitable impurity, and the content of Pd contained as an inevitable impurity in the silver alloy is 15 ppm or less, preferably 10 ppm or less. When Pd is contained in a silver alloy together with Ge as a constituent element of the alloy, the reflectance at a short wavelength of, for example, 400 nm is likely to decrease after a heat resistance test in air at 300 °C for 1 hour. More specifically, the degree of decrease in reflectance at a short wavelength of 400 nm is greater than the degree of decrease in reflectance at wavelengths of 500 nm or 600 nm, i.e., the degree of decrease in reflectance varies greatly depending on the wavelength band. The reason for this decrease in reflectance is that when PdGe precipitates are generated on the surface of the sputtering target and sputtered to form a film, arcing concentrates on the PdGe precipitates, causing particle generation. The generation of particles increases the surface roughness of the film and may cause a decrease in the reflectivity of the film due to the particles. Furthermore, the inclusion of Pd causes the formation of PdGe precipitates, which deteriorates the processability when used as a sputtering target, for example.

[0038] The silver alloy sputtering target material according to this embodiment is formed from the silver alloy according to this embodiment. In the silver alloy according to this embodiment, Cu and Ge are present in trace amounts relative to Ag, so when the silver alloy is produced through melting, the alloy may be in a complete solid solution. For example, in the case of a silver alloy sputtering target, if the crystal grain size is too large, the thickness of the deposited film may be uneven. This is because the sputtering rate varies depending on the crystal plane, and if one crystal grain size is too large, the sputtering rate of that plane may be significantly affected, resulting in uneven film thickness. To prevent this, the crystal grain size should be as small as possible, and it is desirable that the orientation of the crystal planes be random. The crystal grain size of a complete solid solution is refined by plastic processing such as forging and rolling during the production of the sputtering target, and the approximate crystal grain size is determined by subsequent heat treatment. The average crystal grain size is 0.1 μm to 200 μm, preferably 0.3 μm to 150 μm, and more preferably 0.5 μm to 50 μm. The average crystal grain size is calculated, for example, by drawing three line segments randomly on each image taken by a scanning electron microscope (SEM) and calculating according to the line segment method.

[0039] The silver alloy according to this embodiment can be in the form of a silver alloy sputtering target material or a silver alloy paste for producing a silver alloy thin film. A silver alloy thin film can be produced by a sputtering method using the silver alloy sputtering target material. The silver alloy can also be used as a jewelry material.

[0040] By using the above composition, the silver alloy thin film according to this embodiment can achieve a reflectance of 90% or more at 400 nm after heat treatment in air at 300°C for 1 hour. As a result, the degree of decrease in reflectance at short wavelengths of 400 nm is small. Heat treatment in air at 300°C for 1 hour is a more severe condition because it is performed at a higher temperature than heat treatment in air at 250°C for 1 hour. For example, when the silver alloy thin film of Example 1 of Patent Document 4, which has a reflectance of 89.7% at 400 nm, is heat treated in air at 300°C for 1 hour, the reflectance at 400 nm becomes 81.0%. On the other hand, heat treatment in air at 250°C for 1 hour (corresponding to Example 2) for 1 hour resulted in a reflectance of 83.0%. Therefore, the decrease in reflectance due to heat treatment calculated using Equation 1 is 9.7% (at 400 nm in air at 300°C for 1 hour) compared to 7.5% (at 250°C in air for 1 hour). Therefore, the reflectance decreases even more significantly with increasing heat treatment temperature. In contrast, the silver alloy thin film according to this embodiment can maintain a reflectance of 90% or more for light at 400 nm even after heat treatment at 300°C for 1 hour in air, and therefore can be said to have particularly excellent heat resistance and excellent ability to maintain reflectance after a heat resistance test.

[0041] By using the above composition, the silver alloy thin film according to this embodiment can have an arithmetic mean height Sa of 4 nm or less, preferably 3.5 nm or less, after heat treatment in air at 300°C for 1 hour. That is, by using the above composition, the rate of increase in the arithmetic mean height Sa after heat treatment relative to before heat treatment can be kept small, and heat resistance can be sufficiently ensured. The lower limit of the arithmetic mean height Sa after heat treatment in air at 300°C for 1 hour is not particularly limited, but is, for example, 0.5 nm.

[0042] By using the above composition, the silver alloy thin film according to this embodiment can have a resistivity of 3 μΩ cm or less, preferably 2.8 μΩ cm or less, after heat treatment in air at 300° C. for 1 hour. In other words, a resistivity that does not interfere with use in electrodes or wiring can be obtained. There is no particular lower limit to the resistivity after heat treatment in air at 300° C. for 1 hour, but it is, for example, 2 μΩ cm.

[0043] The silver alloy thin film according to this embodiment has excellent heat resistance, and even after heat treatment in air at 300°C for 1 hour, the decrease in reflectance of light at 400 nm is suppressed, so it is suitable for use as a reflective film, a thin semi-transparent film, or a patterned electrode or wiring. These silver alloy thin films are used in applications such as (1) displays, (2) reflective electrodes, (3) electronic components, (4) optical disk media, (5) light components, and (6) electromagnetic wave shielding films.

[0044] In displays, the silver alloy thin film is used as a reflective film, and / or as a perforated semi-transparent film having light-transmitting holes formed therein for transmitting a portion of incident light to the reflective film. Displays include self-emissive displays, flat panel displays, and OLEDs (organic light-emitting diodes, or OLED displays). In particular, OLED elements have a problem of low blue luminous efficiency, and therefore require a film that can provide high reflectance in the short wavelength region including 400 nm, as well as a heat-resistant film that is not deteriorated by heat during the manufacturing process. Therefore, the silver alloy thin film according to this embodiment is preferably used.

[0045] A semi-transparent film can be obtained when the film thickness is as thin as 1 to 50 nm, or can be obtained by forming a perforated semi-transparent film with light-transmitting holes that transmit part of the incident light even when the film thickness exceeds 50 nm.

[0046] As the reflective electrode, a silver alloy thin film is used as a reflective film, and / or a silver alloy thin film is used as a perforated semi-transparent film having light-transmitting holes formed therein to transmit a portion of the incident light to the reflective film, and these films also serve as electrodes.

[0047] As an electronic component, for example, it can be used as an electrode for a resistor or capacitor as a circuit component, or as a contact for a switch, or as wiring for a communication / network unit, a filter, a fuse, a thermistor, an oscillator / resonator, a varistor, a printed wiring board, or as an electrode for a power supply unit, or as wiring for a power supply circuit component, or as an electrode for an integrated circuit, IC, or the like. Furthermore, it can be widely used as an optical component, a sensor, a display component, or an I / O (Input / Output). For example, it can be used as a reflective film for an optical component, or as a contact for an input / output unit, or as a reflective film, wiring, or electrode film for an electronic component such as an LED.

[0048] In optical disk media, a silver alloy thin film is used as a reflective film, and the media may include at least one of a reflective film and a thin semi-transparent film.

[0049] Silver alloy thin films are used as reflective films in lighting components, such as mirrors in headlamps and projector lamps.

[0050] The electromagnetic wave shielding film is an electromagnetic wave shielding film formed on the surface of a support. Specifically, it is applied to an electronic component device having an area covered by the electromagnetic wave shielding film. Examples of the electronic component device include the housing of an electronic device, a wireless device, and a contactless card. The electromagnetic wave shielding film is formed so as to shield electromagnetic waves, with part or all of the electronic component device serving as a support. It is also applied to an electromagnetic wave shielding sheet having an area covered by the electromagnetic wave shielding film. Examples of substrates that serve as supports for the electromagnetic wave shielding sheet include resin sheets, resin films, and resin molded products.

[0051] The silver alloy according to this embodiment has excellent heat resistance, and is inhibited from deteriorating even after heat treatment in air at 300° C. for 1 hour. As a result, the silver alloy paste material containing silver alloy particles formed from the silver alloy according to this embodiment is inhibited from discoloring and from deteriorating due to baking, even after the paste material is baked.

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] Next, a method for producing a silver alloy sputtering target material using the silver alloy according to this embodiment will be described with reference to an example. Each of the metals, Ag (purity 99.99% or more), Cu (purity 99.9% or more), and Ge (purity 99.9% or more), is weighed and placed in a crucible. At this time, a crucible with a low oxygen content, such as a carbonaceous crucible, is selected. An alumina crucible or magnesia crucible may also be used. If a carbonaceous crucible is selected, high-frequency heating is possible, so the carbonaceous crucible containing each metal is placed in a high-frequency melting furnace and vacuum is drawn. The pressure at this time is set to 1.33 Pa or less. The melting chamber is then filled with an Ar atmosphere (1.33 x 10 ４ ~8.0 x 10 ４ The melting temperature was set to 1050 to 1300°C. The blending ratios were in accordance with the ratios of Tests 1 to 10 shown in Table 1.

[0054]

[0055] After the molten state has stabilized, the molten material is poured into a mold to produce an ingot. The mold is a carbonaceous mold with a low oxygen content. Iron molds and alumina molds can also be used. The top of the mold is heated to make it easier to release the gas inside. The top of the mold is heated using a high-frequency coil. After cooling to room temperature, the top of the ingot (the riser) is cut off and removed.

[0056] The ingot is heat treated at 600-900°C, then hot forged and rolled. Annealing is performed during rolling. Annealing is performed when the product is at least twice the wall thickness and in the final stage. The annealing temperature is 300-700°C to ensure fine, uniform crystal grains. Annealing is performed in a vacuum. It can also be performed in an inert gas atmosphere. Afterwards, warping is corrected using a press and leveler.

[0057] The surface or periphery is cut using a lathe, milling machine, or the like to form the product shape. The entire surface of the product may be polished. The surface roughness is adjusted, and finally, the Ag alloy sputtering target material of the present invention can be produced. In the example, the product shape was a disk with a diameter of 50.8 mm and a thickness of 5 mm.

[0058] Next, a method for manufacturing a silver alloy thin film will be described. The silver alloy thin film can be obtained by forming a film by sputtering using the silver alloy sputtering target materials of Tests 1 to 10. Note that the three elements may be split into multiple targets and sputtered simultaneously, and the discharge amount of each element may be controlled to form a film having the silver alloy composition according to this embodiment.

[0059] When forming a silver alloy thin film, an adhesion layer may be provided between the substrate and the thin film. In this case, adhesion-promoting underlayers for various glass substrates include Si, Ta, Ti, Mo, Cr, Al, ITO, ZnO, and SiO. ２ , TiO ２ , Ta ２ O ５ , ZrO ２ is desirable.

[0060] In the examples, the substrate was a non-alkali glass substrate (20 × 40 mm, thickness 0.7 mm). The sputtering conditions were an ultimate vacuum of 5 × 10 －４ The silver alloy thin films were deposited under an Ar atmosphere with a pressure of 0.4 Pa or less, a target output of 150 W, and a thickness of 150 nm. Furthermore, the reflectance of the silver alloy thin films of Tests 1 to 10 was measured using a spectrophotometer (JASCO Corporation, V-750). The wavelength range used was 400 to 800 nm. As a representative example, the reflectance spectrum of the silver alloy thin film having the composition of Test 7 is shown in Figure 1. Next, the silver alloy thin films having the compositions of Tests 1 to 10 were subjected to heat treatment in air at 300°C for 1 hour. Similarly, the reflectance of the silver alloy thin films having the compositions of Tests 1 to 10 after heat treatment was measured. As a representative example, the reflectance spectrum of the silver alloy thin film having the composition of Test 7 after heat treatment is shown in Figure 1.

[0061] (Reflectance of Silver Alloy Thin Film) Table 2 shows the reflectance at 400 nm of the silver alloy thin films of Tests 1 to 10 before heat treatment.

[0062]

[0063] Table 3 shows the reflectance at 400 nm of the silver alloy thin films of Tests 1 to 10 after heat treatment.

[0064]

[0065] Table 4 shows the reflectance at 500 nm of the silver alloy thin films of Tests 1 to 10 before heat treatment.

[0066]

[0067] Table 5 shows the reflectance at 500 nm of the silver alloy thin films of Tests 1 to 10 after heat treatment.

[0068]

[0069] Table 6 shows the reflectance at 600 nm of the silver alloy thin films of Tests 1 to 10 before heat treatment.

[0070]

[0071] Table 7 shows the reflectance at 600 nm of the silver alloy thin films of Tests 1 to 10 after heat treatment.

[0072]

[0073] The reduction rate of reflectance at 400 nm due to heat treatment is shown in Table 8. The reduction rate was calculated using Equation 1. (Equation 1) Reduction rate of reflectance due to heat treatment (%) = {(reflectance before heat treatment - reflectance after heat treatment) / reflectance before heat treatment} x 100

[0074]

[0075] Table 9 shows the reduction in reflectance at 500 nm due to heat treatment.

[0076]

[0077] Table 10 shows the reduction in reflectance at 600 nm due to heat treatment.

[0078]

[0079] Condition 1 is defined as "Cu is 0.20 to 0.50 atomic percent," condition 2 is defined as "Ge is 0.10 to 0.40 atomic percent," and condition 3 is defined as "the total content of Cu and Ge is 0.40 atomic percent or more and less than 0.80 atomic percent." Tests 4, 5, and 7 satisfy all of conditions 1, 2, and 3 and are examples. Figure 2 shows a comparison of the reflectance reduction (%) due to heat treatment of the silver alloy thin films of Tests 1 to 10. As shown in Figure 2, the difference between the degree of reflectance reduction at wavelengths of 500 nm and 600 nm and the degree of reflectance reduction at a short wavelength of 400 nm decreases in the order of Test 4, Test 7, and Test 5, i.e., it was found that the unevenness in the degree of reflectance reduction depending on the wavelength band decreases. Test 5 showed the smallest unevenness in the degree of reflectance reduction depending on the wavelength band.

[0080] Test 1 is a comparative example because it does not satisfy conditions 1 and 2, and Test 6 is a comparative example because it does not satisfy conditions 1 and 3. In both cases, the degree of decrease in reflectance at a wavelength of 600 nm is small, at 0.3% and 0.6%, but the degree of decrease in reflectance at a wavelength of 500 nm is large, at 1.6% and 2.1%, and the degree of decrease in reflectance at a wavelength of 400 nm is even larger, at 5.0% and 4.1%. The reason for this is that Test 1 contains 0.68 at% Cu, slightly exceeding the upper limit of the Cu content in Condition 1, and does not contain Ge. Therefore, when the silver alloy is formed into a thin film, the synergistic heat resistance effect of containing Cu and Ge is not achieved, and when the silver alloy thin film is heat-treated, Cu is easily oxidized and blackened. As a result, the degree of decrease in reflectance increases toward shorter wavelengths, at 500 nm and 400 nm. In addition, Test 6 contained 0.60 at% Cu, exceeding the upper limit of the content in Condition 1, and also contained 0.20 at% Ge. The total amount of Cu and Ge was 0.80 at%, slightly exceeding the upper limit of the total content in Condition 3. However, when the silver alloy was formed into a thin film, the heat resistance was improved due to the synergistic effect of the inclusion of Cu and Ge, and the decrease in reflectance was small when the silver alloy thin film was heat-treated. However, because the total content of Cu and Ge slightly exceeded the upper limit of Condition 3 and the Cu content exceeded the upper limit of Condition 1, the effects of blackening of Cu and light absorption by Cu in Ag were slightly apparent. As a result, the reflectance decreased toward shorter wavelengths, 500 nm and 400 nm.

[0081] Test 2 is a comparative example because it does not satisfy conditions 1, 2, and 3; Test 8 is a comparative example because it does not satisfy conditions 1 and 3; Test 9 is a comparative example because it does not satisfy conditions 1 and 2; and Test 10 is a comparative example because it does not satisfy conditions 1 and 2. In all cases, the reflectance decreases significantly at wavelengths of 400 nm, 500 nm, and 600 nm, and particularly at a wavelength of 400 nm. Specifically, in Tests 2, 8, 9, and 10, the reflectance decreases significantly at a wavelength of 600 nm, being 2.0%, 2.8%, 1.6%, and 1.4%, respectively; at a wavelength of 500 nm, the reflectance decreases significantly at 6.5%, 5.6%, 3.5%, and 3.4%, respectively; and at a wavelength of 400 nm, the reflectance decreases significantly at 10.1%, 7.6%, 8.8%, and 9.2%, respectively. The reason for this is that Test 2 contains 1.40 at% Cu, which exceeds the upper limit of the content in Condition 1, and does not contain Ge. Therefore, when the silver alloy is formed into a thin film, the heat resistance due to the synergistic effect of containing Cu and Ge is not achieved, and when the silver alloy thin film is heat-treated, the Cu is easily oxidized and blackened. As a result, the reflectance decreases more significantly toward shorter wavelengths, such as 500 nm and 400 nm. Test 8 contains 0.60 at% Cu, which exceeds the upper limit of the content in Condition 1, and also contains 0.40 at% Ge, so the total amount of Cu and Ge is 1.00 at%, which exceeds the upper limit of the total content in Condition 3. However, when the silver alloy is formed into a thin film, the heat resistance due to the synergistic effect of containing Cu and Ge is achieved, and the reflectance decreases little when the silver alloy thin film is heat-treated. However, in this composition, the total content of Cu and Ge exceeds that of Test 6, and the Cu content exceeds the upper limit of Condition 1, resulting in slight effects of Cu blackening and light absorption by Cu in Ag. Furthermore, even though the Ge content is at the upper limit of Condition 2, slight effects of Ge oxidation are also observed. As a result, the reflectivity decreases more significantly toward shorter wavelengths, such as 500 nm and 400 nm. Furthermore, in Test 9, the Cu content is 0.10 at%, which is below the lower limit of Condition 1, and the Ge content is 0.50 at%, which is above the upper limit of Condition 2. Therefore, when the silver alloy is formed into a thin film, the synergistic effect of containing Cu and Ge on heat resistance is reduced. Furthermore, when the silver alloy thin film is heat-treated, the Ge content exceeds the upper limit of Condition 2, resulting in the effects of Ge oxidation.As a result, the reflectance decreases more significantly toward the shorter wavelength side, 500 nm and 400 nm. Furthermore, in Test 10, the Ge content is 0.59 at%, which exceeds the upper limit of the content in Condition 2, and the sample does not contain Cu. Therefore, when the silver alloy thin film is formed, the synergistic heat resistance effect of containing Cu and Ge is not achieved. Furthermore, when the silver alloy thin film is heat-treated, the Ge content exceeds the upper limit of Condition 2, which causes the effect of Ge oxidation. As a result, the reflectance decreases more significantly toward the shorter wavelength side, 500 nm and 400 nm.

[0082] Test 3 is a comparative example because it does not satisfy Conditions 1 and 3. The reflectance reduction at wavelengths of 400 nm, 500 nm, and 600 nm is greater than that of the other comparative examples. The reflectance reduction at a wavelength of 400 nm is particularly large. Specifically, Test 3 exhibits a large reflectance reduction of 15.0% at a wavelength of 600 nm, an even larger reduction of 22.4% at a wavelength of 500 nm, and an even larger reduction of 34.4% at a wavelength of 400 nm. The reason for this is that Test 3 contains 0.10 at% Ge, which is the lower limit of the content of Condition 2, but 0.10 at% Cu, which is below the lower limit of the content of Condition 1. Therefore, when the silver alloy is formed into a thin film, the synergistic effect of containing Cu and Ge on heat resistance is extremely small. Therefore, when the silver alloy thin film is heat-treated, the effect of suppressing the growth of microcrystals in the film is small, and surface roughness due to aggregation develops during heat treatment. As a result, the reflectance decreases significantly toward the shorter wavelength side of 500 nm and 400 nm.

[0083] Test 1 and Test 2 will be further considered. Test 1 and Test 2 have Cu contents greater than the upper limit of the range of Condition 1, so they are more likely to blacken after heat treatment, and the reflectance is lower than before heat treatment. In particular, the short wavelengths are significantly lowered. Here, Test 2 has a larger amount of Cu than Test 1, so it is more likely to blacken, and the decrease in reflectance after heat treatment is greater in Test 2 than in Test 1.

[0084] Furthermore, Test 6 and Test 8 will be further considered. In Test 6 and Test 8, the Cu content exceeds the upper limit of the range of Condition 1, and depending on Condition 3, blackening may occur easily after heat treatment, and the reflectance may decrease compared to before the heat treatment. Here, Test 6 and Test 8 have the same amount of Cu, and both satisfy Condition 2 in terms of the Ge content. However, since Test 8 is farther above the range of Condition 3 than Test 6, the amount of Ge oxide after heat treatment is relatively greater. As a result, the decrease in reflectance after heat treatment is greater in Test 8 than in Test 6.

[0085] Further, Test 9 and Test 10 will be considered. In Test 9, the Cu content is less than the lower limit of Condition 1, so the heat resistance due to the synergistic effect of containing Cu and Ge is small. In addition, Test 10 does not contain Cu, so the heat resistance due to the synergistic effect of containing Cu and Ge is not obtained. As a result, even though Cu and Ge are contained, slight blackening of Cu occurs after heat treatment. In Tests 9 and 10, the Ge content is high relative to the range of Condition 2, so the amount of Ge oxide increases after heat treatment, resulting in a decrease in reflectance compared to before heat treatment. Since the amount of Ge is higher in Test 10 than in Test 9, the amount of Ge oxide also increases relatively. Since the total content of Cu and Ge is approximately the same in Tests 9 and 10, the decrease in reflectance after heat treatment in Tests 9 and 10 is approximately the same.

[0086] (Arithmetic mean height Sa, resistivity and reflectivity of silver alloy thin film) Next, further investigation was carried out on the arithmetic mean height Sa, resistivity and reflectivity of the silver alloy thin film. Silver alloy thin films of Tests 11 to 21 were produced in the same manner as Tests 1 to 10, except that the composition was changed. The respective blending ratios are shown in Table 1.

[0087] The reflectance of Tests 11 to 21 was measured in the same manner as in Tests 1 to 10. The arithmetic mean height Sa and resistivity of the silver alloy thin film were measured for Tests 3 to 7, 9, and 11 to 21. The arithmetic mean height Sa (unit: nm) was measured using a scanning probe microscope (AFM100PLUS, manufactured by Hitachi High-Tech Corporation). The resistivity (unit: μΩ cm) was measured using a resistivity measuring device (K-705RS, manufactured by Kyowa Riken Co., Ltd.).

[0088] The arithmetic mean height Sa, resistivity, and reflectivity at 400 nm before heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 11. The reflectivities shown in Table 2 are also shown in Table 11. In Table 11, in the column for one composition, the first row shows the arithmetic mean height Sa, the second row shows the resistivity, and the third row shows the reflectivity.

[0089]

[0090] The arithmetic mean height Sa, resistivity and reflectance at 400 nm after heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 12. The reflectances shown in Table 3 are also shown in Table 12.

[0091]

[0092] The arithmetic mean height Sa, resistivity and reflectance at 500 nm before heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 13. The reflectances shown in Table 4 are also shown in Table 13.

[0093]

[0094] The arithmetic mean height Sa, resistivity and reflectance at 500 nm after heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 14. The reflectances shown in Table 5 are also shown in Table 14.

[0095]

[0096] The arithmetic mean height Sa, resistivity and reflectance at 600 nm before heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 15. The reflectances shown in Table 6 are also shown in Table 15.

[0097]

[0098] The arithmetic mean height Sa, resistivity and reflectance at 600 nm after heat treatment of the silver alloy thin films of Tests 3 to 7, 9, and 11 to 21 are shown in Table 16. The reflectances shown in Table 7 are also shown in Table 16.

[0099]

[0100] Among Tests 3 to 7, 9, 11 to 21, Tests 4, 5, 7, 14, 17, 19, and 20 satisfied all of Conditions 1, 2, and 3 and were examples. Tests 3, 6, 9, 11 to 13, 15, 16, 18, and 21 were comparative examples.

[0101] The silver alloy thin films of Tests 4, 5, 7, 14, 17, 19, and 20, which correspond to Examples among Tests 3 to 7, 9, 11 to 21, had an arithmetic mean height Sa of 4 nm or less after heat treatment in air at 300°C for 1 hour, indicating that they are heat resistant, are less affected by blackening of Cu and oxidation of Ge, and can maintain a reflectivity of 90% or more.Furthermore, the silver alloy thin films of Tests 4, 5, 7, 14, 17, 19, and 20, which correspond to Examples, had a resistivity of 3 μΩ cm or less after heat treatment in air at 300°C for 1 hour, indicating that they are heat resistant and can be used for wiring, electrodes, etc.

[0102] The reduction rates (%) of reflectance of the silver alloy thin films of Tests 11 to 21 due to heat treatment are shown in Table 17.

[0103]

[0104] As shown in Table 17, in Tests 14, 17, 19, and 20, the difference between the degree of decrease in reflectance at wavelengths of 500 nm and 600 nm and the degree of decrease in reflectance at a short wavelength of 400 nm was small, that is, it was found that the unevenness in the degree of decrease in reflectance depending on the wavelength band was small.

[0105] Let us consider the change in reflectivity due to heat treatment. Heat treatment improves the crystallinity of the crystal particles that make up the silver alloy thin film, which contributes to an increase in reflectivity. On the other hand, blackening due to Cu, oxidation of germanium, and deterioration of surface roughness (increase in arithmetic mean height Sa) contribute to a decrease in reflectivity. Therefore, depending on which of the factors that contribute to the increase in reflectivity due to improved crystallinity and the decrease in reflectivity due to blackening due to Cu, oxidation of germanium, and deterioration of surface roughness is greater, the decrease rate in Table 17, for example, will be positive or negative.

Claims

1. A silver alloy containing 0.20 to 0.50 atomic % Cu, 0.10 to 0.40 atomic % Ge, and the balance being Ag and unavoidable impurities, characterized in that the total content of Cu and Ge is 0.40 atomic % or more but less than 0.80 atomic %.

2. A silver alloy sputtering target material characterized by being formed from the silver alloy according to claim 1.

3. A silver alloy thin film formed from the silver alloy according to claim 1.

4. The silver alloy thin film according to claim 3, characterized in that the reflectance of light at 400 nm after heat treatment in air at 300° C. for 1 hour is 90% or more.

5. The silver alloy thin film according to claim 3, wherein the arithmetic mean height Sa after heat treatment in air at 300° C. for 1 hour is 4 nm or less.

6. The silver alloy thin film according to claim 3, which has a resistivity of 3 μΩ·cm or less after heat treatment in air at 300° C. for 1 hour.

7. The silver alloy thin film according to claim 3, which is a reflective film, a thin semi-transparent film, or a patterned electrode or wiring.

8. A display comprising the reflective film according to claim 7 and / or a perforated semi-transparent film having light-transmitting holes formed therein for transmitting a portion of incident light to the reflective film according to claim 7.

9. A reflective electrode comprising the reflective film according to claim 7 or a perforated semi-transparent film having light-transmitting holes formed therein for transmitting a portion of incident light to the reflective film according to claim 7.

10. An electronic component comprising the silver alloy thin film according to claim 3 or 4.

11. An optical disk medium comprising at least one of the reflective film and the thin semi-transparent film according to claim 7.

12. A light component comprising the reflective film according to claim 7.

13. The silver alloy thin film according to claim 3 or 4, which is an electromagnetic wave shielding film.

14. A silver alloy paste material comprising silver alloy particles formed from the silver alloy of claim 1.

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