Metal wiring structure, method for manufacturing metal wiring structure, and sputtering target

Abstract

The present invention provides a metal wiring structure having low resistance, excellent heat resistance, and flexibility, and a method for manufacturing the same. To achieve the above objectives, the metal wiring structure comprises: a metal wiring film having a main component composed of aluminum and an additive element containing 0.005 at% to 0.88 at% of iron added to the main component; and a first covering layer laminated on the metal wiring film. This metal wiring structure provides a metal wiring structure having low resistance, excellent heat resistance, and excellent flexibility.

Description

Technical Field

[0001] The present invention relates to a metal wiring structure, a method for manufacturing the metal wiring structure, and a sputtering target. Background Art

[0002] In thin film transistors (TFTs) such as liquid crystal display elements and organic EL display elements, low-resistance metals such as Al may be used as wiring materials.

[0003] However, since the gate electrode is formed midway through the manufacturing process, it is subject to a thermal history caused by annealing after formation. Therefore, high-melting-point metals (such as Mo) with heat resistance that can withstand this thermal history are often used as gate electrode materials (see, for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-156482. Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, when a high-melting-point metal such as Mo is used as an electrode material for a display having a curved screen or a curved portion of a bendable foldable display, the electrode may break due to bending because the high-melting-point metal does not have sufficient bending resistance.

[0009] Furthermore, high-melting-point metals such as Mo have higher resistivity than low-resistance metals such as Al, and therefore, as the size of a display increases, there is a risk of display delay.

[0010] In view of the above circumstances, an object of the present invention is to provide a metal wiring structure having low resistance and excellent heat resistance and flexibility, a method for producing the metal wiring structure, and a sputtering target.

[0011] Solutions for solving problems

[0012] In order to achieve the above-mentioned purpose, a metal wiring structure of one embodiment of the present invention comprises: a metal wiring film, which has a main component composed of aluminum and an additional element containing iron in an amount of greater than 0.005 at % and less than 0.88 at % added to the above-mentioned main component; and a first covering layer, which is stacked on the above-mentioned metal wiring film.

[0013] Such a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0014] The metal wiring structure described above may further contain vanadium in an amount of 0.01 at % to 0.05 at % as the additional element.

[0015] Such a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0016] The metal wiring structure described above may be composed of the main component described above, the additional elements described above, and inevitable components.

[0017] Such a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0018] In the metal wiring structure, a second cover layer may be provided on the side of the metal wiring film opposite to the first cover layer, and the metal wiring film may be provided between the first cover layer and the second cover layer.

[0019] Such a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0020] In order to achieve the above-mentioned purpose, a method for manufacturing a metal wiring structure according to one embodiment of the present invention includes: forming a metal wiring film on a substrate, the metal wiring film having a main component composed of aluminum and an additional element containing 0.005 at % or more and 0.88 at % or less of iron added to the above-mentioned main component; stacking a first covering layer on the above-mentioned metal wiring film; and heating the above-mentioned metal wiring film at a temperature below 500°C.

[0021] Such a method for producing a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0022] In the above-mentioned method for manufacturing a metal wiring structure, a second covering layer may be formed on a side of the metal wiring film opposite to the first covering layer, and the metal wiring film may be arranged between the first covering layer and the second covering layer.

[0023] Such a method for producing a metal wiring structure can provide a metal wiring structure having low resistance and excellent heat resistance and flexibility.

[0024] In order to achieve the above-mentioned object, a sputtering target for forming the above-mentioned metal wiring structure is provided.

[0025] Effects of the Invention

[0026] As described above, according to the present invention, there are provided a metal wiring structure having low resistance and excellent heat resistance and bendability, a method for manufacturing the metal wiring structure, and a sputtering target. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (a) and (b) are schematic cross-sectional views of a thin film transistor including the metal wiring structure according to this embodiment. Figure 1 (c) and (d) are schematic cross-sectional views of the metal wiring structure according to this embodiment.

[0028] Figure 2 (a) is a graph showing changes in surface roughness of a plurality of Al alloy films immediately after film formation and after heat treatment in the case where no nitride film is provided. Figure 2 (b) is a graph showing changes in surface roughness of a plurality of Al alloy films after heat treatment in the case where a nitride film is provided.

[0029] Figure 3 (a) is a graph showing changes in resistivity ρ (μΩ·cm) of an Al pure metal film and a plurality of Al alloy films immediately after film formation and after heat treatment. Figure 3 (b) is a graph showing the resistivity ρ (μΩ·cm) of an Al alloy film having a nitride film formed as a cap layer before heat treatment. Figure 3 (c) is a graph showing the resistivity ρ (μΩ·cm) of an Al alloy film having a nitride film formed as a cap layer after heat treatment.

[0030] Figure 4 These are surface SEM images of an Al pure metal film and a plurality of Al alloy films after heat treatment in the case where no nitride film is provided.

[0031] Figure 5 These are surface SEM images of an Al pure metal film and a plurality of Al alloy films after heat treatment in the case where a nitride film is provided.

[0032] Figure 6 These are surface SEM images of the Al pure metal film, the Al alloy film, and the stacked film with the cover layer attached when the heating temperature was 450° C. and the heating time was 1.5 hours.

[0033] Figure 7 These are surface SEM images of the Al pure metal film, the Al alloy film, and the stacked film with the cover layer attached when the heating temperature is 500° C. and the heating time is 1.0 hour.

[0034] Figure 8 This is an example of an SEM image of the surface of a glass substrate after etching an Al alloy film formed on the glass substrate.

[0035] Figure 9 This is an example of an SEM image of the surface of a glass substrate after etching a film obtained by further adding a nitride film to an Al alloy film formed on a glass substrate.

[0036] Figure 10 This is a surface SEM image of the laminate film with the cover layer attached when the heating temperature is 500° C. and the heating time is 1.0 hour. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, X, Y, and Z coordinates are sometimes used. In addition, identical components or components having identical functions are sometimes labeled with the same reference numerals, and descriptions of the components are sometimes omitted as appropriate after the components have been described.

[0038] An example of the structure and operation of a device using the metal wiring structure of this embodiment will be described.

[0039] (Thin Film Transistor)

[0040] Figure 1 (a) and Figure 1 (b) is a schematic cross-sectional view of a thin film transistor including the metal wiring structure according to this embodiment. Figure 1 (c) is a schematic cross-sectional view of the metal wiring structure according to this embodiment.

[0041] exist Figure 1 (a) shows a top-gate thin film transistor 1. In the thin film transistor 1, an active layer (semiconductor layer) 11, a gate insulating film 12, a gate electrode 13, and a protective layer 15 are stacked on a glass substrate 10. The active layer 11 is formed of, for example, LTPS (low temperature poly-silicon). The active layer 11 is electrically connected to the source electrode 16S and the drain electrode 16D. In addition, the substrate is not limited to a glass substrate, and may also be a SiOx substrate, a SiNx substrate, a glass substrate with an SiOx film attached, a glass substrate with an SiNx film attached, etc. The following description will be made using the glass substrate 10 as an example.

[0042] Figure 1 The thin-film transistor 2 shown in (b) is a bottom-gate thin-film transistor. In the thin-film transistor 2, a gate electrode 13, a gate insulating film 22, an active layer 21, a source electrode 26S, and a drain electrode 26D are stacked on a glass substrate 10. The active layer 21 is formed, for example, of an IGZO (In-Ga-Zn-O) oxide semiconductor material. The active layer 21 is electrically connected to the source electrode 26S and the drain electrode 26D.

[0043] The thickness of the gate electrode 13 is not particularly limited, and is, for example, not less than 100 nm and not more than 600 nm, preferably not less than 200 nm and not more than 400 nm. When the thickness is less than 100 nm, it is difficult to reduce the resistance of the gate electrode 13. When the thickness exceeds 600 nm, there is a tendency for the bending resistance of the thin film transistor 2 to decrease. The gate electrode 13 is composed of the metal wiring structure of this embodiment. The resistivity of the gate electrode 13 is set to, for example, not more than 15 μΩ·cm, preferably not more than 10 μΩ·cm, more preferably not more than 6.0 μΩ·cm, and even more preferably not more than 3.7 μΩ·cm.

[0044] The gate electrode 13 is formed by forming a solid Al alloy film using a sputtering method, laminating a covering layer such as a nitride film and a metal film, and then patterning it into a predetermined shape. Sputtering methods such as DC sputtering, pulsed DC sputtering, and RF sputtering can be applied. For patterning the solid Al alloy film, either wet etching or dry etching is applied. In addition, for patterning the covering layer, either dry etching or wet etching is applied. The film formation and patterning of the gate electrode 13 are usually performed in the middle of the manufacturing process of the thin film transistors 1 and 2.

[0045] In addition, in thin film transistors 1 and 2, heat treatment (annealing) is performed in the manufacturing process as needed. For example, in thin film transistor 1, after forming the gate electrode 13, a heat treatment of 500°C or less is sometimes performed to activate the active layer 11 or fill the active layer 11 with hydrogen. The heating time can be changed as appropriate, for example, if it is 450°C, it is 90 minutes or less, and if it is 500°C, it is 60 minutes or less. The same heat treatment is also performed in thin film transistor 2. For example, in the active layer 21 or the gate insulating film 22, a heat treatment of 500°C or less is sometimes performed to repair its defects. In this case, the heating time is also changed as appropriate, for example, if it is 450°C, it is 90 minutes or less, and if it is 500°C, it is 60 minutes or less.

[0046] Conventionally, as the material of the gate electrode 13 , a high melting point metal (eg, Mo (molybdenum)) that can withstand a thermal history is generally selected.

[0047] However, recently, thin film transistors 1 and 2 are not only used in flat-panel display devices, but are sometimes also used in curved display devices with curved edges, bendable display devices bent into an arc shape, and foldable display devices that can be folded 180 degrees.

[0048] When a gate electrode composed primarily of a high-melting-point metal (e.g., Mo) is applied to a curved portion of such a display device, cracking may occur in a portion of the gate electrode, potentially leading to breakage, as the high-melting-point metal lacks sufficient bending resistance. The gate electrode forms a channel in the active layer facing each other across the gate insulating film. Therefore, when a gate electrode is applied to a curved portion of a display device, it is preferred that the gate electrode have excellent bending resistance, without cracking or breakage.

[0049] Furthermore, the resistivity of a high melting point metal is relatively high among metals, and as the size of a display incorporating the thin film transistor 1 or 2 increases, display delay of the display may occur.

[0050] To address this issue, one approach is to use pure aluminum metal, which exhibits excellent flexibility and low resistance, as the gate electrode material. However, when the gate electrode is made of pure aluminum metal, the aluminum crystal grain size may increase due to thermal history, generating stress (compressive stress, tensile stress) within the gate electrode and forming hillocks on the electrode surface.

[0051] When such a hillock peels off from the gate electrode, the gate electrode may become highly resistive or disconnected. Furthermore, when another film is formed on the hillock, the film may become highly resistive or disconnected due to the shape of the underlying hillock.

[0052] Furthermore, since either wet etching or dry etching is applied when patterning the gate electrode 13 , it is required to process the gate electrode 13 without leaving any residue by wet etching or dry etching.

[0053] As described above, the electrode material constituting the gate electrode 13 is required not only to have low resistance but also to have excellent bending resistance (flexibility), excellent heat resistance with little hillock formation, and to be capable of being etched without residue.

[0054] (Metal wiring structure)

[0055] In this embodiment, in order to deal with the above problems, the application Figure 1 The metal wiring structure shown in (c) is used as the material of the gate electrode 13. The metal wiring structure is formed by sputtering film formation in a vacuum chamber, for example.

[0056] In the metal wiring structure, a metal wiring film is formed on a substrate such as a glass substrate by sputtering. This metal wiring film comprises a main component composed of aluminum and an additive element including iron added to the main component. A cover layer is then laminated on the metal wiring film. Furthermore, the metal wiring structure is heated at a temperature below 500°C, for example, while heat-treating active layers 11 and 21. Vanadium may also be added to the metal wiring film.

[0057] like Figure 1 As shown in (c), the metal wiring structure includes: an Al alloy film 131, which serves as a metal wiring film; and a covering layer 132 (first covering layer), which is stacked on the Al alloy film 131 and is composed of TiN, MoN, WN, TaN, Ti, Mo, W, Ta, etc. that are not easily diffused into the Al alloy film 131.

[0058] The Al alloy film of this embodiment is a metal wiring film (at%: atom%) having a main component composed of aluminum and an additive element including 0.005 at% to 0.88 at% of iron added to the main component. The metal wiring film may contain 0.01 at% to 0.05 at% of vanadium as an additive element.

[0059] In addition, the Al alloy film may also contain inevitable components. In this case, the Al alloy film is composed of a main component, an element group of iron and vanadium, and inevitable components. Here, as inevitable components, Si, Cu, Mn, or Zn can be cited.

[0060] Here, an iron content of less than 0.005 at % is not preferred because hillocks are likely to form in the Al alloy film when the Al alloy film is heat treated. On the other hand, an iron content exceeding 0.88 at % is not preferred because it makes it difficult to control the target composition and achieve uniform film quality. Furthermore, this also reduces the dry etching performance of the aluminum alloy film, which is not preferred.

[0061] Furthermore, if the vanadium content is less than 0.01 at%, hillocks are likely to form in the Al alloy film when the Al alloy film is subjected to heat treatment, which is not preferred. On the other hand, if the vanadium content exceeds 0.05 at%, the resistivity of the Al alloy film increases, which is also not preferred.

[0062] Using such an Al alloy film can form a low-resistance gate electrode 13 having a resistivity of 3.7 μΩ·cm or less, preferably 3.3 μΩ·cm or less. Furthermore, the Al alloy film has excellent bending resistance and exhibits excellent effects due to the addition of Fe or V elements.

[0063] For example, as an effect of adding Fe or V elements, even if the Al alloy film is heat-treated (maximum 500°C, if it is 450°C, the heating time is less than 90 minutes, if it is 500°C, the heating time is less than 60 minutes), it is difficult to generate hillocks in the Al alloy film. For example, even if the Al alloy film is heat-treated (maximum 500°C, if it is 450°C, the heating time is less than 90 minutes, if it is 500°C, the heating time is less than 60 minutes), the iron concentration between the Al particles in the Al alloy film becomes relatively high, the bonding between adjacent Al particles is suppressed, and the Al particles remain in the state of small particles (small particle size: less than 1 μm). The average particle size of the particles in this embodiment is obtained by laser diffraction method, image analysis using electron microscope images, etc.

[0064] Furthermore, when vanadium is contained in the Al alloy film, since vanadium is a solid solution strengthening element for aluminum, it promotes the solid solution of Al and V in the Al particles. As a result, Al-V intermetallic compounds are dispersed and formed, suppressing the movement of Al in the Al particles (Al migration).

[0065] Furthermore, in the metal wiring structure, Al alloy film 131 is physically covered by cap layer 132. This, in synergy with the aforementioned effects of the added elements, further suppresses the formation of hillocks in the Al alloy film. As a result, even when the Al alloy film is subjected to a heat treatment, the enlargement of Al particles, that is, the formation of hillocks, is suppressed, resulting in an Al alloy film with high heat resistance.

[0066] In addition, if the Al alloy film 131 is attached with the cover layer 132 described above, both the cover layer 132 and the Al alloy film 131 can be etched using dry etching.

[0067] like Figure 1 As shown in (d), the cover layer 132 can be provided not only between the Al alloy film 131 and the gate insulating film 22, but also between the Al alloy film 131 and the glass substrate 10. For example, a cover layer 133 (second cover layer) different from the cover layer 132 is provided on the side of the metal wiring film (Al alloy film 131) opposite to the cover layer 132. The cover layer 133 is made of TiN, MoN, WN, TaN, Ti, Mo, W, Ta, or the like.

[0068] Since the Al alloy film 131 is provided between the capping layer 132 and the capping layer 133 , the capping layer not only functions from above the Al alloy film 131 but also functions from below the Al alloy film 131 , thereby further suppressing the generation of hillocks in the Al alloy film 131 .

[0069] For example, before forming the Al alloy film 131 on the glass substrate 10 , the cover layer 133 is formed on the side of the Al alloy film 131 opposite to the cover layer 132 .

[0070] In order to suppress hillocks in the Al alloy film, there is also a method of adding multiple elements selected from transition elements, semiconductor elements, alkaline earth elements, and lanthanides other than Fe and V in place of Fe and V. However, the multiple elements selected from transition elements, semiconductor elements, alkaline earth elements, and lanthanides may include elements that do not melt together with Al.

[0071] If an element that does not melt with Al is added to the Al film, the element that does not melt with Al may precipitate at the grain boundaries of the Al alloy after heat treatment, forming voids (pores) in the film other than the locations where the element precipitated. In this embodiment, by adding Fe or V to the Al film or using a capping layer, the formation of voids is prevented and the formation of hillocks can be reliably suppressed.

[0072] (Aluminum alloy target)

[0073] As a sputtering target used when forming an Al alloy film, an aluminum alloy target (Al alloy target) is used.

[0074] As an Al alloy target, a target with the same composition as the Al alloy film is prepared. For example, the Al alloy target comprises an Al pure metal sheet with a purity of 5N (99.999%) or higher as the main component, and an element group added to the main component of aluminum. The element group includes 0.005 at% to 0.88 at% of iron (Fe), or 0.005 at% to 0.88 at% of iron (Fe) and 0.01 at% to 0.05 at% of vanadium (V) (at%: atomic %).

[0075] In addition, the Al alloy target may also contain inevitable components totaling 20 ppm or less. In this case, the Al alloy target is composed of a main component, an element group, and inevitable components. Examples of inevitable components include Si, Cu, Mn, and Zn. As an example, Si is 4 ppm or less, Cu is 3 ppm or less, Mn is 1 ppm or less, and Zn is 0.3 ppm or less.

[0076] Al alloy targets are made by mixing a group of elements in pure Al metal flakes and melting the mixture in a crucible using a melting method such as induction heating to form an Al alloy ingot. The Al alloy ingot is then processed into a plate or disc shape by plastic processing such as forging, rolling, and pressing.

[0077] For example, each metal material (metal sheet, metal powder) of Al, Fe, or V is placed in a crucible. Next, each metal material is heated to a melting temperature (e.g., 955°C) that is 300°C higher than the melting point of the Al alloy (e.g., 655°C) by induction heating, and each metal material is melted in the crucible. Next, the molten metal is cooled from the melting temperature to room temperature to form an aluminum alloy ingot. Then, the aluminum alloy ingot is forged as needed and cut into a plate or disc shape. Thus, an Al alloy target is formed.

[0078] One method for forming an alloy ingot for a sputtering target involves melting a metal material at a temperature slightly higher than its melting point and then cooling it from this elevated temperature to form an alloy ingot. This method shortens the cooling time from the molten state to the final state, thereby preventing the precipitation of intermetallic compounds during the cooling process. However, in this method, since the melting temperature is set slightly higher than the melting point, there is a risk that the metal materials may not be fully mixed.

[0079] In contrast, in this embodiment, the metal materials are heated and melted at a melting temperature that is at least 300°C higher than the melting point of the Al alloy, thereby thoroughly mixing the metal materials. It is also believed that the higher the melting temperature, the longer the cooling time from the melting temperature to room temperature, and the more likely intermetallic compounds are to precipitate. However, in this embodiment, the concentration of the added elements is adjusted so that even when the Al alloy ingot is cooled from such a melting temperature that is at least 300°C higher than the melting point of the Al alloy, the precipitation of intermetallic compounds is difficult.

[0080] By setting the amount of the added element group within the above range, an Al alloy ingot is formed in which the temperature difference between the solidus and liquidus in the phase diagram of the metallic compound is reduced, and primary crystals formed from intermetallic compounds and the like are less likely to precipitate in the crucible. The added elements are uniformly dispersed in the Al alloy ingot.

[0081] The Al alloy film formed by sputtering using such an Al alloy target achieves the above-mentioned excellent effects.

[0082] Furthermore, when sputtering targets are made solely of pure aluminum metal, the aluminum ingot may be heated during plastic working processes such as forging, rolling, and pressing, causing aluminum grains to grow within the ingot. Al targets made from such ingots also contain aluminum grains, which, during film formation, can be heated by the plasma and form protrusions on the target surface. These protrusions can cause abnormal discharges or even fly off the target during film formation.

[0083] In contrast, the Al alloy target of this embodiment has Fe or V added to pure Al metal in the aforementioned amounts. Consequently, even when the Al alloy ingot is heated during plastic working processes such as forging, rolling, and pressing, Al alloy grains are less likely to grow within the ingot. Consequently, even when the Al alloy target is exposed to heat from the plasma, protrusions are less likely to form on the target surface, and abnormal discharges and splashing of the protrusions are less likely to occur. Furthermore, because abnormal discharges and splashing of the protrusions are suppressed, the Al alloy target can also be used for high-power sputtering film formation.

[0084] In particular, in an Al alloy ingot (or Al alloy target) to which Fe is added, the Fe content at the grain boundaries between particles is higher than the Fe content within the particles. Furthermore, when vanadium is included as a solid solution strengthening element in the Al alloy ingot (or Al alloy target), the solid solution of Al and V is promoted within the Al particles, and Al-V intermetallic compounds are dispersed and formed. This suppresses the movement of Al within the Al particles. Here, the average particle size of the particles in the Al alloy ingot (or Al alloy target) is adjusted to be greater than 100 μm and less than 200 μm.

[0085] As a result, in the Al alloy ingot (or Al alloy target), the grain boundaries serve as barriers, suppressing the phenomenon in which adjacent fine particles are combined and the fine particles are coarsened. As a result, the heat resistance of the Al alloy target is further improved.

[0086] The following describes the film formation conditions for the metal wiring structure and the properties of each of the multiple metal wiring structures. The metal wiring structure shown below is an example of the above-described composition, and the metal wiring structure of this embodiment is not limited to the following example. As an example, heat treatment is performed at 450°C for 0.5 hours in a nitrogen environment.

[0087] (An Example of Manufacturing Conditions for Al Alloy Film)

[0088] Discharge power: DC discharge, 5W / cm 2

[0089] Film forming temperature: room temperature

[0090] Film forming pressure: 0.3Pa

[0091] Film thickness: 300nm

[0092] (An Example of Nitride Film Manufacturing Conditions)

[0093] Discharge power: DC discharge, 5W / cm 2

[0094] Film forming temperature: room temperature

[0095] Film forming pressure: 0.3Pa

[0096] Film thickness: 70nm, 50nm, and 30nm

[0097] Under the above-mentioned film formation conditions, for example, an Al pure metal film, an Al-0.05 at% Fe film, an Al-0.1 at% Fe film, an Al-0.05 at% Fe-0.05 at% V film, an Al-0.1 at% Fe-0.02 at% V film, an Al-0.2 at% Fe-0.02 at% V film, an Al-0.2 at% Fe-0.05 at% V film, and an Al-0.8 at% Fe-0.02 at% V film were formed. A nitride film, as an example of a capping layer, was also laminated on these Al pure metal films and Al alloy films.

[0098] exist Figure 1 In the device shown, a heat treatment is performed, and therefore the goal is to have no hillocks and low resistance in the metal wiring structure after the heat treatment.

[0099] Figure 2 (a) is a graph showing changes in surface roughness of a plurality of Al alloy films immediately after film formation and after heat treatment in the case where no nitride film is provided. Figure 2 (b) is a graph showing changes in surface roughness of a plurality of Al alloy films after heat treatment in the case where a nitride film is provided.

[0100] Figure 2 The vertical axis of (a) and (b) is the maximum valley depth (PV) of the roughness curve measured by AFM. Figure 2 In (a), “○ (as depo: immediately after film formation)” indicates PV immediately after film formation, and “● (after anneal: after annealing)” indicates PV after heat treatment.

[0101] exist Figure 2 In (a) and (b), the leftmost side shows the results for a pure Al metal film (Pure Al), while the others show the results for various Al alloy films. This indicates that a larger difference ΔPV between the PV immediately after film formation and the PV after heat treatment indicates greater surface irregularities after heat treatment, indicating a higher likelihood of hillock formation after heat treatment.

[0102] exist Figure 2 In the case of (a) where no nitride film is provided, it is confirmed that the Al pure metal film has a larger ΔPV than the Al alloy film. Furthermore, while an increase in ΔPV is observed in the Al alloy film, its value is smaller than that of the Al pure metal film. For example, it is found that the higher the Fe content, the smaller the ΔPV. Furthermore, even at the same Fe content, the addition of V further reduces ΔPV. This indicates that the addition of Fe or V to pure metal Al can suppress the formation of hillocks.

[0103] On the other hand, Figure 2 (b) shows the results after heat treatment when a nitride film is provided. Here, three nitride film (TiN) thicknesses were prepared: 30 nm, 50 nm, and 70 nm. Although ΔPV decreased in the Al pure metal film compared to the case without a nitride film, it did not approach zero.

[0104] In contrast, in the Al-0.05at% Fe film, Al-0.1at% Fe film, Al-0.05at% Fe-0.05at% V film, Al-0.1at% Fe-0.02at% V film, Al-0.2at% Fe-0.02at% V film, Al-0.2at% Fe-0.05at% V film, and Al-0.8at% Fe-0.02at% V film, it can be seen that if a nitride film is set, ΔPV becomes smaller than that of the Al pure metal film.

[0105] For example, in the Al-0.1 at % Fe film, it is found that when the nitride film thickness is 70 nm, ΔPV is closer to 0. In particular, when V is mixed, it is found that ΔPV is closer to 0 even when the nitride film thickness is as thin as 30 nm.

[0106] Figure 3 (a) is a graph showing the changes in resistivity ρ (μΩ·cm) of pure Al metal films and multiple Al alloy films after heat treatment. The dashed line in the graph represents the target resistivity value for a single Al alloy film after heat treatment. The target resistivity for a single Al alloy film is a maximum value of 3.7 μΩ·cm or less.

[0107] When focusing on the resistivity changes of single-layer Al alloy films, it is found that these resistivities are all within the target value (3.7 μΩ·cm or less). In particular, the Al-0.2 at% Fe-0.02 at% V and Al-0.2 at% Fe-0.05 at% V films are 3.5 μΩ·cm or less, and the Al-0.05 at% Fe, Al-0.1 at% Fe, and Al-0.1 at% Fe-0.02 at% V films are 3.3 μΩ·cm or less. In other words, by adding Fe or V to Al, the Al alloy film exhibits resistivity equivalent to that of Al and has higher heat resistance than Al. Furthermore, if V is 0.05 at% or less, there is no weight segregation in the Al alloy, making it possible to produce a target. Furthermore, the diffusion coefficient in Al is small, dislocation movement is less likely to occur, and good heat resistance is maintained. Therefore, even when the nitride film is formed thinly, a low ΔPV is maintained.

[0108] Figure 3(b) is a graph showing the resistivity ρ (μΩ·cm) of an Al alloy film having a nitride film formed as a cap layer before heat treatment. Figure 3 (c) is a graph showing the resistivity ρ (μΩ·cm) of an Al alloy film having a nitride film as a cap layer after heat treatment. The heating temperature is 450°C. Figure 3 (b) and (c) show the resistivity ρ (vertical axis) of the Al pure metal film, Al-0.1at%Fe-0.02at%V film, and Al-0.2at%Fe-0.05at%V film when the TiN film is attached. Figure 3 As shown on the horizontal axis of each of (b) and (c), the thickness of the cover layer was set to 30 nm, 50 nm, or 70 nm in each film.

[0109] The resistivity of the Al alloy film with the capping layer is preferably lower than that of a single-layer Mo film used as the gate electrode 13. For example, it is preferably set to less than half the resistivity of the Mo film. For example, the resistivity of the Al alloy film with the capping layer is preferably set to less than 6 μΩ·cm.

[0110] like Figure 3 As shown in (b), before heat treatment, when a TiN film is used as a capping layer on an Al alloy film, the resistivity of the Al alloy film is higher than that of the pure Al metal film. In particular, the resistivity of the Al-0.2at%Fe-0.05at%V film, which has a higher Fe concentration, is higher than that of the Al-0.1at%Fe-0.02at%V film. Furthermore, it is clear that the resistivity increases with increasing TiN thickness.

[0111] For example, in an Al-0.2 at % Fe-0.05 at % V film having a TiN film thickness of 50 nm or more and a high Fe concentration, the resistivity exceeds 6 μΩ·cm, but in other films, the resistivity is 6 μΩ·cm or less.

[0112] Furthermore, we can know that Figure 3 As shown in (c), after heat treatment, the resistivity of the Al alloy film with the TiN film attached decreases to less than 6 μΩ·cm at all TiN film thicknesses. In particular, when the TiN film thickness is 70 nm, the resistivity of the TiN / Al-0.2 at% Fe-0.05 at% V film reaches 4.1 μΩ·cm. Furthermore, when the TiN film thickness is 30 nm, the resistivity is comparable to that of a single-layer Al alloy film. For example, the resistivity of the TiN / Al-0.1 at% Fe-0.02 at% V film is 3.7 μΩ·cm, and the resistivity of the TiN / Al-0.2 at% Fe-0.05 at% V film is 3.5 μΩ·cm, both below 3.7 μΩ·cm.

[0113] Figure 4 (a)~ Figure 4 (h) is a surface SEM image of the Al pure metal film and the plurality of Al alloy films after heat treatment in the case where no nitride film is provided. Figure 5 (a)~ Figure 5 (h) is a surface SEM image of the Al pure metal film and the plurality of Al alloy films after heat treatment with a nitride film provided. In the surface SEM image, when hillocks are precipitated on the surface of the Al alloy film, the hillocks appear as white particles.

[0114] Generally, when the Fe concentration is reduced without adding V or other additive elements, the Al alloy is close to pure Al metal, so it tends to precipitate hillocks. Figure 4 (a) Al pure metal film, Figure 4 (b) Al-0.05at%Fe film, Figure 4 In the Al-0.1at%Fe film (c), it was observed that the particles that were considered to be hillocks were relatively large. In addition, in the other Al alloy films except these, although Figure 4 (a)~ Figure 4 Compared with the particle size of (c), the particle size is suppressed, but the hillocks are observed as fine particles. However, it seems that the addition of V suppresses the growth of the hillocks.

[0115] In contrast, when a nitride film is provided, although the image of the Al pure metal film ( Figure 5 The particles observed in (a)) that are considered to be hillocks are microparticles, but from the images of other Al alloy films ( Figure 5 (b)~ Figure 5 No particles considered to be hillocks were observed in (h)).

[0116] also, Figure 4 (a)~ Figure 5 The example shown in (h) is the result of heat treatment performed at 450°C for 0.5 hours in a nitrogen environment, but it was found that in the Al alloy film provided with a nitride film (70nm), no hillocks were produced even if the heat treatment was extended for longer than 0.5 hours or the heating temperature was increased to 500°C.

[0117] For example, Figure 6 (a)~ Figure 6 (f) is a surface SEM image of the Al pure metal film, Al alloy film, and stacked film with a cover layer attached when the heating temperature is 450°C and the heating time is 1.5 hours. Figure 6 (a) shows the surface SEM image of Al pure metal film. Figure 6(b) shows a surface SEM image of an Al pure metal film with a nitride film attached thereto. Figure 6 (c) shows the surface SEM image of the Al-0.1at%Fe-0.02at%V film. Figure 6 (d) shows a surface SEM image of an Al-0.1 at % Fe-0.02 at % V film to which a nitride film is attached. Figure 6 (e) shows the surface SEM image of the Al-0.2at%Fe-0.05at%V film. Figure 6 (f) shows a surface SEM image of an Al-0.2at%Fe-0.05at%V film with a nitride film attached thereto.

[0118] like Figure 6 As shown in (a), it is confirmed that hillocks are generated on the Al pure metal film. Figure 6 As shown in (b), it was confirmed that hillocks were generated even when a nitride film was provided on an Al pure metal film. Figure 6 As shown in (c), hillocks are generated on the Al-0.1at%Fe-0.02at%V film, but as shown in Figure 6 As shown in (d), no hillocks were generated on the Al-0.1at%Fe-0.02at%V film with the nitride film attached. Figure 6 As shown in (e), hillocks are generated on the Al-0.2at%Fe-0.05at%V film, but as shown in Figure 6 As shown in (f), no hillocks are generated on the Al-0.2at%Fe-0.05at%V film to which the nitride film is attached.

[0119] Figure 7 (a)~ Figure 7 (f) is a surface SEM image of the Al pure metal film, Al alloy film, and stacked film with a cover layer attached when the heating temperature is 500°C and the heating time is 1.0 hour. Figure 7 (a) shows the surface SEM image of Al pure metal film. Figure 7 (b) shows a surface SEM image of an Al pure metal film with a nitride film attached thereto. Figure 7 (c) shows the surface SEM image of the Al-0.1at%Fe-0.02at%V film. Figure 7 (d) shows a surface SEM image of an Al-0.1 at % Fe-0.02 at % V film to which a nitride film is attached. Figure 7 (e) shows the surface SEM image of the Al-0.2at%Fe-0.05at%V film. Figure 7 (f) shows a surface SEM image of an Al-0.2at%Fe-0.05at%V film with a nitride film attached thereto.

[0120] like Figure 7 As shown in (a), it is confirmed that hillocks are generated on the Al pure metal film. Figure 7 As shown in (b), it was confirmed that hillocks were generated even when a nitride film was provided on an Al pure metal film. Figure 7 As shown in (c), hillocks are generated on the Al-0.1at%Fe-0.02at%V film, but as shown in Figure 7 As shown in (d), no hillocks were generated on the Al-0.1at%Fe-0.02at%V film with the nitride film attached. Figure 7 As shown in (e), hillocks are generated on the Al-0.2at%Fe-0.05at%V film, but as shown in Figure 7 As shown in (f), no hillocks are generated on the Al-0.2at%Fe-0.05at%V film to which the nitride film is attached.

[0121] In addition, in either the case where the heating temperature is above 450°C and the heating time is 1.5 hours, or the case where the heating temperature is above 500°C and the heating time is 1.0 hour, the resistivity of the Al alloy film is the same as that in the case where the heating time is above 450°C and the heating time is 0.5 hour.

[0122] Figure 8 (a)~ Figure 8 (d) shows an example of a SEM image of the surface of a glass substrate after etching the Al alloy film formed on the glass substrate. Figure 8 (a) shows an example of etching an Al-0.1at%Fe film. Figure 8 (b) shows an example of etching an Al-0.05at%Fe-0.05at%V film. Figure 8 (c) shows an example of etching an Al-0.1at%Fe-0.02at%V film. Figure 8 (d) shows an example of etching an Al-0.2at%Fe-0.05at%V film.

[0123] During dry etching, the etching gas is a mixed gas of Cl2 (50 sccm) / Ar (20 sccm). The etching pressure is 1.0 Pa. When the substrate bias power is 400 W, the discharge power is 600 W. In addition, fluorine-based gases (CF4, SF6, CHF3, etc.), chlorine-based gases (BCl3, etc.) can also be used, or a combination of these can be used. As wet etching liquid, a mixed solution containing ammonium fluoride / nitric acid / water (for example: Kanto Chemical KSMF-260), KSMF series (Kanto Chemical), a mixed solution containing phosphoric acid / nitric acid / acetic acid / water (Kanto Chemical, mixed acid Al etching liquid), hydrogen peroxide water, a mixed solution containing hydrogen peroxide water, etc. are used. The liquid temperature is 40°C. Depending on the type and structure of the film, etching gas and etching liquid can be used separately. In addition, dry etching and wet etching can be combined.

[0124] It is known that Figure 8 (a)~ Figure 8 In the Al alloy film shown in (d), both dry etching and wet etching can be performed on the glass substrate without leaving any residue.

[0125] Figure 9 (a) and Figure 9 (b) shows an example of an SEM image of the surface of a glass substrate after etching a film formed by attaching a nitride film (TiN, 70 nm) to an Al alloy film formed on a glass substrate. Figure 9 (a) shows an example of etching TiN film / Al-0.1at%Fe-0.02at%V film, Figure 9 (b) shows an example in which the TiN film / Al-0.2at%Fe-0.05at%V film is etched.

[0126] It is known that Figure 9 In both the Al alloy films with attached nitride films shown in (a) and (b), etching can be performed on glass substrates without residue using dry etching or other methods. During etching, the nitride film is removed along with the Al alloy film. Therefore, even if a nitride film is attached to the Al alloy film as a capping layer, the Al alloy film with attached nitride film can be etched together during the etching process for the Al alloy film.

[0127] In addition, Figure 9 (a) shows the TiN film / Al-0.1at%Fe-0.02at%V film and Figure 9The TiN film / Al-0.2at%Fe-0.05at%V film shown in (b) was treated with a TMAH (Tetramethylammonium hydroxide) solution as a resist developer or an HF solution for removing oxide films. As a result, no roughness occurred on the surface of the TiN film.

[0128] Table 1 shows the results of the bending test of the Al alloy film.

[0129] A polyimide layer (25 μm) was prepared as a substrate for the bending test. Three Al alloy films, namely, an Al-0.1 at% Fe film, an Al-0.1 at% Fe-0.02 at% V film, and an Al-0.2 at% Fe-0.05 at% V film, were formed on the polyimide layer. The thickness of the Al alloy film was 300 nm. Furthermore, a TiN film was formed on each Al alloy film. Three TiN film thicknesses of 30 nm, 50 nm, and 70 nm were prepared. Thus, nine evaluation samples (Samples 1 to 9) were formed.

[0130] Before the bending test, each evaluation sample was annealed at 450°C for 30 minutes. The bending radius was 1 mm, the test speed was 30 rpm, and the number of bends was 1, 1,000, 10,000, and 100,000.

[0131] [Table 1]

[0132]

[0133] The resistance (sheet resistance (Ω / square)) before and after the bending test was measured. The resistance before the bending test was designated as R0, and the resistance after the test was designated as R. Table 1 shows R / R0. The closer R / R0 is to "1", the less change there is in resistance before and after the bending test.

[0134] As shown in Table 1, the resistance of samples 1 to 9 remained unchanged from the initial value (R0) until 10,000 bends. While increases were observed for samples 1, 4, and 7 after 100,000 bends, the resistance of samples 2, 3, 5, 6, 8, and 9 remained unchanged from the initial value (R0). For a bend radius of 1.0 mm, the TiN film thickness is preferably set to 50 nm or less to achieve more reliable bending resistance.

[0135] In addition, Table 2 shows another result of the bending test of the Al alloy film.

[0136] Table 2 shows the bending test results for a bending radius of 1.5 mm. Three samples (Samples 10 to 12) were prepared. For example, a 70 nm thick TiN film was formed on each of three Al alloy films: an Al-0.1 at % Fe film, an Al-0.1 at % Fe-0.02 at % V film, and an Al-0.2 at % Fe-0.05 at % V film.

[0137] [Table 2]

[0138]

[0139] As shown in Table 2, when the TiN film thickness was set to 70 nm, the resistance of samples 10 to 12 remained unchanged from the initial value (R0) even after 100,000 bends. This indicates that excellent bending resistance can be achieved even with a TiN film thickness of 70 nm when the bending radius is set to 1.5 mm.

[0140] In addition, the same bending test as samples 1 to 9 was also attempted for a single-layer Mo film with a thickness of 300 nm. 3 When the bending times reach 10, cracks are generated on the Mo film, and R / R0 is about 50. In a single-layer Mo film, when the bending times reach 10 4 When the cracks were further increased, R / R0 increased to about 65.

[0141] As described above, examples of materials for the capping layer are not limited to TiN films; any film composed of MoN, WN, TaN, Ti, Mo, W, Ta, and the like may also be used. For example, when the W film thickness is 70 nm, the resistivity of a W / Al-0.2at% Fe-0.05at% V film is 4.4 (μΩ·cm); when the Ta film thickness is 70 nm, the resistivity of a Ta / Al-0.2at% Fe-0.05at% V film is 4.3 (μΩ·cm); and when the Mo film thickness is 70 nm, the resistivity of a Mo / Al-0.2at% Fe-0.05at% V film is 4.4 (μΩ·cm). These resistivities are comparable to those of an Al alloy film with TiN attached.

[0142] In particular, the resistivity of Mo and W is close to that of the TiN film, and Mo and W have excellent barrier functions against Al, Fe, and V, so these materials can be replaced with TiN.

[0143] For example, Figure 10 (a)~ Figure 10 (d) is a surface SEM image of the laminated film with the cover layer attached when the heating temperature is 500°C and the heating time is 1.0 hour. Here, as the cover layer, Mo ( Figure 10 (a)), film thickness 70nm Mo ( Figure 10 (b)), W with a film thickness of 30 nm ( Figure 10 (c)), or W with a film thickness of 70 nm ( Figure 10 (d) The Al alloy film is an Al-0.2at%Fe-0.05at%V film (film thickness: 300nm).

[0144] like Figure 10 (a)~ Figure 10 As shown in (d), it can be seen that no hillocks are generated in any of the laminated films.

[0145] Table 3 shows the bending test results for a bending radius of 1.0 mm. Four types of samples were prepared, each consisting of a 300 nm thick Al-0.2 at % Fe-0.05 at % V film with a Mo and W coating layer formed thereon. These samples included a Mo (70 nm) Al-0.2 at % Fe-0.05 at % V film (Sample 13), a Mo (30 nm) Al-0.2 at % Fe-0.05 at % V film (Sample 14), a W (70 nm) Al-0.2 at % Fe-0.05 at % V film (Sample 15), and a W (30 nm) Al-0.2 at % Fe-0.05 at % V film (Sample 16).

[0146] [Table 3]

[0147]

[0148] As shown in Table 3, the resistance of samples 13 to 16 remained unchanged from the initial value (R0) until the bending cycle reached 1,000 times. However, when the bending cycle reached 10,000 times, the R / R0 value began to increase for the 70nm thick Mo or W films. However, for the 30nm thick Mo or W films, the resistance of any stacked film remained unchanged from the initial value (R0) even after the bending cycle reached 100,000 times.

[0149] As such, the cover layer is not limited to TiN; any material with similar mechanical properties can provide the same heat resistance as TiN. Furthermore, by optimizing the type and thickness of the cover layer, both heat resistance and flexibility can be achieved. The materials shown in this embodiment are merely examples, and the thickness of each film or the two-layer or three-layer structure can be adjusted according to specifications for heat resistance, resistivity, and bending resistance.

[0150] While the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible. The embodiments are not limited to being independent, and can be combined as much as possible technically.

[0151] Description of Reference Numerals

[0152] 1, 2: Thin film transistor

[0153] 10: Glass substrate

[0154] 11, 21: Active layer

[0155] 12, 22: Gate insulating film

[0156] 13: Gate electrode

[0157] 15: Protective layer

[0158] 16D, 26D: Drain electrode

[0159] 16S, 26S: Source electrode

[0160] 131: Al alloy film

[0161] 132, 133: Covering layer

Claims

1. A metal wiring structure comprising: A metal wiring film having a main component composed of aluminum and an additive element added to the main component including 0.005 at % to 0.88 at % of iron and 0.01 at % to 0.05 at % of vanadium; and A first covering layer made of TiN, MoN, WN, TaN, Ti, Mo, W, or Ta is stacked on the metal wiring film.

2. The metal wiring structure according to claim 1, wherein A second covering layer made of TiN, MoN, WN, TaN, Ti, Mo, W, or Ta is provided on the side of the metal wiring film opposite to the first covering layer, and the metal wiring film is provided between the first covering layer and the second covering layer.

3. A method for manufacturing a metal wiring structure, comprising: forming a metal wiring film on a substrate, the metal wiring film having a main component composed of aluminum and an additive element added to the main component including 0.005 at % to 0.88 at % of iron and 0.01 at % to 0.05 at % of vanadium; A first covering layer composed of TiN, MoN, WN, TaN, Ti, Mo, W or Ta is stacked on the metal wiring film; as well as The metal wiring film is subjected to a heat treatment at 500° C. or lower.

4. The method for manufacturing a metal wiring structure according to claim 3, wherein: A second covering layer made of TiN, MoN, WN, TaN, Ti, Mo, W or Ta is formed on the side of the metal wiring film opposite to the first covering layer, and the metal wiring film is arranged between the first covering layer and the second covering layer.

Images