US20030180177A1

US20030180177A1 - Ag alloy film and sputtering-target for the Ag alloy film

Info

Publication number: US20030180177A1
Application number: US10/393,993
Authority: US
Inventors: Hideo Murata
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2002-03-25
Filing date: 2003-03-24
Publication date: 2003-09-25
Also published as: KR20030077963A; KR100506474B1; CN1446941A; CN1226446C

Abstract

A composition of an Ag alloy film as a thin film for electronic devices and target material to form thereof by a sputtering process are disclosed. The Ag alloy film consists of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities. The Ag alloy film may be used as a wiring film or a reflective film for flat panel display devices. The sputtering-target material for forming the Ag alloy film consists of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

Description

BACKGROUND OF THE INVENTION

This invention relates to an Ag alloy film and a sputtering-target (i.e. a target material) for the Ag alloy film required to possess satisfactory corrosion resistance, heat resistance, and adhesion properties when applied to various reflective films, flat panel displays, or other thin film devices such as various semiconductor devices, thin film sensors, magnetic heads and so on.

In recent years, Ag films having such advantageous properties as low electric resistivity or high optical reflectance have been of note for application as thin films, especially for electronic devices. While Ag films possess good properties of optical reflectance and resistivity, they have drawbacks of inferior adhesion to the substrates, and heat and corrosion resistance properties.

In recent years, flat panel displays (hereinafter referred to as FPDs) are rapidly becoming popular as a display device replacing conventional cathode-ray tubes. The FPDs include, for example, liquid crystal displays (hereinafter LCDs), plasma display panels (hereinafter PDPs), field emission displays (hereinafter FEDs), electroluminescence displays (hereinafter ELDS), and electrophoretic displays used for electronic papers. The application of Ag to wiring films or reflective films for FPDs involves a problem of film exfoliation during processing because of inferior adhesion of such films onto glass substrates, resin substrates, resin films and metal foils with high corrosion resistance, such as stainless steel foils.

In addition, depending upon a material type of substrates and conditions of a heating atmosphere, such films may contract to impair continuity of the films resulting in a substantial decrease in reflectance or an increase in electric resistivity. Since Ag has inferior corrosion resistance property, Ag films discolor merely under exposure to the air for about one day after film formation, and begin to represent yellowish reflection property (yellowing). The use of Ag for thin films involves a problem to effect a substantial decrease in reflectance or an increase in resistivity because of corrosion induced by chemical solutions employed in fabricating the devices.

To solve such problems, a method to use an Ag alloy target produced by adding 0.1 atomic % of Cu or above into Ag is described in JP-A-8-260135. An Ag alloy comprising 0.1 to 2.5 atomic % of Au and 0.3 to 3 atomic % of Cu is disclosed in JP-A-9-324264. An electrode substrate for reflection type display devices employing an Ag alloy including Pt, Pd, Cu or Ni on an adhesion layer is proposed in JP-A-11-119664. An Ag alloy comprising 0.5 to 4.9 atomic % of Pd is disclosed in JP-A-2000-109943. An Ag alloy comprising 0.1 to 3 weight % of Pd and 0.1 to 3 weight % of Al, Au, Pt or the like is proposed in JP-A-2001-192752. It is reported in JP-A-2002-015464 that reflective films formed from alloys produced by adding Cu and one of Nd, Sn, Ge, Y, Au and the like into Ag and applied as reflective films for optical data storage media demonstrated satisfactory properties of adhesion to the disc substrates or other films as well as oxidation resistance while maintaining desirable reflectance of a laser beam having a specific wavelength.

However, in the case where those elements are added to Ag following the methods disclosed as above, resistivity increases and reflectance on a shorter wavelength side of the visible spectrum, in particular, decreases, and thus no alloy films possessing satisfactory adhesiveness, corrosion resistance and heat resistance as well in addition to low resistivity and high reflectance have been proposed. More specifically, for example in case of Pd, Pt or Ni, if its content becomes 0.2 atomic % or more, reflectance decreases, and if the content exceeds 1 atomic %, resistivity becomes greater than 5 μΩ cm. If Au and Cu are added, changes in reflectance and resistivity remain at a marginal level, but problems arise on heat resistance and adhesion properties.

An object of the present invention is to provide an Ag alloy film having satisfactory adhesiveness, heat resistance, corrosion resistance and patterning properties as well while maintaining low electric resistivity and high optical reflectance properties, and a sputtering-target for producing the Ag alloy film.

BRIEF SUMMARY OF THE INVENTION

Through extensive investigation to solve the above problems, the present inventor has found that, by adding a combination of selected elements to Ag, reflectance becomes essentially a constant value while maintaining high reflectance inherent to Ag within the visible spectrum, low electric resistivity is assured, and corrosion resistance, heat resistance, adhesiveness to the substrate, and patterning properties can be improved, whereby the present invention was accomplished.

According to one aspect of the invention, there is provided an Ag alloy film consisting essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

According to one embodiment of the invention, the Ag alloy film consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities. Preferably, at least one of Au and Cu is contained in an amount of 0.1 to 0.5 atomic % in total.

According to another aspect of the invention, there is provided a sputtering-target for an Ag alloy film consisting essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

According to one embodiment of the invention, the sputtering-target consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities. Preferably, at least one of Au and Cu is contained in an amount of 0.1 to 0.5 atomic % in total.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows the effects of content of rare earth elements on resistivity of the Ag alloy films in Example 1; [0014]
FIG. 2 shows the effects of content of additive elements on resistivity of the Ag alloy films in Example 2; [0015]
FIG. 3 shows the effects of content of rare earth elements on average reflectance of the Ag alloy films in Example 3; [0016]
FIG. 4 shows the effects of content of rare earth elements on differential reflectance of the Ag alloy films in Example 3; [0017]
FIG. 5 shows the effects of Cu content on average reflectance of the Ag alloy films in Example 4; [0018]
FIG. 6 shows the effects of Cu content on differential reflectance of the Ag alloy films in Example 4; [0019]
FIG. 7 shows the effects of Au content on average reflectance of the Ag alloy films in Example 5; [0020]
FIG. 8 shows the effects of Au content on differential reflectance of the Ag alloy films in Example 5; [0021]
FIG. 9 shows reflectance within the optical spectrum of 400 to 700 nm of the Ag alloy films in Example 7; [0022]
FIG. 10 shows reflectance within the optical spectrum of 400 to 700 nm of the Ag alloy films in Example 8; [0023]
FIG. 11 shows the effects of temperatures applied to films on resistivity of the Ag alloy films in Example 9; and [0024]
FIG. 12 shows the effects of temperatures applied to substrates on resistivity of the Ag alloy films in Example 10.[0025]

DETAILED DESCRIPTION OF THE INVENTION

The present invention is characterized by the finding an optimum composition of the Ag alloy films obtaining satisfactory properties such as those of adhesiveness, patterning, corrosion resistance and heat resistance which are drawbacks of Ag films while keeping low resistivity and high reflectance inherent to Ag to the extent possible. [0026]
Herein below there will be provided reasons why the Ag alloy film of the invention has the defined chemical composition. [0027]
When additive elements are added to Ag, while electric resistivity increases and reflectance decreases, heat resistance, corrosion resistance, adhesion, and patterning properties tend to improve as content of such additive elements increases. Therefpre, the inventor noted that in order to solve the above problems accompanied in using Ag, it will be important to identify additive elements and specify necessary minimum contents thereof required to provide satisfactory effects while maintaining low resistivity and high reflectance. [0028]
The inventor paid attention to rare earth elements for employing as additive elements to improve the above shortcomings in film properties. The inventor further considered that the addition of rare earth elements of the IIIa group in the Periodical Table to Ag would have an effect to improve heat resistance property through restraining cohesion of Ag alloy films when the films are heated and also advance corrosion resistance property through modifying properties of Ag itself by forming an intermetallic compound with Ag. [0029]
As a result of diverse examinations and considerations, the inventor has found that Sm, Dy and Tb have distinctive properties apart from the rest of the rare earth elements and when added to Ag alloys are extremely effective in solving the above problems pertaining to heat resistance, corrosion resistance, and patterning properties. [0030]
Although it is not so clear why such elements are effective, it is considered that since Sm, Dy and Tb have smaller atomic radii than lighter rare earth elements such as La, Nd and the like and close to that of Ag, disturbance of crystal lattices will be minimized when added to Ag and offer smaller effects in impeding movement of free electrons. [0031]
However, in the case of Ag alloy films comprising only additive Sm, Dy or Tb, the inventor confronted with a problem that a satisfactory adhesion property can not be obtained due to exfoliation of films during film forming. [0032]
After exploration of other elements that would drastically improve adhesion property without impeding favorable effects of Sm, Dy or Tb the inventor has found that the addition of Au and/or Cu on top of the selected rare earth elements is extremely effective in improving adhesion property. The inventor has also found that addition of Au and/or Cu improves heat and corrosion resistance properties while maintaining low resistivity and high reflectance. [0033]
Although it is not so clear why the additive Au and/or Cu improves the adhesion property, it is assumed that Au and Cu belonging in the same group with Ag tend to dissolve in Ag forming a solid solution and impede atomic migration of Ag resulting in Ag alloy films having a fine and uniform structure, and as a consequence improved adhesion property through restraining cohesion of the Ag alloy films. It is further assumed that as Sm, Dy and Tb are liable to form intermetallic compounds with Au and Cu as well as Ag, a combined addition of Sm, Dy or Tb with Au and/or Cu causes a more effective change in characteristics of Ag resulting in improved corrosion resistance of the Ag alloy films. [0034]
Furthermore, it is assumed that, in the case of such a combined addition of elements, since the additive elements being dissolved, under a non-equilibrium state, in the Ag matrix of the Ag alloy films as sputtered precipitate at grain boundaries as intermetallic compounds, when the Ag alloy films are subjected to heat treatment, so as to inhibit the growth of crystal grains whereby improving heat resistance property of the Ag films and inhibiting intergranular corrosion to improve corrosion resistance property of the same. [0035]
As described above, one of the important characteristics of the invention resides in having found a fact that Sm, Dy or Tb having an effect to improve heat and corrosion resistance properties and Au and/or Cu having an effect to enhance adhesion property can be added to Ag without offsetting respective advantages. In other words, it has now become possible to obtain an Ag alloy film having satisfactory corrosion and heat resistance properties as well as enhanced adhesion property by adding the elements of the above two groups. When content of the additive elements was increased, heat resistance, adhesion, and corrosion resistance properties advanced; on the other hand, electric resistivity and reflectance deteriorated. Therefore, it is important that content of both element groups be controlled to minimum levels while attaining satisfactory property improvement effects. [0036]
Now content of elements to be added to Ag will be described below. [0037]
With the addition of 0.1 atomic % of Sm, Dy or Tb, its improvement effects appeared promptly. But with the addition of more than 0.5 atomic %, resistivity became higher and reflection deteriorated while superior corrosion and heat resistance properties were retained. Therefore, to attain further lower resistivity and higher reflectance, it is desirable to control the quantity of Sm, Dy or Tb to 0.3 atomic % or less. [0038]
The effect of adhesion improvement could be observed if 0.1 atomic % at the smallest of Au and/or Cu was added on top of Sm, Dy or Tb. If content of Cu exceeded 1.0 atomic % resistivity became so high and reflectance dropped significantly, although in case of Au even if more than 1.0 atomic % of Au was added no significant increase in resistivity and decrease in reflectance were observed. If content of Au exceeded 0.5 atomic % generation of residues during etching process took place easily, and with more than 1.0 atomic % the quantity of residues increased and patterning property deteriorated. Thus, to ensure satisfactory patterning property the quantity of Au and/or Cu are desirably be limited to not more than 1.0 atomic %. With more than 0.5 atomic % of Au the generation of residues took place easily and patterning property deteriorated, but the residues could be removed by careful washing. [0039]
Therefore, it is preferable that Ag contains 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb and 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu. It is also preferable that Ag contains 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb and 0.1 to 0.5 atomic % in total of at least one element selected from the group of Au and Cu to materialize an Ag alloy film having higher reflectance, lower resistivity and satisfactory patterning properties. [0040]
As Sm, Dy or Tb is resistive to oxidation as compared with Y or Sc among rare earth elements, the use of Sm, Dy or Tb has a merit enabling chemically stable material supply. This leads to a capability of stable manufacture of sputtering-targets for Ag alloy films. Among the group of Sm, Dy and Tb, for industrial application the use of Sm with lower prices is most preferable, as Dy and Tb are expensive. [0041]
It is preferable to use glass substrates and silicon wafers in forming the Ag alloy film according to this invention. Both substrates have superior process stability in fabricating FPDs and permit application of heat to the substrates as described below in forming the Ag alloy film according to this invention. [0042]
After fabrication the Ag alloy film according to this invention can be further processed into films with lower electric resistivity by heating the substrates. Particularly, heating to not lower than 150° C. permits the Ag alloy film to improve resistivity to 3 μΩ cm or smaller and to not lower than 250° C. to 2.5 μΩ cm or smaller. Thus, the Ag alloy film according to this invention is suitable for a wiring film for such flat panel displays as organic ELDs, LCDs and the like having a process to fabricate polysilicon TFTs that requires to heat glass substrates and silicon wafers. [0043]
If a heating process is applied to conventional Ag—Cu alloys or Ag—Pd alloys, resistivity of films formed from those alloys has become smaller, but adhesion and heat resistance properties have been unsatisfactory. The fact that those problems can also be solved is an additional important advantage of this invention. [0044]
Where ref(max) being the maximum reflectance within the optical wavelength of 400 to 700 nm of the visible spectrum and ref(min) being the minimum reflectance, values of differential reflectance of the Ag alloy film formed according to this invention obtained from a formula between the two variables as (ref(max)−ref(min))/ref(max)×100 becomes 6 or smaller. Thus, reflectance within the visible spectrum required for FPDs becomes essentially a constant value providing a reflective film that have high reflectance, and satisfactory heat resistance, corrosion resistance, adhesion and patterning properties. [0045]
The Ag alloy film according to this invention can be treated into films having essentially constant reflectance within the visible spectrum and high reflectance by heating the substrates after fabrication, and thus is suitable for reflective films for such flat panel displays as reflection type liquid crystal displays and the like having a heating step of glass substrates or silicon wafers. [0046]
In general if a heating process is applied to conventional Ag—Cu alloys or Ag—Pd alloys, reflectance of films formed by those alloys has become smaller most of the time. A thin film having a property to advance reflectance by heating like the Ag alloy film according to this invention is very beneficial to be used as various reflective films for FPDs, and this fact is an additional important advantage of this invention. [0047]
In forming the Ag alloy film according to this invention, a sputtering deposition method with utilization of a target material is most preferable. This is because the sputtering method permits fabrication of films with substantially the same composition with the target material. Thus, it is possible to stably form the Ag alloy film of the invention. For this reason, this invention provides sputtering-target material having substantially the same composition with Ag alloy films for electronic devices. [0048]
Various methods are available for producing target material, and any method which permits high purity, uniform composition, high density and the like required for target material in general may be employed. For example, target material may be produced through a sequence of processes of casting molten metal adjusted to prescribed composition by a vacuum melting method into a metallic mold, forging and rolling the cast material into a plate shape, and machining the plate into a prescribed finished figure. For securing uniform structure, ingots quenched and solidified through a powder sintering method or a splay forming method may be employed. [0049]
Also a sputtering-target for the Ag alloy film according to this invention defines that the balance after counting Sm, Dy or Tb, and Au and/or Cu is essentially Ag and incidental impurities. The incidental impurities may include, to the extent that may not impede the effects of this invention, such gaseous components as Oxygen, Nitrogen, Carbon, transition elements of Fe, Co and Ni, and semi-metals of Al, Si and the like. [0050]
It is preferable, for example, content of respective gaseous components of oxygen, nitrogen and carbon is 50 ppm or less, the transition elements of Fe, Co and [0051] Ni 100 ppm or less; Al 500 ppm or below, and so forth, and the purity excluding the gaseous components is preferably not less than 99.9%.
The substrates to be used for the Ag alloy film according to this invention may be glass substrates, silicon wafers and the like, however, other substrates which allow formation of thin films, for example, resin substrates, resin foils and metal foils may be employed. [0052]
The Ag alloy film for electronic devices according to this invention preferably has a film thickness of 100 to 300 nm to ensure stable electric resistivity. If the thickness is below 100 nm, resistivity will increase because of surface scattering of electrons resulting from the thinness and reflectance will deteriorates due to light transmission to some extent, and also changes in film surface formation tend to take place easily. On the other hand if the thickness exceeds 300 nm such films tend to separate easily due to residual stress in films and represent low reflectance due to roughness of film surfaces caused by crystal growth, and the productivity deteriorates as a result of elongated film formation time. [0053]

EMBODIMENTS

Example 1

In order to confirm the effects of rare earth elements and a group of Au and Cu when they are added to Ag in together, 0.3 atomic % of either Au or Cu and varying quantities of respective rare earth elements, Y, La, Nd, Sm, Tb and Dy, were added to Ag. The alloys were then made into cast Ag alloy ingots by vacuum melting and casting, processed into a plate form by cold rolling, and machined to sputtering-targets having a diameter of 100 mm and a thickness of 5 mm. Then, using the Ag alloy sputtering-targets Ag alloy films having 200 nm thickness were formed on glass substrates. Resistivity values measured by four-probe method in room temperature are shown in FIG. 1. [0054]
As shown in FIG. 1, as content of each rare earth element increased resistivity increased. Ag alloy films formed from alloys containing Sm, Tb or Dy recorded lower resistivity than those containing Y, La or Nd. From these results, it is concluded that Sm, Tb or Dy is preferable as an additive element. When content of respective additive element exceeded 0.5 atomic %, resistivity surpassed 4 μΩ cm canceling out the advantage of low resistivity inherent to Ag. As a result, it is preferable to control content of Sm, Tb or Dy to 0.5 atomic % or less. To obtain lower resistivity, for example 3 μΩ cm or smaller, content is preferable to be 0.3 atomic %. In case when 0.3 atomic % of Au was added in place of Cu, resistivity increased as Sm content increased similarly to the Cu case, but resistivity itself was lower than the Cu case. [0055]

Example 2

A fixed quantity of 0.3 atomic % of Sm was added to Ag, and then varying quantities of Au, Cu, Pd, Ru and Ni, respectively, were further added to produce cast Ag alloy ingots and then sputtering-targets similarly with Example 1. Using the targets, Ag alloy films having a thickness of 200 nm were formed on glass substrates. Resistivity values measured in similar manner with Example 1 are shown in FIG. 2. [0056]
As shown in FIG. 2, resistivity increased as quantities added to Ag increased. Ag alloy films formed from alloys containing Au or Cu recorded lower resistivity than those containing Ru, Ni or Pd. With the addition of not more than 1.0 atomic % of Au or Cu resistivity stayed at 4 μΩ cm or lower. Particularly the addition of Au caused only a marginal increase in resistivity and resistivity of 4 μΩ cm or smaller was kept with the addition even up to 1.5 atomic %. From these results, in adding either Cu or Au to Sm it is preferable that the quantities of Cu are controlled to not more than 1.0 atomic % and of Au to not more than 1.5 atomic %. [0057]

Example 3

A fixed quantity of 0.2 atomic % of Cu was added to Ag, and then varying quantities of Y, La, Nd, Sm and Tb, respectively, were further added to produce cast Ag alloy ingots and then sputtering-targets similarly with Example 1. Using the targets, Ag alloy films having a thickness of 200 nm were formed on glass substrates. Average reflectance within the visible spectrum of 400 to 700 nm was measured by a spectrophotomeric calorimeter (CM2002 made by Minolta Co., Ltd.). The results are shown in FIG. 3. Also where ref(max) being the maximum reflectance within the optical wavelength of 400 to 700 nm and ref(min) being the minimum reflectance, values of differential reflectance obtained from a formula between the two variables as (ref(max)−ref(min))/ref(max)×100 are shown in FIG. 4. [0058]
As shown in FIG. 3, average reflectance decreased as quantities of rare earth elements added to Ag increased. Ag alloy films formed from alloys containing either Sm or Tb recorded smaller deterioration of average reflectance compared to those containing Y, La or Nd. Also as shown in FIG. 4, differential reflectance of Ag alloy films formed from alloys containing Sm or Tb indicated an inclination to become smaller. From these results, Sm or Tb is preferable as an additive element for addition to Ag. By controlling the quantities of Sm or Tb to 0.5 atomic % or less, more preferably 0.3 atomic % or less, Ag alloy films having high reflectance of 97% or above and essentially constant reflectance within the visible spectrum close to paper white with differential reflectance value of 6 or below were made available. [0059]

Example 4

A fixed quantity of 0.2 atomic % of respective rare earth elements, Y, Nd, Sm and Tb, was added to Ag, and then varying quantities of Cu were further added to produce cast Ag alloy ingots and then sputtering-targets similarly with Example 1. Using the targets, Ag alloy films having a thickness of 200 nm were formed on glass substrates by sputtering method. Average reflectance within the visible spectrum of 400 to 700 nm was measured similarly with Example 3. The measurements are shown in FIG. 5. Also values of differential reflectance within the optical wavelength of 400 to 700 nm are shown in FIG. 6. [0060]
As shown in FIG. 5, average reflectance decreased as Cu quantities increased. Ag alloy films formed from alloys containing either Sm or Tb recorded higher average reflectance than those containing Y or Nd. Also as shown in FIG. 6, differential reflectance of Ag alloy films formed from alloys containing Sm or Tb became small and provided reflection properties having essentially constant reflectance within the visible spectrum. Furthermore, when a Cu quantity exceeded 0.5 atomic % reflectance decreased significantly and differential reflectance also became larger. From these results, when Cu is added to Ag together with Sm or Tb, the Cu quantity is preferably be limited up to 0.5 atomic %. [0061]

Example 5

Similarly to Example 4, a fixed quantity of 0.2 atomic % of respective rare earth elements, Y, Nd, Sm and Dy, was added to Ag, and then varying quantities of Au were further added to produce cast Ag alloy ingots and then sputtering-targets similarly with Example 1. Using the targets, Ag alloy films having a thickness of 200 nm were formed on glass substrates by sputtering method. Average reflectance within the visible spectrum of 400 to 700 nm was measured similarly with Example 3. The measurements are shown in FIG. 7. Also values of differential reflectance within the optical wavelength of 400 to 700 nm are shown in FIG. 8. [0062]
As shown in FIG. 7, average reflectance decreased slightly as Au quantities increased. Ag alloy films formed from alloys containing either Sm or Dy recorded higher average reflectance than those containing Y or Nd. Also differential reflectance of Ag alloy films formed from alloys containing Sm or Dy were small and provided reflection properties having essentially constant reflectance within the visible spectrum. Changes in reflectance in response to varying Au quantities were relatively small in comparison with those of Cu, and even if Au quantities were increased changes in reflectance were small. From these results, reflection properties containing Sm or Dy were better than those containing other rare earth elements. [0063]

Example 6

Next, heat resistance, corrosion resistance, adhesion and patterning properties of films formed from Ag alloys containing respective combination of additive elements of Sm plus Cu, Sm plus Au, or Sm plus Cu plus Cu were evaluated. [0064]
In order to evaluate resistivity and reflectance after experiencing similar conditions through which devices for finished products might pass during production processes, resistivity and average reflectance of pure Ag films with a thickness of 200 nm and Ag alloy films formed on glass substrates and silicon wafers, respectively, were measured. Measurements were made at the time just after the film formation, after heating at 250° C. for 2 hours in vacuum, and after exposure to an atmosphere at 85° C. and of 90% humidity for 24 hours for a corrosion test. [0065]
Also to evaluate heat resistance property of films, surfaces of pure Ag films and Ag alloy films heated at 250° C. for 2 hours in atmosphere, respectively, were observed for discoloration, and those samples having no white spots, clouding and yellowing were given a “good” rating. [0066]
Also to evaluate adhesion property of films, cross-cut lines at 2 mm intervals were applied on pure Ag films and Ag alloy films heated in vacuum, respectively, and adhesive tapes were stuck on the surfaces for subsequent peeling off. The number of cross-sections remained on the substrates were counted and expressed in areal ratios against the substrate surface for rating of adhesion property. [0067]

Also for evaluation of patterning property, a photoresist (OFPR-800 made by Tokyo Ohka Kogyo Co., Ltd.) was applied by spin coating on pure Ag films and Ag alloy films, respectively, both of which underwent heating treatments as above. Having exposed the masked photoresist to UV, resist patterns were formed through development with an organic developer, NMD-3, and pure Ag film and Ag alloy film patterns were formed by etching using a solution of phosphoric acid, nitric acid and acetic acid. Pattern edge forms and residues around the edges were examined with a microscope, and those having no film or film-edge exfoliation and retaining no residues were rated to be “good”. The results of measurement and evaluation as above are shown in Tables 1 and 2.

	TABLE 1


	Resistivity (μΩ cm)

		Film	After
Sample		as	heating in	After corrosion
No.	Composition (atomic %)	formed	vacuum	resistance test	Type

1	Ag			2.7	1.8	3.2	Compararive example
2	Ag-0.7	Pd-1.0	Cu	4.1	3.0	4.3	″
3	Ag-0.5	Ru-0.8	Cu	6.8	6.5	7.5	″
4	Ag-1.5	Cu		3.8	3.1	4.5	″
5	Ag-2.0	Nd		6.3	4.9	6.4	″
6	Ag-0.3	Sm		3.1	2.3	3.2	″
7	Ag-0.3	Sm-0.05	Cu	3.2	2.3	3.2	″
8	Ag-0.3	Sm-0.1	Cu	3.2	2.3	3.3	Invention example
9	Ag-0.3	Sm-0.5	Cu	3.2	2.4	3.2	″
10	Ag-0.1	Sm-0.4	Cu	2.9	2.0	2.8	″
11	Ag-0.3	Sm-1.0	Cu	3.8	2.5	3.8	″
12	Ag-0.5	Sm-0.1	Au	3.4	2.7	3.2	″
13	Ag-0.2	Sm-0.4	Au	3.0	2.5	3.0	″
14	Ag-0.15	Sm-0.8	Au	3.0	2.9	3.1	″
15	Ag-0.15	Sm-1.0	Au	3.3	3.5	3.5	″
16	Ag-0.2	Sm-0.2	Cu-0.2 Au	3.0	2.5	3.1	″
17	Ag-0.3	Sm-0.5	Cu-0.5 Au	3.4	2.9	3.6	″
18	Ag-0.3	Sm-0.9	Pd	4.1	3.0	4.3	Comparative example
19	Ag-0.3	Sm-0.4	Ru	8.5	6.2	7.9	″
20	Ag-0.3	Sm-0.5	Cu	3.2	2.4	3.2	Invention example*
21	Ag-0.2	Sm-0.4	Au	3.0	2.5	3.0	″*

	TABLE 2


	Average reflectance (%)

Sample		Film as	After heating	After corrosion
No.	Composition (atomic %)	formed	in vacuum	resistance test

1	Ag			98.5	92.3	78.0
2	Ag-0.7	Pd-1.0	Cu	96.5	95.2	95.1
3	Ag-0.5	Ru-0.8	Cu	96.3	92.6	93.4
4	Ag-1.5	Cu		98.0	85.2	90.8
5	Ag-2.0	Nd		94.3	94.0	94.1
6	Ag-0.3	Sm		98.2	97.8	94.6
7	Ag-0.3	Sm-0.05	Cu	98.2	97.8	96.2
8	Ag-0.3	Sm-0.1	Cu	98.3	98.6	97.5
9	Ag-0.3	Sm-0.5	Cu	97.9	98.5	97.2
10	Ag-0.1	Sm-0.4	Cu	98.5	98.5	97.5
11	Ag-0.3	Sm-1.0	Cu	97.0	97.1	97.0
12	Ag-0.5	Sm-0.1	Au	97.9	98.3	97.6
13	Ag-0.2	Sm-0.4	Au	98.4	98.6	98.2
14	Ag-0.15	Sm-0.8	Au	97.8	97.5	97.4
15	Ag-0.15	Sm-1.0	Au	97.8	97.6	97.4
16	Ag-0.2	Sm-0.2	Cu-0.2 Au	98.0	98.4	98.0
17	Ag-0.3	Sm-0.5	Cu-0.5 Au	97.2	96.9	96.9
18	Ag-0.3	Sm-0.9	Pd	96.3	96.3	96.4
19	Ag-0.3	Sm-0.4	Ru	95.4	95.8	94.6
20	Ag-0.3	Sm-0.5	Cu	97.7	98.4	97.6
21	Ag-0.2	Sm-0.4	Au	98.5	98.6	98.2

Appearance	Adhesiveness	Patterning	Type

Clouding	50	Exfoliation of film	Comparative example
White spots	70	With residues	″
White spots	65	With residues	″
Clouding (yellowing)	70	Good	″
White spots	75	Exfoliation of film edge	″
White spots	60	Exfoliation of film	″
White spots	60	Exfoliation of film	″
Good	75	Good	Invention example
Good	85	Good	″
Good	80	Good	″
Good	85	Good	″
Good	75	Good	″
Good	85	Good	″
Good	85	With residues but good after washing	″
Good	85	With residues but good after washing	″
Good	80	Good	″
Good	85	Good	″
Good	80	Exfoliation of film	Comparative example
Good	65	Good	″
Good	80	Good	Invention example*
Good	80	Good	″*

Referring now to Tables 1 and 2, the pure Ag film (Sample No. 1) showed resistivity smaller than 3.0 μΩ cm at the film formation and a further smaller value after the heat treatments. However, from resistivity increased after the corrosion test, it can be understood that pure Ag film is inferior in corrosion resistance property. The pure Ag film showed the highest average reflectance among the samples at the film formation. However, as reflectance dropped significantly after heating and the film surface clouded after heating in the air, pure Ag film will also have inferior heat resistance property. Furthermore, as adhesion was unsatisfactory and film exfoliation was observed, pure Ag film will have inferior patterning property. Also the Ag alloy films produced through adding Pd, Cu or Ru to Ag as having been proposed in the past (Samples No. 2 and 3) recorded higher resistivity as compared with that of the Ag alloy films according to this invention and resistivity increased after the corrosion resistance test. Also the Ag alloy films according to the prior art indicated lower average reflectance than that of the Ag alloy films according to this invention and smaller reflectance particularly after heating and generated white spots, white round dots on the film surface, after heating in the air. As a result, the Ag alloy films according to the prior art will possess unsatisfactory heat resistance and low adhesion properties, and leave residues after etching. [0070]
The Ag alloy film formed through adding Cu to Ag (Sample No. 4) recorded extremely poor heat resistance, its average reflectance significantly deteriorated after the heating, and its film surface clouded and yellowed. The Ag alloy film formed through adding one of the rare earth elements, Nd, to Ag (Sample No. 5) indicated unsatisfactory heat resistance generating white spots on the film surface and also poor patterning property indicating weak adhesion property and film exfoliation. [0071]
On the other hand, the Ag alloy film formed through adding respective combination of additive elements of Sm plus Cu, Sm plus Au, Sm plus Cu plus Au to Ag according to this invention (Samples No. 8-17) recorded low resistivity smaller than 4 μΩ cm at film formation and retained such low resistivity even after the corrosion test. The Samples No. 8-17 maintained approximately 97% of average reflectance after heating and the corrosion test. The Samples also demonstrated favorable heat resistance as no such changes as clouding, white spotting and yellowing of the film surfaces were observed on top of satisfactory adhesiveness and patterning properties maintaining the above advantageous properties. [0072]
For the Samples No. 20 and 21 silicon wafers were employed in forming Ag alloy films, and as is clear from Table 1 both samples recorded properties similar to those formed on glass substrates. [0073]

Example 7

Spectral reflectance of the Ag alloy film according to this invention produced from an Ag alloy containing 0.3 atomic % of Sm and 0.4 atomic % of Cu was measured just after film formation and after heating in vacuum at the temperature of 250° C. for 1 hour. The measurements are shown in FIG. 9. Reflectance of the Ag alloy film according to this invention formed though adding Sm and Cu to Ag improved with the heating treatment, particularly on a shorter wavelength side, and reflection property having essentially a constant reflection value within the visible spectrum was observed. Where ref(max) being the maximum reflectance within the optical wavelength of 400 to 700 nm and ref(min) being the minimum reflectance, the value of differential reflectance obtained from a formula between the two variables as (ref(max)−ref(min))/ref(max)×100 was 3, demonstrating outstanding reflection property. As a result, in the manufacture of such flat panel displays as liquid crystal displays and the like requiring heating processes, flat display panels having excellent properties which have been unavailable so far will be provided. [0074]

Example 8

Spectral reflectance of an Ag alloy film formed using the Ag alloy sputtering-target containing 0.2 atomic % of Sm and 0.3 atomic % of Au produced for Example 3 and heating the substrate to 150° C. in film formation was measured. The measurements are shown in FIG. 10. Film formation on heated substrate permitted the Ag film to have reflectance higher in the order of 0.5% in the wavelength of 400 to 700 nm. Also forming the film on the heated substrate allowed improvement in adhesion property from 85% to 90%. Employing glass substrates with heat resistance property and applying a heating process in film formation, Ag alloy films having high reflectance and sufficient adhesion will be provided. [0075]

Example 9

An Ag alloy sputtering-target containing 0.3 atomic % of Sm and 0.5 atomic % of Cu was produced similarly to Example 1 and a thin film with a thickness of 200 nm was formed on a silicon wafer. After measuring resistivity, the film was heated in vacuum for 1 hour at varying temperatures, 150° C., 200° C., 250° C. and 350° C. for measurement of resistivity. Effects of heating on resistivity are shown FIG. 11. [0076]
As heating temperature increased, resistivity decreased. Particularly the films fabricated from Ag alloys containing 0.3 atomic % of Sm and 0.5 atomic % of Cu recorded a significant decrease in resistivity in association with the temperature rise providing resistivity of 2.5 μΩ cm or smaller at temperatures of not lower than 200° C. and 2.0 μΩ cm or smaller at temperatures of not lower than 300° C. The pure Ag films showed lower resistivity, but their adhesion and corrosion resistance properties were unsatisfactory as describe above. As the Ag alloy film according to this invention can provide lower resistivity through applying heating after film formation, they are most suitable to wiring films for electronic devices requiring heating steps. Employing the Ag alloy film as a wiring film for polysilicon TFT for flat panel displays to be exposed to elevated temperatures during fabrication will allow manufacture of high response, high quality flat panel display devices. [0077]

Example 10

Using the target for Example 4, Ag alloy films with a thickness of 200 nm were formed on glass substrates heated to 100 to 250° C. during film formation, and changes in resistivity in response to temperatures were measured as shown in FIG. 12. Heating of substrates during film formation resulted in reduction in resistivity. When the substrates were heated to not lower than 150° C., in particular, resistivity significantly decreased, and heated further to not lower than 200° C. or above the Ag alloy films produced from the both kinds of Ag alloys containing 0.3 atomic % of Sm and 0.5 atomic % of Cu, and 0.3 atomic % of Sm and 0.5 atomic % of Au demonstrated resistivity of 2.5 μΩ cm or smaller. Also film formation on heated substrates allowed an increase in adhesion property from 85% to 95%. As explained as above, the Ag alloy film according to this invention is suitable to be employed as an Ag alloy wiring film for electronic devices having low resistivity and appropriate adhesion property by heating the substrates if glass substrates are used. [0078]
According to this invention, an Ag alloy film having low resistivity, high reflectance, satisfactory heat resistance and corrosion resistance properties, and improved adhesion with substrates will be provided stably. The Ag alloy film according to this invention is suitable for such flat panel displays as high resolution LCDs, organic ELDs and PDPs as well as reflection type LCDs used for portable information devices with small power consumption, and also for other various thin film devices, and thus highly worthwhile to apply to industrial usage. [0079]
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. [0080]

Claims

What is claimed is:

1. An Ag alloy film consisting essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

2. An Ag alloy film According to claim 1, which consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

3. An Ag alloy film According to claim 1, which consists essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 0.5 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

4. An Ag alloy film According to claim 1, which consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 0.5 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

5. An Ag alloy film according to claim 1, which is of a wiring film for a flat panel display.

6. An Ag alloy film according to claim 1, which is of a reflective film for a flat panel display.

7. A sputtering-target for an Ag alloy film, which consists essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 1.0 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

8. A sputtering-target for an Ag alloy film according to claim 7, which consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 1.0 atomic % in total of at lest one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

9. A sputtering-target for an Ag alloy film according to claim 7, which consists essentially of 0.1 to 0.5 atomic % of any one element selected from the group of Sm, Dy and Tb, 0.1 to 0.5 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.

10. A sputtering-target for an Ag alloy film according to claim 7, which consists essentially of 0.1 to 0.5 atomic % of Sm, 0.1 to 0.5 atomic % in total of at least one element selected from the group of Au and Cu, and the balance of Ag and incidental impurities.