U.S. patent application number 10/393993 was filed with the patent office on 2003-09-25 for ag alloy film and sputtering-target for the ag alloy film.
This patent application is currently assigned to HITACHI METALS, LTD.. Invention is credited to Murata, Hideo.
Application Number | 20030180177 10/393993 |
Document ID | / |
Family ID | 28043828 |
Filed Date | 2003-09-25 |
United States Patent
Application |
20030180177 |
Kind Code |
A1 |
Murata, Hideo |
September 25, 2003 |
Ag alloy film and sputtering-target for the Ag alloy film
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.
Inventors: |
Murata, Hideo; (Saihaku,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037
US
|
Assignee: |
HITACHI METALS, LTD.
|
Family ID: |
28043828 |
Appl. No.: |
10/393993 |
Filed: |
March 24, 2003 |
Current U.S.
Class: |
420/503 |
Current CPC
Class: |
C23C 14/3414 20130101;
C23C 14/14 20130101; C22C 5/06 20130101 |
Class at
Publication: |
420/503 |
International
Class: |
C22C 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2002 |
JP |
2002-083167 |
Apr 1, 2002 |
JP |
2002-098751 |
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.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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 .mu..OMEGA. 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.
[0007] 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
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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
[0014] FIG. 1 shows the effects of content of rare earth elements
on resistivity of the Ag alloy films in Example 1;
[0015] FIG. 2 shows the effects of content of additive elements on
resistivity of the Ag alloy films in Example 2;
[0016] FIG. 3 shows the effects of content of rare earth elements
on average reflectance of the Ag alloy films in Example 3;
[0017] FIG. 4 shows the effects of content of rare earth elements
on differential reflectance of the Ag alloy films in Example 3;
[0018] FIG. 5 shows the effects of Cu content on average
reflectance of the Ag alloy films in Example 4;
[0019] FIG. 6 shows the effects of Cu content on differential
reflectance of the Ag alloy films in Example 4;
[0020] FIG. 7 shows the effects of Au content on average
reflectance of the Ag alloy films in Example 5;
[0021] FIG. 8 shows the effects of Au content on differential
reflectance of the Ag alloy films in Example 5;
[0022] FIG. 9 shows reflectance within the optical spectrum of 400
to 700 nm of the Ag alloy films in Example 7;
[0023] FIG. 10 shows reflectance within the optical spectrum of 400
to 700 nm of the Ag alloy films in Example 8;
[0024] FIG. 11 shows the effects of temperatures applied to films
on resistivity of the Ag alloy films in Example 9; and
[0025] FIG. 12 shows the effects of temperatures applied to
substrates on resistivity of the Ag alloy films in Example 10.
DETAILED DESCRIPTION OF THE INVENTION
[0026] 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.
[0027] Herein below there will be provided reasons why the Ag alloy
film of the invention has the defined chemical composition.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] Now content of elements to be added to Ag will be described
below.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.degree. C. permits the Ag alloy film to improve
resistivity to 3 .mu..OMEGA. cm or smaller and to not lower than
250.degree. C. to 2.5 .mu..OMEGA. 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.
[0044] 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.
[0045] 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).times.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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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 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%.
[0052] 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.
[0053] 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.
EMBODIMENTS
Example 1
[0054] 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.
[0055] 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 .mu..OMEGA. 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 .mu..OMEGA. 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.
Example 2
[0056] 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.
[0057] 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 .mu..OMEGA. cm or lower. Particularly the
addition of Au caused only a marginal increase in resistivity and
resistivity of 4 .mu..OMEGA. 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 %.
Example 3
[0058] 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).times.100 are shown in FIG. 4.
[0059] 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.
Example 4
[0060] 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.
[0061] 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
%.
Example 5
[0062] 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.
[0063] 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.
Example 6
[0064] 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.
[0065] 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.degree. C. for
2 hours in vacuum, and after exposure to an atmosphere at
85.degree. C. and of 90% humidity for 24 hours for a corrosion
test.
[0066] Also to evaluate heat resistance property of films, surfaces
of pure Ag films and Ag alloy films heated at 250.degree. 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.
[0067] 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.
[0068] 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.
1 TABLE 1 Resistivity (.mu..OMEGA. 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 "* *Note:
Samples with symbol * indicate those formed Ag alloy films on
silicon wafers, otherwise formed on glass substrates.
[0069]
2 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
"* *Note: Samples with symbol * indicate those formed Ag alloy
films on silicon wafers, otherwise formed on glass substrates.
[0070] Referring now to Tables 1 and 2, the pure Ag film (Sample
No. 1) showed resistivity smaller than 3.0 .mu..OMEGA. 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.
[0071] 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.
[0072] 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 .mu..OMEGA. 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.
[0073] 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.
Example 7
[0074] 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.degree. 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).times.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.
Example 8
[0075] 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.degree. 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.
Example 9
[0076] 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.degree. C., 200.degree. C.,
250.degree. C. and 350.degree. C. for measurement of resistivity.
Effects of heating on resistivity are shown FIG. 11.
[0077] 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 .mu..OMEGA. cm or smaller at
temperatures of not lower than 200.degree. C. and 2.0 .mu..OMEGA.
cm or smaller at temperatures of not lower than 300.degree. 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.
Example 10
[0078] 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.degree. 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.degree. C., in particular, resistivity significantly decreased,
and heated further to not lower than 200.degree. 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 .mu..OMEGA.
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.
[0079] 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.
[0080] 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.
* * * * *