U.S. patent application number 10/548778 was filed with the patent office on 2006-08-24 for silver alloy sputtering target for forming reflective layer of optical recording media.
Invention is credited to Akifumi Mishima.
Application Number | 20060188386 10/548778 |
Document ID | / |
Family ID | 32983459 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060188386 |
Kind Code |
A1 |
Mishima; Akifumi |
August 24, 2006 |
Silver alloy sputtering target for forming reflective layer of
optical recording media
Abstract
A silver alloy sputtering target for forming Ag alloy reflective
layer of optical recording media such as magneto-optical recording
disks (MD, MO) and optical recording disks (CD-RW, DVD-RAM) is
provided. The sputtering target is made of (1) a silver alloy
having a composition of 0.5 to 3% by mass of Cu and 0.1 to 3% by
mass in total of one or more elements selected from among Dy, La,
Nd, Tb and Gd, with the remainder consisting of Ag; (2) a silver
alloy having a composition of 0.5 to 3% by mass of Cu and 0.005 to
0.05% by mass in total of one or more elements selected from among
Ca, Be and Si, with the remainder consisting of Ag; or (3) a silver
alloy having composition of 0.5 to 3% by mass of Cu, 0.1 to 3% by
mass in total of one or more elements selected from among Dy, La,
Nd, Tb and Gd and 0.005 to 0.05% by mass in total of one or more
elements selected from among Ca, Be and Si, with the remainder
consisting of Ag.
Inventors: |
Mishima; Akifumi;
(Sanda-shi, JP) |
Correspondence
Address: |
DARBY & DARBY P.C.
P. O. BOX 5257
NEW YORK
NY
10150-5257
US
|
Family ID: |
32983459 |
Appl. No.: |
10/548778 |
Filed: |
March 13, 2003 |
PCT Filed: |
March 13, 2003 |
PCT NO: |
PCT/JP03/03006 |
371 Date: |
September 9, 2005 |
Current U.S.
Class: |
420/502 ;
G9B/7.19; G9B/7.198 |
Current CPC
Class: |
C22C 5/08 20130101; G11B
7/266 20130101; G11B 7/258 20130101; G11B 7/259 20130101; C23C
14/3414 20130101 |
Class at
Publication: |
420/502 |
International
Class: |
C22C 5/08 20060101
C22C005/08 |
Claims
1. A silver alloy sputtering target for forming a reflective layer
of optical recording media comprising: a silver alloy having 0.5 to
3% by mass of Cu; 0.1 to 3% by mass in total of one or more
elements selected from among Dy, La, Nd, Tb and Gd; and the
remainder consisting of Ag.
2. A silver alloy sputtering target for forming a reflective layer
of optical recording media comprising: a silver alloy having 0.5 to
3% by mass of Cu; 0.005 to 0.05% by mass in total of one or more
elements selected from among Ca, Be and Si; and the remainder
consisting of Ag.
3. A silver alloy sputtering target for forming a reflective layer
of optical recording media comprising: a silver alloy having 0.5 to
3% by mass of Cu; 0.1 to 3% by mass in total of one or more
elements selected from among Dy, La, Nd, Tb and Gd; 0.005 to 0.05%
by mass in total of one or more elements selected from among Ca, Be
and Si; and the remainder consisting of Ag.
4. A reflective layer of optical recording medium formed by using
the silver alloy sputtering target according to claim 1.
5. A reflective layer of optical recording medium formed by using
the silver alloy sputtering target according to claim 2.
6. A reflective layer of optical recording medium formed by using
the silver alloy sputtering target according to claim 3.
Description
TECHNICAL FIELD
[0001] The present invention relates to a silver alloy sputtering
target for forming, by the sputtering process, a semi-transparent
reflective layer or a reflective layer (hereinafter collectively
referred to as the reflective layer) that constitutes an optical
recording medium such as optical recording disk (CD-RW, DVD-RAM,
etc.) whereon signals representing audio, visual and/or text
information are reproduced, or recorded, reproduced and erased by
means of a laser beam emitted by a semiconductor laser or the
like.
BACKGROUND ART
[0002] Reflective layers formed from Ag or Ag alloy are used in
optical recording media such as magneto-optical recording disks
(MD, MO) and optical recording disks (CD-RW, DVD-RAM). The
reflective layers formed from Ag or Ag alloy are preferably used
due to high reflectivity for light of broad wavelengths ranging
from 400 to 830 nm, and particularly high reflectivity for laser
beam having a short wavelength used in high density recording of
optical recording media.
[0003] As a method for forming the reflective layers from Ag or an
Ag alloy, it is known to sputter a target made of Ag or the Ag
alloy (refer to Japanese Unexamined Patent Application, First
Publication No. Hei 11-213448, Japanese Unexamined Patent
Application, First Publication No. 2000-109943, and Japanese
Unexamined Patent Application, First Publication No.
2000-57627).
[0004] However, among the optical recording media, in those that
have recording layer formed from a phase change recording material
and are subject to repetitive recording, reproducing and erasing,
reflectivity of the reflective layer formed from Ag or Ag alloy
decreases as the number of repetitions of recording, reproducing
and erasing increases, thus failing to endure repetitive recording
and reproducing operations over a long period of time.
DISCLOSURE OF THE INVENTION
[0005] The present inventors have found that one of the causes of
the problem described above is that, when recording, reproducing
and erasing are carried out repetitively on the optical recording
medium, the Ag reflective layer is repetitively heated by the
irradiation of laser beam and cooled down, during which the Ag
reflective layer recrystallizes to cause the crystal grains to grow
into coarse grains that result in lower reflectivity.
[0006] Accordingly, the present inventors conducted research into
ways to obtain an Ag alloy reflective layer that experiences less
decrease in reflectivity of the reflective layer as the number of
repetitions of recording, reproducing and erasing increases, and
found the following facts:
[0007] (a) Growth of the crystal grains into coarse grains through
repetitive heating by the irradiation with laser beam and cooling
down, and hence the resultant decrease in reflectivity, can be
minimized through an extended period of use, by using an Ag alloy
reflective layer formed by sputtering a silver alloy target that
has a composition of 0.5 to 3% by mass of Cu and 0.1 to 3% by mass
in total of one or more elements selected from among Dy, La, Nd, Tb
and Gd, with the remainder consisting of Ag;
[0008] (b) Growth of the crystal grains into coarse grains through
repetitive heating by the irradiation with laser beam and cooling
down, and hence the resultant decrease in reflectivity, can be
minimized through an extended period of use, by using an Ag alloy
reflective layer formed by sputtering a silver alloy target that
has a composition of 0.5 to 3% by mass of Cu and 0.005 to 0.05% by
mass in total of one or more elements selected from among Ca, Be
and Si, with the remainder consisting of Ag;
[0009] (c) The same effect can be achieved also by including 0.1 to
3% by mass in total of one or more elements selected from among Dy,
La, Nd, Tb and Gd and 0.005 to 0.05% by mass in total of one or
more elements selected from among Ca, Be and Si at the same
time.
[0010] The present invention has been completed based on the
research described above, and is characterized by:
[0011] (1) A silver alloy sputtering target for forming a
reflective layer of optical recording media made of a silver alloy
having a composition of 0.5 to 3% by mass of Cu and 0.1 to 3% by
mass in total of one or more elements selected from among Dy, La,
Nd, Tb and Gd, with the remainder consisting of Ag;
[0012] (2) A silver alloy sputtering target for forming a
reflective layer of optical recording media made of a silver alloy
having a composition of 0.5 to 3% by mass of Cu and 0.005 to 0.05%
by mass in total of one or more elements selected from among Ca, Be
and Si, with the remainder consisting of Ag;
[0013] (3) A silver alloy sputtering target for forming a
reflective layer of optical recording media made of a silver alloy
having composition of 0.5 to 3% by mass of Cu, 0.1 to 3% by mass in
total of one or more elements selected from among Dy, La, Nd, Tb
and Gd and 0.005 to 0.05% by mass in total of one or more elements
selected from among Ca, Be and Si, with the remainder consisting of
Ag.
[0014] The sputtering target for forming the silver alloy
reflective layer of the present invention can be manufactured by
preparing high-purity Ag having purity of 99.99% by mass or higher,
and Cu, Dy, La, Nd, Tb and Gd having purity of 99.9% by mass or
higher as raw materials, melting these materials in high vacuum or
inert gas atmosphere, casting the molten material into an ingot in
high vacuum or inert gas atmosphere and machining the ingot after
applying hot working.
[0015] Ca, Be and Si that hardly form solid solution with Ag are
weighed with Ag in such a proportion that concentration of each
element is 0.20% by mass. They are melted in a high-frequency
vacuum melting furnace and, after melting, with the furnace filled
with Ar gas to atmospheric pressure, and cast in a graphite mold to
make a mother alloy that includes Ca, Be and Si. The mother alloy
and Cu are added into the weighed Ag, melted and cast into an
ingot. Then the target can be made by applying hot working and
machining it.
[0016] Now the reason will be described for setting the composition
of the reflective layer made of the Ag alloy according to the
present invention and the sputtering target for forming the
reflective layer made of the Ag alloy as described above.
Cu:
[0017] Cu has the effects of increasing the strength of crystal
grains by forming a solid solution with Ag, preventing the crystal
grains from recrystallizing, thereby to restrain reflectivity from
decreasing. Recrystallization of the crystal grains cannot be
prevented satisfactorily and therefore reflectivity cannot be
prevented from decreasing, when the Cu content is less than 0.5% by
mass. When the Cu content is higher than 3% by mass, on the other
hand, initial reflectivity of the Ag alloy reflective layer becomes
lower. Accordingly, the Cu content in the Ag alloy reflective layer
and in the sputtering target for forming the Ag alloy reflective
layer is set within the range from 0.5 to 3% by mass (more
preferably from 0.5 to 1.5% by mass).
Dy, La, Nd, Tb, Gd:
[0018] These components react with Ag and form intermetallic
compounds in the grain boundaries that prevent the crystal grains
from agglomerating with each other, thereby preventing the Ag alloy
reflective layer from recrystallizing further. Such an effect
cannot be significantly achieved when the content of one or more of
these elements is less than 0.1% by mass in total. When the content
of one or more of these elements is more than 3% by mass in total,
on the other hand, the target becomes very hard and difficult to
work. Accordingly, the content of these elements in the Ag alloy
reflective layer and in the sputtering target for forming the Ag
alloy reflective layer is set within the range from 0.1 to 3% by
mass (more preferably from 0.2 to 1.5% by mass).
Ca, Be, Si:
[0019] These components hardly form solid solution with Ag, and
precipitate in the grain boundaries so as to prevent the crystal
grains from agglomerating with each other, thereby helping prevent
the recrystallization of the Ag alloy reflective layer further.
Such an effect cannot be significantly achieved when the content of
one or more of these elements is less than 0.005% by mass in total.
When the content of one or more of these elements is more than
0.05% by mass in total, on the other hand, the target becomes very
hard and difficult to make. Accordingly, the content of these
elements in the Ag alloy reflective layer and in the sputtering
target for forming the Ag alloy reflective layer is set within the
range from 0.005 to 0.05% by mass (more preferably from 0.010 to
0.035% by mass).
BEST MODE FOR CARRYING OUT THE INVENTION
Example 1
[0020] High-purity Ag having purity of 99.99% by mass or higher,
and Cu, Dy, La, Nd, Tb and Gd having purity of 99.9% by mass or
higher were prepared as raw materials and were melted in a
high-frequency vacuum melting furnace. The molten material was cast
into an ingot in a graphite mold in Ar gas atmosphere. The ingot
was heated at 600.degree. C. for two hours, then rolled and
machined thereby to make targets Nos. 1 through 22 of the present
invention which dimensions are 125 mm in diameter and 5 mm in
thickness and having compositions shown in Tables 1 and 2,
comparative targets Nos. 1 through 7 and prior art target.
[0021] The targets Nos. 1 through 22 of the present invention, the
comparative targets Nos. 1 through 7 and the prior art target,
which were bonded onto backing plates made of oxygen-free copper
with solder, were then set in a DC magnetron sputtering apparatus.
After pumping the inside of the DC magnetron sputtering apparatus
to vacuum of 1.times.10.sup.-4 Pa, Ar gas was introduced into the
apparatus so as to keep a sputtering gas pressure of 1.0 Pa
therein. Then DC sputtering power of 100 W was supplied from a DC
power source to the target, so as to generate plasma in a space
between the target and a glass substrate, which dimensions are 30
mm in diameter and 0.5 mm in thickness and which is disposed to
oppose the target in parallel to and with a space of 70 mm from the
target, thereby to form the Ag alloy reflective layer having
thickness of 100 nm.
[0022] Reflectivity of the Ag alloy reflective layer formed as
described above was measured with a spectrophotometer immediately
after being formed. Then after leaving the Ag alloy reflective
layer in a temperature and humidity chamber that was controlled to
80.degree. C. in temperature and 85% in relative humidity for 200
hours, reflectivity was measured again under the same conditions.
Based on the reflectivity data thus obtained, reflectivity to light
was determined for wavelengths 400 nm and 650 nm. The results as
shown in Tables 1 and 2 were used to evaluate the durability of the
reflective layer as the optical recording medium in recording and
reproducing of data. TABLE-US-00001 TABLE 1 Reflectivity to
Reflectivity to wavelength 400 nm wavelength 650 nm (%) (%)
Immediately After Immediately After Composition (% by mass) after
200 after 200 Sample No. Cu Dy La Nd Tb Gd Ag forming hours forming
hours Inventive 1 0.52 0.11 -- -- -- -- Remainder 89 88 97 96
targets 2 1.01 0.52 -- -- -- Remainder 87 87 97 96 3 1.51 1.01 --
-- -- -- Remainder 85 84 96 96 4 2.04 2.01 -- -- -- -- Remainder 81
77 95 93 5 2.53 2.54 -- -- -- -- Remainder 79 74 94 92 6 2.98 2.98
-- -- -- -- Remainder 77 71 93 90 7 0.55 -- 0.12 -- -- -- Remainder
89 87 97 96 8 1.04 -- 1.03 -- -- -- Remainder 85 85 96 96 9 1.47 --
2.89 -- -- -- Remainder 79 75 94 92 10 0.52 -- -- 0.11 -- --
Remainder 89 84 97 95 11 0.97 -- -- 1.04 -- -- Remainder 85 84 96
96 12 1.47 -- -- 2.97 -- -- Remainder 79 75 94 92 13 0.53 -- -- --
0.13 -- Remainder 89 86 97 95 14 1.07 -- -- -- 1.02 -- Remainder 85
84 96 96 16 1.46 -- -- -- 2.96 -- Remainder 79 74 94 92
[0023] TABLE-US-00002 TABLE 2 Reflectivity to Reflectivity to
wavelength 400 nm wavelength 650 nm (%) (%) Immediately After
Immediately After Composition (% by mass) after 200 after 200
Sample No. Cu Dy La Nd Tb Gd Ag forming hours forming hours Remarks
Inventive 16 0.51 -- -- -- -- 0.12 Remainder 89 86 97 95 -- targets
17 1.08 -- -- -- -- 1.04 Remainder 85 84 96 96 -- 18 1.52 -- -- --
-- 2.89 Remainder 79 76 94 92 -- 19 0.55 0.06 0.07 -- -- --
Remainder 89 86 97 96 -- 20 1.12 0.14 0.16 0.16 -- -- Remainder 74
86 97 97 -- 21 1.45 0.44 0.48 0.35 0.30 -- Remainder 83 73 96 94 --
22 1.05 0.58 0.61 0.57 0.62 0.58 Remainder 80 75 95 92 --
Comparative 1 0.4* 0.05 -- -- -- -- Remainder 89 70 98 87 --
targets 2 3.6* 3.8* -- -- -- -- Remainder -- -- -- -- Unable to
form 3 1.01 -- 3.2* -- -- -- Remainder 78 67 94 81 -- 4 1.04 -- --
3.4* -- -- Remainder -- -- -- -- Unable to form 5 1.03 -- -- --
3.3* -- Remainder 79 66 94 79 -- 6 1.01 -- -- -- -- 3.2* Remainder
79 67 95 80 -- 7 1.02 1.5* 2.0* -- -- -- Remainder -- -- -- --
Unable to form Prior art targets -- -- -- -- -- -- 100 94 41 98 79
--
[0024] From the results shown in Table 1, it can be seen that the
reflective layers formed by sputtering with the targets Nos. 1
through 22 of the present invention experienced less decrease in
reflectivity than the reflective layers formed by sputtering with
the comparative targets Nos. 1 through 7 or the prior art target,
after being left in a temperature and humidity chamber that was
controlled to 80.degree. C. in temperature and 85% in relative
humidity for 200 hours.
Example 2
[0025] Ag, Cu, Ca, Be and Si having purity of 99.99% by mass or
higher were prepared as raw materials. Since Ca, Be and Si hardly
form solid solution with Ag, these element were weighed with Ag in
such a proportion that concentration of each element became 0.20%
by mass. They were melted in a high-frequency vacuum melting
furnace and, after melting, with the furnace filled with Ar gas to
atmospheric pressure, cast in a graphite mold to make a mother
alloy that included Ca, Be and Si.
[0026] The mother alloy was added together with Cu to Ag, that was
then melted and cast into an ingot. The ingot was heated at
600.degree. C. for two hours, then rolled and machined thereby to
make targets Nos. 23 through 36 of the present invention and
comparative targets Nos. 8 through 13 which dimensions were 125 mm
in diameter and 5 mm in thickness and having compositions shown in
Tables 3 and 4.
[0027] The targets Nos. 23 through 36 of the present invention, and
the comparative targets Nos. 8 through 13 were used to form the Ag
alloy reflective layer having thickness of 100 nm on glass
substrate similarly to Example 1. Reflectivity of the Ag alloy
reflective layer was measured with a spectrophotometer immediately
after being formed. Then after leaving the Ag alloy reflective
layer in a temperature and humidity chamber that was controlled to
80.degree. C. in temperature and 85% in relative humidity for 200
hours, reflectivity was measured again under the same conditions.
Based on the reflectivity data thus obtained, reflectivity to light
was determined for wavelengths of 400 nm and 650 nm. The results as
shown in Tables 3 and 4 were used to evaluate the durability of the
reflective layer as the optical recording medium in recording and
reproducing of data. TABLE-US-00003 TABLE 3 Reflectivity to
Reflectivity to wavelength 400 nm wavelength 650 nm (%) (%)
Immediately After Immediately After Composition (% by mass) after
200 after 200 Sample No. Cu Ca Be Si Ag forming hours forming hours
Inventive 23 0.52 0.005 -- -- Remainder 89 86 97 94 targets 24 1.02
0.025 -- -- Remainder 86 86 96 96 25 1.47 0.049 -- -- Remainder 83
81 95 93 26 0.55 -- 0.006 -- Remainder 89 86 97 95 27 1.08 -- 0.026
-- Remainder 86 86 96 96 28 1.51 -- 0.047 -- Remainder 83 81 95 92
29 0.60 -- -- 0.005 Remainder 89 85 97 95 30 1.09 -- -- 0.025
Remainder 86 85 96 96 31 1.45 -- -- 0.048 Remainder 83 80 95 94 32
0.61 0.002 0.003 -- Remainder 89 87 97 94 33 1.00 -- 0.015 0.014
Remainder 86 86 96 96 34 1.49 0.013 -- 0.016 Remainder 85 85 95 95
35 0.83 0.001 0.002 0.002 Remainder 88 84 97 93 36 1.77 0.015 0.017
0.015 Remainder 83 80 94 91
[0028] TABLE-US-00004 TABLE 4 Reflectivity to Reflectivity to
wavelength 400 nm wavelength 650 nm (%) (%) Immediately After
Immediately After Composition (% by mass) after 200 after 200
Sample No. Cu Ca Be Si Ag forming hours forming hours Remarks
Comparative 8 1.01 0.003* -- -- Remainder 88 73 97 84 -- targets 9
1.03 -- 0.004* -- Remainder 88 74 97 84 -- 10 1.01 -- -- 0.002*
Remainder 88 71 97 82 -- 11 1.04 0.06* -- -- Remainder -- -- -- --
Unable to form 12 1.03 -- 0.06* -- Remainder -- -- -- -- Unable to
form 13 1.01 -- -- 0.06* Remainder -- -- -- -- Unable to form
[0029] From the results shown in Tables 3 and 4, it can be seen
that the reflective layers formed by sputtering with the targets
Nos. 23 through 36 of the present invention experienced less
decrease in reflectivity than the reflective layers formed by
sputtering with the comparative targets Nos. 8 through 13 shown in
Table 4 or the prior art target shown in Table 2, after being left
in a temperature and humidity chamber that was controlled to
80.degree. C. in temperature and 85% in relative humidity for 200
hours.
Example 3
[0030] The raw materials prepared in Example 1 and the mother alloy
including Ca, Be and Si prepared in Example 2 were used to make
targets Nos. 37 through 50 of the present invention having the
compositions shown in Table 5. These targets were used to form the
Ag alloy reflective layers having thickness of 100 nm on glass
substrate similarly to Example 1. Reflectivity of the Ag alloy
reflective layer was measured with a spectrophotometer immediately
after being formed. Then after leaving the Ag alloy reflective
layer in a temperature and humidity chamber that was controlled to
80.degree. C. in temperature and 85% in relative humidity for 200
hours, reflectivity was measured again under the same conditions.
Based on the reflectivity data thus obtained, reflectivity to light
was determined for wavelengths of 400 nm and 650 nm. The results as
shown in Table 5 were used to evaluate the durability of the
reflective layer as the optical recording medium in recording and
reproducing of data. TABLE-US-00005 TABLE 5 Reflectivity to
Reflectivity to wavelength 400 nm wavelength 650 nm (%) (%)
Immediately After Immediately After Composition (% by mass) after
200 after 200 Sample No. Cu Dy, La, Nd, Tb, Gd Ca, Be, Si Ag
forming hours forming hours Inventive 37 0.51 Dy: 0.22 Ca: 0.012
Remainder 87 86 97 97 targets 38 1.03 La: 0.51 Be: 0.020 Remainder
85 85 96 96 39 1.46 Nd: 0.83 Si: 0.029 Remainder 82 82 95 95 40
0.55 Tb: 1.01 Ca: 0.011 Si: 0.018 Remainder 83 83 95 95 41 1.09 Gd:
1.51 Be: 0.031 Remainder 81 81 94 94 42 1.53 Dy: 0.07 Gd: 0.05 Ca:
0.005 Remainder 87 85 96 95 43 0.51 La: 0.05 Tb: 0.14 Be: 0.016
Remainder 87 87 97 96 44 0.97 Nd: 0.54 Dy: 0.55 Si: 0.015 Be: 0.016
Remainder 82 82 95 95 45 1.56 Tb: 1.00 Nd: 1.03 Ca: 0.039 Remainder
78 75 93 91 46 0.61 Gd: 1.43 La: 1.48 Be: 0.049 Remainder 75 74 93
92 47 1.03 Dy: 0.07 Gd: 0.08 Ca: 0.006 Remainder 87 86 97 95 Nd:
0.07 48 1.51 La: 0.34 Tb: 0.37 Be: 0.011 Remainder 83 81 95 94 Dy:
0.35 49 0.58 Nd: 0.67 Dy: 0.70 Si: 0.032 Remainder 80 77 94 92 Gd:
0.73 50 2.96 Tb: 0.75, Nd: 0.65, Ca: 0.015, Be: 0.017 Remainder 74
71 92 91 Gd: 0.75, La: 0.71
[0031] From the results shown in Table 5, it can be seen that the
reflective layers formed by sputtering with the targets Nos. 37
through 50 of the present invention experienced less decrease in
reflectivity for wavelengths of 400 nm and 650 nm than the
reflective layers formed by sputtering with the comparative targets
Nos. 1 through 7 shown in Table 2, the prior art target or the
comparative targets Nos. 8 through 13 shown in Table 4, after being
left in a temperature and humidity chamber that was controlled to
80.degree. C. in temperature and 85% in relative humidity for 200
hours.
INDUSTRIAL APPLICABILITY
[0032] The reflective layer formed by using the silver alloy
sputtering target for forming a reflective layer of optical
recording media according to the present invention experiences less
decrease in reflectivity caused by aging than the reflective layer
formed by using the silver alloy sputtering target for forming a
reflective layer of optical recording media of the prior art does,
and makes it possible to manufacture optical recording media that
can be used over an extended period of time, so as to make great
contribution to the development of the recording media
industry.
* * * * *