U.S. patent application number 13/521148 was filed with the patent office on 2012-11-08 for sb-te-based alloy sintered compact sputtering target.
This patent application is currently assigned to JX NIPPON MINING & METALS CORPORATION. Invention is credited to Yoshimasa Koido, Hideyuki Takahashi.
Application Number | 20120279857 13/521148 |
Document ID | / |
Family ID | 44861426 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120279857 |
Kind Code |
A1 |
Takahashi; Hideyuki ; et
al. |
November 8, 2012 |
Sb-Te-Based Alloy Sintered Compact Sputtering Target
Abstract
Provided is an Sb--Te-based alloy sintered compact sputtering
target having Sb and Te as its main component and which contains
0.1 to 30 at % of carbon or boron and comprises a uniform mixed
structure of Sb--Te-based alloy particles and fine carbon (C) or
boron (B) particles, wherein the average grain size of the
Sb--Te-based alloy particles is 3 .mu.m or less and the standard
deviation thereof is less than 1.00, the average grain size of C or
B is 0.5 .mu.m or less and the standard deviation thereof is less
than 0.20, and, when the average grain size of the Sb--Te-based
alloy particles is X and the average grain size of carbon or boron
is Y, Y/X is within the range of 0.1 to 0.5. The present invention
aims to improve the structure of the Sb--Te-based alloy sputtering
target, inhibit the generation of cracks in the sintered target,
and prevent the generation of arcing in the sputtering process.
Inventors: |
Takahashi; Hideyuki;
(Ibaraki, JP) ; Koido; Yoshimasa; (Ibaraki,
JP) |
Assignee: |
JX NIPPON MINING & METALS
CORPORATION
Tokyo
JP
|
Family ID: |
44861426 |
Appl. No.: |
13/521148 |
Filed: |
April 21, 2011 |
PCT Filed: |
April 21, 2011 |
PCT NO: |
PCT/JP2011/059814 |
371 Date: |
July 9, 2012 |
Current U.S.
Class: |
204/298.13 |
Current CPC
Class: |
G11B 7/266 20130101;
C04B 2235/421 20130101; C23C 14/0623 20130101; C04B 2235/428
20130101; C22C 1/04 20130101; C04B 2235/5445 20130101; C04B 2235/77
20130101; C04B 35/6261 20130101; C04B 35/645 20130101; C04B
2235/5436 20130101; C04B 2235/404 20130101; C22C 28/00 20130101;
C04B 2235/408 20130101; C04B 2235/422 20130101; C04B 2235/785
20130101; C04B 2235/40 20130101; C04B 35/547 20130101; C04B 2235/96
20130101; C22C 12/00 20130101; C23C 14/3414 20130101 |
Class at
Publication: |
204/298.13 |
International
Class: |
C23C 14/14 20060101
C23C014/14; C23C 14/34 20060101 C23C014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2010 |
JP |
2010-101156 |
Claims
1. An Sb--Te-based alloy sintered compact sputtering target having
Sb and Te as its main component and which contains 0.1 to 30 at %
of carbon or boron and comprises a uniform mixed structure of
Sb--Te-based alloy particles and fine carbon (C) or boron (B)
particles, wherein the average grain size of the Sb--Te-based alloy
particles is 3 .mu.m or less and the standard deviation thereof is
less than 1.00, the average grain size of C or B is 0.5 .mu.m or
less and the standard deviation thereof is less than 0.20, and,
when the average grain size of the Sb--Te-based alloy particles is
X and the average grain size of carbon or boron is Y, Y/X is within
the range of 0.1 or more and to 0.5 or less.
2. The Sb--Te-based alloy sintered compact sputtering target
according to claim 1 containing, at a maximum, 30 at % of one or
more types of elements selected from Ag, In, Si, Ge, Ga, Ti, Au,
Pt, and Pd.
3. The Sb--Te-based alloy sintered compact sputtering target
according to claim 2, wherein the target is used for forming a
phase-change recording layer formed from Ag--In--Sb--Te alloy or
Ge--Sb--Te alloy containing carbon or boron.
4. The Sb--Te-based alloy sintered compact sputtering target
according to claim 3, wherein the average deflective strength as an
index of the mechanical strength of ceramics is 100 MPa or
higher.
5. The Sb--Te-based alloy sintered compact sputtering target
according to claim 1, wherein the target is used for forming a
phase-change recording layer formed from Ag--In--Sb--Te alloy or
Ge--Sb--Te alloy containing carbon or boron.
6. The Sb--Te-based alloy sintered compact sputtering target
according to claim 1, wherein an average deflective strength of the
sputtering target as an index of mechanical strength of ceramics is
100 MPa or higher.
Description
TECHNICAL FIELD
[0001] The present invention relates to an Sb--Te-based alloy
sintered compact sputtering target containing carbon or boron and
capable of effectively inhibiting the generation of particles.
BACKGROUND ART
[0002] In recent years, a thin film formed from an Sb--Te-based
material is being used as a material for use in phase change
recording; that is, as a medium for recording information by using
phase transformation. As a method of forming this thin film formed
from the Sb--Te-based alloy material, it is standard to use a means
generally referred to as a physical vapor deposition method such as
the vacuum deposition method or the sputtering method. In
particular, the thin film is often formed using the magnetron
sputtering method from the perspective of operability and film
stability.
[0003] Formation of films by way of the sputtering method is
performed by physically colliding positive ions such as Ar ions to
a target disposed on a cathode, using that collision energy to
discharge materials configuring the target, and laminating a film
having roughly the same composition as the target material on the
opposite anode-side substrate.
[0004] The coating method based on the sputtering method is
characterized in that it is possible to form films of various
thicknesses; for instance, from a thin film of angstrom units to a
thick film of several ten .mu.m, with a stable deposition rate by
adjusting the processing time, power supply and the like.
[0005] When forming a film formed from an Sb--Te-based alloy
material for use in a phase change recording film, particularly
problematic are the generation of abnormal structures such as
nodules (abnormal projections) and craters (abnormal recesses) on
the target surface, generation of micro arcing (abnormal discharge)
based on the foregoing abnormal structures, and the inclusion of
such abnormal structures in the form of clusters (cluster of atoms)
referred to as particles in the thin film.
[0006] Other problems include the generation of cracks or fractures
in the target in the sputtering process, unevenness of the formed
thin film, and the absorption of large amounts of gas components
such as oxygen in the production process of sintered powder for use
in a target which affects the film quality of the sputtered
film.
[0007] These problems encountered in targets and in the sputtering
process will become a significant cause of deteriorating the
quality and yield of the thin film as the recording medium.
[0008] It is known that the foregoing problems are largely affected
by the grain size of the sintering powder or the target structure
or shape. However, conventionally, it was not possible to avoid the
generation of particles, abnormal discharge (arcing), and nodules
and craters on the target in the sputtering process, generation of
cracks or fractures in the target during the sputtering process,
and the inclusion of large amounts of gas components such as oxygen
contained in the target since the target obtained from the
sintering is unable to retain sufficient characteristics upon
producing an Sb--Te-based alloy sputtering target for forming a
phase change recording layer.
[0009] As a conventional production method of an Sb--Te-based
sputtering target, disclosed is a production method of a
Ge--Sb--Te-based sputtering target of preparing powder of Ge--Te
alloy and Sb--Te alloy by way of quenching based on the inert gas
atomization method, evenly mixing alloys wherein the ratios are
Ge/Te=1/1 and Sb/Te=0.5 to 2.0, and thereafter performing pressure
sintering (for instance, refer to Patent Document 1).
[0010] In addition, there is a document that describes technology
pertaining to the method of producing a Ge--Sb--Te-based sputtering
target and a method of producing powder to be used therein by way
of the atomization method including the steps of pouring powder in
which the tap density (relative density) is 50% or higher among the
alloy powders containing Ge, Sb, and Te, performing cold or hot
pressurization thereto, and by sintering a molding material in
which the density after the cold pressurization is 95% or higher
via heat treatment in an Ar or vacuum atmosphere, wherein the
oxygen content of the sintered compact is 700 ppm or less (for
instance, refer to Patent Document 2).
[0011] In addition, there is a document that describes a method of
producing a Ge--Sb--Te-based sputtering target material by
preparing powder from a raw material containing Ge, Sb, and Te by
way of quenching based on the inert gas atomization method, and
using powder among the foregoing powder having a grain size
distribution of 20 .mu.m or greater and in which the specific
surface area per unit weight is 300 mm.sup.2/g or less, and
sintering a compact obtained by performing cold or hot pressure
molding (for instance, refer to Patent Document 3).
[0012] As other technologies of producing a target using atomized
powder, there are the following Patent Documents 4, 5, and 6.
[0013] Nevertheless, the foregoing Patent Documents use the
atomized powder as is, and it is not possible to obtain a
sufficient strength of the target, and it cannot be said that the
refinement and homogenization of the target structure have been
achieved. In addition, there is a problem in that it is
insufficient as an Sb--Te-based sputtering target for forming a
phase change recording layer.
[0014] Moreover, there is also known a sputtering target for
forming an optical disk recording film in which the surface oxide
film or the processing layer is eliminated, and the centerline
average roughness Ra as the surface roughness is .ltoreq.1.0 .mu.m
(refer to Patent Document 7). The object of this target is to
shorten the pre-sputtering time or to eliminate the pre-sputtering
process entirely, and this method is extremely effective for
achieving this object.
[0015] Nevertheless, with recent DVDs and BDs (Blu-ray Discs), even
higher densification is being achieved, and, in order to improve
the production yield, it is extremely important to reduce the
particles caused by the target.
[0016] Accordingly, in addition to the shortening of the
pre-sputtering process, it is necessary to improve the quality of
the overall target and not just the surface of the target in order
to effectively inhibit the generation of particles, abnormal
discharge, and nodules, and the generation of cracks or fractures
in the target.
[0017] Moreover, recently there have been proposals of increasing
the electrical resistance of the phase change recording film,
reducing the current value flowing in the writing and erasing
operation, and reducing the power consumption in order to alleviate
the burden on the circuit. As one such method, a proposal has been
made for mixing carbon powder into the sputtering target to achieve
high resistance (refer to Patent Document 8).
[0018] However, if carbon is mixed into a conventional Sb--Te-based
alloy sputtering target, it will rather become an addition of
foreign matter since carbon powder is non-metal; this will easily
generate abnormal discharge in the sputtering process, the
generation of particles will increase, and, in certain cases,
cracks will occur in the target. There is a problem in that this is
not necessarily a favorable additive.
[0019] In light of the foregoing circumstances, the present
inventors developed an Sb--Te-based alloy sintered compact
sputtering target having Sb and Te as its primary component
comprising a structure where fine carbon or boron particles
encompass the periphery of Sb--Te-based alloy particles, and,
wherein, if the mean diameter of the Sb--Te-based alloy particles
is X and the particle size of carbon or boron is Y, Y/X is within
the range of 1/10 to 1/10000 (refer to Patent Document 9).
[0020] This is innovative technology from the perspective of being
able to inhibit the generation of particles, abnormal discharge
(arcing), and nodules, as well as the generation of cracks or
fractures of the target.
[0021] Nevertheless, with this technology, carbon or boron powder
was adhered to the surface of the Sb--Te-based alloy powder or its
cluster by using airflow or the like, and the diffusion of carbon
powder or boron powder inside the cluster was insufficient. In
addition, there was a problem in that the carbon powder or boron
powder would become a cluster and deteriorate the uniformity, and
there was still room for improvement in this respect. The present
invention is an improvement of the foregoing technology. [0022]
[Patent Document 1] Japanese Unexamined Patent Application
Publication No. 2000-265262 [0023] [Patent Document 2] Japanese
Unexamined Patent Application Publication No. 2001-98366 [0024]
[Patent Document 3] Japanese Unexamined Patent Application
Publication No. 2001-123266 [0025] [Patent Document 4] Japanese
Unexamined Patent Application Publication No. H10-81962 [0026]
[Patent Document 5] Japanese Unexamined Patent Application
Publication No. 2001-123267 [0027] [Patent Document 6] Japanese
Unexamined Patent Application Publication No. 2000-129316 [0028]
[Patent Document 7] Japanese Unexamined Patent Application
Publication No. 2000-169960 [0029] [Patent Document 8] Japanese
Unexamined Patent Application Publication No. 2004-363541 [0030]
[Patent Document 9] International Publication No. WO2008-044626
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0031] The present invention provides an Sb--Te-based alloy
sintered compact target added with carbon or boron for forming the
phase change recording layer capable of overcoming the various
problems described above; namely, a target that is capable of
effectively inhibiting the generation of particles, abnormal
discharge (arcing) and nodules and the generation of cracks and
fractions in the target in the sputtering process. In particular,
the present invention provides an Sb--Te-based alloy sintered
compact sputtering target for forming a phase change recording
layer formed from Ag--In--Sb--Te alloy or Ge--Sb--Te alloy.
Means for Solving the Problem
[0032] As a technical means for overcoming the foregoing problems,
the present inventors discovered that it is necessary to devise the
shape of the powder and structure and characteristics of the target
in order to obtain a stable and homogenous phase change recording
layer. Specifically, the Sb--Te-based alloy powder configuring the
target is refined, and the uniformity in the dispersion of the
mutual position and shape of the carbon powder or boron powder is
improved. In addition, based on the improvement in the uniformity
and refinement, the mechanical strength of the target will improve,
whereby stable sputtering is realized.
[0033] Based on the foregoing discovery, the present invention
provides:
[0034] 1) An Sb--Te-based alloy sintered compact sputtering target
having Sb and Te as its main component and which contains 0.1 to 30
at % of carbon or boron and comprises a uniform mixed structure of
Sb--Te-based alloy particles and fine carbon (C) or boron (B)
particles, wherein the average grain size of the Sb--Te-based alloy
particles is 3 .mu.m or less and the standard deviation thereof is
less than 1.00, the average grain size of C or B is 0.5 .mu.m or
less and the standard deviation thereof is less than 0.20, and,
when the average grain size of the Sb--Te-based alloy particles is
X and the average grain size of carbon or boron is Y, Y/X is within
the range of 0.1 to 0.5.
[0035] The present invention additionally provides:
[0036] 2) The Sb--Te-based alloy sintered compact sputtering target
according to paragraph 1) above containing, at a maximum, 30 at %
of one or more types of elements selected from Ag, In, Si, Ge, Ga,
Ti, Au, Pt, and Pd;
[0037] 3) The Sb--Te-based alloy sintered compact sputtering target
according to paragraph 1) or paragraph 2) above, wherein the target
is used for forming a phase-change recording layer formed from
Ag--In--Sb--Te alloy or Ge--Sb--Te alloy containing carbon or
boron; and
[0038] 4) The Sb--Te-based alloy sintered compact sputtering target
according to any one of paragraphs 1) to 3) above, wherein the
average deflective strength is 100 MPa or higher.
Effect of the Invention
[0039] Since the Sb--Te-based alloy sintered compact of the present
invention is able to inhibit abnormal structures such as lumps
(coarse grains), which are clumps of the added carbon or boron
which is nonmetal, it yields a superior effect of preventing
abnormal discharge with such carbon or boron as the source, inhibit
the generation of particles caused by arcing, and additionally
improving the uniformity of the sputtered film.
[0040] Machining such as cutting work is performed at the stage of
finishing the target, if there is coarsened carbon or boron, there
is a possibility that cracks and the like will occur with such
carbon or boron as the source, and the generation of particles with
cracks as the source could also be considered, and the present
invention is able to achieve a considerable effect of preventing
the foregoing problems from occurring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 shows an SEM photograph of the target surface of
Example 1.
[0042] FIG. 2 shows an SEM photograph of the target surface of the
Comparative Example.
[0043] FIG. 3 shows a diagram of the mechanical strength of the
Ge--Sb--Te alloy upon adding 15 at % of C.
DESCRIPTION OF EMBODIMENT
[0044] The present invention uses an Sb--Te-based alloy powder
obtained by pulverizing Sb--Te-based alloy using a jet mill or the
like, as well as carbon (C) or boron (B) powder, mechanically
mixing the foregoing powders, and thereafter sintering the same to
obtain a sintered compact sputtering target. A vibrational mill,
planetary ball mill or the like may also be used in substitute for
the foregoing jet mill.
[0045] Upon performing the foregoing mixing, as needed, a mixer
such as a blade mixer, mortar, or ball mill may be used. The mixer
desirably comprises a mechanism of being able to destroy the
clusters and physically kneading C or B therein.
[0046] Generally, jet mill pulverization of the Sb--Te-based alloy
powder is able to achieve an extremely fine powder compared to the
gas atomized powder or the machine pulverized powder, and is
characterized in being able to prevent contamination caused by the
use of a pulverizer. A target that is sintered using the jet mill
pulverized powder yields superior characteristics compared to
machine pulverized powder as described later.
[0047] As described above, the use of jet mill pulverized powder is
a preferred mode. Nevertheless, so as long as the conditions of the
present invention are satisfied, there is no particular problem in
using machine pulverized powder other than jet mill pulverized
powder. Upon performing machine pulverization, it is desirable to
perform such machine pulverization in an inert atmosphere in order
to reduce the oxygen content. A vibratory ball mill or the like may
be used for the machine pulverization.
[0048] A significant feature of the Sb--Te-based alloy sintered
compact sputtering target of the present invention is that it
comprises a structure where Sb--Te-based alloy particles and fine
carbon (C) or boron (B) particles are uniformly mixed.
[0049] Carbon or boron is contained in an amount of 0.1 to 30 at %.
The average crystal grain size of the Sb--Te-based alloy particles
is 3 .mu.m or less, and the standard deviation is less than 1.00.
Moreover, the average grain size of C or B is 0.5 .mu.m or less,
and the standard deviation is less than 0.20.
[0050] Moreover, when the average grain size of the Sb--Te-based
alloy particles is X and the average grain size of carbon or boron
is Y, Y/X is within the range of 0.1 to 0.5. Incidentally, the
average grain size of carbon or boron shall include the grain size
of clustered carbon or boron.
[0051] The foregoing target conditions are essential conditions in
order to favorably inhibit the generation of particles, abnormal
discharge (arcing), nodules, as well as the generation of cracks or
fractures of the target in the sputtering process. As a result of
sputtering a target comprising the foregoing conditions, it is
possible to form a film that is more uniform compared to
conventional films.
[0052] In particular, the ratio of the diameter of the Sb--Te-based
alloy particles and the grain size of carbon or boron is important
in relation to the generation of particles. An optimal condition
for this ratio, if Y/X is within the range of 0.1 to 0.5, an effect
is yielded in significantly inhibiting the generation of arcing and
particles.
[0053] It should be easy to understand that the following
conditions; namely, carbon or boron is contained in an amount of
0.1 to 30 at %, the average crystal grain size of the Sb--Te-based
alloy particles is 3 .mu.m or less and the standard deviation
thereof is less than 1.00, and the average grain size of C or B is
0.5 .mu.m or less and the standard deviation thereof is less than
0.20 are important requirements in order to realize Y/X=0.1 to
0.5.
[0054] In cases where Y/X exceeds 1/2, the effect of inhibiting the
generation of arcing and particles is low and the sinterability is
also inferior, and problems such as fractures will arise due to the
resulting low density. Moreover, if Y/X is less than 0.1, producing
the target will be difficult since the carbon powder or boron
powder will fall below the minimum size in which such powders can
be separated and dispersed with this technology.
[0055] Accordingly, it is preferable to keep the values to be
within the foregoing range. The Sb--Te-based alloy particles
preferably have the required grain size in light of the balance
with the grain size of carbon or boron. It is more preferable to be
of a uniform structure where the average crystal grain size of the
Sb--Te-based alloy particles is 3 .mu.m or less and the standard
deviation thereof is less than 1.00.
[0056] In many cases, coarsened Sb--Te-based alloy particles
contain small Sb--Te-based alloy particles, and the mixture of
coarsened Sb--Te-based alloy particles and small Sb--Te-based alloy
particles will cause an uneven structure. Thus, such unevenness
will similarly cause the generation of arcing and particles.
[0057] Moreover, by reducing the crystal grain size of the target,
it is possible to keep the surface of the eroded target smooth even
after the erosion, and there is an advantage of inhibiting the
adhesion, of redepositions onto the unevenness arising on the
eroded surface, such redepositions growing into nodules, and the
generation of particles caused by the collapse of such nodules.
[0058] In addition, when producing a target based on the foregoing
conditions, the selection and mixture of carbon or boron and the
adjustment of the production conditions of their sintered compact
are important. However, so as long as the average crystal grain
size of the Sb--Te-based alloy particles is 3 .mu.m or less, the
standard deviation thereof is less than 1.00, the average grain
size of C or B is 0.5 .mu.m or less and the standard deviation
thereof is less than 0.20, and Y/X can be adjusted to be within a
range of 0.1 to 0.5, it should be understood that there is no
particular limitation on the foregoing production process.
[0059] Consequently, a preferable condition is using jet mill
powder as the raw material of the Sb--Te-based alloy sintered
compact excluding carbon or boron for the foregoing reasons. In
addition, it is desirable that the content of the carbon or boron
to be added is 0.1 to 30 at %. If the additive content is less than
0.1 at %, the effect of addition will be lost, and, if the additive
content exceeds 30 at %, the mechanical strength will diminish due
to the deterioration in the density of the sintered compact, and
problems such as fractures occurring in the production process or
sputtering process will arise.
[0060] Further, the Sb--Te-based alloy sintered compact sputtering
target of the present invention may contain, as an accessory
component, one or more elements selected from Ag, In, Si, Ge, Ga,
Ti, Au, Pt, and Pd in an amount up to 30 at %. In order to yield
the additive effect, the additive amount is usually set to 15 at %
or higher. The Sb content is also added at 15 to 30 at %, and the
remnant is Te.
[0061] When including, as an additive element, one or more elements
selected from Ag, In, Si, Ge, Ga, Ti, Au, Pt, and Pd in an amount
up to 30 at %, it is possible to obtain the intended glass
transition point or transformation speed. In particular, a target
formed from Ag--In--Sb--Te alloy or Ge--Sb--Te alloy containing
carbon or boron is an effective component for forming the phase
change recording layer.
[0062] Moreover, with the Sb--Te-based alloy sintered compact
sputtering target of the present invention, the average deflective
strength is preferably 100 MPa or higher. The average deflective
strength of 100 MPa or higher will become an index of the
mechanical strength of ceramics, and also become a target for
reducing the generation of particles. The present invention is able
to achieve the foregoing numerical value.
[0063] In addition, by increasing the purity of the Sb--Te-based
alloy sintered compact sputtering target, impurities other than the
primary component or the additive accessory component such as
oxides will become the source of abnormal discharge (arcing).
[0064] The present invention has a purity of 4N or higher and is
capable of effectively preventing the arcing caused by such
impurities, and even inhibiting the generation of particles caused
by such arcing. Desirably, the purity is 5N or higher.
[0065] Desirably, the content of gas components as impurities is
set to 1500 ppm or less. The inclusion of gas components such as
oxygen, nitrogen, and carbon could easily become the cause of the
generation of impurities such as oxides, nitrides and carbides. The
reduction of the foregoing impurities will lead to the prevention
of arcing, and the inhibition of the generation of particles caused
by such arcing.
[0066] As described above, with the Sb--Te-based alloy sintered
compact of the present invention, since it is possible to inhibit
the coarsening of the added carbon or boron which is nonmetal, it
yields a superior effect of preventing abnormal discharge with such
carbon or boron as the source, and inhibit the generation of
particles caused by arcing. It is thereby possible to improve the
uniformity of the sputtered thin film.
[0067] Moreover, although machining such as cutting work is
performed at the stage of finishing the target, if there is
coarsened carbon or boron, there is a possibility that cracks and
the like will occur with such carbon or boron as the source, and
the generation of particles with cracks as the source could also be
considered, and the present invention is able to achieve a
considerable effect of being able to prevent the foregoing problems
from occurring.
[0068] As described above, the phase change target having a crystal
structure according to the present invention yields the effect of
being able to reduce the surface unevenness caused by the sputter
erosion, and inhibit the generation of particles caused by the
redeposition detachment onto the target surface. Moreover, with the
foregoing structure, there is also an advantage in that the
composition variation of the sputtered film in the plane and
between lots can be inhibited, and the quality of the phase change
recording layer can be stabilized. Additional effects are yielded
in that the generation of particles, abnormal discharge and nodules
can be effectively inhibited in the sputtering process as described
above, and the uniformity of the thin film can be improved.
[0069] With the Sb--Te-based sputtering target of the present
invention, the content of gas components such as oxygen may be
additionally set to 1500 ppm or less, preferably to 1000 ppm or
less, and more preferably to 500 ppm or less. The reduction of gas
components such as oxygen yields an advantage in being able to
further reduce the generation of particles and abnormal
discharge.
Examples
[0070] The present invention is now explained in detail with
reference to the Examples. These Examples are merely illustrative,
and the present invention shall in no way be limited thereby. In
other words, various modifications and other embodiments based on
the technical spirit claimed in the claims shall be included in the
present invention as a matter of course.
Example 1
[0071] Ge, Sb, Te powder raw materials respectively having a purity
of 4N or higher excluding gas components were mixed and synthesized
to achieve a Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy and this alloy
raw material was pulverized with a jet mill pulverizer in an argon
inert atmosphere. Powder (P) having an average diameter of 3 .mu.m
or less was thereby obtained.
[0072] Subsequently, carbon powder (C) having a grain size of 20 to
750 nm was mixed with the powder (P) at the prescribed mixing
ratios (0.1 to 30 at %) shown in Table 1 using a mortar, a
planetary ball mill, and a vibrational mill.
[0073] This mixing ratio must be set within an appropriate range.
If this is deviated; that is, if the mixing ratio is less than 0.1
at %, there will be no effect of adding the carbon powder (C).
Contrarily, if the addition exceeds 30 at %, the mechanical
strength will diminish due to the deterioration in the density of
the sintered compact, and problems such as fractures occurring in
the production process or sputtering process will arise.
TABLE-US-00001 TABLE 1 amount of carbon powder Example 1 (at %)
method to mix alloy 1-1 0.1 mortar 1-2 0.13 mortar 1-3 0.15 mortar
1-4 0.18 mortar 1-5 0.3 mortar 1-6 0.4 mortar 1-7 0.5 mortar 1-8 15
mortar 1-9 30 mortar 1-10 0.15 planetary ball mill 1-11 0.5
planetary ball mill 1-12 15 planetary ball mill 1-13 0.15
vibrational mill 1-14 0.5 vibrational mill 1-15 15 vibrational
mill
[0074] Subsequently, among the powders mixed as described above,
the raw material powders in which the grain size ratio of the
respective powders (Y/X) was changed as shown in Table 2 based on
the composition ratio of Example 1-3 (the amount of carbon powder:
0.15 at %) were sintered by way of hot pressing, and the obtained
sintered compact was subject to machining and polishing to obtain a
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target containing the
foregoing prescribed amount of carbon. Here, X is the average
crystal grain size of the Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy
particles and Y to is the average grain size of carbon. The
obtained sputtering target comprised a uniform mixed structure of
Sb--Te-based alloy particles and fine carbon (C) particles.
[0075] In the foregoing case, it was possible to achieve the
following; specifically, the average crystal grain size of the
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy particles was 3 .mu.m or
less and the standard deviation thereof was less than 1.00, and the
average grain size of C was 0.5 .mu.m or less and the standard
deviation thereof was less than 0.20.
[0076] It is important that Y/X is within the range of 0.1 to 0.5.
Table 2 shows the density of the target of this Example when the
amount of the carbon powder mixed with mortar was 0.15 at %.
[0077] Since carbon easily becomes a cluster, if the mixed state is
insufficient, there is a problem in that lumps will be generated.
Thus, a uniform mixture is important, and Y/X must be within the
range of 0.1 to 0.5 as a means for achieving such uniform
mixture.
[0078] As shown in Table 2, the density of the targets of Example
1-16 to Example 1-25 was 96.51% to 99.99%, and the number of
generated particles of 0.3 .mu.m or larger was few at 26 to 50.
TABLE-US-00002 TABLE 2 ratio relative density number of particles
Example 1 Y/X of target of target 0.3 .mu.m or larger 1-16 0.101
99.99% 26 1-17 0.120 99.96% 28 1-18 0.133 99.95% 28 1-19 0.139
99.93% 29 1-20 0.145 99.94% 30 1-21 0.159 99.94% 33 1-22 0.213
99.90% 37 1-23 0.254 99.58% 40 1-24 0.326 99.13% 46 1-25 0.497
98.51% 50 Comparison 1-A 0.608 97.50% 81 Comparison 1-B 0.811
96.51% >100
Comparative Example 1
[0079] As a comparative example, the raw material of Example 1-3
was used, and Y/X was adjusted to be 0.608 and 0.811, which is
outside of the range of 0.1 to 0.5, and a
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target was prepared as with
Example 1.
[0080] As shown in table 2, the density of the targets of
comparison 1-A and Comparison 1-B became 97.50% and 96.51% and
deteriorated compared to Example 1. The number of generated
particles increased to 81 and more than 100 respectively, and
showed inferior results.
[0081] Thus, in cases where Y/X exceeds 0.5, the effect of
inhibiting the generation of arcing and particles is low and the
sinterability is inferior, and problems such as fractures occurred
due to the low density. While, in cases where Y/X is less than 0.1,
producing the target was difficult since the carbon powder will
fall below the minimum size in which such powder can be separated
and dispersed with this technology.
[0082] The SEM photograph of the target structure of Example 1-16
is shown in FIG. 1. As shown, defects such as cracks could not be
observed at all, and the target comprised a structure in which fine
carbon particles encompass the periphery of the
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy particles. The number of
generated particles of 0.3 .mu.m or larger which were formed on a
200 mm.phi. Si wafer upon performing sputtering up to 100 kWhr was
26 as described above, and a superior target was obtained.
[0083] The SEM photograph of the target structure of Comparative
Example 1-A is shown in FIG. 2. In FIG. 2, there is a dappled
structure at the center and upper left part, and "lumps" of
coarsened carbon can be observed. When using the target having the
structure shown in FIG. 2, as illustrated in foregoing Comparative
Example 1-A, the number of generated particles of 0.3 .mu.m or
larger formed on the 200 mm.phi. Si wafer increased to 81, and
showed clearly inferior results.
[0084] FIG. 3 shows the mechanical strength of the Ge--Sb--Te alloy
of Example 1 and Comparative Example 1 upon adding 15 at % of C. In
the chart of FIG. 3, it can be said that the farther it is to the
right side, the higher strength (high deflective strength) the
material has. The average deflective strength can be obtained by
multiplying the respective values of the deflective strength and
dividing it by the number of samples.
[0085] The vertical axis in FIG. 3 shows the estimated probability
of fatigue failure which is obtained by dividing the number of
samples prepared from the same specimen by 1. For example, if there
are 4 specimens, the 4 points of 0.25, 0.50, 0.75, and 1.00 can be
plotted.
[0086] In the examples of Comparison 1-A and Comparison 1-B in FIG.
3, since the grain size of Carbon is relatively greater, each line
of the deflective strength is to the left side in the chart and
shows a weak value.
[0087] Meanwhile, Example 1-18, Example 1-21, and Example 1-24 show
that the smaller the grain size of carbon becomes, the more uniform
is the dispersion thereof and the more mechanical strength it
has.
Example 2
[0088] As with Example 1 above, Ge, Sb, Te powder raw materials
respectively having a purity of 4N or higher excluding gas
components were mixed and synthesized to achieve a
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy, and this alloy raw
material was pulverized with a jet mill pulverizer in an argon
inert atmosphere. Powder (P) having an average diameter of 3 .mu.m
or less was thereby obtained.
[0089] Subsequently, boron powder (B) having a grain size of 20 to
750 nm was mixed with the powder (P) at the mixing ratios (0.1 to
30 at %) shown in Table 3 using a mortar, a planetary ball mill,
and a vibrational mill.
[0090] This mixing ratio must be set within an appropriate range.
If this is deviated; that is, if the mixing ratio is less than 0.1
at %, there will be no effect of adding the boron powder (B).
Contrarily, if the addition exceeds 30 at %, the mechanical
strength will diminish due to the deterioration in the density of
the sintered compact, and problems such as fractures occurring in
the production process or sputtering process will arise.
TABLE-US-00003 TABLE 3 amount of boron powder method to mix Example
2 (at %) alloy with 2-1 0.1 mortar 2-2 0.13 mortar 2-3 0.15 mortar
2-4 0.18 mortar 2-5 0.2 mortar 2-6 0.27 mortar 2-7 0.33 mortar 2-8
0.8 mortar 2-9 1.5 mortar 2-10 15 mortar 2-11 30 mortar 2-12 0.25
planetary ball mill 2-13 0.8 planetary ball mill 2-14 15 planetary
ball mill 2-15 0.17 vibrational mill 2-16 0.8 vibrational mill 2-17
3 vibrational mill 2-18 15 vibrational mill
[0091] Subsequently, among the powders mixed as described above,
the raw material powders in which the grain size ratio of the
respective powders (Y/X) was changed as shown in Table 4 based on
the composition ratio of Example 2-10 (15 at % boron powder) were
sintered by way of hot pressing, and the obtained sintered compact
was subject to machining and polishing to obtain a
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target containing the
foregoing prescribed amount of boron. Here, X is the average
crystal grain size of the Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy
particles and Y is the average grain size of boron. These will be
Example 2-19 to Example 2-28.
[0092] The obtained sputtering targets all comprised a uniform
mixed structure of Sb--Te-based alloy particles and boron (B)
particles.
[0093] In the foregoing case, it was possible to achieve the
following; specifically, the average crystal grain size of the
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy particles was 3 .mu.m or
less and the standard deviation thereof was less than 1.00, and the
average grain size of B was 0.5 .mu.m or less and the standard
deviation thereof was less than 0.20.
[0094] Moreover, when the average crystal grain size of the
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy particles is X and the
average grain size of boron is Y, it is important that Y/X is
within the range of 0.1 to 0.5. Table 4 shows the density of the
target of this Example when the amount of the boron powder mixed
with mortar was 15 at %.
[0095] Since fine boron, as with carbon, easily becomes a cluster,
if the mixed state is insufficient, there is a problem in that
lumps will be generated. Thus, a uniform mixture is important, and
Y/X must be within the range of 0.1 to 0.5 as a means for achieving
such uniform mixture.
[0096] Upon observing the SEM photograph of the target surface of
Example 2-19 obtained as described above, it was similar to FIG. 1.
Defects such as cracks could not be observed at all, and the target
comprised a structure in which fine boron particles encompass the
periphery of the Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy
particles.
[0097] The number of generated particles of 0.3 .mu.m or larger
which were formed on a 200 mm.phi. Si wafer upon performing
sputtering up to 100 kWhr was 28 to 66, and a superior target was
obtained. The results are shown in Table 4.
Comparative Example 2
[0098] As a comparative example, the raw material of Example 2-10
was used, and when the average grain size of the Sb--Te-based alloy
particles is X and the average grain size of boron is Y, Y/X was
adjusted to be 0.610 and 0.792, which is outside of the range of
0.1 to 0.5, and a Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target
was prepared as with Example 2.
[0099] As shown, the density of the targets of Comparison 2-A and
Comparison 2-B became 97.13% and 96.36% and deteriorated compared
to Example 2. The number of generated particles of 0.3 .mu.m or
larger increased to 83 and more than 100 respectively, and showed
clearly inferior results.
[0100] Thus, in cases where Y/X exceeds 0.5, the effect of
inhibiting the generation of arcing and particles is low and the
sinterability is also inferior, and problems such as fractures
occurred due to the low density. While, in cases where Y/X is less
than 0.1, producing the target was difficult since the boron powder
will fall below the minimum size in which such powder can be
separated and dispersed with this technology.
[0101] Upon observing SEM photograph of the target, in the cases
where Y/X exceeds 0.5 and Y/X is 0.610, "lumps" of coarsened boron
can be observed, which was similar to FIG. 2.
TABLE-US-00004 TABLE 4 ratio relative density number of particles
Example 2 Y/X of target of target 0.3 .mu.m or larger 2-19 0.109
99.96% 28 2-20 0.118 99.94% 30 2-21 0.127 99.94% 31 2-22 0.140
99.92% 32 2-23 0.142 99.93% 35 2-24 0.163 99.92% 40 2-25 0.221
99.72% 44 2-26 0.267 99.46% 50 2-27 0.335 98.95% 59 2-28 0.493
98.29% 66 Comparison 2-A 0.610 97.13% 83 Comparison 2-B 0.792
96.36% >100
Example 3
Part of Comparative Example 3
[0102] In, Sb, Te powder raw materials respectively having a purity
of 4N or higher excluding gas components were mixed and synthesized
to achieve an In.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy, and this
alloy raw material was pulverized with a jet mill pulverizer in an
argon inert atmosphere. Powder (P) having an average diameter of 3
.mu.m or less was thereby obtained.
[0103] Subsequently, carbon powder (C) and boron powder (B) having
a grain size of 7 to 750 nm was mixed with the powder (P) at the
mixing ratios (0.1 to 30 at %) shown in Table 5 using a mortar.
[0104] This mixing ratio must be set within an appropriate range.
If this is deviated; that is, if the mixing ratio is less than 0.1
at %, there will be no effect of adding the carbon powder (C) and
boron powder (B). Contrarily, if the addition exceeds 30 at %, the
mechanical strength will diminish due to the deterioration in the
density of the sintered compact, and problems such as fractures
occurring in the production process or sputtering process will
arise.
TABLE-US-00005 TABLE 5 amount of carbon and Example 3 boron powder
(at %) method to mix alloy with 3-1 C: 0.05 B: 0.05 mortar 3-2 C:
0.15 B: 0.15 mortar 3-3 C: 0.4 B: 0.4 mortar 3-4 C: 15 B: 15
mortar
[0105] Subsequently, among the powders mixed as described above,
the raw material powders in which the grain size ratio of the
respective powders (Y/X) was changed as shown in Table 6 based on
the composition ratio of Example 3-4 (the amount of carbon powder
and boron powder was 15 at % respectively and 30 at % in total)
were sintered by way of hot pressing, and the obtained sintered
compact was subject to machining and polishing to obtain an
In.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target containing the
foregoing prescribed amount of carbon or boron. Here, X is the
average crystal grain size of the Ge.sub.22.2Sb.sub.22.2Te.sub.55.6
alloy particles and Y is the average grain size of mixed powder of
carbon and boron.
[0106] The obtained Sb--Te-based alloy sintered compact sputtering
target comprised a uniform mixed structure of Sb--Te-based alloy
particles and fine carbon (C) or boron (B) particles.
[0107] In the foregoing case, it was possible to achieve the
following; specifically, the average crystal grain size of the
In.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy particles was 3 .mu.m or
less and the standard deviation thereof was less than 1.00, and the
average grain size of C or B was 0.5 .mu.m or less and the standard
deviation thereof was less than 0.20.
[0108] It is important that Y/X is within the range of 0.1 to 0.5.
Table 6 shows the Y/X ratio of the target and the density of the
target of this Example when the amount of the carbon powder 15 at %
and the boron powder 15 at % was mixed with mortar.
[0109] As shown in Table 6, the density of Example 3-5 to Example
3-14 is 97.85% to 98.35%; high density targets were obtained.
[0110] Since fine carbon and boron easily become a cluster, if the
mixed state is insufficient, there is a problem in that lumps will
be generated. Thus, a uniform mixture is important, and Y/X must be
within the range of 0.1 to 0.5 as a means for achieving such
uniform mixture. Consequently, in cases where Y/X exceeds 0.5, the
effect of inhibiting the generation of arcing and particles is low
and the sinterability is also inferior, and problems such as
fractures occurred due to the low density. While, in cases where
Y/X is less than 0.1, producing the target was difficult since the
carbon powder and boron powder will fall below the minimum size in
which such powder can be separated and dispersed with this
technology.
TABLE-US-00006 TABLE 6 ratio relative density number of particles
Example 3 Y/X of target of target 0.3 .mu.m or larger 3-5 0.103
98.35% 46 3-6 0.115 98.26% 47 3-7 0.129 98.19% 49 3-8 0.138 98.21%
51 3-9 0.146 198.16% 54 3-10 0.160 98.10% 57 3-11 0.225 98.03% 63
3-12 0.261 97.95% 68 3-13 0.328 97.92% 71 3-14 0.494 97.85% 75
Comparison 3-A 0.614 96.62% >100 Comparison 3-B 0.789 95.51%
>100
[0111] Upon observing SEM photograph of the target surface of
Example 3-5 obtained as described above, as with Example 1-16,
defects such as cracks could not be observed at all, and the target
comprised a structure in which fine carbon or boron particles
encompass the periphery of the In.sub.22.2Sb.sub.22.2Te.sub.55.6
alloy particles.
[0112] As Comparative Examples, Comparison 3-A and Comparison 3-B
are shown in Table 6. Upon observing SEM photograph of the target
in which Y/X exceeded 0.5 and Y/X was 0.614 in Table 6, there was a
dappled structure and "lumps" of coarsened carbon or boron could be
observed. The density of Comparison 3-A and Comparison 3-B was
96.62% and 95.51% respectively, was lower compared to Examples.
[0113] In Example 3, the number of generated particles of 0.3 .mu.m
or larger which were formed on a 200 mm.phi. Si wafer was 46 to 75,
and a superior target was obtained though the amount of carbon and
boron was high.
[0114] When using the target of the Comparative Examples in which
Y/X exceeded 1/2, and when Y/X was 0.614 and Y/X was 0.789, the
number of generated particles of 0.3 .mu.m or larger formed on the
200 mm.phi. Si wafer increased to more than 100 and showed clearly
inferior results.
Example 4
Part of Comparative Example 4
[0115] Ag, In, Sb, Te powder raw materials respectively having a
purity of 4N or higher excluding gas components were mixed and
synthesized to achieve a Ag.sub.5In.sub.5Sb.sub.70Te.sub.20 alloy,
and this alloy raw material was pulverized with a jet mill
pulverizer in an argon inert atmosphere. Powder (P) having an
average diameter of 3 .mu.m or less was thereby obtained.
[0116] Subsequently, carbon powder (C) and boron powder (B) having
a grain size of 20 to 750 nm was mixed with the powder (P) at the
mixing ratios (0.1 to 30 at %) shown in Table 7 using a mortar.
[0117] This mixing ratio must be set within an appropriate range.
If this is deviated; that is, if the mixing ratio is less than 0.1
at %, there will be no effect of adding the carbon powder (C) and
boron powder (B). Contrarily, if the addition exceeds 30 at %, the
mechanical strength will diminish due to the deterioration in the
density of the sintered compact, and problems such as fractures
occurring in the production process or sputtering process will
arise.
TABLE-US-00007 TABLE 7 amount of carbon and Example 4 boron powder
(at %) method to mix alloy with 4-1 C: 0.05 B: 0.05 mortar 4-2 C:
0.15 B: 0.15 mortar 4-3 C: 0.4 B: 0.4 mortar 4-4 C: 15 B: 15
mortar
[0118] The powders mixed as described above were sintered by way of
hot pressing, and the obtained sintered compact was subject to
machining and polishing to obtain a
Ag.sub.5In.sub.5Sb.sub.70Te.sub.20 alloy target containing the
foregoing prescribed amount of carbon or boron. The obtained
Sb--Te-based alloy sintered compact sputtering target containing
0.1 to 30 at % of carbon and boron comprised a uniform mixed
structure of Sb--Te-based alloy particles and fine carbon (C) and
boron (B) particles.
[0119] In the foregoing case, it was possible to achieve the
following; specifically, the average crystal grain size of the
Ag.sub.5In.sub.5Sb.sub.70Te.sub.20 alloy particles was 3 .mu.m or
less and the standard deviation thereof was less than 1.00, and the
average grain size of C or B was 0.5 .mu.m or less and the standard
deviation thereof was less than 0.20.
[0120] When the average crystal grain size of the
Ag.sub.5In.sub.5Sb.sub.70Te.sub.20 alloy particles is X and the
average grain size of carbon and boron is Y, it is important that
Y/X is within the range of 0.1 to 0.5.
[0121] Table 8 shows the Y/X ratio of the target and the density of
the target when the amount of boron powder is 15 at %, carbon
powder is 15 at % and 30 at % in total as with this Example mixed
with mortar. The density of Example 4-5 to Example 4-14 was within
the range of 97.80% to 98.25%.
[0122] Fine carbon or boron easily becomes a cluster. If the mixed
state is insufficient; there is a problem in that lumps will be
generated. Thus, a uniform mixture is important, and Y/X must be
within the range of 0.1 to 0.5 as a means for achieving such
uniform mixture.
[0123] As Comparative Examples, Comparison 4-A and Comparison 4-B
are shown in Table 8. The relative density of the respective
Comparison 4-A and Comparison 4-B is 96.52% and 95.40%; was low
compared to Examples. Consequently, in cases where Y/X exceeds 0.5,
the effect of inhibiting the generation of arcing and particles is
low and the sinterability is also inferior, and problems such as
fractures occurred due to the low density.
[0124] In cases where Y/X is less than 0.1, producing the target
was difficult since the carbon powder or boron powder will fall
below the minimum size in which such powder can be separated and
dispersed with this technology.
TABLE-US-00008 TABLE 8 ratio relative density number of particles
Example 4 Y/X of target of target 0.3 .mu.m or larger 4-5 0.102
98.25% 47 4-6 0.123 98.21% 40 4-7 0.130 98.15% 52 4-8 0.134 98.13%
55 4-9 0.143 98.13% 59 4-10 0.155 98.10% 62 4-11 0.231 97.97% 66
4-12 0.249 97.91% 72 4-13 0.319 97.83% 74 4-14 0.499 97.80% 75
Comparison 4-A 0.613 96.52% >100 Comparison 4-B 0.804 95.40%
>100
[0125] Upon observing the SEM photograph of the target surface of
Example 4-5 obtained as described above, as with Example 1-16,
defects such as cracks could not be observed at all, and the target
comprised a structure in which fine boron particles encompass the
periphery of the Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy
particles.
[0126] Upon observing the SEM photograph of the targets of
Comparative Example 4 in which Y/X was 0.613 and Y/X thereof
exceeded 0.5, there was a dappled structure and "lumps" of
coarsened carbon or boron could be observed.
[0127] In Example 4, the number of generated particles of 0.3 .mu.m
or larger which were formed on a 200 mm.phi. Si wafer upon
performing sputtering up to 100 kWhr was 47 or 7580, and a superior
target was obtained even though the amount of carbon and boron
powder that was mixed is higher.
[0128] When using the target of Comparison 4-A and Comparison 4-B
in which Y/X exceeded 0.5, and when Y/X was 0.614 in Comparison
4-A, the number of generated particles of 0.3 .mu.m or larger
formed on the 200 mm.phi. Si wafer increased to more than 100, and
showed clearly inferior results. When using the target of
Comparison 4-B in which Y/X was 0.804, the number of generated
particles of 0.3 .mu.m or larger formed on the 200 mm.phi. Si wafer
increased to more than 100, and showed inferior results.
[0129] The Examples explain a case of using the
Ge.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy target, the
In.sub.22.2Sb.sub.22.2Te.sub.55.6 alloy and the
Ag.sub.5In.sub.5Sb.sub.70Te.sub.20 alloy target to which carbon or
boron was added. The same effects were yielded in the addition of
carbon or boron when adding, as an accessory component, one or more
elements selected from Ag, In, Si, Ge, Ga, Ti, Au, Pt, and Pd.
[0130] That is, one or more elements selected from Ag, In, Si, Ge,
Ga, Ti, Au, Pt, and Pd to become the additive component are
equivalent in a material generally referred to as an Sb--Te-based
alloy material for use as a phase change recording film, and can be
considered equivalents. Accordingly, the foregoing elements yield
the same effects without having to describe them in the Examples.
The same applies to the Sb--Te-based alloy sintered compact
sputtering target of the present invention.
INDUSTRIAL APPLICABILITY
[0131] With the Sb--Te-based alloy sintered compact of the present
invention, since it is possible to inhibit the coarsening of the
grain size of the Sb--Te-based alloy and the added carbon or boron
which is nonmetal, it yields a superior effect of being able to
prevent abnormal discharge with such carbon or boron as the source,
inhibit the generation of particles caused by arcing, and improve
the uniformity of the thin film. Moreover, although machining such
as cutting work is performed at the stage of finishing the target,
if there is coarsened carbon or boron, there is a possibility that
cracks and the like will occur with such carbon or boron as the
source, and the generation of particles with cracks as the source
could also be considered, and the present invention is able to
achieve a considerable effect of being able to prevent the
foregoing problems from occurring. Thus, the present invention is
extremely effective for use as a phase change recording material;
that is, as a medium for recording information by using phase
transformation.
* * * * *