U.S. patent application number 09/846370 was filed with the patent office on 2001-11-08 for refractory metal silicide target, method of manufacturing the target, refractory metal silicide thin film, and semiconductor device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Fukasawa, Yoshiharu, Komatsu, Tohru, Maki, Toshihiro, Sato, Michio, Shizu, Hiromi, Yagi, Noriaki, Yamanobe, Takashi.
Application Number | 20010037938 09/846370 |
Document ID | / |
Family ID | 16478523 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037938 |
Kind Code |
A1 |
Sato, Michio ; et
al. |
November 8, 2001 |
Refractory metal silicide target, method of manufacturing the
target, refractory metal silicide thin film, and semiconductor
device
Abstract
A refractory metal silicide target is characterized by
comprising a fine mixed structure composed of MSi.sub.2 (where M:
refractory metal) grains and Si grains, wherein the number of
MSi.sub.2 grains independently existing in a cross section of 0.01
mm.sup.2 of the mixed structure is not greater than 15, the
MSi.sub.2 grains have an average grain size not greater than 10
.mu.m, whereas free Si grains existing in gaps of the MSi.sub.2
grains have a maximum grain size not greater than 20 .mu.m. The
target has a high density, high purity fine mixed structure with a
uniform composition and contains a small amount of impurities such
as oxygen etc. The employment of the target can reduce particles
produced in sputtering, the change of a film resistance in a wafer
and the impurities in a film and improve yield and reliability when
semiconductors are manufactured.
Inventors: |
Sato, Michio; (Yokohama-Shi,
JP) ; Yamanobe, Takashi; (Yamato-Shi, JP) ;
Komatsu, Tohru; (Yokosuka-Shi, JP) ; Fukasawa,
Yoshiharu; (Yokohama-Shi, JP) ; Yagi, Noriaki;
(Yokohama-Shi, JP) ; Maki, Toshihiro;
(Yokohama-Shi, JP) ; Shizu, Hiromi; (Fujisawa-Shi,
JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Kawasaki-Shi
JP
|
Family ID: |
16478523 |
Appl. No.: |
09/846370 |
Filed: |
May 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09846370 |
May 2, 2001 |
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08397243 |
Mar 20, 1995 |
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08397243 |
Mar 20, 1995 |
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PCT/JP94/01236 |
Jul 27, 1994 |
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Current U.S.
Class: |
204/192.13 ;
419/23; 419/30; 419/31; 419/48 |
Current CPC
Class: |
H01J 37/3491 20130101;
C23C 14/3414 20130101; H01J 37/3426 20130101 |
Class at
Publication: |
204/192.13 ;
419/48; 419/23; 419/30; 419/31 |
International
Class: |
C23C 014/34; B22F
003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 1993 |
JP |
P5-203707 |
Claims
1. A refractory metal silicide target, comprising a fine mixed
structure composed of MSi.sub.2 (where M: at least one kind of a
refractory metal selected from W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co,
Cr, Ni) grains and Si grains, wherein the number of MSi.sub.2
grains independently existing in a cross section of 0.01 mm.sup.2
of the mixed structure is not greater than 15, the MSi.sub.2 grains
have an average grain size not greater than 10 .mu.m, whereas free
Si grains existing in gaps of the MSi.sub.2 grains have a maximum
grain size not greater than 20 .mu.m.
2. A refractory metal silicide target according to claim 1, wherein
when the average value of a Si/M atomic ratio in the entire
sputtering is assumed to be X, the dispersion of the Si/M atomic
ratio in an arbitrary cross section of 1 mm.sup.2 in the mixed
structure is in a range of X.+-.0.02.
3. A refractory metal silicide target according to claim 1, wherein
a density ratio is not less than 99.5% over the entire target.
4. A refractory metal silicide target according to claim 1, wherein
an oxygen content is not greater than 200 ppm and a carbon content
is not greater than 50 ppm.
5. A refractory metal silicide target according to claim 1, wherein
an iron content and an aluminium content are not greater than 1
ppm, respectively.
6. A method of manufacturing a refractory metal silicide target
comprising a fine mixed structure composed of MSi.sub.2 (where M:
at least one kind of a refractory metal selected from W, Mo, Ti,
Ta, Zr, Hf, Nb, V, Co, Cr, Ni) grains and Si grains, wherein the
number of MSi.sub.2 grains independently existing in a cross
section of 0.01 mm.sup.2 of the mixed structure is not greater than
15, the MSi.sub.2 grains have an average grain size not greater
than 10 .mu.m, whereas free Si grains existing in gaps of the
MSi.sub.2 grains have a maximum grain size not greater than 20
.mu.m, the method comprising the processes of: I. preparing a mixed
powder by mixing a high purity refractory metal powder having a
maximum grain size not greater than 15 .mu.m with a high purity
silicon powder having a maximum grain size not greater than 30
.mu.m such that a Si/M atomic ratio is 2-4; II. synthesizing a
refractory metal silicide as well as forming a semi-sintered body
by charging the mixed powder into a vessel and heating the powder
up to 1300.degree. C. in vacuum; III. preparing a crushed powder by
crushing the semi-sintered body in vacuum or in an inert gas
atmosphere; and IV. charging the crushed powder into a compacting
mold, increasing the temperature of the crushed powder to just
below an eutectic temperature in vacuum or in an inert gas
atmosphere at a temperature less than 1200.degree. C. while
applying a low pressing pressure of 10-50 kg/cm.sup.2 to the
crushed powder, and then densifying the powder under a high
pressing pressure of 200-500 kg/cm.sup.2.
7. A method of manufacturing a refractory metal silicide target
according to claim 6, wherein an impurity removing process is
provided between process III and process IV to prepare a high
purity powder by reducing impurities such as oxygen, carbon etc. in
such a manner that the crushed powder prepared in process III is
charged into a vessel and heated to 1100-1300.degree. C. in
vacuum.
8. A method of manufacturing a refractory metal silicide target
according to claim 6, wherein an impurity removing process is
provided between process III and process IV to prepare a high
purity powder by reducing impurities such as oxygen, carbon etc. in
such a manner that the crushed powder prepared in process III is
charged into a vessel and heated to 1100-1300.degree. C. in an
pressure-reduced hydrogen atmosphere.
9. A method of manufacturing a refractory metal silicide target
according to claim 6, wherein the mixed powder to be charged into
the vessel for a heat treatment effected once in process II is set
to a depth not greater than 20 mm.
10. A method of manufacturing a refractory metal silicide target
according to claim 7, wherein the inside diameter of the vessel
into which the crushed powder is charged in the impurity removing
process is set equal to the inside diameter of the compacting mold
into which the crushed powder is charged in process IV.
11. A refractory metal silicide thin film, formed by using a
refractory metal silicide target comprising a mixed structure
composed of MSi.sub.2 (where M: at least one kind of a refractory
metal selected from W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cr, Ni)
grains and Si grains, wherein the number of MSi.sub.2 grains
independently existing in a cross section of 0.01 mm.sup.2 of the
mixed structure is not greater than 15, the MSi.sub.2 grains have
an average grain size not greater than 10 .mu.m, whereas free Si
grains existing in gaps of the MSi.sub.2 grains have a maximum
grain size not greater than 20 .mu.m.
12. A refractory metal silicide thin film according to claim 11,
wherein the refractory metal silicide thin film is a thin film
constituting at least one kind of a gate electrode, source
electrode, drain electrode and wire of a semiconductor device.
13. A semiconductor device, including at least one kind of a gate
electrode, source electrode, drain electrode and wire comprising a
refractory metal silicide thin film formed by using a refractory
metal silicide target comprising a fine mixed structure composed of
MSi.sub.2 (where M: at least one kind of a refractory metal
selected from W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cr, Ni) grains and
Si grains, wherein the number of MSi.sub.2 grains independently
existing in a cross section of 0.01 mm.sup.2 of the mixed structure
is not greater than 15, the MSi.sub.2 grains have an average grain
size not greater than 10 .mu.m, whereas free Si grains existing in
gaps of the MSi.sub.2 grains have a maximum grain size not greater
than 20 .mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refractory metal silicide
target, a method of manufacturing the target, a refractory metal
silicide thin film, and a semiconductor device, and more
specifically, to a refractory metal silicide target, a method of
simply manufacturing the target, a refractory metal silicide thin
film, and a semiconductor device capable of reducing the generation
of particles in sputtering and forming a thin film of high quality
by densifying or fining a mixed structure and making a uniform
composition and further achieving high density and high
purification.
BACKGROUND ART
[0002] A sputtering method is employed as one of the effective
methods of forming a refractory metal silicide thin film used for a
gate electrode, source electrode, drain electrode of semiconductor
devices such as MOS, LSI devices and the like and for wiring. The
sputtering method, which is excellent in mass-productivity and the
stability of a formed film, is a method such that argon ions are
caused to collide with a disc-shaped refractory metal silicide
target and discharge a target constituting metal which is deposited
as a thin film on a substrate disposed in confrontation with the
target. Consequently, the property of the silicide thin film formed
by sputtering greatly depends upon the characteristics of the
target.
[0003] Recently, as a semiconductor device is highly integrated and
miniaturized, it is required that a sputtering target used to form
a refractory metal silicide thin film produces a less amount of
particles (fine grains). That is, since particles produced from a
target during sputtering have a very fine grain size of about
0.1-10 .mu.m, when the particles are mixed into a thin film being
deposited, they cause a serious problem that the yield of
semiconductor devices is greatly reduced by the occurrence of short
circuit between wires of a circuit and insufficient opening of
wires. Thus, the reduction of an amount of particles is strongly
required.
[0004] Since it can become effective means to miniaturize a target
structure, that is, to make the size of MSi.sub.2 grains and free
Si grains as small as possible in order to reduce an amount of
particles produced from a target, there are conventionally proposed
various manufacturing methods of miniaturizing the structure.
[0005] For example, Japanese Patent Application Laid-Open No. Sho
63(1988)-219580 discloses that a high density target having a fine
structure and containing a small amount of oxygen can be obtained
in such a manner that a mixed powder obtained by mixing a high
purity refractory metal powder with a high purity silicon powder is
subjected to a silicide reaction in high vacuum and a semi-sintered
body is formed, then the resultant semi-sintered body is charged
into a pressure-tight sealing canister without being crushed and
the pressure-tight sealing canister is sintered by a hot isostatic
press after having evacuated and sealed. In this case, the thus
obtained target has a fine structure having the maximum grain size
of MSi.sub.2 not greater than 20 .mu.m and the maximum grain size
of free Si not greater than 50 .mu.m and containing oxygen not
greater than 200 ppm with a density ratio not less than 99%.
[0006] Further, Japanese Patent Application Laid-Open No. Hei
2(1990)-47261 discloses that a high density target with a fine
structure can be obtained in such a manner that a mixed powder of a
high purity refractory metal powder and a high purity silicon
powder is subjected to a silicide reaction in high vacuum and a
semi-sintered body is formed, then the semi-sintered body is
crushed to not greater than 150 .mu.m and further added and mixed
with a high purity silicon powder and charged into a pressure-tight
sealing canister, then the pressure-tight sealing canister is
sintered by a hot isostatic press after having evacuated and
sealed. In this case, the thus obtained target has a maximum grain
size of MSi.sub.2 not greater than 20 .mu.m and a density ratio not
less than 99% with only free Si existing in a grain boundary.
[0007] Recently, as a semiconductor device is highly integrated and
miniaturized, a high purity target containing a very small amount
of impurities, which deteriorate the characteristics of the
semiconductor device, is required as a sputtering target used to
form a refractory metal silicide thin film. In particular, it is
strongly required to minimize an amount of oxygen in a target
because oxygen, which concentrates on the interface between a
silicide layer and an under layer and increases a film resistance,
delays signals and lowers the reliability of the device.
[0008] Since it is effective oxygen reducing means to make
deoxidation by heating a semi-sintered body as a material in vacuum
and volatilizing oxygen in the form of silicon oxide (SiO or
SiO.sub.2), the following manufacturing methods of reducing oxygen
are conventionally proposed.
[0009] For example, Japanese Patent Application Laid-Open No. Sho
62(1987)-171911 obtains Mo silicide or W silicide each containing a
small amount of oxygen in such a manner that a mixed powder
obtained by mixing a Mo powder or W powder with a Si powder is
heated in vacuum at a temperature less than 800-1300.degree. C. and
a Mo silicide powder or W silicide powder is synthesized, then the
resultant powder is held in vacuum at 1300-1500.degree. C. to
remove oxygen as SiO by excessive Si.
[0010] On the other hand, a trial for optimizing the grain size of
a material powder and hot pressing conditions from a view point
that the condensation of free Si results to an increase of
particles produced and the following manufacturing method is
proposed.
[0011] For example, Japanese Patent Application Laid-Open No. Sho
63(1988)-74967 obtains a target from which condensed silicon is
removed in such a manner that a mixed powder obtained by adding a
synthesized silicide powder of -100 mesh with a silicon powder of
-42 mesh is heated to 1300-1400.degree. C. while applying a preload
of 60-170 kg/cm.sup.2, then pressed with a pressing pressure of
200-400 kg/cm.sup.2 and held after being pressed.
[0012] Further, Japanese Patent Application Laid-Open No. Sho
64(1989)-39374 obtains a target from which condensed silicon is
removed in such a manner that two types of synthesized silicide
powders of -100 mesh having a different composition are prepared
and a mixed powder adjusted to have an intended composition is hot
pressed under the same conditions as above.
[0013] There is a problem, however, that when all the amounts of a
mixed powder necessary to form a single target is subjected to a
silicide synthesis at once in high vacuum in the above conventional
manufacturing methods, resulting MSi.sub.2 grains are rapidly grown
and coarsened as well as cracks are made to an entire semi-sintered
body by a rapidly increased temperature in a silicide reaction
because the silicide reaction is an exothermic reaction, and when
the semi-sintered body is sintered by pressing in the state as it
is, a resultant sintered body cannot be used because the cracks
remain.
[0014] There is also a problem that since a mixed material powder
overflows from a vessel by the rapid increase of temperature in the
silicide reaction and a composition is out of an intended
composition due to the volatilization of very volatile Si. Thus,
when the semi-sintered body is sintered by pressing in the state as
it is, a target having a desired composition cannot be
obtained.
[0015] Further, there is a problem that even if a semi-sintered
body is crushed and made to a powder, since hard MSi.sub.2
particles which have been grown once and coarsened remain without
being finely crushed, a target having a uniform and fine structure
cannot be obtained as well as an amount of contamination caused by
impurities is increased by crushing and in particular an amount of
oxygen is greatly increased.
[0016] On the other hand, as disclosed in Japanese Patent
Application Laid-Open No. Sho 62(1987)-171911, when a mixed powder
is subjected to a silicide synthesization at 800-1300.degree. C.
and further deoxidized by being heated to high temperature so as to
reduce impurity oxygen, there is a problem that since the sintering
property of a resultant semi-sintered body is excessively improved,
the semi-sintered body cannot be sufficiently crushed in a
subsequent crushing process and formed to a segregated structure in
which MSi.sub.2 and Si are irregularly dispersed, and in
particular, when a heating temperature reaches a temperature region
exceeding 1400.degree. C., this tendency is made more
remarkable.
[0017] Although a semi-sintered body is crushed in an atmosphere
replaced with Ar (argon gas) to prevent an increase of an oxygen
content, it is difficult to completely prevent the contamination by
oxygen when the semi-sintered body is crushed. Further, a problem
also arises in that when a crushed powder is taken out from a
vessel such as a ball mill or the like, the powder surely adsorbs
oxygen to increase oxygen contained therein, and as a result a
finely crushed powder has an increased surface area and an amount
of oxygen adsorbed by the powder is greatly increased.
[0018] On the other hand, even if a synthesized powder was hot
pressed while applying a preload of 60-170 kg/cm.sup.2 thereto
according to the methods of Japanese Patent Application Laid-Open
No. Sho 63(1988)-74967 and Japanese Patent Application Laid-Open
No. Sho 64(1989)-39374, condensed silicon was disadvantageously
produced and a target having a fine and uniform structure could not
be obtained.
[0019] Further, when a synthesized powder was hot pressed without
being applied with a preload, MSi.sub.2 grains obtained by
synthesization was grown as well as a composition has an inclined
distribution in a target and it was difficult to obtain a target
having a fine and uniform structure.
[0020] Japanese Patent Application Laid-Open No. Sho 62(1987)-70270
discloses a refractory metal silicide target having a density ratio
not less than 97%. Further, Japanese Patent Application Laid-Open
No. Sho 62(1987)-230676 discloses a methods of manufacturing a
refractory metal silicide target and describes that a target is
molded by compacting using a single axis under the conditions of
high temperature, high vacuum and high pressing pressure.
[0021] However, the above respective prior arts describe only that
a target is made by subjecting a material powder for the target to
hot pressing and no description is made as to a fine and uniform
structure. Thus, these prior arts cannot achieve an object for
effectively suppressing particles.
[0022] On the other hand, International Patent Application
published according to PCT (No. WO91/18125 discloses a silicide
target having 400.times.10.sup.4 pieces of silicide with a grain
size of 0.5-30 .mu.m existing in a cross section of the mixed
structure of the target of 1 mm.sup.2 with the maximum grain size
of Si not greater than 30 .mu.m and further a silicide target with
the average grain size of silicide of 2-15 .mu.m and the average
grain size of Si of 2-10 .mu.m.
[0023] Since the manufacturing method described in the prior art is
insufficient to obtain a fine uniform target structure, the object
to suppress the occurrence of particles cannot be sufficiently
achieved.
[0024] An object of the present invention is to provide a high
density and purity refractory metal silicide target which has a
fine mixed structure and a uniform composition as well as contains
a less amount of impurities such as oxygen and the like, a method
of manufacturing the target, a refractory metal silicide thin film
and a semiconductor device.
DISCLOSURE OF THE INVENTION
[0025] As a result of a zealous study why particles are generated,
the inventors of this invention have obtained the following
knowledge for the first time:
[0026] (1) since free Si has a sputtering rate larger than that of
MSi.sub.2, as sputtering proceeds, MSi.sub.2 is exposed on an
erosion surface and MSi.sub.2 grains having a weak bonding force
with adjacent grains are liable to be removed from the erosion
surface, and in particular very fine MSi.sub.2 grains remarkably
exhibit this tendency;
[0027] (2) although the form of erosion in a free Si portion
exhibits a wave-shape, as the Si portion increases, the distal end
of the wave-shape is made acute and further the height of the
wave-shape increases, thus the distal end of Si is dropped off or
lacked by the thermal fluctuation in sputtering so that Si is
liable to become particles; and
[0028] (3) when pores remain in the interface between MSi.sub.2 and
free Si of a target or in the interior of free Si, projections are
formed around the pores, and abnormal electric discharge occurs in
the portion where the projections exist in sputtering, by which the
projections are dropped or lacked and made to particles, and the
like.
[0029] Further, the inventors have found it is very effective to
suppress the generation of the particles that:
[0030] (1) a fine mixed structure is formed such that the number of
MSi.sub.2 grains (M: refractory metal) which independently exist on
any arbitrary surface or in a cross section of 0.01 mm.sup.2 of the
mixed structure is not greater than 15, MSi.sub.2 has an average
grain size not greater than 10 .mu.m and free Si existing in the
gaps of MSi.sub.2 has a maximum grain size not greater than 20
.mu.m;
[0031] (2) the mixed structure is arranged such that a Si/M atom
ratio X in 1 mm.sup.2 of the mixed structure has a dispersion of
X.+-.0.02 and free Si is uniformly dispersed; and
[0032] (3) a density ratio is not less than 99.5% over the entire
surface of a target, and the like.
[0033] Further, the inventors have found that the growth of
MSi.sub.2 grains produced can be suppressed and a large dislocation
(dispersion of a composition ratio) of a composition can be
prevented without volatilizing almost all the Si in such a manner
that when silicide is synthesized once in a silicide synthesizing
process, mixed powders each divided to a small amount of lot are
charged into a compacting mold, that is, a depth of the compacting
mold to which the mixed powders are charged is set to not deeper
than 20 mm and the mixed powders are heated in vacuum and
synthesized.
[0034] Further, to reduce impurities in a target and increase its
purity, the inventors have found that:
[0035] (1) a refractory metal silicide semi-sintered body
containing a less amount of oxygen not greater than 200 ppm which
cannot be obtained by prior art can be obtained in such a manner
that a semi-sintered body obtained by synthesizing silicide is
crushed once and a resultant crushed powder is deoxidized by being
heated in vacuum or in a pressure-reduced hydrogen atmosphere in
stead of deoxidizing the semi-sintered body by heating it in the
state as it is;
[0036] (2) when a plurality of powder charging vessels each having
the same inside diameter are prepared and crushed powders are
deoxidized so that semi-sintered bodies can be sintered in a shape
as they are by a hot isostatic press method or the like, since the
semi-sintered bodies have the same shape, a plurality of
semi-sintered bodies can be sintered at the same time and there is
an advantage that the productivity of targets can be improved;
[0037] (3) when the silicide synthesis is performed in a vacuum
furnace using a graphite heater and insulator, a semi-sintered body
obtained by the synthesization is mixed with carbon and iron and
contaminated by them. In contrast, when the silicide synthesis is
performed in a vacuum furnace using a heater and an insulator each
composed of a high purity refractory material, the contamination
can be effectively prevented; and
[0038] (4) contamination caused by impurities contained in a
material can be effectively prevented by crushing a semi-sintered
body in a ball mill having a ball mill main body the inside of
which is lined with a high purity material and crushing mediums
(balls) formed of a high purity material, and the like.
[0039] Further, as a result of a zealous study of hot pressing
conditions effected by using a synthesized powder, the inventors
have found that the size of MSi.sub.2 grains produced is different
depending upon a temperature for applying a pressing pressure and
how the temperature is increased and that the composition in a
target has an inclined distribution in accordance with the
temperature and pressure conditions. More specifically, the
inventors have found that when a synthesized powder is heated up to
just below an eutectic temperature and then applied with a pressing
pressure, MSi.sub.2 grains formed by synthesization are regrown and
that free Si flows in the direction of the end of a target and its
composition has an inclined irregular distribution as the MSi.sub.2
grains grow.
[0040] Further, the inventors have obtained the knowledge that when
a certain degree of a pressing pressure is applied at a temperature
step less than 1200.degree. C. and then heating is effected
stepwise or at a low rate up to just below an eutectic temperature
and further a larger pressing pressure is applied, the growth of
MSi.sub.2 grains is effectively prevented, the composition in a
target is made uniform and a density of the target is increased for
the first time.
[0041] The present invention has been completed based on the above
knowledges.
[0042] More specifically, a refractory metal silicide target
according to the present invention is characterized by comprising a
fine mixed structure composed of MSi.sub.2 (where M: refractory
metal) grains and Si grains, wherein the number of MSi.sub.2 grains
independently existing in a cross section of 0.01 mm.sup.2 of the
mixed structure is not greater than 15, the MSi.sub.2 grains has an
average grain size not greater than 10 .mu.m, whereas free Si
grains existing in the gaps of the MSi.sub.2 grains have a maximum
grain size not greater than 20 .mu.m. Specifically, W, Mo, Ti, Ta,
Zr, Hf, Nb, V, Co, Cr, Ni are used as the metal (M) constituting
the above metal silicide (MSi.sub.2).
[0043] Note, the shape and the number of MSi.sub.2 grains and Si
grains in the above mixed structure are measured as follows. That
is, the maximum grain size, average grain size and number of
MSi.sub.2 grains are measured in such a manner that a photograph
showing the structure of a target sintered body is obtained by
photographing a fracture surface of the sintered body under a
scanning type electron microscope (SEM) at a magnification ratio of
1000 and thus obtained photograph is then analyzed with an image
analyzer. A visual field to be image-analyzed must cover 10
points.
[0044] On the other hand, the maximum grain size, average grain
size and number of free Si grains and chain-shaped (link-formed) Si
grains are measured in such a manner that a photograph showing the
structure of a target sintered body is obtained by photographing a
polished surface of the sintered body under a scanning type
electron microscope (SEM) at a magnification ratio of 1000, then
the photograph is analyzed with an image analyzer. In that case, 5
cross sections obtained by equally dividing the polished surface in
the thickness direction thereof at a pitch of 10 .mu.m were
measured and when Si grains are freed from other Si grains, they
are regarded as free Si, whereas when Si grains are coupled with
other Si grains at any portion thereof, they are regarded as
chain-shaped Si. A visual field must cover 20 points in each cross
section.
[0045] Since Si is more deeply eroded than MSi.sub.2 by sputtering
in the above mixed structure, preferable is a structure arranged
such that MSi.sub.2 grains are coupled each other like a chain and
Si grains exist in the gaps of the MSi.sub.2 grains to reduce
particles generated in a target because MSi, grains are liable to
be removed or dropped from an eroded surface in a portion where
MSi.sub.2 independently exists in Si phase.
[0046] When the size of MSi.sub.2 grains is increased, Si is
selectively scattered from MSi.sub.2 and forms projections like
grains. Since these projections are released and made to particles,
the average grain size of MSi.sub.2 is preferably not greater then
10 .mu.m and more preferably not greater than 5 .mu.m to prevent
the occurrence of the projections. On the other hand, Si is eroded
to a wave-shape by sputtering, and as the size of Si is increased,
the wave-shape is made acute and deep and Si is liable to be lacked
or dropped off. Thus, the maximum grain size of Si is preferably
not greater than 20 .mu.m, more preferably not greater than 15
.mu.m, and further more preferably not greater than 10 .mu.m.
[0047] When the average value of a Si/M atom ratio in an entire
target is assumed to be X, it is preferable that the dispersion of
the Si/M atom ratio in an arbitrary cross section of 1 mm.sup.2 in
the mixed structure is preferably set within the range of
X.+-.0.02. That is, when MSi.sub.2 and Si irregularly disperse even
if a target has a fine structure, in particular when free Si is
locally concentrated and irregularly distributed, since the
structure in the target is greatly changed as well as a plasma
electric discharge is unstably carried out and particles are
induced, the dispersion of the Si/M atom ratio X in an area of 1
mm.sup.2 is preferably X.+-.0.02 and more preferably X.+-.0.01.
[0048] It is preferable to form a high density silicide target in
which the density ratio of a target is not less than 99.5% over the
entire target. When there remain many pores (holes) due to an
insufficient density of a target, the pores exist in an interface
between MSi.sub.2 and Si or in the interior of Si, projections are
formed around the pores in sputtering, an abnormal electric
discharge is caused in the portion of the projections and the
projections are broken and released by the discharge, which results
in the occurrence of particles. Thus, the pores must be reduced as
few as possible, and for this purpose, the density ratio of target
is preferably not less than 99.5%, more preferably not less than
99.7% and further more preferably not less than 99.8% over the
entire target.
[0049] It is preferable that a content of oxygen as an impurity is
set to not greater than 200 ppm and a content of carbon as an
impurity is set to not greater than 50 ppm. When oxygen is taken
into a deposited thin film by sputtering a target containing
oxygen, silicon oxide is formed in the interface of the thin film
and a resistance of the film is increased by the silicon oxide.
Thus, to further reduce the resistance of the film, an oxygen
content in target is preferably set to not greater than 200 ppm and
more preferably not greater than 100 ppm. Further, since carbon
also increases a resistance of the film by forming silicon carbide,
a carbon content in target is preferably set to not greater than 50
ppm and more preferably not greater than 30 ppm to reduce the
resistance of the film.
[0050] The contents of iron and aluminium as impurities are set to
not greater than 1 ppm, respectively. When iron and aluminium are
mixed into a deposited thin film, a deep level is formed in the
interface of the thin film and causes a leakage in connection, by
which a semiconductor is poorly operated and its characteristics
are deteriorated. Thus, an iron content and aluminium content in
target are preferably set to not greater than 1 ppm, respectively
and more preferably not greater than 0.5 ppm, respectively.
[0051] Next, a method of manufacturing a refractory metal silicide
target according to the present invention will be described
below.
[0052] In a process I (step I), a refractory metal powder having a
maximum grain size not greater than 15 .mu.m is blended with a
silicon powder having a maximum grain size not greater than 30
.mu.m such that a Si/M atom ratio (value X in MSi.sub.x) is 2-4 and
these powders are sufficiently mixed each other in a dry state
using a ball mill, V-type mixer or the like so that the silicon
powder uniformly disperses in the refractory metal powder. The
irregularly mixing of them is not preferable because the structure
and composition of a target is made irregular and characteristics
of the film formed by using the target are deteriorated. The
powders are preferably mixed in a vacuum of not higher than
1.times.10.sup.-3 Torr or in an inert gas atmosphere such as an
argon gas to prevent contamination by oxygen. In particular, when a
pulverizer or powder crushing mixer such as a ball mill or the like
is used, contamination by impurities can be effectively prevented
by performing mixing operation in a dry state using a ball mill
having a main body the inside of which is lined with a high purity
material not less than 5N (99.999%) and crushing mediums (balls)
composed of a high purity material so that contamination caused by
impurities from a crusher main body can be prevented.
[0053] The same material as the refractory metal (M) constituting a
target is preferably used as the above high purity material and,
for example, W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cr, Ni etc. are
used.
[0054] As a method of lining the pulverizer main body with the high
purity material, there can be employed a method of lining a high
purity material sheet, a method of integrally forming a high purity
material layer on the inner surface of a main body by various
depositing methods such as CVD, plasma vapor deposition, and the
like.
[0055] The refractory metal powder and silicon powder used as a
target material preferably contain impurities, which deteriorate
characteristics of a semiconductor device, in an amount as small as
possible and preferably have a purity not lower than 5N (99.999%).
Further, since coarse powders coarsen formed MSi.sub.2 grains and
si grains and lowers the dispersing property of Si, the refractory
metal powder preferably has a gain size not greater than 15 .mu.m
and the silicon powder preferably has a grain size not greater than
30 .mu.m. Further, the refractory metal powder preferably has a
grain size not greater than 10 .mu.m and the silicon powder
preferably has a grain size not greater than 20 .mu.m. Furthermore,
the refractory metal powder preferably has a gain size not greater
than 5 .mu.m and the silicon powder preferably has a grain size not
greater than 10 .mu.m.
[0056] A reason why the value X of the Si/M atom ratio is limited
to 2.ltoreq.X.ltoreq.4 is as described below. That is, when the
value X is less than 2, free Si reduces and further disappear in a
silicide target and the structure defined by the present invention
cannot be obtained. On the other hand, when the value X exceeds 4,
since free Si continuously exists, there is obtained a structure in
which MSi.sub.2 grains exist in a Si matrix. Consequently, the
structure of the present invention that MSi.sub.2 grains are
coupled each other like a chain and Si grains exist in the gaps of
the MSi.sub.2 grains is difficult to be obtained. Further, when the
value X is less than 2, since a large tensile strength is produced
in a formed silicide film, the close contact property of the film
with a substrate is deteriorated and the film is liable to be
exfoliated or peeled from the substrate. On the other hand, when
the value X exceeds 4, since a film resistance increases, a
resultant film is improper as an electrode wiring film. Further,
when a mixed powder having the value X not less than 2 is
synthesized to silicide, since free Si exists, there is an
advantage that a crushing property is improved in a process III to
be described below.
[0057] Si is preferably blended in an amount which is a little in
excess of the amount of an intended composition by taking an loss
caused by the volatilization of a Si and SiO.sub.2 film covering
the surface of Si powders into account.
[0058] A process II is a process for synthesizing refractory metal
silicide as well as forming a semi-sintered body by charging the
mixed powder prepared in the process I into a compacting mold and
heating the powder in high vacuum or in an inert gas atmosphere. In
the process II, since an amount of the mixed powder to be charged
into the compacting mold and subjected to a synthesizing operation
effected once affects the size of MSi.sub.2 grains to be produced
and an amount of Si to be volatilized, it is preferable to set an
amount of the mixed powder charged once to a depth not higher than
20 mm. When the depth of charge exceeds 20 mm, formed MSi.sub.2
grains are coarsened due to a temperature increase caused by a
silicide reaction and the powder may be caused to overflow from the
vessel by an explosive reaction. On the other hand, when the mixed
powder to be charged into the vessel has a depth not higher than 1
mm, the number of vessels used for a single target is greatly
increased as well as an amount of production per a synthesizing
treatment is greatly reduced, and productivity is lowered. Thus, a
preferable depth of charge is 1-10 mm. When Mo is used as a
refractory metal powder, however, an amount of the mixed powder to
be charged into a vessel is preferably set to a depth not higher
than 10 mm and more preferably a depth not higher than 5 mm because
a particularly high calorific value is generated by a silicide
reaction.
[0059] A vessel used here is preferably composed of a high purity
Mo, W, Ta, Nb material or the like to prevent the contamination of
the mixed powder caused by impurities generated from the vessel and
thermal deformation. Further, it is preferable to use the same
metal material as a refractory metal (M) constituting intended
refractory metal silicide. Further, the flat portion of the vessel
may be set to such a shape and size as to enable the vessel to be
inserted into calcining equipment such as sintering furnace.
[0060] As a heating pattern, it is preferable to effect heating
stepwise from a temperature 200.degree. C. lower than a silicide
reaction start temperature to suppress the growth of MSi.sub.2
grains and minimize the change of a composition. A temperature
increasing width is preferably 20-200.degree. C. That is, when the
temperature increasing width is less than 20.degree. C., a long
time is needed to synthesization and productivity is lowered,
whereas the width exceeds 200.degree. C. MSi.sub.2 grains are grown
and the powder is caused to overflow from the vessel by an abrupt
increase of temperature, and a composition is changed and the
interior of the furnace is contaminated. Further, each temperature
is preferably held for 0.1-3 hours. When the holding time is less
than 0.1 hour, the temperature of the powder in the vessel is not
made uniform and a temperature difference abruptly increases, and
MSi.sub.2 grains are coarsened. On the other hand, when the holding
time exceeds 3 hours, a long time is needed for synthesization and
productivity is lowered. Note, the temperature increasing width is
preferably set to 20-200.degree. C. and more preferably to
50-100.degree. C. and the holding time is more preferably set to
the range of 0.5-2 hours. In particular, when the temperature is
increased to a temperature of 100.degree. C. or more higher than
the silicide reaction start temperature, it is preferable to set a
long holding time at the silicide reaction start temperature or
within the start temperature+50.degree. C. and the holding time is
preferably not shorter than 1 hour. The silicide reaction start
temperature can be determined by detecting when a degree of vacuum
in the furnace is lowered by the volatilization of Si or silicon
oxide (SiO or Sio.sub.2) caused by a reaction heat.
[0061] Further, the same effect can be achieved by carrying out
heating operation slowly in place of the stepwise heating. In this
case, a heating rate is preferably controlled to 5.degree.
C./minute or less. When the heating rate is excessively large,
MSi.sub.2 grains are grown as well as the powder is caused to
overflow from the vessel, the composition is changed and the
interior of a furnace is contaminated by the abrupt increase of the
temperature.
[0062] A maximum heating temperature in synthesization is
preferably increased up to 1100.degree. C. so that a silicide
reaction starts and synthesization is completed. Since a reaction
temperature is different depending upon an amount of oxygen
contained in the mixed powder, however, the maximum heating
temperature is preferably increased to about 1300.degree. C. by
taking the reduction of the oxygen content into consideration. When
the temperature is increased to higher than 1300.degree. C., the
sintering of a semi-sintered body formed by a silicide reaction
proceeds and its crushing in a process III is made difficult and
further free Si is melted as well as MSi.sub.2 grains are grown and
coarsened by an eutectic reaction. Thus, there is obtained a
structure in which MSi.sub.2 grains and Si grains irregularly
disperse and as a result a silicide target having an intended
crystal structure cannot be obtained. On the other hand, when the
maximum heating temperature is not higher than 1000.degree. C., the
silicide reaction does not start and synthesization is made
impossible except the case that M is Ni. Thus, a more preferable
temperature range is 1150-1250.degree. C.
[0063] Note, when the above maximum heating temperature is
excessively high in the case M is Ni, sintering is liable to
proceed as compared with the case M is other than Ni. Thus, the
temperature is preferably increased up to about 800.degree. C. and
more preferably in the range of 700-800.degree. C. only when Ni is
used.
[0064] When a refractory metal silicide is synthesized as well as a
semi-sintered body is formed in the process II, a vacuum furnace
employed for heating is preferably, for example, a vacuum furnace
using a high purity Mo heater or a high purity W heater and an
insulator composed of a high purity refractory material, by which a
semi-sintered body obtained by synthesization can be effectively
protected from contamination caused by impurities from the heater
and insulator.
[0065] In a process III, a refractory metal silicide semi-sintered
body which is obtained by synthesizing silicide and has an atom
ratio X of 2.ltoreq.X.ltoreq.4, is crushed or pulverized and a
crushed powder is prepared. A powder lump in which free Si
segregated to an aggregation of MSi.sub.2 formed in synthesization
exists is finely crushed and uniformly dispersed by the crushing
process. When this dispersing operation is no effected uniformly,
since the dispersion of MSi.sub.2 and free Si is lowered, the
structure and composition of a target are not uniformly arranged
and a film characteristics are deteriorated, a crushing time is
preferably not shorter than 24 hours. On the other hand, although
the longer the crushing time, the more improved is a crushing
efficiency, since productivity is lowered and an amount of
contamination is increased by oxygen, the crushing time is
preferably not longer than 72 hours. The maximum grain size of a
powder obtained by the crashing is an important factor for
obtaining a fine uniform structure defined by the present
invention. Therefore, the maximum grain size is preferably not
greater than 20 .mu.m and more preferably not greater than 15 .mu.m
in order to obtain the structure defined by the present invention
that MSi.sub.2 grains have an average grain size not greater than
10 m and free Si grains have a maximum grain size not greater than
20 .mu.m.
[0066] The crushing is preferably effected in vacuum or in an inert
gas atmosphere similarly to the process I to prevent the
contamination by oxygen. In particular, when a crushing mixer such
as a ball mill or the like is used, contamination by impurities can
be effectively prevented by carrying out mixing operation in a dry
state using a ball mill having a main body the inside of which is
lined with a high purity material and crushing mediums (balls)
composed of a high purity material so that contamination caused by
impurities from the crusher main body can be prevented.
[0067] Further, it is preferable that the following impurity
removing process is followed by the process III to remove
impurities contained in the crushed power such as oxygen, carbon
etc. That is, the impurity removing process is a process for
heating the crushed powder prepared in the process III and
preparing a high purity powder and a high purity semi-sintered body
by removing impurities such as in particular oxygen and the like
therefrom. A heating temperature is preferably set to
1150-1300.degree. C. to effectively remove oxygen adsorbed to the
crushed power. More specifically, when the heating temperature is
less than 1150.degree. C., it is difficult to obtain a low oxygen
target containing oxygen in a amount not greater than 200 ppm by
volatilizing and removing oxygen as silicon oxide (SiO or
SiO.sub.2). On the other hand, when the heating temperature exceeds
1300.degree. C., a problem arises in that free Si is greatly
volatilized and lost, and it is difficult to obtain a target having
a predetermined composition, and further a semi-sintered body is
cracked, sintering proceeds and an amount of contraction increases,
and the semi-sintered body cannot be hot pressed in the state as it
is. Consequently, a more preferable temperature range is
1200-1250.degree. C.
[0068] In particular, when the heating temperature increases, since
the semi-sintered body is liable to be cracked, it is preferable
that the semi-sintered body is processed while applying a low
pressing pressure thereto. The pressure is preferably in the range
not greater than 10 kg/cm.sup.2.
[0069] Further, the above heating temperature is preferably held
for 1-8 hours. When the holding time is shorter than 1 hour, oxygen
is insufficiently removed, whereas when the time exceeds 8 hours, a
long time is needed and productivity is lowered as well as a large
amount of Si is volatilized and lost, and the dislocation of the
composition of a silicide target increases. Thus, the holding time
is more preferably set to the range of 2-5 hours.
[0070] A degree of vacuum is preferably set to not higher than
10.sup.-3 Torr and further to not higher than 10.sup.-4 Torr to
more effectively reduce oxygen by volatilizing silicon oxide. A
further deoxidizing effect can be obtained and a target containing
a less amount of oxygen can be obtained in such a manner that after
the degree of vacuum is adjusted, hydrogen is introduced into a
heating furnace and the target is heated in a pressure-reduced
hydrogen atmosphere.
[0071] A vessel into which the crushed powder is charged may have a
shape and size equal to those of a compacting mold to be used in a
sintering process such as a hot pressing or the like to be
described later or may be formed to a size determined by taking an
amount of contraction of a semi-sintered body caused by calcination
into consideration. As a result, there can be obtained an advantage
that a deoxidized semi-sintered body can be easily inserted into
the compacting mold and a plurality of semi-sintered bodies can be
simultaneously sintered, and productivity can be greatly improved.
The vessel is preferably composed of a high purity material of Mo,
W, Ta, Nb or the like to prevent the contamination of the crushed
powder by impurities and thermal deformation.
[0072] The crushed powder charged into the vessel is preferably
smoothed by a dedicated pattern and made to flat by moving the
powder forward and backward and in rotation so that the deoxidized
semi-sintered body can be hot-pressed in the state as it is.
[0073] In a process IV, a crushed powder prepared in the process
III or a semi-sintered body having been subjected to the impurity
removing process is subjected to a main sintering and densification
or compaction. The crushed powder or semi-sintered body having been
subjected to the impurity removing process whose Si/M atomic ratio
is adjusted to 2-4 and which is composed of MSi.sub.2 and excessive
Si is charged into the compacting mold and sintered and densified
while setting a temperature and pressure at two steps.
[0074] The compacting mold to be used here is preferably a graphite
compacting mold arranged such that, for example, a BN powder or the
like having an exfoliation resistance at high temperature is coated
on the inner surface of the mold with a spray or brush as a mold
releasing agent and further a partition plate is applied onto the
inside surface through a double-coated adhesive tape, adhesive or
the like. The mold releasing agent is coated to prevent a
compacting mold main body from being fused to the partition plate
in hot pressing. The partition plate is provided to prevent the
direct contact of the semi-sintered body with the mold releasing
agent and isolate the former from the latter. As the partition
plate, a refractory metal such as Mo, W, Ta, Nb etc. enduring high
temperature in sintering and Ni, Ti etc. excellent in workability
and processability is used by being formed to a thickness of
0.1-0.2 mm. When the partition plate is excessively thick, since
its strength is increased, the formability of the plate is lowered
when it is applied onto the compacting mold and workability is
lowered as well as since the partition plate is adhered onto a
sintered body, a long time is needed to remove it by grinding or
the like. On the other hand, when the partition plate is too thin,
since its strength is small, the plate is difficult to handle and
workability is also lowered.
[0075] The fusion of the compacting mold with the partition plate
is prevented as well as the mold releasing agent is not exfoliated
and removed and the mixing of impurities contained in the mold
releasing agent with a sintered body can be effectively prevented
by coating the mold releasing agent on the inner surface of the
mold and further using the compacting mold on which the partition
plate is applied. In particular, even if BN is used as the mold
releasing agent, the contamination of a target caused by inevitably
contained impurities such as aluminium, iron etc. can be
effectively prevented.
[0076] Next, sintering is carried out by applying a low pressing
pressure of 10-50 kg/cm.sup.2 in a high vacuum not higher than
10.sup.-3 Torr and increasing a temperature up to just below an
eutectic temperature stepwise or at a small temperature increasing
rate.
[0077] A pressing pressure is preferably set to 10-50 kg/cm.sup.2
at a first step because the pressure affects the remaining of
aggregated silicon and the grain size of MSi.sub.2. When the
pressing pressure is less than 10 kg/cm, MSi.sub.2 grains grow as
well as a composition is not uniformly distributed. On the other
hand, when the pressure is not less than 50 kg/cm.sup.2, the
ductile flow of free Si is suppressed and aggregated Si remains,
and a structure in which Si is not uniformly dispersed is obtained.
The pressure is more preferably 20-30 kg/cm.sup.2.
[0078] When sintering is carried out by increasing a temperature up
to just below an eutectic temperature while applying a pressure,
heating is preferably effected stepwise or at a low temperature
increasing rate to suppress the growth of MSi.sub.2 grains. A
temperature increasing width is preferably 20-200.degree. C. When
the temperature increasing width is less than 20.degree. C., a long
time is needed for sintering and productivity is lowered, whereas
when the width exceeds 200.degree. C., MSi.sub.2 grains are grown
by an abrupt temperature increases as well as a composition has an
inclined distribution in a target plane due to the flow of free Si.
Further, each temperature is preferably held for 0.1-3 hours. When
the holding time is less than 0.5 hour, the temperature of a
sintered body in a mold is not uniformly distributed, whereas when
the time exceeds 2 hours, a long time is needed and productivity is
lowered. Thus, it is more preferable that the temperature
increasing width is set to the range of 50-100.degree. C. and the
holding time is set to the range of 0.5-2 hours.
[0079] Further, when a heating rate exceeds 20.degree. C./minute in
the heating effected at a low rate, MSi.sub.2 grains are coarsened.
Thus, the heating rate is preferably set to not higher than
20.degree. C./minute. Further, when the heating rate is less than
3.degree. C./minute, since a long time is needed to sintering
operation and productivity is lowered, it is preferably set to the
range of 3-20.degree. C./minute and more preferably to the range of
5-10.degree. C./minute.
[0080] A final sintering temperature T is preferably set to just
below an eutectic temperature, i.e., to the range of
Ts-50.ltoreq.T<Ts. When, for example, W, Mo, Ti, Ta are used as
M, the eutectic temperature Ts is 1400, 1410, 1330, 1385.degree.
C., respectively. Note, the eutectic temperature Ts can be easily
obtained by referring to literatures such as "Constitution of
Binary Alloys" (Dr. phil. Max Hansen and Dr. Kurt Anderko;
McGraw-Hill Book Company, 1958) and the like. When T is not higher
than (Ts-50), pores remain and a desired high density target cannot
be obtained, whereas when T is not less than Ts, free Si is melted
and flows out from the compacting mold and a target with a
dislocated composition is obtained.
[0081] Since a pressing pressure at a second step affects the
density of a resultant sintered body, the pressure is preferably
set to 200-500 kg/cm.sup.2. When the pressing pressure is less than
200 kg/cm.sup.2, a sintered body with a density not less than 99%
cannot be obtained, whereas when the pressure is not less than 500
kg/cm.sup.2, a graphite compacting mold is liable to be broken.
Thus, the pressing pressure is more preferably set to the range of
300-400 kg/cm.sup.2.
[0082] The pressing pressure is preferably applied in 1-5 hours
after a final temperature is reached. When the period of time is
less than 1 hour, the temperature of a semi-sintered body in a mold
is not made uniform and when the pressing pressure is applied in
this state, a problem arises in that a uniform density distribution
and uniform structure cannot be obtained due to an irregular
temperature distribution. On the other hand, when the time exceeds
5 hours, although the temperature of the semi-sintered body in the
mold is completely made uniform, the holding of the semi-sintered
body longer than this time lowers productivity. Thus, the holding
time is preferably 2-3 hours.
[0083] Further, the pressing pressure is preferably held for 1-8
hours. When the holding time is not longer than 1 hour, many pores
remain and a high density target cannot be obtained, whereas when
it is not shorter than 8 hours, since densification does not
further proceed, the manufacturing efficiency of a target is
lowered. Thus, the holding time is more preferably 3-5 hours. The
sintering for the densification is preferably carried out in vacuum
to prevent the contamination caused by the mixture of
impurities.
[0084] An intended sputtering target can be finally obtained by
machining a resultant sintered body to a predetermined shape. At
that time, it is preferable to finish the sintered body by a
machining method which does not produce a surface defect on the
surface of the target.
[0085] A high purity silicide thin film can be formed by effecting
sputtering using the target. Further, various electrodes such as a
gate electrode, source electrode, drain electrode and thin film for
a semiconductor device and a thin film for wiring materials can be
formed by subjecting the thin film to etching and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0086] FIGS. 1A and 1B are electron microphotographs showing the
metal structures of the polished surface and fracture surface of a
target according to Example 1, respectively;
[0087] FIGS. 2A and 2B are electron microphotographs showing the
metal structures of the polished surface and fracture surface of a
target according to Example 6, respectively;
[0088] FIGS. 3A and 3B are electron microphotographs showing the
metal structures of the polished surface and fracture surface of a
target according to Comparative Example 1, respectively;
[0089] FIGS. 4A and 4B are electron microphotographs showing the
metal structures of the polished surface and fracture surface of a
target according to Comparative Example 4, respectively;
[0090] FIG. 5 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Example 11;
[0091] FIG. 6 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Comparative Example 7;
[0092] FIG. 7 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Comparative Example 8;
[0093] FIG. 8 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Example 12;
[0094] FIG. 9 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Comparative Example 9; and
[0095] FIG. 10 is an electron microphotograph showing the metal
structure of the surface of a target semi-sintered body according
to Comparative Example 10.
BEST MODE FOR CARRYING OUT THE INVENTION
[0096] An arrangement and advantage of the present invention will
be described in more detail with reference to the following
examples.
EXAMPLES 1-10
[0097] A high purity M powder (M: W, Mo shown in Table 1) having a
maximum grain size of 15 .mu.m and a high purity Si powder having a
maximum grain size of 30 .mu.m were prepared and the respective
powders were charged into a ball mill the inside of which was lined
with high purity Mo together with high purity Mo balls and then
mixed for 48 hours with the replacement with an Ar gas. Each of the
resultant mixed powders was charged into a high purity Mo vessel
with a charging depth set to 3 mm when M=Mo (weight to be charged
was about 250 g) and to 10 mm when M=W (weight to be charged was
about 750 g) and silicide was synthesized in such a manner that the
temperature of the vessel was increased stepwise from 950.degree.
C. to 1300.degree. C. with a temperature width in each step of
50.degree. C. in a vacuum not higher than 1.times.10.sup.-4 Torr
using a vacuum furnace having a Mo heater and Mo insulator with a
holding time at each step of temperature set to 1 hour. The high
purity materials used had a purity not less than 5N (not less than
99.999%).
[0098] Next, each of semi-sintered bodies obtained by synthesizing
the silicide was charged into a ball mill the inside of which was
lined with high purity Mo together with high purity Mo balls and
then crushed and pulverized for 72 hours with the replacement of
the inner atmosphere of the ball mill with an Ar gas. The resultant
crushed powder was charged into a high purity Mo vessel having a
diameter of 280 mm and deoxidized by heating the vessel at
1250.degree. C. for 4 hours in a vacuum not higher than 10.sup.-4
Torr.
[0099] Further, the resultant semi-sintered body (about 280 mm in
diameter and 40 mm thick) was set to a graphite compacting mold
lined with a Ta foil, heated to 1000.degree. C. in a vacuum not
higher than 10.sup.-4 Torr and then heated stepwise up to
1380.degree. C. with a temperature width in each step of 50.degree.
C. while applying a pressing pressure of 20 kg/cm.sup.2 thereto
with a holding time at each step of temperature set to 1 hour.
Then, the semi-sintered body was hot pressed by a pressing pressure
of 300 kg/cm.sup.2 applied thereto in 2 hours after the temperature
of the semi-sintered body had reached 1380.degree. C., so that a
sintered body having a diameter of 280 mm and a thickness of 14 mm
was prepared.
[0100] The resultant sintered body was subjected to grinding,
polishing and electric discharging processes and finished to a
target having a diameter of 258 mm and a thickness of 10 mm.
COMPARATIVE EXAMPLES 1-6
[0101] As Comparative Examples 1-6, an M powder equal to that used
in Examples 1-10 was mixed with a Si powder having a maximum grain
size of 50 .mu.m and silicide was synthesized in such a manner that
each of the resultant mixed powders was charged into a vacuum
vessel having a conventional carbon (C) heater and carbon (C)
insulator and heated to 1300.degree. C. at a rate of 10.degree.
C./min in a vacuum not higher than 1.times.10.sup.-4 Torr with a
charging depth set to 6 mm when M=Mo and to 20 mm when M=W.
[0102] Next, the crushed powder was charged into in a graphite
compacting mold without being deoxidized and heated to 1000.degree.
C. in vacuum and then heated up to 1380.degree. C. while applying a
pressing pressure of 200 kg/cm thereto, held for 2 hours and then
hot pressed, in the same way as that of Example 1, so that sintered
bodies each having a diameter of 280 mm and a thickness of 14 mm
were prepared.
[0103] The cross-sectional structures of Example 1-10 and
Comparative Examples 1-6 were observed under a scanning type
electron microscope (SEM) and the number of MSi.sub.2 independently
existing in a cross section of 0.01 mm.sup.2, the average grain
size of MSi.sub.2 and the maximum grain size of Si were measured.
Table 1 shows the result of measurement. Further, FIGS. 1A, 2A, 3A
and 4A show electron microphotographs of the metal structures of
the polished surfaces of target sintered bodies relating to
Examples 1 and 6 and Comparative Examples 1 and 4, respectively.
FIGS. 1B, 2B, 3B and 4B show electron microphotographs of the metal
structures of the fracture surfaces of the above, target sintered
bodies, respectively. Note, the measured values are average values
determined by examining a cross section at 20 positions. Further, a
grain size is shown by the diameter of a minimum circle
circumscribing a grain.
1TABLE 1 AVERAGE NUMBER OF AVERAGE MAXIMUM DISPERSION OF
COMPOSITION INDEPENDENT GRAIN SIZE GRAIN SIZE COMPOSITION SPECIMEN
No. OF TARGET MSi.sub.2 (PIECES) OF MSi.sub.2 (.mu.m) OF Si (.mu.m)
(Si/M ATOMIC RATIO) EXAMPLE 1 WSi.sub.2.8 8 8 14 2.80 .+-. 0.01
EXAMPLE 2 WSi.sub.2.8 5 5 15 2.80 .+-. 0.01 EXAMPLE 3 WSi.sub.2.8 8
5 11 2.80 .+-. 0.01 EXAMPLE 4 WSi.sub.2.8 10 6 9 2.80 .+-. 0.01
EXAMPLE 5 WSi.sub.2.8 14 7 13 2.80 .+-. 0.01 EXAMPLE 6 MoSi.sub.2.7
7 8 14 2.70 .+-. 0.01 EXAMPLE 7 MoSi.sub.2.7 6 7 9 2.70 .+-. 0.01
EXAMPLE 8 MoSi.sub.2.7 8 9 10 2.70 .+-. 0.01 EXAMPLE 9 MoSi.sub.2.7
11 6 11 2.70 .+-. 0.01 EXAMPLE 10 MoSi.sub.2.7 14 6 7 2.70 .+-.
0.01 COMPARATIVE WSi.sub.2.8 17 18 35 2.75 .+-. 0.03 EXAMPLE 1
COMPARATIVE WSi.sub.2.8 24 21 42 2.74 .+-. 0.03 EXAMPLE 2
COMPARATIVE WSi.sub.2.8 30 20 32 2.72 .+-. 0.04 EXAMPLE 3
COMPARATIVE MoSi.sub.2.7 19 22 28 2.63 .+-. 0.03 EXAMPLE 4
COMPARATIVE MoSi.sub.2.7 26 24 38 2.61 .+-. 0.03 EXAMPLE 5
COMPARATIVE MoSi.sub.2.7 34 25 42 2.60 .+-. 0.04 EXAMPLE 6
[0104] As is apparent from the result shown in Table 1 and FIG.
1-FIG. 4, Examples 1-10 have a fine uniform structure in which
MSi.sub.2 grains are linked or coupled with each other like chain,
the less number of MSi.sub.2 independently exist, and Si is
dispersed in the gaps of the MSi.sub.2 and further MSi.sub.2 and Si
have a small grain size as compared with Comparative Examples 1-6.
More specifically, it is found that in the metal structures of the
targets of the examples shown in FIGS. 1 and 2, a mixed structure
is formed such that fine MSi.sub.2 grains shown by gray portions
are coupled with each other like a chain and fine Si grains shown
by black portions disperse among them, whereas in the metal
structures of the targets of the comparative examples shown in
FIGS. 3 and 4, coarse MSi.sub.2 grains (gray portions) and Si
grains (black portions) grow as well as a ratio of fine MSi.sub.2
grains independently existing in a Si phase is increased and thus
the targets have a structure in which particles are liable to be
generated.
[0105] Table 1 also shows the result of analysis of a Si/W atom
ratio in a cross section of 1 mm.sup.2 of the mixed structure of
each target effected by a surface analyzing instrument (X-ray
microanalyzer: EPMA). It is found from the result of analysis that
the Examples 1-10 have compositions nearer to an intended
composition as compared with the Comparative Examples 1-6 and
further have uniform compositions.
[0106] Table 2 shows the result of measurement of the densities of
the respective targets and the result of analysis of oxygen,
carbon, iron and aluminium.
2 TABLE 2 DISPERSION OF NUMBER OF AVERAGE COMPOSITION DENSITY RATIO
AMOUNT OF IMPURITY (ppm) PARTICLES SPECIMEN No. OF TARGET (%)
O.sub.2 C Fe Al (PIECES) EXAMPLE 1 WSi.sub.2.8 99.8 .+-. 0.1 153 35
0.3 0.2 5 EXAMPLE 2 WSi.sub.2.8 99.7 .+-. 0.1 130 28 0.2 0.3 12
EXAMPLE 3 WSi.sub.2.8 99.7 .+-. 0.2 186 24 0.4 0.1 19 EXAMPLE 4
WSi.sub.2.8 99.8 .+-. 0.1 120 31 0.5 0.3 25 EXAMPLE 5 WSi.sub.2.8
99.8 .+-. 0.1 87 19 0.4 0.3 30 EXAMPLE 6 MoSi.sub.2.7 99.7 .+-. 0.2
95 24 0.3 0.1 6 EXAMPLE 7 MoSi.sub.2.7 99.7 .+-. 0.1 122 18 0.2 0.2
11 EXAMPLE 8 MoSi.sub.2.7 99.8 .+-. 0.1 105 27 0.4 0.4 20 EXAMPLE 9
MoSi.sub.2.7 99.8 .+-. 0.1 145 36 0.3 0.2 24 EXAMPLE 10
MoSi.sub.2.7 99.7 .+-. 0.1 116 33 0.3 0.1 33 COMPARATIVE EXAMPLE 1
WSi.sub.2.8 99.0 .+-. 0.3 893 128 1.8 1.4 235 COMPARATIVE EXAMPLE 2
WSi.sub.2.8 98.8 .+-. 0.4 952 133 2.3 1.6 280 COMPARATIVE EXAMPLE 3
WSi.sub.2.8 98.5 .+-. 0.3 1025 121 2.1 1.2 322 COMPARATIVE EXAMPLE
4 MoSi.sub.2.7 99.1 .+-. 0.3 1230 158 3.4 2.4 256 COMPARATIVE
EXAMPLE 5 MoSi.sub.2.7 98.8 .+-. 0.4 1304 168 2.8 2.6 293
COMPARATIVE EXAMPLE 6 MoSi.sub.2.7 98.6 .+-. 0.4 1156 150 3.1 2.1
335
[0107] As apparent from the result shown in Table 2, since the
target relating Examples 1-10 have a density ratio not less than
99.5%, it found that Examples 1-10 have a very small content of
impurities as compared with Comparative Examples 1-6.
[0108] The respective sputtering targets relating to Examples 1-10
and Comparative Examples 1-6 were set to a magnetron sputtering
apparatus and sputtered under the condition of an argon pressure of
2.3.times.10.sup.-3 Torr and a silicide film was deposited on a 6
inch Si wafer to about 3000 .ANG. thick. The same operation was
effected 10 times and an amount of mixed particles having a
particle size not less than 0.2 .mu.m was measured and Table 2 also
shows the result of the measurement. As apparent from the result
shown in Table 2, it is found that according to the targets
relating to Examples 1-10, the number of particles mixed onto the 6
inch wafer is not greater than 33 and very small, whereas according
to Comparative Examples 1-6, a lot of particles which are about 10
times those of Examples 1-10 are generated.
EXAMPLE 11
[0109] 4658 g of a high purity (5N) W powder having a maximum grain
size of 8 .mu.m and 1992 g of a high purity (5N) Si powder having a
maximum grain size of 30 .mu.m were prepared, the respective
powders were charged into a ball mill the inside of which was lined
with high purity Mo together with high purity Mo balls and then
mixed for 48 hours with the replacement of the inner atmosphere of
the ball mill with an argon gas. The resultant mixed powder having
a Si/W atomic ratio of 2.80 was divided to each charging depth of 3
mm (weight to be charged was about 250 g) and charged into a high
purity Mo vessel and silicide was synthesized in such a manner that
the temperature of the vessel was increased stepwise from
950.degree. C. to 1300.degree. C. with a temperature width in each
step of 50.degree. C. in a vacuum not higher than 1.times.10.sup.-4
Torr using a vacuum furnace having a Mo heater and Mo insulator
with a holding time at each step of temperature set to 1 hour, so
that semi-sintered bodies of Example 11 were prepared.
COMPARATIVE EXAMPLES 7-8
[0110] On the other hand, a semi-sintered body was prepared as
Comparative Example 7 by heating all the amount of the mixed powder
for a single sheet of a target prepared in Example 11 from
950.degree. C. to 1300.degree. C. in vacuum at a temperature
increasing rate of 10.degree. C./minute. In addition, a
semi-sintered body was prepared as Comparative Example 8 by
dividing a mixed powder similar to that of Example 11 to each
charging depth of 3 mm and then continuously heating the powder up
to 1300.degree. C. at a temperature increasing rate of 10.degree.
C./minute in a vacuum not higher than 1.times.10.sup.-4 Torr.
[0111] The surface metal structures of respective target
semi-sintered bodies of Example 11, Comparative Examples 7 and 8
were magnified and observed under a scanning type electron
microscope (SEM) and microphotographs shown in FIGS. 5, 6 and 7
were obtained. Then, as the result of examination of the maximum
grain sizes of WSi.sub.2 grains and Si grains constituting the
respective metal structures in FIG. 5-FIG. 7, it can be confirmed
that the grain sizes of the respective grains in Example 11 are
smaller than those of Comparative Examples 7 and 8 and a fine
structure is formed and the generation of particles are more
lowered in Example 11.
[0112] Table 3 shows the result of analysis of the compositions of
the semi-sintered bodies obtained by synthesization. As a result,
the degree of dislocation of the composition of Example 11 is
smaller than those of Comparative Examples 7 and 8.
EXAMPLE 12
[0113] 2850 g of a high purity (5N) Mo powder having a maximum
grain size of 5 .mu.m and 2250 g of a high purity (5N) Si powder
having a maximum grain size of 30 .mu.m were prepared, the
respective powders were charged into a ball mill the inside of
which was lined with high purity Mo together with high purity Mo
balls and then mixed for 48 hours with the replacement of the inner
atmosphere of the ball mill with an Ar gas. The resultant mixed
powder having a Si/W atomic ratio of 2.70 was divided to each
charging depth of 1.5 mm (weight to be charged was about 100 g) and
charged into a high purity Mo vessel, silicide was synthesized in
such a manner that the temperature of the vessel was increased
stepwise from 900.degree. C. to 1250.degree. C. with a temperature
width in each step of 50.degree. C. in a vacuum not higher than
1.times.10.sup.-4 Torr using a vacuum furnace having a Mo heater
and a Mo insulator with a holding time at each step of temperature
set to 1 hour, so that a semi-sintered body of Example 12 was
prepared.
COMPARATIVE EXAMPLES 9-10
[0114] On the other hand, a semi-sintered body was prepared as
Comparative Example 9 by heating all the amount of the mixed powder
for a single sheet of the target prepared in Example 12 from
900.degree. C. to 1250.degree. C. in the same vacuum at a
temperature increasing rate of 10.degree. C./minute. In addition, a
semi-sintered body was prepared as Comparative Example 10 by
dividing a mixed powder equal to that of Example 12 to each
charging depth of 1.5 mm and then continuously heating the powder
up to 1250.degree. C. at a heating rate of 10.degree. C./minute in
a vacuum not higher than 1.times.10.sup.-4 Torr.
[0115] The surface metal structures of respective target
semi-sintered bodies of Example 12, Comparative Examples 9 and 10
were magnified and observed under a scanning type electron
microscope (SEM) and microphotographs shown in FIGS. 8, 9 and 10
were obtained, respectively. Then, as the result of measurement of
the grain size of MoSi.sub.2 grains (gray portions) and Si grains
(black portions) constituting respective metal structures and
analysis of dispersion of the compositions of the respective
semi-sintered bodies in FIGS. 8-10, the result shown in Table 3 was
obtained.
3 TABLE 3 AVERAGE DISPERSION OF COMPOSITION SEMI-SINTERED OF SEMI-
BODY SPECIMEN No. SINTERED BODY COMPOSITION EXAMPLE 11 WSi.sub.2.79
2.79 .+-. 0.01 EXAMPLE 12 MoSi.sub.2.68 2.68 .+-. 0.01 COMPARATIVE
WSi.sub.2.65 2.65 .+-. 0.03 EXAMPLE 7 COMPARATIVE WSi.sub.2.69 2.69
.+-. 0.04 EXAMPLE 8 COMPARATIVE MoSi.sub.2.45 2.45 .+-. 0.03
EXAMPLE 9 COMPARATIVE MoSi.sub.2.56 2.56 .+-. 0.04 EXAMPLE 10
[0116] As is apparent from the result shown in Table 3 and FIGS.
8-10, the grain size of MoSi.sub.2 grains in Example 12 is smaller
than that of Comparative Examples 9 and 10 and Example 12 can
obtain a fine uniform metal structure with a small grain size.
[0117] Further, as the result of analysis of the compositions of
the semi-sintered bodies obtained by the synthesization, it is
found that Example 12 can provide a target whose composition is
less dislocated than the targets of Comparative Examples 9 and 12
and which is more homogeneous than the targets thereof.
[0118] Next, a difference of deoxidizing effects will be
described.
EXAMPLE 13
[0119] The semi-sintered body obtained in Example 11 was charged
into a ball mill the inside of which was lined with a high purity
Mo material together with high purity Mo balls and crushed for 48
hours with the replacement of the inner atmosphere of the ball mill
with an Ar gas. The resultant crushed powder was charged into a
high purity Mo vessel having a diameter of 280 mm and the vessel
was heated at 1250.degree. C. for 4 hours in a vacuum not higher
than 1.times.10.sup.-4 Torr.
EXAMPLE 14
[0120] On the other hand, a mixed powder equal to that of Example
13 was heated at 1100.degree. C. for 4 hours in a vacuum not higher
than 1.times.10.sup.-4 Torr as Example 14.
[0121] Table 4 shows the result of analysis of oxygen in the
respective semi-sintered bodies of Example 13 and Example 14.
[0122] As is apparent from the result shown in Table 4, it is
confirmed that an oxygen content of Example 13 is reduced to about
{fraction (1/3)} that of Example 14.
EXAMPLE 15
[0123] The semi-sintered body obtained in Example 12 was charged
into a ball mill the inside of which was lined with a high purity
Mo material together with high purity Mo balls and crushed for 48
hours with the replacement of the inner atmosphere of the ball mill
with an Ar gas. The resultant crushed powder was charged into a
high purity Mo vessel having a diameter of 280 mm and the vessel
was heated at 1250.degree. C. for 4 hours in a vacuum not higher
than lx 10.sup.-4 Torr.
EXAMPLE 16
[0124] On the other hand, a mixed powder equal to that of Example
15 was heated at 1100.degree. C. for 4 hours in a vacuum not higher
than 1.times.10.sup.-4 Torr as Example 16.
[0125] Table 4 shows the result of analysis of oxygen content in
the respective semi-sintered bodies of Example 15 and Example
16.
EXAMPLE 17
[0126] The semi-sintered body obtained in Example 11 was charged
into a ball mill the inside of which was lined with a Mo high
purity material together with high purity Mo balls and crushed for
48 hours with the replacement of the inner atmosphere of the ball
mill with an Ar gas. The resultant crushed powder was charged into
a high purity Mo vessel having a diameter of 280 mm, the vessel was
evacuated to 1.times.10.sup.-4 Torr and hydrogen was introduced
into the vessel and then the vessel was heated at 1250.degree. C.
for 4 hours in an atmosphere reduced to 0.1 Torr. Table 4 shows the
result of analysis of the oxygen content of the resultant specimens
(semi-sintered bodies).
4 TABLE 4 AMOUNT OF OXYGEN SPECIMEN No. (ppm) EXAMPLE 13 110
EXAMPLE 14 380 EXAMPLE 15 140 EXAMPLE 16 140 EXAMPLE 17 85
[0127] As is apparent from the result shown in Table 4, according
to Example 15, the oxygen content of the semi-sintered body is
reduced to about {fraction (1/3)} that of Example 16.
[0128] Further, as shown in Example 17, a higher deoxidizing effect
can be obtained when impurities are removed in a reduced pressure
atmosphere with hydrogen introduced thereinto rather than when they
are removed in a simple vacuum atmosphere.
[0129] As described above, the semi-sintered bodies of the
refractory metal silicide obtained by the manufacturing method of
the examples can easily provide a target with a low oxygen content
because the semi-sintered bodies contain a very small amount of
oxygen. As a result, the employment of the target can reduce a film
resistance and improve the reliability of semiconductor
devices.
EXAMPLES 18-23
[0130] A high purity W powder or high purity Mo powder each having
a maximum grain size of 15 .mu.m was mixed with a high purity Si
powder having a maximum grain size of 30 .mu.m, and silicide was
synthesized by heating the resultant mixed powder in vacuum.
Further, many semi-sintered bodies of 280 mm in diameter and 40 mm
thick having an average composition of WSi.sub.2.8 or MoSi.sub.2.7
were prepared in such a manner that a semi-sintered body obtained
by synthesizing the silicide was crushed in a ball mill and the
resultant crushed powder was deoxidized by being heated in
vacuum.
[0131] Next, silicide targets relating to Examples 18-23,
respectively were made by subjecting the resultant semi-sintered
bodies obtained to hot pressing under a pressing condition and
heating condition each composed of two steps shown in Table 5.
Note, the heating condition was such that the semi-sintered bodies
were continuously heated up to 1000.degree. C. at a temperature
increasing rate of 5-20.degree. C./minute and then heated stepwise
from 1000.degree. C. to 1380.degree. C. with a temperature width in
each step of 50-150.degree. C.
COMPARATIVE EXAMPLES 11-15
[0132] On the other hand, the semi-sintered bodies used in Examples
19-23 were hot pressed under a pressing condition and heating
conditions each composed of two steps, and silicide targets
relating to Comparative Examples 11-15 were made.
[0133] The mixed structures of the resultant silicide targets
relating to Examples 18-23 and Comparative Examples 11-15 were
observed under a scanning type electron microscope and the average
grain size of WSi.sub.2 grains and MoSi.sub.2 grains and the
maximum grain size of Si grains constituting the mixed structures
were measured and the compositions of the respective silicide
targets were analyzed at the center portions and end portions
thereof. Table 5 shows the result of the measurement and
analysis.
5 TABLE 5 AVERAGE COMPOSITION PRESSURIZING HEATING CONDITIONS GRAIN
MAXIMUM OF TARGET AVERAGE CONDITIONS HOLDING SIZE OF GRAIN (Si/M
ATOMIC RATIO) SPECIMEN COMPOSITION 1st STEP 2nd STEP TEMPERATURE
PERIOD MSi.sub.2 SIZE OF Si END CENTER No. OF TARGET (kg/cm.sup.2)
(kg/cm.sup.2) WIDTH (.degree. C.) OF TIME (hr) (.mu.m) (.mu.m)
PORTION PORTION EXAMPLE 18 WSi.sub.2.8 20 300 50 1 8 8 2.78 2.79
EXAMPLE 19 WSi.sub.2.8 30 300 100 2 7 10 2.79 2.79 EXAMPLE 20
WSi.sub.2.8 40 300 150 3 5 14 2.79 2.79 EXAMPLE 21 MoSi.sub.2.7 10
300 50 1 7 7 2.68 2.69 EXAMPLE 22 MoSi.sub.2.7 20 300 100 2 6 10
2.69 2.69 EXAMPLE 23 MoSi.sub.2.7 30 300 150 3 5 14 2.69 2.69
COMPAR- WSi.sub.2.8 250 300 100 2 6 25 2.79 2.79 ATIVE EXAMPLE 11
COMPAR- WSi.sub.2.8 30 300 400 1 12 12 2.77 2.80 ATIVE EXAMPLE 12
COMPAR- MoSi.sub.2.7 150 300 50 1 6 22 2.68 2.69 ATIVE EXAMPLE 13
COMPAR- MoSi.sub.2.7 200 300 100 2 8 27 2.68 2.69 ATIVE EXAMPLE 14
COMPAR- MoSi.sub.2.7 0 300 400 1 15 15 2.65 2.69 ATIVE EXAMPLE
15
[0134] In the targets relating to Examples 18-23, since Si
plastically flows, disperses and moves to the gaps of the
semi-sintered bodies and fills the gaps under the condition of a
low pressing pressure, a less amount of Si is segregated and
uniformly dispersed. Thus, as apparent from the result shown in
Table 5, the WSi.sub.2 grains, MoSi.sub.2 grains and Si grains of
the targets of the respective examples have grain sizes smaller
than those of the comparative examples, so that fine and
miniaturized mixed structures are obtained. Further, it is found
that the composition (Si/M atomic ratio) of each of the targets of
the examples is less dispersed at the center and end portion
thereof and exhibits a composition more uniformly distributed than
that of the comparative examples.
[0135] On the other hand, it is found that when a high pressure is
applied from the initial stage of the start of sintering as in the
targets of Comparative Examples 11, 13, 14, since a Si component is
restricted and plastic flowing is difficult to occur, Si grains are
coarsened and a fine mixed structure cannot be obtained.
[0136] Further, it is also found that when targets are abruptly
heated under a low pressing pressure as in the targets of
Comparative Examples 12 and 15, MSi.sub.2 grains grow and a fine
structure cannot be obtained likewise.
EXAMPLES 24-34
[0137] A high purity M (M: W, Mo, Ti, Zr, Hf, Nb, Ta, V, Co, Cr, Ni
shown in Table 6) powder having a maximum grain size of 15 .mu.m
and a high purity Si powder having a maximum grain size of 30 .mu.m
were prepared and the respective powders were charged into a ball
mill the inside of which was lined with high purity Mo together
with high purity Mo balls and mixed for 48 hours with the
replacement of the inner atmosphere of the ball mill with an Ar
gas. The resultant respective mixed powders were charged into a
high purity Mo vessel. The depth and weight of the mixed powders to
be charged were set to 5 mm and about 2000 g, respectively. The
vessel was then heated stepwise in the temperature range from
800.degree. C. to 1300.degree. C. (different depending upon a
material) in a vacuum not higher than 1.times.10.sup.-4 Torr with a
temperature width in each step of 50.degree. C. with a holding time
at each step temperature set to 1 hour, so that silicide was
synthesized. High purity materials not less than 5N were used as
the respective high purity materials.
[0138] Next, semi-sintered bodies obtained by synthesizing the
suicide were charged into a ball mill the inside of which was lined
with high purity Mo together with high purity Mo balls and then
mixed for 48 hours with the replacement of the inner atmosphere of
the ball mill with an Ar gas. The resultant crushed powders were
charged into a high purity Mo vessel having a diameter of 280 mm
and the vessel was heated at 1250.degree. C. for 4 hours in a
vacuum not higher than 1.times.10.sup.-4 Torr to subject the
powders to a deoxidizing treatment.
[0139] Further, resultant semi-sintered bodies (about 280 mm in
diameter.times.40 mm thick) were set to a graphite compacting mold
the inside of which was lined with a Ta foil and heated to
1000.degree. C. in a vacuum not higher than 1.times.10.sup.-4 Torr.
Then, the temperature of the semi-sintered bodies was increased
stepwise up to a temperature 30.degree. C. lower than the eutectic
temperature of each material (final temperature) with a temperature
width in each step of 50.degree. C. with a holding time of each
temperature set to 1 hour while applying a low pressing pressure of
20 kg/cm to the semi-sintered bodies. Then, the semi-sintered
bodies were hot pressed with a high pressing pressure of 350 kg/cm
in 2 hours after the final temperature was reached, so that
sintered bodies each having a diameter of 280 mm and a thickness of
14 mm were made.
[0140] The resultant sintered bodies were subjected to grinding,
polishing and electric discharging processes and finished to
targets each having a diameter of 258 mm and a thickness of 10
mm.
COMPARATIVE EXAMPLES 16-26
[0141] As Comparative Examples 16-26, an M powder similar to that
of Examples 24-34 was mixed with a Si powder having a maximum grain
size of 50 .mu.m and the resultant respective powders were charged
into a vacuum furnace having a conventional carbon (C) heater and
carbon (C) insulator with a charging depth set to 20 mm and heated
to the temperature range from 800 to 1300.degree. C. (different
depending upon a material) at a rate of 10.degree. C./minute in a
vacuum not higher than 1.times.10.sup.-4 Torr and semi-sintered
bodies were obtained by synthesizing silicide.
[0142] Next, the semi-sintered bodies obtained by synthesizing the
silicide were set to a graphite compacting mold without being
deoxidized and heated to 1000.degree. C. in vacuum. Then, the
temperature of the semi-sintered bodies was increased up to a
temperature 30.degree. C. lower than the eutectic temperature of
each material (final temperature) while applying a pressing
pressure of 200 kg/cm.sup.2 to the semi-sintered bodies. Then, the
semi-sintered bodies were held for 2 hours to be hot pressed, so
that sintered bodies each having a diameter of 280 mm and a
thickness of 14 mm were made and further finished to targets having
the same dimension as that of the above examples.
[0143] The cross-sectional structures of the respective targets
relating to Example 24-34 and Comparative Examples 16-26 were
observed under a scanning type electron microscope (SEM) and the
number of MSi.sub.2 independently existing in a cross section of
0.01 mm.sup.2, the average grain size of MSi.sub.2 and the maximum
grain size of Si were measured. Table 6 shows the result of the
measurement. Note, the measured values are average values
determined by examining a cross section at 20 positions. Further, a
grain size is shown by the diameter of a minimum circle
circumscribing a grain.
6TABLE 6 (To be continued) AVERAGE NUMBER OF AVERAGE MAXIMUM
DISPERSION OF COMPOSITION INDEPENDENT GRAIN SIZE GRAIN SIZE
COMPOSITION SPECIMEN No. OF TARGET MSi.sub.2 (PIECES) OF MSi.sub.2
(.mu.m) OF Si (.mu.m) (Si/M ATOMIC RATIO) EXAMPLE 24 WSi.sub.2.8 9
7 15 2.80 .+-. 0.01 EXAMPLE 25 MoSi.sub.2.7 10 9 13 2.70 .+-. 0.01
EXAMPLE 26 TiSi.sub.2.7 6 7 15 2.70 .+-. 0.01 EXAMPLE 27
ZrSi.sub.2.6 12 9 12 2.60 .+-. 0.01 EXAMPLE 28 HfSi.sub.2.5 10 7 10
2.50 .+-. 0.01 EXAMPLE 29 NbSi.sub.2.7 8 5 11 2.70 .+-. 0.01
EXAMPLE 30 TaSi.sub.2.6 6 8 9 2.60 .+-. 0.01 EXAMVLE 31 VSi.sub.2.5
9 7 13 2.50 .+-. 0.01 EXAMPLE 32 CoSi.sub.2.6 11 9 12 2.60 .+-.
0.01 EXAMPLE 33 CrSi.sub.2.7 7 7 10 2.70 .+-. 0.01 EXAMPLE 34
NiSi.sub.2.7 12 9 13 2.70 .+-. 0.01
[0144] As apparent from the result shown in Table 6, Examples 24-34
have a uniform and fine structure in which the less number of
MSi.sub.2 independently exist and Si disperses in the gaps of the
MSi.sub.2, and further MSi.sub.2 and Si have a small grain size as
compared with Comparative Examples 16-26. Further, in each of the
targets of the respective examples, a mixed structure is formed
such that fine MSi.sub.2 grains shown by white portions are coupled
with each other like a chain and fine Si grains shown by black
portions disperse among them similarly to the metal structures of
the targets of Examples 1 and 6 shown in FIGS. 1 and 2. On the
other hand, it is found that in the targets relating to Comparative
Examples 16-26, coarse MSi.sub.2 grains (gray portions) and Si
grains (black portions) grow as well as a ratio of fine MSi.sub.2
grains independently existing in a Si phase is increased and thus
the targets have a structure in which particles are liable to be
generated similarly to the metal structures of the targets relating
to Comparative Examples 1 and 4 shown in FIGS. 3 and 4.
[0145] Table 6 also shows the result of analysis of a Si/W atomic
ratio in a cross section of 1 mm.sup.2 of the mixed structure of
each target obtained by a surface analyzing instrument (X-ray
microanalyzer: EPMA). It is found from the result of analysis that
the examples have compositions nearer to an intended composition as
compared with the comparative examples and further have uniform
compositions.
[0146] Table 7 shows the result of measurement of the densities of
the respective targets and the result of analysis of oxygen,
carbon, iron and aluminium.
7 TABLE 7 AVERAGE NUMBER OF COMPOSITION DISPERSION OF AMOUNT OF
IMPURITY (ppm) PARTICLES SPECIMEN No. OF TARGET DENSITY RATIO
O.sub.2 C Fe Al (PIECES) EXAMPLE 24 WSi.sub.2.8 99.8 .+-. 0.1 135
30 0.4 0.1 8 EXAMPLE 25 MoSi.sub.2.7 99.8 .+-. 0.1 141 25 0.5 0.3 9
EXAMPLE 26 TiSi.sub.2.7 99.7 .+-. 0.1 185 33 0.6 0.2 15 EXAMPLE 27
ZrSi.sub.2.6 99.8 .+-. 0.1 122 30 0.5 0.3 16 EXAMPLE 28
HfSi.sub.2.5 99.8 .+-. 0.1 179 34 0.7 0.3 13 EXAMPLE 29
NbSi.sub.2.7 99.8 .+-. 0.1 165 25 0.5 0.2 17 EXAMPLE 30
TaSi.sub.2.6 99.7 .+-. 0.2 143 37 0.6 0.3 9 EXAMPLE 31 VSi.sub.2.5
99.7 .+-. 0.1 178 35 0.7 0.3 17 EXAMPLE 32 CoSi.sub.2.6 99.8 .+-.
0.1 188 38 0.6 0.2 18 EXAMPLE 33 CrSi.sub.2.7 99.7 .+-. 0.1 155 31
0.8 0.4 14 EXAMPLE 34 NiSi.sub.2.7 99.7 .+-. 0.2 187 40 0.8 0.3 20
COMPARATIVE EXAMPLE 16 WSi.sub.2.8 99.1 .+-. 0.3 954 117 2.1 2.2
257 COMPARATIVE EXAMPLE 17 MoSi.sub.2.7 99.0 .+-. 0.3 1180 123 3.1
2.3 277 COMPARATIVE EXAMPLE 18 TiSi.sub.2.7 98.5 .+-. 0.4 3475 188
4.5 3.3 327 COMPARATIVE EXAMPLE 19 ZrSi.sub.2.6 98.6 .+-. 0.3 1946
170 3.8 2.2 244 COMPARATIVE EXAMPLE 20 HfSi.sub.2.5 98.8 .+-. 0.3
1737 152 3.2 3.1 217 COMPARATIVE EXAMPLE 21 NbSi.sub.2.7 98.7 .+-.
0.4 2254 162 4.0 2.9 289 COMPARATIVE EXAMPLE 22 TaSi.sub.2.6 98.5
.+-. 0.4 2790 189 4.2 3.1 336 COMPARATIVE EXAMPLE 23 VSi.sub.2.5
98.6 .+-. 0.3 2774 175 3.9 2.7 297 COMPARATIVE EXAMPLE 24
CoSi.sub.2.6 99.0 .+-. 0.3 1995 147 3.5 2.5 207 COMPARATIVE EXAMPLE
25 CrSi.sub.2.7 98.7 .+-. 0.3 2065 155 3.7 2.6 268 COMPARATIVE
EXAMPLE 26 NiSi.sub.2.7 98.4 .+-. 0.4 3358 189 4.5 3.9 357
[0147] As is apparent from the result shown in Table 7, it was
found that the targets relating to Examples 24-34 have a density
ratio not less than 99.5% and a very small content of impurities as
compared with the targets relating to Comparative Examples
16-26.
[0148] The respective targets relating to Examples 24-34 and
Comparative Examples 16-26 were set to a magnetron sputtering
apparatus and sputtered under the condition of an argon pressure of
2.3.times.10.sup.-3 Torr and a silicide film was deposited on a 6
inch Si wafer to about 3000.ANG. thick. The same operation was
repeated 10 times and an amount of mixed particles having a
particle size not less than 0.2 .mu.m was measured. Table 7 also
shows the result of the measurement. As also apparent from the
result shown in Table 7, according to the targets relating to
Examples 24-34, the number of particles mixed on the 6 inch wafer
is not greater than 20 and very small, whereas according to
Comparative Examples 16-26, it is found that a lot of particles
which are about 10 times those of Examples 24-34 are generated.
[0149] Industrial Applicability:
[0150] As described above, the refractory metal silicide targets
according to the present invention have a high purity, high density
fine mixed structure composed of refractory metal silicide grains
and Si grains in which Si grains uniformly disperse and, the
compositions in the targets are uniformly arranged. Consequently,
the employment of the targets reduces particles produced in
sputtering, the change of a film resistance on a wafer surface and
the impurities and the like in the film of the wafer face and can
improve yield and reliability when semiconductors are
manufactured.
* * * * *