U.S. patent application number 09/783259 was filed with the patent office on 2001-08-23 for aluminum nitride sintered body and method of preparing the same.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Murase, Yasuhiro, Nakata, Hirohiko, Natsuhara, Masuhiro, Sasaki, Kazutaka, Tanaka, Motoyuki, Yushio, Yasuhisa.
Application Number | 20010016551 09/783259 |
Document ID | / |
Family ID | 16521919 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010016551 |
Kind Code |
A1 |
Yushio, Yasuhisa ; et
al. |
August 23, 2001 |
Aluminum nitride sintered body and method of preparing the same
Abstract
Provided is an aluminum nitride sintered body excellent in
thermal shock resistance and strength and applicable to a radiating
substrate for a power module or a jig for semiconductor equipment
employed under a strict heat cycle. An aluminum nitride sintered
body obtained with a sintering aid of a rare earth element and an
alkaline earth metal element contains 0.01 to 5 percent by weight
of an alkaline earth metal element compound in terms of an oxide
and 0.01 to 10 percent by weight of a rare earth element compound
in terms of an oxide, and the amount of carbon remaining in the
sintered body is controlled to 0.005 to 0.1 percent by weight,
thereby suppressing grain growth and improving thermal shock
resistance and strength of the sintered body.
Inventors: |
Yushio, Yasuhisa;
(Itami-shi, JP) ; Nakata, Hirohiko; (Itami-shi,
JP) ; Sasaki, Kazutaka; (Itami-shi, JP) ;
Natsuhara, Masuhiro; (Itami-shi, JP) ; Tanaka,
Motoyuki; (Itami-shi, JP) ; Murase, Yasuhiro;
(Osaka, JP) |
Correspondence
Address: |
FASSE PATENT ATTORNEYS, P.A.
P.O. BOX 726
HAMPDEN
ME
04444-0726
US
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
5-33, Kitahama 4-chome. Chuo-ku, Osaka-shi
Osaka
JP
|
Family ID: |
16521919 |
Appl. No.: |
09/783259 |
Filed: |
February 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09783259 |
Feb 13, 2001 |
|
|
|
09357600 |
Jul 20, 1999 |
|
|
|
Current U.S.
Class: |
501/98.5 ;
257/E23.009 |
Current CPC
Class: |
C04B 35/581 20130101;
H01L 23/15 20130101; H01L 2924/0002 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
501/98.5 |
International
Class: |
C04B 035/581 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 1998 |
JP |
10-206353(P) |
Claims
What is claimed is:
1. An aluminum nitride sintered body containing at least 0.005
percent by weight and not more than 0.1 percent by weight of
carbon, at least 0.01 percent by weight and not more than 5 percent
by weight of an alkaline earth metal element in terms of an oxide
thereof and at least 0.01 percent by weight and not more than 10
percent by weight of a rare earth element in terms of an oxide
thereof with a rest mainly composed of aluminum nitride.
2. The aluminum nitride sintered body in accordance with claim 1,
wherein said alkaline earth metal element includes at least one
element selected from a group consisting of Ca, Sr and Ba.
3. The aluminum nitride sintered body in accordance with claim 1,
wherein said rare earth element includes at least one element
selected from a group consisting of Y, La, Ce, Sc, Yb, Nd, Er and
Sm.
4. The aluminum nitride sintered body in accordance width claim 1,
wherein the mean grain size of aluminum nitride grains forming said
sintered body, is not more than 3 .mu.m.
5. The aluminum nitride sintered body in accordance with claim 1,
further comprising a conductive layer or an insulating layer formed
on a surface thereof by a thick film paste method.
6. A method of preparing an aluminum nitride sintered body
comprising steps of: preparing mixed powder containing at least
0.01 percent by weight and not more than 2 percent by weight of
carbon powder, at least 0.01 percent by weight and not more than 5
percent by weight of an alkaline earth metal element in terms of an
oxide thereof and at least 0.01 percent by weight and not more than
10 percent by weight of a rare earth element in terms of an oxide
thereof with a rest mainly composed of powder of aluminum nitride;
forming a compact with said mixed powder; and forming a sintered
body by sintering said compact.
7. The method of preparing an aluminum nitride sintered body in
accordance with claim 6, wherein the content of carbon in said
compact at a temperature of 1500.degree. C. is at least 0.01
percent by weight and not more than 0.1 percent by weight in the
sintering process.
8. The method of preparing an aluminum nitride sintered body in
accordance with claim 6, wherein the sintering temperature is not
more than 1700.degree. C.
9. The method of preparing an aluminum nitride sintered body in
accordance with claim 6, wherein the mean grain size of said powder
of aluminum nitride is at least 0.5 .mu.m and not more than 2.0
.mu.m.
10. The method of preparing an aluminum nitride sintered body in
accordance with claim 6, wherein the content of oxygen in said
powder of aluminum nitride is at least 0.8 percent by weight and
not more than 1.5 percent by weight with respect to the weight of
said aluminum nitride powder.
11. A method of preparing an aluminum nitride sintered body
comprising steps of: preparing mixed powder containing at least
0.01 percent by weight and not more than 20 percent by weight of a
compound liberating carbon, at least 0.01 percent by weight and not
more than 5 percent by weight of an alkaline earth metal element in
terms of an oxide thereof and at least 0.01 percent by weight and
not more than 10 percent by weight of a rare earth element in terms
of an oxide thereof with a rest mainly composed of powder of
aluminum nitride; forming a compact with said mixed powder;
liberating carbon by heat-treating said compact in a non-oxidizing
atmosphere under a condition of at least 150.degree. C. and not
more than 1500.degree. C. in temperature; and forming a sintered
body by sintering heat-treated said compact.
12. The method of preparing an aluminum nitride sintered body in
accordance with claim 11, wherein said compound liberating carbon
includes at least one compound selected from a group consisting of
polyacrylonitrile, polyvinyl alcohol, polyvinyl butyral,
polyethylene terephthalate, glucose, fructose, saccharose,
phenol-formaldehyde resin and stearic acid.
13. The method of preparing an aluminum nitride sintered body in
accordance with claim 11, wherein the content of carbon in said
compact at a temperature of 1500.degree. C. is at least 0.01
percent by weight and not more than 0.1 percent by weight in the
sintering process.
14. The method of preparing an aluminum nitride sintered body in
accordance with claim 11, wherein the sintering temperature is not
more than 1700.degree. C.
15. The method of preparing an aluminum nitride sintered body in
accordance with claim 11, wherein the mean grain size of said
powder of aluminum nitride is at least 0.5 .mu.m and not more than
2.0 .mu.m.
16. The method of preparing an aluminum nitride sintered body in
accordance with claim 11, wherein the content of oxygen in said
powder of aluminum nitride is at least 0.8 percent by weight and
not more than 1.5 percent by weight with respect to the weight of
said aluminum nitride powder.
17. A method of preparing an aluminum nitride sintered body
comprising steps of: preparing mixed powder containing at least
0.01 percent by weight and not more than 5 percent by weight of an
alkaline earth metal element in terms of an oxide thereof and at
least 0.01 percent by weight and not more than 10 percent by weight
of a rare earth element in terms of an oxide thereof with a rest
mainly composed of powder of aluminum nitride; forming a compact
with said mixed powder; and forming a sintered body by sintering
said compact in a non-oxidizing atmosphere having a content of at
least 10 percent by volume and not more than 100 percent by volume
of at least one of carbon monoxide and hydrocarbon.
18. The method of preparing an aluminum nitride sintered body in
accordance with claim 17, wherein the content of carbon in said
compact at a temperature of 1500.degree. C. is at least 0.01
percent by weight and not more than 0.1 percent by weight in the
sintering process.
19. The method of preparing an aluminum nitride sintered body in
accordance with claim 17, wherein the sintering temperature is not
more than 1700.degree. C.
20. The method of preparing an aluminum nitride sintered body in
accordance with claim 17, wherein the mean grain size of said
powder of aluminum nitride is at least 0.5 .mu.m and not more than
2.0 .mu.m.
21. The method of preparing an aluminum nitride sintered body in
accordance with claim 17, wherein the content of oxygen in said
powder of aluminum nitride is at least 0.8 percent by weight and
not more than 1.5 percent by weight with respect to the weight of
said aluminum nitride powder.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an aluminum nitride
sintered body, and more particularly, it relates to an aluminum
nitride sintered body allowing low-temperature sintering and having
high strength and high thermal conductivity and a method of
preparing the same.
[0003] 2. Description of the Prior Art
[0004] Aluminum nitride (AlN) having high thermal conductivity and
a low thermal expansion coefficient is recently employed as the
material for insulated substrates for various types of electronic
components, in place of alumina which has been employed in
general.
[0005] In general, however, aluminum nitride has a relatively high
sintering temperature of at least 1800.degree. C. An existing
sintering furnace or jig component cannot sufficiently withstand
such a high temperature but must be frequently repaired or
discarded/exchanged. Further, aluminum nitride sintered at a high
temperature requires high sintering energy. Therefore, the cost for
an aluminum nitride sintered body is higher than that for an
alumina sintered body, to hinder popularization of aluminum
nitride.
[0006] In order to sinter aluminum nitride which is generally hard
to sinter as compared with alumina, a sintering aid of an alkaline
earth metal element compound or a rare earth element compound is
mainly employed. Particularly in order to lower the sintering
temperature, more specifically to enable sintering at a temperature
of not more than 1700.degree. C., combined use of an alkaline earth
metal element compound and a rare earth element compound is
studied. Typically, various studies have been made on sintering
aids prepared by combining calcium compounds and yttrium
compounds.
[0007] For example, Japanese Patent Laying-Open No. 61-117160
(1986) describes an aluminum nitride sintered body obtained by
normal pressure sintering under a temperature of not more than
1700.degree. C. with a sintering aid prepared by combining an
alkaline earth metal element compound such as CaCO.sub.3 and a rare
earth element compound such as La.sub.2O.sub.3. Japanese Patent
Laying-Open No. 63-190761 (1988) describes a sintering aid for
aluminum nitride prepared by combining CaO and Y.sub.2O.sub.3.
[0008] A technique of reducing an aluminum oxide contained in a
sintered body with carbon or a material liberating carbon for
improving the thermal conductivity of an aluminum nitride sintered
body is generally known. For example, each of Japanese Patent
Publication Nos. 7-5372 to 7-5376 (1995) discloses a method of
increasing the thermal conductivity of aluminum nitride by
nitriding an oxide contained therein through free carbon with a
sintering aid of an yttrium compound. Further, Japanese Patent
Laying-Open No. 58-55377 (1983) describes a method of
reducing/removing oxygen by employing an alkaline metal compound as
a sintering aid and adding carbon powder or the like.
[0009] In addition, it is known that a thick metallized film having
high strength can be formed by introducing a rare earth element or
an alkaline earth metal element into an aluminum nitride sintered
body. For example, Japanese Patent Publication No. 5-76795 (1993)
discloses a circuit board obtained by forming a conductor part or a
dielectric part prepared from at least either paste containing Ag
or paste containing Au on an aluminum nitride sintered body
containing at least one element selected from a rare earth element
and an alkaline earth metal element. Japanese Patent Publication
No. 7-38491 (1995) describes a method of forming a conductive layer
of a high melting point metal such as tungsten or molybdenum on an
aluminum nitride sintered body containing at least one element
selected from a rare earth element and an alkaline earth metal
element.
[0010] As described above, sintering of aluminum nitride under a
low temperature of not more than 1700.degree. C. has been enabled
due to development of a new sintering aid prepared by combining an
alkaline earth metal element compound and a rare earth element
compound. Thus, the thermal conductivity of an aluminum nitride
sintered body is improved, and such an aluminum nitride sintered
body is increasingly applied to a substrate for an exothermic
semiconductor element such as a power device.
[0011] In the aforementioned method employing the sintering aid of
a rare earth element and/or an alkaline earth metal element,
however, a rare earth aluminum oxide, an alkaline earth aluminum
oxide, a rare earth alkaline earth aluminum oxide and the like are
formed between an oxide present in the aluminum nitride sintered
body and the sintering aid. Although formation of these oxides is
necessary for the aforementioned low-temperature sintering under a
temperature of not more than 1700.degree. C., the grain sizes of
the sintered body are increased due to the oxides.
[0012] In recent years, aluminum nitride is frequently applied to a
radiating substrate for a power module or a jig for semiconductor
equipment, which is used under a strict heat cycle. Therefore,
aluminum nitride must be improved in thermal shock resistance as
well as strength for serving as ceramic. In this regard, the mean
grain size of the aluminum nitride sintered body must be not more
than 3 .mu.m, preferably not more than 2 .mu.m. In the conventional
method, however, further improvement of the strength of the
sintered body cannot be attained due to increase of the grain sizes
resulting from formation of a large amount of oxides.
SUMMARY OF THE INVENTION
[0013] In consideration of such general circumstances, an object of
the present invention is to provide an aluminum nitride sintered
body excellent in thermal shock resistance and strength and
applicable to a radiating substrate for a power module or a jig for
semiconductor equipment used under a strict heat cycle by
suppressing grain growth in the case of employing a rare earth
element and an alkaline earth metal element as materials for a
sintering aid and a method of preparing the same.
[0014] In order to attain the aforementioned object, the inventors
have made deep study to find that grain growth can be suppressed
and thermal shock resistance and strength of an aluminum nitride
sintered body can be remarkably improved even if employing a
sintering aid containing a rare earth element and an alkaline earth
metal element by properly selecting the amounts of blending thereof
and controlling the amount of carbon remaining in the sintered
body, to propose the present invention.
[0015] The aluminum nitride sintered body according to the present
invention contains at least 0.005 percent by weight and not more
than 0.1 percent by weight of carbon, at least 0.01 percent by
weight and not more than 5 percent by weight of an alkaline earth
metal element in terms of an oxide thereof and at least 0.01
percent by weight and not more than 10 percent by weight of a rare
earth element in terms of an oxide thereof with a rest mainly
composed of aluminum nitride.
[0016] Preferably, the alkaline earth metal element includes at
least one element selected from a group consisting of Ca, Sr and
Ba.
[0017] Preferably, the rare earth element includes at least one
element selected from a group consisting of Y, La, Ce, Sc, Yb, Nd,
Er and Sm.
[0018] Preferably, the mean grain size of aluminum nitride grains
forming the sintered body is not more than 3 .mu.m.
[0019] Preferably, the aluminum nitride sintered body further
comprises a conductive layer or an insulating layer formed on a
surface thereof by a thick film paste method.
[0020] A method of preparing an aluminum nitride sintered body
according to an aspect of the present invention comprises steps of
preparing mixed powder containing at least 0.01 percent by weight
and not more than 2 percent by weight of carbon powder, at least
0.01 percent by weight and not more than 5 percent by weight of an
alkaline earth metal element in terms of an oxide thereof and at
least 0.01 percent by weight and not more than 10 percent by weight
of a rare earth element in terms of an oxide thereof with a rest
mainly composed of powder of aluminum nitride, forming a compact
with the mixed powder, and forming a sintered body by sintering the
compact.
[0021] Preferably, the content of carbon in the compact at a
temperature of 1500.degree. C. is at least 0.01 percent by weight
and not more than 0.1 percent by weight in the sintering
process.
[0022] Preferably, the sintering temperature is not more than
1700.degree. C.
[0023] Preferably, the mean grain size of the powder of aluminum
nitride is at least 0.5 .mu.m and not more than 2.0 .mu.m.
[0024] Preferably, the content of oxygen in the powder of aluminum
nitride is at least 0.8 percent by weight and not more than 1.5
percent by weight with respect to the weight of the aluminum
nitride powder.
[0025] A method of preparing an aluminum nitride sintered body
according to another aspect of the present invention comprises
steps of preparing mixed powder containing at least 0.01 percent by
weight and not more than 20 percent by weight of a compound
liberating carbon, at least 0.01 percent by weight and not more
than 5 percent by weight of an alkaline earth metal element in
terms of an oxide thereof and at least 0.01 percent by weight and
not more than 10 percent by weight of a rare earth element in terms
of an oxide thereof with a rest mainly composed of powder of
aluminum nitride, forming a compact with the mixed powder,
liberating carbon by heat-treating the compact in a non-oxidizing
atmosphere under a condition of at least 150.degree. C. and not
more than 1500.degree. C. in temperature, and forming a sintered
body by sintering the heat-treated compact.
[0026] Preferably, the compound liberating carbon includes at least
one compound selected from a group consisting of polyacrylonitrile,
polyvinyl alcohol, polyvinyl butyral, polyethylene terephthalate,
glucose, fructose, saccharose, phenol-formaldehyde resin and
stearic acid.
[0027] Preferably, the content of carbon in the compact at a
temperature of 1500.degree. C. is at least 0.01 percent by weight
and not more than 0.1 percent by weight in the sintering
process.
[0028] Preferably, the sintering temperature is not more than
1700.degree. C.
[0029] Preferably, the mean grain size of the powder of aluminum
nitride is at least 0.5 .mu.m and not more than 2.0 .mu.m.
[0030] Preferably, the content of oxygen in the powder of aluminum
nitride is at least 0.8 percent by weight and not more than 1.5
percent by weight with respect to the weight of the aluminum
nitride powder.
[0031] A method of preparing an aluminum nitride sintered body
according to still another aspect of the present invention
comprises steps of preparing mixed powder containing at least 0.01
percent by weight and not more than 5 percent by weight of an
alkaline earth metal element in terms of an oxide thereof and at
least 0.01 percent by weight and not more than 10 percent by weight
of a rare earth element in terms of an oxide thereof with a rest
mainly composed of powder of aluminum nitride, forming a compact
with the mixed powder, and forming a sintered body by sintering the
compact in a non-oxidizing atmosphere having a content of at least
10 percent by volume and not more than 100 percent by volume of at
least one of carbon monoxide and hydrocarbon.
[0032] Preferably, the content of carbon in the compact at a
temperature of 1500.degree. C. is at least 0.01 percent by weight
and not more than 0.1 percent by weight in the sintering
process.
[0033] Preferably, the sintering temperature is not more than
1700.degree. C.
[0034] Preferably, the mean grain size of the powder of aluminum
nitride is at least 0.5 .mu.m and not more than 2.0 .mu.m.
[0035] Preferably, the content of oxygen in the powder of aluminum
nitride is at least 0.8 percent by weight and not more than 1.5
percent by weight with respect to the weight of the aluminum
nitride powder.
[0036] According to the present invention, an aluminum nitride
sintered body having stable strength can be obtained by
low-temperature sintering employing a sintering aid containing a
rare earth element and an alkaline earth metal element, by strictly
controlling the amount of the sintering aid and controlling the
amount of carbon remaining in the sintered body thereby suppressing
grain growth while maintaining excellent basic properties such as
high thermal conductivity.
[0037] In general, an oxide present in a sintered body reacts with
a rare earth element or an alkaline earth metal element blended as
a sintering aid to form a rare earth aluminum oxide or an alkaline
earth aluminum oxide and form liquid phases on grain boundaries to
facilitate sintering. According to study made by the inventors,
however, it has been proved that liquid phases are formed in excess
if no proper amount of carbon is present to activate mass transfer
therethrough, and hence the grain sizes of the sintered body
unnecessarily increase as a result.
[0038] The present invention has been proposed on the basis of such
new recognition that the amount of carbon remaining in the
aforementioned aluminum nitride sintered body is closely related to
the grain sizes and strength of the sintered body. In other words,
low-temperature sintering through liquid phases is enabled while
the grain sizes of the sintered body can be suppressed in a desired
range by adding carbon to the sintered body to remain therein in a
prescribed amount.
[0039] According to the present invention, the amount of carbon is
controlled to remain in the aluminum nitride sintered body by 0.005
to 0.1 percent by weight, while the contents of the alkaline earth
metal element and the rare earth element compound derived from the
sintering aid are set to 0.01 to 5 percent by weight and 0.01 to 10
percent by weight in terms of oxides thereof respectively. Thus,
the strength of the sintered body can be improved by suppressing
grain growth not to increase the grain sizes.
[0040] If the amount of carbon remaining in the aluminum nitride
sintered body is less than 0.005 percent by weight, oxides cannot
be sufficiently reduced due to the insufficient amount of carbon
present in sintering. Thus, grain growth of the aluminum nitride
sintered body is caused beyond necessity to increase the number of
coarse grains, resulting in reduction of the strength of the
sintered body. If carbon remains in excess of 0.1 percent by
weight, such excess carbon causes deficiency of oxides in the
sintered body. Thus, sintering insufficiently progresses under a
low temperature of not more than 1700.degree. C.
[0041] The contents of the alkaline earth metal element and the
rare earth element are set in the aforementioned ranges since the
density of the sintered body is lowered in low-temperature
sintering under a temperature of not more than 1700.degree. C. due
to deficiency of the sintering aid if the contents of the elements
are less than the lower limits of the aforementioned ranges,
leading to inferior quality of the sintered body. If the contents
of the elements exceed the upper limits of the aforementioned
ranges, excess alkaline earth aluminum oxide, rare earth aluminum
oxide and alkaline earth rare earth aluminum oxide are deposited on
the grain boundaries of the aluminum nitride sintered body, to
deteriorate the thermal conductivity.
[0042] The alkaline earth metal element preferably includes at
least one element selected from a group consisting of Ca, Sr and Ba
The rare earth element preferably includes at least one element
selected from a group consisting of Y, La, Ce, Sc, Yb, Nd, Er and
Sm. An aluminum nitride sintered body particularly excellent in
thermal conductivity and other characteristics can be obtained by
employing such alkaline earth metal element and rare earth
element.
[0043] In the aluminum nitride sintered body, grain growth is
suppressed due to reduction of the oxides with carbon as described
above, whereby the mean grain size of the sintered body is reduced.
In particular, the mean grain size of the sintered body is
preferably not more than 3 .mu.m, and more preferably not more than
2 .mu.m. If the mean grain size exceeds 3 .mu.m, the strength and
thermal shock resistance of the aluminum nitride sintered body may
be so lowered that the aluminum nitride sintered body is unsuitable
for application to a radiating substrate for a power module or a
jig for semiconductor equipment employed under a particularly
strict heat cycle.
[0044] The method of preparing an aluminum nitride sintered body
according to the present invention is now described. In this
method, mixed powder is first prepared by adding an alkaline earth
metal element and a rare earth element to aluminum nitride powder
as a sintering aid, by at least 0.01 percent by weight and not more
than 5 percent by weight and at least 0.01 percent by weight and
not more than 10 percent by weight in terms of oxides thereof
respectively and further adding carbon or a compound liberating
carbon. A compact is prepared from this mixed powder, and this
compact is sintered. Thus, an aluminum nitride sintered body
containing carbon is obtained.
[0045] Alternatively, mixed powder is prepared by adding a
sintering aid to aluminum nitride powder in the aforementioned
ratios. A compact is prepared from this mixed powder, and this
compact is sintered in an atmosphere containing carbon monoxide gas
or hydrocarbon gas. Thus, an aluminum nitride sintered body
containing carbon is obtained.
[0046] The inventive method may be carried out through any of three
methods depending on the means of leaving carbon in the obtained
aluminum nitride sintered body. In the first method, carbon powder
is added in the form of carbon black, coke powder, graphite powder
or diamond powder to unsintered material powder of aluminum nitride
powder and a sintering aid. The carbon powder must be added by 0.01
to 2 percent by weight. If the amount of the carbon powder is out
of this range, it is difficult to control the amount of carbon
remaining in the sintered body to 0.005 to 0.1 percent by weight
and to improve the strength of the sintered body by suppressing
increase of the grain sizes.
[0047] In the second method, a compound liberating carbon is
employed when sintering aluminum nitride, in place of the
aforementioned carbon powder. More specifically, at least one
compound is preferably selected from a group consisting of
polyacrylonitrile, polyvinyl alcohol, polyvinyl butyral,
polyethylene terephthalate, glucose, fructose, saccharose,
phenol-formaldehyde resin and stearic acid. With such a compound,
which can be dissolved in an organic solvent or water to be
thereafter added to/mixed with aluminum nitride powder, carbon can
be more homogeneously dispersed in the sintered body as compared
with the aforementioned method adding carbon powder. Stearic acid
can be added in the form of rare earth salt, as a rare earth
element compound forming the sintering aid.
[0048] In the second method employing the compound liberating
carbon, the compact is heated in a non-oxidizing atmosphere at a
temperature of 150 to 1500.degree. C., so that carbon is liberated
from the compound to contribute to reduction of oxides. The amount
of the compound liberating carbon may be in the range of 0.01 to 20
percent by weight, to obtain an effect similar to that in the
aforementioned case of directly adding carbon powder.
[0049] In the third method, a compact prepared from mixed powder of
aluminum nitride powder and a sintering aid is sintered in a
non-oxidizing atmosphere containing at least 10 percent by volume
of gas selected from carbon monoxide gas and hydrocarbon gas. In
this case, oxides in the sintered body can be reduced in a shorter
time than those in the first and second methods, due to high
reactivity of the gas. According to this method, further, the
optimum amount of carbon can be readily left in the sintered body
by controlling the composition of the gas in the aforementioned
range.
[0050] The inventors have observed and studied the sintering
process in the inventive method in detail, to find that an aluminum
nitride sintered body particularly excellent in strength and the
like can be obtained when the amount of carbon contained in the
compact or the sintered body at 1500.degree. C. in the sintering
process is 0.01 to 0.1 percent by weight. If the amount of carbon
is less than 0.01 percent by weight in the stage of starting
sintering at the temperature of 1500.degree. C., the amount of
carbon finally remaining in the sintered body is less than 0.005
percent by weight since carbon is further consumed in the later
step of reducing oxides. If the amount of carbon is in excess of
0.1 percent by weight in this stage, carbon remains in the grain
boundaries of the sintered body to irregularize the color due to
heterogeneous transmittance, or sintering incompletely progresses
to result in defective sintering density. Therefore, the amount of
the remaining carbon at 1500.degree. C. must be controlled by
setting the speed for increasing the temperature at 1.degree.
C./min. in the temperature range of 1300 to 1500.degree. C. or
holding the compact in this temperature range for 1 to 10 hours to
sufficiently progress the reaction of Al.sub.2O.sub.3 +3C
+N.sub.2.fwdarw.2AlN+3CO.
[0051] In the aforementioned method according to the present
invention, the sintering temperature for aluminum nitride is
preferably not more than 1700.degree. C. If the sintering
temperature exceeds 1700.degree. C., grain growth takes place
beyond necessity in the aluminum nitride sintered body even if
addition of carbon or the like is so controlled that the amount of
carbon remaining in the aluminum nitride sintered body is 0.005 to
0.1 percent by weight. Consequently, the mean grain size of the
sintered body exceeds 3 .mu.m to lower the strength of the sintered
body.
[0052] The mean grain size (d.sub.50) of the employed aluminum
nitride powder is preferably in the range of at least 0.5 .mu.m and
not more than 2.0 .mu.m. The term "mean grain size (d.sub.50)"
stands for that having the highest appearance frequency among grain
sizes. If the mean grain size exceeds 2.0 .mu.m, it is difficult to
obtain a sintered body having fine grains of not more than 3 .mu.m
in grain size in particular, due to the excessive initial grain
sizes. If the mean grain size of the aluminum nitride powder is
less than 0.5 .mu.m, bulk density in powder molding is so increased
that it is difficult to increase molding density, and hence the
strength of the compact is lowered.
[0053] Further, the amount of oxygen contained in the aluminum
nitride powder is preferably in the range of at least 0.8 percent
by weight and not more than 1.5 percent by weight. If the oxygen
content is less than 0.8 percent by weight, the amount of liquid
phases formed between oxides and the sintering aid in sintering
tends to be insufficient, to lower the sinterability. If the oxygen
content exceeds 1.5 percent by weight, the amount of the liquid
phases, i.e., grain boundary phases is increased to readily
excessively cause grain growth during sintering.
[0054] In particular, it has been proved that the adhesion strength
of the conductive layer or the insulating layer formed by the thick
film paste method is improved in the aluminum nitride sintered body
according to the present invention. The first reason for this is
that the mean grain size of the sintered body is reduced,
particularly to not more than 3 .mu.m, and the second reason is
that the wettability of the aluminum nitride grains is improved due
to the residual carbon.
[0055] The alkaline earth metal element and the rare earth element
forming the sintering aid have an effect of improving adhesion
between the aluminum nitride grains or adhesion between the
aluminum nitride grains and the insulating layer or the conductive
layer formed thereon. Compounds of the alkaline earth metal element
and the rare earth element are generally present in the vicinity of
the grain boundary phases of the aluminum nitride grains in the
sintered body. Observing the adhesion strength with respect to the
conductive layer or the insulating layer in a microscopic point of
view, adhesion between the aluminum nitride grains and the
insulating layer or the conductive layer is high in portions where
the grain boundary phases of the aluminum nitride grains bonded to
each other through the sintering aid and the conductive layer are
in contact with each other. In portions where the aluminum nitride
grains are directly in contact with the insulating layer, however,
adhesion is conceivably low. Particularly when the mean grain size
is greater than 3 .mu.m, coarse grains of aluminum nitride are
present in the sintered body to result in sparse distribution of
grain boundary phases having high adhesion. Therefore, portions
having insufficient adhesion strength tend to arise to readily
cause peeling when tensile stress is applied between the aluminum
nitride sintered body and the conductive layer or the insulating
layer in measurement of peel strength or the like, to result in
reduction of the adhesion strength.
[0056] According to the present invention, the mean grain size of
the aluminum nitride sintered body can be controlled small,
preferably to not more than 3 .mu.m, as the aforementioned first
reason. Thus, compounds of the alkaline earth metal element and the
rare earth element are homogeneously distributed on the grain
boundaries of such small grains over a wide range with no partial
segregation, to further improve the adhesion strength between the
aluminum nitride grains and the conductive layer or the insulating
layer.
[0057] In addition to such distribution of the compounds around the
grain boundaries, carbon remaining in the aluminum nitride sintered
body reforms the surfaces of the aluminum nitride grains and
improves the wettability with respect to the conductive layer or
the insulating layer. In particular, the wettability between the
metal components and the insulating layer is improved to attain
further improvement of the adhesion strength. If the amount of
carbon is excessive, however, the sinterability is reduced.
Therefore, the amount of carbon remaining in the sintered body is
preferably in the range of at least 0.005 percent by weight and not
more than 0.1 percent by weight.
[0058] Paste employed for the thick film paste method may be
prepared from that generally employed for forming a conductive
layer or a insulating layer, such as Ag, Ag paste such as Ag-Pt or
Ag-Pd paste, conductive paste such as Cu pate or Au paste,
resistive paste of RuO.sub.2, Ru or Bi.sub.2Ru.sub.2O.sub.7,
dielectric paste mainly composed of lead borosilicate glass or the
like, or high melting point paste of W, Mo, TiN or ZrN.
[0059] In order to form the conductive layer or the insulating
layer, a thick film layer may be formed by screen-printing the
paste on the surface of the aluminum nitride sintered body and
heating the same at a prescribed temperature. Alternatively, high
melting point paste of W, Nb, TiN or ZrN may be applied to the
surface of the unsintered compact to be fired simultaneously with
sintering of the compact, to form the conductive layer or the
insulating layer.
[0060] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1
[0061] Samples of mixed powder of 100 percent by weight in total
were prepared by adding aluminum nitride powder (mean grain size:
1.8 .mu.m, oxygen content with respect to aluminum nitride: 1.4
percent by weight) obtained by direct nitriding to carbon black
(BET value (surface area per unit mass calculated by BET adsorption
isotherm): 500 m.sup.2/g), employed as carbon powder, in amounts
shown in Table 1, 1 percent by weight of calcium oxide and 6
percent by weight of yttrium oxide. Polymethyl methacrylate for
serving as a binder, a mixture of dibutyl phthalate and benzyl
butyl phthalate for serving as a plasticizer and a mixture of
methyl ethyl ketone and toluene for serving as a solvent were added
to each sample of the mixed powder and mixed in a ball mill, to
prepare a slurry.
[0062] The obtained slurry was defoamed, and a green sheet of
aluminum nitride was formed as a compact by a doctor blade coater.
Paste mainly composed of tungsten powder having a mean grain size
of 1 .mu.m and containing 5 percent by weight of SiO.sub.2 frit was
applied to a surface of the green sheet, and degassed. Thereafter
the green sheet was fired in a nitrogen atmosphere at a temperature
of 1700.degree. C. for five hours, thereby baking the paste and
simultaneously sintering aluminum nitride. Part of each sample was
taken out in a stage of 1500.degree. C. in temperature in the
sintering process, to measure the carbon content in this stage.
[0063] Thus, a tungsten metallized layer of 10 .mu.m in thickness
was formed on the overall single surface of an aluminum nitride
sintered body of 25 mm by 25 mm having a thickness of 0.635 mm.
Ni-P plating was performed on the tungsten metallized layer of each
sample, which in turn was held in a nitrogen atmosphere at a
temperature of 600.degree. C. for 30 minutes to sinter the plating
layer. No abnormality such as blistering or peeling was observed on
the metallized layer and the plating layer. The thickness of every
plating layer was in the range of 6.+-.0.3 .mu.m.
[0064] An electrolytic copper material of JIS nominal C 1020,
identical in length and width to the aluminum nitride sintered
body, having a thickness of 1 mm was placed on each sample, and the
sample was arranged on a setter in a furnace and subjected to
furnace bonding in a nitrogen atmosphere at a temperature of
970.degree. C. for 30 minutes with no load. Ten test pieces for
each sample prepared in the aforementioned manner were subjected to
a test of repeating a cycle of holding the test pieces at a
temperature of 0.degree. C. for 15 minutes and thereafter holding
the same at a temperature of 100.degree. C. for 15 minutes 100
times. Strength values of the sintered bodies were relatively
compared with each other through ratios (number of cracked test
pieces/10) of cracked aluminum nitride sintered bodies resulting
from the cycle test. Samples of aluminum nitride sintered bodies
having no conductive layers were prepared in a similar manner to
the above, and subjected to evaluation of the mean grain size,
relative density and thermal conductivity. Table 1 shows the
results.
1 TABLE 1 Carbon Characteristics of Amount of Carbon Content in AlN
Sintered Body Carbon Content Sintered Mean Relative Thermal Powder
at 1500.degree. C. Body Grain Size Density Conductivity Sample (wt.
%) (wt. %) (wt. %) Cracking (.mu.m) (%) (W/mK) 1 0.008 0.007 0.004
7/10 3.5 100 100 2 0.013 0.011 0.007 2/10 2.9 100 150 3 0.03 0.03
0.02 1/10 2.8 100 160 4 0.1 0.07 0.06 0/10 2.7 100 160 5 0.3 0.08
0.07 0/10 2.5 100 165 6 1.0 0.09 0.08 0/10 1.8 99 170 7 1.9 0.095
0.09 0/10 1.7 99 170 8 3.0 0.30 0.20 8/10 1.5 95 160
[0065] As understood from the above results, crystal grains grow in
the sintered body due to insufficient reduction of oxides in
sintering if the amount of carbon black is less than 0.01 percent
by weight, to lower the strength of the sintered body and cause
cracking resulting from thermal shock. If the amount of carbon
black exceeds 2 percent by weight, sintering is hindered and the
density of the sintered body is lowered, leading to a tendency of
causing a large number of cracks. It is also understood that the
carbon content at the temperature of 1500.degree. C. in the
sintering process is preferably in the range of at least 0.01
percent by weight and not more than 0.1 percent by weight.
EXAMPLE 2
[0066] Samples Nos. 1 to 8 were prepared by providing tungsten
metallized layers and Ni-P plating layers on aluminum nitride
sintered bodies, similarly to Example 1. A metal layer of 0.2 mm in
thickness and 5.0 mm in width was bonded onto the Ni-P plating
layer of each sample so that the bonding length was 3 mm, and a
grip part of the metal layer perpendicularly projected upward from
an end of the bonded portion was pulled upward at a speed of 20
mm/min., for measuring peel strength of a conductive layer formed
by metallization. Table 2 shows the results.
2 TABLE 2 Sample Peel Strength (kg/mm) 1 1.3.about.2.0 2
1.8.about.2.5 3 2.0.about.2.3 4 2.3.about.2.6 5 2.4.about.2.6 6
2.5.about.2.8 7 2.4.about.2.6 8 1.5.about.1.7
[0067] As understood from the above results, grain growth in the
sintered body was suppressed and compounds of the alkaline earth
metal element and the rare earth element were homogeneously
distributed while wettability between the aluminum nitride grains
and the metals were improved due to the presence of carbon in each
of the samples Nos. 2 to 7 having the amount of carbon black in the
range of at least 0.01 percent by weight and not more than 2
percent by weight, whereby the adhesion strength of the conductive
layer was improved.
[0068] In the sample No. 1 containing the carbon black in the
amount of less than 0.01 percent by weight, however, compounds of
the alkaline earth metal element and the rare earth element were
segregated due to grain growth, to cause portions having
insufficient metallization strength in a microscopic point of view.
Further, the wettability between the metals and the aluminum
nitride grains was lowered due to reduction of the carbon content
in the sintered body. Thus, the peel strength of the sample No. 1
was lowered. In the sample No. 8 containing the carbon black in the
amount exceeding 2 percent by weight, the sinterability was
inhibited to lower the strength of the sintered body. Thus,
cracking was caused inside the aluminum nitride sintered body as a
result of peel strength evaluation, to lower the measured
value.
EXAMPLE 3
[0069] Samples of mixed powder of 100 percent by weight in total
were prepared by adding aluminum nitride powder (mean grain size:
0.8 .mu.m, oxygen content: 1.0 percent by weight) obtained by
reduction nitriding to polyvinyl butyral (PVB), employed as a
compound liberating carbon, in amounts shown in Table 3, 1.13
percent by weight of calcium carbonate in terms of an oxide and 3
percent by weight of neodymium oxide. A green sheet was prepared as
a compact from each sample by a method similar to that in Example
1, and thereafter tungsten paste was printed on the green sheet
similarly to Example 1. The compact was heat-treated in a nitrogen
atmosphere at a temperature of 1000.degree. C. for 10 hours thereby
liberating carbon, and thereafter fired at a temperature of
1650.degree. C. for five hours thereby forming an aluminum nitride
sintered body of 25 mm by 25 mm having a thickness of 0.635 mm,
formed with a tungsten metallized layer of 10 .mu.m in thickness on
its surface.
[0070] An Ni-P plating layer was formed on the tungsten metallized
layer of each sample similarly to Example 1, and thereafter the
sample was subjected to evaluation similar to that in Example 1.
Aluminum nitride sintered bodies haling no such metallized layers
and plating layers were similarly prepared and subjected to
evaluation similar to that in Example 1. Table 3 shows the
results.
3 TABLE 3 Carbon Characteristics of Amount Carbon Content in AlN
Sintered Body of Content Sintered Mean Relative Thermal PVB at
1500.degree. C. Body Grain Size Density Conductivity Sample (wt. %)
(wt. %) (wt. %) Cracking (.mu.m) (%) (W/mK) 9 0.004 0.007 0.004
6/10 3.2 100 90 10 0.013 0.011 0.007 2/10 2.8 100 140 11 0.040
0.030 0.021 1/10 2.6 100 150 12 0.15 0.059 0.044 1/10 2.5 100 152
13 0.50 0.065 0.051 0/10 2.4 99 158 14 2.0 0.071 0.063 0/10 2.3 99
162 15 6.0 0.080 0.071 1/10 2.2 99 164 16 10.0 0.089 0.081 1/10 1.9
99 166 17 18.0 0.095 0.092 2/10 1.8 99 170 18 25.0 0.30 0.15 7/10
1.5 96 150
[0071] It is understood from the above results that an aluminum
nitride sintered body having excellent strength can be obtained
even if employing polyvinyl butyral, calcium carbonate and
neodymium oxide as a carbon source, an alkaline earth metal element
compound and a rare earth element compound respectively, by
controlling the amounts thereof so that carbon remains in the
aluminum nitride sintered body in the range of at least 0.005
percent by weight and not more than 0.10 percent by weight,
similarly to Example 1.
EXAMPLE 4
[0072] Samples of mixed powder of 100 percent by weight in total
were prepared by adding aluminum nitride powder (mean grain size:
1.5 .mu.m, oxygen content with respect to the weight of aluminum
nitride powder: 1.2 percent by weight) obtained by reduction
nitriding to 3.14 percent by weight of barium carbonate in terms of
an oxide and 8 percent by weight of neodymium oxide. Green sheets
were prepared as compacts from these samples of mixed powder by a
doctor blade coater, similarly to Example 1. Paste mainly composed
of tungsten powder of 1 .mu.m in mean grain size and containing 5
percent by weight of SiO.sub.2 frit was applied to each green sheet
and degassed, and thereafter the green sheet was fired in an
atmosphere shown in Table 4 at a temperature of 1600.degree. C. for
six hours, to bake the paste and simultaneously sinter aluminum
nitride.
[0073] Thus, a tungsten metallized layer of 10 .mu.m in thickness
was formed on the overall single surface of each aluminum nitride
sintered body of 25 mm by 25 mm having a thickness of 0.635 mm.
Thereafter an Ni-P plating layer was formed on the tungsten
metallized layer similarly to Example 1, and subjected to
evaluation similar to that in Example 1. Aluminum nitride sintered
bodies formed with no such metallized layers and plating layers
were similarly prepared and evaluated similarly to Example 1. Table
4 shows the results.
4 TABLE 4 Carbon Characteristics of AlN Sintered Body Content in
Mean Grain Relative Thermal Atmosphere in Sintering Sintered Body
Size Density Conductivity Sample (vol. %) (wt. %) Cracking (.mu.m)
(%) (W/mK) 19 nitrogen (100) 0.001 8/10 3.7 100 85 20 methane(5) +
nitrogen(95) 0.003 3/10 3.3 100 110 21 butane(15) + ammonia(85)
0.007 1/10 2.8 100 120 22 acetylene(30) + nitrogen(70) 0.01 0/10
2.5 100 120 23 butane(50) + nitrogen(50) 0.02 0/10 2.3 100 140 24
acetylene(60) + nitrogen(40) 0.04 0/10 2.4 100 130 25 methane(80) +
ammonia(20) 0.06 0/10 1.9 100 140 26 butane(100) 0.08 0/10 1.8 100
130
[0074] It is understood from the above results that the amount of
carbon remaining in the sintered body can be controlled through the
amount of hydrocarbon contained in the firing atmosphere and the
amount of carbon contained in the sintered body can be controlled
to at least 0.005 percent by weight and not more than 0.10 percent
by weight by sintering the compact in the atmosphere containing at
least 10 percent by weight of hydrocarbon gas for obtaining an
aluminum nitride sintered body having excellent strength.
EXAMPLE 5
[0075] Samples of aluminum nitride sintered bodies were prepared by
a method similar to that for the sample No. 15 of Example 3 while
setting only the mean grain sizes of employed aluminum nitride
powder as shown in Table 5, and subjected to evaluation similar to
that in Example 3. Table 5 shows the results.
5 TABLE 5 Mean Carbon Characteristics of Grain Size Carbon Content
in AlN Sintered Body of AlN Content Sintered Mean Relative Thermal
Powder at 1500.degree. C. Body Grain Size Density Conductivity
Sample (wt. %) (wt. %) (wt. %) Cracking (.mu.m) (%) (W/mK) 27 0.4
compact cracked and unsintered 28 0.6 0.13 0.11 4/10 1.9 97 140 15
0.8 0.080 0.071 1/10 2.2 99 164 29 1.3 0.072 0.042 1/10 2.6 99 160
30 1.8 0.044 0.030 1/10 2.8 100 152 31 2.4 0.022 0.015 5/10 3.5 100
130 Note: Sample No. 15 is identical to sample No. 15 in Example
3.
[0076] It is understood from the above results that the binder
enters small clearances between the aluminum nitride grains to
lower the strength of the compact or degreasing is made so
difficult that excess carbon remains in the sintered body to lower
sinterability if the mean grain size of the material aluminum
nitride powder is less than 0.8 .mu.m. If the mean grain size of
the aluminum nitride powder exceeds 2 ,.mu.m, the mean grain size
of the sintered body exceeds 3 .mu.m to lower the strength of the
sintered body as a result.
EXAMPLE 6
[0077] Samples of aluminum nitride sintered bodies were prepared by
a method similar to that for the sample No. 26 of Example 4 while
setting only the oxygen contents in the aluminum nitride powder as
shown in Table 6, and subjected to evaluation similar to that in
Example 4. Table 6 shows the results.
6 TABLE 6 Oxygen Carbon Characteristics of AlN Sintered Body
Content in Content in Mean Relative Thermal AlN Powder Sintered
Body Grain Size Density Conductivity Sample (wt. %) (wt. %)
Cracking (.mu.m) (%) (W/mK) 32 0.5 0.09 5/10 1.7 95 110 33 0.8 0.08
0/10 1.8 100 133 26 1.2 0.08 0/10 1.8 100 130 34 1.5 0.04 1/10 2.9
100 122 35 2.0 0.03 6/10 3.3 100 120 Note: Sample No. 26 is
identical to sample No. 26 in Example 4.
[0078] It is understood from the above results that the strength of
the sintered body may be deteriorated due to reduction of the
sinterability if the oxygen content in the aluminum nitride powder
is less than 0.8 percent by weight, while the oxygen content cannot
be controlled but the mean grain size of the sintered body is
increased if the oxygen content is in excess of 1.5 percent by
weight. Thus, the strength of the sintered body may be lowed also
in this case.
EXAMPLE 7
[0079] Samples of aluminum nitride sintered bodies were prepared by
a method similar to that for the sample No. 3 of Example 1 while
setting only the sintering temperatures as shown in Table 7, and
subjected to evaluation similar to that in Example 1. Table 7 shows
the results.
7 TABLE 7 Carbon Characteristics of Sintering Carbon Content in AlN
Sintered Body Tempera- Content Sintered Mean Relative Thermal ture
at 1500.degree. C. Body Grain Size Density Conductivity Sample
(.degree. C.) (wt. %) (wt. %) Cracking (.mu.m) (%) (W/mK) 36 1600
0.03 0.02 2/10 1.9 99 120 37 1650 0.03 002 2/10 23 100 150 3 1700
0.03 0.02 1/10 2.8 100 160 38 1750 0.03 0.02 7/10 3.7 100 180 39
1800 0.03 0.02 8/10 4.0 100 200 Note: Sample No. 3 is identical to
sample No. 3 in Example 1.
[0080] It is understood from the above results that the mean grain
size of the sintered body exceeds 3 .mu.m if the sintering
temperature exceeds 1700.degree. C. and hence the strength of the
sintered body is lowered to increase the ratio of cracking in the
heat cycle evaluation described with reference to Example 1 as a
result.
EXAMPLE 8
[0081] Samples of aluminum nitride sintered bodies were prepared by
a method similar to that in Example 1 while setting the contents of
yttrium oxide and calcium oxide remaining in the sintered bodies as
shown in Table 8 , and subjected to evaluation similar to that in
Example 1. Table 8 shows the results.
8 TABLE 8 Characteristics of Carbon AlN Sintered Body Content
Content in Mean Carbon Sintered Grain Relative Thermal
Y.sub.2O.sub.3 CaO Powder Body Size Density Conductivity Sample
(wt. %) (wt. %) (wt. %) (wt. %) Cracking (.mu.m) (%) (W/mK) 1 0.005
1.0 0.1 0.06 9/10 1.6 85.0 80 2 0.05 1.0 0.1 0.06 1/10 2.4 99.0 152
3 1 1.0 0.1 0.06 0/10 2.6 100.0 167 4 6 1.0 0.1 0.06 0/10 2.7 100.0
160 5 9 1.0 0.1 0.06 0/10 2.4 99.4 165 6 12 1.0 0.1 0.06 2/10 23
990 110 7 3 0.005 0.1 0.06 10/10 1.1 80.0 75 8 3 0.05 0.1 0.06 1/10
2.3 99.0 154 10 3 1.0 0.1 0.06 0/10 2.6 100.0 169 11 3 3.0 0.1 0.06
0/10 2.5 99.7 157 12 3 7.0 0.1 0.06 6/10 2.0 97.6 98 Note: Sample
No. 4 is identical to sample No. 4 in Example 1.
[0082] It is understood from Table 8 that preferable
characteristics can be obtained if the content of Y.sub.2O.sub.3 is
at least 0.01 percent by weight and not more than 10 percent by
weight and the content of CaO is at least 0.01 percent by weight
and not more than 5 percent by weight.
[0083] According to the present invention, as clearly understood
from the aforementioned Examples, an aluminum nitride sintered body
excellent in thermal shock resistance and strength and improved in
adhesion strength to a conductive layer or an insulating layer
formed by a thick film paste method can be provided by controlling
the amount of carbon thereby suppressing grain growth when
sintering aluminum nitride with a sintering aid containing a rare
earth element and an alkaline earth metal element. Thus, the
aluminum nitride sintered body according to the present invention
is applicable to a radiating substrate for a power module or a jig
for semiconductor equipment used under a strict heat cycle.
[0084] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *