U.S. patent application number 13/348772 was filed with the patent office on 2012-05-03 for semiconductor device and method for manufacturing the same.
This patent application is currently assigned to Kabushiki Kalsha Toshiba. Invention is credited to Tsunehiro INO, Yasushi NAKASAKI.
Application Number | 20120108078 13/348772 |
Document ID | / |
Family ID | 38647556 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120108078 |
Kind Code |
A1 |
INO; Tsunehiro ; et
al. |
May 3, 2012 |
SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME
Abstract
It is made possible to provide a semiconductor device and a
method for manufacturing the semiconductor device that have the
highest possible permittivity and can be produced at low production
costs. A method for manufacturing a semiconductor device, includes:
forming an amorphous film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2-y
(0.81.ltoreq.x.ltoreq.0.99, 0.04.ltoreq.y.ltoreq.0.25,
0.ltoreq.z.ltoreq.1) on a semiconductor substrate, the ranges of
composition ratios x, y, and z being values measured by XPS; and
transforming the amorphous film into an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2 as tetragonal crystals,
by performing annealing at 750.degree. C. or higher on the
amorphous film in an atmosphere containing oxygen.
Inventors: |
INO; Tsunehiro;
(Fujisawa-Shi, JP) ; NAKASAKI; Yasushi;
(Yokohama-Shi, JP) |
Assignee: |
Kabushiki Kalsha Toshiba
Tokyo
JP
|
Family ID: |
38647556 |
Appl. No.: |
13/348772 |
Filed: |
January 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11790854 |
Apr 27, 2007 |
8115261 |
|
|
13348772 |
|
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Current U.S.
Class: |
438/785 ;
257/E21.24 |
Current CPC
Class: |
H01L 27/11526 20130101;
H01L 29/517 20130101; H01L 27/115 20130101; H01L 29/7881 20130101;
H01L 21/02148 20130101; H01L 21/28194 20130101; H01L 29/40117
20190801; H01L 21/31608 20130101; H01L 21/02356 20130101; H01L
21/31641 20130101; H01L 21/02159 20130101; H01L 21/02337 20130101;
C23C 14/08 20130101; H01L 21/31645 20130101; C23C 14/5806 20130101;
H01L 27/11546 20130101; H01L 29/792 20130101; H01L 21/31604
20130101; H01L 21/02161 20130101; H01L 27/11568 20130101; H01L
21/02266 20130101; H01L 29/513 20130101; C23C 14/5853 20130101 |
Class at
Publication: |
438/785 ;
257/E21.24 |
International
Class: |
H01L 21/31 20060101
H01L021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2006 |
JP |
2006-125735 |
Claims
1. A method for manufacturing a semiconductor device, comprising:
forming an amorphous film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2-y
(0.81.ltoreq.x.ltoreq.0.99, 0.04.ltoreq.y.ltoreq.0.25,
0.ltoreq.z.ltoreq.1) on a semiconductor substrate, the ranges of
composition ratios x, y, and z being values measured by XPS; and
transforming the amorphous film into an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2 as tetragonal crystals,
by performing annealing at 750.degree. C. or higher on the
amorphous film in an atmosphere containing oxygen.
2. The method according to claim 1, wherein a pressure in the
atmosphere in which the annealing is performed is atmospheric
pressure.
3. The method according to claim 1, wherein oxygen content in the
atmosphere containing oxygen is 1 ppm or higher.
4. The method according to claim 1, wherein oxygen content in the
atmosphere containing oxygen is 1% or higher.
5-22. (canceled)
23. The method according to claim 1, wherein molecular volume
V.sub.m of tetragonal crystals in the insulating film is in the
range of 0.03353 nm.sup.3.ltoreq.V.sub.m.ltoreq.0.03424 nm.sup.3,
and the insulating film has a physical film thickness of 110 nm or
smaller.
24. The method according to claim 1, wherein lattice constants a,
b, and c of tetragonal unit cells in the insulating film are in the
ranges of 0.3590 nm.ltoreq.a.ltoreq.0.3608 nm, 0.3590
nm.ltoreq.b.ltoreq.0.3608 nm, and 0.5183 nm.ltoreq.c.ltoreq.0.5212
nm, respectively.
25. The method according to claim 1, wherein the insulating film
has relative permittivity ranging from 20 to 26; and molar
polarizability .alpha. of atoms constituting the insulating film is
in the range of 0.00679 nm.sup.3<.alpha..ltoreq.0.00735
nm.sup.3.
26. The method according to claim 1, wherein a' axis of the
tetragonal crystals in the semiconductor film extends substantially
parallel to a film thickness direction of the insulating film.
27. The method according to claim 1, wherein the stress applied
onto the insulating film is 1 GPa or smaller.
28. The method according to claim 1, wherein the insulating film is
a gate insulating film of a CMOSFET.
29. The method according to claim 1, wherein the insulating film is
an interelectrode insulating film of a floating gate type flash
memory.
30. The method according to claim 1, wherein the insulating film is
a blocking insulating film of a MONOS type flash memory.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2006-125735
filed on Apr. 28, 2006 in Japan, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a semiconductor device and
a method for manufacturing the semiconductor device.
[0004] 2. Related Art
[0005] The insulating films in semiconductor devices have become
thinner by the improved semiconductor techniques for producing
smaller devices. In semiconductor production, SiO.sub.2 is an
excellent insulating material, and has been used over a long period
of time. In a gate insulating film, however, the film thickness of
a SiO.sub.2 film has become as small as the size equivalent to a
few atomic layers. As a result, it has become difficult in
principle to restrain current leakage through such a thin
insulating film. Instead of SiO.sub.2, a material having higher
permittivity can be used as an insulating film, and the material
can electrically serve as if it were a thin SiO.sub.2 film. Even if
such a film is thicker than the few atomic layers in the case of a
SiO.sub.2 film, the film is electrically equivalent to the
SiO.sub.2 film. Accordingly, it is assumed that current leakage can
be restrained with such a film.
[0006] In a flash memory or the like, there is an interelectrode
insulating film that isolates the control gate from the floating
gate. However, such an interelectrode insulating film is also
expected to have higher permittivity, as the device size has become
smaller.
[0007] In this trend, high-permittivity insulating films (high-k
films) have been studied, and as of today, gate insulating films
containing hafnium are considered to have the greatest potential.
However, the permittivity of a gate insulating film containing
hafnium is approximately 25 at a maximum. In practice, the
composition ratio of hafnium is highly likely to be lower than
that. Therefore, such a gate insulating film containing hafnium as
a high-k film can achieve relative permittivity as low as 12.
[0008] If a tetragonal crystalline structure can be formed from
zirconia (zirconium oxide) or hafnia (hafnium oxide) through the
first principle calculation, higher relative permittivity might be
achieved. This possibility is suggested in by G. M. Ringanese, X.
Gonze, G. Jun, K. Cho, and A. Pasquarello in Phys. Rev. B69, 184301
(2004) (hereinafter referred to as Reference 1), for example. To
confirm the possibility through experiments, they have tried to
form tetragonal crystalline structures by adding yttrium to
zirconia or hafnia (disclosed by H. Kita, K. Kyuno, and A. Toriumi,
in Appl. Phys. Lett. 86, 102906 (2005)) (hereinafter referred to as
Reference 2).
[0009] Further, increases in permittivity by adding silicon to
hafnia are disclosed by I. Tomida, H. Kita, K. Kyuno, and A.
Toriumi in Appl. Phys. Spring Lectures, 25P-V-3, 2006 (hereinafter
referred to as Reference 3).
[0010] By the technique disclosed in Reference 2, however, a
tetragonal crystalline structure has not successfully been produced
to provide the highest relative permittivity, as can be seen from
the X-ray diffraction profiles.
[0011] In Reference 2, they tried to increase the permittivity by
using rare-earth elements or alkaline-earth elements that were
rarely used in semiconductor processes. Since those elements are
soluble with zirconia and hafnia, it was considered that the
permittivity could be easily increased with those materials.
However, in the real semiconductor manufacturing processes that
thoroughly refuse contamination, it is not easy to predict all the
side effects and adverse influence that might be caused by the
introduction of a rare-earth element or an alkaline-earth element.
Therefore, the costs for introducing rare-earth elements or
alkaline-earth elements are predicted to be very high.
[0012] If the dielectric disclosed in Reference 3 is used as a gate
insulating film in real LSI production, as described later, the
mobility might be reduced due to the stress exerted on the channel
region in direct contact with the gate insulating film, or lattice
relaxation to reduce the relative permittivity to the original
value might be caused in the gate insulating film, or the gate
insulating film might break itself because of the stress. As a
result, the device characteristics might be degraded.
SUMMARY OF THE INVENTION
[0013] The present invention has been made in view of these
circumstances, and an object thereof is to provide a semiconductor
device and a method for manufacturing the semiconductor device that
have the highest possible permittivity and can be produced at low
production costs.
[0014] A method for manufacturing a semiconductor device according
to a first aspect of the present invention includes:
[0015] forming an amorphous film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2-y (0.81
.ltoreq.x.ltoreq.0.99, 0.04.ltoreq.y.ltoreq.0.25,
0.ltoreq.z.ltoreq.1) on a semiconductor substrate, the ranges of
composition ratios x, y, and z being values measured by XPS; and
transforming the amorphous film into an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2 as tetragonal crystals,
by performing annealing at 750.degree. C. or higher on the
amorphous film in an atmosphere containing oxygen.
[0016] A method for manufacturing a semiconductor device according
to a second aspect of the present invention includes: forming an
amorphous film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2-y
(0.76.ltoreq.x.ltoreq.0.985, 0.04.ltoreq.y.ltoreq.0.25,
0.ltoreq.z.ltoreq.1) on a semiconductor substrate, the ranges of
composition ratios x and z being values measured by RBS, the range
of a composition ratio y being values measured by XPS; and
transforming the amorphous film into an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2 as tetragonal crystals,
by performing annealing at 750.degree. C. or higher on the
amorphous film in an atmosphere containing oxygen.
[0017] A semiconductor device according to a third aspect of the
present invention includes: an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2
(0.81.ltoreq.x.ltoreq.0.99, 0.ltoreq.z.ltoreq.1) formed on a
semiconductor substrate, the ranges of composition ratios x and z
being values measured by XPS, the insulating film having a main
phase that is a tetragonal fluorite-type crystalline structure,
molecular volume V.sub.m of tetragonal crystals in the insulating
film being in the range of 0.03353
nm.sup.3.ltoreq.V.sub.m.ltoreq.0.03424 nm.sup.3 per
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2, the insulating film
having a physical film thickness of 110 nm or smaller.
[0018] A semiconductor device according to a fourth aspect of the
present invention includes: an insulating film containing
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2
(0.76.ltoreq.x.ltoreq.0.985, 0.ltoreq.z.ltoreq.1) formed on a
semiconductor substrate, the ranges of composition ratios x and z
being values measured by RBS, the insulating film having a main
phase that is a tetragonal fluorite-type crystalline structure,
molecular volume V.sub.m of tetragonal crystals in the insulating
film being in the range of 0.03353
nm.sup.3.ltoreq.V.sub.m.ltoreq.0.03424 nm.sup.3 per
(Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2, the insulating film
having a physical film thickness of 110 nm or smaller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a flowchart showing the procedures by a method for
manufacturing a semiconductor device in accordance with each
embodiment;
[0020] FIG. 2 shows an X-ray diffraction profile indicating a
tetragonal crystalline state in an insulating film produced by a
manufacturing method in accordance with a first embodiment;
[0021] FIG. 3 shows X-ray diffraction peak intensities calculated
with respect to a variety of zirconia crystalline structures;
[0022] FIG. 4 is a temperature-pressure phase diagram about
zirconia;
[0023] FIG. 5 shows an X-ray diffraction profile indicating a
tetragonal crystalline state in an insulating film produced by a
manufacturing method in accordance with a second embodiment;
[0024] FIG. 6 is a temperature-pressure phase diagram about
hafnia;
[0025] FIG. 7 shows the existence of a Zr-Si bond by XPS in an
insulating film that has an oxygen defect and is produced by a
manufacturing method in accordance with a fourth embodiment;
[0026] FIG. 8 shows X-ray diffraction profiles indicating that
tetragonal crystals are obtained in thin insulating films of 10 nm
or 5 nm in film thickness produced by a manufacturing method in
accordance with the fourth embodiment;
[0027] FIG. 9 shows the relative permittivity observed by examining
the electric properties of insulating films produced by the
manufacturing method in accordance with the fourth embodiment;
[0028] FIG. 10 is a phase diagram of HfO.sub.2 and ZrO.sub.2 at all
ratios;
[0029] FIG. 11 is a cross-sectional view of a CMOS device as a
specific example of a sixth embodiment;
[0030] FIG. 12 is a cross-sectional view of a memory cell of a
floating gate type flash memory as a second specific example of the
sixth embodiment;
[0031] FIG. 13 shows the pressure dependence of the unit call
volume of hafnia crystals;
[0032] FIG. 14 shows the X-ray diffraction profiles of insulating
films of Zr.sub.xSi.sub.1-xO.sub.2 where the composition ratio x of
Zr is 0.86, 0.90, 0.94, 0.98, and 1.00 in XPS measurement; and
[0033] FIG. 15 is a cross-sectional view of a memory cell of a
MONOS type flash memory.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The following is a description of embodiments of the present
invention, with reference to the accompanying drawings.
[0035] In each of the embodiments of the present invention, Si,
which is generally considered not soluble, is added to zirconia or
hafnia, so as to increase the permittivity. In XPS (X-ray
Photoelectron Spectroscopy) measurement, 6 atomic % to 14 atomic %
of Si is added, and in RBS (Rutherford Back-scattering
Spectrometry) measurement, 8 atomic % to 19 atomic % of Si is
added, so as to form a thin film having tetragonal crystals with a
lattice constant approximately 1% smaller than that of conventional
tetragonal crystals. This thin film has a crystalline structure in
which the moving range of oxygen ions in the tetragonal crystals is
wider. As the polarizability is approximately 8% higher, a
permittivity of 20 to 26 that is higher than 17, which is the
relative permittivity of zirconia and hafnia, can be achieved.
[0036] In the following embodiments, in the XPS measurement, the
relative sensitivity coefficient of a Si2p peak is 0.37, the
relative sensitivity coefficient of Zr3d is 2.40, and the relative
sensitivity coefficient of Hf4f is 2.56. In the RBS measurement,
He.sup.+ ions are used with an acceleration voltage of 2.275 MeV, a
scattering angle of 160 degrees, and a dose amount of 40 .mu.c.
First Embodiment
[0037] A method for manufacturing a semiconductor device in
accordance with a first embodiment of the present invention is
described.
[0038] First, as shown in step S1 of FIG. 1, an amorphous
insulating film that had a composition of
Zr.sub.0.86Si.sub.0.14O.sub.1.75 in the XPS measurement with a
smaller amount of oxygen than the oxygen stoichiometry was formed
on a single-crystal silicon substrate that had a natural oxide film
removed with a diluted hydrofluoric acid. The amorphous insulating
film was formed by a sputtering technique, and the film formation
was carried out in a mixed atmosphere of argon and oxygen, with Zr
and Si being the targets. The amount of oxygen loss is the value
obtained on the basis of the ratio of the peak intensity of a Zr-O
bond of Zr3d measured by XPS to the peak intensity of a Zr-Zr or
Zr-Si bond measured by XPS, on the assumption that the peaks of
Zr-Zr and Zr-Si bonds were all caused by the oxygen loss.
[0039] As shown in step S2 of FIG. 1, the substrate having the
amorphous insulating film formed with
Zr.sub.0.86Si.sub.0.14O.sub.1.75 was placed in a heat treatment
chamber, and was subjected to heat treatment. The heat treatment
was performed at 800.degree. C., and the heat treatment time was 30
seconds. The atmosphere gas for the heat treatment was a mixed gas
of nitrogen and oxygen, and the mixed gas was a nitrogen-based gas,
containing only 1 ppm of oxygen. The pressure in the heat treatment
was atmospheric pressure. The oxygen defect in the amorphous
insulating film formed with Zr.sub.0.86Si.sub.0.14O.sub.1.75 was
compensated for in the above heat treatment, and the amorphous
insulating film formed with Zr.sub.0.86Si.sub.0.14O.sub.1.75 was
transformed into an insulating film formed with
Zr.sub.0.86Si.sub.0.14O.sub.2. The fact that there was no oxygen
loss in the sample after the heat treatment was proved by the
phenomenon that there were no peaks of Zr-Zr or Zr-Si bonds in the
XPS measurement.
[0040] Next, X-ray diffraction measurement was carried out for the
insulating film formed with Zr.sub.0.86Si.sub.0.14O.sub.2. The
X-ray diffraction profile obtained as a result of the measurement
is shown in FIG. 2. The X-ray diffraction profile shown in FIG. 2
is similar to the X-ray diffraction profile of tetragonal zirconia
calculated and shown in FIG. 3. Therefore, the insulating film
formed with Zr.sub.0.86Si.sub.0.14O.sub.2 produced by the method of
this embodiment can be considered to be tetragonal zirconia.
However, when the lattice constant of the insulating film formed
with Zr.sub.0.86Si.sub.0.14O.sub.2 produced by the method of this
embodiment was measured through X-ray diffraction and was compared
with the lattice constant (a=b=0.3640 nm, c=0.5270 nm) of
tetragonal zirconia disclosed in "Acta Cryst. 15, 1187, 62", the
lattice constant of the insulating film formed with
Zr.sub.0.86Si.sub.0.14O.sub.2 produced by the method of this
embodiment was approximately 1% lower (a=b=0.3605.+-.0.0003 nm,
c=0.5206.+-.0.0006 nm). FIG. 3 shows the X-ray diffraction peak
intensities calculated with respect to a variety of zirconia
crystalline structures.
[0041] The reason that an insulating film having a tetragonal
zirconia crystalline structure that has been difficult to produce
can be formed by the method of this embodiment is considered to be
the existence of stress applied onto the insulating film. More
specifically, by the method of this embodiment, an amorphous
insulating film that had a composition of
Zr.sub.0.86Si.sub.0.14O.sub.1.75 with a smaller amount of oxygen
than the oxygen stoichiometry was first formed. Annealing was then
performed to compensate for the oxygen defect. As a result, the
volume of the insulating film increased. However, since the
insulating film was attached to the substrate, the insulating film
could not expand in the in-plane direction. Compressive stress was
then applied onto the insulating film, resulting in an
approximately 1% decrease of the lattice constant of the crystals
of the insulating film.
[0042] FIG. 4 is a temperature-pressure phase diagram about
zirconia (see J. M. Leger, P. E. Tomaszewski, A. Atouf, and A. S.
Pereira, Phys. Rev. B47, 14075 (1993)). As is clear from FIG. 4, as
the pressure becomes higher, the temperature at which the
tetragonal crystals in zirconia can stably exist in a crystalline
state becomes lower. Accordingly, since the requirements for
obtaining stable tetragonal crystals at room temperature were
satisfied, the production of tetragonal crystals by the
manufacturing method of this embodiment is considered to be a
success.
[0043] Here, the insulating film disclosed in Reference 3 is again
described. The insulating film disclosed in Reference 3 has a
permittivity increased by adding silicon to hafnia. The molar
polarizability of the atoms in the insulating film disclosed in
Reference 3 is in the range of 0.00669 nm.sup.3 to 0.00673
nm.sup.3, and does not change substantially. In that structure, the
permittivity is increased by reducing the molecular volume (or the
molar volume) by approximately 9%. According to a calculation made
by the inventor, to achieve such a small molecular volume, the
stress exered by distortions in the insulating film must be as
large as 9 GPa. FIG. 13 shows the results of examinations that were
conducted to check changes in lattice constant by applying stress
onto hafnia (see Osamu Ohtaka, Hiroshi Fukui, Taichi Kunisada,
Tomoyuki Fujisawa, Kenichi Funakoshi, Wataru Utsumi, Tetsuo
Irifune, Koji Kuroda, and Takumi Kikegawa, J. Am. Ceram. Soc.,
84[6] 1369-73 (2001)). In FIG. 13, the abscissa axis indicates the
stress to be applied, and the ordinate axis indicates the rate of
the volume V of each unit lattice of hafnia crystals at the applied
pressure to the volume V.sub.0 of each unit lattice of hafnia
crystals at atmospheric pressure. As can be seen from FIG. 13, the
hafnia that is in a thermal equilibrium state at atmospheric
pressure has phase transition to an orthorhombic phase I at a high
pressure, and has further phase transition to an orthorhombic phase
II at a higher pressure. Those crystalline structures are different
from tetragonal crystalline structures, but FIG. 13 shows that a
stress as large as 10 GPa needs to be applied so as to reduce the
molecular volume by 9% in a monoclinic crystalline structure. In
other words, in a hafnia film having a 9% decrease in molecular
volume, a stress as large as 10 GPa is exerted. It is known that
even sapphire, which is the second hardest naturally-produced ore,
only next to diamond, cannot endure such a large stress with
crystals of macroscopic size. In a more precise estimate, the
stress in the film is not smaller than 8 GPa. Therefore, if the
insulating film disclosed in Reference 3 is used as a gate
insulating film in an actual LSI, the mobility might be reduced due
to the stress applied onto the channel region in direct contact
with the gate insulating film, lattice relaxation caused in the
gate insulating film might return the relative permittivity to the
original value, or the gate insulating film might break itself
because of the stress.
[0044] On the other hand, the stress applied onto the insulating
film of this embodiment is 1 GPa or smaller, which is much smaller
than the stress applied onto the insulating film disclosed in
Reference 3. Accordingly, the device characteristics do not
deteriorate.
[0045] Furthermore, Si, which is very often used in semiconductor
processes as an element to be added to zirconia, is used in this
embodiment. Accordingly, the production costs become as low as
possible.
[0046] Also, as described later, the insulating film produced in
this embodiment has a very high permittivity, with the relative
permittivity being 20 to 26, which is higher than the relative
permittivity of zirconia.
[0047] The composition of the above sample after the heat treatment
was determined by a direct measurement method in accordance with
RBS, to obtain the composition values of
Zr.sub.0.81Si.sub.0.19O.sub.2. As long as the measurement carried
out by us is concerned, the molar ratio of [Si]/([Zr]+[Si])
determined by a direct measurement method in accordance with RBS is
considered to be more reliable. On the other hand, in the
semi-quantitative measurement by XPS, it is difficult to achieve
high reliability, as there is surface contamination or the like due
to the exposure of the sample in the atmosphere. However, the
amount of oxygen loss is more accurate in the measurement by the
XPS, since the oxygen peak intensity is very low by RBS.
Accordingly, it is assumed that a composition of
Zr.sub.0.81Si.sub.0.19O.sub.1.75 is obtained by determining the
molar ratio of [Si]/([Zr]+[Si]) by RBS and determining the amount
of oxygen loss by XPS in the sample in an as-depo state before the
heat treatment.
Second Embodiment
[0048] Next, a method for manufacturing a semiconductor device in
accordance with a second embodiment of the present invention is
described.
[0049] First, as shown in step S1 of FIG. 1, an amorphous
insulating film that had a composition of
Zr.sub.0.81Si.sub.0.19O.sub.1.80 in the semi-quantitative
measurement by XPS with a smaller amount of oxygen than the oxygen
stoichiometry was formed on a single-crystal silicon substrate that
had a natural oxide film removed with a diluted hydrofluoric acid.
The amorphous insulating film was formed by a sputtering technique,
and the film formation was carried out in a mixed atmosphere of
argon and oxygen, with Zr and Si being the targets.
[0050] As shown in step S2 of FIG. 1, the substrate having the
amorphous insulating film formed with
Zr.sub.0.81Si.sub.0.19O.sub.1.80 was placed in a heat treatment
chamber, and was subjected to heat treatment. The heat treatment
was performed at 800.degree. C., and the heat treatment time was 8
minutes. The atmosphere gas for the heat treatment was a mixed gas
of argon and oxygen, and the mixed gas was an argon-based gas,
containing only 10 ppm of oxygen. The pressure in the heat
treatment was atmospheric pressure. The oxygen defect in the
amorphous insulating film formed with
Zr.sub.0.81Si.sub.0.19O.sub.1.80 was compensated for in the above
heat treatment, and the amorphous insulating film formed with
Zr.sub.0.81Si.sub.0.19O.sub.1.80 was transformed into an insulating
film formed with Zr.sub.0.81Si.sub.0.19O.sub.2.
[0051] Next, X-ray diffraction measurement was carried out for the
insulating film formed with Zr.sub.0.81Si.sub.0.19O.sub.2. The
X-ray diffraction profile obtained as a result of the measurement
is shown in FIG. 5. The X-ray diffraction profile shown in FIG. 5
is similar to the X-ray diffraction profile of tetragonal zirconia
calculated and shown in FIG. 3. Therefore, the insulating film
formed with Zr.sub.0.81Si.sub.0.19O.sub.2 produced by the method of
this embodiment can be considered to be tetragonal zirconia.
However, when the lattice constant of the insulating film formed
with Zr.sub.0.81Si.sub.0.19O.sub.2 produced by the method of this
embodiment was measured through X-ray diffraction and was compared
with the lattice constant (a=b=0.3640 nm, c=0.5270 nm) of
tetragonal zirconia disclosed in "Acta Cryst. 15, 1187, 62", the
lattice constant of the insulating film formed with
Zr.sub.0.81Si.sub.0.19O.sub.2 produced by the method of this
embodiment was approximately 1% lower (a=b=0.3595.+-.0.0005 nm,
c=0.5190.+-.0.0007 nm). As in the first embodiment, this is because
that compressive stress was applied onto the insulating film
produced by the method of this embodiment, resulting in an
approximately 1% decrease of the lattice constant of the crystals
of the insulating film.
[0052] Thus, as in the first embodiment, a semiconductor device
that has a highest possible permittivity and do not degrade the
device characteristics can also be produced at low production costs
in this embodiment.
[0053] Here, the X-ray diffraction profile shown in FIG. 5 is
described in greater detail. On closer inspection, there is a small
peak of monoclinic zirconia, as indicated by reference numeral 10.
The reason of the existence of this peak may be that the addition
of Si increases to 19 atomic % in terms of the [Si]/([Si]+[Zr])
ratio. However, with such a small amount of monoclinic crystals
being added, the insulating film of this embodiment is still highly
usable as a high-k film.
[0054] The composition of this film after the heat treatment was
determined by a direct measurement method in accordance with RBS,
to obtain the composition values of Zr.sub.0.76Si.sub.0.24O.sub.2.
Accordingly, it can be assumed that a composition of
Zr.sub.0.76Si.sub.0.24O.sub.1.80 is obtained by determining the
molar ratio of [Si]/([Zr]+[Si]) by RBS and determining the amount
of oxygen loss by XPS in the sample in an as-depo state before the
heat treatment.
Third Embodiment
[0055] Next, a method for manufacturing a semiconductor device in
accordance with a third embodiment of the present invention is
described.
[0056] First, as shown in step S1 of FIG. 1, an amorphous
insulating film that had a composition of
Zr.sub.0.99Si.sub.0.01O.sub.1.90 in the measurement by XPS with a
smaller amount of oxygen than the oxygen stoichiometry was formed
on a single-crystal silicon substrate that had a natural oxide film
removed with a diluted hydrofluoric acid. The amorphous insulating
film was formed by a sputtering technique, and the film formation
was carried out in a mixed atmosphere of argon and oxygen, with Zr
and Si being the targets.
[0057] As shown in step S2 of FIG. 1, the substrate having the
amorphous insulating film formed with
Zr.sub.0.99Si.sub.0.01O.sub.1.90 was placed in a heat treatment
chamber, and was subjected to heat treatment. The heat treatment
was performed at 1050.degree. C., and the heat treatment time was 2
minutes. The atmosphere gas for the heat treatment was a pure
oxygen gas. The pressure in the heat treatment was atmospheric
pressure. Through this heat treatment, the amorphous insulating
film formed with Zr.sub.0.99Si.sub.0.01O.sub.1.90 was transformed
into an insulating film formed with
Zr.sub.0.99Si.sub.0.01O.sub.2.
[0058] X-ray diffraction measurement was carried out for the
insulating film formed with Zr.sub.0.99Si.sub.0.01O.sub.2 by the
manufacturing method of this embodiment. The X-ray diffraction
profile obtained as a result of the measurement was similar to the
X-ray diffraction profile of tetragonal zirconia. Therefore, the
insulating film formed with Zr.sub.0.99Si.sub.0.01O.sub.2 produced
by the method of this embodiment can be considered to be tetragonal
zirconia.
[0059] Thus, as in the first embodiment, a semiconductor device
that has a highest possible permittivity and do not degrade the
device characteristics can also be produced at low production costs
in this embodiment.
[0060] As can be seen from the above embodiments, tetragonal
crystals are obtained, with the heat treatment time being in the
range of 30 seconds to 8 minutes, the heat treatment temperature
being in the range of 800.degree. C. to 1050.degree. C., and the
oxygen concentration in the atmosphere gas being in the range of 1
ppm to 100%. Also, tetragonal crystals are obtained, with the
atmosphere gas pressure being varied from 10.sup.-2 Pa to 10.sup.5
Pa (atmospheric pressure).
[0061] As a comparative example, an insulating film having a
composition of Zr.sub.1-xSi.sub.xO.sub.2 without an oxygen defect
was formed. In this insulating film, only monoclinic or cubic
crystals appeared. After the insulating film having a composition
of Zr.sub.1-xSi.sub.xO.sub.2 as a comparative example was subjected
to heat treatment, the monoclinic-cubic ratio was easily
changed.
[0062] By any of the manufacturing methods of the first through
third embodiments, on the other hand, tetragonal crystals can be
maintained with a very wide range of heat treatment conditions. As
described above, it was found that there was a wide range of heat
treatment conditions in a ZrSiO film having tetragonal crystals
produced by any of the manufacturing methods of the first through
third embodiments, and the tetragonal crystals were maintained
after any type of heat treatment in each of the procedures for
manufacturing a real semiconductor device. This means that the
problem with the material disclosed in Reference 3, which cannot be
applied to an actual LSI process, is completely solved, and each of
the embodiments is beneficial in practical use.
[0063] In each of the first through third embodiments, an amorphous
insulating film that had a composition of
Zr.sub.xSi.sub.1-xO.sub.2-y (0.81.ltoreq.x.ltoreq.0.99,
0.10.ltoreq.y.ltoreq.0.25) in the measurement by XPS with an oxygen
defect was formed. However, exactly the same tetragonal crystals as
above can be obtained by using Hf, instead of Zr, and forming an
amorphous insulating film that has a composition of
Hf.sub.xSi.sub.1-xO.sub.2-y (0.81.ltoreq.x.ltoreq.0.99,
0.10.ltoreq.y.ltoreq.0.25) in the measurement by XPS with an oxygen
defect.
[0064] This is because Zr and Hf have chemical properties similar
to each other. Even with the technology as of year 2006, there is
1% of Hf contained in generally available Zr. Although it is
possible to separate the Hf from the Zr, doing so (to emphasize the
small difference between the two materials) is very costly. Like in
Zr, there is 1% of Zr contained in Hf. As is apparent from those
facts, the two materials have almost no differences. In a case
where a Zr oxide is compared with a Hf oxide, for example, a
similar phase diagram can be formed for the Hf oxide, as shown in
FIG. 6 (see O. Ohtaka, H. Fukui, T. Kunisada, T. Fujisawa, K.
Funakoshi, W. Utsumi, T. Irifune, K. Kuroda, and T. Kikegawa, 3.
Am. Ceram. Soc., 84[6] 1369-73 (2001)). Accordingly, it can be
easily assumed that the tetragonal crystals in a Hf oxide can be
stabilized by exactly the same mechanism as the mechanism that can
stabilize the tetragonal crystals in a Zr oxide.
[0065] The composition of this film after the heat treatment was
determined by a direct measurement method in accordance with RBS,
to obtain the composition values of Zr.sub.0.985Si.sub.0.02O.sub.2.
Accordingly, it is assumed that a composition of
Zr.sub.0.985Si.sub.0.0224O.sub.1.90 is obtained by determining the
molar ratio of [Si]/([Zr]+[Si]) by RBS and determining the amount
of oxygen loss by XPS in the sample in an as-depo state before the
heat treatment. Also, it is assumed that a composition of
Hf.sub.xSi.sub.1-xO.sub.2-y (0.76.ltoreq.x.ltoreq.0.985,
0.10.ltoreq.y.ltoreq.0.25) is obtained by determining the molar
ratio of [Si]/([Hf]+[Si]) by a direct measurement method in
accordance with RBS and determining the amount of oxygen loss by
XPS in the above HfSiO film.
Fourth Embodiment
[0066] Next, a method for manufacturing a semiconductor device in
accordance with a fourth embodiment of the present invention is
described.
[0067] First, as shown in step S1 of FIG. 1, a
Zr.sub.xSi.sub.1-xO.sub.2-y was formed on a silicon substrate that
had an interface oxide layer removed through diluted hydrofluoric
acid treatment. In XPS measurement, the formed film is an
insulating film having an oxygen defect, with (x, y) being (1.00,
0.046), (0.99, 0.056), (0.98, 0.053), (0.94, 0.053), (0.90, 0.043),
(0.86, 0.047), (0.86, 0.049), (0.86, 0.057), (0.86, 0.059), (0.86,
0.061), (0.86, 0.062), (0.86, 0.116), or (0.81, 0.083), or an
insulating film without an oxygen defect, with x being 1.00, 0.99,
0.98, 0.90, 0.87, or 0.70.
[0068] When the molar ratio of [Si]/([Zr]+[Si]) is measured by RBS
while the oxygen defect is measured by XPS, the above film is an
insulating film having an oxygen defect, with (x, y) being (1.00,
0.046), (0.985, 0.056), (0.97, 0.053), (0.92, 0.053), (0.86,
0.043), (0.81, 0.047), (0.81, 0.049), (0.81, 0.057), (0.81, 0.059),
(0.81, 0.061), (0.81, 0.062), (0.81, 0.116), or (0.76, 0.083), or
an insulating film without an oxygen defect, with x being 1.00,
0.985, 0.97, 0.86, 0.81, or 0.66.
[0069] In the case of an insulating film having an oxygen defect,
XPS measurement was carried out to confirm that a Zr-Si bond due to
the oxygen defect was observed, as shown in FIG. 7.
[0070] In the case of an insulating film without an oxygen defect,
only an amorphous film or monoclinic crystals or cubic crystals
were formed even by a deposition method or through annealing.
[0071] Next, as shown in step S2 of FIG. 1, annealing was performed
on an insulating film having an oxygen defect. In this case,
substantially perfect tetragonal crystals were formed under any of
the following annealing conditions: (750.degree. C., in a nitrogen
gas, 30 seconds), (750.degree. C., in a nitrogen gas, 60 seconds),
(750.degree. C., in a nitrogen gas, 2 minutes), (750.degree. C., in
a nitrogen gas, 4 minutes), (750.degree. C., in a nitrogen gas, 8
minutes), (750.degree. C., 3% of oxygen and 97% of nitrogen, 30
seconds), (750.degree. C., 3% of oxygen and 97% of nitrogen, 60
seconds), (750.degree. C., 3% of oxygen and 97% of nitrogen, 2
minutes), (750.degree. C., 3% of oxygen and 97% of nitrogen, 4
minutes), (750.degree. C., 3% of oxygen and 97% of nitrogen, 8
minutes), (750.degree. C., in an oxygen gas, 30 seconds),
(750.degree. C., in an oxygen gas, 1 minute), (750.degree. C., in
an oxygen gas, 2 minutes), (750.degree. C., in an oxygen gas, 4
minutes), (750.degree. C., in an oxygen gas, 8 minutes),
(1000.degree. C., in a nitrogen gas, 30 seconds), (1000.degree. C.,
in a nitrogen gas, 60 seconds), (1000.degree. C., in a nitrogen
gas, 2 minutes), (1000.degree. C., in a nitrogen gas, 4 minutes),
(1000.degree. C., in a nitrogen gas, 8 minutes), (1000.degree. C.,
3% of oxygen and 97% of nitrogen, 30 seconds), (1000.degree. C., 3%
of oxygen and 97% of nitrogen, 60 seconds), (1000.degree. C., 3% of
oxygen and 97% of nitrogen, 2 minutes), (1000.degree. C., 3% of
oxygen and 97% of nitrogen, 4 minutes), (1000.degree. C., 3% of
oxygen and 97% of nitrogen, 8 minutes), (1000.degree. C., in an
oxygen gas, 30 seconds), (1000.degree. C., in an oxygen gas, 1
minute), (1000.degree. C., in an oxygen gas, 2 minutes),
(1000.degree. C., in an oxygen gas, 4 minutes), and (1000.degree.
C., in an oxygen gas, 8 minutes).
[0072] There are two purposes of the annealing process in this
case: the first one is to compensate for the oxygen defect; and the
second one is to secure the stability of the structure against the
heat treatment or to make sure that there is no relaxation or
self-destruction in the structure. The results of this embodiment
serve both purposes. Particularly, the second purpose is well
served, as the tetragonal crystals can be maintained as they are
even under the above various heat treatment conditions.
Accordingly, this embodiment should be very useful when applied to
an actual LSI process that involves various heat treatment
procedures.
[0073] When the annealing conditions were more closely examined, it
was confirmed that, with the oxygen concentration in the atmosphere
being 1% or higher, minute silicide crystals unsuitable for a gate
insulating film could be completely prevented from growing at the
interface with the silicon substrate. Accordingly, an oxygen
concentration of 1% or higher in the atmosphere is a more preferred
annealing condition.
[0074] As insulating films each having a composition of (0.86,
0.049) in the XPS measurement and a composition of (0.81, 0.049) in
the RBS measurement, samples of 110 nm, 50 nm, 20 nm, 10 nm, and 5
nm in film thickness were prepared, and the oxygen defect was
compensated for by performing annealing under the following
conditions: (750.degree. C., in an oxygen gas, 30 seconds),
(800.degree. C., in a nitrogen gas, 30 seconds), and (1000.degree.
C., in an oxygen gas, 30 seconds). An in-plane X-ray diffraction
test was conducted for the insulating films of 10 nm and 5 nm in
thickness, and the crystalline structures were examined to find
perfectly tetragonal, fluorite-type crystalline structures, as
shown in FIG. 8. We confirmed that every peak position coincided
with tetragonal one. As for the insulating films of 10 nm in
thickness, the in-plane X-ray diffraction test was conducted only
for the samples annealed under the condition of (800.degree. C., in
a nitrogen gas, 30 seconds), and the result of this test is shown
in FIG. 8.
[0075] There were conventional tetragonal zirconia films that had
silicon added thereto. However, many of them are power samples or
sintered samples, or are thick films of approximately 1 .mu.m in
thickness formed by the sol-gel method or the like.
[0076] Accordingly, thin films of 5 nm and 10 nm in thickness that
can be used as gate insulating films, interpoly insulating films,
or blocking insulating films as disclosed in this embodiment were
unheard of. The molecular volume V.sub.m of those films calculated
on the basis of X-ray diffraction data (lattice constants) was in
the range of 0.03353 nm.sup.3.ltoreq.V.sub.m.ltoreq.0.03424
nm.sup.3 per Zr.sub.xSi.sub.1-xO.sub.2. The molecular volume
reduction rate was 3%. Accordingly, it is reaffirmed that those
films of this embodiment have in-film stress that can endure a LSI
process, unlike the insulating film disclosed in Reference 3, which
has the molecular volume reduction rate of 9%.
[0077] The reason that the in-film stress by the manufacturing
method of this embodiment can endure a LSI process is considered to
be the difference in manufacturing method. By the manufacturing
method of this embodiment, after an amorphous ZrSiO film is formed,
tetragonal crystals are obtained through an annealing process that
is a thermal quasi-equilibrium process. As a result of the semi
thermal equilibrium process, the in-film stress is reduced.
[0078] By the method disclosed in Reference 3, on the other hand, a
HfSiO film is formed by performing sputtering on a HfO.sub.2 target
and a SiO.sub.2 target. It is a well-known fact that a sputtering
process as a thermal nonequilibrium process generates a large
in-film stress.
[0079] In this embodiment, the relative permittivity of each of the
insulating films having the oxygen defect compensated for after the
annealing was measured. The compositions in the XPS measurement
before the annealing were (1.00, 0.046), (0.99, 0.056), (0.98,
0.053), (0.94, 0.053), (0.90, 0.043), and (0.86, 0.047). The
compositions in the XPS measurement after the annealing were (1.00,
0.00), (0.99, 0.00), (0.98, 0.00), (0.94, 0.00), (0.90, 0.00), and
(0.86, 0.00), with the oxygen defect having been compensated
for.
[0080] With the molar ratio of [Si]/([Zr]+[Si]) being measured by
RBS and the oxygen defect amount being measured by XPS, the
composition of the samples before the annealing are considered to
be (1.00, 0.046), (0.985, 0.056), (0.97, 0.053), (0.92, 0.053),
(0.86, 0.043), and (0.81, 0.047). The compositions after the
annealing were (1.00, 0.00), (0.985, 0.00), (0.97, 0.00), (0.92,
0.00), (0.86, 0.00), and (0.81, 0.00). In the estimates of the
amounts of oxygen defect by XPS, the oxygen defect was compensated
for.
[0081] For measurement of electric properties, a gold electrode was
formed on each film after the annealing, so as to make sure that
the electrode resistance was sufficiently low.
[0082] FIG. 9 shows the results of the relative permittivity
measurement. In FIG. 9, the abscissa axis indicates the value of
([Si]/([Si]+[Zr])).times.100 (atomic %) measured by XPS, and the
ordinate axis indicates the relative permittivity of each
insulating film or the ratio of the permittivity .epsilon. of the
insulating film to the permittivity .epsilon..sub.0 of vacuum. As
can be seen from FIG. 9, the relative permittivity was 20 to 26,
with the value of x measured by XPS in a Zr.sub.xSi.sub.1-xO.sub.2
film being in the range of 0.86 to 0.94 (with the value of z in a
Zr.sub.1-zSi.sub.zO.sub.2 film being in the range of 0.06 to 0.14).
Since the relative permittivity of a conventional ZrO.sub.2 film
was approximately 17, increases in permittivity were confirmed.
[0083] In this embodiment, the molar polarizability a of the atoms
in insulating films each having the oxygen defect compensated for
after the annealing was calculated with the use of the above
measured relative permittivity and lattice constant and the
Clausius-Mosotti equation, to find increases to 0.00679
nm.sup.3<.alpha..ltoreq.0.00735 nm.sup.3. This result is
apparently different from the result disclosed in Reference 3,
which is that the molar polarizability of atoms hardly varies even
though the permittivity increases as the crystalline system is
changed to a tetragonal crystalline system. Therefore, this
embodiment should be considered to have successfully produced a
different substance from the substance disclosed in Reference
3.
[0084] When the crystalline structure of each of the insulating
films of Zr.sub.xSi.sub.1-xO.sub.2 formed in this embodiment was
more closely examined, it was found that not only tetragonal
crystals but also an orientation that allows the effective use of
the crystal axis with the higher permittivity was obtained. In a
gate electrode of a transistor, an interelectrode insulating film
of a flash memory, a blocking insulating film of a flash memory, or
a capacitor insulating film, it is the permittivity in the film
thickness direction that affects a real device. Therefore, where
the crystal axis with the higher permittivity is oriented in the
film thickness direction, higher permittivity can be achieved.
[0085] As an examination result, it was confirmed that, in the
sample having a value of 0.90 as the composition ratio x of Zr
measured by XPS, the [110] orientation as the crystal axis with the
higher permittivity in the tetragonal crystals, which is the a'
axis direction, was substantially in parallel with the film
thickness direction, and the permittivity of the sample was
actually the highest (see FIG. 9). Here, the composition ratio x of
Zr as a value measured by RBS was 0.86. With cells twice as many as
the unit cells being taken into account, the [110] orientation in
the unit cells is set as the a' axis of the cells twice as many as
the unit cells. It should be noted that the a' axis is referred to
simply as the "a axis" in some documents.
[0086] Meanwhile, it was confirmed that, in the sample having a
value of 0.94 as the composition ratio x of Zr measured by XPS, the
c axis as the crystal axis with the lower permittivity in the
tetragonal crystals was substantially in parallel with the film
thickness direction, and the permittivity of the sample was
actually the lowest in the tetragonal crystals. Here, the
composition ratio x of Zr as a value measured by RBS was 0.92. In
each of the insulating films of Zr.sub.xSi.sub.1-xO.sub.2 formed in
this embodiment, the c' axis of the cells twice as many as the unit
cells is exactly the same as the c axis of the unit cells.
Furthermore, the difference in length between the a' axis and the
c' axis is approximately 3%, for example, and the length of the a'
axis is always smaller than the length of the c' axis.
[0087] Further, the sample having a value of 0.86 as the
composition ratio x of Zr measured by XPS had a value of 0.81 as
the composition ratio x measured by RBS. However, it was confirmed
that an orientation was not observed though tetragonal crystals
were obtained. Actually, the permittivity of this sample was lower
than the permittivity of the sample having a value of 0.90 as the
composition ratio x of Zr measured by XPS or the sample having a
value of 0.86 as the composition ratio x measured by RBS, but was
higher than the permittivity of the sample having a value of 0.94
as the composition ratio x of Zr measured by XPS or the sample
having a value of 0.92 as the composition ratio x measured by RBS
(see FIG. 9). The estimates made through the first principle
calculations were different from the experimental values
quantitatively, but were proved to be qualitatively correct through
experiments.
[0088] FIG. 14 shows the X-ray diffraction profiles of insulating
films of Zr.sub.xSi.sub.1-xO.sub.2, with the value x of Zr in the
XPS measurement being 0.86, 0.90, 0.94, 0.98, and 1.00, or with the
value of x of Zr in the RBS measurement being 0.81, 0.86, 0.92,
0.97, and 1.00. Since the peak intensities are logarithmically
plotted in FIG. 14, attention is required when the peak intensities
are compared with one another. In this specification, an index is
put to the diffraction peaks in the X-ray diffraction profiles
shown in FIG. 14, with the use of cells twice as many as the unit
cells. The diffraction index used here is a', b', and c, instead of
a, b, and c crystalline system. In FIG. 14, "111", "002", "200",
"112", "202", "220", "113", "311", and "222" represent the
diffraction index a', b', and c crystalline system.
[0089] In the sample having a value of 0.86 as the composition
ratio x of Zr measured by XPS or the sample having a value of 0.81
as the composition ratio x measured by RBS, the diffraction peak of
200 in diffraction index that is the sum of the diffraction peak
200 in the a' axis and the diffraction peak 020 in the b' axis,
which are equivalent to each other, is larger than the peak of 002
in diffraction index in the c-axis as a single peak. Likewise, the
peak of 300 in diffraction index is the sum of the equivalent
diffraction index 131 and the diffraction peak 300, but is larger
than the peak of 113 in diffraction index as a single peak. Since
those peak intensities are affected by minute atom displacements,
the intensity ratio is not always 2:1. However, as long as the
sample has no orientations, the intensity ratio does not change as
much as to reverse the relationship in intensity. In practice, the
intensity ratio is close to 2:1. Accordingly, the sample having a
value of 0.86 as the composition ratio x of Zr measured by XPS or
the sample having a value of 0.81 as the composition ratio x
measured by RBS does not have an orientation. Also, in the sample
having a value 0.90 as the composition ratio x of Zr, the
diffraction peak in the a' axis direction, such as the diffraction
index 200, is very intense, and the a' axis lies in the film
thickness direction. In the sample having a value 0.94 as the
composition ratios x of Zr measured by XPS or the sample having a
value of 0.92 as the composition ratio x measured by RBS, the peaks
having components of the c-axis direction, such as the diffraction
indexes 200, 112, 202, and 113, are relatively intense, and there
is an orientation in the c axis direction.
[0090] As in the above described case, it can be easily assumed
that the tetragonal crystals in a Hf oxide can be stabilized by
exactly the same mechanism as the mechanism that can stabilize the
tetragonal crystals in a Zr oxide.
[0091] Although the heat treatment temperature is in the range of
750.degree. to 1000.degree. C. in this embodiment, it is also
possible to carry out the heat treatment at temperatures in the
range of 750.degree. C. to 1100.degree. C.
Fifth Embodiment
[0092] Next, a semiconductor device in accordance with a fifth
embodiment of the present invention is described. The semiconductor
device of this embodiment is the same as the semiconductor device
produced by any of the manufacturing method of the first through
fourth embodiments, except that the insulating film is replaced
with an insulating film formed with
(Zr.sub.1-zHf.sub.z).sub.xSi.sub.1-xO.sub.2-y (in the XPS
measurement: 0.ltoreq.z.ltoreq.1, 0.86.ltoreq.x.ltoreq.0.99; in the
RBS measurement: 0.ltoreq.z.ltoreq.1, 0.81.ltoreq.x.ltoreq.0.985,
0.04.ltoreq.y.ltoreq.0.25).
[0093] It is a known fact that ZrO.sub.2 and HfO.sub.2 can form
mixed crystals at any ratio. FIG. 10 shows a phase diagram of
ZrO.sub.2 and HfO.sub.2 at all the ratios (see Ruh, H. J. Garrett,
R. F. Domagla, and N. M. Tallan, J. Amer. Ceram. Soc., 51, [1]27
(1968)). The phase diagram of FIG. 10 is a very simple diagram, and
the regions of the respective phases of tetragonal crystals, cubic
crystals, and monoclinic crystals exist for all the compositions
ranging from ZrO.sub.2 to (Hf.sub.zZr.sub.1-z)O.sub.2 to HfO.sub.2.
The boundaries of the respective phases do not cross one another.
It can be considered that such a phase diagram is obtained, because
Zr and Hf have chemical properties very similar to each other.
[0094] Accordingly, as in the first through fourth embodiments, an
amorphous insulating film formed with
(Zr.sub.1-zHf.sub.z).sub.xSi.sub.1-xO.sub.2-y (in the XPS
measurement: 0.ltoreq.z.ltoreq.1, 0.86.ltoreq.x.ltoreq.0.99; with
the molar ratio of [Si]/([Zr]+[Hf]+[Si]) and the molar ratio of
[Hf]/([Zr]+[Hf]) being measured by RBS, with the amount of oxygen
defect being measured by XPS, 0.ltoreq.z.ltoreq.1,
0.81.ltoreq.x.ltoreq.0.985, and 0.ltoreq.z.ltoreq.1,
0.86.ltoreq.x.ltoreq.0.99, 0.04.ltoreq.y.ltoreq.0.25) can be
transformed into (Hf.sub.zZr.sub.1-z).sub.xSi.sub.1-xO.sub.2
(0.ltoreq.z.ltoreq.1, in the XPS measurement:
0.86.ltoreq.x.ltoreq.0.99, in the RBS measurement:
0.81.ltoreq.x.ltoreq.0.985) by annealing, so as to compensate for
the oxygen defect and obtain tetragonal crystals. Since an increase
in permittivity by virtue of the tetragonal crystals is achieved
with ZrO.sub.2 and HfO.sub.2, it is also achieved with
(Zr.sub.1-zHf.sub.z)O.sub.2, which is an intermediate state between
the two oxides. The same applied to cases where tetragonal crystals
are obtained by adding a very small amount (x in this case) of
Si.
[0095] Thus, this embodiment can achieve the same effects as those
of the first through fourth embodiments, with
(Zr.sub.1-zHf.sub.z).sub.xSi.sub.1-xO.sub.2 being used as an
insulating film.
[0096] As described so far, in the first through fifth embodiments
of the present invention, insulating films with such high
permittivity that cannot be formed with conventional high-k
insulating films of zirconia or hafnia can be produced by adding
Si, which is highly compatible with conventional semiconductor
processes. The high-k insulating films of the above described
embodiments are zirconia-based films, hafnia-based films, or films
formed with a mixed material of zirconia and hafnia.
[0097] In each of the first through fifth embodiments of the
present invention, the in-film stress is restricted to 1 GPa or
less, and the molecular volume hardly affects the mechanism of
increasing the permittivity. Accordingly, there are fewer
distortions in the films, and the problem of relaxation and the
problem of self-destruction due to stress can be solved.
Sixth Embodiment
[0098] Next, a semiconductor device in accordance with a sixth
embodiment of the present invention is described.
[0099] The semiconductor device of this embodiment has an
insulating film with compensated oxygen that is disclosed in any
one of the first through fifth embodiments. In this embodiment, the
insulating film is used as a gate insulating film of a MOS,
particularly, as a gate insulating of a CMOS, an interelectrode
insulating film of a flash memory, or a blocking insulating film of
a flash memory.
[0100] FIG. 11 is a cross-sectional view of a semiconductor device
having a CMOSFET as a first specific example of this embodiment.
This semiconductor device as the first specific example includes an
n-channel MOSFET 32 and a p-channel MOSFET 33 that are formed on a
semiconductor substrate 20. The n-channel MOSFET 32 is provided in
a p-well region 22 formed in the semiconductor substrate 20. The
n-channel MOSFET 32 includes a gate insulating film 24 formed on
the p-well region 22, a gate electrode 25 formed on the gate
insulating film 24, source and drain regions 28 formed with
n.sup.+-impurity regions located at portions of the p-well region
22 on either side of the gate electrode 25, and gate sidewalls 27
formed with an insulating material provided on the side faces of
the gate electrode 25.
[0101] The p-channel MOSFET 33 is provided in an n-well region 23
formed in the semiconductor substrate 20. The p-channel MOSFET 33
includes a gate insulating film 24 formed on the n-well region 23,
a gate electrode 26 formed on the gate insulating film 24, source
and drain regions 29 formed with p.sup.+-impurity regions located
at the portions of the n-well region 23 on either side of the gate
electrode 26, and gate sidewalls 27 formed with an insulating
material provided on the side faces of the gate electrode 26. The
p-well region 22 and the n-well region 23 are isolated from each
other by a device isolating region 21. The source and drain regions
28 and 29 have extension regions that extend below the gate
insulating films 24.
[0102] In the semiconductor device as the first specific example,
the gate insulating film 24 of each of the n-channel MOSFET 22 and
the p-channel MOSFET 23 is an insulating film with compensated
oxygen that is disclosed in any one of the first through fifth
embodiments.
[0103] Referring now to FIG. 12, a semiconductor device as a second
specific example of this embodiment is described. This
semiconductor device as the second specific example is a flash
memory, and a cross-sectional view of a memory cell 50 is shown in
FIG. 12. This memory cell 50 includes a tunnel insulating film 42
formed on a semiconductor substrate 40, a gate electrode 44 formed
on the tunnel insulating film 42, source and drain regions 49
formed at the portions of the semiconductor substrate 40 on either
side of the gate electrode 44, and gate sidewalls 48 formed with an
insulating material provided on the side faces of the gate
electrode 44. The gate electrode 44 includes a floating gate 45
formed on the tunnel insulating film 42, an interelectrode
insulating film 46 formed on the floating gate 45, and a control
gate 47 formed on the interelectrode insulating film 46. In this
specific example, the interelectrode insulating film 46 is an
insulating film with compensated oxygen that is disclosed in any
one of the first through fifth embodiments.
[0104] In the second specific example, a floating gate type flash
memory has been described. The insulating film with compensated
oxygen that is disclosed in any one of the first through fifth
embodiments is applicable to a MONOS
(Metal-Oxide-Nitride-Oxide-Silicon) type flash memory. As shown in
FIG. 15, the MONOS type flash memory 50A includes a memory cell
that contains a tunnel insulating film 42 formed on a semiconductor
substrate 40, a gate electrode 44A formed on the tunnel insulating
film 42, source and drain regions 49 formed at the portions of the
semiconductor substrate 40 on either side of the gate electrode
44A, and gate sidewalls 48 formed with an insulating material
provided on the side faces of the gate electrode 44A. The gate
electrode 44A includes a charge storing layer 51 formed on the
tunnel insulating film 42, a blocking insulating film 46A formed on
the charge storing layer 51, and a control gate 47 formed on the
blocking insulating film 46A. The blocking insulating film 46A is
an insulating film with compensated oxygen that is disclosed in any
one of the first through fifth embodiments.
[0105] When the insulating film with compensated oxygen that is
disclosed in any one of the first through fifth embodiments is used
as the interelectrode insulating film or the blocking insulating
film, the insulating film can be a single layer or a stacked
layer.
[0106] Since the gate insulating films 24 of the first specific
example, the interelectrode insulating film 46 of the second
specific example and the blocking insulating film 46A of MONOS type
flash memory of this embodiment are insulating films with
compensated oxygen that are disclosed in any of the first through
fifth embodiments, the in-film stress is restricted to 1 GPa or
less, and the molecular volume hardly affects the mechanism of
increasing the permittivity. Accordingly, there are fewer
distortions in the films, and the problem of relaxation and the
problem of self-destruction due to stress can be solved. Thus,
device characteristics degradation can be prevented.
[0107] For reference, the results of XPS measurement and RBS
measurement of Si compositions in the respective insulating films
of the first through sixth embodiments of the present invention are
shown in the table below.
TABLE-US-00001 TABLE Si Amount XPS RBS composition composition 0%
0% 1% 1.5% 2% 3% 6% 8% 10% 14% 14% 19% 19% 24%
[0108] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concepts as defined by the
appended claims and their equivalents.
* * * * *