U.S. patent application number 10/025899 was filed with the patent office on 2002-06-06 for method for forming gas cluster and method for forming thin film.
Invention is credited to Akizuki, Makoto, Doi, Atsumasa, Harada, Mitsuaki, Matsuo, Jiro, Ogasawara, Satoru, Yamada, Isao.
Application Number | 20020068128 10/025899 |
Document ID | / |
Family ID | 27298594 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068128 |
Kind Code |
A1 |
Akizuki, Makoto ; et
al. |
June 6, 2002 |
Method for forming gas cluster and method for forming thin film
Abstract
In order to deopsit a high-grade and extra-thin film without
causing damage to the substrate at a relatively low temperature,
the present invention provides a method for forming a cluster which
is a lumpy group of atoms or molecules of a reactive substance at
the room temperature under the atmospheric pressure, irradiating
electrons onto clusters, irradiating the resulting cluster ions
onto a substrate surface by accelerating by an acceleration
voltage, and at the same time or alternately, irradiating one or
more component gases of the deposit film onto the substrate
surface, thereby depositing a thin film on the substrate surface
through reaction.
Inventors: |
Akizuki, Makoto; (Gifu,
JP) ; Harada, Mitsuaki; (Gifu, JP) ;
Ogasawara, Satoru; (Gifu, JP) ; Doi, Atsumasa;
(Gifu, JP) ; Yamada, Isao; (Hyogo, JP) ;
Matsuo, Jiro; (Kyoto-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27298594 |
Appl. No.: |
10/025899 |
Filed: |
December 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10025899 |
Dec 26, 2001 |
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09799681 |
Mar 7, 2001 |
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09799681 |
Mar 7, 2001 |
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09566740 |
May 9, 2000 |
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09566740 |
May 9, 2000 |
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08951959 |
Oct 17, 1997 |
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08951959 |
Oct 17, 1997 |
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08650905 |
May 17, 1996 |
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Current U.S.
Class: |
427/248.1 ;
427/595 |
Current CPC
Class: |
C23C 16/4482 20130101;
C23C 14/08 20130101; C23C 14/088 20130101; C23C 16/409 20130101;
C08F 4/65916 20130101; H01J 2237/0812 20130101; C08F 4/6592
20130101; C23C 16/513 20130101; C08F 4/65912 20130101; C08F 10/02
20130101; B01J 37/0215 20130101; C07F 17/00 20130101; C08F 10/02
20130101; B01J 37/347 20130101; C23C 16/405 20130101; C23C 14/0031
20130101 |
Class at
Publication: |
427/248.1 ;
427/595 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 1995 |
JP |
121983/1995 |
Sep 22, 1995 |
JP |
244957/1995 |
Mar 21, 1996 |
JP |
064861/1996 |
Claims
What is claimed is:
1. A method for forming a gas cluster which comprises the steps of
mixing a substance liquid at the room temperature under the
atmospheric pressure and a pressurized gas, and causing the
resultant mixture to spout as a gas from a nozzle to generate a
cluster which is a lumpy group of atoms or molecules.
2. A method as claimed in claim 1, wherein said substance liquid at
the room temperature under the atmospheric pressure is an
oxygen-containing compound.
3. A method as claimed in claim 1 or 2, wherein said substance
liquid at the room temperature under the atmospheric pressure is an
organic metal compound.
4. A method as claimed in any one of claims 1 to 3, wherein said
substance liquid at the room temperature under the atmospheric
pressure is Ti(i-OC.sub.3H.sub.7).sub.4.
5. A method as claimed in any one of claims 1 to 4, wherein said
pressurized gas is an inert gas or a reactive gas.
6. A method as claimed in any one of claims 1 to 5, wherein said
nozzle is an expansion-type nozzle.
7. A method for forming gas cluster ions, which comprises the step
of ionizing the gas cluster formed by the method as claimed in any
one of claims 1 to 6.
8. A method as claimed in claim 7, wherein said ionization is
accomplished by irradiating an electron beam.
9. A method for forming a thin film, which comprises the step of
irradiating the cluster ions formed by the method as claimed in
claim 7 or 8 onto a substrate surface, thereby forming a thin
film.
10. A method as claimed in claim 9, wherein said cluster ions are
accelerated by acceleration voltage.
11. A method for forming a thin film, which comprises the steps of
forming a cluster which is a lumpy group of atoms or molecules of a
reactive substance gaseous at the room temperature, irradiating
cluster ions ionized therefrom onto a substrate surface, and at the
same time or alternately, irradiating a single, or a plurality of,
component gas of a deposit film onto the substrate surface to cause
reaction of the both, thereby depositing a thin film on the
substrate surface; wherein two or more gases to be irradiated
simultaneously are fed after converting same into clusters.
12. A method for forming a thin film, which comprises the steps of
forming a cluster which is an annular group of atoms or molecules
of a reactive substance gaseous at the room temperature,
irradiating cluster ions ionized therefrom onto a substrate
surface, and at the same time or alternately, irradiating a single,
or a plurality of, component gas of a deposit film onto the
substrate surface to cause reaction of the both, thereby depositing
a thin film on the substrate surface; wherein at least one of the
gaseous reactive substances to be converted into cluster is an
oxygen-containing substance.
13. A method for forming a thin film a claimed in claim 11 or 12,
wherein an oxide film is deposited by irradiating cluster ions of a
gas containing oxygen and at least an organic metal compound gas
onto the substrate surface.
14. A method for forming a thin film as claimed in any one of
claims 11 to 13, which comprises the steps of irradiating oxygen
gas cluster ions onto the substrate, and at the same time, or
alternately, irradiating a single,-or a plurality of, component gas
of deposit film onto the substrate surface to cause reaction of the
both, thereby depositing a thin ferroelectric film on the substrate
surface.
15. A method for forming an oxygen-containing gas cluster, which
comprises the step of causing an oxygen-containing pressurized gas
mixed with a rare gas to spout from a nozzle to form a gas
cluster.
16. A method as claimed in claim 15, wherein said nozzle is a
cooled expansion-type nozzle.
17. A method for forming an oxygen-containing gas cluster, which
comprises the step of ionizing the gas cluster formed by the method
as claimed in claim 15 or 16.
18. A method for forming a thin film, which comprises the step of
irradiating the cluster ions formed by the method as claimed in
claim 17 onto a substrate surface, thereby forming a thin film.
Description
FIELED OF THE INVENTION
[0001] The present invention relates to a method for forming a gas
cluster, ionization thereof, and a method for forming a thin film
with this ion beam. More particularly, the present invention
relates to a method for forming a thin film based on a gas cluster
ion, which is a group of reactive substances liquid or gaseous at
the room temperature, which is useful for manufacturing
semiconductors and other electronic devices and for surface
modification of functional materials.
PRIOR ART
[0002] Methods of modifying a surface or forming a thin film on a
substrate surface by irradiating monatomic or monomolecular ions
onto a substrate surface have conventionally been used in practice.
Since it is difficult to obtain a beam having a practically
sufficient density because of the space charge effect between ions
with a low-energy ion irradiation in these methods, it is the usual
practice to use a high incident energy of several keV.
[0003] However, in these conventional methods using ions having a
high incident energy, it is difficult to avoid damages to the
substrate surface to be treated, and deterioration of the substrate
surface and thin film properties.
[0004] Conventionally available methods for depositing a thin film
on a semiconductor substrate have included the vacuum CVD method
and the plasma CVD method. The vacuum CVD method has however a
problem in that a sufficient deposition rate cannot be obtained
unless the substrate temperature is raised to over 400.degree. C.
Consequently, when depositing a thin film such as lead titanate
zirconate (Pb(Zr, Ti)O.sub.3) directly onto a silicon substrate,
for example, Pb, Ti and Zr diffuse throughout the silicon
substrate, resulting in deterioration of electric
characteristics.
[0005] The plasma CVD method, known as a method for forming a thin
film at a low temperature, is defective in that much impurities are
mixed up, and ions damage the substrate surface, with difficulty of
film thickness control of a produced extra-thin film, resulting in
the impossibility to apply for an insulating film or a
ferroelectric film requiring a high quality.
[0006] It has thus been difficult to obtain a high-grade ultra-thin
film because the quality of a thin film has deteriorated according
as the forming temperature of thin film has become lower in the
conventional techniques.
[0007] Under these circumstances as described above, there has been
a strong demand for development of a novel method permitting
surface modification of a substrate and formation of a high-quality
thin film at a lower temperature, or particularly at the room
temperature without heating the substrate, as a basic technique
directed toward progress of a more sophisticated electronics such
as ULSI.
[0008] In this situation of technology, the present inventors have
already proposed a method of forming a lumpy group of atoms or
molecules from a gas-reactive substance gaseous at the room
temperature under the atmospheric pressure and irradiating gas
cluster ions generated by ionizing same onto a substrate
surface.
[0009] This method permits cleaning and flattening of a substrate
surface, as well as even formation of a thin film with a lower
energy, and is therefore attracting the general attention as a
technique for ultra-high-accuracy fine surface fabrication with the
use of a low-energy beam hereafter.
[0010] In spite of the considerable potentiality of this cluster
ion beam, however, the technique has just paved the way to
development, and many problems are still left for future
resolution, including, for example, restriction on the kind of gas
component substances and applications thereof.
[0011] The present invention was developed in view of the
circumstances as described above, and has an-object to provide a
novel method related with gas cluster ion beam, which permits
formation of a high-quality thin film having a flat and smooth
interface in a state free from damage to the substrate at a
relatively low temperature, through further development of the gas
cluster beam technique.
SUMMARY OF THE INVENTION
[0012] As means to solve the above-mentioned problems, the present
invention provides a method for forming a gas cluster, which
comprises the steps of mixing a substance liquid at the room
temperature under the atmospheric pressure and a pressurized gas,
and causing the resultant mixture to spout as a gas from a nozzle
to generate a cluster which is a lumpy group of atoms or molecules
(claims 1 to 6).
[0013] The present invention provides also a method for forming gas
cluster ions, which comprises the step of ionizing the thus formed
gas cluster (claims 7-8), and a method for forming a thin film,
which comprises the step of irradiating the thus formed cluster
ions onto a substrate surface, thereby forming a thin film (claims
9-10).
[0014] Furthermore, the present invention provides a method for
forming a thin film, which comprises the steps of forming a cluster
which is a lumpy group of atoms or molecules of a reactive
substance gaseous at the room temperature, irradiating cluster ions
ionized therefrom onto a substrate surface, and at the same time or
alternately, irradiating a single, or a plurality of, component gas
of a deposit film onto the substrate surface to cause reaction of
the both, thereby depositing a thin film on the substrate surface
(claims 11-14), a method for forming an oxygen-containing gas
cluster, which comprises the step of causing an oxygen-containing
pressurized gas mixed with a rare gas to spout from a nozzle to
form a gas cluster (claims 15-16), a method for forming an
oxygen-containing gas cluster ion resulting from ionization thereof
(claim 17), and a method for forming a thin film, which comprises
the step of irradiating this ion onto a substrate surface, thereby
forming a thin film (claim 18).
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1. shows a sectional view illustrating an
expansion-type nozzle;
[0016] FIG. 2. shows a schematic view illustrating a system for
generating gas clusters from a liquid substance;
[0017] FIG. 3 shows a graph illustrating the He supply pressure
dependency of the cluster beam intensity at a
Ti(i-OC.sub.3H.sub.7).sub.4 temperature of from 60 to 75.degree.
C.;
[0018] FIG. 4 shows a graph illustrating the He supply pressure
dependency of the cluster beam intensity at
Ti(i-OC.sub.3H.sub.7).sub.4 temperatures of 60.degree. C. and
70.degree. C.;
[0019] FIG. 5 shows a graph illustrating the relationship between
the Ti(i-OC.sub.3H.sub.7).sub.4 temperature and the beam intensity
at a partial pressure of 5 of He;
[0020] FIG. 6 shows a graph illustrating the supply pressure
dependency of the O.sub.2 cluster beam intensity whey at various
nozzle temperatures;
[0021] FIG. 7 shows a graph illustrating the relationship between
the O.sub.2/He mixing ratio and the cluster beam intensity at a
nozzle temperature of 300 K;
[0022] FIG. 8 shows a graph illustrating the case with a nozzle
temperature of 250 K corresponding to FIG. 7;
[0023] FIG. 9 shows a graph illustrating the case with a nozzle
temperature of 120 K corresponding to FIG. 7;
[0024] FIG. 10 shows a graph of retarding field spectrum of O.sub.2
ion under various supply pressures at a nozzle temperature of 300
K;
[0025] FIG. 11 shows a graph of retarding field spectrum of O.sub.2
ion at various He mixing ratios at a nozzle temperature of 150
K;
[0026] FIG. 12 shows a graph of retarding field spectra of O.sub.2
ion at a nozzle temperature of 300 K, when decreasing the nozzle
temperature to 140 K, and under conditions including a nozzle
temperature of 140 K and 59% mixing of He gas;
[0027] FIG. 13 shows a graph illustrating the dose dependency of
the thickness of SiO.sub.2 films formed through irradiation of
O.sub.2 and CO.sub.2 cluster ions;
[0028] FIG. 14 shows an XPS spectral diagram of an oxide film
formed through O.sub.2 cluster irradiation;
[0029] FIG. 15 shows a graph illustrating the carbon concentration
in an oxide film;
[0030] FIG. 16 shows a graph illustrating the thickness of an
SiO.sub.2 film as determined from an XPS analysis carried out
before and after an HF treatment of an oxide film formed through
CO.sub.2 cluster irradiation;
[0031] FIG. 17 shows a graph illustrating the thickness of an
SiO.sub.2 film as determined from an XPS analysis carried out
before and after an HF treatment of an oxide film formed through
irradiation of 5 keV O.sub.2 cluster;
[0032] FIG. 18 shows a graph illustrating the thickness of an
SiO.sub.2 film as determined from an XPS analysis carried out
before and after an HF treatment of an oxide film formed through
irradiation of 7 KeV O.sub.2 cluster;
[0033] FIG. 19 shows a graph illustrating high-frequency CV
characteristics of an MOS capacitor using, as a gate oxide film, an
SiO.sub.2 film forced through irradiation of O.sub.2 cluster
ions;
[0034] FIG. 20 shows a retarding field spectral diagram after
ionization of Ti(i-OC.sub.3H.sub.7).sub.4/He mixed gas and He gas,
respectively;
[0035] FIG. 21 shows a diagram illustrating an equipment
configuration for irradiation for generation of clusters and after
ionization thereof;
[0036] FIG. 22 shows an X-ray photoelectron spectral diagram from
Ti2p signal of an Si substrate surface irradiated with
Ti(i-OC.sub.3H.sub.7).s- ub.4 cluster ions;
[0037] FIG. 23 shows an X-ray photoelectron spectral diagram when
irradiating Ti(i-OC.sub.3H.sub.7).sub.4 vapor and O.sub.2 cluster
ions;
[0038] FIG. 24 shows a graph illustrating an X-ray diffraction
pattern when irradiating Pb vapor and O.sub.2 cluster ions;
[0039] FIG. 25 shows a graph illustrating an X-ray diffraction
pattern when irradiating Pb vapor and O.sub.2 cluster ions;
[0040] FIG. 26 shows a graph illustrating the average surface
roughness (Ra) of a sample when irradiating Pb vapor and O.sub.2
cluster ions;
[0041] FIG. 27 shows an X-ray photoelectron spectral diagram from
Ti2p signal when irradiating Ti(i-OC.sub.3H.sub.7).sub.4, Pb vapor
and O.sub.2 cluster ions;
[0042] FIG. 28 shows an X-ray photoelectron spectral diagram from
Pb4f signal corresponding to FIG. 27;
[0043] FIG. 29 shows an X-ray photoelectron spectral diagram from
O21s signal corresponding to FIGS. 27 and 28;
[0044] FIG. 30 shows a graph illustrating an X-ray diffraction
pattern of a PbTiO3 thin film when irradiating
Ti(i-OC.sub.3H.sub.7).sub.4 thin film when irradiating
Ti(i-OC.sub.3H.sub.7).sub.4, PbO vapor and O.sub.2 cluster ions
onto a Pt/Ta/Si substrate at substrate temperatures of 400.degree.
C. and 380.degree. C.;
[0045] FIG. 31 shows a graph illustrating an X-ray diffraction
pattern of a thin film formed by irradiating
Ti(i-OC.sub.3H.sub.7).sub.4, PbO vapor, and various O.sub.2 sources
onto a Pt/Ta/Si substrate at a substrate temperature of 430.degree.
C.; and
[0046] FIG. 32 shows a current-voltage curve of-a PbTiO.sub.3 thin
film obtained by irradiating Ti(i-OC.sub.3H.sub.7).sub.4, PbO vapor
and O.sub.2 cluster ion beam onto a Pt/Ta/Si substrate at a
substrate temperature of 430.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0047] As described above, the present invention makes it
possible:
[0048] 1) to form a gas cluster from a substance liquid at the room
temperature under the atmospheric pressure, to form a gas cluster
ion through ionization thereof, and to form a thin film by means of
this gas cluster ion;
[0049] 2) to form a thin film through simultaneous or alternate
irradiation of the gas cluster ion of a reactive substance liquid
or gaseous at the room temperature under the atmospheric pressure
and other deposit film components; and
[0050] 3) to form a gas cluster and an ion thereof from a mixture
of a rare gas and an oxygen-containing gas, and to form an oxide
film from this ion.
[0051] In the case of the above-mentioned methods, applicable
substances liquid at the room temperature under the atmospheric
pressure include various inorganic and organic compounds,
oxygen-containing compounds such as metal complexes and organic
metal compounds, and applicable pressurized gases include inert
gases and reactive gases.
[0052] The above-mentioned liquid substance may be a gaseous
cluster by transporting same with an inert gas or a rare gas. More
specifically, there has conventionally been known a method of
producing a cluster by charging a solid material into a crucible
and heating it to raise the steam pressure, and clusterization is
possible by a similar method even for a liquid material; This
method has however problems in that, in order to replenish raw
materials, the vacuum unit must be released to the open air, and
the cluster beam cannot be directed downward. In the present
invention, the improvements are such that raw materials can be
replenished outside the vacuum unit by using the method of bubbling
with a carrier gas or the like, and the beam can be directed
downward irrespective of the gravity. In addition, use of the
method of the present invention brings about such effects as an
increase in the cluster size and an increase in the cluster beam
intensity. Because the amount of supplied condensed gas can be
controlled with the amount of supplied carrier gas capable of being
precisely controlled, beam intensity can be stabilized. It is also
possible to form a cluster comprising a mixture of liquid and
gaseous materials by using a reactive gas such as O.sub.2 as a
carrier gas.
[0053] A cluster can be generated from a substance gaseous at the
room temperature under the atmospheric pressure by causing a
pressurized gas to spout through an expansion-type nozzle into a
vacuum unit. In all cases, the thus formed cluster can be ionized
through irradiation of electron or the like.
[0054] The size (lengths l.sub.1 and l.sub.2, and diameters
d.sub.0, d.sub.1, and d.sub.2) of the expansion-type nozzle may be
appropriately determined in response to the amount of generated
cluster, the substance to be formed into a cluster and distribution
of cluster sizes, on the assumption of a circular nozzle having the
shape shown in FIG. 1 as an example. The amount of generated
cluster and the size distribution are dependent particularly on
l.sub.2 and d.sub.0: a smaller d.sub.0 and a longer l.sub.2
correspond to a larger amount of generated cluster and a larger
size. Typical values of l.sub.2 and d.sub.0 include approximately
12=5-50 mm, and d0=0.02-0.2 mm.
[0055] In the examples described later, the following values are
employed, which may approximately be adopted:
[0056] l.sub.1=30 mm, l.sub.2=32 mm,
[0057] d.sub.0=0.1 mm, d.sub.1=12 mm,
[0058] d.sub.2=8 mm.
[0059] The generated gas cluster is usually composed of from
several tens to several thousand atomic or molecular groups. The
extent of size of these groups may be determined, as described
above, in response to the nozzle shape, the structure thereof, the
gas supply pressure, and the kind of the substance to be
treated.
[0060] Applicable reactive substances gaseous at the room
temperature include, for example, oxides and carbides such as
CO.sub.2, CO, O.sub.2N.sub.2O, NO.sub.x, and C.sub.xH.sub.yO.sub.z,
nitrides such as N.sub.2 and NH.sub.3, AsH.sub.3, SiH.sub.4 and
other reacting substances. Any of these substances may be used in
mixture with a rare gas such as Ar and H.sub.2.
[0061] In the case of O.sub.2, mixture with a rare gas and further
the use of a cooled expansion-type nozzle make it possible to form
a gas cluster, to ionize same, and to form an oxide film through
irradiation thereof onto a substrate.
[0062] As a component gas composing a deposit, such organic
substance as an organic metal compound may be used in a gaseous
form in response to the kind of the target deposit film. In this
case, a rare gas capable of being supplied in the form of a halide,
an alcoholate compound or a carbonyl compound of an element such as
Ti, Zr, Pb or Nb may be used as a carrier.
[0063] These components may be supplied in the form of
clusters.
[0064] The method for forming a thin film through a reaction
between a reactive cluster ion beam and the substrate will now be
described further in detail by means of examples.
EXAMPLE 1
[0065] FIG. 2 shows an example of the apparatus for generating a
cluster by transporting vapor of a liquid material by means of a
carrier gas and then causing same to spout from a nozzle. This
demonstrates a case using tetraisopropoxytitanium
(Ti(i-OC.sub.3H.sub.7).sub.4) liquid at the room temperature under
the atmospheric pressure, in which temperature of a thermostat and
a transport piping was raised to about 70 to 75.degree. C. to
increase the vapor pressure to about 1 Torr. He was employed as a
carrier gas. Apart from this, a rare gas such as Ar or H.sub.2 may
be used. A material having a lighter weight results in generation
of a cluster more efficiently.
[0066] FIG. 3 illustrates dependency on He supply pressure of the
beam intensity of gas cluster of tetra-isopropoxytitanium by using
a Ti(i-OC.sub.3H.sub.7).sub.4 mixed gas when causing the raw
material temperature to vary between 60 and 75.degree. C. Results
of supply of He gas alone are also shown. Temperature of the
transport piping and the nozzle was set at 75.degree. C. Beam
intensity was measured as a degree of vacuum by providing a vacuum
gauge on the beam axis. In this case, generation of a cluster
causes a sudden increase in the number of molecules coming into the
vacuum gauge, resulting in a lower degree of vacuum. Generation of
the cluster was confirmed in accordance with this principle. In the
case of He gas alone, no increase in the beam intensity was
observed along with the increase in the supply pressure, thus
suggesting that no cluster was generated. In the case of a mixed
gas, a steep rise of beam intensity is observed under a supply
pressure of over 3 atm. This result clearly indicates that
Ti(i-OC.sub.3H.sub.7).sub.4 was clusterized.
EXAMPLE 2
[0067] FIG. 4 shows dependency on He supply pressure of a
Ti(i-OC.sub.3H.sub.7).sub.4 and He mixed gas beam intensity in the
case with raw material temperatures of 60.degree. C. and 70.degree.
C., and a temperature of the transport piping and the nozzle of
70.degree. C. in Example 1. This similarly suggests that the
Ti(i-OC.sub.3H.sub.7).sub.4 gas was clusterized. Beam intensity
showed a value lower than in the case with a temperature of the
transport piping and the nozzle of 75.degree. C.
[0068] FIG. 5 illustrates the relationship between the source
temperature and the cluster beam intensity under the He gas supply
pressure of 5 atm in the case with a temperature of the transport
piping and the nozzle of 70.degree. C. Increase in the source
temperature leads to a steady increase in the beam intensity.
[0069] These generated clusters can be ionized by the application
of the electron impact technique or the like. Other materials such
as Zr(t-OC.sub.4H.sub.9).sub.4 can also be clusterized.
EXAMPLE 3
[0070] FIG. 6 illustrates the supply pressure dependency of beam
intensity of O.sub.2 gas cluster when the nozzle temperature of
O.sub.2 gas varied between the room temperature and 120 K. While
beam intensity shows only a low value as 0.6.times.10.sup.-4 Torr
at the room temperature under 6 atm, it increases and an increase
in cluster beam intensity is observed according as the nozzle is
cooled. The O.sub.2 gas cluster showed a beam intensity of
4.times.10.sup.-4 Torr at 120 K under 6 atm, or an intensity about
six times as high as that at the room temperature. Generation of a
cluster by nozzle cooling was achieved under a lower supply
pressure. This is useful from the point of view of enlarging the
cluster size and improvement of background degree of vacuum
resulting from a decrease in flow rate.
EXAMPLE 4
[0071] FIG. 7 shows the dependency on mixing ratio of the neutral
beam intensity of an O.sub.2/He mixed gas at a nozzle temperature
of 300 K. Under any of the supply pressures, an increase in the
cluster strength is observed by setting the mixing ratio of He gas
to about 30%. Under an He supply pressure of 6 atm, the beam
intensity shows, under the effect of mixing of He, a value three
times as high as that in the case of O.sub.2 gas.
EXAMPLE 5
[0072] FIGS. 8 and 9 show the dependency on the mixing ratio of
O.sub.2 gas cluster beam intensity in an O.sub.2/He mixed gas when
the nozzle temperature was reduced to 250 K and 120 K,
respectively. In all cases, mixing of He increased the beam
intensity. The case where the nozzle was cooled to 120 K and an He
mixing ratio was appropriately selected showed, as compared with
the case at a nozzle temperature of 300 K and using O.sub.2 gas
only, a beam intensity 20 times as high as that under a supply
pressure of 6 atm and 80 times as high as that under 5 atm. The
maximum beam intensity was 12.times.10.sup.-4 Torr.
[0073] In view of the results presented above, the neutral cluster
beam intensity of O.sub.2 gas could largely be increased through
nozzle cooling and mixing of He by using conditions including a
supply pressure of 5 atm, a nozzle temperature of 120 K and an He
mixing ratio of about 50%. For O.sub.2 cluster, cooling to 120 K
gave a six times as high cluster beam intensity, He dilution, a
three times as high, and a combination of these two methods, a 20
times as high.
EXAMPLE 6
[0074] FIG. 10 illustrates the retarding field spectrum of O.sub.2
cluster ion beam in the case where a nozzle temperature of 300 K
was selected and the supply pressure was varied upon ionization
through irradiation of electron. Even in a positive retarding field
under a supply pressure of over 5 atm, ion current was observed,
suggesting the generation of O.sub.2 cluster ion beam.
[0075] FIG. 11 shows the retarding field spectrum of O.sub.2 ion at
various levels of He mixing ratio. Conditions included a gas supply
pressure of 4.5 atm, an acceleration voltage of 5 kV, and a nozzle
temperature of 150 K. While the case without mixing of He showed a
cluster current density of 2.2 nA/cm.sup.2, He mixing of 35% gave a
current density of 3.9 nA/cm.sup.2, or a cluster current 1.8 times
as high.
EXAMPLE 7
[0076] FIG. 12 shows the retarding field spectrum of O.sub.2 ion in
the case where the nozzle temperature was decreased from 300 K to
140 K, and also in the case where He gas was mixed in an amount of
50% with a nozzle temperature of 140 K. The current density of
cluster ion was increased to 26 nA/cm.sup.2 by nozzle cooling, and
to 80 nA/cm.sup.2 by mixing of 50% He gas. This current value is 16
times as high as the value at the room temperature.
EXAMPLE 8
[0077] FIG. 13 shows the result of XPS investigation of the film
thickness of an oxide film formed by irradiating O.sub.2 gas
cluster ion formed by mixing 50% He and cooling the nozzle to 140 K
onto an Si(100) substrate at the room temperature, together with
the result obtained by using CO.sub.2 gas. These results suggest
formation of an SiO.sub.2 film thinner than 11 nm by the
irradiation of cluster ions. The oxide film thickness demonstrates
a tendency of being saturated at a dose of over about
5.times.10.sup.15 ions/cm.sup.2. Comparison with a constant
acceleration voltage, the oxide film formed by O.sub.2 cluster ions
has a thickness larger than in the case of CO.sub.2 cluster and has
a higher reactivity.
[0078] FIG. 14 illustrates an XPS spectrum of an SiO.sub.2 film
formed at the room temperature by irradiating 7 keV O.sub.2 cluster
ions in an amount of 10.sup.15 ions/cm.sup.2, together with a
spectrum of an SiO.sub.2 film formed at 900.degree. C. by the
application of the thermal oxidation method commonly used in the
LSI manufacturing process. These spectra reveals that the oxide
film of a sample formed by the use of O.sub.2 clusters has a film
structure identical with that of a sample formed by the thermal
oxidation method, and a high-quality SiO.sub.2 thin film is formed
even by the irradiation at the room temperature.
[0079] FIG. 15 shows the carbon concentration in an SiO.sub.2 film
formed by the use of O.sub.2 cluster ion beam in the form of the
relationship between the oxide film thickness and the ratio of
spectral intensity caused by oxygen and carbon. For comparison
purposes, values for an oxide film formed by the use of CO.sub.2
cluster ions and a thermal oxide film are also shown. Because
carbon is not contained in the thermal oxide film to an extent
detectable by the XPS method, these signals are attributable to
organic carbon adhering to the surface after formation of the film
(detection limit of measurement). The carbon concentration in the
oxide film formed by the use of O.sub.2 clusters was reduced to
below a third that in the case with CO.sub.2, thus demonstrating
that a lower carbon concentration was successfully achieved.
EXAMPLE 9
[0080] FIG. 16 shows the thickness of an SiO.sub.2 film as
determined from an XPS analysis after fluoric acid treatment of the
SiO.sub.2 film formed by means of CO.sub.2 cluster ion beam. The
film thickness does not vary between before and after the fluoric
acid treatment with a low dose, so that the oxide film on the
substrate surface is not a high-quality SiO.sub.2 film. Thereafter,
the transition film thickness decreases to 20 .ANG. along with the
increase in dose.
[0081] FIGS. 17 and 18 illustrate the thickness of an SiO.sub.2
film as determined by an XPS analysis before and after a fluoric
acid treatment of the oxide film formed by irradiating 5 keV and 7
keV O.sub.2 cluster ions, respectively. Even with a low ion dose,
the oxide film thickness after the fluoric acid treatment is thin
as about 10 .ANG.. The oxide film has a better quality as compared
with that in the case of CO.sub.2 irradiation, thus suggesting that
a steep interface was formed between the film and the
substrate.
EXAMPLE 10
[0082] FIG. 19 represents high-frequency CV characteristics of an
MOS capacitor using, as a gate insulating film an SiO.sub.2 film of
62 .ANG. formed by the use of O.sub.2 clusters. The substrate is an
n-type Si(100) having a specific resistance of 2 to 3
.OMEGA..multidot.cm. Satisfactory C-V characteristics were
achieved, indicating that this MOS structure has satisfactory
properties as an insulating film for LSI.
EXAMPLE 11
[0083] FIG. 20 shows a retarding field spectrum after ionization of
a Ti(i-OC.sub.3H.sub.7).sub.4/He mixed gas and He gas. Conditions
included a gas supply pressure of 5 atm, an acceleration voltage of
2 kV, and a nozzle temperature of 75.degree. C. In the case of the
Ti(i-OC.sub.3H.sub.7).sub.4/He mixed gas, ion current is observed
within a range of retarding voltage of from 0 to 300 V, thus
suggesting that Ti(i-OC.sub.3H.sub.7).sub.4 cluster ions have been
generated. In this instance, the clusters have an average size of
700 molecules/cluster, and a maximum cluster size of 2,500
molecules/cluster.
EXAMPLE 12
[0084] FIG. 21 illustrates generation of clusters and an outline of
the irradiator. A cluster generating section is provided with a
nozzle having a rare gas mixing mechanism and a cooling mechanism
for generating clusters of oxygen, nitrogen and the like, and a
nozzle having a bubbling mechanism for generating clusters of a
liquid material. A beam analysis/irradiating chamber is provided
with an electrode system for carrying out ionization, acceleration
and mass separation, an ion gauge for analyzing a neutral cluster
beam, and a Faraday cup for analyzing the size of cluster ions. It
is also provided with a substrate holder and an evaporation source
for forming a thin film.
EXAMPLE 13
[0085] FIG. 22 shows an X-ray photoelectron spectrum from a Ti2p
signal of an Si substrate surface in the case where
Ti(i-OC.sub.3H.sub.7).sub.4 cluster ions accelerated with an
acceleration voltage of 7 kV in an oxygen gas atmosphere having an
oxygen partial pressure of 3.times.10.sup.-5 Torr in the apparatus
shown in FIG. 21. The substrate had a temperature of 360.degree. C.
Two peaks observed near binding energies of 459 eV and 464 eV are
signals from TiO2, suggesting that a TiO2 thin film has been
formed. The composition ratio of Ti to O as determined from the
signal intensity ratio of Ti2p and O21s spectra is 1:2, indicating
that a TiO.sub.2 thin film satisfying the stoichiometric ratio has
been formed.
EXAMPLE 14
[0086] FIG. 23 illustrates an X-ray photoelectron spectrum of the
substrate surface in the case where an Si substrate and a Pt thin
film substrate were exposed to Ti(i-OC.sub.3H.sub.7).sub.4 vapor
having a partial pressure of 3.times.10.sup.-5 Torr, and at the
same time, O.sub.2 cluster ions accelerated with 7 kV acceleration
voltage were irradiated. The substrate had a temperature of
360.degree. C. There are observed TiO.sub.2 thin films formed on
the both substrates. The composition ratio of Ti to O as determined
from the signal intensity ratio of Ti2p and O21s spectra is 1:2,
indicating that TiO.sub.2 thin films satisfying the stoichiometric
ratio have been formed. Also in the case where TiO(DPM).sub.2 was
used as a Ti material, a TiO.sub.2 thin film satisfying the
stoichiometric ratio was formed on the Si substrate, showing the
possibility of forming a thin film using various materials by this
method.
[0087] In addition, TiO.sub.2 thin films satisfying the
stoichiometric ratio were formed also in the case where
Ti(i-OC.sub.3H.sub.7).sub.4 cluster ions accelerated with 7 kV
acceleration voltage and O.sub.2 cluster ions accelerated with 7 kV
acceleration voltage were simultaneously irradiated onto an Si
substrate.
EXAMPLE 15
[0088] FIG. 24 shows an X-ray diffraction pattern of a sample
prepared by vapor-depositing Pb by crucible heating at a depositing
rate of 0.7 nm/minute onto an SiO.sub.2 thin film substrate, and at
the same time, irradiating O.sub.2 cluster ion beam at different
acceleration voltages. The result suggests that a PbO thin film
having a preferred (111) orientation was formed by irradiating
O.sub.2 cluster ion beam with an acceleration voltage of at least 5
kV.
EXAMPLE 16
[0089] FIG. 25 shows an X-ray diffraction pattern of a sample
prepared by vapor-depositing Pb onto an SiO.sub.2 thin film
substrate at various depositing rates, and simultaneously,
irradiating O.sub.2 cluster ion beam while accelerating with an
acceleration voltage of 5 kV. While a PbO thin film was formed in
all cases, crystallinity of the PbO thin film is improved by
reducing the depositing rate of Pb to below 1.5 nm/minute. In this
case, O.sub.2 cluster ion beam has a current density of 100
nA/cm.sup.2, and crystallinity may be altered by increasing this
value.
EXAMPLE 17
[0090] FIG. 26 shows the average surface roughness (Ra) of the
surface of a sample prepared by vapor-depositing Pb by crucible
heating onto an SiO.sub.2 thin film substrate at a depositing rate
of 0.7 nm/minute, and at the same time, irradiating O.sub.2 cluster
ion beam. The surface of the PbO thin film is largely flattened by
irradiating O.sub.2 cluster ion beam with an acceleration voltage
of at least 1 kV. With an acceleration voltage of 7 kV, Ra
decreases to 9 .ANG., and an effect of considerable flattening is
obtained.
EXAMPLE 18
[0091] FIG. 27 shows an X-ray photoelectron spectrum from a Ti2p
signal of the surface of a sample prepared by exposing a Pt thin
film substrate heated to 360.degree. C. to a
Ti(i-OC.sub.3H.sub.7).sub.4 atmosphere under a partial pressure of
3.times.10.sup.-5 Torr, vapor-depositing Pb at a depositing rate of
0.7 nm/minute, and at the same time, irradiating O.sub.2 cluster
ion beam accelerated with an acceleration voltage of 7 kV.
[0092] FIG. 28 illustrates an X-ray photoelectron spectrum from a
Pb4f signal of the same sample surface, and FIG. 29, an X-ray
photoelectron spectrum from an O.sub.21s signal of the same sample
surface. The composition ratio determinable from these X-ray
photoelectron spectra of the sample surface is 1:1:3, suggesting
that a PbTiO.sub.3 ferroelectric thin film satisfying the
stoichiometric ratio was formed.
[0093] As is clear from this Example, a ferrodielectric thin film
was formed by using gas cluster ion beam.
EXAMPLE 19
[0094] FIG. 30 shows an X-ray diffraction pattern of a thin film
formed by exposing Pt/Ta/Si substrates heated to 400.degree. C. and
380.degree. C. to Ti(i-OC.sub.3H.sub.7).sub.4 atmosphere having a
partial pressure of 0.4.times.10.sup.-6 Torr, vapor-depositing Pb
at a depositing rate of 0.6 nm/minute, and simultaneously,
irradiating O.sub.2 cluster ion beam having a current density of
100 nA/cm.sup.2, accelerated with an acceleration voltage of 7 kV.
During vapor deposition, the degree of vacuum was 3.times.10.sup.-5
Torr. When using a substrate heated to 400.degree. C., a signal
from a PbTiO.sub.3 thin film having a perovskite crystalline
structure was detected in the X-ray diffraction pattern. A
diffraction in (101) orientation is not observed, whereas there are
observed (001) and (100) preferential orientations. No diffraction
from fixed-dielectric pyrochlore phase is observed in this
PbTiO.sub.3 thin film. With a substrate temperature of 380.degree.
C., the resultant PbTiO.sub.3 thin film is non-crystalline. This
suggests that a PbTiO.sub.3 thin film exhibiting ferroelectricity
at a substrate temperature of at least 400.degree. C. This
substrate temperature is lower by about 100.degree. C. than that in
the application of the CVD method or the sol-gel process. It is
known that, when using the CVD method or the sol-gel process, a
temperature permitting formation of a fixed dielectric pyrochlore
phase exists between the substrate temperature permitting formation
of a non-crystalline phase and the temperature permitting formation
of the perovskite phase. Formation of a pyrochlore phase is not
observed when using gas clusters. It is thus possible to transport
oxygen acting as an oxygen source with a high density, form a thin
film through surface reaction under a high vacuum, and obtain a
high-quality ferroelectric thin film at a low temperature.
EXAMPLE 20
[0095] FIG. 31 shows an X-ray diffraction pattern of a thin film
formed by exposing Ti(i-OC.sub.3H.sub.7).sub.4 to an atmosphere
having a partial pressure of 0.4.times.10.sup.-5 Torr on a Pt/Ta/Si
substrate heated to 430.degree. C., vapor-depositing PbO at a
depositing rate of 0.5 nm/minute, and at the same time, supplying
oxygen under various conditions. When supplying oxygen having a
partial pressure of 3.times.10.sup.-5 Torr as an oxidizing agent,
the resultant thin film is non-crystalline. When irradiating
neutral O.sub.2 clusters not ionized, a single perovskite phase
having sa low crystallinity was obtained. Clusters have a kinetic
energy cluster size times as high as that in a monomolecular state.
Consequently, kinetic energy held by the neutral O.sub.2 clusters
contributes to crystallization, thus making available perovskite.
Crystallinity is largely improved by increasing acceleration
voltage for the O.sub.2 cluster ions to 1 to 7 kV. Even a low
acceleration voltage of 1 kV gave an effect of largely improving
crystallinity.
[0096] In addition to the Pb and Ti sources as described above,
addition of Zr-containing materials and/or La-containing materials
makes it possible to form a Pb-based ferroelectric thin film such
as Pb(Zr, Ti)O.sub.3 and (Pb, La)(Zr, Ti)O.sub.3. By using
Bi-containing materials, Ti-containing materials and Sr-containing
materials as raw materials, it is also possible to form a Bi
laminate ferroelectric thin film such as
BiSr.sub.2Ta.sub.2O.sub.9.
EXAMPLE 21
[0097] FIG. 32 represents current-voltage characteristics of a
capacitor prepared by depositing Au by the sputtering process on an
upper portion of a PbTiO.sub.3 thin film formed by the method of
Example 20 with an acceleration voltage of 3 kV of O.sub.2 cluster
ions. An applied voltage of 5 V leads to a leak current density of
1.times.10.sup.-6 A/cm.sup.2, suggesting that a high-quality thin
film exhibiting a low leak current is formed. The relationship
between field and polarization of the thus formed capacitor shows a
hysteresis history, demonstrating that a ferrodielectric thin film
having a spontaneous polarization property was formed.
[0098] According to the present invention, as described above in
detail, it is possible to convert into gas cluster even a substance
liquid at the room temperature under the atmospheric pressure, to
ionize same, and further, form a thin film thereof. More
specifically, according to the present invention, improvements are
available including the possibility of accomplishing replenishing
of raw materials outside the vacuum unit, and of directing the beam
downward irrespective of the gravity, bringing about such effects
as increase in cluster size, increase in cluster beam intensity,
i.e., the possibility of assisting cooling of
Ti(i-OC.sub.3H.sub.7).sub.4 and promoting growth of
Ti(i-OC.sub.3H.sub.7).sub.4 clusters under the heat absorbing
effect upon release of the carrier gas into vacuum. In addition,
because the amount of supplied condensed gas through the amount of
supplied carrier gas capable of being precisely controlled, it is
possible to stabilize beam intensity. By using a reactive gas such
as O.sub.2, it is also possible to form clusters comprising a
mixture of a liquid material and a gaseous material.
[0099] By irradiating cluster ions of a reactive substance such as
an oxygen-containing compound onto a substrate surface and causing
reaction thereof, it is possible to form various high-quality-thin
oxide films and crystalline composite insulating films at a
relatively low temperature.
* * * * *