U.S. patent application number 09/730564 was filed with the patent office on 2001-08-23 for method for forming a thin film of a composite metal compound and apparatus for carrying out the method.
Invention is credited to Kikuchi, Kazuo, Matsumoto, Shigeharu, Ogura, Shigetaro, Tang, Qi, Yamasaki, Masafumi.
Application Number | 20010015173 09/730564 |
Document ID | / |
Family ID | 14214609 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015173 |
Kind Code |
A1 |
Matsumoto, Shigeharu ; et
al. |
August 23, 2001 |
Method for forming a thin film of a composite metal compound and
apparatus for carrying out the method
Abstract
There is disclosed a method and apparatus for forming a thin
film of a composite metal compound. Independent targets formed of
at least two different metals are sputtered so as to form on a
substrate an ultra-thin film of a composite metal or an
incompletely-reacted composite metal. The ultra-thin film is
irradiated with the electrically neutral, activated species of a
reactive gas so as to convert the composite metal or the
incompletely-reacted composite metal to a composite metal compound
through the reaction of the ultra-thin film with the activated
species of the reactive gas. The formation of the ultra-thin film
and the conversion to the composite metal compound are sequentially
repeated so as to form on the substrate a thin film of the
composite metal compound having a desired thickness.
Inventors: |
Matsumoto, Shigeharu;
(Tokyo, JP) ; Kikuchi, Kazuo; (Tokyo, JP) ;
Yamasaki, Masafumi; (Yokohama-shi, JP) ; Tang,
Qi; (Yokohama-shi, JP) ; Ogura, Shigetaro;
(Kohbe-shi, JP) |
Correspondence
Address: |
LORUSSO & LOUD
3137 Mount Vernon Avenue
Alexandria
VA
22305
US
|
Family ID: |
14214609 |
Appl. No.: |
09/730564 |
Filed: |
December 7, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09730564 |
Dec 7, 2000 |
|
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09092645 |
Jun 9, 1998 |
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6207536 |
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Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 14/08 20130101;
C23C 14/568 20130101; G02B 1/12 20130101; C23C 14/0078 20130101;
Y10S 118/90 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C30B 001/00; H01L
021/20; C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 1998 |
JP |
10-98246 |
Claims
What is claimed is:
1. A method for forming a thin film of a composite metal compound
comprising the steps of: sputtering independent targets formed of
at least two different metals so as to form on a substrate an
ultra-thin film of a composite metal or an incompletely-reacted
composite metal; irradiating the ultra-thin film with the
electrically neutral, activated species of a reactive gas so as to
convert the composite metal or the incompletely-reacted composite
metal to a composite metal compound through the reaction of the
ultra-thin film with the activated species of the reactive gas;
sequentially repeating the step of forming the ultra-thin film and
the step of conversion to the composite metal compound so as to
form on the substrate a thin film of the composite metal compound
having a desired thickness.
2. A method for forming a thin film of a composite metal compound
according to claim 1, wherein the electrically neutral, activated
species of the reactive gas are radicals selected from the group
consisting of atoms having at least one unpaired electron,
molecules having at least one unpaired electron, atoms in an
excited state, and molecules in an excited state.
3. A method for forming a thin film of a composite metal compound
according to claim 1, wherein sputtering is magnetron
sputtering.
4. A method for forming a thin film of a composite metal compound
according to claim 1, wherein a negative voltage applied to each of
the targets is inverted at 1-200 kHz intervals to a positive
voltage ranging between +50 V and +200 V to thereby neutralize,
with electrons in plasma, positive charges which accumulate in a
compound to be formed on the surface of each of the targets.
5. An apparatus for forming a thin film of a composite metal
compound, comprising: film deposition process chambers into which a
working gas is introduced and in which independent targets formed
of at least two different metals are sputtered so as to form on a
substrate an ultra-thin film of a composite metal or an
incompletely-reacted composite metal; a reaction process chamber
for irradiating the ultra-thin film formed in said film deposition
process chambers with the electrically neutral, activated species
of a reactive gas so as to convert the composite metal or the
incompletely-reacted composite metal to a composite metal compound
through the reaction of the ultra-thin film with the activated
species of the reactive gas; and separation means for separating
said reaction process chamber from said film deposition process
chambers in terms of space and pressure by means of shield plates,
wherein said separation means prevents the reactive gas from mixing
with the working gas in said film deposition process chambers so
that there can be sequentially repeated a stable film deposition
process and a reaction process to thereby form on the substrate a
thin film of a composite metal compound having a desired
thickness.
6. An apparatus for forming a thin film of a composite metal
compound according to claim 5, wherein the activated species of the
reactive gas used in said reaction process chamber are electrically
neutral radicals selected from the group consisting of atoms having
at least one unpaired electron, molecules having at least one
unpaired electron, atoms in an excited state, and molecules in an
excited state.
7. An apparatus for forming a thin film of a composite metal
compound according to claim 5, wherein a magnetron sputtering
device serves as a thin film deposition device.
8. An apparatus for forming a thin film of a composite metal
compound according to claim 5, wherein a negative voltage applied
to each of the targets is inverted at 1-200 kHz intervals to a
positive voltage ranging between +50 V and +200 V to thereby
neutralize, with electrons in plasma, positive charges which
accumulate in a compound to be formed on the uneroded portion of
each of the targets.
9. An apparatus for forming a thin film of a composite metal
compound according to claim 5, wherein the activated species are
generated by means of: a radio-frequency discharge chamber
comprising a quartz tube and a radio-frequency coil wound onto the
quartz tube; a radio-frequency power source for applying power to
the radio-frequency coil via a matching box; reaction gas feed
means for introducing a reactive gas from a gas cylinder into the
radio-frequency discharge chamber via a mass flow controller; an
external or internal coil for generating a magnetic field of 20-300
gauss within the radio-frequency discharge chamber; and a
multi-aperture grid or a multi-slit grid disposed between the
radio-frequency discharge chamber and said reaction process
chamber.
10. A method for forming a thin film of a composite metal compound
comprising the steps of: sputtering independent targets formed of
at least two different metals so as to form on a substrate an
ultra-thin film of a composite metal or an incompletely-reacted
composite metal; irradiating the ultra-thin film with the
electrically neutral, activated species of a reactive gas so as to
convert the composite metal or the incompletely-reacted composite
metal to a composite metal compound through the reaction of the
ultra-thin film with the activated species of the reactive gas; and
sequentially repeating the step of forming the ultra-thin film and
the step of conversion to the composite metal compound so as to
form on the substrate a thin film of the composite metal compound
having a desired thickness, whereby the thin film is formed to have
any refractive index within the range between the optical
refractive index intrinsic to a constituent metal compound of the
thin film and the optical refractive index intrinsic to another
constituent metal compound of the thin film.
11. A method for forming a thin film of a composite metal compound
according to claim 10, wherein the electrically neutral, activated
species of the reactive gas are radicals selected from the group
consisting of atoms having at least one unpaired electron,
molecules having at least one unpaired electron, atoms in an
excited state, and molecules in an excited state.
12. A method for forming a thin film of a composite metal compound
according to claim 10, wherein a negative voltage applied to each
of the targets is inverted at 1-200 kHz intervals to a positive
voltage ranging between +50 V and +200 V to thereby neutralize,
with electrons in plasma, positive charges which accumulate in a
compound to be formed on the surface of each of the targets.
13. An apparatus for forming a thin film of a composite metal
compound, comprising: at least two film deposition process
chambers, each being independently enclosed by shield plates; a
reaction process chamber having a radical source for generating the
activated species of a reactive gas; shield means for shielding
said film deposition process chambers; shield means for shielding
said reaction process chamber; a substrate on which a thin film is
formed; and transfer means for sequentially and repeatedly
transferring said substrate between thin film deposition portions
for forming a thin film on said substrate through sputtering, which
thin film deposition portions correspond to said film deposition
process chambers, and an exposure-to-radicals portion for exposing
a thin film to radicals of a reactive gas emitted from a radical
source, which exposure-to-radicals portion corresponds to said
reaction process chamber, wherein a thin film of a composite metal
compound is formed on said substrate through the sequentially
repeated transfer of said substrate between the thin film
deposition portions and the exposure-to-radicals portion, whereby
the thin film is formed to have any refractive index within the
range between the optical refractive index intrinsic to a
constituent metal compound of the thin film of a composite metal
compound and the optical refractive index intrinsic to another
constituent metal compound of the thin film.
14. An apparatus for forming a thin film of a composite metal
compound according to claim 13, wherein said substrate is held by
an electrically-insulated substrate holder so as to prevent the
occurrence of an unusual discharge on said substrate.
15. An apparatus for forming a thin film of a composite metal
compound according to claim 13, wherein the activated species of
the reactive gas used in said reaction process chamber are
electrically neutral radicals selected from the group consisting of
atoms having at least one unpaired electron, molecules having at
least one unpaired electron, atoms in an excited state, and
molecules in an excited state.
16. An apparatus for forming a thin film of a composite metal
compound according to claim 13, wherein a negative voltage applied
to each of the targets is inverted at 1-200 kHz intervals to a
positive voltage ranging between +50 V and +200 V to thereby
neutralize, with electrons in plasma, positive charges which
accumulate in a compound to be formed on the surface of each of the
targets.
17. An apparatus for forming a thin film of a composite metal
compound according to claim 13, wherein the activated species are
generated by means of: a radio-frequency discharge chamber
comprising a quartz tube and a radio-frequency coil wound onto the
quartz tube; a radio-frequency power source for applying power to
the radio-frequency coil via a matching box; reaction gas feed
means for introducing a reactive gas from a gas cylinder into the
radio-frequency discharge chamber via a mass flow controller; an
external or internal coil for generating a magnetic field of 20-300
gauss within the radio-frequency discharge chamber; and a
multi-aperture grid or a multi-slit grid disposed between the
radio-frequency discharge chamber and said reaction process
chamber.
18. An apparatus for forming a thin film of a composite metal
compound according to claim 17, wherein said multi-aperture grid is
formed of a metal or an insulator in which are formed a number of
apertures having a diameter of 0.1-3mm, and is cooled.
19. An apparatus for forming a thin film of a composite metal
compound according to claim 17, wherein said multi-slit grid is
formed of a metal or an insulator in which are formed a number of
slits having a width of 0.1-1mm, and is cooled.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for forming a thin
film of a composite metal compound and an apparatus for carrying
out the method. More particularly, the invention relates to a
method for forming through sputtering a thin film of a composite
metal compound on a substrate in a stable manner and at a high rate
of deposition and to an apparatus for carrying out the method.
[0003] 2. Description of the Related Art
[0004] Conventionally, when optical thin films for various groups
of products are formed through use of only existing vapor
deposition materials, satisfactory performances as required by the
products are very difficult to obtain. That is, designing optical
thin films through use of mere substances existing in the natural
world has proved difficult in terms of attaining optical spectral
characteristics as required by a certain group of products.
[0005] For example, configuration of wide-band antireflection films
requires materials having an intermediate refractive index (between
1.46 and 2.20), which materials rarely exist in the natural
world.
[0006] Generally, in order to decrease the reflectance of, for
example, glass, over the entire wavelength range of visible light,
glass must be coated with a vapor deposition material having a
refractive index of 1.46-2.20, called an intermediate refractive
index. Materials having an intermediate refractive index are
limited, and the refractive index cannot be selected as desired.
Accordingly, the following techniques are known as alternative
techniques for obtaining an intermediate refractive index of the
above-mentioned range.
[0007] (1) A low-refraction material (e.g. SiO.sub.2 (refractive
index: 1.46)) and a high-refraction material (e.g. TiO.sub.2
(refractive index: 2.35)) are concurrently evaporated from
respective evaporation sources, and an intermediate refractive
index (1.46-2.40) is obtained by virtue of their mixing ratio; (2)
a low-refraction material and a high-refraction material are
concurrently evaporated from a single evaporation source in the
form of a mixture, and an intermediate refractive index is obtained
by virtue of their mixing ratio; (3) an intermediate refractive
index is equivalently obtained through the combination of a
low-refraction material and a high-refraction material (called the
equivalent film technique); and (4) a composite target material is
used in sputtering.
[0008] However, the above-mentioned techniques involve the
following disadvantages.
[0009] In the above-mentioned technique (1), wherein a
low-refraction material (e.g. SiO.sub.2 (refractive index: 1.46))
and a high-refraction material (e.g. TiO.sub.2 (refractive index:
2.35)) are concurrently evaporated from respective evaporation
sources and an intermediate refractive index (1.46-2.40) is
obtained by virtue of their mixing ratio, the stable deposition of
a film through the simultaneous control of the rates of deposition
from the two evaporation sources is difficult to achieve, and thus
a desired refractive index is difficult to obtain with good
reproducibility.
[0010] In the above-mentioned technique (2), wherein a
low-refraction material and a high-refraction material are
concurrently evaporated from a single evaporation source in the
form of a mixture and an intermediate refractive index is obtained
by virtue of their mixing ratio, when evaporation continues for a
long period of time, the refractive index changes due to
differences in melting point and vapor pressure between the
low-refraction material and the high-refraction material. As a
result, a desired refractive index is difficult to obtain
stably.
[0011] In the above-mentioned technique (3), wherein an
intermediate refractive index is obtained through use of an
equivalent film formed from combined use of low-refraction and
high-refraction materials, a given refractive index requires the
formation of a very thin layer; thus, the control of film thickness
becomes difficult and complicated.
[0012] As mentioned above, the conventional techniques fail to
concurrently implement a high, stable deposition rate, a wide range
of refractive index variation, and a simple control system.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a method
for forming a thin film of a composite metal compound capable of
controlling the refractive index of a thin film as desired, forming
an ultra-thin film while subjecting the ultra-thin film to
oxidation, nitriding, fluorination, or a like reaction, and forming
on a substrate a thin film of a metallic compound having stable
optical characteristics, dynamic characteristics, and like
characteristics without increasing the substrate temperature and at
a high rate of deposition as well as to provide an apparatus for
carrying out the same.
[0014] Another object of the present invention is to provide a
method for forming a thin film of a composite metal compound
capable of obtaining a wide range of refractive index variation
through use of a simple control system and to provide an apparatus
for carrying out the same.
[0015] The above objects are achieved by the method and apparatus
according to the present invention. Herein, the expression
"ultra-thin film" is used to discriminate a final thin film from a
plurality of ultra-thin films which are deposited to become the
final thin film, and denotes that each of the ultra-thin films is
substantially thinner than the final thin film. The expression
"activated species" refer to radicals, radicals in an excited
state, atoms in an excited state, molecules in an excited state,
and the like. A "radical" refers to an atom or molecule having at
least one unpaired electron. An "excited state" denotes the state
in which the energy level is higher as compared to the stable
ground state having the lowest energy.
[0016] The aspects of the present invention will next be described
in detail.
[0017] First Aspect:
[0018] According to a first aspect of the present invention, there
is provided a method for forming a thin film of a composite metal
compound in which first, independent targets formed of at least two
different metals are sputtered so as to form on a substrate an
ultra-thin film of a composite metal or an incompletely-reacted
composite metal. For example, one of two targets is formed of Si,
while the other target is formed of Ta.
[0019] Next, the thus-formed ultra-thin film (e.g. Si+Ta) on the
substrate is irradiated with the electrically neutral, activated
species of a reactive gas (e.g. activated species of oxygen gas) so
as to convert the composite metal or the incompletely-reacted
composite metal to a composite metal compound (e.g. a composite of
SiO.sub.2 and Ta.sub.2O.sub.2) through reaction of the ultra-thin
film with the activated species of the reactive gas. The
above-mentioned steps of forming an ultra-thin film and converting
the ultra-thin film to a composite metal compound are sequentially
repeated so as to form on a substrate a thin film of a composite
metal compound having a desired thickness.
[0020] In a reactive film deposition step in which a composite
metal compound is obtained from a composite metal or an
incompletely-reacted composite metal, activated species are used
for the following reason. For the chemical reaction in the film
deposition step, chemically active, electrically neutral, activated
species, such as radicals and excited species, are more decisively
important than are charged particles, such as ions and
electrons.
[0021] Activated species are generated through use of a plasma
source for generating high-density plasma connected to a
radio-frequency power source. Specifically, the plasma source is an
inductively-coupled or capacitively-coupled plasma source or a
helicon wave plasma source having an external or internal coil. As
to the capacitively-coupled plasma source, it has an external or
internal coil as the case may be. In order to obtain high-density
plasma, a magnetic field of 20-300 gauss is generated in a plasma
generation unit.
[0022] A voltage (usually a negative voltage) applied to each of
the targets is inverted at 1-200 kHz intervals to a positive
voltage ranging between +50 V and +200 V to thereby neutralize,
with electrons in plasma, positive charges which accumulate in a
compound to be formed on the surface, particularly an uneroded
portion thereof, of each of the targets. Thus, through the
temporary inversion to a positive voltage from a negative voltage,
the positive-charged state on the surfaces-of the targets is
neutralized, so that the voltage of the targets can be held at a
normal level.
[0023] FIGS. 4 to 6 show the relationship between electric power
and optical characteristics, such as refractive index, absorption,
heterogeneity, etc., for Ta.sub.xSi.sub.yO.sub.z films. In FIGS. 4
to 6, optical constants are calculated based on data regarding the
spectral characteristics of a single-layer film. As shown in FIG.
4, the refractive indices of Ta.sub.xSi.sub.yO.sub.z films vary
with the ratio of the power applied to one guide to the power
applied to the other guide.
[0024] As seen from FIG. 4, as the applied power ratio between the
Si cathode and the Ta cathode increases, the refractive index
decreases. Since the vapor deposition rate is fixed at 40 nm/min,
the illustrated relationship between the refractive index and the
applied power ratio holds. As a result, the minimum and maximum
refractive indices at a wavelength of 550 nm are found 1.463 and
2.182, respectively. As the applied power ratio increases, the
refractive index at a wavelength of 550 nm increases from 1.463 to
2.182. Also, the refractive index can be decreased from 2.182 to
1.463.
[0025] In deposition of a thin film of a composite metal compound
having a desired thickness on a substrate as described above, when
two metals are respectively sputtered through, for example,
magnetron sputtering, any refractive index within the range between
the refractive index intrinsic to one metal compound and the
refractive index intrinsic to the other metal compound (e.g. the
range between 1.46 and 2.25, wherein 1.46 is the refractive index
of SiO.sub.2, an Si compound, and 2.25 is the refractive index of
Ta.sub.2O.sub.2, a Ta compound) can be imparted to the thin film
through appropriate control of the power applied to the magnetron
sputtering targets.
[0026] The film deposition process will next be described with
reference to FIG. 3, which illustrates the process of forming a
thin film of a composite metal compound on a substrate.
[0027] First, a substrate is placed in the position of a first
metal target. The first metal target is sputtered so as to form a
very thin metallic film (ultra-thin film) on the substrate. Then,
the substrate is moved to the position of a second metal target.
The second metal target is sputtered so as to form a very thin
metallic film (ultra-thin film) on the substrate. As shown in FIG.
3, the first and second metals are homogeneously deposited on the
substrate to form an ultra-thin film. That is, an ultra-thin film
of a composite metal or an incompletely-reacted composite metal is
formed on the substrate.
[0028] The thus-formed ultra-thin film is finally irradiated with
the electrically neutral, activated species of a reactive gas so as
to convert the composite metal or the incompletely-reacted
composite metal to a composite metal compound through the reaction
of the ultra-thin film with the activated species of the reactive
gas. Specifically, the ultra-thin film is oxidized in the position
of a radical source. The step of forming the ultra-thin film and
the step of conversion to the composite metal compound are
sequentially repeated so as to form on the substrate a thin film of
the composite metal compound having a desired thickness.
[0029] In the present aspect, a substrate may be transferred or
fixed so long as the step of forming an ultra-thin film and the
step of conversion to a composite metal compound are sequentially
repeated so as to form on the substrate a thin film of the
composite metal compound having a desired thickness.
[0030] Second Aspect:
[0031] According to a second aspect of the present invention, there
is provided an apparatus for forming a thin film of a composite
metal compound, comprising a vacuum chamber, film deposition
process chambers, a reaction process chamber, and separation means
(e.g. shield plates). In the film deposition process chambers, a
working gas (e.g. argon gas) is introduced thereinto, and
independent targets formed of at least two different metals (e.g.
Si and Ta in the case of two different metals) are sputtered so as
to form on a substrate an ultra-thin film of a composite metal or
an incompletely-reacted composite metal.
[0032] In the reaction process chamber, the ultra-thin film (e.g.
Si and Ta) formed in the film deposition process chambers is
irradiated with the electrically neutral, activated species of a
reactive gas (e.g. the activated species of oxygen) so as to
convert the composite metal or the incompletely-reacted composite
metal to a composite metal compound (e.g. SiO.sub.2 and
Ta.sub.2O.sub.2) through the reaction of the ultra-thin film with
the activated species of the reactive gas. The separation means is
adapted to separate the reaction process chamber from the film
deposition process chambers in terms of space and pressure by means
of the shield plates.
[0033] The shield plates serving as the separation means define
within the vacuum chamber separate spaces which serve as the
reaction process chamber and the film deposition process chambers.
That is, the thus-defined spaces within the vacuum chamber are not
completely separated from each other, but maintain a substantially
independent state so as to serve as the reaction process chamber
and film deposition process chambers which can be controlled
independently of each other. Thus, the reaction process chamber and
the film deposition process chambers are configured to be least
influential to each other so that optimum conditions can be
established in each of the chambers.
[0034] Thus, the separation means prevents the reactive gas (e.g.
the activated species of oxygen) from mixing with the working gas
(e.g. argon gas) in the film deposition process chambers so that
there can be sequentially repeated a stable film deposition process
and a reaction process to thereby form on a substrate a thin film
of a composite metal compound having a desired thickness.
[0035] As in the case of the first aspect, the activated species of
a reactive gas used in the reaction process chamber are
electrically neutral radicals (atoms or molecules having at least
one unpaired electron, or atoms or molecules in an excited state).
Also, in the present aspect, a magnetron sputtering device may
serve as a thin film deposition device.
[0036] Activated species are generated by means of: a
radio-frequency discharge chamber comprising a quartz tube, around
which a radio-frequency coil is wound; a radio-frequency power
source for applying power to the radio-frequency coil via a
matching box; reaction gas feed means for introducing a reactive
gas from a gas cylinder into the radio-frequency discharge chamber
via a mass flow controller; an external or internal coil for
generating a magnetic field of 20-300 gauss within the
radio-frequency discharge chamber; and a multi-aperture grid, a
multi-slit grid, or a like grid disposed between the
radio-frequency discharge chamber and the reaction process
chamber.
[0037] A multi-aperture grid is formed of a metal or an insulator
in which are formed a number of apertures having a diameter of
0.1-3mm, and is cooled. A multi-slit grid is formed of a metal or
an insulator in which are formed a number of slits having a width
of 0.1-1mm, and is cooled.
[0038] Preferably, a cooling measure, such as a water-cooling
measure, is provided for the multi-aperture grid or multi-slit
grid. The cooling measure may employ a known technique. Such a grid
causes ions and electrons in plasma to mutually exchange charges on
the surface of the grid to thereby introduce into the reaction
process chamber only activated species which are reactive and are
not charged, i.e. which are electrically neutral.
[0039] As in the case of the first aspect, a voltage (usually a
negative voltage) applied to each of the targets is inverted at
1-200 kHz intervals to a positive voltage ranging between +50 V and
+200 V to thereby neutralize, with electrons in plasma, positive
charges which accumulate in a compound to be formed on the surface,
particularly an uneroded portion thereof, of each of the
targets.
[0040] Third Aspect:
[0041] According to a third aspect of the present invention, there
is provided a method for forming a thin film of a composite metal
compound in which a thin film of a composite metal compound having
a desired thickness is formed on a substrate in a manner similar to
that of the first aspect and in which there is imparted to the thin
film any refractive index within the range between the optical
refractive index intrinsic to a constituent metal compound of the
thin film and the optical refractive index intrinsic to another
constituent metal compound of the thin film.
[0042] That is, the present aspects is characterized in that there
is imparted to the thin film any refractive index within the range
between the optical refractive index intrinsic to a constituent
metal compound of a thin film of a composite metal compound and the
optical refractive index intrinsic to another constituent metal
compound of the thin film.
[0043] As described in the section of the first aspect with
reference to FIG. 3, Si serving as a first metal and Ta serving as
a second metal, for example, are sputtered, and the aforementioned
film deposition process is repeated to form a composite oxide
film.
[0044] Through the control of the magnitude of power applied to the
first metal target and that of power applied to the second metal
target, the refractive index of a thin film can be varied. For
example, as shown in FIG. 4, the refractive index of a thin film
varies with the ratio between the power applied to Si serving as
the first metal and the power applied to Ta serving as the second
metal. Accordingly, through the continuous variation of the power
applied to the two targets according to a predetermined rule, a
refractively gradient film can be formed.
[0045] As in the case of the preceding aspects, the electrically
neutral, activated species of a reactive gas are radicals (atoms or
molecules having at least one unpaired electron, or atoms or
molecules in an excited state). Also, the above-mentioned
sputtering may be magnetron sputtering. Further, a voltage (usually
a negative voltage) applied to each of the targets is inverted at
1-200 kHz intervals to a positive voltage ranging between +50 V and
+200 V to thereby neutralize, with electrons in plasma, positive
charges which accumulate in a compound to be formed on the surface,
particularly an uneroded portion thereof, of each of the
targets.
[0046] Fourth Aspect:
[0047] According to a fourth aspect of the present invention, there
is provided an apparatus for forming a thin film of a composite
metal compound, comprising the features of the second aspect and
transfer means for sequentially and repeatedly transferring a
substrate between thin film deposition portions for forming a thin
film through sputtering, which thin film deposition portions
correspond to the aforementioned film deposition process chambers,
and an exposure-to-radicals portion for exposing a thin film to
radicals of a reactive gas emitted from a radical source, which
exposure-to-radicals portion corresponds to the aforementioned
reaction process chamber. A thin film of a composite metal compound
is formed on the substrate through the sequentially repeated
transfer of the substrate between the thin film deposition portions
and the exposure-to-radicals portion. Also, there is imparted to
the thin film any refractive index within the range between the
optical refractive index intrinsic to a constituent metal compound
of a thin film of a composite metal compound and the optical
refractive index intrinsic to another constituent metal compound of
the thin film.
[0048] According to the present aspect, a substrate is held by an
electrically-insulated substrate holder so as to prevent the
occurrence of an unusual discharge on the substrate. As in the case
of the preceding aspects, the activated species of a reactive gas
used in the reaction process chamber are electrically neutral
radicals (atoms or molecules having at least one unpaired electron,
or atoms or molecules in an excited state); a magnetron sputtering
device serves as a film deposition device; and a negative voltage
applied to each of the targets is inverted at 1-200 kHz intervals
to a positive voltage ranging between +50 V and +200 V to thereby
neutralize, with electrons in plasma, positive charges which
accumulate in a compound to be formed on the surface, particularly
an uneroded portion thereof, of each of the targets. Also, a
mechanism of the generation of the activated species, a grid, and
shield means are similar to those of the preceding aspects.
[0049] Fifth Aspect:
[0050] According to a fifth aspect of the present invention, a thin
film of a composite metal compound is formed on a substrate in a
manner similar to that of the first aspect, and any optical
characteristics are imparted to the thin film through the
continuous variation of the refractive index of the thin film in
the direction of the thickness of the thin film within the range
between the optical refractive index intrinsic to a constituent
metal compound of the thin film and the optical refractive index
intrinsic to another constituent metal compound of the thin
film.
[0051] Next will be described, as examples, a 3-layer
antireflection film having an intermediate-refractive-index layer
and a 2-layer antireflection film having a refractively gradient
layer. Their film configurations are, for example, as follows:
[0052] (1)
substrate/M(.lambda./4)/2H(.lambda./2)/L(.lambda./4)/air; and
[0053] (2) substrate/G/L(.lambda./4)/air (G: refractively gradient
layer).
[0054] In this case, the refractive index of the
intermediate-refractive-i- ndex layer M is represented by
n.sub.m=n.sub.1{square root}{square root over (n.sub.s)}, where
n.sub.m is the refractive index of the
intermediate-refractive-index layer M, n.sub.1 is the refractive
index of the low-refractive-index layer, and n.sub.s is the
refractive index of the substrate. The 2-layer antireflection film
is designed based on the conventional 2-layer antireflection design
called w-coat; specifically
substrate/2H(.lambda./2)/L(.lambda./4)/air. FIG. 7 shows the
calculated and measured spectral curves of the 3-layer and 2-layer
antireflection films. As seen from FIG. 7, the calculated values
and the measured values are in good coincidence. In the case of the
2-layer antireflection film, the high-refractive-index layer of the
conventional w-coat is replaced by a refractively gradient layer,
thereby expanding the range of antireflection.
[0055] As mentioned above, through the continuous variation of the
refractive index of a thin film in the direction of the thickness
of the thin film, any optical characteristics can be imparted to
the thin film.
[0056] In the above-described aspects, two sputterers are used for
sputtering two kinds of metals. However, three or more sputterers
may be used. Such a configuration is feasible because the film
deposition process chambers and the reaction process chamber are
separated from each other by the shield means and can be controlled
independently.
[0057] Thus, the present invention yields the following advantages:
the refractive index can be controlled to any value within the
range between the respective refractive indices intrinsic to a
plurality of metals to be sputtered; an ultra-thin film can be
formed while the ultra-thin film is undergoing oxidation,
nitriding, fluorination, or a like reaction; and a thin film of a
metallic compound having stable optical characteristics, dynamic
characteristics, and like characteristics can be formed on a
substrate without increasing the substrate temperature and at a
high rate of deposition. Also, a wide range of refractive index
variation can be obtained through use of a simple control
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] FIG. 1 is a schematic view showing an apparatus for forming
a thin film;
[0059] FIG. 2 is a schematic side view as viewed along the line
A-B-C of FIG. 1;
[0060] FIG. 3 is an explanatory view showing the process of forming
a thin film of a composite metal compound on a substrate;
[0061] FIG. 4 is a graph showing the relation between power ratio
and refractive index;
[0062] FIG. 5 is a graph showing the relation between extinction
coefficient and refractive index;
[0063] FIG. 6 is a graph showing the relation between heterogeneity
and refractive index for a plurality of thin films; and
[0064] FIG. 7 is a graph showing the relation between reflectance
and wavelength for comparison between calculated values and
experimental values.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0065] An apparatus S for forming a thin film according to an
embodiment of the present invention includes a vacuum chamber 11, a
film deposition process chambers 20 and 40, a reaction process
chamber 60, shield plates 31, 51, and 75 (which serve as separation
means or shield means), a substrate holder 13 and drive means
thereof (which serve as transfer means), and means for generating
activated species.
[0066] The vacuum chamber 11 is formed of a closed hollow container
having any shape. The substantially cylindrical substrate holder 13
is disposed at the center of the vacuum chamber 11 in a manner
rotatable at a predetermined speed. The film deposition process
chambers 20 and 40 and the reaction process chamber 60 are disposed
around the substrate holder 13 and within the vacuum chamber
11.
[0067] The film deposition process chambers 20 and 40 are enclosed
with the shield plates 31 and 51, respectively, independently of
each other, and have at least two sputterers.
[0068] The film deposition process chambers 20 and 40 are disposed
opposite to each other with respect to the substrate holder 13. The
film deposition process chambers 20 and 40 are defined by the
shield plates 31 and 51, respectively.
[0069] The shield plates 31, 51, and 75 define separate spaces
which serve as the film deposition process chambers 20 and 40 and
the reaction process chamber 60 (which will be described later),
respectively, in a vacuum atmosphere established within the vacuum
chamber 11. The thus-defined spaces are not completely separated
from each other, but are substantially independent of each other
and serve as the film deposition process chambers 20 and 40 and the
reaction process chamber 60, which are independently
controllable.
[0070] Accordingly, the film deposition process chambers 20 and 40
and the reaction process chamber 60 are configured to be least
influential to each other so that optimum conditions can be
established in each of the chambers 20, 40, and 60. Preferably, the
pressure of the film deposition process chambers 20 and 40 is set
higher than that of the reaction process chamber 60.
[0071] Such pressure setting prevents a reactive gas (e.g. oxygen
gas) in the reaction process chamber 60 from entering the film
deposition process chambers 20 and 40. Thus, there can be prevented
the occurrence of an unusual discharge which would otherwise result
due to the formation of a metallic compound on the surfaces of
targets 29 and 49. For example, the pressure (the degree of vacuum)
of the film deposition process chambers 20 and 40 is preferably
0.8-10.times.10.sup.-3 Torr, and the pressure (the degree of
vacuum) of the reaction process chamber 60 is preferably
0.5-8.times.10.sup.-3 Torr, thereby establishing the condition that
the pressure of the film deposition process chambers 20 and 40 is
greater than that of the reaction process chamber 60.
[0072] The film deposition process chambers 20 and 40 have
sputtering electrodes 21 and 41, respectively. Spaces in front of
the sputtering electrodes 21 and 41 serve as sputtering film
deposition portions.
[0073] The film deposition process chambers 20 and 40 are connected
to sputtering gas cylinders 27 and 47 via mass flow controllers 25
and 45, respectively. A sputtering gas, such as argon, is
introduced from the cylinders 27 and 47 into the film deposition
process chambers 20 and 40, respectively, to thereby establish a
regulated sputtering atmosphere within the film deposition process
chambers 20 and 40. Through the application of power from
sputtering power sources 23 and 43, sputtering is performed. In the
present embodiment, a low-refraction material is used as the target
29. Examples of such a low-refraction material include Si. Also, a
high-refraction material is used as the target 49. Examples of such
a high-refraction material include Ti, Zr, Ta, and Nb.
[0074] The reaction process chamber 60 includes an
activated-species generator 61, which serves as a radical source,
for generating the activated species of a reactive gas and a grid
62. The grid 62 may be a multi-aperture grid or a multi-slit
grid.
[0075] The activated-species generator 61 may be an
inductively-coupled type, a capacitively-coupled type, or a
inductively, capacitively-coupled type and has an external or
internal electrodes. As to a capacitively-coupled type, it has an
external or internal electrodes as the case may be.
[0076] The activated-species generator 61 includes a
radio-frequency (RF) discharge chamber 63 formed of a quartz tube
and a radio-frequency (RF) coil wound on the RF discharge chamber
63. A radio-frequency (RF) power source 69 applies power (a
high-frequency power of 100 kHz to 50 MHz) to the RF coil 65 via a
matching box 67. At the same time, a reactive gas, such as oxygen
gas, is introduced from a reactive gas cylinder 73 into the RF
discharge chamber 63 via a mass flow controller 71. As a result,
the plasma of the reactive gas is generated. Examples of such a
reactive gas include oxidizing gases such as oxygen and ozone,
nitriding gases such as nitrogen, carbonating gases such as
methane, and fluorinating gases such as CF.sub.4.
[0077] In order to obtain a high-density plasma, a magnetic field
of 20-300 gauss is generated within the quartz tube through use of
the external coil 80 or the internal coil 81. The grid 62 disposed
at the connecting portion between the quartz tube and the vacuum
chamber 11 is adapted to release only activated species into the
reaction process chamber 60.
[0078] The multi-aperture grid serving as the grid 62 is formed of
a metal or an insulator in which are formed a number of apertures
having a diameter of 0.1-3mm, and is cooled. The multi-slit grid
serving as the grid 62 is formed of a metal or an insulator in
which are formed a number of slits having a width of 0.1-1mm, and
is cooled.
[0079] Through use of the grid 62, there are selectively introduced
into the reaction process chamber 60 the activated species of a
reactive gas, i.e. radicals, radicals in an excited state, atoms in
an excited state, and molecules in an excited state, while charged
particles such as electrons and ions cannot pass through the grid
62 and thus cannot enter the reaction process chamber 60.
Accordingly, in the reaction process chamber 60, a metallic
ultra-thin film is not exposed to the above-mentioned charged
particles, but is exposed only to electrically neutral activated
species of a reaction gas and reacts with the activated species to
thereby be converted from a metallic thin film of Si and Ta or the
like to a thin film of a composite metal compound (SiO.sub.2 and
Ta.sub.2O.sub.2)
[0080] The transfer means of the present embodiment is adapted to
sequentially and repeatedly transfer a substrate between thin film
deposition portions for forming a thin film through sputtering,
which thin film deposition portions correspond to the film
deposition process chambers 20 and 40, and an exposure-to-radicals
portion for exposing a thin film to radicals of a reactive gas
emitted from a radical source, which exposure-to-radicals portion
corresponds to the reaction process chamber 60.
[0081] The transfer means of the present embodiment will now be
described specifically. As shown in FIGS. 1 and 2, the
substantially cylindrical substrate holder 13 serving as the
transfer means is disposed at the center of the vacuum chamber 11
in a manner rotatable at a predetermined speed. The substrate
holder 13 is rotatably supported by unillustrated bearing portions
in the vacuum chamber 11. The bearing portions may be formed inside
or outside the vacuum chamber 11. The substrate holder 13 is
connected to the output shaft of a rotational drive 17 (motor) and
rotated by the rotating output shaft.
[0082] The rotational drive 17 is configured such that the
rotational speed thereof can be controlled. A substrate (not shown)
is mounted on the substrate holder 13 and transferred sequentially
and repeatedly between the thin film deposition portions for
forming a thin film through sputtering in the film deposition
process chambers 20 and 40 and the exposure-to-radicals portion for
exposing a thin film to radicals of a reactive gas emitted from the
radical source in the reaction process chamber 60.
EXAMPLES
[0083] Sputtering conditions and conditions for generating the
activated species of a reactive gas are as follows:
[0084] (1) Sputtering conditions (Si)
[0085] Applied power: 0-2.8 kW
[0086] Substrate temperature: room temperature
[0087] Argon flux: 300 sccm
[0088] Rotational speed of substrate holder: 100 rpm
[0089] Thickness of ultra-thin film: 2-6 angstroms
[0090] (2) Sputtering Conditions (Ta)
[0091] Applied power: 0-1.5 kW
[0092] Substrate temperature: room temperature
[0093] Argon flux: 200 sccm
[0094] Rotational speed of substrate holder: 100 rpm
[0095] Thickness of ultra-thin film: 1-4 angstroms
[0096] (3) Conditions for Generating Radicals of Reactive Gas
(O.sub.2)
[0097] Applied power: 2.0 kW
[0098] Oxygen flux: 60 sccm
[0099] In order to describe the present invention, there will next
be described, by way of example, the case where a thin film of a
composite metal compound of SiO.sub.2 and Ta.sub.2O.sub.2 is
deposited under the above sputtering conditions and conditions for
generating the activated species of a reactive gas.
[0100] Silicon (Si) is sputtered in the steps of: fixing silicon
serving as the target 29 in place; introducing argon gas into the
film deposition process chamber 20 from the sputtering gas cylinder
27; and applying power to the target 29 from the sputtering power
source 23. Tantalum (Ta) is sputtered in the steps of: fixing
tantalum serving as the target 29 in place; introducing argon gas
into the film deposition process chamber 40 from the sputtering gas
cylinder 47; and applying power to the target 29 from the
sputtering power source 43.
[0101] A refractive index to be obtained depends on the ratio
between the power applied to one magnetron sputtering target and
the power applied to the other magnetron sputtering target in FIG.
3. Oxygen gas is introduced into the activated-species generator 61
from the reactive gas cylinder 73, and the activated-species
generator 61 is activated, thereby generating the activated species
of oxygen gas (oxygen atoms).
[0102] As the substrate holder 13 carrying a substrate is rotated
by the rotational drive 17 (motor), an Si ultra-thin film is
deposited on the substrate when the substrate is located in front
of the sputtering electrode 21 (the sputtering thin-film deposition
portion) in the film deposition process chamber 20. Next, a Ta
ultra-thin film is deposited on the substrate when the substrate is
located in front of the sputtering electrode 41 (the sputtering
thin-film deposition portion) in the film deposition process
chamber 40. The thus-formed thin film of the composite metal is
oxidized by the activated species of oxygen gas when the substrate
is located in front of the grid 62 (the exposure-to-radicals
portion) in the reaction process chamber 60. As a result, the thin
film of the composite metal is converted to a thin film of a
composite metal compound of SiO.sub.2 and Ta.sub.2O.sub.2.
[0103] The substrate holder 13 carrying the substrate is rotated so
as to repeat the deposition of an ultra-thin film of Si and Ta and
the conversion of the ultra-thin film of Si and Ta to a thin film
of a composite compound of SiO.sub.2 and Ta.sub.2O.sub.2 until a
thin film of a composite compound of SiO.sub.2 and Ta.sub.2O.sub.2
having a desired thickness is obtained.
[0104] Spaces in front of the sputtering electrodes 21 and 41 are
enclosed by the shield plates 31 and 51, respectively, and a space
in front of the grid 62 is enclosed by the shield plates 75. A
sputtering gas is introduced into the corresponding enclosed spaces
from the sputtering gas cylinders 27 and 47, and a reaction gas is
introduced into the corresponding enclosed space from the reaction
gas cylinder 73. The thus-introduced gases are evacuated into an
evacuation system by a vacuum pump 15. Accordingly, the sputtering
gas does not enter the space enclosed by the shield plates 75, or
the reactive gas does not enter the spaces enclosed by the shield
plates 31 and 51.
[0105] Also, discharge associated with magnetron sputtering and
discharge associated with the generation of the activated species
of a reaction gas can be controlled independently of each other to
thereby have no effect on each other, and thus are performed
stably, thereby avoiding the occurrence of an unexpected accident
and providing a high reliability. Further, since the
activated-species generator 61 is configured not to expose a
substrate to plasma, the substrate is free from various damages
which would otherwise result due to charged particles. Also, the
substrate temperature can be controlled to 100.degree. C. or lower
to thereby avoid an unfavorable temperature rise. In the case of a
plastic substrate, since the substrate temperature does not exceed
100.degree. C., a glass transition point is not exceeded during
sputtering. Thus, the plastic substrate does not suffer deformation
or like damage.
[0106] The above-mentioned phenomena will now be described with
reference to FIGS. 4 to 7. FIGS. 4 to 7 show the relation among
power and optical characteristics, such as refractive index,
extinction coefficient, and heterogeneity, of
Ta.sub.xSi.sub.yO.sub.z. Optical constants are calculated based on
data regarding the spectral characteristics of a single-layer film.
As shown in FIG. 4, the refractive indices of
Ta.sub.xSi.sub.yO.sub.z films vary with the ratio of the power
applied to one guide to the power applied to the other guide. As
seen from FIG. 4, as the applied power ratio between the Si cathode
and the Ta cathode increases, the refractive index decreases.
[0107] Since the vapor deposition rate is fixed at 40 nm/min, the
illustrated relationship between the refractive index and the
applied power ratio holds. As a result, the minimum and maximum
refractive indices at a wavelength of 550 nm are found 1.463 and
2.182, respectively. As the applied power ratio increases, the
refractive index at a wavelength of 550 nm increases from 1.463 to
2.182. Also, the refractive index can be decreased from 2.182 to
1.463.
[0108] FIG. 5 shows the relation between extinction coefficient and
refractive index, and FIG. 6 shows the relation between
heterogeneity and refractive index for a plurality of thin films.
As shown in FIG. 5, the extinction coefficients of thin films
having a refractive index of 1.463 to 2.00 at a wavelength of 550
nm are smaller than 5.times.10.sup.-4. The extinction coefficients
of thin films having a refractive index of 2.00 to 2.182 are
smaller than 1.times.10.sup.-3. As seen from FIG. 6, the thin films
show a very small heterogeneity. Thin films having a refractive
index not higher than 2.00 are negatively heterogeneous. Thin films
having a refractive index higher than 2.00 are positively
heterogeneous.
[0109] Based on the above findings, a 3-layer antireflection film
having an intermediate-refractive-index layer and a 2-layer
antireflection film having a refractively gradient layer were
designed and fabricated. The fabricated film configurations were as
follows:
[0110] (1)
substrate/M(.lambda./4)/2H(.lambda./2)/L(.lambda./4)/air; and
[0111] (2) substrate/G/L(.lambda./4)/air (G: refractively gradient
layer).
[0112] The refractive index of the intermediate-refractive-index
layer M is represented by n.sub.m=n.sub.1{square root}{square root
over (n.sub.s)}, where n.sub.m is the refractive index of the
intermediate-refractive-index layer M, n.sub.1 is the refractive
index of the low-refractive-index layer, and n.sub.s is the
refractive index of the substrate. The 2-layer antireflection film
was designed based on the conventional 2-layer antireflection
design called w-coat; specifically
substrate/2H(.lambda./2)/L(.lambda./4)/air. FIG. 7 shows the
calculated and measured spectral curves of the 3-layer and 2-layer
antireflection films. As seen from FIG. 7, the calculated values
and the measured values are in good coincidence. In the case of the
2-layer antireflection film, the high-refractive-index layer of the
conventional w-coat was replaced by a refractively gradient layer,
thereby expanding the range of antireflection.
[0113] The present invention includes the following
embodiments:
[0114] An apparatus for forming-a thin film of a composite metal
compound, wherein the multi-aperture grid is formed of a metal or
an insulator in which are formed a number of apertures having a
diameter of 0.1-3mm, and is cooled.
[0115] An apparatus for forming a thin film of a composite metal
compound, wherein the multi-slit grid is formed of a metal or an
insulator in which are formed a number of slits having a width of
0.1-1mm, and is cooled.
[0116] A method for forming a thin film of a composite metal
compound comprising the steps of: sputtering at least two
independent different metals so as to form on a substrate an
ultra-thin film of a composite metal or an incompletely-reacted
composite metal; and irradiating the ultra-thin film with the
electrically neutral, activated species of a reactive gas so as to
convert the composite metal or the incompletely-reacted composite
metal to a composite metal compound through the reaction of the
ultra-thin film with the activated species of the reactive gas,
wherein the step of forming the ultra-thin film and the step of
conversion to the composite metal compound are sequentially
repeated so as to form on the substrate a thin film of the
composite metal compound having a desired thickness, and wherein
there is imparted to the thin film any refractive index within the
range between the optical refractive index intrinsic to a
constituent metal compound of the thin film and the optical
refractive index intrinsic to another constituent metal compound of
the thin film through the continuous variation of the refractive
index of the thin film in the direction of the thickness of the
thin film.
* * * * *