U.S. patent application number 10/849883 was filed with the patent office on 2005-01-13 for process and apparatus for forming oxide film, and electronic device material.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Ide, Shinji, Kitagawa, Junichi, Ozaki, Shigenori.
Application Number | 20050005844 10/849883 |
Document ID | / |
Family ID | 33533147 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050005844 |
Kind Code |
A1 |
Kitagawa, Junichi ; et
al. |
January 13, 2005 |
Process and apparatus for forming oxide film, and electronic device
material
Abstract
An oxide film-forming apparatus, comprising: a process chamber
for disposing an electronic device substrate at a predetermined
position; water vapor supply means for supplying water vapor into
the process chamber; and plasma exciting means for activating the
water vapor with plasma, whereby the surface of the electronic
device substrate can be irradiated with the plasma based on the
water vapor.
Inventors: |
Kitagawa, Junichi;
(Amagasaki-city, JP) ; Ide, Shinji;
(Amagasaki-city, JP) ; Ozaki, Shigenori;
(Amagasaki-city, JP) |
Correspondence
Address: |
Finnegan, Henerson, Farabow
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Assignee: |
TOKYO ELECTRON LIMITED
|
Family ID: |
33533147 |
Appl. No.: |
10/849883 |
Filed: |
May 21, 2004 |
Current U.S.
Class: |
118/715 ;
257/E21.285 |
Current CPC
Class: |
H01L 21/02238 20130101;
H01J 37/32192 20130101; H01L 21/31662 20130101; H01L 21/02164
20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2003 |
JP |
2003-146228(PAT.A |
Claims
What is claimed is:
1. An oxide film-forming apparatus, comprising: a process chamber
for disposing an electronic device substrate at a predetermined
position; water vapor supply means for supplying water vapor into
the process chamber; and plasma exciting means for activating the
water vapor with plasma, whereby the surface of the electronic
device substrate can be irradiated with the plasma based on the
water vapor.
2. An electronic device material, comprising: an electronic device
substrate having at least one trench, and an oxide film covering a
part of the surface of the electronic device substrate; the part
containing at least one trench groove, wherein, in the oxide film
covering the trench groove, the ratio (T.sub.100/T.sub.110) of the
thickness T.sub.100 of the oxide film disposed on the surface (100)
of the electronic device material, to the thickness T.sub.110 of
the oxide film disposed on the surface (110) of the electronic
device material is 0.65 or larger.
3. An oxide film-forming process, comprising: irradiating the
surface of an electronic device substrate with plasma in the
presence of a process gas containing at least water vapor, so as to
form an oxide film on the surface of the electronic device
substrate.
4. An oxide film-forming process according to claim 3, wherein the
oxide film is formed at a temperature of 500.degree. C. or
lower.
5. An oxide film-forming process according to claim 3 or 4, wherein
the plasma is generated on the basis of microwave irradiation
through a plane antenna member having a plurality of slits.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for forming an
oxide film which is capable of suitably forming an oxide film, as
one of fundamental techniques constituting the electronic device
fabrication process, an apparatus for forming an oxide film which
can preferably be used in such an oxide film-forming process, and
an electronic device material which can preferably be formed by
using the oxide film-forming process and apparatus. The process for
forming an oxide film according to the present invention can
preferably be used for forming materials for semiconductors or
semiconductor devices (such as those having an MOS type
semiconductor structure, and those having a thin film transistor
(TFT) structure) or liquid crystal devices.
[0003] 2. Related Background Art
[0004] Along with an increase in the degree or scale of integration
of semiconductor devices in recent years, the element isolation
technique tends to be shifted from LOCOS (Local Oxidation of
Silicon; isolation by a field oxide film) to STI (shallow trench
isolation; isolation by a trench groove). This is because the STI
technique may easily provide an advantage that deeper and more
reliable isolation can be attained.
[0005] When the STI is used, a highly reliable oxide film is first
formed as a base oxide film on the surface of a trench groove, and
then the trench groove is filled with an oxide film by using
chemical vapor deposition (CVD), etc. Heretofore, in this case, the
base oxide film has been formed by using a thermal oxidation
process.
[0006] In the above thermal oxidation process, a high temperature
of about 1000.degree. C. is required. Accordingly, the above STI
(trench oxidation) is only applicable to a very early step among
the entire device fabrication process wherein the thermal damage
due to the thermal oxidation is negligible.
[0007] When the above STI is adopted, the structure obtained
therefrom naturally becomes a three-dimensional structure. In such
a three-dimensional structure, it is necessary to oxidize surfaces
of an Si substrate (or base material) having different crystal
orientations. However, in the thermal oxidation process, the growth
rate is dependent on the crystal orientation, and therefore the
thickness of the resultant oxide film has a strong tendency such
that it varies with different crystal orientations of the Si
substrate in the trench groove having a film which has been
obtained by the thermal oxidation process. Accordingly, when a
minimum film thickness is intended to be secured, there are
produced crystal orientation surfaces which have been oxidized
undesirably thickly, and such a phenomenon has hindered the
fabrication of finer devices.
[0008] Further, in order to enhance the reliability of oxide films,
also in the thermal oxidation process, a wet oxidation process
utilizing (H.sub.2O) or (H.sub.2O.sub.2) is used, and the
development of an oxidation temperature technique capable of
decreasing the rate is in progress. However, the thermal oxidation
process still requires a temperatures of about 800.degree. C. or
higher. In order to secure the element isolation, the substrate is
usually doped so as to provide a predetermined profile of an
impurity. In this case, however, this technique tends to cause a
problem such that the impurity is again dispersed in the processing
due to the thermal oxidation process at 800.degree. C. or
higher.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a process
and apparatus for forming an oxide film which have solved the
above-mentioned problem encountered in the prior art, and an
electronic device material having a high-quality oxide film.
[0010] Another object of the present invention is to provide a
process and apparatus for forming an oxide film which can control
the film thickness of an oxide film, and can provide a high-quality
oxide film, and an electronic device material having such a
high-quality oxide film.
[0011] A further object of the present invention is to provide a
process and apparatus for forming an oxide film which can suppress
the thermal damage to an object to be processed, to a level as
slight as possible, and an electronic device material having such a
high-quality oxide film.
[0012] As a result of earnest study, the present inventors have
found that the above object may be attained extremely effectively,
by irradiating an object to be processed with plasma in the
presence of a process gas containing at least water vapor.
[0013] The process for forming an oxide film according to the
present invention is based on the above discovery, and comprises:
irradiating the surface of an electronic device substrate with
plasma in the presence of a process gas containing at least water
vapor, so as to form an oxide film on the surface of the electronic
device substrate.
[0014] The present invention also provides an oxide film-forming
apparatus, comprising:
[0015] a process chamber for disposing an electronic device
substrate at a predetermined position;
[0016] water vapor supply means for supplying water vapor into the
process chamber; and
[0017] plasma exciting means for activating the water vapor with
plasma,
[0018] whereby the surface of the electronic device substrate can
be irradiated with the plasma based on the water vapor.
[0019] The present invention further provides an electronic device
material, comprising:
[0020] an electronic device substrate having at least one trench
groove, and
[0021] an oxide film covering a part of the surface of the
electronic device substrate; the part containing at least one
trench groove,
[0022] wherein, in the oxide film covering the trench groove, the
ratio (T.sub.100/T.sub.110) of the thickness T.sub.100 of the oxide
film disposed on the surface (100) of the electronic device
material, to the thickness T.sub.110 of the oxide film disposed on
the surface (110) of the electronic device material is 0.65 or
larger.
[0023] In the formation of the oxide film according to the present
invention having the above constitution, plasma irradiation is
conducted in the presence of a process gas containing at least
water vapor (as desired, further comprising O.sub.2 and/or
(O.sub.2+H.sub.2)). According to the present inventors' knowledge
and investigations, it has been confirmed from the spectroscopic
analysis of plasma emission that, when H.sub.2O is produced prior
to the introduction thereof into a processing chamber containing
therein an object to be processed, a larger number of OH groups are
produced (as shown in the graph of FIG. 20 appearing hereinafter).
Based on the presence of such a large number of OH groups, it is
presumed that the present invention can form a highly reliable
oxide film, even at a low temperature, e.g., 500.degree. C. or
lower.
[0024] Further, unlike the conventional oxidation process using
thermal reaction, the present invention provides a process wherein
silicon is oxidized by the supply of oxidizing species, which have
been activated by plasma and such a process is not dependent on the
thermal reaction or thermal diffusion. Accordingly, in the present
invention, it is possible to realize the oxidization which is
relatively less dependent on the surface orientation of a substrate
for an electronic device, and as a result, it is easy to form an
oxide film having a uniform film thickness, even on the surface of
the substrate having a three-dimensional structure (e.g., a trench
groove).
[0025] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic plan view showing an example of a
semiconductor manufacturing equipment for conducting the oxide
film-forming process according to the present invention.
[0027] FIG. 2 is a schematic vertical sectional view showing an
example of the slot plain antenna (plane antenna member) plasma
processing unit which is usable in the oxide film-forming process
according to the present invention.
[0028] FIG. 3 is a block diagram showing an example of the water
vapor generator (WVG) for the oxide film-forming process according
to the present invention.
[0029] FIG. 4 is a graph showing the explosion range of a mixed gas
of oxygen and hydrogen, the operation range for a moisture
generator, and a process range.
[0030] FIG. 5 is a schematic plan view showing an example of the
plane antenna member which is usable in the oxide film-forming
process according to the present invention.
[0031] FIG. 6 is a schematic vertical sectional view of a plasma
processing unit which is usable in the process for forming an
electronic device according to the present invention.
[0032] FIG. 7 is a graph showing an example of the steps of
evacuation, preheating and plasma processing which is preferably
usable in the oxide film-forming process according to the present
invention.
[0033] FIG. 8 is a graph showing the relationship between the
thickness of an oxide film obtained by the oxide film-forming
process according to the present invention and the process gas
preheating time.
[0034] FIG. 9 is a graph showing an example of the relationship
between the intensity of O.sub.2 plasma emission obtained by the
oxide film-forming process according to the present invention and
the process gas preheating time.
[0035] FIG. 10 is a schematic perspective view showing another
example of the water vapor supply means which is preferably usable
in the oxide film-forming process according to the present
invention.
[0036] FIG. 11 is a schematic sectional view showing another
example of the plasma processing apparatus according to the present
invention.
[0037] FIG. 12 is a schematic sectional view showing an example of
the detailed structure of the plasma processing apparatus in FIG.
11.
[0038] FIG. 13 is a schematic sectional view showing an example of
the element isolation obtained by conventional LOCOS.
[0039] FIG. 14 is a schematic sectional view showing an example of
element isolation by a trench groove obtained by STI.
[0040] FIG. 15 is a graph showing an example of the relationship
between the oxide film thickness in the present invention and the
processing time.
[0041] FIG. 16 is a TEM photograph showing the distribution of
oxide film thickness in the vicinity of a trench groove obtained by
the oxide film-forming process according to the present
invention.
[0042] FIG. 17 is a graph showing the comparison of the crystal
orientation dependency of an oxide film obtained by the oxide
film-forming process according to the present invention with that
by the conventional thermal oxidation process.
[0043] FIG. 18 is a schematic sectional view for explaining the
process for evaluating the film quality used in Example 3.
[0044] FIG. 19 is a graph showing the results of evaluation of the
film quality obtained in Example 3.
[0045] FIG. 20 is a graph showing an example of the analytical
result of plasma emission in the present invention.
[0046] FIG. 21 is a schematic sectional view showing an example of
the thickness of an oxide film on a trench groove obtained by the
conventional thermal oxidation process.
[0047] FIG. 22 is a schematic sectional view showing an example of
the thickness of an oxide film on a trench groove obtained by
plasma oxidation of the present invention.
[0048] In the accompanying drawings, the respective reference
numerals have the following meanings.
[0049] W: wafer (substrate to be processed)
[0050] 60: plane antenna member (planar antenna member)
[0051] 2: oxide film
[0052] 2a: nitrogen-containing layer
[0053] 32: plasma processing unit (process chamber)
[0054] 33: plasma processing unit (process chamber)
[0055] 47: heating reactor
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0056] Hereinbelow, the present invention will be described in
detail with reference to the accompanying drawings, as desired. In
the following description, "%" and "part(s)" representing a
quantitative proportion or ratio are those based on mass, unless
otherwise noted specifically.
[0057] (Oxide Film-forming Process)
[0058] In the present invention, the surface of a substrate for an
electronic device is irradiated with plasma in the presence of a
process gas containing at least water vapor, to thereby form an
oxide film on the surface of the electronic device substrate.
[0059] (Electronic Device Substrate)
[0060] The electronic device substrate usable in the present
invention is not particularly limited, and may be one appropriately
selected from known electronic device substrates, or a combination
of two or more of these substrates. Examples of such electronic
device substrates may include: e.g., semiconductor materials and
liquid crystal device materials. Examples of semiconductor
materials may include, e.g., materials mainly comprising
monocrystalline silicon, materials mainly comprising
polycrystalline silicon, and materials mainly comprising silicon
nitride.
[0061] (Oxide Film)
[0062] In the present invention, the oxide film to be disposed on
the electronic device substrate is not particularly limited, as
long as it can be formed by the oxidation of the electronic device
substrate. Such an oxide film may be an oxide film or a combination
of two or more known oxide films to be used for known electronic
devices.
[0063] (Process Gas)
[0064] In the present invention, at the time of forming an oxide
film, the process gas to be used therefor contains at least water
vapor. Another gas (e.g., an inert gas or a rare gas) may be used
in combination therewith, as desired. The rare gas to be used in
such a case is not particularly limited, but may be one
appropriately selected from known rare gases, or a combination of
two or more species thereof. In view of the productivity, it is
preferred to use argon, helium, neon, or krypton as a rare gas.
[0065] (Water Vapor)
[0066] In the present invention, the property or state, production
process and so forth of water vapor are not particularly limited,
as long as it is water vapor which can form an oxide film on an
electronic device substrate in combination with microwave
plasma.
[0067] The water or water vapor (usually, at a pure water level)
which is preferably usable in the present invention, may include,
e.g., those obtained by the following processes.
[0068] (1) A process using a water vapor generator (WVG)
[0069] H.sub.2+O.sub.2------->H.sub.2O (pure water) Heating
(e.g., at about 350.degree. C.)
[0070] (2) A process using a pyrogenic reaction.
[0071] H.sub.2+O.sub.2------->H.sub.2O (pure water) For example,
at 800.degree. C. or higher
[0072] (3) A process using bubbling to obtain water vapor for pure
water.
[0073] (Oxide Film Formation Conditions)
[0074] In an embodiment wherein the present invention is used for
forming an oxide film, the following conditions may preferably be
used, in view of the characteristics of the oxide film to be
formed.
[0075] (1) H.sub.2O: 1-10 sccm, more preferably 5 sccm (about 0.2-2
volume %, more preferably about 1 volume % with respect to a rare
gas),
[0076] (2) Rare gas (e.g., Kr, Ar or He): 250-1000 sccm,
particularly preferably 500 sccm
[0077] (3) Temperature: room temperature (25.degree.
C.)-500.degree. C., particularly preferably 400.degree. C.
[0078] (4) Pressure: 6.67-266 Pa (50-2000 mTorr), particularly
preferably 133 Pa (1000 mTorr)
[0079] (5) Microwave: 2.4-4.9 W/cm.sup.2, more preferably 4.3
W/cm.sup.2.
[0080] In general, in many cases, an impurity is diffused into a
semiconductor substrate in advance to form an active region or
element an isolation region so as to form a device element on the
semiconductor substrate. However, in the conventional thermal
oxidation process, a region containing an impurity can be destroyed
due to the high temperature during the processing time as described
above, to thereby cause a problem.
[0081] In contrast, the present invention permits a low-temperature
processing, and therefore the present invention not only can
protect the impurity region, but also can suppress the damage,
distortion and so forth due to heat. Further, it is also possible
that an oxide film is formed according to the present invention,
and then a desired film (e.g., CVD film) is formed at a relatively
low temperature (about 500.degree. C.), and thereafter, the oxide
film-forming process according to the present invention may
preferably be used in the later oxidation step, whereby the process
control becomes easier.
[0082] (Electronic Device Material Having Oxide Film)
[0083] The present invention may preferably provide an electronic
device material, which has at least one trench groove and has an
oxide film covering at least a portion of the surface of the
electronic device material containing the trench groove. Herein,
the "trench groove" refers to a groove which has been formed in the
electronic device material. The trench groove is present on the
surface of the electronic device substrate at the time of the
formation of the oxide film, but after the formation of the oxide
film, another layer or another structure, etc., may be formed on
the trench groove.
[0084] In the above electronic device material, the ratio
(T.sub.100/T.sub.110) of the thickness T.sub.100 of an oxide film
formed on the surface (100) to the thickness T.sub.110 of an oxide
film formed on the surface (110) may preferably be close to one (1)
in the oxide film covering the trench groove.
[0085] (Apparatus for Forming an Oxide Film)
[0086] The oxide film-forming apparatus according to the present
invention comprises: a process chamber for disposing an electronic
device substrate at a predetermined position; water vapor supply
means for supplying water vapor into the process chamber; and
plasma exciting means for exciting the water vapor by plasma;
whereby the surface of the electronic device substrate can be
irradiated with the plasma based on the water vapor. In the present
invention, the plasma exciting means is not particularly limited,
but may preferably be stand-alone (electric field-free) type plasma
exciting means, such as plasma exciting means utilizing microwave
irradiation, in view of plasma damage. Further, in view of uniform
oxide film formation, the plasma exciting means may particularly
preferably be plasma exciting means which supplies microwave
through a plane antenna member, among those of the stand-alone
plasma type.
[0087] (Plane Antenna Member)
[0088] In the present invention, it is preferred that a
high-density plasma having a low electron temperature is generated
by irradiating microwave via a plane antenna member having a
plurality of slits; and an oxide film is formed on the surface of a
substrate to be processed by utilizing the thus generated plasma.
Such an embodiment can provide a process which accomplishes a light
plasma damage, and a high reactivity at a low temperature.
[0089] For example, a paper (Ultra Clean Technology, Vol. 10
Supplement 1, p. 32, 1998, published by Ultra Clean Society) may be
referred to, with respect to the details of microwave plasma
apparatus which has such a plane antenna having many slits and is
capable of generating plasma having a low electron temperature,
providing a light plasma damage, and a high plasma density.
[0090] When the above new plasma apparatus is used, it can easily
provide a plasma having an electron temperature of 1.5 eV or less,
and plasma sheath voltage of several volts or less. Accordingly, in
this case, the plasma damage can remarkably be reduced, as compared
with that based on the conventional plasma (plasma sheath voltage
of about 50V). A new plasma apparatus comprising this plane antenna
is capable of providing high-density radicals even at a temperature
of about 300.degree. C. to about 700.degree. C., it is considered
that it can suppress the deterioration of device characteristics
due to heating, and it can provide a process having a high
reactivity even at a low temperature.
[0091] (Preferred Plasma)
[0092] The characteristics of plasma to be preferably used in the
present invention are as follows:
[0093] (1) Electron temperature: 1.0 eV or lower
[0094] (2) Density: 1.times.10.sup.12 (1/cm.sup.3) or greater
[0095] (3) Uniformity in plasma density: +/-5% or smaller at
directly beneath the plane antenna.
[0096] As described above, the process for the present invention
can form a high-quality oxide film which enables easy control of
the film thickness (whether the film is either thin a film or a
thick film). Accordingly, when another layer (e.g., an electrode
layer) is formed on the thus formed oxide film, it is possible to
form a semiconductor device structure having an excellent
characteristic.
[0097] The process according to the present invention can form an
oxide film having a high reliability and having a film thickness of
about 10 nm. Accordingly, the present invention is applicable to a
gate oxide film for an MOS type semiconductor, in addition to the
base oxidation for an element isolation trench groove.
[0098] (One Embodiment of Production Process)
[0099] Next, there is described an embodiment of the oxide
film-forming process according to the present invention.
[0100] FIG. 1 is a schematic view (schematic plan view) showing an
example of the total arrangement of a semiconductor manufacturing
equipment 30 for conducting the oxide film-forming process
according to the present invention.
[0101] As shown in FIG. 1, in a substantially central portion of
the semiconductor manufacturing equipment 30, there is disposed a
transportation chamber 31 for transporting a wafer W (FIG. 3).
Around the transportation chamber 31, there are disposed: plasma
processing units 32 and 33 for conducting various treatments on the
wafer, two load lock units 34 and 35 for conducting the
communication/cutoff between the respective processing chambers, a
heating unit 36 for operating various heating treatments, and a
heating reaction furnace 47 for conducting various heating
treatments on the wafer. These units are disposed so as to surround
the transportation chamber 31. Alternatively, it is also possible
to provide the heating reaction furnace 47 independently and
separately from the semiconductor manufacturing equipment 30.
[0102] On the side of the load lock units 34 and 35, a preliminary
cooling unit 45 and a cooling unit 46 for conducting various kinds
of preliminary cooling and cooling treatments are disposed.
[0103] In the inside of transportation chamber 31, transportation
arms 37 and 38 are disposed, so as to transport the wafer W (FIG.
3) between the above-mentioned respective units 32-36.
[0104] On the foreground side of the load lock units 34 and 35 in
this figure, loader arms 41 and 42 are disposed. These loader arms
41 and 42 can put wafer W in and out with respect to four cassettes
44 which are set on the cassette stage 43, which is disposed on the
foreground side of the loader arms 41 and 42.
[0105] In FIG. 1, as the plasma processing units 32 and 33, two
plasma processing units of the same type are disposed in
parallel.
[0106] Further, it is possible to exchange both of the plasma
processing units 32 and 33 with a single-chamber type CVD process
unit. It is possible to set one or two of such a single-chamber
type CVD process unit in the position of plasma processing units 32
and 33.
[0107] When two plasma processing units 32 and 33 are used, it is
possible that an SiO.sub.2 film is formed in the plasma processing
unit 32, and the SiO.sub.2 film is surface-nitrided in the plasma
processing unit 33. Alternatively, it is also possible that the
formation of an SiO.sub.2 film and the surface-nitriding of the
SiO.sub.2 film are conducted in parallel, in the plasma processing
units 32 and 33. Further, it is also possible that an SiO.sub.2
film is formed in another apparatus, and the SiO.sub.2 film is
surface-nitrided in parallel, in the plasma processing units 32 and
33.
[0108] (One Embodiment of Film Formation of Gate Insulator)
[0109] FIG. 2 is a schematic sectional view in the vertical
direction showing a plasma processing unit 32 (or 33) which is
usable in the oxide film formation. FIG. 3 is a block diagram
showing an example of the water vapor generating means which is
preferably usable in the apparatus shown in FIG. 2.
[0110] Referring to FIG. 2, reference numeral 50 denotes a vacuum
container made of, e.g., aluminum. In the upper portion of the
vacuum container 50, an opening portion 51 is formed so that the
opening portion 51 is larger than a substrate (for example, wafer
W). A top plate 54 in a flat cylindrical shape made of a dielectric
such as quartz and aluminum nitride so as to cover the opening
portion 51. In the side wall of the upper portion of vacuum
container 50 which is below the top plate 54, gas feed pipes 72 are
disposed in the 16 positions, which are arranged along the
circumferential direction so as to provide equal intervals
therebetween. A process gas comprising at least water vapor
H.sub.2O (as desired, further comprising an inert such as rare gas)
can be supplied into the plasma region P in the vacuum container 50
from the gas feed pipes 72 evenly and uniformly.
[0111] Referring to FIG. 3, oxygen gas and hydrogen gas can be
supplied to one side of the water vapor generator (WVG), as an
embodiment of the water vapor supply means to be preferably be
usable in the present invention. The other side of the WVG is
connected to the process chamber 50 through an orifice, so that
water vapor can be supplied to the process chamber 50.
[0112] When such a moisture generator is used, an object to be
processed can be oxidized according to the following reaction.
1
[0113] It is generally known in the combustion reaction of H.sub.2
and O.sub.2 that a pressure-temperature characteristic as shown in
FIG. 4 is present. In order to satisfy each of the conditions for
the safe processing, the moisture generator, and oxidation
treatment, the moisture generator may preferably be operated at
about atmospheric pressure, and the oxidation treatment may
preferably be carried out at about 133 Pa, and therefore a pressure
difference should be provided between the process chamber and the
moisture generator by using an orifice.
[0114] On the outside of the top plate 54, there is provided a
radio-frequency power source, via a slit plane member antenna 60
having a plurality of slits, which comprises a slot plane antenna
(SPA) made from a copper plate, for example. As the radio-frequency
power source, a waveguide 63 is disposed on the top plate 54, and
the waveguide 63 is connected to a microwave power supply 61 for
generating microwave of 2.45 GHz, for example. The waveguide 63
comprises a combination of: a flat circular waveguide 63A, of which
lower end is connected to the plane antenna member 60; a circular
waveguide 63B, one end of which is connected to the upper surface
side of the circular waveguide 63A; a coaxial waveguide converter
63C connected to the upper surface side of the circular waveguide
63B; and a rectangular waveguide 63D, one end of which is connected
to the side surface of the coaxial waveguide converter 63C so as to
provide a right angle therebetween, and the other end of which is
connected to the microwave power supply 61.
[0115] In the present invention, a frequency region including UHF
and microwave is referred to as radio-frequency (or high-frequency)
region. The radio-frequency power supplied from the radio-frequency
power source may preferably have a frequency of not smaller than
300 MHz and not larger than 2500 MHz, which may include UHF having
a frequency of not smaller than 300 MHz and microwave having a
frequency of not smaller than 1 GHz. In the present invention, the
plasma generated by the radio-frequency power is referred to as
"radio-frequency plasma".
[0116] In the inside of the above-mentioned circular waveguide 63B,
an axial portion 62 of an electroconductive material is coaxially
provided, so that one end of the axial portion 62 is connected to
the central (or nearly central) portion of the plane antenna member
60 upper surface, and the other end of the axial portion 62 is
connected to the upper surface of the circular waveguide 63B,
whereby the circular waveguide 63B constitutes a coaxial structure.
As a result, the circular waveguide 63B is constituted so as to
function as a coaxial waveguide.
[0117] In addition, in the vacuum container 50, a stage 52 for
carrying the wafer W is provided so that the stage 52 is disposed
opposite to the top plate 54. The stage 52 contains a temperature
control unit (not shown) disposed therein, so that the stage can
function as a hot plate. Further, one end of an exhaust pipe 53 is
connected to the bottom portion of the vacuum container 50, and the
other end of the exhaust pipe 53 is connected to a vacuum pump
55.
[0118] (One Embodiment of Plane Antenna Member)
[0119] FIG. 5 is a schematic plan view showing an example of plane
antenna member 60 which is usable in an apparatus for producing an
electronic device material according to the present invention.
[0120] As shown in this FIG. 5, on the surface of the plane antenna
member 60, a plurality of slots 60a, 60a, are provided in the form
of concentric circles. Each slot 60a is a substantially square
penetration-type groove. The adjacent slots are disposed
perpendicularly to each other and arranged so as to form a shape of
alphabetical "T"-type character. The length and the interval of the
slot 60a arrangement are determined in accordance with the
wavelength of the microwave supplied from the microwave power
supply unit 61.
[0121] (One Embodiment of Heating Reaction Furnace)
[0122] FIG. 6 is schematic sectional view in the vertical direction
showing an example of the heating reaction furnace 47 which is
usable in an apparatus for producing an electronic device material
according to the present invention.
[0123] As shown in FIG. 6, a processing chamber 82 of the heating
reaction furnace 47 chamber is formed into an air-tight structure
by using aluminum, for example. A heating mechanism and a cooling
mechanism are provided in the processing chamber 82, although these
mechanisms are not shown in FIG. 6.
[0124] As shown in FIG. 6, a gas introduction pipe 83 for
introducing a gas into the processing chamber 82 is connected to
the upper central portion of the processing chamber 82, the inside
of the processing chamber 82 communicates with the inside of the
gas introduction pipe 83. In addition, the gas introduction pipe 83
is connected to a gas supply source 84. A gas is supplied from the
gas supply source 84 into the gas introduction pipe 83, and the gas
is introduced into the processing chamber 82 through the gas
introduction pipe 83. As the gas in this case, it is possible to
use one of various gases such as raw material for forming a gate
electrode (electrode-forming gas) such as silane, for example. As
desired, it is also possible to use an inert gas as a carrier
gas.
[0125] A gas exhaust pipe 85 for exhausting the gas in the
processing chamber 82 is connected to the lower portion of the
processing chamber 82, and the gas exhaust pipe 85 is connected to
exhaust means (not shown) such as vacuum pump. On the basis of the
exhaust means, the gas in the processing chamber 82 is exhausted
through the gas exhaust pipe 85, and the processing chamber 82 is
maintained at a desired pressure.
[0126] In addition, a stage 87 for carrying wafer W is provided in
the lower portion of the processing chamber 82.
[0127] In the embodiment as shown in FIG. 6, the wafer W is carried
on the stage 87 by means of an electrostatic chuck (not shown)
having a diameter which is substantially the same as that of the
wafer W. The stage 87 contains a heat source means (not shown)
disposed therein, to thereby constitute a structure wherein the
surface of the wafer W to be processed which is carried on the
stage 87 can be adjusted to a desired temperature.
[0128] The stage 87 has a mechanism which is capable of rotating
the wafer W which carried the stage 87, as desired.
[0129] In FIG. 6, an opening portion 82a for putting the wafer W in
and out with respect to the processing chamber 82 is provided on
the surface of the right side of the processing chamber 82 in this
figure. The opening portion 82a can be opened and closed by moving
a gate valve 98 vertically (up and down direction) in this figure.
In FIG. 6, a transportation arm (not shown) for transporting the
wafer is provided adjacent to the right side of the gate valve 98.
In FIG. 6, the wafer W can be carried on the stage 87, and the
wafer W after the processing thereof is transported from the
processing chamber 82, as the transportation arm enters the
processing chamber 82 and goes out therefrom through the medium of
the opening portion 82a.
[0130] Above the stage 87, a shower head 88 as a shower member is
provided. The shower head 88 is constituted so as to define the
space between the stage 87 and the gas introduction pipe 83, and
the shower head 88 is formed from aluminum, for example.
[0131] The shower head 88 is formed so that the gas exit 83a of the
gas introduction pipe 83 is positioned at the upper central portion
of the shower head 88. The gas is introduced into the processing
chamber 82 through gas feeding holes 89 provided in the lower
portion of the shower head 88.
[0132] (Embodiment of Oxide Film Formation)
[0133] Then, there is described a preferred embodiment wherein an
oxide film is formed on a wafer W (e.g., a silicon substrate) by
using the above-mentioned apparatus.
[0134] Referring to FIG. 1, at first, a gate valve (not shown)
mounted on the sidewall of the process chamber 50 in the plasma
processing unit 32 (FIG. 1) is opened to place the wafer W on the
stage 52 (FIG. 1) by using transportation arms 37 and 38.
[0135] Then, the gate valve is closed to seal the inside thereof,
and thereafter the temperature of the stage 52 is controlled to
heat the wafer W to e.g., 400.degree. C. At this time, for the
purpose of a decrease in the heating time and of the uniformity, a
rare gas such as Argon, a process gas at the time of forming an
oxide film, from the gas supply tube 72 and water vapor are
introduced at a flow rate of 500 sccm and 5 sccm, respectively, to
increase the pressure up to 133 Pa, for example, to thereby
increase the thermal conductivity between the stage and the wafer
and to carry out the first step (preliminary heating).
[0136] After the first step is complete, a microwave of 2.45 GHz
(3500 W), e.g., is generated from the microwave power source 61,
and the microwave is guided through a microwave guide, and
introduced through the plane antenna member 60 and the top plate 54
into the process chamber 50, to thereby generate plasma in the
plasma region P in an upper portion of the process chamber 50.
[0137] Herein, the microwave is transmitted in the rectangular
waveguide 63D in a rectangular mode, and is converted from the
rectangular mode into a circular mode by the coaxial waveguide
converter 63C. The microwave is then transmitted in the cylindrical
coaxial waveguide 63B in the circular mode, and transmitted in the
circular waveguide 63A in the expanded state, and is emitted from
the slots 60a of the plane antenna member 60, and penetrates the
plate 54 and is introduced into the vacuum container 50. In this
case, microwave is used, and accordingly high-density plasma can be
generated. Further, the microwave is emitted from a large number of
slots 60a of the plane antenna member 60, and accordingly the
plasma is caused to have a high plasma density.
[0138] (One Embodiment of Water Vapor Supply)
[0139] Referring to FIGS. 7-9, one embodiment of the water vapor
supply which is preferably be usable in the present invention is
explained. This water vapor supply may preferably include: (1) a
preliminary exhaust step, (2) a preliminary heating step, and (3)
an oxidation step.
[0140] (Preliminary Exhaust Step)
[0141] Referring to FIG. 7, when a process gas containing at least
water vapor is supplied to the process chamber 50, it is preferred
to evacuate the process chamber 50 (about 133 mPa) prior to the
supply in order to prevent the remaining or trace of the prior
history. The evacuation time may differ with various factors, but
in view of balance between the prevention of residual history and
process efficiency, the evacuation time may preferably be about
0.5-1 min. In view of balance between the prevention of residual
prior history and process efficiency, the evacuation may
experimentally preferably be, e.g., 133 mPa and 0.5 to one
minute.
[0142] (Preheating Step)
[0143] Then, an object to be processed (e.g., wafer W) is placed at
the processing position in the process chamber 50, and then the
supply of a process gas containing water vapor into the process
chamber 50 is started. The pressure at this time may preferably be
e.g., about 133 Pa.
[0144] The object to be processed is positioned and gas supply is
started, and then the preheating step is started. At this time, in
order to heat the object to be processed by using the thermal
conductivity of the introduced gas, a higher pressure is preferred.
In view of the simplicity of process flow and efficiency, however,
the preheating step can also be carried out at the same condition
as that of the oxidation condition. For example, the preheating of
400.degree. C., 133 Pa and 1.5-2.0 minutes may experimentally be
preferred.
[0145] (Oxidation Step)
[0146] After the above preheating step, plasma is ignited to start
the processing of the object to be processed. The process gas flow
and processing pressure have been adjusted by the above procedure,
it is possible to transfer the procedure to the main step by only
igniting the plasma.
[0147] (Relationship Between Preheating Time and Resultant Oxide
Film Thickness)
[0148] One example of the dependence of the preheating time on the
predetermined oxidation process is shown in FIG. 8.
[0149] When the preheating is insufficient, it is possible in some
cases that the thickness of the resultant film is thin, the process
reproducibility, for example, becomes problematic.
[0150] (Relationship Between Timing of Introducing Process Gas and
Plasma Emission (Oxygenic Emission))
[0151] FIG. 9 shows an example of the relationship between the
timing of introducing the process gas and the plasma emission. When
a sufficient oxidizing gas atmosphere is not formed at the time of
the plasma ignition, it is possible that the initial rise in the
oxidation process step becomes unstable, and the process stability
becomes problematic.
[0152] (Another Embodiment of Water Vapor Supply)
[0153] The schematic sectional view of FIG. 10 shows another
embodiment of water vapor supply of the present invention. In this
embodiment, water vapor are supplied from the position of the
process chamber 50 which is "hidden" from the plasma (i.e. shadowed
from the plasma). In general, in the vicinity of the gas inlet of
the vacuum chamber, a difference in the gas concentration and in
the pressure tends to occur due to the gas flow, and the plasma
tends to be unstable. Unstable plasma may develop into abnormal
discharge in some cases, and a localized abnormal discharge may hit
the chamber component member with its strong electric field, so as
to cause a contamination in the object to be processed.
Accordingly, the embodiment in FIG. 10 is effective in attaining
stable discharge of the plasma so as to prevent the contamination
of the object to be processed.
[0154] Referring to FIG. 10, in such an embodiment, the upper
portion of the process chamber 50 is composed of an aluminum upper
plate 21 and a ceramic (e.g., alumina Al.sub.2O.sub.3) top plate 22
disposed on the upper plate 21. As shown in FIG. 10, the supply
tube 72 for supplying water vapor (further, a rare gas as desired)
is disposed at a position on the wall of the process chamber 50,
which is "hidden" from the plasma (i.e. shadowed from the
plasma).
[0155] (Another Embodiment of Plasma Processing Apparatus)
[0156] FIG. 11 is a schematic sectional view showing another
example of the plasma processing apparatus according to the present
invention. Referring to FIG. 11, this embodiment is an example
using a plane antenna member as an antenna member.
[0157] As shown in FIG. 11, this plasma processing apparatus 100
has a plasma process chamber 101 entirely shaped into a tubular
form wherein a side wall 101a and the bottom portion 101b are
composed of a conductor such as aluminum, and the interior of the
plasma process chamber 101 is constructed as a sealed space.
[0158] In this plasma process chamber 101, there is housed, on the
upper face thereof, a stage 102 for placing the object to be
processed (e.g., semiconductor wafer W). This stage 102 is formed
in an almost cylindrical shape which is composed of alumite-treated
aluminum, etc., and provide a flat surface and a protruded
portion.
[0159] On the upper surface of the above stage 102, there is
provided an electrostatic chuck or clamp mechanism (not shown) for
retaining thereon a wafer W. Further, this stage 102 is connected
through a feeder line (not shown) to a matching box (not shown) and
a high frequency power source (e.g., for 13.56 MHz; not shown) for
supplying a bias. In the case of CVD, the high frequency power
source 44 is omissible.
[0160] On the other hand, on the side wall of the above plasma
process chamber 101, a gas supply nozzle 103 for introducing the
above water vapor-containing gas into the container is provided as
gas supply means.
[0161] The top portion of the plasma process chamber 101 is opened,
to which an insulating plate 104 (having a thickness of, e.g.,
about 20 mm) which is composed of a ceramic material such as
Al.sub.2O.sub.3 and has permeability to microwave is provided in an
air-tight manner through a sealing member (not shown) such as
O-ring.
[0162] On the top of this insulating plate 104 are provided a plane
antenna member 105 in the form of a circular plate, and a slow wave
material 106 (composed of quartz, Al.sub.2O.sub.3, AiN etc.) having
a high dielectric characteristic. Microwave is transmitted to this
plane antenna member 105 from a coaxial waveguide 107. The
frequency of the microwave is not limited to 2.45 GHz, and other
frequencies such as 8.35 GHz may be used.
[0163] FIG. 12 is a schematic sectional view showing an example of
further details of the structure of FIG. 11. As shown in FIG. 12,
the plasma processing apparatus 100a has a plasma process chamber
101 entirely shaped into a tubular form, of which side wall 101a
and bottom portion 101b are composed of, e.g., a conductor such as
aluminum, and the interior of the plasma process chamber 101 has
been constructed as a sealed space.
[0164] In the plasma process chamber 101, there is housed, on top
thereof, a stage 102 (stage) for placing an object to be processed
(e.g., semiconductor wafer W) on the top thereof. The stage 102 has
a heater (not shown) therein for heating the wafer W as
desired.
[0165] On the other hand, on the side wall of the above plasma
process chamber 101, a gas supply nozzle 103 for introducing the
above water vapor-containing gas into the container is provided as
gas supply means. In this FIG. 12, for rectification of the process
gas, there is disposed a gas baffle plate 109 almost vertically to
the side wall 101a at a height which is almost the same that of the
stage, and further at the inside of the side wall 101a and the gas
baffle plate 109, a liner (made of quartz) for preventing metal
contamination is disposed.
[0166] To the opening of the top portion of the plasma process
chamber 101, an insulating plate 104 (with a thickness of, e.g.,
about 20 mm) which is composed of a ceramic material such as
Al.sub.2O.sub.3 and that has permeability to microwave is provided
in an air-tight manner through a sealing member (not shown) such as
an O-ring.
[0167] On the top of this insulating plate 104 are provided a
discoid plane antenna member 105 and a slow wave material 106
(composed of quartz, Al.sub.2O.sub.3, AiN etc.) having a high
dielectric characteristic. Due to the effect of shortening
wavelength by the slow wave material 106 having the above high
dielectric characteristic, the intratubal wavelength of microwave
can be shortened.
[0168] In this FIG. 12, a cooling plate 112 is disposed on the slow
wave material 106 in order to cool the slow wave material 106 etc.,
and at the inside of the cooling plate 112 and the inside of the
side wall 101a, a coolant path 113 has been provided to cool these
members.
[0169] To the above plane antenna member 105, as described above, a
microwave (a frequency of 2.45 GHz etc.) is transmitted from the
coaxial waveguide 107.
[0170] (One Embodiment of Using Trench Groove)
[0171] For the element isolation formed on an electronic device
substrate, conventionally the so-called local oxidation of silicon
(LOCOS) processing, which effects isolation by an oxide film
locally formed on the substrate, has been mainly used (FIG. 13
shows a schematic sectional view of isolation of element obtained
by LOCOS). However, this had a problem that when this LOCOS is
used, a leak path tends to be formed, and thus the size of element
isolation by LOCOS had to be small.
[0172] Therefore, in recent years, the so-called shallow trench
isolation (STI) that performs element isolation by forming trench
groove in between elements and then forming an oxide film at the
inside of the trench groove have come to be widely used (FIG. 14
shows a schematic sectional view of element isolation obtained by
STI). When this STI technique is used, more secure element
isolation can be attained as compared to the LOCOS mentioned above.
On the other hand, however, when the conventional thermal oxidation
process is used, it is difficult to form an oxide film having a
uniform thickness on the surface of such trench groove, and thus in
view of element isolation function, a plane orientation develops
wherein an unnecessarily thick oxide film is formed, in order to
obtain the minimum film thickness with respect to the plane
orientation wherein growth rate is slow.
[0173] Difference in oxide film thickness generates stress, which
may reduce the reliability of the film or may break it due to
thermal stress imposed on in later steps. Also, an unnecessarily
thick film hinders miniaturization. In contrast, In the present
invention, a highly reliable oxide film which is uniform and
independent of plane orientation can be formed.
[0174] Hereinbelow, the present invention will be described in more
detail with reference to specific Examples.
EXAMPLES
[0175] The present invention will now be explained in more details
with regard to Examples.
Example 1
[0176] (Oxide Film Formation)
[0177] An oxide film was formed on a silicon substrate by the oxide
film-forming process according to the present invention. In the
formation of this oxide film, a process chamber having a plane
antenna member as shown in FIG. 1 and FIGS. 11-12 was used.
[0178] (Substrate)
[0179] As a silicon substrate, a monocrystalline silicon substrate
(wafer) having a specific resistance of 8 (cm, a P type of a
diameter of 200 mm and a plane orientation (100) was used.
[0180] (Prewashing)
[0181] The silicon substrate was washed in the following
procedure.
[0182] 1. Immerse in hyperammonium aqueous solution (10
minutes)
[0183] 2. Rinse in pure water
[0184] 3. Immerse in hyperhydrochloric acid aqueous solution (10
minutes)
[0185] 4. Rinse in pure water
[0186] 5. Immerse in hyperhydrofluoric acid aqueous solution (8
minutes)
[0187] 6. Rinse in pure water
[0188] 7. Dry in nitrogen gas
[0189] (Plasma Oxidation Treatment)
[0190] Microwave output: 3500 W
[0191] Chamber pressure: 133 Pa
[0192] Substrate temperature: 400.degree. C.
[0193] Noble gas flow rate: Ar=500 sccm
[0194] H2O flow rate: 5 sccm
[0195] (Measurement of Processing Time and Oxide Film
Thickness)
[0196] The oxide film thickness was measured using an optical film
thickness meter (ellipsometry). Relationship between the processing
time and the oxide film thickness obtained is shown in the graph of
FIG. 15.
Example 2
[0197] (Measurement of Dependence on Crystal Orientation)
[0198] Using a silicon substrate wherein trench groove had
previously been processed, the same prewashing and plasma
processing as Example 1 was carried out.
[0199] The dependence on crystal orientation of oxide film
thickness was determined by the TEM observation of the cross
section of the oxide film of trench groove. The result of
measurement is shown in TEM photographs in the following (Table 1)
and FIG. 16.
1TABLE 1 Ratio of Position Film thickness Crystal orientation film
thickness 1 200 100 1.00 2 190 1.05 3 230 110 0.87 4 170 1.18 5 200
100 1.00
Comparative Example
[0200] The data obtained in the above measurement were compared to
those obtained by the thermal oxidation process.
[0201] The data by the thermal oxidation process were cited from
"Electronics Technical Directory (3) MOS Device" by Takashi
Tokuyama.
[0202] The comparison of the data obtained by the present invention
and those of the Comparative Example are shown in the graph of FIG.
17.
Example 3
[0203] (Confirmation of Quality of the Oxide Film)
[0204] As shown in the schematic sectional view of FIG. 18,
polysilicon was deposited on the oxide film formed in Example 1 to
prepare a sample for evaluating the quality of the oxide film.
[0205] Using the above sample, the electrical reliability of the
oxide film was evaluated.
[0206] In this evaluation, a voltage was applied on the polysilicon
so that a constant current (0.1 A/cm.sup.2) flows from the
substrate to the polysilicon, and the time to the breakage of the
oxide film was determined. Since the electric current till the
breakage of the oxide film was constant, the scale for evaluation
was represented by (electric current).times.(time)=(electric
amount: Qbd). The result of measurement is shown in the graph of
FIG. 19. It can be evaluated that the greater the electric amount
till the breakage of the oxide film, the more reliable the oxide
film is.
[0207] (Test Condition)
[0208] Constant current stress: -0.1 A/cm2
[0209] Evaluation temperature: 120.degree. C.
[0210] Evaluation size: 10000 .mu.m2
[0211] As described above, the present invention provides an oxide
film-forming process and an oxide film-forming apparatus which can
form a high-quality oxide film, and also can easily control the
film thickness of the oxide film. The present invention provides an
electronic device material having such a high-quality oxide
film.
[0212] In the present invention, an embodiment thereof wherein an
oxide film is formed by using a low temperature (500.degree. C. or
lower) is particularly useful, when an electronic device substrate
having a large diameter (e.g., 300 mm) is used. Conventionally, it
was difficult to uniformly heat or cool such a large-diameter
substrate, as compared with those having a smaller diameter (e.g.,
200 mm)). Accordingly, when a low temperature processing is carried
out according to the present invention, it is easy to minimize the
occurrence of defects which may develop in the electronic device
substrate (wafer) having a large diameter.
[0213] From the invention thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
to be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
[0214] The basic Japanese Application No.146228/2003 filed on May
23, 2003 is hereby incorporated by reference.
* * * * *