U.S. patent application number 10/084935 was filed with the patent office on 2002-10-24 for insulating film and method of producing semiconductor device.
This patent application is currently assigned to SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Fukuda, Takeshi, Sakama, Mitsunori, Uehara, Hiroshi, Uehara, Yukiko, Yamazaki, Shunpei.
Application Number | 20020153565 10/084935 |
Document ID | / |
Family ID | 27295535 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153565 |
Kind Code |
A1 |
Yamazaki, Shunpei ; et
al. |
October 24, 2002 |
Insulating film and method of producing semiconductor device
Abstract
A silicon oxide film is formed to cover an island
non-monocrystalline silicon region by plasma CVD using an organic
silane having ethoxy groups (e.g., TEOS) and oxygen as raw
materials, while hydrogen chloride or a chlorine-containing
hydrocarbon (e.g., trichloroethylene) of a fluorine-containing gas
is added to the plasma CVD atmosphere, preferably in an amount of
from 0.01 to 1 mol % of the atmosphere so as to reduce the alkali
elements from the silicon oxide film formed and to improve the
reliability of the film. Prior to forming the silicon oxide film,
the silicon region may be treated in a plasma atmosphere containing
oxygen and hydrogen chloride or a chlorine-containing hydrocarbon.
The silicon oxide film is obtained at low temperatures and this has
high reliability usable as a gate-insulating film in a
semiconductor device.
Inventors: |
Yamazaki, Shunpei; (Tokyo,
JP) ; Fukuda, Takeshi; (Kanagawa, JP) ;
Sakama, Mitsunori; (Kanagawa, JP) ; Uehara,
Yukiko; (Kanagawa, JP) ; Uehara, Hiroshi;
(Kanagawa, JP) |
Correspondence
Address: |
NIXON PEABODY, LLP
8180 GREENSBORO DRIVE
SUITE 800
MCLEAN
VA
22102
US
|
Assignee: |
SEMICONDUCTOR ENERGY LABORATORY
CO., LTD.
Atsugi-shi
JP
|
Family ID: |
27295535 |
Appl. No.: |
10/084935 |
Filed: |
March 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10084935 |
Mar 1, 2002 |
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09466828 |
Dec 20, 1999 |
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09466828 |
Dec 20, 1999 |
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09190828 |
Nov 12, 1998 |
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6025630 |
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09190828 |
Nov 12, 1998 |
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08734127 |
Oct 21, 1996 |
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5866932 |
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08734127 |
Oct 21, 1996 |
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08455574 |
May 31, 1995 |
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08455574 |
May 31, 1995 |
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08198054 |
Feb 18, 1994 |
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Current U.S.
Class: |
257/347 ;
257/E21.276; 257/E21.279 |
Current CPC
Class: |
H01L 21/02126 20130101;
H01L 21/02216 20130101; H01L 21/02337 20130101; H01L 21/02315
20130101; H01L 21/31629 20130101; H01L 21/31612 20130101; H01L
21/02274 20130101; H01L 21/02131 20130101 |
Class at
Publication: |
257/347 |
International
Class: |
H01L 027/12; H01L
031/0392 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 1993 |
JP |
5-55236 |
Claims
What is claimed is:
1. A semiconductor device comprising: an insulating film comprising
silicon oxide on an insulating surface, wherein the insulating film
includes halogen at a concentration of 5.times.10.sup.20 cm.sup.-3
or less and carbon at a concentration of 5.times.10.sup.19
cm.sup.-3 or less which are detected by second ion mass
spectroscopy.
2. A device according to claim 1, wherein the halogen is
chlorine.
3. A device according to claim 1, wherein the halogen is
fluorine.
4. A device according to claim 1, wherein the insulating film
includes carbon at a concentration of 1.times.10.sup.18 cm.sup.-3
or less which is detected by the second ion mass spectroscopy.
5. A device according to claim 1, wherein the insulating film
includes halogen at a concentration of 1.times.10.sup.17 cm.sup.-3
or more which is detected by the second ion mass spectroscopy.
6. A device according to claim 1, wherein the insulating film is a
gate insulating film.
7. A device according to claim 1, wherein the insulating film is an
insulating film in a thin film transistor.
8. A device according to claim 1, wherein the insulating film
covers an even surface over a glass substrate.
9. A device according to claim 1, wherein the insulating film is
formed by plasma chemical vapor deposition using an organic
silane.
10. A device according to claim 9, wherein the organic silane
comprises at least a material selected from the group consisting of
Si(OC.sub.2H.sub.5).sub.4, Si.sub.2O(OC.sub.2H.sub.5).sub.6,
Si.sub.3O.sub.2(OC.sub.2H.sub.5).sub.8,
Si.sub.4O.sub.3(OC.sub.2H.sub.5).- sub.10 and
Si.sub.5O.sub.4(OC.sub.2H.sub.5).sub.12.
11. A semiconductor device comprising: a crystalline semiconductor
island on an insulating surface; and an insulating film including
silicon oxide to cover the crystalline semiconductor island,
wherein the insulating film includes halogen at a concentration of
5.times.10.sup.20 cm.sup.-3 or less and carbon at a concentration
of 5.times.10.sup.19 cm.sup.-3 or less.
12. A device according to claim 11, wherein the concentrations of
halogen and carbon are detected by secondary ion mass
spectroscopy.
13. A device according to claim 11, wherein the halogen is
chlorine.
14. A device according to claim 11, wherein the halogen is
fluorine.
15. A device according to claim 11, wherein the insulating film
includes carbon at a concentration of 1.times.10.sup.18 cm.sup.-3
or less.
16. A device according to claim 11, wherein the insulating film
includes halogen at a concentration of 1.times.10.sup.17 cm.sup.-3
or more.
17. A device according to claim 11, wherein the insulating film is
formed by plasma chemical vapor deposition using an organic
silane.
18. A device according to claim 17, wherein the organic silane
comprises at least a material selected from the group consisting of
Si(OC.sub.2H.sub.5).sub.4, Si.sub.2O(OC.sub.2H.sub.5).sub.6,
Si.sub.3O.sub.2(OC.sub.2H.sub.5).sub.8,
Si.sub.4O.sub.3(OC.sub.2H.sub.5).- sub.10 and
Si.sub.5O.sub.4(OC.sub.2H.sub.5).sub.12.
19. A semiconductor device including at least a thin film
transistor comprising: a crystalline semiconductor island on an
insulating surface; a silicon oxide film over the crystalline
semiconductor island; and a conductive film including at least one
of aluminum, titanium, and titanium nitride, said conductive film
being formed on the silicon oxide film, wherein the silicon oxide
film includes halogen at a concentration of 5.times.10.sup.20
cm.sup.-3 or less and carbon at a concentration of
5.times.10.sup.19 cm.sup.-3 or less.
20. A device according to claim 19, wherein the concentrations of
halogen and carbon are detected by secondary ion mass
spectroscopy.
21. A device according to claim 19, wherein the halogen is
chlorine.
22. A device according to claim 19, wherein the halogen is
fluorine.
23. A device according to claim 19, wherein the silicon oxide film
includes carbon at a concentration of 1.times.10.sup.18 cm.sup.-3
or less.
24. A device according to claim 19, wherein the silicon oxide film
includes halogen at a concentration of 1.times.10.sup.17 cm.sup.-3
or more.
25. A device according to claim 19, wherein the silicon oxide film
is formed by plasma chemical vapor deposition using an organic
silane.
26. A device according to claim 17, wherein the organic silane
comprises at least a material selected from the group consisting of
Si(OC.sub.2H.sub.5).sub.4, Si.sub.2O(OC.sub.2H.sub.5).sub.6,
Si.sub.3O.sub.2(OC.sub.2H.sub.5).sub.8,
Si.sub.4O.sub.3(OC.sub.2H.sub.5).- sub.10 and
Si.sub.5O.sub.4(OC.sub.2H.sub.5).sub.12.
27. A semiconductor device including at least a thin film
transistor comprising: a crystalline semiconductor island on an
insulating surface; a gate insulating film including silicon oxide
on the crystalline semiconductor island; and a gate electrode on
the gate insulating film, wherein the gate insulating film includes
halogen at a concentration of 5.times.10.sup.20 cm.sup.-3 or less
and carbon at a concentration of 5.times.10.sup.19 cm.sup.-3 or
less.
28. A device according to claim 27, wherein the concentrations of
halogen and carbon are detected by secondary ion mass
spectroscopy.
29. A device according to claim 27, wherein the halogen is
chlorine.
30. A device according to claim 27, wherein the halogen is
fluorine.
31. A device according to claim 27, wherein the gate insulating
film includes carbon at a concentration of 1.times.10.sup.18
cm.sup.-3 or less.
32. A device according to claim 27, wherein the gate insulating
film includes halogen at a concentration of 1.times.10.sup.17
cm.sup.-3 or more.
33. A device according to claim 27, wherein the gate insulating
film is formed by plasma chemical vapor deposition using an organic
silane.
34. A device according to claim 33, wherein the organic silane
comprises at least a material selected from the group consisting of
Si(OC.sub.2H.sub.5).sub.4, Si.sub.2O(OC.sub.2H.sub.5).sub.6,
Si.sub.3O.sub.2(OC.sub.2H.sub.5).sub.8,
Si.sub.4O.sub.3(OC.sub.2H.sub.5).- sub.10 and
Si.sub.5O.sub.4(OC.sub.2H.sub.5).sub.12.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for producing a
gate-insulating film which is used in a thin film device such as a
gate-insulated field effect transistor or the like, at a low
temperature of 650.degree. C. or lower, and also to the insulating
film produced by the method.
BACKGROUND OF THE INVENTION
[0002] Heretofore, in a thin film device such as a gate-insulated
field effect thin-film-transistor (TFT) or the like, a silicon
oxide film with good characteristics, which is obtained by forming
a crystalline silicon followed by heating and oxidizing its surface
at high temperatures falling within a range of from 900 to
1100.degree. C., has been used as a gate-insulating film.
[0003] The oxide film formed by such thermal oxidation is
essentially characterized in that its interfacial level density is
extremely low and that it may be formed on the surface of a
crystalline silicon at a uniform thickness. Accordingly, the former
brings about good on/off characteristics and long-term reliability
on bias/temperature; while the latter reduces the short circuit
between a gate electrode and a semiconductor area (active layer) at
the edges in an island semiconductor region to thereby improve the
production yield of semiconductor devices.
[0004] To use such a thermal oxide film in producing semiconductor
devices, however, a material which is resistant to high
temperatures must be selected as the material for the substrate. In
this respect, since inexpensive glass materials (for example,
alkali-free glass such as Corning 7059, etc.) cannot be used, the
production costs are disadvantageously high especially when
large-area substrates are used. Recently, a technical means for
forming TFT on an alkali-free substrate is being developed, in
which, however, a thermal oxide film cannot be used but a
gate-insulating film shall be formed by sputtering or by physical
or chemical vapor deposition (CVD) such as plasma CVD or reduced
pressure CVD.
[0005] However, it was inevitable that the characteristics of the
silicon oxide film formed by such means were inferior to those of
the thermal oxide film. Namely, the interfacial level density of
the former is generally large and, additionally, the former was
always accompanied by the dangers of alkali ions such as sodium
ions or the like invading the film being formed. In addition, since
the step coverage of the silicon oxide film is not so good, the
film frequently caused the short circuit between the gate electrode
and the active layer at the edges of the island semiconductor
region. For these reasons, it was extremely difficult to obtain
semiconductor devices of the kind satisfying all the
characteristics, the reliability and the production yield by the
prior art technology.
SUMMARY OF THE INVENTION
[0006] The present invention has been made so as to solve at least
one of these problems in the prior art technology. Accordingly, one
object of the present invention is to provide a method for
producing a silicon oxide film with good step coverage. Another
object of the present invention is to provide a silicon oxide film
which is resistant to unfavorable impurities such as alkali ions
and others and also to provide a method for producing the film.
[0007] First, the present invention is characterized in that a film
which has been obtained by plasma CVD using a mixed gas containing
an organic silane having ethoxy groups, oxygen, and hydrogen
chloride or a chlorine-containing hydrocarbon, as the raw material
gas, and consists essentially of silicon oxide is used as a
gate-insulating film.
[0008] Secondly, the present invention is also characterized in
that a film which has been obtained by plasma CVD using a mixed gas
containing an organic silane having ethoxy groups, oxygen, and a
fluorine-containing gas (e.g., NF.sub.3, C.sub.2F.sub.6), as the
raw material gas, and consists essentially of silicon oxide is used
as a gate-insulating film.
[0009] Accordingly, the present invention provides an insulating
film consisting essentially of silicon oxide, which has been formed
on an island non-monocrystalline semiconductor region consisting
essentially of silicon to closely cover the region and is
characterized in that from 1.times.10.sup.17 to 5.times.10.sup.20
cm.sup.-3 of halogens are detected from the film by secondary mass
spectrometry and that 5.times.10.sup.19 cm.sup.-3 or less carbons
are detected therefrom.
[0010] The present invention also provides a first method of
producing a semiconductor device comprising a first step for
forming an island non-monocrystalline semiconductor region
consisting essentially of silicon and a second step for forming a
film consisting essentially of silicon oxide over the
non-monocrystalline semiconductor region in a plasma atmosphere
resulting from a mixed gas containing an organic silane having
ethoxy groups, oxygen, and hydrogen chloride or a
chlorine-containing hydrocarbon.
[0011] The present invention further provides a second method of
producing a semiconductor device comprising a first step for
forming an island non-monocrystalline semiconductor region
consisting essentially of silicon, a second step for exposing the
island semiconductor region to a plasma atmosphere containing
oxygen, and hydrogen chloride or a chlorine-containing hydrocarbon,
and a third step for forming a film consisting essentially of
silicon oxide over the non-monocrystalline semiconductor region in
a plasma atmosphere resulting from a mixed gas containing an
organic silane having ethoxy groups and oxygen.
BRIEF EXPLANATION OF THE DRAWINGS
[0012] FIG. 1(A) is a conceptual cross-sectional view showing a
positive column CVD apparatus used in an example of the present
invention.
[0013] FIG. 1(B) is a conceptual plan view showing the positive
column CVD apparatus shown in FIG. 1(A).
[0014] FIGS. 2(A) to 2(E) shows a flow sheet showing the formation
of TFT in the example.
[0015] FIG. 3 shows the characteristic curves of breakdown voltage
of the insulating films obtained in the example.
[0016] FIGS. 4(A) and 4(B) show the characteristic curves of
V.sub.FB of the insulating films obtained in the example.
DETAILED DESCRIPTION OF THE INVENTION
[0017] As the organic silane having ethoxy groups, preferred are
substances to be represented by chemical formulae.
Si(OC.sub.2H.sub.5).sub.4 (tetraethoxysilane, hereinafter referred
to as TEOS), Si.sub.2O(OC.sub.2H.sub.5).sub.6,
Si.sub.3O.sub.2(OC.sub.2H.sub.5)- .sub.8,
Si.sub.4O.sub.3(OC.sub.2H.sub.5).sub.10 and
Si.sub.5O.sub.4(OC.sub.2H.sub.5).sub.12. Since these organic silane
materials move on the surface of the substrate for a long period of
time to be decomposed on the surface to form a silicon oxide film
thereon, they may well get into even hollows to give an excellent
film with good step coverage.
[0018] As the chlorine-containing hydrocarbon, preferred are
substances to be represented by chemical formulae C.sub.2HCl.sub.3
(trichloroethylene), C.sub.2H.sub.3Cl.sub.3 (trichloroethane) and
CH.sub.2Cl.sub.2 (dichloromethane). The chlorine-containing gas of
the kind is decomposed essentially in a vapor phase to be
compounded with alkali elements such as sodium or the like that
exists in the filming atmosphere, whereupon the resulting compound
removes from the substrate to accelerate the removal of alkali
elements from the silicon oxide film being formed. Some chlorine
atoms still remain in the silicon oxide film formed, and these
function as a barrier therein against alkali elements which will
try to invade the film from the outward later on. As a result, the
reliability of TFT may be improved. The concentration of the
chlorine-containing hydrocarbon is preferably from 0.01 to 1%
relative to the whole mixed gas. If it is more than 1%, the gas
will have bad influences on the characteristics of the film
formed.
[0019] In the insulating film consisting essentially of silicon
oxide, thus formed by the above-mentioned method, halogen elements
(e.g., fluorine or chlorine) are detected in an amount of from
1.times.10.sup.17 from 5.times.10.sup.20 cm.sup.-3 as impurity
elements by secondary ion mass spectrometry, while the carbon
concentration is 5.times.10.sup.19 cm.sup.-3 or less. In
particular, in order to lower the interfacial level density of the
film, it is desired that the carbon concentration is
1.times.10.sup.18 cm.sup.-3 or less. In order to lower the carbon
concentration, the temperature of the substrate during filming may
be 200.degree. C. or higher, preferably 300.degree. C. or
higher.
[0020] On the insulating film to be formed in this manner, many
dangling bonds are often precipitated in the initial stage of its
filming. Therefore, it is preferred to previously expose the
substrate semiconductor layer (this preferably consists essentially
of silicon) to a plasma atmosphere containing oxygen. As a result,
the interfacial level density is lowered while the fluctuations of
the flat band potential in the bias/temperature test are reduced,
and therefore the reliability of the semiconductor device to be
formed is improved. It is also preferred to add to the atmosphere
hydrogen chloride or a chlorine-containing material such as
trichloroethylene, trichloroethane, dichloromethane or the like, in
addition to oxygen, to further improve the effect.
[0021] On the other hand, after the formation of the insulating
film consisting essentially of silicon oxide by the above-mentioned
method, the film may further be heat-treated at temperatures
falling within the range of from 200 to 650.degree. C. to thereby
reduce the fluctuations of the flat band potential. The heat
treatment is preferably conducted in an oxygen-free atmosphere such
as argon, nitrogen or the like. The fluctuations of the flat band
potential are noticeably reduced by the heat treatment at
450.degree. C. or higher and the reduction is saturated at
600.degree. C. or higher.
[0022] The second method of the present invention is characterized
by comprising exposing an island non-monocrystalline semiconductor
region consisting essentially of silicon to a plasma atmosphere
containing oxygen, and hydrogen chloride or a chlorine-containing
hydrocarbon, followed by forming a film consisting essentially of
silicon oxide over the non-monocrystalline semiconductor region by
plasma CVD using a raw material containing an organic silane having
ethoxy groups and oxygen.
[0023] In the second method, hydrogen chloride or a
chlorine-containing hydrocarbon is essentially accumulated in the
chamber during the plasma treatment, which brings about the same
effect as that to be brought about by the above-mentioned first
method where hydrogen chloride or a chlorine-containing hydrocarbon
is added, during the following step of forming the silicon oxide
film. The same as that mentioned above shall apply to the second
step with respect to the improvement in the reliability attainable
by the plasma treatment. To obtain a better result from the second
method, it is also preferred that the chlorine concentration and
the carbon concentration in the silicon oxide film thus formed by
the second method are the same as those in the film formed by the
above-mentioned the first method. It is also preferred in the
second method that the film consisting essentially of silicon oxide
thus formed is subjected to heat treatment at 200 to 650.degree.
C., preferably at 450 to 600.degree. C., after the filming in order
to obtain a further better result.
[0024] The plasma CVD apparatus to be employed in the present
invention may be either an ordinary parallel plate-type apparatus
(in which a pair of electrode plates are located in a chamber,
facing to each other, and one or both of them has/have a sample
substrate mounted thereon) or a positive column-type apparatus such
as that used in the following example.
[0025] However, the latter is preferred to the former in view of
the following two points. One is that the amount of the substrates
to be treated at one time is determined by the area of the
electrodes used in the former, while it is determined by the
discharging volume in the latter. Accordingly, a larger amount of
substrates may be processed at one time by the latter. The other is
that the surface of the substrate treated by the former is much
damaged by the plasma, while the latter is almost free from the
damage by the plasma since it has almost no potential inclination.
In addition, since the uniformity of the film to be formed using
the latter is better than that using the former, the uniform film
has no bad influences on the characteristics of TFT and the
production yield thereof.
[0026] It is necessary that. the chamber of the plasma CVD
apparatus to be used for the filming in the present invention is
sufficiently cleaned, prior to its use, so as to reduce the content
of alkali elements, such as sodium, etc., in the chamber. To clean
the chamber, chlorine, hydrogen chloride or the above-mentioned
chlorine-containing hydrocarbon may be introduced into the chamber
along with oxygen, and thereafter the plasma may be generated
therein. It is preferred that the chamber is heated at 150.degree.
C. or higher, preferably 300.degree. C. or higher, so as to more
effectively carry out the step.
EXAMPLE
[0027] This example demonstrates one embodiment of the present
invention of forming a silicon oxide film, as the gate-insulating
film, on an island non-monocrystalline silicon semiconductor film
by positive column plasma CVD, essentially showing the electric
characteristics of the silicon oxide film formed. The plasma CVD
apparatus used herein is shown in FIG. 1. FIG. 1(A) is a vertical
cross-sectional view of the apparatus, and FIG. 1(B) is a top plan
view of the same. The positive column CVD is characterized in that
the substrate to be coated is located in the positive column region
for plasma discharging and is coated with films therein.
[0028] The RF power sources 102 and 103 give the power to generate
plasma. Regarding the frequency from the sources, radio waves are
typically employed, having a frequency of 13.56 MHz. The power fed
from the two power sources is adjusted by the phase shifter 104 and
the matching boxes 105 and 106 in such a way that the condition of
the plasma to be formed is the best. The power derived from the RF
power sources arrives at the pair of electrodes 107 and 108 that
have been located in parallel to each other in the inside of the
chamber 101 and have been protected by the electrode covers 112 and
113, thus causing discharging between these electrodes. Substrates
to be treated are located between the electrodes 107 and 108. In
order to improve the mass-producibility, the substrates 111 are
cased in a container 109, where they are attached to the both
surfaces of the sample u holders 110. The substrates are
characterized in that they are parallel to each other between the
electrodes. The substrates are heated by the infrared lamp 114 and
kept at suitable temperatures. Though not shown, the apparatus is
fitted with a gas exhauster and a gas-feeding means.
[0029] The filming conditions and the characteristics of the film
formed are mentioned below. The temperature of the substrates was
300.degree. C. Into the chamber, 300 SCCM of oxygen, 15 SCCM of
TEOS and 2 SCCM of trichloroethylene (hereinafter referred to as
TCE) were introduced into the chamber. The RF power was 75 W, and
the whole pressure was 5 Pa. After the filming, the film formed was
annealed in hydrogen atmosphere at 350.degree. C. for 35
minutes.
[0030] FIG. 3 shows the results of the dielectric breakdown test of
the silicon oxide films of 1000 .ANG. thick that had been formed on
high-resistance silicon wafers using the present apparatus. Over
the silicon oxide film, formed was a 1 mm.o slashed.-aluminum
electrode and the relation between the voltage and the current was
plotted. FIG. 3(C) indicates the film that had been formed on the
substrate without any particular treatment of the substrate prior
to the filming, from which it is noted that the breakdown voltage
of the film is low. The films of FIG. 3(A) were formed as follows:
After the substrates were set in the chamber, they were heated at
300.degree. C. and exposed to the plasma atmosphere generated by
introducing 400 SCCM of oxygen and from 0 to 5 SCCM of TCE. The
total pressure of the atmosphere was 5 Pa, and the RF power was 150
W. The plasma exposure was carried out for 10 minutes. (During the
step, no film was formed by the gaseous reaction.) After the plasma
exposure, the silicon oxide films of FIG. 3(A) were formed, and
they showed a high breakdown voltage.
[0031] The films of FIG. 3(B) were formed as follows in the same
manner as in FIG. 3(A) except that the flow rate of TCE in the
filming step was changed to 4 SCCM or more, for example 5 SCCM. As
shown, they had a low breakdown voltage. From these results, it has
been found that the TCE concentration for the filming has the
optimum value.
[0032] FIG. 4(A) shows the result of the bias/temperature test, as
one example of the reliability tests, of the insulating films
formed in this example, indicating the relation between the
fluctuations (V.sub.FB) of the flat band voltage (V.sub.FB) and the
pre-treatment, if any, of the substrates. In the bias/temperature
test, a voltage of +17 V was imparted to the sample at 150.degree.
C. for one hour and the C-V characteristic of the sample was
measured at room temperature. Next, a voltage of -17 V was imparted
to the same sample at 150.degree. C. for one hour and the C-V
characteristic thereof was also measured at room temperature. The
difference in V.sub.FB between the two measurements was obtained to
be V.sub.FB.
[0033] In FIG. 4(A), the substrate of the sample (a) was not
pre-treated. V.sub.FB of the sample (a) was about 5 V and was
relatively large. However, the problem was solved by pre-treating
the substrate. The substrates of the samples (b) and (c) were
pre-treated under the conditions mentioned below.
1 Sample (b) (c) Temperature of Substrate 300.degree. C.
300.degree. C. TCE/Oxygen 0/400 0.5/400 RF Power 150 W 150 W Time
for Treatment 10 min 10 min
[0034] From FIG. 4(A), it is understood that the reliability of the
insulating film was improved much more by pre-treating the
substrate using TCE.
[0035] The same improvement may also be attained by annealing the
insulating film formed. The annealing of the film was carried out
in argon of one atmospheric pressure at 300 to 570.degree. C. for
one hour. The relation between the annealing temperature and
V.sub.FB is shown in FIG. 4(B), from which it is noted that
V.sub.FB was significantly reduced when the film was annealed at
temperatures not higher than 450.degree. C., while it became
gradually constant when the annealing temperature was being near to
600.degree. C. From the result, it was clarified that the annealing
of the insulating film formed is effective in improving the
reliability of the film.
[0036] On the basis of the results obtained from the
above-mentioned experiments, a TFT sample was produced. The flow
sheet for producing it is shown in FIG. 2. First, the silicon oxide
film 202 of 2000 .ANG. thick was formed, as a subbing film, on the
substrate (Corning 7059) 201, by positive column plasma CVD using
TEOS, oxygen and TCE as raw materials. The apparatus used herein
was same as that shown in FIG. 1. The main conditions for the
filming were as follows:
2 Temperature of Substrate: 300.degree. C. Whole Pressure: 5 Pa
Mixed Gas: TOES: 12 SCCM Oxygen: 300 SCCM TCE: 2 SCCM RF Power: 75
W
[0037] Next, an amorphous silicon film of 500 nm thick was
deposited thereover by plasma CVD, and this was patterned to form
the island silicon region 203. This was allowed to stand in
nitrogen atmosphere at 400.degree. C. for 30 minutes to remove
hydrogen therefrom. Next, this was annealed with a laser ray, as
shown in FIG. 2(A), to crystallize the silicon region. As the
laser, used was a KrF excimer laser (having a wavelength of 248 nm
and a pulse width of 20 nsec). The energy density was from 200 to
350 mM/cm.sup.2. During the irradiation of the laser rays, the
substrate was kept at 300 to 500.degree. C., for example
450.degree. C.
[0038] Afterwards, the silicon oxide film 204 of 1000 .ANG. thick
was formed to cover the island silicon region 203, as a
gate-insulating film, by positive column plasma CVD using TEOS,
oxygen and TCE as raw materials, as shown in FIG. 2(B). Prior to
the filming, the substrate was pre-treated, using the same
apparatus as in Example 1. The main conditions for the
pre-treatment were as follows:
3 Temperature of Substrate: 300.degree. C. Whole Pressure: 5 Pa
Mixed Gas: Oxygen: 400 SCCM TCE: 0.5 SCCM RF Power: 150 W Time for
Treatment: 10 minutes
[0039] After the pre-treatment, the film 204 was formed. The main
condition for the filming were mentioned below. After the filming,
the film formed was annealed in argon atmosphere at 550.degree. C.
for one hour.
4 Temperature of Substrate: 300.degree. C. Whole Pressure: 5 Pa
Mixed Gas: TEOS: 15 SCCM Oxygen: 300 SCCM TCE: 2 SCCM RF Power: 75
W
[0040] Next, a 2% silicon-doped aluminum film of 6000 .ANG. thick
was deposited over the film and this was patterned to form the gate
electrode 205. Then, impurity ions (phosphorus or boron) were
introduced into the region 203 in a self-ordered manner by plasma
doping, using the gate electrode 205 as the mask, to form the
impurity regions 206 and 207, as shown in FIG. 2(C). The area into
which the impurities had not been introduced became the
channel-forming region 208. Since the doping was conducted through
the gate-insulating film, it needed an accelerated voltage of 80 kV
for phosphorus and 65 kV for boron. The dose amount was suitable
from 1.times.10.sup.15 to 4.times.10.sub.15 cm.sup.-2.
[0041] Next, the impurities were activated also by annealing with
laser rays, as shown in FIG. 2(D). As the laser, used was the KrF
excimer laser (having a wavelength of 248 nm and a pulse width of
20 nsec). The energy density was from 200 to 350 mJ/cm.sup.2.
During the irradiation of the laser rays, the substrate may be kept
at 300 to 500.degree. C. After the irradiation of the laser rays,
this was annealed at 350.degree. C. in hydrogen atmosphere having a
partial pressure of from 0.1 to 1 atmospheric pressure for 35
minutes.
[0042] Next, the silicon oxide film 209 of 5000 .ANG. thick was
deposited thereover as an interlayer insulating film. The silicon
oxide film 209 was formed by positive column CVD, using TEOS,
oxygen and TCE as raw materials. The apparatus used for the filming
was the same as in Example 1. The main conditions for the filming
were as follows:
5 Temperature of the Substrate: 300.degree. C. Whole Pressure: 5 Pa
Mixed Gas: TEOS: 30 SCCM Oxygen: 300 SCCM
* * * * *