U.S. patent application number 09/739876 was filed with the patent office on 2001-06-07 for apparatus for producing a semiconductor device.
Invention is credited to Itatani, Hideharu, Matsuyama, Naoko, Nakamure, Michihide, Sakai, Masanori, Tsuneda, Masayuki.
Application Number | 20010002585 09/739876 |
Document ID | / |
Family ID | 27306334 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002585 |
Kind Code |
A1 |
Sakai, Masanori ; et
al. |
June 7, 2001 |
Apparatus for producing a semiconductor device
Abstract
A method and apparatus for producing a semiconductor device can
provide a uniform film on a substrate. A substrate is introduced
into a reaction chamber or tube (51) which has gas feed ports (52,
53) and gas exhaust ports (54, 55). The substrate in the reaction
tube (51) is heated to substantially a film forming temperature
while supplying a prescribed gas to the reaction tube (51) through
the gas feed ports (52, 53) and exhausting the prescribed gas from
the reaction tube (51) through all the exhaust ports (54, 55). A
film-forming gas is supplied to the reaction tube (51) to form a
film on the substrate. The substrate with the film formed thereon
is taken out of the reaction tube (51). Moreover, after the film
formation on the substrate, a prescribed gas is supplied to the
reaction tube (51) from the gas feed ports (52, 53) while being
exhausted from the reaction tube (51) through all the exhaust ports
(54, 55), thereby removing a residual gas in the reaction tube.
Inventors: |
Sakai, Masanori; (Tokyo,
JP) ; Tsuneda, Masayuki; (Tokyo, JP) ;
Matsuyama, Naoko; (Tokyo, JP) ; Itatani,
Hideharu; (Tokyo, JP) ; Nakamure, Michihide;
(Tokyo, JP) |
Correspondence
Address: |
MCGINN & GIBB, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Family ID: |
27306334 |
Appl. No.: |
09/739876 |
Filed: |
December 20, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09739876 |
Dec 20, 2000 |
|
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|
09393276 |
Sep 10, 1999 |
|
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|
6204199 |
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Current U.S.
Class: |
118/725 ;
257/E21.274 |
Current CPC
Class: |
H01L 21/02205 20130101;
C23C 16/455 20130101; C23C 16/405 20130101; C23C 16/4412 20130101;
H01L 21/67017 20130101; C23C 16/4408 20130101; C23C 16/45502
20130101; H01L 21/02271 20130101; H01L 21/31604 20130101; H01L
21/02183 20130101 |
Class at
Publication: |
118/725 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 1998 |
JP |
10-258990 |
Mar 30, 1999 |
JP |
11-90035 |
Aug 2, 1999 |
JP |
11-219132 |
Claims
What is claimed is:
1. A method for producing a semiconductor device, comprising the
steps of: introducing a substrate into a reaction chamber which has
at least one gas feed port and at least one gas exhaust port;
heating said substrate in said reaction chamber to substantially a
film forming temperature while supplying a prescribed gas to said
reaction chamber through said at least one gas feed port and
exhausting said prescribed gas from said reaction chamber through
all said exhaust ports; supplying a film-forming gas to said
reaction chamber to form a film on said substrate; and taking said
substrate with said film formed thereon out of said reaction
chamber.
2. The method for producing a semiconductor device according to
claim 1, wherein in said substrate introducing step and said
substrate taking-out step, a prescribed gas is supplied from said
at least one gas feed port to said reaction chamber while being
exhausted from said reaction chamber through all said exhaust
ports.
3. The method for producing a semiconductor device according to
claim 2, further comprising a residual gas removing step for
removing a residual gas remaining in said reaction chamber after
formation of said film on said substrate between said film forming
step and said substrate taking-out step, wherein in said residual
gas removing step, a prescribed gas is supplied to said reaction
chamber from said at least one gas feed port while being exhausted
from said reaction chamber through all said exhaust ports.
4. The method for producing a semiconductor device according to
claim 2, further comprising supplying a prescribed gas to said
reaction chamber from said at least one gas feed port while
exhausting said prescribed gas from said reaction chamber through
all said exhaust ports before said substrate introducing step and
after said substrate taking-out step.
5. The method for producing a semiconductor device according to
claim 4, further comprising a residual gas removing step for
removing a residual gas remaining in said reaction chamber after
formation of said film on said substrate between said film forming
step and said substrate taking-out step, wherein a prescribed gas
is supplied to said reaction chamber from said at least one gas
feed port while being exhausted from said reaction chamber through
all said exhaust ports in said residual gas removing step as
well.
6. The method for producing a semiconductor device according to
claim 1, wherein said at least one exhaust port comprises a
plurality of exhaust ports.
7. The method for producing a semiconductor device according to
claim 1, wherein said substrate having a film-forming surface is
disposed in said reaction chamber substantially horizontally with
said at least one gas feed port and said at least one exhaust port
being positioned in an opposed relation with respect to each other
with said substrate interposed therebetween, and wherein said
film-forming gas flows substantially in parallel with said
film-forming surface of said substrate in said film forming
step.
8. The method for producing a semiconductor device according to
claim 7, wherein said at least one exhaust port comprises a
plurality of exhaust ports.
9. The method for producing a semiconductor device according to
claim 8, wherein in said film forming step, said film-forming gas
is supplied to said reaction chamber a predetermined number of
times while changing the direction of flow of said film-forming
gas.
10. The method for producing a semiconductor device according to
claim 9, further comprising supplying, immediately before and
similar to said film forming step, a prescribed gas to said
reaction chamber from said gas feed port to pass it along said
film-forming surface of said substrate substantially in parallel
therewith and exhausting said prescribed gas from the reaction
chamber through said exhaust port.
11. The method for producing a semiconductor device according to
claim 10, further comprising making the temperature of a portion of
said reaction chamber which adjoins said gas feed port supplying
said prescribed gas different from the temperature of the remaining
portion thereof.
12. The method for producing a semiconductor device according to
claim 11, further comprising making the temperature of a portion of
said reaction chamber which adjoins said gas feed port supplying
said prescribed gas lower than the temperature of the remaining
portion thereof.
13. The method for producing a semiconductor device according to
claim 11, wherein said film-forming gas is a gas mixture containing
a plurality of kinds of gases, said gas mixture containing at least
one kind of a nonreactive gas which is by itself unable to form a
film on said substrate, said nonreactive gas being used as said
prescribed gas.
14. The method for producing a semiconductor device according to
claim 13, wherein said gas mixture contains a first gas which is in
a gaseous state at room temperature and a second gas which is in a
liquid state at room temperature, said first gas being used as said
prescribed gas.
15. The method for producing a semiconductor device according to
claim 1, wherein said prescribed gas is an inert gas which is
unable to form a film on said substrate.
16. The method for producing a semiconductor device according to
claim 1, wherein said film-forming gas contains at least
penta-ethoxy-tantalum.
17. A method for producing a semiconductor device, comprising:
introducing a substrate into a reaction chamber which has at least
one gas feed port and at least one gas exhaust port; heating said
substrate in said reaction chamber to substantially a film forming
temperature; supplying a film-forming gas to said reaction chamber
to form a film on said substrate; removing a residual gas remaining
in said reaction chamber after formation of said film on said
substrate while supplying a prescribed gas to said reaction chamber
from said at least one gas feed port while exhausting said
prescribed gas from said reaction chamber through all said exhaust
ports; and taking said substrate with said film formed thereon out
of said reaction chamber.
18. An apparatus for producing a semiconductor device, comprising:
a reaction chamber having at least one gas feed port and at least
one exhaust port; valves for opening and closing said at least one
gas feed port and said at least one exhaust port; a gas supply
system for supplying a prescribed gas to said reaction chamber from
said at least one gas feed port; and a heater for heating said
substrate in said reaction chamber to substantially a film forming
temperature; wherein at least in a substrate heating step in which
said substrate is heated to substantially the film-forming
temperature by said heater, or in a residual gas removing step in
which a residual gas remaining in said reaction chamber is removed
after a film forming step, said prescribed gas is supplied to said
reaction chamber from said at least one gas feed port while being
exhausted from said reaction chamber through all said exhaust
ports.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a film forming method and
apparatus in which a substrate is introduced into a reaction
chamber having a gas feed port and a gas exhaust port, subjected to
predetermined processing and taken out of the reaction chamber.
More specifically, it relates to such a film forming method and
apparatus in which nonuniformity or irregularities in a film formed
on the substrate can be prevented by precluding film-forming gas
components, which have been attached to the gas exhaust port and
then evaporated therefrom as a film-forming gas, from flowing back
to the reaction chamber.
[0003] Throughout the description which follows, the term "an
exhaust port" refers to an exhaust port and its vicinity in which
the exhaust port is connected with a reaction chamber or tube.
[0004] 2. Description of the Prior Art
[0005] When thin layers or films are to be formed on a substrate, a
film forming apparatus of a sheet-fed type has been used for
example. The term "sheet-fed type" herein used broadly means that
one or more sheets of substrates are simultaneously processed in a
successive manner. As a concrete example of such a film forming
apparatus, a description will be made of the formation of tantalum
oxide (Ta.sub.2O.sub.5) films on a substrate. Generally, tantalum
oxide films are formed by use of a chemical vapor deposition (CVD)
process.
[0006] FIG. 5 is a schematic view showing an example of a
conventional tantalum oxide film producing apparatus.
Penta-ethoxy-tantalum in a liquid state is used as a raw material
for tantalum oxide films. The penta-ethoxy-tantalum liquid is
received in a tank 41 which is disposed in a thermostatic chamber
42. The temperature of the tank 41 is controlled to a constant
value such as, for example, 35 degrees C. by means of the
thermostatic chamber 42. The interior of the tank 41 is pressurized
by a nitrogen (N.sub.2) gas supplied thereto through a nitrogen
feed pipe 48 to push out the penta-ethoxy-tantalum liquid into a
material feed pipe 49. The penta-ethoxy-tantalum liquid is then
supplied from the material feed pipe 49 to a carburetor 43, into
which a nitrogen carrier gas is supplied from the nitrogen feed
pipe 48. The film-forming gas evaporated by the carburetor 43 is
introduced, together with the nitrogen carrier gas, into a reaction
chamber 45 through a feed pipe 44. Simultaneous with this, an
oxygen gas is also introduced from an oxygen tank (not shown) into
the reaction chamber 45, in which the penta-ethoxy-tantalum liquid
is thermally decomposed to form a tantalum oxide film on the
substrate. After the film formation, the atmosphere or gases in the
reaction chamber 45 is exhausted by means of a discharge pump 46
through an exhaust pipe 47.
[0007] In the prior art technology described above, in order to
provide a uniform formation of a tantalum oxide film on a
substrate, certain proposals have been made for the configuration
of the reaction chamber 45, an introduction recipe of the
film-forming gas, an exhaust recipe thereof, etc.
[0008] For example, Japanese Patent Application Laid-Open No. Hei
7-94419 discloses a semiconductor processing apparatus in which a
flat reaction tube is disposed in a heating space defined by a pair
of parallel plate heaters, and a substrate to be processed is
introduced into the flat reaction tube and subjected to a film
forming processing therein. In this semiconductor processing
apparatus, the flat reaction tube is provided at its opposite ends
with gas feed ports and exhaust ports, so that during the
film-forming processing, the direction of flow of a reaction gas,
which is supplied from the gas feed ports to the reaction tube and
exhausted therefrom through the exhaust ports, can be changed
arbitrarily.
[0009] FIG. 6 illustrates a reaction chamber or tube 51 and its
related portions of the semiconductor processing apparatus as
disclosed in the above reference. In this figure, an unillustrated
substrate is horizontally disposed substantially in the center of
the interior of the reaction tube 51, and gas feed ports 52, 53 and
gas exhaust ports 54, 55 are provided at opposite ends of the
reaction tube 51, the gas feed ports 52, 53 being disposed in an
opposed relation with respect to the gas exhaust ports 54, 55,
respectively, with the substrate being interposed therebetween. For
example, a gas supplied from the gas feed port 52 passes through
the reaction tube 51 substantially in parallel with the substrate
to be exhausted from the gas exhaust port 55, as indicated by an
arrow in FIG. 6. At this time, the gas feed port 53 and the gas
exhaust port 54 are both closed by unillustrated valves,
respectively, to interrupt the passage of the gas. With this
conventional apparatus, the direction of the gas flow can be set
reversely in such a manner that a gas is supplied from the gas feed
port 53 to the reaction tube 51 and exhausted from the gas exhaust
port 54 while closing the gas feed port 52 and the gas exhaust port
55.
[0010] Now, a conventional film-forming recipe for forming a
tantalum oxide film on a substrate by use of the semiconductor
processing apparatus as disclosed in the above-mentioned Japanese
Patent Laid-Open No. Hei-94419 will be described while referring to
the accompanying drawings.
[0011] FIGS. 7(a) through 7(c) illustrate the various states of
ventilation or gas flows in the reaction tube 51 from a stand-by
state to the end of a substrate heating step. Here, note that the
substrate heating step is to heat, prior to the formation of a film
thereon, the substrate to a desired temperature by a heater (not
shown) and to make a surface (i.e., film-forming surface) of the
substrate into a uniform state. Preferably, the heater may be of an
electric resistance heater, and it is desired to employ a hot-wall
type heating system in which the temperature of the reaction
chamber is held at the desired temperature before the introduction
of the substrate into the reaction chamber. The heater may, of
course, be a lamp, a high frequency heater, an the like.
[0012] In these figures, note that the opening state and the
closing state of each gas feed port and each gas exhaust port are
indicated by a white circle (valve opening) and a black circle
(valve closing), respectively; that the presence of two of white
circles and/or black circles indicates the degree or extent of
opening or closing of these ports; and that arrows with no symbols
designate flows of gases. Also, one of the gas feed ports and the
gas exhaust ports provided at one end (e.g., at the left side of
FIGS. 7(a) through 7(c)) of the reaction tube 51 is designated by
the term "back-side", and the other of the gas feed ports and the
gas exhaust ports provided at the other end (e.g., at the right
side of FIGS. 7(a) through 7(c)) of the reaction tube 51 is
designated by the term "front-side".
[0013] FIG. 7(a) shows the flow of a gas in the apparatus of the
stand-by state. In this stand-by state, valves 61 through 64
respectively opening and closing the ports 52 through 55 (see FIG.
6) are adjusted such that a nitrogen gas flows in a direction from
the back-side feed port to the back-side exhaust port and further
from front-side feed port to the front-side exhaust port. The gas
passing the reaction tube 51 is discharged to the outside by means
of a discharge pump (DP) through the exhaust pipe 47. Here, note
that the stand-by state means a state prior to the substrate
introducing step in which a substrate is introduced into the
reaction tube 51. Also, though not illustrated, during the
substrate introducing step, all the gas feed ports are closed by
the corresponding valves 61, 62 and all the gas exhaust ports are
opened by the corresponding valves 63, 64 so that the reaction tube
51 is exhausted or vacuum drawn by the discharge pump (DP) from the
exhaust ports via the exhaust pipe 47 so as to keep the interior of
the reaction tube 51 at a desired pressure.
[0014] FIG. 7(b) shows the flow of a gas in the apparatus during
the substrate heating step. In the substrate heating step, a
nitrogen gas supplied from the back-side feed port passes the
reaction tube 51 substantially in parallel with the substrate
disposed therein to be discharged from the front-side exhaust port,
as indicated by an arrow in FIG. 7(b). At this time. the valves 61,
64 are opened, whereas the valves 62, 63 are closed.
[0015] Subsequently, as shown in FIG. 7(c), an oxygen gas is
supplied to the reaction tube 51. The flow of the oxygen gas thus
supplied is the same as that of FIG. 7(b) referred to above. After
the supply of the oxygen gas the substrate heating step is also
finished, and the control process proceeds to the following film
forming step.
[0016] FIGS. 8(a) through 8(e) illustrate the states of ventilation
or gas flows in the reaction tube during the film forming step.
[0017] In FIG. 8(a), a gas flow through the apparatus in a first
stage of the film forming step is shown. A film-forming gas
comprising oxygen and evaporated penta-ethoxy-tantalum is supplied,
together with a carrier gas in the form of a nitrogen gas, to the
heated reaction tube 51 and thermally decomposed there to form a
tantalum oxide film on the substrate (not shown). At this time, the
flow of the film-forming gas is the same as that of FIG. 7(b) but
with the valve 61 being fully opened.
[0018] Subsequently, as shown in FIG. 8(b), the valves 61 through
64 are all opened so that a film-forming gas flows from the
back-side feed port to the back-side exhaust port, and another
film-forming gas flows from the front-side feed port to the
front-side exhaust port. Such valve opening operations are carried
out in order to allow, in a second stage of the film forming step
following the first stage thereof, a fresh film-forming gas to flow
in a direction opposite that in the first stage.
[0019] FIG. 8(c) shows the flow of a gas through the apparatus in
the second stage of the film forming step. In this figure, a
film-forming gas together with a carrier gas in the form of a
nitrogen gas is supplied to the heated reaction tube 51 and
thermally decomposed there to form a tantalum oxide film on the
unillustrated substrate. In the second stage of the film forming
step, the film-forming gas supplied from the front-side feed port
passes the interior of the reaction tube 51 substantially in
parallel with the substrate therein to be exhausted from the
back-side exhaust port, as indicated by arrows in FIG. 8(c), At
this time, the valves 62, 63 are opened (in particular, valve 62 is
fully opened), whereas the valves 61, 64 are closed.
[0020] After the film formation has finished, as shown in FIG.
8(d), the valves 61, 62 are closed and the valves 63, 64 are opened
so that a residual gas in the reaction tube 51 is discharged by
means of the discharge pump (DP) from the back-side exhaust port
and the front-side exhaust port to the outside of the reaction tube
51 through the exhaust pipe 47.
[0021] Finally, as shown in FIG. 8(e), a nitrogen gas is supplied
to the reaction tube 51, as in the stand-by state of FIG. 7(a), and
the entire processings are over. Though not shown, during a
substrate taking-out step in which the substrate having the films
thus formed is taken out of the reaction tube 51, all the valves
61, 62 for the gas feed ports are closed and the interior of the
reaction tube 51 is discharged or vacuum drawn from the exhaust
ports by means of the discharge pump (DP) so as to be at a desired
pressure.
[0022] With the above-mentioned conventional film forming method,
however, a problem arises in that when a tantalum oxide film is to
be formed on a substrate for example, it is difficult to provide
such a tantalum oxide film uniformly on the substrate. For example,
in an attempt to form a tantalum oxide film on a substrate
according to the aforesaid film-forming recipe by using the
semiconductor processing apparatus as disclosed in the
above-mentioned Japanese Patent Application Laid-Open No. Hei
7-94419, residual components of a film-forming gas which has
adhered to the back-side exhaust port are liable to diffuse and
flow back into the reaction chamber as a film-forming gas during
the substrate heating step, thus resulting in the formation of a
thick tantalum oxide film on a portion of the substrate near the
back-side exhaust port.
[0023] Moreover, another problem is that upon removing the residual
gas after the film forming step, as well as during the substrate
introducing step and during the substrate taking-out step, the
residual components of the film-forming gas attached to the gas
exhaust ports are apt to diffuse and flow back into the reaction
chamber as a film-forming gas, thus depositing on the substrate and
deteriorating the uniformity in the film thickness. This is because
even if the reaction chamber is discharged or exhausted through
vacuum drawing with no gas being supplied thereto, it is difficult
to prevent a reverse diffusion into the reaction chamber of the
film-forming gas components remaining in the gas exhaust ports to
any satisfactory manner.
SUMMARY OF THE INVENTION
[0024] Accordingly, the object of the present invention is to
provide a novel and improved film forming method and apparatus
which are capable of uniformly forming a film over a surface of a
substrate.
[0025] Bearing the above object in mind, according to one aspect of
the present invention, there is provided a method for producing a
semiconductor device, which comprises the steps of: introducing a
substrate into a reaction chamber which has at least one gas feed
port and at least one gas exhaust port; heating the substrate in
the reaction chamber to substantially a film forming temperature
while supplying a prescribed gas to the reaction chamber through
the at least one gas feed port and exhausting the prescribed gas
from the reaction chamber through all the exhaust ports; supplying
a film-forming gas to the reaction chamber to form a film on the
substrate; and taking the substrate with the film formed thereon
out of the reaction chamber.
[0026] With the above method, it is possible to prevent components
of the film-forming gas remaining in the exhaust ports from flowing
back into the reaction chamber as a film-forming gas, thereby
obviating the above-mentioned conventional problem that a thick
film of tantalum oxide is formed on a portion of the substrate near
the exhaust ports. Thus, the film formed on the substrate becomes
uniform.
[0027] In a preferred form of the invention, in the substrate
introducing step and the substrate taking-out step, a prescribed
gas is supplied from the at least one gas feed port to the reaction
chamber while being exhausted from the reaction chamber through all
the exhaust ports.
[0028] With this arrangement, in the substrate introducing step and
the substrate taking-out, i.e., from the time when the substrate is
introduced into the reaction chamber until it is taken out
therefrom, except for the film forming step, it is possible to
prevent the film-forming gas remaining in the exhaust ports from
diffusing and flowing back into the reaction chamber as a
film-forming gas, thus ensuring a more uniform formation of the
film on the substrate.
[0029] In another preferred form of the invention, the method
further comprises a residual gas removing step for removing a
residual gas remaining in the reaction chamber after formation of
the film on the substrate between the film forming step and the
substrate taking-out step. In the residual gas removing step, a
prescribed gas is supplied to the reaction chamber from the at
least one gas feed port while being exhausted from the reaction
chamber through all the exhaust ports.
[0030] With this arrangement, in the case where the residual gas
removing step is provided, after the film-forming step, for
removing the residual gas in the reaction chamber, a reverse
diffusion into the reaction chamber of the film-forming gas
components remaining in the exhaust ports can effectively be
precluded in the residual gas removing step as well, resulting in a
uniform film formation on the substrate.
[0031] In a further preferred form of the invention, the method
further comprises supplying a prescribed gas to the reaction
chamber from the at least one gas feed port while exhausting the
prescribed gas from the reaction chamber through all the exhaust
ports before the substrate introducing step and after the substrate
taking-out step.
[0032] With this arrangement, before the substrate introducing step
and after the substrate taking-out step in which there is no
substrate in the reaction chamber, the film-forming gas components
remaining in the exhaust ports can be prevented from diffusing back
into the reaction chamber. That is, except for the film forming
step, such a condition is maintained, thereby making the film
formed on the substrate more and more uniform.
[0033] In a still further preferred form of the invention, the at
least one exhaust port comprises a plurality of exhaust ports.
[0034] Even in such a case, the film-forming gas components
remaining in the exhaust ports are prevented from diffusing and
flowing back into the reaction chamber as a film-forming gas,
making the film formed on the substrate uniform.
[0035] In a further preferred form of the invention, the substrate
having a film-forming surface is disposed in the reaction chamber
substantially horizontally with the at least one gas feed port and
the at least one exhaust port being positioned in an opposed
relation with respect to each other with the substrate interposed
therebetween, whereby the film-forming gas flows substantially in
parallel with the film-forming surface of the substrate in the film
forming step.
[0036] In the aforementioned film-forming apparatus of the
sheet-fed type, the substrate is greatly influenced by a reverse
diffusion into the reaction chamber of the film-forming gas
components remaining in the exhaust ports. With the above
arrangement, however, it is possible to preclude the film-forming
gas components remaining in the exhaust ports from flowing into the
reaction chamber, thereby making the film formed on the substrate
uniform.
[0037] In a further preferred form of the invention, in the film
forming step, the film-forming gas is supplied to the reaction
chamber a predetermined number of times while changing the
direction of flow of the film-forming gas.
[0038] With this arrangement, a uniform formation of the film on
the substrate can readily be attained irrespective of the direction
of flow of the film-forming gas.
[0039] In a further preferred form of the invention, immediately
before and similar to the film forming step, a prescribed gas is
supplied to the reaction chamber from the gas feed port to pass it
along the film-forming surface of the substrate substantially in
parallel therewith, while being exhausted from the reaction chamber
through the exhaust port.
[0040] With this arrangement, turbulence of the film-forming gas at
the beginning of film formation can effectively be prevented,
enabling the more and more uniform formation of the film on the
substrate.
[0041] In a further preferred form of the invention, the
temperature of a portion of the reaction chamber which adjoins the
gas feed port supplying the prescribed gas is made different from
the temperature of the remaining portion thereof.
[0042] In forming a film on a substrate using the aforementioned
prior art film forming method, there is a tendency that a portion
of the substrate near an exhaust port which is not exhausted
immediately before a film forming step for example, i.e., a
substrate surface adjacent a gas feed port supplying a prescribed
gas, becomes thick. With the above arrangement, however, the
temperature of the substrate surface near the gas feed port can be
made slightly lower than that of the remaining portion thereof for
example, so the film-forming speed at that portion of the substrate
surface near the gas feed port can be controlled appropriately,
making it possible to adjust the film thickness during the film
forming step and hence to form a much more uniform film on the
substrate.
[0043] In a further preferred form of the invention, the
temperature of a portion of the reaction chamber which adjoins the
gas feed port supplying the prescribed gas is made lower than the
temperature of the remaining portion thereof.
[0044] In the formation of a film on a substrate according to the
aforementioned prior art film forming method, there is also a
tendency that a portion of the substrate near an exhaust port which
is not exhausted immediately before a film forming step for
example, i.e., a substrate surface adjacent a gas feed port
supplying a prescribed gas, becomes thick. With the above
arrangement, however, the temperature of the substrate surface near
the gas feed port can be made slightly lower than that of the
remaining portion thereof for example, so the film-forming speed
can be made a little slower at that portion of the substrate
surface near the gas feed port than at the remaining portion
thereof, allowing adjustment of the film thickness in the film
forming step and hence enabling a much more uniform film formation
on the substrate.
[0045] In a further preferred form of the invention, the
film-forming gas is a gas mixture containing a plurality of kinds
of gases, the gas mixture containing at least one kind of a
nonreactive gas which is by itself unable to form a film on the
substrate, the nonreactive gas being used as the prescribed
gas.
[0046] The use of the prescribed gas in the form of a nonreactive
gas, which is by itself unable to form a film on the substrate,
does not at all have any adverse effects on the substrate.
Moreover, the nonreactive gas does not adhere to the exhaust ports,
so a reverse flow into the reaction chamber of the film-forming gas
adhered to the exhaust ports due to the diffusion thereof can be
precluded, thus making the film formation on the substrate
uniform.
[0047] In a further preferred form of the invention, the gas
mixture contains a first gas which is in a gaseous state at room
temperature and a second gas which is in a liquid state at room
temperature, the first gas being used as the prescribed gas.
[0048] Using the prescribed gas in the form of a gas that is in a
gaseous state at room temperature does not have any adverse effects
on the substrate. In addition, such a gas does not adhere to the
exhaust ports, so a reverse flow into the reaction chamber of the
film-forming gas adhered to the exhaust ports due to the diffusion
thereof can be precluded, thus ensuring the formation of the
uniform film on the substrate.
[0049] In a further preferred form of the invention, the prescribed
gas is an inert gas which is unable to form a film on the
substrate.
[0050] Using the prescribed gas in the form of an inert gas does
not have any adverse effects on the substrate, and the inert gas
does not adhere to the exhaust ports, and does not cause
undesirable reactions with film-forming gas components.
Consequently, a reverse flow into the reaction chamber of the
film-forming gas adhered to the exhaust ports can be precluded,
thus making the film formed on the substrate uniform.
[0051] In a further preferred form of the invention, the
film-forming gas contains at least penta-ethoxy-tantalum, which
provides marked effects.
[0052] That is, in the case where the film-forming gas contains
penta-ethoxy-tantalum, a tantalum residual component of the
penta-ethoxy-tantalum gas is liable to collect in the interior of
the exhaust ports. In this case, however, it is possible to prevent
a reverse diffusion into the reaction chamber of the residual
component, thereby ensuring a uniform formation of a tantalum oxide
film on the substrate.
[0053] According to another aspect of the present invention, there
is provided a method for producing a semiconductor device, the
method comprising: introducing a substrate into a reaction chamber
which has at least one gas feed port and at least one gas exhaust
port; heating the substrate in the reaction chamber to
substantially a film forming temperature; supplying a film-forming
gas to the reaction chamber to form a film on the substrate;
removing a residual gas remaining in the reaction chamber after
formation of the film on the substrate while supplying a prescribed
gas to the reaction chamber from the at least one gas feed port by
exhausting the prescribed gas from the reaction chamber through all
the exhaust ports; and taking the substrate with the film formed
thereon out of the reaction chamber.
[0054] With this method, it is possible to prevent the film-forming
gas components adhered to the exhaust ports from diffusing and
flowing back into the reaction chamber, thus making the film formed
on the substrate uniform.
[0055] According to a further aspect of the present invention,
there is provided an apparatus for producing a semiconductor
device, the apparatus comprising: a reaction chamber having at
least one gas feed port and at least one exhaust port; valves for
opening and closing the at least one gas feed port and the at least
one exhaust port; a gas supply system for supplying a prescribed
gas to the reaction chamber from the at least one gas feed port;
and a heater for heating the substrate in the reaction chamber to
substantially a film forming temperature. At least in a substrate
heating step in which said substrate is heated to substantially the
film-forming temperature by said heater, or in a residual gas
removing step in which a residual gas remaining in said reaction
chamber is removed after a film forming step, the prescribed gas is
supplied to the reaction chamber from the at least one gas feed
port while being exhausted from the reaction chamber through all
the exhaust ports.
[0056] With this arrangement, it is possible to prevent the
film-forming gas components remaining in the exhaust ports from
flowing back into the reaction chamber as a film-forming gas, thus
making the film formed on the substrate uniform.
[0057] Here, note that Japanese patent No. 2809817 discloses a
means for preventing by-products from collecting in a gas feed
pipe, and Japanese Patent Application Laid-Open Nos. Hei 7-14773
and Hei 8-31743 disclose a means for preventing contaminating
substances such as particles and the like from flowing back into a
reaction chamber. These prior art references, however, do not teach
or suggest at all preventing a film-forming gas remaining in a gas
exhaust port from flowing back into a reaction chamber.
[0058] The above and other objects, features and advantages of the
invention will become more readily apparent from the following
detailed description of the invention when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIGS. 1(a) through 1(c) are views illustrating ventilation
states of a gas during a substrate heating step and immediately
before forming a film according to the present invention.
[0060] FIGS. 2(a) and 2(b) are views illustrating trends of
residual gas components of a film-forming gas remaining in the gas
exhaust ports according to the present invention and a prior art
method, respectively.
[0061] FIG. 3 is a view illustrating uniformity in the film
thickness in the case where tantalum oxide films are formed on two
substrates which are stacked in a vertical direction and held in
position in a reaction tube, according the present invention.
[0062] FIG. 4 is a view illustrating uniformity in the film
thickness in the case where a tantalum oxide film is formed on each
of two substrates which are stacked in a vertical direction and
held in position in a reaction tube according to the prior art
method.
[0063] FIG. 5 is a schematic view illustrating one example of a
prior art apparatus for producing a tantalum oxide film.
[0064] FIG. 6 is a view illustrating a reaction tube of a
semiconductor processing apparatus described in Japanese Patent
Application Laid-Open No. Hei 7-94419.
[0065] FIGS. 7(a) through 7(c) are views illustrating ventilation
(flowing) states of a gas in the reaction tube from a standby state
up to the end of a substrate heating step according to the prior
art.
[0066] FIGS. 8(a) through 8(e) are views illustrating ventilation
(flowing) states of a gas in the reaction tube during a film
forming step and the like according to the present invention and
the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] Now, preferred embodiments of the present invention will be
described in detail while referring to the accompanying
drawings.
[0068] A method for producing a semiconductor device according to
the present invention includes, similar to the aforementioned
conventional technology, introducing a substrate into a reaction
chamber, heating the substrate in the reaction chamber to
substantially a film forming temperature, supplying a film-forming
gas to the reaction chamber to form a film or films on a surface of
the substrate, and taking out the substrate with the film(s) formed
thereon from the reaction chamber.
[0069] Here, note that the reaction chamber may be equipped with at
least one gas feed port and at least one gas exhaust port with any
conditions other than this being not particularly limited.
Specifically, the present invention can be implemented by using a
variety of conventional film forming apparatuses as referred to
above, which includes a reaction chamber or tube capable of
receiving a substrate and provided with at least one gas feed port
and at least one gas exhaust port, valves for opening and closing
the at least one gas feed port and the at least one gas exhaust
port, a valve for supplying a prescribed gas to the reaction
chamber from the at least one gas feed port, and a heater for
heating the substrate in the reaction chamber to substantially a
film forming temperature. Concretely, some examples of such
apparatus equipment usable in implementing the present invention
are ones as shown in FIG. 5 and FIG. 6, respectively. In this case,
as illustrated in FIG. 6, a plurality of gas feed ports and exhaust
ports may be provided.
[0070] The present invention is featured in that at least during a
substrate heating step, a prescribed gas is supplied to the
reaction chamber from the at least one gas feed port while the
prescribed gas is being exhausted from the reaction chamber through
the one gas exhaust port or all the gas exhaust ports (if there are
a plurality of gas exhaust ports). The prescribed gas referred to
herein can be arbitrarily selected depending upon the type of a
film(s) formed on a substrate, and hence is not limited at all. For
example, the prescribed gas can be an inert gas which by itself is
unable to form any film on a substrate.
[0071] Separate from this, the present invention is further
featured in that a residual gas removing step is provided between
the film forming step and the substrate taking-out step, for
removing a residual gas which exists in the reaction chamber after
the film forming step. During the residual gas removing step, a
prescribed gas is exhausted from the reaction chamber through all
the exhaust ports while the prescribed gas is being supplied to the
reaction chamber from the at least one gas feed port.
[0072] As described above, although in the present invention, a
prescribed gas may be supplied to the reaction chamber from the at
least one gas feed port while the prescribed gas may be being
exhausted from the reaction chamber through all the exhaust ports
at least during the substrate heating step or during the residual
gas removing step, it is preferred that supplying a prescribed gas
to the reaction chamber while exhausting it therefrom in the above
manner before and during the substrate introducing step as well as
during and after the substrate taking-out step be carried out,
resulting in the formation of a much more uniform film.
[0073] The substrate heating step according to the present
invention is to heat a substrate to a desired temperature by means
of an appropriate heater so as to make a surface thereof uniform
prior to forming a film thereon. Preferably, the heater may be an
electric resistance heater, and a heating system of a hot wall type
is desirable which can hold the temperature of the reaction chamber
to a desired level prior to introducing the substrate. Of course,
the heater may be a lamp, a high frequency heater or oscillator,
etc.
[0074] The film forming step of the present invention may be
carried out by use of any film forming means or apparatus which can
form a desired film or films on the substrate. In the present
invention, however, particularly remarkable effects or advantages
will be attained when the film forming step is carried out by using
a film forming apparatus of a sheet-fed type in which a substrate
is disposed substantially horizontally in the reaction chamber with
the at least one gas feed port and the at least one exhaust port
being positioned in an opposed relation with respect to each other
with a film-forming surface of the substrate interposed
therebetween, so that a film-forming gas can flow along the
film-forming surface of the substrate substantially in a parallel
relation. That is, the substrate tends to be greatly influenced by
a reverse diffusion into the reaction chamber of the film-forming
gas remaining in the gas exhaust ports, but according to the
present invention, the film-forming gas remaining in the gas
exhaust ports is prevented from flowing back into the reaction
chamber, thereby enabling a uniform formation of a film on the
substrate. Moreover, in the case of performing the film forming
step by using such a film forming apparatus of the sheet-fed type,
it is preferable to supply the film-forming gas at a predetermined
number of times while alternately changing the direction of flow of
the film-forming gas. It is further preferable that a prescribed
gas be supplied, immediately before the film forming step, to the
reaction chamber from the at least one gas feed port and then
discharged from the exhaust port as in the film forming step. In
this regard, it is still preferable to set the temperature of a
portion of the reaction chamber which is adjacent the gas feed port
supplying the prescribed gas to a predetermined value different
from the temperature of the remaining portion thereof. For example,
preferably, the temperature of the portions of the reaction chamber
adjacent or near the gas feed port supplying the prescribed gas is
set to a predetermined value slightly lower than the temperature of
the remaining portion thereof. The portion of the substrate
adjacent or near the gas feed port supplying the prescribed gas is
liable to be influenced by a reverse diffusion of the film-forming
gas from the exhaust ports, so a film formed on the substrate tends
to become thicker at locations adjacent the gas feed port supplying
the prescribed gas than at the other locations. As a consequence,
by setting the temperature of the substrate surface near the gas
feed port supplying the prescribed gas to a value slightly lower
than that of the remaining portion thereof, the speed of film
formation becomes slightly less at a portion of the substrate near
the gas feed port supplying the prescribed gas than at the
remaining portion thereof, thus achieving the formation of a more
uniform film over the surface of the substrate.
[0075] Here, it is to be noted that the film-forming gas may be a
gas mixture containing a plurality of kinds of gases. Specifically,
such a gas mixture may contain at least one kind of nonreactive gas
which is by itself unable to perform a film formation with the
substrate. Further, the gas mixture may contain a gas which is in a
gaseous state at room temperature, and a gas which is in a liquid
state at room temperature. The prescribed gas may be the
nonreactive gas or the gas which is in a liquid state at room
temperature. Also, the prescribed gas may be an inert gas, which is
preferred from a view point that there will be any undesired
reactions with film-forming gas components.
[0076] Now, the present invention will be described in detail in a
case wherein tantalum oxide films are formed on a substrate. Here,
it is needless to say that a method for producing a semiconductor
device and a semiconductor producing apparatus according to the
present invention are not limited to the following method and
apparatus for forming a tantalum oxide film as described
herein.
[0077] As previously described with reference to FIG. 5, a liquid
of penta-ethoxy-tantalum (Ta(OC.sub.2H.sub.5).sub.5), which is in a
liquid state at room temperature, is received in a tank 41 which is
disposed in a thermostatic chamber 42. The temperature of the tank
41 is controlled to be at a predetermined temperature such as, for
example, 35 degrees C. by means of the thermostatic chamber 42. A
nitrogen gas supplied from a nitrogen feed pipe 48 to the tank 41
pressurizes the interior of the tank 41, whereby the
penta-ethoxy-tantalum liquid is pushed out of the tank 41 into the
material feed pipe 49. The penta-ethoxy-tantalum in the liquid
state is supplied from the material feed pipe 49 to a carburetor
43, and a nitrogen carrier gas is also supplied from a nitrogen
feed pipe 48 to the carburetor 43. A film-forming gas evaporated
from the penta-ethoxy-tantalum liquid by the carburetor 43 is
introduced, together with the nitrogen carrier gas, into a reaction
chamber 45 through a feed pipe 44. Simultaneous with this, an
oxygen gas is also introduced from an oxygen tank (not shown) into
the reaction chamber 45 wherein the penta-ethoxy-tantalum is
thermally decomposed to form a tantalum oxide film on the
substrate. After the formation of the film, the atmosphere in the
reaction chamber 45 is discharged through an exhaust pipe 47 by
means of a discharge pump 46.
[0078] According to the present invention, as long as the reaction
chamber 45 is provided with at least one gas feed port and at least
one exhaust port, the configuration of the reaction chamber 45 may
be optional and hence can be the same as in the prior art. For
example, the reaction chamber 45 can be similar to the reaction
tube as referred to in the aforesaid Japanese Patent Application
Laid-Open No. 7-94419 and shown in FIG. 6. Thus, the reaction
chamber 45 may be constructed such that a substrate (not shown) is
horizontally disposed substantially in the center of the reaction
chamber with gas feed ports and gas exhaust ports being provided at
opposite ends of the reaction chamber in an opposed relation with
respect to each other with the substrate interposed therebetween,
as in the gas feed ports 52, 53 and the gas exhaust ports 54, 55 of
the reaction tube 51.
[0079] The present invention is further featured in that at least
in a substrate heating step, a prescribed gas is supplied to the
reaction chamber from at least one gas feed port and discharged to
the outside from all the exhaust ports.
[0080] FIGS. 1(a) through 1(c) illustrate the flowing states of the
prescribed gas during the substrate heating step and immediately
before the formation of a film, according to the present invention.
In these figures, the reaction chamber takes the form of a reaction
tube 51 having at its opposite ends a back-side feed port with a
valve 61 and a front-side feed port with a valve 62 as well as a
back-side exhaust port with a valve 63 and a front-side exhaust
port with a valve 64.
[0081] FIG. 1(a) shows the flow of the prescribed gas in a standby
state of the apparatus. In the standby state of FIG. 1(a), valves
61 through 64 are adjusted in such a manner that a nitrogen gas
flows in a direction from the back-side feed port to the back-side
exhaust port, and from the front-side feed port to the front-side
exhaust port. The gas is supplied from the back-side and front-side
feed ports to the reaction tube 51, passes there and is discharged
to the outside by means of a discharge pump (DP) through an exhaust
pipe 47, as indicated by arrows in FIG. 1(a). Here, note that the
standby state of the apparatus may be during or before the
substrate introducing step in which the substrate is introduced
into the reaction tube 51, or it may be a state in which the
substrate is disposed in the reaction tube 51 prior to the
substrate heating step. Moreover, the prescribed gas in the standby
state is a nitrogen gas, which is an inert gas unable to form by
itself a film on the substrate.
[0082] FIG. 1(b) shows a gas flow in the apparatus during the
substrate heating step. In the substrate heating step of the
reaction tube 51, an oxygen gas supplied from the back-side feed
port to the reaction tube 51 proceeds to the back-side exhaust port
directly opposing the back-side feed port, and discharged therefrom
to the outside, as shown by arrows in FIG. 1(b). Similarly, an
oxygen gas supplied from the front-side feed port to the reaction
tube 51 proceeds to the front-side exhaust port directly opposing
the front-side feed port, and discharged therefrom to the outside.
At this time, the valves 61 through 64 are all opened. The
prescribed gas in the substrate heating step is the oxygen gas. The
oxygen gas is supplied, together with an evaporated
penta-ethoxy-tantalum gas, to the reaction chamber, but it is
unable to form by itself a film on the substrate, and thus called
"a nonreactive gas" in this specification.
[0083] FIG. 1(c) shows the flow of gas immediately before the
formation of a film during the substrate heating step. The oxygen
gas supplied from the back-side feed port to the reaction tube 51
passes through the interior of the reaction tube 51 substantially
in parallel with the substrate, and discharged therefrom to the
outside through the front-side exhaust port, as indicated at arrows
in FIG. 1(c). At this time, the valves 61, 64 are opened (in
particular, valve 61 is fully opened), whereas the valves 62, 63
are closed. After the supply of the oxygen gas, the substrate
heating step is completed, and the process proceeds to the
following film forming step. In this regard, it is desired that the
period of time, in which the gas is forced to flow along the
substrate substantially in parallel therewith immediately before
the film formation as described above, is as short as possible.
Even in such a short time, however, there is a possibility that
film-forming gas components remaining in the back-side exhaust port
flow back therefrom and diffuse into the reaction tube 51 from the
back-side exhaust port which is not exhausted at that time. In this
case, the film formed on the substrate has a tendency that the
thickness of the film becomes greater at a portion of the substrate
near the back-side exhaust port which is not exhausted immediately
before the film forming step, i.e., at a substrate surface near the
back-side feed port from which the prescribed gas is supplied, than
at the other portion thereof. In order to improve this, the
temperature of the reaction tube 51 in the vicinity of the
back-side feed port is adjusted relative to the temperature of the
other portion thereof. For example, the temperature of a portion of
the reaction chamber near the back-side feed port is set to a value
slightly less than the temperature of the other portion thereof. As
a result, the surface temperature of the substrate near the
back-side feed port becomes slightly lower than that of the other
portion thereof, and hence the speed of film formation at that
portion reduces slightly with respect to the other portion thereof,
so that an increase in the film thickness near the back-side feed
port in the film forming step can be properly adjusted.
[0084] The film forming step of the present invention can be
carried out in the same manner as in the prior art. Specifically,
as illustrated in FIG. 8(a), in a first stage of the film forming
step, a film-forming gas comprising an oxygen gas and an evaporated
penta-ethoxy-tantalum gas is supplied to the reaction tube 51
together with a carrier gas such as a nitrogen gas. According to
this embodiment, the film-forming gas may be a gas mixture
containing a plurality of kinds of gases, and the oxygen gas
corresponds to a nonreactive gas. In this connection, note that
oxygen is in a gaseous state at room temperature but
penta-ethoxy-tantalum is in a liquid state at room temperature.
Then, the film-forming gas is heated and thermally decomposed in
the reaction tube 51 to form a tantalum oxide film on the
substrate. At this time, as indicated at arrows in FIG. 8(a), the
film-forming gas is supplied from the back-side feed port to the
reaction tube 51 to pass along the substrate substantially in
parallel therewith, and discharged therefrom through the front-side
exhaust port. During this process, the valves 61, 64 are opened
(valve 61 is fully opened), whereas the valves 62, 63 are
closed.
[0085] Subsequently, as illustrated in FIG. 8(b), the apparatus is
set such that the valves 61 through 64 are all opened, whereby the
film-forming gas flows from the back-side feed port to the
back-side exhaust port and at the same time from the front-side
feed port to the front-side exhaust port. Such an operation is
carried out in view of the fact that in the following second stage
of the film forming step, the film-forming gas is forced to flow in
a direction reverse to the flowing direction thereof in the first
stage of the film forming step.
[0086] Thereafter, as illustrated in FIG. 8(c), the film-forming
gas together with a carrier gas such as a nitrogen gas is supplied
to the reaction tube 51 and thermally decomposed there to form a
new or further tantalum oxide film on the substrate. In the second
stage of the film forming step, as indicated at arrows in FIG.
8(c), the film-forming gas supplied from the front-side feed port
passes the interior of the reaction tube 51 substantially in
parallel with the substrate and discharged from the back-side
exhaust port. At this time, the valves 62, 63 are opened (valve 62
is fully opened), whereas the valves 61, 64 are closed.
[0087] After the film forming step has been finished, a residual
gas removing step is performed, as shown in FIG. 8(e).
Specifically, similar to the standby state of FIG. 1(a), a nitrogen
gas is fed to the reaction tube 51 while at the same time the
interior of the reaction tube 51 is exhausted from all the exhaust
ports, whereby a residual gas in the reaction tube 51 can be
removed, and thus the entire process is finished.
[0088] Here, it is preferable that during and after the substrate
taking-out step in which the substrate processed in the above
manner is taken out of the reaction tube 51, a prescribed gas is
supplied to the reaction tube 51 from at least one gas feed port
while the reaction tube 51 is exhausted from all the gas exhaust
ports.
[0089] As described above, according to the tantalum oxide film
forming method of the present invention, during the substrate
heating step, the residual gas removing step or the like, a gas is
ventilated or passed from the gas feed ports to the gas exhaust
ports which are disposed in opposition to the gas feed ports, e.g.,
from the back-side feed port to the back-side exhaust port and from
the front-side feed port to the front-side exhaust port. With this
arrangement, the film-forming gas components remaining in the gas
exhaust ports can be prevented from diffusing back into the
reaction chamber, thus enabling a uniform formation of thin films
on the substrate.
[0090] FIGS. 2(a) and 2(b) illustrate trends of the components of
the film-forming gas remaining in the gas exhaust ports in the
present invention and the prior art, respectively. In general, the
film-forming gas remains as residual gas components in the exhaust
ports 54, 55 in the vicinity of the reaction tube 51. It is
considered that this phenomenon takes place due to the, fact that
the temperature of the gas exhaust ports 54, 55 is lower than that
of the reaction tube 51.
[0091] FIG. 2(a) shows an embodiment of a method for forming a
tantalum oxide film according to the present invention, in which
during the substrate heating step, ventilation is carried out, for
example, from the back-side feed port to the back-side exhaust port
and the front-side feed port to the front-side exhaust port,
whereby a reverse diffusion into the reaction tube 51 of residual
gas components 80 can be positively prevented. In this connection,
it goes without saying that the reaction tube 51 may be exhausted
through all the exhaust ports while being supplied with the
prescribed gas from either one of the gas feed ports, thus
providing the same effects.
[0092] In contrast to this, according to the prior art shown in
FIG. 2(b), during the substrate heating step, ventilation is
performed from a back-side feed port to a front-side exhaust port,
and hence residual gas components 80 in the back-side exhaust port
will diffuse back in a direction indicated at arrows 81 to invade
into the reaction tube 51, with the result that a tantalum oxide
film is formed on the substrate thicker in a portion thereof near
the back-side feed port than the remaining portion thereof.
Incidentally, Japanese Patent Application Laid-Open No. 7-94419
referred to above does not make any mention of a gas flow in the
substrate heating step prior to the film forming step,
[0093] Moreover, in this prior art, after the end of the film
forming step, a residual gas in the reaction tube 51 is removed in
a way as shown in FIG. 8(d), so the residual gas components in the
exhaust ports will diffuse back into the reaction tube 51 during
the residual gas removing step as well, thereby deteriorating the
uniformity in the film thickness. In addition, in the substrate
introducing step and the substrate taking-out step, the reaction
tube 51 is exhausted by means of a discharge pump so as to be at a
desired pressure with all the gas feed ports closed, as a
consequence of which a similar reverse diffusion of the residual
gas components will take place from the exhaust ports to the
reaction tube 51, resulting in a nonuniform thickness in the films
formed.
[0094] The present invention can be particularly effectively
applied to the formation of tantalum oxide films. This is because
tantalum residual components of the penta-ethoxy-tantalum gas or
vapor contained in the film-forming gas are liable to collect in
the interiors of the exhaust ports 54, 55. Also, it is of course
possible to use the method of the present invention in cases where
another kind of film-forming gas is employed. Further, the
introduction pressure, introduction temperature, introduction time,
introduction amount or flow rate, exhausting pressure, exhausting
time and the like of the film-forming gas or the prescribed gas,
selection of the prescribed gas and the carrier gas, the
temperature employed in the substrate heating step, the extent or
degree of opening or closing of the valves, etc., may be
arbitrarily selected or made while taking account of the kind of a
film to be formed, the scale or size of the film forming apparatus
employed, and so on.
[0095] FIG. 3 illustrates the uniformity in the thickness of thin
films in the case where the present invention is applied to forming
an tantalum oxide film on each of two substrates which are stacked
one over the other in a vertical direction and held in position in
the reaction tube.
[0096] As shown in FIG. 3, the center of an upper one of the
substrates was selected as a reference point of measurement (0 mm),
at which the thickness (angstrom) of thin films on the upper
substrate was measured. Further, additional measurements were
effected at points (indicated at "-50 mm" and "-95 mm" in FIG. 3)
of the upper substrate respectively away from the reference point
(0 mm) distances of 50 mm and 95 mm in a front-side direction, and
at points (indicated at "50 mm" and "95 mm" in FIG. 3) of the upper
substrate respectively away from the reference point (0 mm)
distances of 50 mm and 95 mm in a back-side direction. The results
of these measurement are indicated at a solid line 91 in FIG. 3.
Similar measurements were also made with respect to a lower
substrate, and the results of these measurements are indicated at a
solid line 92 in FIG. 3. Moreover, similar measurements were
effected with respect to a direction (i.e., a left-side to
right-side direction) perpendicular to the front-side to back-side
direction, and the results thereof are indicated at a broken line
93 for the upper substrate and at a broken line 94 for the lower
substrate with a left-side direction and a right-side direction
from the reference point (0 mm) designated by "Left" and "Right",
respectively, in FIG. 3. From the illustration of FIG. 3, it has
been found that by applying the present invention, there could be
formed substantially uniform thin layers or films on the substrate.
Uniformity of the films thus formed were in a range of from 3.9 to
4.8%.
[0097] In contrast, the above-mentioned prior art method did not
give any good results as in the present invention shown in FIG. 3.
In fact, FIG. 4 illustrates uniformity in the thickness of tantalum
oxide films formed on a substrate by means of the prior art method
(i.e., ventilation was effected from the back-side feed port to the
front-side exhaust port during the substrate heating step). The
film-forming conditions and the film-thickness measuring conditions
of FIG. 4 were the same as those of FIG. 3.
[0098] From FIG. 4, it has been found that both of solid lines 95,
96 show great variations in the film thickness in the back-side
direction and the front-side direction, and hence uniformity in the
film thickness has deteriorated. The uniformity or variation of the
film thickness was worsened to 8.4 to 8.7%.
[0099] As apparent from the foregoing, the present invention can
provide a method for producing a semiconductor device and a
semiconductor producing apparatus for implementing this method,
which are capable of forming a uniform thin layer or film on a
substrate.
[0100] While the invention has been described in terms of preferred
embodiments, those skilled in the art will recognize that the
invention can be practiced with modification within the spirit and
scope of the appended claims.
* * * * *