U.S. patent application number 11/802358 was filed with the patent office on 2008-03-20 for semiconductor manufacturing system.
Invention is credited to Takashi Arao, Kenichi Koyanagi, Yuichiro Morozumi, Kazunori Une.
Application Number | 20080066677 11/802358 |
Document ID | / |
Family ID | 38851344 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080066677 |
Kind Code |
A1 |
Morozumi; Yuichiro ; et
al. |
March 20, 2008 |
Semiconductor manufacturing system
Abstract
Disclosed is a technique for effectively suppressing the
generation of particles resulting from peeling-off of unnecessary
films that have unavoidably adhered to the inner surface of the
reaction tube of an ALD film-forming apparatus. A precoating
process utilizing ALD is performed to deposit a metal oxide film,
e.g., an aluminum oxide film, onto the unnecessary films, in order
to prevent peeling-off of the unnecessary films. The type and/or
position of the nozzle for supplying ozone, as a precoat gas, into
the reaction tube during the precoating process is different from
that of the nozzle for supplying ozone, as a film-forming gas, into
the reaction tube during forming of a film on a semiconductor
substrate.
Inventors: |
Morozumi; Yuichiro;
(Nirasaki-shi, JP) ; Koyanagi; Kenichi; (Tokyo-to,
JP) ; Arao; Takashi; (Tokyo-to, JP) ; Une;
Kazunori; (Tokyo-to, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL
1130 CONNECTICUT AVENUE, N.W., SUITE 1130
WASHINGTON
DC
20036
US
|
Family ID: |
38851344 |
Appl. No.: |
11/802358 |
Filed: |
May 22, 2007 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/405 20130101;
C23C 16/45548 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2006 |
JP |
2006-142626 |
Claims
1. A semiconductor manufacturing system, including a reaction
vessel and at least one film-forming nozzle for supplying at least
one film-forming gas into the reaction vessel, configured to form a
film on a semiconductor substrate disposed within the reaction
vessel by supplying the film-forming gas into the reaction vessel
to repeat atomic or molecular level deposition, wherein the
semiconductor manufacturing system further includes at least one
coating nozzle for supplying at least one kind of coating gas into
the reaction vessel to coat a component exposed to an atmosphere
within the reaction vessel, and at least one of said at least one
coating nozzle is separated from said at least one film-forming
nozzle.
2. The semiconductor manufacturing system according, to claim 1,
wherein: said at least one kind of film-forming gas includes a
first film-forming gas and a second film-forming gas, and said at
least one coating gas includes a first coating gas and a second
coating gas; the first film-forming gas is the same as the first
coating gas; and a coating nozzle for supplying the first coating
gas is separated from a film-forming nozzle for supplying the first
film-forming gas.
3. The semiconductor manufacturing system according to claim 2,
wherein: the second film-forming gas is a metal-containing gas; the
second coating gas is a metal-containing gas; and both the first
film-forming gas and the first coating gas are ozone.
4. The semiconductor manufacturing system according to claim 2,
wherein: the semiconductor manufacturing system is a batch-type
system adapted to accommodate a plurality of semiconductor
substrates in the reaction vessel to perform a film forming process
to the semiconductor substrates collectively; the reaction vessel
has an exhaust port for evacuating an interior of the reaction
vessel; the film-forming nozzle for supplying the first
film-forming gas is a distributing nozzle having a plurality of
nozzle holes for discharging the first film-forming gas toward the
plurality of semiconductor substrates from their sides; and the
coating nozzle for supplying the first coating gas has a nozzle
hole which opens in the reaction vessel at a position farther from
the exhaust port than a region in which the plurality of
semiconductor substrates are disposed.
5. The semiconductor manufacturing system according to claim 4,
wherein: the second film-forming gas is a metal-containing gas; the
second coating gas is a metal-containing gas; and both the first
film-forming gas and the first coating gas are ozone.
6. The semiconductor manufacturing system according to claim 2,
wherein: said at least one kind of film-forming gas includes a
third film-forming gas; and the third film-forming gas is the same
as the second coating gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to semiconductor manufacturing
system and particularly to coating apparatus for forming a film of
a desired thickness by repeating atomic or molecular level
deposition. More particularly, the Invention relates to a technique
of effectively precoating the inside of the reaction vessel to
prevent the generation of particles.
BACKGROUND ART
[0002] With higher integration of semiconductor devices, the
miniaturization of their device pattern progresses. For example,
1-gigabit dynamic random access memory (DRAM) has been used in
practical applications. Such large capacity DRAM employs elements
reduced in dimension and hence in surface area. Since DRAM uses the
amount of charge stored on its memory cell capacitors as stored
information, these capacitors must have a capacitance greater than
a certain value. Therefore, memory cell capacitors currently have a
very high aspect ratio. Conventionally, CVD (Chemical Vapor
Deposition) is used to form capacitive dielectric films for
capacitors. However, it is difficult by CVD to uniformly form a
dielectric film in a high aspect ratio groove with a high coverage.
In order to retain its stored data, a memory cell capacitor must
have high capacitance and a low leakage current, which requires the
formation of the thinnest possible uniform film.
[0003] In recent years, in order to solve this problem, ALD (Atomic
Layer Deposition) has been used, which repeatedly deposits a
thickness of a film material on the order of an atomic layer to
form a film having a desired thickness.
[0004] A process, which repeatedly depositing a thickness of a film
material on the order of a molecular layer to form a film having a
desired thickness, is referred to as MLD (molecular layer
deposition) to be distinguished from ALD in some cases. However, in
this specification, the both techniques are commonly referred to as
ALD, since they are based on the same principle. In a case where a
hafnium oxide (hereinafter referred to as an "HfO") film is formed
on a semiconductor substrate by ALD, a gas supply cycle consisting
of the supply of tetrakis(ethylmethylamino)hafnium (hereinafter
abbreviated as "TEMAH"), which is an organic metal material, and
the supply of ozone (O.sub.3) is repeated a plurality of times
while maintaining the semiconductor substrate at a predetermined
temperature. The reaction vessel is evacuated and purged by inert
gas after the supply of one gas and before supply of the other to
ensure that the gases react only on the semiconductor substrate. An
HfO film having a thickness on the order of an atomic layer is
formed on the semiconductor substrate during each cycle. The above
gas supply cycle is repeated a predetermined number of times
determined depending on desired thickness, so that an HfO film can
be formed with excellent film-thickness reproducibility.
[0005] ALD is advantageous in its excellent film-thickness
reproducibility, but is disadvantageous in its long film-forming
time. For example, in forming an HfO film, one cycle deposits a
film of approximately 0.1 nm. Thus, 50 cycles are required to form
a film of thickness of 5 nm. If each cycle takes 1 minute, the
total film forming time will be approximately 50 minutes.
Therefore, the use of a batch-type system is preferable to a single
substrate processing system in terms of productivity.
[0006] FIG. 5 shows the configuration of a conventional batch-type
ALD system for forming an HfO film; and FIG. 6 shows a piping
system associated with this system. Referring to FIG. 5, a vacuum
exhaust port 1103 is provided at the top of a reaction tube 1102
defining a reaction chamber 1101. The vacuum exhaust port 1103 is
connected to a vacuum pump 1105 through an evacuation pipe provided
with a pressure adjusting valve 1104. A boat 1108 having a
plurality of semiconductor substrates 1107 mounted therein is
supported on a boat loader 1106 and loaded in the reaction chamber
1101. A heater 1109 is provided around the reaction tube 1102 to
heat the semiconductor substrates.
[0007] Liquid TEMAH is supplied from a TEMAH supply source 1110
through a liquid flow rate adjuster 1111 to a vaporizer 1112, in
which the liquid TEMAH is vaporized and a TEMAH gas, as a source
gas, is then delivered into the reaction chamber 1101 through a
TEMAH nozzle 1113. Nitrogen gas (N.sub.2) is supplied from a
nitrogen supply source 1114 to the vaporizer 1112 through a flow
rate adjuster 1115 to aid vaporization of the liquid TEMAH. Oxygen
gas (O.sub.2) is supplied from an oxygen supply source (not shown)
through a flow rate adjuster (not shown) to an ozone generator (not
shown) in which the oxygen gas is converted into ozone which is an
oxidizer. The ozone is then delivered into the reaction chamber
1101 through an ozone nozzle 1113. Further, nitrogen gas used as a
purge gas is supplied from the nitrogen gas supply source 1114 to
the reaction chamber 1101 through a flow rate adjuster 1116 and a
nitrogen gas nozzle 1113. There are plural nozzles 1113 each
dedicated to a different gas, although only one nozzle 1113 is
shown in FIG. 5 for simplicity.
[0008] When HfO films are formed on the semiconductor substrates
using the system having the configuration shown in FIG. 5, there
may be a difference in thickness or quality of the films between
the semiconductor substrates mounted in the lower portion and the
upper portion of the boat 1108. The reason is that the
semiconductor substrates disposed in the upper portion of the
reaction chamber 1101 cannot receive sufficient amounts of TEMAH
gas and ozone, since the TEMAH gas and the ozone delivered from
L-shaped nozzles 1113, which are provided in the lowest portion of
the reaction chamber 1101, are mostly consumed by the reaction
occurring in the lower portion of the reaction chamber 1101. Unlike
CVD, in ALD, the supply of excessive amount of source gas does not
result in formation of an unnecessarily large film thickness.
Therefore, excessive TEMAH gas may be supplied into the reaction
chamber 1101 to cause a sufficient amount of TEMAH gas to reach the
upper portion of the reaction chamber 1101. On the other hand,
ozone has a short life under elevated temperature conditions.
Therefore, the supplied ozone progressively disappears as it flows
from the lower portion to the upper portion of the reaction chamber
1101 and, as a result, the upper portion of the reaction chamber
1101 is more likely to lack ozone. To solve this problem, it may be
conceived that an excessive amount of ozone may be supplied to the
reaction chamber 1101. However, the supply of an excessive amount
of ozone causes oxidation damage to the components in the lower
portion of the reaction chamber 1101, which is not desirable.
Furthermore, ozone is consumed by this oxidation reaction.
[0009] In order to solve these problems, a distributing nozzle(s)
1117 such as shown in FIG. 7 may be used. The distributing nozzle
1117 extends from the bottom to the top of the reaction chamber
1101 and includes nozzle holes 1118 each corresponding to
respective semiconductor substrates mounted in the boat 1118. This
arrangement allows processing gas, especially ozone, to be
uniformly supplied to the semiconductor substrates. It should be
noted that the TEMAH gas may be supplied through an L-shaped nozzle
shown in FIG. 5 or the distributing nozzle shown in FIG. 7.
[0010] Incidentally, particle reduction is a critical issue in
semiconductor manufacturing. When a film is formed on the
semiconductor substrates by CVD, ALD, or other chemical deposition
process, deposition of unnecessary films unavoidably occurs on the
inner wall of the reaction tube and on the various components that
are exposed to the atmosphere within the reaction vessel.
Peeling-off of the unnecessary films is a major cause of the
generation of particles, as is well known to those of ordinary
skill in the art. Peeling-off of the unnecessary films tends to
occur when the unnecessary films have a large thickness or when the
inside of the reaction vessel is exposed to the ambient atmosphere.
For example, generation of a large quantity of particles was found
after the inside of reaction vessel was exposed to the ambient
atmosphere for maintenance or repair after performing deposition of
HfO films for many times. Analysis of these particles by EDX
(energy dispersive X-ray spectroscopy) revealed that they were
formed of hafnium oxide. It is thought that the above generation of
particles resulted from the fact that HfO films formed on the inner
wall of the reaction tube absorbed moisture and thereby peeled off
when the inside of the reaction tube was exposed to the ambient
atmosphere for maintenance. It was not possible to visually
recognize the HfO particles since their sizes were very small
(mostly 10 microns or less).
[0011] One of the possible countermeasures against the generated
particles is cycle purging. A trial was conducted to reducing
particles by using the cycle purging. The purging was performed by
repeating a cycle consisting of an ozone flowing step, an
evacuating step, and a nitrogen gas flowing step 50 times (spending
approximately 3 hours), as shown in FIG. 9. In FIG. 9, the
horizontal axis is graduated in 15 sec increments. The ozone
concentration in the ozone flowing step was 200 g/Nm.sup.3; the
oxygen flow rate before the oxygen-to-ozone conversion
(corresponding to the ozone flow rate) was 10 SLM; the pressure in
the reaction vessel in the evacuating step was approximately 5 Pa;
and the nitrogen gas flow rate in the nitrogen gas flowing step was
10 SLM. Dummy semiconductor substrates were placed in the boat and
heated to 300.degree. C. The number and distribution of particles
on the dummy semiconductor substrates were observed after
completion of every predetermined number of cycles. Various
particle distribution patterns were found: locally concentrated
patterns sparsely distributed patterns, etc. FIGS. 10A and 10B show
two examples of the observed particle distribution patterns. FIG.
11 shows change in the number of particles. The number of particles
was not stably reduced even after more than 200 purge cycles
(spending approximately 12 hours). Under such conditions, a
deposition process can not be performed.
[0012] Another possible countermeasure against the generated
particles is cleaning. However, there is no established method for
removing an HfO film by in-situ dry cleaning. Wet cleaning, on the
other hand, requires disassembly of the system, resulting in
significant downtime. Furthermore, wet cleaning should not be
frequently performed, since it shortens the life of the quartz
components. Replacement of components results in shorter downtime.
However, it is not practical since quartz components are
expensive.
SUMMARY OF THE INVENTION
[0013] The present invention has been devised in view of the
foregoing circumstances, and it is therefore the object of the
present invention to provide an effective, in-situ method of taking
countermeasure against particles.
[0014] The present inventors have found that, also in a coating
apparatus that forms a film on semiconductor substrates by repeated
atomic or molecular level depositions, a precoating process that
coats unnecessary film(s) with another film is useful for reducing
particles. It has also been found that such a precoating process
can be performed very effectively, if the gas supply mode during
precoating is different from the gas supply mode during film
formation, in particular, if a gas nozzle for a precoating gas is
provided separately from a gas nozzle for film formation. The
present invention has been made based on those findings.
[0015] Specifically, the present invention provides a semiconductor
manufacturing system including a reaction vessel and at least one
film-forming nozzle for supplying at least one film-forming gas
into the reaction vessel, configured to form a film on a
semiconductor substrate disposed within the reaction vessel by
supplying the film-forming gas into the reaction vessel to repeat
atomic or molecular level deposition, wherein the semiconductor
manufacturing system further includes at least one coating nozzle
for supplying at least one kind of coating gas into the reaction
vessel to coat a component exposed to an atmosphere within the
reaction vessel, wherein at least one of said at least one coating
nozzle is separated from said at least one film-forming nozzle.
[0016] In one preferred embodiment, the at least one kind of
film-forming gas includes a first film-forming gas and a second
film-forming gas, and the at least one coating gas includes a first
coating gas and a second coating gas; the first film-forming gas is
the same as the first coating gas; and a coating nozzle for
supplying the first coating gas is separated from a film-forming
nozzle for supplying the first film-forming gas.
[0017] In one preferred embodiment, the second film-forming gas is
a metal-containing gas; the second coating gas is a
metal-containing gas, and both the first film-forming gas and the
first coating gas are ozone. The at least one kind of film-forming
gas may include a third film-forming gas, and the third
film-forming gas may be the same as the second coating gas.
[0018] In one preferred embodiment, the semiconductor manufacturing
system is a batch-type system adapted to contain a plurality of
semiconductor substrates in the reaction vessel to perform a film
forming process to the semiconductor substrates collectively, the
reaction vessel has an exhaust port for evacuating an interior of
the reaction vessel, the film-forming nozzle for supplying the
first film-forming gas is a distributing nozzle having a plurality
of nozzle holes for discharging the first film-forming gas toward
the plurality of semiconductor substrates from their sides, and the
coating nozzle for supplying the first coating gas has a nozzle
hole which opens in the reaction vessel at a position farther from
the exhaust port than a region in which the plurality of
semiconductor devices are disposed. The semiconductor manufacturing
system may be a vertical, batch-type system that accommodates a
plurality of semiconductor substrates arrayed vertically in
horizontal posture in the reaction vessel, and performs a
film-forming process to the semiconductor substrates
collectively.
[0019] In the most typical embodiment of the present invention
described later with reference to the accompanying drawings, the
first film-forming gas is ozone; the second film-forming gas is
TEMAH gas; the third film-forming gas is trimethyl aluminum
(hereinafter abbreviated as "TMA") gas; the first precoating gas is
ozone; and the second precoating gas is TMA gas. Further, the
semiconductor manufacturing system is a vertical, batch-type system
that accommodates a plurality of semiconductor substrates arrayed
vertically in horizontal posture in the reaction vessel, and
performs a film-forming process to the semiconductor substrates
collectively. Further, the film-forming nozzle for supplying the
first film-forming gas (i.e., ozone) is a distributing nozzle
having a plurality of nozzle holes for discharging the first
film-forming gas toward the plurality of semiconductor substrates
from their sides; and the coating nozzle for supplying the first
coating gas (i.e., ozone) is an L-shaped nozzle having a nozzle
hole which opens in the reaction vessel at a position farther from
an exhaust port than a region in which the plurality of
semiconductor devices are disposed. Ozone is a short-lived gas.
Such a gas is supplied through the distributing nozzle during film
formation, but is supplied from a position far away from the
exhaust port during precoating so that the gas uniformly spreads
within the vessel. Thereby, a film of high quality can be obtained
during film formation, while the entire inside of the reaction
vessel can be coated with a precoat film of high quality with a
small number of deposition cycles during precoating. In this way,
it is possible to effectively prevent generation of particles, and
the system can restart in a short time period after maintenance of
the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a graph showing the number of generated particles
after performing precoating according to the present invention.
[0021] FIG. 2 is a graph showing the thickness distribution of
precoat films.
[0022] FIG. 3 is a vertical cross-sectional view schematically
showing the configuration of an ALD apparatus according to the
present invention.
[0023] FIG. 4 is a schematic diagram showing a gas introducing
portion of the ALD apparatus according to the present
invention.
[0024] FIG. 5 is a schematic vertical cross-sectional view showing
an example of a conventional ALD apparatus.
[0025] FIG. 6 is a diagram showing a piping system in the ALD
apparatus shown in FIG. 5.
[0026] FIG. 7 is a schematic vertical cross-sectional view of
another example of the conventional ALD apparatus.
[0027] FIG. 8 is a side view schematically showing the
configuration of a distributing nozzle.
[0028] FIG. 9 is a time chart illustrating a cycle purge
process.
[0029] FIG. 10 is a diagram showing the distribution of particles
on semiconductor substrates in one example.
[0030] FIG. 11 is a graph showing a relationship between the number
of purge cycles and the number of particles.
[0031] FIG. 12 is a time chart illustrating a precoat process.
[0032] FIG. 13 is a graph showing a relationship between the number
of precoat cycles and the number of particles.
[0033] FIG. 14 is an enlarged view of a portion of the graph of
FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention will be described in detail with
reference to the results of studies and experiments conducted by
the present inventors to achieve the invention.
[0035] A precoating technique has been used to prevent the
generation of particles resulting from peeling-off of unnecessary
films in CVD apparatus. The precoating technique coats potentially
peelable unnecessary films with a film (e.g., an SiO.sub.2 film) to
prevent peeling-off of the unnecessary films. The present inventors
have tried to extend this technique.
[0036] The present inventors conducted an experiment in which an
HfO film was coated with an aluminum oxide (hereinafter referred to
as an "AlO") film. The AlO film was formed by an ALD process that
repeats, a plurality of times, a deposition cycle consisting of a
TMA gas flowing step, an evacuating step, a nitrogen gas flowing
(purging) step, an ozone flowing step, an evacuating step, and a
nitrogen gas flowing (purging) step which were performed in that
order, as shown in FIG. 12. In FIG. 12, the horizontal axis is
graduated in 5 sec increments. This deposition cycle was performed
under the following process conditions. The TMA gas flow rate in
the TMA gas flowing step was 100 SCCM; the ozone concentration in
the ozone flowing step was 200 g/Nm.sup.3; the oxygen flow rate
before the oxygen-to-ozone conversion (corresponding to the ozone
flow rate) was 10 SLM; the pressure in the reaction vessel after
each evacuating step was approximately 5 Pa; and the nitrogen gas
flow rate in the nitrogen gas flowing step was 10 SLM. Several
dummy semiconductor substrates were placed in the boat and heated
to 300.degree. C. Under the aforementioned conditions, 0.1 nm of
AlO film was deposited in each cycle. Thus, a 10 nm thick AlO film
was formed by 100 cycles. 100 cycles spent approximately 2.5
hours.
[0037] This experiment was performed, using an ALD apparatus of the
type shown in FIG. 7 (employing distributing nozzles), according to
the following steps:
[0038] (1) performing a conventional, batch, HfO film coating
process and then exposing the reaction tube to the ambient
atmosphere;
[0039] (2) performing 100 cycles of ALD precoating process under
the foregoing conditions;
[0040] (3) performing a conventional, batch HfO film coating
process in the precoated reaction tube and then counting the number
of particles on the semiconductor substrates; and
[0041] (4) repeating step (2) and step (3).
[0042] FIGS. 13 and 14 are graphs illustrating the results of the
experiment. FIG. 14 is an enlarged view of a portion of the graph
of FIG. 13 (both graphs are based on the same data.) As is apparent
from FIGS. 13 and 14, the number of the particles was stably
reduced after 400 precoating cycles (the resultant AlO precoat film
thickness was 40 nm).
[0043] The experiment indicates that AlO film precoating is useful
for preventing peeling-off of the HfO film. However, it takes
approximately 10 hours to complete 400 precoating cycles. This
precoating process takes much longer time to complete than
conventional SiO.sub.2 film precoating processes by CVD and
therefore is not practical for most applications.
[0044] The present inventors also attempted to combine the above
cycle purging process and the AlO film precoating process, but with
no practically useful results. Approximately 400 cycles of AlO film
precoating were needed to reduce the number of particles regardless
of the number of purge cycles.
[0045] The inventors endeavored to develop a technique of
effectively forming an aluminum oxide precoating to sufficiently
prevent peeling-off of the film. In the course of the development
of such a technique, the inventors have come to a hypothesis that
the use of the distributing nozzle, which is used to effectively
supply ozone during desired film formation, rather avoids formation
of a high-quality precoating.
[0046] To verify this hypothesis, an experiment was performed by
using the ALD apparatus shown in FIG. 3, Note that the ALD
apparatus shown in FIG. 3 is a film-forming system (semiconductor
manufacturing system) in one embodiment of the present invention,
as can be seen from the following description. The ALD apparatus
shown in FIG. 3 will now be described.
[0047] The ALD apparatus shown in FIG. 3 differs from those
described in the "Background Art" section with reference to FIGS. 5
and 7 in that it has a different gas supply system. Duplicative
description of the same components is thus omitted.
[0048] The ALD apparatus shown in FIG. 3 includes a distributing
nozzle 107 and L-shaped nozzles 108. The distributing nozzle 107
extends vertically within the reaction chamber 1101 in the
longitudinal direction of the boat 1108, that is, in the direction
of arrangement of the semiconductor substrates. The distributing
nozzle 107 is configured to jet a gas, through nozzle holes thereof
each arranged at positions corresponding to respective
semiconductor substrates, toward respective semiconductor
substrates from their sides. Each L-shaped nozzle 108 is provided
at the lowest peripheral portion of the reaction chamber 1101 and
configured to supply a gas through a single nozzle hole thereof
from the bottom toward the top of the boat 1108. Note that, in the
ALD apparatus shown in FIG. 3, all components exposed to the
atmosphere within the reaction chamber 1101 are either formed of
quartz or covered with quartz.
[0049] The gas supply system for the ALD system shown in FIG. 3 is
adapted to form an HfO film and an AlO film on the semiconductor
substrates, as well as to form an AlO film as a precoat film on the
inner wall of the reaction tube and on the inner components of the
reaction vessel that are exposed to the atmosphere within the
reaction vessel.
[0050] FIG. 4 is a schematic horizontal cross-sectional view of the
manifold, or gas introducing portion, mounted in the lowermost
portion of the reaction tube (or reaction vessel) 1102 of the ALD
apparatus shown in FIG. 3. Gas lines for introducing various gases
into the reaction chamber 1101 penetrate through the manifold. The
distributing nozzle 107 (see FIG. 8) or the L-shaped nozzle 108
(not shown in FIG. 4) is coupled to the tip of each gas line to
discharge a gas into the reaction chamber 1101. The gas supply
system for the ALD apparatus shown in FIG. 3 includes: an L-shaped
nozzle connected to a TEMAH gas line to supply TEMAH gas when
forming HfO films on the semiconductor substrates; an L-shaped
nozzle connected to a TMA gas line to supply TMA gas when forming
AlO films on the semiconductor substrates; the distributing nozzle
connected to an ozone line to supply ozone when forming the both
HfO films and AlO films on the semiconductor substrates; an
L-shaped nozzle connected to a TMA gas line to supply TMA gas when
forming precoat films on the inner components of the reaction
vessel; and an L-shaped nozzle connected to an ozone line to supply
ozone when forming precoat film on the inner components of the
reaction vessel. Only some of these nozzles are shown in FIG. 3 for
simplicity.
[0051] Note that, when an HfO film is formed as a capacitive
dielectric film, it is common to form an AlO film on the HfO film
to provide enhanced insulation. Therefore, the ALD apparatus shown
in FIGS. 3 and 4 includes a nozzle for forming an AlO film on the
semiconductor substrates, as described above.
[0052] Note that, the ALD apparatus may further include a nitrogen
gas supply nozzle for purging (preferably having an L-shape) (see
FIG. 4). However, the nitrogen gas used as a purge gas is more
preferably supplied through nozzles for supplying TEMAH gas and TMA
gas. There may be a plurality of nozzles each having the same task.
Further, a plurality of nozzles may be disposed locally and
collectively, as shown in FIG. 4, or they may be distributed along
the circumference of the reaction tube 1102.
[0053] The nozzle holes of the L-shaped nozzles 108, especially
those for supplying precoating gases, are arranged at positions
ensuring that the gases discharged from the nozzles is sufficiently
supplied to the surfaces of the components in the lower portion of
the reaction chamber 1101, such as a plate-like member which is a
part of the boat loader 1106 (i.e., the cover for closing the lower
end opening (furnace throat) of the reaction tube 1102) and a
insulating tube. Preferably, the nozzle holes of the L-shaped
nozzles 108 for supplying precoating gases are arranged in the
reaction chamber 1101 at positions farthest from the vacuum exhaust
port 1103. In the example shown in FIG. 3, the nozzle holes of the
L-shaped nozzles 108 are located approximately 100 mm above the
bottom surface of the reaction chamber 1101, i.e., the top surface
of the cover described above.
[0054] Next, an experiment conducted by using the ALD apparatus
shown in FIG. 3 will be described.
[0055] (1) A conventional, batch HfO film coating process (by ALD)
was performed a predetermined number of times by using the ALD
apparatus shown in FIG. 3. The inside of the reaction vessel was
then exposed to the ambient atmosphere. At that time, the TEMAH gas
was supplied through the L-shaped nozzle 168 and the ozone was
supplied through the distributing nozzle 107.
[0056] (2) 100-cycle AlO precoating process was performed by ALD.
The AlO precoating process was performed by repeating, a plurality
of times, an ALD deposition cycle consisting of a TMA gas flowing
step, an evacuating step, a nitrogen gas flowing (purging) step, an
ozone flowing step, an evacuating step, and a nitrogen gas flowing
(purging) which are performed in that order, as shown in FIG. 12.
In FIG. 12, the horizontal axis is graduated in 5 sec increments.
The TMA gas flow rate in the TMA gas flowing step was 100 SCCM; the
ozone concentration in the ozone flowing step was 200 g/Nm.sup.3;
the oxygen flow rate before the oxygen-to-ozone conversion
(corresponding to the ozone flow rate) was 10 SLM; the pressure in
the reaction vessel in the evacuating steps was approximately 5 Pa;
and the nitrogen gas flow rate in the nitrogen gas flowing step was
10 SLM. Several dummy semiconductor substrates were placed in the
boat and heated to 300.degree. C. Both the TMA gas and ozone were
supplied through the L-shaped nozzles.
[0057] (3) A conventional, batch HfO film forming process (by ALD)
was performed once, and then the semiconductor substrates were
checked for particles. The HfO film forming conditions may be
understood just by substituting "TEMAH" for "TMA" in FIG. 12. The
TEMAH gas flow rate in the TEMAH gas flowing step was 1 ml/min
(liquid basis). The flow rates of the other gases and the
temperature and pressure conditions were the same as those for
forming the AlO film described above. At that time, the TEMAH gas
was supplied through an L-shaped nozzle 108 and the ozone was
supplied through the distributing nozzle 107.
[0058] As shown in the graph of FIG. 1, as a result of the
100-cycle precoating, the number of particles (larger than 0.12
microns in size) generated after the subsequent HfO film formation
was 20, sufficiently small. It took approximately 2.5 hours to
complete the 100-cycle precoating. It was thus found that the time
required for precoating was reduced to quarter as compared with the
case where a distributing nozzle was used as an ozone supply nozzle
in which the time required for precoating was approximately 10
hours, as previously described with reference to the previous
experiment result.
[0059] Silicon pieces were placed at positions 101 to 106 within
the reaction chamber 1101 before the above step (2) (see FIG. 3).
The position 101 is located on the inner surface of the cover of
the boat loader 1006 (lower than the nozzle holes of the L-shaped
gas supply nozzles 108); the positions 102 and 103 are on heat
shielding plates of the heat Insulating tube of the boat loader
1006; the position 104 is on the bottom of the boat 1108; the
position 105 is on the dummy semiconductor substrate placed in the
lower portion of the boat 1108; and the position 106 is on the
dummy semiconductor substrate placed in the central portion of the
boat 1108. The thickness of the AlO precoat film formed on each
silicon pieces was measured after the above step (2). In addition,
a comparative experiment was performed in which: a distributing
nozzle for forming the HfO film was used instead of an L-shaped gas
supply nozzle to supply ozone when forming the AlO precoat film
(the other conditions are the same as in the above experiment); and
the thickness of the AlO precoat film formed on the silicon pieces
at each of the positions 101 to 106 was also measured.
[0060] FIG. 2 is a graph illustrating the results of these
experiments. In FIG. 2, symbol A denotes the thickness of the
precoat film formed when the ozone was supplied through an L-shaped
gas supply nozzle; and symbol B denotes the thickness of the
precoat film formed when the ozone was supplied through the
distributing gas supply nozzle. At the positions 104, 105 and 106
in the boat 1108, there was no difference in the thickness of the
AlO precoat films depending on the type of the nozzle. On the other
hand, at the positions 101, 102 and 103, which are lower than the
boat, the AlO precoat film formed by using the L-shaped gas supply
nozzle was approximately 15% thicker than that formed by using the
distributing gas supply nozzle.
[0061] The results of the experiments are summarized below.
[0062] (a) In the case where the ozone was supplied through the
distributing gas supply nozzle, the number of particles was reduced
to a non-problematic level when the thickness of the AlO precoat
film reached approximately 40 nm (400-cycle precoating).
[0063] (b) In the case where the ozone was supplied through the
L-shaped gas supply nozzle, the number of particles was reduced to
a non-problematic level when the thickness of the AlO precoat film
reached approximately 11 nm (100-cycle precoating).
[0064] (c) At positions lower than the boat, the AlO precoat film
formed by using the L-shaped gas supply nozzle was thicker than
that formed by using the distributing gas supply nozzle, but only
by 15%, after 100-cycle AlO precoating.
[0065] The present inventors think the reasons for the above
results (a), (b), and (c) are the following.
[0066] It is apparent that peeling off of the HfO film and hence
the generation of particles can be more effectively prevented in
the case where an AlO precoat film is formed by supplying ozone
using an L-shaped gas supply nozzle, as compared with the case
where a distributing gas supply nozzle is used. The reason for this
relates to the quality or covering properties of the precoat film
rather than its thickness. If ozone is supplied through the
distributing gas supply nozzle. It takes a long time for the ozone
to reach the lower region of the reaction vessel opposite to the
vacuum exhaust port. Thus, a significant amount of ozone may
disappear before reaching that region. As a result, the AlO precoat
film of good quality can not be formed in the lower region of the
reaction vessel. Thus, a large thickness is required in order to
achieve the desired precoating effect with an AlO precoat film of
poor quality. On the other hand, when the ozone is supplied through
an L-shaped gas supply nozzle, it uniformly fills the reaction
vessel and flows smoothly from the nozzle toward the vacuum exhaust
port. This allows the precoat film to be of good quality and hence
have the desired precoating effect even if it has a relatively
small thickness. Note that the boat holds no wafer or only several
dummy wafers during the precoating process. Therefore, it is not
disadvantageous that the L-shaped gas supply nozzle is located far
away from the exhaust port.
[0067] Although the present invention has been described, taking
formation of an HfO film and an AlO precoat film as an example,
based on an ALD system having a specific structure, the prevent
invention is not limited to the foregoing embodiments. It will be
appreciated by those skilled in the art that the broadest scope of
the present invention is that, if the position of a nozzle for
forming a film on the semiconductor substrates (i.e., a
film-forming gas nozzles) are not suitable for forming a precoat
film, a nozzle for supplying a process gas to form a precoat film
(a precoating gas nozzle) may be provided separately from the
film-forming gas nozzle, allowing the process gas for precoating to
be supplied to an appropriate location within the reaction vessel.
Therefore, in a case where another type of film is formed, the
present invention is applicable. Further, the present invention has
been described while focusing on the nozzle for supplying ozone gas
when forming a film on the semiconductor substrates and to the
nozzle for supplying ozone gas for precoating. Since ozone has a
short life, it is true that the advantageous effect of the present
invention is best achieved by providing different nozzles for
supplying ozone when forming a film on the semiconductor substrates
and for supplying ozone when forming a precoat film to allow ozone
to be supplied from optimum positions. However, for example, it is
possible that, for example, when forming an AlO film on the
semiconductor substrates, the TMA gas may be supplied through a
distributing nozzle. In this case, it is considered that an AlO
precoat film of better quality (although the difference may not be
so large as compared with a case of ozone) can be formed by using
an L-shaped gas supply nozzle as a nozzle for supplying the TMA gas
during precoating. In addition, it will be appreciated by those
skilled in the art that the advantageous effects of the present
invention may be expected not only in a case where the film to be
formed on the semiconductor substrates is an HfO film and the
precoat film is an AlO film, but also in a case those films are of
different types (although the advantageous effect may not be the
same degree). Further, although the present invention achieves most
remarkable advantageous effects if it is applied to a vertical
batch system, the advantageous effects can be achieved even if the
present invention is applied to another type of batch system or a
single substrate processing system.
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