U.S. patent application number 12/678765 was filed with the patent office on 2010-11-25 for vaporizing unit, film forming apparatus, film forming method, computer program and storage medium.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Kyoko Ikeda, Sumie Nagaseki, Tatsuro Ohshita, Ikuo Sawada.
Application Number | 20100297346 12/678765 |
Document ID | / |
Family ID | 40467753 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100297346 |
Kind Code |
A1 |
Sawada; Ikuo ; et
al. |
November 25, 2010 |
VAPORIZING UNIT, FILM FORMING APPARATUS, FILM FORMING METHOD,
COMPUTER PROGRAM AND STORAGE MEDIUM
Abstract
A vaporizing unit, in supplying a gas material produced by
vaporizing a liquid material onto a substrate to conduct a film
forming process, can vaporize the liquid material with high
efficiency to suppress generation of particles. With the vaporizing
unit, positively or negatively charged bubbles, which have a
diameter of 1000 nm or less, are produced in the liquid material,
and the liquid material is atomized to form a mist of the liquid
material. Further, the mist of the liquid material is heated and
vaporized. The fine bubbles are uniformly dispersed in advance in
the liquid material, so that very fine and uniform mist particles
of the liquid material are produced when the liquid material is
atomized, which makes heat exchange readily conducted. By
vaporizing the mist of the liquid material, vaporization efficiency
is enhanced, and generation of particles can be suppressed.
Inventors: |
Sawada; Ikuo; (Yamanashi,
JP) ; Nagaseki; Sumie; (Yamanashi, JP) ;
Ikeda; Kyoko; (Yamanashi, JP) ; Ohshita; Tatsuro;
(Yamanashi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
40467753 |
Appl. No.: |
12/678765 |
Filed: |
August 11, 2008 |
PCT Filed: |
August 11, 2008 |
PCT NO: |
PCT/JP2008/064420 |
371 Date: |
May 20, 2010 |
Current U.S.
Class: |
427/248.1 ;
118/726; 392/386 |
Current CPC
Class: |
H01L 21/31645 20130101;
H01L 21/3185 20130101; H01L 21/02271 20130101; H01L 21/31612
20130101; H01L 21/02181 20130101; C23C 16/4486 20130101 |
Class at
Publication: |
427/248.1 ;
118/726; 392/386 |
International
Class: |
C23C 16/448 20060101
C23C016/448; C23C 16/44 20060101 C23C016/44; F02M 15/04 20060101
F02M015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2007 |
JP |
2007-241364 |
Claims
1. A vaporizing unit comprising: a bubble generation device for
generating bubbles having a diameter of 1000 nm or less and charged
positively or negatively in a liquid material for film formation by
supplying a carrier gas for bubble generation into the liquid
material; a vaporizer, connected to the bubble generation device,
for vaporizing the liquid material to obtain a gas material; and a
gas material outlet port, provided at the vaporizer, for
discharging the gas material obtained by vaporization of the liquid
material in the vaporizer, wherein the vaporizer includes a
vaporization chamber for vaporizing the liquid material, an
atomization part, provided at an inlet of the vaporization chamber,
for atomizing the liquid material containing the bubbles supplied
from the bubble generation device to produce a mist of the liquid
material and supply the mist into the vaporization chamber, and a
heater provided in the vaporization chamber to heat and vaporize
the mist of the liquid material supplied from the atomization part
into the vaporization chamber.
2. The vaporizing unit of claim 1, wherein the bubble generation
device generates the bubbles by forming a revolving flow of the
carrier gas.
3. The vaporizing unit of claim 1, wherein the atomization part is
configured as a nozzle for discharging the liquid material
containing the bubbles together with a carrier gas for
atomization.
4. A film forming apparatus comprising: a vaporizing unit for
generating a gas material; and a film forming unit including a
processing chamber connected to the vaporizing unit, a target
object being loaded in the processing chamber and the film forming
unit performing a film forming process on the target object by
using the gas material supplied from the vaporizing unit, wherein
the vaporizing unit includes: a bubble generation device for
generating bubbles having a diameter of 1000 nm or less and charged
positively or negatively in a liquid material for film formation by
supplying a carrier gas for bubble generation into the liquid
material; a vaporizer, connected to the bubble generation device,
for vaporizing the liquid material to obtain the gas material; and
a gas material outlet port, provided at the vaporizer, for
discharging the gas material obtained by vaporization of the liquid
material in the vaporizer, wherein the vaporizer includes a
vaporization chamber for vaporizing the liquid material, an
atomization part, provided at an inlet of the vaporization chamber,
for atomizing the liquid material containing the bubbles supplied
from the bubble generation device to produce a mist of the liquid
material and supply the mist into the vaporization chamber, and a
heater provided in the vaporization chamber to heat and vaporize
the mist of the liquid material supplied from the atomization part
into the vaporization chamber.
5. A film forming method comprising: generating bubbles having a
diameter of 1000 nm or less and charged positively or negatively in
a liquid material for film formation by supplying a carrier gas for
bubble generation into the liquid material; producing a mist of the
liquid material by atomizing the liquid material containing the
bubbles; obtaining a gas material by heating and vaporizing the
mist of the liquid material; and performing a film forming process
on a target object in a processing chamber by supplying the gas
material to the target object.
6. The vaporizing method of claim 5, wherein said generating
bubbles includes forming a revolving flow of the carrier gas.
7. The vaporizing method of claim 5, wherein said producing a mist
of the liquid material includes atomizing the liquid material
containing the bubbles and a carrier gas for atomization through a
nozzle.
8. (canceled)
9. (canceled)
10. The vaporizing unit of claim 2, wherein the atomization part is
configured as a nozzle for discharging the liquid material
containing the bubbles together with a carrier gas for
atomization.
11. The vaporizing method of claim 6, wherein said producing a mist
of the liquid material includes atomizing the liquid material
containing the bubbles and a carrier gas for atomization through a
nozzle.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a technique for supplying a
gas material produced by vaporizing a liquid material to a target
object to perform a film forming process thereon; and more
particularly, to a technique for vaporizing a liquid material.
BACKGROUND OF THE INVENTION
[0002] As one of semiconductor manufacturing processes, there is a
film forming process for forming a specific film on a surface of a
semiconductor wafer (hereinafter, referred to as a "wafer") W. In
the film forming process, a material gas produced by vaporizing a
liquid material is introduced as a film forming gas into an
apparatus.
[0003] As examples of the film forming process using the material
gas produced by vaporizing the liquid material, there are a case in
which a SiO.sub.2 film is formed by using a processing gas obtained
by vaporizing tetra ethyl oxysilane (TEOS) and oxygen (O.sub.2)
gas, and a case in which a silicon nitride (Si.sub.3N.sub.4) film
is formed by using a processing gas obtained by vaporizing
Si.sub.2Cl.sub.6 and ammonia (NH.sub.3) gas.
[0004] A conventional example of a vaporizer for vaporizing the
liquid material is illustrated in FIG. 5. The vaporizer of FIG. 5
includes a vertical cylindrical body 100 that is configured as a
vaporization chamber and has a nozzle 101 installed at an upper
portion thereof. At a leading end portion of the nozzle 101, a
liquid material and a carrier gas are mixed to be discharged in a
mist state into the cylindrical body 100 as in a sprayer. By
heating the inside of the cylindrical body 100, the mist is
vaporized to produce a gas material.
[0005] Meanwhile, recently, a liquid material having a low vapor
pressure may be used due to the development of various devices. For
example, a compound of hafnium (Hf) is employed as a film forming
material.
[0006] For instance, Tetrakis(N-Ethyl-N-Methylamino)Hafnium (TEMAH)
has a vapor pressure of about 0.11 kPa (0.85 Torr) at a temperature
of about 85.degree. C., and Hafnium Tetra-t-Butoxide (HTB) has a
vapor pressure of about 0.55 kPa (4.12 Torr) at a temperature of
about 85.degree. C. These hafnium-based materials have a rather low
vapor pressure, while TEOS has a vapor pressure of about 5.6 kPa
(42 Torr) at a temperature of about 85.degree. C.
[0007] The material having a low vapor pressure is difficult to be
vaporized. For example, when the mist is adhered to an inner wall
of the cylindrical body 100, the mist is dried and solidified at
the inner wall and, then, detached from the inner wall to generate
particles.
[0008] Meanwhile, when a heating temperature is raised to quickly
vaporize the mist, it is difficult to uniformly heat the inside of
the cylindrical body 100, and the mist may be decomposed and
transformed by heating. Further, this phenomenon is more
problematic when it is intended to increase a supply flow rate of
the liquid material. As described above, it is very difficult to
vaporize a low vapor pressure material, which is a problem to be
solved in a film forming process using a new material.
[0009] In this connection, Patent Document 1 discloses a technique
for improving vaporization efficiency by supplying a gas-liquid
mixed fluid to a vaporizer and developing a structure of a nozzle
to obtain a large amount of the gas material. However, a technique
for increasing a flow rate of the gas material is still
required.
[0010] Patent Document 1: Japanese Patent Laid-open Publication No.
2006-100737 (paragraphs [0023] to [0026])
SUMMARY OF THE INVENTION
[0011] The present invention has been devised in order to solve the
problems described above. It is an object of the present invention
to provide a vaporizing unit capable of vaporizing a liquid
material with high efficiency when a film forming process is
performed on a target object by supplying a gas material produced
by vaporizing the liquid material to the target object, a film
forming apparatus, a film forming method, a program for performing
the film forming method and a storage medium storing the
program.
[0012] In accordance with an aspect of the present invention, there
is provided a vaporizing unit including: a bubble generation device
for generating bubbles having a diameter of 1000 nm or less and
charged positively or negatively in a liquid material for film
formation by supplying a carrier gas for bubble generation into the
liquid material; a vaporizer, connected to the bubble generation
device, for vaporizing the liquid material to obtain a gas
material; and a gas material outlet port, provided at the
vaporizer, for discharging the gas material obtained by
vaporization of the liquid material in the vaporizer, wherein the
vaporizer includes a vaporization chamber for vaporizing the liquid
material, an atomization part, provided at an inlet of the
vaporization chamber, for atomizing the liquid material containing
the bubbles supplied from the bubble generation device to produce a
mist of the liquid material and supply the mist into the
vaporization chamber, and a heater provided in the vaporization
chamber to heat and vaporize the mist of the liquid material
supplied from the atomization part into the vaporization
chamber.
[0013] The bubble generation device may generate the bubbles by
forming a revolving flow of the carrier gas.
[0014] The atomization part may be configured as a nozzle for
discharging the liquid material containing the bubbles together
with a carrier gas for atomization.
[0015] In accordance with another aspect of the present invention,
there is provided a film forming apparatus including: a vaporizing
unit for generating a gas material; and a film forming unit
including a processing chamber connected to the vaporizing unit, a
target object being loaded in the processing chamber and the film
forming unit performing a film forming process on the target object
by using the gas material supplied from the vaporizing unit,
wherein the vaporizing unit includes: a bubble generation device
for generating bubbles having a diameter of 1000 nm or less and
charged positively or negatively in a liquid material for film
formation by supplying a carrier gas for bubble generation into the
liquid material; a vaporizer, connected to the bubble generation
device, for vaporizing the liquid material to obtain the gas
material; and a gas material outlet port, provided at the
vaporizer, for discharging the gas material obtained by
vaporization of the liquid material in the vaporizer, wherein the
vaporizer includes a vaporization chamber for vaporizing the liquid
material, an atomization part, provided at an inlet of the
vaporization chamber, for atomizing the liquid material containing
the bubbles supplied from the bubble generation device to produce a
mist of the liquid material and supply the mist into the
vaporization chamber, and a heater provided in the vaporization
chamber to heat and vaporize the mist of the liquid material
supplied from the atomization part into the vaporization
chamber.
[0016] In accordance with still another aspect of the present
invention, there is provided a film forming method including:
generating bubbles having a diameter of 1000 nm or less and charged
positively or negatively in a liquid material for film formation by
supplying a carrier gas for bubble generation into the liquid
material; producing a mist of the liquid material by atomizing the
liquid material containing the bubbles; obtaining a gas material by
heating and vaporizing the mist of the liquid material; and
performing a film forming process on a target object in a
processing chamber by supplying the gas material to the target
object.
[0017] The generating bubbles may include forming a revolving flow
of the carrier gas.
[0018] The producing a mist of the liquid material may include
atomizing the liquid material containing the bubbles and a carrier
gas for atomization through a nozzle.
[0019] In accordance with still another aspect of the present
invention, there is provided a computer program for executing a
film forming method on a computer, wherein the film forming method
includes: generating bubbles having a diameter of 1000 nm or less
and charged positively or negatively in a liquid material for film
formation by supplying a carrier gas for bubble generation into the
liquid material; producing a mist of the liquid material by
atomizing the liquid material containing the bubbles; obtaining a
gas material by heating and vaporizing the mist of the liquid
material; and performing a film forming process on a target object
in a processing chamber by supplying the gas material to the target
object.
[0020] In accordance with still another aspect of the present
invention, there is provided a storage medium storing a computer
program for executing a film forming method on a computer, wherein
the film forming method includes: generating bubbles having a
diameter of 1000 nm or less and charged positively or negatively in
a liquid material for film formation by supplying a carrier gas for
bubble generation into the liquid material; producing a mist of the
liquid material by atomizing the liquid material containing the
bubbles; obtaining a gas material by heating and vaporizing the
mist of the liquid material; and performing a film forming process
on a target object in a processing chamber by supplying the gas
material to the target object.
[0021] In accordance with the present invention, the positively or
negatively charged nano bubbles having a diameter of 1000 nm or
less are generated in the liquid material for the film forming
process of the target object. The liquid material is atomized and
the mist is heated and vaporized. Small bubbles are uniformly
dispersed in advance in the liquid material. Thus, when the liquid
material is atomized, fine and uniform mist can be obtained and
heat exchange is easily performed. Consequently, vaporization
efficiency (heat exchange rate) is improved and generation of the
particles can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 illustrates a schematic configuration of a film
forming apparatus for performing a film forming method in
accordance with an embodiment of the present invention.
[0023] FIGS. 2A and 2B depict an example of a nano bubble
generation device in the film forming apparatus.
[0024] FIG. 3 is a longitudinal cross sectional view of a vaporizer
of the film forming apparatus.
[0025] FIG. 4 schematically shows a process in which a liquid
material is converted into a mist in the vaporizer.
[0026] FIG. 5 is a side view schematically showing a conventional
vaporizer.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0027] Hereinafter, an example of a film forming apparatus for
performing a film forming method in accordance with an embodiment
of the present invention will be described with reference to FIGS.
1 to 3. FIG. 1 illustrates a schematic configuration of a film
forming apparatus for performing a film forming process on a target
substrate such as a semiconductor wafer (hereinafter, referred to
as a "wafer") W. The film forming apparatus includes a liquid
material reservoir 10 storing a liquid material for film formation,
e.g., a compound containing hafnium such as TEMAH, a vaporizing
unit 20a for vaporizing the liquid material of the liquid material
reservoir 10, and a film forming unit 50 for performing a film
forming process by causing a gas material, which is obtained by
vaporizing the liquid material in the vaporizing unit 20a, to react
on the surface of the wafer W.
[0028] In the liquid material reservoir 10, one end of a gas supply
line 14 is provided in an open state at a position higher than a
liquid surface of the liquid material in the liquid material
reservoir 10. The other end of the gas supply line 14 is connected
to a nitrogen gas source 16 for supplying a nonreactive gas, e.g.,
nitrogen gas, via a valve 15. Further, one end of a liquid material
supply line 11 is provided in an open state at a position lower
than the liquid surface of the liquid material in the liquid
material reservoir 10. The other end of the liquid material supply
line 11 is connected to a nano bubble generation device (bubble
generation device) 30 for generating very tiny bubbles, i.e., nano
bubbles, via a mass flow controller 12 and a valve 13. Further, a
heater 17 is provided in the liquid material reservoir 10 to heat
the liquid material to a temperature of, e.g., 50.degree. C.
[0029] Here, nano bubbles refer to bubbles having a diameter of,
e.g., 10 nm or less. The diameter of the bubbles is not limited to
several nm. However, when the bubbles are too large, dispersion in
the liquid deteriorates due to buoyancy and, thus, a uniform
gas-liquid mixed fluid cannot be obtained. Accordingly, the
diameter of the bubbles is required to be smaller than 1000 nm.
Further, these bubbles are required to be charged positively or
negatively to prevent agglutination of the bubbles and, in this
embodiment, they are charged negatively. The nano bubble generation
device 30 for generating the nano bubbles is described with
reference to FIGS. 2A and 2B.
[0030] The nano bubble generation device 30 is configured as, e.g.,
a micro-nano bubble generator made by Nanoplanet Research Institute
Corporation. As shown in FIG. 2A, the nano bubble generation device
30 has a cylindrical housing 31. The liquid material supply line 11
is connected to an upper side of the side surface (circumferential
surface) of the housing 31. Further, a gas supply line 33 for
supplying a carrier gas for generation of nano bubbles is connected
to one end surface of the housing 31. As shown in FIG. 1, a
nonreactive gas supply source 34 storing therein a nonreactive gas
such as Ar gas is connected to an upstream side of the gas supply
line 33 via a valve 36 and a mass flow controller 37. A liquid
material line 35 is connected to the other end surface of the
housing 31, which is opposite to the surface connected to the gas
supply line 33.
[0031] A process of generation of nano bubbles in the nano bubble
generation device 30 will be described. First, when the liquid
material is supplied into the housing 31, the liquid material flows
toward the gas supply line 33 in the housing 31 and, then, flows
toward the liquid material line 35 in the housing 31 while
violently revolving along an inner peripheral surface of the
housing 31. A negative pressure of, e.g., 0.06 MPa (450 Torr) is
generated, as in an aspirator, by the flow of the liquid material.
Accordingly, the gas for nano bubble generation supplied from the
gas supply line 33 is sucked by the negative pressure and, thus,
flows toward the liquid material line 35 at the center of the
revolving flow of the liquid material. The revolving flow of the
liquid material has a revolving radius gradually decreasing as it
goes toward the liquid material line 35. Consequently, at the end
side of the housing 31, as shown in FIG. 2B, the liquid material
and the gas are violently mixed with each other to generate nano
bubbles.
[0032] The nano bubbles have negative charges of, e.g., 40 to 100
mV by friction with the revolving flow of the liquid material (see
"Shrinking Process and Shrinking Pattern of Micro Bubbles",
Hirofumi OHNARI and Yui TSUNAMI, 1st Symposium on Micro-Nano Bubble
Technology). Further, the nano bubbles may be generated by, e.g.,
electrolysis in addition to the aforementioned method.
[0033] As shown in FIG. 1, a vaporizer 20 is connected to the
downstream side of the nano bubble generation device 30 via the
liquid material line 35. Further, the nonreactive gas supply source
34 is connected to the vaporizer 20 via a carrier gas supply line
23 provided with a valve 21 and a mass flow controller 22. The nano
bubble generation device 30, the vaporizer 20 connected to the nano
bubble generation device 30, and a gas material outlet port 24a
provided in the vaporizer 20 constitute the vaporizing unit 20a.
The vaporizer 20 includes, as shown in FIG. 3, a cylindrical
vaporization chamber 24 elongated in a vertical direction, a heater
25 embedded in a sidewall of the vaporization chamber 24, and an
atomization nozzle (atomization part) 26 of, e.g., a double-fluid
nozzle, which is provided at an upper side (inlet) of the
vaporization chamber 24 and has a liquid contacting portion covered
with a nonmetallic material.
[0034] The atomization nozzle 26 has a double-pipe structure
including a liquid material flow path 40 for flowing the liquid
material downward in an inner central portion of the atomization
nozzle 26 and a carrier gas flow path 41 for flowing the carrier
gas of a nonreactive gas therein, the carrier gas flow path 41
surrounding the liquid material flow path 40. The liquid material
flow path 40 and the carrier gas flow path 41 are connected to the
liquid material line 35 and the carrier gas supply line 23,
respectively.
[0035] Further, a leading end portion 42 of the atomization nozzle
26 is configured such that an outer diameter of the carrier gas
flow path 41 rapidly decreases. At the leading end portion 42, the
liquid material is fragmented into small droplets by the pressure
of the carrier gas to produce a mist of the liquid material. The
mist is sprayed into the vaporization chamber 24 through a very
small discharge hole 43 formed at the leading end of the
atomization nozzle 26.
[0036] A first heater 27 is provided at the carrier gas supply line
23. The gas material outlet port 24a is provided at a lower side
surface of the vaporization chamber 24. A gas material outlet line
29 is connected to the gas material outlet port 24a. The gas
material outlet port 24a and the gas material outlet line 29 are
provided with a second heater 28 to prevent re-liquefaction of the
gas material.
[0037] A suction pump 73 is connected to a bottom surface of the
vaporization chamber 24 via a liquid drain line 72 provided with a
valve 71. For instance, the unvaporized mist adhered to the bottom
surface of the vaporization chamber 24 is discharged through the
liquid drain line 72. Further, the structure of the atomization
nozzle 26 is simply illustrated. The film forming unit 50 is
connected to the downstream side of the gas material outlet line 29
via a valve 29a. The film forming unit 50 includes a processing
chamber 60 formed in a mushroom shape having an upper
large-diameter cylindrical part 60a and a lower small-diameter
cylindrical part 60b that are connected to each other. A stage 61
for horizontally mounting the wafer W thereon is provided in the
processing chamber 60. The stage is supported by a supporting
member 62 at a bottom portion of the small-diameter cylindrical
part 60b.
[0038] A heater 61a and an electrostatic chuck (not shown) for
attracting and holding the wafer W are provided in the stage 61.
Further, e.g., three elevating pins 63 (only two pins are shown for
simplicity) for elevating the wafer W to allow the wafer W to be
delivered to/from a transfer unit (not shown) are provided in the
stage 61 such that they can be protruded from and retracted into
the surface of the stage 61. The elevating pins 63 are connected to
a lift mechanism 65 provided outside the processing chamber 60 via
a supporting part 64. A bottom portion of the processing chamber 60
is connected to one end of a gas exhaust pipe 66. A vacuum exhaust
device 67 having a vacuum pump and a pressure controller is
connected to the other end of the gas exhaust pipe 66. Further, a
transfer port 68 that is opened and closed by a gate valve G is
formed at a sidewall of the large-diameter cylindrical part 60a of
the processing chamber 60.
[0039] A gas shower head 69 serving as a gas supply unit is
provided at a central ceiling portion of the processing chamber 60
to face the stage 61. A number of gas supply holes 69a are opened
at a bottom surface of the gas shower head 69 to supply a gas
flowing in the gas shower head 69 to the wafer W. The gas material
outlet line 29 is connected to a top surface of the gas shower head
69. Further, an oxidizing gas source 93 storing therein an
oxidizing gas such as oxygen gas is connected to the top surface of
the gas shower head 69 via an oxidizing gas supply line 92 provided
with a valve 90 and a mass flow controller 91. A gas flow path of
the oxygen gas supplied from the oxidizing gas source 93 and a gas
flow path of the gas material are separately provided in the gas
shower head 69 such that the oxygen gas and the gas material are
not mixed with each other. The oxygen gas is supplied to the wafer
W through oxidizing gas supply holes 94 formed at the bottom
surface of the gas shower head 69.
[0040] The film forming apparatus includes, as shown in FIG. 1, a
control unit 2A having, e.g., a computer. The control unit 2A
includes a data processing part having a program, a memory and a
CPU, and the like. The program includes commands (steps) such that
the control unit 2A transmits control signals to components of the
film forming apparatus to perform the steps. Further, the memory
has a section allowing input of process parameters such as a
process pressure, a process temperature, process time, a gas flow
rate and a power level. When the CPU executes the commands of the
program, the process parameters are read and the control signals
corresponding to the parameters are transmitted to the
corresponding components of the film forming apparatus. The program
(including a program for input and display of the process
parameters) is stored in a computer-readable storage medium, i.e.,
a storage unit 2B such as a flexible disk, a compact disk, a hard
disk, a magneto-optical (MO) disk, and the like, and is installed
in the control unit 2A.
[0041] Next, a film forming method in accordance with the
embodiment of the present invention will be described. First,
nitrogen gas is supplied from the nitrogen gas source 16 to the
liquid material reservoir 10 containing the liquid material
maintained at a temperature of, e.g., 50.degree. C. by the heater
17. At this time, the liquid surface of the liquid material is
pressed by the pressure of the nitrogen gas, so that the liquid
material flows into the nano bubble generation device 30 through
the liquid material supply line 11. Further, when a nonreactive gas
is supplied from the nonreactive gas supply source 34 to the nano
bubble generation device 30, nano bubbles are generated in the
liquid material as described above.
[0042] The nano bubbles have negative charges as described above
and repel each other. Accordingly, the nano bubbles are uniformly
dispersed in the liquid material. Further, the liquid material
having the nano bubbles dispersed therein flows down in the liquid
material flow path 40 formed at the center of the atomization
nozzle 26 of the vaporizer 20. The liquid material is fragmented,
at the leading end portion 42 of the atomization nozzle 26, by the
carrier gas flowing out of the carrier gas flow path 41 provided
outside the liquid material flow path 40.
[0043] As described above, the nano bubbles are uniformly dispersed
in the liquid material to form a uniform gas-liquid mixed fluid.
Accordingly, as shown in FIG. 4, when the liquid material is
fragmented by the carrier gas, fragment lines are interrupted by
the nano bubbles and new fragment lines are generated from the
corresponding nano bubbles. Consequently, the liquid material is
finely and uniformly divided to produce uniform and fine mist
particles 80 of the liquid material at the discharge hole 43 of the
atomization nozzle 26. Thus, the liquid material is atomized into
fine droplets to be supplied into the vaporization chamber 24.
[0044] Further, the nano bubbles are exposed at the surfaces of the
mist particles 80, and the nano bubbles seemingly disappear.
Accordingly, the negative charges of the nano bubbles are
transferred to the mist particles 80 or the air in the vaporization
chamber 24. When the mist particles 80 are provided with negative
charges, the mist particles 80 repel each other, thereby preventing
agglutination after vaporization. When the air is provided with
negative charges, the negative charges combine with positive ions
in the air to be neutralized.
[0045] Meanwhile, the mist particles 80 are heated to a temperature
of, e.g., 150.degree. C. by the heat of the heater 25 provided at
the sidewall of the vaporization chamber 24 and the heat of the
carrier gas. The mist particles 80 have a uniform and small
diameter, so that they can be surely vaporized by rapid heat
exchange to produce a gas material. Further, when the negative
charges of the nano bubbles are transferred to the mist particles
80 and the mist particles have the negative charges, the mist
particles 80 are prevented from being agglutinated and formation of
large droplets is suppressed, thereby achieving further rapid heat
exchange.
[0046] The flow of the gas material is bent at a lower portion of
the vaporization chamber so that the gas material is introduced
into the gas material outlet line 29, while unvaporized particles
of the mist particles 80 are accumulated at the lower portion of
the vaporization chamber 24 by gravity. Thus, gas-liquid separation
is achieved in the vaporization chamber 24. In this case, the heat
exchange rate of the mist particles 80 is high so that the gas
material introduced into the gas material outlet line 29 rarely
includes the mist particles 80. The mist particles accumulated on
the bottom surface of the vaporization chamber 24 are discharged
through the liquid drain line 72 by the suction pump 73 by
regularly opening the valve 71.
[0047] Further, the gas material is supplied into the processing
chamber 60 of the film forming unit 50 through the gas shower head
69 while the re-liquefaction of the gas material is prevented by
the heat of the second heater 28. In the film forming unit 50, the
wafer W is heated in advance and maintained at a predetermined
temperature, and the inside of the processing chamber 60 is
depressurized. In this state, the gas material reacts with the
oxygen gas supplied through the gas shower head 69 on the surface
of the wafer W to produce film forming species. The film forming
species are deposited on the wafer W, thereby forming, e.g., a
hafnium oxide film.
[0048] In accordance with the embodiment of the present invention,
the negatively-charged nano bubbles having a diameter of 1000 nm or
less are generated in the liquid material for the film forming
process of the wafer W. The liquid material is atomized to produce
the mist particles 80 and the mist particles 80 are heated and
vaporized. That is, small bubbles are uniformly dispersed in
advance in the liquid material. Thus, when the liquid material is
atomized, fine and uniform mist particles 80 can be obtained and
heat exchange is easily performed. Consequently, vaporization
efficiency is improved and generation of the particles can be
reduced.
[0049] Further, when the mist particles 80 obtained by atomization
are provided with negative charges, the mist particles 80 repel
each other, thereby preventing agglutination of the mist particles
80. Accordingly, vaporization efficiency is further improved and
generation of the particles can be suppressed.
[0050] Although the film forming process is performed by heating in
the above embodiment, the film forming process may be performed by
using a plasma of the gas material. Further, the film forming
method in accordance with the embodiment of the present invention
may be applied to a case in which a film forming process is
performed in a batch furnace, e.g., a vertical heat treatment
furnace. In this case, a flow rate of the liquid material is
required to be larger than that in a single-wafer film forming
apparatus, but the present invention can be effectively applied
thereto due to improved vaporization efficiency.
[0051] Although the Ar gas is used as a gas for generation of nano
bubbles in the above embodiment, another nonreactive gas such as
nitrogen gas or an active gas such as O.sub.2 gas may be used
instead of Ar gas.
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