U.S. patent application number 10/960762 was filed with the patent office on 2005-06-09 for thermal processing apparatus and a thermal processing method.
Invention is credited to Asano, Takanobu, Fukushima, Hiroki, Nakao, Ken, Okumura, Katsuya.
Application Number | 20050121142 10/960762 |
Document ID | / |
Family ID | 34612842 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050121142 |
Kind Code |
A1 |
Nakao, Ken ; et al. |
June 9, 2005 |
Thermal processing apparatus and a thermal processing method
Abstract
Substrates having surfaces in a highly clean condition are
subjected to a thermal process in a heating furnace. In a thermal
processing apparatus for processing substrates by a predetermined
thermal process that heats the substrates by a heating means, the
substrates are held in a vertical position at horizontal intervals
in a reaction vessel. Cleaning liquids are supplied into the
reaction vessel to clean the substrates, and then the cleaning
liquids are drained away through a drain port, and then a process
gas is supplied into the reaction vessel to process the substrates
by a thermal process. The substrates having the cleaned clean
surfaces are subjected to the thermal process without being exposed
to the ambient atmosphere and can be satisfactorily processed by
the thermal process.
Inventors: |
Nakao, Ken; (Tokyo-To,
JP) ; Asano, Takanobu; (Tokyo-To, JP) ;
Fukushima, Hiroki; (Tokyo-To, JP) ; Okumura,
Katsuya; (Tokyo-To, JP) |
Correspondence
Address: |
Smith, Gambrell & Russell
Suite 800
1850 M Street, N.W.
Washington
DC
20036
US
|
Family ID: |
34612842 |
Appl. No.: |
10/960762 |
Filed: |
October 8, 2004 |
Current U.S.
Class: |
156/345.29 |
Current CPC
Class: |
H01L 21/67109 20130101;
H01L 21/67057 20130101; C23C 16/0227 20130101 |
Class at
Publication: |
156/345.29 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2003 |
JP |
2003-355147 |
Claims
What is claimed is:
1. A thermal processing apparatus for processing substrates by a
predetermined thermal process that heats the substrates by a
heating means, said thermal processing apparatus comprising: a
reaction vessel provided with a drain port; a cleaning liquid
supply means for supplying cleaning liquids into the reaction
vessel to clean the substrates after the substrates have been
loaded into the reaction vessel; and a process gas supply means for
supplying a process gas into the reaction vessel to process the
substrates by the thermal process after the cleaning liquids have
been drained away from the reaction vessel.
2. A thermal processing apparatus for processing substrates by a
predetermined thermal process that heats the substrates by an
external heating means, said thermal processing apparatus
comprising: a reaction vessel provided with a drain port; a lid for
closing an inlet opening of the reaction vessel; a substrate
holding device mounted on the lid to hold the substrates; a
carrying means for carrying the substrate holding device into and
carrying the same out from the processing vessel; a cleaning liquid
supply means for supplying cleaning liquids into the reaction
vessel to clean the substrates after the substrate holding device
holding the substrates has been loaded into the reaction vessel;
and a process gas supply means for supplying a process gas into the
reaction vessel to process the substrates by the thermal process
after the cleaning liquids have been drained away through the drain
port.
3. The thermal processing apparatus according to claim 2, wherein
the substrate holding device holds a plurality of substrates in a
vertical position at horizontal intervals.
4. The thermal processing apparatus according to claim 2, wherein
the cleaning liquid supply means is connected to the lid.
5. The thermal processing apparatus according to claim 2, wherein
the drain port is formed in the lid.
6. The thermal processing apparatus according to claim 1 or 2,
wherein the cleaning liquid supply means is used for filling up the
reaction vessel with the cleaning liquid, and the drain port is
closed while the cleaning liquid is supplied into the reaction
vessel.
7. A thermal processing method comprising the steps of: carrying
substrates into a reaction vessel; cleaning the substrates by
supplying cleaning liquids into the reaction vessel; draining away
the cleaning liquids from the reaction vessel; processing the
substrates by a thermal process by supplying process gases into the
reaction vessel and heating the interior of the reaction vessel
after the cleaning liquids have been drained away.
8. A thermal processing method that processes substrates by a
predetermined thermal process in a reaction vessel by heating the
substrates with an external heating means, said thermal processing
method comprising the steps of: loading a substrate holding device
with the substrates; loading the substrate holding device into the
reaction vessel and hermetically closing an inlet opening of the
reaction vessel by a lid; cleaning the substrate by supplying
cleaning liquids into the reaction vessel; draining away the
cleaning liquids from the reaction vessel; and processing the
substrates by the thermal process by supplying a process gas into
the reaction vessel and heating the interior of the reaction
vessel.
9. The thermal processing method according to claim 8, wherein the
step of loading the substrate holding device with the substrates
loads the substrates onto the substrate holding device such that
the substrates are held in a vertical position at horizontal
intervals.
10. The thermal processing method according to claim 8, wherein the
cleaning liquids are supplied through a discharge port formed in
the lid into the reaction vessel.
11. The thermal processing method according to claim 8, wherein the
cleaning liquids are drained away through a drain port formed in
the lid.
12. The thermal processing method according to claim 7 or 8,
wherein the step of supplying the cleaning liquids into the
reaction vessel fills up the reaction vessel with the cleaning
liquid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a thermal processing
apparatus and a thermal processing method for processing
substrates, such as semiconductor wafers, by a thermal process,
such as a CVD process.
[0003] 2. Description of the Related Art
[0004] A vertical thermal processing apparatus processes
semiconductor wafers (hereinafter referred to simply as "wafers")
in lots by a batch thermal process, such as a batch CVD process
(batch chemical vapor deposition process) for depositing a film on
wafers, a batch oxidation process or a batch diffusion process.
This thermal processing apparatus includes a heating furnace
provided with a vertical reaction tube having an open lower end. A
wafer boat holding a plurality wafers in a stack is mounted on a
lid for closing the open lower end of the reaction tube, the wafer
boat is loaded into the reaction tube by raising the lid, and
processes the wafers by a predetermined thermal process.
[0005] A wafer carrier holding wafers is delivered to process
stations in a factory or to a stocker. Wafers held in the wafer
carrier are contaminated with particles and organic matters and are
oxidized by natural oxidation by the oxidizing effect of the
atmosphere while the wafer carrier is transported. Therefore, it is
a usual procedure to clean wafers by a cleaning apparatus by
successive cleaning processes using some chemical solutions
including a hydrofluoric acid solution, to put the cleaned wafers
in a wafer carrier, and the wafer carrier is carried to the thermal
processing apparatus.
[0006] When the cleaning apparatus is installed in an area
separated from an area in which the thermal processing apparatus is
installed, the cleaned wafers are exposed to the atmosphere and
undergo natural oxidation after cleaning, and an oxide film is
formed on the wafers before the wafers are loaded into the reaction
vessel of the thermal processing apparatus. The adverse effect of
even a little oxide film formed by natural oxidation on the
characteristics of devices becomes more serious as the thickness of
thin films forming devices decreases progressively. Either organic
or inorganic impurities affect the characteristics of devices
adversely. For example, there is a tendency for the desired
thickness of a silicon oxide film as a gate oxide film for CMOS
devices to decrease to thicknesses below 10 nm. Under such
circumstances, it is required to reduce the amount of impurities
carried into the reaction vessel to the least possible extent; that
is it is required to keep the surfaces of wafers as clean as
possible.
[0007] FIGS. 8(a) and 8(b) show a thermal processing apparatus such
as proposed in Patent document 1 to meet such a requirement. This
prior art thermal processing apparatus has a wafer carrier handling
block B1 for receiving and sending out wafer carriers holding
wafers, a cleaning chamber B2 in which wafers taken out of the
wafer carrier are cleaned, and a film forming chamber B3 in which a
film is formed on the cleaned wafers. A wafer boat 11 for holding
wafers W in a stack is placed in the cleaning chamber B2, wafers W
are transferred successively from a wafer carrier to the wafer boat
11, the cleaning chamber B2 is sealed hermetically, and then a
chemical solution is jetted through vertically arranged nozzles 12
onto the wafers W. Then, pure water is jetted through other nozzles
12 onto the wafers W, IPA (isopropyl alcohol) is jetted through
nozzles onto the wafers W, and the wafer boat 11 is rotated by a
motor M to remove water drops remaining on the wafers W by
centrifugal force. Subsequently, the cleaning chamber B2 is filled
up with nitrogen gas, and then the wafer boat 11 is transferred to
an elevator disposed below the film forming chamber B3.
[0008] Patent document 1: JP-A 8-203852 (Paragraph 0028, II. 7 to
9, FIGS. 1, 7 and 9).
[0009] When the wafers W are processed by this prior art thermal
processing apparatus, the wafer W is exposed to the ambient
atmosphere while the cleaned wafers W are transferred from the
cleaning chamber B2 to the film forming chamber B3. Consequently,
for example, an oxide film is formed on the surface of the wafers W
by natural oxidation or impurities floating in the ambient
atmosphere, such as organic substances including hydrocarbons, and
moisture, adhere to the surfaces of the wafers W. If the wafers W
thus contaminated are subjected to, for example, a thermal process
for forming a silicon dioxide film, parts of a film corresponding
to the oxide film formed by natural oxidation are formed in a
thickness greater than that of other parts, a film having an
irregular thickness is formed, and it is possible that a
low-quality silicon dioxide film containing impurities is formed
and such a low-quality silicon dioxide film affects the
characteristics of devices formed on the wafers W adversely.
[0010] Since the thermal processing apparatus has the cleaning
chamber specially for the cleaning process and needs a wafer boat
handling mechanism, the thermal processing apparatus is inevitably
large and needs a large space for installation. There is a tendency
for the vertical thermal processing apparatus to use a reaction
vessel having a low height and capable of batch-processing an
increased number of wafers. Consequently, the pitches of wafers on
a wafer boat are progressively decreased. When the cleaning liquid
is jetted through the nozzles as mentioned in connection with FIG.
8(b), the cleaning liquid cannot be satisfactorily jetted onto the
surfaces of the wafers arranged at short pitches. Consequently, the
wafers cannot be satisfactorily cleaned and it is possible that the
oxide film formed by natural oxidation remains on the surface of
the cleaned wafers.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in view of those
problems and it is therefore an object of the present invention to
provide a thermal processing apparatus and a thermal processing
method capable of keeping the surfaces of substrates in a highly
clean condition in processing the substrates by a thermal process
in a heating furnace.
[0012] A thermal processing apparatus in a first aspect of the
present invention for processing substrates by a predetermined
thermal process that heats the substrates by a heating means
includes: a reaction vessel provided with a drain port; a cleaning
liquid supply means for supplying cleaning liquids into the
reaction vessel to clean the substrates after the substrates have
been loaded into the reaction vessel; and a process gas supply
means for supplying a process gas into the reaction vessel to
process the substrates by the thermal process after the cleaning
liquids have been drained away from the reaction vessel.
[0013] A thermal processing apparatus in a second aspect of the
present invention for processing substrates by a predetermined
thermal process that heats the substrates by an external heating
means includes: a reaction vessel provided with a drain port; a lid
for closing an inlet opening of the reaction vessel; a substrate
holding device mounted on the lid to hold the substrates; a
carrying means for carrying the substrate holding device into and
carrying the same out from the processing vessel; a cleaning liquid
supply means for supplying cleaning liquids into the reaction
vessel to clean the substrates after the substrate holding device
holding the substrates has been loaded into the reaction vessel;
and a process gas supply means for supplying a process gas into the
reaction vessel to process the substrates by the thermal process
after the cleaning liquids have been drained away through the drain
port.
[0014] The substrate holding device may hold a plurality of
substrates in a vertical position at horizontal intervals. The
cleaning liquid supply means may be connected to the lid and/or the
drain port may be formed in the lid. The cleaning liquid supply
means may be used for filling up the reaction vessel with the
cleaning liquid, and the drain port may be closed while the
cleaning liquid is supplied into the reaction vessel.
[0015] A thermal processing method in a third aspect of the present
invention includes the steps of: carrying substrates into a
reaction vessel; cleaning the substrates by supplying cleaning
liquids into the reaction vessel; draining away the cleaning
liquids from the reaction vessel; processing the substrates by a
thermal process by supplying process gases into the reaction vessel
and heating the interior of the reaction vessel after the cleaning
liquids have been drained away.
[0016] A thermal processing method in a fourth aspect of the
present invention that processes substrates by a predetermined
thermal process in a reaction vessel by heating the substrates with
an external heating means includes the steps of: loading a
substrate holding device with the substrates; loading the substrate
holding device into the reaction vessel and hermetically closing an
loading opening of the reaction vessel by a lid; cleaning the
substrate by supplying cleaning liquids into the reaction vessel;
draining away the cleaning liquids from the reaction vessel; and
processing the substrates by the thermal process by supplying a
process gas into the reaction vessel and heating the interior of
the reaction vessel.
[0017] The step of loading the substrate holding device with the
substrates may load the substrates onto the substrate holding
device such that the substrates are held in a vertical position at
horizontal intervals. The cleaning liquids may be supplied through
a discharge port formed in the lid into the reaction vessel. The
cleaning liquids may be drained away through a drain port formed in
the lid. The step of supplying the cleaning liquids into the
reaction vessel may fill up the reaction vessel with the cleaning
liquid.
[0018] The thermal processing apparatus of the present invention
processes the substrates in the reaction vessel by the thermal
process after cleaning the substrates with the cleaning liquids in
the reaction vessel. Thus, the cleaned substrates are not exposed
to the ambient atmosphere, the substrate having the clean surfaces
cleaned by the cleaning process can be subjected to the thermal
process. Consequently, the substrates can be satisfactorily
processed by the thermal process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a plan view of a thermal processing apparatus in a
preferred embodiment according to the present invention;
[0020] FIG. 2 is a longitudinal sectional view of the thermal
processing apparatus embodying the present invention;
[0021] FIG. 3 is a longitudinal sectional view of a heating furnace
included in the thermal processing apparatus;
[0022] FIG. 4 is a plan view of the heating furnace of the thermal
processing apparatus;
[0023] FIG. 5 is a perspective view of a substrate holding device
included in the heating furnace;
[0024] FIG. 6 is a perspective view of a position changing device
included in the thermal processing apparatus;
[0025] FIG. 7 is a view of assistance in explaining a method of
supplying a cleaning liquid into a reaction vessel included in the
thermal processing apparatus; and
[0026] FIG. 8 is a view of assistance in explaining a prior art
thermal processing apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The general configuration of a thermal processing apparatus
in a preferred embodiment according to the present invention will
be described with reference to FIGS. 1 and 2 prior to the
description of the thermal processing apparatus. The thermal
processing apparatus has a transfer port A1 for receiving and
sending out a wafer carrier C holding, for example, fifteen wafers
W, namely, substrates, in a stack, and a loading area A2 where
wafers W are loaded into a heating furnace for carrying out a
thermal process to subject the wafers W to the thermal process. The
transfer port A1 and the loading area A2 are separated by a
partition wall 20 so as to isolate the spaces in the transfer port
A1 and the loading area A2 from each other.
[0028] Installed in the transfer port A1 are a first table 21 for
supporting a wafer carrier C received from an external apparatus, a
second table 22 for supporting a wafer carrier C while wafers W
contained in the wafer carrier C are carried into the loading area
A2, and a carrier carrying mechanism 23 for carrying a wafer
carrier C between the tables 21 and 22. The wafer carrier C is
provided with a lid. The wafer carrier C is sealed hermetically to
prevent exposing the wafers W held therein to the atmosphere when
the wafers W are carried from the preceding process to the thermal
process and from the thermal process to the succeeding process. A
lid operating mechanism combined with a door 24 closing an opening
formed in the partition wall 20 removes the lid to expose the
interior of the wafer carrier C to an atmosphere in the loading
area A2.
[0029] A side flow of clean air is produced in the loading area A2.
Installed in the loading area A2 are a first carrying device 3 and
a second carrying device 4 for carrying a wafer W along
predetermined paths, respectively, a heating furnace 5 in which
wafers W are subjected to the thermal process, and a position
changing deice 6 for changing the position of a wafer between a
horizontal position and a vertical position.
[0030] The first carrying device 3 has a carrier base 32, an arm
unit 31 including a plurality of arms arranged at predetermined
vertical intervals and supported on the carrier base 32 so as to be
horizontally movable to support a peripheral part of each of wafers
W from below the wafer, and a driving system 33 for moving the
carrier base 32 horizontally, i.e., in directions along the width
of the thermal processing apparatus, moving the carrier base 32
vertically and turning the carrier base 32 about a vertical axis.
The first carrying device 3 carries wafers W between a wafer
carrier C and a position changing device 6.
[0031] The second carrying device 4 has a carrier base 42, an arm
unit 41 including a plurality of longitudinally arranged pairs of
arms supported for longitudinal movement on the carrier base 42 to
support wafers W set in a vertical position by the position
changing device 6 by their peripheral parts, i.e., parts outside
their device forming regions, and a driving system 43 for moving
the carrier base 42 horizontally, i.e., in directions along the
width of the thermal processing apparatus, and moving the carrier
base 42 vertically. The second carrying device 4 carries wafers W
between the position changing device 6 and the heating furnace
5.
[0032] The heating furnace 5 will be described with reference to
FIGS. 3 and 4. Referring to FIGS. 4 and 5, a reaction vessel 51 is
placed in a furnace body 50. The reaction vessel 51 has, for
example, a cylindrical shape, is formed of a nonmetallic material,
such as quartz or a ceramic material, and defines a heating space
in which wafers W are placed for the thermal process. The reaction
vessel 51 has an open lower end 53 defining an opening through
which wafers W are carried into and out of the reaction vessel 51.
A lid 7 is disposed under the open lower end 53. The lid 7 is
vertically movable to close and open the open lower end 53 of the
reaction vessel 51. At least the surface of the lid d7 is formed of
a nonmetallic material, such as quartz or a ceramic material. A
wafer boat 71 is supported by a shaft 72 on the lid 7. The wafer
boat 71 is capable of holding a plurality of wafers W, for example,
twenty-five to fifty wafers W, in a vertical position in s
horizontal arrangement. The lid 7 is raised by a boat elevator 73
included in an elevator unit to load wafers W held on the wafer
boat 71 into the reaction vessel 51 and to close the open lower end
53 of the reaction vessel 51 so as to seal the reaction vessel 51
hermetically. A flange 51a is formed on the lower end of the
reaction vessel 51, and an O ring 51b, i.e., a sealing member
formed of a resin, is placed on the lid 7. When the lid 7
supporting the wafer boat 71 is raised and brought into contact
with the flange 51a, the gap between the lid 7 and the open lower
end 53 is sealed hermetically by the O ring 51b.
[0033] More specifically, as shown in FIG. 5, the wafer boat 71
includes a horizontal plate 74, a pair of vertical end plates 75
set on the horizontal plate 74 so as to be opposed to each other,
for example, three support rods 76, i.e., substrate support
members, are extended between the opposite end plates 75. The
support rods 76 are provided with grooves 76a formed at
longitudinal intervals. The second carrying device 4 brings wafers
W from above the wafer boat 71 and inserts peripheral parts of the
wafers W in the grooves 76a to hold the wafers W by the wafer boat
71. If necessary, the horizontal plate 74 and the end plates 75 may
be provided with openings 77 to enable process gases and cleaning
liquids to flow across the horizontal plate 74 and the end plates
75. The openings 77 enable the process gases or the cleaning
liquids to flow smoothly when wafers W are processed. Consequently,
the process gases and the cleaning liquids can be uniformly
supplied into spaces between the wafers W.
[0034] Referring to FIGS. 3 and 4 again, a heater 54, such as a
carbon wire heater, i.e., heating means, is disposed, for example,
in a space between the furnace body 50 and the reaction vessel 51.
A carbon wire heater is preferable because the carbon wire heater
is capable of heating a process atmosphere in the reaction vessel
51 at a high heating rate of, for example, 100.degree. C./min. The
carbon wire heater may be such a heater formed by sealing a carbon
wire formed by twisting a plurality of carbon fiber strands in a
ceramic case, such as a transparent quartz tube having an outside
diameter of ten-odd millimeters. The carbon wire heater is formed
vertically inside the furnace body 50. The heating element of the
heater is not limited to the carbon wire and may be a metal wire,
such as an iron/nickel/chromium alloy wire.
[0035] A process gas supply pipe 8, i.e., process gas supply means,
is connected to a lower part of the side wall of the reaction
vessel 51 so as to open downward. The process gas supply pipe 8 is
connected by a gas supply line 81, such as gas supply pipes, to
process gas sources, i.e., an oxygen source 82 and a steam source
83 in this embodiment. Indicated at V1 to V3 are valves (gas supply
valves. Nitrogen gas supply pipes 84 for carrying dry nitrogen gas,
i.e., inert gas supply pipes for carrying a dry inert gas, are
connected to a lower part of the side wall of the reaction vessel
51. The nitrogen gas supply pipes 84 rise from a lower part to a
middle part of the interior of the reaction vessel 51, and extend
horizontally along the direction of arrangement of the wafers W
held on the wafer boat 71 respectively on the opposite sides of the
arrangement of the wafers W. Outer ends of the nitrogen gas supply
pipes 84 are connected to a valve V4 connected to a nitrogen gas
source 85. The nitrogen gas supply pipes 84 are provided with
blowing holes 84a. Nitrogen gas is blown through the blowing holes
84a against the wafers W held on the wafer boat 71 after cleaning
the wafers W with cleaning liquids to dry the wafers W. A plurality
of nitrogen gas supply pipes 84 may be arranged vertically in a
range corresponding to the height of the wafers W. When the
nitrogen gas supply pipes 84 are arranged so, nitrogen gas can be
more surely blown against the surfaces of the wafers W. The
nitrogen gas supply pipes 84 may be vertically movable. A discharge
line 86, such as a discharge pipe, is connected to a discharge port
52 formed in an upper part of the reaction vessel 51. The discharge
line 86 is connected to a valve V5 connected to a discharge device
87 to discharge gases contained in the reaction vessel 51 from the
reaction vessel 51 by the discharge device 87. A branch line 84a
branched from the nitrogen gas supply line 84 is connected through
a valve V6 to the discharge line 86. The valve V5 is closed and the
valve V6 is opened to supply nitrogen gas from an upper part of the
reaction vessel 51 into the reaction vessel 51.
[0036] A cleaning liquid supply nozzle 9, namely, a cleaning liquid
supply means, is set, for example, vertically so as to project from
the upper surface of the lid 7. The cleaning liquid supply nozzle 9
is connected to a hydrofluoric acid solution source 92, a pure
water source 93 and an IPA (isopropyl alcohol) source 94 by a
cleaning liquid supply line 91, such as a cleaning liquid supply
pipe, extended in the boar elevator 73. The hydrofluoric acid
solution source 92 supplies, for example, a 10% by weight
hydrofluoric acid solution. Indicated at V7 to V9 are valves
(cleaning liquid supply valves), and P1 to P3 are pumps. The lid 7
is provided with a drain port 95. The drain port 95 is connected to
a drain tank, not shown, by a drain line 96, namely, drain pipe. A
valve V10 (drain valve) is placed in the drain line 96 to open and
close the drain port 95.
[0037] The position changing device 6 for changing the position of
wafers W mentioned in connection with FIGS. 1 and 2 will be
described with reference to FIG. 6. A swivel box 61 has an open
front side. Support rails 62 for supporting wafers W thereon are
arranged vertically at intervals corresponding to the thickness of
the wafers W on the inner surfaces of the side walls of the swivel
box 61. The wafers W are inserted in spaces between the support
rails 62 so as to be supported on the support rails 62 in the
swivel box 61. A horizontal shaft 64 is attached to lower back
parts of the side walls of the swivel box 61. The shaft 64 has a
base end connected to a turning mechanism 65. The turning mechanism
65 turns the shaft 64 in opposite directions through 900 about a
horizontal axis to swivel the swivel box 61 forward and backward so
that the wafers W contained in the swivel box 61 are turned between
a horizontal position and a vertical position.
[0038] The swivel box 61 has an open back side 61a. A lifting
device 66 provided with a lifting table 67 is disposed such that
the lifting table 67 is opposite to the open back side 61a of the
swivel box 61 when the swivel box 61 is set in a horizontal
position in which the wafers W held in the swivel box 61 are set in
a vertical position. The lifting table 67 moves through the open
back side 61a into the swivel box 61 when the lifting table 67 of
the lifting device 66 is raised. As shown in FIG. 6(b), the lifting
table 67 is provided in its upper surface with grooves 67a for
receiving peripheral parts of the wafers W. The edges of the
grooves 67a are chamfered. The lifting table 67 is connected by a
shaft 69 to a lifting mechanism 68. The lifting mechanism 68 raises
the lifting table 67 to lift up the wafers W contained in the
swivel box 61. Then, the second carrying device 4 holds the lifted
wafers W to receive the wafers W from the lifting table 67. Thus
the wafers W can be transferred from the lifting device 66 to the
second carrying device 66 and vice versa.
[0039] The thermal process for processing wafers W by the thermal
processing apparatus will be described. An oxidation process, as a
thermal process, for forming a silicon dioxide film on surfaces of
wafers W will be described by way of example. Referring to FIGS. 1
and 2, a waver carrier C is delivered to the first table 21 of the
transfer port A1 by an automatic carrying robot. The carrier
carrying mechanism 23 carries the wafer carrier C to, for example,
a carrier storage unit, not shown, for temporary storage. The
carrier carrying mechanism 23 carries the wafer carrier C from the
carrier storage unit to the second table 22. The lid of the wafer
carrier C is removed after the wafer carrier C has been pressed
against the partition wall 20, and then the door 24 is opened.
[0040] Subsequently, the arm unit 31 of the first carrying device 3
advances into the wafer carrier C, takes out a plurality wafers W,
for example, five wafers W, simultaneously from the wafer carrier C
and carries the wafers W into the swivel box 61 set in a vertical
position. The arm unit 31 repeats this operation to transfer all
the wafers W contained in the wafer carrier C to the swivel box 61.
Then, the turning mechanism 65 turns the shaft 64 to swivel the
swivel box 61 through 90.degree. to set the wafers W held in the
swivel box 61 in a vertical position. Then, the arm unit 41 of the
second carrying device 4 is moved to a position above the swivel
box 61, holds all the wafers W, for example, fifteen wafers W,
lifted up from the swivel box 61 by the lifting device 66, and
carries the wafers W to loads the same on the wafer boat 71. The
arm unit 41 repeats this operation to load the wafer boat 71 with a
predetermined number of wafers W. After the wafer boat 71 has been
thus fully loaded with the wafers W, the second carrying device 4
is retracted.
[0041] Subsequently, the boat elevator 73 is raised to load the
wafer boat 71 holding the wafers W into the reaction vessel 51, and
the open lower end 53 of the reaction vessel 51 is closed by lid 7
to seal the reaction vessel 51 hermetically. Then, the valves V5
and V7 are opened, and the hydrofluoric acid solution, namely, a
cleaning liquid, is supplied through the cleaning liquid supply
nozzle 9 into the reaction vessel 51 to fill up the reaction vessel
51 with the hydrofluoric acid solution as shown in FIG. 7(a). Then,
the hydrofluoric acid solution contained in the reaction vessel 51
is heated by the heater 54 at a temperature, such as 80.degree. C.,
at which the hydrofluoric acid solution will not boil and
interaction between the hydrofluoric acid solution and oxide films
formed by natural oxidation on the wafers W is promoted. A state
where the reaction vessel 51 is filled up with the cleaning liquid
is a state where the level of the cleaning liquid is higher than
that of the upper ends of the wafers W. The oxide films formed by
natural oxidation on the surfaces of the wafers W and impurities
adhering to the surfaces of the wafers W can be removed by
immersing the wafers W in the hydrofluoric acid solution for a
predetermined time. Then, the valves V7 and V5 are closed, and the
valves V6 and V10 are opened to drain the hydrofluoric acid
solution from the reaction vessel 51 and to supply nitrogen gas
into the reaction vessel 51. After the hydrofluoric acid solution
has been completely drained away, the valves V6 and V10 are closed,
and the valves V8 and V5 are opened to fill up the reaction vessel
51 with pure water, namely, cleaning liquid, by supplying pure
water through the cleaning liquid supply nozzle 9 into the reaction
vessel 51. Thus the hydrofluoric acid solution remaining on the
wafers W is rinsed away. Then, the valves V8 and V5 are closed and
the valves V6 and V10 are opened to drain the pure water from the
reaction vessel 51. Then, the valves V6 and V10 are closed, and the
valves V5 and V9 are opened to fill up the reaction vessel 51 with
IPA, namely, cleaning liquid, by supplying IPA trough the cleaning
liquid supply nozzle 9 into the reaction vessel 51. Then, the
valves V9 and V5 are closed, and the valves V6 and V10 are opened
to drain the IPA away from the reaction vessel 51. The IPA reduces
the surface tension of water droplets (droplets of the pure water)
adhering to the surfaces of the wafers W. Consequently, the water
droplets flow along the surfaces of the wafers W held in a vertical
position and drop away from the wafers W.
[0042] The valves V5 to V10 are opened and closed on the basis of a
sequence program stored in a controller, not shown, to supply
hydrofluoric acid solution, pure water and IPA sequentially into
the reaction vessel 51 and to supply and to stop supplying nitrogen
gas into the reaction vessel 51 for the cleaning process. The
valves V1 to V3 and V5 may be opened and closed to supply and to
stop supplying the process gases and a purge gas for the thermal
process, which will be described later, on the basis of a sequence
program stored in the controller. IPA may be supplied in either a
liquid or a vapor. An IPA vapor supply line may be connected to the
lid 7 when IPA is supplied in a vapor.
[0043] Then, the valve V5 is opened, the valves V6 to V9 are
closed, and the valve V4 is opened to supply nitrogen gas, namely,
a dry gas, through the nitrogen gas supply pipes 84 into the
reaction vessel 51 for a drying operation. As mentioned above, the
nitrogen gas supply pipes 84 are provided with the blowing holes
84a corresponding to the wafers W. Nitrogen gas is blown against
the wafers W to dry the wafers W quickly and to purge the reaction
vessel 51 with the nitrogen gas. After the drying operation has
been continued for a predetermined time, the valve V4 is closed to
stop supplying nitrogen gas. The valve V5 in the discharge line 86
is kept open while nitrogen gas is supplied into the reaction
vessel 51 and is closed when nitrogen gas supply is stopped.
[0044] Then, the interior of the reaction vessel 51 is heated by
the heater 54 at a process temperature of, for example,
1000.degree. C.
[0045] A process gas, a mixed gas containing, for example, oxygen
gas and steam, is supplied through the gas supply pipe and the
process gas supply pipe 8 into the reaction vessel, while the
discharge device 87 discharges gases contained in the reaction
vessel 51 from the reaction vessel 51 so as to keep the atmosphere
in the reaction vessel 51 at a predetermined pressure, such as a
slightly reduced pressure. Silicon in the surface layers of the
wafers W is oxidized to form silicon diocese films on the wafers W,
respectively, by the thermal process.
[0046] After continuing the thermal process for a predetermined
time, the valves V1 to V3 are closed to stop supplying the process
gas. The valve V4 is closed after purging the reaction vessel 51
with nitrogen gas, the boat elevator 73 is lowered to a
predetermined lower position, and the lid 7 is opened to release
the reaction vessel 51 from an airtight state. Then, the wafer boat
71 holding the wafers W is unloaded from the reaction vessel 51.
Then the foregoing operation for transferring the wafers W from the
wafer carrier C to the wafer boat 71 is reversed to return the
wafers W to the wafer carrier C; that is, the second carrying deice
4 receives the wafers W from the wafer boat 71 and carries the
wafers W into the swivel box 61, the swivel box 61 is turned
forward to set the swivel box 61 in a vertical position so that the
wafers W are held in a horizontal position in the swivel box 61,
and then the first carrying device 3 transfers the wafers W from
the swivel box 61 to the wafer carrier C. Thus the thermal process
is accomplished.
[0047] The thermal processing apparatus in this embodiment cleans
the wafers W by supplying the cleaning liquids into the heating
furnace 5 by the cleaning liquid supply system, and supplies the
process gas into the heating furnace 5 to process the wafers W by
the thermal process. Therefore, the cleaned wafers W are not
exposed to the ambient atmosphere and silicon dioxide films can be
formed on the clean surfaces of the cleaned wafers W by the thermal
process. Therefore, the silicon dioxide films formed on the
surfaces of the wafers by the thermal process are of very high
quality not containing any oxide film formed by natural oxidation
at all or scarcely containing such an oxide film. Consequently,
high-quality thin gate oxide films can be formed and satisfactory
semiconductor devices can be fabricated on those wafers W. Nitrogen
gas supplied into the reaction vessel 51 works for both drying the
cleaned wafers W and purging the reaction vessel 51 to keep the
surfaces of the wafers W clean. Therefore, the thermal processing
apparatus is simple in construction and is able to operate at a low
operation cost because a nitrogen gas atmosphere does not need to
be created in the loading area A2.
[0048] Although the oxidation process has been described by way of
example, the thermal processing apparatus may be used for carrying
out a CVD process. If films deposited on the inner surfaces of the
reaction vessel 51 and the surfaces of the wafer boat 71 and the
lid 7 during the CVD process are those of substances that can be
removed by the cleaning liquid, both cleaning the interior of the
reaction vessel 51 and cleaning the wafers W can be achieved
simultaneously. An ammonium chloride film is a film that may be
possibly deposited. An ammonium chloride film may be deposited as a
by-product of process, such as a silicon nitride film forming
process that forms a silicon nitride film (Si.sub.3N.sub.4 film)
through the interaction of a silane gas, such as a dichlorosilane
gas, and ammonia gas.
[0049] In the foregoing embodiment, the wafers W held in a vertical
position on the wafer boat 71 are subjected to the cleaning process
and the thermal process. Therefore, the cleaning liquid adheres
scarcely to the vertical surfaces by surface tension, the cleaning
liquid drips off the wafers W by gravity and the cleaning liquid
can be quickly removed from the surfaces of the wafers W to drain
the cleaning liquid from the reaction vessel 51. Consequently,
formation of water marks with the cleaning liquid, particularly
with IPA, can be suppressed when the wafers W are dried by using
nitrogen gas. The drying gas is not limited to nitrogen gas. For
example, high-temperature, high-pressure, dry air having a low
oxygen concentration may be used as the drying gas. The use of such
dry air is more effective than nitrogen gas in suppressing the
formation of water marks.
[0050] When the wafers W held in a vertical position are subjected
to the thermal process, the spaces between the wafers W extend
vertically in which the process gas flows from the bottom toward
the top of the reaction vessel 51 and hence the process gas is able
to flow smoothly upward through the spaces between the wafers W.
Since the wafers W are held in a vertical position that facilitate
the flow of the process gas in the reaction vessel 51, the surfaces
of the wafers W can be uniformly exposed to the process gas.
According to the present invention, wafers W may be processed by
the thermal process in either a batch processing mode as mentioned
above or a single-wafer processing mode. Although the effect
available when wafers W are held in a vertical position, wafers W
held in a horizontal position may be processed.
[0051] According to the present invention, the thermal processing
apparatus does not need necessarily provided with a heater capable
of heating the interior of the reaction vessel 51 at a high heating
rate of 100.degree. C./min as the heater 54. However, when the
cleaning process and the thermal process are carried out in the
same chamber, namely, the processing chamber in the heating furnace
5, it is desirable to keep a low temperature so that the cleaning
liquid may not boil during the cleaning process and to keep a high
temperature such as 1000.degree. C., to promote the reaction of the
process gas during the thermal process. Since the difference
between those temperatures respectively for the cleaning process
and the thermal process is large, the number of cycles of the
thermal process can be increased and the throughput of the thermal
processing apparatus can be increased by employing a high-capacity
heater as the heater 54 to curtail time necessary for raising the
temperature.
[0052] Moreover, since the present invention subjects the wafers to
the thermal process after cleaning, an open wafer carrier may be
used instead of the closed wafer carrier C. A wafer carrier C that
holds wafers W in a vertical position may be used.
* * * * *