U.S. patent application number 11/252212 was filed with the patent office on 2006-04-27 for processing method and processing apparatus.
Invention is credited to Glenn Gale.
Application Number | 20060088959 11/252212 |
Document ID | / |
Family ID | 36206685 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060088959 |
Kind Code |
A1 |
Gale; Glenn |
April 27, 2006 |
Processing method and processing apparatus
Abstract
A processing method of subjecting at least two stacked films,
which comprise a first film and a second film of a target object to
be processed, to a removing process by wet etching comprises
bringing a first process liquid into contact with the first film of
the target object, thereby etching the first film, determining
whether the first film has been removed or not, switching the first
process liquid to a second process liquid differing in a condition
from the first process liquid when it has been determined that the
first film has been removed, and bringing the second process liquid
into contact with the second film, thereby etching the second
film.
Inventors: |
Gale; Glenn; (Tokyo,
JP) |
Correspondence
Address: |
Smith, Gambrell & Russell
Suite 800
1850 M Street, N.W.
Washington
DC
20036
US
|
Family ID: |
36206685 |
Appl. No.: |
11/252212 |
Filed: |
October 18, 2005 |
Current U.S.
Class: |
438/142 ;
257/E21.193; 257/E21.251; 257/E21.528 |
Current CPC
Class: |
H01L 21/31111 20130101;
H01L 29/513 20130101; H01L 21/28167 20130101; H01L 21/6708
20130101; H01L 22/26 20130101; H01L 29/517 20130101; H01L 21/67086
20130101 |
Class at
Publication: |
438/142 |
International
Class: |
H01L 21/8232 20060101
H01L021/8232 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2004 |
JP |
JP 2004-304471 |
Claims
1. A processing method of subjecting at least two stacked films,
which comprise a first film and a second film of a target object to
be processed, to a removing process by wet etching, the method
comprising: bringing a first process liquid into contact with the
first film of the target object, thereby etching the first film;
determining whether the first film has been removed or not;
switching the first process liquid to a second process liquid
differing from the first process liquid in a condition when it is
determined that the first film has been removed; and bringing the
second process liquid into contact with the second film, thereby
etching the second film.
2. The processing method according to claim 1, wherein the first
process liquid dissolves both the first film and the second
film.
3. The processing method according to claim 1, wherein the
determining whether the first film has been removed or not is
performed by measuring the concentration of a prescribed substance
in the first process liquid, which has been brought into contact
with the target object.
4. The processing method according to claim 3, wherein it is
determined that the first film has been removed at the time when
the amount of the component of the first film in the first process
liquid or the rate of increase in the component of the first film
in the first process liquid have become lower than the set
values.
5. The processing method according to claim 3, wherein it is
determined that the first film has been removed at the time when
the amount of the component of the second film in the first process
liquid has increased to exceed the set value.
6. The processing method according to claim 1, wherein the first
film is a high dielectric constant material, the second film is an
interfacial film of silicon oxide (SiO.sub.2) or silicon oxynitride
(SiO.sub.xN.sub.y), and the target object comprises a structure
including a gate insulating film and a gate electrode disposed on a
silicon substrate in this order wherein the gate insulating film
has a two-layer structure consisting of a second film formed on a
silicon substrate and the first film formed on the second film.
7. The processing method according to claim 1, wherein the first
process liquid and the second process liquid differ from each other
in chemical species.
8. The processing method according to claim 1, wherein the first
process liquid and the second process liquid are formed of chemical
liquids of the same kind and differ from each other in the
concentration of the component and/or the pH value.
9. The processing method according to claim 1, wherein the first
process liquid and the second process liquid are formed of chemical
liquids of the same kind and differ from each other in
temperature.
10. A processing method of subjecting at least two stacked films,
which comprise a first film and a second film of a target object,
to a removing process by wet etching, the method comprising:
Bringing a first process liquid into contact with the first film of
the target object, the first process liquid being capable of
etching the first film with a high etching selectivity relative to
the second film; determining whether the first film has been
removed or not; switching the first process liquid to a second
process liquid differing from the first process liquid in a
condition and capable of etching the second film with a high
selectivity relative to the first film when it has been determined
that the first film has been removed; and bringing the second
process liquid into contact with the second film, thereby etching
the second film.
11. The processing method according to claim 10, wherein the first
process liquid dissolves both the first film and the second
film.
12. The processing method according to claim 10, wherein the
determining whether the first film has been removed or not is
performed by measuring the concentration of a prescribed substance
in the first process liquid, which has been brought into contact
with the target object.
13. The processing method according to claim 12, wherein it is
determined that the first film has been removed at the time when
the amount of the component of the first film in the first process
liquid or the rate of increase in the component of the first film
in the first process liquid have become lower than the set
values.
14. The processing method according to claim 12, wherein it is
determined that the first film has been removed at the time when
the amount of the component of the second film in the first process
liquid has increased to exceed the set value.
15. The processing method according to claim 10, wherein the first
film is a high dielectric constant material, the second film is an
interfacial film of silicon oxide (SiO.sub.2) or silicon oxynitride
(SiO.sub.xN.sub.y), and the target object comprises a structure
including a gate insulating film and a gate electrode disposed on a
silicon substrate in this order wherein the gate insulting film has
a two-layer structure consisting of a second film formed on a
silicon substrate and the first film formed on the second film.
16. The processing method according to claim 10, wherein the first
process liquid and the second process liquid differ from each other
in chemical species.
17. The processing method according to claim 10, wherein the first
process liquid and the second process liquid are formed of chemical
liquids of the same kind and differ from each other in the
concentration of the component and/or the pH value.
18. The processing method according to claim 10, wherein the first
process liquid and the second process liquid are formed of chemical
liquids of the same kind and differ from each other in
temperature.
19. A processing apparatus for removing by a wet etching at least
two stacked films, which comprise a first film and a second film of
a target object to be processed, the apparatus comprising: a
housing section housing the target object; a first process liquid
supply section for supplying the first process liquid onto the
target object housed in the housing section, thereby bringing the
first process liquid into contact with the first film for
proceeding the etching of the first film; a second process liquid
supply section for supplying the second process liquid differing in
the condition from the first process liquid onto the target object
housed in the housing section, thereby bringing the second process
liquid into contact with the second film for proceeding the etching
of the second film; a detecting section for detecting the removed
state of the first film; a switching section for switching the
process liquid that is brought into contact with the target object
from the first process liquid to the second process liquid; and a
control section for determining whether the first film has been
removed on the basis of the detected value in the detecting section
and, when it has been determined that the first film has been
removed, for transmitting to the switching section an instruction
to switch the process liquid that is brought into contact with the
target object from the first process liquid to the second process
liquid.
20. The processing apparatus according to claim 19, wherein the
first process liquid is capable of etching the first film with a
high etching selectivity relative to the second film, and the
second process liquid is capable of etching the second film with a
high etching selectivity relative to the first film.
21. The processing apparatus according to claim 19, wherein the
detecting section measures the concentration of a prescribed
substance in the first process liquid in contact with the target
object.
22. The processing apparatus according to claim 19, wherein the
control section determines that the first film has been removed at
the time when the amount of the component of the first film in the
first process liquid, which is detected by the detecting section,
or the rate of increase in the component of the first film in the
first process liquid, which is detected by the detecting section,
has been made smaller or lower that the set value.
23. The processing apparatus according to claim 21, wherein the
control section determines that the first film has been removed at
the time when the amount of the component of the second film in the
first process liquid, which is detected by the detecting section,
or the rate of increase in the component of the second film in the
first process liquid, which is detected by the detecting section,
has been made larger or higher that the set value.
24. The processing apparatus according to claim 19, wherein the
first process liquid supply section and the second process liquid
supply section supply the first process liquid and the second
process liquid, respectively, onto the surface of the target
object.
25. The processing apparatus according to claim 19, wherein the
first process liquid supply section and the second process liquid
supply section supply the first process liquid and the second
process liquid, respectively, into the housing section such that
the target object housed in the housing section is dipped in the
first process liquid and the second process liquid,
respectively.
26. A computer program including a soft ware which, when executed,
causes the computer to control a processing apparatus for removing
by a wet etching at least two stacked films, which comprise a first
film and a second film of a target object to be processed, wherein
the soft ware causes the computer to execute the operations of:
bringing a first process liquid into contact with the first film of
the target object, thereby etching the first film; determining
whether the first film has been removed or not; switching the first
process liquid to a second process liquid differing in a condition
from the first process liquid when it has been determined that the
first film has been removed; and bringing the second process liquid
into contact with the second film, thereby etching the second
film.
27. A storage medium that can be read by a computer, the storage
medium including a soft ware which, when executed, causes the
computer to control a processing apparatus for removing by a wet
etching at least two stacked films, which comprise a first film and
a second film of a target object to be processed, wherein the soft
ware causes the computer to execute the operations of: bringing a
first process liquid into contact with the first film of the target
object, thereby etching the first film; determining whether the
first film has been removed or not; switching the first process
liquid to a second process liquid differing in a condition from the
first process liquid when it has been determined that the first
film has been removed; and bringing the second process liquid into
contact with the second film, thereby etching the second film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a processing method and a
processing apparatus for removing by a wet etching a stacked films
formed of at least two films which comprise a first film and a
second film of a target object to be processed such as a
semiconductor wafer, and a computer program, and a computer
readable storage medium.
[0003] 2. Description of the Related Art
[0004] In recent years, the design rule of the semiconductor
elements constituting an LSI is being made finer and finer in
compliance with the demands for further improvements in the degree
of integration and the operating speed of the LSI. In this
connection, the gate insulating film is required to be made thinner
in the MOS device.
[0005] Conventionally, a silicon oxide film or a silicon oxynitride
film has been used for forming the gate insulating film. In order
to obtain a desired performance by using the gate insulating film
formed of the material noted above, it is necessary to form the
gate insulating film very thin. However, if the gate insulating
film is made thinner, the gate leak current is increased, thereby
increasing the operating power.
[0006] Under the circumstances, a so-called "high-k material" such
as HfO.sub.2, which has a relative dielectric constant higher than
that of the conventional material, attracts attentions. Such being
the situation, a gate insulating film of a two-layer structure
prepared by forming a high-k material film on an interfacial oxide
film consisting of a very thin SiO.sub.2 film has come to be used
in place of the conventional gate insulating film formed of a
silicon oxide film or a silicon oxynitride film.
[0007] After formation of the gate insulating film of the two-layer
structure, a polysilicon film or a metal film is formed on the gate
insulating film, followed by removing the excess portion of the
polysilicon film or the metal film by means of a RIE etching
method, thereby forming a gate electrode. It should be noted in
this connection, that, after formation of the gate electrode, it is
necessary to remove selectively the remaining interfacial oxide
film and the high-k material film in order to expose the source
region and the drain region of the silicon substrate.
[0008] In this case, it is necessary to remove selectively the
interfacial oxide film (SiO.sub.2 film) and the high-k material
film, for example, HfO.sub.2 film by means of the wet etching
because a damage is done to the silicon substrate in the case of
employing the RIE etching method. In the case of employing the wet
etching method, however, serious problems are brought about as
pointed out below.
[0009] A dilute hydrofluoric acid is used in general for removing
the SiO.sub.2 film by the wet etching method. However, the removing
rate of the high-k material film such as a HfO.sub.2 film is very
low under the conditions adapted for the removal of the SiO.sub.2
film to give rise to the difficulty that a long time is required
for the removal of the high-k material film. In addition, SiO.sub.2
exhibits an etching rate higher than that exhibited by the high-k
material to give rise to an inconvenience that SiO.sub.2 in the
element separating region is also removed in the etching stage of
the high-k material film.
[0010] In order to overcome the inconvenience pointed out above, it
is conceivable to use a chemical liquid exhibiting a reverse
selectivity. If the two layers noted above are removed by the
etching with such a chemical liquid, however, another inconvenience
is generated such that an under-cut is generated in the high-k
material film because the high-k material film exhibits a high
etching rate.
[0011] As pointed out above, where the two layers are removed by
the wet etching, an inconvenience accompanying the etching
selectivity is brought about. A technology adapted for overcoming
the inconvenience pointed out above is disclosed in, for example,
Japanese Patent Disclosure (Kokai) No. 2004-179583. Specifically,
it is disclosed in this patent document that a wet etching is
performed by using a dilute hydrofluoric acid as the chemical
liquid and by defining the hydrofluoric acid concentration of the
dilute hydrofluoric acid such that the two layers are etched
non-selectively.
[0012] The technology disclosed in the patent document quoted above
certainly permits overcoming the problems based on the etching
selectivity. However, the etching conditions are not necessarily
satisfactory to the two layers that are to be etched. In some
cases, an inconvenience is generated such that the etching rate is
rendered low.
BRIEF SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a
processing method and a processing apparatus, which do not bring
about a problem in terms of the etching selectivity and which
permit etching at least two stacked films of a target object to be
processed at a sufficiently high etching rate in removing the two
films noted above by the wet etching.
[0014] Another object of the present invention is to provide a
computer program for executing the processing described above and
to provide a storage medium that can be read by a computer.
[0015] According to a first aspect of the present invention, there
is provided a processing method of subjecting at least two stacked
films, which comprise a first film and a second film of a target
object to be processed, to a removing process by wet etching,
comprising bringing a first process liquid into contact with the
first film of the target object, thereby etching the first film,
determining whether the first film has been removed or not,
switching the first process liquid to a second process liquid
differing from the first process liquid in a condition when it is
determined that the first film has been removed, and bringing the
second process liquid into contact with the second film, thereby
etching the second film.
[0016] According to a second aspect of the present invention, there
is provided a processing method of subjecting at least two stacked
films, which comprise a first film and a second film of a target
object, to a removing process by wet etching, the method comprising
Bringing a first process liquid into contact with the first film of
the target object, the first process liquid being capable of
etching the first film with a high etching selectivity relative to
the second film, determining whether the first film has been
removed or not, switching the first process liquid to a second
process liquid differing from the first process liquid in a
condition and capable of etching the second film with a high
selectivity relative to the first film when it has been determined
that the first film has been removed, and bringing the second
process liquid into contact with the second film, thereby etching
the second film.
[0017] According to a third aspect of the present invention, there
is provided a processing apparatus for removing by a wet etching at
least two stacked films, which comprise a first film and a second
film of a target object to be processed, the apparatus comprising a
housing section housing the target object, a first process liquid
supply section for supplying the first process liquid onto the
target object housed in the housing section, thereby bringing the
first process liquid into contact with the first film for
proceeding the etching of the first film, a second process liquid
supply section for supplying the second process liquid differing in
the condition from the first process liquid onto the target object
housed in the housing section, thereby bringing the second process
liquid into contact with the second film for proceeding the etching
of the second film, a detecting section for detecting the removed
state of the first film, a switching section for switching the
process liquid that is brought into contact with the target object
from the first process liquid to the second process liquid, and a
control section for determining whether the first film has been
removed on the basis of the detected value in the detecting section
and, when it has been determined that the first film has been
removed, for transmitting to the switching section an instruction
to switch the process liquid that is brought into contact with the
target object from the first process liquid to the second process
liquid.
[0018] According to a fourth aspect of the present invention, there
is provided a computer program including a soft ware which, when
executed, causes the computer to control a processing apparatus for
removing by a wet etching at least two stacked films, which
comprise a first film and a second film of a target object to be
processed, wherein the soft ware causes the computer to execute the
operations of bringing a first process liquid into contact with the
first film of the target object, thereby etching the first film,
determining whether the first film has been removed or not,
switching the first process liquid to a second process liquid
differing in a condition from the first process liquid when it has
been determined that the first film has been removed, and bringing
the second process liquid into contact with the second film,
thereby etching the second film.
[0019] Further, according to a fifth aspect of the present
invention, there is provided a storage medium that can be read by a
computer, the storage medium including a soft ware which, when
executed, causes the computer to control a processing apparatus for
removing by a wet etching at least two stacked films, which
comprise a first film and a second film of a target object to be
processed, wherein the soft ware causes the computer to execute the
operations of bringing a first process liquid into contact with the
first film of the target object, thereby etching the first film,
determining whether the first film has been removed or not,
switching the first process liquid to a second process liquid
differing in a condition from the first process liquid when it has
been determined that the first film has been removed, and bringing
the second process liquid into contact with the second film,
thereby etching the second film.
[0020] According to the present invention, at least two stacked
films, which comprise a first film and a second film of the target
object is removed by a wet etching. The first film is etched first
with the first process liquid and, then, when it has been
determined that the first film has been removed, the first process
liquid is switched to the second process liquid differing in the
condition from the first process liquid, thereby etching the second
film with the second process liquid. It follows that, if an etchant
that permits etching the first film with a high selectivity is used
as the first process liquid for etching the first film, and if
another etchant that permits etching the second film with a high
selectivity is used as the second process liquid for etching the
second film, both the first and second films can be etched with a
high etching rate without giving rise to a problem in terms of the
etching selectivity.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0021] FIG. 1 is schematic diagram showing as an example the
construction of a processing apparatus used for working the present
invention;
[0022] FIGS. 2A to 2D are cross sectional views for explaining the
processing performed by the processing apparatus shown in FIG.
1;
[0023] FIG. 3 is a flow chart showing the process steps performed
by the processing apparatus shown in FIG. 1;
[0024] FIGS. 4A and 4B collectively show the inconveniences that
are brought about in the case of employing the conventional
method;
[0025] FIG. 5 is schematic diagram showing as another example the
construction of a processing apparatus used for working the present
invention; and
[0026] FIG. 6 is a flow chart showing the process steps performed
by the apparatus shown in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Some embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0028] FIG. 1 is schematic diagram showing as an example the
construction of a processing apparatus 1 used for working the
present invention. As shown in the drawing, the processing
apparatus 1 comprises a chamber 2. A spin chuck 3 for horizontally
holding a semiconductor wafer W that is used as a substrate by
utilizing the vacuum suction is arranged within the chamber 2. The
spin chuck 3 can be rotated by a motor 4. A cup 5 is arranged
inside the chamber 2 in a manner to cover the wafer W held by the
spin chuck 3. An exhaust/drain pipe 6 for exhausting and draining
extends downward from the bottom portion of the cup 5. The pipe 6
extends downward to reach a region downward of the chamber 2.
[0029] A process liquid supply nozzle 10 is arranged above the
wafer W held by the spin chuck 3. The nozzle 10 can be moved by a
driving mechanism (not shown). A process liquid supply pipe 12 is
connected to the process liquid supply nozzle 10, and a switching
valve 13 is mounted to the process liquid supply pipe 12. A pipe 14
extending from a first process liquid supply source 15 and another
pipe 16 extending from a second process liquid supply source 17 are
connected to the switching valve 13. When the switching valve 13 is
operated, it is possible to permit any of the first process liquid
and the second process liquid to flow through the process liquid
supply pipe 12 so as to be discharged from the process liquid
supply nozzle 10 onto the wafer W. These first process liquid and
second process liquid are supplied onto the wafer W while rotating
the wafer W by driving the motor 4, thereby removing two stacked
films formed on the wafer W by the wet etching as described
hereinlater.
[0030] On the other hand, a cleaning/drying nozzle 20 that can be
moved by a driving mechanism (not shown) is arranged above the
wafer W. A pipe 21 is connected to the cleaning/drying nozzle 20,
and a switching valve 22 is mounted to the pipe 21. Further, a pipe
23 extending from a rinsing liquid supply source 24, a pipe 25
extending from an IPA supply source 26 and a pipe 26 extending from
a nitrogen gas supply source 28 for supplying a hot nitrogen gas
are connected to the switching valve 22. When the switching valve
22 is operated, it is possible to permit any of the rinsing liquid,
IPA and the nitrogen gas to flow through the pipe 21 so as to be
spurted from the washing/drying nozzle 20 onto the wafer W. A
rinsing liquid, e.g., a pure water, is supplied from the nozzle 20
onto the wafer W that is kept rotated by driving the motor 4,
thereby cleaning the wafer W and, then, IPA is supplied onto the
wafer W, followed by supplying a hot nitrogen gas onto the wafer W
to dry the wafer W.
[0031] A concentration measuring apparatus 31 is mounted to the
exhaust/drain pipe 6 to detect the concentration of a specified
component of the drain when the first process liquid is supplied
onto the wafer W for performing the wet etching. A CPU 32 is
connected to the concentration measuring apparatus 31. As described
hereinlater, a switching signal is transmitted from the CPU 32 to
the switching valve 13 at the time when a signal, which denotes
that the concentration of the component that is to be measured by
the concentration measuring apparatus 31 has reached a prescribed
value, is transmitted to the CPU 32. The CPU 32 also controls the
operations of the entire substrate processing apparatus 1
including, for example, the operations of the switching valve 22
and the motor 4. A user interface 33 including, for example, a
keyboard for performing the input operation of the command, which
is performed by the process supervisor for supervising the
substrate processing apparatus 1, and a display for visually
showing the operating state of the substrate processing apparatus 1
is connected to the CPU 32. A memory section 34 storing a recipe
recording therein the control program for realizing the various
processing executed by the substrate processing apparatus 1 under
the control of the CPU 32 and the process condition data is also
connected to the CPU 32. An optional recipe is read from the memory
section 34 in accordance with an instruction given from the user
interface 33 to be executed by the CPU 32.
[0032] It is desirable to use the concentration measuring apparatus
31 that permits measuring the concentration of the component that
should be measured with a high accuracy. For example, it is
possible to use suitably an inductively coupled plasma mass
spectroscope (ICPMS) having a detection limit of about 0.1 ppb.
[0033] The process steps that are performed for removing the two
stacked films by using the processing apparatus constructed as
described above will now be described with reference to the cross
sectional views shown in FIGS. 2A to 2D and the flow chart shown in
FIG. 3.
[0034] The following description covers the case where a gate
insulating film of a two-layer structure formed on a silicon
substrate and consisting of an interfacial film formed of silicon
oxide (SiO.sub.2) or silicon oxynitride (SiO.sub.xN.sub.y) and a
high-k material film is removed by the wet etching.
[0035] In the first step, prepared is a wafer W constructed as
shown in FIG. 2A as a target object that is to be subjected to the
wet etching. As shown in the drawing, a very thin interfacial film
41 of silicon oxide (SiO.sub.2) or silicon oxynitride
(SiO.sub.xN.sub.y) is formed on the main surface of a silicon
substrate 40 isolated in the shape of an island by an element
separating region 45 formed of SiO.sub.2. A high-k material film 42
is formed on the interfacial film 41. Further, a gate electrode 43
of polysilicon is formed on the high-k material film 42.
Incidentally, a hard mask positioned above the gate electrode 43 is
not shown in the drawing.
[0036] It is desirable for the high-k material film 42 to be formed
of a high-k material having a relative dielectric constant not
lower than 4.0 including, for example, hafnium oxide (HfO.sub.2),
zirconium oxide (ZrO.sub.2), tantalum oxide (Ta.sub.2O.sub.5),
oxides of rare earth metals, and silicates of these metals, e.g.,
hafnium silicate (HfSiO.sub.x).
[0037] The wafer W of the construction described above is
transferred into the chamber 2 of the substrate processing
apparatus 1 to be disposed on the spin chuck 3 (step 1 shown in
FIG. 3).
[0038] Then, the process liquid supply nozzle 10 is moved to a
position immediately above the center of the wafer W and the first
process liquid capable of etching the high-k material film 42 with
a high selectivity relative to the interfacial film 41 is supplied
from the first process liquid supply source 15 onto the wafer W
through the process liquid supply nozzle 10. As a result, that
portion of the high-k material film 42 which is positioned around
the gate electrode 43 is selectively removed as shown in FIG. 2B
(step 2 shown in FIG. 3).
[0039] Since the first process liquid is brought into contact with
the high-k material film 42 included in the wafer W, thereby
etching the high-k material film 42, the component of the high-k
material film 42 is eluted into the first process liquid. In this
case, the concentration of a prescribed component of the first
process liquid discharged from the exhaust/drain pipe 6 is measured
by the concentration measuring apparatus 31.
[0040] Also, the CPU 32 determines whether the high-k material film
42 has been removed or not (step 3 shown in FIG. 3). When it has
been determined that the high-k material film 42 has been removed,
the first process liquid is switched to the second process liquid
capable of etching the interfacial film 41 with a high selectivity
relative to the high-k material film 42 (step 4 shown in FIG.
3).
[0041] The determination noted above is performed by utilizing the
measured value of the concentration of the prescribed component,
i.e., the concentration obtained by the measurement performed by
the concentration measuring apparatus 31. To be more specific, if
the high-k material film 42 is removed, the interfacial film 41 is
exposed as shown in FIG. 2C. Since the component or the amount of
the component eluted into the first process liquid is changed at
this stage, the CPU 32 recognizes that the change noted above is
reflected by the data measured by the concentration measuring
apparatus 31 so as to determine that the high-k material film 42
has been removed. As a result, a switching instruction is
transmitted to the switching valve 13 so as to perform the
switching from the first process liquid to the second process
liquid.
[0042] To be more specific, when the high-k material film 42 is
removed to expose the interfacial film 41, the amount of the
component of the high-k material that is eluted into the process
liquid is decreased. For example, where HfO.sub.2 is used as the
high-k material, the amount of Hf is decreased. By contraries, if
the first process liquid permits dissolving the material of the
interfacial film 41, e.g., SiO.sub.2, the component of the
interfacial film 41 begins to be eluted into the first process
liquid. It follows that, at the time when the amount of the
prescribed component of the high-k material film 42 forming the
upper layer is decreased to a level lower than the set value or
when the amount of the prescribed component of the interfacial film
41 forming the lower layer is increased to exceed the set value,
the process liquid is switched from the first process liquid to the
second process liquid on the ground that the high-k material film
42 has been removed.
[0043] After the process liquid is switched to the second process
liquid, the interfacial film 41 other than the portion positioned
below the gate electrode 43 is removed by the etching with the
second process liquid, as shown in FIG. 2D (step 5 shown in FIG.
3).
[0044] As described above, the first process liquid and the second
process liquid differ from each other in function and, thus, in the
condition as pointed out below.
[0045] First of all, the first process liquid and the second
process liquid differ from each other in chemical species. It
should be noted that, if an inconvenience is generated by the
mixing of the first and second process liquids, it is desirable to
carry out an intermediate rinsing after the processing with the
first process liquid and before the processing with the second
process liquid.
[0046] A second aspect to be noted is that it is also possible for
the first and second process liquids to be equal to each other in
the chemical species but to differ from each other in the
concentration of the component and/or the pH value. For example, a
dilute hydrofluoric acid that is prepared by diluting hydrofluoric
acid with water is ionized within water
(HF.fwdarw.H.sup.++F.sup.-), and F.sup.- is converted into
HF.sub.2.sup.- by the reaction of
(HF+F.sup.-.fwdarw.HF.sub.2.sup.-). In this case, SiO.sub.2 is
etched mainly by HF.sub.2.sup.-. On the other hand, it is known to
the art that the doped oxides such as BPSG and BSG are etched
directly by the HF molecules. It follows that, if the high-k
material film 42 exhibits such properties as pointed out above, it
is possible to remove the high-k material film 42 and the
interfacial film 41 with a high etching selectivity in the case of
using the first and second process liquids differing from each
other in the HF.sub.2.sup.- or HF concentration. It should also be
noted that the relative concentration of the chemical species is
dependent on the pH value, with the result that the high-k material
film 42 and the interfacial film 41 can be removed with a high
etching selectivity by using the first and second process liquids
differing from each other in the pH value. As pointed out above, in
the case of using the same kind of the chemical liquids, it is
unnecessary to carry out the intermediate rinsing noted above. It
is also possible to add a certain component of the chemical liquid
to increase the concentration of the added component in place of
switching the process liquid between the first process liquid and
the second process liquid. For example, in the case of using an
HF/alcohol type process liquid for the selective etching, the
etching rate of SiO.sub.2 is increased by adding water to the
process liquid. In this case, the switching between the first
process liquid and the second process liquid can be performed
rapidly or gradually depending on the optimum condition that can be
determined by experiments. Incidentally, in order to confirm
whether the concentration of the constituting component of the
process liquid is appropriate, it is desirable to perform the
monitoring on the in-line basis.
[0047] Further, a third aspect to be noted relates to the
temperature. It is possible for the first and second process
liquids of the same composition to differ from each other in
temperature. To be more specific, the reactivity is dependent on
the temperature even if the process liquids have the same
composition. It is possible for the process liquid to have a
temperature adapted for the etching of SiO.sub.2 and another
temperature adapted for the etching of the high-k material. In this
case, it is possible to etch the high-k material film 42 and the
interfacial film 41 with a high etching selectivity by simply
allowing the first process liquid and the second process liquid to
differ from each other in temperature.
[0048] In this embodiment, the etching is performed first with the
first process liquid capable of etching the high-k material film 42
with a high selectivity and, when it has been determined that the
etching of the high-k material film 42 has been finished, the
process liquid is switched to the second process liquid capable of
etching the interfacial oxide film 41 formed of SiO.sub.2 with a
high etching selectivity to etch the interfacial oxide film 41. It
follows that the embodiment makes it possible to overcome the
problems relating to the etching selectivity such as the excessive
etching of the element separating region 45 as shown in FIG. 4A and
the under-cutting of the high-k material film 42 as shown in FIG.
4B. The embodiment also makes it possible to etch the high-k
material film 42 and the interfacial oxide film 41 at a
sufficiently high etching rate.
[0049] Another example of the processing apparatus used for working
the present invention will now be described. FIG. 5 is a schematic
diagram showing another example of the construction of the
processing apparatus 1' used for working the present invention.
[0050] As shown in the drawing, the processing apparatus 1'
comprises a box-shaped inner vessel 51 large enough to house the
wafer W and an outer vessel 52 surrounding the inner vessel 51. The
wafer W is put in and taken out of the inner vessel 51 through an
upper opening. It is possible for a single wafer W or a plurality
of wafers W to be housed in the inner vessel 51 under the state
that the wafer W is supported by a support member (not shown). A
process liquid supply pipe 53 having a switching valve 54 mounted
thereto is inserted into the inner vessel 51. A pipe 55 extending
from a first process liquid supply source 56 and another pipe 57
extending from a second process liquid supply source 58 are
connected to the switching valve 54. It is possible to supply any
of the first process liquid and the second process liquid into the
inner vessel 51 through the process liquid supply pipe 53 by
operating the switching valve 54, with the result that the wafer W
housed in the inner vessel 51 is dipped in any of the process
liquids supplied into the inner vessel 51. The outer vessel 52 is
mounted to surround the upper opening of the inner vessel 51 to
receive the process liquid overflowing the upper edge of the inner
vessel 51.
[0051] A drain line 59 having an opening-closing valve 60 mounted
thereto is connected to the bottom portion of the inner vessel 51.
In replacing the process liquid, the process liquid within the
inner vessel 51 is discharged to the outside through the drain line
59. Also, a circulating line 61 is connected to the bottom portion
of the outer vessel 52 such that the process ilquid is circulated
through the circulating line 61. A reference numeral 62 denotes an
opening-closing valve for opening-closing the circulating line
61.
[0052] On the other hand, a sampling line 63 is connected to the
bottom portion of the inner vessel 51. An opening-closing valve 64,
a concentration measuring apparatus 65 and a pump 66 are mounted to
the sampling line 63, and the other edge of the sampling line 63 is
connected to the bottom portion of the outer vessel 52. It follows
that the sampled process liquid is circulated.
[0053] The concentration measuring apparatus 65 permits detecting
the concentration of a specified component when the first process
liquid is supplied into the inner vessel 51 for applying an etching
to the wafer W. The concentration measuring apparatus 65 is
connected to a CPU 68. As described hereinlater, a switching signal
is transmitted from the CPU 68 to the switching valve 54 at the
time when a signal, which indicates that the concentration of the
component that is to be measured by the concentration measuring
apparatus 65 has reached a prescribed value, has been transmitted
to the CPU 68. The CPU 68 also controls the operations of the
entire substrate processing apparatus 1'. A user interface 69 is
connected to the CPU 68 as in the apparatus shown in FIG. 1. A
memory section 70 storing a recipe recording therein the control
program for realizing the various processings executed by the
substrate processing apparatus 1' under the control of the CPU 68
and also recording therein the process condition data is also
connected to the CPU 68. An optional recipe is read from the memory
section 70 in accordance with the instruction given from the user
interface 69 to be executed by the CPU 68.
[0054] The process steps required for removing the two stacked
films by using the processing apparatus of the construction
described above will now be described with reference to the cross
sectional views shown in FIGS. 2A to 2D and a flow chart shown in
FIG. 6. The process steps for this removing processing of the two
stacked films are basically equal to those in the case of removing
the two stacked films by using the apparatus 1 shown in FIG. 1
described previously.
[0055] In the first step, prepared is a wafer W constructed as
shown in FIG. 2A referred to previously as an object that is to be
subjected to a wet etching and, then, the wafer W of the particular
construction is inserted into the inner vessel 51 of the substrate
processing apparatus 1' shown in FIG. 5 (step 11 shown in FIG.
6).
[0056] Then, the first process liquid capable of etching the high-k
material film 42 with a high selectivity relative to the
interfacial film 41 is supplied from the first process liquid
supply source 56 into the inner vessel 51 such that the wafer W is
dipped in the first process liquid, thereby etching the high-k
material film 42. As a result, the high-k material film 42 around
the gate electrode is selectively removed as shown in FIG. 2B (step
12 shown in FIG. 6).
[0057] Since the first process liquid is brought into contact with
the high-k material film 42 of the wafer W to etch the high-k
material film 42, the component of the high-k material film 42 is
eluted into the first process liquid housed in the inner vessel 51,
with the result that the concentration of the component of the
high-k material film 42 in the first process liquid is increased.
In this case, the concentration of a prescribed component in the
first process liquid, which is sampled by the sampling line 63, is
measured by the concentration measuring apparatus 65.
[0058] Further, the CPU 68 determines whether the high-k material
film 42 has been removed or not (step 13 shown in FIG. 6) and
transmits an instruction to open the opening-closing valve 60 to
the opening-closing valve 60 at the time when it has been
determined that the high-k material film 42 has been removed to
discharge the first process liquid through the drain pipe 59 (step
14 shown in FIG. 6). Still further, the switching valve 54 is
switched to permit the second process liquid capable of etching the
interfacial film 41 with a high selectivity relative to the high-k
material film 42 is supplied from the second process liquid supply
source 58 into the inner vessel 51 through the process liquid
supply pipe 53 (step 15 shown in FIG. 6).
[0059] The determination as to whether the high-k material film 42
has been removed is performed by utilizing the concentration of the
prescribed component measured by the concentration measuring
apparatus 65. To be more specific, the concentration of the
component of the high-k material is increased in proportion to the
etching time as far as the high-k material film 42 has not yet been
removed completely. However, the amount of the component of the
high-k material that is eluted into the first process liquid
substantially ceases to be increased and the amount of the
component of the interfacial film 41 is increased at the time when
the interfacial film 41 has been exposed as shown in FIG. 2C. Such
being the situation, the CPU 68 recognizes that the measured data
of the concentration measuring apparatus 65 reflects the change in
the concentration of the component of the high-k material film 42
in the first process liquid and determines that the high-k material
film 42 has been removed. At the same time, the CPU 68 transmits an
instruction to open to the opening-closing valve 60 and also
transmits a switching instruction to the switching valve 54 so as
to supply the second process liquid into the inner vessel 51.
[0060] After the second process liquid has been supplied into the
inner vessel 51, the interfacial film 41 except the region
positioned below the gate electrode 43 is removed by the etching
with the second process liquid as shown in FIG. 2D (step 16 shown
in FIG. 6).
[0061] Like previous embodiment, the etching is performed first
with the first process liquid capable of etching the high-k
material film 42 with a high etching selectivity and, when it has
been determined that the etching of the high-k material film 42 has
been finished, the process liquid is switched to the second process
liquid capable of etching the interfacial oxide film 41 with a high
etching selectivity to etch the interfacial oxide film 41. It
follows that the embodiment makes it possible to overcome the
problems relating to the etching selectivity such as the
under-cutting of the high-k material film 42 and the excessive
etching of the element separating region 45. The embodiment also
makes it possible to etch the high-k material film 42 and the
interfacial oxide film 41 at a sufficiently high etching rate.
[0062] Incidentally, in the case of the processing apparatus shown
in FIG. 5, a much time is required for replacing the first process
liquid with the second process liquid, with the result that the
amount of the process liquid that is made useless is increased. In
order to avoid this inconvenience, it is effective to store the
first process liquid and the second process liquid in different
vessels. In this case, the wafer W is transferred from within the
vessel storing the first process liquid into the vessel storing the
second process liquid at the time when it has been determined that
the high-k material film 42 has been removed.
[0063] An experiment has been conducted on the etching selectivity
between a HfO.sub.2 film used as the high-k material film and a
SiO.sub.2 film used as the interfacial film.
[0064] In this experiment, used were a dilute hydrofluoric acid
(DHF)/ethanol system process liquid and a dilute hydrofluoric acid
(DHF) process liquid. In the former process liquid, the ethanol
concentration was changed, and in the latter process liquid, the pH
value of the process liquid was changed by using a pH control
agent. These process liquids were brought into contact with the
HfO.sub.2 film and the SiO.sub.2 film to measure the etching rates
of these films. Incidentally, the dilute hydrofluoric acid had a
concentration of 0.05 M at 25.degree. C. Tables 1 and 2 show the
etching rates of the films thus measured. TABLE-US-00001 TABLE 1
ethanol concentration in DHF/ethanol etching rate of etching rate
of process liquid (%) SiO.sub.2 (nm/min) HfO.sub.2 (nm/min) 0 2.5
0.8 20 2.3 1.6 40 2.0 2.3 60 0.5 1.3 80 .about.0 0.2
[0065] TABLE-US-00002 TABLE 2 pH value of DHF etching rate of
etching rate of process liquid SiO.sub.2 (nm/min) HfO.sub.2
(nm/min) 0 0.15 0.3 1 0.2 0.3 2 0.25 0.3 3 0.25 0.2 3.5 0.2 0.03 4
0.18 --
[0066] Table 1 covers the case where the ethanol concentration was
changed in the dilute hydrofluoric acid (DHF)/ethanol system
process liquid. The experimental data support that the SiO.sub.2
film can be etched with a high selectivity relative to the
HfO.sub.2 film in the case where the ethanol concentration is in
the vicinity of 0%, and that the HfO.sub.2 can be etched with a
high selectivity relative to the SiO.sub.2 film in the case where
the ethanol concentration is increased to exceed about 60%. It
should be noted, however, that, if the ethanol concentration is
increased to reach 80%, the etching rate of the HfO.sub.2 film is
lowered, though the HfO.sub.2 film can be etched with a high
selectivity. Such being the situation, it is desirable for the
ethanol concentration to fall within a range of 60 to 80%. Table 2
covers the case where the pH value of the dilute hydrofluoric acid
(DHF) process liquid was changed. The experimental data support
that the HfO.sub.2 film can be etched with a high selectivity
relative to the SiO.sub.2 where the pH value is in the vicinity of
0. However, if the pH value is increased to 3.5 or more, the
SiO.sub.2 film can be etched with a high selectivity relative to
the HfO.sub.2 film. It has been confirmed by the experimental data
that the process liquids can be combined appropriately so as to
etch the HfO.sub.2 film forming the high-k material film with a
high etching selectivity relative to the SiO.sub.2 and, then, to
etch the SiO.sub.2 film with a high etching selectivity relative to
the HfO.sub.2 film so as to remove the laminate film of the
two-layer structure at a sufficiently high etching rate without
giving rise to the problem relating to the etching selectivity.
[0067] It should be noted that the embodiments described above are
simply intended to clarify the technical idea of the present
invention. Naturally, the technical scope of the present invention
should not be construed solely on the basis of the specific
embodiments described above. In other words, the present invention
can be worked in variously modified fashions on the basis of the
spirit of the present invention and within the scope defined in the
accompanying claims.
[0068] For example, the embodiment described above is directed to
the case where a gate insulating film of a two-layer structure
consisting of an interfacial film formed of silicon oxide
(SiO.sub.2) or silicon oxynitride (SiO.sub.xN.sub.y) and a high-k
material film is subjected to the wet etching. However, the target
object to be etched is not limited to the gate insulating film of
the particular two-layer structure. It is also possible to apply
the wet etching of the present invention to at least two stacked
films differing from each other in the material. Also, in the
embodiment described above, it has been determined whether the
upper layer of the two stacked structure has been removed or not by
detecting the concentration of a prescribed component in the
process liquid. However, it is also possible to employ another
method. For example, it is possible to determine whether the upper
film has been removed or not by grasping the state of the film by
using a CCD camera. Further, in the embodiment described above, the
technical idea of the present invention is applied to two stacked
films formed on a semiconductor wafer. However, it is also possible
to apply the technical idea of the present invention to the
processing of another substrate such as a glass substrate for a
liquid crystal display device (LCD) and to the processing of target
objects other than the substrate.
* * * * *