U.S. patent application number 09/805747 was filed with the patent office on 2002-05-09 for methods and apparatus for cleaning an object using an electron beam, and device-fabrication apparatus comprising same.
Invention is credited to Kawata, Shintaro, Okada, Masashi, Shimizu, Sumito.
Application Number | 20020053353 09/805747 |
Document ID | / |
Family ID | 26587270 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020053353 |
Kind Code |
A1 |
Kawata, Shintaro ; et
al. |
May 9, 2002 |
Methods and apparatus for cleaning an object using an electron
beam, and device-fabrication apparatus comprising same
Abstract
Apparatus and methods are disclosed for cleaning an object, such
as a reticle or electron-optical component used in performing
electron-beam microlithography, using an electron beam. The
cleaning can be performed in the presence or absence of a treatment
gas. When performed without a treatment gas, an electron beam is
directed to impinge on the object at an energy sufficient to
volatilize contaminant deposits on the object. When performed with
a treatment gas, the electron beam need not be directed at the
object, but electrons from the beam have an energy sufficient to
ionize molecules of the treatment gas. The ionized molecules
volatilize the contaminant deposits for removal using a vacuum
pump. For example, the beam can be directed to a scattering body
that produces scattered electrons having sufficient energy to
volatilize the contaminant deposits.
Inventors: |
Kawata, Shintaro;
(Kitasama-gun, JP) ; Okada, Masashi;
(Inashiki-gun, JP) ; Shimizu, Sumito;
(Yokohama-shi, JP) |
Correspondence
Address: |
KLARQUIST SPARKMAN CAMPBELL LEIGH &
WHINSTON, LLP
One World Trade Center, Suite 1600
121 S.W. Salmon Street
Portland
OR
97204
US
|
Family ID: |
26587270 |
Appl. No.: |
09/805747 |
Filed: |
March 13, 2001 |
Current U.S.
Class: |
134/1.3 |
Current CPC
Class: |
B08B 7/0035
20130101 |
Class at
Publication: |
134/1.3 |
International
Class: |
C25F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2000 |
JP |
2000-068034 |
Feb 9, 2001 |
JP |
2001-033969 |
Claims
What is claimed is:
1. A contamination-removal device, comprising: a treatment chamber
defining an interior space in which an object, having a deposit of
a contaminant substance and requiring cleaning to remove the
deposit, can be situated; a chamber-evacuation pump in
communication with the treatment chamber, the chamber-evacuation
device being configured to evacuate the interior space of the
treatment chamber; a gas-inlet in communication with the treatment
chamber, the gas-inlet being configured to introduce a treatment
gas into the interior space of the treatment chamber; and an
electron-beam irradiator situated and configured to irradiate an
electron beam in the interior space of the treatment chamber such
that the electron beam ionizes molecules of the treatment gas, and
the ionized molecules of the treatment gas react with molecules of
the contaminant substance on the object to volatilize the
contaminant substance from the object.
2. The contamination-removal device of claim 1, wherein the
treatment gas comprises at least one gas selected from a group
consisting of water vapor, oxygen, ozone, and oxygen radicals.
3. The contamination-removal device of claim 1, further comprising
a lens column and a wafer chamber, wherein the wafer chamber
comprises the treatment chamber.
4. The contamination-removal device of claim 1, wherein the lens
column contains the electron-beam irradiator.
5. The contamination-removal device of claim 4, further comprising
an electron-optical system for illuminating the reticle with an
electron beam.
6. The contamination-removal device of claim 5, wherein: the
electron-optical system comprises the electron-beam irradiator; and
the electron-optical system is situated within the lens column.
7. The contamination-removal device of claim 3, further comprising
a scattering body situated within either the lens column or the
wafer chamber so as to be bombarded with incident electrons from
the electron-beam irradiator and form scattered electrons.
8. A microelectronic-device fabrication apparatus, comprising the
contamination-removal device of claim 1.
9. An electron-beam microlithography apparatus, comprising: a lens
column containing an electron-optical system configured to
illuminate a reticle with an electron beam; a wafer chamber
defining an interior space configured to enclose a substrate to be
exposed with a pattern defined on the reticle and transferred to
the substrate by the electron beam propagating from the reticle to
the substrate; at least one vacuum pump in communication with the
lens column and wafer chamber, the vacuum pump being configured to
evacuate the interior spaces of the lens column and wafer chamber;
a gas-inlet in communication with the wafer chamber, the gas-inlet
being configured to introduce a treatment gas into the interior
space of the wafer chamber; and the wafer chamber being configured
to contain a scattering body situated so as to be irradiated by the
electron beam from the electron-optical system, the electron beam
irradiating the scattering body causing the scattering body to
produce scattered electrons that propagate to any of various
locations in the wafer chamber and lens column to impinge on
contaminant deposits at the various locations and to ionize
molecules of the treatment gas introduced into the interior space,
the ionized molecules reacting with and volatilizing the
contaminant deposits.
10. The apparatus of claim 9, further comprising an electron-beam
source situated in the lens column.
11. The apparatus of claim 9, wherein the treatment gas is at least
one gas selected from a group consisting of water vapor, oxygen,
ozone, and oxygen radicals.
12. An electron-beam microlithography apparatus, comprising: an
electron-beam source; a process chamber defining an interior space;
an electron-optical system situated in the process chamber relative
to the electron-beam source and configured to direct an electron
beam from the source to a substrate situated downstream of the
source; a wafer stage situated in the process chamber, the wafer
stage being configured to hold the substrate as the substrate is
being irradiated by the electron beam; a treatment-gas source
connected to and configured to introduce a treatment gas into the
process chamber; and an electron-scattering body situated in the
process chamber, the electron-scattering body being positionable so
as to be irradiated by the electron beam and produce, from such
irradiation, scattered electrons that propagate to any of various
locations in the process chamber to impinge on contaminant deposits
at the various locations and to ionize molecules of the treatment
gas introduced into the interior space, the ionized molecules
reacting with and volatilizing the contaminant deposits.
13. An electron-beam microlithography apparatus, comprising: a
process chamber defining an interior space; an electron-optical
system situated in the process chamber and comprising an
electron-beam source, the electron-optical system being configured
to irradiate a surface of a substrate selectively with an electron
beam from the source; a treatment-gas source connected to and
configured to introduce a treatment gas into the process chamber;
and an electron-beam irradiation device situated in the process
chamber separately from the electron-optical system, the
electron-beam irradiation device being configured to produce a
respective electron beam that impinges on the treatment gas in the
process chamber so as to ionize molecules of the treatment gas, the
ionized molecules being available to react with and volatilize a
contaminant deposit in the process chamber.
14. The apparatus of claim 13, wherein the treatment gas is at
least one gas selected from a group consisting of water vapor,
oxygen, ozone, and oxygen radicals.
15. A method for removing a deposit of a contaminant in a process
chamber of an apparatus that employs an electron beam to achieve a
desired result, the method comprising the steps: providing a
treatment gas comprising molecules that become ionized when
irradiated by electrons; introducing molecules of the treatment gas
into the process chamber; when the process chamber contains
molecules of the treatment gas, irradiating the molecules of the
treatment gas in the process chamber with the electron beam to
ionize the molecules of the treatment gas; allowing the ionized
molecules of the treatment gas to react with and volatilize the
deposit; and removing the volatilized deposit from the process
chamber.
16. The method of claim 15, wherein the step of removing the
volatilized deposit from the process chamber comprises evacuating
the process chamber.
17. The method of claim 15, wherein the treatment gas is at least
one gas selected from a group consisting of water vapor, oxygen,
ozone, and oxygen radicals.
18. A method for removing a deposit of a contaminant in a process
chamber of an apparatus that employs an electron beam to achieve a
desired result, the method comprising the steps: providing a
treatment gas comprising molecules that become ionized when
irradiated by electrons; introducing molecules of the treatment gas
into the process chamber; placing an electron-scattering body in
the process chamber such that the electron beam can impinge on the
electron-scattering body and thus cause the electron-scattering
body to produce scattered electrons; when the process chamber
contains molecules of the treatment gas, irradiating the
electron-scattering body with the electron beam to produce
scattered electrons that ionize the molecules of the treatment gas;
and allowing the ionized molecules of the treatment gas to react
with and volatilize the deposit.
19. The method of claim 18, wherein the treatment gas is at least
one gas selected from a group consisting of water vapor, oxygen,
ozone, and oxygen radicals.
20. A method for removing a deposit of a contaminant in a process
chamber, comprising the steps: providing a treatment gas comprising
molecules that become ionized when irradiated by electrons;
introducing molecules of the treatment gas into the process
chamber; providing in the process chamber an electron-beam
irradiation device configured to produce an electron beam; placing
an electron-scattering body in the process chamber such that the
electron beam can impinge on the electron-scattering body and thus
cause the electron-scattering body to produce scattered electrons;
when the process chamber contains molecules of the treatment gas,
irradiating the electron-scattering body with the electron beam to
produce scattered electrons that ionize the molecules of the
treatment gas; and allowing the ionized molecules of the treatment
gas to react with and volatilize the deposit.
21. The method of claim 20, wherein the treatment gas is at least
one gas selected from a group consisting of water vapor, oxygen,
ozone, and oxygen radicals.
22. A method for cleaning a reticle in a process chamber of an
electron-beam microlithography apparatus used to transfer an image
of a pattern, defined by the reticle, onto a resist-coated surface
of a substrate, the method comprising the steps: (a) placing the
reticle in an interior space defined by the process chamber; (b)
applying a subatmospheric pressure to the interior space; and (c)
directing an electron beam to impinge on the reticle in the process
chamber, while deflecting electrons of the beam passing through the
reticle away from the resist-coated surface so as not to expose the
resist.
23. The method of claim 22, wherein, in step (c), the electron beam
impinging on the reticle has an energy sufficient to volatilize a
deposit of a contaminant on the reticle as the reticle is being
irradiated with the electron beam.
24. The method of claim 23, wherein the energy of the electron beam
used to clean the reticle is greater than an energy of the electron
beam used to expose the resist-coated surface of the substrate with
the reticle pattern.
25. The method of claim 22, wherein, in step (c), the electron beam
impinging on the reticle has an energy sufficient to confer a
negative charge to a deposit of a contaminant on the reticle and to
cause the deposit to detach from the surface of the reticle.
26. The method of claim 25, further comprising the steps of:
providing a dust collector in the process chamber; providing the
dust collector with a positive charge sufficient to attract the
detached deposit; and collecting the detached deposit using the
dust collector.
27. A method for performing microlithography of a pattern, defined
on a reticle, onto a resist-coated surface of a substrate, the
method comprising: (a) placing the reticle and substrate in the
process chamber, the reticle being situated so as to be irradiated
with an upstream electron beam and to produce a downstream electron
beam carrying an image of an irradiated region of the reticle, and
the substrate being situated such that the resist-coated surface
can be exposed with the image carried by the downstream electron
beam; (b) evacuating the process chamber to produce a
subatmospheric pressure in the process chamber; (c) in a
reticle-cleaning mode of operation, directing the upstream electron
beam to impinge on the reticle while directing the downstream
electron beam away from the resist-coated surface so as to avoid
exposing the resist; and (d) in a substrate-exposure mode of
operation, directing the upstream electron beam to irradiate a
region on the reticle while directing the downstream electron beam
to a corresponding location on the resist-coated surface of the
substrate so as to transfer the pattern from the reticle to the
substrate.
28. The method of claim 27, wherein: in step (c), the electron beam
has a first energy sufficient to volatilize a deposit of a
contaminant on the reticle; in step (d), the electron beam has a
second energy sufficient to expose the resist; and the first energy
is greater than the second energy.
29. The method of claim 27, further comprising the steps of:
providing a dust collector in the process chamber; and during step
(c), providing the dust collector with a positive charge.
30. The method of claim 29, wherein, in step (c): the electron beam
impinging on the reticle has an energy sufficient to confer a
negative charge to a deposit of a contaminant on the reticle and to
detach the deposit from the reticle; and the detached deposit is
attracted to and collected by the dust collector.
31. An electron-beam microlithography apparatus operable to project
an image of a pattern, defined by a reticle, onto a resist-coated
surface of a substrate, the apparatus comprising: a process chamber
defining an interior space; a vacuum pump, in communication with
the interior space, configured to produce a subatmospheric pressure
in the interior space; an electron-beam source situated within the
interior space and configured to produce an electron beam
propagating downstream of the source; a deflector situated within
the interior space and configured, when electrically energized, to
deflect the electron beam propagating from the source; and a main
controller connected to the electron-beam source and to the
deflector, the main controller being configured to operate in first
and second operational modes, wherein in the first operational mode
the electron beam from the source irradiates the reticle, and
electrons of the beam passing through the reticle are deflected by
the deflector away from the resist-coated surface so as not to
expose the resist, and in the second operational mode the electron
beam from the source irradiates a region of the reticle, and
electrons of the beam passing through the reticle are deflected by
the deflector to a corresponding region on the resist-coated
surface so as to imprint the resist-coated surface with the
pattern.
32. The apparatus of claim 31, wherein, in the first operational
mode, the main controller causes the source to produce the electron
beam having a higher intensity than in the second operational mode,
the higher intensity in the first operational mode being sufficient
to volatilize a deposit of a contaminant on the reticle.
33. The apparatus of claim 31, further comprising a dust collector
situated in the process chamber and connected to the main
controller, wherein in the first operational mode the electron beam
has an energy sufficient to confer a negative charge to a deposit
of a contaminant on the reticle and to detach the deposit from the
reticle, and the main controller applies a positive charge to the
dust collector, the positive charge being sufficient to attract the
detached negatively charged deposit of the contaminant.
34. A method for cleaning a reticle for use in performing
charged-particle-beam (CPB) microlithography, comprising the steps:
(a) placing the reticle in a process chamber in which CPB
microlithography of the reticle is performed; (b) directing an ion
beam or electron beam to irradiate a contaminant deposit on the
reticle; and (c) while performing step (b), introducing molecules
of a reactive gas to an area where the ion beam is irradiating the
deposit, wherein the irradiating beam ionizes the molecules of
reactive gas that then react with and volatilize the contaminant
deposit.
35. The method of claim 34, wherein the reactive gas comprises a
first gas selected from a group consisting of gaseous fluoride
compounds, gaseous chloride compounds, and gaseous bromide
compounds.
36. The method of claim 35, wherein the reactive gas comprises a
second gas selected from a group consisting of an inert gas,
nitrogen gas, and oxygen gas.
37. A charged-particle-beam (CPB) microlithography apparatus,
comprising: an illumination-optical system situated and configured
to illuminate a reticle, defining a pattern to be transferred to a
substrate, with a charged-particle illumination beam; a reticle
stage situated and configured to movably hold the reticle as the
reticle is being illuminated by the illumination beam, so as to
produced a patterned imaging beam propagating downstream of the
reticle; a projection-optical system situated and configured to
direct and image the imaging beam on a sensitive substrate; a
substrate stage situated and configured to movably hold the
sensitive substrate as the sensitive substrate is being exposed
with the imaging beam; an ion-beam source and ion-beam optical
system situated and configured to irradiate a focused ion beam onto
a predetermined location on the reticle; and a process chamber
enclosing the illumination-optical system, the reticle stage, the
projection-optical system, the substrate stage, the ion-beam
source, and the ion-beam optical system.
38. A charged-particle-beam (CPB) microlithography apparatus,
comprising: an illumination-optical system situated and configured
to illuminate a reticle, defining a pattern to be transferred to a
substrate, with a charged-particle illumination beam; a reticle
stage situated and configured to movably hold the reticle as the
reticle is being illuminated by the illumination beam, so as to
produced a patterned imaging beam propagating downstream of the
reticle; a projection-optical system situated and configured to
direct and image the imaging beam on a sensitive substrate; a
substrate stage situated and configured to movably hold the
sensitive substrate as the sensitive substrate is being exposed
with the imaging beam; a probe-light source probe-light optical
system situated and configured to irradiate a beam of probe light
onto a surface of the reticle, the probe light being used to
inspect the reticle for a contaminant deposit on the surface of the
reticle; a light detector for detecting a characteristic of the
probe light as the probe light encounters a contaminant deposit on
the reticle; and a process chamber enclosing the
illumination-optical system, the reticle stage, the
projection-optical system, the substrate stage, the probe-light
source, and the probe-light optical system.
39. The apparatus of claim 38, wherein the probe-light optical
system is configured to direct the beam of probe light selectively
on an upstream-facing surface of the reticle and on a side-wall of
an aperture in the reticle.
40. The apparatus of claim 39, wherein the probe light is selected
from the group consisting of UV light, deep UV light, and an
electron beam.
41. A charged-particle-beam (CPB) microlithography apparatus,
comprising: an illumination-optical system situated and configured
to illuminate a reticle, defining a pattern to be transferred to a
substrate, with a charged-particle illumination beam; a reticle
stage situated and configured to movably hold the reticle as the
reticle is being illuminated by the illumination beam, so as to
produced a patterned imaging beam propagating downstream of the
reticle; a projection-optical system situated and configured to
direct and image the imaging beam on a sensitive substrate; a
substrate stage situated and configured to movably hold the
sensitive substrate as the sensitive substrate is being exposed
with the imaging beam; a probe-light source probe-light optical
system situated and configured to irradiate a beam of probe light
onto a surface of the reticle, the probe light being used to
inspect the reticle for a contaminant deposit on the surface of the
reticle; a light detector for detecting a characteristic of the
probe light as the probe light encounters a contaminant deposit on
the reticle; an ion-beam source and ion-beam optical system
situated and configured to irradiate a focused ion beam onto a
predetermined location on the reticle; and a process chamber
enclosing the illumination-optical system, the reticle stage, the
projection-optical system, the substrate stage, the probe-light
source, the probe-light optical system, the ion-beam source, and
the ion-beam optical system.
Description
FIELD OF THE INVENTION
[0001] This invention pertains to apparatus and methods for
fabricating microelectronic devices such as integrated circuits,
displays, and the like, especially such methods and apparatus in
which the subject fabrication is performed in a "process chamber"
(e.g., vacuum chamber). More specifically, the invention pertains
to methods for removing contaminants adhering to a surface inside
such a chamber, such as a surface of a reticle used in a
charged-particle-beam microlithography apparatus. The invention
also pertains to microelectronic-fabrication apparatus operable to
perform removal of contaminants from a surface in a process chamber
of the apparatus.
BACKGROUND OF THE INVENTION
[0002] Fabrication of microelectronic devices (e.g., semiconductor
integrated circuits, displays, magnetic pickup heads, image
sensors, micro-machines) involves a large number of process steps
each performed using a specialized apparatus. Certain fabrication
steps are performed multiple times during fabrication of a device.
For example, microlithography is performed multiple times
(sometimes a hundred times or more) in the fabrication of
contemporary microprocessor chips and the like.
[0003] Continuing further with microlithography as a representative
fabrication method, most microlithography still being performed is
so-called "optical microlithography." In optical microlithography,
light (typically extreme UV light) is used as an energy beam with
which a pattern, defined on a reticle, is transferred onto the
surface of a resist-coated wafer or other substrate. In a related
technique, termed "charged-particle-beam" (CPB) microlithography,
the lithographic energy beam is a charged particle beam such as an
electron beam or ion beam. Whereas optical microlithography need
not be performed in a process chamber, CPB microlithography must be
performed in a vacuum chamber.
[0004] A disadvantage with process chambers in general, especially
vacuum chambers, is their tendency to accumulate deposits of
contaminants. Example contaminants that can accumulate in a vacuum
chamber of a CPB microlithography apparatus include precipitated
gas or gas-reaction products, deposits of resist released from the
wafer, and oil from the vacuum pump. Interaction of the deposits
with the lithographic energy beam can produce deposits of
hydrocarbons and other substances at various locations throughout
the process chamber and on certain components inside the process
chamber. Contaminant deposits also can form on a reticle or
mask.
[0005] Especially in electron-beam microlithography apparatus and
electron microscopes, irradiation of an electron beam over a long
period of time can create conditions leading to increased rates of
contaminant accumulation. Adhesion of contaminants to surfaces of
electromagnetic lenses and the like can affect lens performance in
an adverse manner. Adhesion of contaminants to a reticle can cause
development of irregularities in the transmissivity of the reticle,
which can result in deviations from specifications of the
linewidths and profiles of projected patterns. This results in
decreased accuracy of pattern transfer, and can result in
production of devices that do not function to specifications. In
addition, in an apparatus in which a charged particle beam is used,
charging of contaminant deposits by the beam can generate
extraneous electric fields that undesirably have unpredictable
behavior and alter the beam trajectory, thereby causing decreased
apparatus performance.
[0006] Current methods for removing contaminants from a surface
(e.g., reticle, lens surface, or the like) in the process chamber
typically involve removing the affected item from the process
chamber and wet-cleaning the item. Wet-cleaning normally is
performed using a solvent. This method requires substantial time in
which to turn off the apparatus, open the process chamber, remove
the affected item, clean the item, and replace it in the process
chamber. Also, during cleaning, the apparatus is off and not
performing useful work. This down-time adversely affects throughput
of the fabrication process performed using the apparatus.
[0007] In an optical microlithography apparatus, a thin film known
as a "pellicle" usually is applied to the surface of the reticle to
prevent adhesion of particulate contamination directly to the
reticle. The pellicle keeps the contaminant particles out of the
conjugate plane of the projection lens, thereby preventing
formation of images of the particles on the surface of the
substrate. With a CPB microlithography apparatus, in contrast, a
satisfactory material useful as a pellicle has not yet been found.
Thin-film materials are available that are transmissive to a
charged particle beam. However, passage of the beam through a thin
film usually affects the beam in an adverse manner. Hence,
available materials cannot be used to any substantial degree.
[0008] CPB microlithography apparatus that employ the so-called
"cell-projection" approach generally utilize a small reticle that
is not excessively expensive. A pellicle cannot be used with such a
reticle. Nevertheless, the reticles are relatively inexpensive, so
a contaminated reticle simply is discarded.
[0009] Other CPB microlithography approaches utilize reticles that
are substantially larger than the reticles used in cell projection.
These large reticles are very expensive; hence, it is not practical
simply to discard contaminated reticles. The conventional solution
to this problem is to suppress, as much as possible, contamination
of the reticle and other surfaces inside the process chamber.
Unfortunately, this approach frequently is not successful. For
example, certain exposures are performed while scanning the reticle
stage and wafer stage of the apparatus at high velocity during
exposure of the pattern. Such motions of the wafer stage and
reticle stage tend to generate fine particles. Also, fine particles
can get into the process chambers from the outside environment
during vacuum pump-down and venting. These problems cannot be
avoided, and the introduced particles tend to adhere to the reticle
as contaminants. As a result, reticle cleaning is indispensable for
ensuring accurate transfer of the reticle pattern to the substrate
surface. Again, reticle cleaning by conventional methods as
summarized above undesirably reduces throughput.
SUMMARY OF THE INVENTION
[0010] In view of the shortcomings of conventional methods and
apparatus as summarized above, an object of the invention is to
provide methods and apparatus for removing contaminants adhering to
the reticle or to any of various other components located in a
"process chamber" of a process apparatus, without adversely
affecting the throughput of the process apparatus. An exemplary
process chamber is the vacuum chamber of an electron-beam
microlithography apparatus.
[0011] To such end, and according to a first aspect of the
invention, contamination-removal devices are provided. An
embodiment of such a device comprises a treatment chamber, a
chamber-evacuation pump, a gas-inlet, and an electron-beam
irradiator. The treatment chamber defines an interior space in
which an object, having a deposit of a contaminant substance and
requiring cleaning to remove the deposit, can be situated. The
chamber-evacuation pump is in communication with the treatment
chamber, and is configured to evacuate the interior space. The
gas-inlet is in communication with the treatment chamber, and is
configured to introduce a treatment gas into the interior space.
The electron-beam irradiator is situated and configured to
irradiate an electron beam in the interior space such that the
electron beam ionizes molecules of the treatment gas. The ionized
molecules can react with molecules of the contaminant substance on
the object so as to volatilize the contaminant substance from the
deposit. The volatilized contaminant is removed using the
chamber-evacuation pump.
[0012] The treatment gas desirably is one or more of: water vapor,
oxygen, ozone, and oxygen radicals, which have high reactivity when
ionized by an electron beam.
[0013] The treatment chamber can include a scattering body situated
so as to be bombarded by the electron beam and form scattered
electrons. The scattered electrons propagate to regions in the
treatment chamber that otherwise would be difficult to reach using
the electron beam directly, thereby facilitating rapid cleaning of
such areas.
[0014] The treatment chamber can be a process chamber in which a
fabrication process is conducted. Furthermore, the electron-beam
irradiator can be the same as used to perform the fabrication
process in the process chamber. For example, the electron-beam
irradiator can be an illumination-optical system of an
electron-beam microlithography apparatus. Alternatively, the
electron-beam irradiator can be separate from an electron-optical
system used to perform the fabrication process.
[0015] According to another aspect of the invention, electron-beam
microlithography apparatus are provided that include a process
chamber and an electron-optical system situated in the process
chamber and configured to irradiate a surface of a substrate in a
selective manner with an electron beam from a source. An embodiment
of such an apparatus includes a treatment-gas source connected to
and configured to introduce a treatment gas into the process
chamber. Also inside the process chamber is a separate
electron-beam irradiation device that is separate from the
electron-optical system. The electron-beam irradiation device is
configured to produce a respective electron beam that impinges on
the treatment gas in the process chamber so as to ionize molecules
of the treatment gas. The ionized molecules are available to react
with and volatilize a contaminant deposit in the process chamber.
By including a separate electron-beam irradiation device used for
contaminant removal, this embodiment effectively removes
contaminants from regions inside the process chamber not ordinarily
irradiated by the electron beam from the electron-optical
system.
[0016] According to another aspect of the invention, methods are
provided for removing a deposit of a contaminant in a process
chamber. In an embodiment of such a method, a treatment gas is
provided that comprises molecules that become ionized when
irradiated by electrons. The molecules of the treatment gas are
introduced into the process chamber. When the process chamber
contains molecules of the treatment gas, the molecules of the
treatment gas are irradiated with the electron beam to ionize the
molecules of the treatment gas. The ionized molecules of the
treatment gas are allowed to react with and volatilize the deposit.
Finally, the volatilized deposit is removed from the process
chamber, such as by evacuating the process chamber.
[0017] In another embodiment of the method, a treatment gas is
provided as summarized above. Molecules of the treatment gas are
introduced into the process chamber. In the process chamber, an
electron-beam irradiation device is provided that is configured to
produce an electron beam. An electron-scattering body is placed in
the process chamber such that the electron beam can impinge on the
electron-scattering body to produce scattered electrons. When the
process chamber contains molecules of the treatment gas, the
electron-scattering body is irradiated with the electron beam to
produce scattered electrons that ionize the molecules of the
treatment gas. The ionized molecules are allowed to react with and
volatilize the deposit. An advantage of this method is that the
scattered electrons can propagate to regions inside the process
chamber that otherwise are difficult to reach using a directly
impinging electron beam. In any event, using such a method, there
is no need to remove contaminated objects from the process chamber
or to disassemble the apparatus associated with the process
chamber. Consequently, throughput is not adversely affected to a
significant degree.
[0018] Another method embodiment is directed to methods for
cleaning a reticle in a process chamber of an electron-beam
microlithography apparatus. According to the method, the reticle is
placed in an interior space defined by the process chamber. A
subatmospheric pressure ("vacuum") is applied to the interior
space. An electron beam is directed to impinge on the reticle in
the process chamber as electrons of the beam passing through the
reticle are deflected away from a resist-coated surface of a
lithography substrate so as not to expose the resist.
[0019] The electron beam impinging on the reticle for reticle
cleaning desirably has an energy sufficient to volatilize a deposit
of a contaminant on the reticle as the reticle is being irradiated
with the electron beam. This cleaning energy desirably is greater
than the energy of the beam used to expose the resist-coated
surface of the substrate with the reticle pattern.
[0020] The cleaning energy can be sufficient to confer a negative
charge to the contaminant deposit and to cause the deposit to
detach from the surface of the reticle. In this instance, it is
desirable to provide a "dust collector" inside the process chamber.
The dust collector is provided with a positive charge sufficient to
attract the detached deposit, and thus used to collect the detached
deposit.
[0021] According to another embodiment of a method, according to
the invention, for performing microlithography, the reticle and
substrate are placed in the process chamber. The reticle is
situated so as to be irradiated with an upstream electron beam and
to produce a downstream electron beam carrying an image of the
irradiated region of the reticle. The substrate is situated such
that its resist-coated surface can be exposed with the image
carried by the downstream electron beam. The process chamber is
evacuated to produce a subatmospheric pressure in the process
chamber. In a reticle-cleaning mode of operation, the upstream
electron beam is directed to impinge on the reticle while the
downstream electron beam is directed away from the resist-coated
surface so as to avoid exposing the resist. In a substrate-exposure
mode of operation, the upstream electron beam is directed to
irradiate a region on the reticle while the downstream electron
beam is directed to a corresponding location on the resist-coated
surface of the substrate so as to transfer the pattern from the
reticle to the substrate. In the reticle-cleaning mode, the
electron beam desirably has a first energy sufficient to volatilize
a contaminant deposit on the reticle. In the substrate-exposure
mode, the electron beam desirably has a second energy sufficient to
expose the resist. The first energy desirably is greater than the
second energy.
[0022] Because the reticle is cleaned in situ inside the evacuated
process chamber of the microlithography apparatus, there is no need
to break the vacuum of the process chamber to remove the reticle
for remote cleaning. Hence, the reticle can be cleaned readily
without a significant decrease in throughput. For example, the
reticle can be cleaned before each use.
[0023] In the foregoing method, the process chamber can be provided
with a dust collector that is provided with a positive charge
during the reticle-cleaning mode. Hence, during the
reticle-cleaning mode, the electron beam impinging on the reticle
has an energy sufficient to confer a negative charge to a
contaminant deposit on the reticle and to detach the deposit from
the reticle. The detached deposit thus is attracted to and
collected by the dust collector.
[0024] The foregoing and additional features and advantages of the
invention will be more readily apparent from the following detailed
description, which proceeds with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic elevational depiction (with partial
sections) of a contamination-removal device according to a first
representative embodiment of the invention.
[0026] FIG. 2 is a schematic elevational depiction (with partial
sections) of an electron-optical lens column according to the
second representative embodiment.
[0027] FIG. 3 is a schematic elevational diagram (with control
aspects shown in block-diagram form) of an electron-optical lens
column according to the second representative embodiment.
[0028] FIG. 4 is a schematic elevational depiction (with partial
sections) of certain aspects of an electron-beam microlithography
apparatus according to the third representative embodiment.
[0029] FIG. 5 is a schematic elevational depiction (with partial
sections) of certain aspects of an electron-beam microlithography
apparatus according to the fourth representative embodiment,
including deflection of the beam in a reticle-cleaning mode of
operation.
[0030] FIG. 6 is a schematic elevational depiction (with partial
sections) of certain aspects of the electron-beam microlithography
apparatus according to the fourth representative embodiment, in a
wafer-exposure mode of operation.
[0031] FIG. 7 is a schematic elevational section of a portion of a
scattering-stencil type reticle used in the fourth representative
embodiment, including carbon particles situated on the
upstream-facing surface of the reticle.
[0032] FIG. 8 is a block diagram of certain control relationships
in the fourth representative embodiment.
[0033] FIG. 9 is an elevational schematic diagram of an
electron-beam microlithography apparatus, as described in the fifth
representative embodiment.
[0034] FIG. 10 is an elevational schematic diagram of an
electron-beam microlithography apparatus, as described in the sixth
representative embodiment.
[0035] FIG. 11 is an elevational schematic diagram of an
electron-beam microlithography apparatus, as described in the
seventh representative embodiment.
DETAILED DESCRIPTION
[0036] The invention is described below in the context of
representative embodiments and examples that are not intended to be
limiting in any way.
[0037] First Representative Embodiment
[0038] This embodiment is depicted in FIG. 1, and is directed to a
contamination-removal device 1 according to the invention. The
device 1 of FIG. 1 comprises a process chamber 3 in which the
object 2 to be cleaned is situated, a vacuum pump 5 used to
evacuate the interior of the process chamber 3, and a gas inlet 7
extending through a wall of the process chamber 3. The gas inlet 7
is used for introducing a treatment gas into the interior of the
process chamber 3. During cleaning, the object 2 is mounted or
otherwise placed on a stage 11 situated inside the process chamber
3. The process chamber 3 can be the same chamber in which an actual
fabrication process (e.g., microlithography) is conducted on the
object 2, or can be a separate chamber dedicated to use for
cleaning the object 2. In the latter case, the process chamber 3
can be termed a "treatment chamber."
[0039] The device 1 also includes an electron-beam-irradiation
device 9 situated and configured to irradiate the object 2 with an
electron beam. The electron-beam-irradiation device 9 includes an
electron gun 13 and an electron-optical system 15 that are situated
upstream of the stage 11. The electron gun 13 emits an electron
beam 23 in the downstream direction. The electron-optical system 15
includes multiple electron-lenses and deflectors, and an aperture,
that irradiate the object 2 on the stage 11 with the electron beam
emitted from the electron gun 13.
[0040] An evacuation outlet 17 extends from the process chamber 3
and is connected to the vacuum pump 5 for evacuating the atmosphere
inside the process chamber 3. The gas inlet 7 is connected to a gas
cylinder 21 via valves 19. The gas cylinder 21 provides a supply of
a gas such as water vapor, oxygen, ozone, or oxygen radicals, or a
mixture of such gases.
[0041] For cleaning, the object 2 is placed on the stage 11 inside
the process chamber 3. The vacuum pump 5 is turned on to evacuate
the interior of the process chamber 3. After reaching a desired
vacuum, the vacuum pump is turned off and the valves 19 are opened
to allow flow of the gas from the gas cylinder 21 through the gas
inlet 7 into the process chamber 3. When the interior of the
process chamber 3 is sufficiently filled with the gas, the electron
beam 23 is directed in a downstream direction from the
electron-beam-irradiation device 9. The electron beam 23 ionizes
the gas molecules inside the process chamber 3. The ionized gas
molecules oxidize molecules of the contaminants adhering to the
object 2. As a result, the contaminants are broken down and
volatilized.
[0042] After irradiating the object 2 with the electron beam for a
specified period of time, the vacuum pump 5 is turned on again to
evacuate the process chamber 3. This evacuation draws volatilized
contaminants from the process chamber 3.
[0043] If the area of the object 2 is large, then electron beam 23
can be deflected as required by a deflector or the like of the
electron-optical system 15 to direct the beam 23 to various regions
on the surface of the object 2. This deflection can be in a
scanning manner, or the stage 11 can be moved in a scanning manner
in the horizontal direction (in the figure), to allow the entire
surface of the object 2 to be irradiated with the electron beam
23.
[0044] Second Representative Embodiment
[0045] This embodiment is shown in FIGS. 2 and 3. Turning first to
FIG. 3, an electron-optical lens column 31 is situated in an upper
portion (in the figure) of an electron-beam microlithography
apparatus 30. The lens column 31 is a chamber that can be
evacuated. To such end, a vacuum pump 32 is connected to the lens
column 31. At the upper end (in the figure) of the lens column 31
is an electron gun 33 that emits an electron beam in a downstream
direction. From the electron gun 33, the beam passes through a
condenser lens 34, passes a deflector 35, and impinges on a reticle
M, in that order. The condenser lens 34 converges the electron beam
emitted from the electron gun 33. The electron beam is scanned in
the lateral direction (in the figure) by the deflector 35 to
illuminate every region on the reticle M within the optical field
of the electron-optical system.
[0046] The reticle M is fastened by electrostatic adhesion or the
like to a reticle chuck 40 installed on an upstream-facing surface
of a reticle stage 41. The reticle stage 41 is mounted to and
supported by a base plate 46 or analogous support. The reticle
stage 41 is driven by an actuator 42 connected to the reticle stage
41. The actuator 42 is connected to a controller 45 via a stage
driver 44. A laser interferometer 43 is situated on one side (right
side in the figure) of the reticle stage 41. The laser
interferometer 43 is connected to the controller 45. The laser
interferometer 43 produces data, concerning the position of the
reticle stage 41, that is input to the controller 45. Based on the
data, the controller 45 routes commands to the stage driver 44 to
operate the actuator 42 to drive the reticle stage 41 to a desired
target position.
[0047] A "wafer chamber" 51 (another vacuum chamber, and
representative of a process chamber) is situated downstream of the
base plate 46. A vacuum pump 52 is connected to the wafer chamber
51 (on the right side in the figure) to allow evacuation of the
interior of the wafer chamber 51. Inside the wafer chamber 51 are a
projection lens 54, a deflector 55, and a substrate ("wafer"), in
that order. The electron beam passing through the reticle M is
converged by the projection lens 54 and deflected by the deflector
55 as required to form an image of the illuminated region of the
reticle M in a specified position on the wafer W.
[0048] The wafer W is fastened by electrostatic adhesion or the
like to a wafer chuck 60 situated on the upstream-facing surface of
a wafer stage 61. The wafer stage 61 is mounted on a base plate 66
or analogous support. The wafer stage 61 is movable as required by
an actuator 62 connected to the wafer stage 61. The actuator 62 is
connected to the controller 45 via a stage driver 64. A laser
interferometer 63 is situated to the side of the wafer stage 61
(i.e., on the right side in the figure). The laser interferometer
63 is connected to the controller 45. The laser interferometer 63
produces data concerning the position of the wafer stage 61. This
data is routed to and input to the controller 45. The controller 45
routes commands to the driver 64 to cause the actuator 62 to move
the wafer stage 61 to a desired target position.
[0049] Turning now to FIG. 2, the electron-optical system and
reticle of the apparatus of FIG. 3 are shown in simplified form. As
noted above, the vacuum pumps 32, 52 are connected to the lens
column 31 and wafer chamber 51, respectively, of the apparatus 30.
A gas inlet 71 opens into the lens column 31 or the wafer chamber
51 (or both). The gas inlet 71 is connected to a gas cylinder 75
via valves 73. The gas cylinder 75 supplies a gas such as water
vapor, oxygen, ozone, or oxygen radicals, or a mixture of such
gases.
[0050] To remove contamination from the interior of the apparatus
30, a scattering body 77 can be placed on (for example) the reticle
stage 41 or the wafer stage 61. The scattering body 77 desirably
has a plate configuration and desirably is made of or plated with a
"heavy" metal such as tungsten, tantalum, gold, or platinum. Even
more desirably, the upstream-facing surface of the scattering body
77 defines multiple fine recesses and projections. The valves 73
are opened to introduce the gas from the gas cylinder 75 via the
gas inlet 71 into the lens column 31 and vacuum chamber 51. After
sufficiently filling the respective interiors of the lens column 31
and vacuum chamber 51 with the gas, the upstream-facing surface of
the scattering body 77 is irradiated with an electron beam 81. Such
irradiation generates backscattered electrons 79. The
upstream-facing surface of the scattering body desirably includes
fine recesses and projections to facilitate scattering of electrons
in all directions from the scattering body 77.
[0051] The backscattered electrons 79 ionize molecules of the gas
in the lens column 31 and wafer chamber 51. The ionized gas
molecules react with deposits of contaminants inside the chambers
31, 51, causing breakdown and volatilization of the deposits. Since
the backscattered electrons 79 propagate in all directions inside
the lens column 31 and vacuum chamber 51, regions that ordinarily
are difficult to irradiate (e.g., lenses, deflectors, and the
downstream-facing surfaces of apertures) are irradiated by the
backscattered electrons. Thus, contaminant deposits on all surfaces
inside the chambers 31, 51 are broken down and volatilized. After
irradiating in this manner for a specified period of time, the
vacuum pumps 32, 52 are turned on to evacuate the lens column 31
and wafer chamber 51 and remove the volatilized contaminants.
[0052] Third Representative Embodiment
[0053] This embodiment, directed to an electron-beam
microlithography apparatus 30, is depicted schematically in FIG. 4.
This embodiment includes an electron-beam (e-beam) irradiation
device 83 used for removal of contaminants. The e-beam irradiation
device 83 is situated inside the lens column 31 or wafer chamber 51
(or both). The e-beam irradiation device 83 is separate from the
electron gun 33 used for lithographic exposure. The e-beam
irradiation device 83 includes an electron gun 85 and an
electron-optical system 87. The electron-optical system 87
typically includes multiple lenses, deflectors, and an aperture
(not shown). Vacuum pumps 32, 52 are connected to the lens column
31 and wafer chamber 51, respectively. A gas inlet 71 extends into
the lens column 31 or wafer chamber 51, or both. The gas inlet 71
is connected to a gas cylinder 75 via valves 73. The gas cylinder
75 is filled with a gas such as water vapor, oxygen, ozone, or
oxygen radicals, or mixture thereof.
[0054] To remove contamination from the interior of the apparatus
30, the interiors of the lens column 31 and wafer chamber 51 are
filled with the gas from the gas cylinder 75. The electron beam 81
from the electron gun 33 used for lithographic exposure is
deflected and scanned in the interior of the apparatus 30. Also, an
electron beam 89 is emitted from the e-beam irradiation device 83.
Desirably, the e-beam irradiation device 83 is situated such that
the electron beam 89 emitted therefrom is directed to locations
that are beyond the irradiation range of the exposure electron beam
81, and that are most susceptible to contamination inside the lens
column 31 and wafer chamber 51.
[0055] Gas molecules ionized by the electron beams 81, 89 react
with deposits of contaminants adhering to the interior surfaces of
the chambers 31, 51. Thus, the contaminants are oxidized, broken
down, and volatilized. Electron-beam irradiation is continued for a
specified period of time, after which the vacuum pumps 32, 52 are
turned on to evacuate the lens column 31 and wafer chamber 51.
Thus, the volatilized molecules of the contaminants are removed
from the chambers.
[0056] Any of the various embodiments described above achieve
removal of contaminants from the interior of a chamber of, e.g., a
microlithographic exposure apparatus without reducing throughput or
having to disassemble or remove components from the apparatus.
EXAMPLE 1
[0057] The test object for cleaning was a silicon stencil reticle
with adhering deposits of hydrocarbon contaminants that accumulated
during electron-beam irradiation of the reticle. The test object
was placed in the sample chamber of a scanning electron microscope,
and water vapor was introduced into the sample chamber. The
contaminated test object was scanned and irradiated with an
electron beam, accelerated across a voltage of 20 kV, in a 600-Pa
atmosphere in the sample chamber. Under such conditions, the
contaminants adhering to the silicon stencil reticle were removed
successfully.
EXAMPLE 2
[0058] The test object for cleaning was a silicon stencil reticle
with adhering deposits of hydrocarbon contaminants that accumulated
during electron-beam irradiation of the reticle. The test object
was placed in the sample chamber of a scanning electron microscope,
and oxygen gas was introduced into the sample chamber. The
contaminated test object was scanned and irradiated with an
electron beam, accelerated across a voltage of 20 kV, in a 600-Pa
atmosphere in the sample chamber. Under such conditions, the
contaminants adhering to the silicon stencil reticle were removed
successfully.
EXAMPLE 3
[0059] The test object for cleaning was a silicon stencil reticle
with adhering deposits of hydrocarbon contaminants that accumulated
during electron-beam irradiation of the reticle. The test object
was placed in the sample chamber of a scanning electron microscope,
and ozone gas was introduced into the sample chamber. The ozone gas
was generated using an ozonizer that converts oxygen into ozone.
The contaminated test object was scanned and irradiated with an
electron beam, accelerated across a voltage of 30 kV, in a 400-Pa
atmosphere in the sample chamber. Under such conditions, the
contaminants adhering to the silicon stencil reticle were removed
successfully.
EXAMPLE 4
[0060] The test object for cleaning was a metal aperture, made of
molybdenum, as used in an electron-optical system. The test object
had adhering deposits of hydrocarbon contaminants. The test object
was placed in the sample chamber of a scanning electron microscope,
and a mixture of water vapor and oxygen gas was introduced into the
sample chamber. The contaminated test object was scanned and
irradiated with an electron beam, accelerated across a voltage of
30 kV, in a 600-Pa atmosphere in the sample chamber. Under such
conditions, the contaminants adhering to the metal aperture were
removed successfully.
EXAMPLE 5
[0061] A scattering body was configured as a tungsten plate. The
scattering body was placed on the wafer stage of an electron-beam
microlithography apparatus inside a wafer chamber. Oxygen gas was
introduced into the wafer chamber. The scattering body was
irradiated with an electron beam, accelerated across a voltage of
100 kV, in a 1000-Pa atmosphere in the wafer chamber. Afterward,
the interior of the wafer chamber was evacuated. Under such
conditions, the contaminants adhering to various locations inside
wafer chamber and lens column of the electron-beam microlithography
apparatus were removed.
[0062] Fourth Representative Embodiment
[0063] This embodiment is directed to cleaning of the reticle as
used in a CPB microlithography apparatus. The reticle is cleaned in
situ by the CPB microlithography apparatus operated in a
"reticle-cleaning" mode. Reticle cleaning can be performed prior to
operating the apparatus in a "wafer-exposure" mode, so as to
prepare the reticle for use in exposure. During reticle cleaning,
contaminants are removed by irradiating the reticle with a charged
particle beam (e.g., an electron beam).
[0064] An electron-beam microlithography apparatus according to
this embodiment is shown in FIG. 5. The components used for
exposure and for reticle cleaning are contained in a vacuum chamber
120. For exposure and reticle cleaning, the interior of the vacuum
chamber 120 is maintained at a desired level of "vacuum"
(subatmospheric pressure) by means of a vacuum pump 121. Under such
conditions, it is possible to select either the wafer-exposure mode
or the reticle-cleaning mode without having to change the
vacuum.
[0065] An electron gun 101 emits an electron beam 103 in a
downstream trajectory at an acceleration voltage of, e.g., 100 kV.
A reticle 104 is placed on a reticle stage 105 situated downstream
of the electron gun 101. The electron beam 103 emitted from the
electron gun 101 is collimated by an illumination lens 102 for
irradiation of the reticle 104. At any given instant, the
irradiation field on the reticle 104 is, e.g., 1-mm square.
[0066] The reticle 104 can be a scattering-stencil reticle
comprising a reticle membrane made of a material that scatters
incident electrons of the beam and that defines through-holes that
are transmissive to the incident beam. The pattern of through-holes
in the membrane defines the elements of the pattern to be
transferred to a substrate (wafer) 109. Alternatively, the reticle
can be a scattering-membrane reticle comprising regions of an
electron-scattering material formed on the surface of a thin base
membrane that is relatively transmissive to the incident beam. In
either case, the electron-scattering portions of the reticle are
sufficiently thin to prevent significant absorption of incident
electrons, thereby preventing excessive heating of the reticle that
otherwise would occur by absorption of incident electrons. By way
of example, in a scattering-stencil reticle configuration, the
reticle membrane is made of silicon with a thickness of 2
.mu.m.
[0067] The apparatus of FIG. 5 also includes a first lens 106 and a
second lens 108 of a projection-lens system. The lenses 106, 108
are situated along an optical axis A at a spacing of 50 mm beneath
the reticle 104. A "contrast diaphragm" 107 is situated between the
lenses 106, 108. The contrast diaphragm 107 is made of a tantalum
or other heavy metal plate having a thickness of, e.g., 1 mm and
defining an axial aperture having a diameter of, e.g., 150 .mu.m.
The contrast diaphragm is situated in the vicinity of the Fourier
plane of the reticle 104. The contrast diaphragm 107 blocks
downstream propagation of scattered electrons so that only the
electrons passing through the aperture propagate downstream of the
contrast diaphragm. I.e., electrons scattered while passing through
the reticle 104 are blocked by the contrast diaphragm 107.
[0068] A movable wafer stage 110 is situated in the lower part (in
the figure) of the depicted apparatus. A substrate (wafer) 109 is
mounted on the wafer stage 110 for exposure. So as to be imprinted
with an image of the pattern on the reticle 104, the surface of the
wafer 109 is coated with a resist, either directly or with an
interposed insulating film or conductive film.
[0069] At least one deflector 112 is used to deflect the electron
beam 111 as required. During operation of the apparatus in the
reticle-cleaning mode, the reticle 104 is irradiated by the
electron beam 111. Electrons of the beam passing through the
reticle 104 are deflected laterally by the deflector 112 in a
manner causing the electron beam 111 to enter a Faraday cup 123
situated on the wafer stage 110. Thus, during such deflection, the
electron beam 111 does not irradiate the resist on the wafer 109.
The Faraday cup 123 can be movable so as to be situated on the
wafer stage 110 only in the reticle-cleaning mode. Alternatively,
it is possible to actuate the wafer stage 110 to move the Faraday
cup 123 thereon into a position at which the Faraday cup 123 can
capture the electron beam 111 more easily.
[0070] In the reticle-cleaning mode, the electron beam 103
irradiates the reticle 104 in the same sequence as in the
wafer-exposure mode. Either of the following two methods may be
used to remove contaminants adhering to the reticle 104. In the
first method the contaminants are heated to a high temperature and
volatilized. To such end, the beam intensity (current) of the
electron beam 103 desirably is increased above the beam intensity
used in the wafer-exposure mode, so as to heat the contaminants to
a high temperature as quickly as possible. For example, the beam
intensity can be 50 .mu.A in the wafer-exposure mode and 100 .mu.A
in the reticle-cleaning mode. The electron-beam irradiation time is
described in detail later below. In the second method cleaning is
accomplished by charging the contaminants adhering to the reticle
104 with a negative charge (by electron-beam irradiation). The
contaminants are collected using a dust collector 122 flanking the
reticle 104 and energized with a positive potential. In either
method, the microlithography apparatus shifts to the wafer-exposure
mode after the completing the reticle-cleaning mode.
[0071] FIG. 6 depicts the electron-beam microlithography apparatus
configured for operation in the wafer-exposure mode. In this mode,
the electron gun 101 emits the electron beam 103 in a downward
direction (in the figure), accelerated under a voltage of, e.g.,
100 kV. The electron beam 103 emitted from the electron gun 101 is
collimated by the illumination lens 102 for illumination of the
reticle 104. Also shown are the first and second projection lenses
106, 108, respectively, and the deflector 112. During wafer
exposure, defined regions ("subfields") of the reticle 104 are
irradiated sequentially. Meanwhile, respective images of the
irradiated subfields are formed at predetermined regions on the
wafer 109. These exposure regions on the wafer 109 are determined
by the deflector 112 such that, upon completing exposure of the
reticle pattern onto the wafer 109, the individual subfield images
are "stitched" together properly. As each subfield images is
projected onto the wafer, the resist in the exposure location is
imprinted with the portion of the overall pattern defined by the
irradiated subfield. Usually, the size of the image as formed on
the wafer 109 is "reduced" (demagnified) relative to the size of
the corresponding pattern on the wafer. For example, the reduction
can be 1/4.
[0072] During wafer exposure, exposure time is a function of
exposure parameters such as the resist sensitivity, beam current,
stage velocity, and other variables. For example, the resist can
have a sensitivity of 5 .mu.C/cm.sup.2, and the exposure time for
one subfield can be 62.5 .mu.sec at a beam current (on the reticle)
of 50 .mu.A.
[0073] Beam intensity and irradiation time during the
reticle-cleaning mode (in which contaminants are removed by heating
using the electron beam) are discussed with reference to FIG. 7. In
the figure, a scattering-stencil reticle 104 is shown having
membrane regions 114 and through-holes 115. As representative
particulate contaminants, carbon particles 117 are situated on the
upstream-facing surface of the reticle 104. The particles 117 have
a diameter of 0.4 .mu.m. The electron beam 103 directed onto the
reticle 104 is scattered by the membrane regions 114 and
transmitted by the through-holes 115.
[0074] In the following calculations, the carbon particles 117 are
approximated by cubes measuring 0.4 .mu.m on each side. Assuming
that the carbon particles 117 have the approximate density of
graphite, the density of the particles is 2.27.times.10.sup.6
g/m.sup.3, and the specific heat of the particles is 0.669
J/gK.
[0075] The absorption by the particles 117 of electron-beam energy
can be expressed using the Bethe equation:
dE/dx=1.268.times.10.sup.9 eV/m
[0076] Accordingly, the amount of electron-beam energy absorbed by
a carbon particle (having a thickness of 0.4 .mu.m) is:
dE=(1.268.times.10.sup.9 eV/m)(0.4.times.10.sup.-6
m)=5.07.times.10.sup.2 eV
[0077] Assuming that the electron beam is accelerated under a
voltage of 100 kV, the ratio of the amount of energy absorbed by
the particle to the acceleration energy is:
(5.07.times.10.sup.2 eV)/(10.sup.5 eV).apprxeq.0.5%
[0078] Assuming a beam intensity of 100 .mu.A, the total beam
energy applied in one second to an irradiation area of 1 mm.sup.2
is:
(100 kV)(100 .mu.A)(1 sec)=(1.times.10.sup.5
J/A.multidot.s)(1.times.10.su- p.-4 A)(s)=10 J
[0079] Accordingly, the beam energy irradiated on a carbon particle
measuring 0.4 .mu.m on a side is:
(10 J)[(0.4.times.10.sup.6 m)/(1.times.10.sup.-3
m)].sup.2=1.6.times.10.su- p.-6 J
[0080] Since the energy absorbed by the carbon particles is 0.5% of
the incident beam energy, the absorbed energy is 8.times.10.sup.-9
J.
[0081] The mass of each carbon particle is determined from the
density and volume of the particle:
(2.27.times.10.sup.6 g/m.sup.3)(0.4.times.10.sup.-6
m).sup.3=1.45.times.10.sup.-13 g
[0082] Since the carbon particles merely are resting on the surface
of the reticle with minimal thermal contact with the reticle, it is
assumed that no heat is conducted from the carbon particles to the
reticle. In such a case, the temperature rise .DELTA.T of the
carbon particles is determined as follows:
.DELTA.T=(8.times.10.sup.-9 J)/[(0.669 J/gK)(1.45.times.10.sup.-13
g)]=8.2.times.10.sup.4 K
[0083] In other words, if electron-beam irradiation of the reticle
were performed for 1 second under the conditions described above,
the temperature of each carbon particle would be increased by
approximately 82,000 K. Since the vaporization temperature of
carbon is approximately 4900.degree. C., irradiation with the
electron beam for approximately 60 msec causes the temperature of
the carbon particles to rise approximately 5500 degrees, which
causes the carbon particles to evaporate. Thus, as described above,
reticle cleaning can be accomplished in a short time by irradiating
the reticle with the electron beam having a higher intensity than
used for wafer exposure.
[0084] The reticle 104 shown in FIG. 7 is a scattering-stencil
reticle in which only a small percent of incident beam energy is
absorbed. The heat generated by this absorbed energy is conducted
to the reticle stage. During reticle cleaning as described above,
the temperature rise of the reticle is actually about the same as
encountered by the reticle during the wafer-exposure mode.
Consequently, the reticle temperature does not increase to a level
at which the reticle could be damaged. Also, since the surfaces of
particles of carbon and other contaminants normally are oxidized,
conditions for poor heat conduction between the reticle and the
particles are fairly well satisfied if the thermal-contact
resistance between the reticle and the particles is taken into
account. Furthermore, the electron-beam irradiation conditions are
not limited to the specific conditions described above; actual
conditions should be determined based on the materials and
dimensions of the reticle and the contaminants.
[0085] The example described above was in the context of carbon
particles that exhibit low absorption of the incident electrons of
the beam. Metal particles, on the other hand, exhibit relatively
high absorption of incident electrons. Consequently, metal
particles would be volatilized in a shorter time than carbon
particles.
[0086] In addition, the reticle-cleaning mode can be effective in
removing contaminants (e.g., burned-on carbon-type contaminants)
that cause local accumulations of charge that can affect the beam
trajectory adversely. Whenever charge-accumulation occurs, the
electrical conductivity of the reticle tends to drop, which results
in poorer thermal conductivity between the particulate contaminants
and the reticle. Under such conditions, the contaminants can be
volatilized readily in the same manner as described above.
[0087] A block diagram showing control relationships of this
embodiment is shown in FIG. 8. The intensity of the electron beam
emitted from the electron gun 101 is controlled by an electron-gun
controller 134 connected to a main controller 131. The operational
parameters of the respective lenses 102, 106, 108 are controlled by
a lens-coil power supply 140 also connected to the main controller
131. Similarly, the operational parameters of the deflector 112 are
controlled by a deflector-coil power supply 141 also connected to
the main controller 131.
[0088] The reticle 104 is mounted to the upstream-facing surface of
the reticle stage 105. A reticle-stage controller 133, also
connected to the main controller 131, controls the position of the
reticle stage 105. Respective position detectors 135 (e.g., laser
interferometers) detect the position of the reticle stage 105. Data
produced by the position detectors 135 are routed to the main
controller 131 via respective data interfaces 136. Stage-control
data from the reticle-stage controller 133 are input into a
statistical calculator 132. The statistical calculator 132 is
configured to optimize, from the results of statistical
calculations performed by the statistical calculator, the relative
positions of the reticle and wafer.
[0089] Similarly, a wafer-stage controller 137, also connected to
the main controller 131, controls the position of the wafer stage
110. Respective position detectors 138 (e.g., laser
interferometers) detect the position of the wafer stage 10. Data
produced by the position detectors 138 are routed to the main
controller 131 via respective data interfaces 139. Stage-position
data from the position detector 138 and data from the wafer-stage
controller 137 are input into the statistical calculator 132.
[0090] In the reticle-cleaning mode, the main controller 131
controls the electron-gun controller 134 to cause the electron gun
101 to direct an electron beam toward the reticle 104. The main
controller 131 also controls the deflector-coil power supply 141 so
as to cause the deflector 112 to deflect the electron beam (passing
through the reticle 104) sufficiently to cause the electron beam to
intersect the wafer plane outside an area coated with resist. The
main controller 131 also causes a positive potential to be applied
to the Faraday cup 123 so as to cause the electron beam to be
conducted to the Faraday cup 123.
[0091] In the alternative method in which cleaning is performed by
collecting particulate contaminants, released from the reticle,
using a dust collector 122, the main controller 131 controllably
operates the dust collector 122 in the reticle-cleaning mode.
Specifically, at the time the electron beam is directed toward the
reticle 104, or immediately after such irradiation of the reticle,
a positive potential is applied to the dust collector 122 so that
negatively charged contaminants released from the reticle are
attracted to and collected in the dust collector 122. In cases in
which dust collection is performed simultaneously with
electron-beam irradiation of the reticle, the dust collector
desirably is situated at a position that does not affect the
trajectory of the beam.
[0092] In the wafer-exposure mode, the main controller 131
controllably operates the electron-gun controller 134 to cause the
electron gun 101 to direct the electron beam toward the reticle
104. The main controller 131 also controllably operates the
deflector-coil power supply 141 to cause the deflector 112 to scan
the electron beam over the resist on the wafer so as to imprint the
resist with the reticle pattern as projected onto the wafer
surface.
[0093] Fifth Representative Embodiment
[0094] FIG. 9 shows certain imaging and control relationships of an
electron-beam microlithography apparatus according to a
representative embodiment. Although this embodiment employs an
electron beam as a lithographic energy beam, it will be understood
that the principles of this embodiment can be applied with equal
facility to use of an alternative charged particle beam, such as an
ion beam.
[0095] The apparatus of FIG. 9 comprises an illumination-optical
system IOS and a projection-optical system POS arranged along an
optical axis AX. The illumination-optical system IOS comprises
optical components situated between an electron gun 201 and a
reticle 210, and the projection-optical system POS comprises
optical components situated between the reticle 210 and a substrate
223. So as to be imprinted with the pattern as projected from the
reticle by the projection-optical system POS, the upstream-facing
surface of the substrate 223 is coated with a suitable "resist,"
thereby rendering the substrate "sensitive" to exposure by the
electron beam. The substrate 223 can be any suitable material and
configuration, such as a silicon wafer.
[0096] At the extreme upstream end of the apparatus, the electron
gun 201 emits an electron beam ("illumination beam") in a
downstream direction through the illumination-optical system IOS.
The illumination-optical system comprises first and second
condenser lenses 202, 203, respectively, a beam-shaping aperture
204, a blanking aperture 207, an illumination-beam deflector 208,
and an illumination lens 209. The illumination beam from the
electron gun 201 passes through the condenser lenses 202, 203,
which converge the beam at a crossover C.O. situated at the
blanking aperture 207.
[0097] The beam-shaping aperture 204 is situated downstream of the
second condenser lens 203. The beam-shaping aperture has a profile
(e.g., rectangular) that peripherally trims the illumination beam
as the beam passes through the beam-shaping aperture. Thus, the
illumination beam is trimmed to have a transverse profile that is
shaped and dimensioned to illuminate a single exposure unit (e.g.,
a single subfield) on the reticle 210. For example, the
beam-shaping aperture 204 trims the illumination beam to have a
square transverse profile with side dimensions of slightly greater
than 1 mm as incident on the reticle 210. A focused image of the
beam-shaping aperture 204 is formed on the reticle 210 by the
illumination lens 209.
[0098] As noted above, the blanking aperture 207 is situated,
downstream of the beam-shaping aperture 204, at the crossover C.O.
The blanking aperture includes an aperture plate 207p that defines
an axial through-aperture 207a. During times when the illumination
beam is "blanked" (prevented from propagating to the reticle 210),
the blanking deflector 205 deflects the illumination beam off-axis
as required to cause the beam to be incident on the aperture plate
207p rather than on the through-aperture 207a. Incidence of the
illumination beam on the aperture plate 207p blocks the beam from
propagating to the reticle 210.
[0099] The illumination-beam deflector 208 is situated downstream
of the blanking aperture 207, and is configured mainly for scanning
the illumination beam in the X-direction in FIG. 9 to as to
illuminate successive subfields on the reticle 210 in a sequential
manner. The respective subfields that are illuminated per scan
("sweep") of the beam are in a respective row on the reticle
located within the optical field of the illumination-optical system
IOS. The illumination lens 209 is situated downstream of the
illumination-beam deflector 208. The illumination lens 209 is a
condenser lens that collimates the illumination beam for
impingement on the reticle 210. Also, as noted above, the
illumination lens 209 forms a focused image of the beam-shaping
aperture 204 on the upstream-facing surface of the reticle 210.
[0100] In FIG. 9 only one subfield of the reticle 210 is shown,
situated on the optical axis AX. In actuality, the reticle 210
comprises a large number of subfields, arrayed in the reticle plane
extending in the X- and Y-directions (i.e., the X-Y plane).
Typically, the reticle 210 defines the pattern for a layer of a
microelectronic device, for example an integrated circuit. (The
pattern for one layer need not be defined by only one reticle.) The
pattern normally extends sufficiently to occupy a "die" on the
substrate 223. To ensure that the illumination beam illuminates a
particular subfield on the reticle 210, the illumination-beam
deflector 208 is energized appropriately.
[0101] The reticle 210 is mounted on a reticle stage 211 that can
be moved in the X- and Y-directions. Similarly, the substrate 223
is mounted on a substrate stage 224 that also is movable in the X-
and Y-directions. During imaging of the pattern, the subfields
residing in a particular row within the optical field of the
illumination-optical and projection-optical systems are illuminated
sequentially by scanning ("sweeping") the illumination beam in the
X-direction (synchronously with scanning of the "imaging beam,"
propagating downstream of the reticle 210, in the X-direction). The
respective width of each row in the X-direction on the reticle and
substrate is essentially the width of the optical field of the
illumination-optical system and projection-optical system,
respectively. To progress from one row to the next (and hence
expose subfields outside the optical field), the reticle stage 211
and substrate stage 224 undergo respective continuous scanning
motions in the Y-direction. Both stages 211, 224 are provided with
respective position-measurement systems 212, 225 (typically laser
interferometers) that accurately measure the position of the
respective stage in the X-Y plane in real time. These accurate
positional measurements are critical for achieving proper alignment
and "stitching" together of subfield images as projected onto the
substrate 223.
[0102] The projection-optical system POS comprises first and second
projection lenses 215, 219, respectively, and a deflector 216 all
situated downstream of the reticle 210. As the illumination beam is
irradiated on a selected subfield of the reticle 210, portions of
the beam are transmitted through the reticle while becoming imaged
with the respective portion of the reticle pattern defined by the
particular subfield. Hence, the beam propagating downstream of the
reticle 210 is termed the "imaging beam" or "patterned beam." The
patterned beam passes through the projection-optical system POS to
the substrate 223. In this regard, as the patterned beam passes
through the projection lenses 215, 219, the image carried by the
patterned beam is "demagnified," usually by an integer factor.
Hence, the projection lenses 215, 219 collectively have a
"demagnification ratio" such as 1/4 or 1/5. The patterned beam is
deflected by the deflector 216 and focused at a specified location
on the substrate 223. Also, due to the optical behavior of the
projection-optical system POS, the respective directions of sweeps
of the illumination beam and patterned beam in the X-direction are
mutually opposite, and the respective directions of motion of the
stages in the Y-direction also are mutually opposite.
[0103] As noted above, the upstream-facing surface of the substrate
223 is coated with a suitable resist. Whenever a specified dose of
the patterned beam impinges on the resist, the area of impingement
is imprinted with the image carried by the patterned beam.
[0104] A crossover C.O. is situated on the axis AX at a point at
which the axial distance between the reticle 210 and the substrate
223 is divided according to the demagnification ratio of the
projection lenses 215, 219. A contrast aperture 218 is situated at
the crossover. The contrast aperture 218 blocks portions of the
patterned beam that experienced scattering upon passage through the
reticle 210. Thus, the scattered electrons do not propagate to the
substrate where they otherwise could degrade image contrast.
[0105] A backscattered-electron (BSE) detector 222 is situated
directly upstream of the substrate 223. The BSE detector 222 is
configured to detect and quantify electrons backscattered from
certain marks on the substrate 223 and the substrate stage 224. For
example, a mark on the substrate 223 is scanned by patterned beam
produced by passage of the illumination beam through a
corresponding mark pattern on the reticle 210. Detecting of
backscattered electrons in this manner provides data from which the
relative positional relationship of the reticle 210 and substrate
223 can be determined.
[0106] The substrate 223 is mounted on the substrate stage 224 via
an electrostatic chuck (not shown but well understood in the art).
By simultaneously moving the reticle stage 211 and substrate stage
224 in mutually opposite directions in respective
continuous-scanning motions, it is possible to expose each portion
of the pattern in a sequential manner. Meanwhile, the position
detectors 212, 225 monitor the respective stage position in real
time.
[0107] Each of the lenses 202, 203, 209, 215, 219 and each of the
deflectors 205, 208, 216 is connected to a respective driver 202a,
203a, 209a, 215a, 219a, and 205a, 208a, 216a that supplies
electrical power to the lens or deflector. Similarly, each of the
stages 211, 224, is connected to a respective driver 211a, 224a
that supplies electrical power to the respective stage 211, 224.
Each of the drivers 202a, 203a, 205a, 208a, 209a, 211a, 215a, 216a,
219a, 225a is connected to a main controller 231 that generates and
routes respective control signals for the drivers, thereby
achieving controlled actuation of the lenses, deflectors, and
stages. The main controller 231 also receives respective positional
data from the respective position-measurement systems 212, 225,
which are connected to the main controller 231 via respective
data-interface units 212a, 225a. The data interfaces 212a, 225a
include amplifiers, analog-to-digital (A/D) converters, and other
processing circuitry necessary to interface the data from the
position-measurement systems 212, 225 to the main controller 231. A
similar data-interface 222a connects the BSE detector 222 to the
main controller 231.
[0108] The main controller 231 ascertains and quantifies control
errors associated with stage positions, and actuates the deflector
216 as required to compensate for the control error. Thus, a
reduced (demagnified) image of an irradiated reticle subfield is
accurately transferred to a target position on the substrate 223.
The subfield images are formed on the substrate 223 so as to
"stitch" them together in a contiguous manner to form a complete
die pattern.
[0109] Sixth Representative Embodiment
[0110] This embodiment addresses situations in which irradiation of
the reticle in the manner described in the fourth representative
embodiment could damage the reticle. In other words, heat generated
by directly irradiating the reticle may have an undesired effect
depending upon reticle size and thickness.
[0111] Particulate matter (e.g., particles generated from
mechanical rubbing of machine parts such as stages) are removed by
irradiating a focused ion beam (or electron beam) on the offending
particle on the reticle in the presence of a corrosive gas.
Bombardment of the ion beam on molecules of the gas in the vicinity
of the offending particle ionizes the molecules near the particle.
The ionized molecules are chemically reactive and essentially etch
away the particle by volatilization. The volatilized molecules of
the particle are evacuated using a vacuum pump or analogous
appliance.
[0112] Reference is made to FIG. 10, depicting a process chamber
301 containing an electron-beam microlithography apparatus such as
that shown in FIG. 9 and described in the fifth representative
embodiment. The microlithography apparatus comprises an electron
gun 201 (e.g., as shown in FIG. 9), an illumination-optical system
303, and a projection-optical system 304, all contained within the
process chamber 301. For exposure and cleaning, a reticle 210 is
situated on a reticle stage (not shown, but see the fifth
representative embodiment) between the illumination-optical system
303 and the projection-optical system 304 as shown. The process
chamber 301 is evacuated to a suitable vacuum level by a vacuum
pump 302.
[0113] For inspection, the reticle 210 is moved, by appropriate
lateral motion of the reticle stage, to the left in the figure to a
detecting system 320. (The reticle in the inspection position is
denoted 210'.) Thus, the reticle 210' is situated so as to be
illuminated by a "probe light" produced by the detecting system
320. Specifically, the detecting system 320 comprises a source 321
of probe light, a probe-light illumination system 322, and a
detector 323, all situated within the process chamber 301. The
detector 323 is connected to an image process 324, which is
connected to a memory 325.
[0114] The probe light produced by the source 321 can be, for
example, UV light, deep UV light, or an electron beam. The detector
323 can be a CCD, for example. The probe-light illumination system
322 is configured to direct a beam of the probe light selectively
to any of various locations on the reticle, such as an
upstream-facing surface or a side wall of an aperture in the
reticle.
[0115] During inspection of the reticle 210', the memory 325
preserves data concerning the respective locations of the
contaminant deposit(s) on the reticle 310'. After inspection of the
reticle 210' is completed, the reticle stage returns the reticle
210 to its normal exposure position between the
illumination-optical system 303 and the projection-optical system
304.
[0116] At the exposure position, the reticle 210 can be cleaned.
The reticle stage positions the reticle 210 (according to data
stored in the memory 325) to align the contaminant deposit with an
electron beam or ion beam from the source 301 and passing through
the illumination-optical system 303. Meanwhile, a reactive gas is
introduced into the process chamber, in the vicinity of the reticle
210, by a gas supply 310.
[0117] The gas supply 310 includes a supply 311 of an inert gas, a
supply 312 of a reactive gas, a flow controller 313 to which the
supplies 311, 312 are connected, and a nozzle 314 extending into
the process chamber 301 to discharge gas in the vicinity of the
reticle 210. Exemplary reactive gases include any of various
fluoride gases such as F.sub.2, CF.sub.4, CHF.sub.3, CH.sub.3F,
SF.sub.6, XeF.sub.2, and WF.sub.6 for reaction with Ta or Si; any
of various chloride gases such as Cl.sub.2, CCl.sub.4, CHCl.sub.3,
CH.sub.2Cl.sub.2, CH.sub.3Cl, SiCl.sub.4, and Al.sub.2Cl.sub.6 for
reaction with Al or Cr or Fe--Ni; or any of various bromide gases
such as Br.sub.2 and CBr.sub.4 for reaction with Si.
[0118] The inert gas is used to facilitate, if required, generation
of a plasma of the reactive gas to etch the contaminant deposit.
The inert gas can be, for example, nitrogen or oxygen.
[0119] After cleaning, the reticle 210 is ready (and in position)
for use in making a lithographic exposure.
[0120] Seventh Representative Embodiment
[0121] This embodiment is similar to the sixth representative
embodiment, except for the inclusion of a separate
cleaning-irradiation system 330 for reticle cleaning. The
cleaning-irradiation system 330 is situated inside the process
chamber 301. This embodiment is depicted in FIG. 11, in which all
components that are the same as shown in FIG. 10 have the same
reference numerals and are not described further.
[0122] After inspection, the reticle is moved to the right in FIG.
11 to a cleaning position (the reticle at the cleaning position has
the reference numeral 210"). The cleaning-irradiation system 330
comprises an ion-beam source 331 and an ion-beam optical system
332. The reticle stage positions the reticle 210", based on the
data in the memory 325, such that an ion beam from the source 331
(and passing through the ion-beam optical system 332) is directed
on the contaminant deposit. Suitable ion beams are of Ga ions, Si
ions, or electrons. Meanwhile, the gas supply 310 discharges the
reactive gas (and inert gas if desired) through the nozzle 314.
Cleaning is performed as described above in the sixth
representative embodiment. After cleaning is complete, the reticle
210 is moved to the exposure position between the
illumination-optical system 303 and the projection-optical system
304.
[0123] Whereas the invention has been described in connection with
multiple representative embodiments and examples, it will be
understood that the invention is not limited to those embodiments.
On the contrary, the invention is intended to encompass all
modifications, alternatives, and equivalents as may be included
within the spirit and scope of the invention, as defined by the
appended claims.
* * * * *