U.S. patent application number 11/644986 was filed with the patent office on 2007-08-16 for device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation.
Invention is credited to Anja Bonness, Marcel Choudhury, Karin Eggers, Andreas Frangen, Christoph Hocke, Ruediger Hunger, Norbert Kallis, Wolfgang Keller, Gregor Kubart, Michael Lering, Christoph Noelscher, Michael Roesner.
Application Number | 20070187272 11/644986 |
Document ID | / |
Family ID | 38251270 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070187272 |
Kind Code |
A1 |
Bonness; Anja ; et
al. |
August 16, 2007 |
Device for the storage and use of at least one photomask for
lithographic projection and method for using the device in an
exposure installation
Abstract
The invention relates to a device for the storage of at least
one photomask for lithographic projection and a method for using
the device in an exposure installation. A container is suitable for
receiving a photomask. The container has a housing, a closable
opening device situated at the container housing and serving for
the entry and issuing of the photomask, and one gas inlet opening
arranged to purge the photomask. The invention also relates to a
method for using the device in an exposure installation.
Inventors: |
Bonness; Anja; (Dresden,
DE) ; Choudhury; Marcel; (Durham, NC) ;
Eggers; Karin; (Muncehn, DE) ; Frangen; Andreas;
(Dresden, DE) ; Kallis; Norbert; (Moritzburg,
DE) ; Keller; Wolfgang; (Glen Allen, VA) ;
Hocke; Christoph; (Dresden, DE) ; Lering;
Michael; (Dresden, DE) ; Roesner; Michael;
(Dresden, DE) ; Hunger; Ruediger; (Radeberg,
DE) ; Noelscher; Christoph; (Nuernberg, DE) ;
Kubart; Gregor; (Dresden, DE) |
Correspondence
Address: |
SLATER & MATSIL LLP
17950 PRESTON ROAD
SUITE 1000
DALLAS
TX
75252
US
|
Family ID: |
38251270 |
Appl. No.: |
11/644986 |
Filed: |
December 22, 2006 |
Current U.S.
Class: |
206/455 ;
220/745 |
Current CPC
Class: |
G03F 7/70933 20130101;
G03F 7/70741 20130101; G03F 1/66 20130101 |
Class at
Publication: |
206/455 ;
220/745 |
International
Class: |
B65D 85/48 20060101
B65D085/48; B65D 90/22 20060101 B65D090/22 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2005 |
DE |
10 2005 061 571.6 |
Claims
1. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask with a substantially
laminar flow.
2. The device according to claim 1, wherein the photomask comprises
a transparent substrate, which is provided with a pattern of
absorbent, partly absorbent, phase-shifting or reflective structure
elements on its front side, and comprising a frame, which is
arranged on the front side of the transparent substrate outside the
pattern of absorbent, partly absorbent or phase-shifting structure
elements, and comprises a protective film, which is arranged above
the transparent substrate on the frame in order to protect the
structure elements from particles in an at least partly closed-off
volume.
3. The device according to claim 2, wherein the protective film is
permeable to gaseous substances of the purge gas toward the
volume.
4. The device according to claim 2, wherein the protective film is
provided with one pinhole or a plurality of pinholes in order to
enable a gas exchange between the volume and the region outside the
volume.
5. The device according to claim 2, wherein the frame is provided
with one pinhole or a plurality of pinholes in order to enable a
gas exchange between the volume and the region outside the
volume.
6. The device according to claim 1, wherein the container housing
comprises an electrostatically dissipating coating.
7. The device according to claim 1, wherein the container housing
comprises a reticle holder in order to hold the photomask in a
predetermined position.
8. Device according to claim 7, wherein the closable opening is a
bottom flap and comprises a reticle support in order to hold the
photomask in a predetermined position.
9. The device according to claim 8, wherein the gas inlet opening
and the gas outlet opening are arranged on the bottom flap in a
manner offset with respect to the photomask.
10. The device according to claim 1, wherein the container
comprises a handling flange suitable for transferring the photomask
to an exposure apparatus by means of a mechanical interface.
11. The device according to claim 1, wherein the container and the
bottom flap correspond to an industry standard according to a SEMI
standard.
12. The device according to claim 11, wherein the mechanical
interface corresponds to an industry standard according to a SEMI
standard.
13. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask; and a purge device
comprising at least one gas feed line connected to the gas inlet
opening, the purge device being suitable for purging the container
with a purge gas in order to prevent crystallization on the
photomask, and in which the container comprises a gas outlet
opening and the purge device furthermore comprises at least one gas
discharge line connected to the gas outlet opening.
14. The device according to claim 13, wherein the purging device is
connected to an adapter plate arranged below the bottom flap of the
container, so that the gas feed line is connected to the gas inlet
opening and the gas discharge line is connected to the gas outlet
opening.
15. The device according to claim 14, further comprising a holding
frame suitable for receiving the container, said holding frame
comprises fixings suitable for receiving the adapter plate.
16. The device according to claim 15, wherein the fixings are
embodied in screwable fashion in order to enable the adapter plate
to be exchanged.
17. The device according to claim 14, wherein the adapter plate is
embodied in the holding frame as rack bottom on which the container
with the photomask is placed and can be secured by means of a
hinged mechanism.
18. The device according to claim 14, wherein the positioning of
the container in the holding frame is effected by means of the
handling flange.
19. The device according to claim 14, wherein the positioning of
the photomask in the container is effected by means of constant
contact pressure.
20. The device according to claim 17, wherein the hinged mechanism
is embodied in the form of a clip, which is fitted to the holding
frame in a rotatable manner and can be pivoted into a receiving
position and a holding position.
21. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask with a substantially
laminar flow; and a purge device comprising at least one gas feed
line connected to the gas inlet opening, the purge device being
suitable for purging the container with a purge gas in order to
prevent crystallization on the photomask, and in which the
container comprises a gas outlet opening and the purge device
furthermore comprises at least one gas discharge line connected to
the gas outlet opening, said purging device being arranged below
the bottom flap of the container, so that the gas feed line is
connected to the gas inlet opening and the gas discharge line is
connected to the gas outlet opening.
22. The device according to claim 21, wherein the purge device
comprises a mixing device for purging with a plurality of gases,
the mixing device comprising a T-piece and mixing valve in order to
admix the plurality of gases in the desired mixing ratio.
23. The device according to claim 22, wherein the purge device
feeds a gas mixture for cleaning of organic contaminations as purge
gas.
24. The device according to claim 23, wherein the purge device
feeds a nitrogen-ozone gas mixture.
25. The device according to claim 22, wherein the purge device
feeds a gas mixture for cleaning of inorganic contaminations as
purge gas.
26. The device according to claim 25, wherein the purge device
feeds a nitrogen-argon gas mixture.
27. The device according to claim 22, wherein the purge device
feeds a nitrogen-hydrogen gas mixture.
28. The device according to claim 27, wherein the purge device
feeds a hydrogen-containing gas mixture.
29. The device according to claim 28, wherein the gas mixture is a
forming gas in which the hydrogen proportion is chosen below a
flammability threshold.
30. The device according to claim 22, wherein the purge device
feeds a nitrogen-carbon dioxide gas mixture.
31. The device according to claim 21, wherein the purge device
controls the gas temperature and/or the gas partial pressures of
the purge gas alongside the mixing ratios.
32. The device according to claim 21, wherein the purge device
feeds a gas mixture suitable for removing water from the surface of
the photomask.
33. The device according to claim 32, wherein the purge device
feeds a nitrogen-oxygen gas mixture.
34. The device according to claim 32, wherein the purge device
feeds an air mixture from which water comprises been removed.
35. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask with a substantially
laminar flow; and a microwave source suitable for emitting
microwave radiation comprising a specific wavelength and intensity
from the side of the structure elements onto the photomask.
36. The device according to claim 35, wherein the wavelength and/or
intensity of the microwave radiation of the microwave source is
chosen such that chemical bonds of impurities on the surface of the
transparent substrate, in the volume between the surface of the
transparent substrate and the protective film or on the surface of
the protective film at least partly break up.
37. The device according to claim 36, wherein the wavelength and/or
intensity of the microwave radiation of the microwave source is
furthermore chosen such that hydrogen-oxygen bonds in the
impurities at least partly break up.
38. The device according to claim 37, wherein the impurities
comprise ammonium sulfate present in crystalline form on the
surface of the transparent substrate, in the volume between the
surface of the transparent substrate and the protective film or on
the surface of the protective film.
39. The device according to claim 35, wherein the wavelength of the
microwave radiation of the microwave source is furthermore chosen
such that it lies within a range in which the protective film is at
least partly transparent to microwave radiation.
40. The device according to claim 39, wherein the protective film
comprises a Teflon-containing material.
41. The device according to claim 39, wherein the frequency of the
microwave radiation lies within the range of between 2 GHz and 3
GHz.
42. The device according to claim 41, wherein the frequency of the
microwave radiation is approximately 2455 MHz.
43. The device according to claim 35, wherein the wavelength and
intensity of the microwave radiation of the microwave source are
furthermore chosen such that no or virtually no electrostatic
charging or spark-overs occur on electrically conductive structure
elements on the transparent substrate.
44. The device according to claim 43, wherein the microwave source
is pulsed.
45. The device according to claim 35, wherein the wavelength and
intensity of the microwave radiation is furthermore chosen such
that water at least partly absorbs the microwave radiation.
46. The device according to claim 35, wherein the photomask
comprises a frame, the protective film of the photomask is fixed to
the frame by means of an adhesive, and the wavelength and intensity
of the microwave radiation is furthermore chosen such that the
microwave radiation does not damage the adhesive.
47. The device according to claim 35, wherein the microwave source
comprises a filter comprising the material of the protective
film.
48. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask with a substantially
laminar flow; and an infrared source suitable for emitting infrared
radiation comprising a specific wavelength and intensity from the
side of the structure elements onto the photomask.
49. The device according to claim 48, wherein the wavelength and/or
intensity of the infrared radiation of the infrared source is
suitable for heating impurities on the surface of the transparent
substrate, in the volume between the surface of the transparent
substrate and the protective film or on the surface of the
protective film.
50. The device according to claim 48, wherein the wavelength of the
infrared radiation of the infrared source is furthermore chosen
such that it lies within a range in which the protective film is at
least partly transparent to infrared radiation.
51. The device according to claim 48, wherein the wavenumber of the
infrared radiation lies within the range of between 1000 cm.sup.-1
and 4000 cm.sup.-1.
52. The device according to claim 51, wherein the wavenumber of the
infrared radiation lies within the range of between 1100 cm.sup.-1
and 1400 cm.sup.-1.
53. The device according to claim 51, wherein the wavenumber of the
infrared radiation lies within the range of between 2500 cm.sup.-1
and 3500 cm.sup.-1.
54. The device according to claim 48, wherein the intensity of the
infrared radiation is chosen such that the infrared radiation heats
ammonium sulfate.
55. The device according to claim 48, further comprising a mirror
that directs the infrared radiation of the infrared source onto the
photomask.
56. A device for storage and use of at least one photomask for
lithographic projection, the device comprising: a container
suitable for receiving a photomask, the container comprising a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask, the container comprising at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask through a gas feed line;
and a gasket being arranged between said one gas inlet opening and
said gas feed line, said gasket providing a collapsible seal
between said gas inlet opening and said gas feed line.
57. The device according to claim 56, wherein said container
further comprises at least one gas outlet opening arranged in such
a way that, in the case of purging the photomask, the purge gas is
removed through a gas discharge line and a further gasket being
arranged between said one gas outlet opening and said gas discharge
line, said further gasket providing a collapsible seal between said
gas outlet opening and said gas discharge line.
58. The device according to claim 57, wherein the gasket and/or the
further gasket are formed from a self-inflating material.
59. The device according to claim 58, wherein the gasket is
arranged in a toroidal shape between the gas inlet opening 40 and
the gas feed line.
60. The device according to claim 58, wherein the gasket is
provided as a collapsible gasket having a passive state of being
collapsed.
61. The device according to claim 58, wherein the gasket is
provided as a collapsible gasket having a passive state of being
expanded.
62. The device according to claim 57, wherein the gas inlet opening
is arranged as a stub and the gas feed line is adapted to house the
gas inlet opening in an overlapping manner.
63. The device according to claim 62, wherein the gas discharge
line is arranged as a stub and the gas outlet opening is adapted to
house the gas discharge line in an overlapping manner.
64. The device according to claim 62, wherein the gasket and/or the
further gasket are arranged as a sleeve having a double-walled
cross-section.
65. The device according to claim 64, wherein the sleeve comprises
an outer wall member and an inner wall member which are arranged
such that a passing gas stream unfolds the inner wall member and
the out wall member to provide the collapsible seal.
66. The device according to claim 65, wherein said outer wall
member or said inner wall member comprise an elastic material.
67. The device according to claim 66, wherein said outer wall
member and said inner wall member being subdivided into a plurality
of fins which partially overlap each other.
68. The device according to claim 67, wherein said fins are
arranged such that the purge gas bends the fins in order to provide
the collapsible seal.
69. A device for storage and use of a work piece in semiconductor
manufacturing, the device comprising: a container suitable for
receiving the work piece, the container comprising a container
housing and a closable opening device situated at the container
housing and serving for the entry and issuing of the work piece,
the container comprising at least one gas inlet opening arranged in
such a way that, in the case of purging the work piece, a purge gas
flushes around the work piece through a gas feed line; and a gasket
being arranged between said one gas inlet opening and said gas feed
line, said gasket providing a collapsible seal between said gas
inlet opening and said gas feed line.
70. The device according to claim 69, wherein said work piece
comprises a plurality of semiconductor wafers.
71. The device according to claim 69, wherein said work piece
comprises a photo mask.
72. A method for using a device in a fabrication installation, the
method comprising: providing a fabrication installation comprising
at least one exposure apparatus suitable for receiving the
photomask; feeding the photomask from the container into the
exposure apparatus; carrying out one or more exposure processes
with the exposure apparatus using light from a UV source; removing
the photomask from the exposure apparatus into the container; and
cleaning the photomask in the container by purging with the purge
gas.
73. The method according to claim 72, further comprising: providing
the microwave source; irradiating the photomask with microwave
radiation; and cleaning the photomask in the container by purging
with the purge gas.
74. The method according to claim 72, further comprising: providing
the infrared source; irradiating the photomask with microwave
radiation; and cleaning the photomask in the container by purging
with the purge gas.
Description
[0001] This application claims priority to German Patent
Application 10 2005 061 571.6, which was filed Dec. 22, 2005 and is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to a device for the storage and use of
at least one photomask for lithographic projection and a method for
using the device in an exposure installation.
BACKGROUND
[0003] For the production of integrated circuits, layers provided
with different electrical properties are usually applied on
semiconductor wafers and patterned lithographically in each case. A
lithographic patterning step usually consists in applying a
photosensitive resist, exposing the latter with a desired structure
for the relevant plane and developing it, and subsequently
transferring the resultant resist mask into the underlying layer in
an etching step or using the resist mask as an implantation mask
for altering the electrical properties of the underlying layer in a
targeted manner.
[0004] For the lithographic projection step of a circuit pattern, a
wafer scanner or wafer stepper is usually used as exposure
apparatus. In the exposure apparatus, the photosensitive resist
layer is exposed with electromagnetic radiation having a
predetermined wavelength, which, in present-day exposure
technologies, lies for example in the UV or DUV range at 256 nm,
193 nm or 157 nm. The exposure dose present during the exposure of
the photosensitive resist layer at the location of the
semiconductor wafer is chosen according to the specifications of
the resist layer.
[0005] Each individual layer of the circuit pattern is usually
transferred to the semiconductor wafer by means of a photomask. The
photomask comprises a transparent substrate layer provided with
absorbent elements, such as, e.g., a chromium layer, which simulate
the circuit pattern. The photomask, also called a reticle, is often
provided with a protective film (pellicle). The protective film
serves to protect the structure side of the transparent substrate
layer from deposits. Deposits on the protective film itself are not
normally transferred to the resist layer during lithography since
the protective film lies outside the focal range for imaging onto
the resist layer.
[0006] In large-volume fabrication processes, diverse attempts are
made to optimize the productivity. Besides the miniaturization of
structure dimensions on the semiconductor wafers and the provision
of process installations for semiconductor wafers having a diameter
of 300 mm, a time-saving handling of the semiconductor wafers and
photomasks in the process installations is also an important
optimization variable.
[0007] In order to be able to use process installations from
different manufacturers or of different types, standardized
equipment is typically used. Thus, by way of example, the
standardization committee "SEMI" standardizes a multiplicity of
equipment for the semiconductor industry with regard to the
interoperability thereof.
[0008] SEMI Standard 111-0304 defines the configuration of reticle
containers which are fed to the lithographic projection
installations via a defined interface. Reticle containers which
satisfy said standard are usually referred to as reticle SMIF pod
(SMIF=standard mechanical interface) or by the abbreviation "RSP",
the purpose of which is to enable the reticles to be stored and
transported within wafer fabrication. Reticle containers in
accordance with said standard have a housing and a plate which is
arranged at the bottom of the housing and which can be
automatically closed or opened by the lithographic projection
installations or reticle inspection systems. In this case, RSPs
comprising one reticle and also RSPs comprising six reticles are
used as storage containers.
[0009] In the case of the photomasks used in lithographic exposure
processes, particles or contaminations can attach to the surface by
adhesion from the surrounding atmosphere. Thus, by way of example,
the presence of ammonium ions and/or sulfate ions on the reticle
surface leads to the formation of ammonium sulfate
((NH.sub.4).sub.2SO.sub.4) or to the formation of ammonium oxalate
((NH.sub.4).sub.2C.sub.2O.sub.4H.sub.2O). These crystals can grow
with energy being radiated in by the light source of the exposure
apparatus.
[0010] An example of crystal growth and irradiation with UV light
is described below. Air normally contains hydrogen sulfide
(H.sub.2S) in a low concentration. Together with oxygen, sulfur
dioxide forms in accordance with the reaction equation:
2H.sub.2S+3O.sub.2->2SO.sub.2+2H.sub.2O. [1]
[0011] With light being radiated in during the lithographic
projection, free oxygen radicals are formed which react with sulfur
dioxide in accordance with the following reaction equation:
SO.sub.2+O->SO.sub.3 [2]
[0012] Together with (residual) water from the air, aerosol
particles arise, which are chemically stable, in accordance with
the following reaction equation:
SO.sub.3+H.sub.2O->H.sub.2SO.sub.4 [3]
[0013] In the presence of impurities, in this case ammonia, said
aerosol particles react to form ammonium sulfate, in accordance
with the following reaction equation:
H.sub.2SO.sub.4+2NH.sub.3->(NH.sub.4).sub.2SO.sub.4 [4]
[0014] Photomasks in exposure apparatuses having exposure
wavelengths in the DUV range exhibit a growth of said crystals
which takes place virtually like an avalanche. Consequently, the
photomasks have to be regularly monitored and cleaned.
[0015] This cleaning is usually carried out at the mask company by
the manufacturer of the photomasks. For cleaning purposes, the
photomasks are introduced into an acid bath. By way of example, a
solution containing sulfuric acid is used as the acid bath.
However, it has been found that the surface of freshly cleaned
photomasks is still relatively susceptible to crystal growth.
[0016] In addition to the productivity stoppage and the high costs
due to the cleaning, it can also occasionally happen that a
photomask is destroyed or damaged during cleaning. Furthermore, by
way of example, phase shifter masks can only be cleaned a few times
since the properties of the phase shifters can change.
SUMMARY OF THE INVENTION
[0017] According to an embodiment of the present invention, a
device for the storage and use of at least one photomask for
lithographic projection is provided, which comprises a container
suitable for receiving a photomask. The container includes a
container housing and a closable opening device situated at the
container housing and serving for the entry and issuing of the
photomask. The container has at least one gas inlet opening
arranged in such a way that, in the case of purging the photomask,
a purge gas flushes around the photomask with a laminar flow.
[0018] According to this embodiment of the invention, impurities
directly in the vicinity of the photomask in the volume over the
transparent substrate are removed by means of the chemically active
gases or gas mixtures, thereby suppressing crystal growth on the
surface of the photomask. Consequently, the photomask can be used
significantly longer in a lithographic exposure process without
suffering from the depositing of particles.
[0019] According to a further embodiment of the present invention
of a method for using the device is provided. A fabrication
installation includes at least one exposure apparatus suitable for
receiving the photomask. The photomask is fed from the container
into the exposure apparatus. One or more exposure processes are
carried out with the exposure apparatus using light from a UV
source. The photomask is removed from the exposure apparatus into
the protective container and the photomask is cleaned in the
container by purging with the purge gas.
[0020] In a further embodiment, the following steps are furthermore
performed. A microwave source is provided. The photomask is
irradiated with microwave radiation. The photomask is cleaned in
the container by purging with the purge gas.
[0021] In a further embodiment, the following steps are furthermore
performed. An infrared source is provided. The photomask is
irradiated with infrared radiation and the photomask is cleaned in
the container by purging with the purge gas.
[0022] In accordance with one embodiment of the invention, the
device is used in an exposure apparatus which can be operated with
conventional loading and unloading stations and also storage
containers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will now be explained in more detail with
reference to the accompanying drawings:
[0024] FIG. 1 schematically shows a cross-sectional view through a
device for the storage of a photomask in accordance with one
embodiment of the invention;
[0025] FIG. 2 schematically shows a further cross-sectional view
through a device for the storage of a photomask in accordance with
one embodiment of the invention;
[0026] FIG. 3 schematically shows a further cross-sectional view
through a device for the storage of a photomask in accordance with
one embodiment of the invention;
[0027] FIG. 4 shows a perspective view of a mount in accordance
with one embodiment of the invention;
[0028] FIG. 5 shows a further perspective view of the mount
according to FIG. 4 with a device in accordance with one embodiment
of the invention;
[0029] FIG. 6 schematically shows a further perspective view of a
device in accordance with one embodiment of the invention;
[0030] FIG. 7A schematically shows a further perspective view of a
device in accordance with one embodiment of the invention;
[0031] FIG. 7B schematically shows a further perspective view of a
device in accordance with one embodiment of the invention;
[0032] FIG. 8A schematically shows a further cross-sectional view
through a device in accordance with one embodiment of the
invention;
[0033] FIG. 8B schematically shows a further cross-sectional view
through a device in accordance with one embodiment of the
invention;
[0034] FIG. 9 shows a chemical structural formula of an impurity
for illustrating the procedure according to the invention;
[0035] FIG. 10 shows an absorption spectrum in the infrared range
of an impurity for illustrating the procedure according to the
invention; and
[0036] FIG. 11 shows a transmission spectrum in the infrared range
of a protective film for illustrating the procedure according to
the invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0037] The invention is explained below in the context of the
lithographic patterning of semiconductor wafers, which is carried
out, for example, during the fabrication of microelectronic
circuits. It is appreciated, however, that the present invention
provides many applicable inventive concepts that can be embodied in
a wide variety of specific contexts. The specific embodiments
discussed are merely illustrative of specific ways to apply the
method and to apply the device of the invention, and do not limit
the scope of the invention. Accordingly, the invention can be
applied in a multiplicity of production technologies in which a
patterning step is effected by means of a photomask, thus, for
example, during the production of thin-film components, such as,
e.g., TFT elements, or else in nanotechnology.
[0038] FIG. 1 schematically shows a cross-sectional view through a
photomask for lithographic projection in accordance with a first
embodiment of the invention. The photomask 5 has a transparent
substrate 10, which comprises quartz, by way of example. On the
front side 12, the transparent substrate 10 is provided with a
pattern 14 of structure elements 16. In this case, the pattern 14
corresponds to a level of a circuit design and is usually produced
by means of a suitable CAD program.
[0039] Depending on the type of mask, the structure elements 16 are
embodied in absorbent, partly absorbent or phase-shifting fashion.
The mixture of these properties of the structure elements 16 is
likewise possible. Absorbent structure elements 16 usually comprise
chromium or black chromium. A thinned chromium or molybdenum
silicide is used for partly absorbent structure elements 16. The
phase-shifting properties of the structure elements 16 may be
achieved for example by the use of molybdenum silicide or by an
etch into the mask substrate 10 in order to form trench-like
structure elements. It is, of course, also possible to use
reflective mask types such as are used in EUV lithography by way of
example.
[0040] As is shown in FIG. 1, the photomask 5 has a frame 18
arranged on the front side 12 of the transparent substrate 10
outside the pattern 14 of structure elements 16. The frame 18 is
usually embodied in rectangular or trapezoidal fashion in a plan
view. The frame 18 is adhesively bonded onto the transparent
substrate 10 and encloses the structure elements 16 of the pattern
14.
[0041] A protective film 20, also called pellicle, is furthermore
fixed on the frame 18, for example by adhesive bonding, above the
transparent substrate 10. Said protective film 20, together with
the front side 12 of the transparent substrate 10 and the side
walls of the frame 18, forms an at least spatially closed-off
volume 26.
[0042] The protective film 20 is permeable to gaseous substances of
the purge gas toward the volume 26. For this purpose, the
protective film 20 may be provided with a pinhole, for example, in
order to enable a gas exchange between the volume 26 and the region
outside the volume 26. Other openings or cutouts are likewise
conceivable.
[0043] The device according to the invention furthermore has a
container 30. The container 30 has a container housing 32 and a
bottom flap 34 situated at the container housing 32 as a closeable
opening. Other openings might be provided for example at the
sidewalls of the container 30. The container housing 32 has an
electrostatically dissipating coating, whereby the use of ionizers
or the like is obviated.
[0044] The bottom flap 34 is provided for the entry and issuing of
the photomask 5. Furthermore, the bottom flap 34 has a gas inlet
opening 40 and a gas outlet opening 42, for example in the form of
circular holes within the bottom flap 34. In this case, the
position of the gas inlet opening 40 and of the gas outlet opening
42 within the bottom flap 34 can be chosen freely.
[0045] The container 30 is embodied so as to be able to receive the
photomask 5. For this purpose, the container housing 32 is provided
with a reticle holder 50 in order to hold the photomask 5 in a
predetermined position. The reticle holder 50 may be embodied as a
pin or clamp, for example, thereby preventing the photomask 5 from
slipping in a lateral direction and upward within the container
housing 32. Furthermore, the bottom flap 34 has a reticle support
52 in order to hold the photomask 5 in a predetermined position.
The reticle support 52 is intended to prevent the photomask 5 from
slipping in the direction of the bottom flap 34 within the
container housing 32.
[0046] For simpler use of the device in accordance with FIG. 1
within an exposure installation, the container 30 is provided with
a handling flange 54 fitted to the top side of the container
housing 32. The handling flange 54 serves for transferring the
photomask 5 to an exposure apparatus by means of a mechanical
interface.
[0047] As mentioned in the introduction, for time-saving handling
within semiconductor fabrication installations, a standardization
of the process equipment used is provided. In consequent fashion,
the container 30 and the bottom flap 34 are embodied in accordance
with an industry standard, for example according to the SEMI
Standard. The mechanical interface likewise corresponds to an
industry standard according to one of the SEMI Standards. It goes
without saying that it is likewise conceivable to use standards
appertaining to a different industry standard or else proprietary,
in-house specifications.
[0048] The device in accordance with this embodiment furthermore
has a purge device 44. The purge device 44 serves to remove
impurities by means of the purge gas in the volume 26. As mentioned
in the introduction, said impurities are for example ammonia,
carbon dioxide or else sulfur-containing gases, such as, e.g.,
hydrogen sulfide or sulfur dioxide. Said impurities could cause
crystallization on the photomask 5, which is prevented on account
of the impurities being transported away by means of the purge
gases of the purge device 44.
[0049] For this purpose, as shown on FIG. 3, the purge device 44
has a gas feed line 46 connected to the gas inlet opening 40, and a
gas discharge line 48 connected to the gas outlet opening 42. The
purge device 44 serves to purge the container 30 with a purge gas
in order to prevent crystallization on the photomask 5.
[0050] Particular consideration is given in this case to the
position of the gas inlet opening 40 and the gas outlet opening 42.
In order to prevent the purge gas from flushing around the
photomask 5 in a turbulent flow, the gas inlet opening 40 and the
gas outlet opening 42 are arranged offset with respect to the
photomask. This results in a flow that is as laminar as possible.
The precise position of the gas inlet opening 40 and of the gas
outlet opening 42 can also be determined by means of a computer
simulation.
[0051] As is shown in FIG. 2, the volume within the container 30 is
contaminated with impurities that are present in low concentration
for example as a result of outgassing from the protective film 20,
the container 30 or adhesives used. As mentioned in the
introduction, said impurities grow under irradiation with UV light,
with the result that deposits 24 in crystal form may arise on the
photomask 5.
[0052] The purge device 44 is preferably embodied with a mixing
device for purging with a plurality of gases. For this purpose, a
mixing device comprising a T-piece and a mixing valve may be
provided in order to admix the plurality of gases in a desired
mixing ratio. Moreover, in addition to the mixing ratios, the gas
temperature and/or the gas partial pressures of the purge gas can
be controlled by means of the purge device 44. The container 30 is
shown together with the purge device 44 in FIG. 3.
[0053] A plurality of purge gases is appropriate for eliminating
the impurities. In accordance with reaction equations [1] to [4],
crystal growth is prevented by removing ammonia or
sulfur-containing gases. Generally, a gas mixture for cleaning
organic contaminations or a gas mixture for cleaning inorganic
contaminations may be fed as purge gas. The purge gas used may also
be weakly chemically active, in which case, in particular, the
protective film 20 should not be attacked by the purge gas.
[0054] By way of example, a nitrogen-ozone gas mixture is provided
for cleaning organic contaminations; the cleaning of inorganic
contaminations is effected, e.g., by means of a nitrogen-argon gas
mixture. It is likewise conceivable to feed a nitrogen-hydrogen gas
mixture, for example as a 90% nitrogen and 10% hydrogen forming
gas. A nitrogen-carbon dioxide gas mixture is likewise
possible.
[0055] The impurities within the container are transported away
efficiently on account of the purging with the above-mentioned
purge gases, thereby lengthening the interval between external
cleaning steps in a mask company. As a result, the service life of
the photomask is significantly lengthened, and corresponding
cleaning costs are saved.
[0056] A further aspect is that water is a starting point for many
crystallization processes on the photomask 5. Therefore, provision
is made for choosing the purge gas such that water molecules are
removed from the photomask 5. Water molecules often occur as a
molecular monolayer on the surface of the transparent substrate. By
purging with a dried air mixture, a so-called XDA gas
(XDA=extremely dry air), from which the water component has been
removed to the greatest possible extent, the partial pressure is
shifted correspondingly, resulting in evaporation of the water on
the surface of the photomask.
[0057] FIGS. 4 and 5 show how the above-described concept of
purging the photomask 5 in the container 30 can be applied to
storage systems. The aim is for the storage and repository system
provided in the context of industry standards to be configured
compatibly with the invention.
[0058] As is shown in FIG. 4, a holding frame 56 is provided, which
is able to receive the container 30. The positioning of the
container 30 in the holding frame 56 is effected by means of the
handling flange 54 in this case. For tracking and individualization
of photomasks within a fabrication installation, the container 30
has a barcode identification or electronic identification. The
holding frame 56 is provided with a reader for read-out, which can
be visualized by means of a display 62. It is likewise possible to
transmit read-out results to a central process control by means of
a network connection (not shown in FIG. 4).
[0059] In order to be able to receive a multiplicity of different
containers, the purge device 44, rather than being connected to the
bottom flap 34 directly, is now connected via an adapter plate 58
arranged below the bottom flap 34 of the container. In this case,
the adapter plate 58 is introduced into the holding frame 56. For
this purpose, the holding frame 56 has fixings 60 at its edge in
order to fix the adapter plate 58.
[0060] The adapter plate 58 is embodied in the holding frame 56 as
a rack bottom on which the container 30 with the photomask 5 can be
placed. The fixings 60 are embodied in screwable fashion in order
to enable the adapter plate 58 to be exchanged. The gas feed line
46 is shown as a part of the adapter plate in FIG. 4.
[0061] For receiving the container 30, a hinged mechanism 64 is
provided in the holding frame 56, which mechanism secures the
container 30. As shown in FIG. 4, the hinged mechanism 64 is
embodied in the form of a clip 66 that is fitted to the holding
frame 56 in rotatable fashion and can be pivoted into a receiving
position 59 and a holding position 59' as shown in FIG. 5. A
securing pin 68 in the holding frame 56 or else in the adapter
plate 58 is provided in order to increase the alignment
accuracy.
[0062] To summarize, the holding frame 56 is connected to the purge
device 44, then, so that purging with the purge gases can be
carried out during the storage of photomasks. The combination of
container 30 and holding frame 56 may be embodied in a manner
conforming to an industry standard in this case, for example
according to the SEMI standard.
[0063] This concept is extended below, with reference to FIG. 6, to
a storage system 70 comprising a plurality of receptacle locations
for containers 30. FIG. 6 shows a storage system 70 comprising six
holding frames 56 each for receiving one container 30. The storage
system 70 has a closed-off region accommodating the purge device 44
as storage for a gas system 72. The required gas mixing devices,
T-pieces or mixing valves are likewise accommodated in the storage
for the gas system 72.
[0064] A further embodiment is described making reference now to
FIG. 7A. Depending on the gas used for purging it is not
permissible to blow the purge gases into the atmosphere surrounding
the container due to safety and health regulations to be observed
during operation and/or for cost reasons as uncontrolled gas losses
would increase the amount of purging gas required. Therefore,
attention is drawn to the connection between the gas system and the
container.
[0065] In FIG. 7A, the gas inlet opening 40 and the gas feed line
46 are schematically depicted in a side view. According to this
embodiment, the gas inlet opening is arranged on the closable
opening device 34. Note, that the adapter plate 58 can also be
inserted in-between the gas inlet opening 40 and the gas feed line
46, as described with respect to FIG. 4. Accordingly, the
description given below would then apply to the connection between
the adapter plate 58 and the gas system 44.
[0066] Both, the gas inlet opening 40 and the gas feed line 46 can
be arranged as stubs having respective diameters adapted to house
the gas inlet opening 40 within the gas feed line 46 or vice
versa.
[0067] In FIG. 7A, the gas inlet opening 40 is shown as a
cylindrical stub with a substantially uniform diameter chosen such
that the required gas flow can be achieved. The gas feed line 46 is
formed by a cylindrical stub having two different diameters so as
to result in a step-like cross-section.
[0068] The upper part of the gas feed line 46 has a diameter larger
than the size of the cylindrical stub of gas inlet opening 40.
Accordingly, the gas inlet opening 40 and the gas feed line 46 can
be put together in an overlapping manner. It should be noted that
many different shapes and cross-sections of the gas inlet opening
40 and the gas feed line 46 can be used, including but not limited
to elliptical or rectangular shaped structures having conical,
partially conical or multi-step cross-sections.
[0069] In order to prevent gas from leaking at the joint between
the gas inlet opening 40 and the gas feed line 46, a gasket 36 is
introduced in-between. As shown in FIG. 7A, the gasket is arranged
in the lower part of the gas inlet opening 40 facing the gas feed
lines where gas inlet opening 40 and the gas feed line 46 overlap
with respect to each other.
[0070] The gasket 36 can be of toroidal or ring-like shape as
depicted in FIG. 7A, other shapes are conceivable as well. The
gasket 36 seals the region between the gas inlet opening 40 and the
gas feed line 46. In addition, the gasket 36 can provide a clamping
function in order to retain the container 30 to the gas system
44.
[0071] In order to achieve easily disassembling of the container 30
to the gas system 44, the gasket can be provided as a collapsible
gasket having a passive state of being either collapsed or
expanded. By applying outside pressure, the state of the
collapsible gasket can be selected.
[0072] As an example, self inflatable synthetics can be used which
seal the gas inlet opening 40 and the gas feed line 46 while
inflated. Before removing the container 30 from the gas system 44,
extraction by suction or by applying a vacuum collapses gasket.
During purging of gases, no action has to be taken, as the self
inflatable gasket provides a seal and clamps the gas inlet opening
40 and the gas feed line 46.
[0073] In another conceivable arrangement of the gasket is shown in
FIG. 7B. According to this embodiment, the gas inlet opening 40 is
again formed as a cylindrical shaped stub protruding from the
closable opening device 34. The gas feed line 46 is formed in a
cup-shaped manner so as to allow introduction of the gas inlet
opening 40 as depicted in FIG. 7B.
[0074] The gasket 36 is arranged as a sleeve having a double-walled
cross-section. The double-walled cross-section results in an inner
wall member 37 and an outer wall member 38 joined at cusp 39. As
shown in FIG. 7B, the outer wall member 38 of gasket 36 is attached
to the gas feed line 46, for example by gluing. It is, however,
also conceivable to attach the gasket with the inner wall member or
at the gas inlet opening 40. The gasket 36 is inserted such that
the cusp 39 faces the container 30.
[0075] Generally speaking, the cusp 39 should point in the same
direction with respect to the gas flow purged through the gas feed
line 46. This results in a self-controlled sealing while purging
gas through the gas inlet opening 40. As the incoming gas flow
presses against the inner wall member 37 and outer wall member 38,
a force results which tends to open the inner wall member 37 and
outer wall member 38 with respect to the cusp 39. Accordingly, the
inner wall member 37, or generally speaking the free movable member
of gasket 36, is pressed against the inner wall of the stub of gas
inlet opening 40. As long as gas flow is maintained through the gas
feed line 46, the gasket 36 seals the joint between the gas inlet
opening 40 and the gas feed line 46. In addition, the gasket
provides some clamping of the gas inlet opening 40 and the gas feed
line 46 due to the pressure created by the purging gas.
[0076] In order to provide a seal between the gas inlet opening 40
and the gas feed line 46, an elastic material can be used for the
inner wall member. It is also conceivable to fabricate the entire
gasket using an elastic material such as rubber or the like.
Alternatively, the gasket can be formed using a stiff material,
e.g., a synthetic material, being subdivided into a plurality of
fins which partially overlap each other. The fins are arranged such
that the purge gas bends the fins along the cusp 39 in order to
seal the joint between the gas inlet opening 40 and the gas feed
line 46.
[0077] It should be noted that a further gasket can be arranged in
cases when the container 30 has a gas outlet through which the
purge gas is removed by a gas discharge line. The further gasket is
arranged between the gas outlet opening and the gas discharge line
and provides a similar as described above a collapsible seal
between the gas outlet opening and the gas discharge line. In order
to allow an unfolding by the passing gas stream, the cusp 39
joining the inner wall member 37 and the outer wall member 38 has
to be oriented in the opposite direction so that the discharged gas
unfolds the sleeve formed by the inner wall member 37 and the outer
wall member 38. Accordingly, the gas outlet opening encapsulates
the gas discharge line which can be arranged as a stub, similar to
the embodiment of FIG. 7B.
[0078] In a further embodiment, sealing can be archived with a
magnetic enforced gasket. This could be archived with a metal or
permanent magnet in the one interface side and electro magnet
enforcement at other side (not shown in FIG. 7A or 7B).
[0079] According to the embodiments described with respect to FIGS.
7A and 7B, handling of photomasks with automated equipment is
simplified. For example, a sensor at the shelf operated by a robot
stops gas purging and initiates gasket collapsing for placement and
lifting of the container 30.
[0080] This concept can be extended to the handling of wafer pods
within automated stockers. There, container 30 carries a plurality
of semi-conductor wafers instead of photomask 5. In a
semi-conductor manufacturing unit, the wafer pods are frequently
transported between a shelf and automatic processing units. Here, a
sensor at the shelf operated by a robot stops gas purging and
initiates gasket collapsing for placement and lifting of the
container 30. At the processing units, a placement sensor will open
the gas valve in order to expand the gasket. In case of purging the
semiconductor wafer during processing or storage, it is not
necessary to interrupt the gas flow because there is no gas leakage
and accordingly no human risk present.
[0081] The device described previously is able, by means of the
purge device 44, to effectively purge impurities within the
container 30. On account of relatively long periods of use,
however, it can happen that crystals have nevertheless formed on
the transparent substrate 10 or the structure elements 16. In order
to be able to effectively remove them, a description is given below
of an activation of the crystals by means of electromagnetic
radiation, which can be employed in addition to the measures
already mentioned.
[0082] As is shown in FIG. 8A, a microwave source 80 is used for
this purpose in a first aspect. The microwave source 80 emits
microwave radiation having a specific wavelength and intensity. By
way of example, an arrangement of two electrodes 84 connected to an
RF generator 86 may be provided for this purpose.
[0083] The microwave source 80 may for example also be integrated
into the above-described storage system 70 in accordance with FIG.
4 or be arranged in the vicinity of the holding frame 56 in
accordance with FIG. 4. Generally, the microwave source 80 may be
arranged in the container 30 or outside the container 30. The
container 30 may also be a different container than for normal
storage of the reticles, e.g., a microwave or infrared oven, or be
integrated into the exposure apparatus or a mask inspection
apparatus.
[0084] In the case where the microwave source 80 is integrated into
the storage system 70, the bottom flap 34 is open in this case in
order to allow the microwave radiation to impinge on the photomask
5 unimpeded. In this case, the microwave radiation irradiates the
surface of the transparent substrate 10 and also the structure
elements 16 thereof from the side of the protective film 20. The
wavelength and/or intensity of the microwave radiation of the
microwave source 80 is chosen such that chemical bonds of deposits
24 on the surface of the transparent substrate 10 can break up. It
goes without saying that it is also possible to remove deposits in
the volume 26 between the surface of the transparent substrate 10
and the protective film 20 or on the surface of the protective film
20 itself. The deposits 24 on the surface of the transparent
substrate 10 are usually disruptive for lithographic
projection.
[0085] If the deposits comprise ammonium sulfate, the wavelength
and/or intensity of the microwave radiation of the microwave source
80 should be chosen such that hydrogen-oxygen bonds break up. This
will be explained in more detail again with reference to FIG.
9.
[0086] As is known, bonds within water or OH components are excited
by microwave radiation, and they may break up in the process.
Consequently, an equilibrium arises between the starting product
(NH.sub.4).sub.2SO.sub.4 on the one hand, and the volatile
constituents SO.sub.3, NH.sub.3 and H.sub.2O, on the other hand,
which equilibrium is shifted toward the volatile constituents in
the case of irradiation with microwaves. The formation of particles
on the photomask 5 is thus prevented as a result of the breaking up
of the OH bonds 88 according to the structural formula of ammonium
sulfate in accordance with FIG. 9. It goes without saying that the
procedure mentioned can also be applied to other crystalline
substances.
[0087] In this case, the volatile constituents are entrained by the
purge gas, thereby preventing renewed crystallization. As is shown
in FIG. 8A, the gas feed line 46 and the gas discharge line 48 are
arranged in direct proximity to the photomask 5 in order to remove
the volatile constituents. All the gases already mentioned above in
the discussion of the embodiment in accordance with FIG. 3 are
appropriate as the purge gas. In practice, the use of forming gas
has proved to be particularly effective. As is known, forming gas
is a hydrogen-nitrogen gas mixture, in which case the hydrogen
proportion should be chosen to be below 5.7% here since gases
comprising a higher proportion of hydrogen are highly
flammable.
[0088] The wavelength of the microwave radiation of the microwave
source 80 may be chosen such that it lies within a range in which
the protective film 20 is as transparent as possible to microwave
radiation. In the case of a protective film made of a
Teflon-containing material, the transparent range of the frequency
of the microwave radiation lies between 2 GHz and 3 GHz.
Consequently, it is possible to use a conventional microwave source
having a frequency of the microwave radiation of approximately 2455
MHz, such as is used e.g. in a microwave oven.
[0089] In order to bring the microwave radiation of the microwave
source 80 into the transparent range of the protective film 20, it
is possible to provide a filter 82 comprising, e.g., the material
of the protective film 20. Consequently, only radiation having a
frequency at which the protective film 20 is transparent advances
as far as the photomask 5.
[0090] In a further embodiment, the microwave source 80 may also be
pulsed in order as far as possible to prevent electrostatic
charging or spark-overs on electrically conductive structure
elements on the transparent substrate. Likewise, the microwave
radiation should not damage adhesives for the fixing of the frame
18 or the protective film 20.
[0091] As is shown in FIG. 8B, an infrared source 90 is provided in
a second aspect. The infrared source 90 emits infrared radiation
having a specific wavelength and intensity onto the surface of the
transparent substrate from the side of the protective film. By way
of example, a mirror 94 may also be used for deflection onto the
transparent substrate 10. The infrared source 90 may likewise be
integrated into the above-described storage system 70 in accordance
with FIG. 4 or be arranged in the vicinity of the holding frame 56
in accordance with FIG. 4. The bottom flap 34 is advantageously
open in this case in order to permit the infrared radiation to
impinge on the photomask 5 unimpeded. In this case, the infrared
radiation irradiates the surface of the transparent substrate 10
and also the structure elements 16 thereof from the side of the
protective film 20.
[0092] The infrared source 90 heats crystalline deposits on the
surface of the transparent substrate in order that their volatile
constituents are subsequently removed by means of the purge gas. In
this case, the gas feed line 46 and the gas discharge line 48 are
once again arranged in direct proximity to the photomask 5 in order
to remove the volatile constituents.
[0093] The wavelength of the infrared radiation of the infrared
source 90 is once again chosen such that it lies within a range in
which the protective film 20 is at least partly transparent to
infrared radiation, but the impurities are activated to a
sufficient extent. This necessitates, on the one hand, a high
transmission for infrared radiation in the protective film 20 and a
high absorption for infrared radiation of the impurities.
[0094] A useable frequency range is explained below with reference
to FIGS. 10 and 11.
[0095] FIG. 10 shows an absorption spectrum for ammonium sulfate. A
plurality of absorption edges which can be used for the method
according to the invention lie within the range of a wave number of
the infrared radiation of between 1000 cm.sup.-1 and 4000
cm.sup.-1. Thus the wave number of the infrared radiation could lie
within the range of between 1100 cm.sup.-1 and 1400 cm.sup.-1 or
2500 cm.sup.-1 and 3500 cm.sup.-1.
[0096] FIG. 11 shows a transmission spectrum for a fluoropolymer
which is a customary material for the production of protective
films 20. It is evident that the material of the protective film 20
is sufficiently transparent in the abovementioned ranges. The
transmission values of the protective film 20 are for the most part
above about 90%.
[0097] According to the invention, impurities directly in the
vicinity of the photomask are removed by means of purge gases,
thereby suppressing crystal growth on the surface of the photomask.
Accordingly, the time between photomask cleaning steps can be
significantly lengthened.
[0098] Having described embodiments for a device for the storage
and use of at least one photomask for lithographic projection and a
method for using the device in a fabrication installation and
non-volatile memory cells, it is noted that modifications and
variations can be made by persons skilled in the art in light of
the above teachings. It is therefore to be understood that changes
may be made in the particular embodiments of the invention
disclosed which are within the scope and spirit of the invention as
defined by the appended claims.
[0099] Having thus described the invention with the details and the
particularity required by the patent laws, what is claimed and
desired to be protected by Letters Patent is set forth in the
appended claims.
* * * * *