US20070187272A1

US20070187272A1 - Device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation

Info

Publication number: US20070187272A1
Application number: US11/644,986
Authority: US
Inventors: Anja Bonness; Marcel Choudhury; Karin Eggers; Andreas Frangen; Norbert Kallis; Wolfgang Keller; Christoph Hocke; Michael Lering; Michael Roesner; Ruediger Hunger; Christoph Noelscher; Gregor Kubart
Original assignee: Qimonda AG; Qimonda Richmond LLC
Current assignee: Qimonda AG; Qimonda Richmond LLC
Priority date: 2005-12-22
Filing date: 2006-12-22
Publication date: 2007-08-16
Also published as: CN1996142A; TW200729292A

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.

Description

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

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

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.
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.
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.
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.
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.
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.
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 ((NH₄)₂SO₄) or to the formation of ammonium oxalate ((NH₄)₂C₂O₄H₂O). These crystals can grow with energy being radiated in by the light source of the exposure apparatus.
An example of crystal growth and irradiation with UV light is described below. Air normally contains hydrogen sulfide (H₂S) in a low concentration. Together with oxygen, sulfur dioxide forms in accordance with the reaction equation:
2H₂S+3O₂−>2SO₂+2H₂O. [1]
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:
SO₂+O−>SO₃ [2]
Together with (residual) water from the air, aerosol particles arise, which are chemically stable, in accordance with the following reaction equation:
SO₃+H₂O−>H₂SO₄ [3]
In the presence of impurities, in this case ammonia, said aerosol particles react to form ammonium sulfate, in accordance with the following reaction equation:
H₂SO₄+2NH₃−>(NH₄)₂SO₄ [4]
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.
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.
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

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.
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.
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.
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.
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.
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

The invention will now be explained in more detail with reference to the accompanying drawings:
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;
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;
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;
FIG. 4 shows a perspective view of a mount in accordance with one embodiment of the invention;
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;
FIG. 6 schematically shows a further perspective view of a device in accordance with one embodiment of the invention;
FIG. 7A schematically shows a further perspective view of a device in accordance with one embodiment of the invention;
FIG. 7B schematically shows a further perspective view of a device in accordance with one embodiment of the invention;
FIG. 8A schematically shows a further cross-sectional view through a device in accordance with one embodiment of the invention;
FIG. 8B schematically shows a further cross-sectional view through a device in accordance with one embodiment of the invention;
FIG. 9 shows a chemical structural formula of an impurity for illustrating the procedure according to the invention;
FIG. 10 shows an absorption spectrum in the infrared range of an impurity for illustrating the procedure according to the invention; and
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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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 (NH₄)₂SO₄on the one hand, and the volatile constituents SO₃, NH₃and H₂O, 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.
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.
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.
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.
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.
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.
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.
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.
A useable frequency range is explained below with reference to FIGS. 10 and 11.
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⁻¹and 4000 cm⁻¹. Thus the wave number of the infrared radiation could lie within the range of between 1100 cm⁻¹and 1400 cm⁻¹or 2500 cm⁻¹and 3500 cm⁻¹.
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%.
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.
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.
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.

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 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:

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⁻¹and 4000 cm⁻¹.

52. The device according to claim 51, wherein the wavenumber of the infrared radiation lies within the range of between 1100 cm⁻¹and 1400 cm⁻¹.

53. The device according to claim 51, wherein the wavenumber of the infrared radiation lies within the range of between 2500 cm⁻¹and 3500 cm⁻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

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.