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Device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installationRelated Patent Categories: Special Receptacle Or Package, For Plate Or Sheet, Fragile Or Sensitive (e.g., Glass Mirror), Photo Film Or PlateDevice for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070187272, Device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation. Brief Patent Description - Full Patent Description - Patent Application Claims
[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. Continue reading about Device for the storage and use of at least one photomask for lithographic projection and method for using the device in an exposure installation... 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