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1 Confidential RETICLE STORAGE SYSTEM BACKGROUND [0001] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually 5 onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto 10 a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Modern high resolution tools are generally scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. 15 [0002] Lithography tools have been developed to allow smaller and smaller devices to be patterned on a wafer. Lithographic tools and methods are being developed that utilize multiple exposure. During multiple exposure, two or more reticles are imaged sequentially based on reticle swapping between imaging. Multiple exposure is particularly advantageous in extreme ultra violet (EUV) imaging to overcome undesirably low k1 imaging effects. 20 [0003] A solution to this problem has been implemented in which two or more reticles are stored in vacuum, allowing for faster swap between reticles. It is desirable to all for even faster swap between reticles. DETAILED DESCRIPTION 25 [0004] Before describing embodiments in detail, it is instructive to present an example environment in which embodiments may be implemented. [0005] As shown in Figure 1, a lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or lithocluster, which also includes apparatus to perform one or more pre- and post-exposure processes on a substrate. Conventionally these include one or more spin 30 coaters SC to deposit a resist layer, one or more developers DE to develop exposed resist, one or more chill plates CH and one or more bake plates BK. A substrate handler, or robot, RO picks up a substrate from input/output ports I/O1, I/O2, moves it between the different process devices and delivers it to the loading bay LB of the lithographic apparatus. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory 35 control system SCS, which also controls the lithographic apparatus via lithographic control unit LACU. Thus, the different apparatus may be operated to maximize throughput and processing efficiency. 2 Confidential [0006] Generally, a lithography tool LA can include an exposure chamber, a projection optical system that projects EUV and/or DUV light through a reticle mounted on a reticle stage onto a wafer to print images of a layer of, e.g., an integrated circuit. The lithography tool LA further may include a reticle handling system that exchanges the reticle being exposed as prescribed by the user of the lithography 5 tool LA. [0007] Reticle handling for use in EUV and/or DUV apparatus requires at least some steps wherein the reticles are handled in vacuum. For this purpose, within the lithographic apparatus, a reticle handling subsystem 200 as shown in Figure 2 may be included. The reticle handling subsystem may include a pod transport system 202, which may be an integrated pod transport and manual load station 10 combined. The pod transport system interfaces with an atmospheric module 204. The atmospheric module 204 includes one...