DETAILED DESCRIPTION

[0028] The invention is described below in the context of representative embodiments that are not intended to be limiting in any way.

[0029] First, the overall structure of an electron-beam microlithography system, as well as the general optical relationships of such a system, are depicted schematically in FIG. 4 . The particular type of system depicted in FIG. 4 is a step-and-repeat type as known in the art, and the system is configured for use with load-lock chambers (and other peripherals) as described later below.

[0030] An electron gun 1 is situated at the extreme upstream end of the system and generates an electron beam that propagates in a downstream direction (downward in the figure). The electron beam propagates in a generally axial direction through an illumination-optical system comprising a condenser lens 2 and an illumination lens 3 . The illumination-optical system shapes and directs the beam (termed an “illumination beam” IB) onto a selected region of the reticle 10 . In addition to the lenses 2 , 3 , the illumination-optical system includes a beam-shaping aperture, a blanking deflector, a blanking aperture, an illumination-beam deflector, etc. (not detailed). The illumination beam IB, formed by the illumination-optical system, is moved in a scanning manner across successive regions of the reticle 10 , thereby illuminating exposure regions (“subfields”) of the reticle 10 , situated in the optical field of the illumination-optical system, in a sequential manner.

[0031] As noted above, the reticle 10 defines a large number of exposure regions termed “subfields” each defining a respective portion of the overall pattern defined on the reticle. For exposure the reticle is mounted on a movable reticle stage 11 . Moving the reticle stage 11 in a plane perpendicular to the optical axis AX allows the subfields of the reticle to be illuminated selectively in a sequential manner. This exposure scheme is termed “divided-reticle” exposure and effectively achieves exposure of an entire pattern that covers a much greater area than the optical field of the illumination-optical system.

[0032] Situated downstream of the reticle 10 is a projection-optical system comprising a first projection lens 15 , a second projection lens 19 , and deflectors 16 - 1 to 16 - 6 , the latter being used for aberration correction and image-position adjustment. The electron beam passing through a selected subfield of the reticle 10 is focused by the projection-optical system at a predetermined position on a sensitive substrate 23 (e.g., semiconductor wafer). So as to be imprinted with the projected image, the substrate 23 is coated with a material termed a “resist” that is sensitive to an exposure dose by the electron beam. Typically, the projection-optical system is a “reducing” system, by which is meant that the image as formed on the substrate 23 is smaller, usually by a factor termed a “demagnification factor” (e.g., ¼), than the corresponding pattern as defined on the reticle 10 .

[0033] The electron beam forms a crossover C.O. at a point having an axial location, between the reticle 10 and substrate 23 , that is determined by the demagnification ratio. A contrast aperture 18 is situated at the crossover. The contrast aperture 18 blocks electrons of the beam that were scattered by passage through non-patterned regions of the reticle 10 , thereby preventing the scattered electrons from reaching the substrate 23 .

[0034] The substrate 23 is mounted via an electrostatic chuck (not shown) to a substrate stage 24 that is movable in the XY direction. Each portion of a device pattern, extending wider than the optical field of the projection-optical system, can be exposed in a sequential manner by synchronously scanning the reticle stage 11 and substrate stage 24 in opposite directions.

[0035] FIG. 1 (A) schematically depicts the structure of a microlithography system according to a first representative embodiment. FIG. 1 (B) depicts detail of a region of a rack 66 used for storing (under vacuum) a reticle library for the microlithography system. The system shown in FIG. 1 (A) comprises an illumination-optical system (IOS) lens column 51 that contains the electron gun 1 , condenser lens 2 , illumination lens 3 , etc., summarized above with reference to FIG. 4 . Downstream of the IOS lens column 51 is a reticle chamber 53 that contains a reticle stage 11 . Downstream of the reticle chamber 53 is a projection-optical system (POS) lens column 55 that contains the first projection lens 15 , second projection lens 19 , deflectors 16 , etc., summarized above with reference to FIG. 4 . Downstream of the POS lens column 55 is a wafer chamber 57 that contains a wafer stage 24 . These columns 51 , 55 and chambers 53 , 57 are not necessarily separate, individual chambers; one or more of them can be contiguous with each other. The columns 51 , 55 and chambers 53 , 57 can be evacuated by one or more vacuum pumps (not shown but well-understood in the art) configured to evacuate respective individual columns and chambers or multiple columns and/or chambers.

[0036] A vacuum-side transport robot 63 is situated in a right-hand (in the figure) extension 53 a of the reticle chamber 53 . A vacuum reticle library 64 and reticle load-lock chamber 61 are connected to the extension 53 a to the right (in the figure) of the robot 63 . The vacuum reticle library 64 is effectively a chamber containing an array of reticles 80 stored in a vacuum environment. A first gate valve 62 is interposed between the vacuum reticle library 64 and the reticle load-lock chamber 61 . A second gate valve 71 is provided at the entrance to the reticle load-lock chamber 61 . Inside the vacuum reticle library 64 is a rack 68 having, e.g., multiple shelves (four are shown) that support respective reticles 80 placed on them. In any event, the rack 68 is configured to hold multiple reticles 80 .

[0037] The rack 68 desirably is temperature-controlled, preferably in a manner by which thermal exchange with one or more reticles 80 is by thermal conduction, which is rapid and efficient. To such end, as shown in FIG. 1 (B), at least one shelf of the rack 68 includes a respective fluid conduit 68 a connected to a fluid of which the temperature is controlled. The fluid circulates through the conduits 68 a . An exemplary temperature-control fluid is water. Thus, the vacuum reticle library 64 is configured to regulate the temperature of reticles 80 on the rack 68 by thermal conduction from the fluid to the reticles. The circulating fluid achieves rapid equilibration of the reticles 80 at the desired reticle temperature. In this manner, the temperature of a reticle 80 (that has experienced a temperature change when placed in the vacuum environment and/or that is destined for immediate use in making an exposure) placed on a shelf of the rack 68 can be stabilized quickly to a desired temperature. For example, the temperature of a reticle increases not only from being transported to a vacuum environment but also from being irradiated during use in lithographic exposure. This temperature increase can be predicted, and the temperature of the temperature-control fluid can be set accordingly so as to confer the predicted temperature to the reticles. The temperature of each shelf of the rack 68 need not be identical from shelf to shelf. Rather, the temperature of each shelf can be variable as desired.

[0038] An atmospheric-pressure reticle library 66 is situated to the right (in the figure) of the reticle load-lock chamber 61 , with an atmosphere-side transport robot 65 interposed therebetween. A rack 69 having multiple shelves (four are shown) is provided in the atmospheric-pressure reticle library 66 so as to provide multiple reticles 80 that can be selected quickly for exposure. Each shelf supports a respective reticle cassette 67 . Multiple reticles 80 (which can be the same or different) desirably are stored in each reticle cassette 67 (or each cassette can hold as few as one reticle). To identify the contents of each cassette 67 , a respective bar code (as an exemplary identification symbol) 70 is applied to the cassette 67 and to each reticle 80 situated in the cassette 67 .

[0039] In the context of using a bar code as a representative identification symbol, when transporting a reticle 80 to and from the atmospheric-pressure reticle library 66 , the respective bar code 70 on the reticle 80 and cassette 67 is read by a bar-code reader 59 so as to confirm that the proper reticle from the proper cassette is being transported. Since specific reticles 80 are stored in specific reticle cassettes 67 , each particular reticle desirably is returned to its original reticle cassette after use of the reticle. To ensure no mixups in this regard, the respective bar codes 70 of the reticle 80 and of the reticle cassette 67 are read and confirmed. After making such confirmation is the reticle returned to its cassette. By thus reading the bar code 70 and confirming the identity of the reticle 80 , the reticle is returned to its original reticle cassette without error. The bar codes 70 on the reticle 80 and reticle cassette 67 desirably are read in advance of reticle selection, wherein the read data are stored in a memory and recalled during the confirmation step.

[0040] In other words, reticles desirably remain “paired” with their respective reticle cassettes, wherein, after a reticle is used for exposure it desirably is returned to its original cassette 67 (i.e., the cassette in which the reticle was stored prior to use). Upon reading and confirming the bar codes 70 on reticles 80 and cassettes 67 , the reticle is returned reliably to its proper cassette.

[0041] In FIG. 1 (A) the reticle libraries 64 , 66 are configured desirably for vertical stacking of reticles 80 on a respective stationary rack. Alternatively, it is possible for the reticle libraries to be configured for use with a vertically movable transport robot or such that the reticle libraries 64 , 66 themselves move vertically.

[0042] Whenever a reticle 80 is being transported between the vacuum reticle library 64 and the atmospheric-pressure reticle library 66 , the operator can provide appropriate commands from a keyboard console or the like (not shown), or may operate appropriate controls (not shown) provided at or near the atmospheric-pressure reticle library 66 . If necessary, the bar code 70 applied to the reticle 80 can be read by a bar-code reader 58 .

[0043] Pre-alignment of the reticle may be necessary until the reticle is transported onto the reticle stage 11 . This pre-alignment may be accomplished while transporting the reticle from the atmospheric-pressure reticle library 66 to the load-lock chamber 61 , before placing the reticle in the vacuum reticle library 64 , or while performing both operations.

[0044] A second representative embodiment is depicted in FIG. 2 , and FIG. 3 depicts an example of a load-lock chamber used with this embodiment. The microlithography system shown in FIG. 2 comprises multiple load-lock chambers 61 ′ instead of the vacuum reticle library 64 used in the first representative embodiment, coupled in parallel to the vacuum chamber 53 . Each load-lock chamber 61 ′ contains one or more respective reticles 80 . The operator selects whether the interior of each load-lock chamber 61 ′ is atmospheric pressure or vacuum, or a desired intermediate pressure. Each load-lock chamber 61 ′ can be brought selectively into communication with the vacuum chamber 53 by, e.g., opening a respective gate valve 62 ′. The use of multiple load-lock chambers 61 ′ arranged in this manner facilitates rapid and efficient movement of reticles 80 between the atmosphere side and the vacuum side. As shown in FIG. 3, a respective cassette 67 capable of holding one or more reticles 80 can be situated inside each load-lock chamber 61 ′.

[0045] Reticle cassettes conventionally are made of a rigid plastic resin. If a reticle cassette is moved from an atmospheric-pressure environment to a vacuum environment, the resin tends to outgas, which can degrade the vacuum level. By storing the reticle cassettes 67 in the vacuum environment of the respective load-lock chambers 61 ′, outgassing proceeds and eventually is reduced substantially, thereby avoiding vacuum deterioration. Also, since multiple reticles 80 collectively are stored in the load-lock chambers 61 ′, it is unnecessary to perform outgassing evacuation each time a reticle is exchanged.

[0046] Therefore, according to the embodiments described above, methods and devices are provided that provide easy reticle exchange as well as temperature control of the reticles, if desired.

[0047] Whereas the invention has been described in connection with multiple representative embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.