Patent Application
20070248127
A first embodiment of a cooling device for a reflective mirror is shown in
The heat-conduction member 119 extends to a peripheral region inside the lens barrel or alternatively to outside the lens barrel. Desirably, the heat-conduction member 119 is formed as an integral member from a metal to provide ease of installation and efficient heat conduction. Depending upon circumstances, two or more such members may be linked together. Even when two or more members are used, installation is easier than connecting tubes for liquid coolant. Although the heat-conduction member 119 is mounted within the lens barrel, the danger of liquid leaks associated with use of a coolant tube is eliminated. The heat-conduction member 119 also requires little to no maintenance, and has an extremely small risk (compared to a coolant tube) of conducting or imparting vibrations to the lens barrel. Consequently, the optical system in the lens barrel is less affected by vibrations.
The coolant tube 151 is situated well away from the respective optical element 111, thereby minimizing risk of damage to the element by a coolant leak, and is situated to provide easy access, thereby providing easy maintenance. Also, the coolant tube 151 in this embodiment is substantially shorter than in conventional systems, which improves cooling performance.
As the material of the heat-conduction member 1119, a metal with high thermal conductivity, in particular aluminum or an alloy thereof, is desirable. Other materials that can be used include simple metals having a thermal conductivity of 100 W/(m·K) or higher. These metals include silver, copper, gold, beryllium, tungsten, magnesium, rhodium, silicon, iridium, molybdenum, sodium, zinc, ruthenium, and potassium. Of these alternative metals, tungsten, molybdenum, and zinc are desired from the standpoint of low cost, low toxicity, stability, and other properties.
As the heat-conduction member 119 extends within the lens barrel to the optical element 111, it is desirable to reduce radiative heat propagation from the surface of the member 119 to other surfaces by polishing the surface.
The heat-conduction member 119 may comprise one or more heat pipes. A heat pipe, for example, comprises a sealed vessel that contains a small amount of a volatile fluid (“working fluid”) and that has a capillary-tube structure in its inner walls. One portion (heated portion) of the heat pipe is situated in proximity to the optical element, and the other portion (low-temperature portion) is situated at the peripheral region of the lens barrel or outside the lens barrel. In the heated portion the working fluid is caused to evaporate, and the latent heat of vaporization is absorbed. The vapor of the working fluid moves to the low-temperature portion, condenses in the low-temperature portion, and releases the latent heat of vaporization. The condensed working fluid is recirculated to the heated portion by means of a capillary effect exhibited by the capillary-tube structure. In this way, heat is moved from the heated portion to the low-temperature portion of the heat pipe. When the heat-conduction member 119 comprises one or more heat pipes, the possibility of liquid leaks and of vibrations is reduced compared to a case in which a cooling tube is installed in proximity to the optical element. Further, the above-described metal or other heat-conduction member may be combined with heat pipe(s).
As an electrical current is passed through the Peltier element 117, heat is transferred from its heat-absorbing face to its heat-dissipating face. A temperature sensor (not shown) is installed either on the heat-absorbing face or on the radiative-cooling plate 115. The current passed through the Peltier element 117 is controlled by the output of the temperature sensor, to control heat-transfer. Heat transferred to the heat-dissipating face is conducted to the heat-conduction member 119. The heat-conduction member 119 conducts the heat to a peripheral region within the lens barrel or to a region outside the lens barrel.
The extended portion of the heat-conduction member 119 is attached to the coolant tube 151 by a coupling 153. Thus, the heat-conduction member 119 is cooled by the coolant flowing in the coolant tube 151.
In
Since the coolant tube 151 is situated outside the lens barrel 150, possible damage to components in the lens barrel from coolant leaks is reduced, and maintenance is simplified. Since the coolant tube 151 is straight, bends are eliminated or reduced, with corresponding reduction in incidence and effects of vibrations of the coolant tube 151 on the optical system. Also, by making the coolant tube 151 straight, it length is reduced, thereby maintaining good cooling performance.
The heat-conduction member 119 extends to a peripheral region inside the lens barrel or outside the lens barrel. The structure, materials, and the like of the heat-conduction member 119 are as described with respect to the embodiment shown in
From the standpoint of ease of installation and heat-conduction efficiency, the heat-insulating cover 121 desirably is formed integrally from a metal. Depending on circumstances, two or more members may be linked together to form the heat-insulating cover. The heat-insulating cover 121 desirably is made of a metal having a high thermal conductivity. A particularly advantageous metal in this regard is aluminum or an alloy thereof. Other suitable metals include, but are not limited to, tungsten, molybdenum, and zinc. As the heat-insulating cover 121 extends within the lens barrel, to reduce radiative heat propagation from the surface of the heat-insulating cover to other components in the lens barrel, the surface of the cover desirably is polished.
As an electrical current is passed through the Peltier element, heat is transferred from its heat-absorbing face to its heat-dissipating face. A temperature sensor (not shown) may be mounted on the heat-absorbing face or on the radiative-cooling plate 115. The temperature sensor can be used for feedback-control of the current delivered to the Peltier element according to the output from the temperature sensor, thereby controlling heat transfer. The heat transferred to the heat-dissipating face is conducted to the heat-conduction member 119 and transferred to the peripheral region within the lens barrel or to a region outside the lens barrel.
The extended portion of the heat-conduction member 119 is attached to the coolant tube 151 by a coupling 153, and thus is cooled by the coolant tube 151. Within the lens barrel, since the heat-conduction member 119 is covered by the heat-insulating cover 121, radiative propagation of heat from the heat-conduction member 119 to other reflective mirrors or other components in the lens barrel is prevented.
In the foregoing, features of embodiments of cooling devices, as used with reflective mirrors in a projection-optical system of an exposure apparatus, have been described. Alternatively or in addition, the subject cooling device can be used with a reflective mirror in an illumination-optical system of an exposure apparatus, and/or with another optical element in an exposure apparatus for which temperature regulation is necessary.
The configuration of an embodiment of an exposure apparatus according to the invention is similar in many ways to the exposure apparatus depicted in
The selectable range of the specific material from which the conductive film CL can be made is broad, and includes metals in general (e.g., Cr, Ni, Ta, and other metals and alloys), semiconductors, and the like.
The specific multilayer film ML for use in reflecting incident EUV light depends upon the particular wavelength of EUV light. When, for example, a wavelength of 13-14 nm is used, the multilayer film ML desirably comprises 40 to 50 pairs of layers of Mo (molybdenum) and Si (silicon). The layers desirably alternate with a period equal to approximately half the wavelength, and are formed in a superposed stacked configuration. Using such a multilayer film ML, a reflectivity of approximately 70% is obtained in the normal direction.
In a large-NA (numerical aperture) optical system usable with EUV light, the range of incidence angles at the reticle is extremely large. For an ordinary equal-period multilayer film ML, the reflectivity over the range of incidence angles is broadly distributed between approximately 50% and 74%. The reticle can be formed such that the multilayer film ML has certain regions in which the respective periods are not equal and other regions in which the periods are equal, so as to prevent the reflectivity from the reticle from assuming a distribution, even over a broad range of incidence angle. I.e., with such a reticle, the reflectivity distribution is substantially “flat.” Here, an equal-period multilayer film is a multilayer film in which, for example, Mo (molybdenum) layers of a fixed thickness and Si (silicon) layers of a fixed thickness are stacked repeatedly. In an unequal-period multilayer film of Mo and Si, for example, multiple Mo layers of different thicknesses and multiple Si layers of different thicknesses are stacked.
In the multilayer film ML of the reticle 202, layer thicknesses and the like are optimized according to the incidence wavelength, incidence angle, range of incidence angle, and other optical-system conditions in the exposure apparatus. If a reticle is used that does not conform to the optical-system conditions of the exposure apparatus, the projection-optical system of the exposure apparatus cannot exhibit adequate imaging performance (such as proper focus). By encoding multilayer-film design information for the reticle on a barcode or the like imprinted on the reticle, upon mounting the reticle in the apparatus, the apparatus can “read” the information for the reticle, and provide data or control functions according to whether the reticle conforms to the exposure apparatus.
Among the main steps, wafer processing is key to achieving the smallest feature sizes (critical dimensions) and best inter-layer registration. In the wafer-processing step, multiple circuit patterns are layered successively atop one another on the wafer, forming multiple chips destined to be memory chips or main processing units (MPUs), for example. The formation of each layer typically involves multiple sub-steps. Usually, many operative microelectronic devices are produced on each wafer.
Typical wafer-processing steps include: (1) thin-film formation (by, e.g., sputtering or CVD) involving formation of a dielectric layer for electrical insulation or a metal layer for connecting wires or electrodes; (2) oxidation step to oxidize the substrate or the thin-film layer previously formed; (3) microlithography to form a resist pattern for selective processing of the thin film or the substrate itself; (4) etching or analogous step (e.g., dry etching) to etch the thin film or substrate according to the resist pattern; (5) doping as required to implant ions or impurities into the thin film or substrate according to the resist pattern; (6) resist stripping to remove the remaining resist from the wafer; and (7) wafer inspection. Wafer processing is repeated as required (typically many times) to fabricate the desired microelectronic devices on the wafer.
The process steps summarized above are all well-known and are not described further herein.
As disclosed herein, by providing a cooling device in which the heat-conduction member is in contact with a Peltier element, the cooling device has substantially reduced probability of damage to neighboring components due to leaks of liquid coolant from the coolant tube. Thus, maintenance is simplified, vibrations of the coolant tube are reduced, effects of such vibrations on the optical system are reduced, and good cooling performance is maintained.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2006-119620 | Apr 2006 | JP | national |
