Field of the Invention
The present invention relates to exposure apparatuses, exposure methods, and device manufacturing methods, and more particularly to an exposure apparatus and an exposure method used in a lithography process to produce electronic devices such as a semiconductor device (an integrated circuit) and a liquid crystal display device, and a device manufacturing method which uses the exposure apparatus or the exposure method.
Description of the Background Art
In recent years, in a lithography process for manufacturing electron devices such as a semiconductor device (an integrated circuit), a liquid crystal display device and the like, especially from the aspect of productivity, a projection exposure apparatus is mainly used which reduces and transfers a pattern of a photomask (a mask) or a reticle (hereinafter generally referred to as a “reticle”) that is proportionally enlarged by four to five times the pattern to be formed, onto an object subject to exposure (hereinafter referred to as a “wafer”) via a projection optical system.
In this type of exposure apparatus, the exposure wavelength has been shifted more to the short wavelength side so as to achieve high resolution in correspondence with finer integrated circuits. Currently, the mainstream of the wavelength is 248 nm of the KrF excimer laser, or 193 nm of an ArF excimer laser which belongs to the vacuum ultraviolet region having a shorter wavelength than the 248 nm.
However, with finer design rules of the semiconductor devices, haze (fog) defect of the reticle in the lithography process is becoming a major problem. It is said that reticle haze occurs when a substance which becomes the source of the haze forms on the reticle as a result of an acid-base reaction of acids and bases present on the surface of the reticle and in the atmosphere, or a photochemical reaction of organic impurities, and the source of the haze coheres by moisture inclusion and ultraviolet radiation (energy of exposure) and grows in size to be a cause of defects. Currently, as a cause of reticle haze, ammonium sulfate is seen as the biggest problem. While this problem was recognized in the KrF lithography, it came to have a serious influence on the productivity and production cost in the ArF lithography which uses a shorter wavelength (=higher energy).
It is said that removing volatile impurities (mainly, SOx, NH3, organic matter) which are substances responsible for haze, and moisture which is a substance accelerating the reaction of haze generation from a storage environment and a movement environment of the reticle is an effective measure to comprehensively suppress the haze formation on the reticle. As a concrete example of this effective measure, removing the substance accelerating the reaction of haze generation from the space in the periphery of the reticle in the exposure apparatus can be considered, and to be more precise, supplying a purge gas such as clean dry air (CDA) in the space in the periphery of the reticle and replacing the gas (gas purge) can be considered.
Further, recently, from the aspect of improving processing capacity (throughput), for example, a scanning type projection exposure apparatus by the step-and-scan method (that is, the so-called scanning stepper) which relatively scans the reticle and the wafer while maintaining the image-forming relation during exposure so as to obtain a substantially large exposure field using a projection optical system with high NA but a small field which can easily achieve high NA and low aberration has become mainstream.
As a method to achieve the effective measure to comprehensively suppress the haze formation on the reticle, for example, a method in which the entire reticle stage which holds the reticle is covered with a large air-tight shielding container (reticle stage chamber), and the inside (including the reticle stage and the reticle) is purged overall with gas, as is disclosed in, U.S. Patent Application Publication No. 2004/0057031, is considered effective.
However, when such a shielding container is employed, the exposure apparatus increases in size and weight, which increases the installation area (footprint) per exposure apparatus in a clean room of a semiconductor factory which in turn increases the equipment cost (or running cost), and as a result, productivity of semiconductor devices decreases. Further, access to the vicinity of the reticle becomes difficult, which reduces the workability at the time of maintenance of the reticle stage and the like and increases the time required for maintenance, which also leads to a decrease in productivity of the semiconductor devices.
Especially, the scanning type projection exposure apparatus is equipped with a large reticle stage since the reticle has to be scanned at a high speed during exposure, and the shielding container (reticle stage chamber) covering this large reticle stage entirely increases further in size.
Further, in the projection exposure apparatus, an extremely high accuracy is required concerning alignment (overlay) between layers (a layer) of a circuit element. As one of the factors to influence this overlay accuracy, distortion of the pattern which occurs due to thermal expansion of the reticle by irradiation of the exposure light can be given. In the projection exposure apparatus, because high throughput is required along with accuracy, illuminance of the exposure light shows a tendency of increasing more and more. Therefore, it is becoming difficult to satisfy the overlay accuracy which is required, unless temperature control of the reticle is performed positively.
In the past, as a method of performing temperature control of the reticle, a method (for example, refer to Kokai (Japanese Unexamined Patent Application Publication) No. 10-022196) of blowing air (gas) whose temperature is controlled onto the reticle, or a method of closely attaching a cooling plate in an area besides the exposure range of the reticle has been proposed. However, in the former case, there was an inconvenience that in the case the wind speed was increased to improve the heat transfer rate, particles (so-called dust) were blown up, which adhered to the reticle, and caused defects to occur in the circuit element. Meanwhile, in the latter case, there was an inconvenience that each time the reticle was exchanged, the cooling plate had to be attached to the reticle, which extended the reticle exchange time. As well as this, it is becoming difficult to keep the distortion of the pattern within a permissible value merely by cooling the reticle each time the reticle is exchanged.