Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-10-18
2002-07-02
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S030000, C355S053000
Reexamination Certificate
active
06414743
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an exposure apparatus for use in a lithography process in a production line for manufacturing semiconductor devices, liquid crystal display devices and an exposure method using such exposure apparatus. The present invention also relates to a method for manufacturing circuit devices for use in forming electronic circuit devices on a semiconductor substrate (wafer), glass substrate, and so on.
BACKGROUND TECHNOLOGY
Recently, at plants for manufacturing semiconductor devices such as super LSIs and so on, developments for mass-producing D-RAMs (memory chips), processor chips and the like, having a degree of integration and a fineness of a class of 256 Mbits on a large scale have been carried out extensively with great effort. As developments advance, exposure apparatuses for use in a next-generation lithography process (representatives being processes for coating a resist, exposing, developing resist, etc.) are also required to have a higher precision of alignment, a high resolution and a higher throughput.
At current times, at plants for manufacturing semiconductor devices, a reduced projection exposure apparatus of a step-and-repeat type has been used extensively, which uses i-rays having a wavelength of 365 nm, among emission line mainly from a mercury discharge lamp as illumination light for exposing. The projection exposure apparatus of this type is configured such that i-rays are irradiated as illumination light onto a reticle (a mask substrate) disposed on the object plane side of a projection optical system having a ⅕-fold reduction rate and a circuit pattern formed on the reticle is transcribed on a resist layer on a semiconductor wafer by means of a projection optical system. Further, the projection exposure apparatus of a step-and-repeat type is configured such that a stage with the wafer loaded thereon is transferred in a stepwise and two-dimensional manner in order to allow a sequential transcription of an image of a circuit pattern of the reticle in plural positions (shot regions) on the wafer.
Further, as a trend in these years, in order to avoid that a vision field of the projection optical system should become extremely large attendant upon enlarging a size (a chip size) of a circuit device to be formed on the wafer, a reduced projection exposure apparatus of a step-and-scan type draws attention, which step-and-scan type is to scan and expose an entire image of the circuit pattern of the reticle to the wafer by scanning the reticle in the vision field on the object plane side of the reduced projection optical system in a one-dimensional direction at an equal velocity and at the same time scanning the wafer in the vision field on the image plane side of the reduced projection optical system in a one-dimensional direction at an equal velocity.
Moreover, projection exposure apparatuses of a step-and-repeat type or of a step-and-scan type have been developed, which use ultraviolet pulse light having a wavelength of 248 nm from a KrF excimer laser light source as an exposing illumination light, and they have been begun being launched into production lines on a large scale. As such an excimer laser light source, an ArF excimer laser light source having a shorter wavelength (having a central wavelength of 193 nm) is now being developed, and it is promising in the future as an exposing light source.
In particular, in the case where such an ArF excimer laser light source is used for exposuring, it is required to narrow wavelength characteristics of pulse light to a wavelength that can avoid several absorption bands of oxygen that exist within the wavelength band in a naturally oscillating state of the pulse light. Further, it is required to replenish a majority of an illumination light path extending from the light source to the reticle and a projection light path extending from the reticle to the wafer with inert gases (such as nitrogen gas, helium gas, etc.), in order to provide an environment where oxygen is contained in the least possible amount in both of the such illumination light path and projection light path. An example of the projection exposure apparatus using such an ArF excimer laser light source is disclosed, for example, in U.S. Pat. No. 5,559,584 (Japanese Patent Application Laid-Open Nos. 6-260,385 and 6-260,386).
As an optical glass material for practical use having a desired transmittance for ultraviolet pulse light (wavelength of 250 nm or less) from the such excimer laser light source, there are currently known only two, one being quartz (SiO
2
) and the other being fluorite (CaF
2
). As a matter of course, although there are known other optical glass materials such as magnesium fluoride, lithium fluoride, and so on, they require to solve various problems with processing, durability, and so on before they are applied practically as an optical glass material for use with the projection exposure apparatus.
Moreover, in the case of use of quartz and fluorite for the projection exposure apparatus, achromatism in the projection optical system becomes difficult upon using illumination light. Therefore, a narrow-banded laser light source is preferred from the point of view of easiness of performing achromatism in the projection optical system.
It should be noted herein, however, that a band of such an excimer laser light is originally a broad band, so that a narrow-banded laser light source has its oscillating spectrum narrowed by injection locking, etc. From these reasons, the narrow-banded laser light source suffers from the disadvantages that a laser output is lowered as compared with a broad-band laser light source, and its life is shorter and its costs of production is more expensive than the broad-band laser light source. Therefore, the broad-banded laser light source is more favored in terms of the laser output, life and costs of production than the narrow-banded laser light source. Recently, attempts have been made to use a broad-banded laser light source for a projection optical system having a structure in which achromatism can be done easily.
There are known several types of projection optical systems to be mounted on the projection exposure apparatus. Among them, the types of the projection optical systems for exposure apparatuses which are used for large-scale commercial production lines can be divided into two major types, one being a dioptric type that is composed of a plurality of refractive optical elements (lens elements) only and the other being a catadioptric type that is composed of a combination of such refractive optical elements with reflective optical elements (particularly a concave mirror).
In the case of using a reflection-refraction optical system as of a catadioptric type, the concave mirror is free from chromatic aberration, so that achromatism can be effected easily by locating the concave mirror in a group of refractive lenses. As a result, a broad-banded laser light source can be used which is advantageous in terms of the laser output, life, etc. On the other hand, in the case of using a refractive optical system only as of a dioptric type, too, a broad-banded laser light source can be used because a range of achromatism can be widened by making a rate of fluorite contained in the entire refractive lenses larger.
In a current situation, however, even which type of the projection optical system is adopted, the refractive optical elements (light-transmitting optical elements) have to be used. Therefore, at this point of time, there is no way but using two kinds of glass materials, i.e. quartz and fluorite, for the refractive optical elements. Further, each of the refractive optical elements and the reflective optical elements is produced so as to achieve a desired performance as a single optical element by forming a multi-layer membrane such as a reflection preventive layer, a protective layer, etc. by deposition etc. on a surface of each element. The performance to which attention should be paid herein is how large an absolute value of transmittance or transmissivity of
Kiuchi Toru
Nishi Kenji
Adams Russell
Armstrong Westerman Hattori McLeland & Naughton LLP
Nguyen Hung Henry
Nikon Corporation
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