Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1991-10-08
1993-06-08
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
372 32, G01B 902
Patent
active
052184218
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to a wavelength detecting apparatus for detecting the wavelength of a laser light or the like. More particularly, the present invention relates to a wavelength detecting apparatus preferably employable for a case where a narrow-band oscillating excimer laser light unit is used as a light source for an unit for projecting and exposing an image on a reduced scale for the purpose of producing semiconductor devices.
BACKGROUND ART
Attention has been heretofore paid to utilization of an excimer laser light unit to serve as a light source for an unit for projecting and exposing an image on a reduced scale (hereinafter referred to as a stepper) for the purpose of producing semiconductor devices. This is because of the fact that the excimer laser light unit has many excellent advantages that it is possible to expand a limit of light exposure to the range shorter than 0.5 micron because the wavelength of an excimer laser light is short (about 248.4 nm in the case of a KrF laser light), the excimer laser light has a deep focus depth compared with a g line and an i line generated by a conventional mercury lamp under a condition of same resolvability, a small number of lens apertures (NA) is required, the light exposure range can be enlarged, and a large magnitude of power can be produced with the excimer laser light unit.
In a case where the excimer laser light unit is used as a light source for the stepper, it is required that a laser light to be outputted from the excimer laser light unit is oscillated within the narrow-band oscillatory range. In addition, it is required that the wavelength of the output laser light from the excimer laser light unit which has been oscillated within the narrow-band oscillatory range is stabilized while it is controlled at a high accuracy.
Hitherto, a monitor etalon has been used for the purpose of measuring the wavelength line width of a laser light outputted from a narrow-band oscillating excimer laser light unit or the like, and moreover, detecting the wavelength of the same. The monitor etalon is constructed in the form of an air gap etalon including a pair of partially reflecting mirrors arranged opposite to each other with a predetermined gap therebetween. With such construction, the wavelength of the laser light which has permeated through the air gap etalon is represented by the following equation. opposing pair of partially reflecting mirrors constituting the air gap etalon, n designates a refractivity as measured between the opposing pair of partially reflecting mirrors, and .theta. designates an angle defined by a normal line of the etalon and an optical axis of an incident light.
With respect to the foregoing equation, it is obvious that .theta. varies as the wavelength of the laser light varies, when it is assumed that n, d and are kept constant, respectively. In practice, the wavelength of a light to be detected is practically detected by utilizing the aforementioned nature of the monitor etalon. With the monitor etalon constructed in the above-described manner, however, the above angle .theta. varies as a pressure in the air gap and an environmental temperature vary, even though the wavelength of a light to be detected is kept constant. In view of the above fact, when the monitor etalon is used for performing a detecting operation, the wavelength of the light to be detected is practically detected while the pressure in the air gap and the environmental temperature are controllably kept constant.
However, since it is practically difficult to control the pressure in the air gap and the environmental temperature at a high accuracy, the absolute wavelength of the light to be detected can not be detected at a sufficiently high accuracy.
To obviate the foregoing malfunction, a proposal has been made with respect to an apparatus for detecting the absolute wavelength of a light to be detected by inputting the light to be detected as well as a reference light having a known wavelength (e.g., an argon laser light, an os
REFERENCES:
patent: 4289403 (1981-09-01), Allington
patent: 4650329 (1987-03-01), Barrett et al.
Kobayashi Yukio
Kowaka Masahiko
Wakabayashi Osamu
Kabushiki Kaisha Komatsu Seisakusho
Turner Samuel A.
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