Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1996-04-18
1998-05-05
Nelms, David C.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
372 32, G01B 908
Patent
active
057483167
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a device for detecting the wavelength of a narrow-band excimer laser which is used as a light source for a semiconductor exposure apparatus.
BACKGROUND ART
Conventionally, a monitor etalon is used for the purpose of detecting narrow-band excimer laser wavelength linewidths and wavelengths. A monitor etalon is constituted by using an air-gap etalon in which partially reflecting mirrors are mounted facing each other with a prescribed interval between them, so the transmission wavelength .lambda. of this air-gap etalon can be represented as follows.
It is seen from this equation that, if n, d and m are constant, .theta. changes when the wavelength .lambda. changes. In a monitor etalon, this property is used to detect the wavelength of light that is the object of detection.
However, in the abovementioned monitor etalon, if the pressure in the air gap and the ambient temperature changes, the angle .theta. changes, even if the wavelength is constant. Because of this, there are occasions when it is not possible to detect the wavelength .lambda. accurately on the basis of the angle .theta.. When using a conventional monitor etalon, therefore, it is common practice to perform wavelength detection while controlling the pressure in the air gap and the ambient temperature, etc. to hold them constant.
However, it is difficult to effect highly precise control of the pressure in the air gap and the ambient temperature, and it is therefore not possible to detect absolute wavelengths with satisfactory precision.
There has therefore been proposed a device in which a reference light (eg, mercury lamp light rays) whose wavelength has been determined beforehand is made incident on a monitor etalon together with the light that is the object of detection (output laser light), and the absolute wavelength of the light that is the object of detection is detected with good precision by detecting the relative wavelength of this light with reference to the reference light (eg, the disclosures of Japanese Patent Application Laid-open Nos. 1-101683 and 4-356987).
In a device such as this, light transmitted by the monitor etalon is introduced directly into a light detector such as a CCD image sensor, etc., an interference fringe is formed on the detection surface of this light detector, and the absolute wavelength is detected on the basis of the position of the interference fringe.
However, even in the prior art, if the spectral waveform of the reference light source becomes distorted or changes because of changes in time or the temperature of the reference light source (the spectral waveform changes considerably because of self-absorption of a mercury lamp's 253.7 nm line), there is a resulting distortion of the light intensity distribution of the interference fringe produced by the monitor etalon. In this case, because of the change in the reference light wavelength, it was impossible to highly accurately specify the absolute wavelength of the light to be detected.
There is therefore a demand for a technique whereby reference light which is stable in terms of wavelength changes can be produced, and for a technique for highly precise measurement of the absolute wavelength of reference light.
With the foregoing in view, it is an object of the present invention to provide an excimer laser wavelength detection device with which a stable reference light can be produced and highly precise measurements of the absolute wavelengths of the reference light and of light which is the object of detection can be made.
DISCLOSURE OF THE INVENTION
In the first embodiment of the present invention, a low-pressure mercury lamp is used as a reference light source, and this low-pressure mercury lamp is made such that not less than 49% of a specific isotopic mercury is sealed therein and 253.7 nm line is used, whereby reference light whose spectral wavelength is clear and whose linewidth is narrow is produced.
In the second embodiment of the present invention, a low-pressure mercury lamp is used as a reference
REFERENCES:
patent: 4173422 (1979-11-01), Synder
patent: 4482842 (1984-11-01), Fujimura et al.
patent: 4648951 (1987-03-01), Maya
patent: 4986665 (1991-01-01), Yamanishi et al.
patent: 5173642 (1992-12-01), Matsumoto et al.
patent: 5198872 (1993-03-01), Wakabayashi et al.
patent: 5218421 (1993-06-01), Wakabayashi et al.
patent: 5381076 (1995-01-01), Narone
patent: 5387974 (1995-02-01), Nakatani
Kobayashi Yukio
Wakabayashi Osamu
Komatsu Ltd.
Nelms David C.
Smith Zandra V.
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