Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
1999-03-16
2001-11-13
Evans, F. L. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S326000, C356S328000, C356S329000, C356S450000, C356S515000, C372S032000, C372S102000
Reexamination Certificate
active
06317203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a narrowband module inspection device for inspecting the narrowband efficiency, wavelength selection characteristics, and other narrowband performance of a narrowband module.
2. Description of the Related Art
Attention is focusing on the use of excimer lasers as light sources in steppers used in the fabrication of semiconductor devices. This is because numerous outstanding advantages can be expected. These include the capability to extend the lithography limit to 0.35 &mgr;m and lower as a result of the short wavelengths of an excimer laser; deeper depth of focus than previously-used mercury lamp g-line and i-line peaks at the same resolution; a large exposure area can be achieved with a small numerical aperture (NA) lens; and high power levels.
However, when this excimer laser is utilized as the light source in a semiconductor exposure system, synthetic quartz is the only lens material capable of being fabricated into an optical system for excimer laser wavelengths (the wavelength of a KrF excimer laser is 248 nm, and that of an argon excimer laser is 193 nm); but a synthetic quartz material alone cannot be furnished with a chromatic aberration function.
For example, in the case of spontaneously emitted energy of a KrF excimer laser, the spectral line width is a wide 300 pm, and left as-is, the chromatic aberration of the exposure system lens cannot be ignored, and resolution sufficient for exposure results cannot be achieved.
Accordingly, when utilizing an excimer laser as the light source of a semiconductor exposure system, the bandwidth of the laser light is narrowed by providing inside the laser resonator a narrowband module, comprising a wavelength selection device, such as an etalon, or grating and prism.
When inspecting the performance of a narrowband module such as this, in the past, the narrowband module was mounted into an actual laser, the actual laser light emitted from the laser chamber was incident on the narrowband module, and the outputted light thereof was inspected.
Consequently, with prior art, there are problems such as
(1) an actual laser system is required to confirm the performance of a narrowband module;
(2) it takes time to inspect and adjust a narrowband module; and
(3) when the desired performance is not exhibited in the laser output light, it is impossible to specify whether the cause thereof is a malfunction in the narrowband module, a malfunction in another component element, such as the laser chamber, monitor module, or the like, or a discrepancy in the optical axis adjustment of the resonator.
Further, a technology for inspecting the optical characteristics of a diffraction grating used in an optical disc device and the like is disclosed in Japanese Patent Laid-open No. 2-129844. That is, with this prior art, a single-wavelength collimated beam is incident on a diffraction grating, the positional shift between the light-intercepting position of the first-order light from the diffraction grating and a reference light-intercepting position is measured, and the pitch positional shift of the diffraction grating is inspected on the basis of this measured light-intercepting positional shift. Further, with this prior art, a single-wavelength collimated beam is incident on a diffraction grating, the quantity of light of the first-order light from the diffraction grating, and the quantity of light of a zero-order light are measured, and the groove depth of the diffraction grating is inspected based on a comparison of these light quantities.
As for this prior art, although an inspection related to the physical shape of a diffraction grating in an optical disc device can certainly be performed for a diffraction grating unit, this prior art only detects the physical shape of a diffraction grating utilized in an optical disc device and the like, but does not directly detect the bandwidth-narrowing performance of a diffraction grating.
That is, in the field of lasers, such as an excimer laser, there is a need for an inspection device capable of directly inspecting and adjusting, as a narrowband module unit, a variety of narrowband performance, such as the intensity distribution, spectral line width, center wavelength, narrowband efficiency, and wave front shape of the band-narrowed light beam generated from a narrowband module.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide a narrowband module inspection device, which is capable of inspecting the narrowband performance of a narrowband module as a narrowband module unit.
The invention corresponding to a first embodiment is a narrowband module inspection device for inspecting a narrowband performance of a narrowband module, comprising: light source means for generating a light, which radiates in a wavelength region of a narrowband laser beam; a slit on which the light from the light source means is incident; a collimating converter for converting the light via the slit to a collimated beam, and making the converted light incident on the narrowband module; condensing means for condensing outputted light from the narrowband module; a light detector on which light condensed by the condensing means is incident; a total reflection mirror provided in a removable manner on an optical path between the collimating converter and the narrowband module; and inspecting means for determining a ratio between the output of the light detector in a state wherein the total reflection mirror is provided on the optical path, and the output of the light detector in a state wherein the total reflection mirror is removed from the optical path, and for inspecting a narrowband efficiency of the narrowband module based on the determined ratio.
With such an invention, light emitted in a wavelength region oscillated by a narrowband laser, after passing through a slit and being converting to a collimated beam, is incident on a narrowband module, and the outputted light from the narrowband module is condensed, and incident on a light detector. A total reflection lens is provided in a removable manner on the optical path between the collimating converter and the narrowband module, and based on the output of the light detector, the light intensity Ib in a state, wherein the total reflection mirror is provided, and the light intensity in a state, wherein the total reflection mirror is removed, that is, the light intensity In of light, the bandwidth of which has been narrowed by the narrowband module, is determined, and the narrowband efficiency of the narrowband module is inspected by using the ratio In/Ib thereof as an index. This narrowband efficiency greatly affects laser output.
In this manner, in accordance with the present invention, it becomes possible to inspect narrowband efficiency, which affects laser output, and which is extremely important from the standpoint of the performance of the narrowband module, in accordance with an extremely simple constitution, wherein a total reflection mirror is provided in a removable manner on the optical axis. Further, since it is possible to evaluate the narrowband efficiency of a narrowband module unit without using an actual laser, inspection costs and inspection time can be greatly reduced, and narrowband modules can be manufactured and shipped in volume.
In the invention of a second embodiment, the inspection means of claim
1
inspects wavelength selection characteristics of the narrowband module based on the output of the light detector in the state wherein the total reflection mirror is removed from the optical path.
Therefore, in accordance with the present invention, it becomes possible to evaluate the wavelength selection characteristics (selection center wavelength, spectral line width, and so forth) of a narrowband module without using an actual laser, inspection costs and inspection time can be greatly reduced, and narrowband modules can be manufactured and shipped in volume.
The invention corresponding to a third embodiment is a narrowband
Nakaike Takanori
Wakabayashi Osamu
Evans F. L.
Komatsu Ltd.
Nguyen Sang H.
Varndell & Varndell PLLC
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