JPH0346526A - Wavelength detecting device - Google Patents

Abstract

PURPOSE:To execute the wavelength detection with high accuracy by controlling the position of interference fringes of a reference light so as to be always in a prescribed state. CONSTITUTION:A monitor etalon 32 is irradiated with a reference light 21 generated from a reference light source 20 and light 11 to be detected, and the light which transmits therethrough forms a first and a second interference fringes 33a, 33b corresponding to each wavelength on the detection surface of a photodetector 33. By detecting them by the detector 33, wavelength of the light 11 to be detected is detected. In this case, a signal for showing the detected interference fringes 33a, 33b is inputted to a CPU 40. Subsequently, information of the interference fringe 33a is extracted therefrom and based thereon, by driving a regulator 50 so that the interference fringe 33a become a prescribed position, pressure in an air gap of the etalon 32 is controlled, and by driving a heater or a cooler 60, an ambient temperature of the etalon 32 is controlled. By such a control, the interference fringe 33b shows absolute wavelength of the light 11 to be detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a wavelength detection device for detecting the wavelength of a laser or the like, and particularly to wavelength detection when an excimer laser is used as a light source in a reduction projection exposure device for manufacturing semiconductor devices. The present invention relates to a wavelength detection device suitable for use in.

[Conventional technology]

BACKGROUND ART The use of excimer lasers as light sources for reduction projection exposure apparatuses (hereinafter referred to as steppers) for manufacturing semiconductor devices is attracting attention. This is due to the short wavelength of excimer laser (K r F
Since the wavelength of the laser is approximately 248.4 nm), it is possible to extend the limit of light exposure to 0.5 μm or less, and with the same resolution, the sunspot depth is lower than that of the conventionally used g-line and i-line of mercury lamps. This is because many excellent advantages can be expected, such as being deep, requiring a small numerical aperture (NA) of the lens, increasing the exposure area, and obtaining high power.

By the way, the wavelength of excimer laser is as short as 248.4 nm, so the material that transmits this wavelength is quartz, CaF2 and MaF2':'; Only quartz can be used as a material. For this reason, it is extremely difficult to design a reduction projection lens with chromatic aberration correction. Therefore, when using an excimer laser as a light source for a stepper, it is necessary to narrow the band of the excimer laser's output laser light to the extent that this chromatic aberration can be ignored. It is necessary to perform stabilization control.

Conventionally, a monitor etalon has been used to measure the wavelength line width or detect the wavelength of output light from a narrowband oscillation excimer laser or the like. The monitor etalon is constructed using an air gap etalon in which partially reflecting mirrors are disposed opposite to each other with a predetermined gap, and the transmission wavelength of this air gap etalon is expressed as follows.

mλ−2nd cos θ where m is an integer, d is the distance between the partially reflecting mirrors of the etalon, n is the refractive index between the partially reflecting mirrors, and θ is the angle between the normal to the etalon and the optical axis of the incident light.

From this equation, it can be seen that if n, d, and m are constant, θ changes as the wavelength changes. The monitor etalon uses this property to detect the wavelength of the detected light. By the way, in the above-mentioned monitor etalon, if the pressure in the air gap and the ambient temperature change, the above-mentioned angle θ will change even if the wavelength is constant. Therefore, when a monitor etalon is used, wavelength detection is performed by controlling the pressure within the air gap and the ambient temperature to be constant.

However, it is difficult to control the pressure and ambient temperature of the air gap saw with high precision, and therefore it has not been possible to detect the absolute wavelength with sufficiently high precision.

Therefore, a device has been proposed that detects the absolute wavelength of the detected light by inputting a reference light whose wavelength is known in advance together with the detected light into a monitor etalon and detecting the relative wavelength of the detected light with respect to this reference light. There is.

[Problem to be solved by the invention]

By the way, when the pressure in the air gap of the monitor etalon or the ambient temperature changes, the position of the interference fringes of the reference light (the diameter of the interference fringes) changes accordingly. Here, as the diameter of the interference fringes becomes smaller, the overlap between adjacent fringes increases,
The detection accuracy of the peak position decreases. Therefore, it is preferable that the interference fringes of the reference light be maintained at a predetermined large diameter with high detection accuracy. However, in conventional devices, the position of the interference fringes of the reference light changes due to changes in the pressure in the air gap of the monitor etalon or the ambient temperature, and the position of the interference fringes of the detected light also changes accordingly). It was not possible to always maintain high detection accuracy.

Therefore, it is an object of the present invention to provide a wavelength detection device that can always perform stable and highly accurate wavelength detection while using base light.

[Means to solve the problem]

In order to achieve the above object, the present invention maintains the position of the interference fringes (diameter of the interference fringes) by the reference light at a predetermined state that always provides sufficient detection accuracy, thereby always achieving stable and highly accurate wavelength detection accuracy. I'm trying to get that.

That is, according to the present invention, h (the first interference fringes corresponding to the reference light that are formed by the light that irradiates the etalon with the reference light and the detected light generated from the quasi-light source and are transmitted through the etalon); and a wavelength detection device that detects the wavelength of the detected light by detecting a second interference fringe corresponding to the detected light with a light detection means, detecting a second interference fringe corresponding to the reference light, The apparatus includes a control means for controlling the characteristics of the etalon so that the first interference fringes have a predetermined shape.

[For production]

The position of the interference fringes of the reference light (the diameter of the interference fringes) is controlled so as to always be constant, thereby making it possible to always maintain high wavelength detection accuracy.

〔Example〕

Hereinafter, embodiments of the wavelength detection device according to the present invention will be described.
(See 11 (-1) for detailed explanation.

FIG. 1 shows an embodiment of a wavelength detection device according to the present invention. In this embodiment, the output light 11 of the narrow band oscillation excimer laser 10 is used as the light to be detected.

Further, as the reference light source 20, for example, the wavelength is 632.8n.
He-Ne laser with a wavelength of 496° or Ar with a wavelength of 496°5 nm
A laser or the like can be used.

Narrow: (A part of the laser light 11 output from the beam oscillation excimer laser 10 is sampled by the beam splitter 12, and this sampling light is irradiated onto the beam splitter 13.

Further, the reference light 21 output from the reference light source 20 is irradiated onto the other surface of the beam splitter 13.

The beam splitter 13 transmits a portion of the sampling light sampled by the beam splitter 12 and reflects a portion of the reference light 21 output from the reference light source 20, thereby separating the sampling light and the reference light. Bottom out. The acid-containing light of the sampling light and the static CI light combined by the beam splitter 13 is input to a monitor etalon wavelength detector III (so-called 30), and is irradiated onto the monitor etalon 32 via a condenser lens 311.

The monitor etalon 32 is composed of two transparent plates 32a and 32b whose inner surfaces are partially reflecting mirrors, and each has a different transmission wavelength depending on the angle of the incident light to the monitor etalon 32.

The light transmitted through this monitor etalon 32 is transmitted to the optical position detector 3.
A first interference fringe 33a corresponding to the wavelength of the reference light and a second interference fringe 33b corresponding to the wavelength of the detected light are formed on the detection surface of the photodetector 33.

The photodetector 33 has these first and second interference fringes 33a,
33b is detected.

Note that the photodetector 64 may be a one-dimensional or two-dimensional image sensor, a diode array, or a PSD (1).
O3ITION 5ENSIT! VEDETPJCTO
R), etc. can be configured.

The first -1; interference fringe 33a and the second 1゜ interference fringe 33b detected by the photodetector 33 are not shown;
CPU) 40 is manually powered.

The CPU 40 selects the first signal corresponding to the reference light from the input signal.
Based on this information, the pressure in the air gap of the monitor etalon is controlled by driving the regulator 50 so that the first interference fringe 33a is at a predetermined position (predetermined diameter). , and also controls the ambient temperature of the monitor etalon 32 by driving the heating or cooling device 60 .

With such control, the second interference fringe 33b corresponding to the light to be detected detected by the photodetector 33 represents the absolute wavelength of the light to be detected.

Therefore, the CPU 40 can extract information regarding the second interference fringe 33b corresponding to the detected light from the input signal, and detect the absolute wavelength of the detected light based on this extracted information.

In FIG. 2, the detected light sampled by the beam splitter 12 is introduced using an optical fiber 6, and a mercury lamp (wavelength 253, 7 nm) is used as a reference light source.
This figure shows another embodiment of the present invention using the following.

In this embodiment, the detected light sampled by the beam splitter 12 is input into the optical fiber 16 through the lens 4 and the sleeve 15, and the detected light transmitted through the optical fiber 16 is outputted through the sleeve 17. The output light from the sleeve 17 illuminates the beam splitter 13, and the transmitted light from the beam splitter 13 illuminates the front focal plane 19 of the collimator lens 31 of the monitor etalon wavelength detector 30.

Further, the reference light 23 generated from the reference light source 22 passes through the imaging lens 25, is reflected by the beam splitter 13, and forms an image 26 of the reference light source in front of the front sunspot peak j19 of the collimator lens 31.

According to such a configuration, the reference light source 22 is the image 2 of the reference light source.
6, and the front focal plane of the collimator lens 31 is between the detected light output from the sleeve 17 and the image 26 of this reference light source 22! I! , will be illuminated by wall light.

This illumination light is applied to the collimator lens 31 through the aperture 18, is collimated by the collimator lens 31, and passes through the monitor etalon 32 and the imaging lens 34 onto the detection surface of the photodetector 33 to form the reference light and the detected light. Two interference fringes are formed corresponding to the respective wavelengths.

The CPU 40 drives the regulator 50 based on the first interference fringe corresponding to the reference light among these two interference fringes, controls the pressure of nitrogen N2 in the monitor etalon wavelength detector 30, and controls the pressure of nitrogen N2 in the monitor etalon wavelength detector 30, (diameter of interference fringes) is maintained constant.

Further, the CPU 40 detects the absolute wavelength of the detected light based on the second interference fringe corresponding to the detected light among these two interference fringes.

In FIG. 2, reference numeral 36 indicates an O-ring for maintaining confidentiality within the monitor etalon wavelength detector 30, and reference numeral 35 indicates a bolt for fixing the collimator lens 31 and the imaging lens 34.

In this embodiment, the pressure vessel is formed by the collimator lens 31 and the first imaging lens 36, but a window may be used instead of the collimator lens 31 and the imaging lens 34 to form the pressure vessel. Good too. However, in this case, the collimator lens 31 and the imaging lens 34
must be placed before and after the monitor etalon 32.

FIG. 3 shows still another embodiment using a merging type fiber in which the reference light 21 from the reference light source 20 is also introduced using the optical fiber 28. In this embodiment, the reference light 21 from the reference light source 20 is transmitted to the sleeve 27.
The reference light introduced into the optical fiber 28 through the optical fiber 28 and transmitted through the optical fiber 28 is transmitted through the optical multiplexer 71,
The combined light passes through the optical fiber 72 and is output through the sleeve 73, and illuminates the monitor etalon 32 through the window 37 of the monitor etalon wavelength detector 30. do.

The light transmitted through the monitor etalon 32 forms two interference fringes on the photodetector 33 through the window 38, corresponding to the respective wavelengths of the M Nil light and the detected light. The following operations are similar to those shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects can be obtained.

(1) Detecting a first interference fringe corresponding to the reference light source light, and controlling the temperature of the monitor etalon or the pressure in the air gap so that the first interference fringe has a predetermined shape (predetermined diameter). With this configuration, the absolute wavelength of the detected light can be detected based only on the second interference fringe corresponding to the detected light.

(2) Furthermore, since the first interference fringes are kept constant in a predetermined shape (predetermined diameter), wavelength selection can always be performed with high precision.

(3) By mounting the wavelength detection device of the present invention on a narrow band oscillation excimer laser, the wavelength can be stabilized with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of this invention, FIG. 2 is a diagram showing another embodiment of this invention, and FIG. 3 is a diagram showing still another embodiment of the three inventions. 10...Narrowband oscillation excimer laser, 11...Detected light, 12.13...Beam splitter, 14...
Lens, 15.17, 27.73...Sleeve, 16
゜28.72...Optical fiber, 18...Aperture, one...Collimator lens front focus, 20.22.
... Prefectural quasi-light source, 21.23... Reference light, 24... Filter, 25... Lens, 26... Image of reference light source,
30... Monitor etalon wavelength detector, 31... Collimator lens, 32... Monitor etalon, 34...
Imaging lens, 33... Photodetector, 37.38... Window, 40... CPU, 50... Regulator, 60... Heating or cooling device. 4 0 11

Claims (3)

[Claims] (1) A reference light and a detected light generated from a reference light source are irradiated onto an etalon, and the first interference fringes corresponding to the reference light and the detected light are respectively formed by the light transmitted through the etalon. A wavelength detection device detects the wavelength of the detected light by detecting a second interference fringe with a light detection means, which detects a first interference fringe corresponding to the reference light, and detects a first interference fringe corresponding to the reference light. 1. A wavelength detection device comprising control means for controlling characteristics of the etalon so that the etalon has a predetermined shape. (2) The wavelength detection device according to claim 1, wherein the control means controls the ambient temperature of the etalon. (3) The wavelength detection device according to claim 1, wherein the control means controls the pressure within the air gap of the etalon.