JPH0513858A - Wavelength control equipment - Google Patents

Abstract

PURPOSE:To stabilize glass surface temperature by detecting the glass surface temperature of a low pressure mercury lamp, and making said temperature coincide with a set temperature. CONSTITUTION:One end of an optical fiber 24 is arranged on the surface of a glass tube 20 of a mercury lamp 7, a radiation thermometer 25 is arranged on the other end, and the temperature of the glass tube surface is detected. A tube 30 is arranged around the glass tube 20 to constitute a double tube structure, and cooling medium is circulated in the inside of the tube 30. The cooling medium is stored in a cooling medium vessel 31, the tube 30 and the cooling medium vessel 31 are connected by using a tube 32, and the cooling medium is circulated by a pump 33. A temperature sensor 34 and a heating cooling apparatus 35 are installed in the cooling medium vessel 31, and a temperature controller 36 performs the temperature control of the heating cooling apparatus 35 by using the detection value of the temperature sensor 34 as a feedback signal, so that the cooling medium is kept at a set temperature. Thereby the temperature of the glass tube surface of the mercury lamp 7 can be kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a low-pressure mercury lamp as a reference light source and makes reference light and laser oscillation light generated from the reference light source incident on a wavelength detector and detects the output based on the detection output of the wavelength detector. The present invention relates to a wavelength control device that detects the absolute wavelength of a squeezed light and controls the wavelength of the oscillated light according to the detected absolute wavelength, and more particularly to a technique that considers the temperature fluctuation of the low-pressure mercury lamp.

[0002]

2. Description of the Related Art The use of an excimer laser as a light source of a reduction projection exposure apparatus (stepper) for manufacturing a semiconductor device has attracted attention. This is because the wavelength of the excimer laser is short, so there is a possibility that it can be extended to the light exposure limit of 0.5 μm or less, and if the resolution is the same, the depth of focus is deeper than the g-line and i-line of the mercury lamp that was conventionally used. , That the numerical aperture (NA) of the lens is small and the exposure area can be enlarged.
This is because many excellent advantages such as large power can be expected.

By the way, when an excimer laser is used as a light source for a stepper, it is necessary to narrow the output laser light of the excimer laser, and the wavelength of the narrowed output laser light is controlled with high precision. There is a need to.

Conventionally, a spectroscope using a monitor etalon or a diffracted photon has been used to measure the wavelength line width of the output light of a narrow band oscillation excimer laser and detect the wavelength. The monitor etalon is constructed by using an air gap etalon in which partial reflection mirrors are opposed to each other with a predetermined gap therebetween, 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 refractive index between the partial reflection mirrors of the etalon, and θ is the angle between the normal line of the etalon and the optical axis of the incident light.

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

However, it is difficult to control the pressure in the air gap and the ambient temperature with high precision, and therefore the absolute wavelength cannot be detected with sufficient precision.

Therefore, reference light whose wavelength is known in advance (for example, an argon laser light, an oscillation line of an iron or mercury lamp) is incident on the monitor etalon together with the detected light, and the relative wavelength of the detected light with respect to the reference light is detected. A device for detecting the absolute wavelength of the light to be detected by doing so has been proposed.

In such an apparatus, the transmitted light of the monitor etalon is directly incident on the detection surface of a photodetector such as a CCD image sensor to form interference fringes on the detection surface of the photodetector, and The absolute wavelength is detected based on the detection position.

[0010]

However, when a mercury lamp is particularly used as the reference light of the monitor etalon of the KrF narrow band excimer laser, as shown in FIGS. 5 (a) to 5 (c), several tens of lamps are used. There is a problem that the oscillation lines overlap and the spectrum waveform changes depending on the temperature of the mercury lamp, so that the detected light cannot be detected with high accuracy. Figure 5 shows that the spectrum waveform changes with the glass surface temperature T of the mercury lamp.
It appears prominently when using the 3.7 nm line.

That is, as shown in FIG. 5, the shape of the interference fringes generated by the 253.7 nm line of the low-pressure mercury lamp greatly changes depending on the temperature of the glass surface of the mercury lamp, and the shape of the interference fringes of the glass surface changes. The inventors have found that the temperature is uniquely responded to.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a wavelength control device capable of stabilizing the spectral waveform of the reference light and detecting the absolute wavelength of the output laser light with high accuracy. To aim.

[0013]

According to the present invention, a low-pressure mercury lamp is used as a reference light source, and reference light and laser oscillation light generated from this reference light source are made incident on a wavelength detector, and the detection output of this wavelength detector. In the wavelength control device for detecting the absolute wavelength of the oscillated light based on the above, and controlling the wavelength of the oscillated light according to the detected absolute wavelength, the temperature detection means for detecting the temperature of the glass tube surface of the low-pressure mercury lamp, and A heating / cooling means for heating or cooling the low-pressure mercury lamp, and a temperature control means for controlling the heating / cooling means based on the output of the temperature detecting means to maintain the temperature of the mercury lamp at a predetermined temperature. To do.

[0014]

According to the structure of the present invention, the glass surface of the low-pressure mercury lamp is measured by measuring the temperature of the glass surface of the low-pressure mercury lamp and controlling the temperature of the heating / cooling means so that the measured value matches the set temperature. The surface temperature is stabilized, whereby the spectrum waveform is stabilized, and the absolute wavelength of the output laser light can be detected with high accuracy.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. A KrF narrow band excimer laser 100 is composed of a laser chamber 1 and a band narrowing unit 2. The band narrowing unit 2 includes a wavelength selection element such as an etalon.

The KrF excimer laser light output from the laser chamber 1 is narrowed by the narrowing unit 2 and then emitted through the front mirror 3 and the beam splitter 4. A part of the output laser light is monitored by the beam splitter 4 and input to the wavelength detector 6 via the beam splitter 5.

On the other hand, a low-pressure mercury lamp 7 as a reference light source.
Only the light having the wavelength of 253.7 is selected as the reference light generated by the bandpass filter 8, and the selected light is input to the wavelength detector 6 through the beam splitter 5.

The wavelength controller 8 detects the absolute wavelength of the detected light by detecting the relative wavelength of the detected light with respect to the reference light whose wavelength is known in advance based on the output of the wavelength detector 6, and the detected absolute wavelength. And the selected wavelength of the wavelength selection element such as an etalon arranged in the band narrowing unit 2 is controlled via the driver 9 so as to eliminate the difference between the selected wavelength and the set wavelength.

By the way, in this embodiment, the temperature sensor 10 for detecting the temperature of the glass surface of the mercury lamp 7.
A heating and cooling device 11 for heating or cooling the temperature of the surface of the glass tube of the mercury lamp, and a temperature for driving and controlling the heating and cooling device 11 based on the output of the temperature sensor 10 to control the temperature of the surface of the glass tube of the mercury lamp to a constant temperature. The controller 12 is provided.

FIG. 2 shows a concrete example of the wavelength detector 6. The sampling light of the output laser light is ground glass 13
The light is scattered by a and is input to the wavelength detector 6 including the monitor etalon 13, the condenser lens 14, and the optical position detector 15 via the beam splitter 5.

On the other hand, as the reference light generated from the low-pressure mercury lamp 7, only the light of wavelength 253.7 is selected through the bandpass filter 8, and the selected light is input into the monitor etalon 13 through the beam splitter 5. It

The monitor etalon 13 is composed of two transparent plates 13a and 13b whose inner surface is a partially reflecting mirror, and has different transmission wavelengths depending on the angle of incident light with respect to the etalon 13.

The light transmitted through the etalon 13 is a condenser lens 1.
It is incident on 4. The condenser lens 14 is, for example, an achromatic lens that has been subjected to chromatic aberration correction. By passing through the achromatic condenser lens 14, chromatic aberration is corrected. Such an achromatic lens is used because the wavelength of the KrF excimer laser (248.39 nm) and the wavelength of the reference light (25
(3.7 nm) is slightly different. A concave mirror may be used as the condenser lens.

The optical position detector 15 is, for example, a one-dimensional or two-dimensional image sensor disposed on the focal point of the condenser lens 14, and the light passing through the condenser lens 14 is the optical position detector 1.
5, the first interference fringes 15a corresponding to the wavelength of the reference light and the second interference fringes 15b corresponding to the wavelength of the detected light are formed on the detection surface of the optical position detector 15.

From the optical position detector 15, the above first and second
Signals corresponding to the positions of the interference fringes 15a and 15b are input to the wavelength controller 8.

The wavelength controller 8 detects the absolute wavelength of the detected light (output laser light) from the position signals of these interference fringes, calculates the difference between the detected absolute wavelength and the set wavelength (target value), and calculates the calculated value. The angle of the wavelength selection element (eg, etalon or grating) in the band-narrowing unit (not shown) is changed in accordance with the above. As a result, the wavelength of the excimer laser light transmitted through the wavelength selection element is shifted,
In the embodiment of FIG. 2 in which the wavelength (target value) is fixed, a temperature sensor 10 is provided on the glass surface of the mercury lamp 7 and a fan is provided as a means for stabilizing the surface temperature of the glass tube of the mercury lamp 7. 16 is provided to cool the mercury lamp 7. In this case, the temperature controller 12 uses the detection value of the temperature sensor 10 as a feedback signal to control the number of revolutions of the fan 16 or to control the on / off of the fan to keep the surface temperature of the glass tube of the mercury lamp 7 at the set temperature. There is.

3A to 3C show a specific example of the temperature sensor 10 for detecting the surface temperature of the glass tube of the mercury lamp 7. In the first place, the mercury lamp 7 radiates extremely strong ultraviolet rays, and therefore an organic adhesive cannot be used.

Therefore, in the example of FIG. 3A, the glass tube 20 of the mercury lamp 7 is sandwiched by the metal 21, and the temperature of the metal 21 is detected by the temperature sensor 22. Examples of the metal 21 include copper and aluminum having high thermal conductivity. A notch 23 is provided above the metal 21 to prevent damage to the glass tube 20 due to the difference in thermal expansion coefficient between the glass tube 20 and the metal 21.

In FIG. 3B, the temperature sensor 22 is enclosed inside the glass tube 20 of the mercury lamp 7.

In FIG. 3C, the end of the optical fiber 24 is arranged on the surface of the glass tube 20 of the mercury lamp 7, and the radiation thermometer 25 is arranged on the other end to detect the temperature of the surface of the glass tube. I am trying. Of course, in this case, the radiation thermometer 25 may be directly provided on the surface of the glass tube without providing the optical fiber 24.

FIG. 4 shows a concrete example of a heating / cooling device for heating and cooling the glass tube of the mercury lamp 7. A tube 30 is arranged around the glass tube 20 to form a double tube structure. A cooling medium is circulated inside 30. The cooling medium is stored in the cooling medium tank 31, the pipe 30 and the cooling medium tank 31 are connected by a pipe 32, and the cooling medium is circulated by a pump 33. A temperature sensor 34 and a heating / cooling device 35 are provided in the cooling medium tank 31, and a temperature controller 36 is provided.
Controls the temperature of the heating / cooling device 35 by using the detection value of the temperature sensor 34 as a feedback signal to keep the cooling medium at the set temperature, thereby keeping the temperature of the surface of the glass tube of the mercury lamp 7 constant. . Although the temperature of the cooling medium is detected in this case, the temperature of the surface of the glass tube may be directly detected.

[0033]

As described above, according to the present invention,
The temperature of the low-pressure mercury lamp as the reference light source for wavelength detection is detected, and the temperature of the glass tube surface is controlled to be constant based on the detection result, so the temperature of the glass tube surface of the mercury lamp is stabilized with high accuracy. Therefore, the spectrum waveform of the reference light is extremely stabilized, and the wavelength of the reference light can be detected with high accuracy. Therefore, the absolute wavelength of the output laser light can be detected with high accuracy, and the wavelength of the output laser light can be controlled with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the invention.

FIG. 2 is a diagram showing another embodiment of the invention.

FIG. 3 is a diagram showing a specific example of a temperature sensor.

FIG. 4 is a diagram showing a specific example of a heating / cooling device.

FIG. 5 is an explanatory diagram of a defect phenomenon of the conventional technique.

[Explanation of symbols]

1 ... Laser chamber 2 ... Band narrowing unit 3 ... Front mirror 4 ... Beam splitter 5 ... Beam splitter 6 ... Wavelength detector 7 ... Low pressure mercury lamp 8 ... Wavelength controller 9 ... driver 10 ... Temperature sensor 11 ... Heating / cooling unit 12 ... Temperature controller 13 ... Monitor etalon 14 ... Condensing lens 15 ... Optical position detector 16 ... fan 20 ... Glass tube 21 ... Metal 100 ... KrF narrow band excimer laser

Claims (6)

[Claims] 1. A low-pressure mercury lamp is used as a reference light source, and reference light and laser oscillation light generated from this reference light source are made incident on a wavelength detector, and the absolute value of the oscillation light is detected based on the detection output of this wavelength detector. In the wavelength control device for detecting the wavelength and controlling the wavelength of the oscillated light according to the detected absolute wavelength, the temperature detection means for detecting the temperature of the glass tube surface of the low-pressure mercury lamp, the glass tube surface of the low-pressure mercury lamp Wavelength control comprising heating / cooling means for heating or cooling, and temperature control means for controlling the heating / cooling means based on the output of the temperature detecting means to maintain the temperature of the glass surface of the mercury lamp at a predetermined temperature. apparatus. 2. The wavelength control device according to claim 1, wherein the temperature detecting means includes a metal body sandwiching a glass tube surface of the low-pressure mercury lamp, and a temperature sensor detecting a temperature of the metal body. 3. The wavelength control device according to claim 1, wherein the temperature detecting means is a temperature sensor enclosed in a glass tube of the low-pressure mercury lamp. 4. The wavelength control device according to claim 1, wherein the temperature detecting means is a radiation thermometer. 5. The wavelength according to claim 1, wherein the heating / cooling means is a fan, and the temperature control means maintains the temperature of the mercury lamp at a predetermined temperature by controlling the rotation speed or on / off of the fan. Control device. 6. The heating / cooling means, a cooling medium tank for storing a predetermined cooling medium, a double tube arranged around the glass tube of the low-pressure mercury lamp and through which the cooling medium flows, and the cooling medium. It has a pump that circulates the cooling medium between the tank and the double pipe, and a heating cooler that heats and cools the cooling medium in the cooling medium tank, and the temperature control means controls the temperature of the heating cooler. The temperature of the mercury lamp is maintained at a predetermined temperature by carrying out
The wavelength control device described.