JP2821956B2 - Wavelength controller and low-pressure mercury lamp for wavelength controller - Google Patents

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. The reference light and laser oscillation light generated from the reference light source are incident on a wavelength detector, and are detected based on the detection output of the wavelength detector. The present invention relates to a wavelength control device that detects the absolute wavelength of oscillating light and controls the wavelength of oscillating light according to the detected absolute wavelength, and more particularly to a technique that considers temperature fluctuations of the low-pressure mercury lamp.

[0002]

2. Description of the Related Art Attention has been paid to the use of excimer lasers as light sources for reduction projection exposure apparatuses (steppers) for manufacturing semiconductor devices. This is because the wavelength of the excimer laser is short, so that the light exposure limit may be extended to 0.5 μm or less, and the depth of focus is deeper than the conventional mercury lamp g-line and i-line at the same resolution. 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 a large power can be expected.

When an excimer laser is used as a light source for a stepper, it is necessary to narrow the bandwidth of the output laser light of the excimer laser. 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 output light of a narrow-band oscillation excimer laser or to detect the wavelength. The monitor etalon is configured using an air gap etalon in which partial reflection mirrors are arranged opposite to each other with a predetermined gap therebetween. 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 etalon partial reflection mirrors, and θ is the angle between the normal of the etalon and the optical axis of the incident light.

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

However, it is difficult to control the pressure and the ambient temperature in the air gap with high accuracy, and therefore, it has not been possible to detect the absolute wavelength with sufficient accuracy.

Therefore, reference light (for example, argon laser light, an oscillation line of an iron or mercury lamp) having a known wavelength is incident on the monitor etalon together with the light to be detected, and the relative wavelength of the light to be detected with respect to this reference light is detected. There has been proposed an apparatus for detecting the absolute wavelength of the light to be detected.

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. The absolute wavelength is detected based on the detection position.

[0010]

However, when a mercury lamp is used as the reference light of the monitor etalon of the KrF narrow band excimer laser, as shown in FIGS. 5A to 5C, several tens of lines 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 light to be detected cannot be detected with high accuracy. FIG. 5 shows that the spectrum waveform changes depending on the glass surface temperature T of the mercury lamp.
When a 3.7 nm line is used, it appears remarkably.

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 changes greatly depending on the temperature of the glass surface of the mercury lamp. The present inventors have found that the temperature corresponds uniquely.

The present invention has been made in view of such circumstances, and provides a wavelength control device that can stabilize the spectral waveform of reference light and can detect the absolute wavelength of output laser light with high accuracy. 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 the reference light source are incident on a wavelength detector, and the detection output of the wavelength detector is detected. A wavelength control device that detects the absolute wavelength of the oscillating light based on and detects the temperature of the surface of the glass tube of the low-pressure mercury lamp; A heating / cooling unit for heating or cooling the low-pressure mercury lamp; and a temperature control unit for controlling the heating / cooling unit based on an output of the temperature detection unit to maintain the temperature of the mercury lamp at a predetermined temperature. I 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 and cooling means so that the measured value matches the set temperature. The temperature of the surface 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 be described below 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 includes a laser chamber 1 and a band-narrowing unit 2. The narrowing unit 2 includes a wavelength selecting 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
From the generated reference light, only light having a wavelength of 253.7 is selected via the band pass filter 8, and the selected light is input to the wavelength detector 6 via 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 detects the absolute wavelength of the detected light. The selected wavelength of a wavelength selecting element such as an etalon or a grating disposed in the band narrowing unit 2 is shifted through the driver 9 so that the difference between the wavelength and the set wavelength is eliminated.

In this embodiment, a temperature sensor 10 for detecting the temperature of the glass surface of the mercury lamp 7 is used.
A heating / cooling device 11 for heating or cooling the temperature of the surface of the glass tube of the mercury lamp; and a temperature for controlling the temperature of the surface of the glass tube of the mercury lamp by controlling the driving of the heating / cooling device 11 based on the output of the temperature sensor 10. A controller 12 is provided.

FIG. 2 shows a specific example of the wavelength detector 6, in which the sampling light of the output laser light is applied to a ground glass 50.
Are input to a wavelength detector 6 including a monitor etalon 13, a condenser lens 14, and an optical position detector 15 via a beam splitter 5.

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

The monitor etalon 13 is composed of two transparent plates 13a and 13b whose inner surfaces are partially reflecting mirrors, and has different transmission wavelengths corresponding to angles of incident light with respect to the etalon 13.

The light transmitted through the etalon 13 is collected by the condenser lens 1.
4 is incident. The condensing lens 14 is, for example, an achromatic lens that has been subjected to chromatic aberration correction, and the chromatic aberration is corrected by passing through the achromatic condensing lens 14. Such achromatic lenses are used because the wavelength of the KrF excimer laser (248.39 nm) and the wavelength of the reference light (25.39 nm).
3.7 nm). Note that a concave mirror may be used as the condenser lens.

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

From the optical position detector 15, the first and second
The 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 light to be detected (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 or the like of a wavelength selection element (for example, an etalon or a grating) in a band-narrowing unit (not shown) is changed according to. As a result, the wavelength of the excimer laser light transmitted through the wavelength selection element is shifted,
In the embodiment of FIG. 2 which is fixed at a set wavelength (target value), a temperature sensor 10 is provided on the glass surface of the mercury lamp 7 and a fan is used as a means for stabilizing the glass tube surface temperature of the mercury lamp 7. 16 is provided to cool the mercury lamp 7. In this case, the temperature controller 12 controls the rotation speed or the on / off of the fan 16 using the detection value of the temperature sensor 10 as a feedback signal so as to maintain the surface temperature of the glass tube of the mercury lamp 7 at the set temperature. I have.

FIGS. 3A to 3C show specific examples of the temperature sensor 10 for detecting the surface temperature of the glass tube of the mercury lamp 7. FIG. In the first place, the mercury lamp 7 emits very strong ultraviolet rays, so that an organic adhesive cannot be used.

Therefore, in the example of FIG. 3A, the glass tube 20 of the mercury lamp 7 is sandwiched between the metals 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. The notch 23 is provided above the metal 21 to prevent the glass tube 20 from being damaged due to a difference in the coefficient of thermal expansion between the glass tube 20 and the metal 21.

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

In FIG. 3C, one end of an optical fiber 24 is arranged to measure the temperature of the surface of the glass tube 20 of the mercury lamp 7, and a radiation thermometer 25 is arranged at the other end. The temperature of the surface is detected. Of course, in this case, the temperature of the glass tube surface may be directly measured by the radiation thermometer 25 without passing through the optical fiber 24.

FIG. 4 shows a specific example of a heating / cooling device for heating and cooling the glass tube of the mercury lamp 7. A tube 30 is provided around the glass tube 20 to form a double tube structure. The cooling medium is circulated inside 30. The cooling medium is stored in a cooling medium tank 31, the pipe 30 connects the pipe 30 and the cooling medium tank 31 with a pipe 32, and the pump 33 circulates the cooling medium. In the cooling medium tank 31, a temperature sensor 34 and a heating / cooling device 35 are provided.
By controlling the temperature of the heating / cooling device 35 using the detection value of the temperature sensor 34 as a feedback signal to maintain the cooling medium at the set temperature, the temperature of the surface of the glass tube of the mercury lamp 7 is kept constant. . In this case, the temperature of the cooling medium is detected, but 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 a reference light source for wavelength detection is detected, and the temperature of the glass tube surface is controlled at a constant temperature based on the detection result. Therefore, the spectral waveform of the reference light is greatly 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 control of the output laser light can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present 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 related art.

[Explanation of symbols]

 DESCRIPTION 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 Condenser lens 15 Optical position detector 16 Fan 20 Glass tube 21 Metal 100 KrF narrow band excimer laser

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/106 H01S 3/00

Claims (8)

(57) [Claims] A low-pressure mercury lamp is used as a reference light source, and reference light and laser oscillation light generated from the reference light source are incident on a wavelength detector, and the absolute value of the oscillation light is determined based on the detection output of the wavelength detector. In a wavelength control device that detects a wavelength and controls the wavelength of oscillation light according to the detected absolute wavelength, a temperature detection unit that detects a temperature of a glass tube of the low-pressure mercury lamp, and heats or heats the glass tube of the low-pressure mercury lamp. A wavelength control device comprising: a heating / cooling unit for cooling; and a temperature control unit for controlling the heating / cooling unit based on an output of the temperature detecting unit to maintain a temperature of a glass surface of the mercury lamp at a predetermined temperature. 2. The wavelength control device according to claim 1, wherein said temperature detecting means includes: a metal body for holding a glass tube of said low-pressure mercury lamp; and a temperature sensor for detecting a temperature of said metal body. 3. The wavelength controller according to claim 1, wherein said temperature detecting means is a temperature sensor sealed in a glass tube of said low-pressure mercury lamp. 4. The wavelength control device according to claim 1, wherein said temperature detecting means is a radiation thermometer. 5. The wavelength according to claim 1, wherein said heating / cooling means is a fan, and said temperature control means keeps the temperature of said mercury lamp at a predetermined temperature by controlling the number of revolutions or on / off of said fan. Control device. 6. The heating / cooling means includes: a heating medium tank for storing a predetermined heating medium; a double pipe disposed around a glass tube of the low-pressure mercury lamp, through which the heating medium flows; A pump that circulates the heat medium between a tank and a double pipe; and a heating / cooling unit that heats and cools the heating medium in the heating medium tank, wherein the temperature control unit controls the temperature of the heating / cooling unit. The temperature of the mercury lamp is maintained at a predetermined temperature by performing the operation.
The wavelength control device according to the above. 7. A reference light and a laser oscillation light generated from a reference light source are incident on a wavelength detector, and an absolute wavelength of the oscillation light is detected based on a detection output of the wavelength detector. Accordingly, there is provided a low-pressure mercury lamp for a wavelength control device used as the reference light source of a wavelength control device for controlling the wavelength of oscillation light, the low-pressure mercury lamp, a metal body sandwiching a glass tube of the low-pressure mercury lamp, A low-pressure mercury lamp for a wavelength control device, comprising: a temperature sensor for detecting the temperature of the device; 8. A reference light and a laser oscillation light generated from a reference light source are incident on a wavelength detector, and an absolute wavelength of the oscillation light is detected based on a detection output of the wavelength detector. Therefore, a low-pressure mercury lamp for a wavelength control device used as the reference light source of the wavelength control device for controlling the wavelength of oscillation light, comprising: a low-pressure mercury lamp; and a temperature sensor sealed in a glass tube of the low-pressure mercury lamp. Pressure mercury lamp for wavelength control equipment.