JPH0566297A - Shape stabilization of optical element and optical apparatus using same - Google Patents

Abstract

PURPOSE:To suppress deformation of an optical element resulted from thermal strain thereof and to prevent deterioration of optical performance by measuring temperature distribution of the optical element using a measurement means of temperature distribution, and by heating up the optical element partially using a heating means, based upon signal from the measurement means. CONSTITUTION:The title optical apparatus reflects a synchrotron radiation beam 1 by the use of a multilayered converging mirror 2 and makes the beam converge to a pin spot. The converging mirror 2 is provided with a holder 3 which has a chilling function from both side surface and rear surface thereof by means of a water chilling mechanism. First of all, temperature distribution of the mirror 2 is measured using an infrared measuring means 4 of temperature distribution. Temperature distribution on the rear side of the mirror 2 is also measured using another measuring means 8 of temperature distribution. Surface temperature distribution of the mirror 2 is driven and controlled by a controlling means 9 using a heating means 5 consisting of infra-red lumps 5a, and converging plates 5b, so as to get uniform temperature distribution of an optical element 2 and to eliminate any shape deformation thereof, and moreover the temperature distribution is driven and controlled by a heating means 7 having a heating part 7a by a resisting wire, and a driving part 7b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing the shape of an optical element and an optical device using the same, and particularly to a synchrotron radiation light or a high intensity laser widely used in physics and chemistry research, analysis equipment, manufacturing equipment and the like. The present invention relates to a method for stabilizing the shape of an optical element in which the shape change caused by a partial temperature change of an optical element for light is prevented, and an optical device using the same.

[0002]

2. Description of the Related Art In recent years, a light source that emits a high-intensity light beam such as synchrotron radiation (SR) light or excimer laser has been developed, and optical devices such as physics and chemistry research, analysis equipment, and manufacturing technology have been attracting attention. Research and development of them has become popular.

Generally, in an optical device, reflection, transmission, light collection,
Various optical elements are needed for purposes such as divergence, diffraction, spectroscopy, polarization, imaging. Among them, since the light intensity used is particularly high in an optical device using a high-intensity light source, deformation of the optical element due to a large heat load, performance deterioration, irradiation damage,
Destruction becomes a problem.

For example, in the field of SR light technology, the radiation power from the light source has reached the order of kilowatts due to the progress of the so-called insertion type light source technology such as multi-pole wiggler and undulator in recent years.

Further, the radiation wavelength from the light source is often an electromagnetic wave in the X-ray to vacuum ultraviolet region, and in order to prevent attenuation in the atmosphere, optical elements are often assembled in a vacuum chamber or vacuum beam line. There is. Therefore, in an optical element placed in a vacuum, heat conduction to the atmosphere and heat dissipation due to convection do not occur, and the temperature of the optical element tends to be significantly higher than that in the case where the optical element is placed in the atmosphere.

When such a large heat load is applied, the optical element is deformed due to thermal strain, and the optical performance remarkably deteriorates. In an extreme case, the optical element itself may be destroyed (Tsukamoto et al., Autumn 1990 Committee). Proceedings of Japan Society of Applied Physics P2-
501).

In order to prevent the performance deterioration of the optical element due to the temperature rise, various methods of cooling the optical element have been devised and implemented variously. As a result, the temperature rise of the optical element is largely suppressed as compared with the case where the cooling method is not performed (for example, T. Oversluizen e.
t al. Rev. Sci. Instrum. 601
493 (1989)).

[0008]

However, in an optical device using a light source that emits a high-intensity luminous flux, even if the optical element is cooled, the surface of the optical element generally has a temperature of several to several tens of degrees. The unevenness remains. As a result, the shape of the optical element may be deformed and the optical performance of the optical device may be deteriorated.

For example, in the above-mentioned spectroscopic device using SR light, the surface of the dispersive crystal, which should be a perfect flat surface, is partially deformed to a convex or concave surface with a radius of curvature of 100 m or less even after cooling the element. As a result, there is a problem that the intensity of the spectral light proportional to the intensity of the light source cannot be obtained.

Further, in a projection exposure apparatus for transferring a fine pattern for manufacturing a semiconductor device as disclosed in, for example, Japanese Patent Laid-Open No. 63-18626, temperature unevenness of optical elements such as mirrors is controlled to about 1/100 ° C. Required to do so. However, there is a problem that this cannot be sufficiently dealt with only by cooling the optical element.

The present invention effectively corrects the temperature unevenness of the optical element when a light source that emits a high-intensity luminous flux is used, prevents deformation of the optical element due to thermal distortion, and easily prevents deterioration of optical performance. An object of the present invention is to provide a method for stabilizing the shape of an optical element and an optical device using the method.

[0012]

As a method for stabilizing the shape of an optical element of the present invention, the temperature distribution of the optical element is measured by a temperature distribution measuring means, and the heating means is operated based on a signal from the temperature distribution measuring means. It is characterized in that the optical element is partially heated to control the shape change of the optical element.

In particular, the heating means is provided on the front surface and / or the back surface of the optical element, and the optical element is heated from the front surface and / or the back surface.

A method for stabilizing the shape of an optical element and an optical apparatus using the method include an optical apparatus in which a light beam from a light source is incident on the optical element and the light beam through the optical element is utilized. Provided are temperature distribution measuring means for measuring the temperature distribution of the element and heating means for partially heating the optical element based on a signal from the temperature distribution measuring means and controlling the shape of the optical element due to thermal strain. It is characterized by that.

Further, according to the present invention, when the pattern of the reflective mask surface illuminated by the light beam from the light source is projected onto the wafer surface through the reflecting means, the temperature distribution of the reflective mask surface is measured by the temperature distribution measuring means. Then, the reflective mask is heated by the heating means based on the signal from the temperature distribution measuring means,
It is characterized in that the temperature distribution of the reflective mask is made uniform.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment when the present invention is applied to an optical device using a condenser mirror as an optical element for synchrotron radiation.

In the figure, reference numeral 1 denotes synchrotron radiation light. Reference numeral 2 denotes an optical element, which is composed of a condenser mirror, for example, a surface of silicon carbide or SiC material is polished into a toroidal shape, a multilayer film for soft X-ray reflection is formed on the surface, and synchrotron radiation 1 is reflected. It has an optical effect of condensing in a dot shape.

Reference numeral 3 denotes a holder, which supports the condenser mirror and also has a cooling function of cooling the condenser mirror 2 from the side surface and the back surface by a water cooling mechanism (not shown). Reference numeral 4 denotes a temperature distribution measuring means, which is composed of, for example, an infrared camera using InSb as a sensor.

A heating means 5 has an infrared lamp 5a and a condenser plate (concave mirror) 5b. The heating means 5 controls the temperature distribution of the optical element from the surface side of the optical element 2. The light collector 5b enhances the directivity of infrared rays emitted from the infrared lamp 5a.

Reference numeral 7 denotes the other heating means, which has a heating portion 7a having resistance wires arranged in a mesh and a driving portion 7b for driving and controlling the heating portion 7a. It controls the distribution.

A thermocouple 8 as the other temperature distribution measuring means measures the temperature distribution on the back surface side of the optical element 2. Reference numeral 9 is a control means, and two temperature distribution measuring means 5,
The temperature distribution of the optical element 2 becomes uniform on the basis of the signal from 8, so that the optical element does not change its shape and becomes stable.
The two heating means 5 and 7 are drive-controlled.

In this embodiment, the beam shape of the cross section of the emitted light 1 at the incident position of the condenser mirror 2 perpendicular to the emitted light 1 is about 80.
The size is 8 mm × 8 mm, and the light is incident on the condenser mirror 2 at a viewing angle of 10 ° (incident angle of 80 °). The power (light intensity) of the incident light was about 120 w as determined by referring to the temperature rise of the heat-insulated copper block when the block was irradiated for a certain period of time. The radiated light 1 is obliquely incident on the condenser mirror 2. As a result, the irradiation area on the surface of the condenser mirror 2 is increased, and the heat load density is about 33 mW / mm ² in this embodiment.

The size of the condenser mirror 2 is 200 mm in the incident direction of the emitted light 1 and 100 mm in the direction perpendicular thereto. When the temperature distribution on the surface of the condenser mirror 2 is measured by the infrared camera 4, there is a temperature distribution indicated by the curve a in FIG. 2 in the longitudinal direction of the condenser mirror 2, and the temperature distribution is almost uniform in the vertical direction. there were.

At this time, when the size of the spot at the focus position where the reflected light 1 from the condenser mirror 2 is focused is evaluated by a photographic film exposure method, the diameter is about 7 mm.

Next, the heating means 5 having the elongated infrared lamp 5a is arranged at the position shown in FIG. 1, and the infrared condenser plate 5b and the irradiation power are adjusted to adjust the temperature of the surface of the condenser mirror 2. It was heated and radiated so as to be as uniform as possible. The temperature distribution on the surface of the condenser mirror 2 after this adjustment was a substantially uniform temperature distribution at a temperature of 35 ° C. as shown by the curve b in FIG. At this time, the size of the spot of the reflected light beam at the focal position of the emitted light 1 was about 4 mm in diameter.

Further, while the heating means 7 on the rear surface of the condenser mirror 2 is energized and the temperature of the rear surface is monitored by the thermocouple 7a, the temperature is made equal to the surface temperature of the condenser mirror 2 by the control unit 9. The energization amount of the heating means 7 was adjusted. At this time, the condenser mirror 2
The temperature of the front surface and the back surface was about 40 ° C. When the size of the spot of the reflected beam at the focus position of the condenser mirror 2 was evaluated in this state, the diameter was about 2 mm, and the condensing ability of almost the designed value was obtained.

As described above, in this embodiment, the temperature distribution of the optical element 2 is appropriately controlled, whereby the shape change of the optical element is prevented, and good optical performance can be easily obtained. In this embodiment, a case where a condenser mirror (concave mirror) is used as an optical element is shown, but as an optical element applicable to the present invention, a lens, a reflecting mirror, a beam splitter, a polarizing plate, a dispersive crystal, a diffraction grating. , Optical filters, etalons, multilayer mirrors, masks for exposure equipment, reticles, etc. Any of the optical elements can be applied to an optical device used with a high intensity light source such as SR light or excimer laser.

As the temperature distribution measuring means of the optical element, a one-dimensional or two-dimensional infrared sensor array or the like can be applied in addition to the infrared camera. If temperature measuring elements such as thermocouples and platinum resistors can be embedded or attached to the inside and the front surface or the back surface of the optical element, a plurality of these temperature measuring elements may be installed. This is preferable because the temperature distribution of the optical element can be satisfactorily obtained.

The infrared lamp used as the heating means for the optical element is selected in accordance with the shape of the temperature distribution of the optical element, and a condenser mirror or an aperture is used.
It enables efficient partial heating. It is preferable that the irradiation wavelength width of the infrared lamp is selected so as not to include the wavelength of the light used in the optical device, because noise light can be prevented from entering. Further, the irradiation direction is selected so as not to disturb the optical system of the optical device, thereby preventing deterioration of optical performance.

When a heating element such as a heating wire can be embedded or attached in the optical element and on the front surface or the back surface,
A plurality of the heating elements may be installed in a predetermined portion of the optical element. This is preferable because the optical element can be partially heated and the temperature distribution can be uniformly controlled.

In this embodiment, when the optical element is irradiated with the radiation light, the temperature distribution measuring means is used to measure the temperature distribution of the optical element. Then, a predetermined portion of the optical element is heated by using a heating means so that the temperature distribution becomes uniform so that the shape change due to the thermal strain of the optical element is minimized. The amount of heating is appropriately adjusted by repeatedly measuring the temperature distribution, analyzing the data by the control means, and feeding it back to the heating means.

When the temperature distribution data is fed back from the control means to the heating means, the deformation amount of the optical element due to the temperature distribution is calculated by a calculation means such as the finite element method, and the shape of the optical element is optimized for the purpose of the apparatus. It is also possible to obtain a suitable heating method and feed it back to the heating means.

Particularly in a reflection type optical element, heat is introduced from the front surface by the irradiation of the radiation light from the light source, and a temperature distribution is generated between the heat and the back surface of the optical element. Therefore, it is difficult to eliminate the deformation of the optical element only by making the temperature distribution on the surface of the optical element uniform. Therefore, in the present invention, in the reflection type optical element, it is preferable to provide the heating means on both the front surface and the back surface of the optical element as described above. According to this, the temperature distribution on the front surface and the back surface of the optical element becomes more uniform, and the deformation of the optical element can be further reduced.

FIG. 3 is a schematic diagram of a second embodiment when the present invention is applied to a reduction projection exposure apparatus for manufacturing a semiconductor element for soft X-rays using a laser plasma X-ray source as a light source.

Reference numeral 11 is an excimer laser. The light beam 11a from the excimer laser 11 is condensed by the lens 12 and is applied to the target 13 made of samarium Sm material. As a result, laser plasma X-rays 14 are generated from the target 13. The X-ray 14 generated from the target 13 passes through a beryllium filter 15 and an aperture 16 and irradiates a reflection type mask 17 as an optical element. X-rays reflected from the reflective mask 17 are reduction mirrors 1.
9 and forms an image of the mask 17 on the wafer position 20. Reference numeral 18 denotes a holder, which also has a function of supporting the reflective mask 17 and cooling the mask 17. A heating means 21 has a platinum resistance wire vapor-deposited in a ring shape on the surface of the mask 17, and heats the surface of the mask 17.
Reference numeral 22 is an infrared camera, and 23 is the other heating means for heating the back surface of the reflective mask 17.

On the surface of the reflective mask 17 in this embodiment, a soft X-ray reflection pattern having a multilayer film formed by the method proposed in JP-A-1-175731 is formed.

The surface shape is processed into a curved shape in order to reduce optical aberrations. The reduction mirror 19 can also use a reduction optical system using a plurality of mirrors, and the surface of the reduction mirror 19 is formed of a multilayer film so as to reflect the same wavelength as the soft X-ray reflected by the reflective mask 17. I have a coat. The reduction ratio of the reduction mirror 19 is ⅕. In this embodiment, among the X-rays of various wavelengths generated from the laser plasma X-ray source, soft X-rays having a central wavelength of 130Å are used.

The energy of the excimer laser is 50 mJ
/ Pulse, the repetition frequency is set to 300 Hz, X-rays are generated from the samarium target 13, and the reflection type mask 17 is used.
The surface of the was irradiated with X-rays. A curve C in FIG. 4 is the temperature distribution on the mask surface measured by the infrared camera 22 at this time.
As shown in the figure, the temperature distribution is almost point-symmetrical, and a temperature rise of about 1.2 ° C. was observed in the central portion compared to the surroundings.

At this time, when an image of the mask was formed on the wafer coated with the resist at a position before and after the wafer position 20 and evaluated, there was a focal plane shift of about 10 μm and an image of 0.01% at maximum. There was a distortion of.

Next, the platinum resistance wire 21 on the reflective mask 17
When the heating heater 23a of the heating means 23 on the back surface was energized and the heating amount was adjusted while monitoring with the infrared camera 22, a substantially uniform temperature distribution as shown by the curve d in FIG. 4 was obtained. At this time, when the image formation state was evaluated by the same method as described above, the deviation of the focal plane was 2 μm or less, and the image distortion was 0.002% or less.

[0041]

According to the present invention, the temperature distribution measuring means for the optical element and the heating means for the optical element are provided as described above, and the temperature distribution at the time of irradiating the optical element with light is made uniform.
A method for stabilizing the shape of an optical element, which has the excellent effect of suppressing the deterioration of the optical performance of the optical element and the optical system as a whole by suppressing the amount of the shape deformation of the optical element caused by the uneven temperature rise, and using the method. An optical device can be achieved.

In particular, the method for stabilizing the shape of an optical element of the present invention is effective in an optical device having a high intensity light source such as synchrotron radiation or laser plasma X-ray source, which has been remarkably advanced in technological development in recent years. It has features such as the ability to effectively prevent damage due to thermal strain of the element.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a surface temperature distribution of the optical element of FIG.

FIG. 3 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 4 is an explanatory diagram showing a surface temperature distribution of the reflective mask of FIG.

[Explanation of symbols]

 1 Synchrotron radiation 2 Condenser Mirror 3,18 Holder 4,22 Infrared Camera 5,7,21,23 Heating Means 8 Temperature Distribution Measuring Means 9,24 Control Means 11 Excimer Laser 11a Excimer Laser Beam 12 Condenser Lens 13 Target 15 Beryllium filter 17 Reflective mask 19 Reduction mirror 20 Wafer position

Claims (4)

[Claims] 1. The temperature distribution of an optical element is measured by a temperature distribution measuring means, and the optical element is partially heated by a heating means based on a signal from the temperature distribution measuring means to change the shape of the optical element. A method for stabilizing the shape of an optical element characterized by being controlled. 2. The heating means is provided on the front surface and / or the back surface of the optical element, and the optical element is heated from the front surface and / or the back surface.
Method for stabilizing the shape of optical elements. 3. A light beam from a light source is incident on an optical element,
In an optical device adapted to utilize a light flux passing through the optical element, a temperature distribution measuring means for measuring a temperature distribution of the optical element, and a part of the optical element based on a signal from the temperature distribution measuring means. An optical device comprising: heating means for heating and controlling a shape of the optical element due to thermal strain. 4. When a pattern of a reflective mask surface illuminated by a light beam from a light source is projected onto a wafer surface through a reflecting means, a temperature distribution of the reflective mask surface is measured by a temperature distribution measuring means, An optical device for manufacturing a semiconductor device, wherein the heating means heats the reflective mask based on a signal from the temperature distribution measuring means so that the temperature distribution of the reflective mask becomes uniform.