JP3132086B2 - Optical element shape control method and exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the shape of an optical element and an exposure apparatus, and more particularly to a synchrotron radiation beam or a high-intensity laser beam widely used in physics and chemistry research, analysis equipment, manufacturing equipment and the like. It is suitable for lithography for manufacturing semiconductor elements, in which a shape change caused by a partial temperature change of an optical element is prevented.

[0002]

2. Description of the Related Art In recent years, light sources that emit high-intensity light beams, such as synchrotron radiation (SR) light and excimer lasers, have been developed. The research and development of those are becoming active.

In general, in an optical device, reflection, transmission, light collection,
Various optical elements are required for purposes such as divergence, diffraction, spectroscopy, polarization, and imaging. Of these, the optical device using a high-intensity light source uses a high light intensity, so that a large heat load causes deformation of the optical element, performance degradation, irradiation damage,
Destruction becomes a problem.

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

Further, the radiation wavelength from the light source is often an electromagnetic wave in the range from X-rays to vacuum ultraviolet rays. In order to prevent attenuation in the atmosphere, optical elements are often assembled in a vacuum chamber or vacuum beam line. I have. For this reason, the optical element placed in a vacuum does not conduct to the atmosphere or dissipate heat due to convection, and the temperature of the optical element tends to increase significantly as compared with the case where the optical element is placed in the atmosphere.

[0006] Under such a large thermal load, the optical element is deformed due to thermal strain and the optical performance is remarkably deteriorated. In an extreme case, the optical element itself is destroyed (Tsukamoto et al., Autumn Committee of 1990). Proceedings of the Japan Society of Applied Physics P2-
501).

[0007] In order to prevent performance degradation due to temperature rise of the optical element, various methods of cooling the optical element have been devised and variously implemented. As a result, a rise in the temperature of the optical element is significantly suppressed as compared with the case where the cooling method is not performed (for example, T. Oversluizene).
t al. Rev., Rev .. Sci. Instrum. 601
493 (1989)).

[0008]

However, in an optical device using a light source that emits a high-intensity light beam, the surface of the optical element generally has a temperature of several to several tens of degrees even when the optical element is cooled. Irregularities remain. As a result, the shape of the optical element may be deformed, and the optical performance of the optical device may be reduced.

For example, in the above-mentioned spectroscopic device using SR light, the surface of the spectroscopic crystal, which should be originally a perfect plane, is partially deformed into a convex or concave surface having a radius of curvature of about 100 m or less even after the element is cooled. As a result, there was a problem that the intensity of the spectral light in proportion to the intensity of the light source could not be obtained.

In a projection exposure apparatus for transferring a fine pattern for manufacturing a semiconductor device as disclosed in, for example, JP-A-63-18626, the temperature unevenness of an optical element such as a mirror is controlled to about 1/100 ° C. Is required. However, there is a problem that the cooling of the optical element alone cannot sufficiently cope with this.

The present invention effectively corrects temperature unevenness of an optical element when a light source emitting a high-intensity light beam is used, prevents deformation of the optical element due to thermal distortion, and easily prevents deterioration of optical performance. It is an object of the present invention to provide a method for controlling the shape of an optical element and an exposure apparatus suitable for lithography for manufacturing a semiconductor element.

[0012]

According to a first aspect of the present invention, there is provided a method for controlling the shape of an optical element, comprising measuring temperature distribution information of the optical element, and heating the optical element by heating means based on the measurement. It is characterized in that the temperature unevenness of the element is corrected and deformation of the optical element due to thermal distortion is suppressed. Claim 2
The invention of claim 1 is characterized in that, in the invention of claim 1, the temperature of the optical element is adjusted by heating the optical element from at least one of the front surface and the back surface. According to a third aspect of the present invention, in the first aspect, the heating is performed using at least one of infrared irradiation and heating wire. According to a fourth aspect of the present invention, in the first aspect, the measurement of the temperature distribution information is performed by infrared detection. According to a fifth aspect of the present invention, in the first aspect, the optical element is a reflective mask having a pattern.

According to a sixth aspect of the present invention, there is provided an exposure apparatus for projecting and illuminating a pattern of an illuminated reflective mask onto a wafer through a reduction optical system, and measuring temperature distribution information of the reflective mask. Means, and means for heating the reflective mask by heating means based on the measurement of the measuring means to correct the temperature unevenness of the reflective mask, and for suppressing deformation of the reflective mask due to thermal distortion. Features. According to a seventh aspect of the present invention, in the sixth aspect, the reflection type mask is an X-ray mask having an X-ray reflection portion of a multilayer film.

According to an eighth aspect of the present invention, in the first aspect of the present invention, a holder for supporting the optical element is provided, and the holder also has a cooling function.

A ninth aspect of the present invention is characterized in that, in the sixth aspect of the present invention, a holder for supporting the reflection type mask is provided, and the holder also has a cooling function.

[0016]

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 FIG. 1, reference numeral 1 denotes synchrotron radiation. Reference numeral 2 denotes an optical element, which comprises a condensing mirror. For example, the surface of a silicon carbide or SiC material is polished in a toroidal shape, and a multilayer film for soft X-ray reflection is formed on the surface to reflect the synchrotron radiation 1. It has an optical function of condensing light 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 and the back 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.

Reference numeral 5 denotes a heating means, which has an infrared lamp 5a and a light collector (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 light emitted from the infrared lamp 5a.

Reference numeral 7 denotes the other heating means, which has a heating section 7a in which resistance wires are arranged in a net shape and a driving section 7b for driving and controlling the heating section 7a. Controlling distribution.

Reference numeral 8 denotes a thermocouple as another temperature distribution measuring means, which measures the temperature distribution on the back surface side of the optical element 2. 9 is a control means, and two temperature distribution measuring means 5,
8 so that the temperature distribution of the optical element 2 becomes uniform based on the signal from
The two heating means 5 and 7 are drive-controlled.

In this embodiment, the beam shape of the cross section perpendicular to the radiation light 1 at the position where the radiation light 1 is incident on the condenser mirror 2 is about 80.
mm × 8 mm, and is incident on the condenser mirror 2 at a viewing angle of 10 degrees (incident angle of 80 degrees). The power (light intensity) of the incident light was about 120 w when it was determined with reference to the temperature rise of the insulated copper block when the block was irradiated for a certain time. The radiated light 1 is obliquely incident on the condenser mirror 2, and as a result, the irradiation area on the surface of the condenser mirror 2 becomes large, and in this embodiment, the heat load density is about 33 mW / mm ² .

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

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

Next, a heating means 5 having a long infrared lamp 5a is arranged at a position as shown in FIG. 1, and the infrared light collector 5b and the irradiation power are adjusted so that the temperature of the surface of the collector mirror 2 becomes lower. Heat was emitted to make it as uniform as possible. The temperature distribution on the surface of the condenser mirror 2 after this adjustment was a substantially uniform temperature distribution 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 energizing the heating means 7 on the back surface of the condenser mirror 2 and monitoring the temperature of the back surface with the thermocouple 7a, the control unit 9 controls the temperature to be the same as the surface temperature of the condenser mirror 2. The amount of electricity supplied to the heating means 7 was adjusted. At this time, the focusing mirror 2
The temperature of the front and back surfaces was about 40 ° C. In this state, when the size of the spot of the reflected beam at the focal position of the converging mirror 2 was evaluated, the diameter was about 2 mm, and the light condensing ability of a design value was obtained.

As described above, in the present 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, the case where a condenser mirror (concave mirror) is used as an optical element has been described. However, as an optical element applicable to the present invention, a lens, a reflecting mirror, a beam splitter, a polarizing plate, a spectral 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. When a temperature measuring element such as a thermocouple or a platinum resistor can be buried or attached inside the optical element and on the front surface or the rear surface, a plurality of such temperature measuring elements may be provided. According to this, the temperature distribution of the optical element can be favorably obtained, which is preferable.

The infrared lamp used as the heating means of the optical element selects the shape of the lamp in accordance with the shape of the temperature distribution of the optical element, and uses a condenser mirror, an aperture, etc.
Partial heating can be performed efficiently. It is preferable to select the irradiation wavelength width of the infrared lamp so as not to include the wavelength of light used in the optical device, because it is possible to prevent the incidence of noise light. The irradiation direction is selected so as not to disturb the optical system of the optical device, thereby preventing a decrease in optical performance.

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

In this embodiment, when irradiating the optical element with radiation light, the temperature distribution of the optical element is first measured using the temperature distribution measuring means. Then, a predetermined portion of the optical element is heated using a heating means so that the temperature distribution becomes uniform, so that a change in shape of the optical element due to thermal distortion is minimized. The amount of heating is appropriately adjusted by repeating the temperature distribution measurement, 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 amount of deformation of the optical element due to the temperature distribution is calculated by 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 seek a heating method that makes the heating process easier and feed it back to the heating means.

In particular, in a reflection type optical element, heat flows in from the front surface by irradiation of radiation light from a light source, and a temperature distribution is generated between the optical element and the rear surface. For this reason, it is difficult to eliminate deformation of the optical element only by making the temperature distribution on the surface of the optical element uniform. Therefore, in the present invention, it is preferable to provide the heating means on both the front surface and the back surface of the optical element as described above in the reflection type optical element. 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 view of Embodiment 2 when the present invention is applied to a reduction projection type exposure apparatus for manufacturing a semiconductor device for soft X-rays using a laser plasma X-ray source as a light source.

Reference numeral 11 denotes an excimer laser. A light beam 11a from the excimer laser 11 is condensed by a lens 12 and irradiates a target 13 made of a samarium Sm material. Thus, laser plasma X-rays 14 are generated from the target 13. X-rays 14 generated from the target 13 pass through a beryllium filter 15 and an aperture 16 and irradiate a reflective mask 17 as an optical element. X-rays reflected from the reflective mask 17 are reflected by the reduction mirror 1
At 9, an image of the mask 17 is formed at the wafer position 20. Reference numeral 18 denotes a holder that supports the reflective mask 17 and also has a function of cooling the mask 17. Reference numeral 21 denotes a heating means having a platinum resistance wire deposited in a ring shape on the surface of the mask 17 to heat the surface of the mask 17.
Reference numeral 22 denotes an infrared camera, and reference numeral 23 denotes another heating means for heating the back surface of the reflective mask 17. Heating means 21
Reference numeral 3 denotes one element of a means for changing the temperature distribution of the reflective mask 17.

On the surface of the reflective mask 17 in this embodiment, a soft X-ray reflection pattern provided with a multilayer film by the method proposed in Japanese Patent Application Laid-Open No. 1-175731 is formed.

The surface is processed into a curved surface in order to reduce optical aberrations. It is also possible to use a reduction optical system using a plurality of mirrors as the reduction mirror 19, 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. Coat. The reduction ratio of the reduction mirror 19 is 1/5. In this embodiment, soft X-rays having a center wavelength of 130 ° are used among X-rays of various wavelengths generated from a laser plasma X-ray source.

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

At this time, an image of the mask was formed on the wafer coated with the resist at positions before and after the wafer position 20 and evaluated. As a result, there was a displacement of the focal plane of about 10 μm, and an image of 0.01% at the maximum. Was distorted.

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

[0041]

According to the present invention, the shape of the optical element can be very accurately controlled by adjusting the temperature, and the optical performance of the optical element can be maintained. In particular, it is effective in an X-ray optical device having a high-brightness light source such as a synchrotron radiation source or a laser plasma X-ray source in which the technical development has been remarkably advanced in recent years. Exposure becomes possible.

[0042]

[Brief description of the 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. 1;

FIG. 3 is a schematic diagram of a main part of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a surface temperature distribution of the reflective mask of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synchrotron radiation light 2 Condensing 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 Condensing lens 13 Target 15 Beryllium filter 17 Reflective mask 19 Reduction mirror 20 Wafer position

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G21K 1/06 H05H 13/04

Claims (9)

(57) [Claims] 1. A method of measuring temperature distribution information of an optical element, heating the optical element by a heating means based on the measurement, correcting temperature unevenness of the optical element, and suppressing deformation of the optical element due to thermal distortion. A method for controlling the shape of an optical element. 2. The method for controlling the shape of an optical element according to claim 1, wherein the temperature of the optical element is adjusted by heating the optical element from at least one of a front surface and a rear surface of the optical element. 3. The method according to claim 1, wherein the heating is performed using at least one of infrared irradiation and heating wire. 4. The method according to claim 1, wherein the measurement of the temperature distribution information is performed by detecting infrared rays. 5. The method according to claim 1, wherein the optical element is a reflective mask having a pattern. 6. An exposure apparatus for projecting and illuminating a pattern of an illuminated reflective mask onto a wafer via a reduction optical system, wherein the measuring means measures temperature distribution information of the reflective mask, and the measuring means measures The reflection by the heating means based on
An exposure apparatus comprising: means for heating a mold mask to correct temperature unevenness of the reflective mask, and suppressing deformation of the reflective mask due to thermal distortion. 7. An exposure apparatus according to claim 6, wherein said reflection type mask is an X-ray mask having an X-ray reflection portion formed of a multilayer film. And a holder for supporting said optical element.
And the holder also has a cooling function.
The method for controlling the shape of an optical element according to claim 1. 9. A holder for supporting the reflective mask
Characterized in that the holder also has a cooling function
The exposure apparatus according to claim 6, wherein