JPH0917725A - Projection aligner - Google Patents

Abstract

PURPOSE: To prevent a drop in performance and suppress damages to the optical elements of a projection aligner by two-photon absorption by returning a laser beam onto the same optical axis, which was once divided into two laser beams with different passages having a different length. CONSTITUTION: A laser beam L1 transmitted through a first partial reflecting mirror 11 and transmitted through a second partial reflecting mirror 12, and a laser beam L2 reflected by the first partial reflecting mirror 11, reflected by total reflection mirrors 13 and 14, and also reflected by the second partial reflecting mirror 12, will have a difference in a beam passage equal to the sum of a distance from the first partial reflecting mirror 11 to the total reflection mirror 13 and a distance from the total reflecting mirror 14 to the second partial reflecting mirror 12. Because of this, if the mirrors are arranged in such a manner that the relation of L1/c>Δt is valid where c is the velocity of a beam and Δt is the pulse width of the laser beam, then two pulses returned to the same optical axis by the partial reflecting mirror 12 have been deviated timewise. By doing this, the total energy of the pulse is divided timewise and damages to the optical elements can be restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus using an ArF excimer laser as a light source.

[0002]

2. Description of the Related Art A conventional projection exposure apparatus using an excimer laser as a light source is disclosed in, for example, Japanese Patent Application Laid-Open No. 64-11326, and its schematic structure is shown in FIG.
This projection exposure apparatus has an excimer laser 21 as a light source.
A cylindrical lens 22 and 24 for shaping the beam shape of the laser light, a reflection mirror 23, a fly-eye lens 25 for uniformizing the light distribution, a condenser lens 26 for condensing, and a diaphragm 27. , The condenser lens 2
A reticle 28 as a projection target illuminated by 6;
A projection lens 29 for forming an image of the reticle pattern,
It comprises a wafer 30 as an object to be projected and an XY table 31 for moving the wafer 30 in the plane XY directions.

In this projection exposure apparatus, a laser light source 21 illuminates a reticle 28 on which a desired pattern is formed, and light passing through the reticle 28 is projected and exposed onto a wafer 30 via a projection lens 29. The reticle pattern is transferred onto the wafer 30.

In this type of projection exposure apparatus, with the recent miniaturization and high integration of semiconductor elements, it is required to improve the resolution of the projection exposure apparatus. For this reason, the wavelength of the laser light is being shortened or the wavelength of the light source for illumination is being changed to a single wavelength. Along with this, an ArF excimer laser that generates vacuum ultraviolet light with a wavelength of 193 nm has been attracting attention as a light source.

[0005]

By the way, since the ArF excimer laser is a pulse laser having a pulse width of about 10 nsec, the peak intensity of the output light is high and the photon energy is high due to the short wavelength. The probability of photon absorption is higher than that of mercury lamps and KrF excimer lasers. As a result, in the projection exposure apparatus having the conventional configuration, the optical elements such as the fly's-eye lens, the condenser lens, and the projection lens are damaged due to the absorption of two photons, and the performance of the projection exposure apparatus is degraded. . Further, since an optical element of this type is generally expensive, there is also a problem that repair cost is extremely high when damage occurs.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection exposure apparatus in which damage to optical elements of the projection exposure apparatus due to two-photon absorption is suppressed and performance deterioration is prevented.

[0007]

A projection exposure apparatus according to the present invention comprises a dividing means for dividing a laser beam incident on a projection optical system into two laser beams having different optical paths, and an optical path difference between the divided laser beams. And means for returning the divided laser light having the optical path difference to the same optical axis.

That is, in a preferred aspect of the present invention, the light source is an ArF excimer laser, the means for splitting the optical path into two is a first partial reflection mirror, and the split laser light is on the same optical axis. The means for returning to the second reflection mirror comprises a second partial reflection mirror. The means for providing the optical path difference is a total reflection mirror that reflects the light reflected by the first partial reflection mirror toward the second partial reflection mirror. Further, a first partial reflection mirror and a second partial reflection mirror are arranged on the optical axis connecting the light source and the projection optical system, and four total reflection mirrors are provided as the first and second partial reflection mirrors, respectively. The total reflection mirrors are arranged to face each other and face each other.

[0009]

According to the present invention, the ArF excimer laser light is split into two optical paths by the first partial reflection mirror, and these divided laser lights propagate respectively at different distances, and at the second partial reflection mirror. Since the laser light is returned to the same optical axis again, one pulse of light is 2 on the time axis.
The number of pulse trains is changed to two or more, and the peak of the pulse intensity of the laser light is lowered, and
Damage due to photon absorption is reduced.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a projection exposure apparatus of the present invention. The same or equivalent parts as those of the conventional projection exposure apparatus shown in FIG. 3 are designated by the same reference numerals. That is, the laser light from the ArF excimer laser 21 as a light source is incident on the projection exposure system 2 after passing through the pulse splitting device 1 whose details will be described later. In this projection exposure system 2, the beam shapes of the laser light are shaped by the cylindrical lenses 22 and 24 and the reflection mirror 23, the light distribution is made uniform by the fly-eye lens 25, and the light is condensed by the condenser lens 26 and the diaphragm is used. After being squeezed by 27, the reticle 28 is illuminated. The light passing through the reticle 28 is imaged on the wafer 30 by the projection lens 29, thereby exposing the wafer 30 with the reticle pattern. Also, XY table 3
By moving the wafer 30 in the plane XY direction by 1, the wafer 30 is exposed in chip units.

The pulse splitting device 1 divides and combines laser light into a partial reflection mirror 11 having a reflectance R1 and a partial reflection mirror 12 having a reflectance R2, and a total reflection mirror 13 for giving an optical path difference to the laser light. It is composed of 14, 15, and 16. Then, the partial reflection mirrors 11 and 12 are arranged on the optical axis connecting the light source 21 and the projection optical system, and the total reflection mirrors 13 to 16 are respectively arranged to the partial reflection mirrors 11 and 12.
It is arranged at a position facing 12. In this embodiment, the partial reflection mirrors 11 and 12 are respectively arranged at an angle of 45 ° in the opposite direction to the optical axis, and the total reflection mirrors 13 and 16 are oriented 90 ° from the optical axis with respect to the partial reflection mirror 11. The total reflection mirrors 14 and 15 are arranged in the direction of 90 ° with respect to the optical axis with respect to the partial reflection mirror 12. The total reflection mirrors 13, 16 and 14, 15 are arranged to face each other on the optical path square with the optical axis, and each mirror is oriented at an angle of 45 ° with respect to the optical path.

Therefore, in this projection exposure apparatus, Ar
The laser beam from the F excimer laser is used by the pulse splitting device 1
When incident on the first partial reflection mirror 11, first, a part of the first partial reflection mirror 11 is transmitted along the optical axis, and the other part is reflected toward the total reflection mirror 13. The transmitted light reaches the second partial reflection mirror 12, where a part is transmitted along the optical axis and the other part is reflected toward the total reflection mirror 15. On the other hand, the light reflected toward the total reflection mirror 13 is reflected again by the total reflection mirror 14 and reaches the second partial reflection mirror 12. Then, here, a part thereof is reflected toward the optical axis, and another part is transmitted and directed toward the total reflection mirror 15. Then, each of the lights directed to the total reflection mirror 15 is reflected again by the total reflection mirror 16 and reaches the first partial reflection mirror 11, where a part is reflected toward the optical axis and the other part is reflected. Is transmitted toward the total reflection mirror 13.

Therefore, in order to simplify the explanation, as shown in FIG. 2, the light L transmitted through the first partial reflection mirror 11 and transmitted through the second partial reflection mirror 12.
1 and the light L2 reflected by the first partial reflection mirror 11, reflected by the total reflection mirrors 13 and 14, and further reflected by the second partial reflection mirror 12, both are first. That is, the optical path is different by the sum of the distance between the partial reflection mirror 11 and the total reflection mirror 13 and the distance between the total reflection mirror 14 and the second partial reflection mirror 12. That is, in FIG. 1 and FIG. 2, when the positions of the respective mirrors are indicated by A to F, the light pulse divided by the partial reflection mirror 11 has an optical path difference L1 = AC + CD + DB
There is a difference in time to reach the partial reflection mirror 12 by −AB.

As a result, the speed of light c and the pulse width of the laser light Δ
When the mirrors are arranged so that the relationship of L1 / c> Δt is satisfied at t, the two pulses P1 and P2 returned to the same optical axis by the partial reflection mirror 12 are as shown in FIG.
It will be shifted in time. This causes the total energy of the pulse to be split in time, reducing the peak of the pulse. Therefore, the probability of occurrence of two-photon absorption in the optical element of the projection exposure apparatus thereafter is reduced, and damage to the optical element is suppressed.

Actually, as described above, part of the light reflected by the total reflection mirrors 15 and 16 is reflected on the partial reflection mirrors 11 and 12 and then returned to the optical axis. These lights are added to the above-mentioned pulse, and the pulse intensity is obtained by a complicated calculation formula. Therefore, the output light pulse intensity from the pulse splitting device becomes geometrically smaller each time the splitting of the pulse incident from the light source is repeated, and any output pulse intensity becomes smaller than the incident pulse intensity. On the other hand, on the other hand, since a part of the light is returned to the optical axis with each repetition,
As a result, no energy loss occurs.

That is, in the case where the reflectances of the first and second partial reflection mirrors 11 and 12 are R1 and R2 as described above, the light transmitted through the first partial reflection mirror 11 and reflected from the first partial reflection mirror 11 are reflected as described above. When the trial calculation is performed only when the generated light is combined by the second partial reflection mirror 12, the pulse intensity of the former light is
The incident light intensity is (1−R1) × (1−R2), and the latter light pulse intensity is R1 × R2. 0 <
Since R1 <1 and 0 <R2 <1, both are lower than the input light intensity.

For example, when the partial reflection mirrors 11 and 12 are semi-transmission mirrors, that is, when R1 and R2 are 0.5, the pulse intensity of transmitted light is 0.25 and the pulse intensity of reflected light is 0.25. The peaks of the pulses P1 and P2 shown in FIG. 3 are 0.25, respectively. Then, the remaining 0.5, which is the intensity, is further combined with a time difference, for example, as shown by the broken line in FIG.

In the above-mentioned pulse splitting device, the number and arrangement of the partial reflection mirrors and the total reflection mirrors can be arbitrarily designed, and the optical path difference can be appropriately set according to the design. It is also possible to change the optical path difference by installing glass or the like on the optical path within a range that does not affect the optical characteristics.

[0019]

As described above, according to the present invention, the laser light incident on the projection optical system is split into two laser lights having different optical paths, and an optical path difference is given to the split laser light. In addition, since a pulse splitting device capable of returning the split laser light having an optical path difference to the same optical axis is provided, the ArF excimer laser light as a light source has one pulse of light on the time axis. , The pulse intensity of the laser light is reduced to two or more pulse trains at
Damage due to two-photon absorption in the optical elements of the projection exposure apparatus is reduced.

In particular, the pulse splitting device is arranged on the optical axis connecting the first partial reflection mirror and the second partial reflection mirror to the light source and the projection optical system, and four total reflection mirrors are respectively provided for the first partial reflection mirror. And the second partial reflection mirror so as to face each other, and the total reflection mirrors face each other so that the pulse intensity is divided on the time axis without loss of pulse energy. It is possible to input the light with reduced pulse peaks to the projection optical system.

[Brief description of the drawings]

FIG. 1 is an optical configuration diagram showing an overall configuration of a projection exposure apparatus of the present invention.

FIG. 2 is a diagram showing a comparison between pulse intensity characteristics input to a pulse division device and pulse intensity characteristics output.

FIG. 3 is an optical configuration diagram showing a configuration of a conventional projection exposure apparatus.

[Explanation of symbols]

 1 Pulse Splitter 11, 12 Partial Reflection Mirror 13-16 Total Reflection Mirror 21 Light Source 25 Fly's Eye Lens 26 Projection Lens 28 Reticle 30 Wafer

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[Procedure amendment]

[Submission date] November 24, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is an optical configuration diagram showing an overall configuration of a projection exposure apparatus of the present invention.

FIG. 2 is a view for explaining an optical path difference due to a partial reflection mirror .
It is a block diagram of a pulse division device.

FIG. 3 is a diagram showing a comparison between pulse intensity characteristics input to a pulse division device and pulse intensity characteristics output.

FIG. 4 is an optical configuration diagram showing a configuration of a conventional projection exposure apparatus.

[Explanation of Codes] 1 pulse splitting device 11, 12 partial reflection mirror 13-16 total reflection mirror 21 light source 25 fly's eye lens 26 projection lens 28 reticle 30 wafer

Claims (4)

[Claims] 1. A projection exposure apparatus for exposing a subject to be exposed with a laser beam emitted from a light source by a projection optical system, wherein the laser beam incident on the projection optical system is divided into two laser beams having different optical paths. A splitting unit for splitting, a unit for giving an optical path difference to the split laser beam, and a unit for returning the split laser beam having the optical path difference to the same optical axis. Projection exposure apparatus. 2. The light source is an ArF excimer laser, the means for splitting the optical path into two is a first partial reflection mirror, and the means for returning the split laser light to the same optical axis is a second. 2. The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus is a partial reflection mirror. 3. The projection exposure apparatus according to claim 2, wherein the means for giving an optical path difference is a total reflection mirror for reflecting the light reflected by the first partial reflection mirror toward the second partial reflection mirror. 4. A first partial reflection mirror and a second partial reflection mirror are arranged on an optical axis connecting a light source and a projection optical system, and 4
4. The projection exposure apparatus according to claim 3, wherein each of the total reflection mirrors is arranged to face the first and second partial reflection mirrors, and the total reflection mirrors are arranged to face each other.