JPH09288251A - Pulse width lengthening optical system and exposure device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce average energy within a light emitting time by constituting plural optical paths so that they may have the specified difference of optical path length from each other and executing the pseudo prolongation of the emitting time of pulse light. SOLUTION: The pulse light emitted from a laser light source 1 is made incident on a half mirror 10 and divided into reflected light and transmitted light. The reflected light is made incident on a mirror 14. After the transmitted light is successively reflected by mirrors 11 to 13, it is made incident on the half mirror 10 again. A circulation optical path formed by three mirrors 11 to 13 and the half mirror 10 are set to have the specified optical path length, and functions as a means for giving the difference of the optical path length. The light component reflected at and after the second time by the half mirror 10 is gradually attenuated by an amount equal to the light transmitted through the half mirror 10 in every circulation, and finally all the light is transmitted through the half mirror 10. Therefore, the loss of light quantity is not caused in principle in the case the reflectance of the mirrors 11 to 13 is 100%, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width expanding optical system and an exposure apparatus equipped with the optical system, and more particularly to an optical system for artificially expanding the emission time of pulsed light from a pulse laser light source and the optical system. The present invention relates to a provided exposure apparatus. Furthermore, the present invention relates to a method of manufacturing a semiconductor device using an exposure apparatus equipped with a pulse width expansion optical system.

[0002]

2. Description of the Related Art FIG. 16 is a diagram schematically showing the structure of a conventional exposure apparatus having a pulse laser light source. FIG.
In this exposure apparatus, the light beam emitted from the pulsed laser light source 1 is shaped into a predetermined beam cross-sectional shape by the beam shaping optical system 2, and then the fly-eye lens 3
Incident on. The light flux incident on the fly-eye lens 3 forms a plurality of light source images (secondary light sources) at the focal point on the rear side of the fly-eye lens 3.

Light fluxes from a plurality of secondary light sources are transmitted through the aperture stop 4.
After being limited by the condenser lens 5, the light is condensed by the condenser lens 5 to uniformly illuminate the mask 6 in a superimposed manner. Mask 6
A very fine pattern such as a semiconductor integrated circuit is drawn on the top. The pattern of the mask 6 is reduced or enlarged and projected on the wafer 8 via the projection optical system 7. At this time, the size of the fine pattern that can be formed on the wafer 8 is proportional to the wavelength of the light from the laser light source 1. Therefore, in order to form a finer pattern, it is necessary to make the wavelength of the light from the laser light source 1 as short as possible.

[0004]

However, in the pulsed laser light source, the average energy within the emission time of the pulsed light is very large. For example, wavelength 193nm
In case of ArF excimer laser, the beam cross sectional shape is 20mm
If the emission time is 10 nsec, the average energy within the emission time is 10 MW / cm ² .

Since the average energy within the emission time increases as the wavelength of the laser light decreases, the laser resistance of the optical material tends to decrease. For this reason, in the conventional optical system that uses a laser beam with a short wavelength, the transmittance of the lens material decreases, the performance of the antireflection coat and the reflection mirror deteriorates, and thus the transmittance of the optical system as a whole decreases. The power is reduced and the illuminance uniformity is deteriorated. Further, in a conventional exposure apparatus that uses a laser beam having a short wavelength, aberration may occur due to a change in the refractive index of the lens material of the projection optical system, which may have a serious adverse effect on the imaging performance of the projection optical system.

[0006] For example, when an ArF excimer laser (wavelength: 193 nm), which has been attracting attention in recent years, is used as a light source of an exposure apparatus, only two kinds of optical refraction materials, synthetic quartz glass and fluorite, can be practically used. It was Moreover, in both the synthetic quartz glass and fluorite materials, a gradual decrease in transmittance is observed for laser light having an energy density of a certain threshold value or more. For this reason, in the prior art, in order to avoid deterioration of the performance of the optical system and maintain its durability, the size of the optical system must be increased and the energy density per unit area must be reduced.

The present invention has been made in view of the above-mentioned problems, and a pulse width extension optical system capable of reducing the average energy within the emission time by artificially extending the emission time of pulsed light. Another object of the present invention is to provide an exposure apparatus equipped with the optical system. Another object of the present invention is to provide a method of manufacturing a semiconductor device using an exposure apparatus equipped with a pulse width expansion optical system.

[0008]

In order to solve the above problems, in the first invention of the present invention, a plurality of pulsed light beams are provided in a pulse width expansion optical system for artificially expanding the emission time of the pulsed light beam. The light splitting means for splitting along the optical path and the light synthesizing means for synthesizing the split pulse light along the plurality of optical paths along the same optical path are provided, and the light is synthesized along the same optical path. The plurality of optical paths have a predetermined optical path length difference from each other such that the intensity of the combined pulsed light is substantially smaller than the intensity of the original pulsed light split along the plurality of optical paths. A pulse width stretching optical system is provided.

According to a preferred aspect of the first aspect of the present invention, the predetermined optical path length difference is obtained by multiplying the product of the time when the emission intensity is ½ or more of the peak intensity within the emission time of the original pulsed light and the speed of light. Is also big. Further, in at least one optical path of the plurality of optical paths, a relay optical system for configuring the split surface of the light splitting means and the synthesis surface of the light combining means substantially in a conjugate manner is provided. Is preferred.

Further, in the second aspect of the present invention, an illumination optical system for illuminating a mask having a pattern formed thereon substantially uniformly is provided, and an image of the pattern formed on the mask is formed on a photosensitive substrate. In the exposure apparatus described above, the illumination optical system includes a light source that emits pulsed light, and a pulse width expansion optical system for artificially expanding the emission time of the pulsed light from the light source, and the pulse width expansion optical system is A light splitting means for splitting the pulsed light along a plurality of optical paths,
And a light combining means for combining the divided pulsed lights along the plurality of optical paths along the same optical path, and the intensity of the combined pulsed light combined along the same optical path along the plurality of optical paths. Provided is an exposure apparatus, wherein the plurality of optical paths have a predetermined optical path length difference so that the intensity of the original split pulsed light is substantially smaller.

According to a preferred aspect of the second invention, the illumination optical system forms a multi-light source image for forming a large number of light source images based on the combined pulsed light formed via the pulse width expansion optical system. And a condensing optical system that condenses the light fluxes from the multiple light source images formed by the multi-light source image forming means and illuminates the mask in a superimposed manner.

[0012]

As described above, in the present invention, pulsed light is split along a plurality of optical paths, and then a plurality of split pulsed lights are combined along the same optical path. In this case, the plurality of optical paths are mutually predetermined so that the intensity of the combined pulsed light combined along the same optical path is substantially smaller than the intensity of the original pulsed light divided along the plurality of optical paths. There is an optical path length difference.

As described above, in the present invention, the average energy within the light emission time, that is, the energy per unit time can be reduced by artificially extending the light emission time of the pulsed light. Therefore, in a general optical system using a pulsed light source, it is possible to avoid performance degradation of the optical material due to light irradiation. In particular, in an exposure apparatus that uses a pulsed laser light source, it is possible to satisfactorily form a fine pattern while avoiding a reduction in the imaging performance of the projection optical system due to laser irradiation.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing the configuration of a pulse width expansion optical system according to the first embodiment of the present invention. Further, FIG. 2 is a diagram schematically showing a temporal change in energy of pulsed light emitted from the laser light source of FIG. The pulse width expansion optical system of FIG. 1 includes a laser light source 1 that emits pulsed light of substantially linear polarization. The polarization direction of the pulsed light from the laser light source 1 is assumed to be vertical or parallel to the paper surface of FIG.

The pulsed light emitted from the laser light source 1 enters a half mirror 10 having a semi-transmissive film made of a dielectric multilayer film, and is split into reflected light and transmitted light. The light reflected by the half mirror 10 for the first time becomes split pulse light, enters the mirror 14, and is reflected to the right side in the drawing. On the other hand, the light transmitted through the half mirror 10 for the first time is
After the split pulse light is sequentially reflected by the mirrors 11, 12 and 13, it is incident on the half mirror 10 again.

Of the light that has re-entered the half mirror 10, the light that has passed through the half mirror 10 for the second time is combined along the same optical path as the light that has been reflected by the half mirror 10 for the first time. Of the light that has re-entered the half mirror 10, the light reflected by the half mirror 10 for the second time is sequentially reflected by the mirrors 11, 12 and 13 and then re-enters the half mirror 10. In this way, the half mirror 10 constitutes a light splitting means for splitting pulsed light along a plurality of optical paths and a light combining means for combining split pulsed light along a plurality of optical paths along the same optical path. are doing. The orbital optical path formed by the three mirrors (11 to 13) and the half mirror 10 has three mirrors (11 to 1) so as to have a predetermined optical path length as described later.
3) and the three mirrors (1
1 to 13) function as an optical path length difference providing means.

Of the light that has re-entered the half mirror 10, the light that has passed through the half mirror 10 for the third time is the light that has been reflected by the half mirror 10 for the first time and the half mirror 10.
Is combined along the same optical path as the light transmitted through the second time. In this way, the light components reflected by the half mirror 10 after the second time orbit the same optical path through the mirrors 11, 12 and 13. As described above, when the optical path length of the circular optical path is L and n is an integer of 2 or more, the half mirror 10
The split light passing through n times passes through the half mirror 10 (n-1).
An optical path length difference L is given to the split light that is circulated. The light component reflected by the half mirror 10 after the second time is gradually attenuated by the amount of light passing through the half mirror 10 for each orbit, and finally all the light passes through the half mirror 10. become. Therefore, the mirror 11,
If the reflectances of 12 and 13 are 100%,
In principle, no light quantity loss occurs.

When the emission time of pulsed light (hereinafter referred to as “pulse width”) is δ seconds, the distance of light traveling within the emission time (hereinafter referred to as “pulse length”) is 3 × 10 ⁸ × δ.
[M]. Therefore, if the optical path length of the optical system composed of the half mirror 10 and the mirrors 11, 12 and 13 (hereinafter, referred to as “circulating optical system”) is larger than the pulse length, a plurality of light beams are sequentially combined via the half mirror 10. The split pulse lights do not overlap in time. That is, the plurality of split pulse lights that are sequentially combined via the half mirror 10 have three mirrors (11 to 1) as optical path length difference imparting means.
Since the predetermined optical path length difference is imparted by the action of 3), there is no temporal overlap. FIG. 3 is a diagram showing a change over time in energy of combined pulsed light composed of a plurality of split pulsed lights that do not overlap with each other in time.

As an example, the light emission time, that is, the pulse width δ
When 10nsec., The pulse length becomes 3m. Therefore,
If the optical path length of the circular optical system is set to 3 m or more, the plurality of divided pulse lights to be combined will not temporally overlap. Referring to FIG. 3, it can be seen that the pulse width is artificially extended by the action of the orbiting optical system, and the energy per unit time is greatly reduced.

Even if the optical path length difference (that is, the optical path length of the loop optical system) is equal to or less than the pulse length, the peak position of the emission energy of each split pulsed light is sufficiently shifted in time to average the combined light. The energy, ie the energy per unit time, can be substantially reduced.
By setting the optical path length difference to, for example, a half value pulse length, the energy per unit time can be substantially reduced. Here, as shown in FIG. 2, the time when the emission intensity of the original split pulsed light is equal to or more than half the peak intensity E is defined as a half-value pulse width, and the light travels during the half-value pulse width. The distance is defined as the half value pulse length.

FIG. 4 is a diagram showing the time change of the energy of the combined pulse light when the optical path length difference is equal to the half-value pulse length. Referring to FIG. 4, the peak position of the emission energy of each split pulse light is located outside the half value pulse width of the adjacent pulse light. Thus, even when the optical path length difference is equal to the half-value pulse length, the energy per unit time can be greatly reduced.

The energy of each split pulsed light split by the half mirror 10 is the half mirror 1 for the pulsed light.
It depends on a reflectance of 0. As described above, the semi-transmissive film of the half mirror 10 is composed of a dielectric multilayer film, and the absorption loss and the scattering loss are negligible and can be ignored. Therefore, assuming that the reflectance of the half mirror 10 is R, the transmittance T is expressed as T = 1−R.

The energy of each split pulse light is
It is represented by the following formulas (1) to (4). E1 = E.R (1) E2 = E. (1-R). (1-R) (2) E3 = E. (1-R) .R. (1-R) (3) En = E. (1-R) / R ^(n-2) / (1-R) (4)

Here, E: energy of the original pulsed light split by the half mirror 10 E1: energy of split pulsed light reflected first by the half mirror 10, that is, energy of the first pulsed light E2: 1 round optical system Energy E3 of divided pulsed light, that is, second pulsed light emitted from the half mirror 10 after the orbit, E3: Energy of divided pulsed light, that is, third pulsed light emitted from the half mirror 10 after two turns of the orbiting optical system En: Orbital Energy of the divided pulse emitted from the half mirror 10, that is, the energy of the n-th pulsed light after (n-1) rounds of the optical system

In this case, depending on the reflectance R of the half mirror 10, the energy E1 of the first pulsed light and the energy E2 of the second pulsed light become maximum. Therefore, in order to make the maximum value of the emission intensity of each split pulsed light in the combined light as small as possible, the reflection of the half mirror 10 is made so that the energy E1 of the first pulsed light and the energy E2 of the second pulsed light become substantially equal. It is desirable to set the rate R. That is, E · R = E · (1-R) · (1-R)
So that the reflectance R of the half mirror 10 is 0.3.
It is preferably set to 82. When the reflectance R of the half mirror 10 is 0.382, the ratio of the energy En of each divided pulsed light to the energy E of the original pulsed light is expressed by the following equations (5) to (9).

First pulsed light E1 / E = 38.2% (5) Second pulsed light E2 / E = 38.2% (6) Third pulsed light E3 / E = 14.6% (7) Fourth pulsed light E4 / E = 5.6% (8) Fifth pulsed light E5 /E=2.1% (9)

However, since there is a manufacturing error or fluctuation in the transmittance of the half mirror, the energy of the first pulsed light and the second pulsed light
It is difficult to make the energy of pulsed light exactly equal. Therefore, the energy E1 of the first pulsed light and the second energy
The minimum condition is that the energy E2 of the pulsed light is 50% or less of the original energy E of the pulsed light, and the following conditional expressions (10) and (11) may be set. E ・ R <0.5E (10) E ・ (1-R) ・ (1-R) <0.5E (11)

More specifically, the reflectance R of the half mirror 10 that satisfies the conditional expressions (10) and (11) satisfies the following conditional expression (12). 29.3% <R <50% (12)

Although the pulsed light from the laser light source is linearly polarized light in the first embodiment, it may be non-polarized light, circularly polarized light or random polarized light. However, in the case of non-polarized light, circularly polarized light, or random polarized light, it is desirable that the reflectance of the half mirror for S-polarized light and the reflectance of the half mirror for P-polarized light be equal. When the reflectance of the half mirror for S-polarized light and the reflectance of the half mirror for P-polarized light are different, if the average reflectance of the reflectance for S-polarized light and the reflectance for P-polarized light satisfies conditional expression (12), they are almost equal. The effect of can be obtained. In this case, the ratio of S-polarized light and P-polarized light in the first pulsed light, and S in the second pulsed light
Although the ratio of the polarized light and the P-polarized light will be different, the action and effect of the present invention will not be impaired.

FIG. 5 is a schematic view showing the arrangement of a pulse width expansion optical system according to the second embodiment of the present invention. The pulse width expansion optical system of the second embodiment has a configuration similar to that of the first embodiment, but the transmission and reflection actions of the half mirrors constituting the light splitting means and the light combining means are opposite to those of the first embodiment. . The second embodiment will be described below, focusing on the differences from the first embodiment.

In the pulse width expansion optical system shown in FIG. 5, the pulsed light emitted from the laser light source 1 enters a half mirror 20 having a semi-transmissive film made of a dielectric multilayer film,
It is divided into reflected light and transmitted light. Half mirror 20
The light that has been transmitted the next time becomes split pulse light and proceeds to the right side in the figure. On the other hand, the light reflected by the half mirror 20 for the first time becomes split pulse light and is reflected by the mirrors 21, 22, 23.
And the half mirror 20 after being sequentially reflected by 24.
Re-enters.

The light reflected by the half mirror 20 for the second time among the lights re-incident on the half mirror 20 is combined along the same optical path as the light transmitted through the half mirror 20 for the first time. In addition, of the light that has re-entered the half mirror 20, the light that has passed through the half mirror 20 for the second time is sequentially reflected by the mirrors 21, 22, 23, and 24, and thereafter,
The light enters the half mirror 20 again.

Of the light that has re-entered the half mirror 20, the light reflected by the half mirror 20 for the third time is the light that has passed through the half mirror 20 for the first time and the half mirror 20.
At the second time, the light is combined along the same optical path as the light reflected at the second time. In this way, the light components transmitted through the half mirror 20 after the second time orbit the same optical path via the mirrors 21, 22, 23 and 24. In this way, the orbiting optical path formed by the four mirrors (21 to 24) and the half mirror 20 has four mirrors (2
1 to 24), and the four mirrors (21 to 24) function as optical path length difference providing means. Therefore, assuming that the optical path length of the circulating optical path is L and n is an integer of 2 or more, the split light passing through the half mirror 20 n times passes the optical path with respect to the split light passing through the half mirror 20 (n−1) times. A length difference L is given. Then, the light component transmitted through the half mirror 20 after the second time is gradually attenuated by the amount of the light reflected by the half mirror 20 for each orbit,
Eventually, all the light will be reflected by the half mirror 20. Therefore, if the reflectances of the mirrors 21, 22, 23, and 24 are 100%, no light amount loss occurs in principle.

In the second embodiment, the transmission and reflection actions of the half mirror 20 are completely opposite to those in the first embodiment. Therefore, in the second embodiment, the transmittance T of the half mirror 20 at which the energy of the first pulsed light and the energy of the second pulsed light are substantially equal to each other is the same as the energy of the first pulsed light in the first embodiment. The reflectance R of the half mirror 10 such that the energies of the two pulsed lights are almost equal
be equivalent to. That is, the energy of the first pulsed light and the second pulsed light
The transmittance T of the half mirror 20 may be set to 38.2% in order to make the energy of the pulsed light substantially equal.

Similarly, in order to set the energy E1 of the first pulsed light and the energy E2 of the second pulsed light to 50% or less of the energy E of the original pulsed light, the transmittance T of the half mirror 20 is set as follows. It suffices to construct it so as to satisfy the conditional expression (13). 29.3% <T <50% (13) When the pulsed light from the laser light source 1 is unpolarized light, circularly polarized light or random polarized light, as in the first embodiment, the transmittance for S-polarized light and P If the average transmittance with respect to the polarized light satisfies the above conditional expression (13), almost the same effect can be obtained.

FIG. 6 is a schematic view showing the arrangement of a pulse width expansion optical system according to the third embodiment of the present invention. In the first and second embodiments, the light splitting means and the light combining means are configured by one half mirror, whereas in the third embodiment, the light splitting means and the light combining means are each configured by one polarization beam splitter. are doing. Hereinafter, the third embodiment will be described while paying attention to the difference between the first embodiment and the second embodiment.
An embodiment will be described.

In the pulse width expansion optical system of FIG. 6, the pulsed light emitted from the laser light source 1 is split into P polarized light and S polarized light by the polarization beam splitter 30.
That is, the P-polarized split pulse light that has passed through the polarization beam splitter 30 further passes through the polarization beam splitter 33. On the other hand, the S-polarized split pulse light reflected by the polarization beam splitter 30 is reflected by the mirrors 31 and 3
After being sequentially reflected at 2, the light enters the polarization beam splitter 33.

S incident on the polarization beam splitter 33
The polarized split pulse light is reflected by the polarization beam splitter 33, and is combined along the same optical path as the P-polarized split pulse light transmitted through the polarization beam splitter 33. In this way, the polarization beam splitter 30 constitutes a light splitting means for splitting pulsed light along a plurality of optical paths. Further, the polarization beam splitter 33 constitutes a light combining means for combining the split pulse lights along a plurality of optical paths along the same optical path. The two mirrors (31, 32) pass through the polarization beam splitter 30 and enter the polarization beam splitter 33, and the two mirrors (31, 32) reflect the polarization beam splitter 30 and pass through the two mirrors (31, 32). Then polarization beam splitter 3
It functions as an optical path length difference giving means for giving a predetermined optical path length difference to the optical path of the light traveling toward the optical path 3.

Between the P-polarized split pulse light passing through the polarization beam splitters 30 and 33 and the S-polarization split pulse light passing through the polarization beam splitter 30, the mirrors 31 and 32, and the polarization beam splitter 33. Has a predetermined optical path length difference. As mentioned above, if this optical path length difference is set larger than the pulse length,
In the combined light, the two split pulse lights do not overlap in time. Further, as described above, the energy per unit time of the combined light can be greatly reduced also by setting the optical path length difference to, for example, the half value pulse length.

In the third embodiment, unlike the first and second embodiments in which the loop optical system is present, the original pulsed light is only divided after being divided along the two optical paths and then combined. Therefore, if the original pulsed light, such as non-polarized light, circularly polarized light, or randomly polarized light, is a light whose P-polarized component and S-polarized component are always the same with respect to the polarization beam splitter, the two split light beams are split. The energy of the pulsed light is about 50% of the energy of the original pulsed light.

On the other hand, when the original pulsed light is linearly polarized light or elliptically polarized light, the P polarized light component and the S polarized light component are not always equal to each other with respect to the polarization beam splitter. Therefore, it is preferable to arrange the polarization axis of the polarization beam splitter so that the intensity of the two split pulsed lights is almost equal. That is, when the original pulsed light is linearly polarized light and its polarization direction is vertical or parallel to the paper surface of FIG. 6, it is desirable to arrange the polarization axis of the polarization beam splitter at approximately 45 degrees with respect to the paper surface.

In the third embodiment, half mirrors may be used instead of the polarization beam splitters 30 and 33. However, in this case, in the half mirror (corresponding to the polarization beam splitter of reference numeral 33) that constitutes the light combining means, a light amount loss occurs due to the leakage of light downward in the drawing.

FIG. 7 is a schematic view showing the arrangement of a pulse width expansion optical system according to the fourth embodiment of the present invention. The pulse width expansion optical system of the fourth embodiment has a similar configuration to that of the first embodiment, but basically differs from the first embodiment only in that a wave plate 41 is attached in the optical path of the circular optical system. To do. Less than,
The fourth embodiment will be described, focusing on the differences from the first embodiment.

The pulse-width expanding optical system shown in FIG. 7 is provided with a laser light source 1 which emits pulsed light of substantially linear polarization. The pulsed light from the laser light source 1 is P-polarized light having a polarization direction parallel to the paper surface of FIG.
The P-polarized pulsed light emitted from the laser light source 1 enters the half mirror 40 and is split into reflected light and transmitted light. The light reflected by the half mirror 40 for the first time becomes split pulse light, enters the mirror 14, and is reflected on the right side in the drawing. On the other hand, the light transmitted through the half mirror 40 for the first time becomes split pulse light, which is sequentially reflected by the mirrors 11 and 12 and then enters the ½ wavelength plate 41.

The half-wave plate 41 is made of quartz whose crystal axis forms an angle of 45 degrees with respect to the paper surface. Therefore, the half-wave plate 41 serves to rotate the polarization direction of light passing through the circular optical system by 90 degrees. That is, the P-polarized light is converted into the S-polarized light and the S-polarized light is converted into the P-polarized light each time the light passes through the half-wave plate 41. Therefore, the split pulsed light converted into S-polarized light via the half-wave plate 41 enters the half mirror 40 again.

Of the light that has re-entered the half mirror 40, the light that has passed through the half mirror 40 for the second time is combined along the same optical path as the light that has been reflected by the half mirror 40 for the first time. Further, of the light that has re-entered the half mirror 40, the light that has been reflected by the half mirror 40 for the second time is sequentially reflected by the mirrors 11 and 12, and then enters the half-wave plate 41. The split pulse light converted into P-polarized light via the half-wave plate 41 enters the half mirror 40 again.

Of the light that has re-entered the half mirror 40, the light that has passed through the half mirror 40 for the third time is the light that has been reflected by the half mirror 40 for the first time, and the half mirror 40.
Is combined along the same optical path as the light transmitted through the second time. Thus, the light components reflected by the half mirror 40 from the second time onward are reflected by the mirrors 11, 12, the half-wave plate 41,
And the same optical path through the mirror 13. Then, the polarization state of the light component reflected by the half mirror 40 after the second time alternates between the P-polarized light and the S-polarized light for each circulation, and is gradually attenuated by the amount of the light transmitted through the half mirror 40. Finally, all the light will pass through the half mirror 40.

The energy of each split pulsed light split by the half mirror 40 is the half mirror 4 for the pulsed light.
It depends on a reflectance of 0. That is, assuming that the reflectance of the half mirror 40 for P-polarized light is Rp and the reflectance of the half mirror 40 for S-polarized light is Rs, the first pulsed light
The energies E1 to E3 of the third pulsed light are calculated by the following equation (1
It is represented by 4) to (16).

E1 = E.Rp (14) E2 = E. (1-Rp). (1-Rs) (15) E3 = E. (1-Rp) .Rs. (1-Rp) (16)

In the third embodiment, the polarization direction of the split pulsed light is alternately changed via the half-wave plate 41 provided in the optical path of the circular optical system, whereby the energy E1 of the first pulsed light and , The energy E2 of the second pulsed light and the energy E3 of the third pulsed light can be made substantially equal. When the energies of the respective pulsed lights represented by the formulas (14) to (16) are equal to each other, the reflectance Rp of the half mirror 40 for P-polarized light is 29.3%, and the reflectance Rs of the half mirror 40 for S-polarized light is Rs. Is 58.6%
Becomes

In this case, the energy E of the three pulsed lights
1 to E3 are about 29.3 of the energy E of the original pulsed light.
%. As described above, in the fourth embodiment, the energies E1 and E2 of the two split pulsed lights are optimized to be about 38.2% of the energy E of the original pulsed light, as compared with the first embodiment. It is possible to further reduce the energy per pulsed light.

Further, as described above, considering the error of the reflectance of the half mirror 40, it is necessary that the energies E1 to E3 of the three pulsed lights be about 40% or less of the energy E of the original pulsed light. As the condition, the following conditional expression (17) ~
It can also be configured to satisfy (19).

E.Rp <0.4E (17) E. (1-Rp). (1-Rs) <0.4E (18) E. (1-Rp) .Rs. (1-Rp) <0 .4E (19) When the pulsed light from the laser light source 1 is S-polarized light having a polarization direction perpendicular to the paper surface, Rp and Rs in the above formulas (14) to (19) are exchanged. You can think about it.

FIG. 8 is a schematic view showing the arrangement of a pulse width expansion optical system according to the fifth embodiment of the present invention. The pulse-width expanding optical system of the fifth embodiment has a configuration similar to that of the second embodiment of FIG. 5, but is basically the same as the second embodiment except that a wave plate 51 is provided in the optical path of the circular optical system. Differently.
That is, in the fifth embodiment, as in the fourth embodiment, the first
~ The energies E1 to E3 of the third pulsed light can be made substantially equal to each other. The fifth embodiment will be described below, focusing on the differences from the second and fourth embodiments.

In the fifth embodiment, when the pulsed light from the laser light source 1 is P-polarized light having a polarization direction parallel to the paper surface, the reflectances Rp and R in the fourth embodiment are set.
It suffices to replace s with the transmittances Tp and Ts, respectively. Therefore, when the transmissivity Tp of the half mirror 50 for P-polarized light is 29.3% and the transmissivity Ts of the half mirror 50 for S-polarized light is 58.6%, the energies E1 to E3 becomes equal to each other. When the pulsed light from the laser light source 1 is S-polarized light having a polarization direction perpendicular to the paper surface, the transmissivities Tp and Ts of the half mirror 50 may be exchanged.

FIG. 9 is a schematic view showing the arrangement of a pulse width expansion optical system according to the sixth embodiment of the present invention. The pulse width expansion optical system of the sixth embodiment has a configuration similar to that of the second embodiment of FIG. 5, but a Keplerian relay optical system (61, 62) is additionally provided in the optical path of the loop optical system. Only the difference from the second embodiment is basically the same. The sixth embodiment will be described below, focusing on the differences from the second embodiment.

In the pulse width expansion optical system of FIG. 9, a Kepler type relay optical system (61, 62) additionally provided in the optical path of the loop optical system is a half mirror 2 as a light splitting means.
The division surface of 0 and the combining surface of the half mirror 20 as the light combining means are configured to be substantially conjugate. When a light source with a large divergence angle, such as an excimer laser, is used as the laser light source 1, in the second embodiment of FIG. 5, as the number of times through the orbiting optical system increases, the beam blur due to the divergence angle increases as the number of split pulse lights increases. To do.

FIG. 10 is a diagram schematically showing how, in the second embodiment of FIG. 5, the larger the number of times of splitting pulsed light passing through the circular optical system, the greater the blurring of the beam due to the divergence angle. FIG. 10 shows the first pulsed light, the second pulsed light, and the third pulsed light when they are combined in the half mirror 20.
The cross-sectional shape of the beam intensity of the pulsed light is shown. As shown in FIG. 10, in the second embodiment of FIG. 5, it is understood that the beam cross-sectional shape of each divided pulsed light gradually changes when combining the plurality of divided pulsed lights in the half mirror 20.

In the pulse width extension optical system of the sixth embodiment of FIG. 9, since the Keplerian relay optical system (61, 62) is provided in the optical path of the circular optical system, the number of times through the circular optical system is increased. However, the divergence angle does not increase the beam blur. In the sixth example, since the magnification of the relay optical system (61, 62) is -1, the first pulsed light and the second pulsed light are relatively rotated by 180 degrees and combined. It That is, the odd-numbered pulse light and the even-numbered pulse light are relatively rotated by 180 degrees and are combined.

Therefore, even when the excimer laser light source 1 emits pulsed light having a beam cross-sectional shape with poor symmetry as shown in FIG. 11, odd-numbered pulsed light and even-numbered pulsed light are emitted as shown in FIG. The pulsed light is rotated by 180 degrees and combined. As described above, in the sixth embodiment, by the action of the relay optical system (61, 62) that configures the split surface of the half mirror 20 and the composite surface of the half mirror 20 to be substantially conjugate and has a magnification of −1 times, It is possible to avoid an increase in the blur of the beam due to the divergence angle and improve the beam cross-sectional shape of the combined light to be almost symmetrical.

In the sixth embodiment of FIG. 9, the optical path connecting the laser light source 1 and the half mirror 20 and the mirror 2 are connected.
2 and the optical path connecting the mirror 23 are configured to intersect with each other. However, when the intersection of the optical paths is not desirable, the mirrors 21, 22, 23, 2
It is also possible to avoid the intersection of the optical paths by arranging the surface including 4 and the relay optical system (61, 62) along the direction perpendicular to the paper surface, for example. The magnification of the relay optical system is preferably set to 1 or -1. Further, since the converging point is formed at the intermediate point of the relay optical system, it is necessary to prevent the damage by configuring the optical element so as to be sufficiently away from the converging point.

FIG. 13 is a diagram schematically showing the construction of a pulse width expansion optical system according to the seventh embodiment of the present invention. Seventh
The pulse width expansion optical system of the embodiment has a configuration similar to that of the first embodiment of FIG. 1, except that a Keplerian relay optical system (70, 71) is additionally provided in the optical path of the loop optical system. It is basically different from the first embodiment. Therefore, in the seventh embodiment, similarly to the sixth embodiment, the relay optical system (70, 71) in which the dividing surface of the light dividing means and the combining surface of the light combining means are configured to be substantially conjugate with each other and which has a magnification of -1 times. ),
While avoiding an increase in beam blur due to the divergence angle,
The beam cross-sectional shape of the combined light can be improved to be almost symmetrical.

FIG. 14 is a schematic view showing the arrangement of a pulse width expansion optical system according to the eighth embodiment of the present invention. 8th
The pulse width expansion optical system of the embodiment has a configuration similar to that of the third embodiment of FIG. 6, but a Kepler-type relay optical system (80, 80 is provided in the optical path having the longer optical path length of the two divided optical paths).
81) is basically different from the third embodiment only. Therefore, in the eighth embodiment, similarly to the sixth and seventh embodiments, the relay optical system in which the dividing surface of the light dividing means and the combining surface of the light combining means are substantially conjugate to each other and has a magnification of -1 times. By the action of the system (80, 81), it is possible to avoid an increase in the blur of the beam due to the divergence angle, and to improve the beam cross-sectional shape of the combined light substantially symmetrically.

FIG. 15 is a schematic view showing the arrangement of an exposure apparatus having a pulse width expansion optical system according to the ninth embodiment of the present invention. In the exposure apparatus of the ninth embodiment, an excimer laser light source (ArF excimer laser light source) 6 is used as a pulsed light source that emits pulsed light with a wavelength of 193 nm.
0 is provided. The pulsed light emitted from the excimer laser light source 60 is a Kepler-type relay optical system (91, 9).
The light enters the half mirror 20 via 2). The relay optical system (91, 92) is an excimer laser light source 6
The laser emission port of 0 and the split surface of the half mirror 20 are substantially conjugate with each other.

Further, a Keplerian relay optical system (91,
The magnification 92) is regulated to an appropriate magnification according to the beam cross-sectional shape of the pulsed light from the light source 60 and the size of the half mirror 20. Therefore, even if the light source 60 causes an angle deviation with respect to the optical axis of the relay optical system (91, 92), the pulsed light from the light source 60 can be accurately guided to the half mirror 20.

The pulsed light incident on the half mirror 20 is
Similar to the pulse width expansion optical system of the sixth embodiment of FIG. 9, the pulsed light transmitted through the half mirror 20 and the half mirror 20
It is split into pulsed light that is reflected by and guided to the orbiting optical system. The pulsed light guided to the orbiting optical system is reflected by the mirror 21,
22, 23, 24, Kepler type relay optical system (93,
94) and enters the half mirror 20 again. Thus, as described above, the lights reflected back to the half mirror 20 are sequentially combined along the same optical path. In addition,
The Kepler-type relay optical system (93, 94) has a magnification of -1 and optically conjugates the split surface of the half mirror 20 as the light splitting means and the synthetic surface of the half mirror 20 as the light synthesizing means. Is configured.

As described above, the Keplerian relay optical system (91, 92), the half mirror 20, the mirrors 21, 2 are used.
2, 23, 24, and Kepler type relay optics (9
3, 94) constitutes a pulse width expansion optical system for artificially expanding the emission time of the pulsed light from the light source 60. Also in the pulse width expansion optical system of the exposure apparatus of FIG. 15, the effect of the relay optical system (93, 94) can prevent an increase in the blur of the beam due to the divergence angle of the laser light. Further, even when the pulsed light from the laser light source 60 has a beam cross-sectional shape with poor symmetry, the beam cross-sectional shape of the combined light can be improved to be substantially symmetrical.

As described above, by setting the optical path length of the orbiting optical system larger than, for example, the half-value pulse length, the pulse width can be substantially extended and the average energy within the light emission time can be reduced. it can. As a result, it is possible to avoid performance degradation of the illumination optical system after the pulse width expansion optical system and maintain sufficient durability against laser irradiation.

The pulsed light combined along the same optical path through the half mirror 20 is relayed by a Kepler type relay optical system (95, 96), and then beam-shaped by, for example, a cylindrical lens and a spherical lens. It is incident on the optical system 2. The light shaped into the beam cross-sectional shape according to the shape of the fly-eye lens 3 via the beam-shaping optical system 2 enters the fly-eye lens 3. The fly-eye lens 3 is composed of many lens elements arranged in parallel along the optical axis of the illumination optical system. The light flux incident on the fly-eye lens 3 is divided into a plurality of light fluxes, and a plurality of light source images (secondary light sources) are formed at the rear focal position of the fly-eye lens 3.

The half mirror 20 and the incident surface of the fly's eye lens 3 are formed substantially conjugate with each other by the beam shaping optical system 2. Therefore, even if there is a slight angle difference between the emission direction of the combined pulse light formed via the half mirror 20 and the optical axis of the illumination optical system, all the combined pulse light is incident on the fly-eye lens 3. It is possible to accurately lead to the surface. When the beam shaping optical system 2 includes a cylindrical lens, Japanese Patent Application No. 7-5
As disclosed in the 3579 specification and drawings,
It is desirable that the half mirror 20 and the incident surface of the fly-eye lens 3 be configured to be substantially conjugate in both the vertical direction and the horizontal direction.

Light fluxes from a plurality of secondary light sources are transmitted through the aperture stop 4
After being limited by the condenser lens 5, the light is condensed by the condenser lens 5, and the mask 6 is uniformly illuminated in a superimposed manner through the bending mirror 98. A very fine pattern such as a semiconductor integrated circuit is drawn on the mask 6. The pattern of the mask 6 is reduced or enlarged and projected onto the wafer 8 via the projection optical system 7, and the resist applied on the wafer 8 is exposed. In this way, the light source 60, the pulse width expansion optical system, the relay optical system (95, 96), the beam shaping optical system 2, the fly-eye lens 3, the aperture stop 4, the condenser lens 5, and the folding mirror 98 are provided with the mask 6. An illumination optical system for illuminating substantially uniformly is configured.

As described above, the exposure process (photolithography process) by the exposure apparatus shown in FIG. 15 includes a mask setting process of setting the mask 6 on the object plane of the projection optical system 7 and an image of the projection optical system 7. Wafer 8 as a photosensitive substrate on the surface
After the substrate setting step for setting and the step for setting the mask 6 and the wafer 8, the illumination optical system illuminates the mask 6, and the pattern of the mask 6 is projected and transferred onto the wafer 8 via the projection optical system 7. And a transfer step.

Then, the wafer 8 which has undergone the exposure process (photolithography process) by the exposure apparatus shown in FIG.
After the developing step, an etching step of removing a portion other than the developed resist, a resist removing step of removing unnecessary resist after the etching step, and the like. Then, the steps of exposure, etching, and resist removal are repeated to complete the wafer process. After that, when the wafer process is completed, in the actual assembling process, dicing is performed to cut the wafer into chips for each printed circuit, bonding for providing wiring to each chip, and packaging for each chip. Finally, a semiconductor device such as an LSI is manufactured through each step. Although an example of manufacturing a semiconductor device such as an LSI by a photolithography process in a wafer process using an exposure apparatus has been described above, a liquid crystal display element, a thin film magnetic head are manufactured by a photolithography process using an exposure apparatus. Semiconductor devices such as image pickup devices (CCD, etc.) can also be manufactured.

Although the beam shaping optical system 2 is arranged immediately before the fly-eye lens 3 in the ninth embodiment of FIG. 15, the position of the beam shaping optical system 2 is not limited to this. As described above, as long as the conjugate relationship among the light source 60, the half mirror 20, and the fly-eye lens 3 is satisfied, for example, immediately after the laser light source 60 or in the half mirror 2.
It is also possible to arrange the beam shaping optical system 2 in the optical path between 0 and the lens 95 of the relay optical system (95, 96).

When the projection optical system 7 is composed of a plurality of refractive lenses, it is possible to prevent the influence of the chromatic aberration of the projection optical system 7 and expose a good mask pattern image on the wafer 8 as a photosensitive substrate. Is a narrowing means (etalon, diffraction grating, etc.) for making the wavelength width of the light output from the excimer laser light source 60 10 pm or less.
It is preferable to provide it inside or on the emission side of the excimer laser light source 60. An injection rocking type excimer laser light source can also be used as the light source provided with the narrowing means. Particularly, when the projection optical system 7 is composed of a plurality of quartz lenses, the wavelength width (narrowing width) of the light output from the light source 60 such as an ArF excimer laser should be 1 pm or less. It is preferable that the band is narrowed, and more preferably, the width of the band is 0.5 pm or less.

When the projection optical system 7 is composed of a mixture of a quartz lens and a fluorite lens, the light output from the light source 60 such as an ArF excimer laser has a narrow wavelength band of 3 pm or less. The width of the narrowed band is preferably 1.5 pm or less. When the projection optical system 7 is composed of a mixture of a reflective member such as a mirror and a refractive lens, the wavelength width of the light output from the light source 60 such as an ArF excimer laser is preferably 10 pm or less, More preferably, the width of narrowing is set to 5 pm or less.

As described above, by making the narrowed light incident on the pulse width expansion optical system, it is possible to expose a good mask pattern image on the photosensitive substrate while avoiding the deterioration of the optical characteristics of the exposure apparatus. it can. In the above example,
Although an example in which a mirror is mainly used as the optical path length difference giving means is shown, the invention is not limited to this, and for example, a transparent optical member such as a plane parallel plate is arranged in the split optical path as the optical path length difference giving means. May be. Further, at least one mirror in the optical path length difference providing means can be configured to be movable to make the optical path length difference variable.

Further, as the exposure apparatus shown in FIG.
Not only the so-called step-and-repeat method in which the pattern on the mask 6 is collectively exposed in one shot area on the wafer 8, but the mask 6 is illuminated by an illumination optical system under an arc-shaped or slit-shaped illumination area. However, a method in which a mask stage holding the mask 6 and a substrate stage holding the wafer are moved during exposure to perform scanning exposure may be used.

[0079]

As described above, according to the present invention, the energy per unit time can be reduced by artificially extending the emission time of pulsed light, so that the performance of the optical system can be prevented from deteriorating. be able to. Particularly, in the exposure apparatus, it is possible to satisfactorily form a fine pattern while avoiding the deterioration of the imaging performance of the projection optical system due to laser irradiation. Therefore, a good semiconductor device can be manufactured using this exposure apparatus.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a pulse width expansion optical system according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing a temporal change in energy of pulsed light emitted from the laser light source of FIG.

FIG. 3 is a diagram showing a change over time in energy of combined pulsed light composed of a plurality of divided pulsed lights that do not overlap with each other in terms of time.

FIG. 4 is a diagram showing a change over time in energy of combined pulse light when the optical path length difference is equal to the half-value pulse length.

FIG. 5 is a diagram schematically showing a configuration of a pulse width expansion optical system according to a second embodiment of the present invention.

FIG. 6 is a diagram schematically showing the configuration of a pulse width expansion optical system according to a third embodiment of the present invention.

FIG. 7 is a diagram schematically showing a configuration of a pulse width expansion optical system according to a fourth example of the present invention.

FIG. 8 is a diagram schematically showing a configuration of a pulse width expansion optical system according to a fifth example of the present invention.

FIG. 9 is a diagram schematically showing the configuration of a pulse width expansion optical system according to a sixth embodiment of the present invention.

FIG. 10 is a diagram schematically showing how, in the second embodiment of FIG. 5, the larger the number of times of split pulse light passing through the circular optical system, the greater the blur of the beam due to the divergence angle.

FIG. 11 shows an excimer laser light source 1 in the sixth embodiment.
FIG. 6 is a diagram showing a beam cross-sectional shape with poor symmetry of the pulsed light emitted by the laser.

FIG. 12 is a diagram schematically showing how odd-numbered pulse light and even-numbered pulse light are rotated by 180 degrees and combined in the sixth embodiment.

FIG. 13 is a diagram schematically showing a configuration of a pulse width expansion optical system according to a seventh example of the present invention.

FIG. 14 is a diagram schematically showing a configuration of a pulse width expansion optical system according to an eighth example of the present invention.

FIG. 15 is a view schematically showing the arrangement of an exposure apparatus having a pulse width expansion optical system according to the ninth embodiment of the present invention.

FIG. 16 is a diagram schematically showing a configuration of a conventional exposure apparatus including a pulse laser light source.

[Explanation of symbols]

 1 Laser Light Source 2 Beam Shaping Optical System 3 Fly Eye Lens 4 Aperture Stop 5 Condenser Lens 6 Mask 7 Projection Optical System 8 Wafer 9 Mirror 10 Half Mirror 11-14 Mirror 20 Half Mirror 21-24 Mirror 30, 33 Polarizing Beam Splitter 31, 32 mirror 41, 51 1/2 wavelength plate 50 half mirror 60 excimer laser light source 61, 62 Kepler type relay optical system

Claims (13)

[Claims] 1. A pulse width expansion optical system for artificially expanding the light emission time of pulsed light, comprising: light splitting means for splitting the pulsed light along a plurality of optical paths; and splitting along the plurality of optical paths. And a light combining means for combining the pulsed light along the same optical path, and the intensity of the combined pulsed light combined along the same optical path is divided into the original pulsed light along the plurality of optical paths. The pulse width extension optical system, wherein the plurality of optical paths have a predetermined optical path length difference so as to be substantially smaller than the intensity. 2. The predetermined optical path length difference is such that the emission intensity is 1/2 of the peak intensity within the emission time of the original pulsed light.
The pulse width extension optical system according to claim 1, wherein the pulse width extension optical system is larger than the product of the above time and the speed of light. 3. The optical path length difference giving means for giving the predetermined optical path length difference is provided on at least one optical path split by the light splitting means. The pulse width extension optical system according to. 4. A relay optical system is provided in at least one optical path of the plurality of optical paths so as to configure the split surface of the light splitting means and the synthetic surface of the light combining means substantially in a conjugate manner. The pulse width expansion optical system according to any one of claims 1 to 3, wherein 5. The plurality of optical paths comprises two optical paths,
The pulse width expansion optical system according to claim 1, wherein the light splitting means and the light combining means are the same optical element. 6. An exposure apparatus comprising an illumination optical system for illuminating a mask on which a pattern is formed substantially uniformly, wherein the exposure apparatus forms an image of the pattern formed on the mask on a photosensitive substrate. Includes a light source for pulsed light emission, and a pulse width extension optical system for artificially extending the emission time of the pulsed light from the light source, wherein the pulse width extension optical system directs the pulsed light to a plurality of optical paths. A light splitting means for splitting along the light paths, and a light synthesizing means for synthesizing split pulse lights along the plurality of light paths along the same light path, and a synthesized pulse synthesized along the same light path. The exposure apparatus is characterized in that the plurality of optical paths have a predetermined optical path length difference from each other so that the intensity of the light is substantially smaller than the intensity of the original pulsed light split along the plurality of optical paths. . 7. The multi-light source image forming means for forming a large number of light source images on the basis of the combined pulsed light formed via the pulse width expansion optical system, and the multi-light source image forming means. 7. The exposure apparatus according to claim 6, further comprising a condensing optical system that condenses light beams from a large number of light source images formed by the means to illuminate the mask in a superimposed manner. 8. The optical path length difference giving means for giving the predetermined optical path length difference is provided in at least one optical path divided by the light dividing means. The exposure apparatus according to. 9. The predetermined optical path length difference is such that the emission intensity is 1/2 of the peak intensity within the emission time of the original pulsed light.
9. The exposure apparatus according to claim 6, wherein the exposure apparatus is larger than the product of the above time and the speed of light. 10. A relay optical system is provided in at least one optical path of the plurality of optical paths so as to optically configure a division surface of the light dividing means and a combining surface of the light combining means to be conjugate with each other. 10. The method according to claim 6, wherein
The exposure apparatus according to any one of the above items. 11. The optical path according to claim 6, wherein the plurality of optical paths include two optical paths, and the light splitting means and the light combining means are the same optical element. Exposure equipment. 12. The multi-light source image forming means is a fly-eye lens including a plurality of lens elements arranged in parallel along an optical axis of the illumination optical system, and an incident surface of the fly-eye lens and the light combining means. The exposure apparatus according to any one of claims 7 to 11, characterized in that the exposure surface is positioned substantially conjugate with the composite surface. 13. The method according to any one of claims 6 to 12.
A method of manufacturing a semiconductor device, comprising the step of exposing the pattern formed on the mask to a photosensitive substrate using the exposure apparatus described in the item.