JPH06181159A - Projection aligner - Google Patents

Abstract

PURPOSE:To use a pupil filter having the optimum characteristic according to a mask pattern by selecting the optimum pupil filter in a holder according to a mask to be used for pattern exposure and by exchanging a pupil filter in pupil position for the selected pupil filter. CONSTITUTION:A spatial filter (pupil filter) 23 is arranged in the pupil position of a projection optical system 14, and the predetermined pupil filter 23 is selected by the rotation of a holder 27. The bar-code information 28 of a light- source modulation filter 9 and the pupil filter 23 being optimum for the transfer of a reticule 8 is cut in the reticule 8, and information read by a read section 17 is supplied to a filter selection and operation part 26. The operation results of the operation part 26 are respectively supplied to the actuators 24, 25 of respective holders 21, 27, and the filters 9, 23 optimized for the transfer of the reticule 8 are selected respectively. The pupil surfaces 22 of the projection optical system are provided outside a projection lens group 14 and the pupil surface filter 23 can be mounted to the pupil surface 22.

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 for forming a fine resist pattern required for manufacturing a semiconductor integrated circuit, and more particularly to a projection exposure apparatus for optimizing an optical system by selecting a pupil filter.

[0002]

2. Description of the Related Art In recent years, the progress of photolithography technology has been remarkable, and there is a possibility that a 0.5 μm rule can be realized in a g-line (436 nm) or i-line (365 nm) projection exposure apparatus. This is because the projection exposure apparatus has been improved in performance, and in particular, the NA of the lens has been advanced. However, it is doubtful whether the next-generation 0.3 μm rule can be achieved with the extension so far. The resolution is improved by increasing the NA of the lens and shortening the wavelength of the exposure light, but the depth of focus is reduced, so the practical resolution is not improved so much. Therefore, development of a technique for improving the depth of focus is desired.

FIG. 6 shows a schematic structure of a projection exposure apparatus which is generally used in the past. In this figure, 1 is a mercury lamp, 2 is an elliptical reflecting mirror, 3 is an elliptical reflecting mirror 2.
2nd focal point, 4 is an input lens, 5 is an optical integrator (fly-eye lens), 6 is an output lens, 7 is a collimation lens, 8 is a reticle (mask), 9 is an aperture stop as a uniform stop, 10 is A filter for passing only light of a wavelength whose optical system is corrected for aberration, 11 and 12 are cold mirrors that bend the optical path to lower the height of the device, 13 is a lamp house, 14 is a lens, a mirror or a combination thereof. A projection optical system for projecting an image of the pattern on the reticle 8 onto a wafer, 15 a wafer, and 16 an aperture for determining the numerical aperture.

Although there are many basic structures of the conventional projection exposure apparatus other than those shown in FIG. 6, as shown schematically in FIG. 7A, the light source 1, the first condensing optical system 18, Uniformizing optical system 19, second condensing optical system 20, reticle 8, projection optical system 1
4, the wafer 15 is arranged in this order. The first condensing optical system 18 is a portion corresponding to the elliptical reflecting mirror 2 and the input lens 4 in the example of FIG. 6, and in addition to the elliptic mirror, a spherical mirror, a plane mirror, a lens, etc. are appropriately arranged, and the luminous flux emitted from the light source It has a role of putting it into the homogenizing optical system 19 as efficiently as possible.
The homogenizing optical system 19 is a portion corresponding to the optical integrator 5 in FIG. 6, and an optical fiber, a polyhedral prism, or the like may be used as the other components.

The second condensing optical system 20, which corresponds to the output lens 6 and the collimation lens 7 in FIG. 6, superimposes the light emitted from the homogenizing optical system 19 and further secures the image plane telecentricity. In addition to this, a filter corresponding to the filter 10 of FIG. 6 is inserted at a position where the light beam is parallel to the optical axis, and reflecting mirrors corresponding to the cold mirrors 11 and 12 are also inserted although the positions are not unique.

When the side of light coming from the reticle 8 is viewed in the apparatus constructed as described above, the nature of the light becomes the nature of the light coming out from the homogenizing optical system 19 through the second condensing optical system 20, The emission side of the homogenizing optical system 19 looks like an apparent light source. For this reason, in the case of the above configuration, the emission side 24 of the homogenizing optical system 19 is generally called a secondary light source. When the reticle 8 is projected onto the wafer 15, the formation characteristics of the projection exposure pattern, that is, the resolution and the depth of focus are
It depends on the numerical aperture of the projection optical system 14 and the property of the light that illuminates the reticle 8, that is, the property of the secondary light source 24.

FIG. 7B is an explanatory diagram relating to the reticle illumination light beam and the image formation light beam in the projection exposure apparatus shown in FIG. In FIG. 7B, the projection optical system 14 usually has an aperture stop 16 inside to regulate the angle θa at which the light passing through the reticle 8 can pass, and at the same time, the wafer 15
The angle θ of the light ray incident on the top is determined.

Generally, what is called the numerical aperture NA of the projection optical system is an angle defined by NA = sin θ, and when the projection magnification is 1 / m, there is a relationship of sin θa = sin θ / m. Further, in this kind of apparatus, it is usual that the "image plane telecentric", that is, the principal ray falling on the image plane is constituted perpendicularly to the image plane, and the condition of "image plane telecentric" is satisfied. A real image of the exit surface of the homogenizing optical system 19 in (a), that is, the light source surface of the secondary light source 24 is formed at the position of the aperture stop 16.

Under these conditions, the solid angle when the secondary light source surface is viewed from the reticle 8 through the second condensing optical system 20 is regarded as the range of the light incident on the reticle 8, and its half angle is φ.
Let coherency σ of illumination light be σ = sin φ / sin
When it was defined by θa, it was considered that the pattern formation characteristics could be determined by NA and σ.

Next, the relationship between NA and σ and the pattern formation characteristics will be described in detail. The larger the NA, the higher the resolution, but the shallower the depth of focus, and the aberration of the projection optical system 14 makes it difficult to secure a wide exposure area. Since there is no exposure area and depth of focus (for example, 10 mm square, ± 1 μm) to some extent, it cannot be used in actual applications such as LSI manufacturing, so that the conventional apparatus has a limit of NA = 0.35. On the other hand, the σ value mainly relates to the pattern cross-sectional shape and the depth of focus, and has a correlation with the cross-sectional shape and contributes to the resolution. Since the edge of the pattern is emphasized when the σ value becomes small, the cross-sectional shape becomes a good pattern shape with the side walls approaching the vertical,
The resolution in a fine pattern becomes poor, and the focus range that can be resolved becomes narrow. On the contrary, when the σ value is large, the resolution in a fine pattern and the focus range in which it can be resolved are slightly better, but the side wall inclination of the pattern cross section is gentle, and in the case of a thick resist, the cross-sectional shape is trapezoidal or triangular. Therefore, in the conventional projection exposure apparatus, as a relatively balanced σ value,
σ = 0.5 to 0.7 is fixedly set, and experimentally σ
= 0.3 and so on are only tried. Since the size of the light source surface of the secondary light source 24 may be determined in order to set the σ value, the circular aperture stop 9 for setting the σ value is generally placed immediately after the light source surface of the secondary light source 24.

As one method for improving the depth of focus of such a general projection exposure apparatus, a special diaphragm for inserting the intensity distribution of the secondary light source of the projection exposure apparatus so that the peripheral intensity is larger than the central intensity is inserted. There is an annular illumination exposure method (Japanese Patent Laid-Open No. 61-91662). That is, the filter shown in FIG. 8 is inserted in place of the circular aperture stop 9 for setting the σ value in FIG. The effect of improving the depth of focus obtained by the filter shown in FIG. 8A was evaluated by simulation. Figure 9
Shows the depth of focus with respect to the mask pattern size, and shows the dependence of the central blocking ratio ε of the annular illumination filter. The central shielding rate is defined as ε = r ₂ / by the outer circumferential circle radius r ₁ and the inner circumferential circle radius r ₂ of the ring filter shown in FIGS.
It is represented by r ₁ . The exposure apparatus has an NA of 0.54, a coherence factor of 0.5, and an exposure wavelength of 436 nm (g line). It can be seen that the larger the ε, the greater the effect of improving the limit resolution and the depth of focus.

As another method for improving the depth of focus of the projection exposure apparatus, there is a superflex method in which a spatial frequency filter is inserted in the pupil of the projection exposure apparatus (Proceedings of the 38th Joint Lecture on Applied Physics). , 29a-ZC-
8). According to this, when the images are formed at different positions z = ± β in the optical axis direction and the amplitudes of the two images whose phases are shifted by ± Δφ are combined, (1) the depth of focus increases due to the multiple imaging (FLEX) effect. , (2) A quasi phase shift effect due to phase cancellation at the pattern edge can be obtained at the same time. The amplitude distributions in the lateral (x) direction and the optical axis (z) direction are U (x,
z), such a composite amplitude is U ′ (x, z) = [exp (iΔφ) U (x, z−β)
+ Exp (-iΔφ) U (x, z + β)] / 2

Is given by This amplitude is equal to that obtained by providing the projection lens pupil (aperture) with a spatial filter having a radial distribution of the complex amplitude transmittance represented by the following equation. t (r) = cos (2πβr ² −θ / 2), (where θ = 2Δφ−8πβ / NA ² ) By appropriately selecting β and θ, it is possible to arbitrarily control the distance between the image planes between the two images and the interference effect (or the spatial frequency transfer characteristic).

In order to improve the depth of focus of the projection exposure apparatus, as another method of mounting a spatial frequency filter on the pupil of the projection exposure apparatus, the PCL exposure method (Phase Cont
rastLithograpy) (Proceedings of the 39th Joint Lecture Meeting of the Japan Society of Applied Physics, 30p-NA-4). According to this, in order to maximize the capability of the exposure apparatus, it is necessary to go back to the imaging theory in the partially coherent optical system and determine the parameters (effective light source intensity distribution, mask amplitude transmittance distribution, pupil function) involved in imaging. A method of maximizing the depth of focus and the limiting resolution by optimizing has been proposed. The optimization method is based on a Monte Carlo algorithm called Simulated Annealing. It is used to find the global minimum (large) point when given an appropriate cost function, which sequentially finds the optimal solution.

As an example, L / S = 0.
The DOF (L / S pattern size) when the effective light source radial intensity distribution and the pupil function radial radial phase distribution are optimized so that the depth of focus at 743 (normalized dimension in λ / NA) is maximized. The resist contrast is 60%) is shown in FIG. Further, FIG. 2 shows the effective light source radial direction intensity distribution and the pupil function radial direction phase distribution at that time. L compared to normal exposure
It can be seen that the depth of focus is approximately doubled when /S≧0.743. In order to improve resolution and depth of focus, the above two technologies (super flex method, PCL exposure method)
Is becoming essential.

[0016]

As described above, when the spatial frequency filter is applied to the exposure apparatus, there are the following problems. That is, in a projection exposure apparatus equipped with a spatial frequency filter (pupil filter; a filter that changes the transmittance and the phase) used in the pupil of the projection optical system, the target pattern (pattern type and pattern size) to be formed respectively Since there are differences in the optimum effective light source radial direction intensity distribution, pupil function radial direction phase distribution, and transmittance distribution, it is not possible to always obtain the optimum distribution according to the mask pattern.

The present invention has been made in consideration of the above circumstances, and an object thereof is to use a pupil filter having an optimum characteristic according to a mask pattern, which has a high resolution and a depth of focus. An object of the present invention is to provide a projection exposure apparatus that can perform exposure in a deep state and can improve exposure accuracy.

[0018]

In order to achieve the above object, the present invention adopts the following configuration.

That is, the present invention is a projection exposure apparatus for projecting and exposing a mask pattern onto a wafer via a projection optical system, wherein the exposure light is arranged at a pupil position of the projection optical system and passes through a part of the pupil plane. And the exposure light passing through another portion, a pupil filter that causes a difference in at least one of amplitude or phase among complex amplitudes, a holder that holds a plurality of those having different characteristics of the pupil filter, and a pattern exposure Select the optimal pupil filter in the holder according to the mask used for
A filter exchanging mechanism for exchanging the selected pupil filter with a pupil filter at a pupil position. Moreover, the following are mentioned as a desirable embodiment of this invention.

(1) Interchanging the light source modulation filter (arranged at the position of the secondary light source that illuminates the mask and changing the intensity distribution in the emission surface of the light source) in conjunction with the exchange of the pupil filter. (2) An identification mark such as a bar code is formed on the mask, and each time the mask is replaced, the identification mark is recognized to automatically replace the pupil filter.

[0021]

According to the present invention, a pupil filter suitable for a desired mask pattern can be attached to the pupil position of the projection optical system of the projection exposure apparatus, so that the pupil modulation can be performed. It is possible to maximize the effect of improving the depth of focus and resolution obtained by the technology. Further, by having a structure that can be replaced with a filter that provides suitable exposure characteristics to the mask pattern in conjunction with the mask replacement, not only the exposure accuracy can be improved, but also the throughput can be improved.

[0022]

The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a perspective view showing the schematic arrangement of a projection exposure apparatus according to an embodiment of the present invention. In FIG.
1 is a lamp (light source), 2 is an elliptical reflecting mirror,
The emitted light is reflected by the cold mirror 11. Then, the light passes through the input lens 4, and further through the optical integrator (fly-eye lens) 5, and is irradiated onto the light source modulation filter 9. A plurality of light source modulation filters 9 are set in the revolver holder 21, and a predetermined filter 9 is selected by rotating the holder 21.

The light passing through the filter 9 passes through the output lens 6, is reflected by the cold mirror 12, passes through the collimation lens 7, and is applied to the reticle (mask) 8. The light passing through the reticle 8 is projected by the projection optical system lens 1
The wafer 15 is irradiated with the laser beam passing through 4. Here, the projection optical system 14 is divided into a plurality of parts, and a spatial frequency filter (pupil filter) 23 is arranged between them (at the pupil position of the projection optical system 14). A plurality of pupil filters 23 are set in the revolver type holder 27.
The predetermined filter 23 is selected by the rotation of 7.

The type of the pupil filter 23 set in the holder 27 may be selected in advance so as to be optimal for each of a plurality of mask patterns to be exposed by this apparatus.
Similarly, the type of the light source modulation filter 9 set in the holder 21 may be selected in advance so as to be optimal for each of the plurality of mask patterns to be exposed.

The reticle 8 is engraved with information (for example, bar code information 28) on the light source modulation filter 9 and the pupil filter 23, which are optimal for transferring the reticle 8, and the bar code information 28 is read by the reading section 17. To be The information read by the reading unit 17 is supplied to the filter selection calculation unit 26. The calculation result of the calculation unit 26 is obtained by each holder 21, 2.
7 are supplied to the drive units 24 and 25, respectively. As a result, the filters 9 and 23 that are most suitable for the transfer of the reticle 8 are selected.

The characteristic of this apparatus is the projection optical system, in which the pupil surface 22 of the projection optical system is provided outside the projection lens group 14, and the pupil filter 23 can be attached to this pupil surface 22. For example, if it is desired to maximize the depth of focus with the resolving power and the depth of focus required for this reticle at L / S = 0.743 (normalized dimension in λ / NA), as shown in FIG. A filter that forms the secondary light source intensity distribution and the pupil phase distribution may be attached. However, when resolving power is required up to L / S = 0.5 (normalized dimension in λ / NA) depending on the reticle, from FIG. 3, the light source modulation filter 9 and the pupil filter 23 are set to normal illumination and normal NA. It will be necessary to change to an aperture stop. Alternatively, it is desirable to replace with a light source modulation filter optimized for a desired pattern size and pattern type. In such a case, by operating the filter selection calculation unit 26, the revolver holders 21 and 27 are set to the normal exposure state or the light source modulation filter and the pupil filter optimized for each reticle.

Here, the bar code information 28 is used to obtain information about which filter is preferable for exposing the reticle 8 in advance.
If it is recorded in such a manner that the reticle is exchanged and the optimum filter is automatically exchanged at the same time, the throughput can be improved and a further effect can be expected. Further, the selection means of the suitable filter is not limited to the bar code method, but is applied to other identification methods.

Further, in the above embodiment, the revolver type was shown as the filter exchanging means, but it can be applied to various exchanging means other than those shown in FIGS.
In FIG. 4, the holder 27 that holds the pupil filter 23 is of a slide type. In FIG. 5, the holder 27 that holds the pupil filter 23 is of a magazine type that moves up and down, and a transport arm that transports the pupil filters 23 one by one is used as the drive unit 25.

As described above, according to this embodiment, the light source modulation filter 9 and the pupil filter 23 can be mounted, and the revolver type holders 21 and 27 can be used to easily replace the optimum filter for the desired mask pattern. Therefore, the effects of improving the depth of focus and the resolution obtained by the light source modulation technology and the pupil modulation technology such as the PCL exposure and the super flex method can be maximized, and the exposure accuracy can be greatly improved.

The present invention is not limited to the above embodiment. In the embodiment, both the light source modulation filter and the pupil filter are exchangeable, but only the pupil filter may be exchangeable. Further, the number of filters set in the holder is not limited to four, and can be appropriately changed according to the specifications. Further, the filter exchange mechanism is not limited to the configuration shown in FIGS. 1, 4 and 5, but can be changed as appropriate according to the specifications. In addition, various modifications can be made without departing from the scope of the present invention.

[0032]

As described above in detail, according to the present invention, the pupil filter arranged at the pupil position of the projection optical system is configured to be replaceable, and the pupil filter having the optimum characteristic according to the mask pattern is used. The exposure can be performed in a state where the resolving power is high and the depth of focus is deep, and the exposure accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a filter shape obtained as a result of optimization in the PCL exposure method.

FIG. 3 is a diagram showing DOF with respect to an L / S pattern size when the filter shown in FIG. 2 is attached.

FIG. 4 is a view showing another example of a mechanism for exchanging a light source filter and a pupil filter.

FIG. 5 is a diagram showing still another example of the replacement mechanism of the light source filter and the pupil filter.

FIG. 6 is a schematic configuration diagram showing a conventional projection exposure apparatus.

FIG. 7 is a diagram for explaining a conventional problem.

FIG. 8 is a diagram showing an example of a filter used instead of an aperture stop.

FIG. 9 is a characteristic diagram showing a relationship between a pattern size and a depth of focus in a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 4 ... Input lens 5 ... Optical integrator (fly-eye lens) 6 ... Output lens 7 ... Collimation lens 8 ... Reticle (mask) 9 ... Normal σ diaphragm or light source modulation filter 11, 12 ... Cold mirror 14 ... Projection Optical system 15 ... Wafer 17 ... Filter selection information reading unit 21 ... Holder for attaching light source modulation filter 22 ... Projection optical system pupil 23 ... Spatial frequency filter (pupil filter) 24 ... Driving unit for light source filter replacement 25 ... Pupil filter Drive unit for replacement 26 ... Filter selection calculation unit 27 ... Holder for attaching pupil filter 28 ... Bar code information

Claims (1)

[Claims] 1. A projection exposure apparatus for projecting and exposing a mask pattern onto a wafer through a projection optical system, the exposure light being arranged at a pupil position of the projection optical system, and passing through a part of the pupil plane. Of the exposure light that passes through the portion of the above-described region, a pupil filter that causes a difference in at least one of the amplitude or the phase among the complex amplitudes, a holder that holds a plurality of those having different characteristics of the pupil filter, and a pattern exposure. The projection exposure apparatus comprises a filter exchange mechanism for selecting an optimal pupil filter in the holder according to the mask to be exchanged and exchanging the selected pupil filter with the pupil filter at the pupil position.