JPH07263315A - Projection aligner - Google Patents

Abstract

PURPOSE:To always obtain the optimum oblique-incident lighting position and polarizing direction by controlling the refractive index, transmittance, and polarization of a filter so that the angle and direction of polarization of diffracted light can become equivalent to the optimum oblique-incident lighting position in accordance with the periodic direction and pitch of a mask pattern. CONSTITUTION:A reticle 5 is formed on a transparent substrate and composed of a light shielding section 10 which is made of such a light shielding material as chromium, etc., and does not transmit exposing light and an opening 11 which transmits the exposing light. The refractive index of a filter 9 electrically or optically changes in a cycle of 2D. The angle theta of diffraction of primary diffracted light can be decided from 2Dsintheta=lambda when the variation DELTAn of the refractive index and film thickness (t) of the filter 9 are adjusted. When a mask is irradiated with the diffracted light, two-flux interference is obtained on a wafer.

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 in the manufacture of semiconductor integrated circuits.

[0002]

2. Description of the Related Art In recent years, the progress of photolithography technology has been remarkable, and the wavelength of exposure light has been shortened (i line (365 nm), Kr
It has become possible to form a finer resist pattern on a wafer by improving the performance of the F-excimer laser (248 nm) and the projection exposure apparatus, especially by increasing the NA of the lens.
FIG. 3 shows a schematic configuration of a projection exposure apparatus that is generally used conventionally. The light source 1, the first condensing optical system 2, the homogenizing optical system 3, the second condensing optical system 4, the reticle 5, the projection optical system 6, and the wafer 7 are arranged in this order. The first condensing optical system 2 is a portion corresponding to an elliptical reflecting mirror and an input lens. A spherical mirror, a plane mirror, a lens, and the like other than the elliptic mirror are appropriately arranged, and the light flux from the light source is made as uniform as possible in the homogenizing optical system 3. Has a role to put in. Further, the homogenizing optical system 3 is a portion corresponding to an optical integrator (fly's-eye lens), and an optical fiber, a polyhedral prism, or the like may be used as other portions.

The second condensing optical system 4 is a portion corresponding to the output lens and the collimation lens, superimposes the light emitted from the homogenizing optical system 3, and further secures the image plane telecentricity. In addition, a filter that transmits only the wavelength for which the aberration correction is performed is inserted at a position where the light beam is parallel to the optical axis, and a cold mirror is also inserted, although the position is not unique.

When looking at the side of the reticle 5 where light comes from in the apparatus constructed as described above, the nature of the light becomes the nature of the light coming out of the homogenizing optical system 3 through the second focusing optical system 4. The emission side of the homogenizing optical system 3 looks like an apparent light source. Therefore, in the case of the above-mentioned configuration, the emitting side 8 of the homogenizing optical system 3 is generally called a secondary light source. Chickle 5
Is projected onto the wafer 7, the formation characteristics of the projection exposure pattern, that is, the resolution, the depth of focus, etc., are the numerical aperture NA of the projection optical system 6 and the nature of the light that illuminates the reticle 5, that is, the nature of the secondary light source 8. Depends on

However, if the resolution is increased by shortening the wavelength of the exposure light and increasing the NA of the projection optical apparatus to form a fine pattern on the resist, the depth of focus will be lowered, and the practical resolution will not be improved so much. Therefore, by changing the secondary light source intensity distribution, the reticle, and the complex transmittance distribution of the pupil plane of the projection optical system in the projection exposure apparatus from the conventional one,
Improvements in resolution and depth of focus are being considered.

As a means for improving the resolution, particularly LS
For a pattern having a first-order periodicity (hereinafter abbreviated as L / S) like the wiring pattern in I, as shown in FIG.
The L / S pattern is formed on the transparent substrate by using a mask formed so that the phase difference between the opening 21 of the mask 20 and the exposure light 23 passing through the adjacent opening 22 is approximately 180 degrees. It is known that the resolution is about twice as high as that of a conventional mask formed using a light-shielding substance such as chromium. A publicly known example of this type is JP-A-57-6.
2052 is mentioned.

However, in the case of using the above mask, it is generally difficult to alternate the shifters and it is difficult to make the shifters. Therefore, another method that can obtain an effect almost equal to that of the mask is obtained. Is being considered.

As one of the above-mentioned methods, as shown in FIG. 5, by illuminating from a position decentered from the optical axis 30 in the pattern cycle direction, a phase difference is provided between the lights 32 passing through the adjacent apertures 31, and the resolution is increased. Method (Japanese Patent Laid-Open No. 4-273428)
Is proposed. In this case, conventionally, the filter (σ stop) 33 is formed at the secondary light source position 9 so that the loss of the exposure light in the light shielding portion becomes large.

As a method of solving these problems, a dummy mask 40 is placed above the mask 5 as shown in FIG. 6, and the diffracted light obtained by this is used to obtain an oblique incidence effect on the mask and increase the resolution. The method of improving is proposed (1993 spring adaptation 30p-L-10). A phase shifter-only pattern is used as the dummy mask pattern, and the pattern size is twice the mask pattern size. Oblique incidence illumination is realized by illuminating the mask with the diffracted light obtained thereby. Compared to the case of realizing oblique incidence illumination at the position of the secondary light source, the loss of light amount is reduced when a dummy mask is used, and the optimum oblique incidence position can always be maintained by forming a dummy pattern corresponding to the pattern. It is possible.

However, the dummy mask proposed here is prepared by engraving or adhering a pattern on a transparent substrate, and it is difficult to form the dummy mask when it is integrated with the mask. Even when the mask is formed separately from the mask, it is necessary to replace the dummy mask each time the mask is changed.

[0011]

As described above, when the dummy mask is used, there is a problem in the process of forming the dummy mask and the actual exposure process. The above problem is as a dummy mask
Since the diffracted light is obtained by periodically changing the film thickness of the transparent substrate, one dummy mask must be produced for one pattern.

[0012]

In order to solve the above problems, according to the present invention, in a projection exposure apparatus for projecting and exposing a pattern formed on a mask onto a wafer through a projection optical system, the mask and a light source are provided. In between, a fine region is provided with a filter capable of arbitrarily changing the refractive index, the transmittance and the polarization in the region, according to the periodic direction and pitch of the mask pattern, by the filter The refractive index / transmittance and polarization are controlled electrically and optically by controlling the refractive index / transmittance and polarization of the filter so as to obtain the generated diffracted light angle, and by using an electro-optic material as the filter described above. Provided is a projection exposure apparatus, which is controlled by As the filter material, photorefractive material, liquid crystal, acousto-optic modulator (AOM)
Will be used.

[0013]

According to the present invention, by using the filter as a dummy mask, a periodic pattern having an arbitrary line width / pitch on the mask is generated by this pattern.
The refractive index / transmittance distribution of the filter is formed so that the light enters at a half of the angle formed by the second-order diffracted light and the first-order diffracted light, and the polarization direction is formed so as to be orthogonal to the periodic direction of the pattern. Therefore, it is possible to always obtain the optimum oblique incidence illumination position and polarization direction.

[0014]

EXAMPLE An example of the present invention will be described with reference to FIG. The basic structure of the projection exposure apparatus used in the present invention is the same as that of the conventional apparatus, except that a filter 9 is installed on the reticle 5 in FIG. FIG. 1 shows a basic arrangement of filters and reticles according to an embodiment of the present invention.

The reticle 5 used in this embodiment is formed on a transparent substrate by a light-shielding portion 10 made of a light-shielding material such as chromium that does not transmit exposure light and an opening 11 that transmits exposure light. . As the filter 9 used in the present invention, a filter whose refractive index is changed electrically or optically in a period of 2D is used. By adjusting the refractive index change amount Δn and the filter film thickness t, the diffraction angle θ as the first-order diffracted light can be determined by the following equation.

2Dsin θ = λ By illuminating the mask with this diffracted light 50, the diffracted light 51 obtained is as shown in FIG. 1, and two-beam interference is obtained on the wafer. Thereby, the effect of improving the resolution and the effect of improving the depth of focus can be obtained.

Further, in this case, since the filter and the mask are placed apart from each other by a distance that can be approximated by Fraunhofer diffraction, both of the obliquely incident light can be considered to be incoherent.

Next, the method for forming the above filter will be described in more detail. As a material for constructing a filter, first, a photorefractive material or the like, which is a photoelectric field, is used.
Consider that the refractive index changes in proportion to the power. As shown in FIG. 2, it is assumed that light waves 61 having a wavelength λ and coherent with each other are incident on the material 60 at an incident angle θ. A light intensity distribution having a period P is formed in the filter due to interference.

P = λ / 2 sin θ The refractive index changes according to this light intensity distribution. In a photorefractive material whose refractive index changes in proportion to the square of the electric field, the light intensity distribution and the refractive index change distribution have the same period. Obtained diffracted light is obtained for this refractive index distribution. The light intensity, wavelength, and filter film thickness at the time of formation are adjusted so that the angle of the obtained diffracted light has a desired value. As one of them, if P = 2D and the phase difference of the light passing through the maximum and the minimum of the refractive index is 180 degrees, the diffracted light can be obtained to a substantially desired value.

In the embodiment, D and P in FIGS.
The pitch represented by is not necessarily the pattern size d or D
It does not need to be twice as long as the above, its periodicity does not need to be perfect, and a part of the pattern may be missing.

The filter material does not necessarily have to be a photorefractive material, and it is acceptable as long as the same effect can be obtained by using an element such as liquid crystal. Further, if it is possible to control the polarization direction so as to be orthogonal to the pattern cycle direction in combination with liquid crystal or the like, the effect of further improving the resolution can be obtained. Further, the filter does not necessarily need to discretely generate the diffracted light.

Furthermore, even if multiple exposure is performed by changing the focal plane position on the image plane side or modulation of the complex transmittance distribution of the diffracted light on the pupil plane is added to the present embodiment, the present invention will be realized. It's not a hindrance.

As a preferred embodiment of the present invention, a mask pattern having periodicity is used, a mask made of a light-shielding portion and a transmission portion such as ordinary chromium is used as the mask, and the filter is used. It is possible to use a material whose refractive index distribution can be rewritten.

[0024]

In the projection exposure apparatus for projecting and exposing the pattern formed on the mask onto the wafer through the projection optical system, a fine region is formed between the mask and the light source, and the refractive index in the region is set. Equipped with a filter capable of arbitrarily modulating the transmittance and the polarization, so as to obtain the diffracted light angle and the polarization direction equivalent to the optimum oblique incident illumination position according to the periodic direction and pitch of the mask pattern. By using a projection exposure apparatus characterized by controlling the filter refractive index / transmittance and polarization,
It is possible to perform transfer with a resolution equivalent to that of the oblique incidence illumination method and with little loss of exposure light. Further, by using an electro-optical element or the like as the filter, it is possible to obtain the same effect with one filter for different masks.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a reticle and a light source filter used in an embodiment of the present invention.

FIG. 2 is a functional explanatory diagram of a filter used in an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional projection exposure apparatus.

FIG. 4 is a configuration diagram showing an example of a conventional phase shift mask.

FIG. 5 is a configuration diagram showing an example of conventional oblique incidence illumination.

FIG. 6 is a configuration diagram showing an example of oblique incidence illumination using a conventional dummy mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 1st condensing optical system 3 homogenizing optical system 4 2nd condensing optical system 5 reticle 6 projection optical system 7 wafer 8 secondary light source position 9 filter (dummy mask) 10 reticle opening 11 reticle light shielding part 12 Coherent light to form a filter

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/30 528

Claims (2)

[Claims] 1. A projection exposure apparatus for projecting and exposing a pattern formed on a mask onto a wafer via a projection optical system, wherein the mask, a light source, and the like can be modulated with respect to refractive index, transmittance, and polarization. A filter is provided, and the refractive index / transmittance and polarization of the filter are controlled so as to obtain a diffracted light angle and a polarization direction equivalent to the optimal oblique incidence illumination position according to the periodic direction and pitch of the mask pattern. Projection exposure system. 2. The projection exposure apparatus according to claim 1, wherein an electro-optic material is used as the filter, and the refractive index / transmittance and polarization are electrically and optically controlled.