JPH06112104A - Step and repeat exposure system - Google Patents

Abstract

PURPOSE:To obtain alignment having high accuracy by preventing the detection of asymmetry by an interference even when the thickness of a photo-resist film applied onto an alignment pattern formed onto a substrate such as a wafer is non-uniform and asymmetric and improving resolution and symmetry. CONSTITUTION:In the TTL type alignment detecting optical system of a step and repeat exposure system, light having a wide wavelength band can be used as the illumination light of an alignment mark by a chromatic aberration correcting lens 41, and the alignment mark 31 is lit up by light, in which illumination having a specific wavelength is limited by a wavelength selecting filter 13 and a wavelength limiting filter 14. Reflected light from the alignment mark is image-formed onto an image sensing element 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment detecting optical system, and more particularly to a TTL (Throug) for detecting a mark on a wafer through a projection optical system using light having a wide wavelength band.
The present invention relates to a reduction projection exposure apparatus having an alignment detection optical system of the h The Lens) type.

[0002]

2. Description of the Related Art Conventionally, a stepper for projecting and exposing a circuit pattern on a mask while sequentially moving a wafer has been used for manufacturing a semiconductor. The semiconductor element is
It is manufactured by sequentially aligning a circuit pattern on a wafer coated with a resist, which is a photosensitive material, and a circuit pattern on a mask, and exposing them in superposition. This alignment is performed by detecting an alignment mark on the wafer. In order to perform high-accuracy alignment, T that detects a mark through a projection optical system for exposure is used.
The TL method is effective. Since the resist is applied while rotating the wafer, as shown in FIG. 3, the resist flow causes an asymmetric resist film thickness distribution 312 in the detection direction in the vicinity of the stepped base mark 311. On the other hand, when the resist is irradiated with light having a narrow wavelength width, the detected light intensity changes periodically as shown in FIG. Therefore, if the image of the alignment mark having an asymmetric resist distribution is detected with light having a narrow wavelength width,
As shown in FIG. 4B, the detected waveform is also asymmetrical, which causes a detection error. On the other hand, if illuminated with light with a wide wavelength band,
As shown in FIG. 5A, the detected waveforms are symmetric, which enables highly accurate alignment. However, compatibility of the above-mentioned TTL method and detection with light having a wide wavelength width has the following problems. A projection optical system is generally aberration-corrected only for exposure light in order to transfer a fine pattern.
Therefore, when the TTL method is performed using light with a wide wavelength band, the image points of the respective wavelengths are displaced. That is, since chromatic aberration occurs, the detected waveform is blurred and high-precision alignment cannot be performed. In order to solve this problem, Japanese Patent Laid-Open No. 1-2
As disclosed in Japanese Patent No. 27431, an optical system that corrects chromatic aberration caused by light having a wide wavelength band is used to solve the above problem, and light having a wide wavelength band is used as illumination light. A method has been proposed in which the detection waveform can be detected symmetrically with respect to changes in the resist film thickness.

[0003]

However, in the above-mentioned prior art, since light having a wide wavelength band is used as illumination light, the detected light intensity depends on the thickness of the applied resist and the step of the alignment mark. Since they are different, the wavelength range in which the waveform is asymmetric is also included. Illuminating a wide wavelength range has the effect of suppressing changes in the detected light intensity with respect to changes in the resist film thickness, but if the ratio of the detected light intensity in the wavelength range where the waveform becomes asymmetric is large, this waveform Therefore, the waveform detected in a wide wavelength band is affected, so that an asymmetrical waveform is detected.

For example, as shown in FIG. 6A, an alignment mark having an asymmetric resist film thickness distribution 312 in the detection direction due to the flow of the resist is detected in the vicinity of the stepped base mark 311. Illumination light
When the single wavelengths (monochromatic light) λ1, λ2, and λ3 having a narrow bandwidth (several nm) as shown in FIG. 6A are obtained, the waveforms shown in FIGS. 6B, 6C, and 6D are obtained. . As described above, in the waveform detected with a single wavelength, when the wavelength is different as described with reference to FIG. 4, the detected light intensity is different due to the change in the resist film thickness, so that the waveforms have different shapes. Moreover, at a certain wavelength, as shown in FIG. 6D, a large asymmetry waveform is detected when the change in the light intensity is large with respect to the change in the resist film thickness. Therefore, as shown in FIG. 7B, when the illumination light is in the range from λa to λb having a wide (several tens of nm) bandwidth Δλ including the wavelength band in which the asymmetry is largely detected, FIG. As shown in FIG. 6, the waveform shown in FIG. 6D affects the waveform, resulting in an asymmetrical waveform.

In order to solve the above-mentioned problems of the prior art, an object of the present invention is to detect a change in the light intensity with respect to the change in the resist film thickness in an alignment detection optical system which detects light using a wide wavelength band. An object of the present invention is to provide a reduction projection exposure apparatus that realizes highly accurate alignment by improving the resolution and symmetry of an alignment pattern provided on a substrate such as a wafer by limiting a large wavelength band.

[0006]

In order to achieve the above object, the present invention provides a projection type exposure apparatus provided with a projection lens optimized for only a single wavelength, and a projection substrate via the projection lens. An alignment optical system is provided that includes an illumination optical system that illuminates the above alignment mark with light having a wide wavelength band, and a chromatic aberration correction detection optical system that corrects chromatic aberration that occurs in the projection lens when the alignment mark is detected. Is a projection type exposure apparatus. That is, the chromatic aberration correction detection optical system adjusts the focal length corresponding to each wavelength by the chromatic aberration correction lens mechanism that can be created in the optical path of the illumination light by the method disclosed in, for example, JP-A-1-227431. it can. Further, the illumination optical system combines a filter capable of illuminating with light in a wide wavelength band range and a filter that does not illuminate light within a certain wavelength width range within this wavelength band, thereby increasing the range of the illumination wavelength band. It is possible to limit the wavelength band so that the change of the light intensity with respect to the change of the resist film thickness can be excluded.

[0007]

According to the above-mentioned means, since the chromatic aberration correction lens mechanism is provided in the illumination optical path, it is possible to use the illumination light of the alignment mark having a wide wavelength band. Further, the range of the wavelength band of the illumination light can be illuminated by limiting the range of the illumination wavelength by not illuminating the light in the range of a certain wavelength band.

With the above configuration, the illumination light in the wavelength band in which the change in the light intensity is large with respect to the change in the film thickness of the resist is limited, so that the alignment provided on the substrate such as the wafer is performed. It is possible to improve the resolution and symmetry of the pattern and realize highly accurate alignment.

[0009]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a perspective view of an essential part showing a reduction projection type exposure apparatus which is an embodiment of the present invention. The circuit pattern 100 on the mask 1 is transferred to the wafer 3 via the reduction projection lens 2.
Transcribed on. The reduction projection lens 2 is designed so that the circuit pattern 100 can be resolved best when the exposure light 6 is used. The light emitted from the illumination light source 11 capable of illuminating light having a wide wavelength band is guided by the optical fiber 12, and the wavelength selection filter 13 and the wavelength limiting filter 14 are provided.
Through the illumination lens 15, the beam splitter 16,
By the pair of chromatic aberration correction lenses 41 and the bending mirror 17, the illumination light enters so that the center of the illumination light coincides with the center of the entrance pupil 21 of the reduction projection lens 2, and the reduction projection lens 2
The alignment mark 31 on the wafer 3 is illuminated via. The light reflected by the alignment mark 31 is reduced by the reduction projection lens 2, the bending mirror 17, and the chromatic aberration correction lens 4.
The light enters the image sensor 5 through the beam splitter 16, the image forming lens 42, and the beam splitter 16. The image of the alignment mark 31 is formed on the image sensor 5 by the reduction projection lens 2, the chromatic aberration correction lens 41, and the imaging lens 42.

Next, referring to FIG. 2, the transmission characteristics of the wavelength selection filter 13 and the wavelength limiting filter 14 will be described. (A)
Indicates the transmission characteristic of the wavelength selection filter 13, and the wavelength λa
To λb can be transmitted. (B) shows the transmission characteristics of the wavelength limiting filter 14, and is from wavelengths λc to λd.
It is possible to block light in the range. That is, the light transmitted through the two filters of the wavelength selection filter 13 and the wavelength limiting filter 14 is as shown in (c), and it is possible to limit the transmission of light in a certain wavelength range. If several kinds of filters having different transmission characteristics of the wavelength limiting filter 14 are created and combined with the wavelength selection filter 13, it is possible to change the range of limiting the transmission and the central wavelength, and various transmission characteristics can be obtained. It is possible to illuminate with the given wavelength.

The operation of the above configuration will be described. The wafer 3 is installed at a predetermined position of the reduction lens 2 in order to perform alignment in the detection direction. The light from the illumination light source 11 illuminates the alignment mark 31 with light whose illumination of a specific wavelength is limited by the wavelength selection filter 13 and the wavelength limiting filter 14. The reflected light from the alignment mark forms an image of the alignment mark 31 on the image sensor 5 by the reduction lens 2, the chromatic aberration correction lens 41, and the imaging lens 42, and the position of the alignment mark is detected. FIG. 8 shows an example of the alignment mark 31.
(A) shows the cross-sectional shape of the alignment mark 31.
Near the stepped base mark 311, due to the flow of the resist, the resist film thickness distribution 312 is asymmetric in the detection direction.
Is occurring. A detection waveform of the alignment mark 31 obtained by the detection device having the above configuration is shown in FIG. By limiting the wavelength range in which the change of the light intensity is large with respect to the change of the film thickness of the resist 312 by the wavelength selection filter 13 and the wavelength limiting filter 14, detection with high resolution and symmetry can be performed as shown in FIG. . When the detected waveform becomes asymmetric due to the change of the resist film thickness or the step of the alignment mark 31, the filter having the changed transmission characteristics of the wavelength limiting filter 14 is changed and combined with the wavelength selection filter 13 so that the waveform becomes symmetrical. Ask for. The center position of this detected waveform is obtained by a method not shown, and the wafer 3
The position is detected and alignment is performed.

In this embodiment, the wavelength selection filter 1
Although the wavelength limiting filter 3 and the wavelength limiting filter 14 limit the wavelength with two sheets, the same effect can be obtained by changing the transmittance with one filter. Further, as shown in FIG. 9, even if the wavelength selection filter 13 and the wavelength limiting filter 14 are not installed on the illumination side, they may be arranged in front of the image pickup element 5 to obtain the same effect. Further, as shown in FIG. 10, the same effect can be obtained by arranging the wavelength selection filter 13 and the wavelength limiting filter 14 in the illumination light source 11 and illuminating the light whose wavelength is limited.

[0013]

According to the present invention, a chromatic aberration correction lens mechanism is provided in the illumination optical path, and light having a wide wavelength band is used as the illumination light for the alignment mark. Further, the wavelength range of this illumination light is within a certain wavelength range. Not to illuminate light in the range
By combining and illuminating the wavelength ranges, it is possible to limit the wavelength band in which the change in the light intensity is large with respect to the change in the resist film thickness. Therefore, even if the photoresist film thickness applied to the alignment pattern provided on the substrate such as a wafer is non-uniform and asymmetric, detection of asymmetry due to interference can be prevented, and resolution and symmetry can be improved. It is possible to realize highly accurate alignment.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of an embodiment of an alignment detection system for a projection exposure apparatus.

FIG. 2 is a diagram showing a relationship between transmittances of a wavelength selection filter and a wavelength limiting filter.

FIG. 3 is a diagram showing a cross-sectional view of a background mark and an asymmetric resist film thickness distribution.

FIG. 4 is a relationship between a resist film thickness and a detection intensity and a detection waveform diagram when light with a narrow wavelength width is irradiated.

5A and 5B are a relationship between a resist film thickness and detection intensity and a detection waveform diagram when light with a wide wavelength width is irradiated.

FIG. 6 is a cross-sectional view of an alignment mark having an asymmetric resist film thickness distribution and a detection waveform diagram when detection is performed with a single wavelength.

FIG. 7 is a relational diagram of illumination wavelengths at the time of detection in FIG.

8A and 8B are a cross-sectional view of an alignment mark having an asymmetric resist film thickness distribution and a detection waveform diagram when it is detected in this embodiment.

FIG. 9 is a perspective view of a main part of another embodiment of the alignment detection system for the projection exposure apparatus.

FIG. 10 is a perspective view of a main part of another embodiment of the alignment detection system for the projection exposure apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mask, 2 ... Reduction projection lens, 3 ... Wafer, 5 ... Imaging element, 11 ... Illumination light source, 12 ... Optical fiber, 13 ... Wavelength selection filter, 14 ... Wavelength limiting filter, 16 ... Beam splitter, 17 ... Bending mirror , 31 ... Alignment mark, 41 ... Chromatic aberration correction lens, 42 ... Imaging lens, 311 ... Underground mark, 312 ... Asymmetric resist film thickness distribution.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuhiro Yoshitake 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd.

Claims (3)

[Claims] 1. A projection lens optimized for only a single wavelength, an illumination optical system for illuminating an alignment mark on a projection substrate with light having a wide wavelength band through the projection lens, and the projection when the alignment mark is detected. A reduction projection exposure apparatus comprising an alignment mark detection optical system including a chromatic aberration correction detection optical system for correcting chromatic aberration generated in a lens. 2. The reduction projection exposure apparatus according to claim 1, wherein the illumination optical system is provided with a specific wavelength band which is not illuminated and the bandwidth can be set arbitrarily. 3. The reduction projection exposure apparatus according to claim 1, wherein the illumination optical system is capable of arbitrarily setting a center wavelength of a specific wavelength band not illuminated.