JPH0661122A - Projection aligner - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to increase the contrast of an optical image in a projection exposure apparatus provided with a ring-shaped illumination system. According to the projection exposure apparatus of the present invention, a light attenuation area 32 is provided on a pupil plane in the projection optical system 14, and is used for attenuating especially 0th-order diffracted light among diffracted light diffracted by a pattern on the mask 8. The pupil filter 30 has.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus used in the LSI manufacturing process.

[0002]

2. Description of the Related Art Conventionally, a projection exposure apparatus used in a semiconductor device manufacturing process is known. These are, for example:
It is disclosed in Japanese Patent Laid-Open No. 61-91662.
FIG. 8 is a schematic diagram showing the configuration of the optical system of the conventional projection exposure apparatus disclosed in Japanese Patent Laid-Open No. 61-91662.
Referring to FIG. 8, the conventional projection exposure apparatus further includes a lamp 1, which is a light source, an elliptical reflecting mirror 2 for reflecting the light emitted from the lamp 1, and a light reflected by the elliptic reflecting mirror 2. Cold mirror 11 for inputting, an input lens 4 on which the light reflected by the cold mirror 11 is incident, a filter 10 on which light passing through the input lens 4 is incident, and an optical integrator 5 on which light passing through the filter 10 is incident. And an output lens 6 on which the light passing through the optical integrator 5 is incident,
A cold mirror 12 for reflecting the light passing through the output lens 6, a collimation lens 7 on which the light reflected by the cold mirror 12 enters, and light passing through the collimation lens 7 are irradiated to form a circuit pattern. The mask 8 and the projection optical system 14 for projecting the image of the pattern of the mask 8 onto the wafer 15 upon receiving the light passing through the mask 8 are provided. The projection optical system 14 is composed of a lens, a mirror, or a combination thereof. The projection optical system 14 has an aperture stop 1
6 is provided. An aperture stop 100 is provided between the optical integrator 5 and the output lens 6.

The lamp 1, the elliptical reflecting mirror 2, the input lens 4, the optical integrator 5, the output lens 6, the collimation lens 7, the filter 10, and the cold mirrors 11 and 12 are housed in a lamp house 13.

The input lens 4 plays a role of reducing vignetting of light rays passing through the optical integrator 5 and enhancing light collection efficiency. In addition, the optical integrator 5
Is a bundle of many rod-shaped lenses and is also called a fly-eye lens. The filter 10 is provided to allow only the light of the wavelength whose aberration has been corrected to pass through the optical system. The cold mirrors 11 and 12 serve to bend the optical path and reduce the height of the device. Further, the cold mirrors 11 and 12 also have a function of transmitting long-wavelength photothermal rays and absorbing them in the coolable portion of the lamp house 13.

FIG. 9 is a plan view showing an aperture stop used in the conventional projection exposure apparatus shown in FIG. Referring to FIG. 9, the aperture stop 100 includes a transmissive region 101 that transmits light.
And a light blocking area 102 for blocking light. The aperture stop 100 has a circular light-shielding region 102 at the center of a circular transmission region 101.

Next, the operation will be described with reference to FIGS. 8 and 9. First, light is generated from the lamp 1 installed at the first focus of the elliptical reflecting mirror 2. The light emitted from the lamp 1 is reflected by the elliptical reflecting mirror 2. The light reflected by the elliptical reflecting mirror 2 is further reflected by the cold mirror 11.
Reflected by. As a result, the luminous flux of the light generated by the lamp 1 is once collected near the second focus 3.

The light flux is made substantially parallel by the input lens 4 which shares a focus position with the second focus 3. The light converted into the parallel light flux is incident on the optical integrator 5. By passing through the optical integrator 5, the irradiation uniformity of light is improved. The light emitted from the optical integrator 5 is condensed by the collimation lens 7 via the output lens 6 and the cold mirror 12. The condensed light is irradiated so as to be superposed on the mask 8 on which the circuit pattern is formed and hit. The light beam incident on the optical integrator 5 has an intensity distribution depending on the location, but the light beams emitted from the respective element lenses of the optical integrator 5 are almost the same, and since they are superposed, the irradiation intensity on the mask 8 becomes substantially uniform.

The light emitted from the optical integrator 5 is formed into a ring-shaped illumination system by the aperture stop 100. Light is obliquely incident on the mask 8 by this ring-shaped illumination system. When the oblique illumination by this ring-shaped illumination system is used, the line-and-space (L / S) pattern near the limit resolution is mainly caused by the interference of two light fluxes of the 0th-order diffracted light and the + 1st-order or -1st-order diffracted light. An image is formed and high resolution and high depth of focus can be obtained without changing the wavelength of the light source and the numerical aperture of the projection optical system. That is, in the conventional circular aperture, the amount of light having a small incident angle, which is a component that lowers the resolution, increases. On the other hand, in the ring-shaped illumination system, the component of light with a small incident angle decreases and the component with a large incident angle, which is a component for increasing resolution, increases. As a result, when the ring-shaped illumination system is used, the resolution becomes high and the depth of focus becomes deep accordingly. In oblique irradiation using a ring-shaped illumination system, the resolution and depth of focus improve as the incident angle of irradiation light increases.

The light applied to the mask 8 is projected by the projection optical system 14
Is incident on. The image of the pattern of the mask 8 is projected and transferred onto a resist (not shown) on the wafer 15 by the projection optical system 14. The numerical aperture is determined by the aperture stop 16 provided in the projection optical system 14.

[0010]

However, in general, an aperture stop 100 having a circular light-shielding area 102 as in the prior art is used.
When ring-shaped illumination is formed and exposure is performed, an image is formed with respect to the L / S pattern in the vicinity of the limit resolution mainly by buffering by two light fluxes of 0th-order diffracted light and + 1st-order or -1st-order diffracted light. . Therefore, there is a problem that the contrast of the optical image is low. The present invention has been made to solve the above problems, and an object of the present invention is to provide a projection exposure apparatus that can obtain an optical image having a higher contrast than conventional ones.

[0011]

A projection exposure apparatus according to claim 1 comprises a light source, a condenser lens system for irradiating light emitted from the light source onto a mask having a circuit pattern formed thereon.
An aperture stop provided between the light source and the condenser lens system, a projection optical system for condensing the light passing through the mask on the wafer surface, and a pupil filter arranged at the pupil of the projection optical system. I have it. Further, the aperture stop includes a transmission region for shaping the light emitted from the light source, and a light-shielding region formed in the center of the transmission region so as to shield the light emitted from the light source, and further includes a pupil filter. Has an area that attenuates a part of the light transmitted through the mask.

[0012]

In the projection exposure apparatus according to the first aspect, the pupil filter is arranged in the pupil of the projection optical system, and the pupil filter has a region for attenuating a part of the light transmitted through the mask.
Next-order diffracted light is weakened and exposed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the construction of an optical system of a projection exposure apparatus according to an embodiment of the present invention.

Referring to FIG. 1, the projection exposure apparatus of the present embodiment has a lamp 1 as a light source, an elliptical reflecting mirror 2 for reflecting the light emitted from the lamp 1, and an elliptic reflecting mirror 2 for reflecting the light. Cold mirror 11 for further reflecting reflected light
An input lens 4 on which the light reflected by the cold mirror 11 is incident, a filter 10 on which the light passing through the input lens 4 is incident, an optical integrator 5 on which the light passing through the filter 10 is incident, and an optical integrator 5. Aperture 100 for shaping the light passing through the aperture into a predetermined irradiation shape, the output lens 6 on which the light passing through the aperture stop 100 is incident, and the cold mirror 12 for reflecting the light passing through the output lens 6. And a collimation lens 7 on which the light reflected by the cold mirror 12 is incident. The lamp 1, the elliptical reflecting mirror 2, the input lens 4, the optical integrator 5, the output lens 6, the collimation lens 7, the filter 10, the aperture stop 100 and the cold mirrors 11 and 12 are housed in a lamp house 13.

The projection exposure apparatus of this embodiment further includes a mask 8 having a circuit pattern on which the light passing through the collimation lens 7 is superposed and irradiated, and the light passing through the mask 8 is incident on the mask 8. Image of pattern on wafer 15
And a projection optical system 14 for projecting and exposing the upper resist (not shown). The projection optical system 14 is provided with an aperture stop 16 that determines the numerical aperture, and at the same time, a pupil filter 30 is also provided. The projection optical system 14 is composed of a lens, a mirror, or a combination thereof. Also, the input lens 4,
The roles of the optical integrator 5, the filter 10, and the cold mirrors 11 and 12 are the same as in the conventional case. That is, the input lens 4 plays a role of reducing vignetting of light rays passing through the optical integrator 5 and enhancing light collection efficiency. The optical integrator 5 is a bundle of many rod-shaped lenses and is also called a fly-eye lens. The filter 10 is provided for allowing the optical system to pass only the light of the wavelength whose aberration is corrected. The cold mirrors 11 and 12 serve to bend the optical path and reduce the height of the device. Further, the cold mirrors 11 and 12 also have a function of transmitting long-wavelength photothermal rays and absorbing them in the coolable portion of the lamp house 13.

FIG. 2 is a schematic diagram showing the configuration of the pupil filter shown in FIG. Referring to FIG. 2, the pupil filter 3
0 is a circular transmission region 31 that transmits light, and a circular light attenuation region 32 formed at the center of the circular transmission region 31.
And a light shielding region 33 formed so as to cover the outside of the transmissive region 31. The inner edge of the light shielding region 33 has a size that matches the inner edge of the projection optical system aperture stop 16.

Next, the operation will be described. First, light is generated from the lamp 1 installed at the first focus of the elliptical reflecting mirror 2. The light emitted from the lamp 1 is reflected by the elliptical reflecting mirror 2. The light reflected by the elliptical reflecting mirror 2 is further reflected by the cold mirror 11. As a result, the luminous flux of the light generated by the lamp 1 is once collected near the second focus 3.

The light flux is made substantially parallel by the input lens 4 which shares a focus position with the second focus 3. The light converted into the parallel light flux is incident on the optical integrator 5. By passing through the optical integrator 5, the irradiation uniformity of light is improved. The light emitted from the optical integrator 5 is condensed by the collimation lens 7 via the output lens 6 and the cold mirror 12. The condensed light is irradiated so as to be superposed on the mask 8 on which the circuit pattern is formed and hit. The irradiation light transmitted through the mask 8 is diffracted by the pattern on the mask 8, and the diffracted image is formed on the pupil plane of the projection lens.

Here, an L / S pattern having dimensions near the critical resolution of the projection lens is considered as a mask pattern. Figure 3
FIG. 3 is a schematic diagram showing a diffraction image on a projection lens pupil plane of a line and space (L / S) pattern. Referring to FIG. 3, the 0th-order diffracted light 43 is located at the central portion of the inner edge (edge of the projection lens pupil) 40 in the projection optical system aperture stop 16. Then, the + 1st-order diffracted light 41 and the -1st-order diffracted light 42 are positioned so as to be adjacent to the 0th-order diffracted light 43. The shape of each diffracted light is the shape of the aperture stop 100 (2
The shape of the next light source is similar, and the central part is dark. Here, the pupil filter 30 of the present embodiment mainly plays a role of attenuating the 0th-order diffracted light by 2 / π times among these diffracted lights.

FIG. 4 is a schematic view showing a usage mode of the pupil filter used in this embodiment. Referring to FIG.
The light attenuation region 32 of the pupil filter 30 is installed so as to overlap the 0th-order diffracted light 43. With this structure, the contrast of the optical image can be improved in this embodiment as compared with the conventional case. The principle by which the contrast of an image can be improved by attenuating the 0th-order diffracted light will be described below.

Consider the image formation of the L / S pattern described above.
When the complex amplitude g (X) of the pattern is expanded to the Fourier series, the following expression 1 is obtained.

[0023]

[Equation 1]

Referring to the above formula 1, X is the coordinate of the mask surface, n is the diffraction order, P is the period of the L / S pattern, and j is the imaginary unit. It can be seen from Equation 1 above that the pattern is formed by buffering various diffracted light. Also,
When the ring illumination is used as described above, the optical image is mainly 0.
It is formed by buffering two diffracted lights of the second-order diffracted light and the + 1st-order or -1st-order diffracted light. 0th order diffracted light and 1 for simplification
Assuming that an optical image is formed only by buffering two light beams of the 1st or -1st order diffracted light, the complex amplitude g'of the optical image
(X ') is given by the following Expression 2.

[0025]

[Equation 2]

Referring to the above equation 2, X'is the coordinate of the image plane,
P'is the L / S pattern period on the image plane (mask pattern period multiplied by the transfer magnification). The intensity I ′ (X ′) of the optical image at this time is expressed by the following Expression 3.

[0027]

[Equation 3]

Therefore, the contrast C is given by
become that way.

[0029]

[Equation 4]

Referring to the above equation 4, I'max, I'm
in is the maximum value and the minimum value of the optical image intensity, respectively.

Here, if a filter for increasing the transmittance of the 0th-order diffracted light by m times is installed on the pupil surface of the projection lens, the intensity I '(X') of the optical image is given by the following expression 5.

[0032]

[Equation 5]

From the above expression 5, the contrast C is calculated by the following expression 6
become that way.

[0034]

[Equation 6]

A graph corresponding to the above equation 6 is shown in FIG.
With reference to FIG. 5, it can be seen that the contrast C becomes larger than in the conventional case when the setting is made such that 4 / π ² <m <1. Especially when m = 2 / π, the contrast becomes maximum at C = 1.

Although the case where the shape of the light shielding portion 102 of the aperture stop 100 is circular has been described in the present embodiment,
The present invention is not limited to this, and can be applied to the case where an aperture stop having another shape is used. That is, it can be easily dealt with by changing the shape of the light attenuation region 32 of the pupil filter 30 according to the shape of the light shielding unit 102. FIG. 6 is a plan view showing an aperture stop used in an optical system of a projection exposure apparatus according to another embodiment of the present invention, and FIG. 7 is a plan view of a corresponding pupil filter. 6 and 7, using aperture stop 105 as shown in FIG. 6, corresponding pupil filter 35 becomes as shown in FIG. That is, with reference to FIG.
In FIG. 5, the light shielding area 107 is formed in a cross shape, and the transmission area 106 is divided into four parts. In the pupil filter 35 corresponding to this, the light attenuation region 37 is divided into four portions, and the transmission region 36 is formed so as to fill the gap between them. A light-blocking region 38 is formed so as to cover the outer side of the transmissive region 36, and the inner edge of the light-blocking region 38 is formed to have a size that matches the inner edge of the projection optical system aperture stop 16. In this way, the contrast of the optical image can be easily improved by changing the shape of the light attenuation region of the pupil filter according to the shape of the aperture stop.

[0037]

According to the first aspect of the present invention, by providing the pupil plane of the projection optical system with the pupil filter having the region for attenuating a part of the light transmitted through the mask, the conventional ring-shaped illumination system is provided. In comparison, the ratio of the amplitude of the 0th-order diffracted light to the ± 1st-order diffracted light becomes smaller. As a result, the contrast of the optical image is increased and the resolution and the depth of focus can be improved as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical system of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a pupil filter shown in FIG.

FIG. 3 is a plan view showing a diffraction image on a projection lens pupil plane of a line and space (L / S) pattern.

FIG. 4 is a schematic plan view showing how the pupil filter shown in FIG. 1 is used.

5 is a correlation diagram showing the relationship between the light transmittance of the light attenuation region of the pupil filter used in the embodiment shown in FIG. 1 and the optical image contrast.

FIG. 6 is a plan view showing an aperture stop used in a projection exposure apparatus according to another embodiment of the present invention.

FIG. 7 is a plan view showing a pupil filter used in a projection exposure apparatus according to another embodiment of the present invention.

FIG. 8 is a schematic diagram showing a configuration of an optical system of a conventional projection exposure apparatus.

FIG. 9 is a plan view showing an aperture stop used in a conventional projection exposure apparatus.

[Explanation of symbols]

 1: Lamp 2: Elliptical reflector 3: Second focus of the elliptical reflector 2 4: Input lens 5: Optical integrator 6: Output lens 7: Collimation lens 8: Mask 10: Filter 11: Cold mirror 12: Cold mirror 13: Lamp house 14: Projection optical system 15: Wafer 16: Projection optical system Aperture stop 30: Pupil filter 32: Light attenuation region 35: Pupil filter 100: Aperture stop 105: Aperture stop In the drawings, the same reference numerals are the same or corresponding parts. Indicates.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuya Kamon 4-1-1 Mizuhara, Itami City, Hyogo Prefecture Mitsubishi Electric Co., Ltd.

Claims (1)

[Claims] 1. A light source, a condenser lens system for irradiating light emitted from the light source onto a mask on which a circuit pattern is formed, and an aperture stop provided between the light source and the condenser lens. A projection optical system for condensing the light passing through the mask on the wafer surface, and a pupil filter provided in a pupil of the projection optical system, wherein the aperture stop is configured to detect the light emitted from the light source. A transparent region for molding, and a light blocking region formed so as to block the light emitted from the light source in the central portion of the transparent region, wherein the pupil filter is a part of the light transmitted through the mask. A projection exposure apparatus having a region that attenuates.