JP2634040B2 - Projection exposure equipment - Google Patents

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 the like.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional projection exposure apparatus. FIG.
, 1 is a lamp, 2 is an elliptical reflecting mirror, 3 is a second focal point of the elliptical reflecting mirror 2, 4 is an input lens, 5 is an optical integrator, 6 is an output lens, 7 is a collimation lens, 8 is a reticle, and 9 is uniform. An aperture stop as a stop, 10 is a filter, 11 and 12 are cold mirrors, 13 is a lamp house, 14 is a projection optical system for projecting an image of a pattern on the reticle 8 onto a wafer by a lens or a mirror or a combination thereof, 15 is Wafer,
Reference numeral 16 denotes an aperture stop.

Conventionally, many projection exposure apparatuses of this type use a mercury lamp as a light source lamp 1 and have a g-line of 436 nm, h
A bright line such as a line 405 nm and an i-line 365 nm or a continuous spectrum near these wavelengths is extracted and used. For this reason, the lamp 1 as a light source needs to have a high luminance, and it is better to be close to a point light source in consideration of light collection efficiency and irradiation uniformity. However, since such an ideal light source does not exist in practice, a lamp 1 having a finite size and a distribution of intensity must be used, and the light emitted from such a lamp 1 cannot be reduced. It is important to convert the light into light with good efficiency and uniform irradiation.

The apparatus shown in FIG. 5 is an apparatus having a configuration using a conventional representative light condensing method, in which a lamp 1 is placed at a first focal point of an elliptical reflecting mirror 2 and a second focal point 3 of the elliptical reflecting mirror 2 is placed. Collect the luminous flux once in the vicinity. Then, the light beam is converted into a substantially parallel light beam by the input lens 4 which shares a substantially focal position with the second focal point 3, and is input into the optical integrator 5. The optical integrator 5 is a bundle of a number of rod-shaped lenses, and is also called a fly-eye lens. Passing through the optical integrator 5 is a main factor for improving the irradiation uniformity, and the input lens 4 plays a role in reducing vignetting of the light beam passing through the optical integrator 5 and improving the light collection efficiency. The light that has exited the optical integrator 5 is condensed by the output lens 6 and the collimation lens 7 so that the light beams exiting from the respective small lenses of the optical integrator 5 are superimposed on the reticle 8. Although the light beam incident on the optical integrator 5 has an intensity distribution depending on the place, the light emitted from each small lens of the optical integrator 5 is superimposed almost equally, so that the irradiation intensity on the reticle 8 becomes almost uniform. Naturally, the optical integrator 5
If the intensity distribution of the light incident on the reticle 8 is nearly uniform, the illuminance distribution of the reticle 8 on which the emitted light is superimposed becomes more uniform. An aperture stop 9 is placed on the exit side of the optical integrator 5 to determine the exit side dimensions of the optical integrator 5.

When a mercury lamp is used as the lamp 1 and the light is condensed by the elliptical reflecting mirror 2, the structure of the mercury lamp is vertically elongated as shown in FIG. I can't take it out. Therefore, as shown in FIG. 5, the intensity distribution of light entering the center of the optical integrator 5 may be reduced only by using a convex lens as the input lens 4. Therefore, a biconvex or one-sided convex / concave conical lens may be inserted between the input lens 4 and the optical integrator 5 to make the intensity distribution of light entering the optical integrator 5 more uniform.

The filter 10 is for passing only light having a wavelength whose optical system has been aberration-corrected. The cold mirrors 11 and 12 bend the optical path to lower the height of the apparatus and to provide a long-wavelength photothermal wire. In the lamp house 13 to be absorbed by the coolable portion of the lamp house 13. The light irradiated on the reticle 8 passes through the projection optical system 14, and the image of the fine pattern on the reticle 8 is projected and transferred to the resist on the wafer 15. In the projection optical system 14, there is a stop 16 for determining the numerical aperture.

Although there are many conventional projection exposure apparatuses other than the one shown in FIG. 5, schematically, as shown in FIG.
7, first condensing optical system 18, uniformizing optical system 19, second condensing optical system 20, reticle 8, projection optical system 14, wafer 15
Are 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. 5, and appropriately arranges a spherical mirror, a plane mirror, a lens, etc., in addition to the elliptical mirror, and controls the light flux emitted from the light source as much as possible. It has a role to efficiently enter the uniforming optical system 19. The homogenizing optical system 19 is a portion corresponding to the optical integrator 5 in FIG.

The second condensing optical system 20 is a portion corresponding to the output lens 6 and the collimating lens 7 in FIG. 5, superimposes the light emitted from the uniformizing optical system 19, and secures the image plane telecentricity. . In addition, a filter corresponding to the filter 10 in FIG. 5 is inserted at a position where the light flux is close to the optical axis parallel.
Is also inserted, although the location is not unique.

When the light coming from the reticle 8 is viewed from the apparatus having the above-described configuration, the nature of the light becomes the nature of the light coming out of the homogenizing optical system 19 through the second condensing optical system 20. The exit side of the homogenizing optical system 19 appears as an apparent light source. For this reason, in the case of the above configuration, the exit side 24 of the homogenizing optical system 19 is generally called a secondary light source.

When the reticle 8 is projected onto the web 15, the formation characteristics of the projection exposure pattern, that is, the resolution, the depth of focus, etc., depend on the numerical aperture of the projection optical system 14 and the properties of the light irradiating the reticle 8, It is determined by the properties of the secondary light source 24. FIG. 7 is an explanatory diagram relating to a reticle illumination light beam and an imaging light beam in the projection exposure apparatus shown in FIG.

In FIG. 7, a projection optical system 14 generally has an aperture stop 16 inside, and regulates an angle θa at which light passing through the reticle 8 can pass and an angle θ of a light beam falling on the wafer 15. Have decided. Generally, 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, sin
θa = sin θ / m. In this type of apparatus, it is common that the image plane telecentric, that is, the principal ray falling on the image plane is formed perpendicular to the image. In order to satisfy the condition of this “image plane telecentric”, FIG. The real image of the exit surface of the optical system 19, that is, the light source surface of the secondary light source 24 is formed at the position of the aperture stop 16. Under such conditions, when the secondary light source surface is viewed from the reticle 8 through the second condensing optical system, the angle formed by the reticle 8
When the half angle is φ and the coherency σ of the illumination light is defined as σ = sin φ / sin θa, it has been conventionally considered that the pattern formation characteristic can 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 depth of focus becomes shallow, and it becomes difficult to secure a wide exposure area due to the aberration of the projection optical system 14.
Some exposure area and depth of focus (for example, 10 mm square, ±
Without 1 μm), it cannot be used for actual LSI manufacturing or the like, and the limit of the conventional device is about NA = 0.35. On the other hand, the σ value is mainly related to the pattern cross-sectional shape and the depth of focus, and is related to the resolution in correlation with the cross-sectional shape. When the σ value is small, the edge of the pattern is emphasized, so that the cross-sectional shape becomes a good pattern shape with the side wall approaching perpendicular, but the resolution of a fine pattern is deteriorated and the focus range that can be resolved is narrowed . Conversely, when the σ value is large, the resolution of a fine pattern and the focus range that can be resolved are slightly improved. However, the slope of the side wall of the pattern cross section is small, and in the case of a thick resist, the cross section is trapezoidal or triangular. Therefore, in a conventional projection exposure apparatus, a relatively balanced σ value is fixedly set to σ = 0.5 to 0.7, and experimental conditions such as σ = 0.3 are attempted. It's just that. Since the size of the light source surface of the secondary light source 24 may be determined to set the σ value, a circular aperture stop 9 for setting the σ value is generally placed immediately after the light source surface of the secondary light source 24.

[0012]

In such a conventional apparatus, since only the coherency .sigma. Value controls the properties of the light illuminating the reticle 8, the depth of focus,
When forming a fine pattern while satisfying various conditions such as uniformity in a region and line width controllability, there is a limit determined by NA and σ. Therefore, when the numerical aperture NA of the projection optical system 14 and the size of the secondary light source 24 are determined, the pattern forming characteristics are automatically determined, and the resolution performance cannot be further improved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the problem of pattern resolution after fixing the numerical aperture of a projection optical system and the size of a secondary light source for reticle irradiation. An object of the present invention is to provide a projection exposure apparatus that further improves performance.

[0014]

SUMMARY OF THE INVENTION In order to achieve such an object, the present invention provides a light transmitting device that approaches a periphery instead of a circular diaphragm that determines the size of a secondary light source used in a conventional device. An optical member such as a special diaphragm having a transmittance distribution that is high and continuously changes so as to have low transmittance or complete light blocking when approaching the center is provided.

[0015]

In the present invention, when the resist is thin, the light is exposed only by the light at the peripheral portion of the secondary light source without using the light at the central portion of the secondary light source to improve the resolution.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a secondary light source control diaphragm as a special diaphragm applied to a projection exposure apparatus according to the present invention are shown in FIGS.
As shown in FIG. The stop shown in FIG. 1 is a stop having a ring-shaped pass band, and is manufactured by depositing a light-shielding body such as chromium on a substrate made of quartz, calcium fluoride, lithium fluoride, or the like having high transmittance of irradiation light. Can be. FIG. 2
The stop shown in (a) is a stop having a distribution in transmittance.
As shown in FIG. 2 (b), the aperture distribution is such that the transmittance increases as it approaches the periphery, and the transmittance decreases or the light is completely shielded as it approaches the center. This diaphragm can be manufactured by attaching a light shield to the transmission substrate with a thickness distribution in the radial direction, similarly to the diaphragm shown in FIG. Note that the curve shown in FIG. 2B may be any curve as long as the transmittance increases as approaching the periphery of the circle. The aperture shown in FIG. 3 is an aperture having a small number of small apertures of several or more only in the peripheral portion, and can be manufactured by making a hole in a metal plate or the like. The stop shown in FIG. 4 has a connection portion in a part of the opening of the circular ring in order to easily manufacture a stop similar to the stop shown in FIG. 1 by hollowing out a metal plate or the like.

The configuration of the present invention may be the same as the configuration of the conventional apparatus shown in FIG. 5 or FIG. 6, and the aperture shown in FIGS. When the size of the aperture stop 9 is changed, the smaller the aperture is, that is, the smaller the σ value is, the closer the obtained side wall of the pattern is to the vertical.
On the other hand, when the resolution of a fine pattern is examined,
As the value is larger, adjacent patterns are separated and transferred to a finer pattern. These two trends are:
The smaller the σ value is, the better the cross-sectional shape is. On the other hand, the larger the σ value is, the smaller the pattern can be resolved. There is an appropriate value.
When the thickness of the resist layer to be exposed is reduced in consideration of the use of a multilayer resist or the like, the difference in the cross-sectional shape of the pattern is not so remarkable and only the resolution is a problem. Shifts to the larger σ.

Since there is the above-mentioned relationship between the illumination light and the pattern resolution, in the case of a thin resist layer, the finer the pattern is, the more it is used to the outside of the secondary light source. Therefore, by taking one step further and using only the light at the periphery of the secondary light source necessary for resolving a fine pattern, higher resolution can be achieved. In the projection exposure apparatus according to the present invention using the aperture shown in FIGS. 1 to 4, exposure can be performed only by light around the secondary light source without using light at the center of the secondary light source. If the thickness is reduced, it is possible to obtain a pattern having a fine size that could not be obtained by a conventional apparatus. For example, using an i-line having a wavelength of 365 nm, the projection magnification is 1/10, and the numerical aperture of the projection optical system 14 is 0.3.
5. When a pattern is formed with a resist OFPR800 and a thickness of 0.5 μm, the resolution is only up to a line and space having a line width of 0.5 μm and a pitch of 1 μm under a conventional circular aperture stop with σ = 0.5. Although not obtained, according to an embodiment of the projection exposure apparatus of the present invention using the annular aperture stop shown in FIG. 1, the line width is 0.4 μm and the pitch is 0.8 μm.
It has been confirmed that resolution up to line and space can be achieved. In a circular aperture stop, the higher the resolution, the more the outer rays are used, the higher the resolution.Therefore, the effect differs depending on the outer diameter and inner diameter of the circular aperture stop. The resolution is higher than that of. In addition, even if the apertures shown in FIGS. 2 to 4 are used, an effect corresponding to the distribution of the transmitted light is produced.

Further, according to the present invention, it has been confirmed that the resolution is increased and the depth of focus is increased. For example, in the case of the above resist pattern, the depth of focus is ± 0.5 μm or more for a 0.4 μm line and space, and ± 1 μm or more for a 0.5 μm line and space. Conventionally, even a 0.5 μm line and space is about ± 0.5 μm, which is a considerable improvement.

Although such a special diaphragm can be fixedly installed in the apparatus, it is more advantageous to use the vicinity of the central portion of the secondary light source when the resist film is thick as described above. Therefore, it is more convenient if the conventional uniform aperture such as a circular aperture stop and the special aperture can be exchanged. In addition, the apparatus is configured as shown in FIG. 5, and a conical lens can be attached and detached in front of the optical integrator 5, and the distribution of light entering the optical integrator 5 can be switched between a peripheral ring shape and a centralized type by attaching and detaching the conical lens. If a conventional uniform stop such as a circular stop can be used and a special stop can be used, the light can be used without lowering the light use efficiency. Further, even if the input lens 4 can be replaced so that the focal length and the installation position can be changed so that the size of the light beam entering the optical integrator 5 can be changed, the light collection efficiency can be improved. Generally speaking, based on FIG. 6, when a special aperture is used, a light beam having a shape similar to the transmission portion shape of the special aperture is condensed by the first condensing optical system 18, and
The present invention is more effective if this light beam is allowed to enter the uniforming optical system 19.

[0021]

As described above, according to the present invention, instead of a uniform stop such as a circular stop for determining the size of the secondary light source used in the conventional device, a central portion such as a shape having an annular transmission portion is used. By mounting a special diaphragm with a high transmittance in the peripheral area, a finer pattern can be formed on a thin resist layer with a deeper depth of focus than in the past. This has the effect of greatly improving the degree of integration. Further, since the present invention makes it possible to exchange such a special stop and a conventional uniform stop, there is an effect that it can cope with a resist having a large film thickness.

[Brief description of the drawings]

FIG. 1 is a plan view showing a secondary light source control stop as a special stop applied to a projection exposure apparatus according to the present invention.

FIG. 2 is a plan view showing a secondary light source control stop as a special stop applied to the projection exposure apparatus according to the present invention.

FIG. 3 is a plan view showing a secondary light source control stop as a special stop applied to the projection exposure apparatus according to the present invention.

FIG. 4 is a plan view showing a secondary light source control stop as a special stop applied to the projection exposure apparatus according to the present invention.

FIG. 5 is a configuration diagram showing a conventional typical projection exposure apparatus.

FIG. 6 is a schematic configuration diagram.

FIG. 7 is an explanatory diagram relating to a reticle illumination light beam and an imaging light beam.

[Explanation of symbols]

 Reference Signs List 1 lamp 2 elliptical reflecting mirror 3 second focal point 4 input lens 5 optical integrator 6 output lens 7 collimation lens 8 reticle 9, 16 aperture stop 10 filter 11, 12 cold mirror 13 lamp house 14 projection optical system 15 wafer 17 light source 18 first Condensing optical system 19 Uniformizing optical system 20 Second condensing optical system 24 Secondary light source

Continuation of the front page (72) Inventor Masato Shibuya 3-2-2, Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (56) References 2 outside Kubota “Optical Technology Handbook” Asakura Shoten October 25, 1968 Issued on pages 175-176

Claims (9)

(57) [Claims] 1. A projection exposure apparatus comprising: an illumination optical system for illuminating a reticle; and a projection optical system for projecting and exposing a pattern on the reticle onto a substrate. The illumination optical system uniformly illuminates the reticle. It has a homogenizing optical system and an optical member arranged on the exit side of the homogenizing optical system, and the optical member has a high transmittance as it approaches the periphery and has a low transmittance or complete light blocking when approaching the center. A projection exposure apparatus having a transmittance distribution that continuously changes as described above. 2. The optical member according to claim 1, wherein the optical member includes a transmission substrate having a predetermined transmittance and a light shield having a thickness distribution in a direction from the center to the periphery of the transmission substrate. Projection exposure equipment. 3. The illumination optical system according to claim 1, further comprising optical means for changing a distribution of light incident on said uniformizing optical system to a distribution of light similar to a transmittance distribution of said optical member. The projection exposure apparatus according to claim 1 or 2. 4. The projection exposure apparatus according to claim 3, wherein said illumination optical system has optical means for changing a distribution of light incident on said uniformizing optical system into a distribution of a peripheral ring shape. 5. The projection exposure apparatus according to claim 4, wherein said optical means has a conical lens. 6. An optical member according to claim 1, wherein said optical member is a special stop for increasing the intensity distribution of a secondary light source surface formed on the exit side of said uniformizing optical system such that the peripheral intensity is larger than the central intensity. 3. The apparatus according to claim 1, wherein a uniform stop which does not affect the intensity distribution of a secondary light source surface formed on the exit side of the uniformizing optical system is replaceable.
The projection exposure apparatus according to claim 1. 7. An illumination optical system, comprising: an optical unit for changing a distribution of light incident on the uniformizing optical system to a distribution of light similar to a transmittance distribution of the optical member when the optical member is used. 7. The projection exposure apparatus according to claim 6, further comprising: 8. The optical means has a conical lens provided so as to be insertable into and removable from the illumination optical path. 8. The projection exposure apparatus according to claim 7, wherein the apparatus is switchable between a ring shape and a circular shape. 9. The projection exposure apparatus according to claim 7, wherein said optical means has a plurality of interchangeable input lenses.