JP2634038C - - Google Patents

Description

Description: 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. 2. Description of the Related Art FIG. 5 shows a conventional projection exposure apparatus. In FIG. 5, 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, 9 Is an aperture stop as a uniform stop, 10 is a filter, 11 and 12 are cold mirrors, 13 is a lamp house, 14 is a projection optical system for projecting a pattern image on the reticle 8 onto a wafer by a lens or a mirror or a combination thereof. Reference numeral 15 denotes a wafer, and 16 denotes an aperture stop. Conventionally, many projection exposure apparatuses of this type use a mercury lamp as a light source lamp 1,
Bright lines such as g-line 436 nm, h-line 405 nm, and i-line 365 nm, or continuous spectra in the vicinity of these wavelengths are 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. An input lens 4 which shares a substantially focal position with the second focal point 3
To convert the light beam into a substantially parallel light beam and enter 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. As a matter of course, if the intensity distribution of the light incident on the optical integrator 5 is close to 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, since the structure of the mercury lamp is vertically long and both ends are electrodes 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 lower the height of the apparatus by bending the optical path, and also apply long-wavelength photothermal rays. 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. [0007] There are many configurations of a conventional projection exposure apparatus other than those shown in FIG. 5, but typically, as shown in FIG. 6, a light source 17, a first condensing optical system 18, a uniforming optical system 19, The two condensing optical systems 20, the reticle 8, the projection optical system 14, and the 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. 2, and an optical fiber, a polyhedral prism, or the like may be used as the other components. The second condensing optical system 20 is a portion corresponding to the output lens 6 and the collimation 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 configured as described above, the light has the property 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 characteristics of forming a projection exposure pattern,
That is, the resolution, the depth of focus, and the like are determined by the numerical aperture of the projection optical system 14 and the properties of the light irradiating the reticle 8, that is, the properties of the secondary light source 24. FIG. 7 shows FIG.
FIG. 3 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 usually 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 ray 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, the relationship is 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, an angle formed when the secondary light source surface is viewed from the reticle 8 through the second condensing optical system is regarded as a range of light incident on the reticle 8, and a half angle is φ, and coherency σ of illumination light is 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. Without a certain exposure area and a certain depth of focus (for example, 10 mm square, ± 1 μm), it cannot be used for actual LSI manufacturing and the like, and the conventional apparatus has a limit of about NA = 0.35. On the other hand, the σ value is mainly related to the pattern sectional shape and the depth of focus,
It 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 in a fine pattern is deteriorated and the focus range that can be resolved is narrowed . Conversely, σ
When the value is large, the resolution of a fine pattern and the focus range that can be resolved are slightly improved. However, in the case where the slope of the side wall of the pattern is gentle and the resist is thick, the cross-sectional shape is trapezoidal or triangular. For this reason, in a conventional projection exposure apparatus, a relatively balanced σ
The value is fixedly set to σ = 0.5 to 0.7, and only experimental conditions such as σ = 0.3 have been tried. Since the size of the light source surface of the secondary light source 24 can be determined 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. In such a conventional apparatus, since only the coherency .sigma. Value controls the property of the light illuminating the reticle 8, the depth of focus and the uniformity in the area are controlled. When forming a fine pattern while satisfying various conditions such as the performance and line width controllability, there is a limit determined by NA and σ. Therefore, the numerical aperture NA of the projection optical system 14 and the secondary light source 2
When the size of No. 4 was determined, the pattern forming characteristics were automatically determined, and the resolution performance could not be further improved. The present invention has been made in view of such a point, and an object of the present invention is to resolve a pattern 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. Means for Solving the Problems To achieve such an object, a first invention illuminates a reticle with illumination light,
In a projection exposure method for projecting and exposing an image of a pattern formed on the reticle onto a substrate via a projection optical system, a shape of a secondary light source formed by a uniformizing optical system for uniformly illuminating the reticle may be adjusted. A first step of changing to a shape such that the intensity of the peripheral portion of the secondary light source is greater than the intensity of the central portion or to a circular shape; and the homogenizing optics according to the change in the shape of the secondary light source. And a second step of changing the distribution of the illumination light on the incident side of the system. Further, the second invention is an exposure apparatus having an illumination optical system including a uniformizing optical system for uniformly illuminating a reticle, and a projection optical system for projecting an image of a pattern formed on the reticle onto a substrate. The shape of the secondary light source formed by the uniformizing optical system that uniformly illuminates the reticle is changed to one of a shape in which the intensity of the peripheral portion of the secondary light source is greater than the intensity of the central portion and a circular shape. First changing means for changing; and second changing means for changing the distribution of the illumination light on the incident side of the uniformizing optical system in accordance with a change in the shape of the secondary light source. 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. FIG. 1 to FIG. 4 show embodiments of a secondary light source controlling aperture as a special aperture applied to the projection exposure apparatus according to the present invention. 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. The stop shown in FIG. 2A 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, conversely, as the σ value is larger, adjacent patterns are separated and transferred to the finer pattern. From these two tendencies, that is, the smaller the σ value is, the better the cross-sectional shape is, while the larger the σ value is, the finer the pattern can be resolved. , There is an appropriate value of σ value that passes through the finest pattern. 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 up 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, the numerical aperture of the projection optical system 14 is 0.35, and the resist OFPR800, 0.5
When a pattern is formed with a thickness of μm, the resolution can be reduced only to a line and space having a line width of 0.5 μm and a pitch of 1 μm under an apparatus condition of σ = 0.5 with a conventional circular aperture stop. According to the embodiment of the projection exposure apparatus of the present invention using the shown annular aperture stop, it has been confirmed that resolution up to a line and space having a line width of 0.4 μm and a pitch of 0.8 μm is possible. 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 transmitted light is produced, and any other shape may be used as long as it has a high transmittance on the outside. Further, according to the present invention, it has been confirmed that the resolution increases and the depth of focus increases. 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 center of the secondary light source when the resist film thickness is large 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. Further, the apparatus is configured as shown in FIG. 5, and a conical lens is detachable 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, the first luminous flux having a shape similar to the transmission portion shape of the special aperture is used.
The present invention is more effective if the light is condensed by the condensing optical system 18 and this light beam is input to the homogenizing optical system 19. As described above, according to the present invention, a central portion such as a shape having a ring-shaped transmission portion is used instead of a uniform stop such as a circular stop for determining the size of the secondary light source used in the conventional device. By mounting a special diaphragm with 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. In this case, there is an effect that the degree of integration can be greatly improved. 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. [Description of Signs] 1 lamp 2 elliptical reflecting mirror 3 second focus 4 input lens 5 optical integrator 6 output lens 7 collimation lens 8 reticle 9, 16 aperture stop 10 filters 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

Claims (1)

1. A projection exposure method for illuminating a reticle with illumination light and projecting and exposing an image of a pattern formed on the reticle onto a substrate via a projection optical system. Changing the shape of the secondary light source formed by the uniformizing optical system that illuminates the light source into one of a shape in which the intensity of the peripheral portion of the secondary light source is greater than the intensity of the central portion and a circular shape. A projection exposure method, comprising: a first step; and a second step of changing a distribution of the illumination light on the incident side of the uniformizing optical system according to a change in a shape of the secondary light source. 2. The first step includes: a first optical member having a light transmitting region having a shape such that the intensity of a peripheral portion of the secondary light source is greater than the intensity of a central portion thereof; and the circular light transmitting portion. 2. The projection exposure method according to claim 1, further comprising the step of setting one of a second optical member having a region and an exit side of the uniforming optical system. 3. The projection exposure method according to claim 1, wherein the second step includes a step of changing the distribution of the illumination light on the incident side of the uniformizing optical system by an optical unit. 4. The optical unit has a conical lens provided so as to be insertable into and removable from an illumination optical path on an incident side of the uniformizing optical system, and the second step is performed by inserting and removing the conical lens. 4. The projection exposure method according to claim 3, wherein the light quantity distribution on the incident side of the uniformizing optical system is converted into a circular shape and a circular shape. 5. The optical unit includes a plurality of input lenses provided interchangeably with respect to an illumination light path on an incident side of the uniformizing optical system, and the second step includes: 4. The projection exposure method according to claim 3, wherein the magnitude of the illumination light on the incident side of the uniforming optical system is changed by replacing the light. 6. An exposure apparatus comprising: an illumination optical system including a uniformizing optical system for uniformly illuminating a reticle; and a projection optical system for projecting an image of a pattern formed on the reticle onto a substrate. The shape of the secondary light source formed by the uniformizing optical system that uniformly illuminates the light source into one of a shape in which the intensity at the peripheral portion of the secondary light source is greater than the intensity at the central portion and a circular shape A projection exposure apparatus comprising: a first changing unit that changes the distribution of the illumination light on the incident side of the uniformizing optical system according to a change in the shape of the secondary light source. . 7. The first optical member having a light transmission region having a shape such that the intensity of the peripheral portion of the secondary light source is greater than the intensity of the central portion, and the first optical member. 7. The projection exposure apparatus according to claim 6, further comprising: a second optical member provided so as to be exchangeable with each other and having the circular light transmitting region. 8. An optical unit for changing the distribution of the illumination light on the incident side of the homogenizing optical system according to exchange of the first optical member and the second optical member. The projection exposure apparatus according to claim 7, further comprising: 9. The optical unit inserts into and removes from the illumination optical path on the entrance side of the homogenizing optical system in order to convert the light quantity distribution on the entrance side of the homogenizing optical system into a circular shape and an annular shape. 9. The projection exposure apparatus according to claim 8, further comprising a conical lens provided so as to be able to be provided. 10. The optical means are interchangeably provided with respect to an illumination light path on an incident side of the homogenizing optical system in order to change a size of the illumination light on an incident side of the homogenizing optical system. 9. The projection exposure apparatus according to claim 8, comprising a plurality of input lenses provided.