JP2006080150A - Exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure device capable of obtaining uniform resolution over the whole wafer by equalizing the temperature distribution in the diameter direction of a medium between a projection lens and a wafer. <P>SOLUTION: The space between the lens 12A of a projection optical system 12 and a wafer W is filled by fluid LQ in a liquid bath 13. In the inside of the liquid bath 13, an annular spacer 14 (temperature-distribution equalizer) intervenes between the wafer W and a wall 13B so that the same side as the wafer W may substantially be constituted. The surface of the spacer 14 has the same reflection factor substantially with the surface of the wafer W. Furthermore, it is preferred that its thermal conductivity is substantially the same with the wafer W. The liquid temperature of the periphery of the wafer W substantially becomes the same temperature with the center of the wafer W so that the equalization of the temperature distribution is attained in a diametric direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exposure apparatus for exposing a resist layer on a wafer surface with a fine circuit pattern, and more particularly to a so-called immersion type exposure apparatus that fills and exposes a liquid between a projection lens and a wafer.

  Miniaturization of circuit patterns is progressing in order to increase the integration of semiconductor elements such as LSI (Large Scale Integrated circuit) and increase the operation speed, but a reduction projection exposure apparatus is widely used to form the circuit patterns. It has been. For example, a 193 nm ArF excimer laser is used as the light source of the reduction projection exposure apparatus, and the resolution is said to be 65 nm. However, it has become possible to improve the resolution without drastically changing the design of the exposure apparatus by using the immersion exposure technique developed in recent years. This immersion exposure technique is a technique in which a liquid is filled between a projection lens of a reduction projection exposure apparatus and a wafer for exposure. For example, the medium between the projection lens and the wafer, which has been conventionally air, is used as pure water. In theory, the resolution is reduced to 45 nm.

By the way, the above resolution is
Resolution = k (process coefficient) · λ (wavelength of illumination light) / NA (1)
It is represented by NA is determined by n · sin θ. n is the refractive index of the medium between the projection lens and the wafer, where n = 1 when the medium is air and n = 1.44 when pure water. θ is a refraction angle, and as the refractive index of the medium increases, the value of sin θ decreases according to Snell's law. Therefore, the resolution is not dramatically improved by the rate of increase of the refractive index of the medium, but the development cost can be kept lower than the shortening of the wavelength of the light source, and it is possible to provide a low-cost exposure apparatus. It becomes.

  In this way, the immersion exposure apparatus has many advantages, but several problems must be solved in order to put this immersion exposure apparatus into practical use. The handling of the medium between wafers is mentioned. Specifically, when a temperature distribution is generated in the radial direction in this medium, a refractive index distribution is generated in the radial direction, and as a result, a resolution distribution is generated in the radial direction. As a method for solving this problem, for example, Patent Document 1 discloses a technique for adjusting a distance (working distance) between a projection lens of a reduction projection exposure apparatus and a wafer.

JP-A-10-303114

  However, in Patent Document 1, the cause of the temperature distribution in the radial direction in this medium is not clarified, and only a solution based on the assumption that there is a temperature distribution in the radial direction is presented. This solution does not prevent the temperature distribution from occurring in the radial direction. Therefore, this problem cannot always be solved by this solution when the wavelength is further shortened.

  The present invention has been made in view of such a problem, and the object thereof is not dependent on the refractive index of the medium between the projection lens and the wafer or the wavelength of the exposure light, and the medium between the projection lens and the wafer. It is an object of the present invention to provide an exposure apparatus capable of uniforming the temperature distribution in the radial direction and obtaining uniform resolution over the entire wafer.

The exposure apparatus of the present invention equalizes the resolution of the entire wafer by including the following components (A) to (D).
(A) Illumination optical system for illuminating a photomask on which a circuit pattern is drawn (B) Projection optical system for projecting a circuit pattern on the photomask illuminated by the illumination optical system onto a resist layer on the wafer surface (C) Projection optics A liquid tank (D) for holding a liquid that fills the space between the system and the wafer is provided with a bottom portion having a wafer placement region, a side wall portion surrounding the wafer placement region, a wafer portion, and a wafer. A temperature distribution uniformizing unit interposed between the wafer mounted on the mounting region and the side wall portion, and configured to make the temperature distribution of the entire wafer surface uniform by constituting substantially the same surface as the wafer surface; Including

  In this exposure apparatus, the temperature distribution uniformizing section that is substantially flush with the wafer makes the liquid temperature in the peripheral portion of the wafer substantially the same as that of the surface portion of the wafer, thereby achieving uniform temperature distribution. It is done. More specifically, the temperature distribution uniformizing section has a reflectance that is substantially the same as that of the wafer surface, and more preferably a thermal conductivity that is substantially the same as that of the wafer. The entire temperature distribution is uniform including the central portion and the peripheral portion of the wafer.

The temperature distribution uniformizing unit may be formed integrally with the side wall and bottom of the liquid tank, but may be separated from the liquid tank as a spacer. In this case, for example, the spacer is formed by forming a thin film on the surface of the base material. As the substrate, a ceramic, Arton, ZEONOR, acrylic, polycarbonate, and those made of glass or of silicon carbide (SiC), and a thin _{film, SiO 2, TiO 2, ZnO} 2, MgF 2, a-Si, a- It is assumed to be composed of C, SiN, SiON, SiC, SiOC, TiN, TiON, or the like.

  According to the exposure apparatus of the present invention, the temperature distribution uniformizing unit is provided between the wafer placed in the wafer mounting region and the side wall in the liquid bath, and the temperature distribution uniformizing unit provides the surface of the wafer. Since the same surface is formed and the temperature distribution in the radial direction in the entire wafer surface is made uniform, the resolution is made uniform over the entire wafer surface.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of an exposure apparatus 1 according to an embodiment of the present invention. The exposure apparatus 1 includes an illumination optical system 11 for illuminating a photomask 10 on which a circuit pattern is drawn, and a circuit pattern on the photomask 10 illuminated by the illumination optical system 11 as a resist layer on the surface of the wafer W. And a liquid tank 13 directly below the projection optical system 12. The liquid tank 13 holds a liquid LQ having a refractive index larger than 1 as described later, and fills the space between the projection optical system 12 and the wafer.

  The illumination optical system 11 is composed of, for example, a laser light source as an exposure light source, an optical integrator, a condenser lens, and the like (not shown). The laser light source is, for example, an F2 excimer laser light source with a wavelength of 157 nm, an ArF excimer laser light source with a wavelength of 193 nm, a KrF excimer laser light source with a wavelength of 248 nm, or a mercury light source with a wavelength of 365 nm. It is projected onto the photosensitive resist layer R on the surface. The optical integrator is composed of, for example, a fly-eye lens, and forms a secondary light source image (a collection of a plurality of point light sources) by dividing the laser light emitted from the laser light source. The condenser lens converts the light from the secondary light source image formed by the fly-eye lens into illumination light having a uniform illuminance distribution.

  The photomask 10 is, for example, a circuit pattern (reticle) drawn four times on a substrate such as synthetic quartz or calcium fluoride having a high transmittance with respect to light emitted from a laser light source. The projection optical system 12 is composed of a plurality of lenses made of, for example, synthetic quartz or calcium fluoride having a high transmittance with respect to light emitted from the laser light source, and a circuit pattern drawn on the photomask 10 is, for example, The image is reduced to 1/4 and projected onto the resist layer R.

  The liquid tank 13 has a bottomed cylindrical shape, for example, a circular bottom portion 13A having a wafer placement region in the center, and a side wall portion 13B provided so as to surround the wafer placement region at the periphery of the bottom portion 13A. It is equipped with. The wafer W is placed on the wafer placement region in the liquid tank 13, and in this embodiment, a ring as a temperature distribution uniformizing portion is placed between the placed wafer W and the side wall portion 13B. Unlike the conventional case, a liquid spacer 14 is interposed between the side surface portion of the wafer W and the side wall 13B. The spacer 14 is separate from the main body (the bottom portion 13A and the side wall portion 13B) of the liquid tank 13.

The main body of the liquid tank 13 is made of, for example, aluminum, stainless steel, or ceramic. As shown separately from the wafer W in FIG. 2, the spacer 14 has a thickness that is substantially flush with the surface of the wafer W, and the reflectance of the surface is substantially the same as that of the wafer W. Thus, the temperature distribution on the entire surface including the central portion and the peripheral portion (edge region) of the wafer W is made uniform. Specifically, the spacer 14 has a configuration in which a thin film 14A is formed on a substrate 14B, for example. Thin film 14A is almost the same material as that of the wafer W is the reflectance of the surface, for _{example, SiO 2, TiO 2, ZnO} 2, MgF 2, a-Si, a-C, SiN, SiON, SiC, SiOC, TiN Or it consists of TiON etc., and is comprised by the single layer film or multilayer film with a film thickness of about 10-300 nm. Here, the reflectances of the thin film 14A and the wafer W are substantially the same, not only in the strict sense of the same, but also due to the difference between the central portion and the peripheral portion of the wafer W. If the resolution is uniform and the non-uniformity of resolution caused by this is of a level that does not cause a problem in practice, the difference is included (for example, 0.05% or less).

  In order to achieve a uniform temperature distribution on the surface of the wafer W in this way, it is desirable that not only the reflectance but also the thermal conductivity of the spacer 14 is as close as possible to that of the wafer W. In this case, as in the case of the reflectance, if the temperature non-uniformity generated between the central part and the peripheral part of the wafer W due to the difference and the non-uniformity of resolution caused by this are not problematic in practice, this is allowed. (For example, 0.05% or less). For this reason, examples of the material of the substrate 14B include ceramic, arton, zeonore, acrylic, polycarbonate, glass, and silicon carbide (SiC).

Examples of the liquid LQ include pure water (refractive index 1.44), perfluorinated polyether (refractive index 1.3), Cs ₂ SO ₄ (refractive index 1.6), H ₂ SO ₄ (refractive index 1.65) or Those having a refractive index greater than 1 such as H ₃ PO ₄ (refractive index 1.5) are used.

  Note that the gap D between the spacer 14 and the wafer W when installed in the liquid tank 13 is preferably as small as possible so that the liquid LQ does not enter the gap D, but there is a gap D of 50 μm or more and 100 μm or less. It does not matter (see FIG. 2).

  Next, the operation of the exposure apparatus 1 having such a configuration will be described.

  First, the illumination optical system 11, the photomask 10, and the projection optical system 12 are arranged in this order so that each optical axis coincides with the optical axis AX, and the liquid tank 13 is arranged immediately below the projection optical system 12. In the liquid tank 13, a ring-shaped spacer 14 is fitted between the wafer W and the side wall 13B. Subsequently, the wafer L and the spacer 14 in the liquid tank 13 are filled with the liquid LQ, the tip of the projection optical system 12 (lens 12A) is immersed in the liquid LQ, and the position of the wafer W is the position of the projection optical system 12. The upper and lower positions of the liquid tank 13 are adjusted so as to be the working distance. Thereafter, laser light is emitted from the illumination optical system 11 to irradiate a circuit pattern on the photomask 10 and an imaging light beam from the circuit pattern is applied to the surface of the wafer W through the projection optical system 12 and the liquid LQ. An image is projected onto the resist layer R.

  At this time, the light emitted from the projection optical system 12 is not only absorbed by the resist layer R but also reflected on the surface of the resist layer R, or transmitted through the resist layer R and then reflected on the surface of the wafer W. . The amount of the reflected light has a property of changing according to the wavelength of light emitted from the illumination optical system 11 and the NA (numerical aperture) of the projection optical system 12. Specifically, when the wavelength of light emitted from the illumination optical system 11 is shortened or the NA of the projection optical system 12 is increased, the focal length of the projection optical system 12 is shortened, and accordingly the incident angle to the wafer W is increased. Becomes smaller, the amount of the reflected light increases.

  When the amount of reflected light increases in this way, standing waves generated by incident light and reflected light become conspicuous in the resist layer R of the wafer W, thereby changing the resolution. This variation in resolution can be eliminated by providing an antireflection film under the resist layer R to suppress standing waves, but this is due to the occurrence of the temperature distribution in the radial direction of the wafer W as described above. Variations in resolution cannot be resolved.

  Here, the effect of the present embodiment will be described by comparing with a comparative example. The comparative example has the same configuration as that of the present embodiment except that the spacer 14 is not provided.

  In the comparative example, since the spacer 14 is not provided as described above, the side surface of the wafer W is also filled with the liquid LQ. Accordingly, the depth of the liquid LQ is not constant in the radial direction, and changes rapidly at the peripheral edge (near the edge) of the wafer W. Further, since the reflectivity and thermal conductivity of the wafer W and the liquid tank 13 are generally different, the reflectivity and thermal conductivity are not constant in the radial direction but change rapidly in the vicinity of the edge of the wafer W. For these reasons, the degree to which the temperature of the liquid LQ rises due to the reflected light and heat radiation is not uniform in the radial direction, and is lower than the central region near the edge of the wafer W.

  As a result, the temperature distribution of the liquid LQ is not uniform in the radial direction of the wafer W, and the refractive index of the liquid LQ is not uniform in the radial direction, so that the resolution is not uniform in the radial direction. Further, since the stray light of the reflected light is reduced near the edge as compared with the central region of the wafer W, the influence of the stray light on the resolution is reduced. Furthermore, since the turbulent flow of the liquid LQ tends to occur in the vicinity of the edge of the wafer W, there is a possibility that bubbles are generated and an exposure defect occurs.

  On the other hand, in the present embodiment, as described above, the spacer 14 is present around the wafer W, and there is no liquid LQ in the gap between the wafer W and the spacer 14, or even if there is very little. is there. Accordingly, the depth of the liquid LQ is uniform in the radial direction and does not change near the edge of the wafer W. Further, since the spacer 14 is a separate body from the main body of the liquid tank 13, the reflectance and the thermal conductivity can be adjusted independently, so that the reflectance and the thermal conductivity of the wafer W and the spacer 14 are substantially reduced. Can be the same. Accordingly, the reflectance and the thermal conductivity are uniform in the radial direction and do not change near the edge of the wafer W. For these reasons, the degree to which the temperature of the liquid LQ rises due to the reflected light and the heat radiation becomes uniform in the radial direction, and the degree of temperature rise in the central region and the vicinity of the edge of the wafer W is the same.

  As a result, the temperature distribution of the liquid LQ is uniform in the radial direction, and thus the refractive index of the liquid LQ is also uniform in the radial direction, so that the resolution is uniform in the radial direction. Further, since the amount of the stray light of the reflected light is the same between the central region of the wafer W and the vicinity of the edge, the influence of the stray light on the resolution is the same. In addition, since the turbulent flow of the liquid LQ does not occur in the vicinity of the edge of the wafer W, there is no possibility that bubbles are generated and an exposure defect occurs.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above embodiment, it has been described that the reflectance and the thermal conductivity of the wafer W and the spacer 14 are preferably the same (substantially the same), but the present invention is not limited to this. If the thermal conductivity of the wafer W is sufficiently small, the thermal conductivity of the spacer 14 may be different from that of the wafer W. If the reflectance of the wafer W is sufficiently small, the reflection of the spacer 14 is not necessary. The rate may be different from that of the wafer W.

  Further, the liquid tank 13 is not limited to that shown in FIG. 1, and a configuration of a modified example as shown in FIG. 3 or FIGS. 4A to 4C can be selected. In FIG. 3, a wafer holder 15 is interposed between the bottom 13A of the liquid tank 13 and the wafer W, and the thickness of the spacer 14 is equal to the total thickness of the wafer holder 15 and the wafer W.

  4 (A) to 4 (C) show the case where the independent spacer 14 of the above embodiment is eliminated. 4A, the tray 16 having a holding groove 16A for holding the wafer W instead of the spacer 14 is accommodated in the liquid tank 13. In FIG. FIG. 4B is a view in which the bottom 13A of the liquid tank 13 of the above embodiment is thickened, and a holding groove 17 for holding the wafer W is provided on the bottom 13A. FIG. The bottom portion 13A is thickened, a holding groove 18 is provided in the bottom portion 13A, and the wafer holder 19 and the wafer W are stacked and accommodated in the holding groove 18. In any of the examples, the wafer W and the surrounding portion constitute the same plane and are in close contact, and the reflectance, more preferably the thermal conductivity, is substantially the same as in the above embodiment. That is, the tray 16 (FIG. 4A) and the main body of the liquid tank 13 may be made of the materials shown in the above embodiment.

It is a schematic block diagram of the exposure apparatus which concerns on one embodiment of this invention. It is a perspective view for demonstrating a structure of a spacer. It is sectional drawing showing the structure of the modification of a liquid tank. It is sectional drawing showing the structure of the other modification of a liquid tank.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Exposure apparatus, 10 ... Photomask, 11 ... Illumination optical system, 12 ... Projection optical system, 13 ... Liquid tank, 13A ... Bottom part, 13B ... Side wall part, LQ ... Liquid, R ... Resist layer, W ... Wafer

Claims (8)

An illumination optical system for illuminating a photomask on which a circuit pattern is drawn, and
A projection optical system that projects a circuit pattern on a photomask illuminated by the illumination optical system onto a resist layer on the surface of the wafer;
An exposure apparatus comprising: a liquid tank that holds a liquid that fills a space between the projection optical system and the wafer,
The liquid tank is provided integrally with the bottom portion having a wafer placement region, a sidewall portion surrounding the wafer placement region, a wafer placed in the wafer placement region, and the sidewall portion. An exposure apparatus comprising: a temperature distribution uniformizing unit that is interposed between the first and second wafers and forms a surface substantially the same as the surface of the wafer to uniform the temperature distribution of the entire wafer surface. The exposure apparatus according to claim 1, wherein the temperature distribution uniformizing unit has substantially the same reflectance as that of the wafer surface. The exposure apparatus according to claim 1, wherein the temperature distribution uniformizing unit has a thermal conductivity substantially the same as that of the wafer. 4. The exposure apparatus according to claim 1, wherein a gap between the temperature distribution uniformizing unit and the wafer is 50 μm or more and 100 μm or less. 5. The exposure apparatus according to any one of claims 1 to 4, wherein the temperature distribution uniformizing unit is a separate spacer from the side wall and the bottom. The exposure apparatus according to any one of claims 1 to 4, wherein the temperature distribution uniformizing unit is formed integrally with the side wall and the bottom. The exposure apparatus according to claim 5, wherein the spacer is formed by forming a thin film on a surface of a base material. The substrate is a ceramic, Arton, ZEONOR, acrylic, polycarbonate, formed by glass or SiC, the thin _{film, SiO 2, TiO 2, ZnO} 2, MgF 2, a-Si, a-C, SiN, SiON, The exposure apparatus according to claim 7, wherein the exposure apparatus is made of SiC, SiOC, TiN, or TiON.

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