JP2005311020A - Exposure method and method of manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure method for implementing highly precise exposure by decreasing the influence of the anisotropy image forming property of a projection optical system, mainly center astigmatism, caused by lighting conditions. <P>SOLUTION: Under lighting conditions where light intensity distribution in a fourier transform equivalent surface to the surface of the pattern of reticle R in which the pattern is formed (for example, pupil surfaces of a lighting optical system, a projection optical system PL or the like) is rotationally asymmetric on an optical axis (for example, dipole lighting condition and the like), center astigmatism generated in the projection optical system is corrected. The pattern is transferred to a wafer W via the projection optical system after the correction. This makes it possible to implement highly precise exposure since the influence of the center astigmatism of the projection optical system caused by the lighting conditions is decreased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exposure method and a device manufacturing method, and more specifically, an exposure method used in a lithography process in manufacturing an electronic device (microdevice) such as a semiconductor element or a liquid crystal display element, and a device manufacturing method including the exposure method. About.

  Conventionally, various exposure apparatuses have been used when manufacturing a semiconductor element or a liquid crystal display element in a photolithography process. At present, a pattern of a photomask or a reticle (hereinafter, collectively referred to as “reticle”) is used. , A projection exposure apparatus for transferring onto a substrate such as a wafer or a glass plate having a photosensitive agent such as a photoresist coated on the surface via a projection optical system, for example, a so-called step-and-repeat reduction projection exposure apparatus (so-called stepper) ) Is used.

  In recent years, along with the high integration of semiconductor elements, the reticle pattern is projected onto the projection optical system by illuminating the reticle with rectangular or arc-shaped illumination light and synchronously scanning the reticle and substrate with respect to the projection optical system in a one-dimensional direction. A scanning exposure apparatus such as a so-called slit scan system or a so-called step-and-scan system that sequentially transfers images onto a substrate via a substrate has been developed. According to such a scanning exposure apparatus, it is possible to transfer a reticle pattern using only a part (central part) of the effective exposure field of the projection optical system with the least aberration, and therefore, compared with a static exposure apparatus. It becomes possible to expose a fine pattern with higher accuracy. Further, according to the scanning exposure apparatus, the exposure field can be enlarged in the scanning direction without being restricted by the projection optical system, so that a large area exposure is possible, and the reticle is used with respect to the projection optical system. In addition, the relative scanning of the wafer has an averaging effect, and there is an advantage that improvement of distortion, depth of focus, uniformity of exposure amount distribution, and the like can be expected.

  On the other hand, in the scanning exposure apparatus, the illumination area that illuminates the reticle has a rectangular or arc shape elongated in the non-scanning direction, so that the projection optical system absorbs the illumination light, thereby orthogonally intersecting the optical axis. Imaging characteristics with different changes in the biaxial directions (hereinafter also referred to as “anisotropic imaging characteristics” in the present specification), for example, rectangular distortion, center ass, etc. The imaging characteristics change according to the absorption of illumination light. Here, the center ass means the anisotropy of the focus in the vicinity of the optical axis center of the projection optical system, and more specifically, the first pattern and the second pattern whose periodic directions are orthogonal to each other. Means the imaging characteristics of the projection optical system in which the imaging positions of the first pattern and the second pattern (positions in the optical axis direction) are shifted when placed near the optical axis of the projection optical system. To do. The focus anisotropy is nothing but astigmatism. In this specification, terms such as “center ass” and “focus anisotropy” are used in this sense.

  An invention relating to a projection optical system capable of suppressing deterioration of anisotropic imaging characteristics due to absorption of illumination light in a scanning exposure apparatus, and changes in anisotropic imaging characteristics due to absorption of illumination light by the projection optical system An invention related to a scanning exposure apparatus that suppresses and improves exposure accuracy has been proposed previously by the present applicant (see, for example, Patent Document 1).

  By the way, in a recent exposure apparatus, modified illumination using two-beam interference, for example, dipole illumination, as a kind of super-resolution technique that improves the resolving power without reducing the effective depth of focus more than necessary. (Dipole illumination) and the like have come to be used relatively frequently during exposure with a periodic pattern as a transfer target.

  When the above-described dipole illumination or the like is employed in the scanning exposure apparatus, the inventors of the present invention are significantly larger than the center as a result of the illumination area that illuminates the reticle being elongated in the non-scanning direction. The center ass was found to be caused by the dipole illumination. The center ass due to the rotationally asymmetric illumination condition such as dipole illumination is not limited to the scanning exposure apparatus, but also occurs in a stationary exposure apparatus such as a stepper.

  However, the technique described in the above-mentioned Patent Document 1 can cope with the center ass caused by the illumination area being elongated in the non-scanning direction, but it is sufficient for the center ass when the dipole illumination is adopted. It is difficult to respond. In addition, there is no technology that can sufficiently cope with the center ass when the dipole illumination is adopted.

Japanese Patent Laid-Open No. 11-258498

  The present invention has been made under such circumstances. The first object of the present invention is to reduce the anisotropic imaging characteristics of the projection optical system caused mainly by illumination conditions, mainly the influence of the center ass. An object of the present invention is to provide an exposure method that realizes accurate exposure.

  A second object of the present invention is to provide a device manufacturing method capable of improving the productivity of microdevices.

  The invention according to claim 1 is an exposure method in which a mask is illuminated with illumination light, and a pattern formed on the mask is transferred onto a photosensitive object via a projection optical system, wherein the pattern is formed. The exposure method includes a step of correcting a center spot generated in the projection optical system under an illumination condition in which a light amount distribution on a surface corresponding to a Fourier transform with respect to a pattern surface of a mask is rotationally asymmetric with respect to an optical axis.

  In this specification, “rotational asymmetry” means “not rotationally symmetric”. Here, “rotation symmetry” is different from “rotation symmetry” in the usual meaning, that is, “a property that does not change even if a figure or the like is rotated by a certain angle around a certain axis (symmetry axis)”. , "A property that does not change even if one figure or the like is rotated at any angle of 0 ° to 360 ° around a certain axis (symmetric axis)", and in all other cases, it is rotationally asymmetric. In this specification, the terms “rotational symmetry” and “rotational asymmetry” are used in this sense.

  According to this, the illumination condition in which the light quantity distribution on the plane corresponding to the Fourier transform with respect to the pattern surface of the mask on which the pattern is formed (for example, the pupil plane of the illumination optical system or the pupil plane of the projection optical system) is rotationally asymmetric with respect to the optical axis. Under the illumination conditions where the light quantity distribution on the plane corresponding to the Fourier transform with respect to the pattern surface is rotationally asymmetric with respect to the optical axis, such as dipole illumination conditions. The center ass occurring in the projection optical system is corrected, and the pattern is transferred onto the photosensitive object by the corrected projection optical system. Therefore, it is possible to reduce the influence of the center assault of the projection optical system caused by the illumination conditions, and to realize highly accurate exposure.

  In this case, as in the exposure method according to claim 2, the illumination condition is such that a light quantity distribution having a maximum value is formed at two positions decentered by substantially the same distance from the optical axis on a surface corresponding to Fourier transform with respect to the pattern surface. The dipole illumination condition can be determined.

  According to a third aspect of the present invention, there is provided an exposure method for illuminating a mask with illumination light and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system. A first transfer step of transferring a first pattern onto a photosensitive object under a predetermined first illumination condition such that an error occurs in the projection optical system; an anisotropy generated in the projection optical system under the first illumination condition; A second transfer step of transferring the second pattern onto the photosensitive object under a second illumination condition in which an imaging characteristic that relieves the imaging characteristic is generated in the projection optical system. is there.

  According to this, the first pattern is transferred onto the photosensitive object under a predetermined first illumination condition that causes anisotropic imaging characteristics to occur in the projection optical system (first transfer step), and the first pattern is transferred to the first pattern. The second pattern is transferred onto the photosensitive object under a second illumination condition in which an imaging characteristic that relaxes the anisotropic imaging characteristic generated in the projection optical system under the illumination condition is generated in the projection optical system ( Second transfer step).

  For this reason, the second pattern is transferred onto the photosensitive object in a state where the anisotropic imaging characteristics are relaxed, and at least when the second pattern is transferred, the projection optical system generated due to illumination conditions It is possible to reduce the influence of the anisotropic imaging characteristics, for example, center ass, and to realize highly accurate exposure.

  In this case, as in the exposure method according to claim 4, the first illumination condition is that the surface corresponding to the Fourier transform with respect to the pattern surface of the mask on which the first pattern is formed is substantially from the optical axis with respect to the first axis direction. It is a first dipole illumination condition in which a light quantity distribution having a maximum value is formed at two positions decentered by the same distance, and the second illumination condition is a Fourier with respect to the pattern surface of the mask on which the second pattern is formed. The second dipole illumination condition is such that a light quantity distribution having local maximum values is formed at two positions that are decentered from the optical axis by substantially the same distance in the second axis direction orthogonal to the first axis direction on the conversion equivalent surface. be able to. In such a case, the temperature distribution resulting from the absorption of the illumination light of the projection optical system approaches rotational symmetry, and it becomes possible to reduce anisotropic imaging performance, for example, center ass.

  In each of the exposure methods according to claims 3 and 4, as in the exposure method according to claim 5, the first pattern is mainly a periodic pattern having a direction corresponding to the first illumination condition as a periodic direction. In addition, the second pattern may mainly include a periodic pattern having a direction corresponding to the second illumination condition as a periodic direction.

  In each of the exposure methods according to claims 3 to 5, as in the exposure method according to claim 6, the first transfer step and the second transfer step can be performed alternately. . In such a case, not only the second pattern but also the first pattern is transferred onto the photosensitive object in a state where anisotropic imaging characteristics are relaxed. This is because the first illumination condition and the second illumination condition alleviate anisotropic imaging characteristics, such as center ass, that occur in the projection optical system under one illumination condition, under the other illumination condition. It is because of the relationship.

  In this case, as in the exposure method according to claim 7, the first transfer step and the second transfer step are alternately executed every time one lot of the photosensitive object is processed. Can do.

  In each of the exposure methods according to claims 3 to 7, as in the exposure method according to claim 8, in the first transfer step, the first pattern is transferred onto a photosensitive object by a scanning exposure method. In the two-transfer process, the second pattern can be transferred onto the photosensitive object by a scanning exposure method.

  In this case, as in the exposure method according to the ninth aspect, the scanning direction can be changed by 90 ° between the first transfer step and the second transfer step.

  In each of the exposure methods according to claims 8 and 9, as in the exposure method according to claim 10, the projection optical system is a catadioptric system in which an illumination area that illuminates the pattern is decentered from the optical axis. In this case, at least one of the first transfer step and the second transfer step, the wavefront aberration of the projection optical system caused by the eccentricity of the illumination area is series-expanded using a Zernike polynomial (Fringe-Zernike polynomial). It is possible to perform exposure in consideration of the 1θ component term among the plurality of Zernike terms.

  The invention according to claim 11 is an exposure method in which a mask is illuminated with illumination light, and a pattern formed on the mask is transferred onto a photosensitive object via a projection optical system. When the pattern is transferred under a predetermined illumination condition as occurs in the above, the position of the photosensitive object with respect to the optical axis direction of the projection optical system is focused on a periodic pattern having a direction corresponding to the illumination condition as a periodic direction. An adjustment step for adjusting the pattern; and a transfer step for transferring the pattern onto the photosensitive object whose position in the optical axis direction is adjusted.

  Here, the “direction according to the illumination condition” means that the resolution of the periodic pattern whose center direction is the predetermined direction is mainly improved under the predetermined illumination condition in which the center ass is generated in the projection optical system. It means the periodic direction of the pattern to be improved.

  According to this, when the pattern is transferred under the predetermined illumination condition, the position of the photosensitive object with respect to the optical axis direction of the projection optical system is focused on the periodic pattern whose direction is the direction according to the illumination condition. It is adjusted (adjustment process). For example, when transferring a pattern mainly including a pattern whose periodic direction is the first axial direction in a plane orthogonal to the optical axis of the projection optical system (including a pattern composed only of a pattern whose periodic direction is the first axial direction). The position of the photosensitive object with respect to the optical axis direction of the projection optical system is adjusted so that the surface of the photosensitive object coincides with the best focus position of the pattern having the first axis direction as the periodic direction. Further, for example, a pattern mainly including a pattern whose periodic direction is the second axial direction orthogonal to the first axial direction in a plane orthogonal to the optical axis of the projection optical system (consists only of a pattern whose periodic direction is the second axial direction). (Including the pattern), the position of the photosensitive object in the optical axis direction of the projection optical system is adjusted so that the surface of the photosensitive object coincides with the best focus position of the pattern having the second axis direction as the periodic direction.

  Then, the pattern is transferred under the above illumination conditions onto the photosensitive object whose position in the optical axis direction has been adjusted as described above (transfer process).

  Therefore, by focusing only on the pattern in the target periodic direction, it becomes possible to expose the target pattern with the best focus, reducing the influence of the center assault of the projection optical system caused by the illumination conditions. Highly accurate exposure can be realized.

  In this case, as in the exposure method according to claim 12, the illumination condition is an illumination condition in which a light amount distribution rotationally asymmetric with respect to the optical axis is generated on a plane corresponding to a Fourier transform with respect to a pattern surface on the mask on which the pattern is formed. Can be.

  In this case, as in the exposure method according to claim 13, the illumination condition is such that a light amount distribution having a maximum value is formed at two positions decentered by substantially the same distance from the optical axis on a surface corresponding to a Fourier transform with respect to the pattern surface. The dipole illumination condition can be determined.

  The invention described in claim 14 is a device manufacturing method including a lithography process, wherein the exposure method according to any one of claims 1 to 13 is executed in the lithography process. Is the method.

  According to the exposure method of the present invention, it is possible to reduce the anisotropic imaging characteristics of the projection optical system caused mainly by the illumination conditions, mainly the influence of center ass, and to realize highly accurate exposure. is there.

  Moreover, according to the device manufacturing method of the present invention, there is an effect that the productivity of the microdevice can be improved.

<< First Embodiment >>
A first embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 shows a schematic configuration of a scanning exposure apparatus 100 according to the first embodiment suitable for carrying out the exposure method of the present invention. The scanning exposure apparatus 100 is a so-called step-and-scan projection exposure apparatus.

  This scanning exposure apparatus 100 includes an illumination system including a light source 1 and illumination optical systems (2A, 2B, 3 to 10), a reticle stage RST that holds a reticle R as a mask, a projection optical system PL, and a projection optical system PL. An imaging characteristic correction mechanism 14 that corrects imaging characteristics such as magnification and aberration, a lens controller 15 that controls the imaging characteristic correction mechanism 14, a wafer stage WST that holds a wafer W as a photosensitive object, and these A control system is provided.

  The illumination system includes a light source 1, a diffractive optical unit 2A, a zoom optical system 2B, a vibrating mirror 3, a fly-eye lens 4 as an optical integrator, a half mirror 5, an integrator sensor 6, a reticle blind 7, a bending mirror 8, and a condenser lens system. 9 and the reflectance sensor 10 and the like. The optical integrator 4 is not limited to a fly-eye lens. For example, an internal reflection type integrator (such as a rod integrator) or a diffractive optical element may be used, or along the optical axis IX in the illumination optical system. A plurality of optical integrators (types may be different) may be arranged.

  The diffractive optical unit 2A is composed of a rotating plate in which a plurality of diffractive optical elements (DOEs) are arranged at predetermined angular intervals, and the rotating plate is driven by a motor (not shown). Here, the plurality of diffractive optical elements are planes corresponding to the Fourier transform of the pattern surface of the reticle R, specifically, the exit-side focal plane of the fly-eye lens 4 (pupil plane of the illumination optical system) and its conjugate plane (for example, projection) The light intensity distribution of the illumination light on the pupil plane of the optical system PL), that is, for setting various illumination conditions, is selected according to the pattern of the reticle R to be transferred to the wafer W, for example, by driving the rotating plate. One diffractive optical element most suitable for the illumination condition is arranged on the optical path of the illumination optical system. The plurality of diffractive optical elements are substantially the same from the optical axis IX of the illumination system (corresponding to the optical axis AX of the projection optical system) with respect to the X-axis direction (the direction orthogonal to the paper surface in FIG. 1) on the plane corresponding to the Fourier transform of the pattern surface. A DOE for setting an X-axis dipole illumination condition (first dipole illumination condition) in which a light quantity distribution having a maximum value is formed at two positions decentered by a distance, and a Y-axis direction (FIG. 1) in a plane corresponding to the Fourier transform of the pattern surface Y-axis dipole illumination conditions in which a light quantity distribution having a maximum value is formed at two positions decentered by substantially the same distance from the optical axis IX of the illumination system (coincided with the optical axis AX of the projection optical system) 2nd dipole illumination condition) DOE for setting, DOE for annular illumination condition setting for distributing illumination light in an annular shape outside the optical axis on the surface corresponding to the Fourier transform of the pattern surface Normal DOE etc. for illumination condition setting to distribute a circular area around the optical axis illumination light and in the Fourier transform corresponding surface of the pattern surface are included. The diffractive optical elements provided in the diffractive optical unit 2A are not limited to the four types described above. For example, the light amount distribution of illumination light on the pupil plane of the illumination optical system is decentered by substantially the same distance from the optical axis IX. It may include a diffractive optical element applied to quadrupole illumination having a maximum value at four positions, or small σ illumination in which a coherence factor (σ value) is set smaller than the above-described normal illumination.

  The zoom optical system 2B includes at least a zoom lens system (afocal system), and is a normal illumination (including small σ illumination), annular illumination, and multipolar illumination (including dipole illumination, quadrupole illumination, etc.). In each case, the size of the illumination light on the pupil plane of the illumination optical system (corresponding to the aforementioned σ value) is variable. In this embodiment, the diffractive optical unit 2A and the zoom optical system 2B described above constitute a shaping optical system that can arbitrarily set the illumination condition of the reticle.

  Note that the zoom optical system 2B may include a plurality of prisms (conical prisms, pyramid prisms, etc.) whose at least one is movable along the optical axis IX of the illumination optical system and whose interval is variable. And at least one of the plurality of prisms, the σ value and the annular ratio (ratio between the inner diameter and the outer diameter) in annular illumination, and the σ value and the light quantity distribution on the pupil plane of the illumination optical system are maximized in multipolar illumination. The position (interval with the optical axis IX) and the like can be arbitrarily changed. When an internal reflection type integrator is used as the optical integrator 4, the zoom optical system 2B collects the illumination light generated from the diffractive optical element and passing through the zoom lens system, and enters the internal reflection type integrator. At this time, the condensing point is set such that its position is different from the incident surface of the internal reflection type integrator. Further, a variable aperture stop (iris stop) that cuts flare light (including light unnecessary for illumination of the reticle R generated by the diffractive optical element) generated in the illumination optical system, for example, an exit surface of the fly-eye lens 4 (Ie, arranged on the pupil plane of the illumination optical system or its conjugate plane).

  In addition, the incident-side focal plane (incident plane) of the fly-eye lens 4 and each diffractive optical element (DOE) on the diffractive optical unit 2A are substantially maintained in a Fourier transform relationship via the zoom optical system 2B. It has become.

  On the other hand, the exit-side focal plane of the fly-eye lens 4 substantially coincides with the Fourier transform plane (pupil plane of the illumination optical system) of the pattern surface of the reticle R. Of course, the entrance-side focal plane and the exit-side focal plane of the fly-eye lens 4 are in a Fourier transform relationship. Therefore, in the present embodiment, the exit-side focal plane of the fly-eye lens 4 has an imaging relationship (conjugate) with the diffractive optical element.

Here, the components of the illumination system will be described together with their actions. The illumination light IL as the exposure light generated by the light source 1 passes through a shutter (not shown) and then enters one of the DOEs of the diffractive optical unit 2A. . Thereby, the diffracted light generated from the DOE enters the zoom optical system 2B. As the illumination light IL, for example, KrF excimer laser light (wavelength 248 nm), ArF excimer laser light (wavelength 193 nm), F ₂ laser light (wavelength 157 nm), or the like is used.

  The light beam emitted from the zoom optical system 2B is bent in the horizontal direction through the vibrating mirror 3 for smoothing interference fringes and weak speckles generated on the irradiated surface (reticle surface or wafer surface), and fly-eye. The lens 4 converts the illuminance distribution (intensity distribution) into a substantially uniform light beam. That is, a secondary light source (surface light source) composed of a number of point light sources (light source images) is formed on the exit-side focal plane of the fly-eye lens 4. In the present embodiment, the pupil plane of the illumination system, which is the exit-side focal plane of the fly-eye lens 4, is distributed in a circular area including the optical axis as a whole, according to the DOE selectively arranged on the optical path. Secondary light source (corresponding to normal illumination conditions) consisting of a large number of point light sources (light source images), from a large number of point light sources (light source images) distributed in two circular regions decentered by the same distance from the optical axis in the X-axis direction Secondary light source (corresponding to the X-axis dipole illumination condition), secondary light source (Y-axis) consisting of a number of point light sources (light source images) distributed in two circular regions decentered by the same distance from the optical axis in the Z-axis direction Corresponding to dipole illumination conditions), secondary light sources composed of a large number of point light sources (light source images) distributed in a ring-shaped region centered on the optical axis, and the like are formed.

  And most (about 97%) of the light (pulse illumination light) IL emitted from the secondary light source passes through the half mirror 5 and illuminates the reticle blind 7 with uniform illuminance.

  Here, the reticle blind 7 is composed of two movable blinds and a fixed blind having a fixed opening shape disposed in the vicinity thereof. The slit-shaped illumination area IAR for illuminating the reticle R by the reticle blind 7 can be set to a rectangular shape having a desired shape and size.

  The light beam that has passed through the reticle blind 7 reaches a folding mirror 8 where it is bent vertically downward to illuminate an illumination area IAR portion of the reticle R on which a circuit pattern or the like is drawn via a condenser lens system 9.

  On the other hand, the remaining illumination light IL (about 3%) is reflected by the half mirror 5 and received by the integrator sensor 6. The integrator sensor 6 can detect the amount of illumination light with respect to the reticle R. A light amount signal from the integrator sensor 6 is supplied to the main controller 21.

  The reflectivity monitor 10 is used for measuring wafer reflectivity (reflected light amount), which is a basis for calculating fluctuations in imaging characteristics (various aberrations) due to illumination light absorption of the projection optical system PL, that is, irradiation fluctuations. The amount of light returned from the projection optical system PL side through the condenser lens system 9, the bending mirror 8, and the reticle blind 7 is detected. A light amount signal from the reflectance monitor 10 is also supplied to the main controller 21. The method for measuring the wafer reflectivity is disclosed in, for example, the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 11-258498) and the like and is not described in detail because it is known.

On reticle stage RST, reticle R is fixed, for example, by vacuum suction. Note that the material used for the reticle R needs to be properly used depending on the type of the illumination light IL. That is, in the case where KrF excimer laser light or ArF excimer laser light is used as the illumination light IL, synthetic quartz can be used in addition to fluorite, but when F ₂ laser light is used, fluorite is used. Need to form.

  The reticle stage RST is driven on a reticle base (not shown) by a reticle driving unit 41 configured by a linear motor or the like, and is in a plane perpendicular to the optical axis IX of the illumination system (matching the optical axis AX of the projection optical system PL). Thus, it is movable within a predetermined stroke range in a predetermined scanning direction (here, Y-axis direction).

  The position of the reticle stage RST is constantly measured by a reticle laser interferometer system (not shown) with a resolution of about 0.5 to 1 nm, for example. The position information of the reticle stage RST from this reticle laser interferometer system is mainly The main controller 21 controls the reticle stage RST via the reticle drive unit 41 based on the position information of the reticle stage RST. Note that, for example, two measurement axes of the reticle laser interferometer system are provided in the scanning direction and one axis in the non-scanning direction.

  The projection optical system PL is arranged below the reticle stage RST in FIG. 1, and the direction of the optical axis AX (coincident with the optical axis IX of the illumination system) is the Z-axis direction. This projection optical system PL uses a birefringent optical system composed of a plurality of lens elements (lenses) 30a to 30j (see FIG. 2) having a telecentric reduction system on both sides and a common optical axis in the Z-axis direction. . In FIG. 2, reference numeral 30p indicates the pupil plane of the projection optical system PL.

  The projection magnification β of the projection optical system PL is, for example, 1/4 or 1/5. Therefore, when the illumination area IAR on the reticle R is illuminated by the illumination light IL from the illumination system, a part of the circuit pattern of the reticle R is passed through the projection optical system PL by the illumination light IL that has passed through the reticle R. Is reduced and projected onto the wafer W whose surface is coated with a photoresist.

  Further, as described above, the imaging characteristic correction mechanism 14 is provided in the projection optical system PL. As the imaging characteristic correction mechanism 14, as disclosed in Patent Document 1 and the like, a plurality of specific lens elements (hereinafter referred to as “movable lens”) among the plurality of lenses 30 a to 30 j constituting the projection optical system PL. ) Is driven independently using a piezo element or the like in the optical axis AX direction (Z direction) and the tilt direction with respect to the XY plane. Each of the movable lenses described above can be driven in the optical axis AX direction (Z direction) and the tilt direction with respect to the XY plane. Further, the driving amount of the support point of each movable lens by each piezoelectric element is monitored by a sensor (not shown). According to this imaging characteristic correction mechanism 14, by driving or tilting each of the plurality of movable lenses in the optical axis direction, various imaging characteristics change, and each movable lens is driven in the optical axis direction. The rotationally symmetric aberration (imaging characteristics) can be adjusted to a desired state by any combination of tilt driving.

  In the present embodiment, the magnification and the aberration (at least one of the five Zeisel aberrations), specifically, the curvature of the field are caused by the imaging characteristic correction mechanism 14 in the same manner as disclosed in, for example, Patent Document 1 above. , Distortion, coma aberration, and spherical aberration are corrected, and this imaging characteristic correction mechanism 14 and lens controller 15 constitute an imaging characteristic correction apparatus that corrects the imaging characteristics of the pattern image of the reticle R. Has been. In addition to driving the lens, the imaging characteristic correction device may adjust the imaging characteristic by controlling the light source 1 and slightly shifting the wavelength of the illumination light, for example.

In the case where KrF excimer laser light or ArF excimer laser light is used as the illumination light IL, as a material of each lens element constituting the projection optical system PL, synthetic quartz or the like can be used in addition to fluorite. In the case of using the F ₂ laser light, fluorite is all used as the material of the lens element used in the projection optical system PL. Besides fluorite, fluoride single crystals such as lithium fluoride, magnesium fluoride and strontium fluoride, composite fluoride crystals of lithium-calcium-aluminum, composite fluoride crystals of lithium-strontium-aluminum, zirconium -Fluorine glass composed of barium-lanthanum-aluminum, quartz glass doped with fluorine, quartz glass doped with hydrogen in addition to fluorine, quartz glass containing OH groups, OH groups contained in addition to fluorine Improved quartz such as quartz glass may be used.

Further, in the exposure apparatus 100 of the present embodiment, as shown in FIG. 2, a fiber (particularly a fiber in which the inner surface of a hollow glass tube is coated with aluminum) FB is introduced into the projection optical system PL from the outside. ing. In this case, actually, as shown in FIG. 3, a plurality of fibers FB _{1 to} FB _n are respectively arranged at predetermined angular intervals along the outer periphery of the optical member, for example, the lenses (30c, 30d, 30g). Has been introduced. These fibers FB are connected to an infrared irradiation source (not shown) provided outside the projection optical system PL. In this case, an infrared irradiation mechanism is constituted by a plurality of fibers FB _{1 to} FB _n and an infrared irradiation source (not shown).

Here, for example, when the F ₂ laser light is used as illumination light IL, a lens 30a~30j for constituting the projection optical system PL, fluorite is used. In this case, infrared rays having a wavelength of about 6 to 10 μm, which are absorbed relatively well by the fluorite lens, are irradiated from the fibers FB ₁ to FB _n constituting the infrared irradiation mechanism by the lenses (30c, 30d, 30g). . As an infrared irradiation source in this case, for example, a semiconductor laser using a compound semiconductor such as lead sulfur selenide, lead tin selenide, lead tin telluride or the like can be used.

  In the present embodiment, the main controller 21 controls the infrared irradiation mechanism in accordance with the reticle pattern and illumination conditions used for the exposure. This point will be described later.

  Wafer stage WST includes a Y-axis direction (horizontal direction in FIG. 1) which is a scanning direction on a base (not shown) including a linear motor and a voice coil motor, and an X-axis orthogonal thereto. 1 (longitudinal direction in FIG. 1) with a long stroke, and Z direction, θz direction (rotation direction around Z axis), θx direction (rotation direction around X axis), and θy direction (Y axis) It is finely driven in the rotation direction).

  Wafer W is sucked and held via wafer holder 17 on wafer stage WST. On wafer stage WST, an irradiation amount sensor 20 that detects an irradiation amount that reaches the wafer surface through reticle R and projection optical system PL is provided. The detection value of the dose sensor 20 is supplied to the main controller 21.

  The position in the XY plane of wafer stage WST (ie, wafer W) is always measured by a wafer laser interferometer system (not shown) with a resolution of about 0.5 nm to 1 nm, for example. Wafer laser interferometer system is an X-axis interferometer that measures the positions of wafer stage WST in the X-axis direction and the Y-axis direction by irradiating laser beams onto the reflecting surfaces provided (or formed) on wafer stage WST, respectively. , Each Y-axis interferometer has. These X-axis and Y-axis interferometers are composed of multi-axis interferometers having a plurality of measurement axes. In addition to the X and Y positions of wafer stage WST, rotation (yawing (θz rotation that is rotation around the Z axis)), pitching (Θx rotation that is rotation around the X axis) and rolling (θy rotation that is rotation around the Y axis)) can also be measured. In addition, the multi-axis interferometer described above tilts the laser beam to a reflection surface installed on a gantry (not shown) on which the projection optical system PL is mounted via a reflection surface installed on wafer stage WST with an inclination of 45 °. Irradiation may be performed to detect relative position information regarding the optical axis direction (Z-axis direction) of the projection optical system PL.

  The position information of wafer stage WST from the wafer laser interferometer system is sent to main controller 21, and main controller 21 moves wafer W in the XY plane via wafer drive unit 42 based on the position information of Z stage 17. Position control.

  Further, in the scanning exposure apparatus 100 of the present embodiment, two autofocus detection systems, that is, reticle autofocus, which are integrally attached to the projection optical system PL (or its mount) via a holding member (not shown). A detection system (hereinafter referred to as “reticle AF system”) 12 (12a, 12b) and a wafer autofocus detection system (hereinafter referred to as “wafer AF system”) 19 (19a, 19b) are provided.

  The wafer AF system 19 includes an irradiation optical system 19a that irradiates the wafer W with a detection beam obliquely, and a light receiving optical system 19b that receives reflected light from the wafer W surface of the detection beam. An oblique incidence type focal position detection system is used to detect the position. As this wafer AF system 19, for example, a focal position detection system disclosed in Japanese Patent No. 3316833 is used.

  The reticle AF system 12 also includes an obliquely incident optical system 12a that irradiates the pattern surface of the reticle R with a detection beam obliquely and a light receiving optical system 12b that receives reflected light from the reticle surface of the detection beam. An optical focus position detection system is used. The reticle AF system 12 is for detecting the position in the Z direction of the optical axis IX of the pattern surface of the reticle R and the area in the vicinity thereof. As the reticle AF system 12, one having the same configuration as that disclosed in the above-mentioned Japanese Patent No. 3316833 can be used.

  Note that the AF system is not limited to the oblique incidence type, and for example, an interferometer that measures the Z position of the wafer surface and the reticle surface and an autofocus sensor that directly measures the distance between the projection optical system and the wafer or reticle are adopted. You may do it.

  Furthermore, the scanning exposure apparatus 100 of the present embodiment is provided with an environmental sensor 36 that detects a change in the environment in the vicinity of the projection optical system PL. As the environmental sensor 36, various sensors such as an atmospheric pressure sensor (pressure sensor), a temperature sensor, and a humidity sensor can be provided. However, the main part of the exposure apparatus that normally includes the projection optical system is placed in a chamber in which the temperature and humidity are strictly controlled. It is considered small. Therefore, in the present embodiment, an atmospheric pressure sensor is provided as the environment sensor 36. However, depending on the arrangement and configuration of the air conditioning system of the exposure apparatus, the atmospheric pressure is not necessarily the same inside and outside the projection optical system PL. Therefore, in this embodiment, as shown in FIG. An internal pressure sensor 36a that detects the pressure of the gas inside the projection optical system PL (hereinafter referred to as “internal pressure” as appropriate) and the atmospheric pressure (hereinafter referred to as “external pressure” as appropriate) in a chamber outside the projection optical system PL are measured. An external atmospheric pressure sensor 36b is provided. In FIG. 1, it is assumed that the internal pressure sensor 36a and the external pressure sensor 36b are representatively shown as the environmental sensor 36. The calculation method of the imaging characteristic change due to the change in the atmospheric pressure (the above-described external pressure and internal pressure) is disclosed in, for example, Patent Document 1 and the like, and thus the description thereof is omitted.

  In addition, the scanning exposure apparatus 100 of the present embodiment is also provided with an off-axis type alignment system (not shown) for detecting alignment marks (not shown) attached to each shot area on the wafer W. Yes. The main controller 21 detects the position of the alignment mark on the wafer W using an alignment system prior to scanning exposure, which will be described later. Based on the detection result, the reticle driving unit 41 and the wafer driving device 42 perform reticle detection at the time of scanning exposure. The synchronous movement of R and the wafer W is performed.

Next, the principle of scanning exposure in the scanning exposure apparatus 100 of this embodiment will be briefly described. The reticle R is illuminated by a rectangular (slit-shaped) illumination area IAR having a longitudinal direction in a direction (X-axis direction) perpendicular to the scanning direction (Y-axis direction) of the reticle R, and the reticle R is illuminated during exposure by the illumination area IAR. Is moved relative to each other at a speed V _R in one direction (for example, −Y direction), and the entire pattern area is illuminated. The illumination area IAR (center substantially coincides with the optical axis AX) is projected onto the wafer W via the projection optical system PL, and a slit-shaped projection area conjugate to the illumination area IAR, that is, the exposure area IA is formed. Since an inverted image of the reticle pattern is formed in the exposure area IA, the wafer W is placed on the reticle R in a direction (+ Y direction) opposite to the scanning direction of the reticle R (here, the −Y direction) with respect to the exposure area IA. The relative movement is performed at the speed V _W in synchronization, and the entire shot area on the wafer W is scanned and exposed with illumination light. In this scanning exposure, the reticle R and the wafer W, that is, the reticle stage RST and the wafer stage WST are accurately matched to the reduction magnification of the projection optical system PL by the reticle driving unit 41, the wafer driving device 42, and the main control device 21. Are moved synchronously at a speed ratio V _W / V _R (= 1/4 or 1/5), and the pattern area pattern of the reticle R is accurately reduced and transferred onto the shot area on the wafer W. The

  During the scanning exposure, the pattern surface of the reticle R and the surface of the wafer W are conjugated with respect to the projection optical system PL based on the detection signals of the wafer AF system 19 and the reticle AF system 12 (that is, the exposure area IA). At least one of wafer stage WST and reticle stage RST is moved in the Z-axis direction via wafer drive device 42 by main controller 21 so that the image plane of projection optical system PL and the surface of wafer W substantially coincide with each other. The drive is controlled, and focus correction described later is executed. At this time, tilt driving of at least one of the reticle R and the wafer W, that is, leveling control is also performed.

  In the scanning exposure apparatus 100, the reticle pattern transfer by scanning exposure on the shot area on the wafer W and the stepping operation to the acceleration start position (scanning start position) for exposure of the next shot area are repeated. By doing so, step-and-scan exposure is performed, and the reticle pattern is transferred to all shot regions on the wafer W.

  Next, focus correction in the scanning exposure apparatus 100 will be described. First, the simplest case where the focus change of the projection optical system PL itself is not considered will be described.

First, in order to obtain a conjugate relationship between reticle R and wafer W, a position (Z position) in the Z-axis direction of wafer stage WST serving as a reference is obtained. That is, a measurement reticle on which a predetermined measurement mark is drawn is mounted at a predetermined location on the reticle stage RST, and the measurement mark is moved while stepping the wafer stage WST in the Z-axis direction and the X-axis or Y-axis direction. Transferred onto the wafer W coated with a photosensitive agent. Next, the Z position Z _best of the mark shape baked by observing the wafer W with an optical microscope is best (eg mark shape is greatest or mark edges are most standing) wafer stage WST, the memory Is found on the basis of the data on the correspondence between each target value Z _i and the position P _i stored in. Then, the position Z _best is set as a reference position, and the outputs of the reticle AF system 12 and the wafer AF system 19 when the Z position of the wafer stage WST is at the reference position are stored in the memory as the respective AF reference positions. Subsequent focus fluctuation correction is managed by displacement from this reference position.

  Note that it is assumed that the best focus plane varies depending on the periodic direction (X-axis direction and Y-axis direction) of the pattern due to an anisotropic focus shift described later. Therefore, the focus described here refers to an average best focus plane in consideration of anisotropic focus. The reticle AF system 12 and the wafer AF system 19 can measure position information at a plurality of points in the illumination area IAR and the exposure area IA, respectively, and the above-mentioned AF reference positions are obtained at the plurality of points, respectively, in the memory. It is remembered. Further, instead of the trial baking, for example, the projection image of the reticle mark or the reference mark of the reticle stage RST is detected by the photoelectric sensor of the wafer stage WST, so that projections in the Z-axis direction are performed at a plurality of points in the exposure area IA. The image plane position (focus position) of the optical system PL may be obtained.

  Then, during actual scanning exposure, the main controller 21 prevents the outputs of the reticle AF system 12 and the wafer system AF 19 from fluctuating from the respective AF reference positions (that is, the optical relationship between the reticle R and the wafer W). Wafer stage WST is driven and controlled in the direction of the optical axis (so that a certain distance is kept constant). In this way, focus correction is performed.

More specifically, assuming that the detected reticle R and wafer W side displacement relative to the AF reference position are Rz and Wz, and the projection magnification is ML, the focus displacement ΔF is
ΔF = Rz × ML ² −Wz (1)
It is expressed. By moving wafer stage WST in the Z-axis direction so that ΔF becomes 0, the conjugate relationship between reticle R and wafer W is maintained (ie, image of projection optical system PL in exposure area IA during scanning exposure). The surface and the surface of the wafer W substantially coincide).

  Next, correction when the focus of the projection optical system PL itself fluctuates due to factors such as changes in atmospheric pressure and absorption of illumination light will be described. At this time, it is possible to cope with the focus change of the projection optical system PL itself by using the following equation (2) obtained by expanding the above equation (1).

ΔF = FL + Rz × ML ² −Wz (2)

  In the above equation (2), FL corrects the focus change due to atmospheric pressure change (focus atmospheric pressure change), the focus change due to illumination light absorption (focus irradiation change), and the above five types of imaging characteristics. Therefore, this is the focus change of the projection optical system PL itself, which combines the focus change that occurs as a side effect by moving the movable lens. The focus change that occurs as a side effect due to the movement of the movable lens is to correct imaging characteristics other than the focus (that is, at least one of the five types of imaging characteristics in this embodiment). When the movable lens is driven, the focus fluctuates accordingly, which means that this influence needs to be taken into account for focus correction.

Regarding the calculation method of the amount of change in imaging characteristics (various aberrations) of the projection optical system including the focus due to atmospheric pressure change, and the amount of change in imaging characteristics (various aberrations) of the projection optical system including the focus due to illumination light absorption Since it is disclosed in detail in Patent Document 1 and the like, detailed description is omitted. In the latter case, the exposure dose Q ₁ is calculated based on the following equation (3), and is used to calculate the amount of change in the imaging characteristics (various aberrations) of the projection optical system including the focus due to illumination light absorption. .

Q ₁ = Q ₀ × I ₁ / I ₀ (3)
In the above equation (3), Q ₀ is a dose stored in advance in the memory as a function corresponding to the scanning position of the reticle R, and I ₀ is stored in the memory as a function corresponding to the scanning position of the reticle R. The output of the integrator sensor 6 stored in advance according to the scanning position of the reticle R stored in advance, and I ₁ is the output of the integrator sensor 6 at the time of exposure.

Further, the integrator sensor 6, using a reflectance monitor 10, for example by the methods disclosed in, Patent Document 1, obtained in advance calculation formula of the wafer reflectivity R _W, at the time of actual exposure scanning position of the reticle R depending on outputs of the integrator sensor 6 of the reflectance sensor 10 has been stored, and based on the outputs of the integrator sensor 6 of the reflectance sensor 10 during exposure, and calculates the wafer reflectivity R _W, lighting It is used to calculate the amount of change in imaging characteristics (various aberrations) of the projection optical system including the focus due to light absorption.

  Note that the amount of change in various aberrations such as focus due to illumination light absorption is calculated using a calculation method using a predetermined model function disclosed in, for example, Patent Document 1 described above.

  Also, a method for correcting the imaging characteristics of the projection optical system PL, specifically, field curvature, magnification, distortion, coma aberration, and spherical aberration (particularly each rotationally symmetric component) (calculation of the driving amount of the movable lens for correction) As a method, for example, as disclosed in Patent Document 1, the relationship between the curvature of field, magnification, distortion, coma, spherical aberration, and the product of the imaging characteristic change coefficient and the driving amount of the movable lens It is possible to use a method for solving a new simultaneous legal formula in which a change in imaging characteristics other than an arbitrary imaging characteristic in the five-way linear simultaneous equation is set to zero. In this case, in order to correct the above five types of imaging characteristics using the obtained movable lens drive amount, it is necessary to separately calculate the amount of focus change that occurs as a side effect by driving the movable lens. .

  Next, an anisotropic imaging characteristic of the projection optical system PL of the scanning exposure apparatus 100 of the present embodiment, mainly a center astigmatism correction method will be described.

  Prior to the description of this correction method, the reason why the center ass will occur will be described with reference to FIGS.

  Here, as shown in FIG. 10, a case is considered in which a composite pattern CP as shown in FIG. 11 is formed on the pattern surface (lower surface) of the reticle R.

  The composite pattern CP includes a line and space (L / S) pattern (hereinafter referred to as “H pattern”) HP having a predetermined period in the scanning direction and an L / S pattern (hereinafter referred to as “V pattern”) having a predetermined period in the non-scanning direction. It is a composite pattern consisting of VP.

  This composite pattern CP is approximately from the optical axis IX of the illumination system (corresponding to the optical axis AX of the projection optical system) with respect to the X-axis direction that is the non-scan direction on the Fourier transform equivalent surface (pupil plane of the illumination optical system) of the pattern surface. Assume that projection is performed on a wafer under X-axis dipole illumination conditions in which a light quantity distribution having a maximum value is formed at two positions decentered by the same distance. At this time, it is assumed that the composite pattern CP is arranged at the center of the illumination area on the reticle R (that is, on the optical axis of the projection optical system PL).

  FIG. 4 shows the light amount distribution on the aforementioned lenses (30c, 30d, 30g) in the vicinity of the pupil plane of the projection optical system under the X-axis dipole illumination condition. In this figure, the shaded area indicates the irradiation area of the illumination light IL.

  Under this X-axis dipole illumination condition, a rotationally asymmetric temperature distribution as shown in FIG. 6 is generated in the projection optical system PL (in the vicinity of the pupil plane) by absorption of illumination light.

  At this time, the lens in the vicinity of the pupil plane of the projection optical system PL, for example, the lens 30c, is shown in FIG. 8 which is a cross-sectional view taken along line AA in FIG. 6 and FIG. 9 which is a cross-sectional view taken along line BB in FIG. As described above, thermal deformation is performed in different shapes in the X-axis direction and the Y-axis direction. The other lenses 30d, 30g, etc. are similarly thermally deformed. However, when the entire projection optical system PL is regarded as one large lens, the projection optical system PL may be considered to be thermally deformed into a shape as shown in FIGS.

  As a result, the diffracted light generated from the V pattern VP and distributed in the non-scanning direction passes through the surface of the projection optical system PL where the curvature change is relatively gentle, and passes through a predetermined imaging plane (V pattern best focus shown in FIG. 10). Image). On the other hand, the diffracted light generated from the H pattern HP and distributed in the scanning direction passes through a surface having a relatively large curvature change of the projection optical system PL and passes through a predetermined image plane (the H pattern best focus surface shown in FIG. 10). ). As a result, a deviation occurs between the V pattern best focus surface and the H pattern best focus surface. In this way, under the X-axis dipole illumination condition, an imaging plane shift (focus anisotropy) in the orthogonal biaxial direction occurs in the vicinity of the optical axis of the projection optical system PL, that is, “center ass”. Note that, under the X-axis dipole illumination condition, the focus anisotropy similarly occurs in places other than the vicinity of the optical axis of the projection optical system PL.

  The above-described composite pattern CP is converted into the optical axis IX of the illumination system (to the optical axis AX of the projection optical system) with respect to the direction corresponding to the Y-axis direction that is the scan direction on the Fourier transform equivalent plane (pupil plane of the illumination optical system) of the pattern surface. When projecting onto a wafer under a Y-axis dipole illumination condition in which a light quantity distribution having a maximum value is formed at two positions that are decentered by substantially the same distance from the coincidence), the above-mentioned near the pupil plane of the projection optical system A light amount distribution as shown in FIG. 5 is generated on the lenses (30c, 30d, 30g). In this figure, the shaded area indicates the irradiation area of the illumination light IL.

  Under this Y-axis dipole illumination condition, a rotationally asymmetric temperature distribution as shown in FIG. 7 is generated in the projection optical system PL (in the vicinity of the pupil plane) by absorption of illumination light.

  At this time, the lens in the vicinity of the pupil plane of the projection optical system PL, for example, the lens 30c, has a cross section taken along line AA as shown in FIG. 9, and a cross section taken along line BB as shown in FIG. Thermally deforms. The other lenses 30d, 30g, etc. are similarly thermally deformed. Also in this case, when the entire projection optical system PL is regarded as one large lens, the projection optical system PL may be considered to be thermally deformed in the same manner as described above.

  As a result, under the Y-axis dipole illumination condition, a center ass in which the V pattern best focus plane and the H pattern best focus plane are in the opposite positional relationship as shown in FIG. 10 occurs in the projection optical system PL. . Note that, under the Y-axis dipole illumination condition, the focus anisotropy occurs similarly in a place other than the vicinity of the optical axis of the projection optical system PL.

In the present embodiment, during the scanning exposure described above, the illumination conditions are set by the main controller 21 using the diffractive optical unit 2A and the zoom optical system 2B (shaping optical system) according to the pattern to be exposed. At this time, the main control device 21 calculates the light amount distribution of the illumination light IL for the lenses (30c, 30d, 30g) constituting the projection optical system PL, and the lens (30c, 30c, 30) is calculated based on the calculated light amount distribution of the illumination light IL. 30d, 30g) predicting the uneven distribution state of heat, corresponding to the prediction result, appropriately selecting a fiber from the plurality of fibers FB _{1 to} FB _n , and infrared rays from the selected fiber (30c, 30d, 30g) is irradiated (see FIG. 3).

As an example, when the X-axis dipole illumination condition is set as the illumination condition and the lens (30c, 30d, 30g) is predicted to be in a heat generation state (temperature distribution) as shown in FIG. By irradiating infrared rays from fibers other than FB _m and FB _n , the heat generation state of the projection optical system PL is brought close to a rotationally symmetric shape. As a result, each lens constituting the projection optical system PL undergoes rotationally symmetric deformation, and the anisotropic imaging performance such as the center ass is corrected. After this correction, the lens is rotated using the imaging characteristic correction mechanism described above. The pattern of the reticle R is transferred in a good state by correcting the symmetrical imaging characteristics.

  As described above, according to the exposure apparatus 100 of the present embodiment, the light quantity distribution on the plane corresponding to the Fourier transform with respect to the pattern surface of the reticle R on which the pattern is formed (for example, the pupil plane of the illumination system or the pupil plane of the projection optical system). Is rotationally asymmetric with respect to the optical axis, and the illumination light IL is not irradiated as described above under the illumination condition in which the lenses constituting the projection optical system PL are locally (non-uniformly) heated by the illumination light IL. By irradiating the remaining portion of the lens with infrared rays by an infrared irradiation mechanism and heating it, the temperature distribution of the lens can be made substantially uniform as a result. As a result, it is possible to suppress the occurrence of rotationally asymmetric aberration, for example, center ass, which is difficult to correct the projection optical system PL due to the uneven temperature distribution of the lens. In other words, if the lens is heated after the occurrence of the center ass, the center ass is corrected. For this reason, the center projection generated in the projection optical system due to the illumination condition in which the light quantity distribution on the plane corresponding to the Fourier transform with respect to the pattern plane is rotationally asymmetric with respect to the optical axis, for example, the dipole illumination condition is corrected, and the corrected projection A pattern is transferred onto the wafer via the optical system PL. Therefore, it is possible to reduce the influence of the center assault of the projection optical system caused by the illumination conditions, and to realize highly accurate exposure.

  In this case, since the heating of the lens by the infrared irradiation mechanism can be performed even during the exposure, the occurrence of rotationally asymmetric aberration of the projection optical system can be more reliably suppressed. Therefore, it is possible to realize highly accurate exposure by performing exposure while maintaining good imaging characteristics of the projection optical system.

  In addition, heating of a lens with infrared rays differs from heating with a contact-type heating mechanism (heat source) or cooling with a contact-type cooling mechanism, so there is no contact with the lens, so the lens is distorted due to contact with the heating or cooling mechanism. There is no possibility that the lens will vibrate, and there is no possibility that the lens will vibrate as in the case of cooling by air blowing.

  In the first embodiment, the lens is heated by the infrared irradiation mechanism from the viewpoints of suppressing the distortion of the lens and suppressing the vibration. However, the present invention is not limited to this. Other temperature adjustment mechanisms (such as a heating mechanism or a cooling mechanism) may be used as long as the temperature of the lens can be adjusted (partial heating or cooling). For example, heating by a contact-type heating mechanism such as a combination of a heat sink and a heat source, cooling by a contact-type cooling mechanism using a Peltier element, or heating or cooling by blowing a temperature-adjusted gas, or these Arbitrary combinations and the like may be adopted.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, the same reference numerals are used for the same or equivalent components as in the first embodiment described above, and descriptions thereof are omitted.

  The exposure apparatus according to the second embodiment is provided with a barcode reader (not shown) that reads a barcode attached to the reticle R in the reticle conveyance path, and the infrared irradiation mechanism described above. Except for this point, it is configured in the same manner as the exposure apparatus 100 described above.

  By the way, the V pattern best focus plane and the H pattern best focus plane described above vary as the irradiation time of the illumination light IL elapses, for example, as shown in FIG. Therefore, in the second embodiment, the V pattern best focus surface and the H pattern best focus surface under the X-axis dipole illumination condition and the Y-axis dipole illumination condition described above are obtained in advance and stored in the memory. .

  Next, an exposure sequence in the second embodiment will be briefly described.

  The reticle R is loaded onto the reticle stage RST via a reticle loader (not shown), and a barcode attached to the reticle R is read by a barcode reader (not shown) while the reticle R is being transferred. Information read by the code reader is sent to the main controller 21.

  Based on the information, main controller 21 obtains information on the pattern formed on reticle R, and determines the illumination conditions suitable for the transfer of the pattern according to the type of pattern, and diffractive optics in the illumination system. Setting is performed as described above using the unit 2A and the zoom optical system 2B.

  For example, when the pattern formed on the pattern surface of the loaded reticle R mainly includes the aforementioned V pattern (when the ratio of the V pattern to the H pattern is high, or when only the V pattern is included), the main controller 21. Sets the aforementioned X-axis dipole illumination conditions as illumination conditions.

  Further, for example, when the pattern formed on the pattern surface of the loaded reticle R mainly includes the H pattern described above (when the ratio of the H pattern to the V pattern is high or only the H pattern is included), the main control is performed. The device 21 sets the aforementioned Y-axis dipole illumination condition as the illumination condition.

  Then, under the set illumination conditions, basically, the reticle R pattern is applied to each shot area on the wafer W by the step-and-scan method in the same procedure as in the first embodiment described above. Transcribed. At this time, during the above-described scanning exposure, based on the detection signals of the wafer AF system 19 and the reticle AF system 12, the main controller controls so that the pattern surface of the reticle R and the surface of the wafer W are conjugate with respect to the projection optical system PL. The wafer stage WST is driven and controlled in the Z-axis direction by the wafer drive device 42 by 21 to perform focus correction. At this time, the V pattern described above is stored in the memory in accordance with the pattern on the reticle R. Focus is corrected with the best focus plane or the H pattern best focus plane as a target. That is, in the exposure apparatus according to the second embodiment, an appropriate illumination condition and its main body are provided according to the periodic direction of the pattern required in each process (which one of V pattern and H pattern is included). Paying attention to the periodic direction of the pattern, the position of the wafer W with respect to the optical axis direction of the projection optical system PL is adjusted.

  As described above, according to the second embodiment, for example, a pattern (X axis) mainly including a pattern (V pattern) whose periodic direction is the X axis direction in a plane orthogonal to the optical axis of the projection optical system PL. (Including a pattern composed only of a pattern (V pattern) whose direction is a periodic direction) is transferred, the Z position of the wafer W is adjusted so that the surface of the wafer W coincides with the best focus position of the V pattern. Further, for example, a pattern mainly including a pattern whose periodic direction is the Y-axis direction in a plane orthogonal to the optical axis of the projection optical system PL (including a pattern consisting only of a pattern whose periodic direction is the Y-axis direction (H pattern)). Is transferred, the Z position of the wafer W is adjusted so that the surface of the wafer W coincides with the best focus position of the H pattern.

  Then, the pattern is transferred under the above illumination conditions onto the wafer W whose Z position has been adjusted as described above.

  Therefore, in the second embodiment, it is possible to expose the target pattern with the best focus by focusing only on the pattern in the target periodic direction, and the projection optical system generated due to the illumination condition It is possible to reduce the influence of the center ass and realize high-precision exposure.

  In this case, as can be seen from FIG. 12, when transferring either the V pattern or the H pattern, when the focus is adjusted to the average focus surface of the V and H patterns, a focus shift occurs. In the exposure method of this embodiment, occurrence of such a focus shift can be effectively suppressed.

  Next, using the exposure apparatus according to the second embodiment, a step of transferring the first pattern onto the wafer by the step-and-scan method under the X-axis dipole illumination condition as the first illumination condition; Consider a case where the process of transferring the second pattern onto the wafer by the step-and-scan method under the Y-axis dipole illumination condition as the second illumination condition is alternately performed for each lot of wafers. In this case, the first pattern is a pattern mainly including a periodic pattern (V pattern) having a direction corresponding to the X-axis dipole illumination condition (X-axis direction) as a periodic direction, and the second pattern is a Y-axis dipole illumination condition. It is assumed that the pattern mainly includes a periodic pattern (H pattern) having a direction corresponding to (Y-axis direction) as a periodic direction.

  Due to such alternate exposure under the X-axis dipole illumination condition and the Y-axis dipole illumination condition, the projection optical system PL has a temperature distribution as shown in FIG. As shown in FIG. 13, the AA line cross section of the projection optical system PL regarded as one large lens is thermally deformed after the illumination light is absorbed as shown in FIG. The cross section taken along the line BB is thermally deformed as shown in FIG. In this case, as compared with FIGS. 8 and 9 described above, the shapes of the AA axis cross section which is the scanning direction and the BB axis cross section which is the non-scanning direction of FIG. 13 are similar.

  In other words, anisotropic imaging characteristics are obtained by alternately repeating the process of transferring the first pattern under the X-axis dipole illumination condition and the process of transferring the second pattern under the Y-axis dipole illumination condition. The first pattern is transferred onto the wafer under X-axis dipole illumination conditions such that (for example, center ass) occurs in the projection optical system, and then anisotropic imaging that occurs in the projection optical system under the X-axis dipole illumination conditions The second pattern is transferred onto the wafer under a Y-axis dipole illumination condition in which an imaging characteristic that relaxes the characteristic (for example, center ass) occurs in the projection optical system.

  For this reason, the second pattern is transferred onto the wafer in a state where anisotropic imaging characteristics (for example, center ass) are relaxed, and at least the second pattern is transferred due to illumination conditions. The anisotropic imaging characteristics of the resulting projection optical system, for example, the influence of center ass can be reduced, and high-accuracy exposure can be realized.

  In FIG. 16, the state of the center ass occurring in the projection optical system PL in this case is shown with the horizontal axis as the time axis. As is clear from FIG. 16, when the first pattern (mainly V pattern) is continuously exposed under X-axis dipole illumination conditions (state shown by a dotted line in FIG. 16), the above method was used. When the maximum amount of center ass occurring in the projection optical system is seen, the former is b and the latter is a (<b). Therefore, by performing alternate exposure under the above-described X-axis dipole illumination condition and Y-axis dipole illumination condition, it is possible to reduce center ass and to realize highly accurate exposure. Of course, also in this case, it goes without saying that the pattern is exposed with the best focus at any time during the transfer of the first pattern and the second pattern.

  In addition, since irradiation of illumination light is not performed between lots (and during reticle exchange), it can be seen from FIG.

  In the above description, the step of transferring the first pattern under the X-axis dipole illumination condition and the step of transferring the second pattern under the Y-axis dipole illumination condition are alternately repeated. However, the present invention is not limited to this, and a pattern under a predetermined illumination condition that causes anisotropic imaging characteristics to occur in the projection optical system is transferred onto the photosensitive object, and the anisotropy generated in the projection optical system under the illumination condition is transferred. Another pattern may be transferred onto the photosensitive object under different illumination conditions that cause the imaging characteristic to relax the imaging characteristic in the projection optical system.

  In this case, each pattern is transferred onto the photosensitive object in a state where the anisotropic imaging characteristics are relaxed, and the anisotropic imaging characteristics of the projection optical system caused by illumination conditions, for example, It is possible to reduce the influence of center ass and realize high-precision exposure.

  Depending on the combination of illumination conditions and the pattern to be transferred, the pattern to be transferred in one exposure process may not be transferred with the required accuracy. After completing exposure of a predetermined reticle under illumination conditions, the reticle is exchanged, and the illumination conditions are changed as necessary to expose another pattern on the wafer (double exposure), and then to the desired A pattern may be formed. In this double exposure, a method of alternately repeating the step of transferring the first pattern under the X-axis dipole illumination condition and the step of transferring the second pattern under the Y-axis dipole illumination condition is adopted. In such a case, double exposure is possible in a state where the influence of the anisotropic imaging characteristics (for example, center ass) of the projection optical system caused by the illumination conditions described above is reduced. Is even more effective. Further, the present invention can be applied not only to double exposure but also to stitching exposure.

  In order to obtain the same effect as described above, the following configuration may be employed.

  That is, even when the same reticle pattern is continuously transferred to a plurality of wafers, each time a predetermined number of wafers are exposed, the reticle and wafer placement directions are passed through the reticle loader and wafer loader. Is rotated 90 ° in the horizontal plane (in the XY plane), and under the instruction of the main controller 21, the illumination conditions are set so that the illumination area rotates 90 ° around the optical axis in the horizontal plane. By doing so, the lens of the projection optical system PL has the same heat distribution as that in FIG. 13, so that the generation of non-rotationally symmetric aberration and the occurrence of center astigmatism are reduced as much as possible. An equivalent effect can be obtained.

  In this case, the scanning direction of wafer stage WST and reticle stage RST also needs to be changed (specifically, changed from the Y-axis direction to the X-axis direction), but reticle stage RST is configured to be movable in a two-dimensional direction. The reticle blind 7 can also be opened and closed in the Z-axis direction and can also be opened and closed in the X-axis direction. In this case, the exposure may be performed not only for a predetermined number of wafers but also for each wafer with the scanning direction rotated by 90 °.

  When the same reticle pattern is continuously transferred to a plurality of wafers, the projection optical system PL may be rotated only 90 ° about the optical axis every time exposure of a predetermined number of wafers is completed. . Even if it does in this way, it is possible to acquire the effect equivalent to the said 2nd Embodiment.

  In each of the above embodiments, a refractive system is used as the projection optical system. However, the present invention is not limited to this, and a refractive optical element and a reflective optical element (such as a concave mirror or a beam splitter) are combined. In the case of the so-called catadioptric system (catadioptric system), the illumination area that illuminates the pattern is often decentered from the optical axis, but in addition to the correction of the anisotropic imaging characteristics (for example, center as described above) It is desirable to correct the distortion or coma aberration caused by the decentering of the illumination area, that is, the wavefront aberration of the projection optical system by combining the 1θ component terms of a plurality of Zernike terms that are series-expanded using a Zernike polynomial. In this case, distortion or coma may be corrected using the above-described imaging characteristic correction mechanism.

  Further, when a catadioptric system is used as the projection optical system, two catadioptric paths are provided in the projection optical system (mirrors are arranged on both sides of the optical axis), and two paths each time a predetermined time elapses. It is good also as switching and using.

  In each of the above-described embodiments, as described in Patent Document 1, the anisotropic adjustment of image formation characteristics caused by the illumination area elongated in the non-scanning direction is also corrected by initial adjustment of image formation characteristics. It's also good.

In each of the above embodiments, F ₂ laser light, ArF excimer laser light, KrF excimer laser light, or the like is used as the illumination light IL for exposure. However, the present invention is not limited to this, and other vacuum ultraviolet light, for example, In addition to Kr ₂ laser light and Ar ₂ laser light, ultraviolet bright lines (g-line, i-line, etc.) from an ultra-high pressure mercury lamp can be used. For example, as a vacuum ultraviolet light, an infrared or visible single wavelength laser light oscillated from a DFB semiconductor laser or fiber laser is doped with, for example, erbium (Er) (or both erbium and ytterbium (Yb)). Alternatively, harmonics amplified with a fiber amplifier and converted into ultraviolet light using a nonlinear optical crystal may be used.

  In each of the above embodiments, the case where the present invention is applied to a scanning exposure apparatus such as a step-and-scan method has been described, but the scope of the present invention is of course not limited thereto. That is, the present invention can be suitably applied to a step-and-repeat reduction projection exposure apparatus. In addition, the present invention may be applied to an immersion type exposure apparatus that is disclosed in, for example, International Publication No. WO99 / 49504 and the like and is filled with a liquid between the projection optical system PL and the wafer. The immersion exposure apparatus may be a scanning exposure system using a catadioptric projection optical system, or a static exposure system using a projection optical system with a projection magnification of 1/8. In the latter immersion type exposure apparatus, it is preferable to adopt a step-and-stitch method in order to form a large pattern on the substrate.

  In addition, an illumination unit composed of a plurality of lenses and a projection optical system are incorporated into the exposure apparatus main body, optical adjustment is performed, and a wafer stage (including a reticle stage in the case of a scanning type) consisting of a large number of machine parts is exposed The exposure apparatus according to the present invention, such as the exposure apparatus of each of the above-described embodiments, can be manufactured by connecting the wiring and pipes to each other and performing overall adjustment (electrical adjustment, operation check, etc.). The exposure apparatus is preferably manufactured in a clean room where the temperature, cleanliness, etc. are controlled.

  The present invention is not limited to an exposure apparatus for manufacturing a semiconductor, but is used for manufacturing a display including a liquid crystal display element. An exposure apparatus for transferring a device pattern onto a glass plate and a device used for manufacturing a thin film magnetic head. The present invention can also be applied to an exposure apparatus that transfers a pattern onto a ceramic wafer, and an exposure apparatus that is used for manufacturing an imaging device (CCD or the like), micromachine, organic EL, DNA chip, and the like. Further, in order to manufacture reticles or masks used in not only microdevices such as semiconductor elements but also light exposure apparatuses, EUV exposure apparatuses, X-ray exposure apparatuses, electron beam exposure apparatuses, etc., glass substrates or silicon wafers, etc. The present invention can also be applied to an exposure apparatus that transfers a circuit pattern. Here, in an exposure apparatus using DUV (far ultraviolet) light, VUV (vacuum ultraviolet) light, or the like, a transmission type reticle is generally used. As a reticle substrate, quartz glass, fluorine-doped quartz glass, meteorite, Magnesium fluoride or quartz is used. Further, in a proximity type X-ray exposure apparatus or an electron beam exposure apparatus, a transmission mask (stencil mask, membrane mask) is used, and a silicon wafer or the like is used as a mask substrate.

<Device manufacturing method>
Next, an embodiment of a device manufacturing method using the above-described exposure apparatus in a lithography process will be described.

  FIG. 17 shows a flowchart of a manufacturing example of a device (a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine, etc.). As shown in FIG. 17, first, in step 201 (design step), device function / performance design (for example, circuit design of a semiconductor device) is performed, and pattern design for realizing the function is performed. Subsequently, in step 202 (mask manufacturing step), a mask on which the designed circuit pattern is formed is manufactured. On the other hand, in step 203 (wafer manufacturing step), a wafer is manufactured using a material such as silicon.

  Next, in step 204 (wafer processing step), using the mask and wafer prepared in steps 201 to 203, an actual circuit or the like is formed on the wafer by lithography or the like as will be described later. Next, in step 205 (device assembly step), device assembly is performed using the wafer processed in step 204. Step 205 includes processes such as a dicing process, a bonding process, and a packaging process (chip encapsulation) as necessary.

  Finally, in step 206 (inspection step), inspections such as an operation confirmation test and durability test of the device created in step 205 are performed. After these steps, the device is completed and shipped.

  FIG. 18 shows a detailed flow example of step 204 in the semiconductor device. In FIG. 18, in step 211 (oxidation step), the surface of the wafer is oxidized. In step 212 (CVD step), an insulating film is formed on the wafer surface. In step 213 (electrode formation step), an electrode is formed on the wafer by vapor deposition. In step 214 (ion implantation step), ions are implanted into the wafer. Each of the above-described steps 211 to 214 constitutes a pre-processing process at each stage of wafer processing, and is selected and executed according to a necessary process at each stage.

  At each stage of the wafer process, when the above pre-process is completed, the post-process is executed as follows. In this post-processing process, first, in step 215 (resist formation step), a photosensitive agent is applied to the wafer. Subsequently, in step 216 (exposure step), the circuit pattern of the mask is transferred to the wafer by the exposure apparatus and exposure method described above. Next, in step 217 (development step), the exposed wafer is developed, and in step 218 (etching step), the exposed members other than the portion where the resist remains are removed by etching. In step 219 (resist removal step), the resist that has become unnecessary after the etching is removed.

  By repeatedly performing these pre-processing steps and post-processing steps, multiple circuit patterns are formed on the wafer.

  If the device manufacturing method of this embodiment described above is used, the exposure apparatus and the exposure method according to each of the above embodiments are used in the exposure step (step 216), so that the reticle pattern can be accurately transferred onto the wafer. it can. As a result, the productivity (including yield) of a highly integrated device (microdevice) can be improved.

  As described above, the exposure method of the present invention is suitable for illuminating a mask with illumination light and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system. The device manufacturing method of the present invention is suitable for manufacturing electronic devices (microdevices) such as semiconductor elements and liquid crystal display elements.

It is a figure which shows schematically the structure of the scanning exposure apparatus which concerns on 1st Embodiment suitable for implementing the exposure method of this invention. It is a figure which shows schematically the internal structure of the projection optical system of FIG. 1 with an atmospheric pressure sensor. It is a figure which shows the example of arrangement | positioning of the fiber introduce | transduced in the projection optical system. It is a figure which shows light quantity distribution on the lens (30c, 30d, 30g) of the pupil plane vicinity of a projection optical system on X-axis dipole illumination conditions. It is a figure which shows light quantity distribution on the lens (30c, 30d, 30g) of the pupil plane vicinity of the projection optical system under Y-axis dipole illumination conditions. It is a figure which shows the temperature distribution of the projection optical system under the illumination conditions of FIG. It is a figure which shows the temperature distribution of the projection optical system on the illumination conditions of FIG. It is a figure which shows the AA line cross section of FIG. It is a figure which shows the BB line cross section of FIG. It is a figure which shows the state which the center ass in the projection optical system generate | occur | produced. It is a figure which shows the composite pattern which consists of H pattern and V pattern which were formed on the reticle R. It is a figure relevant to the 2nd Embodiment of this invention, Comprising: It is a figure which shows the irradiation fluctuation | variation of a H pattern best focus surface and a V pattern best focus surface. It is a figure which shows the temperature distribution produced in the projection optical system by the alternating exposure on X-axis dipole illumination conditions and Y-axis dipole illumination conditions. It is AA sectional view taken on the line of the projection optical system of FIG. FIG. 14 is a sectional view taken along line BB of the projection optical system in FIG. 13. It is a figure which shows the mode of the center assault which generate | occur | produces in a projection optical system by the alternating exposure under X-axis dipole illumination conditions and Y-axis dipole illumination conditions on a horizontal axis. It is a flowchart for demonstrating the device manufacturing method which concerns on this invention. It is a flowchart which shows the specific example of step 204 of FIG.

Explanation of symbols

IL: illumination light, R: reticle (mask), PL: projection optical system, W: wafer (photosensitive object).

Claims (14)

An exposure method for illuminating a mask with illumination light and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system,
An exposure method comprising a step of correcting a center spot generated in the projection optical system under an illumination condition in which a light amount distribution on a plane corresponding to a Fourier transform with respect to a pattern surface of the mask on which the pattern is formed is rotationally asymmetric with respect to an optical axis.   The illumination condition is a dipole illumination condition in which a light quantity distribution having a maximum value is formed at two positions decentered by substantially the same distance from the optical axis on a plane corresponding to Fourier transform with respect to the pattern surface. An exposure method according to 1. An exposure method for illuminating a mask with illumination light and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system,
A first transfer step of transferring a first pattern onto a photosensitive object under predetermined first illumination conditions such that anisotropic imaging characteristics occur in the projection optical system;
The second pattern is exposed under the second illumination condition in which an imaging characteristic that relaxes the anisotropic imaging characteristic generated in the projection optical system under the first illumination condition is generated in the projection optical system. A second transfer step of transferring onto the object. The first illumination condition is a light quantity distribution having a maximum value at two positions decentered by substantially the same distance from the optical axis in the first axis direction on a plane corresponding to a Fourier transform with respect to a pattern surface of the mask on which the first pattern is formed. Is a first dipole illumination condition in which is formed,
The second illumination condition includes two positions that are decentered from the optical axis by substantially the same distance with respect to a second axis direction orthogonal to the first axis direction on a plane corresponding to a Fourier transform with respect to a pattern surface of the mask on which the second pattern is formed. The exposure method according to claim 3, wherein the exposure condition is a second dipole illumination condition in which a light quantity distribution having a maximum value is formed. The first pattern mainly includes a periodic pattern whose periodic direction is a direction according to the first illumination condition,
5. The exposure method according to claim 3, wherein the second pattern mainly includes a periodic pattern having a direction corresponding to the second illumination condition as a periodic direction. 6.   The exposure method according to claim 3, wherein the first transfer step and the second transfer step are performed alternately.   The exposure method according to claim 6, wherein the first transfer step and the second transfer step are alternately performed every time one lot of the photosensitive object is processed. In the first transfer step, the first pattern is transferred onto a photosensitive object by a scanning exposure method,
The exposure method according to any one of claims 3 to 7, wherein, in the second transfer step, the second pattern is transferred onto a photosensitive object by a scanning exposure method.   The exposure method according to claim 8, wherein the scanning direction is changed by 90 ° between the first transfer step and the second transfer step. The projection optical system is a catadioptric system in which an illumination area that illuminates the pattern is decentered from the optical axis,
At least one of the first transfer step and the second transfer step, 1θ of a plurality of Zernike terms in which the wavefront aberration of the projection optical system due to the eccentricity of the illumination area is series-expanded using a Zernike polynomial. 10. The exposure method according to claim 8, wherein exposure is performed in consideration of component terms. An exposure method for illuminating a mask with illumination light and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system,
When transferring the pattern under a predetermined illumination condition such that a center ass is generated in the projection optical system, the optical axis of the projection optical system is focused on a periodic pattern having a direction corresponding to the illumination condition as a periodic direction. An adjusting step of adjusting the position of the photosensitive object with respect to a direction;
A transfer step of transferring the pattern onto the photosensitive object whose position in the optical axis direction has been adjusted.   12. The exposure method according to claim 11, wherein the illumination condition is an illumination condition that generates a rotationally asymmetric light amount distribution with respect to an optical axis on a surface corresponding to a Fourier transform with respect to a pattern surface on a mask on which the pattern is formed.   The illumination condition is a dipole illumination condition in which a light quantity distribution having a maximum value is formed at two positions decentered by substantially the same distance from the optical axis on a surface corresponding to a Fourier transform with respect to the pattern surface. An exposure method according to 1. A device manufacturing method including a lithography process,
In the said lithography process, the exposure method as described in any one of Claims 1-13 is performed, The device manufacturing method characterized by the above-mentioned.

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