JP2005116831A - Projection aligner, exposure method, and device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably illuminate a mask by an illumination light in a prescribed polarized state when a rod type integrator is used for an illuminance uniformizing member. <P>SOLUTION: The projection aligner includes an illumination lighting system ILS for illuminating the illumination light from an exposure light source 1 to a reticule R, and a projection light system PL for projecting the image of the pattern of the reticule R onto a wafer W. The illumination lighting system ILS includes the rod integrator 14R of a substantially rectangular solid shape made of cubic system crystals with its lengthwise direction working as (100) direction of the crystal in order to uniformize illumination distribution on the reticule R, the rod integrator 14R in its lengthwise direction is arranged substantially in parallel with the optical axis AX2 of the illumination lighting system ILS, and its illumination light includes a prescribed linearly polarized light as a principal component. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exposure technique used in a lithography process for manufacturing various devices such as a semiconductor integrated circuit (LSI or the like), an image sensor, or a liquid crystal display, and more specifically, a mask pattern is formed with light in a predetermined polarization state. It is related with the exposure technique illuminated with. The present invention also relates to a device manufacturing technique using the exposure technique.

  When forming a fine pattern of an electronic device such as a semiconductor integrated circuit or a liquid crystal display, a pattern of a reticle (or a photomask, etc.) as a mask drawn by enlarging the pattern to be formed approximately 4 to 5 times is projected. A method is used in which an exposure transfer is performed by reducing on a wafer (or glass plate or the like) as a substrate to be exposed (photosensitive member) via an optical system. For the exposure transfer, a stationary exposure type projection exposure apparatus such as a stepper and a scanning exposure type projection exposure apparatus such as a scanning stepper are used. The resolution of the projection optical system is approximately a value obtained by dividing the exposure wavelength by the numerical aperture (NA) of the projection optical system. The numerical aperture (NA) of the projection optical system is obtained by multiplying the sine of the maximum incident angle of the illumination light beam for exposure to the wafer by the refractive index of the medium through which the light beam passes.

Therefore, in order to cope with miniaturization of semiconductor integrated circuits and the like, the exposure wavelength of the projection exposure apparatus has been made shorter. At present, the main exposure wavelength is 248 nm of the KrF excimer laser, but the 193 nm of the shorter wavelength ArF excimer laser is also entering the practical stage. Further, there has been proposed a projection exposure apparatus using a so-called vacuum ultraviolet exposure light source such as an F ₂ laser having a shorter wavelength of 157 nm or an Ar ₂ laser having a wavelength of 126 nm. In addition to shortening the wavelength, it is possible to increase the resolution by increasing the numerical aperture (increasing NA) of the projection optical system. Therefore, development has been made to further increase the NA of the projection optical system. The NA of the current state-of-the-art projection optical system is about 0.8.

  On the other hand, as a technique for improving the resolution of a transferred pattern while using a projection optical system having the same exposure wavelength and the same NA, a method using a so-called phase shift reticle and a distribution of incident angles of illumination light beams on the reticle are predetermined distributions. So-called super-luminal illumination (see, for example, JP-A-61-91662), 2-pole illumination, and 4-pole illumination (see, for example, JP-A-4-101148 and JP-A-4-225357) Resolution technology has also been put into practical use. Furthermore, an attempt to improve the resolution and the depth of focus by making the polarization state of the illumination light linearly polarized, particularly when the pattern directivity on the reticle is aligned in one specific direction has been proposed (for example, , See Patent Document 1).

Incidentally, in order to operate an electronic device such as a semiconductor integrated circuit at a high speed, it is necessary to uniformly transfer the line width of a pattern to be transferred to each position on the wafer to a predetermined value. For this purpose, it is necessary to make the distribution of the exposure intensity (illumination light intensity) over the entire exposure field of the projection exposure apparatus uniform, and the illumination optical system has conventionally had a uniform illumination intensity such as a fly eye integrator or a rod integrator. An optical integrator was provided. Among these, the rod integrator is an elongated quadrangular prism-shaped solid member made of glass or optical crystal, and by using this, relatively good illuminance uniformity can be achieved with a relatively inexpensive member.
See JP-A-7-245258

As described above, linearly polarized illumination is effective in improving the resolution when exposing a one-dimensional pattern having a uniform direction in one specific direction. However, in an illumination optical system using a rod integrator, the polarization direction of linearly polarized light is rotated by the birefringence of the optical material constituting the rod integrator, and it may be difficult to illuminate the reticle with the desired linearly polarized light. Arise.
In particular, when the exposure wavelength is shortened to about 193 nm or less, the absorption loss of glass or synthetic quartz with respect to the exposure light increases, and it becomes difficult to use these materials for the rod integrator. Therefore, in the wavelength range of about 193 nm or less, it is necessary to configure the rod integrator with a fluoride crystal having high transparency to ultraviolet rays. However, among the fluoride crystals, magnesium fluoride having particularly good ultraviolet transmittance is difficult to use because it is a birefringent material having uniaxial crystallinity.

  In addition, fluorite (calcium fluoride crystal) and barium fluoride crystal are optical crystals belonging to a highly symmetrical cubic system, and are not birefringent in the visible light region, but for ultraviolet light having a wavelength of about 200 nm or less. As a result, intrinsic birefringence due to the crystal structure occurs. For this reason, when these materials are applied to the rod integrator, the polarization state of the illumination light changes due to intrinsic birefringence, and the reticle may not be illuminated with a desired linearly polarized light.

The present invention has been made in view of such problems, and when a rod integrator is used as an illuminance uniforming member, the mask can be stably illuminated with illumination light in a predetermined polarization state, and the mask pattern can be changed. An object of the present invention is to provide an exposure technique capable of transferring at a high resolution.
A further object of the present invention is to provide a device manufacturing technique that can manufacture a device with high accuracy using the exposure technique.

  A projection exposure apparatus according to the present invention projects an illumination optical system (ILS) that irradiates illumination light from a light source (1) onto a first object (R), and an image of the first object on a second object (W). In the projection exposure apparatus having the projection optical system (23), the illumination optics is used to internally reflect at least a part of the illumination light on a part of the optical path between the light source and the first object. The system comprises a cubic crystal, and has a substantially rectangular parallelepiped rod-type integrator (14) whose long side direction is the (100) direction of the crystal. The long-side direction of the rod-type integrator is the illumination The illumination light that is disposed substantially parallel to the optical axis of the optical system and is incident on the rod-type integrator is one of two parallel side surfaces along the long-side direction of the rod-type integrator. Parallel side surfaces (14e, 14f As a main component linearly polarized light to the electric field direction either perpendicular second direction to the first direction or the other parallel sides perpendicular (14c, 14d) to.

According to the present invention, since the long-side direction of the rod-type integrator is aligned with the predetermined direction of the crystal, the polarization state of the illumination light passing through the rod-type integrator is stably maintained in the almost incident state. The Therefore, the first object (mask) can be stably illuminated with illumination light in a predetermined polarization state (for example, linearly polarized light).
In this case, as an example, the side surface of the rod integrator may substantially coincide with the (100) plane of the crystal. In this configuration, even if the polarization state of the illumination light is linearly polarized light parallel to either the first direction or the second direction, when the illumination light is internally reflected by the side surface, the polarization state is almost incident. Is maintained.

As another example, the side surface of the rod-type integrator may substantially coincide with the (110) plane of the crystal. Even in this configuration, when the illumination light is internally reflected by the side surface, the polarization state is maintained substantially at the time of incidence.
Further, the illumination optical system may further include an angle variable mechanism (9a, 9b, 10) that makes the incident angle range of the illumination light to the rod integrator variable. Thereby, for example, the light amount distribution on the surface corresponding to the pupil plane of the illumination optical system can be controlled.

Further, the angle variable mechanism may include a diffractive optical element. In this case, the angle variable mechanism may include a mechanism for exchanging the diffractive optical element (9a) with another diffractive optical element (9b).
The angle variable mechanism may include a polyhedral prism (41, 42), and the angle variable mechanism may further include a zoom optical system (5, 6).

  The angle variable mechanism further includes an angle limiting mechanism that limits the incident angle range of the illumination light to the first object to a plurality of discrete ranges separated in a direction corresponding to the first direction, The illumination light incident on the rod integrator may be mainly composed of linearly polarized light whose second direction is the electric field direction. In this case, for example, a pattern formed by arranging a plurality of line patterns elongated in the second direction at a fine pitch on the first object can be transferred with high resolution.

  Further, the variable angle mechanism has an effective σ value of 0.7 or more in the direction corresponding to the first direction as the incident angle range of the illumination light with respect to the first object, and corresponds to the second direction. The illumination light incident on the rod-type integrator may include linearly polarized light whose first direction is an electric field direction as a main component. .

  In this case, the effective σ value of the illumination light in the predetermined direction on the first object is a sine of the maximum value of the incident angle of the illumination light on the first object in the predetermined direction. A value obtained by dividing the value obtained by multiplying the refractive index of the medium by the numerical aperture in the predetermined direction on the first object side of the projection optical system. Therefore, when the effective σ value of the illumination light becomes larger in the first direction than the second direction, the incident angle range in the first direction becomes wider than that in the second direction. In the region on the pupil plane, the numerical aperture in the second direction is substantially larger in the vicinity of the optical axis than in the vicinity. Therefore, the image formed on the second object is an optical image with substantially different numerical apertures added incoherently (intensity added). Therefore, the spatial coherency of the image on the second object is reduced by the averaging effect, the fluctuation due to the change in the pitch of the transfer line width is reduced, and the OPE (Optical Proximity Error) characteristic that is an error due to the optical proximity effect. Is improved. Further, by setting the effective σ value in the second direction to 0.2 or less, the resolution is determined in the same principle as so-called small σ illumination with respect to the second direction when a predetermined pattern such as a phase shift pattern is used. Will improve.

In addition, the cubic crystal is, for example, a fluoride crystal. In this case, the fluoride crystal is, for example, a calcium fluoride crystal.
The illumination light may be ultraviolet light having a wavelength of 200 nm or less. Furthermore, the illumination light is, for example, ultraviolet light having a wavelength of 193 nm emitted from an ArF excimer laser.
Next, the exposure method according to the present invention uses the projection exposure apparatus of the present invention to expose the photoconductor (W) as the second object with the pattern image of the mask (R) as the first object. It is. According to the present invention, since the mask can be illuminated with light having a desired polarization state (for example, linearly polarized light), resolution and depth of focus can be improved.

In this case, the pattern of the mask may include a rectangular pattern, and the longitudinal direction of the rectangular pattern may substantially coincide with the direction corresponding to the second direction.
The mask pattern may include a spatial frequency modulation type phase shift pattern, and the longitudinal direction of the phase shift pattern may substantially coincide with the direction corresponding to the first direction. As a result, the OPE characteristics are improved, and a reduction in the depth of focus in a pattern having a predetermined pitch can be prevented.

  Next, a device manufacturing method according to the present invention is a device manufacturing method including a lithography process, and a pattern is transferred to a photoreceptor using the exposure method of the present invention in the lithography process. According to the present invention, a fine pattern can be transferred onto a photoreceptor with high accuracy, and a device having a fine pattern can be manufactured with high accuracy.

According to the present invention, when an illumination optical system including a rod-type integrator is used, the first object (mask) can be stably illuminated with illumination light in a predetermined polarization state.
In particular, when the wavelength of the illumination light (exposure beam) is about 200 nm or less, it is difficult to maintain the polarization state at the time of incidence simply by disposing the optical material, so that the effect of the present invention is enhanced.

  By applying the present invention, for example, when exposing a pattern formed on the first object and having a uniform direction in one direction, the illumination light having the polarization state optimized in the pattern direction is optimized within the optimum incident angle range. The first object can be irradiated from any incident direction, and the resolution and depth of focus of the pattern can be improved with a relatively inexpensive configuration. Furthermore, when the first object is a phase shift mask and the pattern is a phase shift pattern, the OPE characteristics can be improved along with the improvement in resolution and depth of focus.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings. In this example, the present invention is applied to the case where exposure is performed by a scanning exposure type projection exposure apparatus (scanning stepper) having a step-and-scan method.
FIG. 1 is a partially cutaway view showing a schematic configuration of the projection exposure apparatus of this example. In FIG. 1, the projection exposure apparatus of this example includes an illumination optical system ILS and a projection optical system 23. ing. The former illumination optical system ILS includes a plurality of optical members arranged along optical axes (illumination system optical axes) AX1, AX2, AX3 from the exposure light source 1 to the condenser lens 18 (details will be described later). The illumination field of exposure on the pattern surface (reticle surface) of the reticle R as a mask is illuminated with a uniform illuminance distribution by using illumination light (exposure light) IL as an exposure beam from. The latter projection optical system 23 reduces an image obtained by reducing the pattern in the illumination field of the reticle R at the projection magnification β (β is a reduction magnification such as 1/4, 1/5, etc.) under the illumination light. Projection is performed on an exposure area on one shot area on the wafer W coated with a photoresist as a substrate to be exposed (substrate). Reticle R and wafer W can also be regarded as a first object and a second object, respectively. The wafer W is a disk-shaped substrate having a diameter of about 200 to 300 mm, such as a semiconductor (silicon or the like) or SOI (silicon on insulator). The projection optical system 23 of this example is a refractive optical system, for example, but a catadioptric system or the like can also be used.

  In FIG. 1, the projection optical system 23, reticle R, and wafer W are scanned and exposed in a plane (XY plane) that takes the Z axis parallel to the optical axis AX4 of the projection optical system 23 and is perpendicular to the Z axis. A description will be given by taking the Y axis along the scanning direction of the reticle R and the wafer W (direction parallel to the paper surface of FIG. 1) and taking the X axis along the non-scanning direction (direction perpendicular to the paper surface of FIG. 1). To do. In the illumination optical system ILS, the Z axis is taken along the optical axes AX1, AX2, and AX3 as will be described later, and the X and Y directions in the projection optical system 23 and the like are within a plane perpendicular to the Z axis. The corresponding directions will be described as the X direction and the Y direction, respectively. In this case, the illumination field of the reticle R is an elongated area in the X direction, which is the non-scanning direction, and the exposure area on the wafer W is an elongated area conjugate with the illumination field. Further, the optical axis AX4 of the projection optical system 23 coincides with the illumination system optical axis AX3 on the reticle R.

  First, the reticle R on which a pattern to be exposed and transferred is sucked and held on the reticle stage 20, and the reticle stage 20 moves on the reticle base 19 in the Y direction at a constant speed and X is corrected so as to correct the synchronization error. The reticle R is scanned by slightly moving in the direction, the Y direction, and the rotation direction around the Z axis. The position of the reticle stage 20 in the X and Y directions and the rotation angle are measured by a movable mirror 21 and a laser interferometer 22 provided thereon. Based on this measurement value and control information from the main control system 31, the reticle stage drive system 29 controls the position and speed of the reticle stage 20 via a drive mechanism (not shown) such as a linear motor. Above the periphery of the reticle R, a reticle alignment microscope (not shown) for reticle alignment is arranged.

  On the other hand, the wafer W is sucked and held on the wafer stage 24 via a wafer holder (not shown), and the wafer stage 24 can move on the wafer base 27 at a constant speed in the Y direction and step in the X and Y directions. It is placed so that it can move. The wafer stage 24 also incorporates a Z leveling mechanism for aligning the surface of the wafer W with the image plane of the projection optical system 23 based on the measurement value of an autofocus sensor (not shown). The X- and Y-direction positions and the rotation angle of the wafer stage 24 are measured by a movable mirror 25 and a laser interferometer 26 provided thereon. Based on this measurement value and control information from the main control system 31, the wafer stage drive system 30 controls the position and speed of the wafer stage 24 via a drive mechanism (not shown) such as a linear motor. Also, in the vicinity of the projection optical system 23, for example, an FIA (Fie1d Image A1ignment) type alignment sensor 28 is disposed by an off-axis method for detecting the position of the alignment mark on the wafer W for wafer alignment. ing.

  Prior to exposure by the projection exposure apparatus of this example, alignment of the reticle R is performed by the reticle alignment microscope described above, and the position of the alignment mark formed together with the circuit pattern in the previous exposure process on the wafer W is an alignment sensor. By detecting at 28, alignment of the wafer W is performed. Thereafter, the reticle stage 20 and the wafer stage 24 are driven in a state where the illumination field on the reticle R is irradiated with the illumination light IL, and the reticle R and one shot area on the wafer W are synchronously scanned in the Y direction. The operation of stopping the emission of the illumination light IL and driving the wafer stage 24 to move the wafer W stepwise in the X and Y directions is repeated. The ratio of the scanning speed between the reticle stage 20 and the wafer stage 24 during the synchronous scanning is such that the projection magnification of the projection optical system 23 is maintained in order to maintain the imaging relationship between the reticle R and the wafer W via the projection optical system 23. equal to β. By these operations, the pattern image of the reticle R is exposed and transferred to all shot areas on the wafer W by the step-and-scan method.

Next, the configuration of the illumination optical system ILS of this example will be described in detail. In FIG. 1, an ArF (argon fluorine) excimer laser (wavelength 193 nm) is used as the exposure light source 1 of this example. Other exposure light sources include F ₂ (fluorine molecule) laser (wavelength 157 nm), Kr ₂ (krypton molecule) laser (wavelength 146 nm), Ar ₂ (argon molecule) laser (wavelength 126 nm), and harmonics of YAG laser. A generation light source, a harmonic generator of a solid-state laser (such as a semiconductor laser), or the like can also be used. Further, for example, a KrF (krypton fluorine) excimer laser (wavelength 247 nm) or a mercury lamp can be used as an exposure light source.

  The illumination light IL emitted from the exposure light source 1 enters the polarization control member 4 (details will be described later) via the relay lenses 2 and 3 along the illumination system optical axis AX1. Illumination light IL emitted from the polarization control member 4 passes through a zoom optical system (5, 6) composed of a combination of a concave lens 5 and a convex lens 6, is reflected by a mirror 7 for bending the optical path, and is reflected on the illumination optical axis AX2. The light then enters a diffractive optical element (DOE) 9a. The diffractive optical element 9a is composed of a phase type diffraction grating, and the irradiated illumination light is diffracted in a predetermined direction and travels.

  As will be described later, the diffraction angle and direction of each diffracted light from the diffractive optical element 9a correspond to the incident angle and direction of illumination light on the reticle R. Therefore, a plurality of diffractive optical elements 9a and other diffractive optical elements 9b having a different diffractive action are arranged on the turret-shaped member 8. Then, the member 8 is driven by the exchange mechanism 10 and the diffractive optical element 9a and the like at an arbitrary position on the member 8 is loaded at a position on the illumination system optical axis AX2, so that the reticle according to the pattern of the reticle R is obtained. The incident angle range and directionality of the illumination light to R can be set to desired values. The incident angle range can be finely tuned by moving the concave lens 5 and the convex lens 6 constituting the zoom optical system (5, 6) in the direction of the illumination system optical axis AX1. I can do it. The mechanism including the member 8, the diffractive optical elements 9a and 9b, the exchange mechanism 10, and the zoom optical system (5, 6) corresponds to the angle variable mechanism.

  Illumination light (diffracted light in this case) IL emitted from the diffractive optical element 9a is a plane corresponding to the pupil plane of the relay lens 11 and the illumination optical system ILS along the illumination system optical axis AX2 (hereinafter referred to as “pupil equivalent plane”). It passes through 12R and the relay lens 13R, and enters the incident surface 14aR of a rectangular parallelepiped rod integrator 14R having a long side in the direction of the illumination system optical axis AX2. Then, the illumination light IL that travels straight in the rod integrator 14R as an illuminance uniforming member (optical integrator) or is internally reflected by the side surface of the rod integrator 14R is emitted from the emission surface 14bR. The rod integrator 14R corresponds to the rod type integrator of the present invention.

  The exit surface 14bR of the rod integrator 14R is arranged on a conjugate plane (surface having an imaging relationship) with respect to the reticle surface, and the illumination field on the reticle R can be limited by the field stops 15a and 15b provided here. . Further, if necessary, the field stops 15a and 15b may be of a scanning type, and scanning may be performed in synchronization with the scanning of the reticle stage 20 and the wafer stage 24. In this case, the field stop may be divided into a fixed field stop and a movable field stop.

The illumination light IL emitted from the rod integrator 14R illuminates the reticle R via the condenser lens 18 along the illumination system optical axis AX3 through the condenser lens 16R and the optical path bending mirror 17. The illuminated pattern on the reticle R is projected onto the wafer W and transferred by the projection optical system 23 as described above.
Although the optical path bending mirrors 7 and 17 are not essential in terms of optical performance, the overall height (the height in the Z direction) of the projection exposure apparatus increases when the illumination optical system ILS is arranged in a straight line. Therefore, for the purpose of space saving, the mirrors 7 and 17 are arranged at appropriate positions in the illumination optical system ILS. Further, the illumination system optical axis AX1 coincides with the illumination system optical axis AX2 by reflection of the mirror 7, and the illumination system optical axis AX2 coincides with the illumination system optical axis AX3 by reflection of the mirror 17.

As a material of the rod integrator 14R of this example, a fluoride crystal material belonging to a cubic system such as fluorite (calcium fluoride: CaF ₂ ), barium fluoride (BaF ₂ ), or lithium fluoride (LiF) is used. To do. Even in the case of a fluoride crystal, magnesium fluoride (MgF ₂ ) is a uniaxial crystal and has a large birefringence, and thus is not suitable for the rod integrator 14R of this example.

  However, since the band gap of magnesium oxide (MgO) is 7.8 eV, that is, the energy of light is 159 nm in terms of wavelength, it has good transparency to ArF excimer laser light, and its crystal structure is also Since it is a rock salt structure type cubic system, its birefringence is relatively small and suitable for the material of the rod integrator 14R. Also, other crystal materials are suitable for the material of the rod integrator 14R of this example as long as they are materials belonging to a cubic system and having good transparency with respect to the exposure wavelength.

Next, the rod integrator 14R in FIG. 1 will be described in detail with reference to FIGS.
FIG. 2 is a perspective view showing the illumination optical system 1LS from the pupil equivalent surface 12R to the reticle R of the projection exposure apparatus shown in FIG. However, for convenience of explanation, in FIG. 2, the mirror 17 in FIG. 1 is omitted, so that the illumination system optical axis AX2 coincides with the illumination system optical axis AX3 and is parallel to the Z axis. Further, the pupil equivalent surface 12R, the relay lens 13R, the rod integrator 14R, and the condenser lens 16R in FIG. 1 are denoted by reference numerals 12, 13, 14, and 16 with the last reference sign R removed in FIG. In this case, the directions of the pupil equivalent surface 12, the relay lens 13, the rod integrator 14, and the condenser lens 16 in FIG. 2 are different from the corresponding members in FIG. 1, but their configurations and functions are as shown in FIG. Identical to the corresponding member inside.

  In the projection exposure apparatus of this example, the reticle R is scanned in the Y direction. Therefore, the field of the projection optical system 23, that is, the illumination field IAR on the pattern surface (reticle surface) of the reticle R is as shown in FIG. Furthermore, it is desirable that the rectangle has a long side in the X direction. Therefore, the exit surface 14b of the rod integrator 14 in a conjugate relationship (imaging relationship) via the illumination field IAR and the condenser lenses 16 and 18 is also a rectangle whose X direction is the long side direction.

  4 is a side view showing a part of the optical members of FIG. 2. In FIG. 4, the illumination light IL incident on the rod integrator 14 is changed according to the incident angle to the incident surface 14a of the rod integrator 14. It goes straight in the integrator 14 or is internally reflected by the side surfaces 14c and 14d to reach the exit surface 14b. That is, a light beam incident at a small incident angle (an angle close to vertical incidence) travels straight through the rod integrator 14 as shown by a solid line in FIG. 4 to reach the exit surface 14b, and enters at a medium incident angle. 4 is reflected internally by the side surfaces 14c and 14d of the rod integrator 14 as shown by a broken line in FIG. 4 and then reaches the exit surface 14b. A light beam incident at a large incident angle is shown in FIG. The inner surface is repeatedly reflected by the side surfaces 14c and 14d, and reaches the exit surface 14b.

  A plurality of illumination lights having different incident angles with respect to the incident surface 14a are superimposed on the exit surface 14b, and the illuminance in the exit surface 14b is made uniform by averaging the illumination lights. In FIG. 4, the light beam IL having an incident angle spread in the X direction has been described as an example. However, even in the case of a light beam having an incident angle spread in the Y direction, internal reflection on the side surface in the Y direction of the rod integrator 14 is performed. Thus, the averaging effect can be obtained. Accordingly, the illuminance in the illumination field IAR on the reticle R conjugate with the exit surface 14b is also made uniform.

  Further, since the rod integrator 14 has no refracting action, the exit angles in the X direction and the Y direction of the light beam exiting from the exit surface 14b are reversed when the inner surface reflection is an odd number, The absolute value maintains the incident angle θ of the light beam incident on the incident surface 14a. Therefore, by setting the incident angle range of the light beam incident on the incident surface 14a of the rod integrator 14 to a predetermined value, the emission angle range of the light beam emitted from the exit surface 14b of the rod integrator 14 is set to a predetermined value. As a result, the incident angle range of the illumination light incident on the reticle R can be set to a predetermined value.

  For this reason, the pupil equivalent surface 12 which becomes the pupil plane via the relay lens 13 with respect to the incident surface 14a of the rod integrator 14 is an optical member (the relay lens 13 to the condenser lens) after the relay lens 13 in the illumination optical system ILS. 18) corresponds to the pupil plane with respect to the reticle plane. That is, on the pupil equivalent surface 12, the illumination light flux passing through a position away from the illumination system optical axis AX2 by a predetermined distance (for example, the distance IX in the X direction) is refracted by the refraction action of the relay lens 13 whose focal length is f1. The light is incident on the incident surface 14a of the rod integrator 14 while being inclined in the X direction by an incident angle θ that satisfies the following relationship.

IX = f1 × sin θ (1)
This light beam exits from the exit surface 14b with an inclination of + θ or −θ in the X direction, and is irradiated onto the reticle R at a predetermined incident angle.
The incident angle on the reticle R varies depending on the imaging magnification of the exit surface 14b of the rod integrator 14 and the illumination field IAR on the reticle R. As an example, if this magnification is four times, the incident on the reticle R The angle φ is an angle φ that satisfies the following expression.

sin φ = sin θ / 4 (2)
By the way, the distribution of the illumination light quantity on the pupil equivalent plane 12 can take various shapes. For example, when the reticle R is a spatial frequency modulation type phase shift reticle, so-called small σ illumination is suitable for the illumination light to the reticle R. This small σ illumination can be realized by concentrating the illumination light amount distribution on the pupil equivalent surface 12 on a circular area 12d having a small radius on the illumination system optical axis AX2, as shown in FIG. That is, as the diffractive optical element 9a in FIG. 1, an element that does not have a great diffractive action may be used so that diffracted light is generated within a minute diffraction angle range. In FIGS. 5A, 5B, 5C, and 4D, the pupil equivalent planes 12 in FIGS. 2 and 4 are represented by pupil equivalent planes 12c, 12e, 12h, and 12k, respectively.

  The light amount distribution shown in FIG. 5B is so-called dipole illumination, and small circular light amount regions 12f and 12g are located at predetermined distances in the −X direction and the + X direction from the illumination system optical axis AX2. Exists. This dipole illumination is suitable for exposure of a pattern PX having periodicity in the X direction on the reticle R shown in FIG. When the pitch in the X direction of the pattern PX in FIG. 5E is P and the exposure wavelength is λ, the incident angle of the illumination light to the reticle R is tilted by ± λ / (2P) in the X direction. And the depth of focus of the projected image can be greatly increased. The positions of the regions 12f and 12g having a large amount of light in FIG. 5B are determined based on the above relationship so that the incident angle of the illumination light to the reticle R is the angle (± λ / (2P)). That's fine. Further, in order to form such two polar regions 12f and 12g having a large light quantity on the pupil equivalent surface 12e, the diffractive optical element 9a in FIG. 1 is used as the Z direction in FIG. 1 (in FIG. 5B). It is preferable to use a phase type diffraction grating having a longitudinal direction (corresponding to the Y direction) and periodicity in the X direction in FIG. The diffractive optical element 9a in this case corresponds to an angle limiting mechanism.

  Further, the light amount distribution on the pupil equivalent surface 12 can be changed by changing the pitch and directionality of the diffractive optical element 9a. That is, if a diffractive optical element having a structure obtained by rotating the diffractive optical element 9a by 90 ° is used, the optical axis AX2 is positioned at a predetermined distance in the + Y direction and the −Y direction as shown in FIG. Regions 12i and 12j having a large amount of light can be formed. Such illumination light quantity distribution is suitable for exposure of a pattern having a periodicity in the Y direction obtained by rotating the pattern PX of the reticle R shown in FIG. 5E by 90 °.

  Here, assuming that a line and space pattern having a line width of 65 nm having periodicity in the X direction is exposed on the wafer by a projection exposure apparatus having an exposure wavelength of 193 nm, the pitch is 130 nm on the wafer. Furthermore, when the projection magnification β of the projection optical system 23 is set to ¼, the pattern pitch P on the reticle R corresponding to the line and space pattern is 520 nm (= 130 × 4). Therefore, when exposing such a pattern, the incident angle of the illumination light to the reticle R is tilted in the X direction by ± φ using an angle φ (= 10.7 °) satisfying the following equation according to the above relationship. Is desirable.

sinφ = 193 / (520 × 2) (3)
Furthermore, when the imaging magnification between the exit surface 14b of the rod integrator 14 and the illumination field IAR on the reticle R is set to 4 times the above, the exit angle of illumination light from the exit surface 14b of the rod integrator 14 satisfies the following equation. It is desirable to be ± θ using the angle θ (= 47.9 °).
sin θ = 4 × sin φ (4)
As described above, since this coincides with the desired incident angle θ of the illumination light to the incident surface 14a of the rod integrator 14 (Equation (1)), the pitch and directionality of the diffractive optical element 9a are optimized to increase the amount of light. The positions of the regions 12f and 12g may be set to satisfy the above relationship.

Correspondingly, the traveling direction of the illumination light in the rod integrator 14 also proceeds in a direction inclined by an angle ψ in the X direction with respect to the Z axis that is the optical axis of the rod integrator 14. The angle ψ depends on the refractive index n of the optical crystal constituting the rod integrator 14 and satisfies the following relationship.
n × sin ψ = sin θ (5)
If the optical crystal constituting the rod integrator 14 is fluorite, the refractive index of fluorite with respect to a light beam with a wavelength of 193 nm is 1.501, so ψ = 29.6 °.

  By the way, when exposing a pattern PX having periodicity in the X direction as shown in FIG. 5E and having a longitudinal direction in a direction perpendicular to the X direction, the polarization direction of the reticle R (vibration direction of the electric field of light) is Y. By illuminating with illumination light whose main component is linearly polarized light, the contrast and depth of focus of the projected image can be increased. This is reported, for example, in Reference 1 (Thimothy A. Brunner, et al .: “High NA Lithographic imaging at Brewster's ange1”, SPIE Vo1.4691, pp.1-24 (2002)).

Therefore, it is desirable that the illumination light having a light amount distribution in which the light amount increases in the regions 12f and 12g in FIG. 5B also has a polarization state in which the linearly polarized light in the Y direction in FIG. 5B is a main component. .
However, even when cubic fluorite is used, birefringence is not generated for a light beam having a wavelength of 200 nm or less and traveling in a direction about 30 ° away from the optical axis as described above. May occur. This birefringence is a birefringence due to a crystal lattice structure called intrinsic birefringence, and occurs not only in fluorite but in all cubic crystals. The amount of birefringence varies depending on the relationship between the traveling direction of the light beam and the crystal orientation, and is maximized for light traveling in the (110) direction of the crystal and travels in the (111) and (100) directions of the crystal. 0 for light. Specifically, when light having a wavelength of 193 nm travels 1 cm in the (110) direction in a fluorite crystal, an optical path difference of 3.2 nm occurs due to intrinsic birefringence between linearly polarized lights orthogonal to each other.

Therefore, even if linearly polarized illumination light is incident on the rod integrator 14 made of fluorite or other crystal material, the plane of polarization of the linearly polarized light is rotated or elliptically polarized by the intrinsic birefringence (intrinsic birefringence) of the crystal. In some cases, it is not possible to obtain emitted light while maintaining a desired linearly polarized state.
Therefore, FIG. 3 shows the rod integrator 14 in FIG. 2, and in this example, as shown in FIG. 3, the (100) direction of a crystal belonging to a cubic system such as fluorite constituting the rod integrator 14 is shown. The direction of the long side of the rod integrator 14, that is, the optical axis direction of the illumination optical system ILS is assumed to match. Here, the (100) direction is an axis optically equivalent to the direction of the <100> axis (an axis in which the arrangement of numbers is replaced or the sign is further inverted, that is, the <010> axis, the <001> axis , <-100> axis, <0-10> axis, <00-1> axis). A crystal plane orthogonal to the (100) direction is defined as a (100) plane. Therefore, the entrance surface 14a and the exit surface 14b of the rod integrator 14 correspond to the (100) plane of the crystal. As an example, in this example, the direction of the <001> axis of the crystal is matched with the direction of the long side of the rod integrator 14 in the (100) direction.

Further, as shown in FIG. 3, in the rod integrator 14, the X-axis direction coinciding with the direction of one side of the rectangular illumination field on the reticle R in FIG. 2 is the <100> crystal axis, and the Y-axis orthogonal to the X-axis. Are aligned with the <010> crystal axis. Accordingly, the side surfaces 14c, 14d, 14e, and 14f of the rod integrator 14 are all (100) surfaces.
Hereinafter, the reason will be described with reference to FIGS.

  6 proceeds at a predetermined angle with respect to the optical axis in a fluorite crystal in which the optical axis direction (long-side direction) coincides with the <001> crystal axis, like the rod integrator 14 shown in FIG. It shows the birefringence characteristics generated with respect to the light beam. The horizontal axis in FIG. 6 represents a deviation angle RX in the X direction from the optical axis direction (<00-1> axial direction which is the −Z direction) in the traveling direction of the light beam, and the vertical axis in FIG. Represents a deviation angle RY of the traveling direction from the optical axis direction to the Y direction. Further, the positions of the black circles arranged two-dimensionally in FIG. 6 represent the traveling direction of the light beam determined from the horizontal axis and the vertical axis, and the birefringence characteristics generated for the light beam traveling at that angle are: It is shown as a line segment centered on each black circle. The direction of this line segment represents the fast axis of birefringence (the direction of linearly polarized light that minimizes the refractive index), and its length represents the amount of birefringence. The relationship between the length of the line segment and the amount of birefringence is as shown in the scale at the lower right in FIG.

  In this case, four points of RX = + 45 ° and RX = −45 ° on the horizontal axis and RY = + 45 ° and RY = −45 ° on the vertical axis in FIG. 6 correspond to the (110) direction of the crystal. Therefore, the amount of birefringence is maximized. In addition, the (111) direction of the crystal is near the center of each quadrant in FIG. 6, and birefringence is zero here. Also, since the origin is in the (100) direction, the birefringence at the origin is zero. When viewed from the (100) direction, the cubic crystal has four-fold rotational symmetry, so that the birefringence characteristic also has four-fold rotational symmetry as shown in FIG.

Illumination light that is optimal for exposing a line-and-space pattern with a line width of 65 nm having periodicity in the X direction at the exposure wavelength of 193 nm (ArF excimer laser light) is the optical axis direction (− It proceeds at an angle away from the (Z direction) by ± 29.6 ° in the X direction. The polarization state is preferably linearly polarized light in the Y direction.
FIG. 7A is an enlarged view of a portion corresponding to the direction in which the illumination light travels in FIG. 6, and the center 7AC of FIG. 7A is RX = 30 ° in FIG. Corresponds to RY = 0 °. The circle in FIG. 7A represents the angle range of the illumination light beam, and the radius thereof is the coherence factor (σ value) of the illumination system when the numerical aperture NA of the projection optical system 23 is 0.9 under the above conditions. ) Is a range corresponding to σ = 0.15, which is about 5 ° in angular range. The relationship between the length of the line segment and the amount of birefringence at this time is as shown in the scale shown in the lower right of FIG.

  As shown in FIG. 7A, the intrinsic birefringence generated within this traveling angle range is relatively large, but the fast axis (the direction of the line segment extending from each black circle) is generally in the RX direction, that is, the X direction. Parallel to That is, the linearly polarized light polarized in the Y direction travels through the fluorite rod integrator 14 with almost no change in the polarization state because the polarization direction substantially coincides with the slow axis (the direction orthogonal to the fast axis). To do.

In addition, also when the inner surface is reflected by the side surface 14d of the rod integrator 14 in FIG. 3, the light linearly polarized in the Y direction becomes almost perfect S-polarized light with respect to the reflecting surface, so that the polarization state hardly reflects. To do.
The traveling direction after reflection at the side surface 14d is a direction inclined by about 30 ° from the optical axis direction (−Z direction) to the −X direction. As is clear from FIG. 6, RX = Even for a light beam traveling in the direction of −30 ° and RY = 0 °, the fast axis is substantially parallel to the RX direction, that is, the X direction. Therefore, linearly polarized light polarized in the Y direction is still in its polarization state. It proceeds through the fluorite rod integrator 14 with almost no change. The illumination light is repeatedly reflected on the side surfaces 14d and 14c, and then emitted from the exit surface 14b of the rod integrator 14 while maintaining the polarization state of linearly polarized light polarized in the Y direction. The linearly polarized illumination light is illuminated.

  When the reticle pattern is a pattern having periodicity in the Y direction, as shown in FIG. 5C, a position away from the optical axis AX2 by a predetermined distance in the + Y direction and the −Y direction on the pupil equivalent plane 12h. It is desirable from the viewpoint of increasing the image contrast and the depth of focus to use the polarized light having the regions 12i and 12j having a large amount of light and the polarization state of which is mainly the linearly polarized light in the X direction. When the pattern to be transferred is a line-and-space pattern (pitch: 130 nm) having a line width of 65 nm on the wafer as described above, the illumination light passes through the rod integrator 14 at RX = 0 °, RY = Proceed in a direction centered around ± 29.6 °.

  Also in this case, the birefringence characteristic with respect to the angular range is obtained by rotating the characteristic shown in FIG. 7A by 90 ° from the symmetry of the crystal, as is apparent from FIG. The direction is approximately orthogonal to the fast axis RY direction, that is, the Y direction. Therefore, the light beam polarized in the X direction travels through the rod integrator 14 with almost no change in the polarization state. Even when the light is reflected by the side surfaces 14e and 14f, the polarization state is not changed in the same manner as described above. Therefore, the illumination light is emitted from the emission surface 14b while maintaining the linearly polarized light in the X direction, and is applied to the reticle R. Is illuminated with the desired linearly polarized illumination.

It should be noted that the actual pattern on the reticle R is not formed only from patterns that are all aligned in one direction. Therefore, the optimal dipolar and linearly polarized illumination for a pattern having a specific direction as described above is the pattern with the finest line width among the patterns on the reticle R, and therefore difficult to expose. It may be optimized and used.
By the way, as can be seen from FIG. 6, the direction of the fast axis with respect to each incident angle when the optical axis (Z axis) coincides with the (100) direction is substantially aligned with the radial direction. Therefore, by simply matching the optical axis of the rod integrator 14 with the (100) direction of the crystal, the side surface of the rod integrator 14 does not need to specify the crystal plane, and the linear polarization of the incident light in the above-described dipole illumination can be obtained. It is possible to configure the rod integrator 14 that can be ejected while maintaining a certain state.

For example, when the rod integrator 14 is configured so that the side surfaces 14c, 14d, 14e, and 14f of the rod integrator 14 coincide with the (110) plane of the crystal, the birefringence characteristic is 45 as shown in FIG. The rotation characteristic is obtained (the AA ′ direction in FIG. 6 coincides with the horizontal axis).
FIG. 7B shows the birefringence characteristics for a light beam traveling in a range of a radius of about 5 ° centered in the direction of RX = 30 ° and RY = 0 ° in that case. In this case, compared to the result shown in FIG. 7A, the angle of deviation of the fast axis of each light beam from the X-axis is particularly shown in FIG. 7B at the upper and lower end positions 7BU and 7BB in FIG. It is larger than the result shown in (A). However, the birefringence amount itself for each light beam is small.

  Since the final change in the polarization state is determined by the product of the birefringence amount and the traveling distance and the angular relationship between the fast axis and the polarization direction, the side surfaces 14c to 14f of the rod integrator 14 are made to coincide with the (110) plane. It is not generally possible to determine which of the cases where the side surfaces 14c to 14f of the rod integrator 14 are coincident with the (100) plane is advantageous. Therefore, it is preferable to select an optimum crystal direction (rotation angle around the Z direction) as the direction of each of the side surfaces according to the shape of the rod integrator 14 (particularly the length in the optical axis direction).

On the other hand, when the long side direction of the rod integrator 14 is matched with the (111) direction of the crystal, it is difficult to form the rod integrator 14 that can preserve the polarization direction of linearly polarized light as described above.
FIG. 8 shows the fluorite crystal in which the optical axis (Z axis) coincides with the <111> axis of the crystal, as in FIG. 6, in the optical axis direction (<-1-1 in the -Z direction). The birefringence characteristics generated for a light beam traveling at a predetermined angle with respect to (> axial direction) are shown. When viewed from the (111) direction, the cubic crystal has three-fold rotational symmetry, and therefore the birefringence characteristic also has three-fold rotational symmetry as shown in FIG. In FIG. 8, the side surfaces 14c and 14d in the X direction of the rod integrator 14 are made to coincide with the {−211} plane, and therefore the side surfaces 14e and 14f in the Y direction of the rod integrator 14 are made to coincide with the {0-11} surface. The birefringence characteristics are shown.

At this time, with respect to illumination light suitable for exposure of the above-described pattern having periodicity in the X direction, that is, illumination light traveling at an angle of ± 29.6 ° in the X direction from a direction parallel to the optical axis (−Z direction) The birefringence characteristics are shown in FIGS. 9 (A) and 9 (B).
FIG. 9A shows the birefringence characteristics of a light beam traveling within a radius of about 5 ° with a direction inclined −30 ° in the X direction as the center 9AC, and FIG. 9B is inclined + 30 ° in the X direction. The birefringence characteristic of a light beam traveling in a radius of about 5 ° with the direction as the center 9BC is shown. The amount of birefringence is indicated by the length of the line segment centered on each black circle, and the scale is as shown in the lower right of each figure.

From the result shown in FIG. 9A, the amount of birefringence acting on the light beam traveling in the direction inclined by −30 ° in the X direction is small, and the direction of the fast axis is generally the RX direction, that is, the X direction. Parallel to For this reason, the linearly polarized light in the Y direction travels in the above direction with almost no change in the polarization state.
Further, from the result shown in FIG. 9B, although the amount of birefringence acting on the light beam traveling in the direction inclined by + 30 ° in the X direction is large, the direction of the fast axis is approximately the RY direction, that is, Y The direction of polarization of the linearly polarized light in the Y direction is hardly changed when traveling in the above direction. Therefore, even if a fluorite crystal whose optical axis (Z axis) is aligned with the (111) direction of the crystal is used as the material of the rod integrator 14, a pattern having periodicity in one direction (X direction in the above). In this exposure, it is possible to realize dipole illumination having good linear polarization characteristics.

However, in actual circuit pattern exposure, even if the periodicity of the pattern is limited to the X direction in a specific exposure process, it is necessary to expose a pattern having periodicity in the Y direction in other exposure processes. Become.
The illumination light of the dipole illumination that is optimal for exposing a pattern having a periodicity of 130 nm pitch (on the wafer) in the Y direction passes through the rod integrator 14 as described above, RX = 0 °, RY = ± 29.6. A light beam traveling at an angle of ° and linearly polarized in the X direction.

FIG. 9C shows the birefringence characteristics of a light beam traveling within a radius of about 5 ° with the direction inclined by + 30 ° in the Y direction in FIG. 8 as the center 9CC, and FIG. 9D shows the Y direction in FIG. 2 shows the birefringence characteristics of a light beam traveling within a radius of about 5 ° with the direction inclined by −30 ° as the center 9DC. The scale of the amount of birefringence is as shown in the lower right of each figure.
As shown in FIGS. 9C and 9D, both light beams generate a relatively large amount of birefringence in the traveling direction, and the fast axis is the X direction in which the light beam is polarized. That is, it is greatly inclined from the RX direction in the figure. For this reason, the polarization direction of the illumination light beam is greatly influenced by the intrinsic birefringence of fluorite, and the desired linearly polarized light cannot be maintained.

  As described above, the dipole illumination having the optimum linear polarization characteristic with respect to the pattern having at least one periodicity in the X direction or the Y direction cannot be realized. This is because the (111) direction is set as the optical axis. This is due to the three-fold rotational symmetry of the refractive characteristics. Therefore, it is a problem that cannot be solved no matter how the rod integrator 14 made of fluorite crystal is rotated with the (111) direction as the rotation axis.

Therefore, as in this example, the crystal direction of the optical crystal used in the rod integrator 14 should be parallel to the (100) direction with respect to the illumination system optical axis AX2 in FIG.
By the way, when exposing a spatial frequency modulation type phase shift reticle as shown in FIG. 10, generally so-called small σ illumination with high spatial coherence is preferable.
FIG. 10 is a plan view showing a phase shift reticle R of the spatial frequency modulation type. In FIG. 10, line patterns LC, LL1, LL2, LR1, and LR2 made of a light-shielding film such as chrome are arranged at a pitch PT in the Y direction on a transmissive reticle substrate RP. The XY coordinates in FIG. 10 are the same as the coordinates on the reticle R in FIGS. 1 and 2. The longitudinal direction of each line pattern LC, LL1, LL2, LR1, LR2 coincides with the X direction, and the line width in the Y direction, which is the short direction, is WD. Further, light shielding patterns CL and CR are arranged on the outer sides of the line patterns LL2 and LR2 at both ends, separated by an interval (inter-side interval) SP, respectively.

  At intervals between the line patterns LC, LL1, LL2, LR1, and LR2 and the light shielding pattern CR, phase shift portions PS1, PS2, and PS3 are formed at every other portion, and the phase of transmitted light at that portion is another reticle substrate. A spatial frequency modulation type phase shift pattern (spatial frequency modulation type phase shift reticle) shifted by 180 ° with respect to the transmitted light from the RP is configured. The phase shift portions PS1, PS2, and PS3 are formed, for example, by digging the reticle substrate RP by etching.

  In this case, the small σ illumination is an illumination condition in which the incident angle range of illumination light to the reticle is narrow. That is, the small σ illumination is illumination in which the coherence factor (σ value), which is the ratio of the numerical aperture of the illumination light to the reticle to the numerical aperture on the reticle side of the projection optical system 23, is as small as about 0.3 or less. . In order to improve the resolution with respect to the phase shift pattern and expand the depth of focus, it is necessary to reduce the σ value to about 0.15.

  However, in such small σ illumination, the optical proximity is such that the line width of the pattern transferred onto the wafer W varies even if the pattern has the same pattern line width WD due to the change in the pitch PT of the phase shift pattern. The problem of OPE (Optica1 Proximity Error), which is an error due to the effect, becomes obvious. Furthermore, there arises a problem that the depth of focus for a pattern having a specific pitch is reduced.

  In this example, upon exposure of such a phase shift pattern, the illumination light amount distribution on the pupil equivalent surface 12 in FIG. 2 is shown in the X direction with the illumination system optical axis AX2 as the center, as shown in FIG. The amount of light is increased in a region 121 that is wide and narrow in the Y direction. More specifically, the effective angle value of the incident angle range of the illumination light IL with respect to the reticle R in the X direction (direction corresponding to the first direction) becomes as large as 0.7 or more as shown in the following equation. The direction (direction corresponding to the second direction) is set so that the effective σ value is as narrow as 0.2 or less.

Effective σ value in X direction ≧ 0.7 (6)
0 <effective σ value in Y direction ≦ 0.2 (7)
Thereby, the reduction of the focal depth at the OPE and the specific pitch can be greatly improved. In this case, the effective σ value of the illumination light in the predetermined direction on the reticle R is the refractive index of the medium in the sine of the maximum value of the incident angle of the illumination light on the reticle R in the predetermined direction. (In this example, this refractive index is substantially 1) is obtained by dividing the value obtained by multiplying by the numerical aperture in the predetermined direction on the reticle R side of the projection optical system 23.

  Hereinafter, this effect will be described using optical simulation results. The optical conditions used in this simulation are an exposure wavelength of 193 nm and a wafer-side numerical aperture NA of the projection optical system 23 of 0.92. The pattern used is the phase shift pattern shown in FIG. 10, and each dimension of the pattern is converted into a dimension on the wafer in consideration of the projection magnification, and the line width WD = 50 nm and the interval SP = 140 nm. The width of the light shielding patterns CR and CL in the Y direction = 10 μm, and the length of each pattern in the X direction = 10 μm. The pitch PT of the line patterns LC, LL1, LL2, LR1, and LR2 is made variable for the evaluation of the OPE characteristics and the depth of focus at each pitch.

Further, in order to improve the imaging performance with respect to the line patterns LC, LL1, LL2, LR1, and LR2 having the longitudinal direction in the X direction, the polarization state of the illumination light is changed to the linearly polarized light in the X direction (first direction). It was. These conditions are the same in the simulation under the illumination conditions of the present example below and the simulation under the conventional illumination conditions shown for comparison.
Next, a simulation method will be described.

  FIG. 11 is a cross-sectional view taken along the line AA ′ in FIG. 10 among the projected images generated when the reticle pattern shown in FIG. 10 is projected onto the wafer using the projection exposure apparatus of this example. The image intensity distribution Img is obtained by optical simulation. In FIG. 11, the line width when the line pattern LC at the center in FIG. 10 is transferred onto the wafer is the portion corresponding to the line pattern LC in the image intensity distribution Img (dark part IC), which is a predetermined slice. It can be calculated as the slice width PW when crossing at the level SL. Using this method, simulation evaluation was performed by the following method.

In the evaluation of the OPE characteristic, first, the image intensity distribution Img when the pitch PT of the line pattern LC or the like is 600 nm is calculated under each illumination condition, and the slice level SL is determined with the slice width PW of the dark part IC of the image being 35 nm. .
Subsequently, the image intensity distribution Img at each pitch PT is calculated with the pitch PT being variable, and the line width PW of the transfer pattern is obtained from the slice width of the dark portion IC of each image at the slice level SL. As a result, the relationship between the line width PW of the transfer pattern and the pattern pitch PT is obtained.

  Also in the evaluation of DOF (depth of focus), the pitch PT of the line pattern LC or the like was changed, the depth of focus at each pitch PT was calculated, and the relationship between DOF and pitch PT was obtained. For the calculation of DOF, the ED-Tree method (for example, Reference 2 (Burn J. Lin et al .: “Methods to Print Optical Images at Low-k1 Factors”, SPIE Vol. 1264, pp. 2-13 (1990)) Applied). At that time, the target line width was set to 35 nm, and the assumed errors were an allowable line width error of ± 2.8 nm and an exposure dose error of ± 2.5%. As for the pattern, a WD = 53 nm pattern assuming a manufacturing error of +3 nm for the reticle line width and a WD = 47 nm pattern assuming a manufacturing error of -3 nm for the reticle line width were obtained, and the common depth of focus was obtained. .

For both OPE and DOF, the four line patterns LL1, LL2, LR1, and LR2 are removed from the pattern in FIG. 10, and the light-shielding patterns CL and CR are separated from each other by a distance between the sides of the center line pattern LC and SP. Evaluation was also made on “one pattern”, which is a deformation pattern shifted to the center side.
Hereinafter, the result will be described with reference to FIG. 12, FIG. 13, and FIG.

The simulation results of OPE and DOF assuming the use of normal illumination with σ = 0.15, which is a conventional exposure method, are as shown in FIGS. 13A and 13B, respectively.
Since the reticle pattern to be exposed is a spatial frequency modulation type phase shift pattern, with a small σ illumination of σ = 0.15, the pattern pitch PT (horizontal axis) is from 140 nm as shown in FIG. A large DOF (vertical axis) can be obtained in a 200 nm minute pitch pattern. However, in the range of about 290 nm to 340 nm, which is a medium pitch PT, the DOF is less than 150 nm, and the depth of focus is reduced in a pattern having a so-called specific pitch.

  Securing the DOF of 150 nm or more is extremely important for securing the yield in LSI mass production, and it is difficult to apply the exposure technique to mass production with a DOF of less than 150 nm. As a result, in order to form a circuit pattern with this conventional exposure method, it may be necessary to restrict the design (layout) of the circuit pattern and eliminate a pattern having a pitch in this range.

  Further, as shown in FIG. 13A, the change of the transfer line width PW (vertical axis) accompanying the change of the pattern pitch PT (horizontal axis) is large, and the change width is within the range where the pitch PT is 250 nm to 600 nm. It reaches 10.5 nm for the pattern. Note that Iso and black circles at the right end of the horizontal axis in the diagrams shown in FIGS. 13A and 13B represent the simulation results of the above-described single pattern, and the same applies to the following drawings. is there.

  On the other hand, the simulation results of OPE and DOF assuming the use of conventional illumination with conventional σ = 0.30 are as shown in FIGS. 14 (A) and 14 (B), respectively. Since the spatial coherence of the illumination light is reduced by increasing the illumination σ value to 0.3, the OPE characteristic shown in FIG. 14A is a change in the pitch PT compared to that shown in FIG. The fluctuation of the transfer line width PW is reduced and improved. Numerically, the change width of the transfer line width PW when the pitch PT is in the range of 250 nm to 600 nm is reduced to 5.5 nm.

However, the DOF decreases due to the increase in the illumination σ value, and for patterns with a pitch PT of 260 nm or less, the DOF is less than 150 nm, and it becomes extremely difficult to transfer a fine pitch pattern.
On the other hand, as an example of the illumination condition of this example, the simulation results of OPE and DOF when the effective σ value in the X direction is 0.85 and the effective σ value in the Y direction is 0.15 are as follows: FIG. 12 (A) and FIG. 12 (B) are as shown. That is, the OPE characteristic is as shown in FIG. 12A, and the change width of the transfer line width PW is 5.5 nm when the pitch PT is in the range of 250 nm to 600 nm, which is shown in FIG. 14A. Is as small and good as in the case of illumination with σ = 0.3.

Also, as shown in FIG. 12B, a DOF of 150 nm or more is secured in any of the ranges where the pitch PT is 140 nm to 600 nm and the single pattern indicated as Iso at the right end in FIG. 12B. Has been.
From the above, it can be seen that under the illumination conditions of this example, the exposure transfer can be performed with a practical depth of focus with respect to a wide range of pitch PT patterns while suppressing the OPE.

  In this example, the incident angle range of the illumination light to the reticle is set to 0.85 for the effective σ value in the X direction and 0.15 for the effective σ value in the Y direction. The range of incident angles of light on the reticle is not limited to this value. That is, if the effective σ value in the X direction is 0.7 or more and the effective σ value in the Y direction is 0.2 or less, the above effect can be exhibited.

In order to form such a rectangular illumination light quantity distribution on the pupil equivalent plane 12, the diffractive optical element 9a in FIG. 1 has a longitudinal direction in the Y direction and a different pitch in a predetermined range in the X direction. It is preferable to use a phase type diffraction grating group having the same. In this diffraction grating group, the pitches of the phase gratings formed thereon differ depending on the position in the plane.
By the way, the shape of the region 121 having a large light amount in the illumination light amount distribution shown in FIG. 5D is not limited to a rectangular shape that is long in the X direction, and the phase shift pattern has a longitudinal direction in the Y direction. If the pattern has periodicity, it should have a rectangular shape that is long in the Y direction. In this case, it goes without saying that the polarization direction of linearly polarized light should also be the Y direction.

  Of course, in the projection exposure apparatus of this example, it is possible to irradiate the reticle R with illumination light having an illumination light quantity distribution as shown in FIG. 5D while maintaining the desired linear polarization state. On the pupil equivalent plane 12 in FIG. 2, the light flux corresponding to the light quantity distribution shown in FIG. 5D has the optical axis direction coincided with the (100) direction of the fluorite crystal, and the side faces 14c to 14f In the rod integrator 14 matched with the (100) plane of the stone crystal, it is distributed almost on the horizontal axis (-RX to + RX) in FIG. 6 showing the relationship between the traveling direction of the light beam and the birefringence characteristics. Since the fast axis in this region is substantially in the RX direction, that is, parallel to the X direction, the illumination light whose polarization direction is the X direction travels through the rod integrator 14 with almost no change in the polarization state. The reticle R can be illuminated with the desired linearly polarized light (here, linearly polarized light in the X direction).

This is substantially the same for illumination light having a light amount distribution obtained by rotating the light amount distribution of FIG. 5D by 90 ° and linearly polarized in the Y direction. The reticle R can be illuminated with the desired linearly polarized light (here, linearly polarized light in the Y direction).
Note that the projection exposure apparatus of this example is used only when the spatial frequency modulation type phase shift reticle shown in FIG. 10 or the one-dimensional line and space pattern shown in FIG. 5E is exposed. However, it is also used when exposing patterns of other shapes.

  Therefore, among the diffractive optical elements 9a and 9b arranged on the turret-shaped member 8 in FIG. 1, elements for realizing illumination with a normal σ value of about 0.7, or similar σ It is desirable that an element for realizing annular illumination is also installed so that the switching mechanism 10 can be switched and used. Further, the reticle R can be exposed at a high speed so that the exposure of one wafer W can be performed by exchanging two reticles and selecting and exchanging the illumination conditions from any of the above-mentioned various illumination conditions. It is preferable to provide a mechanism.

Depending on the illumination conditions, there are cases where it is desirable for the illumination light to be randomly polarized. In addition, as described above, the polarization direction of linearly polarized light needs to be switched λ to the X direction or the Y direction. In the projection exposure apparatus of this example, such polarization state control is performed by the polarization control member 4 in the illumination optical system ILS of FIG. Hereinafter, the polarization control member 4 will be described.
In FIG. 1, when an excimer laser or a fluorine laser is used as the exposure light source 1, the illumination light IL emitted from the exposure light source 1 is essentially linearly polarized light. Therefore, as the polarization control member 4, a member that converts (rotates) the polarization direction of the linearly polarized light into a desired direction may be used. That is, the polarization control member 4 is provided with a half-wave plate made of an optical material having birefringence, such as quartz (silicon dioxide crystal) or magnesium fluoride crystal, so as to be rotatable around the illumination system optical axis AX1. This can be achieved. In this case, the polarization direction of the illumination light IL illuminated on the reticle R can be controlled by setting the rotation angle of the half-wave plate.

  On the other hand, when the exposure light source 1 emits a light beam other than linearly polarized light such as a mercury lamp or a randomly polarized laser, a polarization filter or a polarizing beam splitter that transmits only linearly polarized light in a predetermined direction is used as the polarization control member 4. Can be used. However, even if the illumination light applied to the reticle R is not completely linearly polarized, the effect of the above example can be achieved if the majority of the illumination light intensity (for example, about 80% or more) is predetermined linearly polarized light. Therefore, it is sufficient that the polarization selectivity of the polarizing filter or the polarizing beam splitter is about 80% or more.

Incidentally, as described above, it may be preferable that the polarization state of the illumination light illuminated on the reticle is non-polarized. In this case, it is desirable that the polarization control member 4 of the projection exposure apparatus of this example be configured to be detachable or generate non-polarized illumination light.
For example, when the exposure light source 1 is a laser light source that emits a substantially linearly polarized light beam, two polarization plates arranged in series with respect to the illumination system optical axis AX1 are used as the polarization control member 4, and light By rotating the two wave plates with the axis AX1 as the center of rotation, the emitted light beam can be made into linearly polarized light or circularly polarized light (that is, substantially non-polarized light).

  Note that, depending on the design and manufacturing method of the diffractive optical elements 9a and 9b and the like, an example of the illumination light amount distribution on the pupil equivalent surface 12 in FIG. 2 is an example of the amount of light in the two regions 12f and 12g in FIG. In a large light amount distribution or the like, an unnecessary light amount distribution may occur in addition to a predetermined position (position where the regions 12f and 12g should be). Therefore, an interchangeable diaphragm (deformed diaphragm) is provided in the vicinity of the pupil equivalent surface 12, and this modified diaphragm is also replaced and arranged in accordance with the exchange of the diffractive optical elements 9a, 9b, etc., and only the desired light quantity distribution is obtained. It is also possible to selectively transmit light and shield unnecessary light amount distribution.

By the way, in the said embodiment, the mechanism containing the diffractive optical element 9a, 9b of FIG. 1 and the exchange mechanism 10 is shown as an angle variable mechanism which prescribes | regulates and makes variable the incident angle range of the illumination light beam to the rod integrator 14 of FIG. Although used, this angle variable mechanism is not limited to this, and other members can be used.
For example, as shown in FIG. 15, the first polyhedral prism 41 whose exit surface 41b has a concave shape is disposed on the exposure light source side, and the second polyhedral prism 42 whose incident surface 42a has a convex shape is disposed on the rod integrator side. A polyhedral prism pair arranged in the above may be used. In this case, the distribution of the illumination light beam on the pupil equivalent surface 12 can be made variable by making the polyhedral prism pair rotatable about the illumination system optical axis AX2 and making the interval DD of the polyhedral prism pair variable. You can also.

In the above embodiment, the structure of the rod integrator 14 in FIG. 2 is a rectangular parallelepiped, but the incident surface 14a side may have some chamfering or the like in the periphery thereof. Therefore, the rod integrator 14 may have a substantially rectangular parallelepiped shape.
Next, an example of a semiconductor device manufacturing process using the projection exposure apparatus of the above embodiment will be described with reference to FIG.

  FIG. 16 shows an example of a semiconductor device manufacturing process. In FIG. 16, a wafer W is first manufactured from a silicon semiconductor or the like. Thereafter, a photoresist is applied on the wafer W (step S10), and in the next step S12, a reticle (provisionally R1) is loaded on the reticle stage of the projection exposure apparatus of the above embodiment (FIG. 1). Then, the pattern of the reticle R1 (represented by the symbol A) is transferred (exposed) to all the shot areas SE on the wafer W by the scanning exposure method. At this time, double exposure is performed as necessary. The wafer W is, for example, a wafer having a diameter of 300 mm (12 inch wafer), and the size of the shot area SE is, for example, a rectangular area having a width of 25 mm in the non-scanning direction and a width of 33 mm in the scanning direction. Next, in step S14, a predetermined pattern is formed in each shot region SE of the wafer W by performing development, etching, ion implantation, and the like.

  Next, in step S16, a photoresist is applied on the wafer W, and then in step S18, a reticle (provisionally R2) is loaded onto the reticle stage of the projection exposure apparatus of the above-described embodiment (FIG. 1). Then, the pattern of the reticle R2 (represented by the symbol B) is transferred (exposed) to each shot area SE on the wafer W by the scanning exposure method. In step S20, a predetermined pattern is formed in each shot region of the wafer W by performing development and etching of the wafer W, ion implantation, and the like.

  The above exposure process to pattern formation process (steps S16 to S20) are repeated as many times as necessary to manufacture a desired semiconductor device. Then, a semiconductor device SP as a product is manufactured through a dicing process (step S22) for separating each chip CP on the wafer W one by one, a bonding process, a packaging process, and the like (step S24). .

According to the device manufacturing method of this example, since exposure is performed under the illumination conditions of the above-described embodiment, it is possible to manufacture a semiconductor integrated circuit that is more highly integrated than in the past with a high yield. As a result of the above effects, according to the device manufacturing method of this example, it is possible to manufacture a highly integrated and high performance semiconductor integrated circuit at low cost.
Further, the projection exposure apparatus of the above-described embodiment includes an illumination optical system composed of a plurality of lenses, a projection optical system incorporated in the exposure apparatus main body, optical adjustment, and a reticle stage and wafer stage made up of a large number of mechanical parts. Is attached to the exposure apparatus main body, wiring and piping are connected, and further comprehensive adjustment (electrical adjustment, operation check, etc.) is performed. The exposure apparatus is preferably manufactured in a clean room where the temperature, cleanliness, etc. are controlled.

Further, the present invention can be applied not only to a scanning exposure type projection exposure apparatus but also to a batch exposure type projection exposure apparatus such as a stepper. The magnification of the projection optical system used may be not only a reduction magnification but also an equal magnification or an enlargement magnification. Furthermore, the present invention can be applied to an immersion type exposure apparatus disclosed in, for example, International Publication (WO) No. 99/49504.
Further, the use of the projection exposure apparatus of the present invention is not limited to the exposure apparatus for manufacturing a semiconductor device, but for example, a liquid crystal display element formed on a square glass plate or a display apparatus such as a plasma display. The present invention can be widely applied to an exposure apparatus and an exposure apparatus for manufacturing various devices such as an image sensor (CCD or the like), a micromachine, a thin film magnetic head, and a DNA chip. Furthermore, the present invention is also applied to an exposure process (exposure apparatus) when manufacturing a mask (a photomask including an X-ray mask, a reticle, etc.) on which a mask pattern of various devices is formed using a photolithography process. be able to.

  In addition, this invention is not limited to the above-mentioned embodiment, Of course, a various structure can be taken in the range which does not deviate from the summary of this invention.

  According to the device manufacturing method of the present invention, the performance of various devices such as semiconductor integrated circuits can be improved, and the manufacturing cost of various devices can be reduced.

It is the figure which partly cut off showing the schematic structure of the projection exposure apparatus of an example of embodiment of this invention. FIG. 2 is a perspective view showing the optical member of the illumination optical system from the pupil equivalent surface 12R (12) to the reticle R in FIG. It is a perspective view which shows the rod integrator 14 in FIG. FIG. 3 is a side view showing optical members from a pupil equivalent surface 12 to a rod integrator 14 in FIG. 2. (A), (B), (C) and (D) are diagrams showing examples of illumination light quantity distribution on the pupil equivalent plane 12 of FIG. 2, and (E) is a plan view showing an example of a pattern of a reticle R to be transferred. It is. It is a figure which shows the birefringence characteristic produced with respect to the light beam which advances at a predetermined angle with respect to an optical axis in the fluorite crystal which made the optical axis direction correspond to the <001> crystal axis. (A) is an enlarged view showing the birefringence characteristics for a light beam traveling in a radius range of about 5 ° centering on the directions of RX = 30 ° and RY = 0 ° in FIG. 6, and (B) is FIG. FIG. 5 is an enlarged view showing the birefringence characteristics for a light beam traveling in a radius range of about 5 ° centering around RX = 30 ° and RY = 0 ° in the birefringence characteristics rotated clockwise by 45 °. It is a figure which shows the birefringence characteristic produced with respect to the light beam which advances at a predetermined angle with respect to an optical axis in the fluorite crystal which made the optical axis direction correspond to the <111> crystal axis. (A) and (B) are enlarged views showing the birefringence characteristics with respect to a light beam traveling in a radius range of about 5 ° centered in the direction of RX = ± 30 ° and RY = 0 ° in FIG. 8, (C). And (D) are enlarged views showing the birefringence characteristics with respect to a light beam traveling in a radius range of about 5 ° centered in the direction of RX = 0 ° and RY = ± 30 ° in FIG. It is a top view which shows an example of a phase shift reticle of a spatial frequency modulation type. It is a figure which shows an example of the intensity distribution of the image corresponding to the part in alignment with the AA 'line of FIG. It is a figure which shows the result of having calculated transfer line width PW and DOF (depth of focus) with respect to pattern pitch PT by the optical simulation under the illumination conditions of an example of embodiment of this invention. It is a figure which shows the result of having calculated transfer line | wire width PW and DOF (depth of focus) with respect to pattern pitch PT by the optical simulation which assumed use of conventional normal illumination ((sigma) = 0.15). It is a figure which shows the result of having calculated transfer line width PW and DOF (depth of focus) with respect to pattern pitch PT by the optical simulation which assumed use of the conventional normal illumination ((sigma) = 0.30). It is a figure which shows a pair of polyhedral prism as another example of an angle variable mechanism. It is a figure which shows an example of the lithography process for manufacturing a semiconductor device using the projection exposure apparatus of embodiment of this invention.

Explanation of symbols

R ... reticle, W ... wafer, ILS ... illumination optical system, AX2 ... illumination system optical axis, 1 ... exposure light source, 4 ... polarization control member, 8 ... turret-shaped member, 9a, 9b ... diffractive optical element, 10 ... exchange Mechanism, 12R (12) ... pupil equivalent plane, 14R (14) ... rod integrator, 23 ... projection optical system, 41, 42 ... polyhedral prism

Claims (18)

In a projection exposure apparatus having an illumination optical system that irradiates a first object with illumination light from a light source, and a projection optical system that projects an image of the first object onto a second object,
In order to internally reflect at least a part of the illumination light on a part of the optical path between the light source and the first object, the illumination optical system includes a cubic crystal (100) of the crystal. ) Having a substantially rectangular parallelepiped rod-type integrator whose direction is the long side direction,
The long side direction of the rod integrator is disposed substantially parallel to the optical axis of the illumination optical system,
The illumination light incident on the rod integrator is incident on the first direction or the other parallel side surface perpendicular to one of the two parallel side surfaces along the long side direction of the rod integrator. A projection exposure apparatus comprising, as a main component, linearly polarized light whose electric field direction is any one of vertical second directions.   2. The projection exposure apparatus according to claim 1, wherein the side surface of the rod integrator substantially coincides with a (100) plane of the crystal.   The projection exposure apparatus according to claim 1, wherein the side surface of the rod integrator substantially coincides with a (110) plane of the crystal.   The projection exposure apparatus according to any one of claims 1 to 3, wherein the illumination optical system further includes an angle varying mechanism that varies an incident angle range of the illumination light to the rod-type integrator. .   The projection exposure apparatus according to claim 4, wherein the angle variable mechanism includes a diffractive optical element.   6. The projection exposure apparatus according to claim 5, wherein the angle variable mechanism includes a mechanism for exchanging the diffractive optical element with another diffractive optical element.   The projection exposure apparatus according to claim 4, wherein the angle variable mechanism includes a polyhedral prism.   The projection exposure apparatus according to claim 4, wherein the angle variable mechanism further includes a zoom optical system. The angle variable mechanism further includes an angle limiting mechanism that limits an incident angle range of the illumination light to the first object to a plurality of discrete ranges separated in a direction corresponding to the first direction,
9. The projection exposure apparatus according to claim 4, wherein illumination light incident on the rod-type integrator is mainly composed of linearly polarized light having the second direction as an electric field direction. The variable angle mechanism has an incident angle range of the illumination light with respect to the first object,
The effective σ value for the direction corresponding to the first direction is 0.7 or more,
Including a condition that an effective σ value in a direction corresponding to the second direction is 0.2 or less;
The projection exposure apparatus according to any one of claims 4 to 8, wherein the illumination light incident on the rod-type integrator is mainly composed of linearly polarized light having the first direction as an electric field direction.   The projection exposure apparatus according to claim 1, wherein the cubic crystal is a fluoride crystal.   The projection exposure apparatus according to claim 11, wherein the fluoride crystal is a calcium fluoride crystal.   The projection exposure apparatus according to claim 1, wherein the illumination light is ultraviolet light having a wavelength of 200 nm or less.   14. The projection exposure apparatus according to claim 13, wherein the illumination light is ultraviolet light having a wavelength of 193 nm emitted from an ArF excimer laser.   An exposure method comprising: exposing a photoconductor as the second object with an image of a mask pattern as the first object using the projection exposure apparatus according to claim 1. .   The exposure method according to claim 15, wherein the mask pattern includes a rectangular pattern, and a longitudinal direction of the rectangular pattern substantially coincides with a direction corresponding to the second direction.   16. The mask pattern includes a spatial frequency modulation type phase shift pattern, and a longitudinal direction of the phase shift pattern substantially coincides with a direction corresponding to the first direction. An exposure method according to 1. A device manufacturing method including a lithography process,
A device manufacturing method, wherein a pattern is transferred to a photoconductor using the exposure method according to any one of claims 15 to 18 in the lithography step.

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