JPH05226217A - Projection type exposure system - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain the optimum imaging characteristics of the projection optical system according to the illumination conditions. [Configuration] First illumination system (5, 7) and second illumination system (6
0, 61, 62) are provided in the optical integrator block 6. The block 6 can be moved by the drive system 54, and the first and second illumination systems can be switched. In addition, the reticle R, the lens elements 20, 21,
22 and 23 are movable by drive elements 29, 25, 27, 57 and 58. Depending on the switching between the first and second illumination systems, the reticle R or the lens element (20,
By moving (21, 22, 23), the imaging characteristics of the projection optical system are optimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type exposure apparatus,
In particular, the present invention relates to changing the image forming characteristics of a projection optical system of a projection type exposure apparatus for manufacturing semiconductor integrated circuits and liquid crystal devices.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type has a Fourier transform plane (hereinafter referred to as a pupil plane of the illumination optical system) in an illumination optical system with respect to a plane where a pattern is present on a reticle, or in a plane in the vicinity thereof. The reticle is illuminated by limiting the illumination light flux to a substantially circular shape (or rectangular shape) centered on the optical axis of the illumination optical system (hereinafter referred to as normal illumination). Thus, in normal illumination, the intensity of the illumination light from each direction within the incident angle range of the illumination light to the reticle pattern (numerical aperture of the illumination light flux) is almost uniform, and the numerical aperture of the illumination light flux and the projection The ratio (σ value) to the reticle side numerical aperture of the optical system is 0.5 to 0.
It was about 7. In normal illumination, when the exposure wavelength is λ and the wafer-side numerical aperture of the projection optical system is NA _W , the resolution is approximately 0.7 × λ / NA _W , and the depth of focus is ± λ / 2.
Given by (NA) ² .

In ordinary illumination, in order to expose a finer pattern, it is necessary to use an exposure light source having a shorter wavelength or a projection optical system having a larger numerical aperture. However, it is difficult to make the wavelength of the exposure light source shorter than that at present (for example, 200 nm or less) at the present time because there are no suitable optical materials and there is no stable light source capable of obtaining a large amount of light. Also,
When the numerical aperture of the projection optical system is increased, the depth of focus decreases in inverse proportion to the square of the numerical aperture, so that it is difficult to realize an optical system with high resolution and sufficient depth of focus.

Therefore, a phase shift provided with a phase shifter for shifting the phase of the transmitted light from a specific portion of the transmitted portion of the circuit pattern of the reticle by π (rad) with respect to the transmitted light from other transmitting portions. The use of reticles has also been proposed. The phase shift reticle is disclosed in, for example, Japanese Patent Publication No. 62-50811, and the use of this phase shift reticle has the effect of improving the resolution.

Further, recently, a ring-shaped illumination and a reticle pattern that shields only a central portion within an incident angle range of an illumination light flux on a reticle pattern (limits a light amount distribution on a pupil plane of an illumination optical system to a ring-shaped). A specific (discrete) illumination light flux is incident from multiple directions (the light amount distribution on the pupil plane of the illumination optical system is maximum at multiple discrete positions decentered from the optical axis of the illumination optical system. Modified light sources have been proposed which limit the illumination flux so that it has a value. When the annular illumination or the modified light source is used, the resolution and depth of focus of the projection optical system can be improved, although the light amount loss and the illuminance uniformity are deteriorated.

Here, in manufacturing a semiconductor integrated circuit, high resolution is naturally required, but the depth of focus (focus margin) is also an extremely important factor. On the other hand, there is also a method of increasing the depth of focus by giving a specific aberration (particularly spherical aberration) to the projection optical system without using the above-mentioned modified light source.
It is proposed in Japanese Patent No. 234411. This utilizes the fact that the photosensitive material (photoresist) on the wafer has a thickness of about 1 μm, and the depth of focus increases although there is a slight decrease in contrast.

[0007]

In the prior art as described above, the aberration of the projection optical system, especially the spherical aberration, is fixed at the time of manufacture or adjustment and cannot be easily changed thereafter. It was If the above-mentioned annular illumination, modified light source, and phase shift reticle are applied to a projection optical system that has a predetermined spherical aberration in accordance with normal illumination to increase the depth of focus, the predetermined spherical aberration will be reduced. Adversely affect. That is, when the annular illumination, the modified light source, and the phase shift reticle are used, conversely, due to spherical aberration, the depth of focus is reduced, or the focus position changes depending on the line width (pitch). Therefore, there is a problem that the effective depth of focus is reduced as compared with the case where the predetermined spherical aberration is not provided.

Further, even in an optical system which does not give spherical aberration in particular, distortion or the like may occur due to changes in illumination conditions. The present invention has been made in view of the above problems, and it is a projection type that can be used by switching between normal illumination, modified light source, annular illumination, and phase shift reticle, and maximizes the depth of focus under each illumination condition. The purpose is to realize an exposure apparatus.

[0009]

In order to solve the above problems, the present invention forms illumination light from a light source into a substantially uniform intensity distribution, and the uniform illumination light is used as a mask having a fine pattern. In a projection type exposure apparatus including an illumination optical system for irradiating and a projection optical system for image-projecting an image of the pattern of the mask onto a photosensitive substrate, the illumination condition for the mask is changed according to the pattern of the mask. Illumination condition changing means, image forming characteristic control means for controlling the image forming characteristics of the projection optical system, and adjusting means for adjusting the image forming characteristic control means in conjunction with the illumination condition changing means are provided.

[0010]

[Function] Switching between normal illumination and annular illumination, switching between ordinary illumination and modified light source, switching between regular illumination (normal reticle) and phase shift reticle, switching between annular illumination and modified light source, and switching By moving the lens element of the projection optical system in accordance with the above, it is possible to change the distortion and the spherical aberration, and to obtain the optimum imaging characteristics of the projection optical system according to each illumination condition.

[0011]

1 is a plan view showing a schematic structure of a projection exposure apparatus according to an embodiment of the present invention. In FIG. 1, the ultra-high pressure mercury lamp 1 generates illumination light (i-line or the like) IL in a wavelength range that exposes the resist layer. Exposure illumination light source 1
In addition to bright lines such as a mercury lamp, a laser light source such as a KrF or ArF excimer laser or a harmonic such as a metal vapor laser or a YAG laser may be used. The illumination light IL is reflected by the elliptical mirror 2 and focused on the second focal point f ₀ thereof, and then enters the optical integrator block 6 via the mirror 3 and the relay lens 4.

FIG. 1 shows a case where the optical integrator block 6 includes two types of optical integrator systems, and the two types of optical integrator systems are replaceable. The first optical integrator system is composed of an input lens 5 and a fly-eye lens 7, and the light amount distribution on the exit-side surface 7a of the fly-eye lens 7 is almost uniform within a circular area in the plane perpendicular to the optical axis AX. The distribution is similar (normal lighting). The exit surface 7a of the fly-eye lens 7 has an optical Fourier transform relationship with the reticle pattern of the reticle R.
Therefore, the light amount distribution on the exit surface 7a of the fly-eye lens 7 corresponds to the distribution of the illumination light amount on the reticle pattern surface within the incident angle range.

The second optical integrator system comprises a polyhedral prism 60, an input lens 61 and two fly-eye lenses 62A and 62B as an input optical system. The multi-sided prism 6 includes a V-shaped concave prism 60a and a V-shaped concave prism 60a.
Illumination light I from the light source 1
Divide L into two. The respective light fluxes from the polygonal prism 60 enter the fly-eye lenses 62A and 62B via the input lenses 61a and 61b. The exit surfaces 62a and 62b of the fly-eye lenses 62A and 62B also have an optical Fourier transform relationship with the reticle pattern of the reticle R. In this way, the illumination light flux passing through the pupil plane of the illumination optical system, its conjugate plane, or a plane in the vicinity thereof is centered at a position decentered by a predetermined amount from the optical axis AX of the illumination optical system. By defining the reticle R in a local region, the illumination light beam irradiated on the reticle R is tilted in a predetermined direction by an angle corresponding to the fineness of the reticle pattern (hereinafter, simply referred to as a multiple tilt illumination method).

In FIG. 1, the first optical integrator system is arranged in the optical path and shows the state of normal illumination. An aperture stop 8 for varying the numerical aperture NA _IL of the illumination optical system is arranged near the exit surface (reticle side focal plane) 7 a of the fly-eye lens 7. The illumination light IL emitted from the fly-eye lens 7 is relay lenses 9 and 1.
1, passes through the variable blind 10 and the main condenser lens 12, reaches the mirror 13, and is reflected almost vertically downward there, and then illuminates the pattern area PA of the reticle R with a substantially uniform illuminance. Since the surface of the variable blind 10 has a conjugate relationship with the reticle R, a plurality of movable blades forming the variable blind 10 are opened and closed by a motor (not shown) to change the size and shape of the opening, thereby changing the size of the reticle R. The illumination field can be set arbitrarily. The reticle R is held by a reticle holder 14, and the holder 14 is placed on a reticle stage RS that can be two-dimensionally moved in a horizontal plane by a plurality of expandable and contractible drive elements 29 (only two are shown in FIG. 1). . Therefore, by controlling the amount of expansion and contraction of the drive element 29 by the drive element control unit 53, the reticle R can be translated in the optical axis direction and can be tilted in any direction with respect to the plane perpendicular to the optical axis. Has become. More on that later,
With the above configuration, it is possible to correct the image forming characteristic of the projection optical system, particularly the pincushion type or barrel type distortion. still,
The reticle R is positioned so that the center point of the pattern area PA coincides with the optical axis AX.

The illumination light IL that has passed through the pattern area PA enters the projection optical system PL that is telecentric on both sides, and the projection optical system PL forms a projected image of the circuit pattern of the reticle R on which a resist layer is formed. Projection (imaging) is performed by superimposing it on one shot area on the wafer W held so that its surface is substantially coincident with the best imaging plane. still,
In this embodiment, some of the lens elements (20, 21, 22, 23 in the figure) that form the projection optical system PL can be independently driven, and the projection optical system P
It is possible to adjust the imaging characteristics of L, for example, the projection magnification, spherical aberration, distortion, field curvature, astigmatism, etc. (details will be described later).

Further, a variable aperture stop 32 is provided in the pupil plane Ep of the projection optical system PL or in a plane in the vicinity thereof, so that the numerical aperture NA of the projection optical system PL can be changed. .. The wafer W is vacuum-sucked by a wafer holder (θ table) 16 and held on the wafer stage WS via the holder 16. The wafer stage WS can be tilted in any direction with respect to the best image plane of the projection optical system PL by the motor 17 and can be finely moved in the optical axis direction (Z direction). Also, this stage WS
Is configured to be two-dimensionally movable by a step-and-repeat method, and when transfer exposure of the reticle R onto one shot area on the wafer W is completed, stepping is performed to the next shot position. The wafer stage WS
For the configuration and the like, see, for example, Japanese Patent Laid-Open No. 62-274201.
It is disclosed in the publication. A moving mirror 19 that reflects the laser beam from the interferometer 18 is provided at the end of the wafer stage WS.
Is fixed, and the two-dimensional position of the wafer stage WS is constantly detected by the interferometer 18 with a resolution of, for example, about 0.01 μm.

Further, in FIG. 1, an image forming light beam for forming an image of a pinhole or a slit toward the best image forming surface of the projection optical system PL is obliquely supplied to the optical axis AX. Irradiation optical system 30 and wafer W of the image forming light beam
An oblique-incidence type focus detection system including a light-receiving optical system 31 that receives a light beam reflected on the surface of the light via the beam is provided. The structure of this focus detection system is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112, and the position of the wafer surface in the vertical direction (Z direction) with respect to the image plane is detected to detect the wafer W and the projection optical system. The in-focus state with PL is detected.

By the way, in FIG. 1, a main controller 50 for controlling the entire apparatus and a bar code BC representing the name formed on the side of the reticle pattern while the reticle R is being conveyed right above the projection optical system PL. A bar code reader 52 for reading, a keyboard 51 for inputting commands and data from an operator, and a drive system (motor) for driving an optical integrator block 6 to which a plurality of fly-eye lens groups including a fly-eye lens 7 are fixed. , Gatren, etc.) 54. In the main controller 50, the names of a plurality of reticles to be handled by this projection exposure apparatus (for example, stepper) and the operation parameters of the stepper corresponding to each name are registered in advance. When the bar code reader 52 reads the reticle bar code BC, the main controller 50 uses one of the operating parameters corresponding to the name as a pre-registered illumination condition (type of reticle, periodicity of reticle pattern, etc.). (Corresponding to (1)), one of the fly-eye lens groups most suitable for the optical integrator block 6 is selected, and a predetermined drive command is output to the drive system 54. Further, as operating parameters corresponding to the above names, optimum setting conditions of the variable aperture diaphragms 8 and 32 and the variable blind 10 under the fly eye lens group selected previously, and the projection optical system PL
Computation parameters (optimal imaging characteristics under each illumination condition, constants representing the rate of change of each imaging characteristic change amount with respect to the drive amount of the lens element) used to correct the image forming characteristic of the It is registered and these conditions are set at the same time when the fly-eye lens group is set.
As a result, the optimum illumination condition is set for the reticle R placed on the reticle stage RS. The above operation can also be executed by the operator directly inputting commands and data to the main controller 50 from the keyboard 51.

Next, a mechanism for correcting the image forming characteristic of the projection optical system PL will be described. As shown in FIG. 1, in the present embodiment, the driving element controller 53 drives the reticle R and the lens elements 20, 21, 22, and 23 independently to correct the image forming characteristics of the projection optical system PL. It is possible. The image forming characteristics of the projection optical system PL include a focal position, a projection magnification, a spherical aberration, a distortion, a field curvature, an astigmatism, and the like, and these values can be individually adjusted. In the example, in order to simplify the description, a case where the focal position, the projection magnification, the distortion, the spherical aberration, and the field curvature are adjusted in the bilateral telecentric projection optical system will be described.
In this embodiment, the barrel-type or pincushion-type distortion is corrected by moving the reticle R.

Now, the lens element 20 is the support member 2
4 is fixed to the lens element 21 (21a, 21a
b) is fixed to the support member 26. The lens element 22 is fixed to the support member 55, and the lens element 23 is fixed to the support member 56. The lens elements other than the lens elements 20, 21, 22, and 23 are fixed to the lens barrel portion 28 of the projection optical system PL, and in this embodiment, the optical axis AX of the projection optical system PL is fixed to the lens barrel portion 28. The optical axis of the lens element that is being used.

A plurality of support members 24 (for example, 3
Then, the two driving elements 25 (shown in the drawing) are connected to the supporting member 26, and the supporting member 26 is connected to the lens barrel portion 28 by a plurality of expandable and contractable driving elements 27.
Further, the support member 55 is connected to the support member 56 by the extendable drive element 57, and the support member 56 connects the drive element 5 with the support member 56.
It is connected to the lens barrel portion 28 by 8. Drive element 2
As 5, 27, 29, 57, 58, for example, an electrostrictive element or a magnetostrictive element is used, and the displacement amount of the drive element according to the voltage or magnetic field applied to the drive element is obtained in advance. Although not shown here, in consideration of the hysteresis of the drive element, a position detector such as a capacitive displacement sensor or a differential transformer is provided in the drive element, and the position of the drive element corresponding to the voltage or magnetic field applied to the drive element is provided. Is monitored to enable highly accurate driving. With the above configuration, the drive element control unit 5
3 is capable of independently moving the lens elements 20, 21, 22, 23 and the peripheral points 3 to 4 of the reticle R in the optical axis direction by an amount corresponding to the drive command given from the main controller 50. As a result, the lens elements 20, 21, 2
Each of 2, 23 and the reticle R can be translated in the optical axis direction and can be tilted in an arbitrary direction with respect to a plane perpendicular to the optical axis AX. In addition, a drive element that is movable in the direction perpendicular to the optical axis may be provided so that each lens element and reticle can be moved in a plane perpendicular to the optical axis.

Here, when each of the lens elements 20 and 21 is moved in the optical axis direction, each of the projection magnification M, the field curvature C, and the focus position F changes at a change rate corresponding to the amount of movement. Further, when each of the lens elements 22 and 23 is moved in the optical axis direction, the spherical aberration S changes. The driving amount of the lens element 20 is x ₁ , the lens element 2 is
The drive amount of 1 is x ₂ , the drive amount of the lens element 22 is x
₃ , assuming that the driving amount of the lens element 22 is x ₄ , each of the change amounts ΔM, ΔC, ΔF, ΔS of the projection magnification M, the field curvature C, the focus position F and the spherical aberration S is expressed by the following equations. ..

ΔM = C _M1 × x ₁ + C _M2 × x ₂ (1) ΔC = C _C1 × x ₁ + C _C2 × x ₂ (2) ΔF = C _F1 × x ₁ + C _F2 × x ₂ (3) ΔS = C _S1 × x ₃ + C _S2 × x ₄ (4) Incidentally, C _M1 , C _M2 , C _C1 , C _C2 , C _F1 , C _F2 , C _S1 , C _S2
Is a constant representing the rate of change of each change amount with respect to the drive amount of the lens element.

By the way, as described above, the focus detection system 30,
Reference numeral 31 is for detecting the amount of deviation of the wafer surface from the optimum focus position with the optimum focus position of the projection optical system as a zero point reference. Therefore, an appropriate electrical or optical offset amount x ₅ is applied to the focus detection systems 30 and 31,
By positioning the wafer surface using the focus detection systems 30 and 31, the lens elements 20 and 21,
It is possible to correct the focus position shift due to the driving of 22 and 23. At this time, the above equation 3 is expressed as the following equation.

ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₅ (5) Similarly, when the reticle R is translated in the optical axis direction, the distortion D and the focus position are changed at a rate corresponding to the amount of movement. Each of F changes. Drive amount of reticle R is x
Assuming ₆ , each of the distortion D and the change amounts ΔD and ΔF of the focus position F is expressed by the following equations.

ΔD = C _D6 × x ₆ (6) ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₅ + C _F6 × x ₆ (7) where C _D6 and C _F6 are the reticle R of each variation amount. It is a constant indicating the rate of change with respect to the drive amount. From the above, Equation 1,
By setting the drive amounts x _{1 to} x ₆ at _2, 4, _6, and 7, the change amounts ΔM, ΔC, ΔD, ΔF, and ΔS can be arbitrarily adjusted. Here, a case has been described in which five types of image forming characteristics are simultaneously adjusted (set to a predetermined image forming characteristic) and corrected. Here, regarding the correction, if the amount of change in the image forming characteristic of the projection optical system due to the change of the illumination condition is negligible, it is not necessary to correct the image forming characteristic, and When the image forming characteristics other than the five types described in the embodiment change greatly, it is necessary to correct the image forming characteristics. Further, in the present embodiment, an example in which correction is performed by moving the reticle R and the lens element as the image forming characteristic adjusting mechanism has been shown, but the adjusting mechanism suitable in the present embodiment may be any other method, for example, two A method of sealing the space sandwiched between the lens elements and adjusting the pressure of this sealed space may be adopted.

Here, in the present embodiment, the drive element controller 53
Depending on the reticle R and the lens elements 20, 2
Although the lens elements 1, 22 and 23 can be moved, the lens elements 20 and 21 are particularly easy to control as compared with other lens elements because the influences on the respective characteristics such as projection magnification, distortion, field curvature and astigmatism are large. Therefore, the lens elements 22 and 23 have a larger influence on the spherical aberration than the other lens elements and are easier to control.

Further, in the present embodiment, the lens elements for controlling the projection magnification, distortion and the like have a two-group structure (lens elements 20, 21), but three or more groups may be used. By using 3 or more groups, it is possible to increase the range of movement of the lens element while suppressing fluctuations in other aberrations, and to cope with various shape distortions (distortions such as trapezoids and rhombuses), field curvature, and astigmatism. It will be possible. Further, the lens element that controls the spherical aberration is not limited to the two-group configuration (lens elements 22 and 23). By adopting the adjusting mechanism having the above configuration, it is possible to sufficiently cope with a change in illumination condition.

In the above, the apparatus provided with the first optical integrator system and the second optical integrator system is used, but the optical integrator block 6 is used.
Is not limited to switching between two types of illumination states, and may be a block including a plurality of types of optical integrator systems as shown in FIG. FIG. 2 shows an example in which a third optical integrator system and a fourth optical integrator system are provided between the first optical integrator system and the second optical integrator system. Third
The optical integrator system of (1) is composed of a fly-eye lens 63 and an input lens 5a (not shown) whose central portion is shielded from light and realizes annular illumination. The fourth optical integrator system has four fly-eye lenses 64A and 64A.
B, 64C, 64D and input lenses 61a ₁ , 61a
It realizes a modified light source in which the secondary light source is divided into four (it realizes a plurality of inclined illuminations), which is configured by b ₁ , 61c ₁ , 61d ₁ and the polygonal prism 60A. The polyhedral prism 60A is composed of a quadrangular pyramid (pyramidal) concave prism 60Aa and a convex prism 60Ab. The exit surfaces of the fly-eye lenses of the third optical integrator system and the fourth optical integrator system also have an optical Fourier transform relationship with the reticle pattern surface.

By moving the optical integrator block 6 provided with these optical integrator systems, the illumination conditions can be switched.
Further, the switching of the illumination condition is made to switch the optical integrator system, but it is not limited to this.
For example, a light blocking plate having a ring-shaped opening or a light blocking plate having a plurality of openings may be replaceably provided near the exit surface of the fly-eye lens 7.

Further, the optical system of the second and fourth optical integrator systems for injecting the light beam into the fly-eye lens is not limited to the polyhedral prism, but may be provided with a mirror, a fiber, a diffraction grating or the like. Further, as described above, in the multi-tilt illumination method, the position of the fly-eye lens (passing position of the illumination light beam) depends on the periodicity (pitch) of the reticle pattern.
Therefore, a plurality of optical integrator systems with different positions of the fly-eye lens may be provided in the block 6. Also in the annular illumination, a plurality of optical integrator systems in which the size of the fly-eye lens 63 and the size of the light shielding portion are different may be provided in the block 6.

Next, the measuring mechanism of the image forming characteristics of the projection optical system PL will be described with reference to FIG. As shown in FIG. 6B, a grid pattern 15m including two sets of slit patterns Gx and Gy is formed on the surface of the reference member 15, and the grid pattern 15m includes the mirror 80 and the lens 8.
1, the illumination light transmitted by the optical fiber 82, the lens 83 and the mirror 84 illuminates from below.
It is desirable that this illumination light is light in the substantially same wavelength range as the exposure illumination light IL, and for example, a part of the illumination light IL from the light source 1 may be branched and guided by a beam splitter. The illumination light transmitted through the reference member 15 reaches the reticle R via the projection optical system PL, is reflected by the back surface (pattern surface) thereof, and returns to the reference member 15 via the projection optical system PL again. Further, the reflected light transmitted through the grating pattern 15m again passes through the optical fiber 82 and the like, and then enters the photodetector 85 composed of Photomal or SPD, and is photoelectrically converted there to generate a photoelectric signal corresponding to the light intensity. Output. The main controller 50 inputs, for example, a detection signal from the focus detection system (light receiving optical system 31) together with the photoelectric signal from the photodetector 85. Then, the wafer stage WS
Is moved in the Z direction, and the level change of the photoelectric signal of the photodetector 85 at that time is obtained. The result is shown in FIG. In the figure, the position f at which the signal level has a peak is the optimum focus position (best focus position) at any one point in the image field. For example, the measurement is performed while moving the reference member 15 in the image field. By repeatedly performing, the focus position, field curvature, astigmatism, etc. can be obtained as the imaging characteristics of the projection optical system PL. Since the projection magnification and the distortion cannot be measured with the above configuration, for example, the marks formed at a plurality of positions on the reticle R are photoelectrically detected via the reference marks provided on the wafer stage. It is desirable to keep.

Although not shown in FIG. 6A,
In this embodiment, the exit surface of the optical fiber 82 (reference member side)
It is assumed that a plurality of spatial filters can be exchangeably arranged in the vicinity. Accordingly, the illumination condition for the reference member 15 (for example, the numerical aperture (σ of the optical fiber 82 (σ
Value), orbicular zone illumination, multiple-inclination illumination described later, etc.) can be arbitrarily changed. At this time, it is desirable to provide slit patterns with a plurality of pitches on the surface of the reference member 15 in correspondence with the reticle pattern.

In this embodiment, the angle of the parallel flat glass (plane parallel) (not shown) provided inside the light receiving optical system 31 is adjusted in advance so that the image plane becomes the zero point reference, and the focus detection system. Shall be calibrated. Further, for example, a horizontal position detecting system as disclosed in Japanese Patent Laid-Open No. 58-113706 is used, or the focal position can be detected at arbitrary plural positions in the image field of the projection optical system PL. By configuring a focus detection system (for example, forming a plurality of slit images in an image field), it is assumed that the inclination of a predetermined region on the wafer W with respect to the image plane can be detected. Next, with reference to FIG. 3 and FIG. 4, an example of the multiple tilt illumination method (deformed light source) and its principle will be described.

FIG. 3 is a diagram showing how diffracted light is generated from a circuit pattern and an image is formed when a reticle is illuminated by using the multiple tilt illumination method. On the lower surface of the reticle R (on the side of the projection optical system PL), a one-dimensional line-and-space pattern composed of a transmissive portion Ra and a light shielding portion Rb is drawn as a circuit pattern. In the projection exposure apparatus (FIG. 1) used in this embodiment, the local region through which the illumination light flux passes has a center at a position decentered from the optical axis in the pupil plane of the illumination optical system, as will be described later. There is. Therefore, the illumination light flux L0 that illuminates the reticle R is
The light is incident on the reticle R at a predetermined incident angle ψ from a direction (X direction) substantially perpendicular to the direction in which the circuit pattern of (1) is drawn (periodic direction). The incident angle ψ and the incident direction are uniquely determined by the position of the diffracted light generated by the pattern on the reticle in the pupil plane of the projection optical system.

Now, from the pattern on the reticle, putter
0th order in the direction of the diffraction angle according to the fineness (width, pitch)
Diffracted light D_o, + 1st order diffracted light D_p, -1st order diffracted light D_mFrom
To live. The resolution limit of the pattern by the conventional illumination method is
Whether ± 1st order diffracted light can pass through the projection optical system
Is determined by. In FIG. 3, the light is transmitted through the projection optical system PL.
The one that reaches the roof W is the 0th-order diffracted light of the above three light beams.
D_oAnd + 1st order diffracted light D _p2 light fluxes, and these 2 light fluxes
Form an interference fringe, that is, an image of a circuit pattern on the wafer W.
To achieve. That is, the apparent NA increases. Therefore,
Conventionally, when the pattern pitch is P, P> λ / NA
The pattern size given by the degree is the resolution limit.
On the other hand, in the multiple tilt illumination method in this embodiment,
The resolution limit is approximately P> λ / 2NA.

Further, in FIG. 3, 0th-order diffracted light D _o and +
The first-order diffracted light D _p passes through an optical path that is substantially symmetrical with respect to the optical axis AX. This is because the incident angle ψ of the illumination light flux Lo is sin
It can be realized by setting ψ = sin θ / 2 = λ / 2P. At this time, when defocusing the wafer W, 0
The order diffracted light D _o and the + 1st order diffracted light D _p generate almost the same amount of wavefront aberration (due to defocus). This is because the wavefront aberration with respect to the defocus amount ΔF is ½ × ΔF sin ² t (where t is the incident angle of each diffracted light on the wafer), and here the 0th-order diffracted light and the + 1st-order diffracted light are incident on the wafer. This is because the incident angles t are almost equal. By the way, the cause of collapsing (defocusing) the pattern image on the wafer is the difference in wavefront aberration between the respective light beams. However, in the apparatus used in this embodiment (for example, FIG. 5), the 0th-order diffracted light D _o and the + 1st-order diffracted light D _p irradiated on the wafer have almost the same wavefront aberration, and therefore the defocus amount ΔF is the same. However, the degree of blurring is less than that of the conventional exposure apparatus. That is, the depth of focus is deep.

Further, in FIG. 3, the 0th-order diffracted light D _o and +
The first-order diffracted light D _p is assumed to be substantially symmetrical with respect to the optical axis AX, but in order to increase the depth of focus, the pupil plane Ep
It is not necessary that these two diffracted lights are symmetrical with respect to the optical axis AX, and may pass through positions that are substantially equidistant from the optical axis AX. Here, since the fineness (line width, pitch) and directionality of the pattern of the reticle used in the exposure apparatus are not specified to one type, the pupil of the illumination optical system of the projection exposure apparatus used in this embodiment is The center position of the local area through which the illumination light flux passes, for example, the positions of the two fly-eye lens groups 62A and 62B shown in FIG. 1 in the pupil plane of the illumination optical system are variable (exchangeable) depending on the type of pattern. ) Is desirable.

The optimum position of the fly-eye lens will be briefly described. FIG. 4A is a so-called one-dimensional line-and-space pattern in which the transmissive portions Ra and the light-shielding portions Rb extend in the Y direction and are regularly arranged in the X direction at a pitch P. At this time, for example, the individual fly-eye lens groups 62A and 62B in FIG. 1 (that is, the positions of the secondary light source groups)
4B, the optimum position is on the assumed Y-direction line segment Lα in the pupil plane 70 of the illumination optical system and on the line segment Lβ.
It will be any position above. FIG. 4B is a view of the pupil plane 70 of the illumination optical system corresponding to the reticle pattern RP ₁ viewed from the optical axis AX direction, and the coordinate system XY defined in the pupil plane 70.
Is the reticle pattern RP ₁ seen from the same direction in FIG.
Same as (A).

Now, as shown in FIG. 4B, on the pupil plane 70, the distances α and β from the optical axis AX (center of the pupil) to the respective line segments Lα and Lβ are α = β. α and β correspond to the incident angle ψ _X of the illumination light with respect to the reticle in the X direction, and are the distances that satisfy the above sin ψ _X = λ / 2Px, where λ is the exposure wavelength. Therefore, the fly-eye lens groups 62A, 6
If the positions of the centers of 2B (that is, the centers of gravity of the light amount distribution of the secondary light source group) are on the line segments Lα and Lβ, the fly-eye lens group 62A is used for the line-and-space pattern as shown in FIG. , 62B, the two diffracted lights, one of the 0th-order diffracted light and the ± 1st-order diffracted light, which are generated by the illumination light, are approximately equidistant from the optical axis AX in the pupil plane Ep of the projection optical system PL. You will pass through the position. Therefore, as described above, the depth of focus for the line and space pattern (FIG. 4A) can be maximized and high resolution can be obtained.

On the other hand, FIG. 4C shows the case where the reticle pattern is a so-called isolated space pattern, and the X-direction (horizontal direction) pitch of the pattern RP ₂ is Px and the Y-direction (longitudinal direction) pitch is Py. It is assumed that Figure 4
FIG. 4D is a diagram showing the optimum position of each fly-eye lens group in this case, and the position and rotation relationship with FIG.
This is the same as the relationship between (A) and (B). In the case of the two-dimensional pattern RP ₂ , it is desirable to form four local areas (illumination light flux) on the pupil plane 70 of the illumination optical system. Therefore, in the device (FIG. 1) having the above configuration, the fourth optical region is formed. It is sufficient to provide four fly-eye lens groups as in the integrator system (FIG. 2).

Now, the two-dimensional pattern R as shown in FIG.
When the illumination light is incident on P ₂ , diffracted light is generated in the two-dimensional direction according to the periodicity of the pattern RP _{2 in} the two-dimensional direction (pitch X: Px, pitch Y: Py). 2 as shown in FIG. 4 (C)
Also in the dimensional pattern RP ₂ , one of the 0th order diffracted light and the ± 1st order diffracted light in the diffracted light is projected by the projection optical system P.
The depth of focus can be maximized by passing the position on the pupil plane Ep of L that is substantially equidistant from the optical axis AX.

As shown in FIG. 4D, if the centers of the two fly-eye lens groups (secondary light source groups) are located on the line segments Lα and Lβ, the depth of focus for the X-direction component of the two-dimensional pattern RP ₂ is determined. Can be maximum. Similarly, when the incident angle of the illumination light on the reticle in the Y direction is ψ _Y , γ, ε
Be a distance that satisfies sin ψ _Y = λ / 2Py, and the line segment L
Two fly-eye lens groups (secondary light source group) on γ and Lε
If there is each center of, the depth of focus can be maximized for the Y-direction component of the two-dimensional pattern RP ₂ .

As described above, the illumination light flux from the fly-eye lens group (secondary light source group) arranged at each position in the pupil plane 70 shown in FIG. 4 (B) or (D) becomes the reticle pattern RP ₁ or RP ₂ . Upon incidence, either the + 1st-order diffracted light component D _p or the −1st-order diffracted light component D _m from the reticle pattern and the 0th-order light diffracted light component D _o from the optical axis AX at the pupil plane Ep of the projection optical system PL. It will pass through positions that are almost equidistant. Therefore, as described above, a projection type exposure apparatus having a high resolution and a large depth of focus can be realized.

Here, the reticle pattern shown in FIG.
Although only the two examples shown in (A) or (C) were considered, the + 1st-order diffracted light component or -1 from the pattern is paid attention to the periodicity (fineness) of other patterns.
The pupil plane 70 of the illumination optical system is so arranged that two light fluxes of one of the second-order diffracted light components and the zero-order diffracted light component pass through the position on the pupil plane Ep of the projection optical system PL that is substantially equidistant from the optical axis AX. Fly's eye lens group (secondary light source group) in
Set the center position of. The other diffracted light, for example, one of ± 2nd-order diffracted light and the 0th-order diffracted light may have a positional relationship substantially equal to the light source AX on the pupil plane of the projection optical system.

Further, when the reticle pattern includes a two-dimensional periodic pattern as shown in FIG.
When focusing on the second-order diffracted light component, the pupil plane E of the projection optical system PL
On p, a first-order or higher-order diffracted light component distributed in the X direction (first direction) centering on the one zero-order diffracted light component,
There may be first-order or higher-order diffracted light components distributed in the Y direction (second direction). Therefore, assuming that a two-dimensional pattern is satisfactorily formed on one specific 0th-order diffracted light component, one of the higher-order diffracted light components distributed in the first direction,
One of the higher-order diffracted light components distributed in the second direction and a specific 0
The three 0th-order diffracted light components are distributed at substantially equal distances from the optical axis AX on the pupil plane Ep so that the specific 0th-order diffracted light component (1
It suffices to adjust the positions of the two fly-eye lens groups (secondary light source groups). For example, in FIG. 4D, the respective center positions of the fly-eye lens group (secondary light source group) are set to points Pζ, Pη, P
It is better to match either κ or Pμ. Points Pζ, P
η, Pκ, and Pμ are all line segments Lα or Lβ (the optimum position for the periodicity in the X direction, that is, the 0th-order diffracted light and X
Direction ± 1st order diffracted light is at an equal distance from the optical axis on the pupil plane Ep of the projection optical system), and an intersection of the line segment Lγ or Lε (the optimum position for the periodicity in the Y direction). Therefore, the light source position is optimum in either the X direction or the Y direction.

Although a pattern having a two-dimensional directivity at the same location on the reticle is assumed as a two-dimensional pattern in the above, when a plurality of patterns having different directivities exist at different positions in the same reticle pattern. The above method can be applied to. When the pattern on the reticle has a plurality of directions or fineness, the optimum position of each fly-eye lens group corresponds to each direction and fineness of the pattern as described above. Alternatively, each fly-eye lens group may be arranged at the average position of each optimum position. Further, this average position may be a weighted average in which a weight corresponding to the fineness or importance of the pattern is added.

Further, the light fluxes emitted from the respective fly-eye lens groups are obliquely incident on the reticle. At this time, if the direction of the light amount center of gravity of these inclined incident light beams (plurality) is not perpendicular to the reticle, the position of the transferred image shifts in the in-plane direction of the wafer when the wafer W is slightly defocused. To do. In order to prevent this, the direction of the light amount centroid of the illumination light fluxes (plurality) from each fly-eye lens group is set to be perpendicular to the reticle pattern, that is, parallel to the optical axis AX. That is, when an optical axis (center line) is assumed for each fly-eye lens group, a position vector in the Fourier transform plane of the optical axis (center line) with reference to the optical axis AX of the projection optical system PL, and It suffices that the vector sum of the product of the light amount emitted from the fly's eye lens group becomes substantially zero. Also, as an easier way,
The number of secondary light sources is 2m (m is a natural number), and the positions of m of them are determined by the above-described optimization method (FIG. 4), and the remaining m are positions that are substantially symmetrical with respect to the above-mentioned m and the optical axis AX. Should be placed in

Next, the operation of the projection exposure apparatus according to this embodiment will be described. Here, an example of a switching operation between the first optical integrator system and the second optical integrator system will be described. First, a case where the first optical integrator system is arranged will be described. A reticle R ₁ suitable for normal illumination is set on the reticle stage RS. At this time, the first optical integrator system (5, 7) is arranged in the optical path of the illumination optical system based on the information of the bar code BC provided on the reticle R ₁ . Here, the apparatus of FIG. 6 described above performs focus calibration and adjusts the outputs of the focus sensors 30 and 31 to zero when the wafer W is placed at the image formation position.

As described above, in normal lighting,
Having a predetermined amount of spherical aberration improves the depth of focus. For this reason, here, the information about the spherical aberration amount to be adjusted is recorded in the bar code BC, and the main controller 50 uses the constant C _S regarding the spherical aberration amount and the spherical aberration amount described above to determine the lens drive amount (reference value). The driving amount of the lens from the position) is calculated. Then, the spherical aberration on the wafer W side is
For example, the lens 2 may have the spherical aberration curve shown in FIG.
Move 1 and 22. FIG. 5 is a diagram showing the spherical aberration characteristic, in which the direction of the Z axis is an optical code and the direction away from the lens is plus (+). ΔSA indicates the amount of spherical aberration at a predetermined NA, and ΔSA is preferably about 2 to 5 μm for a lens having an NA of about 0.6. Thus, when spherical aberration is generated, the best focus position is Z = 0.
The position in the Z direction is slightly shifted to the plus (+) side from (the position without spherical aberration). This defocus amount ΔZ is added as an offset to the focus sensors 30 and 31. The wafer stage WS aligns the surface of the wafer W with a position displaced in the optical axis direction by the offset amount ΔZ. The defocus amount may be corrected by driving the lens. Incidentally, the driving amount of the lens may be recorded directly on the bar code BC.

Next, the case of switching to the second optical integrator system will be described. The reticle R ₂ using multiple tilt illumination is set on the reticle stage RS, and the main control system 50 controls the drive system 54 based on the information from the barcode BC of the reticle R ₂ . Drive system 54
Switches the optical integrator block and arranges the second optical integrator system (60, 61, 62) in the optical path of the illumination optical system. In addition, the main control system 50
Sets the σ value of the illumination optical system to an appropriate value. Here, the σ value is set to 0.1 to 0.3.

The second optical integrator system (6
0, 61, 62), the lenses 21 and 22 are returned to the reference positions because the depth of focus is larger without spherical aberration. At this time, the offset amounts of the focus sensors 30 and 31 become zero. Note that, here, the focus calibration of the focus sensors 30 and 31 is an example in the case where there is no spherical aberration, and if the calibration is performed when spherical aberration is given, the offset amount is zero with spherical aberration. Therefore, it has a predetermined offset amount without spherical aberration.

Similarly, the spherical aberration can be adjusted according to the switching between the first fly-eye lens system and the third and fourth fly-eye lens systems. Even when the phase shift reticle is used in the first fly-eye lens system, the lens systems 22 and 23 are moved so as to make the spherical aberration zero by the same operation. Also, switching of illumination conditions (switching between the first optical integrator system and the second, third, and fourth optical integrator systems, or the second, third, and fourth optical integrator systems).
By switching between optical integrator systems, switching between a regular reticle and a phase shift reticle, and switching between optical integrator systems with different fly-eye lens positions, the position where the light flux passes in the projection optical system changes. , The distortion varies. In each of the switching of the illumination conditions, the change amount of the image forming characteristic is registered in the bar code BC, and the main controller 50 calculates the lens drive amount in the same manner as the above operation. Based on this, the reticle R (or the lens elements 20, 2,
1) should be moved. If the focus position changes accordingly, the focus sensors 30 and 31 are offset as described above, and the wafer stage WS is moved to offset the focus reference position by a predetermined amount. The wafer W is placed on. Alternatively, the focus offset may be adjusted by moving the lens as described above.

Although the operation focusing on the distortion has been described above, the lens 20 may be changed with respect to other optical characteristic changes such as field curvature and magnification variation in accordance with the switching of the illumination conditions as described above. , 21, 22 and the position of the reticle are moved. In addition, every time the lighting conditions are switched,
The focus may be calibrated or the distortion or the like may be measured for correction.

In the above embodiment, the reticle R or the lens elements 20, 21, 22, 2 of the projection optical system are used.
Although 3 is moved, the aberration state can be changed by moving the entire projection optical system. Therefore, the present invention can be realized even if the entire projection optical system is moved up and down collectively by the drive member. Further, the movement of the entire reticle R and the projection optical system and the movement of part of the lenses may be performed together.

Although the projection type exposure apparatus has been described above, it may be a reflection type or a catadioptric type. Further, when the projection optical system is a catadioptric type including a reflecting mirror, the same effect can be obtained by moving the reflecting mirror instead of the lens.

[0057]

As described above, according to the present invention, the illumination condition can be changed according to the reticle pattern, and the best image forming characteristic can be obtained under each illumination condition. In particular, by adjusting the spherical aberration in accordance with the switching of the normal illumination, the annular zone, and the modified light source, it becomes possible to obtain the optimum depth of focus under each illumination condition.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus according to an embodiment of the present invention,

FIG. 2 is a diagram showing an exchange mechanism for arranging a plurality of optical integrator systems in an exchangeable manner according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating the principle of a multi-tilt illumination method used in an embodiment of the present invention;

FIG. 4 is a view for explaining the arrangement of fly's eye lens groups in the multiple tilt illumination method adopted in an embodiment of the present invention;

FIG. 5 is a diagram showing a spherical aberration characteristic in normal illumination adopted in an embodiment of the present invention,

FIG. 6 is a diagram illustrating a measurement operation of an image forming characteristic of a projection optical system using a reference member.

[Explanation of symbols]

 6 ... Optical integrator block 7, 62, 63, 70 ... Fly-eye lens 8, 32 ... Variable aperture diaphragm 20, 21, 22, 23 ... Lens element 25, 27, 29, 57, 58 ... Driving element 30, 31 ... Focus Sensor 50 ... Main controller 53 ... Control unit 54 ... Drive system R ... Reticle W ... Wafer WS ... Wafer stage

Claims (4)

[Claims] 1. An illumination optical system for shaping illumination light from a light source into a substantially uniform intensity distribution and irradiating the mask with a fine pattern with the uniform illumination light, and an image of the pattern of the mask on a photosensitive substrate. A projection type exposure apparatus including a projection optical system for image-forming and projecting onto an image, an illumination condition changing means for changing an illumination condition for the mask according to a pattern of the mask, and an imaging characteristic of the projection optical system. A projection type exposure apparatus comprising: an image forming characteristic control unit for adjusting the image forming characteristic; and an adjusting unit for adjusting the image forming characteristic control unit in association with the illumination condition changing unit. 2. The image forming characteristic control means moves at least one of an optical member forming the projection optical system and the mask in an optical axis direction of the projection optical system, or the optical axis. 2. The projection type exposure apparatus according to claim 1, further comprising a movable member that is inclined with respect to a plane perpendicular to the plane. 3. The projection type exposure apparatus according to claim 1, wherein the image forming characteristic adjusting means changes a spherical aberration of the projection optical system. 4. The illumination condition changing means limits a light flux passing on a Fourier transform surface of the mask in the illumination optical system to a predetermined area including an optical axis of the illumination optical system. A second illumination condition for limiting the light flux passing on the Fourier transform surface in an annular shape centered on the optical axis of the illumination optical system, and the center of the light flux passing on the Fourier transform surface with respect to the illumination optical system. 2. The projection type exposure apparatus according to claim 1, further comprising a switching unit that switches between a third illumination condition that limits at least two local areas decentered from the optical axis.