JPH0770471B2 - Projection exposure method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for manufacturing semiconductor integrated circuits and liquid crystal devices, which requires high-precision image forming performance, and more particularly to maintaining the image forming performance of a projection optical system.

[0002]

2. Description of the Related Art In a photolithography process for forming a circuit pattern of a semiconductor element or the like, a method of transferring a pattern formed on a reticle (mask) onto a substrate (semiconductor wafer, glass plate, etc.) is usually adopted. It A photosensitive photoresist is coated on the substrate, and the circuit pattern is transferred to the photoresist according to the irradiation light image, that is, the pattern shape of the transparent portion of the reticle pattern. In a projection exposure apparatus (for example, a stepper or the like), an image of a reticle pattern is image-projected on a wafer via a projection optical system.

In this type of apparatus, in the plane of the illumination optical system (hereinafter referred to as the pupil plane of the illumination optical system), which is the Fourier transform plane of the plane on which the pattern on the reticle exists, or in the plane in the vicinity thereof, The illumination light flux is limited to a substantially circular shape (or a rectangular shape) about the optical axis of the illumination optical system to illuminate the reticle. Therefore, the illumination light flux is incident on the reticle at an angle that is almost vertical. Further, on a reticle (a glass substrate such as quartz) used in this apparatus, a transmissive portion (reticle bare surface portion) having a transmittance of almost 100% for an illumination light flux and a light shielding portion having a transmittance of almost 0%. A circuit pattern composed of (chrome etc.) was drawn.

Now, the illumination light beam irradiated on the reticle as described above is diffracted by the reticle pattern, and 0th order diffracted light and ± 1st order diffracted light are generated from the pattern. These diffracted lights are condensed by the projection optical system and an interference fringe, that is, an image of a reticle pattern is formed on the wafer. At this time, the angle θ (reticle side) formed by the 0th order diffracted light and the ± 1st order diffracted light is sin θ = λ / P, where λ (μm) is the wavelength of the exposure light and NA is the reticle side numerical aperture of the projection optical system. Determined by

By the way, if the pattern pitch becomes finer,
If sin θ becomes larger and sin θ becomes larger than the reticle-side numerical aperture (NA) of the projection optical system, the ± 1st-order diffracted light becomes the Fourier transform surface of the reticle pattern. It is limited by the effective diameter of the surface) and cannot pass through the projection optical system. In other words, only the 0th-order diffracted light reaches the wafer, and no interference fringe (pattern image) is generated. Therefore, in the conventional exposure method as described above, when a reticle consisting of only the above-mentioned transmissive portion and light-shielding portion (hereinafter referred to as a normal reticle) is used, the fineness of the reticle pattern that can be resolved on the wafer (minimum pattern pitch ) P is P ≈ P from sin θ = NA
It is given by the relational expression λ / NA.

Therefore, the minimum pattern size is the pitch P.
Therefore, the minimum pattern size is 0.5 × λ /
Although it is about NA, in the actual photolithography process, the influence of the wafer curvature, the step difference of the wafer due to the process,
Alternatively, some depth of focus is required due to the thickness of the photoresist itself. Therefore, the practical minimum resolution pattern size is expressed as k × λ / NA. Here, k is called a process coefficient and is usually about 0.6 to 0.8.

From the above, in the conventional exposure method
Shorter for exposing and transferring finer patterns
Wavelength exposure light source, or higher numerical aperture
It was necessary to use a fine projection optical system. But Naga
Have a shorter wavelength of the exposure light source (for example, 200 nm or less).
Below) is suitable for use as a transmissive optical member.
Absence of optical material, stable with high light output
It is difficult at this point due to the lack of a light source.
Also, the numerical aperture of the projection optical system is already at the theoretical limit.
It is almost hopeless that a larger aperture will be created soon. Tentative
± λ / NA even if a larger aperture than the shape is possible ²
The depth of focus, which is determined by, decreases sharply as the numerical aperture increases.
Therefore, the depth of focus required for actual use will be smaller,
There is a problem that it cannot be a general purpose exposure apparatus.

Therefore, a phase shifter (dielectric thin film) 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 transparent portions. It has also been proposed to use a phase shift reticle with The phase shift reticle is disclosed in, for example, Japanese Patent Publication No. 62-50811, and the use of this phase shift reticle makes it possible to transfer a finer pattern than in the case of using a normal reticle. That is, there is an effect of improving the resolution. When using this phase shift reticle,
The numerical aperture (coherence factor σ) of the illumination optical system needs to be optimized. Various types of phase shift reticles have been proposed so far, but typical ones are a spatial frequency modulation type, a shifter light shielding type, and an edge emphasis type.

[0009] Recently, attempts have been made to enable transfer of fine patterns by optimizing the illumination conditions or devising the exposure method. There has been proposed a method of improving resolution and depth of focus by selecting a combination of a numerical value (σ value) and a numerical aperture (NA) of a projection optical system for each pattern line width. Furthermore, the light quantity distribution of the illumination light flux on the pupil plane of the illumination optical system or in the vicinity of the pupil plane is regulated in a ring-shaped manner, and the ring-shaped illumination method that illuminates the reticle pattern with the illumination light flux, or the periodicity of the reticle pattern is supported. There is also proposed an inclined illumination method or the like in which an illumination light beam is inclined from a specific direction and emitted at a predetermined angle. However, in any of the above methods, it is not effective for all reticle patterns, that is, the line width and shape thereof, and it is necessary to select an optimum illumination method or condition for each reticle or its pattern, The projection exposure apparatus requires a structure that allows the illumination conditions (σ value, etc.) in the illumination optical system to be variable.

By the way, in the projection exposure apparatus, in recent years, it has become more and more required to maintain the image forming characteristics of the projection optical system at a constant value with high accuracy. Therefore, various image forming characteristics are corrected. A method has been proposed and put to practical use.
Among them, the method for correcting the fluctuation of the image forming characteristic due to the absorption of the exposure light of the projection optical system is disclosed in, for example, JP-A-60-
It is disclosed in Japanese Patent No. 78454. In the disclosed method, the amount of energy (amount of heat) accumulated in the projection optical system along with the incidence of exposure light on the projection optical system is sequentially calculated, and the change amount of the imaging characteristic due to the accumulated energy amount is obtained, It has been proposed to finely adjust the imaging characteristics by a predetermined correction mechanism. As this correction mechanism, for example, there is a method of sealing a space sandwiched by two lens elements of a plurality of lens elements forming a projection optical system and adjusting the pressure of the sealed space.

The image forming characteristics corrected as described above mainly include the projection magnification, the focus position, the distortion aberration, etc., but in the projection exposure apparatus which needs to maintain the image forming characteristics with higher accuracy, other than these. Since it is difficult to correct the image-forming characteristics, and the fluctuation amount according to the accumulated energy amount (heat accumulated amount) is not so large, attention is paid also to the field curvature etc. which has not been conventionally corrected. ing. That is, a limit value (reference value) of the heat accumulation amount is determined in advance so that the amount of change in the imaging characteristic corresponding to the heat accumulation amount of the projection optical system due to the absorption of exposure light does not exceed a predetermined amount, and the step-and-repeat method is used. When sequentially exposing the reticle pattern on the wafer with, the exposure operation is stopped when the heat accumulation amount of the projection optical system exceeds the reference value, and the exposure operation is prohibited until this heat accumulation amount becomes less than the reference value. A method to continue (stop) has been proposed. Specifically, exactly the same as the method disclosed in the above publication, the heat accumulation amount accumulated in the projection optical system due to the incidence of exposure light is sequentially calculated, and it is calculated for each one-shot exposure or each wafer exchange. By comparing the heat storage amount calculated by the calculation with the predetermined reference value, it is determined whether or not the exposure to the next shot is performed.

[0012]

However, in the prior art as described above, when the illumination condition of the illumination optical system is changed as described above, or when the phase shift reticle is used, the inside of the projection optical system, especially the vicinity of the pupil plane, is used. In (lens element), the distribution of the amount of transmitted light can change. Since the illumination light originally concentrates and passes near the pupil plane, a change in the light amount distribution here has a large effect on the fluctuation of the imaging characteristics due to the absorption of the illumination light of the projection optical system. (Rate of change, time constant, etc.) will also change. That is, even if the total amount of energy of the illumination light incident on the projection optical system (that is, the amount of accumulated heat) is the same, the change characteristic of the image formation characteristic is different for each illumination condition, and the aberration amount is the same even under the same reference value. Can be different from each other. For this reason, when the illumination conditions are changed as described above, the reference value for determining the execution or prohibition of the exposure operation does not exist as a constant value, and the conventional method cannot be applied as it is. Depending on the situation, there is a problem that the image forming characteristic is deteriorated, and conversely, the exposure operation is prohibited more than necessary and the productivity (throughput) is lowered even though the aberration amount does not exceed the predetermined amount.

The present invention has been made in consideration of the above points. The reticle and the reticle pattern (type, periodicity,
Illumination conditions (numerical aperture of illumination optical system,
That is, even if the σ value, the numerical aperture of the projection optical system, the annular illumination, the tilted illumination, etc.) is changed, the pattern on the photosensitive substrate is always kept under the highly accurate imaging characteristics without lowering the throughput more than necessary. The object is to obtain a projection exposure apparatus that can perform exposure.

[0014]

In order to solve such a problem, in the present invention, the illumination light (I) from the light source (1) is used.
Illumination optical system (1-12) for irradiating the mask (R) with L)
And a projection optical system (PL) for projecting the image of the pattern of the mask (R) onto the photosensitive substrate (W), the pattern image of the mask (R) is projected in a predetermined image formation state. In order to achieve this, the amount of heat accumulated in the projection optical system (PL) due to the incidence of the illumination light (IL), or the amount of change in the optical characteristics of the projection optical system (PL) caused by the amount of heat accumulation or environmental changes, and a predetermined reference value Exposure control means (50) for controlling the start or stop of the exposure operation on the photosensitive substrate, and the illumination light (I) on the pupil plane (Fourier transform plane) of the illumination optical system.
By changing at least one of the distribution state of L), the pattern on the mask to be projected on the photosensitive substrate (W), and the numerical aperture of the projection optical system (PL), the projection optical system (PL)
Exposure condition changing means (variable aperture diaphragms 8 and 32, variable blind 10, turret plate 7 and drive system 54, or mask exchange mechanism) for changing the distribution state of the light flux on the pupil plane (Ep) of the projection optical system ( A means (50) for changing the reference value according to the change of the distribution state of the light flux on the pupil plane (Ep) of PL) is provided.

[0015]

In the present invention, when the illumination condition is changed in accordance with the mask or its pattern, the reference value of the heat storage amount of the projection optical system for judging the start or prohibition of the exposure operation is changed. It was decided to change to an optimum value under the lighting conditions. Therefore, even if the illumination condition is changed, it is possible to maintain good imaging characteristics of the projection optical system without lowering the throughput more than necessary.

[0016]

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. As the exposure illumination light source 1, a bright line such as a mercury lamp, a laser light source such as a KrF or ArF excimer laser, or a harmonic wave of a metal vapor laser or a YAG laser may be used. Illumination light I
L is reflected by the elliptical mirror 2 and condensed at its second focal point f ₀ , and then enters the optical integrator (fly-eye lens group) 7A via the cold mirror 5 and the condensing optical system 6 including a collimator lens and the like. To do. A variable 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) of the fly-eye lens group 7A. Here, the fly-eye lens group 7A is
The focal plane on the reticle side is arranged in the in-plane direction perpendicular to the optical axis AX so that the focal plane on the reticle substantially coincides with the Fourier transform plane (pupil conjugate plane) of the reticle pattern. In the vicinity of the second focal point f ₀ , the motor 4 closes the optical path of the illumination light IL,
A shutter (for example, a four-blade rotary shutter) 3 for opening is arranged.

In the present embodiment, a plurality of fly-eye lens groups (FIG. 2) including a fly-eye lens group 7A are provided on the holding member (rotary turret plate) 7, and a drive system 54 allows an arbitrary fly-eye lens group. The lens group is configured to be replaceably arranged in the illumination optical path. Therefore,
By configuring the plurality of fly-eye lens groups to be replaceable together with the variable aperture stop 8, it is possible to change the illumination condition according to the type of reticle, the periodicity of the pattern, etc. (details will be described later).

The illumination light IL emitted from the fly-eye lens group 7A is relay lenses 9 and 11, a variable blind 10,
And the mirror 1 passing through the main condenser lens 12.
3, the pattern area PA of the reticle R is illuminated with a substantially uniform illuminance after being reflected almost vertically downward. Since the surface of the variable blind 10 has a conjugate relationship with the reticle R, the variable blind 10 can be moved by a motor (not shown).
By changing the size and shape of the opening by opening and closing the plurality of movable blades constituting the reticle, the illumination visual field of the reticle R can be arbitrarily set. The reticle R is held by the reticle holder 14, and the reticle holder 14 is mounted on the reticle stage RS which can be two-dimensionally moved in a horizontal plane by a plurality of expandable and contractible drive elements 29 (only two of which are shown in FIG. 1). There is. Therefore, the drive element controller 53
The reticle R is translated in the optical axis direction by controlling the amount of expansion and contraction of the drive element 29 by.
It can be tilted in any direction with respect to a plane perpendicular to the optical axis. As will be described in detail later, the above-described configuration can correct the image forming characteristics of the projection optical system, in particular, the pincushion type and barrel type distortions. 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 constituting the projection optical system PL, that is, each of 20, 21 and 22 in FIG. It is possible to correct the imaging characteristics of the system PL, such as projection magnification and distortion (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 a wafer holder (θ table) 1
6 is vacuum-sucked and held on the wafer stage WS via the holder 16. The wafer stage WS is
The motor 17 can be tilted in any direction with respect to the best image plane of the projection optical system PL, can be finely moved in the optical axis direction (Z direction), and can be two-dimensionally moved by a step-and-repeat method. When the transfer exposure of the reticle R onto one shot area on the wafer W is completed, the stepping is performed to the next shot position. still,
The structure of the wafer stage WS is disclosed in, for example, Japanese Patent Laid-Open No. 62-274201. A movable mirror 19 that reflects the laser beam from the interferometer 18 is fixed to the end of the wafer stage WS, and the two-dimensional position of the wafer stage WS is determined by the interferometer 18 with a resolution of, for example, about 0.01 μm. Always detected.

Further, an irradiation amount monitor (photoelectric sensor) 33 is provided on the wafer stage WS so as to substantially coincide with the surface position of the wafer W. The photoelectric sensor 33 is composed of, for example, a photodetector having a light-receiving surface having substantially the same area as the image field of the projection optical system PL or the projection area of the reticle pattern, and outputs optical information regarding this irradiation amount to the main controller 50. To do. This light information serves as basic data for obtaining the amount of change (aberration amount) in the imaging characteristics corresponding to the amount of energy accumulated in the projection optical system PL with the incidence of illumination light.

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 supplied obliquely with respect to the optical axis AX. Irradiation optical system 30 and wafer W of its image forming light beam
An oblique-incidence type focus detection system including a light-receiving optical system 31 that receives a light beam reflected by the surface of the light via the beam is provided. The configuration 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.

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. It is assumed that the focus detection system is configured (for example, a plurality of slit images are formed in the image field) so that the inclination of a predetermined region on the wafer W with respect to the image plane can be detected.

By the way, in FIG. 1, a main controller 50 for integrally controlling the entire apparatus and a bar code BC representing a name formed on the side of the reticle pattern while the reticle R is being conveyed right above the projection optical system PL. To drive a bar code reader 52 for reading, a keyboard 51 for inputting commands and data from an operator, and a holding member (rotary turret plate) 7 to which a plurality of fly-eye lens groups including a fly-eye lens group 7A are fixed. Drive system (motor, gatoren, etc.) 54 of FIG. In the main controller 50, the names of a plurality of reticles to be handled by this projection exposure apparatus (eg stepper) and the stepper operation parameters corresponding to each name are registered in advance. When the bar code reader 52 reads the reticle bar code BC, the main control unit 50 pre-registers the illumination condition (type of reticle, periodicity of the reticle pattern, etc.) as one of the operation parameters corresponding to the name. (Corresponding to (1)), one fly-eye lens group most suitable for (1) is selected from the holding members 7, 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 image forming characteristics of the projection optical system PL. A calculation parameter (details will be described later) used for correcting by the correction mechanism described later is also registered, and these condition settings are also performed 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 each of the reticle R and the lens elements 20, (21, 22) independently to correct the imaging characteristics of the projection optical system PL. It is possible. As the image forming characteristics of the projection optical system PL,
There are focal position, projection magnification, distortion, field curvature, astigmatism, etc., and these values can be corrected individually. Focus position in optical system,
A case of correcting the projection magnification, distortion, and field curvature will be described. In this embodiment, the reticle R
To correct barrel or pincushion distortion.

The lens element 20 of the first group closest to the reticle R is fixed to the support member 24, and the lens element (21, 22) of the second group is fixed to the support member 26. Lens elements below the lens element 23 are fixed to the lens barrel portion 28 of the projection optical system PL. In the present embodiment, the optical axis AX of the projection optical system PL
Is the optical axis of the lens element fixed to the lens barrel portion 28.

A plurality of support members 24 (for example, 3
Then, 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.
The drive elements 25, 27, 29 are, for example, electrostrictive elements,
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 the magnetic field applied to the drive element is provided. Is monitored to enable high-precision driving.

Here, the lens elements 20, (21,
When each of 22) is translated in the optical axis direction, each of the projection magnification M, the field curvature C, and the focus position F changes at a rate of change corresponding to the amount of movement. Assuming that the driving amount of the lens element 20 is x ₁ and the driving amount of the lens element (21, 22) is x ₂ , the projection magnification M, the field curvature C, and the change amounts ΔM, ΔC, and ΔF of the focus position F are , Is expressed by the following equation.

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) C _M1 , C _M2 , C _C1 , C _C2 , C _F1 , and C _F2 are constants that represent 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, when an appropriate electrical or optical offset amount x ₃ is applied to the focus detection systems 30 and 31, the wafer surface is positioned by using the focus detection systems 30 and 31, and the lens element 20 is thus positioned. ,
It is possible to correct the focus position shift due to the driving of (21, 22). At this time, the above expression 3 is expressed as the following expression.

ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₃ (4) 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
_{If 4} , the distortion D and the change amounts ΔD and ΔF of the focus position F are expressed by the following equations.

ΔD = C _D4 × x ₄ (5) ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₃ + C _F4 × x ₄
(6) Note that C _D4 and C _F4 are constants representing the rate of change of each amount of change with respect to the drive amount of the reticle R. From the above, Equation 1,
By setting the drive amounts x _{1 to} x ₄ in 2, 5, and 6, the change amounts ΔM, ΔC, ΔD, and ΔF can be arbitrarily corrected. Although the case where four types of image forming characteristics are simultaneously corrected is described here, if the change amount of the image forming characteristics of the projection optical system due to the absorption of the illumination light is negligible, It is not necessary to perform the above correction, and when the image forming characteristics other than the four types described in the present embodiment change significantly, it is necessary to correct the image forming characteristics. Further, when the amount of change in field curvature is corrected to zero or less than the allowable value, the amount of change in astigmatism is also corrected to zero or less than the allowable value. No correction shall be made. In the present embodiment, as for the change amount ΔF (formula 6) of the focus position, for example, the change amount ΔF to the focus detection systems 30 and 31 is electrically calculated.
Alternatively, it is optically provided as an offset, and the wafer W is moved in the Z direction using the focus detection systems 30 and 31 to set the wafer surface at the best image plane (best focus position) of the projection optical system PL. And Further, in the present embodiment, an example in which the image forming characteristic is corrected by the movement of the reticle R and the lens element has been shown, but a suitable correcting mechanism in this embodiment may be any other system.
For example, a method of sealing a space sandwiched between two lens elements and adjusting the pressure in this sealed space may be adopted.

Here, in the present embodiment, the drive element controller 53
The reticle R and the lens element 20,
Although (21, 22) can be moved, in particular, the lens elements 20, (21, 22) have influences on other characteristics such as projection magnification, distortion, and field curvature (astigmatism) on other lens elements. Compared to this, it is easier to control. In this embodiment, the movable lens element is composed of two groups, but it may be composed of three or more groups. In this case, the range of movement of the lens element can be increased while suppressing the fluctuation of other aberrations, and various lens elements can be used. It is possible to cope with the shape distortion (distortion such as trapezoid and rhombus) and the field curvature (astigmatism). By adopting the correction mechanism having the above-mentioned configuration, it is possible to sufficiently cope with a change in the image forming characteristic of the projection optical system PL due to absorption of exposure light.

With the above configuration, the drive element control section 53
Can independently move the lens elements 20, (21, 22) of the second group 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 second group of lens elements 20,
Each of (21, 22) and the reticle R can be translated in the optical axis direction and can be tilted in any direction with respect to a plane perpendicular to the optical axis AX.

The illumination method adopted in the projection exposure apparatus according to this embodiment will be briefly described with reference to FIG. As an example of the illumination method adopted in this embodiment, the illumination light flux passing through the pupil plane of the illumination optical system, its conjugate plane, or the plane in the vicinity thereof is decentered by a predetermined amount from the optical axis AX of the illumination optical system. By defining at least two local areas having the center at the position, a plurality of illumination light beams irradiated on the reticle R are symmetrically formed with respect to the optical axis AX in a predetermined direction by an angle corresponding to the fineness of the reticle pattern. It is tilted (hereinafter, simply referred to as a multi-tilt illumination method).

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 including 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 (period 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.

From the pattern on the reticle, 0th-order diffracted light _Do , + 1st-order diffracted light _Dp , and -1st-order diffracted light _Dm are generated in the direction of the diffraction angle according to the fineness (width, pitch) of the pattern. In FIG. 3, what reaches the wafer W after passing through the projection optical system PL is the 0th-order diffracted light D _o and +1 of the above three light fluxes.
It is shown as two light beams of the next diffracted light D _p , and these two light beams form an interference fringe, that is, an image of a circuit pattern on the wafer W. The resolution limit of the pattern by the conventional illumination method is determined by whether or not ± 1st order diffracted light can pass through the projection optical system. That is, conventionally, when the pattern pitch is P, the pattern size given by P> λ / NA is the resolution limit. On the other hand, in the multi-tilt illumination method of this embodiment, P> λ / 2NA is almost satisfied.
Is the resolution limit.

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 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, 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 the 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 not limited. The center position of the local area where the illumination light flux passes on the surface, for example, the positions of the two fly-eye lens groups 7B ₁ and 7B ₂ shown in FIG. 2 in the pupil plane of the illumination optical system are variable according to the type of pattern. Is desirable. That is, this is because each of the incident direction and the incident angle of the illumination light flux on the reticle is determined by the direction in which the pattern is drawn, the width, and the pitch. For example, in the case of a one-dimensional line-and-space pattern arranged in the X direction as shown in FIG. 3, the illumination light flux L0 is
It may be incident from the direction shown in the figure. That is, the illumination light flux L0 is incident on the reticle R parallel to the paper surface. In addition, 0th-order diffracted light D ₀ and + generated from the pattern
If the incident angle of the illumination light flux L0 is determined so that the first-order diffracted light D _p passes through the position on the pupil plane Ep that is substantially equidistant from the optical axis AX, the depth of focus of the image on the wafer W can be increased. it can.

The eccentric direction from the optical axis AX of the central position of the local area where the illumination light flux passes within the pupil of the illumination optical system is determined according to the incident direction thus determined, and the line width of the pattern is determined. Or the optical axis A according to the incident angle determined by the periodicity
The amount of eccentricity from X will be determined. The center position of the local area (corresponding to the fly-eye lens group) where the illumination light flux passes in the pupil plane of the illumination optical system is determined as described above.

Further, when illuminating a pattern drawn in a two-dimensional direction, it is advisable to illuminate the illumination light beam from two directions in accordance with the direction of each pattern. Further, the illumination luminous flux is not in two directions, that is, two luminous fluxes, but two luminous fluxes which are symmetrical with respect to the optical axis of the projection optical system are added to each of the luminous fluxes, so that a total of four luminous fluxes (for example, a fly shown in FIG. 2). Eye lens group 7
D ₁ corresponds to ~7D ₄₎ preferably used. In that case, since the light amount centroid direction of these light fluxes coincides with the optical axis of the projection optical system, it is possible to prevent the lateral displacement (telecentric displacement) of the image that occurs when the wafer is slightly defocused. Further, for a periodic pattern arranged in a direction inclined by 45 ° with respect to the X and Y directions, the four light beams used for illuminating the two-dimensional pattern as described above are provided on the pupil plane of the illumination optical system. It is advisable to perform illumination in a state of being rotated by 45 ° about the optical axis. Also, when illuminating a reticle having a one-dimensional line-and-space pattern as shown in FIG. 3, it is also preferable to perform multi-tilt illumination with two light beams that are substantially symmetrical with respect to the optical axis of the projection optical system. When illuminating a one-dimensional pattern, if the intensity ratio of the 0th-order diffracted light and the 1st-order diffracted light generated from the pattern is exactly 1: 1, illumination is performed with two light beams from a direction symmetrical to the optical axis. No need. However, this is limited to the case where there is only one pattern pitch.

Here, only the one-dimensional pattern shown in FIG. 3 was considered as the reticle pattern, but other patterns are also focused on their periodicity (fineness), and the + 1st order diffracted light component or − from that pattern is obtained. The pupil plane of the illumination optical system is so arranged that two light fluxes, one of the first-order diffracted light component and the zero-order diffracted light component, pass through the pupil plane Ep of the projection optical system PL at a position substantially equidistant from the optical axis AX. Each local area in, ie, fly-eye lens group (secondary light source group)
Set the center position of. The other diffracted light, for example, one of ± 2nd-order diffracted lights 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. In addition, when a pattern having a two-dimensional directivity exists at the same position on the reticle as a two-dimensional pattern, or when a plurality of patterns having different directivities exist at different positions in the same reticle pattern. The above method can be applied. Furthermore, if the pattern on the reticle has multiple directions or fineness, the optimum position of each fly-eye lens group corresponds to each directionality and fineness of the pattern, or Each fly-eye lens group may be arranged at the average position of. Further, this average position may be a weighted average in which a weight corresponding to the fineness or importance of the pattern is added.

Next, with reference to FIG. 2, a change mechanism of the fly-eye lens group used for changing the illumination condition, particularly for switching between the normal illumination and the plurality of inclined illuminations will be described.
As shown in FIG. 2, in the present embodiment, four types of fly-eye lens groups 7A are fixed with different eccentricity states with respect to the optical axis AX depending on the periodicity of the reticle pattern.
7D are integrally provided on the holding member 7, and the drive system 5
By driving (rotating) the holding member 7 by 4, each of the plurality of fly-eye lens groups 7A to 7D can be exchangeably arranged in the optical path of the illumination optical system. Here, when each of the fly-eye lens groups 7B to 7D is arranged in the illumination optical path, the fly-eye lens groups are arranged substantially symmetrically with respect to the optical axis AX. Incidentally, FIG.
Shows that the fly-eye lens group 7A used during normal illumination is arranged in the illumination optical path. In FIG. 2, for example, when the fly-eye lens groups 7B ₁ and 7B ₂ are arranged in the illumination optical path, the respective centers thereof (in other words, the secondary light source images in the fly-eye lens groups 7B ₁ and 7B ₂ respectively) are formed. The fly-eye lens groups 7B ₁ and 7B ₂ are integrally held so that the center of gravity of the light amount distribution is set at a discrete position decentered with respect to the optical axis AX by an amount determined according to the periodicity of the reticle pattern. Material (rotating turret plate)
It is held at 7. The fly-eye lens groups 7B to 7
In each of D, it is desirable that the position of each fly-eye lens group can be moved according to the periodicity of the reticle pattern.

FIG. 2 is a diagram showing a specific structure of the holding member, and here, four types of fly-eye lens groups 7 are used.
A to 7D are arranged at intervals of about 90 ° on a holding member (turret plate) 7 that is rotatable around the rotation shaft 7a. Each of the four types of fly-eye lens groups 7A to 7D is
The fly-eye lens groups hold different eccentric states (that is, positions in a plane substantially perpendicular to the optical axis AX) with respect to the optical axis AX (center of the holding member) according to the periodicity of the reticle pattern. Has been done. The fly-eye lens groups 7B and 7C are both two fly-eye lens groups (7B
₁ , 7B ₂ ), (7C ₁ , 7C ₂ ), and when these fly-eye lens groups are arranged in the illumination optical system, they are fixed so that their arrangement directions are substantially orthogonal to each other. . Fly-eye lens unit 7D are approximately equidistant to place the four fly's eye lens 7D ₁ ～7D ₄ from its center 7d (optical axis AX), and fixed. Fly's eye lens group 7
A is the optical axis A when its center is placed in the illumination optical system.
It is fixed so that it almost coincides with X, and is used when the conventional exposure is performed. As is clear from FIG. 2, according to the information of the reticle barcode BC as described above, the turret plate 7 is rotated by the drive element 55 including a motor and a gear, and each of the four types of fly-eye lens groups 7A to 7D. Therefore, it is possible to arrange a desired holding member according to the periodicity (pitch, arrangement direction, etc.) of the reticle pattern in the illumination optical system. At this time, since the drive element 55 is also used for positioning, it is desirable to provide a rotation angle measuring member such as a rotary encoder.

Here, each position of the plurality of fly-eye lens groups shown in FIG. 2 (position in the plane perpendicular to the optical axis), in other words, the holding member to be selected, depends on the reticle pattern to be transferred. It is good to decide. Decision (selection) in this case
As described above, the illumination light flux from each fly-eye lens group is incident on the reticle pattern so as to obtain the optimum resolution for the fineness (pitch) of the pattern to be transferred and the effect of improving the depth of focus. A holding member having a fly-eye lens group at or near the position (incident angle ψ) is used. When it is necessary to strictly set the angle of incidence of the illumination light flux on the reticle pattern, each of the plurality of fly-eye lens groups in the holding member is arranged in the radial direction (radiation direction) about the optical axis AX. It may be configured such that it can be slightly moved, and each of the plurality of fly-eye lens groups can be rotated around the optical axis AX. Further, in each of the plurality of fly-eye lens groups 7A to 7D shown in FIG. 2, the exit end area of each fly-eye lens group is the numerical aperture of the illumination light flux passing through the fly-eye lens group with respect to the reticle R and the projection optical system. PL reticle side numerical aperture (N
It is desirable to set the ratio with A _R ), so-called σ value, to be about 0.1 to 0.3. The configuration for changing the illumination condition, that is, for changing the light amount distribution on the pupil plane of the illumination optical system is not limited to that shown in FIG.

Next, an example of changing the illumination conditions, which is the main operation of the apparatus according to this embodiment, and the light amount distribution in the vicinity of the pupil plane of the projection optical system under each illumination condition will be described. Here, when the pattern is formed substantially uniformly on the reticle R over the entire exposure field of the projection optical system PL, among the plurality of lens elements forming the projection optical system PL, near the reticle R or the wafer W. In the lens element (1), the illumination light passes almost uniformly over the entire surface regardless of the illumination conditions. On the other hand, in the vicinity of the pupil plane Ep of the projection optical system PL, the illuminance distribution differs depending on the illumination condition. Therefore, the temperature distribution generated in the lens element near the pupil plane also differs for each illumination condition. Particularly, in the vicinity of the pupil plane, the illumination light flux passes through in a concentrated manner, so it can be said that the illuminance (temperature) distribution that differs depending on the illumination conditions has a great influence on the imaging characteristics. Therefore, a case of changing the σ value of the illumination optical system as the illumination condition will be described with reference to FIG. In FIG. 4, members having the same functions and functions as those in FIG. 1 are designated by the same reference numerals.

The coherence factor of the illumination optical system, the so-called σ value, is the ratio of the numerical aperture NA _IL of the illumination optical system and the numerical aperture NA _R of the projection optical system (reticle side), that is, σ = NA _IL / NA _R. = Sin θ ₁ / sin θ ₂
Here, as shown in FIG. 4A, θ ₁ is the angle of the illumination light that illuminates the reticle R, and θ ₂ is the angle of the illumination light that can pass through the aperture stop 32 of the projection optical system PL. In FIG. 4, the numerical aperture N _R of the projection optical system is constant and the numerical aperture N of the illumination optical system is N.
4A shows the case where A _IL is changed, and FIG. 4A shows the case where the σ value is large, and FIG. 4B shows the case where the σ value is small. As is clear from FIG. 4, in the present embodiment, the σ value can be arbitrarily set by the variable aperture stop 8 arranged near the exit surface of the fly-eye lens group 7A (that is, the pupil plane of the illumination optical system). In the present embodiment (FIGS. 1 and 4), the variable aperture stop is used as a means for changing the σ value. However, for example, the condensing optical system 6 (FIG. 1) may be used as a zoom lens system, or Even if the illumination optical system (fly-eye lens group or the like) is configured to be replaceable, the σ value can be made variable in the same manner as above.

As shown in FIGS. 4A and 4B, the 0th-order diffracted light of the illumination light flux that has passed through the reticle R is incident on the projection optical system PL at the same angle θ ₁ as the incident angle of the illumination light. The wafer W reaches the wafer W by advancing as shown by a solid line. Although not shown, the first-order and higher-order diffracted light travels outside the 0th-order diffracted light and reaches the wafer W. A variable aperture stop 32 is provided on the pupil plane Ep of the projection optical system PL.
Numerical aperture NA _W (on the wafer side) is represented by NA _W = sin θ ₃ . Here, looking at the light quantity distribution on the pupil plane of the projection optical system PL, the 0th-order diffracted light passes through almost the center (hatched portion) of the pupil plane within the plane defined by the aperture stop 32, and the first-order or higher order The diffracted light will pass through the outside. Generally, the intensity of the 0th-order diffracted light is higher than that of the 1st-order or higher-order diffracted light, so that the lens element particularly near the pupil plane has a small σ value (see FIG. 4).
It is considered that the illumination light flux is concentrated on the center of the pupil and the temperature rises when it is larger than in (B)) (FIG. 4A). When pattern exposure is actually performed, the optimum illumination conditions corresponding to these types of reticle (for example, normal reticle or phase shift reticle), pattern line width, shape, periodicity, etc. Numerical aperture NA _W (further, fly-eye lens group) is set to variable aperture diaphragms 8 and 32.
It is set by driving the (turret plate 7).

Next, a method of calculating the amount of change in the image forming characteristic of the projection optical system PL will be briefly described. In the present embodiment, four types of image forming characteristics, that is, the projection magnification, the field curvature, the distortion, and the focus position are dealt with, but these image forming characteristics have different generation mechanisms and their variation characteristics are Each imaging characteristic needs to be calculated independently as they may differ from each other. However, since the calculation methods of these imaging characteristics are the same, the projection magnification will be described as an example here. In addition, in the present embodiment, the case where the σ value of the illumination optical system is changed as the illumination condition will be described.

Generally, the temperature of an object when heat is absorbed by the object is determined by the balance between the amount of heat absorbed by the object and the amount of heat released from the object. This is generally called a first-order lag system, and it is considered that the change characteristic of the projection magnification has the same behavior. Fig. 5 shows the fluctuation characteristics of the first-order lag system.
Shown in. FIG. 5 shows the change characteristic of the projection magnification when the projection optical system PL is irradiated with a certain amount of illumination light for a certain period of time. The change characteristic shown in FIG. 5 can be determined by two values, that is, the ratio ΔM / E of the final amount ΔM of change of the projection magnification with respect to the irradiation energy, and the time constant T representing the change over time. Figure 5
, The time constant T is ΔM with respect to the final change amount ΔM.
It can be expressed as a time that changes by x (1-e ^-1 ). That is, the smaller the time constant T, the faster the change. The ratio ΔM / E and the time constant T may be obtained by measuring the projection magnification while actually illuminating the projection optical system PL with the illumination light to obtain the change characteristic as shown in FIG. In reality, since the structure of the projection optical system PL is complicated, it may not be shown as a simple change characteristic as shown in FIG. 5, but may be expressed as the sum of several first-order delay systems. In this embodiment, in order to simplify the description, a case where a simple change characteristic is shown will be described.

Now, in FIG. 1, when the reticle R is exchanged, the wafer stage WS is driven to move the photoelectric sensor 33 to the optical axis position of the projection optical system PL, and the amount of illumination light incident on the projection optical system PL is measured. . Next, main controller 50 determines ratio ΔM / E obtained in advance, time constant T, irradiation energy detected by photoelectric sensor 33, and shutter 3.
The amount of change in the projection magnification is calculated by calculation based on the opening / closing time.

Here, when the σ value of the illumination optical system changes as described above, the light amount distribution, that is, the temperature distribution, in the lens element near the pupil plane Ep of the projection optical system PL changes. For example, when the σ value is small, the irradiation energy is concentrated on the center of the pupil and the temperature of the central part becomes high (FIG. 4 (B)),
It is considered that the lens element undergoes large thermal deformation near the center. On the other hand, when the σ value is large (FIG. 4 (A)),
It is considered that the temperature of the lens element as a whole rises and a particularly large thermal deformation cannot occur. Therefore, even if the total irradiation energy amount is the same, the change of the projection magnification is larger when the σ value is smaller than when the σ value is large,
That is, the ratio ΔM / E is considered to be large.

On the other hand, when the .sigma. Value is small, the temperature of the peripheral portion does not rise so much, and it is considered that the lens temperature suddenly drops when the irradiation of the illumination light is interrupted. On the other hand, when the σ value is large, the temperature of the lens gradually decreases because the lens temperature is increasing as a whole. Therefore, it is considered that when the σ value is small, the temporal change is larger than when the σ value is large, that is, the time constant T is small. From the above, it can be seen that both ΔM / E and T are changed by changing the σ value.

In the above description, the case where the σ value is changed has been taken as an example, but other illumination conditions (annular zone illumination, multiple tilt illumination, etc.) can be considered in exactly the same manner. Also,
Even when the phase shift reticle is used, the angle at which the diffracted light from the reticle pattern is incident on the projection optical system is different from that of a normal reticle, and therefore, it can be considered that the imaging characteristics similarly change. For example, Japanese Patent Publication 62-
When the spatial frequency modulation type phase shift reticle as disclosed in Japanese Patent No. 50811 is used, a light quantity distribution similar to that when the multiple tilt illumination method is adopted is generated on the pupil plane of the projection optical system.

Next, as the illumination light enters, the projection optical system P
A method of inhibiting the exposure operation according to the amount of heat accumulated in L will be described. In the image formation characteristic correction mechanism as described above, the items to be corrected (focal position, projection magnification, various aberrations, etc.) have been explained, but as a practical matter, all image formation characteristics that can fluctuate according to the amount of heat accumulation are corrected. It is impossible to do so, and it is general to select one or two from those having a large influence on the image formation pattern (projection image of the reticle pattern) and correct. Therefore, for an item that is not corrected by the correction mechanism, if the exposure operation is not executed when the influence (change amount) is within a predetermined allowable value, a sufficiently high resolution pattern exposure is performed. I can't do it. In addition, regarding the items for which the above correction is performed, it is impossible in reality to set the correction error (change amount) to zero, and the exposure operation is performed when the correction error is also within the allowable value. I have to do it. From the above, the reference value of the heat accumulation amount is set so that the change amount of the image forming characteristic corresponding to the heat accumulation amount of the projection optical system PL due to the exposure light absorption does not exceed the predetermined amount, and the actual heat accumulation amount is There has been proposed a method of performing an exposure operation when the value is below a reference value.

Now, in this embodiment, regardless of whether or not the correction is performed as described above, attention is paid to the image forming characteristic which is the most problematic in practical use. Here, as the imaging characteristics,
Consider, for example, coma. It should be noted that coma aberration is not included in the image forming characteristics corrected by the image forming characteristic correcting mechanism as described above. By the way, the projection optical system P by absorbing the illumination light
The change characteristic of the coma aberration corresponding to the heat storage amount of L is represented as a first-order lag system or the sum of the first-order lag system, just like the projection magnification described above. Therefore, if a model of the change characteristic of coma aberration obtained in advance by experiments or simulations is stored in the main controller 50 (memory not shown), it is disclosed in Japanese Patent Laid-Open No. Sho 60-78454. As described above, by sequentially calculating the heat storage amount of the projection optical system, the change amount of the coma aberration due to the heat storage amount can be obtained. Thus, by comparing the calculated value with the allowable limit value of the coma aberration (change amount), it becomes possible to determine whether or not the exposure operation should be interrupted. still,
Actually, it is not necessary to obtain the change amount of coma aberration as described above, and the relationship between the heat accumulation amount of the projection optical system and the change amount of coma aberration is obtained in advance by experiments or simulations and the allowable limit value of coma aberration is set. The corresponding heat accumulation amount is stored as a reference value, the heat accumulation amount sequentially calculated by the above calculation is compared with the reference value, and the exposure operation is stopped when the heat accumulation amount reaches the reference value. May be.

By the way, various concrete sequences for preventing the deterioration of the image formation pattern due to the above-mentioned coma aberration can be considered, but here, the variation amount of the coma aberration (aberration amount) and the permissible limit value are changed every wafer exchange. It is assumed that (or the heat storage amount and the reference value) are compared and will be described with reference to FIG.
In FIG. 6, the vertical axis represents the amount of change in coma ΔG, and the horizontal axis represents the time t. Here, the projection optical system PL has cooled down sufficiently after the end of the previous exposure operation,
That is, the heat accumulation amount is almost zero, and the exposure operation is started from this state. FIG. 6 shows the case where the exposure operation is started at time t ₀ . Also, time T
₁ represents the exposure processing time (including stepping time) for all shot areas on one wafer, and time T ₂
Represents the time during which operations other than exposure such as wafer exchange and wafer alignment are performed. Actually, since exposure is performed by the step-and-repeat method, time T ₁
Even in the inside, the shutter 3 repeatedly closes and opens the illumination optical path, that is, the illumination light does not enter the projection optical system PL while the wafer stage is moving (during stepping), and the variation Δ
G decreases. Therefore, the curve representing the amount of change ΔG within the time T ₁ does not become smooth as shown in FIG. 6 but becomes a jagged curve, but it is expressed here as an average. Figure 6
As shown in (4), the amount of change ΔG gradually increases as the exposure process on the wafer continues. G _{L1 in} FIG. 6 represents an allowable limit value of the amount of change ΔG, and if it is determined whether or not the exposure operation on the wafer is continued using this limit value G _L1 , the exposure operation on a certain wafer is in progress. The change amount ΔG is the limit value G
_{Since L1} is exceeded (curve G _{V2 in} FIG. 6), the exposure for the remaining shot area of the wafer is performed in a state where the image formation pattern is deteriorated. Therefore, actually, the limit value G _L1 is slightly smaller than the limit value G _L1 , for example, the change amount ΔG increased by the exposure process on one wafer.
_A value G _L2 smaller than _L1 is set as a limit value, and this limit value G _L2 is used as a reference for determining whether or not to continue the exposure operation.

As shown in FIG. 6, the coma aberration change amount ΔG exceeds the limit value G _L2 at the time ta, and if the exposure operation is continued in this state, the change amount ΔG changes as the curve G _{V2. It} exceeds _L1 . Therefore, before the exposure operation on the next wafer is started (time ta), the change amount ΔG is compared with the limit value G _L2, and the exposure operation is interrupted based on the comparison result, and the change amount ΔG is equal to or less than the limit value G _L2. The exposure operation continues to be stopped until. Then, by restarting the exposure operation at the time when the change amount ΔG reaches the limit value G _L2 (time tb), the change amount ΔG is always maintained at the limit value G _L1 or less, that is, the image formation pattern due to coma aberration. The exposure is performed with the deterioration suppressed within a predetermined allowable range (curve G _{V1 in} FIG. 6).

According to the above method, the stop time (tb-t
Since a) occurs, the number of wafers processed per unit time decreases, and the productivity (throughput) of the apparatus may decrease.
It is possible to reduce the occurrence of defective products due to the deterioration of the imaging characteristics and prevent the yield from decreasing. Although the description has been given here taking coma as an example, the types and number of image forming characteristics to which the above method should be applied, and the allowable limit value of the change amount thereof have a small influence on the image forming pattern. ,throughput,
It may be determined in consideration of yield and the like. Further, in the above method, the case where the variation ΔG and the limit value G _L2 are compared every time the wafer is exchanged has been described, but other than this, the comparison may be performed every shot. That is, the comparison may be performed for each unit shot, each unit wafer (or each lot), or each unit time. Alternatively, in order to prevent the above-described stop time (tb-ta) from occurring, the amount of change in the imaging characteristics that should be reduced within the exposure stop time between shots (corresponding to the stepping time) is obtained in advance, and the change is made by that amount. The wafer stage WS may be stepped with the exposure stop time required for reducing the amount. This method is effective when a so-called die-by-die method is adopted in which exposure is performed while aligning each shot when the reticle patterns of the second and subsequent layers are superposed and exposed. Further, the stepping speed can be slowed down to reduce the vibration of the apparatus, and further, the wafer stage WS can be slowly driven into the target stop position (exposure position) over time, thereby improving the positioning accuracy. It is possible to obtain the effect that it becomes possible.

Next, the operation of suppressing the amount of change in the image forming characteristic of the projection optical system to the allowable limit value (or the heat storage amount of the projection optical system which is the reference value) or less will be briefly described. Now,
As described above, the change amount and the change characteristic (time constant) of the image forming characteristic (especially aberration) change for each illumination condition. Therefore, the image forming characteristic that should interrupt the exposure operation so as to keep the amount of change below the permissible limit value, that is, "the image forming characteristic that poses the most practical problem"
Can also differ for different lighting conditions. For example, coma aberration can be considered in the multiple tilt illumination method, and spherical aberration can be considered when the σ value is small. Further, in the above description (example of coma aberration), the "imaging characteristic which is the most problematic in practical use" is determined by the magnitude of the change amount of each imaging characteristic (the influence on the imaging pattern). Actually, it is necessary to consider the change characteristics, that is, the speed of change (rate of change).
For example, FIG. 7 shows the relationship between the change amount Δ of the imaging characteristics and the time t when a high irradiation energy amount is given to the projection optical system PL under a predetermined illumination condition. FIG. 7 shows the fluctuations of the three imaging characteristics a to c, the vertical axis represents the amount of change Δ normalized by the allowable limit value Δ _L , and the horizontal axis represents the time t. Further, in FIG. 7, the allowable limit value Δ _{L of the} imaging characteristic is 1.0
The exposure operation is started at time t ₀ . It should be noted that all three curves CVa to CVc in FIG. 7 are jagged curves like the curve G _{V2 in} FIG. 6, but here they are averaged and shown smoothly.

If attention is paid only to the magnitude of the amount of change in FIG. 7, the "imaging characteristic which is the most problematic in practice" is the characteristic b (curve CVb), and the amount of change Δ is the limit value Δ _{L as} described above. It suffices to stop the exposure operation at the time point (time t ₂ ) at which the exposure time reaches. However, since the excess of the limit delta _L with characteristic a (curve CVa) the change amount delta is the time t _1, must be stopped the exposure operation actually focused on characteristic a at time t _1. On the other hand, when performing the exposure while stopping the exposure operation by paying attention to only the characteristic a, as compared with the case where the exposure operation is not stopped as shown in FIG. if the amount of energy incident on the 1 / 1.2, can be kept below the amount of change tolerance limits delta _L. However, in order to make the characteristic b equal to or less than Δ _L , the amount of energy must be 1 / 1.5 on average. That is, if attention is paid only to the characteristic a, the characteristic b will exceed the limit value Δ _L when the stop time has sufficiently passed. Therefore, if the imaging characteristics as shown in FIG. 7, the characteristics a, so as to sequentially check the amount of change for each b, so as to always both equal to or less than the limit value delta _L, at least one of a limit value delta _L It is necessary to adopt a sequence in which the exposure operation is stopped when the value exceeds.

From the above, when the illumination conditions are changed, it is necessary to successively calculate the amount of change under the changed illumination conditions as the "imaging properties most practically problematic" in advance. Must be selected, and during the exposure operation, the amount of change must be sequentially calculated only for the selected image forming characteristic and comparison with the allowable limit value must be performed.
In the example shown in FIG. 7, the characteristics a, may be calculated to the amount of change for each b, the characteristics a, if the amount of change b is sufficient that both smaller than the permissible limit value delta _L, characteristic c (curve CV
Since c) is always less than or equal to the limit value Δ _L, it is not necessary to calculate the change amount of the characteristic c. Of course, if the change characteristics (time constant) of the imaging characteristics are almost the same for each aberration,
It suffices to select (determine) the imaging characteristics for which the above calculation should be performed, focusing only on the amount of change. Further, when the image forming characteristic selected as described above is such that the image forming characteristic correcting mechanism (FIG. 1) corrects the change amount, it is not necessary to newly perform another calculation to obtain the change amount. without it the limit value of the calculated amount of change for use in the correction mechanism delta _L
It may be used for comparison with.

Further, in the above description, the permissible limit value of the amount of change for each imaging characteristic is a constant value under a predetermined illumination condition, but in reality, even if the illumination condition is the same,
The limit value may change depending on the fineness (line width, pitch, etc.) and shape (arrangement state in the pattern surface, etc.) of the reticle pattern to be exposed. Therefore, if information about the reticle pattern is not input to the exposure apparatus, the allowable limit value must be determined under the strictest conditions, and throughput may be unnecessarily reduced depending on the reticle pattern. Therefore, for example, information about the reticle pattern (line width or the like) is provided as a bar code on the reticle, or is stored in the memory of the apparatus main body in association with the reticle name (bar code BC). And Reticle R
When the lens is mounted on the holder 14, the bar code reader 52 reads the bar code to automatically set the illumination condition, and also to change the amount of change in the imaging characteristic most suitable for the condition and the reticle pattern. The permissible limit value (or the reference value of the heat storage amount of the projection optical system) may be determined, and thereby it is possible to prevent the throughput from being lowered more than necessary.

Further, in the above description, after the illumination condition is changed sufficiently long, the influence of the illumination condition before the change has already disappeared (that is, the heat accumulation amount remaining in the projection optical system as a history is almost It is assumed that the value is zero), and the exposure operation is started in this state. Therefore,
Consider, for example, a case where after changing the illumination condition during the exposure operation for one wafer, immediately restarting the exposure operation under the next illumination condition, the projection optical system PL has the condition before the illumination condition is changed. Since the history under
The change amount of the imaging characteristic cannot be expressed as a simple sum of the change amounts under the two conditions before and after the illumination condition change.
Therefore, by simply changing the allowable limit value (or the reference value of the heat accumulation amount) of the change amount due to the change of the illumination condition to a value most suitable for the changed illumination condition, the change amount of the imaging characteristic can be determined. It is difficult to keep within the allowable range of. Further, in order to obtain the amount of change in the imaging characteristics by sequential calculation, it is necessary to calculate the temperature distribution of the lens element in the transient state when the illumination condition is changed and to know the corresponding amount of change. It is theoretically possible to do this, but in reality, the lighting conditions before and after the change overlap, which is very complicated and impractical.

Therefore, after the shutter is closed to change the illumination condition and the exposure operation is stopped, a predetermined time until the influence (history) of the illumination condition before the change becomes sufficiently small, for example, the variation amount Δ of the imaging characteristic. The exposure operation is continuously stopped until is reduced to a constant level (threshold value) Ms, and the shutter is opened when the variation Δ reaches the constant level Ms, and the exposure operation is performed under the changed illumination condition. Just start. According to this method, the history of the illumination conditions before the change as described above can be eliminated, and the allowable limit value of the change amount of the imaging characteristics (or the reference value of the heat accumulation amount) is set as the changed illumination condition. By simply switching to the most suitable value, the amount of change in the imaging characteristics can be suppressed within a predetermined allowable range. It should be noted that the level Ms is a predetermined allowable value when the difference (calculation error) between the amount of change in the image formation characteristic that is sequentially calculated under the changed illumination condition (calculation parameter) and the amount of change in the actual image formation characteristic. It may be determined so as to be within (uniquely determined according to the control accuracy of the imaging characteristic). At this time, it is desirable to set the level Ms to a value as large as possible so as not to reduce the throughput of the apparatus, that is, to shorten the exposure stop time. Actually, it is advisable to previously obtain the level Ms corresponding to various combinations of illumination conditions by experiments or simulations.

On the other hand, when the exposure operation is not stopped at the time of changing the illumination condition and the exposure is started immediately after the change, for example, for each combination of the illumination conditions, the irradiation amount (heat amount) to the projection optical system before and after the illumination condition is changed. (Accumulation amount) and exposure stop time when changing the illumination conditions, etc., the allowable limit value (or the heat accumulation amount) corresponding to the change amount of the imaging characteristics in the transient state when changing the illumination condition is preliminarily tested or simulated. It suffices to strictly obtain the reference value) by calculation. Considering the number of combinations of lighting conditions and the variation (type) of the irradiation amount under each lighting condition, it is too complicated and realistic to determine the allowable limit value of the change amount for each of these conditions. I can not say. Furthermore, in addition to determining the allowable limit value, when starting the exposure operation continuously immediately after changing the illumination conditions, considering that it is extremely difficult to successively calculate the amount of change in the imaging characteristics as described above. There must be. However, if the variation of the light amount distribution on the pupil plane of the projection optical system or the variation amount of the imaging characteristic or the variation characteristic due to the change of the illumination condition is small, the above calculation can be performed relatively easily. Therefore, the exposure operation may be started immediately after changing the illumination condition.

When the amount of change in the image forming characteristic exceeds the allowable limit value (or the amount of heat accumulated in the projection optical system is the reference value) or the exposure operation is stopped by changing the illumination condition, the image forming characteristic is changed. The amount of change (or the amount of heat accumulation) gradually decreases, but since the amount of change is obtained by sequential calculation due to the imaging characteristic correction mechanism as described above, the amount of change attenuation must be calculated. You don't have to do anything special.

Next, an example of the processing in the main controller 50 will be described with reference to the flowchart shown in FIG. Here, an example will be described in which the illumination conditions are not changed for the same reticle, and the reticle is not exchanged while the same wafer is exposed. Although not shown in FIG. 1, the main controller 50 changes the illumination conditions and starts the exposure operation.
In addition to controlling the stoppage, the control unit that controls the entire device as a whole, determines the allowable limit value (or the reference value of the heat storage amount) of the change amount of the imaging characteristics for each illumination condition and reticle pattern, and changes the imaging characteristics. Amount (or heat accumulation amount of the projection optical system) and an operation parameter corresponding to the name of each reticle, such as illumination conditions and heat accumulation amount of the projection optical system (or corresponding to this). It is assumed to be configured with a storage unit (memory) that stores calculation parameters and the like for calculating (amount of change in image formation characteristic).

As shown in FIG. 8, first in step 101, main controller 50 confirms whether or not the reticle is placed on holder 14, and the operator inputs information from keyboard 51 or the information is input in advance. Based on a program (exposure sequence) or the like, whether or not the reticle is loaded on the holder 14 immediately, the reticle is immediately loaded, and when the reticle is loaded, a new reticle is loaded on the holder 14 or not. Judge whether or not reticle replacement is required. Here, it is assumed that the reticle is exchanged, and the process proceeds to the next step 102. In step 102, the main controller 50 determines whether the state of the exposure apparatus (setting condition), that is, whether the illumination condition is set to normal illumination, annular illumination, or multiple tilt illumination, and the σ value of the illumination optical system, The numerical aperture of the projection optical system PL and the aperture shape / position of the variable blind 10 are confirmed. This is performed by recognizing the setting states of the drive system 54, the variable aperture diaphragms 8 and 32, the variable blind 10, and the like. It may be performed by simply reading out various conditions inside the memory corresponding to the reticle R (bar code BC) on the reticle holder 14.

At the next step 103, the holder 1 is newly added.
The bar code BC of the reticle R loaded in No. 4 is read. Then, the main controller 50 uses the barcode BC
The operation parameter corresponding to (reticle name) is read from the memory. As a result, the most suitable (optimal) illumination conditions that match the type of reticle (normal reticle, phase shift reticle), the fineness of the pattern, the periodicity, etc., that is, normal illumination, annular illumination, or multiple tilt illumination, are used. Or
Furthermore, conditions such as inner diameter, outer diameter, and annular ratio (ratio of inner diameter to outer diameter) are used for ring illumination, conditions such as the number of fly-eye lens groups and their positions are used for multi-tilt illumination, and the illumination optical system σ
Value, numerical aperture of projection optical system PL, and variable blind 10
The opening shape, position, etc. of are recognized.

Next, main controller 50 drives holding member 7, variable aperture diaphragms 8 and 32, variable blind 10 and the like based on the illumination conditions read out in step 103, and illuminates optimum reticle R and its pattern. The conditions are set (step 104). In step 104, the change may be made only for the condition different from the illumination condition confirmed in the previous step 102, and if the illumination condition need not be changed at all, the process immediately proceeds to step 105. As an example of changing the illumination condition, for example, when the reticle pattern is a fine two-dimensional line-and-space pattern, the control unit rotates the holding member 7 to arrange the fly-eye lens group 7D in the illumination optical path, and the pattern pitch thereof. the positions of the fly-eye lens unit 7D ₁ ~7D ₄ in a pupil plane near the illumination optical system is finely adjusted in accordance with or periodic direction. Further, if necessary, the variable aperture diaphragms 8 and 32 and the variable blind 10
You can readjust it.

Here, when the illumination condition is changed as described above, for example, when the normal illumination (fly-eye lens group 7A) is changed to a plurality of inclined illuminations (fly-eye lens group 7D), the projection optical system PL changes the illumination light flux. The passing area is completely different before and after changing the lighting conditions. Therefore, under this changed illumination condition, the projection magnification and various aberrations of the projection optical system PL (distortion, field curvature, astigmatism, coma aberration, spherical aberration, etc.) are optimum values, or zero or an allowable range. Inside the projection optical system P by the imaging characteristic correction mechanism in FIG.
It is desirable to adjust the image forming characteristic of L. It should be noted that when the history (heat accumulation) does not remain in the projection optical system PL in advance, or the amount of change in the imaging characteristics due to the history is at the level Ms or less, the imaging characteristics correction mechanism for each illumination condition is used. The correction amount (the driving amount of the reticle or lens element, etc.) is obtained, and the image formation characteristic correction mechanism is controlled based on the correction amount before the exposure operation is started under the new illumination condition. It suffices to adjust the image forming characteristics of the optical system PL. As for aberrations (coma aberration, spherical aberration, etc.) that cannot be corrected by the imaging characteristic correction mechanism, for example, the aberrations can be largely changed among the lens elements constituting the projection optical system PL, and other aberrations can be changed. The lens element which is hardly changed can be finely moved, and the aberration amount can be adjusted by driving this element.

Next, main controller 50 determines the reticle and the image forming characteristics to be noted under the illumination conditions, that is, "the image forming characteristics that pose the most practical problems". The image forming characteristic determined here is the image forming characteristic a in FIG. 7 as described above,
In some cases, a plurality of imaging characteristics are set as shown in b. Further, when the imaging characteristic (hereinafter referred to as the focused imaging characteristic) to be calculated for which the allowable limit value of the change amount is set as described above is determined, the focused imaging under the new illumination condition is determined. The change amount (or change rate) of the characteristic and the change characteristic (time constant) are also read from the memory, and set so that the calculation unit can successively calculate the change amount of the characteristic (step 105). Then, even pattern information of the reticle R to be exposed (line width, density distribution in the pattern surface, etc.) is read from the memory,
An allowable limit value (corresponding to G _L2 in FIG. 6) of the amount of change in the focused image-forming characteristic set previously is determined (step 106). With the above, the setting of various conditions in main controller 50 is completed.

Next, main controller 50 determines whether or not the illumination conditions have been changed (step 107). Here, it is assumed that the illumination condition read from the memory under the new reticle R is different from the condition confirmed in the previous step 102, and the change is made, and the process proceeds to the next step 108.
If it is determined in step 107 that the illumination conditions have not been changed, the process immediately proceeds to step 110.

In step 108, whether or not the history of the illumination conditions before the change remains in the projection optical system PL, that is, whether the change amount of the image forming characteristic of the projection optical system PL due to the history is below the level Ms or not. Determine whether or not. Here, the exposure operation is stopped due to the change of the illumination condition, and the change amount is gradually reduced accordingly. However, the attenuation calculation of the change amount of the image formation characteristic is the calculation parameter under the illumination condition before the change. The exposure operation is continuously performed based on (time constant, etc.). Therefore, main controller 50 compares this calculated value with level Ms, and if the calculated value is less than level Ms, no history remains in projection optical system PL, that is, under the changed illumination condition. It is determined that the change amount of the image forming characteristic can be sequentially calculated using the calculation parameter of (1), and the process proceeds to the next step 110.

On the other hand, when it is determined that the history remains in the projection optical system PL, the process proceeds to step 109, waits for a fixed time (for example, about several seconds), and then returns to step 108 to determine the amount of change in the imaging characteristic. It is determined whether or not the level is below the level Ms. If it is determined that the history remains, the process proceeds to step 109 again, and the following steps 108,
109 is repeatedly executed, and when the amount of change in the imaging characteristic becomes equal to or lower than the level Ms, the process proceeds to step 110. Here, the above determination is made at regular time intervals. However, for example, the waiting time until the change amount of the imaging characteristics becomes equal to or less than the level Ms is calculated from the attenuation calculation by the calculation parameter, and the calculated time is calculated. After waiting for just that, the process may proceed to step 110 immediately.

It should be noted that the imaging characteristics for which it is necessary to determine whether or not the amount of change is equal to or less than the level Ms are the illuminations after the change determined in the previous step 104 even if all the aberrations including the projection magnification are included. Only the focused image forming characteristic under the condition may be used. Further, when the focused image forming characteristic is different before and after the change of the illumination condition, for example, when the change amount of the focused image forming characteristic under the illumination condition before the change becomes equal to or less than the level Ms,
Alternatively, the amount of change in the focused imaging characteristic under the changed illumination condition is newly calculated using the calculated parameters under the changed illumination condition, and the calculated value becomes equal to or lower than the level Ms. At that point, the process may proceed to step 110.

At the next step 110, the main controller 5
In 0, it is determined whether or not the amount of change in the focused imaging characteristic is equal to or less than the allowable limit value. This is performed in exactly the same way as in step 108 by comparing the amount of change calculated successively and the allowable limit value, and if the amount of change (calculated value) is below the allowable limit value, immediately proceed to step 112. Then, the exposure of the wafer is started. On the other hand, if the change amount exceeds the allowable limit value, the process proceeds to step 111,
Here, after waiting for a fixed time (for example, about 1 second), the process returns to step 110 again, and it is determined whether or not the amount of change is less than or equal to the allowable limit value. Hereafter, steps 110 and 11
1 is repeatedly executed, and the process proceeds to step 112 when the change amount becomes equal to or less than the allowable limit value. Here, similarly to step 111, the waiting time until the amount of change becomes equal to or less than the allowable limit value is calculated from the attenuation calculation using the calculation parameter, and after waiting for the time calculated here, the process may immediately proceed to step 112. .

In step 112, the pattern of the reticle R is sequentially exposed on the wafer W under new illumination conditions. After the exposure is completed, main controller 50 determines whether or not the next wafer is to be exposed (step 113).
Since only the first wafer has been exposed here,
Proceeding to next step 114, wafer exchange is executed. Further, main controller 50 determines whether or not the reticle should be replaced for the next (second) wafer (step 10).
2). Here, it is assumed that the pattern of the same reticle is exposed, and the process proceeds to step 110. In step 110, the change amount of the image forming characteristic of interest is compared with the permissible limit value in exactly the same manner as described above. To do. Hereinafter, the above sequence is repeatedly executed until the exposure of all the wafers to be exposed is completed. As a result, it becomes possible to perform the pattern exposure on the wafer always under the highly accurate imaging characteristics.
When the reticle is replaced, the steps 102-
When step 106 is executed and the illumination condition is changed, steps 108 and 109 may be executed. If the illumination conditions are not changed even after reticle replacement, step 10
It is not necessary to perform steps 5 and 106.

Here, if the exposure sequence is such that the reticle is not exchanged for all the wafers to be exposed, in the flowchart shown in FIG. 8, step 110 is executed immediately after step 114 is completed. good. At this time, it is premised that the amount of change in the imaging characteristic in step 110 is compared with the allowable limit value every time the wafer is exchanged. Although FIG. 8 shows a sequence in which the illumination condition is not changed for the same reticle, the illumination condition may be changed for each unit number of wafers (or each shot area) or each lot even for the same reticle. Any sequence may be adopted. Further, although the reticle was not exchanged for the same wafer, even if the same wafer is used, a reticle exchange may be performed for each unit shot (for example, for each shot), and the illumination condition may be changed. good. The present invention is particularly effective when exposing a wafer under various illumination conditions while changing the illumination conditions as described above.

Even when the reticle is changed from the normal reticle to the phase shift reticle in step 102 (or vice versa), the process proceeds from step 102 to step 110 in FIG. 8, so that the illumination condition is particularly changed (holding member 7). Drive or change of σ value) is not performed. However, since the light amount distribution changes on the pupil plane of the projection optical system PL, it is assumed that the reticle exchange as described above corresponds to the change of the illumination condition, and the steps 108 and 10 are performed.
9 is adopted. It should be noted that, other than the phase shift reticle, a reticle that changes the light amount distribution on the pupil plane of the projection optical system PL, for example, a normal reticle and a light blocking member (chrome or the like) that constitutes the pattern thereof is partially In the case of a so-called halftone reticle that gives a light transmittance, it is desirable to execute steps 108 and 109 by regarding it as a change in illumination condition. Further, even when exposure is performed on the same reticle while changing the illumination condition, the same effects can be obtained by directly applying the present embodiment.

As described above, in this embodiment, step 10
8 and 110, the amount of change in the imaging characteristic was sequentially calculated and compared with the level Ms and the allowable limit value. However, the amount of heat accumulated in the projection optical system PL due to absorption of illumination light and The relationship with the corresponding change amount of the image forming characteristic is obtained, and the allowable limit value (or level M) of the change amount of the image forming characteristic is obtained.
The amount of heat accumulation corresponding to s) is stored as a reference value,
In steps 108 and 110, only the heat storage amount of the projection optical system PL is sequentially calculated, and by comparing the heat storage amount (calculated value) with a reference value, it is determined whether or not the exposure operation is started. Is also good.

In this embodiment, the main control device 50 controls the start and stop of the exposure operation as described above, but a dedicated control unit is prepared separately from the main control device 50, and the unit concerned is It is also possible to input the illumination conditions and the like to control the exposure operation, and the main controller 50 only gives various conditions and calculation results to the unit. Although not shown in FIG. 1, a display device (a cathode ray tube or the like) for notifying the operator of the calculation result in the main control device 50 and the operation state of the exposure device is provided, and the exposure operation is stopped in steps 109 and 111, for example. During this time, the operator may be informed of how long the exposure stop time is. At this time, the exposure stop time can be easily obtained from the attenuation calculation of the change amount of the image formation characteristic.

Further, in the above embodiment, the permissible limit value is set for the variation amount of the focused image forming characteristic such as coma aberration and spherical aberration, and the exposure operation is stopped when the variation amount exceeds the limit value. Regarding other imaging characteristics, such as projection magnification, distortion, field curvature, astigmatism, etc., it is assumed that the imaging characteristic correction mechanism sequentially corrects the variation so that the variation is always within the allowable range. I was there. However, the combination of the image forming characteristic to be selected as the image forming characteristic of interest and the image forming characteristic corrected by the correction mechanism may be arbitrary, and for example, coma aberration and field curvature may be selected as the image forming characteristic of interest. Absent. Depending on the type of the reticle or its pattern and the illumination conditions, the projection magnification and the distortion may be sequentially corrected by the correction mechanism, and only the coma aberration may be selected as the focused image forming characteristic.

Further, in the above embodiment, the image forming characteristic to be selected as the focused image forming characteristic and the image forming characteristic to be corrected by the correcting mechanism are clearly distinguished, but the change amount is sequentially corrected by the correcting mechanism. Even if the imaging characteristic is selected as the focused imaging characteristic, that is, the permissible limit value of the change amount is set, and the change amount and the permissible limit value that are successively calculated in the same manner as above are compared to perform the exposure operation. It may be determined whether or not to start. This is because even if the image forming characteristic is such that the amount of change is sequentially corrected by the correction mechanism, there is a limit to correction of the amount of change (aberration amount) by the correction mechanism depending on the type (for example, curvature of field). This is because the amount cannot be completely corrected and gradually increases, and eventually the amount of change (sum of residual correction errors) may exceed the allowable limit value.

Further, in step 110, when the variation amount of the image forming characteristic of interest exceeds the allowable limit value, the exposure operation is stopped until the variation amount becomes equal to or less than the limit value. Using the imaging characteristic correction mechanism,
Alternatively, the amount of change may be positively made equal to or less than the allowable limit value by driving the lens element that is effective for correcting the amount of change in the focused imaging characteristic. At this time, the relationship between the amount of heat accumulated in the projection optical system PL and the amount of change in the imaging characteristics corresponding thereto can change, so the relationship is updated based on the previous correction amount (driving amount), and thereafter It is desirable to successively calculate the amount of change in the imaging characteristic based on this updated relationship and compare it with the allowable limit value.

Further, in the above embodiment, the projection optical system PL corresponding to the type of reticle, its pattern, and the illumination conditions.
Of the light intensity (illuminance) in the vicinity of the pupil surface of the lens, the image formation characteristic is also affected by a change in the illuminance distribution of the lens element of the projection optical system PL near the reticle due to a change in the density distribution of the reticle or its pattern. Can fluctuate,
Even in such a case, it is possible to suppress the amount of change in the imaging characteristics to the allowable limit value or less, as in the above embodiment. That is, when the illumination light is unevenly irradiated to the lens elements near the reticle due to the change of the illumination field of view by the variable blind 10 or the change of the density distribution of the reticle pattern, even if the illumination amount is the same, It is conceivable that the imaging characteristics of the lens element will change as compared with the case where the lens element is irradiated almost uniformly. Therefore, in such a case, not only in the vicinity of the pupil plane of the projection optical system PL but also in the illuminance distribution in the lens element near the reticle, the illuminance distribution here is considered as one of the illumination condition changes, and the variation amount is sequentially changed. By performing the calculation, it becomes possible to perform more strict control of the imaging characteristics.

Further, in the above-mentioned embodiment, the change of the image forming characteristic due to the heat accumulation amount of the projection optical system due to the absorption of the illumination light was considered, but the fluctuation is relatively small as compared with the absorption of the illumination light.
The amount of change may be sequentially calculated in consideration of even changes in the imaging characteristics due to changes in the environment (atmospheric pressure, temperature, etc.) around the projection optical system PL. Further, recently, while the wafer stage WS is moved in the optical axis direction of the projection optical system PL, the exposure light transmitted to the inside of the wafer stage WS by an optical fiber or the like causes a reference pattern provided substantially in the same plane as the wafer surface. And the photoelectrically detecting the reflected light on the lower surface (pattern surface) of the reticle R of the pattern image through the reference pattern, the focus position at an arbitrary point in the exposure field of the projection optical system PL is determined. It is proposed to detect. In this type of focus position detection system, in order to accurately detect the focus position for each illumination condition, for example, a plurality of spatial filters are replaceably arranged near the exit end face of the optical fiber and formed on the pupil plane of the projection optical system PL. The illuminance distribution is set to be substantially equal to the illuminance distribution for each illumination condition (including the phase shift reticle etc.) of the illumination optical system. Therefore, even when the focus position is detected by the apparatus having the above-described configuration, the projection optical system PL can absorb the exposure light and the imaging characteristics thereof can change, so that the amount of heat accumulated in the projection optical system due to the absorption of the exposure light can be increased. It is desirable to calculate the amount of change in the image forming characteristic in consideration of the above.

In the above embodiment, the case where the normal illumination is changed to the multi-inclined illumination as the illumination condition is described. However, for example, when only the σ value of the illumination optical system is changed, the normal illumination is changed to the annular illumination ( In the case of multiple tilt illumination, the fly-eye lens groups 7B to 7D are exchanged with each other according to the periodicity of the reticle pattern, or even if the fly-eye lens groups are the same, the individual fly-eye lens groups are slightly moved. The present invention is also effective when the illumination blind field is changed by the variable blind 10 or when the numerical aperture of the projection optical system PL is changed.

According to the above-mentioned embodiments, the image forming characteristics of the projection optical system PL are always maintained in good condition, but the reduction of productivity (throughput) due to interruption of the exposure operation cannot be avoided. Therefore, in order to make up for the above drawbacks, the waiting time in steps 109 and 111 in FIG.
It is desirable to effectively use it for self-calibration of the exposure apparatus including checking (measurement) of the focus position of L, projection magnification, or various aberrations, baseline check of the alignment sensor, and the like. Although the projection optical system PL in FIG. 1 is composed of only a refracting element, a reflecting element,
Alternatively, a combination of a refraction element and a reflection element may be used.

[0091]

As described above, according to the present invention, even if the change amount (change characteristic) of the image forming characteristic of the projection optical system due to the absorption of the illumination light changes according to the change of the illumination condition, the projection is performed for each illumination condition. Set a predetermined allowable limit value (or a predetermined reference value for the heat storage amount) to the amount of change in the imaging characteristics corresponding to the heat storage amount of the optical system,
The exposure operation is stopped (interrupted) while the amount of change exceeds the allowable limit (or the amount of heat accumulation exceeds the reference value).
I decided to do it. For this reason, it is possible to always suppress the deterioration of the image formation pattern due to the variation of the image formation characteristic for each illumination condition within the allowable value. Further, by determining the image forming characteristic for which the allowable limit value should be set for each illumination condition, and paying attention only to the determined image forming characteristic and comparing the variation amount with the allowable limit value, the exposure operation is started and stopped. Therefore, it is possible to minimize the decrease in productivity (throughput) due to the stop time.

[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 a specific configuration of an exchange mechanism that exchangeably arranges a plurality of fly-eye lens groups in an optical path of an illumination light flux.

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 diagram showing an optical path from a fly-eye lens group to a wafer before and after changing an illumination condition (σ value) and a light amount distribution near a pupil plane of a projection optical system.

FIG. 5 is a diagram illustrating a change characteristic of an image forming characteristic (projection magnification) of a projection optical system due to absorption of illumination light.

FIG. 6 is a diagram for explaining an allowable limit value to be set for the amount of change in the imaging characteristics of the projection optical system due to absorption of illumination light.

FIG. 7 is a diagram illustrating a method of setting an allowable limit value for the amount of change in image formation characteristics.

FIG. 8 is a flowchart showing an example of a control operation of image forming characteristics of the projection optical system.

[Explanation of symbols]

 3 Shutter 10 Variable blind 20-23 Lens element 25, 27, 29 Driving element 33 Irradiation amount monitor (photoelectric sensor) 50 Main controller R Reticle PL Projection optical system Ep Pupil surface W Wafer WS Wafer stage

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 7352-4M 527

Claims (6)

[Claims] 1. The projection optical system according to the incidence of the illumination light in order to project an image of a pattern of a mask irradiated with illumination light from a light source onto a photosensitive substrate in a predetermined image formation state via a projection optical system. Projection exposure method for controlling start or stop of exposure operation on the photosensitive substrate based on a heat accumulation amount of the system or an amount of change in optical characteristics of the projection optical system caused by heat accumulation or environmental change and a predetermined reference value In the step of determining the reference value according to a change in the distribution state of the light flux on the pupil plane of the projection optical system; and after the change in the distribution state of the light flux, using the determined reference value. And a step of performing the exposure operation. 2. A distribution state of the illumination light on a pupil plane of an illumination optical system that illuminates the mask with the illumination light, a pattern on the mask to be projected on the photosensitive substrate, and a numerical aperture of the projection optical system. The projection exposure method according to claim 1, wherein the distribution state of the light flux on the pupil plane of the projection optical system is changed by changing at least one of them. 3. When the distribution state of the light flux on the pupil plane of the projection optical system changes, the exposure operation is stopped until the amount of heat accumulation or the amount of change in the optical characteristics becomes a predetermined allowable value or less. 3. The projection exposure method according to claim 1 or 2. 4. The projection exposure method according to claim 3, wherein the optical characteristic of the projection optical system or the baseline of the alignment sensor is measured while the exposure operation is stopped. 5. A projection exposure apparatus comprising: an illumination optical system for irradiating a mask with illumination light from a light source; and a projection optical system for projecting an image of the pattern of the mask onto a photosensitive substrate,
In order to project the pattern image of the mask in a predetermined image formation state, the amount of heat accumulated in the projection optical system due to the incidence of the illumination light, or the amount of change in the optical characteristic of the projection optical system caused by heat accumulation or environmental change And an exposure control means for controlling the start or stop of the exposure operation on the photosensitive substrate based on a predetermined reference value; and a distribution state of the illumination light on the pupil plane of the illumination optical system,
Exposure condition changing means for changing the distribution state of the light flux on the pupil plane of the projection optical system by changing at least one of the pattern on the mask to be projected on the photosensitive substrate and the numerical aperture of the projection optical system. A projection exposure apparatus comprising: means for changing the reference value according to a change in the distribution state of the light flux on the pupil plane of the projection optical system. 6. The exposure control means, when the distribution state of the light flux on the pupil plane of the projection optical system changes, the heat accumulation amount or the change amount of the optical characteristic becomes equal to or less than a predetermined allowable value. The projection exposure apparatus according to claim 5, wherein the exposure operation is stopped.