JPH07147224A - Projection aligner - Google Patents

Abstract

PURPOSE:To excellently correct the fluctuation amount of image formation characteristics which is generated by thermal deformation of a mask, in a projection allgner of, in particular, a scan exposure system. CONSTITUTION:A slit-shaped illumination region on a mask R is illuminated with an illumination light from a light source 1, a pattern image in the illumination region is projected and exposed on a wafer W through a projection optical system PL, and the wafer W is scanned in the X direction simultaneously with the scanning of the mask R in the X direction. The relative velocity between the mask R and atmospheric gas is approximately measured from the measured value of an interferometer 16, and the thermal deformation amount of the mask R is measured from the relative velocity, irradiation energy to the mask R, etc. Then the change amount of image formation characteristics caused by the thermal deformation amount is cancelled via an image formation characteristics control part 12.

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 having a function of correcting an image forming characteristic used when manufacturing a semiconductor element or the like in a photolithography process, and more particularly, to a mask and a photosensitive substrate for exposure. Is suitable for application to a so-called slit scan exposure system or step-and-scan system projection exposure apparatus that sequentially exposes the pattern image of the mask onto the photosensitive substrate while scanning in parallel.

[0002]

2. Description of the Related Art In a photolithography process for manufacturing a semiconductor integrated circuit or the like, a wafer (or a glass plate or the like) on which a pattern image of a photomask or a reticle (hereinafter referred to as "mask") is coated with a photoresist or the like. A) a projection exposure apparatus is used to expose the above. In such a projection exposure apparatus, as the circuit pattern to be transferred is further miniaturized, the allowable range of the variation amount of the image forming characteristic of the projection image by the projection optical system is narrowed. Therefore, in a conventional projection exposure apparatus, in order to correct a variation amount of image forming characteristics (for example, magnification, focal position, etc.) caused by absorption of illumination light by a projection optical system, Japanese Patent Application Laid-Open No. 60-7 has been proposed.
As disclosed in Japanese Patent No. 8455 or Japanese Patent Laid-Open No. 63-58349, the amount of light incident on the projection optical system is detected, and the fluctuation amount of the imaging characteristic of the projection optical system is corrected according to the detected light amount. The image forming characteristic correcting mechanism is provided.

The mechanism disclosed in, for example, Japanese Patent Laid-Open No. 60-78455 will be briefly described. A wafer corresponding to the variation characteristic of the image forming characteristic of the projection optical system is prepared in advance and the wafer is placed on the wafer. The amount of light energy incident on the projection optical system is calculated at a predetermined time interval by a photoelectric sensor on the stage, and the integrated value of this amount of light energy is applied to the model to calculate the amount of fluctuation of the imaging characteristics. . In this case, the exposure time for obtaining the integrated value of the light energy incident on the projection optical system is calculated, for example, by constantly monitoring the signal indicating that the shutter for opening and closing the illumination light is in the open state. Therefore, it is possible to calculate the current variation amount of the imaging characteristic of the projection optical system according to the model, and perform the correction based on this variation amount. As a result, the problem of the change in the image forming characteristic due to the absorption of the illumination light of the projection optical system has been solved.

However, since the illumination light also passes through the mask, the mask is thermally deformed by the absorption of the illumination light, which also causes a problem that the image forming characteristic is changed. In particular, since the mask has a pattern formed by a light-shielding film such as a chrome film, the light-shielding film absorbs a large amount of heat unlike the glass substrate portion having a high transmittance. Further, in recent years, there is a tendency to adopt a technique of reducing the reflection of the light-shielding film on the mask for the purpose of preventing flare of the optical system, but this further increases heat absorption in the light-shielding film.

Further, the circuit pattern formed by the light-shielding film of the mask is not always uniformly distributed over the entire mask but may be distributed unevenly. In this case, the temperature of the mask locally rises and anisotropic strain may occur. Also, when exposing only a part of the pattern of the mask using a variable field stop (reticle blind) or the like, anisotropic distortion may similarly occur. The distortion of the mask thus generated causes anisotropic distortion in the projected image. In this case, it is not sufficient to correct only the magnification component.

Further, regarding the thermal deformation of the mask, it is difficult to uniformly correct it because the amount of thermal deformation, and hence the amount of change in the imaging characteristics, differs depending on the type of mask used. That is, for example, the variation amount of the image formation characteristic of the mask used for adjusting the image formation characteristic of the projection exposure apparatus at the time of shipping is recognized as the variation characteristic of the image formation characteristic of the projection exposure apparatus and corrected. However, if other masks are used, the amount of thermal deformation will be different and accurate correction will not be possible.

In particular, when the masks are exchanged one after another and the exposure is performed, if the thermal deformation amount of each mask is not taken into consideration, the variation amount of the image forming characteristic may be accumulated and cause a large error. As a countermeasure against this, for example, a method of cooling the mask to a constant temperature can be considered, but since the temperature of the glass surface of the mask and the temperature of the light-shielding film such as a chrome film cannot be equal, the whole is cooled uniformly without heat distribution. Is extremely difficult. Further, since cooling is a phenomenon involving heat conduction, the response is poor, and there is a problem that it cannot follow the opening / closing operation of the shutter for opening / closing the illumination light, which is unrealistic. A projection exposure apparatus capable of satisfactorily correcting the change in the optical characteristics caused by the thermal deformation of the mask is disclosed in Japanese Patent Laid-Open No. 4-192317.

[0008]

However, the conventional method of correcting the image forming characteristic has been proposed on the premise of the collective exposure method (full field method). However, in recent years, the pattern area of the mask is illuminated in a slit shape, the mask is scanned with respect to the slit-shaped illumination area, and the exposure area conjugate with the slit-shaped illumination area is synchronized with the scanning of the mask. The so-called step-and-scan exposure method or slit-scan exposure method (hereinafter, referred to as "scan exposure method") projection in which the mask pattern is sequentially projected and exposed on each shot area of the wafer by scanning the wafer. Exposure equipment has been developed. This scan exposure method has an advantage that a large area can be exposed without being restricted by the field size of the projection optical system in the scanning direction.

In such a scan exposure system,
Since the mask is scanned with respect to the illumination area during exposure, the factors to be considered for the mask (such as the mask cooling effect accompanying mask scanning) have increased, and the calculation of the thermal deformation amount of the mask is performed by the batch exposure method. There is an inconvenience that it becomes more complicated than the case. The present invention has been made in view of the above problems, and an object of the present invention is to make it possible, particularly in a scan exposure type projection exposure apparatus, to satisfactorily correct the amount of variation in the imaging characteristics caused by thermal deformation of the mask.

[0010]

A projection exposure apparatus according to the present invention is, for example, as shown in FIG. 1, an illumination optical system for illuminating a predetermined illumination area on a mask (R) on which a transfer pattern is formed. (1 to 7), a projection optical system (PL) for projecting a pattern image of the mask (R) onto the photosensitive substrate (W), and a mask (R) for holding the mask (R) and illuminating the area.
Stage (RST) which scans the photosensitive substrate (W) and a substrate stage (WST) which holds the photosensitive substrate (W) and scans the photosensitive substrate (W) with respect to a region conjugate with the predetermined illumination region.
And scanning the mask (R) at a predetermined speed via the mask stage (RST), at a speed corresponding to the projection magnification of the projection optical system (PL) via the substrate stage (WST) in synchronization with the scanning. In a projection exposure apparatus that sequentially scans and exposes a pattern image of a mask (R) on a photosensitive substrate (W) by scanning the photosensitive substrate (W), image formation for correcting the image formation state of a projection optical system (PL) It has a state correction means (12).

Further, according to the present invention, the relative velocity measuring means for measuring the relative velocity of the mask (R) and the gas in contact with the mask, the measurement result of the relative velocity measuring means and the illumination optical system for the mask (R). The amount of thermal deformation of the mask (R) is calculated from the irradiation energy from the deformation amount calculation means (20), and projection is performed via the imaging state correction means (12) based on the calculation result of this thermal deformation amount calculation means. Optical system (P
The control means (20) for correcting the image forming state of L) is provided.

In this case, mask side position measuring means (15, 16) for measuring the position of the mask stage (RST) may be provided, and the mask side position measuring means may also serve as the relative speed measuring means. Further, as the relative speed measuring means, for example, the anemometer (35) shown in FIG. 7 may be used.

[0013]

In the present invention, in the scan exposure method, the mask is cooled by the atmospheric gas by the scanning of the mask (R), and the cooling action is the scanning speed of the mask, more accurately, the mask and the atmospheric gas. The fact that it changes depending on the relative speed of That is, the relative velocity between the mask and the atmospheric gas is measured by the relative velocity measuring means, and the thermal deformation amount of the mask is calculated from the relative velocity and the irradiation energy of the illumination optical system with respect to the mask.

As a method for obtaining the thermal deformation amount of the mask (R), its relative speed, the kind of the light shielding film such as a chromium film used in the mask or the heat absorption rate of the light shielding film, and the density distribution of the pattern on the mask , Illumination intensity of the illumination light on the mask, irradiation time of the illumination light (when using a shutter,
There is a method of calculating a typical amount of thermal deformation at several points in the mask by numerical calculation based on information such as the open / closed state) and the speed (scanning speed) at which the mask passes through the illumination area of the illumination light. From the thermal deformation amount of the mask thus obtained, the amount of change in the image formation state is obtained by applying a theoretical calculation or a formula in which the actual measurement result is formulated. The image formation state of the projection optical system (PL) is corrected via the image formation state correction means (12) so as to cancel out this change amount. As the image formation state correction means (12), the projection optical system (P) that changes the atmospheric pressure of the pressure chamber between the predetermined lenses in the projection optical system (PL) is used.
Well-known means for changing the image formation state of the projected image can be used by moving or tilting a predetermined lens element in L) in the optical axis direction, or moving or tilting the mask (R) in the optical axis direction. .

As a result, in the scan exposure system,
Even when the scanning speed of the mask is changed, the image formation state can be maintained constant, or the influence of the change in the image formation state can be minimized. In addition, the mask stage (RS
Mask side position measuring means (15, 1) for measuring the position of (T)
When 6) also serves as the relative velocity measuring means, the scanning velocity of the mask (R) is approximately used as the relative velocity between the mask (R) and the atmospheric gas. This is a simple method when the atmospheric gas can be regarded as stationary.

On the other hand, when the anemometer (35) shown in FIG. 7 is used as the relative speed measuring means, even when air for cooling is blown from the air blower or the like to the mask (R). , The relative speed can be measured accurately.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the projection exposure apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a scan exposure type projection exposure apparatus of the present embodiment. In FIG. 1, the illumination light IL generated by a light source 1 passes through a shutter (not shown), and then a collimator lens and a fly are used. The illuminance homogenizing optical system 2 including an eye lens converts the illuminance distribution into a substantially uniform luminous flux. Examples of the illumination light IL include excimer laser light such as KrF excimer laser light and ArF excimer laser light, harmonics of copper vapor laser and YAG laser, or ultraviolet emission lines (g line, i line, etc.) from an ultrahigh pressure mercury lamp. ) Etc. are used. When a laser light source is used, light emission may be switched on / off by a power source unit of the laser light source instead of the shutter.

The illumination light emitted from the illuminance homogenizing optical system 2 is
The beam reaches the beam splitter 4A via the relay lens 3, and most of the light passes through the beam splitter 4A to reach the variable field stop 5. The variable field stop 5 is arranged on a surface optically conjugate with the pattern formation surface of the mask R and the exposure surface of the wafer W, and includes a plurality of movable light shielding portions (for example, two L-shaped movable light shielding plates). The size of the opening (slit width, etc.) is adjusted by opening and closing with a motor. By adjusting the size of the opening, the illumination area IAR for illuminating the mask R is set to a desired shape and size.

On the other hand, the illumination light reflected by the beam splitter 4A is received by an integrator sensor 4B composed of a photoelectric conversion element via a condensing optical system (not shown), and an output signal of the integrator sensor 4B is supplied to the main control system 20. Has been done. The wafer W is integrated by integrating (or integrating in the case of pulsed light emission) output signals of the integrator sensor 4B.
It is possible to monitor the cumulative exposure amount for the mask R and the cumulative irradiation energy for the mask R. The light flux that has passed through the variable field diaphragm 5 illuminates a mask R having a circuit pattern and the like drawn through a relay lens 6 and a dichroic mirror 7. The mask R is vacuum-sucked on the mask stage RST, and the mask stage RST finely moves two-dimensionally in a plane perpendicular to the optical axis IX of the illumination optical system to position the mask R.

Further, the mask stage RST can be moved at a designated scanning speed in a predetermined direction (scanning direction) by a mask driving section (not shown) composed of a linear motor or the like. The mask stage RST has a moving stroke that allows the entire surface of the mask R to cross at least the optical axis IX of the illumination optical system. A movable mirror 15 that reflects the laser beam from the interferometer 16 is fixed to the end of the mask stage RST.
The position of T in the scanning direction is determined by the interferometer 16, for example, 0.
It is constantly detected with a resolution of about 01 μm. Interferometer 1
The position information of the mask stage RST from 6 is sent to the stage control system 19, and the stage control system 19 is based on the position information of the mask stage RST, and a mask drive part (not shown).
The mask stage RST is driven via. A mask R is set at a predetermined reference position by a mask alignment system (not shown).
The mask stage RS so that the
Since the initial position of T is determined, the position of the mask R can be measured with sufficiently high accuracy simply by measuring the position of the movable mirror 15 with the interferometer 16. Further, in this embodiment, the interferometer 1
The measurement result of 6 is also supplied to the main control system 20, and the main control system 2
0 calculates the thermal deformation amount of the mask R from the measurement result and the irradiation energy with respect to the mask R (described later).

Now, the illumination light IL that has passed through the mask R is
For example, it is incident on a projection optical system PL that is telecentric on both sides, and the projection optical system PL has a projected image obtained by reducing the circuit pattern of the mask R by, for example, 1/5 or 1/4, and a photoresist (photosensitive material) is applied to the surface thereof. It is formed on the wafer W. As shown in FIG. 2, in the projection exposure apparatus of the present embodiment, the mask R is formed by the rectangular (slit-shaped) illumination area IAR having the longitudinal direction in the direction perpendicular to the scanning direction (x direction) of the mask R. is illuminated, the mask R is scanned at a velocity V _R in the -x direction (or x direction) at the time of exposure.
The illumination area IAR (the center of which is substantially coincident with the optical axis IX) is projected onto the wafer W via the projection optical system PL to form a slit-shaped exposure area IA. Since the wafer W has an inverted imaging relationship with the mask R, the wafer W is scanned at the speed V _W in synchronization with the mask R in the x direction (or −x direction) opposite to the direction of the speed V _R , The entire surface of the shot area SA on the wafer W can be exposed. Scanning speed ratio V _W
/ V _R is made to those corresponding to the reduction magnification β of exactly the projection optical system PL, the pattern of the pattern area PA of the mask R is accurately reduced and transferred onto the shot area SA on the wafer W. The width of the illumination area IAR in the longitudinal direction is set to be wider than the pattern area PA on the mask R and smaller than the maximum width of the light shielding area ST, and the entire surface of the pattern area PA is illuminated by scan exposure. It has become.

Returning to the explanation of FIG. 1, the wafer W is vacuum-sucked on the wafer holder 9, and the wafer holder 9 is held on the wafer stage WST. The wafer holder 9 can be tilted in an arbitrary direction with respect to the best imaging plane of the projection optical system PL by a driving unit (not shown), can be finely moved in the optical axis IX direction (z direction), and can be moved in the optical axis IX. It is also possible to rotate around. On the other hand, wafer stage WST is configured not only to move in the scan direction (x direction) described above, but also to move in a direction (y direction) perpendicular to the scan direction so that it can be arbitrarily moved to a plurality of shot areas. , A step-and-scan operation in which the operation of scanning and exposing each shot area on the wafer W and the operation of moving to the next shot exposure start position are repeated. The wafer stage drive unit (not shown) such as a motor is mounted on the wafer stage WST.
Are driven in the xy directions.

An interferometer 1 is provided at the end of wafer stage WST.
The movable mirror 17 that reflects the laser beam from the laser beam No. 8 is fixed, and the position of the wafer stage WST in the xy plane is constantly detected by the interferometer 18 with a resolution of, for example, about 0.01 μm. The position information (or speed information) of wafer stage WST is sent to stage control system 19, and stage control system 19 controls wafer stage WST based on this position information (or speed information).

Further, in the vicinity of the wafer holder 9 on the wafer stage WST, a dose monitor 22 composed of a photoelectric conversion element so that the light receiving surface is at the same height as the exposure surface of the wafer W.
Is installed and the output signal of the dose monitor 22 is the main control system 2
It is being supplied to 0. The dose monitor 22 is connected to the projection optical system P.
Wafer W by moving into the L exposure field
The exposure amount (irradiation energy) on the exposure surface of can be monitored. In this embodiment, as will be described later, the transmittance distribution of the mask R (distribution of pattern existence rate) is measured by using the dose monitor 22.
To measure.

Further, in FIG. 1, a TTL (through the lens) type wafer alignment system for detecting the position of an alignment mark (wafer mark) for alignment on the wafer W is provided, and the alignment system thereof is provided. Is supplied to the main control system 20 that controls the operation of the entire apparatus, and the main control system 20 calculates the array of shot areas on the wafer W from the measured positions of the wafer marks.

In the wafer alignment system, as the light source 23, a light source such as a He-Ne laser beam that emits light having a wavelength that does not expose the photoresist to light is usually used. The light flux generated by the light source 23 enters the beam splitter 26. The light beam reflected by the beam splitter 26 is reflected by the mirror 25 and then projected by the projection optical system P.
The wafer mark for alignment on the wafer W is illuminated via L. The reflected light or diffracted light from the wafer mark is again received by the photoelectric sensor 24 via the projection optical system PL, the mirror 25, and the beam splitter 26. This detection signal is supplied to the main control system 20, and the main control system 20 obtains the array coordinates of the chip patterns already formed in each shot area on the wafer W from the measured coordinates of the wafer mark. As a result, the wafer W that was previously exposed and processed
Mask R for the chip pattern of each shot area of
The wafer W is aligned so that the projected images of are accurately superimposed and exposed. Although various methods for aligning the wafer W have been proposed, other methods can be used as well.

Further, the apparatus shown in FIG. 1 supplies an image forming light beam for forming a pinhole or a slit image toward the best image forming plane of the projection optical system PL from an oblique direction with respect to the optical axis IX direction. The oblique incidence type wafer position detection system (focus detection system) including the irradiation optical system 13 and the light receiving optical system 14 that receives the reflected light flux of the imaged light flux on the surface of the wafer W through the slit is projected. It is fixed to a support portion (not shown) that supports the optical system PL. The configuration of the wafer position detection system is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112, and the position deviation of the wafer surface in the vertical direction (z direction) with respect to the image plane by the wafer position detection systems 13 and 14 is described. Is detected, the wafer holder 9 is driven in the z direction so that the wafer W and the projection optical system PL maintain a predetermined distance. Wafer position information from the wafer position detection system is transferred to the main control system 20.
To the stage control system 19 via. The stage control system 19 determines the wafer holder 9 based on the wafer position information.
Are driven in the z direction.

In the present embodiment, the angle of the parallel flat glass (plane parallel) (not shown) provided inside the light receiving optical system 14 is adjusted in advance so that the image plane becomes the zero point reference, and the wafer position is detected. The system shall be calibrated. Further, for example, Japanese Patent Laid-Open No. 58-113706
The horizontal position detection system as disclosed in Japanese Patent Publication No. JP-A-2003-242242 is used, or the wafer position detection system is configured so as to be able to detect the focal positions at arbitrary plural positions within the exposure field of the projection optical system PL (for example, By forming a plurality of slit images in the exposure field), the inclination of a predetermined area on the wafer W with respect to the image plane may be detected.

Further, the apparatus shown in FIG. 1 is provided with a correction mechanism for correcting the image forming characteristic of the projection optical system PL. This correction mechanism corrects changes in the image forming characteristics of the projection optical system PL itself due to atmospheric pressure changes, absorption of illumination light, and the like, and at the same time, the pattern of the mask R is adjusted so as to cancel the distortion of the projected image due to thermal deformation of the mask R. It works to distort the projected image. The correction mechanism will be described below. The imaging characteristics of the projection optical system PL include focal position, field curvature, distortion, magnification error, astigmatism, etc., and mechanisms for correcting them are conceivable, but here, the distortion and magnification error of the projection image are related. Only the correction mechanism will be described.

As shown in FIG. 1, in this embodiment, the imaging characteristic control unit 12 drives the mask R or the lens element 27 in the projection optical system PL to correct the imaging characteristic. In the projection optical system PL, the lens element 27 closest to the mask R is fixed to the support member 28, and the lens element 2 following the lens element 27 is fixed.
.. are fixed to the main body of the projection optical system PL. In the present embodiment, the optical axis IX of the projection optical system PL indicates the optical axis of the main body of the projection optical system PL below the lens element 29. A plurality of support members 28 are expandable and contractible (at least two or more, two are shown in FIG. 1)
Is connected to the main body of the projection optical system PL via the drive element (for example, piezo element) 11.

Here, the lens element 27 has the optical axis IX.
When the image is translated in the direction of, the projection magnification (enlargement / reduction rate of the size of the projected image) changes at a rate of change according to the amount of movement.
Next, when the lens element 27 is inclined with respect to the plane perpendicular to the optical axis IX, a trapezoidal distortion occurs in the originally rectangular projected image. Next, the case of driving the mask R will be described. The mask R is mounted on the mask stage RST as described above. Mask stage R
ST is a plurality of expandable and contractible (at least two, two in FIG. 1) drive elements (eg, piezo elements) 10
Is connected to a mask base (not shown). Since the mask base and the projection optical system PL are fixed to a main body (not shown) of the projection exposure apparatus, the distance between the projection optical system PL and the mask R can be changed by the drive element 10. Here, when the mask R moves in parallel in a predetermined direction along the optical axis IX, so-called pincushion distortion occurs, and when the mask R moves in the opposite direction, so-called barrel distortion occurs.

When the mask R or the lens element 27 is driven as described above, the focus position or the image plane changes accordingly, but the amount varies from each drive amount to the main control system 2.
0 can be calculated. Then, the main control system 20 adds an offset to the zero reference of the wafer position detection systems 13 and 14 by the amount calculated, and controls so that the exposure surface of the wafer W is always at the focus position. Accordingly, even if the focus position or the image plane position of the projection optical system PL changes due to the driving of the mask R or the lens element 27, the focus position or the image plane position is adjusted according to the change.

In the case of the batch exposure method, the exposure can be performed by canceling the influence of the thermal deformation amount of the mask R by changing the projected image of, for example, a square into an arbitrary shape by a combination of the above methods. . However, when the exposure is performed by the scan exposure method, the mask R is scanned with respect to the illumination area, and thus the thermal deformation amount of the mask R is accurately obtained as follows.

First, let us consider the transfer of the amount of heat between two objects, for example. It is considered that the movement of the amount of heat in this case is basically proportional to the temperature difference between the two objects. Further, the rate of change of the temperature change due to the movement of the heat amount is proportional to the movement amount of the heat amount. The amount of heat transferred is ΔQ, the temperatures of two objects are T ₁ and T, respectively.
_2, the elapsed time t, when the the K _1, K _2, K ₃ proportional constant, the following relation.

[0035]

[Formula 1] ΔQ = K ₁ (T ₁ −T ₂ ), (T ₁ > T ₂ ).

[0036]

## EQU2 ## dT ₁ / dt = -K ₂ ΔQ

[0037]

## EQU3 ## dT ₂ / dt = K ₃ ΔQ From (Equation 1) to (Equation 3), the following equation is established using the coefficients K ₄ and K ₅ .

[0038]

## EQU4 ## dT ₁ / dt = -K ₄ (T ₁ -T ₂ )

[0039]

## EQU5 ## dT ₂ / dt = K ₅ (T ₁ −T ₂ ) These are first-order lag systems, as is well known, and when there is a temperature difference between the temperatures T ₁ and T ₂ , Both draw an exponential curve and reach a certain temperature. The heat distribution on the mask R is calculated based on the above equation.

In this case, as shown in FIG. 3A, the mask R is vertically and horizontally divided into, for example, 4 × 4 blocks B1 to B16. P1 is the center of each of the blocks B1 to B4
~ P4. Attention is first focused on block B1 in FIG. The block B1 exchanges heat with the adjacent blocks B5 and B2 (heat conduction). In addition, the mask stage RST of FIG.
Also, heat is exchanged with the air, but here, for simplicity, the temperature of the air and the temperature of the mask stage RST are constant. The temperature of each block B1 to B16 is set to T ₁ to
Assuming that T _{16 is} the temperature of the air contacting the mask R, T _{0 is} the temperature of the mask stage RST, and T _H is the temperature of the mask stage RST, the following expression holds for the temperature T _{1 of the} block B1.

[0041]

[6] _{dT 1 / dt = K 12 (} T 2 -T 1) + K 15 (T 5 -T 1) + K 10 (T H -T 1) + K 0 (T 0 -T 1) + K P η 1 P Here, dT ₁ / dt is the time derivative of T ₁ , K ₁₂ and K ₁₅ are coefficients (heat diffusion coefficient) of heat transfer between the block B1 and the blocks B2 and B5, respectively, and K ₁₀ is the mask stage RS.
The thermal diffusion coefficient between T and the block B1, K ₀ is the thermal diffusion coefficient between each block and air, η ₁ is the pattern existence rate of the block B1, P is the power of the light source, and the dose monitor 22
The value K _P corresponding to the output of is a coefficient that correlates the amount of heat absorbed by each block of the illumination light with η ₁ and P.
The thermal diffusion coefficient K ₀ is represented by a function (K ₀ = F (V _R )) of the scanning speed V _R of the mask stage RST, and shows the state of the cooling effect by the scanning of the mask stage RST.

The last term of (Equation 6) shows the amount of heat absorbed from the illumination light, and the other terms show the process in which the absorbed heat diffuses. Here, T _H and T ₀ are constant, T _H = T _0, and the temperature of each block is (T ₀ + Δ
T _i ), and considering that all blocks on the mask R are made of quartz glass, K ₁₂ , K ₁₃ , ... Like

[0043]

## EQU7 ## dΔT ₁ / dt = K _R (ΔT ₂ −ΔT ₁ ) + K _R (ΔT ₅ −T ₁ ) + K _H (−ΔT ₁ ) + K ₀ (−ΔT ₁ ) + K _P η ₁ P = (− 2K _R− K _H −K ₀ ) ΔT ₁ + K _R ΔT ₂ + K _R ΔT ₅ + K _P η ₁ P, (K _R = K ₁₂ = K ₁₃ = ...) (Equation 7) is obtained for each of the blocks B1 to B16. , Matrix expression is as follows.

[0044]

[Equation 8]

This is a 16-dimensional system of simultaneous differential equations, and can be solved by a numerical method.
Alternatively, it is also possible to solve the problem by expressing the differential form as a difference of a certain minute time (calculation cycle of a computer in the main control system 20) in a difference form, that is, a difference method. In (Equation 8), the so-called external force term is the final term, so if the values of each block per unit time, that is, the values of η ₁ , P ₁ , η ₂ , P ₂ ... ΔT ₁ , Δ for each
The value of T ₂ can be obtained. The pattern existence ratios η ₁ , η ₂ ... Are obtained by the method described later, and the incident light amounts P ₁ , P ₂ ... Are obtained from the output signal of the integrator sensor 4B in FIG.

Further, each coefficient K_R, K₀ , K_H, K_PIs
Mask R, physical properties of air, flow velocity of air, scanning speed of mask R
Degree V_RIt is possible to calculate from the above. Furthermore, the seed
Experiments were carried out for various masks R, and each coefficient was actually the best match.
It is also possible to decide so. Next, (Equation 8)
To solve, the pattern existence rate η of each block of the mask R is₁
~ Η ₁₆However, the pattern existence rate is a mask
It is obtained by measuring the partial transmittance of R.
Thus, in FIG. 1, the partial transmittance of the mask R is
To obtain, the irradiation amount on the wafer stage WST
A projected image of each block of the mask R on the light receiving surface of the monitor 22.
Provide a smaller light receiving opening. And the dose monitor
22 is set in the exposure field of the projection optical system PL.
In this state, the mask R is scanned and the irradiation amount monitor 22 outputs it.
Divide the force signal by the output signal without mask R
Yes.

However, when the exposure light source is a pulse light source such as an excimer laser light source, the exposure energy for each pulse emission varies, so that the output signals of the integrator sensor 4B are simultaneously detected and irradiation is performed using the output signal of the integrator sensor 4B. It is necessary to correct the output signal obtained by the quantity monitor 22. Then, the following two methods are conceivable as a method for obtaining the distribution of the pattern existence rate of the mask R from the transmittance distribution thus measured. The first method is a method of obtaining the pattern existence rate of the mask R using the average value of the output signals of the irradiation amount monitor 22 (further, the integrator sensor 4B) during the first first scanning. This method is effective when the pattern is uniformly distributed over the entire surface of the mask R or when the scanning speed V _R is high.

On the other hand, when the average value causes a large error from the actual output signal, the second method is used. In the second method, when obtaining the pattern existence rate, the transmittance of the mask R is stored in correspondence with the coordinates of the mask stage RST, and the read transmittance is used according to the coordinates of the mask stage RST. . This method
Or have the pattern on the mask R is present are concentrated in certain portions, in the method using the average value as in the first method slow scanning speed V _R, if the error becomes large is effective like.

Next, by scanning the mask R, wind (air flow) hits the surface of the mask R to cool the mask R. The effect is that the irradiation energy of the illumination light causes thermal expansion of the pattern on the mask R. The effect on the The effect of cooling the surface of the mask R by scanning the mask R is that the scanning speed V _R (more accurately, the relative speed between the mask R and the atmospheric gas) and the thermal diffusion coefficient on the surface of the mask R. The correlation with K ₀ as shown in FIG. 4 may be measured.
The thermal diffusion coefficient K ₀ is, as introduced in (Equation 6),
It is a coefficient representing the transfer of heat between each block of the mask R and the air in contact with it.

FIG. 5 is an explanatory diagram of the thermal diffusion coefficient K _0. The horizontal axis of FIG. 5 shows the elapsed time t from the start of exposure, and the vertical axis shows the average temperature T _R of the mask R at time t. In this case, in the curves 32A to 32D, the scanning speeds of the mask R during scanning exposure are V _{RA to} V _RD (V _RA <V _RB <V _RC <, respectively.
V _RD ) and the temperature characteristics when the speed is gradually increased. From FIG. 5, as the scanning speed of the mask R is increased, the irradiation energy accumulated in the mask R becomes more efficient to the surrounding gas (air). It can be seen that the temperature rise of the mask R is small due to diffused diffusion. Thus, the scanning speed V of the mask R
_Since the thermal diffusion efficiency from the mask R increases as _R becomes faster, the thermal diffusion coefficient K _{0 in} FIG. 4 also becomes larger as the scanning speed V _R becomes faster. However, the degree of increase is gradually decreasing.

[0051] Therefore, although the thermal diffusivity K ₀ from the characteristics of FIG. 5 is determined, the scanning speed V _R of the first mask for the
It is necessary to accurately detect (more accurately, the relative velocity between the mask R and the atmospheric gas). A method of detecting the scanning speed V _R of the mask R will be described. The position of the mask stage RST on which the mask R is placed is constantly measured in the scanning direction by the mask-side interferometer 16. Therefore, the main control system 20 can obtain the scanning speed V _R by performing processing such as differentiating the output signal from the interferometer 16. Position of the thus mask stage RST is constantly measured by the interferometer 16 of the mask side, since the scanning speed V _R of the mask R from the output signal is ready to constantly detected, differences and the scanning speed V _R, the mask The degree of correction of the image formation state due to thermal expansion of the mask R can be adjusted by the difference such as whether R is scanning or stopped.

FIG. 6 shows the amount of change in the image forming characteristics in various cases. In FIG. 6, straight lines 33A and 33B show the image forming characteristics when the scanning speed V _R is high and low during exposure, respectively. The change amount trends, and the straight lines 33C, 33D, and 33E respectively show the change amount tendency of the imaging characteristics when the scanning speed V _R is high, low, and 0 during non-exposure. The slopes of the straight lines 33A to 33E indicate the rate of change in the imaging characteristics, and the negative slopes of the straight lines 33C to 33E indicate that the temperature of the mask R gradually decreases during non-exposure. The slopes of the straight lines 33A and 33B are respectively tan θ ₁
And tan θ ₂ , the slopes of the straight lines 33C, 33D and 33B are −tan θ ₃ , −tan θ ₄ and −tan θ _{5 respectively.}
Then, the following relationship is established.

[0053]

[Mathematical formula-see original document] θ ₁ <θ ₂ and θ ₃ > θ ₄ > θ _{5 As} can be seen from FIG. 6, the imaging speed changes due to the change in the scanning speed V _{R in} both cases of exposure and non-exposure. Change rate is different. Therefore, it is necessary to calculate (Equation 8) using the thermal diffusion coefficient K ₀ , which is a function of the scanning speed V _R , as a parameter.

In the above description, the mask R
Scanning speed V_RAnd coefficient of thermal expansion (or coefficient of thermal diffusion K₀) Relationship
I am looking for a person in charge, but more accurately, the problem is the scanning speed
Degree V _RNot by the relative velocity of the mask R and the atmosphere gas
Yes, the thermal expansion amount of the mask R changes according to this relative speed
To do. Therefore, the mass obtained by the interferometer 16 on the mask side
Scan speed V of R_ROf the relative velocity with the atmosphere gas
Used as an approximation. In this regard, actually a mask
To accurately measure the relative velocity between R and the atmosphere gas,
If you install an anemometer at one end of the 1st mask stage RST
Good. If you use the measurement result of the wind speed with this anemometer,
An air conditioner in the environmental chamber where the shadow exposure device is installed
Accurate phase considering the influence of the wind sent from
It can measure the velocity versus speed and correct the thermal expansion of the mask R more accurately.
It can be carried out.

As described above, the scanning speed V_R(More accurate
, The relative velocity between the mask R and the atmospheric gas is measured.
And from FIG. 4, the thermal diffusion coefficient K₀Is required. in this way
Thermal diffusion coefficient K obtained by₀Substituting into (Equation 8)
From the temperature distribution ΔT of each block of the mask R₁~ ΔT₁₆
Is required. Of these and the quartz glass that is the material of the mask R
Based on the coefficient of thermal expansion, each block B of the mask R in FIG.
Center point P of 1 to B16 ₁~ P₁₆The mutual distance change of
And the movement of each point on the mask R can be determined,
For example, the mask R is deformed as shown in FIG. This
When the amount of thermal deformation of the mask R is obtained, the image of the mask R
Projection when the wafer is projected onto the wafer W via the projection optical system PL.
The variation amount of the image, that is, the variation amount of the image forming characteristic is obtained. So
Here, the main control system 20 of FIG.
Then, the image formation characteristic is adjusted so as to cancel out the variation in the image formation characteristic.
Make a correction. This allows the same mask R to be used for scanning.
Even if the exposure is repeated, it is projected on the wafer W.
The pattern image of the mask R is always kept constant
It

Next, a modification of the above embodiment will be described. First, in the above-described embodiment, the temperature distribution of the mask R is obtained from (Equation 8) after obtaining the thermal diffusion coefficient K ₀ . However, the total coefficient of thermal expansion of each block of the mask R including the coefficient of thermal expansion of the pattern of the mask R may be directly measured. According to this method, the thermal diffusion coefficient K ₀
As compared with the case where is independently calculated as a function of the scanning speed V _R , factors such as the material of the pattern of the pattern area PA of the mask R and the pattern existence rate in the pattern area PA can be accurately considered. And the overall thermal expansion of the mask R, an example of obtaining the relationship between the scanning speed V _R, the mask R
The material of the pattern of the pattern area PA that is drawn on a mask R (light shielding film), the pattern existence ratio in the pattern area PA, irradiation energy of the illumination light, based on the scanning speed V _R of a mask or the like R, theoretically This is a method of obtaining the overall coefficient of thermal expansion. Further, as another way of obtaining, while scanning the mask R at a constant speed, the mask R is continuously irradiated with the illumination light, and the pattern image of the mask R is printed on the wafer W at regular intervals to obtain the pattern image. There is also a method in which the thermal expansion amount of the mask R is measured by actually measuring the distortion and the magnification, and thereby the total thermal expansion coefficient is obtained.

In addition, the scanning speed V _R is changed to various values, the mask R is scanned, and the temperature distribution on the surface of the mask R is measured while the illumination light is being radiated to the mask R. , The state of heat transfer between the light-transmitting portion and the light-shielding portion in the pattern area PA of the mask R, the state of expansion of the pattern area PA, and the like are examined, and from these results, the overall heat of the mask R with respect to the scanning speed V _R is examined. There is also a method of obtaining the expansion coefficient.

Next, in the above-mentioned embodiment, the relative velocity between the mask R and the atmospheric gas is measured and corrected. However, the surface of the mask R is constantly exposed to the air of a constant wind velocity so that the mask R There is also a method of eliminating a change in the imaging characteristic due to the presence or absence of the scanning and the difference in the scanning speed V _R and always applying a constant correction to the imaging characteristic. FIG. 7 shows a main part of a system configuration for keeping the wind speed constant. In FIG. 7, the mask stage RST holding the mask R is slidable in the x direction on the mask base 34 via the drive element 10. The coordinate of the mask stage RST in the x direction is constantly measured by the interferometer 16. The air blower 36 of the air blower is arranged in the side surface of the mask stage RST in the x direction, and the air whose velocity is variable is blown from the air blower 36 to the mask stage RST. Further, an anemometer 35 is fixed to one end of the mask stage RST on the side of the blower port 36, and the anemometer 35 measures the relative velocity of the mask stage RST and thus the mask R and the atmospheric gas (air). Therefore, the scanning speed V of the mask stage RST
Even if _R changes, the relative speed between the mask R and the atmospheric gas can be made constant by controlling the wind speed or the air volume of the blower so that the wind speed measured by the anemometer 35 becomes constant.

However, unlike the arrangement of FIG. 7, air may be blown to the mask R from the air blower at a constant speed in a direction (non-scanning direction) perpendicular to the paper surface of FIG. Even in this case, the relative velocity between the mask R and the atmospheric gas can be regarded as substantially constant by setting the wind velocity of the air to be considerably higher than the scanning velocity V _R of the mask R. In addition to using the anemometer 35 as described above, the temperature distribution on the surface of the mask R in FIG. 7 is constantly monitored by a temperature sensor or the like so that the temperature of the surface of the mask R is always constant. The amount of air blown onto the mask R may be controlled. By this method, the state of the mask R (heat-deformed state) is always kept constant, and the image formation state can be kept excellent.

In addition, the pattern of the mask R is set on the wafer W.
Even when it is not exposed to light, the mask R may be scanned to cool the mask R and return to a state where the correction of the imaging characteristic using the imaging characteristic control unit 12 of FIG. 1 is not performed as much as possible. . This principle will be described with reference to FIG. Figure 8
Shows the relationship between the correction amount C of the image forming characteristic by the image forming characteristic control unit 12 and the corresponding change amount F of the image forming state. In FIG. 8, the straight line 37 represents the correction amount C of the image forming characteristic and The theoretical relationship with the corresponding change amount F of the image formation state is shown. However, in reality, the correction amount C of the image formation characteristic by the image formation characteristic control unit 12 has variations in reproducibility. Assuming that the variation in reproducibility is ΔC, in the range 38 where the correction amount C is equal to or less than ΔC in the straight line 37, the variation in the image formation characteristic variation F may become too large due to the image formation characteristic correction. In other words, if the image forming characteristic is not corrected in the range 38, the image forming characteristic may be better maintained. Therefore, the image forming characteristic is not corrected in the range 38.

On the straight line 37, the correction amount C is ΔC.
In the range 39 exceeding the range, the amount of change F of the imaging characteristics is corrected by the correction by exceeding the variation of the reproducibility. Therefore, in the range 39, it is desirable to perform the correction using the imaging characteristic control unit 12. Further, in the range 39, since the image forming characteristic varies due to the correction of the image forming characteristic, the state of the mask R is set to the range 38 so that the correction is not required. It is this method to scan R and cool mask R as fast as possible.

Further, in FIG. 1, position detecting marks are periodically formed in the pattern area of the mask R vertically and horizontally, and the positions of these position detecting marks are directly measured by a position detecting device (not shown). Therefore, a method of obtaining the thermal deformation amount of the mask R can be considered. Next, a thin film (so-called pellicle) for preventing foreign matter adhesion may be stretched on both surfaces (may be one surface) of the mask R via a rectangular frame. When the pellicle is stretched on the mask R in this way, even if the mask R is scanned, the wind does not hit the surface of the mask R, so that the cooling effect due to the wind accompanying the scanning of the mask R cannot be expected. In this case, the scanning speed V of the mask R
_R (more accurately, the relative velocity with the atmospheric gas) is removed from the correction formula for thermal expansion, and a correction formula corresponding to (Equation 8) is obtained from a theoretical formula or an empirical formula obtained by actually irradiating the mask R. Seeking,
It is necessary to distinguish the correction method depending on the presence or absence of the pellicle.

As described above, the present invention is not limited to the above-mentioned embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0064]

According to the present invention, the relative velocity between the mask and the atmospheric gas is measured, the thermal deformation amount of the mask is calculated based on the measurement result and the irradiation energy, and the projected image resulting from this thermal deformation amount is calculated. By correcting the image forming characteristic of the projection optical system so as to cancel out the distortion of the image forming apparatus, it is possible to favorably correct the variation amount of the image forming characteristic caused by the thermal deformation of the mask in the scan exposure type projection exposure apparatus. is there. This also improves the overlay accuracy when exposing a multi-layered pattern on the photosensitive substrate.

Further, since a light-absorbing material can be used as the material of the light-shielding film for forming the mask pattern, the light-shielding film does not adversely affect the optical system such as the projection optical system such as flare. You can choose. Also,
When the mask side position measuring means for measuring the position of the mask stage is provided, and this mask side position measuring means also serves as the relative speed measuring means, the relative speed measuring means is not particularly provided, and the relative position is measured by a simple device configuration. Velocity can be measured approximately.

When the relative velocity measuring means is an anemometer, even when the atmospheric gas is flowing,
The relative velocity between the atmospheric gas and the mask can be measured with higher accuracy.

[Brief description of drawings]

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

FIG. 2 is a perspective view for explaining a scan exposure method.

FIG. 3A is a plan view showing a state in which the mask is divided into 16 blocks, and FIG. 3B is a view showing a modified example of the center of each block of the mask.

FIG. 4 is a diagram showing a relationship between a mask scanning speed V _R and a thermal diffusion coefficient K ₀ .

FIG. 5 is a diagram showing an example of changes over time in the temperature T _R of the mask when the scanning speed V _R of the mask changes.

FIG. 6 is a diagram showing an example of the amount of change in the imaging characteristics depending on the scanning speed V _R of the mask during exposure and during non-exposure.

FIG. 7 is a modification of the embodiment, which is a mask stage RST.
It is a block diagram which shows the principal part when the anemometer 35 is provided above.

FIG. 8 is a diagram showing the relationship between the correction amount of the image formation characteristic and the change amount of the image formation characteristic.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 illuminance distribution uniforming optical system 3, 6 relay lens 4B integrator sensor 5 variable field diaphragm R mask PL projection optical system W wafer RST mask stage WST wafer stage 10, 11 drive element 12 imaging characteristic control unit 16 mask side Interferometer 18 Interferometer on wafer side 19 Stage control system 20 Main control system 22 Irradiation amount monitor 27 Lens element

Claims (3)

[Claims] 1. An illumination optical system for illuminating a predetermined illumination area on a mask on which a transfer pattern is formed, a projection optical system for projecting a pattern image of the mask onto a photosensitive substrate, and a mask for holding the mask. A mask stage that scans the mask with respect to the illumination region, and a substrate stage that holds the photosensitive substrate and scans the photosensitive substrate with respect to a region conjugate with the predetermined illumination region, By scanning the photosensitive substrate through the substrate stage at a speed corresponding to the projection magnification of the projection optical system in synchronization with scanning the mask at a predetermined speed through the mask stage, a pattern image of the mask is obtained. In a projection exposure apparatus for sequentially projecting and exposing on the photosensitive substrate, an imaging state correction means for correcting the imaging state of the projection optical system, a phase of the mask and a gas in contact with the mask. Relative velocity measuring means for measuring the velocity, deformation amount calculating means for calculating the thermal deformation amount of the mask from the measurement result of the relative velocity measuring means and the irradiation energy from the illumination optical system to the mask, A projection exposure apparatus comprising: a control unit that corrects the image formation state of the projection optical system via the image formation state correction unit based on the calculation result of the deformation amount calculation unit. 2. The projection exposure apparatus according to claim 1, further comprising mask-side position measuring means for measuring the position of the mask stage, wherein the mask-side position measuring means also serves as the relative speed measuring means. 3. The projection exposure apparatus according to claim 1, wherein the relative speed measuring means is an anemometer.