JPH0883752A - Device and method for projection exposure - Google Patents

Abstract

PURPOSE: To improve the base line measuring accuracy of a projection exposing device by correcting the interval value between a detection center and the projected point of a reference point in accordance with the deviated amount of a prescribed height position against a reference plane in the direction of optical axis. CONSTITUTION: A reference mark FM1 is detected by means of an off-axis alignment system. A main control system MCS stores the detection error amount (correcting amount) of the mark FM1 on the basis of detected results when the off-axis alignment system detects the mark FM1 at the best focusing position in a storage device 21 by correlating the error amount with the deviated amount of the alignment system in Z-direction from the best focusing position of the alignment system at the height position of the mark FM1. At the time of performing base line measurement, the system MCS corrects the amount of the base line by outputting a correcting amount from the storage device 21 in accordance with the error amount between the best focusing position of a projection optical system PL and the best focusing position of the alignment system.

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 which exposes a pattern formed on a mask onto a photosensitive substrate such as a semiconductor wafer or a glass plate for liquid crystal, and particularly, to increase the baseline of an off-axis alignment system. The present invention relates to a projection exposure apparatus and method having a function of accurately controlling.

[0002]

2. Description of the Related Art Conventionally, regarding the baseline measurement of a projection exposure apparatus equipped with an off-axis alignment system,
It is disclosed in Japanese Patent Laid-Open No. 5-324923. A reference plate is provided on a wafer stage that holds a photosensitive substrate (wafer). Off-axis
A first fiducial mark detectable by the alignment system,
A second fiducial mark, which can be detected by a through-the-reticle (TTR) type alignment system, is juxtaposed in a predetermined design positional relationship. Then, the position of the stage is fixed at a predetermined position, and the amount of positional deviation between the mark on the mask (reticle) and the second reference mark is detected by the TTR type alignment system, and at the same time, the off-axis alignment system is used to detect the position deviation. 1 The amount of displacement of the reference mark from the detection center is detected. A projection point of the center point of the reticle by the projection optical system, based on these detected two positional deviation amounts and a design distance (including manufacturing error) between the first reference mark and the second reference mark, Calculate the distance (baseline amount) from the detection center of the off-axis alignment system.

When a pattern on a reticle is exposed on a wafer, an alignment mark attached to each of a plurality of shot areas already formed on the wafer is detected by an off-axis alignment system. The off-axis alignment system irradiates the alignment mark on the wafer with light and detects the image of the alignment mark by the reflected light with a television camera (CCD camera). At this time, the height position of the alignment mark (the position in the optical axis direction of the projection optical system) is controlled so that the image of the alignment mark taken by the CDD camera becomes the best. Hereinafter, this height position is defined as "the best focus position of the off-axis alignment system". Then, by controlling the position of the wafer stage based on the detection result of the alignment mark by the off-axis alignment system and the previously obtained baseline amount, the pattern in the shot area and the projected image of the pattern on the reticle can be obtained. It is possible to accurately overlay and expose.

[0004]

In the conventional technique as described above, when measuring the baseline amount, the surface of the reference plate is aligned with the image plane of the projection optical system. Therefore, the distance between the projection point of the reticle center point in the image plane of the projection optical system by the projection optical system and the detection center of the off-axis alignment system is detected as the baseline amount. At this time, the best focus position of the off-axis alignment system coincides with the height position of the image plane of the projection optical system (hereinafter, this height position is referred to as the "best focus position of the projection optical system"). Not necessarily. When the projection exposure apparatus is manufactured, even if these two best focus positions are at the same height position, the best focus positions may be displaced due to, for example, fluctuations in atmospheric pressure.

In the off-axis alignment system, if the height position of the mark to be detected is different, an error will occur in each detection result. One of the causes for this is, for example, the inclination of the optical axis of the off-axis alignment system with respect to the optical axis of the projection optical system (hereinafter, this inclination is referred to as "telecentric inclination"). Another cause is aberrations (such as astigmatism and coma) of the optical system of the alignment system.

From the above, if the best focus position of the projection optical system and the best focus position of the off-axis alignment system are different at the time of baseline measurement, the above-mentioned telecentric inclination, aberration, etc. are added to the calculated baseline amount. There is a problem in that an error corresponding to is generated. The present invention has been made in view of the above conventional problems, and an object of the present invention is to obtain a projection exposure apparatus and method in which the baseline measurement accuracy is improved.

[0007]

A projection exposure apparatus according to the present invention is a projection optical system (PL) for projecting an image of a pattern of a mask (R) onto a photosensitive substrate (W) as shown in FIG. 1, for example.
And a stage (WS) which holds the photosensitive substrate (W) and is movable in a plane perpendicular to the optical axis (AX) of the projection optical system (PL).
T) and a reference plate (F) provided on the stage (WST) and having a reference pattern of a predetermined shape formed thereon.
P) and the photosensitive substrate (W) are arranged at a predetermined height position in the optical axis direction of the projection optical system (PL), and a first pattern for alignment formed on the photosensitive substrate (W) is formed. First pattern detection system for detection (4 to 7, 20, MC
S), a reference point on the mask (R), or a second pattern and a reference pattern formed at a predetermined point on the mask (R) having a fixed positional relationship with the reference point, and a projection optical system (P).
L) to detect the relative positional relationship between the second pattern and the reference pattern.
8), the first pattern detection system (4 to 7, 20, MCS) and the second pattern detection system are used for the reference pattern arranged in a predetermined reference plane perpendicular to the optical axis (AX). Based on each detection result when (10 to 18) is detected, the detection center of the first pattern detection system (4 to 7, 20, MCS) in the reference plane and the projection optical system (PL) of the reference point are used. Measuring means (MCS) for obtaining the distance from the projection point and correction means for correcting the value of the distance obtained by the measuring means (MCS) according to the amount of deviation of a predetermined height position with respect to the reference plane in the optical axis direction. 20, MC
S) and.

In the projection exposure method of the present invention, the image of the pattern of the mask (R) is projected and exposed on the photosensitive substrate (W) through the projection optical system (PL). ) Projection optics of the detection center of the pattern detection system (4 to 7) for detecting the alignment pattern formed on the mask and the projection point of the reference point on the mask (R) by the projection optical system (PL). An interval in a predetermined reference plane perpendicular to the optical axis (AX) of the system (PL) is obtained, and the pattern detection system (4 to
In the projection exposure method of arranging the photosensitive substrate (W) at a predetermined exposure position according to the detection result and the interval when 7) detects the alignment pattern, the pattern detection system (4 to
7) depending on the amount of deviation in the optical axis direction between the height position in the optical axis direction of the projection optical system (PL) in which the photosensitive substrate (W) is arranged when detecting the alignment pattern, and the reference plane. The position of the photosensitive substrate (W) in the direction perpendicular to the optical axis (AX) is adjusted, and the photosensitive substrate (W) is placed at the exposure position.

[0009]

According to the present invention, for example, as shown in FIG. 7, by using a reference pattern formed on a reference plate, a reference point on a mask (reticle) on a predetermined reference plane (image plane of the projection optical system) The distance between the projection point of the projection optical system and the detection center point of the first pattern detection system is measured as the baseline amount. Here, the height position where the photosensitive substrate is arranged when the first pattern detection system detects the pattern formed on the substrate is the position of Z ₂ shown in FIG. 7. This position is the best focus position of the first pattern detection system. The correction means is a shift amount (Z ₁ − between the height position Z ₁ of the image plane of the projection optical system and the best focus position Z ₂ of the first pattern detection system).
Correct the baseline amount according to Z ₂ ). At this time, the correction means, for example, corrects the correction amount of the baseline amount by the shift amount (Z
₁ -Z ₂₎ is calculated based on. Further, the correction amount may be stored in advance in association with the shift amount (Z ₁ −Z ₂ ).

As described above, the image plane of the projection optical system and the first
Even if the best focus position of the pattern detection system is deviated in the optical axis direction of the projection optical system, the baseline amount can be measured with high accuracy.

[0011]

1 is a diagram showing a schematic construction of a projection exposure apparatus according to an embodiment of the present invention. In FIG. 1, the reticle R is provided with a circuit pattern to be exposed on the wafer W and reticle marks RM ₁ and RM ₂ for alignment. The reticle stage RST can be moved in the X and Y directions by a drive system RSC such as a motor, and can further rotate in the XY plane. The moving amount or moving position is successively measured by three laser interferometers IRX, IRY, and IRθ. In FIG. 1, the laser interferometer I
Although only RX is shown, laser interferometers IRY and IRθ are arranged in a direction (Y direction) perpendicular to the plane of FIG. The rotation amount of the reticle stage RST about the Z axis (coordinate axis parallel to the optical axis AX) is obtained by the difference between the measurement values of the interferometers IRY and IRθ, and the movement amount in the Y axis direction is the interference system I.
It is calculated by the addition average value of the measured values of RY and IRθ, and the movement amount in the X-axis direction is calculated by the interferometer IRX.

The reticle R is irradiated with illumination light from an illumination optical system (not shown), and the circuit pattern on the reticle R is image-projected onto the wafer W via the projection optical system PL. The wafer W is suction-held on the wafer stage WST, and the wafer stage WST is two-dimensionally moved in the XY plane by the drive system WSC. Wafer stage WS
The moving amount or moving position of T is determined by three laser interferometers IF.
It is sequentially measured by X, IFY ₁ , and IFY ₂ . FIG.
In FIG. 1, only the laser interferometer IFX is shown, but the laser interferometers IFY ₁ and IFY ₂ are arranged in a direction (Y direction) perpendicular to the paper surface of FIG. Further, on the wafer stage WST, a reference plate F on which marks FM1, FM2A, FM2B for baseline measurement described later are formed.
P is provided. The surface of the reference plate FP is arranged in substantially the same plane as the surface of the wafer W.

The XY coordinate positions of the reticle stage RST and wafer stage WST detected by the laser interferometers arranged on the reticle side and the wafer side, respectively, are output to the main control system MCS, and the main control system MCS outputs these signals. Command signal to the drive system RSC, WST based on
Control the movement of each stage. The projection exposure apparatus in this embodiment has an off-axis type alignment system. This off-axis alignment system
The projection lens PL is composed of a reflection prism (or mirror) 7 fixed near the lower end, an objective lens 6, a mirror 5, a detection system 4, and the like. An index plate having a conjugate optotype mark, a CCD camera, and the like are provided inside the detection system 4, and an image of the alignment mark on the wafer W is taken by the CCD camera together with the conjugate index mark. At this time, the Z position of the alignment mark on the wafer W is CC
It is desirable that the position of the image of the alignment mark imaged by the D camera be in the best focus (the best focus position of the off-axis alignment system).
Further, in the present embodiment, the optical axis of the objective lens 6 falling on the wafer stage WST via the prism 7 and the projection lens PL
The optical axis AX is separated from the optical axis AX by a constant distance only in the X direction, and there is almost no positional difference in the Y direction.

FIG. 2 is a plan view showing the arrangement of each member on the wafer stage WST. The wafer W is the wafer stage WS.
The wafer is placed on a wafer holder WH that can be slightly rotated on T and is vacuum-sucked. In this embodiment, the linear notch OF of the wafer W is mechanically pre-aligned so as to be parallel to the X axis and then placed on the wafer holder WH. As shown in FIG. 2, the center of the diameter (optical axis AX) of the lower end of the lens barrel of the projection lens PL and the field of view of the objective lens 6 of the off-axis alignment system are arranged as close as possible. As described above, when the projection lens PL and the reference plate FP are arranged, the wafer W moves most from the position directly below the projection lens PL to the diagonally lower right in the figure. Unloading is possible.

Further, as shown in FIG. 2, a laser interferometer IF is provided on two adjacent sides of the outer periphery of wafer stage WST.
A movable mirror IMx that reflects the beam from X and a movable mirror IMy that reflects the beam from each of the laser interferometers IFY ₁ and IFY ₂ are fixed. The beam from the interferometer IFX is perpendicular to the reflecting surface of the movable mirror IMx extending in the Y direction, and the extension line of the beam is orthogonal to the extension line of the optical axis AX of the projection lens PL. The beam from the interferometer I FY ₂ is X
It is perpendicular to the reflecting surface of the movable mirror IMy extending in the direction, and the extension line of the beam is also orthogonal to the extension line of the optical axis AX. Another one
The beams from the two interferometers IFY ₁ are perpendicular to the reflecting surface of the moving mirror IMy and are parallel to the beams of the interferometers IFY ₂ .

Further, the wafer stage WS of the objective lens 6
The extension line of the optical axis falling on T is orthogonal to the extension line of the beam of the interferometer IFX and the extension line of the beam of the interferometer IFY ₁ . The arrangement of such an interferometer is described in detail in JP-A 1-3
It is disclosed in Japanese Patent Publication No. 09324. As shown in FIG. 1 and FIG. 2, the reference plate FP is disposed on the wafer stage WST at a corner portion surrounded by two movable mirrors IMx and IMy, and is disposed on the surface of a transparent material having a low expansion coefficient such as a quartz plate. A light-shielding layer such as chrome is formed, and a part of the light-shielding layer is used as fiducial marks FM1, FM2A,
It is etched into the shape of FM2B. The fiducial mark FM1 is an off-axis alignment system (4
~ 7) detected fiducial marks FM2A and FM
2B is a TTR alignment system (1A, 1
B).

These reference marks FM1, FM2A, FM
The 2B interval in the X direction is accurately made with sub-micron accuracy, but if there is a residual placement error amount, that value is precisely measured in advance and obtained as a device constant. It is assumed to be stored in the storage device 21 shown. FIG. 3 shows the reference marks FM1, FM2A, F on the reference plate FP.
It is a top view which shows the detailed mark arrangement of M2B.

In FIG. 3, the reticle mark R is provided at two symmetrical points across the intersection of the straight line LX and the straight line LY _2.
M _1, the reference mark FM2 corresponding to the RM ₂ of the respective arrangement
A and FM2B are provided. This mark FM2A,
FM2B is obtained by etching a chrome layer on the reference plate FP with cross-shaped slits. The mark FM2A is aligned with the reticle mark RM _1, and the mark FM2B is aligned with the reticle mark RM ₂ . Further, at the time of baseline measurement, the intersection of the straight line LX parallel to the X axis and the straight line LY ₂ parallel to the Y axis is substantially coincident with the optical axis AX of the projection lens PL.

A circular area PIF whose origin is the intersection of the straight line LX and the straight line LY ₂ is the projection visual field area of the projection lens PL. On the other hand, the straight line LY _{1, which} is set apart from the straight line LY _{2 in the} X direction by a certain distance, is parallel to the Y axis.
A reference mark FM1 having a size that can be included in the visual field MIF of the objective lens 6 of the off-axis alignment system is formed on the intersection of Y ₁ and the straight line LX. Mark FM1
In order to enable two-dimensional alignment, a plurality of line patterns extending in the Y direction are arranged in the X direction at a constant pitch, and a plurality of line patterns extending in the X direction are arranged in the Y direction at a constant pitch. It is formed as a dimensional pattern. As is clear from the above description, the reference plate F
In P, the straight line LY ₁ is as close as possible to the center line (measurement axis) of the beam of the interferometer IFY _{1 in} the XY plane, and the straight line LY ₂ is the center line (measurement axis of the beam of the interferometer IFY ₂ ). ) Is fixed as much as possible (that is, rotation deviation is prevented as much as possible) on the wafer stage WST.

Next, a method of detecting the reference mark FM1 by the off-axis alignment system (4 to 7) will be described. FIG. 4 is a diagram showing an index plate 4F provided in the detection system 4. As shown in FIG. 4, the index plate 4F is an index mark TMX ₁ , TMX ₂ , TM formed of a line pattern of a plurality of (for example, four) light-shielding portions on a transparent glass.
Y ₁ and TMY ₂ are formed. FIG. 4 shows the intersection of the straight lines LX and LY ₁ set on the reference plate FP and the indicator plate 4
The state where the center of F coincides is shown. Index mark TMX
₁ , TMX ₂ are provided so as to sandwich the reference mark FM ₁ on the reference plate FP in the X direction, and the index marks TMY ₁ , T
MY ₂ is provided so as to sandwich the reference mark FM ₁ in the Y direction.

Now, each index mark on the optotype plate 4F and the image of the reference mark FM ₁ (or the mark on the wafer) are stored in the detection system 4 via an imaging lens for image pickup, a beam splitter and the like. It is magnified and imaged on two CCD cameras. The image pickup area of one CCD camera is set to the area 40X in FIG. 4 on the optotype plate 4F, and the index marks TMX ₁ and TMX _{2 are set.}
The horizontal scanning line is defined in the X direction orthogonal to the line pattern. The image pickup area of the other CCD camera is the area 40Y.
And the horizontal scanning line is defined in the Y direction orthogonal to the line pattern of the index marks TMY ₁ and TMY ₂ . The image signal from each CCD camera is a circuit for digitally sampling the signal level for each pixel, a circuit for converting and averaging image signals (digital values) obtained for each of a plurality of horizontal scanning lines,
Waveform processing circuits, such as a circuit which computes each X-direction and Y-direction position shift amount of the index mark TM and the reference mark FM ₁ at high speed, are processed.
Sent to CS.

Next, returning to FIG. 1 again, a TTR type alignment system for detecting the reference marks FM2A and FM2B on the reference plate FP will be described. In this embodiment, two alignment systems having the same configuration are provided, but the configuration of the TTR alignment system having the objective lens 11 will be described here. The projection optical system 13 is composed of a light source that generates light having an exposure wavelength, a condenser lens, an illumination field stop, and the like. The light emitted from the projection optical system 13 illuminates the reticle mark RM ₁ via the lens system 14, the beam splitter 12, and the mirror 10. Reticle mark RM
The reflected light from ₁ is reflected by the beam splitter 12 via the mirror 10 and the objective lens 11, and enters the imaging lens 15. The image light flux of the mark RM ₁ is divided into two by the half mirror 16, and the imaging lens 15 forms the CCD camera 17 for detecting the X direction and the CCD camera 1 for detecting the Y direction.
The images are enlarged and formed on the respective image pickup surfaces of 7Y. The CCD cameras 17X and 17Y are arranged such that the horizontal scanning lines with respect to the magnified image of the mark RM ₁ are orthogonal to each other.

Mark RM₁Is in the X direction, as shown in FIG.
Double slit mark RM extended to ₁extended in the x and Y directions
Double slit mark RM₁consists of y and
RM₁x, RM₁y is transparent surrounded by a rectangular shading band SB
It is made as a dark part in the window. As shown in FIG.
The frames 17X and 17Y are cross-shaped stripes of the reference mark FM2A.
Image the lit as a black line. The image processing circuit 18X is
Digital waveform processing of image signal from CCD camera 17X
And a slit extending in the Y direction of the reference mark FM2A,
Reticle mark RM₁Double slit mark RM₁x
Then, the amount of positional deviation between and in the X direction (horizontal scanning line direction) is obtained.
The image processing circuit 18Y receives an image signal from the CCD camera 17Y.
Signal is processed by digital waveform and the X direction of the reference mark FM2A
Slit extending in the direction and reticle mark RM₁The double
Slit mark RM₁Y direction with y (horizontal scan line direction)
Find the amount of positional deviation. The main control system MCS is a processing circuit 1
Reference mark FM2A and reticle obtained by 8X and 18Y
Le Mark RM₁The amount of misalignment in the X and Y directions with
If it is outside the allowable range, the reticle stage RST
Control the drive system RSC to correct the position of the reticle R
It As shown in FIG. 5, the fiducial mark FM2A has a cross-shaped stripe.
Of the lits, the slit that extends in the X direction is a double slip.
Tomark RM₁Slit sandwiched by x and extending in the Y direction
Is a double slit mark RM₁Ideal to be sandwiched between y
Alignment will be achieved.

Further, in the projection exposure apparatus of this embodiment, as shown in FIG. 1, the optical axis AX is provided on the side of the projection optical system PL.
A projection system 1 for projecting a slit pattern image at a predetermined measurement point in the exposure field of the projection optical system PL obliquely with respect to
And the reflected light from the measurement point is received to re-image the slit pattern image, and a focus signal corresponding to the amount of deviation of the re-imaged position from the reference position is generated to generate the main control system MCS. An autofocus system including a light receiving system 2 for supplying the light is provided. The autofocus system includes a parallel flat plate glass 3 in the optical path of a light beam emitted from the light projecting system 1, and the parallel flat plate glass 3 has a rotation axis extending in a direction perpendicular to the plane of FIG. The mechanism is rotatable with respect to the rotation axis within a predetermined angle range. Main control system M
CS controls the rotation angle of the parallel plate glass 3 and the measurement point is the image plane of the projection optical system PL (best focus plane).
Calibration is performed so that the reflected light from the measurement point is incident on the reference position of the light receiving system 2, that is, the focus signal from the light receiving system 2 becomes 0, From the value of the focus signal, for example, the position shift amount (defocus amount) of the exposure surface of the wafer W from the best focus surface in the optical axis AX direction is detected.

Further, the projection exposure apparatus according to the present embodiment is equipped with a pressure controller 20 for correcting a variation in magnification of the projection lens due to a variation in atmospheric pressure. The pressure control unit 20 outputs an output signal corresponding to the atmospheric pressure to the main control system MCS, and controls the pressure of a predetermined air chamber (lens interval of the objective lens) in the projection optical system according to the signal. In the pressure control unit 20, the amount of change in atmospheric pressure and the amount of change in pressure of the air chamber necessary for correcting the change in projection magnification of the projection optical system are stored in advance in association with each other. The detailed structure of the pressure control unit 20 is described in, for example, Japanese Patent Application Laid-Open No. 60-7.
It is disclosed in Japanese Patent No. 8454.

Further, since the Z position (the best focus position of the projection optical system) of the image plane of the projection optical system fluctuates according to the fluctuation of the atmospheric pressure, the main control system MCS controls the atmospheric pressure from the pressure control unit 20. The angle of the parallel flat plate glass 3 of the autofocus system is controlled on the basis of the signal corresponding to the measurement point, and the measurement point on the wafer W is the image plane of the projection optical system PL (best focus plane)
Calibration is performed so that the reflected light from the measurement point is incident on the reference position of the light receiving system 2 in the state where Further, the main control system MCS centrally controls the entire device based on various device constants and measurement result values stored in the storage device.

Next, an example of the baseline measurement and alignment operation by the projection exposure apparatus of this embodiment will be described. FIG. 6 is a flowchart illustrating a typical sequence. First, the main control system MCS conveys the reticle R stored in a predetermined storage and loads it onto the reticle stage RST depending only on the mechanical positioning accuracy and the delivery accuracy (step 500). In this case, loading accuracy of reticle R, double slit mark RM ₁ x and the size of the window region of the reticle mark shown in FIG. 5 (inside the light-shielding band SB) of about 5mm square,
If the length of RM ₂ y is about 4 mm, it is desirable that the length is ± 2 mm or less.

Next, the main control system MCS preliminarily roughly aligns the position of the reticle R in step 501 so that the marks RM ₁ and RM ₂ of the reticle R are normally detected by the TTR alignment system. Perform pre-alignment. At this time, the reticle mark RM
₁ , the plain surface of the reference plate FP is arranged at the projection position by the projection optical system PL at the position where RM ₂ is likely to exist, and in that state, the reticle marks RM ₁ and RM ₂ are read by the CCD cameras 17X and 17Y shown in FIG. Take an image. By this pre-alignment, the centers of the marks RM ₁ and RM ₂ of the reticle R can be pre-aligned with the accuracy of about several μm to the centers in the image pickup areas of the CCD cameras provided in the two TTR alignment systems, respectively.

Next, the main control system MCS starts the reticle alignment operation from step 502.
The drive system W is arranged so that each of the two reference marks FM2A and FM2B is located at the designed position within the visual field PIF of the projection lens PL.
SC is the interferometer IFX and the interferometer IFY ₂ (or IFY ₁ )
The wafer stage WST is positioned by controlling according to the measured values of When the wafer stage WST is positioned, the reference mark FM2A the reticle mark RM _1, reference mark FM2B the CCD camera 17X in a state of being aligned reticle mark RM ₂ and each generally, imaged by 17Y. At this stage, the processing circuits 18X and 18Y in FIG. 1 are operated to move the reticle mark RM ₁ with respect to the reference mark FM2A in the X and Y directions (ΔXR ₁ and ΔYR).
₁ ) and reticle mark R for fiducial mark FM2B
Amount of displacement of M ₂ in X and Y directions (ΔXR ₂ , ΔYR ₂ )
And measure.

Next, at step 503, it is judged whether or not each positional deviation amount is within an allowable value, that is, whether the positional deviation amount of the reticle R in the X, Y, and θ directions is within a predetermined allowable range. To do. Then, when the deviation amount of the reticle R in the X, Y, and θ directions is larger than the allowable value, the reticle stage RST is finely moved in step 504. At this time, as is apparent from the shapes and arrangements of the _two reticle marks RM ₁ and RM ₂ , the alignment of the reticle R in the X direction is such that the reticle marks RM ₁ and RM ₁ are aligned with the center points of the reference marks FM 2 A and FM 2 B. _When the center points of ₂ are displaced toward the reticle center CC as positive, and when displaced in the opposite direction as negative, the polarities and absolute values of the displacement amounts ΔXR ₁ and ΔXR _{2 in} the X direction are equal. It is achieved by doing.

Similarly, when the center points of the reticle marks RM ₁ and RM ₂ are deviated in the positive direction of the Y axis of the stationary coordinate system, the Y direction and the θ direction of the reticle R are aligned in the Y direction. This is achieved by making the polarities and absolute values of the deviation amounts ΔYR ₁ and ΔYR ₂ equal to each other. Then Reticle R
The main control system MCS repeats the operation from step 502 again because it is necessary to confirm whether or not the target position is accurately aligned by the fine movement of.

By the above steps 502-504,
The reticle R has two reference marks FM2 on the reference plate FP.
It means that the A and FM2B are aligned with the designed coordinate position. Next, in the main control system MCS, step 5
The operation from 05 is executed. In step 505, the coordinate values of wafer stage WST at the time when the reticle alignment is achieved are stored, and interferometers IFX, IF are stored.
The drive system 116 of wafer stage WST is servo-controlled so that the measured value of Y ₂ (or IFY ₁ ) always matches the stored value.

Next, in step 506, the main control system MCS performs fiducial mark detection using the TTR alignment system and the off-axis alignment system at the same time. In general,
When the reticle stage RST is finely moved to the target position and alignment is achieved in the previous step 504, the reticle stage RST is fixed by vacuum suction or the like to the column side serving as the base. At the time of this suction, the reticle stage RST may be laterally displaced by a minute amount. This lateral shift is a slight one, but it is one of the error factors in baseline management, and it is necessary to fully recognize it. The recognition is performed by again using the CCD camera of the TTR alignment system to perform the measurement operation of step 502, or monitoring the amount of change in the measurement values of the interferometers IRX, IRY, and IRθ from the time when the reticle alignment is achieved. It is possible with. However, in the present embodiment, since the lateral displacement is also managed as the baseline amount, only the lateral displacement amount need not be individually calculated.

By the way, at the stage of step 506, the reference mark FM1 on the reference plate FP is already located in the detection area of the off-axis alignment system. Therefore, the main control system MCS uses a CCD camera of an off-axis alignment system as shown in FIG. 4 to shift the position of the optotype mark TM and the reference mark FM1 in the optotype plate 4F in the X and Y directions ( ΔXF, ΔYF) is obtained as the actual size on the wafer. At the same time, by using the CCD cameras 17X and 17Y of the TTR alignment system, the positional deviation amount (ΔXR ₁ , ΔYR ₁ ) between the reticle mark RM ₁ and the reference mark FM2A.
When, by TTR alignment system having an objective lens 21 shown in FIG. 1, the reticle mark RM ₂ and the reference mark F
The amount of positional deviation from M2B (ΔXR ₂ , ΔYR ₂ ) is measured as the actual size on the wafer side. At this time, since the CCD camera is used as a photoelectric sensor in both the TTR method and the off-axis method, the processing circuits 18X and 18Y are arranged so that the timing signals of the image signal waveforms corresponding to the picked-up mark images in the memory are matched as much as possible. Etc. Further, since the position of the reference plate FP is servo-locked by the interferometer, the acquisition of the image signal waveform in the TTR method and the acquisition of the image signal waveform in the off-axis method are caused by fluctuations in the refractive index of air. It is necessary to make the interval sufficiently shorter than the time of the fluctuation of the wafer stage position.

Next, the main control system MCS executes step 507,
At 508, calculation for obtaining the baseline amount is performed.
The calculation of the baseline amount will be described with reference to FIG. Here, the off-axis alignment system 8 in FIG. 7 is the same as the off-axis alignment system (4 to 7) shown in FIG. 1 for convenience. As described above, the projection exposure apparatus in this embodiment is provided with the pressure control unit 20 that outputs a signal according to the atmospheric pressure to the main control system MCS. Then, the main control system MCS obtains the amount of fluctuation from the reference atmospheric pressure based on this signal, and
A deviation amount of the best focus position of the projection optical system PL caused by the atmospheric pressure fluctuation is calculated. Then, the rotation angle of the parallel plate glass 3 is controlled according to the deviation amount, and the calibration of the autofocus system is performed. Similarly, the main control system MCS also calculates the amount of deviation of the best focus position of the off-axis alignment system that occurs due to atmospheric pressure fluctuations. The best focus position of the projection optical system PL,
The best focus position of the off-axis alignment system 8 is set in advance to a predetermined Z coordinate position Z ₀ , as shown by the broken line in FIG. 7, but the projection optical system PL and the off-axis alignment system 8 are set. When the atmospheric pressure around 8 fluctuates, for example, the best focus position of the projection optical system PL fluctuates to Z ₁ shown in FIG. 7, and the best focus position of the off-axis alignment system 8 fluctuates to Z ₂ . These best focus positions are obtained by the main control system MCS. Therefore, in the previous step 506, with the surface of the reference plate FP arranged on the image plane of the projection optical system PL, the shift amounts (ΔXF, ΔYF), (ΔXR ₁ ,
ΔYR ₁ ) and (ΔXR ₂ , ΔYR ₂ ) are measured.

Here, in this embodiment, since the image plane of the projection optical system and the best focus position of the TTR type alignment system are at the same height position (Z = Z ₁ ), the surface of the reference plate FP is Baseline measurement is performed according to the image plane of the projection optical system. However, if the image plane of the projection optical system and the best focus position of the TTR alignment system are at different height positions, the surface of the reference plate FP is set to T.
The baseline amount can be measured with higher accuracy when the best focus position of the TR alignment system is adjusted.

Next, an example of a method of calculating the baseline amount by the main control system MCS will be described. In the storage device 21, as a design constant value, each distance (ΔXfa, ΔXfa, between the center point of the reference mark FM1 and the reference mark FM2A in the X and Y directions.
ΔYfa), the center point of the reference mark FM1 and the reference mark F
Distances (ΔXfb, ΔYfb) in the X and Y directions from M2B are stored in advance with the straight line LX as a reference. Then, based on the constant values ΔXfa and ΔXfa, the fiducial mark FM2A,
The distance LF in the X direction between the bisector of the line segment connecting the central points of FM2B and the central point of the reference mark FM1 is stored.

LF = (ΔXfa + ΔXfb) / 2 (1) In the main control system MCS, 1/2 of the difference between the deviation amounts ΔXR ₁ and ΔXR _{2 in} the X direction obtained by the two TTR alignment systems is measured on the wafer side. Is calculated as ΔXcc. ΔXcc = (ΔXR ₁ −ΔXR ₂ ) / 2 (2) where ΔXR ₁ and ΔXR ₂ are reticle marks RM ₁ and R
When M ₂ is displaced in the direction of the reticle center with respect to each of the reference marks FM2A and FM2B, it is assumed that the displacement in the opposite direction is a negative value.

When the value ΔXcc obtained by the equation (2) is zero, the projection point of the center CC of the reticle R is precisely located on the bisector in the X direction of the center points of the two reference marks FM2A and FM2B. It is in agreement with. Next, the main control system MCS
Is based on the measured value ΔXF and the calculated values LF and ΔXcc,
The projection point CP of the center point CC of the reticle R on the imaging plane of the projection optical system PL (the best focus position in the alignment system of the TTR system) and the center point of the index plate 4F of the off-axis alignment system 8 in the X direction. Projection point FP1 of (divided point between index marks TMX ₁ and TMX ₂ )
The distance BLx in the X direction between

BLx = LF−ΔXcc−ΔXF (3) where ΔXF is the reference mark FM1 with respect to the bisecting point of the index marks TMX ₁ and TMX _{2 in} the X direction.
It is assumed that a positive value is obtained when the shift is detected in the direction of L (reference marks FM2A, FM2B), and a negative value is detected when the shift is detected in the opposite direction.

However, as will be described later, the point at which the off-axis alignment system 8 actually detects the alignment mark on the wafer W is the best focus position of the off-axis alignment system 8, that is, the point FP2 shown in FIG. Is. Therefore, X is fed from the position where the alignment mark on the wafer is actually detected by the off-axis alignment system 8 to the exposure position immediately below the projection optical system PL.
The amount in the direction, that is, the baseline amount in the X direction is the distance BLOX in the X direction between the point FP2 and the point CP shown in FIG.

Here, the optical axis of the off-axis alignment system 8 is tilted with respect to the optical axis of the projection optical system PL.
The value of this inclination (telecentric inclination) is measured in advance when the projection exposure apparatus is manufactured and is stored in the storage device 21 as an apparatus constant. In this embodiment, the angle of the telecentric tilt in the X direction is θFx, and the angle of the telecentric tilt in the Y direction is θFy.

[0043] Now, the main control system MCS obtains the error amount ΔZ of the best focus position Z ₂ of the best focus position Z ₁ and the off-axis alignment system 8 of the projection optical system PL (step 507), the error amount ΔZ And storage device 2
X of off-axis alignment system 8 input from 1
The baseline amount BLOx in the X direction is measured using the telecentric inclination θFx in the direction (step 508).

BLOx = BLx + Δx = BLx−ΔZ · tan θFx = LF−ΔXcc−ΔXF−ΔZ · tan θFx (4) where ΔZ · tan θFx is when the telecentric is inclined in the −X direction as shown in FIG. It takes a positive value, and takes a negative value when tilting in the opposite direction (+ X direction).

Similarly, the main control system MCS is a reticle R.
The deviation amount ΔYcc in the Y direction between the projection point of the center point CC of the reference mark and the bisector of the line segment connecting the center point of the reference mark FM2A and the center point of the FM2B, and the center points of the reference marks FM2A and FM2B are connected. A deviation amount ΔYf ₂ in the Y direction between the bisector of the line segment and the center point of the reference mark FM1 is obtained, and the measured value ΔYF, the telecentric inclination θFy of the off-axis alignment system 8 in the Y direction, and the projection optical PL. based on the error amount ΔZ of the best focus position Z ₂ of the best focus position Z ₁ and the off-axis alignment system 8 of the system, to calculate a Y-direction baseline value by the following equation (step 508).

BLOy = ΔYcc−ΔYf ₂ −ΔYF−ΔZ · tan θFy (5) where ΔZ · tan θFy is positive when the telecentric tilt in the Y direction of the off-axis alignment system is tilted in the + Y direction, − When it is tilted in the Y direction, it takes a negative value. By the above calculation, off-axis
Baseline amount of alignment system 8 (BLOx, BLOx
y) is always obtained with high accuracy.

In this embodiment, the baseline amount is corrected by considering only the telecentric inclination of the off-axis alignment system. However, by taking into account the aberration of the optical system of the alignment system, the base amount can be more accurately measured. The line amount can be measured. First, the fiducial mark FM1 is placed at a predetermined coordinate position and detected by an off-axis alignment system. At this time, the height position of the reference mark FM1 is moved within a predetermined range centered on the best focus position of the off-axis alignment system. The main control system MCS uses the detection error amount (correction amount) of the reference mark FM1 based on the detection result when the reference mark FM1 is detected at the best focus position of the off-axis alignment system as the height of the reference mark FM1. The storage device 21 is associated with the shift amount of the position in the Z direction from the best focus position of the off-axis alignment system.
Remember. During the baseline measurement, correction from the storage device 21 according to the error amount ΔZ of the best focus position Z ₂ of the best focus position Z ₁ and the off-axis alignment system 8 of the projection optical system PL as in this embodiment The amount is output, and the baseline amount is corrected using this correction amount. With the above operation, the baseline amount can be accurately measured.

Further, as in this embodiment, the distance B shown in FIG.
The positional deviation amount (ΔXF, Δ) between the optotype mark TM and the reference mark FM1 in the optotype plate 4F in the X and Y directions without obtaining Lx.
YF), the previously calculated correction amount (ΔZ · tan θF
It goes without saying that the baseline amount may be obtained after adding x, ΔZ · tan θFy). On the wafer W, a plurality of exposed regions, that is, shot regions in which the pattern of the reticle R has already been exposed are two-dimensionally arranged. And in each shot area, the alignment mark detected by the off-axis alignment system,
It is formed in a fixed relationship with the center point of the shot area. In many cases, the alignment marks on those wafers are provided in the street lines. Although several methods or sequences are conventionally known as an actual wafer alignment method, only the basic wafer alignment will be described here.

FIG. 8 shows the arrangement of the shot areas and marks on the wafer W, with the centers SCn and X of the shot areas SAn.
The distance in the X direction from the direction mark WMx is ΔXwm, the center S
The width between Cn and the Y mark WMy for the Y direction in the Y direction is Δ.
Designated as Ywm. First, when the off-axis alignment system 8 is used, the mark WMx of an arbitrary shot area SAn is sandwiched between the index marks TMX ₁ and TMX ₂ in the detection area of the off-axis alignment system 8 on the wafer. Position the stage WST. At this time, since the best focus position of the off-axis alignment system 8 is obtained by the main control system MCS at the time of the previous baseline measurement, by controlling the Z position of the stage based on this value, the wafer The alignment mark on W can be accurately arranged at the best focus position of the off-axis alignment system 8.

Then, the main control system MCS reads the coordinate position Xm of the positioned wafer stage WST in the X direction from the interferometer IFX. Further, by processing the image signal from the CCD camera 4X in the off-axis alignment system, X between the center point of the index plate 4F and the center point of the mark WMx is processed.
The deviation amount ΔXp in the direction is detected. Next, the wafer stage W
Move ST and mark W on the wafer with index marks TMX ₁ and TMX _{2 of} the off-axis alignment system.
The wafer stage WST is positioned so that My is sandwiched. The coordinate position Ym in the Y direction at this time is determined by the interferometer I.
Read from F ₁ . Then, the amount of deviation ΔYp in the Y direction between the center point of the index plate 4F and the center point of the mark WMy is obtained by imaging with the CCD camera 4Y.

After the above mark position detection is completed, the coordinate position of the wafer stage WST for aligning the center SCn of the shot area SAn with the projection point of the center CC of the reticle R at the time of exposure (only by calculation of the following equation) Xe, Y
e) is required. Xe = Xm- [Delta] Xp + (BLOx- [Delta] Xwm) (6) Ye = Ym- [Delta] Yp + (BLOy- [Delta] Ywm) (7) The present invention is a mark detected by the TTR alignment system as in the above-described embodiment. And both marks detected by the off-axis alignment system are provided on the reference plate, and each mark is simultaneously detected by the TTR alignment system and the off-axis alignment system to measure the baseline amount. However, instead of detecting them at the same time, the wafer stage is scanned and the position when the mark is detected by each alignment system is measured with a laser interferometer etc., and the difference is calculated as the baseline amount. It can also be applied in cases.

Further, although the exposure apparatus described in the embodiment exposes the projected image of the pattern on the reticle R onto the wafer W by the step-and-repeat method, the present invention uses the reticle and the wafer. The same can be applied to a step scan type exposure apparatus that simultaneously scans in a direction perpendicular to the optical axis of the projection optical system. The present invention can also be applied to an X-ray aligner using an X-ray source such as SOR and an X-ray stepper.

[0053]

As described above, according to the present invention, the height position at which the photosensitive substrate is arranged when the first pattern detection system detects the pattern on the photosensitive substrate serves as a reference when measuring the baseline amount. Even if it does not coincide with the plane (image plane of the projection optical system), the baseline amount is corrected according to the shift amount. Therefore, even if there is a telecentric inclination or aberration in the optical system of the first pattern detection system, the baseline amount can always be measured with high accuracy.

Even if environmental conditions such as atmospheric pressure change,
Since the amount of deviation between the best focus position of the first pattern detection system and the image plane of the projection optical system can be obtained according to the change, the amount of baseline can be obtained accurately.

[Brief description of drawings]

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

FIG. 2 is a plan view showing an arrangement of reference mark plates on a wafer stage.

FIG. 3 is a plan view showing the arrangement of various marks on a reference mark plate.

FIG. 4 is a diagram showing a pattern arrangement of an index plate of an off-axis alignment system.

FIG. 5 is a diagram showing an example of the shape of a reticle alignment mark.

FIG. 6 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 7 is a diagram illustrating an error in a baseline amount due to atmospheric pressure fluctuation.

FIG. 8 is a plan view showing the arrangement of shot arrays and wafer marks on a wafer.

[Explanation of symbols for main parts]

R ... Reticle W ... Wafer PL ... Projection lens MCS ... Main control system RST ... Reticle stage WST ... Wafer stage FP ... Reference plate FM1 ... Off-axis alignment Reference mark for system FM2A, FM2B ... TTR alignment reference mark for system IFX, IFY ... Laser interferometer for wafer stage RM ₁ , RM ₂ ... Reticle mark 8 ... Off-axis alignment System 20 ... Pressure control unit 21 ... Storage device

Claims (5)

[Claims] 1. A projection optical system for projecting an image of a mask pattern onto a photosensitive substrate, a stage which holds the photosensitive substrate and is movable in a plane perpendicular to the optical axis of the projection optical system.
A reference plate provided on the stage, on which a reference pattern having a predetermined shape is formed, and the photosensitive substrate are arranged at a predetermined height position in the optical axis direction of the projection optical system, and formed on the photosensitive substrate. First for aligned alignment
The first pattern detection system for detecting a pattern, the second pattern formed on a reference point on the mask, or a predetermined point on the mask having a fixed positional relationship with the reference point, and the reference pattern are projected. In a projection exposure apparatus having a second pattern detection system that detects a relative positional relationship between the second pattern and the reference pattern through an optical system, the projection exposure apparatus is arranged in a predetermined reference plane perpendicular to the optical axis. Based on the respective detection results when the first pattern detection system and the second pattern detection system detect the reference pattern, the detection center of the first pattern detection system and the reference point in the reference plane are Measuring means for obtaining a distance from the projection point by the projection optical system, and the measuring hand according to the amount of deviation of the predetermined height position with respect to the reference plane in the optical axis direction. Projection exposure apparatus characterized by having a correction means for correcting the value of the interval sought. 2. The reference pattern includes a first reference pattern detected by the first pattern detection system and the second reference pattern.
A second reference pattern detected by a pattern detection system, wherein the first reference pattern and the second reference pattern are the detection center of the first pattern detection system and the second reference pattern of the second pattern detection system in the reference plane. The device according to claim 1, wherein the device is arranged in parallel on the reference plate in a positional relationship according to a distance from a detection center. 3. The correction means has an environmental condition measuring means for measuring an environmental condition around the projection optical system and the first pattern detection system, and a change in the environmental condition measured by the environmental condition measuring means. The apparatus according to claim 2, wherein the shift amount is obtained based on the amount. 4. A pattern detection system for detecting an alignment pattern formed on the photosensitive substrate prior to projecting and exposing a mask pattern image on the photosensitive substrate via a projection optical system. The distance between the center and the projection point of the reference point on the mask by the projection optical system in a predetermined reference plane perpendicular to the optical axis of the projection optical system is determined, and the pattern detection system is used for the alignment. In a projection exposure method for arranging the photosensitive substrate at a predetermined exposure position according to a detection result when a pattern is detected and the interval, the photosensitive substrate is used when the pattern detection system detects the alignment pattern. In the direction perpendicular to the optical axis of the photosensitive substrate according to the amount of deviation in the optical axis direction between the height position of the projection optical system in which the optical axis direction is arranged and the reference plane. Projection exposure method characterized by adjusting the location, placing the photosensitive substrate to the exposure position. 5. The method according to claim 4, wherein an environmental condition around the projection optical system and the pattern detection system is detected, and the deviation amount is measured based on the detection result.