JP3003990B2 - Projection exposure method, projection exposure apparatus and circuit manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure method and a projection exposure apparatus, and more particularly to a projection exposure method for manufacturing a semiconductor integrated circuit and a focus position control for aligning a projection lens in an optical axis direction in the projection exposure apparatus. It is.

[0002]

2. Description of the Related Art In a lithography process in the manufacture of a semiconductor integrated circuit, a step-and-repeat type reduction projection exposure apparatus, a so-called stepper, plays a central role. In general, a projection lens having a large numerical aperture (NA) is used for this stepper. However, recently, a numerical aperture (N.A.) corresponding to the minimum line width of a circuit pattern formed on the order of submicrons has been used. .
A. ) Is further increased, and the practical depth of focus of the projection lens is very small. In addition, when exposure is performed continuously for a long time, the projection lens absorbs the irradiation energy of the exposure light and the temperature rises. In accordance with the temperature change of the projection lens, that is, the amount of heat stored in the projection lens by the irradiation energy. Since the focal position changes in the optical axis direction within the image plane of the projection lens, the image plane may fluctuate. For this reason, unless a projected image of a circuit pattern formed on a mask or a reticle (hereinafter, referred to as a reticle) is accurately formed on a photosensitive substrate (hereinafter, referred to as a wafer), a blurred pattern is formed on the wafer. The problem of poor resolution arises. For this reason, for example, the image forming plane of the projection lens and the wafer plane are made to coincide with each other by using an apparatus disclosed in Japanese Patent Application Laid-Open No. 60-168112 filed by the present applicant. In this apparatus, a so-called through-the-lens (TTL) type optical system for detecting a first mark on a reticle and detecting a second mark on a wafer via a projection lens is provided. This optical system is adjusted to perform focusing, and then the second mark is focused by changing the distance between the wafer and the projection lens in the optical axis direction.
Thus, the reticle and the wafer are maintained conjugate with respect to the projection lens, and the projection image of the circuit pattern of the reticle is always projected on the wafer in a focused state (best focus).

[0003]

However, in this type of apparatus, the first mark on the reticle is formed in the periphery of the exposure field of the projection lens in association with the pattern area, and is focused only at the end of the exposure field. Position detection will be performed. Therefore, the focal position at the center of the exposure field is not detected, and the curvature of field of the projection lens cannot be measured. Therefore, there is a problem that a trial printing or the like must be performed in order to measure the field curvature. Further, a rectangular mark formed extending in a sagittal direction (hereinafter, referred to as an S direction) on a reticle is usually used to detect a focal position at the mark position. (Hereinafter referred to as the focal position in the S direction) and the meridional direction (M direction)
Focus position detected from a rectangular mark extending
(Referred to as a focal position in the M direction), an offset occurs due to astigmatism of the projection lens. As a result, there is a problem that the accuracy of detecting the focal position is reduced and the resolution limit of the projection lens, which is discussed with the focal positions in the S and M directions, is reduced. Furthermore, the surface position of the wafer cannot be controlled by following the fluctuation of the imaging surface according to the amount of heat accumulated in the projection lens due to the irradiation energy. There is also a problem that the imaging performance at the time of exposure is deteriorated.

The present invention has been made in consideration of the above points, and detects a focal position and follows a change of an image forming surface according to a heat accumulation amount of a projection lens, thereby achieving high accuracy and short time. It is an object of the present invention to obtain a projection exposure apparatus which can set a wafer surface at an optimum exposure position and always perform exposure in a focused state (best focus).

[0005] In the present invention for solving the above problems, a method of a pattern formed on a mask through a projection optical system for projecting onto the substrate, wherein the irradiation energy by the energy beam incident on the projection optical system a step of storing the optical axis direction of the variation characteristic of the projection optical system at a plurality of points in the image plane of the projection optical system caused in accordance with the heat accumulated amount accumulated in the projection optical system, through the mask
The irradiation energy incident on the projection optical system is
Calculating the amount of heat accumulated in the projection optical system; calculating the state of the imaging plane of the projection optical system based on the variation characteristics and the amount of heat accumulation; and Adjusting the relative position between the imaging surface and the substrate according to the state of the surface.

In an apparatus for projecting a pattern formed on a mask onto a substrate via a projection optical system, an irradiation energy by an energy ray incident on the projection optical system is provided.
Measuring means for measuring a variation characteristic of a plurality of points in an image plane of the projection optical system in an optical axis direction of the projection optical system, which is generated in accordance with an amount of heat accumulated in the projection optical system by the projection optical system; means for storing a characteristic, said through the mask
Irradiation energy per unit time incident on the projection optical system
Means for measuring the irradiation energy, and the irradiation energy per unit time.
When the energy ray enters the projection optical system
Heat accumulation in the projection optical system based on the
Calculating the amount , based on the variation characteristics and the heat accumulation amount, calculating means for calculating the state of the imaging surface of the projection optical system, based on the calculation result, the imaging surface and the And adjusting means for adjusting the relative position with respect to the substrate. Further, in a circuit manufacturing method for projecting a pattern formed on a mask onto a substrate via a projection optical system, the irradiation energy by an energy ray incident on the projection optical system is provided.
A step of storing the optical axis direction of the variation characteristic of the projection optical system at a plurality of points in the image plane of the projection optical system caused in accordance with the heat accumulated amount accumulated in the projection optical system by chromatography, wherein
Irradiation energy incident on the projection optical system via a mask
Calculate the amount of heat accumulated in the projection optical system by
And calculating a state of an imaging plane of the projection optical system based on the fluctuation characteristics and the heat accumulation information ;
Adjusting the relative position between the imaging plane and the substrate according to the calculated state of the imaging plane.

When a test reticle having a reticle mark composed of, for example, rectangular marks extending in the S and M directions, respectively, is used, the focus position can be detected without causing an offset. . Then, the focus positions in the S direction and the M direction at a plurality of points in the exposure field are detected for each appropriate heat accumulation amount, and S generated by the heat accumulation amount is detected.
The fluctuation of the projection optical system in the direction and the M direction is stored. Based on the fluctuation characteristics of the projection optical system on the memory, the state of the image plane of the projection optical system (field curvature, image plane inclination, etc.) is calculated, and the fluctuation of the state of the image plane is calculated. By following the surface position of the exposure area on the wafer and controlling the surface of the exposure area at the optimal exposure position, it is possible to prevent the occurrence of poor resolution due to defocus or curvature of field, etc. (Best focus) for exposure.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a stepper having a focusing function according to a first embodiment of the present invention. In FIG. 1, the exposure illumination light source (not shown) is g-line, i
Illumination light having a wavelength (exposure wavelength) that exposes a resist such as a line is generated. The illumination light passes through a fly-eye lens 1 and a beam splitter 2, reaches a condenser lens 4 via a mirror 3, and is exposed to a reticle. The pattern area Pa of the reticle R held on the stage 5 is illuminated with uniform illuminance. Here, as shown in FIG. 2A, an alignment mark RMb having a cross mark formed of a chrome layer on a transparent window as an alignment mark RM on the reticle R.
RMe is associated with the pattern area Pa and the projection lens 6
Are provided in the exposure field IF. FIG.
(B) shows a schematic configuration of the test reticle TR. In the figure, reticle marks Rb to Re correspond to alignment marks RMb to RMe of reticle R, respectively.
The reticle mark Ra is disposed in the exposure field 1F of the projection lens 6, and is provided at the center of the test reticle TR. As shown in FIG. 3, the reticle marks Ra to Re, for example, the reticle marks Rb are rectangular marks Rb extending in the Y-axis and X-axis directions on the transparent window and formed of a chrome layer.
x and Rby. Now, as shown in FIG. 1, the bilateral or one-side telecentric projection lens 6 projects the image of the circuit pattern or the alignment mark RM drawn in the pattern area Pa of the reticle R onto the wafer W coated with the resist. However, the alignment mark RM
May be shielded by a reticle blind (not shown) during actual device exposure. The wafer W is held on a tilting stage (hereinafter, referred to as a leveling stage) 7 via a wafer holder (not shown) (not shown). The leveling stage 7 is provided on a wafer stage 9 and can be tilted in an arbitrary direction by a driving unit 8.

The position of the wafer stage 9 in the X direction is detected by a laser interferometer 10 and a plane mirror 10m provided on the wafer stage 9. Wafer stage 9
Above, a photoelectric detector (detector) 12 that detects the amount of exposure light that has passed through the projection lens 6 is provided. The size of the light receiving surface of the detector 12 is determined to be equal to or larger than the size of the projected image of the pattern area Pa of the reticle R, and receives all the exposure light passing through the reticle R and the projection lens 6. In addition, a reference member 20 such as a glass substrate provided with a fiducial mark FM used for performing focusing, baseline measurement, and the like on the wafer stage 9 is substantially aligned with the surface position of the wafer W. Is provided. On the reference member 20, rectangular marks FMx and FMy, which are light-transmitting slit patterns extending in the Y-axis and X-axis directions used for focusing and the like, are formed as fiducial marks FM. I have.

[0010] The fiducial mark FM is a g-line transmitted under the reference member 20 using the fiber 21,
Illumination light (exposure light) such as i-line illuminates the lens 22 and mirror 23 from below (inside the wafer stage 9). The illumination light transmitted through the fiducial mark FM forms a projection image of the fiducial mark FM on the pattern surface of the reticle R via the projection lens 6. Further, the light transmitted through the reticle R without being blocked by the alignment mark RM passes through the condenser lens 4, the beam splitter 2, and the like to the half mirror 24.
Incident on. The illumination light divided into two by the half mirror 24 is divided into light splitters 25x, 2x2 at positions Epx and Epy substantially conjugate to the pupil plane Ep of the projection lens 6, respectively.
6y. Here, as shown in FIG. 4A, the light splitter 25x divides the pupil image Ep 'of the projection lens 6 into wavefronts in the X-axis direction, and the two divided illumination lights Exa and Exb are detected by detectors 25a and 25b, respectively. Is received by the The light splitter 25x and the detectors 25a, 25
The first focus position detection system 25 composed of b is used at the time of focus position detection using a rectangular mark portion extending in the Y-axis direction of the alignment mark RM (cross mark). Similarly, the light splitter 26y shown in FIG. 4B splits the pupil image Ep 'into wavefronts in the Y-axis direction, and divides the illumination light Ey into two.
a and Eyb are received by the detectors 26a and 26b, respectively. The second focus position detection system 26 including the light splitter 26y and the detectors 26a and 26b is used at the time of focus position detection using a rectangular mark portion extending in the X-axis direction of the alignment mark RM.

In FIG. 1, an image forming light beam for forming an image of a pinhole or a slit toward an image forming surface of the projection lens 6 is inclined through a beam splitter 33 with respect to the optical axis of the projection lens 6. An oblique incident light type focus detection system 31 is provided which includes an irradiation optical system 31a for supplying light from the direction and a light receiving optical system 31b for receiving, via a beam splitter 34, a light beam reflected by the surface of the wafer W of the image forming light beam. ing. The configuration and the like of the focus detection system 31 are described in, for example, Japanese Patent Application Laid-Open No.
No. 2, the vertical position of the surface of the wafer W with respect to the reference plane is detected, and the wafer W and the projection lens 6 are detected.
Is to detect the in-focus state with the image forming plane. further,
An irradiation optical system 32 that supplies a parallel light beam from a direction oblique to the optical axis of the projection lens 6 via a beam splitter 33.
a and a light receiving optical system 32 for receiving, via a beam splitter 34, a light beam reflected by the surface of the wafer W of the parallel light beam
A horizontal position detection system 32 consisting of b is provided. The configuration and the like of the horizontal position detection system 32 are disclosed in, for example, Japanese Patent Application Laid-Open No. 58-113706 filed earlier by the present applicant, and the wafer W with respect to the optical axis of the projection lens 6 is
The vertical position of the surface, that is, the horizontal position is detected.
Main controller 30 controls the position of projection lens 6 of wafer stage 9 in the optical axis direction (Z-axis direction) based on the output signal of first focus position detection system 25 or second focus position detection system 26. And the overall operation of the apparatus including the focus detection system 31, the horizontal position detection system 32, and the like. Further, the drive unit 8 of the leveling stage 7 is controlled in accordance with the value calculated by the main controller 30 and the amount of displacement detected by various alignment systems.
And a predetermined drive command to the drive unit 11 of the wafer stage 7 and the like.

The beam splitter 2 is a switching mirror provided in the illumination optical path so as to be insertable and removable, and can be retracted out of the optical path by a driving device (not shown). Further, actually, a beam splitter section having a reflectance of several percent and a total reflection mirror section are provided on the mirror surface, and are switched to the total reflection mirror at the time of detecting the focal position in this embodiment, and to the beam splitter at the time of detecting the reflectance of the wafer W. It is desirable to configure as follows.

Next, the operation of the apparatus constructed as in this embodiment will be described. In FIG. 1, main controller 30
FIG. 2B shows, using the test reticle TR shown in FIG. 2B, for each appropriate heat accumulation amount, the focal position at a predetermined position on the imaging surface of the projection lens 6 corresponding to the heat accumulation amount, that is, the fluctuation characteristic of the focal position. To detect. First, the reticle mark R shown in FIG.
b, focus position detection using reticle mark Rb (test reticle TR) and fiducial mark FM
The amount of positional deviation (defocus amount) of the projection lens 6 with respect to the (reference member 20) in the optical axis direction is detected. At this time, a rotary shutter (not shown) provided in the optical path of the illumination light for exposure and closing and opening the optical path is used to close the optical path to prevent the exposure light from entering the projection lens 6.

Therefore, main controller 30 is driven by drive unit 11.
To move the wafer stage 9 in the Z direction,
1 to a predetermined position (coordinate value Z).₁)
Position. Then, the reference member 20 is connected to the fiber 21.
From below with the illumination light transmitted by
Mark FMx on the pattern surface of test reticle TR
Is formed. Next, in FIG.
As shown, the projected image FMx ′ relatively moves the mark Rbx by X
The wafer stage 9 is finely moved in the X direction so as to scan in the X direction.
Move. At this time, without being blocked by the mark Rbx,
The illumination light transmitted through the test reticle TR is
Via lens 4, mirror 3 and beam splitter 2
The light enters the half mirror 24. And half mirror 2
The illumination light reflected at 4 is the first focal position detection system 25
To the X-axis direction by the beam splitter 25x.
Divided and received by detectors 25a and 25b respectively
Is done. At this time, the projected image FMx ′ and the mark Rbx are combined.
Light passing through the test reticle TR
And the amount of light increases sequentially according to the shift. Next
The photoelectric signals output from the detectors 25a and 25b
The signal is output to the waveform processing device 27,
In this case, the photoelectric signal is transferred to the wafer stay by the laser interferometer 10.
Processing is performed in synchronization with the position signal of the edge 9. As a result, FIG.
Waveform signal S as shown in (b)₁, S_TwoIs detected and the wave
The shape processor 27 generates the waveform signal S₁, S _TwoThe main controller
Output to 30. Here, projection is performed using the light splitter 25x.
At a position Epx substantially conjugate to the pupil plane Ep of the lens 6, the illumination light
Since the light is divided (so-called pupil division), the divided illumination light
The principal rays of Exa and Exb are the light of the projection lens 6 respectively.
Tilt with respect to the axis (hereinafter this tilt is called telecentric tilt)
). Therefore, the reference member 20 is moved to a predetermined position (coordinate value Z).
₁), The image forming position of the projection lens 6 on the reticle side
Is shifted in the X-axis direction in the pattern of the reticle R.
You. Therefore, the main controller 30 is controlled by the light splitter 25x.
Projection image FM by illumination light Exa and Exb divided into two
x ′ and the position where the mark Rbx matches, that is,
Waveform signal S₁, S _TwoX axis of the positions a and b where
Direction is detected, and its value is represented by a coordinate value X.₁, X_TwoNote as
Remember

Next, the wafer stage 9 is moved in the Z direction via the drive unit 11, and the reference member 20 is positioned at a predetermined position (coordinate value Z ₂ ) using the focus detection system 31. Then, the illumination light Ex at the coordinate value Z _{2 by} the same operation as described above.
The position where the mark Rbx matches the projected image FMx ′ by a and Exb is detected, and the detected value is stored as coordinate values X ₁ ′ and X ₂ ′. FIG. 5C shows the relationship between the focus position and the matching position obtained as a result. In FIG. 5C, the intersection of the two straight lines is the position where the image shift of the projected image FMx 'does not occur, that is, the position where the defocus amount between the reticle R and the reference member 20 becomes zero (the in-focus position Z ₀ ). And the inclination of each straight line corresponds to the telecentric inclination of the illumination light Exa, Exb.
Therefore, main controller 30 sets projected image FMx ′ and mark Rb
The defocus amount between the reticle R and the reference member 20 is calculated based on the position where x matches and the telecentric inclination of the illumination lights Exa and Exb, and the value is stored as ΔZbs. In order to improve the accuracy of the defocus amount detection, the above-described measurement is preferably performed a plurality of times, and the defocus amount calculated from the average straight line obtained as a result is preferably stored.

Next, the main controller 30 uses the mark Rby to determine the defocus amount ΔZbm between the test reticle TR and the reference member 20 in the Y direction using the second focal position detection system 26 in the same manner as the above operation. To detect. The main controller 30 detects the S direction (for example, the X-axis direction) and the M direction (for example, the Y-axis direction) detected using the marks Rbx and Rby.
For example, based on the defocus amounts ΔZbs and ΔZbm, an average value thereof is taken to determine the defocus amount at the position of the reticle mark Rb. Further, main controller 30 uses reticle marks Ra, Rc, Rd, and Re to detect the defocus amounts in the S and M directions at each reticle mark in the same manner as in the above-described operation, and to determine the values and the values thereof. From the value, the exact defocus amount Δ at the position of the reticle mark
Za, ΔZc, ΔZd, and ΔZe are determined. Then, these detection results are stored as defocus amounts when the heat accumulation amount of the projection lens 6 is substantially zero.

Next, the main controller 30 drives the rotary shutter to open the optical path, and causes the exposure light to enter the projection lens 6. Then, the above-described detection of the defocus amount at the position of the reticle mark is performed for each of the reticle marks Ra to Re of the test reticle TR for each appropriate amount of heat accumulation while irradiating the projection lens 6 with exposure light. The amount of defocus at the position of the reticle marks Ra to Re corresponding to the amount of heat accumulation is detected. The main controller 30 determines the amount of heat accumulated in the projection lens 6 by the output signal of the detector 12 (the amount of irradiation energy per unit time) and the time during which the exposure light is incident on the projection lens 6 (that is, the opening of the rotary shutter). Time). As a result, curves A (t) and B representing the relationship between the amount of heat accumulation and the amount of defocus at the positions of reticle marks Ra to Re as shown in FIG.
(T), C (t), D (t) and E (t) are obtained. For example, when each curve can be approximated by a function, the main control device 30 formulates a graph and stores it in the memory 28. When the curve cannot be approximated, the main controller 30 stores the relationship in the memory 28 for each measurement point. Then, the defocus amount at the position of at least one reticle mark, for example, the defocus amount ΔZbs at the mark Rbx is detected, and the defocus amount ΔZb at this mark position considering the offset due to astigmatism of the projection lens 6 is calculated. In addition to the detection, the defocus amounts ΔZa, ΔZc, ΔZd, and ΔZe at the positions of the other four reticle marks Ra, Rc, Rd, and Re can be similarly detected.

By the above operation, data (variation characteristics of the focal position) used for the positioning (focusing) in the Z-axis direction, that is, at the position of each reticle mark corresponding to the heat accumulation amount E as shown in FIG. Memory 2 for defocus amount ΔZ
8 is completed. Incidentally, depending on the shape of the circuit pattern formed in the pattern area Pa, the test reticle TR
The transmittance differs for each reticle R, and the amount of irradiation energy per unit time of the exposure light incident on the projection lens 6 may change due to the difference in the transmittance and the attenuation of the exposure illumination light source. Therefore, at the time of actual exposure, an offset occurs in the fluctuation characteristic of the focal position detected as described above. Therefore, to detect the radiation energy per unit of exposure light time enters the projection lens 6 by using a detector 12 when the test reticle TR use, stores the read value in the memory 28 as K _1.

Next, instead of the above-described test reticle TR,
In addition, the alignment marks RMa to RMa shown in FIG.
Reticle R having RMe is placed on reticle stage 5.
Cut. Here, after setting reticle R,
Exposure light incident on the projection lens 6 using the
The amount of irradiation energy per unit time is detected, and this value K _Two
And the value K stored in the memory 28₁And the ratio (K_Two/ K₁)
Is calculated as a correction constant K and stored in the memory 28.
Good. Further, it is stored in the memory 28 using the correction constant K.
The variation amount of the variation characteristic is corrected, that is, the variation amount is multiplied by K,
The variation characteristic of the focal position multiplied by K is stored in the memory 28.
Keep it. And the reticle mark of the test reticle TR
Alignment mark RMb of reticle R corresponding to Rb
And the alignment mark RM is operated in the same manner as described above.
b, that is, deformation at a rectangular mark extending in the Y-axis direction.
The waste amount ΔZbs is detected. And this defocus
The amount ΔZbs and the data in the memory 28 (K times the focal position
Of the alignment marks Rc, R
Defocus amounts ΔZc, ΔZd, Δ at positions d and Re
Ze and the defocus amount ΔZ at the center position of the reticle R
a is obtained from the value on the memory 28. Next,
Projection based on the defocus amounts ΔZa to ΔZe
Optimal focus position considering field curvature of lens 6
The defocus amount ΔZ is calculated from the following equation (1).

[0020]

(Equation 1)

Further, the image plane tilt amount Δθ in the X-axis and Y-axis directions
x and Δθy are calculated from the following equations (2) and (3). However, each alignment mark RMb from the center of reticle R
Let l be the distance from RMe to.

[0022]

(Equation 2)

Next, main controller 30 drives wafer stage 11 via drive unit 11 so that the detection value at a predetermined position (coordinate value Z ₂ ) of the exposure area of wafer W by focus detection system 31 changes by ΔZ. 9 is moved by the defocus amount ΔZ in the Z-axis direction. Further, the drive unit 8 controls the horizontal position detection system 32 so that the detection values in the X-axis and Y-axis directions in the exposure area on the wafer W coincide with the image plane tilt amounts Δθx and Δθy, respectively.
The leveling stage 7 is tilted through. Accordingly, the reticle R and the exposure area on the wafer W are set at conjugate positions with respect to the projection lens 6, and the occurrence of poor resolution due to the curvature of the field of the projection lens 6, the tilt of the field, and the like is prevented. Positioning (focusing) in the Z-axis direction ends.
Note that the defocus amount ΔZ calculated from the above equation (1)
Are averaged from the defocus amounts ΔZa to ΔZe at the alignment marks RMa to RMe, and the position of the exposure area on the wafer W is adjusted in accordance with the average value, thereby performing more accurate alignment in the Z-axis direction. be able to.

If the exposure is continuously performed for a long time, the state of the image forming surface of the projection lens 6 fluctuates according to the amount of accumulated heat, and poor resolution may occur. Therefore, when exposure is performed continuously for a long time, an arbitrary alignment mark, for example, a rectangular mark portion extending in the Y-axis direction of the alignment mark RMb is used, and the defocus amount ΔZ
bs. Then, the defocus amount ΔZbs
Exceeds the predetermined allowable range, the defocus amount ΔZ
bs and the data on the memory 28, the defocus amount at each alignment mark position is obtained, and based on the defocus amount at each position, the defocus amount ΔZ and the image plane tilt are calculated from Expressions (1) to (3). The amounts Δθx and Δθy are calculated. Next, main controller 30 responds to this result to drive units 8 and 11.
, A predetermined drive command is output to set an exposure area on the wafer W to an optimal exposure position. By repeating this operation as appropriate, it is possible to perform positioning in the Z-axis direction while following a change in the state of the imaging surface according to the heat accumulation amount E of the projection lens 6.

When the thickness unevenness of the resist or the like occurs on the wafer W, the offset is generated by the defocus amount ΔZ calculated by the above equation (1), that is, the optimum focus position is set to the zero point reference. Then, the angle of the parallel flat glass (plane parallel) provided inside the light receiving optical system 31b is adjusted, and the focus detection system 31 is calibrated. Then, the position of the exposure area on the wafer W in the Z-axis direction is detected for each exposure area using the focus detection system 31, and the focus detection system 3 is adjusted so that the difference between this position and the zero point reference becomes zero.
By moving the wafer stage 9 in the Z-axis direction based on the output signal of No. 1, it is possible to prevent the occurrence of poor resolution or the like due to unevenness in the thickness of the resist. Further, in parallel with the focusing by the focus detection system 31, a horizontal position detection system 32 is used for each exposure area, and based on an output signal of the horizontal position detection system 32, the inclination of the exposure area surface is determined by the image plane inclination amount Δθx, If the leveling stage 7 is driven so as to coincide with Δθy, occurrence of poor resolution or the like is similarly prevented, and high-precision exposure can be performed on the entire surface of the wafer W.

In this embodiment, the first focus position detecting system 25 is used.
And the second focus position detection system 26 are provided to perform the focus position detection. However, it is not necessary to use two sets of focus position detection systems. For example, the pupil image Ep ′ of the projection lens 6 is converted to a surface of the coordinate system XY. The light splitter is provided at a position substantially conjugate to the pupil plane Ep of the projection lens 6 so as to split the wavefront in a direction inclined by 45 degrees within the direction of the projection lens 6 so as to receive the illumination light split by the light splitter. If two detectors are arranged, it is clear that the same effect can be obtained even with one set of focus position detection systems.

In this embodiment, the defocus amount ΔZbs (ΔZb) in the S direction (or M direction) at the position of at least one alignment mark (for example, RMb).
m) is detected, and the defocus amount ΔZbs and the memory 2
8, the defocus amount ΔZ and the field curvature amounts Δθx and Δθy are calculated from the equations (1) to (3). However, the heat accumulation amount E is calculated from the output signal of the detector 12 (irradiation energy amount per unit time) and the closing and opening times of the rotary shutter, and the heat accumulation amount E is used instead of the above-described defocus amount. Based on the heat accumulation amount E and the data in the memory 28, the equations (1) to (3)
From the defocus amount ΔZ and the field curvature amounts Δθx and Δθy
, The same effect can be obtained.

[0028]

As described above, according to the present invention, even if the state of the imaging surface of the projection optical system changes in accordance with the amount of irradiation energy of the exposure light which is accumulated in the projection optical system, this image formation can be achieved. image
Since the correction is performed in accordance with the state of the surface, the precision of the focus position control with respect to the practical depth of focus of the projection optical system can be increased, and the exposure can always be performed in a focused state (best focus).

If the focal position at that position is determined from the focal positions in the S direction and the M direction, the focal position can be detected with high accuracy without causing an offset due to astigmatism of the projection lens. be able to.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a stepper having a focusing function according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a schematic configuration of a device reticle. (B) The figure which shows the schematic structure of a test reticle.

FIG. 3 is a plan view showing a schematic configuration of a reticle mark used for focus position detection.

FIG. 4A is a diagram for explaining an arrangement of a light splitter used when detecting a focal position using a mark extending in a Y-axis direction. (B) A diagram for explaining the arrangement of a light splitter used when detecting a focal position using a mark extending in the X-axis direction.

FIG. 5A is a diagram provided for explanation when a projected image of a fiducial mark scans a reticle mark. (B) A diagram showing a waveform signal obtained when detecting a change in the light amount of the detector in synchronization with the position signal of the wafer stage. FIG. 3C is a diagram for describing detection of a defocus amount.

FIG. 6 is a diagram illustrating a change in an image forming surface due to a change in temperature of a projection lens.

[Explanation of Signs of Main Parts]

7: Leveling stage, 9: Wafer stage, 12: Detector (irradiation energy amount detector), 20: Reference member, 24: Half mirror,
25x, 26y ... light splitter, 25a, 25b, 26
a, 26b: detector, 27: waveform processing device, 28: memory, 30: main controller, 31
a, 31b: focus detection system; 32a, 32b: horizontal position detection system; R: reticle; W: wafer.

Claims (9)

(57) [Claims] 1. A method of projecting a pattern formed on a mask onto a substrate via a projection optical system, comprising: irradiating energy with energy rays incident on the projection optical system.
Process and for storing the optical axis direction of the variation characteristic of the projection optical system at a plurality of points in the image plane of the projection optical system caused in accordance with the heat accumulated amount accumulated in the projection optical system by Energy; the mask Irradiation energy that enters the projection optical system through
The amount of heat accumulated in the projection optical system by energy
Calculating; and calculating a state of an imaging plane of the projection optical system based on the fluctuation characteristics and the heat accumulation amount ; and calculating the state of the imaging plane according to the calculated state of the imaging plane. Adjusting the relative position between the substrate and the substrate. 2. The projection exposure method according to claim 1, wherein adjusting the relative position includes adjusting a position of the substrate with respect to the projection optical system. 3. The projection optical system according to claim 1, wherein the variation characteristics in the optical axis direction of the projection optical system in two different directions at a plurality of points in an image plane of the projection optical system are stored. Projection exposure method. 4. The projection exposure method according to claim 3, wherein said two different directions are a sagittal direction and a meridional direction. 5. An apparatus for projecting a pattern formed on a mask onto a substrate via a projection optical system, wherein the irradiation energy by an energy ray incident on the projection optical system is provided.
Measuring means for measuring the optical axis direction of the variation characteristic of the projection optical system at a plurality of points in the image plane of the projection optical system caused in accordance with the heat accumulated amount accumulated in the projection optical system by Energy; the Means for storing a variation characteristic; unit time for entering the projection optical system via the mask
Means for measuring irradiation energy per unit time ; irradiation energy per unit time ;
Based on the time information at which the ray enters the projection optical system,
Calculating the amount of heat stored in the projection optical system
If, on the basis of the variation characteristics and the heat storage amount, the calculation means for calculating a state of the focal plane of the projection optical system; based on the calculation result, the relative position between the substrate and the imaging plane A projection exposure apparatus, comprising: an adjusting unit that adjusts the distance. 6. An adjusting means for adjusting a relative position between the imaging surface and the substrate with respect to an optical axis direction of the projection optical system, and adjusting a relative inclination between the imaging surface and the substrate. The projection exposure apparatus according to claim 5, further comprising an adjustment mechanism that performs at least one of the following. 7. The mask has two measurement marks extending in two different directions at each of a plurality of measurement points, and the measurement means uses the measurement marks to measure the plurality of points of the projection optical system. The projection exposure apparatus according to claim 5, wherein a fluctuation characteristic in an optical axis direction is measured. 8. The projection exposure apparatus according to claim 7, wherein said two different directions are a sagittal direction and a meridional direction. 9. A circuit manufacturing method for projecting a pattern formed on a mask onto a substrate via a projection optical system, the method comprising: irradiating energy by an energy ray incident on the projection optical system.
Process and for storing the optical axis direction of the variation characteristic of the projection optical system at a plurality of points in the image plane of the projection optical system caused in accordance with the heat accumulated amount accumulated in the projection optical system by Energy; the mask Irradiation energy that enters the projection optical system through
The amount of heat accumulated in the projection optical system by energy
Calculating; and calculating a state of an imaging plane of the projection optical system based on the fluctuation characteristics and the heat accumulation amount ; and calculating the state of the imaging plane according to the calculated state of the imaging plane. Adjusting the relative position between the substrate and the substrate.