JPH10209030A - Method and apparatus for projection exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always ensure a high-accuracy exposure, without influence of partial irregularity of exposing regions on a photosensitive substrate surface. SOLUTION: Before exposure, a wafer W is moved in a two-dimensional plane, the positions at measuring points e.g. P4-P6 on the optical axis (Z) of the wafer surface are measured to see the irregularity, and the best imaging plane Fo of a projection optical system is measured. Face elements 62 of a wafer holder 25 for vacuum chucking the back side of the wafer W are driven by specified lengths along the optical axis to align the wafer surface with the best imaging plane Fo of the optical system, thus always ensuring a high- accuracy exposure.

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 optical system which illuminates a mask on which a pattern is formed by exposure light and projects an image of the pattern formed on the mask. And a projection exposure apparatus to which the exposure method is applied.

[0002]

2. Description of the Related Art A projection exposure apparatus for exposing an image of a mask pattern on a photosensitive substrate on a stage through a projection optical system using exposure light such as ultraviolet light is used for various precision processing such as manufacturing of semiconductor elements. Has been put to practical use.

In these projection exposure apparatuses, a focusing mechanism that sets a current exposure area (shot area) of a photosensitive substrate within a range of a depth of focus of an imaging surface of a projection optical system, that is, an autofocus mechanism is required.

[0004] Such focusing mechanisms are generally classified into a direct system and an indirect system. In the direct method of
The focal point of the image of the mask pattern on the reference surface provided on the stage is directly detected using the exposure light. Specifically, as disclosed in, for example, JP-A-1-286418, an image of a special mark formed on the mask pattern surface is projected on the reference surface. Then, the projected image of the mark formed on the reference plane is observed through the projection optical system and the mark, and the focal point is determined by detecting the peak of the light amount of the projected image narrowed down by the mark.

On the other hand, in the indirect method, a measuring means for measuring the height of the stage with respect to the projection optical system is separately provided, and the origin of the measuring means is adjusted to the focal point determined in advance using the direct method described above. The height of the exposed surface of the photosensitive substrate is detected using a measuring unit, and the exposed surface is indirectly guided to the focal point. For example, Japanese Patent Laid-Open No. 1-41
Japanese Patent Application Laid-Open No. 962 or Japanese Patent Application Laid-Open No. S60-168112 discloses an example of a means for measuring the height of a stage using an oblique incidence type optical system fixed outside the projection optical system. A mechanism for measuring the height of the exposure surface immediately below is disclosed.

A special example of a focusing mechanism is disclosed in, for example, Japanese Patent Application Laid-Open No. 57-212406, in which a special mark formed on a pattern surface of a mask is directly projected on an exposure surface of a photosensitive substrate. Is detected directly through the projection optical system and the mark to directly determine the focal point.

In the conventional projection exposure apparatus, the line width of the pattern to be exposed is not very fine, and there is a certain margin in the depth of focus of the projection optical system. Did not have to consider much.

[0008]

By the way, integrated circuits are becoming more and more integrated year by year, and pattern line widths are becoming finer and finer. Accordingly, even in a projection exposure apparatus, an increasingly higher processing accuracy is required in recent years. It has become. For this reason, the resolution of the projection exposure apparatus has been improved by shortening the wavelength of the exposure light and increasing the numerical aperture (NA) of the projection optical system. .A.)
Increasing the value has a surface on the other hand that the depth of focus becomes shallower.

For example, in recent manufacture of a semiconductor memory device having particularly high processing accuracy, a wavelength of 365 nm is used as exposure light.
A projection exposure apparatus using a projection optical system that uses m i-lines and has a focal depth of 1 μm or less is used. In this case, an accuracy of 0.1 μm or less is usually required as the focusing accuracy of the focal point. For example, Japanese Patent Publication No. Sho 62-50811
In a special projection exposure system using the interference phenomenon of exposure light disclosed in Japanese Patent Application Laid-Open Publication No. HEI 7-303, extremely high accuracy of 0.05 μm or less is required.

As described above, the depth of focus of the projection optical system of the projection exposure apparatus becomes increasingly shallow, and the above-described autofocus mechanism makes the entire surface of a shot area on a photosensitive substrate such as a wafer average in the optical axis direction of the shot area. With the conventional method of aligning with a plane, it is becoming difficult at present to fit the entire shot area within the depth of focus of the projection optical system when there is partial unevenness or the like in an exposure shot. is there.

Further, the projection optical system has a considerable amount of curvature of field and the like. Strictly speaking, since the imaging surface is not a plane, the curvature of field and the like are reduced as the depth of focus becomes shallower. The influence of the imaging characteristics on the focusing accuracy is becoming increasingly negligible.

The present invention has been made under such circumstances, and an object of the present invention is to always perform high-precision exposure without being affected by partial unevenness of a region to be exposed on the surface of a photosensitive substrate. And a projection exposure method.

It is another object of the present invention to provide a projection exposure apparatus capable of always performing high-precision exposure without being affected by partial unevenness or the like of a region to be exposed on the surface of a photosensitive substrate. .

[0014]

According to the first aspect of the present invention, an image of a pattern (PA) formed on a mask (R) is exposed on a photosensitive substrate (W) via a projection optical system (PL). Prior to exposure, the photosensitive substrate (W) is moved in a two-dimensional plane while the position of the surface of the photosensitive substrate (W) in the direction of the optical axis of the projection optical system (PL) is exposed. The photoelectric substrate detects the change in the photosensitive substrate (W)
A first step of measuring surface irregularities; and the projection optical system (P
L) a second step of measuring the imaging characteristic; and, based on the results of the first step and the second step, the area to be exposed (SE) on the photosensitive substrate (W) is changed to the projection optical system (PL). A third step of setting the shape of the surface of the photosensitive substrate (W) so as to coincide with the best image forming plane.

According to this, prior to exposure, the change in the position of the surface of the photosensitive substrate in the optical axis direction of the projection optical system is photoelectrically detected while moving the photosensitive substrate in a two-dimensional plane in the first step. Then, the irregularities on the surface of the photosensitive substrate are measured, and the imaging characteristics of the projection optical system are measured in the second step. Here, the image forming characteristic of the projection optical system to be measured in the second step means the image forming characteristic used to match the exposed area on the photosensitive substrate with the best image forming plane of the projection optical system. This means, for example, an imaging characteristic related to the two-dimensional distribution of the best imaging point in the optical axis direction in the field of view of the projection optical system, such as field curvature.

In the third step, the surface shape of the exposed area (shot area) of the photosensitive substrate is changed based on the measurement result of the unevenness on the surface of the photosensitive substrate and the measurement result of the imaging characteristics of the projection optical system. The surface shape of the photosensitive substrate is set so as to coincide with the best image forming plane. Here, "matching with the best imaging plane" means that the entire surface of the exposure region is included within the width of the depth of focus of the projection optical system, and that the entire surface of the exposure region of the photosensitive substrate is focused. Means

When exposure is started in a state where the entire surface of the region to be exposed on the photosensitive substrate coincides with the best image forming plane of the projection optical system, the pattern image of the mask is integrated through the projection optical system. The area to be exposed on the photosensitive substrate in the focused state is projected and exposed. Therefore, high-precision exposure can always be performed without being affected by partial irregularities on the surface of the photosensitive substrate.

According to a second aspect of the present invention, an image of a pattern (PA) formed on a mask (R) is projected onto a projection optical system (PL).
A projection exposure apparatus for exposing a photosensitive substrate (W) held on a stage (18) movable in a two-dimensional direction through the stage, and holding the photosensitive substrate (W) on the stage (18). A substrate holding mechanism (25) capable of changing the shape of the contact surface with the photosensitive substrate (W); and the projection optical system (PL) at predetermined measurement points (P1 to P9) on the surface of the photosensitive substrate (W). ), A detecting means (40, 42) for photoelectrically detecting the position of the projection optical system (P) in the direction of the optical axis (AX).
L), the best image plane (Fo) at any point in the projection field of view.
A) imaging characteristic measuring means (30) for measuring a position; said detecting means (40, 42) and imaging characteristic measuring means (30).
Based on the measurement result, the exposure area (SE) on the photosensitive substrate (W) coincides with the best imaging plane of the projection optical system (PL). Control means (44) for changing the shape of the contact surface with W).

According to this, prior to exposure, while the stage holding the photosensitive substrate is moved in a two-dimensional plane, the change in the position of the surface of the photosensitive substrate in the optical axis direction of the projection optical system is detected by the detecting means. Then, the unevenness of the photosensitive substrate surface is measured. Similarly, while moving the stage in a two-dimensional plane, the distribution of the best imaging plane position in the projection field of view of the projection optical system is measured by the imaging characteristic measuring means. Then, the control means controls the substrate holding mechanism based on the measurement results of the detection means and the imaging characteristic measuring means so that the exposure area (shot area) on the photosensitive substrate coincides with the best imaging plane of the projection optical system. Change the shape of the contact surface with the substrate. Here, "matching with the best imaging plane" means that the entire surface of the exposure area is included within the width of the depth of focus of the projection optical system, as in the case of the first aspect of the present invention. This means that the entire surface of the region to be exposed on the photosensitive substrate is focused.

When exposure is started in a state where the entire surface of the region to be exposed on the photosensitive substrate coincides with the best image forming plane of the projection optical system, the entire pattern image of the mask is projected through the projection optical system. Projection exposure is performed on a region to be exposed on the photosensitive substrate in a focused state. Therefore, high-precision exposure can always be performed without being affected by partial irregularities on the surface of the photosensitive substrate.

In this case, the substrate holding mechanism that can hold the photosensitive substrate on the stage and change the shape of the contact surface with the photosensitive substrate changes the exposure area (shot area) of the photosensitive substrate to the projection optical system. Any structure may be used as long as the surface shape of the photosensitive substrate can be set so as to match the image forming surface. For example, as described in the third aspect of the present invention, the substrate holding mechanism (25) includes a stage ( 18) A large number of surface elements (62) provided on the photosensitive substrate (W) and constituting a holding member of the photosensitive substrate (W), and each surface element (62) is independently extended in the optical axis (AX) direction of the projection optical system (PL). A configuration having a number of driving mechanisms (68) for driving may be employed. According to the substrate holding mechanism having such a configuration, it is possible to easily change (set) the shape of the photosensitive substrate surface to a desired shape by independently driving each surface element by the driving mechanism.

Further, the imaging characteristic measuring means measures at least one of field curvature and astigmatism of the projection optical system (PL) as in the invention according to claim 4. Is also good.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG.

FIG. 1 shows a schematic configuration of a projection exposure apparatus 10 according to one embodiment. This projection exposure apparatus 10
Is a so-called step-and-repeat type reduction projection type exposure apparatus.

The projection exposure apparatus 10 includes an illumination optical system (not shown) for illuminating a reticle R as a mask, a reticle holder 36 for holding the reticle R, and an image of a pattern formed on the reticle R as a photosensitive substrate. It has a projection optical system PL for projecting onto the wafer W, a stage device 14 for mounting and moving the wafer W, and a main controller 44 for controlling the entire projection exposure apparatus 10.

An illumination optical system (not shown) includes, for example, a light source such as a mercury lamp, an elliptical mirror for condensing exposure light emitted from the light source, and converts the collected exposure light into a substantially parallel light beam. An input lens, a fly-eye lens into which a light beam output from the input lens enters to form a number of secondary light sources on a rear (reticle side) focal plane, and collects exposure light emitted from these secondary light sources. It can be configured to include a condenser lens system or the like that illuminates the reticle R with uniform illuminance by emitting light. In the present embodiment, two L-shaped movable blades 45A and 45 are provided in the illumination optical system.
B. A movable blind as a variable field stop having B (hereinafter referred to as a “movable blind 45
A, 45B "), and the arrangement surface of the movable blinds 45A, 45B is conjugate with the pattern surface of the reticle R. In addition, this movable blind 45
A fixed blind 46 whose opening shape is fixed is arranged near A and 45B. The fixed blind 46 is, for example, a field stop surrounding a rectangular opening with four knife edges, and the rectangular opening defines an area that can be exposed by the projection optical system.

The movable blinds 45A and 45B are driven in the X and Z directions in the XZ plane by the movable blind drive mechanisms 43A and 43B, whereby a part of the illumination area on the reticle R defined by the fixed blind 46 is reduced. Masked, illumination area of any shape (including size)
As a result, the exposure area SE (see FIG. 7) on the wafer W, which is conjugate to the illumination area on the reticle R, is also set to a rectangular area of any shape (including size). That is, in the present embodiment, the exposure area SE on the wafer W is set by the movable blinds 45A and 45B. The operations of the drive mechanisms 43A and 43B are controlled by the main controller 44 in accordance with blind setting information (masking information) from a main computer (not shown).

The reticle R illuminated by the illumination optical system (not shown) is held by a reticle holder 36.

The reticle holder 36 has four
A vacuum suction portion 34 is provided at one corner portion, and the reticle R is held on the reticle holder 36 via the vacuum suction portion 34. The reticle holder 36 has an opening (not shown) corresponding to a pattern area PA on the reticle R where a circuit pattern is formed, and is driven by a driving mechanism (not shown) in the X, Y, and θ directions (Z direction). (Rotational direction around the axis), whereby the center (reticle center) of the pattern area PA is aligned with the projection optical system PL.
Of the reticle R so as to pass through the optical axis AX.

Further, in the present embodiment, when the wafer W is located within the pattern projection area by the projection optical system PL,
In order to detect the position of the surface of the wafer W in the Z direction (the optical axis AX direction), a first focus detection system (40, 4) of the oblique incidence method is used.
2) is provided. The first focus detection system includes an irradiation optical system 40 including an optical fiber bundle 81, a condenser lens 82, a slit plate 83, a lens 84, a mirror 85, and an irradiation objective lens 86; a condenser objective lens 87; The light receiving optical system 42 includes a plate 88, an imaging lens 89, a light receiving slit plate 93, and a photo sensor 90 such as a silicon photodiode or a phototransistor.

Here, the first focus detection system (40, 4)
Explaining the operation of each component of the configuration 2), illumination light having a wavelength that is different from the exposure light EL and does not expose the photoresist on the wafer W is guided from an unillustrated illumination light source via an optical fiber bundle 81. The illumination light emitted from the optical fiber bundle 81 illuminates the slit plate 83 via the condenser lens 82. The illumination light that has passed through the slit (opening) of the slit plate 83 passes through the lens 84, the mirror 85, and the irradiation objective lens 8
6 irradiates the wafer W obliquely. At this time, if the surface of the wafer W is on the best image forming plane, an image of the slit of the slit plate 83 is formed on the surface of the wafer W by the lens 84 and the irradiation objective lens 86. Further, the angle between the optical axis of the objective lens 86 and the wafer surface is set to about 5 to 12 degrees,
The center of the slit image of the slit plate 83 is located at the projection optical system PL.
Is located at a point where the optical axis AX intersects the wafer W.

The slit image light beam reflected by the wafer W passes through the converging objective lens 87, the rotation direction vibration plate 88, and the imaging lens 89, and falls on the light receiving slit plate 93 disposed on the front side of the photo sensor 90. It is re-imaged. The rotation direction vibration plate 88 minutely vibrates a slit image formed on the light receiving slit plate 93 in a direction orthogonal to the longitudinal direction. Here, the imaging lens 89 and the light receiving slit plate 9
3, the relative relationship between the slit on the light receiving slit plate 93 and the vibration center of the reflected slit image from the wafer W is
A plane parallel for shifting in the direction orthogonal to the longitudinal direction of the slit may be arranged.

Here, the main controller 44 includes an oscillator (OS
C. ) Is built in, and this OSC. The vibrating device 92 driven by the drive signal from the
8 is vibrated.

When the slit image vibrates on the light receiving slit plate 93 in this manner, the light beam transmitted through the slit of the slit plate 93 is received by the photo sensor 90. Then, a detection signal (photoelectric conversion signal) from the photo sensor 90 is supplied to the signal processing device 91. The signal processing device 91 has a built-in synchronous detection circuit (PSD).
OSC. An AC signal having the same phase as the drive signal from is input. Then, the signal processing device 91 performs synchronous rectification based on the phase of the AC signal, and the detection output signal, that is, the focus position detection signal FS is output to the main control device 44. The focus position detection signal FS is called a so-called S-curve signal, and becomes a zero level when the center of the slit of the light receiving slit plate 93 coincides with the center of vibration of the reflected slit image from the wafer W, and the wafer W changes from that state. Positive level when displaced upward, wafer W
Is at a negative level when is displaced downward. Therefore, the height position (position in the optical axis direction) of the wafer W at which the focus position detection signal FS becomes zero level is detected as the focal point.

However, in such an oblique incidence method, there is no guarantee that the height position of the wafer W at the focal point (the signal FS is zero level) always coincides with the best imaging plane. That is, the focus position detection signal FS is a signal indicating the position of the reference mark plate FM or the wafer W in the optical axis direction of the projection optical system PL, and is a signal indicating the focus position in an indirect manner. Therefore, in order to detect the in-focus point using the focus position detection signal FS, the reference mark plate FM is directly determined in advance.
Alternatively, the in-focus state of the wafer W with respect to the projection optical system PL is checked, and the level of the focus position detection signal FS at the true in-focus position or at a position near the true in-focus position is determined at a predetermined level (this is referred to as “pseudo” Adjustment (first focus detection system (40, 42))
Of the substrate table 18 so that the signal FS becomes the pseudo focus level thereafter.
What is necessary is just to control the axial movement. For example, 0 is used as the pseudo focus level.

In such a case, in order to calibrate the first focus detection system (40, 42) by setting a predetermined offset to the level of the focus position detection signal FS at the focal point or the like, optical and Although there is an electrical method, in order to set optically, the distribution of the amount of light on the light receiving surface of the photo sensor 90 is determined in a state where the reference mark plate FM or the like is at a predetermined position in the Z-axis direction. Should be changed to the position. For example, as described above, when the plane parallel is arranged on the front surface of the photosensor 90 and the angle of the plane parallel is changed, the distribution of the amount of light on the light receiving surface of the photosensor 90 changes. be able to. Further, an offset may be electrically added so that the value of the signal FS becomes the in-focus level.

As described above, since the focus position detection signal FS is a signal indicating a focal point in the indirect method, the focus position detection signal FS is generated when the position of the image plane (focal point) of the projection optical system PL changes due to exposure light absorption or the like. May have a difference between the focal point at which the signal FS becomes a pseudo-focusing level and the actual focal point. Therefore, in the present embodiment, the offset setting of the focus position detection signal FS (the calibration of the first focus detection system (40, 42)) is performed using the calibration signal KS. For this reason, in the present embodiment, the best imaging plane of the projection optical system PL is detected and the calibration signal K is detected.
A second focus detection system 30 that outputs S to the main controller 44 is provided.

Next, a second focus detection system 3 as imaging characteristic measuring means for detecting the best imaging plane of the projection optical system PL.
0 will be described with reference to FIG.

FIG. 2 shows the configuration of the second focus detection system 30 of the TTL system for detecting the best focus plane of the projection optical system PL constituting the projection exposure apparatus 10 according to the present embodiment.

The second focus detection system 30 includes a reference mark plate FM (more precisely, a reference pattern on the reference mark plate) fixed on a substrate table 18 to be described later at a height substantially equal to the surface of the wafer W. A mirror M1, an objective lens 50 for illumination, and an optical fiber 51 provided below the reference mark plate FM (inside the substrate table 18);
1 is provided with a beam splitter 52, lens systems 53 and 54, and a photoelectric sensor 55 provided on the incident end side.

In FIG. 2, a projection optical system PL is schematically shown divided into a front group and a rear group with a stop surface (pupil surface) EP interposed therebetween.
The optical axis AX passes through the center of the reticle R, that is, the center of the pattern area PA, perpendicularly to the reticle pattern surface.

On the upper surface of the reference mark plate FM, as shown in FIG. 3, an amplitude type diffraction grating mark 28A composed of lines / spaces having a constant pitch and the diffraction grating mark 28A are each set at 45 ° in a counterclockwise direction. , 90 ° and 135 °, diffraction grating marks 28B, 28C and 28D are formed. The reference pattern 28 is constituted by these four types of diffraction grating marks 28A to 28D. The formation of the diffraction grating marks in various directions in this way is for eliminating the influence of the pattern on the reticle R, and in the sagittal (S) direction and the meridional (M) at an arbitrary point in the image field of the projection optical system PL. This is because the focus position (astigmatism) in the direction (1) can be measured. The diffraction grating mark forming surface of the reference mark plate FM and the exposure surface of the wafer W are set to have the same height in the optical axis direction of the projection optical system PL. Note that the pattern formed on the reference mark plate FM may be a phase type diffraction grating mark.

In FIG. 2, the illumination light EL for exposure is introduced into the optical fiber 51 via the lens system 53 and the beam splitter 52 arranged on the incident end side of the optical fiber 51. This illumination light is emitted from the emission end of the optical fiber 51, is collected by the objective lens 50, and is
1, the diffraction grating marks 28A-28 of the reference mark plate FM
Both 28D are irradiated from the back side. Here, the illumination light EL
Is preferably obtained from a light source for reticle R illumination (a mercury lamp, an excimer laser, or the like), but a dedicated light source may be separately prepared. However, when a different light source is used, it is necessary to use illumination light having the same wavelength as the exposure illumination light or a wavelength very similar thereto.

The illumination condition of the reference mark plate FM by the objective lens 50 is matched as much as possible with the illumination condition of the projection optical system PL during pattern projection, that is, the projection optical system PL
Numerical aperture (NA) of illumination light on the image side of objective lens 50
Numerical aperture (NA) of illumination light from the camera to the fiducial mark plate FM
It is desirable to make approximately the same.

From the diffraction grating marks 28A to 28D on the reference mark plate FM irradiated by the illumination light EL, an image light beam to be transmitted to the projection optical system PL is generated. In FIG. 2, it is assumed that the substrate table 18 is set so that the reference mark plate FM is located slightly below the best imaging plane (reticle conjugate plane) Fo of the projection optical system PL. At this time, the image light beam L1 generated from one point on the reference mark plate FM passes through the center of the pupil plane EP of the projection optical system PL and converges on a plane Fr slightly shifted downward from the pattern plane of the reticle R and then diverges. Then, after being reflected by the pattern surface of the reticle R, the light returns to the original optical path. Here, the surface Fr is at a position conjugate with the reference mark plate FM with respect to the projection optical system PL. Projection optical system PL
Is a telecentric system, the reference mark plate FM
The image luminous fluxes from the upper diffraction grating marks (light emission marks) 28A to 28D are regularly reflected on the lower surface (pattern surface) of the reticle R and are again reflected by the diffraction grating marks (light emission marks) 28A to 28D.
It returns to overlap with D. However, if the reference mark plate FM is displaced from the imaging plane Fo as shown in FIG. 2, blurred reflection images of the marks 28A to 28D are formed on the reference mark plate FM, and the reference mark plate FM When coincident with the surface Fo, the surface Fr also coincides with the pattern surface of the reticle R, and each mark 28 is placed on the reference mark plate FM.
A sharp reflected image of A to 28D is formed so as to be superimposed on each mark. In the double-sided telecentric projection optical system PL, the reflected image from the pattern surface of the reticle R is projected onto the light-emitting marks 28A to 28D as its own source. When the reference mark plate FM is defocused, the reflected image becomes larger than the shapes and dimensions of the marks 28A to 28D, and the illuminance per unit area also decreases.

Therefore, of the reflected image formed on the reference mark plate FM, the light flux of the image portion not shielded by the original marks 28A to 28D is received by the optical fiber 51 via the mirror M1 and the objective lens 50, and the beam is received. The light is received by the photoelectric sensor 55 via the splitter 52 and the lens system 54. The light receiving surface of the photoelectric sensor 55 is arranged almost conjugate with the pupil plane (Fourier transform plane) EP of the projection optical system PL.

In the configuration shown in FIG.
The contrast signal can be obtained simply by moving in the vertical direction (Z direction).

FIG. 4 shows an output signal of the photoelectric sensor 55, that is, a signal level characteristic of the calibration signal KS. 4, the horizontal axis represents the position of the substrate table 18 in the Z-axis direction, that is, the height position of the reference mark plate FM in the optical axis AX direction. Here, FIG. 4A shows a signal level when the light emitting marks 28A to 28D are back-projected onto a chrome portion in the pattern surface of the reticle R,
FIG. 4B shows a signal level when back-projected onto a glass portion (transparent portion) in the pattern plane. Normally, the chrome portion of the reticle is deposited on a glass (quartz) plate with a thickness of about 0.3 to 0.5 μm, and the reflectance of the chrome portion is, of course, much higher than the reflectance of the glass portion. However, since the reflectivity at the glass portion is not completely zero, the detection is possible although the level is considerably small as shown in FIG. 4B. In general, since the reticle for manufacturing an actual device has a high pattern density, it is considered that the probability that all back-projected images of the light emitting marks 28A to 28D are simultaneously applied to the glass portion (transparent portion) in the reticle pattern is extremely small.

In any case, when the surface of the reference mark plate FM is moved in the optical axis direction so as to cross the best imaging plane Fo, the signal level becomes a maximum value at the position Zo in the Z direction. Therefore, the position of the best imaging plane Fo is determined by simultaneously measuring the position of the substrate table 18 in the Z-axis direction and the output signal KS and detecting the position in the Z-axis direction when the signal level is maximized. In this detection method, the imaging plane Fo can be detected at an arbitrary position in the reticle R. That is, as long as the reticle R is set on the object side of the projection optical system PL, the absolute focus position (best imaging plane Fo) can be measured at any position in the projection visual field (image field) at any time. Also, as described above, reticle R
The thickness of the chromium layer is 0.3 to 0.5 μm, and the detection error of the best imaging plane Fo caused by this thickness is (0.3) when the projection magnification of the projection optical system PL is reduced by, for example, ５.
^{~0.5) × (1/5) 2 =} 0.012~0.02μm next, which is a value almost negligible.

Returning to FIG. 1, the stage device 14 includes a base 11, a Y stage 16 which can reciprocate on the base 11 in the Y-axis direction (left-right direction on the paper) of FIG.
An X stage 12 that can reciprocate on the Y stage 16 in an X axis direction (a direction orthogonal to the paper surface) orthogonal to the Y axis direction;
And a substrate table 18 provided on the X stage 12. A wafer holder 25 as a substrate holding mechanism is mounted on the substrate table 18, and the wafer W is held by the wafer holder 25 by being vacuum-sucked. The stage device 14 can be moved along the optical axis AX of the projection optical system PL by a Z stage (not shown).

FIG. 7 is a plan view of the wafer holder 25 with the wafer W mounted thereon, and FIG. 8 is an exposure area (shot area) SE on the wafer W shown in FIG.
An enlarged plan view of the wafer holder 25 corresponding to the portion is shown. As shown in FIG. 8, the wafer holder 25
Has many surface elements 62 arranged in a matrix. Here, the shape of each surface element 62 is circular, but the shape of the surface element is not limited to a circle, and may be, for example, a triangle, a quadrangle, or another polygonal shape.

FIG. 9A is a schematic sectional view taken along line AA of FIG. As shown in FIG. 9A, a suction hole 64 is formed at the center of each of the surface elements 62 constituting the wafer holder 25, and the back surface of the wafer W is connected to each of the surface elements via the suction hole 64. 62 holds it by suction.

FIG. 10A shows one surface element 62 and its vicinity in a partially cutaway manner.
FIG. 2B is a plan view of the surface element 62 shown in FIG. As shown in FIG. 10A, one end of a support shaft 66 is connected to the surface of the surface element 62 opposite to the wafer holding surface (the upper surface in FIG. 10A). At the end, the support shaft 66 is
It is connected to one end of a drive mechanism 68 that drives in the vertical direction (Z-axis direction) in FIG. The drive mechanism 68 is formed of, for example, a piezo element, which is a piezoelectric element. The amount of displacement of the surface element 62 in the Z-axis direction via the support shaft 66 is approximately 5/100 μm in accordance with the amount of voltage applied to the drive mechanism 68. It can be adjusted with the precision of. The drive mechanism 68
Does not necessarily need to be composed of piezo elements,
Other actuators such as an ultrasonic linear motor may be employed as long as the actuator can achieve the accuracy of about 5/100 μm.

The suction hole 64 has a vacuum pipe 70.
And the other end of the vacuum pipe 70 is connected to a vacuum pump or the like (not shown). The vacuum pump operates so that the back surface of the wafer W is suctioned to the surface element 62 through the suction hole 64. It has become.

As shown in FIG. 9B, the respective surface elements 62 are attracted to the rear surface of the wafer W by the respective drive mechanisms 68 in the optical axis AX direction (Z-axis direction) of the projection optical system PL. And deforms the rear surface of the wafer W to set the surface shape of the wafer W to a desired shape. In FIG. 9B, when the best imaging plane Fo of the projection optical system PL is a plane, the plane element 62 is driven such that the shot area SE of the wafer W coincides with the best imaging plane Fo. The state is shown.

A drive mechanism 68 for driving each surface element 62 in the Z-axis direction is independently controlled by the main controller 44 shown in FIG.

Next, with reference to FIG. 5, an example of the overall operation when the focus position detection signal FS is calibrated by the projection exposure apparatus 10 according to the present embodiment will be described. In this case, it is assumed that the position of the Z-axis coordinate ZB of the substrate table 18 has been set as the focal point by the previous calibration or the like.

First, in step 101 of FIG. 5, the main controller 44 controls the X stage 1
2. By operating the Y stage 16, the reference mark plate FM is moved to a desired measurement point in the image field of the projection optical system PL. In the next step 102, the main controller 44 moves the Z-axis coordinate of the substrate table via the driving device 21 downward by Z from the current focal point ZB. The interval ΔZ is the maximum expected absolute value of the fluctuation of the imaging plane of the projection optical system PL in the Z-axis direction, ZMAX.
Then, it is selected such that ΔZ> ZMAX.

Then, main controller 44 determines in step 10
3, the Z-axis coordinate of the substrate table 18 is changed to (ZB-.DELTA.Z) via the driving device 21 and a Z.theta. Driving mechanism (not shown).
From above at an almost constant speed. When this scanning is started, in step 104, the main controller 44
Synchronizes with a predetermined sampling pulse, fetches a calibration signal KS and a focus position detection signal FS in parallel, and writes them in an internal memory. Then, in step 105, the main controller 44 checks whether or not the Z-axis coordinate of the substrate table has reached (ZB + ΔZ).
If the Z-axis coordinate has not reached (ZB + ΔZ), the process returns to step 103 to continue scanning in the Z-axis direction. If the Z-axis coordinate has reached (ZB + .DELTA.Z) in step 105, the process proceeds to step 106.

In the above steps 102 to 105, for example, a series of address areas in the first storage area in the internal memory of the main controller 44 are indicated by a solid curve 38 in FIG. The calibration signal KS is stored in a series of address areas in the second storage area in the internal memory, and the focus position detection signal FS that changes in an S-shape around 0 as shown in FIG. Is stored. The horizontal axis in FIGS. 6A and 6B is an address. Since the sampling pulse of this embodiment is a pulse train that becomes a high level “1” at regular time intervals, the address is regarded as time t. Can be. Further, since the substrate table 18 rises at a substantially constant speed, an approximate value of the Z-axis coordinates of the substrate table 18 can be obtained by performing a primary conversion on the time t (or the address value).

Returning to FIG. 5, in step 106, the main controller 44 sets a pseudo focal point obtained from the Z-axis coordinate of the true focal point or a position near the true focal point obtained from the calibration signal KS and the focal position detection signal FS. The deviation amount δZ from the Z-axis coordinate of the focal point is calculated.

For example, in the example of FIG. 6, the address when the calibration signal KS becomes the maximum is the true focal point Z.
The address when the focus position detection signal FS becomes 0 in the S-curve characteristic is the address corresponding to the focal point ZB set in the previous calibration. When the grid mark formed on the reference mark plate FM is a phase grating, the signal KS is the signal shown in FIG.
(A), the value becomes the minimum at the true focal point ZC as shown by the one-dot chain line curve 39 in FIG. Therefore, in any case, the signal FS is obtained from the convex or concave peak address of the signal KS.
The deviation amount δZ on the Z-axis coordinate is obtained by subjecting the deviation address amount obtained by subtracting the address of the zero-cross point to a predetermined primary operation.

In this case, as shown in step 107 in FIG. 5, the accuracy of measurement of the amount of deviation can be increased by repeating the operations of steps 102 to 106 n times (n is an integer of 2 or more). Further, as shown in step 108, each time one deviation amount is calculated, the driving device 21
, The X stage 12, the Y stage 16, and a Z / θ drive mechanism (not shown) are operated to displace the reference mark plate FM in a plane perpendicular to the optical axis of the projection optical system PL by a small amount. . As a result, the position of the reticle R on which the images of the diffraction grating marks 28A to 28D of the reference mark plate FM are projected in the pattern area PA is also displaced by a small amount, so that the influence of the pattern of the pattern area PA is eliminated, and the measurement accuracy is reduced. Is prevented from decreasing.

It is a matter of course that the sequence may return to step 102 immediately when it is determined in step 107 that the measurement has not been performed n times.

Thereafter, in step 109, the main controller 44 sets the deviation δZ between the Z-axis coordinate of the true focus or a position near the true focus and the Z-axis coordinate of the pseudo focus obtained from the focus position detection signal FS. Is stored in an internal memory. Thereafter, main controller 44 sets Z set by the previous calibration.
A value obtained by adding <δZ> to the axis coordinate value ZB (ZB +
<ΔZ>) is regarded as the focal point, and the offset is adjusted so that the focal position detection signal FS at this focal point has a predetermined pseudo-focusing level.

According to the second focus detection system 30 according to the present embodiment, as long as the reticle R is set on the object side of the projection optical system PL, the absolute focus position can be set at any position in the image field at any time. (Best imaging plane Fo) can be measured as described above. Therefore, the second focus detection system 30 and the first focus detection system (40,
42), the above steps 102 to 102 are used for each measurement point.
It is not necessary to particularly explain that the processing of 106 can measure the curvature of field of the projection optical system PL.

Therefore, in the present embodiment, the substrate table 1
8 is moved in the XY two-dimensional plane, the field curvature data of the projection optical system PL measured using the first focus detection system (40, 42) and the second focus detection system 30 is stored in the substrate table 18. A memory 96 that is stored in association with the XY coordinate positions is provided in the main control device 44. The specific use of the data stored in the memory 96 will be described later in detail.

Next, the projection optical system PL in the projection exposure apparatus 10 according to the present embodiment configured as described above.
Will be described when the exposure is performed using the entire area of the exposure-possible area as the exposure area SE.

In the case of this exposure operation, the reticle alignment by a reticle microscope (not shown) has been completed as a premise, and the above-mentioned measurement data of the field curvature of the projection optical system is stored in the memory 96. Shall be.

First, the CPU in the main controller 44 waits until the input of the shot size, the total number of shots N, the shot arrangement, parameters for process correspondence, and the like is completed.

In this waiting state, the operator operates the keyboard to input the shot size, the total number N of shots, the shot arrangement, parameters for process correspondence, and the like.
When a command indicating that the input of the parameters has been completed is input, main controller 44 sets surface element 62 and wafer W on wafer W in order to match the surface shape of wafer W with the best imaging plane of projection optical system PL for each shot area. Is obtained by calculation.

This calculation is performed based on the shot size, the shot arrangement (the arrangement data of each shot on the wafer W), and the arrangement data of the surface elements 62 stored in the memory in advance. That is, since the wafer W can be positioned (pre-aligned) with a certain degree of accuracy with respect to the wafer holder 25, the positional relationship between the surface element 62 and each exposure area can be easily determined only by specifying the shot size and the shot arrangement. Can be calculated, and the surface element 62 used for controlling each exposure area SE can be obtained according to the positional relationship.

As described above, the correspondence between each exposure area SE and the surface element 62 to be driven is clarified in advance, so that it is necessary to adjust irregularities in each exposure area SE described later in detail. This can be used when calculating the vertical drive correction amount of the surface element 62. Here, a description will be given assuming that the relative positional relationship between the surface element 62 and the exposure region SE on the wafer W is as shown in FIG.

Next, the main controller 44 drives one or both of the Y stage 16 and the X stage 12 via the driving device 21 so that the reference mark plate FM is positioned below the projection optical system PL. The substrate table 18 is moved, and the output of the laser interferometer 31 at this time is stored in an internal memory (not shown). In the main controller 44, the reference mark plate F
The substrate table 18 is moved by driving one or both of the Y stage 16 and the X stage 12 via the driving device 21 so that M is located below the alignment sensor (not shown). And the output of the laser interferometer 31 are stored in an internal memory (not shown). That is, the baseline measurement is performed in this manner. Note that the sequence of the baseline measurement is the same as that of the conventional projection exposure apparatus also in the present embodiment, and a detailed description thereof will be omitted.

Subsequently, the main controller 44 moves the substrate table 18 via the driving device 21 so that the alignment mark on the wafer W is positioned below the alignment sensor (not shown), and the output of the alignment sensor is determined. The position of the alignment mark is detected based on the output of the laser interferometer 31. In this way, based on the measured value of the alignment mark position attached to the predetermined sample shot and the design value of the shot array, all shot array coordinates on the wafer are obtained by statistical calculation using the least squares method, Based on this, a so-called enhanced global alignment (hereinafter, referred to as “EGA”) calculation for positioning each shot area at the exposure position is performed. Note that this E
Since the GA operation is disclosed in detail in the above-mentioned Japanese Patent Application Laid-Open No. 61-44429, a detailed description thereof will be omitted.

By using such an EGA calculation result, each shot area (for example, corresponding to each semiconductor chip in the case of taking one chip per shot) is projected onto the projection optical system PL.
Substrate table 1 so that it is positioned accurately sequentially
8 can be position-controlled.

Therefore, first, each exposure area SE is positioned below the projection optical system PL based on the EGA calculation, and each measurement point on the wafer W surface in each exposure area SE (for example, as shown in FIG. 8). P1 to P9) are sequentially moved to the center position of the optical axis of the projection optical system PL, and the first focus detection system (illumination optical system 40, light receiving optical system 42) of the oblique incidence system is used to move the measurement points in the Z direction. The position is measured, and the Z-direction position is stored in the memory in correspondence with each measurement point. Here, the number of measurement points on the surface of the wafer W is set to nine for one exposure area SE. However, the present invention is not limited to this. The surface shape of the wafer W may be grasped more accurately by performing 25-point measurement at a position corresponding to the position of 62. in this way,
How to measure the points may be determined as appropriate in consideration of the required resolution, throughput, and the like of the projection exposure apparatus.

As described above, the best imaging plane Fo of the projection optical system PL stored in the memory (the second focus detection system 30
The main controller 44 obtains the best results from the surface of the wafer W at the position of each surface element 62 on the basis of the position of each measurement point on the surface of the wafer W (obtained by the first focus detection system). The amount of positional shift (the amount of defocus) in the Z-axis direction up to the image plane Fo is calculated and stored in the memory. The amount of displacement (the amount of defocus) in the Z-axis direction at the position of each surface element 62 stored in this memory is the amount of drive (correction amount) of the surface element 62 described later. In the case of FIG. 8, the surface element 62 whose position coincides with each measurement point (P1 to P9)
As for, the amount of displacement in the Z-axis direction from the best imaging plane (Fo) to the surface of the wafer W becomes the driving amount of the surface element 62 as it is, but the driving amount of the surface element 62 that does not correspond to the measurement point is , Can be obtained by calculation based on the amount of displacement at the measurement points in the peripheral part.

Next, a case where each surface element 62 is driven by the driving mechanism 68 will be described.

When measuring the shape of the wafer surface described above, as shown in FIG. 9A, the driving mechanism of all the surface elements 62 is arranged so that all the surface elements 62 are arranged on the same plane. By applying the same voltage to the surface element 62, the surface element 62 is initialized. Then, when the exposure area SE to be subjected to the exposure processing is determined and the surface element 62 corresponding to the exposure area SE is determined, the main controller 44 reads out the driving amount (correction amount) of the corresponding surface element 62 stored in the memory. , Each drive mechanism 68 is individually driven. Thereby, each surface element 62 moves to a predetermined position in the Z-axis direction and stops. That is, in the exposure area SE, FIG.
As shown in FIG. 9B, the irregularities on the surface of the wafer W placed on the wafer holder 25 shown in FIG.
When the surface element 62 of the wafer holder 25 that holds the wafer W is driven, the best imaging plane Fo of the projection optical system PL is driven.
The surface of the wafer W can be made to match. Therefore, it is possible to perform high-resolution and high-accuracy exposure. In the case of FIG. 9B, the best imaging surface Fo of the projection optical system PL is a flat surface, and the surface of the wafer W is corrected to be flat so as to coincide with this. When the surface Fo is curved, the surface of the wafer W is corrected according to the curved surface.

In this manner, while correcting the position of the surface of the wafer W in the Z-axis direction for each exposure area SE (shot area) on the wafer W, each shot area on the wafer W is step-and-repeat. Are successively exposed.

As described above, according to the projection exposure apparatus 10 of this embodiment, each of the measurement points P 1 to P
9, the amount of misalignment at the position of the surface element 62 constituting the wafer holder 25 is calculated in advance based on the amount of misalignment between the Z-axis position in FIG. 9 and the best imaging plane Fo of the projection optical system PL. The correction amount. When the exposure process is performed on the exposure area SE, the driving mechanism 68 is driven for each surface element 62 in accordance with the correction amount, so that each surface element 6 is exposed.
2 moves in the Z-axis direction with the wafer 2 being attracted to the back side of the wafer W, and can be deformed so that the surface shape of the wafer W matches the best imaging plane Fo of the projection optical system PL.

Therefore, according to the projection exposure apparatus 10 of the present embodiment, even when a high resolution is required and the depth of focus is reduced when performing the exposure process for each exposure area SE, the projection depth is always within the range of the depth of focus. , The entire surface of the wafer W in the exposure region enters, so that highly accurate exposure processing can be performed.

In the above embodiment, the case where the photoelectric first focus detection system for detecting the position of the surface in the Z-axis direction at one point on the wafer W is used is exemplified. May be used, and a multi-point focus position detection system that simultaneously detects the positions of the plurality of measurement points in the Z optical axis direction on the wafer surface may be used. In this case, the Z light of the wafer W may be used. The position measurement in the axial direction can be performed in a shorter time.

In the above embodiment, the case where the wafer holder 25 is provided on the Z stage 18 which moves only in the Z axis direction for the sake of simplicity has been described. It is also possible to provide a Z-leveling stage capable of tilting with respect to the Z-axis direction along with the movement of the direction, and to provide the wafer holder 25 on this Z-leveling stage.

Further, in the above-described embodiment, as shown in FIG. 8, the arrangement and number of the surface elements 62 or the arrangement state with respect to the exposure area SE have been specified, but the present invention is naturally limited to this example. Instead, the size, number, and arrangement of the surface elements 62 may be changed, and the size and shape of the exposure region SE itself can be arbitrarily set using the movable blind 45 or the like. In this case,
The correction amount of each surface element 62 can be calculated by appropriate calculation based on known data.

In the above embodiment, the relationship between the surface element 62 and the exposure area SE has been described with reference to FIG. 8, but the movable blinds 45A and 45B shown in FIG. By changing the size (change of shot size) or changing the arrangement of adjacent exposure areas SE (change of shot arrangement), the positional relationship is appropriately changed. In such a case, since there is no guarantee that each measurement point on the surface of the wafer W coincides with the plane element 62,
The main controller 44 determines the exposure area S based on the amount of displacement in the Z-axis direction between the surface of the wafer W and the best imaging plane Fo at each measurement point and the positional relationship between the measurement point and the surface element 62.
The drive amount of each surface element 62 used for correcting the surface shape of E can be obtained by calculation.

Further, in the above embodiment, the surface shape of the wafer W is measured in advance for all the shot areas using the first focus detection system. However, the present invention is not limited to this. Alternatively, the measurement points of the sit area may be sequentially measured.

In the above embodiment, the case where the projection exposure apparatus of the step-and-repeat type is applied has been described. However, the scope of the present invention is not limited to this, and the reticle R and the wafer W It is also possible to apply the present invention to a projection exposure apparatus such as a step-and-scan method in which exposure is performed while relatively scanning is performed.

[0090]

As described above, according to the first aspect of the present invention, it is possible to obtain a highly accurate image in a state where the surface shape of the area to be exposed on the surface of the photosensitive substrate coincides with the best imaging plane of the projection optical system. A projection exposure method capable of performing exposure is provided.

According to the present invention, high-precision exposure can be performed while the shape of the region to be exposed on the surface of the photosensitive substrate coincides with the best imaging plane of the projection optical system. It is possible to provide an excellent projection exposure apparatus that has never been achieved before.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a projection exposure apparatus according to an embodiment.

FIG. 2 is a diagram illustrating a configuration of a second focus detection system of a TTL system for detecting a best image plane of a projection optical system included in the projection exposure apparatus of FIG. 1;

FIG. 3 is a view showing a diffraction grating mark formed on an upper surface of a reference mark plate FM of FIG. 1;

4A and 4B are diagrams illustrating signal level characteristics of a calibration signal, wherein FIG. 4A is a diagram illustrating a signal level when a light emitting mark is back-projected onto a chrome portion in a pattern surface of a reticle, and FIG. It is a figure which shows the signal level when it is back-projected on the glass part (transparent part) in a pattern surface.

FIG. 5 is a flowchart illustrating a calibration operation of a focus position detection signal FS in the projection exposure apparatus of the present embodiment.

6A is a diagram showing a calibration signal KS, and FIG. 6B is a diagram showing a focus position detection signal FS.

FIG. 7 is a plan view showing a relationship between a wafer holder and an exposure area.

FIG. 8 is an enlarged view of an exposure area of FIG. 7;

9A and 9B are schematic cross-sectional views taken along line AA of FIG. 8, wherein FIG. 9A is a diagram showing a state of the wafer W before correction, and FIG. 9B is a diagram showing a state of the wafer W after correction. .

10 (A) is a partially cutaway view of one surface element of FIG. 9 and a portion in the vicinity thereof, and FIG. 10 (B) is a plan view of FIG. 9 (A).

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 projection exposure apparatus 18 X stage 25 wafer holder 30 second focus detection system 40 illumination optical system 42 light receiving optical system 44 main controller 62 surface element 68 drive mechanism EL exposure light AX optical axis SE exposure area R reticle PL projection optical system W Wafer

Claims (4)

[Claims] 1. A projection exposure method for exposing an image of a pattern formed on a mask onto a photosensitive substrate via a projection optical system, wherein the photosensitive substrate is moved in a two-dimensional plane prior to exposure. A first step of measuring unevenness of the surface of the photosensitive substrate by photoelectrically detecting a change in a position of the surface of the photosensitive substrate in the direction of the optical axis of the projection optical system; and measuring an imaging characteristic of the projection optical system. A second step; setting a shape of the surface of the photosensitive substrate based on a result of the first step and the second step such that a region to be exposed on the photosensitive substrate coincides with a best imaging plane of the projection optical system. And a third exposure step. 2. A projection exposure apparatus for exposing an image of a pattern formed on a mask to a photosensitive substrate held on a stage movable in a two-dimensional direction via a projection optical system. A substrate holding mechanism for holding the photosensitive substrate and changing a shape of a contact surface with the photosensitive substrate;
Detecting means for photoelectrically detecting a position in the optical axis direction of the projection optical system at a predetermined measurement point on the surface of the photosensitive substrate; and forming a best imaging plane position at an arbitrary point in a projection field of view of the projection optical system. Image characteristic measuring means; and, based on the measurement results of the detecting means and the image forming characteristic measuring means, the substrate holding mechanism is arranged such that the exposed area on the photosensitive substrate coincides with the best image forming plane of the projection optical system. Control means for changing the shape of the contact surface with the substrate. 3. The substrate holding mechanism is provided on the stage, and drives a number of surface elements constituting a holding member of the photosensitive substrate, and independently drives each of the surface elements in an optical axis direction of the projection optical system. 3. The projection exposure apparatus according to claim 2, further comprising a number of drive mechanisms. 4. The projection exposure apparatus according to claim 2, wherein said imaging characteristic measuring means measures at least one of field curvature and astigmatism of said projection optical system.