JP2002260986A - Method of measuring optical characteristic, method for exposure, and method of manufacturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of measuring optical characteristics by which the optical characteristics of a projection optical system can be measured in a short time with high accuracy and high reproducibility. SOLUTION: In the method of measuring optical characteristics, the image of a pattern for measurement containing at least two land-and-space patterns having different duty ratios is projected through the projection optical system (PL), and the formed states of the images of the land-and-space patterns contained in the pattern for measurement are detected at a plurality of positions with respect to the direction along optical axis of the projection optical system. Then the optical characteristic of the projection optical system is measured based on the detected results of the formed states.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical characteristic measuring method, an exposure method, and a device manufacturing method, and more particularly, to an optical characteristic measuring method for measuring an optical characteristic of a projection optical system, and measuring by the optical characteristic measuring method. The present invention relates to an exposure method for performing exposure using a projection optical system adjusted in consideration of the obtained optical characteristics, and a device manufacturing method using the exposure method.

[0002]

2. Description of the Related Art Conventionally, in a lithography process for manufacturing a semiconductor device, a liquid crystal display device, or the like, a pattern formed on a mask or a reticle (hereinafter, collectively referred to as a “reticle”) is resisted through a projection optical system. There is used an exposure apparatus that transfers a wafer or a glass plate or the like onto which a substrate or the like is applied (hereinafter, also appropriately referred to as a “wafer”). In recent years, as an apparatus of this kind, from the viewpoint of emphasizing throughput, a step-and-repeat type reduction projection exposure apparatus (so-called “stepper”) or a step-and-scan type scanning type apparatus which is an improvement of this stepper has been used. 2. Description of the Related Art Sequentially moving projection exposure apparatuses such as exposure apparatuses are relatively frequently used.

In addition, semiconductor elements (integrated circuits) and the like are becoming highly integrated year by year. Accordingly, projection exposure apparatuses, which are apparatuses for manufacturing semiconductor elements and the like, require higher resolution, that is, finer patterns with higher precision. The ability to transfer has been required. In order to improve the resolving power of the projection exposure apparatus, it is necessary to improve the imaging performance of the projection optical system. Therefore, it is important to accurately measure and evaluate the optical characteristics of the projection optical system.

However, accurate measurement of the optical characteristics of the projection optical system, for example, the image plane (best image plane) is based on the premise that the best focus position at each evaluation point (measurement point) can be accurately measured. As a method of detecting a best focus position in a conventional projection exposure apparatus, the following three methods are mainly known.

[0005] First, a predetermined reticle pattern (for example, a line and space pattern) is used as a test pattern, and the test pattern is transferred to a test wafer at a plurality of wafer positions in the optical axis direction of the projection optical system. Then, the line width value of the resist image (transferred pattern image) obtained by developing the test wafer is visually measured using a scanning electron microscope (SEM) or the like, and the line width value and the projection are measured. A method of determining the best focus position based on a correlation with a wafer position in the optical axis direction of the optical system (hereinafter also referred to as “focus position” as appropriate) is known as a so-called CD / focus method.

Secondly, a resist image of a wedge mark is formed on a wafer at a plurality of focus positions, and a change in a line width value of the resist image due to a difference in the focus position is amplified to a dimensional change in a longitudinal direction. The length of the resist image in the longitudinal direction is measured using a mark detection system such as an alignment system for detecting a mark on the wafer after replacement. A method of slicing the vicinity of the maximum value of the approximate curve indicating the correlation between the focus position and the length of the resist image at a predetermined slice level and determining the middle point of the obtained focus position range as the best focus position is a so-called method. Known as the SMP focus measurement method.

Third, the test pattern is transferred to the test wafer at a plurality of focus positions while changing the exposure amount. Then, by determining the presence or absence of the resist image of the test pattern on the test wafer for each focus position, the exposure amount when the resist image disappears is measured, and the correlation between the focus position and the measured exposure amount is shown. A method of determining the maximum value of the approximate curve as the best focus position is known as a so-called overexposure focus measurement method.

Then, for various test patterns,
Based on the best focus position obtained in this way, astigmatism, field curvature, and the like, which are optical characteristics of the projection optical system, are measured.

[0009]

However, the above-mentioned CD
In the focus method, for example, the line width value of the resist image is set to SE
In order to measure at M, it is necessary to strictly focus the SEM, and the measurement time per point is extremely long, and several to several tens of hours are required to measure at many points. I was In addition, the test pattern for measuring the optical characteristics of the projection optical system has been miniaturized,
It is expected that the number of evaluation points in the field of view of the projection optical system will also increase. Therefore, the conventional measurement method using the SEM has a problem that the throughput until a measurement result is obtained is significantly reduced. In addition, higher levels of measurement errors and reproducibility of measurement results have been required, and it has become difficult to cope with the conventional measurement methods. Further, as an approximation curve indicating the correlation between the focus position and the line width value, a fourth-order or higher approximation curve is used to reduce the error. There was a constraint that a width value had to be determined. In addition, the difference between the line width value at the focus position shifted from the best focus position (including both the + direction and the − direction with respect to the optical axis direction of the projection optical system) and the line width value at the best focus position is an error. Is required to be 10% or more in order to reduce the value, but it has become difficult to satisfy this condition.

In the above-described SMP focus measurement method, since the measurement is usually performed with monochromatic light, the influence of interference differs due to the difference in the shape of the resist image, which may lead to a measurement error (dimensional offset). Can be Furthermore, in order to measure the length of the resist image of the wedge-shaped mark by image processing, it is necessary to capture in detail the information up to both ends in the longitudinal direction where the resist image becomes thinnest. However, there is a problem that the resolution of a camera or the like is not sufficient. In addition, since the test pattern is large, it has been difficult to increase the number of evaluation points in the field of view of the projection optical system.

Further, in the above-described over-exposure focus measurement method, the measurement result is apt to fluctuate before and after the exposure amount at which the resist image disappears due to the influence of errors in the exposure amount, focus position, and the like. Is reduced.

The present invention has been made under such circumstances, and a first object of the invention is to provide an optical characteristic measuring method capable of measuring the optical characteristics of a projection optical system in a short time with high accuracy and reproducibility. Is to provide.

It is a second object of the present invention to provide an exposure method capable of realizing highly accurate exposure.

It is a third object of the present invention to provide a device manufacturing method capable of improving the productivity of a highly integrated device.

[0015]

According to a first aspect of the present invention, there is provided an optical characteristic measuring method for measuring an optical characteristic of a projection optical system (PL) for projecting a pattern on a first surface onto a second surface. A mask (R) on which a measurement pattern including at least two line and space patterns having different duty ratios is formed is arranged on the first surface, and an image of the measurement pattern is projected on the second surface by the projection optical system. Side, and detects the state of image formation of each line and space pattern in the measurement pattern at a plurality of positions in the optical axis direction of the projection optical system, and based on the detection result, the optical system of the projection optical system This is an optical characteristic measuring method characterized by obtaining characteristics.

Here, there are several methods for displaying the duty ratio of the line and space pattern. In this specification, the duty ratio is indicated by the ratio of the width of the line portion to the width of the space portion in the line and space pattern. When the duty ratio is "increased", it means that only the width of the line portion is increased without changing the period, and when the duty ratio is "decreased", only the width of the line portion is reduced without changing the period. It means becoming. Further, in the present specification, the “minimum value” of the duty ratio refers to at least two values having the same cycle.
When comparing two line and space patterns,
This means the duty ratio of the line and space pattern having the narrowest line portion width.

In this specification, the term "pattern image" means, for example, an image (a visible image such as a resist image and a latent image) formed on a substrate when the substrate is disposed on the second surface side. ) As well as a spatial image (projected image) of the pattern. Therefore, the detection of the image formation state includes not only the detection of the transfer image formation state but also the detection of the aerial image formation state by so-called aerial image measurement.

According to this, first, a measurement pattern including at least two line and space patterns formed on the mask and having different duty ratios is projected on the second surface side via the projection optical system. Then, the image formation state of each line and space pattern in the measurement pattern is detected at a plurality of positions in the optical axis direction of the projection optical system, and the optical characteristics are obtained based on the detection results.

Here, the measurement pattern may be at least two line and space patterns having different duty ratios. For this reason, many measurement patterns can be arranged in the pattern plane of the mask, and the number of evaluation points whose optical characteristics should be detected in the field of view of the projection optical system can be increased. Can be narrowed. Therefore, as a result, the measurement accuracy of the optical characteristics and the reproducibility of the measurement result can be improved. In addition, a plurality of line and space patterns having different duty ratios are used as measurement patterns. For this reason, the exposure amount is constant and the image amount in the optical axis direction of the projection optical system is changed while adopting a measurement method in which only the detection target position of the pattern image formation state in the optical axis direction of the projection optical system is changed. The optical characteristics can be obtained by using an analysis method similar to a measurement method that changes both the detection target position of the formation state of the laser beam and the detection target position. Therefore, compared to a measurement method that changes both the exposure amount and the detection target position of the image formation state in the optical axis direction of the projection optical system, the optical characteristics can be obtained in a short time, and the optical characteristic measurement can be performed. Throughput can be improved. In addition, since the exposure amount is constant, the variation in the measurement result is small compared to the method of changing the exposure amount (for example, the over-exposure focus measurement method described above), and as a result, the measurement accuracy and the reproduction of the measurement result are reduced. It is possible to improve the performance.

Therefore, according to the optical characteristic measuring method of the first aspect, the optical characteristics of the projection optical system can be obtained in a short time with high accuracy and reproducibility.

In this case, as the line and space pattern in the measurement pattern, various types can be considered, but as in the optical characteristic measuring method according to claim 2, the periodic direction of each line and space pattern May be the same.

In the optical characteristic measuring method according to the first aspect of the present invention, the measurement pattern may be different in the duty ratio and the periodic direction may be different from the first direction, as in the optical characteristic measuring method according to the third aspect. A first pattern consisting of at least two line and space patterns, and a second pattern consisting of at least two line and space patterns having different duty ratios and a periodic direction as a second direction. And a first pattern including at least two line and space patterns having different duty ratios and the same first period, as in the optical characteristic measuring method according to claim 4, and the duty ratio is different. Second pattern comprising at least two line and space patterns having the same second period And emissions, may include a.

In each of the optical characteristic measuring methods according to the first to fourth aspects, as in the optical characteristic measuring method according to the fifth aspect, each of the line and space patterns is formed in a specific direction on the pattern surface of the mask. It is good also as being arranged in a line along.

In each of the optical characteristic measuring methods according to the third and fourth aspects, as in the optical characteristic measuring method according to the sixth aspect, each of the line and space patterns constituting the first pattern is the same as that of the mask. The line and space patterns arranged on the pattern surface along the predetermined row in the specific direction, and forming the second pattern, the line and space patterns on the pattern surface are different from the specific row in the specific direction. They may be arranged along one line.

In this case, as in the optical characteristic measuring method according to claim 7, the predetermined pattern on which the first pattern is arranged on the pattern surface and the second pattern are arranged. It may further include a light-shielding pattern formed between the other rows.

In each of the optical characteristic measuring methods according to the fifth to seventh aspects, as in the optical characteristic measuring method according to the eighth aspect, the rows of the line and space patterns arranged along the specific direction may be arranged in a line. The pattern may include at least one of a portion where the duty ratio of the pattern gradually increases from one side to the other side in the specific direction and a portion where the duty ratio gradually decreases.

[0027] In each of the optical characteristic measuring methods according to the first to eighth aspects, the image of the measurement pattern is formed on the second surface side of the projection optical system as in the optical characteristic measuring method according to the ninth aspect. The images may be transferred to different regions on the substrate by the projection optical system at a plurality of positions on the substrate (W) arranged in the optical axis direction of the projection optical system.

In this case, various methods are conceivable for detecting the formation state of the image of each line and space pattern in the measurement pattern, but as in the optical characteristic measuring method according to claim 10, Even if the image formation state of each line-and-space pattern in the measurement pattern is detected by pattern matching between each imaging data of the image of the measurement pattern transferred to a different area above and predetermined template pattern data. good.

In the optical characteristic measuring method according to the tenth aspect, as in the optical characteristic measuring method according to the eleventh aspect, a pattern is provided near the pattern area on the mask where the measurement pattern is formed. A blank area that does not exist may be present.

In this case, as in the optical characteristic measuring method according to the twelfth aspect, the template pattern data may be image data of the blank area on the mask projected on the substrate.

In each of the optical characteristic measuring methods according to the ninth to twelfth aspects, as in the optical characteristic measuring method according to the thirteenth aspect, the detection target of the formation state is a latent image formed on the substrate. However, the resist image may be a resist image obtained by developing the substrate, as in the optical characteristic measuring method according to claim 14. Here, the photosensitive layer for detecting the state of image formation on the substrate,
The photoresist is not limited to a photoresist, but may be any as long as an image (a latent image and a visible image) is formed by irradiation of light (energy).
For example, the photosensitive layer may be an optical recording layer, a magneto-optical recording layer, or the like. Therefore, the object on which the photosensitive layer is formed is not limited to a wafer or a glass plate. A possible plate or the like may be used.

In each of the optical characteristic measuring methods according to the first to fourteenth aspects, various optical characteristics can be considered. For example, as in the optical characteristic measuring method according to the fifteenth aspect, the image forming state As a result of the detection, the minimum value of the duty ratio of the line and space pattern in which the image is detected is obtained for each position in the optical axis direction of the projection optical system, and the position of the projection optical system in the optical axis direction and The best focus position may be determined based on the correlation with the minimum value, and as a result of detection of the image formation state, the image is detected as in the optical characteristic measurement method according to claim 16. A range in the optical axis direction of the projection optical system is obtained for each duty ratio of the line-and-space pattern, and the best focus is obtained based on the correlation between the range and the duty ratio. It is also possible to determine the scum position.

According to a seventeenth aspect of the present invention, a mask (R) is irradiated with an energy beam for exposure, and a pattern formed on the mask is transferred onto a substrate (W) via a projection optical system (PL). 17. An exposure method, comprising:
Adjusting the projection optical system in consideration of the optical characteristics measured by the optical characteristic measurement method according to any one of the preceding claims; and a pattern formed on the mask via the adjusted projection optical system. Transferring to the substrate;
Is an exposure method.

According to this, the projection optical system is adjusted so that optimum transfer is performed in consideration of the optical characteristics of the projection optical system measured by each of the optical characteristic measuring methods according to claims 1 to 16, and the adjustment thereof is performed. Since the pattern formed on the mask is transferred onto the substrate via the projected projection optical system, the fine pattern can be transferred onto the substrate with high accuracy.

The invention according to claim 18 is a device manufacturing method including a lithography step, wherein the lithography step uses the exposure method according to claim 17.

According to this, in the lithography step, a fine pattern can be accurately transferred onto the substrate by the exposure method according to claim 17, and as a result, the productivity (yield rate) of a highly integrated device can be reduced. Included) can be improved.

[0037]

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 an exposure apparatus 100 according to an embodiment suitable for carrying out a method for measuring optical characteristics of a projection optical system and an exposure method according to the present invention. This exposure apparatus 10
Reference numeral 0 denotes a step-and-repeat reduction projection exposure apparatus (so-called stepper).

The exposure apparatus 100 includes an illumination system IOP and a reticle stage R for holding a reticle R as a mask.
ST, a wafer W as a substrate coated with a photosensitive agent (photoresist) by applying an image of a pattern formed on reticle R
A projection optical system PL for projecting upward, an XY stage 20, X which holds a wafer W and moves on a two-dimensional plane (within an XY plane)
A drive system 22 for driving the Y stage 20 and a control system for these components are provided. This control system is composed of a work station (or microcomputer) provided with various interfaces, and is mainly configured with a main control device 28 that integrally controls the entire apparatus.

The illumination system IOP includes a light source such as a KrF excimer laser or an ArF excimer laser, a fly-eye lens or a rod-type (internal reflection type) integrator as an optical integrator or a homogenizer, a relay lens, a condenser lens, and a reticle blind. (All are not shown). The illumination system IOP illuminates the pattern on the lower surface (pattern forming surface) of the reticle R with a uniform illuminance distribution by illumination light IL for exposure from a light source.

The reticle stage RST includes an illumination system I
It is located below the OP in FIG. A reticle R is attracted and held on the reticle stage RST via a vacuum chuck or the like (not shown). The reticle stage RST is driven by a driving system (not shown) in the X-axis direction (the horizontal direction in FIG. 1) and the Y direction. It can be minutely driven in the axial direction (the direction perpendicular to the plane of FIG. 1) and in the θz direction (the direction of rotation around the Z axis perpendicular to the XY plane). Thus, reticle stage RST can position reticle R (reticle alignment) in a state where the center of the pattern of reticle R (reticle center) substantially matches optical axis AXp of projection optical system PL. FIG. 1 shows a state in which this reticle alignment has been performed.

The projection optical system PL is arranged below the reticle stage RST in FIG. 1 so that the direction of the optical axis AXp is the Z-axis direction orthogonal to the XY plane. The projection optical system PL is a reduction system that is telecentric on both sides, and has a common optical axis A in the Z-axis direction.
A refractive optical system (not shown) including a plurality of lens elements having X is used. A specific plurality of lens elements are controlled by an imaging characteristic correction controller (not shown) based on a command from the main controller 28, and the optical characteristics of the projection optical system PL, such as magnification, distortion, coma, and The field curvature and the like can be adjusted.

The XY stage 20 is actually a Y stage that moves on a base (not shown) in the Y-axis direction.
An X stage is configured to move on the stage in the X-axis direction, and these are shown as XY stages 20 in FIG. A wafer table 18 is mounted on the XY stage 20, and a wafer W is held on the wafer table 18 via a wafer holder (not shown) by vacuum suction or the like.

The wafer table 18 minutely drives the wafer holder for holding the wafer W in the Z-axis direction and the tilt direction with respect to the XY plane. This wafer table 1
8 is provided with a movable mirror 24, which projects a laser beam on the movable mirror 24 and receives the reflected light, thereby measuring the position of the wafer table 18 in the XY plane. A total 26 is provided to face the reflecting surface of the movable mirror 24. Actually, the moving mirror is provided with an X moving mirror having a reflecting surface orthogonal to the X axis and a Y moving mirror having a reflecting surface orthogonal to the Y axis. An X laser interferometer for directional position measurement and a Y laser interferometer for Y direction position measurement are provided,
In FIG. 1, these are representatively the moving mirror 24, the laser interferometer 2
6 is shown. The X laser interferometer and Y laser
A laser interferometer is a multi-axis interferometer having a plurality of measuring axes,
In addition to the X and Y positions of the wafer table 18, rotation (yaw (θz rotation about the Z axis)), pitching (X
Rotation (θx rotation around the axis) and rolling (θy rotation around the Y axis) can also be measured. Therefore, in the following description, it is assumed that the laser interferometer 26 measures the positions of the wafer table 18 in the five degrees of freedom directions of X, Y, θz, θy, and θx.

The measurement value of the laser interferometer 26 is stored in the main controller 2
And the main controller 28 controls the laser interferometer 26
By driving the XY stage 20 via the drive system 22 while monitoring the measurement values of the above, the wafer table 18 is positioned.

The Z direction position and the tilt amount of the surface of the wafer W are
For example, the measurement is performed by a focus sensor AFS including an oblique incidence type multipoint focal position detection system having a light transmitting system 50a and a light receiving system 50b disclosed in Japanese Patent Application Laid-Open No. 6-283403. The measurement value of the focus sensor AFS is also supplied to the main controller 28,
The main controller 28 controls the position and inclination of the wafer W in the optical axis direction of the projection optical system PL by slightly driving the wafer table 18 via the drive system 22 based on the measurement value of the focus sensor AFS. Has become.

That is, the position and orientation of the wafer W in the directions of five degrees of freedom of X, Y, Z, θx and θy are controlled via the wafer table 18 in this manner. Note that the remaining error of θz (yawing) is calculated based on the wafer table 18 measured by the laser interferometer 26.
Is corrected by rotating at least one of the reticle stage RST and the wafer table 18 based on the yawing information.

On the wafer table 18, a reference plate FP whose surface is the same as the surface of the wafer W is provided.
Has been fixed. On the surface of the reference plate FP, various reference marks including a reference mark used for so-called baseline measurement or the like are formed.

Further, in this embodiment, an off-axis type alignment detection system AS as a mark detection system is provided on the side surface of the projection optical system PL. This alignment detection system AS uses FIA (Filed Image Alignment).
It has an alignment sensor called a system, and is used for measuring the positions of the reference mark on the reference plate FP and the alignment mark on the wafer in the X and Y two-dimensional directions. This FI
A system is broadband (broadband) such as halogen lamp
The sensor illuminates the mark with light and processes the mark image to measure the mark position.

The alignment control unit 16 A / D converts the information DS from the alignment detection system AS, and further performs arithmetic processing on the digitized signal to detect a mark position. This detection result is supplied from the alignment control device 16 to the main control device 28.

Further, in the exposure apparatus 100 of the present embodiment, although not shown, a reticle is provided above the reticle R via a projection optical system PL disclosed in, for example, JP-A-7-176468. A pair of reticles composed of a TTR (Through The Reticle) alignment system using an exposure wavelength for simultaneously observing a reticle mark on R or a reference mark on reticle stage RST (both not shown) and a mark on reference plate FP. An alignment microscope is provided. The detection signals of these reticle alignment microscopes are supplied to the main controller 28 via the alignment controller 16.

Next, in this embodiment, the projection optical system P
An example of a reticle used for measuring the optical characteristics of L will be described.

FIG. 2 shows an example of a test reticle R _T (hereinafter abbreviated as “reticle R _T ”) used for measuring the optical characteristics. FIG. 2 shows a reticle R _T
2 is a plan view seen from the pattern surface side (the lower surface side in FIG. 1). The reticle _RT has a pattern area PA at the center of a glass substrate 42 as a substantially square mask substrate.
Are provided, and a plurality of patterns as described later are arranged in the pattern area PA. Further, a pair of reticle alignment marks RM1 and RM2 are provided on both sides in the X-axis direction of the pattern area PA passing through the center of the pattern area PA, that is, the center of the reticle _RT (reticle center).
Are formed.

Here, in this embodiment, a description will be given of a measurement pattern RPA arranged in the pattern area PA of the reticle _RT for measuring the optical characteristics of the projection optical system.

As shown in FIG. 3, the measurement pattern RPA has nine pattern cells CA 1 to CA 9 of the same size.
9.

Each of the pattern cells CA1 to CA9 has a line and space (hereinafter abbreviated as “L / S”) pattern in which ten line patterns are periodically arranged, and a predetermined line width. And a frame-like frame pattern. The L / S pattern is arranged at a predetermined position in the frame pattern. Further, the frame pattern has a line width necessary for reliably forming a resist image. this is,
This is because it serves as a kind of marker used for extracting image data at the time of image processing to be described later.

The L / S patterns in each of the pattern cells CA1 to CA9 have the same cycle direction (first cycle direction) and the same cycle (first cycle), and differ only in the duty ratio. . In the present embodiment, the periodic direction of the L / S pattern in each of the pattern cells CA1 to CA9 is, for example, the horizontal direction (X-axis direction) in FIG.

Although there are several methods of displaying the duty ratio of the L / S pattern, in this specification, the width (L) of the line portion and the width (S) of the space portion in the L / S pattern are used.
And it is shown by the ratio. Further, the duty ratio being “increased” means that only the width L of the line portion is increased without changing the cycle, and the duty ratio is “decreased”.
Means that only the width L of the line portion becomes narrow without changing the period.

Each of the pattern cells CA1 to CA9 has
As shown in FIG. 3, they are arranged in a line at equal intervals along the vertical direction (Y-axis direction) in FIG. 3, which is a specific direction. The L / S pattern in each of the pattern cells CA1 to CA9 corresponds to the upper side (−Y
Side) to the lower side of the drawing (+ Y side), the duty ratio gradually decreases.

In the present embodiment, as an example, the duty ratio (first duty ratio) of the pattern cell CA1 is
L: S = 1.4: 0.6, and the duty ratio (second duty ratio) of the pattern cell CA2 is L: S = 1.3:
0.7, the duty ratio (third duty ratio) of the pattern cell CA3 is L: S = 1.2: 0.8, and the duty ratio (fourth duty ratio) of the pattern cell CA4 is
L: S = 1.1: 0.9, and the duty ratio of pattern cell CA5 (fifth duty ratio) is L: S = 1.0:
1.0, the duty ratio (sixth duty ratio) of the pattern cell CA6 is L: S = 0.9: 1.1, and the duty ratio (seventh duty ratio) of the pattern cell CA7 is
L: S = 0.8: 1.2, and the duty ratio (eighth duty ratio) of the pattern cell CA8 is L: S = 0.7:
1.3, the duty ratio (ninth duty ratio) of the pattern cell CA9 is L: S = 0.6: 1.4.

On the lower side (+ Y side) of the pattern cell CA9 in FIG. 3, a blank cell CA10 as a blank area having no pattern is arranged.
This blank cell CA10 is composed of only the frame pattern. The purpose of this frame pattern is the same as in the case of the aforementioned pattern cells CA1 to CA9.

The pattern cells CA1 to CAC
When it is not necessary to distinguish A9 from the blank cell CA10, they are collectively referred to as "cells" as appropriate.

On the pattern surface of reticle _RT ,
With alignment of reticle _RT performed, measurement pattern RPA and blank cell CA10 are arranged at positions corresponding to a plurality of evaluation points in the field of view of projection optical system PL.

Further, in the area where the measurement pattern RPA and the blank cell CA10 in the pattern area PA are not arranged, chrome for light shielding is deposited.

Next, the reticle pattern is transferred onto the wafer W by the exposure apparatus 100 of this embodiment, and the projection optical system P
An operation flow for forming a resist image for measuring the optical characteristics of L will be briefly described.

First, wafer W is loaded on wafer table 18 by a wafer loader (not shown), and reticle _RT is loaded on reticle stage RST by a reticle loader (not shown).

Main controller 28 determines that the midpoint of a pair of reference marks (not shown) formed on the surface of reference plate FP provided on wafer table 18 substantially coincides with the optical axis of projection optical system PL. Thus, the reference plate FP is moved. This movement is performed by moving the XY stage 20 via the drive system 22 while monitoring the measurement result of the laser interferometer 26 by the main controller 28. Next, the main controller 28
Adjusts the position of reticle stage RST such that the center (reticle center) of reticle _RT substantially matches the optical axis of projection optical system PL. At this time, for example, reticle alignment marks RM1 and RM via projection optical system PL by a reticle alignment microscope (not shown) described above.
The relative position between the reference mark 2 and the corresponding reference mark is detected.

Then, main controller 28 controls reticle alignment marks RM1 and RM2 based on the result of detection of the relative position detected by the reticle alignment microscope.
The position of the reticle stage RST in the XY plane is adjusted via a drive system (not shown) so that the relative position error between the reticle stage and the corresponding reference mark is minimized. As a result, the center (reticle center) of reticle _RT is aligned with projection optical system PL.
And the rotation angle of the reticle _RT also exactly matches the coordinate axis of the rectangular coordinate system defined by the length measurement axis of the laser interferometer 26. That is, the reticle alignment is completed.

Next, main controller 28 controls illumination system IOP.
The size and the position of the opening of the reticle blind (not shown) are adjusted so that the irradiation area of the illumination light IL matches the pattern area of the reticle _RT , and the opening of the reticle blind (not shown) in the illumination system IOP. Adjust the size and position of. At the same time, the main controller 28 monitors the measurement result of the laser interferometer 26 and
The stage 20 is moved. As a result, the wafer W is projected so that the image of the pattern of the reticle _RT is transferred to a virtual partitioned area (hereinafter, referred to as a “shot area”) on which the first exposure is to be performed. It is moved to a predetermined position below the optical system PL.

[0070] Further, the main controller 28, so that the position of the wafer W about the optical axis of the projection optical system is Z _1,
While monitoring the measurement value from the focus sensor AFS, the wafer table 18 is minutely driven in the Z-axis direction and the tilt direction. In this embodiment, as an example, and changing the position of the wafer W about the optical axis of the projection optical system from Z ₁ to _{Z 11 (= Z 1 + 10} × ΔZ) in [Delta] Z increments.

Exposure is performed in this state, and the pattern of the reticle _RT is projected onto the photoresist layer on the wafer W by the projection optical system P.
Transfer via L. Thereby, the image of the measurement pattern RPA and the image of the blank cell CA10 are respectively transferred to a plurality of points in the first shot area. The plurality of points correspond to a plurality of evaluation points whose optical characteristics (in this embodiment, the best focus position) are to be detected in the field of view of the projection optical system PL, and are hereinafter referred to as “evaluation corresponding points”.

Next, the main controller 28 sets D (see FIG. 4) to the length of one side of the image of the frame pattern, which is estimated from the length of one side of the frame pattern and the projection magnification of the projection optical system. Predetermined pitch ΔX somewhat larger than
Only, the XY stage 20 is moved in the −X direction in the same manner as described above. Thus, the first shot area on the wafer W moves by ΔX in the −X direction. That is, a region apart from the first shot region by ΔX in the + X direction becomes a next shot region (second shot region). Further, main controller 28 monitors the measurement value of focus sensor AFS in the Z direction of wafer table 18 so that the position of wafer W in the optical axis direction of the projection optical system becomes Z ₂ (= Z ₁ + ΔZ). Set the position to a predetermined pitch ΔZ
Only in the + Z direction. That is, the position of the wafer W in the optical axis direction of the projection optical system is changed. Then, exposure is performed in this state, and the pattern of the reticle _RT is transferred onto the wafer W via the projection optical system PL.

Hereinafter, similarly, the position of the wafer W in the optical axis direction of the projection optical system is changed to Z ₁₁ (= Z ₁ + 10 × Δ).
The above processing is repeated until Z). That is, the exposure of the same pattern is repeated on the eleven shot areas on the wafer W by the step-and-repeat method. As a result, the image of the measurement pattern RPA and the image of the blank cell CA10 are transferred for each evaluation corresponding point in each shot area.

[0074] When the position of the wafer W about the optical axis of the projection optical system exposure at Z ₁₁ is completed, the wafer W
Is unloaded from above the wafer table 18 by a wafer unloader (not shown) according to an instruction from the main controller 28, and then exposed by the wafer transfer system (not shown).
Is transported to a coater / developer (not shown) connected inline with the printer.

The wafer W is developed in the coater / developer. Upon completion of the development, the wafer W
A resist image is formed. Here, focusing on one evaluation point in the field of view of the projection optical system PL, as shown in FIG. 4 as an example, measurement patterns having different positions of the wafer W with respect to the optical axis direction of the projection optical system at the time of transfer. Eleven resist images RWA1 to RWA11 each including an RPA and a blank cell CA10 are formed. Here, each of the resist image RWA1~RWA11, the position of the wafer W about the optical axis of the projection optical system during each transfer corresponds to the case of _{Z 1 ~Z} 1 1. Each of the resist images RWA1 to RWA11 has a resist image of 10 cells (9 pattern cells and 1 blank cell), so that the projection optical system P
There are a total of 110 (= 10 × 11) cells of resist images corresponding to one evaluation point in the L visual field. The area where the resist images of the 110 cells are present is hereinafter referred to as “evaluation point corresponding area”. That is, there are as many evaluation point corresponding areas as the number of evaluation points in the field of view of the projection optical system PL.

Next, in the resist image of each pattern cell thus formed on the wafer W, the state of formation of the image of the L / S pattern is detected. There are various possible states of forming an image of the L / S pattern.
In the present embodiment, attention is paid to whether or not a resist image of the L / S pattern is formed on the wafer W as one of the formation states of the image of the L / S pattern. Various methods are conceivable for detecting whether or not the resist image of the L / S pattern is formed. In the present embodiment, as an example,
It is assumed that an image processing method using pattern matching with predetermined template pattern data is used. Therefore, first, an apparatus used for the image processing will be described.

In the present embodiment, as shown in FIG.
Image processing of the resist image is performed using the scanning electron microscope 500 and the image processing device 550. This scanning electron microscope 5
Reference numeral 00 includes a microscope main body 501 for enlarging a resist image, and a CCD imaging device 505 for imaging the resist image enlarged by the microscope main body 501 and outputting digital data (imaging data).

On the other hand, the image processing device 550 includes a processing unit 551 for performing predetermined image processing based on image data supplied from the CCD image capturing device 505 via the cable 520, and a display for displaying image processing results and the like. Part 552,
An input unit 553 for the operator to input commands and the like
A printing unit 554 for printing an image processing result or the like;
And a storage unit 555 for storing imaging data and the like.

Further, the CCD image pickup device 505 is a pixel (hereinafter referred to as a “CCD pixel”) which is an area in which information of a resist image enlarged by the microscope main body 501 formed on a light receiving surface (not shown) is divided in a matrix. Output). Here, the CCD image pickup device 50
Reference numeral 5 denotes monochrome correspondence, in which image information (shading) at the position of each CCD pixel is represented by 8-bit data (0 to 25).
5) That is, output is performed in 256 gradations. However, 0 means white and 255 means black.

Next, a method for performing image processing of a resist image using the scanning electron microscope 500 and the image processing device 550 will be described.

First, after the operator holds the wafer W (or a part of the wafer W) at a predetermined position on the microscope main body 501, a resist image (hereinafter, referred to as "a") is enlarged on a screen (not shown) of the microscope main body 501 at a predetermined magnification. When the enlarged resist image is displayed, the information of the enlarged resist image is converted into 8-bit digital data for each CCD pixel by the CCD image pickup device 505. Then, the digital data is supplied to the image processing device 550 via the cable 520 as imaging data. The processing unit 551 of the image processing device 550 displays an image corresponding to the enlarged registration image on the display unit 552 based on the image data. That is, the display unit 552 displays an image substantially equivalent to the enlarged resist image displayed on a screen (not shown) of the microscope main body 501.

Then, the operator refers to the image displayed on the display section 552 and refers to the registration images RWA1 to RWA1 in the predetermined evaluation point corresponding area to be subjected to the image processing.
The microscope main body 501 is adjusted so that an image corresponding to the enlarged resist image of the WA 11 (hereinafter, referred to as a “display resist image”) is displayed on the display unit 552.

Subsequently, when the operator instructs execution of image processing via the input unit 553, the processing unit 551
The imaging data from the CD imaging device 505 is stored in the storage unit 555.

Here, in order to distinguish display resist images on a cell-by-cell basis, arrays DA _{i, j} (i = 1 to 11, j = 1 to 1)
0) will be used. In this embodiment,
As shown in FIG. 6, the subscript i indicates the position of the wafer W in the optical axis direction of the projection optical system. That is,
DA _{1, j to} DA _{11, j} (j = 1 to 10) indicate that the position of the wafer W in the optical axis direction of the projection optical system is Z ₁ to Z _1, respectively.
Shows a display resist image transferred in the case of Z _11. The subscript j indicates a difference in the duty ratio of the L / S pattern in the pattern cell when j = 1 to 9. That is, DA _{i, 1 to} DA _{i, 9} (i = 1 to
11) shows display resist images of the pattern cells CA1 to CA9, respectively. For example, DA _5,9, the position of the wafer W about the optical axis of the projection optical system means displaying resist image of the pattern cell CA9 transcribed in the case of Z _5. Therefore, the rightward direction of the paper (i-value increasing direction) in FIG. 6 is a direction in which the value of the position Z of the wafer W with respect to the optical axis direction of the projection optical system during transfer gradually increases, and the downward direction of the paper (the j-value L / S of the pattern cell)
This is a direction in which the line width of the line pattern in the pattern gradually becomes smaller (the duty ratio becomes smaller). Note that j
In the case of = 10, it means a display resist image of the blank cell CA10. Also, i and j used in the following description have the same meaning as described above.

In this embodiment, as an example, FIG.
As shown in FIG. 2, each display resist image DA _{i, j}
It is divided into a 3 × 23 matrix of minute regions, and each minute region is divided into target pixels GA _{m, n} (m = 1 to 23, n = 1 to 2).
3). For example, the target pixels GA _{12 and 22} mean pixels at positions separated from the target pixel GA _{1,1 at the} lower left of the paper in FIG. 7 by 21 pixels in the right direction on the paper and 11 pixels upward in the paper. . The target pixels correspond one-to-one with the CCD pixels in the CCD image pickup device 505, and each target pixel GA _{m, n} has 8-bit image data (hereinafter referred to as “pixel data”). ing. That is, the display resist image corresponding to one cell is 52
It has 9 (= 23 × 23) 8-bit data.

Next, the processing section 551 searches the image data stored in the storage section 555 for 110 frame patterns, and extracts the image data in each frame pattern. Then, the processing unit 551 converts the extracted imaging data into each of the display resist images DA _{i, j} (i = 1 to 11, j = 1).
10) to 10), and saves them in the storage unit 555 as imaging data files.

Further, the processing section 551 performs pattern matching with the following template to thereby display resist images DA _{i, j} (i = 1 to 11, j = 1 to 1) of the pattern cells.
The pixel data of each target pixel in 9) is binarized. In this embodiment, imaging data of a display resist image of a blank cell transferred simultaneously with a pattern cell to be processed is used as template pattern data.

[0088] First, the processing unit 551, a blank cell as a display resist image DA _{1, 1} and the template pattern data pattern cells CA1 transfer when the position of the wafer W about the optical axis of the projection optical system of Z ₁ Each target pixel GA in the display resist image DA _{1, 10} of CA10
The pixel data of _{m and n} is extracted from the image data file stored in the storage unit 555.

Then, the processing section 551 outputs the target pixel GA
_m, each _n, display resist image DA _{1, 1} a calculates the difference between the pixel data and the pixel data _{DA 1, 10} corresponding thereto, the correlation coefficient of the operation result C _m, n _(m = 1~ 2
3, n = 1 to 23). For example, the display resist image D
The pixel data of the target pixel GA _1,1 of A _1,10 is 45, and the target pixel GA of the corresponding display resist image DA _1,1 is 45.
_If the pixel data of _1,1 is 60, the correlation coefficient C
_1,1 becomes 15. That is, the correlation coefficient C _{m, n} is 0 to
It has a value up to 255, and the closer to 0, the higher the matching degree.

Next, the processing unit 551 calculates the correlation coefficient
C_{m, n}And a predetermined reference value (for example, 200)
And display resist image DA_1,1Each target pixel GA_{m, n}To
The pixel data in this is binarized into 0 and 1. That is, an example
For example, when the predetermined reference value is 200, the correlation coefficient
C_{m, n}Is greater than 200, "0", the correlation coefficient C
_{m, n}Is less than 200 is defined as “1”. The above
The predetermined reference value is arbitrarily set within a range of 0 to 255.
be able to. FIG. 8 shows a display resist image DA._{1 , 1}To
Target pixel GA after binarization processing_{m, n}Painting in
An example of raw data is shown.

The processing section 551, like the display resist images DA ₁ , ₁ described above, processes other display resist images DA.
_{1, j} (j = 2-9) and DA _{i, j} (i = 2-11, j
= 1 to 9), binarization processing of pixel data at each target pixel GA _{m, n} is performed. The binarized data thus obtained is stored in the storage unit 55 as a binarized file.
5 is stored.

Subsequently, the processing section 551 makes each display resist image DA _{i, j} (i = 1 to 11, j =
It is detected whether or not an image of the L / S pattern exists in 1) to 9). It is assumed that a plurality of thresholds used for detection are registered in the image processing device 550 in advance.

First, the processing unit 551 refers to the binarized file stored in the storage unit 555, and generates a binary image for each display resist image DA _{i, j} (i = 1 to 11j = 1 to 9). The number of “0” in the pixel data after the conversion is counted.
Then, the processing unit 551 determines that the number of “0” is the first threshold S
If V1 or more, it is determined that an image of the L / S pattern exists, and the determination value is set to “0” as a detection result. on the other hand,
If the number of “0” is less than the first threshold value SV1, the processing unit 551 determines that the image of the L / S pattern does not exist,
The determination value is set to “1” as the detection result. In the present embodiment, as an example, a detection result as shown in FIG. 9 is obtained.

Next, the processing unit 551 checks the detection results.
Of the L / S pattern in the measurement pattern based on
For each duty ratio, the projection optical system whose judgment value is “0”
The position range of the wafer W in the optical axis direction is obtained, and
Median M_j(J = 1 to 9) is calculated. Specifically, for example
For example, as shown in FIG. 9, j = 1 (first duty
Ratio), the judgment value is “0” in the range of i = 1 to 11.
So that its median M₁Becomes 6. Similarly, j
= 2 (second duty ratio) ₂Is 6,
Median value M when j = 3 (third duty ratio)₃Is
5, median value M when j = 4 (fourth duty ratio)₄
Is the center when 5.5 and j = 5 (fifth duty ratio)
Value M₅Is in the case of 5, j = 6 (sixth duty ratio)
Median M₆Is 5.5, j = 7 (seventh duty ratio)
Median value M₇Is 5.5, j = 8 (the eighth duty
Median M for ratio)₈Is 5, j = 9 (the ninth Deute
Median M in the case of₉Becomes 5. Note that this embodiment
In the state, the position of the wafer W in the optical axis direction of the projection optical system
Is changing at a constant pitch ΔZ.
The median value is calculated using the values, but if the pitch is
If not constant, the wafer in the optical axis direction of the projection optical system
It is necessary to use the value of the position of W itself.

Further, the processing unit 551 calculates the median M
₁~ M₉Of the first threshold SV
The sub best focus position at 1. Note that this embodiment
In the embodiment, as an example, the sub-best file at the first threshold value SV1 is set.
The focus position is 5.4 (= Z ₅And Z₆More than the middle position of
And Z₅).

Next, the processing section 551 changes the first threshold value to the second threshold value SV2 (> SV1), and, similarly to the above, displays the display resist images DA of all pattern cells.
_{For i, j} (i = 1 to 11, j = 1 to 9), the presence or absence of the image of the L / S pattern is detected. In the present embodiment, as an example, a detection result as shown in FIG. 10 is obtained.

Then, based on these detection results, the processing unit 551 determines, for each duty ratio of the L / S pattern in the measurement pattern, the wafer W in the optical axis direction of the projection optical system whose judgment value is “0”. Is obtained, and the median value _Mj (j = 1 to 9) is calculated. For example, FIG.
As shown in the case of j = 1, since the determination value in the range of i = 2 to 11 is "0", the median _{M 1} becomes 6.5. Similarly, the median M2 when j = ₂ is 6.
5, j = median _{M 3} in the case of 3 6, j = 4 is the median _{M 4} in the case of 6, j = 5 median _{M 5} 5.5 in the case of, j
The median M6 in the case of = ₆ is 5.5, and the median M7 in the case of j = ₇ is 5.5. When j = 8,9, i = 1 to
In the range of 11, all the judgment values are “1”, so there is no median.

Then, the processing unit 551 calculates the median M
₁~ M₇Of the second threshold SV
The sub best focus position at 2 is set. Note that this embodiment
In the embodiment, as an example, the sub-best file at the second threshold value SV2 is set.
The focus position is 5.9 (= Z ₆Somewhat Z₅Leaning)
You.

Further, the processing section 551 changes the second threshold value to the third threshold value SV3 (> SV2), and similarly to the above, the display resist images DA of all the pattern cells.
_{For i, j} (i = 1 to 11, j = 1 to 9), the presence or absence of the image of the L / S pattern is detected. In the present embodiment, as an example, a detection result as shown in FIG. 11 is obtained.

Then, based on these detection results, the processing unit 551 determines, for each duty ratio of the L / S pattern in the measurement pattern, the wafer W in the optical axis direction of the projection optical system whose judgment value is “0”. Is obtained, and the median value _Mj (j = 1 to 9) is calculated. For example, FIG.
As shown in the case of j = 1, since the determination value in the range of i = 2 to 9 is "0", the median _{M 1} becomes 5.5. Similarly, the median M2 when j = ₂ is 6, and j =
The median M _{3 for 3} is 5, and the median M _{4 for} j = ₄
Is 5.5, and the median M5 when j = ₅ is 5. In the case of j = 6 to 9, in the range of i = 1 to 11, all the judgment values are “1”, so that there is no median value.

Then, the processing unit 551 calculates the median M
₁~ M₅Is calculated, and the average value is calculated as the third threshold value SV.
3 is the sub best focus position. Note that this embodiment
In the state, for example, the sub-best file at the third threshold value SV3 is used.
The focus position is 5.4 (= Z ₅And Z₆More than the middle position of
And Z₅Leaning).

Subsequently, the processing section 551 obtains sub-best focus positions for various threshold values in the same manner as described above, and when the change in the sub-best focus position is smallest with respect to the change in the threshold value as shown in FIG. Is set as the best focus position. In the present embodiment, as an example, somewhat Z ₅ side of the Z ₆ is the best focus position. The processing unit 551 stores the result in the storage unit 555 and displays the result on the display unit 552.
A message requesting the next instruction from the operator is displayed on the display unit 552.

Next, the operator adjusts the microscope main body 501 so that the display resist image in another evaluation point corresponding area is displayed on the display unit 552, and then instructs the image processing device 550 to execute image processing. .

The processing section 551 obtains the best focus position in the same manner as described above.

In this way, the best focus position is obtained in all the evaluation point corresponding areas in the same manner as described above, and the best focus position is printed out from the printing unit 554.

By performing an approximation process using the least squares method based on the best focus position obtained for each of a plurality of evaluation points in the field of view of the projection optical system in this manner, the optical characteristics of the projection optical system can be obtained. One field curvature can be calculated.

Further, at a plurality of evaluation points in the field of view of the projection optical system, based on the line width value in the transfer image of the same pattern cell (for example, CA5) at the best focus position,
By performing the approximation processing using the least squares method, it is possible to obtain the line width uniformity in the field of view of the projection optical system, which is one of the optical characteristics of the projection optical system. Here, the line width value may be obtained by a conventional line width measurement method using a scanning electron microscope, but can also be obtained by image processing.

The optical characteristic data of the projection optical system obtained in this way is input to the main controller 28 of the exposure apparatus 100 and stored in a storage device (not shown). Then, main controller 28 instructs an imaging characteristic correction controller (not shown) based on the optical characteristic data, for example, the position of at least one optical element (lens element in the present embodiment) of projection optical system PL (lens element). The curvature of field of the projection optical system PL is adjusted by changing the inclination of the projection optical system PL (including the distance from other optical elements). The optical elements used for adjusting the imaging characteristics of the projection optical system PL are not only refractive optical elements such as lens elements, but also reflective optical elements such as concave mirrors, or aberrations (distortion, spherical aberration, etc.) of the projection optical system PL. ), Especially an aberration correction plate for correcting the non-rotationally symmetric component. Further, the method of correcting the imaging characteristics of the projection optical system PL is not limited to the movement of the optical element. For example, a method of controlling the exposure light source to slightly shift the center wavelength of the illumination light IL, or a method of correcting the projection optical system A method of changing the refractive index in a part of the PL may be used alone or in combination with the movement of the optical element.

In the exposure apparatus 100 of the present embodiment,
Exposure is performed using the projection optical system PL whose optical characteristics have been adjusted as described above in the same procedure as the operation of forming a resist image for measuring the optical characteristics of the projection optical system PL described above.

As described above, according to the optical characteristic measuring method of the exposure apparatus 100 of the present embodiment, since a plurality of line and space patterns having different duty ratios are used as the measurement patterns, the exposure amount is constant. An analysis method in a measurement method in which both the exposure amount and the position of the wafer W in the optical axis direction of the projection optical system are changed while the measurement method only changes the position of the wafer W in the optical axis direction of the projection optical system. The best focus position, which is one of the optical characteristics, can be obtained by using an analysis method similar to. Therefore, the best focus position can be obtained in a shorter time as compared with a measurement method in which both the exposure amount and the position of the wafer W in the optical axis direction of the projection optical system are changed. Can be improved. In addition, since the exposure amount is constant, the variation in the measurement result is small compared to the method of changing the exposure amount (for example, the over-exposure focus measurement method described above), and as a result, the measurement accuracy and the reproduction of the measurement result are reduced. Performance can be improved. In addition, the exposure amount at this time does not need to be the best exposure amount, and is ± 20 of the best exposure amount.
%.

Since the measurement pattern is composed of a plurality of line-and-space patterns formed under the same forming conditions except for the duty ratio, the measurement pattern includes a plurality of line-and-space patterns having different periodic directions. Compared with the case where the projection optical system includes the projection optical system, the optical characteristics of the projection optical system in the predetermined periodic direction can be obtained more accurately in a shorter time.

Each of the pattern cells CA1 to CA9 constituting the measurement pattern corresponds to the upper side (−Y
Side) to the lower side of the drawing (+ Y side), the duty ratio gradually decreases. As a result, the formation state of the image of the L / S pattern can be efficiently detected for each duty ratio, so that the optical characteristics measured based on the detection result can be obtained in a short time, and as a result, the optical characteristics can be obtained. It is possible to improve the measurement throughput.

Further, in the present embodiment, the degree of matching (correlation coefficient) between each image data and a predetermined template pattern data is obtained by pattern matching, which is an objective and quantitative method. Since the state of formation of the image of the L / S pattern is detected based on the number, the conventional method of measuring a dimension (for example, the aforementioned CD)
/ Focus method or SMP focus measurement method), it is possible to detect an image formation state in a short time and with high accuracy. Therefore, it is possible to improve the measurement accuracy of the optical characteristics determined based on the detection result and the reproducibility of the measurement results, and as a result, it is possible to improve the throughput of the optical characteristics measurement.

In addition, since the size of the measurement pattern can be reduced as compared with the conventional method of measuring dimensions, it is possible to arrange a large number of measurement patterns in the pattern area PA of the reticle. Therefore, the number of evaluation points can be increased, and the interval between each evaluation point can be narrowed. As a result, the measurement accuracy of the optical characteristic measurement can be improved.

In this embodiment, since the cells are arranged in a line along the Y-axis direction which is a specific direction on the pattern surface PA of the reticle _RT , the cells are arranged in a direction perpendicular to the cell column direction ( By transferring the pattern while moving the shot area on the wafer W in the (X-axis direction) at regular intervals,
Many images can be transferred onto the wafer W. Moreover, in the resist image, the duty ratio of the L / S pattern changes in the Y-axis direction of the wafer W,
In the X-axis direction, since the cells are transferred so that the position of the wafer with respect to the optical axis of the projection optical system changes at a constant pitch, the detection of the image formation state of the L / S pattern and the detection result The calculation of the sub best focus position based on this can be performed efficiently. Therefore, the best focus position can be obtained in a shorter time as compared with the case where the cells constituting the measurement pattern are not arranged in a line, and the throughput of optical characteristic measurement can be improved.

Further, in the area where the measurement pattern is not arranged in the pattern area PA, chrome for light shielding is deposited, so that many measurement patterns can be transferred onto the wafer W. As a result, In addition, it is possible to improve the measurement accuracy of the optical characteristic measurement and the reproducibility of the measurement result.

Further, since a blank cell exists as a blank area not including a pattern in the vicinity of the measurement pattern in the pattern area PA of the reticle _RT, a pattern cell which is a detection target of an image formation state is projected. It is possible to transfer a blank area where no pattern exists in the same shot area as the shot area. By using the image data of this blank area as template pattern data, the accuracy of pattern matching is improved, and an image is formed with high accuracy. The state can be detected. Therefore, it is possible to improve the accuracy of the optical characteristics determined based on the detection result.

Further, in the present embodiment, based on the detection result of the image formation state, the range of the position of the wafer W in the optical axis direction of the projection optical system where the image is detected is changed for each duty ratio of the L / S pattern. The best focus position is determined based on the sub best focus position calculated from the correlation between the range and the duty ratio. This determination method is similar to the determination method used in the conventional measurement method for changing the exposure amount (for example, the above-described over-exposure focus measurement method), but includes an error caused by changing the exposure amount. Therefore, it is possible to accurately determine the best focus position, which is one of the optical characteristics.

Further, in the relationship between the sub-best focus position and the threshold value, the best focus position is determined from the position of the wafer W in the optical axis direction of the projection optical system when the variation of the sub-best focus position is smallest with respect to the change of the threshold value. Since the determination is made, it is possible to improve the reproducibility of the measurement result of the optical characteristic measurement.

Further, according to the exposure method of the present embodiment, the focus control target value at the time of exposure is set in consideration of the best focus position determined as described above. It is possible to transfer the image with high precision.

Next, the analysis method used for measuring the best focus position in the present embodiment will be described with reference to FIGS.
5 will be described in detail.

First, L / S with respect to the best focus position
The influence of the duty ratio of the pattern and the influence of the period of the L / S pattern on the best focus position are determined.

For example, three types of L / S patterns PA1 to PA3 having a constant period and different duty ratios and three types of L / S patterns PB1 to PB having a constant line width and different periods.
3 are arranged at a plurality of positions corresponding to a plurality of evaluation points in the field of view of the projection optical system PL in the pattern area PA of the reticle _RT . Then, the image of each pattern is transferred to a plurality of shot areas on the wafer W while changing the position of the wafer W in the optical axis direction of the projection optical system PL. The wafer W is developed, the line width value of the resist image of each pattern formed on the wafer W is measured, and the contrast of each pattern is calculated from the line width value. Here, the contrast means a ratio between a value obtained by multiplying the line width of the pattern by the projection magnification of the projection optical system and the line width value of the resist image actually formed on the wafer W. Then, for each evaluation point, an approximate curve indicating the correlation between the contrast and the position of the wafer W in the optical axis direction of the projection optical system is calculated for each L / S pattern, and the contrast is determined based on the approximate curve. The position of the wafer W in the direction of the optical axis of the projection optical system when the local maximum value is taken is defined as the best focus position.

FIG. 13 shows a certain evaluation point (first evaluation point).
The correlation between the contrast of the L / S patterns PA1 to PA3 and the position of the wafer W in the direction of the optical axis of the projection optical system at a point on the wafer W corresponding to. According to this, the local maximum value of the contrast shows a different value depending on the duty ratio of the L / S pattern, but the best focus position can be uniquely obtained regardless of the duty ratio of the L / S pattern. FIG. 14 shows the L / S patterns PA1 to PA at points on the wafer W corresponding to different evaluation points (second evaluation points).
3 shows the correlation between the contrast of No. 3 and the position of the wafer W in the optical axis direction of the projection optical system. According to this, similarly to FIG. 13, the maximum value of the contrast is L / S
Although different values are shown depending on the duty ratio of the pattern, the best focus position can be uniquely obtained regardless of the duty ratio of the L / S pattern. That is, if the period is constant, the best focus position is L / S
It does not depend on the duty ratio of the pattern.

FIG. 15 shows the L / S patterns PB1 to PB at a point on the wafer W corresponding to the first evaluation point.
3 shows the correlation between the contrast of No. 3 and the position of the wafer W in the optical axis direction of the projection optical system. According to this, the best focus position differs depending on the value of the period. That is, when the line width of the L / S pattern is constant and the period is different, the best focus position cannot be uniquely obtained.

Further, as shown in FIGS. 13 and 14, when the period is constant, the contrast of the image of the L / S pattern decreases as the line width of the line pattern decreases. Further, as the difference between the position of the wafer and the best focus position with respect to the optical axis of the projection optical system increases, the contrast of the image of the L / S pattern decreases.

That is, L / L of the same exposure amount and the same cycle
When projecting the S pattern, the smaller the duty ratio is,
Also, as the deviation of the wafer position from the best focus position is larger, the image of the L / S pattern is less likely to be formed on the wafer.

In this embodiment, utilizing this phenomenon, a plurality of L / S patterns having a constant period and different duty ratios are transferred while changing the wafer position with respect to the optical axis of the projection optical system, and the L / S pattern is transferred. Is detected at each duty ratio of the L / S pattern, and the best focus position is obtained based on the detection result. Therefore, the best focus position can be obtained with high accuracy. As a result, the measurement accuracy of the optical characteristic measurement can be improved. 13 to 15, the position of the wafer W with respect to a predetermined reference position in the optical axis direction of the projection optical system is taken as the focus position on the horizontal axis.

In the present embodiment, it is also possible to measure the best exposure amount. That is, at the best focus position determined as described above, the measurement pattern is transferred while changing the energy amount (exposure dose) of the exposure light irradiated onto the wafer W, and for example, the duty of the L / S pattern is changed. Pattern cell C with ratio L: S = 1: 1
The best exposure can be obtained from the exposure dose when the duty ratio of the L / S pattern in the A5 resist image is closest to L: S = 1: 1, that is, the exposure dose when the contrast is the highest.

As a method for obtaining the best focus position from the image data, apart from the above-described method using the sub best focus position, an image of the L / S pattern at each position of the wafer W in the optical axis direction of the projection optical system is provided. There is a method of utilizing the minimum value of the duty ratio (hereinafter, referred to as “limit duty ratio”) in which is formed. As an example, a specific description will be given using a detection result (see FIG. 10) obtained when the threshold value is the second threshold value SV2.

In this case, as shown in FIG.
In the case of 2, the limit duty ratio is j = 2 (second duty ratio DR ₂ ), and in the case of i = 3, the limit duty ratio is j =
3 (third duty ratio DR ₃ ), the limit duty ratio when i = 4 is j = 3 (third duty ratio DR ₃ ),
When i = 5, the limit duty ratio is j = 7 (seventh duty ratio DR ₇ ), when i = 6, the limit duty ratio is j = 7 (seventh duty ratio DR ₇ ), and when i = 7 In this case, the limit duty ratio is j = 4 (the fourth duty ratio D
R ₄ ), when i = 8, the limit duty ratio is j = 3 (third duty ratio DR ₃ ), when i = 9, the limit duty ratio is j = 3 (third duty ratio DR ₃ ), i = 1
The limit duty ratio when j is 0 is j = 2 (second duty ratio DR ₂ ), and when i = 11 is j.
= 2 (second duty ratio DR ₂ ). Next, FIG.
As shown in FIG. 6, an approximation curve indicating the correlation between the position of the wafer W in the optical axis direction of the projection optical system and the limit duty ratio is obtained by an approximation process using the least squares method. Then, the position of the wafer W in the optical axis direction of the projection optical system when the approximation curve shows the minimum value is set as the best focus position. That is, the position of the wafer W in the optical axis direction of the projection optical system when the L / S pattern having the smallest duty ratio is formed on the wafer W is set as the best focus position. Here, the best focus position, _{Z 5} and _{Z 6}
And almost coincides with the case where the above-described sub best focus position is used. Further, the average value (simple average or weighted average) of the plurality of best focus positions obtained as described above from the determination results at the plurality of threshold values can be obtained with high accuracy.

Here, based on the detection result of the image formation state, the minimum value of the duty ratio of the L / S pattern in which the image is detected is obtained for each position of the wafer W in the optical axis direction of the projection optical system. The best focus position is determined from the correlation between the position of the wafer W in the optical axis direction of the projection optical system and the minimum value of the duty ratio. This decision method is
This method is similar to the determination method used in the conventional measurement method for changing the exposure amount (for example, the above-described over-exposure focus measurement method), but does not include an error due to the change in the exposure amount, so that it can be accurately performed. The best focus position, which is one of the optical characteristics, can be obtained.

Further, paying attention to the contrast of the resist image, the position of the wafer W in the optical axis direction of the projection optical system when the contrast is maximized for each duty ratio of the L / S pattern is obtained, and the average value (simple average) is obtained. Or a weighted average) may be used as the best focus position. The contrast can be obtained from the line width value of the image of the pattern measured by a scanning electron microscope or the like, but can also be obtained by image processing.

Further, in the present embodiment, the sub best format
The focus position is determined by all the duty ratios at which the image is formed.
Median M at_jIs calculated from the average value of
It is not limited, for example, the first shown in FIG.
If the threshold is₃, M ₅, M₇, M₉like,
Every other median M_jSub-best focus from average
The position may be obtained, and M₅~ M₉Dew as
Median M when tee ratio is small_jSub-best from the average of
The focus position may be obtained. Or different multiple
Calculate the average value with the combination of
It is also possible to use the average value as the sub best focus position.
You. Further, in the present embodiment, the average value is obtained by a simple average.
However, it may be obtained by a weighted average.

Further, in the present embodiment, the duty ratio of the L / S pattern of the measurement pattern RPA gradually decreases from the upper side (−Y side) to the lower side (+ Y side) of FIG. , Nine types of pattern cells are arranged, but the present invention is not limited to this.
For example, conversely, the pattern cells may be arranged so that the duty ratio of the L / S pattern gradually increases from the upper side (−Y side) to the lower side (+ Y side) in FIG. In either case, the image formation state can be efficiently detected for each duty ratio. In addition, the number of line patterns and the duty ratio of each L / S pattern in the present embodiment are examples, and are not limited thereto. Also, the number of pattern cells is not limited to nine. Furthermore, the arrangement position of the blank cell CA10 is not limited to the lower side (+ Y side) of the pattern cell CA9 in FIG.
As long as it is in the vicinity of the measurement pattern, for example, it may be arranged on the upper side (−Y side) of the pattern cell CA1 in FIG.

In place of the measurement pattern RPA,
As shown in Figure 17, the pattern area PA of the reticle _{R T,} eleven patterns cell CB2～CB12,
Measurement patterns RPB arranged from the upper side of the drawing (−Y side) to the lower side of the drawing (+ Y side) at regular intervals in a line along the Y-axis direction which is the specific direction can be used. Here, the cells CB2 to CB12 are pattern cells including L / S patterns having the same period direction and the same period. The duty ratio of the L / S pattern gradually increases from the pattern cell CB2 to the pattern cell CB7, and the duty ratio of the L / S pattern gradually decreases from the pattern cell CB7 to the pattern cell CB12. For example, the pattern cell CB2
The L / S pattern of the pattern cells CB12 and CB12 has the sixth duty ratio, the L / S pattern of the pattern cells CB3 and CB11 has the fifth duty ratio, and the L / S pattern of the pattern cells CB4 and CB10. The pattern has the fourth duty ratio and the L / S of pattern cells CB5 and CB9.
The pattern has the third duty ratio, the L / S pattern of the pattern cells CB6 and CB8 has the second duty ratio, and the L / S pattern of the pattern cell CB7 is the first duty ratio. Can have a ratio.
That is, the same pattern cell can be included in the measurement pattern. The cells CB1 and CB13 are blank cells as blank areas, and the blank cell CB1 is
The blank cell CB13 is arranged below the pattern cell CB12 (+ Y side).

FIG. 18 shows the measurement pattern RP described above.
As in the case of A, an example of the resist image on the wafer W after exposing the measurement pattern RPB and the blank cells CB1 and CB13 and completing development is shown. Then, the relationship between the sub-best focus position and the threshold is determined in the same manner as described above, and the sub-best focus position when the change in the sub-best focus position with respect to the change in the threshold is the smallest is set as the best focus position. According to this, two correlations between the sub-best focus position and the threshold are obtained, and by calculating the average value of the best focus positions obtained from each correlation, the best focus position can be obtained with higher accuracy. . In this case, three or more pattern cells having the same duty ratio of the L / S pattern can be included in the measurement pattern. In addition, the number of pattern cells is not limited to 11 as a matter of course, and the portion where the duty ratio gradually increases from one side to the other side in the specific direction and the duty ratio It suffices that at least one part each having a gradually decreasing size is included. Furthermore, it is also possible to make the period direction of the L / S pattern different between a portion where the duty ratio gradually increases from one side to the other side in a specific direction and a portion where the duty ratio gradually decreases. This is because the best focus position can be individually obtained for a portion where the duty ratio gradually increases and a portion where the duty ratio gradually decreases.

In place of the measurement pattern RPA,
As shown in FIG. 19, in the pattern area PA of the reticle _RT , the measurement pattern RPA as the first pattern having the first periodic direction and the second pattern RPa having the second periodic direction are provided. It is also possible to use the measurement patterns RPC arranged in a line along the Y-axis direction which is a specific direction. Note that blank cells are arranged as blank regions below the first pattern RPA and the second pattern RPa (+ Y side). Here, the second periodic direction is a direction obtained by rotating the first periodic direction by 90 degrees in the plane of the paper. Thus, the best focus position for each periodic direction can be obtained in the same manner as described above. In the case where the first pattern RPA and the second pattern RPa are patterns formed under the same forming conditions (period, duty ratio, etc.) except in the periodic direction, the best focus obtained from the first pattern is used. location and,
The astigmatism of the projection optical system can be obtained from the difference from the best focus position obtained from the second pattern.
That is, based on the difference between the best focus position obtained based on the measurement pattern having the periodic direction of the sagittal direction and the meridional direction arranged at the evaluation point at an arbitrary image height position in the field of view of the projection optical system PL. Astigmatism can be calculated. Furthermore, the average value (simple average or weighted average) of the best focus position obtained from the first pattern and the best focus position obtained from the second pattern can be set as the best focus position at the evaluation point. is there. Thereby, the best focus position can be obtained with high accuracy. That is, the optical characteristics can be obtained for each of the first and second periodic directions, and the difference in the optical characteristics due to the change in the periodic direction can be obtained. By using the average value of the optical characteristics, the optical characteristics can be obtained with higher accuracy.

Further, an approximation process by the least square method is performed on a plurality of evaluation points in the field of view of the projection optical system based on the astigmatism of the projection optical system calculated in this manner, so that the astigmatism plane is obtained. Uniformity can be determined.

The total focal difference of the projection optical system can be obtained from the astigmatism in-plane uniformity and the field curvature.

Further, the difference between the first periodic direction and the second periodic direction may be other than 90 degrees, and the chromium as a light shielding pattern is provided in the pattern area PA of the reticle _RT. The first pattern may be disposed along a predetermined row in the Y-axis direction, which is a specific direction, and the second pattern may be disposed along another row in the Y-axis direction, with the deposition region interposed therebetween. L having three or more types of periodic directions
The / S pattern may be included in the measurement pattern. Thus, a difference in the best focus position due to a difference in the periodic direction can be obtained. Further, an average value (simple average or weighted average) of the best focus positions in each cycle direction may be set as the best focus position at the evaluation point.

Further, instead of the measurement pattern RPA,
As shown in FIG. 20, in the pattern area PA of the reticle _RT , a chromium deposition area VC as a light-shielding pattern is provided.
The measurement pattern RPA as a first pattern having a first cycle is disposed along a predetermined row in the Y-axis direction which is a specific direction, with a second cycle having a second cycle.
A measurement pattern in which the pattern RPD is arranged along another row in the Y-axis direction can be used. This allows
The image of the first pattern and the image of the second pattern can be easily distinguished, the formation state of the images of both patterns can be detected efficiently, and the optical characteristics based on the first pattern and
The optical characteristics based on the second pattern can be obtained in a short time. Therefore, compared with the case where the first pattern and the second pattern are mixed, the throughput of the optical characteristic measurement can be improved. Further, it is possible to obtain the best focus position with higher accuracy from the average value (simple average or weighted average) of the best focus position in each cycle obtained in the same manner as described above. Further, if the first pattern and the second pattern are patterns formed under the same forming conditions except for the period, the effect of the period of the L / S pattern on the best focus position can be obtained. That is, optical characteristics can be obtained for each of the first cycle and the second cycle,
The difference in the optical characteristics due to the change in the period can be obtained, and the optical characteristics can be obtained with higher accuracy by using the average value of the optical characteristics obtained for each period.

Further, by moving the shot area on the wafer W at regular intervals in the X-axis direction, the image of the first pattern can be transferred adjacent to the image of the first pattern. Since the image of the second pattern can be transferred adjacent to the image, the transfer area of the image of the first pattern and the transfer area of the image of the second pattern can be separated. Therefore, the optical characteristics based on the detection result of the image formation state of the first pattern and the optical characteristics based on the detection result of the image formation state of the second pattern can be efficiently obtained.
As a result, it is possible to improve the throughput of optical characteristic measurement. Note that the first pattern and the second pattern may be arranged along the predetermined row.

In the present embodiment, the image data of the resist image of the blank cell is used as the template pattern data. However, at least the image of the L / S pattern substantially does not exist in the image data of the resist image of the pattern cell. The imaging data of one pattern cell may be used as template pattern data. In this case, it is not always necessary to arrange a blank cell near the measurement pattern in the pattern area PA of the reticle _RT . Here, when imaging data of a plurality of pattern cells is used as template pattern data, an average value (simple average or weighted average) of the imaging data is obtained for each corresponding target pixel, and the average value is used as template pattern data. May be used.

Further, in the present embodiment, the CCD image pickup device 505 converts the information of the enlarged resist image into 8-bit digital data corresponding to the density of black and white for each CCD pixel, but is not limited to this. However, it can be changed to a value other than 8 bits (for example, 4 bits) if necessary. Also, using a color-capable CCD imaging device,
For example, corresponding to (red), G (green), and B (blue), respectively, the data may be converted into 8-bit digital data (24-bit data in total). In this case, in pattern matching with the template pattern data, the pixel data of each target pixel is compared with the template pattern data for each of R, G, and B.

In the pattern matching with the template, the area to be compared is set to 529 (= 23 × 23).
(Target pixel), but the present invention is not limited to this. Further, it is not always necessary to make the number of target pixels coincide with the number of CCD pixels of the CCD imaging device 505 in the region to be compared. It is meaningless to make the number of target pixels larger than the number of CCD pixels.
By making the number smaller than the number of D pixels, the time required for image processing can be shortened. In this case, for example, 9
If one CCD pixel corresponds to one target pixel, 9
The average value (simple average or weighted average) of the CCD pixel data may be used as the pixel data of the target pixel.

In this embodiment, a scanning electron microscope is used to obtain image data of a resist image, but the present invention is not limited to this. For example, the exposure apparatus 1
Alternatively, an alignment sensor (such as an alignment detection system AS used for wafer alignment) provided at 00 may be used. In this case, by supplying image data from the alignment detection system AS to the image processing device 550, the best focus position can be obtained in the same manner as described above. Further, the optical characteristics of the projection optical system PL can be adjusted based on the above-described measurement results (such as the best focus position) without the intervention of an operator or the like. That is, the exposure apparatus can have an automatic adjustment function. Further, the resist image (or latent image) may be detected by a method other than the image processing method.

In this embodiment, the position of the wafer W in the direction of the optical axis of the projection optical system is set to + Z at a constant pitch ΔZ.
Although the direction is changed, the present invention is not limited to this. For example, the pitch ΔZ may be changed to a smaller pitch in a range considered to be near the best focus position in order to improve measurement accuracy.

Further, in the present embodiment, the shot area is moved at regular intervals in the direction orthogonal to the cell column direction, but the present invention is not limited to this. It is sufficient that the position of the wafer W in the direction of the optical axis of the projection optical system at the time of transfer is clear during the process of detecting the image formation state. That is, it is only necessary that the imaging data file can be created correctly.

Further, in the present embodiment, the image processing device 5
Numeral 50 captures image data (image data of 110 cells) of one evaluation point corresponding region at one time, and for example, captures image data (image data of 11 cells) of each position of the wafer W a plurality of times. (10 times). This relates to the resolution (the number of CCD pixels) of the CCD imaging device 505, the magnification of the scanning electron microscope 500, and the like. Of course, it is also possible to take in the resist images of the cells one by one. In addition, the processing unit 551 may perform the image processing after the imaging data of all the images are prepared.

In this embodiment, the case where the photosensitive layer for detecting the state of image formation on the substrate is a photoresist has been described. However, the photosensitive layer is not limited to the photoresist, and is not limited to the photoresist. What is necessary is just to form an image (latent image and visible image) by irradiation. For example, the photosensitive layer may be an optical recording layer, a magneto-optical recording layer, or the like. Therefore, the object on which the photosensitive layer is formed is not limited to a wafer or a glass plate. A possible plate or the like may be used. However, if the object to be imaged is a latent image, it is necessary to convert the latent image into a visible image, and the method of converting the latent image into a visible image differs depending on the recording method of the latent image.

Further, the detection of the image formation state may be performed by aerial image measurement for measuring a projection image (aerial image) of the pattern projected by the projection optical system. For example, a pattern plate on which a slit-shaped or rectangular opening pattern is formed, the pattern plate is scanned in a predetermined direction in a two-dimensional plane perpendicular to the optical axis of the projection optical system, and light received through the opening When performing aerial image measurement using a so-called aerial image measurement device that performs photoelectric conversion, for each position in the optical axis direction of the projection optical system, Fourier-transform the photoelectric conversion signal from the aerial image measurement device, for example, The image formation state can be detected from the amplitude ratio (also called contrast) between the first-order frequency component and the zero-order frequency component. Then, the position in the optical axis direction of the projection optical system when the amplitude ratio (contrast) is maximized for each duty ratio is obtained, and the average value (simple average or weighted average) can be set as the best focus position.

Further, in the present embodiment, whether or not an image of the L / S pattern is formed is detected by using a technique called pattern matching with template pattern data. However, the present invention is not limited to this. Instead, for example, a reference value may be set in advance instead of the template pattern data, and the detection may be performed based on a result of comparing the reference value with the target pixel data in the image of each cell. Alternatively, all the target pixel data in the cell may be added and compared with a predetermined reference value to detect whether or not the image of the L / S pattern is formed.

The image may be enlarged by an optical microscope, a scanning electron microscope, or the like, and whether or not the image of the L / S pattern is formed may be visually detected.

Further, in the present embodiment, in the binarization processing of the target pixel data, the correlation value is calculated from the difference between the target pixel data of the display resist image of the target pattern cell and the target pixel data of the display resist image of the blank cell. Although the binarization of the target pixel data is performed by comparing the correlation value with a predetermined reference value, the present invention is not limited to this, and the binarization processing may be performed based on another algorithm. good. For example, when calculating the correlation value, instead of using only the pixel data of each target pixel, a simple average value of a plurality of pixel data around each target pixel or a weighted average value thereof can be used. It is.

In this embodiment, each cell has a frame pattern. However, if the transfer position of each cell on the substrate can be detected by other means, the frame pattern may not be provided. Alternatively, only some of the cells may have a frame pattern. Furthermore, the frame pattern does not necessarily have to be frame-shaped, and may be, for example, a contact hole, as long as the purpose as a marker for detecting the position of an image is achieved. Further, in the present embodiment, the image forming characteristic of the projection optical system PL is adjusted via the image forming characteristic correction controller. However, for example, only the image forming characteristic correction controller sets the image forming characteristic within a predetermined allowable range. When the control cannot be performed, at least a part of the projection optical system PL may be replaced, or at least one optical element of the projection optical system PL may be reworked (aspherical processing or the like). In particular, when the optical element is a lens element, the eccentricity may be changed or the optical element may be rotated around the optical axis. At this time, when a registration image or the like is detected using the alignment sensor of the exposure apparatus 100, the main control device 28 displays a warning on a display (monitor) or informs an operator or the like of necessity of assistance to the operator through the Internet or a mobile phone. The notification may be given, or information necessary for adjusting the projection optical system PL, such as a replacement portion of the projection optical system PL and an optical element to be reworked, may be notified together. As a result, not only the operation time for measuring the optical characteristics (including the imaging characteristics) but also the preparation period can be shortened, and the stop period of the exposure apparatus can be shortened, that is, the operation rate can be improved.

In the above embodiment, the case where the present invention is applied to the step-and-repeat type reduction projection exposure apparatus has been described. However, the scope of the present invention is not limited to this. That is, step
The present invention can be suitably applied to an AND scan method, a step and stitch method, a mirror projection aligner, a photo repeater, and the like. Further, the projection optical system PL may be any of a refraction system, a catadioptric system, and a reflection system, and may be any of a reduction system, an equal magnification system, and an enlargement system.

In particular, the step-and-scan type reduction projection exposure apparatus uses a conventional method of measuring the optical characteristics of the projection optical system by changing the exposure amount (for example, the above-described over-exposure focus measurement method). In such a case, there is a problem that the measurement result varies greatly before and after the exposure amount at which the resist image disappears due to the influence of the exposure amount, focus position, vibration, synchronization accuracy between the reticle and the wafer, and the reproducibility of the measurement result is reduced. Furthermore, since the exposure amount when the resist image disappears is significantly different from the normally used best exposure amount, there is a problem that the state of vibration and synchronization accuracy at the time of exposure is not always the same as the normal use state. . However, in the present invention, since the optical characteristics of the projection optical system are measured under the same exposure amount, it is possible to suppress the occurrence of the above problem, and as a result, it is possible to improve the reproducibility of the measurement result. .

Further, the light source of the exposure apparatus to which the present invention is applied is not limited to a KrF excimer laser or an ArF excimer laser, but may be an F ₂ laser (wavelength: 157 nm) or another pulsed laser light source in the vacuum ultraviolet region. good. In addition, a fiber doped with, for example, erbium (or both erbium and ytterbium) is used as the exposure illumination light, for example, a single-wavelength laser beam in the infrared or visible range oscillated from a DFB semiconductor laser or a fiber laser. A harmonic that has been amplified by an amplifier and wavelength-converted to ultraviolet light using a nonlinear optical crystal may be used.

Further, the present invention relates to an exposure apparatus for transferring a device pattern onto a glass plate, which is used not only for an exposure apparatus used for manufacturing a semiconductor element but also for a display including a liquid crystal display element and a plasma display. Exposure equipment used in the manufacture of thin-film magnetic heads for exposing device patterns onto ceramic wafers, imaging devices (such as CCDs), micromachines, and DNA chips, as well as exposure used in the manufacture of masks or reticles. It can also be applied to devices and the like.

Further, by applying the image processing apparatus used in the present embodiment, a simple contrast measurement can be performed by obtaining the density of a predetermined area of an image. It can be used for evaluating the accuracy of the apparatus of the exposure apparatus main body.

Further, as the image processing device 550, C
A personal computer having an interface with the CD imaging device 505 can be used. in this case,
The function of the processing unit 551 is stored in the storage unit 555 as a computer program, and is called by an operator's instruction.

<< Device Manufacturing Method >> Next, an embodiment of a device manufacturing method using the above-described exposure apparatus and exposure method will be described.

FIG. 21 shows devices (semiconductor chips such as ICs and LSIs, liquid crystal panels, CCDs, thin-film magnetic heads,
A flow chart of a manufacturing example of a DNA chip, a micromachine, etc.) is shown. As shown in FIG. 21, first, in step 301 (design step), a function / performance design of a device (for example, a circuit design of a semiconductor device) is performed, and a pattern design for realizing the function is performed. Subsequently, in step 302 (mask manufacturing step), a mask on which the designed circuit pattern is formed is manufactured. On the other hand, in step 303 (wafer manufacturing step), a wafer is manufactured using a material such as silicon.

Next, in step 304 (wafer processing step), an actual circuit or the like is formed on the wafer by lithography using the mask and the wafer prepared in steps 301 to 303, as will be described later. Next, step 305 (device assembly step)
In, device assembly is performed using the wafer processed in step 304. This step 305 includes processes such as a dicing process, a bonding process, and a packaging process (chip encapsulation) as necessary.

Finally, step 306 (inspection step)
In step 305, inspections such as an operation confirmation test and a durability test of the device manufactured in step 305 are performed. After these steps, the device is completed and shipped.

FIG. 22 shows a detailed flow example of step 304 in the case of a semiconductor device. In FIG. 22, step 311 (oxidation step)
In, the surface of the wafer is oxidized. Step 312
In the (CVD step), an insulating film is formed on the wafer surface. In step 313 (electrode forming step), electrodes are formed on the wafer by vapor deposition. Step 3
At 14 (ion implantation step), ions are implanted into the wafer. Steps 311 to 314 described above
Each of them constitutes a pre-processing step in each stage of wafer processing, and is selected and executed according to a necessary process in each stage.

In each stage of the wafer process, when the above-mentioned pre-processing step is completed, the post-processing step is executed as follows. In this post-processing step, first, in step 3
In 15 (resist forming step), a photosensitive agent is applied to the wafer. Subsequently, in step 316 (exposure step), the circuit pattern of the mask is transferred to the wafer by the exposure apparatus and the exposure method of the above embodiment. Next, in step 317 (development step), the exposed wafer is developed, and in step 318 (etching step), the exposed members other than the portion where the resist remains are removed by etching. Then, in step 319 (resist removing step), unnecessary resist after etching is removed.

By repeating these pre-processing and post-processing steps, multiple circuit patterns are formed on the wafer.

If the device manufacturing method of the present embodiment as described above is used, the exposure apparatus and the exposure method of the above embodiment are used in the exposure step. High-precision exposure is performed via the projection optical system adjusted in consideration of the characteristics, and a highly integrated device can be manufactured with high productivity.

[0171]

As described above, according to the optical characteristic measuring method of the present invention, there is an effect that the optical characteristics of the projection optical system can be obtained in a short time with high accuracy and reproducibility.

Further, according to the exposure method of the present invention, there is an effect that highly accurate exposure can be realized.

According to the device manufacturing method of the present invention, the productivity of a highly integrated device can be improved.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of a reticle used for measuring optical characteristics of a projection optical system.

FIG. 3 is a diagram for explaining a measurement pattern used for measuring optical characteristics of a projection optical system.

FIG. 4 is a diagram for explaining a resist image formed on a wafer.

FIG. 5 is a diagram for explaining an apparatus used for performing image processing of a resist image.

FIG. 6 is a diagram for explaining an array DA _{i, j} used to specify each cell in a display resist image.

FIG. 7 is a diagram for explaining pixels GA _{m, n} in a region to be compared in pattern matching.

FIG. 8 is a diagram illustrating an example of a result of binarization processing of pixel data in the display resist images DA _{1, 1} .

FIG. 9 is a diagram illustrating an example of a result of detection of an L / S pattern image formation state in a display resist image in a case of a first threshold value SV1.

FIG. 10 shows a second threshold value SV2 in a display resist image.
FIG. 14 is a diagram illustrating an example of a result of detection of an L / S pattern image formation state in the case of FIG.

FIG. 11 shows a third threshold value SV3 in a display resist image.
FIG. 14 is a diagram illustrating an example of a detection result of a state of forming an image of an L / S pattern in the case of FIG.

FIG. 12 is a diagram illustrating a relationship between a sub best focus position and a threshold.

FIG. 13 shows three types of L having the same cycle but different duty ratios.
FIG. 7 is a diagram illustrating a relationship between contrast in an image of the / S pattern and a wafer position in an optical axis direction of a projection optical system.

FIG. 14 is a diagram showing the relationship between the contrast and the wafer position in the optical axis direction of the projection optical system in images of three types of L / S patterns having the same cycle and different duty ratios at evaluation points different from FIG. is there.

FIG. 15 is a diagram showing a relationship between contrast in images of three types of L / S patterns having the same line width and different periods, and the wafer position in the optical axis direction of the projection optical system.

FIG. 16 is a diagram illustrating a relationship between a minimum value (limit duty ratio) of a duty ratio at which an image of an L / S pattern is formed in a display resist image and a wafer position in an optical axis direction of a projection optical system.

FIG. 17 is a view for explaining a measurement pattern different from the measurement pattern of FIG. 3;

18 is a diagram showing a resist image of the measurement pattern of FIG.

FIG. 19 is a diagram for explaining a measurement pattern different from the measurement patterns of FIGS. 3 and 17;

20 is a diagram for explaining a measurement pattern different from the measurement patterns of FIGS. 3, 17 and 19. FIG.

FIG. 21 is a flowchart illustrating an embodiment of a device manufacturing method according to the present invention.

FIG. 22 is a flowchart of a process in step 304 of FIG. 21.

[Explanation of symbols]

28: Main control unit, 100: Exposure unit, 500: Scanning electron microscope, 550: Image processing unit, CA10: Blank cell (blank area), PL: Projection optical system, R: Reticle (mask), RPA: For measurement Pattern (first pattern: first)
, The first direction), RPa... Second pattern (second period), RPB... Measurement pattern (first period, first period), RPD... Second pattern (second Cycle), VCR: light-shielding pattern, W: wafer (substrate).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03F 9/02 H01L 21/30 516A F-term (Reference) 2G086 HH07 2H095 BA02 BB01 BB02 BB31 5F046 DB05 DB10 EA03 EA09 FC04 FC06

Claims (18)

[Claims] 1. An optical characteristic measuring method for measuring an optical characteristic of a projection optical system for projecting a pattern on a first surface onto a second surface, wherein the measuring pattern includes at least two line and space patterns having different duty ratios. Is arranged on the first surface, an image of the measurement pattern is projected on the second surface side by the projection optical system, and the image is projected at a plurality of positions in the optical axis direction of the projection optical system. An optical characteristic measuring method comprising: detecting an image forming state of each line and space pattern in a measurement pattern; and obtaining an optical characteristic of the projection optical system based on the detection result. 2. The method according to claim 1, wherein the line and space patterns have the same periodic direction. 3. The measurement pattern includes: a first pattern including at least two line-and-space patterns having different duty ratios and a periodic direction as a first direction; and a second pattern having different duty ratios and a second periodic direction. A second pattern comprising at least two line and space patterns as directions.
The optical characteristic measurement method described in 1. 4. The measurement pattern includes a first pattern including at least two line-and-space patterns having different duty ratios and the same first period, and a second pattern having different duty ratios and the same second pattern. A second pattern comprising at least two line-and-space patterns having a period.
The optical characteristic measurement method described in 1. 5. The optical device according to claim 1, wherein the line and space patterns are arranged in a line on a pattern surface of the mask along a specific direction. Characteristics measurement method. 6. The line and space pattern constituting the first pattern is arranged along a predetermined line in the specific direction on a pattern surface of the mask, and the line constituting the second pattern is provided. The optical property measuring method according to claim 3, wherein the AND space pattern is arranged on the pattern surface along another row in the specific direction different from the predetermined row. 7. The light-shielding pattern formed between the predetermined row on which the first pattern is arranged on the pattern surface and the other row on which the second pattern is arranged. 7. The method according to claim 6, further comprising a pattern. 8. A row of the line and space patterns arranged along the specific direction includes a portion where a duty ratio of the pattern gradually increases from one side to the other side in the specific direction and a portion where the duty ratio gradually decreases. The optical characteristic measuring method according to any one of claims 5 to 7, comprising at least one portion of: 9. The image of the measurement pattern is provided by the projection optical system at a plurality of positions of a substrate arranged on the second surface side of the projection optical system in an optical axis direction of the projection optical system. The method according to claim 1, wherein the images are respectively transferred to different upper areas. 10. An image of each line and space pattern in the measurement pattern by pattern matching between each image data of the image of the measurement pattern transferred to a different region on the substrate and predetermined template pattern data. The method for measuring optical characteristics according to claim 9, wherein a formation state is detected. 11. The optical characteristic measuring method according to claim 10, wherein a blank area where no pattern exists exists near the pattern area on the mask where the measurement pattern is formed. 12. The template pattern data includes:
12. The optical characteristic measuring method according to claim 11, wherein the image data is imaging data of the blank area on the mask projected on the substrate. 13. The image to be detected for the formation state,
The optical characteristic measuring method according to claim 9, wherein the method is a latent image formed on the substrate. 14. An image to be detected for the formation state,
The optical characteristic measuring method according to claim 9, wherein the resist image is a resist image obtained by developing the substrate. 15. As a result of detecting the state of formation of the image, a minimum value of a duty ratio of the line and space pattern where the image is detected is obtained for each position in the optical axis direction of the projection optical system. The optical characteristic measuring method according to claim 1, wherein a best focus position is determined based on a correlation between a position of the optical system in the optical axis direction and the minimum value. 16. As a result of detecting the state of formation of the image, a range in the optical axis direction of the projection optical system in which the image is detected is obtained for each duty ratio of the line-and-space pattern. 15. The optical characteristic measuring method according to claim 1, wherein the best focus position is determined based on a correlation with the ratio. 17. An exposure method for irradiating a mask with an energy beam for exposure and transferring a pattern formed on the mask onto a substrate via a projection optical system, wherein the exposure method comprises the steps of: A step of adjusting the projection optical system in consideration of the optical characteristics measured by the optical characteristic measurement method according to the paragraph; and a pattern formed on the mask via the adjusted projection optical system on the substrate. And a transferring step. 18. A device manufacturing method including a lithography step, wherein the lithography step uses the exposure method according to claim 17.