JP2004079585A - Method for measuring imaging characteristics, and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve measuring capabilities in the measurement of projection optical system imaging characteristics. <P>SOLUTION: The number of lines in a line and space pattern to be transcribed to a wafer is changed from 5 to 2 in this method for measuring imaging characteristics such as comatic aberration. This reduces the effect of defocusing of line widths or the like in the line pattern to be imaged on the wafer and also decreases the effect of reticle formation errors or the like, and enables a high-precision measurement of projection optical system imaging characteristics. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging characteristic measuring method and an exposure method, and more particularly, to an imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system, and an imaging characteristic is measured by the imaging characteristic measuring method. And an exposure method for performing exposure using a projection optical system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, when a semiconductor element or a liquid crystal display element or the like is manufactured by a photolithography process, a pattern of a photomask or a reticle (hereinafter, collectively referred to as a “reticle”) is formed on a surface through a projection optical system. A projection exposure apparatus for transferring onto an object such as a wafer or a glass plate coated with a photosensitive agent, for example, a step-and-repeat type reduction projection exposure apparatus (so-called stepper), and a step-and-scan type scanning projection exposure An apparatus (a so-called scanning stepper) or the like is used.
[0003]
In this type of projection exposure apparatus, the accuracy of a projected image greatly changes due to a focus shift during exposure (transfer of a reticle pattern onto a wafer) or an aberration of a projection optical system. There is a need for a technique for accurately measuring imaging characteristics such as aberrations and the like.
[0004]
As a method of measuring the best focus position of the above-described projection optical system, for example, a test printing of a predetermined pattern is performed on a resist-coated wafer, and then the wafer is developed, and the line width of the pattern is set to, for example, SEM ( A technique of measuring the best focus position using a scanning electron microscope and comparing it with a designed line width value, or using a relationship between the focus position and the line width (CD / focus) Law).
[0005]
For example, in the case of a stepper, a line and space having, for example, five linear patterns (hereinafter, abbreviated as L / S) having five linear patterns with respect to the arrangement of shot areas on a wafer is changed in a trial printing while changing a focus position by a fixed amount. The test pattern of (1) is transferred onto the wafer. Then, the line width of the linear resist pattern in each shot area formed after development is immediately measured, and the focus position when exposing the shot area having the smallest line width in all shots is determined as the best. It is determined as the focus position.
[0006]
Regarding the aberration of the projection optical system, five L / S patterns transferred onto the wafer are measured again at the best focus position determined as described above, and the amount of aberration is defined.
[0007]
[Problems to be solved by the invention]
However, 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, transfer of finer patterns with high precision. Is required. For this reason, test patterns for measuring the imaging characteristics of the projection optical system have been miniaturized. For this reason, the line width of the L / S pattern has naturally become narrower, and is currently about 130 nm.
[0008]
As described above, when the L / S pattern of the test pattern is thinned to the current level, the line width of the two line patterns at both ends of the five line pattern images formed on the wafer is reduced. However, a phenomenon occurs in which the line widths of the three line pattern images on the inner side are thinner than those, and depending on certain exposure conditions, these images may disappear completely.
[0009]
The image of the line patterns at both ends is an important element for measuring the imaging characteristics of the projection optical system, particularly, coma aberration. There is a demand for a method capable of measuring characteristics with high accuracy.
[0010]
The present invention has been made under such circumstances, and a first object of the present invention is to provide an imaging characteristic measurement method capable of improving the measurement capability when measuring the imaging characteristic of a projection optical system. Is to do.
[0011]
A second object of the present invention is to provide an exposure method capable of realizing highly accurate exposure.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is an imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system (PL) for projecting a pattern on a first surface onto a second surface, wherein the predetermined interval (D) Marks (DM) formed by two predetermined patterns (LP1, LP2) having a predetermined width (L) disposed at a predetermined distance. ₁ ~ DM ₅ ) Is disposed on the first surface, and the mark is transferred onto an object (W) disposed on the second surface via the projection optical system; and A measurement step of measuring the size of the mark image (for example, L1, L2); and a calculation step of calculating the imaging characteristics of the projection optical system based on the information on the measured size of the mark image. This is an image characteristic measuring method.
[0013]
According to this, a mark formed by two predetermined patterns having a predetermined width arranged at a predetermined interval is transferred onto an object, and the projection optical system is connected based on information on the size of the image of the mark. Image characteristics are calculated. By doing so, the number of patterns projected on the object is reduced as compared with the case where five L / S pattern marks are used, so that the accuracy of forming an image of the predetermined pattern is adversely affected. Fewer numbers. Therefore, the degree of the change in the size of the image of the two predetermined patterns with respect to the change in the defocus amount or the magnitude of the above-described mark manufacturing error decreases. Therefore, in the imaging characteristic measuring method of the present invention, the influence of other factors such as the defocus amount and the mark manufacturing error on the size of the two predetermined pattern images is reduced, and the imaging characteristics of the projection optical system are measured. In this case, the measurement capability can be improved.
[0014]
In this case, the measurement of the size of the mark image may be performed on a latent image formed on the object without developing the object, or on the object on which the mark image is formed. May be performed on a resist image formed on the object or an image (etched image) obtained by etching the object on which the resist image is formed. The size of the mark image is determined by, for example, an alignment detection system of an exposure apparatus (an LSA system or an alignment detection system of an image processing method for forming an image of the alignment mark on an image sensor, a so-called FIA (Field Image Alignment) system). The measurement may be performed by using such a method. The shape of the mark image may be linear, rhombic, or another shape.
[0015]
In this case, as in the imaging characteristic measuring method according to claim 2, the predetermined interval is such that, in the measuring step, two predetermined pattern images in the mark image formed on the object are separated from each other. The interval can be measured.
[0016]
As a result of examination by the present applicant, when measuring the size of the above-described mark image in order to calculate the imaging characteristics of the projection optical system, the narrower the interval between two predetermined patterns on the mark, the more the It has been confirmed that the imaging characteristics of the projection optical system can be accurately determined based on the size of the image formed on the object. However, if the interval between the two predetermined patterns on the mark is too small, it is difficult to distinguish the images of the two predetermined patterns formed on the object, and it is impossible to measure the size of the two predetermined patterns. Become. Therefore, it is necessary to set the interval between two predetermined patterns on the mark, that is, the predetermined interval to be an interval at which the images of the two predetermined patterns on the mark can be separated and measured.
[0017]
In this case, as in the imaging characteristic measuring method according to claim 3, the calculating step includes calculating an imaging characteristic of the projection optical system based on information on a difference between the sizes of the images of the two predetermined patterns. can do.
[0018]
As a typical imaging characteristic of the projection optical system which can be calculated by the imaging characteristic measuring method of the present invention, there is coma aberration. The coma aberration can be obtained by using, as an index value, the difference between the sizes of the images of the two predetermined patterns formed on the object. In the calculation step, the coma aberration of the projection optical system is measured based on the information on the difference between the sizes. I do.
[0019]
Further, in this case, as in the imaging characteristic measuring method according to claim 4, the predetermined interval includes a difference between the sizes of the images of the two predetermined patterns included in the information of the size difference. The interval may be larger than the size of the noise component to be used.
[0020]
The degree of formation of the images of the two predetermined patterns formed on the object depends on the exposure conditions such as the exposure dose and the focus position of the projection optical system, and the exposure conditions and the optimal exposure conditions when these images are formed. Is a noise component when measuring the size of the mark image. Further, even when the size of the mark image is measured, the noise component is included in the information on the size of the mark image depending on the measurement state. In order to measure the coma aberration of the projection optical system, the difference between the sizes of the two predetermined patterns is calculated as described above, and the information of the difference between the sizes includes the above-described noise component. I have. Therefore, in order to extract the value of the difference included in the information of the size difference, the level of the noise component included in the information needs to be smaller than the value of the difference. It has been confirmed that the level of the noise component depends on the interval between two predetermined patterns in the mark. In the present invention, the interval between the two predetermined patterns is defined as described above.
[0021]
In the image forming characteristic measuring method according to claim 1 or 2, as in the image forming characteristic measuring method according to claim 5, in the calculating step, a best focus position and an astigmatism are used as image forming characteristics of the projection optical system. At least one of the aberration, the spherical aberration, the field curvature, and the coma aberration may be calculated based on information on the size of the image of the two predetermined patterns.
[0022]
In the imaging characteristic measuring method according to any one of claims 1 to 5, as in the imaging characteristic measuring method according to claim 6, the predetermined interval is substantially equal to a predetermined width of the predetermined pattern. Good, but it is preferable that the width is set smaller than the predetermined width.
[0023]
The invention according to claim 7 is an exposure method for transferring a pattern of a mask (R) onto an object (W) via a projection optical system (PL), and is an exposure method according to any one of claims 1 to 6. Measuring the imaging characteristics of the projection optical system by the imaging characteristics measurement method described in the above; adjusting the conditions at the time of exposure in consideration of the measured imaging characteristics, the mask pattern Transferring onto an object.
[0024]
According to this, the imaging characteristic of the projection optical system is accurately measured by the imaging characteristic measuring method according to any one of the first to sixth aspects. Then, the conditions of the exposure are adjusted in consideration of the measured imaging characteristics, and the pattern of the mask is transferred onto the object. The adjustment of the exposure condition typically includes, for example, adjustment of the imaging characteristics of the projection optical system based on the measured imaging characteristics, adjustment of the alignment error between the mask and the object caused by the imaging characteristics, and the like. In any case, since the conditions for exposure are adjusted, highly accurate exposure can be performed.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0026]
FIG. 1 shows an exposure apparatus 100 according to an embodiment suitable for carrying out the imaging characteristic measuring method and the exposure method according to the present invention. The exposure apparatus 100 is a step-and-scan type projection exposure apparatus.
[0027]
The exposure apparatus 100 includes an illumination system IOP, a reticle stage RST (mask stage) for holding a reticle R as a mask, and a wafer as an object on which a photosensitive agent (photoresist) is applied by forming an image of a pattern formed on the reticle R. A projection optical system PL for projecting onto the W, an XY stage 20 (object stage) that holds the wafer W and moves in a two-dimensional plane (XY plane), a drive system 22 that drives the XY stage 20, and a control system thereof. Etc. are provided. The control system is mainly configured by a main controller 28 that controls the entire apparatus.
[0028]
The illumination system IOP includes a light source such as a KrF excimer laser or an ArF excimer laser, an optical integrator or a homogenizer (a fly-eye lens or a rod-type (internal reflection type) integrator, a diffractive optical element, or the like), a relay lens, and a variable ND filter. , A condenser lens, a reticle blind (or a masking blade), and an illumination optical system including a dichroic mirror (all not shown). In the illumination system IOP, a rectangular slit-shaped illumination area elongated in the X-axis direction is substantially uniform with the illumination light IL within the visual field of the projection optical system PL defined by the reticle blind on the reticle R on which a circuit pattern or the like is drawn. Illuminate with an appropriate illuminance.
[0029]
The reticle stage RST is arranged below the illumination system IOP in FIG. A reticle R is suction-held on the reticle stage RST via a vacuum chuck or the like (not shown). The reticle stage RST can be finely driven in the Y-axis direction (the left-right direction on the paper surface in FIG. 1), the X-axis direction (the direction perpendicular to the paper surface in FIG. 1), and the θz direction (the rotation direction around the Z-axis perpendicular to the XY surface). At the same time, it can be driven at a scanning speed specified in a predetermined scanning direction (here, the Y-axis direction). Note that reticle stage RST may include a fine moving unit that finely moves reticle R with at least three degrees of freedom (for example, the X-axis and Y-axis directions and the θz direction), and a coarse moving unit that has a long stroke in the scanning direction.
[0030]
A moving mirror 15 that reflects a laser beam from a reticle laser interferometer (hereinafter, referred to as “reticle interferometer”) 21 is fixed on reticle stage RST. The position of the reticle stage RST in the moving plane is constantly detected by the reticle interferometer 21 with a resolution of, for example, about 0.5 to 1 nm. Here, actually, on reticle stage RST, a moving mirror (or a retroreflector) having a reflecting surface orthogonal to the Y-axis direction and a moving mirror having a reflecting surface orthogonal to the X-axis direction are provided. A reticle Y interferometer and a reticle X interferometer are provided corresponding to the movable mirror. However, in FIG. 1, these are representatively shown as the movable mirror 15 and the reticle interferometer 21. Here, one of the reticle Y interferometer and the reticle X interferometer, for example, the reticle Y interferometer is a two-axis interferometer having two measurement axes, and the reticle stage RST is controlled based on the measurement value of the reticle Y interferometer. In addition to the Y position, rotation in the θz direction can be measured.
[0031]
Position information of reticle stage RST from reticle interferometer 21 is sent to main controller 28. Main controller 28 drives reticle stage RST via drive system 29 based on the position information of reticle stage RST.
[0032]
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. Here, as the projection optical system PL, a dioptric system composed of a plurality of lens elements having a common optical axis AXp in the Z-axis direction, which is a telecentric reduction system, is used here. Specific plural lenses among the lens elements are controlled by an imaging characteristic correction controller (not shown) based on a command from the main controller 28, and optical characteristics (including imaging characteristics) of the projection optical system PL, for example, projection. The magnification, distortion, coma, field curvature and the like can be adjusted.
[0033]
The XY stage 20 is actually composed of a Y stage that moves on a base (not shown) in the Y-axis direction and an X stage that moves on the Y stage in the X-axis direction. Are integrally shown as an XY stage 20. A wafer table 18 is mounted on the XY stage 20, and a wafer W is held on the wafer table 18 by vacuum suction or the like via a wafer holder (not shown).
[0034]
The XY stage 20 moves not only in the scanning direction (Y-axis direction) but also in the scanning direction so that a plurality of shot areas on the wafer W can be positioned in a projection area in a visual field conjugate to the illumination area. Are also movable in a non-scanning direction (X-axis direction) perpendicular to the direction. Then, a step-and-scan operation of repeating an operation of scanning (scanning) exposing each shot area on the wafer W and an operation of moving to a scan start position (acceleration start position) for exposure of the next shot is performed.
[0035]
The wafer table 18 minutely drives a wafer holder that holds the wafer W in the Z-axis direction and the tilt direction with respect to the XY plane. A movable mirror 24 is provided on the upper surface of the wafer table 18, and the position of the wafer table 18 in the XY plane is measured by projecting a laser beam onto the movable mirror 24 and receiving the reflected light. A laser interferometer 26 is provided to face the reflecting surface of the movable mirror 24. Actually, as the movable mirror, there are provided an X movable mirror having a reflecting surface orthogonal to the X axis and a Y movable mirror having a reflective surface orthogonal to the Y axis. Although an X laser interferometer for position measurement and a Y laser interferometer for position measurement in the Y-axis direction are provided as laser interferometers, these are representatively shown as a movable mirror 24 and a laser interferometer 26 in FIG. Is illustrated. The X laser interferometer and the Y laser interferometer are multi-axis interferometers having a plurality of measurement axes, and in addition to the X and Y positions of the wafer table 18, rotation (yaw (θz rotation which is rotation about the Z axis)) , Pitching (θx rotation around the X axis) and rolling (θy rotation around the Y axis) can also be measured. Therefore, in the following description, it is assumed that the position of the wafer table 18 in the directions of five degrees of freedom of X, Y, θz, θy, and θx is measured by the laser interferometer 26.
[0036]
The measurement value of the laser interferometer 26 is supplied to a main controller 28. The main controller 28 monitors the measurement value of the laser interferometer 26 and drives the XY stage 20 through the drive system 22 to thereby control the wafer. The position of the table 18 is controlled.
[0037]
The position and the amount of tilt in the Z-axis direction of the surface of the wafer W can be determined by, for example, a focus sensor including an oblique incidence type multipoint focus position detection system having a light transmission system 50a and a light reception system 50b disclosed in Japanese Patent Application Laid-Open No. 6-283403. It is measured by AFS. The measurement value of the focus sensor AFS is also supplied to the main control device 28. The main control device 28 slightly drives the wafer table 18 via the drive system 22 based on the measurement value of the focus sensor AFS, thereby performing projection. The position and the inclination of the wafer W with respect to the optical axis direction of the optical system PL are controlled.
[0038]
That is, the position and orientation of the wafer W in the X, Y, Z, θx, and θy directions of five degrees of freedom are controlled via the wafer table 18 in this manner. The remaining error of θz (yaw) is corrected by rotating at least one of reticle stage RST and wafer table 18 based on yaw information of wafer table 18 measured by laser interferometer 26.
[0039]
Further, a reference plate FP is fixed on the wafer table 18 so that the height of the surface is the same as the surface of the wafer W. On the surface of the reference plate FP, various reference marks including a reference mark used for so-called baseline measurement of an alignment detection system AS described later are formed.
[0040]
Further, in the present embodiment, an off-axis type alignment detection system AS as a mark detection system for detecting an alignment mark formed on the wafer W is provided on a side surface of the projection optical system PL. The alignment detection system AS has, for example, an alignment sensor called an LSA system or an FIA system, and measures the positions of the reference marks on the reference plate FP and the alignment marks on the wafer W in the X and Y two-dimensional directions. It is possible.
[0041]
Here, the LSA system is the most versatile sensor that irradiates a mark with a laser beam and measures the position of the mark by using diffracted and scattered light, and has conventionally been used for a wide range of process wafers. . The FIA system is a sensor that illuminates a mark with broadband (broadband) light such as a halogen lamp and measures the mark position by processing the mark image, and is effectively used for an asymmetric mark on an aluminum layer or a wafer surface. You.
[0042]
Not only the FIA system, but also an alignment sensor such as an LSA system that irradiates a target mark with coherent detection light and detects scattered light or diffracted light generated from the target mark, and two diffraction lights generated from the target mark. Of course, it is possible to use an alignment sensor that detects light by interfering with light (for example, the same order) alone or in an appropriate combination.
[0043]
The alignment control device 16 performs A / D conversion of the information DS from the alignment detection system AS, and further calculates 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.
[0044]
Further, in the exposure apparatus 100 of the present embodiment, a reticle mark on the reticle R or a reticle stage RST above the reticle R via the projection optical system PL disclosed in, for example, JP-A-7-176468. A pair of reticle alignment detection systems (not shown) including a TTR (Through The Reticle) alignment system using light of an exposure wavelength for simultaneously observing a reference mark (both not shown) and a mark on the reference plate FP are provided. Have been. The detection signals of these reticle alignment detection systems are supplied to main controller 28 via alignment controller 16. When actually performing scanning exposure with the exposure apparatus 100, these reticle alignment detection systems use a reticle mark on the reticle R or a reference mark on the reticle stage RST (both not shown) and a mark on the reference plate FP. Are detected, and the coordinate system of the reticle stage RST defined by the measurement axis of the reticle interferometer 21 and the measurement of the wafer interferometer 26 are determined from the measured values of the reticle interferometer 21 and the wafer interferometer 26 at that time. The reticle alignment is performed by obtaining the relationship with the coordinate system of the XY stage 20 defined by the long axis.
[0045]
Next, an example of a reticle used in the imaging characteristic measuring method of the present embodiment will be described.
[0046]
FIG. 2 shows an example of a reticle RT used for measuring the imaging characteristics of the projection optical system PL. FIG. 2 is a plan view of reticle RT as viewed from the pattern surface side (the lower surface side in FIG. 1). In the reticle RT, a pattern area PA is provided in the center of a glass substrate 42 as a substantially square mask substrate, and a total of 5 points including a center of a slit-shaped illumination area indicated by a dotted line and a square portion in the pattern area PA is provided. Measurement mark DM in place ₁ ~ DM ₅ Is formed. Note that, for example, a pair of reticle alignment marks RM1 and RM2 are formed 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). In the pattern area PA, the measurement mark DM ₁ ~ DM ₅ The portion excluding is a light shielding portion.
[0047]
FIG. 3 shows the measurement mark DM ₁ Is shown as an example. As shown in FIG. 3, the measurement mark DM ₁ Is a mark formed by the line patterns LP1 and LP2. The line patterns LP1 and LP2 are both linear patterns extending in the X-axis direction and parallel to each other, have a line width L in the Y-axis direction, and are arranged at intervals D in the Y-axis direction. . In this embodiment, the narrower the distance D between the line patterns LP1 and LP2, the more accurately the imaging characteristics of the projection optical system PL can be obtained based on the size of those images formed on the wafer W. . However, if the distance D between the line patterns LP1 and LP2 on the mark is too small, the images of the line patterns LP1 and LP2 formed on the wafer W will be in a connected state. It becomes difficult to measure the line width of the images of the patterns LP1 and LP2. Therefore, the interval D is the measurement mark DM ₁ The interval must be set so that the images of the upper line patterns LP1 and LP2 can be measured separately from each other. In the present embodiment, the measurement mark DM ₁ In, the line patterns LP1 and LP2 are light shielding portions, and the other portions are light transmitting portions. Note that other measurement marks DM ₂ ~ DM ₅ Also measurement mark DM ₁ It has the same configuration as.
[0048]
Further, the degree of formation of the images of the line patterns LP1 and LP2 formed on the wafer W is also affected by exposure conditions such as the exposure dose at the time of exposure and the focus position of the projection optical system PL. ₁ ~ DM ₅ , For example, the line widths of the images of the line patterns LP1 and LP2 include not only components due to the imaging characteristics of the projection optical system PL such as aberration but also components due to these exposure conditions. This component is a noise component when measuring the imaging characteristics of the projection optical system PL such as aberration. Further, a measurement mark DM obtained in a measurement process described later. ₁ ~ DM ₅ The information related to the size of the image includes noise due to the measurement state. For example, to measure the coma aberration of the projection optical system PL, the line width difference between the images of the line patterns LP1 and LP2 is measured as described above. The noise component described above is included. Therefore, the index value of the coma aberration included in the information of the line width difference needs to be higher than the level of the noise component included in the information. The level of this noise component is determined by the measurement mark DM ₁ ~ DM ₅ Has been confirmed to be affected by the distance D between the line patterns LP1 and LP2, and in the present embodiment, the line width difference L1-L2 of the image of the line patterns LP1 and LP2 included in the line width difference information is determined. The interval D between the line patterns LP1 and LP2 needs to be defined so as to be larger than the size of the noise component included in the information. In the present embodiment, for example, the measurement mark DM in which the line width of the line patterns LP1 and LP2 is 130 nm and the interval D is 120 nm. ₁ ~ DM ₅ Shall be used.
[0049]
Next, a flow of a measurement operation for measuring the imaging characteristics of the projection optical system PL by the exposure apparatus 100 of the present embodiment will be briefly described.
[0050]
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).
[0051]
Main controller 28 adjusts the center of a pair of fiducial marks (not shown) formed on the surface of fiducial plate FP provided on wafer table 18 so as to substantially coincide with the optical axis of projection optical system PL. The wafer table 18 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, main controller 28 adjusts the position of reticle stage RST via drive system 29 such that the center (reticle center) of reticle RT substantially matches the optical axis of projection optical system PL. At this time, for example, the relative position between the reticle alignment marks RM1 and RM2 and the corresponding reference mark is detected by the reticle alignment detection system (not shown) via the projection optical system PL.
[0052]
The main controller 28 drives the reticle alignment marks RM1 and RM2 based on the detection result of the relative position detected by the reticle alignment detection system such that the relative position error between the reticle alignment marks RM1 and RM2 and the corresponding reference mark is minimized. The position of the reticle stage RST in the XY plane is adjusted via the system 29. Thereby, the center of the reticle RT (reticle center) almost exactly coincides with the optical axis of the projection optical system PL, and the rotation angle of the reticle RT coincides with the coordinate axis of the rectangular coordinate system defined by the length measurement axis of the laser interferometer 26. Exact match.
[0053]
Next, the main controller 28 moves the XY stage 20 via the drive system 22 while monitoring the measurement result of the laser interferometer 26, and in this embodiment, applies a positive resist as a photosensitive agent on the surface. The moved wafer W is moved to a position below the projection optical system PL.
[0054]
In this state, main controller 28 performs exposure. Here, since the purpose is to measure the imaging characteristics of the projection optical system PL, the reticle RT and the wafer W, ie, the reticle stage RST and the XY stage 20, are kept stationary during exposure. In the present embodiment, coma aberration or an index value (referred to as an abnormal line width or a line width difference) is measured as the imaging characteristic of the projection optical system PL, and the best focus position of the projection optical system PL is already determined. It is assumed that measurement and calibration of the focus sensor AFS have been completed. Therefore, the exposure is performed after the imaging plane of the projection optical system PL and the surface of the photoresist layer of the wafer W are substantially matched in the irradiation area of the illumination light IL using the focus sensor AFS. Thereby, measurement mark DM of reticle RT ₁ ~ DM ₅ The images of the line patterns LP1 and LP2 are reduced and transferred onto the photoresist layer on the wafer W via the projection optical system PL (exposure step). At this time, exposure is performed at a normal exposure dose (that is, an appropriate amount according to the sensitivity characteristics of the resist).
[0055]
When the exposure is completed, the wafer W is unloaded from above the wafer table 18 by a wafer loader (not shown) in accordance with an instruction from the main controller 28, and then inline with the exposure apparatus 100 by a wafer transfer system (not shown). Is transported to a coater / developer (not shown), which is connected to the printer.
[0056]
The wafer W is developed in the coater / developer. Upon completion of the development, a transfer image LP1W of the line pattern LP1 and a transfer image LP2W of the line pattern LP2 are formed on the wafer W as shown in FIG.
[0057]
Next, measurement mark DM formed on wafer W ₁ ~ DM ₅ , That is, the transfer image LP1W of the line pattern LP1 and the transfer image LP2W of the line pattern LP2 (line width measurement) are measured as follows (measurement step). At this time, since the line patterns LP1 and LP2 on the reticle RT are arranged at the interval D, the transfer image LP1W of the line pattern LP1 and the transfer image LP2W of the line pattern LP2 are separated on the wafer W. And their line widths can be measured.
[0058]
First, upon receiving the notification of the completion of development from the coater / developer, the main controller 28 instructs a wafer transfer system (not shown) to transfer the wafer W into the exposure apparatus 100, and transfers the transferred wafer W to the wafer loader. To load on the wafer table 18 again.
[0059]
Then, main controller 28 moves transfer image LP1W of line pattern LP1 and transfer image LP2W of line pattern LP2 formed on wafer W directly below alignment detection system AS, and uses, for example, an FIA system or the like. The line width L1 of the transfer image LP1W of the line pattern LP1 and the line width L2 of the transfer image LP2W of the line pattern LP2 are measured (see FIG. 4). Those measurement marks DM detected by the alignment detection system AS ₁ ~ DM ₅ Is transmitted to the main controller 28 via the alignment controller 16.
[0060]
Next, main controller 28 calculates the imaging characteristics of projection optical system PL based on line width L1 of transfer image LP1W of line pattern LP1 and line width L2 of transfer image LP2W of line pattern LP2 (calculation step). .
[0061]
In the present embodiment, a case where coma aberration is calculated as the imaging characteristic of the projection optical system will be described. For example, when the L / S pattern is usually transferred onto the wafer W via the projection optical system PL, the coma aberration is a phenomenon in which the line widths of line images located at both ends of the transferred image are greatly different. Is known to be detectable. In order to express the coma aberration by this phenomenon, the line widths of the transfer images of the line patterns located at both ends in the best focus state are defined as D1 and D2.
| D1-D2 | / (D1 + D2) (1)
A so-called abnormal line width value (a line width change amount due to coma aberration) defined by the following equation is used.
[0062]
Therefore, in the present embodiment, the amount represented by the following equation may be defined as an abnormal line width value as an index of coma aberration from the line widths L1 and L2 of the transfer images LP1W and LP2W of the line patterns LP1 and LP2.
[0063]
Line width abnormal value = | L1-L2 | / (L1 + L2) (2)
[0064]
In main controller 28, measurement mark DM ₁ ~ DM ₅ The average value of the line width L1 of the transfer image LP1W of each line pattern LP1 and the average value of the line width L2 of the transfer image LP2W of the line pattern LP2 are substituted for L1 and L2 in the above equation (2). The calculated result may be calculated as an abnormal line width value. In the present embodiment, coma is measured as one of the imaging characteristics of the projection optical system PL. However, various other parameters such as a best (best) focus position, astigmatism, spherical aberration, and field curvature are used. Can also be measured. In this case, at least one of the line width L1 and the line width L2 is used as an index of each aberration.
[0065]
In the exposure apparatus 100 of the present embodiment, the main controller 28 controls each unit of the apparatus and measures the imaging characteristics of the projection optical system PL by the imaging characteristic measurement method described above before the start of exposure. Then, main controller 28 adjusts various conditions at the time of exposure in consideration of the measured imaging characteristics, and performs scanning exposure while performing synchronous control of XY stage 20 and reticle stage RST.
[0066]
The adjustment of various conditions at the time of exposure typically includes, for example, adjusting the imaging characteristic of the projection optical system PL based on the measurement result via the above-described imaging characteristic correction controller. Further, for example, when the imaging characteristic is curvature of field or the like, at least one of the reticle R and the wafer W in the Z-axis direction and the tilt angle may be adjusted during the scanning exposure. At this time, the adjustment of the imaging characteristics by the imaging characteristic correction controller may be used together.
[0067]
If the imaging characteristics cannot be adjusted within the predetermined accuracy range, main controller 28 displays a warning on a display (monitor) or assists an operator or the like through the Internet (e-mail or the like) or a mobile phone. May be notified. Further, in this case, information necessary for adjustment of each drive system and sensors may be notified together. As a result, not only the work time for measuring various data, but also the preparation period can be shortened, and the stop period of the exposure apparatus 100 can be shortened, that is, the operation rate can be improved.
[0068]
As described in detail above, the measurement mark DM formed by the two line patterns LP1 and LP2 having the line width L arranged at the interval D. ₁ ~ DM ₅ Are transferred onto the wafer W, and the imaging characteristics of the projection optical system PL are measured based on the images of the measurement marks, ie, the transfer images LP1W and LP2W of the line patterns LP1 and LP2. You.
[0069]
FIG. 5 shows a case where an L / S pattern mark having five line patterns is used as a measurement mark of the imaging characteristics of the projection optical system PL, and a case where two line patterns are used as in the present embodiment. The characteristics of the size of the transferred image when the mark of the L / S pattern is used are shown. In addition, when the line width difference of the transfer images of the line patterns at both ends of the L / S pattern having five line patterns is L1′−L2 ′, and the coma aberration is measured using the measurement mark of this pattern, It is assumed that an abnormal line width value obtained by the same equation as the above equation (2) is used as an index value of coma aberration.
[0070]
In FIG. 5A, the horizontal axis indicates the defocus amount, and the vertical axis indicates the line width abnormal value represented by the above equation (2). Further, the characteristic of the abnormal line width value of the transferred image when the mark of the L / S pattern using the two line patterns is used is indicated by a solid line (L1−L2), and the L having the five line patterns The characteristic of the abnormal line width value of the transferred image of the line pattern at both ends of the / S pattern is indicated by a dotted line (L1'-L2 ').
[0071]
As shown in FIG. 5A, the line width index value of both measurement marks changes depending on the focus position at the time of exposure, and becomes minimum at the best focus position where the defocus amount is 0, and the defocus amount is reduced. It increases as it gets bigger. Therefore, when the measurement mark for measuring the coma aberration is transferred to the wafer, it is desirable to set the defocus amount to the best focus position where the defocus amount is zero. However, in actual measurement, it is difficult to expose the measurement mark with the defocus amount completely set to zero.
[0072]
As shown in FIG. 5A, the ratio of the change of the abnormal line width value to the change of the defocus amount is smaller in L1−L2 than in L1′−L2 ′. Therefore, when L1−L2 is measured, the change in the abnormal line width due to the defocus amount becomes smaller. Therefore, even when the defocus amount is not 0, the coma aberration can be measured with higher accuracy. .
[0073]
In FIG. 5B, the horizontal axis indicates a reticle manufacturing error, and the vertical axis indicates the line width of a line image formed on the reticle, which is transferred onto a wafer. Further, the line width characteristic of the transferred image when the mark of the L / S pattern using two line patterns is used is shown by a solid line (L2), and the L / S pattern having five line patterns is shown. The characteristic of the line width abnormal value of the transfer image of the line pattern at both ends is indicated by a dotted line (L2 ′).
[0074]
As shown in FIG. 5B, it can be seen that the line widths L2 and L2 ′ of the transferred image both of the measurement marks increase as the reticle manufacturing error increases. Therefore, when a measurement mark is transferred to a wafer to measure aberrations such as coma aberration, it is desirable to reduce the manufacturing error of the measurement mark, that is, the reticle manufacturing error as much as possible. However, it is difficult to completely eliminate the reticle manufacturing error. As shown in FIG. 5B, the degree of the change in the abnormal line width with respect to the change in the reticle manufacturing error is smaller in L2 than in L2 '. This tendency is the same for the other line widths L1 and L1 '. Therefore, when L2 is measured, the error in the line width of the transferred image due to the reticle manufacturing error becomes smaller, and thus aberrations such as coma can be measured with higher accuracy.
[0075]
As described above, the measurement characteristic of the coma aberration has a smaller number of patterns to be projected than when five L / S pattern measurement marks are used, and thus affects the degree of pattern image formation at the measurement marks. And the number of other patterns that give For this reason, the degree of the change in the size of the image of the two line patterns with respect to the change in the defocus amount or the magnitude of the manufacturing error of the mark becomes small. Therefore, in the imaging characteristic measuring method according to the present embodiment, the influence of other factors such as the defocus amount and the mark reticle manufacturing error on the size of the line widths L1 and L2 of the transfer images LP1W and LP2W of the line patterns LP1 and LP2. Can be reduced, and the measurement capability when measuring the imaging characteristics of the projection optical system PL can be improved.
[0076]
In this case, the measurement mark DM ₁ ~ DM ₅ Of the size of the transferred image may be performed on the latent image formed on the wafer W without developing the wafer W, or the measurement mark DM ₁ ~ DM ₅ After developing the wafer W having the transferred image formed thereon, the process is performed on the resist image formed on the wafer W or an image (etched image) obtained by etching the wafer W having the resist image formed thereon. May be.
[0077]
Further, in the present embodiment, the transfer images LP1W and LP2W are linear images, but the present invention is not limited to this, and may be rhombic images or other shapes. In the case of a rhombic image, it is desirable to measure the size using the LSA system instead of the FIA system. Further, in the present embodiment, in order to measure the coma aberration or the index value thereof, the exposure is performed by arranging the wafer at the best focus position of the projection optical system PL. However, it is clear from the description of FIG. As described above, it is not always necessary to expose the wafer at the best focus position.
[0078]
In the above embodiment, the value represented by the right side of the above equation (2) is used as the index value of the coma aberration. However, the numerator | L1-L2 | You may make it.
[0079]
Further, according to the exposure apparatus 100 of the present embodiment, the imaging characteristics of the projection optical system PL are accurately measured by the above-described imaging characteristics measuring method. Then, various conditions during exposure are adjusted in consideration of the measured imaging characteristics, and the pattern of reticle R is transferred onto wafer W. The adjustment of the exposure condition typically includes, for example, adjustment of the imaging characteristics of the projection optical system PL based on the measured imaging characteristics, adjustment of the alignment error between the reticle R and the wafer W caused by the imaging characteristics, and the like. Can be In any case, since various conditions at the time of exposure are adjusted, highly accurate exposure can be performed.
[0080]
In the above embodiment, the case where the longitudinal direction of the line patterns LP1 and LP2 is the X-axis direction is described. However, the present invention is not limited to this, and the longitudinal direction of the line patterns LP1 and LP2 is the Y-axis direction. May be present, or may be in another direction on the XY plane. Further, a plurality of sets of line patterns LP1 and LP2 having different longitudinal directions may be used as one measurement mark. Further, a plurality of sets of line patterns LP1 and LP2 in which at least one of the line width and the interval D is different may be used as one measurement mark.
[0081]
Further, in the above-described embodiment, the measurement mark DM whose interval D is smaller than the line width of the line patterns LP1 and LP2. ₁ ~ DM ₅ However, the interval D may be approximately equal to the line width, or the interval D may be larger than the line width. In particular, in the former, comparison of the measurement results with the conventional five line patterns Becomes easier.
[0082]
Further, in the above-described embodiment, the measurement marks of the reticle RT are provided at a total of five locations including the center and the four corners of the area in the pattern area PA, but the present invention is not limited to this, and the reticle is not limited to this. A large number of measurement marks may be arranged on the RT pattern area PA.
[0083]
In the above embodiment, the line width of the resist image is measured. However, for example, the line width of a latent image or an image obtained by etching a wafer on which a resist image is formed may be measured. good. In the above embodiment, the line widths L1 and L2 of the transferred image are measured using the alignment detection system AS of the exposure apparatus 100. However, other than the exposure apparatus, for example, a dedicated line width measurement apparatus (SEM or the like) is used. You may.
[0084]
Further, in the above embodiment, the line widths L1 and L2 of the transfer images LP1W and LP2W are optically detected by the alignment detection system AS or the like. However, the present invention is not limited to this. For example, an ECD (Electrical Critical Dimension) : A measuring method using electric resistance). In this case, it is necessary to add an electrode pattern for measuring electric resistance to the line pattern to be measured.
[0085]
Further, in the above embodiment, a positive photoresist is used as a photoresist as a photosensitive agent applied to the wafer, but a negative photoresist may be used.
[0086]
Further, in the above-described embodiment, the line patterns LP1 and LP2 are used as the light-shielding portions. However, the line patterns LP1 and LP2 may be used as the light-transmitting portions, and the surrounding portions may be used as the light-shielding portions. In this case, it is desirable to use a negative photoresist.
[0087]
Further, a drawing error or the like of a measurement mark formed on the reticle may be detected in advance, and the error may be added to the calculation result of Expression (2). Further, in the above embodiment, when measuring the imaging characteristics of the projection optical system PL, the measurement mark DM ₁ ~ DM ₅ Was transferred to the wafer. Alternatively, the measurement mark may be transferred by a scanning exposure method, or the measurement mark may be transferred by both a static exposure method and a scanning exposure method. The imaging characteristics may be determined for each.
[0088]
In the above embodiment, the case where the line widths L1 and L2 of the transferred image are measured using the FIA system of the alignment detection system AS has been described. However, the present invention is not limited to this. Of course, the line widths L1 and L2 of the transferred image may be measured using the above-described alignment sensor that detects two diffracted lights (for example, the same order) generated from the mark by causing interference. Even in this case, the imaging characteristics of the projection optical system PL can be obtained in the same manner as in the above embodiment.
[0089]
Further, in the above-described embodiment, the case where the present invention is applied to the step-and-scan type scanning exposure apparatus has been described. However, the scope of the present invention is not limited to this. That is, the present invention can be suitably applied to a step-and-repeat method, a step-and-stitch method, a mirror projection aligner, a photo repeater, and the like. In particular, in the case of a step-and-repeat type projection exposure apparatus, in the exposure step, the exposure is performed while the object stage and the mask stage are stationary, thereby forming the image forming characteristic of the projection optical system PL in the same manner as in the above embodiment. Can be requested.
[0090]
Further, the projection optical system PL may be any one of a refraction system, a catadioptric system, and a reflection system, and may be any one of a reduction system, an equal magnification system, and an enlargement system. Further, the reticle may be of a reflection type as well as a transmission type.
[0091]
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 a continuous light source such as a mercury lamp that generates g-line, i-line, or the like. ₂ A laser (wavelength: 157 nm) or another pulsed laser light source in the vacuum ultraviolet region may be used. In addition, for example, a single-wavelength laser beam in the infrared or visible range oscillated from a DFB semiconductor laser or a fiber laser is used as the exposure illumination light, for example, a fiber doped with erbium (or both erbium and ytterbium). A harmonic that has been amplified by an amplifier and wavelength-converted to ultraviolet light using a nonlinear optical crystal may be used. Further, EUV light or the like may be used as the illumination light for exposure. In this case, a reflection type reticle is used.
[0092]
Furthermore, the present invention is not limited to an exposure apparatus used for manufacturing a semiconductor element, but also an exposure apparatus used for manufacturing a display including a liquid crystal display element and a plasma display, which transfers a device pattern onto a glass plate, and a thin film magnet. For exposure equipment used to manufacture device masks, such as exposure devices that transfer device patterns onto ceramic wafers, imaging devices (such as CCDs), micromachines, and DNA chips, as well as exposure devices that are used to manufacture masks or reticles. Can also be applied.
[0093]
【The invention's effect】
As described above in detail, according to the imaging characteristic measuring method according to the present invention, there is an effect that the imaging characteristic of the projection optical system can be accurately and efficiently measured.
[0094]
Further, according to the exposure method of the present invention, since various conditions at the time of exposure are adjusted, highly accurate exposure can be performed.
[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 an imaging characteristic of a projection optical system.
FIG. 3 is an enlarged view showing a measurement mark on the reticle shown in FIG. 2;
FIG. 4 is a view showing a transferred image formed on a resist layer when exposure is performed using the reticle on which the measurement mark shown in FIG. 3 is formed.
FIG. 5 is a graph showing a characteristic of a size of a transferred image in various measurement marks.
[Explanation of symbols]
DM ₁ ~ DM ₅ ... Measurement marks, LP1, LP2, line pattern, PL, projection optical system, R, mask, W, wafer.

Claims (7)

An imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system that projects a pattern on a first surface onto a second surface,
A mark formed by two predetermined patterns having a predetermined width arranged at a predetermined interval is arranged on the first surface, and the mark is arranged on the second surface via the projection optical system. An exposing step of transferring the image onto an object;
A measuring step of measuring a size of an image of the mark formed on the object;
A calculating step of calculating an imaging characteristic of the projection optical system based on the information on the size of the measured mark image. The said predetermined space | interval is the space | interval which can separate the image of two predetermined patterns in the image of the said mark formed on the said object in the said measurement process mutually, and can be measured. Imaging characteristic measurement method. The imaging characteristic measuring method according to claim 2, wherein the calculating step calculates an imaging characteristic of the projection optical system based on information on a difference between the sizes of the images of the two predetermined patterns. The predetermined interval is an interval such that a difference between the sizes of the images of the two predetermined patterns included in the information on the size difference is larger than a size of a noise component included in the information. The imaging characteristic measuring method according to claim 3. In the calculating step, at least one of a best focus position, astigmatism, spherical aberration, field curvature, and coma aberration is defined as an imaging characteristic of the projection optical system based on information on an image size of the two predetermined patterns. The imaging characteristic measuring method according to claim 1, wherein the calculation is performed by calculation. The imaging characteristic measuring method according to claim 1, wherein the predetermined interval is set smaller than a predetermined width of the predetermined pattern. An exposure method for transferring a pattern of a mask onto an object via a projection optical system,
A step of measuring an imaging characteristic of the projection optical system by the imaging characteristic measuring method according to any one of claims 1 to 6;
Transferring the pattern of the mask onto the object by adjusting conditions for exposure in consideration of the measured imaging characteristics.

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