JP4798353B2 - Optical characteristic measuring method and pattern error measuring method - Google Patents

Description

  The present invention is a measurement technique that can be used, for example, when measuring optical characteristics of a projection optical system mounted on a projection exposure apparatus used for transferring a mask pattern onto a substrate, and errors in the pattern for measuring the optical characteristics. About.

  Conventionally, a wafer (or glass plate) coated with a resist (photosensitive material) through a projection optical system in a lithography process for manufacturing a semiconductor element, an image sensor (CCD, etc.), a liquid crystal display element, etc. For example, batch exposure type and scanning exposure type projection exposure apparatuses are used. In these projection exposure apparatuses, as the degree of integration of semiconductor elements and the like is further improved, it is required to further improve the line width accuracy of the circuit pattern after transfer. One of the optical characteristics of the projection optical system that affects the line width accuracy is an optical proximity effect characteristic (hereinafter referred to as OPE characteristic). The OPE characteristic means that the line width of a resist pattern obtained by developing a projected image changes depending on the pitch of the pattern.

Conventionally, in order to measure the OPE characteristic, the line width of the resist pattern actually formed from the projected image of the pattern for characteristic evaluation has been measured with a scanning electron microscope or the like. In addition to the measurement of the OPE characteristic, for example, a method of processing a detection signal obtained by scanning a predetermined mark image with a slit in order to measure the position of a projected image has been proposed (for example, Patent Documents). 1).
Japanese Patent Laid-Open No. 2003-218024

In the conventional measuring method of OPE characteristics, it is necessary to perform development of the resist and measurement of the line width of the resist pattern. Furthermore, the conventional method of scanning a mark image with a slit changes the detection signal depending on the slit width, so that it is difficult to apply it to the measurement of OPE characteristics as it is.
In addition, if the shape of the pattern for characteristic evaluation used for evaluating the OPE characteristic includes an error, it causes a measurement error. Therefore, the shape error of the pattern for characteristic evaluation is accurately measured in advance. It is desirable to keep it.

In view of such a point, the first object of the present invention is to provide an optical characteristic measurement technique capable of measuring optical characteristics such as OPE characteristics efficiently and with high accuracy.
A second object of the present invention is to provide a pattern error measurement technique capable of measuring a pattern error that can be used when measuring such optical characteristics with high accuracy.

The optical characteristic measurement method according to the present invention is an optical characteristic measurement for obtaining optical characteristics of a projection optical system based on light amount information obtained by scanning a pattern image by the projection optical system (PL) with a predetermined aperture (122). In the method, a first step of obtaining a spatial frequency component of the predetermined aperture, and a spatial frequency component obtained by Fourier transforming the light quantity information as a spatial frequency component of the predetermined aperture obtained in the first step. And a second step of obtaining an optical characteristic of the projection optical system based on intensity distribution information recovered by performing an inverse Fourier transform on the corrected spatial frequency component.

According to the present invention, optical characteristics such as OPE characteristics can be efficiently measured based on light amount information obtained by scanning an aerial image with the predetermined aperture. In addition, the measurement accuracy of the optical characteristics is improved by obtaining the spatial frequency component of the predetermined aperture in advance.
Further, the pattern error measurement method according to the present invention is a pattern error measurement for obtaining a shape error of a pattern based on light amount information obtained by scanning a periodic pattern (PM) image with a predetermined aperture (122). In the method, a first step of obtaining a spatial frequency component of the predetermined aperture, and information on a region of m times (m is an integer greater than or equal to 1) the pitch of the pattern image among the light quantity information is Fourier transformed. A second step of correcting the obtained spatial frequency component with the spatial frequency component of the predetermined aperture obtained in the first step, and performing an inverse Fourier transform on the corrected spatial frequency component to restore the intensity distribution; And a third step of obtaining a shape error of the pattern based on information obtained by binarizing the intensity distribution recovered in the second step with a predetermined threshold value. According to the present invention, by using a predetermined aperture whose spatial frequency component is known, the shape error of the pattern can be measured with high accuracy.

Further, in the optical characteristic measuring method according to the present invention , as an example, the first step includes an estimation step for estimating a spatial frequency component of the first pattern, and an image of the first pattern by the projection optical system having the predetermined aperture. Measurement process for actually measuring the spatial frequency component by Fourier-transforming the light quantity information obtained by scanning with, the space of the predetermined aperture based on the estimated spatial frequency component and the measured spatial frequency component A calculation step of calculating a frequency component.
At this time, the first step may include a step of estimating a spatial frequency component based on the actually measured value of the shape error of the first pattern.
Further, when the first pattern has a periodic pattern (PM) , the shape error of the first pattern is determined using an image formed using a first set of diffracted light from the first pattern, and You may make it obtain | require based on the image formed using the 2nd set of diffracted light different from the said 1st set of diffracted light from a 1st pattern . At this time, since the amount of light of the two sets of diffracted light changes according to the shape error of the first pattern, the shape error can be measured with high accuracy based on images formed from the two sets of diffracted light. .

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a scanning stepper type projection exposure apparatus 10 of this example. In FIG. 1, a projection exposure apparatus 10 includes a light source 14 (exposure light source) that generates a laser beam LB, an illumination optical system 12, a reticle stage RST that holds and moves a reticle R as a mask, a projection optical system PL, and a wafer W. It includes a wafer stage WST that holds and moves (substrate), a main controller 50 that controls these, and the like. An ArF excimer laser light source (oscillation wavelength 193 nm) is used as the light source 14, but instead, harmonics of a KrF excimer laser (wavelength 248 nm), an F ₂ laser (wavelength 157 nm), and a solid-state laser (semiconductor laser, etc.) A generator or a mercury lamp can also be used.

  The illumination optical system 12 includes a beam shaping optical system 18, a fly-eye lens 22 as an optical integrator, an illumination system aperture stop plate 24, a relay optical system comprising relay lenses 28A and 28B, and a fixed reticle blind that defines the shape of the illumination area. 30A, a movable reticle blind 30B for preventing exposure to unnecessary portions during scanning exposure, a mirror M, a condenser lens 32, and the like. Hereinafter, the laser beam LB emitted from the fly-eye lens 22 is referred to as illumination light IL as an exposure beam.

  The light source 14 and the illumination optical system 12 are also used as an illumination system for a later-described aerial image measurement. The illumination system aperture stop plate 24 is disposed on the pupil plane of the illumination optical system in the vicinity of the exit-side focal plane of the fly-eye lens 22 and is arranged at substantially equal angular intervals, for example, for normal illumination, annular illumination, and modified illumination ( A plurality of aperture stops for dipole illumination and the like are arranged. The main control device 50 rotates the illumination system aperture stop plate 24 via the drive device 40, whereby the illumination conditions can be set. The illumination light IL reflected by the beam splitter 26 disposed on the exit surface side of the illumination system aperture stop plate 24 is incident on an integrator sensor 46 composed of a light receiving element via a condenser lens 44. A detection signal of the integrator sensor 46 is supplied to the main controller 50 via the signal processing device 80, and exposure amount control for the wafer W, for example, is performed based on the detection signal.

  The illumination light IL emitted from the illumination optical system 12 during exposure illuminates the illumination area IAR on the pattern surface (lower surface) of the reticle R with a uniform illuminance distribution. Under the illumination light IL, the pattern of the reticle R is resist (photosensitive material) at a projection magnification of 1/4 or 1/5, for example, via a telecentric projection optical system PL on both sides (or one side on the wafer side). ) Is projected onto the exposure area IA on the coated wafer W. As shown in FIG. 2, a variable aperture stop AS for controlling the numerical aperture NA of the projection optical system PL is disposed in the vicinity of the pupil plane PP of the projection optical system PL. Hereinafter, the Z-axis is taken in a direction parallel to the optical axis AX of the projection optical system PL, the X-axis is taken in a direction perpendicular to the paper surface of FIG. 1 within a plane perpendicular to the Z-axis, and the direction parallel to the paper surface of FIG. A description will be given taking the Y axis. In this example, the scanning direction of reticle R and wafer W during scanning exposure is the Y direction, and illumination area IAR and exposure area IA are elongated areas in the non-scanning direction (X direction) orthogonal to the scanning direction.

  In FIG. 1, a reticle R is fixed on a reticle stage RST by, for example, vacuum suction. Reticle stage RST can be finely driven two-dimensionally (in the X direction, Y direction, and rotation directions about the Z axis) in the XY plane on reticle base RBS by a reticle stage drive system 56R including a linear motor and the like. At the same time, it is movable on the reticle base RBS at a scanning speed designated in the Y direction.

  A movable mirror 52R that reflects a laser beam from a laser interferometer (hereinafter referred to as “reticle interferometer”) 54R is fixed on the reticle stage RST. The position of the reticle stage RST in the XY plane is the reticle stage RST. For example, the interferometer 54R always detects with a resolution of about 0.1 to 1 nm. Position information of reticle stage RST from reticle interferometer 54R is sent to stage controller 70 and main controller 50 via this. The stage controller 70 controls the movement of the reticle stage RST via the reticle stage drive system 56R according to an instruction from the main controller 50.

In addition, a reticle mark plate RFM on which an aerial image measurement mark is formed is arranged near the end of the reticle stage RST in the −Y direction so as to be aligned with the reticle R. The aerial image measurement mark may be formed in a part of the pattern area of the reticle R.
In FIG. 1, wafer stage WST includes XY stage 42 and Z tilt stage 38 mounted on XY stage 42. The XY stage 42 is two-dimensionally driven in the X direction and the Y direction by a linear motor (not shown) constituting a wafer stage drive system 56W on the wafer base 16. A wafer W is held on the Z tilt stage 38 via a wafer holder 25 by vacuum suction or the like. The Z tilt stage 38 aligns the surface of the wafer W or a later-described slit plate 90 with the image plane of the projection optical system PL based on the measurement result of the autofocus sensor including the irradiation system 60a and the light receiving system 60b.

  In FIG. 1, a movable mirror 52 </ b> W that reflects a laser beam from a laser interferometer (hereinafter referred to as “wafer interferometer”) 54 </ b> W is fixed on the Z tilt stage 38. The position of the Z tilt stage 38 (wafer stage WST) in the X and Y directions is always detected by the wafer interferometer 54W, for example, with a resolution of about 0.1 to 1 nm. Further, based on the measurement value of the wafer interferometer, the rotation angles of the Z tilt stage 38 around the X axis, Y axis, and Z axis are also measured, and information on the position and rotation angle of the wafer stage WST is stored in the stage controller 70. , And this is supplied to the main controller 50. Stage control device 70 controls the position of wafer stage WST in the XY plane via wafer stage drive system 56W in accordance with an instruction from main control device 50. Further, an off-axis alignment sensor ALG for aligning the wafer W is provided on the side surface of the projection optical system PL.

  At the time of exposure, under the control of the main controller 50, the reticle stage RST and the wafer stage WST are driven in a state where the illumination light IL is irradiated, and the reticle R and the wafer W are projected in the Y direction by the projection optical system PL. The scanning exposure operation that moves in synchronization with the magnification as the speed ratio, and the operation that stops the irradiation of the illumination light IL, drives the wafer stage WST, and moves the wafer W stepwise in the X and Y directions. The pattern image of the reticle R is sequentially exposed to each shot area on the wafer W by repeating the scan method.

  Next, an example of a method for measuring OPE (Optical Proximity Effect) characteristics as optical characteristics of the projection optical system PL in the projection exposure apparatus of this example will be described. As an example, the OPE characteristic is an error with respect to the designed line width of each mark image (for example, resist pattern) when a plurality of marks having the same line width and different pitches are projected through the projection optical system PL. And the pitch. For this purpose, an aerial image measuring device 59 is provided on the wafer base 16, and a part of the optical system constituting the aerial image measuring device 59 is disposed inside the Z tilt stage 38.

  FIG. 2 is a partially cutaway view showing the aerial image measuring device 59. In FIG. 2, the aerial image measuring device 59 is a stage-side component provided on the Z tilt stage 38, that is, a slit plate 90. , A relay optical system comprising lenses 84 and 86, a mirror 88 for bending the optical path, a light transmission lens 87, and a component outside the stage provided outside the wafer stage WST, that is, a mirror 96, a light receiving lens 89, such as a photomultiplier tube. The photoelectric sensor 94 which consists of these is included. The light receiving lens 89 and the photoelectric sensor 94 are accommodated in a column fixed to the wafer base 16 in a cylindrical member 92 fixed via a connecting member 93, and the mirror 96 is also cylindrically connected via a connecting member (not shown). A fixed member 92 is fixed.

  More specifically, the slit plate 90 is fitted from above to a projecting portion 58 provided on the Z tilt stage 38 of the wafer stage WST and having an opening at the top so as to cover the opening. Yes. The slit plate 90 is configured by forming a reflective film 83 that also serves as a light-shielding film on the upper surface of a glass substrate 82 that transmits flat illumination light IL parallel to the XY plane. As shown to (A), the slit-shaped opening pattern (henceforth a slit) 122 of width 2D of the Y direction is formed.

  In the state of FIG. 2, measurement marks PM (characteristic measurement patterns) made of line and space patterns formed on the reticle mark plate RFM at a predetermined pitch in the Y direction are provided in the illumination area of the illumination light IL. The image of the mark by the projection optical system PL is projected onto the slit plate 90. The reticle mark plate RFM is also formed with a number of marks (not shown) having the same or different line width as the measurement mark PM and different pitches. In the following description, data such as the line width and pitch of the measurement mark PM are values in a projection image by the projection optical system PL. Then, wafer stage WST is driven, and as shown in FIG. 3 (A), slit 122 is scanned in the Y direction (or −Y direction) indicated by arrow F with respect to image PM ′ of measurement mark PM. However, the light beam that has passed through the slit 122 is received by the photoelectric sensor 94 via the lens 84, the mirror 88, the lens 86, the light transmission lens 87, the mirror 96, and the light receiving lens 89 of FIG. 2, and the detection signal S3 of the photoelectric sensor 94 is received. Is supplied to the signal processing device 80 of FIG. In the signal processing device 80, the detection signal S3 is captured as digital data S3 (Y) corresponding to the Y coordinate of the wafer stage WST, and an arithmetic processing described later is performed, whereby the intensity distribution of the image of the measurement mark PM ( The light intensity distribution).

  First, the basic operation of the OPE characteristic measurement of this example will be described. Therefore, the transmittance distribution S2 (Y) of the slit 122 (predetermined opening) in FIG. 2 at a certain point in time is set to 1 within the range where the width in the Y direction is 2D, as shown in FIG. In other cases, it is assumed to be 0. Also, the intensity distribution of the image PM ′ of the measurement mark PM in FIG. 2 by the projection optical system PL is the intensity distribution S1 (Y) of the pitch P in FIG. 3C (actually the OPE characteristic of the projection optical system PL). 2), the detection signal S3 (Y) (light quantity distribution information) in FIG. 2 is the intensity distribution S1 (Y ) And the transmittance distribution S2 (Y). The integration range of the integration symbol ∫ is from −∞ to + ∞.

S3 (Y) = ∫S2 (Y−u) · S1 (u) du (1)
That is, due to the influence of the width 2D of the slit 122, the detection signal S3 (Y) has a dull waveform with respect to the intensity distribution S1 (Y) of the image PM ′, as shown in FIG. In this case, the intensity distribution S1 (Y), the transmittance distribution S2 (Y), and the detection signal are defined with the spatial frequency of the Y axis of the image PM ′ being f [cycle / μm] (the number of bright portions or dark portions per 1 μm). Assuming that FS1 (f), FS2 (f), and FS3 (f) are Fourier functions (spatial frequency components) obtained by Fourier-transforming S3 (Y) with respect to the Y-coordinate, a predetermined value is obtained from a well-known convolution theorem. Except for the proportionality factor: In the signal processing device 80 of FIG. 1, the Fourier function FS3 (f) can be calculated by subjecting the detection signal S3 (Y) of the equation (1) to discrete Fourier transform.

FS3 (f) = FS1 (f) · FS2 (f) (2)
In this example, as an example, the Fourier function FS2 (f) of the transmittance distribution S2 (Y) is obtained in advance, and the inverse function thereof is stored as, for example, the device function in the memory 51 of FIG. 1 (first step). Note that the spatial frequency characteristic of the aerial image measuring device 59 also changes depending on the numerical aperture of the optical system following the slit 122 in FIG. 2, and therefore the Fourier function FS2 (f) is obtained in consideration of the numerical aperture of the optical system. Is desirable. During the subsequent measurement of the OPE characteristic, the signal processing device 80 obtains a function FS3 (f) / FS2 () obtained by multiplying the Fourier function FS3 (f) of equation (2) by the device function (1 / FS2 (f)). By performing inverse Fourier transform on f), the intensity distribution S1 (Y) of the image PM ′ is recovered as follows (the first half of the second step). In the following equation, the symbol invF means inverse Fourier transform.

invF (FS3 (f) / FS2 (f)) = invF (FS1 (f))
= S1 (Y) (3)
The maximum value of the space frequency of the image of the projection optical system PL in FIG. 2 is 2NA / λ using the numerical aperture NA of the projection optical system PL and the wavelength λ of illumination light. In addition, since the calculation of equation (3) is actually performed discretely by digital processing, the pitch of the image PM ′ is P, a predetermined integer of 1 or more is m, and a variable consisting of an integer is i. As an example, the functions FS2 (f) and FS3 (f) are calculated at discrete positions having a spatial frequency of i / P (or i / mP) in a region having a width P (or m · P). Note that the initial value of the variable i is 1, the maximum value is I (or I ′), and the maximum spatial frequency value I / P (or I ′ / mP) is a maximum value of 2 NA / λ or less as follows. It is. An example of arithmetic processing such as the expression (3) is also disclosed in Japanese Patent Laid-Open Nos. 2002-14005 and 2003-218024. Moreover, it is also applicable to this example that the functions used when calculating the Fourier functions FS2 (f) and FS3 (f), which are disclosed in these publications, may be unequal intervals with respect to the position Y.

I / P (or I ′ / mP) ≦ 2 · NA / λ (4)
By binarizing the recovered intensity distribution S1 (Y) with a predetermined threshold, the line width in the Y direction of each bright part of the image PM ′ can be obtained. The line width is supplied to the main controller 50. In the main controller 50, for example, the average value of the line width is expressed as a function of the pitch of the measurement mark PM, thereby obtaining the OPE characteristic of the projection optical system PL ( Second half of the second step).

Next, a method for obtaining the Fourier function FS2 (f) of the slit 122 in the equation (2) will be described. In the first method, the width 2D of the slit 122 is measured with, for example, a scanning electron microscope, the width 2D, the numerical aperture of the optical system in the aerial image measuring device 59 in FIG. 2, and the wavelength λ of the illumination light. Is used to theoretically calculate the Fourier function FS2 (f).
In the second method, the Fourier function FS1 (f) of the measurement mark PM in FIG. 2 is theoretically calculated (estimated), and the image obtained by scanning the projection optical system PL with the slit 122 is detected. The signal S3 (Y) is obtained, Fourier transformed to obtain the Fourier function FS3 (f) (measured), and the Fourier function FS2 (f) of the slit 122 is calculated from the equation (2). The calculation in this case is performed at discrete positions where the spatial frequency is i / P (or i / mP) and 2 · NA / λ or less as described above. Further, although the Fourier function has an amplitude component and a phase component, the calculation may be performed using only the amplitude component (so-called spatial frequency characteristics) approximately.

As a mark for calculating the Fourier function (having a known Fourier function), a line and space pattern having a simple shape and a duty of 50% is desirable. In the calculation, it is desirable to perform an optical simulation including the optical system in the aerial image measuring device 59 of FIG. 2 together with the projection optical system PL.
The solid line Fourier function FS2 (f) in FIG. 4 shows an example of the function thus calculated. In FIG. 4, the horizontal axis is the spatial frequency f [cycle / μm], and the vertical axis is the amplitude P of the function. is there. The inverse function 1 / FS2 (f) of the function FS2 (f) is stored as a device function.

  As described above, when the Fourier function FS1 (f) of the measurement mark PM in FIG. 2 is theoretically calculated in advance, it is desirable to measure the shape error (manufacturing error) of the mark. Usually, the pitch error of the reticle mark plate RFM or the periodic mark on the reticle is sufficiently small, and it is sufficient to measure the line width error. This is because the line width changes due to an error in the development process, an error in the beam size of the electron beam drawing apparatus, and the like, whereas the pattern pitch depends only on the drawing position determination accuracy of the electron beam drawing apparatus. The measurement mark PM is usually drawn in a minute region having a side of about several μm to several tens of μm. The drawing position determination accuracy in such a minute region is usually very small.

As an example, when the design line width of the measurement mark has a duty of 50%, that is, a mark having the same width between the light shielding region and the transmission region, how much the duty of the mark deviates from the designed value of 50%. Measured by the following method.
1) Measurement by Second Harmonic Amplitude As shown in FIG. 2, when projecting an image of a measurement mark (designated PM) having a duty of 50% through the projection optical system PL as shown in FIG. By controlling the three-beam interference state of the zero-order light D0 and the ± first-order light D (−1), D (+1), the zero-order light D0, the ± first-order light D (−1), D (+1) ), And two imaging states of the ± second-order light D (−2) and D (+2) and the five-beam interference state are sequentially set. If the mark has a duty of exactly 50%, even second-order or higher-order diffracted light is not generated unless there is a manufacturing error. Therefore, the second order from the detection signal S3 obtained by scanning the slit 122 in the two imaging states. By obtaining harmonics and comparing the measured values of their amplitudes with design values (simulation values), it is possible to estimate the deviation from 50% of the duty and thus the line width of the mark.

When obtaining the detection signal S3 in the two imaging states, by adopting a value when the amplitude of the second harmonic becomes maximum while changing the focus position (Z position) of the slit plate 90, an even function Accurate line width can be measured without being affected by component aberration. Similarly, in the simulation, it is desirable to perform calculation at the focus position where the second harmonic is maximized.
2) Measurement by diffracted light intensity For example, when measuring the shape error of the measurement mark PM in FIG. 2, adjustment of the tilt angle (telecentricity) of the principal ray of the illumination light from the illumination optical system 12 in FIG. By adjusting the variable aperture stop AS of the second projection optical system PL, only a desired order of diffracted light from the measurement mark PM is allowed to pass through the projection optical system PL, and a photoelectric sensor (not shown) on the wafer stage WST is shown. ) To measure the intensity of the diffracted light. For example, the line width of the measurement mark PM can be obtained by comparing the intensity of the second-order diffracted light with the intensity of the second-order diffracted light calculated by performing a simulation while gradually changing the line width at the same pitch.

3) Method of using known Fourier function of slit 122 (predetermined opening) As described above, Fourier function FS2 (f) of slit 122 is obtained in advance using a mark with a duty of 50% (first step), and then A detection signal S3 (light quantity information) is obtained by scanning an image of a mark to be measured with the slit 122, and information on an area of m times the pitch of the image (m is an integer of 1 or more) is 1 / (m · P). To 2 · NA / λ, a function obtained by multiplying a Fourier function FS3 (f) obtained by Fourier transform in the spatial frequency range from the inverse function of the Fourier function FS2 (f) as shown in equation (3). Is subjected to inverse Fourier transform to recover the intensity distribution S1 (Y) (second step). Thereafter, a shape error of the pattern is obtained based on a waveform obtained by binarizing the recovered intensity distribution with a predetermined threshold (third step).

4) Measurement of the phase shift amount of the harmonic with respect to the coma aberration A method of measuring the amount of coma aberration from the phase shift amount of the fundamental wave and the harmonic of the aerial image, and the amount of the phase difference of the coma aberration depending on the line width of the pattern Are also known to be different (see, for example, Japanese Patent Application Laid-Open No. 2003-218024). Therefore, also in this example, the phase shift amount between the fundamental wave and the harmonic wave is obtained from the spatial image of the measurement mark PM in FIG. 2, the coma aberration is obtained from the phase shift amount, and the line width is estimated from the coma aberration. be able to. Since this coma aberration does not depend on the width of the slit 122, the line width of the pattern can be estimated with high accuracy.

5) The pattern line width may be directly measured by a scanning electron microscope.
6) The variable aperture stop AS of the projection optical system PL of FIG. 2 is stopped, only the 0th order light from the measurement mark PM is allowed to pass through the projection optical system PL, and the measured value of the intensity of the 0th order light is the simulation result. The pattern line width may be estimated by comparison.
It is desirable to obtain the Fourier function FS2 (f) of the slit 122 after measuring the line width by any of the line width measurement methods listed above (except method 3). An example of the Fourier function FS2 (f) thus obtained is shown as the Fourier function FS2A (f) in FIG.

Next, simulation results of actual image restoration using the apparatus function (1 / FS2 (f)) of FIG. 4 are shown in FIGS.
FIG. 5 shows a simulation result of a periodic measurement mark having an image pitch P1 of about 350 nm and a duty of about 50%, and a transmitted light design intensity distribution represented by S1, and the horizontal axis represents Y. The coordinate [μm] and the vertical axis represent the light intensity or the relative value of the detection signal. The width of the measurement mark image in the period direction is several μm to several tens of μm. FIG. 6 is an enlarged view of the 2 μm wide region in the center of FIG. 5. In FIGS. 5 and 6, the detection signal S 3 is the amount of light obtained by scanning the measurement mark image with the slit 122 of FIG. The intensity distribution S4 corresponds to S1 (Y) in the equation (3) that is recovered by performing the inverse Fourier transform by substituting the Fourier function of the detection signal S3 into the equation (3). Yes.

  In the calculation, since the detection signal S3 in FIG. 6 (center part in FIG. 5) can be regarded as a part of the periodic pattern of the pitch P1 accurately, as an example, the spatial frequency from 1 / P1 in the range of the pitch P1. Calculations may be performed at 1 / P1 intervals in a range up to I1 / P1 ≦ 2NA / λ (I1 is the largest integer in the range). At this time, the pitch P1 may be obtained by binarizing the detection signal S3 with an appropriate threshold value Th1 as an average pitch of rising edges or falling edges of the binarized waveform, or a design value may be used. Alternatively, n1 may be an integer of 2 or more, and a waveform obtained by averaging the waveforms of n1 pitches P1 may be subjected to Fourier transform. In this case, since the electrical and optical noise can be removed by the averaging effect, the accuracy is improved.

  When it is desired to recover the mark image corresponding to the entire intensity distribution S1 in FIG. 5 and to measure a long-period line width change, the pitch P1 is obtained by the above-described method, and an integer m (in FIGS. 5 and 6). In the region of P1 · m using an integer of 2 or more), the intensity distribution S4 may be recovered after performing calculations at 1 / (m · P1) intervals in the range of spatial frequencies from 0 to 2NA / λ. . In this calculation, the apparatus function (1 / FS2 (f)) in FIG. 4 may be calculated at an interval of 1 / (m · P1) from the beginning, but in order to reduce the calculation amount, Data calculated at P1 intervals may be interpolated and used.

The recovered intensity distribution S4 is binarized with a threshold Th2 corresponding to the photosensitive level of the resist, and the interval between the falling edge and the rising edge of the binarized signal, that is, the line width of the resist pattern is measured. By performing the above line width measurement on the measurement marks having various pitches, the OPE characteristic of the projection optical system PL in FIG. 1 can be measured.
Next, FIG. 7 shows a simulation result of a periodic measurement mark in which the image pitch P2 is about 500 nm and the duty is out of 50%, and the transmitted light design intensity distribution is represented by S1A. 8 is an enlarged view of the 2 μm wide region in the center of FIG. 7. In FIGS. 7 and 8, the detection signal S3A is obtained by scanning the image of the measurement mark with the slit 122 of FIG. In the light amount distribution, the intensity distribution S4A corresponds to S1 (Y) in the equation (3) recovered by performing the inverse Fourier transform by substituting the Fourier function of the detection signal S3A into the equation (3).

  Also in the recovery, the pitch P2 is determined by the threshold Th3 in FIG. 8, and the calculation is performed with the spatial frequency of 1 / P2 interval or 1 / (m · P2) interval in the range of pitch P2 or P2 · m. Thus, the intensity distribution S4A may be recovered. Thereafter, the recovered intensity distribution S4A is binarized with a threshold value Th4 that is the photosensitive level of the resist, and the line width of the resist pattern can be obtained.

  Moreover, although the said embodiment applies this invention when measuring the optical characteristic of the projection optical system of a scanning exposure type projection exposure apparatus, this invention is a batch exposure type projection exposure apparatus, such as a stepper. For example, the present invention can also be applied to the case where the optical characteristics of the projection optical system are measured by an immersion type exposure apparatus disclosed in International Publication No. 99/49504 pamphlet. As described above, the present invention is not limited to the above-described embodiment, and various configurations can be taken without departing from the gist of the present invention.

  The present invention can be used when measuring the optical characteristics of a projection optical system of a projection exposure apparatus used when manufacturing a semiconductor device or the like.

It is a figure which shows the projection exposure apparatus of an example of embodiment of this invention. It is a figure which shows the aerial image measuring device with which the projection exposure apparatus of FIG. 1 was equipped. It is explanatory drawing of the slit 122 and detection signal S3 of FIG. It is a figure which shows an example of the apparatus function used in order to perform image restoration by embodiment of this invention. It is a figure which shows the detection signal etc. of the image of the measurement mark of pitch P1. It is an enlarged view which shows the center part of FIG. It is a figure which shows the detection signal etc. of the image of the measurement mark of pitch P2. It is an enlarged view which shows the center part of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 12 ... Illumination optical system, 14 ... Light source, PL ... Projection optical system, 50 ... Main controller, 59 ... Aerial image measuring device, 80 ... Signal processing device, 90 ... Slit plate, 122 ... Slit, RFM ... Reticle mark plate, PM ... Mark for measurement

Claims (10)

In an optical characteristic measurement method for obtaining optical characteristics of the projection optical system based on light amount information obtained by scanning a pattern image by the projection optical system with a predetermined aperture,
A first step of obtaining a spatial frequency component of the predetermined aperture;
The spatial frequency component obtained by Fourier transforming the light quantity information is corrected with the spatial frequency component of the predetermined aperture obtained in the first step, and the corrected spatial frequency component is recovered by inverse Fourier transform. And a second step of obtaining an optical characteristic of the projection optical system based on the intensity distribution information.   The first step includes an estimation step of estimating a spatial frequency component of the first pattern, and Fourier transform of light amount information obtained by scanning the image of the first pattern by the projection optical system with the predetermined aperture. An actual measurement step of measuring a spatial frequency component; and a calculation step of calculating a spatial frequency component of the predetermined aperture based on the estimated spatial frequency component and the measured spatial frequency component. The optical property measuring method according to claim 1.   The optical characteristic measuring method according to claim 2, wherein the first step includes a step of estimating a spatial frequency component based on an actual measurement value of a shape error of the first pattern.   The optical characteristic measurement method according to claim 3, wherein the shape error of the first pattern is obtained using intensity information of diffracted light of the first pattern.   4. The optical according to claim 3, wherein the shape error of the first pattern is obtained by using an amplitude of a harmonic in a spatial frequency component obtained by Fourier transforming the spatial image of the first pattern. Characteristic measurement method. Wherein the first pattern has a periodic pattern,
The shape error of the first pattern is different from the image formed using the first set of diffracted light from the first pattern and the second set different from the first set of diffracted light from the first pattern. The optical characteristic measuring method according to claim 3, wherein the optical characteristic measuring method is obtained based on an image formed using diffracted light. Based on a spatial frequency component of a predetermined order of an image formed using the first set of diffracted light and a spatial frequency component of the predetermined order of an image formed using the second set of diffracted light. The optical characteristic measuring method according to claim 6 , wherein a shape error of the first pattern is obtained. The first set of diffracted light is zero-order light and ± first-order light, and the second set of diffracted light is zero-order light, ± first-order light, and ± second-order light. The optical characteristic measuring method according to claim 6 or 7 . In a pattern error measurement method for obtaining a shape error of the pattern based on light amount information obtained by scanning an image of a pattern having periodicity with a predetermined aperture,
A first step of obtaining a spatial frequency component of the predetermined aperture;
Of the light quantity information, the predetermined aperture obtained in the first step is a spatial frequency component obtained by Fourier-transforming information of an area of m times the pitch of the pattern image (m is an integer of 1 or more). A second step of correcting the spatial frequency component of the corrected spatial frequency component and performing an inverse Fourier transform on the corrected spatial frequency component to recover the intensity distribution;
And a third step of determining a shape error of the pattern based on information obtained by binarizing the intensity distribution recovered in the second step with a predetermined threshold. The wavelength of illumination light that illuminates the pattern is λ, the numerical aperture of the projection optical system that projects the image of the pattern is NA, and the pitch of the image of the pattern is P. 10. The method according to claim 9 , further comprising: performing a Fourier transform on information of an area m times the pitch of the pattern image in a spatial frequency range of at least 1 / (m · P) to 2 · NA / λ. Pattern error measurement method.

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