JPH0453220A - Projection optical device - Google Patents

Abstract

PURPOSE:To obtain a best focus position by a simple constitution of device in a short measurement time in a highly precise manner by a method wherein rediffracted beams which is generated at angles different with each other and obtained by making diffracted lights of different angle with each other is incident on a lattice pattern, are detected by the detector provided on an almost conjugated surface of an optical system. CONSTITUTION:At least two diffracted beams of U(-1), U(0) and U(epsilon+1), which are generated at different angle with one another, are made incident on a projection optical system by projecting a first pattern on a first object at the periodic structure of the prescribed pitch. When the above-mentioned diffracted beams are projected on the second pattern which is formed on a second object in the same direction in the periodic structure of the prescribed pitch, at least the two rediffracted beams {U'(-1), U'(0) and U'(epsilon+1)} generated by rediffraction are received on the surface which is almost conjugated with the pupil surface of the projection optical system, and a plurality of adaptable signals are outputted. The second pattern and the diffracted beams are relatively shifted, the relative phase difference between signals is detected by the plurality of signals which are outputted after modulation by the prescribed amplitude by the above-mentioned relative movement, and the amount of deviation from the conjugated position of the first object and the above-mentioned second object is worked out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a projection optical device used in a semiconductor integrated circuit manufacturing process, particularly in a lithography process.

[Conventional technology]

In recent years, the degree of integration of semiconductor integrated circuits has increased more and more, and it has become necessary to form circuits with a minimum line width of submicron. Accordingly, projection optical devices for producing semiconductor integrated circuits are also required to have higher resolution and alignment accuracy. In order to improve the resolution, it may be possible to use exposure light with a shorter wavelength, and excimer lasers are currently attracting attention as an exposure light source.

Excimer lasers are high-intensity, high-power pulsed lasers with many oscillation wavelengths in the ultraviolet region, and are attracting the most attention as light sources for next-generation exposure equipment.

Conventionally, projection optical devices using this type of laser as a light source do not have a mechanism for automatically determining the best focus position of the optical system, and the best focus position has been determined by, for example, performing trial printing on a wafer.

Also, as shown in Japanese Patent Application Laid-Open No. 63-70104,
A telecentric optical system is provided between a reticle having a pattern and a wafer having a second pattern, and the first pattern is projected across the wafer and a slit-shaped light emitting section provided on approximately the same plane as the wafer. a detector provided on the opposite side of the lens and outputting information regarding the alignment state between the image of the first pattern by the projection lens and the second pattern; In an exposure apparatus equipped with a shutter that selectively switches the light passing through a plurality of different regions and a moving stage that changes the optical path length between the reticle and the wafer, the light from the light emitting slit is conjugated to the pupil. A device that converts telecentric light into non-telecentric light by partially blocking light with a surface is being considered.In the second case, while changing the optical path length between the reticle and the wafer in stages,
Before and after this change, the reticle and wafer are moved relative to each other, and the positions of the reticle and wafer are detected. Next, the shutter changes the light-blocking area on the pupil conjugate plane to an unblocked area, and similarly detects the positions of the reticle and the wafer. Finally, a technique is known in which the best focus position is determined based on the relative relationship between the optical path length between the reticle and the wafer and the positions of the wafer and reticle before and after switching the shutter.

[Problem to be solved by the invention]

However, in the case of test printing, it is very time-consuming and time-consuming to prepare the wafer, expose it, develop it, and measure the line width, and the measurement accuracy was about 0.3 μm in resolution. Further, in the method using non-telecentric light, the stage has to be moved multiple times, which causes a problem in that the throughput decreases. The present invention has been proposed in order to solve the above-mentioned problems, and aims to provide a projection optical device that has a simple device configuration, shortens the measurement time, and can determine the best focus position with high measurement accuracy.

[Means to solve problems]

In order to solve this problem, the present invention provides a projection optical device for projecting a first object onto a second object via a projection optical system, wherein a periodic structure formed at a predetermined pitch on the first object is provided. When one pattern is irradiated, at least two diffracted lights (U (-1
), U(+1)) to enter the projection optical system; and the at least two diffracted lights (U(-],), U(+1)) from the first pattern.
When a second pattern formed in a periodic structure with a predetermined pitch in the same direction as the first pattern is irradiated onto the second object through the projection optical system, the second pattern is diffracted again by the second pattern, At least two re-diffracted lights (U' (-1), U' (+1)) generated at different angles from each other are received by a plane substantially conjugate with the pupil plane of the projection optical system, and the at least two re-diffracted lights are Light (U' (-1), U'(
+1))), and detecting means for outputting a plurality of signals corresponding to each of the second pattern and the at least two diffracted lights (U (-1), U (10N)) in the pitch direction of the second pattern. and a position for detecting a relative phase difference between the plurality of signals based on the plurality of Iho signals modulated with a predetermined amplitude and output from the detection means by the relative movement. A phase difference detection means and a calculation means for calculating a deviation amount from a conjugate position of the first object and the second object in the projection optical system based on the phase difference are provided.

For 1 work The principle of the present invention will be explained using FIG.

In the present invention, diffracted lights (U (-1), U (0),
The re-diffracted light (U(+1)) generated at different angles obtained by entering the grating pattern GM2
' (-1), U' (0), U' (+1))
, a detector (D
(-1), D (0), D (+1)
The defocus amount is calculated from the phase difference between the photoelectric signals corresponding to the intensities of at least two re-diffracted lights among the respective re-diffracted lights obtained by detection with ').

The phase difference between the photoelectric signals is determined by the grating pattern GM2 and the diffracted light (U
(, -1), U (0), U (+1)) by comparing the phases of the modulation signals when the signals are relatively displaced. Here, U(-1) is -1st order diffracted light (counterclockwise direction in the paper is - (minus)), U
(0) is the 0th-order diffracted light, U (+1) is the +1st-order diffracted light (clockwise in the paper is + (plus)), and U'
(-1), U' (0), U' (+1) are each -
These are 1st-order, 0th-order, and +1st-order re-diffracted lights. Diffracted light U (-
1), U(0).

U(+1) is generated by irradiating the transmission grating pattern GMI with a laser beam emitted from the 1-noser light source 1 via a mirror from the direction opposite to the projection optical system PL.

The solid lines represent the GMI lattice planes W and G through the projection lens PL.
This shows a state in which the M2 lattice plane R is in a conjugate relationship, and hereinafter this will be referred to as a focused state.

In this state, the diffracted light U (
-], ), U (0), and U (+1), there is no phase difference between them, and the re-diffracted light U' (-]), U' (0)
It is clear that there is no phase difference between =7 U' (+]). Therefore, the diffracted light (U (-1,), U (0)
.

When the diffracted light and the grating GM2 were moved relative to each other in the direction of movement of U(+1)) with respect to the grating GM2, the re-diffracted light U' t,-1) was detected by the detector D(-1). Detection signal 5 (-1), re-diffracted light U' (0) detected by detector D (0), detection signal 5 (0), re-diffracted light U' (+1) detected by detector D (+1) The signals S(+1) are modulated in phase. Here, the detectors D(-1,), D(0), D(+
1. ) is installed on a surface that is substantially conjugate to the pupil of the projection optical system PL.

Next, a broken line indicates a state where the grating GMI and W are shifted by Z in a direction away from the projection optical system PL from the focused state to become a W plane. Case 7 on the grating 0M2 side across the projection optical system PL.
- The GMI image plane is formed on the R'' plane at a position shifted toward the projection optical system PL by Z'' according to the magnification of the projection optical system PL. This situation is shown in FIG. Here, P represents the point where the two diffracted lights U (-1), U (0), and U (+1) are focused on the R' plane, and Ql is the point where the diffracted light U (0) enters the grating GM2. The point Q2 represents the point where the diffracted light U(+1) is incident on the grating GM2. Further, the grating GM2 is a grating with a duty of 1:1, and when considering the constituent components of the re-diffracted light, only the zero-order and first-order constituent components are focused.

(If the duty is 1:l, no second-order diffracted light is generated, so
Further, it is assumed that the configuration is such that other high-order light does not need to be taken into consideration. ) First, considering the re-diffracted light U' (-1), U' (-1) is the re-diffracted light U' (0°=1) which has a -1 component of the diffracted light U(0) and the diffracted light U(+1
) re-diffracted light U' (-1-L O
).

Re-diffracted light U' (0, -1) and U' (+1.O)
If the phase difference between them is φ and the diffraction angle of the re-diffracted light is θ, both diffracted lights are U' (0,1)A-elk(slnθ・X + co
Ilθ4') 田(interest 0)=A' +elk(811
It can be expressed as 1θX→coxlLZ')-Ill.

Here, the phase difference φ is expressed as φ=k (, PQ 2 - PQ 1) = k (PQ2 - PQl cos θ) λ ・ COS θ, and if the pitch of the grating GM2 is P and the wavelength of the laser beam is λ, then P- From λ/sinθ, φ is expressed as Z゛φ=2π ta, nθ...(1).

Considering the re-diffracted light U'' (0) in the same way, it becomes U' (0)
is U' (+1. +1), U' (0,0), U
' (-1,-]), U' (+1.+1), U(-1,-
1) each have a phase difference of (1) with respect to U' (0, O).

Here, referring to FIG. 1, the re-diffracted light U' (+1) is composed of two re-diffracted light components, U' (0, -z) and U' (1,0), and Similarly, there is a phase difference (1) between the diffracted lights. Grating GM2 and diffracted light (U (-1), U (0).

Considering the change in the interference light intensity of each re-diffracted light when U(+1)) is relatively moved, the re-diffracted light U'
(0) detected by detector D(0) Detection signal 5
(0) is the component U' (+1°+1), U'
The phase difference of (-1, -1) is canceled, and U
' It becomes a modulated signal corresponding to the component of (0, O).

In addition, both detection signals S (-1) and s (+1), which are obtained by detecting the re-diffracted light U' (-]) and U' (+1) by the detectors D (-1) and D (+1), respectively, are 5. The modulated signal has the opposite sign to the (0) signal and is out of phase by (1).

By detecting this phase difference, the amount of deviation ΔZ on the grating 0M1 side W is determined. The +1st-order diffraction angle θ1 on the side of the grating GMI surface W is uniquely determined by the wavelength (λ) and the pitch PI (duty 11) of the grating GMI, and is determined by θ1=sin-' (2) I.

Incidentally, the pitch PI has a relationship of Px=P/m, assuming that the magnification of the projection optical system PL is 17 m.

Phase shift amount 2 between S (-1) and S (+1) signals
Letting ΔX be the amount of movement of the grating GMI in the X direction (rightward in the paper) corresponding to Δφ, it becomes 2π. Sensitivity is doubled by taking the difference between the S (-1) and S (+1) signals.

From formula (1), ΔZ is 2π ・tanθ 1 can be obtained from the phase difference Δφ by calculating .

By using such a method, it is possible to obtain a high resolution, and in principle, the result can be obtained in one scan, so the measurement can be completed in a very short time.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 3 shows an overall configuration diagram of the apparatus in the first embodiment of the present invention.

In this embodiment, an exposure apparatus using an excimer laser as a light source will be described. Pulsed light from an excimer laser light source 1 enters a beam shaping optical system 3 via a movable mirror 2 and a fixed mirror M1, and is shaped into a predetermined cross-sectional shape and size.

The pulsed light from the beam shaping optical system 3 is reflected by a swinging mirror 5 that swings within a predetermined angle by a drive unit 4, and then enters a fly-eye lens FL that functions as an optical integrator, and is connected to a large number of secondary light sources. (spot light). Each spot light of the excimer beam formed on the exit side of each element lens of the fly eye lens PL is transmitted through a beam splitter BS, and is then connected to a condenser lens system 6.
The light beams are superimposed on the reticle blind (illumination field aperture) RB so as to have a substantially -like intensity distribution. The excimer light that has passed through the reticle blind RB is sent to lens system 7.
, the circuit pattern area of the reticle R is illuminated through the fixed mirror M2, the main condenser lens 8, and the fixed mirror M3.

Here, the reticle blind RB is conjugated with the reticle R by a lens system 7 and a main condenser lens 8. Reticle R is a dedicated reticle blind type 9X
, 9Y with respect to the main body of the apparatus in the X1Y and θ directions. The image of the circuit pattern on the reticle R is reduced and projected onto the wafer W by the projection lens 10. The wafer W is placed on an X stage IIX, and this X stage 11X is a Y stage that moves on the base in the X direction], I
Move on Y in the X direction. As a result, the wafer W moves two-dimensionally along the projection image plane, and step-and-repeat exposure or the like is performed.

Now, on the X stage 11X'2, an index plate 12 having a transmission type diffraction grating pattern is provided at approximately the same height as the wafer W. The movable mirror 2 is movable, and by moving the movable mirror 2 during focus calibration, the laser light emitted from the laser light source 1 is guided to the index plate 12 by the mirror system. Here, the laser beam is appropriately reduced or expanded by the beam expander 14 and illuminates the aperture 15. By changing the magnification of this beam expander 14, the illuminance with which the aperture 15 is illuminated can be changed. A mirror 13 fixed to the X stage IIX is provided below the index plate 12.

The index plate 12 transmits pulsed light from the excimer laser light source l to the beam expander 14 when the movable mirror 2 is retracted from the illustrated position. Aperture 15. Beam splitter M4 fixed on a plurality of mirrors and Y stage IIY. It is arranged so as to be received from the bottom surface via a mirror 13.

The excimer beam incident on the beam splitter M4 is a substantially parallel light beam, parallel to the Y axis, and the excimer beam enters the beam splitter M4.
A part of the light beam is reflected perpendicularly to the X direction, and is reflected vertically upward by the mirror 13 below the index plate 12. Therefore, no matter how the X stage llX1Y stage IIY moves, the excimer beam is always incident on the lower surface of the index plate 12. It is assumed here that the index plate 12 is formed substantially on the same plane as the wafer surface, and the wafer W and reticle R are in a conjugate relationship with the projection lens 10.

On the other hand, the light beam transmitted through the beam splitter M4 enters the power detector 20 provided on the Y stage IIY. Further, images of a large number of secondary light sources formed by a fly's eye lens FL are formed on the entrance pupil of the projection lens 10 to perform Koehler illumination. Also, wafer W
The upper one shot area is exposed with tens of pulses or more in order to reduce optical noise such as speckles and interference fringes and to increase exposure control accuracy. Among optical noises, the interference fringes on the image plane that are generated by using the fly-eye lens FL can be reduced by oscillating laser pulses while deflecting the swinging mirror 5 by minute angles, thereby changing the interference fringes in the pitch direction. After one shot of exposure is completed, the contrast of the interference fringes on the wafer is reduced to a level that does not affect practical use (contrast value of approximately ±196).

Next, the diffraction grating pattern according to this embodiment will be explained using FIG. The index plate 12'2 is provided with transmission type diffraction grating patterns 22X and 22Y with a partial pitch as shown in FIG. It is equivalent. (Furthermore, a center detection pattern 23 is provided on the index plate 12''.

) Also, as shown in FIG. 4(a), the reticle is also changed in size by the reciprocal of the magnification of the projection lens 10, and is formed in the same direction as the patterns 22X and 22Y on the index plate 12. Patterns 22X'' and 22Y' are provided outside the exposure area, and correspond to the second pattern formed with a periodic structure with a predetermined pitch according to the present invention.

Now, by moving the movable mirror 2 shown in FIG. 3 from the optical path, the laser beam enters the index plate 12, and
The diffracted light diffracted by the transmission type diffraction patterns 22X and 22Y provided on the reticle 2 is back-projected and imaged onto the reticle R by the projection lens IO. Furthermore, this diffracted light is diffracted again by the transmission diffraction patterns 22X' and 22Y' on the reticle R, and this re-diffracted light travels through the illumination optical system in the opposite direction and passes through the fixed mirrors M, l, and I. Nons 7,
6 and a lens system 17 to enter a photoelectric element 18 . The photoelectric element 18 is arranged at a position substantially conjugate with the pupil of the projection lens 10.

Stage IIX, on which the wafer is placed, moves to the exposure position for each area one by one, and uses a well-known oblique incidence type focus sensor 21 to determine the amount of deviation from the best focus position for each exposure area. Stage 1 by the amount of error. After moving in the IX and Z directions (optical axis direction of the projection lens 10) and positioning to the best focus position in the Z direction, exposure is performed.

Here, FIG. 5 shows a photoelectric element 18 according to an embodiment of the present invention.
The configuration is shown below.

This detector 18 is expanded in two dimensions and can detect signals corresponding to the diffracted light diffracted by the patterns 22X22Y' in both the X and Y directions on the reticle. Sensor XA that detects +1st order light in the X direction (detects -] order light), XB (detects +1st order light), sensor YA that detects +1st order light in the X direction (detects -1st order light) ), YB (which detects +1st order light), and sensor L which detects 0th order light are installed on the same rotating substrate SR.

The rotating substrate SR is placed on an X-direction fine movement stage position, and the X stage position is placed on a Y-direction fine movement stage position. Therefore, by rotation and translation, the sensor can be easily aligned with the light spots of the respective diffracted lights converging on the pupil conjugate plane.

Next, FIG. 6 shows a block diagram representing signal processing according to an embodiment of the present invention. The signals photoelectrically converted by the sensors XA, XB, and L of the photoelectric element 18 are sent to amplifiers 24A, 24B, and 24.
Each signal is amplified to an appropriate size by L. The signals amplified by amplifiers 24A, 24B, and 24L are then input to dividers 25A, 25B, and 25L via peak hold circuits 30A, 30B, and 30L. Further, the signal photoelectrically converted by the power detector 20 is sent to an amplifier 31.
The amplified signals are input to the dividers 25A, 25B and 25L via the peak hold circuit 32, respectively. Each side multiplier 25A, 25B, 25L uses the signal from the power detector 20 as a reference signal,
Amplifier 24A.

Processing is performed to divide the signals from 24B and 24L by this reference signal. This is because when an excimer laser is used as a light source, the energy of the excimer laser light varies by a few percent to several tens of percent for each pulse.
A photoelectric signal from a power detector 20 provided to receive the pulsed light transmitted through the upper beam splitter M4 is captured for each pulse emission, and the level of the photoelectric signal of the photoelectric element 18 is normalized using a divider or the like. This is because it is necessary. Due to this standardization, even if the output of the laser light source changes during operation, it does not affect the photoelectric signal from the photoelectric element 18 after being standardized. On the other hand, the position of stage IIX is monitored by a laser interferometer 26, and the position of stage IIX is 001.
Generates up/down pulses every μm. This up-down pulse enters a frequency divider 27, which generates pulses at appropriate sampling intervals. Stage 1. IX is scanned in one direction, and in synchronization with the position signal at this time, A/D converters (analog-to-digital converters) 28A, 28B, 2
8L digitally samples the signals from the dividers 25A, 25B, and 25L, and synchronizes this converted digital signal with the position signal to store the stage position and memory (RAM).
)29 so that it uniquely corresponds to the memory 2 address.
Store in 9.

The CPU 1.9 is an A/D converter 2 stored in the memory 29.
The defocus amount is calculated based on the data from 8A, 28B, and 28L, and the defocus amount is corrected as the offset amount of the focus sensor 21.

Note that the coordinate values of stage IIX are also input to the CPU 19 and used for various position measurements and laser beam control.

Next, the focus calibration operation according to the first embodiment of the present invention will be described.

The pitch of the grating pattern 22X provided on the index plate 12 is P1. (duty is 1:1) and the magnification of the projection lens 10 is I/m, then the pitch P of the diffraction grating pattern 22X' provided on the reticle is mP.
l, and the rotation of the reticle has been removed in advance,
By scanning the stage 11X in the X direction at a position where pattern 22X and pattern 22X' generally overlap, the diffracted light diffracted again by pattern 22X' is transmitted to sensor X.
A.

The light is received by XB and L, and a signal that is modulated with a predetermined amplitude and output is detected.

Next, the relationship between the relative movement of the grating pattern 22X' and the diffracted light during focusing and defocusing, and the phase difference of the detection signal will be explained using FIGS. 7, 8, and 9. First, using FIG. 7, the movement of stage IIX and the relative movement between the diffracted light and the pattern 22X" will be explained. Mirror 13
The laser light from the laser light source 1 that enters the diffraction grating pattern 22X through the diffraction grating pattern 2 on the index plate 12
2X, the -1st-order diffracted light U(-1), the 0th-order diffracted light U(0), and the +1st-order diffracted light U(+1) are emitted from the pattern 22X on the W plane. When the stage 1 on which the index plate 12 is mounted, X is stationary, no modulation signal is obtained from the photoelectric element 18, and no phase difference can be detected. When stage IIX is moved in one direction (X direction: right direction on the page), re-diffracted light (-1st order: U'
(-1), 0th order: U' (0), +1st order: U
' (+1)) A modulation signal modulated with an amplitude corresponding to the optical intensity can be obtained. Here, when the wafer stage is moved in the X direction, the moving direction of the diffracted light incident on the grating pattern 22X' with respect to the grating pattern 22X' is M
direction (opposite to the direction of movement of the wafer stage).

Next, the relative movement of the pattern 22X and the diffracted light will be explained with reference to FIG.

■ indicates the state in focus (pattern 22X and pattern 22X' are in a conjugate relationship); at this time, pattern 22
The X image plane R' and the pattern 22X and R match.

■ indicates rear focusing (when the index plate 12 is in a position farther away from the projection lens PL by ΔZ than when in focus), and at this time, the R゛ plane is closer to the projection lens PL by ΔZ'' than the second plane. ■ is when the front focus is on (when the index plate 12 is closer to the projection lens 10 by ΔZ than when in focus)
In this case, the R' plane is formed at a position farther from the projection lens PL than the two planes. First, the case of ■ focusing will be explained. Stage or X direction (toward the right side of the page)
Even if the diffracted lights move in the M direction (to the left in the drawing), each of the diffracted lights enters the pattern 22X at the same time.

Therefore, the re-diffracted light U' (+), U' (0), U
' Signals S (-1) corresponding to (+1),
S (0) and S (+1) are modulated signals with the same phase. This situation is shown in (■) in FIG.

In FIG. 9, the vertical axis of the waveform diagram represents the signal intensity (1) corresponding to the intensity of interference light, and the horizontal axis represents the position (X) of the stage.

■In the case of rear focus, as the stage moves (according to the moving direction of the diffracted light), the diffracted light enters the pattern 22X' in the order of U (+1), U (0), U (1). Therefore, the phase of the 5(-1,) signal composed of the re-diffracted light of U(+1) and U(0) becomes a modulated signal that is advanced relative to the phase of the 5(0) signal. Also, U(-1)
The phase of the S(+]) signal, which is composed of the re-diffracted light of U(0) and U(0), is delayed with respect to the phase of the 5(0) signal. This situation is shown in Figure 9 (■).

■In the case of front focus,■Contrary to the case of rear focus, the diffracted light with respect to the grating pattern 22X' is U(1), U(0),
It will be incident in the order of U (+1), and 5(-1,)
(The phase of the signal becomes a modulated signal that is delayed with respect to the 5 (0) signal, and the S (+1) signal becomes a modulated signal that is advanced with respect to the 5 (0) signal. This situation is illustrated in Figure 9. If each phase difference is Δφ, the phase difference of the signal corresponding to the ±1st-order re-diffracted light corresponding to the defocus amount ΔZ is 2Δφ, and the diffraction angle on the pattern 22X side (wafer surface side) is 01
Then, the defocus amount ΔZ can be precisely determined using the above-mentioned equation (4).

In this embodiment, it is assumed that the approximate best focus position is determined in advance (°C), and the gear reputation of the focus sensor 21 is first performed at this approximate best focus position (designed value). Then, the amount of focus deviation with respect to this approximate best focus position is determined by the method described above, this amount of deviation is corrected as the offset amount of the focus sensor 21, and focus calibration is performed. From then on, focusing is performed with respect to the best focus position. .

For example, the phase difference can be detected by analyzing the data stored in the memory 29 for each pulse of the frequency divider 27. If the resolution of the interferometer is 001 μm, then Δ
If the pitch (Pl) of the grating on the wafer side is 2 μm and the wavelength (λ) is 0.248 μm, we can obtain a resolution of about 0.01 μm in terms of the X direction, (2), (3), (from formula 41, tan (sin-') #0.08 μm, so a resolution of about 0.08 μm can be obtained.

Here, the phase difference between the signal for the 0th-order male diffracted light and the signal for the ±1st-order refracted light is determined, and the defocus amount is determined from the phase difference between the signals for the ±1st-order refracted light. The amount of defocus can be calculated from the phase difference between the signal for the second-order diffracted light and the signal for the +1st-order refracted light, the signal for the 0th-order diffracted light, and the signal for the 11th-order diffracted light, or directly between the signals for the ±1st-order diffracted light. It is also possible to determine the defocus amount from the phase difference.

However, from the viewpoint of sensitivity, it is preferable to detect the phase difference between the signals corresponding to the ±1st-order refracted light.

Furthermore, by utilizing the fact that the specific pitch of the alignment mark is known in advance from the design, the relationship between the structure of the alignment mark and its detection scanning direction can be obtained as a sinusoidal periodic signal or a measurement signal through relative scanning. There is also a method of determining the phase difference by determining the phase difference as follows. In this method, the obtained measurement signal can be taken into memory as a function f (x) with respect to the moving distance X of the stage.

In this case, the period T (therefore, the frequency V) of the fundamental wave component is uniquely determined by the pitch of the alignment marks in the scanning direction, and this is known as a design value. The function signal thus obtained is subjected to calculations, Fourier integration is performed, and its phase component φ is determined according to the following equation.

S-=f f (x) ・s in (2πV-x)
・dxC=ff (x)-cos (2πV-x)
-dxφ1=tan-' (S/C) (rad) Here, S is the sine component of the Fourier transform of frequency U, C is the cosine component, and φ1 is f (x) for the sine wave in equation (1).
is the phase angle of

The sin/cos functions for such calculations are executed by the CPU 19.
It can be generated within.

Since the Fourier integral method is used, its phase component,
That is, the highest correlation peak position can be found by integrating only two sine and cosine times, and the number of calculations is extremely reduced, resulting in results being obtained in a short time.

Incidentally, although the above-mentioned distance X is described here, the same applies to the case where a function regarding time t is taken.

With the method of detecting the phase of a moiré signal as in the present invention, high-resolution signal detection can be expected, and it is also less susceptible to noise.

Further, in this embodiment, only one direction, the X direction, is shown as the moving direction of the stage, but the stage can be moved in the XX direction. Calculation of the defocus amount is also performed for the lattice patterns 22Y/22Y' in the X direction. this is,
Generally, the projection lens 10 has astigmatism, and therefore,
This is because the amount of defocus caused by the lattice patterns 22X/22X' in the X direction and the amount of defocus caused by the lattice patterns 22Y/22Y' in the X direction may be different.

In this way, when the defocus amounts for the X and Y lattice patterns are different, the average value of both may be used as the defocus amount. Also, using the zero-order light signal detected by the sensor L of the light-receiving element 18, reticle position measurement (measurement for converting the reticle position to the wafer stage position) is simultaneously measured during the aforementioned focus calibration using the index plate 12. If this is the case, the throughput will be further improved.

Next, a second embodiment of the present invention will be described with reference to FIG. 1O. The same members as in the first embodiment are given the same reference numerals.

In the first embodiment, focus calibration has been described using the transmission type diffraction grating patterns 22X and 22Y on the index plate 12, or as shown in FIG. Pattern 22X'', 22Y
”, and a configuration in which the laser beam is incident through the mirror 33 (
It is assumed that the configuration is such that laser light is incident on the mirror 33 from the laser light source 1. ) as a reflection grating pattern 22X
The reflected diffracted light diffracted by "22Y"" is re-diffracted by the diffraction grating patterns 22X" and 22Y' on the reticle, and the re-diffracted light is received, and signals for the ±1st-order diffracted light are obtained in the same manner as above. , the amount of defocus is determined from the phase difference between these signals. The other configurations are the same as in the first embodiment.

Furthermore, the above 1. In the second embodiment, the diffracted light diffracted on the wafer side is re-diffracted by the pattern 22X22Y' on the reticle and the re-diffracted light is photoelectrically detected. The patterns 22X and 22Y on the wafer are used as the second pattern according to the present invention, and the pattern 2 of the reticle is
The same effect can be obtained by re-diffracting the diffracted light diffracted by 2X22Y by the patterns 22X and 22Y on the index plate I2, and by providing a detector under the index plate 12 to detect the re-diffracted light. It will be done.

Further, the means for moving the diffracted light and the pattern relative to each other is not limited to stage movement, but may be configured such that, for example, a plane parallel device is provided in the optical path and is moved slightly in response to the pulses of the interferometer 26. Furthermore, the projection optical system is not limited to a projection lens.

〔Effect of the invention〕

As described above, according to the present invention, the best focus position of the projection optical device can be determined with high accuracy and in a short time by moving the diffracted light and the pattern one or several times, thereby improving the throughput. I can do it. Furthermore, it is possible to measure the reticle position simultaneously with the focus position, which further improves throughput.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of calculating the amount of defocus from the phase difference of the present invention, Fig. 2 is a diagram showing the phase shift of re-diffracted light due to the defocus of the present invention, and Fig. 3 is a diagram showing the principle of calculating the amount of defocus from the phase difference of the present invention. FIG. 4 is a diagram showing a pattern on a reticle and a pattern on an index plate according to the first embodiment. FIG. 5 is a diagram showing a photoelectric element according to the first embodiment of the present invention. Figure, 6th
The figure is a block diagram showing signal processing according to the first embodiment of the present invention, and FIG. 7 shows the movement of the stage and the relative movement between the 9 diffracted light and the pattern on the reticle according to the first embodiment of the present invention. FIG. 8 is a diagram showing the relative movement of the diffracted light and the pattern on the reticle according to the first embodiment of the present invention,
FIG. 9 is a diagram showing a modulated signal obtained by the photoelectric device according to the first embodiment of the invention, and FIG. 10 is a diagram showing the second embodiment of the invention. [Explanation of symbols of main parts] 1...Laser light source, 2...Switching mirror, 10...
・Projection lens, 11X...X stage, IIY...
X stage, 12... index plate, 18... light receiving element,
19...CPU, 20...Power detector, 21
...Grand incidence AF sensor, 22X, 22Y...Pattern on index plate, 22X', 22Y'...Pattern on reticle, R...Reticle, W...Wafer, EP...Projection Pupil plane of lens 10

Claims (2)

[Claims] (1) In a projection optical device that projects a first object onto a second object via a projection optical system, a first pattern formed in a periodic structure with a predetermined pitch is irradiated onto the first object; illumination means for causing at least two diffracted lights generated at different angles from one pattern to enter the projection optical system; the at least two diffracted lights from the first pattern pass through the projection optical system, When a second pattern formed in a periodic structure with a predetermined pitch in the same direction as the first pattern is irradiated onto an object, at least two re-diffracted lights are diffracted again by the second pattern and generated at mutually different angles. a detection means for receiving the light on a plane substantially conjugate with the pupil plane of the projection optical system and outputting a plurality of signals corresponding to each of the at least two re-diffracted lights; the second pattern and the at least two diffracted lights; moving means for relatively moving the light in the pitch direction of the second pattern; based on the plurality of signals modulated with a predetermined amplitude and output from the detection means by the relative movement; a phase difference detection means for detecting a relative phase difference; and a calculation means for calculating a deviation amount from a conjugate position of the first object and the second object with respect to the projection optical system based on the phase difference; A projection optical device characterized by (2) The at least two diffracted lights generated at different angles from the first pattern are ±1st-order lights, and the at least two re-diffracted lights are 0th-order light and +1st-order light, or 0th-order light and -1st-order light. The projection optical device according to claim 1, characterized in that the projection optical device is light, or +1st order light and -1st order light.