JPH06241728A - Detection method for position deviation and gap - Google Patents

Abstract

PURPOSE:To provide a position deviation detection method high in detection resolution to a large detection extent and capable of separately detection posi tion deviation quantities DELTAx, DELTAz in two-dimensional directions. CONSTITUTION:Two pairs of two monochromatic lights having slightly mutually different frequencies f1, f2, are used. In each pair, the two light fluxes are mutually different in incident angles on both sides of the light axis, concerning the light axis, in asymmetrical relation, (theta1<theta2). The two pairs are incident on the diffraction lattices 32, 32 for a first object M and a second object W, respectively, from the two directions in reverse symmetrical relation on both sides of the light axes. Diffraction lights of two or more beams, subjected to light heterodyne interference, are taken out from two positions symmetrical on both sides of the each light axis. Accordingly, two-dimensional phase fluctuation quantities in x and 2 directions, phix, phiz, are separately calculated on the basis of phases phixz and phixz' of light heterodyne detection signals occurring from light path difference fluctuation quantities due to position deviation in x and 2 directions in both diffraction lattices 32, 32. And thus, the displacement quantities or both objects M, W, are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor ultra-fine processing apparatus (proximity exposure apparatus such as SOR aligner / stepper, liquid crystal stepper) and a registration ultra-precision registration measuring superposition accuracy of a pattern exposed on a photosensitive substrate. The present invention relates to a position shift detection method using optical heterodyne interference light in measurement or the like.

[0002]

2. Description of the Related Art In the ultra-precision alignment of aligners for synchrotron radiation photolithography, photosteppers, etc., it is necessary to accurately detect the positional deviation of two objects to be aligned in the X direction (in-plane direction). Therefore, for that purpose, for example, JP-A-62-261003 and JP-A-64-89323.
JP-A-H09-242, et al. Propose a position shift detection method using optical heterodyne interference light. On the other hand, JP-A-63-3810
No. 2 proposes a configuration in which an incident light system from the third-order diffraction angle direction is added to the position detection optical system because measurement in the Z direction (out-of-plane gap direction) is also performed.

Both of these interfere with the diffracted light extracted from the diffraction gratings of the two objects, and detect the phase difference of the beat signals generated in each of these two objects to detect the amount of positional deviation between the two objects. It is expected to dramatically improve the ability to detect and resolve misalignment.

[0004]

However, in these methods, when the phase shift is more than one cycle, pitch jumping / shifting in alignment occurs, which is inaccurate.
There is a limit to the detection range in which the displacement must be within a certain range in advance. In particular, if the grating pitch of the diffraction grating is reduced, the detection resolution is improved, but the detection range is narrowed, and conversely, if the pitch is increased, the opposite relationship occurs.

Therefore, in order to achieve the improvement of the detection resolution and the expansion of the detection range, which are contradictory to each other by the present applicant,
We proposed a structure in which a plurality of diffraction gratings with different grating pitches are arranged side by side on two objects for detection.

Further, if the light is incident from the direction of the optical axis, the ± 1st order, ± 2nd order, ± 3rd order of the diffracted light obtained (two directions symmetrical about the optical axis) ) From the opposite direction (when the incident direction is referred to as the incident order here by borrowing this diffraction order), the closer the incident order is to 0, the smaller the change amount of the optical path difference becomes. Is wide and the interference of low-order diffracted light is strong, so that a strong diffracted light intensity can be obtained, but the detection resolution is lowered. On the contrary, the farther the incident order is from 0, the opposite of the above case.

Therefore, the applicants have proposed a structure adopting a system in which the incident orders are plural, and when the absolute value of the orders becomes large, the defect that the diffracted light intensity is lowered is compensated, so that the diffraction grating is specially designed. Another proposal was made to increase the intensity of diffracted light by superposing the 0th-order diffracted light on the diffracted light of a specific order by using a shape (blaze grating).

However, the first method of arranging a plurality of diffraction gratings having different grating pitches is not practical because it takes time to form such a diffraction grating, and the second proposal in which a plurality of incident orders are provided is as follows. The problem is that the optical system becomes too complicated, and the third proposal using a specially shaped diffraction grating is very difficult to form a diffraction grating with such a shape, and is not practical, in addition to the complicated optical system. A point was pointed out.

Further, it is impossible to measure the displacement in the Z direction unless another incident light system is added as in JP-A-63-38102, and an alignment error in the Z direction caused by the tilt or vibration of the optical axis. There were often problems because the factors could not be corrected sufficiently. Even with the configuration in which the incident light system shown in the same item is added, it is difficult to adjust the wavefront of the two light beams for high-order incidence, and diffracted light of another order (for example, -3rd order diffracted light) is superimposed on the detection signal in the X direction. As a result, the detection accuracy is lowered, the S / N ratio of the detection signal is lowered, and multiple interference is also exerted, which adversely affects the alignment.

The present invention was devised in view of the above problems of the prior art, and does not complicate the configuration and adjustment of the optical system, has a wide detection range and high detection resolution,
A position shift detection method capable of separately detecting the position shift amounts Δx and Δz in the two-dimensional direction is provided so that the correction can be performed even when there is an inclination of the optical axis or there is an amplitude in the Z direction. It is what

[0011]

Before describing the structure of the present invention, the diffraction order of the diffracted light obtained from the diffraction grating of the present application will be defined in advance.

FIG. 1 and FIG. 2 show the states of coincidence of the incident angle and the diffraction angle of the reflection diffraction grating. First, when monochromatic light having a frequency f is incident on the reflection diffraction grating 32 having a grating pitch P with an inclination of an incident angle θi from the optical axis, the diffracted light with a diffraction order of m and n = 0 is specularly reflected. Those diffracting to the optical axis side are m, n = -1, -2, -3, and so on. Those diffracting to the minus order or the opposite side are m, n = +1 and +.
2, +3, and so on, plus order (diffraction angles corresponding to these diffraction orders are denoted by θm and θn). The relationship between the incident angle θi and the diffraction angles θm and θn at this time is expressed by the following formulas 3 and 4 according to the basic formula of the diffraction grating.

[0013]

[Equation 3] Sinθm-Sinθi = m · λ / P

[0014]

[Equation 4] Sinθn-Sinθi = n · λ / P

The position shift detecting method of the present invention will be described based on the above definitions. As shown in FIG. 3, two monochromatic light sets having slightly different frequencies (that is, f ₁ and f ₂ ) are used. Two sets (that is, a total of four beams) are used, and the two beams of each set have different incident angles with respect to the optical axis on both sides of the optical axis (that is, θ ₁ and θ ₂ where θ ₁ <θ ₂ ). From the asymmetrical direction, and between the pairs, there is a direction of reversal symmetry on both sides of the optical axis (that is, a pair of blank arrows f ₁ and f ₂ and a shaded f).
The pair of ₁ and f ₂ is symmetrical with respect to the optical axis in the left-right inversion in the drawing) to the diffraction gratings 32a and 32b of the first object M and the second object W, respectively (these grating pitches are P). ) And take out the diffracted light of two or more beams of optical heterodyne interference from the positions symmetrical to both sides of the optical axis. Then, the optical path difference due to the X-direction positional deviation and the Z-direction positional deviation of both diffraction gratings 32a and 32b is extracted. From the phases φ _xz and φ _xz ′ shown in the following equations 1 and 2 generated based on the variation amount, the two-dimensional phase variation amount φ _{x in the} X and Z directions is calculated by the sum and difference of these two equations. The basic feature is that the displacement amounts of both objects M and W are obtained by separately calculating φ _z and φ _z , respectively.

[0016]

[ _Formula 1] φ _{x z} = φ _x + φ _z

[0017]

(2) φ _xz ′ = φ _x −φ _z

As in the above-mentioned method of the invention, when two sets of two light beams shifted left and right with respect to the optical axis are made into four light beams having left-right inversion symmetry and are made incident from both sides thereof, it is shown in FIG. 4 (a). As described above, one or more optical heterodyne-interfered diffracted lights obtained from a set in which the light flux of the left side frequency f ₁ and the right side light of the frequency f ₂ are shifted to the right side as a whole are obtained in the state of the left tilt (light When the interfering diffracted light emerges on both sides of the axis, the entire light beam is shifted to the left. On the other hand, as shown in FIG. 7B, the light flux with the frequency f _{1 on} the left side and the light flux with the frequency f ₂ on the right side are totally One or more optical heterodyne interference diffracted light obtained from another set that is shifted to the left is obtained in the state of right tilt (if interference diffracted light appears on both sides of the optical axis, it is shifted to the right as a whole. Will be). In the beat signal detected from the interference diffracted light thus obtained, when the two objects M and W have a shift in the X direction, both the beat signal derived from the diffracted light with the left tilt and the beat signal derived from the diffracted light with the right tilt , If there is always a phase shift (phase variation amount) φ _x in the constant direction with respect to the reference signal, and if there is a shift in the Z direction, the beat signal derived from the diffracted light with the left tilt and the beat derived from the diffracted light with the right tilt The signal causes a phase shift φ _z in the opposite direction with respect to the reference signal. As a result, the phase shift φ _xz of the beat signal derived from the diffracted light with the left tilt that is actually detected is obtained as shown in the above equation 1, and the reference of the beat signal derived from the diffracted light with the right tilt is obtained. As the phase shift φ _xz ′ with respect to the signal, the one expressed by the above-mentioned equation 2 is obtained. Therefore, it is possible to separately calculate the two-dimensional phase fluctuation amounts φ _x and φ _z in the X direction and the Z direction from the sum and difference of both equations.

[0019]

EXAMPLES Hereinafter, specific examples of the method of the present invention will be described in detail.

FIGS. 5 and 6 are a perspective view showing an example of the configuration of an optical system device used for carrying out the method of the present invention for detecting the positional deviation between the mask M and the wafer W, and a detailed view of the optical path of the optical system.

In FIG. 5, first, a monochromatic laser light whose polarization planes are orthogonal to each other from the two-wavelength orthogonal polarization laser light source 12 and whose frequencies are slightly different (f ₁ , f ₂ ) (that is, the frequency f ₁ component is represented by →). P-polarized light, or S-polarized light represented by ↑ for the frequency f ₂ component) is generated. Reference numeral 10 is a controller for the light source 12, which is electrically processed to produce a first REF 11
The reference beat signal having the frequency of | f ₁ −f ₂ | is output from a. The light source 12 may be replaced with a structure in which a frequency shifter including two acousto-optic elements (AOM) is used to obtain a light source having two frequencies.

The alignment light emitted from the light source 12 is normally elliptically polarized at a laser emission port of about 3 to 4%, and this is converted into a two-frequency component by a phase plate (rotation correction optical component) called a λ / 4 plate 13. Correct the orthogonal state of to a more correct posture. Then, the beam of alignment light reaches the polarization beam splitter (PBS) 14, and the S-polarized (f ₂ frequency) component reaches the λ / 2 plate 15 from there. It is incident on the λ / 2 plate 15 from the direction of 45 ° with respect to the crystal axis, and the S-polarized light of frequency f ₂ is rotated 90 ° to be P-polarized light which is the same as f ₁ frequency. The λ
The F ₂ frequency P-polarized light emitted from the / 2 plate 15 has its optical path changed by the mirror 16, and the f ₂ frequency alignment beam can be moved in the Z and X directions in the figure, and can also be tilted or rotated by θ. The optical axis direction is changed by 17 to reach the lens 18.
This lens 18 focuses the laser beam f ₂ (collection)
Then, the state position where the beam diameter is most narrowed is created at two positions indicated by beam waist BW of 24 and 25 in the figure. This is for forming a light flux that crosses in parallel on a field stop AS27, which will be described later, and for configuring a telecentric optical system.

On the other hand, the P-polarized alignment beam of frequency f ₁ transmitted through the polarization beam splitter 14 is reflected by the lens 19
Leading to. Like the lens 18, the lens 19 narrows the laser beam to two beam waists BW 24, 25. The incident positions of the laser beams narrowed down by the lenses 18 and 19 are adjusted and are made incident on the non-polarizing beam splitter NPBS20. On the non-polarizing beam splitter NPBS20, the distance between the beams of the frequencies f ₁ and f ₂ is adjusted by the mirror 17 so that the interference diffracted light of the desired diffraction order (-1, -1) can be obtained later. The incident illumination angle to the diffraction grating 32 by the objective lens 31 described later is
Since the frequency is determined by the beam spacing between f ₁ and f ₂ , it is adjusted precisely. The reflection / transmission surface of the non-polarization beam splitter NPBS20 can adjust the wavefronts of two light fluxes by tilting and rotating axes.
Wavefront aberration is removed so that the wavefronts of the light beams are the same. Frequency f incident on non-polarizing beam splitter NPBS20
Both the ₁ and f ₂ alignment beams are split together in two directions as parallel beams.

The two light fluxes of frequencies f ₁ and f ₂ reaching the mirror 21 change the optical axis direction, and the non-polarizing beam splitter NPBS23
Leading to. Similarly, the two light fluxes reaching the mirror 22 change the optical axis direction and are shifted by a predetermined amount by the mirror 22 which can be rotated and tilted in the X and Z directions, and a non-polarized beam splitter NPBS23.
The four light beams (f ₂ f ₂ f ₁ f ₁ ) are arranged above, and are precisely adjusted so as to be symmetrical left and right with respect to the optical axis. If a lateral shift occurs with respect to the optical axis, a non-telecentric state occurs, and a minute shift occurs in the diffraction grating 32 that is the image plane, and the two detection range lengths differ. In the figure, the four light beams emitted from the non-polarizing beam splitter NPBS23 to the right side are for the other axes, but it is preferable to replace them if a cube-shaped beam splitter having two mirror surfaces can be produced.

The four light beams emitted from the non-polarization beam splitter NPBS23 are arranged symmetrically with respect to the optical axis in the left-right direction and reach the lens 26. The lenses 26, 28, 31, 33 are both telecentric optics and have a field stop AS27.
Image has a conjugate (image forming) relationship for forming an image on the diffraction grating 32 of the mask M and the wafer W. When the image of the field stop AS27 is formed on the diffraction grating 32 by such a telecentric arrangement, the image forming magnification of the image becomes constant even if there is defocus (focal position shift). For example, the Franhofer diffraction image from the field stop AS27, which occurs when the optical system is tilted or the lens is decentered, causes an alignment error, but the influence is reduced because it is imaged by both telecentric optical systems. it can. The four light beams emitted from the lens 26 are narrowed down on the field stop AS27 arranged at the focal position of the rear surface of the lens 26 so that the four light beams cross each other in parallel, and an alignment beam having a field stop diameter is formed and injected.
A pupil plane EP70, which will be described later, located at the focal point of the rear surface of the lens 28, forms four parallel light beams. The four-beam parallel light is emitted from the lens 28, travels in parallel to the optical axis, and is focused on the pupil plane EP70 where the Fourier transform image of the diffraction grating 32 is obtained at the front focus position of the objective lens 31 as if it were a point light source. Like Since the arrangement of the four light fluxes on the pupil plane EP70 is inverted by the lenses 26 and 28, the arrangement of the four light fluxes is changed from (f ₂ f ₂ f ₁ f ₁ ) to (f
₁ f ₁ f ₂ f ₂ ) and the reverse position.

The four beams of P-polarized light (→) all pass through the polarization beam splitter PBS29 and reach the λ / 4 plate 30. The four light fluxes that have passed through the λ / 4 plate 30 become counterclockwise circularly polarized light, and travel by expanding the beam diameter as parallel light to the objective lens 31. As shown in FIG. 7, the four light fluxes transmitted through here are
The objective lens 31 makes incident illumination with an outer angle θ ₂ and an inner angle θ ₁ with respect to the optical axis. When such incident illumination is performed, four-beam is arranged in a position of Fb · sin [theta ₂ and Fb · sin [theta ₁ on the pupil plane EP70 respect to the optical axis (Fb is the surface focal length of the objective lens 31 ), The light is incident on the diffraction grating 32 at an angle which is symmetrical with respect to the optical axis.

Furthermore, in this embodiment, the interference diffracted light is received by the following light receiving optical system. Diffracted light obtained by illuminating two sets of two light fluxes is in a state as shown in FIG. That is, since the high-order diffracted light is centered on the specularly reflected light (0th-order light) in the direction opposite to the incident angles θ ₁ and θ ₂ , the pitch P intervals are arranged.
Two sets of two light beams are diffracted without being mixed. In this figure, the diffraction orders (-1, -1) from which the interference beat signal is obtained
(-1, -1) (-3, +1) (-3, +1) (+1,
Only -3) (+1, -3) is specified. Here, the interference diffracted light that detects the beat signal is the above-mentioned six light beams, but this is determined by the effective diameter of the lens 31, and if the lens has a high NA (aperture ratio), the higher order interference diffraction light is used. It is possible to collect light.

Next, a method for isolating the incident illumination light and the interference diffracted light will be described. The obtained diffracted light is diffracted at an angle symmetric with respect to the optical axis, becomes circularly polarized light that rotates in the opposite direction to the circularly polarized light when incident, and is condensed by the objective lens 31. The interference 6 light beams become parallel light, and when passing through the λ / 4 plate 30, the polarization direction becomes S-polarized (↑) (shown by the polarized light ◎ perpendicular to the paper surface in FIG. 6). It is reflected by the separation surface of the beam splitter PBS29. Here, polarizing beam splitter PBS 29 and λ / 4 plate 30
The incident light and diffracted light are completely separated by. The reflected diffracted light whose traveling direction is changed reaches the lens 33 having the front focal length on the pupil plane EP70, and is further imaged at the position of the rear focal length. This position has a conjugate (image forming) relationship with the field stop AS27. Lenses 33 and 34 are afocal magnifying lenses, which magnify and relay the image forming surface on the front surface. This magnified image becomes a Fourier image on the rear surface of the lens 34.

The six light fluxes that have passed through the lens 34 are perforated mirrors.
By (35), only the central (-1, -1) (-1, -1) th order diffracted light passes through and the other light beams are reflected. The two passed light fluxes reach the lens 36, stray light and ambient light are blocked by the slit 38, and reach the four-divided detector 37. On the surface of the four-divided detector 37 is a surface on which the image of the diffraction grating 32 is enlarged and projected,
Here, the beat signals of the wafer W and the mask M are separated and received by the respective detection surfaces. On the other hand, as for the high-order diffracted light reflected by the perforated mirror 35, only the desired diffracted light is taken out by the spatial filter 39, and thereafter, it is received by a lens and a detector (not shown), respectively.

In this embodiment, two beams are used to create four parallel light beams.
Although the non-polarizing splitters NPBS20 and 25 are used, four parallel light fluxes can be created by using the transmitted light of the diffraction grating having the same pitch as the diffraction grating 32 of the mask M and the wafer W. Figure 8 (a)
Is a drawing showing a conventional method for producing parallel 2 light fluxes, and FIG. 7B is a drawing for explaining a method for producing parallel 4 light fluxes using a diffraction grating. In the conventional method, when laser light along the optical axis illuminates the diffraction grating 50, diffracted light is generated on the transmission side. The (51, 0, +1) diffracted light that can be condensed by the lens 51 is extracted, and the spatial filter 52 extracts the 0th order (regular reflection light).
Is cut to create −1st and + 1st order parallel light fluxes.
This configuration is applied to four parallel light fluxes, which illuminate the diffraction grating 50 with two laser light fluxes from different directions with respect to the optical axis.
The respective diffracted lights are arranged at desired intervals, and the parallel light is extracted by the lens 51 as the parallel light by the spatial filter 52 in the same manner to extract the −1st and + 1st order light fluxes.
As an actual configuration, as shown in FIG. 9, two P-polarized laser beams of frequencies f ₁ and f ₂ are made incident on a non-polarized beam splitter NPBS20 through lenses 18 and 19 in a direction orthogonal to each other and are made parallel to each other. A laser beam of frequencies f ₁ and f ₂ after being split into two as a light beam has a beam waist B in the figure.
The aperture is narrowed down at the position of W53, and the interval is set so that desired parallel light can be obtained. Two parallel light beams are formed by the lens 54, and the diffraction grating
The diffracted light on the transmission side obtained by illuminating 50 passes through the lens 51 though it is shown by the shaded line for the frequency f _{1 and} the white line for the frequency f _2. Are converted into parallel light, and the spatial filter 52 cuts the 0th-order light, respectively, and the +1, -1, -1, and + first-order four-beam parallel light is extracted. The diffraction grating 50 is arranged at a position conjugate with the mask M and the wafer W. In the configuration of the above embodiment, the diffraction grating 54 is arranged in the field stop AS27. In another embodiment, a Wollaston prism (P-polarized light, S-polarized light separation / extraction element) may be used to create four parallel light beams.

As shown in this embodiment, two pairs of two light fluxes which are left-shifted and right-shifted with respect to the optical axis are left-right inverted symmetrically.
As a light flux, as shown in FIG. 10, the mask M and the wafer W
When each of the diffraction gratings 32 is illuminated, two (-1, -1) th order diffracted lights are obtained at positions symmetrical to the optical axis for both the mask M and the wafer W (other diffraction orders are omitted in the drawing). Has been). As shown in FIG. 4B, with respect to the incident light that is left-shifted with respect to the optical axis, diffracted light having a right tilt opposite to the incident direction with respect to the optical axis is obtained according to the law of reflection. To be Similarly, for incident light that is shifted to the right with respect to the optical axis, diffracted light that is tilted to the left is obtained as shown in FIG. The reason why the four-beam illumination is performed is to measure the phase change in the two-dimensional direction (X direction, Z direction) at the same time.
The reason why two sets of two light fluxes are incident and illuminated symmetrically with respect to the optical axis is to make the phase amounts corresponding to the obtained movement amounts of Δx and Δz the same amount.

Next, in the present embodiment, it will be described that two (-1, -1) th order diffracted lights are obtained at symmetrical positions with respect to the optical axis. FIG. 7 is a principle explanatory diagram showing an interference model of two wavelengths with incident light to the diffraction grating formed on the wafer W and diffracted light up to (−3rd to + 3rd). In the present embodiment, as shown in FIG. 6F, the duty ratio of the diffraction grating 32 has the best first-order diffraction efficiency (P-
a) 1 / P = 1/2 was used. The same figure (c)
The one shown in (d) is from the diffraction grating 32.
F _{1 of} the order that can be condensed by the objective lens 31 up to + 3rd order,
It is the intensity distribution of the m-th and n-th order diffracted light of f ₂ .

First, a set of two light beams (frequency f ₁ and f ₂ ) shifted leftward from the optical axis will be described. The pupil plane EP70 at the front focal length of the objective lens 31 shown in (e) of the figure is a plane on which the Fourier transform image of the diffraction grating 32 is obtained, and this plane serves as a point light source in the optical arrangement of the illumination system. 4 Narrow the light flux. Illumination light (white arrow) having a frequency f ₁ incident at an outer incident angle θ ₂ is incident and illuminated on the diffraction grating 32, and its specularly reflected light (0th order light) is incident on the pupil plane EP70 with respect to the optical axis. And return to the opposite position. With this position as the center, as shown in (R1) of FIG. Similarly, the frequency f ₂ incident at the inner incident angle θ ₁
Illumination light (white arrow) is also incident on the diffraction grating 32 and illuminated.
The specularly reflected light returns to the position opposite to the incident position with respect to the optical axis on the pupil plane EP70 as the specularly reflected light (0th order light), and as shown in (R2) of FIG. As +1 order ~
-3rd order diffracted light is obtained. At this time, the interval between the incident illumination light having the frequency f ₁ (white arrow) and the incident illumination light having the same frequency f ₂ (white arrow) on the pupil plane EP70 is (m = −1, It is set so that the n = −1) th order diffracted light interferes (overlaps). The interference diffracted light of the (-1, -1) th order obtained in such a situation is obtained at the diffracted light position tilted to the right (black solid line arrow) with respect to the optical axis, and is shifted to the right of the optical axis. Other than this, the diffracted light enters the interference state (-3,
It is also in the (+1) th and (+ 1, -3) th positions.

On the other hand, another set of two light fluxes of frequency f ₁ and f ₂ (hatched arrows) is also shifted to the right about the optical axis at the time of the incident illumination, and therefore the above-mentioned center is set about the optical axis. The interference diffracted light is obtained at the position reversed from the case. That is, as shown in (L1, L2) of FIG.
The interference diffracted light of the 1st and -1) th order is obtained at the diffracted light position that is tilted to the left with respect to the optical axis (the hatched arrow) and is shifted to the left of the optical axis on the pupil plane EP70. In addition to this, the diffracted light enters the interference state also at the (-3, +1) th and (+1, -3) th positions.

The interference diffracted light having the left tilt and the right tilt obtained as described above is obtained at a symmetrical position with respect to the optical axis without the interference diffracted lights overlapping with each other, as shown in FIG. In front of the detector 37 or the like for detecting the interference diffracted light, they are separated as shown in FIG.

Next, the principle of separating the phase fluctuation amount in the Δx direction and the phase fluctuation amount in the Δz direction by the sum and difference of predetermined formulas will be described. 11 to 13 show left-right symmetrical incident illumination with an incident angle of θ (Symmetric, FIG. 11).
And the case where the incident illumination light is shifted to the right with the incident angles θ ₁ and θ ₂ (Left, FIG. 12) and the case where the incident illumination light is shifted to the left under the same conditions (Rig
ht, FIG. 13), and −1st order interference diffracted light. At the same time, the phase shift direction of the beat signal with respect to the reference signal when there are minute fluctuation amounts Δx and Δz are also shown in these drawings by a black arrow and a white arrow.

As is clear from these figures, the phase shift directions with respect to the shift in the Δx direction are the same in all three cases. This can be judged from the fact that the change in the optical path length due to the movement is always long for the frequency f ₁ and is always short for the frequency f ₂ as shown in FIGS. 14 to 16 described later. That is, the optical path difference [L] with respect to the illumination light of frequency f ₁ when the illumination light of frequency f ₂ is used as a reference
(1) -L (2)] has a long optical path length of L (1),
Also, since the optical path length of L (2) becomes short, it always becomes positive,
Therefore, the phase shift direction is always the same direction.

On the other hand, in the case of symmetrical incidence of FIG. 11 with respect to the movement of Δz, the variation amounts of the optical path lengths of the incident illumination lights of the frequencies f ₁ and f ₂ are always equal, and the optical path difference [L (1) -L
(2)] becomes 0, and the amplitude intensity changes, but
The phase does not change and no phase shift occurs. This is an advantage that the symmetrical optical arrangement does not affect the variation in the Δz gap direction.

In the case of left asymmetry or right asymmetry, the amount of phase fluctuation associated with each Δz movement occurs in the opposite direction depending on the inclination direction from the optical axis (white arrows → and ←).

The change in optical path length in the above case is
This will be specifically shown in FIGS. 14 to 16. These drawings show that the beam of frequency f _{1 and} the beam of frequency f ₂ are Δx and Δz.
It shows the optical path lengths L (1) and L (2) when moving from the position P to P ′ as the position moves by a minute. In these drawings, the optical path change length of the incident light generated at that time is circle A, circle B.
Also, the change amount of the optical path of the diffracted light is shown by a circle C, and the optical path length is shown by a thick solid line. Of these, the optical path length circle C of the diffracted light is the optical path length generated in the same direction at the frequencies f ₁ and f ₂ , and the optical path difference [L
(1) -L (2)] = (Circle A + Circle C) − (Circle B + Circle C)
= (Circle A−circle B), the circle C does not contribute to the optical path difference and can be excluded from the calculation of the optical path difference. That is, the optical path difference may be considered as the optical path length generated for incident light of frequencies f ₁ and f ₂ .

Therefore, first, let us consider a superposition of _two waves u ₁ and u _{2 which} have substantially equal amplitudes and slightly different frequencies (several tens KHz to several hundred KHz) and which travel in the same direction.

U ₁ and u ₂ can be written as light waves represented by the following equations (5) and (6).

[0043]

[Equation 5] u ₁ = a ₁ exp {i [ω ₁ t−2πL (1) / λ ₁ −φ _{R (1)} ]}

[0044]

[Equation 6] u ₂ = a ₂ exp {i [ω ₂ t−2πL (2) / λ ₂ −φ _{R (2)} ]} where a ₁ , a ₂ ...... u ₁ , and the amplitude of u ₂ ω ₁ ...... u ₁ Angular frequency ω ₂ …… u ₂ angular frequency λ ₁ , λ ₂ …… u ₁ , u ₂ wavelength φ _{R (1)} , φ _{R (2)} …… u ₁ , u ₂ initial phase (constant value ) L (1) ...... u ₁ optical path length L (2) …… u ₂ optical path length

The beat frequency (beat) is a repetition frequency of amplitude fluctuation and can be expressed by the following equation (7).

[0046]

[Equation 7] Δf = (ω ₁ −ω ₂ ) / 2π

When the sum of the amplitudes of the two waves u ₁ and u ₂ is squared to obtain the superposition strength of the waves, the following equation 8 is obtained.

[0048]

[Equation 8]

[L (1) / λ ₁ -L (2) /
It can be seen from the λ ₂ ] term that the phase term is delayed or advanced due to the change in the optical path difference [L (1) -L (2)].

In the optical heterodyne alignment method, this phase difference is measured, but this phase difference is ± 18.
Since the angle detection range is fixed within 0 °,
[L (1) / λ ₁ −L (2) / λ ₂ ], the optical path difference [L (1) −L (2)] is the detection range and the phase advance.
It is an item that affects the direction of delay. The _two laser beams of the frequencies f ₁ and f ₂ used have slightly different wavelengths, and the frequency of the beat signal (f ₁ −f ₂ ) is about 2.4 × 10 ⁵ Hz.
Since it is sufficiently smaller than the optical frequency of about 5 × 10 ¹⁴ Hz,
The laser wavelength can be λ ₁ = λ ₂ ≈λ. Therefore, 2π [L
The term of (1) / λ ₁ −L (2) / λ ₂ ] is 2π [L (1) −
L (2)] / λ.

Next, based on FIGS. 14, 15 and 16, the optical path difference [-1st order diffracted light of f ₁ frequency component and −1st order diffracted light of f ₂ frequency component in the optical axis direction in the case of FIG. L (1)-
L (2)].

FIG. 14 is a diagram showing changes in the optical path length of a symmetrically arranged incident light illumination arrangement. Θ shown here is
It is the incident angle when the illumination lights of frequencies f ₁ and f ₂ are incident in the opposite directions from the directions of the ± first-order diffracted light obtained when the illumination light is incident in the optical axis direction. The optical path ellipse A of the incident light on the optical path L (1) having the frequency f ₁ is represented by the following Expression 9.

[0053]

[Equation 9] L (1) = Δz / cos θ + (Δx−Δz · tan θ) sin θ = Δx · sin θ + Δz (1 / cos θ−tan θ) sin θ = Δx · sin θ + Δz (1 / cos θ−sin ² θ / cos θ) = Δx · sin θ + Δz · cos θ

Similarly, the optical path length circle B of the incident light on the optical path L (2) of the frequency f ₂ is expressed by the following equation (10).

[0055]

[Equation 10] L (2) = Δz / cos θ− (Δx + Δz · tan θ) sin θ = −Δx · sin θ + Δz · cos θ

Optical path difference [L of light of frequency f ₁ and frequency f ₂
(1) -L (2)] is given by the following equation 11 from the above equations 9 and 10.

[0057]

[Equation 11] L (1) −L (2) = Δx · sin θ + Δz · cos θ − (− Δx · sin θ + Δz · cos θ) = Δx (sin θ + sin θ) −Δz (cos θ−cos θ) = 2Δx · sin θ

As can be seen from the above equation, in the case of bilaterally symmetric incidence, the incident angles θ are equal to the optical axis, so no optical path difference occurs in the Z direction, and only Δx changes. This is the advantage of the bilaterally symmetrical incidence type.

On the other hand, as shown in FIG. 15 and FIG. 16, when the diffracted light is extracted with the light being left-shifted or right-shifted with respect to the optical axis (rightward or rightward). Asymmetry or left asymmetry), left and right are unbalanced, and as is clear from the fact that the incident angles θ are actually θ ₁ and θ ₂ in the term of (cos θ-cos θ) in the above equation 11, the displacement of Δz becomes The optical path difference also occurs.

FIG. 15 shows the optical path length change (R) of diffracted light to the right due to the left-shift incident light and its optical path difference, and FIG.
Shows the optical path length change (L) of the left tilt diffracted light due to the right-shift incident light and the optical path difference. As aforementioned,
θ ₁ and θ ₂ are the respective incident angles with respect to the incident light with respect to the optical axis, and the inner incident angle θ ₁ <the outer incident angle θ ₂ .

Optical path length circle A'circle A "in both figures is the optical path length of the incident light of frequency f ₁ , circle B'circle B" is the optical path length of the incident light of frequency f ₂ and circle C'circle C "is the frequency f ₁ And the optical path length of the f ₂ diffracted light.
(2)], and the optical path length of the circle C ′ in the diffraction direction can be excluded from the calculation of the optical path difference because the diffraction directions are the same direction. In both figures, the diffraction angle between the diffracted light and the optical axis is Not specified, which means that the optical path difference can be specified by the incident angles of the incident lights of frequencies f ₁ and f ₂ .

Then, when the mask M moves from the position P to the position P ', the optical path lengths L (1) and L (2) for the incident lights of the frequencies f ₁ and f ₂ in FIG. 15 are obtained, respectively.
The following equations 12 and 13 are obtained.

[0063]

[Equation 12] L (1) = Δz / cos θ ₂ + (Δx−Δz · tan θ ₂ ) sin θ ₂ = Δx · sin θ ₂ + Δz · cos θ ₂

[0064]

[Equation 13] L (2) = Δz / cos θ ₁ − (Δx + Δz · tan θ ₁ ) sin θ ₁ = −Δx · sin θ ₁ + Δz · cos θ ₁

From the above two equations, the optical path difference based on the incident light of frequency f ₂ is as shown in the following equation (14).

[0066]

[Equation 14] L (1) -L (2) = (sin θ ₁ + sin θ ₂ ) Δx − (cos θ ₁ −cos θ ₂ ) Δz

The first term on the right side of the above equation is a term relating to Δx, and
The second term is the term relating to Δz, and the second term is the difference of cosθ. Since θ ₁ <θ ₂ , (cos
The term [theta] _1- cos [theta] ₂ ) is positive, so entering-indicates a negative sign. 2π / λ [L of the above equation 8
The term (1) -L (2)] is the phase term (-
180 ° to + 180 °), the amount of change in the phase terms of Δx and Δz can be expressed by the following expression 15, as in the expression 14 described above.

[0068]

[Equation 15] φ _xz ′ = φ _x −φ _z

Similarly, in FIG. 16, when the optical path length when moving from P to P ′ is obtained, the following equations 16 and 17 are obtained by exchanging θ ₁ and θ ₂ of the equations 12 and 13. .

[0070]

[Equation 16] L (1) = Δz / cos θ ₁ + (Δx−Δz · tan θ ₁ ) sin θ ₁ = Δx · sin θ ₁ + Δz · cos θ ₁

[0071]

[Equation 17] L (2) = Δz / cos θ ₂ − (Δx + Δz · tan θ ₂ ) sin θ ₂ = −Δx · sin θ ₂ + Δz · cos θ ₂

Therefore, the optical path difference [L (1) -L (2)] based on the optical path L (2) is as shown in the following expression 18.

[0073]

[Equation 18] L (1) -L (2) = (sin θ ₁ + sin θ ₂ ) Δx + (cos θ ₁ −cos θ ₂ ) Δz

When this is represented by the amount of phase change as in the equation 15, the following equation 19 is obtained.

[0075]

[Formula 19] φ _xz = φ _x + φ _z

In this embodiment, since the left-shifted and right-shifted illumination light beams are incident at the same time, the phase fluctuation amounts φ _x and φ _z are separated from each other by the sum and difference of the equations (15) and (19). Can be measured.

As described above, the incident angle is θ ₁ = θ ₂ = θ in the case of bilaterally symmetric incidence, and the term relating to Δz in the second item on the right side of the equations 14 and 18 is 0. Also the first on the right side
The item is 2Δx · sin θ. That is, as Δx and Δz move, the optical path length in the X direction becomes longer for the incident light of frequency f ₁ and becomes shorter for the incident light of frequency f ₂ , whereas the optical path length in the Z direction becomes Both f ₁ and f ₂ are long, but the amount of change is the same.

On the other hand, when diffracted light having a right asymmetry and a left asymmetry is obtained by the incidence of the left-shifted and right-shifted illumination light, the asymmetry causes the term relating to Δz in the second term of the equations (14) and (18). (Cos θ ₁ −cos θ ₂ ) is generated in an amount proportional to the gradient difference between θ ₁ and θ ₂ and the incident angle θ ₁
By illuminating two asymmetrical groups of θ and θ ₂ symmetrically with respect to the optical axis, the same amount [(cos θ ₁ − is different in the direction [(cos θ ₁ −cos θ ₂ ))] in the opposite direction. cos
θ ₂ )] can be generated. Also, the first terms of the equations 14 and 18 are (sin θ ₁ + sin
θ ₂ ), which is the same as the traveling direction of Δx regardless of the tilt angle.

At this time, the detection range of Δx is (sin θ ₁ +
Although the amount is proportional to sin θ ₂ ), the detection range for Δz is cos θ ₁ −cos θ ₂ ).
Since the difference is s, it becomes longer than Δx, and on the other hand, the detection resolution decreases.

Although the above-described embodiment utilizes the optical heterodyne interference by the (-1, -1) th order diffracted light,
Similarly, due to the interference in which the detection range lengths of the (-1, 0) th order and the (0, -1) th order are doubled, similarly, an asymmetric set of the incident angles θ ₁ ′ and θ ₂ ′ is ₂ with respect to the optical axis. It is possible to perform incident illumination in a pair symmetry. A description will be given below to another embodiment in which the (-4, 0) -th order and the (0, -1) -th order optical heterodyne interference signals are obtained and the four light fluxes are left-right inverted symmetrically.

As shown in FIGS. 17 and 18, a light beam having a frequency f ₁ (indicated by a white solid line in FIG. 18) is incident at an angle θ ₂ ′ and is positioned at the opposite position (the same position) with respect to the optical axis according to the law of reflection. In the figure, the specularly reflected light returns to the position where the light flux of frequency f ₂ ′ is incident). As for the diffracted light, −3rd to + 3rd order diffracted light is obtained centered on this specularly reflected light, and the intensity distribution is shown in (R1) of FIG. 18D. The other frequency f
The light flux ₂ (white solid line in the figure) is incident and illuminated at an angle θ ₁ ′ smaller than the incident angle θ ₂ ′, and the specularly reflected light is at the opposite position (at the position where the light flux having the frequency f ₁ ′ is incident in the figure). ) Return to. Diffracted light is centered around this specularly reflected light and is −3rd to +3
The next diffracted light is obtained, and its intensity distribution is shown in (R2) of FIG. Therefore, when the diffraction order m of the light flux of frequency f ₁ and the diffraction order n of frequency f ₂ are expressed, the (m = −1, n = 0) order and (m = 0, n = asymmetrical with respect to the optical axis.
-1) The following interference diffracted light is obtained.

Another set of _two light fluxes having the frequencies f ₁ ′ and f ₂ ′ are incident from the positions where the light fluxes having the frequencies f ₁ and f ₂ are diffracted in the opposite direction (thick lines shaded in the figure). Similarly, the diffracted light is obtained centering on the respective specularly reflected light positions.
As shown in the intensity distribution at (L1, L2) in (c), the (m = -1, n = 0) and (m = 0, n = -1) -order interferences are asymmetric with respect to the optical axis. Diffracted light is obtained. Therefore, the interference light in front of the detector is arranged in a straight line and symmetrically arranged with respect to the optical axis without being mixed.

19 to 21 show the case of bilaterally symmetric incident illumination where the incident angle is θ '(S1 / 2, FIG. 19), the incident illumination light is set to the right with incident angles θ ₁ ′ and θ ₂ ′. In the case of left asymmetry shifted (L1 / 2, FIG. 20) and in the case of right asymmetry incident illumination light shifted left under the same conditions (R1 / 2,
21) and (0, −1) -th order interference diffracted light states in FIG. At the same time, the minute variation Δ
The phase shift directions of the beat signal with respect to the reference signal in the case of x and Δz are also shown in these drawings by a black arrow and a white arrow.

As shown in FIG. 19, in the case of bilaterally symmetric incident illumination, the phase does not change even if there is movement in the Z direction. On the other hand, in the case of the left asymmetrical incidence shown in FIG. 20, when there is a movement in the Z direction, the phase advances in the same direction by the same amount. Also in FIG.
In the case of right asymmetrical incidence, as shown in (4), when there is a movement in the Z direction, the phase advances in the opposite direction by the same amount. By utilizing this fact, the phases in the X direction and the Z direction can be separated and measured by the sum and the difference as in the above-mentioned embodiment.

22 to 24, the phase change amount due to the change in the optical path length and the phase advance / delay directions will be described.

FIG. 22 shows the case of bilaterally symmetric incident illumination. If the position P is moved by Δx, Δz to the position P ′, an optical path difference indicated by a thick solid line is generated. Here, there is a relationship of circle A ₁ = circle A ₂ and circle C ₁ = circle C ₂ because the incident illumination is symmetrical with respect to the optical axis. The incident angle at this time is about half of the diffraction angle θ of the ± first-order diffracted light that would be obtained if the illumination light was incident and illuminated from the optical axis direction. ,
θ / 2. The optical path length in this case can be expressed by the following equations 20 and 21.

[0087]

[Equation 20] Circle A ₁ = Circle A ₂ = Δz / cos (θ / 2) + [Δx−Δz · tan (θ / 2)] sin (θ / 2) = Δx · sin (θ / 2) + Δz · cos (θ / 2)

[0088]

[Equation 21] Circle C ₁ = Circle C ₂ = Δz / cos (θ / 2)-[Δx + Δz · tan (θ / 2)] sin (θ / 2) = − Δx · sin (θ / 2) + Δz · cos (θ / 2) )

At this time, the diffraction order of the f ₁ frequency component is m,
When the diffraction order of the f ₂ frequency component is n and two optical path differences of two interference diffracted lights (m = 0, n = −1) and (m = −1, n = 0) are calculated respectively, m = 0, n =-
1) The optical path difference of the next interference diffracted light is given by the following equation 22 (2 in the circle ₂ of C ₂ means round trip), and the equation 20 and the equation 2
From 1, the term of Δz is eliminated as shown in the following equation 23.

[0090]

[Equation 22] L (1) -L (2) = ( round A ₁ + round C ₁₎ -2 Round C ₂ = round A ₁ - Round C ₂

[0091]

[Equation 23] L (1) -L (2) = 2Δx · sin (θ / 2)

The optical path difference of the interference diffracted light of the (m = −1, n = 0) order is given by the following equation 24 (2 of 2 circles A ₁ means round trip), which is the same as the above equation 23.

[0093]

[Equation 24] L (1) -L (2) = 2 circle A _1- (circle A ₂ + circle C ₂ ) = circle A ₁ -circle C ₂ = 2Δx · sin (θ / 2)

This means that in the case of left-right asymmetry in FIG.
This indicates that the direction of phase change in the X direction is equal to the amount of change. Further, since the term of Δz is deleted, there is no phase fluctuation due to Δz.

On the other hand, FIGS. 23 and 24 show the case of left-right asymmetrical incidence. In these drawings, circle A ₁ , circle B ₁ , circle C ₁ , circle A ₂ , circle B ₂ , circle C ₂ , circle A ₁ ′ circle B ₁ ′ circle C ₁ ′ circle A ₂ ′ circle B ₂ ′ circle C ₂ 'refers to an optical path length indicated by the thick solid line, circles a ₁
= Circle A ₁ ′ = Circle A ₂ ′, Circle B ₁ = Circle A ₂ = Circle B ₁ ′, Circle C ₁
= Circle C ₂ = Circle C ₂ ′, Circle B ₂ = Circle C ₁ ′ = Circle B ₂ ′ are divided into four groups. This combination causes an optical path difference. The optical path lengths of these are summarized below, where the inner incident angle is θ ₁ ′ and the outer incident angle is θ ₂ ′ with respect to the optical axis.
The optical path difference is calculated respectively.

[0096]

[Equation 25] Circle A ₁ = Circle A ₁ ′ = Circle A ₂ ′ = Δz / cos θ ₂ ′ + (Δx−Δz · tan θ ₂ ′) sin θ ₂ ′ = Δx · sin θ ₂ ′ + Δz · cos θ ₂ ′

[0097]

[Equation 26] Circle B ₁ = Circle A ₂ = Circle B ₁ ′ = Δz / cos θ ₁ ′ + (Δx−Δz · tan θ ₁ ′) sin θ ₁ ′ = Δx · sin θ ₁ ′ + Δz · cos θ ₁ ′

[0098]

[Equation 27] Round C ₁ = round C ₂ = round _{C 2 '= Δz / cosθ 2} ' - (Δx + Δz · tanθ 2 ') sinθ 2' = -Δx · sinθ 2 '+ Δz · cosθ 2'

[0099]

[Equation 28] Round B ₂ = round C ₁ '= round _{B 2' = Δz / cosθ 1} '- (Δx + Δz · tanθ 1') sinθ 1 '= -Δx · sinθ 1' + Δz · cosθ 1 '

What can be understood from these equations (25) to (28) is that the coefficient of Δz is positive and tends to increase, but there is a combination of increasing or decreasing Δx.

The optical path difference in the case of left asymmetry due to the right-shifted incident light in FIG. 23 is (m = 0, n = -1)
The next optical path difference is the following equation 29, (m = −1, n = 0)
The next optical path difference is given by the following equation (30).

[0102]

[Equation 29] L (1) -L (2) = (Round B ₁ ′ + Round C ₁ ′) − (Round C ₂ ′ + Round B ₂ ′) = Round B ₁ ′ −Round C ₂ ′ = (sin θ ₁ ′ + sin θ ₂ ′) Δx + (cos θ ₁ ′ −cos θ ₂ ′) Δz

[0103]

[Equation 30] L (1) -L (2) = (Round B ₁ ′ + Round A ₁ ′) − (Round C ₂ ′ + Round A ₂ ′) = Round B ₁ ′ −Round C ₂ ′ = (sin θ ₁ ′ + sin θ ₂ ′) Δx + (cos θ ₁ ′ −cos θ ₂ ′) Δz

When the optical path difference in the case of right asymmetry due to the left shift incident light in FIG. 24 is calculated, (m = 0, n = −
1) The next optical path difference is given by the following equation 31, and (m = −1, n =
0) The next optical path difference is given by the following equation 32.

[0105]

[Equation 31] L (1) -L (2) = ( round A ₁ + round C ₁₎ - (Round B ₂ + round C ₂₎ = round A ₁ - circle _{B 2 = (sinθ 1 '+} sinθ 2') Δx- (cosθ ₁ ′ -cos θ ₂ ′) Δz

[0106]

[Equation 32] L (1) -L (2) = ( round A ₁ + round B ₁₎ - (Round B ₂ + round A ₂₎ = round A ₁ - circle _{B 2 = (sinθ 1 '+} sinθ 2') Δx- (cosθ ₁ ′ -cos θ ₂ ′) Δz

To summarize the above, in the case of right asymmetry due to the left-shift incident light in FIG. 24, the optical path difference is determined by the difference between the optical path circles A ₁ and B ₂ , and the phase shift direction of Δx is the rightward arrow direction (thick solid line). (Arrow), and the phase shift direction of Δz is the opposite direction (white arrow), and the variation amount thereof is the same for both the (0, -1) th order and the (-1, 0) th order. Further, the variation amount of Δx is, as is clear from the above equations 31 and 32,
From the sum of sin of the first term on the right side, the variation amount of Δz can be known from the difference of cos of the second term. On the other hand, in the case of left asymmetry due to the right-shift incident light in FIG. 23, the phase shift direction of Δx is the rightward arrow direction (thick solid arrow) and the same as the phase shift direction of Δz (white arrow). Therefore, by detecting these phases, Δx can be calculated from the sum.
It is possible to detect the phase fluctuation amount in the direction and the phase fluctuation amount in the Δz direction separately from the difference.

[0108]

According to the position shift detecting method of the present invention described in detail above, the structure of the optical system and its adjustment are not complicated,
The detection resolution is high while having a wide detection range, and it becomes possible to separately detect the positional deviation amounts Δx and Δz in the two-dimensional direction. Further, even if there is an inclination of the optical axis or there is an amplitude in the Z direction, the correction can be performed.
It should be noted that the use of this position shift detection method can also be applied to a vibration detection method or device for measuring the scanning / vibration state of the device or measuring the vibration of a detection object such as a sample.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of diffraction orders of diffracted light when incident on the left side of the optical axis.

FIG. 2 is an explanatory diagram of a diffraction order of diffracted light when the light is incident on the right side of the optical axis.

FIG. 3 shows frequencies f ₁ and f ₂ at incident angles of θ ₁ and θ ₂ with respect to the optical axis.
FIG. 3 is an explanatory diagram showing an example of the configuration of the present invention showing a state of interference diffracted light when two sets of the illumination light are made incident from positions of two-sided inversion symmetry with respect to the optical axis.

FIG. 4 is an explanatory diagram showing a diffracted light heterodyne position and a phase shift direction when right shift incident illumination and left shift incident illumination are performed.

FIG. 5 is a perspective view showing an example of the configuration of an optical system device used for carrying out the method of the present invention.

FIG. 6 is a detailed view of the optical path of the optical system.

FIG. 7 is an explanatory diagram showing an optical heterodyne interference model when illuminating light is incident and a diffraction grating is irradiated with the light by a Fourier transform lens in the present embodiment.

FIG. 8 is an explanatory diagram illustrating the principle of obtaining a parallel light flux using a diffraction grating.

FIG. 9 is a detailed view of an optical system showing the specific configuration thereof.

FIG. 10 is a perspective view when two sets of two light beams that are left-shifted and right-shifted with respect to the optical axis are made into four light beams that are symmetrical in left-right inversion and are incident on the diffraction gratings of the mask and the wafer.

FIG. 11 is an explanatory diagram showing a state of −1st order interference diffracted light in the case of left-right symmetric incident illumination with an incident angle of θ.

FIG. 12 is an explanatory diagram showing a state of −1st order interference diffracted light in the case of left asymmetry in which incident illumination light is shifted to the right with incident angles of θ ₁ and θ ₂ .

FIG. 13 is an explanatory diagram showing a state of −1st order diffracted diffracted light in the case where the incident illumination light is shifted to the left and is asymmetrical to the right when the incident angles are θ ₁ and θ ₂ .

FIG. 14 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) in the case of bilaterally symmetrical incident illumination.

FIG. 15 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) when left-shift incident illumination is performed in the present embodiment.

FIG. 16 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) when right-shift incident illumination is performed in this example.

FIG. 17 is a (−1, 0) (0, −1) order when two sets of two light beams that are left-shifted and right-shifted with respect to the optical axis are incident on the diffraction gratings of the mask and the wafer in a left-right inverted symmetrical manner. FIG. 6 is a perspective view when the interference diffracted light of is obtained.

FIG. 18 is an explanatory diagram showing an optical heterodyne interference model when illuminating light is incident and a diffraction grating is irradiated with the light by a Fourier transform lens in the present embodiment.

FIG. 19 is an explanatory diagram showing a state of interference diffracted light of (−1,0) (0, −1) order in the case of left-right symmetric incident illumination with an incident angle of θ ′.

FIG. 20 shows (−1,0) in the case of left asymmetry in which incident illumination light is shifted to the right with incident angles of θ ₁ ′ and θ ₂ ′.
It is explanatory drawing which shows the state of the interference diffraction light of a (0, -1) order.

FIG. 21 shows (−1,0) in the case of right asymmetry in which incident illumination light is shifted to the left with incident angles θ ₁ ′ and θ ₂ ′.
It is explanatory drawing which shows the state of the interference diffraction light of a (0, -1) order.

FIG. 22 is an explanatory diagram showing an optical path difference between both optical paths when symmetrically incident illumination is performed.

FIG. 23 is an explanatory diagram showing an optical path difference between both optical paths when left-shift incident illumination is performed in this example.

FIG. 24 is an explanatory diagram showing an optical path difference between both optical paths when right-shift incident illumination is performed in this example.

[Explanation of symbols]

 31 Fourier transform lens 32, 50 Diffraction grating 37 4-division detector 70 Pupil plane EP M mask W wafer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 20, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Patent application title: Position shift and gap detection method

[Claims]

[Equation 1]

[Equation 2]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor ultra-fine processing apparatus (proximity exposure apparatus such as SOR aligner / stepper, liquid crystal stepper) and a registration ultra-precision registration measuring superposition accuracy of a pattern exposed on a photosensitive substrate. Position shift using optical heterodyne interference light in measurement etc.
And a gap detection method.

[0002]

2. Description of the Related Art In the ultra-precision alignment of aligners for synchrotron radiation photolithography, photosteppers, etc., it is necessary to accurately detect the positional deviation of two objects to be aligned in the X direction (in-plane direction). Therefore, for that purpose, for example, JP-A-62-261003 and JP-A-64-89323.
Issue, two objects using optical heterodyne interference light
There has been proposed a highly accurate position deviation detection method in the X direction (in-plane direction) . On the other hand, in JP-A-63-38102,
Since the measurement in the Z direction (out-of-plane gap direction) is also performed,
A configuration has been proposed in which an incident light system from the third-order diffraction angle direction is added to the position detection optical system.

[0003] These were taken out from the diffraction grating of the two objects both -1st order, causing interference -1-order diffracted light, detecting the phase difference of the beat signal produced in each of these two objects Since it measures the amount of positional deviation between both objects and does not undergo intensity change due to gap fluctuation , it is expected that the positional deviation detection accuracy and resolution will be dramatically improved.

[0004]

However, in these methods, when the phase shift is more than one cycle, pitch jumping / shifting in alignment occurs, which is inaccurate.
There is a limit to the detection range in which the displacement must be within a certain range in advance. In particular, if the grating pitch of the diffraction grating is reduced, the detection resolution is improved, but the detection range is narrowed, and conversely, if the pitch is increased, the opposite relationship occurs.

Therefore, in order to achieve the improvement of the detection resolution and the expansion of the detection range, which are contradictory to each other by the present applicant,
We proposed a structure in which a plurality of diffraction gratings with different grating pitches are arranged side by side on two objects for detection.

Further, if the light is incident from the direction of the optical axis, the ± 1st order, ± 2nd order, ± 3rd order of the diffracted light obtained (two directions symmetrical about the optical axis) ) From the opposite direction (when the incident direction is referred to as the incident order here by borrowing this diffraction order), the closer the incident order is to 0, the smaller the change amount of the optical path difference becomes. Is wide and the interference of low-order diffracted light is strong, so that a strong diffracted light intensity can be obtained, but the detection resolution is lowered. On the contrary, the farther the incident order is from 0, the opposite of the above case.

[0007] The present applicants have conducted a proposal configuration employing the method of entering orders becomes more and if the absolute value of the next number is large, to compensate for the disadvantages diffracted light intensity decreases, the diffraction Another proposal has been made to increase the intensity of diffracted light by superposing the 0th-order diffracted light on the diffracted light of a specific order by using a specially shaped grating (blazed grating).

However, the first method of arranging a plurality of diffraction gratings having different grating pitches is not practical because it takes time to form such a diffraction grating, and the second proposal in which a plurality of incident orders are provided is as follows. The problem is that the optical system becomes too complicated, and the third proposal using a specially shaped diffraction grating is very difficult to form a diffraction grating with such a shape, and is not practical, in addition to the complicated optical system. A point was pointed out.

Further, it is impossible to measure the displacement in the Z direction unless another incident light system is added as in JP-A-63-38102, and an alignment error in the Z direction caused by the tilt or vibration of the optical axis. There were often problems because the factors could not be corrected sufficiently. Even with the configuration in which the incident light system shown in the same item is added, it is difficult to adjust the wavefront of the two light beams for high-order incidence, and diffracted light of another order (for example, -3rd order diffracted light) is superimposed on the detection signal in the X direction. As a result, the detection accuracy is lowered, the S / N ratio of the detection signal is lowered, and multiple interference is also exerted, which adversely affects the alignment.

The present invention was devised in view of the above problems of the prior art, and does not complicate the configuration and adjustment of the optical system, has a wide detection range and high detection resolution,
In-plane position shift (Δx) is detected and stable during exposure
Provide a method for detecting the position shift and gap that can directly separate and detect the gap (Δz) between two objects, and can correct the gap even when there is an inclination of the optical axis or there is an amplitude in the Z direction. It is something like this.

[0011]

Before describing the structure of the present invention, the diffraction order of the diffracted light obtained from the diffraction grating of the present application will be defined in advance.

FIG. 1 and FIG. 2 show the states of coincidence of the incident angle and the diffraction angle of the reflection diffraction grating. First, when monochromatic light having a frequency f is incident on the reflection diffraction grating 32 having a grating pitch P with an inclination of an incident angle θi from the optical axis, the diffracted light with a diffraction order of m and n = 0 is specularly reflected. Those diffracting to the optical axis side are m, n = -1, -2, -3, and so on. Those diffracting to the minus order or the opposite side are m, n = +1 and +.
2, +3, and so on, plus order (diffraction angles corresponding to these diffraction orders are denoted by θm and θn). The relationship between the incident angle θi and the diffraction angles θm and θn at this time is expressed by the following formulas 3 and 4 according to the basic formula of the diffraction grating.

[0013]

[Equation 3]

[0014]

[Equation 4]

Based on the above definitions, the positional deviation and
The cap detection method will be described. As shown in FIG. 3, the frequencies are slightly different (that is, f ₁ and f ₂ ).
Two monochromatic light groups (that is, a total of four luminous fluxes) are used, and the two luminous fluxes of each of these groups have different incident angles with respect to the optical axis on both sides of the optical axis (that is, θ ₁ and θ ₂ θ ₁ <θ ₂ ) From the asymmetrical direction, and between the pairs, there is a direction of reversal symmetry on both sides of the optical axis (that is, a pair of blank arrows f ₁ and f ₂ and a hatched f ₁ ). (The set of f ₂ is symmetrical with respect to the optical axis in the left-right inversion in the drawing) to each of the diffraction gratings 32a and 32b (these grating pitches are P) of the first object M and the second object W, respectively. Diffracted light that is made incident and has two or more beams of light heterodyne interfered with each other from the positions symmetrical on both sides of the optical axis, and then the X-direction position shift and Z direction of both diffraction gratings 32a and 32b are extracted.
Phase variation amount shown in the following equations 1 and 2 of the optical heterodyne detection signal generated based on the variation amount of the optical path difference due to the gap
From [Delta] [phi _xz and [Delta] [phi _xz 'by calculating two-dimensional phase deviation delta phi _x and delta phi _z respectively separation of X and Z directions by the sum and difference of these two equations, the amount of displacement of both objects M, W The basic feature is to seek. In the figure, the diffraction grade
The objective lens 31 located at the rear focal length F from the child 32
The surface on which the diffraction grating image of the diffraction grating 32 is obtained by
(This surface is the surface on which the Fourier transform image of the diffraction grating 32 was obtained.
So it is also called the Fourier plane). And this pupil EP
Is at the front focal length F of the objective lens 31.

[Equation 1] Δφ _xz = Δφ _x + Δφ _z

[Equation 2] Δφ _xz ′ = Δφ _x −Δφ _z

As in the above-mentioned method of the invention, when two sets of two light beams shifted left and right with respect to the optical axis are made into four light beams having left-right inversion symmetry and are made incident from both sides thereof, it is shown in FIG. 4 (a). As described above, one or more optical heterodyne-interfered diffracted lights obtained from a set in which the light flux of the left side frequency f ₁ and the right side light of the frequency f ₂ are shifted to the right side as a whole are obtained in the state of the left tilt (light When the interfering diffracted light emerges on both sides of the axis, the entire light beam is shifted to the left. On the other hand, as shown in FIG. 7B, the light flux with the frequency f _{1 on} the left side and the light flux with the frequency f ₂ on the right side are totally One or more optical heterodyne interference diffracted light obtained from another set that is shifted to the left is obtained in the state of right tilt (if interference diffracted light appears on both sides of the optical axis, it is shifted to the right as a whole. Will be). In the beat signal detected from the interference diffracted light thus obtained, when both objects M and W have a positional deviation in the X direction, the beat signal derived from the diffracted light with the left tilt and the beat signal derived from the diffracted light with the right tilt In both cases, a phase shift (amount of phase fluctuation) Δφ _x is always generated in a fixed direction with respect to the reference signal, and the gap in the Z direction is
When there is a fluctuation, the beat signal derived from the diffracted light with the left tilt and the beat signal derived from the diffracted light with the right tilt cause a phase shift Δφ _z in the opposite direction with respect to the reference signal. As a result, the phase shift Δφ _xz of the beat signal derived from the diffracted light with the left tilt that is actually detected is obtained as shown in the above equation 1, and the beat signal derived from the diffracted light with the right tilt is obtained. As the phase shift Δφ _xz ′ with respect to the reference signal, the one expressed by the equation 2 is obtained. Therefore, from the sum and difference of both equations, the two-dimensional phase fluctuations Δφ _x and Δ in the X and Z directions are obtained.
It is possible to separately calculate φ _z .

[0019]

EXAMPLES Hereinafter, specific examples of the method of the present invention will be described in detail.

FIG. 5 and FIG. 6 are a perspective view showing an example of the configuration of an optical system device used for carrying out the method of the present invention for detecting the positional deviation and the gap between the mask M and the wafer W, and a detailed view of the optical path of the optical system. is there.

In FIG. 5, first, a monochromatic laser light whose polarization planes are orthogonal to each other from the two-wavelength orthogonal polarization laser light source 12 and whose frequencies are slightly different (f ₁ , f ₂ ) (that is, the frequency f ₁ component is represented by →). P-polarized light, or S-polarized light represented by ↑ for the frequency f ₂ component) is generated. Reference numeral 10 is a controller for the light source 12, which is electrically processed to produce a first REF 11
The reference beat signal having the frequency of | f ₁ −f ₂ | is output from a. The light source 12 may be replaced with a structure in which a frequency shifter including two acousto-optic elements (AOM) is used to obtain a light source having two frequencies.

The alignment light emitted from the light source 12 is normally elliptically polarized at a laser emission port of about 3 to 4%, and this is converted into a two-frequency component by a phase plate (rotation correction optical component) called a λ / 4 plate 13. Correct the orthogonal state of to a more correct posture. Then, the beam of alignment light reaches the polarization beam splitter (PBS) 14, and the S-polarized (f ₂ frequency) component reaches the λ / 2 plate 15 from there. It is incident on the λ / 2 plate 15 from the direction of 45 ° with respect to the crystal axis, and the S-polarized light of frequency f ₂ is rotated 90 ° to be P-polarized light which is the same as f ₁ frequency. The λ
The F ₂ frequency P-polarized light emitted from the / 2 plate 15 has its optical path changed by the mirror 16, and the f ₂ frequency alignment beam can be moved in the Z and X directions in the figure, and can also be tilted or rotated by θ. The optical axis direction is changed by 17 to reach the lens 18.
The lens 18 narrows (collects) the laser beam f ₂ to create a state position where the beam diameter is most narrowed at two positions indicated by the beam waist BW of 24 and 25 in the figure. This is for forming a light flux that crosses in parallel on a field stop AS27, which will be described later, and for configuring a telecentric optical system.

On the other hand, the P-polarized alignment beam of frequency f ₁ transmitted through the polarization beam splitter 14 is reflected by the lens 19
Leading to. Like the lens 18, the lens 19 narrows the laser beam to two beam waists BW 24 and 25. Laser focused by lenses 18 and 19
The incident positions of the beams are adjusted and are made incident on the non-polarization beam splitter NPBS20. On the non-polarizing beam splitter NPBS20, the distance between the beams of the frequencies f ₁ and f ₂ is adjusted by the mirror 17 so that the interference diffracted light of the desired diffraction order (-1, -1) can be obtained later. The incident illumination angle on the diffraction grating 32 by the objective lens 31 which will be described later is determined by the beam interval between the frequencies f ₁ and f _{2 and} is therefore adjusted precisely. The reflection / transmission surface of the non-polarization beam splitter NPBS20 can adjust the wavefronts of the two light beams by tilting and rotating axes, and removes the wavefront aberration so that the wavefronts of the two light beams become the same. Both alignment beams of frequencies f ₁ and f ₂ incident on the non-polarizing beam splitter NPBS20 are branched into two directions together as a parallel light beam.

The two light fluxes of frequencies f ₁ and f ₂ reaching the mirror 21 change the optical axis direction, and the non-polarizing beam splitter NPBS23
Leading to. Similarly, the two light fluxes reaching the mirror 22 change the optical axis direction and are shifted by a predetermined amount by the mirror 22 which can be rotated and tilted in the X and Z directions, and a non-polarized beam splitter NPBS23.
The four light beams (f ₂ f ₂ f ₁ f ₁ ) are arranged above, and are precisely adjusted so as to be symmetrical left and right with respect to the optical axis. If a lateral shift occurs with respect to the optical axis, a non-telecentric state occurs, and a minute shift occurs in the diffraction grating 32 that is the image plane, and the two detection range lengths differ. In the figure, the four light beams emitted to the right of the non-polarizing beam splitter NPBS23 are used for the other axes, but if a cube-shaped beam splitter having two mirror surfaces can be formed, it is desirable to replace them.

The four light beams emitted from the non-polarization beam splitter NPBS23 are arranged symmetrically with respect to the optical axis in the left-right direction and reach the lens 26. The lenses 26, 28, 31, 33 are both telecentric optics and have a field stop AS27.
Image has a conjugate (image forming) relationship for forming an image on the diffraction grating 32 of the mask M and the wafer W. When the image of the field stop AS27 is formed on the diffraction grating 32 by such a telecentric arrangement, the image forming magnification of the image becomes constant even if there is defocus (focal position shift). For example, if there is tilt of the optical system or decentering of the lens,
The Franhofer diffraction image causes alignment errors, but since it is imaged by both telecentric optical systems,
The effect can be further reduced. 4 emitted from the lens 26
The light flux is focused on a field diaphragm AS27 arranged at the focal point of the rear surface of the lens 26 so that the four light fluxes intersect in parallel,
An alignment beam having a field stop diameter is formed and ejected, and becomes four parallel light beams on a pupil plane EP70, which will be described later, at the focal point of the rear surface of the lens 28. The four-beam parallel light is emitted from the lens 28, travels in parallel to the optical axis, is at the front focal point of the objective lens 31, and the Fourier transform image of the diffraction grating 32 is obtained.
It is condensed at P70 and looks like a point light source. Since the arrangement of the four light fluxes on the pupil plane EP70 is inverted by the lenses 26 and 28, the arrangement of the four light fluxes is changed from (f ₂ f ₂ f ₁ f ₁ ) to (f ₁ f ₁
f ₂ f ₂ ) and the reverse position.

The four beams of P-polarized light (→) all pass through the polarization beam splitter PBS29 and reach the λ / 4 plate 30. The four light fluxes that have passed through the λ / 4 plate 30 become counterclockwise circularly polarized light, and travel by expanding the beam diameter as parallel light to the objective lens 31. As shown in FIG. 7, the four light fluxes transmitted through here are
The objective lens 31 makes incident illumination with an outer angle θ ₂ and an inner angle θ ₁ with respect to the optical axis. When such incident illumination is performed, four-beam is arranged in a position of Fb · sin [theta ₂ and Fb · sin [theta ₁ on the pupil plane EP70 respect to the optical axis (Fb is the surface focal length of the objective lens 31 ), The light is incident on the diffraction grating 32 at an angle which is symmetrical with respect to the optical axis.

Furthermore, in this embodiment, the interference diffracted light is received by the following light receiving optical system. Diffracted light obtained by illuminating two sets of two light fluxes is in a state as shown in FIG. That is, since the high-order diffracted light is centered on the specularly reflected light (0th-order light) in the direction opposite to the incident angles θ ₁ and θ ₂ , the pitch P intervals are arranged.
Two sets of two light beams are diffracted without being mixed. In this figure, the diffraction orders (-1, -1) from which the interference beat signal is obtained
(-1, -1) (-3, +1) (-3, +1) (+1,
Only -3) (+1, -3) is specified. Here, the interference diffracted light that detects the beat signal is the above-mentioned six light beams, but this is determined by the effective diameter of the lens 31, and if the lens has a high NA (aperture ratio), the higher order interference diffraction light is used. It is possible to collect light.

Next, a method for isolating the incident illumination light and the interference diffracted light will be described. The obtained diffracted light is diffracted at an angle symmetric with respect to the optical axis, becomes circularly polarized light that rotates in the opposite direction to the circularly polarized light when incident, and is condensed by the objective lens 31. The interference 6 light beams become parallel light, and when passing through the λ / 4 plate 30, the polarization direction becomes S-polarized (↑) (shown by the polarized light ◎ perpendicular to the paper surface in FIG. 6). It is reflected by the separation surface of the beam splitter PBS29. Here, polarizing beam splitter PBS 29 and λ / 4 plate 30
The incident light and diffracted light are completely separated by. The reflected diffracted light whose traveling direction is changed reaches the lens 33 having the front focal length on the pupil plane EP70, and is further imaged at the position of the rear focal length. This position has a conjugate (image forming) relationship with the field stop AS27. Lenses 33 and 34 are afocal magnifying lenses, which magnify and relay the image forming surface on the front surface. This magnified image becomes a Fourier image on the rear surface of the lens 34.

The six light fluxes that have passed through the lens 34 are perforated mirrors.
By (35), only the central (-1, -1) (-1, -1) th order diffracted light passes through and the other light beams are reflected. The two passed light fluxes reach the lens 36, stray light and ambient light are blocked by the slit 38, and reach the four-divided detector 37. On the surface of the four-divided detector 37 is a surface on which the image of the diffraction grating 32 is enlarged and projected,
Here, the beat signals of the wafer W and the mask M are separated and received by the respective detection surfaces. On the other hand, as for the high-order diffracted light reflected by the perforated mirror 35, only the desired diffracted light is taken out by the spatial filter 39, and thereafter, it is received by a lens and a detector (not shown), respectively.

In this embodiment, two beams are used to create four parallel light beams.
Although the non-polarizing splitters NPBS20 and 25 are used, four parallel light fluxes can be created by using the transmitted light of the diffraction grating having the same pitch as the diffraction grating 32 of the mask M and the wafer W. Figure 8 (a)
Is a drawing showing a conventional method for producing parallel 2 light fluxes, and FIG. 7B is a drawing for explaining a method for producing parallel 4 light fluxes using a diffraction grating. In the conventional method, when laser light along the optical axis illuminates the diffraction grating 50, diffracted light is generated on the transmission side. The (51, 0, +1) diffracted light that can be condensed by the lens 51 is extracted, and the spatial filter 52 extracts the 0th order (regular reflection light).
Is cut to create −1st and + 1st order parallel light fluxes.
This configuration is applied to four parallel light fluxes, which illuminate the diffraction grating 50 with two laser light fluxes from different directions with respect to the optical axis.
The respective diffracted lights are arranged at desired intervals, and the parallel light is extracted by the lens 51 as the parallel light by the spatial filter 52 in the same manner to extract the −1st and + 1st order light fluxes.
As an actual configuration, as shown in FIG. 9, two P-polarized laser beams of frequencies f ₁ and f ₂ are made incident on a non-polarized beam splitter NPBS20 through lenses 18 and 19 in a direction orthogonal to each other and are made parallel to each other. A laser beam of frequencies f ₁ and f ₂ after being split into two as a light beam has a beam waist B in the figure.
The aperture is narrowed down at the position of W53, and the interval is set so that desired parallel light can be obtained. Two parallel light beams are formed by the lens 54, and the diffraction grating
The diffracted light on the transmission side obtained by illuminating 50 passes through the lens 51 though it is shown by the shaded line for the frequency f _{1 and} the white line for the frequency f _2. Are converted into parallel light, and the spatial filter 52 cuts the 0th-order light, respectively, and the +1, -1, -1, and + first-order four-beam parallel light is extracted. The diffraction grating 50 is arranged at a position conjugate with the mask M and the wafer W. In the configuration of the above embodiment, the diffraction grating 50 is arranged in the field stop AS27. In another embodiment, a Wollaston prism (P-polarized light, S-polarized light separation / extraction element) may be used to create four parallel light beams.

As shown in this embodiment, two pairs of two light fluxes which are left-shifted and right-shifted with respect to the optical axis are left-right inverted symmetrically.
As a light flux, as shown in FIG. 10, the mask M and the wafer W
When each of the diffraction gratings 32 is illuminated, two (-1, -1) th order diffracted lights are obtained at positions symmetrical to the optical axis for both the mask M and the wafer W (other diffraction orders are omitted in the drawing). Has been). As shown in FIG. 4B, with respect to the incident light that is left-shifted with respect to the optical axis, diffracted light having a right tilt opposite to the incident direction with respect to the optical axis is obtained according to the law of reflection. To be Similarly, for incident light that is shifted to the right with respect to the optical axis, diffracted light that is tilted to the left is obtained as shown in FIG. The reason why the four-beam illumination is performed is to measure the phase change in the two-dimensional direction (X direction, Z direction) at the same time.
The reason why two sets of two light fluxes are incident and illuminated symmetrically with respect to the optical axis is to make the amount of phase fluctuation corresponding to the obtained amount of movement of Δx and Δz the same.

Next, in the present embodiment, it will be described that two (-1, -1) th order diffracted lights are obtained at symmetrical positions with respect to the optical axis. FIG. 7 is a principle explanatory diagram showing an interference model of two wavelengths with incident light to the diffraction grating formed on the wafer W and diffracted light up to (−3rd to + 3rd). As shown in FIG. (F) In the present embodiment, data of the diffraction grating 32
The first-order diffraction efficiency is the best as the duty ratio ( Pa )
A 1: 1 ratio of / P = 1/2 was used. The same figure (c)
The one shown in (d) is from the diffraction grating 32.
F _{1 of} the order that can be condensed by the objective lens 31 up to + 3rd order,
It is the intensity distribution of the m-th and n-th order diffracted light of f ₂ .

First, a set of two light beams (frequency f ₁ and f ₂ ) shifted leftward from the optical axis will be described. The pupil plane EP70 at the front focal length of the objective lens 31 shown in (e) of the figure is a plane on which the Fourier transform image of the diffraction grating 32 is obtained, and this plane serves as a point light source in the optical arrangement of the illumination system. 4 Narrow the light flux. Illumination light (white arrow) having a frequency f ₁ incident at an outer incident angle θ ₂ is incident and illuminated on the diffraction grating 32, and its specularly reflected light (0th order light) is incident on the pupil plane EP70 with respect to the optical axis. And return to the opposite position. With this position as the center, as shown in (R1) of FIG. Similarly, the frequency f ₂ incident at the inner incident angle θ ₁
Illumination light (white arrow) is also incident on the diffraction grating 32 and illuminated.
The specularly reflected light returns to the position opposite to the incident position with respect to the optical axis on the pupil plane EP70 as the specularly reflected light (0th order light), and as shown in (R2) of FIG. As +1 order ~
-3rd order diffracted light is obtained. At this time, the interval between the incident illumination light having the frequency f ₁ (white arrow) and the incident illumination light having the same frequency f ₂ (white arrow) on the pupil plane EP70 is (m = −1, It is set so that the n = −1) th order diffracted light interferes (overlaps). The interference diffracted light of the (-1, -1) th order obtained in such a situation is obtained at the diffracted light position tilted to the right (black solid line arrow) with respect to the optical axis, and is shifted to the right of the optical axis. Other than this, the diffracted light enters the interference state (-3,
It is also in the (+1) th and (+ 1, -3) th positions.

On the other hand, another set of two light fluxes of frequency f ₁ and f ₂ (hatched arrows) is also shifted to the right about the optical axis at the time of the incident illumination, and therefore the above-mentioned center is set about the optical axis. The interference diffracted light is obtained at the position reversed from the case. That is, as shown in (L1, L2) of FIG.
The interference diffracted light of the 1st and -1) th order is obtained at the diffracted light position that is tilted to the left with respect to the optical axis (the hatched arrow) and is shifted to the left of the optical axis on the pupil plane EP70. In addition to this, the diffracted light enters the interference state also at the (-3, +1) th and (+1, -3) th positions.

The interference diffracted light having the left tilt and the right tilt obtained as described above is obtained at a symmetrical position with respect to the optical axis without the interference diffracted lights overlapping with each other, as shown in FIG. In front of the detector 37 or the like for detecting the interference diffracted light, they are separated as shown in FIG.

Next, the principle of separating the phase fluctuation amount in the Δx direction and the phase fluctuation amount in the Δz direction by the sum and difference of predetermined formulas will be described. 11 to 13 show left-right symmetrical incident illumination with an incident angle of θ (Symmetric, FIG. 11).
And the case where the incident illumination light is shifted to the right with the incident angles θ ₁ and θ ₂ (Left, FIG. 12) and the case where the incident illumination light is shifted to the left under the same conditions (Rig
ht, FIG. 13), and −1st order interference diffracted light. At the same time, the phase shift direction of the beat signal with respect to the reference signal when there are minute fluctuation amounts Δx and Δz are also shown in these drawings by a black arrow and a white arrow.

As is clear from these figures, the phase shift directions with respect to the shift in the Δx direction are the same in all three cases. This can be judged from the fact that the change in the optical path length due to the movement is always long for the frequency f ₁ and is always short for the frequency f ₂ as shown in FIGS. 14 to 16 described later. That is, the optical path difference [L] with respect to the illumination light of frequency f ₁ when the illumination light of frequency f ₂ is used as a reference
(1) -L (2)] has a long optical path length of L (1),
Also, since the optical path length of L (2) becomes short, it always becomes positive,
Therefore, the phase shift direction is always the same direction.

On the other hand, in the case of symmetrical incidence of FIG. 11 with respect to the movement of Δz, the variation amounts of the optical path lengths of the incident illumination lights of the frequencies f ₁ and f ₂ are always equal, and the optical path difference [L (1) -L
(2)] becomes 0, and the amplitude intensity changes, but
The phase does not change and no phase shift occurs. This is an advantage that the symmetrical optical arrangement does not affect the variation in the Δz gap direction.

In the case of left asymmetry or right asymmetry, the amount of phase fluctuation associated with each Δz movement occurs in the opposite direction depending on the inclination direction from the optical axis (white arrows → and ←).

The change in optical path length in the above case is
This will be specifically shown in FIGS. 14 to 16. These drawings show that the beam of frequency f _{1 and} the beam of frequency f ₂ are Δx and Δz.
It shows the optical path lengths L (1) and L (2) when moving from the position P to P ′ as the position moves by a minute. In these drawings, the optical path change length of the incident light generated at that time is circle A, circle B.
Also, the change amount of the optical path of the diffracted light is shown by a circle C, and the optical path length is shown by a thick solid line. Of these, the optical path length circle C of the diffracted light is the optical path length generated in the same direction at the frequencies f ₁ and f ₂ , and the optical path difference [L
(1) -L (2)] = (Circle A + Circle C) − (Circle B + Circle C)
= (Circle A−circle B), the circle C does not contribute to the optical path difference and can be excluded from the calculation of the optical path difference. That is, the optical path difference may be considered as the optical path length generated for incident light of frequencies f ₁ and f ₂ .

Therefore, first, let us consider a superposition of _two waves u ₁ and u _{2 which} have substantially equal amplitudes and slightly different frequencies (several tens KHz to several hundred KHz) and which travel in the same direction.

U ₁ and u ₂ are wave forms as shown in the following formulas 5 and 6.
You can write in a formula .

[0043]

[Equation 5]

[0044]

[Equation 6]

The beat frequency (beat) is a repetition frequency of amplitude fluctuation and can be expressed by the following equation (7).

[0046]

[Equation 7]

When the sum of the amplitudes of the two waves u ₁ and u ₂ is squared to obtain the superposition strength of the waves, the following equation 8 is obtained.

[0048]

[Equation 8]

[L (1) / λ ₁ -L (2) /
It can be seen from the λ ₂ ] term that the phase term is delayed or advanced due to the change in the optical path difference [L (1) -L (2)].

In the optical heterodyne alignment method, this phase difference is measured, but this phase difference is ± 18.
Since the angle detection range is fixed within 0 °,
[L (1) / λ ₁ −L (2) / λ ₂ ], the optical path difference [L (1) −L (2)] is the detection range and the phase advance.
It is an item that affects the direction of delay. The _two laser beams of the frequencies f ₁ and f ₂ used have slightly different wavelengths, and the frequency of the beat signal (f ₁ −f ₂ ) is about 2.4 × 10 ⁵ Hz.
Since it is sufficiently smaller than the optical frequency of about 5 × 10 ¹⁴ Hz,
When the high speed is C, the beat frequency Δf is | C / λ ₁ −
Since C / λ ₂ | and Δf << C, the laser wavelength can be set as λ ₁ = λ ₂ ≈λ. Therefore, 2π [L (1) / λ ₁
The term of −L (2) / λ ₂ ] is 2π [L (1) −L (2)] /
can be replaced with λ.

Next, based on FIGS. 14, 15 and 16, the optical path difference [-1st order diffracted light of f ₁ frequency component and −1st order diffracted light of f ₂ frequency component in the optical axis direction in the case of FIG. L (1)-
L (2)].

FIG. 14 is a diagram showing changes in the optical path length of a symmetrically arranged incident light illumination arrangement. Θ shown here is
It is the incident angle when the illumination lights of frequencies f ₁ and f ₂ are incident in the opposite directions from the directions of the ± first-order diffracted light obtained when the illumination light is incident in the optical axis direction. The optical path ellipse A of the incident light on the optical path L (1) having the frequency f ₁ is represented by the following Expression 9.

[0053]

[Equation 9]

Similarly, the optical path length circle B of the incident light on the optical path L (2) of the frequency f ₂ is expressed by the following equation (10).

[0055]

[Equation 10]

Optical path difference [L of light of frequency f ₁ and frequency f ₂
(1) -L (2)] is given by the following equation 11 from the above equations 9 and 10.

[0057]

[Equation 11]

As can be seen from the above equation, in the case of bilaterally symmetric incidence, the incident angles θ are equal to the optical axis, so no optical path difference occurs in the Z direction, and only Δx changes. This is the advantage of the bilaterally symmetrical incidence type.

On the other hand, as shown in FIG. 15 and FIG. 16, when the diffracted light is extracted with the light being left-shifted or right-shifted with respect to the optical axis (rightward or rightward). Asymmetry or left asymmetry), left and right are unbalanced, and as is clear from the fact that the incident angles θ are actually θ ₁ and θ ₂ in the term of (cos θ-cos θ) in the above equation 11, the displacement of Δz becomes The optical path difference also occurs.

FIG. 15 shows the optical path length change (R) of diffracted light to the right due to the left-shift incident light and its optical path difference, and FIG.
Shows the optical path length change (L) of the left tilt diffracted light due to the right-shift incident light and the optical path difference. As aforementioned,
θ ₁ and θ ₂ are the respective incident angles with respect to the incident light with respect to the optical axis, and the inner incident angle θ ₁ <the outer incident angle θ ₂ .

Optical path length circle A'circle A "in both figures is the optical path length of the incident light of frequency f ₁ , circle B'circle B" is the optical path length of the incident light of frequency f ₂ and circle C'circle C "is the frequency f ₁ And the optical path length of the f ₂ diffracted light.
(2)], and the optical path length of the circle C ′ in the diffraction direction can be excluded from the calculation of the optical path difference because the diffraction directions are the same direction. In both figures, the diffraction angle between the diffracted light and the optical axis is Not specified, which means that the optical path difference can be specified by the incident angles of the incident lights of frequencies f ₁ and f ₂ .

Then, when the mask M moves from the position P to the position P ', the optical path lengths L (1) and L (2) for the incident lights of the frequencies f ₁ and f ₂ in FIG. 15 are obtained, respectively.
The following equations 12 and 13 are obtained.

[0063]

[Equation 12]

[0064]

[Equation 13]

From the above two equations, the optical path difference based on the incident light of frequency f ₂ is as shown in the following equation (14).

[0066]

[Equation 14]

The first term on the right side of the above equation is a term relating to Δx, and
The second term is the term relating to Δz, and the second term is the difference of cosθ. Since θ ₁ <θ ₂ , (cos
The term [theta] _1- cos [theta] ₂ ) is positive, so entering-indicates a negative sign. 2π / λ [L of the above equation 8
The term (1) -L (2)] is the phase term (-
180 ° to + 180 °), the phase of Δx and Δz
The fluctuation amount can be expressed as in the following Expression 15, as in Expression 14 above.

[0068]

[Equation 15]

Similarly, in FIG. 16, when the optical path length when moving from P to P ′ is obtained, the following equations 16 and 17 are obtained by exchanging θ ₁ and θ ₂ of the equations 12 and 13. .

[0070]

[Equation 16]

[0071]

[Equation 17]

Therefore, the optical path difference [L (1) -L (2)] based on the optical path L (2) is as shown in the following expression 18.

[0073]

[Equation 18]

When this is represented by the amount of phase change as in the equation 15, the following equation 19 is obtained.

[0075]

[Formula 19]

In this embodiment, since the left-shifted and right-shifted illumination lights are incident at the same time, the phase fluctuation amounts Δ φ _x and Δ φ _z can be calculated from the sum and difference of the above equations (15) and (19).
Can be measured separately.

As described above, the incident angle is θ ₁ = θ ₂ = θ in the case of bilaterally symmetric incidence, and the term relating to Δz in the second item on the right side of the equations 14 and 18 is 0. Also the first on the right side
The item is 2Δx · sin θ. That is, as Δx and Δz move, the optical path length in the X direction becomes longer for the incident light of frequency f ₁ and becomes shorter for the incident light of frequency f ₂ , whereas the optical path length in the Z direction becomes Both f ₁ and f ₂ are long, but the amount of change is the same.

On the other hand, when diffracted light having a right asymmetry and a left asymmetry is obtained by the incidence of the left-shifted and right-shifted illumination light, the asymmetry causes the term relating to Δz in the second term of the equations (14) and (18). (Cos θ ₁ −cos θ ₂ ) is generated in an amount proportional to the gradient difference between θ ₁ and θ ₂ and the incident angle θ ₁
By illuminating two asymmetrical groups of θ and θ ₂ symmetrically with respect to the optical axis, the same amount [(cos θ ₁ − is different in the direction [(cos θ ₁ −cos θ ₂ ))] in the opposite direction. cos
θ ₂ )] can be generated. Also, the first terms of the equations 14 and 18 are (sin θ ₁ + sin
θ ₂ ), which is the same as the traveling direction of Δx regardless of the tilt angle.

At this time, the detection range of Δx is (sin θ ₁ +
Although the amount is proportional to sin θ ₂ ), the detection range for Δz is cos θ ₁ −cos θ ₂ ).
Since the difference is s, it becomes longer than Δx, and on the other hand, the detection resolution decreases.

Although the above-described embodiment utilizes the optical heterodyne interference by the (-1, -1) th order diffracted light,
Similarly, due to the interference in which the detection range lengths of the (-1, 0) th order and the (0, -1) th order are doubled, similarly, an asymmetric set of the incident angles θ ₁ ′ and θ ₂ ′ is ₂ with respect to the optical axis. It is possible to perform incident illumination in a pair symmetry. A description will be given below to another embodiment in which the (-4, 0) -th order and the (0, -1) -th order optical heterodyne interference signals are obtained and the four light fluxes are left-right inverted symmetrically.

As shown in FIGS. 17 and 18, a light beam having a frequency f ₁ (indicated by a white solid line in FIG. 18) is incident at an angle θ ₂ ′ and is positioned at the opposite position (the same position) with respect to the optical axis according to the law of reflection. In the figure, the specularly reflected light returns to the position where the light flux of frequency f ₂ ′ is incident). As for the diffracted light, −3rd to + 3rd order diffracted light is obtained centered on this specularly reflected light, and the intensity distribution is shown in (R1) of FIG. 18D. The other frequency f
The light flux ₂ (white solid line in the figure) is incident and illuminated at an angle θ ₁ ′ smaller than the incident angle θ ₂ ′, and the specularly reflected light is at the opposite position (at the position where the light flux having the frequency f ₁ ′ is incident in the figure). ) Return to. Diffracted light is centered around this specularly reflected light and is −3rd to +3
The next diffracted light is obtained, and its intensity distribution is shown in (R2) of FIG. Therefore, when the diffraction order m of the light flux of frequency f ₁ and the diffraction order n of frequency f ₂ are expressed, the (m = −1, n = 0) order and (m = 0, n = asymmetrical with respect to the optical axis.
-1) The following interference diffracted light is obtained.

Another set of _two light fluxes having the frequencies f ₁ ′ and f ₂ ′ are incident from the positions where the light fluxes having the frequencies f ₁ and f ₂ are diffracted in the opposite direction (thick lines shaded in the figure). Similarly, the diffracted light is obtained centering on the respective specularly reflected light positions.
As shown in the intensity distribution at (L1, L2) in (c), the (m = -1, n = 0) and (m = 0, n = -1) -order interferences are asymmetric with respect to the optical axis. Diffracted light is obtained. Therefore, the interference light in front of the detector is arranged in a straight line and symmetrically arranged with respect to the optical axis without being mixed.

19 to 21 show the case of bilaterally symmetric incident illumination where the incident angle is θ '(S1 / 2, FIG. 19), the incident illumination light is set to the right with incident angles θ ₁ ′ and θ ₂ ′. In the case of left asymmetry shifted (L1 / 2, FIG. 20) and in the case of right asymmetry incident illumination light shifted left under the same conditions (R1 / 2,
21) and (0, −1) -th order interference diffracted light states in FIG. At the same time, the minute variation Δ
The phase shift directions of the beat signal with respect to the reference signal in the case of x and Δz are also shown in these drawings by a black arrow and a white arrow.

As shown in FIG. 19, in the case of bilaterally symmetric incident illumination, the phase does not change even if there is movement in the Z direction. On the other hand, in the case of the left asymmetrical incidence shown in FIG. 20, when there is a movement in the Z direction, the phase advances in the same direction by the same amount. Also in FIG.
In the case of right asymmetrical incidence, as shown in (4), when there is a movement in the Z direction, the phase advances in the opposite direction by the same amount. By utilizing this fact, the phases in the X direction and the Z direction can be separated and measured by the sum and the difference as in the above-mentioned embodiment.

22 to 24, the phase variation amount due to the change in the optical path length and the phase advance and delay directions will be described.

FIG. 22 shows the case of bilaterally symmetric incident illumination. If the position P is moved by Δx, Δz to the position P ′, an optical path difference indicated by a thick solid line is generated. Here, there is a relationship of circle A ₁ = circle A ₂ and circle C ₁ = circle C ₂ because the incident illumination is symmetrical with respect to the optical axis. The incident angle at this time is about half of the diffraction angle θ of the ± first-order diffracted light that would be obtained if the illumination light was incident and illuminated from the optical axis direction. ,
θ / 2. The optical path length in this case can be expressed by the following equations 20 and 21.

[0087]

[Equation 20]

[0088]

[Equation 21]

At this time, the diffraction order of the f ₁ frequency component is m,
When the diffraction order of the f ₂ frequency component is n and two optical path differences of two interference diffracted lights (m = 0, n = −1) and (m = −1, n = 0) are calculated respectively, m = 0, n =-
1) The optical path difference of the next interference diffracted light is given by the following equation 22 (2 in the circle ₂ of C ₂ means round trip), and the equation 20 and the equation 2
From 1, the term of Δz is eliminated as shown in the following equation 23.

[0090]

[Equation 22]

[0091]

[Equation 23]

The optical path difference of the interference diffracted light of the (m = −1, n = 0) order is given by the following equation 24 (2 of 2 circles A ₁ means round trip), which is the same as the above equation 23.

[0093]

[Equation 24]

This means that in the case of left-right symmetry in FIG.
It indicates that the direction of phase change in the direction and the amount of change are the same. Further, since the term of Δz is deleted, there is no phase fluctuation due to Δz.

On the other hand, FIGS. 23 and 24 show the case of left-right asymmetrical incidence. In these drawings, circle A ₁ , circle B ₁ , circle C ₁ , circle A ₂ , circle B ₂ , circle C ₂ , circle A ₁ ′ circle B ₁ ′ circle C ₁ ′ circle A ₂ ′ circle B ₂ ′ circle C ₂ 'refers to an optical path length indicated by the thick solid line, circles a ₁
= Circle A ₁ ′ = Circle A ₂ ′, Circle B ₁ = Circle A ₂ = Circle B ₁ ′, Circle C ₁
= Circle C ₂ = Circle C ₂ ′, Circle B ₂ = Circle C ₁ ′ = Circle B ₂ ′ are divided into four groups. This combination causes an optical path difference. The optical path lengths of these are summarized below, where the inner incident angle is θ ₁ ′ and the outer incident angle is θ ₂ ′ with respect to the optical axis.
The optical path difference is calculated respectively.

[0096]

[Equation 25]

[0097]

[Equation 26]

[0098]

[Equation 27]

[0099]

[Equation 28]

What can be understood from these equations (25) to (28) is that the coefficient of Δz is positive and tends to increase, but there is a combination of increasing or decreasing Δx.

The optical path difference in the case of left asymmetry due to the right-shifted incident light in FIG. 23 is (m = 0, n = -1)
The next optical path difference is the following equation 29, (m = −1, n = 0)
The next optical path difference is given by the following equation (30).

[0102]

[Equation 29]

[0103]

[Equation 30]

When the optical path difference in the case of right asymmetry due to the left shift incident light in FIG. 24 is calculated, (m = 0, n = −
1) The next optical path difference is given by the following equation 31, and (m = −1, n =
0) The next optical path difference is given by the following equation 32.

[0105]

[Equation 31]

[0106]

[Equation 32]

To summarize the above, in the case of right asymmetry due to the left-shift incident light in FIG. 24, the optical path difference is determined by the difference between the optical path circles A ₁ and B ₂ , and the phase shift direction of Δx is the rightward arrow direction (thick solid line). (Arrow), and the phase shift direction of Δz is the opposite direction (white arrow), and the variation amount thereof is the same for both the (0, -1) th order and the (-1, 0) th order. Further, the variation amount of Δx is, as is clear from the above equations 31 and 32,
From the sum of sin of the first term on the right side, the variation amount of Δz can be known from the difference of cos of the second term. On the other hand, in the case of left asymmetry due to the right-shift incident light in FIG. 23, the phase shift direction of Δx is the rightward arrow direction (thick solid arrow) and the same as the phase shift direction of Δz (white arrow). Therefore, by detecting these phases, Δx can be calculated from the sum.
It is possible to detect the phase fluctuation amount in the direction and the phase fluctuation amount in the Δz direction separately from the difference.

[0108]

The position shift and the gap of the present invention described in detail above.
According to-up detection method, construction and adjustment of the optical system does not become complicated, large detection resolution while having a detection range is high, the in-plane positional displacement detection, stably continuously even during exposure
To be able to directly detect the gap between two objects
become. Further, even if there is an inclination of the optical axis or there is an amplitude in the Z direction, the correction can be performed.
By using this position shift and gap detection method, it is possible to apply it to a vibration detection method or device for measuring the scanning / vibration state of the device or measuring the vibration of a detection object such as a sample.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of diffraction orders of diffracted light when incident on the left side of the optical axis.

FIG. 2 is an explanatory diagram of a diffraction order of diffracted light when the light is incident on the right side of the optical axis.

FIG. 3 shows frequencies f ₁ and f ₂ at incident angles of θ ₁ and θ ₂ with respect to the optical axis.
FIG. 3 is an explanatory diagram showing an example of the configuration of the present invention showing a state of interference diffracted light when two sets of the illumination light are made incident from positions of two-sided inversion symmetry with respect to the optical axis.

FIG. 4 is an explanatory diagram showing a diffracted light heterodyne position and a phase shift direction when right shift incident illumination and left shift incident illumination are performed.

FIG. 5 is a perspective view showing an example of the configuration of an optical system device used for carrying out the method of the present invention.

FIG. 6 is a detailed view of the optical path of the optical system.

FIG. 7 is an explanatory diagram showing an optical heterodyne interference model when illuminating light is incident and a diffraction grating is irradiated with the light by a Fourier transform lens in the present embodiment.

FIG. 8 is an explanatory diagram illustrating the principle of obtaining a parallel light flux using a diffraction grating.

FIG. 9 is a detailed view of an optical system showing the specific configuration thereof.

FIG. 10 is a perspective view when two sets of two light beams that are left-shifted and right-shifted with respect to the optical axis are made into four light beams that are symmetrical in left-right inversion and are incident on the diffraction gratings of the mask and the wafer.

FIG. 11 is an explanatory diagram showing a state of −1st order interference diffracted light in the case of left-right symmetric incident illumination with an incident angle of θ.

FIG. 12 is an explanatory diagram showing a state of −1st order interference diffracted light in the case of left asymmetry in which incident illumination light is shifted to the right with incident angles of θ ₁ and θ ₂ .

FIG. 13 is an explanatory diagram showing a state of −1st order diffracted diffracted light in the case where the incident illumination light is shifted to the left and is asymmetrical to the right when the incident angles are θ ₁ and θ ₂ .

FIG. 14 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) in the case of bilaterally symmetrical incident illumination.

FIG. 15 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) when left-shift incident illumination is performed in the present embodiment.

FIG. 16 is an explanatory diagram showing an optical path difference between an optical path L (1) and an optical path L (2) when right-shift incident illumination is performed in this example.

FIG. 17 is a (−1, 0) (0, −1) order when two sets of two light beams that are left-shifted and right-shifted with respect to the optical axis are incident on the diffraction gratings of the mask and the wafer in a left-right inverted symmetrical manner. FIG. 6 is a perspective view when the interference diffracted light of is obtained.

FIG. 18 is an explanatory diagram showing an optical heterodyne interference model when illuminating light is incident and a diffraction grating is irradiated with the light by a Fourier transform lens in the present embodiment.

FIG. 19 is an explanatory diagram showing a state of interference diffracted light of (−1,0) (0, −1) order in the case of left-right symmetric incident illumination with an incident angle of θ ′.

FIG. 20 shows (−1,0) in the case of left asymmetry in which incident illumination light is shifted to the right with incident angles of θ ₁ ′ and θ ₂ ′.
It is explanatory drawing which shows the state of the interference diffraction light of a (0, -1) order.

FIG. 21 shows (−1,0) in the case of right asymmetry in which incident illumination light is shifted to the left with incident angles θ ₁ ′ and θ ₂ ′.
It is explanatory drawing which shows the state of the interference diffraction light of a (0, -1) order.

FIG. 22 is an explanatory diagram showing an optical path difference between both optical paths when symmetrically incident illumination is performed.

FIG. 23 is an explanatory diagram showing an optical path difference between both optical paths when left-shift incident illumination is performed in this example.

FIG. 24 is an explanatory diagram showing an optical path difference between both optical paths when right-shift incident illumination is performed in this example.

[Explanation of symbols] 31 Fourier transform lens 32, 50 Diffraction grating 37 Quadrant detector 70 Pupil plane EP M mask W wafer

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─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 21/027 H01S 3/00 F 8934-4M

Claims (1)

[Claims] 1. Two sets of two monochromatic lights having slightly different frequencies are used, and two light fluxes of each set are generated from asymmetrical directions having different incident angles with respect to the optical axis on both sides of the optical axis. In addition, between these sets, these two sets of light fluxes are made incident on the diffraction gratings of the first object and the second object, respectively, from the directions in which they are inversion symmetry on both sides of the optical axis, and the two sides of the optical axis are symmetrical on both sides. Diffracted light of two or more beams caused by optical heterodyne interference is extracted from any position, and the following equations (1) and (2) are used for the optical heterodyne detection signal generated based on the optical path difference fluctuation amount due to the X-direction position shift and the Z-direction position shift of both diffraction gratings. Phase φ _xz shown in
And φ _xz ′, the two-dimensional phase fluctuation amounts φ _x and φ _z in the X direction and the Z direction are separately calculated from the sum and difference of these two equations, respectively, to detect the positional deviation. [Equation 1] φ _xz = φ _x + φ _z [ _Equation 2] φ _xz ′ = φ _x −φ _z