JP3106490B2 - Positioning apparatus and exposure apparatus having the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for aligning a substrate on which a diffraction grating is formed, and particularly to a semiconductor exposure apparatus (stepper,
This is suitable for an alignment device used for an aligner or the like.

[Conventional technology]

In recent years, as a device for transferring a fine pattern such as a semiconductor element onto a semiconductor wafer with high resolution, a projection type exposure device,
So-called steppers have been used frequently. In particular, recently, it has been required to increase the density of LSIs manufactured thereby, and it is necessary to transfer a finer pattern onto a wafer. To cope with this, higher-precision alignment is indispensable.

Therefore, many diffraction grating interference type alignment devices have been proposed as higher resolution alignment sensors.

There are several types of diffraction grating interference type alignment sensors, but typically, Japanese Patent Application Laid-Open Nos. 59-192917, 60-67932, or 62-56722. And the two-beam homodyne interference method disclosed in JP-A-61-187615, JP-A-62-56818, JP-A-63-283129, or JP-A-2-116116. A two-beam heterodyne interference system as disclosed is known.

In either method, the diffraction grating formed on the substrate (semiconductor wafer or mask) is irradiated with a laser beam or the like from two directions to form one-dimensional interference fringes on the diffraction grating. In the heterodyne method, a certain frequency difference (usually 1 MHz or less) is given to beams from two directions, and interference fringes are run at high speed in the pitch direction.

In the two-beam homodyne method, the intensity of interference light (for example, interference light generated when ± 1st-order diffracted light travels in the same direction) from the diffraction grating that changes when the diffraction grating and the interference fringe are mechanically moved in the pitch direction. The light beam itself corresponds to the displacement of the diffraction grating. On the other hand, in the two-beam heterodyne system, since the intensity of the interference light from the diffraction grating always changes with the frequency difference (beat frequency), the photoelectric signal is an AC signal that changes in a sinusoidal manner at the beat frequency. Therefore, in the heterodyne method, a signal (reference signal) of a beat frequency serving as a reference is prepared in advance, and a phase difference between the signal and a measurement signal (beat frequency) generated by receiving the interference light from the diffraction grating is obtained. The displacement of the diffraction grating is detected.

FIG. 2 is a perspective view showing a basic configuration of a conventionally known diffraction grating interference type alignment sensor.
The two parallel laser beams LB ₁ and LB ₂ are inclined by angles −θ _FS and θ _{FS with} respect to the optical axis AXa of the alignment system, and intersect on the illumination field stop FS. A rectangular aperture AP is formed in the stop FS, and the two beams L ₁ and L ₂ that have passed through the aperture AP pass through the lens system 3.
a, the mirror MR, the beam splitter BS, and the lens system 3b intersect again on the one-dimensional diffraction grating (mark) WM on the substrate 4. The composite system of the lens systems 3a and 3b functions as an imaging optical system for forming an image of the aperture AP of the stop FS on the substrate 4, and a pupil plane (Fourier plane) EP exists between the lens systems 3a and 3b. I do.

The principal rays of the _two beams L ₁ and L ₂ irradiating the substrate 4 are symmetrically inclined with respect to the optical axis AXa in the XZ plane in FIG. Therefore, in the pupil plane EP, the two beams L ₁ and L ₂
Spots SP ₁ and SP ₂ symmetrically separated in the X direction across AXa
Focus on

According to such a configuration, a plurality of interference fringes arranged at a constant pitch in the X direction are formed on the diffraction grating WM of the substrate 4 by the interference of the beams L ₁ and L ₂ . Therefore, the pitch direction of the diffraction grating WM is set to the X direction, and the pitch Pf of the interference fringes and the diffraction grating WM
When the intersection angle 2θ _FS of the original beams LB ₁ and LB ₂ is set so that the pitch Pg of the light beam becomes 2Pf = Pg, the diffraction grating WM
Then, an interference light BTL of ± 1st-order diffracted light is generated in parallel with the optical axis AXa. This interference light BTL is transmitted through the lens 3b and the beam splitter BS.
The light is received by a photoelectric detector (photomultiplier, photodiode, etc.) PD via the. Here, the photoelectric detector PD is arranged on the pupil plane (Fourier plane) to receive the spot light of the interference light BTL.

In the homodyne method, since the interference fringes formed on the substrate 4 are stationary, the substrate 4 is slightly moved in the X direction. With this fine movement, the level of the photoelectric signal from the detector PD changes sinusoidally. In the heterodyne method, since there is a frequency difference Δf between the beams LB ₁ and LB ₂ , even if the substrate 4 is not moved,
The photoelectric signal becomes an AC signal having a frequency Δf.

Therefore, in the homodyne method, if the substrate 4 is slightly moved so that the level of the photoelectric signal becomes a predetermined value, the alignment of the diffraction grating 4 in the X direction with reference to the interference fringes is completed. On the other hand, in the case of the heterodyne method, the phase difference (± 180 °) between the reference signal serving as a reference (alternating current having a frequency Δf) and the photoelectric signal of the detector PD is obtained, whereby the diffraction grating WM in the X direction from the reference position is obtained. The amount of deviation is obtained in the range of ± 1/4 Pg.

[Problems to be solved by the invention]

In the above-mentioned prior art, the diffraction grating WM is also one-dimensional because it is premised on one-dimensional alignment exclusively.
When performing two-dimensional displacement detection at the same point above,
The diffraction grating WM is a two-dimensional grating and has two beams L ₁ and L
₂ (or LB ₁ , LB ₂ ) may be rotated around the optical axis AXa by 90 degrees from the case of FIG.

However, the same applies to the case of a one-dimensional diffraction grating.
In the case of a two-dimensional diffraction grating, the overall shape is generally substantially square (or rectangular). Therefore, the aperture AP of the illumination field stop FS also becomes square (or rectangular). This aperture FS
Limits the illumination field on the substrate 4 of the _two beams L ₁ and L ₂ ,
It has a function of preventing unnecessary irradiation of a pattern (a part of a circuit pattern or the like) other than the diffraction grating WM. That is, it prevents light reflected from patterns other than the diffraction grating WM (particularly, diffraction and scattered light) from entering the detector PD as noise light in advance.

However, it has been found that the diffracted light generated by the field stop FS has an adverse effect on the detection accuracy. Therefore,
In order to facilitate the following description, the effect of the field stop FS will be described with reference to FIG. 3 which shows the system of FIG. 2 in a simplified manner.

As shown by the solid line in FIG. 3, the coherent parallel beams LB ₁ and LB ₂ having different frequencies irradiate the rectangular diaphragm FS from two directions having a predetermined incident angle θ _FS, and then the lens system 3a
Beam spots on the pupil plane EP (Fourier plane)
The light is collected as SP ₁ and SP ₂ .

Thereafter, the two beams pass through the lens system 3b and irradiate the illumination area of the diffraction grating (hereinafter referred to as a mark) WM formed on the substrate 4 from two directions having a predetermined incident angle ± θ _WM .

Here, it is assumed that the incident angle ± θ _WM is set so that ± first-order diffracted light is generated in the direction of the normal line (optical axis) of the mark WM.

However, in practice, when the field stop FS having the rectangular aperture AP is irradiated with beams LB ₁ and LB ₂ having different frequencies from two directions having a predetermined intersection angle (± θ _FS ), the rectangular stop FS Diffracted light is generated at the edge of.

Since the two beams LB ₁ and LB ₂ incident on the rectangular stop FS can be handled as plane waves, the pupil plane EP of the lens systems 3a and 3b can be analyzed as a Fraunhofer diffraction.

The distribution of the Fraunhofer diffracted light on the pupil plane EP is determined by the incident angle θ _{FS of} the _two beams LB ₁ and LB ₂ with respect to the stop _FS , the wavelength λ, and the directionality of the edge of the aperture AP.

As shown in FIG. 2, the edges of two opposite sides of the aperture AP are aligned with the direction of the line formed by the plane including both the principal rays of the _two beams LB ₁ and LB ₂ intersecting the plane of the stop FS. When orthogonal,
A part of the franfofer diffraction light generated at this edge is
There is a problem that the quality of the two beams irradiating the substrate 4 (particularly, the frequency uniformity of each beam) is deteriorated.
Therefore, the Fraunhofer diffraction caused by the aperture AP of the stop FS will be described with reference to FIG.

Qualitatively, as shown in FIG. 4, a lens system 3a, the 3b of the pupil plane EP (Fourier plane), and the diffraction intensity distribution DF ₁ by the beam LB ₁ shown by a solid line, the diffraction intensity of the beam LB ₂ shown by a broken line It formed a distribution DF ₂ Hitomi Toga center O symmetrically.

Here, especially, the diffracted light that has a bad influence on the detection accuracy will be described.

As shown, the beam LB ₁ intensity I _O to form a beam spot at the position of SP ₁ of the pupil plane EP, the beam L having an intensity I _N
While diffracted light B ₂ is mixed, the beam LB ₂ intensity I _O to form a beam spot at the position of SP ₂ of the pupil plane EP, the diffracted light beam LB ₁ having an intensity I _N is mixed.

From this fact, in the FIG. 3 described above, as shown by the broken line, the noise diffracted beam l generated by the beam LB ₁ frequency f ₁
b ₁ is, in order to advance the same optical path and the beam LB ₂ frequency f _2, the beam LB ₂ will be irradiated a mark WM at an incident angle of - [theta] _WM while beat by noise light lb _1.

On the other hand, the mark in a state noise diffracted light lb ₂ generated by the beam LB ₂ of frequency f ₂ also, in order to advance the same optical path and the beam LB ₁ frequency f _1, the beam LB ₁ is obtained by beat by noise light lb ₂ WM is irradiated at an incident angle of + θ _WM .

FIG. 5 shows how diffracted light is generated from the mark WM under the above conditions. As shown in FIG. 5, the -1st-order diffracted light LB ₂ of the beam LB ₂ extends in the direction of the normal (optical axis) of the mark WM. (-
With 1) and the -1st-order diffracted light lb ₁ noise diffracted light lb ₁ and (-1) is generated, the beam LB ₁ +1 order diffracted light LB ₁ (+
1) and the + 1st-order diffracted light lb ₂ (+1) of the noise diffracted light lb ₂ is generated.

Further, in FIG. 4 just described, it can be seen that the diffracted light of each beam LB ₁ and LB ₂ is also mixed in the center O of the pupil position of the lens systems 3a and 3b. For this reason, in FIG. 3, the noise diffracted light beams lb ₁ ′ and lb ₂ ′ of the beams LB ₁ and LB ₂ by the field stop FS having a rectangular opening progress on the optical axis in a beat state, The mark WM is irradiated vertically. Then
As shown in FIG. 5, zero-order diffracted light beams lb ₁ (0) ′ and lb ₂ (0) ′ are generated in the normal direction of the mark WM.

As described above, the detector PD provided on the pupil plane EP (or a position conjugate with the pupil plane) detects all the light generated in the normal direction (optical axis direction) of the mark WM as the interference light BT. If noise diffracted light is included in the light, the detected interference beat signal will include a large error (phase error).

In the above description, the mark WM is diffracted as a one-dimensional diffraction grating, but even when a two-dimensional diffraction grating is used,
The effect of the Franchoff diffraction due to the aperture AP of the aperture FS can be exactly the same.

Therefore, the present invention solves the above-mentioned problems, and prevents the diffracted light generated by the illumination field stop from adversely affecting the position detection accuracy of the diffraction grating, and enables highly accurate and stable alignment at all times. It is an object of the present invention to provide a positioning device which is provided.

[Means for solving the problem]

The present invention provides a light source that emits coherent light or quasi-monochromatic light, an illumination optical system for irradiating light from the light source onto a two-dimensional diffraction grating formed on a substrate to be aligned, and the two-dimensional light source. A detection optical system for detecting a plurality of diffracted lights generated from the diffraction grating, and a photodetector that receives a specific diffracted light of the plurality of diffracted lights via the detection optical system and that corresponds to the intensity of the specific diffracted light A photoelectric detector that outputs a signal; and a device that two-dimensionally positions the substrate based on the photoelectric signal. The feature is that the illumination field stop defined by the opening edge inclined with respect to any of the two pitch directions of the two-dimensional diffraction grating is positioned at a position substantially conjugate with the substrate in the illumination optical system. It has been established in.

Further, the present invention provides a method for manufacturing a substrate, comprising: a one-dimensional first diffraction grating having a pitch in a predetermined first direction; and a one-dimensional second diffraction grating having a pitch in a second direction different from the first direction. A beam irradiation means for irradiating a parallel beam of coherent light or quasi-monochromatic light from a light source, and a detection optical system for detecting the first diffraction grating or the diffraction light generated from the second diffraction grating by irradiating the parallel beam, A photoelectric detector that receives the diffracted light through the detection optical system and outputs a photoelectric signal corresponding to the intensity of the diffracted light, and moves the substrate in the first direction and the second direction based on the photoelectric signal. Alignment device for at least one of the directions.

The feature is that the beam irradiating means intersects the light from the light source at a predetermined angle on the substrate and on the conjugate plane with the irradiation optical system for forming a plane conjugate with the substrate. A two-beam forming means for converting the two parallel beams into two parallel beams to be guided to the irradiation optical system; and arranged on the conjugate plane and defined by edges inclined in both the first direction and the second direction. An illumination field stop having an aperture is provided, and further between the light source and the illumination field stop,
A switching means is provided for selectively switching the direction of an intersecting line formed between the surface including the two beams from the two light beam forming means and the substrate between the first direction and the second direction.

[Action]

As shown in FIG. 5, marked by the irradiation of the beam LB ₁ W
The amplitude of the + _1st-order diffracted light LB ₁ (+1) generated in the normal direction of M is A ₁ , and the amplitude of the -1st-order diffracted light LB ₂ (-1) generated in the normal direction of the mark WM by the irradiation of the beam LB ₂ is A ₂ , beam LB ₂
-1st-order diffracted light lb ₁ (−) generated in the normal direction of the mark WM by irradiation of the noise light diffracted light lb ₁ traveling on the same optical path as
The amplitude of 1) is b ₁ , and the amplitude of the + _1st- order diffracted light lb ₂ (+1) generated in the normal direction of the mark WM by irradiation of the noise diffracted light lb ₂ traveling on the same optical path as the beam LB ₁ is b ₂ . When
The optical beat signal _SWM photoelectrically detected by the detector is given by the following equation.

S _WM = A ₁ cos (ω ₁ t + φ ₁ ) + A ₂ cos (ω ₂ t + φ ₂ ) + b ₁ cos (ω ₁ t + δ ₁ ) + b ₂ cos (ω ₂ t + δ ₂ )
(1) Since the signal detected by the detector is a time average of the intensity (square of the amplitude), the detected signal intensity when Δω = ω ₁ −ω ₂ is as follows.

Now, assuming that the pitch of the mark WM is Pg, for example, when the substrate is displaced by Δx in the X direction, the corresponding phase change amount is: Becomes

Therefore, to make the explanation easier, A ₁ = A ₂ ≡A,
Assuming that b ₁ = b ₂ ≡b and all initial phases other than the phase difference due to the movement of the wafer are zero, the equation (2) is given by the following equation. As can be seen from the equation (3), the optical beat signal observed by the detector is only the second and third terms on the right side of the equation (3), and the second term depends on the displacement of the substrate in the X direction. Only the phase changes, and the third term is a noise component that is completely unrelated to the displacement of the substrate in the X direction.

Therefore, the optical beat signal S observed by the detector
_The phase difference between the _{WM and} the reference signal is expressed by the second value on the right side of the equation (3).
It can be understood that the difference is detected as a difference from the combined wavelength of the term and the third term.

Here, a change α in phase due to a displacement Δx in the X direction of the substrate
Can be expressed by the following equation.

Due to the adverse effect of the error component term of the third term in the equation (3), the actually detected phase difference becomes α _P as shown in the vector diagram of FIG. 6, and the phase error is maximized. The time is when α = π / 2.

In this case, if A ² + b ² >> 2Ab,
The phase error amount α _e (= α−α _P ) is Can be approximated.

Further, assuming that A >> b, this equation (5) becomes: Can be approximated.

As described above, in the actual alignment, the relative phase difference between the reference signal and the light beam signal _SWM obtained by the detection is detected in accordance with the displacement amount of the substrate. It can be understood that the error has a great effect on the detection accuracy.

Here, the phase error alpha _e, when the pitch of the diffraction grating mark WM formed on the substrate and Pg, pitch Pf is because Pg / 2 of the interference fringes formed on the mark, position error X _e of the substrate
Is Becomes

As an example, if the pitch of the mark WM is 8 μm and the required position error detection resolution of the substrate is 0.02 μm or less,
From (4) in the above equation, Becomes

In this case, the intensity ratio of the noise diffracted lights lb ₁ and lb ₂ generated by the existence of the rectangular aperture FS to the beams LB ₁ and LB ₂ satisfies the following condition from b / A = α _e / 2 of the equation (6). There is a need.

Therefore, the amplitude of the noise diffracted light actually mixed into each of the beams LB ₁ and LB ₂ is obtained on the pupil plane EP (Fourier plane) of the lens system. On this pupil plane, as described above, since it can be analyzed as a Fraunhofer diffraction, the sine value of the exit angle of the diffracted light generated from the field stop FS is defined as ξ, and this ξ is defined as the pupil plane (Fourier plane). ), The amplitude distribution of each diffracted light on the pupil plane is given by the following equation.

However, the amplitude of the diffracted light is b, the amplitude of the plane wave incident on the field stop FS is A _o , and the wavelengths of the beams LB ₁ and LB ₂ are λ (strictly, the wavelengths are different, but the frequency difference is 1 MHz or less. It can be said that they are practically the same when thinking with
Beam spot SP from center O of pupil plane (point intersecting with optical axis)
₁ , the distance to SP ₂ is ± ξ ₀ (= sin ± θ _FS = ± λ / 2
P _FS ), the incident angles of the beams LB ₁ and LB ₂ irradiating the field stop FS are ± θ _FS , and the pitch of the interference fringes formed on the field stop is P
_FS , sin 0/0 = 1.

Figure 7 is (9) is obtained by actually graphed equation diffraction amplitude of FIG. 7 (a) is generated in the FS stop irradiation of the beam LB ₂ in the lens system 3a, 3b of the pupil plane EP shows a distribution diagram the 7 (b) shows the lens system 3a, 3b diffraction amplitude distribution generated by the FS stop by irradiation of the light beam LB ₁ at the pupil plane EP of. It can be seen that these two figures are supported by the diffraction intensity distribution shown in FIG.

For example, in the pupil plane EP, as shown in FIG.
The amplitude b of the noise diffracted light beam lb ₂ at the beam spot position SP ₁ (ξ = + ξ ₀ ) of the beam LB ₁ or FIG. 7B
As shown, the beam spot position SP ₂ of the beam LB ₂ (ξ =
When the magnitude of the amplitude b of the noise diffracted light lb ₁ at −ξ ₀ ) is obtained, the expression (9) is as follows.

As an example, the pitch of interference fringes formed on the field stop
_Assuming that P _FS is 4 μm and the width w of the rectangular aperture is 50 μm, the expression (10) becomes: Which is larger than the value of b / A ₀ ≦ 0.016 in the equation (8) described above.

That is, in this case, in the configuration in which the rectangular field stop FS is applied, due to the effect of diffraction from the stop FS, 0.02
It can be seen that it is difficult to ensure the accuracy (position error detection resolution) of μm or less.

The amplitude b of another noise light that travels from the rectangular aperture FS in the optical axis direction and passes through the center O (ξ = 0) of the pupil plane EP is
From equation (9), If the width w of the field stop and the pitch P _{FS of the} interference fringes formed on the field stop are the same as the values described above, Is larger than the condition value 0.016 of the expression (8) described above, and as a result, it is difficult to perform high-precision alignment.

Based on the above analysis, in the present invention, the extremum point on the distribution of the Franchoffer diffraction that appears due to the presence of the illumination field stop on the pupil plane of the system matches the pupil passing position of the original beam for mark illumination. The direction of the aperture edge was determined so as not to generate noise light.

Although the above analysis was performed for the heterodyne method, even in the homodyne method, the diffracted light generated at the aperture may have an adverse effect as noise light, and the error due to the noise light may be quantitatively determined by the same analysis method. it can.

〔Example〕

1 (a) and 1 (b) show a configuration of a positioning apparatus according to a first embodiment of the present invention, and FIG. 1 (a) shows an example in which the positioning apparatus is incorporated in a projection type exposure apparatus (such as a stepper). The projection lens PL projects the circuit pattern of the reticle (mask) onto the shot area 4a on the wafer, as shown in FIG. 1 (a).
Here, illustration of the reticle is omitted. Projection lens
A pupil plane (Fourier plane) ep also exists inside the PL. The optical axis AXa of the alignment optical system is provided so as to pass off the axis of the projection lens PL. The basic configuration of the optical system for positioning is the same as that of the conventional one (FIG. 2), but here, the lens system 3b is particularly called an objective lens, and the lens system 3a is located between the lens system 3a and the objective lens 3b. It is assumed that a position conjugate with the pupil ep of the projection lens PL is created, and the position substantially coincides with the pupil plane EP of the positioning optical system.

In the present embodiment, a two-dimensional diffraction grating is used as the mark WM on the wafer. In FIG. 1 (a), the mark WM is X
It is assumed that a periodic structure (pitch) is provided in two directions, a direction and a Y direction.

In FIG. 1A, the two beams LB ₁ and LB ₂ are inclined on a wafer in a plane parallel to the XZ plane through the aperture AP of the stop FS, and the position of the mark WM in the X direction. Misalignment is detected.

The optical axis AXa of the alignment optical system is set so as to pass at least through the center of the pupil ep of the image-side telecentric projection lens PL, whereby two beams are formed on the image side (wafer side) of the projection lens PL. Symmetry center line of LB ₁ and LB ₂ (optical axis AX
a) becomes parallel to the optical axis AX of the projection lens PL. That is,
The telecentricity of the illumination beam is compensated. The aperture FS is
The lens system 3a and the objective lens 3b are conjugate with the spatial position Pr below the mirror MR, and are also conjugate with the wafer surface via the projection lens PL. In this embodiment, the four edges of the aperture AP of the field stop FS provided at the intersection (image conjugate plane) of the _two beams LB ₁ and LB ₂ are aligned in the X direction on the wafer.
They were arranged so as not to be parallel to any of the Y directions. The meaning will be described later in detail.

FIG. 1B shows a configuration of a two-beam forming means for generating _two beams LB ₁ and LB ₂ toward the stop FS in FIG. 1A. Laser light source not shown (He-Ne, Ar ion, He-Cd
Etc.) (or their second harmonic) LB
Is separated into two by the beam splitter BS _1, One beam is reflected by the mirror Mr _1, incident on the AOM (acousto-optic modulator) 10a driven by the high-frequency signal of the frequency f _1. The other beam from beam splitter BS ₁ has frequency f
AOM 10b is driven by the high frequency signal of ₂ . AOM
10a outputs the first-order diffraction beams LB ₁ only high frequency f ₁ with respect to the original frequency f ₀ of the beam LB, the beam LB ₁ is 0
The light passes through the next light cut filter 11a and enters the lens 12a.

AOM10b outputs first-order diffraction beams LB ₂ of high frequency by f ₂ for the frequency f ₀ of the beam LB, the beam LB ₂ is incident on the lens 12b passes through the 0-order light cut filter 11b.

The beams LB ₁ and LB ₂ before being incident on the lenses 12a and 12b are both parallel beams.

Now, the beam LB _{1 that} has passed through the lens 12a becomes a converged light beam and is incident on the beam splitter BS ₂ for synthesis.
The beam LB ₂ that has passed through the after being reflected by the mirror Mr ₂ becomes convergent light beam is incident on the beam splitter BS _2. The beam splitter BS ₂ is to synthesize such that the two principal rays of beams LB _1, LB ₂ in parallel to each other, and at predetermined intervals. Two beams LB _1, LB ₂ that has been synthesized by the beam splitter BS ₂ is amplitude divided further by the beam splitter BS _3. Two beams L reflected by beam splitter BS ₃
B ₁ and LB ₂ enter the beam splitter BS ₄ via the mirror Mr ₃ without being interrupted by the shutter SHx. The two beams LB ₁ and LB ₂ transmitted through the beam splitter BS ₃ are blocked by the shutter SHy. The shutters SHx and SHy are selectively switched. When the shutter SHx is open, the beams LB ₁ and LB ₂ are oriented so as to detect the displacement of the mark WM on the wafer in the X direction. When is open, the beams LB ₁ and LB ₂ are oriented so as to detect a displacement in the Y direction. When the shutter SHy is open, the two beams LB ₁ and LB ₂ are reflected by the mirror Mr ₃ and then incident on the image rotator IRT, where the two beams L
After B ₁ and LB ₂ are rotated by 90 ° around the optical axis,
It enters the beam splitter BS _4. The two beams LB ₁ and LB ₂ from the mirror Mr ₄ are parallel in the XY plane in the figure, and one of the two beams is amplitude-divided by the beam splitter BS ₄ via the lens 13. They intersect on the stop FS in FIG. Beam splitter BS ₄ from two beams that have missing upward lens 13, crossing over reference grid 15 of the transmission through the mirror Mr _5. After lens 13 and lens 14, 2
Both the main beams LB ₁ and LB ₂ are parallel light beams.

Therefore, one-dimensional interference fringes flow on the reference grating 15 at a speed corresponding to the frequency difference (f ₁ −f ₂ = Δf) due to interference between the two beams.

The photoelectric detector PD ₂ generates +1 generated vertically from the reference grid 15
Order diffracted light (frequency f ₀ + f ₁ ) and −1 order diffracted light (frequency f ₀ +
f ₂ ), and receives a reference beat signal Bref. Reference signal from the detector PD ₂ is the frequency difference Delta] f (f
_1- f ₂ ), which is used for detecting a phase difference with the signal from the photoelectric detector PD _{1 in} FIG. 1 (a).

FIG. 8A shows a mark WM formed on a wafer.
In this figure, square minute lattice elements (convex or concave) are regularly arranged in the X and Y directions at a duty of 50%. The mark WM is formed in a scribe line area (about 50 to 100 μm in width) that divides the shot area 4a on the wafer.

FIG. 8B shows a planar arrangement relationship between the shape of the aperture AP of the field stop FS and the mark WM, and in this embodiment, the stop FS
The opening AP is a square, and is rotated by an angle θ about the optical axis AXa with respect to the outer shape of the mark WM in the XY plane (plane perpendicular to the optical axis AXa).

That is, four edges e ₁ , e ₂ ,
Each of e ₃ and e ₄ defines four sides (X
(Parallel to either the axis or the Y-axis).

When the edge of the stop FS is inclined by θ with respect to the X and Y axes in this manner, the diffraction light distribution due to the aperture AP formed on the pupil plane ep of the projection lens PL is as shown in FIGS. 9 (a) and 9 (b). become.
9 (a) and 9 (b) show the pupil plane ep viewed obliquely, the origin 0 is the pupil center (intersection with the optical axis AX), and the coordinate system ξ−η
Is defined by the sine value of the exit angle corresponding to the X and Y directions of the diffracted light from the stop FS.

FIG. 9A shows that two beams LB ₁ and LB ₂ are X (ξ).
Shows the diffracted light intensity distribution when set for direction measurement,
FIG. 9 (b) shows the diffracted light intensity distribution when set for Y (η) direction measurement.

Since the principle is the same in the X direction and the Y direction, the following description will be made only with reference to the case of the X direction measurement in FIG. 9A.

In FIG. 9A, the spot positions SP ₁ , SP ₂ of the _two beams LB ₁ , LB _{2 formed} on the pupil plane ep are symmetrically located about the point 0 on the ξ axis. Accordingly, the coordinate values of the spot positions SP ₁ and SP ₂ are (ξ ₀ , 0) and (−
ξ ₀ , 0).

Diffracted light distribution D generated at stop FS by irradiation of beam LB ₁
F ₁ is spread while repeating some of the maximum value toward the peripheral takes a maximum value at the position SP _1. Diffracted light distribution DF ₁
The spread is mainly along each of the lx ₁ axis and the ly ₁ axis. Axis lx
₁ and ly ₁ are orthogonal to each other in the ξ-η plane with the point SP ₁ as the origin, but each of the ξ axis and the η axis corresponds to the inclination angle of the diaphragm FS in the ξ-η plane. And tilted by θ.

Distribution of the diffracted light along the axis lx ₁ was caused by the edge e _1, e ₂ of the stop FS shown in Figure No. 8 (b), axial ly
The distribution of the diffracted light along ₁ is caused by the edges e ₃ and e ₄ of the stop FS.

Diffracted light emitted by the stop FS by the irradiation of the beam LB ₂ distribution DF ₂
For also the distribution characteristics are identical to the diffracted light distribution DF _1, distributed in two dimensions along the axis lx _2, ly ₂ around the position SP _2. The axes lx ₂ and ly ₂ are also inclined by θ with respect to the axes ξ and η, respectively.

Here, FIG. 10 shows the diffraction light intensity distribution of FIG. 9 (a) in a plan view. In FIG. 10, the black circles indicated by SP ₁ and SP ₂ represent the spots of the beams LB ₁ and LB ₂ (maximum values in the diffracted light distributions DF ₁ and DF ₂ ), respectively. This represents the maximum value in the light distributions DF ₁ and DF ₂ .

9 and 10, a plane conjugate with the pupil plane ep of the projection lens PL (or a plane conjugate with the wafer).
In order to reduce the influence of the noise light reaching the detector PD ₁ arranged at the position, when the beams LB ₁ and LB ₂ are transmitted to the mark WM, the maximum value in the diffracted light distribution generated on the pupil plane ep by the aperture FS is reduced. ,
Two beam spot positions SP ₁ , SP ₂ and pupil center point O
What is necessary is just to determine the inclination angle θ of the edge of the aperture FS so as to deviate from the above.

Therefore, how to determine the inclination angle of the edge of the aperture FS will be described below.

FIG. 11 is a generalized representation of the aperture shape of the stop FP shown in FIG. 8 (b). The opposing edges e ₁ and e ₂ are parallel to each other and have an interval a ₂ , and the edges e ₁ and e A line perpendicular to ₂ (ly ₁ , l
The inclination between y ₂ ) and the Y axis is denoted by φ. Similarly, opposing edges e ₃ and e ₄ are parallel to each other and have an interval a _1, and edges e ₃ and e ₄
And the inclination between the line (lx ₁ , lx ₂ ) perpendicular to the X axis and the X axis. In the example shown in FIG. 8 (b), a ₁ = a ₂ , φ = ψ = θ
It is.

The amplitude distribution u generated on the pupil plane when the _two beams LB ₁ and LB ₂ are incident on the stop FS at an angle of ± θ _FS from the vertical is represented by the axis ly ₁ (FIG. 11). ly ₂ ) and axis lx
Oblique coordinate system with ₁ (lx ₂ ) as the coordinate axis Is represented by the following equation.

Oblique coordinate system Is associated with the orthogonal coordinate system ξη (XY) as follows.

Note that k in the equation (12) is k = 2π / λ, and since the pitch of the diffraction grating WM on the wafer is Pg, sin θ
_FS = λ / Pg (provided that the projection magnification is 1).

By the way, there are two factors regarding the entry of noise light due to the aperture of the field stop FS as described with reference to FIG. Therefore, description will be made again with reference to FIG.
In FIG. 12, consider _one light transmission beam LB1.
When this beam LB ₁ passes through the aperture of the stop FS, the noise light component lb ₁ passing through the same optical path as the other light transmission beam and the noise light component lb ₁ ′ toward the center of the pupil EP are obtained by the Frann-Fore diffraction. Occurs.

Among noise light lb ₁ is diffracted by the grating WM on the wafer 4, returns to the center of the pupil EP becomes first-order diffracted light N (lb _1). Since the noise light lb ₁ ′ is perpendicularly incident on the grating WM on the wafer 4, its zero-order diffracted light (specular reflection light) N (l
b ₁ ) returns to the center of the pupil EP. Therefore, in addition to the first-order diffracted light BTL as signal light generated vertically from the grating WM, the noise light N (l
b ₁ ) and N (lb ₁ ′) are mixed and photoelectrically detected.

Therefore, the respective amplitude reflectances of the 0th-order light and the 1st-order light in the grating WM are defined as r ₀ and r _1, and the amplitude distribution on the pupil plane of the franfofa diffraction light traveling toward the wafer 4 through the pupil EP is represented by u (ξ , Η), the amplitude of the signal light BTL on the pupil Is represented by the following equation.

Furthermore, the combined amplitude of the two noise lights N (lb ₁ ) and N (lb ₁ ′) on the pupil Is represented by the following equation.

The amplitude of these signal components And the amplitude of the noise component Is actually measured as a vector-like sum, and this is the amount of error when measuring the phase difference. FIG. 13 shows this state, which means substantially the same as FIG. As shown in FIG. 13, the phase difference corresponding to the displacement of the grating WM actually measured from the result of the photoelectric detection is φm, and the true phase difference is φt.

Therefore the noise component The error amount Δ on the phase difference due to the above is included. So the noise component Assuming the condition that the error amount Δ due to And noise components Are orthogonal to each other, the error amount Δ becomes maximum. From this, the phase measurement error amount Δ is expressed by the following equation.

On the other hand, assuming that the allowable error amount at the time of alignment (measurement of the position of the lattice mark) is ε, it is necessary that 2kε sin θ _FS > Δ (17).

From the above equation (16), assuming that Δ is sufficiently small, Equation (17) can be approximated by

Actually, as shown in FIG. 12, there is not one light transmitting beam, but another symmetrical light transmitting beam LB ₂ exists simultaneously as shown in FIG. Therefore, the amplitudes of the noise light components lb ₂ and lb ₂ ′ due to the beam LB _{2 on} the pupil plane are N (lb ₂ ) and N (l
b ₂ ′), the amplitude Ψ of light (light that is photoelectrically detected) appearing at the center of the pupil is expressed by the following equation.

In this equation (19), E ₁ is the amplitude of the beam LB ₁ and E ₂ is the beam LB ₂
, W ₁ and w ₂ are the angular frequencies of beams LB ₁ and LB ₂ , respectively.
Is a complex number.

When this equation (19) is converted into the intensity I, it is expressed as equation (20).

Where r ₁ E ₁ + r ₀ N (lb ₁ ′) + r ₁ N (lb ₁ ) = A ₁ r ₂ E ₂ + r ₀ N (lb ₂ ′) + r ₁ N (lb ₂ ′) = A ₂ r ₀ N _{(lb 1 ') + r 1} N (lb 1) = N 1 r 0 N (lb 2') + r 1 N (lb 2) = is the N _2.

Here, r ₁ ^* , E ₁ ^* , E ₂ ^* , N ₁ ^* , and N ₂ ^* represent conjugate complex numbers.

In this equation (20), if the noise light components N ₁ and N ₂ are ignored because they are sufficiently small with respect to the signal light components E ₁ and E ₂ , the error amount tanΔ is calculated according to the same concept as in the above expression (16). It is in the relationship of the expression

Here, for the sake of simplicity, assuming that the intensity of the _two transmitted light beams LB ₁ and LB ₂ is equal and the intensity of each diffracted light is symmetric, E ₁ = E ₂ = E, N (lb ₁ ′) = N (lb ₂ ') = No N
(Lb ₁ ) = N (lb ₂ ) = Nd, and the equation (21) can be exchanged as follows.

From the fact that there is a relationship of the above equations (16) and (18) and the amplitude distribution u (ｕ, η) on the pupil plane, No, N in the equation (22)
Since d and E can be specified, Holds.

Here, the amplitude distribution u (ξ, η) of the pupil plane in the orthogonal coordinate system ξη (XY) can be exchanged as in the following equation based on the above equations (12) and (13).

Thus, the amplitude distribution u (0,0) at the center of the pupil and the amplitude distribution u (sin θ at the position where the _two light transmission beams LB ₁ and LB ₂ pass.
_FS , 0) and u (−sin θ _FS , 0) are obtained as follows.

Therefore, equation (23) can be summarized as follows.

From the above equation (25), the relationship between the angle 成 formed with the X (ξ) axis of the line l _x1 (l _x2 ) orthogonal to the edges e ₃ and e _{4 of} the aperture FS and the edge intervals a ₁ and a ₂ is It is given as in equation (26).

This equation is an analysis in the case of measurement in the X direction in which the _two beams LB ₁ and LB ₂ are inclined and incident on a plane including the XZ axis and perpendicular to the plane of the stop FS. An analysis at the time of measurement is also possible. In this case, the amplitude distribution u (sin θ _FS , 0), u (−sin θ _FS ,
0) are u (0, sin θ _FS ) and u (0, −sin θ
_FS ). Therefore, u (0, sin θ _FS ), u (0,
−sin θ _FS ) is given by equation (24). And this equation may be substituted into equation (23). However, as in equation (25), the term of sin in the numerator of the fraction that appears during the calculation process is treated as 1 (worst value).

In this way, when the conditional expression in the case of measuring in the Y direction is derived,
Basically, similarly to the above equation (26), the edge e _{1 of the} aperture FS,
Angle φ of line ly ₁ (ly ₂ ) orthogonal to e ₂ with respect to η (Y) axis
And a relational expression between the edge spacing a ₁ , a _2, etc. of the aperture of the stop FS.

By the way, in the above analysis, the pupil EP of the projection lens PL
Expression (19) or (20) representing the amplitude of the interference beat light BTL received by the photoelectric sensor conjugate with the mark WM on the wafer 4
Was not considered. So again the twelfth
With reference to the drawings, an analysis in which the positional deviation amount Δx of the mark WM is considered will be described. Here, two light transmission beams LB ₁ and LB ₂
Are simultaneously incident on the lens systems 3a and 3b (see FIG. 12), the intensity distribution on the pupil of each diffracted light from the pupil plane EP toward the wafer 4 is represented by two beams LB ₁ , Assuming that the intensities of LB ₂ are equal, u ₁ (sin θ _FS , 0) = u ₂ (−sin θ _FS , 0) = U (0) u ₁ (0, 0) = u ₂ (0, 0) = U (1) u ₁ (−sin θ _FS , 0) = u ₂ (sin θ _FS , 0) = U (2)

The intensity I (absolute value) of light diffracted by the mark WM on the wafer 4 and photoelectrically detected is obtained by the following equation.

Here r (0), r (-1 ), r (1) represents the zero order light, -1 order light, reflectance to each of the + 1-order light of the mark WM, theta _WM is two beams LB ₁ , LB _{2 on} the wafer 4. Assuming that the diffraction efficiencies are the same, the beat frequency component photoelectrically detected includes the signal components generated by the beams LB ₁ and LB ₂ and the beams lb ₁ ′ and LB ₂ or the beam lb ₂ ′.
And LB ₁ or beam lb ₁ and LB ₂ or beam l
obtained as the synthesis of a noise component caused by contamination of the b ₂ and LB _1.

In the above equation (27), the intensity distributions U (0), U
Substituting each of (1) and U (2) and summing up, the intensity of the signal component Is Intensity of noise component due to mixing of beam lb ₁ ′ and LB ₂ or beam lb ₂ ′ and LB ₁ Is And the intensity of the noise component due to the mixing of the beams lb ₁ and LB ₂ or the beams lb ₂ and LB ₁ Is It is expressed as

Actually, other minute components also enter as noise light, but the amount is extremely small and can be ignored in practical use.

The noise component in the above equation (29) has a sensitivity that the phase difference measured for one pitch shift of the wafer mark WM changes exactly one cycle (360 °), and changes in proportion to the positional shift amount Δx. The noise component of the above equation (30) is a component that is not related to the displacement of the mark WM. Equation (28)
Has a sensitivity such that the phase difference changes by two periods (720 °) with respect to a shift of one pitch of the mark WM.

From the above equations (29) and (30), equations (29) and (30) are set such that the sum of the amplitudes of the noise components is smaller than the preset alignment tolerance (ε) or the phase difference measurement tolerance.
Medium amplitude terms, 4r (1) r (0) U (0) U (1) and 4r (1) ² U
(0) intensity distributions U (0), U that determine the value of U (2)
After obtaining (1) and U (2), similar to the previous analysis,
The inclination angle of each edge of the stop FS that satisfies the intensity distribution may be obtained.

As is clear from the above embodiment, the noise light component generated from the diffraction grating mark WM and mixed into the measurement light received by the photoelectric detector due to the influence of the franfoa diffraction generated at the aperture of the field stop FS is aligned. , The accuracy of the position measurement of the lattice mark WM can be improved.

FIG. 14 is a view showing an example of an aperture shape of a field stop FS according to another embodiment of the present invention. FIG. 14 (A) shows that all four sides are 45 with respect to the measurement directions X and Y of the two-dimensional diffraction grating mark WM.
This is a square opening AP arranged at ゜. FIG. 14 (B) shows a rhombic opening AP in which the diagonal line is aligned with the measurement directions X and Y of the mark WM. FIG. 14 (C) shows a rectangular (rectangular) opening AP rotated by a predetermined amount, and FIG. 14 (D) shows that none of the two opposing edges of the four edges are parallel and Each side shows an unequal leg trapezoidal opening in which none of the sides is parallel to the measurement directions X and Y. FIG. 14 (E) shows an opening in which the overall shape is a square, but the portion corresponding to each side is stepped with minute edges extending in a direction intersecting the X and Y directions.

FIG. 14 (F) shows a circular opening containing the mark WM,
FIG. 14 (G) shows an elliptical aperture. In the circular aperture and the elliptical aperture, the inclination of the edge continuously changes, and an annular interference fringe is generated. Therefore, it is necessary to determine the diameter of the aperture AP so that the light intensity diffracted toward the center of the pupil becomes zero. In the case of a circular aperture, this is a value of the diameter at which the Bessel function becomes zero. Each of the aperture shapes shown in FIGS. 14A to 14G can be used as it is not only for the two-dimensional mark WM but also for the case where the one-dimensional diffraction grating is symmetric.

Further, in the above embodiment, a two-dimensional diffraction grating mark whose measurement direction is orthogonal is considered, but the present invention can be similarly applied to a case where a grating mark whose measurement direction is not orthogonal is detected.

In FIG. 1 (b) of the further embodiment, the X direction and the Y direction are shown.
Switching between the _two beams LB ₁ and LB ₂ for the direction is performed by two AOs.
The shutters SHx and SHy after M10a and 10b were used, but after splitting the beam from the laser light source into two, two AOMs for measuring the X direction were provided for one optical path, and the other optical path was used. , Two AOMs for measurement in the Y direction are provided. In the measurement in the X direction, the high-frequency drive signal to the two AOMs for the Y direction is cut off. The drive signal may be cut off. Only the zero-order light is emitted from the AOM from which the drive signal has been cut off, and the zero-order light is emitted from the slit 11 in FIG. 1 (b).
All are blocked at a and 11b. Therefore, two X direction
Two beams from the AOM and two from the AOM for the Y direction
Alternatively, the beam is synthesized at the position of the beam splitter BS4 in FIG. 1 (b). When using four AOMs like this, an image rotator as shown in Fig. 1 (b)
IRT and shutter SHx, SHy are unnecessary. Also 4 AOMs
Is used, a method may be adopted in which beam incidence on two AOMs for the X direction and beam incidence on two AOMs for the Y direction are selectively switched. At this time, switching may be performed by a mechanical shutter, but a combination of an acousto-optic deflector (AOD) 100 and an apex mirror 102 as shown in FIG. 15 (a), or as shown in FIG. 15 (b) A combination of a deflection beam splitter (PBS) 104 and a rotatable half-wave plate 106 can be similarly switched.

FIG. 16 shows a configuration in which the present invention is applied to a TTR (through-the-reticle) type alignment system. Two beams
After LB ₁ and LB ₂ are reflected by the mirror MR, the irradiation field stop FS
Cross on In the case of FIG. 16, it is assumed that the beams LB ₁ and LB ₂ are inclined in a plane perpendicular to the sheet of FIG. The two beams LB ₁ and LB ₂ that have passed through the stop FS pass through an optical element (tilted parallel flat glass or the like) 120 that corrects astigmatism or coma caused by differences in color (wavelength) with the projection lens PL. Incident on the Fourier transform lens 122. Lens 122 has two beams
The principal rays of LB ₁ and LB ₂ are made parallel, and the beams LB ₁ and L
The B ₂ to converge as a spot in the pupil plane (Fourier plane). The beam is further incident on a telecentric objective lens 126 via a beam splitter 124 and a mirror 127
And irradiates the mark (diffraction grating shape) RM on the reticle R.

Here, since the projection lens PL is telecentric on both sides, the optical axis of the objective lens 126 is parallel to the optical axis AX of the projection lens PL on both the reticle R side and the wafer W side.

The two parallel beams LB ₁ and LB ₂ passing through the transparent window around the mark RM on the reticle R pass through positions symmetrical with respect to the center of the pupil EP of the projection lens PL, and are again reflected by the mark WM on the wafer W. They intersect as parallel beams.

Interference beat light (measurement light) generated vertically from mark WM
After the BTL passes through the center of the pupil EP of the projection lens PL, the transparent portion around the mark RM of the reticle R, the mirror 127, the objective lens 12
6, and return to the light receiving system 130 via the beam splitter 124. The light receiving system 130 simultaneously operates the mark RM on the reticle R.
And the reflected diffracted light from The drive control system 132 controls the hardware 128 for holding the objective lens 126 and the mirror 127 integrally.
Change the alignment position in the image field of the projection lens PL by moving it to the dimension (change the position of the mark RM)
It corresponds to. Further, the drive control system 132
There is a drive motor for finely moving S in the optical axis direction of the objective lens 126 or tilting the S in an arbitrary direction with respect to the optical axis. Here, the hardware 128 moves in the optical axis direction of the objective lens 126, and thus corresponds to the marks RM existing at different image height positions in the image field of the projection lens PL. When the position of the mark RM must be changed two-dimensionally, the entire alignment system including the hardware 128,
Alternatively, a part may be moved in a direction perpendicular to the optical axis of the objective lens 126 in the XY plane. By the way, the way of inserting the _two beams LB ₁ and LB _{2 in} FIG. 16 is to detect the grid mark WM for measuring the X direction on the wafer W and the grid mark RM for measuring the X direction on the reticle R. It corresponds to that. Therefore, the pitch direction of the marks WM and RM is a direction perpendicular to the paper surface of FIG.

Further, since the beams LB ₁ and LB ₂ have wavelengths (for example, 633 nm of a He-Ne laser) far apart from the wavelength of illumination light (436 nm, 356 nm, 284 nm, or the like) used for projection exposure, various chromatic aberrations (axial Upper chromatic aberration, lateral chromatic aberration, color-based coma, astigmatism, etc.) occur. Of these, due to the influence of axial chromatic aberration, when trying to cross the _two beams LB ₁ and LB ₂ at the mark WM on the wafer W, it may not be possible to cross the reticle R any longer.

FIG. 17 shows this state, and at the wavelength of the _two beams LB ₁ and LB ₂ , there is a plane IMP conjugate with the wafer W at a distance ΔZC above the reticle R. In this case, ΔZC is called an axial chromatic aberration amount, and may be several + mm or more depending on the projection lens. Therefore, the two parallel beams LB ₁ and LB ₂ emitted from the objective lens 126 are set to intersect at the plane IMP. Then, the two beams pass on the reticle R while being separated from each other (or partially overlapped), but the projection lens
When the light reaches the wafer W via the PL, it crosses exactly on the mark WM. Therefore, the illumination field stop FS is the surface IM
What is necessary is just to arrange in conjugate with P.

Now, when two beams are separated on the reticle R,
As shown in Fig. 17, the reticle grating mark RM is
₁ and LB ₂ are provided separately at the location where they pass. These two marks
The pitch directions of the RMs are both the Y direction, and the continuity of the pitch is maintained. At the center of the two marks RM, a transparent portion for passing the interference beat light BTL from the wafer mark WM is provided, and the interference beat light BTL is received by a pupil conjugate photoelectric detector in the light receiving system 130. .

On the other hand, the zero-order light beam LB ₁ from the reticle mark RM (regular reflected light) but 1-order diffracted light LB ₁₁ with LB ₁₀ occurs, marked as the primary light LB ₁₁ returns the same optical path and the beam LB ₁ The pitch of the RM is determined. Similarly, from the mark RM 0 order light LB ₂₀ with 1-order diffracted light LB ₂₁ of beam LB ₂ is generated so as to reverse the optical path of the beam LB _2. After these primary lights (beams) LB ₁₁ and LB ₂₁ intersect once at the plane IMP, the light receiving system 130 passes through the objective lens 126 and the beam splitter 124.
Incident on. In the light receiving system 130, a lens system to create a surface IMP plane conjugate, are provided and the reticle reference grating of the transmission type disposed in the conjugate plane, the two beams LB _11, LB ₂₁ reticle reference grid The interference beat light (even though ± 1st-order diffracted light becomes coaxial and interferes) generated by irradiating the light is received by the photoelectric detector. The photoelectric signal (alternating current of beat frequency Δf) from the photoelectric detector and the interference beat light from the mark WM
The phase difference between the signal from the photoelectric detector receiving the BTL (AC of Δf) corresponds to the amount of displacement between the reticle R and the wafer W. Now, in such a configuration, when a reticle having a different size of the circuit pattern area on the reticle R is mounted, the position of the mark RM naturally changes, so that the hardware 128 moves so that the mark RM can be detected. At this time, if curvature of field or the like occurs due to significant aberrations due to the wavelengths of the beams LB ₁ and LB ₂ , the conjugate plane of the stop FS is shifted from the wafer surface before and after moving the hardware 128, that is, The aperture image of the aperture FS is blurred on the wafer W.
Therefore, the drive control system 132 stores the amount of field curvature corresponding to each alignment position in the image field of the projection lens PL as a map in advance, and finely moves the diaphragm FS in the optical axis direction in conjunction with the movement of the hardware 128. . When the amount of astigmatism, coma, or the like changes in accordance with the change in the alignment position, the optical element 120 may be moved and appropriately adjusted.

As described above, in each embodiment of the present invention, it is assumed that a two-dimensional diffraction grating mark is used. However, the one-dimensional grating mark for X-direction measurement and the one-dimensional grating mark for Y-direction measurement are adjacent to each other (or (At a fixed distance), and each of these two one-dimensional grid marks is
Even when the two beams LB ₁ and LB ₂ are switched between the X direction and the Y direction through a single objective optical system, exactly the same effects as those of the present invention can be obtained.

Further, the measurement direction by the diffraction grating mark does not necessarily need to be orthogonal to each axis direction of the orthogonal coordinate system XY, and may be inclined at an arbitrary angle. Further, the present invention can be similarly implemented even in a homodyne system in which no frequency difference is given to the _two light transmission beams LB ₁ and LB ₂ .

〔The invention's effect〕

As described above, according to the present invention, when measuring the alignment mark position two-dimensionally, the noise light component mixed into the measurement light from the mark due to the influence of the diffracted light generated by the field stop provided in the mark illumination system. Since it can be suppressed to almost zero, there is an effect that the measurement accuracy of the mark position is enhanced.

Further, by using a two-dimensional diffraction grating mark as shown in the embodiment, the mark area occupied on the wafer surface can be halved. Furthermore, since the mark detection system is configured to enable two-dimensional measurement, throughput is high and one-dimensional lattice marks can be used as they are, so wafers with different mark forms (one-dimensional or two-dimensional) can be used as they are. There is also an advantage that it can be processed.

[Brief description of the drawings]

1 (a) and 1 (b) are perspective views showing the configuration of an alignment device according to an embodiment of the present invention, FIG. 2 is a perspective view showing the configuration of a conventional device, and FIG. 3 is an illumination field stop. FIG. 4 is a diagram illustrating an example of the intensity distribution of the Fraunhofer diffracted light on the pupil plane of the system, FIG. 5 is a diagram illustrating the mixing of noise light, and FIG. FIG. 7 (a) and FIG. 7 (b) are diagrams showing the intensity of the Fraunhofer diffraction on the pupil plane, and FIGS. 8 (a) and 8 (b) are diagrams of the present invention. FIGS. 9 (a) and 9 (b) are plan views showing the shape of a two-dimensional diffraction grating mark and the shape of an illumination field stop based on the first embodiment, and FIGS. 9 (a) and 9 (b) are generated by the field stop according to the first embodiment. FIG. 10 is a perspective view showing the intensity distribution on the pupil plane of the Fraunhofer diffraction, FIG. 10 is a plan view showing the state of FIG. 9 (a) on the pupil plane, and FIG. FIG. 12 is a diagram showing a general shape for analyzing the planar shape of the illumination field stop, FIG. 12 is a diagram showing a system for analyzing noise light mixing caused by one beam passing through the aperture opening, FIG. 13 is a vector diagram for explaining an error caused by noise, and FIGS.
(G) is a plan view showing another opening shape of the illumination field stop, and FIG.
FIGS. 15 (a) and 15 (b) show another example of a beam switching method for switching the measurement direction, and FIGS. 16 and 17 show projection exposure of the positioning apparatus according to the second embodiment of the present invention. It is a figure showing the composition at the time of applying to an apparatus. BRIEF DESCRIPTION OF REFERENCE NUMERALS] LB _1, LB ₂ ...... laser beam, FS ...... illumination field stop, AP ...... opening, PL ...... projection lens, WM ...... 2-dimensional solutions Kaisetsuko mark.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kazuya Ota 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nikon Oi Works Co., Ltd. (56) References JP-A-3-9204 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H01L 21/027

Claims (16)

(57) [Claims] An illumination optical system for irradiating a light from the light source onto a two-dimensional diffraction grating formed on a substrate to be aligned; and a plurality of diffracted lights generated from the two-dimensional diffraction grating. And a photoelectric detector that receives a specific diffracted light of the plurality of diffracted lights via the detection optical system and outputs a photoelectric signal corresponding to the intensity of the specific diffracted light; An apparatus for two-dimensionally aligning the substrate based on the photoelectric signal, comprising: a field stop having an opening edge inclined with respect to any of two pitch directions of the two-dimensional diffraction grating; An alignment device, wherein the alignment device is arranged at a substantially conjugate position. 2. An illumination optical system comprising: a telecentric objective lens system; and a light source for converting light from the light source into two beams which are substantially parallel to an optical axis and pass symmetrically at a pupil plane of the objective lens system. And a two-beam unit for intersecting the two beams at a predetermined angle on the two-dimensional diffraction grating via the objective lens system; and the field stop comprises an optical path of the two-beam unit. 2. The device according to claim 1, wherein the device is provided at a position substantially conjugate with the two-dimensional diffraction grating. 3. The apparatus according to claim 2, wherein said two beam forming means gives a frequency difference between said two beams. 4. The apparatus according to claim 2, wherein said two beams by said two beam forming means have the same frequency. 5. When the two pitch directions of the two-dimensional diffraction grating are x and y directions orthogonal to each other, all the aperture edges of the four sides of the field stop are set in both the x and y directions. 5. The device according to claim 1, wherein the device comprises at least one of an inclined rectangular opening, a parallelogram opening and a trapezoidal opening. 6. The inclination of the aperture edge of the field stop is:
5. The device according to claim 1, wherein the device changes continuously. 7. The apparatus according to claim 6, wherein said field stop has a circular aperture or an elliptical aperture. 8. A substrate on which a one-dimensional first diffraction grating having a pitch in a predetermined first direction and a one-dimensional second diffraction grating having a pitch in a second direction different from the first direction are formed. Beam irradiation means for irradiating a parallel beam from a light source; a detection optical system for detecting diffracted light generated from the first diffraction grating or the second diffraction grating by irradiating the parallel beam; A photoelectric detector that receives the diffracted light and outputs a photoelectric signal according to the intensity of the diffracted light; and wherein the substrate is positioned with respect to at least one of the first direction and the second direction based on the photoelectric signal. In the apparatus for matching, the beam irradiation means includes: an irradiation optical system for forming a plane conjugate with the substrate; and two light beams intersecting light from the light source at a predetermined angle on the substrate and on the conjugate plane. To a parallel beam And an illumination field stop disposed on the conjugate plane and having an aperture defined by an edge inclined with respect to both the first direction and the second direction. Having, further disposed between the light source and the illumination field stop,
A position provided with switching means for selectively switching the direction of an intersecting line formed by the substrate and the plane including the two beams from the two light beam generating means between the first direction and the second direction. Matching device. 9. An exposure apparatus for transferring a pattern on a reticle onto a wafer, wherein the aligning apparatus according to claim 1, detects at least one of the positions of the reticle and the wafer. An exposure apparatus comprising: 10. An exposure illumination means for illuminating said reticle with a predetermined wavelength, wherein a wavelength of light from said light source is different from a wavelength of said exposure illumination means. An apparatus according to claim 1. 11. The apparatus according to claim 11, wherein said reticle and said wafer are
11. A projection optical system for forming an image of the pattern on the reticle is arranged.
An apparatus according to claim 1. 12. A two-dimensional diffraction grating formed on a substrate to be aligned, which is irradiated with light from a light source, and receives a specific diffraction light of a plurality of diffraction lights generated from the two-dimensional diffraction grating; Outputting a photoelectric signal according to the intensity of the specific diffracted light,
A method of two-dimensionally aligning the substrate based on the photoelectric signal, comprising: an opening edge disposed at a position substantially conjugate with the substrate and inclined with respect to any of two pitch directions of the two-dimensional diffraction grating. And outputting the photoelectric signal based on light passing through a field stop having the following. 13. Assuming that two pitch directions of the two-dimensional diffraction grating are x and y directions orthogonal to each other, all four opening edges of the field stop are in any of the x and y directions. At least one of an inclined rectangular opening, a parallelogram opening, and a trapezoidal opening
13. The method of claim 12, wherein: 14. The method of claim 12, wherein the slope of the aperture edge of the field stop changes continuously. 15. The method of claim 14, wherein said field stop has a circular or elliptical aperture. 16. An exposure method for transferring a pattern on a reticle onto a wafer, wherein the position of at least one of the reticle and the wafer is detected by using the alignment method according to any one of claims 12 to 15. An exposure method, comprising the step of: