JP2001267211A - Position detecting method and apparatus, and exposure method and apparatus using the position detecting method - Google Patents

Abstract

(57) [Problem] To reduce a position detection error due to asymmetry of a diffraction grating mark, and perform positioning of a test object with high accuracy. SOLUTION: Two light beams L03 and L30 having different frequencies are incident on a diffraction grating mark WM formed on a wafer at a predetermined incident angle, and ± 3rd-order diffraction light generated from the diffraction grating mark WM is photoelectrically detected. Detected by the detector 33. Next, two beams L04 and L40 having different frequencies from each other are made incident on the diffraction grating mark WM at a predetermined angle of incidence different from the incidence angles of the two light beams L03 and L30, and ± 4 generated from the diffraction grating mark. Next-order diffracted light is detected by the photoelectric detector 33. Based on the beat signal obtained by detecting the ± 3rd-order diffracted light and the beat signal obtained by detecting the ± 4th-order diffracted light, the detection error due to the asymmetry of the sectional shape of the diffraction grating mark WM is corrected, and the position of the wafer is corrected. Perform alignment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterodyne interference type position detecting method and position detecting apparatus, and more particularly to a photodetector for manufacturing a semiconductor device, a liquid crystal display device, an image pickup device (such as a CCD), or a thin film magnetic head. It is suitable for use in an alignment system of an exposure apparatus used for exposing a mask pattern on a photosensitive substrate in a lithography process.

[0002]

2. Description of the Related Art In order to form a fine pattern of a semiconductor device or the like, a pattern of a reticle (or a photomask or the like) as a mask is transferred onto a wafer (or a glass plate or the like) as a photosensitive substrate via a projection optical system. An exposure apparatus such as a projection exposure apparatus such as a stepper or a proximity type exposure apparatus for directly transferring a reticle pattern onto a wafer is used. For example, since a semiconductor element is formed by stacking a large number of circuit patterns on a wafer in a predetermined positional relationship, when a circuit pattern is transferred to the second and subsequent layers on the wafer, each of the previously formed circuit patterns is formed. It is necessary to perform high-accuracy alignment (alignment) between the circuit pattern in the shot area and the reticle pattern to be transferred from now on.

[0003] Conventionally, a diffraction grating mark (alignment mark) provided on a reticle and a wafer has been conventionally used to position the reticle and the wafer with high accuracy.
LIA (Laser Interferometric Alig) that irradiates two position detection lights from two directions in two directions and measures the position of the mark from the phase of the interference light obtained from the two generated diffraction lights.
nment) type alignment devices have been used.

[0004] This LIA type alignment apparatus includes:
A method of irradiating position detection light from the ± N-order direction with respect to the periodic direction of the mark grating and receiving the generated interference light (a composite light beam of ± N-order diffracted light of both incident lights: N is a natural number)
This is referred to as “± N-order light detection method”. ) And position detection light from the ± N / 2-order directions with respect to the period direction of the mark lattice, and the 0th-order light of one incident light (first incident light) and the other incident light (second incident light). A method of independently receiving a combined light beam of the N-th order diffracted light of the second incident light and the N-th order diffracted light of the first incident light (hereinafter, “0-N”). Next light detection method ").

[0005] The LIA type alignment apparatus is
It is roughly classified into a homodyne system in which the frequencies of the two position detection lights are the same and a heterodyne system in which the two position detection lights have a certain frequency difference. As the light detection system, both of the heterodyne system and the homodyne system can be used.

[0006]

As described above, in the conventional exposure apparatus, an alignment apparatus such as an LIA method has been used to align the reticle and the wafer with high accuracy. However, the alignment mark is formed with a small step on the surface of the wafer or the like, and when the cross-sectional shape of the alignment mark becomes asymmetric due to a wafer process such as etching or sputtering in a semiconductor manufacturing process, this alignment mark is formed. There is a disadvantage that the position detection accuracy is reduced due to the asymmetry of the mark.

For this reason, Japanese Patent Application Laid-Open No. 9-219362 discloses a method for reducing detection errors due to mark asymmetry by using light of a plurality of wavelengths as position detection light. In addition, WO 98/39689 proposes a method of reducing a detection error due to mark asymmetry by using a plurality of position detection light beams having different orders in a homodyne system.

However, in the method of using light of a plurality of wavelengths as position detection light disclosed in Japanese Patent Application Laid-Open No. 9-219362, only a single order such as ± 1st-order diffracted light is detected.
ing: chemical mechanical polishing) when performing alignment of a low-step wafer, there is a disadvantage that the wafer is easily affected by mark asymmetry.

In the method of using a plurality of position detection lights having different orders from each other in the homodyne method, it is necessary to provide the same number of detectors as the number of types of position detection light to be used, which complicates the configuration of the apparatus. There was an inconvenience. Also,
For configuration reasons, it can only be used with ± Nth order light detection method,
Since the signal intensity of the ± Nth-order light detection method is extremely small as compared with the 0-Nth-order light detection method, sufficient detection accuracy may not be obtained.

In view of the above, the present invention has a simple configuration,
It is another object of the present invention to provide a position detection method capable of reducing a position detection error due to asymmetry of a diffraction grating mark and performing alignment of a test object with high accuracy. Still another object of the present invention is to provide a position detecting device capable of performing such a position detecting method, and an exposure method and an apparatus using such a position detecting method.

[0011]

According to the position detecting method of the present invention, a mark (RM, W) formed on an object (1, 4) is formed.
M) is a position detecting method for measuring the position, wherein a first two light beams (L03, L30) having a predetermined wavelength are made to enter the mark from two different directions at a first incident angle θ1, A second two light beams (L04, L40) having the predetermined wavelength and different from the first two light beams are transmitted to the mark in two different directions from the first incident angle different from the first incident angle. Incident at an incident angle θ2, and the first and second
The position information of the mark is obtained based on the diffracted beams generated from the mark due to the incidence of the light beam.

According to the present invention, as an example, a first interference beam between diffracted beams of a predetermined order generated from the mark due to the incidence of the first two light beams is detected, and the second two light beams are detected. A second interference beam generated from the mark by the incident light and having a different order from the predetermined order is detected. When the position of a mark is detected by the LIA method, the detection error due to the asymmetry of the cross-sectional shape of the mark generally decreases as the order of the detected interference beam increases. Therefore, for example, the relationship between the order of the interference beam and the detection error is obtained in advance by simulation or experiment, and the detection error due to the asymmetry of the mark is estimated and corrected from this relationship, so that the detection error due to the asymmetry of the mark is reduced. Therefore, the position of the object can be accurately adjusted.

Further, a diffracted beam generated from the mark by the incidence of the first two light beams and a diffracted beam generated from the mark by the incidence of the second two light beams are detected by using the same photoelectric detector. This has the advantage that the configuration of the device can be simplified. Further, based on the order of the diffracted beams constituting each of the interference beams, the S / N ratio of a signal based on the interference beam, or the strength of the signal, any one of the first interference beam and the second interference beam is used. It is desirable to select one of them and to obtain the position information of the mark based on the detection result of the selected interference beam. In this case, the detection error due to the asymmetry of the mark can be corrected with higher accuracy, and the positioning of the object can be performed with higher accuracy.

It is desirable to temporally switch between a state in which the first two light beams enter the mark and a state in which the second two light beams enter the mark. In this case, for example, the first and second two light beams can be generated using the same acousto-optic element, and there is an advantage that the configuration of the device is simplified. Also, the first 2
It is desirable to spatially separate the light beam and the second two light beams. Also in this case, for example, the first and second two light beams can be generated using the same acousto-optic element, and there is an advantage that the configuration of the device is simplified.

Next, an exposure method according to the present invention is an exposure method for forming a predetermined pattern on an object (4) using an exposure beam, and is a method for detecting a mark (WM) detected by the position detecting method according to the present invention. The positioning of the object is performed based on the position information, and the predetermined pattern is exposed on the aligned object. According to the present invention, since the position information of the mark is detected by the position detection method of the present invention, the positioning of the object can be performed with high accuracy, and the predetermined pattern can be accurately positioned on the object. Can be exposed.

Next, a position detecting device according to the present invention is a position detecting device for measuring the position of a mark (RM, WM) formed on an object (1, 4), and comprises a first detecting device having a predetermined wavelength. Two light beam generating means (10 to 13, 17, 60) for generating two light beams (L03, L30) and a second two light beams (L04, L40) having the predetermined wavelengths, and first and second light beams; Irradiation means (18a, 18b, 21, 22, 22) for making two light beams enter the mark from two different directions.
26, 27, 37, 38, 3) and detection means (33, 36) for detecting a diffraction beam generated from the mark by irradiation of the first and second two light beams.
Are incident on the mark at an incident angle different from the incident angle of the second two light beams on the mark. According to the position detecting device of the present invention, the position detecting method of the present invention can be implemented.

An exposure apparatus according to the present invention is an exposure apparatus for forming a predetermined pattern on an object (4) by using an exposure beam, and the position of a mark (WM) detected by the position detecting apparatus according to the present invention. The position of the object is aligned based on the information, and the predetermined pattern is exposed on the aligned object. According to the present invention, the position of the object can be accurately adjusted by the position detection device of the present invention, and the predetermined pattern can be exposed on the object with high accuracy.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to an alignment system of a TTR (through the reticle) system provided in a stepper type projection exposure apparatus and of a heterodyne interference system. FIG. 1 shows a projection exposure apparatus of the present embodiment. In FIG. 1, a reticle 1 is held on a reticle stage 2 which is movable two-dimensionally. A circuit pattern for transfer is formed on the pattern surface of the reticle 1, and a diffraction grating mark RM as an alignment mark (reticle mark) is formed on the pattern surface near the circuit pattern.

An illumination optical system 40 is disposed obliquely above the reticle 1, and at the time of exposure, exposure light from the illumination optical system 40 emits dichroic mirrors 6 inclined at an angle of 45 ° above the reticle 1. Is reflected downward by
The circuit pattern on the reticle 1 is illuminated with a uniform illuminance distribution. Under the exposure light, the circuit pattern on the reticle 1 is projected through the projection optical system 3 to the wafer 4 at a predetermined projection magnification β.
Each of the upper shot areas is projected and exposed. A photoresist is applied to the surface of the wafer 4, and the surface is held on a plane conjugate with the pattern surface of the reticle 1 with respect to the projection optical system 3. In the vicinity of each shot area on the wafer 4, a diffraction grating mark WM as an alignment mark (wafer mark) similar to the diffraction grating mark RM on the reticle 1 is formed. In the following description, the z-axis is taken in parallel with the optical axis of the projection optical system 3, the x-axis is taken in a plane perpendicular to the z-axis, parallel to the plane of FIG. 1, and the y-axis is taken perpendicular to the plane of FIG. .

The wafer 4 is held on a wafer stage 5 which moves two-dimensionally in the x and y directions in a step-and-repeat manner, and transfers and exposes a pattern of the reticle 1 to one shot area on the wafer 4. Is completed, the next shot area to be exposed on the wafer 4 is stepped to the exposure field of the projection optical system 3. X direction in reticle stage 2 and wafer stage 5, y
Each stage is provided with an interferometer (not shown) for independently detecting the position in the direction and the rotational direction (θ direction), and each stage is driven by an attached drive motor in each direction.

On the other hand, an alignment optical system for detecting the positions of the diffraction grating marks RM and WM is provided above the dichroic mirror 6. In this alignment optical system, the light source 10 is a white light source such as a xenon (Xe) lamp or a halogen lamp that supplies broadband light different from the exposure light. The white light from the light source 10 is converted into a parallel light beam through a variable aperture 11 and a condenser lens 12 having a variable aperture, and then converted into a light beam L through a bandpass filter 13 that extracts light in a predetermined wavelength range. 1 acousto-optic element (hereinafter, referred to as “AOM”)
It is incident on 17. The first AOM 17 is driven by a high-frequency signal SF1 having a frequency f1, and the AOM 17 emits a zero-order light L0 of the light beam L and a first-order diffracted light L3 frequency-modulated by f1 by anisotropic Bragg diffraction.

Thereafter, the zero-order light L0 and the first-order diffracted light L3
Passes through the lens 18a, the mirror 20, and the lens 18b,
The second AO driven by the high frequency signal SF2 having the frequency f2
It is incident on M60. At this time, the lenses 18a and 18b
The relay optical systems 18a and 18b
The center of the ultrasonic operation region of No. 17 and the center of the ultrasonic operation region of the AOM 60 are conjugate. Also, the relay optical system 18
Light beams other than the zero-order light L0 and the first-order diffracted light L3 from the first AOM 17 are cut off by the spatial filter 19 arranged in each of the first and second AOMs 17a and 18b.

Considering the reverse projection by the relay optical systems 18a and 18b and the reverse by the mirror 20, the AOM 6
0 is driven by the high-frequency signal SF2 in the direction opposite to the case of the AOM 17. As a result, the first-order diffracted light (hereinafter, simply referred to as “light flux”) L03 and 1 that is frequency-modulated at f2 by the anisotropic Bragg diffraction of the 0th-order light L0 at the AOM 60.
Zero-order light (hereinafter simply referred to as “light flux”) L30 in the AOM 60 of the second-order diffracted light L3 is emitted in different directions. Since both the light beam L30 and the light beam L03 are polarized in a direction perpendicular to the paper surface of FIG. 1, the light beam L30 and the light beam L03
, A heterodyne beam of the frequency (f1-f2) is obtained.

The light beam L30 and the light beam L03 pass through the lens 21 and the spatial filter 61, respectively, and are split into two by the beam splitter 22. The light beam L03 and the light beam L30 transmitted through the beam splitter 22 are
Then, interference fringes flowing along the pitch direction are formed on the reference diffraction grating 24 provided at the focusing position. The diffracted light passing through the diffraction grating 24 is photoelectrically detected as a reference optical beat signal by a photoelectric detector 25 including a photodiode or the like.

On the other hand, the light beam L03 and the light beam L30 reflected by the beam splitter 22 pass through a relay optical system 26 including lenses 26a and 26b, a relay lens 27, a beam splitter 28, and a plane parallel plate 37. The parallel plane plate 37 is provided at or near the pupil conjugate position of the projection optical system 3 so as to be tiltable with respect to the optical axis of the alignment optical system, and has a function of maintaining telecentricity. Light beam L03 and light beam L3 that have passed through parallel plane plate 37
Numeral 0 illuminates the diffraction grating mark RM on the reticle 1 from two directions having a predetermined intersection angle via the objective lens 38 and the dichroic mirror 6.

Thus, on the diffraction grating mark RM,
Interference fringes flowing along the pitch direction are formed, and in the normal direction of the diffraction grating mark RM (the optical axis direction of the projection optical system 3),
A -3rd order diffracted light of the light beam L03 and a + 3rd order diffracted light of the light beam L30 are generated. The crossing angles when the light beams L03 and L30 illuminate the diffraction grating mark RM from two directions are as follows: the pitch of the diffraction grating mark RM is PRM; the reference wavelength of the light supplied from the light source 10 is λ0;
Alternatively, when the incident angle of the light beam L30 with respect to the diffraction grating mark RM is θRM, the setting is made so as to satisfy the following relationship.

PRM · sin θRM = 3λ0 (1) Accordingly, the ± 3rd-order diffracted light generated from the diffraction grating mark RM is again converted into the dichroic mirror 6 and the objective lens 3
8. After passing through the parallel plane plate 37, the beam splitter 2
After being reflected at 8, the light reaches a field stop 34 via a lens 29 and a beam splitter 30.

The field stop 34 is provided at a position conjugate with the reticle 1. Specifically, as shown by the hatched portion in FIG. 3A, only the diffracted light from the diffraction grating mark RM of the reticle 1 passes. An opening SRM is provided at a position conjugate with the diffraction grating mark RM so as to allow the opening. The diffracted light from the diffraction grating mark RM that has passed through the field stop 34 is filtered by a spatial filter 35 that blocks the 0th-order diffracted light, and only the ± 3rd-order diffracted light reaches the photoelectric detector 36. An optical beat signal including the position information of the reticle 1 is photoelectrically detected.

Now, the light beam L03 and the light beam L30 illuminate the diffraction grating mark RM on the reticle.
2A, a transmission window P0 for alignment light is provided in parallel with the diffraction grating mark RM, as shown in FIG. 2A, and the transmission window P0 on the wafer 4 as shown in FIG.
A diffraction grating mark WM is formed at a position corresponding to 0.

In FIG. 1, the light beam L03 and a part of the light beam L30 that have passed through the transmission window P0 of the reticle 1 have a predetermined intersection angle with the diffraction grating mark WM on the wafer 4 via the projection optical system 3. Illumination is performed in two directions, whereby interference fringes flowing along the pitch direction are formed on the diffraction grating mark WM. In the normal direction of the diffraction grating mark WM (the direction of the optical axis of the projection optical system 3), a -3rd-order diffracted light of the light beam L03 and a + 3rd-order diffracted light of the light beam L30 are generated.
The ± 3rd-order diffracted light generated from the diffraction grating mark WM passes through the projection optical system 3, the transmission window P0 (see FIG. 2A), the dichroic mirror 6, the objective lens 38, and the plane-parallel plate 37 again. After that, the light reaches the field stop 31 via the lens 29 and the beam splitter 30. The field stop 31 is provided at a position conjugate with the wafer 4. Specifically, as shown by the hatched portion in FIG. 3B, only the diffracted light from the diffraction grating mark WM on the wafer 4 passes. An opening SWM is provided at a position conjugate with the diffraction grating mark WM.

Therefore, the diffracted light from the diffraction grating mark WM that has passed through the field stop 31 is filtered by a spatial filter 32 that blocks the 0th-order diffracted light, and only the ± 3rd-order diffracted light reaches the photoelectric detector 33. Photoelectric detector 33
A photoelectric signal containing an optical beat signal containing positional information on the wafer 4 is detected. Here, the spatial filters 32 and 35 are located at positions substantially conjugate with the pupil of the alignment optical system, that is, the projection optical system 3.
And the diffraction grating marks RM, WM formed on the reticle 1 and the wafer 4
Is set so as to block the 0th-order light (specular reflection light) from the light source and to pass only the ± 3rd-order diffraction light (diffraction light generated in the direction perpendicular to the diffraction grating mark on the reticle 1 and the wafer 4). . The photoelectric detectors 33 and 36 are arranged so as to be substantially conjugate with the reticle 1 and the wafer 4 with respect to the objective lens 38 and the lens 29, respectively.

The three photoelectric signals obtained from each of the photoelectric detectors 25, 33, and 36 have the same frequency Δf (=
f1-f2), which includes a sinusoidal optical beat signal,
Each is supplied to the phase detection system 50 of FIG. An optical beat signal extracting unit (Fourier transform circuit) in the phase detection system 50 electrically Fourier-transforms the three photoelectric signals to accurately extract a sinusoidal optical beat signal having a frequency Δf. The phase difference between the optical beat signals is detected.

Now, assuming that the reticle 1 and the wafer 4 are stopped at arbitrary positions without being aligned.
The corresponding two optical beat signals will be shifted by a certain phase. Here, the phase difference (within ± 180 °) of each optical beat signal from the reticle 1 and the wafer 4 is a relative position within １ ／ of the grating pitch of the diffraction grating marks formed on the reticle 1 and the wafer 4 respectively. It uniquely corresponds to the deviation amount.

For this reason, the relative displacement between the reticle 1 and each of the shot areas on the wafer 4 is reduced to less than 1/2 of the grating pitch of each of the diffraction grating marks RM and WM by the pre-alignment and search alignment steps. Perform positioning. Then, in the phase detection system 50, for example, the phase difference between the optical beat signal corresponding to the diffraction grating mark RM and the optical beat signal corresponding to the diffraction grating mark WM is obtained.
The main control system 5 which controls the operation of the entire apparatus by controlling the phase difference.
Feed to 1. Accordingly, the main control system 51 moves the reticle stage 2 or the wafer stage 5 via the servo system 52 two-dimensionally so that the phase difference supplied from the phase detection system 50 becomes zero or a predetermined value. I do.

The reference optical beat signal obtained by the photoelectric detector 25 is used as a reference signal, and the phase difference between the reference signal and the optical beat signal from each of the diffraction grating marks RM and WM is zero or a predetermined value. Positioning may be performed to obtain a value. Further, a beat signal obtained by mixing high-frequency signals for driving the AOMs 17 and 60 can be used as a reference signal.

Next, a portion for generating two light beams having different frequencies will be described in detail with reference to FIG. FIG.
1, the relay optical systems 18a and 18b in FIG. 1 are represented by the relay optical system 18, and the mirror 20 is omitted. Therefore, the application direction of the high-frequency signal SF2 in the AOM 60 is opposite to that in FIG. In FIG. 4, AO
The center (diffraction point) CA of the ultrasonic action area in the acousto-optic medium 17a of M17 and the center (diffraction point) CB of the ultrasonic action area in the acousto-optic medium 60a of the AOM 60 are conjugate with respect to the relay optical system 18. ing.

The AOM 17 is made of, for example, tellurium dioxide (TeO ₂ ), quartz, or lead molybdate (PbMoO ₄ ).
A transducer 17b such as a piezoelectric element is adhered to an acousto-optic medium 17a such as
1 is applied. Similarly, the AOM 60 has a transducer 60b attached to the acousto-optic medium 60a, and a high-frequency signal SF2 having a frequency f2 is applied from the oscillator 59 to the transducer 60b.

The light beam L is polarized in a direction parallel to the plane of FIG. 4 and is incident on the AOM 17, and is about 50% by the transverse ultrasonic traveling wave A in the acousto-optic medium 17 a of the AOM 17.
Undergoes anisotropic Bragg diffraction and is a first-order diffracted light beam L3
And the light passes through the AOM 17 in parallel with the optical axis as a light beam L0, most of which is the zero-order light. The light beam L3 is
While receiving the frequency modulation of f1, the polarization direction is rotated in the direction perpendicular to the paper surface of FIG. 4, and the polarization direction of the zero-order light L0 is the same as that at the time of incidence. The light beam L3 and the light beam L0 enter the AOM 60 via the relay optical system 18 so as to intersect at the center CB of the ultrasonic action area in the acousto-optic medium 60a of the second AOM 60.

The light beam L0 is substantially 100% diffracted by the ultrasonic traveling wave B in the acousto-optic medium 60a of the AOM 60, and becomes a light beam L03, which is a first-order diffracted light having undergone frequency modulation of f2, and the light beam L3 is an AOM 60. Is transmitted as it is to become a light beam L30 which is the zero-order light. The light beam L03 has a polarization direction shown in FIG.
Is rotated in a direction perpendicular to the plane of the drawing, and is equal to the polarization direction of the light beam L30. Therefore, the light flux L03 and the light flux L
30 can be used as a light beam for position detection.

The 0th-order light L00 may be slightly generated by the AOM 60 of the 0th-order light L0.
00 is shielded by the spatial filter 61 of FIG. In this example, almost 50% of the light beam L incident on the AOM 17 is f
Since the light beam L30 has been subjected to the frequency modulation of 1 and almost all of the remaining light beam has become the light beam L03 subjected to the frequency modulation of f2, the diffraction efficiency is extremely high.

By the way, as shown in FIG. 5, the groove bottom of the line constituting the diffraction grating mark WM has, for example, a difference in the direction of the grating period due to the inclination φ.
When the cross-sectional shape has an asymmetry, the absolute value and the phase of the amplitude reflectance of the diffraction grating mark also become asymmetric. As a result, the diffracted light generated from the diffraction grating mark also has different intensities and phases between, for example, the positive order generated in the right direction and the negative order generated in the left direction with respect to the 0th order light. Accuracy deteriorates. In particular, when a low-level wafer subjected to processing such as CMP is used, the detection error increases.

Therefore, in this example, utilizing the fact that the detection error due to the asymmetry of the diffraction grating mark becomes smaller as higher order diffracted light is used as shown in FIG. The error curve of FIG. 6 is obtained in advance by simulation, and the position of the diffraction grating mark WM is detected by using the ± 4th-order diffracted light in addition to the above-mentioned ± 3rd-order diffracted light. Estimate and correct errors. Detection by ± 4th-order diffracted light is performed by the oscillators 16 and 59 shown in FIG.
This is performed by changing the frequencies f1 and f2 applied to 0b, changing the light beams L03 and L30 indicated by solid lines to light beams L04 and L40 indicated by dotted lines, and changing the angle of incidence on the diffraction grating mark WM.

First, when detecting by ± 3rd-order diffracted light, for example, the frequencies f1 and f2 of the ultrasonic waves applied to the AOMs 17 and 60 in FIG.
Hz, and light fluxes L03 and L30 are generated. As shown in FIG. 9, the light fluxes L03 and L30 are incident on the diffraction grating mark WM at an incident angle θ1, and on the diffraction grating mark WM,
An interference fringe having a pitch of 2 μm is formed, and the diffraction grating mark W
In the normal direction of M, the third-order diffracted light L3A of the light beam L30
And a + 3rd-order diffracted light L3B of the light beam L03 are generated. Here, the pitch P of the diffraction grating marks WM is 12 μm.
m, and the intersection angle when the light beam L03 and the light beam L30 illuminate the diffraction grating mark WM from two directions is such that when the reference wavelength of the light supplied from the light source 10 is λ, the following relationship is satisfied. It has become.

P · sin θ1 = 3λ (2) As a result, the ± 3rd-order diffracted lights L3A and L3B generated from the diffraction grating mark WM reach the photoelectric detector 33 and include the positional information on the wafer 4 as described above. An optical beat signal is photoelectrically detected. At this time, the frequency of the optical beat signal is 10
0 kHz. This frequency can be easily stabilized on the order of ppm and can be set with extremely high precision. Further, when the sound speed of the ultrasonic waves is 4000 m / sec, the pitch of the ultrasonic waves traveling in the AOMs 17 and 60 is 80 μm, and the pitch of the interference fringes is 4 μm because the 0-order light is shielded. The reduction magnification of the optical system including the projection optical system 3 between the diffraction grating marks WM is 1/20.

Next, when performing detection by ± 4th-order diffracted light, for example, the frequencies f1 and f2 of the ultrasonic waves applied to the AOMs 17 and 60 in FIG.
Switching to 6.77 MHz, the light fluxes L04 and L40 are generated. As shown in FIG. 9, the light beams L04 and L40 are incident on the diffraction grating mark WM at an incident angle θ2, and interference fringes having a pitch of 1.5 μm are formed on the diffraction grating mark WM. In the normal direction of the light beam L40
-4th-order diffracted light L4A and + 4th-order diffracted light L of light beam L04
4B respectively occur. Here, the intersection angle when the light beam L04 and the light beam L40 illuminate the diffraction grating mark WM from two directions satisfies the following relationship.

P · sin θ2 = 4λ (3) Accordingly, the ± 4th-order diffracted lights L4A and L4B generated from the diffraction grating mark WM reach the photoelectric detector 33, and an optical beat signal including the position information of the wafer 4 is generated. Photoelectrically detected.
The frequency of this optical beat signal is also 100 kHz. In the main control system 51, the error curve shown in FIG. 6, the detected values of the ± 3rd-order diffracted lights L3A and L3B and the ± 4th-order diffracted lights L4A and L4
The detection error due to the asymmetry of the diffraction grating mark WM is estimated and corrected based on the detected value of 4B, and the wafer stage 5 is two-dimensionally moved via the servo system 52 for positioning.

As described above, the frequency of the ultrasonic waves applied to the AOMs 17 and 60 is switched over time, and the ± 3rd-order diffracted light L
By detecting the 3A, L3B and ± 4th-order diffracted lights L4A, L4B, errors due to asymmetry of the diffraction grating mark WM can be reduced, and highly accurate alignment can be performed. Further, according to this example, the light beams L03 and L30 and the light beams L04 and L40 can be generated by the same AOM 17, 60, and the detection of the ± 3rd-order diffracted lights L3A and L3B and the ± 4th-order diffracted lights L4A and L4B. Can be performed by the same photoelectric detector 33, and the diffraction grating mark W
There is an advantage that the position of M can be detected with high accuracy.

In addition, the switching between the detection using the ± 3rd-order diffracted light and the detection using the ± 4th-order diffracted light can be performed in a very short time by changing the frequency of the ultrasonic waves applied to the AOMs 17 and 60 on the order of μsec. Since the detection of the lattice mark WM can be performed in a very short time, it can be performed in a very short time. Therefore, ± 3rd order diffracted light and ±
The fourth-order diffracted light is apparently detected at the same time.
Further, two kinds of frequencies can be simultaneously applied to the ultrasonic waves applied to the AOMs 17 and 60.

The order of the diffracted light used for detection is 3
The order is not limited to the fourth and fourth orders, and higher order diffracted lights such as the fifth and sixth orders may be used.
Low-order diffracted light such as second-order diffracted light may be used. Alternatively, a detected value of the diffracted light having the best SN ratio of the optical beat signal or the detected value of the highest-order diffracted light may be selected as a detection reference or a true value.

For each layer, for example, an error curve is obtained in advance before the alignment of the head wafer of the rod, for example.
It is also possible to store the offset of the detection error and fix the order of the diffracted light as a reference for detection to, for example, the third order. Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment in that a portion for generating two light beams incident on the diffraction grating mark WM is changed. In FIG. 7, portions corresponding to FIG. The detailed description is omitted.

In FIG. 7, the light beam emitted from the light source 10 is frequency-modulated by the AOMs 17 and 60 and enters the beam splitter 70 via the lens 21. The light beam L1 that has passed through the beam splitter 70 is
1, the beam is split into the diffraction grating mark WM at an incident angle θ via the beam splitter 73 and the spatial filter 61 to the objective lens 38, and ± 1 of the light flux L1 in the normal direction of the diffraction grating mark WM. Next-order diffracted light is generated. Here, the intersection angle when the light beam L1 illuminates the diffraction grating mark WM from two directions is set so as to satisfy the following relationship.

P · sin θ = λ (4) Accordingly, the ± first-order diffracted light generated from the diffraction grating mark WM reaches the photoelectric detector 33, and the photoelectric detector 33 includes positional information on the wafer 4. An optical beat signal is photoelectrically detected. On the other hand, the light beam L3 reflected by the beam splitter 70 is reflected by the mirrors 72a and 72d and the lens 72.
b, 72c, and 72e, through the magnifying optical system 72,
Reflected by the beam splitter 73, the spatial filter 6
1 to the diffraction grating mark WM at a predetermined angle of incidence via the objective lens 38. Magnifying optical system 72
Is larger than the magnification of the optical system of the light path of the light beam L1 including the lens 71. In this example, the magnification of the light beam L3 in the normal direction of the diffraction grating mark WM is ±. Light beam L3 at an incident angle such that third-order diffracted light is generated
Are incident on the diffraction grating mark WM. Then, the ± 3rd-order diffracted light of the light beam L3 generated in the normal direction of the diffraction grating mark WM reaches the photoelectric detector 33, and the optical beat signal containing the position information on the wafer 4 is detected by the photoelectric detector 33. Is done.

As described above, the two light beams are spatially divided, and one of the two light beams is recombined with a different magnification from the other two light beams, so that the incident angle with respect to the diffraction grating mark WM is made different. Can be. Further, when only high-order diffracted lights such as ± 3rd-order diffracted light and ± 4th-order diffracted light are used as in the first embodiment, the detection ranges are narrowed to 2 μm and 1.5 μm, respectively. Although alignment becomes difficult, when ± 1st-order diffracted light is used as in this example, the detection range is 6 μm, which is practical for rough alignment.

In each of the above embodiments, the ± N-order light detection method is used. However, since the high-order diffracted light generally has low diffraction efficiency, a sufficient signal intensity can be obtained by the ± N-order light detection method. If not, it is preferable to use the 0-Nth order light detection method as described below. FIG. 10 shows a state near the diffraction grating mark WM when the 0-Nth order light detection method is used. In FIG. 10, the light beams L03 and L30 are incident on the diffraction grating mark WM at an incident angle θ3. It has become. Then, the light beam L generated from the diffraction grating mark WM
The zero-order light 30 and the third-order diffracted light L3C of the light beam L03 reach the photoelectric detector 33A, and a photoelectric beat signal including the positional information of the diffraction grating mark WM is photoelectrically detected by the photoelectric detector 33A. Further, the zero-order light of the light beam L03 and the third-order diffracted light of the light beam L03 reach the photoelectric detector 33B, and the optical detector 33B photoelectrically detects an optical beat signal including the positional information of the diffraction grating mark WM. Here, the crossing angles when the light beams L03 and L30 illuminate the diffraction grating mark WM from two directions are set so as to satisfy the following relationship.

2P · sin θ3 = 3λ (5) The light beams L04 and L40 are incident on the diffraction grating mark WM at an incident angle θ4, and the zero-order light of the light beam L40 generated from the diffraction grating mark WM. And the third-order diffracted light L4C of the light beam L04 reach the photoelectric detector 33A, and a photoelectric beat signal including the positional information of the diffraction grating mark WM is photoelectrically detected by the photoelectric detector 33A. Further, the light beam L0
4 and the third-order diffracted light of the light beam L40 form the photoelectric detector 3
3B, the photoelectric detector 33B photoelectrically detects an optical beat signal including the position information of the diffraction grating mark WM. Here, the light beams L04 and L40 are the diffraction grating marks W
The intersection angle when illuminating M from two directions is set so as to satisfy the following relationship.

2P · sin θ4 = 4λ (6) As described above, by using the 0-Nth order light detection method, a higher signal intensity can be obtained than in the case of using the ± Nth order light detection method. As shown in FIG. 8, the 0th-order light L30 and the −3rd-order diffracted light L3D are converted by the photoelectric detector 33A into
The 0th-order light L03 and the 3rd-order diffracted light L3C are converted into a photoelectric detector 33B.
Thus, the detection may be performed without using a beam splitter or the like.

By the way, assuming that the frequency of the ultrasonic wave applied to the acousto-optic medium of the AOM is f, care must be taken to properly select the parameter Q given by the following equation. Q = (2πLλf ² ) / nV ² (7) where L is the length of the ultrasonic action area, λ is the center wavelength of the light beam used, n is the refractive index of the acousto-optic medium, and V is the velocity of the ultrasonic wave. It is. Then, the value of Q is about 4π (≒ 12.6)
, Bragg diffraction occurs, and Raman-Nath diffraction occurs when the value of Q is around 2. And that Q
The pitch of the traveling wave in the acousto-optic medium can be changed to some extent by adjusting the frequency f of the ultrasonic wave within a range that almost satisfies the condition of the value of the two light beams incident on the diffraction grating mark WM. Can be changed. Further, as in the second embodiment, by dividing two light beams and recombining one of the two light beams with a different magnification from the other two light beams, if the incident angles with respect to the diffraction grating mark WM are different from each other. In this case, the intersection angle can be changed over a wider range.

Further, in each of the above embodiments, the present invention has
Although applied to a TR type alignment system, the present invention can also be applied to an off-axis type alignment system. Further, in each of the above embodiments, the present invention is applied to an alignment system of a stepper type projection exposure apparatus. However, the present invention relates to a step-and-scan type projection exposure apparatus, and furthermore, a projection optical system. The present invention can also be applied to an alignment system such as a proximity type exposure apparatus that is not used.

Further, the projection exposure apparatus of the above embodiment adjusts the illumination optical system and the projection optical system, and assembles each component electrically, mechanically or optically. The work in this case is desirably performed in a clean room where the temperature is controlled. Then, the wafer 4 exposed as described above undergoes a developing step, a pattern forming step, a bonding step, and the like, whereby devices such as semiconductor elements are manufactured.

The present invention is not limited to the above-described embodiment, but may take various configurations without departing from the spirit of the present invention.

[0061]

According to the present invention, the detection error due to the asymmetry of the mark can be reduced, and the object can be positioned with high accuracy. Further, it is possible to detect, using the same photoelectric detector, a diffracted beam generated from the mark by the incidence of the first two light beams and a diffracted beam generated from the mark by the incidence of the second two light beams. There is an advantage that the configuration of the apparatus can be simplified. Further, when the present invention is applied to a case where a predetermined pattern is formed on an object using an exposure beam, the predetermined pattern can be exposed on the object with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in a first embodiment of the present invention.

FIG. 2A is a plan view showing a diffraction grating mark and a transmission window on a reticle, and FIG. 2B is a plan view showing a diffraction grating mark on a wafer.

3A is a diagram illustrating a field stop conjugate with a reticle, and FIG. 3B is a diagram illustrating a field stop conjugate with a wafer.

4 is a diagram showing an alignment system of the projection exposure apparatus of FIG.

FIG. 5 is a sectional view showing a diffraction grating mark having asymmetry in a sectional shape in a grating direction.

FIG. 6 shows a detection error δ due to the order N of diffracted light and the asymmetry of the diffraction grating mark when performing alignment by the LIA method.
6 is a graph showing an example of the relationship with.

FIG. 7 is a view showing an alignment system of a projection exposure apparatus used in a second embodiment of the present invention.

FIG. 8 is a diagram showing the vicinity of a diffraction grating mark when alignment is performed by the 0-Nth order light detection method.

FIG. 9 is a diagram showing the vicinity of a diffraction grating mark when alignment is performed by the ± N-order light detection method.

FIG. 10 is a diagram showing the vicinity of a diffraction grating mark when alignment is performed by the 0-Nth order light detection method.

[Explanation of symbols]

RM, WM: diffraction grating mark, 1: reticle, 3: projection optical system, 4: wafer, 10: light source, 11: variable aperture, 1
2 ... condenser lens, 13 ... band pass filter, 1
7, 60 ... acousto-optic element (AOM), 18a, 18b ...
Relay optical system lens, 19, 61 ... spatial filter, 2
5, 33, 36: photoelectric detector, 38: objective lens, 71
... Lens, 72 ... Magnifying optical system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 21/30 507R F term (Reference) 2F065 AA03 AA14 BB02 BB28 CC20 DD00 DD02 FF48 FF49 FF52 GG02 GG03 GG04 GG24 HH12 JJ01 JJ05 JJ18 LL00 LL20 LL46 LL57 LL59 NN08 PP12 UU01 UU07 2H051 AA10 BA53 BA72 CE12 CE14 2H097 CA16 GB00 KA20 LA10 LA12 5F046 AA20 BA02 BA03 CB17 DA12 DB05 EA07 EA09 FA06 FA09 FC04

Claims (17)

[Claims] 1. A position detecting method for measuring a position of a mark formed on an object, comprising: a first incident light beam having a predetermined wavelength and a first incident angle with respect to the mark from two different directions. A second light beam having the predetermined wavelength and different from the first two light beams.
Are incident on the mark from two different directions at a second angle of incidence different from the first angle of incidence, based on a diffracted beam generated from the mark by the incidence of the plurality of light beams. And position information of the mark. 2. A first interference beam between diffraction beams generated in a predetermined direction from the mark by the incidence of the first two light beams is detected, and a first interference beam from the mark is detected in the predetermined direction by the incidence of the second two light beams. The position detecting method according to claim 1, wherein a second interference beam between the generated diffraction beams is detected, and position information of the mark is obtained based on a detection result of the first and second interference beams. 3. The position according to claim 2, wherein the first interference beam includes a diffraction beam of a predetermined order, and the second interference beam includes a diffraction beam of an order different from the predetermined order. Detection method. 4. The first interference beam and the second interference beam, based on an order of a diffraction beam constituting each of the interference beams, an S / N ratio of a signal based on the interference beam, or an intensity of the signal. 4. The position detection method according to claim 2, wherein one of the above is selected, and the position information of the mark is obtained based on the detection result of the selected interference beam. 5. The method according to claim 1, wherein a state in which the first two light beams enter the mark and a state in which the second two light beams enter the mark are temporally switched. 5. The position detection method according to claim 4. 6. The position detecting method according to claim 1, wherein the first two light beams and the second two light beams are spatially separated. 7. The position detecting method according to claim 1, wherein the first two light beams have different frequencies, and the second two light beams also have different frequencies. 8. An exposure method for forming a predetermined pattern on an object using an exposure beam, based on position information of the mark detected by the position detection method according to any one of claims 1 to 7. And exposing the predetermined pattern to the object on which the alignment has been performed. 9. A position detecting device for measuring the position of a mark formed on an object, wherein the position detecting device generates a first two light beams having a predetermined wavelength and a second two light beams having the predetermined wavelength. Light beam generating means; irradiation means for causing the first and second two light beams to enter the mark from two different directions; diffracted beams generated from the mark by irradiation of the first and second two light beams Detecting means for detecting the second light flux, wherein the first two light fluxes correspond to the second
A position detecting device, which is incident on the mark at an incident angle different from an incident angle of a light beam. 10. The detection means includes: a first interference beam between diffracted beams generated in a predetermined direction from the mark by the incidence of the first two light beams; and the mark from the mark by an incidence of the second two light beams. 10. The mark according to claim 9, wherein a second interference beam between the diffraction beams generated in a predetermined direction is detected, and the position information of the mark is obtained based on the detection results of the first and second interference beams. Position detection device. 11. The apparatus of claim 10, wherein the first interference beam includes a diffraction beam of a predetermined order, and the second interference beam includes a diffraction beam of a different order from the predetermined order. Position detection device. 12. The first interference beam and the second interference beam based on an order of a diffraction beam constituting each of the interference beams, an S / N ratio of a signal based on the interference beam, or an intensity of the signal. 11. The position detecting device according to claim 9, further comprising a selection unit that selects any one of the following: and obtaining position information of the mark based on a detection result of the selected interference beam. 13. The two-beam generating means includes an acousto-optic device, and generates the two beams having different incident angles by changing the frequency of an ultrasonic wave applied to the acousto-optic device. The position detecting device according to claim 9. 14. The two-light east generating means changes the frequency of the ultrasonic wave applied to the Masami Mae acousto-optic hands in a time-sharing manner, so that the first two luminous fluxes and the second luminous flux having different incident angles are different from each other. 14. The position detecting device according to claim 13, wherein the two light beams are generated by time division. 15. The two light beam generating means, comprising: an ultrasonic wave having a plurality of frequencies according to an incident angle of the first light beam;
By applying ultrasonic waves of a plurality of frequencies according to the incident angle of the luminous flux to the acousto-optic element substantially simultaneously,
14. The position detecting device according to claim 13, wherein the first two light beams and the second two light beams having different incident angles are generated substantially simultaneously. 16. The position detecting device according to claim 9, wherein said first two light beams have different frequencies from each other, and said second two light beams also have different frequencies from each other. 17. An exposure apparatus for forming a predetermined pattern on the object using an exposure beam, wherein the position information of the mark detected by the position detection apparatus according to claim 9 is provided. An exposure apparatus, comprising: aligning the object based on the predetermined pattern; and exposing the predetermined pattern on the aligned object.