JPH04361103A - Method and apparatus for detecting relative position - Google Patents

Abstract

PURPOSE:To execute stable position detection by a method wherein first and second position detection marks are formed at pitches changed in a prescribed direction, an interference light is applied to the marks, diffracted lights from the marks are separated, detection signals are processed and thereby position alignment is conducted. CONSTITUTION:Laser beams of two wavelengths which are emitted from a light source 1 and of which the frequencies are different slightly from each other and the planes of polarization orthogonal to each other are turned into interference lights by a movable mirror 7 and applied to a mark 14 and a mark 16. The pitches of the marks 14 and 16 are the same in the direction X and different in the direction Y. The light reflected and diffracted by the mark 14 is reflected by SBS1 11 and SBS2 17, a beat frequency is detected therefrom by a photoelectric detector 21 and it is inputted as a beat signal to a signal processing circuit 22. Meanwhile, the light reflected and diffracted by the mark 16 is reflected by the SBS. 11 and then transmitted through the SBS2 17, the beat frequency is detected therefrom by a photoelectric detector 19 and it is inputted as the beat signal to the signal processing circuit 22. In this circuit 22, a phase difference between the beat signals is detected and converted into the amount of positional slippage between a mask 13 and a wafer 15.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a relative position detection device, and in particular to a relative position detection device that can be suitably applied to an exposure device for manufacturing semiconductor ICs and LSIs, and a pattern evaluation device. be.

0002

[Background Art] With the miniaturization of semiconductor ICs and LSIs in recent years, when mask patterns are exposed and transferred onto a wafer all at once or by a step-and-repeat method, it is necessary to position the mask and wafer with respect to each other with high precision. Technology to match these needs has become indispensable.

As such alignment techniques, conventionally proposed methods utilize optical heterodyne interference to measure minute displacements between a mask and a wafer, or to perform precise alignment. As an example of such a method, a method using double diffracted light generated by two diffraction gratings as shown in FIG. 5 is disclosed in JP-A-56-61608.

In FIG. 5, reference numeral 23 indicates a transmission type diffraction grating, 24 indicates a reflection type diffraction grating, 25 and 26 indicate incident light having two wavelengths whose frequencies are slightly shifted from each other, 27 and 28 indicate desired diffracted light, and 25 -23, 26-23 are -1st-order transmitted diffracted lights from the transmission type diffraction grating 23, 25-23', 26
-23' is the -1st-order reflected diffraction light from the reflection type diffraction grating 24 of the transmitted diffraction lights 25-23 and 26-23, and 25-2
4, 26-24 is the +1st-order reflected diffraction light from the reflection-type diffraction grating 24 of the light that has passed through the transmission-type diffraction grating 23 in the 0th order, and 29 is the reflection-type diffraction grating 24 of the light that has passed through the transmission-type diffraction grating 23 in the 0th-order. This light is a combination of −1st-order reflected and diffracted light from . The grating pitch P1 of the transmission type diffraction grating 23 is configured to be 1/2 of the grating pitch P2 of the reflection type diffraction grating.

In general, a diffraction grating with a grating pitch P has a wavelength λ.
When the light is incident from the vertical direction, the diffracted light is θ=si
It becomes strong only in the direction of θ expressed as n-1 (m・λ/P) (m=0, ±1, ±2,...), and depending on the value of m, m
This is called the next diffracted light.

In FIG. 5, incident lights 25 and 26 are diffracted by a transmission type diffraction grating 23 and become -1st-order transmitted diffracted lights 25-23 and 26-23, respectively.
The next-order transmitted diffraction lights 25-23 and 26-23 are diffracted again by the reflection type diffraction grating 24, and become -1st-order reflected diffraction lights 25-23' and 26-23', respectively. - The directions of incidence of the first-order transmitted diffraction lights 25-23 and 26-23 on the reflection type diffraction grating 24 are θ-1=sin-1(-λ1/P2) θ-2=si
The incident light 25 is
, 26, the speed of light is C and the wavelength λ
The frequencies of the incident light of 1 and λ2 are respectively f1 and f2
Then, the frequency difference Δf between the two incident lights, that is, the frequency of the beat signal, is Δf=|f1 −f2 |=|1
/λ1 −1/λ2 |・C. Here, Δf is
The value is about several kHz to several hundred kHz, and since this value is sufficiently small compared to the speed of light, it can be regarded as θ-1=-θ+1. Since the beams 25-23' and 26-23' are each diffracted in the vertical direction of the diffraction grating 24, they are optically combined to form the desired diffracted beam 27.

Furthermore, the incident lights 25 and 26 are 0th-order diffracted by the transmission type diffraction grating 23, and further reflected and diffracted by the reflection type diffraction grating 24, resulting in +1st-order reflected diffraction lights 25-24 and 26.
-24. These +1st-order reflected diffraction lights 25-24,
26-24 is on the back surface of the transmission type diffraction grating 23, and Ψ-1=sin-1(-λ1/P1)Ψ+1=si in the vertical direction of this back surface.
Since the light enters from the n-1 (λ2/P1) direction, that is, the direction of the ±1st-order diffracted light toward the back surface of the transmission diffraction grating 23, it is diffracted by the transmission diffraction grating 23 in the -1st order and becomes vertically diffracted light. , are similarly optically combined into the desired diffracted light 28.

The phase of the beat signal resulting from optical heterodyne interference obtained from these diffracted lights 27 and 28 changes depending on the relative displacement between diffraction gratings 23 and 24 shown in FIG. Therefore, for example, when aligning a semiconductor wafer and a mask, the incident light 25, 26
An optical system is configured in advance to branch out the same light from the light source and combine the respective lights to obtain a reference beat signal.The reference beat signal obtained from this optical system and the wafer The mask and wafer can be aligned by detecting the phase difference between the beat signal and the diffracted lights 27 and 28 obtained by being diffracted by the diffraction grating formed over the mask.

[0009]

However, as shown in FIG. 5, in the conventional method described above, there is a diffracted light 29 in addition to the diffracted lights 27 and 28 necessary for alignment. In this diffracted light 29, the incident lights 25 and 26 are 0th-order diffracted by the transmission type diffraction grating 23, and this light is transmitted to the reflection type diffraction grating 24.
are incident at incident angles of θ-1 and θ+1, respectively, and are reflected and diffracted there, and -1st-order reflected diffraction light from the reflection type diffraction grating 24 is optically synthesized, and the light is perpendicular to the transmission type diffraction grating 23. It is something that has progressed in that direction. Since this diffracted light 29 is generated in the same direction as the desired diffracted lights 27 and 28, interference occurs between the diffracted light 29 and the desired diffracted lights 27 and 28. Moreover, the diffracted light 29 is a composite diffracted light generated by diffracting only by the reflection type diffraction grating 24, whereas the desired diffraction lights 27 and 28 are diffracted by the transmission type diffraction grating 23 and the reflection type diffraction grating 24. This is the double diffracted light generated by this process. Therefore, the diffracted light intensity of the diffracted light 29 is the double diffracted light 27, 2
8 and becomes the main component of the diffracted light generated in the direction of travel of the desired diffracted light, so it acts as noise in the diffracted lights 27 and 28, which serve as position information signals. A beat signal due to optical heterodyne interference generated between this diffracted light 29 and desired diffracted lights 27 and 28 is generated by the diffraction grating 2.
Even if a relative displacement occurs between 3 and 24, no phase change occurs,
Therefore, alignment cannot be performed using the diffracted light 29. Furthermore, the beat signal obtained from the diffracted lights 27 and 28 and the beat signal obtained from the diffracted light 29 cause interference with each other, and this interference causes a difference between the reference beat signal and the desired beat signal from the diffracted lights 27 and 28. This has the disadvantage that the phase difference with the signal fluctuates and the accuracy of alignment deteriorates.

The present invention has been made to solve the above-mentioned problems, and provides relative position detection that extracts only the diffracted light necessary for position alignment, obtains a stable beat signal, and improves position detection accuracy. The purpose is to provide a device.

[0011]

[Means and operations for solving the problems] In order to solve the above problems, the relative position detection method of the present invention provides a first alignment mark and a second alignment mark whose relative positions are to be detected. The first and second alignment marks are irradiated with interference light obtained by interfering with a plurality of light beams formed at different pitches and having slightly different frequencies, respectively, and the first and second alignment marks A first diffracted light diffracted in a predetermined direction and a second diffracted light separated from the first diffracted light in the predetermined direction by the second alignment mark are detected. , the relative positional deviation of the first and second alignment marks is detected from the relative relationship between the first and second diffracted lights. Further, the relative position detection device of the present invention includes a light source that generates a plurality of light beams having slightly different frequencies, and an interference light generation means that generates interference light by causing the plurality of light beams emitted from the light source to interfere with each other. , an interference light irradiation means for irradiating the interference light onto first and second alignment marks whose relative positions are to be detected, and a first pitch in a first direction that is the same as a pitch of interference fringes of the interference light a first diffracted light generated by the first alignment mark, which is formed at a second pitch different from the pitch of the interference fringes in a second direction perpendicular to the first direction; The second alignment marks are formed at the first pitch in the first direction and at a third pitch different from the second pitch in the second direction. A second diffracted light that is separated from the diffracted light,
The relative positional deviation of the first and second alignment marks is determined from the relative relationship between the separate detection means that detect each separately and the diffracted light from each alignment mark detected by the separate detection means. It is characterized by comprising a signal processing means for calculating the amount.

The concept of the relative position detection method of the present invention will be explained below with reference to FIGS. 1 and 2. As shown in Figure 1,
ω1 (=ω0 +Δω) and ω2 (=ω0−
Two laser beams 31 with plane wavefronts having an angular frequency of Δω)
, 32 at a predetermined angle θ, the intensity I at point A is I(x,t)=I0 cos2 (Δωt+k・x・s
inθ). Here, I0 is the laser intensity, k
is ω0/c, where c is the speed of light.

[0013] Therefore, the interference intensity of the interference caused by the laser beams 31 and 32 differs depending on the position, and
Its intensity changes over time. That is, interference fringes having a pitch determined by the incident angle θ of the laser beams 31 and 32 become interference light flowing due to the difference in frequency of the respective incident beams.

FIG. 2 is a diagram showing the configuration of first and second position detection marks whose relative positions are to be detected. here,
An explanation will be given by taking an exposure mask and first and second alignment marks formed on a semiconductor wafer as an example. In FIG. 2, the exposure mask 13 and the semiconductor wafer are arranged to overlap in a direction perpendicular to the paper surface, and the exposure mask 13 and the semiconductor wafer 15 have first and second alignment marks 1.
4 and 16 are arranged in a matrix. A light transmitting portion 14a is provided in a portion of the exposure mask 13 that faces the alignment mark 16 formed on the semiconductor wafer 15.
is provided, and the incident light is configured to pass through this light transmitting portion 14a and illuminate the second alignment mark 16. The first alignment mark 14 on the exposure mask 13 is formed to have a pitch of P1 in the X direction and a pitch of Pm in the Y direction, while the second alignment mark 16 on the semiconductor wafer 15 is formed to have a pitch of P1 in the X direction and a pitch of Pm in the Y direction. The pitch in the X direction is P1, and the pitch in the Y direction is PW. That is, the first and second alignment marks have a pitch P1 in the X direction that is the same, and a pitch Pm in the Y direction,
PW is formed differently.

The two laser beams 31 and 32 mentioned above are
The pitch of flowing interference fringes caused by the interference of these laser beams is determined by the pitch of the flowing interference fringes caused by the interference of these laser beams.
By making the interference light incident on the exposure mask 13 and the semiconductor wafer 15 at an angle matching the pitch P1 in the X direction of 6, the interference light is aligned with the first and second alignment marks 1.
4, 16 From the mark edge in the Y direction, the light is diffracted only in the Y direction at diffraction angles corresponding to the respective pitches Pm and PW, and Y direction diffracted light is generated.

[0016] For example, considering each of the +1st-order diffracted lights of these Y-direction diffracted lights, each of the +1st-order diffracted lights is aligned with the alignment marks 14 and 16.
In the vicinity of the Fourier plane of , the above-mentioned pitches PW and P
The light is separated and focused at a position determined by m. Therefore, by giving a predetermined pitch difference to the alignment marks 14 and 16 in the Y direction, it is possible to separate and detect each diffracted light. In this way, when each +1st order diffracted light is photoelectrically detected and detected separately, since optical heterodyne interference has occurred in the illumination light illuminating the alignment marks 14 and 16, each +1st order diffracted light has a beat. A signal is generated. A phase difference occurs between the beat signals depending on the amount of deviation d of the alignment marks 14 and 16 in the X direction, and by detecting this phase difference, the amount of positional deviation d can be calculated.

That is, according to the relative position detection method of the present invention, the first alignment mark whose relative position is to be detected and the second alignment mark are arranged so that the pitch in the first direction is the same. On the other hand, the pitches in the second direction orthogonal to the first direction are configured to be different from each other, and the optical heterodyne interference light is configured such that the pitch of the interference fringes is the same as the pitch in the first direction. First
and by irradiating the second alignment mark,
The diffracted light containing the position information of each mark is
The diffracted light diffracted by the first alignment mark and the second alignment mark differ depending on the pitch difference between the alignment marks in the direction of
It is now possible to separate and detect the diffracted light diffracted by the alignment mark, and from the relative relationship of these separately detected diffracted lights, the relative positional deviation between the two alignment marks can be determined. can be found.

Furthermore, in the relative position detection device of the present invention, a plurality of light beams emitted from a light source and having slightly different frequencies are caused to interfere with each other to generate interference light, and this interference light is used to detect a relative position. The irradiation is applied to first and second alignment marks, and is separated and diffracted by the first and second alignment marks according to the pitch difference in a predetermined direction between the first and second position detection marks. The diffracted lights are detected separately, and from the relative relationship of the thus detected diffracted lights, that is, the diffracted lights containing positional information of the respective alignment marks, it is possible to determine the position of the first and second alignment marks. It is configured to calculate a relative positional shift amount. Therefore, the zero-order light that acts as noise, which occurs when double diffracted light is detected, is not generated as in the conventional example, and the diffracted light necessary for alignment generated at each position detection mark is separated. It becomes possible to take it out. Therefore, a stable beat signal can be obtained and position detection accuracy can be improved.

[0019]

Embodiment FIG. 3 is a diagram showing a schematic configuration of an embodiment of the relative position detecting device of the present invention. This embodiment is an example in which the relative position detection device of the present invention is applied to an X-ray exposure device for manufacturing semiconductor ICs and LSIs.

In FIG. 3, reference numeral 1 denotes a two-wavelength orthogonally polarized laser light source (hereinafter abbreviated as "light source") that generates two wavelengths of light with slightly different frequencies and mutually orthogonal polarization planes, and 2 a beam expansion 3 is a beam splitter (hereinafter referred to as “
4 and 6 are 1/4λ plates, 5 is a fixed mirror, 7 is a movable mirror whose angle can be adjusted, 8 is a polarizer, and 10
, 12, 18, 20 are lenses, 13 is a mask, 1
4 is a first alignment mark formed on the mask 13; 15 is a semiconductor wafer; 16 is a second alignment mark formed on the mask 16; 11 and 17 are Fourier marks of the wafer 15 or the mask 13. A special beam splitter (hereinafter referred to as "SBS1", "
(abbreviated as “SBS2”), 19 and 21 are photoelectric detectors, 2
2 is a signal processing circuit. Note that the mask 13 includes a first
The alignment mark 14 of the light transmitting portion 1 is formed.
4a is formed, a part of the light irradiating the mask 13 is diffracted by the first alignment mark 14, and the other part is transmitted through the light transmitting part 14a and is located below the mask 13. The second alignment mark 16 formed on the wafer 15 is irradiated with light, and the light is diffracted there. Further, the first alignment mark 14 and the second alignment mark 16 are formed according to the relationship shown in FIG. 2. That is, the pitches Pm and Pw of each mark in the Y direction are formed to be different so that the pitch P1 in the X direction is the same.

FIG. 4 shows the diffracted light diffracted by the first alignment mark 14 formed on the mask 13 and the wafer 1.
The diffracted light diffracted by the second alignment mark 16 formed on the beam splitter SBS1 11,SB
It is a figure which shows the state observed on S217 surface.

The mask 13 is mounted on a mask stage (not shown), and this mask stage has X, Y
The mask stage is configured to be able to be driven in the direction and rotated about an arbitrary line on the stage surface passing through the center of the mask stage. The mask 13 is positioned at a predetermined position using a positioning mechanism (not shown). After the positioning is completed using the relative position detection device of the present embodiment, light of a wavelength effective for exposing the resist coated on the surface of the wafer 15 (for example, exposure light including an X-ray region) is masked. The wafer 15 is irradiated via the wafer 13. By illuminating with this exposure light,
The mask pattern formed on the mask 13 is exposed in close contact with the surface of the wafer 15.

On the other hand, the wafer 15 is also configured to be movable in the X, Y, and Z directions, and, like the above-mentioned mask stage, can be rotated about an arbitrary line on the stage surface passing through the center of the wafer mounting surface. The wafer is placed on a wafer stage (not shown) configured as follows. This stage is X, Y, Z
A fine movement mechanism (not shown) such as a motor is provided to enable fine movement adjustment in the direction and rotation direction. The position of the stage in the X and Y directions is constantly detected with a precision of, for example, 0.04 μm using a measuring means such as a laser interferometer. However, the fine movement adjustment mechanism of the stage in the X and Y directions is capable of fine movement adjustment of about 2 nm. The relative position detection device of the present invention determines the amount of relative positional deviation between the mask 13 and the wafer 15, and completes the positioning by feeding back the amount of positional deviation to, for example, a wafer stage drive mechanism (not shown).

A laser beam of two wavelengths, whose frequencies are slightly different and whose planes of polarization are perpendicular to each other, emitted from the light source 1 is expanded to a predetermined beam width by a beam expander 2, and then converted into a P-polarized light component by a PBS 3. and an S-polarized component. Of these, the P-polarized laser beam passes through the PBS 3, passes through the λ/4 plate 4, becomes circularly polarized light, is reflected by the fixed mirror 5, enters the λ/4 plate 4 again, becomes S-polarized light, and becomes P-polarized light.
It is reflected to the polarizer 8 side by BS3. On the other hand, the S-polarized light component is reflected by the PBS 3, passes through the λ/4 plate 4, becomes circularly polarized light, is reflected by the movable mirror 7 set to be tilted at a predetermined angle with respect to the PBS 3, and is returned to the λ/4 plate. The light enters, becomes P-polarized light, and passes through the PBS3. These P-polarized laser beams and S-polarized laser beams pass through a polarizer 8 and become laser beams having a common plane of polarization. These two laser beams have slightly different frequencies and a predetermined angular difference between them by the movable mirror 7, so they become interference lights, and the beat frequency of this interference light creates interference fringes in the X direction. Flowing. This interference light is transmitted to the lens 10, SBS1
11. The light passes through the lens 12 and illuminates the alignment mark 14 formed on the mask 13 and the wafer position detection mark 16 formed on the wafer 15. In this embodiment as well, as explained with reference to FIG.
4a is provided, and the interference light is configured to pass through this light transmitting portion 14a and illuminate the wafer alignment mark 16.

The light reflected and diffracted by the alignment mark 14 formed on the mask 13 passes through the lens 12, is reflected by the SBS1 11, and is further reflected by the SBS2 17.
The light is reflected by the lens 18 and collected by the photoelectric detector 19.
incident on . The beat frequency is detected by the photoelectric detector 19 and is input to the signal processing circuit 22 as a beat signal. On the other hand, the light reflected and diffracted by the alignment mark 16 formed on the wafer 15 passes through the lens 12 and is reflected by the SBS 1 11.
2 17, is focused by a lens 20, and enters a photodetector 21. Here, the beat frequency is similarly detected and input to the signal processing circuit 22 as a beat signal. The signal processing circuit 22 detects the phase difference between these beat signals and converts it into the amount of positional deviation between the mask 13 and the wafer 15.

As described above, in the relative position detection device of the present invention, the fixed mirror 4 is provided parallel to the PBS 3, whereas the movable mirror 7 is tilted at a predetermined angle with respect to the PBS 3. Since a predetermined angle difference is provided between the fixed mirror 4 and the movable mirror 7, the light irradiating the mask 13 and the wafer 15 becomes interference light, and the X
Interference fringes flowing in the direction are generated.

Now, adjust the direction of the movable mirror 7,
If the pitch of the interference fringes of the light irradiated onto the mask 13 or wafer 15 is made to match the pitch P1 of the position detection marks 14 and 16 in the X direction, the Y
Diffracted lights 41 and 42 are generated respectively. The thus generated diffracted lights 41 and 42, excluding the zero-order light, contain positional information of the marks 14 and 15.

FIGS. 4A and 4B show the diffracted light 41 diffracted in the Y direction by the first position detection mark 14 formed on the mask 13 and the second position detection mark formed on the wafer 15. The diffracted light 42 diffracted in the Y direction by the mark 16 is transmitted to SBS1 11 and SBS2 1, which are installed at positions substantially conjugate to the Fourier plane of the mask 13 or wafer 15.
7 is a diagram observed above. In Figures 4(a) and (b), ○
is the diffracted light 41 diffracted by the first alignment mark 14
, and ● indicates the ±1st order light of the diffracted light 42 diffracted by the second alignment mark 16 . In addition, ◎ indicates the 0th-order light of the diffracted lights 41 and 42.

[0029] When paying attention to each ±1st-order diffracted light,
The diffraction angle is determined by the pitches Pm and PW of the position detection marks 14 and 16 in the Y direction, respectively. Pitch P of both position detection marks 14 and 16 in the Y direction
Since m and PW are formed to differ by a predetermined amount, as shown in FIG. The ±1st-order diffracted lights of the diffracted lights 42 are separated according to this pitch, and are separated into SBS1 11,
The light is focused on SBS2 17.

As shown in FIGS. 4(a) and 4(b), the SBS1 11 and the SBS2 17 are constructed so that their reflectances partially differ greatly. That is, FIG. 4(a)
A transmission film 11a is provided at the center of the SBS 111 shown in FIG. The secondary light ◎ is transmitted, and the ±1st order light ○ and ● are reflected and further guided in the direction of SBS2. As shown in FIG. 4(b), the SBS2 17 has a transmission film 1 wider than the transmission film 11a of the SBS 111 in the center.
7a is provided, and a reflective film is provided on both sides of the transmitting film 17a, so that the ±1st-order light ○ of the diffracted light 41 diffracted by the first alignment mark 14 is transmitted, and the second alignment mark The ±1st-order light ● of the diffracted light 42 diffracted by the beam 16 is reflected. The ±1st-order diffracted light transmitted through the SBS2 17 and diffracted by the first alignment mark 14 is transmitted through the lens 18.
The light is collected by the laser beam detector 19 and made incident on the first photoelectric detector 19 to detect the first beat signal. On the other hand, the ±1st-order diffracted light reflected by the SBS2 17 and diffracted by the second alignment mark 16 is focused by a lens 20, and is incident on a second photoelectric detector 21 to detect a second beat signal. .

These first and second photoelectric detectors 19
, 21, there is a phase difference between the first and second beat signals detected by the mask 13 and the wafer 15 in accordance with the amount of deviation d in the X direction. Therefore, the first and second beat signals are input to the signal processing circuit 22, the phase difference between the two beat signals is detected, and the mask 13 and the wafer 15 are
Calculate the relative positional deviation amount. The amount of relative positional deviation calculated in this way is fed back to the adjustment mechanism of the wafer stage (not shown) to adjust the positions of the wafer and the mask.

In the above-mentioned embodiment, in order to facilitate understanding and improve precision, marks formed in a matrix are used as respective alignment marks. Even if one mark with a difference is provided for each object whose positional deviation is to be detected, a desired beat signal can be obtained. In addition, in this embodiment, a close exposure type in which the mask and wafer are brought into close contact with each other for exposure has been described, but as long as the conjugate relationship between the mask and wafer and SBS1 11 and SBS2 17 is not significantly disrupted, projection is possible. A structure in which a lens is inserted between a mask and a wafer may also be used. Furthermore, first and second alignment marks may be formed on the wafer 15, as in the case of measuring overlay accuracy. In addition, in this embodiment, for ease of explanation, the position detection mark formed on the mask 13 and the wafer 1
Although the position detection marks formed in 5 are arranged in the Y direction, they may be formed anywhere within the illumination range of the incident light.

[0033]

As described above, according to the relative position detection method and apparatus of the present invention, the first and second position detection marks to be aligned are formed with different pitches in a predetermined direction, Interference light is applied to these alignment marks, the diffracted light containing the mark's position information is separated and diffracted from each mark, and the signals detected from this diffracted light are processed to perform alignment. I have to. Therefore, it is possible to eliminate the influence of 0th order diffracted light that inhibits position detection accuracy, which has been a problem in the past, making it possible to perform stable position detection and achieve high-precision positioning such as mask and wafer alignment. It can be applied very effectively to devices requiring technology. Furthermore, the method of the present invention can be suitably applied not only to alignment between a mask and a wafer, but also to measurement of minute displacement of an object, measurement of overlay error of two objects, detection and control of coordinate positions, etc. be able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the concept of a relative position detection method and apparatus of the present invention.

FIG. 2 is a diagram illustrating the relative relationship of first and second alignment marks in the method and apparatus of the present invention.

FIG. 3 is a diagram showing the overall configuration of the device of the present invention.

FIGS. 4A and 4B are diagrams showing the state of diffracted light on beam splitters SBS1 and SBS2, which partially have greatly different reflectances; FIGS.

FIG. 5 is a diagram for explaining the principle of alignment using conventional optical heterodyne interference.

[Explanation of symbols]

1 Light source 2 Beam expander 3 Polarizing beam splitter 4, 6 λ/4 plate 5 Fixed mirror 7 Movable mirror 8 Polarizer 10, 12, 18, 20 Lens 11, 17
Beam splitter 11a, 17a Transmissive section 11b, 17b Reflective section 13 Mask 14 First alignment mark 14a Light transmissive section 15 Wafer 16 Second alignment mark 19, 21 Photoelectric converter 22 Signal processing circuit

Claims (3)

[Claims] 1. A first alignment mark and a second alignment mark whose relative positions are to be detected are formed at different pitches in a predetermined direction, and a plurality of light beams having slightly different frequencies are caused to interfere with each other. The first and second alignment marks are irradiated with interference light, and the first diffracted light diffracted in the predetermined direction by the first alignment mark and the first diffracted light diffracted in the predetermined direction by the second alignment mark are The first diffracted light is detected from the second diffracted light that is separated and diffracted in the predetermined direction, and the first and second diffracted lights are detected based on the relative relationship between these first and second diffracted lights. 2
A relative position detection method characterized by detecting a relative positional shift of alignment marks. 2. The relative position detection method according to claim 1, wherein the first alignment mark is formed on an exposure mask, and the second alignment mark is formed on a semiconductor wafer, A relative position detection method, characterized in that a relative positional shift between the exposure mask and the semiconductor wafer is detected from the relative relationship between the first and second diffracted lights. 3. A light source that generates a plurality of light beams having slightly different frequencies, and an interference light generating means that generates interference light by causing the plurality of light beams emitted from the light source to interfere with each other.
interference light irradiation means for irradiating the interference light onto first and second alignment marks whose relative positions are to be detected; and a first diffracted light generated by the first alignment mark formed at a second pitch different from the pitch of the interference fringes in a second direction perpendicular to the first direction; The first diffraction is caused by the second alignment mark formed at the first pitch in one direction and at a third pitch different from the second pitch in the second direction. The separation detection means for separately detecting the second diffracted light generated separately from the light, and the relative relationship between the diffracted lights from the respective alignment marks detected by the separation detection means, A relative position detection device comprising: a signal processing means for calculating a relative positional deviation amount between the first and second alignment marks.