JPH04148808A - Position detecting method and position aligning method - Google Patents

Abstract

PURPOSE:To simplify an optical system for guiding out diffracted light and to facilitate the adjustment of an optical axis by detecting the amounts of displacements of first and second objects based on the phase different between beat signals having equal frequencies. CONSTITUTION:The electric signal which is detected in a mask-signal light receiving part 6a of the signal light receiving parts (detectors) of a bisected sensor 6 contains the beat signals having two beat frequencies fa and fb. The signal is divided into two signals. The signals are filtered through a low-pass filter 7a having the threshold value of f = 0.5 MHz and a bypass filter 7b which satisfy the condition of fa<f<fb. The + or -first mask signal and the + or -first wafer signal and the + or -fourth mask signal and the + or -fourth wafer signals obtained in this way are inputted into first and fourth phase meters 8a and 8b. Thus each phase is measured. When the + or -first and + or -fourth phase signals are detected at the same time in this way, the broad detecting range with the + or -first light can be covered, and the super-high resolution in the + or -fourth light can be achieved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention provides a position detection method using optical heterodyne interference light in semiconductor ultra-fine processing, ultra-precision Il+q determination, etc., and a position detection configuration using the position detection method to detect two objects. The present invention relates to an alignment method for performing ultra-precise alignment.

[Conventional technology]

For precision position detection technology such as synchrotron radiation lithography aligners and photosteppers, for example,
Optical heterodyne position detection methods are beginning to be put into practical use at the prototype level, as in Patent No. 261003 and Japanese Patent Application Laid-Open No. 64-89323.

The basic configuration of these methods is to irradiate coheren I light with two slightly different frequencies onto each of the diffraction gratings of the first and second objects from ±n-order directions, respectively. Detects the diffracted light generated in the vertical direction,
In addition, by interfering the two frequency components at the time of the diffraction or in the middle of the diffracted optical path to produce an optical heterodyne interference diffracted light, beat signals are respectively generated based on this, and the phase difference of these beat signals is measured. This is to detect the displacement amounts of the fourth and second objects.

In the optical heterodyne position detection method described above, the larger the grating constant of each diffraction grating, that is, the grating pitch P, the wider the signal detection range, and the relationship between them is as follows: Signal detection range 2 Diffraction grating pitch P / 2 n ·
... (2) However, n = the absolute value of the order in the irradiation direction of the coherent light, for example, if n or 1, the detection range is 172 of -1 - pitch (2). However, the opposite relationship holds true for detection resolution, and if the accuracy of the phase meter resolution is about 1°, then the detection resolution is: detection resolution 2 signal detection range / 360°...
(2) The smaller the absolute value n of the order in the light irradiation direction, or the larger the grating pitch I), the lower the accuracy of the detection resolution. Therefore, if you try to increase the detection resolution by changing the angle of light irradiated to each diffraction grating, increasing the absolute value n of the order, or using a diffraction grating with a small grating pitch P, the signal detection range will be 1: , becomes extremely narrow as is clear from the equation below.

Therefore, the present inventors proposed a new position detection and alignment configuration that can expand the detection range while maintaining the necessary detection resolution.

In these prior art techniques proposed by the present inventors, the grating pitch of the diffraction grating and the grating pitch, which have a direct effect on the signal detection range and detection resolution (these are in a contradictory relationship as described in J-2). For each absolute value n of the order of the ±n-th irradiation direction determined by 2 for each of the second objects A and B
It is possible to have diffraction gratings (Ia) (Ib) with a grating pitch P (in the drawing, Pl and P2, where p□>p2) of type 1-1, or with the absolute value n of the order as shown in FIG. The coherent light is irradiated onto each of the first and second objects A and B in a plurality of irradiation directions (for example, ±1-order and ±4-order directions) with different directions.

In such a configuration, the value of P or n in the formula (-1) is 2.
Since it has two different values, from this equation 0 and the equation 0 above, the phase difference of the signal can be obtained as a signal waveform as shown in FIG. )(c)
The signal detection range is very wide as shown in the figure (b).
As shown in (d), detection resolution with very high precision can be obtained.

[Problem that the invention seeks to solve]

However, in all of these configurations, the extraction of the diffracted light is performed in the direction perpendicular to the ±nth order irradiation direction when viewed in the grating width direction of the diffraction gratings (la) (lb), so the first and second There is a possibility that two or more diffracted lights generated by the objects Δ and B may be extracted in an overlapped manner. In order to avoid this, in these configurations, 1) (b)
As shown in , coherent light is irradiated at oblique incidence states of 01.02 with different inclination angles, and the diffracted light is also extracted at an inclination angle of 01.0 corresponding to these angles.
The structure is such that it can be taken out in 2...

Therefore, the arrangement of optical systems such as various mirrors and disks, and the adjustment of the optical axes of each optical system become complicated. In particular, in the detection optical system, two sets of detectors D, D4, etc. per axis (first and second objects There is a problem in that the number of parts that require adjustment of the optical system increases. Also, the space occupied by the optical system becomes larger, and synchro 1
~ When installed in an exposure device that uses soft X-rays from Ron synchrotron radiation, it is practically extremely important to avoid the exposure area, synchrotron radiation transmission window, etc., and arrange the optical system in an oblique incidence configuration as described above. It's difficult.

The present invention was devised in view of the new problems inherent in the technology proposed by the inventors as described above, and it simplifies the optical system, allows optical axis adjustment to be easily performed on one floor, and saves space. The aim is to provide a configuration that can be used.

[Means for solving problems]

Therefore, the present invention improves the configuration proposed by the present inventors, and uses a position detection method for detecting the positional relationship between the first and second objects and this position detection configuration as is. This is a proposal for an alignment method for aligning the first and second objects (between the first invention and the second invention, between the third invention and the fourth invention, between the fifth invention and the sixth invention).
There is such a relationship between the inventions and between the seventh invention and the eighth invention).

In addition, when viewed from the width direction of the diffraction grating, each of the diffracted lights taken out in the vertical direction overlaps even when viewed from the side in the longitudinal direction of the grating, that is, first, as an incident configuration, each cohesin beam is overlapped when viewed from the side in the longitudinal direction of the grating. 1- All the light irradiated onto the diffraction grating is obliquely incident at the same inclination angle, and when extracting the diffracted light, the first
The optical axes of the diffracted light beams overlap the object A and the second object B, respectively, so that the light beams are extracted in parallel biaxial state. Then, these beat signals are detected while the diffracted lights on each optical axis overlap, and in the process of detection, the beat signals of the diffracted lights of different origins are separated, or the diffracted lights of each of these optical axes are detected immediately before detection. These beat signals are detected after eliminating the overlap of the lights and making them respective interference diffraction lights.

When detecting these beat signals while the diffracted lights overlap as in the former case, first, as shown in Figure 1 (a), the frequencies are slightly different (for example, f, and f2, and f3 and f4). frequency components, or f, f2 and f2
and f) that can interfere with each other during diffraction (their planes of polarization match during diffraction), and calculate the frequency of each set of beat signals generated during the diffraction. will differ between these pairs (e.g.,
fa=lf, -f21 and fb=lfJ-f.

A set of a plurality of coherent lights (faf: fb at both beat frequencies of The configuration according to the proposal and the configuration also proposed by the present inventor that irradiates from two or more irradiation directions in which the absolute value n of the order differs for the ±n-th irradiation direction are used for these incident lights. ). When these interference diffraction lights are detected as a beat signal, these beat signals are detected in a combined state as shown in Figure 2 (a), so as shown in Figure 1 (b). Pan 1-pass filter 131 as shown in ? It is filtered by □ to PF to separate them into beat frequencies as shown in Figure 2 (b) and (c), and finally the first object with the same beat frequency is derived from a person. The phase difference between the beat signals from the second object B and the second object B is measured.

- On the other hand, when detecting a beat signal by eliminating the overlap of the diffracted lights just before detection, as in the latter case, the frequencies are slightly different and interfere with each other during diffraction, as shown in Figure 3 (a). The plane of polarization will be different between these pairs (for example, the plane of polarization of one set will be different). is vertical, and the polarization plane of the other set is horizontal, and the beat frequencies do not necessarily have to match.) A plurality of sets of coherent lights are used as incident light. Before detecting these interference diffraction lights, a polarizing beam splitter PBS is used as shown in the same figure (b).
,, PRS4 etc. are used to eliminate the overlap of the diffracted lights and separate them into interference diffracted lights each having a single plane of polarization (for example, even if the beat frequencies of both interference diffracted lights are f8, or fa Even in the two cases of (fl) and (fl), the light is extracted separately into one with a vertical polarization plane and one with a horizontal polarization plane). Ultimately, all of these are detected as beat signals by detectors D1 to D4, etc., but the first object with the same polarization plane (for example, the polarization plane is vertical or horizontal) and the second The phase difference between the beat signals originating from object B will be measured.

Hereinafter, only the position detection method of the present invention will be described in detail.

First, the first invention is to set a set of elements that have slightly different frequencies and can interfere with each other during diffraction, and the frequencies of the beat signals of each set generated during the interference will differ between these sets. A set of multiple coherent lights,
For each set, the diffraction gratings of the first and second objects are irradiated from the ±n-order directions, and the beams are irradiated from multiple directions with different absolute values n of the orders at the same inclination angle. Interference light that is diffracted in the vertical direction from each of the diffraction gratings of the first and second objects upon incidence and taken out at the same tilt angle is obtained from each of the diffraction gratings of the first and second objects. The synthesized signal of the beat signals obtained from these interference lights is filtered with a bandpass filter and separated into signals with a single beat frequency (
The basic feature is that the phase difference between the Be-I signals having the same frequency as above is measured, and the displacement amount of the first and second objects is detected based on these phase differences.

Further, the third invention provides a method in which two or more types of diffraction gratings having different grating constants are arranged side by side on each of the first and second objects, and
A set of coherent light beams that have slightly different frequencies and can interfere with each other during diffraction is used, and the frequency of the beat signal of each set that is generated during the interference differs between these sets of coherent lights. , the incidence is made at the same inclination angle for each set from the ±n-th order direction determined according to each lattice constant of the diffraction grating, and by these incidences, each of the diffraction gratings of the first and second objects is incident in the vertical direction, respectively. The interference light beams obtained from each diffraction grating of the first and second objects are detected separately, and a composite signal of the beat signals obtained from these interference lights is detected. The beat signals of the first and second objects are filtered with a bandpass filter and separated into beat signals of a single frequency, and the phase difference between the beat signals of the same frequency is measured. It is characterized by detecting the amount of displacement.

The fifth invention is to form a plurality of sets of coherent lights whose polarization planes differ between each set, each set consisting of a set of light beams having slightly different frequencies and which can interfere with each other during diffraction. For each diffraction grating of the first and second objects to be irradiated from the ±n-order direction, it is made incident at the same inclination angle from multiple directions with different absolute values D of the orders, and by these incidences, The interference light diffracted in the vertical direction from each diffraction grating of the first and second objects and extracted at the same tilt angle is divided into those obtained from each diffraction grating of the first and second objects and detected. At the same time, these interference lights are separated for each plane of polarization, the phase differences of the beat signals obtained from the interference lights of the same planes of polarization are each measured, and the first signal is calculated based on these phase differences. and detecting the amount of displacement of the second object.

Furthermore, the seventh invention is such that two or more types of diffraction gratings with different r-constants are arranged side by side and placed on each of the first and second objects, and the diffraction gratings have slightly different frequencies and can interfere with each other during diffraction. A set of coherent lights whose planes of polarization differ between these sets,
The light is incident on each set at the same inclination angle from the ±n-th order direction determined according to each grating constant of the diffraction grating, and by these incidences, the light is vertically directed from each of the diffraction gratings of the first and second objects. Interfering light that is diffracted and extracted at the same tilt angle is detected separately into those obtained from each diffraction grating of the first and second objects, and these interference lights are separated for each plane of polarization. , the phase difference between the Bea-1 signals obtained from the interference light beams having the same plane of polarization is measured, and the amount of displacement of the first and second objects is detected based on these phase differences. It is said that

〔Example〕

Specific examples of the present invention will be described below.

FIGS. 4(a) and 4(b) show an embodiment of the position detection method of the eleventh invention.

As shown in Figure (a), coherent light emitted from a small laser light source (2a) consisting of a semiconductor laser (or a He-Na laser etc. may also be used) is transmitted through a half mirror.
Divide into two by (3a) and use frequency shifter (4a) (4b)
(Two are used in the drawing, but you can use only one and shift only one frequency) to set the beat frequency f a = 0.1 M! (Two linearly polarized lights of z (2
If the frequencies of the two polarized lights are f□ and f2, respectively, fa is determined by fa=lf1 f2). The planes of polarization of these coherent lights match. The two polarized lights are transferred to a diffraction grating (Ia
)(], b) from the ±1st direction (angle α) (at this time, as shown in the same figure (b), the inclination angle θ
irradiated at an oblique incidence).

Similarly, the light from another laser light source (zb) (or the beam may be split from the aforementioned light source (2a) using a half mirror (not shown)) is divided into two by a half mirror (3b), Beat frequency f b = 1. using frequency shifter (4c) (4d). It produces two linearly polarized lights at t4Hz (all planes of polarization are identical to those of the two legs). These two polarized lights are similar to the two polarized lights in Figure 4 (b).
) as shown in FIG.
, a diffraction grating (
la) (lb) is irradiated from the ±4th direction (angle β), respectively.

And both diffraction gratings (1,a) of mask A and wafer B
The diffracted light from (1,b) becomes an optical heterodyne interference diffracted light having each beat frequency fa and fb at the time of diffraction, and all of the diffracted light is vertical in the grating width direction and at the same angle of inclination as the above-mentioned inclination angle O in the grating longitudinal direction. It is emitted at an angle of These diffracted lights are expanded to an appropriate size by a beam expander (5) and separated into a mask signal and a wafer signal by a two-split sensor (6).

The electric signal detected by the mask signal light receiving part (6a) of the signal light receiving part (detector) of the two-part sensor (6) is as follows.
Two beat frequencies fa and f as shown in Figure 2(a)
Contains the beat signal of b.

This signal is branched into two, and each is filtered by a low-pass filter (7a) and a bypass filter (7b) having a threshold value of f=0.5 MIIZ that satisfies the condition fa<f<fb. The signal that has passed through the low-pass filter (7a) is a ±1st-order mask signal of the beat frequency fa from which the fb acid component has been removed, as shown in FIG. 3(b). Further, the signal that has passed through the bypass filter (7b) is a ±4th-order mask signal of the beat frequency fb from which the fa acid component has been removed, as shown in FIG. 3(c).

On the other hand, the wafer signal receiving section (6) of the two-part sensor (6)
The electrical signal detected in b) also includes two beat frequencies fa and fb. Therefore, this signal is split into two, and each is filtered with a low-pass filter (7C) and a bypass filter (7d) that have a threshold of 0.5 Mllz2.The signal that has passed through this low-pass filter (7C) is filtered by fb acid. Component removed beat frequency fa 1
Next is the wafer signal. Further, the signal passed through the bypass filter (7d) is a ±4th-order wafer signal of the beat frequency fb from which the fa acid component has been removed.

The ±1st mask signal and ±1st wafer signal obtained as described above, as well as the ±4th mask signal and ±4th wafer signal, are captured by phase meters (8a) and (8b), respectively, and each Measure the phase. In this way, by simultaneously detecting the ±1st-order and ±4th-order phase signals, it is possible to cover a wide detection range with the ±1st-order light, and also achieve the ultra-high resolution of the ±4th-order light. Become.

Furthermore, if the value detected here is sent to the signal processing section (9) as shown by the broken line in FIG. 4(b) and fed back to the mask stage and wafer stage, the mask Δ and the wafer B are aligned. You can also do that.

In addition, when receiving the diffracted light, the above-mentioned two-split sensor (6
) instead of using a knife mirror (10) and two photodetectors Da, D as shown in FIG.
This can also be done by using b. However, the two-split sensor (6) has two signal receivers (6a) (6b).
), and this dead zone reduces the crosstalk between the diffracted light from the mask A side and the diffracted light from the wafer B side, so it is better to use the two-split sensor (6). However, the device configuration becomes more compact.

〔Effect of the invention〕

- As described in detail, according to the method of the present invention, after extracting the diffracted light in an overlapping state, the overlap is eliminated immediately before detection, or signal separation is performed during the detection process, and the final result is Since it becomes possible to measure the phase difference between signals with the same beat frequency, the optical system for extracting the diffracted light can be simplified, optical axis adjustment becomes easier, and the installation space for these optical systems can be saved. can also be made smaller.

Further, in particular, the first to fourth methods of the invention do not use a polarizing beam splitter or a /2 wavelength plate, so that polarization leakage components are not generated and effects such as deterioration of signal linearity are less likely to occur.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are explanatory diagrams showing the basic signal detection method of the first to fourth invention methods, and FIGS. 2(a), (b), and (c) are (i) before and after filtering of the detection signal. Waveform diagrams showing divided waveforms, Figures 3(a) and (b) are explanatory diagrams showing the basic signal detection method of the fifth to eighth invention methods, and Figures 4(a) and (b) are diagrams showing the basic signal detection methods of the fifth invention method to the eighth invention method. Figure 5 is a front view and side view showing a specific example of the method; Figure 5 is a schematic diagram showing an example of a light receiving configuration that can be used in place of the two-split sensor used in this example;
The figure is a perspective view showing a position detection configuration proposed by the inventor;
FIG. 7 is a perspective view showing another position detection configuration similarly proposed by the inventor, and FIG. 8 (a) (b) (c) (d)
9A and 9B are waveform diagrams showing the signal waveforms of beat signals obtained by these proposed configurations, and FIGS. 9A and 9B are explanatory diagrams that do not show oblique incidence and oblique emission states in these proposed configurations. In the figure, (Ia) and (Ib) are diffraction gratings, (2) (2a)
(2b) is a laser light source, (3) (3a) (3b)
is half mirror 1 (4a) (4b) (4c) (4d
) is a frequency shifter, (5) is a beam expander, (6
) is a two-split sensor, (6a) (6b) is a light receiving part, (7
a) (7c) is a low-pass filter, (7b) (7d) is a bypass filter, (8a) (8b) is a phase meter, (9)
is a signal processing control unit, (10) is a Knifezi Miller, and A
is the first object, B is the second object, D3, D2, D3, D
4 indicates each detector. No. 1 (a) Draft procedure amendment (voluntary) July 12, 1990

Claims (8)

[Claims] (1) A set of elements with slightly different frequencies that can interfere with each other during diffraction, and a plurality of coherent signals in which the frequencies of the beat signals of each set that occur during the interference differ between these sets. In order to irradiate each set of light from the ±n-order directions to each diffraction grating of the first and second objects, it is possible to irradiate each set of light from the ±n-order directions at the same inclination angle from multiple directions with different absolute values n of the orders. The interference light beams are diffracted in the vertical direction from each of the diffraction gratings of the first and second objects by these incidences, and are extracted at the same inclination angle from each of the diffraction gratings of the first and second objects. The synthesized signal of the beat signals obtained from these interference lights is filtered with a bandpass filter and divided into beat signals of a single beat frequency. A position detection method that measures phase differences and detects displacement amounts of the first and second objects based on these phase differences. (2) A set of elements with slightly different frequencies that can interfere with each other during diffraction, and a plurality of coherent signals in which the frequencies of the beat signals of each set that are generated at the time of interference differ between these sets. In order to irradiate each set of light from the ±n-order directions to each diffraction grating of the first and second objects, it is possible to irradiate each set of light from the ±n-order directions at the same inclination angle from multiple directions with different absolute values n of the orders. The interference light beams are diffracted in the vertical direction from each of the diffraction gratings of the first and second objects by these incidences, and are extracted at the same inclination angle from each of the diffraction gratings of the first and second objects. The synthesized signal of the beat signals obtained from these interference lights is filtered with a bandpass filter and divided into beat signals of a single beat frequency. An alignment method that measures phase differences and aligns the first and second objects based on these phase differences. (3) Two or more types of diffraction gratings with different grating constants are arranged side by side on each of the first and second objects, and a set of gratings with slightly different frequencies that can interfere with each other during diffraction, A plurality of sets of coherent light beams, in which the frequency of each set of beat signals generated at the time of interference differs between these sets, are separated for each set from the ±n-th direction determined according to each grating constant of the diffraction grating. are incident on the first and second objects at the same inclination angle, and the interference light beams are diffracted in the vertical direction from the respective diffraction gratings of the first and second objects and taken out at the same inclination angle as a result of these incidences. The beat signals obtained from each diffraction grating of the object are detected separately, and the composite signal of the beat signals obtained from these interference lights is filtered with a bandpass filter and divided into each beat signal of a single beat frequency. A position detection method that measures phase differences between identical beat signals and detects displacement amounts of the first and second objects based on these phase differences. (4) Two or more types of diffraction gratings with different grating constants are arranged side by side on each of the first and second objects, and a set of gratings with slightly different frequencies that can interfere with each other during diffraction is formed, A plurality of sets of coherent light beams, in which the frequency of each set of beat signals generated at the time of interference differs between these sets, are separated for each set from the ±n-th direction determined according to each grating constant of the diffraction grating. are incident on the first and second objects at the same inclination angle, and the interference light beams are diffracted in the vertical direction from the respective diffraction gratings of the first and second objects and taken out at the same inclination angle as a result of these incidences. The beat signals obtained from each diffraction grating of the object are detected separately, and the composite signal of the beat signals obtained from these interference lights is filtered with a bandpass filter and divided into each beat signal of a single beat frequency. An alignment method that measures phase differences between beat signals between objects and aligns the first and second objects based on these phase differences. (5) A set of coherent light beams with slightly different frequencies that can interfere with each other during diffraction is created, and each set of coherent light beams has a different plane of polarization. In order to irradiate each diffraction grating of the first and second objects from the ±n-order directions, the beams are incident at the same inclination angle from multiple directions with different absolute values n of the orders, and these incidences cause the first and detecting the interference light that is diffracted in the vertical direction from each diffraction grating of the second object and taken out at the same tilt angle into those obtained from each of the diffraction gratings of the first and second objects, and , separate these interference lights for each plane of polarization, measure the phase difference of the beat signals obtained from the interference lights of the same plane of polarization, and calculate the first and second beat signals based on these phase differences. 2. A position detection method for detecting the amount of displacement of an object. (6) A set of light beams with slightly different frequencies that can interfere with each other during diffraction is created, and each set of coherent light beams has a different plane of polarization. In order to irradiate each diffraction grating of the first and second objects from the ±n-order directions, the beams are incident at the same inclination angle from multiple directions with different absolute values n of the orders, and these incidences cause the first and detecting the interference light that is diffracted in the vertical direction from each diffraction grating of the second object and taken out at the same tilt angle into those obtained from each of the diffraction gratings of the first and second objects, and , separate these interference lights for each plane of polarization, measure the phase difference of the beat signals obtained from the interference lights of the same plane of polarization, and calculate the first and second beat signals based on these phase differences. 2. Alignment method for aligning objects. (7) Two or more types of diffraction gratings with different grating constants are arranged side by side on each of the first and second objects, and a set of gratings with slightly different frequencies that can interfere with each other during diffraction is formed. A plurality of sets of coherent lights whose polarization planes differ between these sets are made incident at the same inclination angle for each set from ±n-th directions determined according to each lattice constant of the diffraction grating. , interference light diffracted in the vertical direction from each of the diffraction gratings of the first and second objects by these incidences, and extracted at the same inclination angle, is
In addition to separately detecting the signals obtained from each diffraction grating of the second object, these interference lights are separated for each plane of polarization, and the beat signals obtained from the interference lights of those with the same plane of polarization are detected. A position detection method that measures phase differences and detects displacement amounts of the first and second objects based on these phase differences. (8) Two or more types of diffraction gratings with different grating constants are arranged side by side on each of the first and second objects, and a set of gratings with slightly different frequencies that can interfere with each other during diffraction is formed, A plurality of sets of coherent lights whose polarization planes differ between these sets are made incident at the same inclination angle for each set from ±n-th directions determined according to each lattice constant of the diffraction grating. , interference light diffracted in the vertical direction from each of the diffraction gratings of the first and second objects by these incidences, and extracted at the same inclination angle, is
In addition to separately detecting the signals obtained from each diffraction grating of the second object, these interference lights are separated for each plane of polarization, and the beat signals obtained from the interference lights of those with the same plane of polarization are detected. An alignment method that measures phase differences and aligns the first and second objects based on these phase differences.