JPH0635928B2 - Position detection method and position alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a position detection method utilizing optical heterodyne interference light in semiconductor ultrafine processing, ultraprecision measurement, etc. The present invention relates to a positioning method for performing ultra-precision positioning.

[Prior Art] A precision position detecting technique such as an aligner for synchrotron radiation photolithography and a photostepper is disclosed in, for example, JP-A-62-62.
Optical heterodyne position detection methods such as those described in Japanese Patent Laid-Open No. 261003 and Japanese Patent Laid-Open No. 64-89323 have begun to be put to practical use at the level of prototypes.

The basic configuration of these methods is to irradiate the diffraction gratings of the first and second objects with coherent light of two slightly different frequencies from the directions of the ± nth order, respectively, so that the diffraction gratings are perpendicular to each of the diffraction gratings. Direction diffracted light is detected, and two frequency components are interfered at the time of the diffraction or in the middle of the diffracted light path to generate optical heterodyne interference diffracted light, and beat signals are generated based on the diffracted light. The amount of displacement of the first and second objects is detected by measuring the phase difference of.

In the above optical heterodyne position detection method, the larger the grating constant of each diffraction grating, that is, the larger the grating pitch P, the wider the signal detection range, and the relationship between them is: signal detection range = diffraction grating pitch P / 2n ... = Absolute value of the order in the irradiation direction of coherent light. For example, when n is 1, 1/2 of the pitch P is the detection range. However, the opposite relationship holds true for the detection resolution, and if the accuracy of the phase meter resolution is about 1 °, the detection resolution is: detection resolution = signal detection range / 360 °. The smaller the absolute value n of the order in the irradiation direction and the larger the grating pitch P, the lower the accuracy of the detection resolution. Therefore, in order to increase the detection resolution, if the irradiation angle of light to each diffraction grating is changed to increase the absolute value n of the order or to use a diffraction grating with a small grating pitch P, the signal detection range is calculated from the above equation. As you can see, it becomes extremely narrow.

Therefore, the inventors of the present invention have proposed a new position detection and alignment configuration capable of expanding the detection range while maintaining the required detection resolution.

In these prior arts proposed by the present inventors, the grating pitch of the diffraction grating and the grating which directly affect the signal detection range and the detection resolution (these have a contradictory relationship as shown in the above equation) Absolute value of the order of ± n-order irradiation direction [diffraction equation n · λ = P · sin θn (λ is the light source wavelength, n is a positive integer, θn is the incident angle of light with respect to the normal to the lattice plane)] determined by the pitch P For n, there are two or more types of pitches, or two or more different irradiation directions (or two or more different diffraction directions).
For example, as shown in FIG. 6, first and second objects A,
Each of B is provided with two or more kinds of diffraction gratings P (P ₁ and P _{2 in} the drawing, where P ₁ > P ₂ ) of diffraction gratings (1a) (1b),
As shown in FIG. 7, coherent light is emitted to each of the first and second objects A and B so that the absolute values n of the orders are different in a plurality of irradiation directions (for example, ± 1st order and ± 4th order). It is designed to irradiate.

In such a configuration, since the value of P or n in the above equation has two or more different values, the phase difference of the signals is as shown in FIG. 8 from this equation and the above equation. It is obtained as a signal waveform, and one with a very wide signal detection range as shown in (a) (c) of the figure and one with extremely high detection resolution accuracy as shown in (b) (d) of the figure. Will be obtained together.

[Problems to be solved by the invention]

However, in all of these configurations, when the extraction of diffracted light is performed in the direction perpendicular to the ± nth order irradiation direction when the diffraction widths of the diffraction gratings (1a) and (1b) are viewed in the width direction, There is a risk that two or more diffracted lights generated by each of the objects A and B may be overlapped and extracted. In these configurations to avoid it,
As shown in FIGS. 9 (a) and (b) as seen from the side right in the longitudinal direction of the grating, coherent light is emitted in oblique incident states θ ₁ , θ ₂ ... With different inclination angles, and the diffracted light is also extracted. The inclination angles θ ₁ , θ _2, ... Corresponding to these angles are taken out.

Therefore, the arrangement of optical systems such as various mirrors and detectors and the adjustment of the optical axis of each optical system become complicated, and especially in the detection optical system, two sets of detectors D _{1 to} D ₄ are provided for each axis (first and second).
There is a problem in that there are many parts that require adjustment of the optical system, such as one set for each of the objects A and B). In addition, the space occupied by the optical system becomes wider, and when installing in an exposure device that uses soft X-rays of synchrotron radiation, avoid the exposure area and radiation transmission window, and enter the oblique incidence as described above. It is actually very difficult to arrange the optical system in the configuration.

The present invention was created in view of the new problems inherent in the technique proposed by the present inventor as described above, and the optical system can be simplified to easily adjust the optical axis, and space saving can be realized. It does not provide a configuration.

[Means for solving problems]

Therefore, the present invention is an improvement over the configuration proposed by the present inventor, and uses the position detection method for detecting the positional relationship between the first and second objects and this position detection configuration as they are. The invention proposes 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, and the fifth invention and the sixth invention).
There is such a relationship between inventions and between the seventh invention and the eighth invention).

In addition, when the diffracted lights respectively extracted in the vertical direction when viewed from the diffraction grating width direction overlap with each other when viewed from the lateral side in the longitudinal direction of the grating, that is, first, as a configuration of incidence, each coherent when viewed from the lateral direction in the longitudinal direction of the grating. All the irradiation of the light to the diffraction grating is made to be obliquely incident at the same inclination angle, and when the diffracted light is taken out, the optical axes of the diffracted light overlapping the first object A and the second object B are respectively formed, and the two parallel light beams are formed. It is taken out in the axial state. And these beat signals are detected while the diffracted lights in each optical axis are overlapped, or the beat signals of different diffracted lights originating in the process of the detection are separated,
Immediately before detection, the overlapping of the diffracted lights of the respective optical axes is eliminated to form respective interference diffracted lights, and then the beat signals are detected.

When the beat signals are detected while the diffracted lights are overlapped as in the former case, first, the frequencies are slightly different (for example, f ₁ , f ₂ and f ₃ as shown in FIG. 1 (a)).
And f ₄ frequency components, or f ₁ and f ₂ and f ₂ and f ₃ frequency components that can interfere with each other during diffraction (polarization planes match during diffraction) , The frequencies of the beat signals of each set generated at the time of the interference will be different between these sets (for example, fa = | f ₁ −
For both beat frequencies f ₂ | and fb = | f ₃ −f ₄ |, fa ≠ fb
A plurality of sets of coherent light are used as incident light (a diffraction grating having two or more types of pitches is provided in the first object and the second object, respectively, the configuration proposed by the present inventor, and ± n The same proposed configuration of the present inventor, which irradiates from two or more irradiation directions in which the absolute value n of the order is different depending on the next irradiation direction, is used for these incident lights).
When these interference diffracted lights are detected as beat signals, these beat signals are detected in a combined state as shown in FIG. 2 (a).
As shown in (b), the frequency filters PF _{1 to} PF _{4 are used} for filtering so that each of them has a single beat frequency as shown in FIGS. From the first object A and the second object B having the same
The phase difference between the beat signals of the origins will be measured respectively.

On the other hand, in the latter case, when the beat signal is detected by eliminating the overlapping of the diffracted light immediately before the detection, the frequencies are slightly different as shown in FIG. (For example, those having frequency components of f ₁ and f ₂ and having the same polarization plane) are set as one set, and the polarization planes are different between these sets (for example, the polarization plane of one set is vertical). Direction, and the polarization plane of the other set is horizontal, and the beat frequencies do not necessarily need to match.) A plurality of sets of coherent light are used as incident light. And before detecting these interference diffracted light, the same figure (b)
As shown in Fig. ₂ , polarization beam splitters PBS ₁ and PBS ₂ etc. are used to eliminate the overlapping of the diffracted lights and separate them into interference diffracted lights with a single polarization plane (for example, both interference diffracted lights have the same beat frequency). Even in the case of fa, or fa and f
Even in the case of two types of b, it is extracted separately into one having a vertical polarization plane and one having a horizontal polarization plane). Eventually, these are detected as beat signals by the detectors D _{1 to} D _4, etc., but the first object A having the same plane of polarization (for example, the plane of polarization is vertical or horizontal).
The phase difference of the beat signal between the source and the source of the second object B will be measured respectively.

Hereinafter, the configuration of the present invention will be described in detail only with respect to the position detecting method.

First, in the first aspect of the invention, a set of beat signals having slightly different frequencies and capable of interfering with each other at the time of diffraction is set, and the frequencies of the beat signals of the respective sets generated at the time of the interference are different between the sets. A set of multiple coherent lights,
When the diffraction gratings of the first and second objects are radiated from the ± n-order directions for each set, they are incident at the same tilt angle from a plurality of directions in which the absolute values n of the orders are different, and these The interference light which is vertically diffracted by the respective diffraction gratings of the first and second objects and is extracted at the same inclination angle is divided into those obtained from the respective diffraction gratings of the first and second objects. Detected, and the combined signal of beat signals obtained from these interference lights is filtered by a frequency filter to be divided into single beat frequencies, and the phase difference between the beat signals of equal frequencies is measured. The basic feature is to detect the displacement amounts of the first and second objects based on these phase differences.

Further, according to the third invention, two or more kinds of diffraction gratings having different grating constants are arranged side by side and arranged in each of the first and second objects, and
A set of coherent light beams whose frequencies are slightly different and can interfere with each other at the time of diffraction is set as one set, and the frequencies of the beat signals of each set generated at the time of interference are different between these sets. , Incident at the same inclination angle for each set from directions of ± nth order determined according to the respective grating constants of the diffraction grating, and by these incidences, the diffraction gratings of the first and second objects are respectively caused to be in the vertical direction. The interference light that is diffracted into and extracted at the same tilt angle is divided into those obtained from the diffraction gratings of the first and second objects and detected, and the combined signal of the beat signals obtained from these interference lights is detected. The signals are filtered by a frequency filter to be divided into those having a single beat frequency, the phase differences between the beat signals having the same frequency are measured, and the first and second phases are determined based on these phase differences. It is characterized by detecting the displacement amount of the object.

A fifth aspect of the invention is to set a plurality of sets of coherent light beams whose polarization planes are different between these sets, each set having a slightly different frequency and capable of interfering with each other during diffraction. For each diffraction grating of the first and second objects to be irradiated from the ± order directions, the absolute value of the order n
Which are incident from a plurality of directions which are different from each other at the same inclination angle, and are diffracted in the vertical direction from the respective diffraction gratings of the first and second objects by these incidences and taken out at the same inclination angle. The light is divided into those obtained from the diffraction gratings of the first and second objects to be detected, and these interference lights are separated for each polarization plane, and the interference lights of the same polarization plane are obtained respectively. The phase difference of the beat signals to be measured, and the first and second phase differences are measured based on these phase differences.
The feature is that the displacement amount of the object is detected.

Furthermore, in the seventh invention, two or more kinds of diffraction gratings having different grating constants are arranged side by side and arranged in each of the first and second objects,
A plurality of sets of coherent light beams whose polarization planes are different between these sets are set as the respective lattice constants of the diffraction grating, as a set of those having slightly different frequencies and capable of interfering with each other at the time of diffraction. From each of the ± n-order directions, which are determined according to the angle of incidence, by the same inclination angle for each group, and by these incidences, the diffraction gratings of the first and second objects are respectively diffracted in the vertical direction and have the same inclination angle. The interfering light extracted in step 1 is divided into those obtained from the diffraction gratings of the first and second objects and detected, and the interfering light is separated for each polarization plane so that those having the same polarization plane are separated from each other. It is characterized in that the phase differences of the beat signals respectively obtained from the interference light are measured and the displacement amounts of the first and second objects are detected based on these phase differences.

〔Example〕

 Specific examples of the present invention will be described below.

4 (a) and 4 (b) show an embodiment of the position detecting method of the first invention.

As shown in FIG. 1A, a small laser light source (2a) composed of a semiconductor laser (or a He-Ne laser or the like may be used).
The coherent light emitted from is divided into two by half mirror (3a), and frequency shifters (4a) and (4b) (two in the drawing are used, but only one frequency may be used to shift only one frequency) Thus, two linearly polarized lights having a beat frequency fa = 0.1 MHz (if the frequencies of the two polarized lights are f ₁ and f ₂ , respectively, this fa is determined by fa = | f ₁ −f ₂ |). The polarization planes of these coherent lights are the same. The two polarized light is reflected by the mirrors M ₁ and M ₂ to form the mask A which is the first and second objects.
And a diffraction grating (1 with a grating pitch P formed on the wafer B
Irradiation is performed from the ± 1st direction (angle α) with respect to a) and (1b) (at this time, irradiation is performed in an oblique incidence state with an inclination angle θ as shown in FIG.

Similarly, the light from another laser light source (2b) (or the beam from the above-mentioned light source (2a) may be split using a half mirror (not shown)) is split into two by the half mirror (3b), The frequency shifters (4c) and (4d) are used to create two linearly polarized lights with a beat frequency fb = 1 MHz (these planes of polarization are all the same as above). Similar to the above-mentioned two-polarized light, the two-polarized light is a diffraction grating (1a) (1b) formed on the mask A and the wafer B in the oblique incidence state with the inclination angle θ as shown in FIG. 4 (b). The irradiation is performed from the ± 4th order (angle β).

The diffracted light from both the diffraction gratings (1a) and (1b) of the mask A and the wafer B becomes interference diffracted light having beat frequencies of fa and fb at the time of diffraction, all in the vertical direction in the grating width direction and in the grating longitudinal direction. In the direction, the light is emitted at the same angle as the tilt angle θ. These diffracted light beam expanders (5) are expanded to an appropriate distance and divided into a mask signal and a wafer signal by a two-division sensor (6).

The electric signal detected by the mask signal light receiving portion (6a) of the signal light receiving portion (detector) of the two-divided sensor (6) is shown in FIG.
It includes beat signals of two beat frequencies fa and fb as shown in (a). This signal is split into two, and each is f
Filtering is performed by the low-pass filter (7a) and the high-pass filter (7b) having a contingency value of f = 0.5 MHz satisfying the condition of a <f <fb. The signal passed through the low pass filter (7a) has a beat frequency f from which the fb component is removed as shown in FIG.
± 1st order mask signal of a. In addition, a high-pass filter (7
The signal passed through b) is a ± 4th order mask signal of beat frequency fb from which the fa component is removed as shown in FIG.

On the other hand, the electric signal detected by the wafer signal light receiving portion (6b) of the two-divided sensor (6) is the same as the two beat frequencies f.
Includes a and fb. So this signal is split into two,
Each is filtered by a low-pass filter (7c) and a high-pass filter (7d) with a threshold value of 0.5 MHz. The signal passed through the low pass filter (7c) is a ± 1st order wafer signal of beat frequency fa from which the fb component is removed. The signal passed through the high pass filter (7d) is a ± 4th order wafer signal of beat frequency fb from which the fa component is removed.

The ± 1st order mask signal and the ± 1st order wafer signal, and the ± 4th order mask signal and the ± 4th order wafer signal obtained as described above are respectively captured by the phase meters (8a) and (8b), and the respective phases are acquired. taking measurement. By detecting the ± 1st order and ± 4th order phase signals at the same time in this way, it is possible to cover a wide detection range by the ± 1st order light and to achieve the ultrahigh resolution of the ± 4th order light. Become.

Further, if the value detected here is sent to the signal processing unit (9) as shown by the broken line in FIG. 4 (b) and fed back to the mask stage and the wafer stage, the alignment of the mask A and the wafer B is performed. You can also

In addition, when receiving the diffracted light, the above-mentioned two-division sensor (6)
Instead of using, a knife edge mirror (10) and two photodetectors Da and Db can be used as shown in FIG. But a two-part sensor
In the case of (6), there is a dead zone between the two signal receiving portions (6a) and (6b), and the dead zone reduces the crosstalk at the time of separating the diffracted light from the mask A side and the diffracted light from the wafer B side. Therefore, using the two-divided sensor (6) makes the device configuration more compact.

〔The invention's effect〕

As described above in detail, according to the method of the present invention, after the extraction of the diffracted light is performed in a state where there is overlap, the overlap is eliminated immediately before detection, or signal separation is performed in the detection process to finally obtain the beat frequency. Since it becomes possible to measure the phase difference between signals having equal values, the optical system for extracting the diffracted light can be simplified and the optical axis adjustment becomes easy,
The installation space for these optical systems can also be reduced.

Further, in particular, in the first to fourth invention methods, since the polarization beam splitter, the half-wave plate and the like are not used, the polarization leakage component does not occur and the influence such as the deterioration of the signal linearity is less likely to occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and (b) are explanatory views showing the basic signal detection method of the first to fourth invention methods, and FIGS. 2 (a) (b) (c) are detection methods. Waveform diagram showing signal waveforms before and after signal filtering, Fig. 3 (a) (b)
Is an explanatory view showing a basic signal detecting method of the fifth invention method to the eighth invention method, FIGS. 4 (a) and (b) are front views and side views showing a concrete embodiment of the first invention method, FIG. 5 is a schematic view showing an example of a light receiving structure that can be used in place of the two-division sensor used in this embodiment, and FIG. 6 is a perspective view showing a position detecting structure proposed by the present inventor. FIG. 8 is a perspective view showing another position detection configuration similarly proposed by the present inventor, and FIG. 8 (a) (b) (c)
FIG. 9 (d) is a waveform diagram showing the signal waveform of the beat signal obtained by these proposed configurations, and FIGS. 9 (a) and 9 (b) are explanatory diagrams showing oblique incidence and oblique emission states in these proposed configurations. . In the figure, (1a) (1b) is a diffraction grating, (2) (2a) (2b) is a laser light source, (3) (3a) (3b) is a half mirror, (4a) (4b) (4c) (4d ) Is a frequency shifter, (5) is a beam expander, (6) is a 2-split sensor, (6a) and (6b) are light receiving parts, (7a) and (7c) are low-pass filters, and (7b) and (7d) are high-pass filters. , (8a) (8b) are phase meters,
(9) is a signal processing control unit, (10) is a knife edge mirror, A
Is a first object, B is a second object, and D ₁ , D ₂ , D ₃ and D ₄ are detectors.

Claims (8)

[Claims] 1. A plurality of sets, each having a slightly different frequency and capable of interfering with each other at the time of diffraction, as a set, and the frequencies of beat signals of the respective sets generated at the time of the interference will be different between these sets. When the respective sets of coherent light are radiated to the respective diffraction gratings of the first and second objects from the ± n-order directions, the same inclination is obtained from a plurality of directions in which the absolute values n of the orders are different. The incident light is made incident at an angle, and the incident light is diffracted in the vertical direction from the diffraction gratings of the first and second objects, respectively, and the interference light extracted at the same inclination angle is diffracted by the first and second objects. The signals obtained from the grating are detected separately, and the combined signal of the beat signals obtained from these interference lights is filtered by a frequency filter to be divided into those with a single beat frequency. Position detecting method for detecting a displacement amount of the first and second objects on the basis of these phase difference a phase difference between the bets signals respectively measured by. 2. A plurality of sets, each having a slightly different frequency and capable of interfering with each other at the time of diffraction, as a set, and the frequencies of beat signals of the respective sets generated at the time of the interference will be different between these sets. When the respective sets of coherent light are radiated to the respective diffraction gratings of the first and second objects from the ± n-order directions, the same inclination is obtained from a plurality of directions in which the absolute values n of the orders are different. The incident light is made incident at an angle, and the incident light is diffracted in the vertical direction from the diffraction gratings of the first and second objects, respectively, and the interference light extracted at the same inclination angle is diffracted by the first and second objects. The signals obtained from the grating are detected separately, and the combined signal of the beat signals obtained from these interference lights is filtered by a frequency filter to be divided into those with a single beat frequency. Alignment method for performing alignment of the first and second objects on the basis of these phase difference a phase difference between the bets signals respectively measured by. 3. A set of two or more kinds of diffraction gratings having different lattice constants arranged side by side in each of the first and second objects, and having a slightly different frequency and capable of interfering with each other during diffraction. As a plurality of sets of coherent light beams in which the frequencies of the beat signals of the respective sets generated at the time of the interference differ from each other from the directions of the ± nth order determined according to the respective lattice constants of the diffraction grating. Each set is made to enter at the same inclination angle, and by these incidences, the interference light which is diffracted in the vertical direction from each diffraction grating of the first and second objects and is extracted at the same inclination angle is The second object is detected by being divided into those obtained from each diffraction grating, and the combined signal of beat signals obtained from these interference lights is filtered by a frequency filter to be divided into those having a single beat frequency, Position detecting method for detecting a displacement amount of the first and second objects on the basis of these phase difference the phase difference of the beat signals between equal wavenumber respectively measured by. 4. A set of two or more kinds of diffraction gratings having different lattice constants arranged side by side in each of the first and second objects, and having a slightly different frequency and capable of interfering with each other during diffraction. As a plurality of sets of coherent light beams in which the frequencies of the beat signals of the respective sets generated at the time of the interference differ from each other from the directions of the ± nth order determined according to the respective lattice constants of the diffraction grating. Each set is made to enter at the same inclination angle, and by these incidences, the interference light which is diffracted in the vertical direction from each diffraction grating of the first and second objects and is extracted at the same inclination angle is The second object is detected by being divided into those obtained from each diffraction grating, and the combined signal of beat signals obtained from these interference lights is filtered by a frequency filter to be divided into those having a single beat frequency, Alignment method for performing alignment of the first and second objects on the basis of these phase difference the phase difference of the beat signals between equal wavenumber respectively measured by. 5. A plurality of sets of coherent light, each having a slightly different frequency and capable of interfering with each other when diffracted, are set as a set, and a plurality of sets of coherent light whose polarization planes are different between the sets are provided. When the diffraction gratings of the first and second objects are irradiated from the ± n-order directions for each of them, they are incident at the same inclination angle from a plurality of directions in which the absolute values n of the orders are different. Interfering light that is diffracted in the vertical direction from each diffraction grating of the first and second objects and is extracted at the same inclination angle is detected separately by the interference light obtained from each diffraction grating of the first and second objects. At the same time, these interference lights are separated for each polarization plane, the phase differences of the beat signals respectively obtained from the interference lights having the same polarization plane are measured, and the first difference is calculated based on these phase differences. And the displacement of the second object Position detection method for detecting. 6. A plurality of sets of coherent light whose polarization planes are different between these sets, each set having a slightly different frequency and capable of interfering with each other during diffraction. When the diffraction gratings of the first and second objects are irradiated from the ± n-order directions for each of them, they are incident at the same inclination angle from a plurality of directions in which the absolute values n of the orders are different. Interfering light that is diffracted in the vertical direction from each diffraction grating of the first and second objects and is extracted at the same inclination angle is detected separately by the interference light obtained from each diffraction grating of the first and second objects. At the same time, these interference lights are separated for each polarization plane, the phase differences of the beat signals respectively obtained from the interference lights having the same polarization plane are measured, and the first difference is calculated based on these phase differences. And the position of the second object Alignment method of performing. 7. Diffraction gratings having two or more different grating constants are arranged side by side in each of the first and second objects, and the frequencies are slightly different from each other and can interfere with each other during diffraction. As a set, a plurality of sets of coherent light beams whose polarization planes are different between these sets are provided with the same inclination angle for each set from the ± nth order determined depending on each grating constant of the diffraction grating. Interference light that is diffracted in the vertical direction from the respective diffraction gratings of the first and second objects and is extracted at the same tilt angle by these incidences. And the interference light is separated for each polarization plane, and the phase difference of the beat signals obtained from the interference light of the same polarization planes is measured and Based on the phase difference Position detecting method for detecting a displacement amount of the first and second objects. 8. A set of two or more kinds of diffraction gratings having different grating constants arranged side by side in each of the first and second objects, and having a slightly different frequency and capable of interfering with each other during diffraction. As a plurality of sets of coherent light beams whose polarization planes are different between these sets, with the same inclination angle for each set from the ± nth order determined depending on each grating constant of the diffraction grating. From the diffraction gratings of the first and second objects, the interference light that is incident on the diffraction gratings of the first and second objects is vertically diffracted by the incidences and is extracted at the same inclination angle. In addition to detecting the obtained signals separately, these interference lights are separated for each polarization plane, and the phase difference of the beat signal obtained from the interference lights of the same polarization planes is measured to obtain these positions. Based on the phase difference Alignment method of performing alignment of the first and second objects.