JP5943717B2 - Position detection system, imprint apparatus, device manufacturing method, and position detection method - Google Patents

Description

  The present invention relates to a position detection system, an imprint apparatus, a device manufacturing method, and a position detection method for obtaining a relative position between objects.

  The demand for miniaturization of semiconductor devices has advanced, and in addition to the conventional photolithography technology, a microfabrication technology called an imprint technology has attracted attention. This technique is also called an imprint technique, and can form a fine structure on the order of several nanometers on a substrate. For example, as one of imprint techniques, there is a photocuring method. In an imprint apparatus using this photocuring method, first, a resin (imprint material, photocurable resin) is applied to a shot that is an imprint area on a substrate (wafer). Next, the resin applied to the substrate is molded with a mold. Then, after the resin is cured by irradiating light (ultraviolet rays), the resin and mold are separated (released), whereby a resin pattern is formed on the substrate.

  An imprint apparatus suitable for this photocuring method is disclosed in Patent Document 1, for example. For alignment between the substrate and the mold in the imprint apparatus, when the substrate and the mold are brought into contact with each other (pressing mold), alignment marks formed on the substrate and the mold are observed for each shot. A so-called die-by-die method is adopted in which the amount of deviation obtained from the observation result is corrected and the resin is cured.

  In the imprint apparatus, diffraction gratings having a period (repeated pattern) in the measurement direction are formed on the mold and the substrate as alignment marks. The periods of the diffraction gratings formed on the mold and the substrate (repetitive pattern pitch) are slightly different from each other. When diffraction gratings having different pitches are overlapped, interference fringes (so-called moire fringes) appear due to interference between diffracted lights from the two diffraction gratings. Since the phase of the moire fringe changes depending on the relative position of the two diffraction gratings, the relative position of the mold and the substrate can be matched by observing the moire fringe. In order to detect moire fringes, the imprint apparatus includes an illumination optical system that illuminates the diffraction grating and a detection optical system that detects moire fringes.

  Conventionally, in order to obtain the phase of the moire fringes, the phase is obtained using the entire area of the moire fringes detected by the light receiving element of the detection optical system, and the relative positions of the mold and the substrate are matched. The moire fringes detected by the light receiving element of the detection optical system are disclosed in FIG. 3 (3C, 3D) of Patent Document 2.

Special table 2008-522412 gazette JP 2011-243664 A

  In order to detect light other than the specularly reflected light that illuminates the diffraction grating formed on the mold and the substrate, as in the imprint apparatus of Patent Document 1, at least one diffraction grating of the mold and the substrate is measured. A checkerboard-like diffraction grating having a period in a direction orthogonal to the direction. By using a diffraction grating having a period in a direction orthogonal to the measurement direction (non-measurement direction), it is possible to detect light diffracted from the illumination optical system in the non-measurement direction.

  Since the size of the diffraction angle is determined by the interval (pitch) of the diffraction grating in the non-measurement direction, the period of the diffraction grating formed in the non-measurement direction depends on the size of the diffraction angle and the area where the alignment mark can be formed. (Number of repetitions) may be reduced. It was found that an intensity distribution asymmetric in the non-measurement direction is generated in the intensity of the moire fringes (interference pattern of diffracted light) detected by the detection optical system depending on the pitch and the number of periods of the diffraction grating formed in the non-measurement direction. For this reason, when the detection area used for measurement is limited to the non-measurement direction from the moire fringes detected by the detection system, it has been found that the phase obtained from the moire fringes is shifted depending on the position of the detection area in the non-measurement direction. In FIG. 3 of Patent Document 2, three periods of moire fringes are used. If an asymmetric intensity distribution occurs in the non-measurement direction, the detection accuracy may be reduced.

  The present invention has been made in view of such a situation, and is a method for obtaining a relative position of two objects using a diffraction grating having a period in a non-measurement direction, and the relative position is determined with accuracy. Provided is a position detection system that can be obtained well.

  The position detection system of the present invention has a first diffraction grating having a period in a first direction, and a second period different from the first direction having a period different from the period of the first diffraction grating in the first direction. An illumination optical system that illuminates a second diffraction grating having a period in the direction, and a detection optical system that detects an interference pattern due to light from the first diffraction grating and the second diffraction grating illuminated by the illumination optical system A position detection system that detects a relative position of the first diffraction grating and the second diffraction grating in a first direction from a detection result of the detection optical system, The control unit uses the detection area limited to the second direction in the first direction among the interference patterns periodically changed in the first direction detected by the detection optical system. In the first direction of the diffraction grating and the second diffraction grating And obtaining the kick relative positions.

  According to the present invention, there is provided a method for obtaining a relative position between two objects using a diffraction grating having a period in a non-measurement direction, and capable of obtaining the relative position with high accuracy. be able to.

It is a figure which shows the structure of the imprint apparatus which concerns on 1st embodiment of this invention. It is a figure which shows the alignment mark which produces | generates a moire fringe. It is a figure which shows the alignment mark for X directions which concerns on 1st embodiment of this invention. It is a figure which shows an example of a structure of the mark detection part which concerns on 1st embodiment of this invention. It is a figure which shows an example of a structure of the mark detection part which concerns on 1st embodiment of this invention. It is a figure which shows the pupil plane of the mark detection part which concerns on 1st embodiment of this invention. It is a figure which shows the mode of the diffracted light at the time of the moire fringe measurement which concerns on 1st embodiment of this invention. It is a figure which shows the Y direction alignment mark which concerns on 1st embodiment of this invention. It is a figure which shows a mode that the moire fringe for the alignment of a X direction and a Y direction is observed using the position detection apparatus which concerns on 1st embodiment of this invention. It is a figure which shows the alignment mark and moire fringe which concern on 1st embodiment of this invention. It is a figure which shows the alignment mark and moire fringe which concern on 1st embodiment of this invention. It is a figure which shows the light intensity of the interference fringe which concerns on 1st embodiment of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
(About device configuration)
First, the configuration of the imprint apparatus 1 according to the first embodiment of the present invention will be described with reference to FIG. The imprint apparatus of this embodiment shall employ a photocuring method. In the following description, as shown in FIG. 1, an X axis and a Y axis orthogonal to each other in a plane parallel to the substrate and the mold are taken, and a direction perpendicular to the X axis and the Y axis is taken as a Z axis.

  The imprint apparatus 1 includes an irradiation unit 2, a mark detection unit 3, a mold holding unit 4 that holds a mold 7, a substrate stage 5 that holds a substrate 8, and an application unit 6 that applies (supplies) resin 9 to the substrate 8. .

  The irradiation unit 2 irradiates the mold 7 with light in order to cure the resin 9 after contacting (pressing) the mold 7 and the resin 9. The irradiating unit 2 includes a light source (not shown) and a plurality of optical elements for uniformly irradiating light emitted from the light source with a predetermined shape onto a later-described concavo-convex pattern 7a serving as an irradiated surface. Here, as the light source, for example, a high-pressure mercury lamp, various excimer lamps, an excimer laser, or a light emitting diode can be employed. The light source is appropriately selected according to the characteristics of the resin 9, but the present invention is not limited by the type, number, or wavelength of the light source.

  The mark detection unit 3 optically detects a mold side mark 10 (first diffraction grating) formed on the mold 7 and a substrate side mark 11 formed on the substrate 8. The mark detection unit 3 is an optical system for measuring the relative position between the mold 7 and the substrate 8, and is a position detection system that performs measurement for alignment between the mold 7 and the substrate 8. The optical axis of the optical system is arranged so as to be perpendicular to the mold 7 or the substrate 8. The mark detection unit 3 is configured to be driven in the X-axis direction and the Y-axis direction according to the position of the mark arranged on the mold 7 or the substrate 8. Furthermore, the optical system is configured so that it can be driven in the Z-axis direction in order to focus the optical system at the mark position. Based on the relative position information of the mold 7 and the substrate 8 measured based on the mark detected by the mark detection unit 3, the driving of the mold holding unit 4 and the substrate stage 5 is controlled.

  The mold holding unit 4 attracts and holds the mold 7 by vacuum suction or electrostatic suction. The mold holding unit 4 includes a chuck unit that holds the mold 7 and a drive mechanism that drives the mold 7 in the Z-axis direction to bring the mold 7 and the resin 9 into contact with each other. Further, the mold holding unit 4 may be provided with a magnification correction mechanism that corrects distortion of a pattern transferred to the resin 9 by deforming the mold 7 in the X-axis direction and the Y-axis direction. Note that each of the pressing and releasing operations of the imprint apparatus 1 may move the mold 7 in the Z direction, but may move the substrate stage 5 (substrate 8) in the Z direction, or both. May be moved.

  The substrate stage 5 (substrate holding unit) holds the substrate 8 by vacuum suction or electrostatic suction. The substrate stage 5 includes a chuck unit that holds the substrate 8 and a drive mechanism that drives the substrate 8 in the XY plane.

  The application unit 6 is application means for applying (supplying) the resin 9 onto the substrate 8. Here, the resin 9 will be described using a photocurable resin having a property of being cured by being irradiated with ultraviolet rays. The resin 9 is appropriately selected depending on the type of semiconductor device. As shown in FIG. 1, the application unit 6 is not installed inside the imprint apparatus 1, but a separate application apparatus is prepared outside, and the substrate 8 previously coated with the resin 9 by the application apparatus is placed inside the imprint apparatus 1. There may be a configuration to be introduced.

  The mold 7 has a predetermined pattern (for example, an uneven pattern 7 a such as a circuit pattern) formed on the surface with respect to the substrate 8. The material of the mold 7 is quartz or the like that can transmit the light irradiated from the irradiation unit 2.

(About imprint operation)
Next, an imprint operation by the imprint apparatus 1 will be described. First, the substrate 8 is transferred to the substrate stage 5 by a substrate transfer unit (not shown). Subsequently, the substrate 8 is moved to the application position of the application unit 6 by the substrate stage 5. The application unit 6 applies the resin 9 to a predetermined shot (imprint region) of the substrate 8 (application process).

  Next, the substrate stage 5 is moved so that the resin 9 applied on the substrate 8 is positioned immediately below the mold 7. At this time, the mold side mark 10 and the substrate side mark 11 are detected by the mark detection unit 3, the alignment between the mold 7 and the substrate 8, and the magnification correction of the mold 7 by the magnification correction mechanism provided in the mold holding unit, etc. To implement. Next, the mold 7 is driven by the mold holding part 4 to bring the resin 9 and the mold 7 into contact (pressing process). The mark detection by the mark detection unit 3 may be performed after the resin 9 and the mold 7 are brought into contact with each other.

  When the flow of the resin 9 to the concave / convex pattern 7a, the alignment between the mold 7 and the substrate 8, and the magnification correction of the mold are sufficiently performed, the irradiation unit 2 irradiates light for curing the resin 9 (irradiation process). . At this time, when the mark detection unit 3 blocks the optical path, the mark detection unit 3 retracts so as not to block the optical path. Next, when the mold 7 is driven by the mold holding portion and the mold 7 is separated from the cured resin 9 (mold release process), the concave / convex pattern 7 a of the mold 7 is transferred onto the substrate 8. The series of imprint operations and mark detection described below are controlled by the control unit 12.

(About mark detection)
Next, details of the mark detection unit 3 (position detection system), the mold side mark 10 formed on the mold 7, and the substrate side mark 11 formed on the substrate 8 will be described.

  For alignment between the mold 7 and the substrate 8, diffraction gratings having slightly different periods (pitch of repeated patterns) as shown in FIGS. 2A and 2B are used as the mold side mark 10 and the substrate side mark 11. 31 and a diffraction grating 32 are used. When these two diffraction gratings are overlapped, the diffracted light from the respective diffraction gratings interfere with each other, and an interference pattern (moire fringes) as shown in FIG. 2C having a period reflecting the difference in period between the two diffraction gratings. ) Occurs. The moiré fringes change the position of light and dark (the phase of the fringes) according to two relative positions. For example, when one side is slightly shifted, the moire fringes in FIG. 2C change as shown in FIG. This moire fringe enlarges the actual relative displacement between the diffraction gratings and is generated as a fringe with a large pitch. Therefore, even if the resolution of the detection optical system is low, the relative position between the two objects can be accurately obtained. Can be measured. In the present invention, as will be described later, a relative position between two objects is measured using a signal having an even period among the generated moire fringes.

  Here, in order to detect moire fringes (moire signal), the diffraction gratings of FIGS. 2A and 2B are detected in a bright field (illuminated from the vertical direction and diffracted light is detected from the vertical direction). Then, zero order light from the diffraction grating 31 and zero order light from the diffraction grating 32 are also detected. Zero order light from the diffraction grating of either the mold side mark 10 or the substrate side mark 11 causes a reduction in the contrast of moire fringes.

  Therefore, the mark detection unit 3 of the present embodiment has a dark field configuration in which zero-order light is not detected. Further, the diffraction grating of either the mold side mark 10 or the substrate side mark 11 has a checkerboard-like shape as shown in FIG. 3A so that the moire fringes can be detected even in the configuration of a dark field illuminated with oblique incidence. A diffraction grating is used. It is basically the same whether the mold side mark 10 or the substrate side mark 11 is a checkerboard-like diffraction grating, but in the following, an example in which the mold side diffraction grating is made a checkerboard-like will be described.

  FIGS. 3A and 3B show a mold side mark 10 and a substrate side mark 11 for detecting the relative positions of the mold and the substrate in the X direction, respectively. The mold side mark 10 is a checkerboard-like diffraction grating 10a (second diffraction grating) having a period of Pmm in the X direction and Pmn in the Y direction, and the period Pmm and the period Pmn may be different or the same. . The substrate side mark 11 is a diffraction grating 11a (first diffraction grating) having a period Pw different from the period Pmm in the X direction.

  Hereinafter, the principle of detecting moire fringes by the mark detection unit 3 in a state where the two diffraction gratings 10a and the diffraction grating 11a are overlapped will be described.

  FIG. 4 is a diagram illustrating an example of the configuration of the mark detection unit 3 of the present embodiment. The mark detection unit 3 includes a detection optical system 21 and an illumination optical system 22. The illumination optical system 22 guides the light emitted from the light source 23 onto the same optical axis as the detection optical system 21 using an optical member such as a prism 24, and illuminates the mold side mark 10 and the substrate side mark 11.

  For example, a halogen lamp or LED is used as the light source 23, and the light source 23 is configured to emit visible light or infrared light different from the light emitted from the irradiation unit 2. Thus, by using light that does not cure the resin 9 for the light source 23, it is possible to prevent the resin from being cured at the time of mark detection.

  The detection optical system 21 and the illumination optical system 22 are configured to share a part of the optical members constituting them, and the prism 24 is disposed on or near the pupil plane of the detection optical system 21 and the illumination optical system 22. ing. The mold side mark 10 and the substrate side mark 11 are each composed of a diffraction grating, and the detection optical system 21 generates an interference pattern due to interference of diffracted light from two diffraction gratings illuminated by the illumination optical system 22. The interference pattern is an interference pattern (so-called moire fringes) having a period reflecting a period difference between two diffraction gratings, and forms an image on the image sensor 25. A CCD, CMOS, or the like is used for the image sensor 25.

  The prism 24 has a reflection film 24a for reflecting light near the pupil plane of the illumination optical system 22 on the bonding surface. The reflective film 24a also functions as an aperture stop that defines the size of the pupil (or detection NA: NAo) on the pupil plane of the detection optical system 21. Here, the prism 24 may be a half prism having a semi-permeable film on the bonding surface, or a plate-like optical member having a reflective film formed on the surface thereof.

  Like the mark detection unit 3 shown in FIG. 5, the detection optical system 21 and the illumination optical system 22 may be provided with individual aperture stops 26 and 27 on their pupil surfaces, respectively. Thus, the position where the prism 24 according to the present embodiment is disposed does not necessarily have to be in the pupil plane of the detection optical system 21 and the illumination optical system 22 or in the vicinity thereof. At this time, for the prism 24, a half prism having a semipermeable membrane on its bonding surface is used.

The relationship between the effective light source distribution on the pupil plane of the illumination optical system 22 of the mark detection unit 3 and the size NAo of the pupil (detection aperture) on the pupil plane of the detection optical system 21 will be described with reference to FIG. In FIG. 6, the size of the pupil on the pupil plane is indicated by the numerical aperture NA. The effective light source distribution of the illumination optical system of the present embodiment is composed of four poles IL1 to IL4. IL1 to IL4 are circular poles each having a diameter NAp. The poles IL1 and IL2 are arranged on the Y axis of the pupil plane at positions separated by NAil in the plus direction and the minus direction from the optical axis, respectively. The poles IL3 and IL4 are located on the X axis of the pupil plane from the optical axis. They are arranged at positions separated by NAil in the positive and negative directions, respectively. That is, the illumination optical system 22 is configured to perform oblique incidence illumination on the mold side mark 10 and the substrate side mark 11, and the incident angle θ is θ = sin ⁻¹ (NA _il ) Equation 1
It is. NAo, NAp, and NAil satisfy the following formula 2.
_{NA O <NA il -NA P /} 2 Equation 2
That is, a dark field configuration is employed in which regular reflection light (zero-order diffracted light) from the mold side mark 10 and the substrate side mark 11 is not detected. Moreover, Total_NA in FIG. 6 indicates the size of the numerical aperture necessary for forming the illumination optical system 22.

  Next, the principle of generation of moire fringes and relative position detection using moire fringes will be described.

  7A and 7B are views of the diffraction grating 10a and the diffraction grating 11a viewed from the X-axis direction and the Y-axis direction, respectively. Moire fringes for detecting a relative position in the X direction (first direction) are generated by the poles IL1 and IL2 arranged on the Y axis (parallel to the second direction) on the pupil plane.

Here, the diffraction angle φ by the diffraction grating is expressed by the following equation, where d is the period of the diffraction grating, λ is the wavelength of light, and n is the diffraction order.
sinφ = nλ / d Equation 3
Therefore, if the diffraction angles in the X direction and the Y direction by the diffraction grating 10a are φmm and φmn, respectively, and the diffraction angle by the diffraction grating 11a is φw,
sinφmm = nλ / Pmm Equation 4
sinφmn = nλ / Pmn Equation 5
sinφw = nλ / Pw Equation 6
It becomes.

  In FIG. 7A, first, the diffraction grating 10a and the diffraction grating 11a are arranged in the Y axis direction (non-measurement direction) by the pole IL1 and the pole IL2 arranged on the Y axis that is the non-measurement direction (second direction) on the pupil plane. Illuminated obliquely. The light (zero-order diffracted light) D1 and D1 ′ specularly reflected by the diffraction gratings 10a and 11a does not enter the detection optical system 21 because the mark detection unit 3 satisfies Expression 2.

Next, D2 and D2 ′ indicate light diffracted in the ± 1st order only on the mold side, D3 is diffracted in +/− 1 order by the diffraction grating 10a on the mold side, and − / + 1 by the diffraction grating 11a on the substrate side. Next, the diffracted diffracted light is shown. D3 is diffracted light used for detection. Lights D2, D2 ′, D3 diffracted by the angle φmn by the mold side diffraction grating 10a having a period of Pmn in the Y-axis direction are emitted at an angle detected by the detection optical system 21 with respect to the Y-axis. In this embodiment, Pmn, NAo, NAil, and NAp satisfy the following conditions in order to detect ± first-order diffracted light having the highest diffraction intensity among diffracted light except zero-order light.
_{| NAil- | sinφmn || = | NA} il -λ / Pmn | <NA O + NA P / 2 Equation 7
In other words, diffracted light in the Y-axis direction can be detected at a wavelength λ in a range that satisfies Expression 7.

Here, since the first-order diffracted light can be detected most efficiently when D3 is perpendicular to the Y-axis direction, if the center wavelength of the illumination light output from the light source is λc,
NA _il −λc / Pmn = 0 Equation 8
It is desirable that the illumination conditions and the period of the diffraction grating on the mold side are adjusted so that

  As described above, with respect to the Y-axis direction (non-measurement direction), the diffraction grating 10a on the mold side is illuminated obliquely, and diffracted light diffracted in the non-measurement direction is detected by the diffraction grating 10a.

  Next, the diffracted light in the X-axis direction (measurement direction) will be described with reference to FIG.

The pole IL1 and the pole IL2 arranged on the Y axis of the pupil plane enter the diffraction gratings 10a and 11a from a direction perpendicular to the X axis. Considering +/− 1 order diffracted light as in the Y-axis direction,
The diffracted light D3 diffracted by the diffraction grating 10a on the mold side in the +/− 1 order and diffracted by the − / + 1 order by the diffraction grating 11a on the substrate side has a small angle with respect to the X axis because Pmm and Pw are close to each other. The light enters the detection optical system 21.

  FIG. 7C shows how the diffracted light D3 is diffracted. A solid line arrow represents diffracted light that has been diffracted in +/− 1 order by the diffraction grating 10a on the mold side, diffracted by − / + 1 order by the diffraction grating 11a on the substrate side, and transmitted through the mold. The dotted arrow represents the diffracted light that has passed through the diffraction grating 10a on the mold side, diffracted at the − / + 1 order by the diffraction grating 11a at the substrate side, and diffracted at the +/− 1 order by the diffraction grating 10a at the mold side. ing.

  The diffraction angle φΔ at this time is expressed by the following equation.

If | Pw−Pmm | / (Pmm · Pw) = 1 / (PΔ) in Equation 9, sin φΔ = λ / (PΔ) Equation 10
It becomes. This means that an interference pattern with a period PΔ appears by the diffracted light D3. This interference pattern of diffracted light is moire fringes, and its period depends on the difference between the periods of the diffraction grating on the mold side and the diffraction grating on the substrate side. However, in this embodiment, since the diffraction grating on the mold side has a checkerboard shape, the period of the generated moire fringes is (PΔ) / 2. At this time, since the relative misalignment between the mold and the substrate is enlarged to the bright and dark misalignment of the moire fringes, the alignment can be performed with high accuracy even using a detection optical system having a low resolving power.

Next, the light D2 and D2 ′ first-order diffracted only by the diffraction grating 10a on the mold side or the light D4 and D4 ′ first-order diffracted by only the diffraction grating 11a on the substrate side are emitted at an angle φmm or φw (FIG. 7). (B)). Since D2, D2 ′, D4, and D4 ′ become noise without generating moire fringes, it is desirable that they are not detected by the detection optical system 21. For this reason, in this embodiment, the period of the diffraction grating and the mark detection unit 3 are adjusted so as to satisfy the following expressions 11 and 12.
NA _O + NA _P / 2 <| sinφmm | = λ / Pmm Equation 11
NA _O + NA _P / 2 <| sinφw | = λ / Pw Equation 12

  Further, the light (zero-order diffracted light, FIG. 7B, D1, D1 ′) that is not diffracted in the X-axis direction by either the mold-side diffraction grating 10a or the substrate-side diffraction grating is detected optical system with respect to the X-axis. Inject at the angle detected at 21. In addition, the diffraction grating on the mold side did +/− n order diffraction and − / + n order diffraction in the X-axis direction before and after reflection on the substrate without being diffracted by the diffraction grating on the substrate side (total zero order). Diffracted light is also emitted at an angle detected by the detection optical system 21 with respect to the X axis. These lights do not generate moiré fringes, but reduce the contrast of the moiré fringes. However, in this embodiment, since the diffraction grating 10a on the mold side has a checkerboard shape, the diffracted light from adjacent gratings is not generated. The phases are shifted by π and cancel each other. Therefore, the intensity of D5 is suppressed, and moire fringes can be measured with good contrast.

  FIG. 7 (d) is a three-dimensional representation of FIGS. 7 (a) and 7 (b). D1 and D1 ′ are not described because the strength is suppressed.

  As described above, the detection of the moire fringe for the relative position measurement in the X direction of the mold 7 and the substrate 8 has been described. However, the detection of the moire fringe for the relative position measurement in the Y direction can be performed by changing the alignment mark and the illumination direction. It is basically the same just by switching between X and Y.

  As shown in FIG. 8, a checkerboard diffraction grating 10b having a period of Pmn in the X direction and Pmm in the Y direction is used for the mold side mark 10, and a period Pw different from Pmm in the Y direction is used for the substrate side mark 11. Is used. Further, moire fringes for measuring the relative position in the Y direction are generated by illuminating the diffraction gratings 10b and 11b with the poles IL3 and IL4 arranged on the Y axis.

  In the above, the case where the periods of the diffraction grating 10a and the diffraction grating 10b are the same and the periods of the diffraction grating 11a and the diffraction grating 11b are the same has been described. By making the periods of the diffraction gratings the same, the distance from the optical axis to IL1 and IL2 can be made equal to the distance from the optical axis to IL3 and IL4, and the condition under which diffracted light is detected in the X and Y directions There is no need to design separately. Therefore, signal processing for relative position measurement can be made common from the detected moire fringes. However, the present invention is not limited to this. If the conditions for detecting diffracted light in the X direction and Y direction are changed, the periods of the diffraction grating 10a and the diffraction grating 10b may be different from each other, and the periods of the diffraction grating 11a and the diffraction grating 11b are different from each other. Also good. Furthermore, the distance from the optical axis to IL1 and IL2 and the distance from the optical axis to IL3 and IL4 may be different. In this case, the signal processing method differs between the X direction and the Y direction, and it is necessary to change the size of an integration region (detection region) used for position detection described later.

  In the present embodiment, the quadrupole illumination in which two poles are formed in the X direction and the Y direction as the effective light source distribution on the pupil plane of the illumination optical system as shown in FIG. 6 has been described. As the shape of the light intensity distribution, a dipole illumination in which two poles are formed in the X direction or the Y direction may be used. In addition, here, a region having a light intensity stronger than the surroundings on the pupil plane is called a pole. Therefore, there may be light between the poles. Further, the shape of the effective light source distribution may be an annular shape (annular illumination). In this case, two light intensity peaks (poles) are formed in each of the X direction and the Y direction. Therefore, even if annular illumination is used, the illumination optical system can irradiate light having a plurality of poles in the non-measurement direction.

  Further, the mark detection unit 3 of the present embodiment performs oblique incidence illumination from two directions on the diffraction grating and detects in the vertical direction, but in order to detect moire fringes, the oblique incidence illumination from at least one direction is performed. That's fine. For example, in order to detect moire fringes using the diffraction grating shown in FIG. 3, it is sufficient to irradiate one of the light beams IL1 and IL2. If oblique illumination is performed from two directions, twice the amount of light can be secured as compared to the case where oblique incidence illumination is performed from one direction and a mark is detected from the oblique direction as described in Patent Document 1. . Therefore, the relative positions of the two objects can be detected with high accuracy.

  Since the mark detection unit of the present embodiment has an effective light source distribution and a detection aperture as shown in FIG. 6, oblique incidence illumination can be performed simultaneously from the X direction and the Y direction. Therefore, the moiré fringes in the X direction and the Y direction are observed at the same time by simultaneously placing the marks in which the diffraction gratings 10a and 11a and the diffraction gratings 10b and 11b are overlapped in the visual field 40 of the mark detection unit 3 as shown in FIG. be able to. That is, the mark detection unit 3 according to the present embodiment can simultaneously acquire relative position information in two directions.

(Asymmetry of moire fringes)
When detecting the diffracted light of the checkerboard diffraction grating using a high resolution scope (mark detection unit) as in this embodiment, if the number of repetitive patterns in the non-measurement direction is small, the detected moire fringes It was found that asymmetry occurred.

  The asymmetry generated in the moire fringes will be described with reference to FIGS. Since one of the two diffraction gratings has a checkerboard shape, there are two patterns of Type_A and Type_B in the way of overlapping the mold side mark and the substrate side mark.

  Type_A in FIG. 10 will be described. FIG. 10A and FIG. 10B are schematic views of a diffraction grating used for relative position detection. FIG. 10A shows a diffraction grating of the mold side mark 10 and represents a checkerboard-like diffraction grating. FIG. 10B is a diffraction grating of the substrate side mark 11 and represents a line-and-space diffraction grating. The black portion represents a light shielding pattern (light shielding portion) such as Cr, and the white portion represents a transmission pattern (transmission portion). The X-axis direction is the measurement direction, and the Y-axis direction is the non-measurement direction.

  FIG. 10C shows moiré fringes on the XY plane obtained by light intensity simulation by electromagnetic field analysis when the diffraction grating of the mold side mark 10 and the diffraction grating of the substrate side mark 11 are arranged. Diffraction gratings of the mold side mark 10 and the substrate side mark 11 are arranged in the range of the mark region MR shown in FIG. 10 (a) and 10 (b) are exaggerated by enlarging the scale as compared with FIG. 10 (c). The contour lines indicate the intensity of the light intensity of the moire fringes. Moire fringe images are asymmetric in the Y-axis direction with respect to the mark center.

  FIG. 10D shows an integrated waveform obtained by integrating the light intensity of the moire fringes shown in FIG. 10C in the non-measurement direction in the integration region (detection region) in which the range is limited in the non-measurement direction. is there. It is a result when integrating | accumulating the light intensity of the integration area | region shown in FIG.10 (c). The horizontal axis represents the position of moire fringes, and the vertical axis represents the light intensity of moire fringes. Frequency analysis is performed on this integrated waveform using Fourier transform or the like. The phase component of the moire fringe is obtained based on the period of the moire fringes calculated from the period of the diffraction grating of the mold side mark 10 and the substrate side mark 11 to specify the position of the moire fringes. As described above, the period of the moire fringes is determined as (PΔ) / 2 from the period of the marks.

  Similarly, Type_B in FIG. 11 will be described. FIG. 11A shows a diffraction grating of the mold-side mark 10 and represents a checkerboard-like diffraction grating. FIG. 11B shows a diffraction grating of the substrate side mark 11 and represents a line-and-space diffraction grating. FIG. 11C shows moiré fringes on the XY plane obtained by light intensity simulation by electromagnetic field analysis when the diffraction grating of the mold side mark 10 and the diffraction grating of the substrate side mark 11 are arranged. 11 (a) and 11 (b) are exaggerated by enlarging the scale as compared with FIG. 11 (c). The image of moire fringes shown in FIG. 11C is also asymmetric in the Y-axis direction with respect to the mark center.

  FIG. 11 (d) shows an integrated waveform obtained by integrating the light intensity of the moire fringes shown in FIG. 11 (c) in the non-measurement direction in the integration region (detection region) in which the range is limited in the non-measurement direction. is there. It is a result when integrating | accumulating the light intensity of the integration area | region shown in FIG.11 (c).

  As shown in FIG. 10 and FIG. 11, there are two types of overlapping patterns of Type_A and Type_B as the overlapping method of the mold side mark and the substrate side mark where the moiré fringe intensity reaches a peak. The difference between Type_A and Type_B is that the light shielding portion and the transmissive portion of the checkerboard shown in FIGS. 10A and 11A are inverted. Therefore, when moire fringes are detected with a scope having a high resolving power with respect to the period of the mark, the strength of the moire fringes seen in Type_A and Type_B appears to be reversed. Specifically, as shown in Type_A in FIG. 10C and Type_B in FIG. 11C, the intensity of the moire fringes is asymmetric in the Y-axis direction with respect to the mark center and becomes an inverted intensity. FIG. 10C and FIG. 11C both show a light portion having moire fringes on the + X side (right side) and the −X side (left side) in the X-axis direction. In FIG. 10C, the bright part on the −X side is shifted to the + Y side (up) compared to the bright part on the + X side, and in FIG. 11C, the bright part on the + X side is bright on the −X side. It shows what is shifted to the + Y side (up) compared to the part.

  Since the moiré fringes are asymmetric in the Y-axis direction (asymmetric in the non-measurement direction), when the light intensity is accumulated from the detected moire fringes, the light intensity is shifted to the position of the peak depending on the area to be accumulated (fooled). May occur. This is because the phase obtained as a result of performing frequency analysis on the integrated waveform using Fourier transform or the like differs depending on the integration region. This deviation of the peak position becomes an error in the position of the moire fringe in the measurement direction. That is, an error occurs in the relative position detection between the mold 7 and the substrate 8.

  An example will be described with reference to FIG. As shown in FIG. 11C, an integration region is defined in the mark region, and the light intensity in the region is integrated to obtain a moire fringe waveform. FIG. 11C shows an integration region (i) in which the integration region is shifted from the mark center in the non-measurement direction (Y-axis direction) to the Y-axis direction − side and an integration region (ii) in which the integration region is shifted to the Y-axis direction + side. . Since the integration region (i) and the integration region (ii) moire fringes are asymmetrical, the integrated waveform at this time is a waveform in which a difference occurs in the measurement direction as shown in FIG. That is, it can be seen that when the area where the light intensity of the moire fringes is integrated moves in the Y-axis direction from the center of the mark area, the center of gravity position of the moire fringes shifts in the X-axis direction which is the measurement direction.

  In Type_A in FIG. 10 as well, Type_B in FIG. 11 is similar to Type_B in that the moiré fringes are asymmetric in the Y-axis direction. The position of the center of gravity shifts in the X axis direction, which is the measurement direction. However, Type_A and Type_B have inverted moire fringes asymmetry appearing in the Y-axis direction. For this reason, the deviation in the X-axis direction due to the integration region appears in the opposite direction between Type_A and Type_B.

  The moire fringes detected by the mark detection unit are repetitions of the above-described moire fringes of Type_A and Type_B. An example of a schematic diagram of a diffraction grating and moire fringes used for relative position detection is shown in FIG. 12A shows the diffraction grating of the mold side mark 10, and FIG. 12B shows the diffraction grating of the substrate side mark 11. FIG. 12C shows moire fringes obtained by two diffraction gratings. FIG. 12D shows an integrated waveform obtained by integrating the light intensity of moire fringes in the non-measurement direction in the integrated region (iii) shown in FIG. In the present embodiment, this integration area (iii) is used as a detection area for detecting the alignment mark.

  As shown in FIG. 12C, two types of signals, Type_A and Type_B, are periodically repeated. That is, in the integrated waveform shown in FIG. 12D, detected asymmetric moire fringes are repeated every two cycles.

  Therefore, a solution for the problem of asymmetry in the non-measurement direction is to detect the position using two types of moire fringes (moire fringes for two periods) of Type_A and Type_B. That is, an integrated waveform is obtained using moire fringes for two cycles. Frequency analysis is performed on the integrated waveform for two cycles using Fourier transform or the like. By performing frequency analysis on the integrated waveform for two cycles, measurement errors due to the asymmetry of moire fringes can be reduced. This is because the asymmetry appearing in the non-measurement direction is reversed between Type_A and Type_B, so that a shift occurring in the measurement direction can be reduced.

  As shown in FIG. 12D, the detection signal of the moire fringe that is asymmetric in the measurement direction is repeated every two cycles. Therefore, the detection region regarding the measurement direction is not limited to two cycles, and may be four cycles or six cycles. By using moire fringes with an even period, the influence of asymmetric moire fringes can be reduced. In this way, frequency analysis is performed on the integrated waveform obtained by integrating the light intensities of even numbers from the detected moire fringes using Fourier transform or the like. For example, the fundamental frequency component of the periodic structure of the moire fringes is extracted from the detected moire fringes by frequency analysis. The relative displacement between the mold side mark and the substrate side mark is obtained from the phase component of the moire fringes thus obtained. If a state without a phase component is set as a reference position for alignment, the relative positional deviation is proportional to the magnitude of the phase component.

  In addition, the detection area may be obtained by extracting a signal for an even period from the interference pattern of the interference light detected by the image sensor 25 of the mark detection unit 3, and the light incident on the image sensor 25 is an even period. As shown, a slit or a light shielding plate may be provided. Further, the image sensor 25 may be a line sensor extending in the measurement direction.

  Furthermore, the magnification of the detection optical system may be adjusted so that moiré fringes for an even number of periods are detected on the image sensor. As described above, if the period of the mark on the mold side and the period of the mark on the substrate side are known, the period of moire fringes (interference pattern) can be obtained. Since the period of the moire fringes is (PΔ) / 2, an even period region on the detection surface of the image sensor 25 can be obtained by multiplying the magnification of the detection optical system. The pitch of the diffraction grating on the mold side and the diffraction grating on the substrate side may be designed so that the period of the moire fringes is detected in accordance with the length of the detection region in the measurement direction. In this way, the size of the detection area can be determined in advance. Alternatively, two light intensity peaks that are continuous from the moire fringes detected by the image sensor 25 may be identified and used to determine an even period region. The series of position detection processing is controlled by the control unit 12.

  The problem of asymmetry of moire fringes in the non-measurement direction can be reduced by increasing the number of repetitive patterns of diffraction gratings in the non-measurement direction. However, since the substrate side mark is formed on the scribe line, the area of the alignment mark is limited. Therefore, the number of repetitions of the diffraction grating period cannot be easily increased in the non-measurement direction. Since marks in the measurement direction are formed along the scribe line, the non-measurement direction coincides with the width direction of the scribe line. Since it is desired to make the pattern region formed on the substrate as large as possible, the width of the scribe line cannot be easily increased.

  Further, when detecting the first-order diffracted light from the diffraction grating, the interval (pitch) between repeated patterns in the non-measurement direction must be increased depending on the position of the detection system. For example, as compared with the case of performing oblique incidence illumination on the diffraction grating and detecting first-order diffracted light in the direction of oblique incidence illumination, oblique incidence illumination is performed and the first-order diffracted light is emitted in a direction perpendicular to the alignment mark. The diffraction angle for detection is small. Therefore, the interval (pitch) between the repeating patterns of the diffraction grating in the non-measurement direction becomes large. As described above, the interval between the repetitive patterns of the diffraction grating may be increased depending on the direction in which the diffracted light from the diffraction grating is detected (the diffraction angle with respect to the incident light). If the mark area cannot be increased, the number of repetitive patterns of diffraction gratings in the non-measurement direction must be reduced. FIG. 12A shows a case where the number of cycles (the number of repetitions) of the diffraction grating in the non-measurement direction is one cycle. The present invention is particularly effective when detecting moire fringes of a diffraction grating having four periods or less.

  The influence of the asymmetry of the moire fringes in the non-measurement direction can be reduced by setting the detection area for detecting the mark in the non-measurement direction to be larger than the mark area in a sufficiently wide area. However, in this case, since the contrast of the moire fringes to be processed is lowered, the measurement accuracy may be lowered. Further, when there is another mark adjacent to the mark to be detected, light from the mark may enter the detection region, which causes a measurement error. Therefore, the contrast of the detected mark can be improved if the detection area for detecting the moire fringes is not made larger than necessary. In the present embodiment, an area limited in the non-measurement direction is defined as a detection area.

  In this way, when detecting light diffracted from the diffraction grating from the detection region by the detection optical system, it is possible to reduce the occurrence of deviation in the detection result by using the signal of the even period of the diffracted light in the measurement direction. it can. The positional deviation in the measurement direction that occurs when the detection area is shifted in the non-measurement direction occurs in the reverse direction every cycle. For this reason, a measurement error due to asymmetry is generated so as to cancel out with a signal of two cycles, so that the measurement error can be reduced by using an even-cycle signal. It has been found that even if the detection area is shifted in the non-measurement direction, the detection result hardly changes depending on the measurement position in the measurement direction obtained by detecting the moire fringes.

  On the other hand, when the length of the detection area for detecting the moire fringes in the measurement direction is longer or shorter than two periods of the diffracted light, the measurement direction is displaced. The magnitude of the positional deviation is proportional to the magnitude of the deviation between the detection area in the measurement direction and the length of two cycles. Depending on the mark detection accuracy, the length in the measurement direction of the detection region for detecting moire fringes may not be exactly two cycles (even cycles) of moire fringes. The detection area can be determined according to the allowable detection accuracy.

(Second embodiment)
(About device manufacturing method)
Subsequently, a device manufacturing method according to an embodiment of the present invention will be described.

  A method for manufacturing a device (semiconductor integrated circuit element, liquid crystal display element, etc.) as an article includes a step of forming a pattern on a substrate (wafer, glass plate, film-like substrate) using the above-described imprint apparatus. Furthermore, the manufacturing method may include a step of etching the substrate on which the pattern is formed. In the case of manufacturing other articles such as patterned media (recording media) and optical elements, the manufacturing method may include other processes for processing a substrate on which a pattern is formed instead of etching. The method for manufacturing an article according to the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of the article as compared with the conventional method.

  In the above embodiment, the position detection system and the position detection method for detecting the alignment mark used for the alignment of the mold of the imprint apparatus and the substrate have been described, but the present invention is not limited to this. The present invention can be used in any apparatus that uses a diffraction grating in which moire fringes are generated to align two different objects. For example, it can be used for alignment of a substrate and a mask of a proximity type exposure apparatus that transfers a mask pattern to the substrate by providing a minute gap between the substrate and the mask.

  In the above embodiment, the mark detection unit 3 has been described as a method of detecting the first-order diffracted light diffracted in the vertical direction from the alignment mark by performing oblique incidence illumination on the alignment mark. Is not limited to this. For example, a method of illuminating light from a direction perpendicular to the alignment mark and detecting diffracted light from an oblique direction can be mentioned. Also, a method of detecting the zero-order diffracted light by irradiating the alignment mark with oblique incidence, and a method of detecting the first-order diffracted light from an oblique position by irradiating the alignment mark with oblique incidence as in Patent Document 1. Etc. In either case, it is necessary to use a diffraction grating having a period in the non-measurement direction for at least one of the mold side mark and the substrate side mark. Thus, when detecting the moire fringes of the diffraction grating having a period in the non-measurement direction, the above-described detection method can be used.

  It is desirable that the wavelength λ of the illumination light used in the mark detection unit 3 described with reference to FIG. 4 is variable as wide as possible, and the conditions of illumination light suitable for mark detection can be set by the process of creating the substrate 8. For example, the wavelength λ of the illumination light used in the mark detection unit 3 may be cut out of a desired wavelength band with a bandpass filter or the like using a halogen lamp having a broad wavelength as the light source 23, or a single color such as an LED. A plurality of light sources having different center wavelengths may be provided and switched. The mark detection unit 3 may detect diffracted light of light having a plurality of wavelengths by illuminating the diffraction grating with light having a plurality of wavelengths.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 1 Imprint apparatus 2 Ultraviolet irradiation part 3 Mark detection part 4 Type | mold holding part 5 Substrate stage 6 Application | coating part 7 Type 8 Substrate 9 Resin 10 Type | mold side alignment mark 11 Substrate side alignment mark

Claims (14)

A first diffraction grating having a period in a first direction, and a second diffraction having a period in the first direction different from the period in the first direction of the first diffraction grating and a period in a second direction different from the first direction. An illumination optical system for illuminating the grating;
A detection optical system for detecting an interference pattern by light from the first diffraction grating and the second diffraction grating illuminated by the illumination optical system;
A control unit,
A position detection system that detects a relative position of the first diffraction grating and the second diffraction grating in a first direction from a detection result of the detection optical system,
The control unit is a detection region limited in the second direction at an even period in the first direction, among the interference patterns periodically changing in the first direction formed by the light detected by the detection optical system. A position detection system characterized in that a relative position in the first direction of the first diffraction grating and the second diffraction grating is obtained using.   The control unit obtains a phase component of the interference pattern by performing frequency analysis on the interference pattern detected by the detection optical system, and uses the phase component to determine a first direction of the first diffraction grating and the second diffraction grating. The position detection system according to claim 1, wherein a relative position is obtained.   The control unit uses the integrated waveform obtained by integrating the light intensity of the interference pattern in the detection area detected in the detection optical system and limited in the second direction in the second direction. The position detection system according to claim 1, wherein a relative position of the grating and the second diffraction grating in the first direction is obtained. A first diffraction grating having a period in a first direction, and a second diffraction having a period in the first direction different from the period in the first direction of the first diffraction grating and a period in a second direction different from the first direction. An illumination optical system that illuminates the first diffraction grating and the second diffraction grating from an oblique direction parallel to a second direction;
A detection optical system for detecting an interference pattern from the first diffraction grating and the second diffraction grating illuminated by the illumination optical system in a direction perpendicular to the first diffraction grating and the second diffraction grating;
A control unit,
A position detection system that detects a relative position of the first diffraction grating and the second diffraction grating in a first direction from a detection result of the detection optical system,
The control unit uses the detection area limited in the second direction with an even period in the first direction among the interference patterns periodically changed in the first direction detected by the detection optical system. A position detection system characterized in that a relative position of a first diffraction grating and the second diffraction grating in a first direction is obtained. The illumination optical system illuminates light having a pole in the second direction on the pupil plane;
The period of the second diffraction grating in the second direction is P1, the numerical aperture of the detection optical system on the pupil plane of the detection optical system is NAo, and the pole of the illumination optical system on the pupil plane from the optical axis When the distance is NAil1, the size of the pole is NAp1, and the wavelength of light illuminated from the illumination optical system is λ,
It is characterized by satisfying | NAil1-λ / P1 | <NAo + NAp1 / 2 at least for some wavelengths λ,
The position detection system according to claim 4.   The position detection system according to claim 5, wherein the illumination optical system illuminates light having a plurality of poles in the second direction on the pupil plane.   The position detection system according to any one of claims 1 to 6, wherein the first direction and the second direction are orthogonal to each other.   2. The size of an even period region of the interference pattern is obtained using a period in the first direction of the first diffraction grating and a period in the first direction of the second diffraction grating. The position detection system according to any one of 1 to 7. A imprint apparatus for forming on a substrate a pattern of the resin by using a mold,
An imprint apparatus, wherein the relative position between the mold and the substrate is obtained using the position detection system according to claim 1. Forming a pattern on a substrate using the imprint apparatus according to claim 9;
Processing the substrate on which the pattern is formed in the step;
A device manufacturing method comprising: A first diffraction grating having a period in a first direction, and a second diffraction having a period in the first direction different from the period in the first direction of the first diffraction grating and a period in a second direction different from the first direction. Illuminate the grid,
Detecting an interference pattern that periodically changes in a first direction by light from the illuminated first diffraction grating and the second diffraction grating;
A position detection method for obtaining a relative position of the first diffraction grating and the second diffraction grating in a first direction from a detection result of detecting the interference pattern,
Among the interference patterns formed by the detected light, the first diffraction grating and the second diffraction grating in the first direction are relative to each other using a detection region that is even-numbered in the first direction and limited in the second direction. A position detection method characterized by obtaining a specific position.   The phase component of the interference pattern is obtained by frequency analysis of the interference pattern formed by the detected light, and the relative positions of the first diffraction grating and the second diffraction grating in the first direction are determined from the phase component. The position detection method according to claim 11, wherein the position detection method is obtained.   Relative in the first direction of the first diffraction grating and the second diffraction grating using an integrated waveform obtained by integrating the light intensity of the interference pattern in the detection region restricted in the second direction in the second direction. The position detection method according to claim 11, wherein a specific position is obtained.   12. The size of an even period region of the interference pattern is obtained using a period in the first direction of the first diffraction grating and a period in the first direction of the second diffraction grating. 14. The position detection method according to any one of items 13 to 13.

Images