Interferometer system, wavefront analysis system, projection system, lithography apparatus, and method for analyzing the wavefront of a light beam in a heterodyne interferometer system.

Abstract

The interferometer system comprises a light source that provides a light beam, and an optical system arranged to split the light beam into a measurement beam and a reference beam having different wavelengths, guide the measurement beam to a reflection measurement surface, guide the reference beam to a reflection reference surface, and recombine the reflection measurement beam with the reflection reference beam to provide a reflected light beam. A reference detector receives the light beam and provides a reference detector signal, and / or a measurement detector receives the reflected light beam and provides a measurement detector signal. A ToF camera receives the reflected light beam and a demodulated signal based on the reference detector signal or the measurement detector signal and provides a camera signal representing the wavefront difference between the reflection measurement beam and the reflection reference beam, demodulated by the demodulated signal. The interferometer system analyzes the wavefront difference based on the camera signal.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of European Application No. 23158336.0 filed on February 23, 2023, which is incorporated herein by reference in its entirety.

[0002]

[0002] The present invention relates to an interferometer system and a wavefront analysis system for analyzing the wavefront difference of a reflected light beam of a heterodyne interferometer system. The present invention further relates to a projection system and / or a lithography apparatus for optical lithography comprising such an interferometer system, and a method for analyzing the wavefront difference of a reflected light beam of a heterodyne interferometer system. s

Background Art

[0003]

[0003] A lithography apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, also alternatively called a mask or a reticle, can be used to generate the circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target portion (e.g., including a part of one or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, one substrate includes a network of adjacent target portions to which patterns are sequentially applied. Conventional lithography apparatuses include so - called steppers in which each target portion is irradiated by exposing the entire pattern to the target portion in one go, and so - called scanners in which the substrate is scanned synchronously in a given direction (the "scan" direction) parallel or antiparallel to a given direction (the "scan" direction) while scanning the pattern with a radiation beam in the given direction, whereby each target portion is irradiated. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern on the substrate.

[0004]

[0004] In embodiments of lithography apparatus, an interferometer system is used to determine the position of a movable object with high precision. Examples of these movable objects include substrate supports and optical elements, such as mirrors in a projection optical system. The interferometer system may also be used, for example, in a wavelength tracker to accurately determine the path length to a stationary object.

[0005]

[0005] The interferometer system may include a light source device, an optical system, and a measurement detector. The light source device is arranged to provide a light beam that is guided to the optical system. The optical system is arranged to split the light beam into a measurement beam and a reference beam, to guide the measurement beam along the measurement path to the reflection measurement surface, and to guide the reference beam along the reference path to the reflection reference surface. After the measurement beam is reflected by the reflection measurement surface and the reference beam is reflected by the reflection reference surface, the optical system may recombine the measurement beam with the reference beam to provide a reflected light beam. The measurement detector is arranged to receive the reflected light beam and provide a measurement detector signal. This measurement detector signal represents the position of the reflection measurement surface. A processing device may be provided to determine the position of the reflection measurement surface based on the measurement detector signal.

[0006]

[0006] Interferometer systems may have measurement errors that depend on the inclination of the reflection measurement surface. These inclination-dependent errors are often related to the wavefront quality of the reflected light beam, in particular to the wavefront quality of the reflection measurement beam relative to the reflection reference beam. In addition, other factors such as the alignment of the optical elements of the optical system, manufacturing tolerances, and fiber noise may affect the wavefront quality of the reflected light beam.

[0007]

[0007] A Shack-Hartmann sensor can be installed to measure the wavefront gradient using a segmented microlens array, and the gradient can be integrated to create a wavefront map. However, a Shack-Hartmann sensor can only measure the wavefront gradient and cannot measure the beam phase offset. [Overview of the project]

[0008]

[0008] An object of the present invention is to provide an improved system for analyzing, for example, characterizing, the wavefronts of the reflectance beam and reference beam of an interferometer optical system. In particular, an object of the present invention is to provide an interferometer system that can be used to analyze the wavefront difference of the reflectance beam and reference beam of a heterodyne interferometer system and to determine wavefront deformation for diagnosis and / or calibration of the interferometer system.

[0009]

[0009] The objective is also to provide an improved or at least alternative method for analyzing the wavefront difference of the reflected light beam of a heterodyne interferometer system.

[0010]

[0010] According to one aspect of the present invention, A light source device arranged to provide a light beam, An optical system arranged to split a light beam into a measurement beam and a reference beam, wherein the measurement beam has a first wavelength and the reference beam has a second wavelength, and the first and second wavelengths are different, and the system is arranged to guide the measurement beam along a measurement path to a reflection measurement surface, guide the reference beam along a reference path to a reflection reference surface, the measurement beam is reflected by the reflection measurement surface, and after the reference beam is reflected by the reflection reference surface, the reflection measurement beam is recombined with the reflection reference beam to provide a reflected light beam, A reference detector arranged to receive a light beam and provide a reference detector signal, and / or a measurement detector arranged to receive a reflected light beam and provide a measurement detector signal, The system includes a ToF camera that receives a reflected light beam and a demodulated signal based on a reference detector signal or a measurement detector signal, and is configured to provide a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal, It is positioned to analyze the wavefront difference based on the camera signal. We provide interferometer systems.

[0011]

[0011] According to one aspect of the present invention, a wavefront analysis system for analyzing the wavefront difference of a reflected light beam of a heterodyne interferometer system, wherein the interferometer system provides a reflected light beam and a reference detector signal and / or a measurement detector signal, the reflected light beam includes a reflected measurement beam and a reflected reference beam, the reflected measurement beam having a first wavelength and the reflected reference beam having a second wavelength, and the first wavelength and the second wavelength being different, A ToF camera is configured to receive a reflected light beam and a demodulated signal based on a reference detector signal or a measurement detector signal, and to provide a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal. A processing device that analyzes wavefront differences based on camera signals, We provide a wavefront analysis system equipped with the following features.

[0012]

[0012] According to one aspect of the present invention, a projection system and / or lithography apparatus for optical lithography is provided, comprising an interferometer system.

[0013]

[0013] According to one aspect of the present invention, a method for analyzing the wavefront difference of a reflected light beam in a heterodyne interferometer system, The steps of providing a light beam and The steps include splitting the light beam into a measurement beam having a first wavelength and a reference beam having a second wavelength, which are different wavelengths from each other, The steps include: guiding the measurement beam along the measurement path toward the reflection measurement surface on the object of interest; The steps include: guiding a reference beam along a reference path toward a reflective reference surface on a reference object; The steps include: the measurement beam being reflected by the reflection measurement surface, the reference beam being reflected by the reflection reference surface, and then recombining the reflection measurement beam and the reflection reference beam to provide a reflected light beam; The steps include receiving a light beam with a reference detector and providing a reference detector signal, and / or receiving a reflected light beam with a measurement detector and providing a measurement detector signal, The ToF camera receives a demodulated signal based on a reflected light beam and a reference detector signal or a measurement detector signal. The steps include measuring a camera signal that represents the wavefront difference between the reflection measurement beam and the reflection reference beam of the reflected light beam demodulated with the demodulated signal, and The steps involve analyzing the camera signal to analyze the wavefront difference, This provides a method that includes [something]. [Brief explanation of the drawing]

[0014]

[0014] Embodiments of the present invention will be described below with reference to the attached schematic diagrams in which the corresponding reference numerals indicate the corresponding parts, but these are merely illustrative examples.

[0015] [Figure 1] A schematic diagram of a lithography apparatus is shown. [Figure 2] One embodiment of the interferometer system according to the present invention is shown. [Figure 3] A first alternative embodiment of the interferometer system according to the present invention is shown. [Figure 4] A second alternative embodiment of the interferometer system according to the present invention is shown. [Modes for carrying out the invention]

[0016]

[0015] Figure 1 schematically shows a lithography apparatus according to one embodiment of the present invention. This apparatus includes an illumination system IL, a support structure MT, a substrate table WT, and a projection system PS.

[0017]

[0016] The illumination system IL is configured to adjust the radiation beam B. The support structure MT (e.g., a mask table) is constructed to support the patterning device MA (e.g., a mask) and is connected to a first positioner PM configured to accurately position the patterning device according to certain parameters. The substrate table WT (e.g., a wafer table) is constructed to hold a substrate (e.g., a resist-coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate according to certain parameters. The projection system PS is configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0018]

[0017] The illumination system IL can include various types of optical components such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiation.

[0019]

[0018] As used herein, the term "radiation beam" encompasses not only particle beams such as ion beams or electron beams, but also any type of electromagnetic radiation including ultraviolet (UV) radiation (e.g., having a wavelength of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm or 126 nm, or around these wavelengths) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 nm to 20 nm).

[0020]

[0019] The support structure MT supports the patterning device MA, i.e., it bears its weight. The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithography apparatus, and conditions such as whether the patterning device MA is held in a vacuum environment. The support structure MT can hold the patterning device MA using mechanical, vacuum, electrostatic or other clamping techniques. The support structure MT may be, for example, a frame or table that can be fixed or movable as needed. The support structure MT may ensure that the patterning device MA is in a desired position relative to, for example, the projection system PS.

[0021]

[0020] The term “patterning device” as used herein should be interpreted broadly to refer to any device that can be used to impart a pattern to a cross section of a radiation beam B in order to generate a pattern on a target portion C of a substrate W. Note that the pattern imparted to the radiation beam B may not precisely correspond to a desired pattern on the target portion C of the substrate W, for example, if the pattern includes phase-shift features or so-called assist features. Generally, the pattern imparted to the radiation beam corresponds to a specific functional layer of a device, such as an integrated circuit, that is generated on the target portion C.

[0022]

[0021] The patterning device MA may be transparent or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary masks, Levenson (alternating) phase-shift masks, halftone (attenuated) phase-shift masks, and various hybrid mask types. As an example of a programmable mirror array, a matrix array of small mirrors is used, each of which can be individually tilted to reflect the incident radiation beam B in a different direction. The tilted mirrors impart a pattern to the radiation beam B reflected by the mirror matrix.

[0023]

[0022] The term “projection system” as used herein should be interpreted broadly to encompass any type of projection system, including, for example, refractive optical systems, reflective optical systems, reflector-refractor optical systems, magneto-optical systems, electromagnetic optical systems, and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used or other factors such as the use of immersion liquid or vacuum.

[0024]

[0023] As shown herein, the device is of the transmissive type (for example, using a transmissive mask). Alternatively, the device may be of the reflective type (for example, using a programmable mirror array of the type mentioned above or using a reflective mask).

[0025]

[0024] The lithography apparatus may be of a type having two or more substrate tables WT (and / or two or more mask tables). In such a “multistage” machine, additional tables may be used in parallel, or preparation steps may be performed on one or more tables while one or more other tables are being used for exposure. In addition to one or more substrate tables WT, the lithography apparatus may have a measurement stage positioned below the projection system PS when the substrate tables WT are away from their position. The measurement stage may be equipped with sensors for measuring the characteristics of the lithography apparatus instead of supporting the substrate W. For example, the projection system may project an image onto sensors on the measurement stage and determine the image quality.

[0026]

[0025] The lithography apparatus may be of a type in which at least a portion of the substrate W is covered with a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system and the substrate. An immersion liquid may be applied to other spaces within the lithography apparatus, such as between the patterning device MA and the projection system PS. Immersion techniques are well known in the art as a technique for increasing the numerical aperture of a projection system. As used herein, the term “immersion” does not mean that a structure such as the substrate W needs to be immersed in a liquid, but rather that a liquid is present between the projection system PS and the substrate W during exposure.

[0027]

[0026] Referring to Figure 1, the illumination system IL receives the radiant beam B from the radiant source SO. The radiant source SO and the lithography apparatus may be separate components, for example, when the radiant source SO is an excimer laser. In such cases, the radiant source is not considered to form part of the lithography apparatus, and the radiant beam B is delivered from the radiant source SO to the illumination system IL with the help of a beam delivery system BD, which includes, for example, a suitable guide mirror and / or beam expander. In other cases, for example, when the radiant source SO is a mercury lamp, the radiant source SO may be an integral part of the lithography apparatus. The radiant source SO and the illuminator IL may, if necessary, be called a radiant system together with the beam delivery system BD.

[0028]

[0027] The illumination system IL may include an adjuster AD for adjusting the angular intensity distribution of the radiant beam B. Generally, the outer and / or inner radial ranges of the intensity distribution at the pupil plane of the illumination system (generally referred to as σ-outer and σ-inner, respectively) can be adjusted. The illumination system IL may also include various other components such as an integrator IN and a capacitor CO. The radiant beam B may be adjusted using the illuminator IL to obtain the desired uniformity and intensity distribution across its cross-section.

[0029]

[0028] The radiant beam B is incident on a patterning device MT held on a support structure MT, and a pattern is formed by the patterning device MA. The radiant beam B, having crossed the patterning device MA, passes through a projection system PS and is focused by the projection system PS onto a target portion C of the substrate W. With the help of a second positioner PW and a position sensor IF (e.g., an interferometer, linear encoder, or capacitance sensor), the substrate table WT can be precisely moved to position, for example, various target portions C within the path of the radiant beam B. Similarly, a first positioner PM and another position sensor (not shown in Figure 1) can be used to precisely position the patterning device MA relative to the path of the radiant beam B after mechanical removal from the mask library or during scanning. In general, the movement of the support structure MT can be achieved using long-stroke modules and short-stroke modules that form part of the first positioner PM. The long-stroke modules can provide coarse positioning over the large range of movement of the short-stroke modules. The short-stroke module can provide fine positioning of the support structure MT relative to the long-stroke module over a small range of movement. Similarly, the movement of the substrate table WT can be achieved using the long-stroke and short-stroke modules forming part of the second positioner PW. The long-stroke module can provide coarse positioning over the large range of movement of the short-stroke module. The short-stroke module can provide fine positioning of the substrate table WT relative to the long-stroke module over a small range of movement. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to or fixed only to the short-stroke actuator. The patterning device MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.As shown in the figure, substrate alignment marks P1 and P2 occupy dedicated target areas, but may also be located in the space between target areas C (known as scribe line alignment marks). Similarly, in situations where multiple dies are provided on a patterning device MA, mask alignment marks M1 and M2 may be placed between the dies.

[0030]

[0029] The illustrated apparatus can be used in at least one of the following modes:

[0031]

[0030] 1. In the first mode, the so-called step mode, the support structure MT and the substrate table WT are kept essentially stationary, while the entire pattern applied to the radiation beam B is projected onto the target portion C in one pass (i.e., single static exposure). Next, the substrate table WT is moved in the X and / or Y directions so that another target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C on which an image is formed in a single static exposure.

[0032]

[0031] 2. In the second mode, the so-called scan mode, the support structure MT and the substrate table WT are scanned synchronously, while the pattern applied to the radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the mask table MT can be determined by the scaling (reduction) and image inversion characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion (in the non-scanning direction) in single dynamic exposure, and the length of the scan operation determines the height of the target portion (in the scanning direction).

[0033]

[0032] 3. In the third mode, the support structure MT is kept essentially stationary, holding the programmable patterning device, and projects the pattern applied to the radiation beam B onto the target portion C while the substrate table WT is moved or scanned. In this mode, a pulsed radiation source is generally used to update the programmable patterning device as needed each time the substrate table WT is moved, or between consecutive radiation pulses during scanning. This mode of operation is readily available for maskless lithography using programmable patterning devices such as the programmable mirror arrays of the type mentioned above.

[0034]

[0033] Combinations and / or variations of the above usage modes, or completely different usage modes may also be adopted.

[0035]

[0034] Figure 2 shows an interferometer system 100 according to one embodiment of the present invention. The interferometer system 100 is arranged to measure changes in the position of a movable object 200. The movable object 200 is part of the lithography apparatus shown in Figure 1. The interferometer system 100 may be used, for example, to measure the position of a mirror or lens element of a projection system PS, a patterning device support MT, or a substrate support WT. The movable object 200 includes a reflectance measuring surface 201. The change in the position of the movable object 200 is determined with respect to a reference object 300 having a reference reflectance surface 301. If the starting position of the movable object 200 is known, the actual absolute position of the movable object 200 can be determined based on the starting position and the measured change in position.

[0036]

[0035] The interferometer system 100 includes a light source device 101 that provides a light beam 102. The light source device 101 includes, for example, a stabilized laser light source 103, a first polarization-frequency shift device 104, a second polarization-frequency shift device 105, and a rosion prism 106.

[0037]

[0036] The interferometer system 100 is a heterodyne interferometer system. Light emitted from the light source 103 is split into a first optical beam and a second optical beam. The first optical beam is supplied to the first polarization-frequency shift device 104 with a first polarization and a first wavelength. The second optical beam is supplied to the second polarization-frequency shift device 105 with a second polarization and a second wavelength. The first and second polarizations are orthogonal to each other. The first and second wavelengths are different. The difference between the first frequency of the first optical beam and the second frequency of the second optical beam may be in the range of 0.5 to 50 MHz, or for example, in the range of 5 to 20 MHz. The first optical beam is for forming a measurement beam, and the second optical beam is for forming a reference beam.

[0038]

[0037] The first polarization-frequency shift device 104 and the second polarization-frequency shift device 105 may each include a separate polarization unit and a frequency shift unit. The frequency shift unit may include, for example, a photoacoustic modulator. The first and second light beams are recombined in the lochon prism 106. Any other suitable optical component other than the lochon prism 106 may be used to recombine the first and second light beams.

[0039]

[0038] In practice, one of the first wavelength of the first light beam or the second wavelength of the second light beam may be the same as the wavelength of light provided by the light source 103, but the other of the first or second wavelength may be shifted by the respective polarization-frequency shift devices 104, 105. It is clear that a frequency shift device is also unnecessary for the one of the first or second wavelength that is not shifted.

[0040]

[0039] As an alternative to this configuration, a free-space Zeeman split laser may be applied. Such a free-space Zeeman split laser may provide a light beam having a first light beam portion and a second light beam portion, the first and second beam portions having mutually orthogonal polarization and different wavelengths.

[0041]

[0040] Thus, the light source system 101 provides a light beam 102 having a first light beam section and a second light beam section, the first beam section and the second beam section having mutually orthogonal polarization and different wavelengths.

[0042]

[0041] The light beam 102 is guided into an optical system including a polarizing beam splitter 107. The polarizing beam splitter 107 is arranged to split the light beam into a first light beam section and a second light beam section, providing a measurement beam based on the first light beam section and a reference beam based on the second light beam section.

[0043]

[0042] The measurement beam is guided along the measurement path 205 toward the reflection measurement surface 201 on the object 200. The reference beam is guided along the reference path 305 toward the reflection reference surface 301 on the reference object 300.

[0044]

[0043] After the measurement beam is reflected by the reflective measurement surface 201 and the reference beam is reflected by the reflective reference surface 301, the measurement beam and the reference beam are recombined in the polarizing beam splitter 107 to form the reflected light beam 108. The reflected light beam 108 is guided to a measurement detector 109, which is, for example, an avalanche photodiode. The measurement detector 109 measures a measurement detector signal based on the reflected light beam 108.

[0045]

[0044] The measurement detector signal may be directed to the processing device 110. Based on the measurement detector signal, the relative movement of the movable object 200, i.e., the change in path length Lx, can be determined with high accuracy. The movement of the movable object 200 causes a phase shift in the phase signal. Based on these phase shifts in the phase signal, the processing device 110 can determine the relative displacement of the movable object 200 with respect to the reference object 300. If the starting position of the movable object 200 is known, the position of the movable object 200 can be determined.

[0046]

[0045] A portion of the light beam 102 from the light source device 101 is directed by a translucent mirror 111 to a reference detector 112, which is, for example, an avalanche photodiode. This portion of the light beam 102 does not interact with either the reflection measurement surface 201 or the reflection reference surface 103. The reference detector 112 measures a reference detector signal based on the light beam 102. This reference detector signal may be directed to a processing device 110 for further processing. This reference detector signal may be used, for example, as a reference signal for first and second wavelengths and represents the light beam 102 directed towards the optical system of the interferometer system 110, particularly the polarizing beam splitter 107, thereby improving the measurement accuracy of the interferometer system. The reference detector 112 provides a reference detector signal representing the light beam 102.

[0047]

[0046] The interferometer system 100 in Figure 2 may have measurement errors that depend on the inclination of the reflection measurement surface 201. These inclination-dependent errors are often related to the wavefront quality of the reflected light beam 108, for example, the wavefront of the measurement beam relative to the reference beam. In addition, other factors such as the alignment of the optical elements of the optical system, manufacturing tolerances, and fiber noise may affect the quality of the wavefront difference of the reflected light beam 108.

[0048]

[0047] It is desirable to obtain insights into the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam 108. To analyze the wavefront difference of the reflected light beam 108, the interferometer system 100 is provided with a ToF camera 115 positioned to receive the reflected light beam 108. To guide the reflected light beam 108 toward the ToF camera 115, the optical system of the interferometer system 100 includes a translucent mirror 109 that divides the reflected light beam 108 into a first portion guided toward a measurement detector 109 and a second portion guided toward the ToF camera 115. The ToF camera is a digital camera capable of providing depth values ​​at each pixel of the camera.

[0049]

[0048] The measurement detector 109 and the ToF camera 115 may include at least one polarizer to cause interference between the orthogonally polarized reflection measurement beam and the reflection reference beam. Similarly, the reference detector 112 may include at least one polarizer to cause interference between the orthogonally polarized measurement beam and the reference beam.

[0050]

[0049] In order to analyze the wavefront difference between the measurement beam and the reference beam of the reflected light beam 108, the reflected light beam is demodulated with a demodulation signal. In the embodiment shown in Figure 2, the measurement detector signal provided by the measurement detector 109 is guided to the ToF camera 115 as a demodulation signal for demodulating the reflected light beam 108.

[0051]

[0050] The wavefront difference of the reflected light beam 108, particularly the reflectance measurement beam, with respect to the reflectance measurement beam may be determined by demodulating the reflected light beam 109 using the measurement detector signal. In an alternative embodiment, the reference detector signal may be used as the demodulated signal to demodulate the reflected light beam 108 received by the ToF camera 115.

[0052]

[0051] The ToF camera 115 provides a camera signal representing the wavefront difference between the wavefront of the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated with the demodulated signal to a processing device 110 for further processing of the camera signal. The processing device that processes the camera signal may be a separate processing device from the processing device 110 that processes the measurement detector signal and the reference detector signal received directly from the measurement detector and the reference detector.

[0053]

[0052] The camera signal contains information about the wavefront difference of the reflected light beam 108. This information may be determined by analyzing the camera signal. The processing device may be configured, for example, to unwrap the camera signal representing the wavefront difference of the reflected light beam. By unwrapping the camera signal, the spatial representation of the wavefront may be determined. This spatial representation facilitates the analysis of wavefront quality.

[0054]

[0053] The processing device 110 may be configured to determine the wavefront deformation of the wavefront of the reflected light beam, the reflectance measurement beam and / or the reflectance reference beam, in particular the wavefront deformation of the reflectance measurement beam of the reflected light beam relative to the reflectance reference beam of the reflected light beam. The wavefront deformation may be due to, for example, air turbulence and / or position / tilt-dependent deformation resulting from the alignment and / or manufacturing tolerances of the optical elements of the optical system, for example, imperfections in the reflectance measurement surface 201 may cause ghost reflections.

[0055]

[0054] By analyzing the wavefront deformation of the reflected light beam 108, the measurement quality and robustness of the interferometer system 100 can be diagnosed. Wavefront analysis may be added to existing interferometer systems 100 to diagnose the performance of these interferometer systems 100. Furthermore, in new interferometer configurations, wavefront analysis can also be used to determine the product quality with respect to the wavefront difference of the reflected light beam 108.

[0056]

[0055] The wavefront analysis system may be integrated with the interferometer system 100, or it may be provided as a separate device that can be easily used to diagnose the wavefront characteristics of different interferometer systems 100.

[0057]

[0056] The processing device 110 may be configured to calculate correction and / or compensation values ​​for correcting and / or compensating for wavefront deformation of the wavefront of the reflected light beam, the reflection measurement beam and / or the reflection reference beam. Such correction and / or compensation values ​​can be used to calibrate the interferometer system 100 so that, for example, software correction of the measurement results obtained by the measurement detector 109 and / or the measurement results obtained by the ToF camera 115 can correct and / or compensate for undesirable wavefront deformation of the wavefront of the reflection measurement beam and / or the reference beam by the interferometer system 100. The correction may include subtracting a pre-calibrated reference.

[0058]

[0057] The wavefront of the measurement beam or the reference beam may be pre-calibrated so that the wavefront of this beam is known. The ToF camera 115 can then be used to determine the absolute wavefront of the other of the measurement beam or the reference beam. For example, if the wavefront of the reference beam is pre-calibrated, the ToF camera 115 can then be used to determine the absolute wavefront of the measurement beam. Pre-calibration may be performed using a complete or known reference wavefront before mixing one of the measurement beam or the reference beam with the wavefront difference sensor 115, or it may be performed using another type of absolute wavefront measuring device such as a Shack-Hartmann sensor. This sensor used for absolute measurement should be used for either the measurement beam or the reference beam.

[0059]

[0058] Furthermore, it is also possible to guide only one of the first and second optical beams to the optical system of the interferometer 100 and the other directly to the ToF camera 115. For example, the first optical beam, which is for forming the measurement beam, may be guided to the polarization beam splitter 107 so as to travel along the measurement path 205, while the second optical beam, which is for forming the reference beam, may not be guided to the polarization beam splitter 107 but directly to the ToF camera 115. The reflectance measurement beam and the second optical beam may be mixed immediately before being detected by the ToF camera 115. The second optical beam may be a fully collimated beam originating from a high-quality or pre-calibrated collimator, or the second optical beam may be emitted from the fiber end without going through the optical system and emitted as a perfect spherical wavefront as a known wavefront reference. The first and second light beams may be inverted, for example, so that the second light beam is guided to the optical system of the interferometer 100, and the first light beam is guided directly to the ToF camera 115 to analyze the wavefront quality of the reference beam's wavefront.

[0060]

[0059] Figure 3 shows a first alternative embodiment of the interferometer system 100, which includes a wavefront analysis system. In this embodiment, both the reference detector signal and the measurement signal can be used as demodulated signals. In this embodiment, wavefront analysis is provided as a wavefront analysis system 400 comprising a ToF camera 115, a demodulated signal selection device 116, and a separate processing device 117.

[0061]

[0060] The wavefront analysis system 400 provides a reflected light beam 108 through a translucent mirror 113, and provides a reference detector signal from the reference detector 112 and a measurement detector signal from the measurement detector 113, and allows one of the reference detector signal and the measurement signal to be selected as the demodulated signal. As an alternative to the transparent mirror 113, a polarizing beam splitter or a combination of a waveplate and a polarizing beam splitter may be provided, which is aligned so that the reflected measurement beam and the reflected reference beam interfere with each other. The wavefront analysis system 400 can be implemented without additional signal loss to the detector 109. The measurement detector 109 and the ToF camera 115 detect a heterodyne signal that is 180° out of phase.

[0062]

[0061] The demodulated signal is provided to the ToF camera 115 by the demodulated signal selection device 116. The demodulated signal selection device 116 is connected to the reference detector 112 to receive the reference detector signal and is connected to the measurement detector 109 to receive the measurement detector signal. The demodulated signal selection device 116 is configured to selectively guide the selected one of the reference detector signal and the measurement detector signal to the ToF camera 115 as the demodulated signal in order to demodulate the reflected light beam 108.

[0063]

[0062] By demodulating the reflected light beam using the reference detector signal as a demodulated signal, a camera signal is obtained that represents the wavefront difference between the measurement beam and the reference beam, including the displacement of the reflection measurement surface 201. By demodulating the reflected light beam using the measurement detector signal as a demodulated signal, a camera signal is obtained that represents the wavefront of the reflected light beam, excluding the displacement of the reflection measurement surface 201.

[0064]

[0063] The demodulated signal selection device 116 may be directly controlled by the processing device 117 of the wavefront analysis system 400, as shown by the dashed arrow in Figure 3, and may select the desired one of the reference detector signal and the measurement signal as the demodulated signal. In an alternative embodiment, the demodulated signal selection device 116 may be controlled by another device, such as the processing device 110.

[0065]

[0064] Figure 4 shows a second alternative embodiment of the interferometer system 100 equipped with a wavefront analysis system. In this embodiment, both the reference detector signal and the measurement signal can be used as demodulated signals. Corresponding to the embodiment in Figure 3, the demodulated signal selection device 116 is arranged to selectively guide either the reference detector signal or the measurement detector signal to the ToF camera 115. In this embodiment, the demodulated signal selection device 116 and the ToF camera 115 are integrated into the interferometer system, but they may be provided as separate systems, as shown in Figure 3.

[0066]

[0065] The demodulated signal selection device 116 may be directly controlled to select one of the reference detector signal and the measurement signal as the demodulated signal, or the demodulated signal selection device 116 may be controlled by another device, such as the processing device 110, as shown by the dashed arrow in Figure 4.

[0067]

[0066] In the embodiment shown in Figure 4, the reference detector signal measured by the reference detector 112 and the measurement detector signal measured by the measurement detector 109 are not directly transmitted to the processing device 110. In this embodiment, the ToF camera 115 is used not only for the analysis of the wavefront of the reflected light beam 108, in particular the wavefront of the reflected measurement beam relative to the reflected reference beam, but also for determining the displacement of the reflected measurement surface 201, i.e., the movable object 200.

[0068]

[0067] To determine the displacement of the reflection measurement surface 201, the reference detector signal is used as the demodulated signal. If it is desirable to continuously measure the displacement of the reflection measurement surface 201 and there is no need to analyze the wavefront of the reflected light beam 108 which has no displacement, the demodulated signal selection device 116 may be omitted, and the reference detector signal of the reference detector 112 may be directly guided to the ToF camera 115 as the demodulated signal.

[0069]

[0068] The above describes an interferometer system in which a ToF camera is configured to receive a reflected light beam and a demodulated signal and analyze the wavefront difference between a reflected measurement beam and a reflected reference beam. The demodulated signal is based on a reference detector signal or a measurement detector signal. In alternative embodiments, any signal having a wavelength identical to or close to the wavelength of the measurement beam or the reference beam, or a wavelength between the wavelength of the measurement beam and the wavelength of the reference beam, for example, a split frequency between the wavelength of the measurement beam and the wavelength of the reference beam, may be used. The demodulated signal may be measured by a measurement detector or a reference detector, or it may be obtained, for example, from a drive signal used in a light source device to introduce a wavelength difference between a first light beam section and a second light beam section.

[0070]

[0069] While this text specifically refers to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein has other applications. For example, these include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like. In light of these alternative applications, it will be recognized by those skilled in the art that where the terms “wafer” or “die” are used herein, they may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. The substrates described herein may be processed before or after exposure with, for example, a track (usually a tool for coating a layer of resist onto the substrate and developing the exposed resist), a metronome tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to the above and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example to produce a multilayer IC, and therefore the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

[0071]

[0070] While we have made particular reference to the use of embodiments of the present invention in the field of optical lithography, it should be understood that the present invention can be used in other fields, such as imprint lithography, depending on the context, and is not limited to optical lithography. In imprint lithography, a topography in a patterning device defines the pattern to be created on a substrate. The topography of the patterning device is imprinted into a resist layer supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, and once the resist has cured, the pattern remains inside.

[0072]

[0071] Although specific embodiments of the present invention have been described above, it should be understood that the present invention can be practiced in ways other than those described. For example, the present invention may take the form of a computer program that includes one or more sequences of machine-readable instructions describing the methods disclosed above, or a data storage medium (e.g., semiconductor memory, magnetic or optical disk) that stores such a computer program internally.

[0073]

[0071] The above description is illustrative and not limiting. Therefore, it will be apparent to those skilled in the art that modifications to the invention described can be made without departing from the claims. Other aspects of the invention are described in the following numbered clauses.

[0074] 1. A light source device arranged to provide a light beam, An optical system arranged to split a light beam into a measurement beam and a reference beam, wherein the measurement beam has a first wavelength and the reference beam has a second wavelength, and the first and second wavelengths are different, and the system is arranged to guide the measurement beam along a measurement path to a reflection measurement surface, guide the reference beam along a reference path to a reflection reference surface, the measurement beam is reflected by the reflection measurement surface, and after the reference beam is reflected by the reflection reference surface, the reflection measurement beam is recombined with the reflection reference beam to provide a reflected light beam, A reference detector arranged to receive a light beam and provide a reference detector signal, and / or a measurement detector arranged to receive a reflected light beam and provide a measurement detector signal, The system includes a ToF camera that receives a reflected light beam and a demodulated signal based on a reference detector signal or a measurement detector signal, and is configured to provide a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal, It is positioned to analyze the wavefront difference based on the camera signal. Interferometer system. 2. The interferometer system according to Clause 1, wherein a reference detector is arranged to receive a light beam and provide a reference detector signal, a measuring detector is arranged to receive a reflected light beam and provide a measuring detector signal, and the demodulated signal is a selected one of the reference detector signal and the measuring detector signal. 3. The interferometer system according to Clause 2, comprising a demodulation signal selection device connected to a reference detector to receive a reference detector signal and connected to a measurement detector to receive a measurement detector signal, wherein the modulation signal selection device is arranged to selectively guide one of the reference detector signal and the measurement detector signal to a ToF camera as a demodulation signal for demodulating a reflected light beam. 4. An interferometer system as described in Clause 1, comprising a processing device for analyzing the wavefront difference of the reflected light beam. 5. The interferometer system as described in Clause 4, wherein the processing device is arranged to unwrap the camera signal representing the wavefront difference of the reflected light beam. 6. The interferometer system as described in Clause 4, wherein the processing device is arranged to determine the wavefront deformation of the wavefront of the reflected light beam, the reflectance measurement beam and / or the reflected reference beam. 7. The interferometer system as described in Clause 6, wherein the processing device is arranged to calculate correction and / or compensation values ​​for correcting and / or compensating for wavefront deformation of the reflected light beam, the reflectance measurement beam and / or the reflected reference beam. 8. The interferometer system according to Clause 7, wherein the light beam includes a first light beam portion having a first polarization and a second light beam portion having a second polarization, the first light beam portion having a different wavelength from the second light beam portion, the first light beam portion being for forming a measurement beam, and the second light beam portion being for forming a reference beam. 9. The interferometer system according to Clause 8, comprising an optical system which divides a light beam into a first light beam section and a second light beam section to provide a measurement beam and a reference beam, and a polarizing beam splitter which is arranged to recombine the measurement beam and the reference beam after the measurement beam has been reflected by a reflection measurement surface and the reference beam has been reflected by a reflection reference surface to provide a reflected light beam. 10. The interferometer system according to any one of the clauses 1 to 9, wherein the movable object is a substrate support for a lithography apparatus, a patterning device support, or an optical element of a projection system. 11. A wavefront analysis system for analyzing the wavefront difference of a reflected light beam of a heterodyne interferometer system, wherein the interferometer system provides a reflected light beam and a reference detector signal and / or a measurement detector signal, and the reflected light beam includes a reflected measurement beam and a reflected reference beam, wherein the reflected measurement beam has a first wavelength and the reflected reference beam has a second wavelength, and the first wavelength and the second wavelength are different. The wavefront analysis system is A ToF camera is configured to receive a reflected light beam and a demodulated signal based on a reference detector signal or a measurement detector signal, and to provide a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal. A processing device that analyzes wavefront differences based on camera signals, A wavefront analysis system equipped with the following features. 12. The wavefront analysis system according to Clause 11, comprising a demodulation signal selection device connected to a reference detector to receive a reference detector signal and connected to a measurement detector to receive a measurement detector signal, wherein the modulation signal selection device is arranged to selectively guide one of the reference detector signal and the measurement detector signal to a ToF camera as a demodulation signal for demodulating a reflected light beam. 13. A projection system for optical lithography comprising an interferometer system as described in any of clauses 1 to 10. 14. A lithography apparatus comprising an interferometer system as described in any of clauses 1 to 10. 15. A method for analyzing the wavefront difference of a reflected light beam in a heterodyne interferometer system, The steps of providing a light beam and The steps include splitting the light beam into a measurement beam having a first wavelength and a reference beam having a second wavelength, which are different wavelengths from each other, The steps include: guiding the measurement beam along the measurement path toward the reflection measurement surface on the object of interest; The steps include: guiding a reference beam along a reference path toward a reflective reference surface on a reference object; The steps include: the measurement beam being reflected by the reflection measurement surface, the reference beam being reflected by the reflection reference surface, and then recombining the reflection measurement beam and the reflection reference beam to provide a reflected light beam; The steps include receiving a light beam with a reference detector and providing a reference detector signal, and / or receiving a reflected light beam with a measurement detector and providing a measurement detector signal, The ToF camera receives a demodulated signal based on a reflected light beam and a reference detector signal or a measurement detector signal. The steps include measuring a camera signal that represents the wavefront difference between the reflection measurement beam and the reflection reference beam of the reflected light beam demodulated with the demodulated signal, and The steps involve analyzing the camera signal to analyze the wavefront difference, Methods that include... 16. The steps of receiving the light beam with a reference detector and providing a reference detector signal, The steps include receiving the reflected light beam with a measuring detector and providing a measuring detector signal, A step of selecting one of the reference detector signal and the measurement detector signal as the demodulated signal, The method described in Article 13, including the method described in Article 13. 17. The method further includes the step of selectively inducing a reference detector signal or a measurement detector signal as a demodulated signal to a ToF camera in order to demodulate the reflected light beam, By demodulating the reflected light beam using the reference detector signal as the demodulated signal, a camera signal representing the wavefront difference of the reflected light beam, including the displacement of the reflection measurement surface, is obtained. The method according to Clause 15, wherein a camera signal representing the wavefront difference of the reflected light beam, which does not include the displacement of the reflection measurement surface, is obtained by demodulating the reflected light beam using the measurement detector signal as a demodulated signal. 18. The method of Clause 15, wherein the analysis of the camera signal includes unwrapping the camera signal which represents the wavefront difference of the reflected light beam. 19. The method according to Clause 15, wherein analyzing the camera signal includes determining the wavefront deformation of the wavefront of the reflected light beam, the reflectance measurement beam and / or the reflected reference beam. 20. The method according to Clause 19, wherein the analysis of the camera signal includes calculating correction and / or compensation values ​​to correct and / or compensate for wavefront deformation of the wavefront of the reflected light beam, the measurement beam and / or the reference beam.

Claims

1. A light source device arranged to provide a light beam, An optical system arranged to split the aforementioned light beam into a measurement beam and a reference beam, wherein the measurement beam has a first wavelength and the reference beam has a second wavelength, the first wavelength and the second wavelength are different, the measurement beam is guided along a measurement path to a reflection measurement surface, the reference beam is guided along a reference path to a reflection reference surface, the measurement beam is reflected by the reflection measurement surface, and after the reference beam is reflected by the reflection reference surface, the reflection measurement beam is recombined with the reflection reference beam to provide a reflected light beam, A reference detector arranged to receive the light beam and provide a reference detector signal, and / or a measurement detector arranged to receive the reflected light beam and provide a measurement detector signal, The system includes a ToF camera that receives the reflected light beam and a demodulated signal based on the reference detector signal or the measurement detector signal, and is configured to provide a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal, A system is arranged to analyze the wavefront difference based on the camera signal. Interferometer system.

2. The reference detector is arranged to receive the light beam and provide a reference detector signal. The measurement detector is arranged to receive the reflected light beam and provide a measurement detector signal. The interferometer system according to claim 1, wherein the demodulated signal is a selected one of the reference detector signal and the measurement detector signal.

3. The interferometer system includes a demodulation signal selection device connected to the reference detector and receiving the reference detector signal, and connected to the measurement detector and receiving the measurement detector signal, The interferometer system according to claim 2, wherein the modulation signal selection device is arranged to selectively guide one of the reference detector signal and the measurement detector signal to the ToF camera as the demodulated signal in order to demodulate the reflected light beam.

4. The interferometer system according to claim 1, further comprising a processing device for analyzing the wavefront difference of the reflected light beam.

5. The interferometer system according to claim 4, wherein the processing device is arranged to unwrap the camera signal representing the wavefront difference of the reflected light beam.

6. The interferometer system according to claim 4, wherein the processing device is arranged to determine the wavefront deformation of the wavefront of the reflected light beam, the reflectance measurement beam and / or the reflectance reference beam.

7. A wavefront analysis system for analyzing the wavefront difference of a reflected light beam of a heterodyne interferometer system, wherein the interferometer system provides a reflected light beam and a reference detector signal and / or a measurement detector signal, the reflected light beam includes a reflection measurement beam and a reflection reference beam, the reflection measurement beam having a first wavelength and the reflection reference beam having a second wavelength, and the first wavelength and the second wavelength being different, The waveplane analysis system is, A ToF camera is provided that receives the reflected light beam and a demodulated signal based on the reference detector signal or the measurement detector signal, and provides a camera signal representing the wavefront difference between the reflected measurement beam and the reflected reference beam of the reflected light beam demodulated by the demodulated signal. A processing device that analyzes the wavefront difference based on the camera signal, A wavefront analysis system equipped with the following features.

8. The wavefront analysis system includes a demodulation signal selection device connected to the reference detector and receiving the reference detector signal, and connected to the measurement detector and receiving the measurement detector signal, The wavefront analysis system according to claim 7, wherein the modulation signal selection device is arranged to selectively guide one of the reference detector signal and the measurement detector signal to the ToF camera as the demodulated signal in order to demodulate the reflected light beam.

9. A projection system for optical lithography comprising the interferometer system described in any one of claims 1 to 6.

10. A lithography apparatus comprising the interferometer system described in any one of claims 1 to 6.

11. A method for analyzing the wavefront difference of a reflected light beam in a heterodyne interferometer system, The steps of providing a light beam and The steps of dividing the light beam into a measurement beam having a first wavelength and a reference beam having a second wavelength, which are different wavelengths from each other, The steps include: guiding the measurement beam along the measurement path toward the reflection measurement surface on the object of interest; The steps include: guiding the reference beam along a reference path toward a reflective reference surface on a reference object; The steps include: the measurement beam being reflected by the reflection measurement surface, the reference beam being reflected by the reflection reference surface, and then recombining the reflection measurement beam and the reflection reference beam to provide a reflected light beam; The steps include receiving the aforementioned light beam with a reference detector to provide a reference detector signal, and / or receiving the reflected light beam with a measurement detector to provide a measurement detector signal, The steps include receiving the reflected light beam and the demodulated signal based on the reference detector signal or the measurement detector signal with a ToF camera, The steps include measuring a camera signal that represents the wavefront difference between the reflection measurement beam and the reflection reference beam of the reflected light beam demodulated with the demodulated signal, The steps include analyzing the camera signal and analyzing the wavefront difference, Methods that include...

12. The steps include receiving the light beam with the reference detector and providing the reference detector signal, The steps include receiving the reflected light beam with the measuring detector and providing the measuring detector signal, The steps include selecting one of the reference detector signal and the measurement detector signal as the demodulated signal, The method according to claim 11, including the method described in claim 11.

13. The method further includes the step of selectively inducing the reference detector signal or the measurement detector signal as the demodulated signal to the ToF camera in order to demodulate the reflected light beam, By demodulating the reflected light beam using the aforementioned reference detector signal as a demodulated signal, a camera signal representing the wavefront difference of the reflected light beam, including the displacement of the reflection measurement surface, is obtained. The method according to claim 11, wherein a camera signal representing the wavefront difference of the reflected light beam, which does not include the displacement of the reflection measuring surface, is obtained by demodulating the reflected light beam using the measurement detector signal as a demodulated signal.

14. The method according to claim 11, wherein analyzing the camera signal includes unwrapping the camera signal representing the wavefront difference of the reflected light beam.

15. The method according to claim 11, wherein analyzing the camera signal includes determining the wavefront deformation of the wavefront of the reflected light beam, the reflectance measurement beam and / or the reflectance reference beam.

Images