Height measurement error determination

Abstract

A method for determining a substrate height measurement error, the method comprising: providing a laser beam modulated at a given frequency, the laser beam having a wavelength and polarization; directing the modulated laser beam onto the substrate at an acute angle relative to a normal extending from the substrate; detecting a position of the modulated laser beam after the modulated laser beam has been reflected from the substrate; using a detection based on the frequency of the modulation applied to the laser beam to measure a modulation of the detected position of the modulated laser beam; and determining the height measurement error based on the measured modulation of the detected position of the modulated laser beam wherein the wavelength or the polarization is modulated.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European application 23165575.4, filed on March 30, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to determining substrate height measurement error. Substrate height measurement error can be determined in a photolithography apparatus. Background Technology

[0004] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project, for example, a pattern (often referred to as a “design layout” or “design”) from a patterning apparatus (e.g., a mask also known as a photomask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] As semiconductor manufacturing processes continue to advance, the size of circuit elements has shrunk dramatically over the decades, while the number of functional elements, such as transistors, per device has steadily increased, following a trend commonly known as "Moore's Law." To keep pace with Moore's Law, the semiconductor industry is pursuing technologies that enable the creation of increasingly smaller features. Photolithography equipment uses electromagnetic radiation to project patterns onto a substrate. The wavelength of this radiation determines the minimum size of the feature patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to photolithography equipment using radiation with a wavelength, for example, 193 nm, photolithography equipment using extreme ultraviolet (EUV) radiation with wavelengths in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on a substrate.

[0006] Typically, a substrate may comprise multiple layers containing one or more materials (each layer having been patterned by a photomask), and each of the multiple layers may comprise multiple repetitions of the same pattern. The patterns of each layer may be arranged in a two-dimensional array. Any and all references to “substrate” should be understood to include a “base” substrate, such as a silicon or glass substrate or any other suitable base substrate, and any layers disposed thereon, including but not limited to previously exposed and treated patterned layers and / or photoresist.

[0007] Different points across the surface of the substrate can be at different heights, and therefore, the lithographic radiation focused on the surface of the substrate at the first point (at the first height) may not be focused at the second point (at the second height). In order to maintain focus on the surface of the substrate, the height of the substrate surface is measured and the lithography equipment is adjusted accordingly.

[0008] A height measurement system can be used to measure the height of a substrate's surface. However, it is known that the light used by the height measurement system to measure the height of a substrate's surface can partially penetrate into the substrate surface, rather than being reflected only from the substrate surface. This partial reflection of light may occur in a layer located below the substrate surface. This partial reflection causes errors in the substrate height measurement.

[0009] Substrate height measurement error can be referred to as height process dependence (HPD) or apparent surface deposition (ASD).

[0010] It can be expected to provide systems that avoid or mitigate one or more problems associated with existing technologies. Summary of the Invention

[0011] According to a first aspect of this disclosure, a method for determining a substrate height measurement error is provided, the method comprising: providing a laser beam modulated at a given frequency, the laser beam having a wavelength and polarization; directing the modulated laser beam onto the substrate at an acute angle relative to a normal extending from the substrate; detecting a position of the modulated laser beam after the modulated laser beam has been reflected from the substrate; using the detection based on the frequency of modulation applied to the laser beam to measure modulation of the detected position of the modulated laser beam; and determining a height measurement error based on the measured modulation of the detected position of the modulated laser beam, wherein the wavelength or polarization is modulated.

[0012] Advantageously, this method determines height measurement error in a manner different from existing techniques. Advantageously, this method can be performed quickly and can be performed within a photolithography apparatus (e.g., before or during substrate exposure).

[0013] The height measurement error can be an absolute value determined by the known refractive index of a layer on a reference substrate.

[0014] The height measurement error can be a relative value determined by comparing the measured modulation of the detected position of the modulated laser beam with a measured calibrated modulation obtained using a different substrate with a layered structure corresponding to the layered structure of the substrate being measured.

[0015] Height measurement error can be determined as a relative value by comparing the modulation measured at different locations on the substrate by a modulated laser beam.

[0016] The detection can use harmonics of the frequency modulated by the wavelength or polarization of the laser beam to measure the modulation of the detected position of the modulated laser beam.

[0017] The detection can be a lock-in detection based on the amplitude of the first harmonic, second harmonic, or other harmonic of the modulation frequency, which is automatically selected among the first harmonic, second harmonic, or other harmonics.

[0018] The wavelength of a laser beam can be modulated to 1 / 100th of the laser beam's wavelength.

[0019] The wavelength of the laser beam can be modulated up to 100 pm.

[0020] The laser beam can be provided by a single-frequency laser.

[0021] According to a second aspect of this disclosure, a method for determining the height of a substrate is provided, the method comprising: measuring the height of the substrate; determining a substrate height measurement error using the method of the first aspect of this disclosure; and adjusting the measured height of the substrate using the determined substrate height measurement error.

[0022] According to a third aspect of this disclosure, a substrate height measurement error determination system is provided, comprising: a projection unit including a laser, the projection unit being configured to guide a laser beam emitted by the laser onto a substrate, the laser beam having a wavelength and polarization; a detection system including a detector configured to detect a position of the laser beam after reflection from the substrate; a modulator configured to apply modulation at a given frequency to the wavelength or polarization of the laser beam emitted by the laser to obtain a modulated laser beam; a lock-in amplifier configured to receive an output from the detection system and to measure modulation of the detected position of the modulated laser beam based on the frequency of modulation applied to the wavelength or polarization of the laser beam; and a processor configured to determine a substrate height measurement error using the measured modulation of the detected position.

[0023] Advantageously, the third-party system determines height measurement errors in a manner different from existing methods. Advantageously, the system allows for rapid determination of height measurement errors. Advantageously, the height measurement error system can be implemented within a photolithography apparatus.

[0024] The detector can be a lock-in detector. Both the modulator and the detector can be part of a lock-in amplifier.

[0025] The lock detector can automatically select between the first harmonic, the second harmonic, or other harmonics based on the amplitude of the first harmonic, the second harmonic, or other harmonics of the modulated frequency.

[0026] The modulator can be configured to modulate the wavelength or polarization of the laser beam to 1 / 100 of the laser beam's wavelength.

[0027] The modulator can be configured to modulate the wavelength of the laser beam to 100 pm.

[0028] The laser can be a single-frequency laser.

[0029] According to a fourth aspect of this disclosure, a measurement system is provided, comprising: a substrate height measurement error determination system according to a third aspect; and a substrate height measurement system, wherein a processor is configured to adjust the measured height of the substrate obtained by using the determined substrate height measurement error.

[0030] The detection system may include a portion of the substrate height measurement system.

[0031] The projection unit may include a portion of the substrate height measurement system.

[0032] According to a fifth aspect of this disclosure, a lithography apparatus is provided that includes a measurement system according to a fourth aspect of this disclosure.

[0033] The different aspects of this disclosure can be combined together. Attached Figure Description

[0034] Embodiments of this disclosure will now be described by way of example only with reference to the accompanying drawings, in which:

[0035] - Figure 1 A lithography apparatus, including a system for determining substrate height measurement error, is schematically depicted according to embodiments of the present disclosure; and

[0036] - Figure 2 A schematic depiction in more detail of the method used to determine Figure 1 A system for measuring substrate height error. Detailed Implementation

[0037] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 nm to 100 nm).

[0038] The terms “mask,” “mask,” or “patterning apparatus” as used herein can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of a substrate.

[0039] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the patterning apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0040] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, via a beam delivery system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination of said refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in the cross-section of the radiation beam B at the plane of the pattern forming apparatus MA.

[0041] The term "projection system" PS as used herein should be broadly interpreted to encompass various types of projection systems suitable for the exposure radiation used and / or for other factors such as immersion in liquids or vacuum, including refractive, reflective, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination of such refractive, reflective, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0042] Photolithography equipment (LA) can fall into a category where at least a portion of the substrate can be covered by a liquid with a relatively high refractive index, such as water, to fill the space between the projection system (PS) and the substrate (W)—this is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0043] Photolithography equipment (LA) can also be of the type with two or more substrate supports (WT). In such a "multi-platform" machine, multiple substrate supports (WT) can be used in parallel, and / or a subsequent exposure step for preparing substrate W on one of the substrate supports (WT) can be performed, while another substrate W on other substrate supports (WT) is used to expose patterns on other substrates (WT).

[0044] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask) MA held on a mask support MT and patterned by a pattern (design layout) present on the pattern forming apparatus MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, a first positioner PM and possibly another position sensor (the other position sensor is located in…) Figure 1 (Not explicitly depicted) can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. The patterning apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they can be located in the space between target portions. When substrate alignment marks P1, P2 are located between target portions C, these substrate alignment marks are referred to as scribing alignment marks.

[0045] For the purposes of this disclosure, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes: the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is called an Rx rotation. A rotation about the y-axis is called an Ry rotation. A rotation about the z-axis is called an Rz rotation. The x-axis and y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system is not limiting of this disclosure and is only used for illustration. Rather, another coordinate system, such as a cylindrical coordinate system, may be used to illustrate this disclosure. The orientation of the Cartesian coordinate system can be different, for example, such that the z-axis has a component along the horizontal plane. In the figures, the height of the substrate W is indicated in the Z direction.

[0046] A height measurement system LS is arranged to measure the top surface topography of a substrate W. The height measurement system LS can be referred to as a horizontal sensor or a topography measurement system. A graph of the height (z) of the substrate as a function of its position (x, y) on the substrate can be generated using the height measurement system LS. This height graph can then be used to adjust the vertical position of the substrate W and / or adjust the projection system PS during the projection of a pattern from the patterning apparatus MA onto the substrate.

[0047] The height measurement system LS can be stationary. The substrate stage WT and substrate W can move below the height measurement system LS in a scanning motion. This allows the height measurement system to measure the height across the surface of substrate W and thereby generate a height map.

[0048] The height measurement system LS includes a projection unit 10, a detection system 12, and a processor 15. The projection unit 10 is configured to provide a light beam incident on a substrate W (including any patterned layers located on the substrate W) and subsequently detected by the detection system 12. The position of the light beam incident on the detection system 12 depends on the height of the substrate W. This allows for the measurement of the height of the substrate W. The projection unit 10 includes a diffraction grating (not depicted), which may be referred to as a projection grating. The detection system 12 includes a diffraction grating (not depicted), which may be referred to as a detection grating. An image of the projection grating is formed at the detection grating, and this grating image provides a height measurement relative to the position of the detection grating.

[0049] The height measurement system LS may include multiple lasers (or other light sources). The height measurement system LS may, for example, include a broadband light source, such as a white light source emitting light across the visible spectrum. The height measurement system may, for example, include multiple lasers configured to emit light at different wavelengths. The output from the detection system 12 can be processed by the processor 15 to obtain the measured height of the substrate W. The measured height of the substrate may include measurement errors caused by reflections of light from multiple layers of the substrate (as described below). Figure 2 (Further explanation follows).

[0050] The lithography equipment also includes a height measurement error determination system (ES). The height measurement error determination system (ES) uses some of the same components as the height measurement system (LS), and these components are... Figure 1 It is indicated as a shared component.

[0051] The height measurement error determination system ES includes at least one single-frequency laser 18. The single-frequency laser may have a bandwidth of, for example, 10 MHz or less, such as about 1 MHz. Laser 18 may form part of projection unit 10. The position of reflection of the laser beam 16 provided by projection unit 10 is detected by detection system 12. A signal module 14, including a modulation unit (or modulator) and a lock-in amplifier, is arranged. The modulator is configured to modulate the wavelength and / or polarization of the laser beam 16 emitted by projection unit 10. The lock-in amplifier is configured to receive an output signal from detection system 12. The detected position of the reflected laser beam is modulated due to the wavelength or polarization modulation of the laser beam. The lock-in amplifier provides an output, which is a measurement result of the modulated detected position. Processor 15 uses the output from the lock-in amplifier to determine the height measurement error. The height measurement error may be applied to the measured height of the substrate. The height measurement error may be referred to as height process dependence (HPD).

[0052] The height measurement error determination system ES is described in more detail. Figure 2 In the above-mentioned system, some components of the height measurement error determination system ES can also form part of the height measurement system LS. The projection unit 10 includes a single-frequency laser 18 and a diffraction grating 20. The diffraction grating 20, referred to as the projection grating 20, applies a periodic structure to the laser beam 16. The laser beam 16 is incident on the substrate W. The laser beam 16 is at an acute angle θ relative to the normal extending from the substrate W (in other words, relative to the Z direction).

[0053] Laser 18 is configured to emit a laser beam 16 with a bandwidth of less than 2 nm and may be referred to as a narrowband laser. The modulator of signal module 14 can apply modulation to the wavelength of the laser beam 16 emitted by laser 18. The modulator can, for example, change the wavelength of the laser beam 16 by about 1 pm. The modulator can change the wavelength of the laser beam by up to 10 pm or up to 50 pm. The modulator can change the wavelength by a greater amount, for example, up to 100 pm. However, if a larger wavelength modulation, such as 100 pm, is used, the output from the lock-in amplifier may no longer be linear (this will depend on the substrate structure).

[0054] Typically, the wavelength modulation can reach 1 / 100 of the center wavelength of the laser beam 16.

[0055] The light emitted by a laser is usually polarized light. However, the light source arranged in the projection unit 10 (or the unit itself) can be equipped with a polarizer. Figure 2 (Not shown) to provide a beam 16 with the desired polarization. The analytical polarization element can be arranged in the detection system 12 ( Figure 2 (Not shown in the diagram).

[0056] The modulator of signal module 14 can apply modulation to the polarization of the laser beam 16 emitted by laser 18. For example, a polarization modulator can be arranged to interact with the laser beam 16 within projection unit 10. The polarization modulator can be a liquid crystal-based modulator (or polarization rotator) or an electro-optic element that controls the polarization state of beam 16 by an externally applied voltage. With the aid of the polarization module, the polarization state of beam 16 can be modulated at a predefined frequency.

[0057] Typically, the substrate will consist of many patterned layers. However, for the sake of simplicity, Figure 2 The substrate W depicted has only two layers: a lower silicon layer 32 (which may be referred to as the "base" substrate) and an upper optical resist layer 30 (which may be referred to as the resist). The main portion 16a of the laser beam 16 is reflected from the upper surface 22 of the resist 30. The reflected main portion 16a of the laser beam is reflected toward the detection system 12.

[0058] The detection system 12 includes a diffraction grating 24 and a pair of detectors 26a and 26b. The diffraction grating 24 may be referred to as the detection grating 24. The reflected main portion 16a of the laser beam forms an image of the projection grating 20 at the detection grating 24. The detection grating 24 may be periodic, corresponding to the periodicity of the grating image formed by the reflected main portion 16a of the laser beam. The position of this grating image will depend on the height of the upper surface 22 of the resist 30. The detection grating 24 guides the laser to the first detector 26a and the second detector 26b. The proportion of laser light received by each detector 26a, 26b depends on the position of the grating image relative to the detection grating 24. Therefore, the signal output from the detectors 26a, 26b depends on the height of the upper surface 22 of the resist 30. A differential amplifier 28 can be used to determine the difference between the signals output from the detectors 26a, 26b. The output from the differential amplifier 28 is provided to the signal module 14. Other position detection systems can be used to detect the position of the reflected laser beam.

[0059] The projection unit 10 and the detection system 12 may include other optical elements, such as lenses and / or mirrors (not depicted), along the path of the laser beam 16 (e.g., between the projection grating 20 and the detection grating 24).

[0060] As mentioned above, the main portion 16a of the laser beam is reflected from the upper surface 22 of the resist 30. However, the resist 30 is not a perfect reflector, and therefore a portion 16b of the laser beam 16 passes through the resist. This secondary portion 16b of the laser beam is reflected from the interface between the resist 30 and the silicon substrate 32. The secondary portion 16b of the laser beam is a relatively small proportion of the incident laser beam 16, for example, 10% or less of the incident laser beam (e.g., 1% or less of the incident laser beam). This is schematically depicted by the secondary portion 16b of the laser beam, which is a line with a smaller thickness compared to the main portion 16a of the laser beam.

[0061] The secondary portion 16b of the laser beam also forms an image of the projection grating 20 at the detector grating 24. However, this grating image is formed at a lower position, different from the grating image formed by the main portion 16a of the laser beam. (As shown from...) Figure 2 As can be seen, the position of the detector grating image provided by the secondary portion 16b of the laser beam is determined by the height of the silicon substrate 32. The height offset between the position of the grating image provided by the main portion 16a of the laser beam and the position of the grating image provided by the secondary portion 16b of the laser beam will depend on the thickness T of the resist.

[0062] The grating image formed by the secondary portion 16b of the laser beam introduces a measurement error into the signals output from detectors 26a and 26b. The signals output from detectors 26a and 26b indicate that the height of the upper surface 22 of the resist is lower than the actual height of the upper surface of the resist. The height measurement error determination system ES determines this height measurement error. The height measurement error can be used to adjust the use of the height measurement system LS (see [link to system description]). Figure 1 The height measurement value obtained is obtained from this.

[0063] The height measurement error determined by the system ES can be an absolute measurement value, i.e., a value indicating the offset between the measured height of the upper surface 22 of the resist 30 and the actual height of the upper surface of the resist. The height measurement error can also be a relative value, for example, indicating whether the height measurement error at a given area of ​​the substrate is greater than or less than the height measurement error at different areas of the substrate.

[0064] For reference Figure 2 The measurements obtained by the height measurement error determination system ES will be explained in more detail. The optical path difference L between the main part 16a and the secondary part 16b of the laser beam can be expressed as:

[0065]

[0066] The reflected laser beam 16, considered as a single beam, has a complex amplitude:

[0067]

[0068] Where A is the amplitude of the main portion 16a of the laser beam and a is the amplitude of the secondary portion 16b of the laser beam. It can be assumed that... and (where n1 is the refractive index of resist 30 and n2 is the refractive index of silicon substrate 32). Therefore, it can be assumed that the reflection 16b from silicon substrate 32 is weaker than the reflection 16a from resist 30. When a << A, the phase of the reflected laser beam 16 is:

[0069]

[0070] In the assumption In this case, the height measurement error HPD caused by the secondary portion 16b of the laser beam can be expressed as:

[0071]

[0072] Equation 4 includes the following terms:

[0073]

[0074] This indicates that the measurement error HPD will oscillate according to the wavelength of the laser beam 16. Embodiments of this disclosure obtain information about the height measurement error HPD by modulating the wavelength of the laser beam 16.

[0075] The modulator of signal module 14 provides a modulation signal to control the operation of laser 18, such that the center wavelength of laser beam 16 is modulated. The modulation is at a given frequency (e.g., selected by the user or automatically by a lock-in amplifier). This causes modulation of the position of the reflected laser beam 16 detected by detectors 26a, 26b.

[0076] The lock-in amplifier of signal module 14 uses the frequency of modulation applied to the laser beam to measure the modulation of the detected position of laser beam 16. The lock-in amplifier is configured to identify harmonics (e.g., a first harmonic) of the signal output from computational amplifier 28 (or other output signals in the case of a different position detection system). The lock-in amplifier identifies the harmonics as components of the output signal having the frequency of the modulation harmonic applied to laser 18. The lock-in amplifier of signal module 14 provides an output signal with an amplitude indicating the amplitude of the detected harmonic. Processor 15 receives the output signal from the lock-in amplifier. Processor 15 uses the output signal to determine the altitude measurement error. As mentioned above, the altitude measurement error can be an absolute value or a relative value. The altitude measurement error can be used to adjust the altitude measurement value obtained by the altitude measurement system LS.

[0077] In some cases, the first harmonic of the signal received by the lock-in amplifier can have a lower amplitude than, for example, the second harmonic. The relative amplitudes of the different harmonics will depend on... Figure 2 The refractive index and thickness of the resist layer 30 in the scenario depicted are shown. The lock-in amplifier can be configured to automatically select the harmonic that provides the maximum signal amplitude. In other scenarios (not depicted) where the substrate has multiple layers, the relative amplitudes of different harmonics will depend on the refractive index and thickness of each layer. Furthermore, the lock-in amplifier can be configured to automatically select the harmonic that provides the maximum signal amplitude. For example, for some substrates, the first harmonic can provide a stronger signal that can be used to determine the height measurement error. For other substrates, the second harmonic can provide a stronger signal that can be used to determine the height measurement error. Other harmonics can be used. Typically, lock-in detection is based on the automatic selection of the amplitudes of the first harmonic, the second harmonic, or other harmonics of the modulation frequency.

[0078] Similar to controlling the (center) wavelength of laser 18 via a modulation signal, the polarization of the beam (laser beam) 16 may be controlled by a modulation signal provided to a polarization module. The polarization state of the laser beam 16 is changed by the polarization module. That is, the polarization is rotated by a certain degree: approximately 1° or greater, approximately 5° or greater, approximately 10° or greater, 15° or greater, 30° or greater, 45° or greater, and may depend on the frequency response of the polarization module. In such a case, the polarization of the incident light is modulated to obtain a signal related to the product structure. Since the product structure affects the intensity of light reflected from it, the polarization-modulated light can be used to reduce the influence of the product structure on the detected light.

[0079] Typically, lock-on detection is used to measure the modulation of a detected position (e.g., detected by detectors 26a, 26b) to a laser beam of modulated wavelength. Lock-on detection is achieved by modulating the laser beam at a given frequency and then using said frequency to identify the modulation of the detected position. Both the modulation of the laser beam and the lock-on detection can be performed by the signal module 14.

[0080] In this embodiment, the broadband light source (or other light source) of the height measurement system LS can be provided as a laser 18 adjacent to the height measurement error determination system ES. In this case, the projection grating 20, the detection grating 24, and the detector 26 can be shared between the two systems. Systems LS and ES can operate simultaneously. That is, the height measurement system LS can measure the height map of the substrate W, and the height measurement error determination system ES can simultaneously determine the height measurement error. The height measurement error determination system ES can provide a height measurement error map.

[0081] exist Figure 2In the scenario described, the determined adjustment can be an absolute measurement of the height measurement error HPD, i.e., the value indicating the offset between the measured height of the upper surface 22 of the resist 30 and the actual height of the upper surface of the resist. Referring to equation (5), the refractive index n1 of the resist 30 is known, the incident angle θ of the laser beam 16 is known, and the wavelength λ of the laser beam is known. The relative amplitudes a and A of the first laser beam portion 16a and the second laser beam portion 16b can be measured during calibration. Therefore, the height measurement error HPD can be considered as an absolute value dependent on the unique unknown T. The height measurement error HPD can be subtracted from the measured height of the upper surface 22 of the resist to obtain the corrected height.

[0082] The above are examples of substrates with relatively simple structures. In practice, a substrate may include more than two layers, for example, five or more layers, ten or more layers, etc. In this case, the absolute value of the height measurement error (HPD) may not be directly obtainable. As can be understood from equation (4), the height measurement error (HPD) will depend on the thickness and refractive index of each layer of a multi-layered substrate. Because the height measurement error (HPD) depends on many different parameters, the height measurement error (HPD) may not provide an absolute value directly, but can be obtained by subtracting the absolute value from the measured height to obtain the corrected height. However, in such a context, embodiments of the present disclosure can still provide useful information. Specifically, a relative measurement of the height measurement error (HPD) can be used to adjust the measured height. For example, the height measurement error (HPD) can be converted into an absolute value for height correction by comparing it with a previous calibration measurement. For example, the height adjustment can be determined for a substrate with a given layer structure (e.g., by comparing the output of a broadband level sensor LS with an output obtained using an air gauge). Embodiments of the present disclosure can determine the height measurement error (HPD) for a calibrated substrate. This provides a calibration of the height measurement error (HPD) relative to the difference between the output of the broadband level sensor LS and the actual substrate height. The height measurement error (HPD) for another substrate with the same layer structure can then be measured as part of the photolithography exposure. The height measurement error (HPD) can be compared with the height measurement error (HPD) obtained using a calibrated substrate. The result of the comparison can be used to obtain a height adjustment. The height adjustment can then be used to obtain the corrected height of the exposed substrate.

[0083] In another embodiment, the height measurement error can be used as one of a plurality of error measurements for adjusting the measured substrate height.

[0084] Typically, more than two hundred dies are exposed on the substrate, and in some cases, more than six hundred dies are exposed on the substrate. Each of the dies has been exposed using the same series of patterning apparatus and has undergone the same processing. Therefore, each of the dies should have the same properties, including the same height measurement error. In practice, the height measurement error can vary across the entire substrate. This can occur, for example, due to the effects of processing the substrate layers. In one example, metal can be deposited into a structure formed in the substrate, and excess metal can be removed from the substrate using grinding. Grinding can, for example, remove slightly more material from one side of the substrate compared to the opposite side (e.g., a gradient of metal thickness across the substrate may exist). Embodiments of this disclosure can provide height measurement error values ​​that vary gradually across the surface of the substrate. The height measurement error values ​​can be used to adjust the expected height measurement error of the substrate. This adjusted expected height measurement error can be used as a height adjustment applied to the measured height of the substrate.

[0085] Calibration of a height measurement error determination system according to embodiments of this disclosure may include determining the relative amplitudes of the main portion 16a and the secondary portion 16b of the reflected beam. Calibration may include directing the laser beam 16 onto the substrate and changing the (center) wavelength of the laser beam 16 by a few nanometers, for example, 10 nm. Similarly, calibration may include directing the laser beam 16 onto the substrate and changing the polarization of the laser beam 16 by several degrees: about 1° or greater, about 5° or greater, about 10° or greater, 15° or greater, 30° or greater, 45° or greater, and may depend on the frequency response of the polarization module. Calibration may be performed at a single location on the substrate. Calibration may be performed at multiple locations for a given die on the substrate. Calibration may be performed for each measurement site on the substrate.

[0086] An initial calibration of the height measurement error determination system can be performed. This initial calibration, which may be referred to as electronic calibration, aims to determine the system gain. For this initial calibration, a substrate W with a known structure is used. The substrate W can be, for example, a substrate that has not yet received any device patterning, which includes alignment marks (the properties of such substrates are well known). The substrate W may comprise two layers. A laser beam 16 is directed onto the substrate W and detected. The output is provided from a lock-in amplifier in the signal module 14. The processor 15 compares the output from the lock-in amplifier with the known thickness of the upper layer of the substrate. This provides a gain value, i.e., a factor that can be used to multiply the signal output from the system during subsequent use. The initial calibration may use more than one measurement.

[0087] The outputs of detectors 26a and 26b will be received by the locked input channel. A phase-locked loop will lock onto the signal and extract the amplitude and phase of the reflected light 16a and 16b. Both signals are available, and the amplitude of the first harmonic will have a strong correlation with the product (layer) structure. The original height map (main signal) from the horizontal sensor LS and the output of the error determination system ES (HPD signal) are also available. Several methods exist to use the HPD signal as a reference or as a second detector signal to clean the relevant portion of the main signal. These methods may require calibration. This will be a problem of solving a set of linear equations to reduce the HPD contribution to the error. In the same way, the outputs of the horizontal sensor LS and the error determination system ES, as two detectors measuring this two event, produce a mixed signal. This is also known as the "cocktail party" problem. Several methods exist to make the two signals unmixed without specific calibration. An example of such a technique is called blind signal separation (BSS) or blind source separation.

[0088] To effectively cover the surface of the substrate W, embodiments of this disclosure can be configured to project a laser beam array 16 onto the surface of the substrate W. This provides an array of measurement regions on the substrate that covers a large measurement area.

[0089] The embodiments described in this disclosure include a height measurement system LS and a separate height measurement error determination system ES. However, in some embodiments, a single system may be used. That is, the height measurement error determination system ES can determine the height measurement error and can also provide a substrate height measurement.

[0090] Embodiments of the present invention are described as including a single-frequency laser with a bandwidth of 10 MHz or less, such as about 1 MHz. Embodiments of the present invention may include a single-frequency laser with a bandwidth of up to 20 MHz. Such embodiments can provide useful height measurement error. However, the dynamic range of such embodiments will be smaller than that of a single-frequency laser with a narrower bandwidth.

[0091] Although the methods described herein have been described with respect to substrates W that have been exposed or will be exposed to lithographic radiation (i.e., radiation beam B), it will be apparent to those skilled in the art that the methods (and corresponding apparatus) can be advantageously adapted for use with substrates that have not been exposed to lithographic radiation.

[0092] In the embodiments described in this invention, wavelength / polarization modulation and harmonic detection are performed by a lock-in amplifier system. However, any suitable device can be used to apply wavelength modulation, and any suitable device can be used to detect the harmonics of the applied modulation. Typically, any of null detection, heterodyne detection, and quadrature detection can be used. These are examples of lock-in detection. Detection can be performed using hardware or software.

[0093] Altitude measurement systems and altitude measurement error determination systems can be collectively referred to as measurement systems.

[0094] Embodiments of this disclosure can form portions of a lithography apparatus or metrology apparatus, for example, as depicted. Embodiments of this disclosure can form portions of a lithography tool. Other examples of lithography tools are further mentioned below.

[0095] Similarly, although the methods described herein have been described with respect to DUV lithography radiation, it will be apparent to those skilled in the art that the methods (and corresponding apparatus) can be advantageously adapted for use with EUV lithography radiation (and corresponding apparatus).

[0096] While specific references can be made to the use of lithography equipment in IC manufacturing herein, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include the fabrication of integrated optical systems, patterning for guiding and detecting magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0097] While specific reference may be made herein to embodiments of this disclosure within the context of a photolithography apparatus, embodiments of this disclosure can be used in other apparatuses. Embodiments of this disclosure can form part of a mask inspection apparatus, a measurement apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatuses). These apparatuses are generally referred to as photolithography tools. Such photolithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0098] While the foregoing has been specifically referenced to the embodiments of this disclosure in the context of optical lithography, it should be understood that this disclosure is not limited to optical lithography and can be used in other applications, such as imprint lithography, where circumstances permit.

[0099] Where circumstances permit, embodiments of this disclosure may be implemented in hardware, firmware, software, or any combination of hardware, firmware, and software. Embodiments of this disclosure may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any means for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.). Additionally, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that these descriptions are merely for convenience, and those actions are actually caused by a computing device, processor, controller, or other means that execute firmware, software, routines, instructions, etc., and may, in execution, cause actuators or other devices to interact with the physical world.

[0100] The invention is set forth in the following aspects.

[0101] 1. A method for determining substrate height measurement error, the method comprising:

[0102] Provides a laser beam with a wavelength or polarization modulated at a given frequency;

[0103] A modulated laser beam is directed onto the substrate at an acute angle relative to the normal extending from the substrate.

[0104] Detect the position of the modulated laser beam after it has been reflected from the substrate;

[0105] The modulation of the detected position of the modulated laser beam is measured using detection based on the frequency of modulation based on the wavelength or polarization applied to the laser beam; and

[0106] The height measurement error is determined based on the modulation measured at the detected position of the modulated laser beam.

[0107] 2. A method for determining substrate height measurement error, the method comprising:

[0108] Provide a laser beam modulated at a given frequency, the laser beam having a wavelength and polarization;

[0109] The modulated laser beam is guided onto the substrate at an acute angle relative to the normal extending from the substrate;

[0110] Detect the position of the modulated laser beam after it has been reflected from the substrate;

[0111] The modulation of the detected position of the modulated laser beam is measured using detection based on the frequency of the modulation applied to the laser beam; and

[0112] The height measurement error is determined based on the measured modulation of the detected position of the modulated laser beam, wherein the wavelength or polarization is modulated.

[0113] 3. The method according to aspect 1 or 2, wherein the height measurement error is an absolute value determined by the known refractive index of a layer of the reference substrate.

[0114] 4. The method according to aspect 1 or 2, wherein the height measurement error is a relative value determined by comparing the measured modulation of the detected position of the modulated laser beam with a measured calibration modulation obtained using a different substrate having a layer structure corresponding to the layer structure of the measured substrate.

[0115] 5. The method according to aspect 1 or 2, wherein the height measurement error is a relative value determined by comparing the measured modulations at different measured locations on the substrate by the modulated laser beam.

[0116] 6. The method according to any of the foregoing aspects, wherein the modulation of the detected position of the modulated laser beam is measured using harmonics of the frequency modulated by the wavelength or polarization of the laser beam.

[0117] 7. The method according to aspect 6, wherein the detection is a lock-in detection based on the automatic selection of the amplitude of a first harmonic, a second harmonic, or other harmonic of the modulation frequency among the first harmonic, the second harmonic, or other harmonics.

[0118] 8. The method according to any of the foregoing aspects, wherein the wavelength is modulated, and the modulation of the wavelength of the laser beam reaches 1 / 100 of the wavelength of the laser beam.

[0119] 9. The method according to any of the foregoing aspects, wherein the wavelength is modulated, and the modulation of the wavelength of the laser beam reaches 100 pm.

[0120] 10. The method according to any of the foregoing aspects, wherein the laser beam is provided by a single-frequency laser.

[0121] 11. A method for determining the height of a substrate, the method comprising: measuring the height of the substrate; determining a substrate height measurement error using the method according to any of the preceding claims; and adjusting the measured height of the substrate using the determined substrate height measurement error.

[0122] 12. A substrate height measurement error determination system, comprising:

[0123] A projection unit, the projection unit including a laser, the projection unit being configured to guide a laser beam emitted by the laser onto a substrate, the laser beam having a wavelength and polarization;

[0124] A detection system, the detection system including a detector configured to detect the position of a laser beam after reflection from a substrate;

[0125] A modulator configured to apply modulation at a given frequency to the wavelength or polarization of a laser beam emitted by a laser.

[0126] A detector configured to receive output from a detection system and to measure the modulation of the detected position of the modulated laser beam based on the frequency of modulation of the wavelength or polarization applied to the laser beam; and

[0127] A processor configured to determine substrate height measurement error using measured modulation of the detected location.

[0128] 13. The substrate height measurement error determination system according to aspect 12, wherein both the modulator and the lock-in amplifier are part of a signal module.

[0129] 14. The substrate height measurement error determination system according to aspect 12, wherein the lock-in amplifier automatically selects between the first harmonic, the second harmonic, or other harmonics based on the amplitude of the first harmonic, the second harmonic, or other harmonics of the modulation frequency.

[0130] 15. A substrate height measurement error determination system according to any one of aspects 12 to 14, wherein the wavelength is modulated, and the modulator is configured to modulate the wavelength of the laser beam to 1 / 100 of the wavelength of the laser beam.

[0131] 16. The substrate height measurement error determination system according to any one of aspects 12 to 15, wherein the wavelength is modulated and the modulator is configured to modulate the wavelength of the laser beam to 100 pm.

[0132] 17. A substrate height measurement error determination system according to any one of aspects 12 to 16, wherein the laser is a single-frequency laser.

[0133] 18. A measurement system comprising a substrate height measurement error determination system according to any one of aspects 12 to 17, and a substrate height measurement system, wherein a processor is configured to adjust the measured height of the substrate obtained by using the determined substrate height measurement error using the substrate height measurement system.

[0134] 19. The measurement system according to aspect 18, wherein the detection system includes a portion of the substrate height measurement system.

[0135] 20. The measurement system according to aspect 18 or aspect 19, wherein the projection unit includes a portion of the substrate height measurement system.

[0136] 21. A photolithography apparatus comprising a measurement system according to any one of aspects 18 to 20.

[0137] While specific embodiments of this disclosure have been described above, it will be understood that this disclosure may be practiced in other ways than those described. The above description is intended to be exemplary and not restrictive. Therefore, those skilled in the art will understand that modifications to the described disclosure may be made without departing from the scope of the claims set forth below.

Claims

1. A method for determining substrate height measurement error, the method comprising: Provide a laser beam modulated at a given frequency, the laser beam having a wavelength and polarization; The modulated laser beam is directed onto the substrate at an acute angle relative to the normal extending from the substrate; Detect the position of the modulated laser beam after it has been reflected from the substrate; The modulation of the detected position of the modulated laser beam is measured using the detection of the frequency based on the modulation applied to the laser beam. as well as The height measurement error is determined based on the measured modulation of the detected position of the modulated laser beam, wherein the wavelength or the polarization is modulated.

2. The method according to claim 1, wherein, The height measurement error is an absolute value determined with reference to the known refractive index of the layer of the substrate.

3. The method according to claim 1, wherein, The height measurement error is a relative value determined by comparing the measured modulation of the detected position of the modulated laser beam with a measured calibrated modulation obtained using a different substrate with a layered structure corresponding to the layered structure of the substrate being measured.

4. The method according to claim 1, wherein, The height measurement error is a relative value determined by comparing the modulation measured at different locations on the substrate by the modulated laser beam.

5. The method according to any of the preceding claims, wherein, The detection uses harmonics of the frequency of the modulation applied to the laser beam, or the frequency of the modulation applied to the laser beam, to measure the modulation at the detected position of the modulated laser beam.

6. The method according to claim 5, wherein, The detection is a lock-in detection based on the automatic selection of the amplitude of a first harmonic, a second harmonic, or other harmonic of the modulated frequency among the first harmonic, the second harmonic, or other harmonics.

7. The method according to any of the preceding claims, wherein, The wavelength is modulated, and the modulation of the wavelength of the laser beam reaches 1 / 100 of the wavelength of the laser beam.

8. The method according to any of the preceding claims, wherein, The wavelength is modulated, and the modulation of the wavelength of the laser beam reaches 100 pm.

9. A method for determining the height of a substrate, the method comprising: Measure the height of the substrate. The substrate height measurement error is determined using the method according to any of the preceding claims, and The measured height of the substrate is adjusted using the determined substrate height measurement error.

10. A substrate height measurement error determination system, comprising: A projection unit, the projection unit including a laser, the projection unit being configured to guide a laser beam emitted by the laser onto a substrate, the laser beam having a wavelength and polarization; The detection system includes a detector configured to detect the position of the laser beam after reflection from the substrate; A modulator configured to apply modulation at a given frequency to the wavelength or polarization of the laser beam emitted by the laser to obtain a modulated laser beam; A lock-in amplifier configured to receive an output from the detection system and to measure the modulation of the detected position of the modulated laser beam based on the frequency of the modulation of the wavelength or polarization applied to the laser beam. as well as A processor configured to determine substrate height measurement error using measured modulation of the detected location.

11. The substrate height measurement error determination system according to claim 10, wherein, Both the modulator and the lock-in amplifier are part of the signal module.

12. The substrate height measurement error determination system according to claim 11, wherein, The lock-in amplifier automatically selects between the first harmonic, the second harmonic, or other harmonics based on the amplitude of the first harmonic, the second harmonic, or other harmonics of the modulated frequency.

13. The substrate height measurement error determination system according to any one of claims 10 to 12, wherein, The wavelength is modulated, and the modulator is configured to modulate the wavelength of the laser beam to 1 / 100 of the wavelength of the laser beam.

14. The substrate height measurement error determination system according to any one of claims 10 to 13, wherein, The wavelength is modulated, and the modulator is configured to modulate the wavelength of the laser beam to 100 pm.

15. A measurement system comprising a substrate height measurement error determination system according to any one of claims 10 to 14, and a substrate height measurement system, wherein, The processor is configured to adjust the measured height of the substrate obtained using the substrate height measurement system using the determined substrate height measurement error.

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