Height measurement error detection

Abstract

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

Description

Technical Field

[0001] [Cross-reference to Related Applications] This application claims the priority of European Application No. 23165575.4 filed on March 30, 2023, the entire content of which is incorporated herein by reference.

[0002] [Technical Field] The present disclosure relates to determining a substrate height measurement error. The substrate height measurement error may be determined in a lithography apparatus.

Background Art

[0003] A lithography apparatus is an apparatus configured to apply a desired pattern onto a substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithography apparatus may project, for example, a pattern of a patterning device (also often referred to as a mask, e.g., a reticle) (often also referred to as a “design layout” or “design”) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] As semiconductor manufacturing processes continue to advance, following a trend commonly known as "Moore's Law," the number of functional elements such as transistors per device has steadily increased over the past several decades, while the dimensions of circuit elements have continuously decreased. The semiconductor industry is pursuing technologies that enable the generation of increasingly smaller features to keep pace with Moore's Law. To project patterns onto a substrate, lithography equipment may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Lithography equipment using extreme ultraviolet (EUV) radiation with wavelengths in the range between 4 nm and 20 nm (e.g., 6.7 nm or 13.5 nm) may be used to form smaller features on a substrate than, for example, lithography equipment using radiation with a wavelength of 193 nm.

[0005] Typically, a substrate may comprise multiple layers of one or more materials (each layer patterned by a reticle), and each layer may comprise multiple repetitions of the same pattern. The patterns of each layer may be arranged as a two-dimensional array. Some or all of the references to “substrate” are understood to comprise a “base” substrate, e.g., a silicon or glass substrate, or any other suitable base substrate, and any layers provided thereon (including, but not limited to, a previously exposed and processed patterning layer and / or photoresist).

[0006] Different points across the substrate surface may be at different heights, and lithographic radiation focused at the first point (first height) on the substrate surface may not be in focus at the second point (second height). To maintain focus on the substrate surface, the height of the substrate surface is measured, and the lithography apparatus is adjusted accordingly. [Overview of the project] [Problems that the invention aims to solve]

[0007] The surface height of a substrate may be measured using a height measuring system. However, it is known that the light used by the height measuring system to measure the surface height of a substrate may not simply be reflected from the substrate surface, but may partially penetrate into the substrate surface. This partial reflection of light may occur from layers beneath the substrate surface. This partial reflection can lead to errors in substrate height measurement.

[0008] Substrate height measurement errors may be expressed as height process dependence (HPD) or ASD (apparent surface depression).

[0009] It is desirable to provide a system that prevents or mitigates one or more problems related to prior art. [Means for solving the problem]

[0010] A first aspect of this disclosure provides a method for determining a substrate height measurement error, comprising: providing a laser beam modulated at a given frequency having wavelength and polarization; directing the modulated laser beam onto the substrate at an acute angle with respect to a normal extending from the substrate; detecting the position of the modulated laser beam after it has been reflected from the substrate; using the detection based on the modulation frequency applied to the laser beam to measure the 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, where the wavelength or polarization is modulated.

[0011] Advantageously, the method determines height measurement errors in a manner different from prior art methods. Advantageously, the method may be performed rapidly or within a lithography apparatus (e.g., before or during exposure of the substrate).

[0012] The height measurement error may also be an absolute value determined by referring to the known refractive index of the substrate layer.

[0013] The height measurement error may also be 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 substrate being measured.

[0014] The height measurement error may also be a relative value determined by comparing the measured modulations of the detected position of the modulated laser beam for different locations on the substrate.

[0015] Detection may involve measuring the modulation of the detected position of the modulated laser beam using harmonics of the modulation frequency applied to the wavelength or polarization of the laser beam.

[0016] The detection may also be a lock-in detection that automatically selects between the first harmonic, the second harmonic, or other harmonics of the modulation frequency, based on the amplitude of these harmonics.

[0017] The modulation of the laser beam wavelength can be as small as 1 / 100th of the laser beam wavelength.

[0018] The wavelength modulation of the laser beam can be as low as 100 pm.

[0019] The laser beam may be provided by a single-frequency laser.

[0020] According to a second aspect of this disclosure, a method for determining the height of a substrate is provided, comprising: measuring the height of the substrate; determining a substrate height measurement error using the method of a first aspect of this disclosure; and adjusting the measured height of the substrate using the determined substrate height measurement error.

[0021] According to a third aspect of the present disclosure, a projection unit configured to direct a laser beam emitted by a laser, having a wavelength and polarization, onto a substrate, a detection system including 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 in order to obtain a modulated laser beam, a lock-in amplifier configured to receive an output from the detection system and measure the modulation of the detected position of the modulated laser beam based on the frequency of the modulation applied to the wavelength or polarization of the laser beam, and a processor configured to use the measured modulation of the detected position to determine a substrate height measurement error, a substrate height measurement error determination system is provided.

[0022] Advantageously, the system of the third aspect determines a height measurement error in a manner different from prior art methods. Advantageously, the system enables the height measurement error to be determined quickly. Advantageously, it may be executed within a lithography apparatus (e.g., before or during exposure of the substrate). The height measurement error system may be within the lithography apparatus.

[0023] The detector may be a lock-in detector. The modulator and the detector may both be part of a lock-in amplifier.

[0024] The lock-in detector may automatically select between the first harmonic, the second harmonic, or other harmonics of the modulation frequency based on the amplitudes of these harmonics.

[0025] The modulator may be configured to modulate the wavelength or polarization of the laser beam by up to 1 / 100 of the wavelength of the laser beam.

[0026] The modulator may be configured to modulate the wavelength of the laser beam by up to 100 pm.

[0027] The laser may be a single-frequency laser.

[0028] According to a fourth aspect of the present disclosure, there is provided a measurement system comprising a substrate height measurement error determination system according to the third aspect and a substrate height measurement system, wherein the processor is configured to use the determined substrate height measurement error to adjust the measured height of the substrate obtained using the substrate height measurement system.

[0029] The detection system may form part of the substrate height measurement system.

[0030] The projection unit may form part of the substrate height measurement system.

[0031] According to a fifth aspect of the present disclosure, there is provided a lithographic apparatus comprising the measurement system according to the fourth aspect of the present disclosure.

[0032] The features of different aspects of the present disclosure may be combined together.

Brief Description of the Drawings

[0033] Hereinafter, embodiments of the present disclosure will be described by way of example only, with reference to the following accompanying drawings. FIG. 1 schematically shows a lithographic apparatus including a system for determining a substrate height measurement error according to an embodiment of the present disclosure. FIG. 2 schematically shows in more detail the system for determining the substrate height measurement error of FIG. 1.

Embodiments for Carrying Out the Invention

[0034] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation including ultraviolet radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 - 100 nm).

[0035] The terms “reticle,” “mask,” or “patterning device” as used in this text may be broadly interpreted to refer to any general patterning device that can be used to impart a patterned cross section to an incident radiation beam, corresponding to a pattern to be generated on a target portion of a substrate.

[0036] Figure 1 schematically shows a lithography apparatus LA. The lithography apparatus LA includes an illumination system (also referred to as an illuminator) IL configured to adjust a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to specific parameters; a substrate support (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to precisely position the substrate support according to specific parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern formed by the patterning device MA onto the radiation beam B onto a target portion C of the substrate W (e.g., including one or more dies).

[0037] During operation, the illumination system IL receives the radiated beam from the radiation source SO, for example, via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling the radiation. The illuminator IL may be used to adjust the radiated beam B so that it has a desired spatial and angular intensity distribution in its cross-section, in the face of the patterning device MA.

[0038] The term “projection system” PS as used herein should be interpreted broadly to encompass all types of projection systems, including refractive, reflective, reflective-refracting, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, that are appropriate for the exposure radiation in use and / or other factors such as the use of immersion liquid or vacuum. The use of the term “projection lens” herein may be interpreted as synonymous with the more general term “projection system” PS.

[0039] The lithography apparatus LA may be of a type in which at least a portion of the substrate is covered with a liquid such as water having a relatively high refractive index to fill the space between the projection system PS and the substrate W (also referred to as immersion lithography). More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0040] The lithography apparatus LA may be of a type having two or more substrate support WTs. In such a “multistage” apparatus, the substrate support WTs may be used in parallel, and / or, while one substrate W is being used on the other substrate support WT to expose a pattern on the other substrate W, the preparation steps for subsequent exposure of the substrate W may be performed on the substrate W positioned on one of the substrate support WTs.

[0041] During operation, the radiant beam B is incident on a patterning device such as a mask MA held on a mask support MT, and a pattern is formed by the pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiant beam B passes through a projection system PS that focuses the beam onto a target portion C of the substrate W. A second positioner PW and a position measurement system IF can precisely drive the substrate support WT to position different target portions C at focusing and alignment positions along the path of the radiant beam B, for example. Similarly, a first positioner PM and other appropriate position sensors (not explicitly shown in Figure 1) may be used to precisely position the patterning device MA relative to the path of the radiant beam B. The patterning device MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The illustrated substrate alignment marks P1, P2 occupy dedicated target portions, but they may be located in the spaces between target portions. The substrate alignment marks P1 and P2, positioned between target portions C, are known as scribe line alignment marks.

[0042] To illustrate this disclosure, a Cartesian coordinate system is used. The 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 around the x-axis is denoted as an Rx rotation. A rotation around the y-axis is denoted as a Ry rotation. A rotation around the z-axis is denoted as an Rz rotation. The x-axis and y-axis define the horizontal plane, and the z-axis defines the vertical direction. The Cartesian coordinate system is not limiting to this disclosure and is used solely for illustrative purposes. Alternatively, other coordinate systems, such as a cylindrical coordinate system, may be used to illustrate this disclosure. For example, the orientation of the Cartesian coordinate system may differ, such as the z-axis having a component along the horizontal plane. In the figure, the height of the substrate W is shown as the Z direction.

[0043] A height measurement system LS is provided for measuring the topography of the substrate W. The height measurement system LS may also be referred to as a level sensor or topography measurement system. A map of the substrate height (z) as a function of the position (x, y) on the substrate may be generated from the measurement results obtained using the height measurement system LS. This height map may be used to adjust the vertical position of the substrate W and / or to adjust the projection system PS during the projection of a pattern onto the substrate from a subsequent patterning device MA.

[0044] The height measurement system LS may be stationary. The substrate table WT and substrate W may be driven during scanning movement below the height measurement system LS. This allows the height measurement system to measure the height across the surface of the substrate W and generate a height map.

[0045] The height measurement system LS comprises a projection unit 10, a detection system 12, and a processor 15. The projection unit 10 is configured to provide a beam of light that, after being incident on a substrate W (including any pattern-forming layer thereon), is detected by the detection system 12. The position at which the beam of light is incident in the detection system 12 depends on the height of the substrate W. This allows the height of the substrate W to be measured. The projection unit 10 includes a diffraction grating (not shown), which may be referred to as a projection grating. The detection system 12 includes a diffraction grating (not shown), which may be referred to as a detection grating. An image of the projection grating is formed on the detection grating, and the position of this grating image relative to the detection grating provides height measurement.

[0046] The height measurement system LS may comprise multiple lasers (or other light sources). The height measurement system LS may comprise, for example, a broadband light source (e.g., a white light source emitting light across the visible spectrum). The height measurement system may comprise multiple lasers configured to emit light at different wavelengths. The output from the detection system 12 may 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 due to light reflection from multiple substrate layers (further explanation below with respect to Figure 2).

[0047] The lithography apparatus further includes a height measurement error detection system ES. The height measurement error detection system ES uses some of the same components as the height measurement system LS, which are shown as common components in Figure 1.

[0048] The height measurement error determination system ES comprises at least one single-frequency laser 18. The single-frequency laser may have a bandwidth of, for example, 10 MHz or less (e.g., a bandwidth of about 1 MHz). The laser 18 may constitute part of the projection unit 10. The position of reflection of the laser beam 16 provided by the projection unit 10 is detected by the detection system 12. A signal module 14 is provided, comprising a modulation unit (or modulator) and a lock-in amplifier. The modulator is configured to modulate the wavelength and / or polarization of the laser beam 16 emitted by the projection unit 10. The lock-in amplifier is configured to receive an output signal from the detection system 12. The detected position of the reflected laser beam is modulated for modulation of the wavelength or polarization of the laser beam. The lock-in amplifier provides an output which is the measurement result of the detected position modulation. The 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 expressed as height process dependency (HPD).

[0049] The height measurement error detection system ES is shown in more detail in Figure 2. As previously mentioned, some components of the height measurement error detection system ES may constitute part of the height measurement system LS. The projection unit 10 comprises 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 makes an acute angle θ with respect to the normal extending from the substrate W (in other words, with respect to the Z direction).

[0050] Laser 18 is configured to emit a laser beam 16 with a bandwidth smaller than 2 nm and may be described as a narrowband laser. The modulator of signal module 14 may apply modulation to the wavelength of the laser beam 16 emitted by laser 18. The modulator may change the wavelength of the laser beam 16 by, for example, about 1 pm. The modulator may change the wavelength of the laser beam by up to 10 pm, or up to 50 pm. The modulator may change the wavelength by a larger amount (e.g., up to 100 pm). However, when larger wavelength modulations such as 100 pm are used, the output from the lock-in amplifier may not be in a linear regime (this depends on the substrate structure).

[0051] Generally, the wavelength modulation can be as small as 1 / 100th of the central wavelength of the laser beam 16.

[0052] Light emitted by a laser is typically polarized. A polarizer (not shown in Figure 2) may be provided in the light source provided in the projection unit 10 (or the unit itself) to provide a light beam 16 with the desired polarization. An analytical polarization element may be provided in the detection system 12 (not shown in Figure 2).

[0053] The modulator of the signal module 14 may apply modulation to the polarization of the laser beam 16 emitted by the laser 18. For example, a polarization modulator may be provided to interact with the laser beam 16 within the projection unit 10. The polarization modulator may be a liquid crystal based modulator (or polarization rotor), or an electro-optic element that controls the polarization state of the light beam 16 by an externally applied voltage. The polarization module can modulate the polarization state of the light beam 16 at a predetermined frequency.

[0054] Generally, a substrate has many pattern-forming layers. However, for the sake of simplicity, the substrate W shown in Figure 2 has only two layers: a lower layer of silicon 32 (which may be referred to as the "base" substrate) and an upper layer of photoresist 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 towards the detection system 12.

[0055] The detection system 12 comprises a diffraction grating 24 and a pair of detectors 26a and 26b. The diffraction grating 24 may also be referred to as the detection grating 24. The main portion 16a of the reflected laser beam forms an image of the projection grating 20 on the detection grating 24. The detection grating 24 may have a periodicity corresponding to the periodicity of the grating image formed by the main portion 16a of the reflected laser beam. The position of this grating image depends on the height of the top surface 22 of the resist 30. The detection grating 24 directs the laser light toward the first and second detectors 26a and 26b. The proportion of laser light received by each detector 26a and 26b depends on the position of the grating image relative to the detection grating 24. Therefore, the signal output from the detectors 26a and 26b depends on the height of the top surface 22 of the resist 30. A differential amplifier 28 may be used to determine the difference between the signal outputs from the detectors 26a and 26b. The output from the differential amplifier 28 is provided to the signal module 14. Other position detection systems may be used to detect the position of the reflected laser beam.

[0056] The projection unit 10 and detection system 12 may include further optical elements such as lenses and / or mirrors (not shown) along the path of the laser beam 16 (for example, between the projection grid 20 and the detection grid 24).

[0057] As described 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 as a result, a portion 16b of the laser beam 16 passes through the resist. This secondary laser beam portion 16b is reflected from the interface between the resist 30 and the silicon substrate 32. The secondary laser beam portion 16b is a relatively small proportion of the incident laser beam 16 (e.g., less than 10% of the incident laser beam (e.g., less than 1% of the incident laser beam)). This is schematically represented by the secondary laser beam portion 16b, which is a thinner line than the main laser beam portion 16a.

[0058] The secondary laser beam portion 16b also forms an image of the projection grating 20 on the detector grating 24. However, this grating image is formed at a different position, lower than the grating image formed by the main laser beam portion 16a. As can be seen from Figure 2, the position of the detector grating image provided by the secondary laser beam portion 16b is determined by the height of the silicon substrate 32. The height offset between the position of the grating image provided by the main laser beam portion 16a and the position of the grating image provided by the secondary laser beam portion 16b depends on the thickness T of the resist.

[0059] The grating image formed by the secondary laser beam portion 16b introduces a measurement error into the signal output from detectors 26a and 26b. The signal output from detectors 26a and 26b indicates that the height of the top surface 22 of the resist is lower than the actual height of the top surface of the resist. The height measurement error determination system ES determines this height measurement error. The height measurement error may be used to adjust the height measurement results obtained using the height measurement system LS (see Figure 1).

[0060] The height measurement error determined by the system ES may be an absolute value (i.e., a value indicating the offset between the measured height of the top surface 22 of the resist 30 and the actual height of the top surface of the resist). The height measurement error may also be a relative value (e.g., a value indicating whether the height measurement error in a given area of ​​the substrate is greater than or less than the height measurement error in a different area of ​​the substrate).

[0061] The measurement results obtained by the height measurement error detection system ES will be explained in more detail with reference to Figure 2. The optical path difference L between the main laser beam portion 16a and the secondary laser beam portion 16b may be expressed as follows.

number

number

number

number

number

[0062] The modulator of signal module 14 provides a modulation signal that controls the operation of the laser 18 so that the central wavelength of the laser beam 16 is modulated. The modulation is at a given frequency (e.g., selected by the user or automatically selected by the lock-in amplifier). This results in modulation of the position of the reflected laser beam 16, which is detected by detectors 26a and 26b.

[0063] The lock-in amplifier of signal module 14 measures the modulation of the detected position of the laser beam 16 using the modulation frequency applied to the laser beam. The lock-in amplifier is configured to identify harmonics (e.g., the first harmonic) of the signal output from op-amp 28 (or other output signals if a different position detection system is used). The lock-in amplifier identifies harmonics as components of the output signal, which have a frequency that is the harmonic of the modulation applied to the laser 18. The lock-in amplifier of signal module 14 provides an output signal having an amplitude that indicates 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 height measurement error. As previously stated, the height measurement error may be an absolute or relative value. The height measurement error may be used to adjust the height measurement results obtained by the height measurement system LS.

[0064] In some examples, the first harmonic of the signal received by the lock-in amplifier may have a lower amplitude than, for example, the second harmonic. In the scenario shown in Figure 2, the relative amplitudes of different harmonics depend on the refractive index and thickness of the resist 30 layer. The lock-in amplifier may be configured to automatically select the harmonic that provides the largest signal amplitude. In other scenarios (not shown) where more layers are provided on the substrate, the relative amplitudes of different harmonics depend on the refractive index and thickness of each layer. Again, the lock-in amplifier may be configured to automatically select the harmonic that provides the largest signal amplitude. For example, for some substrates, the first harmonic may provide a strong signal that can be used to determine height measurement errors. For other substrates, the second harmonic may provide a strong signal that can be used to determine height measurement errors. Other harmonics may be used. Generally, lock-in detection automatically selects between the first harmonic, the second harmonic, or other harmonics of the modulation frequency based on the amplitudes of these harmonics.

[0065] Similar to the control of the (center) wavelength of the laser 18 by a modulation signal, the polarization of the light beam (laser beam) 16 can be controlled by a modulation signal provided to a polarization module. The polarization state of the laser beam 16 can be changed by the polarization module. That is, the polarization can be rotated by several angles (about 1° or more, about 5° or more, about 10° or more, 15° or more, 30° or more, 45° or more) and may depend on the frequency response of the polarization module. In this case, the polarization of the incident light is modulated to obtain a signal correlated with the product structure. Since the product structure affects the intensity of the light reflected from it, polarization-modulated light can be used to reduce the influence of the product structure on the detected light.

[0066] Generally, lock-in detection is used to measure the modulation (detected by detectors 26a and 26b) of a detected position in a modulated wavelength laser beam. Lock-in detection is achieved by modulating the laser beam at a given frequency and using that frequency to identify the modulation at the detected position. Both the laser beam modulation and lock-in detection may be performed by the signal module 14.

[0067] In one embodiment, the broadband light source (or other light source) of the height measurement system LS may be provided in close proximity to the laser 18 of the height measurement error determination system ES. In this case, the projection grid 20, detection grid 24, and detector 26 may be common to both systems. Systems LS and ES may operate simultaneously. That is, the height measurement system LS may measure a height map for the substrate W, and the height measurement error determination system ES may simultaneously determine height measurement errors. The height measurement error determination system ES may provide a height measurement error map.

[0068] In the scenario shown in Figure 2, the adjustment to be determined may also be an absolute value of the height measurement error HPD (i.e., a value indicating the offset between the measured height of the top surface 22 of the resist 30 and the actual height of the top 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, A of the first and second laser beam portions 16a, b may be measured during calibration. Thus, the height measurement error HPD can be treated as an absolute value that depends only on the unknown T. The height measurement error HPD may be subtracted from the measured height of the top surface 22 of the resist to obtain a corrected height.

[0069] The above is an example for a substrate with a relatively simple structure. In reality, the substrate may have more than two layers (e.g., five or more layers, ten or more layers, etc.). In this case, it may not be possible to directly obtain an absolute value for the height measurement error HPD. As can be understood from equation (4), the height measurement error HPD depends on the thickness and refractive index of each layer of the multilayer substrate. Because the height measurement error HPD depends on many different parameters, it may not directly provide an absolute value that can be subtracted from the measured height to obtain a corrected height. However, even in such a scenario, embodiments of the present disclosure may still provide useful information. In particular, a relative measurement of the height measurement error HPD may be used to adjust the measured height. For example, the height measurement error HPD may be converted to an absolute value for height correction through comparison with a previous calibration measurement. For example, the height adjustment value may be determined for a substrate having a given layer structure (e.g., by comparing the output of a broadband level sensor LS with an output obtained using an air gauge). One embodiment of the present disclosure may determine the height measurement error HPD for the calibrated substrate. This provides calibration of the height measurement error (HPD) for the difference between the output of the broadband level sensor LS and the actual substrate height. Subsequently, the height measurement error (HPD) for other substrates with the same layer structure may be measured as part of the lithography exposure. The height measurement error (HPD) may be compared with the height measurement error (HPD) obtained using the calibrated substrate. The results of the comparison may be used to obtain a height adjustment value. The height adjustment value may be used to obtain a corrected height for the substrate being exposed.

[0070] In other embodiments, a height measurement error may be used as one of several error measurements used to adjust the measured substrate height.

[0071] Typically, more than 200 dies are exposed on a substrate, and in some cases, more than 600 dies are exposed on a substrate. Each die is exposed using the same series of patterning device exposure and undergoes the same processing. Therefore, each die should have the same characteristics, including the same height measurement error. In practice, the height measurement error may vary across the substrate. This can occur, for example, due to the effects of processing the substrate layers. In one example, a metal film may be deposited within a structure formed on the substrate, and polishing may be used to remove excess metal from the substrate. Polishing may remove slightly more material from one side of the substrate than from the other side (for example, there may be a gradient in the thickness of the metal across the substrate). Embodiments of this disclosure may provide as an output a height measurement error value that gradually changes across the surface of the substrate. The height measurement error value may be used to adjust for the expected height measurement error for the substrate. This adjusted expected height measurement error may be used as a height adjustment value applied to the measured height of the substrate.

[0072] Calibration of the height measurement error determination system according to the embodiments of this disclosure may include determining the relative amplitude of the primary reflected beam portion 16a and the secondary reflected beam portion 16b. Calibration may include directing the laser beam 16 to the substrate and changing the (center) wavelength of the laser beam 16 by several nanometers, for example, 10 nm. Similarly, calibration may include directing the laser beam 16 to the substrate and changing the polarization of the laser beam 16 by several angles (about 1° or more, about 5° or more, about 10° or more, 15° or more, 30° or more, 45° or more), and may depend on the frequency response of the polarization module. Calibration may be performed at a single position on the substrate. Calibration may be performed at multiple positions on a given die on the substrate. Calibration may be performed at each measurement location on the substrate.

[0073] An initial calibration of the height measurement error detection system may be performed. This initial calibration, which may be referred to as electronic calibration, is intended to determine the system's gain. For this initial calibration, a substrate W having a known structure is used. The substrate W may be, for example, a substrate that has not yet received a device pattern including alignment marks (the characteristics of such a substrate are well known). The substrate W may have two layers. A laser beam 16 is detected, directed onto the substrate W. 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 multiple measurements.

[0074] The outputs of detectors 26a and 26b are received by a lock-in input channel. A lock-in phase-locked loop locks onto the signal and extracts the amplitude and phase of the reflected light 16a and 26b. Two signals are available, with the amplitude of the first harmonic having a strong correlation with the product (layer) structure. The output of the original height map from the level sensor LS (main signal) and the output of the error determination system ES (HPD signal). There are a few methods to clean up the correlated portion of the main signal by using the HPD signal as a reference or second detector signal. These methods may require calibration. This is a problem of solving a set of linear equations to reduce the HPD's contribution to the error. Similarly, the outputs of the level sensor LS and the error determination system ES as two detectors that measure these two events, which produce a mixed signal. This is also known as the "cocktail party" problem. There are a few methods to separate these two signals without requiring specific calibration. An example of such a technique is known as BSS (blind signal separation) or blind source separation.

[0075] To effectively cover the surface of the substrate W, embodiments of the present disclosure may be configured to project an array of laser beams 16 onto the surface of the substrate W. This provides an array of measurement areas on the substrate that covers a larger measurement range.

[0076] The embodiments of the present disclosure described herein comprise a height measurement system LS and a separate height measurement error detection system ES. However, in one embodiment, a single system may be used. That is, the height measurement error detection system ES may determine height measurement errors and may also provide substrate height measurements.

[0077] Embodiments of the present invention have been described as comprising a single-frequency laser having a bandwidth of 10 MHz or less, for example, a bandwidth of about 1 MHz. Embodiments of the present invention may also comprise a single-frequency laser having a bandwidth of up to 20 MHz. Such an embodiment may provide useful height measurement error. However, the dynamic range of such an embodiment is smaller than that of a single-frequency laser with a narrower bandwidth.

[0078] The method described herein is described in relation to a substrate W that has been exposed to or will be exposed to lithographic radiation (i.e., radiation beam B), but as will be apparent to those skilled in the art, the method (and corresponding apparatus) may, advantageously, be adapted for use with substrates that have not been exposed to lithographic radiation.

[0079] In the embodiments of the present invention described, wavelength / polarization modulation and harmonic detection were performed by a lock-in amplifier system. However, any suitable device may be used to apply wavelength modulation, and any suitable device may be used to detect the harmonics of the applied modulation. Generally, homodyne detection, heterodyne detection, or quadrature detection may be used. These are examples of lock-in detection. Detection may be performed using hardware or software.

[0080] The height measurement system and the height measurement error detection system may be collectively referred to as the measurement system.

[0081] Embodiments of this disclosure may constitute part of a lithography apparatus (e.g., as shown) or a measuring apparatus. Embodiments of this disclosure may constitute part of a lithography tool. Furthermore, examples of lithography tools are mentioned below.

[0082] Similarly, although the method described herein is described in relation to DUV lithography radiation, as will be apparent to those skilled in the art, the method (and corresponding apparatus) may, advantageously, be adapted for use with EUV lithography radiation (and corresponding apparatus).

[0083] While this text may have provided specific references to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications. Possible other applications 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.

[0084] While specific references to embodiments of the disclosure in the context of lithography apparatus may be made in this text, embodiments of the disclosure may be used in other apparatuses. Embodiments of the disclosure may constitute part of a mask inspection apparatus, a measuring apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be referred to as lithography tools. Such lithography tools may operate under vacuum conditions or atmospheric (non-vacuum) conditions.

[0085] While specific references to the use of embodiments of this disclosure in the context of optical lithography may have been made above, it is understood that this disclosure may be used in other applications, such as imprint lithography, to the extent that the context permits, and is not limited to optical lithography.

[0086] To the extent permitted by context, embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may be implemented as instructions stored on a machine-readable medium which may be read and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, the 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 transmitted signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described as performing specific actions. However, such descriptions are merely for convenience and should be understood that such actions are actually brought about by computing devices, processors, controllers, or other devices that execute firmware, software, routines, instructions, etc., and cause actuators or other devices to interact with the physical world.

[0087] Aspects of the present invention are presented in the following sections. Item 1: A method for determining a substrate height measurement error, To provide a laser beam with wavelength or polarization modulated at a given frequency, The modulated wavelength laser beam is directed onto the substrate at an acute angle with respect to the normal extending from the substrate, The position of the modulated laser beam after it has been reflected from the substrate is detected, To measure the modulation of the detected position of the modulated laser beam, the detection is used based on the frequency of the modulation applied to the wavelength or polarization of the laser beam, The height measurement error is determined based on the measured modulation of the detected position of the modulated laser beam. A method for providing this. Item 2: A method for determining a substrate height measurement error, To provide a laser beam modulated at a given frequency, having wavelength and polarization, The modulated laser beam is directed onto the substrate at an acute angle with respect to the normal extending from the substrate, The position of the modulated laser beam after it has been reflected from the substrate is detected, To measure the modulation of the detected position of the modulated laser beam, the detection is used based on the frequency of the modulation applied to the beam, The height measurement error is determined based on the measured modulation of the detected position of the modulated laser beam, which is modulated by the wavelength or polarization. A method for providing this. Item 3: The method according to item 1 or 2, wherein the height measurement error is an absolute value determined by referring to the known refractive index of the substrate layer. Item 4: The method according to item 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 substrate being measured. Item 5: The method according to item 1 or 2, wherein the height measurement error is a relative value determined by comparing the measured modulations of the detected position of the modulated laser beam for different locations on the substrate. Item 6: The method according to any one of items 1 to 5, wherein the detection measures the modulation of the detected position of the modulated laser beam using harmonics of the frequency of the modulation applied to the wavelength or polarization of the laser beam. Item 7: The method according to item 6, wherein the detection is a lock-in detection that automatically selects between a first harmonic, a second harmonic, or other harmonics of the frequency of the modulation based on the amplitudes of these harmonics. Item 8: The wavelength is modulated, The modulation of the wavelength of the laser beam is at most 1 / 100 of the wavelength of the laser beam. The method described in any of items 1 through 7. Item 9: The wavelength is modulated, The modulation of the wavelength of the laser beam is up to 100 pm. The method described in any of items 1 through 8. Item 10: The laser beam is provided by a single-frequency laser, as described in any one of items 1 to 9. Item 11: A method for determining the height of a circuit board, Measuring the height of the substrate, Determine the substrate height measurement error using one of the methods described in items 1 through 10, Using the determined substrate height measurement error, the measured height of the substrate is adjusted. A method for providing this. Item 12: A projection unit equipped with a laser having wavelength and polarization, configured to direct the laser beam emitted by the laser onto a substrate, A detection system comprising 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, A detector that receives an output from the detection system and is configured to measure the modulation of the detected position of the modulated laser beam based on the frequency of the modulation applied to the wavelength or polarization of the laser beam, A processor configured to use the measured modulation of the detected position in order to determine a substrate height measurement error, A circuit board height measurement error detection system equipped with the following features. Item 13: The modulator and the lock-in amplifier are both part of the signal module in the substrate height measurement error determination system described in item 12. Item 14: The substrate height measurement error determination system according to item 12, wherein the lock-in amplifier automatically selects between the first harmonic, the second harmonic, or other harmonics of the modulation frequency based on the amplitude of these harmonics. Item 15: The wavelength is modulated, The modulator is configured to modulate the wavelength of the laser beam by a maximum of 1 / 100 of the wavelength of the laser beam. A substrate height measurement error detection system as described in any of items 12 to 14. Item 16: The wavelength is modulated, The modulator is configured to modulate the wavelength of the laser beam by up to 100 pm. A substrate height measurement error detection system as described in any of items 12 to 15. Item 17: The aforementioned laser is a single-frequency laser, a substrate height measurement error determination system according to any one of items 12 to 16. Item 18: A substrate height measurement error determination system described in any of items 12 to 17, A substrate height measurement system, Equipped with, The processor is configured to use the determined substrate height measurement error to adjust the measured height of the substrate obtained using the substrate height measurement system. Measurement system. Item 19: The detection system is a part of the substrate height measurement system, as described in item 18. Item 20: The measurement system according to item 18 or 19, wherein the projection unit constitutes part of the substrate height measurement system. Item 21: A lithography apparatus comprising a measurement system as described in any of items 18 to 20.

[0088] Although specific embodiments of the Disclosure have been described above, it should be understood that the Disclosure may be implemented in ways different from those described. The above descriptions are illustrative and not intended to limit the Disclosure. Accordingly, it will be apparent to those skilled in the art that modifications may be made to the described Disclosure without departing from the scope of the following claims.

Claims

1. A method for determining a substrate height measurement error, To provide a laser beam modulated at a given frequency, having wavelength and polarization, The modulated laser beam is directed onto the substrate at an acute angle with respect to the normal extending from the substrate, The position of the modulated laser beam after it has been reflected from the substrate is detected, To measure the modulation of the detected position of the modulated laser beam, the detection is used based on the frequency of the modulation applied to the beam, The height measurement error is determined based on the measured modulation of the detected position of the modulated laser beam, which is modulated by the wavelength or polarization. A method for providing this.

2. The method according to claim 1, wherein the height measurement error is an absolute value determined by referring to the known refractive index of the layers 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 calibration modulation obtained using a different substrate having a layer structure corresponding to the layer 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 measured modulations of the detected position of the modulated laser beam for different locations on the substrate.

5. The method according to any one of claims 1 to 4, wherein the detection measures the modulation of the detected position of the modulated laser beam using harmonics of the frequency of the modulation applied to the wavelength or polarization of the laser beam.

6. The method according to claim 5, wherein the detection is a lock-in detection that automatically selects between a first harmonic, a second harmonic, or other harmonics of the frequency of the modulation based on the amplitudes of these harmonics.

7. The wavelength is modulated, The modulation of the wavelength of the laser beam is at most 1 / 100 of the wavelength of the laser beam. The method according to any one of claims 1 to 6.

8. The wavelength is modulated, The modulation of the wavelength of the laser beam is up to 100 pm. The method according to any one of claims 1 to 7.

9. A method for determining the height of a circuit board, Measuring the height of the substrate, Determining a substrate height measurement error using the method according to any one of claims 1 to 8, Using the determined substrate height measurement error, the measured height of the substrate is adjusted. A method for providing this.

10. A projection unit equipped with a laser having wavelength and polarization, configured to direct the laser beam emitted by the laser onto a substrate, A detection system comprising 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 in order to obtain a modulated laser beam, A lock-in amplifier configured to receive an output from the detection system and measure the modulation of the detected position of the modulated laser beam based on the frequency of the modulation applied to the wavelength or polarization of the laser beam, A processor configured to use the measured modulation of the detected position in order to determine a substrate height measurement error, A circuit board height measurement error detection system equipped with the following features.

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

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

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

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

15. A substrate height measurement error determination system according to any one of claims 10 to 14, A substrate height measurement system, Equipped with, The processor is configured to use the determined substrate height measurement error to adjust the measured height of the substrate obtained using the substrate height measurement system. Measurement system.

Images