Calibration apparatus

Abstract

A calibration apparatus for a wavelength-tunable deep ultraviolet (DUV) light source includes a plasmonic device in a path of a light beam from a discharge chamber; and a calibration detector that receives the light beam exiting the plasmonic device. The calibration detector is configured to detect a fluence of the light beam.

Description

CALIBRATION APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 553,745, filed February 15, 2024, titled CALIBRATION APPARATUS, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The disclosed subject matter relates to a calibration apparatus for a metrology apparatus of a deep ultraviolet (DUV) light source.BACKGROUND

[0003] One kind of gas discharge light source used in photolithography is termed an excimer light source or laser. Typically, an excimer laser uses a combination of one or more noble gases, which can include argon, krypton, or xenon, and a reactive gas, which can include fluorine or chlorine. The excimer laser can create an excimer (or exciplex), a pseudo-molecule, under appropriate conditions of electrical simulation (energy supplied) and high pressure (of the gas mixture), the excimer only existing in an energized state. The excimer in an energized state gives rise to amplified light in the ultraviolet range. An excimer light source can use a single gas discharge chamber or a plurality of gas discharge chambers. When the excimer light source is performing, the excimer light source produces a deep ultraviolet (DUV) light beam. DUV light can include wavelengths from, for example, about 190 nanometers (nm) to about 280 nm.

[0004] The DUV light beam can be directed to an exposure apparatus, such as an inspection system or a photolithography system (e.g, a stepper or a scanner), which is a machine that applies a desired pattern onto a target portion of a substrate (such as a silicon wafer). The DUV light beam interacts with a projection optical system, which projects the DUV light beam through a mask onto the photoresist of the wafer. In this way, one or more layers of chip design is patterned onto the photoresist and the wafer is subsequently etched and cleaned.SUMMARY

[0005] In some general aspects, a calibration apparatus is configured for a wavelength-tunable deep ultraviolet (DUV) light source. The calibration apparatus includes: a plasmonic device in a path of a light beam produced by a light source; and a calibration detectorthat receives the light beam exiting the plasmonic device, the calibration detector configured to detect a fluence of the light beam.

[0006] Implementations can include one or more of the following features. For example, a controller can be configured to command a wavelength tuning apparatus to scan the wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within the tuning range of the DUV light source. Thecontroller can be in communication with the calibration detector and can be configured to analyze the detected change of fluence induced by the localized surface plasmon resonance. The localized surface plasmon resonance can correspond to an absorption extreme (such as a dip or a peak) in the detected fluence. The controller can be in communication with a metrology apparatus that estimates a wavelength of the light beam. The controller can be configured to determine a calibration error of the metrology apparatus based on an analysis of the output of the calibration detector relative to the wavelength estimated by the metrology apparatus. The controller can be configured to adjust the calibration of the metrology apparatus based on the determined calibration error. The calibration error can correspond to a difference between the known wavelength at the localized surface plasmon resonance and an apparent wavelength corresponding to an extreme in the fluence of the output of the calibration detector.

[0007] The plasmonic device can include a two or three-dimensional matrix of metallic nanostructures arranged relative to a non-metallic substrate. The calibration detector can be arranged to receive the light beam that is transmitted through the plasmonic device. The metallic nanostructures can be hemispheres or tubes. The substrate can include a DUV transparent material. The substrate can include sapphire, SiCh with multiwalled carbon nanotubes matrix composites, or Si-doped Ga2C>3. The light beam can have an operating range within the DUV wavelength range between 190 nanometers (nm) and 280 nm. The metallic nanostructures can include aluminum, gallium, tin, titanium, lead, bismuth, indium, or hafnium (IV) oxide.

[0008] The plasmonic device can include a two or three-dimensional matrix of nanostructures, each nanostructure including a metal, a substrate at which the matrix is arranged, and a base material, the base material and the matrix being separated by the substrate, thereby producing a locally enhanced electric field through plasmonic coupling. The calibration detector can be arranged to receive the light beam that is reflected from the plasmonic device. The metallic nanostructures can be hemispheres or tubes. The base material can be made of the same metal as the metallic nanostructures, and the substrate can be non-metallic and DUV transparent. An absorbing wavelength and a spectral bandwidth of the plasmonic material can be partly determined by a thickness of the substrate. The light beam can have an operating range within the DUV wavelength range between 190 nanometers (nm) and 280 nm. The metallic nanostructures can include aluminum, gallium, tin, titanium, lead, bismuth, indium, or hafnium (IV) oxide.

[0009] The plasmonic device can include a two- or three-dimensional matrix of plasmonic nanostructures, each plasmonic nanostructure having a scale that is smaller than the wavelength of the light beam. Adjacent nanostructures can be spaced apart from each other by a distance in a range between 5 nm and 20 nm.

[0010] The plasmonic device can be a solid-state material.

[0011] The calibration apparatus can further include a diffuser that diffuses a light beam before it enters the plasmonic device.

[0012] In other general aspects, a method is performed for calibrating a metrology apparatus of a deep ultraviolet (DUV) light source. The method includes: generating a wavelength -tunable light beam from the DUV light source; directing the generated light beam along a calibration path to interact with a plasmonic device; detecting a fluence of the light beam that has interacted with the plasmonic device; and calibrating the metrology apparatus based on the detected fluence.

[0013] In other general aspects, a photolithography system includes: a gain medium, an energy pump, and an optical resonator configured to generate a light beam; a metrology apparatus configured to measure a wavelength of the generated light beam; a calibration apparatus; and a controller in communication with the metrology apparatus and the calibration apparatus. The calibration apparatus includes a plasmonic device in a calibration path of the light beam, and a calibration detector that receives the light beam exiting the plasmonic device. The calibration detector is configured to detect a fluence of the light beam. The controller is configured to calibrate the metrology apparatus based on the detected fluence of the light beam.

[0014] Implementations can include one or more of the following features. For example, the controller can be configured to command a wavelength tuning apparatus to scan the wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within a tuning range of the DUV light source. The controller can be configured to compare the known wavelength of the light beam at the localized surface plasmon resonance with the apparent center wavelength of the light beam measured by the metrology apparatus.

[0015] In other general aspects, a process of making a semiconductor device includes calibrating a metrology apparatus of a deep ultraviolet (DUV) light source and subsequently exposing a photoresist on a semiconductor substrate with light from the DUV light source. The calibrating includes: generating a wavelength-tunable light beam from the DUV light source; directing the generated light beam along a calibration path to interact with a plasmonic device; detecting a fluence of the light beam that has interacted with the plasmonic device; and calibrating the metrology apparatus based on the detected fluence.

[0016] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.DRAWING DESCRIPTION

[0017] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable a person skilled in the relevant art(s) to make and use implementations described herein.

[0018] Fig. 1 is a block diagram of a calibration apparatus arranged relative to a metrology apparatus configured to measure or sense one or more aspects relating to a light beam produced by a light source, the calibration apparatus including plasmonic device and a calibration detector;

[0019] Fig. 2 is a block diagram and a schematic illustration of an implementation of a metrology apparatus that includes a spectral analysis module that includes an optical separation apparatus and a sensor;

[0020] Fig. 3 is a block diagram of an implementation of an optical separation apparatus that can be used in a spectral analysis module of a metrology apparatus;

[0021] Fig. 4 is a block diagram of an implementation of a plasmonic device for use in a calibration apparatus, the plasmonic device including a matrix of plasmonic nanostructures;

[0022] Fig. 5 A is a block diagram of an implementation of a plasmonic device for use in a calibration apparatus;

[0023] Fig. 5B is a perspective view of the plasmonic device of Fig. 5A;

[0024] Fig. 6A is a block diagram of an implementation of a plasmonic device for use in a calibration apparatus;

[0025] Fig. 6B is a perspective view of the plasmonic device of Fig. 6A;

[0026] Fig. 7A is a block diagram of an implementation of a plasmonic device for use in a calibration apparatus;

[0027] Fig. 7B is a perspective view of the plasmonic device of Fig. 7A;

[0028] Fig. 8 A is a block diagram of an implementation of a plasmonic device for use in a calibration apparatus;

[0029] Fig. 8B is a perspective view of the plasmonic device of Fig. 8A;

[0030] Fig. 9 is a block diagram of an implementation of a calibration apparatus arranged relative to a metrology apparatus;

[0031] Fig. 10 is a block diagram of an implementation of a photolithography system including an implementation of a light source that produces a light beam directed to a photolithography exposure apparatus; and

[0032] Fig. 11 is a flow chart of a procedure for calibrating a metrology apparatus.

[0033] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DESCRIPTION

[0034] Referring to Fig. 1, a calibration apparatus 100 is arranged relative to a metrology apparatus 160. The metrology apparatus 160 is configured to measure or sense one or more aspects relating to a light beam 151 produced by an ultraviolet light source 150, the light beam 151 being provided to and used by an output device 155. For example, the metrology apparatus 160 can be configured to estimate a wavelength or a bandwidth of the light beam 151 based on a measurement relating to a diagnostic light beam 15 Im. In various applications, the diagnostic light beam 15 Im supplied to metrology apparatus 160 is a sample of the light beam 151. For example, the diagnostic light beam 15 Im can be a beam generated by a beam splitter in the path of the light beam 151. In other applications, the diagnostic light beam 15 Im can be a reference beam with known characteristics, such as a known center wavelength and / or a known power spectrum. The ultraviolet light source 150 can operate in the deep ultraviolet (DUV) wavelength range and can be wavelength-tunable, which means that the wavelength of light beam 151 can be adjusted within a sub-range in the DUV wavelength range, and such sub-range can be controlled or determined by the output device 155. The DUV wavelength range is between 190 nanometers (nm) and 280 nm. And, in some specific designs of the light source 150 that use argon fluoride (ArF) or krypton fluoride (KrF) for a gain medium, the DUV wavelength sub-range can encompass wavelengths of approximately 193 nm (in one sub-range) or approximately 248 nm (in another sub-range), respectively.

[0035] During operation, because of various unwanted effects, the accuracy of the measurement performed by the metrology apparatus 160 can degrade over time. This degradation may arise from physical or optical changes that occur over time, for example, over months or years, as the metrology apparatus 160 is being used. For example, operation of the metrology apparatus 160 can rely on precise aspects of an optical path travelled by the diagnostic light beam 15 Im within the metrology apparatus 160, such as an optical path length within an etalon or a reference cavity. If mechanical changes in the metrology apparatus 160 cause this path to change overtime, those changes can lead to erroneous assessments of a spectral feature (such as a peak wavelength or a center wavelength) of an optical spectrum of the light beam 151. The measured aspect can correspond to this measured spectral feature. The optical path length is related not only to a geometric length of the path followed by the diagnostic light beam 15 Im through the metrology apparatus 160, but also to the refractive index of the medium or media through which the diagnostic light beam 15 Im propagates. Over time, a relevant path length within the metrology apparatus 160 can change due to mechanical instabilities or thermal effects or stress-relief effects. Such changes can be due to changes in any one or more of the refractive index and the geometric path length. Changes in the optical path length experienced by the diagnostic light beam 15 Im can cause errors in the measurement of the spectral feature (wavelength) of the diagnostic light beam 15 Im performed by the metrology apparatus 160. This, in turn, makes it difficult to control the spectral features (such as the wavelength) and optical spectrum of the light beam 150. Moreover, the output device 155 may require certain spectral features or a particularoptical spectrum of the light beam 151 for proper operation. When the wavelength is not correct, the output device 155 may operate at a lower efficiency or effectiveness.

[0036] In order to maintain the accuracy of the measurements performed by the metrology apparatus 160, the metrology apparatus 160 is calibrated using the calibration apparatus 100. The calibration apparatus 100 is in a path of a light beam 151c. The light beam 151c can be the light beam 151 or 15 Im, or it can be a portion of the light beam 151 or 15 Im that has been split off or separated from the light beam 151, 15 Im. During calibration, one or more operating parameters of the metrology apparatus 160 are adjusted to compensate for the degradation in the metrology apparatus 160. Calibration of the metrology apparatus 160 can take a few seconds, tens of seconds, or even up to a minute or more. During calibration, the light beam 151 is not available for use by the output device 155. Thus, the operating time of the output device 155 is halted in order to perform a calibration.

[0037] The calibration apparatus 100 includes a plasmonic device 105 and a calibration detector 130 that receives a light beam 151c’ exiting the plasmonic device 105. The plasmonic device 105 provides a known wavelength reference. This reference enables calibration of the metrology apparatus 160, as discussed in more detail below. The plasmonic device 105 includes a metamaterial, which can be a solid-state material. The metamaterial is an artificial three-dimensional volumetric medium that includes a bulk metallic and / or dielectric constituent elements. The calibration detector 130 is configured to detect one or more properties (such as a fluence) of the light beam 151c’ output from the plasmonic device 105.

[0038] In various situations, the use of plasmonic device 105 provides improved performance and reliability of the calibration apparatus 100 in relation to prior calibration systems that provide a wavelength reference. Specifically, the plasmonic device 105 may have a smaller form factor and take up less space as compared to prior calibration devices. This compactness may provide a benefit in that the region or volume around the light source 150 can be used for other purposes. Moreover, the plasmonic device 105 may require less time to warm up from standby as compared to prior calibration devices. For example, in some implementations, the plasmonic device 105 does not need to warm up and is immediately ready for use from standby because it is a solid state material. In other implementations, warm up may require less than 1 second. This improved speed means that calibration times can be reduced, which means that the output device 155 is halted for a shorter period of time for calibration than in prior calibrations. The plasmonic device 105 typically does not require a power supply to operate; that is, it is a passive device, and it may be less prone to malfunctioning than prior calibration devices. The plasmonic device 105 may further enable a wavelength resolution on the order of nanometers, picometers, or sub-picometers at the calibration detector 130.

[0039] As mentioned above, the plasmonic device 105 is a device that uses a metamaterial (or a plasmonic metamaterial). A metamaterial is a synthetic composite that exhibits properties not found in natural materials. The plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve certain optical properties or to influence optical properties. The surface plasmons are packets ofelectrical charge that collectively oscillate at the surfaces of metals at optical frequencies. Plasmons are produced from the interaction of the light beam 151c with metal -dielectric metamaterials within the plasmonic device 105 that are formed by nanoparticles or nanostructures. The plasmons are local to these nanostructures, or on the surface of the nanostructure, instead of being localized across a metal -dielectric interface, and the plasmons propagate along the surface of the nanostructure. A localized surface plasmon (LSP) is the result of the confinement of the surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. When a small, for example, spherical, metallic nanoparticle is irradiated by light, the oscillating electric field causes the conduction electrons to oscillate coherently. The interaction of light (the light beam 151c) with the metamaterial changes (for example, an absorption changes) depending on the chemicals in the metamaterial and also depending on the shape of the metamaterial. For example, hemispherical nanostructures produce a different interaction (or absorption by the light beam 151c) than nanorods / nanocylinders, stars, or spheres. Other properties that affect the interaction between the light beam 151c and the metamaterial include the polarization of the light beam 151c and the relative refractive index between the metamaterial and the surrounding materials.

[0040] Referring to Fig. 2, an implementation 260 of the metrology apparatus 160 includes a spectral analysis module 261. The spectral analysis module 261 includes an optical separation apparatus 262 (such as an etalon) and a sensor 266. The spectral analysis module 261 can include other components not shown, such as one or more of diffusers, windows, and reflective or refractive optical components. In the example of Fig. 2, the property measured by the spectral analysis module 261 includes a wavelength of the diagnostic light beam 15 Im that is produced by the light source 150. The spectral analysis module 261 is configured to sense the wavelength of the diagnostic light beam 15 Im by sensing and analyzing a spectral profile 252 of the diagnostic light beam 15 Im. The spectral profile 252, which is also referred to as an optical spectrum, is a spectral shape or intensity spectrum of the diagnostic light beam 15 Im (and the light beam 151) as a function of the wavelength (or frequency) of the diagnostic light beam 15 Im. Thus, the spectral profile 252 contains information about how the optical energy or power of the light beam 15 Im or 151 is distributed over different wavelengths (or frequencies). The diagnostic light beam 15 Im is directed through an aperture 267 of the spectral analysis module 261 to the optical separation apparatus 262. The diagnostic light beam 15 Im travels along an optical path that is defined by an optical path length within the optical separation apparatus 262. The optical separation apparatus 262 interacts with the diagnostic light beam 15 Im and outputs a plurality of spatial components 253 (such as interference fringes or a fringe pattern) that are indicative of the spectrum of the diagnostic light beam 15 Im. In operation, the spectral analysis module 261 can generate the spectral profile 252.

[0041] The spatial components (or fringe pattern) 253 are indicative of the distribution of optical energy or power, shown as a spectral intensity 254i, of the light beam 15 Im over the different wavelengths 254w. The spatial components 253 correspond to the values of the spectral intensity 254imapped into a two-dimensional space. In this way, the optical separation apparatus 262 transforms the spectral information, such as the wavelength, of the light beam 15 Im into spatial information that can be sensed or detected by the sensor 266. The transformation maps the spectral information to different positions in space such that the spectral information can be observed by the sensor 266. If the output of the optical separation apparatus 262 is detected at a linear sensor 266, then the detected fringe pattern 253 is displayed as a linear pattern 255, which is indicative of the spectral profde 252.

[0042] The sensor 266 receives and senses the output spatial components 253. The sensor 266 can be defined by a plane that indicates generally the active area of its sensing region. The plane of the sensing region can be perpendicular to the direction of propagation of the spatial components 253. The sensor 266 can be a detector that receives and senses the output spatial components 253. For example, one type of suitable detector that can be used to measure along one dimension is a linear photodiode array. The linear photodiode array consists of multiple elements of the same size, formed in a linear arrangement at an equal spacing in one package. The photodiode array is sensitive to the wavelength of the light beam 15 Im, and if the light beam 15 Im has a wavelength in the deep ultraviolet range, then the photodiode array is sensitive to light having a wavelength in the deep ultraviolet range. In various implementations, the sensor 266 can be a two-dimensional sensor. For example, the sensor 266 can be a one -dimensional or a two-dimensional charged coupled device (CCD) or a one-dimensional or two-dimensional complementary metal oxide semiconductor (CMOS) sensor. In some implementations, the sensor 266 is able to read out data (such as the value of the wavelength) at a fast enough rate, for example, at about 6 kHz. In some implementations, the sensor 266 is able to read, analyze, process, and report out the fringe pattern 255 at a rate that exceeds 10 kHz.

[0043] The output of the sensor 266 is connected to a control module 269 that measures a property of the spatial components 253 and analyzes the measured properties to calculate an estimate of the spectral feature (such as the wavelength or the bandwidth) of the light beam 15 Im (and 151). The spectral feature estimate of the diagnostic light beam 15 Im and the light beam 151 is provided to the light source 150, the output device 155, or to a control apparatus associated with one or more of the light source 150 and the output device 155. The control module 269 can be connected to the sensor 266 through a data connection and can also be in communication with the light source 150 and / or the output device 155. The control module 269 can perform the measurement, analysis, and calculation for each pulse of the light beam 15 Im (and 151) or for a set of pulses of the light beam. The control module 269 can also be connected to or in communication with the calibration apparatus 100 (Fig. 1).

[0044] In the example of Fig. 2, the calculated estimate of the spectral property is a wavelength XI 51 of the light beam 15 Im, 151. The estimated wavelength X151 can correspond to or be based on a center wavelength 256 of the spectral profde 252 of the light beam 15 Im. During operation, the spectral analysis module 261 senses or measures aspects of the spectral profde 252 including the center wavelength 256. The value of the estimated wavelength X151 of the light beam 15 Im, 151 canbe based on this measured center wavelength 256. The value of the estimated wavelength X151 can be based on the spatial components 253 that are sensed by the sensor 266 as well as a calibrated model of the optical path length of the optical separation apparatus 262. For example, a diameter of the rings visible in the spatial components 253 can be indicative of the center wavelength 256 and the optical path length of the optical separation apparatus 262. Over time, the optical path length within the optical separation apparatus 262 can change due to changes in any one or more of the refractive index or the physical separation of the optical flats 368A, 368B or other factors. Because the measurement of the wavelength Z 15 1 of the diagnostic light beam 15 Im is sensitive to the optical path length of the optical separation apparatus 262, degradations such as a changed optical path length experienced by the diagnostic light beam 15 Im can cause errors in the measurement of the wavelength, including the center wavelength 256 of the spectral profde 252, of the diagnostic light beam 15 Im performed by the spectral analysis module 261.

[0045] The calibration apparatus 100 communicates with the spectral analysis module 261 of the metrology apparatus 260 during operation to thereby calibrate the spectral analysis module 261 and the metrology apparatus 260, thus compensating for degradation of the metrology apparatus 260 over time. The calibration apparatus 100 calibrates the metrology apparatus 260 (and the spectral analysis module 261) by adjusting one or more operating parameters of the spectral analysis module 261. For example, the calibration apparatus 100 can adjust any one or more of software parameters, control parameters, and physical parameters of the spectral analysis module 261. In various implementations, the calibration apparatus 100 is configured to deduce an updated measurement of the optical path length of the optical separation apparatus 262. This updated value of the optical path length can then be used for future measurements made by the spectral analysis module 261.

[0046] Referring to Fig. 3, an implementation 362 of the optical separation apparatus 262 is shown. The optical separation apparatus 362 includes an input lens 3621, an etalon 362E, and an output lens 3620. Referring also to Fig. 2, the aperture 267 can be placed at a focal plane of the input lens 3621. By locating the aperture 267 at the focal plane of the input lens 3621, each point from the focal plane acts as a point source and, accordingly, the input lens 3621 acts to collimate the diagnostic light beam 15 Im before entering the etalon 362E. The output lens 3620 is positioned at the exit of the etalon 362E such that a focal plane of the output lens 3620 overlaps the active area of the sensor 266 (Fig. 2). The etalon 362E includes a pair of partially reflective glass or optical flats 368A, 368B, which can be spaced a short distance (for example, sub-millimeters, millimeters, or centimeters) apart with the reflective surfaces facing each other. In other implementations, the etalon 362E includes a single plate with two parallel reflecting surfaces. The flats 368A, 368B can be made in a wedge shape to prevent the rear surfaces from producing interference fringes. The rear surfaces can also have an anti- reflective coating. As the light beam 15 Im passes through the paired flats 368A, 368B, the light beam 15 Im is multiply reflected, and produces a plurality of transmitted rays, which are collected by the output lens 3620 and brought to the active region of the sensor 266 (Fig. 2). The etalon 362E interactswith the light beam 15 Im and outputs the plurality of spatial components (such as the spatial components 253 of Fig. 2) that are indicative of the spectrum of the light beam 15 Im, 151. The etalon 362E transforms the spectral information including the wavelength of the light beam 15 Im, 151 into spatial information that is sensed or detected by the sensor 266. The spatial components produced by the etalon 362E are an interference pattern that appear as a set of concentric rings (such as the spatial components 253 of Fig. 2). The sharpness of the rings depends on the reflectivity of the flats 368A, 368B of the etalon 362E. Thus, when the reflectivity of the flats 368A, 368B is high and the light beam 15 Im is a monochromatic light beam, the etalon 362E produces a fringe pattern of narrow, bright rings against a dark background (as shown in Fig. 2).

[0047] Referring again to Fig. 1, in some implementations, a controller 120 receives the output from the calibration apparatus 100 and the output from the metrology apparatus 160. Specifically, the controller 120 can be in communication with the calibration detector 130 of the calibration apparatus 100 and the control module 269 (Fig. 2) of the metrology apparatus 160. The controller 120 communicates with a wavelength tuning apparatus 121 that is associated with the light source 150.

[0048] In general, the controller 120 includes or has access to memory, which can be read-only memory and / or random access memory. The controller 120 can also include one or more user input devices and one or more user output devices. The controller 120 includes one or more programmable processors, and one or more computer program products tangibly embodied in a machine -readable storage device for execution by a programmable processor. The programmable processor can execute a program of instructions to perform desired functions by operating on input data (such as from the calibration apparatus 100, the metrology apparatus 160, or the light source 150) and generating appropriate output (which can be provided to one or more of the calibration apparatus, the metrology apparatus 160, and the light source 150). The programmable processor can receive instructions and / or data from the memory. The controller 120 can include one or more modules, with each module dedicated to a certain task. Although the controller 120 is represented as a box in which all components can be co-located, it is possible for the controller 120 to be made up of components that are physically remote from each other, or even physically co-located with one or more of the metrology apparatus 160, the light source 150, the calibration apparatus 100, and the output device 155.

[0049] In particular, the controller 120 (under instruction from one or more of the calibration apparatus 100 and the metrology apparatus 160) can command the wavelength tuning apparatus 121 to adjust the wavelength of the light beam 151 so that it temporally varies, or scans, across a range of wavelengths. During calibration, the controller 120 commands the wavelength tuning apparatus 121 to scan across at least one localized surface plasmon resonance of the plasmonic device 105 that is within a tuning range of the light source 150. The localized surface plasmon resonance can correspond to an extreme value (such as a dip or a peak) in the absorption that is detected as the fluence at the calibration detector 130. With respect to the output from the calibration detector 130,the controller 120 can be configured to analyze the detected change of fluence as a function of wavelength induced by the localized surface plasmon resonance. This change in fluence is dependent on the characteristics of the localized surface plasmon resonance, which do not significantly change over time. Analyzing the detected change in fluence as a function of wavelength can be used to detect calibration errors of the metrology apparatus 160, as discussed in more detail below with reference to Fig. 9. The calibration detector 130 can be an optical detector such as a photodiode detector or a photomultiplier tube that measures an intensity or fluence of the light beam 151c’ that has interacted with the plasmonic device 105.

[0050] Referring to Fig. 4, an implementation 405 of the plasmonic device 105 is shown. In order to improve the clarity, the scale of the features of the plasmonic device 405 is not accurate. In this implementation, an optical diffuser 404 is positioned and configured to diffuse the light beam 151c before it enters the plasmonic device 405. The optical diffuser 404 acts to spread the optical power of incoming light beam 151c, that is, to diffuse the optical energy in the beam profile of the light beam 151c, making the spatial and / or angular distribution of the light smoother than the original incoming light beam 151c. The optical diffuser 404 homogenizes and smooths the profile of the light beam 151c. The optical diffuser 404 can operate by transmission (with the light beam 151c passing through) or by reflection (with the light beam 151c reflecting from it).

[0051] The plasmonic device 405 includes a matrix 406 of plasmonic nanostructures 407. The nanostructures 407 can be any suitable shape such as, for example, hemispherical (as shown in Fig. 4 and also Figs. 5A, 5B, 7A, and 7B), tubular or cylindrical (as shown in Figs. 6A, 6B, 8A, and 8B) or other shapes such as, for example, star-shaped, conical, spherical, or trapezoidal. The matrix 406 can extend as an array in a two-dimensional plane, the X_p, Y_p plane.

[0052] In some implementations, each plasmonic nanostructure has a scale or extent that is smaller than a wavelength of the light beam 151c. For example, if the light beam 151c has a wavelength of 193 nm (in the DUV range), then each nanostructure 407 has an extent or scale that is smaller than 193 nm and if the light beam 151c has a wavelength of 248 nm (in the DUV range), then each nanostructure 407 has an extent or scale that is smaller than 248 nm. In other implementations, some or all of the nanostructures 407 have an extent or scale that is comparable to the wavelength of the light being analyzed. As shown in the insert of Fig. 4, the scale or extent of the nanostructure 407 is given along a direction in the plane X_p, Y_p as 407el and along a direction Z_p that is perpendicular to the plane as 407e2. The extent 407el and the extent 407e2 can be smaller than 193 nm or smaller than 248 nm, in the examples above. In some implementations, the extent 407el and the extent 407e2 are smaller than 100 nm, smaller than 50 nm, smaller than 20 nm, or on the order of 1 nm. In some implementations, the extent 407el and the extent 407e2 are on the order of 10 nm to 50 nm. Additionally, as shown in the inset of Fig. 4, adjacent nanostructures 407 can be spaced apart or separated from each other in the X_p, Y_p plane by a distance 407d that is smaller than the wavelength of the light beam 151c, and can be in a range of between 5 nm and 20 nm. The overallextent of the matrix 406 in the X_p, Y_p plane can be any size suitable to receive the diffused beam from the optical diffuser 404, such as, for example, on the order of 1-10 centimeters (cm). The overall extent of the matrix 406 along the Z_p direction can be on the order of millimeters (mm), submillimeter, or hundreds of nanometers.

[0053] The plasmonic nanostructures 407 are configured to be optically transparent to the wavelength of the light beam 151c. The plasmonic nanostructures 407 can be metallic. For example, the plasmonic nanostructures 407 can be made of any of the following materials: aluminum, gallium, tin, titanium, lead, bismuth, indium, or hafnium (IV) oxide.

[0054] Next, different implementations of the plasmonic device 105 are discussed with reference to Figs. 5A-8B, which show general schematic depictions of the plasmonic device 105. As noted below, in order to facilitate clarity, the scale of the features of the plasmonic devices in these images is not accurate. In the implementations discussed next, the plasmonic devices of Figs. 5A, 5B, 6A, and 6B are optically transmissive devices while the plasmonic devices of Figs. 7A, 7B, 8A, and 8B are optically reflective devices. Each plasmonic device in Figs. 5A-8B includes a two-dimensional matrix of plasmonic nanostructures, with each plasmonic nanostructure having a scale or extent that is smaller than a wavelength of the light beam 151c.

[0055] Referring to Figs. 5A and 5B, an implementation 505 of the plasmonic device 105 is shown. The plasmonic device 505 includes a two-dimensional matrix 506 of nanostructures 507 arranged relative to a substrate 510. Specifically, the matrix 506 is applied to (that is, fixed to) a surface 508 of the substrate 510 and is formed as an array that extends in the X_p, Y_p plane. The nanostructures 507 can be partly embedded in the surface 508, as depicted in Fig. 5B. In this implementation 505, the plasmonic device 505 is a transmissive device, and thus, the light beam 151c passes through the matrix 506 and the substrate 510 and the calibration detector 130 (Fig. 2) is arranged to receive the light beam 151c’ that is transmitted through the plasmonic device 505. In the plasmonic device 505, the nanostructures 507 are hemispheres or hemispherical in shape. The matrix 506 and the substrate 510 are optically transparent to the wavelength of the light beam 151c; thus, if the light beam 151c is in the DUV range, then the matrix 506 and the substrate 510 are optically transparent to DUV light.

[0056] Referring to Figs. 6A and 6B, another implementation 605 of the plasmonic device 105 is shown. The plasmonic device 605 is similar to the plasmonic device 505, except that the plasmonic device 605 includes a two-dimensional matrix 606 of tubular or cylindrical nanostructures 607 arranged relative to a substrate 610. The matrix 606 is applied to (that is, fixed to) a surface 608 of the substrate 610 and is formed as an array that extends in the X_p, Y_p plane. The nanostructures 607 can be partly embedded in the surface 608, as depicted in Fig. 6B. The calibration detector 130 (Fig. 2) is arranged to receive the light beam 151c’ that is transmitted through the plasmonic device 605. The matrix 606 and the substrate 610 are optically transparent to the wavelength of the light beam 151c; thus, if the light beam 151c is in the DUV range, then the matrix 606 and the substrate 610 are optically transparent to DUV light.

[0057] Referring to Figs. 7A and 7B, an implementation 705 of the plasmonic device 105 is shown. The plasmonic device 705 includes a two-dimensional matrix 706 of nanostructures 707 arranged relative to a substrate 710. The plasmonic device 705 also includes a base material 711. The substrate 710 acts as a spacer and separates the matrix 706 and the base material 711. The matrix 706 is applied to (that is, fixed to) a surface 708 of the substrate 710 and is formed as an array that extends in the X_p, Y_p plane. The nanostructures 707 can be partly embedded in the surface 708, as depicted in Fig. 7B. In this implementation, the plasmonic device 705 is a reflective device. Thus, the light beam 151c passes through the matrix 706 and the substrate 710, and is reflected from the base material 711, passing back through the substrate 710 and the matrix 706 and then directed to the calibration detector 130 (Fig. 2). The calibration detector 130 is arranged to receive the light beam 151c’ that is reflected from the plasmonic device 705. In the plasmonic device 705, the nanostructures 707 are hemispheres or hemispherical in shape. The matrix 706 and the substrate 710 are optically transparent to the wavelength of the light beam 151c; thus, if the light beam 151c is in the DUV range, then the matrix 706 and the substrate 710 are optically transparent to DUV light. The arrangement of the base material 711 relative to the substrate 710 produces locally enhanced electric field through plasmonic coupling. The base material 711 acts as an optical mirror.

[0058] Referring to Figs. 8A and 8B, another implementation 805 of the plasmonic device 105 is shown. The plasmonic device 805 is similar to the plasmonic device 705, except that the plasmonic device 805 includes a two-dimensional matrix 806 of tubular or cylindrical nanostructures 807 arranged relative to a substrate 810. The matrix 806 is applied to (that is, fixed to) a surface 808 of the substrate 810 and is formed as an array that extends in the X_p, Y_p plane. The nanostructures 807 can be partly embedded in the surface 808, as depicted in Fig. 8B. The calibration detector 130 (Fig.2) is arranged to receive the light beam 151c’ that is reflected from the plasmonic device 805. The matrix 806 and the substrate 810 are optically transparent to the wavelength of the light beam 151c; thus, if the light beam 151c is in the DUV range, then the matrix 806 and the substrate 810 are optically transparent to DUV light.

[0059] In general, the nanostructures 507, 607, 707, 807 are configured to be transparent to the wavelength of the light beam 151c. As discussed above, the nanostructures 507, 607, 707, 807 can be made of any of the following metals: aluminum, gallium, tin, titanium, lead, bismuth, indium, or hafnium(IV) oxide. Moreover, as discussed with reference to Fig. 4, the scale of each nanostructure 507, 607, 707, 807 is smaller than the wavelength of the light beam 151c. As shown in Fig. 5A, the scale or extent of the nanostructure 507 is given along a direction in the X_p, Y_p plane as 507el and along a direction Z_p perpendicular to the plane as 507e2. As shown in Fig. 6A, the scale or extent of the nanostructure 607 is given along a direction in the X_p, Y_p plane as 607el and along a direction Z_p perpendicular to the plane of the surface 608 as 607e2. As shown in Fig. 7A, the scale or extent of the nanostructure 707 is given along a direction in the X_p, Y_p plane as 707el and along a direction Z_p perpendicular to the plane as 707e2. As shown in Fig. 8A, the scale or extent of thenanostructure 807 is given along a direction in the X_p, Y_p plane as 807el and along a direction Z_p perpendicular to the plane as 807e2.

[0060] Each of the substrates 510, 610, 710, 810 can be non-metallic. As mentioned, the substrates 510, 610, 710, 810 are made of a material that is optically transparent to the wavelength of the light beam 151c and also compatible with the material of the nanostructures 507, 607, 707, 807. The substrates 510, 610, 710, 810 can be in a solid state. In some implementations, the substrate 510, 610, 710, 810 is made of sapphire (AI2O3). In other implementations, the substrate 510, 610, 710, 810 is made of Si O2 with multiwalled carbon nanotubes matrix composites. In other implementations, the substrate 510, 610, 710, 810 is made of Si-doped Ga2C>3. The substrates 510, 610, 710, 810 can generally have a refractive index that is dependent on a wavelength of the light beam 151c. For example, different wavelengths of the light beam 151c can interfere in different ways with the atoms in the substrate 510, 610, 710, 810. Similarly, the refractive index of the nanostructures 507, 607, 707, 807 can depend on the wavelength of the light beam 151c, the material of the nanostructures, and the orientation of the nanostructures. For example, hafnium can have a refractive index of about 2.2 for light having a wavelength in the DUV range. As another example, sapphire can have a refractive index of 1.7 for light having a wavelength of 500 nm at a specific crystal orientation 0001. Aluminum nanospheres can have a refractive index of 1 at a wavelength of 120 nm and a refractive index of 1.7 at a wavelength of 220 nm.

[0061] With reference to the plasmonic device 705, 805 of Figs. 7A, 7B and 8A, 8B, respectively, the base material 711, 811 can be a material in a solid state . The base material 711, 811 can be made of the same material as the nanostructures 707, 807. For example, if the nanostructures 707, 807 are a particular metal, then the respective base material 711 , 811 is the same particular metal . In one implementation, the nanostructures 707, 807 are made of aluminum and the base material 711, 811 is made of aluminum.

[0062] As discussed above, at least one localized surface plasmon resonance of the plasmonic device 105, 405, 505, 605, 705, 805 is within a tuning range of the light source 150. The localized surface plasmon resonance can correspond to an extreme value such as a dip or a peak in the absorption that is detected as the fluence at the calibration detector 130. The wavelength at which there is a dip / peak in the fluence may correspond to a change in the absorption and may be dependent on a thickness of the underlying substrate 510, 610, 710, 810, the thickness taken along the Z_p direction. A spectral bandwidth of the plasmonic material within the nanostructures 507, 607, 707, 807 may be determined in part by a thickness of the underlying substrate 510, 610, 710, 810.

[0063] In the plasmonic device 705, 805 of Figs. 7A, 7B and 8A, 8B, respectively, the base material 711, 811 and the nanostructures 707, 807 may both be plasmonic materials. If a distance D7, D8 between the respective matrix 706, 806 and the respective base material 711, 811 is small enough, then the effects can be coupled, which means that they can produce a locally enhanced electric field. The distance D7 or D8 directly affects an intensity of the coupling and the tunability of the opticalresponse of the plasmonic device 705, 805, respectively. Moreover, by coupling these plasmonic structures (the nanostructures 707, 807 and the respective base materials 711, 811), the symmetry of the electromagnetic field intensity and distribution is shared and broken, and this allows for multiple orders of modes of plasmonic excitement to develop.

[0064] In one implementation of the plasmonic devices 505, 605, the nanostructures 507, 607 are made of aluminum and the substrates 510, 610 are made of sapphire. The optical response to the light beam 151c can be selected by modifying the shape or diameter / extent of the nanostructures 507, 607, and the refractive index of the sapphire substrate 510, 610. For example, for a first extent of the nanostructure 507, 607 and a first refractive index of the substrate 510, 610, a nanostructure 507 that is a hemisphere that is partly embedded in a high refractive index sapphire can exhibit a localized surface plasmon resonance near about 193 nm. As another example, for a second extent of the nanostructure 507, 607 and a second refractive index of the substrate 510, 610, a hemispherical nanostructure 507 that is partly embedded in a high refractive index sapphire can exhibit a localized surface plasmon resonance near about 248 nm.

[0065] Moreover, when aluminum nanostructures 707, 807 are embedded in a respective sapphire substrate 710, 810 with an aluminum base material 711, 811, respectively (Figs. 7A, 7B, 8A, 8B), their symmetry can be broken and there can be a plurality of localized surface plasmon resonances, at least one being within the DUV wavelength sub-range of the light source 150. For example, a coupling of dipolar and quadripolar modes can give sharp / strong resonances within the DUV wavelength range that are tunable depending on the size or extent of the nanostructures 707, 807 and the thickness D7, D8 of the respective substrate 710, 810. As an example, it is possible for hemispherical aluminum nanostructures 707, 807 having a 50 nm extent on a 15 nm thick sapphire substrate 710, 810 to exhibit a localized surface plasmon resonance near 193 nm. As a further example, it is possible for hemispherical aluminum nanostructures 707, 807 having a 50 nm extent on a 10 nm thick sapphire substrate 710, 810 to exhibit a localized surface plasmon resonance near 248 nm. The dimensions noted (the shape and extent of the nanostructures and the refractive index of the materials) can be changed to tune this resonance.

[0066] In other implementations of the plasmonic device 405, the matrix 407 of plasmonic nanostructures 407 can be a three-dimensional matrix and thus it can extend as an array in the three- dimensional space, the X_p, Y_p, Z_p space.

[0067] Referring to Fig. 9, an implementation 960 of the metrology apparatus 160 is arranged relative to an implementation 900 of the calibration apparatus 100. The metrology apparatus 960 can be designed like the metrology apparatus 260 and include an aperture 967 through which the light beam 151m passes. The calibration apparatus 900 includes an aperture 901, a plasmonic device 905, and a calibration detector 930. In other implementations, the calibration apparatus 900 can include additional components than those shown in Fig. 9. The controller 120 communicates with thecalibration detector 930 and the metrology apparatus 960 (and specifically the control module 969) through one or more data connections, each of which can be wired or wireless.

[0068] The calibration apparatus 900 receives the diagnostic light beam 151c from the light source 150 through the aperture 901. An optical diffuser 904 is positioned and configured to diffuse the light beam 151c before it enters the plasmonic device 905. The diagnostic light beam 151c interacts with the plasmonic device 905 to produce an extinction (for example, absorption) profile 915 of the energy transition (the localized surface plasmon resonance) of the plasmonic device 905, and the calibration detector 930 detects this absorption profile 915. The absorption profile 915 shows the relationship between a characteristic associated with the interaction between the diagnostic light beam 151c and the plasmonic device 905, and the wavelength of the diagnostic light beam 151c (as reported by the metrology apparatus 960). Thus, the absorption profile 915 is displayed as a graph of the characteristic (measured by the calibration detector 930) versus the wavelength of the diagnostic light beam 151c. In order to detect the extreme value (that is, the dip or the peak) in the absorption profile 915, the wavelength of the diagnostic light beam 151c is scanned across the energy transition (for example under control of the controller 120 and the wavelength tuning apparatus 121 of Fig. 1). This scan is performed while keeping an output energy of the light beam 151 (and the light beams 151c, 151m) constant.

[0069] The plasmonic device 905 has at least one known localized surface plasmon resonance at a wavelength rcf that coincides with the wavelength range of the diagnostic light beam 151c (and also the light beam 151). When the wavelength of the light beam 151c coincides with the absorption wavelength (at the known localized surface plasmon resonance), a substantial reduction in the fluence signal (for example, a reduction of 10-50%) is observed at the calibration detector 930. During the scan, two corresponding sets of data are taken, the signal from the calibration detector 930 and the wavelength as measured by the metrology apparatus 960. The signal from the calibration detector 930 is plotted against the wavelength reported by the metrology apparatus 960.

[0070] Specifically, the wavelength of the light beam 15 Im is scanned by the wavelength tuning apparatus 121, and the metrology apparatus 960 outputs the estimated wavelength 1151 (Fig. 2) of the light beam 15 Im (based on the center wavelength 256) and this is provided to the controller 120. As discussed above, the spectral analysis module 261 (within the metrology apparatus 960) can estimate the wavelength 1151 of the light beam 15 Im based on the measurement relating to the spatial components 253 that are sensed by the sensor 266 as well as the calibrated model of the optical path length of the optical separation apparatus 262. Moreover, as the wavelength of the light beam 15 Im is scanned by the wavelength tuning apparatus 121, the calibration detector 930 outputs the absorption profile 915 of the light beam 151c to the controller 120.

[0071] The controller 120 analyzes the data from the calibration detector 930 and determines an apparent center wavelength Xc, which corresponds to the center of the extreme in the fluence (which, in this example, is the absorption dip) in the profile 915. Since the true wavelength Zrcf of thelocalized surface plasmon resonance is known with precision, the calibration error (depicted as CE) can be calculated by the controller 120. The calibration error corresponds to a difference (Xref - Zc) between the known or true wavelength Zrcf and the apparent wavelength Xc. The controller 120 uses the error (Zrcf - c) to automatically correct the calibration constants used in the algorithms of the metrology apparatus 960. For example, the controller 120 can adjust one or more operating parameters of the spectral analysis module 261 within the metrology apparatus 960 until it determines that the internally reported wavelength Xc is equal to or close enough to the value Xref. Once these two values (Xc and Xref) are equal or within an acceptable range of each other, then the spectral analysis module 261 and the metrology apparatus 960 is calibrated.

[0072] The calibration of the metrology apparatus 960 performed by the calibration apparatus 900 can take several minutes to perform and complete. For example, a calibration can take one (1) to five (5) minutes to perform and complete. During calibration of the metrology apparatus 960, the output device 155 (Fig. 1) is not receiving the light beam 151 within a required specification, and therefore the output device 155 is not operating. This down time in operation of the output device 155 due to calibration reduces the output and production of the output device 155. For this reason, the calibration apparatus 900 is designed with the plasmonic device 905 to thereby reduce the down time in operation of the output device 155.

[0073] Referring to Fig. 10, in some implementations, a photolithography system 1070 includes a light source 1050 that produces a light beam 1051 having a wavelength that is nominally at a center wavelength and is directed to a photolithography exposure apparatus or scanner 1055 by way of a beam preparation system 1071 that can include beam directing and beam modification optics. The light source 1050 is an implementation of the light source 150 and the exposure apparatus 1055 is an implementation of the output device 155 of Fig. 1. The photolithography system 1070 also includes an implementation 1060 of the metrology apparatus 160, an implementation 1000 of the calibration apparatus 100 arranged relative to the metrology apparatus 1060, and an implementation 1020 of the controller 120. The metrology apparatus 1060 receives the diagnostic light beam 105 Im, which is the portion of the light beam 1051 that has been split off from the light beam 1051 by a beam splitter 1072.

[0074] The light beam 1051 is produced by an optical source 1073 and is directed to a wafer 1040 in the exposure apparatus 1055 to thereby pattern microelectronic features on the wafer 1040. The light beam 1051 has a wavelength in the DUV range, for example, about 248 nanometers (nm) or about 193 nm. The size of the microelectronic features patterned on the wafer 1040 depends on the wavelength of the light beam 1051, with a lower wavelength resulting in a smaller minimum size. When the wavelength of the light beam 1051 is 248 nm or 193 nm, the minimum size of the microelectronic features can be, for example, 50 nm or less.

[0075] Various disturbances (such as, for example, temperature gradients, pressure gradients, optical distortions) act on the optical source 1073 and the light beam 1051 to modify the spectral properties orfeatures (such as the wavelength) of the light beam 1051. Thus, the photolithography system 1070 includes other components, such as, for example, a spectral feature selection system 1074 which can be a part of the wavelength tuning apparatus 121, the metrology apparatus 1060 that is configured to measure aspects (such as the wavelength) relating to the light beam 1051, and a control system 1075, that are used in combination to determine the impact of the disturbances on the light beam 1051 and to correct for the effect of such disturbances on the light beam 1051. In some implementations, the controller 1020 is a dedicated system apart from the control system 1075 while in other implementations, one or more components of the controller 1020 can be implemented within the control system 1075.

[0076] The spectral feature selection system 1074 and / or the wavelength tuning apparatus 121 can include one or more optical elements that interact with a pre-cursor light beam 105 Ip and an actuation system that is configured to control one or more of the optical elements. These optical elements can include at least one dispersive optical element such as an optical grating and a beam expander including a set of refractive optical elements such as prisms. The optical elements are made of materials that are suitable for interacting with the wavelength of the pre-cursor light beam 105 Ip.

[0077] In some implementations, the optical source 1073 is an excimer optical source that outputs the pulsed light beam 1051 (which can be a laser beam). As the pulsed light beam 1051 enters the photolithography exposure apparatus 1055, it is directed through a projection optical system 1041 and projected onto the wafer 1040 to form one or more features on a photoresist on the wafer 1040. The features on the photoresist may include exposure patterns that serve as a key basis for, for example, etching, deposition, implantation, metallization, and / or other semiconductor fabrication steps. These steps can be used to form semiconductor devices, integrated circuits, microelectronic devices, or other electronic devices based on these exposure patterns. The photolithography exposure apparatus 1055 can also include a controller 1042 that can communicate with one or more of the control system 1075 and the controller 1020.

[0078] In the implementation shown, the optical source 1073 is a two-stage system that includes a master oscillator (MO) 1073MO that provides a seed light beam to a power amplifier (PA) 1073PA. The MO 1073MO and the PA 1073PA can be considered to be subsystems of the optical source 1073 or systems that are part of the optical source 1073. The power amplifier 1073PA receives the seed light beam from the master oscillator 1073MO and amplifies the seed light beam to generate the light beam 1051 for use in the photolithography exposure apparatus 1055. For example, the master oscillator 1073MO can emit a pulsed seed light beam with seed pulse energies of approximately 1 millijoule (mJ) per pulse, and these seed pulses can be amplified by the power amplifier 1073PA to about 10 to 15 mJ. The master oscillator 1073MO includes a MO discharge chamber having two elongated electrodes (which constitute an excitation mechanism), a gain medium that is a gas mixture, and a fan for circulating gas between the electrodes. A resonator is formed between the spectral feature selection system 1074 on one side of the discharge chamber of the master oscillator 1073MOand an output coupler on a second side of the discharge chamber master oscillator 1073MO. The power amplifier 1073PA includes a beam coupling optical system that receives the seed light beam from the master oscillator 1073MO and directs the seed light beam through a PA discharge chamber, and to a beam turning optical element, which modifies or changes the direction of the seed light beam so that it is sent back into the PA discharge chamber. The PA discharge chamber includes a pair of elongated electrodes, a gain medium that is a gas mixture, and a fan for circulating the gas mixture between the electrodes.

[0079] The gas mixture of the gain media used in respective discharge chambers can be any gas suitable for producing a light beam at the wavelength and bandwidth required for the application at the output device 155 (such as the photolithography exposure apparatus 1055). For an excimer source, the gas mixture can contain a noble gas (rare gas) such as, for example, argon or krypton, a halogen, such as, for example, fluorine or chlorine and traces of xenon apart from helium and / or neon as buffer gas. Specific examples of the gas mixture include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, krypton fluoride (KrF), which emits light at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of about 351 nm. The excimer gain medium (the gas mixture) is pumped with short (for example, nanosecond) current pulses in a high- voltage electric discharge by application of a voltage (the excitation signal) to the respective elongated electrodes. The light beam 1051 is a pulsed light beam and can include one or more bursts of pulses that are separated from each other in time. Each burst can include one or more pulses of light. In some implementations, a burst includes hundreds of pulses, for example, 100-400 pulses. As discussed above, when the gain medium within the MO and the PA is pumped by applying voltage to the electrodes, the gain medium in the MO or PA emits light. When the voltage is applied to the electrodes in pulses, the light emitted from the gain medium is also pulsed. Thus, the repetition rate of the pulsed light beam 1051 is determined by the rate at which voltage is applied to the electrodes, with each application of voltage producing a pulse of light. The pulse of light propagates through the gain medium and exits the chamber through the output coupler. Thus, a train of pulses is created by periodic, repeated application of voltage to the electrodes. The repetition rate of the pulses can range between about 500 Hz and 6,000 Hz. In some implementations, the repetition rate is be greater than 6,000 Hz, and can be, for example, 12,000 Hz or greater. The pulsed light beam 1051 can have an average output power in the range of tens of watts, for example, from about 50 W to about 130 W. The irradiance (that is, the average power per unit area) of the light beam 1051 at the output may range from 60 W / cm2 to 80 W / cm2.

[0080] Referring to Fig. 11, a procedure 1180 is performed to calibrate the metrology apparatus 160. The wavelength-tunable light beam 151 is generated (1181). For example, the light source 150 generates the light beam 151, 15 Im, 151c (Fig. 1) in accordance with instructions from the output device 155 and also based on the settings in the wavelength tuning apparatus 121. The generated light beam is directed along a calibration path to interact with a plasmonic device (1182). For example, thelight beam 151c is directed to interact with the plasmonic device 105 within the calibration apparatus 100. The fluence of the light beam that has interacted with the plasmonic device is detected (1183). For example, the calibration detector 130 within the calibration apparatus 100 detects a fluence of the light beam 151c’ that has interacted with the plasmonic device 105. The metrology apparatus is calibrated based on the detected fluence (1184). For example, the controller 120 can receive the output from the calibration detector 130 and the data from the metrology apparatus 160 to analyze the fluence of the light beam 151c’, determine the calibration error of the metrology apparatus 160, and adjust parameters of the metrology apparatus 160 to reduce or eliminate the calibration error.

[0081] The implementations can be further described using the following clauses.1. A calibration apparatus for a wavelength-tunable deep ultraviolet (DUV) light source, the calibration apparatus comprising: a plasmonic device in a path of a light beam from a discharge chamber; and a calibration detector that receives the light beam exiting the plasmonic device, the calibration detector configured to detect a fluence of the light beam.2. The calibration apparatus of clause 1, wherein a controller is configured to command a wavelength tuning apparatus to scan the wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within the tuning range of the DUV light source.3. The calibration apparatus of clause 2, wherein the controller is in communication with the calibration detector and is configured to analyze the detected change of fluence induced by the localized surface plasmon resonance.4. The calibration apparatus of clause 3, wherein the localized surface plasmon resonance corresponds to an absorption extreme in the detected fluence.5. The calibration apparatus of clause 3, wherein the controller is in communication with a metrology apparatus that estimates a wavelength of the light beam.6. The calibration apparatus of clause 5, wherein the controller is configured to determine a calibration error of the metrology apparatus based on an analysis of the output of the calibration detector relative to the wavelength estimated by the metrology apparatus.7. The calibration apparatus of clause 6, wherein the controller is configured to adjust the calibration of the metrology apparatus based on the determined calibration error.8. The calibration apparatus of clause 6, wherein the calibration error corresponds to a difference between the known wavelength at the localized surface plasmon resonance and an apparent wavelength corresponding to an extreme in the fluence of the output of the calibration detector.9. The calibration apparatus of clause 3, wherein the controller is in communication with a metrology apparatus that estimates a bandwidth of the light beam.10. The calibration apparatus of clause 9, wherein the controller is configured to determine a calibration error of the metrology apparatus based on an analysis of the output of the calibration detector relative to the bandwidth estimated by the metrology apparatus.11. The calibration apparatus of clause 1, wherein the plasmonic device comprises a two or three- dimensional matrix of metallic nanostructures arranged relative to a non-metallic substrate.12. The calibration apparatus of clause 11, wherein the calibration detector is arranged to receive the light beam that is transmitted through the plasmonic device.13. The calibration apparatus of clause 11, wherein the metallic nanostructures are hemispheres or tubes.14. The calibration apparatus of clause 11, wherein the substrate includes a DUV transparent material.15. The calibration apparatus of clause 14, wherein the substrate includes at least one of sapphire, SiCh with multiwalled carbon nanotubes matrix composites, and Si-doped Ga2C>3.16. The calibration apparatus of clause 11, wherein the light beam has an operating range within the DUV wavelength range between about 190 nanometers (nm) and about 280 nm.17. The calibration apparatus of clause 11, wherein the metallic nanostructures comprise at least one of aluminum, gallium, tin, titanium, lead, bismuth, indium, and hafhium(IV) oxide.18. The calibration apparatus of clause 1, wherein the plasmonic device comprises a two or three- dimensional matrix of nanostructures comprising a metal, a substrate at which the matrix is arranged, and a base material, the base material and the matrix being separated by the substrate, thereby producing a locally enhanced electric field through plasmonic coupling.19. The calibration apparatus of clause 18, wherein the calibration detector is arranged to receive the light beam that is reflected from the plasmonic device.20. The calibration apparatus of clause 18, wherein the metallic nanostructures are hemispheres or tubes.21. The calibration apparatus of clause 18, wherein the base material is made of the same metal as the metallic nanostructures, and the substrate is non-metallic and DUV transparent.22. The calibration apparatus of clause 18, wherein an absorbing wavelength and a spectral bandwidth of the plasmonic material is partly determined by a thickness of the substrate.23. The calibration apparatus of clause 18, wherein the light beam has an operating range within the DUV wavelength range between about 190 nanometers (nm) and about 280 nm.24. The calibration apparatus of clause 18, wherein the metallic nanostructures include at least one of aluminum, gallium, tin, titanium, lead, bismuth, indium, and hafnium (IV) oxide.25. The calibration apparatus of clause 1, wherein the plasmonic device comprises a two- or three- dimensional matrix of plasmonic nanostructures, each plasmonic nanostructure having a scale that is smaller than the wavelength of the light beam.26. The calibration apparatus of clause 25, wherein adjacent nanostructures are spaced apart from each other by a distance in a range between about 5 nm and about 20 nm.27. The calibration apparatus of clause 1, wherein the plasmonic device is a solid-state material.28. The calibration apparatus of clause 1, further comprising a diffuser that diffuses a light beam before it enters the plasmonic device.29. A method of calibrating a metrology apparatus of a deep ultraviolet (DUV) light source, the method comprising: generating a wavelength-tunable light beam from the DUV light source; directing the generated light beam along a calibration path to interact with a plasmonic device; detecting a fluence of the light beam that has interacted with the plasmonic device; and calibrating the metrology apparatus based on the detected fluence.30. An exposure apparatus comprising: a gain medium, an energy pump, and an optical resonator for generating a light beam; a metrology apparatus configured to measure a wavelength of the generated light beam; a calibration apparatus comprising: a plasmonic device in a calibration path of the light beam; and a calibration detector that receives the light beam exiting the plasmonic device, the calibration detector configured to detect a fluence of the light beam; and a controller in communication with the metrology apparatus and the calibration apparatus, the controller configured to calibrate the metrology apparatus based on the detected fluence of the light beam.31. The exposure apparatus of clause 30, wherein the controller is configured to command a wavelength tuning apparatus to scan the wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within a tuning range of the DUV light source.32. The exposure apparatus of clause 31, wherein the controller is configured to compare the known wavelength of the light beam at the localized surface plasmon resonance with the apparent center wavelength of the light beam measured by the metrology apparatus.33. The exposure apparatus of clause 30, wherein the plasmonic device comprises a plurality of metallic nanostructures arranged relative to a non-metallic substrate, and the non-metallic substrate includes a material transparent to a wavelength range between about 190 nanometers (nm) and 280 nm.34. The exposure apparatus of clause 33, wherein each metallic nanostructure has a first dimension extending along a direction in parallel to the beam light, the first dimension being smaller than 193 nm.35. A process of making a semiconductor device comprising calibrating a metrology apparatus of a deep ultraviolet (DUV) light source and subsequently exposing a photoresist on a semiconductor substrate with light from the DUV light source, wherein the calibrating comprises: generating a wavelength-tunable light beam from the DUV light source; directing the generated light beam along a calibration path to interact with a plasmonic device; detecting a fluence of the light beam that has interacted with the plasmonic device; and calibrating the metrology apparatus based on the detected fluence.

[0082] The above-described implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A calibration apparatus for a wavelength-tunable deep ultraviolet (DUV) light source, the calibration apparatus comprising: a plasmonic device in a path of a light beam from a discharge chamber; and a calibration detectorthat receives the light beam exiting the plasmonic device, the calibration detector configured to detect a fluence of the light beam.

2. The calibration apparatus of claim 1, wherein a controller is configured to command a wavelength tuning apparatus to scan a wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within a tuning range of the DUV light source.

3. The calibration apparatus of claim 2, wherein the controller is in communication with the calibration detector and is configured to analyze the detected change of fluence induced by the at least one localized surface plasmon resonance.

4. The calibration apparatus of claim 3, wherein the at least one localized surface plasmon resonance corresponds to an absorption extreme in the detected fluence.

5. The calibration apparatus of claim 3, wherein the at least one controller is in communication with a metrology apparatus that estimates the wavelength of the light beam, and the controller is configured to determine a calibration error of the metrology apparatus based on an analysis of an output of the calibration detector relative to the wavelength estimated by the metrology apparatus.

6. The calibration apparatus of claim 5, wherein the controller is configured to adjust the calibration of the metrology apparatus based on the determined calibration error.

7. The calibration apparatus of claim 5, wherein the calibration error corresponds to a difference between a known wavelength at the localized surface plasmon resonance and an apparent wavelength corresponding to an extreme in the fluence of the output of the calibration detector.

8. The calibration apparatus of claim 1, wherein the plasmonic device comprises a two or three-dimensional matrix of metallic nanostructures arranged relative to a non-metallic substrate, and the metallic nanostructures are hemispheres or tubes.

9. The calibration apparatus of claim 8, wherein the non-metallic substrate includes at least one of sapphire, SiCh with multiwalled carbon nanotubes matrix composites, and Si-doped Ga2C>3.

10. The calibration apparatus of claim 1, wherein the plasmonic device comprises a two or three-dimensional matrix of nanostructures comprising a metal, a substrate at which the matrix is arranged, and a base material, the base material and the matrix being separated by the substrate, thereby producing a locally enhanced electric field through plasmonic coupling.

11. The calibration apparatus of claim 1, wherein the plasmonic device comprises a two- or three-dimensional matrix of plasmonic nanostructures, each plasmonic nanostructure having a scale that is smaller than the wavelength of the light beam, and adjacent nanostructures are spaced apart from each other by a distance in a range between 5 nm and 20 nm.

12. A method of calibrating a metrology apparatus of a deep ultraviolet (DUV) light source, the method comprising: generating a wavelength-tunable light beam from a discharge chamber; directing the generated light beam along a calibration path to interact with a plasmonic device, wherein the plasmonic device includes a two or three-dimensional matrix of metallic nanostructures arranged relative to a non-metallic substrate; detecting a fluence of the light beam that has interacted with the plasmonic device; and calibrating the metrology apparatus based on the detected fluence.

13. The method of claim 12, wherein the two or three-dimensional matrix of metallic nanostructures have a hemisphere or tube configuration.

14. An exposure apparatus comprising: a gain medium, an energy pump, and an optical resonator for generating a light beam; a metrology apparatus configured to measure a wavelength of the generated light beam; a calibration apparatus comprising: a plasmonic device in a calibration path of the light beam; and a calibration detector that receives the light beam exiting the plasmonic device, the calibration detector configured to detect a fluence of the light beam; and a controller in communication with the metrology apparatus and the calibration apparatus, the controller configured to calibrate the metrology apparatus based on the detected fluence of the light beam.

15. The exposure apparatus of claim 14, wherein the controller is configured to command a wavelength tuning apparatus to scan the wavelength of the light beam across at least one localized surface plasmon resonance of the plasmonic device, the at least one localized surface plasmon resonance being within a tuning range of the DUV light source.

16. The exposure apparatus of claim 15, wherein the controller is configured to compare the known wavelength of the light beam at the localized surface plasmon resonance with the apparent center wavelength of the light beam measured by the metrology apparatus.

17. The exposure apparatus of claim 14, wherein the plasmonic device comprises a plurality of metallic nanostructures arranged relative to a non-metallic substrate, and the non-metallic substrate includes a material transparent to a wavelength range between about 190 nanometers (nm) and 280 nm.

18. The exposure apparatus of claim 17, wherein the metallic nanostructures include at least one of aluminum, gallium, tin, titanium, lead, bismuth, indium, and hafnium(IV) oxide.

19. The exposure apparatus of claim 17, wherein each metallic nanostructure has a first dimension extending along a direction in parallel to the beam light, the first dimension being smaller than 193 nm.

20. The exposure apparatus of claim 14, further comprising a diffuser that diffuses the light beam before it enters the plasmonic device.

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