Electron spectroscopy apparatus and method

Abstract

A method for determining the chemical composition of a sample using electron spectroscopy is described, the method including ablating material from a region by irradiating a surface of the sample with one or more laser pulses on the region, irradiating at least a portion of the region with an excitation beam of electron radiation or electromagnetic radiation, measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam, and repeating the steps of ablat- ing material, irradiating with the excitation beam, and measuring the intensity and energy to determine a quantitative surface depth profile of the chemical composition of at least a portion of the sample. An electron spectroscopy apparatus for determining the chemical composition of a sample is also described.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for electron spectroscopy, including depth profiling. In particular, the apparatus and method provide improved compositional accuracy, faster depth profiling, and increased depth of investigation. [Background technology]

[0002] Surfaces and interfaces of materials represent the boundary between a solid and its environment, or between two contacting surfaces. As such, surfaces and interfaces are the sites of fundamentally important chemical, physical, electrical, and mechanical processes that enable and influence the operation and performance of structures, machines, devices, and organisms.

[0003] In engineering applications, important physiochemical processes such as corrosion, oxidation, wear, and adhesion occur at surfaces and interfaces. Understanding such phenomena allows material scientists and engineers to optimize their benefits and mitigate their detrimental effects. Such mitigation measures include surface engineering processes, such as the deposition of protective coatings, or enhancing the mechanical properties of surfaces through hardening or strengthening processes. Meanwhile, stronger adhesives are being developed through the optimization of chemical formulations, allowing for the formation of stronger bonds between the adhesive and the material surface.

[0004] Surfaces and interfaces are crucial for the operation of functional devices. The performance of optoelectronic and electrochemical devices, sensors, actuators, etc., depends on both the properties of the bulk material and the efficiency of chemical and electrical processes at the surface / interface. To achieve the desired multifunctional properties of the device, multilayer structures of different materials are often fabricated, and the layer thicknesses can vary from a few microns to a single atomic layer.

[0005] Accurate and reliable chemical analysis of solids in bulk, at their surfaces, and at their interfaces with other solids is key to understanding the fabrication and properties of technologically important materials and devices, developing new multifunctional materials, and understanding material failures.

[0006] Two of the most widely used and highly developed surface chemical analysis techniques are electron spectroscopy: X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). XPS is a photoelectron spectroscopy technique in which electron core-level and valence-band spectra from atoms in a solid are obtained by irradiating the material with an X-ray beam. Chemical state information is extracted from the spectrum in the form of electron binding energy shifts due to variations in the local chemical environment. AES is similar to XPS but is based on the analysis of Auger electrons that are released as part of the relaxation process following core-level excitation. In AES, excitation occurs via incident radiation, either X-rays or an electron beam.

[0007] Both XPS and AES can quantify surface chemical composition to a depth of approximately 5 nm with a sensitivity of 0.1-1 atomic % for all elements except hydrogen and helium. Both methods provide information about the chemical state of elements, but in this respect XPS is superior to AES for most elements.

[0008] In many cases, it is important to determine the chemical composition at depths beyond the analytical depth of XPS / AES. For example, this is the case when examining the chemical composition of a submicron multilayer optical filter, i.e., a 1-5 μm multi-process surface treatment for protective purposes. To accomplish this, material must be removed from the surface and the XPS / AES analysis repeated on the new surface revealed by the material removal. This cycle of material removal and XPS / AES analysis continues until the chemical composition is recorded for the depth of interest. The elemental composition at each level is calculated and plotted as a function of the number of cycles, known as a depth profile. If the depth is measured under the assumption that the material removal rate is constant, the depth profile can be plotted in terms of chemical composition as a function of actual depth. For example, as shown in Figure 1A, thin films with thicknesses of 50-500 nm can be analyzed using existing XPS depth profiling techniques. Thicker thin films, up to approximately 5 μm thick, can also be analyzed, but this analysis requires significant time to perform using conventional techniques.

[0009] In the XPS / AES depth profiling process, material removal is typically achieved using ion beam bombardment by an ion gun attached to a spectrometer. The ion beam is aligned with an X-ray spot (in the case of XPS) or an electron beam (in the case of AES) on the surface of the sample, allowing for the execution of a periodic depth profiling process. Upon impact with the surface, the ion gun accelerates ions to high energies sufficient to remove surface atoms in a process known as sputtering. Figure 1B is a schematic diagram of a conventional XPS apparatus using an ion beam. The apparatus includes a vacuum chamber (such as an UHV chamber 10) into which a sample 20 for analysis is inserted. An X-ray source 30 is provided, which directs an X-ray beam toward a target area on the surface of the sample. The surface material emits electrons that are collected by a detector 50, and the electron energy is measured by an electron analyzer 40. The apparatus further includes an ion gun 60. The ion gun can generate a beam of monoatomic ions or (polyatomic) cluster ions, which are directed at the sample surface to remove layers from the surface by sputtering. Argon is commonly used to generate the ions, although other ion sources can be used.

[0010] Commercially available AES and XPS spectrometers became available as scientific tools around 1970. Since then, sputtering has been used as the only practical method for generating XPS / AES depth profiles. However, even though sputter depth profiling has been in use for 50 years and is the only current method for generating XPS / AES depth profiles, sputter depth profiling has its drawbacks, as explained below.

[0011] (i) Sample damage and preferential sputtering Many materials are ion beam sensitive. This means that the sputtering process damages the underlying surface, resulting in changes in the chemical composition recorded by XPS / AES throughout the depth profile. For certain compounds, this can take the form of preferential sputtering, where some elements are sputtered more than others, a phenomenon known as preferential sputtering. This is particularly observed for inorganic materials. For polymeric materials, in addition to preferential sputtering of elements such as oxygen from the polymer, the ion beam can also damage the molecular structure. Therefore, for ion beam-sensitive materials, the ability of XPS / AES to provide accurate quantitative composition information can be compromised, resulting in inaccurate chemical composition recorded throughout the XPS / AES sputter depth profile. Furthermore, the degree of preferential sputtering varies depending on the ion beam conditions and material composition. The degree of preferential sputtering cannot be reliably predicted for any new material or ion beam conditions. As a result, when performing depth profiling of materials that may be ion beam sensitive, analysts often do not know whether preferential sputtering is altering the apparent composition of the collected depth profile. The inaccurate composition recorded during depth profile measurements, and the inability to know whether this is occurring in the material under investigation, is a significant problem for a technique that is considered to be able to provide an accurate chemical composition.

[0012] The aforementioned argon cluster ion beam or gas cluster ion beam (GCIB) has made it possible to significantly reduce damage to most thermopolymers during depth profiling. GCIB has also been shown to reduce, but not completely eliminate, preferential sputtering in metal oxides. However, this has also introduced new problems resulting from thermal spikes associated with GCIB bombardment.

[0013] (ii) low material removal rate; Another problem with sputtering is the relatively low sputter rate for many materials, especially inorganic materials. While sputter rates can be improved by using higher ion beam energy and current, increased energy generally results in more surface damage. Using ion beam energies of 0.5 to 3 keV and typical currents delivered by ion guns used in modern XPS / AES instruments, sputter rates of tens to hundreds of nanometers per hour are achieved. For analyses requiring material removal of more than 1 to 2 microns, XPS / AES depth profiling is typically performed overnight, considering the total time for both sputtering and analysis for thick layers requiring significant material removal or multilayer structures requiring many cycles of sputtering and measurement. XPS / AES depth profiling using ion beam-induced sputtering to depths greater than approximately 5 microns is generally considered impractical. Therefore, it is desirable to seek a solution that addresses the problem of performing XPS / AES depth profiling across thicker layers. For example, to analyze bulk materials, interlayers, or buried interfaces, as shown in Figure 1A.

[0014] The paper "Integrated experimental setup for angle resolved photoemission spectroscopy of transuranic materials" by Graham et al. (Review of Scientific Instruments, 84, 093902, September 2013) describes work to develop angle resolved photoemission spectroscopy (ARPES) for transuranic materials. The Los Alamos National Laboratory technical report "Combining X-Ray Photoelectron Spectroscopy with Laser Ablation for Nuclear Forensics of Pu and U" by Joyce et al. (Report No. LA-UR-14-23989) describes a method for cleaning oxides from Pu and U based materials and the analysis of Pu and U based materials. Summary of the Invention

[0015] The present invention aims to solve problems related to (a) inaccurate determination of the chemical composition of materials and / or (b) limited material removal rates during XPS / AES depth profiling. The present invention is particularly advantageous in that it can improve the accuracy of chemical composition and chemical state information during depth profiling of polymers, metal oxides, other inorganics, semiconductors, alloys, and other materials. Compared to ion beam depth profiling, the ability to access increased depths for analysis allows access to subsurface regions of various chemical compositions, buried interfaces, and individual subsurface layers.

[0016] This is achieved by the use of laser pulses for material ablation in conjunction with electron spectroscopy such as XPS and AES.

[0017] The present invention provides a method for determining the chemical composition of a sample using electron spectroscopy, comprising ablating material from a region of a surface of the sample by irradiating the region with one or more pulses of a laser, irradiating at least a portion of the region with an excitation beam of electron radiation or electromagnetic radiation, measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam, and repeating the steps of ablat- ing material, irradiating with the excitation beam, and measuring the intensity and energy to determine a quantitative surface depth profile and yield a chemical composition of at least a portion of the sample. In a preferred embodiment, the method further comprises, prior to initially ablating material from the region, irradiating at least a portion of the unablated region with an excitation beam of electron radiation or electromagnetic radiation and measuring the intensity and energy of electrons emitted from at least a portion of the unablated region of the sample as a result of the excitation beam.

[0018] The method may further include determining the elemental composition of at least a portion of the ablated region from the intensity and energy of the emitted electrons, and optionally determining the chemical state of the element from the energy of the emitted electrons. The method may further include determining the depth or relative depth of one or more ablated regions, for example, relative to an unablative surface adjacent to the ablated region or relative to the surface of the sample before ablation. To determine the depth or relative depth of one or more ablated regions, the method may further include determining the ablation rate per pulse of material present in the surface depth profile. Additionally, the method may further include converting the number of pulses to depth. Alternatively, the depth may be determined independently by measuring the final crater depth using, for example, profilometry, microscopy, white light interferometry, or other methods.

[0019] One or more of the pulses of the laser beam may be femtosecond pulses.

[0020] The method may further include repeating the steps of ablating the material, irradiating with the excitation beam, and measuring the intensity and energy of the emitted electrons to determine a depth profile, for example, to a depth of greater than 5 μm, greater than 10 μm, greater than 100 μm, or greater than 200 μm.

[0021] Each step of ablating material can involve removing a layer of about 1 to several hundred nanometers, or even about one atomic layer, for example, 0.3 nm to 10 μm (e.g., 0.3 nm to 1000 nm, or 1 nm to 10 μm, 1 nm to 1000 nm, or 10 nm to 500 nm).

[0022] The excitation beam may be a beam of X-rays and the spectroscopy may be XPS or AES, or the excitation beam may be a beam of electrons and the spectroscopy may be AES.

[0023] The method may further include tilting the sample relative to the ablation laser beam. Tilting the sample relative to the laser beam may reduce the roughness of the crater bottom and / or enable a deeper depth profile. The method may also include rotating or partially rotating the sample between ablation layers or steps (e.g., less than 90°, e.g., 15-85°, or 25-75°, or 35-75°, or 45-65°, or 50-60°, e.g., about 45, 55, or 65°). This may also reduce the roughness of the crater bottom and / or enable a deeper depth profile and greater depth resolution of the measurement compared to simple laser ablation. The method may include incremental rotation of the sample surface between ablation layers or steps or between laser pulses, or may include continuous rotation of the sample surface during the method. Sample surface rotation, which is a rotational movement in the plane of the surface, has the effect of varying or randomizing the laser direction relative to the surface over multiple ablation steps. Otherwise, if there are multiple laser pulses using the same direction at the surface, undesirable laser-induced periodic surface structures (LIPSS) may accumulate. Thus, the rotation of the sample surface should preferably avoid rotation steps that are multiples of 90 degrees, such as 90 degrees or 180 degrees; for example, a 55-degree rotation works well over many pulses. The laser beam may be a linearly polarized laser beam. The method may include incremental or continuous rotation of the angle of the linearly polarized laser beam during ablation or between ablation steps. In other words, the orientation of the polarization plane of the laser beam may be rotated, for example, incrementally or continuously, during ablation or between ablation steps or laser pulses. Similar to rotating the sample surface, rotating the polarization of the laser beam has the effect of varying or randomizing the laser direction relative to the surface over multiple ablation steps.Similarly, to avoid undesirable LIPSS, rotation of the laser polarization should preferably avoid rotation steps that are multiples of 90 degrees, such as 90 degrees or 180 degrees; for this reason, a 55-degree rotation, for example, works well across many pulses. The method may include rotating the laser polarization by less than 90 degrees between ablation layers or steps, such as by 15-85 degrees, 25-75 degrees, 35-75 degrees, 45-65 degrees, or 50-60 degrees, e.g., 45, 55, or 65 degrees. Alternatively, the method may include converting a linearly polarized beam to a beam with circular or elliptically polarized light. The use of a circularly or elliptically polarized laser beam can optionally be combined with sample rotation and / or polarization.

[0024] Thus, some embodiments of the present methods may include either (i) rotating the sample in the plane of its surface between ablation steps and / or between laser pulses, and / or (ii) rotating the plane of polarization of the laser pulses between ablation steps and / or between laser pulses, or (iii) converting the polarization of the laser pulses to circular or elliptical polarization. Rotating the sample, rotating the polarization, and / or converting the polarization may reduce the roughness of the crater bottom and / or enable achieving a deeper depth profile.

[0025] The one or more pulses can ablate material by Coulomb explosion and / or thermal processes, and the method can include adjusting one or more of the pulse energy, pulse length, and other parameters depending on the material to provide an ablation process that is optimal for analytical purposes.

[0026] The step of determining the chemical composition may include determining the concentration of the chemical elements. The concentration of the chemical elements may be stated in atomic percentage (atomic %) or stoichiometry, or otherwise. The chemical concentration of the elements may be quantitatively determined from the relative measured intensities. The chemical elements and chemical states of the elements may be determined from the measured energies.

[0027] The step of ablating material may form a crater in the surface of the specimen, and at least a portion of the area irradiated with the excitation beam of x-rays / electrons may include an area at the base of the crater.

[0028] The crater preferably has a substantially flat bottom, and the excitation beam preferably irradiates at least a portion of the substantially flat bottom. The excitation beam preferably irradiates at least a portion of the substantially flat bottom, and preferably does not irradiate the edges or sidewalls of the crater. The ratio of crater width (across the crater bottom) to excitation beam spot size can be at least 3:1, or at least 4:1, or at least 5:1. A ratio of at least 5:1 is preferred.

[0029] The width of the substantially flat bottom of the crater can be greater than the width of the excitation beam, which is the full width at half maximum (FWHM) of the beam intensity, 1 / e 2 It may be determined to be the diameter or other measure of the beam width within which most of the beam's energy is contained.

[0030] Ablating material from a region of the specimen may include moving the relative position of the laser pulse to scan the pulse across a region of the surface of the specimen to ablate craters in the surface.

[0031] The relative position of the laser pulses can be moved by scanning the laser or by scanning the position of the sample, which can include irradiating the sample with one or more pulses at multiple overlapping pixel locations.

[0032] The method can include passing a laser pulse through an optical setup that converts a typically Gaussian intensity laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the sample surface. The laser pulse can generate a crater having a width corresponding to the width of the flat-top or top-hat intensity profile. The beam-shaping element can include a diffractive optical element. Alternatively, the beam-shaping element can be a refractive optical element or other optical element.

[0033] A combination of scanning and a flat top or top hat beam profile may also be used.

[0034] The laser pulses may each have a duration of less than 1 nanosecond (ns), less than 1 picosecond (ps), less than 500 femtoseconds (fs), less than 100 fs, less than 10 fs, or less than 1 fs. As example ranges, the laser pulses may have durations in the range of 1 fs to 1 ns, or 1 fs to 1 ps, or 1 fs to 500 fs, or 1 fs to 200 fs, or 1 fs to 100 fs. The lower end of the range may be lower than 1 fs, for example, 0.1 fs.

[0035] The laser pulse energy in one or more repetitions (pulses), preferably one pulse, should be sufficient to ablate the material. In some embodiments, the energy per laser pulse can be in the range of 10 nJ to 1000 μJ, or 1 μJ to 1000 μJ, or 10 μJ to 1000 μJ, such as 50 to 500 μJ. Alternatively, the repetitions can be bursts or pulse trains, with the bursts or pulse trains having these energies.

[0036] The diameter of the laser pulse at the sample surface can be in the range of 1 to 1000 μm, such as 10 to 300 μm, or 50 to 150 μm.

[0037] The method may further include setting or adjusting, by a controller, one or more parameters of the pulses of the laser based on compositional information about the specimen and performing the step of ablating material, wherein the parameters of the laser pulses are set or adjusted by the controller. The controller may be a computing device having a memory and a processor.

[0038] The one or more parameters of the laser pulse that may be set or adjusted by the controller include one or more of pulse duration, pulse energy, repetition frequency, wavelength, and spot size.

[0039] The setting or adjusting step may further include receiving input from a user indicating compositional information about the specimen, and the controller adjusting one or more laser parameters based on the compositional information.

[0040] The method may further include performing a survey scan or survey profile to determine approximate measurements of elemental constituents in the sample, and generating one or more parameters of the laser pulse based on the approximate measurements.

[0041] The method may further include performing mechanical profilometry or microscopy (e.g., atomic force microscopy) or white light interferometry (WLI) of the sample surface, and generating or adjusting one or more parameters of the laser pulse based on the profilometry, microscopy, or interferometry.

[0042] The controller can use a reference database or algorithm to determine the laser parameters based on information about the sample.

[0043] The method may include ablating material, irradiating an excitation beam, and measuring electron intensity and energy, followed by adjusting one or more parameters of the laser based on measured or predicted compositional information about the sample at a depth after ablation, and repeating the steps of ablating material, irradiating an excitation beam, and measuring electron intensity and energy using the adjusted one or more parameters of the laser.

[0044] The method may further include repeating the steps of adjusting, ablating material, irradiating with the excitation beam, and measuring electron intensity and energy until the sample is analyzed to the target depth.

[0045] The method may include placing a sample on a sample stage in a vacuum chamber, followed by ablating material, irradiating with an excitation beam, and measuring the intensity and energy of the emitted electrons, wherein the sample may not be moved more than the laser spot or scan size between the ablation and excitation beam irradiation steps.

[0046] The laser pulse and the excitation beam may be spatially coincident at the sample surface. In this context, the term coincident does not mean that the laser pulse and the excitation beam must have exactly the same spatial extent and position at the sample surface, but rather that there is at least an overlap. Preferably, the spot size of the excitation beam is smaller than the spot size of the laser pulse. The excitation pulse may be centered on the laser pulse.

[0047] The ablation step may include raster scanning an ablative laser pulse across the sample surface, the excitation beam coinciding with at least a portion of the ablated sample surface area.

[0048] The present invention provides further methods as described herein, which methods can be combined in any combination.

[0049] 1. A method of electron spectroscopy comprising: ablating material from a region of a surface of a sample by irradiating the region with one or more pulses of a laser, the ablation forming a crater in the surface of the sample; irradiating at least a portion of the ablated region at the base of the crater with an excitation beam of electromagnetic radiation, such as electron radiation or X-rays; measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam; and determining the chemical composition of the surface of the crater based on the measured intensity and energy of the emitted electrons. The ablation step can be repeated to form deeper craters.

[0050] 1. A method of electron spectroscopy comprising: ablating material from a region of a surface of a sample by irradiating the region with one or more pulses of a laser, the laser pulses having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; and irradiating at least a portion of the ablated region with an excitation beam of electromagnetic radiation, such as electron radiation or X-rays. The method may further include measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam, and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons.

[0051] 1. A method of electron spectroscopy comprising: setting, by a controller, one or more parameters of pulses of a laser based on compositional information about the sample; ablating material from a region of the sample by irradiating a region of a surface of the sample with one or more pulses of the laser, the pulse parameters of the pulses being set by the controller; irradiating at least a portion of the region with an excitation beam of electromagnetic radiation, such as electron radiation or x-rays; measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons.

[0052] 1. A method of electron spectroscopy comprising: placing a sample on a sample stage in a vacuum chamber; ablating material from a region of the sample by irradiating a region of a surface of the sample with one or more pulses of a laser; irradiating at least a portion of the region with an excitation beam of electromagnetic radiation, such as electron radiation or X-rays; measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons; wherein the sample is not moved between the ablation step and the excitation beam irradiating step by no more than the size of the laser spot or scan area.

[0053] 1. A method of electron spectroscopy comprising: placing a sample on a sample stage in a vacuum chamber; ablating material from a region of the sample by irradiating a region of a surface of the sample with one or more pulses of a laser configured to direct the pulses toward the sample surface; irradiating at least a portion of the region with an excitation beam of electromagnetic radiation, such as electron radiation or X-rays; measuring the intensity and energy of electrons emitted from at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons, wherein the laser pulse and the excitation beam are spatially coincident at the sample surface.

[0054] The present invention provides an electron spectroscopy apparatus for determining the chemical composition of a sample, the apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron detector and analyzer configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a quantitative surface depth profile of the chemical composition of the sample.

[0055] The electron analyzer and detector may be further configured to determine the elemental composition of the target region from the intensity and energy of the emitted electrons, and optionally, to determine the chemical state of elements in the elemental composition from the intensity and energy of the emitted electrons. The electron analyzer may comprise an electrostatic toroidal capacitor analyzer, e.g., an electrostatic concentric hemispherical analyzer. Other types of electron analyzers, such as cylindrical mirror analyzers, may be used. Electrons may be detected using one or more electron multipliers. The electron multiplier may comprise a single channeltron, an array of channeltrons, or a microchannel plate. The detector, also known as an electron counter, may comprise one or more channel electron multiplier (channeltron) detectors. Alternatively, a channel plate multiplier used in conjunction with a position-sensing element, such as a delay line detector (DLD) or a resistive anode divider, may be used to simultaneously detect the number of electrons and the landing position of each electron.

[0056] The laser is preferably configured to generate nanosecond, or picosecond, or more preferably femtosecond pulses.

[0057] The excitation beam source may be configured to generate an X-ray beam or an electron beam.

[0058] The excitation beam source can be configured to generate a beam of X-rays, and the electron detector and analyzer are configured to measure photoelectrons and Auger electrons. Alternatively, the excitation beam source is configured to generate an electron beam, and the electron analyzer is configured to measure Auger electrons. When the excitation beam is an X-ray beam, the electrons are photoelectrons, and the spectroscopy is XPS. When the excitation beam is an electron beam, the electrons are Auger electrons, and the spectroscopy is AES.

[0059] The sample stage can be configured to tilt relative to the ablation laser beam.

[0060] The sample stage may include a positioning device to move the sample in an orthogonal direction in the sample plane, for example to raster scan the sample relative to the location of incidence of the ablative laser pulse.

[0061] The laser may be equipped with mirrors to adjust the position of incidence of the laser pulse on the sample so as to raster scan the laser pulse across the sample.

[0062] The laser may be equipped with a beam shaping element to convert the laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the sample surface.

[0063] The laser beam shaping element may be configured to transform the laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the sample surface, the diameter at the surface of the sample preferably being larger than the diameter of the excitation beam at the surface of the sample.

[0064] The beam-shaping element may comprise a diffractive optical element, a refractive optical element, or other optical element.

[0065] The laser can be configured to generate pulses each having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs.

[0066] The laser is configured to produce pulses having an energy in the range of 10 nJ to 1000 μJ, or 1 to 1000 μJ, or 10 μJ to 1000 μJ per pulse, for example 50 to 500 μJ.

[0067] The laser may be configured to produce pulses having a spot size at the sample surface in the range of 1-1000 μm, for example 10-300 μm, or 50-150 μm.

[0068] The controller can be configured to adjust one or more parameters of the pulses of the laser based on compositional information about the sample.

[0069] The one or more parameters of the laser pulse set by the controller may include one or more of pulse duration, pulse energy, repetition frequency, wavelength, and spot size.

[0070] The controller may be configured to receive input from a user indicating compositional information about the sample and adjust one or more laser parameters based on the compositional information.

[0071] The controller may be configured to reference a reference database or algorithm to determine the laser parameters based on information about the sample.

[0072] The laser source and the excitation beam source may be configured to direct the laser pulses and the excitation beam, respectively, to spatially coincide at the sample surface.

[0073] The present invention provides further devices as described below, which can be combined in any combination.

[0074] 1. An electron spectroscopy apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample, the laser configured to ablate material to form a crater in the surface of the sample; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron analyzer and detector configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

[0075] 1. An electron spectroscopy apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample, the laser configured to generate pulses having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron analyzer and detector configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

[0076] 1. An electron spectroscopy apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample; a controller configured to adjust or set one or more parameters of the pulses of the laser based on information about the sample; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron analyzer and detector configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

[0077] 1. An electron spectroscopy apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron analyzer and detector configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample, wherein the sample stage is configured for a maximum travel corresponding to a size of the sample.

[0078] 1. An electron spectroscopy apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample; an excitation beam source configured to generate an excitation beam of electron radiation or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; and an electron analyzer and detector configured to measure the intensity and energy of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample, wherein the laser source and excitation beam source are configured to direct the laser pulses and the excitation beam, respectively, to spatially coincide at the sample surface.

[0079] In each of the above methods and apparatus, the excitation beam may be a beam of electromagnetic radiation, such as an electron beam or x-rays. [Brief explanation of the drawings]

[0080] Hereinafter, embodiments of the present invention and aspects of the prior art will be described with reference to the accompanying drawings. [Figure 1A] FIG. 1 is a schematic diagram illustrating the depth of analysis that can be achieved using conventional XPS. [Figure 1B] FIG. 1 is a schematic diagram of an XPS apparatus equipped with an ion source for sputtering away a layer of material. [Figure 2] 1 is a schematic diagram of an XPS apparatus equipped with an ablation laser according to the present invention; [Figure 3A] 1 is a schematic diagram of an engineering setup for an ablation laser according to the present invention. [Figure 3B] Schematic diagram showing the rotation of the sample surface and / or the rotation or translation of the laser polarization during the ablation step. [Figure 4A] 1 is a process flow diagram of steps for performing a method of electron spectroscopy using laser ablation to generate a composition depth profile. [Figure 4B]1 shows the different depth resolutions obtained when depth profiling through a nickel / chromium multilayer structure with (left graph) and without (right graph) rotating the laser polarization between pulses. [Figure 5A] These are, respectively, an XPS spectrum showing the background signal of the Ag 3d XPS spectrum and a peak fit of the C 1s XPS spectrum showing the individual peaks of carbon in different chemical states. [Figure 5B] These are, respectively, an XPS spectrum showing the background signal of the Ag 3d XPS spectrum and a peak fit of the C 1s XPS spectrum showing the individual peaks of carbon in different chemical states. [Figure 6a] 1A-1C show examples of quantified XPS depth profiles of laser ablation plotted as a function of ablation level and depth, respectively. [Figure 6b] 1A-1C show examples of quantified XPS depth profiles of laser ablation plotted as a function of ablation level and depth, respectively. [Figure 7a] FIG. 1 is a schematic diagram of a beam scanning approach to laser ablation. [Figure 7b] 1 is a schematic cross-sectional view through an ablated region on which an excitation beam is incident. [Figure 8] FIG. 1 is a schematic diagram of Gaussian beam overlap capable of achieving uniform intensity across a pixel for ablation. [Figure 9] FIG. 1 is a schematic diagram of an optical setup for generating a top-hat or flat-top beam intensity profile. [Figure 10] 1 is a plot of a top-hat intensity profile of a laser pulse showing intensity in plan and cross-section. [Figure 11] 11 is a graph showing a mechanical profilometry trace across a crater on a sample surface formed by a raster scan pulse according to FIG. 10; [Figure 12a]Depth profiles of the chemical composition of TiO samples obtained using laser ablation, conventional sputtering, and cluster ion beam sputtering. [Figure 12b] Depth profiles of the chemical composition of TiO samples obtained using laser ablation, conventional sputtering, and cluster ion beam sputtering. [Figure 12c] Depth profiles of the chemical composition of TiO samples obtained using laser ablation, conventional sputtering, and cluster ion beam sputtering. [Figure 12d] The corresponding photoelectron spectroscopy spectrum. [Figure 12e] The corresponding photoelectron spectroscopy spectrum. [Figure 12f] The corresponding photoelectron spectroscopy spectrum. [Figure 13a] 1A and 1B are surface depth profiles of InP obtained using laser ablation and sputtering, respectively. [Figure 13b] 1A and 1B are surface depth profiles of InP obtained using laser ablation and sputtering, respectively. [Figure 14a] Regarding the surface depth profile of the iron oxide layer on iron obtained using laser ablation, Figure 14a shows XPS spectra from three different layered regions (Fe2+ / 3+, Fe2+, and Fe0) in the surface profile of Figures 14b and 14c. [Figure 14b] Regarding the surface depth profile of the iron oxide layer on iron obtained using laser ablation, Figure 14a shows XPS spectra from three different layered regions (Fe2+ / 3+, Fe2+, and Fe0) in the surface profile of Figures 14b and 14c. [Figure 14c] Regarding the surface depth profile of the iron oxide layer on iron obtained using laser ablation, Figure 14a shows XPS spectra from three different layered regions (Fe2+ / 3+, Fe2+, and Fe0) in the surface profile of Figures 14b and 14c. [Figure 15a]1 is a surface depth profile of PET on steel obtained using laser ablation. [Figure 15b] The corresponding XPS spectrum from the PET layer is shown. [Figure 15c] The corresponding XPS spectrum from the PET layer is shown. DETAILED DESCRIPTION OF THE INVENTION

[0081] FIG. 2 is a schematic diagram of an X-ray photoelectron spectroscopy (XPS) apparatus 100 according to one embodiment of the present invention. The apparatus includes a vacuum chamber 110, which may be a UHV vacuum chamber similar to the vacuum chamber 10 shown in FIG. 1B. The apparatus further includes a sample stage capable of receiving a sample 120. An X-ray source 130 is provided for generating an excitation beam of X-rays. Alternatively, for Auger electron spectroscopy (AES), an electron source may be provided for generating an excitation beam of electrons. An electron analyzer 140 is provided for analyzing photoelectrons and Auger electrons generated by the incidence of the excitation beam on the sample surface before they are detected by a detector 150. A laser 160, such as a femtosecond laser, is provided for irradiating and ablating the sample surface so that XPS or AES can be performed at a certain depth. The laser replaces the argon ion gun or etching source 60 shown in FIG. 1B. The apparatus may further include a controller 180 for controlling, for example, laser parameters. As shown in FIG. 2, the sample stage receives the sample 120 within the vacuum chamber 110. The sample stage 120 may be a movable sample stage equipped with a positioning mechanism to adjust the position of the sample in two orthogonal directions in the sample plane, such as the x- and y-directions. The positioning mechanism may also have z-direction (height) adjustment. The sample stage may also be equipped with a positioning mechanism for in-plane rotational motion, such as rotation in the xy plane. This in-plane rotational motion is further shown in FIG. 3B. The sample stage may also be equipped with a tilting mechanism for tilting the sample relative to the ablation laser beam.

[0082] The electron analyzer 140 may comprise an electrostatic toroidal capacitor analyzer, for example, an electrostatic concentric hemispherical analyzer. Other types of electron analyzers, such as a cylindrical mirror analyzer, may also be used. The electron analyzer measures the energy of the emitted electrons.

[0083] The detector, also known as the electron counter 150, may comprise one or more channel electron multiplier (channeltron) detectors. Alternatively, a channel plate multiplier used in conjunction with a position-sensitive element such as a delay line detector (DLD) or a resistive anode divider can be used to simultaneously detect the number of electrons and the landing position of each electron. The detector measures the intensity of the emitted electrons.

[0084] The X-ray or electron source 130 is configured to generate and direct electrons or X-rays toward the sample surface. The X-rays may be monochromatic and may be generated from a high-energy electron gun positioned to accelerate electrons toward a target anode. The target anode may be aluminum so that the resulting X-rays are generated at the appropriate energy. The X-rays may be directed into the chamber through a monochromator crystal and focused toward the sample surface. The X-rays pass through an opening, or aperture, to reach the sample surface. Upon impinging on the sample surface, the X-rays cause the emission of photoelectrons or Auger electrons.

[0085] Because electron emission can cause positive charge to build up on the sample, the instrument can further include a flood gun 131 to perform charge neutralization at the sample surface during analysis. This is most severe when the sample surface is insulating, because the accumulated charge remains on the surface and is not dissipated by charge transport through the sample. Positive charge can affect the XPS spectrum by shifting peaks to higher binding energies and distorting them. The flood gun can be of any suitable type, such as the gun disclosed in GB 2411763(A). The flood gun neutralizes the charge on the sample surface by replenishing the emitted electrons. Neutralization stabilizes and controls the charging of the sample surface.

[0086] The apparatus may further include one or more video cameras 132, 133. These may be mounted outside the vacuum chamber and configured to provide an image of the sample stage. The video camera may be mounted to collect an image of the sample on the sample stage through an optical window in the vacuum chamber. Two cameras are shown in Figure 2. A lamp 134 is shown illuminating the sample from above, e.g., in the same direction as electrons are emitted from the sample. Light from the lamp 134 may be directed toward the sample via a pair of mirrors 135, 136. Mirror 136 may be an annular mirror positioned so that electrons emitted from the sample pass through its central hole. The pair of mirrors provides a periscope configuration that allows convenient placement of the lamp. Camera 132 is positioned to view the sample from above using the annular mirror 136. Mirror 135 is a two-way or semi-transparent mirror that reflects light from the lamp directed toward the sample while allowing at least a portion of the light from the sample to enter camera 132. Camera 132 has the advantage of viewing the sample from directly above, providing a good view of the surface from which electrons are emitted. The second camera 133 can view the sample more directly, but at a sharper angle, so it cannot see the surface as well, but no image is lost compared to camera 132, which views through the annular mirror 136. A secondary lamp 137 can be provided. Although not apparent from the schematic, this secondary lamp 137 can illuminate the sample from a similar direction to how camera 133 views the sample. A laser 160 can also be mounted outside the vacuum chamber, and the ablation pulse can be directed to pass through a window into the vacuum chamber and onto the sample 120. Figure 3A shows further details of an embodiment of the laser 160. The laser can include a femtosecond (fs) laser source 210. In other embodiments, the laser can be a picosecond or nanosecond laser. The fs laser source 210 can be based on a diode-pumped Yb medium, which can provide a range of pulse lengths, pulse wavelengths, and pulse energies. The pulses output from the laser source pass through a series of optical elements that condition the pulses and direct them to a target area on the sample surface, as shown in FIG. 3A.The beam expander 215 functions to size and collimate the beam suitable for the flat-top shaper 220, which converts the Gaussian beam into a beam with a flat-top intensity profile. The mirror 225 directs the beam or pulse to the variable attenuator 230 and polarization adjustment optics 235. The variable attenuator 230 can be used to reduce the beam power / energy as needed. The polarization adjustment optics 235 can comprise a zeroth-order half-wave plate or a zeroth-order quarter-wave plate and can be rotatable. In this way, the polarization of the laser beam can be rotated (relative to linearly polarized laser light) or converted to circular or elliptically polarized light, both of which are shown in FIG. 3B. In some embodiments, it may be possible to use two or more of the aforementioned wave plates in series and / or to use wave plates operating at different (non-zero) orders. Other birefringent materials, for example in the form of prisms, may also be used. Generally, controlling the polarization state of the incident laser provides a way to suppress the formation of laser-induced periodic surface structures (LIPSS). There are various ways in which such control of polarization can be achieved in practice; the key requirement is to control the phase difference between orthogonally polarized components of the incident laser beam at its operating wavelength. In this way, the polarization of the laser beam can be rotated (relative to linearly polarized laser light) or converted to circular or elliptically polarized light. This can be achieved through the use of single or multiple zero-order or multi-order wave plates, or through the use of other types of single- or multi-layer birefringent optical materials, waveguides, and components. A second beam expander 240 can be placed before mirror 245 to adjust the spot size of the beam at the focal point. Although the laser is described in terms of a beam, pulses or bursts of pulses are generally implied, since continuous wave beams are not generated by femtosecond laser sources. Mirror 245 directs the pulse through focusing lens 250, which focuses the pulse to the desired spot size on the sample surface. The pulse passes through window 255, such as a glass window, into the vacuum chamber of the XPS or AES spectrometer so that it is incident on a target area on the surface of sample 260.The controller 280 can control the fs laser source 210, the variable attenuator 230, and the polarization adjustment optics 235 to set the laser parameters as desired. The controller can also control one or both of the beam expanders 215 and 240, as needed. This embodiment of the laser optics can achieve smooth, flat-bottomed craters and therefore good profiling performance. Changing the linear polarization direction between pulses, achieved using the polarization adjustment optics, can minimize potential ripple morphology due to laser-induced periodic surface structures (LIPSS) that may appear on the surface during profiling. The method can include incremental or continuous rotation of the angle of the linearly polarized laser beam during ablation or between ablation shots. Alternatively, the method can include converting the linearly polarized beam to a beam with circular or elliptically polarized light. Sample rotation, polarization rotation, and / or polarization conversion can reduce the roughness of the crater bottom and / or enable the achievement of deeper depth profiles.

[0087] In some embodiments, the femtosecond laser has a wavelength of 1030 nm and a pulse length of 160 fs. Alternatively, the laser wavelength can be 515 nm. Shorter or longer pulses can be used, such as in the range of 10 fs to 10 ps, ​​or 10 fs to 1 ps, or even less than 1 fs to 1 ns. The spot size of the laser pulse on the sample surface can vary. In some embodiments, the spot size ranges from about 50 to 150 μm. The energy of each pulse can vary depending on the material and the amount of ablation required, such as 10 nJ to 1000 μJ, or more preferably 50 to 500 μJ. In one embodiment, the energy of each pulse can be about 600 μJ. The pulse repetition rate can vary. In some embodiments, pulse repetition rates of up to about 10 kHz can be used. By combining laser beam scanning with stage rastering, depths of hundreds of microns can be achieved.

[0088] The controller 180 can be configured to receive input from a user to set appropriate laser parameters for the sample under investigation. For example, the pulse energy, spot size, and / or pulse duration can be adjusted to provide energy at the sample surface above the material's ablation threshold, but below sufficient energy or duration to cause damage to the remaining surface chemistry. The controller 180 can receive input from a user interface or another computer. The input can include settings for adjusting one or more of the spot size, pulse energy, pulse duration, pulse repetition frequency, and wavelength. Alternatively, the input can indicate an expected material or material type. The controller can include, for example, an algorithm, lookup table, library, or database that, when executing a computer program on the controller's processor, provides laser parameters optimized for the expected material or material type to ablate the surface while avoiding or minimizing damage to the underlying chemical composition. The parameters can be further optimized to provide rapid ablation while minimizing damage to the underlying chemical composition.

[0089] A further method for determining how to adjust laser parameters for different sample materials is to perform a survey scan of the sample surface to be ablated. This may include performing electron spectroscopy methods such as XPS or AES, as described herein. Other sample survey scanning techniques may also be used. In one example, for a single-layer sample, the survey scan can determine the elemental composition within the surface layer. A library of similar materials can then be used to optimize settings such as fluence, frequency, pulse duration, and / or wavelength to achieve a desired ablation rate (i.e., level or nm per pulse) that captures chemical information of the surface layer. The number of pulses can then be set for the desired depth or level of the profile. Crater morphology, such as size, shape, and / or surface roughness, or amount of variation, can also be considered. For multilayer samples, the single-layer approach can be repeated for each layer. Alternatively, for multilayer samples, either prior knowledge of the composition of each layer or a survey profile can be used to determine the laser parameters to use. For example, the survey profile may include an approximate assessment of the composition followed by optimization of the settings for the single layer using a library of similar materials. If the library is insufficient or inaccurate for the sample, the ablation rate can be determined by ex-situ analysis (e.g., mechanical profilometry, microscopy, or white light interferometry) of craters formed using various fluences and numbers of pulses / levels.

[0090] The ablation rate (i.e., nm per level or pulse) is material dependent and can be determined by ex-situ analysis (e.g., mechanical profilometry, microscopy, or white light interferometry) of craters formed using various fluences and numbers of pulses / levels.

[0091] Returning to Figure 2, the laser 160 and the X-ray or electron source 130 are configured to direct the laser pulse and the X-ray or electrons, respectively, to the same target area of ​​the sample surface, i.e., so that the laser pulse and the X-ray or electrons coincide at the sample surface. The alternating operation of the laser to remove layers from the sample surface and the X-ray or electron source to irradiate the sample surface to eject electrons from the sample allows for the construction of a compositional depth profile of the sample. The use of a femtosecond laser is particularly advantageous because it avoids or reduces damage to the composition of the sample surface compared to ion beam sputtering.

[0092] A method of operation of the apparatus of FIG. 2 will now be described in more detail. FIG. 4A is a process flow chart of a method 300 for operating the apparatus of FIG. 2. The process begins in step 310 with placing a sample in the vacuum chamber of the apparatus. This may include placing the sample on a sample stage within the chamber and moving the sample stage to position the sample so that the ablation beam and excitation beam are incident on a target area of ​​the sample. The sample may be introduced into the chamber by breaking the vacuum, placing the sample on the sample stage, and then evacuating the chamber, or the sample may be introduced through a vacuum load lock. The method may additionally or alternatively include adjusting the laser and X-ray or electron source so that their beams are incident on a precise location on the sample. In one configuration, coarse alignment may be performed using a sample stage positioner, and fine alignment may be achieved by adjusting the position of the laser and X-ray or electron source beam. Preferably, in step 315, prior to ablation, an excitation beam of X-rays or electrons is generated and directed toward the natural surface of the sample. The X-rays or electrons can be directed at the natural surface within the region to be ablated. Alternatively, in this step, the X-rays or electrons can be directed at any region of the sample's surface, such as outside the region to be ablated, if the sample has a uniform composition, as is often the case with thin films. In step 320, a detector and electron analyzer are used to measure the intensity and energy of the emitted electrons. The emitted electrons of interest are photoelectrons and / or Auger electrons. Optionally, in step 325, the controller 280 can adjust the laser to adjust pulse parameters for the sample material. For example, pulses can be adjusted to ablate more material quickly or to reduce damage to the surface composition. Different materials may require lower pulse energies for ablation and / or may be more easily damaged with longer pulses.Although step 325 is shown as following the initial irradiation step 315 and measurement step 320, this optional step may be performed at one or more different points in the method, any time before the ablation step, such as before or after optional steps 315 and 320. In step 330, the laser generates a pulse to ablate the sample surface. After ablation, an excitation beam of x-rays or electrons is generated and directed at the new surface created by ablation, as shown in step 340. This step is performed without the need to move the sample, since the excitation beam and the ablation pulse are substantially spatially coincident. In step 350, a detector and electron analyzer are used to measure the intensity and energy of the emitted electrons. The emitted electrons of interest are photoelectrons and Auger electrons. As shown in step 360, the steps of laser ablation, excitation beam irradiation, and electron intensity and energy measurement can be repeated to accumulate compositional information about a layer of the sample. Between each step of laser ablation 330, or between each laser pulse used in each step of laser ablation 330, the sample surface and / or the polarization plane of the laser beam are rotated in steps, for example, 55 degrees. The degree of rotation between each laser pulse can be selected to effectively suppress LIPSS formation, and can be a rotation of 10 to 80 degrees, such as 40 to 70 degrees, for example, 55 degrees. Alternatively, the laser pulses can be converted to elliptically or circularly polarized light to suppress LIPSS formation. In step 370, a composition depth profile is generated or calculated.

[0093] The physical process of using femtosecond laser ablation and its advantages over other material removal techniques will now be described in more detail.

[0094] In laser ablation, the material removal process involves two competing mechanisms, depending on the laser pulse length: thermal and electrostatic processes, also known as Coulomb explosion. In both cases, laser photon energy is primarily absorbed by electrons. In thermal processes, excited electrons relax through electron-phonon interactions, and the lattice equilibrates after a few picoseconds due to localized heating. Material is ejected as a result of mechanisms including evaporation and hydrodynamic expansion of the heated material, the exact mechanism depending on the laser pulse length and energy. In the Coulomb explosion mechanism, the strong electric field associated with high-intensity, short pulses of light allows for the occurrence of strong-field ionization and processes such as multiphoton and tunnel ionization, resulting in a high concentration of ions in the surface region. When the electrostatic attraction between emitting electrons or the electrostatic repulsion between positively charged ions exceeds the local bond strength, ions are ejected from the surface of the material during Coulomb explosion. As the laser pulse length is shortened to the ultrashort femtosecond range, there is insufficient time for electronic and solid relaxation processes to occur, leading to a significant decoupling of these processes. As a result, Coulomb explosion dominates the thermal mechanism for ultrashort pulse-induced ablation.

[0095] Conventional techniques of monatomic ion sputtering and cluster ion sputtering have drawbacks compared to ultrafast laser ablation. In monatomic ion sputtering, incident ions penetrate the surface layer, causing a momentum cascade with atoms in a localized region. When enough energy is transferred to surface atoms so that bonds with neighboring atoms can be broken, the surface atoms are ejected (sputtered) into the vacuum. In cluster ion sputtering, the low average energy of the ions and collisions between ions within the cluster upon impact with the surface result in much less or no penetration of the incident ions, but still cause multiple collisions between surface atoms, which are then ejected into the vacuum. The high average energy per atom in monatomic sputtering leads to chemical damage of the surface, which can be analyzed by XPS or AES. In polymers, this leads to effects such as preferential removal of functional groups and modification of bonds, resulting in irregular graphitic carbonaceous structures. In inorganic materials, chemical damage often takes the form of preferential sputtering, in which one element in a compound is preferentially sputtered compared to another. The much lower average energy per atom in cluster ion sputtering results in much less or minimal damage to the polymer, yet still results in preferential sputtering of the inorganic material.

[0096] The preferential sputtering of one element in a compound over another is generally believed to be caused by two effects: mass difference and surface binding energy. The mass difference effect considers the variation in energy transfer to elements of different masses when incident ions enter the surface of the compound and the effect this has on the sputtering yield of each element. The surface binding energy is the energy required to remove an atom from the outer atomic layer. The surface binding energy considers the variation in the binding energies of different atoms in a compound and is often expressed as the sublimation enthalpy of the surface composition. Generally, for inorganic compounds, the mass difference effect is the primary mechanism that results in preferential sputtering.

[0097] In femtosecond laser ablation, high-energy, ultrashort pulses of a laser beam cause multiphoton ionization, which promotes electrons from the valence band to the conduction band. Further absorption of energy by inverse bremsstrahlung results in avalanche ionization and space charge effects. Electrons are ejected into the vacuum. Electrostatic repulsion between ions remaining in the surface region and attraction to the ejected electrons results in a Coulomb explosion in which ions are "pushed" or "pulled" from the surface, resulting in ablation. In femtosecond laser ablation, the absorption of pulse energy occurs over a short time frame in which energy is transferred to electrons but not directly to phonons, resulting in minimal heating.

[0098] In the laser ablation Coulomb explosion mechanism, bonds between the departing ions and the underlying atoms are broken, but there tends to be no interatomic momentum transfer, as occurs in sputtering processes. Therefore, there is no effect of mass difference. Furthermore, because it is not necessarily the surface layer of atoms that is ablated, surface bond energy is not important in the process. As a result, neither of the two effects that result in preferential sputtering in sputter depth profiling occurs in laser ablation. Therefore, using optimized laser parameters, analysis of the material surface following laser ablation can result in minimal or much less damage to the ablated crater surface compared to ion beam sputtering and more accurate determination of surface composition by XPS / AES.

[0099] Femtosecond laser ablation is an extremely fast process (10 -15 ~10 -12The volume of material removed depends on the energy and spot size of the laser pulse and the operating mode of the laser. Pulsed laser operating modes can vary from single to repetitive pulses at different frequencies. The amount of material removed by a single pulse can range from a few nanometers to over 500 nanometers as energy increases. Therefore, using laser ablation as a material removal process allows tens to hundreds of microns of material to be removed in practical timescales. Therefore, in contrast to sputter depth profiling, which is impractical for accessing such depths, XPS / AES depth profiles can be recorded over much greater depths and deep buried layers and interfaces exposed using laser ablation depth profiling.

[0100] An important process occurring during repeated laser ablation of a surface is the formation of laser-induced periodic surface structures (LIPSS), which exhibit ripple morphology. LIPSS formation is a complex process, and various theories have been proposed to explain this phenomenon [J. Bonse, S. Graf Laser Photonics Reviews 14 (2020) 2000-215]. The formation of LIPSS at surfaces is problematic for electron spectroscopy depth profiling. This is because ripple morphology can roughen the surface and degrade the depth resolution of the depth profile, resulting in poorly resolved layers and / or unclear interfaces in the profile. One of the most accepted theories for LIPSS formation is that incident light is scattered by surface roughness [Bonse and Graf, ibid.]. Other surface waves, such as surface plasmon polaritons, can also be excited. Incident radiation interferes with the primary scattered radiation and surface plasmon polaritons, resulting in spatial variations in the incident beam energy distribution and a ripple morphology that develops on the material surface as the number of ablation pulses increases. Many factors, such as sample roughness, polarization direction, angle of incidence, and material dielectric constant, influence the various LIPSS structures that form [Bonse, and Graf, ibid.]. Because sample roughness and polarization direction are important factors in the formation of LIPSS, various experimental and optical strategies can be used to slow or limit the formation of LIPSS and promote the formation of smoother crater bottoms in the depth profile. To achieve this goal, one or more of the following can be performed: (i) In the optical setup, the plane of polarization of the linearly polarized laser beam is (a) Continuously rotate, (b) converting the light into a circularly or elliptically polarized beam before it hits the sample; and / or (c) Rotating the angle from 0 to 360 degrees stepwise between each laser pulse. and / or (ii) The sample is rotated continuously or rotated between 0 and 360 degrees between each laser pulse.

[0101] FIG. 4B shows the different depth resolutions obtained when depth profiling through a nickel / chromium multilayer structure with (left graph) and without (right graph) rotating the laser polarization between pulses.

[0102] Quantification Electron spectroscopy instruments count the number (intensity) and energy of electrons emitted from the surface of a material following excitation by an energy source (e.g., by X-ray, UV, or electron irradiation). The total electron intensity is plotted as a function of electron (bond or kinetic) energy. Quantification in electron spectroscopy is based on the direct relationship between the intensity of the photoelectron peak and / or the intensity of the Auger electron peak and the mole fraction concentration of the element within the analysis depth. This relationship is expressed by the following equation (1), where I is the peak intensity, J is the photon flux, ρ is the concentration of the atom or ion, σ is the cross section for electron emission, K is the spectrometer coefficient, and L is the electron attenuation length. I=JρσKL (1) The emission cross section σ is the probability that a photoelectron or Auger electron will be emitted from exposure to an energy source. The cross section varies with the element, electron orbital, and total angular moment. The spectrometer factor K accounts for the variability in detector performance from instrument to instrument and incorporates both the transmission function (i.e., the fraction of electrons transmitted through the detector as a function of kinetic energy) and the detector efficiency (i.e., the fraction of transmitted electrons that contribute to the detected signal). The inelastic mean free path represents the distance traveled by the emitted electrons before inelastic scattering. However, a more accurate term, the attenuation length (L), is used in Equation (1) to correct the inelastic mean free path for elastic scattering, allowing for the determination of the intensity emitted from a given depth in a given direction. Inelastic scattering results in electrons that do not contribute to the photoelectron and / or Auger electron peak intensities.

[0103] The contributions of each of the above factors (σ, K, L) to the photoelectron / Auger electron peak intensity for any particular peak in the spectrum are combined into a single term known as the sensitivity factor, F, which allows the relative proportion of that element at the analysis depth to be determined (see Equation (2) below). Sensitivity factors can be obtained from a library of theoretically determined values, experimentally determined values, or user-defined values. If library values ​​are determined for / with electron spectrometers having different transmission functions, a correction for the different transmission functions is required.

[0104] Peak intensities are typically measured graphically as the integrated areas of photoelectron and / or Auger electron peaks after subtracting background signals using appropriate methods. Figure 5A shows the Ag 3d photoelectron peak. The background, C, is calculated using various methods, including the linear, Shirley, or Tougaard methods. Other methods exist for determining peak intensities, such as using peak height instead of peak area or measuring the peak-to-peak derivative spectrum seen in electron-excited Auger spectroscopy.

[0105] Using equation (1) and obtaining a constant photon flux, the normalized peak intensities can be used to calculate element concentrations as atomic percent, assuming a homogeneous mixture of elements exists within the analysis depth. Based on this assumption, the concentration of element A in a multi-element material is given by equation (2) below: [A]atom% = [(I A / F A ) / Σ(I / F)]×100 (2) I and F represent the peak intensity and sensitivity coefficient of the elements detected in the spectrum (I A is the peak intensity of element A, and F A(where is the sensitivity factor for element A). However, in the case of Auger electrons generated using an electron source, corrections for matrix effects are required. Although the sample is assumed to contain a homogeneous mixture of elements within the analysis depth for the quantification of photoelectron and Auger electron spectra, other methods can be used to more accurately describe the elemental distribution within the analysis depth if such a distribution is known or expected to occur within the analysis depth.

[0106] Peak convolution can occur due to overlapping energy peaks or the presence of multiple chemical states. This is shown in Figure 5B. To quantify the different chemical states in such cases, it is necessary to perform peak fitting to separate the peak intensity contributions from the various components present and then quantify them separately, as described in the previous section. The bond / kinetic energies for the different chemical states of the elements are determined from recording standard spectra of such materials with known compositions or from available spectroscopic libraries. Figure 5B shows an example of the C 1s region from an XPS spectrum, including contributions from carbon C-C, C-O, and C=O in different chemical states. Peak fitting was used to determine the relative peak intensities corresponding to each chemical state, allowing for quantification of the various chemical states. The relative atomic concentrations of C-C, C=O, and CO are 77.73%, 12.74%, and 9.53%, respectively.

[0107] To construct a depth profile, electron spectroscopy spectra are recorded from the surface, following each laser ablation cycle. The spectra are quantified, and the chemical composition is determined based on equation (2). For each surface and each cycle / depth for which an electron spectrum was recorded, the fractional composition or elemental chemical state of each element is plotted as a function of the number of laser ablation cycles or depth. The conversion of cycle number to depth can be achieved by measuring the depth or through prior knowledge of the layer thickness. Figures 6a and 6b show examples of quantified laser ablation XPS depth profiles plotted as a function of ablation level and depth, respectively.

[0108] Crater formation The above describes how the ablation beam and the excitation beam are spatially coincident at the sample surface. If the excitation beam is larger or similar in size relative to the area incident on the ablated sample surface region, the excitation beam may be incident on the edge or sidewall of the ablated region. This may cause electrons originating from the edge or sidewall to be emitted and analyzed in addition to electrons emitted from the surface desired to be investigated. These electrons from the edge or sidewall may be from a different chemical composition than the crater surface desired to be investigated, thus causing inaccurate measurements. Therefore, it is desirable for the ablated region to have an area larger than the area of ​​the excitation beam when incident on the sample surface.

[0109] One approach to increasing the surface area of ​​the ablated region is to scan the ablation beam across the sample surface. Another approach is to use a wider beam to ablate a larger area. These options are discussed below.

[0110] Figure 7a is a schematic diagram of a beam scanning technique for generating a larger ablation area on a sample surface. Focused laser pulses 141 from a laser 130 are raster-scanned in a box pattern. The scan consists of overlapping pixels. Each pixel can be ablated by one or more pulses, and then the pulse position is moved to the next pixel. The number of pixels required is determined by the dimensions of the ablated area and the pitch between pixels. In Figure 7, the ablated area has a width of X μm and a length of Y μm. The pixel pitch is x μm in the width direction and y μm in the length direction. At each pixel, the laser delivers a single pulse or multiple pulses at a given repetition rate. By setting a given number of passes to complete the box pattern, the process can be repeated, increasing the crater depth. The sample can also be rotated by a given angle around the center point of the raster area between passes to reduce the roughness of the crater bottom. For example, in the first scan, the pulse position is first moved in the x direction, and after completing a set of x pixels, the position is advanced in the y direction, and these steps are repeated to build a raster scan of area XY. For the next layer, the scanning process can be rotated 90 degrees so that the first scan of pixels is in the y direction, and then the position is advanced in the x direction. Other scan patterns are possible.

[0111] The beam can be moved across the sample by including a movable mirror in the optical system, such as mirror 260 in Figure 3A. In one embodiment, the beam is moved across a sample with a maximum area of ​​2 mm 2 Although preferably 100 nm, it can be larger in other embodiments. Larger areas are useful for accessing deeper layers by overcoming aspect ratio issues that may exist with smaller areas. However, larger areas take longer to ablate.

[0112] Figure 8 is a schematic diagram of Gaussian beam overlap that can be used to achieve uniform radiation intensity on a sample surface for ablation. The diagram shows possible beam overlap conditions, based on full width at half maximum (FWHM), to achieve uniform radiation intensity across a rastered area and thus a flat-bottom crater. As shown in the diagram, the beams at two adjacent pixel locations overlap so that the FWHM of one pixel location just touches the FWHM of the adjacent location.

[0113] Figure 7b is a schematic cross-section of the crater depth showing the flat bottom profile. For comparison, a narrower width excitation beam (such as an X-ray beam) is shown at 151.

[0114] In the X-ray spot size range of 10-400 μm, it is preferable to use the largest possible spot size while maintaining the recommended ratio of crater width to X-ray spot size of 5:1. The center of the X-ray spot for XPS analysis is located at the center of the crater.

[0115] Instead of scanning the beam while keeping the sample position fixed as described above, an alternative approach is to move the sample while keeping the beam position fixed. The laser pulses are focused to a fixed point in x, y, and z that coincides with the focal point of the X-ray beam. The sample stage is raster-scanned with laser ablation steps at each pixel in a similar manner to that described above. After each pass, the stage is returned to the center of the raster area to perform XPS analysis. Again, the sample can be rotated by a given angle around the center of the raster area between passes to reduce roughness at the crater bottom.

[0116] For AES analysis, the electron beam focal position is also centered on the center of the crater, and the same recommended spot size ratios as explained above apply.

[0117] As mentioned above, another alternative is to use a wider beam to ablate that area. Figure 9 is a schematic diagram of an optical setup for generating a top-hat shaped beam or pulse intensity. A top-hat (or flat-top) beam profile is formed using a diffractive optical element (DOE) beam shaping element as part of the optical setup. As shown, the top-hat intensity profile is formed near, but not at, the minimum focused spot. The laser pulse first passes through a beam expander to increase the cross-sectional area of ​​the beam. This may correspond to the beam expander 215 in Figure 3A. The incident Gaussian beam (TEM 00 ) is the nominal diameter 1 / e required by the selected DOE element 2 and is collimated using a variable beam expander. A top-hat or flat-top beam shaping element may correspond to the flat shaper 220 in FIG. 3A. The Gaussian intensity profile is transformed into a uniform intensity spot that is either circular, square, or rectangular at a given working distance from the objective focusing lens. The spot size is determined by the incident beam size, incident beam wavelength, and the effective focal length (EFL) of the focusing lens.

[0118] With this technique, the maximum uniform top hat area is likely to be approximately 500 μm x 500 μm. Therefore, unless this technique is combined with one of the scanning processes mentioned above, the maximum ablation area will also be approximately 500 μm x 500 μm. Using an ideal crater width to x-ray spot size ratio of 5:1, x-ray spot sizes up to 100 μm would be possible, such as in the 10-100 μm range.

[0119] Figure 10 shows the top-hat profile achieved to generate an elliptical crater resulting from a laser at a 45-degree angle relative to the sample surface. Generally, the laser can be at any angle of incidence relative to the sample surface between 0 and 90 degrees, such as between 30 and 60 degrees. In this figure, the flat top was achieved after the focal plane rather than before it, as shown in Figure 9. In the top plot of Figure 10, the solid ellipse indicates the FWHM. In the bottom figure, the intensity profile is taken along the X and Y directions of the top figure. The FWHM in the X direction is approximately 404 μm, and the FWHM in the Y direction is approximately 544 μm.

[0120] Figure 11 shows an example mechanical profilometry trace across the central region of a crater formed on a GaAs single crystal sample using the beam profile in Figure 10. In this example, the beam profile was scanned across the entire sample surface. In Figure 11, a 3 × 3 pixel stage raster was used with an x / y pitch of 200 μm. A single shot was applied per pixel, with 15 levels of ablation and 90° rotation between levels. The pulse energy was approximately 200 μJ per pulse. The pixel positions had approximately 50% overlap, resulting in a smooth crater bottom. Larger crater depths can be achieved with less overlap, which removes more material but at the expense of increased crater surface roughness.

[0121] The advantage of using a scanning approach (i.e., beam or stage scanning) compared to a stationary beam approach (i.e., either Gaussian or top-hat) is an increase in the maximum achievable crater size. Therefore, the maximum profiling depth can also be increased, as the resulting crater aspect ratio allows the X-ray and flood gun beams to access the crater floor at greater depths. This can enable depths in the hundreds of microns range. Conversely, a disadvantage of the scanning approach is the increase in ablation time as the number of pixels increases. In addition, careful determination of pixel pitch may be required to avoid rough crater bottoms from overlapping pulses, which may also result in reduced depth resolution. A combination of the scanning approach and the stationary approach may be preferable when using the scanning approach to mill a channel around the stationary beam crater to provide the X-ray and flood gun beams with access to the crater floor. With the scanning approach, the typical beam size, and therefore the pulse energy, can be reduced compared to the stationary approach. For example, in a scanning approach, the beam diameter may range from 10 to 100 μm and the pulse energy may range from 0.01 to 10 μJ, while in a stationary beam approach, the beam diameter may range from 100 to 500 μm and the pulse energy may range from 10 to 1000 μJ. Lower pulse energies within the range may require multiple pulses in a burst at each pixel and / or level, using repetition rates in the range of 0.001 to 200 kHz.

[0122] result Figures 12-15 show the results of using the laser setup shown in Figure 3A for XPS depth profiling of femtosecond laser ablation. The laser pulse duration used in each case was 160 fs and the wavelength was 1030 nm. A comparison with sputter depth profiling is also provided. Figures 12 and 13 show the extent to which the preferential sputtering effect is avoided for two technologically important inorganic materials, TiO2 and InP, by using femtosecond laser ablation.

[0123] Figure 12 shows XPS depth profiles obtained for a bulk TiO2 sample. Figure 12a shows compositional depth profiles obtained using femtosecond laser ablation for nine ablation levels (energy per pulse: 120 μJ). Figure 12b shows compositional depth profiles obtained using conventional sputtering with a 500 eV argon ion beam. Compositional data was recorded after 10 seconds of etching, and the etch-measurement cycle continued for a total time of 90 seconds with a 10-second etching period. Figure 12c shows compositional depth profiles obtained using conventional sputtering with an 8 keV 300 argon atomic GCIB. Compositional data was recorded after 30 seconds of etching, and the etch-measurement cycle continued for a total time of 270 seconds with a 30-second etching period. The elements in the sample and their chemical states are determined using XPS based on the intensity and energy of the emitted electrons.

[0124] As shown in Figure 12(d), in the Ti 2p peak, the chemical state of Ti in TiO2 is Ti with a binding energy of 459.0 eV. 4+ 12(e) and 12(f) show the lower oxidation states of Ti, i.e., Ti with binding energies of 457.7 eV and 456.5 eV, respectively, as explained below. 3+ and Ti 2+ Shows.

[0125] The sample composition at the surface (initial period) differs from the composition after the first ablation / ion etching due to the presence of surface hydrocarbon contamination. The hydrocarbon XPS C 1s contamination signal has been removed from the profile as it is not relevant for determining the TiO stoichiometry. Measurements after the initial period relate to bulk TiO. In Figure 12a, the O concentration was found to be 67 atomic % and the Ti concentration was 33 atomic %, indicating that the TiO stoichiometry was determined for the femtosecond laser ablation method. 2.0 In Figures 12b and 12c, the O concentration is about 62 atomic % and the Ti concentration is about 38 atomic %. Therefore, the stoichiometry is + TiO for ion sputtering1.65 and 8 keV Ar 300 + Cluster sputtering of TiO 1.70 The Ti 2p spectra (Fig. 12d-f) show a Ti 2p profile (Fig. 12d) similar to that expected for TiO2. 4+ Although only the presence of Ar at 500 eV is shown, + Ion sputtering (Fig. 12e) and 8 keV Ar 300 + For both cluster sputtering (Fig. 12f), the Ti sputtering was due to the preferential sputtering of O as a result of the ion beam bombardment. 3+ State and Ti 2+ The existence of the state can be clearly observed.

[0126] Figure 13 shows the InP 1.0 Figure 13a shows the profile produced by femtosecond laser ablation with pulses of approximately 120 μJ over 18 repetitions. Figure 13b shows the profile produced for 500 eV argon ion sputtering over 390 seconds. In the case of femtosecond laser ablation, the In and P concentrations are very similar at 50 atomic %, whereas in the case of sputtering, the In concentration is significantly higher than the P concentration. As a result, in the femtosecond laser depth profile, the recorded stoichiometry is InP 1.0 In sputtering, InP 0.7 This is due to the preferential sputtering of P from the sample.

[0127] To demonstrate the rapid depth profiling capabilities and ability to extend the femtosecond laser ablation XPS technique to multi-micron depths, an analysis of an iron oxide layer is shown in Figure 14. Femtosecond laser ablation XPS depth profiling was performed on a 7 μm layer of iron oxide grown on iron. The sample underwent approximately 100 ablation passes (four passes at each repetition level) with an energy of approximately 300 μJ per pulse (with a 1-second pause between laser shots). After this, the iron substrate was reached. Each laser ablation shot removed approximately 70 nm of material, and the profile was performed in approximately 1.5 minutes, excluding XPS analysis time. As shown in Figure 14b, the metal oxide exhibits two distinct layers, with the outer layer exhibiting a higher O concentration and the inner layer having a lower O content. Figure 14a shows the Fe 2p spectra from three distinct regions: the outer layer, the inner layer, and the substrate. Fe 0 The spectrum is from the iron metal substrate. The other two spectra represent different chemical forms of iron oxide in the layer, namely Fe 2+ (FeO) and Fe 2+ / Fe 3+ The figure shows spectral features (peak shifts and shake-up satellites) indicative of Fe3O4. Fe3O4 is evident in the first four ablation iterations, then changes to FeO from around iterations 8 to 18. Starting at iteration 18, the oxidation signal rapidly decreases as the Fe at the bottom approaches. Therefore, as can be seen, important chemical information is retained. Principal component analysis can be used to identify "fingerprint spectra" associated with different chemical states of Fe and extract the regions within the profile where those individual spectra reside. Thus, in Figure 14c, the chemical composition of each layer can be plotted, revealing the Fe3O4 / FeO layered structure of the oxide. For comparison, a high-current, fast etch rate using a 500 eV argon ion beam etches at a rate of around 10 nm / min, resulting in a total etch time of 700 min (11.7 h) for a similar depth. Furthermore, iron oxide undergoes preferential sputtering of O, while Fe 3+ The species is Fe under ion beam bombardment. 2+and further reduced to metallic Fe, so sputter depth profiling does not retain important chemical information of the different oxides formed.

[0128] A further example of the benefits of the femtosecond laser ablation XPS technique is shown in Figure 15 for a polymer sample, namely, PET. The sample is a 12 μm layer on steel. Figure 15a shows 24 iterations of femtosecond laser ablation with a single-shot pulse energy of 300 μJ per iteration. The total time for this ablation and measurement sequence was approximately 10 minutes. As the number of iterations and depth into the PET layer increased, the carbon:oxygen ratio remained constant, indicating no chemical changes with increasing depth. After 7–8 pulses, the presence of iron in the steel rapidly became apparent. Figures 15b and 15c show the C 1s and O 1s spectra, respectively, for the first 7–8 iterations of ablation. Good uniformity is observed between the traces in each plot, indicating the correct chemical state and relative intensities of the PET, with no signs of chemical damage. Seven to eight iterations of ablation and measurement were achieved after approximately 2.5 minutes. In comparison, argon ion cluster sputtering is required to preserve the chemical information of PET, as seen in the femtosecond laser ablation C 1s and O 1s XPS spectra, and the etch depth reached after 3 hours of sputtering (excluding the XPS measurement time) would be only about 5 μm.

[0129] Those skilled in the art will readily appreciate that various modifications and variations can be made to the above-described methods and apparatus. Modifications may be made without departing from the scope of the appended claims. For example, the pulse parameters of the ablation laser or the size and shape of the ablated region can be changed. Method steps from different embodiments can be combined, and alternative components can be used for the ablation laser.

[0130] Embodiments of the present invention are described in the following clauses. A1. A method for determining the chemical composition of a sample using electron spectroscopy, the method comprising: ablating material from a region on a surface of the sample by irradiating the region with one or more pulses of a laser; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; repeating the steps of ablating material, irradiating with an excitation beam, and measuring intensity and energy to determine a quantitative surface depth profile of the chemical composition of at least a portion of the sample. A2. The method of clause A1, further comprising, prior to initially ablating material from the region, irradiating at least a portion of the unablative region with an excitation beam of electron radiation or electromagnetic radiation, and measuring the intensity and energy of electrons emitted from at least a portion of the unablative region of the sample as a result of the excitation beam. A3. The method of clause A1 or clause A2, further comprising determining the chemical states of elements in the chemical composition from the intensity and energy of the emitted electrons. A4. The method of any of clauses A1-A3, further comprising determining the depth or relative depth of one or more ablated regions. A5. The method of any of clauses A1-A4, wherein one or more pulses of the laser beam each have a duration of less than 1 ns or less than 1 ps. A6. The method of any of clauses A1-A5, further comprising repeating the steps of ablating material, irradiating with an excitation beam, and measuring the energy and intensity of the emitted electrons to determine a depth profile to a depth of greater than 5 μm. A7. The method of any of clauses A1-A6, wherein each step of ablating material includes removing a layer having a thickness in the range of 0.3 nm to 1 μm. A8. The method of any of clauses A1-A7, wherein the excitation beam is a beam of X-rays. A9. The method of any of clauses A1-A8, wherein the excitation beam is a beam of X-rays and the spectroscopic method is XPS. A10. The method of any of clauses A1-A9, further comprising tilting the sample relative to the ablative laser beam. A11. The method of any of clauses A1-A10, further comprising either (i) rotating the sample in the plane of its surface between ablation steps and / or between laser pulses, and / or (ii) rotating the plane of polarization of the laser pulses between ablation steps and / or between laser pulses, or (iii) converting the polarization of the laser pulses to circular or elliptical polarization. A12. The method of any of clauses A1-A11, wherein the one or more pulses ablate material by Coulomb explosion. A13. The method of any of clauses A1-A12, wherein the step of ablating material forms a crater in the surface of the specimen, and at least a portion of the area irradiated with the excitation beam of electrons includes an area at the base of the crater. A14. The method of clause A13, wherein the crater has a substantially flat bottom and the excitation beam irradiates at least a portion of the substantially flat bottom. A15. The method of any of clauses A14, wherein the excitation beam irradiates at least a portion of the substantially flat bottom and does not irradiate the edges or sidewalls of the crater. A16. The method of any of clauses A13-A15, wherein the width of the substantially flat bottom of the crater is greater than the width of the excitation beam. A17. The method of any of clauses A13-A16, wherein the step of ablating material from a region of the sample includes moving the relative position of the laser pulse to scan the pulse across a region of the surface of the sample to ablate a crater in the surface. A18. The method according to clause A17, wherein the relative position of the laser pulse is moved by scanning the laser or by scanning the position of the sample. A19. The method of clause A17 or A18, wherein scanning includes irradiating the sample with one or more pulses at a plurality of overlapping pixel locations. A20. The method of any of clauses A1-A19, wherein the laser is incident at an angle other than normal to the surface being ablated, such as 30-60 degrees. A21. The method of any of clauses A13-A20, further comprising passing the laser pulse through a beam shaping element to convert the laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the sample surface. A22. The method of any of clauses A13-A21, further comprising passing the laser pulses through a polarization adjusting optics to change the direction of linear polarization of the laser beam or convert the linear polarization of the laser beam to circular or elliptical polarization of the laser beam. A23. The method of clause A21 or A22, wherein the beam-shaping element comprises a diffractive optical element or a refractive optical element. A24. The method of any of clauses A1-A23, wherein the laser pulses have durations of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs, respectively. A25. The method of any of clauses A1-A24, wherein the energy per laser pulse is in the range of 10 nJ to 1000 μJ, such as 50 to 500 μJ. A26. The method of any of clauses A1-A25, wherein the spot size of the laser pulse on the sample surface is in the range of 1 to 1000 μm. A27. setting, by the controller, one or more parameters of the pulses of the laser based on compositional information about the sample; The method of any of clauses A1-A26, further comprising performing the step of ablating material, wherein parameters of the laser pulses are set by the controller. A28. The method of clause A27, wherein the one or more parameters of the laser pulse set by the controller include one or more of pulse duration, pulse energy, repetition frequency, wavelength, and spot size. A29. The setting step includes receiving input from a user indicating compositional information about the sample; The method of clause A27 or A28, further comprising: the controller adjusting one or more laser parameters based on the composition information. A30. performing a survey scan or survey profile to determine approximate measurements of elemental constituents in the sample; The method of any one of clauses A27-A28, further comprising: generating one or more parameters of the laser pulse based on the estimated measurements. A31. The method of any of clauses A27-A30, further comprising: performing mechanical profilometry, microscopy, or white light interferometry of the sample surface; and generating or adjusting one or more parameters of the laser pulses based on the profilometry, microscopy, or white light interferometry. A32. The method of any of clauses A27-A31, further comprising the controller using a reference database or algorithm to determine the laser parameters based on information about the sample. A33. The method of any of clauses A27-A32, further comprising, following the steps of ablating material, irradiating with an excitation beam, and measuring electron intensity and energy, adjusting one or more parameters of the laser based on measured or predicted compositional information about the sample at a depth after ablation, and repeating the steps of ablating material, irradiating with an excitation beam, and measuring electron intensity and energy using the adjusted one or more parameters of the laser. A34. The method of clause A33, further comprising repeating the steps of adjusting, ablating material, irradiating with the excitation beam, and measuring electron intensity and energy until the sample is analyzed to the target depth. A35. Further comprising placing a sample on a sample stage in a vacuum chamber, followed by the steps of ablat- ing material, irradiating with an excitation beam, and measuring the intensity and energy of the emitted electrons; The method according to any one of clauses A1 to A34, wherein the sample is not moved an amount greater than the size of the sample between the ablation step and the excitation beam irradiation step. A36. The method of any of clauses A1-A35, wherein the laser pulse and the excitation beam are spatially coincident at the sample surface. A37. The method of clause A35, wherein the ablation step includes raster scanning an ablative laser pulse over the sample surface, the excitation beam being coincident with the ablated sample surface. B38. A method of electron spectroscopy comprising: ablation of material from an area on a surface of a specimen by irradiating the area with one or more pulses of a laser, the ablation forming a crater on the surface of the specimen; irradiating at least a portion of the ablated region at the bottom of the crater with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; and determining the chemical composition of the surface of the crater based on the measured intensity and energy of the emitted electrons. C39. A method of electron spectroscopy comprising: ablation of material from a region of the sample by irradiating the region of the surface of the sample with one or more pulses of a laser, the laser pulse having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; irradiating at least a portion of the ablated region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; and determining the chemical composition of the surface based on the measured intensity and energy of the emitted electrons. D40. Electron spectroscopy method comprising: setting, by the controller, one or more parameters of the pulses of the laser based on compositional information about the sample; ablation of material from a region of the sample by applying one or more pulses of a laser to the region of the surface of the sample, the pulse parameters being set by a controller; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; and determining the chemical composition of the surface based on the measured intensity and energy of the emitted electrons. E41. A method of electron spectroscopy comprising: placing a sample on a sample stage within a vacuum chamber; ablation of material from a region of a surface of the sample by irradiating the region with one or more pulses of a laser; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; determining the chemical composition of the surface based on the measured intensity and energy of the emitted electrons; The method, wherein the sample is not moved an amount greater than the size of the sample between the ablation step and the excitation beam irradiation step. F42. A method of electron spectroscopy comprising: placing a sample on a sample stage within a vacuum chamber; ablation of material from a region of a surface of the sample by irradiating the region with one or more pulses of the laser, the laser being configured to direct the pulses toward the surface of the sample; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from at least a portion of the area of ​​the specimen as a result of the excitation beam; determining the chemical composition of the surface based on the measured intensity and energy of the emitted electrons; A method in which the laser pulse and the excitation beam are spatially coincident at the sample surface. G43. Electron spectroscopy equipment for determining the chemical composition of a sample, the equipment comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam and determine a quantitative surface depth profile of the sample's chemical composition. G44. The apparatus of clause G43, wherein the electron analyzer is further configured to determine the chemical states of elements in the chemical composition from the intensity and energy of the emitted electrons. G45. The apparatus of clause G43 or G44, wherein the laser is configured to generate pulses having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs. G46. An apparatus described in any of clauses G43 to G45, wherein the excitation beam source is configured to generate a beam of X-rays. G47. An apparatus described in any of clauses G43 to G45, wherein the excitation beam source is configured to generate a beam of X-rays and the electron analyzer is configured to measure photoelectrons. G48. An apparatus described in any of clauses G43 to G47, wherein the sample stage is configured to tilt relative to the ablation laser beam. G49. A method according to any of clauses G43 to G48, wherein (i) the sample stage is configured to rotate the sample in the plane of the sample's surface, and the controller is configured to control the sample stage to rotate between ablation steps and / or between laser pulses, and / or the laser comprises a polarization controller configured to (ii) rotate the plane of polarization of the laser pulses between ablation steps and / or between laser pulses, or (iii) convert the polarization of the laser pulses to circular or elliptical polarization. G50. An apparatus according to any one of clauses G43 to G49, wherein the sample stage comprises a positioning device for moving the sample in an orthogonal direction in the sample plane so as to raster scan the sample relative to the incidence position of the ablation laser pulse. G51. An apparatus according to any one of clauses G43 to G50, wherein the laser is provided with a mirror to adjust the position of incidence of the laser pulse on the sample so as to raster scan the laser pulse across the sample. G52. An apparatus according to any of clauses G43 to G51, wherein the laser is provided with a beam shaping element to convert the laser pulse to have a substantially flat-top intensity profile or a top-hat intensity profile across its diameter incident on the sample surface. G53. An apparatus as described in clause G52, wherein the laser beam shaping element is configured to transform the laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the sample surface, the diameter at the surface of the sample being greater than the diameter of the excitation beam at the surface of the sample. G54. An apparatus according to clause G52 or G53, wherein the beam-shaping element comprises a diffractive optical element or a refractive optical element. G55. An apparatus described in any of clauses G43 to G54, wherein the laser is configured to generate pulses having an energy in the range of 10 nJ to 1000 μJ per pulse. G56. An apparatus described in any of clauses G43 to G55, wherein the laser is configured to generate pulses having a spot size at the sample surface in the range of 1 to 1000 μm. G57. The apparatus of any of clauses G43-G56, further comprising a controller configured to adjust one or more parameters of the pulses of the laser based on compositional information about the sample. G58. An apparatus described in any of clauses G43 to G57, wherein the one or more parameters of the laser pulse set by the controller include one or more of pulse duration, pulse energy, repetition frequency, wavelength, and spot size. G59. The controller receiving input from a user indicating compositional information regarding the sample; The apparatus of any of clauses G43-G58, configured to adjust one or more laser parameters based on the composition information. G60. An apparatus described in any of clauses G43 to G59, wherein the controller is configured to determine the laser parameters based on information about the sample by reference to a reference database or algorithm. G61. An apparatus described in any of clauses G43 to G60, wherein the laser source and the excitation beam source are configured to direct the laser pulses and the excitation beam, respectively, to spatially coincide at the sample surface. H62. An electron spectrometer, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen, the laser configured to ablate material to form a crater in the surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the sample's chemical composition. I63. An electron spectrometer, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct them to a target area of ​​the sample to ablate a surface of the sample, the laser configured to generate pulses having a duration of less than 1 ns, 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the sample's chemical composition. J64. An electron spectrometer, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; a controller configured to adjust or set one or more parameters of the pulses of the laser based on information about the sample; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the sample's chemical composition. K65. Electron spectroscopy equipment, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the sample's chemical composition; The sample stage is configured for a maximum travel that corresponds to the size of the sample in the apparatus. L66. Electron spectroscopy equipment, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward a target area of ​​the specimen; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the sample surface in response to the excitation beam to determine a surface depth profile of the sample's chemical composition; The apparatus, wherein the laser source and the excitation beam source are configured to direct the laser pulse and the excitation beam, respectively, to spatially coincide at the sample surface.

Claims

1. 1. A method for determining the chemical composition of a sample using electron spectroscopy, the method comprising: ablation of material from a region of a surface of a specimen by irradiating the region with one or more laser pulses; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; repeating the steps of ablating the material, irradiating the excitation beam, and measuring the intensity and energy to determine a quantitative surface depth profile of the chemical composition of at least a portion of the sample.

2. 10. The method of claim 1, further comprising, prior to initially ablating material from the region, irradiating at least a portion of an unablated region with an excitation beam of electron radiation or electromagnetic radiation, and measuring the intensity and energy of electrons emitted from the at least a portion of the unablated region of the specimen as a result of the excitation beam.

3. 3. The method of claim 1 or claim 2, further comprising determining chemical states of elements in the chemical composition from the intensities and the energies of the emitted electrons.

4. The method of any one of claims 1 to 3, further comprising determining a depth or relative depth of the ablated region or regions.

5. The method of any one of claims 1 to 4, wherein the one or more pulses of the laser beam each have a duration of less than 1 ps.

6. 6. The method of claim 1, further comprising repeating the steps of ablating the material, irradiating with the excitation beam, and measuring the energy and intensity of the emitted electrons to determine a depth profile to a depth of more than 5 μm.

7. A method according to any one of claims 1 to 6, wherein each step of ablating material comprises removing a layer having a thickness in the range of 0.3 nm to 1 μm.

8. The method according to any one of claims 1 to 7, wherein the excitation beam is a beam of X-rays.

9. The method according to any one of claims 1 to 8, wherein the excitation beam is a beam of X-rays and the spectroscopy method is XPS.

10. The method of any one of claims 1 to 9, further comprising tilting the sample relative to the ablation laser beam.

11. 11. The method of claim 1, further comprising either (i) rotating the sample in the plane of the surface of the sample between the ablation steps and / or between the laser pulses, and / or (ii) rotating the plane of polarization of the laser pulses between the ablation steps and / or between the laser pulses, or (iii) converting the polarization of the laser pulses to circular or elliptically polarized light.

12. The method of any one of claims 1 to 11, wherein the one or more pulses ablate material by Coulomb explosion.

13. 13. The method of any one of claims 1 to 12, wherein the step of ablating material forms a crater in the surface of the specimen, and wherein the at least part of the area irradiated with the excitation beam of electrons comprises an area at the base of the crater.

14. The method of claim 13 , wherein the crater has a substantially flat bottom, and the excitation beam illuminates at least a portion of the substantially flat bottom.

15. The method of claim 14 , wherein the excitation beam illuminates the at least a portion of the substantially flat bottom and does not illuminate an edge or sidewall of the crater.

16. The method according to any one of claims 13 to 15, wherein the width of the substantially flat bottom of the crater is greater than the width of the excitation beam.

17. 17. The method of any one of claims 13 to 16, wherein ablating material from a region of the specimen comprises moving the relative position of the laser pulse to scan the pulse across the region of the surface of the specimen to ablate the crater in the surface.

18. 18. The method of claim 17, wherein the relative position of the laser pulse is moved by scanning the laser or by scanning the position of the sample.

19. 19. The method of claim 17 or 18, wherein the scanning comprises irradiating the sample with one or more pulses at a plurality of overlapping pixel locations.

20. 20. The method of any one of claims 1 to 19, wherein the laser is incident at a non-normal angle to the surface to be ablated, such as 30 to 60 degrees.

21. 21. The method of any one of claims 13 to 20, further comprising passing the laser pulse through a beam shaping element to convert the laser pulse to have a substantially flat-top or top-hat intensity profile across its diameter incident on the surface of the sample.

22. 22. The method of any one of claims 13 to 21, further comprising passing the laser pulses through polarization adjusting optics to change the direction of linear polarization of the laser beam or convert the linear polarization of the laser beam to circular or elliptical polarization of the laser beam.

23. 23. The method of claim 21 or 22, wherein the beam-shaping element comprises a diffractive or refractive optical element.

24. The method of any one of claims 1 to 23, wherein the laser pulses have a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs, respectively.

25. A method according to any one of the preceding claims, wherein the energy per laser pulse is in the range of 10 nJ to 1000 μJ, such as 50 to 500 μJ.

26. The method of any one of claims 1 to 25, wherein the spot size of the laser pulse on the surface of the sample is in the range of 1 to 1000 µm.

27. setting, by a controller, one or more parameters of the laser pulse based on compositional information about the sample; The method of any one of claims 1 to 26, further comprising performing the step of ablating the material, wherein the parameters of the laser pulses are set by the controller.

28. 28. The method of claim 27, wherein the one or more parameters of the laser pulse set by the controller include one or more of pulse duration, pulse energy, repetition frequency, wavelength, and spot size.

29. The step of configuring includes receiving input from a user indicating the compositional information for the sample; 29. The method of claim 27 or 28, further comprising: the controller adjusting the one or more laser parameters based on the composition information.

30. performing a survey scan or survey profile to determine approximate measurements of elemental constituents in the sample; 29. The method of claim 27 or 28, further comprising generating the one or more parameters of the laser pulse based on the approximate measurements.

31. 31. The method of any one of claims 27 to 30, further comprising: performing mechanical profilometry, microscopy, or white light interferometry of a surface of the sample; and generating or adjusting the one or more parameters of the laser pulses based on the mechanical profilometry, microscopy, or white light interferometry.

32. 32. The method of any one of claims 27 to 31, further comprising the controller using a reference database or algorithm to determine the laser parameters based on the information about the specimen.

33. 33. The method of any one of claims 27 to 32, further comprising, following the steps of ablating material, irradiating with an excitation beam, and measuring electron intensity and energy, adjusting the one or more parameters of the laser based on measured or predicted composition information for the sample at a depth after the ablation, and repeating the steps of ablating material, irradiating with the excitation beam, and measuring electron intensity and energy using the adjusted one or more parameters of the laser.

34. 34. The method of claim 33, further comprising repeating the steps of adjusting, ablating material, irradiating with the excitation beam, and measuring electron intensity and energy until the sample is analyzed to a target depth.

35. further comprising placing the sample on a sample stage in a vacuum chamber, followed by the steps of ablating the material, irradiating with the excitation beam, and measuring the intensity and energy of the emitted electrons; 35. The method of any one of claims 1 to 34, wherein the sample is not moved an amount greater than the size of the sample between the ablation step and the excitation beam irradiation step.

36. The method of any one of claims 1 to 35, wherein the laser pulse and the excitation beam are spatially coincident at the surface of the sample.

37. 36. The method of claim 35, wherein the ablation step comprises raster scanning the ablative laser pulses across a surface of the specimen, the excitation beam being coincident with the ablated specimen surface.

38. 1. A method of electron spectroscopy comprising: ablation of material from an area on a surface of a specimen by irradiating the area with one or more laser pulses, the ablation forming a crater in the surface of the specimen; irradiating at least a portion of the ablated area at the bottom of the crater with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface of the crater based on the measured intensity and energy of the emitted electrons.

39. 1. A method of electron spectroscopy comprising: ablation of material from a region of a surface of the sample by irradiating the region with one or more laser pulses, the laser pulses having a duration of less than 1 ns, less than 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; irradiating at least a portion of the ablated region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons.

40. 1. A method of electron spectroscopy comprising: setting, by the controller, one or more parameters of the laser pulse based on compositional information about the sample; ablation of material from the region of the sample by applying the one or more laser pulses to the region of the surface of the sample, the parameters of the pulses being set by the controller; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; and determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons.

41. 1. A method of electron spectroscopy comprising: placing a sample on a sample stage within a vacuum chamber; ablation of material from a region of the surface of the sample by irradiating the region with one or more laser pulses; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons; The method, wherein the sample is not moved an amount greater than the size of the sample between the ablation step and the excitation beam irradiation step.

42. 1. A method of electron spectroscopy comprising: placing a sample on a sample stage within a vacuum chamber; ablation of material from a region of the surface of the sample by irradiating the region with one or more laser pulses, the laser configured to direct pulses toward the surface of the sample; irradiating at least a portion of the region with an excitation beam of electron or electromagnetic radiation; measuring the intensity and energy of electrons emitted from the at least a portion of the region of the sample as a result of the excitation beam; determining a chemical composition of the surface based on the measured intensity and energy of the emitted electrons; The method, wherein the laser pulse and the excitation beam are spatially coincident at the surface of the sample.

43. 1. An electron spectroscopy apparatus for determining the chemical composition of a sample, said apparatus comprising: a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam and determine a quantitative surface depth profile of the chemical composition of the sample.

44. An electron spectroscopy apparatus, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen, the laser configured to ablate material to form a crater in the surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

45. An electron spectroscopy apparatus, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the sample to ablate a surface of the sample, the laser configured to generate pulses having a duration of less than 1 ns, 1 ps, less than 500 fs, less than 100 fs, less than 10 fs, or less than 1 fs; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

46. An electron spectroscopy apparatus, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; a controller configured to adjust or set one or more parameters of the pulses of the laser based on information about the sample; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample.

47. An electron spectroscopy apparatus, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample; The apparatus, wherein the sample stage is configured for a maximum amount of movement corresponding to a size of the sample.

48. An electron spectroscopy apparatus, a vacuum chamber; a sample stage mounted within the vacuum chamber, the sample stage configured to receive a sample to be analyzed; a laser configured to generate laser pulses and direct the laser pulses toward a target area of ​​the specimen to ablate a surface of the specimen; an excitation beam source configured to generate an excitation beam of electron or electromagnetic radiation and direct the excitation beam toward the target area of ​​the sample; an electron analyzer and detector configured to measure the energy and intensity of electrons emitted from the surface of the sample in response to the excitation beam to determine a surface depth profile of the chemical composition of the sample; The apparatus, wherein the laser light source and the excitation beam source are configured to direct the laser pulse and the excitation beam, respectively, to spatially coincide at the surface of the sample.

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