System and method for characterizing a film by X-ray photoelectron and low-energy X-ray fluorescence spectroscopy

Systems and methods for characterizing films by X-ray photoelectron spectroscopy (XPS) are disclosed. For example, a system for characterizing a film may include an X-ray source for generating an X-ray beam having an energy below the k-edge of silicon. A sample holder may be included for positioning a sample in a pathway of the X-ray beam. A first detector may be included for collecting an XPS signal generated by bombarding the sample with the X-ray beam. A second detector may be included for collecting an X-ray fluorescence (XRF) signal generated by bombarding the sample with the X-ray beam. Monitoring/estimation of the primary X-ray flux at the analysis site may be provided by X-ray flux detectors near and at the analysis site. Both XRF and XPS signals may be normalized to the (estimated) primary X-ray flux to enable film thickness or dose measurement without the need to employ signal intensity ratios.

BACKGROUND

Embodiments of the invention are in the field of X-ray photoelectron spectroscopy (XPS) Analysis and, in particular, systems and methods for characterizing films by XPS.

2) Description of Related Art

X-ray photoelectron spectroscopy (XPS) is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra may be obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top, e.g., 1 to 10 nm of the material being analyzed. XPS analysis commonly employs monochromatic aluminum Kα (AlKα) X-rays, which may be generated by bombarding an aluminum anode surface with a focused electron beam. A fraction of the generated AlKα X-rays is then intercepted by a focusing monochromator and a narrow X-ray energy band is focused onto the analysis site on a sample surface. The X-ray flux of the AlKα X-rays at the sample surface depends on the electron beam current, the thickness and integrity of the aluminum anode surface, and crystal quality, size, and stability of the monochromator.

X-ray fluorescence (XRF) is the emission of characteristic “secondary” (or fluorescent) X-rays from a material that has been excited by bombarding with higher energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science and archaeology.

XPS analysis and XRF analysis each have their own advantages and drawbacks as techniques for sample characterization. Thus, advances are needed in analyses based on XPS and/or XRF detection.

SUMMARY

Embodiments of the present invention pertain to systems and methods for characterizing films by X-ray photoelectron spectroscopy (XPS).

In an embodiment, a system for characterizing a film includes an X-ray source for generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. A sample holder is included for positioning a sample in a pathway of the X-ray beam. A first detector is included for collecting an XPS signal generated by bombarding the sample with the X-ray beam. A second detector is included for collecting an XRF signal generated by bombarding the sample with the X-ray beam.

In another embodiment, a method for characterizing a film having a metal or element species includes generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. A sample is positioned in a pathway of the X-ray beam. An XPS signal generated by bombarding the sample with the X-ray beam is collected. An XRF signal generated by bombarding the sample with the X-ray beam is also collected.

In another embodiment, a monochromator for focusing an X-ray beam having an energy below the absorption edge (k-edge) of silicon includes a layer of indium antimonide (InSb) disposed directly on and conformal with a substrate layer of glass.

In another embodiment, a monochromator for focusing an X-ray beam having an energy below the absorption edge (k-edge) of silicon includes a layer of indium antimonide (InSb) disposed on and conformal with a layer of silicon. The layer of silicon is disposed above and conformal with a substrate layer of glass.

In another embodiment, a system for characterizing a film includes an X-ray source for generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. A sample holder is included for positioning a sample in a pathway of the X-ray beam. A monochromator is positioned between the X-ray source and the sample holder and in the pathway of the X-ray beam. The monochromator includes a layer of indium antimonide (InSb) disposed on and conformal with a layer of silicon. The layer of silicon and InSb is disposed above and conformal with a substrate layer of glass having a suitable doubly curved shape, e.g., ellipsoidal or toroidal). In one such embodiment, the monochromator structure (e.g., InSb/Si/Substrate) provides point-to-point focusing of X-rays emitted from the X-ray source (e.g., an anode) into a monochromatic X-ray spot focused at the sample. A detector for collecting an XPS signal generated by bombarding the sample with the X-ray beam is also included.

DETAILED DESCRIPTION

Systems and methods for characterizing films by X-ray photoelectron spectroscopy (XPS) are described. In the following description, numerous specific details are set forth, such as calibration techniques and system arrangements, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known features such as entire semiconductor device stacks are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

Various electronic events may occur when a sample including a layer disposed above a substrate is bombarded with X-rays. For example, an electron may be released from the sample. X-ray photoemission may occur for an electron generated within the top, e.g., 10 nanometers of the sample. Most information from an XPS measurement is usually obtained near the surface since attenuation of the electron signal occurs as the electrons travel through material on their way out. For measurements deeper in the sample (e.g., 0.1->2 microns deep), X-ray fluorescence (XRF) may be used since XRF signals typically attenuate 1000 times less than XPS photoelectron signals and are thus less susceptible to effects of depth within a sample.

XPS analysis commonly employs monochromatic aluminum Kα (AlKα) X-rays, which may be generated by bombarding an aluminum anode surface with a focused electron beam. The Al-based X-rays are typically focused with a quartz crystal monochromator. XPS signals obtained from samples bombarded with such radiation are typically strong and therefore often provide very meaningful data. However, as mentioned above, XRF measurements may also be needed to obtain information from deeper within a sample or information that is largely independent of layer thickness or depth. AlKα X-rays could also be utilized as a primary source for X-ray fluorescence analysis. However, the AlKα X-ray energy (1486.7 eV) is too low to generate useable XRF signals from a number of technologically important materials, including Al, Hf, and Ta. It is therefore desirable to utilize primary X-rays of somewhat higher energy than AlKα. At the same time, it is desirable to keep the excitation energy below the absorption edge for Si Kα X-ray generation for XRF (and XPS) analysis, about 1840 eV. By doing so, we avoid swamping the XRF measurement with a silicon signal from the Si substrate. Another approach to minimizing the competition with the Si signal would be to use X-ray energies well above the Si absorption edge (W Kα at 59 keV, Mo Kα at 17.5 keV, Ag Kα at 22 keV, Cr Kα at 5.4 keV, Cu Kα at 8 keV). These X-ray energies do preferentially excite higher-energy XRF signals and enhance their detection (for example for Hf or Zr), but at the expense of light element XRF detection (such as Al, O, or N). The higher X-ray energies also lead to a substantial loss in XPS photoelectron emission cross section (detectable signal).

In accordance with an embodiment of the present invention, X-rays with an energy less than the absorbing edge of silicon are used for XPS measurements. By using X-rays with an energy below the absorbing edge of silicon, enhanced XRF measurements without silicon signal interference may be made while accessing a broader range of element coverage of relevant materials (i.e., Al and Hf). For example, in one embodiment, XPS measurements are made using tungsten-sourced (W Mα) X-rays. Both XPS and XRF measurements are collected and are used together to aid in characterization of the sample. In an embodiment, an indium antimonide (InSb) monochromator is used with a tungsten-based X-ray source. In one such embodiment, a monochromator composed of a thin crystalline InSb layer bonded to a curved substrate surface is employed. In another such embodiment, a bilayer monochromator of InSb disposed on a layer of silicon (Si) is used and is bonded to a curved surface. Monitoring/estimation of the primary X-ray flux at the analysis site may be provided by X-ray flux detectors near and at the analysis site. Both XRF and XPS signals may be normalized to the (estimated) primary X-ray flux to enable film thickness or dose measurement without the need to employ signal intensity ratios.

In an aspect of the present invention, a film measurement system includes both an XPS detector and an XRF detector. For example,FIG. 1is an illustration representing a film measurement system having XPS and XRF detection capability, in accordance with an embodiment of the present invention.

Referring toFIG. 1, a film measurement system100includes an XPS/XRF generation and detection system housed in a chamber101coupled with a computing system122. The XPS/XRF generation and detection system includes an electron beam source102provided for generating an electron beam104. Electron beam104is used to generate an X-ray beam108by bombarding an anode106. A monochromator109is provided for transporting a monochromatized X-ray beam110from X-ray beam108. A sample holder111may be used to position a sample199in a pathway of monochromatized X-ray beam110.

An XPS detector114is provided for collecting an XPS signal112generated by bombarding sample199with monochromatized X-ray beam110. An XRF detector116is provided for collecting an XRF signal118also generated by bombarding sample199with monochromatized X-ray beam110. In an embodiment, system100is configured to collect XRF signal118and XPS signal112simultaneously or near simultaneously, representing single sampling event. The XPS signal112and XRF signal118are composed of photo-electrons and fluorescent X-rays, respectively. Additionally, a flux detector120may be provided for determining an estimated flux of monochromatized X-ray beam110. In one such embodiment, flux detector120is positioned at sample holder111, as depicted inFIG. 1. In another embodiment, an X-ray flux detector121is placed near the monochromator to partially intersect small fraction of the primary X-rays in order to monitor the X-ray flux while the sample holder111is positioned at the analysis site.

In an embodiment, X-ray beam108has an energy below the absorption edge (k-edge) of silicon. For example, in one embodiment, the energy is less than 1800 eV. In a particular embodiment, the anode106ofFIG. 1(e.g., the X-ray source) is or includes a tungsten (W) target. The W target may be used to provide a line below the silicon absorption edge (e.g., the M-line of tungsten). In an embodiment, by including a W target instead of, e.g., an aluminum (Al) target or molybdenum (Mo) target which provides a line in the absorption range of silicon, an XRF measurement taken on a non-silicon species on or above silicon may be greatly enhanced. However, the enhancement of the XRF signal may be obtained to some detriment of the quality of the XPS signal generated. That is, the signal strength of the XPS signal may be less for a W-target based X-ray beam versus an Al-target-based X-ray beam if generated under identical conditions. To overcome any such detriment to the XPS signal, in an embodiment, the W target is irradiated/heated by a higher current density electron beam to increase the flux of the X-ray beam generated from the target. It is possible to increase the current density on the W target, compared to a similar Al target, because of the higher melting point of W versus Al. Increased flux in turn leads to a stronger XPS signal. In an alternative embodiment, tantalum (Ta) is used in place of tungsten.

In an embodiment, the monochromator109is suitable for optimizing the focusing of an X-ray beam having an energy below the absorbing edge of silicon. For example, in one embodiment, the monochromator109is positioned between a tungsten X-ray source and the sample holder111and in the pathway of an X-ray beam generated from the tungsten source. In a particular such embodiment, the monochromator109is composed of a layer of indium antimonide (InSb) disposed on and conformal with a layer of silicon. The layer of silicon is disposed above and conformal with a substrate layer of glass of suitable shape and orientation to direct a monochromatic X-ray beam to the sample holder111.

In accordance with an embodiment of the present invention, system100is configured to characterize a film. For example, since the X-ray beam108has an energy below the absorption edge (k-edge) of silicon, XPS and XRF measurements taken from a sample including a substantial amount of silicon, such as a silicon substrate, may be made with little to no interference or swamping by a silicon signal. In one embodiment, characterization of metal species in a film disposed on or above a silicon substrate is performed with high accuracy using an arrangement such as system100.

In an embodiment, an XRF signal generated from system100is used to supplement the information of XPS signals generated from system100while referencing both XRF and XPS signals to the primary X-ray flux as measured with Flux detector120or121. Computing system122includes a user interface124coupled with a computing portion126having a memory portion128. Computing system122may be configured to calibrate an XPS signal detected by XPS detector114. Computing system122may be configured to calibrate the XRF signal detected by XRF detector116. Computing system122may be configured to monitor the primary X-ray flux as measured by Flux detector120and/or121. In accordance with an embodiment of the present invention, computing system322is for normalizing an XPS signal detected by XPS detector114, as well as an XRF signal detected by XRF detector116with the primary X-ray flux measured by Flux detector120or121. In one embodiment, memory portion328has stored thereon a set of instructions for, when executed, using monochromatized X-ray beam110to generate XPS signal112and XRF signal118from sample199.

Flux detector120may be used to determine an estimated flux of monochromatized X-ray beam110. By positioning flux detector120at the point where monochromatized X-ray beam110meets sample holder111, as depicted inFIG. 1, flux detector120may not be able to collect a portion of monochromatized X-ray beam110at the same time that sample199is in place on sample holder111. Thus, in an embodiment, when flux detector120is positioned at the point where monochromatized X-ray beam110meets sample holder111, an estimated flux of monochromatized X-ray beam110is determined when sample199is not present on sample holder111. The flux is referred to as an ‘estimated’ flux, as opposed to a ‘measured’ flux which would be determined when a sample is actually present. In one embodiment, the estimated flux of the X-ray beam is obtained approximately immediately prior to generating the XPS signal from sample199. In one embodiment, the estimated flux of the X-ray beam is obtained approximately immediately subsequent to generating the XPS signal from sample199.

In an embodiment Flux detector121is used to provide a proxy X-ray flux measurement for Flux detector120for estimated flux of monochromatized X-ray beam110. By positioning flux detector121at near the monochromator to intersect a small portion of the primary X-ray flux above the sample111, the primary X-ray flux can be monitored while the monochromatized X-ray beam110meets sample holder111, as depicted inFIG. 1, and while XPS and XRF signals118and112are recorded by XRF detector116and XPS detector114.

In another aspect of the present invention, a monochromator is provided optimized for use with an X-ray beam having an energy below the absorption edge (k-edge) of silicon. For example,FIG. 2illustrates a bottom-up view (2A), a cross-sectional view taken in the Y-direction (2B), and a cross-sectional view taken in the X-direction, of a monochromator, in accordance with an embodiment of the present invention.

Referring toFIGS. 2A-2C, a monochromator200includes a layer of indium antimonide (InSb)202disposed on and conformal with a layer of silicon204. The layer of silicon204is disposed above and conformal with a layer of glass208. However, in another embodiment, the layer of silicon204is omitted and the layer of InSb202is disposed directly on and conformal with the layer of glass208. In an embodiment, the monochromator200is suitable for focusing an X-ray beam having an energy below the absorption edge (k-edge) of silicon. Such a pairing may permit more X-rays per unit of time (flux) as compared to coupling with a conventional monochromator such as a quartz monochromator. In a specific such embodiment, the monochromator is for focusing an X-ray beam generated from a tungsten (W) source.

In an embodiment, the substrate layer of glass208has a curved (ellipsoidal) shape, e.g., a curve in more than one dimension as would otherwise be the case for a cylindrical curve. For example, referring toFIGS. 2B and 2C, the monochromator200is displaced from a horizontal surface by an amount “a” in both the x-axis and the y-axis. In one such embodiment, the monochromator200has a latitudinal dimension (along the x-axis) approximately in the range of 1-5 centimeters, a longitudinal dimension (along the y-axis) approximately in the range of 3-15 centimeters. The latitudinal shape of the monochromator ellipsoid (minor axis) has to satisfy the Bragg condition and maintain a Bragg angle of approximately 68.9 degrees for InSb to deliver a monochromated W Mα X-ray beam to the sample111. The longitudinal shape of the monochromator focusing ellipsoid is given by minor ellipsoid axis and corresponding distance of the ellipsoid foci via the well known ellipsoid focusing equation.

In one particular embodiment, the shape of the monochromator ellipsoid has a major ellipsoid axis of a approximately in the range of 9-12 centimeters, a minor ellipsoid axis of b approximately in the range of 8-11 centimeters and thus a spacing of the foci of 2× approximately 35-40 centimeters, using InSb (2d-lattice spacing of approximately 7.4812 and Bragg angle of approximately 68.91 degree) to monochromate and focus W Ma X-rays from the anode to the analysis spot on the sample111. Alternate focusing configurations may be obtained as long as the Bragg angle for InSb, as well as the ratios b/a approximately in the range of 0.85-1.0 and c/b approximately in the range of 0.35-0.42 are satisfied.

In an embodiment, the monochromator200further includes an interfacial region206between the silicon layer204and the glass layer208, as depicted inFIGS. 2B and 2C. The interfacial region206may enable bonding between the silicon layer204and the glass layer208. In one such embodiment, the monochromator200includes the layer of InSb202having a thickness of approximately 5-15 microns, the layer of silicon204having a thickness less than 90 microns, the substrate layer of glass208having a thickness approximately in the range of 2-10 centimeters, and further includes an interfacial silicon dioxide (SiO2) layer206disposed between the layer of silicon204and the layer of glass208. The interfacial SiO2layer has a thickness approximately in the range of 50-150 nanometers. In a particular embodiment, if the layer of silicon204has a thickness greater than 90 microns, it may be brittle and break during coupling to the ellipsoidal surface of the glass substrate208.

In an embodiment, the InSb layer202is first bonded to a flat silicon layer prior to forming the monochromator202. Once the flat bonding is performed, the InSb/Si pairing is bonded to the appropriate ellipsoidal surface of the glass substrate layer208. In one embodiment, the InSb/Si pairing may be replaced with a InSb/Ge pairing, which is subsequently bonded to the ellipsoidal glass substrate208.

In another aspect of the present invention, an XPS system need not include XRF capability but may be arranged in a manner suitable for generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. For example,FIG. 3is an illustration representing a film measurement system having XPS detection capability, in accordance with an embodiment of the present invention.

Referring toFIG. 3, a film measurement system300includes an XPS generation and detection system housed in a chamber301coupled with a computing system318. The XPS generation and detection system includes an electron beam source302provided for generating an electron beam304. Electron beam304is used to generate an X-ray beam308by bombarding an anode306. A monochromator309is provided for focusing a monochromatized X-ray beam310from X-ray beam308. A sample holder311may be used to position a sample399in a pathway of monochromatized X-ray beam310.

An XPS detector314is provided for collecting an XPS signal312generated by bombarding sample399with monochromatized X-ray beam310. Additionally, a flux detector316may be provided for determining an estimated flux of monochromatized X-ray beam310. In one such embodiment, flux detector316is positioned at sample holder311, as depicted inFIG. 3. Computing system318includes a user interface320coupled with a computing portion322having a memory portion324.

In an embodiment, system300is for characterizing a metal-species-containing film and includes an X-ray source for generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. For example, in one embodiment, the energy is less than 1800 eV. In one embodiment, the X-ray source is or includes a tungsten (W) target. In an embodiment, the monochromator309is positioned between the X-ray source (e.g., anode306) and the sample holder311and in the pathway of the X-ray beam308, as depicted inFIG. 3. In one embodiment, the monochromator309includes a layer of indium antimonide (InSb) disposed on and conformal with an ellipsoidal glass substrate. In another embodiment, the monochromator309includes a layer of indium antimonide (InSb) disposed on and conformal with a layer of silicon. The layer of silicon is disposed above and conformal with an ellipsoidal glass substrate. Thus, in accordance with an embodiment of the present invention, an XPS system includes a tungsten (or the like) target for generating an X-ray beam with an energy below the absorption edge of silicon, and also includes a InSb-based monochromator particular suited from focusing such lower energy X-ray beams, such as W Mα, onto a sample for analysis.

In an aspect of the invention, an XPS measurement may be made upon introduction of a sample into an XPS system, such as but not limited to XPS systems100and300. In accordance with an embodiment of the present invention, the sample is bombarded with an X-ray beam. In response to bombardment by the X-ray beam, and XPS signal (composed of photo-electrons) may be emitted from the sample and collected in a detector. In an embodiment, the XPS signal is correlated with the atomic dose of a particular atomic species in the sample. In one embodiment, the atomic dose is correlated with a sample property such as, but not limited to, the thickness of a film in the sample, the depth to which the particular atomic species is incorporated into the sample or a concentration ratio of several atomic species in the sample. Additionally, one or more of the species may be a metal species. For example, in a particular embodiment, an XPS signal for a dielectric layer such as, but not limited to, silicon dioxide, silicon oxy-nitride, aluminum oxide or hafnium oxide, is obtained. In accordance with an embodiment of the present invention, the XPS signal is correlated to a property of the dielectric film without having to obtain, reference or ratio an XPS signal of, e.g., an underlying substrate or reference film. In one embodiment, the XPS signal is calibrated with a simultaneously or near simultaneously collected XRF signal, as well as the estimated X-ray flux recorded by X-ray Flux detectors120or121.

In an aspect of the present invention, as described briefly above, an XRF measurement may be used to glean additional information from an XPS measurement made from a sample. The sample may include a metal species of other element species such as oxygen or nitrogen. For example,FIG. 4is a Flowchart400representing a series of operations in a method for characterizing a film, in accordance with an embodiment of the present invention.FIG. 5Aillustrates a cross-sectional view of a sample including metal species for characterization by XPS and XRF.FIG. 5Bincludes equations used for analysis of XPS and XRF signals emitted from the sample ofFIG. 5A.

Referring to operation402of Flowchart400and to correspondingFIG. 5A, a method for characterizing a film includes generating an X-ray beam502having an energy below the absorption edge (k-edge) of silicon. In an embodiment, generating the X-ray beam502has an energy less than 1800 eV. In an embodiment, the X-ray beam502is generated from a tungsten (W) target. In an embodiment, the film includes one or more metal species such as, but not limited to, hafnium, aluminum, lanthanum or titanium. In another embodiment, the film includes oxygen or nitrogen.

Referring to operation404of Flowchart400and to correspondingFIG. 5A, the method optionally also includes positioning an X-ray Flux detector (e.g., X-ray Flux detector120fromFIG. 1) in the pathway of the X-ray beam502. The X-ray flux is measured prior to placing the sample500in a pathway of the X-ray beam502. In an alternative implementation, an X-ray flux detector (e.g., X-ray flux detector121fromFIG. 1) may be used to monitor the X-ray flux stability during XPS and XRF measurements while the sample500is placed in a pathway of the X-ray beam502. The X-ray flux measurement serves as reference for the measured XPS504and XRF506signal intensities. Both the XPS and the XRF signal intensity are directly proportional to the primary X-ray flux (120or121) for a given sample structure and measurement configuration. Normalization of measured XRF and XPS intensities by the X-ray flux permits thickness/dose measurement without the need for XRF or XPS signal intensity ratios (as is commonly used in XPS analysis).

Referring to operation406of Flowchart400and to correspondingFIG. 5A, the method also includes positioning a sample500in a pathway of the X-ray beam502. In an embodiment, the sample500includes one or more films having metal species. For example, in a specific embodiment, the sample500includes a first layer of titanium nitride (TiN)500A having thickness T1disposed above a layer including aluminum (Al)500B having thickness T2which, in turn, is disposed above a second layer of titanium nitride (TiN)500C having thickness T3, as depicted inFIG. 5A. The stack of layers500A,500B,500C is disposed on or above a silicon substrate.

Referring to operation408of Flowchart400and to correspondingFIG. 5A, the method also includes collecting an XPS signal504generated by bombarding the sample500with the X-ray beam502. For example, an XPS signal504obtained from the layer including aluminum (Al)500B may be collected, as depicted inFIG. 5A. An XPS spectra may be obtained by irradiating the sample500with a beam of X-rays502while simultaneously measuring the kinetic energy and number of electrons that escape from the top, e.g., 1 to 10 nm of the sample500.

Referring to operation410of Flowchart400and to correspondingFIG. 5A, the method also includes collecting an XRF signal506generated by bombarding the sample500with the X-ray beam502. For example, an XRF signal506obtained from the layer including aluminum (Al)500B may be collected, as depicted inFIG. 5A. An XRF spectra may be obtained may be obtained by irradiating the sample500with a beam of X-rays502and measuring the emission of characteristic secondary (or fluorescent) X-rays there from. Referring to operation412, in an embodiment, the method optionally further includes performing a Flux measurement following completion of the above analysis.

In an embodiment, the method further includes combining the measurement result from the XPS signal504and the XRF signal506. In a specific example, a repeating layer structure may be used as a sample, such as the repeating layer structure500which includes more than one layer of titanium nitride. Referring toFIG. 5Aand equations (i) and (ii) ofFIG. 5B, the intensity (I(Al)) of the XPS signal504generated from layer500B (having thickness T2) is attenuated by layer500A based on the thickness (t, or T1) of layer500A and the photoelectron attenuation length associated with the Al signal504(λAl). On the other hand, since the XRF signal506is largely not depth dependent at or below the 100 nm scale, the signal is not attenuated. Accordingly, the XRF signal506may be used to determine an amount of aluminum present in sample500. The amount of aluminum I(Al) determined from XRF signal506may be used in equation (iv) ofFIG. 5Balong with the measured XPS signal504(I measured) to determine the thickness (t, or T1) of the top titanium nitride layer. That is, the XRF signal506, which provides an amount of aluminum present (equation (iii)), may be used to determine the depth of the aluminum, which directly corresponds to the thickness (T1) of the titanium nitride layer500A and the thickness (T2) of the aluminum containing layer500B. XRF (and XPS) measurement of the Ti signal yields the total TiN thickness of the stack (T1+T3). The thickness of TiN layer (T3) thus follows directly, as the top TiN layer thickness (T1) has already been determined from XPS and XRF measurements of the respective Al signal intensities.

Thus, in accordance with an embodiment of the present invention, a method further includes determining, for a film including the metal species disposed below one or more other films, and the XPS signal having an attenuated signal intensity of the metal species, and an XRF signal having an essentially non-attenuated signal of the metal species. In one such embodiment, calibrating the XPS signal to the XRF signal includes determining a quantity of the metal species from the XRF signal and, subsequently, determining, from the XPS signal and the quantity, a depth of the film below the one or more other films.

In another, alternative embodiment, a method further includes calibrating the XPS signal with the XRF signal for the very top film of a stack of films on a silicon substrate. In one such example, a quantity of the metal (or atomic element) species is determined from the XRF signal (normalized to the X-ray flux) and, subsequently, a thickness of the top film including the metal species is determined from the XPS signal and the quantity provided by the XRF measurement. This approach may provide for ease of XPS calibration for new film materials, particularly if the XRF signal is normalized to the X-ray flux.

The computer system600may further include a network interface device608. The computer system600also may include a video display unit610(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device612(e.g., a keyboard), a cursor control device614(e.g., a mouse), and a signal generation device616(e.g., a speaker).

The secondary memory618may include a machine-accessible storage medium (or more specifically a computer-readable storage medium)631on which is stored one or more sets of instructions (e.g., software622) embodying any one or more of the methodologies or functions described herein. The software622may also reside, completely or at least partially, within the main memory604and/or within the processor602during execution thereof by the computer system600, the main memory604and the processor602also constituting machine-readable storage media. The software622may further be transmitted or received over a network620via the network interface device608.

Thus, systems and methods for characterizing films by XPS have been described. In accordance with an embodiment of the present invention, a system for characterizing a film includes an X-ray source for generating an X-ray beam having an energy below the absorption edge (k-edge) of silicon. The system also includes a sample holder for positioning a sample in a pathway of the X-ray beam. The system also includes a first detector for collecting an XPS signal generated by bombarding the sample with the X-ray beam. The system also includes a second detector for collecting an XRF signal generated by bombarding the sample with the X-ray beam. In one embodiment, the X-ray source includes a tungsten (W) target. In one embodiment, the XRF signal is for calibrating the XPS signal.