Characterization of structures with small dimensions using low energy X-ray beams.

Abstract

A system for characterizing a structure having microscopic dimensions, comprising: (i) an electron optics system configured to illuminate the structure with an X-ray beam having an X-ray beam energy close to but not exceeding the k-edge energy of a chemical element in the structure; (ii) at least one detector: an X-ray photoelectron spectroscopy (XPS) detector that collects an XPS signal generated by the illumination of the structure; or an X-ray fluorescence (XRF) detector that collects an XRF signal generated by the illumination of the structure; and (iii) a computing device configured to determine chemical element information regarding the amount and concentration of the chemical element in the structure based on at least one of the XPS signal or the XRF signal.

Description

[Technical Field]

[0001] This invention relates to the evaluation of structures with microscopic dimensions using low energy X-ray beams. [Background technology]

[0002] X-ray photoelectron spectroscopy (XPS) is a quantitative spectroscopic technique that measures the composition, empirical formula, chemical state, and electronic state of elements present in a material. XPS spectra are obtained by irradiating a material with an X-ray beam, while simultaneously measuring the kinetic energy and number of electrons emitted from the upper part of the analyzed material, e.g., 1–10 nm. XPS analysis typically uses monochromatic aluminum Kα (AlKα) X-rays, which are generated by irradiating an aluminum anode surface with a focused electron beam. A portion of the generated AlKα X-rays is blocked by a focusing monochromator, and a narrow X-ray energy band is focused at the analyzed region on the 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 the crystal quality, size, and stability of the monochromator.

[0003] X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from materials excited by irradiation with higher-energy X-rays or gamma rays. This phenomenon is widely used in elemental and chemical analysis, particularly in the investigation of metals, glass, ceramics, and building materials, as well as in geochemistry, forensics, and archaeology.

[0004] XPS and X-ray fluorescence analysis each have their own advantages. XPS provides surface-sensitive information for material systems, where the analysis depth is limited by the escape depth of the excited and emitted photoelectrons. When the excitation X-ray energy is hv, the excited and emitted photoelectrons with binding energy BE have a kinetic energy of hv-BE. The lower the excitation X-ray energy, the smaller the kinetic energy of the emitted photoelectrons, and consequently the smaller the escape depth of the photoelectrons. This means that XPS enables highly surface-sensitive sampling. On the other hand, XRF provides deeper compositional information, determined by the range of the primary excitation X-rays in the material and the range and attenuation of the fluorescent X-rays excited and emitted from the material. However, advances are needed in analyses based on XPS and / or XRF detection. Summary of the Invention

[0005] A system, method, and non-transitory computer-readable medium storing instructions therefor are provided for evaluating structures having fine dimensions.

[0006] In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0007] [Figure 1] An example system and sample are shown. [Figure 2] An example system and sample are shown. [Figure 3] An example system and sample are shown. [Figure 4] An example system and sample are shown. [Figure 5] An example system and sample are shown. [Figure 6] Examples of parts of the system and samples are shown. [Figure 7] Examples of parts of the system and samples are shown. [Figure 8]An example of the expected XPS signal for a thin SiON / HfOx / SiON layer on a silicon substrate is shown, extending from the surface through the milling process to the interface where the second layer is exposed. [Figure 9] 1 shows an example of the progression of an XPS signal through a second HfOx / SiON layer. [Figure 10] FIG. 10 is a diagram showing an example of the progression of an XPS signal from a third layer to a silicon substrate. [Figure 11] The expected K Kα XRF intensity throughout the SiON / HfOx / SiON stack and the N Kα intensity during milling from the top surface to the silicon interface are shown. [Figure 12] An example of an N1s depth profile from the surface to bulk silicon is shown. [Figure 13] An example of the method is shown below. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0009] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, the invention, both as to organization and method of operation, together with its objects, features, and advantages, may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

[0010] It will be understood that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0011] In this specification, any reference to one of a system, a method, and a non-transitory computer-readable medium shall apply mutatis mutandis to any other of the system, method, and non-transitory computer-readable medium. For example, a reference to a system shall apply mutatis mutandis to a method executable by the system and to a non-transitory computer-readable medium capable of storing instructions executable by the system.

[0012] At least one embodiment of the illustrated invention, much of which can be implemented using electronic components and circuitry known to those skilled in the art, will not be described in detail beyond what is deemed necessary as illustrated above for the understanding and appreciation of the concepts underlying the invention and in order not to obscure or detract from the teachings of the invention.

[0013] The following illustrative numbers and values ​​should be considered as non-limiting examples.

[0014] For low-Z elements such as boron and nitrogen, X-ray beams with X-ray beam energies close to (but not exclusively close to) the k-edge energy (k-absorption edge energy) of the structural chemical elements are sometimes referred to as PKECE X-ray beams. Efficient excitation can also be expected for high-Z elements, even at the L, M, and other edge proximity of the excitation X-rays. Regarding proximity, the energy of the PKECE X-ray beam 24 should ideally not exceed, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 2, or 2.5 times the k-edge energy of the structural chemical elements. It should be noted that the photoelectron cross section, like the XRF Kα cross section, decreases significantly with increasing excitation X-ray energy ratio.

[0015] Sometimes you want to know the dose and concentration of a chemical element in a structure.

[0016] By irradiating a sample structure with the PKECE X-ray beam, the amount and concentration of chemical elements in the structure can be measured with high sensitivity and accuracy. The energy of the PKECE X-ray beam is a fraction (e.g., 5-55%) of the beam energy of conventional technologies.

[0017] The structures may have microscale dimensions. For example, the thickness of the structures may be in the range of 1 to 50 angstroms. The structures may also be thin films of other structures.

[0018] The system may perform only XPS measurements to obtain chemical element information regarding the amount and concentration of chemical elements near the surface of the structure.

[0019] The system may perform only XRF measurements to obtain chemical element information regarding the amount and concentration of chemical elements within the structure as well as on its surface.

[0020] The system may perform both XRF and XPS measurements.

[0021] Various examples are given of systems that perform both XRF and XPS measurements (also called XRF / XPS systems), and references to such systems can also apply mutatis mutandis to systems that perform only XRF or XPS measurements.

[0022] FIG. 1 shows an example of an XRF / XPS system 11-1.

[0023] The XRF / XPS system 10-1 includes an electron optical system 13, an XPS detector 18 that collects an XPS signal 28 generated by illumination of a structure, an XRF detector 19 that collects an XRF signal 29 generated by illumination of the structure, and a computing device 30.

[0024] The electron optics 13 is configured to irradiate the structure with a PKECE X-ray beam target. The electron optics 13 may include, for example, an electron beam source 12 that generates an electron beam 21. The electron beam 21 is used to generate an initial X-ray beam 22 by bombarding an anode 13. A monochromator 14 is provided to convert the initial X-ray beam 22 into a monochromated PKECE X-ray beam 24, which is incident on a structure 41 of a sample 40. The initial X-ray beam 22 exhibits a wider bandwidth than the monochromated PKECE X-ray beam 24.

[0025] Referring to 10-2, the computing device 30 is configured to determine chemical element information regarding the dose and concentration of the chemical elements in the structure based on at least one of the XPS signal or the XRF signal.

[0026] For example, the chemical element can be boron and the structure can include silicon and germanium. The energy of the PKECE X-ray beam is approximately 278 electron volts. The term "approximately" allows for a deviation of 1-20%.

[0027] For example, the chemical element can be nitrogen and the structure can include silicon oxide. The PKECE X-ray beam has an energy of greater than or equal to 405 electron volts to about 452.2 electron volts.

[0028] XPS detector 18 is highly sensitive to emissions from the surface of the structure. When using XPS detector 18, computing device 30 can be configured to generate surface chemical element information, including surface chemical element information related to the amount and concentration of chemical elements at the surface of the structure.

[0029] The XRF detector 19 is sensitive to emission from the structure, including surface and subsurface emissions.

[0030] When using XRF detector 19, computing device 30 can be configured to generate surface chemical element information, including overall chemical element information regarding the amounts and concentrations of chemical elements within the structure.

[0031] The XRF / XPS system 10-1 can perform one or more XRF measurements in parallel with an XPS measurement, or can perform one or more XRF measurements at different times from the XPS measurement.

[0032] XRF / XPS system 10-1 can be configured to perform multiple measurements during multiple illumination iterations.

[0033] 4 and 10-4, the sample and structure can be milled (etched, milled, or otherwise) layer by layer using a milling system 35 between measurement iterations to provide extensive information about the structure, and in particular to receive surface chemical element information about the surface of the structure between different milling iterations. Milling iterations can be performed between measurement iterations.

[0034] As milling progresses, the XPS detector can acquire new information about each successively exposed surface, and the XRF signal is expected to decrease over time as the overall volume of the structure decreases during milling iterations.

[0035] The XPS detector is configured to collect one or more XPS signals generated during one or more illumination iterations of the plurality of iterations, and the computing device 30 is configured to determine surface chemical element information related to the amounts and concentrations of chemical elements at the surface of the structure based on the one or more XPS signals.

[0036] The XRF detector is configured to collect one or more XRF signals generated during one or more of the illumination iterations of the plurality of iterations, and the computing device 30 is configured to determine overall chemical element information regarding the amounts and concentrations of the chemical elements within the structure based on the one or more XRF signals.

[0037] 2 shows an example of an XRF system 10-2. The XRF system 10-2 differs from the XPS / XRF system 10-1 in FIG. 1 in that it does not include an XPS detector.

[0038] 3 shows an example of an XPS system 10-3. The XPS system 10-3 differs from the XPS / XRF system 10-1 in FIG. 1 in that it does not include an XRF detector.

[0039] 4 and 5 show an example of an XPS / XRF system 10-4. XPS / XRF system 10-4 differs from XPS / XRF system 10-1 of FIG. 1 by including, for example, a charged particle miller or other surface monolayer removal device 35. FIG. 4 shows XPS / XRF system 10-4 during a milling iteration, in which the charged particle mill is milling a structure using milling beam 27. FIG. 5 shows XPS / XRF system 10-4 during an illumination iteration.

[0040] Figures 6 and 7 show examples of portions of an XPS system 10-5. Figure 6 shows a portion of an XPS system 10-5 during an illumination iteration. Figure 7 shows a portion of an XPS / XRF system 10-5 during a milling iteration in which a charged particle mill 35 mills a structure using a milling beam 27.

[0041] Portions of the XPS system 10-5 include an XPS detector 18 that collects an XPS signal 28 generated by illumination of the structure, and an electron beam source 12 that generates an electron beam 21. The electron beam 21 is used to bombard an anode 13 to generate an initial X-ray beam 22. A monochromator 14 is provided to convert the initial X-ray beam 22 into a PKECE X-ray beam 24 that is incident on a structure 41 of a sample 40. The initial X-ray beam 22 exhibits a wider bandwidth than the PKECE X-ray beam 24.

[0042] Figures 8, 9, and 10 show examples of XPS signals 100-1 to 100-11 obtained during various illumination iterations during milling iterations of a near-surface nitrogen-containing structure. The XPS signal changes during the milling process.

[0043] Figure 11 shows the expected N Kα XRF intensity (dotted line) through a complete SiON / HfOx / SiON stack, demonstrating negligible attenuation of the N Kα signal through the structure, i.e., due to the relatively large range of the exciting and exiting X-rays through the measurement stack, ∼99.5% of the total nitrogen is captured and measured. The ideal response of N Kα intensity during milling through the stack structure is shown by the solid line from zero (perfect stack) to the silicon bulk interface at ∼20 Å. Naturally, the excitation and emission fractions of the XRF signal are specific to the thickness and composition of the stack structure.

[0044] Figure 12 shows an example of an N1s depth profile from the surface to bulk silicon. The structure includes a 5 Å SiON top layer followed by a 10 Å high-k material middle layer, followed by a 5 Å SiON bottom layer.

[0045] The lower layer does not contribute to the surface signal. The decay length of N1s inside the SiON is 39 Å. The decay of N1s inside the SiON is significant.

[0046] FIG. 13 illustrates an example method 200 for evaluating structures with fine dimensions.

[0047] Method 200 begins at step 210 by irradiating the structure with an X-ray beam having an X-ray beam energy proximate to the k-edge energy of the chemical elements of the structure (PKECE X-ray beam) via an electron optics system.

[0048] Step 210 is followed by step 220, in which at least one detection signal is generated, which is an X-ray photoelectron spectroscopy (XPS) detection signal or an X-ray fluorescence (XRF) detection signal.

[0049] Step 220 is followed by step 230, in which chemical element information relating to the amount and concentration of chemical elements in the structure is determined based on the at least one detection signal.

[0050] The method 200 can be performed by any of the systems described above.

[0051] Steps 210, 220, and 230 may be repeated (iterated) multiple times.

[0052] The repetition of steps 210, 220, and 230 may be followed by a step 240 of milling the structure. Step 240 may be followed by step 210.

[0053] Any arrangement of components to achieve the same functionality is substantially "associated" such that the desired functionality is achieved. Thus, for purposes of this specification, any two components that combine to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of architecture or intervening components. Likewise, any two components so associated can also be considered to be "operably connected" or "operably coupled" with each other to achieve the desired functionality.

[0054] Furthermore, those skilled in the art will recognize that the boundaries between operations (acts) described above are merely illustrative. Multiple operations may be combined into a single operation, a single operation may be distributed into additional operations, and operations may be performed with at least partial overlap in time. Furthermore, alternative embodiments may include multiple instances of an operation, and the order of operations may be changed in various other embodiments.

[0055] Also, for example, in one embodiment, the illustrated embodiment may be implemented as circuits located on a single integrated circuit or within the same device, or the illustrated embodiment may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in any suitable manner.

[0056] Also, for example, embodiments or portions thereof may be implemented as a soft or code representation of a physical circuit, or a logical representation that can be translated into a physical circuit, such as any suitable type of hardware description language.

[0057] However, other modifications, variations, and alternatives are possible. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

[0058] In the claims, reference signs placed between parentheses shall not be construed as limiting the scope of the claim. The word "comprising" does not exclude the presence of other elements or steps recited in the claim. Furthermore, as used in this specification, the words "a" or "an" are defined as one or more. Furthermore, the use of introductory phrases such as "at least one" and "one or more" in a claim shall not be construed as meaning that the introduction of another claim element with the indefinite article "a" or "an" limits a particular claim containing such introduced claim element to inventions containing only one such element, nor shall the presence of the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" in the same claim be construed as meaning that the particular claim containing such introduced claim element is limited to inventions containing only one such element. The same applies to the use of definite articles. Unless otherwise specified, terms such as "first" and "second" are used to arbitrarily distinguish between elements described by such terms. Accordingly, these terms are not necessarily intended to indicate any chronological or other priority of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0059] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

[0060] Any reference to the words "comprise", "comprise" or "have" may apply mutatis mutandis to the words "consisting of" and / or "consisting essentially of".

Claims

1. an electron-optical system configured to illuminate the structure with an X-ray beam having an X-ray beam energy close to a k-edge energy of a chemical element of the structure; at least one detector: (i) an X-ray photoelectron spectroscopy (XPS) detector that collects XPS signals produced by illumination of the structure; or (ii) an X-ray fluorescence (XRF) detector that collects XRF signals produced by illumination of the structure; and a computing device configured to determine chemical element information regarding amounts and concentrations of chemical elements in the structure based on at least one of the XPS signal or the XRF signal; A system for evaluating structures having small dimensions.

2. 10. The system of claim 1, wherein the x-ray beam energy does not exceed two times the k-edge energy of the chemical elements of the structure.

3. 2. The system of claim 1, wherein said chemical element is boron, said structure further comprises silicon germanium, and said x-ray beam energy is about 278 electron volts.

4. 10. The system of claim 1, wherein said chemical element is nitrogen, said structure further comprises silicon oxide, and said x-ray beam energy is greater than or equal to 402 electron volts.

5. 10. The system of claim 1, wherein the at least one detector is an XPS detector, and the chemical element information comprises surface chemical element information relating to amounts and concentrations of chemical elements at a surface of the structure.

6. 10. The system of claim 1, wherein the at least one detector is an XRF detector, and the chemical element information includes global chemical element information regarding amounts and concentrations of chemical elements within the structure.

7. 2. The system of claim 1, wherein the at least one detector includes an XPS detector and an XRF detector, and the chemical element information includes (i) surface chemical element information related to the amount and concentration of chemical elements at the surface of the structure, and (ii) global chemical element information related to the amount and concentration of chemical elements within the structure.

8. The system of claim 1 , wherein the electron-optics system is configured to illuminate the structure during multiple illumination iterations.

9. 9. The system of claim 8, wherein the at least one detector comprises an XPS detector, the XPS detector configured to collect one or more XPS signals generated during one or more illumination iterations of the plurality of iterations, and the computing device configured to determine surface chemical element information related to amounts and concentrations of chemical elements at a surface of the structure based on the one or more XPS signals.

10. 9. The system of claim 8, wherein the at least one detector comprises an XRF detector, the XRF detector configured to collect one or more XRF signals generated during one or more illumination iterations of the plurality of iterations, and the computing device configured to determine overall chemical element information regarding amounts and concentrations of chemical elements in the structure based on the one or more XRF signals.

11. The system of claim 1 , wherein the structure is milled between at least one pair of adjacent illumination iterations.

12. The system of claim 1 , comprising a mill configured to mill the structure during one or more milling iterations that do not overlap any of the illumination iterations.

13. irradiating the structure with an X-ray beam having an X-ray beam energy close to the k-edge energy of a chemical element of the structure by an electron optics system; generating at least one detection signal of an X-ray photoelectron spectroscopy (XPS) detection signal or an X-ray fluorescence (XRF) detection signal; determining chemical element information regarding the amount and concentration of the chemical element in the structure based on the at least one detection signal; A method for evaluating structures with small dimensions.

14. 14. The method of claim 13, wherein the x-ray beam energy does not exceed two times the k-edge energy of the chemical elements of the structure.

15. 14. The method of claim 13, wherein the chemical element is boron, the structure further comprises silicon germanium, and the x-ray beam energy is about 278 electron volts.

16. 14. The method of claim 13, wherein the chemical element is nitrogen, the structure further comprises silicon oxide, and the x-ray beam energy is 402 electron volts or greater.

17. 14. The method of claim 13, wherein the at least one detector is an XPS detector, and the chemical element information comprises surface chemical element information relating to amounts and concentrations of chemical elements at the surface of the structure.

18. 14. The method of claim 13, wherein the at least one detector is an XRF detector, and the chemical element information comprises global chemical element information regarding amounts and concentrations of chemical elements in the structure.

19. 14. The method of claim 13, wherein the at least one detector comprises an XPS detector and an XRF detector, and the chemical element information comprises: (i) surface chemical element information relating to the amount and concentration of chemical elements at the surface of the structure, and (ii) global chemical element information relating to the amount and concentration of chemical elements within the structure.

20. 14. The method of claim 13, wherein the electron-optical system illuminates the structure during multiple illumination iterations.

21. 21. The method of claim 20, wherein the at least one detector comprises an XPS detector, wherein the XPS detector collects one or more XPS signals generated during one or more illumination iterations of the plurality of iterations, and wherein the computing device determines surface chemical element information related to amounts and concentrations of chemical elements at a surface of the structure based on the one or more XPS signals.

22. 21. The method of claim 20, wherein the at least one detector comprises an XRF detector, wherein the XRF detector collects one or more XRF signals generated during one or more illumination iterations of the plurality of iterations, and wherein the computing device determines overall chemical element information regarding amounts and concentrations of chemical elements in the structure based on the one or more XRF signals.

23. 14. The method of claim 13, wherein the structure is milled between at least one pair of adjacent illumination iterations.

24. 14. The method of claim 13, comprising a mill configured to mill the structure during one or more milling iterations that do not overlap any of the illumination iterations.

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