Evaluation of structures with microscopic dimensions using low energy x-ray beams

Abstract

A system for evaluating a structure having microscopic dimensions, the system comprising: (i) an electro-optical device configured to irradiate the structure with an X-ray beam having an X-ray beam energy close to but not exclusive of k-edge energy of chemical elements of the structure; (ii) at least one detector selected from (i) an X-ray photoelectron spectroscopy (XPS) detector for collecting X-ray fluorescence (XRF) signals generated by irradiating the structure, and (ii) an XRF detector for collecting X-ray fluorescence (XRF) signals generated by irradiating the structure; and (iii) a computing device configured to determine chemical element information regarding the dose and concentration of chemical elements in the structure based on at least one of the XPS signal and the XRF signal.

Description

Background Art

[0001] 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 present within a material. An XPS spectrum can be obtained by irradiating a material with an X-ray beam while measuring the kinetic energy and number of electrons escaping from the top (e.g., 1 nm to 10 nm) of the material being analyzed. XPS analysis typically employs monochromatic aluminum Kα (AlKα) X-rays that can be generated by irradiating the surface of an aluminum anode with a focused electron beam. A portion of the generated AlKα X-rays is then intercepted by a focusing monochromator that focuses a narrow X-ray energy band onto an analysis site 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.

[0002] X-ray fluorescence (XRF) is the characteristic "secondary" (or fluorescent) X-ray emission from a material that has been excited by being bombarded with higher-energy X-rays or gamma rays. This phenomenon is widely used for elemental and chemical analysis, particularly in the investigation of metals, glass, ceramics, and building materials and in studies in geochemistry, forensic science, and archaeology.

[0003] XPS analysis and XRF analysis each have their own advantages. XPS provides surface-sensitive information about a material system, where the analysis depth is limited by the escape depth of the excited and emitted photoelectrons. For an excitation X-ray energy hv, the excited and emitted photoelectrons with a binding energy BE will have a kinetic energy of hv - BE. The lower the excitation X-ray energy, the lower the kinetic energy of the emitted photoelectrons, resulting in a smaller escape depth of the photoelectrons, i.e., resulting in highly surface-sensitive sampling via XPS. On the other hand, XRF provides compositional information up to much greater depths, which is 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, analysis based on XPS and / or XRF detection requires improvement. Summary of the Invention

[0004] A system, method, and non-transitory computer-readable medium for storing instructions for evaluating a structure having a microscopic size can be provided. Brief Description of the Drawings

[0005] To understand the present 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:

[0006] Figure 1 An example of a system and a sample is shown;

[0007] Figure 2An example of the system and the sample is shown;

[0008] Figure 3 An example of the system and the sample is shown;

[0009] Figure 4 An example of the system and the sample is shown;

[0010] Figure 5 An example of the system and the sample is shown;

[0011] Figure 6 An example of a part of the system and the sample is shown;

[0012] Figure 7 An example of a part of the system and the sample is shown;

[0013] Figure 8 An example of the XPS signals expected from the surface and the milling steps until the second layer becomes the exposed interface for a thin SiON / HfOx / SiON on a silicon substrate layer is shown;

[0014] Figure 9 An example of the XPS signal progression through the second HfOx / SiON layer is shown;

[0015] Figure 10 An example of the XPS signal; the progression through the third layer until the silicon substrate;

[0016] Figure 11 An example of the expected N Kα XRF intensity through the complete SiON / HfOx / SiON stack and the intensity of the N Kα intensity when milling from the top surface to the silicon interface is shown;

[0017] Figure 12 An example of the Nls depth profile from the surface to the bulk silicon is shown; and

[0018] Figure 13 An example of the method is shown. Detailed Description

[0019] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, those skilled in the art will understand 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.

[0020] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, the organization and method of operation of the present invention, 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.

[0021] It should be understood that, for simplicity and clarity of illustration, the elements shown in the figures are not necessarily drawn to scale. For example, for clarity, the dimensions of some of the elements may be exaggerated relative to other elements. In addition, where considered appropriate, reference numerals may be repeated in the figures to indicate corresponding or similar elements.

[0022] Any reference in the specification to any one of a system, a method, and a non-transitory computer-readable medium should be applied, mutatis mutandis, to any other one of the system, the method, and the non-transitory computer-readable medium as appropriate. For example, any reference to a system should be applied, mutatis mutandis, to a method that can be performed by the system and a non-transitory computer-readable medium that can store instructions executable by the system.

[0023] Since at least one illustrated embodiment of the present invention can be implemented mostly using electronic components and circuits known to those skilled in the art, details will not be explained to any greater extent than considered necessary above in order to understand and appreciate the basic concepts of the present invention and in order not to obscure or distract from the teachings of the present invention.

[0024] Any numbers or values described below should be regarded as non-limiting examples.

[0025] An X-ray beam having an X-ray beam energy that is close (but not exclusively) to the k-edge energy of the chemical element of the structure can also be referred to as a PKECE X-ray beam for low-Z elements such as boron or nitrogen. Similar highly efficient excitation can be expected for the L, M, etc. edges of the excitation X-rays for high-Z elements. With regard to proximity, the energy of the PKECE X-ray beam 24 can desirably not exceed, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 2, 2.5 times the k-edge energy of the chemical element of the structure. It should be noted that the higher the excitation x-ray energy ratio becomes, the significantly smaller the photoelectron cross-section and the XRF Kα cross-section become.

[0026] It may be desirable to find the dose and concentration of the chemical elements within the structure.

[0027] Irradiating the structure of the sample with a PKECE X-ray beam helps to highly sensitively and accurately measure the dose and concentration of the chemical elements of the structure. The beam energy of the PKECE X-ray beam is a part of the prior art beam energy (for example, between 5% and 55%).

[0028] The structure can be of microscopic dimensions - for example, the structure can have a thickness that can range between 1 angstrom and 50 angstroms. The structure can be a thin film of any other structure.

[0029] The system can perform only XPS measurements to obtain chemical element information about the dose and concentration of chemical elements near the surface of the structure.

[0030] The system can perform only XRF measurements to obtain chemical element information about the dose and concentration of chemical elements within the structure and not just at the surface of the structure.

[0031] The system can perform both XRF measurements and XPS measurements.

[0032] Various examples are for a system that performs both XRF measurements and XPS measurements (also referred to as an XRF / XPS system). Any reference to such a system can be applied, mutatis mutandis, to a system that performs only one of XRF measurements or XPS measurements, as the case may be.

[0033] Figure 1 An example of an XRF / XPS system 11-1 is shown.

[0034] The XRF / XPS system 10-1 includes electron optics 13, an XPS detector 18 for collecting XPS signals 28 generated by irradiating the structure, an XRF detector 19 for collecting XRF signals 29 generated by irradiating the structure, and a computing device 30.

[0035] The electron optics 13 is configured to irradiate the structure with a PKECE X-ray beam target. The electron optics 13 can include, for example, an electron beam source 12 for generating 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 monochromatic PKECE X-ray beam 24 that is incident on the structure 41 of the sample 40. The initial X-ray beam 22 exhibits a wider bandwidth than the monochromatic PKECE X-ray beam 24.

[0036] Referring to 10-2, the computing device 30 is configured to determine chemical element information about the dose and concentration of chemical elements in the structure based on at least one of the XPS signal and the XRF signal.

[0037] For example, the chemical element can be boron, and the structure can also include silicon germanium. The energy of the PKECE X-ray beam can be about 278 electron volts. The term "about" can allow a deviation of 1% to 20%.

[0038] For example, the chemical element can be nitrogen, and the structure can also include silicon oxide. The energy of the PKECE X-ray beam can be higher than 405 electron volts or about 452.2 electron volts.

[0039] The XPS detector 18 is very sensitive to emissions from the surface of the structure. When the XPS detector 18 is used, the computing device 30 can be configured to generate surface chemical element information that includes surface chemical element information regarding the dose and concentration of chemical elements in the surface of the structure.

[0040] The XRF detector 19 is sensitive to emissions from the structure, including emissions from the surface and emissions below the surface.

[0041] When the XRF detector 19 is used, the computing device 30 can be configured to generate surface chemical element information that includes total chemical element information regarding the dose and concentration of chemical elements within the structure.

[0042] The XRF / XPS system 10-1 can perform one or more XRF measurements in parallel with the XPS measurement, or perform one or more XRF measurements at a different time than the XPS measurement.

[0043] The XRF / XPS system 10-1 can be configured to perform multiple measurements during multiple irradiation iterations.

[0044] Referring Figure 4 to 10-4 in, the sample and the structure can be milled layer by layer between one measurement iteration and another by means of the milling system 35 in order to provide extensive information about the structure, especially receiving surface chemical element information regarding the surface of the structure between different milling iterations. The milling iteration can be carried out between one measurement iteration and another.

[0045] As the milling progresses, the XPS detector can obtain new information about the surface (one exposed surface after another), and the XRF signal is expected to decrease over time - because the overall volume of the structure shrinks during the milling iteration.

[0046] The XPS detector is configured to collect one or more XPS signals generated during one or more irradiation iterations among multiple iterations. The computing device 30 is configured to determine surface chemical element information regarding the dose and concentration of chemical elements in the surface of the structure based on the one or more XPS signals.

[0047] The XRF detector is configured to collect one or more XRF signals generated during one or more irradiation iterations among multiple iterations. The computing device 30 is configured to determine total chemical element information regarding the dose and concentration of chemical elements within the structure based on the one or more XRF signals.

[0048] Figure 2 An example of the XRF system 10-2 is shown. The XRF system 10-2 is related to Figure 1The XPS / XRF system 10-1 is different in that it does not include an XPS detector.

[0049] Figure 3 An example of the XPS system 10-3 is shown. The XPS system 10-3 is different from Figure 1 the XPS / XRF system 10-1 in that it does not include an XRF detector.

[0050] Figure 4 and Figure 5 An example of the XPS / XRF system 10-4 is shown. The XPS / XRF system 10-4 is different from Figure 1 the XPS / XRF system 10-1 in that it includes, for example, a charged particle milling device or other surface monolayer removal device 35. Figure 4 The XPS / XRF system 10-4 during a milling iteration is shown, during which the charged particle milling device mills the structure with a milling beam 27. Figure 5 The XPS / XRF system 10-4 during an irradiation iteration is shown.

[0051] Figure 6 and Figure 7 An example of a part of the XPS system 10-5 is shown. Figure 6 A part of the XPS system 10-5 during an irradiation iteration is shown. Figure 7 A part of the XPS / XRF system 10-5 during a milling iteration is shown, during which the charged particle milling device 35 mills the structure with a milling beam 27.

[0052] The part of the XPS system 10-5 includes an XPS detector 18 for collecting the XPS signal 28 generated by irradiating the structure, and an electron beam source 12 for generating 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 PKECE X-ray beam 24, which is incident on the structure 41 of the sample 40. The initial X-ray beam 22 exhibits a wider bandwidth than the PKECE X-ray beam 24.

[0053] Figure 8 、 Figure 9 and Figure 10 Examples of the XPS signals 100-1 to 100-11 obtained during different irradiation iterations between milling iterations of a structure including near-surface nitrogen are shown. During the milling process, the XPS signals change.

[0054] Figure 11Shows the expected N Kα XRF intensity (dashed line) through the complete SiON / HfOx / SiON stack, indicating negligible attenuation of the N Kα signal through the structure, i.e., the total nitrogen dose measurement obtained by capturing ~99.5% of the total nitrogen dose due to the relatively large range of the excitation and outgoing X-rays of the measured stack. The ideal response of the N Kα intensity when milling through the stack structure is indicated by the solid line from zero (complete stack) to the silicon bulk interface at ~20 Å. Naturally, the excitation and emission parts of the XRF signal will be specific to the thickness and composition of the stack structure.

[0055] Figure 12 Shows an example of the Nls 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 intermediate layer, which in turn is followed by a 5 Å SiON bottom layer.

[0056] The bottom layer does not contribute to the surface signal. The attenuation length of Nls within SiON is 39 Å. There is significant attenuation of Nls within SiON.

[0057] Figure 13 Shows an example of method 200 for evaluating a structure with microscopic dimensions.

[0058] Method 200 can start with step 210 of irradiating the structure with an X-ray beam (PKECE X-ray beam) having an X-ray energy close to the k-edge energy of the chemical elements of the structure by an electron optical device.

[0059] After step 210 can be step 220 of generating at least one detection signal among an X-ray photoelectron spectroscopy (XPS) detection signal and an X-ray fluorescence (XRF) detection signal.

[0060] After step 220 can be step 230 of determining chemical element information about the dose and concentration of chemical elements in the structure based on the at least one detection signal.

[0061] Method 200 can be executed by any one of the systems mentioned above.

[0062] Multiple iterations of steps 210, 220, and 230 can be provided.

[0063] After the iterations of steps 210, 220, and 230 can be step 240 of milling the structure. After step 240 can be step 210.

[0064] Any arrangement of components that perform the same function is effectively "associated" to achieve the desired function. Thus, any two components that are combined to perform a particular function can be considered to be "associated" with each other to achieve the desired function, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "operably connected" or "operably coupled" to each other to achieve the desired function.

[0065] In addition, those skilled in the art will recognize that the boundaries between the above operations are merely illustrative. Multiple operations can be combined into a single operation; a single operation can be distributed over additional operations, and operations can be performed at least partially overlapping in time. In addition, alternative embodiments can include multiple instances of an operation, and the order of operations can be changed in various other embodiments.

[0066] For example, in one embodiment, the illustrated examples can be implemented as circuitry located on a single integrated circuit or within the same device. Alternatively, the examples can be implemented as any number of separate integrated circuits or separate devices interconnected in a suitable manner.

[0067] For example, an example or a portion thereof can be implemented as a soft or code representation of a physical circuitry system or a soft or code representation that can be converted into a physical circuitry system (such as in any suitable type of hardware description language).

[0068] However, other modifications, variations, and alternatives are possible. Thus, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

[0069] In a claim, any reference numeral placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in a claim. In addition, as used herein, the term "a" or "an" is defined as one or more than one. Further, the use of the introductory phrases (such as "at least one" and "one or more") in a claim shall not be construed to imply that the introduction of another claim element by the indefinite article "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" as well as the indefinite article (such as "a" or "an"). The same holds true for the use of the definite article. Unless otherwise stated, terms (such as "first" and "second") are used arbitrarily to distinguish the elements so described. Thus, these terms are not necessarily intended to indicate the temporal or other precedence 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.

[0070] Although certain features of the present invention have been illustrated and described herein, many modifications, substitutions, changes and equivalents will now occur to those of ordinary skill in the art. Accordingly, it is to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the present invention.

[0071] Any reference to any of the terms "comprising", "including", "having" may, where appropriate and with necessary modifications, be applied to the terms "consisting of" and / or "consisting essentially of".

Claims

1. A system for evaluating a structure having a microscopic size, the system comprising: an electron optical device configured to irradiate 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; at least one detector selected from (i) an XPS detector for collecting an X-ray photoelectron spectroscopy (XPS) signal generated by irradiating the structure, and (ii) an XRF detector for collecting an X-ray fluorescence (XRF) signal generated by irradiating the structure; and a computing device configured to determine chemical element information regarding the dose and concentration of the chemical element in the structure based on at least one of the XPS signal and the XRF signal.

2. The system according to claim 1, wherein The X-ray beam energy does not exceed twice the k-edge energy of the chemical element of the structure.

3. The system according to claim 1, wherein, The chemical element is boron and the structure further includes silicon germanium, and wherein the X-ray beam energy is about 278 electron volts.

4. The system according to claim 1, wherein, The chemical element is nitrogen and the structure further includes silicon oxide, and wherein the X-ray beam energy is higher than 402 electron volts.

5. The system according to claim 1, wherein The at least one detector is the XPS detector; and wherein the chemical element information includes surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure.

6. The system according to claim 1, wherein The at least one detector is the XRF detector; and wherein the chemical element information includes total chemical element information regarding the dose and concentration of the chemical element within the structure.

7. The system according to claim 1, wherein The at least one detector includes the XPS detector and the XRF detector; and wherein the chemical element information includes (i) surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure, and (ii) total chemical element information regarding the dose and concentration of the chemical element within the structure.

8. The system according to claim 1, wherein The electron optical device is configured to irradiate the structure during multiple irradiation iterations.

9. The system according to claim 8, wherein, The at least one detector includes the XPS detector, wherein the XPS detector is configured to collect one or more XPS signals generated during one or more of the irradiation iterations in the multiple iterations; and wherein the computing device is configured to determine surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure based on the one or more XPS signals.

10. The system according to claim 8, wherein, The at least one detector includes the XRF detector, wherein the XRF detector is configured to collect one or more XRF signals generated during one or more of the irradiation iterations in the multiple iterations; and wherein the computing device is configured to determine total chemical element information regarding the dose and concentration of the chemical element within the structure based on the one or more XRF signals.

11. The system according to claim 1, wherein, The structure is milled between at least a pair of adjacent irradiation iterations.

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

13. A method for evaluating a structure having a microscale size, the method comprising: irradiating the structure with an X-ray beam by an electron optical device, the X-ray beam having an X-ray beam energy close to the k-edge energy of a chemical element of the structure; generating at least one detection signal selected from an X-ray photoelectron spectroscopy (XPS) detection signal and an X-ray fluorescence (XRF) detection signal; and determining chemical element information regarding the dose and concentration of the chemical element in the structure based on the at least one detection signal.

14. The method according to claim 13, wherein, The X-ray beam energy does not exceed twice the k-edge energy of the chemical element of the structure.

15. The method according to claim 13, wherein, The chemical element is boron and the structure further includes silicon germanium, and wherein the X-ray beam energy is about 278 electron volts.

16. The method according to claim 13, wherein, The chemical element is nitrogen and the structure further includes silicon oxide, and wherein the X-ray beam energy is higher than 402 electron volts.

17. The method according to claim 13, wherein At least one detector is an XPS detector; and wherein the chemical element information includes surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure.

18. The method according to claim 13, wherein At least one detector is an XRF detector; and wherein the chemical element information includes total chemical element information regarding the dose and concentration of the chemical element within the structure.

19. The method according to claim 13, wherein, At least one detector includes an XPS detector and an XRF detector; and wherein the chemical element information includes (i) surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure, and (ii) total chemical element information regarding the dose and concentration of the chemical element within the structure.

20. The method according to claim 13, comprising: irradiating the structure by the electron optical device during multiple irradiation iterations.

21. The method according to claim 20, wherein, At least one detector includes an XPS detector, wherein the method comprises: collecting, by the XPS detector, one or more XPS signals generated during one or more of the irradiation iterations in the multiple iterations; and determining, by a computing device, surface chemical element information regarding the dose and concentration of the chemical element in the surface of the structure based on the one or more XPS signals.

22. The method according to claim 20, wherein, At least one detector includes an XRF detector, wherein the method comprises: collecting, by the XRF detector, one or more XRF signals generated during one or more of the irradiation iterations in the multiple iterations; and determining, by a computing device, total chemical element information regarding the dose and concentration of the chemical element within the structure based on the one or more XRF signals.

23. The method according to claim 13, wherein, The structure is milled between at least a pair of adjacent irradiation iterations.

24. The method according to claim 13, comprising: milling the structure by a milling device during one or more milling iterations that do not overlap with any of the irradiation iterations.

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