Patterned X-ray emitting targets

Abstract

The present invention provides improved patterned X-ray emitting targets, X-ray sources including patterned X-ray emitting targets, X-ray reflection and scattering measurement (XRS) systems utilizing such X-ray emitting targets, as well as X-ray photoelectron spectroscopy (XPS) systems and X-ray fluorescence analysis (XRF) systems.

Description

Technical Field

[0005]

[0001] (Related Application) Reference is made to U.S. Patent No. 9,588,066 and U.S. Patent Publication No. 2017 / 0160081, owned by the assignee of this invention, the disclosures of which are hereby incorporated herein by reference. This application relates to patterned X-ray emitting targets, X-ray sources including patterned X-ray emitting targets, and X-ray reflectance scatterometry (XRS) systems, X-ray photoelectron spectroscopy (XPS) systems, and X-ray fluorescence (XRF) systems that use such X-ray emitting targets.

Background Art

[0002] Various types of patterned X-ray emitting targets, X-ray sources including patterned X-ray emitting targets, and X-ray reflectance scatterometry (XRS) systems, X-ray photoelectron spectroscopy (XPS) systems, and X-ray fluorescence (XRF) systems that use such X-ray emitting targets are known.

Disclosure of the Invention

[0003] This invention provides improved patterned X-ray emitting targets, X-ray sources including patterned X-ray emitting targets, and X-ray reflectance scatterometry (XRS) systems, X-ray photoelectron spectroscopy (XPS) systems, and X-ray fluorescence (XRF) systems that use such X-ray emitting targets.

[0004] This invention will be more fully understood from the following detailed description taken in conjunction with the drawings.

Brief Description of the Drawings

[0005] [Figure 1]This is a simplified diagram of an X-ray target constructed and operating according to a preferred embodiment of the present invention, which is particularly useful for XPS and XRF measurements. [Figure 2] This is a simplified (not to exact scale) cross-sectional view of the X-ray target in Figure 1, along the line II-II in Figure 1. [Figure 3] This is a simplified diagram of an X-ray target constructed and operating according to another preferred embodiment of the present invention, which is particularly useful for XRS and XRD measurements. [Figure 4] This is a simplified (not to exact scale) cross-sectional view of the X-ray target in Figure 3, along the IV-IV line in Figure 3. [Figure 5] This is a schematic diagram of an X-ray inspection system using an X-ray target according to an embodiment of the present invention. [Figure 6] This is a schematic diagram of an XPS or XRF X-ray measurement system using an X-ray target according to an embodiment of the present invention. [Figure 7] This is a schematic diagram of an XRS or XRD X-ray measurement system using an X-ray target according to an embodiment of the present invention. [Examples]

[0006] Referring to Figures 1 and 2, Figures 1 and 2 are a simplified diagram and a cross-sectional view of a patterned X-ray target 100 constructed and operating according to a preferred embodiment of the present invention, respectively.

[0007] The patterned X-ray target 100 preferably comprises a patterned X-ray impermeable mask 102, which is typically made of gold and has one or more openings 104 defining at least one X-ray passage window. The mask 102 is preferably made of gold with a thickness of about 1 μm. It should be understood that the mask 102 can be made thinner or thicker, such as up to 2 μm, depending on the desired level of shielding.

[0008] Preferably, an active layer 106, such as an aluminum (Al) layer with a thickness of about 2 μm, is provided beneath the mask 102. Alternatively, tungsten (W), tantalum (Ta), magnesium (Mg), or other suitable material can be selected as the active layer 106.

[0009] A diamond substrate 110 is bonded beneath the active layer 106 via a plurality of intermediate layers 108. These intermediate layers 108 provide a graded transition between the pure metal of the active layer 106 and the carbon diamond crystalline structure of the diamond substrate 110. The intermediate layers 108 facilitate the transition between the two different materials, thereby improving the bonding between them. Various employable structures and compositions of the intermediate layers 108 are described in U.S. Patent No. 7,359,487, which is incorporated herein by reference.

[0010] The diamond substrate 110 is preferably 0.5 mm thick and is located below the intermediate layer 108.

[0011] The properties of the diamond substrate 110 can be modified in several ways. In some situations, it may be desirable to dopage the diamond with boron to increase its electrical conductivity (while lowering its thermal conductivity), thereby allowing charge to be dissipated from the electron beam used to excite X-ray radiation. In other situations, the thermal conductivity can be increased by optimizing the impurities, grain size, grain boundaries, or surface roughness of the diamond.

[0012] A heat sink 114 is bonded to the diamond substrate 110 via a plurality of additional intermediate layers 112. The intermediate layers 112 can be selected from the group consisting of titanium, chromium, nickel, gold, silver, aluminum, copper, any alloy thereof, and any combination thereof.

[0013] Alternatively, the diamond substrate 110 may be bonded to the heat sink 114 by soldering using one or more intermediate solder layers. The one or more solder layers can be made of a low-melting-point material that does not cause excessive oxidation of the ionizing radiation forming layer when heated to the soldering temperature. The heat sink 114 is preferably made of a high thermal conductivity material such as beryllium oxide (BeO), tungsten, silicon carbide, aluminum nitride, copper, aluminum, silver, cement diamond (ScD), and any combination thereof.

[0014] One or more apertures can be of any shape / dimension, such as spot-shaped or strip-shaped (straight, curved, etc.), defining any desired pattern (1D, 2D, periodic, random, etc.). In the case of a strip-shaped aperture (trench) (elongated groove), the mask can block the electron beam and / or excited X-rays along only one axis (1D). Such a configuration may be useful, for example, in case of grazing angles of X-ray incidence, or when further shaping of the X-rays achieved by directing optics (slits, focusing elements, etc.) is required. The patterned X-ray target 100 and / or electron beam can be moved continuously or stepwise along one or two axes, for example, along the strip-shaped aperture.

[0015] Referring to Figures 3 and 4, Figures 3 and 4 are a simplified and cross-sectional view, respectively, of a patterned X-ray target 200 constructed and operating according to a preferred embodiment of the present invention.

[0016] The patterned X-ray target 200 preferably comprises a patterned X-ray opaque mask 202, which is typically formed from gold and has one or more apertures 204 that define one or more X-ray passage windows. The mask 202 preferably has a thickness in the range of about 0.1 pm to 0.2 pm. It should be understood that the mask 202 should not be too thick to avoid any “geometrical” obstruction that may occur to the grazing angle exit photons.

[0017] A diamond substrate 210, typically 0.5 mm thick, is bonded beneath the mask 202 via multiple intermediate layers 208. In this embodiment, the diamond substrate 210 functions as an active layer.

[0018] The properties of the diamond substrate 210 can be modified in several ways. In some situations, it may be desirable to dopage the diamond with boron to increase its electrical conductivity (while lowering its thermal conductivity), for example, to dissipate charge from an electron beam used to excite X-ray radiation. In other situations, the thermal conductivity can be increased by optimizing the impurities, grain size, grain boundaries, or surface roughness of the diamond.

[0019] The multiple intermediate layers 208 described above provide a stepwise transition between the carbon-diamond crystalline structure of the diamond substrate 210 and the pure metal of the mask 202. The intermediate layers 208 facilitate the transition between the two different materials, thereby improving the bonding between the two materials. The disclosure of U.S. Patent No. 7,359,487 describing the structure of the intermediate layers 208 is incorporated herein by reference.

[0020] Below the diamond substrate 210, a heat sink 214 is coupled via a plurality of additional intermediate layers 212. The intermediate layer 212 can be selected from the group consisting of titanium, chromium, nickel, gold, silver, aluminum, copper, any alloy thereof, and any combination thereof.

[0021] Alternatively, the diamond substrate 210 may be bonded to the heat sink 214 by soldering using one or more intermediate solder layers. The one or more solder layers can be a low melting point material that does not cause excessive oxidation of the ionization radiation forming layer when heated to the soldering temperature. The heat sink 214 is preferably composed of a high thermal conductivity material such as beryllium oxide (BeO), tungsten, silicon carbide, aluminum nitride, copper, aluminum, silver, cemented diamond (ScD), and any combination thereof.

[0022] The one or more openings can have any shape / dimension, such as spot-shaped or strip-shaped (linear, straight, etc.), and define any desired pattern (1D, 2D, periodic, random, etc.). In the case of a strip-shaped opening (trench), the mask can block an electron beam or excited X-rays along only one axis (1D). Such a configuration can be useful, for example, when the X-ray incident angle is glancing or when further shaping of the X-rays is required by a directional optical system (slit, edge, focusing element, etc.).

[0023] Referring to FIG. 4, the intermediate layer 208 is preferably opened so as to be aligned with one or more openings 204.

[0024] Referring to FIG. 5, FIG. 5 is a simplified schematic diagram of an X-ray inspection system using a patterned X-ray target according to an embodiment of the present invention.

[0025] Referring to Figure 5, an electron beam 306 is provided by an electron beam gun 310. The electron beam 306 strikes the surface of an X-ray target 316, preferably an X-ray target of the type described above and shown in Figures 1 to 4, thereby generating ionizing radiation 318, preferably X-rays. The ionizing radiation 318 can be used for any suitable purpose.

[0026] In the illustrated embodiment, the ionizing radiation 318 strikes a monochromator 320, for example, a Bragg crystal monochromator, and preferably the ionizing radiation 327 reflected from the monochromator 320 strikes a sample 330 placed on a sample holder 332, more specifically, the target sample surface 334 to be inspected. The reflected ionizing radiation 327, such as X-rays, is reflectable, i.e., scattered by its impact on the sample 330. In addition to or instead of this, such impacts may result in the generation of photoelectrons. A suitable detector 340 detects the reflected radiation 342. In one embodiment, the data generated by the detector 340 is transmitted to a computer 350 and further processed to generate useful information and / or images.

[0027] Referring to Figure 6, Figure 6 is a schematic diagram of an XPS or XRF X-ray measurement system 700 using an X-ray target according to one embodiment of the present invention.

[0028] Referring to Figure 6, the X-ray measurement system 700 includes an electron beam source 702 that generates an electron beam 704. The electron beam 704 collides with an X-ray target 706, preferably of the type described above and shown in Figures 1 to 4, thereby generating an X-ray beam 708. A monochromator 709 receives the X-ray beam 708, generating a monochromatic X-ray beam 710. A sample holder 712 allows a sample 713 to be placed in the path of the monochromatic X-ray beam 710.

[0029] An XPS detector 714 may be provided for the XPS signal 715 generated by the collision of the monochromatic X-ray beam 710 with the sample 714. Alternatively, or in addition to this, an XRF detector 716 may be provided for the XRF signal 718 generated by the collision of the monochromatic X-ray beam 710 with the sample 714.

[0030] The XRF signal 718 and the XPS signal 715 can be detected simultaneously or nearly simultaneously and represent a single sampling event. The XPS signal 715 and the XRF signal 718 result from the detection of photoelectron and fluorescent X-rays, respectively. In addition, a flux detector 721' may be provided to determine the estimated flux of the monochromatic X-ray beam 710. In one embodiment, the flux detector 721' is positioned in the sample holder 712 as shown in Figure 6. In another embodiment, the X-ray flux detector 721 is positioned near the monochromator 709 so as to partially intersect with a small portion of the primary X-rays of the X-ray beam 708, and the X-ray flux is monitored when the sample holder 712 is positioned at the analysis site.

[0031] The computing system 728 preferably includes a user interface 720, a computing engine 722, and memory 724. The computing system 728 can be configured to process the XPS signal 715 output by the XPS detector 714 and / or the XRF signal 718 output by the XRF detector 716. The computing system 728 can also be configured to monitor the primary X-ray flux measured by the flux detector 721 or 721'. In one embodiment of the invention, the computing system 728 operates to normalize the XPS signal 715 detected by the XPS detector 714 and the XRF signal 718 detected by the XRF detector 716 according to the X-ray flux measured by the flux detector 721 or 721'.

[0032] Referring to Figure 7, Figure 7 is a simplified diagram of an X-ray measurement system 800 of XRS and / or XRD that uses an X-ray target according to an embodiment of the present invention and operates to provide X-ray reflectance scatterometry.

[0033] Referring to Figure 7, the X-ray measurement system 800 includes an electron beam source 802 that generates an electron beam 804. The electron beam 804 collides with an X-ray target 806, preferably of the type described above and shown in Figures 1 to 4, thereby generating an X-ray beam 808, preferably with an energy of about 1 keV or less. A monochromator 810 receives the X-ray beam 808, generating a monochromatic X-ray beam 812. A magnetic electron suppression device 813 is provided between the X-ray target 806 and the monochromator 810.

[0034] Preferably, a sample holder 814 positions a sample 816, preferably having a periodic structure, within the path of the monochromatic X-ray beam 812. The monochromator 810 also operates to focus the X-ray beam 808 to provide the focused monochromatic X-ray beam 812 to the sample holder 814. The detector 818 receives at least a portion of the X-ray beam 819 scattered from the sample 816.

[0035] In the illustrated embodiment, the X-ray target 806 is designed to generate low-energy X-rays, but for higher-energy XRF, the diamond substrate 212 may contain molybdenum (Mo) or rhodium (Rh) in addition to carbon.

[0036] It will be apparent to those skilled in the art that this invention is not limited to what is specifically shown and described above. Rather, the scope of this invention includes both combinations and subcombinations of the various features described above, as well as their modifications and variations, which are not found in the prior art.

Claims

1. An X-ray source for generating an X-ray beam, the X-ray source comprising: an electron gun configured to generate an electron beam; and a patterned X-ray emitting target, the patterned X-ray emitting target comprising: an X-ray blocking mask having one or more apertures; one or more structural elements comprising an x-ray generating structural element located below the x-ray blocking mask, the one or more structural elements including a top structural element; the x-ray producing structure is configured to (a) receive electrons of the electron beam that pass through the x-ray blocking mask, and (b) reflect the x-ray beam that passes through the x-ray blocking mask; a sample holder for positioning a sample having a periodic structure; a monochromator positioned between the X-ray source and the sample holder, the monochromator directing the X-ray beam from the X-ray source to the monochromator toward the sample holder; and a detector for collecting at least a portion of the X-ray beam scattered by the sample; Equipped with X-ray measurement system.

2. 2. The x-ray metrology system of claim 1, wherein said electron gun is fixed and said patterned x-ray emitting target moves continuously along an axis.

3. 2. The x-ray metrology system of claim 1, wherein said electron gun is fixed and said patterned x-ray emitting target is rotated relative to said electron gun.

4. 2. The x-ray metrology system of claim 1, wherein the one or more apertures are configured to compensate for focal aberrations of the monochromator.

5. 10. The x-ray metrology system of claim 1, wherein the electron gun is operative to provide an electron beam having a spatially varying intensity.

6. The X-ray measurement system of claim 1, wherein the one or more apertures are configured to generate X-rays having a desired X-ray pattern by taking into account downstream distortions of the X-ray beam passing through at least one of the apertures.

7. 2. The x-ray metrology system of claim 1, wherein the x-ray blocking mask has a plurality of different non-zero thicknesses at a plurality of different locations thereof.

8. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is an X-ray generating substrate, and the patterned X-ray emitting target also includes at least one adhesive layer disposed between the X-ray generating substrate and the X-ray blocking mask.

9. 2. The x-ray metrology system of claim 1, wherein the x-ray blocking mask is formed from a plurality of materials having different x-ray absorption characteristics.

10. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is an X-ray generating substrate, and the X-ray generating substrate is configured to have enhanced thermal conductivity properties at a location not under the at least one opening.

11. The x-ray measurement system of claim 1, wherein the x-ray generating structural element is an x-ray generating substrate, the x-ray generating substrate being patterned and doped with boron.

12. The x-ray measurement system of claim 1, wherein the x-ray generating structural element is an x-ray generating substrate, and the x-ray generating substrate is formed with a patterned thermally conductive layer configured to provide enhanced thermal conduction at locations not under the at least one opening.

13. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is an X-ray generating substrate, the X-ray generating substrate being mounted such that its position varies in at least one direction during operation.

14. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is an X-ray emitting layer, and the patterned X-ray emitting target has at least one adhesive layer disposed between the high thermal conductivity substrate and the X-ray emitting layer, and between the X-ray emitting layer and the X-ray blocking mask.

15. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is selected from an X-ray emitting layer formed on at least one surface of an X-ray generating substrate or a thermally conductive substrate.

16. The X-ray measurement system of claim 1, wherein the X-ray generating structural element is an X-ray emitting layer formed on at least one surface of a thermally conductive substrate, and the thermally conductive substrate is made of a thermally conductive material selected from beryllium oxide (BeO), tungsten, silicon carbide, aluminum nitride, copper, aluminum, silver, and cemented diamond (ScD).

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