Abstract
Disclosed is a radiation window structure. The radiation window structure including a substrate made of silicon nitride and a coating layer grown from a vapor phase on outer surface of the substrate. Also disclosed is a method for manufacturing a radiation window structure.
Claims
1-15. (canceled)
16. A radiation window structure, comprising: a substrate made of silicon nitride, and a coating layer grown from a vapor phase on outer surface of the substrate.
17. The radiation window structure according to claim 16, wherein the coating layer is made of pyrolytic carbon.
18. The radiation window structure according to claim 16, wherein the substrate is between 5 and 500 nanometers thick.
19. The radiation window structure according to claim 16, wherein the coating layer is between 20 nanometers and 5 micrometers thick.
20. The radiation window structure according to claim 16, comprising a mesh layer made of silicon between the substrate and the coating layer at least on one surface of the substrate.
21. The radiation window structure according to claim 20, comprising a silicon nitride layer between the mesh layer on at least one surface of the substrate and the coating layer.
22. The radiation window structure according to claim 20, wherein the mesh layer is between 20 nanometers and 500 micrometers thick.
23. The radiation window structure according to claim 21, wherein the silicon nitride layer is between 5 and 500 nanometers thick.
24. A method for manufacturing a radiation window structure, the method comprising: growing a coating layer from a vapor phase on outer surface of a substrate made of silicon nitride.
25. The method according to claim 24, wherein the growing of the coating layer is provided simultaneously on the whole outer surface of the substrate.
26. The method according to claim 24, wherein the coating layer grown from the vapor phase is made of pyrolytic carbon.
27. The method according to claim 24, wherein said growing comprises pyrolysis.
28. The method according to claim 24, wherein the gas used in said growing the coating layer from the vapor phase is methane.
29. The method according to claim 24, comprising producing a mesh layer between the substrate and the coating layer at least on one surface of the substrate.
30. The method according to claim 29, comprising producing a silicon nitride layer between the mesh layer on at least one surface of the substrate and the coating layer.
Description
BRIEF DESCRIPTION OF FIGURES
[0026] The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.
[0027] FIG. 1 illustrates a method and a radiation window according to an embodiment of the invention.
[0028] FIG. 2 illustrates a method and a radiation window according to another embodiment of the invention.
[0029] FIG. 3 illustrates a method and a radiation window according to yet another embodiment of the invention.
[0030] FIG. 4 illustrates a method and a radiation window according to yet another embodiment of the invention.
DESCRIPTION OF SOME EMBODIMENTS
[0031] In this description we use the following vocabulary. A layer means a quantity of essentially homogeneous material that by its form has much larger dimensions in two mutually orthogonal directions than in the third orthogonal direction. In most cases of interest to the present invention, the dimension of a layer in said third orthogonal direction (also referred to as the thickness of the layer) should be constant, meaning that the layer has uniform thickness. A foil is a structure, the form of which may be characterised in the same way as that of a layer (i.e. much larger dimensions in two mutually orthogonal directions than in the third orthogonal direction) but which is not necessarily homogeneous: for example, a foil may consist of two or more layers placed and/or attached together. A mesh is a special case of a layer or foil, in which the constituents do not make up a continuous piece of material but define an array of (typically regular, and regularly spaced) openings. A radiation window foil is a foil that has suitable characteristics (such as low absorption, sufficient gas tightness, sufficient mechanical strength etc.) for use in a radiation window of a measurement apparatus. A radiation window is an entity that may comprise a piece of radiation window foil attached to a (typically annular) support structure so that electromagnetic radiation may pass through an opening defined by the support structure without having to penetrate anything else than said piece of radiation window foil and the (typically gaseous) medium that otherwise exists within said opening. In this application a term radiation window structure corresponds to the term radiation window foil.
[0032] FIG. 1 illustrates a workpiece in various steps of a method for manufacturing a radiation window structure according to an embodiment of the invention. The topmost step illustrates a substrate 102 made of silicon nitride. The substrate 102 may be provided in a silicon frame in order to ease the handling of the radiation window structure. The substrate 102 may be between 5 and 500 nanometers thick. Preferably, the substrate 102 is between 40 to 50 nanometers thick. If the substrate 102 was thinner, its mechanical strength would be so low that the need for additional support solutions could be required. If the substrate 102 was thicker, its absorption might come too high concerning very sensitive X-ray fluorescence measurements, like the detection of sodium. The use of a substrate 102 made of silicon nitride enables manufacturing a thin and gastight radiation window.
[0033] In the next step of the method illustrated in FIG. 1 a coating layer 104 is grown from a vapor phase on outer surface of the substrate 102. In the other words the substrate 102 is coated with the coating layer 104. The gas may be methane, for example. The coating layer 104 may be grown on the whole surface of the substrate 102 simultaneously and at the same speed. In other words all the outer surfaces of the substrate 102 are coated with the coating layer 104 simultaneously. By growing the coating layer 104 simultaneously and at the same speed on the whole surface of the substrate 102, as illustrated in FIG. 1, deformation of the coating layer 104 and/or defects in the coating layer 104 may be at least partly reduced. Thus, also the quality of the coating layer 104 may be improved at least partly. The material for the coating layer 104 may preferably be selected so that the thermal expansion coefficient of the coating layer 104 material is close to the thermal expansion coefficient of the substrate 102 material. The thermal expansion coefficient of the silicon nitride is 3.27.Math.10.sup.6 C..sup.1. Preferably, the thermal expansion coefficient of the coating layer 104 material may differ from the thermal expansion coefficient of the silicon nitride less than 3.Math.10.sup.6 C..sup.1. The coating layer 104 may be made of pyrolytic carbon. The thermal expansion coefficient of the pyrolytic carbon is 0.5.Math.10.sup.6 C..sup.1. The use of pyrolytic carbon in the coating layer 104 is preferable, because of at least the following reasons: the pyrolytic carbon is not toxic, the atomic number of the pyrolytic carbon is small, helium leakage through the pyrolytic carbon is low. However, the substrate made of silicon nitride is a good diffusion barrier that assures that the radiation window is gastight. The thickness of the coating layer 104 may be between 20 nanometers and 5 micrometers. If the coating layer 104 was thinner, the manufacturing of the coating layer might become unreliable and more challenging. If the coating layer 104 was thicker, its absorption might come too high. Preferably, the coating layer 104 may be between 300 and 500 nanometers.
[0034] Pyrolysis may be used to grow the coating layer 104 from a vapor phase. Pyrolysis is a reaction used to coat a preformed substrate with a layer of pyrolytic carbon. Pyrolysis occurs at high temperature, such as 1000 to 2000 degrees Celsius. The gas used in pyrolysis may be methane, for example.
[0035] FIG. 2 illustrates part of a radiation window manufacturing method according to yet another embodiment of the invention. The first step is comparable to corresponding step in FIG. 1 earlier. Thus, the topmost step illustrates a substrate 102 made of silicon nitride. At the second step of FIG. 2 a mesh layer 202 is produced on at least on one surface of the substrate 102. In
[0036] FIG. 2 the mesh layer 202 is produced on the second surface of the substrate 102. Alternatively or in addition, the mesh layer 202 may be produced on the first surface of the substrate 102. FIG. 3 illustrates part of a radiation window manufacturing method according to yet another embodiment of the invention, wherein the mesh layer 202 is produced on the first surface of the substrate 102 and on the second surface of the substrate 102. Otherwise, the steps in FIG. 3 are comparable to corresponding steps in FIG. 2. The mesh layer 202 may be manufactured using a thin film deposition technique. Suitable methods for depositing the mesh layer 202 include, but are not limited to, chemical vapour deposition and pulsed laser deposition. At first, the mesh layer 202 is uniform. The mesh layer 202 may be made of silicon, for example. The criteria to be applied in choosing the material for the mesh layer 202 include reasonable mechanical strength, good binding to the substrate 102, suitability to etching with an etching method and/or agent that does not affect the substrate 102 to a significant extent, low absorption of radiation, absence of disturbing fluorescence peaks and/or other awkwardly handled anomalities at the wavelengths of electromagnetic radiation at which the radiation window is to be used, as well as easy handling in a thin film deposition process. Preferably, the mesh layer 202 may be between 20 nanometers and 500 micrometers thick.
[0037] In the third step in FIG. 2, regularly spaced portions of the originally uniform mesh layer 202 are removed to turn said uniform layer into a mesh. In FIG. 2 regularly spaced mesh is used as an example, but also irregular mesh may be used. The characteristic dimensions of the mesh may include for example a diameter of openings in the order of 1 to 5000 micrometres, and a width of the ribs in the mesh in the order of 50 to 5000 micrometres. Assuming that the process of turning the originally uniform layer into a mesh does not significantly affect those parts of the layer that are to form the ribs, the height (the dimension in the vertical direction in FIG. 2) of the ribs constituting the mesh will be essentially the same as the original thickness of the uniform layer. These dimensions are examples only, and the eventual selection of characteristic dimensions should be made in accordance with the mechanical strength that the completed radiation window should have. Several methods for turning a previously uniform, thin-film-deposited layer into a mesh layer are known, including but not being limited to photolithography, wet etching, dry etching, plasma etching, electron beam lithography, and ion beam lithography. The method should naturally be selected so that it still leaves the window continuous. The mesh layer 202 may be used to improve the mechanical strength of the window structure.
[0038] At the last step in FIG. 2, a coating layer 104 is grown from a vapor phase on outer surface of the combined structure comprising substrate 102 and at least one mesh layer 202 as described above. Thus, the mesh layer 202 is provided between the substrate 102 and the coating layer 104 at least on one surface of the substrate 102. The last step in FIG. 2 is comparable to corresponding last step in FIG. 1 earlier. The mesh layer 202 between the substrate 102 and the coating layer 104 enables that the coating layer 104 may be thinner than without the mesh layer 202. Preferably, the thickness of the coating layer 104 may be similar to the thickness of the substrate 102 if the mesh layer 202 is provided between the substrate 102 and the coating layer 104.
[0039] FIG. 4 illustrates part of a radiation window manufacturing method according to yet another embodiment of the invention. The first three steps are comparable to corresponding steps in FIG. 2 earlier. Thus, the topmost step illustrates a substrate 102 made of silicon nitride. At the second step of FIG. 4 a mesh layer 202 is produced on at least on one surface of the substrate 102. In the third step in FIG. 4, regularly spaced portions of the originally uniform mesh layer 202 are removed to turn said uniform layer into a mesh. At the next step in FIG. 4 a silicon nitride layer 402 is produced on the at least one mesh layer 202. The silicon nitride layer 402 may be manufactured using a thin film deposition technique. Suitable methods for depositing the silicon nitride layer 402 include, but are not limited to, chemical vapour deposition and pulsed laser deposition. Preferably, the silicon nitride layer 402 is between 5 and 500 nanometers thick. The silicon nitride layer 402 on top of the mesh layer 202 may be used to improve at least partly the mechanical strength of the window structure.
[0040] At the last step in FIG. 4, a coating layer 104 is grown from a vapor phase on outer surface of the combined structure comprising substrate 102, at least one mesh layer 202, and silicon nitride layer 402 as described above. Thus, the silicon nitride layer 402 is provided between the mesh layer 202 on at least one surface of the substrate 102 and the coating layer 104. The last step in FIG. 4 is comparable to corresponding last step in FIGS. 1 and 2 earlier.
[0041] The method for manufacturing a radiation window structure described above may be implemented to manufacture a single radiation window structure that may be attached to a support structure. Alternatively, the method may be implemented to manufacture a plurality of radiation window structures on a one wafer. The plurality of the radiation window structures may be cut from the wafer. Furthermore, the plurality of the cut radiation window structures may be attached to corresponding support structures.
[0042] Advantages of the invention include the possibility of manufacturing radiation windows where the radiation window foil is very thin and yet gastight, and causes very little unwanted absorption or spurious responses in a measurement involving X-rays. Furthermore, the invention enables manufacturing radiation windows where the mechanical stress caused for example by thermal expansion may be at least partly reduced. Additionally, the pyrolytic carbon used in the coating layer of the radiation window structure is not toxic and it is environmentally sustainable also in the long term.
[0043] The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.
