Method for manufacturing a carbon-based radiant window and a carbon-based radiant window

Abstract

The present invention relates to a method for manufacturing a radiation window (100) for an X-ray measuring apparatus. The method includes depositing an amorphous carbon layer (102) on the surface of a carrier (101) (120), mounting a composite structure (103) comprising the amorphous carbon layer (102) and the carrier (101) in a region surrounding an opening (104) in the housing (105) such that the amorphous carbon layer (102) faces the housing (105) (140), and removing at least a portion of the carrier (101) (150). The present invention also relates to a radiation window (100) for an X-ray measuring apparatus.

Description

Technical Field

[0001] The present invention generally relates to the technical field of radiation windows. In particular, the present invention relates to a radiation window for an X-ray measuring device.

Background Art

[0002] A radiation window is a part of a measuring device that transmits a desired portion of electromagnetic radiation, such as X-ray radiation. In many cases, the radiation window must be gas-tight in order to seal and protect an accommodation space in a reduced-pressure state and / or in which a specific gas component is present. Nevertheless, in order to reduce the absorption of the desired radiation as much as possible, the main part of the radiation window preferably needs to be composed of a thin film made of a material containing only elements with a small atomic number. The radiation window foil can be attached to the housing of the radiation window by a selected bonding method.

[0003] Beryllium is known to be a good material as a material for a radiation window foil, especially in an X-ray measuring device, because it has a small atomic number (4) and as a result, the absorption of X-rays is very small. Another property that makes beryllium very useful as a radiation window foil is its excellent bending rigidity. At the time of writing this specification, the thinnest commercially available beryllium foil for use in a radiation window has a thickness of approximately 8 micrometers. At the time of writing this specification, it has not yet been shown that a method of manufacturing a beryllium foil by rolling from an ingot can produce a beryllium foil that has sufficient gas tightness and a thickness of less than 8 micrometers, and in that sense, it seems to have reached a limit. This phenomenon is due to the relatively large crystal grain size (larger than the foil thickness). Grain boundaries in the beryllium foil tend to cause gas leakage through the foil. Furthermore, beryllium is toxic and thus has disadvantages as a material. This will impose additional requirements on the manufacturing process. Also, the use of beryllium has become uncertain due to the tightening of regulatory requirements by national authorities.

[0004] Boron carbide is a preferred material, particularly for manufacturing radiation window foils in X-ray measuring devices. Boron carbide is non-toxic and is an environmentally sustainable material in the long term. If the boron carbide layer is thin, for example, less than 0.5 micrometers, its mechanical strength is too low, making the layer brittle. However, if the thickness of the boron carbide layer is increased beyond, for example, 2 micrometers, the crystal size within the boron carbide layer begins to increase, resulting in the layer becoming brittle. Therefore, increasing the thickness of the boron carbide layer does not improve the mechanical strength of boron carbide. Typically, radiation window foils made of boron carbide require one or more additional radiation filter layers to block electromagnetic radiation of unwanted wavelengths, such as ultraviolet (UV), visible light (VIS), and / or infrared (IR) radiation. The aforementioned one or more radiation filter layers are typically made of aluminum. However, aluminum already has a higher atomic number (13) compared to beryllium (4) and boron (5). Therefore, radiation filter layers, i.e., radiation shielding layers, or other layers made of aluminum impair the bandpass performance of X-rays, especially in applications where efficient light filtering, i.e., blocking, is required, such as shielding from sunlight. Another drawback of aluminum relates to its heat resistance. The construction of X-ray detectors typically involves a vacuum sealing process, which is carried out at temperatures exceeding 150°C to remove moisture and other potential outgassing sources. Although the sealing temperature is well below the melting point of aluminum, it is high enough to cause clustering and pinhole formation in thin aluminum layers. Aluminum containing clustered pinholes has reduced shielding efficiency, resulting in decreased performance and yield.

[0005] Graphene is another selective material, particularly for manufacturing radiation window foils in X-ray measuring devices. However, single-layer graphene does not provide sufficient mechanical strength. To improve the mechanical strength of radiation window foils, multilayer graphene structures can be used. Multilayer graphene structures typically consist of tens, hundreds, or thousands of layers of graphene monolayers stacked in layers. Preferably, a multilayer graphene structure includes at least 350 layers of graphene monolayers. However, stacking single layers of graphene becomes impractical. While it may be possible to stack tens or hundreds of single layers of graphene, the achievable thickness in a multilayer graphene structure consisting of tens or hundreds of single layers of graphene is limited because the ideal thickness of a single layer of graphene is 0.345 nanometers. This limits the production of large-area radiating windows, for example, because larger radiating windows experience greater stress than smaller ones, thus requiring thicker window foils. Furthermore, high-quality multilayer graphene structures cannot be grown directly on silicon wafers. A catalyst is required to grow high-quality multilayer graphene structures on silicon wafers. However, multilayer graphene structures grown on catalysts exhibit heterogeneity, resulting in weakened window foils.

[0006] Therefore, it is necessary to develop solutions to mitigate the aforementioned problems and provide a thin, gastight radiation window. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The following is a simplified summary to provide a basic understanding of some aspects of various embodiments of the present invention. This summary is not a comprehensive overview of the present invention, nor is it intended to identify any important or essential elements of the present invention, or to define its scope. The following summary merely presents some concepts of the present invention in a simplified form prior to a more detailed description of exemplary embodiments of the present invention.

[0008] One object of the present invention is to provide a radiation window for an X-ray measuring device and a method for manufacturing a radiation window. Another object of the present invention is to provide a radiation window for an X-ray measuring device and a method for manufacturing a radiation window that is thin, has very little X-ray absorption, and has a radiation window foil that absorbs electromagnetic radiation of unwanted wavelengths, including ultraviolet (UV), visible light (VIS), and infrared (IR) radiation, without using an aluminum layer.

[0009] The object of the present invention is achieved by the methods and radiation windows defined by each independent claim. [Means for solving the problem]

[0010] According to a first aspect, a method is provided for manufacturing a radiation window for an X-ray measuring apparatus, the method comprising depositing an amorphous carbon layer on the surface of a carrier, mounting a composite structure comprising the amorphous carbon layer and the carrier in a region surrounding an opening in a housing such that the amorphous carbon layer faces the housing, and removing at least a portion of the carrier. The amorphous carbon layer may be deposited on the carrier surface by thermal decomposition. The removal of at least a portion of the carrier may include removing the central region of the carrier to form an additional support structure. The carrier may be a silicon wafer. The thickness of the amorphous carbon layer may be between 0.5 and 3 micrometers.

[0011] According to a second embodiment, a radiation window for an X-ray measuring apparatus is provided, the radiation window comprising a housing defining an opening and a radiation window foil having an amorphous carbon layer attached to the housing in a region surrounding the opening so as to cover the opening of the housing. The amorphous carbon layer may be provided by pyrolysis deposition technology. The radiating window foil may further include additional support structures on the surface of the amorphous carbon layer opposite to the housing. The additional support structure may be made of silicon. The thickness of the amorphous carbon layer may be between 0.5 and 3 micrometers.

[0012] Various exemplary and non-limiting embodiments of the present invention relating to both structure and operation, as well as additional objectives and advantages associated therewith, will be best understood from the following description of specific exemplary and non-limiting embodiments, which will be read in conjunction with the accompanying drawings.

[0013] The verbs “to comprise” and “to include” as used herein are used as open limitations, neither excluding nor requiring the existence of features not described herein. Features described in dependent claims may be freely combined with each other unless otherwise expressly stated herein. Furthermore, the use of “a” or “an,” i.e., the singular form, throughout this specification should be understood not as excluding the plural. Embodiments of the present invention are shown in the accompanying drawings as examples, not limitations. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 schematically shows a method for manufacturing a radiation window and an example of a radiation window. [Figure 2] Figure 2 schematically shows a non-limiting example of a radiant window that further includes one or more additional layers and / or structures. [Modes for carrying out the invention]

[0015] In this specification, the following terms are used: A layer means a quantity of essentially homogeneous material in which, by its form, the dimensions in two mutually orthogonal directions are significantly larger than the dimensions in a third orthogonal direction. In most cases relating to the present invention, the dimensions of the layer in the third orthogonal direction (also referred to as the thickness of the layer) should be constant, meaning that the layer has a uniform thickness. A foil is a structure whose form can be characterized in the same way as layers (i.e., dimensions in two mutually orthogonal directions are significantly larger than dimensions in a third orthogonal direction), but which may consist of one or more layers. If a foil consists of two or more layers, these two or more layers are arranged and / or joined to each other. A radiation window foil 107 is a foil having properties suitable for use in a radiation window 100 of a measuring device, such as an X-ray measuring device (low absorption of desired radiation, sufficient gastightness, sufficient mechanical strength, etc.). The radiation window 100 is a structure in which a part of the radiation window foil 107 is attached to an annular housing (i.e., a support structure) 105, thereby allowing electromagnetic radiation to pass through the opening 104 defined by the housing 105 without penetrating anything other than that part of the radiation window foil 107.

[0016] Figure 1 shows an example of a workpiece in each step of an exemplary method for manufacturing a radiation window 100 for an X-ray measuring device. Figure 1 shows a cross-sectional view of the workpiece in each step of the exemplary method. The X-ray measuring device may, but is not limited to, an X-ray fluorescence (XRF) spectrometer or a radiation detector. The top step 110 of the exemplary method shown in Figure 1 shows a carrier 101. At least one surface of the carrier 101 may be polished. In Figure 1, the polished surface is facing upwards. The carrier 101 may be a silicon wafer. For example, silicon wafers are routinely polished to an RMS (root mean square) roughness value on the order of a fraction of a nanometer, which is sufficient for the purposes of the present invention. In addition to or instead of silicon, the carrier 101 may be made from other solid materials that can be polished to the required level of smoothness and, preferably, can be etched with relatively common and easy-to-handle etchants. In a non-limiting example, the thickness of the carrier 101 may be approximately 725 micrometers.

[0017] In the next step 120 of the exemplary method shown in Figure 1, an amorphous carbon layer 102 is formed on the surface of the carrier 101. Preferably, the amorphous carbon layer 102 is formed on the polished surface of the carrier 101. The amorphous carbon layer 102 is formed by deposition on the surface of the carrier 101. For example, the amorphous carbon layer 102 may be deposited on the surface of the carrier 101 by pyrolysis, i.e., the amorphous carbon layer 102 may be formed on the surface of the carrier 101 using pyrolysis deposition techniques. In other words, the material of the amorphous carbon layer 102 is pyrolysis deposited carbon composed mainly or entirely of amorphous carbon. The thickness of the amorphous carbon layer 102 can be, for example, 0.5 to 3 micrometers. Amorphous carbon is a carbonaceous material without a crystal structure. Amorphous carbon is an alloy with a small atomic number (6) and imparts strength to the radiation window structure 100. Due to the small atomic number of amorphous carbon, the amorphous carbon layer 102 has very little absorption of X-rays, that is, it can transmit a part of the desired electromagnetic radiation such as X-ray radiation, and is particularly effective in the energy range important for energy dispersive analysis of elements such as X-ray fluorescence analysis. Amorphous carbon suppresses the propagation of cracks more effectively compared to materials having a crystal structure such as graphene, for example. The amorphous carbon layer 102 also functions as an etch stop layer. This means that in the radiation window 100, a separate etch stop layer is not necessary, but it can also be provided optionally. The purpose of the etch stop layer is to block an etchant that can be used to remove at least a part of the carrier 101 in the method step 150 described later. In other words, the amorphous carbon layer 102 is impermeable to the etchant. When one or more additional layers are formed on the amorphous carbon layer 102, the amorphous carbon layer 102 as an etch stop layer prevents the etchant from affecting the one or more additional layers that can be formed on the amorphous carbon layer 102. The amorphous carbon layer 102 also functions as a radiation filter layer for blocking electromagnetic radiation of unnecessary wavelengths such as ultraviolet (UV), visible light (VIS), and / or infrared (IR) radiation. This means that, for example, there is no need to provide a separate radiation filter layer made of aluminum in the radiation window 100, but it can also be provided optionally. The separate radiation filter layer is typically composed of aluminum. Therefore, the use of the amorphous carbon layer 102 reduces the need for the use of aluminum. The amorphous carbon layer 102 provides a gas-tight radiation window. This means that separate layers, such as a separate etch-stop layer, are not required to provide a gas-tight radiation window. Various carbonaceous materials, such as amorphous carbon, graphene, multilayer graphene, and highly oriented pyrolysis graphite (HOPG), are well known to have their own unique Raman spectra. Therefore, different carbonaceous materials can be distinguished from each other based on their Raman spectra. In other words, by using Raman spectroscopy, it is possible to determine whether the carbonaceous material of the radiation window 100 is amorphous carbon or another carbonaceous material.

[0018] In the next step 130 of the exemplary method shown in Figure 1, the composite structure 103, including the carrier 101 and the amorphous carbon layer 102, is cut into single pieces (e.g., single chips) of a size suitable for use in one radiation window 100. For example, the carrier 101 may originally be a silicon wafer with a diameter of several inches, while the diameter of a piece large enough for the radiation window 100 may be, for example, between 1 and 2 centimeters. On the other hand, the present invention does not limit the maximum size of the radiation window 100 to be manufactured. In another example, the radiation window 100 according to one example may have a diameter of 10 millimeters for the opening 104 covered with foil through which radiation passes. Cutting the composite structure 103 into pieces in this step of the method is not an essential requirement of the manufacturing method, but it is advantageous in that a large number of finished radiation windows 100 can be manufactured very practically from a single original workpiece.

[0019] In the next step 140 of the exemplary method shown in FIG. 1, a piece of the composite structure 103 including the carrier 101 and the amorphous carbon layer 102 is attached (i.e., joined) to an annular region around the opening 104 in the housing 105 (i.e., the support structure) such that the amorphous carbon layer 102 faces the housing 105. In other words, the composite structure 103 is attached to the surrounding region of the opening 104 in the housing 105 so as to cover the opening 104 of the housing 105, and at this time, the housing 105 is located on the surface of the amorphous carbon layer 102 opposite to the carrier 101. The material of the housing 105 can be, for example, kovar, nickel, zirconium, or stainless steel, but is not limited thereto. To attach the composite structure 103 to the housing 105, various joining methods can be used. For example, soldering or adhesion can be used to attach the composite structure 103 to the housing 105, but the present invention is not limited thereto, and any other joining method can be used. The solder material used for soldering can be, for example, indium. The adhesive material used for adhesion can be, for example, an epoxy-based adhesive. FIG. 1 schematically shows a cross-section of a layer of adhesive or solder 106 drawn exaggeratedly thick. The illustration of the adhesive or solder 106 in FIG. 1 is merely schematic and does not mean that a flat adhesive layer or solder layer formed on the flat surface between the housing 105 and the amorphous carbon layer 102 is the only option. The fact that the carrier 101 still exists in the process of attaching the composite structure to the housing 105 makes handling easier and there is no need to worry about wrinkles or other types of deformations of the radiation window foil 107 at this stage.

[0020] The term "annular" should be understood in a broad sense. The present invention does not require the annular housing 105 (or other annular structure) to have, for example, a circular shape. For example, it is sufficient that the housing structure 105 has several edges and / or regions around the opening 104 to which the radiating window foil 107 can be firmly and sufficiently attached so that the radiating window foil 107 is securely held in place in the finished structure, and furthermore, in applications where gastightness is required, it is sufficient that a gastight seal can be formed.

[0021] In the final step 150 shown in the example in Figure 1, at least a portion of the carrier 101 is removed. If the carrier 101 is completely removed, the radiating window foil 107, which includes the amorphous carbon layer 102, is left covering the opening 104 of the housing 105. Alternatively, if the carrier 101 is partially removed, the radiating window foil 107 covering the opening in the housing 105 may further include an additional support structure 101a formed by the remaining portion of the carrier 101. For example, an annular additional support structure 101a may be formed by removing the central region of the carrier 101. Since the annular additional support structure 101a does not extend to the central part of the radiating window 100 where the opening 104 in the housing 105 is located, it does not obstruct the transmission of desired electromagnetic radiation through the radiating window 100, nor does it cause unwanted absorption or spurious responses. The annular additional support structure 101a is shown by a dashed line in Figure 1 to indicate that the carrier 101 may be partially or completely removed. The step of removing at least a portion of carrier 101 may include, for example, removing at least a portion of carrier 101 by etching. Alternatively, other methods may be used to remove at least a portion of carrier 101. Etching is considered the most advantageous method for carefully removing carrier 101 while preserving other layers. For example, if carrier 101 is composed of silicon, potassium hydroxide (KOH) is one suitable etching agent.

[0022] After the method steps described above, post-processing steps such as cleaning, drying, and testing may be applied as needed. The manufactured radiation window 100 can be mounted on an X-ray measuring device.

[0023] For example, the radiant window foil 107 of the radiant window 100 may further include one or more additional layers and / or structures 202, 203, 204, 205. For example, a separate etch stop layer 202 may be formed between the carrier 101 and the amorphous carbon layer 102. In other words, an additional method step for forming, i.e., depositing, the separate etch stop layer 202 may be performed between step 110 and step 120, in which case the etch stop layer 202 may be formed on the polished surface of the carrier 101, and then the amorphous carbon layer 102 may be formed on the opposite side of the etch stop layer 202 than the carrier 101. The etch stop layer 202 extends across the entire polished surface of the carrier 101; that is, the etch stop layer 202 is positioned across the entire area between the polished surface of the carrier 101 and the amorphous carbon layer 202. The material for the etch stop layer 202 should be depositable as a thin layer (e.g., on the order of 5 to 200 nanometers) and should not significantly absorb radiation or cause undesirable abnormalities at the wavelength of electromagnetic radiation used by the radiation window 100. For example, when the carrier 101 is composed of silicon, one suitable material for the etch stop layer 202 is silicon nitride. Other suitable alternative materials for the etch stop layer 202 include, but are not limited to, aluminum oxide and silicon dioxide. Suitable methods for depositing the etch stop layer 202 include, but are not limited to, chemical vapor deposition, pulsed laser deposition, and atomic layer deposition. For example, after the carrier 101 is at least partially removed in step 150, the etch stop layer 202 may be left on the amorphous carbon layer 102. In this case, the etch stop layer 202 needs to be very thin and have very low X-ray absorption. For example, the material of the etch stop layer 202 left on the amorphous carbon layer 102 may be silicon nitride. When the etch stop layer 202 is left on the amorphous carbon layer 102, the etch stop layer 202 can also function as a gastight barrier layer. Alternatively, after the carrier 101 is at least partially removed in step 150, the etch stop layer 202 may be at least partially removed. If the carrier 101 is partially removed, for example, if the central portion of the carrier 101 is removed, preferably the corresponding portion of the etch stop layer 202, i.e., the corresponding central portion of the etch stop layer 202, may also be removed. If the etch stop layer 202 is removed from at least the region of the aperture 104, the etch stop layer 202 will not obstruct the transmission of desired electromagnetic radiation through the radiation window 100, nor will it cause more unwanted absorption or spurious responses. For example, the material of the etch stop layer 202 that is removed at least partially may be aluminum oxide or silicon dioxide. The removal of at least partially of the etch stop layer 202 may be carried out using an etching method different from the etching method used to remove the carriers at least partially in step 150. Alternatively, or in addition to this, after at least a portion of the carrier 101 is removed in step 150, one or more additional layers 203 may be formed on the exposed amorphous carbon layer 102. For example, the radiation window foil 107 may further include a first radiation filter layer as an additional layer 203. Alternatively, or in addition to this, before the installation in step 140, at least one of a second radiation filter layer and / or other layers 204 may be formed on the side of the amorphous carbon layer 102 facing the housing 105. The at least one radiation filter layer 203, 204 may be composed of, for example, zirconium, niobium, or silver, but is not limited to these. The at least one radiation filter layer 203, 204 may be composed of aluminum, but as mentioned above, the use of aluminum has known drawbacks. Therefore, aluminum is not a preferred material for the at least one radiation filter layer 203, 204, i.e., the first and second radiation filter layers. In a non-limiting example, the thickness of the at least one thin film layer 203, 204 may be, for example, between 10 and 300 nanometers. Alternatively, or in addition to the above, the radiant window 100 may include an annular edge reinforcement structure 205 between the amorphous carbon layer 102 and the housing 105 (or, if the radiant window foil 107 further includes a second radiation filter layer 204, between the second radiation filter layer 204 and the housing 105). The edge reinforcement structure 205 may be positioned so as to overlap the opening 104 when the radiant window foil 107 is attached to the housing 105. The edge reinforcement structure 205 improves the strength of the radiant window foil 107 attached to the housing 105 by distributing point stresses that may occur on the radiant window foil 107 due to, for example, sharp objects on the housing 105 or other non-ideal factors, over a wider area on the radiant window foil 107, thereby preventing or at least reducing breakage of the radiant window foil 107. Figure 2 schematically shows a non-limiting example of a radiation window 100 further including one or more additional layers and / or structures. In the example of Figure 2, the radiation window 100 includes an etch-stop layer 202, a first radiation filter layer 203, a second radiation filter layer 204, and an edge reinforcement structure 205, but the radiation window 100 may include one or more of these additional layers and structures. In the example of Figure 2, after the carrier 101 is partially removed, the etch-stop layer 202 is partially removed, i.e., the central portion of the etch-stop layer 202 corresponding to the central portion of the carrier 101 that has been removed.

[0024] The advantages of the present invention, as described above, include the possibility of manufacturing a radiation window for an X-ray measuring device in which the radiation window foil 107 is gastight despite being very thin, absorbs very little X-rays, absorbs electromagnetic radiation of unwanted wavelengths without using an aluminum layer, and has good intensity.

[0025] The dimensions shown in the drawings are not to scale, nor are they comparable to each other; they were selected solely for the purpose of visual clarity in the drawings.

[0026] The specific examples provided in the above description should not be construed as limiting the applicability and / or interpretation of the attached claims. The list and group of examples shown in the above description are not exhaustive unless otherwise expressly stated.

Claims

1. Depositing an amorphous carbon layer (102) on the surface of a carrier (101) (120); Attaching the composite structure (103) including the amorphous carbon layer (102) and the carrier (101) to the area surrounding the opening (104) in the housing (105) such that the amorphous carbon layer (102) faces the housing (105) (140); and To remove at least a portion of the carrier (101) (150) A method for manufacturing a radiation window (100) for an X-ray measuring device, including the above.

2. The method according to claim 1, wherein the amorphous carbon layer (102) is deposited on the surface of the carrier (101) by thermal decomposition.

3. The method according to claim 1 or 2, wherein removing at least a portion of the carrier (101) (150) includes removing the central region of the carrier (101) to form an additional support structure (101a).

4. The method according to any one of claims 1 to 3, wherein the carrier (101) is a silicon wafer.

5. The method according to any one of claims 1 to 4, wherein the thickness of the amorphous carbon layer (102) is between 0.5 and 3 micrometers.

6. A housing (105) defining the opening (104); and A radiating window foil (107) including an amorphous carbon layer (102) is attached to the housing (105) in the region surrounding the opening (104) so ​​as to cover the opening (104) of the housing (105). A radiation window (100) for an X-ray measuring device, including the above.

7. The radiant window (100) according to claim 6, wherein the amorphous carbon layer (102) is formed by thermal decomposition deposition technology.

8. The radiant window (100) according to claim 6 or 7, wherein the radiant window foil (107) further includes an additional support structure (101a) on the surface of the amorphous carbon layer (102) opposite to the housing (105).

9. The radiation window (100) according to claim 8, wherein the additional support structure (101a) is made of silicon.

10. The radiation window (100) according to any one of claims 6 to 9, wherein the thickness of the amorphous carbon layer (102) is between 0.5 and 3 micrometers.

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