GB2561439A

GB2561439A - Radiation window

Info

Publication number: GB2561439A
Application number: GB1802342.4A
Authority: GB
Inventors: Chekurov Nikolai; Nenonen Seppo; Andersson Hans; Talvitie Heli
Original assignee: Oxford Instruments Technologies OY
Current assignee: Oxford Instruments Technologies OY
Priority date: 2017-02-15
Filing date: 2018-02-13
Publication date: 2018-10-17
Anticipated expiration: 2038-02-13
Also published as: GB201802342D0; DE102018000848A1; GB2561439B; FI128876B; FI20175121L

Abstract

Silicon wafer 510 has mask layers 514, 512 e.g. silicon oxide or silicon nitride, on first and second sides. Etching occurs from first and second sides of the wafer to obtain, at least partly from the silicon of the wafer, a radiation window layer. This is, for example, at least partially transparent to X-rays, e.g. soft x-rays with energy below about 1 KeV, perhaps for use in a radiation measurement device to convey rays to a detector placed in vacuum. Increasing durability for a thin radiation window e.g. between 0.4 and 0.6 micrometres thick, the radiation window layer has a support structure e.g. a mechanical grid built of the silicon wafer via the first mask layer. Also disclosed is a method of obtaining a radiation window layer from a compound silicon wafer with mask layer between wafers, and a radiation window construct with support structure comprised of a compound wafer.

Description

(71) Applicant(s):

Oxford Instruments Technologies Oy

Technopolis Innopoli 1, Tekniikantie 12, Espoo 02150,

Finland (51) INT CL:

G01T 7/00 (2006.01) (56) Documents Cited:

WO 2012/091715 A1 DE 102014103546 A1 US 6477225 B1 US 4862490 A US 20080317209 A1

DE 003707130 A1 US 6477226 B1 US 5418833 A US 20130051535 A1 US 20040146139 A1

Field of Search:

INT CL G01T, G03F, H01J, H01L Other: WPI, EPODOC (72) Inventor(s):

Nikolai Chekurov Seppo Nenonen Hans Andersson Heli Talvitie (74) Agent and/or Address for Service:

Withers 8, Rogers LLP

More London Riverside, LONDON, SE1 2AU, United Kingdom (54) Title of the Invention: Radiation window

Abstract Title: Radiation window layer and support structure comprised of a silicon wafer (57) Silicon wafer 510 has mask layers 514, 512 e.g. silicon oxide or silicon nitride, on first and second sides. Etching occurs from first and second sides of the wafer to obtain, at least partly from the silicon of the wafer, a radiation window layer. This is, for example, at least partially transparent to X-rays, e.g. soft x-rays with energy below about 1 KeV, perhaps for use in a radiation measurement device to convey rays to a detector placed in vacuum. Increasing durability for a thin radiation window e.g. between 0.4 and 0.6 micrometres thick, the radiation window layer has a support structure e.g. a mechanical grid built of the silicon wafer via the first mask layer. Also disclosed is a method of obtaining a radiation window layer from a compound silicon wafer with mask layer between wafers, and a radiation window construct with support structure comprised of a compound wafer.

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FIGURE 14

RADIATION WINDOW

FIELD [00011 The present invention relates to window constructs that are at least partially 5 transparent to radiation, such as x-rays.

BACKGROUND [00021 Radiation measurement devices operate by determining a reaction of a detector device to incoming radiation. For example, an x-ray camera may receive x-rays and determine their intensity as a function of location on a two-dimensional chargecoupled device, CCD, array. A spectrometer, on the other hand, may be configured to determine spectral characteristics of incoming radiation, for example to determine an astrophysical redshift or to identify characteristic emission peaks of elements to analyse elemental composition of a sample.

[0003] When measuring soft x-rays, by which it may be meant, for example, x-rays with energy below about 1 keV, providing the radiation to a detector presents with challenges. For example, air scatters soft x-rays and many materials absorb soft x-rays, wherefore the radiation most conveniently is conveyed to a detector through vacuum, wherein the detector may be placed in the vacuum. On the other hand, magnesium, for example, exhibits characteristic emissions around 1.2 keV. Most elements exhibit characteristic emissions above 1 keV.

[0004] When operating in atmospheric conditions, a suitable window may be arranged to admit soft x-rays into the vacuum where a detector may be arranged to analyse the radiation. Such a window would ideally be transparent to the soft x-rays and durable of construction, and impermeable to air to protect a detector unit.

[0005] Transparency may be increased by reducing the thickness of the window. For example, beryllium windows have been used, wherein the thinner the window is, the larger a fraction of incoming radiation is admitted through the window. On the other hand, the thinner the window is, the likelier it is to break in real-life circumstances.

[00061 To increase durability of a window, the window may be supported with a mechanical grid or it may be sandwiched between supporting structures. Supporting structures may take the form of web-like support structures, which partially cover and partially expose the window material. In parts where the window material is exposed by supporting structures, the window is maximally transparent to incoming radiation.

SUMMARY OF THE INVENTION [00071 The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0008] According to a first aspect of the present invention, there is provided a method comprising obtaining a silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon.

[0009] Various embodiments of the first aspect may comprise at least one feature from the following bulleted list:

• the method comprises removing the mask layer • building a support structure for the radiation window layer · the window layer is obtained by etching also from a first side of the silicon wafer • the radiation window layer is of a thickness of between 0.02 micrometres and 2 micrometres • the radiation window layer is of a thickness of between 0.2 micrometres and 2 micrometres · the radiation window layer is of a thickness of between 0.3 and 0.8 micrometres • the radiation window layer is of a thickness of between 0.4 and 0.6 micrometres • a timed etch or real-time monitoring is employed to stop the etching • providing a dopant in the silicon wafer underneath the mask layer • the dopant is provided into the silicon before the mask layer is obtained on the silicon wafer • the dopant comprises boron • the dopant is provided into the silicon by annealing the silicon wafer together with a dopant containing layer • the dopant is employed as an etch stop in the etching • the silicon wafer comprises a compound silicon wafer comprised of a first silicon wafer and a second silicon wafer, there being disposed a second mask layer between the first silicon wafer and the second silicon wafer • the second mask layer comprises either a silicon oxide layer or a silicon nitride layer • the second mask layer comprises the silicon nitride layer and the method comprises leaving the second mask layer on the radiation window layer • the method comprises etching a support structure for the radiation window layer. [0010] According to a second aspect of the present invention, there is provided a radiation window construct, comprising a radiation window layer comprised of at least one of silicon, silicon carbide and boron nitride, and wherein the radiation window layer is continuously exposed on at least one side.

[0011] Various embodiments of the second aspect may comprise at least one feature from the following bulleted list:

• the radiation window construct comprises a support structure of the radiation window layer • the radiation window layer is of a thickness of between 0.02 micrometres and 2 micrometres • the radiation window layer is of a thickness of between 0.3 and 0.8 micrometres • the radiation window layer is of a thickness of between 0.4 and 0.6 micrometres • the radiation window layer comprises a dopant • the dopant comprises boron • the radiation window layer comprises thereon a supplementary layer • the supplementary layer comprises at least one of: a silicon nitride layer, an aluminium layer and a graphene layer [00121 According to a third aspect of the present invention, there is provided an xray detector comprising a radiation window construct in accordance with the second aspect. The x-ray detector may comprises an enclosure with vacuum or low pressure therein, and wherein the radiation window construct is exposed on one side to the vacuum or low pressure and on another side to environmental conditions outside the enclosure

BRIEF DESCRIPTION OF THE DRAWINGS [00131 FIGURE 1 illustrates an example system capable of being operated with at least some embodiments of the present invention;

[00141 FIG. 2A - FIG. 2C illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0015] FIG. 3A - FIG. 3E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0016] FIG. 4A - FIG. 4E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0017] FIG. 5A - 5D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0018] FIG. 6A - 6E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0019] FIG. 7A - 7D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0020] FIG. 8A - 8E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[0021] FIG. 9A - 9D illustrate an example manufacturing process in accordance 25 with at least some embodiments of the present invention;

[0022] FIG. 10A - 10D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[00231 FIG. 11A - 11D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[00241 FIG. 12A - 12D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention;

[00251 FIG. 13 A - 13D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention, and [00261 FIGURE 14 is a flow graph of a method in accordance with at least some embodiments of the present invention;

EMBODIMENTS [0027] Radiation windows have been made of toxic materials, such as berylliumbased materials. On the other hand, radiation windows may benefit from layers deposited thereon, to enhance their desired characteristics, which may include gas impermeability, optical properties or spectral selectivity, for example. To facilitate provision of such layers, and/or to use non-toxic materials, radiation windows in accordance with at least some embodiments of the present invention may comprise a window layer constructed of silicon, optionally leaving at least one side of the window layer without a supporting structure connected thereto. By being constructed of silicon, it may be meant, for example, that the window layer is constructed of crystalline silicon.

[0028] FIGURE 1 illustrates an example system capable of being operated with at least some embodiments of the present invention. The illustrated system relates to x-ray fluorescence, to which the present invention is not limited, rather, windows built in accordance with the present invention may find application also more broadly.

[0029] FIGURE 1 illustrates an analytic device 110, which comprises an x-ray detector 120. X-ray detector 120 is in this example configured to determine spectral characteristics of x-rays incident on itself, for example to enable elemental composition analysis based on characteristic emissions. In the illustrated example, x-ray detector 120 is in an enclosure formed by a housing of analytic device 110. Alternatively, x-ray detector 120 could be in an enclosure formed separately inside the housing.

[00301 In use, the arrangement of FIGURE 1 irradiates sample 130 with primary xrays 102 from primary x-ray source 140, stimulating matter comprised in sample 130 to emit, via fluorescence, secondary x-ray radiation 103, spectral characteristics of which are determined, at least partly, in x-ray detector 120. The primary x-rays may be generated from radioactive decay of an isotopic source or by accelerating charged particles, for example. In some embodiments, a source of primary x-rays may be comprised in, or provided with, analytic device 110.

[00311 X-ray detector 120 comprises a window region 115, which is arranged to admit x-rays into X-ray detector 120. Window region 115 is illustrated in an enlarged view 115E at the bottom of FIGURE 1, wherein a gap in the outer housing of detector 120 is shown. Arranged in the gap is a window layer 117, preventing inflow of air from outside X-ray detector 120 to inside X-ray detector 120 while allowing x-rays, such as, for example, soft x-rays, to enter X-ray detector 120, so that these x-rays may be analysed in x-ray detector 120. Window layer 117 may be comprised of silicon, for example, such as crystalline silicon.

[0032] A benefit of a window layer 117 constructed of silicon is that manufacture of silicon window layers is repeatable and simple. This is so compared to window layers of other materials, such as beryllium-based materials. Beryllium-based materials, such as beryllium oxide, furthermore, are toxic substances therefore it is advisable to avoid using them in products used by humans. Beryllium-based materials are, further, difficult to manufacture in precisely controlled thicknesses. Some products define a beryllium-based foil thickness as 8 + 5 micrometres, which amounts to a relative thickness tolerance of >60%.

[0033] A silicon window layer 117 having soft x-ray performance similar to a tenmicrometre thick beryllium-based window layer may have a thickness of about 0.5 micrometres. This is so, since beryllium is more transparent to x-rays. The relative thickness of membranes made of silicon may be better than 20%. Alternatively to silicon, silicon carbide or boron nitride may be employed to similar effect, in various embodiments of the present invention. A silicon, silicon carbide or boron nitride window layer may be between 100 and 300 nanometres in thickness, for example.

[00341 Window layer 117 is supported by supporting structure 119 to form a window construct. Supporting structure 119 may be constructed of silicon, such as crystalline silicon, for example. In some embodiments, supporting structure 119 is constructed, at least partly, of a same silicon wafer as window layer 117.

[00351 In some embodiments, such as the one illustrated in FIGURE 1, enlarged view 115E, supporting structure 119 leaves both sides of window layer 117 continuously exposed.

[00361 In some embodiments of the invention, window layer 117 may be overlaid by supporting structure 119, for example by being constructed of a wafer from which supporting structure 119 is also constructed, such that the supporting structure is built using a mask, for example. Supporting structure 119 may be constructed by etching, for example. Supporting structure 119 may, in some embodiments, support window layer 117 on one side but not the other side, in other words, supporting structure 119 overlay may be limited to one side of window layer 117. Such an overlaid support structure 119a is illustrated in FIGURE 1 supporting window layer 117a. The need for support structure 119 to overlay window layer 117 may depend, for example, on a size of window layer 117. A smaller window layer 117 may be sufficiently rigid without an overlaid support structure 119, as in enlarged view 115E, while a larger window layer 117a may need a web-like overlaid support structure 119a attached and overlaid on one or both sides of window layer 117a, to provide it with additional structural rigidity. The window construct comprised of window layer 117a and support structure 119a is an alternative to the window construct illustrated in enlarged view 115E. Although window layer 117a is illustrated in FIGURE 1 as separated from the overlaid support structure 119a by a gap, this is for clarity of illustration purposed only. In reality, window layer 117a touches support structure 119a in areas where the two are overlaid.

[0037] In general, supporting structure 119a, where attached to and overlaid with window layer 117a, may partially obscure and partially expose window layer 117a. In detail, a part of window layer 117a touching support structure 119a will be obscured by it, by which it is meant that x-rays passing through window layer 117a will at these places be partially prevented, by support structure 119a, from reaching x-ray detector 120. In parts of window layer 117a not touching support structure 119a, x-rays that penetrate window layer 117a may proceed directly to x-ray detector 120. The larger the part of window layer 117a touching, and obscured by, supporting structure 119a, the stronger is the support provided to window layer 117a and the larger the effect supporting structure 119a has on x-rays incoming through window layer 117a. The strength of supporting structure 119a may thus be seen as a trade-off between x-ray transmittance through window layer 117a and strength of the radiation window construct which comprises window layer 117a and supporting structure 119a. In general, window layer 117a may be completely exposed on a first side and partly exposed on a second side, the supporting structure being on the second side. By completely exposed, or continuously exposed, it is meant window layer 117a is exposed in a manner that an area of window layer 117a in active use is not obstructed by a support structure on the exposed side.

[00381 Window layer 117 or 117a may be continuous in nature, by which it is meant the layer is not interrupted, for example, in accordance with the support structure. A continuous layer may be planar in the sense that it lies in a single plane.

[0039] Window layer 117 or 117a may be thin, in the half-micrometre range, for example, while extending over an opening which is in the order of a few millimetres, or centimetres, in size.

[0040] Window layer 117 or 117a may have, on one or both sides, at least one supplementary layer. Examples of supplementary layers include a thin aluminium layer and a graphene layer. An aluminium layer may block, at least partly, visible light from entering through window layer 117. Graphene, on the other hand, may enhance an ability of window layer 117, for example when made of crystalline silicon, to prevent gas molecules such as ones found in air from penetrating through window layer 117. When at least one side of window layer 117 is clear from supporting structures, such supplementary layers may be applied easier and the resulting supplementary layers have fewer defects. This provides the beneficial technical effect that the layers function better in their respective purposes.

[0041] In general a compound silicon wafer may comprise a construct wherein two or three silicon wafers are attached one on top of another. There may be a layer or layers arranged in between the silicon wafers comprised in the compound silicon wafer.

[0042] FIG. 2A - FIG. 2C illustrate an example manufacturing process in accordance with at least some embodiments of the present invention. The process begins at the situation of FIG. 2A, where a silicon wafer 210 is obtained, comprising at least an optional first silicon oxide layer 214, and, optionally, a second silicon oxide layer 212. While the layers are herein referred to as silicon oxide layers, in general other materials are usable, as well. In other words, silicon oxide is herein employed as an example material used in a mask layer.

[00431 As the process advances to the situation illustrated in FIG. 2B, second silicon oxide layer 212 has been patterned, by removing part thereof. The patterning may open an opening to expose the crystalline silicon that forms the bulk of silicon wafer 210, for example.

[00441 As the process advances to the situation illustrated in FIG. 2C, silicon wafer

210 has been etched until only a thin membrane of silicon remains, the thin membrane forming the window layer. Silicon oxide layer 214 and/or 212 may be removed in a subsequent, optional phase. Such removing exposes the window layer also from the other side. In some embodiments, etching is done from both sides to obtain the window layer.

[0045] While the process of FIGs 2 A - 2C is simple, it requires careful control of the etching process to ensure a membrane of desired thickness, for example 0.5 micrometres, remains at the end of the etch. Errors in the etching may cause this method to have relatively low yield of acceptable resulting window layers. A real-time endpoint detection method may be employed to enhance the yield by triggering and end to the etching as the membrane is at an acceptable thickness.

[0046] As a numerical example, where a nominal etch rate is 0.6 micrometres/minute, a sixteen-hour etch may need to be stopped at an accuracy of roughly ten seconds, to produce an acceptable window layer.

[0047] FIG. 3A - FIG. 3E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0048] FIG. 3A illustrates an initial phase, where a silicon wafer 310 is provided with a spin-on-glass layer 312. Spin-on-glass, SOG, is a type of glass that can be applied as a liquid and cured to form a layer of glass having characteristics similar to those of SiO2. SOG may contain a dopant.

[00491 As the process advances to the phase illustrated in FIG. 3B, silicon wafer 310 has been annealed until a dopant layer 314 penetrates from the SOG into silicon wafer 310, to a desired depth. The dopant may comprise boron, for example. An advantage of this procedure is that it is highly repeatable. Dopant layer 314 may be comprised of crystalline silicon into which dopant atoms or dopant molecules have been introduced.

[00501 Alternatively, an ion implantation method may be employed in providing the dopant layer 314 in silicon wafer 310. In ion implantation, ions may be accelerated using an electrical field and impacted into a solid, such as silicon wafer 310. A strength of the electrical field may be selected in dependence of a desired thickness of dopant layer 314, as the stronger the electrical field, the higher the energy of the ions and the deeper they can penetrate into silicon wafer 310.

[00511 Alternatively or in addition to boron, another dopant may be employed, which is usable, when penetrated in the silicon, as an etch stop as will be described below. The depth of dopant layer 314 may be selected according to the desired thickness of the resulting window layer.

[0052] As the process advances to the phase illustrated in FIG. 3C, the spin-on-glass layer 312 has been removed, and silicon oxide layers 316 and 318 have been obtained on either side of silicon wafer 310, as illustrated in FIG. 3C. Silicon oxide layer 316 covers dopant layer 314. Silicon oxide is here used as an example of a material mask layer 318 may be comprised of.

[0053] As the process advances to the phase illustrated in FIG. 3D, silicon oxide layer 318 is opened on a side opposite the side with dopant layer 314. This exposes the crystalline silicon that silicon wafer 310 is comprised of.

[0054] As the process advances to the phase illustrated in FIG. 3E, the window layer is constructed of silicon wafer 310 by etching until the dopant layer 314, which forms an etch stop. For example, KOH/TMAH/Electochemical etch/Dry etch or their combination may be employed. Optionally, the oxide layer(s) may be removed in a subsequent process phase, which is not illustrated in FIGs 3A - 3E. The bottom side of the resulting window layer may be rough. An advantage of the method of FIGs 3 A - 3E is that the method is relatively accurate, which is useful in constructing a thin window layer. The dopant may remain in the window layer.

[00551 FIG. 4A - FIG. 4E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[00561 In FIG 4A, a layered silicon wafer 410 is obtained, with silicon oxide layers

412 and 414. The layer on top of silicon oxide layer 414 is comprised of crystalline silicon, like the rest of the wafer. This layer on top of silicon oxide layer 414 will become the window layer, as described herein below. In some embodiments, layer 414 and/or 412 is of another suitable substance, rather than silicon oxide.

[00571 As the process advances to the phase illustrated in FIG. 4B, a silicon oxide layer 416 is added on a first side of the wafer of FIG. 4A.

[00581 As the process advances to the phase illustrated in FIG. 4C, silicon oxide layer 412 is patterned into a mask, by removing part thereof, to expose silicon of silicon wafer 410 on a second side.

[0059] As the process advances to the phase illustrated in FIG. 4D, silicon wafer 410 is etched to expose, from the second side, silicon oxide layer 414.In this etch, wet or dry etching may be employed.

[0060] As the process advances to the phase illustrated in FIG. 4E, at least one of silicon oxide layers 416, 414 and 412 are removed, completing construction of the window layer of silicon of silicon wafer 410. Parts of silicon oxide layer 414 will remain in between layers of silicon wafer 410, as illustrated in FIG. 4E.

[0061] A level of accuracy that may be attained may depend on the wafer used in the method of FIGs 4A - 4E. Wafers, located between mask layers 414 and 416, with layer thickness accuracy from +-0.5 um to 0.01 um are commercially available.

[0062] FIGs 5 A - 5D through to FIGs 13 A - 13D illustrate manufacturing methods that furnish a silicon window layer with a supporting structure, to enhance its durability, stiffness and/or mechanical properties in general.

[0063] FIG. 5A - 5D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0064] In the phase of FIG. 5 A, a blank silicon wafer 510 is obtained. On wafer 510 are disposed mask layers 512 and 514, these mask layers being composed of silicon oxide, for example. Top mask layer 514 is patterned with a shape of a supporting structure, which may comprise a net shape, for example. Bottom mask layer 512 is patterned with an opening to define a shape of a resulting window.

[00651 As the process advances to the phase illustrated in FIG. 5B, etching, for 5 example timed etching, is performed from the bottom side to selectively thin down wafer

510 to a thickness of, approximately, the eventual supporting structure. This thickness may be, for example, about 20 micrometres.

[00661 As the process advances to the phase illustrated in FIG. 5C, etching, for example timed etching, is performed from the top side to form a window layer of silicon of silicon wafer 510, leaving the supporting structure attached to the window layer. The support structure is formed of silicon of silicon wafer 510, as is the window layer.

[0067] Optionally, at least one of the mask layers may be removed. The resulting structure is illustrated in FIG. 5D.

[0068] In general, according to the embodiment of FIGs 5 A - 5D, there is provided a method comprising obtaining a silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed on a first side of the silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the silicon wafer by etching from the first side of the silicon wafer.

[0069] FIG. 6A - 6E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0070] In the phase of FIG. 6 A, a blank silicon wafer 610 is obtained. On wafer 610 are disposed mask layers 612 and 614, these mask layers being composed of silicon oxide, for example. Top mask layer 614 is patterned with a shape of a supporting structure, which may comprise a net shape, for example. Bottom mask layer 612 is patterned with an opening to define a shape of a resulting window.

[0071] As the process advances to the phase illustrated in FIG. 6B, etching, for example timed etching, is performed from the bottom side to selectively thin down wafer

610 to a thickness of, approximately, the eventual supporting structure. This thickness may be, for example, about 20 micrometres.

[00721 As the process advances to the phase illustrated in FIG. 6C, an etch stop layer 616 is implanted on the bottom side. Metallization may be used if needed for contact for electrochemical etching.

[00731 As the process advances to the phase illustrated in FIG. 6D, etching, for example wet etching with the etch stop layer 616 , is performed from the top side to form a window layer of silicon of silicon wafer 610, leaving the supporting structure attached to the window layer. The support structure is formed of silicon of silicon wafer 610, as is the window layer.

[00741 Optionally, at least one of the mask layers may be removed. The resulting structure is illustrated in FIG. 6E.

[0075] In general, according to the embodiment of FIGs 6 A - 6E, there is provided a method comprising obtaining a silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed on a first side of the silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the silicon wafer by etching from the first side of the silicon wafer. An etch stop layer is provided on an exposed surface of the second side after etching from the second side, and the etching from the first side is performed until the etch stop layer is reached.

[0076] FIG. 7A - 7D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0077] In the phase of FIG. 7 A, a structure composed of two silicon wafers 710 and 720 is obtained. Silicon oxide layer 714 is disposed between the two silicon wafers, and silicon oxide layer 712 on the bottom side of wafer 710.

[0078] As the process advances to the phase illustrated in FIG. 7B, top silicon oxide layer 722 is obtained on wafer 720 and the top silicon oxide layer 722 is patterned with a shape of a supporting structure, which may comprise a net shape, for example. Bottom silicon oxide layer 712 is patterned with an opening to define a shape of a resulting window. Silicon oxide layer 722 may be obtained on wafer 720 by oxidizing or by depositing, for example.

[00791 As the process advances to the phase illustrated in FIG. 7C, etching is performed from the bottom side. The exposed part of silicon oxide layer 714 may optionally be removed.

[00801 Finally, as the process advances to the phase illustrated in FIG. 7D, timed etching is done from the top side to build the supporting structure of silicon of wafer 720.

[00811 In general, according to the embodiment of FIGs 7 A - 7D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed on a first side of the compound silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the compound silicon wafer by etching from the first side of the silicon wafer. The etching from the second side is herein done until an etch stop layer buried in the compound silicon wafer is reached. The buried etch stop layer may comprise a silicon oxide layer.

[0082] FIG. 8A - 8E illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0083] In the phase of FIG. 8 A, a structure composed of two silicon wafers 810 and 820 is obtained. Silicon oxide layer 814 is disposed between the two silicon wafers, and silicon oxide layer 812 on the bottom side of wafer 810.

[0084] As the process advances to the phase illustrated in FIG. 8B, top silicon oxide layer 822 is obtained on wafer 820 and the top silicon oxide layer 822 is patterned with a shape of a supporting structure, which may comprise a net shape, for example. Bottom silicon oxide layer 812 is patterned with an opening to define a shape of a resulting window. Silicon oxide layer 822 may be obtained on wafer 820 by oxidizing or by depositing, for example.

[0085] As the process advances to the phase illustrated in FIG. 8C, etching is performed from the bottom side. The exposed part of silicon oxide layer 814 may be removed.

[00861 As the process advances to the phase illustrated in FIG. 8D, an etch stop layer 824 is implanted from the bottom side. Finally, as the process advances to the phase illustrated in FIG. 8E, etching is done from the top side to build the supporting structure of silicon of wafer 820. The layer with the etch stop 824 forms, in this embodiment, the window layer.

[00871 In general, according to the embodiment of FIGs 8 A - 8E, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed on a first side of the compound silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the compound silicon wafer by etching from the first side of the silicon wafer. The etching from the second side is herein done until an etch stop layer buried in the compound silicon wafer is reached. The buried etch stop layer may comprise a silicon oxide layer, and the buried etch stop layer may be replaced with a second buried etch stop layer. The etching may be done from the first side is done until the second etch stop layer is reached. The second etch stop layer may comprise an implanted etch stop layer, for example.

[0088] FIG. 9A - 9D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0089] In the phase of FIG. 9 A, a structure composed of two silicon wafers 910 and 920 is obtained. Silicon oxide layer 914 is disposed between wafer 910 and wafer 920, and silicon oxide layer 912 is on the bottom side of the structure. Layer 914 has been patterned, before attaching the wafers to each other, with a shape of a supporting structure.

[0090] As the process advances to the phase illustrated in FIG. 9B, silicon oxide layer 912 is removed and a silicon nitride layer 922 is attached to the bottom side of wafer 910. Likewise, a silicon nitride layer 924 is attached on the top side of silicon wafer 920. The presence of silicon oxide layer 912 in this embodiment is optional. Another material similar to silicon nitride may be alternatively employed in layers 924 and 922.

[0091] As the process advances to the phase illustrated in FIG. 9C, silicon nitride layer 922 has been patterned with a shape of the radiation window that is desired, and etching from the bottom side has been performed, to expose silicon oxide layer 914, which acts as a mask for constructing a supporting structure.

[00921 As the process advances to the phase illustrated in FIG. 9D, a timed etch may be employed from the bottom side, to construct the supporting structure, using layer 914 as a mask, and also obtain the radiation window. Subsequently, layers 922, 924 and/or the exposed parts of layer 914 may be removed.

[00931 In general, according to the embodiment of FIGs 9A - 9D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed buried in the compound silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the compound silicon wafer by etching from the second side of the silicon wafer, in accordance with the buried mask layer. The buried etch stop layer may comprise a silicon oxide layer for example.

[0094] FIG. 10A - 10D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[0095] In the phase of FIG. 10A, a structure composed of two silicon wafers 1010 and 1020 is obtained. Silicon oxide layer 1014 is disposed between wafer 1010 and wafer 1020, and silicon oxide layer 1012 is on the bottom side of the structure. Layer 1014 has been patterned, before attaching the wafers to each other, with a shape of a supporting structure.

[0096] As the process advances to the phase illustrated in FIG 10B, an etch stop layer 1024 is obtained on the top side of silicon wafer 1020. Layer 1024 may therefore be a doped layer. This may be obtained using silicon-on-glass, SOG, or ion implantation, for example. Silicon oxide layer 1012 is replaced with a protective layer 1022, of silicon nitride, for example.

[0097] As the process advances to the phase illustrated in FIG 10C, layer 1022 has been patterned with a desired shape of a resulting radiation window, and etching has been performed from the bottom side to expose silicon oxide layer 1014, which forms a mask for building a support structure.

[00981 As the process advances to the phase illustrated in FIG 10D, etching is continued from the bottom side until the etch stop layer 1024 is reached. This etching may comprise, for example, wet or electrochemical etching. In this process, the supporting structure is built of silicon of wafer 1020. Optionally, the oxide layer may, in exposed parts, be removed.

[00991 In general, according to the embodiment of FIGs 10A - 10D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed buried in the compound silicon wafer, and the method comprises building a support structure for the radiation window layer of silicon of the compound silicon wafer by etching from the second side of the silicon wafer, in accordance with the buried mask layer, until an etch stop layer on a first side of the compound silicon wafer is reached. The buried etch stop layer may comprise a silicon oxide layer for example [00100] FIG. 11A - 11D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[00101] In the phase of FIG. 11 A, a structure of FIG. 10C is obtained as a starting point of the method of FIGs 11A - 11D. In other words, doped etch stop layer 1124 is on silicon wafer 1120, which is attached to silicon wafer 1110 such that silicon oxide mask layer 1114 is disposed thereinbetween. Silicon nitride layer 1122 is attached on the bottom side of silicon wafer 1110, [00102] As the process advances to the phase illustrated in FIG 1 IB, regions that are unprotected by silicon oxide mask layer 1114 are doped, These doped regions are illustrated in FIG 11B, FIG. 11C and FIG. 11D as regions 1126. As the process advances to the phase illustrated in FIG. 11C, the exposed parts of mask layer 1114 are removed. Finally, as the process advances to the phase illustrated in FIG 1 ID, etching is done from the bottom side to build the radiation window structure and the supporting structure of silicon of wafer 1120.

[00103] A benefit of the embodiment of FIGs 11A - 11D is having the same doping level on both sides of the supporting structure, which reduces stress-related bending.

[001041 In general, according to the embodiment of FIGs 11A - 11D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. A second mask layer is disposed buried in the compound silicon wafer, and the method comprises obtaining, using doping and using the second mask layer, a further mask layer, and building a support structure for the radiation window layer of silicon of the compound silicon wafer by etching from the second side of the silicon wafer, in accordance with the further mask layer, until an etch stop layer on a first side of the compound silicon wafer is reached. The buried etch stop layer may comprise a silicon oxide layer for example.

[001051 FIG. 12A - 12D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[00106] In the phase of FIG. 12A, a structure is obtained which comprises silicon wafers 1210, 1220 and 1230. Silicon oxide layer 1214 is disposed between wafers 1210 and 1220, and silicon oxide layer 1224 is disposed between wafers 1220 and 1230. A further silicon oxide layer 1222 is attached on the bottom side of silicon wafer 1210, as illustrated in FIG. 12A.

[00107] As the process advances to the phase illustrated in FIG 12B, a further silicon oxide layer 1232 is obtained on silicon wafer 1230. Fayer 1232 is then patterned with a shape of a supporting structure, and layer 1222 is patterned with a desired shape of a resulting radiation window.

[00108] As the process advances to the phase illustrated in FIG 12C, etching from the bottom side is done until oxide layer 1214 is partially exposed. As the process advances to the phase illustrated in FIG 12D, etching from the top side is done until oxide layer 1224 is partially exposed. Finally, optionally, the exposed oxide layers may be removed. In this embodiment, the window layer is formed of silicon of silicon wafer 1220 and the supporting structure is formed of silicon of silicon wafer 1230.

[00109] In general, according to the embodiment of FIGs 12A - 12D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. The compound silicon wafer comprises three wafers, with two buried silicon oxide layers in between the wafers. The etching from the second side is done until a first one of the buried silicon oxide layers is exposed, and a support structure for the radiation window layer is constructed by etching, from a first side of the compound silicon wafer, until a second one of the buried silicon oxide layers is exposed. The etching from the first side may be done in accordance with a second mask layer on the first side of the compound silicon wafer.

[001101 FIG. 13 A - 13D illustrate an example manufacturing process in accordance with at least some embodiments of the present invention.

[001111 In the phase of 13A, a structure is obtained which comprises silicon wafers 1310, 1320 and 1330. Silicon oxide layer 1324 is disposed between wafers 1320 and 1330, and silicon oxide layer 1314 is disposed between wafers 1310 and 1320. Silicon oxide layer 1314 has been patterned with a shape of a supporting structure before wafers 1310 and 1320 were attached together.

[00112] As the process advances to the phase illustrated in FIG 13B, layer 1312 is patterned with a shape of the desired radiation window. As the process advances to the phase illustrated in FIG 13C, etching from the bottom side is done, as illustrated, to expose, partly, silicon oxide layers 1314 and 1324. Finally, in the phase illustrated in FIG 13D, the oxide layers are removed, where exposed, resulting in a silicon window layer supported by a supporting structure constructed of silicon of silicon wafer 1320.

[00113] In general, according to the embodiment of FIGs 13A - 13D, there is provided a method comprising obtaining a compound silicon wafer comprising a mask layer on a second side, and etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. The compound silicon wafer comprises three wafers, with two buried silicon oxide layers in between the wafers. The etching from the second side is done until both of the buried silicon oxide layers are exposed at least partly, such that this etching partly uses a first one of the buried silicon oxide layers as a mask in building a support structure for the radiation window layer.

[001141 As a further variant at least one of the wafers could be etched prior the attaching of the two wafers, which may be used in facilitating etching processes.

[001151 FIGURE 14 is a flow graph of a method in accordance with at least some embodiments of the present invention.

[001161 Phase 1410 comprises obtaining a silicon wafer comprising a mask layer on a second side. Phase 1420 comprises etching from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon. Optional phase 1430 comprises removing the silicon oxide layer. [001171 As described herein above, the etching may comprise, for example, a timed etch, an etch stopped at dopant-based etch stop layer, or an etch stopped at a mask layer disposed inside the silicon wafer. Where a dopant is present, it may remain in the resulting radiation window layer.

[001181 It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. [00119] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[00120] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[001211 Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[001221 While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[00123] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of a or an, that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY [00124] At least some embodiments of the present invention find industrial application in measurement devices, such as soft x-ray measurement devices, for example.

ACRONYMS LIST

CCD charge-coupled device keV kiloelectronvolt

SOG

Spin-on-glass

REFERENCE SIGNS LIST

110	Analytic device
120	X-ray detector
115	Window region
115E	Window region, enlarged view
117, 117a	Window layer
119, 119a	Supporting structure
130	Sample
102, 103	Primary x-rays, secondary x-rays
210	Silicon wafer
212	Second silicon oxide layer
214	First silicon oxide layer
310	Silicon wafer
312	SOG layer
314	Dopant layer
316, 318, 712, 714, 722, 812, 814, 822, 912, 914, 1012, 1014, 1114, 1214, 1224, 1222, 1232, 1312, 1314, 1324, 1334	Silicon oxide layer
410, 510, 610, 710, 720, 810, 820, 910, 920, 1010, 1020, 1110, 1120, 1210, 1220, 1230, 1310, 1320, 1330	Silicon wafer
412, 512, 612, 414, 514, 614,	mask layer

416
616, 824, 1024, 1124, 1126	Etch stop layer
924, 922, 1022, 1122	Silicon nitride layer
1410-1430	Phases of the method of FIGETRE 14

Claims

CLAIMS:

1. A method comprising:

- obtaining (1410) a silicon wafer comprising a mask layer on a second side, and

- etching (1420) from the second side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon,

- building a support structure for the radiation window layer, characterized in that

- the window layer is obtained by etching, using a second mask layer, the silicon of the silicon wafer also from a first side of the silicon wafer.

2. The method of claim 1, wherein the support structure for the radiation window layer is built of the silicon of the silicon wafer.

3. The method of claim 1, wherein the radiation window layer is of a thickness of between 0.02 micrometres and 2 micrometres.

4. The method of claim 3, wherein the radiation window layer is of a thickness of between 0.3 and 0.8 micrometres.

5. The method of claim 4, wherein the radiation window layer is of a thickness of between 0.4 and 0.6 micrometres.

6. The method of any of claims 1-5, wherein a timed etch or real-time monitoring is employed to stop the etching (1420).

7. The method of claim 1, further comprising providing a dopant on a first side of the silicon wafer.

8. The method of claim 7, wherein the dopant is provided into the silicon before the mask layer is obtained on the silicon wafer.

9. The method of any of claims 7-8, wherein the dopant comprises boron.

10. The method of any of claims 7-9, wherein the dopant is provided into the silicon by annealing the silicon wafer together with a dopant containing layer.

11. The method of any of claims 7 - 10, wherein the dopant is employed as an etch stop in the etching (1420).

12. A method comprising:

- obtaining (1410) a silicon wafer comprising a mask layer on a first side, and

- etching (1420) from the first side of the silicon wafer to obtain, at least partly, from silicon of the silicon wafer, a radiation window layer comprised of the silicon, characterized in that the silicon wafer comprises a compound silicon wafer comprised of a first silicon wafer and a second silicon wafer, there being disposed a second mask layer between the first silicon wafer and the second silicon wafer.

13. The method of claim 12, wherein the second mask layer comprises either a silicon oxide layer or a silicon nitride layer.

14. The method of claim 13, wherein the second mask layer comprises the silicon nitride layer and the method comprises leaving the second mask layer on the radiation window layer.

15. The method of any of claims 12 - 14, further comprising etching a support structure for the radiation window layer.

16. A radiation window construct, comprising:

- a radiation window layer (920, 1024, 1124) comprised of silicon;

- a support structure (920, 914, 910, 922, 1020, 1014, 1010, 1022, 1120, 1126, 1114, 1110) of the radiation window layer (920, 1024, 1124);

- wherein the radiation window layer (920, 1024, 1124) is continuously exposed on at least one side, characterized in that

- the radiation window layer (920, 1024, 1124) and the support structure (920, 914, 910, 922, 1020, 1014, 1010, 1022, 1120, 1126, 1114, 1110) are comprised of silicon of a first silicon wafer (920, 1020, 1120) of a compound silicon wafer which further comprises a mask layer (914, 1014, 1114) between the first silicon wafer (920, 1020, 1120) and a second silicon wafer (910, 1010, 1110) of the compound silicon wafer.

17. The radiation window construct of claim 16, wherein a shape of the support structure (920, 914, 910, 922, 1020, 1014, 1010, 1022, 1120, 1126, 1114, 1110) is defined by the mask layer (914, 1014, 1114).

18. The radiation window construct of claim 16 or 17, wherein the radiation window layer (920, 1024, 1124) is of a thickness of between 0.02 micrometres and 2 micrometres.

19. The radiation window construct of claim 18, wherein the radiation window layer (920, 1024, 1124) is of a thickness of between 0.3 and 0.8 micrometres.

20. The radiation window construct of claim 19, wherein the radiation window layer (920, 1024, 1124) is of a thickness of between 0.4 and 0.6 micrometres.

21. The radiation window construct of any of claims 16 - 20, wherein the radiation window layer (920, 1024, 1124) comprises a dopant.

22. The radiation window construct of claim 21, wherein the dopant comprises boron.

23. The radiation window construct of any of claims 16 - 22, wherein the radiation window layer (920, 1024, 1124) comprises thereon a supplementary layer.

24. The radiation window construct of claim 23, wherein the supplementary layer comprises at least one of: a silicon nitride layer, an aluminium layer and a graphene layer.

25. An x-ray detector (120) comprising a radiation window (920, 1024, 1124) construct in accordance with at least one of claims 16-24.

26. The x-ray detector (120) of claim 25, wherein the x-ray detector comprises an enclosure with vacuum or low pressure therein, and wherein the radiation window construct is exposed on one side to the vacuum or low pressure and on another side to environmental conditions outside the enclosure.

Intellectual

Property

Office

Application No: GB 1802342.4