Patent Application
20230094257
The present application is related to x-ray windows.
X-ray windows are used in expensive systems requiring high reliability. High system requirements result in demanding characteristics of the x-ray window.
The following definitions, including plurals of the same, apply throughout this patent application.
As used herein, the term “identical material composition” means exactly identical or identical within normal manufacturing tolerances.
As used herein, the term “g/cm3” means grams per cubic centimeters.
As used herein, the term “minimum thickness” means the smallest / minimum thickness of the specified material in the aperture 15 or 35.
As used herein, the terms “on”, “located at”, and “adjacent” mean located directly on or located over with some other solid material between. The terms “located directly on”, “adjoin”, “adjoins”, and “adjoining” mean direct and immediate contact.
As used herein, the term “nm” means nanometer(s).
As used herein, the term “parallel” means exactly parallel, parallel within normal manufacturing tolerances, or nearly parallel such that any deviation from exactly parallel would have negligible effect for ordinary use of the device.
As used herein, the terms “top-side” and “bottom-side” refer to top and bottom-sides or faces in the figures, but the device may be oriented in other directions in actual practice. The terms “top” and “bottom” are used for convenience of referring to these sides or faces.
10, 30, 50, 60, and 70 are x-ray window embodiments.
The support-frame 11 can encircle an aperture 15. The support-frame 11 can include an inner-side 11i facing the aperture 15 and an outer-side 11o facing outward and opposite of the inner-side 11i. The support-frame 11 can include a top-side 11T and a bottom-side 11B opposite of each other.
The boron-film 12 can include a near-side 12N (nearer the support-frame 11) and a far-side 12F (farther from the support-frame 11). Method step 90 shows an upper-boron-film 12u and a lower-boron-film 12L.
The annular-film 32 can include an aperture 35, a near-side 32N (nearer the support-frame 11) and a far-side 32F (farther from the support-frame 11).
The thin-film 52 can be an aluminum-film or a film made of another material. The thin-film 52 can be a stack of multiple layers / multiple thin-films.
80 and 90 are steps in a method of making x-ray windows. Wafer 81 has a top-side 81T and a bottom-side 81B. Wafer 81 is located in an oven 82.
Useful characteristics of x-ray windows include low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, made of low atomic number materials, corrosion resistance, high reliability, and low-cost. Each x-ray window design is a balance between these characteristics.
An x-ray window can combine with a housing to enclose an internal vacuum. The internal vacuum can aid device performance. For example, an internal vacuum for an x-ray detector (a) minimizes gas attenuation of incoming x-rays and (b) allows easier cooling of the x-ray detector.
Permeation of a gas through the x-ray window can degrade the internal vacuum. Thus, low gas permeability is a desirable x-ray window characteristic.
Outgassing from x-ray window materials can degrade the internal vacuum of the device. Thus, selection of materials with low outgassing is useful.
The x-ray window can face vacuum on one side and atmospheric pressure on an opposite side. Therefore, the x-ray window may need strength to withstand this differential pressure.
Visible and infrared light can cause undesirable noise in the x-ray detector. The ability to block transmission of visible and infrared light is another useful characteristic of x-ray windows.
A high x-ray flux through the x-ray window allows rapid functioning of the x-ray detector. Therefore, high x-ray transmissivity through the x-ray window is useful.
Detection and analysis of low-energy x-rays is needed in some applications. High transmission of low-energy x-rays is thus another useful characteristic of x-ray windows.
X-rays can be used to analyze a sample. X-ray noise from surrounding devices, including from the x-ray window, can interfere with a signal from the sample. X-ray noise from high atomic number materials are more problematic. It is helpful, therefore, for the x-ray window to be made of low atomic number materials.
X-ray windows are used in corrosive environments, and may be exposed to corrosive chemicals during manufacturing. Thus, corrosion resistance is another useful characteristic of an x-ray window.
X-ray window failure is intolerable in many applications. For example, x-ray windows are used in analysis equipment on Mars. High reliability is a useful x-ray window characteristic.
X-ray window customers demand low-cost x-ray windows with the above characteristics. Reducing x-ray window cost is another consideration.
The present invention is directed to various x-ray windows, and methods of making x-ray windows, that satisfy these needs. Each x-ray window or method may satisfy one, some, or all of these needs.
As illustrated in
The boron-film 12 can be the main support structure spanning the aperture 15 of the support-frame 11, and can be thicker than any other material spanning the aperture 15. Example lower limits of a minimum thickness Th12 of the boron-film 12 across the aperture include: Th12 ≥ 25 nm, Th12 ≥ 50 nm, Th12 ≥ 100 nm, Th12 ≥ 300 nm, or Th12 ≥ 500 nm. Example upper limits of a minimum thickness Th12 of the boron-film 12 across the aperture include: and Th12 ≤ 500 nm, Th12 ≤ 750 nm, ≤ 1200 nm, Th12 ≤ 1500 nm, Th12 ≤ 3000 nm, or Th12 ≤ 10,000 nm.
The support-frame 11 can have a ring shape, can encircle the aperture 15, or both. The support-frame 11 can have a top-side 11T and a bottom-side 11B, which can be opposite of each other and parallel with respect to each other. The support-frame 11 can have an inner-side 11i facing the aperture 15 and an outer-side 11o opposite of the inner-side 11i. The inner-side 11i and the outer-side 11o can extend between and can join the top-side 11T and the bottom-side 11B. The support-frame 11 (and the wafer 81 described below) can comprise silicon, such as for example ≥ 30, ≥ 50, ≥ 90, or ≥ 95 mass percent silicon. The support-frame 11 (and the wafer 81 described below) can comprise silicon dioxide, such as for example ≥ 30, ≥ 50, ≥ 90, or ≥ 95 mass percent silicon dioxide.
The boron-film 12 can have a near-side 12N (nearer the support-frame 11) and a far-side 12F (farther from the support-frame 11), opposite of each other. The near-side 12N of the boron-film 12 can adjoin and/or be hermetically-sealed to the top-side 11T of the support-frame 11. The hermetic-seal can be a direct bond between the top-side 11T of the support-frame 11 and the boron-film 12. The hermetic-seal can be free of aluminum or an aluminum-film.
Example weight percentages of boron, throughout the entire boron-film 12, include ≥ 80, ≥ 90, ≥ 95, ≥ 97, ≥ 98, or ≥ 99 weight percent. Example weight percentages of hydrogen, throughout the entire boron-film 12, include ≥ 0.01, ≥ 0.05, ≥ 0.1, ≥ 0.5, ≥ 0.9, ≥ 2, or ≥ 4 weight percent hydrogen. Example density, throughout the entire boron-film 12, includes ≥ 1.94 g/cm3, ≥ 2.04 g/cm3, or ≥ 2.1 g/cm3 and ≤ 2.18 g/cm3, ≤ 2.24 g/cm3, or ≤ 2.34 g/cm3. For example, the boron-film 12 can have 99.1 weight percent boron, 0.9 weight percent hydrogen, and density of 2.14 g/cm3. A window with these material properties can be manufactured as noted in the METHOD section below.
The aperture 15 of the support-frame 11 can consist of thin films spanning the entire aperture. The aperture 15 of the support-frame 11 can be free of material of the support-frame 11, free of ribs, or both.
As illustrated in
Addition of the annular-film 32 can improve the ability of the x-ray window to withstand thermal stress during rapid or large temperature changes and can improve bonding of the x-ray window to a housing. The above benefits are particularly applicable if the annular-film 32 is similar in material and thickness to the boron-film 12,
X-ray windows 30 and 70, with the annular-film 32, can be combined with any other x-ray window examples described herein, including those shown in any of
As illustrated in
The thin-film 52 can be located on the far-side 12F of the boron-film 12, as illustrated in
The thin-film 52 on the far-side 12F of the boron-film 12 can be combined with the annular-film 32 (
An outer portion or outer ring of the near-side 12N of the boron-film 12 can be attached to or adjoin the support-frame 11. A junction of the boron-film 12 and the support-frame 11 can be free of the thin-film 52.
The thin-film 52 can extend onto, cover, or adjoin the inner-side 11i and the bottom-side 11B of the support-frame 11, as illustrated in
Because aluminum has a higher atomic number than boron, it can be useful to have a relatively thin layer of aluminum. Thus for example, Th52 ≤ 0.5*Th12, Th52 ≤ 0.3*Th12, Th52 ≤ 0.1 *Th12, where Th52 is a minimum thickness of the thin-film 52 in the aperture 15 and Th12 is a minimum thickness of the boron-film 12 in the aperture 15. Other example relationships, for the thin-film 52 to have sufficient thickness, include Ths2 ≥ 0.001 *Th12, Th52 ≥ 0.01*Th12, or Th52 ≥ 0.1*Th12.
The boron film 12 can be the primary film or only film spanning the aperture 15. Thus, for example, ThF ≤ 1.1*Th12, ThF ≤ 1.25*Th12, ThF ≤ 1.5*Th12, or ThF ≤ 2*Th12.
The aluminum-film and the boron-film 12 can be the only solid structures spanning the aperture 15 of the support-frame 11. The boron film 12 and the aluminum-film can be the primary films, or only films, spanning the aperture 15. Thus, for example, ThF ≤ 1.1*(Th12 + Th52), ThF ≤ 1.25*(Th12 + Th52), ThF ≤ 1.5*(Th12 + Th52), or ThF ≤ 2*(Th12 + Th52). ThF is a minimum thickness of the films in the aperture 15.
The x-ray window can be hermetically sealed to a housing, with an internal vacuum. The boron-film 12 can face atmospheric pressure and the aluminum-film can face a vacuum.
A method of manufacturing an x-ray window can comprise some or all of the following steps, which can be performed in the following order. There may be additional steps not described below. These additional steps may be before, between, or after those described.
The method can comprise placing a wafer 81 in an oven 82; introducing a gas into the oven 82, the gas including boron, and forming boron-film(s) 12 on the wafer 81 (step 80 in
Deposition temperature can be adjusted to control percent hydrogen and percent boron. Lower (higher) temperature can result in in increased (decreased) hydrogen in the boron-film 12. For example, a temperature of 390° C. can result in about 1% H in the boron-film 12. Other example temperatures in the oven 82, during formation of the boron-film(s) 12, include ≥ 50° C., ≥ 100° C., ≥ 200° C., ≥ 300° C., or ≥ 340° C., and ≤ 340° C., ≤ 380° C., ≤ 450° C., ≤ 525° C., ≤ 550° C., or ≤ 600° C.
Formation of the boron-film 12 can be plasma enhanced, in which case the temperature of the oven 82 can be relatively lower. A pressure in the oven can be relatively low, such as for example 60 pascal. Higher pressure deposition might require a higher process temperature.
As illustrated in
Here is an example of deposition to form boron-film(s) 12 with about 99.1 weight percent boron, 0.9 weight percent hydrogen, and density of 2.14 g/cm3: A wafer 81 is loaded into the oven 82. The furnace is evacuated (about 450 mTorr) and temperature stabilized at ~390° C. A gas with 15 molar percent diborane and 85 molar percent argon is introduced into the oven, resulting in deposition of the boron-film(s) 12. Oven 82 pressure is controlled by an adjustable butterfly valve at the vacuum inlet.
After step 80, the method can further comprise etching through a center of the wafer 81 at the bottom-side 81B to form a support-frame 11 encircling an aperture 15 (see
After step 90, the method can further comprise etching through a center of the lower-boron-film 12s to form an annular-film 32 and etching through a center of the wafer 81 at the bottom-side 81B to form a support-frame 11 encircling an aperture 15 (see
A resist can be used to form the desired annular-shape of the annular-film 32 or the support-frame 11. A solution of potassium ferricyanide, a fluorine plasma (e.g. NF3, SF6, CF4), or both, can be used to etch the lower-boron-film 12s. Example chemicals for etching the wafer 81 include ammonium hydroxide, cesium hydroxide, potassium ferricyanide, potassium hydroxide, sodium hydroxide, sodium oxalate, tetramethylammonium hydroxide, or combinations thereof. The resist can then be stripped, such as for example with sulfuric acid and hydrogen peroxide (e.g. Nanostrip).
Some (e.g. ≥ 25%, ≥ 50%, ≥ 75%, or ≥ 90%) of the near-side 12N and the far-side 12F of the boron-film 12 can both face atmospheric pressure, a gas, or both at this step in the process (after etch and before the deposition of thin-film 52 / aluminum-film).
A thin-film 52 (e.g. an aluminum-film) can be deposited on the far-side 12F of the boron-film 12 (
A thin-film 52 (e.g. an aluminum-film) can be deposited on the near-side 12N of the boron-film 12 (or the near-side 12N of the upper-boron-film 12U), on the inner-side 11i of the support-frame 11, on the bottom-side 11B of the support-frame 11, or combinations thereof (
The x-ray window can then be sealed to a housing with a vacuum inside of the housing. The boron-film 12 (or upper-boron-film 12U) can face atmospheric pressure outside of the housing, and the aluminum-film can face the vacuum.
The support-frame 11, boron-film(s) 12, annular-film 32, and the thin-film(s) 52 can have properties as described above.
This application is a continuation of U.S. Pat. Application Number US17/228,846, filed on Apr. 13, 2021, which claims priority to U.S. Provisional Pat. Application No. 63/023,385, filed on May 12, 2020, which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63023385 | May 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17228846 | Apr 2021 | US |
| Child | 17994832 | US |
