Ultra-high energy resolution analysis crystal and preparation method thereof

Abstract

The present invention discloses an ultra-high energy resolution analytical crystal and a method for preparing the same. The ultra-high energy resolution analytical crystal of the present invention comprises a concave substrate, an intermediate layer, and a crystal. The lower surface of the crystal, the upper and lower surfaces of the intermediate layer, and the concave spherical surface of the concave substrate are plated with Au. The lower surface of the crystal and the upper surface of the intermediate layer are bonded to form a combined body, and the upper surface of the crystal serves as the upper surface of the combined body. The lower surface of the combined body is bonded to the concave spherical surface of the concave substrate. The upper surface of the combined body is grooved to cut through the crystal. The present invention can produce spherically curved analytical crystals with an energy resolution of 1 meV.

Description

Technical Field

[0001] The present invention belongs to the field of synchrotron radiation X-ray spectroscopy and optical element technology, and relates to a high-precision silicon spherical analytical crystal, and specifically to an ultra-high energy resolution analytical crystal based on metal thermal diffusion bonding and a preparation method thereof. Background Art

[0002] As the core optical element of the IXS spectrometer, the spherically curved analytical crystal achieves energy screening through Bragg diffraction: nλ=2dsinθ; where d is the lattice spacing, θ is the Bragg angle, and n is the diffraction order. Single-crystal silicon spherical crystals have the best intrinsic energy resolution under backscattering geometry (Bragg angle close to 90°). When high-order reflections with Si(nnn) n>13 are used, sub-meV monochromatization capabilities can be achieved. Although theoretical calculations show that single-crystal silicon systems have the potential for sub-meV resolution, they face three challenges in actual manufacturing: ① Lattice perfection is limited by crystal growth technology, and the dislocation density needs to be controlled at <10 3 / cm² level; ② The residual stress generated by the press-bending process causes crystal plane distortion, with a typical stress gradient exceeding 200 MPa / mm; ③ The temperature stability and lattice parameter drift caused by thermal deformation need to be controlled at the mK level.

[0003] There are three traditional methods for preparing spherical curvature analysis crystals:

[0004] 1. The solution described in R. Verbeni's 2005 article is as follows: ① First, a 3.2 mm thick crystal is cut into a 1 x 1 mm array using silicon wafer grooving technology, leaving a 0.2 mm silicon substrate to support the array. ② A first chemical etching is performed to eliminate stress introduced during crystal cutting. ③ Glue is dispensed robotically onto the array and bonded to a concave borosilicate glass surface, which is then heated to 170° to cure. ④ The remaining 0.2 mm silicon substrate is polished away using a grinding technique. ⑤ A final chemical etching is performed using nitric and hydrofluoric acids.

[0005] 2. Daisuke Ishikawa, in J. Synchrotron Rad. (2015), 22, 3–9, describes a method for fabricating ultra-high energy resolution analysis crystals by combining anodic bonding, gluing, and temperature gradient techniques. The specific steps are as follows: ① Double-sided polishing of a single-crystal silicon wafer and TEMPAX glass, followed by chemical etching to remove stress. ② Bonding the silicon to the glass wafer. ③ Using a dicing saw, slice through the silicon without breaking the glass. ④ Chemical etching to remove the groove stress. ⑤ Grooving the spherical Invar alloy and applying glue. ⑥ Bonding and curing the grooved silicon / glass assembly to the Invar alloy. ⑦ Applying a temperature gradient to the assembly to correct for geometric aberrations caused by the detector's deviation from the Rowland circle.

[0006] 3. In a 1996 article, C. Masciovecchio reported obtaining high-energy-resolution analytical crystals by chemically etching to remove the substrate. The specific steps are: ① Double-sided polishing of a melt-zone high-resistance single-crystal silicon wafer. ② Grooving the wafer, leaving a 200µm layer of material as the substrate. ③ Chemical etching to eliminate cutting stress. ④ Applying glue to the cut surface and bonding it to the concave silicon crystal. ⑤ Final chemical etching to eliminate stress and the remaining substrate.

[0007] The main drawbacks of existing technologies include: First, the use of adhesive bonding results in large surface errors in concave crystals due to uneven adhesive layer thickness. Second, substrate removal often involves grinding, chemical etching, and other techniques, which results in prolonged crystal etching and increased surface roughness due to chemical etching or grinding. Because meV energy-resolved analysis crystals require high surface accuracy, and the orientation accuracy of each small grain after grooving must be controlled to the order of 10urad, existing technologies struggle to achieve this surface accuracy and sub-meV energy resolution.

[0008] Inelastic X-ray scattering (IXS), a core technique for studying low-energy excited states in materials, can effectively detect collective elementary excitations such as phonons and magnetic excitations by precisely measuring the energy-momentum transfer generated by X-ray interactions with matter. Currently, the key limitation to achieving sub-millielectronvolt (meV) energy resolution with this technique lies in the performance optimization and preparation of spherically curved analytical crystals. Currently, spherical analytical crystal systems constructed from single-crystal silicon achieve X-ray monochromatization through high diffraction orders in a backscattering geometry, with theoretical Darwin widths reaching millielectronvolts. However, in practical applications, existing analytical crystals struggle to achieve energy resolution better than 1 meV due to limitations such as crystal lattice perfection, stresses induced by bending and grooving, and thermodynamic stability. This severely limits the detection and precise interpretation of weak excitation signals in complex quantum materials. Summary of the Invention

[0009] To address the challenges of the prior art, the present invention aims to provide an ultra-high energy resolution analytical crystal and its preparation method, capable of producing spherically curved analytical crystals with an energy resolution of 1 meV. This invention is an advanced energy analysis optical element based on high-energy resolution inelastic X-ray scattering (IXS), suitable for synchrotron radiation inelastic X-ray scattering and X-ray Rowland circle spectrometers.

[0010] This invention innovatively proposes a method that utilizes metal thermal diffusion bonding, combined with flat-cut pixel technology, to improve the normal alignment accuracy of single crystal particles after grooving to the order of tens of urads. By optimizing the process flow and technical parameters, the mechanical stress during the processing is significantly removed, and the thermal stability and energy resolution capability of the analyzed crystal are improved.

[0011] This invention utilizes gold-gold diffusion bonding technology to combine homogeneous silicon and concave silicon to produce an ultra-high energy resolution analysis crystal, effectively avoiding the internal stress generated by two materials with different thermal expansion coefficients during temperature changes. It also avoids the dilemma of anodic bonding being limited to specific materials.

[0012] The present invention combines gold-gold diffusion bonding and flat-cut pixel crystal technology to improve the consistency of the crystal orientation of single crystal particles and avoid the surface error problem caused by uneven glue layer thickness.

[0013] The technical solution of the present invention is:

[0014] An ultra-high energy resolution analytical crystal based on metal thermal diffusion bonding is characterized in that it includes a concave substrate, an intermediate layer and a crystal; wherein, the lower surface of the crystal, the upper and lower surfaces of the intermediate layer, and the concave spherical surface of the concave substrate are plated with an Au layer; the lower surface of the crystal and the upper surface of the intermediate layer are bonded to each other to form a combination, and the upper surface of the crystal is the upper surface of the combination; the lower surface of the combination is bonded to the concave spherical surface of the concave substrate; the upper surface of the combination is grooved to cut through the crystal.

[0015] Furthermore, the crystal is a zone-melting single-crystal silicon Si(111) crystal; the material of the intermediate layer is Si(100); and the material of the concave substrate is Si(100).

[0016] Furthermore, the thickness of the zone-melting single-crystal silicon Si(111) crystal is 3-5 mm and the resistivity is greater than 10,000 ohm-cm; the intermediate layer is 0.5 mm thick Si(100); one side of the 16 mm thick Si(100) is polished into a concave spherical surface with a curvature radius of 6-12 meters to obtain the concave substrate.

[0017] Furthermore, a Ti / Cr layer with a thickness of 10-30 nm is prepared as a transition layer on the lower surface of the crystal, the upper and lower surfaces of the intermediate layer, and the concave spherical surface of the concave substrate, and an Au layer with a thickness of 500 nm-1 um is plated on the transition layer.

[0018] Furthermore, the crystal, the intermediate layer, and the concave substrate are subjected to precision polishing and chemical etching to eliminate stress on the crystal, the planar substrate, and the intermediate layer.

[0019] A method for preparing an ultra-high energy resolution analysis crystal based on metal thermal diffusion bonding, comprising the following steps:

[0020] Step 1: Select a crystal, a planar substrate, and a concave substrate and perform precision polishing and chemical etching on them to eliminate stress on the crystal, the planar substrate, and the concave substrate;

[0021] Step 2, plating an Au layer on the lower surface of the crystal, the upper and lower surfaces of the planar substrate, and the concave spherical surface of the concave substrate;

[0022] Step 3: placing the lower surface of the crystal and the upper surface of the planar substrate opposite to each other in a metal thermal diffusion bonding machine for bonding to a combination; wherein the upper surface of the crystal is the upper surface of the combination;

[0023] Step 4: Grooving the upper surface of the combined body, cutting through the crystal so that the bottom of the groove is the Au layer plated on the upper surface of the planar substrate;

[0024] Step 5: Place the lower surface of the grooved combination opposite to the concave spherical surface of the concave substrate in a metal thermal diffusion bonding machine for bonding to obtain an ultra-high energy resolution analysis crystal;

[0025] Step 6: Chemically etch the ultra-high energy resolution analysis crystal to eliminate bending stress and slotting stress.

[0026] Furthermore, the crystal is a zone-melting single-crystal silicon Si(111) crystal; the material of the planar substrate is Si(100); and the material of the concave substrate is Si(100).

[0027] Furthermore, the thickness of the zone-melting single-crystal silicon Si(111) crystal is 3-5 mm and the resistivity is greater than 10,000 ohm-cm; the planar substrate is 0.5 mm thick Si(100); and the concave substrate is obtained by polishing one side of the 16 mm thick Si(100) into a concave spherical surface with a curvature radius of 6-12 meters.

[0028] Furthermore, a Ti / Cr layer with a thickness of 10-30 nm is prepared as a transition layer on the lower surface of the crystal, the upper and lower surfaces of the planar substrate, and the concave spherical surface of the concave substrate, and then an Au layer with a thickness of 500 nm-1 um is plated on the transition layer.

[0029] Furthermore, the etching solution used in the chemical etching of step 1 and step 6 is a mixed solution of nitric acid and hydrofluoric acid, and the etching time is 10 minutes; wherein, the ratio of nitric acid to hydrofluoric acid in the etching solution is 10:1; and the polishing precision PV value reaches 1 / 20 of the wavelength.

[0030] The advantages of the present invention are as follows:

[0031] 1. The present invention can realize the combination of silicon and silicon homogeneous materials, effectively avoiding material stress caused by temperature stability.

[0032] 2. The present invention can achieve a higher-precision surface shape. Since there is no flowing intermediate layer, the surface shape will depend on the polishing accuracy of the concave single crystal silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart for making ultra-high energy resolution analysis crystals based on gold-gold thermal diffusion bonding. DETAILED DESCRIPTION

[0034] The present invention will be described in further detail below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0035] This patented invention utilizes metal hot-compression diffusion bonding to achieve adhesive-free bonding of the same material. This technology ensures that the bonding material and substrate are the same material, avoiding the internal stress problems caused by two materials with different thermal expansion coefficients during temperature changes. The specific process flow is as follows:

[0036] 1) First, prepare the single crystal material. Zone-melted single-crystal silicon (Si(111)) is preferred, with a thickness of 3-5 mm and a resistivity greater than 10,000 ohm-cm. A 0.5 mm thick Si(100) is used as a planar substrate. A 16 mm thick Si(100) is polished into a concave spherical surface to create a concave substrate with a radius of curvature of 6-12 m. All three materials require precision polishing and chemical etching to eliminate machining-induced stress. Chemical mechanical polishing is used, achieving a peak-to-valley (PV) polishing accuracy of 1 / 20 of a wavelength.

[0037] 2) The lower surface of the Si(111) crystal, the upper and lower surfaces of the thin silicon wafer Si(100), and the concave spherical surface are gold-plated using a vacuum electron beam magnetron sputtering evaporation coating method. The Au layer thickness is 500nm-1um, and a 10-30nm Ti / Cr layer is used as a transition layer to ensure a firm bond between gold and silicon.

[0038] 3) Place the lower surface of the Si(111) crystal and the upper surface of the Si(100) flat substrate opposite to each other in a metal thermal diffusion bonding machine for bonding to obtain a combination, with a heating temperature of 350-450 degrees Celsius, a pressure of >40KN, a time of 20-45 minutes, and a vacuum environment; wherein the upper surface of the Si(111) crystal is the upper surface of the combination.

[0039] 4) Grooving is performed on the upper surface of the combination. The groove depth is slightly greater than the thickness of the Si(111) crystal. The Si(111) crystal is cut through. The groove size is 1*1mm.2 , groove width 120um. Cutting through can not only prevent the bending stress from being transmitted to or affecting the upper surface of the crystal, but also improve the energy resolution.

[0040] 5) The lower surface of the grooved assembly is aligned with the concave spherical surface of the concave substrate and metal diffusion bonding is performed again to combine the two to obtain an ultra-high energy resolution analysis crystal; the bonding temperature is 400 degrees, the pressure is 1-5 MPa, the time is 55-65 minutes, and the environment is vacuum.

[0041] 6) Finally, the ultra-high energy resolution analysis crystal is chemically etched to eliminate bending stress and slotting stress.

[0042] While specific embodiments of the present invention have been disclosed for illustrative purposes, intended to facilitate understanding and implementation of the present invention, those skilled in the art will appreciate that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the disclosure of the preferred embodiments, and the scope of protection claimed in the present invention shall be determined by the scope of the claims.

Claims

1. An ultra-high energy resolution analysis crystal, characterized in that: The invention comprises a concave substrate, an intermediate layer and a crystal; wherein, an Au layer is plated on the lower surface of the crystal, the upper and lower surfaces of the intermediate layer and the concave spherical surface of the concave substrate; the lower surface of the crystal and the upper surface of the intermediate layer are bonded to form a combination, and the upper surface of the crystal is the upper surface of the combination; the lower surface of the combination is bonded to the concave spherical surface of the concave substrate; the upper surface of the combination is grooved to cut through the crystal; wherein, the lower surface of the crystal and the upper surface of the intermediate layer are placed relative to each other in a metal thermal diffusion bonding machine for bonding to obtain the combination, and the heating temperature is 350 degrees to 450 degrees.

2. The ultra-high energy resolution analysis crystal according to claim 1, characterized in that The crystal is a zone-melting single-crystal silicon Si(111) crystal; the material of the intermediate layer is Si(100); and the material of the concave substrate is Si(100).

3. The ultra-high energy resolution analysis crystal according to claim 2, characterized in that The thickness of the zone-melting single-crystal silicon Si(111) crystal is 3-5 mm and the resistivity is greater than 10,000 ohm-cm; the intermediate layer is 0.5 mm thick Si(100); one side of the 16 mm thick Si(100) is polished into a concave spherical surface with a curvature radius of 6-12 meters to obtain the concave substrate.

4. The ultra-high energy resolution analysis crystal according to claim 2 or 3, characterized in that A Ti / Cr layer with a thickness of 10-30 nm is prepared as a transition layer on the lower surface of the crystal, the upper and lower surfaces of the intermediate layer, and the concave spherical surface of the concave substrate, and an Au layer with a thickness of 500 nm-1 um is plated on the transition layer.

5. The ultra-high energy resolution analysis crystal according to claim 1, 2 or 3, characterized in that: The crystal, the intermediate layer and the concave substrate are subjected to precision polishing and chemical etching to eliminate stress on the crystal, the planar substrate and the intermediate layer.

6. A method for preparing an ultra-high energy resolution analytical crystal, comprising the steps of: Step 1: Select a crystal, a planar substrate, and a concave substrate and perform precision polishing and chemical etching on them to eliminate stress on the crystal, the planar substrate, and the concave substrate; Step 2, plating an Au layer on the lower surface of the crystal, the upper and lower surfaces of the planar substrate, and the concave spherical surface of the concave substrate; Step 3: Place the lower surface of the crystal and the upper surface of the planar substrate opposite to each other in a metal thermal diffusion bonding machine for bonding to obtain a combination; wherein the upper surface of the crystal is the upper surface of the combination, and the heating temperature is 350°C to 450°C; Step 4: Grooving the upper surface of the combined body, cutting through the crystal so that the bottom of the groove is the Au layer plated on the upper surface of the planar substrate; Step 5: Place the lower surface of the grooved combination opposite to the concave spherical surface of the concave substrate in a metal thermal diffusion bonding machine for bonding to obtain an ultra-high energy resolution analysis crystal; Step 6: Chemically etch the ultra-high energy resolution analysis crystal to eliminate bending stress and slotting stress.

7. The method according to claim 6, characterized in that The crystal is a zone-melting single-crystal silicon Si(111) crystal; the material of the planar substrate is Si(100); and the material of the concave substrate is Si(100).

8. The method according to claim 7, characterized in that The thickness of the zone-melting single-crystal silicon Si(111) crystal is 3-5 mm and the resistivity is greater than 10,000 ohm-cm; the planar substrate is 0.5 mm thick Si(100); one side of the 16 mm thick Si(100) is polished into a concave spherical surface with a curvature radius of 6-12 meters to obtain the concave substrate.

9. The method according to claim 7 or 8, characterized in that A Ti / Cr layer with a thickness of 10-30 nm is prepared as a transition layer on the lower surface of the crystal, the upper and lower surfaces of the planar substrate, and the concave spherical surface of the concave substrate, and then an Au layer with a thickness of 500 nm-1 um is plated on the transition layer.

10. The method according to claim 6, 7 or 8, characterized in that: The etching solution used in the chemical etching of step 1 and step 6 is a mixed solution of nitric acid and hydrofluoric acid, and the etching time is 10 minutes; wherein, the ratio of nitric acid to hydrofluoric acid in the etching solution is 10:1; and the polishing precision PV value reaches 1 / 20 wavelength.

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