Soft x-ray grazing incidence mirror with integrated protective layer and method of making the same

Abstract

The application relates to a soft X-ray grazing incidence mirror with an integrated protective layer and a preparation method thereof, which comprises an optical substrate, a metal reflecting layer, and a protective layer directly covering the surface of the metal reflecting layer. The application has the beneficial effects that the service life is significantly improved, the service life in a plasma environment is 5-10 times longer than that of the prior art, the maintenance cost of an optical system is greatly reduced, the reflection performance is stable, the soft X-ray reflectivity attenuation is significantly slowed down after long-term operation, and the performance consistency of the optical system is ensured.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, and particularly relates to a soft X-ray grazing incidence mirror with an integrated protective layer and its preparation method. Background Technology

[0002] In soft X-ray lithography, soft X-ray source diagnostics, and high-power soft X-ray optical systems, grazing incidence mirrors (GI mirrors) are often deployed near plasma sources due to their relatively simple requirements for film structure and good broadband adaptability. Examples include laser plasma source (LPP) or discharge plasma (DPP) light collection systems, front-end reflective components of soft X-ray spectrometers, and soft X-ray plasma diagnostic optical paths.

[0003] Currently, ruthenium (Ru) is the most widely used material for the reflective layer of grazing incidence mirrors in engineering. Its core advantage lies in the fact that Ru has a high imaginary part contrast of refractive index in the soft X-ray band and exhibits high reflectivity under small incident angle conditions, thus becoming the mainstream choice in existing technologies.

[0004] However, existing Ru grazing incidence mirrors face unavoidable degradation mechanisms in actual operation, which seriously affect their service life and performance stability: 1. High-energy ion etching: Metal ions and other impurity ions generated in the plasma continuously bombard the Ru surface in the energy range of tens to hundreds of eV, resulting in atomic-level sputtering etching and a rapid increase in surface RMS roughness (>0.3nm), which in turn causes a significant decrease in grazing incidence reflectivity; 2. Contamination deposition: The Ru surface has a high adsorption energy for Sn, C, Si and their oxides. Once the contamination layer is formed, it is difficult to remove by low temperature methods, and it will further absorb soft X-rays and cause local hot spots, accelerating the destruction of the Ru layer structure. 3. Thermal load and thermal stress issues: Grazing incidence mirrors directly bear the energy deposition of soft X-ray photons, plasma radiation heat and secondary electron energy deposition. However, Ru has limited thermal conductivity, and heat accumulates in the film layer, which can easily lead to problems such as thermal stress concentration in the film layer, metal film cracking or interface peeling, and substrate surface distortion.

[0005] In summary, a single Ru reflective layer is no longer sufficient to meet the long-term stability requirements of high-power soft X-ray systems. There is an urgent need for a novel grazing incidence mirror structure and fabrication method that can solve the aforementioned degradation problem. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a soft X-ray grazing incidence mirror with an integrated protective layer and its preparation method.

[0007] Firstly, a soft X-ray grazing incidence mirror with an integrated protective layer is provided, comprising, from bottom to top: an optical substrate, a metal reflective layer, and a protective layer directly covering the surface of the metal reflective layer.

[0008] Preferably, the material of the metal reflective layer includes at least one of ruthenium, molybdenum, silicon, nickel, or boron carbide; the thickness of the metal reflective layer is from 5 nm to 300 nm.

[0009] Preferably, the material of the protective layer is selected from any one or a combination of diamond-like carbon, silicon carbide, nanocrystalline diamond, doped diamond, boron carbide, boron nitride, and silicon nitride; the thickness of the protective layer is 1 nm to 10 nm.

[0010] Preferably, the surface roughness RMS value of the protective layer is less than or equal to 0.2 nm.

[0011] Preferably, a transition bonding layer is also included between the metal reflective layer and the protective layer.

[0012] Preferably, the material of the transition bonding layer includes Cr, Ti, Si, C or compounds thereof; the thickness of the transition bonding layer is 0.5 nm to 1 nm.

[0013] Preferably, the optical substrate is made of monocrystalline silicon, aluminum alloy, or ultra-low expansion glass.

[0014] In a second aspect, a method for fabricating a soft X-ray grazing incidence mirror with an integrated protective layer as described in any of the first aspects is provided, comprising: S1, Provides an optical substrate; S2. A metallic reflective layer is deposited on the surface of the optical substrate; S3. A protective layer is deposited on the surface of the metal reflective layer to form a protective layer.

[0015] Preferably, after S2, the method further includes: depositing a transition bonding layer on the surface of the metal reflective layer; S3 specifically involves depositing a protective layer on the surface of the transition bonding layer.

[0016] Preferably, in S2, the metal reflective layer is deposited using magnetron sputtering or ion beam deposition; in S3, the protective layer is deposited using ion beam sputtering, ion beam-assisted deposition, high-power pulsed magnetron sputtering, microwave plasma chemical vapor deposition, or plasma-enhanced chemical vapor deposition.

[0017] The beneficial effects of this invention are: 1. This invention significantly improves service life, extending it by 5–10 times compared to existing technologies in plasma environments, and greatly reduces the maintenance cost of optical systems; furthermore, this invention provides stable reflectivity, with a significant slowdown in soft X-ray reflectivity decay after long-term operation, ensuring consistent optical system performance.

[0018] 2. The protective layer made of diamond-like carbon and other materials in this invention has low surface energy, which significantly reduces the adhesion of contaminant particles, allowing them to be removed by simple cleaning methods without complicated treatment. Furthermore, the diamond-like carbon protective layer has excellent thermal conductivity, which can quickly dissipate surface heat, effectively reducing the thermal gradient and surface drift of the mirror and ensuring optical accuracy.

[0019] 3. This invention is highly compatible with existing processes, and the preparation process can be directly integrated into the existing soft X-ray mirror manufacturing process without large-scale modification of production equipment, thus possessing good engineering application feasibility. Attached Figure Description

[0020] Figure 1 A schematic diagram of the soft X-ray grazing incidence mirror structure with integrated diamond-like protective layer provided by the present invention; Figure 2 A schematic diagram of the fabrication process of the soft X-ray grazing incidence mirror with diamond-like protective layer provided by the present invention; Figure labeling: 1. Protective layer; 2. Grazing incidence reflective layer; 3. Smooth substrate; 4. Monocrystalline silicon. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0022] Example 1: Embodiment 1 of this application provides a grazing incidence mirror structure that combines high soft X-ray grazing incidence reflectivity, high resistance to ion etching, high resistance to contamination, and excellent thermal management performance, in order to solve the core problems of short lifespan and rapid performance degradation of existing Ru grazing incidence mirrors in plasma environments.

[0023] Specifically, by integrating an ultrathin diamond-like carbon or other protective layer on the surface of the Ru reflective layer, the following objectives can be achieved without significantly reducing the grazing incidence reflectivity of soft X-rays: physical blocking of high-energy ion bombardment; chemical passivation of contaminants such as Sn / O / C / Si / Cu; rapid lateral and longitudinal diffusion of surface thermal load; and orders of magnitude improvement in the overall service life of the reflector.

[0024] like Figure 1As shown, the soft X-ray grazing incidence mirror with integrated protective layer includes, from bottom to top: an optical substrate, a metal reflective layer, and a protective layer directly covering the surface of the metal reflective layer.

[0025] The metal reflective layer may be a grazing incidence reflective coating such as ruthenium (Ru), molybdenum / silicon (Mo / Si), nickel (Ni), or boron carbide (B4C), with a thickness of 5–300 nm, preferably 30–50 nm.

[0026] The protective layer is selected from any one or a combination of diamond-like carbon (DLC), silicon carbide (SiC), nanocrystalline diamond, doped diamond, boron carbide (B4C), boron nitride (BN), and silicon nitride (Si3N4) thin films, with a thickness ranging from 1 to 10 nm, preferably 2 to 4 nm.

[0027] The surface roughness RMS value of the protective layer is less than or equal to 0.2 nm, preferably ≤ 0.1 nm, to ensure high soft X-ray reflectivity at grazing incidence angles of 1°–10°.

[0028] In addition, the thermal conductivity of the protective layer is ≥100 W·m -1 ·K -1 It is used as a rapid diffusion channel for surface heat. Example 2: Based on Embodiment 1, Embodiment 2 of this application provides a more specific soft X-ray grazing incidence mirror with an integrated protective layer, which, from bottom to top, includes: an optical substrate, a metal reflective layer, and a protective layer directly covering the surface of the metal reflective layer.

[0029] The optical substrate is a smooth substrate such as single-crystal silicon, aluminum alloy, or ultra-low expansion glass.

[0030] In addition, a transition bonding layer is provided between the metal reflective layer and the protective layer.

[0031] The transition bonding layer is made of Cr, Ti, Si, C or their compounds; the thickness of the transition bonding layer is 0.5 nm to 1 nm, and it is used to alleviate the mismatch of thermal expansion coefficients between the metal and the protective layer and improve the interfacial bonding strength.

[0032] Based on the above structure, under ion bombardment conditions with energies ≥50 eV, its surface etching rate is reduced by at least one order of magnitude compared to the unprotected Ru layer.

[0033] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 1 can be referred to each other, and will not be repeated in this application.

[0034] Example 3: Based on Example 2, Example 3 of this application provides a method for fabricating a soft X-ray grazing incidence mirror with an integrated protective layer, including: S1, Provides an optical substrate.

[0035] Specifically, an ultra-smooth optical substrate is provided, the substrate being selected from single-crystal silicon, silicon carbide, or low-expansion glass, with a surface RMS roughness ≤ 0.2 nm.

[0036] For example, a 4-inch single-crystal silicon wafer is selected as the optical substrate. The RMS roughness of the substrate surface is controlled within 0.15 nm by chemical mechanical polishing. Then, acetone and isopropanol are used for ultrasonic cleaning for 15 min in sequence to remove organic contaminants on the surface. Finally, the substrate is treated with a plasma cleaner for 5 min to further remove surface residues.

[0037] In addition, aluminum alloy or low-expansion glass can be used instead of monocrystalline silicon substrate, as long as the RMS roughness of the substrate surface is ≤0.2 nm.

[0038] S2. A metallic reflective layer is deposited on the surface of the optical substrate.

[0039] Specifically, a 30–50 nm thick Ru reflective layer is deposited on the substrate surface using magnetron sputtering or ion beam deposition.

[0040] For example, a magnetron sputtering device is used at a vacuum level of 5 × 10⁻⁶. -4 In an environment of Pa, using a pure Ru target as the sputtering source, with a sputtering power of 100 W and an argon flow rate of 30 sccm, a 15 nm thick Ru reflective layer was deposited on the substrate surface, with the deposition rate controlled at 0.5 nm / s.

[0041] In addition, after S2, it also includes: depositing a transition bonding layer on the surface of the metal reflective layer; S3 specifically involves depositing a protective layer on the surface of the transition bonding layer.

[0042] In addition, ion beam deposition can be used instead of magnetron sputtering, with the deposition parameters adjusted to an ion beam energy of 500 eV and a beam current density of 10 mA / cm², to ensure that the Ru layer thickness is controlled within 10–20 nm.

[0043] S3. A protective layer is deposited on the surface of the metal reflective layer to form a protective layer.

[0044] Specifically, processes such as ion beam sputtering deposition (IBD), ion beam assisted deposition (IAD), high power pulsed magnetron sputtering (HiPIMS), microwave plasma chemical vapor deposition (MPCVD), or plasma enhanced chemical vapor deposition (PECVD) are used to deposit 2–4 nm thick diamond-like carbon (DLC), silicon carbide (SiC), or other high-performance protective layers on the Ru surface.

[0045] For example, a microwave plasma chemical vapor deposition (MPCVD) device was used, with methane and hydrogen as reactant gases, a gas flow ratio of 1:99, a microwave power of 800 W, a deposition pressure of 10 Torr, to deposit a 3 nm thick diamond-like carbon (DLC) protective layer on the Ru reflective layer surface, and the deposition temperature was controlled below 200 °C.

[0046] In addition, nanocrystalline diamond, boron-doped diamond, silicon carbide (SiC), boron carbide (B4C), silicon nitride (Si3N4), and boron nitride (BN) can be used instead of DLC. Regarding deposition methods, ion beam assisted deposition (IAD), plasma-enhanced CVD (PECVD), or high-power pulsed magnetron sputtering (HiPIMS) can also be used to deposit the diamond-like carbon protective layer. The IAD deposition parameters are: ion beam energy 300 eV, beam current density 5 mA / cm², and deposition temperature 150 °C; the plasma-enhanced CVD deposition parameters are: RF power 300 W, reaction gases acetylene and hydrogen (flow ratio 2:98), and deposition pressure 5 Tor.

[0047] It should be noted that the method provided in this embodiment is the corresponding preparation method of the product provided in Embodiment 2. Therefore, the parts that are the same as or similar to those in Embodiment 2 in this embodiment can be referred to each other, and will not be repeated in this application.

Claims

1. A soft X-ray grazing incidence mirror with an integrated protective layer, characterized in that, From bottom to top, it includes: an optical substrate, a metal reflective layer, and a protective layer that directly covers the surface of the metal reflective layer.

2. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 1, characterized in that, The material of the metal reflective layer includes at least one of ruthenium, molybdenum, silicon, nickel, or boron carbide; the thickness of the metal reflective layer is from 5 nm to 300 nm.

3. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 2, characterized in that, The material of the protective layer is selected from any one or a combination of diamond-like carbon, silicon carbide, nanocrystalline diamond, doped diamond, boron carbide, boron nitride, and silicon nitride; the thickness of the protective layer is 1 nm to 10 nm.

4. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 3, characterized in that, The surface roughness RMS value of the protective layer is less than or equal to 0.2 nm.

5. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 4, characterized in that, It also includes a transition bonding layer disposed between the metal reflective layer and the protective layer.

6. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 5, characterized in that, The material of the transition bonding layer includes Cr, Ti, Si, C or their compounds; the thickness of the transition bonding layer is 0.5 nm to 1 nm.

7. The soft X-ray grazing incidence mirror with integrated protective layer according to claim 6, characterized in that, The optical substrate is made of monocrystalline silicon, aluminum alloy, or ultra-low expansion glass.

8. A method for preparing a soft X-ray grazing incidence mirror with an integrated protective layer as described in any one of claims 1 to 7, characterized in that, include: S1, Provides an optical substrate; S2. A metallic reflective layer is deposited on the surface of the optical substrate; S3. A protective layer is deposited on the surface of the metal reflective layer to form a protective layer.

9. The method for preparing a soft X-ray grazing incidence mirror with an integrated protective layer according to claim 8, characterized in that, Following S2, the process also includes: depositing a transition bonding layer on the surface of the metal reflective layer; S3 specifically involves depositing a protective layer on the surface of the transition bonding layer.

10. The method for preparing a soft X-ray grazing incidence mirror with an integrated protective layer according to claim 9, characterized in that, In S2, the metal reflective layer is deposited using magnetron sputtering or ion beam deposition. In S3, the protective layer is deposited using ion beam sputtering, ion beam-assisted deposition, high-power pulsed magnetron sputtering, microwave plasma chemical vapor deposition, or plasma-enhanced chemical vapor deposition.

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