Laser incidence window anti-pollution method suitable for pulse laser deposition system

Abstract

The invention discloses a laser incidence window anti-pollution method suitable for a pulse laser deposition system, and belongs to the technical field of pulse laser deposition. According to the method, the distance between a laser incidence window and a target material is prolonged to 800-1200 mm, a matched long-focal-length focusing lens is adopted to keep the laser focusing capacity, and a metal extension pipe is connected with a vacuum cavity in a sealed mode. An extinction structure or an anti-reflection coating is arranged on the inner surface of the extension pipe to inhibit laser scattering, and the window is made of quartz glass and coated with a magnesium fluoride / silicon dioxide film. During implementation, the vacuum cavity is maintained at 10 <-3 >-10 <-6 > Pa or process gas is introduced, and the light transmittance of the laser incident window is still higher than 91% after 50 times of continuous deposition. The method effectively avoids a plasma plume main sputtering area, reduces window pollution, ensures stable laser energy density, is suitable for continuous high-quality deposition of materials such as high-temperature superconducting and oxide films, and remarkably reduces the equipment maintenance frequency.

Description

Technical Field

[0001] The invention belongs to the technical field of pulsed laser deposition, and in particular relates to a laser incident window anti-pollution method applicable to a pulsed laser deposition system. Background Art

[0002] Pulsed laser deposition (PLD) is a vacuum thin-film deposition technology commonly used to prepare high-quality thin-film materials. It is particularly suitable for preparing thin films with complex components such as oxide superconductors, functional ceramics, and thin-film batteries. Its basic principle is to focus high-energy laser pulses onto the surface of a solid target, generating a high-temperature plasma plume that deposits a thin film onto a substrate.

[0003] In conventional PLD systems, to maintain high-quality laser beam incidence on the target surface, an optical glass window is typically required to isolate the vacuum environment and configure a focusing lens system to precisely focus the laser on the target. However, during the thin film deposition process, sputtering generated by high-energy laser bombardment on the target surface diffuses with the plume, and some particles are reversely deposited on the laser incident window, causing glass contamination, reduced light transmittance, and ultimately a significant decrease in the laser energy density received by the target. To maintain stable operation of the equipment, operators must frequently remove, clean, or replace the window glass, increasing the system maintenance burden and experimental uncertainty.

[0004] Although PLD systems currently widely use a laser transmission method that uses an incident window and a lens, the following issues exist: the laser incident window is typically close to the target (e.g., 30-50 cm), making it susceptible to contamination by back-sputtered particles. Once window contamination worsens, laser transmittance decreases, leading to a decrease in the laser energy density on the target surface, affecting film composition uniformity and growth quality. Operators must frequently interrupt experiments to clean or replace the window glass, reducing work efficiency and equipment stability. Existing methods lack effective physical structural designs to completely prevent laser window contamination. These drawbacks severely limit the long-term operation and stability of PLD technology for high-quality thin film production. Summary of the Invention

[0005] The present invention proposes a laser incident window anti-contamination method suitable for a pulsed laser deposition system. The main idea is to extend the distance between the laser incident window and the target material, thereby preventing sputtering from being deposited on the window glass.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preventing contamination of a laser incident window of a pulsed laser deposition system, comprising the following steps:

[0008] Extend the distance between the laser incident window and the target to 800-1200 mm;

[0009] A focusing lens with a focal length of 800-1200 mm is used to focus the laser beam on the target surface;

[0010] The laser incident window is sealed and connected to the vacuum cavity through a metal extension tube, and a matte structure or an anti-reflection coating is provided inside the extension tube.

[0011] In the above technical solution, the distance between the laser incident window and the target material is 1000 mm, and the focal length of the focusing lens is 1000 mm.

[0012] In the above technical solution, the material of the metal extension tube is stainless steel or aluminum alloy, and the inner surface thereof is sandblasted or anodized to form a matte structure.

[0013] In the above technical solution, the anti-reflection coating is a magnesium fluoride or silicon dioxide film, which is coated on the outer surface of the laser incident window.

[0014] In the above technical solution, the focusing lens is made of quartz or calcium fluoride, and the light transmission wavelength covers 193-355nm.

[0015] In the above technical solution, the background pressure of the vacuum chamber is maintained at 10 -3 -10 -6 Pa, or introduce oxygen or nitrogen process gas.

[0016] In the above technical solution, the laser incident window is made of quartz glass with a thickness of 3-8 mm.

[0017] In the above technical solution, the transmittance of the laser incident window remains above 91% after 50 consecutive depositions.

[0018] In the above technical solution, the method is suitable for the deposition of high-temperature superconducting films, high-temperature superconducting coated conductors, iron-based superconductors or oxide functional materials.

[0019] In the above technical solution, the laser is output by an excimer laser, and the single pulse energy is 150-800 mJ.

[0020] Beneficial effects:

[0021] The present invention can significantly reduce laser window pollution without changing the original laser source and target material system, and is suitable for the transformation of various existing or newly built PLD equipment.

[0022] 1. Significantly reduced pollution: The laser window is as far as 1 meter away from the target material, effectively avoiding the main propagation area of ​​the feather sputtering, and there is almost no deposition pollution on the window;

[0023] 2. Improved energy density stability: The transmittance of the incident window remains stable, ensuring that the target always receives uniform laser energy density, improving film quality and repeatability;

[0024] 3. Reduced maintenance workload: No need to frequently replace or clean the incident window, reducing operation interruption time and improving experimental continuity;

[0025] 4. Simple structure and easy to implement: only need to add extension structure and replace lens, suitable for direct modification of existing equipment, low cost and strong adaptability;

[0026] 5. Wide application universality: This solution can be extended to multiple PLD application fields such as high-temperature superconducting films, iron-based superconductors, and oxide functional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the PLD device structure.

[0028] Figure 2 Schematic diagram of the extension tube structure.

[0029] Figure 3 It is a transmittance comparison curve.

[0030] Among them, 1 is the extension tube, 2 is the optical path, 3 is the lens, 4 is the coated flange window, 5 is the inner wall sandblasting, and 6 is the flange connector. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are intended only to explain the present invention, and the scope of protection of the present invention should include the entire contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement the entire contents of the claims of the present invention.

[0032] Example 1

[0033] like Figure 1 and Figure 2 As shown, this embodiment proposes a laser incident window anti-contamination method suitable for a pulsed laser deposition system, which adopts the following structure: Extension tube 1: Made of stainless steel, with a total length of 1000 mm, an inner diameter of 50 mm, and a wall thickness of 3 mm. The extension tube 1 is sealed with the vacuum chamber through a flange connector 6 to ensure that the vacuum degree of the chamber is maintained at 10 -3 -10 -6 The inner surface is sandblasted 5 times to form a matte structure to suppress laser scattering.

[0034] Optical path 2: After being emitted from the external excimer laser, the laser beam propagates along the axial center of the extension tube 1, passes through the lens 3 and is focused on the surface of the target material, forming a high-energy density spot with a diameter of about 1 mm.

[0035] Lens 3: Installed at the entrance end of the extension tube 1 and fixed by a precision bracket to ensure that the laser light path 2 is strictly aligned with the axis of the extension tube 1 to avoid optical path deviation.

[0036] Coated flange window 4: Located at the connecting flange between the extension tube 1 and the vacuum chamber, the window is made of 5mm thick quartz glass with an anti-reflection coating on its outer surface, which is optimized for wavelength and effectively improves light transmittance.

[0037] Flange connector 6: A standard flange is used, which is fastened to the vacuum chamber and the extension tube 1 by bolts, and is combined with a copper gasket to achieve vacuum sealing.

[0038] Overall workflow: After being focused by lens 3, the laser beam passes through a coated flange window 4 and enters the extension tube 1. Sandblasting the inner wall 5 suppresses scattered light reflections, ultimately allowing the laser beam to precisely impact the target surface. This structure extends the optical path (800–1200 mm), positioning the window away from the primary sputtering zone of the plasma plume. Combined with extinction and anti-reflection design, this significantly reduces contamination risk and ensures consistent transmittance.

[0039] Example 2: Extension tube structure design

[0040] 1. Technical parameters

[0041] Extension tube material: stainless steel (SUS 304), wall thickness 3 mm;

[0042] Total length: 1000 mm (adapting to the distance between the target and the window);

[0043] Inner diameter: 50 mm (matching the laser spot diameter);

[0044] Connection method: flange sealing (ISO-KF40 standard interface).

[0045] Internal processing:

[0046] Matt structure: the inner surface is sandblasted (sand grain size 80 mesh), roughness Ra = 1.6 μm;

[0047] Anti-reflection coating: The outer surface is coated with a magnesium fluoride (MgF2) thin film with a thickness of 300 nm (optimized for 248 nm laser wavelength).

[0048] 2. Implementation steps

[0049] 2.1. Extension tube processing:

[0050] The stainless steel tube is processed by CNC lathe to ensure the smoothness of the inner wall (Ra≤0.8 μm);

[0051] The inner wall is sandblasted to form a diffuse reflection surface to reduce the laser scattering energy.

[0052] 2.2 Coating preparation:

[0053] A MgF2 anti-reflection coating was deposited on the outer surface of the laser incident window (quartz material) using a magnetron sputtering process;

[0054] The transmittance of the coating increased from 92% to 98% at a wavelength of 248 nm.

[0055] 2.3 System Integration

[0056] Connect the extension tube to the vacuum chamber through the flange and test the sealing performance with a helium mass spectrometer (leak rate ≤ 1×10 -9 Pa·m 3 / s);

[0057] Laser optical path calibration: The CCD camera monitors the position of the light spot to ensure that the focus coincides with the target surface.

[0058] Example 3: Transmittance Test Verification

[0059] Test conditions

[0060] PLD system configuration:

[0061] Laser: KrF excimer laser (wavelength 248 nm, pulse energy 300 mJ, repetition rate 5 Hz);

[0062] Target material: YBCO superconducting target (diameter 50 mm);

[0063] Substrate: SrTiO3 single crystal substrate, heated to 700℃;

[0064] Vacuum background pressure: 5×10 -4 Pa, and oxygen was introduced (flow rate 20 sccm).

[0065] Comparison group:

[0066] Traditional method: the window is 40 cm away from the target and no extension tube is used;

[0067] The method of the present invention: the window is 800 mm away from the target material, and contains a sandblasting matt extension tube.

[0068] Benchmark transmittance measurements:

[0069] The initial light transmittance (248 nm wavelength) was measured using a spectrophotometer;

[0070] Traditional window: initial light transmittance 92%; window of the present invention: initial light transmittance 97%.

[0071] Continuous deposition experiment:

[0072] Each group performed 50 depositions (30 minutes each, 25 hours cumulatively);

[0073] The window transmittance was measured after every 10 depositions.

[0074] Table 1: Test results

[0075]

[0076] Data Analysis

[0077] like Figure 3 As shown, the traditional method: the light transmittance decreases at a rate of about 0.84% ​​per time (a cumulative decrease of 42% after 50 times), and the window needs to be cleaned every 20 times; the method of the present invention: the light transmittance decreases at a rate of about 0.12% per time (only a decrease of 6% after 50 times), and no mid-process maintenance is required.

[0078] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preventing contamination of a laser incident window of a pulsed laser deposition system, characterized in that: The following steps are involved: Extend the distance between the laser incident window and the target to 800-1200 mm; A focusing lens with a focal length of 800-1200 mm is used to focus the laser beam on the target surface; The laser incident window is sealed and connected to the vacuum cavity through a metal extension tube, and a matte structure or an anti-reflection coating is provided inside the extension tube.

2. The anti-pollution method according to claim 1, characterized in that: The distance between the laser incident window and the target material is 1000 mm, and the focal length of the focusing lens is 1000 mm.

3. The anti-pollution method according to claim 1, characterized in that: The metal extension tube is made of stainless steel or aluminum alloy, and its inner surface is sandblasted or anodized to form a matte structure.

4. The anti-pollution method according to claim 1, characterized in that: The anti-reflection coating is a magnesium fluoride or silicon dioxide film, which is coated on the outer surface of the laser incident window.

5. The anti-pollution method according to claim 1, characterized in that: The focusing lens is made of quartz or calcium fluoride, and its light transmission wavelength covers 248-355 nm.

6. The anti-pollution method according to claim 1, characterized in that: The background pressure of the vacuum chamber is maintained at 10 -3 -10 -6 Pa, or introduce oxygen or nitrogen process gas.

7. The anti-pollution method according to claim 1, characterized in that: The laser incident window is made of quartz glass with a thickness of 3-8 mm.

8. The anti-pollution method according to claim 1, characterized in that: The light transmittance of the laser incident window remains above 91% after 50 consecutive depositions.

9. The anti-pollution method according to claim 1, characterized in that: The method is suitable for depositing high-temperature superconducting films, high-temperature superconducting coating conductors, iron-based superconductors or oxide functional materials.

10. The anti-pollution method according to any one of claims 1 to 9, characterized in that: The laser is output from an excimer laser, and the single pulse energy is 150-800 mJ.

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