The following is a detailed explanation of the use of the dual angle evaporation system:
1、 Core parameter setting and control
Dual tilt angle collaborative adjustment mechanism
One evaporation stage: A small angle (5 ° -20 °) is used to achieve tilted orientation of liquid crystal molecules, which requires precise control of the angle between the evaporation beam and the substrate to ensure that the long axis of the molecules is aligned along the evaporation direction.
Secondary evaporation stage: After rotating the substrate by 90 °, a planar orientation is formed at a larger angle (20 ° -45 °). This process requires synchronous adjustment of the tilt angles of both axes to avoid uneven pre tilt angles caused by azimuth deviation.
Dynamic compensation algorithm: For large-area coating, integrated real-time angle sensor feedback is used to correct mechanical drift through PID control, ensuring an angle accuracy of ± 0.5 °.
Temperature and vacuum joint control
Segmented heating strategy: In the initial stage, low-speed evaporation (<100 ℃) is used to remove adsorbed water vapor. In the main evaporation stage, the boiling point of the material is raised to ± 5 ℃, and after the end, the temperature is lowered to below the melting point to prevent agglomeration.
Vacuum gradient management: Pre treat with vacuum degree ≤ 5 × 10 ⁻⁴ Torr for degassing, maintain 10 ⁻⁶ -10 ⁻⁷ Torr during the evaporation stage to reduce collision scattering, and combine with helium mass spectrometer leak detector for real-time monitoring of leakage rate.
2、 Standardization of operating procedures
Substrate loading and positioning
Magnetic adsorption is used to fix the substrate, and a laser interferometer is used to calibrate the flatness (error<2 μ m). The curved base needs to be matched with a specialized fixture with a curvature radius of ≥ 50mm to avoid stress deformation.
Multi stage vapor deposition execution
Pre cleaning: Plasma bombardment of the substrate surface for 5 minutes reduces the contact angle to<10 ° to improve adhesion.
Dual axis linked vapor deposition: The first layer of SiO ₂ is deposited diagonally at a rate of 8 Å/s (θ ₁=70 °), generating a pre tilt angle of 5 ° -35 °; The second layer of metal electrode rotates the substrate and is evaporated at θ ₂=60 ° to construct a TN box shaped molecular arrangement.
In situ annealing: Immediately start the temperature control module after the evaporation is completed, cool to room temperature at a rate of 5 ℃/min, and release residual stress.
3、 Common problem solutions
Uniformity optimization
Shadow effect suppression: Gaussian curvature evaporation source (K>0) is used to increase the edge deposition rate by 30%, offsetting the center thin edge thick defects caused by traditional planar sources.
Planetary carrier motion compensation: Set the ratio of revolution speed to rotation speed to 3:1 to eliminate the "comet tail" stripes.
Quick fault diagnosis
Film cracking alarm: Immediately pause vapor deposition, check the grounding resistance of the substrate table (normally<1 Ω) and the response time of the baffle opening and closing (≤ 0.2s).
Sudden drop in vacuum degree: sequentially detect the compression amount of the sealing ring (recommended Shore hardness 70 ± 5), the closing clearance of the gate valve (<0.1mm), and rule out the possibility of atmospheric diffusion.
4、 Maintenance and upkeep standards
routine maintenance
Use a dust-free cloth dipped in ethanol daily to clean the residue inside the chamber, with a focus on wiping off the carbon deposits on the blocking parts.
Replace the pump oil every week and record the vacuum recovery time (standard ≤ 30 minutes to reach 5 × 10 ⁻⁴ Torr).
Periodic calibration
Quarterly maintenance: Use a quartz crystal oscillator to calibrate the rate sensor, and replace the probe when the deviation exceeds ± 5%.
Annual overhaul: Disassemble the rotary joint to clean the oxide, and update the thermal conductive silicone grease layer (thickness 0.2mm).
The above are the core points of the dual angle evaporation system. Strictly following these technical specifications is necessary to fully leverage the performance advantages of the equipment and promote the progress of optical component manufacturing processes.