In the production of elliptical zinc selenide (ZnSe) polishing wafers, ultrasonic cleaners are primarily employed in the post-polishing cleaning stage to remove contaminants such as polishing compound residues, cooling oil, and dust. Specifically, the cleaning process is applied at two critical nodes:

1. Post-Polishing and Pre-Coating Cleaning:

After polishing, the wafer surface retains organic contaminants including polishing compounds, cooling oils, and microscopic particles. Ultrasonic cleaning utilizes high-frequency vibrations to generate cavitation effects, efficiently stripping these contaminants in a non-contact manner, thereby providing a clean substrate surface for subsequent coating processes.

2. Post-Coating Cleaning:

During the coating process, impurities such as photoresist residues, target sputtering particles, and dust from handling may accumulate. Ultrasonic cleaning effectively removes these submicron-level contaminants, particularly achieving comprehensive cleaning around edges, grooves, and other complex geometries—eliminating blind spots inherent in manual cleaning.

System Overview

The VGT-1509FH Optical Ultrasonic Cleaning System demonstrates high compatibility with elliptical ZnSe polishing wafers, with the following specifications:

• Frequency Range: 40 kHz – 100 kHz (adjustable), balancing aggressive contaminant removal with precision cleaning.

• Temperature Control: ≤ 50°C, preventing thermal stress damage to the ZnSe wafers.

Core Advantages: Non-contact cleaning protects the coating layer; cavitation effects efficiently remove submicron particles and organic residues; excellent cleaning uniformity.

Machine Architecture

The equipment comprises 15 functional tanks, with all subsystems operating independently yet cooperatively. The cleaning section and the slow-pull plus hot-air drying section are each governed by independent electrical control systems.

Core Subsystems

1. Ultrasonic Cleaning System

• Generator: VGT's proprietary fourth-generation ultrasonic generator.

• Frequency Range: 40 kHz – 120 kHz (adjustable).

  • Low frequency (40 – 60 kHz): Suitable for removing heavy oils, cutting fluids, and stubborn contaminants.

  • High frequency (80 – 120 kHz): Suitable for submicron-level particle cleaning of precision optical components.

• Power Adjustment: 50 W – 300 W (adjustable), preventing excessive power from damaging coatings or brittle materials.

• Transducers: Equipped with internationally advanced Honda transducers, delivering strong and uniformly distributed vibration with energy conversion efficiency ≥ 95%.

• Cleaning Principle: Cavitation generates instantaneous high pressure exceeding 1,000 atmospheres, effectively stripping nanoscale particles from the workpiece surface.

2. Oscillation (Lifting) System

• Drive Method: The oscillation motor drives a linear slide via an eccentric wheel for vertical motion.

• Oscillation Speed: 3 – 10 cycles/min (adjustable).

• Functions:

  • Eliminates ultrasonic cleaning dead zones.

  • Increases relative friction between the workpiece and cleaning solution, enhancing contaminant removal efficiency.

  • Prevents lightweight workpieces from stacking and colliding under intense ultrasonic conditions.

  • Reduces bubble shielding effects, ensuring uniform ultrasonic energy distribution.

3. Multi-Stage Filtration and Circulation System

• Filtration Precision: 1 – 50 μm (adjustable).

• Configuration: Dual filtration with a pre-pump removable strainer and a post-pump filter.

• Circulation Pump: Equipped with a SANSON magnetic drive pump.

• Oil-Water Separation: The reservoir tank features a dual-chamber partitioned structure for automatic oil separation and recovery.

• Pressure Monitoring: A pressure gauge is installed before the filter, triggering an automatic alarm when clogging occurs to prompt filter replacement.

• Effectiveness: Significantly extends cleaning solution service life, reducing chemical consumption by over 30%.

4. Automatic Constant Temperature System

• Heating Power: 4.5 kW stainless steel heating tubes.

• Temperature Range: Ambient to 100°C.

• Control Method: Real-time feedback from temperature sensors, in conjunction with cooling water solenoid valves, achieves precise constant temperature control.

5. Slow-Pull Dewatering System

• Principle: Utilizing the characteristic of ultrapure water (resistivity ≥ 15 MΩ·cm) achieving maximum surface tension at elevated temperatures, the workpiece is slowly and obliquely lifted out of the water, causing the water to rapidly contract into spherical droplets and slide off, resulting in water-spot-free drying.

• Temperature Control: OMRON digital temperature control system, range ambient to 120°C.

• Tank Structure: Serrated overflow structure on the tank surface, with 10 mm insulating cotton applied externally.

• Anti-Recontamination: Exhaust apertures at the top of the tank draw away escaping water vapor, preventing it from re-condensing on the extracted products.

6. IPA Vapor Rinsing and Drying System

• Cleaning Medium: Isopropyl alcohol (IPA) vapor.

• Heating Method: Indirect heating via externally jacketed high-temperature oil, achieving uniform vapor density.

• Cooling System: Equipped with a 10 HP chiller to minimize IPA volatilization and ensure drying effectiveness.

• Function: Effectively removes water spots and polar contaminants, achieving advanced-level drying.

7. Top FFU Clean System

• An FFU (Fan Filter Unit) is installed atop the drying tank, creating a localized positive pressure zone above it.

• The majority of water vapor is extracted through the tank surface exhaust ports, effectively reducing secondary contamination of cleaned workpieces by ambient dust.

• Fundamentally improves product yield.

8. PLC Intelligent Control System

• Human-machine interface (HMI) enabling precise control over all process variables including water filling/draining, cleaning temperature, ultrasonic power, processing time, and drying parameters.

• Supports programming and storage of multiple process recipes, enabling "one-touch" switching between different cleaning protocols.

• The robotic manipulator is driven by a servo motor, offering high speed, stability, and positioning accuracy.

Structure and Materials

• Cleaning Tank Material: 316L stainless steel, corrosion-resistant and durable.

• Frame Structure: 304 stainless steel square tubing, clad with PP panels.

• Exterior Housing: 1.0 mm electro-galvanized sheet with powder coating, equipped with acrylic access doors and observation windows.

• Ultrasonic Transducer Plates: Immersible type, offering minimal energy loss and easy maintenance.

• Safety Protection: Integrated CO₂ automatic fire suppression system and overflow alarm.

• Cleaning Basket: Specially designed for optimal liquid drainage.

• Cleanliness: Equipped with a negative-pressure air filter, ensuring high cleanliness within the cleaning chamber.