Common wafer holding methods in wafer handling mainly include mechanical clamping, mechanical vacuum adsorption, and Bernoulli chucks. For non-standard parts such as air path connectors, orifice plates, and floating support rings used in Bernoulli chucks, Hansheng Automation provides single-piece or small-batch precision machining based on customer drawings.
I. Common Wafer Holding Methods
Mechanical Clamping
Principle: Uses support plates and telescopic rods to clamp the wafer with materials such as silicone.
Advantages: Suitable for larger wafers, can quickly clamp the wafer for processing, and improves production efficiency.
Disadvantages: Relatively lower stability and precision, and may cause certain mechanical damage to the wafer.
Mechanical Vacuum Adsorption
Principle: Uses a vacuum pump to seal the wafer surface with the chuck and form negative pressure, thereby fixing the wafer.
Advantages: Provides stable adsorption force to ensure wafer stability during processing; suitable for wafers of different sizes and types with high flexibility; relatively simple maintenance.
Disadvantages: If vacuum fails or operation is improper, the wafer may be damaged; may not be the best choice for extremely fragile or ultra-thin wafers.
Bernoulli Chuck
Principle: Based on the Bernoulli principle, high-speed airflow creates a low-pressure area on the chuck surface, generating adsorption force and enabling non-contact wafer holding.
Advantages: Almost no physical contact between the wafer and the chuck, reducing potential mechanical damage and contamination; inert gas can be used as the air cushion, allowing stable operation under various temperature and chemical environments; airflow can be adjusted to accommodate wafers of different sizes and shapes.
Disadvantages: Higher cost; higher requirements for wafer flatness.
II. Detailed Explanation of Bernoulli Chucks
1. Working Principle of Bernoulli Chucks
The Bernoulli chuck is a non-contact chuck based on the Bernoulli principle. The principle states that in fluid flow, an increase in fluid velocity leads to a decrease in fluid pressure. During operation, externally supplied compressed air flows at high speed through the small gap between the chuck and the object surface. As the airflow velocity increases, the air pressure in the gap drops, forming a low-pressure area between the chuck and the object. The surrounding air at higher pressure pushes the wafer toward the low-pressure area, achieving non-contact adsorption.
2. Application of Bernoulli Chucks in Single-Wafer Cleaning Equipment
In fully automatic single-wafer cleaning equipment, large and thin wafers are sensitive to clamping force, and wafers have different warpage levels, placing higher demands on gripping and transfer. The Bernoulli chuck plays a major role here. It uses blown vacuum rather than suction vacuum to grip the wafer. When compressed air enters the workpiece and blows toward the wafer, it rapidly spreads radially from the center of the disc, making the airflow above the wafer much higher than below it. According to the Bernoulli principle, increased flow velocity leads to lower pressure, so the pressure under the wafer is higher than above it, allowing the chuck to hold the wafer without contact. This non-contact gripping method effectively avoids wafer breakage and contamination during handling.
3. Advantages of Bernoulli Chucks
Non-contact gripping reduces physical contact between the wafer and the chuck, lowering the risk of mechanical damage and contamination. It is highly adaptable, with adjustable airflow for wafers of different sizes and shapes. It offers good stability under various temperature and chemical environments. The simplified design also contributes to long service life and reduced maintenance downtime.
4. Limitations of Bernoulli Chucks
Cost is relatively high. It also requires good wafer flatness; insufficient flatness may affect adsorption performance.
In summary, the common wafer holding methods each have advantages and disadvantages. As a non-contact adsorption technology, the Bernoulli chuck has significant advantages in reducing mechanical damage and contamination, and is particularly suitable for applications with high requirements for wafer flatness, though its cost is higher. In practical applications, the appropriate wafer holding method should be selected based on specific needs and conditions.
