The surface contamination of wafers, especially by particle contaminants, has been one of the major problems in the semiconductor industry since its inception. The yield on fully processed silicon wafers is inversely related to the defect density of the wafers.
One way to decrease defect density is to use efficient cleaning techniques that remove particle contaminants efficiently. Small particles are especially difficult to remove from wafers because of the strong electrostatic forces between the particles and the substrate. It is therefore imperative to find an effective way to remove particles from wafers with efficiency and without damage to the wafers.
Modern wafer manufacturing facilities use stringent contamination control protocols, including the use of cleanroom suits, latex gloves, and highly purified ventilation systems. In combination with these protocols, modern manufacturing facilities use various methods of cleaning wafers, often involving pressurized water jet scrubs, rotating wafer scrubbers, wet chemical baths and rinses, and similar systems. These processes, however, are prone to damaging the wafer.
In addition, the chemical processes have inherent dangers associated with the use of chemicals, such as sulfuric acid, ammonium hydroxide, and isopropyl alcohol.
Ultrasonic cleaning involves a variety of complex mechanisms, including cavitation, mechanical vibration, etc., depending on whether liquids are used in the cleaning process or not. A typical ultrasonic source is a plane surface that oscillates at a single frequency, producing a longitudinal wave. Vibrational energy transmitted subsequently propagates through the fluid.
From: “Efficient Cleaning Of Silicon Wafers Using Ultrasonic Technology”