Sonic cleaning is defined as a system of removing undesired or foreign matters from an object or group of objects. This is used in a number of applications but in this article we will highlight its use in the semiconductor industry. The process involves high frequency vibration generation in a fluid medium using a transducer. Generated frequency vibrations perform a scrubbing action ideal for cleaning devices with crevices or blind holes common in semiconductors or memory disks.
Sonic Cleaning Process
1. A transducer from the outside of a tank is used to generate high frequency vibrations propagated through a fluid medium;
2. Vibrations (waves) oscillate between maximum and minimum pressure.
3. When the pressure minimum is below the vapor pressure of the fluid medium, bubbles are formed in the fluid medium. When the pressure increases to maximum pressure, the bubbles implode, sending out an intense shockwave of energy as the fluid rushes in to fill the void left by the collapsed bubble.
4. The shockwaves of energy (aka cavitation energy) become an agent for removing contaminants or foreign particles from a substrate.
Megasonics vs. Ultrasonics
There are a number of factors that can affect the intensity of the cavitation energy in a sonic process. Such factors are the following: the surface tension of the fluid medium; the distance of the substrate from the transducer. However, a critical factor is the frequency of the sonic waves. When it is categorized as Ultrasonic Cleaning Process, the frequency is less than 100kHz. With this range, bubbles have longer time to form and grow which create more cavitation energy when they collapse. On the other hand, Megasonic Processes apply frequencies from 600 to 2000 kHz producing smaller amount of cavitation energy as bubbles have less time to grow and are smaller when they collapse.
In the semiconductor industry, Ultrasonic cleaning is becoming increasingly unpopular. High cavitation energy generated in Ultrasonic process can damage substrates most especially those with sensitive components. Megasonic gentle waves can clean substrates without damaging sensitive parts.
Riza Deshpande is an Internet enthusiast who loves to share useful information on electronics and industry-related topics. Specifically she wants to share her knowledge on topics like sapphire etching and semiconductor cleaning devices.