As silicon microscopic circuits and structures shrink in size, the elimination of contaminants from becomes increasingly important. When silicon wafer cleaning is effective, it removes particles as small as 0.1 µm to prevent them from affecting the silicon fabrication process. Traditional wafer cleaning with chemicals may leave some of the smallest particles in place and production line output quality can suffer. The semiconductor components produced may be of inferior quality or fail completely. Megasonic cleaning with sound waves in the MHz range generated in a water cleaning solution can remove particles down to 0.1 µm in size and improve cleaning performance.
How the Megasonic Process Cleans
The Megasonic Cleaning System consists of a high-frequency generator, transducers that convert the electric signal from the generator to sound waves in the water, and a cleaning tank to hold the cleaning solution and the silicon wafers. Sound waves in the MHz frequency range travel through the cleaning liquid and generate microscopic cavitation bubbles in the low-pressure wave troughs. When the bubbles collapse in the high-pressure wave peaks, they produce tiny jets of water.
When the bubbles collapse near a wafer, the resulting jets hit the silicon and dislodge any particles adhering to the surface. The particles are carried away by the water currents and the microscopic bubbles are so numerous that all surfaces are cleaned. The bubbles and the cleaning effect are present throughout the liquid and they penetrate into holes, crevices and microscopic structures, cleaning completely.
In addition to cleaning silicon wafers and removing microscopic particles more effectively than traditional cleaning methods, Megasonic Cleaning provides several other benefits over the use of chemicals. The rise in output quality is accompanied by lower costs, a safer process environment and shorter process times.
When a semiconductor fabrication facility uses fewer chemicals for cleaning wafers, costs decrease. The facility has to purchase smaller amounts of chemicals, storage costs are lower and costs for disposal are less. Depending on the process, Megasonic Cleaning may allow a facility to eliminate certain chemicals completely, resulting in even higher savings.
The Megasonic Cleaning process is safe and environmentally friendly. The megasonic waves and the cleaning solution do not present any danger to equipment or operators who can set a timer and come back when the cleaning process is finished. The water-based solution is not toxic and does not require special disposal. Compared to chemical cleaning, the storage and handling of Megasonic cleaning materials is safe and easy, power consumption is lower and less water is required.
Modutek’s Megasonic Cleaning System
The Modutek Megasonic Cleaning System was developed together with ultrasonic technology leader Kaijo Corporation to reflect the specific demands of silicon wafer cleaning. The high operating frequency in the MHz range ensures gentle but effective cleaning of delicate materials without pitting the silicon surface or damaging the silicon wafer structures.
Modutek’s partnership with Kaijo lets the company offer an integrated system that features the Quava Megasonic generator and transducer within Modutek’s cleaning baths. Megasonic’s baths are available in the indirect heating MSI series that can heat the cleaning solution up to 140 degrees centigrade while the direct heating MSD series can heat the cleaning solution up to 70 degrees centigrade. Both baths are ideal for submicron particle removal with a high power density and high efficiency.
The Megasonic System is available with 600 W, 900 W and 1200 W power ratings at the standard 950 kHz frequency. Frequencies of 200 kHz, 430 kHz, 750 kHz and 2 MHz are also available for applications that require the more robust cleaning action from the lower frequencies or for very delicate components at the higher frequency. In any case, Modutek can advise customers to make sure they select the ideal Megasonic Cleaning configuration for their specific silicon wafer cleaning applications.
