When it comes to small and smallest particles on surfaces, the use of Megasonic is known for years (i.e. ultrasonic waves in the higher frequency range, usually 400kHz upwards). Most notably, if particles smaller 1 micron shall be removed, the method is quite successful. Thereby, it doesn’t damage the sensitive micro- and nanostructures of the substrate, since the cavitation bubbles are much smaller than with traditional ultrasound. Typical applications are wafer cleaning, MEMS and microstructure cleaning and etching, removal of photoresist in photo masks and many others.
The latest trends with this technology look at even higher frequencies, that is more than currently 5 MHz for even smoother cleaning and the control systems become more advanced. With future generations it will be possible to digitally control the nozzles, allowing for a wide control range and very short cycles of on/off times.
Nowadays nozzles are available in a single or dual versions, meaning, that either one frequency – e.g. 1MHz – or a combination of two frequencies – e.g. 1+3 MHz – is applied. The fully metal-free design with a housing made of PTFE (Polytetrafluoroethylene ) allows to meet the high requirements in the semiconductor industry. The medium passes by at the internal piezo ceramic which modulates the high frequency ultrasound into the water stream and is finally focused by a quartz glass nozzle outlet with a width of approx. 4mm, resulting in a Megasonic jet stream to effectively cleaning your surface.
This way, for example a 200mm/8” Si-wafer can be cleaned within 1 minute from silicon nitrite (Si3N4) and silicon dioxide (SiO2) particles, depending on cleaning media and temperature up to a PRE of >= 98%.
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