Direct Observation of Single Bubble Cavitation Damage for MHz Cleaning

It is well known that the physical force cleaning such as megasonic (MS) and ultrasonic (US) cleaning are used in FEOL (front-end-of-line) and BEOL (back-end-of-line). Recently, with scaling down below 43 nm, the influence of pattern damage by physical force methods such as MS and US irradiation has been reported. Hence, for the 2x and 3x nm node devices, it will be very difficult to apply MS cleaning for particle removal process without understanding the cavitation force. Cavitation is a complex phenomena based on bubble formation and explosion in the liquid. To control “MS cleaning” and “cavitation” induced pattern damage, many studies using “Sonoluminescence” have been reported. This method is able to demonstrate the existence of high energy fields such as cavitation throughout the megasonic field. The damage clustering distribution was investigated for the damage size and damage length in batch MS conditions using gate structure patterned [1]. In this method, it is difficult to discuss the cavitation force, quantitatively. And this method can not obtain the quantitative physical force on the wafer surface, directly. To understand “cavitation force” induced pattern damage, the observation of “cavitation force” is highlighted with “imaging films” such as blanket aluminum film and resist film, directly.