Megasonic cleaning system with buffered cavitation method
An acoustic energy cleaning system and method which fosters micro-bubble formation for effective cleaning while buffering micro-bubble growth which would otherwise damage the wafer. In one embodiment, the invention includes combining a first frequency signal and a second frequency signal having a positive amplitude bias component so as to form a combined signal. The combined signal, which has a positive amplitude offset, is applied to a transducer system that converts the combined signal into acoustic waves. The acoustic waves can be applied to the object to be cleaned in a cleaning fluid.
1 . A method for cleaning an object comprising:
a) combining a first frequency signal and a second frequency signal having a bias component so as to form a combined signal;
b) applying the combined signal to a transducer system, the transducer system converting the combined signal into acoustic waves, the acoustic waves having regions of positive pressure greater than without the bias component added; and
c) applying the acoustic wave to the object to be cleaned in a cleaning fluid.
2 . The method of claim 1 further comprising adjusting at least one of a period and an amplitude of the second frequency signal to increase micro-bubble formation.
3 . The method of claim 1 further comprising adjusting at least one of a period and an amplitude of the bias component to buffer micro-bubble growth.
4 . The method of claim 1 wherein the combined signal is positively biased.
5 . The method of claim 1 wherein the combined signal is unbalanced.
6 . The method of claim 1 wherein step a) further comprises combining the first frequency signal, the second frequency signal and a third frequency signal to form the combined signal, the third frequency signal having a frequency that is less than the frequency of the first signal.
7 . The method of claim 1 wherein the second frequency signal is a quasi-direct voltage bias signal.
8 . The method of claim 1 wherein the first frequency signal has a megasonic frequency and the second frequency signal is a quasi-direct voltage bias signal.
9 . The method of claim 8 wherein step a) further comprises combining the first frequency signal, the second frequency signal and a third frequency signal to form the combined signal, the third frequency signal having an ultrasonic frequency.
10 . The method of claim 1 wherein the second frequency signal has only a positive amplitude.
11 . The method of claim 1 further:
wherein step a) further comprises combining the first frequency signal, the second frequency signal and a third frequency signal to form the combined signal, the third frequency signal having a frequency that is less than the frequency of the first signal;
adjusting the timing of the first frequency signal through a first trigger;
adjusting the amplitude of the first frequency signal through a first preamplifier; and
buffering micro bubble growth while increasing micro bubble formation through at least one of the adjustment of the first trigger and adjustment of the first preamplifier.
12 . The method of claim 11 wherein the buffering is accomplished in real-time.
13 . The method of claim 1 further:
wherein step a) further comprises combining the first frequency signal, the second frequency signal and a third frequency signal to form the combined signal, the third frequency signal having a frequency that is less than the frequency of the first signal;
adjusting the timing of the third frequency signal through a second trigger;
adjusting the amplitude of the third frequency signal through a second preamplifier; and
buffering micro bubble growth while increasing micro bubble formation through at least one of the adjustment of the second trigger and adjustment of the second preamplifier.
14 . The method of claim 1 wherein the object being cleaned is a semiconductor wafer.
15 . A method for cleaning an object comprising:
a) combining a first frequency signal and a second frequency signal having a positive amplitude bias component so as to form a combined signal;
b) applying the combined signal to a transducer system, the transducer system converting the combined signal into acoustic waves; and
c) applying the acoustic wave to the object to be cleaned in a cleaning fluid.
16 . The method of claim 15 further comprising adjusting at least one of a period and an amplitude of the second frequency signal to increase micro-bubble formation.
17 . The method of claim 15 further comprising adjusting at least one of a period and an amplitude of the bias component to buffer micro-bubble growth.
18 . The method of claim 1 wherein the second frequency has only a positive amplitude.
19 . A method for cleaning an object comprising:
generating a combined signal including at least a first megasonic component and a second megasonic component, the second megasonic component of lower frequency than the first megasonic component;
applying the combined signal to a transducer system, the transducer system converting the combined signal into acoustic waves in a cleaning fluid; and
the combined signal creating an acoustic longitudinal wave having regions of positive slope greater than without the bias component added, to clean the object with the acoustic waves.
20 . The method of claim 19 , further comprising adjusting at least one of a period and an amplitude of the second megasonic component, to increase micro-bubble formation.