Real-time monitoring of excimer laser ablation of multilayer thin films by detecting acoustic emission

Guangyu Liu; Erol C. Harvey; Dario J. Toncich; Jason P. Hayes; Choon K. Ng; Hengyi Jin; Matthew Solomon

doi:10.1117/12.469427

13 November 2002 Real-time monitoring of excimer laser ablation of multilayer thin films by detecting acoustic emission

Guangyu Liu, Erol C. Harvey, Dario J. Toncich, Jason P. Hayes, Choon K. Ng, Hengyi Jin, Matthew Solomon

Proceedings Volume 4936, Nano- and Microtechnology: Materials, Processes, Packaging, and Systems; (2002) https://doi.org/10.1117/12.469427
Event: SPIE's International Symposium on Smart Materials, Nano-, and Micro- Smart Systems, 2002, Melbourne, Australia

Abstract

In micromachining, excimer laser ablation was a key process for producing featured by removing parts of a photoresist layer. One hurdle was that the seed layer (e.g., copper), on which the photoresist was spun, was easily attacked or damaged in laser ablation of the photoresist. To overcome this, an acoustic emission transducer (AET) was coupled to the X-Y stage of an excimer laser system to acquire surface acoustic waves (SAWs) arising from pulsed laser-material interaction. The characteristics of such a process could then be investigated by analysing this feedback AE signal. Analysis of the frequency spectrum showed that there was a dominant frequency correlating with the ablation process through one material to another. Specifically, the amplitude of the dominant frequency had an abrupt change when laser beam approached the interface of two layers. The RMS values and the variance values of raw acoustic waves were also indicative of such a process. The exact number of shots machining through one material was indicated by properly calibrating such a correlation at given laser parameters. Furthermore, the etch rate of machined material could be calculated by averaging the thickness of this material with the associated number of shots. Finally, a real-time monitoring scheme of complex laser micromachining process was addressed on the basis of taking SAWs as feedback signals.

Citation Download Citation

Guangyu Liu, Erol C. Harvey, Dario J. Toncich, Jason P. Hayes, Choon K. Ng, Hengyi Jin, and Matthew Solomon "Real-time monitoring of excimer laser ablation of multilayer thin films by detecting acoustic emission", Proc. SPIE 4936, Nano- and Microtechnology: Materials, Processes, Packaging, and Systems, (13 November 2002); https://doi.org/10.1117/12.469427

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