Thin-film adhesion: A comparative study between colored picosecond acoustics and spontaneous buckles analysis

Abstract

This paper presents some quantitative measurements of the adhesion energy of thin WTi films deposited on Si substrate. Two different techniques are applied to the same sample series. One is a mechanical test based on the analysis of spontaneously formed defects. The second is based on acoustic waves whose reflection at the interface between the thin-film and the substrate is sensitive to the adhesion. An excellent correlation is obtained between both approaches: the adhesion energy measured by buckles analysis and acoustic reflection coefficient measured by picosecond acoustics. The acoustic approach offers several advantages among which a nondestructive character, a compatibility with complex stacks and a sensitivity to detect adhesion anomaly even if no defect is formed.