| Popis: |
The semiconductor manufacturing industry is continuously trying to increase the number of electrical components that fit on computer chips in order to keep fulfilling Moore's empirical law. Therefore, recently, chip manufacturers started stacking computer chips on top of each other, creating three-dimensional stacks of integrated circuits. During the fabrication of these multi-layer structures, it is crucial that all layers are electrically connected with each other via vertical interconnects. Therefore, accurate alignment of the wafer with respect to the illumination source is crucial for the functionality of the chips. To align the wafer so-called "alignment markers" are etched in the bottom layer of the wafer. However, after a few (possibly opaque) layers, the alignment markers are no longer optically visible and therefore alignment of the wafer cannot occur. To overcome this issue, it has been proposed to use laser-induced sound waves to detect the optically buried alignment markers. An ultrashort high-intensity laser pulse illuminates the top surface of the multi-layer stack, launches an acoustic wave inside the sample. The acoustic wave travels through the multi-layer stack and reflects off the buried alignment marker. Here, the acoustic wave copies the shape of the alignment marker such that the wavefront of the acoustic wave resembles that of the alignment marker. The acoustic replica of the marker travels back to the top surface where, for a short amount of time, it deforms the surface in the same spatially periodic manner as the alignment marker. The acoustic replica of the alignment marker can then be optically detected, resulting in an indirect detection of the buried alignment marker. In this thesis we demonstrate techniques to increase the photo-acoustic signal strength. Both enhanced detection and enhanced excitation using a surface plasmon polariton resonance have been shown. We also demonstrate the ability to generate extremely high-frequency acoustic waves using thin metal layers. Furthermore, high-power laser-induced damage on nanostructured gold has been investigated to better understand the damage mechanism, which is a limiting factor in the excitation of high amplitude acoustic waves. |
