Fluorocarbon Film Deposition Using Reactive Ion Etcher and Its Application for Physical Analysis of 3D Stacking TSV, Micro Bump and Hybrid Bonding

Through-silicon via (TSV), micro bump, and hybrid bonding are three critical structures for three-dimensional (3D) integrated circuits (IC) stacking technology. The large-scale (~urn level) feature size will be the challenge for conventional physical analysis and the development of new techniques must be considered. During the sample preparation process in focused ion beam (FIB), a protection layer deposition is necessary to avoid the damage by subsequent ion milling, especially for samples where the region of interest (ROI) is on the surface. It consumes time and only small area is capable due to the low deposition rate in FIB. Besides, the material contrast in scanning electron microscope (SEM) images is low if only metallic precursors in FIB can be selected. Therefore, a new protection layer which is non-metallic material and can be deposited over a large area is considered. This paper investigates the possibility of fluorocarbon film deposition utilizing the reactive ion etcher (RIE) as a new option for the protection layer. The precursor trifluoromethane (CHF3) is generally used for silicon oxide etching in RIE. However, the literature indicates that it can also be used for fluorocarbon film deposition under specific process conditions. The experiment results show that the fluorocarbon film can be deposited successfully in RIE using CHF3 without oxygen (O2). Lower radio frequency (RF) power and higher chamber pressure enhance the deposition rate. The profile can be observed by SEM images and energy dispersive spectroscopy (EDS) verified the existence of carbon and fluorine compounds on the surface. The fluorocarbon film is further applied as the protection layer on TSV, micro bump and hybrid bonding samples for subsequent FIB cross-sectional preparation. It not only saves the deposition time in FIB, but also provides high transparency for target navigation by top view and better material contrast for cross-sectional images. This study successfully develops a new technique for physical analysis in 3D stacking technology and creates a deposition function on the etching tool, which is a significant achievement in the physical and failure analysis laboratory.