Larry E. Frisa

Characterization of PVD tin uniformity

Abstract The thickness and uniformity of TiNx layers, which are widely used as diffusion barriers, is routinely determined using sheet resistance measurements. However, resistivity is sensitive to stoichiometry as well as to film thickness. In this paper it is shown that: (1) the thickness of TiNx derived from resistivity measurements may be incorrect due to composition variations; (2) good resistivity uniformity does not guarantee that the thickness uniformity is also good since these characteristics are sensitive to different deposition parameters; and (3) uniformities of both resistivity and thickness of a TiNx layer can be balanced by optimization of deposition parameters. Such optimization requires simultaneous and independent measurement of the thickness and composition variations in the film. This requirement identifies ellipsometry as a natural choice for TiNx characterization. Use of multiple angle-of-incidence (MAI) ellipsometry with a blue Ar laser (458 nm) allows thickness and composition effects to be decoupled and ensures accurate measurements over 1000 A. Comparison of MAI ellipsometry, spectroscopic ellipsometry (SE), profilometry, and resistivity measurements of TiNx films on specially prepared wafers confirms the reliability and accuracy of MAI ellipsometry measurements. Variations in TiNx composition and thickness across the wafers were found to be consistent for MAI ellipsometry, SE, and profilometry measurements.

Control of PVD TiN thickness measurements

Abstract TiN is widely used as a diffusion barrier layer. Uniformity of the thickness and composition of this layer is dependent on the deposition conditions and is important for production yield. This uniformity is routinely derived from the sheet resistance measurements. Due to the correlation between composition and thickness in resistivity measurements, thus derived thickness can be incorrect. Use of the multiple angles of incidence (MAI) ellipsometry with a blue Ar + laser (458 nm) allows to decouple thickness and composition effects and ensures accurate measurements over 1000 A for TiN x ( x ≥ 1.1). Comparison of the MAI ellipsometry, spectroscopic ellipsometry (SE), profilometry and resistivity measurements of TiN layer on a specially prepared wafers confirms reliability and accuracy of the MAI ellipsometry measurement. Tracking of the composition and thickness variation of the TiN across the wafers with the MAI ellipsometry is found consistent with the SE and profilometry measurements.

Self-aligned silicide process technology for sub-0.25-μm geometries

This work compares the extendibility of titanium with pre- deposition amorphizing implant (PAI) and cobalt salicides to sub-0.25 micrometer technologies. Cobalt salicide has low sheet resistance and a tighter distribution of sheet resistances than titanium salicide with PAI for narrow linewidths. The reaction of cobalt with silicon is not affected by dopants in the silicon as the reaction of titanium is. Less cobalt need be deposited than titanium for a given sheet resistance target. Cobalt salicide requires fewer process steps than titanium salicide with PAI. Cobalt salicide has lower diodes for shallow junctions, requires a smaller thermal budget, and provides a lower contact resistances than titanium salicide. Thus, cobalt salicide process technology has better process control, is more compatible with sub-0.25 micrometer devices, and more compatible with interlayer connections than titanium salicide with PAI.