Electromigration Reliability in Nanoscale Cu Interconnects

Electromigration behavior in Cu damascene wires was studied for various Cu grain struc-tures. The grain size was modulated by Cu linewidth and thickness, and by adjusting the wafer annealing process step after Cu electroplating and before Cu chemical mechanical polishing. A larger variation of Cu grain size between the samples was achieved on CMOS 65 nm node tech-nology than previous nodes which was due to the finer line width and thinner metal thickness. The Cu lifetime and mass flow in samples with bamboo, near bamboo, bamboo-polycrystalline mixture, and polycrystalline grain structures were measured. The effects of a Cu(2.5 wt.% Ti) alloy seed, Cu surface pre-clean, and selective electroless CoWP deposition techniques on Cu electromigration were also observed and a significantly improved Cu lifetime was found. The electromigration activation energies for Cu in Cu(Ti) alloy, along Cu/amorphous a-SiCxNyHz in-terface and grain boundary were found to be 1.3, 0.95 and 0.79 ± 0.05 eV, respectively. In addition the Cu line size effect on the Cu conductivity for Cu area less than 4×104 nm2 was found to be a linear function of the Cu line area.

Quanto: a Rietveld program for quantitative phase analysis of polycrystalline mixtures

Quantitative determination of phase abundance in a multicomponent polycrystalline mixture is a basic goal in materials characterization. Because of several advantages compared with traditional techniques, the Rietveld method has been increasingly applied to this task. Further progress in this direction would be to carry out the analysis automatically. The new Rietveld packageQuantois devoted to the automatic estimation of the weight fraction of each crystalline phase in a mixture. The amorphous content can be estimated by means of the internal-standard method. Corrections for preferred orientation and microabsorption effects are available. A user-friendly graphical interface facilitates interaction. A data bank including several organic and inorganic phases is supplied with the program.

The Effect of Microstructure and Processing Procedures on the Resistivity of Co-Sputtered W-Si Layers on GaAs Substrates

ABSTRACTThe relationship between microstructure, composition, resistivity and processing procedures of W-Si layers on (100) GaAs was examined for both “as deposited” specimens and specimens annealed at temperatures between 100°C and 1000°C. TEM, EDAX, SIMS, AUGER and four point probe resistivity measurements were employed.The layers, exhibiting a columnar growth structure typical of sputter deposition, are amorphous below ≈ 800°C. At 700°C, the formation of pits, attributed to the outdiffusion of Ga and As into the W-Si layer, is observed at the W-Si/GaAs interface. The Ga and As outdiffusion was confirmed for temperatures above 700°C. The layers annealed between 800°C and 1000°C consist of a polycrystalline mixture of αW, βW and W5Si3 with coarse particles, thought to be W5Si3 precursors, formed along the W-Si/GaAs interface and protruding into the substrate. As the frequency of these protrusions increases with increasing temperature, the resistivity of the W-Si layers decreases.Both the composition and the resistivity of the W-Si thin films are affected by the processing procedure. The Si/W ratio of the W-Si thin films decreases whilst their resistivity significantly increases as a result of etching away the Si3N4 capping layer using HF. It is thought that this is due to the removal of Si-oxides formed within the layer during the W and Si sputtering. The decrease in the Si/W ratio and the increase in resistivity are not observed if an A1N capping layer is used.

Kinetics of the Icosahedral -to- Approximant Transformation in Al-Cu-Fe

The kinetics of an icosahedral to approximant phase transformation were investigated in cast alloys in the composition range Al(63.65)Cu(20–25)Fe(12–15). Perfect icosahedral crystals are stable in the temperature range below the peritectic melting temperature and above approximately 700°C, below which they transform to a textured polycrystalline mixture of small microcrystals of an icosahedral approximant. The transformation is isocompositional and does not appear to occur by nucleation and growth. The kinetics of the transformation under continuous cooling and isothermal conditions were investigated using conventional and high resolution electron microscopy. The transformation is reversible, takes place over a range of compositions, temperatures and times and results in distinctive strain contrast in the electron microscope.