"XPS characterisation of dielectric layers for microelectronic applications"

Prof Greg Hughes

Physics Dept., Dublin City University

greg.hughes@dcu.ie

The application of XPS characterisation to two different types of dielectric layers used in semiconductor device fabrication will be presented. The high dielectric constant hafnium oxide (HfO2) is a leading candidates to replace SiO2 as the transistor gate dielectric in future device technologies. In almost all dielectric growth processes on silicon, oxide interfacial layers are formed during the deposition. The presence of an intermediate SiO2 layer between the HfO2 and the silicon is detrimental to the equivalent oxide thickness (Eot) of the oxide gate structure. This study investigates the chemical species present at the HfO2/Si interface formed by ion assisted e-beam deposition using XPS. HfO2 layers (2.5nm) were deposited on n and p type (100)silicon surfaces at 150oC from using (i) e-beam evaporation, (ii) plasma assisted e-beam evaporation with low energy Ar ion bombardment and (iii) a two stage process combining (i) and (ii). The use of low energy Ar ion bombardment during high-k film deposition has the potential for film densification during film growth.

The second application is a study investigating the fluorocarbon based plasma etching (FBPE) of low dielectric constant (ULK) carbon doped oxide (CDO) films, which have a k value of 2.4. The effects of different ion density power and ion energy power settings on the chemical composition of the fluorocarbon layer deposited during the etch process were investigated. XPS was used to analyze the chemical composition of the post-etched low-k CDO films. XPS spectra of the C1s core levels reveals that relative concentration of CFx species in the fluorocarbon films reduced as ion density source power and ion energy power levels were increased and this can be correlated with a higher etch rate and thinner fluorocarbon layers. Plasma conditions which resulted in the absence of a fluorocarbon layer showed a 50% reduction in the carbon concentration in the upper part of the low-k layer. However, the depletion of carbon from the CDO was minimized when plasma conditions resulted in the presence of a fluorocarbon layer on the CDO surface during etching of the low-k.