Paper EM-FrM2
Effect of Annealing Temperature on the Chemical Composition, Chemical Depth Profile,and Film Morphology of High-k Gate Dielectrics by AR-XPS and AFM

Friday, October 19, 2007, 8:20 am, Room 612

Hf-based films are alternative gate dielectric films to SiON because of their high dielectric constant and their relatively wide band gap. These films should stay amorphous after activation annealing at T>1000 °C because grain boundaries may serve as paths of dopant diffusion. Pure HfO2 is not a good gate dielectric film because it crystallizes at a low temperature of 500 °C. In this work the effect of different annealing temperatures on chemical composition, and atomic depth profile of HfSiON films is studied by AR-XPS, AFM and TEM. HfSiON films with different N concentrations were annealed at temperatures ranging from 500C to 1050C. These films are thermally stable up to T=1000°C. AR-XPS analysis shows that Hf concentration remains constant, while the N concentration increases linearly with decoupled plasma nitridization power (DPN). All the samples show one layer of HfSiON on Si substrate with thickness of about 20Å. The AR-XPS depth profile shows that Hf and N are evenly distributed in the films, and carbon is observed as a contaminant element on the film surface. The film roughness by AFM is RMS=2Å. The temperature of T=1050C is most commonly used in the CMOS processes, because it is the temperature of Si recovery after dopants implantation. At this temperature the film should remain amorphous and thermodynamically stable. The set of films previously studied, was then annealed at T=1050C. AR-XPS analysis shows that the concentrations of both Hf and N drop significantly, while the N concentration still increases as the DPN power increases. The resulting films consist of two stacked layers of SiOx/HfSiON/Si whose total thickness ranges between of 24Å and 36Å. The AR-XPS depth profile shows that Hf is closer to the Si interface, N is buried in the middle of the film and a significant fraction of carbon is present both in the surface and in the bulk. These AR-XPS results can be explained only if crystallization occur. TEM images show the appearance of micro islands. AFM analysis shows that the film roughness increases by a factor of 20 compared to that of the film annealed at T=1000C. Based on the high film roughness, we conclude that AR-XPS technique on films at T=1050C produces meaningless results in term of composition and depth profile data. However, increasing the amount of N in the film prevents film crystallization. These films show a relative low roughness, and the AR-XPS results are similar to those of the samples annealed below T=1000C.