Experimental study of the boron redistribution in bilayer films silicon-based by SIMS technique
The present work focuses on the study two sets of films bilayers obtained by Low Pressure Chemical Vapor Deposition (LPCVD), for use as material to MOS gate structures (transistors, chemical sensor ISFET, etc.). The first series of films are composed by two layers, silicon amorphous un-doped layer (poly1) and polysilicon boron doped in situ (poly2). The second series are constituted by boron doped polysilicon (polySi) and nitrogen doped polysilicon (NIDOS). These films (poly1/poly2 and polySi/NIDOS) are annealed in tem the same conditions of deposit and annealing. The boron concentration is monitored by secondary ion mass spectrometry (SIMS). The superposition between the SIMS profiles of poly1/poly2 and polySi/NIDOS films have shown that low thermal annealing budget at 600°C/2h, ensures long boron redistribution to the interface poly2/SiO2. At the contrary, a high thermal budget the second layer (poly2) was recristallyzed and reached to the doped oxide. For polySi/NIDOS films, SIMS profiles confirmed the presence of low nitrogen (X = 1%) which can effectively suppress the boron penetration at the interface NIDOS/SiO2.
Ambient and dopant effects on boron diffusion in oxides
Diffusion of boron from ion implanted polycrystalline silicon source through 12.5 nm oxides was measured as a function of annealing ambience and doping concentrations of phosphorus or arsenic in the polycrystalline silicon. For comparison, boron ion implanted into 500 nm oxides was also investigated. In both cases, annealing in forming gas (90% N2, 10% H2) increases the diffusion rate of boron over that in nitrogen and the rate increase is the result of a large increase in the pre‐exponential term. Diffusion of ion implanted boron in oxides is much slower than that from an ion implanted polycrystalline silicon source. The lowering of the rate is the result of the five orders of magnitude decrease in the pre‐exponential term, even though concurrently there is also a decrease in the activation energy. Co‐doping of polycrystalline silicon with either phosphorus or arsenic lowers the pre‐exponential term by approximately 10%. Therefore, we conclude that boron diffusion through oxides is entropy dominated.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.