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.