AN ANNEALING STUDY OF La_2O_3-SiO_2 AND ZrO_2-SiO_2 GATE DIELECTRICS

摘要

The crystallization behavior and thermodynamic stability of candidate replacement dielectrics from the La_2O_3-SiO_2 and ZrO_2-SiO_2 (or HfO_2-SiO_2) systems have been studied. We emphasize the differences in behavior between these systems. We note that the La-based dielectrics are somewhat more resistant to crystallization, for a given SiO_2 concentration. We also note that the Zr and Hf systems are characterized by phase segregation accompanying crystallization. This phenomenon strongly impacts the resultant dielectric microstructures, and contrasts with the La-based system. We have studied the oxidation (of the Si interface) and reduction (of the dielectric) for the systems, and note that all compositions are susceptible to both reduction and oxidation. Each dielectric composition, if no oxygen barrier is introduced, has only a narrow window of pO_2 and temperature conditions within which both oxidation and reduction is limited. By paying attention to these conditions, it has been possible to process the dielectrics at temperatures around 1000C while maintaining acceptable capacitor properties. However, it should be noted the oxygen activities required fall within a smaller range than currently utilized in CMOS processing, and furthermore, crystallization does occur at these temperatures.