The reaction behavior of the Interfacial Layer (IL) in an HfAlO
x/SiO
2 and SiON structure during a post deposition annealing (PDA) in an N
2-diluted oxygen ambient was examined. After a PDA at 1,050
oC for 1 s, the 0.7 nm-thick IL was reduced if the O
2 concentration was lower than 0.02%. The reduction of the IL led to the formation of defects and the Si migration to the HfAlO
x surface, resulting in an increase in the C-V hysteresis. The amount of Si migrated to HfAlO
x surface decreases with increasing the O
2 concentrations during PDA and changing the interfacial layer from SiO
2 to SiON. Even if SiON is used for interfacial layer, the decreasing of mobility was caused by nitrogen which stay in interface between SiON and substrate. Optimization of nitrogen in SiON interfacial layer is necessary. Electron and hole mobility of 75/77% of that for SiO
2 were obtained for HfAlO
x/SiON with EOT = 1.6 nm because of optimization of PDA O
2 concentration and nitrogen profile in SiON.
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