Incipient amorphous-to-crystalline transition in HfO2 as a function of thickness scaling and anneal temperature

Abstract

A series of 1.4, 1.8, and 4.0nm thick HfO2 films deposited on Si(100) substrates have been measured by extended X-ray absorption fine-structure prior to anneal processing, following a standard post deposition anneal of 700°C for 60s in NH3 ambient, and following an additional rapid thermal anneal cycle of 1000°C for 10s in N2 ambient. Analysis of the second coordination shell gives clear evidence of increased ordering with increasing film thickness at each temperature. Similarly, increased ordering with increasing anneal temperature is evident for each film thickness. Although X-ray diffraction and high resolution transmission electron microscopy indicated the 1.4nm HfO2 samples to be amorphous, EXAFS has distinguished nanocrystalline from amorphous states for these films.