Phase control of HfO2-based dielectric films for higher-k materials

In this work, attempts were made to increase the k values of the HfO2 film by transforming its structure from monoclinic to tetragonal phase. The tetragonal seed HfO2 layer and multilayer approaches were tested based on the fact that the HfO2 film deposited via atomic layer deposition (ALD) using O2 as the oxygen source induced tetragonal-phase HfO2 after the post deposition annealing (PDA) at temperatures higher than 700 °C. Both approaches, however, failed to transform the monoclinic HfO2 layer grown via ALD using O3 as the oxygen source, which suggests that the driving force for forming the thermodynamic stable phase (monoclinic) overwhelms the interface energy effect between the two different phases, which would have induced the desired transformation. As another approach, the HfO2 films were alloyed with ZrO2, which was an effective method of changing the structure from monoclinic to tetragonal. While the k values of the Hf1−xZrxO2 (HZO) film could be tuned by the Zr concentration and the PDA temperature, the increase of the PDA temperature to over 800 °C induced the compositional segregation of HZO, which largely increased the leakage current. A critical Zr concentration was found (between 50 and 70%), in which the k-value increase was quite abrupt but the increase in leakage was not very evident after the PDA at 700 °C.