Selective wet etching of atomic layer deposited ferroelectric hafnium zirconium oxide and hafnium oxide thin films

The cointegration of conventional CMOS with high-k hafnium oxide (HfO2) as the gate dielectric and ferroelectric field effect transistors (FeFETs) with hafnium zirconium oxide (HZO) as the ferroelectric gate dielectric has attracted substantial interest owing to several pragmatic applications, viz., embedded nonvolatile memory, neuromorphic computation, content addressable memories, etc. Such a cointegration requires patterning on HfO2 and HZO thin films. In this study, selective wet etching of HZO and HfO2 has been investigated. The etch rates of amorphous as-deposited HfO2 and HZO films on the silicon substrate and etch resistance of the annealed HfO2 film (crystalline) in hydrofluoric solution (HF) have been examined. It is observed that upon depositing HZO film over annealed HfO2 (A-HfO2), the as-deposited HZO layer inherits the crystallinity from underneath A-HfO2 and, thus, becomes impervious to HF solution. By incorporating silicon oxide (SiO2) as a barrier layer between A-HfO2 and HZO (Si/A-HfO2/SiO2/HZO), the replication of crystallinity from underlying A-HfO2 is prevented. Therefore, the HZO film (amorphous) along with the SiO2 barrier layer can be etched in HF solution, while underneath A-HfO2 is still unaffected. These findings can be applied toward realizing a novel selective wet etching of HfO2/HZO, which is crucial for the cointegration of FeFET and traditional CMOS.