Influence of low energy ion irradiation on oxygen deficient hafnium oxide (HfO2) thin films

Changes in various properties of Hafnium Oxide (HfO2) high k-dielectric thin films, grown on Silicon (Si) substrate by 500 cycles and 1000 cycles of Atomic Layer Deposition (ALD) technique; having nominal thickness of around 50 nm and 120 nm were studied as a function of Low Energy Ion Beam (LEIB) irradiation. In this article, we have attentively studied (i) 350 keV Xe for 50 nm films and (ii) 275 keV Ne and 450 keV Kr for 120 nm films LEIB irradiation defect induced modifications in HfO2 thin films. The pristine and irradiated films were studied by various techniques. The variation of grain size as a function of low energy ion irradiation was measured by Field Emission Scanning Electron Microscopy (FESEM) while the substantial Root Mean Square (RMS) surface roughness and particle size distribution was measured by Atomic Force Microscopy (AFM). Structural changes studied using X-Ray Diffraction (XRD) revealed the change of state from amorphous to crystalline nature of the films for thickness < 100 nm while the samples with thickness > 100 nm changed from monoclinic crystal phase to orthorhombic. Systematic X-Ray Photoelectron Spectroscopy (XPS) study showed that deposited films are highly oxygen deficient (HfOx<2) and post-irradiation of films at high energy, having thickness > 120 nm, the films underwent complete oxidation leading to the formation of a new carbon compound CxHfyOz. Relative study of < 100 nm and > 100 nm films showed that, the 50 nm films has low resistivity compared to 120 nm thick films. So, films > 100 nm can be used in a Metal Oxide Semiconductor (MOS) device to reduce the leakage current.