Characterisation of ALCVD Al2O3–ZrO2 nanolaminates, link between electrical and structural properties

Abstract

Al2O3 and ZrO2 mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al2O3 and ZrO2 films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO2 on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al2O3. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al2O3 and ZrO2 films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1–1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.