Physical and electrical characterization of Hafnium oxide and Hafnium silicate sputtered films

Hafnium oxides and hafnium silicate films were investigated as a possible r eplacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar at mosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the sil ane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temp eratures of 22 degreesC and 500 degreesC. The chemical composition of the f ilms was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by tr ansmission electron microscopy (TEM) and the electrical properties were mea sured with capacitance-voltage and current-voltage measurements using alumi num gate capacitors. TEM and electrical measurement showed that a SiO2 inte rfacial layer of about 3 nm formed at the Si interface due to the oxidizing sputter ambient. This precluded the growth of Hf based high-K films with s mall equivalent thickness. After correction for the interfacial oxide layer , the dielectric constant was found to decrease from about 21 for Hf oxide to about 4-5 for the Hafnium silicates with low Hf content (3 at. % Hf and 32 at. % Si). The optical band gap was found to increase from 5.8 eV for Hf oxide to about 7 eV for the silicate films. After annealing at 1000 degree sC followed by a 300 degreesC postmetallization anneal, negligible flat ban d voltage shift were measured on hafnium silicate films and good interface passivation was observed. However, leakage currents increased due to the hi gh temperature processing. (C) 2001 American Institute of Physics.