Impact of deposition and annealing temperature on material and electrical characteristics of ALD HfO₂

Hafnium oxide (HfO₂) is one of the most promising high-k materials to replace SiO₂ as a gate dielectric. Here we report material and electrical characterization of atomic layer deposition (ALD) hafnium oxide and the correlations between the results. The HfO₂ films were deposited at 200, 300, or 370°C and annealed in a nitrogen ambient at 550, 800, and 900°C. Results indicate that deposition temperature controls both the material and the electrical properties. Materials and electrical properties of films deposited at 200°C are most affected by annealing conditions compared to films deposited at higher temperatures. These films are amorphous as deposited and become polycrystalline after 800°C anneals. Voids are observed after a 900°C anneal for the 200°C deposited films. The 200°C deposited films have charge trapping and high leakage current following anneals at 900°C. The 300°C deposited films have lower chlorine content and remain void-free following high-temperature anneals. These films show a thickness-dependent crystal structure. Annealing the films reduces leakage current by four orders of magnitude. Finally, films deposited at 370°C have the highest density, contain the least amount of impurities, and contain more of the monoclinic phase of HfO₂ than those deposited at 300 and 200°C. The best electrical performance was obtained for films deposited at 370°C.