Research On Preparation Technology And Properties Of HfO₂ Thin Films

With the continuous advancement of science and technology,people have higher and higher requirements for the performance and size of optoelectronic devices,which has triggered an upsurge in the research of nano-film materials.Hafnium oxide(HfO₂)film has become one of materials that people pay attention to because of its high transmittance,large optical band gap,high dielectric constant and good thermal stability.How to improve the density,insulation and stability,reduce defects,and improve the optical and electrical properties has become a hotspot in the current research of HfO₂ films.The structural properties,optical properties and electrical properties of HfO₂ films are inseparable from the film preparation technology.Exploring the key technical parameters and process rules that affect the mechanical,optical and electrical properties of HfO₂ films can provide an important theoretical and experimental basis for the process control and performance adjustment of HfO₂films.In this dissertation,magnetron sputtering and atomic layer deposition(ALD)technology combined with rapid photothermal annealing(RPT)and microwave annealing(MWA)processes were used to prepare HfO₂ films with different microstructures,and the effects of different parameters on the film structure and performance were studied.ALD alternate deposition technology was used to prepare Hf Al O high dielectric gate composite film,and the film was successfully used it to make charge trap memory(CTM)devices.The main research contents are as follows:(1)The HfO₂ films were deposited by magnetron sputtering technology,and the effects of oxygen-argon ratio,sputtering time,sputtering power and substrate temperature on the structure and performance of HfO₂ films were investigated.The results show that the HfO₂ films are mainly amorphous with a small amount of monoclinic phase;the refractive index is most affected by the sputtering time;the elastic modulus and hardness increase with the increase of the sputtering time,and with the ratio of oxygen to argon;the sputtering power and substrate temperature increase first and then decrease;the residual stresses are all tensile stresses,which increase with the increase of sputtering time and substrate temperature,and decrease with the increase of oxygen-argon ratio;the leakage current has increased to varying degrees,and the sputtering power and substrate temperature have a greater impact on the leakage current.(2)The HfO₂ film was prepared by ALD technology,and the effects of deposition temperature and deposition cycle on the structure and performance of the film were studied.The results show that as the deposition temperature increases,the film thickness decreases slightly,the surface roughness first increases and then decreases,the hardness and elastic modulus decrease,the residual stress increases,and the breakdown strength and dielectric constant first increase and then decrease,the refractive index increases from 2.04 to 2.08;as the deposition cycle increases,the crystallinity of the film increases,the surface grain size,roughness and refractive index increase,the transmittance decreases,the residual stress increases slowly,and the elastic modulus,hardness,the breakdown voltage,leakage current,and dielectric constant all increase,and the optical band gap increases from 5.57 e V to 5.82 e V.(3)RPT was used to anneal the HfO₂ film.The results show that as the annealing temperature increases,the crystallinity of the HfO₂ film increases;after annealing by RPT,the average grain size of the HfO₂ film increased from 6.5 nm to 10.4 nm,its roughness gradually increased,the refractive index of the HfO₂ film remains almost unchanged,and the dielectric constant of the film decreases to 11.7.(4)The HfO₂ film was annealed using MWA technology.The results show that in the range of 300°C-600°C,compared with RPT annealing,the grain size of MWA annealed samples is significantly larger,and the grains are more uniform and dense;when the annealing temperature is 300°C,surface roughness is the largest(1.663 nm);as the annealing temperature increases,the refractive index of the film increases,the transmittance and dielectric constant decreases;under the same conditions,the overall quality of the film annealed by MWA is better than that by RPT.(5)Using ALD alternate deposition technology,the(HfO₂)_0.8(Al₂O₃)_0.2high-dielectric gate dielectric composite film was prepared,and its microstructure and photoelectric properties were preliminary studied.The results show that the film still remains amorphous and has higher transparency after annealing at 700°C.The Hf Al O film was used to instead of the traditional Si₃N₄ as the storage layer,the fabricated CTM device exhibits a relatively obvious counterclockwise hysteresis storage window;after 10⁵ write/erase operations,the storage window of the device decreases by only 8%.