High-Throughput Growth And Structural Controlling Of HfO₂ Films By Laser Chemical Vapor Deposition

The advantages of Hafnium Oxide（HfO₂）,such as a high permittivity,sufficient breakdown field strength,low thermal conductivity,high melting point and hardness,have facilitated recent advances in high-density microchips.HfO₂ films were expected to realize the manufacturing of composite dielectric layers with abilities of dielectric,heat,as well as wear resistances.However,HfO₂ films have disadvantages of a low growth rate,poor controllability,high preparation cost,and lack of systematic research on the internal relationship between the microstructure and growth mechanism.This study explored the change law of the microstructure and properties of HfO₂ films at different deposition conditions via the laser chemical vapor deposition（LCVD）.Ulteriorly,the high-throughput growth with a large gradient temperature field（1000K/cm）was introduced to obtain the evolution of growth models.Finally,the high-throughput growth and structure control of HfO₂ films were obtained,to improve the experimental efficiency and optimize experimental conditions.Firstly,Hf（acac）₄ was selected as the precursor to prepare HfO₂ films on Si（100）substrates.The laser distribution of high-throughput LCVD was adjusted to achieve a stable control of the large gradient（1000 K/cm）temperature field.When T_dep=1600K,R_dep reached the maximum value of 362μmh^-1.The results of FWHM andηshowed that the crystallinity was the highest at 1400 K,but R_dep was lower(61.8μmh^-1).According to TEM observation,the top surfaces of the vein-like structure at 1300 K were（002）and（111）planes,which were perpendicular to the growth direction.The top faces of the pyramid-like structure at 1400 K were（111）and（111）planes,corresponding to the sides of the square cone.When T_dep=1300～1400 K,E_a was 160～220 k J/mol,which fitted the laminate-island growth model.When T_dep=1500～1600K,E_a decreases to 80～100 k J/mol,which conformed to the island growth model.Secondly,the effects of the deposition temperature,total pressure and time on the structures and properties of HfO₂ films were investigated.When T_dep=1400 K and P_tot=100 Pa,the deposition rate reached 174μmh^-1,which was 10²-10³ times higher than other CVD methods.Meanwhile,it has the highest dielectric constant,breakdown field strength,fracture toughness,volume density and lowest porosity.According to TEM observation,a large number of twin boundaries and stacking faults were observed along the[111]direction,and the defect density was 1×10³μm^-2 approximately.Finally,the evolution law of the growth mechanism under different deposition parameters was explored.ln R_dep showed an Arrhenius lineal relationship with T_dep^-1.When T_dep<1200 K,the film displayed a needle-like structure.The apparent reaction activation energy E_a was 230～260 k J/mol,and the reaction process manifested as the chemical reaction regime.When T_dep=1200～1400 K,the surface morphology changed into an angular spindle structure.E_a was 115～140 k J/mol,and the reaction process manifested as the mass transfer regime.When T_dep>1400 K,due to the precipitation of t-HfO₂ and airflow etching on the substrate surface,R_dep decreased with the increase of T_dep.The film changed into a granular or semi-spherical structure with a smooth surface.