Preparation And Application Of PEALD-based Al₂O₃ Films

In recent years,the semiconductor industry has developed rapidly.The traditional gate dielectric material SiO2 can no longer meet the trend of "proportional shrinking" of microelectronic devices.Using high-κ materials with high dielectric constant,wide bandgap,high stability,and good compatibility with silicon to replace SiO2 is an effective way to improve device performance.Aluminum oxide(Al2O3)is a high-κ film with good performance.Its dielectric constant is close to 9,and it has stable thermal and chemical properties,good interface with silicon,easy preparation,and low cost.It is a good gate dielectric layer and has broad application prospects.Plasma-enhanced atomic layer deposition(PEALD)is a thin film deposition technique that uses plasma-assisted deposition on the basis of atomic layer deposition(ALD).It has advantages such as low deposition temperature,adjustable parameters,and in-situ plasma treatment.This paper focuses on the process parameters of PEALD and studies the effects of different process parameters on the properties of Al2O3 films and their applications in thin film transistors(TFTs)and charge trapping memories(CTMs).The specific research results are as follows:(1)The effects of PEALD process temperature and oxygen plasma pulse time on the properties of Al2O3 films.The PEALD process temperature and oxygen plasma pulse time can affect the properties of Al2O3 films.This experiment studied the properties of Al2O3 films prepared by PEALD at different process temperatures(50℃-250℃)and different oxygen plasma pulse times(5 s-40 s),and characterized their electrical parameters through MOS capacitors of Al/Al2O3/p-Si structure.The study found that the process temperature had little effect on the dielectric constant of Al2O3 films.Al2O3 films prepared at different temperatures all contained negative oxide layer charges.As the deposition temperature increased,the content of negative charge defects in the Al2O3 film or at the interface gradually decreased,and the breakdown field strength gradually increased to above 11 MV/cm.Al2O3 films prepared under different oxygen plasma pulse times all contained negative oxide layer charges.As the oxygen plasma pulse time prolonged,the border trap charge in the Al2O3 film gradually increased,and the hysteresis voltage of the MOS capacitor gradually increased.(2)The application of Al2O3 films prepared under different PEALD process parameters in TFTs.In order to explore the application of Al2O3 films in TFTs,the gate control capability of Al2O3 films deposited under different PEALD process conditions was studied,and Al2O3 films prepared at different process temperatures(50℃-250℃)and different oxygen plasma pulse times(5 s-40 s)were used as the gate dielectric layer of indium-gallium-zinc oxide TFTs(IGZO TFTs),and their performance was investigated.The study found that as the process temperature increased,the TFT had a smaller subthreshold swing and higher mobility,which was attributed to the decrease in defects in the Al2O3 film and better interface quality between the Al2O3 film and IGZO.As the oxygen plasma pulse time prolonged,the threshold voltage of the TFT gradually increased,and the mobility and current on-off ratio gradually decreased.The Al2O3 film deposited at a deposition temperature of 100 ℃ and an oxygen plasma pulse time of 5 s allowed the TFT to achieve a mobility of 9.2 cm2V-1s-1 and a current on-off ratio of 108.(3)The application of PEALD-deposited Al2O3 films in CTMs.Al2O3 films deposited using different oxygen sources have different properties.This experiment analyzed the composition,band structure,and surface morphology of Al2O3 films deposited using different oxygen sources,and performed bias stress tests on MOS capacitors and TFTs based on Al2O3 films.The study found that Al2O3 films prepared using oxygen plasma as an oxygen source had certain storage performance.This experiment used it as a charge trapping layer to prepare a charge trapping memory,and the storage window could reach 8.31 V,and the charge could be erased by UV light assistance.