Preparation And Applications Of Al₂O₃ Films In Gate Stacks Of Charge Trapping Memories

As the demand for data storage continues to increase,the status of semiconductor memory in the international market is increasing,and research and development of semiconductor memory has important strategic significance.Charge trapping memory(CTM),as an emerging semiconductor memory,has the characteristics of fast programming/erasing speed,high density,low power consumption,and non-volatility.The device structure originated from the floating gate type CTM was first proposed in 1967,and continuously improved on the basis of MNOS(Metal-Nitride-Oxide-Silicon),developed to SNOS(Poly-Silicon-Nitride-Oxide-Silicon),SONOS(Poly-Silicon-Oxide-Nitride-Oxide-Silicon)and then MANOS(Metal-Aluminum-Nitride-Oxide-Silicon).Under the requirements of shrinking device sizes,the method of using high-k materials as blocking layer,charge trapping layer,and tunneling layer has been extensively studied and has been proven to improve the storage efficiency of CTM.Alumina(Al2O3),as a typical high-k material,has the advantages of higher band gap and stability,and has been widely used in various types of memory.In this paper,by studying the preparation of aluminum oxide film and the application of charge trap memory,based on the characteristics of Al2O3,Metal-Oxide-Semiconductor(MOS)capacitor,Thin Film Transistor(TFT)and other devices were prepared.Then the role of Al2O3 and the impact of the device performance factors,study the feasibility of Al2O3 as blocking layer and tunneling layer in CTM,and apply Al2O3 in CTM devices to analyze its memory performance.The blocking layer in CTM should have a smaller trap density and better dielectric properties on the basis of suppressing the leakage of electrons from the charge trapping layer to the gate electrode.Based on the characteristic requirements of the blocking layer,the experiment used the ALD growth process with high film formation quality to prepare Pd/Al2O3/Si MOS devices with Al2O3 as the gate dielectric layer,and through the I-V measurement,C-V measurement,AFM measurement and other characterization methods.The performance of devices with different deposition and annealing conditions was analyzed.We found that the deposition temperature of Al2O3 has an effect on device leakage and surface morphology.When the gate is applied by a low electric field,the increase of the deposition temperature has little effect on the leakage current;devices with a higher Al2O3 deposition temperature under a high electric field will have a larger leakage current and a lower breakdown voltage.The dielectric constant increases with the increase of the deposition temperature.For the device annealed at the deposition temperature of 200?,the dielectric constant can reach 9.02,which is very close to the theoretical value of the dielectric constant of Al2O3.The flat band voltage shifts positively as the deposition temperature increases.In addition,the forming gas composed of H2 and Ar can effectively reduce leakage and improve dielectric performance after annealing at 400?C.The surface of the film after annealing will also be smoother.The quality of the tunneling layer depends on the contact between the layer and the Si substrate and the quality of its thin film.During the programming/erasing process,the electric field on the tunneling layer with a relatively thin thickness is very strong.Based on the characteristics of the tunneling layer,Al/IGZO/Al2O3/Si TFT devices were fabricated,and it was found that TFT showed good output characteristics and transfer characteristics,and parameters such as mobility and switching current ratio were extracted for analysis,the mobility in the saturation region is 4.66 cm2/Vs,the sub-threshold swing is 76 mV/dec,and the switching current ratio in the saturation region reaches 2.1 ×108.And annealing was found the TFT device prepared after the treatment has improved device performance.Through the preparation of Pd/Al2O3/HfAlO/SiO2/Si CTM device,we studied its memory performance.According to the C-V characteristic curve,its memory window is obtained.It shows a window of 5.04 V when the scanning voltage is 10 V,and after annealing,the memory window has been effectively improved,showing a trend of increasing with the increase of annealing temperature.The retention characteristic of CTM is an important indicator of memory performance.Through testing and fitting,the change curve of flat band voltage within 10 years is fitted.We found that CTM with Al2O3 as blocking layer can effectively suppress the leakage of electric charge and show good memory retention characteristics.