Studies On The Electrical Characteristics Of ALD-Grown Hafnium Oxide Thin-Film Devices

With the advent of the information age,the explosive growth of data requires the non-volatile memory of computers and mobile devices to rapidly increase for higher storage capabilities.As Moore's Law limit to being approached,a proportional reduction in device size has a fundamental impact on device performance.As a technique to solve the above problems,charge trapping memory has attracted attention.At the same time,the excellent properties of high-k materials make them introduced into charge trapping memories to improve device performance.In this thesis,study on HfO2 growth process based on the Atomic Layer Deposition(ALD),the electrical performance of capacitors and charge-trapped memories using HfO2 thin films as dielectric and storage layers,respectively,is analyzed.The main contents are as follows:ALD equipment was used to obtain HfO2 films with different purge time and growth temperature.Based on HfO2 films with different growth conditions,MOS capacitors were fabricated,and their electrical properties were analyzed in various aspects.In studying the influence of growth temperature on device performance,we conducted C-V,I-V and constant voltage stress(CVS)tests on MOS capacitors,and analyzed the effect of ALD growth temperature on HfO2 thin film MOS capacitors from three perspectives.Firstly,the influence of growth temperature on the boundary traps in MOS capacitors was analyzed by the C-V curve.Studies have shown that there are many boundary traps in HfO2 thin film MOS capacitors grown at high temperatures,which can reach?1012 cm-2.Secondly,based on the I-V curves of devices on different substrates,the transport mechanism of charges in MOS capacitors is analyzed,which lays a foundation for the subsequent analysis of the transfer mechanism of charges in Pd/Al2O3/HfO2/Al2O3/Si(MAHAS)charge-trapping memories.The I-V analysis found that when the MOS capacitor is working at low field strength(<3 MV),the charge is transmitted by Schottky emission;when it is working at high field strength(>3 MV),the charge is transmitted by F-N(Fowler-Nordheim)or P-F(Poole-Frenkel)mechanism,in which P-F transmission is the main transmission mechanism.The CVS test results show that the HfO2-MOS capacitor with a growth temperature of 150?,after applying a gate voltage of-6 V for 50 s,found that the C-V curve of the HfO2-MOS capacitor has an offset of 1.25 V,Based on this,it was speculated that there were a large number of hole traps in the HfO2 film and it was found that the HfO2 film grown at low temperature may have many defects.Finally,in order to analyze the origin of hole traps in the HfO2 film,the X-Ray electron Spectrum analysis(XPS)test was used to analyze the states and states of each element of the HfO2 film.The existence of amorphous lattice 0 bonds was found from the test.And the number of amorphous lattice O bonds will decrease as the ALD growth temperature increases.It can be inferred that a large number of hole traps in the HfO2 film are caused by the action of the amorphous lattice O bond,and when the ALD growth temperature is low,the number of hole traps in the HfO2 film is the lower.In order to investigate the effect of amorphous lattice O bonds on the performance of CTM devices in the HfO2 film as a memory layer,we prepared CTM devices with MAHAS structure and studied them.Using HfO2 films grown at different temperatures as storage layers,write and erase speed tests and pulse C-V tests were performed on MAHAS devices.It can be found that the hole trap caused by the amorphous lattice O bond in the HfO2 film has a significant effect on the device:1)The hole trap affects the write and erase speed of the CTM device,making the writing process difficult,but accelerated erase process;2)The hole trap affects the size of the storage window of the CTM device.The storage window decreases from 8 V to 5 V as the growth temperature increases,so the number of hole traps directly affects the storage capacity of the device.The number of hole traps caused by the amorphous lattice O in the HfO2 film is directly related to the ALD growth temperature.Therefore,the performance of the CTM device can be improved by optimizing the ALD growth process.