Performance Of High-k Dielectric Charge Trapping Memories Based On Defect Engineering

With the gradually reduction of device feature size,the complexity of the process makes the conventional charge trapping memories(CTM)face the problem of decreased reliability such as high charge leakage and poor retention characteristic.The defect engineering is used to simplify the preparation process of the CTM,which can effectively improves the retention characteristic and reduces the power consumption of the devices.In this paper,the charge storage layers with rich defects are mainly prepared by nitrogen plasma treatment and oxygen vacancy formation.Combined with the first-principles theory analysis,the performance impacts of the CTM prepared by different defect introducing methods are explored.The following research work has been carried out in nitrogen plasma treatment:the memory samples with Al/Hf O₂/Hf ON/Hf O₂/Si(MONOS-Hf O₂)structure are prepared by atomic layer deposition(ALD),whose nitride storage layers are formed by prepared by N₂or NH₃plasma.Combined with material and electrical characterization,we found that the energy of the nitrogen plasma treatment is not enough to introduce nitrogen defects into Al₂O₃,so no memory windows appears in the electrical characteristics of the devices.However,the MONOS-Hf O₂memories with N₂or NH₃plasma treatments both appear memory windows.At the same time,because of the higher ionization rate of NH₃,the nitrogen doping amount in storage layer of NH₃is more than N₂.Therefore,the memory with NH₃plasma appears a bigger memory window of 2.641 V with the programming/erasing voltage of±6 V than it with N₂plasma of 1.106 V.Because the nitrogen content introduced by nitrogen plasma treatment is very small,which cannot form a stable,uniform and high doped nitride,the charge loss rate of the memory is 82.3%.According to the first-principle simulation,we find that a small amount of nitrogen doping in Hf O₂will slightly reduces the forbidden band width,and introduces a shallow defect energy level of about 0.448 e V from the top of the valence band.But,due to the shallow defect level at the bottom of the conduction band,the retention characteristics of the device are very poor.The other research work has been carried out on the formation of oxygen vacancy:the memory samples with Al/Al₂O₃/Hf O_x/Al₂O₃/Si(MOHOS-Hf O_x)structure are prepared by ALD,where the Hf O_xcharge storage layer with oxygen vacancies are prepared by changing the injection amount of TDMA-Hf source in ALD.Compared with the Al/Al₂O₃/Hf O₂/Al₂O₃/Si(MOHOS-Hf O₂)memory,where the Hf O₂with less oxygen vacancies as the storage layer,MOHOS-Hf O_xshows a bigger memory window of 5.50 V with the programming/erasing voltage of+8/-10 V.It is found that Al₂O₃tunneling layer with 1 min 400?N₂-PDA can significantly improve the leakage characteristics of the memory devices,and reduce the charge loss rate from 70.5%to 23.2%.Moreover,a high working rate of 50 ns and a 3.02 V memory window appears at a low voltage(+3/-10 V),which greatly reduces the power consumption of the memory.This is because the uniform distributed oxygen vacancies in Hf O_xdeposited by ALD show good stability.In addition,based on the first-principles theory analysis,different coordination oxygen vacancies in monoclinic phase of Hf O₂(m-Hf O₂)will introduce deep trap levels as electron trapping levels in the forbidden bands,which have well ability to capture charges.Therefore,MOHOS-Hf O_xhave better memory characteristic than MOHOS-Hf O₂.