纳米晶及纳米叠层基电荷俘获型存储器的研究

发布时间：2018-06-06 07:03

本文选题：电荷俘获型 + 非易失性存储器　；参考：《南京大学》2012年博士论文

【摘要】：自从非易失性半导体存储器诞生以来,浮栅型存储器一直是存储器市场上的主流产品。随着半导体器件特征尺寸逐渐缩小和集成度的不断提高,浮栅型非易失性存储器件已经很难满足存储器的微型化要求。特别是当半导体器件的特征尺寸减小到22nm以后,基于传统的浮栅型存储技术将走到物理和技术的极限。因此,寻找一种拥有高存储密度、快速编程、低成本、低能耗的非易失性存储器,成为目前存储器研究领域的热点。多晶硅-氧化硅-氮化硅-氧化硅-硅衬底(SONOS)型电荷俘获型存储器以其优良的性能,例如低功耗、低编程电压、编程速度快,良好的数据保持能力和抗疲劳性能逐渐引起了人们的注意。传统的SONOS型存储器采用Si3N4替代多晶硅浮栅层,电荷被Si3N4存储层中的分立的陷阱能级捕获,从而很大程度上避免了浮栅型结构中的应力诱导漏电效应。正是基于分立能级的考虑,传统的SONOS型存储器不断得到发展。为了提高存储层中的陷阱数量,high-k材料被用于存储层；半导体或者金属纳米晶被用作存储介质以提高器件性能。本文系统研究了ZrO：纳米晶基存储器的电学性能,微观结构和可靠性问题；同时提出一种新型纳米叠层基电荷俘获型存储结构,并对其存储性能进行了初步研究,主要结果概括如下： 1.利用(Zr02)0.8(Si02)0.2(ZSO)伪二元氧化物代替传统Si3N4作为存储层,Al2O3作为隧穿层和阻挡层,借助原子层气相沉积和脉冲激光沉积制备了电荷俘获型ZrO2纳米晶基存储单元。XRD和TEM分析结果表明,经过高温退火处理,ZrO2纳米晶作为存储介质从过饱和的ZSO母相中析出,ZrO2纳米晶被非晶母相包围。测试结果表明该存储单元有优良的性能：当扫描电压为±8V时,存储窗口达到7.5V。即使在150℃下,器件写入/擦出105次后,存储窗口变化较小,表明该器件具有良好的抗疲劳特点。不同温度(25℃,85℃和150℃)下,经过105次写入擦除操作的器件的电荷损失量分别为6.6%,8.3%和12%(保持时间为4×104秒)。 2.首次系统研究了退火过程中ZrO2纳米晶的析出过程、形态演变、及其尺寸和密度对器件存储性能的影响。结果表明未经过退火处理的ZSO薄膜为非晶态。随着退火时间的增加,薄膜开始析出ZrO2纳米晶；当退火时间为60s,纳米晶的密度达到最大值；当退火时间达到90s后,纳米晶的密度有所下降。而ZrO2纳米晶尺寸一直呈现逐渐增大的趋势。实验发现,经过60s退火处理的存储器件具有最宽的存储窗口4.4V,最小的(5%)的电荷损失量和最佳的耐疲劳特性。X-射线光电子能谱(XPS)能带分析结果表明,在60s退火处理的ZrO2纳米晶基电荷俘获型存储单元中,Al2O3和ZSO之间具有1.3eV的导带补偿,正是高的势垒导致器件具有良好的数据保持能力。 3.首次设计和制备了一种纳米叠层基电荷俘获型存储器结构：利用ZrO2/Al2O3纳米叠层代替传统SONOS型中的氮化硅或者high-k电介质作为存储层。为了研究存储层中界面对存储特性的影响,我们制备并研究了一系列具有相同存储层总厚度但是叠层数不同的样品。实验发现,相同扫描电压下,随着界面数量的增加,器件的存储窗口逐渐增大。结果表明,ZrO2/Al2O3纳米叠层中的界面对器件性能起着关键作用,电子主要是被界面所俘获；然而当界面数量过多时,存储窗口反而变小,这主要是由于静电排斥作用以及高温退火之后,界面距离减小,导致界面结构变得弥散。当界面数量为8时,器件具有6.3V的存储窗口以及10年后7.5%的电荷损失量。通过研究ZrO2/Al2O3纳米叠层基存储单元异质结构的能带排列,ZrO2/Al2O3纳米叠层之间具有1.7eV的势垒高度。Al2O3和ZrO2薄膜之间的深势阱提高了器件的数据保持能力。
[Abstract]:The invention relates to a non - volatile memory with high storage density , fast programming , low cost and low energy consumption .
semiconductor or metal nanocrystals are used as storage media to improve device performance .

In this paper , the electrical properties , microstructure and reliability of the ZrO _ 2 nanocrystalline based memory are studied .
At the same time , a novel nano - stack - based charge - trapping storage structure is proposed , and its storage performance is preliminarily studied .

1 . Using ( Zr02 ) 0.8 ( Si02 ) 0.2 ( ZSO ) pseudo - binary oxide instead of traditional Si3N4 as a storage layer , Al2O3 as a tunneling layer and a barrier layer , a charge trapping type ZrO2 nanocrystalline base unit was prepared by atomic layer vapor deposition and pulsed laser deposition .

2 . The evolution of ZrO2 nanocrystals during the annealing process was studied for the first time . The effects of size and density on the storage properties of the devices were studied . The results show that the annealed ZSO films are amorphous . As the annealing time increases , the films begin to precipitate ZrO2 nanocrystals .
when the annealing time is 60s , the density of the nanocrystalline reaches the maximum value ;
The results of X - ray photoelectron spectroscopy ( XPS ) band analysis show that there is a conduction band compensation of 1.3 eV between Al2O3 and ZSO , which leads to good data retention capability of the device .

In order to study the influence of the interface on the storage characteristics , a series of samples with the same total thickness but different number of layers have been prepared and studied . The results show that the interface in the ZrO2 / Al2O3 nano - stack plays a key role in the performance of the device , and the electrons are mainly captured by the interface .
However , when the number of interfaces is too large , the storage window becomes smaller , mainly due to electrostatic repulsion and high temperature annealing , the interface distance is reduced , resulting in dispersion of the interface structure . When the number of interfaces is 8 , the device has a storage window of 6.3 V and a charge loss amount of 7.5 % after 10 years . By studying the energy band arrangement of the heterogeneous structure of the ZrO2 / Al2O3 nano - stack - based storage unit , the barrier height of 1.7 eV is formed between the ZrO2 / Al2O3 nano - stacks . The deep potential well between the Al2O3 and the ZrO2 thin film improves the data retention capability of the device .
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：TP333

【共引文献】