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1、 I I 摘要 I 摘要摘要 闪速存储器（Flash Memory）是目前占据统治地位的非易失性半导体存储器 （NVSM） 。它具有低功耗，小体积，高密度，可重复擦写等优异的特性。浮栅 器件作为闪存中的主流技术被广泛使用，但是当器件尺寸减小到 65nm以下时， 传统多晶硅浮栅器件将遇到很大的挑战， 其中最突出的就是器件擦写速度和可靠 性的矛盾，这主要 与存储器件隧穿介质层的厚度有关：一方面要求隧穿介质层 比较薄，以实现快速有效的P/E操作；另一方面又要求较厚的隧穿介质层，以实 现足够的保持时间。为了克服这个问题，引入高介电常数材料对隧穿氧化层进行 优化，通过多介质复合隧穿介质层的方法来解决：主
2、要有VARIOT和CRESTED 两种堆叠隧穿结构。 本文首先介绍了浮栅存储器的广泛应用和它具有的优势， 接着介绍了浮栅存 储器件的结构和特性，工作原理，及其目前所面临的挑战。 本文结合纳米晶和VARIOT堆叠结构，制作了VARIOT堆叠隧穿层的Au纳米 晶MOS存储结构：Si/ SiO2/ HfO2/Au 纳米晶/Al2O3/Al，主要是通过电子束蒸发 加快速热退火成晶的方法，在VARIOT(高k/ SiO2)堆叠隧穿层上制备了Au金属纳 米晶材料。针对该存储结构的电荷存储能力和电荷保持特性进行测试，并对测试 结果进行分析。VARIOT堆叠隧穿层中引入高k材料HfO2，其介电常数是SiO2材
3、 料的五倍，保证了相同等效氧化层厚度(EOT)的HfO2介质可以提供数倍于SiO2 材料的物理厚度，有利于提供更好的数据保持特性。实验数据表明隧穿氧化层在 相同等效厚度情况下，VARIOT堆叠隧穿介质具有比单层SiO2隧穿介质更高的物 理厚度，有效降低了漏电流，进一步提高器件的保持特性。 我们还通过理论和MEDICI软件仿真两种方法分析了CRESTED(高k/ SiO2/高 k)堆叠隧穿结构对浮栅存储器件编程速度的影响。分析表明要折中考虑 CRESTED中高k材料的介电常数和势垒高度，才能设计出合理的CRESTED结构 从而提高存储器件的编程速度。并通过MEDICI模拟得出，在相同等效厚度情况
4、 下，Si3N4/SiO2/Si3N4和Y2O3/SiO2/ Y2O3两种CRESTED堆叠隧穿层浮栅存储器 件的FN隧穿速度是传统浮栅存储器的 100 倍左右。 关键字：非易失性存储器；VARIOT 堆叠隧穿层；冠状势垒隧穿层；高 k 介质。 Abstract II Abstract Flash Memory dominates the field of NonVolatile Semiconductor Memory today. It has the attractive characteristic of low power, small size, high integration,
5、 and rewritability. A device based on floating gate which is mainstream technology is used widely in flash memory. However, this device will encounter bigger challenge when the feature size is scaling down to sub-65nm.The most conspicuous one stems from the tradeoff between the operation speed and r
6、eliability: on the one hand, a thinner tunneling oxide is required to allow fast and efficient programming and erasing. One the other hand, a thicker tunneling oxide is needed to guarantee enough isolation under retention. To overcome this problem, we can use high-k materials to optimize tunneling l
7、ayer. This work focus on two new tunneling layer structures: VARIOT and CRESTED tunneling layer. Firstly, the application and superiority of flash memory are introduced followed by its structure and characteristics. Working principle and the encountered challenge are introduced. In this paper, we in
8、vestigated the feasibility of e-beam evaporation combined with rapid thermal annealing process to fabricate metal nanocrystals. Based on the optimized process parameters founded, the MOS memory structure with Au nanocrystals embedded in the VARIOT tunneling dielectric was fabricated: Si/ SiO2/ HfO2/
9、Au Ncs/Al2O3/Al. The charging characteristics and the charge retention performances were electrically investigated, and the test result was analyzed. The dielectric constant of High-k material HfO2 is five times for SiO2. In the same equivalent oxide thickness, the physics thickness of HfO2 is five
10、times for SiO2, it makes the memory having better retention performance. The experiment datasheet indicate that when VARIOT tunneling dielectric and the single SiO2 tunneling dielectric have the same equivalent oxide thickness, the VARIOT tunneling dielectric VARIOT tunneling dielectric has larger p
11、hysic thickness, reduces the leakage current efficiency and improves the memory retention without affecting the charging 多介质复合隧穿层的闪存器件研究 III characteristics. We identify the factors that influence the program/erase speed of the floating gate memory with CRESTED tunneling layer by theory calculation
12、and MEDICI simulation. Research results indicate that: high-k dielectrics are used in the flash memories with CRESTED tunnel dielectrics requiring a trade-off between barrier height and dielectric constant to designing a reasonable CRESTED tunneling layer for improving the memory programming speed.
13、MEDICI simulation indicate that, in the case of the same equivalent oxide thickness, the FN tunneling speed of floating gate memory with CRESTED tunneling layer as Si3N4/SiO2/Si3N4 or Y2O3/SiO2/Y2O3 is one hundred times to the FN tunneling speed of traditional floating gate memory. Key words: nonvolatile memory, VARIOT tunneling layer, CRESTED tunneling layer, high-k dielectric. 目录 IV 目录目录 摘要. I Abstract . II 目录. IV 第一章 绪论. 1 1.1 非易失性存储器 . 1 1.2 Flash 存储器的应用和市场 . 4 1.3 Flash 发展面临的挑战 . 6 1.4 本文主要内容 . 8 第二章 浮栅存储器件中高k材料的应用. 10 2.1 常见高k介质及其电学特性 . 10 2.2 高k介质在闪存中的应用 .
