【作者】 卢伟；

【导师】 殷江；

【作者基本信息】 南京大学 ， 材料科学与工程， 2016， 博士

【摘要】 多晶硅-氧化硅-氮化硅-氧化硅-硅(SONOS)型存储器作为电荷俘获型存储器(CTM)的一种,已经受到了相当多的关注。人们为了获得更高的数据存储密度、更快的编程/擦除速度、更低的操作电压和更小的功耗,半导体器件的基本单元尺寸一直在减小,但是一些固有的限制使得SONOS型器件的尺寸达到了一个临界值。其中一个挑战就是SONOS型器件的电荷存储层中储存的电子数会随着存储单元尺寸的变小而迅速减少。通过用high-k材料来替代传统的Si3N4介质作为电荷俘获型存储器件的电荷存储介质可以改善器件的电荷俘获能力和数据保持性能,但还是无法根本解决电荷存储密度不高的问题。为了解决这个问题,人们研究发现high-k复合介质作为电荷俘获介质可以有效解决上述问题。high-k复合介质的高电荷存储密度可以归结为两种high-k氧化物材料之间的互扩散形成的高密度缺陷态。本文研究了 Hf0.5Zr0.5O2复合氧化物薄膜的缺陷态密度,研究比较了Ta0.5Al0.5Ox(TaAlO-55)和 Zr0.5Al0.5Ox(ZrAlO-55)不同体系 high-k 复合介质的存储性能,并系统研究了不同掺杂比例Ta-Hf-O体系high-k复合介质的存储性能,最后研究了具有不同价态金属阳离子的high-k复合介质的电荷存储密度。主要研究结果如下:1.利用原子层沉积技术和射频磁控溅射技术制备了 Pt/Al2O3/Hf0.5Zr0.5O2/Al2O3/p-Si存储结构,同时利用高分辨透射电子显微镜(HRTEM)表征了其微结构。通过表征存储结构的高频(1 MHz)电容-电压(C-V)性能确定了Hf0.5Zr0.5O2 high-k薄膜中电荷的存储密度为6.63×1012 cm-2,进一步计算出存储结构中的体缺陷密度近似为2.21×1019 cm-3。Hf0.5Zr0.502薄膜在氮气氛围中退火处理之后,薄膜中的氧空位被氮原子占据导致薄膜中的缺陷态密度降低,电荷存储能力下降。2.利用原子层沉积技术和射频磁控溅射技术制备了 Pt/Al2O3/TaAlO-55/Al2O3/p-Si和Pt/Al2O3/ZrAlO-55/Al2O3/p-Si结构的电荷俘获型存储器原型器件,同时利用高分辨透射电子显微镜(HRTEM)表征了其微结构。由于TaAlO-55与p-Si衬底导带底间的势能差小于ZrAlO-55与p-Si衬底导带底间的势能差,在相同的扫描电压下,电子从p-Si衬底通过A12O3层隧穿到电荷俘获层的几率更大。TaAlO-55器件展现了更好的存储性能,当施加±7 V的操作电压时TaAlO-55器件的电荷存储密度达到了 2.88×1013 cm-2,并可推算出器件在进行编程/擦除操作后,在10年后可以保留60%的电荷。3.利用Ta0.5Al0.5Ox(TaHfO-55)和 Ta0.3Hf0.7Ox(TaHfO-37)复合介质制备了TaHfO-55和TaHfO-37电荷俘获存储器原型器件。利用HRTEM表征了这两种器件的微观结构,并测试了 TaHfO-55和TaHfO-37器件的C-V曲线。当扫描电压为±11 V时TaHfO-55器件的存储窗口达到了 9.53 V,存储电荷密度(Nt)为3.65 ×1013cm-2。由于TaHfO-55复合介质中Ta2O5和HfO2的互扩散最有效,产生的缺陷态密度最高,因而在相同的扫描电压下TaHfO-55器件的电荷存储密度最大。疲劳测试结果显示经过1×105次编程/擦除操作,TaHfO-55和TaHfO-37器件的存储窗口损失很小。编程/擦除速度测试表明从脉冲宽度为10-4s的脉冲信号开始,TaHfO-55和TaHfO-37器件开始有明显的响应。随着脉冲宽度的增加,平带电压的偏移量迅速增大。将数据保持的结果外推至10年,TaHfO-55器件的电荷损失量为50%,TaHfO-37器件的电荷损失量为60%。相对于TaHfO-37,TaHfO-55与p-Si导带底间的势能差(PBCB)要低0.3 eV。较低的势能差使电子从p-Si衬底通过A12O3层隧穿进入电荷俘获层的几率更大。因而TaHfO-55器件的编程/擦除、疲劳和数据保持性能更优异。4.制备了利用 Hf0.5Zr0.5O2(ZrHfO-55)、Hf0.5Al0.5Ox(HfA1O-55)和Ta0.5Hf0.5Ox(TaHfO-55)high-k复合介质作为电荷存储介质的电荷俘获型原型存储器件,研究了将具有不同价态阳离子的high-k复合氧化物介质做为电荷存储层对电荷俘获型存储器的存储性能的影响。在相同的扫描电压下,ZrHfO-55器件存储的电荷密度最小,HfAlO-55次之,TaHfO-55器件的电荷存储密度最大。当扫描电压为±11 V时TaHfO-55器件的电荷存储密度为3.59×1013 cm-2。由于ZrO2与HfO2结构类似,而且Zr4+与Hf4+价态相同,因此当这两种介质复合时,两种介质的复合界面处的缺陷态密度不会发生质的跃升。而由于Al3+和Hf4+价态不同,因此在A12O3和HfO2的各自表面处,阳离子及氧离子的空间分布状态则完全不一样,其电荷分布(或电子云分布)也有巨大差异。因此当这两种high-k介质复合时,在两种介质界面处会形成新的能带结构,这种能带结构与各自high-k介质的能带结构有巨大差异,在复合介质的带隙中形成高的缺陷态密度。对于Ta2O5和HfO2情况完全类似。因此TaHfO-55及HfAlO-55存储器件具有高的电荷存储密度。而相对于HfAlO-55复合介质,TaHfO-55复合介质与p-Si衬底间导带底的势能差要小0.5 eV,因而TaHfO-55存储器件的电荷存储密度最高。更多还原

【Abstract】 Silicon-oxide-nitride-oxide-silicon(SONOS)-type memory device as one of the charge-trapping memory devices(CTM)has received considerable interest.With continuous down-scaling the cell dimension to obtain high data-storage density,high programing/erasing speeds,low operating voltage and low power consumption,some intrinsic limitations make this kind of memory rapidly approach the scaling limit.One of the challenges is that the number of electrons stored in the charge-trapping dielectric of SONOS-type memory device decreases significantly with the continual down-scaling of the cell size.An improvement of the charge-trapping capability and retention performance can be obtained by using high-k materials or band-gap-engineered charge-trapping layer to replace traditional Si3N4.However,they still suffer the same few-storage-electron limitation.Recently,high-k composite dielectric has been employed as the charge-trapping layer.It was suggested that the excellent charge-trapping efficiency of high-k composite should be ascribed to the high density of defect states formed due to the inter-diffusion between two kinds of high-k oxides.In this work,we studied the density of the defect states in Hf0.5Zr0.5O2 high-k film and the storage performance of charge trapping memories employing Ta0.5Al0.5Ox(TaAlO-55)and Zr0.5Al0.5Ox(ZxAlO-55)high-k composites as the charge trapping layer.The storage performances of charge trapping memories employing Ta0.5Hf0.5Ox(TaHfO-55)and Ta0.3Hf0.7Ox(TaHfO-37)high-k composites as the charge trapping layer were studied systematically too.Finally,the density of the trapped charges in the charge trapping memories employing high-k composites with different valence states as the charge trapping layer were investigated.The main achievements are as followed:1.A memory structure Pt/Al2O3/Hf0.5Zr0.5O2/Al2O3/p-Si was fabricated by using atomic layer deposition and rf-magnetron sputtering techniques,and its microstructure has been investigated by using the high resolution transmission electron microscopy(HRTEM).By measuring the applied gate-voltage dependence of the capacitance for the memory structure,the planar density of the trapped charges in Hf0.5Zr0.5O2 high-k film was estimated as 6.63×1012 cm-2,indicating a body defect density of larger than 2.21×1019 cm-3.It was observed that the post-annealing process in N2 can reduces the defect density in Hf0.5Zr0.5O2 film,which was ascribed to the occupancy of oxygen vacancies by nitrogen atoms.2.The charge-trapping memory structures Pt/Al2O3/TaAlO-55/Al2O3/p-Si and Pt/Al2O3/ZrAlO-55/Al2O3/p-Si were fabricated by using rf-sputtering and atomic layer deposition techniques and their microstructures have been investigated by using the high resolution transmission electron microscopy(HRTEM).With a lower PBCB(potential at the bottom of the conduction band)difference between TaAlO-55 and p-Si than that between ZrAlO-55 and p-Si,TaAlO-55 CTM device shows a better charge-trapping performance.A density of trapped charges 2.88 ×1013 cm-2 at an applied voltage of±7V was obtained for TaAlO-55 CTM device,and it could keep about 60%of the initially trapped charges after 10 years.3.The charge-trapping memory structures Pt/Al2O3/TaHfO-55/Al2O3/p-Si and Pt/Al2O3/TaHfO-37/Al2O3/p-Si were fabricated by using rf-sputtering and atomic layer deposition techniques and their microstructures have been investigated by using the high resolution transmission electron microscopy(HRTEM).Under an applied voltage of±11 V,the memory window of TaHfO-55 CTM device is about 9.53 V and the density of the stored charges in TaHfO-55 CTM device is about 3.65 × 1013cm-2.The TaHfO-55 CTM device shows the maximum storage density under the same applied voltage due to the most effective inter-diffusion between Ta2O5 and HfO2.After 1×105 programming/erasing cycles,the memory windows of TaHfO-55 and TaHfO-37 CTM device decrease little.The programming/erasing speed test shows that TaHfO-55 and TaHfO-37 CTM devices respond to a voltage pulse with a pulse width of 10-4 s obviously.With the increase of the pulse width,the shift in the flat band voltage increases rapidly.After 10 years,the charge loss of TaHfO-55 devices was estimated as about 50%,and the charge loss of TaHfO-37 devices was estimated as about 60%.With a lower PBCB difference between TaHfO-55 and p-Si than that between TaHfO-37 and p-Si,TaHfO-55 CTM device shows a better charge-trapping performance.4.Hf0.5Zr0.5O2(ZrHfO-55)、Hf0.5Al0.5Ox(HfAl0-55)and Ta0.5Hf0.5Ox(TaHfO-55)CTM devices were fabricated to investigate the effect of different chemical valence of cations in individual high-k dielectric for high-k composite on the density of the stored charges of CTM devices with high-k composite as the charge storage layer.Under the same applied voltage,the density of the stored charges in ZrHfO-55 CTM device was the lowest,and the density of the stored charges in TaHfO-55 CTM device is the largest.A density of the trapped charges 3.59 × 1013 cm-2 at an applied voltage of±11 V was obtained for TaHfO-55 CTM device.Due to the similar structure between ZrO2 and HfO2,and the same chemical valence of Zr4+and Hf4+,the density of the defect state at the interface between both high-k dielectrics will not be large.Because of the different chemical valence between Al3+ and Hf4+,the space distributions of cations and oxygen ions will be quite different with those in amorphous Al2O3 and HfO2 dielectrics,and the charge distributions(or the distributions of electron cloud)also will be quite different with those in amorphous Al2O3 and HfO2 dielectrics.So when the high-k composite was formed,a new energy band structure quite different with those of amorphous Al2O3 and HfO2 dielectrics will be formed at the interface of both high-k dielectrics,resulting in the formation of the defect states with a high density in the band gap of high-k composite.For Ta2O5 and HfO2 composites,the situation is completely similar.Therefore,TaHfO-55 and HfAlO-55 CTM devices show higher densities of the trapped charges.The PBCB difference between TaHfO-55 and p-Si is lower about 0.5 eV than that between HfAlO-55 and p-Si,so TaHfO-55 CTM device shows a largest density of the trapped charges.更多还原