Structures and Generation Mechanisms of Defects in High-k Dielectric Films for Silicon ULSIs

在即将到来的亚65 nm互补金属氧化物半导体(CMOS)技术中，HfO_2、Hf_xSi_(1-x&gt；O_y)、ZrO_2(ZrO_2)、Zr_xSi_(t；1-x&gt；O_y)等高k材料有望取代SiO_2成为栅电介质的基本材料。然而，这些高k候选者的带隙中存在大量由于缺陷而引起的局域态的可能性很高。这些局域态被认为会导致各种介质故障，如高泄漏电流、低击穿电压和阈值变化。因此，对于局域态的详细和系统的研究对于理解缺陷对电学性质的影响是必不可少的。从这个角度出发，我们利用光致发光(PL)作为一种可以提供带隙能量和局域态的基本信息的工具，对HfO_2、Hf_xSi_&lt；1-x&gt；O_y、ZrO_2和ZrxSi_&lt；1-x&gt；O_y进行了基础研究。X射线ph值…还进行了更多的耳电子能谱(XPS)分析，以研究谱带分布。此外，还研究了热处理对高k材料电学性能的影响。用XPS研究了夹在蒸发Au电极和Si衬底之间的非晶态Hafnia和Hfn硅酸盐薄膜的能带分布。价带偏移量和导带偏移量随着Si和Au侧Hf含量的增加而减小，直至基本不变。在文献中，硅酸锆的价带偏移量也有类似的下降。测量了等离子体增强化学气相沉积沉积的非晶态和氧化锆、脉冲激光沉积的非晶态氧化氢和晶态氧化钛(YSZ)的紫外光致发光光谱。无论结晶度、氧缺陷、来源醇盐、沉积方法或衬底材料的差异，所有Hafnia和Zirconia样品的光致发光峰都出现在2.7到2.9 eV左右。在所有样品中，光致发光的衰变曲线也是相似的。这些结果表明，光致发光是氢氧化铝和氧化锆所固有的，而不是由于杂质、氧空位或样品与衬底之间的界面缺陷造成的。从光致发光激发(PLE)和真空-紫外(VUV)吸收测量中发现，光致发光被紫外光激发到了带边的尾态。当样品在90 0℃下退火时，除YSZ外，其余样品在4.2 eV附近出现一个新的光致发光峰。PLE和VUV吸收测量表明，4.2 eV的PL是由于带间吸收而被激发的。本文还讨论了硅酸盐和Hf中诱导的PL的机制。在两种硅酸盐中都观察到了从2.0 eV到5.0 eV的宽广的光致发光谱。这种光致发光有两个组分，它们的峰值分别在2.8~3.0 eV和3.8 eV附近，硅酸锆在2.7~3.0 eV和3.8 eV左右。时间分辨光致发光和光致发光衰变测量表明，光致发光成分的起源在2.7(2.8)eV到3.0 eV之间，而在Hafnia和Zirconia中，发光成分的来源在2.7到2.9 eV之间。此外，PLE和VUV吸收测量表明，在2.7(2.8)~3.0 eV和3.8 eV附近的光致发光分量都被激发到了带边的尾态。通过这些研究，假设了Hf-SiO_3、Zr-SiO_3、Ha_2O_3和ZrO_2在它们的带隙中都有发光中心，它们的上下能级具有一定的固定能量差，与Hf或Zr的含量无关。此外，我们还研究了后处理对Hf和Zr硅酸盐电学性质的影响。当样品在一氧化氮(NO)中进行后处理时。漏电流和电容-电压(C-V)滞环宽度显著减小。根据ESR测量，认为样品与硅衬底界面上的顺磁缺陷是造成漏电流和C-V滞后的原因。此外，XPS的深度分布表明，后氮化有效地终止了这些界面缺陷，并有助于改善电学性能。较少

For the coming sub-65 nm complementary metal-oxide-semiconductor (CMOS) technology, high-k materials such as hafnia (HfO_2), hafnium silicate (Hf_xSi_<1-x>O_y), zirconia (ZrO_2), and zirconium silicate (Zr_xSi_<1-x>O_y) are expected to take the place of SiO_2 as the basic material for gate dielectrics. However, there is a high possibility that a lot of localized states due to defects are present in the band gap of these high-k candidates. These localized states are assumed to cause various dielectric malfunctions such as high leakage current, low breakdown voltage, and threshold variation. Therefore, detailed and systematic research on the localized states is indispensable to understand the effects of the defects on electrical properties.From this viewpoint, we have carried out basic studies on HfO_2, Hf_xSi_<1-x>O_y, ZrO_2, and ZrxSi_<1-x>O_y, using photoluminescence (PL) as a common tool that can provide fundamental information about the band gap energy and localized states. X-ray ph … More otoelectron spectroscopy (XPS) analyses were also carried out to investigate the band profiles. Furthermore, the effects of postannealing on the electrical properties of the high-k materials were also studied.Energy band profiles were investigated by XPS for amorphous hafnia and hafnium silicate films sandwiched between an evaporated Au electrode and a Si substrate. Valence band offset and conduction band offset decrease until they become almost constant with an increase in hafnium content at both Si and Au sides. In literature, similar decrease in the valence band offset was reported in zirconium silicate.Photoluminescence spectra induced by UV photons were measured for amorphous hafnia and zirconia deposited by plasma-enhanced chemical-vapor deposition, amorphous hafnia deposited by pulse laser deposition, and crystalline yttria-stabilized zirconia (YSZ). A PL peak appears around 2.7 to 2.9 eV similarly in all hafnia and zirconia samples, irrespective of the difference in crystallinity, oxygen deficiency, source alkoxide, deposition method, or the substrate material. The decay profile of the PL is also similar in all the samples. These results indicate that the PL is inherent in hafnia and zirconia, and is not due to impurities, oxygen vacancy, or interface defects between the sample and the substrate. From PL excitation (PLE) and vacuum-ultraviolet (VUV) absorption measurements, the PL was found to be excited by UV photons to tail states at the band edges. When the samples were annealed at 900℃, a new PL peak appears around 4.2 eV in all the samples except YSZ. The PLE and VUV absorption measurements indicate that the 4.2-eV PL is excited due to the interband absorption.Mechanisms of PLs induced in hafnium and zirconium silicates were also discussed. A broad PL spectrum was observed from 2.0 to 5.0 eV similarly in both silicates. This PL has two components with peaks around 2.8 to 3.0 eV and 3.8 eV for hafnium silicates and those around 2.7 to 3.0 eV and 3.8 eV for zirconium silicates. Time-resolved PL and PL decay measurements indicate that the origin of the PL component around 2.7(2.8) to 3.0 eV is the same as that of the PL component around 2.7 to 2.9 eV in hafnia and zirconia. Furthermore, PLE and VUV absorption measurements show that both the PL components around 2.7(2.8) to 3.0 eV and 3.8 eV are excited to tail states at the band edges. Through these studies, it is assumed that hafnium silicate, zirconium silicate, hafnia, and zirconia have luminescent centers in their band gaps with their respective upper and lower states that have a certain fixed energy difference irrespective of the hafnium or zirconium content.Furthermore, effects of postannealing on the electrical properties of hafnium and zirconium silicates were investigated. When the samples were postannealed in nitrogen monoxide (NO). leakage current and capacitance-voltage (C-V) hysteresis width are decreased drastically. From ESR measurement, it is assumed that paramagnetic defects at the interface between the sample and the Si substrate are responsible for the leakage current and the C-V hysteresis. Furthermore, depth profile by XPS shows that the postnitridation effectively terminates these interface defects and contributes to the improvement in electrical properties. Less