【作者】 匡潜玮；

【导师】 刘红侠；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 随着大规模集成电路VLSI （Very Large Scale Integrated circuits）技术的迅猛发展，半导体器件的特征尺寸遵循着摩尔定律不断地减小，在进入到45nm工艺节点下，MOS晶体管的栅氧化层的等效厚度降低到了1nm左右，如果仍采用常规的SiO₂栅介质，将带来不可接受的栅漏电流，并引起可靠性下降等严重问题，这给集成电路的的进一步发展带来了巨大的阻碍，意味着传统的SiO₂作为器件的栅介质已经达到了物理极限。解决这个问题的唯一办法是用具有较高介电常数的电介质材料取代SiO₂用作栅介质层。高k栅介质可以在保持等效厚度不变的条件下增加栅介质层的物理厚度，可以大大减小直接隧穿效应和栅介质层承受的电场强度。本文对高k栅介质材料与器件进行了系统地研究，取得的主要研究成果如下：1.对ALD生长工艺进行了研究。通过实验得出了生长温度、pluse time、purgetime和氧化剂对使用ALD设备生长高k栅介质材料的影响。结果表明，只有当循环数大于某一数值后，生长速率才基本保持稳定。不同工艺参数和氧化剂对使用ALD设备生长的栅介质材料影响较大，主要体现在杂质含量、高温特性、原子化学计量比和平带电压表现出了较大的差异。在HfO₂和SiO₂界面采用Al预处理技术进行平带电压调整，进而达到阈值电压调节的目的，实验证明，Al预处理技术可以对高k栅器件的阈值电压进行有效地调节。2.通过对椭偏测试结果进行转换和分析，得到了高k介质的禁带宽度。受量子限域效应的影响，介质的禁带宽度与厚度成反比关系，并且随着厚度的增加，禁带宽度趋于稳定；退火后介质的禁带宽度会略微增大。与H2O生长的HfO₂相比，O₃作为氧源生长的HfO₂的禁带宽度要略小，但是生长温度对O₃作为氧源生长的HfO₂的禁带宽度有较大影响。由于高k栅结构价带差和导带差的重要性，利用XPS谱图，结合价带谱以及椭偏对不同厚度HfO₂禁带宽度的测量结果，对不同厚度HfO₂的导带差和价带差进行了计算，得到了精确的HfO₂-Si体系的能带结构。3.采用ALD淀积工艺生长了高k栅介质薄膜，制备了相应的高k栅介质器件，对高k栅器件的I-V漏电机制进行了研究和分析。研究了ALD淀积工艺生长的高k栅MOS器件中的频率色散效应。根据样品的测量结果发现，高频条件下积累区电容出现了频率色散现象。针对双频C-V法测量高k栅MOS电容中制备工艺和测量设备引入的寄生效应，给出了改进的等效电路模型，消除了频率色散效应。4.分析了不同退火温度和电应力对HfO₂高k栅介质应变Si和应变SiGe MOS器件的特性的影响。对比了同样栅氧层厚度的HfO₂Si、HfO₂应变Si、应变SiGe以及HfO₂MOS器件的栅电流，受氧化层势垒高度和界面态密度的影响，HfO₂应变Si MOS器件中的栅漏电流最小，而HfO₂应变SiGe MOS器件中的栅漏电流最大。分析了电应力对HfO₂应变SiGe和HfO₂应变Si MOS器件栅极I-V特性的影响，发现正压应力会使得HfO₂应变器件的栅漏电流减小,而负压应力对器件栅极I-V特性影响不大。5.通过结合主要的散射机制极化光学声子散射和声学声子散射，经过系综蒙特卡罗，系统地研究了高k栅介质HfO₂中电子高场输运机理。研究发现，尽管声学声子散射对能量弛豫没有贡献，但由于在电子能量比较高的时候，声学声子散射率急剧增加，可以极大的增加电子在通过HfO₂介质时的运行距离，增加了电子在经过栅介质时候发生光学声子散射的几率，使得HfO₂高k栅介质可以在较高的电场下仍然能保持系统能量平衡，增加了栅氧层的击穿电压阈值点，并得到了与实验基本相符的结果。更进一步，结合蒙特卡罗仿真的结果，对能量弛豫长度进行了研究，给出了在不同电场，不同初始能量下的能量弛豫长度。最后，给出了电子穿过HfO₂时的平均漂移速度。更多还原

【Abstract】 Through efforts of several decades, semiconductor devices have been dramaticallyscaled down to nano-scale in order to achieve higher device density and performance.As the technology node comes to45nm, the equivalent thickness of silicon oxide gatedielectric is only around1nm, which causes the intolerable gate leakage current, andmakes silicon oxide come to its fundamental physical limit. To reduce the substantialgate leakage current resulting from direct quantum mechanical tunneling across thedielectric layer, high-k dielectrics which can give large gate capacitances with dielectricfilms physically thicker than those of corresponding silicon oxide gate dielectrics areneeded. In this dissertation, high-k gate materials and devices are researchedsystematically, and the author’s major contributions are outlined at follows:1. The ALD deposition process is studied. The relationship between ALD processparameters and high k gate material is given. The research result shows that growth ratewill keep stable when the growth cycle is in a big value. Variation of depositionparameters and the type of oxide source will significantly influence the quality of high kgate material deposited by ALD, which mainly appear in impurities, high temperaturecharacteristic, atom chemical stoichiometry and flat band voltage. The aluminumpretreatment is done at the interface of HfO₂and SiO₂, aiming to tune the VFB. Theexperiment results show the fact that the aluminum pretreatment can effectively tune theVFBof high k devices.2. The bandgap of the high k dielectric is obtained from the VASE testing result,indicating that the bandgap of the high k dielectric will decrease with the increment ofthe thickness, and this trend will gradually disappear as the thickness increases.Compares to the H2O-based HfO₂, the bandgap of the O₃-based HfO₂is smaller, and thedeposition temperature has more influence on the O₃-based HfO₂than that of theH2O-based HfO₂. Based on the VASE and XPS testing results, the VBO and CBO ofHfO₂with different thickness are calculated, for which the accurate band structure ofHfO₂-Si system are obtained.3. The leakage current mechanism of high k gate device is investigated. Thefrequency dispersion effect of high k gate MOS device deposited by ALD is studied.The C-V curves show that the accumulation capacitances take on the frequency dispersion at high frequency. For MOS capacitor high k gate, different fabricationprocess and measurement equipments will cause parasitic effect. Therefore, anequivalent circuit model is proposed, and is finally proved to be effective in eliminatingthe frequency dispersion effect.4. The effects of different annealed temperatures on HfO₂gate dielectrics strainedSi MOS and HfO₂gate dielectrics strained SiGe MOS are analyzed. Compared HfO₂Si-based strained MOS to HfO₂Si MOS, it’s found that the gate leakage current in HfO₂strained Si MOS is the smallest and the one in HfO₂strained SiGe MOS is the highest,which is the effect of interfacial and the barrier at the oxide semiconductor interface.The SILC on HfO₂strained Si MOS and HfO₂strained SiGe MOS is also studied. It’slearned negative voltage stress have less effect on the MOS structures. And positivevoltage stress decrease the gate leakage current in both of HfO₂strained Si MOS andHfO₂strained SiGe MOS.5. Through the main scattering mechanism of optical phonon scattering andacoustic phonon scattering, the high field electron transport mechanism of HfO₂gate issystematically researched by ensemble Monte Carlo method. It is found that acousticphonon scattering rate will dramaticalyy increase when electron is in a high energy state,which can increase the optical phonon scattering rate. It will allow electrons keep thesystem energy balance even in the high field environment, which increase thebreakdown voltage. With the result of Monte Carlo simulation, the energy relaxationlength is researched. It is figured out for different initial energy and electric field.Finally, the average drift velocity when electrons get through HfO₂is also given.更多还原