硅基高κ材料的分子束外延生长

【作者】 徐闰；

【导师】 蒋最敏；

【作者基本信息】 复旦大学 ， 凝聚态物理， 2005， 博士

【摘要】 在过去二十多年里,Si基元器件的大小遵循Moore定律按比例的持续减小。对于下一代金属氧化物半导体场效应管（MOSFET）器件,原来的栅极介电材料SiO₂已经不再适合使用。人们需要寻找适合的高k（k指介电常数）材料作为MOSFET器件中新的栅极材料。这其中,有两类材料最受关注。其中之一是IVB族金属氧化物,包括HfO₂和ZrO₂;另一类是ⅢA和ⅢB族氧化物,包括Al₂O₃和Y₂O₃,CeO₂等其他一些稀土金属氧化物。在这篇论文里,我们主要研究高k氧化物HfO₂和Er₂O₃的生长及其特性。 第一、二章将分别介绍研究背景和实验仪器。 在第三章中,我们将研究HfO₂的生长及其基本的物理和化学性质。HfO₂薄膜由电子束蒸发法获得。X射线光电子能谱（XPS）研究证明薄膜是符合化学剂量比的。透射电子显微镜（TEM）结果显示薄膜呈多晶状。原子力显微镜（AFM）结果表明薄膜表面非常平整,无空洞。对12nm厚的HfO₂而言,其均方根粗糙度为0.16nm。由电学方法得出薄膜总的介电常数为18。 第四章主要研究了以下四个方面。第一,Si基HfO₂薄膜的热稳定性。对在900℃和一个大气压的N₂气氛下快速退火30s的HfO₂薄膜,扫描电子显微镜（SEM）和AFM结果发现薄膜表面依然很平整,无空洞。这表明在这种条件下薄膜未发生分解反应,其热稳定性良好。但是,同步辐射光电子能谱研究表明在超高真空条件下HfO₂薄膜在温度为750℃时开始分解。第二,HfO₂薄膜与Si的能带偏差。基于光电子能谱的方法用于研究HfO₂薄膜与Si的价带偏差,其值约为3.46eV。第三,HfO₂薄膜的禁带宽度。从01s的能量损失谱上可获得HfO₂的禁带宽度值约为5.0ev。第四,我们采用在位的光电子能谱方法研究HfO₂薄膜的初期生长。实验观察到,即使对非常薄的HfO₂薄膜,界面处存在富Si的硅酸盐（silicate）层。这层界面层的形成与Hf可能促进氧化的作用有关。 第五章中主要论述Er₂O₃薄膜在Si（001）和Si（111）上的外延生长,也包括Si衬底表面的薄SiO₂层对Er₂O₂外延生长的影响。Er₂O₃薄膜和Si的外延关系由XRD和RHEED来确定。在Si（001）衬底上,其外延关系为Er₂O₃（110）//Si（001）,Er₂O₃[001]//Si[110]或Er₂O₃[110]//Si[110]。在Si（111）衬底上,其外延关系为Er₂O₃（111）//Si（111）。在较低的生长气压或/和较低的生长温度下,Er的硅更多还原

【Abstract】 For continued technology scaling, high k materials are required to replace SiO₂ as gate dielectric in the next generation metal oxide field effect transistors （MOSFET）. Two kinds of materials are most promising. One is Group IVB metal oxides such as HfO₂ and ZrO₂; the other is Group IIIA and Group IIIB metal oxides including Al₂O₃, Y₂O₃ and some other rare earth oxides. In this thesis, we have studied the growth and characterization of high k materials HfO₂ and Er₂O₃.Here, the first two chapters introduce the research background and experimental equipments.In Chapter 3, the MBE growth and characterization of HfO₂ films are discussed. HfO₂ films were grown by electron beam evaporation using a metallic Hf source. Firstly, the basic physical and chemical properties of the as-grown films were characterized by using the corresponding methods. The as-deposited films are stoichiometric and polycrystalline, as verified by X-ray spectroscopy （XPS） and transmission electron microscopy （TEM） results, respectively. Atomic force microscopy （AFM） images show an extremely smooth surface obtained, with a root-mean-square （rms） roughness of about 0.16 nm for a 12 nm thick HfO₂ film. The films exhibit the overall dielectric constant of 18.Chapter 4 includes the following four sections. Firstly, the thermal stability of HfO₂ films on Si substrates. For the HfO₂ films upon rapid temperature annealing （RTA） at 900℃ in 1 atm N₂ for 30 s, both scan electron microscopy （SEM） and AFM results show a flat surface, and no voids or pits are found, indicating a good thermal stability of HfO₂ films upon annealing in the N₂ ambient. However, HfO₂ films begin to decompose at about 750℃ under the ultrahigh vacuum （UHV） condition, as verified by synchrotron radiation photoemission spectroscopy （SRPES） results. Secondly, band offset of HfO₂ films on Si（001）. The photoemission based method proposed by Kraut et al. is used to determine the band offset of HfO₂ with Si. Accordingly, the valence band offset of HfO₂ with Si is 3.46 eV. Thirdly, the band gap of HfO₂. By using the O 1s energy loss spectrum, the band gap of HfO₂ films is roughly measured to be about 5.0 eV. The relatively small value obtained mainly arises from the lower energy resolution due to the non-monochromatic Mg ka x-ray used. The last section concerns in situ photoemission study on initial growth of HfO₂ films on Si（001） is also included in Chapter 4. Interfacial layers between HfO₂ and the Si substrate are observed even for very thin HfO₂ films and confirmed to be Si-rich更多还原