导　　师： 邹志强

学科专业： 080903

授予学位： 博士

作　　者： ;

机构地区： 上海交通大学

摘　　要： 金属硅化物具有低电阻率和高温稳定性，其外延生长与传统的硅基集成电路（IC）工艺兼容，有望用作集成电路器件中的欧姆接触或肖特基势垒接触、低阻的互连线及有源电子器件等。金属硅化物在IC中的应用对减小栅极和内部互连线级的RC延迟有实际意义。与其他金属硅化物相比，锰的硅化物具有更多复杂的化学组成，如Mn/_6Si/_1、Mn/_9Si/_2、Mn/_3Si、Mn/_5Si/_2、Mn/_5Si/_3、MnSi以及非化学配比的MnSi/_/(～1.7/)。Mn/_5Si/_3和MnSi均具有金属性，有望用作低阻的互连线等；Mn/_5Si/_3具有反铁磁性, MnSi是B20型的金属间化合物，薄膜相的MnSi是至今发现的少数几种具有铁磁性的硅化物材料之一，且可以外延生长在Si衬底上，是电子自旋注入的很好的候选者；MnSi/_/(～1.7/)是带宽约为0.7eV的直接带隙半导体材料，是一种很有应用前景的高温热电材料，外延生长在Si衬底上的MnSi/_/(～1.7/)薄膜有望用于制作与现行硅工艺兼容的光电子器件，如光纤连接器和红外探测器阵列等。本文在以往研究的基础上，利用超高真空扫描隧道显微镜、扫描电子显微镜和透射电子显微镜对锰的硅化物薄膜和多种纳米结构在Si/(111/)-7×7和Si/(100/)-2×1表面上的固相外延生长（金属锰先在室温下沉积随后退火）和反应外延生长（金属锰直接沉积在加热的衬底上）进行了系统研究,主要研究成果如下： （1）锰的硅化物在Si/(111/)-7×7表面的反应外延生长：当衬底温度低于260℃时，沉积在硅衬底上的锰原子与衬底不反应，生成占据在衬底7×7元胞的半个单胞的锰团簇；当衬底温度控制在260℃-500℃，锰纳米团簇和平板状MnSi岛共存；当衬底温度高于500℃时，生成MnSi平板状岛、MnSi1.7纳米线和不规则的Mn/_5Si/_3三维岛等三种纳米结构。390℃-610℃温度范围内锰硅化物岛的成核密度符合传统成核理论。 （2）使用反应外延生长法，精确控制各项生长参数，在Si/_/(111/)-7×7表面上制备了具有大的长宽比的锰的硅化物纳米线。单位时间内衬底可以提供的自由硅原子数量对硅化物纳米线的生长起至关重要的作用。较高的生长温度和较小的锰沉积速率有利于纳米线的生长，同时亦能有效地抑制其他种类硅化物的生成。纳米线的生长由应力最小化驱动，是衬底和硅化物之间晶格失配的各向异性作用的结果。由扫描隧道谱（I-V）知纳米线是具有~0.8ev带隙的半导体。透射电子显微镜结果表明，纳米线成分为Mn/_Si/_/(1.7/)。 （3）研究了室温-~750℃，锰硅化物在Si/_/(111/)-7×7表面的固相外延生长情况。锰的覆盖度控制在0.6-1ML，室温沉积后生成由占据着衬底7×7元胞半胞的锰团簇构成的有序蜂窝状结构。250℃退火，锰团簇开始与衬底反应生成硅化物；~250℃-500℃退火，小的三维岛（富锰的硅化物）和平板状岛（Mn/_Si/_）在Si/_/(111/)表面上共存；500℃退火，小的三维岛全部转化为平板状的Mn/_Si/_岛；600℃退火，平板状岛又全部转化为由富硅的硅化物构成的大尺寸的三维岛。随着退火温度的升高和退火时间的延长，硅化物岛的密度降低，平均尺寸增大。大岛的形成是小岛消融的结果，遵从熟化机制。 （4）使用锰源和硅源双源共蒸发法，在Si/_/(111/)-7×7表面上制备了具有原子级平整度的Mn/_Si/_薄膜，膜厚~0.7nm，使用透射电子显微镜确定了薄膜的成分。薄膜与衬底间的晶格失配度约为-3.2/%，晶体取向关系为：/(111/)Si/_/////(111/)Mn/_Si/_,/[101/]Si/_/////[121/]Mn/_Si/_。研究发现较低的退火温度（250-300℃）和充足的退火时间有利于薄膜的生成，Mn/_Si/_薄膜的生长是通过Mn/_Si/_平板状岛的横向分形扩展生长实现的。扫描隧道谱显示Mn/_Si/_薄膜呈现金属性。 （5）研究了锰的硅化物纳米结构在Si/_/(100/)-2×1表面的反应外延生长情况。当生长温度高于~310℃时，沉积在硅衬底上的锰原子全部与衬底反应并生成两种形貌的硅化物：屋状的三维岛和纳米棒。研究表明，随着生长温度的提高，两种纳米结构的尺寸线性增大，成核密度成指数规律衰减，符合传统成核理论。 （6）研究了室温-~750℃，锰的硅化物在Si/_/(100/)-2×1表面的固相外延生长情况。室温下沉积在Si/_/(100/)-2×1表面的锰原子形成由不规则锰团簇构成的无定形结构。~280℃-305℃退火，开始发生硅化反应生成不规则外形的硅化物；430℃退火，不规则的硅化物全部转化为三维岛；600℃退火，三维岛全部转化为平板状岛。扫描隧道谱（I-V）表明，生成的硅化物都是具有~0.8ev禁带宽度的半导体，很可能由MnSi/_/(1.7/)构成。岛的长大过程遵从熟化机制。 Metal silicides have low resistivity and high temperature stability. The epitaxygrowth of metal silicides on silicion surface are eminently compatible with traditionalintergrated circuit /(IC/) process and can be used as Ohmic or Schottky barrier contactsand as low resistive interconnections. The application of metal silicides caneffectively reduce the RC delay between the gates and the inner interconnections.Compared with other metal silicides, manganese silicides have more possiblechemical composition，such as Mn/_6Si/_1、Mn/_9Si/_2、Mn/_3Si、Mn/_5Si/_2、Mn/_5Si/_3、MnSi andMn/_Si/_1.7. Mn/_5Si/_3and MnSi are metallic and can be used as low resistiveinterconnections; MnSi is a B20-type intermetallic compound, MnSi thin films werefound to be ferromagnetic and can epitaxally grow on silicon surface, its magneticproperties make it a promising candidate as spin injectors in future spintronic devices;On the other hand, MnSi/_/(1.7/)is semiconducting with a direct band gap of about0.7eVand is a potential material for many optoelectronic applications such as silicon-basedinfrared detectors and light sources. In this dissertation, based on previous researches,the solid-phase /(SP/) epitaxial growth /(manganese deposition at room temperaturefollowed by annealing/) and the reactive epitaxial growth /(deposition on a heatedsilicon substrate/) of manganese silicide nanostructures on Si/(111/)-7×7surfaces were studied by ultra-high vacuum scanning tunneling microscope /(UHV-STM/)，scanningelectronic microscope /(SEM/) and transmission electronic microscope /(TEM/). Themajor results are summarized as follows: /(1/) Reactive epitaxy growth of Mn silicide nanostructures on Si /(111/)-7×7surfaces:below260℃, there is no reaction between Mn atoms and the substrate，small clusterswith congruent size which occupy single7×7unit cell halves formed; between260℃and500℃, Mn nanoclusters and various Mn/_silicide islands coexist with bare Sisurface; above500℃, three kinds of large silicide islands /(nanowires, tabular islandsand3-D irregular-shaped islands/) have been distinguished. Besides, from390℃to610℃the nucleation density of silicide islands can be well described by conventionalnucleation theory. /(2/) Manganese silicide nanowires /(NWs/) with a large length//width ratio have beenpredominantly formed on Si/_/(111/)-7×7surfaces with the reactive epitaxy method by adelicate control of growth parameters. The supply of free Si atoms per unit time playsa crucial role in the formation of the NWs. High growth temperature and low Mn/_deposition rate are favorable for the growth of long NWs with a large length//widthratio and the formation of islands with other shapes can be greatly restrained underthese conditions. The formation of NWs is driven by the minimization of the strainenergy caused by the lattice mismatch between the silicide and substrate. Scanningtunneling spectroscopy measurements show that the NWs exhibit a semiconductingcharacter with a band gap of～0.8eV. TEM result shows that NWs are composed ofMnSi/(1.7/). /(3/) Solid-phase epitaxial growth of manganese silicides on a Si /(111/)-7×7surface attemperatures between room temperature and~750°C has been studied using scanningtunneling microscopy. The as-deposited Mn film of~0.6–1ML shows an orderedhoneycomb structure with each Mn cluster occupying a half of the7×7unit cell. TheMn clusters begin to react with the Si substrate to form silicides at~250°C. Twotypes of silicides, the three-dimensional /(3D/) and tabular islands, respectivelycorresponding to Mn-rich silicides and monosilicide MnSi, respectively, coexist onthe Si /(111/) surface at annealing temperatures between250and500°C. At500°C annealing, all3D islands convert into tabular islands and Mn/_Si/_is the only Mn silicidephase. Above600°C, the tabular islands convert into large3D islands that are likelyto be Si-rich manganese silicides. With increasing annealing temperature and time, thenumber density of silicide islands decreases, while the average size /(area/) of theremaining islands increases. The growth of large islands is a result of the dissolutionof small ones, which can be understood in the context of Ostwald ripeningmechanism. /(4/) Atomically flat MnSi thin films with few defects have been formed on Si /(111/)-7×7surfacewith the solid-phase epitaxy method by the codeposition of Mn and Si atoms. The thickness of thefilms is about~0.7nm. The crystallographic structure of the films is studied by transmissionelectron microscopy /(TEM/). The crystallographic orientation relationship between the silicionsubstrate and MnSi films can be /(111/)Si/////(111/)MnSi,/[101/]Si/////[121/]MnSi, with a lattice mismatchof-3.2/%. Comparatively low annealing temperature /(250-300℃/) and long annealing timeare favorable for the growth of thin films, and the growth of Mn/_Si/_thin films isaccomplished by the lateral expansion of Mn/_Si/_tabular islands. Scanning tunnelingspectroscopy measurements show that the Mn/_Si/_films exhibit a metallic character. /(5/) The growth of Mn silicide nanostructures on Si/(100/)-2×1surfaces with thereactive epitaxy method was studied using scanning tunneling microscopy. Growthtemperature being set above~310℃, all the incident Mn/_atoms react with thesubstrate and two kinds of silicide nanostructures are formed:3-D hut like islands andnanorods. With the increasing of growth temperature, nanostructures grow largelineally, but the nucleation density of silicide islands declined exponentially andfollows the conventional nucleation theory. /(6/) The growth of Mn silicide nanostructures on Si/(100/)-2×1surfaces with thesolid-phase epitaxy method between RT-~750℃was studied using scanning tunnelingmicroscopy. Mn amorphous structures are formed with RT deposition. When theannealing temperature is within the range of~280℃-305℃, silicide reaction takesplace and irregular-shaped silicide nanostructures form; after annealing at430℃, allthe irregular-shaped silicides convert into3-D islands; after annealing at600℃, only tabular islands form on the Si/(100/) surface. Scanning tunneling spectroscopymeasurements show that the silicides exhibit a semiconducting character with a bandgap of～0.8eV, which implies that they are composed of MnSi/_/(1.7/). The growth oflarge islands is a result of the dissolution of small ones, which can be understood inthe context of Ostwald ripening mechanism.

关 键 词： 外延生长 超高真空扫描隧道显微镜 固相外延生长 反应外延生长 锰的硅化物纳米结构 纳米线

分 类 号： [TN304]

领　　域： [电子电信]