立方碳化硅的多光谱技术研究

发布时间：2018-05-17 13:39

本文选题：立方碳化硅 + 椭圆偏振光谱　；参考：《广西大学》2017年硕士论文

【摘要】：随着电子工业与技术的迅速发展,第一代半导体Si及第二代化合物半导体GaAs,GaP,InP等代表材料已经不能满足现代军事的发展需求。因此,第三代化合物半导体材料SiC迅速发展起来。SiC半导体材料其禁带宽度为2.3～3.3 eV,在930℃高温下仍具有较低的本征载流子浓度、高电流击穿电场、较高的电子饱和漂移速度及高热导率等以上物理特性,使得SiC材料在高温、高频及高功率器件应用中可成为替代Si的理想材料。为了进一步提高SiC薄膜的晶体质量,促进碳化硅半导体材料的工业生产,了解SiC材料的物理特性,如光学常数,载流子浓度,应力分布及晶格声子振动显得尤为重要。因此本论文,对一系列采用化学气相沉淀方法生长的以Si为基底的3C-SiC薄膜进行多光谱技术测量与分析,如椭圆偏振光谱,拉曼散射光谱等。论文的主要研究内容从以下几个方面进行,如:(1)通过变角度和变温椭圆偏振光谱研究以上薄膜光学性质。从样品表面及界面的反射光中测量得到椭圆偏振光偏振状态变化。在三个不同入射角度,光谱范围270～1700nm(0.73～4.6eV),温度变化范围从25～500℃条件下的进行椭圆偏振光谱测量。立方碳化硅的复杂介电常数采用Cody-Lorentz模型进行建模拟合,在全光谱范围获得较满意的拟合结果,从而得到不同温度下不同厚度的3C-SiC/Si薄膜的光学常数。(2)对一系列不同厚度3C-SiC/Si样品进行不同激发波长的拉曼散射光谱测量,并结合两种理论模型对其谱线进行理论分析。通过比较可见光及紫外光激发拉曼测量光谱,结果表明激光穿透深度及相应穿透深度的晶体质量是影响拉曼散射强度的主要原因。通过空间相关模型,对532 nm及325 nm激发波长下的横向光学声子模(TO)进行分析,比较不同激发波长TO模的强度,发现随着激光穿透深度的不同TO声子模强度的不同主要是相应穿透深度下样品的晶体质量决定。为了进一步获得3C-SiC/Si相应载流子浓度,采用另一理论模型拉曼光谱纵光学声子-等离子体激元耦合(LOPC)拟合。为了得到较好的拟合结果,采用差分拉曼的方法移去Si基底在相应波数下的Si二阶拉曼峰。通过拟合结果得到,325 nm激发波长拉曼光谱中得到的载流子浓度n大于532 nm激发,可见接近样品表面的上表面层与晶体的内层其电学及光学性质有很大的不同。同时也对不同取值的等离子阻尼常数及声子阻尼常数对LO拉曼模的谱线影响进行了相应分析。(3)由于3C-SiC与Si之间存在大于20%的晶格失配而产生高密度的晶界混乱,导致其存在较大的晶界应力。因此3C-SiC/Si外延层中存在相应残余应力。为了分析以Si为基底的3C-SiC薄膜中应力分布,采用横截面拉曼散射光谱的方法对3C-SiC-C4样品的残余应力进行分析。结合Stefan Rohmfeld教授提出的TO及LO声子模拉曼频率ω与平面应变△a‖/a0公式。该关系式在所研究的应变方程上是线性的,并且线性回归产生。由于基底Si较强的二阶拉曼信号及等离子体激元耦合模的影响,3C-SiC薄膜的LO拉曼中心频率不能准确得到。根据上述公式,及测量得到的TO拉曼频率可以计算得到相应的残余应力ε0。由于3C-SiC薄膜和Si基底之间的晶格失配度,通过以上分析最大的应力在晶界处被发现。(4)采用变温拉曼光谱对不同掺杂浓度及不同厚度的3C-SiC薄膜进行分析。两片3C-SiC薄膜的TO拉曼频移随着温度的升高均逐渐向低波数移动。通过拟合分析可知,TO拉曼频移随温度的升高向低波数移动,主要是由于四声子非谐振耦合起主导作用。对两片具有不同载流子浓度的3C-SiC薄膜的LOPC峰进行分析,重掺杂样品C3的LOPC拉曼频移出现异常,随着温度升高先向高波数移动,再向低波数移动。这种随着温度变化的LOPC拉曼频移异常的现象,主要是由于低温下杂质电离不完全电离,热膨胀效应、晶格失配存在的残余应力及声子的非谐振耦合作用引起。
[Abstract]:With the rapid development of electronic industry and technology, the first generation of semiconductor Si and the two generation compound semiconductor GaAs, GaP, InP and other representative materials have been unable to meet the needs of modern military development. Therefore, the third generation compound semiconductor material SiC has rapidly developed.SiC semiconductor materials with a band gap of 2.3 to 3.3 eV, and still remains at the high temperature of 930. With low intrinsic carrier concentration, high current breakdown electric field, high electron saturation drift velocity and high thermal conductivity, the SiC material can be an ideal substitute for Si in high temperature, high frequency and high power devices. In order to further improve the crystal quality of SiC thin film, the silicon carbide semiconductor material can be promoted. In industrial production, it is particularly important to understand the physical properties of SiC materials, such as optical constants, carrier concentration, stress distribution and lattice phonon vibration. Therefore, in this paper, a series of Si based 3C-SiC films, such as ellipsometry spectrum and Raman scattering light, are measured and analyzed by a series of chemical vapor deposition methods. The main contents of the paper are as follows: (1) study the optical properties of the above film through the variable angle and temperature variable ellipsometry spectrum. The polarization state of elliptically polarized light is measured from the reflected light of the surface and interface of the sample. At three different angles of entry, the spectrum range is from 270 to 1700nm (0.73 ~ 4.6eV) and temperature. The degree variation ranges from 25~500 C to the ellipsometry spectrum measurement. The complex permittivity of cubic silicon carbide is modeled and fitted by Cody-Lorentz model. The satisfactory fitting results are obtained in the spectrum range. The optical constants of 3C-SiC/Si films with different thickness at different temperatures are obtained. (2) a series of different thickness 3C-SiC/Si samples are measured by Raman scattering spectra at different excitation wavelengths, and the spectral lines are analyzed with two theoretical models. The results show that the laser penetration depth and the crystal mass of the corresponding penetration depth are the main factors affecting the Raman scattering intensity by comparing the visible light and ultraviolet light excited Raman spectra. Through space correlation model, the transverse optical phonon mode (TO) at 532 nm and 325 nm excitation wavelengths is analyzed, and the intensity of TO modes at different excitation wavelengths is compared. It is found that the difference of the intensity of the TO phonon modes with the different penetration depth of the laser is mainly determined by the crystal mass of the sample under the corresponding penetration depth. In order to further obtain the corresponding 3C-SiC/Si load of the TO. In order to get better fitting results, the Raman peaks of the Si two of the Si substrate under the corresponding wave number are removed by the method of differential Raman. The carrier concentration n in the Raman spectra of the 325 nm excitation wavelengths is obtained by using the differential Raman method. More than 532 nm excitation, it can be seen that the electrical and optical properties of the upper surface layer near the sample surface and the inner layer of the crystal are very different. At the same time, the influence of the different values of the plasma damping constant and the phonon damping constant on the spectral lines of the LO Raman mode is also analyzed. (3) the lattice mismatch between 3C-SiC and Si is greater than 20%. In order to analyze the stress distribution in the Si based 3C-SiC thin film, the residual stress in the 3C-SiC thin film is analyzed. The residual stress of the 3C-SiC-C4 sample is analyzed by means of cross section Raman scattering spectroscopy. Combined with Professor Stefan Rohmfeld, the analysis of the residual stress in the 3C-SiC film on the epitaxial layer is analyzed. The formula of TO and LO phonon mode Raman frequency omega and plane strain Delta a /a0 formula. This formula is linear in the strain equation studied and linear regression. The frequency of LO Raman center of 3C-SiC film can not be accurately obtained because of the strong two order Raman signal and plasma excimer coupling mode of the base Si. According to the above formula, And the measured TO Raman frequency can be calculated to obtain the corresponding residual stress e 0. due to the lattice mismatch between the 3C-SiC film and the Si substrate. The maximum stress of the above analysis is found at the grain boundary. (4) the 3C-SiC thin films with different doping concentration and different thickness are analyzed by the variable Winraman spectrum. The TO of two 3C-SiC films The Raman shift gradually moves to the low wave number as the temperature rises. Through the fitting analysis, it is found that the TO Raman shift moves to the low wave number with the increase of temperature, mainly due to the leading role of the four phonon non resonant coupling. The LOPC peak of the 3C-SiC film with different carrier concentration is analyzed, and the LOPC Raman frequency of the heavy doped sample C3 is found. The anomalous shift appears as the temperature rises first to the high wave number and then to the low wave number. This abnormal LOPC Raman shift is mainly due to the incomplete ionization of impurities, the thermal expansion effect, the residual stress in lattice mismatch and the non resonant coupling of the acoustic phonon at low temperature.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.24;O657.3

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