發(fā)布時間：2018-05-17 13:39

  本文選題：立方碳化硅 + 橢圓偏振光譜��； 參考：《廣西大學》2017年碩士論文

【摘要】：隨著電子工業(yè)與技術(shù)的迅速發(fā)展,第一代半導體Si及第二代化合物半導體GaAs,GaP,InP等代表材料已經(jīng)不能滿足現(xiàn)代軍事的發(fā)展需求。因此,第三代化合物半導體材料SiC迅速發(fā)展起來。SiC半導體材料其禁帶寬度為2.3～3.3 eV,在930℃高溫下仍具有較低的本征載流子濃度、高電流擊穿電場、較高的電子飽和漂移速度及高熱導率等以上物理特性,使得SiC材料在高溫、高頻及高功率器件應(yīng)用中可成為替代Si的理想材料。為了進一步提高SiC薄膜的晶體質(zhì)量,促進碳化硅半導體材料的工業(yè)生產(chǎn),了解SiC材料的物理特性,如光學常數(shù),載流子濃度,應(yīng)力分布及晶格聲子振動顯得尤為重要。因此本論文,對一系列采用化學氣相沉淀方法生長的以Si為基底的3C-SiC薄膜進行多光譜技術(shù)測量與分析,如橢圓偏振光譜,拉曼散射光譜等。論文的主要研究內(nèi)容從以下幾個方面進行,如:(1)通過變角度和變溫橢圓偏振光譜研究以上薄膜光學性質(zhì)。從樣品表面及界面的反射光中測量得到橢圓偏振光偏振狀態(tài)變化。在三個不同入射角度,光譜范圍270～1700nm(0.73～4.6eV),溫度變化范圍從25～500℃條件下的進行橢圓偏振光譜測量。立方碳化硅的復雜介電常數(shù)采用Cody-Lorentz模型進行建模擬合,在全光譜范圍獲得較滿意的擬合結(jié)果,從而得到不同溫度下不同厚度的3C-SiC/Si薄膜的光學常數(shù)。(2)對一系列不同厚度3C-SiC/Si樣品進行不同激發(fā)波長的拉曼散射光譜測量,并結(jié)合兩種理論模型對其譜線進行理論分析。通過比較可見光及紫外光激發(fā)拉曼測量光譜,結(jié)果表明激光穿透深度及相應(yīng)穿透深度的晶體質(zhì)量是影響拉曼散射強度的主要原因。通過空間相關(guān)模型,對532 nm及325 nm激發(fā)波長下的橫向光學聲子模(TO)進行分析,比較不同激發(fā)波長TO模的強度,發(fā)現(xiàn)隨著激光穿透深度的不同TO聲子模強度的不同主要是相應(yīng)穿透深度下樣品的晶體質(zhì)量決定。為了進一步獲得3C-SiC/Si相應(yīng)載流子濃度,采用另一理論模型拉曼光譜縱光學聲子-等離子體激元耦合(LOPC)擬合。為了得到較好的擬合結(jié)果,采用差分拉曼的方法移去Si基底在相應(yīng)波數(shù)下的Si二階拉曼峰。通過擬合結(jié)果得到,325 nm激發(fā)波長拉曼光譜中得到的載流子濃度n大于532 nm激發(fā),可見接近樣品表面的上表面層與晶體的內(nèi)層其電學及光學性質(zhì)有很大的不同。同時也對不同取值的等離子阻尼常數(shù)及聲子阻尼常數(shù)對LO拉曼模的譜線影響進行了相應(yīng)分析。(3)由于3C-SiC與Si之間存在大于20%的晶格失配而產(chǎn)生高密度的晶界混亂,導致其存在較大的晶界應(yīng)力。因此3C-SiC/Si外延層中存在相應(yīng)殘余應(yīng)力。為了分析以Si為基底的3C-SiC薄膜中應(yīng)力分布,采用橫截面拉曼散射光譜的方法對3C-SiC-C4樣品的殘余應(yīng)力進行分析。結(jié)合Stefan Rohmfeld教授提出的TO及LO聲子模拉曼頻率ω與平面應(yīng)變△a‖/a0公式。該關(guān)系式在所研究的應(yīng)變方程上是線性的,并且線性回歸產(chǎn)生。由于基底Si較強的二階拉曼信號及等離子體激元耦合模的影響,3C-SiC薄膜的LO拉曼中心頻率不能準確得到。根據(jù)上述公式,及測量得到的TO拉曼頻率可以計算得到相應(yīng)的殘余應(yīng)力ε0。由于3C-SiC薄膜和Si基底之間的晶格失配度,通過以上分析最大的應(yīng)力在晶界處被發(fā)現(xiàn)。(4)采用變溫拉曼光譜對不同摻雜濃度及不同厚度的3C-SiC薄膜進行分析。兩片3C-SiC薄膜的TO拉曼頻移隨著溫度的升高均逐漸向低波數(shù)移動。通過擬合分析可知,TO拉曼頻移隨溫度的升高向低波數(shù)移動,主要是由于四聲子非諧振耦合起主導作用。對兩片具有不同載流子濃度的3C-SiC薄膜的LOPC峰進行分析,重摻雜樣品C3的LOPC拉曼頻移出現(xiàn)異常,隨著溫度升高先向高波數(shù)移動,再向低波數(shù)移動。這種隨著溫度變化的LOPC拉曼頻移異常的現(xiàn)象,主要是由于低溫下雜質(zhì)電離不完全電離,熱膨脹效應(yīng)、晶格失配存在的殘余應(yīng)力及聲子的非諧振耦合作用引起。
[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.
【學位授予單位】：廣西大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN304.24;O657.3

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