低温激光退火多晶硅薄膜的光学常数研究

用分光反射光谱(SR)和分光椭偏光谱(SE)来分析低温激光退火多晶硅薄膜的光学特性。利用多层光学和Braggeman有效介质近似模型(B-EMA),对薄膜光学常数和结构参数(膜厚度,表面粗糙度和非均匀性)的退火功率依存关系进行解析。解析结果表明,有一个临界退火功率存在。退火达到这个功率时,多晶硅薄膜的光学常数非常接近单晶硅。由于受增大晶粒尺寸影响,在这个功率时,薄膜表面粗糙度和非均匀性也显示了一峰值。在整个退火区域,膜厚度有大约8%变化。     

Ultra-thin SiO2 film studies: index, thickness, roughness and the initial oxidation regime

Special techniques are needed to reliably measure the ultra thin film and interfacial properties. For this purpose we have used and/or further developed several techniques: Fowler–Nordheim (FN) electron tunneling current oscillations (FNCOs); spectroscopic ellipsometry (SE); a novel application of SE called spectroscopic immersion ellipsometry (SIE); atomic force microscopy (AFM) along with Fractal analysis. In this study we review our recent results on ultra thin SiO₂ films for film thickness measurements, the kinetics of the initial regime of Si oxidation, and interfacial roughness and the effects of roughness on Si oxidation and interfacial electronic properties.     

Surface roughness and optoelectronic properties of intrinsic and doped nc-Si:H prepared by Rf-magnetron sputtering at low temperature

The correlation between the surface roughness and optoelectronic properties of a series of intrinsic and doped nanocrystalline silicon samples deposited by rf-magnetron sputtering at low temperature has been deduced from atomic force microscopy, spectroscopic ellipsometry, optical transmission and reflection and Raman spectroscopy measurements. Atomic force microscopy observations and spectroscopic ellipsometry analysis of the surface layers reveal that the Root Mean Square (rms) surface roughness for the doped samples increases with increasing sample thickness, while for the intrinsic samples we obtain lower rms surface roughness values which are found to be independent of the film thickness. The surface roughness is related to the microstructure of crystalline grains at the layer surface as verified by analysis of the experimental pseudo-dielectric function. However optical reflectance measurements obtained show that the film thickness affects the surface roughness, but not significantly the complex refractive index.     

同步辐射光刻的X射线反射谱表征

采用X射线反射（XRR）谱对同步辐射导致的氧化物薄膜的刻蚀进行了在位测试,结果表明波长为0．154nm的单色X光在室温下可对MgO和Cr2O3产生轻微的刻蚀。与文献中大量报道的同步辐射X射线光刻及烧蚀不同．这是单色X射线光刻的首次报道。尽管刻蚀速率极慢,但利用XRR谱的高分辨率,成功地检测到了膜厚的减薄。     

Infrared reflectance analysis of GaN epitaxial layers grown on sapphire and silicon substrates

Infrared reflectance (IR) of GaN grown on sapphire and silicon substrates has been studied both theoretically and experimentally. The theoretical calculation of the IR spectra is based on the transfer matrix method. The IR spectral characteristics influenced by several factors, such as film thickness, incident angle, free carriers, are systematically examined. Combined with experimental results, surface scattering and interface layer effects are also studied. For GaN epilayers grown on sapphire, carrier concentrations and mobility are determined by fitting to the IR reststrahlen band and compared with the Hall measurement. The interface effect is demonstrated to cause a damping behaviour of the interference fringes away from the reststrahlen band. For GaN grown on Si, the IR spectra predicted the large surface roughness of the epilayers. A variation of IR reststrahlen band is correlated to the microstructures of the films, i.e. their polycrystalline nature of the GaN films grown on Si. A three-component effective medium model is proposed to calculate the IR spectra for polycrystalline GaN, and a qualitative correlation between the IR spectra and structure of the film is established. All results show that IR, as a non-destructive method, is efficient for characterising GaN epilayers in semiconductor processing.     

紧凑型光谱薄膜测厚仪的研制

为了开发一种用于测量各向同性均匀薄膜介质厚度的紧凑型薄膜测厚仪,采用了共光路垂直入射设计,利用薄膜干涉原理,通过非线性优化算法对反射光谱进行了拟合,反演计算出了薄膜样品的厚度。采用该仪器测量部分SiO2/Si薄膜样件,测量结果与商业椭偏仪测量结果之间的相对偏差小于0.5%,而单次测量时间仅为70ms。结果表明,该薄膜测厚仪具有对测量距离不敏感、光路简洁、结构紧凑及重复性精度良好等优点,对实现在线实时测量功能具有积极意义。     

溶胶-凝胶工艺制备SrTiO3纳米薄膜的研究

采用溶胶-凝胶方法,以醋酸锶、钛酸四丁酯为前驱体,乙酰丙酮为螯合剂,乙二醇甲醚为溶剂,乙酸为助溶剂和催化剂制备溶胶,用旋涂法在Si(100)衬底上制备出了具有典型钙钛矿型结构的SrTiO3纳米薄膜.用XRD、AFM、SEM和椭圆偏光仪等手段分析了薄膜的性能,结果显示薄膜的表面均匀、无裂纹、厚度20～30nm,折射率1.75～1.85,晶粒度35～60nm,表面平均粗糙度RMS为3.4～3.8 nm,晶粒形貌呈类圆锥形态.     

Optical diagnostics of plasma chemistries and chamber conditions in gate oxide stack etch

Various kinds of plasma chemistries were used in the study of polysilicon gate stack etch. Different degrees of gate oxide surface roughness were observed. Stable gate oxide thickness and smooth surface were found when using fluorine-based plasma chemistries. In contrast, non-fluorine-based chemistry tends to give uneven gate oxide thickness and rough surface. The stability of the gate oxide thickness can be controlled by chamber seasoning when using non-fluorine-based chemistry. It is also noticed that fluorine-based chemistries always result in thicker remaining gate oxide than the one without fluorine. The type of wafer used for seasoning can also have influence on chamber condition and subsequently the etch rates and gate oxide thickness. From the trends of emission intensity of Si, it is believed that etch byproducts as well as chamber wall polymer have potential impacts on the observed variation of gate oxide surface roughness, thickness, and etch rates.     

Simulation and analysis of polycrystalline silicon photovoltaic cells surface color differences based on transfer matrix method

Following the previous work, in this paper, the antireflective films thicknesses, refractive indexes and reflectance spectra of different color categories of the polycrystalline silicon cells are tested and compared. It is found that the color difference of polycrystalline silicon cells is mainly caused by the antireflective film. Then the matrix transfer method is used to simulate the reflection spectra according to the actual tested parameters of the samples, and the effectiveness of the simulation is verified. Finally, according to the distribution of the spectral solar irradiance, the total solar absorption of the polycrystalline silicon cells with different antireflective film thicknesses is simulated. The optimal value of the antireflective film thickness of the polycrystalline silicon cell is calculated. This study has important guiding significance for photovoltaic (PV) enterprises to realize the optimal production of plasma enhanced chemical vapor deposition (PECVD) process in production.     

Back-etch method for plan view transmission electron microscopy sample preparation of optically opaque films

Back-etch methods have been widely used to prepare plan view transmission electron microscopy (TEM) samples of thin films on membranes by removal of the Si substrate below the membrane by backside etching. The conventional means to determine when to stop the etch process is to observe the color of the light transmitted through the sample, which is sensitive to the remaining Si thickness. However, most metallic films thicker than 75 nm are opaque, and there is no detectable color change prior to film perforation. In this paper, a back-etch method based on the observation of an abrupt change of optical reflection contrast is introduced as a means to determine the etch endpoint to prepare TEM samples for these films. As the acid etchant removes the Si substrate material a rough interface is generated. This interface becomes a relatively smooth and featureless region when the etchant reaches the membrane (film/SiO2). This featureless region is caused by the mirror reflection of the film plane (film/SiO2 interface) through the optically transparent SiO2 layer. The lower etch rate of SiO2 (compared with Si) gives the operator enough time to stop the etching without perforating the film. A clear view of the morphology and control of Si roughness during etching are critical to this method, which are discussed in detail. The procedures of mounting wax removal and sample rinsing are also described in detail, as during these steps damage to the membrane may easily occur without appropriate consideration. As examples, the preparation of 100-nm-thick Fe-based amorphous alloy thin film and 160-nm-thick Cu-thin film samples for TEM imaging is described.     

Characterization of organic thin films for OLEDs using spectroscopic ellipsometry

We report the optical characterization of thin, evaporated organic films used in fabrication of organic light emitting diodes (OLEDs): N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-l,l'biphenyl-4,4'diamine,or TPD,andtris(8-hydroxy)quinolato aluminum, or Alq3. In particular, we have obtained and analyzed spectroscopic eliipsometry (SE) data using a multi-sample approach, to determine the optical constants for Alq₃ and TPD films over the wavelength range 250-850 nm. We show that bi-layer Alq₃/TPD films on Si can be analyzed for individual layer thicknesses, even though the refractive index is nearly identical for these films in the visible region. Simulations of in situ monitoring are also presented, which show sub-nm thickness resolution for organic layer growth on a Si monitor wafer. SE has great utility for process control, either by ex situ or in situ thickness measurement.     

SiO_2薄膜致密性的表征

论述了表征SiO2薄膜致密性的三种方法:红外光谱法、折射率法和腐蚀速率法,分析了它们各自的特点。制备了不同衬底和不同工艺的三个热氧化SiO2薄膜样品,利用红外光谱法和折射率法对样品进行了对比测试。结果表明,采用红外光谱法表征SiO2薄膜的致密性时,主特征吸收峰频率不仅与薄膜致密性相关,还与样品的厚度和衬底等因素有关;而折射率法受这些因素的影响较小,是表征SiO2薄膜致密性较为适用的方法。     

玻璃基底和表面粗糙度在氮化硅薄膜椭偏测量中的影响

在光谱椭偏测量中,玻璃基底的背反射会给测量结果造成较大影响。针对平板显示器件玻璃基底表面氮化硅镀膜进行了椭偏测量和模型计算。采用相干背反射模型“空气基底空气”计算并拟合得到与厂商数据符合较好的玻璃基底折射率。对氮化硅薄膜采用Tauc Lorentz色散模型进行了分析拟合,讨论了薄膜与基底界面层、表面粗糙度对光学常数及模型拟合的影响,表明在薄膜与基底间晶格失配的情况下,界面层的引入对改善拟合度是必要的。给出了薄膜体系的光学常数、薄膜结构的分析结果。     

硅各向异性浅槽腐蚀实验研究

通过实验分析,对比了异丙醇(IPA)和超声波对Si(100)面在KOH溶液和四甲基氢氧化氨(TMAH)溶液中的浅槽腐蚀速率及其表面形态的影响。实验结果表明,IPA能降低TMAH溶液的腐蚀速率,但IPA在KOH溶液中腐蚀速率降低不明显;IPA加入到较高浓度的KOH溶液中,会在Si表面产生较大小丘,恶化了Si腐蚀表面的质量,但在TMAH溶液中加入一定量的IPA会改善腐蚀表面的质量;超声波能加快腐蚀速率并能改善Si腐蚀表面质量,但对于加入IPA的较高浓度KOH溶液,超声波未能消除Si腐蚀表面的小丘,另外,超声波还能减弱腐蚀过程中微尺寸沟槽的尺寸效应;在腐蚀条件和配比一定情况下,TMAH溶液的腐蚀质量比KOH溶液好。     

In situ sensors for monitoring and control in molecular beam epitaxial growth of Hg1−xCdxTe

The current status of the implementation and refinement of two wafer state sensors forin situ monitoring and control during molecular beam epitaxial (MBE) growth of Hg_1−xCd_xTe will be reported. First a rapid scan spectral ellipsometer has been developed and employed for precisely measuring compositions of Hg_1−xCd_xTe alloys during growth. MBE films in the composition range x = 0.20 to 0.30 have been grown andin situ spectra taken at the growth temperature (180°C) and at room temperature. The MBE films were treated as single layers without the need to invoke any surface film (due to surface roughness, oxide, or of any different composition) as required for exsitu data. The least squares fit over the whole spectral range was used as a measure of the precision. The film composition was also determinedex situ by wavelength dispersive analysis of x-rays and by Fourier transform infrared (FTIR) spectrometry after verifying that there was no lateral variation. A precision of better than ±0.0015 has so far been demonstrated usingin situ spectral ellipsometry for Cd composition or CdTe mole fraction, x, measurements. This compares with ±0.003 for single wavelength ellipsometry. The composition of Hg_1−xCd_xTe films were also monitored during growth. A spectral pyrometer based on a FTIR spectrometer has also been developed for substrate temperature measurements during growth. The spectral pyrometer measures both the emission and reflectance to give the emissivity of a growing sample over a range of wavelengths spanning the peak of the grey body emission. From the reflectivity measurements, the thickness (in excess of 1 μm) of the growing film is also determined from the interference fringes. The spectral ellipsometer is only capable of measuring thicknesses up to C.a 5000°A (i.e. optically thin). Excellent agreement is obtained between thein situ (at growth temperature) andex situ (at room temperature) thickness measurements. The small discrepancy can be explained by the refractive index of Hg_1−xCd_xTe being 5% higher at the growth temperature than at room temperature. The combination ofin situ sensors now provides a means of continuously monitoring the composition and thickness of the growing Hg_1−xCd_xTe film.     

Effects of controlled texturization of the crystalline Si surfaceon the SiO2/Si effective barrier height

A two-stage plasma etch texturination process to control the level of crystalline silicon surface roughness has been investigated. Initially, a Cl₂ plasma etch is used to produce a very rough Si surface. This is followed by an isotropic SF₆ plasma etch, whose etch time is used to reduce and control the level of surface roughness created by the previous step. Oxides grown on texturized Si surfaces with short SF₆ etch times exhibit lower effective SiO₂/Si barrier height and greater electron injection enhancement than those with longer SF₆ etch times     

基于双D型光纤表面等离子共振折射率传感研究

以双D型光纤作为传输载体,研究了一种基于表面等离子共振技术的双D型光纤折射率传感器。利用时域有限差分法,分析了双D型光纤剩余包层厚度、金膜厚度、金膜表面粗糙度以及双通道传输对光纤SPR传感器性能的影响。仿真结果表明,当剩余包层厚度为300~500nm、覆盖的金膜厚度为50nm时,双D型光纤SPR传感器的性能得到优化;金膜表面粗糙度也是影响传感器性能的重要因素,当金膜表面粗糙度的均方根值低于2nm或其相关长度大于160nm时,金膜表面粗糙度对传感器性能的影响显著减小,且在折射率为1.33~1.36的传感环境下具有较好的线性度;在双D型光纤两侧覆不同的金属膜,可以实现信号的双通道测量。     

Parameterized complex dielectric functions of CuIn1−xGaxSe2: applications in optical characterization of compositional non‐uniformities and depth profiles in materials and solar cells

In‐situ spectroscopic ellipsometry (SE) was employed to extract the complex dielectric functions ε = ε₁ + iε₂ over the spectral range of 0.75–6.5 eV for a set of polycrystalline CuIn_1−xGa_xSe₂ (CIGS) thin films with different alloy compositions x = [Ga]/{[In] + [Ga]}. For highest possible accuracy in ε for each CIGS thin film, specialized SE procedures were adopted including (i) deposition to a thickness of ~600 Å on smooth native oxide covered crystal silicon wafers, which minimizes the surface roughness on the film and thus the required corrections in data analysis, and (ii) measurement in‐situ, which minimizes ambient contamination and oxidation of the film surface. Assuming an analytical form for each of the ε spectra for these CIGS films, oscillator parameters were obtained in best fits, and these parameters were fit in turn to polynomials in x. With the resulting database of polynomial coefficients, the ε spectra for any composition of CIGS can be generated from the single parameter, x. In addition to enabling accurate contactless determination of bulk and surface roughness layer thicknesses of CIGS films by high speed multichannel SE, the database enables characterization of the composition and its profile with depth into these films, and even how the depth profile varies spatially within the plane of the films. In this study, depth profile parameters were found to correlate spatially with solar cell performance parameters. As a result, SE provides the capability of contactless compositional analysis of production‐scale CIGS photovoltaic modules at high speed. Copyright © 2016 John Wiley & Sons, Ltd.     

Stabilization of sheet resistance for metal lines by formation of etch stop layer (ESL) trench structure

Sheet resistance of metal lines is mainly affected by critical dimension (CD), etch depth, and chemical mechanical planarization amount in damascene process. Therefore, these factors must be stably controlled in order to stabilize the sheet resistance of metal lines. Especially the etch depth, which is sensitive to the pattern density and the equipment conditions bring not only the variation of sheet resistance of metal lines but also the connection problem to the under-layered contacts. The objective of this study is to reduce the variation of the sheet resistance of metal lines by stabilization of the etch depth with etch stop layer (ESL). SiN film was used as an ESL while the intermetal dielectric (IMD) films were employed by the conventional fluorine-doped silicate glass (FSG)/SiH₄ film with an increment of thickness by the employment of SiN film as an ESL. The selectivity of oxide-to-nitride was about 6.4:1 for etch stop step. While the stop layers were removed after the etch stop step, the pre-metal dielectric was also etched at the same time for the stable connection to the under-layered contacts. Comparing the ESL method to the conventional method, more stable metal lines were formed with the in-line CD measurement, thickness measurement, cross-sectional scanning electron microscopy analysis, and sheet resistance measurement from the view point of the connection to the under-layered contacts. The stable sheet resistance of metal lines was also obtained with the changes in etch time or thickness.