Ge覆盖层诱导晶化多晶Si薄膜的晶化特性研究

采用电子束蒸发技术在衬底温度为180℃条件下生长具有Ge覆盖层的非晶Si薄膜,并于500℃、600℃、700℃真空退火5h.采用Raman散射、X射线衍射(XRD)、全自动数字式显微镜等对所制备薄膜的晶化特性进行研究.结果表明,Ge覆盖层具有诱导非晶Si薄膜晶化的作用,且随着退火温度的升高a-Si薄膜晶化越显著.具有Ge覆盖层非晶薄膜经500℃退火5h沿Si(400)方向开始晶化,对应晶粒尺寸约为4.9 nm.将退火温度升高到700℃时,非晶硅薄膜几乎全部晶化,晶化多晶Si薄膜在Si(400)方向表现出很强的择优取向特性,晶粒尺寸高达23.3μm.与相同条件下制备的无Ge覆盖层的非晶Si薄膜相比,晶化温度降低了300℃.     

常规退火与光退火固相晶化的对比

为研究传统炉子退火与光退火固相晶化的不同特点,用石英玻璃作衬底,在室温、350℃和450℃下用PECVD法直接沉积非晶硅(a-Si:H)薄膜,把沉积的样品分别在850℃下用传统炉子退火3h、用光快速热处理(RTP)5min,然后用Raman、XRD和SEM分析对比,发现传统炉子退火后的晶粒分布不均匀,光退火后的晶粒分布均匀.XRD分析发现两种方法晶粒尺寸均为30nm左右.     

玻璃衬底上中温制备多晶硅薄膜的量子态现象

用PECVD法直接沉积的非晶硅(a-Si:H)薄膜用传统炉在中温退火,然后用拉曼光谱、XRD和SEM分析,发现晶粒大小随退火温度和退火时间呈现量子态现象.分析发现在传统炉中850℃下退火三个小时晶粒大小出现极大值,平均晶粒尺寸为30nm左右.     

单晶硅衬底上Ge填埋层低温应力诱导重结晶制备多晶硅薄膜

本文采用电子束蒸发法,室温下在Si(400)的基片上生长含锗(Ge)填埋层的非晶硅薄膜,其结构为a-Si/Ge/Sisubstrate,并在真空中进行后续退火.采用Raman散射(Raman Scattering)、X射线衍射(X-ray Diffraction)、高分辨电子扫描显微镜(HRSEM)、光学显微镜和热重差热分析(DSC)等手段,研究退火后样品晶化特性和晶化机理.结果表明,室温下生长的含有250 nm Ge填埋层的生长态样品在400℃退火5h,薄膜基本全部实现晶化,并表现出明显的Si (111)择优取向.样品分别在400℃、500℃、600℃和700℃退火后薄膜的横向光学波的波峰均在519cm-1附近,半高宽大约为6.1 cm-1,且均在Si(111)方向高度择优生长.退火温度为600℃的样品对应的晶粒尺寸约为20 μm.然而,在相同的薄膜结构(a-Si/Ge/Si substrate)的前提下,当把生长温度提高到300℃时,温度高达到700℃退火时间5h后,薄膜依然是非晶硅状态.差热分析表明,室温生长的样品,在后续退火过程中伴随界面应力的释放,从而诱导非晶硅薄膜重结晶成多晶硅薄膜.     

利用快速热退火法制备多晶硅薄膜

为了制备优质的多晶硅薄膜,该论文研究了非晶硅薄膜的快速热退火(RTA)技术.先利用PECVD设备沉积非晶硅薄膜,然后把其放入快速热退火炉中进行退火.退火前后的薄膜利用X射线衍射(XRD)仪、Raman光谱仪及扫描电子显微镜(SEM)测试其晶体结构及表面形貌,利用电导率测试设备测试其暗电导率.研究表明退火温度、退火时间以及沉积时的衬底温度对非晶硅薄膜的晶化都有很大的影响.     

非晶硅薄膜制备及其晶化特性研究

用磁控溅射法在K9玻璃上沉积了非晶硅(a-Si)膜和a-Si/Al膜,并将其在流动的N2气氛下进行退火.对退火前后的样品进行Raman光谱、XRD和SEM表征和分析.Raman光谱表明随着退火温度的升高,a-Si膜的散射峰出现了明显的蓝移,但XRD结果表明薄膜仍为非晶态;而a-Si/Al膜在温度很低时就已经开始晶化.     

HWCVD低温制备超薄硼掺杂纳米晶硅薄膜

采用热丝化学气相沉积(HWCVD)技术在低温条件下(100℃)制备超薄(～30 nm)的硼掺杂硅薄膜.系统研究了氢稀释比例RH对薄膜的微结构和电学性能的影响.当RH由55增加至115,薄膜的有序度增加,晶化率升高,载流子浓度增加,暗电导率增加;同时,薄膜的缺陷密度增加、霍尔迁移率降低.实验证实,当RH=55～70时,超薄硅薄膜开始晶化,这是薄膜由非晶到纳米晶的转化区.快速热退火工艺进一步提高了薄膜导电率.在RH=115、衬底温度为100℃沉积条件下,经过420℃、80 s退火,获得电导率为6.88 S/cm的超薄硼掺杂纳米晶硅薄膜.     

温度对快速热退火制备多晶硅薄膜结构与电学性能的影响

采用快速热退火方法对热丝CVD沉积的非晶硅薄膜进行了晶化处理.利用傅里叶红外光谱研究了非晶硅薄膜脱氢处理前后Si-Hx含量的变化;用X射线衍射(XRD),拉曼(Raman)光谱和扫描电子显微镜研究了硅薄膜的结构性能与退火温度的关系;利用电导率测试研究了硅薄膜的电学性能对退火温度的依赖性.研究发现,脱氢处理可以有效的抑制快速热退火引起的硅薄膜中微裂纹的出现.随着退火温度由700℃升高至1100℃,硅薄膜的结晶性逐渐升高,在1100℃下快速热退火15 s制备的多晶硅薄膜的晶化率高达96.7;.同时,硼掺杂硅薄膜的电导率也由700℃退火的1.39×10-6 S·cm-1提高至1100℃退火的16.41 S·cm-1,增大了7个数量级.     

基于PECVD制备多晶硅薄膜研究

基于PECVD以高纯SiH4为气源研究制备多晶硅薄膜,在衬底温度550℃、射频(13.56MHz)电源功率为20W直接沉积获得多晶硅薄膜.采用X射线衍射仪(XRD) 和场发射扫描电子显微镜(SEM) 对多个样品薄膜的结晶情况及形貌进行分析,薄膜结晶粒取向均为<111>、<220>、<311>晶向.对550℃沉积态薄膜在900℃、1100℃时进行高温退火处理,硅衍射峰明显加强.结果表明,退火温度越高,退火时间越长,得到多晶硅薄膜表面晶粒趋于平坦,择优取向为<111>晶向,晶粒也相对增大.     

光退火制备多晶硅薄膜的量子态现象

用PECVD法直接沉积的非晶硅(a-Si:H)薄膜在中温情况下光退火,然后用XRD、Raman光谱和SEM分析,发现晶粒大小随退火温度和退火时间呈现量子态现象.平均晶粒大小为30nm左右.     

Crystallization of silicon thin films by current‐induced joule heating using a tungsten overcoat

A modified crystallization process using current‐induced joule heating under vacuum is presented. A thin layer of high temperature resistant tungsten was sputtered on the amorphous silicon as the conducting and annealing medium. The thin film thickness was measured by α‐stepper. The high current density provided effective means in crystallizing the amorphous silicon layer. The crystalline morphology was studied by scanning electron microscopy (SEM) after Secco‐etch, transmission electron microscopy (TEM), and x‐ray diffraction (XRD), under different annealing conditions. The grain size was controlled in the range of 0.1‐0.5 μm and could be increased with annealing time. No tungsten silicide was found. Some defects were formed due to electron‐migration effect near the electrodes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of absorption coefficient spectra in a-Si:H films near the transition from amorphous to crystalline phase measured by resonant photothermal bending spectroscopy

Optical absorption spectra of a widegap hydrogenated amorphous silicon film have been estimated by resonant photothermal bending spectroscopy. It is found that excess absorption exists over the photon energy region of 1.2–1.6 eV. This excess absorption decreases by light illumination and does not recover through thermal annealing. The decrease in the excess absorption may be due to oxidization of the film by light illumination.     

Processing of intensities of electron scattering from amorphous silicon by methods of continuous wavelet analysis

It is shown that intensities of electron scattering from amorphous silicon can be processed by the methods of wavelet analysis. The coordination radii for amorphous silicon at various annealing temperatures are calculated using the intensity distribution of coefficients of the wavelet transform.     

Thermal annealing of a-Si/Au superlattice thin films

The superlattice films, which consist of amorphous silicon (a-Si) and amorphous gold (Au), were prepared by ultra-high vacuum evaporation system. The first layer was grown a-Si with a thickness of 4.2 nm and the second layer was grown Au with a thickness of 0.8 nm. Thermal annealing was performed at 473, 673, and 873 K, respectively. The structural properties of the films were investigated using transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman scattering spectroscopy. The electrical property was assessed by the temperature dependence of electrical conductivity. A crystallization of Si and a forming of Au nanoparticles were observed in all of the annealing films. The crystalline volume fraction reached 70% by annealing time for 15 min. An average diameter of the Au nanoparticles embedded in Si matrix also increased with increasing the annealing temperature. At annealing temperature above 873 K, Au atoms migrated toward the film surface. It was observed that the electrical conductivity changed in several temperatures.     

Temperature dependent formation of microcrystal and amorphous silicon by vacuum evaporation

In silicon films deposited in vacuum by electron beam evaporation of solid silicon, the substrate temperature dependence of the formation temperature of amorphous silicon and crystalline silicon is determined. On steel and alumina substrates, below 520°C, the silicon film is amorphous. Above this temperature, the film is crystalline with a pronounced optical band gap of 1.7 eV. With thermal treatment in vacuum, a transformation from an amorphous to a crystalline state is observed at 650°C.     

Spectroscopic ellipsometry study of nickel induced crystallization of a-Si

The aim of this work is to present a spectroscopic ellipsometry study focused on the annealing time effect on nickel metal induced crystallization of amorphous silicon thin films. For this purpose silicon layers with 80 and 125 nm were used on the top of which a 0.5 nm Ni thick layer was deposited. The ellipsometry simulation using a Bruggemann Effective Medium Approximation shows that films with 80 nm reach a crystalline fraction of 72% after 1 h annealing, appearing to be full crystallized after 2 h. No significant structural improvement is detected for longer annealing times. On the 125 nm samples the crystalline volume fraction after 1 h is only around 7%, requiring 5 h to get a similar crystalline fraction than the one achieved with the thinner film. This means that the time required for full crystallization will be strongly determined by the Si layer thickness. Using a new fitting approach the Ni content within the films was also determined by SE and related to the silicon film thickness.     

Hydrogenated amorphous silicon with substrate-dependent structure

Hydrogenated amorphous silicon (a-Si:H) thin films grown at 250°C on (1 0 0) crystalline substrate using plasma-enhanced chemical vapor deposition (PECVD) with SiH₄/H₂ gas flow ratio equal to 5/1 (sccm) are investigated by transmission electron microscopy. It is found that the thin film is totally amorphous when grown on a glass substrate. But when the substrate is changed to crystalline silicon, some crystalline grains are found embedded in the amorphous structure in certain regions even if the thickness of the film reaches 600 nm. It is suggested that the amorphous silicon film grown on a crystalline silicon substrate at a temperature of 250°C without heavy H₂ dilution is a mixed network of a small amount of crystalline silicon and the major portion of amorphous silicon.     

Analysis of IBAD silicon oxynitride film for anti-reflection coating application

A SOI-based optoelectronic device needs a high-quality anti-reflection coating on both faces of the device to minimize the optical reflectance from the face. In this work amorphous silicon oxynitride films were deposited on silicon substrates by ion beam assisted deposition (IBAD). The main purpose was to use silicon oxynitride film as single layer anti-reflection coating for SOI-based optoelectronic devices. This application is primarily based on the ability to tune the silicon oxynitride optical functions to the values optimal by changing deposition parameters. The chemical information was measured by X-ray photoelectron spectroscopy (XPS). Spectroscopic ellipsometry (SE) was applied to measure the refractive index and thickness. Single-side polished silicon substrate that was coated with silicon oxynitride film exhibited low reflectance. Double-side polished silicon substrate that was coated with silicon oxynitride film exhibited high transmittance. The results suggested silicon oxynitride film was a very attractive single layer anti-reflection coating for SOI-based optoelectronic device.     

Remote plasma deposition of microcrystalline silicon thin-films: Film structure and the role of atomic hydrogen

Microcrystalline silicon films grown in an expanding thermal plasma, i.e. in the absence of ion bombardment, are found to be porous and rich in nano-sized voids. By carrying out an extensive investigation on the material quality of films deposited in the amorphous-to-microcrystalline transition regime, on the microcrystalline silicon growth development, and on the influence of the substrate temperature, it is concluded that the inferior material quality is related to the lack of a sufficient amount of amorphous silicon tissue. As possible cause for the insufficient amount of amorphous silicon tissue, the interaction of atomic hydrogen with amorphous silicon films has been studied in order to highlight a possible competition between film growth and H-induced etching of amorphous silicon, and between film growth and H-induced surface/film modification. The etch rates obtained are too low to compete with film growth. Furthermore, atomic H cannot be considered responsible for the poor quality of amorphous tissue present in the microcrystalline silicon films, as the H up-take mainly takes place in divacancies. These results suggest that ion bombardment may be a necessary condition to provide good quality microcrystalline silicon films.     

Influence of electron beam annealing on optical properties of a-Si from ellipsometric spectrum study

The optical properties of a-Si films prepared by rf sputtering and annealed by an electron beam under different conditions have been measured by the spectroscopic ellipsometry technique in the ultraviolet-visible range. The results show that the optical properties of these samples obviously changed with suitable annealing conditions, and the amorphous silicon can be gradually transformed to crystalline silicon.