非晶硅薄膜的低温快速晶化及其结构分析

在镀铝的廉价玻璃衬底上高速沉积的非晶硅薄膜在不同的温度下退火10min.退火温度为500℃时,薄膜表面形成了硅铝的混合相,非晶硅薄膜开始呈现了晶化现象 退火温度为550℃时,大部分(约80%)的非晶硅晶化为多晶硅,平均晶粒尺寸为500nm 退火温度为600℃时,几乎所有的非晶硅都转化为多晶硅,其平均晶粒尺寸约为15μm.     

非晶硅薄膜的低温快速晶化及其结构分析

在镀铝的廉价玻璃衬底上高速沉积的非晶硅薄膜在不同的温度下退火10min.退火温度为500℃时,薄膜表面形成了硅铝的混合相, 非晶硅薄膜开始呈现了晶化现象;退火温度为550℃时,大部分(约80%)的非晶硅晶化为多晶硅,平均晶粒尺寸为500nm;退火温度为600℃时,几乎所有的非晶硅都转化为多晶硅,其平均晶粒尺寸约为1.5μm.     

退火对Ge诱导晶化多晶Si薄膜结晶特性的影响

本文采用磁控溅射法, 衬底温度500 ℃下在硅衬底上分别制备具有Ge填埋层的a-Si/Ge 薄膜和a-Si薄膜, 并进行后续退火, 采用Raman光谱、X射线衍射、原子力显微镜及场发射扫描电镜等对所制薄膜样品进行结构表征. 结果表明, Ge有诱导非晶硅晶化的作用, 并得出以下重要结论: 衬底温度为500 ℃时生长的a-Si/Ge薄膜, 经600 ℃退火5 h Ge诱导非晶硅薄膜的晶化率为44%, 在相同的退火时间下退火温度提高到700 ℃, 晶化率达54%. 相同条件下, 无Ge填埋层的a-Si薄膜经800 ℃退火5 h薄膜实现晶化, 晶化率为46%. 通过Ge填埋层诱导晶化可使在相同的条件下生长的非晶硅晶薄膜的晶化温度降低约200 ℃. Ge诱导晶化多晶Si薄膜在Si(200)方向具有高度择优取向, 且在此方向对应的晶粒尺寸约为76 nm. 通过Ge诱导晶化制备多晶Si薄膜有望成为制备高质量多晶Si薄膜的一条有效途径.     

大尺寸化学Ni源金属诱导晶化多晶硅的研究

用无电电镀的化学方法，在VHF-PECVD沉积获得的非晶硅薄膜表面形成镍诱导源，在550℃下退火若干小时，可以诱导产生微米量级的多晶硅晶粒.用此法形成的镍源可以均匀地分布在非晶硅薄膜的表面.非晶硅薄膜上形成晶核的数量取决于镍溶液的浓度、pH值和无电电镀的时间等参量.当成核密度比较低时可以观察到径向晶化现象.用VHF-PECVD非晶硅薄膜作为晶化前驱物，晶化后多晶硅的最大晶粒尺寸可达到90μm.用此多晶硅试制的TFT，获得了良好的器件特性. 关键词： 金属诱导晶化 化学源 多晶硅 薄膜晶体管     

溶液法铝诱导晶化制备多晶硅薄膜

采用铝（Al）盐溶液作为诱导源进行了非晶硅晶化成多晶硅的研究.光学显微镜观测与Raman光谱分析表明,合适配比的铝盐溶液能够将非晶硅予以诱导晶化.采用剥层XPS测试分析,探究了Al盐溶液与硅表面可能的化学反应以及随之发生的硅-铝层交换的过程.最后对溶液法诱导晶化的机理进行了讨论. 关键词： 铝诱导晶化 多晶硅薄膜 溶液法     

变温退火制备铝诱导大晶粒多晶硅薄膜的机理研究

为了缩短铝诱导法制备大晶粒多晶硅薄膜的退火时间,用射频磁控溅射法在玻璃衬底上沉积了a-Si/SiO2/Al叠层膜,并用两种方法进行变温退火.分析了变温退火工艺对铝诱导晶化过程的影响,着重讨论了退火过程中温度由低温升到高温时不形成小晶粒的机理和条件.研究表明,当退火温度升高时,是否形成小晶粒取决于晶粒半径、耗尽层厚度和相邻晶粒间距三者之间的关系.     

化学源金属诱导多晶硅研究

以硝酸镍溶液为化学源，对于用不同方法沉积得到的非晶硅膜作晶化前驱物，都能予以不同程度的晶化.用VHF-PECVD方法获得的非晶硅膜作前驱物，易于去氢并更容易晶化.当化学源浓度不同时，晶化效果会存在一定差别，在一定的范围内，溶液浓度越高，晶化后形成的晶粒越大.退火气氛对晶化结果产生某些影响，可以发现，在N₂气氛下退火，比在大气下有更好的晶化效果.最后对物理源与化学源作诱导金属的晶化结果进行了比较，结果表明，对诱导金属源而言，化学源显示出更为有效的晶化趋势. 关键词： 金属诱导晶化 多晶硅薄膜 低温制备 退火处理     

532nm连续激光晶化非晶硅薄膜的原位拉曼光谱研究

用磁控溅射制备了非晶硅薄膜,用波长为532 nm的连续激光退火和显微Raman光谱原位测试技术和场发射扫描电子显微镜研究了非晶硅薄膜在不同激光功率密度和不同扫描速度下的晶化状态。结果表明,激光照射时间10 s,激光功率密度大于2.929×105W/cm2时,能实现非晶硅薄膜晶化。在激光功率密度为5.093×105W/cm2,扫描速度为10 mm/s时非晶硅开始向多晶硅转化。在5.093×105W/cm2的功率密度下,以1.0 mm/s的扫描速度退火非晶硅薄膜,得到的晶粒直径为740 nm。     

不同退火温度下晶化硅薄膜的电学输运性质

采用等离子体化学气相沉积技术制备氢化非晶硅薄膜,经过不同温度下的热退火处理,使薄膜由非晶结构向晶化结构转变,得到含有纳米晶粒的晶化硅薄膜.在晶化过程中,采用Raman技术对样品的结构进行表征.通过变温电导率的测试,对薄膜的电学输运性质进行了分析.研究结果表明：退火温度为700 ℃时,样品中开始有纳米晶形成,随着退火温度的增加,样品的晶化比增大,在1000 ℃时,薄膜的晶化比达到90%以上.在700 ℃退火时,薄膜中晶化成分较低,载流子的传输特性主要受到与硅悬挂键有关的缺陷态影响,表现为带尾定域态的跳跃电导 关键词： 氢化非晶硅 退火 纳米硅 电输运     

磁控共溅射低温制备多晶硅薄膜及其特性研究

多晶硅在光电子器件领域具有较为重要的用途。利用磁控溅射镀膜系统,通过共溅射技术在玻璃衬底上制备了非晶硅铝(α-Si/Al)复合膜,将Al原子团包覆在α-Si基质中,膜中的Al含量可通过Al和Si的溅射功率比来调节。复合膜于N₂气氛中进行350 ℃,10 min快速退火处理,制备出了多晶硅薄膜。利用X射线衍射仪、拉曼光谱仪和紫外-可见光-近红外分光光度计对多晶硅薄膜的性能进行表征,研究了Al含量对多晶硅薄膜性能的影响。结果表明：共溅射法制备的α-Si/Al复合膜在低温光热退火下晶化为晶粒分布均匀的多晶硅薄膜;随着膜中Al含量逐渐增加,多晶硅薄膜的晶化率、晶粒尺寸逐渐增加,带隙则逐渐降低;Al/Si溅射功率比为0.1时可获得纳米晶硅薄膜,Al/Si溅射功率比为0.3时得到晶化率较高的多晶硅薄膜,通过Al含量的调节可实现多晶硅薄膜的晶化率、晶粒尺寸及带隙的可控。     

AlCl3-induced crystallization of amorphous silicon thin films

It is reported that the direct contact between Al and amorphous silicon (a-Si) enhances the crystallization of a-Si films. But the polycrystalline silicon (poly-Si) films crystallized by the direct contact of Al metal film suffer the problems of rough surface. In our study, we utilized the AlCl₃ vapor during the a-Si films deposition instead of Al metal film to enhance crystallization. X-ray diffraction (XRD) shows that the AlCl₃ vapor so successfully enhanced the crystallization of a-Si films that the crystallization was completed in 5 h at 540 °C. And the orientation of the poly-Si film deposited with AlCl₃ vapor is much more random than that of annealed with Al metal under layer. But the average grain size is much larger than that. Moreover, the surface of the AlCl₃-induced crystallized poly-Si film was much smoother than that of the Al-induced poly-Si film. The Al and Cl incorporation into the poly-Si film was confirmed using X-ray photoelectron spectroscopy (XPS) and found that the quantity of Al and Cl incorporated into the Si film was below the detection limit of XPS.     

Evolution of surface morphology during the growth of amorphous and polycrystalline silicon films

The evolution of the surface morphology of LPCVD poly-Si films (deposition temperature 620°C), a-Si films (deposition temperature 550°C) and poly-Si films, obtained by the crystallization of a-Si is investigated in the thickness range 40–500 nm. It is found that upon an increase in the thickness from 40 to 500 nm, the surface roughness (parameters S _q , S _z , S _v ) is increased for poly-Si, while in the case of a-Si and poly-Si obtained by crystallization a-Si, on the contrary, decreases. The correlation length (S _al ) increases for all three types of silicon films. Poly-Si films, obtained by the crystallization of a-Si, as compared to LPCVD poly-Si films have a significantly lower surface roughness, respectively, S _q two times less at a thickness of 40 nm and sixteen times less at 500 nm. In contrast to thick films, thin a-Si films (at thicknesses of less than 40 nm) have a granular structure, which is especially pronounced at an average thickness of about 20 nm and there is a maximum on the dependence of the roughness S _q on the thickness.     

Microwave-induced low-temperature crystallization of amorphous Si thin films

Microwave heating was utilized for low-temperature crystallization of amorphous Si (a-Si) films. Microwave heating lowered the annealing temperature and reduced the annealing time. By microwave heating the hydrogen in the amorphous films was diffused out long before the nucleation of polycrystalline Si (poly-Si). The combination of NiCl₂ coating on a-Si and microwave heating greatly reduced crystallization temperature. The combination of metal-induced crystallization and microwave-induced crystallization might be a useful technique to develop high-quality poly-Si films at low temperature.     

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 °C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 °C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 °C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).     

Low-Temperature (<100°C) Poly-Si Thin Film Fabrication on Glass

Polycrystalline silicon (poly-Si) thin-film is fabricated on Al-coated planar glass substrates at the temperature below 100°C, using aluminium-induced crystallized (AIC) amorphous silicon (a-Si) deposited by dc-magnetron sputtering under an electric field. The properties of NA poly-Si films (AIC of dc-magnetron sputtered silicon non-annealing) are characterized by Raman spectroscopy and x-ray diffraction (XRD) spectroscopy. A narrow and symmetrical Raman peak at a wave number of about 521cm^-1 is observed for samples, showing that the films are fully crystallized. XRD spectra reveal that the films are preferentially (111) oriented. Furthermore, the XRD spectrum of the sample prepared without electric field does not show any XRD peaks for poly-Si, which only appears at about 38°for Al (111) orientation. It is indicated that the electric field plays an important role in crystallization of poly-Si during the dc-magnetron sputtering. Thus, high quality poly-Si film can be obtained at low temperature and separate post-deposition step of AIC of a-silicon can be avoided.     

Modeling of CW laser diode irradiation of amorphous silicon films

The purpose of this work is to determine the optimal parameters required to crystallize thin amorphous silicon films on glass substrate with a continuous wave (CW) laser diode (λ = 808 nm), using a numerical model developed in COMSOL Multiphysics. The numerical simulation of the laser crystallization process takes into account the solid-liquid phase change and the difference between the melting temperature of amorphous (Tm_a-Si = 1420 K) and that of crystalline silicon (Tm_c-Si = 1690 K). We have varied the main parameters controlling the crystallization process, namely the power and the scan speed of the laser beam. Furthermore the initial temperature as well as the thickness of the a-Si:H layer were also taken as a parameter to optimize the process. We have determined the melting, crystallization and ablation energy threshold versus the different operational parameters.     

Effects of gas temperature on optical and transport properties of a-Si:H films deposited by PECVD

Effects of silane temperature (T _g) before glow-discharge on the optical and transport properties of hydrogenated amorphous silicon (a-Si:H) thin films were investigated. The optical measurements show that the refractive index increases with increasing T _g. The transport characterizations show that when T _g increases, the dark conductivity increases. However, the temperature coefficient of resistance decreases. In addition, after holding at 130°C for 20 h, the resistance variation, ΔR/R, of the films deposited at T _g = room temperature (10.8%) is much larger than those deposited at silane temperatures of 80°C (3%) and 160°C (2%). This can be attributed to different rates of defect creation in a-Si:H films caused by various T _g.     

In situ spectromicroscopic study of nickel induced lateral crystallization of amorphous silicon thin film using SPESM

Scanning photoelectron spectromicroscopy (SPESM) has been used to study nickel metal induced lateral crystallization (Ni-MILC) of amorphous silicon (a-Si) thin films, produced by in situ annealing of vacuum deposited Ni patterned films on a-Si. The spatial variations in the chemical composition of the Ni-MILC of a-Si were directly imaged. High-resolution photoemission spectra of both Si 2p and Ni 3p core levels and valence band were used to evaluate morphological changes and chemical interactions. Our direct spectromicroscopic characterization clearly shows that the Ni-MILC process in UHV leads to the lower crystallization temperature and a faster crystallization speed of a-Si, and a poly-Si film with high-crystallinity can be obtained. A unified mechanism for the enhanced growth rate of the high-crystallinity poly-Si film produced by Ni-MILC in UHV is proposed.     

Preparation and characterization of transparent NiO thin films deposited by spray pyrolysis technique

Nickel oxide thin films were successfully fabricated with various deposition time (t_d = 5, 10, and 15 min) on glass substrates using spray pyrolysis technique. The deposited films undergo thermal treatment at 350 °C for various annealing time (t_a = 0, 15, 30 and 60 min). In this study, the effect of t_d and t_a on film thickness was observed and their influence on structural, morphological and optical properties were investigated. The films deposited with t_d = 5 min showed amorphous structure while the films grown at higher deposition time became partially crystallized with preferred growth along (1 1 1) direction. Heat treatment carried out in air allowed us to tune the polycrystalline structure and the diffraction intensity at preferred peak increases with the increase in t_a which is a consequence of better crystallinity. This was reflected in the AFM micrographs of the films which suggested that the thermal annealing (or increasing t_a) facilitates the process of grain-growth, and improves the crystalline microstructure. The optical transmission of the films was found to vary with t_d and t_a and thus film thickness. The thinner films show higher transparency in the UV–vis spectral region. The optical band gap was blue-shifted from 3.35 eV to 3.51 eV depending on t_a. The effect of t_a on the various optical constants of the NiO films has also been discussed.