Influence of laser wavelength and beam profile on Nd:YAG laser assisted formation of polycrystalline-Si films

Influence of wavelengths and beam profiles of a pulsed Nd³⁺:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd³⁺:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm² to 560 mJ/cm², where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm² to 480 mJ/cm². On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm² was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd³⁺:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization.     

Laser marking on microcrystalline silicon film

We present a compact dot marker using a CW laser on a microcrystalline silicon (Si) thin film. A laser annealing shows a continuous crystallization transformation from nano to a large domain (> 200 nm) of Si nanocrystals. This microscale patterning is quite useful since we can manipulate a two-dimentional (2-D) process of Si structural forms for better and efficient thin-film transistor (TFT) devices as well as for photovoltaic application with uniform electron mobility. A Raman scattering microscope is adopted to draw a 2-D mapping of crystal Si film with the intensity of optical-phonon mode at 520 cm(-1). At a 300-nm spatial resolution, the position resolved the Raman scattering spectra measurements carried out to observe distribution of various Si species (e.g., large crystalline, polycrystalline and amorphous phase). The population of polycrystalline (poly-Si) species in the thin film can be analyzed with the frequency shift (delta omega) from the optical-phonon line since poly-Si distribution varies widely with conditions, such as an irradiated-laser power. Solid-phase crystallization with CW laser irradiation improves conductivity of poly-Si with micropatterning to develop the potential of the device application.     

铝诱导晶化P型非晶硅薄膜实验研究

利用PECVD设备在普通玻璃基片上沉积硼掺杂P型非晶硅薄膜,采用铝诱导晶化法（AIC）在氮气气氛保护下进行退火处理制备出P型多晶硅薄膜,研究了不同厚度的金属铝膜和热处理温度对非晶硅薄膜的微观结构、表面形貌的影响。实验结果表明：铝膜相对厚度越厚,对a—Si的晶化诱导效果则越好,在一定温度条件下,相对较厚的铝膜可以缩短a—Si晶化为polv-Si的时间,并且能使a—Si的晶化更加完整,产生尺寸较大的硅晶颗粒。在铝膜厚度相同,退火温度相同的条件下,热处理的时间越长,则晶化发生的程度越深,晶化越为彻底。     

聚酰亚胺/二氧化硅复合薄膜的热物性及其影响因素

应用自行研制的亚微米/微米薄膜激光脉冲法热扩散率测定仪和差示扫描量热仪(DSC)分别测定了聚酰亚胺(PI)薄膜和PI/SiO_2复合薄膜在不同温度下的热扩散率、热导率和比热,解决了激光脉冲法测定热导试样的透光问题.研究了PI/SiO_2复合薄膜的热物性随SiO_2添加量和温度的变化关系.结果表明:随着温度的升高,PI薄膜及PI/SiO_2复合薄膜的热扩散率下降,比热和热导率线性增加.在PI薄膜中添加SiO_2颗粒可降低PI薄膜的比热,明显增强导热性能,但是不会改变PI薄膜热导率随温度升高而增大的变化规律.     

多晶硅薄膜的表面处理工艺

采用NH3和N2O的等离子体分别对p-Si（多晶硅）薄膜表面进行了钝化处理,处理后的p-Si TFT（薄膜晶体管）具有比未处理FTF更优越的性能,通电试验与热应力试验后,处理后的器件呈现出更好的承受电负荷和热应力能力,钝化的微观机理是NH3和N2O等离子体中和了p-Si薄膜的悬挂键,形成牢固的Si-N键,减少了表面态密度。     

多晶硅薄膜的铝诱导晶化法制备及其晶粒的择优取向特性

采用铝诱导非晶硅薄膜晶化技术制备了多晶硅薄膜,并研究了多晶硅的成核和生长特性。非晶硅薄膜采用等离子体增强化学气相沉积法制备,其表面沉积铝薄膜后经不同温度的氮氛围退火处理。结果表明,退火后的硅薄膜层与铝层发生置换,所生长的多晶硅颗粒的平均尺寸约为150nm。X射线衍射分析结果揭示,薄膜的晶向显著依赖于退火温度,较低温度下,铝诱导晶化速率较慢,薄膜的优化晶向与非晶硅薄膜中团簇的初始原子排列趋势紧密相关。而较高温度下,铝诱导晶化促使多晶硅(111)择优成核及随后的固相生长。     

Influence of the Crystal Growth Temperature on the Formation of Zr Reach Crystalline Phases in a Nuclear Waste Confinement Glass Ceramic

Many glass ceramics are potential candidates for the confinement of radioactive waste. This is the case of glasses embedding radiation-resistant ceramics as zirconolites, pyrochlores or pyroxenes. This study deals with the influence of the crystal growth temperature on the formation of such phases in a nuclear glass ceramic in the system： Al203-SiO2-CaO-MgO-ZrO2-TiO2. The materials with six contents of ZrO2, ranging from 1.00 to 6.40 m.%, are synthesized by a discontinuous method, consisting in a double-melting at 1,350℃, followed by both a nucleation at 564℃, and a crystal growth treatment at： 900, 100 and 1,100 ℃. For the whole of the materials, the morphology reveals a glassy feature, with a opaque aspect. One can also evidence a different crystallization process from the bulk to the surface. The glass ceramics X-ray diffraction analysis （XRD） show that the main identified crystalline skeletons are those of： 2M-zirconolite, CaZrTi207 and ZrO2, depending on the content ofZrO2 in materials and the crystal-growth temperature. The material with the middle content in ZrO2 （4.5 m.%） and crystallized at the middle value ofTc （1,010℃） show the greatest content in zirconolite （87 %）, doped with either lanthanides or alcalin-earth elements, due to the complexity of the mixture of oxides. The temperature of 1,010 ℃ appears to be more selective with regard to the formation of the 2M-zirconolite.     

Excimer laser annealed poly-Si thin film transistor with self-aligned lightly doped drain structure

We have made an excimer laser annealed poly-Si thin film transistor (TFT). The stress of the poly-Si films crystallized by excimer laser annealing is studied by Raman spectroscopy. The transverse-optic phonon frequency is independent of the excimer laser energy, but dependant on the precursor a-Si film thickness. The nMOS TFT with a self-aligned lightly doped drain (LDD) structure shows low leakage current. The large leakage current of the pMOS TFT with non-LDD structure is reduced by the off-state stress. The gate to channel capacitance as a function of gate voltage for nMOS TFT shows the characteristic parallel shift of the capacitance–voltage curves with frequency variation.     

Performance enhancement of excimer laser crystallized poly-Si thin film transistors with fluorine implantation technology

Polycrystalline silicon thin film transistors (poly-Si TFTs) with the ion implantation of fluorine elements were investigated in this study. The electrical performance and reliability were reported comprehensively. Experimental work has shown the electrical characteristics of excimer laser crystallized F-ions-implanted poly-Si TFTs are improved effectively, especially for field effect mobility. It is also found that the fluorine piled up at the poly-Si interface during thermal annealing, for the TFT fabricated without a prior deposition of pad oxide. The stronger Si-F bonds replace the Si-Si/Si-H, leading to the superior electrical reliability. However, the dose of F ions is critical in poly-Si, or the electrical characteristics of TFT devices will be degraded.     

Thin film growth of epitaxial, polycrystalline and amorphous SrRuO3

The SrRuO₃ thin films were grown on amorphous fused silica and (100) single crystal LaAlO₃ substrates by pulsed laser deposition method. On fused silica substrates, polycrystalline SrRuO₃ thin film was obtained and below the crystallization temperature, SrRuO₃ thin films show an amorphous phase. For the case of epitaxial growth on (100) single crystal LaAlO₃ substrate, the crystallization temperature of SrRuO₃ thin film was increased by ∼ 100 °C indicating that additional energy is necessary in order to obtain the epitaxial thin film. By using the eclipse method and the control of substrate temperature, the variations of surface morphologies and grain size were observed by atomic force microscope. Below the crystallization temperature, amorphous SrRuO₃ thin film shows hopping transport property of an insulator.     

准分子激光引起的非晶硅薄膜晶化行为的研究

利用KrF准分子激光对非晶硅薄膜的表层进行了晶化.研究了激光能量密度和照射脉冲数对薄膜结晶度的影响,并对晶化后薄膜的形貌和结构进行了表征.结果表明:该非晶硅薄膜晶化阈值约为110 mJ/cm2,且不受照射脉冲数的影响;激光能量密度是影响薄膜结晶度的首要因素,但在较低的能量密度时,增加照射脉冲数也会显著的提高薄膜结晶度;结构及形貌表征发现,薄膜晶化层厚度约为400～500 nm,平均晶粒尺寸为30～50 nm.     

Direct growth of large grain polycrystalline silicon films on aluminum-induced crystallization seed layer using hot-wire chemical vapor deposition

Large grain polycrystalline silicon (poly-Si) films on glass substrates have been deposited on an aluminum-induced crystallization (AIC) seed layer using hot-wire chemical vapor deposition (HWCVD). A poly-Si seed layer was first formed by the AIC process and a thicker poly-Si film was subsequently deposited upon the seed layer using HWCVD. The effects of AIC annealing parameters on the structural and electrical properties of the poly-Si seed layers were characterized by Raman scattering spectroscopy, field-emission scanning electron microscopy, and Hall measurements. It was found that the crystallinity of seed layer was enhanced with increasing the annealing duration and temperature. The poly-Si seed layer formed at optimum annealing parameters can reach a grain size of 700 nm, hole concentration of 3.5 × 10¹⁸ cm^− 3, and Hall mobility of 22 cm²/Vs. After forming the seed layer, poly-Si films with good crystalline quality and high growth rate (> 1 nm/s) can be obtained using HWCVD. These results indicated that the HWCVD-deposited poly-Si film on an AIC seed layer could be a promising candidate for thin-film Si photovoltaic applications.     

Fabrication of excimer laser annealed poly-Si thin film transistor by using an elevated temperature ion shower doping

We have investigated the effect of an ion shower doping of laser annealed poly-Si films at elevated substrate temperatures. The substrate temperature was varied from room temperature to 300°C when the poly-Si film was doped with phosphorus by a non-mass-separated ion shower. Optical, structural, and electrical characterizations have been performed in order to study the effect of the ion shower doping. The sheet resistance of the doped poly-Si films was decreased from 7 × 10⁶ Ω/sq to 700 Ω/sq when the substrate temperature was increased from room temperature to 300°C. This large change in sheet resistance is due to the fact that the doped films do not become amorphous but remain in the polycrystallinephase. The mildly elevated substrate heating appears to contribute mainly to reduction of ion damages incurred in the poly-Si films in addition to the activation of dopants during the ion shower doping. From the fabricated n-channel poly-Si TFTs, the current crowding effect do not occur because of the low contact source-drain resistance and the field effect mobility of 120 cm²/(V s) has been obtained.     

金属镍诱导p型多晶硅薄膜的光电性能研究

利用电子束蒸镀方法及重掺杂p型硅为蒸发源在K8玻璃衬底上沉积非晶硅薄膜,采用镍诱导晶化法在氮气氛围下进行退火处理制备出p型多晶硅薄膜.研究了不同温度热处理条件对p型多晶硅薄膜的光电性能的影响,通过霍尔测量、拉曼光谱、原子力显微镜、紫外-可见光吸收光谱等测试手段对薄膜进行分析.结果表明,随着晶化温度的提高晶化程度先增强后...     

Crystallization of Au-Si/glass thin film: a real-time synchrotron X-ray scattering study

The crystallization of amorphous, Si-rich, Au28Si72/glass thin film was studied in real-time synchrotron X-ray scattering experiments. The amorphous film crystallizes first into Au and Si phases at a low temperature of 206 degrees C. At annealing temperatures above eutectic temperature (T(E) = 360 degrees C), the Au phase melts while the Si phase rapidly grows further. The crystallized Au28Si72 thin film has nanowire-type grains with 1000-nm-length and 10-nm-diameter. We confirm that the Au liquid phase contributes to the low-temperature crystallization of the Si solid phase for Si-nanowire growth.     

A Numerical Simulation to Propose a Flash Method for In Situ Detection of the Thermal Diffusivity of Anisotropic Thin Film Materials

Strong anisotropy of thermal diffusivity is frequently observed in thin film materials. We propose an in situ experimental method to remotely measure radial and axial components of the thermal diffusivity. The method is based on the traditional laser flash technique but is specialized to also highly challenging experimental situations such as sample manufacture and use phase when thin films may be exposed to very high pressures or temperatures and to high temperature gradients. The method requires laser pulses of very short duration and fast measurement of transient temperature excursions in only radial directions on the surface of the thin film samples. The accuracy of the method is checked by comparison with results from a finite element calculation for a graphite sheet with high anisotropic conductivity that simulates a thermo-physical experiment.     

Crystallization of amorphous Si thin films by the reaction of MoO3/Al nanoengineered thermite

In this work, we investigated a new crystallization method for amorphous silicon (a-Si) using a mixture of nano-energetic materials: molybdenum oxide and aluminum (MoO₃/Al). The purpose of using nano-energetic materials is to improve the performance of a-Si films with a self-propagating exothermic reaction over a period of microseconds without any substrate damage. The mixture of MoO₃/Al nanopowders was used for a thermite reaction for crystallization of a-Si thin films.Characterization results showed that a-Si thin films were successfully crystallized to poly-Si as evidenced by a Raman peak near 519 cm^− 1. The crystalline volume fraction of poly-Si after the nanoengineered thermite reaction was about 94.7% and poly-Si grains was uniformly distributed with an average grain size of around 40-50 nm. These results indicate that high quality poly-Si thin films were successfully prepared on the substrate.     

Characterization of laser annealed polycrystalline silicon films on various substrates

The structure and property of eximer laser annealed poly-Si films on various substrate materials such as MoW, Cr, were studied. It was found that the crystallinity of the film depended on the recrystallization energy density and substrate materials. The crystallinity of the film on substrate was the highest quality, and the higher the thermal conductivity of the substrate, the poorer the crystallinity of the poly-Si films at the same laser energy density. In the lower laser energy region than optimum, the grain size and surface roughness were increased with increasing laser power due to the increase of the crystallinity and decreased intrinsic stress. On the other hand, in the higher power region than optimum, with the increase of laser power, X-ray intensity and grain size were decreased due to the fast solidification velocity. There was no metal diffusion into poly-Si film but small amount of Si, less than 3 atomic percent, diffused into the metal film during the recrystallization process.     

Poly-Si films with long carrier lifetime prepared by rapid thermal annealing of Cat-CVD amorphous silicon thin films

Polycrystalline silicon (poly-Si) films thicker than 1.5 μm, consisting of dense small grains called nano-grain poly-Si (ngp-Si), are formed by flash lamp annealing (FLA) of amorphous silicon (a-Si) films prepared by catalytic chemical vapor deposition (Cat-CVD) method. Crystallinity of the ngp-Si films can be controlled by changing lamp irradiance. Secondary ion mass spectroscopy (SIMS) profiles of dopants in the ngp-Si films after FLA shows no serious diffusion. A minority carrier lifetime of over 5 μs is observed from these ngp-Si films after defect termination process using high pressure water vapor annealing (HPWVA), showing possibility of application for high-efficient thin film solar cells.     

Effect of low oxygen pressure on structural and magnetic properties of quenched SrFe12O19 thin films

Strontium hexaferrite thin films have been grown on glass substrates at room temperature in oxygen environment by pulsed laser deposition method. The effect of oxygen pressure (p_o2) on the structural and magnetic properties has been investigated. The as-deposited films were found to be amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 850 °C in air. The thickness of the film increased with p_o2. The film grown at p_o2 = 0.455 Pa had a clear hexagonal structure. The values of coercivity for the films were found to increase with p_o2.