脉冲激光退火纳米碳化硅的光致发光

采用XeCl准分子脉冲激光退火技术制备了纳米晶态碳化硅薄膜(nc-SiC),并对薄膜的光致发光(PL)特性进行了分析。结果表明,纳米SiC薄膜的光致发光表现为300～600 nm范围内的较宽发光谱带,随退火激光能量密度的增加,nc-SiC薄膜398 nm附近的发光峰相对强度增加,而470 nm附近发光峰相对减小。根据nc-SiC薄膜的结构特性变化, 认为这两个发光峰分别来源于6H-SiC导带到价带间的复合发光和缺陷态发光,并且这两种发光过程存在竞争。     

脉冲激光晶化非晶硅薄膜的有限差分模拟

 根据热传导原理,建立了脉冲激光晶化非晶硅薄膜的理论模型。运用有限差分方法研究了不同激光波长、能量密度等因素对薄膜温度变化及相变过程的影响。计算了不同波长激光器对厚度500 nm非晶硅晶化的阈值能量密度。结果发现,准分子晶化的阈值能量密度最低,但是在同样的能量密度下,熔融深度却不及使用更长波长的激光器。计算并分析了升高衬底温度对结晶速度和晶粒尺寸的影响,模拟结果较好地验证了实验结论和规律。     

脉冲激光晶化超薄非晶硅膜的分子动力学研究

利用准分子脉冲激光晶化非晶硅薄膜是制备高密度尺寸可控的硅基纳米结构的有效方法之一.本文将脉冲激光对非晶硅超薄膜的影响处理为热传导问题,采用了基于Tersoff势函数的分子动力学方法模拟了在非晶氮化硅衬底上2.7 nm超薄非晶硅膜的脉冲激光晶化过程.研究了不同激光能量对非晶硅薄膜晶化形成纳米硅的影响,发现在合适的激光能量窗口下,可以获得高密度尺寸可控的纳米硅薄膜,进而模拟了在此能量作用下非晶硅膜中成核与生长的机理与微观过程,并对晶化所获得的纳米硅薄膜的微结构进行了分析. 关键词： 非晶硅 分子动力学 脉冲激光晶化     

KrF准分子激光退火氢化非晶碳化硅薄膜的晶化研究

介绍了利用KrF准分子脉冲激光对氢化非晶碳化硅(a-SiC∶H)薄膜进行激光退火以实现薄膜的结晶化。利用等离子增强化学气相沉积(PECVD)在单晶Si(100)衬底上制备a-SiC∶H薄膜, 再用不同能量密度的激光对薄膜样品进行退火。分析表明, 选用合适能量密度的激光退火能够实现a-SiC∶H薄膜的结晶化, 且结晶颗粒大小随着入射激光能量密度的增加而增大; 显微图表明当入射能量密度超过200 mJ/cm2时, 薄膜表面出现由热弹性波引起的表面波纹现象, a-SiC∶H薄膜结晶过程为液相结晶; 傅里叶红外谱(FTIR)表明随着入射能量密度增加, 薄膜中氢含量降低, Si-C峰增强并且峰位出现蓝移, 薄膜的结晶度提高。     

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。     

非晶硅薄膜的激光晶化及深度剖析喇曼光谱研究

利用共焦显微喇曼光谱仪，对采用PECVD方法制备的非晶硅薄膜进行了退火晶化。晶化后薄膜的喇曼光谱表明。薄膜由非晶硅结构转变为微晶硅结构，同时根据微晶硅结构的喇曼光谱的晶化峰位的移动。可以计算出晶化后微晶硅晶粒尺寸为5nm左右。在对晶化后的薄膜进行深度剖析喇曼光谱研究中，对光谱进行分峰拟合，根据晶化峰的积分强度和非晶峰的积分强度的深度剖析曲线。可以看出晶化程度最高的部分位于薄膜中央，也就是在薄膜上层和接近衬底底部材料结构仍是非晶硅结构。而位于薄膜中间的材料结构转变为微晶硅结构。     

氢化硅薄膜的晶化机理研究

采用PECVD工艺制备了非晶,微晶和多形硅薄膜,研究了电极间热梯度对氢化硅薄膜结构的影响.根据拉曼光谱得到了微晶硅的晶化率,并在椭偏仪中用BEMA模型验证了其准确性.根据理论模型研究了热梯度对微晶和多形硅薄膜沉积机理的影响.研究薄膜厚度对晶化率的影响表明微晶薄膜底端和表面之间存在晶化梯度,而多形硅薄膜中无晶化梯度存在.采用Tauc-Lorentz模型拟合得到薄膜的结构参数表明非晶硅薄膜的致密度和有序度低,而多形硅和微晶硅薄膜的有序度、致密度相近,且明显高于非晶硅. 关键词： 氢化硅 晶化 热梯度 结构     

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.     

非晶硅薄膜晶化过程中微结构的分析

使用X射线衍射技术和高分辨率电子显微镜(HREM),分析研究了在非晶硅薄膜由非晶相向微晶相转化过程中其网络结构的变化特征,由此,给人们一个直观的信息,并加深对非晶硅薄膜微结构的认识。 关键词：     

Mg-Ni-Nd非晶合金晶化温度与晶化驱动力的预测

通过对Buschow提出的预测二元非晶态合金晶化温度的“最小空位”模型进行扩展,并进一步结合Miedema理论得到了一种预测三元非晶态合金晶化温度和晶化驱动力的理论方法.利用该方法计算了(Mg_70.6Ni_29.4)_1-xNd_{x(x＝5,10,15)非晶态合金的晶化温度、晶化驱动力以及晶化焓.其中晶化温度和晶化焓的理论预测值与实验值的相对误差分别小于8%和7%.同时发现较高的晶化驱动力会降低 关键词： 非晶态合金 晶化温度 晶化驱动力}     

Nanocrystalline silicon films prepared by laser—induced crystallization

The excimer laser-induced crystallization technique has been used to investigate the preparation of nanocrystalline silicon (nc-Si) from amorphous silicon ($\al$-Si) thin films on silicon or glass substrates. The $\al$-Si films without hydrogen grown by pulsed-laser deposition are chosen as precursor to avoid the problem of hydrogen effluence during annealing. Analyses have been performed by scanning electron microscopy, atomic force microscopy, Raman scattering spectroscopy and high-resolution transmission--electron microscopy. Experimental results show that silicon nanocrystals can be formed through laser annealing. The growth characters of nc-Si are strongly dependent on the laser energy density. It is shown that the volume of the molten silicon predominates essentially the grain size of nc-Si, and the surface tension of the crystallized silicon is responsible for the mechanism of nc-Si growth.     

Nickel-disilicide-assisted excimer laser crystallization of amorphous silicon

Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi多晶硅 受激准分子激光器结晶 结晶化 界面晶粒生长polycrystalline silicon, excimer laser crystallization,Ni-disilicide, Ni-metal-induced lateral crystallization, two-interface grain growthProject supported by the National High Technology Development Program of China (Grant No 2002AA303250) and by the National Natural Science Foundation of China (Grant No 60576056).9/7/2005 12:00:00 AM3/6/2006 12:00:00 AMPolycrystalline silicon （poly-Si） thin film has been prepared by means of nickel-disilicide （NiSi2） assisted excimer laser crystallization （ELC）. The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon （a-Si） coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy （SEM）, another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization （Ni-MILC） model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.     

UV–visible spectral characterization and density functional theory simulation analysis on laser-induced crystallization of amorphous silicon thin films

The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon （a-Si：H） thin films was studied both theoretically and experimentally. The thin films were irritated by a frequency-doubled （λ= 532 nm） Nd：YAG pulsed nanosecond laser. An effective density functional theory model was built to reveal the variation of bandgap energy influenced by thermal stress after laser irradiation. Experimental results establish correlation between the thermal stress and the shift of transverse optical peak in Raman spectroscopy and suggest that the relatively greater shift of the transverse optical （TO） peak can produce higher stress. The highest crystalline fraction （84.5%） is obtained in the optimized laser energy density （1000 mJ/cm2） with a considerable stress release. The absorption edge energy measured by the UV- visible spectra is in fairly good agreement with the bandgap energy in the density functional theory （DFT） simulation.     

激光干涉结晶法制备一维周期结构的纳米硅阵列

利用激光干涉结晶方法,采用周期为400 nm的一维(1D)移相光栅掩模调制KrF准分子激光器的脉冲激光束斑的能量分布,在不同厚度的超薄氢化非晶硅(a-Si:H)膜内直接制备1D有序纳米硅(nc-Si)阵列.拉曼散射谱表明,样品上呈条状分布的受辐照区域发生晶化.原子力显微镜和透射电子显微镜测试结果表明：1D的nc-Si阵列的周期和移相光栅掩模一样.随着a-Si:H膜厚度从10nm降至4nm,通过控制激光的能量密度,每个周期中nc-Si条状分布区宽度可达到30nm.nc-Si条状分布区的高分辨电子显微镜照片显 关键词： 纳米硅 激光干涉结晶 移相光栅 定域晶化     

Dynamical resolidification behavior of silicon thin films during frontside and backside excimer laser annealing

Excimer laser annealing (ELA) is frequently employed to fabricate low-temperature polycrystalline silicon films on glass substrate. The grain size and crystallinity of polycrystalline silicon films are significantly affected by the resolidification behavior during ELA. A real-time in situ time-resolved optical measurement system is developed to record the rapid phase transformation process during ELA. The average solidification velocity of liquid-Si is calculated from these optical spectra using MATLAB and Excel softwares. Field emission scanning electron microscopy images reveal maximum grain size of poly-Si films with a diameter of 1 μm, which is obtained in the complete melting regime of both frontside ELA and backside ELA. Recrystallization mechanisms of complete melting of Si thin films in frontside ELA and backside ELA are demonstrated. Resolidification scenarios of partial melting, near-complete melting and complete melting in frontside ELA and backside ELA are proposed.     

Evaluation of probe lasers employed in optical diagnostics for phase transformation of thin films during excimer laser crystallization

The stability and reliability of probe laser is an important factor affecting the inspection of the phase transformation process of Si thin films during excimer laser crystallization using in-situ time-resolved optical measurements. The changes in 2D intensity profile, peak power density, and beam wander of the commonly used helium–neon (He–Ne) and diode laser are investigated experimentally. It is found that the peak power density of He–Ne laser is higher than that of diode laser, while the total power of He–Ne laser is lower than that of diode laser. Although the instability in the peak power density of He–Ne laser will increase with increasing the operation time, the beam stability of He–Ne laser is better than that of diode laser. For long-time operation (>24 h) of optical measurements, the diode laser is a good candidate of probe laser. Conversely, the diode laser is suitable for the short-time operation (<24 h) of optical measurements because the beam-wander is higher than that of He–Ne laser.     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.     

Evolution of microstructure in polycrystalline silicon thin films upon excimer laser crystallization

Polycrystalline silicon (poly-Si) films fabricated by pulsed excimer laser crystallization (ELC) have been investigated using time-resolved optical measurements, scanning-electron microscopy, and cross-sectional transmission-electron microscopy. Detailed crystallization mechanisms are proposed to interpret the microstructure evolution of poly-Si films for both frontside and backside ELC. It is found that the backside ELC is a good candidate for the manufacturing of low-temperature polycrystalline silicon because of the high laser efficiency and low surface roughness of the poly-Si films.