多晶硅薄膜低温生长中晶粒大小的控制

以SiCl4H2为气源,用等离子体增强化学气相沉积(PECVD)方法低温快速沉积多晶硅薄膜.实验发现,在多晶硅薄膜的生长过程中,气相空间各种活性基团的相对浓度是影响晶粒大小的重要因素,随功率、H2/SiCl4流量比的减小和反应室气压的增加,晶粒增大.而各种活性基团的相对浓度依赖于PECVD工艺参数,通过工艺参数的改变,分析生长过程中空间各种活性基团相对浓度的变化,指出“气相结晶”过程是晶粒长大的一个重要因素. 关键词： 气相结晶 多晶硅薄膜 晶粒生长 SiCl4     

纳米引晶法选择性生长金刚石薄膜

通过传统的光刻工艺和纳米引晶技术,在抛光的单晶Si衬底上形成带有 超细金刚石纳米粉的引晶图案,并利用该图案与抛光Si处金刚石成核密度的巨大差异,实现 金刚石薄膜的高选择比生长。该方法具有工艺简单、沉积效率高、选择比高、对底无任何损 伤等优点。同时,这种方法很容易在不同衬底上实现金刚石薄膜的大面积选择性生长。     

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。     

Raman scattering analysis of the residual stress in metal-induced crystallized amorphous silicon thin films using nickel

Raman scattering analysis is used to study the residual stress in metal-induced crystallized amorphous silicon thin film. The influence of the crystallization parameters on thin film properties is investigated as a function of annealing temperature, annealing time, and nickel top-seed-layer thickness. Thin films produced under optimal annealing conditions are measured to have crystallization efficiency of about 98%, which is full crystallization. Residual stress analysis reveals clear stress reduction with prolonged annealing time and Ni capping layer thickness. A very low tensile stress of about 87 MPa is achieved. The relationships between optimal crystallization temperature, crystallization time, and Ni-layer thickness are described.     

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.     

Hysteresis suppression improvement of polycrystalline silicon thin-film transistors by two-step hydrogenation

The effect of two-step hydrogenation, consisting of plasma hydrogenation and annealing in hydrogen, on the hysteresis phenomenon of metal-induced unilaterally crystallized silicon thin-film transistors (MIUC-Si TFTs) was investigated. The large hysteresis level of the conventional MIUC-Si TFTs caused a wide variation of the drain current with the previous gate voltage. As the plasma exposure time increased, the plasma hydrogenation commonly used for stability in poly-Si TFTs was found to increase the hysteresis level of MIUC-Si TFTs after a minimum point. This is because plasma-induced damages correlated with unique defects of MIUC-Si such as metal-related weak bonds, are accompanied by passivation. The following annealing repaired the damages. Consequently the hysteresis level was lower, which resulted in a narrower variation of the drain current.     

改进的DLA方法模拟薄膜二维生长

对经典的DLA模型进行改进，研究了薄膜的二维生长过程.通过改变表征吸附原子在基底扩散 能力的参量D_T，D_C以及表征沉积速率的参量D_V，得到 了与实验一致的薄 膜分形生长模式和团状生长模式.分析了薄膜的形核阶段原子团的大小分布，以及不同条件 下原子团的数目和大小随覆盖度的变化. 关键词： DLA 薄膜生长 分形生长 团状生长     

氮化硅纳米薄膜非平衡热导率实验研究

3ω实验方法是一种可以对薄膜热导率进行瞬时测量的方法。根据3ω方法测试原理,搭建了薄膜导热系数测试平台,并且分别测试低频率段和高频段薄膜与基底的温升以及薄膜热导率。测试结果表明:Si3N4薄膜的热导率随温度的升高而增大;高频段下,热导率受频率影响大,误差大;在低频段下薄膜热导率与频率变化基本无关;基于电子与声子的局部热平衡运输方程假设,S i3N4薄膜的热导率具有极度非平衡性;通过比较电阻、热导率与温度的关系可以看出加热器的尺寸大小会影响薄膜的热导率,最佳加热器的宽度选用20μm左右。     

生长初期Ta膜的表面动态演化行为

用磁控溅射方法在单晶Si衬底上沉积膜厚为15—250nm的Ta膜.基于原子力显微镜获得的薄膜表面形貌，用动力学标度理论量化表征薄膜表面动态演化行为.结果表明：当膜厚d<50nm时，薄膜生长指数β≈0.17，而d>50nm后β≈0.45；随着d增加，粗糙度指数α由0.24逐渐增加到0.69，且在d>50nm后趋于稳定.Ta膜的表面动态演化行为揭示了其由小岛聚合结构向连续膜演化的生长过程.与自阴影等非局域效应引起的非稳定行为不同的是，当d<50nm时，薄膜表面动态演化的非稳定行为来源于生长初期的小岛聚合，表面小岛沿膜面切向的生长优于沿法向的生长.随着d继续增加，薄膜以连续膜形式生长，表面动态演化趋于稳定.     

Influence of silicon cluster on epitaxial growth of silicon carbide

Precursor concentration dependences of growth rate, doping concentration and surface morphology have been investigated in the epitaxial growth of 4H-SiC(0001) epilayers with horizontal hot-wall CVD system using various precursor concentrations under constant C/Si ratio. Form the experimental data it is found that silicon cluster which is formed through gas phase nucleation plays an important role in controlling the doping concentration and epitaxial growth rate of the silicon carbide. It was observed that t...     

Simulation of kinetically limited growth of electrodeposited polycrystalline Ni films

A kinetic Monte Carlo (KMC) technique was adopted to simulate the growth dynamics of electrodeposited polycrystalline Ni thin films under kinetically limited conditions with a two-dimensional triangle lattice mapping the cross-section of the film. Effects of surface diffusion and surface-energy anisotropy on the microstructures of the plated film such as shape and size of grains, density, surface roughness, and textures were examined. This work focuses on the microstructure evolutions for different deposition parameters (for example, deposition rate and electrolyte temperature). We obtained the growth exponent β=0.46, which characterizes the scaling behavior of this growth. Preferential orientation of 1 1 1 and 1 0 0 have been observed at elevated temperature and at elevated deposition rate, respectively. To simulate the evolution of texture, the influence of hydrogen absorption on the surface energy of six main surfaces of nickel was investigated.     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用. 关键词： 大气压等离子体射流 发射光谱 电子激发温度 多晶硅薄膜沉积     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用.     

硅掺杂铝镓氮薄膜场发射性能研究

利用脉冲激光沉积,分别制备了一系列不同Si掺杂浓度的铝镓氮(AlGaN)薄膜.对此薄膜进行场致电子发射测试表明,Si掺杂浓度为1％的AlGaN薄膜具有最好的场发射特性.相对于非掺杂样品,其场发射电流明显增加,场发射开启电场显著降低.掺杂带来载流子浓度的提升,为场发射提供足够的电子源,使样品的场发射性能提升.但掺杂浓度的进一步提高,薄膜缺陷增加,电子迁移率降低,其薄膜内部电子输运能力降低大于电子浓度的增加对场电子发射的贡献,导致场发射性能开始变差.     

非均匀基底上三维薄膜生长的模拟研究

考虑原子在基底表面的扩散、沿岛周界的扩散和不同层间的扩散以及非均匀基底上表面吸附能分布的各向异性，建立起非均匀基底表面上原子扩散和三维薄膜生长的动力学蒙特卡罗模型.模拟得到在不同生长条件下出现的层状生长、岛状生长和混合生长三种生长模式和相应的多层薄膜生长形貌图.通过统计三维薄膜中原子在各层的分布，计算薄膜的表面粗糙度，得到薄膜生长模式与生长条件之间的关系. 关键词： 薄膜生长 非均匀基底 动力学蒙特卡罗模拟     

Deposition pressure effect on the surface roughness scaling of microcrystalline silicon films

The scaling behaviour of surface roughness evolution of microcrystalline silicon (μc-Si:H) films prepared by very-high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) has been investigated by using a spectroscopic ellipsometry (SE) technique. The growth exponent β was analysed for the films deposited under different pressures P_g. The results suggest that films deposited at P_g = 70 Pa have a growth exponent β about 0.22, which corresponds to the definite diffusion growth. However, abnormal scaling behaviour occurs in the films deposited at P_g = 300 Pa. The exponent β is about 0.81 that is much larger than 0.5 of zero diffusion limit in the scaling theory. The growth mode of μ c-Si:H deposited at P_g= 300 Pa is clearly different from that of μc-Si:H at P_g = 70 Pa. Monte Carlo simulations indicate that the sticking process and the surface diffusion of the radicals are two key factors to affect the growth mode under different pressures. Under P_g= 300 Pa, β>0.5 is correlated with the strong shadowing effect resulting from the larger sticking coefficient.     

Delta doping in silicon

Two-dimensional doping sheets (“δ-doping”) are integral parts of many novel semiconductor device concepts. Their practical realization in silicon (Si), however, was long delayed by the difficulty to introduce dopants into Si in a well-controlled way during epitaxial growth. Recent advances in the understanding of epitaxial growth and the incorporation of dopants in Si have overcome these difficulties and opened a new field in Si materials and device research. In this article, we review the growth, processing, and characterization of epitaxially grown 5-doped Si. Furthermore, we discuss the electronic subband states of such structures. Finally, we give an overview of device concepts that use 5-doping and analyze their properties.     

Electron scattering characteristics of polycrystalline metal transition films by in-situ electrical resistance measurements

In-situ electrical resistance measurements were performed to obtain the scattering characteristics of very thin polycrystalline metal transition magnetic alloys grown by ion beam deposition (IBD) on specific underlayers. The experimental curves show size effects at small film thicknesses and important differences between Co₈₅Fe₁₅ and Ni₈₁Fe₁₉ thin layers grown on identical underlayers of Ta70 Å/Ru13 Å. The largest difference was observed in Ni₈₁Fe₁₉ films grown on underlayers of amorphous Ta70 Å. The experimental curves of electrical resistivity/conductivity variation with layer thickness were well fit within the Mayadas and Shatzkes (M-S) model, assuming specific formulations for grain growth with layer thickness.     

分步法高速沉积微晶硅薄膜

为提高微晶硅薄膜的纵向结晶性能, 在甚高频等离子体增强化学气相沉积技术的基础上, 采用过渡参数缓变和两步法相结合的方法在普通玻璃衬底上高速沉积薄膜. 当功率密度为2.1 W/cm², 硅烷浓度在6%和9.6%之间变化时, 从薄膜方向和玻璃方向测算的Raman晶化率的差异维持在2%以内. 硅烷浓度为9.6%时, 薄膜沉积速率可达3.43 nm/s, 从薄膜方向和玻璃方向测算的Raman晶化率分别为50%和48%, 差异的相对值仅为4.0%. 合理控制过渡阶段的参数变化, 可使两个方向的Raman晶化率差值下降到一个百分点. 表明采用新方法制备薄膜, 不仅可以抑制非晶孵化层的形成, 改善微晶硅薄膜的纵向结构, 还为制备优质薄膜提供了较宽的参数变化空间. 关键词： 微晶硅薄膜 非晶孵化层 高速沉积 甚高频等离子体增强化学气相沉积     

Molecular dynamics simulations of atomic assembly in the process of GaN film growth

Molecular dynamics simulations using a Coulomb–Buckingham potential have been used to investigate the process of wurtzite GaN films growth, including the appearance of films in early stage, regulation of growth, structure of the surface and the dynamic features. The simulations show that the N atoms and Ga atoms are absorbed on the lattice of substrate and take on a distinct sandwich structure. Time evolution of the mean square displacements and diffusion coefficient of the deposited atoms are observed, the results show that the clusters will become stable with the increase of time steps and the atoms reach the initial stable state after 25 ps; N atoms reach the equilibrium positions more quickly than Ga atoms. It is proved by radial distribution function and the ratio of vacancy of every deposited layer that the crystalline characters of the films will become better as the time steps increase and weaker from bottom to top.