Simulation of the transport of sputtered atoms and effects of processing conditions

Sputter deposition is a complex process; it is obvious that the energy and direction of the particles arriving at the substrate is in close relation with the transport process from the target to the substrate, it is desirable to model this transport of atoms through the background gas. The transport of sputtered Ag atoms during sputter deposition through the gas phase in the facing targets sputtering system studied by Monte Carlo simulation is presented. The model calculates the flux of the atoms arriving at the substrate, their energy, direction and number of collisions they underwent. The dependence of the deposition rates of Ag atoms on the gas pressure and the distance between the targets and substrate were investigated.     

Texturing effects in molybdenum and aluminum nitride films correlated to energetic bombardment during sputter deposition

Molybdenum films sputter-deposited at low pressure show a (110) to (211) texture turnover with increasing film thickness, which is accompanied by a transition from a fiber texture to a mosaic-like texture. The degree of (002) texturing of sputtered aluminum nitride (AlN) films strongly depends on nitrogen pressure in Ar/N₂ or in a pure N₂ atmosphere. For the understanding of these phenomena, the power density at the substrate during sputter deposition was measured by a calorimetric method and normalized to the flux of deposited atoms. For the deposition of Mo films and various other elemental films, the results of the calorimetric measurements are well described by a model. This model takes into account the contributions of plasma irradiation, the heat of condensation and the kinetic energy of sputtered atoms and reflected Ar neutrals. The latter two were calculated by TRIM.SP Monte Carlo simulations. An empirical rule is established showing that the total energy input during sputter deposition is proportional to the ratio of target atomic mass to sputtering yield. For the special case of a circular planar magnetron the radial dependence of the Mo and Ar fluxes and related momentum components at the substrate were calculated. It is concluded that mainly the lateral inhomogeneous radial momentum component of the Mo atoms is the cause of the in-plane texturing. For AlN films, maximum (002) texturing appears at about 250 eV per atom energy input. Received: 23 June 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

用自洽的蒙特卡罗—流体结合模型模拟溅射过程

 采用自洽的蒙特卡罗－流体结合模型对溅射过程进行模拟,以了解等离子体粒子行为与溅射参数的关系。溅射过程包括气体放电和溅射原子传输。对于气体放电,蒙特卡罗部分模拟快电子和快气体原子,而流体部分则描述离子和慢电子。对于溅射原子传输,蒙特卡罗部分模拟溅射原子的碰撞过程,而流体部分则描述溅射原子的扩散和漂移。模拟的结果包括：等离子体粒子的密度和能量分布;不同电离机制对气体原子和溅射原子电离的贡献;不同等离子体粒子对阴极溅射碰撞的贡献;溅射原子的密度分布;溅射场和溅射粒子相对于入射离子能量和角度的分布;溅射原子经碰撞后在整个等离子体区的分布。     

Plume dynamics during film and nanoparticles deposition by pulsed laser ablation

The gas dynamics of pulsed laser ablation of silicon target in the helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. A shock driven process is clearly observed. It is shown that the interaction of the shock front with the target surface and the vapor front induce significant backward flux of ablated particles and oscillating behavior of vapor front. A confined layer mixed with high density Si and He atoms is formed around the contact front. Its behavior is important to the nanoparticle formation and deposition.     

Arq+(q=0-12)离子掠射到单晶铜表面的能损谱

采用蒙特卡罗模拟方法,对低速高电荷态Arq+离子掠射到单晶铜表面时的能损谱与表面结构的依赖关系进行研究。在能损计算中,包含了四种可能的能损机制。对于Ar原子沿着晶列方向掠射时,发现能损谱为一两峰结构,其中在能损比较大的区间新出现一个明显的小峰结构。通过研究Arq+以不同条件掠射到表面的能损,对观察到的沟道效应进行论述。能损谱的计算结果与实验结果吻合得比较好。     

Sputtering studies with the Monte Carlo Program TRIM.SP

The Monte Carlo Program TRIM.SP (sputtering version of TRIM) was used to determine sputtering yields and energy and angular distributions of sputtered particles in physical (collisional) sputtering processes. The output is set up to distinguish between the contributions of primary and secondary knock-on atoms as caused by in- and outgoing incident ions, in order to get a better understanding of the sputtering mechanisms and to check on previous theoretical models. The influence of the interatomic potential and the inelastic energy loss model as well as the surface binding energy on the sputtering yield is investigated. Further results are sputtering yields versus incident energy and angle as well as total angular distributions of sputtered particles and energy distributions in specific solid angles for non-normal incidence. The calculated data are compared with experimental results as far as possible. From this comparison it turns out that the TRIM.SP is able to reproduce experimental results even in very special details of angular and energy distributions.     

MONTE CARLO STUDIES OF RADIATION DAMAGE INDUCED BY FUSION:DYNAMIC SIMULATION OF SPUTTERING

In this paper, the sputtering caused by fusion of ⁴He particles in the first wall materials is investigated by using the dynamic Monte Carlo simulation, which is based on the binary collision approximation. The dependences of sputtering yields on the incident energy and angle, as well as the comparisons of results calculated using the Monte Carlo methed with results from experiments, are discussed. Energy spectrum and angular distributions of sputtered species, the depth of origin of the sputtered particles as well as range distributions of incident ions are given. From a comparison between the related experimental data and the calculated results with static and dynamic simulation it has been found that a better agreement is obtained for dynamic simulation.     

MONTE CARLO STUDIES OF RADIATION DAMAGE INDUCED BY FUSION DYNAMIC SIMULATION OF SPUTTERING

In this paper, the sputtering caused by fusion of ⁴He particles in the first wall materials is investigated by using the dynamic Monte Carlo simulation, which is based on the binary collision approximation. The dependences of sputtering yields on the incident energy and angle, as well as the comparisons of results calculated using the Monte Carlo methed with results from experiments, are discussed. Energy spectrum and angular distributions of sputtered species, the depth of origin of the sputtered particles as well as range distributions of incident ions are given. From a comparison between the related experimental data and the calculated results with static and dynamic simulation it has been found that a better agreement is obtained for dynamic simulation.     

Computer simulation of gas rarefaction effects and film deposition characteristics in a magnetron sputtering apparatus

Ar gas is known to be rarefied in front of a magnetron sputtering cathode due to the collisional heating by energetic sputtered atoms. The effects of the Ar rarefaction in a magnetron sputtering apparatus used for Ti-film deposition were investigated using the direct simulation Monte Carlo (DSMC) method which is capable of taking gas rarefaction effects into account. The calculated film deposition rate on a substrate and the film coverage in a small hole were larger than those calculated by the conventional simulation where the gas rarefaction is not included. This shows that the gas rarefaction improves both the film deposition rate and the film coverage.     

离子轰击入射角对溅射参数的影响

本文用基于两体碰撞近似的蒙特-卡罗模拟方法研究离子轰击入射角对溅射参数的影响,讨论了入射角与溅射产额、溅射粒子能谱、角分布和阈能的关系,并把计算结果与某些半经验公式和实验数据进行了比较。 关键词：     

不同温度下团簇生长的Monte Carlo模拟

引入基底表面束缚能、最近邻粒子间的耦合能以及应力场,对粒子扩散势垒进行修正,采用Monte Carlo方法对不同温度下薄膜生长过程进行模拟研究.结果表明,当400 K≤T ≤ 480 K,所得团簇的平均分支宽度基本保持不变,其值近似为单粒子直径.当500 K≤T ≤ 680 K,团簇分支宽度随着温度的升高而逐渐增大至约4个粒子.随着温度的继续升高,由于粒子较高的活跃性而无法凝聚形成大团簇,团簇包含粒子数的平均值小于2.还研究了不同温度下团簇在生长过程中的形貌演化过程以及团簇数变化规律.     

Dynamic Monte Carlo simulation of film–substrate interface mixing in the deposition of Co on Cu (001)

Dynamic Monte Carlo simulations are performed to investigate the interface mixing of Co atoms deposited on a Cu (001) substrate. A tight-binding potential was used to determine the input parameters (jump probabilities and energy barriers) for the Dynamic Monte Carlo model. The results show that more Co adatoms penetrate into the substrate as the temperature rises and/or as the deposition rate decreases, and that the intermixing between the layers becomes concomitantly more pronounced. Cu atoms migrating into the Co layer via exchange processes during the growth of consecutive Co layers are proposed to be responsible for the intermixing. Furthermore, an initial Co clustering followed by a layer-by-layer growth mode was observed in the simulations, with the surface concentration of Cu atoms depending on the fraction of migrating Cu atoms and decaying into the Co film following a power law. The fraction of Cu atoms migrating into the Co layer can be adjusted by varying the deposition rate and the substrate temperature.     

Sputtered-atom energy relaxation in a plasma

The Monte Carlo method has been used to examine the migration of sputtered atoms, whose transport may be described by a diffusion equation. The position of the virtual source in the plasma is determined. The energy relaxation has also been examined by experiment. The theoretical and experimental results are in agreement.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–8, October, 1982.     

基于蒙特卡罗正算输运的全局减方差方法

蒙特卡罗方法是当前形势下辐射屏蔽计算的首选分析工具。小概率深穿透问题则是屏蔽计算的关键与亟待解决的核心问题,需要使用有效的减方差技巧。针对全局问题,利用蒙特卡罗正算输运得到的粒子通量或探测响应来构建权重窗参数,将现有的粒子位置偏移拓展到位置和能量偏倚。利用国际屏蔽基准题进行测试验证,通过使用该方法,粒子被引导到模型的所有位置。平均相对误差降低到10%以下,几乎所有网格区域都有粒子统计。结果表明,基于蒙特卡罗正算输运的输运偏倚参数构建方法能够实现全局减方差。     

Energy deposition,reflection and sputtering in hyperthermal rare-gas→Cu bombardment

Using molecular-dynamics simulation, we study the scattering and penetration of normally incident hyperthermal (5–400 eV) Ne, Ar, and Xe atoms off a Cu crystal. We find that between 80% and 98% of the incident energy is deposited in the solid; the fraction depends primarily on the projectile mass, and — for not too low energies — only slightly on the bombarding energy. At low energy, the major part of the non-deposited energy is carried away by the reflected projectile. At energies above the sputter threshold, an increasingly important contribution of between 2% and 6% of the incident energy is carried away by sputtered particles. These results compare well with experiment. Electronic inelastic losses show only little influence on this behaviour. We demonstrate that the inclusion of a realistic attractive interaction between the projectile and the target atoms influences the energy deposition considerably at energies below around 100 eV.     

非均一相互作用能对超薄膜生长影响的Monte Carlo模拟研究

利用Monte Carlo (MC)模拟技术研究了非均一的吸附原子与基底相互作用能在一定的生长条件下对超薄膜生长过程的影响.非均一相互作用能是由基底表面原子在垂直和水平方向上实际位置与理想晶格原子位置的偏差所造成.本文用高斯分布来表示这种非均一相互作用能.模拟结果表明:非均一相互作用能对超薄膜的生长过程及薄膜的形貌有显著的影响.这种影响同时受到生长条件的限制,在中等温度时相互作用能的非均一性对岛的个数、平均大小的影响最显著;温度的增加在一定程度上可抵御相互作用能的非均一性对薄膜生长的影响. 关键词： 薄膜生长 Monte Carlo 模拟 相互作用能     

非平衡磁控溅射系统的离子束流控制

在非平衡磁控溅射沉积非磁性金属薄膜过程中,离子,原子到达比、沉积速率等参数是影响薄膜结构和性能的重要因素。根据非平衡磁控溅射沉积过程中离子的分布特点,分别考虑离子和中性粒子的传输,导出了对圆形平面靶非平衡磁控溅射沉积薄膜的放电功率、气压和离子束流密度等参数之间的关系,阐明了放电参数对于沉积过程离子束流密度等参数的影响。在Ar放电条件下,测量了系统的伏安特性;采用偏压平面离子收集电极测量了溅射系统轴向离子束流密度随不同的气压、溅射电流和空间位置的变化规律。结果表明模型分析的结论和实验数据的变化趋势相符合。     

低场低能区金刚石内载流子飞行时间的蒙特卡洛模拟

金刚石是一种重要的宽禁带半导体材料,对金刚石内载流子输运过程的研究将有助于了解金刚石用作各种电子器件的潜能。利用Monte Carlo模拟方法,研究了在低场低能区金刚石内载流子的飞行时间。在模拟中考虑了抛物线型能带模型和声学声子散射机制,以及样品对光的吸收和载流子在Brillouin区边界的Bragg反射。通过模拟,得到了低场低能区金刚石材料内载流子的飞行时间分布,并与相关的实验结果进行了比较分析,验证了该模拟模型的正确性。研究结果表明,在低场低能区,金刚石材料内主要的散射机制是声学声子散射。在研究金刚石材料内载流子的迁移输运问题时,可以采用较为简单的抛物线型能带模型,但在研究薄样品中的载流子输运时应当考虑材料的光吸收对初始载流子分布的影响,而且在场强较高以及样品厚度较大时,应当考虑载流子在Brillouin区边界的Bragg反射。     

Three-dimensional spatiokinetic distributions of sputtered andscattered products of Ar+ and Cu+ impacts onto theCu surface: molecular dynamics simulations

Energy and angular distributions of reflections and sputtered atoms are essential inputs for feature profile evolution simulations. Molecular dynamics simulations are used to compute the three-dimensional energy and angular distributions for reflected and sputtered products when both Ar⁺ and Cu⁺ ions bombard a copper surface. We term these “spatiokinetic” distribution functions (SKDF's). We show by example that SKDF's for reflected Ar⁺ ions focus as the incident angle &thetas;_i (normal=0°) is increased from 60-75° and broaden as the incident energy E_i is increased from 55-175 eV. We show that the SKDF's for glancing-angle reflected Cu⁺ ions focus when E_i is increased from 55-175 eV. We show that the SKDF's for copper atoms sputtered by 175 eV Ar⁺ are insensitive to &thetas;_i;. We report total sputter yields for Ar⁺ and Cu⁺ ions at 55 and 175 eV for incident angles between 0° and 85°, and sticking probabilities for Cu⁺ ions for these energies and angles. Comparison to representative experimental results (Doughty et al., 1997) is given     

低能中子在锆中产生的辐照损伤的计算机模拟研究

以GEANT4为基础采用蒙特卡罗方法对能量为1 MeV的中子在锆 材料中的输运过程进行了模拟分析. 首先计算得出: 反冲核的能量主要分布在1 keV和15 keV之间, 中子和靶核发生两次弹性碰撞的平均空间距离为29.47 mm. 由于中子和靶核在发生连续两次弹性碰撞过程中产生的两个反冲核能量较低, 它们的空间距离又比较大, 由此可以推测出: 由初级离位原子产生的后续级联碰撞可以看做是一系列独立的子级联碰撞过程, 同时也计算了中子在靶材的不同深度区域内产生的反冲核数目和平均能量. 其次, 利用蒙卡方法计算得到的结果, 采用分子动力学方法, 分别计算了五种不同能量下的初级离位原子产生的级联碰撞情况, 给出了初级离位原子的能量与其产生的次级离位原子数目之间的关系以 及不同能量下的初级离位原子产生的损伤区域范围等情况, 通过蒙特卡罗方法和分子动力学方法的结合, 给出了能量为1 MeV的中子在锆材料中产生的初级辐照损伤分布图像. 关键词： 辐照损伤 级联碰撞 蒙特卡洛模拟 分子动力学