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。     

Heating of condensation surface during magnetron sputtering

Chromium films deposited by magnetron sputtering on non-heated substrates from non-thermalized atoms crystallize in regular bcc Cr phase, with non-uniform microstructure and lattice constant along the thickness. These non-uniformities decrease with elevation of the substrate temperature and vanish at a certain value. However films deposited on non-heated substrates from thermalized atoms crystallize in a low-temperature Cr phase and have almost uniform microstructure. We have developed a model explaining this effect, which is based on the supposition of the formation of a “hot” layer on the growth surface during deposition, whose temperature depends on the flux of energy delivered to the condensation surface and can be noticeably higher than the substrate temperature. Detailed investigation of the structure of Cr films deposited at various temperatures and energy fluxes delivered to the growth surface, correlate well with the above model.     

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     

Systematic investigation of the reactive ion beam sputter deposition process of SiO<Subscript>2</Subscript>

Ion beam sputter deposition (IBSD) is an established physical vapour deposition technique that offers the opportunity to tailor the properties of film-forming particles and, consequently, film properties. This is because of two reasons: (i) ion generation and acceleration (ion source), sputtering (target) and film deposition (substrate) are locally separated. (ii) The angular and energy distribution of sputtered target atoms and scattered primary particles depend on ion incidence angle, ion energy, and ion species. Ion beam sputtering of a Si target in a reactive oxygen atmosphere was used to grow SiO₂ films on silicon substrates. The sputtering geometry, ion energy and ion species were varied systematically and their influence on film properties was investigated. The SiO₂ films are amorphous. The growth rate increases with increasing ion energy and ion incidence angle. Thickness, index of refraction, stoichiometry, mass density and surface roughness show a strong correlation with the sputtering geometry. A considerable amount of primary inert gas particles is found in the deposited films. The primary ion species also has an impact on the film properties, whereas the influence of the ion energy is rather small.     

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.     

Control of the structure and stress state of thin films and coatings in the process of their preparation by ion-plasma methods

A system analysis of the influence of the substrate temperature during deposition on two main factors (nanodimensionality of structural aggregates and high stresses) responsible for the nonequilibrium state of the materials of ion-plasma-deposited films and coatings has been performed. It has been shown that an increase in the temperature during deposition leads to a preferred growth of nanocrystallites in the direction of incidence of film-forming particles, which, in turn, results in the formation of an anisometric crystal structure. The main causes of the generation of high elastic stresses in ion-plasma condensates are the ion/atom bombardment in the process of deposition (which stimulates the development of compressive stresses) and the difference in the thermal expansion coefficients of the condensate and substrate materials (which initiates the development of thermal stresses; the sign is determined by the difference between the thermal expansion coefficients of the condensate and substrate materials). An increase in the temperature during deposition results in the relaxation of compressive stresses stimulated by the ion/atom bombardment and in an enhancement of the influence of thermal stresses on the state of the ion-plasma condensate. This makes it possible to control the stress state of ion-plasma films and coatings by purposefully varying the substrate temperature during deposition.     

Effect of the oxygen flow rate on the structure and the properties of Ag-Cu-O sputtered films deposited using a Ag/Cu target with eutectic composition

Ag-Cu-O films were deposited on glass substrates by reactive sputtering of a composite Ag₆₀Cu₄₀ target in various Ar-O₂ mixtures. The films were characterised by energy dispersive X-ray analysis, X-ray diffraction, UV-visible spectroscopy and using the four point probe method. The structure of the films is strongly dependent on the oxygen flow rate introduced in the deposition chamber. The variation of the oxygen flow rate allows the deposition of the following structures: Ag-Cu-(O) solid solution, nc-Ag + nc-Cu₂O, nc-Ag + nc-(Ag,Cu)₂O and finally X-ray amorphous. UV-visible reflectance measurements confirm the occurrence of metallic silver into the deposited films. The increase of the oxygen flow rate induces a continuous increase of the film oxygen concentration that can be correlated to the evolution of the film reflectance and the film electrical resistivity. Finally, the structural changes vs. the oxygen content are discussed in terms of reactivity of sputtered atoms with oxygen.     

Monte Carlo simulation of thermalization process of sputtered particles

The transport process of sputtered particles in plasma sputter deposition was studied by computer simulation using the Monte Carlo method, with particular attention to the understanding of the thermalization process. Due consideration was taken of the momentum loss as well as of the energy loss of sputtered particles colliding with sputter gas molecules. The results clearly showed that with increasing target-substrate distance, the energy distribution of sputtered copper atoms arriving at the substrate shifts toward lower kinetic energies, but still contains a considerable fraction of high energy particles. In addition, it was found that the arrival rate of sputtered copper atoms at the substrate decreases exponentially with the target-substrate distance, while the return rate to the target first increases and then becomes constant. It was concluded that the present Monte Carlo simulation can be successfully used for a quantitative estimation of the transport process of sputtered particles.     

Formation of two-component two-phase metal films at elevated temperatures

This paper is devoted to the study of two-component thin films deposited at elevated temperatures. The dependence of plasma-assisted film deposition from a flow of sputtered Cu and Fe atoms on the substrate temperature and type, concentration of sputtered components in the flow, and film thickness is investigated.     

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by keV Ar+ ion bombardment

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys under 3 keV AR⁺ ion bombardment were measured to understand the preferential sputtering. The surface composition of sputter-deposited Au-Cu films on substrates mounted at different ejection angles was analyzed by Auger electron spectroscopy and electron probe microanalysis. Although the result indicated that the proportion of sputtered Cu atoms to the Au atoms in the Au-Cu alloy depends on the ejection angle, marked enhancement of the lighter component in the direction normal to the surface has not been observed in spite of the larger mass ratio of the constituent atoms of the Au-Cu alloy.     

Tailored Ceramic Film Growth at Low Temperature by Reactive Sputter Deposition

Reactive sputter deposition of ceramic films with tailored structure is addressed in this article. We begin with a brief overview of reactive sputter deposition specifically related to oxide and nitride films, including techniques for in situ plasma diagnostics. We identify two flux components in the plasma that have a controlling influence on film structure and stoichiometry: (1) the flux bearing sputtered target species, which consists of atoms (M) or reacted molecules (MO_x or MN_x), and (2) the reactive gas flux-containing species in various states of activation. Nonelectronic plasma reactions in which one partner is an excited rare gas species are described, and their role in modifying the sputtered flux, as well as in creating activated reactive gas species, is discussed. We then illustrate the general concepts presented in the overview using four examples of technologically interesting materials grown by rf diode sputter deposition at temperature below 300°C, including: (1) fifth period metal (Zr, Y, Nb) oxides, (2) zirconia-alumina and zirconia-yttria nano-laminates, (3) nanocrystalline aluminum nitride, and (4) vitreous sp² and sp³-bonded boron nitride. Together, these diverse examples form a complementary set that demonstrates the ability to tailor film properties once the chemical and energetic parameters of the deposition process are understood.     

Cobalt redistribution over the surface of inhomogeneous cobalt-copper alloy films

The surfaces of electrodeposited 1-μm-thick Co_xCu_100−x (x=8, 11, and 20 at. %) films and also of 0.2-μm-thick films obtained by sputtering targets made of the electrodeposited films with an argon ion beam are analyzed by atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). XPS data indicate that cobalt is absent on the surface of the electrodeposited films but is present in the bulk and on the surface of the sputtered films. The difference in the XPS spectra of copper in the electrodeposited and sputtered films of the same composition is less significant. The data obtained are explained within the framework of a qualitative model according to which subgrains of the basic (copper) component coalesce into large clusters, which subsequently take on a regular oval shape on the free surface. This process favors cobalt atom migration from the free surface to near-surface voids. High-energy particles existing in the flux of the target sputtering products bombard the growth front of the ion-sputtered films, causing the fastest sputtered cobalt atoms to penetrate into the copper matrix as point defects.     

Self-organization of quasi-equilibrium steady-state condensation in accumulative ion-plasma devices

We consider both theoretically and experimentally self-organization process of quasi-equilibrium steady-state condensation of sputtered substance in accumulative ion-plasma devices. It has been shown that the self-organization effect is caused by self-consistent variations of the condensate temperature and the supersaturation of depositing atoms. Two possible types of self-organization process have been found out on the basis of the phase-plane method. The aluminium condensation experimental data confirming the self-organization nature of quasi-equilibrium steady-state condensation are discussed.     

On the characterization of sculptured columnar Mn thin films; correlation between nanostructure and the optical and electrical properties using experimental and simulation results

Mn columnar (nanorod shaped) thin films of 40 and 150?nm thicknesses were deposited on glass substrates at different deposition angles, using oblique angle deposition technique. The concept of local homogenization proposed by Bruggeman is used for optical analyses of these samples. Results of this simulation method are compared with the experimental data and values for void fraction and film thickness are predicted. In addition, using the perturbation simulation method, variation of relative resistance of these thin films was obtained as a function of material inclusion. It is observed that both simulation and experimental results show that the thinnest samples with the least amount of material inclusion have the highest electrical resistance. Results showed a rise at about 30° deposition angle, which may be attributed to the surface diffusion effect or thermal vibration causing rearrangement of atoms as well as crystallographic available sites for relaxation of adatoms deposited at this certain direction, though this requires a thorough investigation.     

Sputtered deposited nanocrystalline ZnO films: A correlation between electrical, optical and microstructural properties

Zinc oxide thin films were prepared by dc (direct current) and rf (radio frequency) magnetron sputtering on glass substrates. ZnO films produced by dc sputtering have a high resistance, while the films produced using rf sputtering are significantly more conductive. While the conductive films have a compact nodular surface morphology, the resistive films have a relatively porous surface with columnar structures in cross section. Compared to the dc sputtered films, rf sputtered films have a microstructure with smaller d spacing, lower internal stress, higher band gap energy and higher density. Dependence of conductivity on the deposition technique and the resulting d spacing , stress, density, band gap, film thickness and Al doping are discussed. Correlations between the electrical conductivity, microstructural parameters and optical properties of the films have been made. PACS 73.25.+i; 81.15.cd; 81.05.ys     

Calculation of the flow of sputtered atoms returning to a target with a surface relief during sputtering in glow discharge

A model is constructed that describes the transport of a sputtered substance near a target with a relief surface that is sputtered in glow discharge. For a periodic relief with small amplitude, distribution of a return flow of sputtered atoms from a discharge gap is calculated by a perturbation method. It is shown that nonuniform repeated deposition of the substance sputtered from the target could be one of the causes of formation of a relief on its surface.     

Effect of substrate temperature on the morphological,structural,and optical properties of RF sputtered Ge_(1-x)Sn_x films on Si substrate

In this study, Ge_(1-x)Sn_x alloy films are co-sputtered on Si(100) substrates using RF magnetron sputtering at different substrate temperatures. Scanning electron micrographs, atomic force microscopy(AFM), Raman spectroscopy, and x-ray photoemission spectroscopy(XPS) are conducted to investigate the effect of substrate temperature on the structural and optical properties of grown Ge Sn alloy films. AFM results show that RMS surface roughness of the films increases from 1.02 to 2.30 nm when raising the substrate temperature. This increase could be due to Sn surface segregation that occurs when raising the substrate temperature. Raman spectra exhibits the lowest FWHM value and highest phonon intensity for a film sputtered at 140?C. The spectra show that decreasing the deposition temperature to 140?C improves the crystalline quality of the alloy films and increases nanocrystalline phase formation. The results of Raman spectra and XPS confirm Ge–Sn bond formation. The optoelectronic characteristics of fabricated metal-semiconductor-metal photodetectors on sputtered samples at room temperature(RT) and 140?C are studied in the dark and under illumination. The sample sputtered at 140?C performs better than the RT sputtered sample.     

脉冲激光沉积法制备的ZnO薄膜的低阈值电抽运紫外随机激射

分别采用直流反应溅射法和脉冲激光沉积法在硅衬底上沉积ZnO薄膜, 用X射线衍射、扫描电镜、光致发光谱等手段对两种方法沉积的ZnO薄膜的结晶状态、 表面形貌和光致发光等进行了表征. 进一步对比研究了以上述两种方法制备的ZnO薄膜作为发光层的金属-绝缘体-半导体结构器件的电抽运紫外随机激射. 结果表明, 与以溅射法制备的ZnO薄膜作为发光层的器件相比, 以脉冲激光沉积法制备的ZnO薄膜为发光层的器件具有更低的紫外光随机激射阈值电流和更高的输出光功率. 这是由于脉冲激光沉积法制备的ZnO薄膜中的缺陷更少, 从而显著地减少了紫外光在光散射过程中的光损耗. 关键词： 随机激射 ZnO薄膜 脉冲激光沉积 溅射     

Influence of growth mode on stoichiometry in epitaxial calcium ruthenate thin films

Clear evidence about the influence of growth orientation on the stoichiometry of sputtered oxide thin films is reported and discussed. The growth of stoichiometric and of non-stoichiometric films is respectively obtained, from the same CaRuO₃ target, on the surface of (110) and (100) perovskite substrates. Such phenomenon has been systematically investigated by deposition of pairs of samples in the same deposition run. Our data show that in samples deposited on (100) perovskites, Ca excess leads to the formation of a single Ca-rich phase with stoichiometry Ca_{1 + x} Ru_1-x O₃, resulting in a dramatic effect on transport properties. Structural characterization based on X-ray diffraction proves that the orthorhombic structure is preserved in a wide stoichiometry range. The striking evidence that substrate orientation influences film stoichiometry is discussed in terms of growth kinetics and chemical properties of sputtered species.Received: 13 April 2004, Published online: 30 September 2004PACS: 68.55.-a Thin film structure and morphologyF. Bevilacqua: Present address: STMicroelectronics, Arzano, ItalyF. Ricci: Present address: Pirelli Labs, Italy     

FTIR法研究BCN薄膜的内应力

采用射频磁控溅射技术,用六角氮化硼和石墨为溅射靶,以氩气(Ar)和氮气(N₂)为工作气体,在Si(100)衬底上制备出硼碳氮(BCN)薄膜。利用傅里叶变换红外光谱(FTIR)考察了不同沉积参数(溅射功率为80～130 W、衬底温度为300～500 ℃、沉积时间为1～4 h)条件下制备的薄膜样品。实验结果表明,所制备薄膜均实现了原子级化合。并且沉积参数对BCN薄膜的生长和内应力有很大影响,适当改变沉积参数能有效释放BCN薄膜的内应力。在固定其他条件只改变一个沉积参数的情况下,得到制备具有较小内应力的硼碳氮薄膜的最佳沉积条件：溅射功率为80 W、衬底温度为400 ℃、沉积时间为2 h。