Control of plasma process instabilities during thin silicon film deposition

Fourier transform infrared absorption spectroscopy (FTIR), optical emission spectroscopy (OES), self-bias voltage and plasma impedance controls were applied as in situ process diagnostics during the deposition of amorphous silicon thin-films. The diagnostic abilities of OES and FTIR are compared. The FTIR in-situ direct measurement of silane concentration in exhaust line is more precise than OES control. All in situ process diagnostics clearly indicates the inconsistency of plasma properties and therefore of deposition conditions. The drifts are comparable with the film deposition time. The FTIR measurement of reactant concentration in the process chamber evidence that the strong silane concentration drop (about 50%) in a plasma is the cause of the short-term drift of OES signals (SiH? emission), plasma impedance and self-bias voltage signals. The influences of the deposition chamber geometry and technological parameters on process drifts are considered. The decrease of the gas residence time in the reactor leads to a decrease of Initial Transient State phenomena. Finally, the improvement of solar cell performance based on thin silicon films is demonstrated when drifts are reduced.     

Role of ex-situ oxygen plasma treatments on the mechanical and optical properties of diamond-like carbon thin films

Role of ex-situ oxygen plasma (OP) treatment on mechanical properties of diamond-like carbon (DLC) thin films is explored. The DLC film after this treatment shows superhardness behaviour, maximum hardness of 46.3 GPa and elastic modulus of 423.2 GPa are obtained when film grown at self bias of 100 V followed by 10 min OP treatment. Moreover, the colour of the coating is fed after OP treatment, leading it to a colourless coating with significantly enhanced transmittance and improved antiglare property. Such OP treated DLC films may find their applications as protective coatings on cutting tools, automobile parts, magnetic storage media and colourless coating in packaging, as the DLC films posses brown colour.     

H-assisted plasma CVD of Cu films for interconnects in ultra-large-scale integration

H-assisted plasma CVD (HAPCVD), in which Cu(hfac)₂ is supplied as the source material, realizes control of qualities of Cu films, since H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness. Conformal deposition in fine trenches can be realized by decreasing dissociation degree of Cu(hfac)₂ using the HAPCVD. Cu(hfac) is identified as the radical mainly contributing to the deposition. Based on the results, we proposed a model in which Cu(hfac) and H react on surfaces to deposit Cu films. We also demonstrated conformal deposition of smooth Cu films of 30 nm thickness and 1.9 mV cm resistivity and almost complete Cu filling in trenches 0.35mm wide and 1.6 mm deep using the HAPCVD.     

H-assisted plasma CVD of Cu films for interconnects in ultra-large-scale integration

H-assisted plasma CVD (HAPCVD), in which Cu(hfac)₂ is supplied as the source material, realizes control of qualities of Cu films, since H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness. Conformal deposition in fine trenches can be realized by decreasing dissociation degree of Cu(hfac)₂ using the HAPCVD. Cu(hfac) is identified as the radical mainly contributing to the deposition. Based on the results, we proposed a model in which Cu(hfac) and H react on surfaces to deposit Cu films. We also demonstrated conformal deposition of smooth Cu films of 30 nm thickness and 1.9 μΩ cm resistivity and almost complete Cu filling in trenches 0.35 μm wide and 1.6 μm deep using the HAPCVD.     

Intermediate gas phase precursors during plasma CVD of HMDSO

In plasma enhanced chemical vapor deposition (PECVD) from complex molecules like hexamethyldisiloxan (HMDSO) often not the molecules themselves but intermediate and reactive radicals or molecules are the precursors for film growth. Additionally, such PECVD processes are volume or mass flow limited under many process conditions. In these cases growth rate and film homogeneity is mainly dominated by the precursor content and its spatial distribution in the gas or plasma phase. Therefore the identification of such intermediate precursors is an important task to optimize a PECVD process and also helps us to understand the plasma chemical reactions during PECVD. A combined mass spectrometry and IR absorption study is used to identify intermediate gas phase precursors in HMDSO/O₂ PECVD remote plasmas. For this study a microwave plasma CVD system was used with HMDSO/O₂ ratios between 0.1 and 1 at typical operating pressures between 20 and 70 Pa. Three reactive intermediate species are proposed to act as a precursor for SiO_x film growth from HMDSO/O₂ plasmas. All three having a mass of 148 amu. The related reactive groups are the silanon (Si=O), silanol (Si-OH) and aldehyde (C=O) groups.     

Nanocrystalline yttria films by plasma-assisted liquid injection (PA-LI) CVD technique using metallorganic precursors

Nanocrystalline cubic Y₂O₃ film deposition by PA-LICVD was studied at 773 K in a N₂/O₂ plasma environment with methanol and triglyme solution of aquatris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium(III) and its polyether adduct complexes as precursors. The X-ray powder patterns are analyzed and found to be triclinic and monoclinic for Y(tmhd)₃·H₂O(1) and Y₂(tmhd)₆·triglyme (2). Y₂O₃ film with (111) plane as the dominant orientation was obtained on graphite under a deposition pressure of 0.8–1.2 mbar.     

CVD技术在制备含硅化合物膜层中的应用

本文综述了近十几年来CVD技术在不同基底材料上制取含硅化合物膜层的研究应用 ,并提出了目前存在的问题     

Linear antenna microwave plasma CVD deposition of diamond films over large areas

Diamond thin films were grown by linear antenna microwave plasma CVD process over large areas (up to 20 × 10 cm²) from a hydrogen based gas mixture. The influence of the gas composition (H₂, CH₄, CO₂) and total gas pressure (0.1 and 2 mbar) on the film growth is presented. For CH₄/H₂ gas mixtures, the surface crystal size does not show dependence on the methane concentration and total pressure and remains below 50 nm as observed by SEM. Adding CO₂ (up to 10%) significantly improves the growth rate. However, still no significant change of morphology is observed on films grown at 2 mbar. The crucial improvement of the diamond film purity (as detected by Raman spectroscopy) and crystal size is found for deposition at 0.1 mbar. In this case, crystals are as large as 500 nm and the growth rate increases up to 38 nm/h.     

微波等离子体化学气相沉积装置的工作原理

微波等离子体化学气相沉积（ＭＰＣＶＤ）是制备金刚石膜的一种重要方法。用简单实验方法给出了ＭＰＣＶＤ装置中微波模式转换、微波与等离子体耦合等工作原理。矩形波导中的ＴＥ１０模式经微波模式转换器转变为同轴线中的ＴＥＭ模式，再由ＴＥＭ模式转变为圆波导的ＴＭ０１模式。ＴＭ０１模式激发低压气体形成等离子体，等离子体严重影响微波模式分布。在国内首次成功运行了５ｋＷ天线耦合石英窗式ＭＰＣＶＤ装置。     

Al2O3陶瓷上沉积金刚石薄膜的研究

以酒精为碳源，用热丝ＣＶＤ法对不同表面状态的Ａｌ２Ｏ３衬底进行了金刚石薄膜沉积的比较，用扫描电镜，喇曼光谱和Ｘ射线衍射等方法检测了沉积出的金刚石膜的质量，并讨论了它们对成核和生长的影响。     

CVD Polymers for Devices and Device Fabrication

Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high‐purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro‐ and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.     

Diamond like carbon coatings deposited by microwave plasma CVD: XPS and ellipsometric studies

Diamond-like carbon (DLC) films were deposited by microwave assisted chemical vapour deposition system using d.c. bias voltage ranging from −100 V to −300 V. These films were characterized by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry techniques for estimating sp ³/sp ² ratio. The sp ³/sp ² ratio obtained by XPS is found to have an opposite trend to that obtained by spectroscopic ellipsometry. These results are explained using sub-plantation picture of DLC growth. Our results clearly indicate that the film is composed of two different layers, having entirely different properties in terms of void percentage and sp ³/sp ² ratio. The upper layer is relatively thinner as compared to the bottom layer.     

Silica nanofilms deposited by atmospheric pressure plasma liquid deposition

Silica coatings were deposited onto pure silicon surfaces by a deposition technique known as atmospheric pressure plasma liquid deposition using liquid tetraethylorthosilicate (TEOS) as a precursor. Deposition parameters were varied, including power, TEOS flow rate, helium flow rate, and substrate distance, in order to assess their influence on the growth rates and refractive index as well as the formation of surface particulates and organic content of the coatings. Growth rates were accurately controlled in the range of 0.5 nm s^− 1 to 7.2 nm s^− 1, with thin-films having refractive indices ranging from 1.1 to 1.4, indicative of layers with different levels of porosity. The results suggest that, with careful selection of deposition parameters, this (atmospheric pressure) plasma-based deposition technique could be used to achieve coherent, particulate free, smooth dense inorganic silica coatings.     

复合抛光对 CVD金刚石薄膜表面光洁度的改进研究

采用激光抛光和热化学抛光相结合的方法，对通过热丝CVD方法生长的金刚石薄膜进行了复合抛光处理．并利用X射线衍射仪（XRD）、拉曼光谱仪（Raman）、扫描电子显微镜（SEM）和原子力显微镜（AFM）对金刚石薄膜进行了表征．结果表明，所合成的金刚石薄膜是高质量的多晶（111）取向膜；经复合抛光后，金刚石薄膜的结构没有因抛光而发生改变，金刚石薄膜的表面粗糙度明显降低，光洁度大幅度提高，表面粗糙度Ra在100nm左右，基本可以达到应用的要求．     

生长温度对CVD金刚石薄膜的影响

系统研究了ＣＶＤ金刚石薄膜成膜过程中生长温度对薄膜质量、生长率和力学性能的影响。研究结果表明：在典型沉积条件下，生长温度愈高、薄膜的晶体质量愈好；但薄膜的应力状况和附着性能变坏；在８００℃时，金刚石薄膜的生长速率最大。讨论了ＣＶＤ金刚石薄膜作为机械工具涂层的最佳生长温度。     

CVD金刚石膜的场发射机制

利用热灯丝化学气相沉积方法在光滑的钼上沉积了金刚石膜,用扫描电子显微镜和Raman谱对金刚石膜进行了分析。结果表明金刚石膜是由许多金刚石晶粒组成,晶粒间界主要是石墨相,并且在膜内有许多缺陷。金刚石膜的场发射结果表明高浓度CH4形成的金刚石膜场发射阈位电场较低浓度CH4形成的金刚石为低。这意味着杂质（如石墨）和缺陷（悬挂键）极大地影响了膜的场发射性能。根据以上结果,提出了一种CVD金刚石膜的场发射机制即膜内的缺陷增强膜内的电场,石墨增大电子的隧穿系数以增强CVD金刚石膜的场发射。     

Direct current electrical conduction mechanism in plasma polymerized thin films of tetraethylorthosilicate

The plasma polymerized tetraethylorthosilicate (PPTEOS) thin films were deposited on to glass substrates at room temperature by a parallel plate capacitively coupled glow discharge reactor. The current density-voltage (J-V) characteristics of PPTEOS thin films of different thicknesses have been observed at different temperatures in the voltage region from 0.2 to 15 V. In the J-V curves two slopes were observed — one in the lower voltage region and another in the higher voltage region. The voltage dependence of current density at the higher voltage region indicates that the mechanism of conduction in PPTEOS thin films is space charge limited conduction. The carrier mobility, the free carrier density and the total trap density have been calculated out to be about 2.80 × 10^− 15m²V^− 1s^− 1, 1.50 × 10²²m^− 3 and 4.16 × 10³³m^− 3 respectively from the observed data. The activation energies are estimated to be about 0.13 ± 0.05 and 0.46 ± 0.07 eV in the lower and higher temperature regions respectively for an applied voltage of 2 V and 0.09 ± 0.03 and 0.43 ± 0.10 eV in the lower and higher temperature regions respectively for an applied voltage of 14 V. The conduction in PPTEOS may be dominated by hopping of carriers between the localized states at the low temperature and thermally excited carriers from energy levels within the band gap in the vicinity of high temperature.     

Grain-Scale Modeling of CVD of Polycrystalline Diamond Films

The evolution of grain size, grain-size distribution, morphological and crystallographic texture, surface roughness, and the contribution of various surface facets to the growth of polycrystalline diamond films is performed by carrying out a series of two-dimensional computer simulations. The films are assumed to grow from a set of randomly oriented, {100}- and {111}-faceted nuclei by the motion of their vertices (the points where the adjoining facets of the same or neighboring grains meet). The vertex velocities are found to be a function of the orientation and the growth rate of the adjoining facets. To quantify the latter, a {100} to {111} growth-rate parameter is used. The results show that the evolution of the grain size and its distribution, surface roughness, morphological and crystallographic texture, and the portion of the film grown from different surface facets are all mutually linked and governed by the magnitude of the growth-rate parameter. The latter can be controlled by the CVD processing conditions, such as the substrate temperature, reactor pressure, mole fraction of carbon-source gas (e.g., CH₄, C₂H₂).     

Influence of plasma heating of wafer substrates on SiO2 deposition rate in a TEOS/O2 high-density plasma CVD system

The influence of plasma heating of the Si and glass wafer substrates on silicon dioxide (SiO₂) deposition rates by a tetraethylorthosilicate/O₂ supermagnetron (high-density) plasma CVD were investigated. With a fixed RF power of 100 W supplied to both upper and lower electrodes, the SiO₂ deposition rate on the Si wafer substrate decreased with increasing wafer-stage temperature, showing a negative activation energy for the deposition rate. When Si and glass wafers were attached to the electrode using adherent thermal conductors, the film thickness increased almost linearly with regard to the deposition time, and both deposition rates became almost the same (about 310 Å/min). When both wafers were simply laid on the electrode without an adhesive bond and hence with poor thermal contact, the film thickness increased nonlinearly with deposition time, showing a gradual decrease in deposition rate with time, being as low as 80 and 150 Å/min, respectively for Si and glass wafers, for a deposition time of 15 min. The difference between the two deposition rates on Si and glass wafers in the case of poor thermal contact to the lower electrode is thought to be caused by plasma heating and related mainly to differences in optical absorption characteristics of the two wafer substrates. Variations in measured thickness distributions across the substrate surface were attributed to an antisymmetric plasma density distribution in the direction perpendicular to the magnetic field lines caused by E×B electron drift.     

用发射天线式微波等离子体CVD装置沉积大面积金刚石薄膜

在国内首次研制成功了高气压发射天线式微波等离子体辅助化学气相沉积金刚石薄膜装置，用该装置成功地在３英寸的单晶硅衬底上沉积了Φ７０ｍｍ的金刚石薄膜。这一成果填补了国内空白，对我国金刚石薄膜研究领域的设备更新换代和开发应用具有重要意义。