High performance poly-crystalline silicon thin film transistorsfabricated using remote plasma chemical vapor deposition of SiO2

A remote plasma chemical vapor deposition (RPCVD) of SiO₂ was investigated for forming an interface of SiO₂/Si at a low temperature below 300°C. A good SiO₂/Si interface was formed on Si substrates through decomposition and reaction of SiH₄ gas with oxygen radical by confining plasma using mesh plates. The density of interface traps (D_it) was as low as 3.4×10¹⁰ cm^-2eV^-1. N- and p-channel Al-gate poly-Si TFTs were fabricated at 270°C with SiO₂ films as a gate oxide formed by RPCVD and laser crystallized poly-crystalline films formed by a pulsed XeCl excimer laser. They showed good characteristics of a low threshold voltage of 1.5 V (n-channel) and -1.5 V (p-channel), and a high carrier mobility of 400 cm²/Vs     

Advances in remote plasma-enhanced chemical vapor deposition for low temperature In situ hydrogen plasma clean and Si and Si1-xGex epitaxy

Remote plasma-enhanced chemical vapor deposition (RPCVD) is a low temperature growth technique which has been successfully employed inin situ remote hydrogen plasma clean of Si(100) surfaces, silicon homoepitaxy and Si_{1- x}Ge_x heteroepitaxy in the temperature range of 150–450° C. The epitaxial process employs anex situ wet chemical clean, anin situ remote hydrogen plasma clean, followed by a remote argon plasma dissociation of silane and germane to generate the precursors for epitaxial growth. Boron doping concentrations as high as 10²¹ cm^?3 have been achieved in the low temperature epitaxial films by introducing B₂H₆/He during the growth. The growth rate of epitaxial Si can be varied from 0.4Å/min to 50Å/min by controlling therf power. The wide range of controllable growth rates makes RPCVD an excellent tool for applications ranging from superlattice structures to more conventional Si epitaxy. Auger electron spectroscopy analysis has been employed to confirm the efficacy of this remote hydrogen plasma clean in terms of removing surface contaminants. Reflection high energy electron diffraction and transmission electron microscopy have been utilized to investigate the surface structure in terms of crystallinity and defect generation. Epitaxial Si and Si_1-xGe_x films have been grown by RPCVD with defect densities below the detection limits of TEM (~10⁵ cm^-2 or less). The RPCVD process also exploits the hydrogen passivation effect at temperatures below 500° C to minimize the adsorption of C and 0 during growth. Epitaxial Si and Si_1-xGe_x films with low oxygen content (~3 × 10₁₈ cm^-3) have been achieved by RPCVD. Silicon and Si/Si_1-xGe_x mesa diodes with boron concentrations ranging from 10¹⁷ to 10¹⁹ cm^-3 in the epitaxial films grown by RPCVD show reasonably good current-voltage characteristics with ideality factors of 1.2-1.3. A Si/Si_1-xGe_x superlattice structure with sharp Ge transitions has been demonstrated by exploiting the low temperature capability of RPCVD.In situ plasma diagnostics using single and double Langmuir probes has been performed to reveal the nature of the RPCVD process.     

Defect microstructure in low temperature epitaxial silicon grown by RPCVD

Defect characterization of epitaxial silicon films grown by low temperature remote plasmaenhanced chemical vapor deposition (RPCVD) under various conditions is discussed. The film morphology and crystallinity have been examined by defect etching/Nomarski optical microscopy and transmission electron microscopy. Prior to epitaxial growth, anex situ wet chemical clean and anin situ remote hydrogen plasma clean were performed to remove the native oxide as well as other surface contaminants such as carbon. A damage-free (100) Si surface with extremely low concentrations of carbon and oxygen as confirmed byin situ Auger electron spectroscopy can be achieved using this cleaning technique at temperatures as low as 250°. Low temperature Si homoepitaxy was achieved by RPCVD on lightly doped (100) Si substrates. Growth parameters such as silane flow rate (partial pressure), chamber pressure, and substrate temperature were varied during epitaxial growth to investigate the dependence of film quality on these parameters. For comparison,in situ remote hydrogen plasma and epitaxial growth were also performed on heavily dopedp-type (100) Si substrates. Finally, the results of epitaxial growth at temperatures as low as 150° are presented.     

Defect microstructure in single crystal silicon thin films grown at 150° C-305° C by remote plasma-enhanced chemical vapor deposition

Defect microstructure in terms of defect density and impurity concentration of epitaxial Si films grown by low temperature Remote Plasma-enchanced Chemical Vapor Deposition (RPCVD) in the temperature range of 150–305° C has been investigated using Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), Reflection High Energy Electron Diffraction (RHEED) and defect etching/Nomarski microscopy. Defect density in the epitaxial Si films is found to be a strong function of growth temperature in the temperature range under study, indicating that thermal excitation is an important source of energy, in addition to plasma excitation, for driving surface reactions in the RPCVD expitaxial process. Impurity concentrations of H, O and C in the epitaxial films have been determined by SIMS analysis. The trace amounts (∼1 ppm) of oxygen and water vapor in the reactant gas (2%SiH₄/He) was identified to be an important source of oxygen in the epitaxial Si films. An oxygen concentration as low as 3 × 10¹⁸ cm^-3 in the epitaxial Si film grown at 150° C has been achieved through the use of a gas purifier. The higher hydrogen concentration in the films grown at lower temperatures is believed to be due to insufficiently rapid hydrogen desorption from the surface during growth. The results of characterization using TEM and SIMS are discussed to elucidate the atomistic mechanisms of Si epitaxial growth by RPCVD.     

Structural analysis of Ge x Si1−x /Si layers by remote plasma-enhanced chemical vapor deposition on Si (100)

In this work, remote plasma-enhanced chemical vapor deposition (RPCVD) has been used to grow Ge _x Si_1−x /Si layers on Si(100) substrates at 450° C. The RPCVD technique, unlike conventional plasma CVD, uses an Ar (or He) plasma remote from the substrate to indirectly excite the reactant gases (SiH₄ and GeH₄) and drive the chemical deposition reactions. In situ reflection high energy electron diffraction, selected area diffraction, and plan-view and cross-sectional transmission electron microscopy (XTEM) were used to confirm the single crystallinity of these heterostructures, and secondary ion mass spectroscopy was used to verify abrupt transitions in the Ge profile. XTEM shows very uniform layer thicknesses in the quantum well structures, suggesting a Frank/ van der Merwe 2-D growth mechanism. The layers were found to be devoid of extended crystal defects such as misfit dislocations, dislocation loops, and stacking faults, within the TEM detection limits (∼10⁵ dislocations/cm²). Ge _x Si_1−x /Si epitaxial films with various Ge mole fractions were grown, where the Ge contentx is linearly dependent on the GeH₄ partial pressure in the gas phase for at leastx = 0 − 0.3. The incorporation rate of Ge from the gas phase was observed to be slightly higher than that of Si (1.3:1).     

RPCVD生长SiGe薄膜及其性能研究

利用应用材料公司外延设备,在Si(001)衬底上,通过RPCVD方式生长出完全应变、无位错的SiGe外延层.通过X射线衍射和原子力显微镜测试技术,得到了外延层Ge摩尔分数、外延层厚度、生长速率以及表面粗糙度等参数,研究了运用RPCVD方法制备的应变SiGe外延层的生长特性以及薄膜特性.结果表明,在660℃所生长的薄膜,其XRD图像均出现了Pendelossung条纹,表明薄膜质量较好.Ge摩尔分数高达16.5%.薄膜表面粗糙度RMS在0.3～0.6nm.     

CeO_2高K栅介质薄膜的制备工艺及其电学性质

研究了 Ce O2 作为高 K (高介电常数 )栅介质薄膜的制备工艺 ,深入分析了衬底温度、淀积速率、氧分压等工艺条件和利用 N离子轰击氮化 Si衬底表面工艺对 Ce O2 薄膜的生长及其与 Si界面结构特征的影响 ,利用脉冲激光淀积方法在 Si(10 0 )衬底生长了具有 (10 0 )和 (111)取向的 Ce O2 外延薄膜 ;研究了 N离子轰击氮化 Si衬底表面处理工艺对 Pt/ Ce O2 / Si结构电学性质的影响 .研究结果显示 ,利用 N离子轰击氮化 Si表面 /界面工艺不仅影响 Ce O2 薄膜的生长结构 ,还可以改善 Ce O2 与 Si界面的电学性质     

Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD

Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 °C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 °C. Root mean square of roughness (RMS) of ∼0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. ∼4 × 10⁸ cm⁻² for a 4.7 μm thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 °C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as ∼7 × 10⁵ cm⁻² is achieved for 4.7 μm Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of ∼0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated.     

Role of CF2 in the etching of SiO2, Si3N4 and Si in fluorocarbon plasma

The CF2 density and etch rate of SiO2, Si3N4 and Si are investigated as a function of gas pressure and 02 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO2 etch rate increases. Previous study has shown that SiO2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO2 etching. Generally, the CF2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO2 etching. When more CF2 radical in plasma, SiO2 etch rate is increased because more fluorine can be provided. In this case, CF2 is considered as a reactant for SiO2 etching. The etch rate of Si3N4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF2 density in plasma. Etching results obtained by varying O2 flow rate also support the proposition.     

碳氟等离子体中CF2对SiO2，Si3N4和Si刻蚀的作用

The CF2 density and etch rate of SiO2, Si3N4 and Si are investigated as a function of gas pressure and O2 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO2 etch rate increases. Previous study has shown that SiO2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO2 etching. Generally, the CF2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO2 etching. When more CF2 radical in plasma, SiO2 etch rate is increased because more fluorine can be provided. In this case, CF2 is considered as a reactant for SiO2 etching. The etch rate of Si3N4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF2 density in plasma. Etching results obtained by varying O2 flow rate also support the proposition.     

电子耗空对喷焰尘埃等离子体离子波不稳定性的影响

在离子波不稳定性增长率的计算过程中增加对自洽尘埃电荷数的考虑, 以考察电子耗空效应对尘埃等离子体离子波不稳定性增长率的影响.通过比对多个算例的计算结果发现:随着尘埃数密度的增大, 电子耗空的加剧可以导致不稳定性增长率减小; 喷焰释放早期的离子波不稳定性增长率可以更低; 无论是尘埃数密度还是中性分子数密度单独增大, 均可以导致离子波不稳定性增长率的减小.这表明现有理论方法中隐含的假设不是恒成立.     

Effect of substrate bias on the properties of plasma deposited organosilicone (pp-HMDSN) thin films

Organosilicone thin films have been deposited by plasma polymerization (pp) in a plasma enhanced chemical vapor deposition (PECVD) system using hexamethyldisilazane (HMDSN:C6H19Si2N) as a monomer precursor, at different biases of the stainless-steel substrate holder. The substrate bias affected film thickness, surface morphology, chemical composition and photoluminescence (PL) emission. For a negatively biased substrate, it is found that the film thickness is the minimum, while the porosity and PL emission are the maximum. For a positively biased substrate, the thickness and the ratio of Si/N are the maximum which correspond to a blue shift of the PL emission in comparison with the case of non-biased grounded substrate. In addition, the characterization of the plasma using a single cylindrical Langmuir probe has been performed to obtain information about both the electron density and the positive ion energy, where it can be concluded that the ion energy plays a major role in determining film thickness.     

Cleaning and passivation of the Si(100) surface by low temperature remote hydrogen plasma treatment for Si epitaxy

This paper presents the results of a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment which serves the dual purpose of cleaning and passivating the Si(100) surface prior to low temperature Si epitaxy by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The remote hydrogen plasma treatment was optimized for the purposes of cleaning and passivation, respectively. To achieve a clean, defect-free substrate surface, the remote hydrogen plasma process was first optimized using Transmission Electron Microscopy (TEM) and Auger Electron Spectroscopy (AES). For hydrogen passivation, the substrate temperature was varied from room temperature to 250° C in order to investigate the degree of passivation as a function of substrate temperature by examining the amount of oxygen readsorbed on the substrate surface after air exposure. Low temperature Si expitaxy was subsequently performed on the air-exposed substrates without further cleaning to evaluate the effectiveness of the hydrogen passivation. It was found that better Si surface passivation is achieved at lower substrate temperatures as evidenced by the fact that less oxygen is observed on the surface using AES and Secondary Ion Mass Spectroscopy (SIMS) analyses. The amount of readsorbed oxygen on the H-passivated Si surface after a two hour air exposure was found to be as low as 0.1 monolayer from SIMS analysis. Using Reflection High Energy Electron Diffraction (RHEED) analysis, different surface reconstructions ((3 × 1) and (1 × 1)) were observed for H-passivated Si surfaces passivated at various temperatures, which was correlated to the results of AES and SIMS analyses. Epitaxial growth of Si films at 305° C was achieved on the air-exposed Si substrates, indicating a chemically inert Si surface as a result of hydrogen passivation. A novel electron-beam-induced-oxygen-adsorptiom phenomena was observed on the Hpassivated Si surface. Scanning Auger Microscopy (SAM) analysis was performed to study the reaction kinetics as well as the nature of Si—H bonds on the H-passivated Si surface. Preliminary results show that there is a two-step mechanism involved, and oxygen adsorption on the H-passivated Si surface due to electron beam irradiation may be due to the formation of O-H groups rather than the creation of Si—O bonds.     

A New View of Microcrystalline Silicon: The Role of Plasma Processing in Achieving a Dense and Stable Absorber Material for Photovoltaic Applications

To further lower production costs and increase conversion efficiency of thin‐film silicon solar modules, challenges are the deposition of high‐quality microcrystalline silicon (μc‐Si:H) at an increased rate and on textured substrates that guarantee efficient light trapping. A qualitative model that explains how plasma processes act on the properties of μc‐Si:H and on the related solar cell performance is presented, evidencing the growth of two different material phases. The first phase, which gives signature for bulk defect density, can be obtained at high quality over a wide range of plasma process parameters and dominates cell performance on flat substrates. The second phase, which consists of nanoporous 2D regions, typically appears when the material is grown on substrates with inappropriate roughness, and alters or even dominates the electrical performance of the device. The formation of this second material phase is shown to be highly sensitive to deposition conditions and substrate geometry, especially at high deposition rates. This porous material phase is more prone to the incorporation of contaminants present in the plasma during film deposition and is reported to lead to solar cells with instabilities with respect to humidity exposure and post‐deposition oxidation. It is demonstrated how defective zones influence can be mitigated by the choice of suitable plasma processes and silicon sub‐oxide doped layers, for reaching high efficiency stable thin film silicon solar cells.     

Silicon-Carbon alloy film formation on Si(100) using SiH4 and CH4 reaction under low-energy ECR Ar plasma irradiation

Epitaxial growth of Si-C alloy films on Si(100) were achieved in the C fraction range up to about 5 at% by surface reaction of SiH₄ and CH₄ under low-energy Ar plasma irradiation without substrate heating in electron-cyclotron-resonance (ECR) plasma chemical-vapor deposition (CVD). Moreover, it was found that the Si-C alloy (C fraction of 1.4 at%) with an about 1%-larger vertical lattice constant than unstrained Si could be epitaxially grown on Si(100) under perfect lattice matching, which was different from the generally-reported results of tensile-strained Si-C alloy epitaxy on Si(100) at relatively higher temperatures. It was also found that deposition interruption effectively improved crystal quality of the film with an increased strain.     

Deposition of GaN thin film on ZnO/Si by DIBD method

The GaNis a semiconductor material witha widefor-bidden band(Eg=3.36eV).It has many unique advan-tages such as high electron drift velocity,small dielectricconstant,goodthermal conduction et al.It is a favorablematerial for making electric devices with hi…     

VHF plasma deposition for thin-film solar cells

Fast deposition rates, typical for very high frequency (VHF) plasma deposition, up to now have mainly been attributed to a more efficient silane decomposition as the results of an enhanced density of high-energy electrons in the plasma. In this work a-Si:H was prepared at excitation frequencies in a wide frequency range between 25 and 250 MHz and at otherwise constant conditions. In order to understand the processes leading to the observed increase in deposition rate with frequency, the plasma was investigated by optical emission spectroscopy and mass spectrometry. Plasma-substrate interactions were studied by impedance analysis and ion flux measurements. the results show that the high deposition rates are mainly the result of an increased surface reactivity of film precursors resulting from the ions impinging on the growth surface. It is shown that variation of the excitation frequency allows a flexible control of ion flux and energies. Conditions were optimized for the preparation of a-Ge:H films, which require a flux of high-energy ions to the substrate. Material properties were obtained that were comparable to results from deposition on the cathode of a radio frequency (RF) discharge.     

Remote plasma-enhanced CVD of silicon: Reaction kinetics as a function of growth parameters

The reaction kinetics in Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) have been studied for a chamber pressure of 200 mTorr, rf powers between 4 and 8 W, diluted silane flow rates between 5 and 40 sccm, and temperatures between 190 and 480° C. The observed temperature dependence of growth rate reveals a change in activation energy at 300–325° C, suggesting that hydrogen desorption is the rate limiting step in the deposition reaction. A strong dependence of growth rate on rf power has been attributed in part to the extension of the glow discharge region closer to the substrate at higher rf powers. Growth rate has been shown to increase when the sample is positioned closer to the glow, indicating that the reaction precursor is a short-lived species, probably SiH₂ or SiH₃. Growth rate has been shown to exhibit a sublinear dependence on silane partial pressure. Oxygen incorporation in the deposited films has been studied using Secondary Ion Mass Spectroscopy (SIMS), and it has been found that the main source of oxygen contamination is the process gases. However, it has also been found that “point of use” purification of the process gases reduces water and oxygen contamination significantly, reducing the oxygen incorporation in the films by an order of magnitude.     

GaN在Si(001)上的ECR等离子体增强MOCVD直接生长研究

研究了用电子回旋共振(ECR)等离子体增强金属有机物化学气相沉积(PEMOCVD)技术在Si(001)衬底上,低温(620～720℃)下GaN薄膜的直接外延生长及晶相结构.高分辨透射电镜(HRTEM)和X射线衍射(XRD)结果表明:在Si(001)衬底上外延出了高度c轴取向纤锌矿结构的GaN膜,但在GaN/Si(001)界面处自然形成了一层非晶层,其两个表面平坦而陡峭,厚度均匀(≈2nm).分析认为,在初始成核阶段N与Si之间反应所产生的这层SixNy非晶层使GaN的β相没有形成.XRD和原子力显微镜(AFM)结果表明,衬底表面的原位氢等离子体清洗,GaN初始成核及后续生长条件对GaN膜的晶体质量非常重要.     

GaN在Si(001)上的ECR等离子体增强MOCVD直接生长研究

研究了用电子回旋共振(ECR)等离子体增强金属有机物化学气相沉积(PEMOCVD)技术在Si(001)衬底上,低温(620～720℃)下GaN薄膜的直接外延生长及晶相结构.高分辨透射电镜(HRTEM)和X射线衍射(XRD)结果表明:在Si(001)衬底上外延出了高度c轴取向纤锌矿结构的GaN膜,但在GaN/Si(001)界面处自然形成了一层非晶层,其两个表面平坦而陡峭,厚度均匀(≈2nm).分析认为,在初始成核阶段N与Si之间反应所产生的这层SixNy非晶层使GaN的β相没有形成.XRD和原子力显微镜(AFM)结果表明,衬底表面的原位氢等离子体清洗,GaN初始成核及后续生长条件对GaN膜的晶体质量非常重要.