低气压下制备金刚石薄膜的研究

利用我们自己研制的磁约束直流等离子体设备，在低气压（＜１Ｔｏｒｒ）下。用Ａｒ＋Ｈ２＋ＣＨ４的混合气体在基片上进行了沉积金刚石薄膜的工艺研究。利用扫描电镜和拉曼光谱对不同的进气方式所制备出的金刚石薄膜的形貌和质量进行了比较。结果表明。当在基片表面附近引入碳源气体和大约５０％氢气时，可以大大提高薄膜质量。     

MIM capacitor fabrication and assessment for GaAs MMICs

Metal-insulator-metal, MIM, capacitors have been fabricated using plasma deposited silicon nitride, SiN_x, films deposited under varying deposition conditions. The electrical properties of the MIM capacitors and the corresponding physical properties of the SiN_x films have been determined. The breakdown field strength of the films, which varied between 0.4–3.0 MVcm⁻¹, has been related to the amount of hydrogen incorporated in the SiN_x layers during deposition. Frenkel-Poole conduction through the silicon nitride has been observed at room temperature and this conduction mechanism is shown to be predominant and independent of the breakdown field strength, for the films investigated.     

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.     

Dependence of surface morphology of CVD diamond films on deposition conditions

ＤｅｐｅｎｄｅｎｃｅｏｆｓｕｒｆａｃｅｍｏｒｐｈｏｌｏｇｙｏｆＣＶＤｄｉａｍｏｎｄｆｉｌｍｓｏｎｄｅｐｏｓｉｔｉｏｎｃｏｎｄｉｔｉｏｎｓＹＡＮＧＧｕｏｗｅｉ（Ｄｅｐｔ．ｏｆＰｈｙｓ．，ＸｉａｎｇｔａｎＵｕｉｖｅｒｓｉｔｙ，Ｘｉａｎｇｔａｎ４１１１０５...     

Growth of diamond films on si(100) with and without boron nitride buffer layer

Diamond films were grown on Si(100) and boron nitride deposited Si(100) substrates using hot filament chemical vapor deposition (HFCVD) technique. Microstructure and morphology of diamond films have been investigated systematically as a function of CH₄ and H₂ ratio and the ambient pressure. The deposited films were characterized by employing techniques such as scanning electron microscopy (SEM) and laser Raman spectroscopy. The average size and growth rate of diamond particles were found to increase with the CH₄ to H₂ ratio and decrease with the ambient pressure. Maximum growth rate of synthetic diamond deposited on Si(100) was found to be ∼3.5 µm/hr for the film deposited at 20 Torr with CH₄:H₂ ∼ 1.5:100 (substrate temperature ∼850°C). In most of these depositions, the morphology of the diamond crystals was cubic with significant secondary nucleation at higher methane concentrations and ambient pressure. The diamond film deposited on Si(100) with BN buffer layer shows an improvement in growth rate and the coverage, and the secondary nucleation was found to be substantially reduced, resulting in relatively smooth morphology. MicroRaman investigations show less amorphous graphite formation and better structural quality of diamond film than the one deposited without the BN buffer layer. On leave from Department of Physics University of Poona, Pune-411007 INDIA     

A study of the local electronic and atomic structure in <Emphasis Type="Italic">a</Emphasis>-Si<Subscript>x</Subscript>C<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> amorphous alloys using ultrasoft X-ray emission spectroscopy

X-ray spectroscopy has been used to obtain data on the local electronic and atomic structure of a-Si_xC_1?x:H(Er) alloys produced by plasma-enhanced chemical vapor deposition (PECVD) with various relative amounts of silane and methane in the gas mixture (x=0.3–0.9). It is shown that the alloys contain silicon and carbon atoms in different coordination environments. Silicon is observed as elementary amorphous silicon and silicon carbide, and the relative amounts of these phases in the films depend on the composition of the gas mixture. Carbon atoms can form bonds with silicon in a coordination close to that found in crystalline silicon carbide, with a noticeable amount of C-H bonds also appearing. In addition, carbon can form an elementary carbon phase with various coordination numbers characteristic of graphite and diamond in the film.     

Selective silicon epitaxy by photo-chemical vapor deposition at a very low temperature of 160°C

We have grown epitaxial Si films by the photo-chemical vapor deposition (photo-CVD) technique with SiH₄ and H₂ at a very low-temperature of 160°C. Epitaxial films were grown on silicon substrates, while amorphous-like films were deposited on glass substrates. Furthermore, it was found from the atomic hydrogen etching which was produced by photo-dissociation of hydrogen that the etching rate of amorphous silicon was much higher than that of crystal silicon. By using these selectively, we have demonstrated selective epitaxial growth of silicon by the photo-CVD technique followed by the atomic hydrogen photo-etching. Furthermore, heavily phosphorus-doped silicon films (>1 × 10²¹ cm¹⁻³) were also selectively grown by this novel technique.     

Dependence of surface morphology of CVD diamond films on deposition conditions

The diamond films have been deposited by the hot filament CVD method on molybdenum substrates from the mixture reactant gas of acetone and hy-drogen.The surface morphologies of the obtained diamond films under various de-position conditions have been observed by scanning electron microscope (SEM).The experimental results strongly indicate that the surface morphologies of the re-sulting films have closely related to the deposition conditions,i.e.,reaction pres-sure.For molybdenum substrates,under the lower reaction pressure the surface morphologies of the grains comprising the resulting films mainly display the small single crystal cubo-octahedron and double small crystal cubo-octahedron;under the higher reaction pressure ,the surface morphologies mainly display the large cauliflower-like .These results show that there are various crystal habits for CVD diamond under various deposition conditions .     

An a-Si:H vacuum-compatible photoresist process for fabricating device structures in HgCdTe

A process for transferring patterns into HgCdTe epilayers using a hydrogenated amorphous silicon (a-Si:H) photomask has been demonstrated. a-Si:H films were grown using plasma enhanced chemical vapor deposition (PECVD). A latent image of a projected mask pattern was created at the a-Si:H surface by ultraviolet enhanced oxidation in the load lock of the PECVD vacuum chamber. This image was transformed into a mask by hydrogen plasma removal of the unexposed areas. A hydrogen plasma etch selectivity value greater than 500:1 for oxide and a-Si:H allows patterns as thick as 700 nm to be generated. a-Si:H masks were used to create arrays of mesas in planar HgCdTe epilayers by etching in an electron cyclotron resonance (ECR) plasma reactor. Etch selectivity between a-Si:H and HgCdTe during an ECR hydrogen plasma etch was measured to be greater than 18:1. R_oA values > 10³ were obtained for mid-wavelength infrared diodes made from HgCdTe heterojunctions using a-Si:H masks.     

Low-Temperature deposition of dielectric films by microwave plasma enhanced decomposition of hexamethyldisilazane

Hexamethyldisilazane (HMDS) has been used as an organosilicon source for the deposition of dielectric films at low temperatures (200-250° C) by microwave plasma enhanced CVD technique. Hydrogenated films of variable composition of silicon carbonitride, silicon oxynitride and silicon dioxide have been deposited by decomposition of HMDS in the presence of additive gases like NH₃, O₂ and H₂ under different process conditions. Deposited films have been characterized by the measurement of refractive index and buffered HF etch rate, and by the analysis of XPS and infrared transmission spectra. An increase in HMDS partial pressure generally results in the decrease of refractive index. The films show stable C-V characteristics of metal-insulator-semicon-ductor (MIS) capacitors with positive insulator charge density.     

Highly rectifying Au-contacts on diamond-on-silicon substrate

Au Schottky diodes have been fabricated on highly oriented diamond (HOD) films, grown on silicon using AC-bias nucleation and microwave plasma chemical vapor deposition. The active layers were selectively grown and doped by solid boron source. High rectification ratios were obtained up to 500°C in a bias voltage range up to ±15 V. A current density of more than 1 A/cm² and a breakdown field strength up to 2.0·10⁶ V/cm for point contacts has been demonstrated     

循环刻蚀工艺对金刚石膜形貌和电阻率的影响

为了制备新型金刚石薄膜辐射剂量计,针对目前金刚石薄膜质量较差,难于满足辐射剂量计要求的问题,采用微波等离子体CVD法,研究了循环刻蚀生长阶段工艺参数(甲烷浓度,基片温度)和刻蚀方法对薄膜形貌、电阻率的影响。结果表明,循环刻蚀生长有利于提高金刚石薄膜的纯度和取向性。当?(甲烷)为0.34%,基片温度为960℃时,可获得[100]晶面取向的、电阻率达1011Ω·cm的金刚石膜,和采用常规工艺所得金刚石薄膜相比,其电阻率提高了3个数量级。     

Effects of nitrogen trifluoride on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon films

The effects of nitrogen trifluoride (NF₃) on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon (DLC) films were investigated. The addition of NF₃ increases the deposition rate of DLC film due presumably to the removal of activated hydrogen species by the fluorine radical (F⁻). Diamond-like carbon films deposited in a methane/NF₃ mixture have a higher refractive index, a lower bulk resistivity, and a lower optical bandgap compared to films deposited in pure methane due to a lower hydrogen content in the films. Moreover, the bulk resistivity of methane/NF₃ DLC films remains constant for annealing temperatures below 400°C. Thus, DLC films deposited with NF₃ are more stable than DLC films deposited without NF₃.     

Thin-film transistors in polycrystalline silicon by blanket andlocal source/drain hydrogen plasma-seeded crystallization

Thin film n-channel transistors have been fabricated in polycrystalline silicon films crystallized using hydrogen plasma seeding, by using several processing techniques with 600 to 625°C or 1000°C as the maximum process temperature. The TFTs from hydrogen plasma-treated films with a maximum process temperature of 600°C, have a linear field-effect mobility of ~35 cm²/Vs and an ON/OFF current ratio of ~10⁶, and TFTs with a maximum process temperature of 1000°C, have a linear field-effect mobility of ~100 cm²/Vs and an ON/OFF current ratio of ~10⁷. A hydrogen plasma has also then been applied selectively a in the source and drain regions to seed large crystal grains in the channel. Transistors made with this method with maximum temperature of 600°C showed a nearly twofold improvement in mobility (72 versus 37 cm² /Vs) over the unseeded devices at short channel lengths. The dominant factor in determining the field-effect mobility in all cases was the grain size of the polycrystalline silicon, and not the gate oxide growth/deposition conditions. Significant increases in mobility are observed when the grain size is in order of the channel length. However the gate oxide plays an important role in determining the subthreshold slope and the leakage current     

微米金刚石聚晶薄膜场发射点的研究

采用微波等离子化学气相沉积方法,以甲烷和氢气为反应气体,在镀有金属钛的陶瓷衬底上,制备了微米金刚石聚晶薄膜.利用扫描电镜、拉曼光谱、X射线光电子能谱对薄膜的化学组成、微观结构和表面形貌进行了表征.用二级结构的场发射仪和扫描隧道显微镜研究了薄膜的场发射性能,结果表明微米金刚石聚晶薄膜发射点主要来源于聚晶颗粒.进一步研究了单个聚晶颗粒表面不同区域的发射性能,发现多种因素对场发射的性能有影响.     

金刚石基底上制备(002)AlN薄膜的研究

首先采用微波等离子体化学气相沉积(MPCVD)方法,在O2/H2/CH4混合气体气氛下利用大功率微波在(100)Si片上生长出了异质外延金刚石膜,X-射线衍射(XRD)、拉曼光谱和场发射扫描电子显微镜(FESEM)对薄膜的表征分析结果表明,制备的金刚石膜具有很高的金刚石相纯度,且晶粒排列紧密;继而采用射频磁控反应溅射法,在抛光的金刚石基底上成功制备了高C轴择优取向的氮化铝(AlN)薄膜,研究了不同的溅射气压、靶基距对AlN薄膜制备的影响,XRD检测结果表明,溅射气压低,靶基距短,有利于AlN(002)面择优取向,相反则更有利于AlN薄膜的(103)面和(102)面择优取向;研究了AlN薄膜在以N终止的金刚石基底和纯净金刚石基底两种表面状态上的生长机制,结果发现,以N终止的金刚石基底非常有利于AlN(002)面择优取向生长;从Al-N化学键的形成以及溅射粒子平均自由程的角度,探讨了其对AlN薄膜择优取向的影响。     

Bulk passivation of multicrystalline silicon solar cells induced by high‐rate‐deposited (> 1 nm/s) silicon nitride films

Silicon nitride (a‐SiN_x:H) films deposited by the expanding thermal plasma at high rate (> 1 nm/s) have been studied for application as anti‐reflection coatings for multicrystalline silicon (mc‐Si) solar cells. Internal quantum efficiency measurements have revealed that bulk passivation is achieved after a firing‐through process of the a‐SiN_x:H as deposited from NH₃/SiH₄ and N₂/SiH₄ plasmas. However, the a‐SiN_x:H films deposited from N₂/SiH₄ show a lower passivation quality than those deposited from NH₃/SiH₄. This has been attributed to a poorer thermal stability of the films deposited from the N₂/SiH₄ plasma, resulting in structural changes within the film during the firing step. Copyright © 2002 John Wiley & Sons, Ltd.     

Low-temperature growth of polycrystalline SiC by catalytic CVD from monomethylsilane

Microcrystalline silicon carbide (μc-SiC) has several applications, such as solar cells, light-emitting diodes and as optical coating for solar cells. Hydrogenated amorphous silicon carbide (a-SiC:H) grows by plasma enhanced CVD, even under hydrogen diluted conditions. High concentration of atomic hydrogen from catalytic CVD could promote lower temperature growth of μc-SiC under the same conditions as a-SiC:H without plasma. In the present study, μc-SiC films have been successfully grown by catalytic CVD (hot-filament catalysis) from monomethylsilane and hydrogen on (1 0 0) silicon substrates maintained at 300 °C. The optimal chamber pressure is 1.0 Torr and the optimal concentration of monomethylsilane in the hydrogen carrier gas is 1%. FTIR spectra of films obtained under these conditions show strong Si-C peaks.     

Deposition,opto-electronic and structural characterization of polymorphous silicon thin films to be applied in a solar cell structure

In this study we analyze the optoelectronic properties and structural characterization of hydrogenated polymorphous silicon thin films as a function of the deposition parameters. The films were grown by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of argon (Ar), hydrogen (H₂) and dichlorosilane (SiH₂Cl₂). High-resolution transmission electron microscopy images and Raman measurements confirmed the existence of very different internal structures (crystalline fractions from 12% to 54%) depending on the growth parameters. Variations of as much as one order of magnitude were observed in both the photoconductivity and effective absorption coefficient between the samples deposited with different dichlorosilane/hydrogen flow rate ratios. The optical and transport properties of these films depend strongly on their structural characteristics, in particular the average size and densities of silicon nanocrystals embedded in the amorphous silicon matrix. From these results we propose an intrinsic polymorphous silicon bandgap grading thin film to be applied in a p–i–n junction solar cell structure. The different parts of the solar cell structure were proposed based on the experimental optoelectronic properties of the pm-Si:H thin films studied in this work.     

本征微晶硅薄膜的结构演变及其对太阳电池光伏性能的影响

采用高压射频等离子体增强化学气相沉积(RF-PECVD)方法制备本征硅薄膜和n-i-P结构太阳电池,研究了氢稀释率对本征硅薄膜的电学特性和结构特性的影响.采用光发射谱(OES)和喇曼(Raman)散射光谱研究了处于过渡区的本征硅薄膜的纵向结构演变过程.结果表明:光发射谱和喇曼散射光谱可以作为研究硅薄膜的纵向结构演变有效手段.随着氢稀释率的增加,硅薄膜从非晶相向微晶相过渡时,其纵向结构的改变会严重影响硅薄膜太阳电池的光伏性能.