纳米硅薄膜制备技术进展

本文综述了纳米硅薄膜制备新技术的进展。着重介绍了高氢稀释硅烷蚀刻法，微波氢基团增强化学气相沉积，逐层法和高频数值等离子体化学气相沉积技术制备纳米硅薄膜的沉积过程和生长机制．本文指出氢基团为各项新技术发展的关键并将在今后纳米硅薄膜制备技术发展中起重要作用。     

纳米硅薄膜的低压化学气相沉积和电学性能研究

利用普通低压化学气相沉积技术在玻璃衬底上制备了大面积的纳米硅薄膜。不同温度下薄膜暗电导率的测试研究表明 ,薄膜的室温暗电导率随成膜温度的升高而增加 ,相应的电导激活能降低。热激活隧道击空机制可以较好地解释纳米硅薄膜特殊的电学性能。原位后续热处理研究表明 ,延长热处理时间以及采用低温成膜、高温后续退火的热处理方法均能有效提高其室温暗电导率。     

微波等离子体化学气相沉积方法制备纳米金刚石薄膜

为了制备出大面积均匀连续的纳米金刚石薄膜,并探索温度、气氛等条件对最终生长出的纳米金刚石薄膜样品的影响,使用微波等离子体化学气相沉积(MPCVD)方法,改变CH4、H2、Ar气体比例以及衬底温度,在不同生长条件下制备了5组金刚石薄膜样品.5组样品分别使用ESEM和拉曼光谱进行成膜质量、形貌、结构以及组分的表征,分析了不...     

HWP-CVD氮化硅薄膜的结构和光学特性

采用傅立叶红外吸收谱和紫外-可见透射谱研究了螺旋波等离子体增强化学气相沉积法制备的氢化非晶氮化硅薄膜的原子间键合结构和光学特性。结果表明,在不同硅、氮活性气体配比R下,薄膜表现出不同的Si/N比和H原子键合方式,富氮样品中H原子主要和N原子结合,而富硅样品中主要和Si原子结合。随着R的增加,薄膜的光学带隙E_g和E₀₄逐渐减小,此结果关联于薄膜结构无序性程度的增加,而薄膜的(E₀₄-E_g)和Tauc斜率B值之间存在着相互制约关系。     

特种化学气相沉积法制备大面积纳米硅薄膜的微结构和电学性能研究

采用可与Si平面工艺兼容的特殊设计的化学气相沉积系统在玻璃衬底上制备了大面积的纳米Si薄膜.高分辨率电子显微镜和选区电子衍射分析表明,成膜温度对薄膜微结构有关键影响,衬底温度的升高促进了薄膜晶态率的提高和Si晶粒的长大.660℃成膜时非晶Si薄膜基体中镶嵌了尺寸为8～12nm,晶态率为50%的纳米Si晶粒,具有明显的纳米Si薄膜微结构特征.用变温薄膜暗电导率测试系统研究表明,随成膜温度的升高,薄膜的晶态率提高、室温暗电导率提高而相应的电导激活能降低,用热激活隧道击穿机制解释了纳米Si薄膜微结构与特殊电学性能的关系.研究了原位后续热处理对薄膜微结构和电学性能的影响,发现延长热处理时间以及采用低温成膜、高温后续退火的热处理方法能有效提高纳米Si薄膜的晶态率,进而提高其室温暗电导率.     

纳米硅薄膜的低压化学气相沉积和电学性能研究

利用普通低压化学气相沉积技术在玻璃衬底上制备了大面积的纳米硅薄膜。不同温度下薄膜暗电导率的测试研究表明，薄膜的室温暗电导率随成膜温度的升高而增加，相应的电导激活能降低。热激活隧道击空机制可以较好地解释纳米硅薄膜特殊的电学性能。原位后续热处理研究表明，延长热处理时间以及采用低温成膜、高温后续退火的热处理方法均能有效提高其室温暗电导率。     

化学气相沉积制备纳米结构碳化钨薄膜

采用氟化钨(WF6)和甲烷(CH4)为前驱体,采用等离子体增强化学气相沉积(PECVD)方法制备具有纳米结构的碳化钨薄膜。采用SEM、XRD、EDS等方法表征了碳化钨薄膜的形貌、晶体结构和化学组成。通过表征,表明在前驱体混合气体中的甲烷与氟化钨气体的流量比(碳钨比)为20、基底温度为800℃的条件下得到的碳化钨薄膜是由直径为20～35nm的圆球状纳米晶构成。通过分析影响薄膜的晶体结构、化学组成的因素后,认为要得到具有纳米晶结构的碳化钨薄膜,主要应控制前驱体气体中的碳钨比以及基底温度。     

等离子体化学气相法沉积金刚石薄膜

本文介绍和评述了化学气相沉积法制备人造金刚石薄膜及其进展，重点评述了反应机理，发展历史，沉积方法，补底材料，检测手段，论述了有利于形成立方晶系金刚石材料的沉积条件。     

等离子体增强化学气相沉积氮化钛薄膜

等离子增强化学气相沉积法(PCVD)是在物理气相沉积(PVD)和化学气相沉积(CVD)基础上发展起来的一种沉积方法。它兼有 PVD 和 CVD 方法的优点。介绍了 PCVD的原理和所研制的一台 PCVD 设备。分析了用 CVD 法和 PCVD 法制备的硬质膜的性能。所分析的性能有:显微硬度、抗弯强度、粘结牢度、机加工性能。     

Structural and optical properties of four-hexagonal polytype nanocrystalline silicon carbide films deposited by plasma enhanced chemical vapor deposition technique

Four-hexagonal polytype films of nanocrystalline silicon carbide (4H-nc-SiC) were deposited by plasma enhanced chemical vapor deposition method with more than 3×10⁴ W m⁻² threshold of power density, high hydrogen dilution ratio, and bias pretreatment. The source gases were silane, methane and hydrogen. Our work showed that under conditions similar to those used for the growth of μc-SiC—except a higher power densities over a threshold, a bigger bias pretreatment on substrates, and a moderate bias deposition—nc-SiC films could indeed be achieved. The Raman spectra and transmission electron microscopy diffraction patterns demonstrated that the as-grown films from the H₂-CH₄-SiH₄ plasma consist of amorphous network and phase-pure crystalline silicon carbide which has the 4H polytype structure. The microcolumnar 4H-SiC nanocrystallites of a mean size of approximately 1.6×10⁻⁸ m in diameter are encapsulated by amorphous SiC networks. The photoluminescence spectra of 4H-SiC at room temperature, peaking at 8.10×10⁻⁷ m using a wavelength of 5.145×10⁻⁷ m of argon ion laser, were obtained at room temperature; the luminescence mechanism is thought to be related to transitions in the energy band gap which could be ascribed to the surface states and defects in the structure of 4H-SiC nanocrystalline in these films due to its small size. The as-grown films showed an optical transmittance of 89% at 6.58×10⁻⁷ m. This higher transmittance is believed to be from the small size and amorphous matrix.     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.     

Fabrication of nanocrystalline silicon carbide thin film by helicon wave plasma enhanced chemical vapour deposition

Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapour deposition on Si substrates using the mixture of SiH₄, CH₄, and H₂ at a low substrate temperature of 300 °C. The infrared absorption spectroscopy analyses and microstructural characteristics of the samples deposited at various magnetic fields indicate that the high plasma intensity in helicon wave mode is a key factor to the success of growing nanocrystalline silicon carbide thin films at a relative low substrate temperature. Transmission electron microscopy measurements reveal that the films consist of silicon carbide nanoparticles with an average grain size of several nanometers, and the light emission measurements show a strong blue photoluminescence at room temperature, which is considered to be caused by the quantum confine effect of small size silicon carbide nanoparticles.     

Piezoresistive properties of nanocrystalline silicon thin films deposited on plastic substrates by hot-wire chemical vapor deposition

The piezoresistive property of n-type and p-type nanocrystalline silicon thin films deposited on plastic (PEN) at a substrate temperature of 150 °C by hot-wire chemical vapor deposition, is studied. The crystalline fraction decreased from 80% to 65% in p-type and from 84% to 62% in n-type films, as the dopant gas-to-silane flow rate ratio was increased from 0.18% to 3-3.5%. N-type films have negative gauge factor (− 11 to − 16) and p-type films have positive gauge factor (9 to 25). In n-type films the higher gauge factors (in absolute value) were obtained by increasing the doping level whereas in p-type films higher gauge factors were obtained by increasing the crystalline fraction.     

Structural and optical properties of microcrystalline silicon films deposited by plasma enhanced chemical vapour deposition

Hydrogenated microcrystalline (c) silicon films were prepared by plasma enhanced chemical vapour deposition using an Ar-diluted SiH₄ gas at various deposition conditions. The substrate temperature and RF power were varied from 150 to 400 C and from 10 to 120 W, respectively. Structure and microstructure were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Hydrogen bonding and optical properties were investigated by FTIR spectra and UV transmission spectra. The crystal fraction of the films increased as the deposition temperature decreased and RF power increased. More definite columnar morphology was developed with increasing crystal fraction. The existence of c-Si above a critical RF power (>30 W) suggests that SiH₂ radical in plasma plays an important role for the formation of columnar morphology and c-Si. IR absorption analysis showed that the SiH₂/SiH bonding ratio in the silicon films increased as the crystal fraction increased. The UV absorption coefficient of the films became smaller as the deposition temperature and RF power increased.     

Evolution of optical properties with deposition time of silicon nitride and diamond-like carbon films deposited by radio-frequency plasma-enhanced chemical vapor deposition method

The paper presents investigations of the optical properties of thin high-refractive-index silicon nitride (SiN_x) and diamond-like carbon (DLC) films deposited by the radio-frequency plasma-enhanced chemical vapor deposition method for applications in tuning the functional properties of optical devices working in the infrared spectral range, e.g., optical sensors, filters or resonators. The deposition technique offers the ability to control the film's optical properties and thickness on the nanometer scale. We obtained thin, high-refractive-index films of both types at deposition temperatures below 350 °C, which is acceptable under the thermal budget of most optical devices. In the case of SiN_x films, it was found that for short deposition processes (up to 5 min long) the refractive index of the film increases in parallel with its thickness (up to 50 nm), while for longer processes the refractive index becomes almost constant. For DLC films, the effect of refractive index increase was observed up to 220 nm in film thickness.     

Bulk and interface properties of low-temperature silicon nitride films deposited by remote plasma enhanced chemical vapor deposition

Hydrogenated silicon nitride (a-SiN_x:H) films were deposited at temperatures ranging from 50 to 300 °C with remote plasma enhanced chemical vapor deposition (RPECVD) from NH}_{3 and SiH}_{4. The effect of the operating variables, such as deposition temperature and especially the partial pressure ratio of reactant (R=NH₃/SiH₄) on the properties of the Sa-SiN_x:H interface was investigated. The H^* radical was dominantly observed and the deposition rate was proportional to the NH^* radical concentration. The density of highly energetic N ₂ ^* radicals increased in the high plasma power regime in which the film surface was roughened, but they promote surface reactions even at low temperature. The refractive index was more closely related to the film stoichiometry than film density. The interface trap density is related to the amount of silicon intermediate species and Si–NH bonds at the Si/SiN_x:H interface and it can be minimized by reducing the intermediate Si species and Si–NH bonding state. The films showed a midgap interface trap density of 2 × 10¹¹ - 2 × 10¹²cm^-2. © 2001 Kluwer Academic Publishers     

Optical and structural properties of silicon oxynitride deposited by plasma enhanced chemical vapor deposition

We present an overview of the properties of silicon oxynitride material (SiON) deposited by plasma enhanced chemical vapor deposition (PECVD) for photovoltaic applications. SiON films were deposited using silane (SiH₄), ammonia (NH₃) and nitrogen protoxide (N₂O) as precursor gases in a low frequency PECVD. Varying the gas flow mixture leads to a whole range of SiON layers starting from the silicon oxide to the silicon nitride with unique stoichiometries and properties. Thanks to spectroscopic ellipsometry measurements we have confirmed the suitability of SiON for antireflection coating layers due to the range of the refractive indexes attainable. SiON structure was analyzed by X-ray photo-electron spectroscopy. We have thus highlighted the critical role of oxygen behavior on the SiON network and the progressive replacement of nitrogen by oxygen atoms when the oxygen precursor increases. The type of chemical bonds present in SiON layers was also investigated by infrared spectroscopy. The SiON layers also contain a non-negligible amount of hydrogen which might be useful for passivation applications. The behavior of hydrogen content was thus analyzed by elastic recoil decay analysis and desorption characterization. A typical rapid thermal annealing was performed on the SiON samples in order to simulate the solar cells contact annealing and to investigate its impact on the dielectric film properties. It was found that hydrogen becomes weakly bonded to the films and strongly decreases in quantity with the annealing. The surface passivation effect is presented in the last part of this paper. The trend before and after a rapid thermal annealing showed opposite results which could be explained by the high porosity of the layers and the formation of Si-O bonds.     

Annealing effects on structural and electrical properties of fluorinated amorphous carbon films deposited by plasma enhanced chemical vapor deposition

The annealing effects on the structural and electrical properties of fluorinated amorphous carbon (a-C:F) thin films prepared from C₆F₆ and Ar plasma are investigated in a N₂ environment at 200 mTorr. The a-C:F films deposited at room temperature are thermally stable up to 250 °C, but as the annealing temperature is increased beyond 300 °C, the fluorine incorporation in the film is reduced, and the degree of crosslinking and graphitization in the film appears to be enhanced. At the annealing temperature of 250 °C, the chemical bond structures of the film are unchanged noticeably, but the interface trapped charges between the film and the silicon substrate are reduced significantly. The increased annealing temperature contributes the decrease of both the interface charges and the effective charge density in the a-C:F film. Higher self-bias voltage is shown to reduce the charge density in the film.     

Mechanical properties of carbon-modified silicon oxide barrier films deposited by plasma enhanced chemical vapor deposition on polymer substrates

Cohesive and adhesive properties of silicon oxide barrier coatings deposited from an oxygen/hexamethyldisiloxane gas mixture by plasma enhanced chemical vapor deposition, with controlled incorporation of carbon on 12 μm thick polyethylene terephtalate films were investigated. The reactor was equipped with a 2.45 GHz slot antenna plasma source and a 13.56 MHz-biased substrate holder. The two plasma sources were operated separately or in a dual mode. It was found that no or negligible internal stresses were introduced in the silicon oxide coatings as long as the increase of energy experienced by the film was compensated by the densification of the oxide. For a range of process parameters and carbon content on the changes of the crack onset strain, adhesion, and cohesion were found to be similar. Generally a high crack onset strain or good adhesion and cohesion were measured for films with an increased carbon content, although this was obtained at the expense of the gas barrier performance. Promising approaches towards high-barrier thin films with good mechanical integrity are proposed, based on coatings with a gradient in the carbon content and in the mechanical properties, on nano-composite laminates, and on organo-silane treatments.