氢化微晶硅薄膜的两因素优化及高速沉积

采用甚高频等离子体辅助化学气相沉积技术(VHF-PECVD)分别对薄膜沉积参数进行了功率密度-沉积气压和硅烷浓度-气体总流量两因素优化.主要研究沉积参数对薄膜沉积速率和结晶状况的影响,结果表明:高沉积压强下,功率密度的提高对微晶硅薄膜(μc-Si∶H)沉积速率的影响减弱,硅烷浓度和气体总流量影响作用相对增强,高硅烷浓度有利于材料的利用,最终在高压强(600Pa)条件下,使微晶硅薄膜的沉积速率提升到2.1nm·s-1.同时,利用分步沉积法对薄膜的纵向结构均匀性进行了初步研究.     

高气压下氢化微晶硅薄膜的高速沉积

利用甚高频等离子增强化学气相沉积(VHF-PECVD)制备了一系列微晶硅(μc-Si:H)薄膜。研究分析了功率密度、硅烷浓度和气体流量在较高沉积气压(500 Pa和600 Pa)下对薄膜生长速率、结晶状况和电学特性的影响。研究表明:在高压强条件下,硅烷浓度和气体流量对沉积速率影响显著,而功率密度影响较弱;高沉积速率生长的薄膜孵化层较厚;电学特性较好的薄膜位于非晶/微晶过渡区。经过工艺的初步优化,在高压强(600 Pa)条件下,使微晶硅薄膜的沉积速率提升到2.1 nm/s。     

沉积条件对硅基薄膜非晶转微晶相变、沉积速率及其光电性能的影响(英文)

本文采用HWA-MWECR-CVD系统制备了微晶硅薄膜。研究了氢稀释比、反应压强以及微波功率对微晶硅薄膜非晶转微晶相变及其相关性能的影响。实验结果表明:当氢稀释比为94%、反应压强为1.5Pa以及微波功率为500W时,高质量的微晶硅薄膜可以被获得,如2.86*104的高光敏性,1nm左右的沉积速率以及8.9%的光致衰退速率等。     

射频功率对微晶硅薄膜微结构和光电性能的影响

采用射频等离子体增强化学气相沉积(rf-PECVD)技术,在玻璃和硅衬底上沉积微晶硅(μc-Si:H)薄膜。利用拉曼光谱、AFM和电导率测试对不同射频功率下沉积的薄膜的结构特性及光电性能进行分析。研究表明:随着射频功率的增加,薄膜的晶化率和沉积速率也随之增加,而当射频功率增加到一定的程度,晶化率和沉积速率反而减小。薄膜的暗电导率与晶化率的变化情况相对应。     

TiO_2磁控溅射工艺参数对薄膜沉积速率的影响

为了经济、有效、准确地在线测量光学薄膜厚度,采用射频磁控反应溅射法在玻璃衬底上制备TiO2薄膜。用自制的简易监测系统对TiO2薄膜在生长过程中的沉积速率进行了即时测量,研究了射频功率、气体流量、工作气压等工艺参数对TiO2薄膜沉积速率的影响规律。结果表明:沉积速率监测系统对膜厚变化反应灵敏,能够实时监测薄膜生长速率;溅射过程中,射频功率、氧氩流量比和工作气压对薄膜沉积速率有较大的影响,射频功率从120 W增加到240 W,薄膜沉积速率增加;氧气流量从1 mL/min增加到5 mL/min,薄膜沉积速率先逐渐增大后减小,存在一个临界点;工作气压从0.3 Pa增加到0.8 Pa,薄膜沉积速率缓慢增加,但临界点后迅速下降。     

脉冲磁控溅射沉积微晶硅薄膜工艺研究

采用脉冲磁控溅射法制备氢化微晶硅薄膜,利用X射线衍射、拉曼光谱、扫描电子显微镜和四探针测试仪对薄膜结构和电学性能进行表征和测试,研究了衬底温度、氢气稀释浓度和溅射功率对硅薄膜结构和性能的影响。结果表明:在一定范围内,通过控制合适的衬底温度、增大氢气稀释浓度及提高溅射功率,可以制备高质量的微晶硅薄膜。在衬底温度为400℃、氢气稀释浓度为90%及溅射功率为180W的条件下制备的微晶硅薄膜,其晶化率为72.2%,沉积速率为0.48nm/s。     

硅烷浓度对微晶硅薄膜微结构及电学性质的影响

采用RF-PECVD技术,在玻璃衬底上低温沉积了优质微晶硅薄膜,并深入研究了硅烷浓度对微晶硅薄膜微结构及电学性质的影响.研究结果表明,微晶硅薄膜的沉积速率、平均晶粒尺寸、晶化率和电导率均呈现相似的变化规律,而谱中出现的拐点由硅烷浓度决定.该变化规律可通过相应的薄膜生长的微观理论得到合理的解释.     

微晶硅p-i-n薄膜太阳电池研究进展

相对于单晶硅和非晶硅来说,微晶硅薄膜太阳电池具有更多的优势。高速沉积高效微晶硅太阳电池已经成为当前研究的热点。综合介绍了微晶硅p-i-n太阳电池的结构以及基本原理、研究现状和存在的问题,并对其发展前景进行了展望。     

反应溅射GexC1—x薄膜的沉积速率

系统地研究了射频磁控反应溅射中工艺参数ＧｅｘＣ１－ｘ薄膜沉积率的影响，结果表明，当气体流量比过某值后，沉积速率较大的下降。沉积速率随射频率功率的增大而增大，某工作气压下有沉积速率的最大值，薄膜厚度时间增长规律在出现靶中毒及未出的靶中毒的情况下略有差别。     

HfO2薄膜的制备与光学性能

采用射频磁控反应溅射法，以高纯热压HfO2陶瓷为靶材，在Si衬底上成功制备出HfO2薄膜。系统研究了工艺参数对薄膜沉积速率的影响规律，并对薄膜的光学性能进行了研究。结果表明，射频功率对薄膜沉积速率的影响最为明显，O2／Ar流量比和衬底温度对沉积速率的作用不明显，所制备薄膜的折射率较高在近红外波段趋于1．95，在500-1650nm波段范围内薄膜几乎无吸收，透过率较高。     

High-rate deposition of amorphous silicon films using hot-wire CVD with a coil-shaped filament

To reduce the manufacturing cost of amorphous silicon (a-Si:H)-based photovoltaic devices, it is important to deposit high-quality a-Si:H and related materials at a high deposition rate. To this end, we designed and constructed a hot-wire deposition chamber with a coiled filament design and with multiple gas inlets. The process gas could be directed into the chamber through the filament coil and have maximum exposure to the high-temperature filament surface. Using such a chamber design, we deposited a-Si:H films at high deposition rates up to 800 Å s⁻¹ and dense, low-void a-Si:H at rates up to 240 Å s⁻¹.     

High-speed preparation of c-axis-oriented YBa2Cu3O7-δ film by laser chemical vapor deposition

YBa₂Cu₃O_7-δ (YBCO) films were prepared by laser chemical vapor deposition using Y(DPM)₃, Ba(DPM)₂/Ba(TMOD)₂ and Cu(DPM)₂ as precursors with enhancement by a continuous wave Nd:YAG laser. A c-axis-oriented YBCO film almost entirely in a single phase was obtained. The YBCO film consisted of rectangular grains about 30 μm in size. The highest deposition rate was about 100 μm h^− 1, which was 10-1000 times higher than that of conventional MOCVD.     

Structure and electrical properties of ITO thin films deposited at high rate by facing target sputtering

High rate deposition of ITO thin films at a low substrate temperature was attempted by using a facing target sputtering (FTS) system. Deposition rate as high as 53 nm/min was realized on polycarbonate film substrate of 80-μm thickness. When the film was deposited at a deposition rate above 80 nm/min, polycarbonate film substrate was thermally damaged. The film deposited by FTS has much smaller compressive film stress than the film deposited by conventional magnetron sputtering. The film stress was reduced significantly by increasing the sputtering gas pressure and stress-free films can be obtained by adjusting the sputtering gas pressure. This may be mainly caused by the fact that bombardment by high energy negative oxygen ions to substrate surface during deposition can be completely suppressed in the FTS. Film structure and electrical properties changed little with substrate position, and uniform films were obtained by the FTS.     

Dynamic behaviour of high strength steel parts developed through laser assisted direct metal deposition

High strength steel alloys are good candidates for many engineering applications particularly those involving high strains and impact loads. Such applications in energy absorption devices require materials that can sustain dynamic loading and remain strong under demanding conditions. But the processing cost of these alloys has been a prohibitive factor, thus re-enforcing the research on porous and cellular structures made of stainless steels. Direct metal deposition (DMD) is a process which employs the power of a CO₂ laser to melt and deposit metallic powders onto steel substrates. Such structures offer advantages of creating novel configurations only by computer control of laser “tool path”. This research investigates the mechanical behaviour of solid and porous parts with prismatic cavities under quasi-static and dynamic compressive loading. Apart from two main deficiencies of relatively large variations of properties among the test specimen and sufficiently low modulus of elasticity, the stress strain behaviour is very close to the commercial grades of stainless steel produced by rolling and forming. The energy absorption behaviour of porous specimen is also very encouraging and renders DMD as a suitable process for manufacturing of customized sandwich and graded structures that can be used as a substitution for many engineering applications such as monolithic compression plates and explosion shields.     

Photoconducting a-Si:H films grown at high deposition rates by pulsing a VHF 100 MHz discharge

In a novel experiment hydrogenated amorphous silicon films were deposited by modulating the very high frequency (VHF) (100 MHz) discharges, at low frequency (2 Hz) with a nonzero low power level, using pure as well as 25% hydrogen and 25% helium diluted silane as the source gases. During these studies deposition rate is found to depend on the dwell time as in the case of RF pulsed plasma CVD reported earlier by the authors. The films were characterised for optical bandgap, dark and photoconductivity, hydrogen content, microstructure factor, Urbach energy and defect density. The results indicate that, unlike the RF pulsed plasma case, there is an order of magnitude improvement in the photoconductivity of the material due to pulsing the VHF discharges. Urbach energy and defect density studies also indicate an improvement in the film quality. The improvements are more pronounced in diluted silane deposited films. Controlled ion bombardment (of high flux and lower energy) and the resulting ion bombardment induced preparation of the growth surface in the VHF discharges are believed to be the main factors contributing to the observed results. Thus, a more favourable sheath characteristics as obtained during pulsed VHF discharge conditions over RF (13.56 MHz). Silane discharges holds the key to obtain high growth rate deposition of a-Si:H films of acceptable opto-electronic quality     

AlGaN/GaN-heterostructures on (111) 3C-SiC/Si pseudo substrates for high frequency applications

We present the realization of high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures, which were grown on silicon substrates using an ultrathin SiC transition layer. The growth of AlGaN/GaN heterostructures on 3C-SiC(111)/Si(111) was performed using metalorganic chemical vapour deposition (MOCVD). The 3C-SiC(111) transition layer was realized by low pressure CVD and prevented Ga-induced meltback etching and Si-outdiffusion in the subsequent MOCVD growth. The two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface showed an electron sheet density of 1.5 × 10¹³ cm^− 3 and a mobility of 870 cm²/Vs. The HEMTs DC and RF characteristics were analysed and showed a peak cut-off frequency as high as 29 GHz for a 250 nm gate length.     

High-rate deposition and mechanical properties of SiOx film at low temperature by plasma enhanced chemical vapor deposition with the dual frequencies ultra high frequency and high frequency

A high efficiency, high-rate deposition process was developed for silicon oxide films using plasma enhanced chemical vapor deposition (PECVD) with an additional ultra high frequency (UHF) power with high frequency (HF) bias. The effect of the UHF input power with HF bias on the anti-scratch properties of the silicon oxide films was examined. The hybrid plasma process was also examined by advanced plasma source. Dissociation of the octamethylycyclodisiloxane (OMCTS) precursor was controlled by the plasma processing parameters. SiO_x films were deposited on polycarbonate substrates by PECVD using OMCTS and oxygen carrier gas. The rate of SiO_x film deposition increased with increasing input energy. The plasma was analyzed by optical emission spectroscopy. The deposition rate was characterized using an alpha-step. The mechanical properties of the coatings were examined using a nano-indenter and pencil hardness measurements. The chemical properties of the coatings were examined by Fourier transform infrared spectroscopy. The deposition rate of the SiO_x films was controlled by the dissociation of OMCTS using the appropriate intensity of excited neutrals, ionized atoms and input UHF input power with HF bias at room temperature.     

Mitigating the geometrical limitations of conventional sputtering by controlling the ion-to-neutral ratio during high power pulsed magnetron sputtering

High power pulsed magnetron sputtering has been used to grow thin chromium layers on substrates facing and orthogonal to the target. It is demonstrated that at low peak target current density, j_T < 0.6 A/cm² corresponding to a low ion-to-neutral flux ratio, films grown on substrates facing the target exhibit in-plane alignment. This is due to the rectangular shape of the target that yields an asymmetry in the off-normal flux of sputtered species. With increasing j_T the biaxial alignment degrades, as the major portion of the incoming flux (ions) can be effectively steered by the electric field of the substrate to remove asymmetry imposed by geometrical restrictions. Eventually, at j_T = 1.7 A/cm² a fiber texture is obtained. For films grown on substrates orthogonal to the target, the large column tilt characteristic for growth at low j_T, decreases with increasing ion content in the flux and almost disappears at the highest value of j_T. The latter indicates that material flux to the substrate is highly ionized so that deposition takes place along substrate normal despite the high nominal inclination angle. Thus, in the limit of high j_T the artifacts of conventional physical vapor deposition, resulting from the line-of-sight deposition, are effectively eliminated and the film growth proceeds more or less unaffected by the substrate orientation. Samples mounted orthogonally thus possess a similar texture, morphology, and topography as those facing the target.     

Studies of medium frequency high power density magnetron sputtering discharges

Optical emission spectroscopy and Langmuir probe have been used to study the power dependence of medium frequency, 100 kHz, pulsed magnetron sputtering discharge. Copper target was sputtered in the argon atmosphere. The examined power ranged from 0.5 to 4.5 kW which gave an average power density on target surface from 25 to 115 W/cm². Optical spectroscopy did not reveal any significant changes of copper ion contribution to the sputtering process. The electron temperature and plasma potential changed a little with applied power. The electron density depended linearly on the sputtering power.