Structural and electrical properties of plasma-deposited silicon nitride from SiH4-N2 gas mixture

Plasma-deposited silicon nitride films were produced from SiH₄-N₂ gas mixture. Their composition, chemical bonds, and electrical properties were investigated by varying the deposition conditions. The silicon nitride films from SiH₄-N₂ gas mixture exhibit (i) less hydrogen, (ii) higher thermal endurance, (iii) higher density, and (iv) smaller etching rate than those of the films deposited from SiH₄, and NH₃ gas mixture. These results can be partly attributed to lower hydrogen concentration. As the Si/N ratio approaches the stoichiometric value, 0.75, the resistivity and the breakdown strength are increased. They are 10¹⁵Ωcm and 9MV/cm, respectively, at Si/N≃0.85. Interface state density between silicon and silicon nitride layers is as low as 1& #x223C; 5xl0¹¹cm⁻² eV⁻¹. On leave from The Northwest Telecommunication Engineering Institute, Xi’an, The People’s Republic of China.     

Oxygen and carbon incorporation in low temperature epitaxial Si films grown by rapid thermal chemical vapor deposition (RTCVD)

Using SIMS analysis, we have measured oxygen and carbon concentrations in epitaxial Si films grown between 550 and 900° C. The films were grown by rapid thermal chemical vapor deposition from SiH₄ as well as several different SiH₂Cl₂ sources. We have found that at low deposition temperatures (∼750° C or lower), oxygen incorporation is first dictated by source gas impurities and then by residual chamber gases. For the case of SiH₂Cl₂, which can have substantial oxygen content due to its reactivity with H₂O, oxygen concentrations of about 10²⁰ cm^-3 are typical at low deposition temperatures. SiH₄, however, can be obtained in higher purity, and oxygen concentrations of 10¹⁸ cm^-3 can be realized at low temperatures. At higher deposition temperatures (750-900° C), SiO volatilizes, leaving the films grown from all sources with low oxygen concentrations, typically less than 5 × 10¹⁷ cm^-3. Carbon incorporation is much less of a problem since it is present to a lesser extent both in the chamber background and in the source gases. Carbon levels less than or equal to 10¹⁸ cm^-3 can be obtained at all deposition temperatures greater than about 650° C. The performance ofp/n junctions is shown to degrade significantly for junctions grown below 850° C. We conclude that for growth of long lifetime Si films in the temperature range <800° C, that low residual H₂O partial pressures (<10^-10 Torr) are desired. Therefore, CVD chambers should be loadlocked and also capable of base pressures as low as about 10^-9 Torr.     

Optical and electrical properties of Al2O3 films containing silicon nanocrystals

Optical, electrical, and structural properties of Al₂O₃ films subjected to silicon-ion implantation and annealing were investigated by means of photoluminescence measurements, current-voltage measurements and transmission electron microscopy. Transmission electron microscopy revealed that silicon nanocrystals were epitaxially formed in ϑ-Al₂O₃. Visible photolum inescence was observed, for the first time, from Al₂O₃ films containing silicon nanocrystals. Observed visible photoluminescence seems to be related to quantum size effects in silicon nanocrystals as well as localized radiative recombination centers located at the interface between silicon nanocrystals and matrix, similar to porous Si and other Si nanostructures. The conduction mechanism in the samples was studied by using dc current-voltage measurements. The conduction properties depend on temperature and applied electric fields. The conduction behavior in low electric fields consists of thermally activated region dominated by the Schottky conduction and nonthermally activated region in which carrier transport is controlled by space-charge-limited currents. The conduction behavior under relatively high electric fields is almost independent of temperature and well fitted by space-charge-limited conduction.     

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO₂ layer at the Ta₂O₅/Si interface is observed by annealing in dry O₂ or N₂ and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta₂O₅ films decreases as the annealing temperature increases when annealed in dry O₂ or N₂. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta₂O₅. The effect is larger in thicker Ta₂O₅ films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO₂ layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO₂. The electrical properties of Ta₂O₅ as a function of annealing conditions do not depend on the fabrication method of Ta₂O₅ but strongly depend on the thickness of Ta₂O₅ layer.     

The CVD growth of Cu films using H2 as carrier gas

Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethylvinylsilane (Cu(hfac)TMVS) was studied using a low pressure chemical vapor deposition system of a cold wall vertical reactor. The Cu films deposited using H₂ as a carrier gas revealed no impurities in the films within the detection limits of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Using hydrogen as a carrier gas, the hydrogen not only acts as a reducing agent, but also reacts with the residual fragment of precursor. As a result, using H₂ as a carrier gas for Cu(hfac)TMVS resulted in Cu films of lower resistivity, denser microstructure and faster deposition rate than using Ar or N₂ as the carrier gas. Moreover, we found that N₂ plasma treatment on the substrate surface prior to Cu deposition increased the deposition rate of Cu films.     

Characterization of Si homoepitaxial films grown with and without surface photoactivation by ArF excimer laser-induced photodissociation of Si2H6

Silicon homoepitaxial films have been grown by photodissociation of Si₂H₆ by the 193 nm line of an ArF excimer laser in an ultra-high vacuum system. Silicon epitaxy has been achieved in two ways: one, in which the laser shines into the chamber parallel to the substrate and another, in which the laser is directly incident on the substrate at grazing angles (87° with respect to the substrate normal). Controllable growth rates of 0.5–4Å/min have been achieved for crystalline films by the first method using substrate temperatures as low as 250° C, Si₂H₆ partial pressures of 20 mTorr and photon flux densities of 10¹⁶ photons/pulse.cm². In the second method, where the laser beam is directly incident on the wafer at grazing angles, very high growth rates of up to 80Å/min have been achieved at 300° C, 20 mTorr Si₂H₆ partial pressure and a photon flux density of 2 × 10¹⁵ photons/pulse.cm². A comparison of the microstructure of the films grown by the two methods is presented on the basis ofin situ reflection high energy electron diffraction (RHEED) analysis and selected area transmission electron microscopy (TEM) studies. In both cases, the growth rates are found to be linearly dependent on the photon flux density for the process parameter ranges studied.     

甲烷流量对8.5代非晶硅光伏组件P层材料结构和光学性质的影响

本文研究了甲烷流量对作为工业非晶硅光伏组件的p层材料—非晶碳化硅结构和光学性质的影响.p层非晶碳化硅薄膜采用硅烷和甲烷混合气体在射频等离子体增强化学气相沉积(RF-PECVD)设备中沉积制得,该设备是应用材料公司制造的尺寸为2.2 m × 2.6 m的8.5代系统.采用红外光谱和透射/反射谱分析与沉积工艺相关的键结构和光学性质.相同工艺条件下,当甲烷含量从3000 sccm增加到8850 sccm, p层非晶碳化硅薄膜的光学带隙逐步增加. p层非晶碳化硅薄膜的沉积速率随甲烷流量的增加而逐渐减小,其原因是硅烷-甲烷等离子体中SiH3粒子的减少.文中还通过在不同位置取样和分析沉积速率研究了大面积薄膜的均匀性.     

Reaction pathways and sources of OH groups in low temperature remote PECVD silicon dioxide thin films

Silicon oxides deposited by remote plasma-enhanced chemical-vapor deposition (Remote PECVD) can be grown under conditions which produce hydrogen-free SiO₂, and under conditions which promote the incorporation of bonded-hydrogen in either SiH or SiOH groups, but generally not in both. In this paper, we investigate the relationship between the deposition conditions leading to OH incorporation, and other post-deposition pathway(s) by which OH can also be incorporated. Two ways by which OH can be incorporated into the oxides are by: (i)intrinsic pathways which are associated with the heterogeneous chemical reactions responsible for film growth; and (ii)extrinsic pathways which refer to incorporation after film deposition stops. The results of our experiments to date show no evidence to support the intrinsic process; all of the infrared (ir) detectable OH is shown to derive from post-deposition or extrinsic sources. We have found two distinct post-deposition sources, one from the deposition chamber ambient during cool-down and one from atmospheric moisture. Each of these sources has a particular spectroscopic signature. We show that OH incorporated from atmospheric moisture occurs as spatially correlated near-neighbor Si-OH groups, whereas OH groups incorporated in the deposition chamber ambient are randomly distributed in the SiO₂ host material.     

用热蒸发法制备的Cu2ZnSnS4 薄膜的光电性能

在室温下用真空热蒸发法在玻璃基片上制备Sn/Cu/ZnS 前躯体膜层,然后对其在550C 下在硫气氛中硫化3小时以制得Cu₂ZnSnS₄ (CZTS) 多晶薄膜。对该薄膜进行X射线衍射（XRD）、能量色散X射线光谱（EDX）、紫外可见近红外分光光度计、霍尔测量系统和3D光学显微镜等分析测试。实验结果表明,当[Cu]/([Zn] [Sn]) =0.83和[Zn]/[Sn] =1.15时,该CZTS薄膜在光子能量范围在1.5 - 3.5 eV 时其吸收系数大于4.010₄cm_-1 ,直接带隙为1.47 eV。其载流子浓度、电阻率和迁移率分别为7.9710₁₆ cm_-3, 6.06 Ω.cm, 12.9 cm₂/(V.s), 导电类型为p型。因此,所制备出的CZTS 薄膜适合作为太阳电池的吸收层材料。     

衬底温度对磁控溅射生长HMGZO薄膜特性的影响

为适应高效Si基薄膜太阳电池对宽光谱透明导电 薄膜的需求,采用磁控溅射技术 生长了不同衬 底温度氢化作用下Ga和Mg共掺杂ZnO(HMGZO)透明导电氧化物(TCO)薄膜。研究了不同衬底温 度(200～280 ℃)对HMGZO薄膜 结晶特性及光电特性的影响。实验结果表明,制备的HMGZO薄膜均为具有六角纤锌矿结构的 多晶薄膜,呈 现(002)晶面择优生长。随着衬底温度的升高,薄膜中Mg含量逐渐增加,并且薄膜表面新型 锥状结构趋于 致密和均匀化。在各元素含量和结晶质量的共同影响下,其电阻率随着温度的升高从6．70×10－4 Ω·cm增加至7．63×10－4 Ω·cm。所有薄膜在可 见光区域(380～800 nm)的透过率均在80%以上,由于载流子共振吸收的作用,近红外区域的 透过率有所下降。MgO扩展带隙的作用和 Burstein-Moss(BM)效应的影响共同促进了薄膜光学带隙E_g展 宽,使得E_g达到了3.75 eV。当衬底温度为280 ℃ 时,薄膜方块电阻为4.91 Ω/sq,电阻率为7.63×10－4 Ω·cm,光电性能指数ΦTC值达0.022 Ω－1。     

Cu2ZnSnS4四种晶型的电子结构、光学性质和力学性质

本文采用密度泛函理论详细计算了Cu₂ZnSnS₄四种晶型的晶体结构、电子结构、光学性质和力学性质。结果表明它们之间在光学性质和力学性质方面没有非常明显的差异,计算结果与文献报道的实验数据基本一致。根据计算结果,Cu2ZnSnS4的基本带隙是由孤立导带的带宽来决定。Cu₂ZnSnS₄的载流子有效质量非常小,尤其是闪锌矿衍生的Cu₂ZnSnS₄在导带底具有极小的电子有效质量。根据所计算的力学常数矩阵可知,四种晶型的Cu₂ZnSnS₄; 均符合Born稳定性条件,而且较高的B/G比例表明Cu2ZnSnS4的四种晶型都具有突出可塑性。     

Ti掺杂对Sb2Te3薄膜的结构及光学性质的调控

对Sb₂Te₃薄膜的结构、线性光学及非线性吸收性质的Ti掺杂影响进行了系统性探究。利用磁控溅射和高温退火手段制备了不同Ti掺杂浓度的晶态Sb₂Te₃薄膜。X射线光电子能谱分析显示Sb₂Te₃薄膜中的Ti元素以Ti⁴⁺化学态以TiTe₂的形式存在。线性光学性质结果表明,在保持非线性器件中宽工作波长特性的同时,Ti掺杂可以提高Sb₂Te₃薄膜的透射率,并降低光学带隙从1.32 eV至1.25 eV,根据Burstein-Moss理论,这取决于载流子的减少。利用自主搭建的开孔Z扫描系统,测试了薄膜样品在132 GW/cm²强度下800 nm飞秒激光激发的非线性吸收性质,结果显示的Ti掺杂引起的饱和吸收可调谐行为可归因于光学带隙减小与晶化抑制的竞争效应。此外,Ti掺杂将Sb₂Te₃薄膜的激光损伤阈值从188.6 GW/cm²提高到了265.5 GW/cm²。总而言之,Ti掺杂Sb₂Te₃薄膜在非线性光学器件领域具有广泛的应用前景。     

Selective chemical etching of polycrystalline SiGe alloys with respect to Si and SiO2

Polycrystalline SiGe etches that are selective to silicon dioxide as well as silicon are needed for flexibility in device fabrication. A solution of NH₄OH, H₂O₂, and H₂O has been found to selectivity etch polycrystalline silicon-germanium alloys over both silicon and silicon dioxide. Optimum composition of the solution was determined by maximizing etch rates for SiGe films with several germanium compositions. The dependence of etch rates on germanium content, etching temperature, and doping concentration are reported. The etch rate and selectivity are approximately exponentially proportional to the germanium content. Etching was found to be insensitive to deposition method, doping method, and annealing conditions of the SiGe films. In addition, etching leaves a smooth silicon substrate surface after removal of SiGe films.     

退火温度对电子束沉积Ag/TiO2薄膜光学性质和光催化性能的影响

研究了退火温度对电子束制备Ag/TiO₂薄膜光学 性质和光催化性能的影响。在石英玻璃、硅片 上沉积了Ag/TiO₂复合薄膜,在空气氛围下,进行了400℃, 500℃的退火一小时.用紫外-可见分光光度 计、X射线衍射仪(XRD) 、原子力显微镜(AFM)对沉积和退火后的薄膜分别进行光学、结构、 形貌分析。结 果表明:300℃下制备的Ag/TiO₂复合薄膜为无定形结构,400℃以上薄呈多晶态。吸光度和表面粗糙度 随退火温度的增加而增大,薄膜的光学带隙随退火温度的增加而减小。锐钛矿相表现出了更 好的光催化性能。     

Low temperature sintering properties of Y-doped BaTiO3 ceramics by BaB2O4 sintering aid

The sintering process of semiconducting Y-doped BaTiO₃ ceramics added with BaB₂O₄ as low temperature sintering aid were investigated. When the low temperature sintering aid BaB₂O₄ added Y-doped BaTiO₃ ceramics prepared by Sol-Gel method, the sintering temperature of BaTiO₃-based ceramics would be greatly decreased, and also widen sintering range. Y-doped BaTiO₃ ceramics with BaB₂O₄ addition can be obtained at 1050 °C. Ceramics samples with room temperature resistivity 60-80 Ω cm, ratio of the maximum resistivity to minimum resistance (Rmax/Rmin) 10⁴ and temperature coefficient of resistivity (α) 10%/°C were obtained.     

Improvement in dielectric properties of low temperature PECVD silicon dioxide by reaction with hydrazine

The dielectric properties of plasma-enhanced chemical vapor deposition (PECVD) SiO₂ deposited at 150°C were improved by reaction with anhydrous hydrazine vapor at 150–350°C. The permittivity and loss decreased ~32% and ~86%, respectively, after reaction with hydrazine at 150°C. The decrease in permittivity and loss correlated with a decrease in the dipole concentration (silanol + water). During exposure to humid conditions, water uptake in the SiO₂ films degraded the dielectric properties. A nitrogen anneal at 350°C did not improve the dielectric properties of the PECVD SiO₂. Although water was removed from the films, silanol remained. When the PECVD SiO₂ deposited at 150° was reacted with hydrazine vapor at 150°C, both silanol and water were removed from the films. The dielectric properties and resistance to water absorption improved.     

银纳米颗粒修饰TiO2薄膜的结构,光学及光催化性能

采用电子束沉积技术在石英玻璃、硅片基板上沉积了TiO₂薄膜,利用热蒸发技术在TiO₂薄膜表面沉积了不同厚度的Ag膜,研究了Ag膜厚度对TiO₂薄膜结构、形貌、光学和光催化 性能的影响。利 用紫外-可见分光光度计(UV-VIS)、X射线衍射仪(XRD)、冷场发射电子显微镜(SEM)对沉积 后的薄膜分别 进行光学、结构、形貌分析。利用能谱仪测定了元素成分及含量。用光催化降解亚甲基橙(M O)的速率评 价了合成的Ag-TiO₂的光催化性能。结果表明:Ag纳米粒子在TiO₂表面均匀分布;制备 的Ag修饰多孔TiO₂纳米薄膜具有优异的光催化性能。测试结果表明:在250 ℃下制备的T iO₂薄膜为无定形结构;随着Ag膜厚度 的增加,样品的光催化活性提高。当Ag膜厚度为3.7 nm时,光催化活 性最高;与纯TiO₂相比,Ag-TiO₂具有更高的光催化活性。     

K2MgSiO4:Eu3+红色荧光粉的制备与发光性能

采用高温固相反应合成了适合近紫外光-蓝光激 发的K₂MgSiO₄:Eu³⁺红色荧光粉,并对其发光特性进行了研究。X射线衍 射(XRD)测试结果表明,合成样品为纯相晶体。样品激发光谱由O2-→Eu³⁺电 荷迁 移带波长为(200～350nm)和Eu³⁺的特征激发峰(波长为350～500nm) 组成,主峰位于396nm波长处,次级峰位于466nm波长处。在396nm和466nm波长分别激发 下,样品发射峰均由Eu³⁺的⁵D₀→⁷FJ(J=0,1,2,3,4)能级跃迁产生,其中619nm波长处发射强度最大。 随着Eu³⁺掺杂浓度的增加,荧光粉的发光强度增大。在实验测定的浓度范 围内,未出现浓度猝灭现象。样品的色坐标位于红光区,且非常接近NTSC标准。样品发光强 度随温度增加出现温度猝灭现象,发 射峰位置并未出现明显红移。样品中,Eu³⁺在⁵D₀能 级上的荧光寿命约为0.535ms。     

热处理温度对Li2SrSiO4:Eu2+发光性能的影响

采用高温固相反应法制备一种白光发光二极管(LED )用黄色荧光粉Li₂Sr(1－x)SiO₄:xEu²⁺, 研究测试温度和退火温度对Li₂Sr(1－x)SiO₄:xEu²⁺荧光粉发光性能的影响。实验发现,对于 不同掺杂浓度的样品,在不同测试温度下,经过热处理后的样品与未处理样品相 比,激发和发射光谱强度得到普遍提高,原因是热处理后晶体结构的完整性得到 提高。在变温测试下,Li₂Sr(1－x)SiO₄:xEu²⁺的发光性能总体是随着测试温度升高而 下降,但在短波长(500～550nm)范围内的发光性能随着温度升高 而增强。分析表明,这与Li₂SrSiO₄基质材料的晶体结构和掺杂元素有关。     

低温退火对具有HfO2/TiN栅结构的MOS电容电学性能的影响

The effects of low temperature annealing,such as post high-k dielectric deposition annealing(PDA),post metal annealing(PMA)and forming gas annealing(FGA)on the electrical characteristics of a metal–oxide–semiconductor(MOS)capacitor with a TiN metal gate and a HfO2dielectric are systematically investigated.It can be found that the low temperature annealing can improve the capacitance–voltage hysteresis performance significantly at the cost of increasing gate leakage current.Moreover,FGA could effectively decrease the interfacial state density and oxygen vacancy density,and PDA could make the flat band positively shift which is suitable for P-type MOSs.