硅及硅基半导体材料中杂质缺陷和表面的研究

随着超大规模集成电路设计线宽向深亚微米级（<0.5μm）和亚四分之一微米级（<0.25μm）发展,对半导体硅片及其它硅基材料的质量要求越来越高,研究上述材料中各种杂质的行为,控制缺陷类型及数量,提高晶体完整性,降低表面污染和采用缺陷工程的方法改善材料质量显得尤为重要。文章阐述了深亚微米级和亚四分之一微米级集成电路用大直径硅材料中铁、铜金属和氧、氢、氮非金属杂质元素的行为,点缺陷及其衍生缺陷的本质与控制方法,硅片表面形貌、表面污染与检测方法的研究热点。同时还介绍了外延硅、锗硅及绝缘体上硅（SOI）等硅基材料的特性、制备及工艺技术发展趋势,展望了跨世纪期间硅及硅基材料产业发展的技术经济前景。     

硅离子注入引入纳米晶对SIMOX材料进行总剂量辐射加固

本研究工作采用硅离子注入和高温退火工艺对SIMOX材料的BOX层进行总剂量辐射加固.辐射实验结果证明了该加固方法的有效性.PL谱和HRTEM图像显示了硅离子注入及退火工艺在材料的BOX层中引入了Si纳米晶,形成电子陷阱能级,有效俘获电子,从而提高了材料BOX层的抗总剂量辐射能力.     

氢气氛退火对硅上低温外延制备的硅锗薄膜性能的影响

采用反应型热化学气相沉积系统在硅(100)衬底上外延生长富锗硅锗薄膜。四氟化锗作为锗源, 乙硅烷作为还原性气体。通过设计表面反应, 在低温条件下(350℃)制备了高质量的富锗硅锗薄膜。研究了氢退火对低温硅锗外延薄膜微结构和电学性能的影响。结果发现退火温度高于700℃时, 外延薄膜的表面形貌随着退火温度的升高迅速恶化。当退火温度为650℃时, 获得了最佳的退火效果。在该退火条件下, 外延薄膜的螺旋位错密度从3.7×10⁶ cm^-2下降到4.3×10⁵ cm^-2, 表面粗糙度从1.27 nm下降到1.18 nm, 而外延薄膜的结晶质量也有效提高。霍尔效应测试表明, 经退火处理的样品载流子迁移率明显提高。这些结果表明, 经过氢退火处理后, 反应型热化学气相沉积制备的低温硅锗外延薄膜可以获得与高温下硅锗外延薄膜相比拟的性能。     

超高真空CVD生长锗硅外延层及其双晶X射线衍射研究

利用自行研制的超高真空化学气相沉积系统 ,在直径 3英寸的衬底硅片上生长了锗硅应变外延层 ,并进行了实时掺杂生长。利用双晶X射线衍射技术测试了外延层 ,确定外延层的组分与晶体质量 ,并利用二次离子质谱仪进行了纵向组分分布剖析 ,利用扩展电阻仪确定外延层的电学特性。研究了锗硅应变外延层的生长特性和材料特性 ,生长速率随锗组分的增加而降低 ,以氢气为载气的硼烷对锗硅合金的生长速率有促进作用。还通过生长锗组分渐变的缓冲层 ,改善了外延层的晶体质量     

高温氢气退火提高硅片质量的研究

研究了硅片高温氢气退火的工艺技术,实验显示,在高温1150℃,在高纯氢气氛中退火处理至少60min,在硅片表面产生约50μm以上的洁净层。测试了退火后硅片中氧的深度分布,发现硅片表面有一层低氧区,能提高硅片的质量,使氧化层错的密度降低一个数量级,测试数据还表明高温氢退火对降低COP缺陷的密度和提高氧化层的质量也有一定的效果。     

在SOI材料上制备高质量的氧化铪薄膜

用电子束蒸发氧化铪靶的方法．在SOI(绝缘体上硅)材料上制备了氧化铪薄膜，随后在氮气中进行快速退火(600℃．300s)。借助掠角X射线衍射(GAXRD)、X射线光电子能谱(XPS)、高分辨透射电镜(HRTEM)技术分析了样品的微观结构．研究了样品在退火前后发生的组成及结构变化．结果表明退火后氧化铪薄膜由退火前的非晶态转变为单斜结构的多晶态，薄膜中的O／Hf原子比较退火前更接近化学计量比2。借助扩展电阻探针(SRP)技术考察了退火前后薄膜的电学性能．证明在SOI材料上制备的多晶氧化铪薄膜同样具有较好的电介质绝缘性能。     

一种光聚合共混树脂抗原子氧侵蚀的机理

采用双酚A型环氧树脂E-44与有机硅环氧树脂ES-06的共混改性树脂体系进行紫外光辐照聚合,制备了光聚合含硅聚合物;使用原子氧效应地面模拟设备对光聚合含硅聚合物进行原子氧侵蚀试验,比较了试验前后试样的质量、表面形貌和成分的变化,研究了原子氧的侵蚀机理.结果表明,在紫外光辐照固化后改性树脂的表面形成一层含C的氧化硅(SiOx)膜,经原子氧暴露试验后进一步氧化转变为富含SiO2的保护膜,具有较好的耐原子氧性能.原子氧对含硅共混物的侵蚀是多种效应协同作用的结果,以发生化学反应为主,通过提氢,插入和置换等机理产生含碳挥发性物质和H2O等,导致聚合物的质量损失.生成的硅氧化物留在聚合物表面,能有效地阻止原子氧对基底聚合物材料的进一步侵蚀.     

具有室温铁磁性和高空穴迁移率的锰掺杂硅锗薄膜（英文）

本文采用超高真空化学气相沉积系统在锗衬底上外延生长了第IV族硅锗薄膜,然后通过离子注入和快速热退火进行锰元素掺杂.结构测试表明,外延的硅锗薄膜是具有均匀拉伸应变的单晶,随后的离子注入和快速热退火使其变为多晶.磁性测试表明,退火后的薄膜表现出依赖于锰掺杂浓度的铁磁性,居里温度最高可达309 K; X射线磁圆二色谱揭示了替代位锰元素的自旋和轨道磁矩.为最大限度地减少反常霍尔效应的影响,磁输运测试在高达31 T的强磁场下进行,该薄膜在300 K温度下空穴迁移率达到创纪录的～1230 cm²V^-1s^-1.此高迁移率归因于样品较高的结晶质量和拉伸应变对能带的调制.本文首次展示了具有室温铁磁性和高载流子迁移率的锰掺杂硅锗薄膜,有望促进基于第IV族半导体的自旋电子材料与器件的实际应用.     

离子注入改性SOI材料总剂量辐射退火效应和机理研究

基于绝缘体上硅(SOI)的CMOS电路具有天然的抗单粒子优势,但绝缘埋层的存在使得其总剂量效应尤为突出和复杂。本文研究了利用离子注入改性SOI材料的总剂量辐射和退火效应、基于赝MOS技术的SOI材料辐射效应评估技术和离子注入改性提高SOI材料抗辐射性能的机理。实验结果表明,采用该技术制备的绝缘体上硅材料抗总剂量能力达到1Mrad(Si);离子注入改性SOI材料在经过室温和高温退火后,辐射导致的固定电荷和界面态可以完全恢复;离子注入和高温退火在二氧化硅薄膜中形成硅纳米团簇结构,从而引入深电子陷阱,补偿总剂量辐射引起的绝缘埋层中的空穴积累。     

超高真空CVD生长锗硅外延层及其双晶X射线衍射研究

利用自行研制的超高真空化学气相沉积系统，在直径３英寸的衬底硅片上生长了锗硅应变外延层，并进行了实时掺杂生长。利用双晶Ｘ射线的衍射技术测试了餐延层，确定外延层的组分怀晶体质量，并利用二次离子质谱仪进行了纵向组分分布剖 析，利用扩展电阻仪确定外延层的电学特性，研究了锗硅应变外延层的生长特性和材料特性，生长速率随锗组分的增加而降低，以氢气为载气的硼烷对锗硅合金的生长速率有促进作用。还通过生长锗 组分渐变     

Capacitorless single transistor dynamic random-access memory devices fabricated on silicon-germanium-on-insulator substrates

Capacitorless single transistor dynamic random-access memory (1T-DRAM) cells on silicon-germanium-on-insulator (SGOI) substrates with various Ge mole fractions in the relaxed-SiGe layers were investigated. SGOI substrates with strained-Si channels showed higher on-currents and carrier mobility than a silicon-on-insulator (SOI) substrate with unstrained-Si channels. SGOI 1T-DRAM devices had larger memory windows than a similar device with SOI; memory window increased with increasing Ge mole fraction in the relaxed-SiGe layer. The SGOI 1T-DRAMs showed degraded retention times. High-temperature annealing reduced the effects of crystalline defects and thus improved the electrical properties of the SGOI substrates, leading to higher carrier mobility, larger memory window, and longer data retention.     

Defect control by Al deposition and the subsequent post-annealing for SiGe-on-insulator substrates with different Ge fractions

SiGe-on-insulator (SGOI) substrates with different Ge fractions (Ge%) were fabricated using Ge condensation technique. High acceptor concentration (N_A) in SGOI layer and interface-trap density (D_it) at SGOI/buried oxide (BOX) interface were found by using back-gate metal-oxide-semiconductor field-effect transistor method. For the reduction of high N_A and D_it, Al deposition and the subsequent post-deposition annealing (Al-PDA) were carried out. As a comparison, a forming gas annealing (FGA) was also performed in H₂ ambient. It was found that both Al-PDA and FGA effectively reduced N_A and D_it for low-Ge% SGOI. However, with an increase in Ge%, FGA became less effective while Al-PDA was very effective for the reduction of N_A and D_it.     

Evolution of SiO2/Ge/HfO2(Ge) multilayer structure during high temperature annealing

Use of germanium as a storage medium combined with a high-k dielectric tunneling oxide is of interest for non-volatile memory applications. The device structure consists of a thin HfO₂ tunneling oxide with a Ge layer either in the form of continuous layer or discrete nanocrystals and relatively thicker SiO₂ layer functioning as a control oxide. In this work, we studied interface properties and formation kinetics in SiO₂/Ge/HfO₂(Ge) multilayer structure during deposition and annealing. This material structure was fabricated by magnetron sputtering and studied by depth profiling with XPS and by Raman spectroscopy. It was observed that Ge atoms penetrate into HfO₂ layer during the deposition and segregate out with annealing. This is related to the low solubility of Ge in HfO₂ which is observed in other oxides as well. Therefore, Ge out diffusion might be an advantage in forming well controlled floating gate on top of HfO₂. In addition we observed the Ge oxidation at the interfaces, where HfSiO_x formation is also detected.     

Low temperature synthesis and electrical characterization of germanium doped Ti-based nanocrystals for nonvolatile memory

Chemical and electrical characteristics of Ti-based nanocrystals containing germanium, fabricated by annealing the co-sputtered thin film with titanium silicide and germanium targets, were demonstrated for low temperature applications of nonvolatile memory. Formation and composition characteristics of nanocrystals (NCs) at various annealing temperatures were examined by transmission electron microscopy and X-ray photon-emission spectroscopy, respectively. It was observed that the addition of germanium (Ge) significantly reduces the proposed thermal budget necessary for Ti-based NC formation due to the rise of morphological instability and agglomeration properties during annealing. NC structures formed after annealing at 500 °C, and separated well at 600 °C annealing. However, it was also observed that significant thermal desorption of Ge atoms occurs at 600 °C due to the sublimation of formatted GeO phase and results in a serious decrease of memory window. Therefore, an approach to effectively restrain Ge thermal desorption is proposed by encapsulating the Ti-based trapping layer with a thick silicon oxide layer before 600 °C annealing. The electrical characteristics of data retention in the sample with the 600 °C annealing exhibited better performance than the 500 °C-annealed sample, a result associated with the better separation and better crystallization of the NC structures.     

Fabrication of multilayered Ge nanocrystals by magnetron sputtering and annealing

Multilayered Ge nanocrystals embedded in Si and Ge oxide films have been fabricated on Si?substrate by a (SiO(2)+Ge)/(SiO(2)+GeO(2)) superlattice approach, using an rf magnetron sputtering technique with a Ge+SiO(2) composite target and subsequent thermal annealing in N(2) ambient at 750?°C for 5?min. X-ray diffraction (XRD) measurements indicated the formation of Ge nanocrystals with an average size estimated to be 9.8?nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode shifted downwards to 298.8?cm(-1), which was caused by quantum confinement of phonons in the Ge nanocrystals. X-ray photoemission spectroscopy (XPS) analysis demonstrated that the Ge chemical state is mainly Ge(0) in the (SiO(2)+Ge) layer and Ge(4+) in the (SiO(2)+GeO(2)) layer in the superlattice structure. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (SiO(2)+Ge) layers, and had good crystallinity. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction compared with the conventional Ge-ncs fabrication method using a single and thick SiO(2) matrix film.     

Epitaxial growth of relaxed germanium layers by reduced pressure chemical vapour deposition on (110) and (111) silicon substrates

The growth of Ge on (110) and (111) oriented Si substrates is of great interest to enhance the mobility of both holes and electrons in complementary metal oxide semiconductor transistors. However, the quality of thick, relaxed Ge layers grown epitaxially on these surfaces is usually much lower than similar layers grown on (100) Si, resulting in both higher defect densities (i.e. threading dislocations and stacking faults) and rougher surfaces. In this work we have investigated the growth of Ge layers on (110) and (111) Si substrates by reduced-pressure chemical vapour deposition using a two temperature process. We have found that the combination of suppressing the Ge seed layer roughness and high temperature post-growth annealing can reduce the rms surface roughness of (110) Ge layers to below 2 nm and the threading dislocation density to below 1 × 10⁷ cm^− 2. Thick (111) Ge layers were found to exhibit a very high density of stacking faults, that could not be reduced by post-growth annealing and a higher rms surface roughness of around 12 nm, which was limited by the Ge seed layer.     

Microstructure and dielectric functions of Ge nanocrystals embedded between amorphous Al2O3 films: study of confinement and disorder

Ge nanocrystals (6–9?nm) embedded between amorphous Al₂O₃ films were produced in a cluster beam deposition system. The microstructural evaluation and compressive stress experienced by the Ge nanocrystals due to the presence of an oxide layer, nanoparticle size distribution and their changes due to thermal annealing were studied by X-ray diffraction, HRTEM and Raman spectroscopy. Spectroscopic ellipsometry was used to measure the dielectric functions of the deposited films. A multilayer model based on the effective medium approximation was used to analyze the variation of percentage of defects and the extent of disorder with particle size of the nanocrystals. The correlation between the microstructural characteristics and optical properties was established by evaluating standard sum rules. Germanium nanocrystals show visible photo luminescence at room temperature around 3.0 and 2.8?eV. However, a peak shift towards lower energies with increasing particle size due to thermal annealing was not detected. The experimentally observed luminescence is presumably originated due to the presence of oxide-related defect centers at the interface between the germanium nanocrystals and the embedded oxide layers.     

Phase transformation and optical characteristics of porous germanium thin film

In this study, we proposed a method to prepare GeO₂ by treating porous Ge thin film with thermal annealing in O₂ ambient. After annealing, the morphological transformation from porous thin film to an island structure was observed. The crystallization and composition of the porous Ge thin film prepared using different annealing time in O₂ ambient were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectra. Initial Ge composition was gradually oxidized to GeO₂ with increasing annealing time. Comparing the photoluminescence (PL) results between Ge and GeO₂, it was found that the visible photoluminescence originated from the germanium oxide. Photoluminescence measurements obtained at different temperatures exhibited a maximum integrated PL intensity at around 200 K. A possible explanation for this behavior might be the competition between radiative recombination and nonradiative hopping process.     

体硅上外延超薄Si1-xGex用于制备SGOI材料

采用减压化学气相沉积的方法在Si衬底上制备了高质量的Si0.75Ge0.25/Si/Si0.86Ge0.14叠层材料,通过TEM、光学显微镜和XRD分析表明,外延的SiGe薄膜具有完好的晶格结构,平整的表面质量,SiGe薄膜处于完全应变状态.通过与Si上外延渐变缓冲层制备的SiGe材料比较发现,使用这种超薄的全应变Si...     

Ge/Si heterojunction photodetector for 1.064 µm laser pulses

Isotype and anisotype heterojunction Ge/Si photodetectors have been made by depositing Ge layer onto monocrystalline Si using vacuum evaporation technique. These detectors before and after annealing were utilized to detect 1.064 μm Nd:YAG laser pulses. The study also includes determination of the optimum Ge thickness and annealing conditions. The experimental results show that the photoresponse highly improve after classical thermal annealing (CTA) and rapid thermal annealing (RTA).The voltage responsivity and rise time results are strongly dependent on annealing type and conditions. It is found that the optimum conditions can be obtained for n-Ge/p-Si photodetector prepared with 200 nm Ge thick and annealed with RTA at 500°C/25 sec.