Study of oxygen and carbon species on Si substrate during in-situ cleaning prior to high-quality epitaxial deposition

We investigated the effect of in-situ cleaning with ECR (Electron Cyclotron Resonance) hydrogen plasma. This cleaning was effective in removing oxygen and carbon on the wafer surface because of its high density and low substrate damage and, thus, high quality epitaxial films were deposited. The contents of the oxygen or carbon species were correlated with the structural quality of the interface and film. The possible reaction mechanisms for the cleaning of oxygen and carbon species were scrutimized. The removal of oxygen rather than of carbon, was crucial in obtaining high quality epitaxial films.     

Critical misfit of epitaxial growth metallic thin films

The critical misfit of epitaxial growth metallic thin films fc was thermodynamically considered. It is found that there exists a competition between the energy of the misfit dislocation of film and non-coherent interface energy of film-substrate. Equilibrium between these energies was present at a critical atomic misfit ft. When the atomic misfit is larger than the critical value, epitaxial growth does not occur. The critical misfit of the epitaxial growth thin films can be predicted. The results show that fe is proportional to the non-coherent interface energy of the film-substrate, and inversely proportional to the elastic modulus and the thickness of the film.     

铝板带清洗工艺对表面质量的影响

对铝板带清洗工艺进行了深入的分析研究。重点介绍了各种清洗技术的工艺流程、技术特点,对比了各种清洗技术对板带材表面质量的影响。结果表明:采用碱清洗工艺对提高铝板带产能、改善其表面质量等比其他清洗工艺有较为明显的优势。     

Si粉微合金化对钢-铝复合材料界面的影响

采用粉末轧制工艺,在界面添加4％ Si粉进行界面微合金化调控,成功制备出界面结合良好的钢-铝复合材料.研究了界面微合金化设计、扩散退火处理工艺对钢-铝复合材料界面区元素扩散、生成物相的影响规律,探讨了元素Si界面调控的作用机理.结果表明:添加4％ Si粉界面微合金设计,在500℃扩散退火,保温1h热处理工艺下,复合材料界面未出现金属间化合物,600℃扩散退火,保温1h热处理工艺下,仅出现少量化合物Fe2Al5,Si粉界面微合金化处理能延缓界面化合物相生成,使生成Fe2Al5相的扩散温度向高温推移;Si扩散固溶到Fe、Al基体中形成连续固溶体,提高了界面两侧物理及力学性能的连续性,改善复合材料的界面结合.     

Effect of in-situ plasma cleaning on the crystalline quality of silicon homoepitaxial films

Low temperature processing, which includes in-situ cleaning and epitaxial deposition, is not only important for future silicon ULSI (Ultra Large Scale Integration) technology but also for silicon based heterostructures. Low temperature processing cannot volatilize or dissolve the surface contaminants by heating the substrate, as was accomplished in the traditional high temperature epitaxial growth. In this study, electron cyclotron resonance (ECR) hydrogen plasma was used and films were deposited thermally at a low temperature. The epitaxial films, which were deposited in our chemical vapor deposition systems, immediately after the insitu cleaning processes were characterized by cross-sectional transmission electron microscopy, etc. The role of a hydrogen ion in the in-situ cleaning was clarified by investigating the cleaning efficiencies for a variety of conditions. Process variables such as cleaning temperature and d.c. bias were investigated, and the d.c bias turned out to play a crucial role in low-temperature in-situ cleaning processes. Also, the effect of the in-situ cleaning temperature on the cleaning efficiency was investigated and discussed.     

Effect of hydrogen annealing on characteristics of polycrystalline silicon

The characteristics of mc-Si used for solar cells during H2 ambient annealing at 800-1200 ℃ were investigated by means of FTIR and QSSPCD. The results reveal that grain boundaries or defects in mc-Si may facilitate the formation of oxygen precipitates, and the formation of oxygen precipitates has deleterious effect on the lifetime of mc-Si. Decreasing lifetime could result from the formation of new recombination during annealing. Additionally, It is found that hydrogen may facilitate the formation of oxygen precipitates in mc-Si. On the other hand, the diffusion of hydrogen may passivate the defects/boundaries and it is beneficial to the lifetime of mc-Si.     

Comparison of measurements and simulation results in 300 mm CZ silicon crystal growth

A special thermal modeling tool, CrysVUn, which was developed by Crystal Growth Laboratory (CGL) of Fraunhofer Institute of Integrated Systems and Devices Technology in Erlangen of Germany, was used for numerical analysis of growth interface situation. The heat transportation, argon flow and melt convection have been considered. Cauchy's first and second laws of motion have been the governing partial equations for stress calculation. The measurement results and simulation results were compared and the interface shape and thermal stress distribution during 300 mm Czochralski (CZ) silicon crystal growth with different growth rates were predicted.     

Suppressing the surface roughness and columnar growth of silicon nitride films

The growth and structure evolution of silicon nitride films prepared by radio frequency magnetron sputtering at low pressure were investigated for thickness changes. Grazing-incidence X-ray reflectivity, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to study the structure, surface roughness and composition, respectively, of the films. It was found that with an increase in thickness from 5 to 830 nm, the silicon nitride films have a similar surface structure and their surface roughness only slightly increases. The surface roughness of all the silicon nitride films is only a little more than 0.2 nm, much less than previously reported results. AFM measurement of the fractured film surface indicated that thin silicon nitride films with a thickness below approximately 300 nm have a dense, smooth and uniform structure, and columnar structures gradually appear only in thick films. These results are mainly attributed to the special design of the sputtering system and the energetic particle bombardment of the growing surface, by which the surface roughness and columnar growth were suppressed.     

Effects of argon gas flow rate and guide shell on oxygen concentration in Czochralski silicon growth

φ200 mm silicon single crystals were grown in the φ450 mm hot zone of a Czochralski （CZ） furnace. By modifying the pattern and the velocity of the argon flow, the silicon single crystals with different oxygen concentrations were obtained. Through numerical simulation, the velocity of the argon gas flow was plotted for the first time. The experiment resuits were analyzed and the optimum condition of the argon flow with the lowest oxygen concentration was obtained.     

Effect of oxygen precipitates in solar grade silicon on minority carrier lifetime and efficiency of solar cells

The effect of oxygen precipitates on minority carrier lifetime and performance of solar cell was studied by means of Fourier Transform Infrared Spectroscopy (FTIR), quasi-steady state photoconductance (QSSPCD), optical microscope, spectrumresponse and solar cell efficiency test. The minority carrier lifetime and performance of solar cell reduced depend on oxygen precipitates. A few of oxygen precipitates have formed after single-step annealing; and they do not impact the efficiency dramatically. Pre-annealing at 650 ℃ for 4 h enhances the oxygen precipitation when it is subjected to middle temperature annealing. The solar cells performance decayed sharply. Especially annealing at 950 ℃ for 3 h, the V os and I sc of cells decrease 12% and 25% respectively. Few oxygen precipitates have formed in silicon after high temperature annealing at about 1050 ℃ whether pre-annealing is used or not, and the performance of cells is notbe affected.     

激光清洗对SMA490BW钢接头表面应力及腐蚀的影响

为提高耐候钢焊接质量,将皮秒脉冲激光清洗技术引入到耐候钢焊接的清洗中,并研究了皮秒脉冲激光清洗对SMA490BW耐候钢焊接接头抗应力腐蚀性能的影响. X射线残余应力测试试验结果表明,激光清洗后试样表面残余拉应力增加130 ~ 200 MPa,不利于应力腐蚀性能的提高. 但周期浸润腐蚀试验证明,激光清洗使试件表面的耐蚀性明显提高,这有利于提高接头的抗应力腐蚀性能. 最后,通过三点弯应力腐蚀试验证明,激光清洗提高了耐候钢接头的抗应力腐蚀性能. 其原因为激光清洗使试样表面形成微米级（0.8 ~ 1.2 μm）紧密堆积的柱状颗粒,提高了试件表面的耐蚀性大于表面残余拉应力带来的影响.     

脉冲激光对6106铝合金表面形貌及氧含量的影响

研究了脉冲激光清洗在不同的清洗速度以及不同的脉冲重复频率下铝合金表面形貌以及表面氧元素含量的影响。试验结果表明,在清洗速度较低时(0.1～0.6 m/min),铝合金激光清洗过的表面呈溅射重叠的状态,当清洗速度大于0.8 m/min时,脉冲激光在铝合金表面的形成的冲击坑逐渐变得分散、独立;铝合金表面氧元素整体的含量随清洗速度的增减呈先下降后增加的趋势,在清洗速度较小或者较大时,氧元素含量均接近母材表面氧元素含量水平,氧元素含量分布具有明显的区域性,脉冲激光冲击坑的位置氧元素含量明显高于周围未冲击位置。随脉冲重复频率的增加,铝合金表面形貌由独立冲击坑逐渐过渡为溅射重叠的状态,表面氧元素整体含量明显下降,约为母材氧含量的1/2,氧元素的分布也逐渐变为弥散。     

Interface diffusion of sputtered CoZrNb films on silicon substrate

The amorphous CoZrNb films were deposited by DC magnetron sputtering.The depth distributions of the elements were analyzed by Rutherford backscattering spectrometry (RBS).The results indicate that when the deposition time is longer than 37 min, the film composition keeps constant along the depth.When the deposition time is longer than 45 min, the Co concentration at the interface of the silicon substrate is higher than the average value in the whole film.When the deposition time is longer than 52 min, the Co atoms diffuse into the substrate during the deposition.According to the Co composition profile in the substrate, which were determined from the RBS spectra, the Co diffusion coefficients in the substrate were calculated using the solution of Fick's second law corresponding to an infinite source with a constant diffusion coefficient.The calculated diffusion coefficients indicate an interstitial assisted diffusion mechanism.     

Oxygen concentration inhomogeneity in the silicon melt of the czochralski single crystal growth system

The momentum, heat and mass transfer in the silicon melt of the Czochralski crystal growth system were calculated with a three dimensional numerical simulation technique. Several types of non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt with axisymmetrical boundary conditions. Since the asymmetric profiles and the rotations of fluid, temperatures and oxygen concentration fluctuated in the melt. The correlations between both fluctuations at the same point became larger, as the convection grew stronger. The calculation also showed that the temperature and oxygen concentration near the interface also fluctuated. The results suggested that the oxygen concentration could be considered one of the causes of the striation pattern in grown silicon single crystals.     

激光表面熔凝处理对共晶铝硅合金疲劳裂纹扩展的影响

研究了共晶铝硅合金在激光表面熔凝处理后的显微组织变化及激光表面熔凝处理对合金疲劳裂纹扩展的影响.结果表明,激光表面熔凝处理使试验合金的表层微观组织发生显著变化,熔凝层中的初生α-Al枝晶相和共晶Si相均有明显细化,熔凝层的硬度显著提高;在应力比R为0.1和0.5的试验条件下,激光表面熔凝处理能显著提高共晶铝硅合金的疲劳裂纹扩展抗力.     

坩埚表面改性对冶金法多晶硅电学性能的影响

冶金法制备太阳能级多晶硅所用石墨坩埚含有不同类型的金属杂质,这些杂质通常会降低硅锭的电阻率和少于寿命等电学性能.本文研究了坩埚表面改性对冶金法多晶硅电阻率和少子寿命的影响.通过在不同冷凝速率条件下,对工业硅原料在改性前后的坩埚内提纯.经对铸锭切片的电阻率测试得出:坩埚表面改性使冶金法多晶硅锭的电阻率得到了明显的提高,电阻率的最高值由原来冷凝速率为20μ m/s时的110mΩ·cm提高列30μm/s时227mΩ·cm;经对铸锭切片的少于寿命测试得出:冶金法多晶硅的少子寿命在冷凝速率20μn/s时最高,坩埚表面改性使少子寿命由原来的0.81μs提高到1.91μs.     

Structure Heredity Effect of Mg-10Y Master Alloy in AZ31 Magnesium Alloy

研究了高铌TiAl合金Ti-44Al-8Nb-0.2W-0.1B-0.1Y (at％)分别与Al2O3/ZrO2/Y2O3坩埚的界面反应.测得界面反应层的厚度分别为40,170和20 μm.研究中最大的发现在于Ti-44Al-8Nb-0.2W-0.1B-0.1Y(at％)合金在3种坩埚中凝固后显微组织的转变.经测定该合金在3种坩埚中凝固获得的试样中氧含量分别为0.35,0.41和0.11 (at％).由于在合金熔化和凝固过程中,坩埚中的氧元素扩散进入合金基体,较高的氧含量导致合金显微组织发生转变,在与Al2O3和ZrO2坩埚反应的合金中发生了包晶反应.作为对比,选取一种低铌含量的TiAl合金Ti-49.5Al-2Cr-2Nb.经测定在3种坩埚中反应的氧含量分别为0.40,0.63和0.25 (at％),但是组织却没有明显的差异.     

Effect of substrate surface roughness on the adherence of NiCrAlY thermal spray coatings

The adherence of plasma sprayed NiCrAlY bond coats can be improved by an appropriate substrate surface finish. The interface fracture energy for crack propagation along the coating/substrate interface has been measured for different surface roughness by means of a specially designed four-point bending test. An increase of the interface fracture energy of about 15% was observed for a three times higher surface roughness. In addition, four-point bending tests with the coating on the side face of bending specimens were performed to analyze the fracture and spalling behavior of the coatings both under large tensile and compressive substrate deformations.     

Research on spraying and fusing of non-self-fluxing copper powdered alloy on cast iron surface

0IntroductionIt is well known that not every powdered alloy can beused for spraying and fusing. There are two important de-mands to powdered alloy for this usage: Firstly, its moltenpoint should be below that of the matrix; secondly itshould be self-fluxing. Meanwhile not only the coatingquality but also the feasibility of some technologies are in-fluenced greatly by the property of the powder, obviouslythe development and research on the powder is a choke-point that restricts the development …