Mechanism of hemispherical-grained Si formation for dynamic random access memory cells by rapid thermal chemical vapor deposition

An uneven coating made of hemispherical-grained Si (HSG) was formed on an amorphous Si layer by a rapid thermal chemical vapor deposition (CVD) (RTCVD) process. The uneven coating increases the effective surface area of a capacitor electrode in dynamic random access memory (DRAM) cells. The formation of the HSG consists of “seeding” and subsequent isothermal annealing stages. During the seeding stage, nanometer size Si single crystals are formed on the surface of the amorphous Si layer. During rapid thermal annealing at 665°C, under high vacuum, the Si grains grow linearly with increasing temperature and reach an average size of 95 nm after 20 sec. The nucleation and growth of the HSG occurs within a narrow range of temperature and time, which is sufficient for a short diffusion path of Si atoms on the surface of the amorphous Si layer, but insufficient for crystallization of the amorphous Si layer: The HSG coating increases the capacitance of a memory cell by a factor of 2.     

An investigation of LPCVD and PECVD of in situ doped polycrystalline silicon for VLSI

In general, high-temperature processes cause thermal stresses and diffusion of dopants, resulting in reduced device yields. It is thus desirable to reduce the number of high-temperature steps and the use of an in situ doping technique eliminates one such step. In this investigation, low-pressure chemical vapour deposition (LPCVD) and plasma-enhanced chemical vapour deposition (PECVD) have been utilised to deposit in situ doped polycrystalline silicon films. The process characteristics and properties such as spreading resistance, grain structure, etch rate using a plasma and dopant concentrations of these films have been investigated and explained using a simple model for dopant activation and grain growth. It is shown that good-quality films suitable for VLSI can be produced.     

Observation of unequal densities for sulfur defects in silicon predeposited by low fluence ion implantation*

The dynathermal current and capacitance responses of two isotopes of sulfur, 32s and 34s predeposited by low fluence ion implantation into siliconp ⁺- n junction diodes are presented. As opposed to all previous studies, in this work unequal densities are seen for the shallow and deep sulfur defects, for both the 32_s− and 34₋ related defects. Additionally, the dynathermal response of the deep 34_s center is seen to exhibit a shift of 3 K from that of 32_S at a fixed heating rate of 9.5 ±0.1 K/s, consistent with the isotope dependence of the thermal emission process observed earlier for these cen-ters by isothermal capacitance measurements. The work was conducted as part of the Semiconductor Technology Program at NBS. Portions of this work were supported by the Division of Electric Energy Systems, Department of Energy (Task Order A021-EES), the Defense Advanced Research Projects Agency (Order No. 2397), and the NBS. Not subject to copyright. NBS-NRC Postdoctoral Research Associate.     

Theoretical approach to estimate laser process parameters for drilling in crystalline silicon

This paper presents a simple method for estimating the ablation rate during drilling processes in crystalline silicon wafers. Using data from literature, the physical process of material heating, melting, and ejection can be estimated on a time scale and leads to a temporal separation of the pulse duration in two parts. The latter one offers a theoretical determination of the expected average ablation rate. The results of this approximation coincide with experimental values and offer solutions to increase drilling efficiency. The experiments were done with a q‐switched solid‐state laser emitting at 1064 nm wavelength at pulse durations between 810 ns and 1440 ns. Copyright © 2010 John Wiley & Sons, Ltd.     

硅片线锯砂浆中硅粉与碳化硅粉的泡沫浮选分离回收

以对碳化硅表面有选择性的脂肪酸作为捕收剂,采用泡沫浮选分离方法来分离回收硅片线锯砂浆中的和碳化硅粉。研究了捕收剂浓度、起泡剂浓度、浮选溶液的温度及pH值对分离效果的影响。当浮选溶液中捕收浓度为0.315mol/L,起泡剂浓度为0.18mol/L,温度为70℃,pH值为4.5时,分离效果最佳:浮起产物中碳化粉质量分数为99.3%,沉淀产物中硅粉质量分数为95.9%。     

电解电容器铝箔横向隧道孔的生长控制

在酸性介质中已经产生隧道孔的铝箔表面,继续在中性电解液中采取直流阳极溶解时,隧道孔密度及长度与二次侵蚀时电解质类别相关。在此基础上,通过二次侵蚀前铝箔表面的酸浸泡成膜处理,以及二次侵蚀过程中在中性氯化钠介质中添加复合有机物,达到控制此过程中隧道孔生长方向的目的,使其在原隧道孔的孔壁沿着与铝箔表面平行的方向产生新的隧道孔,这为提高铝箔表面积提出了新的途径,为进一步提高铝电解电容器比容提供了可能性。     

Optimisation of implantation conditions for the formation of buried SiO2 layers in silicon

The substrate temperature dependence of the IR transmission spectra of buried silicon dioxide layers formed by high dose ion implantation (~1017) was investigated for an ion dose ranging from 1017 to 1018 ions/cm2 at 250°C of 16O+ at 100 keV energy. The IR spectra indicate that the silicon/silicon-dioxide/silicon can be obtained after thermal annealing treatment of the implanted sample for 10 mm in hydrogen ambient at 1100°C.     

变温LPCVD沉积氮化硅薄膜的均匀性优化

以低压化学气相沉积(LPCVD)热壁立式炉为实验平台,由二氯硅烷和氨通过LPCVD工艺合成氮化硅薄膜,利用降温成膜提高氮化硅薄膜的膜厚均匀度.基于气体碰撞理论建立了氮化硅薄膜沉积速率与反应气体浓度的关系式.分析比较了LPCVD炉内不同升温速率沉积氮化硅薄膜的表面性能.发现在变温沉积阶段,选择合适的降温速率是实现薄膜沉积...     

Formation of titanium and cobalt germanides on Si (100) using rapid thermal processing

Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid thermal annealing in either Ar or N₂ ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The sheet resistance was found to be dependent on annealing ambient (Ar or N₂) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides were found to be 20 μΩ-cm and 35.3μΩ-cm, corresponding to TiGe₂ and Co₂Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti₆Ge₅ phase forms prior to TiGe₂. The TiGe₂ phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures (425° C); however, the stability of the material is poor at elevated temperatures.     

Characterization of silicon ion-implantation damage in single-strained-layer (InGa)As/GaAs quantum wells

We have characterized the structural effects of silicon ion implantation and controlled-atmosphere annealing on single quantum wells of In_0.14Ga_0.86As strained to match the in-plane lattice spacing of bulk GaAs. Cantilever-beam techniques were applied to measure implantation-induced stresses, while Rutherford backscattering, double-crystal x-ray diffraction, and cross-sectional transmission electron microscopy were applied to characterize the resulting microstructure. Samples were examined in both the as-implanted state and also after implantation and annealing under an arsenic overpressure at 800° C for 10 minutes. For implants whose energies produced maximum implanted ion density near the center of the 20 nm-thick quantum well, a maximum in the implantation-induced stresses were observed to occur at a silicon ion fluence of 1 × 10¹⁴/cm². Annealing of the implanted samples resulted in small dislocation loops in the ion range zone with survival of the strained quantum well. Electrical activation of the implants was found to be similar to identical implants into bulk GaAs.     

Optimization of dry etch process conditions for HgCdTe detector arrays

A key technology required for fabricating single and multi-band mesa photodiodes with pixel sizes less than or equal to 25 μm is the development of an anisotropic etch process for HgCdTe. The primary approach investigated for this purpose has been electron cyclotron resonance (ECR) dry etching. This paper reviews an experiment used to optimize the ECR etch process at Lockheed Martin IR Imaging Systems, Inc. and then the use of the process to produce state-of-the-art LW photodiodes. In this work, a Ar:H plasma was used in a Plasma Therm series 700 ECR plasma etcher. Reactor variables were optimized by a designed experiment against the following response parameters: anisotropy, etch uniformity and “damage,” as measured by the photodiode zero bias and reverses bias impedance characteristics. The critical process variables of Ar:H gas pressure, lower magnet current, and electrode height were all optimized. The optimized process parameters were then utilized to fabricate arrays with 80K cut-off wavelengths in excess of 11 μm, R₀As of 29 Ω-cm², Rd_20mV/Rd_0mV>13 and quantum efficiency>71%.     

Deposition of highly efficient microcrystalline silicon solar cells under conditions of low H2 dilution: the role of the transient depletion induced incubation layer

This paper addresses the plasma deposition of highly efficient microcrystalline silicon (μc‐Si:H) p‐i‐n solar cells under conditions of high SiH₄ utilization and low H₂ dilution. It was established that the transient depletion of the initially present SiH₄ source gas induces the formation of an amorphous incubation layer that prevents successful crystallite nucleation in the i‐layer and leads to poor solar cell performance. The effect of this transient depletion induced incubation layer on solar cells was made visible through dedicated solar cell deposition series and selected area electron diffraction measurements. Applying a gas flow procedure at plasma ignition it was succeeded to prepare state‐of‐the‐art μc‐Si:H material and solar cells under low hydrogen dilution conditions, highlighted by μc‐Si:H solar cells of up to 9·5% efficiency prepared using an undiluted source gas flow consisting solely of SiH₄. Copyright © 2007 John Wiley & Sons, Ltd.     

Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (T_g) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When T_g increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.     

The influence of oxidation-sirtl etch condition on the stacking fault generation in (111) silicon wafers

The successive oxidation-Sirtl etch technique has been investigated to evaluate the perfection of silicon crystals by detecting extrinsic stacking faults produced during oxidation. Experiments were performed in (111) epitaxial wafers. Measured densities of stacking faults were found to epend on the conditions of thermal oxidation, and stacking fault densities were a maximum at an oxidation temperature of around 1100°C. The stacking fault densities were reduced appreciably when epitaxial wafers were chemically etched to remove several tens of microns prior to the test. The generation of stacking faults is thought to occur by heterogeneous nucleation due to a very small amount of unidentified impurity found in epitaxial crystals.     

Optimization of the deposition and annealing conditions of fluorine-doped indium oxide films for silicon solar cells

Fluorine-doped indium oxide (IFO) films are deposited onto (pp ⁺)Si and (n ⁺ nn ⁺)Si structures made of single-crystal silicon by ultrasonic spray pyrolysis. The effect of the IFO deposition time and annealing time in an argon atmosphere with methanol vapor on the IFO chemical composition, the photovoltage and fill factor of the Illumination-U _oc curves of IFO/(pp ⁺)Si structures, and the sheet resistance of IFO/(n ⁺ nn ⁺)Si structures, correlating with the IFO/(n ⁺)Si contact resistance, is studied. The obtained features are explained by modification of the properties of the SiO _x transition layer at the IFO/Si interface during deposition and annealing. Analysis of the results made it possible to optimize the fabrication conditions of solar cells based on IFO/(pp ⁺)Si heterostructures and to increase their efficiency from 17% to a record 17.8%.     

电解电容器用铝箔腐蚀工艺研究

采用正交实验方法,选择腐蚀溶液的组成、腐蚀电压、腐蚀温度和时间四因素,探索影响环保型铝电解电容器用腐蚀箔性能的工艺参数。结果表明:当ψ(H2SO4∶HCl)为3∶1,电压为8V,温度为85℃,腐蚀时间85s时,可以获得高比容(0.59)高强度(弯折次数140)兼顾的性能。腐蚀溶液的组成、电压是影响腐蚀箔性能的主要因素。     

AC PDP介质保护膜材料的选择

随着对交流等离子体显示板电压变化原因的探讨，新型表面保护材料的开发研究以及为除去污染而对制造工艺的调整，ＡＣＰＤＰ正在获得极好寿命特性。介质保护膜直接与放电气体相接触，其材料和表面状况是决定ＡＣＰＤＰ寿命及放电性的重要因素，因而保护膜材料的选择尤为重要。     

Evaluation of a PECVD advanced barrier (k = 3.7) for 32 nm CMOS technology and below

An advanced dielectric barrier proposed for sub-45 nm CMOS technology nodes is firstly characterized on 300 mm full sheet wafers. The barrier is a bi-layer deposited by PECVD. The copper diffusion barrier property is ensured by a depositing dense initiation layer with the efficiency of a standard SiCN barrier (k = 5.0). The top layer, thicker, with lower density, enables the decrease of the barrier k-value to 3.66 and plays the role of etch stop layer. Combined with a PECVD porous a-SiOC:H dielectric (k-value = 2.5), the advanced dielectric barrier is successfully integrated in a C65 dual damascene architecture reaching a 3% gain in RC. A high via chain resistance yield is evidence of good via opening. Finally, the advanced barrier shows the same electromigration performance than the standard SiCN barrier.     

Nature of the nuclei for thermal donor formation in silicon (or another variant of accelerated oxygen diffusion)

The influence of preliminary heat treatment at 800 °C on the accumulation and annealing kinetics of thermal donors formed at 450 °C in silicon single crystals is investigated by performing four-point measurements of the electrical resistivity. The activation energies for the generation and annealing of thermal donors were found to increase appreciably after preliminary heat treatment at 800 °C. The experimental results are discussed with consideration of the role of the various phase states of oxygen in as-grown Si. An interpretation is proposed with allowance for the effect of the internal elastic stresses created by microfluctuations of the oxygen and thermal donor concentrations in the Si lattice on the diffusion coefficient of oxygen atoms. A quantitative estimation of the dimensions of the microfluctuations gives a value on the order of hundreds of angstroms. The generation and annealing kinetics of thermal donors are described within the Kaizer-Frisch-Reiss model with allowance for the locally accelerated (within the microfluctuations) diffusion of oxygen. The microfluctuations contain roughly 1–3% of the total number of oxygen atoms in the crystal. This low percentage complicates the observation of the accelerated diffusion of oxygen by direct methods, but is sufficient for thermal donor generation. Fiz. Tekh. Poluprovodn. 33, 1423–1427 (December 1999)     

Role of impurities in the formation of silicyne (long-chain silicon): Theory and experiment

The short-range order structure of amorphous silicon prepared by various methods is investigated by electron diffraction analysis. The influence of impurities in the as-prepared films and those irradiated with neon, oxygen, and carbon ions at doses up to 1×10¹⁶ cm⁻² on the character of structural transformations and the formation of interatomic silicon multiple bonds during annealing are investigated. The structure of films annealed at 500 °C is found to depend on the type of impurities and the nature of their chemical bond with silicon atoms. In particular, oxygen (>0.2 at. %), unlike hydrogen and carbon, acts as an inhibitor for the formation of silicyne. Good agreement is also noted between the experimentally determined short-range order parameters and those calculated by the nonempirical Hartree-Fock method. Fiz. Tekh. Poluprovodn. 33, 1253–1259 (October 1999)