Iron trichloride as oxidizer in acid slurry for chemical mechanical polishing of Ge2Sb2Te5

The effect of iron trichloride （FeC13） on chemical mechanical polishing （CMP） of Ge2Sb2Te5 （GST） film is inves- tigated in this paper. The polishing rate of GST increases from 38 nm/min to 144 nm/min when the FeC13 concentration changes from 0.01 wt% to 0.15 wt%, which is much faster than 20 nm/min for the 1 wt% H2O2-based slurry. This polish- ing rate trends are inversely correlated with the contact angle data of FeCl3-based slurry on the GST film surface. Thus, it is hypothesized that the hydrophilicity of the GST film surface is associated with the polishing rate during CMP. Atomic force microscope （AFM） and optical microscope （OM） are used to characterize the surface quality after CMP. The chemical mechanism is studied by potentiodynamic measurements such as Ecorr and Icorr to analyze chemical reaction between FeCl3 and GST surface. Finally, it is verified that slurry with FeCl3 has no influence on the electrical property of the post-CMP GST film by the resistivity-temperature （RT） tests.     

Thermal effect of Ge_2Sb_2Te_5 in phase change memory device

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1in In film composed of In/InOx core–shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.     

Current Controlled Relaxation Oscillations in Ge_2Sb_2Te_5-Based Phase Change Memory Devices

The relaxation oscillation of the phase change memory(PCM) devices based on the Ge_2Sb_2Te_5 material is investigated by applying square current pulses.The current pulses with different amplitudes could be accurately given by the independently designed current testing system.The relaxation oscillation across the PCM device could be measured using an oscilloscope.The oscillation duration decreases with time,showing an inner link with the shrinking threshold voltage V_(th).However,the relaxation oscillation would not terminate until the remaining voltage V_(on) reaches the holding voltage V_h.This demonstrates that the relaxation oscillation might be controlled by V_(on).The increasing current amplitudes could only quicken the oscillation velocity but not be able to eliminate it,which indicates that the relaxation oscillation might be an inherent behavior for the PCM cell.     

Impulse response of Ge_2Sb_2Te_5-based ultrafast photodetector integrated with SOI waveguide

The impulse response for a phase-change material Ge_2Sb_2Te_5(GST)-based photodetector integrated with a silicon-on-insulator(SOI) waveguide is simulated using finite difference time domain method. The current is calculated by solving the drift-diffusion model for short pulse(～10 fs) excitation for both of the stable phases.Full width at half-maximum values of less than 1 ps are found in the investigation. The crystalline GST has higher 3 dB bandwidth than the amorphous GST at a 1550 nm wavelength with responsivities of 21 A/W and18.5 A/W, respectively, for a 150 nm thick GST layer biased at 2 V. A broad spectrum can be utilized by tuning the device using the phase-change property of material in the near infrared region.     

Structural Evolution and Phase Change Properties of C-Doped Ge_2Sb_2Te_5 Films During Heating in Air

We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbondoped Ge_2 Sb_2 Te_5(C-GST) films during heating in air. Both the C-GST films without and with a thin SiO_2 capping layer(C-GST and C-GST/SiO_2) are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO_2 films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy,Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistancetemperature measurement reveals an unusual smooth decrease in resistance above 110℃ during heating. Xray diffraction result has excluded the possibility of phase change in the C-GST film below 170℃. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe_(4-n) Ge_n(n = 0, 1) units above 110℃ in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.     

Mechanism of amorphous Ge2Sb2Te5 removal during chemical mechanical planarization in acidic H2O2 slurry

In this paper, chemical mechanical planarization (CMP) of amorphous Ge2Sb2Te5 (a-GST) in acidic H2O2 slurry is investigated. It was found that the removal rate of a-GST is strongly dependent on H2O2 concentration and gradually increases with the increase in H2O2 concentration, but the static etch rate first increases and then slowly decreases with the increase in H2O2 concentration. To understand the chemical reaction behavior of H2O2 on the a-GST surface, the potentiodynamic polarization curve, surface morphology and cross-section of a-GST immersed in acidic slurry are measured and the results reveal that a-GST exhibits a from active to passive behavior for from low to high concentration of H2O2 . Finally, a possible removal mechanism of a-GST in different concentrations of H2O2 in the acidic slurry is described.     

Mechanical effects of polishing pad in copper electrochemical mechanical deposition for planarization

ECMD (electrochemical mechanical deposition) process consists of a traditional ECP (electrochemical plating) mechanism and a mechanical component. That is, this technique involves both electrochemical plating and mechanical sweeping of the material surface by the polishing pad. The mechanism of the ECMD process may be achieved through two mechanisms. The first mechanism may be the electrochemical plating on the surface where mechanical sweeping of polishing pad does not reach, and the second mechanism may be that the plating rate in the area that is mechanically swept may be reduced by the polishing pad. In this study, the effects of the mechanical component were investigated through various polishing pad types and hole ratios. In comparison to various polishing pad types using the manufactured the ECMD system, the plating rate and WIWNU (within wafer non-uniformity) using the experimental non-pore polishing pad were better than those of the experiments using other polishing pads.     

Sb_2Te_3热电薄膜的离子束溅射制备与表征

采用离子束溅射技术交替沉积Sb-Te-Sb多层薄膜后进行高真空热处理,直接制备Sb2Te3薄膜.利用X射线衍射(XRD)仪、霍尔系数测试仪、薄膜Seebeck系数测量系统对所制备的薄膜特性进行表征.XRD测量结果显示,薄膜的主要衍射峰与Sb2Te3标准衍射峰相同,在[101]/[012]晶向取向明显,存在较多的Te杂质峰;霍尔系数测试结果表明,薄膜为p型半导体薄膜,薄膜电阻率较低,其电导率接近于金属电导率,载流子浓度量级为1023cm-3,具有良好的电学性能;Seebeck系数测量结果显示,薄膜具有良好的热电性能,在不同条件下制备的薄膜的Seebeck系数在7.8—62μV/K范围;在所制备的薄膜中,退火时间为6h、退火温度为200℃的薄膜其Seebeck系数达到最大,约为62μV/K,且电阻率最小.     

Electrochemical characterization of surface complexes formed on Cu and Ta in succinic acid based solutions used for chemical mechanical planarization

Open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H₂O₂, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. The data analysis steps are discussed in detail to demonstrate how the D.C. and A.C. electrochemical probes can be combined in the framework of the RDE technique to design and test CMP slurry solutions.     

Study micromechanism of surface planarization in the polishing technology using numerical simulation method

With the development of semiconductor industry, the chemical mechanical polishing technology has already became the main stream method of realize the surface global flatness. In order to understanding physical essence underlying this technology, the author carried out nanometer polishing experiment of silicon wafer using molecular dynamics (MD) simulation method. The simulation result shows that larger slurry grain generate much more vacancy, dislocation, larger residual stress and intensive plastic deformation than that of small one although the larger grain acquire better surface quality.     

Time-dependent evolution process of Sb_2Te_3 from nanoplates to nanorods and their Raman scattering properties

High-quality Sb_2Te_3 nanostructures are synthesized by a simple hydrothermal method. The morphologies of the nanostructures change from hexagonal nanoplates to nanorods with the extension of growth time. Secondary nucleation is the dominant factor responsible for the change of the morphologies. Structural analyses indicate that all the obtained nanostructures are well crystallized. IR-active phonons are mainly observed in the Raman spectra of the nanoplates and nanorods. The slight deviations are observed in the Raman modes between the nanoplates and nanorods, which could originate from confinement effect in the nanostructures.     

纳米氧化铈的制备及其抛光性能的研究

采用溶胶-凝胶法制备了纳米CeO2粉体,并采用XRD、TOF-SIMS对其进行了表征。结果表明平均晶粒度在13.3nm,粒度分布均匀。进而研究了纳米CeO2在玻璃基片抛光中的抛光性能。ZYGO形貌仪表明,抛光后其表面平均粗糙度值(Ra)可降低到0.6nm左右。原子力显微镜(AFM)在5μm×5μm范围内测得基片表面粗糙度Ra值为0.281nm,表面光滑,划痕等表面微观缺陷明显改善。     

Phase transition,elastic and electronic properties of topological insulator Sb_2Te_3 under pressure: First principle study

The phase transition, elastic and electronic properties of three phases(phase Ⅰ,Ⅱ, and Ⅲ) of Sb_2Te_3 are investigated by using the generalized gradient approximation(GGA) with the PBESOL exchange–correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus,Young's modulus, Poisson's ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa(Ⅰ→Ⅱ) and 14.1 GPa(Ⅱ→Ⅲ), which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases Ⅰ and Ⅲ are brittle, while phaseⅡ is ductile. Of the three phases, phaseⅡ has the most serious degree of elastic anisotropy and phase Ⅲ has the slightest one.Finally, we investigate the partial densities of states(PDOSs) of three phases and find that the three phases possess some covalent features.     

Effect of additives for higher removal rate in lithium niobate chemical mechanical planarization

High roughness and a greater number of defects were created by lithium niobate (LN; LiNbO₃) processes such as traditional grinding and mechanical polishing (MP), should be decreased for manufacturing LN device. Therefore, an alternative process for gaining defect-free and smooth surface is needed. Chemical mechanical planarization (CMP) is suitable method in the LN process because it uses a combination approach consisting of chemical and mechanical effects. First of all, we investigated the LN CMP process using commercial slurry by changing various process conditions such as down pressure and relative velocity. However, the LN CMP process time using commercial slurry was long to gain a smooth surface because of lower material removal rate (MRR). So, to improve the material removal rate (MRR), the effects of additives such as oxidizer (hydrogen peroxide; H₂O₂) and complexing agent (citric acid; C₆H₈O₇) in a potassium hydroxide (KOH) based slurry, were investigated. The manufactured slurry consisting of H₂O₂-citric acid in the KOH based slurry shows that the MRR of the H₂O₂ at 2 wt% and the citric acid at 0.06 M was higher than the MRR for other conditions.     

Localized corrosion effects and modifications of acidic and alkaline slurries on copper chemical mechanical polishing

This study demonstrates the CMP performance can be enhanced by modifying the corrosion effects of acidic and alkaline slurries on copper. A corrosion test-cell with a polishing platform is connected with the potentiostat to investigate the corrosion behaviors of copper CMP in various alumina slurries. Experiments show that the slurry needs to be maintained in acidic pH<4.56 or alkaline pH>9.05 surroundings and thus better dispersion of alumina particles and less residual contaminant on copper surface can be obtained. The surface defects after copper CMP using acidic and alkaline slurries are described by pitting corrosion mechanisms, and these mechanisms can be regarded as a basis to modify their corrosion effects. Experimental results indicate that it is necessary to modify the dissolution of HNO₃ and oxidization of NH₄OH for copper CMP slurries. Consequently, the slurries of 5 wt.% HNO₃ by adding 0.1 wt.% BTA or 5 wt.% KNO₃ by adding 1 wt.% NH₄OH achieve good CMP performance for copper with higher CMP efficiency factor (CMPEF), 1460 and 486, and lower surface roughness (R_q), 4.019 and 3.971 nm, respectively. It is found that AFM micrographs can support the effectiveness of corrosion modifications for copper CMP in various slurry chemistries.     

Optical Recording Performance of In_（47）Sb_（14）Te_（39）Phase Change Thin Films using 514．5nm Wavelength Laser Beam

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Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.     

Relative roles of acetic acid, dodecyl sulfate and benzotriazole in chemical mechanical and electrochemical mechanical planarization of copper

The efficiency of chemical mechanical or electrochemical mechanical planarization (CMP or ECMP) carried out in the fabrication of integrated circuits is largely governed by the functional chemicals used in these processes. In this work, we study the individual and combined chemical and electrochemical effects of a selected set of such chemicals that can potentially support both CMP and ECMP of copper. These chemicals include acetic acid (HAc) as a complexing agent, H2O2 as an oxidizer, and ammonium dodecyl sulfate (ADS) as a dissolution inhibitor. Surface passivating effects of ADS under both CMP (open circuit) and ECMP (voltage activated) conditions are compared with those of a standard dissolution inhibitor for Cu, benzotriazole (BTAH), and the combined effects of a BTAH-ADS mixture also are explored. The experiments are performed in the absence of mechanical polishing using static and rotating Cu disc electrodes, and electro-dissolution of Cu for ECMP is activated using a voltage pulse modulation technique. A mechanism of surface reactions is proposed to describe the relative roles of HAc, H2O2, ADS and BTAH as electrolyte components for CMP and ECMP of Cu.     

Er3+/Tm3+共掺杂Ga5Ge20Sb10S65玻璃的发光特性及能量传递

采用高温熔融急冷法制备了系列Er3+/Tm3+共掺杂的Ga5Ge20Sb10S65玻璃,测试了样品的吸收光谱,以及分别在980 nm和800nm LD激发下样品的荧光光谱.运用Judd-Ofelt理论计算了Er3+离子在Ga5Ge20Sb1oS65玻璃中的强度参数Ω(i=2,4,6)、自发辐射跃迁几率A和辐射寿命τ等光...     

Modeling effects of abrasive particle size and concentration on material removal at molecular scale in chemical mechanical polishing

A novel material removal model as a function of abrasive particle size and concentration was established in chemical mechanical polishing (CMP) based on molecular scale mechanism, micro-contact mechanics and probability statistics. A close-form equation was firstly developed to calculate the number of effective particles. It found nonlinear dependences of removal rate on the particle size and concentration, being qualitatively agreement with the published experimental data. The nonlinear relation results from the couple relationship among abrasive number, slurry concentration and surface atoms’ binding energy with the particle size. Finally, the system parameters such as the operational conditions and materials properties were incorporated into the model as well.