Nano-scale gap filling and mechanism of deposit-etch-deposit process for phase-change material

Ge2Sb2Te5 gap filling is one of the key processes for phase-change random access memory manufacture.Physical vapor deposition is the mainstream method of Ge2Sb2Te5 film deposition due to its advantages of film quality,purity,and accurate composition control.However,the conventional physical vapor deposition process cannot meet the gapfilling requirement with the critical device dimension scaling down to 90 nm or below.In this study,we find that the deposit-etch-deposit process shows better gap-filling capability and scalability than the single-step deposition process,especially at the nano-scale critical dimension.The gap-filling mechanism of the deposit-etch-deposit process was briefly discussed.We also find that re-deposition of phase-change material from via the sidewall to via the bottom by argon ion bombardment during the etch step was a key ingredient for the final good gap filling.We achieve void-free gap filling of phase-change material on the 45-nm via the two-cycle deposit-etch-deposit process.We gain a rather comprehensive insight into the mechanism of deposit-etch-deposit process and propose a potential gap-filling solution for over 45-nm technology nodes for phase-change random access memory.     

Chemical mechanical planarization of Ge_2Sb_2Te_5 using IC1010 and Politex reg pads in acidic slurry

In the paper, chemical mechanical planarization(CMP) of Ge2Sb2Te5(GST) is investigated using IC1010 and Politex reg pads in acidic slurry. For the CMP with blank wafer, it is found that the removal rate(RR) of GST increases with the increase of pressure for both pads, but the RR of GST polished using IC1010 is far more than that of Politex reg. To check the surface defects, GST film is observed with an optical microscope(OM) and scanning electron microscope(SEM). For the CMP with Politex reg, many spots are observed on the surface of the blank wafer with OM, but no obvious spots are observed with SEM. With regard to the patterned wafer, a few stains are observed on the GST cell, but many residues are found on other area with OM. However, from SEM results, a few residues are observed on the GST cell, more dielectric loss is revealed about the trench structure. For the CMP with IC1010, the surface of the polished blank wafer suffers serious scratches found with both OM and SEM, which may result from a low hardness of GST, compared with those of IC1010 and abrasives. With regard to the patterned wafer, it can achieve a clean surface and almost no scratches are observed with OM, which may result from the high-hardness SiO2 film on the surface, not from the soft GST film across the whole wafer. From the SEM results, a clean interface and no residues are observed on the GST surface, and less dielectric loss is revealed. Compared with Politex reg, the patterned wafer can achieve a good performance after CMP using IC1010.     

自组织InAs/GaAs量子点垂直排列生长研究

利用自组织生长InAs/GaAs量子点的垂直相关排列机制，生长了上下两层用6.5nm GaAs间隔的InAs结构.下层InAs已经成岛，由于应力传递效应，上层InAs由二维生长向三维成岛生长的转变提前发生，临界厚度从1.7ML变成小于1.5ML.透射电子显微镜截面象显示形成上下两层高度差别很大的InAs量子点，但是由于两层量子点之间存在强烈的电子耦合，光致发光谱中只有与包含大量子点的InAs层相对应的一个发光峰.     

相变型半导体存储器研究进展

文章系统地介绍了相变型半导体存储器的原理、相变材料、特点、器件结构设计、研究现状及面临的几个关键器件工艺问题．C—RAM由于具有非易失性、循环寿命长、元件尺寸小、功耗低、可多级存储、高速读取、抗辐照、耐高低温、抗振动、抗电子干扰和制造工艺简单等优点，被认为最有可能取代目前的FLASH、DRAM和SRAM而成为未来半导体存储器主流产品．     

Simulation of the Propagation Property of Metal Wires Terahertz Waveguides

The propagation property of metal wires terahertz waveguides is studied and simulated under the framework of the Sommerfeld model. The group velocity dispersion, attenuation amplitude, transverse magnetic mode and propagating energy have been obtained by numerically solving the complex eigenvalue equation for the propagation constant. It is found that the group velocity dispersion and attenuation amplitude decrease with the increasing radii of metal wires. The energy power within the dielectric layer increase with the increase of radiation frequency.     

Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films

Ge_2Sb_2Te_5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge_2Sb_2Te_5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge_2Sb_2Te_5 film is due to the amorphous －Te－-Te－ stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe_4 and the Sb－Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb－Sb (Te_2) and (Sb_2) Sb－Sb (Te_2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge_2Sb_2Te_5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te_2) Sb－Sb (Te_2).     

Single Cell Element of Chalcogenide Randoul Access Memory Fabricated with the Focused Ion Beam Method

A singie cell element of chalcogenide random access memory was fabricated by using the focused ion beam method.The contact size between the Ge2Sb2Te5 Phase change film and the top electrode film is about 600nm (diameter) and the contact area is caiculated to be 0.28μm^2.The thickness of the phase change film is 83nm.The current-voltage characteristics of the cell element are studied using the home-made current-voltage tester in our laboratory.The minimum threshold current of about 0.6mA is obtained.     

Si1Sb2Te3 phase change material for chalcogenide random access memory

This paper investigated phase change Si1Sb2Te3 material for application of chalcogenide random access memory. Current-voltage performance was conducted to determine threshold current of phase change from amorphous phase to polycrystalline phase. The film holds a threshold current about 0.155 mA, which is smaller than the value 0.31 mA of Ge2Sb2Te5 film. Amorphous Si1Sb2Te3 changes to face-centred-cubic structure at ~ 180℃ and changes to hexagonal structure at ~ 270℃. Annealing temperature dependent electric resistivity of Si1Sb2Te3 film was studied by four-point probe method. Data retention of the films was characterized as well.     

Characteristics of Sn-Doped Ge2Sb2Te5 Films Used for Phase-Change Memory

Sn-doped Ge2Sb2Te5 thin films deposited on Si（100）/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystallization temperatures of the 3.58 at.%, 6.92 at.% and 10.04 at.% Sn-doped Ge2Sb2Te5 thin films have decreases of 5.3, 6.1 and 0.9℃, respectively, which is beneficial to reduce the switching current for the amorphous-to-crystalline phase transition. Due to Sn-doping, the sheet resistance of crystalline Ge2Sb2Te5 thin films increases about 2-10 times, which may be useful to reduce the switching current for the amorphous-to-crystalline phase change. In addition, an obvious decreasing dispersibility for the sheet resistance of Sn-doped Ge2Sb2Te5 thin films in the crystalline state has been observed, which can play an important role in minimizing resistance difference for the phase-change memory cell element arrays.     

不同组分InxGa1-xAs(0≤x≤0.3)覆盖层对自组织InAs量子点的影响

研究了不同In组分的In_xGa_1-xAs(0≤x≤0.3)覆盖层对自组织InAs量子点的结构及发光特性的影响.透射电子显微镜和原子力显微镜表明,InAs量子点在InGaAs做盖层时所受应力较GaAs盖层时有所减小,并且x＝0.3时,InGaAs在InAs量子点上继续成岛.随x值的增大,量子点的光荧光峰红移,但随温度的变化发光峰峰位变化不明显.理论分析表明InAs量子点所受应力及其均匀性的变化分别是导致上述现象的主要原因. 关键词： 量子点 盖层 应力 红移