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The electrical resistance on the crystallization process of sputtered-deposited Ge1Cu2Te3 film was investigated by two-point probe method. It was found that the amorphous Ge1Cu2Te3 film crystallizes into a single Ge1Cu2Te3 phase with a chalcopyrite structure, which leads to a large resistance drop. The crystallization temperature of the Ge1Cu2Te3 amorphous film was about 250 °C, which is about 70 °C higher than the conventional Ge2Sb2Te5 amorphous film. The activation energy for the crystallization of the Ge1Cu2Te3 amorphous film was higher than that of the Ge2Sb2Te5 amorphous film. The Ge1Cu2Te3 compound with a low melting point can be expected to be suitable as the phase change material for PCRAM.
The electrical resistance change of amorphous SixTe100-x (x: 10-23) films during heating was investigated by a two-point probe method. The SixTe100-x films showed two-stage crystallization processes. The film was firstly crystallized to Te and subsequently crystallized to Si2Te3 with an electrical resistance drop. The first crystallization temperature Tx1st slightly increased with increasing Si content, while the second crystallization temperature Tx2nd was independent on the composition and was a constant temperature of 310 °C. In all films, the electrical resistance once increased in the temperature range from 250 to 295 °C before the crystallization of the Si2Te3. This temporal resistance increase could be explained by considering a formation of high-resistivity Si-rich amorphous phase.
A thin-amorphous MnOx layer using self-forming barrier process with a Cu-Mn alloy shows good adhesion and diffusion barrier properties between copper and dielectric layer, resulting in excellent reliability for stress and electromigration. Meanwhile, chemical vapor deposition (CVD) can be employed for conformal deposition of the barrier layer in narrow trenches and vias for future technology node. In our previous research, a thin and uniform amorphous MnOx layer could be formed on TEOS-oxide by thermal metal-organic CVD (MOCVD), showing a good diffusion barrier property. In addition, a good adhesion strength is necessary between a Cu line and a dielectric layer not only to ensure good SM and EM resistance but also to prevent film delamination under mechanical or thermal stress conditions during fabrication process such as chemical mechanical polishing or high temperature annealing. To date, no information is available with regard to the adhesion property of CVD-MnOx. In this work, we report diffusion barrier property in further detail and adhesion property in PVD-Cu/CVD-MnOx/SiO2/Si. The temperature dependence of the adhesion property is correlated with the chemical composition and valence state of Mn investigated with SIMS and Raman spectroscopy.
Substrates were p-type Si wafers having a plasma-TEOS oxide of 100nm in thickness. CVD was carried out in a deposition chamber. A manganese precursor was vaporized and introduced into the deposition chamber with H2 carrier gas. After the CVD, a Cu overlayer was deposited on some samples using a sputtering system in load lock chamber of the CVD machine. The diffusion barrier property of the MnOx film was investigated in annealed samples at 400 oC for 100 hours in a vacuum of better than 1.0×10-5 Pa. The Adhesion property of Mn oxide was investigated by Scotch tape test in the as-deposited and in the annealed Cu/CVD-MnOx/TEOS samples. The obtained samples were analyzed for thickness and microstructure with TEM, chemical bonding states of the MnOx layer with XPS, and composition of each layer with SIMS.
In the CVD deposition below 300 °C, no Cu delamination was observed both in the as-deposited and in the annealed Cu/CVD-MnOx/SiO2 samples. On the other hand, in the CVD deposition at 400 °C, the Cu films were delaminated from the CVD-MnOx/TEOS substrates. The XPS peak position of Mn 2p and Mn 3s spectra indicated that the valence state of Mn in the as-deposited barrier layer below 400 °C was 2+. Composition analysis with SIMS as well as Raman also indicated the presence of a larger amount of carbon at 400 °C than at less than 300 °C. The good adhesion between Cu and MnO could be attributed to an amount of carbon inclusion in the CVD barrier layer.
An ultrathin barrier layer of MnOx was grown using metal organic chemical vapor deposition (MOCVD) at an interface between Cu and SiO2 dielectric. The electronic transport properties of Cu/MnOx/SiO2/p-Si metal oxide semiconductor (MOS) devices showed leakage current density within the range of 10-8-10-7A/cm2 up to an electric field of 4MV/cm. The current density remained within the same range after bias temperature aging test at 3MV/cm for 6×103s at 550K. The capacitance-voltage curves of the MOS device having the MnOx layer grown at 473K do not show significant shift of flat band voltage after thermal annealing at 673K for 3.6×103s as well as after bias temperature aging test at 1MV/cm, 550K for 2.4×103 s. These results indicate that the ultrathin layer of MnOx is stable under the above conditions and prevents sufficiently Cu ion diffusion into the SiO2 dielectric.
GeTe-Sb2Te3 pseudobinary compounds are attracting considerable attention as phase change materials for optical disk and phase change random access memory (PRAM). In these compounds, Ge2Sb2Te5 (GST) has been used for an optical disk memory such as DVD-RAM because the crystallization by laser beam heating is very fast (∼20ns). Recently, the GST has been much considered as material for PRAM and, therefore, the electrical resistance change due to crystallization and the phase change by applying an electrical current have been widely investigated. On the other hand, although GeTe compound has been suggested as the phase change material for the optical disk by Chen et al in 1986, the study focusing on the phase change material for PRAM is limited. Since GeTe is known to show the phenomenon of electrical switching, this compound has a potential of PRAM. In this study, the electrical resistance and crystalline structural changes on crystallization process in Ge-Te thin films were investigated.
Films of amorphous Ge100–xTex (x : 46-94) with 200 nm thickness were deposited by sputtering of GeTe alloy target or co-sputtering of GeTe and Te targets on SiO2/Si substrates. In-situ electrical resistance measurements during heating process of these films were performed by two point probe method in a heating rate of 2∼50°C/min. X-ray diffraction (XRD) analysis was employed for the structural identification of thin films for 10-60° in 2′ using X-ray diffractometer with Cu-K. Transmission electron microscope (TEM) analysis was carried out to investigate the microstructure and to identify crystalline structure. The compositions of these films were confirmed by energy dispersive X-ray spectroscopy (EDS) attached TEM.
All as-deposited Ge-Te films were confirmed amorphous by XRD and TEM. From the in-situ electrical resistance measurements, it is found that resistance change with crystallization process depends on the composition and the stoichiometric GeTe compound shows abrupt electrical resistance change at around 190 °C. The crystallization temperature of GeTe was higher than that of GST and resistance difference between the amorphous and the crystal was also larger. While the electrical resistance of GST film gradually decreased with increasing temperature after the crystallization at around 160 °C, that of GeTe film showed small temperature dependence after crystallization. It was found by X-ray measurement observation that the amorphous GeTe compound film crystallized first into a cubic state, and then into a stable rhombohedral state by further heating. The crystallization kinetics of Ge-Te thin films will be also presented.
A manganese oxide layer was formed by thermal chemical vapor deposition(CVD) on a tetraethylorthosilicate (TEOS) oxide substrate. The thickness of the Mn oxide layer could be varied 2.6 to 10 nm depending on deposition temperature. Heat-treated samples of PVD Cu / CVD Mn oxide /SiO2 indicated no interdiffusion. The CVD Mn oxide was found to be a good diffusion barrier layer.
Self-forming barrier process was carried out on a porous low-k material with the Cu-Mn alloys. The effects of various surface treatments were investigated in the sample having a pore size of 0.9 nm and a porosity of 25%. Before and after annealing, samples were analyzed in cross section with transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). Concentration profile was also analyzed with time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicated the penetration of Cu into the low-k interior during deposition, followed by the segregation of Cu at the low-k/Si interface during subsequent annealing. Although a diffusion barrier layer was formed and no further Cu penetration was not observed during annealing, initial Cu penetration in the deposition process was detrimental and should be prevented by restoring the plasma damage on the low-k surface.
Deformation mechanisms of electroplated Cu thin films on TaN/SiO2/Si were investigated by performing isothermal annealing above 200 °C. Stress relaxation behavior during isothermal annealing was analyzed by curve fitting using exponential decay equations. During heating, fast relaxation and subsequent slow relaxation processes were observed. In contrast, during cooling, only slow relaxation process was observed. Among possible mechanisms for stress relaxation, diffusion creep was found to be the most plausible mechanism based on the obtained values of the activation energy. It was suggested that the slow relaxation process observed both in the heating and in the cooling processes was attributed to a grain-boundary diffusion creep. On the other hand, the fast relaxation process observed during heating was attributed to a surface-diffusion controlled mechanism. The surface diffusion mechanism was considered to be characteristic to Cu thin films that did not form stable surface oxide.
A magnesium (Mg) solid solution with a long periodic hexagonal structure was found in a Mg97Zn1Y2 (at.%) alloy in a bulk form prepared by warm extrusion of atomized powders at 573 K. The novel structure has an ABACAB-type six layered packing with lattice parameters of a = 0.322 nm and c = 3 × 0.521 nm. The Mg solid solution has fine grain sizes of 100 to 150 nm and contains 0.78 at.% Zn and 1.82 at.% Y. In addition, cubic Mg24Y5 particles with a size of about 7 nm are dispersed at small volume fractions of less than 10% in the Mg matrix. The specific density (ρ) of the extruded bulk Mg–Zn–Y alloy was 1.84 Mg/m3. The tensile yield strength (σy) and elongation (δ) are 610 MPa and 5%, respectively, at room temperature, and the specific yield strength defined by the ratio of σy to ρ is as high as 3.3 × 105 Nm/kg. High σy values exceeding 400 MPa are also maintained at temperatures up to 473 K. It is noticed that the σy levels are 2.5 to 5 times higher than those for conventional high-strength type Mg-based alloys. The Mg-based alloy also exhibits a high-strain-rate superplasticity with large δ of 700 to 800% at high strain rates of 0.1 to 0.2 s−1 and 623 K. The excellent mechanical properties are due to the combination of the fine grain size, new long periodic hexagonal solid solution containing Y and Zn, and dispersion of fine Mg24Y5 particles. The new Mg-based alloy is expected to be used in many fields.
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