Materials Science Forum Vol. 815

Abstract: Though the quality of epitaxial wafer prepared by barrel type epitaxial furnace is inferior to that by traditional single wafer furnace, it has a series of advantages such as high yield and low cost. The key issues and difficulties of the epitaxy process for buried layers IC wafers prepared by barrel type epitaxial furnace were discussed. By optimizing the epitaxy process parameters and tightly controlling the production procedure such as cleaning and inspecting, barrel type epitaxial furnace can meet the special requirement for buried layer epitaxial process. The characteristics of the epilayers prepared by barrel type epitaxial furnace were close or equivalent to that by single wafer furnace. The ways to suppress the auto doping in the double buried layer epitaxial process were introduced. The ideal transition width of the epilayers was obtained by the two-step epitaxy.

Abstract: A novel Ru thin film formation method was proposed to deposit metallic Ru thin films on TiN substrate for future backend of line process in semiconductor technologies. RuO₂ thin films were first grown on TiN substrate by oxygen plasma-enhanced atomic layer deposition technique. The deposited RuO₂ thin films were then reduced into metallic Ru thin films by H₂/N₂-assisted annealing.

Abstract: With the development of power electronic devices, the market demand for acid etched wafers of monocrystalline silicon, which has good surface properties and minimum surface roughness, increases rapidly. But there has been rarely report about the impact of acid etching process on the wafer surface roughness. This paper studied the surface roughness of the wafer, which was etched by mixture of HNO₃, HF and HAC. The results showed that the surface roughness became smaller with the increase of wafer remove amount, while the roughness became worse with the service life extension of the acid; however, fluid infusion discharge method could be adopted in the etching process so that the etching acid system could achieve a relatively balanced state and wafer roughness became stabilized. The process mechanism was studied and analyzed in this investigation.

Abstract: Graphene is a novel two dimensional material with exceptional properties. Chemical vapor deposition of graphene on metal substrates is widely used to prepare high quality graphene film. However, the graphene films need to be transferred to oxide substrates for device applications. A chemical vapor deposition approach for direct growth of graphene films on zinc oxide was demonstrated in the present investigation. Raman spectra were used to characterize the grown graphene films. The impact of the growth temperature, time and gas flow ratio on the layer number and crystallite size of graphene was investigated.

Abstract: Current ULSI circuits have features with dimensions in the nanoscale region. As the critical dimension shrinks, Cu BEOL systems face reliability impacts. Alloying has been proved to be a promising technique to retard grain boundary electro-migration (EM). In this paper, dilute Cu Alloys such as Cu-Al, Cu-Mn for dual-damascene interconnect applications have been investigated. The alloy chosen principle for nanoscale interconnects has been discussed. The ultrahigh purity copper alloy target properties including purity, alloy composition, grain size and sputtering performance were investigated, to lay the foundation for the application of the large-size ultrahigh purity copper alloy target used for 300mm wafer fabrication. The relationships between deposited film behaviors and sputtering target properties in some applications were also discussed. In order to acquire high quality thin film, the properties of sputtering target such as alloy composition homogeneity, grain size and uniformity et al. have to be well controlled by proper fabrication techniques.

Abstract: Metal-insulator-semiconductor (MIS) diodes with Si₃N₄/Al₂O₃ bilayer gate dielectric films deposited on an AlGaN/GaN heterostructure were fabricated, where the Si₃N₄ layer played a role of etching stopped layer to protect the Al₂O₃ film from being damaged. Compared with traditional Schottky diodes, a distinct suppression of gate leakage current was achieved for the MIS diodes both at forward and reverse bias, and the dominant leakage current mechanism is Fowler–Nordheim tunneling. The 2DEG density extracted from C-V curves was 3~7 ́10¹³cm^-2, in the same order of magnitude as Schottky diodes and hall measurement. Although the existence of the bilayer dielectric did not affect the 2DEG density at the interface of AlGaN/GaN, Si₃N₄ layer shared more gate bias and led to more gate bias required to deplete 2DEG and turn down the devices, moreover, Si₃N₄ layer had no effect on suppressing the forward or reverse gate leakage current due to its narrow band gap width and band bending compared with a single Al₂O₃ film. The experimental results provided a reference for the design of gate dielectric film structure for AlGaN/GaN high-electron-mobility transistors (HEMTs).

Abstract: A new type of fully self-aligned technology for graphene field-effect transistors was presented, in which a PVD SiO₂ layer was taken as mask for the deposition of self-aligned source, drain and gate contacts. In this key process, the dielectric edge-sides exposure phenomenon during metal thermal evaporation was exploited. In the prepared self-aligned GFETs, both parasitic capacitance of the gate overlapped source and drain areas and series resistance of the spacing areas between gate and source and drain contacts were eliminated. The DC characterization and on-chip microwave measurement of the fabricated GFETs with channel length of 1give a maximum transconductanceof 2.32,field-effect mobilities of electrons and holes of 6924and 7035, and intrinsic cutoff frequencyof 0.5GHz, respectively, showing a significant improvement of both DC and RF performance.

Abstract: Electron beam (EB) annealing was used to acquire a reasonable and stable component in Si-Sb-Te material. For Si₂Sb₂Te₅ phase change material, EB irradiation can induce phase separation and some regions have remained unchanged, which manifests as Si_xSb₂Te₃. The component of these steady areas was considered as reasonable in which Sb₂Te₃ is a stable compound. The crystallized Si_3.3Sb₂Te₃ film after EB irradiation exhibited nanoscale grains with well-proportioned distribution and these grains were all with Sb₂Te₃ structure surrounded by amorphous. This unique structure brings fast phase change speed which is at least 12 times more rapidly than Si₂Sb₂Te₅ material because it localizes atoms’ diffusion in a nanoarea during reversible phase transition process.

Abstract: The lowest-energy geometrical structures of a cluster containing 55 atoms were searched by using the Density Functional Tight Binding (DFTB) combined with unbiased global optimization genetic algorithms (GAs) method. Two lowest-energy structures were obtained for the Si₅₅ cluster with the appearance of “Y shape” and “like-spherical shape” configurations. The configuration dependence average energy, highest occupied and lowest unoccupied molecular (HOMO-LUMO) gap, electron transfer and molecular dipole moment were also discussed in details for this cluster.