Papers by Keyword: ULSI

Abstract: One of promising candidates as dopants for forming ultra-shallow and high conductive source/drain in future silicon devices has been proposed to be dimer or trimer co-dopants containing pairs or trios of different impurity elements. Making choice of a combination of the impurity elements with a small ionization energy is essential for the appropriate dimers and trimers. In this work we calculated total energies of silicon with substitutional or ineterstitial impurity elements and derived formation energies for the substitutional and interstitial impurity elements for the atomic number 1 to 83 with the exception of inert gas and lanthanum series elements. We present here the periodic table with the formation energies of the substitutional and interstitial impurity elements for determining the most stable site of the impurity elements in Si lattice. We can use this table as a database for calculating ionization energies of the impurity element.

Abstract: One of promising candidates as dopants for forming ultra-shallow and high conductive source/drain in future silicon devices has been proposed to be dimer or trimer co-dopants containing pairs or trios of different impurity elements. Making choice of a combination of the impurity elements with a small ionization energy is essential for the appropriate dimers and trimers. In this work we calculated total energies of silicon with substitutional or ineterstitial impurity elements and derived formation energies for the substitutional and interstitial impurity elements for the atomic number 1 to 83 with the exception of inert gas and lanthanum series elements. We present here the periodic table with the formation energies of the substitutional and interstitial impurity elements for determining the most stable site of the impurity elements in Si lattice. We can use this table as a database for calculating ionization energies of the impurity element.

Abstract: High gate leakage current, as a central problem, has decelerated the downscaling of minimum feature size of the field effect transistors In this paper, a combination of density functional theory and non equilibrium Green’s function formalism has been applied to the atomic scale calculation of the tunnel currents through CeO₂, Y₂O₃, TiO₂ and Al₂O₃ dielectrics in MOSFETs. The tunnel currents for different bias voltages applied to Si/Insulator/Si systems have been obtained along with tunnel conductance v/s bias voltage plots for each system. The results are in agreement to the use of high dielectric constant materials as gate dielectric so as to enable further downscaling of MOSFETs with reduced gate leakage currents thereby enabling ultra large scale integration. When used as dielectric, TiO₂ exhibits extremely low tunnel currents followed by Y₂O₃ while CeO₂ and Al₂O₃ exhibit high tunnel currents through them at certain bias voltages.

Abstract: Electronic structures of silicon with carbon, indium, or indium-carbon dimers were calculated to investigate the interaction between indium and carbon in X center due to the indium-carbon dimers. Ab initio calculations were carried out mainly for basic Si₇₁H₆₀, C-Si₇₀H₆₀, In-Si₇₀H₆₀, and InC-Si₆₉H₆₀ clusters. The results showed that : (i) the X level was observed at E_HOMO + 0.42 eV in the InC-Si₆₉H₆₀ which was a little bit shallower than E_HOMO + 0.44 eV of the corresponding substitutional In in the In-Si₇₀H₆₀, (ii) dominant constituents of density of states of the X level were the partial densities of states of In and Si, and (iii) the X level had the antibonding nature between In and C.

Abstract: It is known that acceptor-carbon complexes have ionization energies less than those of the corresponding substitutional, separate acceptors in silicon. We present the formation mechanism for a shallower acceptor energy level called an X level that is due to an indium- carbon pair. Ab initio calculation methods were used to evaluate electronic structures and lattice relaxations of silicon with indium, carbon or a carbon-indium dimer. The results shows that the bonding interaction between the 5p orbitals of the indium atom and the 3sp orbitals of the silicon atoms bound with the indium atom mainly determines the ionization energy of the X level, and the ionic bonding interaction of the carbon atomic orbitals with the indium atomic orbitals in the X level enables the bonding interaction of the orbitals between the indium atom and the silicon atom to lower the corresponding indium acceptor level, and then to form the shallower X level.

Abstract: The total energies of donor-acceptor-donor D₂A trimer codopants (D = As and Sb, A = B, Al, Ga, In and Tl) in Si and their electronic geometrically stable structures were studied using ab initio calculations in order to propose new dopants for the formation of ultra shallow junctions with high carrier concentrations in the source/drain regions. The results of the calculations indicated that the trimer codopants were formed in Si and were stable. The trimer codopants are also able to activate the inactive complexes As₂V and Sb₂V by codoping acceptor atoms that occupy vacant sites. In particular, As₂Al, As₂Ga, Sb₂B and Sb₂Ga resulted in both shallower donor levels and higher solid solubility compared to traditional single donor atoms such as As and Sb.

Abstract: We numerically evaluate the accumulation of dislocations in periodic structure of the shallow trench isolation (STI) type ULSI cells which has generally been adopted as the latest semiconductor device structure. STI type ULSI cells with gate length less than 62 nm and various trench depths are employed and subjected to a temperature drop from the initial value of 1000 °C. Dislocation accumulation is evaluated by a technique of crystal plasticity analysis. Relations between the geometry of the STI type ULSI cells and dislocation accumulation are discussed.

Abstract: This paper discusses the effect of plating condition on the mechanical properties and residual stress of electroplated Cu film. The inlaid copper structure was fabricated on silicon wafer where silicon oxide was thermally grown. Seed layer was deposited by sputtering method followed by copper electro-deposition. Copper was electrodeposited with IBM paddle type electroplating machine Residual stress, hardness, elastic modulus, and surface roughness of electroplated copper film were investigated at various organic additives in plating solution and current types with a nanoindenter and a surface profilometer. The dishing amounts in chemical mechanical polishing (CMP) was also investigated at various additives. The results show that, in the case of residual stress, the copper film deposited at higher additive or PC current result in lower residual stress. The additives do not significantly affect the mechanical properties of Cu deposit.

Abstract: With the highest brilliance synchrotron radiation X-ray (SPring-8) and TEM observations, Cu oxides ranged 2-nm to 10-nm in thickness formed on sputtered Cu has been evaluated. For the plasma-assisted Cu oxide, weak Cu2O and/or CuO X-ray diffraction pattern is observed, while no diffraction pattern in native and thermally (170°C) grown oxides. Those native and thermal oxides show Cu2O coordination observed by XANES (X-ray Absorption Near Edge Structure) method. This suggests that Cu oxide formed at low temperatures consists of stoichiometric Cu2O in an amorphous structure. According to the Fowler-Nordheim (F-N) current emission model, the current emission taking place at Cu2O decreases with increasing of the oxide thickness and its mean barrier height (φB) in the MIM band structure. In case of current density at 106A/cm2 of 1V, it is estimated that the allowable thickness of Cu oxides is approximately 1.5-nm at 1 eV of barrier height.

Abstract: The dishing phenomena of soft materials in chemical mechanical polishing (CMP) process were problematic in delineating inlaid metal patterns. The inlaid copper structures were fabricated on Si wafer where SiO2 was thermally grown. Seed layer was deposited by thermal evaporate method followed by copper electrodeposition. Copper was electrodeposited with IBM paddle type electroplating machine to obtain uniform thickness of coating. The dishing amounts were measured at various current density and current type. The dishing amounts with pattern density and line width were also measured. The losses of copper were not sensitively dependent on current density however those were dependent on current type. The dishing amount of copper was decreased at high pattern density especially over 50% and increased with line width. Surface topology and grain size of coating were investigated with surface profilometer and FESEM.