Tetsuya Yoshikawa

Hydrogen Promoted Copper Migration in the High Pressure Anneal Process

To meet the requirement of lower processing temperature in the high pressure anneal process (HiPA), Cu films deposited by physical vapor deposition (PVD) with addition of hydrogen were investigated. Experimental results on the hole filling performance under high pressure, the grain growth, the micro-hardness measurement and the film stress measurement revealed that the hydrogen addition markedly changes the properties of the Cu film. It is especially effective in softening the PVD-Cu film and/or in promoting the Cu atom diffusion which also promotes grain growth. As a result the processing temperature may be lowered down to around 400°C, which is the highest temperature allowable for the interconnection structures with organic low-k dielectric layers.

Effects of the high-pressure annealing process on the reflow phenomenon of copper interconnections for large scale integrated circuits

The embedding effect of physical vapour deposited and electrochemical deposited copper films due to a high-pressure annealing process at 400 °C and 150 MPa was investigated in order to apply this high-pressure annealing process to dual-damascene fabrication technology for copper interconnections. The experimental results support a thermal elasticity and plasticity analysis using a finite-element method which predicts that additional external pressure acts to push copper films to the via holes. This analytical result agrees well with the hole filling performance under the high-pressure annealing of test element group specimens on which via holes of 0.28 μm in diameter and 1.2 μm in depth were previously formed. The residual stress left after lowering the temperature and pressure has no dependence on the additional external pressure and therefore does not reduce the reliability of the copper interconnections. However, the additional external pressure reduces the incremental creep strain of copper during the heating and holding step and reduces the stress transition point during the cooling step. This indicates that the additional external pressure on annealing at approximately 400 °C is effective for the perfect filling of copper into via holes without minute voids and in suppressing the siphoning phenomenon in copper from via holes.

Preparation of alloy thin films by the CAPD process

Abstract Brass (CuZn), nickel-silver (CuZnNi) and stainless steel (Fe18Cr8Ni) thin films were deposited by the cathodic arc plasma deposition process onto SUS304 in order to study the chemical composition change from that of the target and to determine surface roughness. The deposition variables investigated were substrate temperature and arc current. The chemical composition of each target and the prepared thin films were analyzed by atomic absorption spectrochemical analysis. The composition of both the brass and nickel-silver alloy films were studied in relation to the targets used as a function of substrate temperatures. Surface roughness was measured by the stylus method. As-deposited thin films displayed very high roughness.

Supercritical resist dry technique for electron-beam projection lithography (EPL)

A single-layer resist process for a technology nodes at or below 65nm utilizing a novel supercritical dry technique and Electron-beam Projection Lithography (EPL) technology is discussed. EPL is inhernelty advantageous in imaging sub-65nm geometries with high aspect ratios. Pattern collapse of these high aspect ratio (resist) structures, however, is a critical and limiting issue. By employing our novel supercritical carbon dioxide (SCCO2) dry technique, 70nm and 60nm lines and spaces patterns with a resist thickness of 250nm, whose aspect ratio is 3.5 and 4.2 respectively, have been successfully demonstrated without resist pattern collapse.

Highly-enhanced reflow characteristics of sputter deposited Cu alloy thin films for large scale integrated interconnections

An attempt to improve the reflow characteristics of sputtered Cu films was made by alloying the Cu with various elements. We selected Y, Sb, Nd, Sm, Gd, Dy, In, Sn, Mg, and P for the alloys, and “the elasto-plastic deformation behavior at high temperature” and “the filling level of Cu into via holes” were estimated for Cu films containing each of these elements. From the results, it was found that adding a small amount of Sb or Dy to the sputtered Cu was remarkably effective in improve the reflow characteristics. The microstructure and imperfections in the Cu films before and after high-temperature high-pressure annealing were investigated by secondary ion micrographs and positron annihilation spectroscopy. The results imply that the embedding or deformation mechanism is different for the Cu-Sb alloy films compared to the Cu-Dy alloy films. We consider that the former is embedded by softening or deformation of the Cu matrix, which has a polycrystalline structure, and the latter is embedded by grain bounda...

Hydrothermal Reaction of Copper and Water.

Experiments to investigate the reaction between copper and water were carried out. A copper powder sample was encapsulated with water in a Cu capsule and annealed at 120 MPa, 9000 s, at temperatures from 300°C to 400°C. Observation of the processed sample using an optical microscope and X-ray diffraction analysis showed that copper and water react and form Cu(OH)2 and Cu2O. To date the mechanisms of the reaction are not clear, however the dissipation of hydrogen and oxygen appears to play an important role.

Highly-enhanced reflow characteristics of sputter deposited Cu interconnections of large scale integrated devices by optimizing sputtering conditions

Improving the reflow characteristics of sputtered Cu films was attempted by optimizing the sputtering conditions. The reflow characteristics of films deposited under various sputtering conditions were evaluated by measuring their filling level in via holes. It was found that the reflow characteristics of the Cu films are strongly influenced by the deposition parameters. Deposition at low temperatures and the addition of H2 or N2 to the Ar sputtering gas had a significant influence on the reflow characteristics. Imperfections in the Cu films before and after the high-temperature, high-pressure treatments were investigated by positron annihilation spectroscopy. The results showed that low temperature and the addition of H2 or N2 led to films containing a large number of mono-vacancies, which accelerate atomic diffusion creep and dislocation core diffusion creep, improving the reflow characteristics of the Cu films.