Yukimasa Yoshida

A New High-Density Plasma Etching System Using A Dipole-Ring Magnet

A new high-density plasma etching system has been developed using a dipole-ring magnet (DRM). The system utilizes a parallel magnetic field up to 600 G with excellent uniformity extending over 250 mm in diameter. The nonuniformity of plasma was compared with that of a conventional permanent-magnet-enhanced plasma using a gate oxide integrity test. The plasma generated using DRM produced no gate oxide degradation, while the conventional magnetron plasma produced some gate oxide degradation under the most highly accelerated conditions. Si etch rate is shown to depend strongly on magnetic field strength, increasing from 1.3 µm/min at 120 G to 2.1 µm/min at 600 G.

Mechanism of corrosion in Al-Si-Cu

An Al-Cu local cell was formed between the Cu precipitation and adjacent Al in an Al-Si-Cu alloy when Cu was added in excess to the alloy. Once an Al-Cu local cell was formed, corrosion took place simply by dipping the alloy in deionized water without any contamination. Furthermore, it was found that corrosion was enhanced at the Al-Si-Cu lines in contact with the p+-n junction of Si. The reason for this is that holes are injected into Al-Si-Cu from p+-Si due to electromotive force produced by light irradiation and an external circuit connecting the alloy and n-Si formed by the adsorption of moisture on the surface. Furthermore, it was found that the irradiation of light with a wavelength between 320 to 380 nm was most effective in enhancing the corrosion reaction.

Profile Control of SiO2 Trench Etching for Damascene Interconnection Process

The purpose of the present study is to reveal a microtrench generation mechanism in the damascene trench etch process for SiO2 film. Experiments are discussed for the CO gas flow and the pressure change, employing a C4F8/CO magnetron etch system. Increasing the CO gas flow or the pressure prevents the microtrench generation. Moreover, the microtrench ratio A/B that is defined by the depth at the edge of the trench bottom, A and the trench depth at the center of the trench bottom, B becomes higher in accordance with increasing larger space size. In previous reports, the main effect of CO gas and pressure increase is identified as decreasing CFx radical density by dilution of C4F8 or by increasing the residence time. The reduction of CFx radical flux may prevent microtrench generation by decreasing the formation of fluorocarbon film at the trench bottom. These results suggest that the microtrench generation is caused by thicker formation of fluorocarbon films at the center of the trench bottom which has a larger solid angle than at the edge of the trench bottom.

Microtrench Generation in SiO2 Trench Etching for Damascene Interconnection Process

The mechanism of microtrench generation in SiO2 trench etching in fluorocarbon gas chemistry is presented using the magnetron etch system under a 40–80 mTorr pressure condition. In the previous study, we pointed out that the microtrench is caused by the etch rate increase at the trench bottom edge where the fluorocarbon film is thin, because the thicker fluorocarbon film was formed more easily at the center of the trench bottom where the solid angle is larger than at the edge of the trench bottom. In this study, the experimental condition is extended to lower pressures. The microtrench ratio becomes higher in accordance with a larger pattern size at pressures higher than 40 mTorr. However, the pattern dependence of the microtrench ratio is reversed at 20 mTorr. This is explained by the effect of a constant residence time, the dilute gas effect, and the inverse-reactive ion etching (RIE) lag which is observed at 20 mTorr. In conclusion, the microtrench formed by the shadowing effect for fluorocarbon radicals is offset by increasing the bombarded ions at the trench bottom with the decrease of pressure to a condition such as 20 mTorr pressure.

Dual Damascene Etching Process Using Sacrificial Spin-on-Glass Film

The dual damascene (DD) formation process for sub 0.2 µm feature size devices has been investigated. The via-first DD process, where via holes are first formed, followed by trench formation, used the antireflection film in via holes after the trench pattern lithography process. In subsequential trench etch process, crownlike etch residues of SiO2 were formed around via holes due to etch inhibiting effect of antireflection films in via holes. A spin-on-glass (SOG) film is filled in via holes as a sacrificial film before trench pattern lithography was used. It could eliminate the crownlike etch residues because of the absence of an antireflection film in via holes. Moreover, it could give via holes a rounded profile at their top edges. This DD process used for fabricating films with no etch residues and rounded via holes reduces the aspect ratio of via holes and was confirmed to be effective for subsequential metal filling process.

Gate Oxide Breakdown Phenomena in Magnetron Plasma

Gate oxide breakdown phenomena in a magnetron plasma were investigated from the viewpoint of the effect of magnetic field distribution on the radiation damage. It was found that strong parallel and normal magnetic field regions simultaneously present on a wafer induced surface potential difference along the wafer, and could cause gate oxide breakdown. An optimized magnetic field, consisting of flux lines parallel to the wafer, was found to reduce the degradation of the gate oxide.