Motoo Suwa

Stress migration resistance and contact characterization of Al–Pd–Si interconnects for very large scale integrations

Stress‐induced migration resistance and contacts to silicon of Al–0.3%Pd–1%Si interconnections for submicron process integrated circuit devices have been investigated and compared to Al–0.5%Cu–1%Si. Using creep tests, Pd has been found to be an excellent additional element to Al for reducing grain boundary diffusion. Palladium improved the stress‐induced migration resistance and reduced void and hillock formation in Al–Si conductors. Aluminum palladium precipitates in Al–Pd–Si alloys were found to be formed at higher temperatures than aluminum copper compounds and may be the reason for the improvements. The contact resistance of Al–Pd–Si was found to be similar to that of Al–Cu–Si. The reliability and yield data from 1.2 μm ROM test devices using Al–Pd–Si conductors is better than that of Al–Cu–Si conductors.

Effects of ultrahigh pressure on the crystallization temperature of Ni80P20 amorphous alloys

Abstract The pressure dependence of the crystallization temperature of splat-quenched Ni80P20 amorphous alloy ribbons has been studied over the pressure range 0–12 GPa. The crystallization temperature increased up to 10 GPa but a sudden drop occurred between 10 GPa and 10.5 GPa. The crystallization temperature then started to increase again with the increase in pressure. From the X-ray diffraction analysis and the transmission electron microscope observations, it was confirmed that the precipitates which appeared in the crystalline phase above 10 GPa were different from those observed in the lower pressure range. It becomes clear now that the aforementioned sudden drop is closely related to this difference in the precipitates.

High-reliability interconnections for ULSI using Al-Si-Pd-Nd/Mo layered films

An Al-Si-Pd-Nb alloy and a bilayered interconnection using this alloy with molybdenum have been investigated for ULSI interconnections. The electromigration lifetime of Al-Si-0.3 wt.% Pd-0.4 wt.% Nb was 5 times better as compared to Al-Si-0.5 wt.% Cu. In addition, layering this alloy with low-resistivity molybdenum improved the electromigration resistance considerably as compared to Al-Si-Cu layered with a high-resistivity metal, i.e., TiW. PdO was thought to be formed on the Al-Si-0.3 wt.% Pd-0.4 wt.% Nb alloys surface. The corrosion resistance of this alloy is much better than that of Al-Si-Cu because of this PdO. The ease in patterning the alloy at submicrometer linewidths (to 0.5 mu m) is quite satisfactory. The Al-Si-Pd-Nb/Mo layered system is therefore thought to be promising for future interconnection applications requiring durability against high current densities. >

Development of highly reliable Al-Si-Pd alloy interconnections for VLSI

An Al-Si-Pd alloy developed to improve the reliability of VLSI interconnections is discussed. Dry etching characteristics of the Al-Si-Pd alloy in submicrometer patterning proved to be much better than those of the Al-Si-Cu alloy used previously. Both electro- and stress-induced migration resistances of the Al-Si-Pd alloy were at least at the same level as those of the Al-Si-Cu alloy. Long-term reliability tests of resin-molded 1.3- mu m-process MOS devices using an Al-Si-Pd alloy interconnection gave satisfactory results. >

Development of a new flip-chip bonding process using multi-stacked /spl mu/-Au bumps

A novel flip-chip bonding (FCB) process was developed for improving the packaging of high frequency ICs operating at more than 10 GHz. This process, which uses multi-stacked /spl mu/-Au bumps, a lower apparatus cost than that of the FCB process using PbSn bumps. Tests have confirmed that the new FCB process is sufficiently reliable and that ICs made with this process has satisfactory high-frequency characteristics in IC operation of up to 15 GHz.<<ETX>>

Study on step coverage and (111) preferred orientation of aluminum film deposited by a new switching bias sputtering method

A new switching bias sputtering method capable of improving both the step coverage at the small contact holes and the quality of aluminum film has been developed for the formation of reliable interconnection of very large scale integrated circuits. The method features alternating operation of standard and bias sputtering in 5×10−4 Torr of argon. Aluminum film deposited using this method is seen to have seven times higher (111) orientation and four times higher electromigration resistance than simple bias‐sputtered aluminum film. Additionally, the step coverage is raised to 50% for a perpendicular step with 1 μm depth and 1 μm width.

Effects of Si on electromigration of Al–Cu–Si/TiN layered metallization

This work investigates electromigration (EM) in Al‐1 wt %Si, Al‐1 wt %Si‐0.5 wt % Cu and Al‐0.5 wt % Cu films with TiN barrier metals. The EM resistance of the Al‐0.5 wt % Cu layered metallization was found to be higher than that of the Al‐1 wt % Si‐0.5 wt % Cu layered metallization. The electromigration test results show that the reaction between Al films and underlying TiN layer degrades the electromigration performance of the Al‐1 wt % Si, Al‐1 wt % Si‐0.5 wt % Cu films. The reaction kinetics between Al alloys and TiN layers was studied by transmission electron microscopy and by investigating the resistance rise mechanism. Si was found to enhance thin intermetallic compound formation between the Al alloys and TiN on samples annealed at 450 °C.

Stress migration resistance of Al-Si-Pd alloy interconnects

Al-Si-Pd alloy with high stress-induced migration resistance was developed for VLSI interconnects. Pd was selected to depress grain boundary diffusion of Al alloys. The microstructures of Al matrices alloyed with Pd and Cu were investigated. The morphologies of precipitation in Al alloy conductors were examined after high-temperature heat treatment. The stress-induced migration resistances of the Al-Si-Pd and Al-Si-Cu were found to be influenced by the microstructures of Al matrices.<<ETX>>

Development of Corrosion-Resistant Aluminum Alloy Wire

A study was undertaken to find a corrosion-resistant aluminum alloy wire for improving the reliability of resin-molded devices using aluminum ball bonding. Palladium (Pd) was selected to be alloyed to aluminum matrix in order to improve corrosion resistance on the basis of the passivation theory that some metals are passivated when certain noble elements are dispersed uniformly in the matrix. AI-Pd alloy wires were made containing magnesium (Mg) which was added to improve bondability between aluminum balls and aluminum electrodes. It was found that AI-Pd-Mg alloy wires exhibit outstanding corrosion resistance compared with AI-Si and AI-Mg wires in both the pressure cooker test (PCT) and another test in which the wires were dipped into a bath of boiling water together with resin powder. Intergranular corrosion was recognized in AI-Si and AI-Mg wires in PCT. AI-Pd-Mg wire hardly corroded even after 500 h of PCT. Dissolution of the wires was observed in the dipping test. However, dissolution of the AI-Pd-Mg wire is much less than that of the other wires. A good quality aluminum ball, highstrength bonding, and good looping characteristics can be realized using AI-Pd-Mg wire. It is concluded that AI-Pd-Mg wire satisfies all the major requirements of bonding wires. The corrosion protection mechanism of AI-Pd alloy was explained as the strengthening of surface protection film on the aluminum matrix by the addition of Pd.

Influence of silicon concentration and layering of molybdenum silicide on the reliability of Al–Si–Cu interconnections

The influence of Si concentration on the stress induced migration resistance and the electrical resistivity change from silicon precipitates of Al–Si–Cu and Al–Si–Cu/MoSi2 interconnections was investigated. Electromigration of Al–Si–Cu/MoSi2 was examined as a function of MoSi2 thickness. A 1.5 wt. % Si concentration in aluminum alloy prevented grain growth and improved the stress induced migration resistance of the interconnections. However, this amount of Si addition caused resistance increases, because Si precipitates grew to the point that they were the same size as the interconnection linewidth. Layering of the Al–Si–Cu alloy containing 0.7 wt. % Si with MoSi2 improved the stress induced migration resistance of aluminum interconnections and prevented the resistance increases. Furthermore, increasing MoSi2 thickness improved electromigration resistance of layered interconnections. For MoSi2 thickness of >30 nm, electromigration resistance was better than that of single layer Al–Si–Cu interconnections.