Yasushi Koubuchi

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.

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. >

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.

Corrosion resistance of Al-Pd-Si conductor

An Al-Pd-Si alloy conductor which has higher corrosion resistance than an Al-Si conductor after resin molding is discussed. A palladium oxide-rich (PdO-rich) area is formed by annealing in the surface oxide film on the Al-Pd-Si alloy conductors. It is responsible for the increased corrosion resistance of Al-Pd-Si with over 0.3 wt.% Pd. >

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.

Interaction between Al-Si-Cu alloys and MoSi2

The interaction at the metal–metal interface of the Al–Si–Cu/MoSi2 bilayer system has been investigated as a function of the Cu concentration. The Al in the Al–Si–Cu alloy reacts with the MoSi2 at temperatures above 400 °C. Al atoms diffuse into the MoSi2 and the excess Si diffuses into the Al layer. After the reaction, the amorphous MoSi2 becomes crystalline Mo(Al,Si)2. The excess Si in the MoSi2 layer forms precipitates in the Al layer. The Cu concentration in the Al alloy affects the reaction rate with 1% Cu having the largest effect followed by 0.5% Cu and then 3% Cu. A model is presented that explains this phenomenon. The Al–Si alloy without Cu does not react with MoSi2 below 450 °C.

Photochemical Characterization of the Surface Oxide Films of Al‐Pd‐Si and Al‐Si

The effect of Pd addition to the Al alloy on the photoelectrochemical response is described. The oxide films are characterized by photoelectrochemical methods. The addition of Pd decreases the photocurrent during illumination. The properties of the surface oxide films on thin Al‐Pd‐Si and Al‐Si alloy films are discussed. The surface oxide film property is related to the increased corrosion resistance of Al‐Pd‐Si. A model of the aluminum oxide film structure on the Al‐Pd‐Si film is also proposed.