Segregation of Si and Cu at AlSiCu / TiN Interfaces
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A. KAMEYAMA, A. YAOITA, T. KITANO, AND S. SAITO NEC Corporation, ULSI Device Development Laboratories, Sagamihara, Kanagawa 229, Japan
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Shimokuzawa,
ABSTRACT The behavior of Cu and Si in the Al-alloy / TiN interface has been demonstrated by techniques of SIMS, GDS, XRD and AES. Cu and Si were observed to segregate at the AlSiCu / TiN interfaces just after sputtered. This segregation occurred to form a layered structure, not an island one. As these materials at the interface remained to exist even after annealing, the distribution of Cu and Si after annealing would be governed by that just as sputtered. The segregation behavior of Cu in A1Cu / TiN structure was the same as that of AlSiCu / TiN.
INTRODUCTION In order to improve circuit reliability, it is important to understand the stability of thin films and the interfacial reactions. Al / TiN structures have been widely used for VLSIs interconnection. However, this layered structure has a problem such as the increase of contact resistance by annealing. Wittmer found that Al had decomposed TiN to form AIN and TiA13 after annealingi. Similar results have been shown by other workers 2 -4 . Though TiN has been utilized as barrier material to suppress interfacial reaction between Al and Si,
it reacts Al itself to increase contact resistance 4 . Small amounts of Cu and Si have been added to Al to obtain higher electromigration performance. It is of interest to know the behavior of these additive materials, especially at the AlSiCu / TiN interface in the point of view of circuit reliability. In this work, we have demonstrated the segregation phenomenon of Si and Cu at the AlSiCu / TiN interface. To clarify this, behavior of Si and Cu was investigated from the points of TiN-sputtering conditions, annealing treatments and Al-alloy thickness.
EXPERIMENTAL In this study, we used several kinds of layered structures: (1) AlSiCu(200 nm)/ barrier metal(30-80 nm) / AlSiCu(200 nm) / Si02 / Si substrate, which barrier metal was TiN / Ti or Ti, (2) AlSiCu(100 nm) / TiNx (100 nm) / Si02 / Si substrate, where x was obtained during the TiN reactive sputtering process by varying the N2 / Ar ratio in the gas mixture 2,5, (3) Al-alloy(10 - 100 nm) / TiN (100 nm) / Si02 / Si substrate, which Al-alloy was AlSiCu or AICu. In these work, Si or Cu content was I % or 0.5%, respectively. For the first series of structures, Al-alloy films were deposited by conventional reflow sputtering at 400 - 450 VC.The other structures were fabricated as follows; Al-alloy and 407 Mat. Res. Soc. Symp. Proc. Vol. 382 01995 Materials Research Society
barrier metal were consecutively deposited without exposing to air at room temperature, and then, some part of these samples were annealed at 350 - 550 'C for 15 minutes under nitrogen ambient. Secondary Ion Mass Spectrometry (SIMS) and Glow Discharge Spectroscopy (GDS) were used to examine depth profiles. Structural analysis was carried out by X-Ray reflective diffraction (XRD). Elemental analysis was performed by Auger Electron Spectrometry (AES).
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