Makiko Kageyama

AL-SI CRYSTALLOGRAPHIC-ORIENTATION TRANSITION IN AL-SI/TIN LAYERED STRUCTURES AND ELECTROMIGRATION PERFORMANCE AS INTERCONNECTS

Formation of aluminum‐silicon (Al‐Si) alloy/titanium nitride (TiN) layered structures and their electromigration (EM) performance have been investigated. The crystallographic structure of the TiN film changes with the sputter‐deposition conditions. A large negative substrate bias in reactive sputtering induces a structural transition in the TiN film. The crystal orientation normal to the film surface is easily controlled from the 〈111〉 to the 〈200〉 direction. The crystallographic orientation of the Al‐Si alloy film has been successfully controlled by the film deposition on an orientation controlled barrier TiN film. The Al‐Si alloy film grows epitaxially on TiN at the initial stage of deposition and this causes the Al‐Si alloy’s preferred orientation to the underlying TiN film. These layered structures with different levels of Al‐Si alloy preferred orientation have been subjected to EM tests, and the Al‐Si alloy film with stronger 〈111〉 orientation was found to have a longer EM lifetime. The best EM resis...

Formation of texture controlled aluminum and its migration performance in Al-Si/TiN stacked structure

An Al/TiN stacked structure has been investigated with respect to texture control of the films and their migration resistance. The Al on TiN film was observed to have the same preferred crystal orientation as the underlayer TiN film. TiN film texture can be controlled by changing its deposition conditions. Texture controlled Al films can be formed by using these TiN films. In these stacked structures, Al film with stronger

Microstructural study on the C49-to-C54 phase transformation in TiSi2 formed from preamorphization implantation

Microstructural characteristics of C49–TiSi2 in narrow lines have been investigated by transmission electron microscopy. The C49–TiSi2 formed by a preamorphization treatment exhibits small grain size and heavily faulted structures. C54 grains are also observed sporadically in the C49 matrix in spite of relatively low temperature range. Moreover, defects circularly distribute around a less-defective region in the vicinity of the C54 grains. The C49 grains in these regions are well aligned with identical crystallographic orientations. These results indicate two-dimensional growth of C49–TiSi2, and the circular defects are introduced by internal stress associated with the growth process. Also the internal stress is considered to enhance the heterogeneous C54 nucleation.

Texture Control and Electromigration Performance in Al-Based and Cu-Based Layered Interconnects

Texture control of Al and Cu by underlying refractory metal is discussed. Al texture can be controlled with underlayer metals like as Ti and TiN which have the same atomic arrangement within 3% misfits to Al. Cu texture can be also controlled by underlayer TiN in spite of a large difference in inter-atomic distance of Cu and TiN. Since the epitaxial growth of TiN on Cu is observed, it is suggested that epitaxial growth may occur at the early stage of Cu deposition on TiN. The electromigration performance was evaluated in double level interconnects with W-stud via. It is confirmed that highly textured Al and Cu have high electromigration resistance. Both the diffusion of Cu in Al-Cu and Al drift are suppressed in textured Al-alloy interconnects, and Cu drift is also suppressed in Cu damascene lines formed on textured TiN. Grain boundary diffusion and the interfacial diffusion would be suppressed in highly textured metals with underlayer and it is speculated that interfacial diffusion is more important in Cu damascene lines.

Effect of preamorphization implantation on C54–TiSi2 formation in salicided narrow lines

The effect of the preamorphization implantation (PAI) process on TiSi2 phase transformation has been investigated by using arrays of submicron TiSi2 lines. The C49–C54 transformation of TiSi2 during annealing is promoted by the PAI process. The promotion of phase transformation cannot be explained only by the difference in grain size of the C49–TiSi2; hence, the nucleation site density for the phase transformation was estimated. The epitaxial relation with the Si substrate also retards the C49–C54 phase transformation. The epitaxial growth of C49–TiSi2 on the Si substrate is observed in a large portion of C49–TiSi2 grains in the sample without PAI, whereas orientation of C49–TiSi2 in the sample with PAI has no relation to that of the Si substrate. Epitaxial C49–TiSi2 is more stable and is difficult to phase transform. After phase transformation, the C54–TiSi2 oriented to the 〈004〉 direction is predominant in the samples without PAI. The strong orientation of C54〈004〉 resulted from one-dimensional growth a...

Electromigration performance of Al–Si–Cu filled vias with titanium glue layer

Abstract Electromigration performance of vias filled with high temperature (480°C) sputtered Al alloys on Ti glue layers was investigated in comparison with W-stud vias. Electromigration lifetime and failure mode are quite different according to via structures and kinds of Al alloys used. Electromigration lifetime of W-stud via chain and Al–Cu filled via chain depends on the via to via distances, while that of Al–Si–Cu filled via chain does not depend on the via to via distances. Failure mode observations revealed that voids were formed only at a few locations in the test structure in Al–Si–Cu filled via chain while voids were formed at every via in W-stud via chains and Al–Cu filled via chains. It is supposed that Al moves through the Al–Si–Cu filled vias during electromigration test in spite of the existence of the Ti glue layer at the via bottom. The Al transportation, however, was prohibited at W-stud vias and Al–Cu filled vias. Glue Ti deposited at via bottom was converted to Al–Ti–Si alloy in Al–Si–Cu filled vias, while Al 3 Ti alloy was formed at Al–Cu filled via bottom. It is speculated that Al transportation occurs through via bottom Al–Ti–Si alloy layer during electromigration test in the case of Al–Si–Cu filled vias.

Transmission Electron Microscopic Studies of TiSi2 Microstructures and the C49-C54 Phase Transformation in Narrow Lines

Transmission electron microscopy was used to study phase transformation of TiSi2 from C49 to C54 phases. By the pre-amorphization implantation (PAI) treatment, the metastable C49 grain size is reduced and shows heavily defective structures. In particular, circular distributed defects surrounding a less-defective region are frequently observed for the C49 matrix. These regions are found to have mosaic structures while maintaining specific orientation. The results indicate two-dimensional growth of C49 from the less-defective region to the circular defective region. Furthermore, heterogeneous nucleation of C54 is often observed at the defective regions. This suggests local stress associated with this two-dimensional growth which enhances the heterogeneous nucleation of C54. On the contrary, strong epitaxial relationships between C49 grains and Si substrate are observed with high concentration in non-PAI samples. Since these C49 grains aligned on the substrate are considered to be stable even at relatively high temperatures, C54 nucleation sites are assumed to markedly decrease in narrow lines.

Deoxidization of Water Desorbed from APCVD TEOS ­ O 3 SiO2 Film with Thin Titanium Cap Film

The water absorption characteristics and desorption characteristics of atmospheric-pressure chemical vapor deposited (APCVD) tetraethylorthosilicate and ozone (TEOS-O 3 ) film have been studied in detail to apply TEOS-O 3 film to LSI intermetal dielectric film. TEOS-O 3 film absorbs a large amount of water from the air, and desorbs the water at 200°C or less. It has also been found that titanium thin film deposited on TEOS-O 3 film suppresses water desorption from TEOS-O 3 film completely. Titanium thin film deoxidizes water desorbed from TEOS-O 3 film to hydrogen even at 200°C or less. The reliability of aluminum wiring with TEOS-O 3 intermetal dielectric film has not been sufficient because of aluminum film bursting in the via-hole formed on TEOS-O 3 film during high-temperature storage testing at 150°C or more. However, if titanium thin film is used as the lowest layer of the accumulating aluminum wiring structure on TEOS-O 3 film, aluminum bursting in the via-hole is suppressed completely. We consider the aluminum bursting to be caused by water pressure during the high-temperature storage testing, and the suppression by the titanium thin film to be caused by titanium deoxidization of water to hydrogen.

Influence of Interface Structure between Overlayered Titanium Nitride Film and Aluminum on Multilayered Interconnects

Aluminum film with overlayered titanium nitride (TiN), which was formed as antireflective material, has been investigated. The effect of TiN film on aluminum film properties and the layered-metal line reliability as an interconnect depend on its deposition process. Aluminum grain enlargement after annealing was largely promoted by compressive stress of TiN, when TiN was deposited on aluminum after the aluminum was exposed to air. When TiN is deposited successively on aluminum in the same vacuum, aluminum grain size does not increase with TiN compressive stress. In this case, TiN has been found to have epitaxial continuity with the underlayer aluminum. This crystal continuity suppresses Al atom movement. Electromigration resistance of the TiN/Al/TiN layered line was found to have a longer lifetime when the overlayered TiN was deposited successively on aluminum. It is considered that this crystal continuity also influences the electromigration resistance of the layered-metal lines.

Influence of Interface Structure between Overlayer TiN and Al on Multilayered Interconnects

With the frend of increasing packing density of VLSI, multilayered metallization came to be indispensable technique for high reliable interconnects. For Al-alloy lines with TiN barrier metal, relation between aluminum texture and underlayer TiN has been clarified by our group[]. Aluminum was found to have the same texture as underlayer TiN texture which can be controlled by changing deposition condition, and electro-migration resistance of Al/TiN layered line was shown to be improved by promoting Al<111> preferred oiientation. This time, the effect of TiN overlayer on Al-alloy was examined. Some investigation on electromigration of aluminum with W, TiW,TiN or MoSi* overlayer were reported[2],[3]. However, the effect of overlayer metal was not clear. TiN is one of the most effective anti-reflective material for patterning deep submicron lines, and TiN/Al[iN layered interconnects is the most prevailing structure. In addition, TiN, which has very close lattice constant as aluminum, is expected to improve the metal reliability. In this point of view, we investigated the Alalloy lines with TiN overlayer, and found that the effect of TiN is different if TiN was deposited successively in vacuum or not. Though aluminum grain enlargement is easy to occur for air exposed sample, the successive deposited sample is more reliable for electromigration because of continuous crystal sffucture at TiN and Al interface. PA4-3