Yasuhiko Kojima

Cu Wettability and Diffusion Barrier Property of Ru Thin Film for Cu Metallization

The main issue of Cu metallization is the electromigration of Cu through the interface between Cu and the barrier or capping layer. To improve electromigration resistance at the Cu and barrier metal interface, insertion of a glue layer which enhances the adhesion of Cu onto the under layer may be effective. The wettability of Cu on Ru and Ta glue layers was evaluated as the index of Cu adhesion strength onto glue layers. The wetting angle of Cu (43°) on a Ru substrate was three times lower than that of Cu (123°) on a Ta substrate after annealing. Lower wetting angle of Cu on a Ru substrate indicates a good adhesion property between Cu and Ru and may imply a high electromigration resistance. The better Cu wettability of Ru compared to Ta can be explained by the concept of lattice misfit. A Ru(002) plane has lower lattice misfit, which suggests lower interface energy, and enhanced the adhesion of Cu onto Ru. However, the Ru film showed poor Cu diffusion barrier properties, which suggests Ru should be used as a glue layer in combination with another barrier layer.

Material Consideration on Ta, Mo, Ru, and Os as Glue Layer for Ultra Large Scale Integration Cu Interconnects

The electromigration resistance of ultra-large scale integration (ULSI) Cu interconnects can be improved by inserting an adhesion promoter between Cu and the diffusion barrier. A metallurgical survey was accomplished to select the element having a good Cu adhesion property. For adoption as an interconnect material, it should have a low resistivity and should not react with Cu to avoid increasing the resistance of Cu interconnects. Ru, Os, Mo, W, and Ta satisfied the above conditions. The Cu adhesion property of these elements was estimated by the lattice misfit concept. The Cu adhesion property was experimentally examined and compared hcp elements (Ru and Os), which have a good matching interface with fcc Cu, with the bcc elements (Mo and Ta). Ru and Os, which had lower lattice misfit values, showed a better adhesion property than the bcc elements having higher lattice misfit values. Among these elements, Ru had the best Cu adhesion property and thus it can be an optimum glue layer element for Cu interconnects.

Influence of Crystal Orientation of Ru Under-Layer on Initial Growth of Copper Chemical Vapor Deposition

The effect of Ru crystal orientation on the deposition behavior of chemical vapor deposition (CVD) Cu was investigated. The crystal orientation of Ru films was modulated by adjusting sputtering temperature. Ru(001) and random orientation films were obtained by sputtering at 300 °C and room temperature, respectively. CVD Cu on Ru with the (001) crystal orientation had a smooth morphology and a strong (111) peak. However, CVD Cu on the Ru film with the random orientation had a rough surface and a random orientation. A low lattice misfit between Cu(111) and Ru(001) realized a good morphology and a strong (111) orientation of CVD Cu films, which coincide with our lattice misfit concept.

ESR detection of non-equivalent scandium trimer

The existence of non-equivalent Sc trimer was confirmed by ESR measurements after the HPLC separation of a Sc-trimer enriched portion from carbon soot. The newly observed ESR signal consists of well-resolved hyperfine structures reproducible by a non-equivalent Se trimer structure. The observed hyperfine structures and line widths were compared with those of Sc@C82 and Sc3@C82, by which the stabilization of the non-equivalent trimer structure is discussed in terms of the hindered molecular motion of the trimer embedded in a fullerene-like carbon network.

Addition of Chemicals for Deposition of Copper by Chemical Vapor Deposition Using Cu(hfac)tmvs Precursor

The effects of some additive chemicals on the deposition of copper by chemical vapor deposition with Cu(hfac)tmvs have been investigated. Diethylamine and acetaldehyde had no effect on copper film deposition. Use of triethylsilanol slightly increased the deposition rate, with a maximum at the molecular triethylsilanol/Cu(hfac)tmvs ratio of 0.4%. Water and formic acid markedly increased the deposition rate and the number of reactions per molecule of these additives was determined to be more than one, implying that they act as catalysts. The effects of water and formic acid on copper films purity have also been investigated.

Stability of Metallofullerene LaC82 on UV Light Irradiation.

The effect of UV light on the stability of metallofullerenes containing lanthanum was investigated using laser desorption time-of-flight mass spectrometry and ESR. The decomposition rate of LaC82 in toluene solution was about 100 times faster than that of C60. Moreover, decomposition of both metallofullerene and C60 toluene solutions induced by UV light irradiation in air would mainly occur without oxide formation. In these decomposition reactions by UV light irradiation, both dissolved oxygen and photo excited toluene molecules would play important roles.