Yusuke Harada

Study of crystal orientation in Cu film on TiN layered structures

The effect of underlayer texture on Cu film orientation has been studied. Cu texture correlates well with the underlayer texture. The Cu〈111〉 crystallographic orientation is enhanced on TiN film with a strong TiN〈111〉 orientation. Cu preferred orientation can be controlled by choosing an appropriate underlayer. Cross-sectional transmission electron microscope observation revealed that the Cu(111) plane grows epitaxially on the TiN(111) plane in spite of the large lattice mismatch between Cu and TiN. The atomic arrangement between Cu(111) and TiN(111) planes in TiN film deposited on Cu film has a rotational angle within ±10° around the 〈111〉 axis. On the other hand, in Cu film deposited on TiN film, there are two rotational angles: a rotational angle of 25°–30° in large Cu grain region and little rotation with rotational angle distributions less than 10° in a small Cu grain region. These results can be explained by consideration of superlattice mismatch. Cu(111) plane rotation occurs so as to have more ene...

Texture and electromigration performance in damascene interconnects formed by reflow sputtered Cu film

We have investigated the Cu texture in damascene interconnect structures formed by the reflow method of sputtered Cu film and electromigration (EM) performance in Cu damascene interconnects. The texture of reflowed Cu film depends on Cu deposition temperature and line width. Improved 〈111〉 texture in blanket films is obtained when Cu is deposited at temperatures over 200 °C. However, Cu films form voids in the trench patterns at deposition temperatures of 350 °C or more, and the voids cannot be filled even after the reflow process. Thus, it is necessary to choose the optimum deposition temperature to fabricate void-free Cu damascene interconnects. It was found that the Cu (111) peak intensity in reflowed Cu lines measured by using x-ray diffraction decreases as trench width decreases. This can be explained by aspect ratio changes of Cu lines in trenches, which affect the dominating Cu texture components originating from sidewall or bottom nucleations. Underlayer metals at sidewalls affect the Cu texture. ...

Cu crystallographic texture control in Cu/refractory-metal layered structure as interconnects

The effect of underlayer texture on Cu film orientation has been studied. The crystallographic orientation of sputter-deposited Cu film depends strongly on the underlayer refractory-materials. Cu (111) orientation can be controlled by changing the preferred orientation of the TiN underlayer that has the same cubic structure as Cu. TEM observation of the Cu/RTN–TiN interface has revealed that the Cu (111) plane grows epitaxially on the TiN (111) plane. It has been also clarified that the atomic arrangement between the Cu (111) and TiN (111) planes has a rotational angle within ±10° around the 〈111〉 axis.

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...

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.

Oxidation and Reduction Characteristics of Sputter-Deposited Cu Thin Films

The oxidation and reduction characteristics of sputter-deposited Cu thin film with a preferred orientation have been studied. It was found that Cu oxide, which is identified as Cu 2 O phase, is easily formed by annealing at 200°C in an O 2 ambient. The linear relation between Cu 2 O thickness and the square root of oxidation time indicates that the oxidation process of Cu films obeys a parabolic rate law at temperatures from 200 to 280°C. The activation energy of the oxidation reaction in the Cu film was 0.89 eV. The oxidized Cu films were reduced by H 2 annealing at 300°C. The Cu 2 O formed in the Cu metal of a partially oxidized film was reduced at about 5 min, and the sheet resistance decreased to that of an as-deposited Cu film. The sheet resistance of a fully oxidized Cu film decreased with annealing time and saturated after about 10 min. As a result, the preoxidation sheet resistance could not be recovered. This incomplete recovery is due to the formation of voids in the reduced Cu film. Void-free reduced Cu films with low sheet resistance can be obtained by using appropriate temperatures and pressures during the H 2 annealing.