Characterization of Self-Formed Ti-Rich Interface Layers in Cu(Ti)/Low-k Samples

Abstract

In our previous studies, thin Ti-rich diffusion barrier layers were found to be formed at the interface between Cu(Ti) films and SiO 2 /Si substrates after annealing at elevated temperatures. This technique was called self-formation of the diffusion barrier, and is attractive for fabrication of ultralarge-scale integrated (ULSI) interconnects. In the present study, we investigated the applicability of this technique to Cu(Ti) alloy films which were deposited on low dielectric constant (low-k) materials (SiO x C y ), SiCO, and SiCN dielectric layers, which are potential dielectric layers for future ULSI Si devices. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary-ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) films. It was concluded that the Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The primary factor to control the composition of the self-formed Ti-rich interface layers was the C concentration in the dielectric layers rather than the enthalpy of formation of the Ti compounds (TiC, TiSi, and TiN). Crystalline TiC was formed on the dielectric layers with a C concentration higher than 17 at.%.

Effects of Dielectric-Layer Composition on Growth of Self-Formed Ti-Rich Barrier Layers in Cu(1 at%Ti)/Low-k Samples

“…As we mentioned in the previous study, 15) the C concentration in the dielectric layers was believed to play an important role in determining compositions of the self-formed Ti-rich interface layers. Although the Si concentration in the low-k layers is similar, the C concentration of 14 at% in the low-k4 layer is lower than that in the low-k1 (17 at%).…”

“…In the previous study, 15) Ti segregation was to occur at the Cu(Ti)/dielectric-layer interface and the Cu(Ti) surface after annealing at Ar atmosphere. In the present study, Ti segregation was observed only at the interface after annealing in UHV.…”

“…This is similar to the result in which the formation of TiC or TiSi at the Ti-rich interface layers was determined by the C concentration in the dielectric layers. 15) The resistivity decrease for the annealed Cu(Ti)/low-k3 and Cu(Ti)/low-k4 samples from 400 C to 500 C was smaller than those of Cu(Ti)/low-k1 and Cu(Ti)/low-k2 samples. However, the resistivity decrease from 500 C to 600 C was larger.…”

“…In addition to formation of amorphous Ti oxides in the Ti-rich interface layers in all the samples, formation of TiC was observed in the Cu(Ti)/ low-k1, Cu(Ti)/SiCO and Cu(Ti)/SiCN samples, while formation of TiSi was observed in the Cu(Ti)/SiO 2 and Cu(Ti)/ low-k4 samples after annealing at 400 C. This is consistent with the previous study. 15) 3.3 Growth of the self-formed Ti-rich interface layers…”

“…We recently succeeded in forming Ti-rich barrier layers using Cu(Ti) alloy films prepared on SiO 2 /Si substrates after annealing at 400 C. [12][13][14] In our previous study, 15) seven dielectric layers such as low-k1(SiO x C y ), low-k2, low-k3, low-k4, SiCO, SiCN and SiO 2 layers were prepared and thin Ti-rich diffusion barrier layers were found to be formed at the interface between the Cu(Ti) films and the dielectric-layer/Si substrates after annealing at elevated temperatures. The Tirich interface layers formed in the Cu(10 at%Ti) alloy films deposited on the dielectric layers after annealing at 500 and 600 C consisted of crystalline TiC or TiSi in addition to amorphous Ti oxides.…”