Atsushi Noya

Properties of TaNx films as diffusion barriers in the thermally stable Cu/Si contact systems

The properties of Ta2N and TaN compound films as a diffusion barrier between Cu and Si have been investigated by examining compositional depth profiles obtained by Auger electron spectroscopy. The use of a Ta2N barrier is effective for improving the thermal stability of the contact system by raising the silicide formation temperature as compared with the use of a Ta barrier. The contact system of Cu/TaN/Si is fairly stable due to annealing for 1 h even at 750 °C. This is interpreted by the stability of the TaN compound, which is chemically inert to Si as well as Cu at this temperature. Eliminating the grain growth of TaN due to annealing is also effective for suppressing the physical diffusion through the barrier.

Diffusion barrier properties of ZrN films in the Cu/Si contact systems

A thermally stable Cu/ZrN/Si contact system using a ZrN diffusion barrier of low resistivity was developed. In the contact system, the growth of an oriented ZrN(100) layer on Si(100), and subsequent growth of a Cu(110) layer on ZrN(100) were observed. The obtained contact system was fairly stable after annealing even at 750 °C for 1 h without any diffusion and/or reactions at either the interface of Cu/ZrN or ZrN/Si. It was revealed that the ZrN layer with low electrical resistivity showed a high performance as a diffusion barrier, and was one of the excellent materials for the use in ultralarge scale integration technology.

Preparation of WNx Films and Their Diffusion Barrier Properties in Cu/Si Contact Systems.

We prepared thin WNx films with various compositions by reactive sputtering and examined their characterizations and barrier properties applied to Cu/WNx /Si contact systems. The results indicate that the W65N35 barrier, which is in the W2N phase with preferred orientation in the (111) plane, shows excellent barrier properties for Cu metallization. The obtained Cu/W2N/Si system is fairly stable without diffusion and/or reaction even after annealing at 800° C for 1 h. This system stability is speculated to originate from the thermal stability of the W2N film itself, which is chemically inert and scarcely changes in structure due to annealing.

Stoichiometry of Ta–N Film and Its Application for Diffusion Barrier in the Al3Ta/Ta–N/Si Contact System

In order to obtain a stable contact structure applicable to Si–LSI thin film technology, we have produced the contact structure of Al3Ta/Ta–N/Si by interposing the Ta–N film as a diffusion barrier between Al3Ta film and Si substrate. The contact structure was heat-treated at various temperatures in vacuum, and the behavior of mass transport across the interfaces of both Al3Ta/Ta–N and Ta–N/Si caused by the heating process was examined by Auger depth analysis. Also, on the basis of X-ray diffraction and XPS analysis, the barrier properties of the Ta–N film were examined with respect to the crystalline state and the chemical bonding state of the film. It is revealed that the thermal stability of this contact structure is closely related to the stoichiometry of the Ta–N film used as a diffusion barrier.

Solid-phase reactions of diffusion barriers of Ti and TiN to copper layers on SiO2

Thin films of Ti and TiN interposed between the Cu layer and SiO2 are examined as a diffusion barrier as well as an adhesion-promoting layer for Cu metallization technology. Solid-phase reactions and/or interdiffusion taking place in the Cu/Ti/ SiO2/Si and Cu/TiN/ SiO2/Si systems are examined by X-ray diffraction and the depth profiling method using Auger electron spectroscopy and X-ray photoelectron spectroscopy. The reduction of SiO2 through the formation of Ti-oxides occurs at the Ti/ SiO2 interface even in the as-deposited Cu/Ti/ SiO2/Si system. In addition to this, the formation of Ti5Si3 and interdiffusion which result in the formation of Cu–Ti intermetallic compounds due to annealing at 450° C are evident, and lead to intermixing of the whole system. The use of TiN instead of Ti drastically suppresses the reaction and interdiffusion, and the Cu/TiN/ SiO2/Si system is stable even after annealing at 850° C, though the incorporation of a small amount of Ti into the Cu layer is observed.

Formation of metal‐rich silicides in the initial stage of interfacial reactions in Nb/Si systems

The interfacial reaction of Nb thin films on (100) Si indicates the first phase nucleation of metal‐rich silicide and the occurrence of multiphases under certain annealing conditions. Nb3Si was identified as being the first nucleated phase at the annealing temperature of 550 °C, and subsequently Nb5Si3 is found to be formed by annealing at 600 °C. The multiphases of Nb3Si, Nb5Si3, and NbSi2 were observed to be formed simultaneously in the specimen annealed at 650 °C. The growth of NbSi2 by the out‐diffusion of Si, which overcame the metal‐rich phase, was observed at annealing temperatures over 700 °C.

Auger electron spectroscopy study on the stability and the interfacial reaction of Ta, Ta-N and TaN films as a diffusion barrier between Cu9Al4 film and Si

The diffusion barrier properties of Ta, Ta-N and TaN films to Si and the Cu9Al4 compound have been studied by examining depth profiles obtained from Auger electron spectroscopy. The contact system degrades with the silicide formation at the interface between the barrier and the Si substrate. The silicide formation temperature of these films was 650°C for the Ta barrier and 700°C for the Ta-N one. The contact system using the TaN compound barrier tolerates a temperature of 750°C. Ta atoms are the diffusing species for silicide formation in the present study, which protects the contact system from catastrophic failure due to the intermixing of all elements at higher temperatures.

Application of thin nanocrystalline VN film as a high-performance diffusion barrier between Cu and SiO2

Thin nanocrystalline vanadium nitride (VN) films of low resistivity were examined as an extremely thin diffusion barrier to provide thermal stability in Cu∕VN∕SiO2∕Si systems. A 10-nm-thick VN barrier with grains ranging from several to ∼10nm in diameter provided excellent barrier properties. After annealing at 600°C for 1h, the barrier showed scarcely any change in structure and absence of Cu diffusion and/or decisive interfacial reaction in the system. This was interpreted to mean that the present barrier, which is made of a thermochemically stable δ-VN compound phase with a slightly nitrogen-rich composition and a nanocrystalline structure, was preferable to suppress the solid-phase reaction and/or diffusion, as well as the structural change upon annealing. It was revealed that the nanocrystalline VN barrier is an excellent candidate as a barrier in a forthcoming Cu metallization scheme.

Transmission electron microscopy of the sequence of phase formation in the interfacial solid-phase reactions in Ta/Si systems

The interfacial reaction of Ta thin films on (100) Si was investigated by high-resolution transmission electron microscopy. An amorphous layer was observed at the as-deposited Ta/Si interface. A phase of Ta5Si3 was first found to form at the interface between a Ta overlayer and the amorphous layer after annealing at 560 °C for 1 h. Annealing at 630 °C for 1 h led to the formation of another interlayer due to the outdiffusion of Si between the amorphous layer and Si. The phase in this interlayer transformed from a metastable one to TaSi2 due to annealing at 680 °C for 1 h. The first nucleation of Ta5Si3 at the interface between Ta and the amorphous layer implies that the initially formed amorphous layer has a metal-rich composition close to Ta5Si3. The formation of the interlayer between the amorphous layer and Si prior to the nucleation of TaSi2 was considered as a result of a kinetic constraint to favor the nucleation of TaSi2.

Thermal stability of Cu/W/Si contact systems using layers of Cu(111) and W(110) preferred orientations

A thermally stable Cu/W/Si contact system using Cu(111) and W(110) films with preferred orientations has been developed. The application of the W diffusion barrier with the [110] preferred orientation effectively suppresses the grain boundary diffusion of Si as well as the fast diffusion of Cu through the barrier due to annealing, resulting in raised silicidation temperatures above 670 °C and an effective suppression of Cu diffusion. The contact system tolerates annealing at 690 °C for 1 h, at which the W layer also stands as an effective barrier, although the W barrier is uniformly consumed by the silicidation reaction at the W/Si interface.