Si Contact System Research Articles

Effectiveness of Al12W Layer on Suppression of Spontaneous Reaction in Al/Al12W/W2N/Si Contact Systems

The effectiveness of the interposed Al12W layer in realizing a thermally stable Al/Al12W/W2N/Si contact was examined by varying its thickness. It was revealed that an interposed Al12W layer whose thickness is greater than the diffusion length of the species that participates in the spontaneous reaction of the Al12W formation upon annealing was required to realize a thermally stable interface in the contact. The effectiveness of the interposed Al12W layer depended on the kinetics of the spontaneous reaction between Al and W in the contact.

Mn(Thin-Film)/Si(Substrate) Contacts: Analysis of the Buried Interface by Soft X-Ray Emission Spectroscopy

Electron-probe soft X-ray emission spectroscopy (SXES) has been applied to the nondestructive analysis of the buried interface of a Mn(thin-film)/Si(substrate) contact system, where the energy of the primary electrons, Ep, is varied below 20 keV. An important point of this analysis is that SXES gives a specific signal for each chemical element in different chemical bonding states. The Mn(thin-film)/Si(100) specimen not subjected to heat treatment did not show any additional phase except for Mn and Si at the interface region within the detection limit of the present experiment. The specimen subjected to heat treatment at 350°C for 3 min showed a layered structure of Mn/MnSi/MnSi1.7/Si(100) from the top to the substrate.

Application of Al3Hf/Hf Bilayered Film as a Diffusion Barrier to Al Metallization System of Si Large-Scale Integration

We have attempted to improve the reliability of Al metallization system of Si-LSI, using Hf3Si2 silicide with the lowest contact resistivity. Al3Hf/Hf bilayered films were interposed as a diffusion barrier between Al and Si in order to realize both preservation of the Al overlayer and sufficiently low contact resistivity at the Si interface. We have investigated the interfacial solid-phase reaction of the Al/Al3Hf/Hf/Si contact system by means of X-ray diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses, and compared it with that of the Al/Hf/Si system. It is revealed that the Al/Al3Hf/Hf/Si system is satisfactorily stable up to 420°C at which the formation of the Hf3Si2 phase occurs at the Si interface.

Effect of H2O partial pressure and temperature during Ti sputtering on texture and electromigration in AlSiCu/Ti/TiN/Ti metallization

The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO2/Si substrates has been investigated. The Ti (002) and TiN (111) preferred texture of the films deposited at 350 °C was found to be improved drastically by increasing the H2O partial pressure from 1×10−9 to 3×10−8 Torr. Both the Ti (002) and TiN (111) texture showed a similar H2O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti (002) texture was attributed to the self-assembly of Ti atoms on the SiO2 surface, which had a low surface free energy due to the formation of surface OH groups. The AlSiCu/Ti/TiN/Ti layered film fabricated with the highly textured TiN/Ti film showed a strong Al (111) texture and had a smooth surface. Moreover, interconnects from this improved film had longer electromigration lifetimes. It was also confirmed that the increased H2O partial pressure (3×10−8 Torr) does not affect the contact resistance and junction leakage current of the AlSiCu/Ti/TiN/Ti/(n+Si or p+Si) contact system.

Investigation of Pt/Ta diffusion barrier using hybrid conductive oxide (RuO2) for high dielectric applications

The Pt/Ta diffusion barrier using hybrid conductive oxide (RuO2) for dynamic random access memory and ferroelectric random access memory capacitor bottom electrodes is proposed. The thermal stability of Pt+RuO2 (50 nm)/Ta+RuO2 (50 nm)/TiSi2/poly-Si/SiO2/Si contact system is investigated and compared to that of the Pt(50 nm)/Ta(50 nm)/TiSi2/poly-Si/SiO2/Si contact system. The Pt+RuO2/Ta+RuO2/TiSi2/poly-Si/SiO2/Si contact system sustained its structure up to 650 °C, whereas Pt/Ta/TiSi2/poly-Si/SiO2/Si contact system was completely degraded after annealing at 650 °C. In the former case, the addition of ruthenium dioxide (RuO2) into the Pt bottom electrode layer led to retardation of the oxygen indiffusion, preventing the indiffusion of oxygen up to 650 °C. In addition, the Ta+RuO2 diffusion barrier showed an amorphous structure and RuO2 is bound to the Ta matrix, inhibiting the interdiffusion of O, Pt, and Si through grain boundaries which can act as fast diffusion paths up to high temperatures. Therefore, it appeared that the barrier properties of Pt/Ta diffusion barrier are improved by using hybrid conductive oxide (RuO2).

Preparation of Cu 10Zr 7 Intermetallic Compound Film and Its Application as a Diffusion Barrier in Cu/Cu 10Zr 7/ZrN/Si Contact System

We investigated the diffusion barrier properties of Cu10Zr7 intermetallic compound film for possible application to Cu metallization technology. First, a Cu/Zr bilayered film was heat-treated in vacuum at various temperatures for 1h, to confirm the most stable Cu–Zr compound formed by solid-phase reaction. It was found that a single phase of Cu10Zr7 compound can be obtained at temperatures above 550°C and that this compound film is stable up to 600°C. On the other hand, by the co-sputtering method, although CuZr2–Cu10Zr7 mixture alloy film was prepared, no Cu10Zr7 single-phase compound film was obtained. We heat-treated the Cu/CuZr2–Cu10Zr7 bilayered film for 2h at 500°C, which was lower than the temperature necessary for the formation of Cu10Zr7 by solid-phase reaction. In this way, we prepared the stoichiometric Cu10Zr7 film. Then, we produced the Cu/Cu10Zr7/ZrN/Si contact system using this Cu10Zr7 film as a diffusion barrier and investigated its thermal stability. We found that the system is satisfactorily stable up to 650°C without any Si diffusion, although a slight diffusion of Cu was observed at the interface of Cu/Cu10Zr7.

Soft X-ray emission spectroscopy study of CaF 2(film)/Si(111): non-destructive buried interface analysis

A soft X-ray emission spectroscopy (SXES) study under an energetic electron irradiation is first applied to a non-destructive buried interface analysis of a CaF 2(film ∼ 40 nm)/Si(111) contact system, where the energy of primary electrons, E p, is ≤ 5 keV. The present work has explored the usefulness of the application of the SXES method to the interface study to give rise to the following findings: the CaF 2/Si(111) interface shows rather sharp transition from the top CaF 2 to the substrate Si, there certainly is a Ca-silicide layer at the CaF 2/Si(111) interface, the thickness of the silicide layer is estimated to be less than several nm, and the e-beam excited SXES non-destructive study is very powerful to analyze a specimen with rather thick top film (> 40 nm) and thin interface layer (< several nm).

Solid-Phase Reactions in Polymorphic Epitaxial Contact Systems of bfAl/YSi2-x/Si

Solid-phase reactions taking place in an epitaxial Al/YSi2-x /Si contact system are examined by X-ray diffraction and depth profiling using Auger electron spectroscopy. The diffusion of Al into YSi2-x and the subsequent reaction between Al and Y forming Al3Y take place after annealing for 1 h at 400 and 450° C, respectively. Although an out-diffusion of Si and Y leads to failure of the contact system, the distribution of Al is restricted to within the initially formed YSi2-x layer without forming Al spikes.

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.

The effect of carbon on strain relaxation and phase formation in the Ti/Si1−x−yGexCy/Si contact system

We report the first study of interfacial reactions of a metal with Si1−x−yGexCy epitaxially grown on Si. The Ti/Si1−x−yGexCy/Si (0&amp;lt;y&amp;lt;1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1−xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C-containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations.

Diffusion barrier effects of Al3Zr/Zr bilayered films interposed between Al and Si

AbstractThe interfacial solid‐phase reactions taking place in the Al/Al3Zr/Zr/Si contact systems have been investigated to evaluate the effectiveness of Al3Zr/Zr bilayered films as a diffusion barrier in Al‐metallization technology. The interposition of an intermediate Al3Zr layer can successfully suppress the possible spontaneous rections between the Al and Zr layers because nearly‐minimum free energy states are realized at interfaces of both Al/Al3Zr and Al3Zr/Zr. It is revealed that the present system tolerates heat treatment at temperatures of up to 470°C and the formation of a Zr‐silicide layer is observed at the Zr/Si interface after heat treatment in the temperature range of 450 ∼ 470°C.

Surface and Interface Analysis of Thin-Film/Si(Substrate) Contacts by Sxes

AbstractA soft X-ray emission spectroscopy(SXES) study under an energetic electron irradiation has been applied to a nondestructive buried interface analysis of a thin-film(e.g., Cr)/Si(substrate) contact system, where the energy of primary electrons, Ep , is less than 20keV. An interesting point of this method is that we can have a specific signal for an element to be used as a finger print, otherwise it is difficult. By using this e-beam excited SXES, we can study an interface buried deep in a rather thick overlayer, e.g., more than a hundred of nm, which is due to the fact that a mean free path of a soft X-ray or an X-ray production depth is much larger than the mean free path of an energetic electron in solids. Electronic structural study of silicides by SXES is also shown.

Rapid thermal nitridation of titanium on Cu/Si contact system

The TiN/TiSi 2 bilayer formed on n +- p junction by rapid thermal annealing (RTA) process was investigated. The various thicknesses of titanium film (10–80 nm) were sputtered on the n +Si substrate, then annealed by RTA at a temperature of 850°C for 30 s in a N 2 ambient (850°C/30 s/N 2). Junction leakage current densities of the n +- p diodes with TiN/TiSi 2 bilayers were about 10 nA/cm 2 for the initial Ti film thickness below 65 nm. The TiN/TiSi 2 bilayer was used as a diffusion barrier between Cu and n +Si. Leakage current density and specific contact resistance measurements were performed on the Cu/TiN/TiSi 2/ n +Si contact system after thermal stress on various temperatures (250–600°C). The thermal stability temperature increasing with initial Ti film thickness was found. The optimum diffusion barrier for Cu n + Si contact system was the sample with initial Ti film thickness 50 nm after RTA 850°C/30s/N 2. It possessed the TiN (20 nm)/TiSi 2 (100 nm) bilayer and the thermal stability temperature up to 475°C for the Cu n + Si contact system. We also displayed cross-section transmission electron microscopy and glancing angle incident X-ray diffraction data at various sintering temperatures and studied the failure mechanism.

Thermal stability study of TiN/TiSi2 diffusion barrier between Cu and n+Si

The failure mechanism of the TiN/TiSi2 bilayers as diffusion barriers between Cu and n+Si was investigated. The TiN/TiSi2 bilayers were formed by either annealing Ti (50 nm)/n+Si via various rapid thermal processes or reactively sputtering TiN (50 nm) on TiSi2. The degradation study of the Cu/TiN/TiSi2/n+Si contact system was undertaken by scanning electron microscopy, cross-section transmission electron microscopy (XTEM), secondary-ion-mass spectrometry (SIMS), and diode leakage current and contact resistance measurements. Leakage current measurements indicated no deterioration of n+-p diode junctions up to 475 °C for 30 min in a N2 ambient. For the sintering temperature at 500 °C, the leakage current increased abruptly and SIMS profiles revealed a large amount of Cu atoms diffusing into the junctions of n+-p diodes. XTEM showed that the small pyramidal-shaped Cu3Si crystallite (with a size 0.25 μm) precipitated in the n+Si substrate. The formation of Cu3Si increased the occupied volume, then generated the gap between TiSi2 and n+Si, and gradually increased the specific contact resistance. The diffusion resistance, depending on the thickness of TiN film, was also observed.

Effect of the phase transition of Ti silicide on the thermal stability of Si‐interface in the Cu/CuTi2/Ti/Si contact system

AbstractIn an attempt to realize a stable Cu metallization in Si‐LSI, a Cu/CuTi2/Ti/Si contact system was prepared and its thermal stability was studied. As a result, although the phase transition from the intermediate CuTi2 phase to the CuTi phase was observed with increasing annealing temperature in the contact system, the interface between the metallization layers (Cu and CuTi) and Si in the system suppressed the excess diffusion of Si at temperatures up to 570°C. the reason is that the Ti silicide formed at the Si interface acts as an Si diffusion barrier until its chemical state transforms into TiSi2, which is the final phase of Ti silicide. However, the contact system failed due to a direct chemical reaction between Ti and/or Cu in CuTi and Si which diffused into the upper layer through TiSi2 when Ti silicide at Ti/Si interface formed TiSi2 at 600°C. Then the contact system resulted in the phase‐separated bilayer structure of silicide. It was revealed from these results with the thermal stability of this contact system is related closely to the phase transition of the Ti silicide layer at the Si interface with increasing annealing temperature.

Auger electron spectroscopy study on the thermal stability of the Al/Al12W/W2N/Si contact system

The thermal stability of the Al/Al12W/W2N/Si contact system has been studied using Auger electron spectroscopy analysis. The interposed Al12W layer between the Al overlayer and the W2N barrier layer effectively suppresses the possible spontaneous reaction between Al and W, which can be carried out by bringing about a chemical equilibrium state at each interface of Al/Al12W and Al12W/W2N. This is achieved by the successive combination of the thin-film assembly; the materials bordering each other consist of one common constituent metal and form a compound at least on one side, which leads the interfaces to a lower free-energy state, i.e., an equilibrium. It is shown that the present contact system tolerating heat treatment at temperatures up to 600 °C is one of the most stable multilayered configurations among those of Al metallization technology.

Thermal Stability Study on Cu/Tin/TiSi2/Si

ABSTRACTWe have investigated TiN/TiSi2 films as diffusion barriers between copper and silicon. The TiN/TiSi2 films were formed by annealing Ti/Si via rapid thermal process at a temperature of 850'C for 30 seconds in N2 ambient. The contact resistance and leakage current of the Cu/TiN/TiSi 2/n+-p Si contact system were measured after sintering at 350-600°C for 30 minutes in an N2 ambient. We found an abrupt increase of contact resistance occurred at a sintering temperature of 600°C. From the leakage current of n+-p diode, we observed that the thermally stable temperature was about 475ycC. Meanwhile, XTEM photographs showed small Cu3Si crystallites with size of about 0.25 μm precipitated in the n+Si substrate at a sintering temperature 500°C. The formation of Cu3Si increases the occupied volume, generates the gap between TiSi2 and n+Si, and gradually increases the specific contact resistance. SIMS profiles also showed that a certain amount of Cu atoms diffused into the n+-p Si junction and that Si atoms existed in the Cu film. The Cu3Si formation across the n+-p junction can explain the abrupt increase in the leakage current measurement at 500°C. So the failure mechanisms for contact resistance and leakage current are different.

Influence of contact treatments on the electrical characteristics of shallow-junction titanium-based contacts

A comparison of the electrical characteristics of Al-Si/TiW/TiSi 2/Si, Al-Si/TiW/Ti/Si and Al-Si/Si contact structures has been carried out. The influence of a contact implantation and anneal on the electrical characteristics of the TiSi 2 contacted shallow junctions has also been investigated. Compared with the Al-Si/TiW/TiSi 2/Si contact system, the Al-Si/TiW/Ti/Si contact was shown to be a more suitable metalization scheme for the shallow junction contact technology, due to its lower contact resistance and junction leakage as well as its simplicity of fabrication process. The contact resistance of the Ti/ n +-Si system was found to be lower than that of the TiSi 2/ n +-Si system. The low contact resistance of Ti/ n +-Si3 is attributed to the presence of a uniform amorphous interlayer as well as significantly less influence of As on Ti/a-alloy/ n +-Si compared to TiSi 2/ n +. A contact anneal was found to reduce contact resistance for both TiSi 2/ n +-Si and TiSi 2/ p +-Si contact systems. With an additional P + implantation and anneal, the contact resistances are drastically reduced for the n +-Si contacts. On the other hand, a B + contact implantation and anneal did not significantly improve the contact performance of the TiSi 2/ p +-Si system. The difference is thought to arise from the lower degree of recovery of B + implantation damage resulted from the contact implantation of TiSi 2/ p +-Si contact compared to that of TiSi 2/ n +-Si contact. The addition of the contact P + implantation increased the total dopant concentration underneath the surface to such an extent that it leads to a reduction in contact resistance.

Electronic and atomic structures of metal(Ni, Co, Au) /Si(111) contacts: soft X-ray spectroscopy and photoelectron spectroscopy

A nondestructive surface and interface structure analysis was successfully carried out using the soft X-ray emission spectroscopy (SXES) method for transition metal (Ni, Co) silicides and metal(very-thin-layer)/Si(substrate) contact systems. The method is based on the following facts: (1) the Si L 2.3 valence band SXES spectrum of a Si-compound (or alloy) shows a clear difference from that of Si crystal. (2) The soft X-ray production depth increases with increasing incident electron energy. The valence band electronic structure was also discussed in comparison with the X-ray photoelectron spectroscopy study.

Sxes Study of Transition Metal Silicide Films and their Contacts to Semiconductors

AbstractSpectra obtained by a new soft x-ray emission spectroscopy(SXES) apparatus again exhibited clear differences among Si-compounds and Si crystal. A non-destructive analysis of an annealed transition metal(TMSi:film)/Si(111) contact system was carried out using either the distinct differences of Si L2, 3 SXES spectra between TMSi's and Si single crystals or the fad that the soft x-ray production depth increases in a solid with the energy of the primary electron, Ep. It was shown that the apparatus was capable of exploring electronic and atomic structures of a multi-layered contact system grown on a Si(111) substrate.