Ti Diffusion Barrier Research Articles

알루미늄 하부층이 탄소나노튜브의 성장 및 전계방출 특성에 미치는 영향

We studied the effect of an Al underlayer on the growth of carbon nanotubes (CNTs) and their field emission characteristics, First of all, CNTs were grown on the Invar catalyst layers with different thickness of 1 to 10 nm, showing that the CNT length was saturated for the catalyst 5 nm or thicker. The CNTs grown on the 5-nm-thick catalyst were <TEX>${\sim}10{\mu}m$</TEX> long and <TEX>${\sim}30nm$</TEX> in diameter. Second, an Al underlayer was applied between the catalyst layer and the Ti diffusion barrier to reduce the diameters of CNTs for better field emission properties by forming spherical Al oxide particles on which smaller catalyst nanoparticles would occur. The optimal thickness of an Al underlayer underneath the 5-nm-thick catalyst was <TEX>${\sim}15nm$</TEX>, producing the CNTs with the length of <TEX>${\sim}15{\mu}m$</TEX> and the diameter of <TEX>${\sim}15nm$</TEX>. The field emission measurements, following the tape activation, showed that the thinner and longer CNTs gave rise to better field emission performance with the lower turn-on and threshold electric fields.

Electrode metallization for high permittivity oxide RF thin film capacitors

High permittivity oxide thin film capacitors for RF components should be integrated on the chip to form a complete miniaturized module, with other semiconductor or thin film components such as inductors, isolation capacitors, and bias resistors. The quality factor ( Q) values of the RF capacitors are strongly dependent on electrode conductivity. Alas the best conducting metals (e.g. Ag, Cu, Al) are not thermodynamically stable during deposition of high permittivity oxide films with high temperature and oxygen atmosphere. On the other hand, refractory metals (e.g. Mo, W) endure high temperatures, but are prone to oxidation. Therefore, a diffusion barrier is a prerequisite for integrating refractory metals to achieve a stable electrode structure. In this study both non-reactive and sacrificial diffusion barriers with Mo metallization were investigated on Si/SiO 2 substrates. Also, noble metals (Au and Pt) as oxidation resistant materials were examined. Annealing at 650 °C was performed to the electrode stacks in an open-end air furnace and in vacuum with protective gas. The chemically inert materials Au and Pt failed to endure the high annealing temperature. Au became extremely rough and cracks appeared. Massive grain growth and adhesion loss occurred with Pt film. Mo electrode withstood the oxidizing ambient conditions with a sacrificial Si or Al–Ti diffusion barrier. Moderate increase in surface roughness was observed after the annealing due to oxidation. Also, thermally stable AlN, Si 3N 4, and SiO 2 diffusion barriers were able to block oxygen from the Mo electrode.

Formation of Ti diffusion barrier layers in Thin Cu(Ti) alloy films

In order to study a formation mechanism of thin Ti-rich layers formed on the surfaces of Cu(Ti) wires after annealing at elevated temperatures, the 300-nm-thick Cu(Ti) alloy films with Ti concentration of 1.3 at.% or 2.9 at.% were prepared on the SiO2/Si substrates by a co-sputter deposition technique. The electrical resistivity and microstructural analysis of these alloy films were carried out before and after annealing at 400°C. The Ti-rich layers with thickness of ∼15 nm were observed to form uniformly both at the film surface and the substrate interfaces in the Cu(2.9at.%Ti) films after annealing (which we call the self-formation of the layers) using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Both the resistivities and the microstructures of these Cu(Ti) films were found to depend strongly on the Ti concentrations. The resistivities of the films decreased upon annealing due to segregation of the supersaturated Ti solutes in the alloy films to both the top and bottom of the films. These Ti layers had excellent thermal stability and would be applicable to the self-formed diffusion barrier in Cu interconnects of highly integrated devices. The selection rules of the alloy elements for the barrier self-formation were proposed based on the present results.

A comparative molecular dynamics study of copper trench fill properties between Ta and Ti barrier layers

The copper atoms deposition on tantalum diffusion barrier layer in a damascene process was studied using molecular dynamics simulation with the embedded atom method (EAM) as interaction potential for the present alloy metal system which is based on invariance-preserving alloy model. The present results are discussed in terms of void formation, coverage percentage and alloy fraction. The effects of different process parameters on the trench-filling morphologies and microstructures including incident energies of depositing atoms and substrate temperatures were investigated. Comparing with Ti diffusion barrier under the same process parameters, it is found that due to better thermal stability that significant improvement in coverage percentage can be obtained using the tantalum barrier layer, especially at high incident energies and high substrate temperatures.

Effects of Ti Thickness on Ti Reactions in Cu/Ti/SiO2 System upon Annealing

The reactions of <TEX>$Cu/Ti/SiO_2$</TEX> structures at temperatures ranging from 200 to <TEX>$700^{\circ}C$</TEX> have been studied for various Ti thicknesses. The reaction products initially formed, at around <TEX>$300^{\circ}C$</TEX>, were a series of Cu-Ti intermetallics (<TEX>$Cu_3$</TEX>Ti/CuTi) with the oxygen dissolved in the Ti moving from the compounds into the remaining unreacted Ti. At <TEX>$500^{\circ}C$</TEX>, the <TEX>$Cu_3$</TEX>Ti was converted into Cu-rich intermetallics, <TEX>$Cu_4$</TEX>Ti, which grew at the expense of the CuTi due to the increased oxygen content in the Ti. In addition, the outdiffusion of Ti, to the Cu surface, and the <TEX>$Ti-SiO_2$</TEX> reactions, caused an abrupt increase in the oxygen content in the Ti layer, which placed thermodynamic restraints on further Ti reactions. Furthermore, thinner Ti layers showed a higher increasing rate of oxygen accumulation for the same consumption of Ti, which led to significantly reduced Ti consumption. The <TEX>$SiO_2$</TEX> film under the Ti diffusion barrier was more easily destroyed with increasing Ti thickness.

Real-time x-ray scattering study on the thermal evolution of interface roughness in CoSi2 formation

The thermal evolution of interface roughness during cobalt silicide formation in the Co/Ti/Si(001) and Co/Si(001) systems was investigated using real-time synchrotron x-ray scattering measurement. We find that the enhancement of the CoSi2/Si(001) interface roughness is caused by the retardation of silicide phase formation almost up to the CoSi2 nucleation temperature. In the Co(120 Å)/Ti(50 Å)/Si(001), the interface roughness increases only to 6 Å during silicidation, by suppressing the reaction between the Co overlayer and Si substrate with a Ti diffusion barrier nearly up to the CoSi2 nucleation temperature of 660 °C. In the Co(120 Å)/Si(001), however, the reaction already starts at a low temperature of 300 °C, resulting in a significant rise of the interface roughness up to 13 Å, which is mainly attributed to the formation of Si{111} facets that act as the nucleation sites of misoriented CoSi2 grains.

Low-temperature intermediate Au-Si wafer bonding; eutectic or silicide bond

The actual mechanism involved in Au-Si wafer bonding is controversial. Usually a titanium or chromium layer is deposited in between the (oxidized) silicon substrate and the gold layer to ensure adhesion. The resulting bond of two such wafers after annealing is generally considered to be eutectic, however, the bond temperature required is higher than would be expected from the Au-Si eutectic temperature. Moreover, silicide grains are formed at the bonding interface. In this paper it is proposed that the actual bonding is initiated by the dissolution of the oxide layer by silicidation of the titanium adhesion/barrier layer. The subsequent direct Au-Si contact enables the formation of the euteetic phase. The silicidation is required to obtain the eutectic alloy with 19 at.% Si despite the Ti diffusion barrier. The bonding temperature required is, therefore, set by the silicidation process rather than by the eutectic phase. Several experiments have been designed to support this theory. AI-Si eutectic bonding has been investigated, as it is not complicated by an adhesion metal and experiments demonstrate reliable bonding close to its eutectic temperature. Moreover, a Ti/Au/Si/Au stack has been fabricated to be used as a eutectic solder, giving bonding at a temperature not affected by silicidation. Keywords Eutectic bonding Gold Silicide bonding Silicon Wafer bonding

Ti-diffusion barrier in Cu-based metallization

Reliability investigations, with or without a barrier layer, have been performed to study the penetration of copper into thermal oxide as a function of temperature and applied electric field. No copper diffusion was detected without a barrier into 100 nm thick oxide for temperature stress as high as 450°C for one hour and for bias temperature stress (BTS) as high as 300°C for 8 h at 1 MV/cm. This absence of diffusion was observed when thermal annealing was performed under vacuum. A 20 nm thick titanium layer was used as a diffusion barrier/adhesion promoter between the copper and the oxide. The devices using this barrier were not affected by a temperature stress of 600°C for 10 h and by BTS even at 450°C for 2 h at 1 MV/cm.

Evaluation of in situ formed W–Ti and MoSi2 as a diffusion barrier to Al for CoSi2 silicided contact

A simple metallization process to form a shallow CoSi2 silicided contact and W–Ti diffusion barrier simultaneously has been developed. The process starts with depositions of a Co–Ti alloy layer and an overlying W layer on silicon wafers using a dual e-beam evaporation system; this is followed by a single-step annealing treatment in a normal flowing-nitrogen furnace. On the other hand, bilayer self-aligned shallow MoSi2/CoSi2/Si silicided contact can be derived from the W/Co–Mo/Si system by a two-step annealing treatment performed in the same environment. I–V characteristics for silicided p+n diodes with the diffusion barriers formed in situ were measured after they had been finished with Al deposition and post-Al annealing at temperatures from 350 to 600 °C in N2. For comparison, Al/CoSi2/p+n and Al/p+n structures were also investigated. It turns out that the integrity of Al/W–Ti/CoSi2/p+n and Al/MoSi2/CoSi2/p+n silicided contacts can be preserved up to 550 and 500 °C, respectively, for a 20 min annealing, while that of Al/CoSi2/p+n can be kept only up to 450 °C.

Nanoscale CoSi2 contact layer growth from deposited Co/Ti multilayers on Si substrates

In this letter, we describe procedures for forming continuous, planar, and thermally stable 12-nm-thick CoSi2 layers via Co/Si interaction through an interfacial Ti(O) diffusion barrier layer. Three Co and three Ti layers were deposited sequentially on Si-(100) substrates by dual source thermal evaporation with Ti as the first layer. Oxygen was found to be selectively incorporated into all Ti layers during deposition. Following a 550 °C, 2 h anneal the morphology of the silicide layer depended strongly on the thickness of the initial Ti(O) layer. For an initial Ti(O) layer of ∼5 nm, both Co and Si readily diffused to form a Co silicide interfacial layer with a very rough, faceted interface. Increasing the Ti(O) thickness to ∼10 nm stopped Si out diffusion and reduced Co in diffusion such that a uniform 6 nm CoSix interfacial layer formed. Selective removal of the upper layers and a 750/800 °C annealing produced a 12 nm CoSi2 layer with a resistivity of ∼28 μΩ cm.

Interfacial Morphology of Selicides Formed Via Rta of Sputtered Bi- and Multi-Layer Co/Ti(O,C) on Si

ABSTRACTCobalt silicide formed by diffusion of Co through a Ti compound has been reported for both bilayer and multilayer Co/Ti-Si structurest[2-4]. To compare the bilayer and multilayer systems in terms of the Co silicide interfacial morphology, both bilayers and six layers of 20nm Co and lOnm Ti were sputter deposited on (100)Si in a system where background. oxygen and carbon were gettered by each Ti layer. The samples were annealed from 550°C to 800°C for 60 sec by lamp RTA in N2 ambient. XTEM micrographs revealed that significant differences in interfacial morphology existed between bilayer and multilayer samples. The interfacial amorphous Ti(O.C) diffusion barrier layer was found to be more effective in the multilayer system producing uniform CoSix layers as thin as ∼5nm after 550°C RTA, whereas the silicide formed in the bilaver samples under the same condition was rough. RBS analysis showed that the transformation temperature from CoSi to CoSi2 was 800°C in bilayers and even higher for multilayers. The higher transformation temperature is attributed to the additional Co available in the multilayer system and its effect on Co monosilicide phase stability as previously reported[10].

Aluminum-Titanium Multilayer Interconnect With Titanium Diffusion Barrier

ABSTRACTThe metallurgical reaction at 450°C in forming gas ambient between the Ti diffusion barrier and Al, causing the contact degradation in the Al (1% Si)-Ti multilayer interconnects has been studied. The Ti-Al reaction is reduced by preheating the Ti layer in N2 using rapid thermal processing (RTP) at 2.500°C. The curtailed reaction is attributed to the thin surface titanium oxynitride layer. It was found that a 1000-Å Ti layer inserted between the multilayer and Si is effective as a sacrificial diffusion barrier against contact degradation, but 500-Å Ti is not. RTP of the thin Ti film rendered it effective as a diffusion barrier.

Diffusion of aluminum in ion-implanted α-Ti

The diffusion of Al in polycrystalline ion-implanted α-Ti has been studied in the temperature range 600–850 °C using ion-beam techniques. Diffusion couples were created by ion implantation. The time-dependent concentration profiles were monitored by the use of the nuclear resonance broadening technique through the 27Al(p,γ) 28Si reaction. The effect of the implantation energy and implanted dose on the diffusivity of Al has been investigated. The value of 1.62±0.11 eV for the activation energy and (7.4±9.8)×10−7 cm2/s for the frequency factor was obtained. The present result is discussed in the framework of the Ti diffusion barrier used in semiconductors.

Interdiffusion and Schottky-barrier-height variations in Au–W(Ti)/n-GaAs contacts

Au–W(Ti)/n-GaAs diodes were constructed for the purpose of examining the thermal stability of the metal–GaAs interface and the integrity of the W(Ti) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(Io), determined by measurement of the zero voltage current intercept, Io, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(Io) up to 500°C. Above 500°C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation, and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished.