G. Ramanath

High‐speed (104 °C/s) scanning microcalorimetry with monolayer sensitivity (J/m2)

We introduce a high sensitivity (1J/m2) scanning microcalorimeter that can be used at high heating rates (104u2009°C/s). The system is designed using ultrathin SiN membranes that serve as a low thermal mass mechanical support structure for the calorimeter. Calorimetry measurements of the system are accomplished via resistive heating techniques applied to a thin film Ni heating element that also serves as a thermometer. A current pulse through the Ni heater generates heat in the sample via Joule heating. The voltage and current characteristics of the heater were measured to obtain real‐time values of the temperature and the heat delivered to the system. This technique shows potential for measuring irreversible heat of reactions for processes at interfaces and surfaces. The method is demonstrated by measuring the heat of fusion for various amounts of thermally evaporated Sn ranging from 50 to 1000 A.

1 000 000 °C/s thin film electrical heater: In situ resistivity measurements of Al and Ti/Si thin films during ultra rapid thermal annealing

We introduce a new technique for rapidly heating (106u2009°C/s) thin films using an electrical thermal annealing (ETA) pulse technique. By applying a high‐current dc electrical pulse to a conductive substrate‐heater material (Si), joule heating occurs thus heating the thin film. This method was demonstrated by heating thin films of aluminum at rates ranging from 103 to 106u2009°C/s. The temperature of the system is measured by using the substrate heater as a thermistor and is found to be within ≊±10u2009°C during anneals at ≊105u2009°C/s. Phase transformations in the Ti‐Si system were also observed using in situ resistivity measurements during ETA at ≊104u2009°C.

Heat capacity measurements of Sn nanostructures using a thin-film differential scanning calorimeter with 0.2 nJ sensitivity

We have developed a new thin-film differential scanning calorimetry technique that has extremely high sensitivity of 0.2 nJ. By combining two calorimeters in a differential measurement configuration, we have measured the heat capacity and melting process of Sn nanostructures formed via thermal evaporation with deposition thickness down to 1 A. The equivalent resolution of the calorimeter is 1 nanogram in mass or 0.4 A in thickness. We have observed a decrease of up to 120°C in the melting point of Sn nanostructures.

Gas‐phase transport of WF6 through annular nanopipes in TiN during chemical vapor deposition of W on TiN/Ti/SiO2 structures for integrated circuit fabrication

Delamination of TiN/Ti bilayers on SiO2 is a serious problem during W chemical vapor deposition (CVD) using WF6 to form vertical interconnects in integrated circuits. In order to obtain insight into the delamination mechanism, we have determined depth‐distributions of W and F in sputter‐deposited TiN/Ti bilayers on SiO2 as a function of WF6 exposure time tWF6 at 445u2009°C. Even for tWF6<6 s, significant concentrations of both W (≊3.5 at.u2009%) and F (≊2 at.u2009%) penetrate through the 106‐nm‐thick TiN film. W piles up at the TiN/Ti interface, while F rapidly saturates the TiN layer and accumulates in the Ti underlayer at concentrations up to ≊10 at.u2009% for tWF6=60 s. Cross‐sectional and scanning transmission electron microscopy analyses demonstrate that WF6 penetrates into the TiN layer through nanometer‐scale intercolumnar voids spanning the entire film thickness and reacts with the Ti underlayer. We propose that the high F concentrations in the Ti layer weakens the Ti/SiO2 interface leading to adhesion failure of...

W deposition and titanium fluoride formation during WF6 reduction by Ti: Reaction path and mechanisms

Reaction of WF6 with air-exposed 27- and 250-nm-thick Ti films has been studied using Rutherford backscattering spectroscopy, scanning and high-resolution transmission electron microscopy, electron and x-ray diffraction, and x-ray photoelectron spectroscopy. We show that W nucleates and grows rapidly at localized sites on Ti during short WF6 exposures (≈6 s) at 445u200a°C at low partial pressures pWF6 0.35 results in the formation of a network of elongated microcracks in the W film which allow WF6 to diffuse through and attack the underlying Ti, consuming the 27-nm-thick Ti film through the evol...

Evolution of microstructure in nanocrystalline Mo-Cu thin films during thermal annealing

The evolution of microstructure in Mo‐Cu thin films during annealing has been investigated by in situ sheet resistance measurements, ex situ x‐ray diffraction, and in situ hot‐stage as well as conventional transmission electron microscopy. Mo‐Cu thin films, deposited on various glass substrates by magnetron sputtering at ∼30u2009°C, were supersaturated solid solutions of Cu in Mo with a nanocrystalline microstructure. The as‐deposited films had large compressive residual stresses owing to the low homologous deposition temperature and low Ar pressure during deposition. Annealing results showed two distinct sets of microstructural changes occurring in the temperature ranges between ∼300 and 500u2009°C, and ∼525 and 810u2009°C. In the lower‐temperature range, anisotropic growth of nanocrystallites was accompanied by stress relaxation without any observable phase separation. At temperatures greater than ∼525u2009°C, the metastable solid solution collapsed and Cu precipitated at the grain boundaries. Increasing temperature resulted in the coarsening of Cu precipitates and simultaneous growth of Mo grains. At temperatures greater than ∼700u2009°C, phase separation and grain growth approached completion.The evolution of microstructure in Mo‐Cu thin films during annealing has been investigated by in situ sheet resistance measurements, ex situ x‐ray diffraction, and in situ hot‐stage as well as conventional transmission electron microscopy. Mo‐Cu thin films, deposited on various glass substrates by magnetron sputtering at ∼30u2009°C, were supersaturated solid solutions of Cu in Mo with a nanocrystalline microstructure. The as‐deposited films had large compressive residual stresses owing to the low homologous deposition temperature and low Ar pressure during deposition. Annealing results showed two distinct sets of microstructural changes occurring in the temperature ranges between ∼300 and 500u2009°C, and ∼525 and 810u2009°C. In the lower‐temperature range, anisotropic growth of nanocrystallites was accompanied by stress relaxation without any observable phase separation. At temperatures greater than ∼525u2009°C, the metastable solid solution collapsed and Cu precipitated at the grain boundaries. Increasing temperature re...

Kinetics of thin-film reactions of Cu/a-Ge bilayers

The kinetics of the Cu3Ge phase formation during reactions between 600 nm polycrystalline Cu (poly-Cu) and 600 nm amorphous Ge (a-Ge) layers on Si (100) substrates have been studied as a function of annealing conditions. Monoclinic Cu3Ge nucleated rapidly, resulting in smooth Cu3Ge layers. The room-temperature resistivity of the Cu3Ge was ∼8 μΩu2009cm (∼4.5 times that of pure Cu). The real-time resistance versus temperature [R(T)] characteristics were nearly identical for heating rates of 0.1–5u2009°C/min. Modeling of the R(T) data indicates that the reaction was predominantly diffusion controlled with a rate of (4×10−3u2009cm2/s) exp [−0.85±0.01 eV/kT] where k=8.617×10−5u2009eV/K. Secondary ion mass spectrometry profiles and R(T) data for the films annealed to various temperatures indicate that the Cu3Ge/Ge interface is stable for T<300u2009°C.

Au-mediated low-temperature solid phase epitaxial growth of a SixGe1-x alloy on Si(001)

The evolution of microstructure during Au‐mediated solid phase epitaxial growth of a SixGe1−x alloy film on Si(001) was investigated by in situ sheet resistance measurements, x‐ray diffraction, conventional and high‐resolution transmission electron microscopy, energy dispersive x‐ray spectroscopy, and Rutherford backscattering spectrometry. Annealing amorphous‐Ge/Au bilayers on Si(001) to temperatures below 120u2009°C caused changes primarily in the microstructure of the Au film. Near ≊130u2009°C, Ge from the top layer diffused and crystallized along the grain boundaries of Au. The Ge that had reached the Au/Si (001) interface mixed with Si from the substrate, to form epitaxial SixGe1−x islands on Si (001). Si from the substrate had dissolved into Au before entering the growing epitaxial islands. Meanwhile, the Au that was displaced by Ge that filled the Au grain boundaries, diffused into the top layer along columnar voids in the amorphous Ge film. With increasing temperature, more Au was displaced to the top by ...

An ultrafast thin-film microcalorimeter with monolayer sensitivity (J/m{sup 2})

The authors introduce a high-sensitivity ({approximately}1 J/m{sup 2}) scanning microcalorimeter that can be used to perform direct calorimetric measurements on thin film samples at ultrafast heating rate ({approximately} 10{sup 4} C/s). This novel microcalorimeter is fabricated by utilizing SiN thin-film membrane technology, resulting in dramatically reduced thermal mass of the system. Calorimetric measurements are accomplished by applying a dc-current pulse to the thin-film metal (Ni) heater which also serves as a thermometer, and monitoring the real-time voltage and current of the heater. The temperature of the system and the energy delivered to the system are then determined. This calorimetric technique has been demonstrated by measuring the melting process of thin Sn films with thickness ranging from 13 to 1,000 {angstrom}, and shows potential for calorimetric probing of irreversible reactions at interfaces and surfaces, as well as transformations in nanostructured materials,

Evolution of Microstructure During Low-Temperature Solid Phase Epitaxial Growth of Si ξ Ge 1-ξ on Si(001)

The evolution of microstructure during Au-mediated solid phase epitaxial growth of a SiGe alloy film on Si(001) (c-Si) was investigated by in situ resistance measurements, X-ray diffraction, conventional and high-resolution transmission electron microscopy, and chemical microanalyis. Annealing a-Ge/Au bilayers on c-Si to temperatures below 120°C caused changes primarily in the microstructure of the Au film. Increases in temperature to ≃150°C resulted in the diffusion of Ge through the grain boundaries of Au. The Au, displaced by crystalline Ge at the grain boundaries, diffused along columnar voids of amorphous Ge (a-Ge) leading to the formation of Au-rich crystallites in the top layer. Results indicate that the Ge that had reached the Au/c-Si interface grew epitaxially on c-Si at temperatures below 150°C. As the temperature was further increased, some Si from the substrate dissolved into Au and got incorporated in the growing epilayer. At 310°C, the initial Au film was displaced completely by a laterally continuous Si ξ Gei. ξ (ξ ∼ 0.2) epilayer whose thickness was limited by that of the initial Au film. Twins, and residual amounts of Au near the SiGe/c-Si interface, were the predominant defects observed in the SiGe epilayer.