H.‐C. W. Huang

Hillock growth kinetics in thin Pb-In-Au films

Abstract Hillock growth has been studied in films 100–500 nm thick of Pb-12wt %In-4wt%Au deposited onto oxidized Si substrates at room temperature. Overlying SiO layers were used to suppress hillock formation everywhere except within 4μ × 4μm size openings in the SiO where hillock growth could be observed. Hillock growth was initiated in these openings by heating the samples in a scanning electron microscope. The dependence of hillock growth on time, temperature and sample geometry were investigated. In addition, an X-ray technique was used to determine the elastic strain in the Pb-alloy films. Analysis of the results indicates that the driving force for hillock formation is the compressive stress generated in the film during heat treatment produced by the thermal expansion coefficient difference between the Pb-alloy film and the Si substrate. A one-dimensional stressdriven diffusion model has been developed to analyse the hillock growth behaviour. By fitting the model to the data, values of an effective ...

Schottky barrier height measurement by electron‐beam induced voltage

We demonstrate that electron‐beam induced voltage (EBIV) technique can be used for direct measurement of Schottky (or p‐n junction) barrier height. Schottky barrier heights of PtSi, Pd2Si, and TiSi2 on n‐type (111) Si measured by this technique were found to be 0.84, 0.74, and 0.57 eV, respectively, in excellent agreement with values obtained by the standard current‐voltage technique. Because of no complication due to leakage current in EBIV measurement, this technique is particularly suited for studying the formation of low barrier height Schottky diodes. Furthermore, this technique can be extended for in situ measurements of barrier height to supplement surface electron spectroscopy studies on the electrical and chemical characteristics of silicide/Si interfaces.

Oxygen‐doped Pb‐In‐Au films suitable for Josephson tunnel junction base electrodes

The effects of oxygen doping during film deposition on film microstructures, surface morphology, strain behavior, and electrical resistivity have been studied by using transmission and scanning electron microscopies, x‐ray diffraction, and electrical resistivity measurements for 0.2‐μm‐thick Pb and Pb‐12 wt.% In‐4 wt.% Au films prepared at ∼77 K. The average grain size of both types of films was found to decrease with increasing oxygen partial pressure during the film deposition: one order of magnitude smaller grains, compared with those prepared in a high vacuum (≲5×10−8 Torr), were obtained when the oxygen pressure was higher than 1×10−6 Torr. The finest average grain size obtained in the present experiments was ≲15 nm, which is over 10 times smaller than the film thickness. The surfaces of both films were found to be smooth when the films were prepared at oxygen pressures below 1×10−5 Torr. Strain relaxation upon cooling to 4.2 K was observed for oxygen‐doped Pb films, but no strain relaxation was obse...

Generation of interface states due to emission of leakage electrons from silicon substrate into silicon dioxide

Experimental evidence of interface state generation due to the emission of leakage electrons from the silicon substrate into SiO2 is presented. Interface states were measured on MNOS capacitors before and after temperature‐bias stress, where the electron emission process occurred, using the high‐frequency and quasistatic C‐V technique. Electrical access to the silicon surface to vary the space‐charge width was made by the use of a very small diffusion underneath the field plate. The generation of interface states which can in turn cause device degradation is undoubtedly a reliability concern.

Platinum silicide contact to arsenic‐doped polycrystalline silicon

PtSi contacts to As‐doped polycrystalline silicon have been studied with respect to dopant redistribution, microstructure, and contact resistance. Arsenic was found to pileup at the PtSi‐polysilicon interface upon silicide formation. Cross‐sectional transmission‐electron microscopy revealed columnar PtSi grains and a relatively flat interface between PtSi and polysilicon. These observations are similar to those reported for the case of PtSi formed on the single‐crystal silicon. The specific contact resistance (ρc) has been investigated as a function of As concentration ranging from 8×1019 to 2×1021 cm−3 and of its dependence on substrate preclean procedures prior to Pt deposition. It was found that ρc decreases with increasing As concentration, as expected from theory. However, the contact resistance to As‐doped polysilicon is about ten times higher than contacts to similarly doped single‐crystal Si. The origin of this difference is attributed to the fact that not all of the implanted As was activated. Ha...

Thermal stability of Pb‐alloy Josephson junction electrode materials. VIII. Effects of Au addition to Pb‐Bi counterelectrodes

In previous studies, strain‐relaxation‐induced changes in film microstructure, such as grain rotation, hillock formation, and dislocation slip bands, were observed after repeated thermal cycling between 298 and 4.2 K in 0.4‐μm‐thick e‐phase Pb‐Bi films that are used as the counterelectrode material of experimental Pb‐alloy Josephson junction devices. In the present paper, the effects of small additions of Au (1–8 nm thickness) to the Pb‐Bi films on the changes in the film microstructure were studied by using x‐ray diffraction, and scanning and transmission electron microscopy. It was found that the changes in microstructure observed in the Pb‐Bi films were significantly reduced by the Au addition, although the average level of strain relaxation in the Pb‐Bi alloy films upon thermal cycling between 298 and 4.2 K was not influenced by the Au addition. Experimental junctions were made using fine‐grained Pb‐In‐Au films prepared at 77 K as the base electrode material, and Pb‐Bi or Pb‐Bi‐Au films prepared at 27...

Thermal stability of Pb‐alloy Josephson junction electrode materials. VII. Concentration range of single ε‐phase Pb‐Bi films used in counterelectrodes

From the viewpoint of mechanical stability upon repeated thermal cycling between 298 and 4.2 K, Pb‐Bi films with single e‐phase have been found to be desirable as the counterelectrode material of Pb‐alloy Josephson junction devices. The Bi concentration range of the e‐phase was studied by using x‐ray diffraction and electron microprobe techniques for Pb‐Bi films with various Bi contents prepared by evaporation from an alloy source. The film composition was determined by controlled‐potential coulometry. From the lattice constants and phase identification experiments, the Bi content range of the single e‐phase was determined to be 27.5∼31.8 wt. % (±0.3 wt. %) at room temperature. The lower limit of the Bi content of the e‐phase agrees reasonably well with those reported previously, but the upper limit of the Bi content is ∼1 wt. % higher than that of Preece and King, and ∼2 wt. % lower than that of Predel and Schwermann. Although Predel and Schwermann indicated that there would be a eutectoid at 27.5 wt. % ...

Ring formation of Kirkendall voids in Pb‐alloy thin‐film diffusion couples

Ring formation has been observed in thin‐film diffusion couples consisting of a 400‐nm‐thick Pb0.71Bi0.29 (in weight fraction) or Pb layer above a 200‐nm‐thick Pb0.84In0.12Au0.04 layer with a very thin (∼6 nm) rf‐grown oxide diffusion barrier in between. When interdiffusion was initiated by a rupture in the oxide barrier, concentric rings were observed to form in Pb‐Bi or Pb layer centering at the rupture site as interdiffusion proceeded. Rings were found to be a string of voids resulting from Kirkendall interdiffusion. In addition, relatively high concentrations of indium and oxygen were found at rings. Although the mechanism for ring formation is not clear at present, factors which influence ring formation are discussed.

Advanced single precursor based pSiCOH k = 2.4 for ULSI interconnects

A single precursor, octamethylcyclotetrasiloxane (OMCTS), was used to develop a pSiCOH interconnect dielectric with an ultralow dielectric constant k = 2.4. With no added porogen, the advanced pSiCOH dielectric has low pore size and low pore interconnectivity. The new OEx2.4 dielectric has a high carbon content with a significant fraction in the form of Si-CH2-Si bridging bond resulting in a film with relatively high modulus and increased resistance to process induced damage. The new OEx2.4 film shows significant improvement in device reliability (time dependent dielectric breakdown) over the reference k 2.55 and other k 2.4 dielectrics. This dielectric not only addresses the integration challenges but also provides capacitance benefit by retaining an overall lower integrated k value over the reference films. The results discussed in this paper indicate that the single-precursor OMCTS-based advanced pSiCOH, OEX2.4 dielectric is a strong candidate for sub-10 nm Cu/low k interconnects.

SFG analysis of the molecular structures at the surfaces and buried interfaces of PECVD ultralow-dielectric constant pSiCOH

PECVD deposited porous SiCOH with ultralow dielectric constant has been successfully integrated as the insulator in advanced interconnects to decrease the RC delay. The effects of NH3 plasma treatment and the effectiveness of the dielectric repair on molecular structures at the surface and buried interface of a pSiCOH film deposited on top of a SiCNH film on a Si wafer were fully characterized using sum frequency generation vibrational spectroscopy (SFG), supplemented by X-ray photoelectron spectroscopy. After exposure to NH3 plasma for 18 s, about 40% of the methyl groups were removed from the pSiCOH surface, and the average orientation of surface methyl groups tilted more towards the surface. The repair method used here effectively repaired the molecular structures at the pSiCOH surface but did not totally recover the entire plasma-damaged layer. Additionally, simulated SFG spectra with various average orientations of methyl groups at the SiCNH/pSiCOH buried interface were compared with the experimental...