G.M. Crean

Selective electroless copper metallization on a titanium nitride barrier layer

Abstract Electroless copper plating is demonstrated as a novel low temperature, selective technique for metallization of TiN. The properties of the as-deposited copper from two electroless plating baths of different composition were examined. It was found that the as-deposited Cu layer (0.50 μm) from a commercial bath, containing high amounts of Na and K, had a resistivity of ∼2.70 μΩ cm, and the as-deposited Cu layer (0.50 μm) from a research bath with low mobile ion levels had a lower resistivity of ∼2.20 μΩ cm. The topography of both deposits was examined using SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy). ICP (Inductively Coupled Plasma) and SIMS (Secondary Ion Mass Spectrometry) techniques were used to examine the contaminant levels in the plating solutions and in the Cu surface, respectively. The uniformity of the Cu layer on TiN was also examined for both the commercial and research systems and it was found that the uniformity of sheet resistance was better when the commercial plating bath was used to deposit Cu, at an average value of ∼4% as compared to the average value of ∼35% for the research bath. This improvement in deposit uniformity could be due to the greater amount of stabilisers and additives included in the composition of the commercial solution.

Refractive femtosecond laser beam shaping for two-photon polymerization

Three dimensional microstructure fabrication by two-photon polymerization is an established technique that normally uses single beam serial writing. Recently the use of a micro-optical element, to give multipoint beam delivery, was reported to give a degree of parallel processing. The authors describe an alternative approach to parallel processing using an axicon lens. This is a refractive element that, in combination with a high power microscope objective, efficiently transforms the laser beam from a Gaussian spot to an annulus. The authors demonstrate that the beam can polymerize a three dimensional shape, with nanoscale resolution. The use of more sophisticated refractive beam shaping is also discussed.

Si'SiGe electron resonant tunneling diodes with graded spacer wells

Resonant tunneling diodes have been fabricated using graded Si1−xGex (x=0.3→0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the peak current density is achieved. Peak current densities of 0.08 A/cm2 with peak-to-valley current ratios of 1.67 have been achieved for a low peak voltage of 40 mV at 77 K. This represents an improvement of over an order of magnitude compared to previous work.

Atmospheric pressure excimer lamp-assisted photoselective activation process for electroless plating

Abstract Photoselective activation technologies for electroless metallisation have significant potential in minimising the number of activation process steps. In this work, a novel photo-selective activation process for electroless plating is described. The process is based on the selective photodecomposition of a palladium based precursor using a purpose built 222 nm KrCl* excimer lamp contact mask aligner. The photoexposure conditions to produce a selective palladium activation are detailed. Previously reported maximum pressure thresholds (1 mbar) for an efficient photoprocess have been overcome. This has been achieved using a triple excimer lamp source to increase ultraviolet (UV) intensity, a substrate temperature of 70–85°C and an organometallic precursor having a ligand to metal charge transfer optical absorption peak at 224 nm corresponding to the peak output of the KrCl* excimer lamp. Activation is reported at atmospheric pressure in a N 2 ambient, removing the need for processing under vacuum. Electroless copper features with a lateral resolution of 50 μm are demonstrated. The electroless metallisations are characterised in terms of adhesion performance, resistivity and resistance to peel-off during sawing.

Silicon quantum integrated circuits – an attempt to fabricate silicon-based quantum devices using CMOS fabrication techniques

An introduction to the methodology, design concepts, fabrication routes and potential applications is presented of research to fabricate quantum devices on a complementary metal oxide semiconductor (CMOS) fabrication line. Si/Si1−xGex heterostructure field effect transistors, velocity modulation transistors and resonant tunnelling diodes are considered and initial fabrication stages discussed.

Optical characterisation of thin film benzocyclobutene (BCB) based polymers

Optical properties of benzocyclobutene (BCB)-based polymer films deposited on Si are characterised using variable angle spectroscopic ellipsometry (VASE) as a function of spin and cure parameters. Thicknesses extracted from VASE are correlated to scanning electron microscopy (SEM) analysis. The extent of cure and heat flow characteristics of these films as a function of process parameters are extracted from Fourier transform infra-red (FTIR) and differential scanning calorimetry (DSC) measurements.

Defect study of GaInP/GaAs based heterojunction bipolar transistor emitter layer

Defects in the emitter region of Ga0.51In0.49P/GaAs heterojunction bipolar transistors (HBTs) were investigated by means of deep-level transient spectroscopy. Both annealed (635 °C, 5 min) and as grown metalorganic chemical vapor deposition epitaxial wafers were investigated in this study, with an electron trap observed in the HBT emitter space-charge region from both wafers. The deep-level activation energy was determined to be 0.87±0.05 eV below the conduction band, the capture cross section 3×10−14 cm2 and the defect density of the order of 1014 cm−3. This defect was also found to be localized at the emitter–base interface.

Optical and structural properties of InGaP heterostructures

In this study, optical and structural properties of InGaP/GaAs epitaxial heterostructures are investigated as a function of growth temperature and substrate orientation (2 and 108). Both ordered and disordered InGaP layers were grown by metal organic vapour phase epitaxy (MOVPE). The complex refractive index both above and below the fundamental band gap has been determined using spectroscopic ellipsometry (SE). In particular an InGaP/GaAs intermixing layer, in addition to the InGaP oxide overlayer was identified and introduced in order to improve the accuracy of the extracted refractive index. Variations in Raman TOm mode and photoluminescence (PL) emission efficiencies show different degrees of ordering, which are correlated to different PL peak energies or bandgaps extracted from SE data. Misfit strain and lattice mismatch are also investigated. q 2000 Elsevier Science S.A. All rights reserved.

POLYCRYSTALLINE DIAMOND FILMS FOR ACOUSTIC WAVE DEVICES

Abstract A laser ultrasonics technique has been used to measure acoustic wave velocities in polycrystalline CVD diamond for the first time. Lamb (plate) waves propagate with very high velocities in the range 8700–12 200 m s −1 ; the lowest values are recorded for films with the lowest crystal quality and highest non-diamond content. High-quality films with differing crystal textures [(100), (110)] or thickness (250–535 μm) show little variation. The results are discussed in terms of the fabrication of a high-sensitivity flexural plate wave (FPW) device for sensing applications in hostile environments.

Characterization of acoustic Lamb wave propagation in polycrystalline diamond films by laser ultrasonics

The propagation of acoustic Lamb waves in free standing chemical vapor deposited polycrystalline diamond has been studied using a laser ultrasonic technique. The influence of film morphology, quality, and thickness on the waves has been assessed. Acoustic waves with high velocities in the range 8700–12 200 ms−1 were observed; the lowest values were recorded for films with the lowest crystal quality and highest nondiamond content. High quality films with differing crystal textures or thickness show little variation. The influence of temperature on the dispersion characteristics of Lamb wave propagating in a 50 mm diam polycrystalline diamond wafer were also investigated. Little variation was apparent across the range studied (30–250 °C). Material parameters extracted from the dispersion chracteristics of the acoustic signal together with scanning electron microscopy studies suggested that void, microcrack, and grain boundary density most influences the propagation of low frequency Lamb waves in free standi...