Topographic Evolution in the Atomic Scale Growth and Erosion Continuum

This review gives a detailed survey of the range of fascinating surface features which develop under growth or erosion conditions under the combined influence of thermal and more energetic atomic particle fluxes. Collisionally induced atomic ejection and migration, and thermally and radiation induced atom and defect diffusion processes are outlined and their relevance to topographic initiation and evolution explored. A range of experimental observations of surface feature elaboration is discussed from net growth to net erosion conditions and models for their explanation are considered. It is concluded that while much data have been accumulated, much of these have been in so diverse experimental conditions that precise modelling in atomic terms is difficult and generalisations are treacherous. A clear need for structured, extensive studies exists with very precise parameter definition and control

Numerical and experimental studies of the sputter yield amplification effect

Recently we have demonstrated the existence of the so called sputter yield amplification SYA effect, based on the preferential sputtering of the lighter species during ion bombardment of composite solids and resulting in enhanced partial sputtering yield of the lighter species as compared to the elemental sputtering yield. In specific cases the enhancement of the sputtering yield could reach one order of magnitude or more. This effect has been both numerically studied and experimentally observed during low energy ion bombardment of i thin films of low mass on heavy substrates; ii thin films of high mass on light substrates; iii simultaneous high mass atom deposition on light substrates; iv simultaneous low mass atom deposition on heavy substrates. In all cases sputter yield enhancement of the low mass species is observed but in each individual case different specific goals are achieved. For example, in case i much faster etch rate of the thin film is achieved than what is expected from the elemental sputtering yield. In cases ii and iii faster erosion of the target is achieved in view of sputter deposition processes. In case iv a nearly complete removal of the deposited species with a partial sputtering yield substantially higher than the elemental sputtering yield is achieved in view of selective ion beam assisted deposition. The SYA effect is also observed in the net growth regime, i.e. during the deposition of composite films with ion co bombardment. In this case the composition of the growing film differs from that of the deposition flux. This work presents systematic numerical and experimental studies of the SYA effect in all these cases as a function of the ion energy, mass and angle of incidence as well as the target species. The simulations have been performed with the T DYN program. General rules are given as to when the amplification effect is most pronounced. Potential applications are also discusse

Structural and electroacoustic studies of AIN thin films during low temperature radio frequency sputter deposition

AIN is a material used in a wide variety of applications such as electroacoustic devices, blue diodes, IR windows, thermal conductors, metal-insulator-semiconductor structures, integrated circuit packaging, etc. In this work thin piezoelectric AIN polycrystalline films have been grown on Si and SiO2 using rf magnetron sputter deposition in an Ar/N-2 gas mixture. The structural properties of the film have been optimized by varying the deposition parameters, such as process pressure, gas mixture, substrate temperature, discharge power, etc. [K. Tominaga et al., Jpn. J. Appl. Phys., Part 1 35, 4972 (1996); H. Okana et al., ibid. 31, 3446 (1992); K. Kazuya, T. Hanabusa, and K. Tominaga, Thin Solid Films 281-282, 340 (1996)]. It was found that the best film texture was obtained for a particular set of parameters, namely process pressure of 4 mTorr, substrate temperature 350 degreesC, discharge power 350 W, and a gas mixture of 25% Ar and 75% N-2. The films as examined by x-ray diffraction exhibited a columnar structure with a strong (001) texture, and a fall width at half maximum (FWHM) rocking curve of 1.6 degrees. Atomic force microscopy measurements indicated a surface roughness with a rms value of 8 Angstrom. Classical nonapodized transversal surface acoustic wave filters operating at a frequency of 534 MHz were fabricated to characterize the electroacoustic properties of the films. The measurements indicated a coupling coefficient of 0.37% and a phase velocity of 4900 m/s. Further, thin epitaxial films were grown on (001)alpha -Al2O3 (sapphire) under the same deposition conditions except the substrate temperature. The films exhibited a (001)AlN//(001)alpha -Al2O3 plane orientation with a (002) rocking curve FWHM value of about 0.4 degrees, showing a relatively good alignment of the c axis. The in-plane orientation was [110]AlN//[120]alpha -Al2O3 corresponding to a rotation of the AIN film of 30 degrees with respect to the (001)alpha -Al2O3 surface. Cross-sectional transmission electron microscopy studies indicated a population of both thread and edge dislocations with decreasing concentrations with film thickness. (C) 2001 American Vacuum Society

UV sensing using film bulk acoustic resonators based on Au/n-ZnO/ piezoelectric-ZnO/Al structure

A new type of ultraviolet (UV) light sensor based on film bulk acoustic wave resonator (FBAR) is proposed. The new sensor uses gold and a thin n-type ZnO layer deposited on the top of piezoelectric layer of FBAR to form a Schottky barrier. The Schottky barrier’s capacitance can be changed with UV light, resulting in an enhanced shift in the entire FBAR’s resonant frequency. The fabricated UV sensor has a 50 nm thick n-ZnO semiconductor layer with a carrier concentration of , 1017 cm23 . A large frequency downshift is observed when UV light irradiates the FBAR. With 365 nm UV light of intensity 1.7 mW/cm2 , the FBAR with n-ZnO/ Au Schottky diode has 250 kHz frequency downshift, much larger than the 60 kHz frequency downshift in a conventional FBAR without the n-ZnO layer. The shift in the new FBAR’s resonant frequency is due to the junction formed between Au and n-ZnO semiconductor and its properties changes with UV light. The experimental results are in agreement with the theoretical analysis using an equivalent circuit model of the new FBAR structure