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The conformality of thin films grown by atomic layer deposition (ALD) is studied using all-silicon test structures with long narrow lateral channels. A diffusion model, developed in this work, is used for studying the propagation of ALD growth in narrow channels. The diffusion model takes into account the gas transportation at low pressures, the dynamic Langmuir adsorption model for the film growth and the effect of channel narrowing due to film growth. The film growth is calculated by solving the diffusion equation with surface reactions. An efficient analytic approximate solution of the diffusion equation is developed for fitting the model to the measured thickness profile. The fitting gives the equilibrium constant of adsorption and the sticking coefficient. This model and Gordon's plug flow model are compared. The simulations predict the experimental measurement results quite well for Al2O3 and TiO2 ALD processes.

The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes with Ni, Ti, and TiW seed layers and subsequent integration into thin film bulk acoustic wave resonators. The crystalline structure and morphology of the Mo and c-axis oriented AlN films were found to vary strongly with seed layer material and thickness. The smoothest Mo electrodes were obtained on thin Ti films. Reactive sputtering of AlN on top of these optimized electrodes resulted in a dense columnar grain structure with a well-aligned (002) crystal orientation and good electro-acoustic properties, including an effective coupling coefficient of 6.89% and quality factor above 1000.

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/SiO2 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, Si3N4, and SiO2 diffusion barriers were able to block oxygen from the Mo electrode.

In the first edition of "The Nano-Micro Interface," we discussed the piezoelectric quality of zinc oxide (ZnO) thin films. In this second edition's chapter, we have extended our view and included other piezoelectric materials like AlN, Sc-alloyed AlN, PZT (lead zirconate titanate) {Pb(ZrTi)O3}, and leadfree compounds. The focus of applying these thin piezoelectric films is in BAW (thin film bulk acoustic wave resonator) technology, which is used in all smart mobile devices from phones to tablets for wellness, health, and entertainment. BAW technology is based on the venerable crystal oscillator principle (such as quartz resonator) extended to the GHz frequency range by utilizing thin film technology to shrink the dimensions of the oscillator to the micrometer-scale. The main application of BAW is in telecommunications. The BAW filters show promise to be even smaller and have higher performance than SAW (surface acoustic wave) filters. Two different approaches of BAW filters are reviewed and compared: bridge-type technology and acoustic-mirror-based technology. Piezoelectric materials in thin film form using microelectronics fabrication methods and nanolevel control of piezoelectric film growth will be emphasized.

A detailed model for the operation of a flow type atomic layer deposition (ALD) reactor is developed and tested with the growth of tantalum pentoxide thin films. The model incorporates evaporation, diffusion, and convection phenomena in mass transport and a kinetic description of the surface reactions and film growth. The theory gives a quantitative estimate for the deposition rate and thickness uniformity of the film. The necessary conditions for an ALD operation are discussed. The experiments support the predictions provided a pure ALD mode is prevailing.

CaF2, SrF2, and ZnF2 thin films have been deposited on glass substrates for the first time using atomic layer deposition (ALD) at temperatures between 260 and 400°C. The source materials used are alkaline earth β‐diketonates, zinc acetate dihydrate, and hydrogen fluoride in nitrogen atmosphere. The growth rate of films varies from 20 to 90 pm/cycle depending on materials and temperature. The crystallinity, orientation, stoichiometry, atomic density, optical and electrical properties together with growth properties of the films have been characterized. Also, multilayer structures with alternating materials of high ZnS and low (fluoride) index of refraction have been prepared by ALD.

CaF 2 , SrF 2 , and ZnF 2 thin films have been deposited on glass substrates for the first time using atomic layer deposition (ALD) at temperatures between 260 and 400 o C. The source materials used are alkaline earth β-diketonates, zinc acetate dihydrate, and hydrogen fluoride in nitrogen atmosphere. The growth rate of films varies from 20 to 90 pm/cycle depending on materials and temperature. The crystallinity, orientation, stoichiometry, atomic density, optical and electrical properties together with growth properties of the films have been characterized. Also, multilayer structures with alternating materials of high (ZnS) and low (fluoride) index of refraction have been prepared by ALD

A simple model is developed for calculating lateral acoustical coupling between adjacent thin film BAW resonators forming an electrical N-port. The model is based on plate wave dispersion properties of different regions of the device and solution of lateral eigenmodes and eigenfrequencies. Mechanical and electrical response of the device is calculated as a superposition of eigenmodes according to voltage drive at one electrical port at a time while extracting current induced in the other ports, leading to a full Y-parameter description of the device. Comparison of model prediction with experimental results from adjacent large square resonators and narrow finger-like resonators is performed. Large resonators exhibit comb-shaped oscillating transmission characteristics over wide frequency band, while narrow finger create a single pass-band. Fair qualitative agreement is obtained.

As a test vehicle to measure the piezoelectricity of zinc oxide films, bulk acoustic wave (BAW) re-sonators were fabricated using standard microelectronics deposition, photolithography, and etching tech-niques on 100 mm Corning glass or silicon wafers. Resonators and filters were of solidly mounted re-sonator (SMR) type. The acoustic quarter wavelength mirror consisted of high and low acoustic impe-dance materials, which were either three pairs of molybdenum and silicon dioxide or two pairs of tungs-ten and silicon dioxide, respectively. Mirrors were designed for 1 and 2 GHz frequencies. Material pro-perties of the zinc oxide films have been studied by x-ray diffraction (including rocking curve), scanning electron microscopy and atomic force microscopy. Resonators were measured from 0.5 to 6 GHz using network analyzer. The highest acoustic coupling coefficient, K2 = 10.4% at 1.6 GHz, for thin film zinc oxide was achieved. Also a passband filter, fulfilling the complete E-GSM specifications, was fabricated using zinc oxide piezoelectric in the resonators.

Spurious resonance suppression in ZnO based thin film BAW resonators by the boundary ring method of (1) is studied. Electrical responses of resonators with varying width of the boundary ring structure are measured. Very clean resonator response is reached with optimum dimensions. Emergence of the piston mode and simultaneous spurious resonance suppression is demonstrated by 2D FEM simulation with a model corresponding to the measured devices. Good correlation between measurement and simulation is found. I. INTRODUCTION Thin film bulk acoustic wave resonators and filters for the GHz range have been intensively developed during the last ca. 10 years due to great demand in the mobile communications industry. Main application of the thin film BAW devices is in the band pass filters of the antenna circuit of mobile phones. With the thin film BAW technology, low insertion loss, high power handling, steep pass band skirts and small footprint are sought together with low manufacturing cost. The BAW filters are also inherently better applicable for higher frequencies (> 2 GHz) than SAW filters due to the lack of critical dimensions. Also as BAW resonators do not rely on a special crystalline substrate, possibility to integrate them with silicon IC:s exists. In order to create high performance filters, the BAW resonators they consist of, must fulfill certain performance criteria. Most importantly the effective coupling coefficient K 2 determines the attainable bandwidth of the filter and the Q- values affect the insertion loss and pass band skirt steepness. In addition, the resonator should not have ripple in or near the inductive region of its electrical response. In a low insertion loss filter this is only attained by suppressing the spurious resonances in some manner.

We have probed ultrasonic vibrations of a piezoelectric thin film utilizing a scanning laser interferometric technique. The vibrations are also simulated using a "toy" model of a membrane of zero thickness, and applying 2D FEM modeling for the solution of the eigenmodes. Despite the strong truncations used in the modeling, the agreement between our simulations and the measurements for several of the modes is striking. The samples were fabricated by patterning thin films photolithographically.

Insulating films consisting of thin layers of tantalum oxide and aluminum oxide were deposited using the atomic layer epitaxy technique at a temperature of 300 °C from metallic chlorides and H2O. The average film composition can be modified between pure aluminum oxide and pure tantalum oxide by varying the pulsing ratio. The effective refractive index is adjustable between 1.67 and 2.23 and the relative permittivity between 8.4 and 24. The leakage current of tantalum oxide is significantly reduced by thin interposed layers of aluminum oxide. These multilayers will potentially be useful, for example for applications in future memory integrated circuit and large-area display technologies.

The growth rate in atomic layer deposition (ALD) or epitaxy (ALE) is usually saturated to a constant level when appropriate operation conditions are attained. The layer thickness deposited in one cycle is limited by adsorption. A simple molecular description for chemisorption and surface reactions is suggested and shows that both reaction steps have an effect on the growth rate. A model is developed for the calculation of the growth rate from the geometry of the reactant molecules and the density of the adsorption sites on the surface. The results are compared with experimental values of binary oxide, sulphide and fluoride thin films. In most cases, a surface configuration is found that gives the observed growth rate.

An optical method for determining the layer thicknesses in a multilayer thin film structure is developed and its performance in terms of accuracy and resolving power is characterized. The effects of layer thicknesses, their indices of refraction, light absorption, measurement wavelength range, thickness non-uniformity and unintentional transition layers are characterized. The measurement procedure is applied to oxide, sulphide and fluoride thin film multilayer structures, up to nine individual layers thick, deposited on a glass substrate using atomic layer deposition. In most cases the method is found reliable and error estimates of film thickness vary between 1 and 50 nm depending on the thin film structure in the sample.