The material transfer from the target to the substrate involved in pulsed laser deposition is described with respect to chemical reactions in the processing gas atmosphere in order to derive the laser parameters and the processing variables necessary for the deposition to thin films with application-adapted properties. The heating and removal are described by the conversion of the optical energy into internal energy followed by a phase transition form the condensed to the gaseous state. The delivered energy becomes distributed into different channels of decomposition in accordance to the temperature. The dynamics of the volatile species is calculated by the use of non- dissipative continuum mechanical equations of the conversion laws of mass, momentum, and energy. The flow field patterns of the gas phase during the material transfer of the polymers PE, PP and PMMA and the ceramic Al2O3 are calculated. The modeling calculating are direction towards the spatial and temporal dependence of the total and partial pressures either of the materials to be processed or of the processing gas species. The mathematical models are applied to the polymers PE, PP, and PMMA and to the ceramic Al2O3 following the chemical composition in thermodynamic equilibrium. The main emphasis of the calculations is to derive parameters and processing variables for pulsed laser film deposition in the case of other material properties.

The deposition of different hard ceramics coatings as Al2O3, ZrO2, c-BN and DLC thin films by pulsed laser deposition (PLD) has been of increasing interest as alternative process compared to the latest progress in CVD and PVD deposition. For instance, in pulsed laser deposition, the properties of the resulting thin films are influenced by the composition, ionization state, density, kinetic and excitation energies of the particles of the vapor/plasma. In order to deposit hard ceramics with different properties and applications, various substrates as Pt/Ti/Si multilayer, glass (fused silica), steel, polymethylmethacrylate (PMMA), polycarbonate (PC), Si(100) and Si(111) are used. These thin films are deposited either by excimer laser radiation (lambda = 248nm) or by CO2 laser radiation (lambda = 10,6 mum). To characterize the structural, optical and mechanical properties of the hard ceramics thin films, different techniques as Raman spectroscopy, ellipsometry, FTIR-spectroscopy and nanoindentation are used.

Holes in polypropylene (PP) and polymethylmethacrylate (PMMA) plates, 0.5 mm in thickness were drilled by irradiation with up to 3000 pulses of KrF-excimer laser radiation (λ = 248 nm) at fluences per pulse ɛ in the range 0.1–10 J/cm2, conditions which yield a laser-induced plasma/vapor plume. The process was analyzed experimentally in terms of material removal rate, optical emission of the laser-induced plasma, hole geometry, debris production at the hole edge, and chemical changes in the polymer induced by the laser irradiation. Additionally, the process was simulated using a model based on degradation of the polymer induced by optical absorption and heating, leading to gas-phase products. Such characteristics as the material removal rate as a function of fluence, the nature of the gas phase products and the deposition of debris were calculated.

The pulsed laser deposition of thin ceramic (Al2O3, BN, ZrO2) films with pulsed excimer or CO2 laser radiation on various substrates (steer: Si) is described for various laser parameters and processing variables. The variables produce vapor and/or plasma states represented in the type, number, momentum and energy of the ensemble of species generated, which are used to deposit thin films with defined propel-ties according to applications in view of optical and mechanical properties illustrated by examples.

In Pulsed Laser Deposition the laser parameters pulse duration, repetition rate, and average output power are important parameters for control of the resulting Nm properties. In order to obtain high deposition and coverage rates the use of powerful laser radiation sources is required. A new approach is the use of Q-switch CO2-lasers, making accessible the range of kW average output powers for PLD. A common industrial fast axial gas Bow rf-excited CO2-laser is equipped with a mechanical Q-switch assembly. The characteristic properties of this laser radiation source are studied by measurements of the average output power and of the spatial and temporal intensity distribution of the laser radiation. Results show, that the laser operates in multimode or in TEM10 mode depending on the use of apertures in the resonator. Variation of the electrical rf-excitation (in synchronization with the Q-switch) influences the pulse duration and shape, repetition rate, and average output power. Based on the experimental findings model calculations are carried out, in order to predict the pulse energy and average output power of the laser radiation source, when operating with different Q-switch parameters, e.g. higher repetition rates.

Sintered targets of Al2O3 are removed by CO2- and excimer laser radiation and deposited as thin films onto steel and silicon substrates. Micro Raman spectroscopy and atomic force microscopy are used to characterize the morphological and structural properties of the films. Mechanical properties are investigated by nanoindentation measurements and a laser-acoustic method, optical properties are studied by ellipsometry. Al2O3 films deposited using CO2-laser radiation show an inhomogeneous surface structure with droplets embedded in a matrix, whereas the films deposited using excimer laser radiation are smooth, which is explained by different material removal mechanisms. The microhardness (i.e. ratio of indentation load to residual area of the indent) of the amorphous matrix structure is similar to 8 GPa, the crystalline droplets are softer at similar to 2 GPa. Varying the processing gas pressures in the range of 0.01-0.6 mbar yields a change in the index of refraction of the films, which is close to the bulk value for gas pressures <0.1 mbar. The decrease of the index of refraction is caused by a lowered film density, correlating with a lowered mean energy of the particles impinging on the substrate, which is calculated. The results show the possibility of scaling-up the pulsed laser deposition process for industrial applications by use of CO2-laser radiation. (C) 1998 Elsevier Science S.A.

Raman spectroscopy is employed for structural characterization of BaTiO3, ferroelectric thin films, deposited by a hybrid DC-field enhanced pulsed laser deposition (PLD)-process. Pulsed excimer laser radiation (KrF, lambda=248 nm, tau=25 ns) is used for material removal from a sintered BaTiO3-target in an O-2 processing gas atmosphere (pressure p(O-2)approximate to 1*10(-1) mbar) with subsequent deposition on a substrate. Additional energy is supplied to the laser-induced plasma via a system of two concentric ring electrodes lying on different electric potentials (difference Delta V up to several hundred V), leading to further activation of the plasma and ignition of a DC-discharge in the processing gas atmosphere. Micro-Raman spectroscopy is performed with Ar+ laser radiation (lambda=488 nn), using a microscope unit to achieve a high spatial resolution in the range of 1 mu m. The Raman spectra of the BaTiO3, films show peaks typical for the tetragonal/cubic Perovskite structure. Polarization-dependent measurements reveal a mean c-axis orientation normal to the substrate surface, regardless whether a DC-field is applied or not. Using low DC-bias voltages (Delta V=50 V) allows lowering the substrate temperature without affecting the crystal quality of the films, as determined from the full width at half maximum (FWHM) of the Raman peaks, which is a measure for the crystal quality. High DC-bias voltages (Delta V=700 V), however, lead to amorphous films. The dielectric constant of the BaTiO3, films is strongly correlated to the crystal quality.

A rf-pumped CO2-laser in combination with a mechanical Q-switch is used for Pulsed Laser Deposition (PLD). Exemplary results of experimental and/or theoretical investigations of the laser radiation source output and of the material removal, transfer, and film deposition in PLD are presented. Variation of the electrical rf-excitation of the laser medium influences the pulse duration and shape, repetition rate, and average output power. Different characteristic pulses concerning pulse shape and duration are used for PLD of Al2O3. By model calculations the amount of the laser pulse energy utilised for target material removal, target heating and generation of the plasma state is determined. The weight loss as a function of fluence in the range of 5 - 20 S/cm(2) is calculated; it increases monotonically with the fluence. Al2O3 films deposited onto steel and silicon substrates exhibit an inhomogeneous structure with crystalline droplets embedded in an amorphous matrix, which is explained by thermal and non-thermal material removal processes. The microhardness of the droplets (approximate to 2 GPa) is lower than that of the matrix structure (approximate to 8 GPa) as determined by nanoindentation tests.

Sintered targets of ZrO2 and Al2O3 are ablated by KrF excimer laser radiation. The processing gas atmosphere consists of O2 at typical pressures of 10−3-1 mbar. Films with a thickness of 200–700 nm are deposited on a Pt/Ti/Si multilayer substrate. The analytical techniques used for the determination of structural characteristics of the films are X-ray diffraction and electron microscopy. The thickness and the complex refraction index are determined by ellipsometry by fitting a model for the film geometry to the measured data. The optical film thickness at different wavelengths is determined using interference reflection photometry. The investigations concentrate on the influence of the oxygen pressure, the target-to-substrate distance and the laser fluence on the refraction index of the films, which is correlated with the film density. The compaction of the films is achieved by particles impinging with kinetic energies above 30 eV on the growing surface. The kinetic energy of the particles depending on the processing parameters is modelled and related to the resulting film properties.

Material removal from sintered Al2O3-targets in a PLD process is examined experimentally and theoretically using an rf-pumped CO2-laser with a mechanical Q-switch (chopper). Laser pulse shape, repetition rate, and average output power are influenced by variation of chopper parameters and rf-pump voltage. The typical pulse duration ranges from 0.75 - 2.8 mu s (FWHM) at a repetition rate of 3.08 kHz and an average output power of < 300 W. The absorptivity of the target is examined with FTIR-spectroscopy, the surface morphology by scanning electron microscopy. The unirradiated target has an absorptivity of > 0.8, increasing after material removal with the target surface having a wavelike structure with dendrites and cracks. The target weight loss is determined by micro-balancing, yielding a material removal threshold of 4 J/cm(2). The weight loss per pulse is < 10 ng for the investigated fluences of 2 - 8 J/cm(2), re-deposition of removed material on the target is observed. Using model calculations the amount of the laser pulse energy used for material removal, target heating and for building up the plasma state is determined. The weight loss as a function of fluence in the range of 5 - 20 J/cm(2) is calculated; it increases monotonically with the fluence.

BaTiO3 thin films are deposited onto (111)-Si/Ti/Pt using a hybrid DC-field enhanced pulsed laser deposition (PLD)-technique with excimer laser radiation. Space- and time-resolved plasma emission spectroscopy (PES) is used for determination of the mean velocity of the particle species within the plasma/vapour. The structural properties of the films are characterised by XRD-measurements and micro-Raman spectroscopy. The electrical properties are analysed by impedance measurements. The electric field influences the number of excited and ionised particles within the ambient gas and plasma, caused by a discharge in the ambient gas and interaction between ambient gas and plasma. The hybrid process allows production of crystalline films of the tetragonal phase at reduced deposition temperatures. Dielectric constants of up to epsilon(r)=320 are obtained.

Sintered targets of Pb0.52Ti0.48O3 are used in a pulsed laser deposition (PLD) process to deposit thin ferroelectric films onto a Pt/Ti/Si(lll) substrate for electrical applications. Repetition rates vary between 1 and 200 Hz, the deposition temperature ranges from 500-800 degrees C. After thin film deposition the films are treated with different post-annealing procedures. The influence of repetition rate, deposition temperature and post-annealing procedures on the morphology, stoichiometry, crystalline phase, and the resulting electrical properties of the deposited films is investigated. Analytical methods used are scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, micro-Raman spectroscopy, and impedance measurements. A model for the dependence of film thickness and stoichiometry on repetition rate and substrate temperature is presented and compared to the experimental results. (C) 1997 Elsevier Science S.A.