Guenter Reisse

Titanium nitride thin film deposition by laser CVD

Abstract Investigations aimed at the development of a laser induced chemical vapor deposition process for use in structured deposition of titanium nitride coatings on tool steel were performed. Experiments were carried out using a focused argon ion laser beam, where lateral film growth is realized by laser scanning. In particular, the deposition of titanium nitride from TiCl4/N2/H2-precursor gas mixtures at atmospheric pressure was investigated. The deposited TiN films are adherent, hard, rough and porous. The double layer capacitance of those films is approximately one order of magnitude higher than that of smooth and dense TiN films. In order to estimate the laser induced temperatures in the film-substrate-system, lateral and temporal temperature fields were calculated.

Laser based chemical vapour deposition of titanium nitride coatings

Abstract Investigations concerning the development of a chemical vapour deposition process for the structures deposition of titanium nitride coatings onto tool steel at low substrate temperatures are presented. In order to stimulate local film growth of hard coatings, excimer and argon ion laser beams were used respectively. In the experiments with the excimer laser, the beam projection method was used. The TiNx coatings were deposited from the precursor gas tetrakis-(dimethylamido)-titanium (Ti(N(CH3)2)4), in a reactive atmosphere of nitrogen and hydrogen at the excimer wavelengths 248 nm and 351 nm in combination with an additional r.f. or d.c. discharge. Experiments using an argon ion laser were carried out with a focused laser beam, where lateral film growth was induced by laser scanning. In particular, the deposition of TiNx from TiCl4N2H2 and TiCl4NH3 gas mixtures was inves tigated.

Characterization of ion-assisted pulsed laser deposited cubic boron nitride films

Abstract Cubic boron nitride films were deposited by pulsed laser deposition from a boron nitride and a boron target using a KrF-excimer laser, where the growing films were bombarded by a nitrogen or a nitrogen/argon ion beam. The variation of the film properties with laser and ion beam parameters and substrate temperature has been investigated by infrared spectroscopy, cross-section and plan-view high-resolution transmission electron microscopy, electron-energy-loss spectroscopy and in situ ellipsometry. It will be shown that c -BN films with high phase purity can be prepared at sufficiently strong ion bombardment as well as substrate temperatures above 160°C. The c -BN phase was found to grow exclusively on top of the well-known hexagonal interlayer with c -axis orientation parallel to the substrate surface. Two types of nucleation were observed, the first characterized by c -BN (111) and the second by c -BN (001) lattice planes growing parallel to the (0002) lattice planes of the initially formed h- BN layer. c -BN films were prepared at maximum growth rates of 16 nm/min. Additional UV-photon irradiation of the growing films results in distinct modifications of the microstructure of the BN films. Using laser pulse energy densities on the substrate surface above 200 mJ/cm 2 the laser irradiation leads to the formation of turbostratic h- BN even though the unirradiated film regions of the same sample show the cubic structure. In contrast, films irradiated at 100 to 160 mJ/cm 2 are cubic. Electron microscopic observations show that in this range the mean diameter of crystallite in the excimer laser irradiated regions increased by a factor of two in comparison with unirradiated regions of the same sample. The experimental results will be discussed in context with the results of temperature field calculations.

Properties of pulsed laser deposited boron nitride films

Pulsed laser ablation using an excimer laser of 248 nm wavelength was applied to prepare boron nitride films, where the ablation from boron nitride as well as elemental boron targets was studied. The growing films were bombarded by a nitrogen or a nitrogen/argon ion beam to obtain stoichiometric films and to investigate ion induced modifications of structure and properties. Depending on deposition parameters the refractive index of the boron nitride films in the visible wavelength range varies between 2.5 and 1.7 and the optical energy band gap between 2.0 and 4.5 eV. Most films were found to be completely sp2-bonded and amorphous to nanocrystalline with a turbostratic microstructure. Only boron nitride films deposited from the boron target and bombarded with nitrogen/argon ions show also an absorption peak in the infrared spectrum that indicates the presence of the cubic phase.

Deposition of optical coatings by pulsed laser ablation

Abstract Hafnia, zirconia and yttria films for optical applications were prepared by pulsed laser deposition using an excimer laser at 248 nm wavelength. The growing films were bombarded by oxygen ions. Films were investigated with regard to refractive index, absorption and laser damage thresholds. Based on the findings that the refractive index varies with ion bombardment and growth rate it is shown that multilayer systems with regard to refractive index consisting of only one material can be prepared. Such multilayers were investigated with regard to reflectivity and laterally resolved absorptivity.

Laser-induced structural phase changes in i-carbon films

Abstract Amorphous i-C films were irradiated as-deposited or during the growth process with laser pulses of wavelengths 1.06 μm, 308 nm and 248 nm and ns-pulse duration. Films irradiated during deposition at the ultraviolet wavelengths contained a remarkably high proportion of microcrystals (up to 40% of the film material). Analysis of different patterns indicate that these microcrystals consist of cubic diamond.

Laser-induced chemical vapour deposition of conductive and insulating thin films

Abstract Investigations concerning the laser-induced chemical vapour deposition of Mo, W, Co and TiSi2 conductive thin film structures from Mo(CO)6, W(CO)6, Co2(CO)8, TiCl4 and SiH4 using a direct writing method are presented. SiO2 thin films were deposited from SiH4 and N2O in a large area deposition process stimulated by an excimer laser by using a parallel beam configuration.

Ion and laser induced modification of optical and structural properties of i-carbon films

Abstract i-Carbon films were prepared by ion beam sputter deposition, a dual-beam method and direct ion beam deposition in order to investigate the effects of ions of specific energy on the optical properties of these films. With increasing ion bombardment the refractive index decreases, and the films become remarkably less absorbent in the visible and near-IR spectral region. Irradiation of as-deposited and growing i-C films with laser pulses of wavelengths 1.06 μm, 308 nm and 248 nm and nanosecond duration results in the formation of various metastable carbon phases. In particular laser modification of these films during the growth process using UV wavelengths leads to the formation of crystallites within the films which have a cubic structure according to transmission electron diffraction analysis.

Properties of laser-ablated amorphous carbon films

Excimer laser ablation of a polycrystalline graphite target was used to prepare amorphous carbon films. Optical properties of the films were investigated in dependence of the laser power density and the hydrogen supply during deposition. The hydrogen content of the films was 0.7 to 37.5 at % in dependence of the deposition conditions. An optical bandgap up to 1.6 eV was found for films with low hydrogen content. Applying an additional hydrogen plasma during deposition the optical bandgap increased up to 1.95 eV. The laser power density was varied between 1.5 and 3.4 X 107 W/cm2. Generally, the lower power densities near the ablation threshold lead to larger optical bandgaps. An additional excimer laser irradiation of the growing carbon films with a laser power density up to 106 W/cm2 leads to graphitization within the otherwise amorphous films. An increase of the laser power density to 2 X 106 W/cm2 induce the formation of microcrystallites. Those microcrystallites could be identified as cubic diamond by means of transmission electron microscopy (TEM) investigations.

Absorption and laser damage threshold studies of ion assisted pulsed laser deposited oxide films

The laterally resolved absorption and the laser damage thresholds at 1.06 micrometers wavelength of yttria and hafnia films prepared by pulsed laser deposition with oxygen ion bombardment of the growing films were investigated. Depending on the laser and ion beam parameters films with low average absorption can be prepared by that method. Consequently, high predominantly intrinsic absorption induced laser damage thresholds D1 comparable with those of continuously evaporated films can be prepared. The more defect induced laser damage thresholds D0, however, are largely determined by a certain number of micron- sized particulates embedded inside the films. Their number can be reduced by optimizing the laser pulse power density and the laser beam cross-section on the target, while their influence on laser damage thresholds can be reduced by increasing the ratio of oxygen ion bombardment to growth rate.