J. Röhrich

Physical properties of high pressure reactively sputtered TiO2

We present a study of the physical properties of TiO2 thin films deposited at 200°C on Si by high pressure reactive sputtering, a nonconventional deposition method. Just after deposition, the TiO2 films were in situ annealed in the deposition chamber at temperatures between 600 and 900°C in O2 atmosphere. Morphological, compositional, structural and electrical characterization of the samples was performed by means of several techniques, including transmission electron microscopy, heavy-ion elastic recoil detection analysis, infrared spectroscopy, x-ray and electron diffraction and capacitance-voltage measurements. Microscopy images show that the TiO2 films are polycrystalline, and that a SiO2 film spontaneously grows at the TiO2∕Si interface. The unannealed TiO2 films are oxygen rich, as shown by compositional measurements. By annealing this oxygen excess is released. For temperatures above 600°C the TiO2 films are stoichiometric. Infrared spectroscopy and diffraction measurements show that as-deposited f...

Composition and optical properties of silicon oxynitride films deposited by electron cyclotron resonance

Silicon oxynitride films covering the whole composition range from silicon nitride to silicon oxide have been deposited by electron cyclotron resonance chemical vapor deposition from SiH4, O2 and N2 gas mixtures. The composition of the films has been determined by heavy-ion elastic recoil detection analysis (HI-ERDA), providing absolute concentrations of all elements, including H, and by Auger electron spectroscopy. Additionally, Fourier transform infrared (FTIR) spectroscopy and ellipsometry measurements have been performed on the same samples for optical characterization. n nThe concentration of the different species (Si, O, N and H) and the density of the films have been calculated and compared to the theoretical values for stoichiometric films. The presence of N–H bonds and non-bonded H results in a significant decrease of the Si concentration with respect to the theoretical value, especially for samples close to silicon nitride composition. The decrease of the Si concentration results in a decrease of both the N and O concentrations. The overall result is a decrease of the density and therefore a decrease of the refractive index with respect to stoichiometric films. n nThe total H content determined by ERDA has been compared with the area of the FTIR N–H stretching band, which is frequently used to obtain the H content. It has been found that the calibration factor for this band depends on composition, increasing with increasing the O content.

High-pressure reactively sputtered HfO2: Composition, morphology, and optical properties

Hafnium oxide films were deposited by high pressure reactive sputtering using different deposition pressures and times. The composition, morphology, and optical properties of the films, together with the sputtering process growth kinetics were investigated using heavy ion elastic recoil detection analysis, Fourier transform infrared spectroscopy, ultraviolet-visible-near infrared spectroscopy, x-ray diffraction, and transmission electron microscopy. The films showed a monoclinic polycrystalline structure, with a grain size depending on the deposition pressure. All films were slightly oxygen rich with respect to stoichiometric HfO2 and presented a significant amount of hydrogen up to 6 at. %, which is attributed to the high affinity for moisture of the HfO2 films. The absorption coefficient was fitted to the Tauc law, obtaining a band gap value of 5.54 eV. It was found that the growth rate of the HfO2 films depends on the deposition pressure P as P x7f1.75 . This dependence is explained by a diffusion model of the thermalized atoms in high-pressure sputtering. Additionally, the formation of an interfacial silicon oxide layer when the films were grown on silicon was observed, with a minimum thickness for deposition pressures around 1.2 mbars. This interfacial layer was formed mainly during the initial stages of the deposition process, with only a slight increase in thickness afterwards. These results are explained by the oxidizing action of the oxygen plasma and the diffusion of oxygen radicals and hydroxyl groups through the polycrystalline HfO2 film. Finally, the dielectric properties of the HfO2/SiO2 stacks were studied by means of conductance and capacitance measurements on Al/HfO2/SiO2/Si devices as a function of gate voltage and ac frequency signal.

Optical and structural properties of SiOxNyHz films deposited by electron cyclotron resonance and their correlation with composition

SiOxNyHz films were deposited from O2,u2002N2, and SiH4 gas mixtures at room temperature using the electron cyclotron resonance plasma method. The absolute concentrations of all the species present in the films (Si, O, N, and H) were measured with high precision by heavy-ion elastic recoil detection analysis. The composition of the films was controlled over the whole composition range by adjusting the precursor gases flow ratio during deposition. The relative incorporation of O and N is determined by the ratio Q=φ(O2)/φ(SiH4) and the relative content of Si is determined by R=[φ(O2)+φ(N2)]/φ(SiH4) where φ(SiH4), φ(O2), and φ(N2) are the SiH4, O2, and N2 gas flows, respectively. The optical properties (infrared absorption and refractive index) and the density of paramagnetic defects were analyzed in dependence on the film composition. Single-phase homogeneous films were obtained at low SiH4 partial pressure during deposition; while those samples deposited at high SiH4 partial pressure show evidence of separatio...

Bonding configuration and density of defects of SiOxHy thin films deposited by the electron cyclotron resonance plasma method

The composition, bonding configuration, hydrogen content, and paramagnetic defects of SiOxHy thin films were studied. Films were deposited by the electron cyclotron resonance plasma method at room temperature using SiH4 and O2 as precursor gases. The film composition was measured by heavy ion elastic recoil detection analysis and energy dispersive x-ray spectroscopy. Suboxide films with compositions ranging from SiO2 to SiH0.38 were obtained. Infrared spectroscopy showed the presence of different Si–O and Si–H vibration modes. The usual estimation of the oxygen to silicon ratio by the wave number of the Si–O–Si stretching band was not accurate for films far from stoichiometry. These off-stoichiometric films also showed a broader Si–O–Si stretching peak than the stoichiometric ones, indicating a higher bonding disorder. The position of the Si–O–Si bending and rocking modes did not depend on the film composition. On the other hand, the peak position of the Si–H modes were found strongly dependent on the Si ...

Compositional analysis of amorphous SiNx:H films by ERDA and infrared spectroscopy

The composition of amorphous SiN x : H films grown by the electron cyclotron resonance (ECR) plasma method was studied by heavy-ion elastic recoil detection analysis (ERDA) with 129 Xe ion beams of 1.1 and 1.8 MeV amu -1 and time-of-light (ToF) mass separation. This technique allows simultaneous determination of the absolute atomic concentrations and depth profiles of all involved elements, including hydrogen. Radiation damage at extended ion beam exposure was found to decrease the N/Si ratio and the hydrogen concentration. By measuring the dose dependence, this effect was quantified in order to support correction to zero dose conditions. Monitoring the damage effects by infrared (IR) spectroscopy revealed an increase of the Si-H bond density at the expense of N-H bonds. The results suggest that the damage process is initiated by breaking of N-H bonds and that recapturing of hydrogen by Si appears as an effective competitive process to hydrogen release. Combining the ERDA and IR data, the oscillator strength ratio of the N-H and Si-H stretching bands is found to be 1.4 ± 0.2.

Influence of H on the composition and atomic concentrations of “N-rich” plasma deposited SiOxNyHz films

The influence of H on the composition and atomic concentrations of Si, O, and N of plasma deposited SiOxNyHz films was investigated. The bonding scheme of H was analyzed by Fourier-transform infrared spectroscopy. The composition and absolute concentrations of all the species present in the SiOxNyHz, including H, was measured by heavy-ion elastic recoil detection analysis (HI–ERDA). Samples were deposited from SiH4, O2, and N2 gas mixtures, with different gas flow ratios in order to obtain compositions ranging from SiNyHz to SiO2. Those samples deposited at higher SiH4 partial pressures show both Si–H and N–H bonds, while those deposited at lower SiH4 partial pressures show N–H bonds only. The Si–H and N–H bond concentrations were found to be proportional to the N concentration. The concentration of H was evaluated from the Si–H and N–H stretching absorption bands and compared to the HI–ERDA results, finding good agreement between both measurements. The deviation from H-free stoichiometric SiOxNy composit...