F. L. Martı́nez

Rapid thermal annealing effects on the structural properties and density of defects in SiO2 and SiNx:H films deposited by electron cyclotron resonance

The effect of rapid thermal annealing processes on the properties of SiO2.0 and SiN1.55 films was studied. The films were deposited at room temperature from N2 and SiH4 gas mixtures, and N2, O2, and SiH4 gas mixtures, respectively, using the electron cyclotron resonance technique. The films were characterized by Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance spectroscopy. According to the FTIR characterization, the SiO2.0 films show continuous stress relaxation for annealing temperatures between 600 and 1000 °C. The properties of the films annealed at 900–1000 °C are comparable to those of thermally grown ones. The density of defects shows a minimum value for annealing temperatures around 300–400 °C, which is tentatively attributed to the passivation of the well-known E′ center Si dangling bonds due to the formation of Si–H bonds. A very low density of defects (5×1016 cm−3) is observed over the whole annealing temperature range. For the SiN1.55 films, the highest struct...

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. The 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. The 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.

Defect structure of SiNx:H films and its evolution with annealing temperature

The structure of defects of SiNx:H films is investigated by electron-spin resonance. It is found that a relaxation process takes place at annealing temperatures below 600 °C for those compositions in which the nitrogen-to-silicon ratio is above the percolation threshold of the Si–Si bonds in the nitride lattice. The nature of this process is discussed and attributed to a thermally activated charge transfer between metastable defects. No such relaxation occurs in the films with a composition below the percolation threshold, possibly due to a positive correlation energy and a structural lack of flexibility. For higher annealing temperatures, an increase of the defect density is observed and associated with the thermal release of hydrogen.

Thermally induced changes in the optical properties of SiNx:H films deposited by the electron cyclotron resonance plasma method

We analyze the effect of thermal processes on the optical properties (refractive index, optical gap, Tauc coefficient, and Urbach energy) of SiNx:H films. Films with three different nitrogen to silicon ratios (x=0.97, x=1.43, and x=1.55, respectively) were deposited by a chemical vapor deposition technique assisted by an electron cyclotron resonance generated plasma. After deposition they were subjected to rapid thermal annealing at temperatures ranging from 300 °C to 1050 °C. We found that the percolation threshold for Si–Si bonds (at x=1.1) separates films with different response to thermal treatments. The changes of the Tauc coefficient and the Urbach energy at moderate annealing temperatures indicate a structural relaxation of the network for the films with x above the percolation threshold, while at higher temperatures the trends are inverted. In the case of x below the percolation limit the inversion point is not observed. These trends are well correlated with the width of the Si–N infrared stretchi...

Temperature effects on the electrical properties and structure of interfacial and bulk defects in Al/SiNx:H/Si devices

Bulk properties of SiNx:H thin film dielectrics and interface characteristics of SiNx:H/Si devices are studied by a combination of electrical measurements (capacitance–voltage and current–voltage characteristics) and defect spectroscopy (electron spin resonance). The SiNx:H films were deposited by an electron cyclotron resonance plasma method and subjected to rapid thermal annealing postdeposition treatments at temperatures between 300 and 1050 °C for 30 s. It is found that the response of the dielectric to the thermal treatments is strongly affected by its nitrogen to silicon ratio (N/Si=x) being above or below the percolation threshold of the Si–Si bonds in the SiNx:H lattice, and by the amount and distribution of the hydrogen content. The density of Si dangling bond defects decreases at moderate annealing temperatures (below 600 °C) in one order of magnitude for the compositions above the percolation threshold (nitrogen rich, x=1.55, and near stoichiometric, x=1.43). For the nitrogen rich films, a good...

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.

Thermal stability of a-SiNx:H films deposited by plasma electron cyclotron resonance

We analyze the influence of rapid thermal annealing on Al/SiNx:H/Si structures with a nitrogen to silicon ratio of 1.55 in the insulator bulk. The SiNx:H is deposited by the electron cyclotron resonance plasma method and the films were annealed at temperatures ranging from 300 to 1050 °C. We have related the changes of the interface trap density with those of the insulator bulk density of dangling bonds, resistivity, and breakdown field. A sharp dip in the dangling bond density is observed at moderate annealing temperatures, from 1.8×1018 cm−3 for the as-deposited film down to 9.6×1016 cm−3 at the point of inversion of the trend between 500 and 600 °C. The density of interface states is also reduced in this range of temperatures from 3.6×1011 to 1.2×1011 eV−1 cm−2. Resistivity and breakdown field are maintained in the range 5×1014–5×1015 Ω cm and 6.4–6.6 MV/cm, respectively, up to a temperature of 600 °C. We attribute the improvement of the interface characteristics and the decrease of dangling bonds to a...

Photovoltage effects under sinusoidal illumination

A theory is presented for open-circuit voltage (PV) and short-circuit current (SI) effects when a p-n junction diode is illuminated through a slit with a sinusoidal pattern moving across it. The amplitude of PV oscillations is strongly reduced due to annihilation of photocarriers diffusing to the metal contacts on the surface so as to keep the voltage beneath the contacts constant. From the dependence of the oscillation amplitude on the wave vector of the illumination pattern, the lateral diffusion length of the photocarriers can be deduced. The short-circuit currents under sinusoidal and uniform illumination are equal. A combination of PV and SI measurements should reveal anisotropy in the diffusivities of photocarriers in the plane of the diode and perpendicular to it. Recent results on quantum well diodes are discussed.