A. del Prado

Full composition range silicon oxynitride films deposited by ECR-PECVD at room temperature

Abstract Silicon oxynitride films were deposited at room temperature using the ECR-PECVD technique. Precursor gases were O 2 , N 2 and SiH 4 . The composition of the films can be controlled by regulating the gases flow ratio. R = (O 2 + N 2 )/SiH 4 and R′ = O 2 /SiH 4 have proved to be the key deposition parameters. FTIR spectroscopy, AES and ellipsometric measurements were performed in order to characterise the films. A single Si O/Si N stretching band is observed in the FTIR spectrum for all compositions, indicating single-phase homogeneous SiO x N y films. FWHM of the stretching band shows a maximum for the composition corresponding to the same number of Si O and Si N bonds. Samples cover the whole composition range from silicon nitride to silicon oxide including nitrogen-rich films, even though the gas flow ratio R″ = N 2 /O 2 during deposition was small (from r″ = 1.0 for SiO 1.9 N 0.04 to R″ = 6.7 for SiO 0.26 N 1.2 ). Silicon oxide composition samples (SiO 2.0 ) show essentially the same IR features as the thermal oxide: Si O stretching band located at 1072 cm −1 , with a FWHM of 96 cm −1 and a shoulder/peak ratio of 0.30, while nitrogen-rich samples (SiO 0.26 N 1.2 ) show a total bonded hydrogen content below 2 × 10 22 cm −3 .

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...

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. 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.

Sub-bandgap absorption in Ti implanted Si over the Mott limit

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 × 1020 cm−3, which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm2) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 × 103 and 104 cm−1. These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.

Sub-bandgap spectral photo-response analysis of Ti supersaturated Si

We have analyzed the increase of the sheet conductance (ΔG□) under spectral illumination in high dose Ti implanted Si samples subsequently processed by pulsed-laser melting. Samples with Ti concentration clearly above the insulator-metal transition limit show a remarkably high ΔG□, even higher than that measured in a silicon reference sample. This increase in the ΔG□ magnitude is contrary to the classic understanding of recombination centers action and supports the lifetime recovery predicted for concentrations of deep levels above the insulator-metal transition.

Influence of interlayer trapping and detrapping mechanisms on the electrical characterization of hafnium oxide/silicon nitride stacks on silicon

Al/HfO2/SiNx:H/n-Si metal-insulator-semiconductor capacitors have been studied by electrical characterization. Films of silicon nitride were directly grown on n-type silicon substrates by electron cyclotron resonance assisted chemical vapor deposition. Silicon nitride thickness was varied from 3 to 6.6 nm. Afterwards, 12 nm thick hafnium oxide films were deposited by the high-pressure sputtering approach. Interface quality was determined by using current-voltage, capacitance-voltage, deep-level transient spectroscopy (DLTS), conductance transients, and flatband voltage transient techniques. Leakage currents followed the Poole–Frenkel emission model in all cases. According to the simultaneous measurement of the high and low frequency capacitance voltage curves, the interface trap density obtained for all the samples is in the 1011 cm−2 eV−1 range. However, a significant increase in this density of about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride interfacial layers. In thi...

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

SiOxNyHz films were deposited from O2, N2, 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...

Effect of interlayer trapping and detrapping on the determination of interface state densities on high-k dielectric stacks

The influence of the silicon nitride blocking layer thickness on the interface state densities (Dit) of HfO2/SiNx:H gate-stacks on n-type silicon have been analyzed. The blocking layer consisted of 3 to 7 nm thick silicon nitride films directly grown on the silicon substrates by electron-cyclotron-resonance assisted chemical-vapor-deposition. Afterwards, 12 nm thick hafnium oxide films were deposited by high-pressure reactive sputtering. Interface state densities were determined by deep-level transient spectroscopy (DLTS) and by the high and low frequency capacitance-voltage (HLCV) method. The HLCV measurements provide interface trap densities in the range of 1011 cm−2 eV−1 for all the samples. However, a significant increase in about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride barrier layers. In this work we probe that this increase is an artifact due to the effect of traps located at the internal interface existing between the HfO2 and SiNx:H films. Because charge trapp...

Optical spectroscopic study of the SiN∕HfO2 interfacial formation during rf sputtering of HfO2

High-k stacks formed by chemical-vapor-deposited SiN and high-pressure sputtered HfO2 in either O2 or Ar atmosphere have been studied. The introduction of a SiN layer is proposed to prevent the uncontrollable SiO2 growth while sputtering. The formation of Si–O bonds after the sputtering of the HfO2 film in O2 atmosphere was observed by infrared spectroscopy. Optical diagnosis of the plasma demonstrated a high density of O radicals in the system when working with O2. The small radius and high reactivity of these O radicals are the source of the SiN oxidation. However, the structure of the SiN film is preserved during Ar sputtering.