E. San Andrés

A comparative study of the electrical properties of TiO2 films grown by high-pressure reactive sputtering and atomic layer deposition

Oxide–semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO2 films annealed in O2 at temperatures ranging from 600 to 900 °C, and atomic layer deposited (ALD) TiO2 films grown at 225 or 275 °C from TiCl4 or Ti(OC2H5)4, and annealed at 750 °C in O2, has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900 °C in oxygen atmosphere exhibit the best characteristics, with Dit density being the lowest value measured in this work (5–6 × 1011 cm−2 eV−1), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO2 film thickness and the crystallinity, since in the films annealed at 900 °C rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600–800 °C, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700 °C annealed HPRS films than for 750 °C annealed ALD TiO2 films, whereas 800 °C annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.

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.

A Reliable Metric for Mobility Extraction of Short-Channel MOSFETs

When comparing the extracted carrier mobility of long- and short-channel transistors, special consideration must be given to the metallurgical gate length (Lmet), neglecting the impact of source and drain junction profiles. Lmet can be identified with nanometer precision by using RF split-C-V measurements, and physical and electrical analysis can demonstrate the accuracy of the method. Another important parameter, the external transistor resistance (Rsd), can be identified with linear current measurements of short-channel devices. However, it is important to quantify the mobility dependence from the gate length in order to obtain an accurate result. A method to estimate the electrical field (Eeff) of short-channel devices is proposed. The extracted short-channel mobility shows a universal behavior identical to the classical long-channel one.

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...

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.

Characterization of nitrogen-rich silicon nitride films grown by the electron cyclotron resonance plasma technique

Amorphous hydrogenated silicon nitride films have been deposited by the electron cyclotron resonance plasma technique, using N2 and SiH4 as precursor gases. The gas flow ratio, deposition temperature and microwave power have been varied in order to study their effect on the properties of the films, which were characterized by Rutherford back-scattering spectrometry, elastic recoil detection analysis (ERDA), Fourier transform infrared spectroscopy and ellipsometry. All samples show N/Si ratios near or above the stoichiometric value (N/Si = 1.33). The hydrogen content determined from ERDA measurements is significantly higher than the amount detected by infrared spectroscopy, evidencing the presence of non-bonded H. As the N2/SiH4 gas flow ratio is increased (by decreasing the SiH4 partial pressure), the Si content decreases and the N–H concentration increases, while the N content remains constant, resulting in an increase of the N/Si ratio. The decrease of the Si content causes a decrease of the refractive index and the density of the film, while the growth ratio also decreases due to the limiting factor of the SiH4 partial pressure. The infrared Si–N stretching band shifts to higher wavenumbers as the N–H concentration increases. The increase of deposition temperature promotes the release of H, resulting in a higher incorporation of N and Si into the film and a decrease of the N/Si ratio. The effect of increasing the microwave power is analogous to increasing the N2/SiH4 ratio, due to the increase in the proportion of nitrogen activated species.

Thermally induced modifications on bonding configuration and density of defects of plasma deposited SiOx:H films

The bonding configuration, hydrogen evolution, and defect content of rapid thermally annealed (RTA) SiOx:H films of different compositions were studied. Infrared absorption measurements showed that all the hydrogen present in the films is lost at annealing temperatures below 600 °C without any change in the oxygen to silicon ratio of the films. The activation energy of the hydrogen release is in the 0.21–0.41 eV range independently of film composition, suggesting that the process occurs via network bond reactions. For annealing temperatures higher than 700 °C, a change in the Si–O–Si stretching wave number from the initial unannealed value to the 1070–1080 cm−1 range was promoted, independently of the initial film composition. Electron spin resonance measurements showed that all the films contain two type of bulk paramagnetic defects: the E′ center (•Si≡O3) and the silicon dangling bond center (•Si≡Si3). The RTA process promotes a general decrease of defect concentration for annealing temperatures below 4...

Optimization of Sub-Melt Laser Anneal: Performance and Reliability

A thermo-mechanical stress model (TMS) is presented to explain the impact of sub-melt laser anneal (LA) on SiON dielectric and on the overall transistor performance. An Lgmin reduction of 15nm/5nm for nMOS/pMOS over our poly-Si/SiON reference, with 8% capacitance and 10% source and drain resistance (RSD) improvement, is demonstrated. Best device performance and NBTI immunity are reached by lowering the laser power and optimizing the nitrogen and fluorine profile. This minimizes the increase of Si dangling bonds at the SiON/Si interface and the oxide fixed charges, generated by the thermo-mechanical stress (TMS) during the LA fast thermal gradient. The full potential of LA is demonstrated by skipping the RTA. An Lgmin gain of 25nm/20nm is achieved for metal gate nMOS/FUSI gate pMOS devices over the junction RTA reference. Optimal 0.26 fF/mum overlap capacitance values (at Vdd= | 1 | V), 18%/ 23% for nMOS/pMOS lower CV/I product and pMOS improved RSD are demonstrated