Fluorinated Silicon Nitride Films Research Articles

Influence of substrate temperature on the properties of fluorinated silicon-nitride thin films deposited by IC-RPECVD

Fluorinated silicon-nitride films have been prepared from an Ar/SiF4/NH3 gas mixture by inductively coupled remote plasma-enhanced chemical vapor deposition (IC-RPECVD) at different substrate temperatures, ranging from 150 to 300°C. All of the resulting deposited silicon-nitride films were free of Si-H bonds, showed high dielectric breakdown fields (≥8 MV cm−1), and had root mean square (rms) surface roughness values below 3 A. The films’ refractive indices and the contents of O and F remain constant, but Si/N ratios drop from 5 to 2 and N-H bond concentrations decrease in the range (1.3–0.9) × 1022 cm−3 as the substrate temperature increases. The density of interface states (Dit) with c-Si was reduced from 2.4 × 1012 to 8 × 1011 eV−1 cm−2 at substrate temperatures ≥250°C.

Role of hydrogen on the deposition and properties of fluorinated silicon-nitride films prepared by inductively coupled plasma enhanced chemical vapor deposition using SiF4∕N2∕H2 mixtures

Fluorinated silicon-nitride films have been prepared at low temperature (250°C) by remote plasma enhanced chemical vapor deposition using mixtures of SiF4, N2, Ar, and various H2 flow rates. The deposited films were characterized by means of single wavelength ellipsometry, infrared transmission, resonant nuclear reactions, Rutherford backscattering analysis, and current-voltage measurements. It was found that films deposited without hydrogen grow with the highest deposition rate, however, they result with the highest fluorine content (∼27at.%) and excess of silicon (Si∕Nratio≈1.75). These films also have the lowest refractive index and the highest etch rate, and exhibit very poor dielectric properties. As a consequence of the high fluorine content, these films hydrolize rapidly upon exposure to the ambient moisture, forming Si–H and N–H bonds, however, they do not oxidize completely. The addition of hydrogen to the deposition process reduces the deposition rate but improves systematically the stability and insulating properties of the films by reducing the amount of both silicon and fluorine incorporated during growth. All the fluorinated silicon-nitride films deposited at hydrogen flow rates higher than 3.5sccm resulted free of Si–H bonds. In spite of the fact that films obtained at the highest hydrogen flow rate used in this work are still silicon rich (Si∕Nratio≈1.0) and contain a considerable amount of fluorine (∼16at.%), they are chemically stable and show acceptable dielectric properties.

Composition, structural, and electrical properties of fluorinated silicon–nitride thin films grown by remote plasma-enhanced chemical-vapor deposition from SiF4/NH3 mixtures

Fluorinated silicon–nitride films (SiNx:F) have been prepared at 250 °C by remote plasma-enhanced chemical-vapor deposition using mixtures of SiF4/NH3 in different proportions. The structure, relative composition, and fluorine content of the films were evaluated by Fourier-transform infrared spectroscopy, Rutherford backscattering, ellipsometry, and resonant nuclear-reaction analysis. The electrical properties of the films were also assessed from the current–voltage characteristics of Al–SiNx:F–Si metal–insulating–semiconductor structures. It was found that the SiF4/NH3 ratio produces little influence on the refractive index and density of the films, but this ratio has important effects on the fluorine content, deposition rate, and electrical properties. In general, these SiNx:F films are free of Si–H bonds, chemically stable, and show breakdown fields above 8 MV/cm.

Composition, oxidation, and optical properties of fluorinated silicon nitride film by inductively coupled plasma enhanced chemical vapor deposition

Amorphous fluorinated silicon nitride films have been deposited with the variation of NF3 flow rate using SiH4, N2, Ar, and NF3 gases by inductively coupled plasma enhanced chemical vapor deposition for the first time, and the absolute composition, oxidation mechanism, and optical properties were investigated. The absolute composition including hydrogen was performed by means of elastic recoil detection time of flight. It was found that the oxygen and fluorine contents in the film dramatically increased, but the hydrogen content decreased to below 4 at.% as the NF3 flow rate increased. The oxidation mechanism could be explained in terms of the incorporation of the activated residual oxygen species in the chamber into the film with unstable open structure by the fluorine-added plasma. It was shown that the density and optical properties such as refractive index, absorption coefficient, and optical energy gap depended on the film composition. The variations of the above properties for fluorinated silicon nitride film could be interpreted by the contents of fluorine and oxygen with high electronegativity.

ChemInform Abstract: Remote Plasma‐Enhanced CVD of Fluorinated Silicon Nitride Films.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Fluorinated silicon nitride film for the bottom antireflective layer in quarter micron optical lithography

Fluorinated silicon nitride thin film as a bottom antireflective layer (BARL) material, being suitable for line-patterning in KrF excimer laser (248 nm) lithography, has been studied by film fabrication/characterization and computer simulation. Three-dimensional reflectance simulation process suggests that the 0% reflectance between photoresist (PR) and BARL can be achieved by selecting proper combinations of film optical properties such as refractive index (n), extinction coefficient (k) and thickness (d). For the PR/300 Å BARL/c-Si or PR/300 Å BARL/W-Si structure at a wavelength of 248 nm, the simulation process reveals that nearly 0% reflectance could be obtained when the n and k values of the film are 2.109 and 0.68 or 2.052 and 0.592 respectively. The fluorinated silicon nitride films prepared by ICP enhanced CVD have been evaluated with the variations of flow rates under the two conditions of and 3:20 (sccm). The film n and k values at 248 nm vary in the ranges of 1.665 - 2.352 and 0.007 - 0.695 respectively, depending on gas flow ratio. As it is very sensitive to the film thickness, the reflectance could be reduced, using compoter simulation, to almost 0% by changing the film thickness. Furthermore, the ARL performance for line/space processed by the KrF excimer laser stepper and the stripping ability/selectivity show this material to be a superior candidate for deep-UV microlithography applications.

Remote Plasma-Enhanced CVD of Fluorinated Silicon Nitride Films

An investigation has been made of the effect of dilution of nitrogen with NF3 on the properties of silicon nitride deposited by remote plasma-enhanced CVD (PECVD). For NF3/N2 mixtures with < 1.5% NF3, fluorinated films with the structure of silicon nitride are formed but the total concentration of bonded hydrogen in the films decreases with increasing NF3 flow rate, which leads to an improvement of the electrical properties of the films compared with unfluorinated films. Such films could be of interest for device applications. For NF3/N2 mixtures with NF3 > 1.5 %, films with the structure of silicon dioxide are formed, but they do not contain enough oxygen to give typical SiO2 IR spectra. It is suggested that the silicon dioxide structure arises because of isoelectronic substitution of oxygen by NF.

The Applicability of Fluorinated Silicon Nitride Film As Bottom Antireflective Layer In Deep Ultraviolet Lithography

AbstractThis study describes the use of fluorinated silicon nitride film as a bottom antireflective layer (BARL) material suitable for line-patterning in quarter-micron KrF excimer laser lithography. For the structures of photoresist/BARL (300Å)/c-Si and photoresist/BARL (300 Å )/W-Si at a wavelength of 248nm, 0% reflectance could be achieved when the refractive index (n) and extinction coefficient (k) values of the film are 2.11 and 0.68 or 2.05 and 0.59, respectively. The fluorinated silicon nitride thin films on p-type (100) Si substrates obtained by inductively coupled plasma enhanced CVD have been evaluated with the variations of NF3 flow rates under the two conditions of SiH4:N2=2:15 and 3:20 (seem). The films optical constants and reflectance were investigated by spectroscopic ellipsometry combined with a reflectance simulation program. The film n and k values at 248nm vary in the ranges of 1.67~2.35 and 0.01~0.69, respectively, depending on gas flow ratio of SiH4:N2:NF3. Low reflectance of below 5% can be obtained from reflectance simulation for two deposition conditions with a BARL thickness of 300Å. In addition, the reflectance could be reduced to almost 0% by controlling film thickness. Finally, the antireflective layer performance was investigated using KrF excimer laser lithography.

I.r. spectra resolution in fluorinated silicon nitride films

The broad I.r. Si-N band (700–1200 cm−1) in fluorinated silicon nitride films has been resolved. I.r. spectra of the samples have been fitted using Gaussian curves centred in positions determined from the maxima of the negative second derivative of the digitized spectra. In silicon nitride films deposited by plasma-assisted chemical vapour deposition from SiH4-NF3-NH3-N2 gas mixtures-SiFn radicals (n=1–3) incorporated in their structures have been detected. The relative concentrations of the different fluorine radicals present in the network depend on the NF3 flow ratio used. As the flow ratio increases above 0.5, -SiF and-SiF2 concentrations in the film reach the steady state. However, an appreciable increase in-SiF3 and [-SiF2-] n concentrations has been observed.

Oxidation kinetics of plasma-enhanced chemical vapor deposition silicon nitride films deposited from SiH4/NH3/NF3/N2 mixtures

Fluorinated silicon nitride films have been deposited by plasma-enhanced chemical vapor deposition (PECVD) varying the relative [NF3]/([NH3]+[NF3]) flow ratio in the range 0–1. The as-deposited films show an increase in the –NH radicals and a decrease in the –SiH radicals when the flow ratio increases above 0.5. In addition, these films are very unstable in hot water as well as in normal air atmospheres. The oxidation kinetics has been explained in terms of a direct oxidation reaction of the silicon nitride lattice accompanied by the formation of fluorinated complexes which also react with moisture to give finally SiO2.

ChemInform Abstract: Properties of Fluorinated Silicon Nitride Films for Applications to Device Processes.

AbstractFluorinated silicon nitride films are deposited by plasma‐CVD using SiF4/N2/H2 or Si2F6/N2/H2 gas mixtures as sources.

Oxygenated and Fluorinated Amorphous Silicon Nitride Films and their Use in Thin Film Transistors

ABSTRACTWe present a comparison of the properties of films of amorphous silicon nitride, amorphous silicon oxynitride, and amorphous fluorinated silicon nitride deposited by plasma enhanced chemical vapor deposition. The properties of fluorinated silicon nitride films degrade when exposed to air. TFT devices fabricated with silicon nitride and silicon oxynitride insulators show thteshold voltages ≤3 V and source drain current ON/OFF ratios exceeding 107 for gate voltages smaller than 20 V, whereas TFTs with fluorinated silicon nitride insulators show an inferior performance. We also present ideas on the possible relation between the stress in the insulator film and the reliability of TFTs fabricated using these layers.

Properties of Fluorinated Silicon Nitride Films for Applications to Device Processes

Fluorinated silicon nitride films were deposited by plasma‐CVD from or gas mixture. The deposition rate was increased by using the latter gas system, typically as high as 50 nm/min, which was comparable to that of the conventional hydrogenated silicon nitride deposited from . The fluorinated silicon nitride exhibited (i) lower hydrogen content, (ii) higher stability against hydrogen outdiffusion, and (iii) higher thermal endurance. Successful applications as final passivation layers, diffusion or annealing masks, and gate insulator can be expected.

Bonding configuration of fluorine in fluorinated silicon nitride films

Bonding configuration of constituent elements in fluorinated silicon nitride insulating films prepared by reactive plasma of SiF4 (or SiF2), N2, and H2 gas mixture is investigated by means of optical absorption analysis and electron-spin resonance study. Fluorine is bonded to silicon rather than to nitrogen. Slight variations of spin density and optical gap with chemical composition are attributed to the complemental increase of fluorine with decrease of nitrogen, and to the passivation of silicon dangling bonds by fluorine atoms.

Electrical properties of plasma-deposited fluorinated silicon nitride

Electrical properties of fluorinated silicon nitride films deposited from glow discharges of SiH 4-He-NH 3-NF 3 and SiH 4-He-NH 3-F 2 mixtures are investigated via high frequency capacitance-voltage and current-voltage techniques. The results are compared with those for unfluorinated silicon nitride films deposited from SiH 4-He-NH 3 plasmas. All films exhibit counterclockwise hysteresis, indicating charge trapping in the film. When fluorine is added to the film, the dielectric constant decreases and the dielectric strength increases. Bias temperature stress measurements are performed to determine flatband voltages and fixed charge densities for fluorinated and unfluorinated films. Fluorinated films have more negative charge than unfluorinated films.

Structure and optical properties of plasma-deposited fluorinated silicon nitride thin films

The deposition chemistry, optical properties, and structure of plasma-deposited fluorinated silicon nitride films are studied and compared to available results of other researchers. Fluorinated films show an increase in deposition rate and optical band gap, and a decrease in refractive index and film stress compared to unfluorinated silicon nitride films. Fluorine concentration in the films ranges from 5 to 25 at. %. The total hydrogen concentration of fluorinated films is lower than that of unfluorinated films. The improved thermal stability of fluorinated films as compared to unfluorinated films is explained by a significant decrease in hydrogen bonded to silicon. All films hydrolyze to some extent and films with large fluorine concentrations hydrolyze rapidly to silicon dioxide. The microstructure of fluorinated films consists of clustered silicon-fluorine and nitrogen-hydrogen regions within an amorphous silicon-nitrogen matrix.

Frequency effects and properties of plasma deposited fluorinated silicon nitride

The properties of low-hydrogen, fluorinated plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films grown using NF3/SiH4/N2 feed mixtures in 200 kHz and 14 MHz discharges were compared. High-energy ion bombardment at 200 kHz is expected to enhance surface diffusion and chemical reconstruction. Compared to fluorinated silicon nitride deposited at 14 MHz under otherwise comparable conditions, the 200 kHz films had a lower Si–H bond concentration (≲1×1021 cm−3), lower total hydrogen content (5–8×1021 cm−3), better resistance to oxidation, lower compressive stress (−0.7 to −1.5 Gdyne/cm), and higher density (3.1 g/cm3). The dielectric constant of better low-frequency Class I films was constant to 500 MHz, while that of high-frequency films fell up to 15% between 100 Hz and 10 MHz. The absorption edges of low-frequency PECVD fluorinated silicon nitride films were between 5.0 and 6.1 eV, which compare with 4.4 to 5.6 eV for the high-excitation frequency fluorinated material and 3 to 4 eV for conventional PECVD nitride. However high-frequency films may have fewer trap centers and a lower dielectric constant. 14 MHz p-SiN:F films grown with NH3 as an auxiliary nitrogen source showed absorption edges similar to low-frequency material grown from NF3/SiH4/N2, but they have substantially more N–H bonding. The dielectric constant and absorption edge of these films were comparable to those of low-frequency p-SiN:F from NF3/SiH4/N2.

Plasma enhanced chemical vapor deposition of fluorinated silicon nitride using SiH4-NH3-NF3 mixtures

Fluorinated silicon nitride films are deposited by the plasma enhanced reaction of SiH4-NH3-NF3 gas mixtures. The deposition rate with NF3 increases to a maximum of approximately six times that of SiNxHy deposited using only SiH4 and NH3. Optical and electrical properties of the SiNxHy films are also affected. The addition of NF3 to the deposition atmosphere significantly reduces the concentration of H bonded to Si. The films display dielectric properties similar to SiNxHy films deposited using SiH4 and NH3. All films containing F hydrolyze on exposure to air. When less than 10 at. % F is present in the as-deposited films, film stability is achieved after initial hydrolysis. Essentially total hydrolysis to SiO2 occurs when the F content exceeds 10 at. %.

Electrical properties of silicon nitride films plasma-deposited from SiF4, N2, and H2 source gases

The electrical properties of the fluorinated silicon nitride films deposited from reactive plasma of SiF4-N2-H2 or SiF2-N2-H2 gas mixtures were investigated by changing the source SiF4 flow rate. A resistivity and breakdown strength as high as 1014–1016 Ω cm and 5–10 MV/cm, respectively, were reproducibly observed over a wide range of the N/Si ratio. The deep-trap densities and energy levels are not very dependent on the film composition. Their slight variation in the present deposition conditions can be understood by the slight variation of the spin density and the optical gap. The dielectric constant and the interface state density between silicon and silicon nitride are 4.8–6.0 and (1–5)×1012 cm−2 eV−1, respectively.