Plasma Deposited Silicon Nitride Films Research Articles

Passivation of III/V-based Compound Semiconductor Devices Using High-Density Plasma Deposited Silicon Nitride Films

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Influence of the high-temperature “firing” step on high-rate plasma deposited silicon nitride films used as bulk passivating antireflection coatings on silicon solar cells

The influence of a short high-temperature step, comparable to the so-called “firing” of the metallization on silicon solar cells, on properties of high-rate (>0.5 nm/s) plasma deposited silicon nitride (a-SiNx:H) films has been investigated. These a-SiNx:H films are used as antireflection coating on multicrystalline silicon (mc-Si) solar cells and, after the firing process, they also induce hydrogen bulk passivation in the mc-Si. Three different types of remote plasma deposited a-SiNx:H films have been investigated: (i) expanding thermal plasma (ETP) deposited a-SiNx:H films from a N2–SiH4 gas mixture, (ii) ETP deposited a-SiNx:H films from a NH3–SiH4 mixture, and (iii) microwave plasma deposited a-SiNx:H films from a NH3–SiH4 mixture. The atomic composition and optical and structural properties of the films have been studied before and after the high-temperature step by the combination of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. It has been observed that the high-temperature step can induce significant changes in hydrogen content, bonding types, mass density, and optical absorption of the films. These thermally induced effects are more enhanced for Si- than for N-rich films, which in some cases have a high thermal stability. Furthermore, the material properties and the influence of the high-temperature step have been related to the bulk passivation properties of the a-SiNx:H coated mc-Si solar cells. It is found that in particular the density and thermal stability of the a-SiNx:H films seem to be important for the degree of the bulk passivation obtained.

Plasma-deposited silicon oxide and silicon nitride films on poly(ethylene terephthalate): A multitechnique study of the interphase regions

The “interphase” region between the deposited layer [e.g., plasma-enhanced chemically vapor deposited (PECVD) SiO2 or SiN] and the poly(ethylene terephthalate) (PET) substrate has been investigated and compared to physical vapor deposited (PVD) (electron beam evaporated) SiO2. Composition profiles determined by time-of-flight elastic recoil detection, electron microprobe analysis, and x-ray photoelectron spectroscopy all show an extended interphase region more than 50 nm in width, while the profile of the PVD SiO2 is narrower. However, since these analytical techniques are invasive and prone to artifacts, we have also examined ultrathin (about 10 and 20 nm) SiO2 and SiN PECVD layers on 50 nm spin-coated PET substrates by nondestructive infrared (IR) techniques. The IR spectra confirm that the thin PECVD deposits also comprise an organosilicon phase with Si–CHx bonds. We explain these observations in terms of a fragmentation/redeposition mechanism: During the earliest stage of PECVD, interaction between the plasma and the polymer surface produces volatile organic species, which intermix with the reagent gas feed, thus giving rise to the observed organosilicon-like deposit with gradually decreasing carbon content.

Substrate Surface Morphology and Growth Evolution of Low Temperature Silicon Nitride on Transparent Plastics

AbstractSurface morphology and nucleation are important for forming electronic thin films on plastic substrates. We have used atomic force microscopy (AFM) with an oscillating cantilever to examine various transparent substrates, including 7059 glass, polyethylene terephthalate (PET), indium tin oxide (ITO)-coated PET, and polycarbonate, and studied the effect of deposition processes on these surfaces. Studies include: 1) differences in dielectric nucleation on plastics and glass; 2) dielectric growth evolution; and 3) the effect of plasma exposure on surface roughness. The surface morphology of the different substrate materials varied significantly with the PET showing the largest roughness values; all the polymers were more rough than typical 7059 glass (rms <0.5 nm). Furthermore, the initial nucleation on both polymers were different than on glass. Very thin layers (<30Å nominal thickness) of plasma deposited silicon nitride films on polycarbonate and glass produced flat, smooth surfaces, with rms roughness of ≈0.5 nm. On the PET substrates, the nitride growth began with broad, thin deposits and developed a coarse, large-grained structure as growth progressed. With exposure to a NH3 + N2 plasma, the glass and PET surfaces showed detectable changes in surface roughness, which are discussed below. These results demonstrate that plasma-deposited insulators nucleate and grow differently on plastic substrates than on glass, which has implications for electronic devices fabricated directly on plastics.

Nitrogen plasma instabilities and the growth of silicon nitride by electron cyclotron resonance microwave plasma chemical vapor deposition

Nitrogen plasma instabilities have been identified through fluctuations in the ion current density and substrate floating potential. The behavior of the plasma instabilities was found to be confined to the pressure regime 0.9 mTorr<P<1.6 mTorr. The onset of instabilities in the nitrogen plasmas occurred following the transition from an underdense to overdense plasma, where an overdense plasma is defined for densities greater than the critical density nc=7.4×1010 cm−3. The instabilities are a consequence of the nonlinear dynamics present in electron cyclotron resonance (ECR) plasmas and indicative of a transition between plasma modes as the pressure increases from 0.9 to 1.6 mTorr. The plasma instabilities are suppressed with the introduction of silane for the deposition of silicon nitride, although the plasma still undergoes a transition from an underdense to overdense plasma at 1.0 mTorr. The transition pressure delineated regions of poor and optimum electrical properties of silicon nitride films deposited from a dilute nitrogen-silane (N2/SiH4=5) plasma. To evaluate growth conditions, the flux of energetic ions to deposited atoms was approximated by examination of the ratio of ion current density to deposition rate. This ratio was found to be well correlated to the electrical properties of ECR microwave plasma deposited silicon nitride films for pressures above the underdense to overdense transition at 1.0 mTorr.

Plasma-deposited silicon nitride films with low hydrogen content for amorphous silicon thin-film transistors application

A comparative study of the vibrational properties of PECVD amorphous silicon nitride films obtained from SiH4 + NH3 and SiH4 + N2 precursor gas mixtures has been performed by FT-IR transmission spectroscopy. The bonded hydrogen, calculated from the absorption spectra, shows important quantitative and qualitative differences depending on the precursor gas mixtures used. The hydrogen content of near-stoichiometric films obtained from SiH4 + N2 mixture is 10 times lower than that of films prepared from SiH4 + NH3 mixture. In addition, hydrogen is mainly bonded to nitrogen atoms in films from SiH4 + NH3, whereas it is mainly bonded to silicon atoms in films from SiH4 + N2. These low-hydrogenated silicon nitride films, obtained from mixtures containing N2, have been applied as insulator layers in the preparation of amorphous silicon thin-film transistors (a-Si TFTs). The TFTs were of normal staggered type composed of the structure Al/a-SiN:H/a-Si:H grown on NiCr source and drain electrodes deposited on glass substrates. TFTs with a 0.2 μm thick a-Si:H layer and 10 μm channel length have on-off current ratios of 5 × 104, electron field-effect mobilities of about 1.5 cm2/V s and threshold voltages around 5 V.

Densification of plasma deposited silicon nitride films by hydrogen dilution

The effects of hydrogen dilution on the bonding characteristics, composition, and properties of SiN films deposited from a SiH 4/NH 3 mixture by r.f. plasma enhanced chemical vapor deposition were studied. The addition of relatively small amounts of hydrogen increased the Si/N ratio resulting in a corresponding increase in the SiH/NH bonding ratio. At higher hydrogen dilutions, the Si/N ratio decreased towards stoichiometric with significant changes in the hydrogen bonding characteristics. Changes in the physical properties are discussed in terms of the measured changes in bonding structure. Changes normally associated with changes in bulk film density were found to be well correlated to the SiN bond density. The effects of substrate temperature and NH 3/SiH 4 ratio on films deposited under conditions of high hydrogen dilution were similar to those widely reported in the literature for plasma-enhanced chemical vapor deposition films deposited without hydrogen. Films deposited by remote plasma using hydrogen as the excitation exhibited high SiN bond densities and low hydrogen. Experiments are planned to clarify the mechanism responsible for the observed changes in film properties.

Properties of very low temperature plasma deposited silicon nitride films

Plasma enhanced deposition of silicon nitride films is shown to have less N–H bonds and provide better heat resistance using SiH4–N2 than SiH4–NH3–N2 plasmas at 100 °C. Properties of silicon nitride using SiH4–N2 plasma are studied versus various deposition parameters such as radio frequency power, silane flow ratio, and deposition pressure. The experimental data indicate that the deposition process at 100 °C has a N2-reaction-controlled mechanism.

The effect of diluent gas and rapid thermal annealing on the properties of plasma-deposited silicon nitride films

The effects of diluent gases on the deposition rate, content of hydrogen bonds, etch rate, refractive index and fixed charge density of plasma-enhanced chemical vapour deposition silicon nitride films have been studied for various gas compositions. Post-rapid thermal annealing (RTA) of as-grown films was also performed in the temperature range 500–1100°C. From the results of optical emission spectroscopy it is suggested that metastable N2 molecules can contribute to silicon nitride film formation as an extra nitrogen source. Metastable N2 molecules may enhance the dissociation of other feed gases. Lower refractive index, higher deposition rate and higher NH bond density were obtained for silicon nitride films grown in N2 diluent as compared with films grown in H2 diluent. As the RTA temperature was increased, the content of hydrogen bonds was reduced and the film density increased. Hence the etch rate of silicon nitride films in buffered HF solution decreased with increasing RTA temperature. A minimum value of fixed charge density was obtained at the RTA temperature of 900°C for all the films investigated.

Physico-Chemical Properties of Plasma Deposited Silicon Nitride Films

The physico-chemical properties of plasma deposited silicon nitride films from Si-enriched ones to those containing excessive nitrogen (relative to stoichiometric Si3N4) are investigated. The film composition is calculated from the data of IR-spectroscopy. The rate of growth and etching, the density, and the index of refraction are measured. A model of the SiNxHy structure is proposed based on the assumption that groups of atoms are absent in the regulary lattice of silicon nitride. Some quantitative estimates are made at the basis of the percolation theory for the explanation of the exponential increase of the etching rate. Russian text ignored

The influence of underlying metals on the hydrogen evolution from plasma-deposited silicon nitride films

The influence of underlying metals on hydrogen evolution from plasma-enhanced chemical vapor deposited silicon nitride (P-SiN) films was investigated. Titanium (Ti), tungsten (W), and tungsten silicide (WSix:x=2.3) cap layers were deposited onto pure-Al, Al-1%Si, Al-0.5%Cu and Al-1%Si-0.5%Cu films on oxidized silicon wafers. The bilayers and Al-alloys were covered with P-SiN films and heated. It was found that the hydrogen evolution rates for the P-SiN films were influenced by the underlying bilayers as well as Al-alloys. Copper (Cu) addition to underlying Al films raised the hydrogen evolution rate peak temperature for the cover P-SiN film, due to the suppression of cover P-SiN film blistering and cracking as a result of Al-Cu hardening. Titanium thin-film capping on the Al-alloy also raised the hydrogen evolution rate peak temperature for the P-SiN film, as results of Ti adhesive layer and thermally stable intermetallic compound formation, TiAl3.

An x-ray photoelectron spectroscopic analysis of plasma deposited silicon nitride films

The effect of deposition conditions on the structure and composition of plasma deposited silicon nitride films was studied using x-ray photoelectron spectroscopy. Plasma deposited silicon nitride films were transferred directly from the deposition chamber into a surface analysis system, thereby permitting analysis of as-deposited films without modification due to ion sputtering. Plasma deposited silicon nitride films with N:Si ratios from 1.8–0.3 were deposited using SiH4, NH3, N2, and H2 as the source gases. The N:Si ratio in the films increased with increasing nitrogen concentration in the gas phase. Changes in the deposition power or the substrate temperature also influenced the N:Si ratio. Large differences in the film structure were observed for plasma deposited silicon nitride films formed with NH3 compared to N2 with respect to deposition temperature variations.

Mechanisms of dehydrogenation during ArF excimer laser patterning of plasma-deposited silicon nitride films

Using Fourier-transformed infrared spectroscopy, we show that pulsed ArF excimer laser irradiation of plasma-deposited silicon nitride films causes a large reduction in NH (∼100%) and SiH (∼50%) in the top ∼500 Å, and further show that this is responsible for the large suppression of the etch rate in buffered HF solution. Temperature rise calculations qualitatively predict the observed maximum falloff in etch rate and in SiH and NH concentration at the surface of the film. The observed reduction of the effect in thin films, which is due to the heat-sink effect of the underlying substrate, is also predicted. Both are strong indications that NH and SiH bonds are broken in a laser heating process. H2 has been detected as a product evolved during laser irradiation; however, most H2 remains trapped in the film.

Effects of post-deposition argon implantation on the memory properties of plasma-deposited silicon nitride films

Post-deposition ion implantation has been used to introduce argon into plasma-enhanced chemically vapor deposited silicon nitride films in an attempt to influence the transfer, trapping, and emission of charge during write/erase exercising of the metal-silicon nitride-silicon oxide-silicon structure. Argon was implanted into the SiH4 -NH3 -N2 deposited films at energies ranging from 25 to 75 keV, current densities ranging from 0.1 to 75 μA/cm2 and fluences ranging from 1×1012 to 1×1016 ions/cm2. Physical properties of the films were studied by ellipsometry and infrared spectroscopy, while high frequency capacitance-voltage (C-V) curves were used to obtain programming, retention, and endurance characteristics.

Adhesion, friction, and wear of plasma-deposited thin silicon nitride films at temperatures to 700 °C

An investigation examined the adhesion, friction and wear behavior of silicon nitride films deposited by low and high frequency plasmas (30 kHz and 13.56 MHz) at various temperatures up to 700 °C in vacuum. The results of the investigation indicated that the Si/N ratios were much greater for the films deposited at 13.56 MHz than for those deposited at 30 kHz. Amorphous silicon was present in both low and high frequency plasma-deposited silicon nitride films. However, more amorphous silicon occurred in the films deposited at 13.56 MHz than in those deposited at 30 kHz. Temperature significantly influenced adhesion, friction and wear of the silicon nitride films. Wear occurred in the contact area at high temperature. The wear correlated with the increase in adhesion and friction for the low and high frequency plasma-deposited films above 600 °C and 500 °C respectively. The low and high frequency plasma-deposited thin silicon nitride films exhibited a capability for lubrication (low adhesion and friction) in vacuum at temperatures to 500 °C and 400 °C respectively.

The effect of Ar+ sputtering on the x-ray photoelectron spectra of plasma-deposited silicon nitride films

The effects of argon-ion sputtering and atmospheric exposure on the composition and structure of plasma-deposited (PD) silicon nitride films were studied using x-ray photoelectron spectroscopy. PD silicon nitride samples were transferred directly from the plasma deposition chamber into the analysis chamber without ambient exposure. Samples exposed to ambient oxidized, with an oxidation rate that depended upon deposition temperature. Ion energies of 500–4000 eV were used to sputter sample surfaces. Preferential sputtering was observed at all energies, with the lower energies creating less compositional and structural modification. Films deposited at lower temperatures exhibited pronounced preferential sputtering of nitrogen, particularly NHx species. Ion milling was found to be unacceptable as a means of surface cleaning PD silicon nitride since even qualitative N:Si composition trends were modified by sputtering.

Direct pattern replication in plasma deposited silicon nitride films by 193 nm ArF excimer laser-induced suppression of etching

Exposure of plasma deposited silicon nitride to 193 nm ArF excimer laser radiation suppresses the etch rate in buffered HF solution by as much as a factor of 50. Using a contact mask, 0.23 μm lines and spaces were transferred into silicon nitride by this exposure and etching technique. The mechanism involves transient thermal annealing induced by the 15 ns laser pulses, which reduces the concentration of NH and SiH groups.

Correlation of G/sub m/ degradation of submicrometer MOSFETs with refractive index and mechanical stress of encapsulation materials

Evaluations of five different plasma-deposited silicon nitride films for use as an encapsulation material for polysilicon-gate MOSFETs are discussed. The films were (1) a-SiN:H; (2) Applied Materials a-SiN:H process B; (3) Applied Materials a-SiN:H process D; (4) silicon oxynitride, a-SiON:H; and (5) fluorinated silicon nitride, a-SiNF:H. Submicrometer MOSFET devices that aged the least as measured by transconductance degradation were encapsulated with films having the lowest refractive index (a-SiON:H and a-SiNF:H). The results show that films with low refractive index and low absolute value of mechanical stress age the least. The results are interpreted in terms of the Meyer-Fair model where the lower refractive index films are more porous to H leaving the device than the higher refractive index films. >

Low-temperature hydrolysis (oxidation) of plasma-deposited silicon nitride films

Low-temperature hydrolysis (oxidation) of plasma-deposited silicon nitride films

Correlation of refractive index and silicon content of silicon oxynitride films

The refractive index of plasma-deposited silicon nitride and silicon oxynitride films may be used to estimate the atomic per cent silicon in the films. This linear correlation is different from previously reported correlations and can even be applied to high temperature low pressure chemically vapour deposited silicon oxynitride films. While the refractive index can be used to monitor plasma nitride and plasma oxynitride films, it is important to remember that oxynitride films with different nitrogen and oxygen contents can have the same refractive index. The Bruggeman effective medium approximation with silicon and silicon dioxide as the two phases can be used to model the correlation. Although physically unreal, the model suggest that the large polarizability of silicon in the film controls the refractive index and that the polarizabilities of voids, hydrogen, nitrogen, oxygen and fluorine can be grouped together with an effective refractive index of 1.46.