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Influence of substrate temperature on the properties of fluorinated silicon-nitride thin films deposited by IC-RPECVD
Abstract
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 Å. 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.
... However, the use of high hydrogen dilutions can contribute to an excessive incorporation of weak Si H bonds into the pm-Si, resulting unsuitable for thin-film, photovoltaic applications [8][9][10]. For this reason, alternative passivating atoms with higher mass and lower diffusion coefficient than hydrogen, such as deuterium, fluorine and chlorine, are being investigated [11,12]. Chlorinated silanes, i.e., SiH 2 Cl 2 , SiHCl 3 and SiCl 4 have been used aiming at the improvement of material properties [13][14][15]. ...
Several electronic devices, such as perovskite solar cells (PSCs) and organic light‐emitting diodes (OLEDs), are very vulnerable to water vapor. Therefore, they require an ultrahigh‐performance gas barrier (water vapor transmission rate [WVTR]: less than 10−5 g m−2 d−1). The barrier performance of solution‐processed gas barriers is inferior to that of vacuum‐processed gas barriers; however, they possess advantages such as high resource efficiency, high throughput, low fabrication cost, and printability, which facilitate sustainable manufacturing and digital fabrication. The simultaneous realization of solution processability and ultrahigh barrier performance is highly desired. Herein, this work reports solution‐processed gas barriers developed using perhydropolysilazane (PHPS)‐derived SiN (PDSN) layers densified by vacuum ultraviolet (VUV) irradiation in a nitrogen atmosphere at room temperature. The appropriate PDSN thickness and irradiated VUV dose result in an excellent WVTR of 4.8 × 10−5 g m−2 d−1 (a barrier performance close to that of glass), which makes it among the best‐performing water vapor barriers recorded to date. The barrier performance is achieved with a thickness of only 990 nm and a short VUV irradiation time (2.4 min per PHPS layer). An ultrahigh‐performance barrier with rapid processability such as this expands the possibility of solution‐processed barrier technology. The water vapor transmission rate (WVTR) of 10−5 g m−2 d−1 can be achieved by an all‐solution‐processed ultrahigh barrier using perhydropolysilazane‐derived SiN films densified by vacuum UV irradiation (only 2.4 min per layer) under a nitrogen atmosphere. The barriers show significant potential for solution‐processed barriers to be applicable to products vulnerable to water vapor, such as perovskite solar cells and organic light‐emitting diodes.
Gas barrier films are widely used in electronic and packaging applications. They are also critical components of flexible organic light-emitting diodes (FOLEDs) that require high gas barrier performance. Among the various film manufacturing techniques, solution-processed thin-film encapsulation (TFE) represents a low-cost FOLED fabrication method. The nanometer-thick SiN films produced following the vacuum ultraviolet (VUV)-induced densification of solution-processed perhydropolysilazane (PHPS) films in a N2 atmosphere can potentially serve as TFE barrier films. However, the nanometer-thick PHPS densification process has not been examined in sufficient detail. We investigated and discussed the effects of the Si–N bond number, PHPS film composition, and free volume (present in the produced Si–N network) on the VUV-induced PHPS densification process. It was found that VUV irradiation caused rapid hydrogen release and film densification through the formation of Si–N bonds. The results obtained using the X-ray photoelectron spectroscopy and dynamic secondary ion mass spectrometry techniques, and the calculated residual hydrogen ratios, revealed that the film composition was strongly related to the number of residual hydrogen atoms and Si–N bonds. Notably, nanometer-thick PHPS film densification was a relatively slow process, in which the free volume in the Si–N network was considerably reduced by the atomic rearrangement induced by the simultaneous cleavage of several Si–N bonds during VUV irradiation. We believe that the results presented herein can potentially serve as a guideline for developing solution-processed nanometer-thick SiN films with relatively high density and excellent gas barrier performance (that is comparable to that exhibited by vacuum-processed barrier films).
Tantalum oxide and tantalum - aluminum oxide films have been prepared by pyrosol using alcoholic start solution of tantalum chloride and aluminum acetylacetonate at substrates temperatures of 250 degrees C. All films are amorphous independent of the deposition conditions. X-ray diffraction shows that aluminum incorporation in deposited materials stabilizes the amorphous phase even after annealing at 525 degrees C and 900 degrees C. Energy dispersive spectroscopy, Rutherford backscattering, refractive index, and FTIR results indicate that the relative chemical composition of the deposited films is about [Ta] = 20 atom % and [O] = 80 atom %, probably containing hydroxide or oxohydroxide groups. The concentration of aluminum in films depends on the concentration of aluminum acetylacetonate in start solution with a ratio [Al atom % in film]/ [ Al atom % in solution] approximate to 0.1. The rms roughness has values of < 1 nm. The effect of incorporation of aluminum in deposited material and its annealing at 525 degrees C on the electrical characteristics of metal-oxide - metal structures increases the breakdown electric field and decreases the current density. The dielectric constant decreases as the aluminum concentration increases and annealing has a densification effect on the TAO films. (c) 2007 The Electrochemical Society.
Silicon nitride films have been deposited using inductively-coupled plasma high-density plasma chemical vapor deposition (HDP CVD), plasma-enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) methods. Characterization and comparison of the three films were performed using Fourier-transform infrared spectroscopy, secondary-ion mass spectroscopy, Rutherford backscattering spectrometry, and hydrogen forward-scattering spectrometry, in addition to wet-etch rate and stress measurement studies. It was found that silicon nitride films deposited using HDP CVD method have several advantages over the silicon nitride films that were deposited using the LPCVD and PECVD methods. The HDP CVD silicon nitride film can be deposited at much lower temperatures (⩽400 °C) than LPCVD silicon nitride, and has substantially less hydrogen (5.5 at. %) than the PECVD film. In addition, the PECVD film contains some oxygen in the film. The wet-etch rate of HDP CVD silicon nitride film is comparable to that of LPCVD film and is significantly less than that of PECVD film in both hot phosphoric acid and buffered HF solutions. The stress of the HDP CVD film is similarly compressive to the PECVD silicon nitride, and not as highly tensile as that of LPCVD silicon nitride. © 2000 American Vacuum Society.
The dynamic roughening of amorphous silicon nitride growth front
prepared by a plasma-enhanced chemical vapor deposition is presented.
Morphology of the films grown at different substrate temperatures (from
50 to 350 °C) for various lengths of deposition time was measured ex
situ using atomic force microscopy. The dynamic scaling exponents are
measured as α~0.77, β~0.40, and 1/z~0.28, and do not change
significantly under the investigated substrate temperature range. An
attempt has been made to describe the plasma growth process using a
multiparticle reemission model where the incident flux distribution,
sticking coefficient, shadowing, surface diffusion, and desorption
mechanisms all contributed to the growing morphology.
Silicon nitride (SiN) from plasma-enhanced chemical vapour deposition is widely used in PV industry as an antireflection coating. In addition the large amount of hydrogen (of up to 25 at%) (J. Appl. Phys. 49 (1978) 2473) incorporated in the SiN layer can be driven into the solar cell during the contact firing step, leading to an excellent bulk passivation as demonstrated by several research institutes during the last decade (Proceedings of the 12th EC PVSEC, Amsterdam, The Netherlands, 1994, p. 1018). Despite these advantages sometimes a problem occurs during the firing of the SiN layer, called blistering. Supposing that the blistering effect can be influenced by the surface preparation we performed a short ammonia plasma activation step prior to the SiN deposition. This step results in no damage of the surface which is shown in the form of solar cell results and lifetime measurements. On the contrary a positive effect on lowly doped emitters is possible.
Ultrathin fluorinated silicon nitride (SiNx) films of 4 nm in thickness were formed on a Si substrate at 350 °C in the downflow of electron cyclotron resonance plasma-enhanced chemical vapor deposition employing ammonia and tetrafluorosilane (NH3/SiF4) gases. Ultrathin fluorinated SiNx film was evaluated for use as a gate dielectric film. The observed properties indicated an extremely low leakage current, one order of magnitude lower than thermal SiO2 of identical equivalent oxide thickness, as well as an excellent hysteresis loop (20 mV) and interface trap density (Dit=4×1011 cm-2) in the capacitance-voltage characteristics. The film structures and the surface reactions for the fluorinated SiNx film formation were examined via in situ x-ray photoelectron spectroscopy. in situ Fourier-transform infrared reflection absorption spectroscopy, in situ atomic force microscopy, and thermal desorption mass spectroscopy. The control of the fluorine concentration in the SiNx films was found to be a key factor in the formation of fluorinated SiNx films of high quality at low temperatures. Fluorinated SiNx is the effective material for application in ultrathin gate dielectric film in ultralarge-scale integrated circuits.
Control of substrate temperature (TS) during plasma etching and film deposition using fluorinated silicon gases has profound effects on etch and deposition rates as well as the overall composition of deposited materials. How TS directly affects individual species and reactions at the plasma-surface interface, however, is not fully understood. Using the imaging of radicals interacting with surfaces technique, we have measured the effect of TS on SiF and SiF2 surface reactivity in SiF4 and SiF4:H2 plasmas under a variety of plasma conditions. At TS=300 K, there is significantly more SiF2 than SiF emanating from the surface. This is expected as SiF2 is a known etch product. Interestingly, higher substrate temperatures result in significant increases in surface scatter for both molecules. These results are discussed with respect to the role that each molecule plays in etching and deposition mechanisms, as well as in comparison to results for plasma species in other plasma systems. In addition to surface interaction measurements, rotational temperatures (thetaR) for SiF and SiF2 were measured in a 170 W plasma as 450+/-50 and 752+/-100 K, respectively.
Fabrication on thin-film transistors (TFTs) on flexible plastic substrates for large-area imagers and displays has been made possible by lowering the deposition temperatures, which reduces the thermal deformation of plastic substrates, greatly facilitating substrate preparation and device patterning. Furthermore, at extremely low deposition temperatures, much wider variety of low-cost substrates, plastics or otherwise, are available for use. In this article, we report on a-Si:H TFTs fabricated at 75 °C on glass and plastic substrates. The TFTs were fabricated using inverted-staggered topology, in a full wet etch process. The TFT structures consisted of 140 nm of sputtered Mo for gate, 380 nm of plasma-enhanced chemical vapor deposition (PECVD) a-SiNx:H gate dielectric optimized for 75 °C, 50 nm of PECVD a-Si:H channel material, 50 nm of PECVD n+ a-Si:H for source/drain contacts, and sputtered Al for contact metallization. Current-voltage characteristics were measured, and relevant transistor parameters were calculated. TFTs exhibited the leakage current below 10-12 A, and on/off current ratio exceeding 105. The results were compared to those for high temperature a-Si:H TFTs, and the differences are discussed.
Dielectric materials with lower permittivity (low k) are required for isolation to reduce the interconnect RC delay in deep submicron integrated circuit. In this work, carbon-doped silicon oxide films are investigated as a potential low k material. The films were prepared by the radio frequency plasma-enhanced chemical vapor deposition (PECVD) technique from trimethylsilane (3MS) in an oxygen (O2) environment. The O2/3MS flow ratio (in sccm) was varied from 50:600 to 900:600 to investigate its effects on the properties of the films. The films were also annealed at 400 °C in an N2 atmosphere for 30 min to determine the thermal stability of their properties. Thickness and refractive index were measured by opti-probe. Chemical structures were characterized by Fourier transform infrared spectroscopy (FTIR). Dielectric constants were measured using a Si/insulator/mercury probe structure. It was found that the deposition rate increased almost three times while the refractive index decreased from 1.46 to 1.39 with increasing oxygen concentration in the gas feed. Dielectric constants as low as 2.9 have been obtained for the as-prepared film with a O2/3MS flow ratio of 100:600. FTIR spectra revealed that more Si–CH and Si–CH3 groups were introduced into the silicon dioxide backbone of the films at this flow ratio, and the low dielectric constant obtained is attributed to the increased incorporation of carbon in the form Si–CH3 bond, which has lower polarizability compared to the Si–O bonds that were replaced. The annealing has been found to lower the dielectric constant of the films, but has no effect on their composition and chemical structure.
In this paper, the effect of chemical–mechanical polishing (CMP) of silicon nitride films was investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Silicon nitride films with different deposition methods (PECVD and LPCVD) and two different silica-based slurries were studied. The surface chemical structure of as-deposited LPCVD film is slightly better than that of as-deposited PECVD film, and the surface morphologies (RMS roughness ∽0.3 nm for LPCVD film, and 1.9 nm for PECVD film) are much different. After CMP, the LPCVD film was more dramatically oxidized, and the surface became rougher for the process conditions used. The PECVD film was less dramatically oxidized, a subsilicon nitride (SiNx) appeared on the surface, and the surface became smoother. These results suggest that the quality of as-deposited nitride film, as well as the CMP process conditions, impact significantly on the quality of the polished surface.
Silicon-rich, nearly stoichiometric and nitrogen-rich silicon nitride films have been prepared by the glow-discharge decomposition of silane and ammonia with nitrogen dilution, with and without ammonia plasma pre-treatment of the silicon substrate. A considerable improvement in the silicon nitride/silicon interface, as evident from the large reduction in the minimum interface state density (Dit)min, due to ammonia plasma pretreatment is observed.