Amorphous Silicon Nitride

Amorphous silicon nitride (a-Si3N4) is used extensively in the microelectronics industry in the form of thin films, which are prepared by both normal and reactive sputtering, chemical vapor deposition (CVD), ion-beam-assisted deposition, and ion 

The density of amorphous Si3N4 (up to 3 gcm ) is less than that of its crystalline forms. Rather, the most important properties of a-Si3N4 are its low permeability towards sodium, oxygen, H2O, and hydrogen (because of the rigid covalent stmc-ture), its high electrical resistivity (lO fim), hardness, and its good resistance to chemical attack [2, 11, 12]. 

On heating, a-Si3N4 is converted to crystalline a-Si3N4 the time-temperature domain boundary for complete crystallization runs from about 10 min at 1400 °C to Ih at 1250 °C, and to 4h at 1100 °C [13]. 

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For 3C-SiC substrates, not nitridation but low temperature buffer layer growth without nitridation has been used as an initial process, under the apprehension that amorphous silicon nitride layers are formed... 

Tris transaminates readily with ammonia or primary amines when catalyzed by carbon dioxide or strong organic acids. The polysilazane products range from discrete solid disilazanes, to liquid distillable oligomers, and to highly cross-linked infusible polymers. Some of these polysilazanes can be pyro-lyzed to amorphous silicon nitride or mixtures of silicon nitride and silicon carbide below 1550 or to crystalline ceramics above that temperature. 

Micro-Raman spectroscopy was used to characterise 4H-SiC layers grown from a variety of precursor systems.381 FTIR data were able to characterise hydrogenated amorphous silicon nitride films with embedded nanoparticles. Oxidation leads to the appearance of an Si O feature at 1070 cm 1,382 Raman spectra were used to determine the degree of micro-crystallinity of pc Si I I layers, using the intensity ratio of bands at 520 cm-1 and 480 cm-1.383 IR and Raman spectra were used to determine the effects of neutron irradiation on a-SiC H films.384 A range of a-SiCx I I and a-SiCxNy H films were studied using IR spectroscopy 385 similar experiments were carried out on a-Si i xGcx Il,F films.386... 

The photodiode-lever separation can be measured sufficiently accurately to ensure that it is a negligible source of error. The value of this distance varies slightly om scan to scan, depending on the beam alignment, but is typically 12.0 mm. Finally one must consider the geometrical and mechanical properties of the cantilever. Because the stoichiometry of the cantilevers can vary from that of bulk amorphous silicon nitride, the values of the Young s modulus and Poisson ratio are not very accurately known. We have used quoted values for bulk silicon nitride, but the accuracy of these values is hard to assess. As mentioned earlier, the quoted thickness of the levers was checked by measuring the lever resonant frequency, and frie width of the levers is accurately known (10 pm). 

Amorphous silicon nitride films, which are resistant to water vapor, salts, and other chemicals and, therefore, are applied as a final encapsulating layer for ICs, are effectively produced using PECVD. A typical feed-gas mixture for PECVD is SiH4-NH3. The process is performed in plasma at pressures of 0.25-3 Torr conventional substrate temperatures are in the range 250-500°C. Deposition rates of silicon nitride films under such conditions are about 20-50 nm/min. The plasma deposited silicon nitride film can usually be characterized... 

In conclusion, we have reviewed some of the structural optical and electrical properties of amorphous silicon/amorphous silicon nitride superlattices. The regularity and smoothness of the layers, the abruptness of the interfaces. 

A report has appeared (12) on the formation of a high surface area amorphous silicon nitride from a solution phase reaction of tetrachloro-silane with liquid ammonia. In our hands (7) this reaction gave a material with a surface area of 90 m g both the form of the BET isotherm and transmission electron microscopy indicated that the surface area was derived from the external surface of small particles, i.e. a non-porous material. An... 

R. M. Laine, F. Babonneau, K. Y. Blohowiak, R. A. Kennish, J. A. Rahn, and G. J. Exharos, The evolutionary process during pyrolytic transformation of poly(n-methylsilazane) from a preceramic polymer into an amorphous silicon nitride/carbon composite, J. Am. Ceram. Soc. 1995, 78, 137-145. 

Stoichiometric and hydrogenated amorphous silicon nitrides (Si3N4, and a-SiNx H, respectively) have many uses in the microelectronics industry, such as to passivate various capless devices and to act as a diffusion barrier against species such as H2O or Na+. Silicon nitride is also employed as a diffusion barrier in selective silicon oxidation (because of the low oxidation rate) and as an interlayer insulator material [2]. 

H. Matsuo, 0. Funayama, T. Kato, H. Kaya and T. Isoda, Crystallization behavior of high purity amorphous silicon nitride fiber, J. Ceram. Soc. Japan, 102 [5], 409-413 (1994). 

We observed similar decarbonization when we pyrolyzed PNMS, ONMS, APNMS, and APNES in the presence of ammonia. The ceramic yields and chemical compositions are shown in Table 4. The pyrolysis of ONMS and PNMS in the presence of ammonia provides an amorphous silicon nitride with a highly reduced level of residual carbon relative to those obtained by pyrolysis in nitrogen. The amount of elemental carbon can be lower than 1 wt%. 

The chemical structure of the films and particularly the incorporation of hydrogen were studies by FTIR (Perkin Elmer 1760). Fig. 8 shows infrared transmittance spectra of silicon carbonitride films (a) and silicon nitride films (b) deposited at 1123 K. The clusters of absorption peaks that appear in both spectra in the 1300 to 1940 and 3320 to 3900 wavenumber (cm i) regions are attributed to atmospheric moisture. CO2 is also detected at around 2345 cm i. For spectrum (b), the strong band at 847 cm-i indicates the formation of amorphous silicon nitride [161. The much weaker peak at 3326 cm i which is due to a N—H stretching vibration indicates the existence of N—H bonds in the films. The Si—N band at 847 cm i appeared to be broadened near its base line around 1173 cm i. This is due to the existence of N-H bonds which exhibit another bending mode at 1170 cm l All the films displayed similar spectra, and there was no indication of an Si—H bond in silicon nitride. In addition to the stro line at 837 cm, resulting from the fundamental stretching of silicon carbonitride [17], the main difference between spectra (a) arid (b) is the presence of a weak Si—H band, which is observed to be more intense in the films deposited below 1123 K. None of the films exUbited the C—H band around 2900 cm i, which is present in the IR spectrum of the precursor. 

Is ambiguous (Figure 10)12 he value of the Sl/N atomic ratio, determined from XPS measurements is found to obey a linear relationship with refractive index and thus it is possible to express the fraction of NH bonds as a function of the stoichiometry of the film (Figure 11). It can be seen from this relationship that it is possible to tune the amorphous silicon nitride to the required refractive index, e.g. for optical waveguide applications, within the range 1.6 to 2.1. 

Matsunaga, K., Iwamoto, Y. (2001). Molecular dynamics study of atomic structure and diffusion behavior in amorphous silicon nitride containing boron. Journal of the American Ceramic Society, 84(10), 2213-2219. doi 10.1111/j.l 151-2916.2001. tb00990.x. 

Riedel, R., Seher, M. (1991). CrystalUzation behaviour of amorphous silicon nitride. Journal cfthe European Ceramic Society, 7(1), 21-25. doi 10.1016/0955-2219(91)90049-6. 

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