Silicon Nitride and Oxynitride

Stoichiometric silicon nitride (Si3N4) often is used for chemical passivation and encapsulation of silicon bipolar and MOS devices, because it serves as an extremely good barrier to diffusion of water and sodium ions. Water causes device metallization to corrode and sodium causes devices to become electrically unstable. Silicon nitride is also used as a mask for the selective oxidation of silicon, and as a strong dielectric in MNOS (metal-nitride-oxide-silicon) structures. 

The deposition of Si3N4, like that of Si02, is a broadly practiced industrial process. In general, films are either grown by LPCVD or PECVD with comparable properties. Table 5-9 summarizes the properties of silicon nitride grown in typical commercial systems. 

Silicon precur- Nitrogen sor source Carrier gas (diluent) CVD method Deposition temp. [°C] Growth rate [Amin- ] Comments Ref. 

A summary of frequently employed CVD systems for silicon nitride thin films is given in Table 5-10. 

PECVD of SiN using SiH4/N2 generally leads to electronically leaky films due to the porous nature of the films [153]. However, if an electron cyclotron resonance (ECR) plasma is employed, SiN films of high quality may be deposited on ambient temperature substrates [154]. 

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Progress in the design and fabrication of high-quality optical microresonators is closely related to the development of novel optical materials and technologies. The key material systems used for microresonator fabrication include silica, silica on silicon, silicon, silicon on insulator, silicon nitride and oxynitride, polymers, semiconductors such as GaAs, InP, GalnAsP, GaN, etc, and crystalline materials such as lithium niobate and calcium fluoride. Table 2 smnmarises the optical characteristics of these materials (see Eldada, 2000, 2001 Hillmer, 2003 Poulsen, 2003 for more detail). 

Table 4.6. A selection of chemical shifts for silicon nitride, silicon oxynitride and SiAION compounds and related metal silicon nitrides and oxynitrides, with respect to TMS.

Andrievskii RA, Lyutikov RA (1996) Russ J Phys Chem 70 526 Durham SJP, Shanker K, Drew RAL (1991) Canadian Metallurgical Quarterly 30 39 Hendry A (1977) Thermodynamics of silicon nitride and oxynitride. In Riley FL (ed) Nitrogen Ceramics. Proc Nato Advanced Study Institute on Nitrogen Ceramics, Noordhoff, Leyden, p 183... 

IR data (vSiN 820-833 cm ) were used to characterise SiN films formed by a variety of CVD techniques. The IR spectra of amorphous SiOxN3 thin films included vSiO and vSiN features at 1105 cm", 865 cm respectively Two other reports have been made of IR spectra of CVD-produced silicon nitride and oxynitride films " " The FTIR spectrum of an SisN4 powder shows a feature at 1200 cm corresponding to the presence of Si-O units ... 

Silicon Nitride and Oxynitride Fibres from Poly(carbosilane)s... 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH4, and nitrous oxide, N20, for deposition of silicon nitride. The most common CVD films used are silicon dioxide, silicon nitride, and silicon oxynitrides. 

Mixed oxide, Al203-Si02, bond phases are generally the next most corrosion resistant to acids including low quantities of HF. Silicon nitride and silicon oxynitride bonded silicon carbides perform similarly to mixed oxide bonds. Table 19-2 shows typical weight loss and retained strength values for these products in contact with common acidic solutions for the times and temperatures shown. ... 

Besides clay-bound ware, there are also products composed of pure SiC, which, however, require very high firing temperatures and are utilized in special applications only. Silicon nitride or oxynitride can also serve as the binding phase the materials are highly refractory and can be produced at comparatively low temperatures by reactive sintering (cf. Chapter IV, Section 6.5). 

C. Synthesis of Silicon Nitride and Silicon Oxynitride Fibers from Polycarbosiianes... 

The nitridation of polycarbosilane (with ammonia) begins at about 500°C and terminates almost completely at about 800°C. There is scarcely any carbon in the nitride obtained at 1400°C. Chemical analysis indicates its composition to be Si3N3.72, almost that of pure silicon nitride, Si3N4 [39]. Up to 1300°C, the X-ray diffraction pattern of nitride fiber is broad and characteristic of the amorphous state, whereas those at 1400°C indicate crystalline a-SisN4 (Fig. 11). Both silicon nitride and silicon oxynitride fibers have been obtained by the heat... 

Mutin PH. Control of the composition and structure of silicon oxycarbide and oxynitride glasses derived from polysUoxane precursors. J. Sol-Gel Sci. Technol. 1999 14 27-38 Nomura K., Takasuka Y., Kamiya K., Nasu H. Preparation ofNbN fibres by nitridation of sol-gel derived Nb20s fibres. J. Mater. Sci., Electronics 1994 5 53-58... 

Silicon Nitride and Sialon. In this section we discuss both silicon nitride and sialon, a material with similar properties. Silicon nitride, SijN4, exhibits very high resistance to heat and corrosion, and is exceptionally strong. Sialon, a family of sUicon-aluminmn-sihca oxynitrides, has properties comparable to those of silicon nitride, and is much easier to manufacture and form into complex shapes. 

Poly(carbosilane) fibres have been employed recently as precursors to silicon nitride and silicon oxynitride fibres. The preparation of silicon nitride fibres involves a two-stage process. The precursor fibres are first crosslinked by electron irradiation then heated in ammonia at temperatures up to 1400 °C. Electron irradiation is used to effect the crosslinking reaction without incorporation of oxygen. The nitridation reaction takes place between 500 and 800 °C. At a pyrolysis temperature of 1400 °C, essentially all the carbon in the precursor is lost, giving a composition close to that of pure silicon nitride. At this temperature, however, the fibre was extensively crystallized and the tensile strength was very low. The tensile strength of the fibre was shown to reach a maximum level of about 1.4 GPa at a nitridation temperature of 1300°C. 

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

The other platform is dielectrics, for example, silicon dioxide, silicon nitride, silicon oxynitride, tantalum pentoxide, and titanium dioxide. They can be deposited by various methods, such as plasma-enhanced chemical vapor deposition, thermal evaporation, electron-beam evaporation, and sputtering. There are a number of dielectrics with refractive indices ranging from 1.45 to 2.4, facilitating diverse waveguide designs to satisfy different specification. Dielectrics have two other... 

Materials made of silicon nitride, silicon oxynitride, or sialon-bonded silicon carbide have high thermal shock and corrosion resistance and may be used for pump parts, acid spray nozzles, and in aluminum reduction cells (156—159). A very porous silicon carbide foam has been considered for surface combustion burner plates and filter media. It can also be used as a substrate carrying materials such as boron nitride as planar diffusion source for... 

Siaions consist of three-dimensional arrays of (Si—Al) (O.N)4 tetrahe-dra. These oxynitrides are traditionally fabricated with silicon nitride An example is beta-sialon, where the O and Si are partially replaced by N and Al, respectively. Advanced sialons are now being researched to enhance fracture toughness and iinpioved cieep properties,... 

This model goes a long way towards explaining most experimental results reported in the literature for ISFETs with oxide or nitride surfaces. Unfortunately, the properties of these materials prepared in different laboratories are very different. It is known that silicon nitride (really silicon oxynitride SisNztOx) forms an oxygen-rich layer at the surface, whose thickness depends on the deposition conditions. This passivation layer forms rapidly (in a matter of hours) and is very stable, even under continuous exposure to aqueous electrolyte. The hydration of this layer seems to fit the requirements and predicted behavior of the Sandifer model. Consequently, ISFETs that have been exposed to aqueous solution for more than one hour show no adsorption effects which would be expected from the SBT model. 

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