Physical properties silicon nitride

Within the past decade, research on the development of new Si3N4 compositions has greatly intensified. These efforts have resulted in a proliferation of new synthetic procedures. Preparative routes have been developed with increasing emphasis on the control of purity and physical properties. Silicon nitride powders, fibers, coatings, and composites each have their own characteristic requirements, which can dictate the choice of a particular route (i). 

As a consequence of their superior physical and chemical properties, silicon nitride and silicon carbonitride films have become increasingly important for both structural and microelectronic device applications. Chemical vapor depositions (CAH)) has become a major technique for the synthesis of these thin film materials flO]. 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (SijN ), and boron nitride (BN) offer a wide variety of unique physical properties such as high hardness and high structural stability under environmental extremes, as well as varied electronic and optical properties. These advantageous properties provide the driving force for intense research efforts directed toward developing new practical applications for these materials. These efforts occur despite the considerable expense often associated with their initial preparation and subsequent transformation into finished products. 

The carbides and nitrides are well known for their hardness and strength, and this section will briefly compare a number of these properties with those of the pure metals. Concentration will be placed here on the first row compounds, since these constitute a complete series, and Mo and W, since these are the most commonly studied metals. As will be shown, the physical and mechanical properties of carbides and nitrides resemble those of ceramics not those of metals. Comparisons will be made with boron carbide (B4C), silicon carbide (SiC), aluminium nitride (AIN), silicon nitride (Si3N4), aluminium oxide (A1203), and diamond, as representative ceramic materials. 

NISTCERAM National Institute of Standards and Techology Gas Research Institute, Ceramics Division mechanical, physical, electrical, thermal, corrosive, and oxidation properties for alumina nitride, beryllia, boron nitride, silicon carbide, silicon nitride, and zirconia... 

Although CVD and plasma deposited films offer excellent properties as a passivation layer, the inability to reproduce chemical and physical properties has been a problem. Depending on gas flow rates and deposition conditions, free Si, H, C and 0 may be Incorporated into the films. Characterization of these films has been restricted almost exclusively to surface analytical techniques and ellipsometry. AES and XPS have been used to determine the C, N, 0, and Si content of CVD silicon nitride. 

For silicon nitride films made in a cold-wall, pa rail el-pi ate reactor operating at 50 kHz, 200 mTorr, gas flows of SiH4/NH3/N2 = 140/270/800 seem and 500 watts of power, we can compare chemical and physical properties with thermally-deposited silicon nitride. Such a comparison is shown in Table 1.2... 

Whenever silicon nitride is synthesized in the presence of aluminum-containing compounds (frequently used as a flux material in process of growing whiskers), there is a high probability of the formation of /3 -SiA10Ns. Up to two-thirds of the silicon in /3-Si3N4 can be substituted by Al without a change of structure. The /3 -SiAl()N has mechanical and physical properties similar to y3-Si3N4. It is, however, thermodynamically more stable than silicon nitride. 

PHYSICAL AND CHEMICAL PROPERTIES OF SILICON NITRIDE FILMS FROM SiH4 + NH3 + N2 [195]... 

Silicon carbide is noted for its extreme hardness [182-184], its high abrasive power, high modulus of elasticity (450 GPa), high temperature resistance up to above 1500°C, as well as high resistance to abrasion. The industrial importance of silicon carbide is mainly due to its extreme hardness of 9.5-9.75 on the Mohs scale. Only diamond, cubic boron nitride, and boron carbide are harder. The Knoop microhardness number HK-0.1, that is the hardness measured with a load of 0.1 kp (w0.98N), is 2600 (2000 for aAl203, 3000 for B4C, 4700 for cubic BN, and 7000-8000 for diamond). Silicon carbide is very brittle, and can therefore be crushed comparatively easily in spite of its great hardness. Table 8 summarizes some typical physical properties of the SiC ceramics. 

Silicon nitride, Si3N4, has physical, chemical, and mechanical properties that make it a useful industrial... 

The common commercially available fibers used in composites are fiberglass, graphite (carbon), aramid, polyethylene, boron, silicon carbide, and other ceramics such as silicon nitride, alumina, and alumina silica. Many matrix choices are available, both thermosetting and thermoplastic. Each type has an impact on the processing technique, physical properties, and environmental resistance of the finished composite. The most common resin matrices include polyester, vinyl esters, epoxy, bismaleimides, polyimides, cyanate ester, and triazine. 

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