Hydrogen silicon nitride

Reactions (1), (2) and (3), which all use ammonia, have a tendency to deposit silicon nitride with a high ratio of included hydrogen, especially at the lower temperatures and if a plasma is used. This tendency is often detrimental but it can be remedied, at least to some degree, by using nitrogen instead of ammonia ... 

The reinforcing fibers are usually CVD SiC or modified aluminum oxide. A common matrix material is SiC deposited by chemical-vapor infiltration (CVI) (see Ch. 5). The CVD reaction is based on the decomposition of methyl-trichlorosilane at 1200°C. Densities approaching 90% are reported.b l Another common matrix material is Si3N4 which is deposited by isothermal CVI using the reaction of ammonia and silicon tetrachloride in hydrogen at 1100-1300°C and a total pressure of 5 torr.l" " ] The energy of fracture of such a composite is considerably higher than that of unreinforced hot-pressed silicon nitride. 

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

As a second example of the application of ion-beam analysis techniques to semiconductors, we take the calibration of IR absorption measurements of the hydrogen content of sputtered amorphous silicon and silicon nitride. In early measurements, the hydrogen content of glow-discharge a-Si H deduced from IR absorption measurements, using ablsinitio calculations of the absorption cross section of the Si—H IR absorption bands, was com-... 

The passivation of silicon, motivated by the centrality of this semiconductor to the microelectronics industry, has been well studied. In addition to excellent passivation allowed by the silicon oxide, silicon can also be passivated with silicon nitride (Si3N4), other dielectrics, metal layers, and hydrogen. Here we focus only on hydride termination, since in addition to acting as a passivating layer for the underlying silicon, the hydride groups provide a versatile starting point for subsequent attachment chemistry. 

Silicon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between silicon carbide and a variety of compounds at relatively high temperatures. Sodium silicate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal silicide. Silicon carbide decomposes in fused alkalies such as potassium chromate or sodium chromate and in fused borax or cryolite, and reacts with carbon dioxide, hydrogen, air, and steam. Silicon carbide, resistant to chlorine below 700°C, reacts to form carbon and silicon tetrachloride at high temperature. SiC dissociates in molten iron and the silicon reacts with oxides present in the melt, a reaction of use in the metallurgy of iron and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new silicon nitride-bonded type exhibits improved resistance to cryolite. 

Plasma-deposited silicon nitride contains large amounts of hydrogen, typically in the range of 20—25 atomic % H, and has polymer-like properties. The electrical resistivity of the film depends on the deposition temperature, the film stoichiometry, and the amounts of hydrogen and oxygen in the film. 

Silicon nitride powder can be made by the reaction of silicon tetrachloride vapor with gaseous ammonia. The by-product is gaseous hydrogen chloride. Write a balanced equation for the reaction. 

Figure 12. Hydrogen concentration versus temperature for silicon nitride layers deposited by PECVD. (seem is standard cubic centimeters per minute.) (Reproduced with permission from reference 221. Copyright 1985 The Electrochemical Society, Inc.)...

Franz et al. [93] developed a palladium membrane micro reactor for hydrogen separation based on MEMS technology, which incorporated integrated devices for heating and temperature measurement. The reactor consisted of two channels separated by the membrane, which was composed of three layers. Two of them, which were made of silicon nitride introduced by low-pressure chemical vapor deposition (0.3 pm thick) and silicon oxide by temperature treatment (0.2 pm thick), served as perforated supports for the palladium membrane. Both layers were deposited on a silicon wafer and subsequently removed from one side completely... 

Silicon nitride films produced by this technique proved to be comparable to those created in parallel-plate reactors in terms of stoichiometry and hydrogen content, as evidenced by the data presented in Figures 17 and 18. 

Silicon nitride films deposited in para 11 el-pi ate, plasma-enhanced CVD reactors will be discussed in greater detail in a later chapter. However, they typically have a refractive index on the order of 2.0, partly because of hydrogen incorporated into the layer, and the ECR films appear similar. Also, as... 

The first three items relate to the chemical nature of the film. An outstanding feature of PECVD silicon nitride films is that their stoichiometry can be controlled, and that they can have as much as 30 atomic percent hydrogen in them. The last two items relate to the mechanical behavior of such films. If they are not dense enough, they will net be effective barriers to moisture... 

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