Silicon in semiconductors

Contacfs and diffusion-barriermefallizafion and selecfive deposition on silicon in semiconductor applications (experimental). 

A potential application is as an insulator coating on silicon in semiconductor devices. 

Following a concise review of direct access storage devices, a treatise on the properties and electrochemistry of magnetically soft materials is provided by P. C. An-dricacos and L. T. Romankiw. The chapter is focused on the fundamentals of the magnetics and electrochemistry of Permalloy, a material which has similar importance in magnetic storage as has silicon in semiconductor devices. 

Inorganic (non-polymer) basecoats can provide layers to aid in adhesion (adhesion layer or glue layer) of a film to a surface. For example, in the Ti-Au metallization of oxides, the titanium adhesion layer reacts with the oxide to form a good chemical bond and the gold alloys with the titanium. The layers may also be used to prevent interdiffusion (diffusion barrier) between subsequent layers and the substrate. For example, the electrically conductive compound TiN is used as a barrier layer between the aluminum metallization and the silicon in semiconductor device manufacturing. 

Figure Bl.22.4. Differential IR absorption spectra from a metal-oxide silicon field-effect transistor (MOSFET) as a fiinction of gate voltage (or inversion layer density, n, which is the parameter reported in the figure). Clear peaks are seen in these spectra for the 0-1, 0-2 and 0-3 inter-electric-field subband transitions that develop for charge carriers when confined to a narrow (<100 A) region near the oxide-semiconductor interface. The inset shows a schematic representation of the attenuated total reflection (ATR) arrangement used in these experiments. These data provide an example of the use of ATR IR spectroscopy for the probing of electronic states in semiconductor surfaces [44]-...

SEMICONDUCTORS - SILICON-BASED SEMICONDUCTORS] (Vol 21) -gelatin in [GELATIN] (Vol 12)... 

To produce silicon, used in semiconductors, from sand (Si02), a reaction is used that can be broken down into three steps ... 

Silicon in the elemental state has important electronic applications as a semiconductor that were developed only during the last decade. The discovery of these uses was possible only after methods were developed for preparing silicon of extremely high purity. Reduction of Si02 with... 

An important step toward the understanding and theoretical description of microwave conductivity was made between 1989 and 1993, during the doctoral work of G. Schlichthorl, who used silicon wafers in contact with solutions containing different concentrations of ammonium fluoride.9 The analytical formula obtained for potential-dependent, photoin-duced microwave conductivity (PMC) could explain the experimental results. The still puzzling and controversial observation of dammed-up charge carriers in semiconductor surfaces motivated the collaboration with a researcher (L. Elstner) on silicon devices. A sophisticated computation program was used to calculate microwave conductivity from basic transport equations for a Schottky barrier. The experimental curves could be matched and it was confirmed for silicon interfaces that the analytically derived formulas for potential-dependent microwave conductivity were identical with the numerically derived nonsimplified functions within 10%.10... 

A more elaborate example of induct on heating is shown in Fig. 5.8, which showsareactordesignedforthedeposition of silicon epitaxy in semiconductor devices (see Ch. 13).Thepowerissuppliedby a solid-state high-frequency (20 KHz) generator. A radiation reflector, shown in Detail A, increases the efficiency and uniformity of deposition. Pressure varies from 100 mbar to 1 atm. 

Experimental applications include the direct deposition of patterns as small as 0.5 im in semiconductor applications using holographic methods, and the production of rods and coreless boron and silicon carbide fibers (see Ch. 19). 

Polycrystalline Silicon (Polysilicon). Polycrystalline silicon is used extensively in semiconductor devices. It is normally produced by the decomposition of silane at low pressure (ca. 1 Torr) as follows ... 

A common deposition reaction, used widely in semiconductor processing, combines ammonia with silane as the silicon source ... 

The market for silicon nitride is fast growing, particularly in structural and chemical resistance applications and as a thin film in semiconductor devices.P 1... 

A widely used glass is phosphosilicate (PSG), which is used extensively in semiconductor devices as a passivation and planarization coating for silicon wafers. It is deposited by CVD by the reaction of tetraethyl orthosilicate (TEOS) (C2H50)4Si, and trimethylphosphate PO(OCH3)3, in a molecular ratio corresponding to a concentration of 5 to 7% P. Deposition temperature is usually 700°C and pressure is 1 atm. 

Li, S. H. and Miller, R., Chemical Mechanical Polishing in Silicon Processing, Semiconductor Semimet., Vol. 63, New York Academic Press, 2000. 

The main source of silicon for semiconductor chips is silicon dioxide (silica). Silica can be reduced directly to elemental form by intense heating with coke in an electric arc furnace. At the temperature of the furnace, silicon is... 

A major and growing use of the minor metalloids is in semiconductor fabrication. Germanium, like silicon, exhibits semiconductor properties. Binary compounds between elements of Groups 13 and 15 also act as semiconductors. These 13-15 compounds, such as GaAs and InSb, have the same number of valence electrons as Si or Ge. The energy gap between the valence band and the conduction band of a 13-15 semiconductor can be varied by changing the relative amounts of the two components. This allows the properties of 13-15 semiconductors to be fine-tuned. 

In semiconductors such as silicon, each atom in the structural lattice has four outer electrons, each of which covalently pairs with an electron from one of the four neighboring atoms to form the interatomic bonds, i.e.- the "diamond" structure. Completely pure silicon thus has essentially no electrons available at room temperature for electron conduction, making it a very poor conductor. However, the key is getting the silicon pure enough. Originally, silicon was thought to be a natural semi-conductor until really pure silicon became available. 

In SAM the electron beam can be focussed to provide a spatial resolution of < 12 nm, and areas as small as a few micrometers square can be scanned, providing compositional information on heterogeneous samples. For example, the energy resolution is sufficient to distinguish the spectrum of elemental silicon from that of silicon in the form of its oxide, so that a contaminated area on a semiconductor device could be identified by overlaying the Auger maps of the two forms of silicon obtained from such a specimen. 

Soft, silver white metal that melts in the hand (29.8 °C) and remains liquid up to 2204 °C (difference 2174 °C, suitable for special thermometers). Gallium is quite widespread, but always in small amounts in admixtures. Its "career" took off with the advent of semiconductors. Ga arsenide and Ga phosphide, which are preferential to silicon in some applications, have extensive uses in microchips, diodes, lasers, and microwaves. The element is found in every mobile phone and computer. Ga nitride (GaN) is used in UV LEDs (ultraviolet light-emitting diodes). In this manner, a curiosity was transformed into a high-tech speciality. 

The majority of important semiconducting materials are isoelectronic with elemental silicon. Important semiconductor materials include the III-V (13-15) materials such as GaAs or InP, and II-VI (12-16) materials such as CdS or ZnSe (Table 1). These compound semiconductors are most often formed by combining elements displaced on either side of silicon by one place (i.e., Ill = Ga or In and V = N or As for a III-V material) or two places (i.e., II = Zn or Cd and VI = S or Se for a II-VI material) in the periodic table. Other materials are of specialist importance, especially ternary materials such as CuInE2 (E = S and Se), which find applications in solar cell technologies, as do materials of III-VI composition such as InxS, although their properties are often complicated by the potential for the formation of a wide range of similar phases. 

---