Solid source diffusion

The occurrence of etch rate reduction on highly boron doped materials appears to be independent of doping methods, whether by solid-source diffusion, epitaxial growth, or ion implantation. However, the boron concentration at which significant reduction occurs is different for different methods of doping. The critical boron concentration for etch rate reduction to occur is affected by the defect density in different doped materials. It is found that for similar boron concentrations the amount of etch rate reduction in KOH solutions decreases with increasing defect densityIn... 

The process uses four mask levels (PAD METAL, SOI, TRENCH, and BLANKET METAL) that are used to pattern fine metal features on the device layer, holes through the device layer, holes through the substrate, and shadow-masked metal features on the device and substrate layers. The process starts off with a 4 in. SOI wafer (substrate 1-10 Q-cm, n-type, device layer 110 Q-cm) that is heavily phosphorus doped at the surface (15 25 Q/n) by solid source diffusion from a PSG layer during a 1 h anneal at 1050°C in argon. The PSG is then stripped in a wet etch. 

The apparatus for open-tube diffusion consists of a silica furnace tube with a continuously flowing gas. The exit end may be at atmospheric pressure or at reduced pressure. The impurity source may be a vaporizing solid whose vapors are carried to the semiconductor by a carrier gas. The carrier gas may be bubbled through a liquid impurity source. The carrier gas takes up source molecules, which then decompose at elevated temperatures. Liquid sources are maintained at or near room temperature. This arrangement has an advantage over the use of solid sources in terms of easier control of source temperature and, thus, impurity concentrations in the carrier gas. 

Liquid doping sources are usually of two forms (1) a solution of dopant material is directly applied to the semiconductor surface and dried prior to diffusion or (2) a carrier gas is bubbled through the liquid source and the source molecules are carried into an open-tube furnaee. Doping may then occur from the gas phase or from a deposited solid phase on the semiconductor. Also, in some cases solid sources deposited on semiconductors become liquid at diffusion temperatures (e.g., borosilicate glasses containing ca. 30 mol% B2O3 become liquid at 1000°C)L... 

Some ceramic materials are not found widely or at all in nature, and thus are synthesized for use. To prepare more complex ceramic compositions such as perovskites of general structural formula ABO3, and ferrites, of formula MFc204, the individual oxides or salts of the cations A, B, and M are often combined as powders and then reacted at high temperature by a solid-state diffusion mechanism. Silicon nitride (Si3N4) can be manufactured from either the nitridation of silicon metal or from the reaction of silicon tetrachloride with ammonia. Silicon carbide (SiC) is obtained from the reduction of silica with a carbon containing source. 

A particularly interesting series of experiments has recorded the direct observation of diffusion broadening of the Mdssbauer line [60]. A Co/Cu source or a Fe/Cu absorber shows the onset of considerable line broadening between 1000° and 1060°C due to solid-state diffusion, although the data show considerable discrepancies from prediction by a simple diffusion-jump model. 

Figure 7.7 Graphical representation of the solution to Pick s second law for a thin planar source diffusing into a semi-infinite solid. The curves show concentration versus distance after various times and the units have been chosen arbitrarily.

Similarly, for the point source diffusing in an infinite solid the solution for C in three dimensions is... 

When a positron is emitted from a source and then penetrates into a solid, it quickly loses kinetic energy until it reaches the thermal level (Figure 4.26). This thermalised positron moves around in the solid by diffusion and finally annihilates with an electron. 

When a positron is emitted from a source, and penetrates into a solid, it quickly loses its kinetic energy to thermal energy. The thermalised positron moves around in the solid by diffusion and finally annihilates with one of the electrons in its surroundings. All of the energy from the electron-positron annihilation is converted into two annihilation y-rays, which can be detected. The annihilation rate of a positron is determined by the local electron density in the locale of the positron. Thus, positrons... 

Smith, K. and Wang, C.Y. (2006) Solid-state diffusion limitations on pulse operation of a lithium ion cell for hybrid electric vehicles. /. Power Sources, 161 (1), 628-639. 

Dislocation theory as a portion of the subject of solid-state physics is somewhat beyond the scope of this book, but it is desirable to examine the subject briefly in terms of its implications in surface chemistry. Perhaps the most elementary type of defect is that of an extra or interstitial atom—Frenkel defect [110]—or a missing atom or vacancy—Schottky defect [111]. Such point defects play an important role in the treatment of diffusion and electrical conductivities in solids and the solubility of a salt in the host lattice of another or different valence type [112]. Point defects have a thermodynamic basis for their existence in terms of the energy and entropy of their formation, the situation is similar to the formation of isolated holes and erratic atoms on a surface. Dislocations, on the other hand, may be viewed as an organized concentration of point defects they are lattice defects and play an important role in the mechanism of the plastic deformation of solids. Lattice defects or dislocations are not thermodynamic in the sense of the point defects their formation is intimately connected with the mechanism of nucleation and crystal growth (see Section IX-4), and they constitute an important source of surface imperfection. 

The retarding influence of the product barrier in many solid—solid interactions is a rate-controlling factor that is not usually apparent in the decompositions of single solids. However, even where diffusion control operates, this is often in addition to, and in conjunction with, geometric factors (i.e. changes in reaction interfacial area with a) and kinetic equations based on contributions from both sources are discussed in Chap. 3, Sect. 3.3. As in the decompositions of single solids, reaction rate coefficients (and the shapes of a—time curves) for solid + solid reactions are sensitive to sizes, shapes and, here, also on the relative dispositions of the components of the reactant mixture. Inevitably as the number of different crystalline components present initially is increased, the number of variables requiring specification to define the reactant completely rises the parameters concerned are mentioned in Table 17. 

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