Silicon oxidation growth rate

An important point is that the micro- and nanopowders consisting of pyramidal crystallites (prepared by grinding silicon waste from semiconductor manufacturing) and single-crystal Si are identical in the temperature variation of the silicon oxide growth rate. At the same time, the nanopowders prepared via silane decomposition in an rf plasma and the micropowders consisting of spherical crystallites differ markedly in the temperature variation of the oxidation rate. The nanopowders are less sensitive to the oxidation temperature. 

The substrate condition plays an important role in the growth of native oxide on silicon. The growth rate of native oxide films is similar for lowly and moderately doped silicon substrates. An increased growth rate is observed with high dopant concentration >10 Vcm on both n- and silicon substrates. Figure 2.17 shows that for n type, the oxide grows faster on heavily doped substrates. In addition, it shows that... 

Thermal oxidation of silicon can be achieved under dry or wet oxidation condition. In dry oxidation, oxygen is the oxidant whereas in wet oxidation, water molecule is the oxidant. Thermal oxidation is often carried out at elevated temperatures, such as 600-1250°C. The oxide growth rate is generally faster in wet oxidation compared to dry oxidation. Also, the growth rate of the oxide depends on the crystallographic orientation of the silicon, that is, the linear oxidation rate of silicon qualitatively is [110] > [111] > z[100]. However, crossover in growth rate is possible for instance, the oxide growth rate at 700-1000°C, [111] > [110], but not at 1100°C. 

Many theories on the formation mechanisms of PS emerged since then. Beale et al.12 proposed that the material in the PS is depleted of carriers and the presence of a depletion layer is responsible for current localization at pore tips where the field is intensified. Smith et al.13-15 described the morphology of PS based on the hypothesis that the rate of pore growth is limited by diffusion of holes to the growing pore tip. Unagami16 postulated that the formation of PS is promoted by the deposition of a passive silicic acid on the pore walls resulting in the preferential dissolution at the pore tips. Alternatively, Parkhutik et al.17 suggested that a passive film composed of silicon fluoride and silicon oxide is between PS and silicon substrate and that the formation of PS is similar to that of porous alumina. 

When the surface is completely covered by an oxide film, dissolution becomes independent of the geometric factors such as surface curvature and orientation, which are responsible for the formation and directional growth of pores. Fundamentally, unlike silicon, which does not have an atomic structure identical in different directions, anodic silicon oxides are amorphous in nature and thus have intrinsically identical structure in all orientations. Also, on the oxide covered surface the rate determining step is no longer electrochemical but the chemical dissolution of the oxide.1... 

In contrast to acidic electrolytes, chemical dissolution of a silicon electrode proceeds already at OCP in alkaline electrolytes. For cathodic potentials chemical dissolution competes with cathodic reactions, this commonly leads to a reduced dissolution rate and the formation of a slush layer under certain conditions [Pa2]. For potentials slightly anodic of OCP, electrochemical dissolution accompanies the chemical one and the dissolution rate is thereby enhanced [Pa6]. For anodic potentials above the passivation potential (PP), the formation of an anodic oxide, as in the case of acidic electrolytes, is observed. Such oxides show a much lower dissolution rate in alkaline solutions than the silicon substrate. As a result the electrode surface becomes passivated and the current density decreases to small values that correspond to the oxide etch rate. That the current density peaks at PP in Fig. 3.4 are in fact connected with the growth of a passivating oxide is proved using in situ ellipsometry [Pa2]. Passivation is independent of the type of cation. Organic compounds like hydrazin [Sul], for example, show a behavior similar to inorganic ones, like KOH [Pa8]. Because of the presence of a passivating oxide the current peak at PP is not observed for a reverse potential scan. 

Initially the growth rate is lower than on crystalline silicon. It is known that hydrogen has the ability to passivate the crystalline silicon surface and so its presence on the a-Si H film is probably the reason for the slower rate. The different oxidation properties of PVD and CVD films are a dramatic illustration of the different a-Si H structures that can be produced. 

H O, a mixture which incidentally can combust or explode. Ozone (O3) is also used to accelerate oxidization, usually for cases of less-reactive precursors such tetraethoxysilane (TEOS). N O and CO are also used as oxidizers, as in SiH Cl -I- 2Np SiO (s) -I- 2 HCl -I- 2 N, or ZrCl + 2 CO -I- 2 H ZrO (s) -i-2 CO -1- 4 HCl. Hydrolysis reactions are often used with metal chloride precursors 2 AICI3 -1- 3 H O Al303(s) + 6 HCl, or TiCl -1- 2 Hp TiO (s) + 4 HCl. Solid substrates can also be directly oxidized, as in the steam oxidation of silicon Si(s) + 2 Hp SiO Cs) -I- 2 H. This gives a high-quality oxide, but at a relatively slow growth rate. 

Kang and Rhee grew bismuth oxide films at 225-425 °C by direct liquid injection MOCVD, using Bi(thd)3 dissolved in n-BuOAc. Temperatures above 325 °C tend to decrease the growth rate due to gas-phase dissociation processes. Annealing at temperatures up to 650 °C is necessary to obtain monoclinic o -Bi203. Temperatures above 750 °C convert a-Bi203 into cubic bismuth silicate due to the reaction with the silicon substrate. 

In contrast to C and N, Si-metabolism is metabolicaUy inexpensive for a given cell size, a silicon frustule requires ca. 1/10 the total metabolic energy of an equivalent cell wall composed of carbon compounds (Raven, 1983). Si-metabolism is also not directly coupled to photosynthesis. Si-transport and deposition are driven by oxidative phosphorylation (Blank and SuUivan, 1979 Blank et al, 1986 Sullivan, 1976), while serine and glycine, the amino acids which provide the main fraction of the protein matrix for Si-deposition (Werner, 1977), are terminal substances produced during photorespiration (Burris, 1977). Si-metaboHsm is instead Hnked to the regulation of cell division (Fig. 37.2) and growth rates (Brzezinski et al, 1990 Martin-Jezequel et al, 2000 Volcani, 1981). 

The oxidation rate of the micro- and nanopowders was found to be faster than that of bulk single-crystal silicon, hich can be rationalized as follows. At the initial stages of the oxide growth oxygen adsorption on micro- and nanoparticles leads to SiO formation. The oxidation is then due to an enhanced oxidant diffusion over the particle surface. During the oxidation of the powders, the amount of the oxidant penetrating into the bulk of a particle is so small that its contribution to the oxidation process in the bulk of the particle is insignificant. In this case, the oxidation of the micro- and nanopowders is... 

---