Deal-Grove oxidation rate constants for the controlled combustion-based radical oxidation of silicon wafers in a batch reactor were determined, thus providing insight into the rate-limiting factors. Re-examination of the oxidation rates of wafers with different crystal orientations provides an estimate of the enhancement of the linear rate constant in radical oxidations as compared to standard wet and dry oxidation processes.Oxidation of silicon wafers via atomic oxygen radicals is becoming increasingly desirable and has already supplanted conventional wet or dry thermal oxidation for some applications. Growth rates for radical oxidation depend much less on crystal orientation than for thermal dry or wet oxidation, a vital characteristic for threedimensional transistor designs 1,2 and shallow-trench isolation ͑STI͒ liner oxides, for which the lack of sufficient corner rounding from thermal oxidation is a liability. 3 Radical-based oxide films have been shown to have superior breakdown voltages and leakage properties compared to thermal oxides. 4 At low temperatures, oxide growth rates from oxygen radicals are much higher than thermal oxidation rates. Radicals even enable wafer processing at temperatures below 400°C, a temperature range otherwise only accessible with plasmas. Various methods have long been explored to produce high-quality silicon dioxide at reduced temperatures. Examples include ozone oxidation, UV-assisted oxidation, and plasma oxidation. One single-wafer-based radical oxidation system, known as in situ steam generation ͑ISSG͒, utilizes oxygen and hydroxyl radicals created through chemical reactions of hydrogen and oxygen. Its success relies on two critical conditions. First, the process must be run at low pressures to achieve a sufficiently long radical lifetime. Second, a high volume of oxygen and hydrogen must be used to reduce the chemical residence time. 5,6 The reactants are premixed at relatively low temperatures, e.g., 100°C, and flow over a heated silicon wafer. The reactants are heated by the wafer within the thermal boundary layer. Due to the low operating pressure and high mass flow rate, reactants flow over the wafer at high speeds. The silicon wafer has to be heated and maintained at a sufficiently high temperature to initiate and sustain the gas-phase combustion process. This raises the minimum temperature at which combustion-based radical oxidation can be performed, compared to a hotwall reactor, for example.The challenge for producers of capital equipment for semiconductor manufacturing has been to design radical oxidation systems that are not cost prohibitive, have high throughput, and produce wafers with superior oxide properties ͑e.g., thickness uniformity͒. With these targets in mind, it becomes important to understand the nature of the radical-based oxidation, that is, to identify the ratelimiting factors, factors that have been long understood for thermal oxidation. Recently a model for the oxidation kinetics in two combustion-based systems was proposed in which an initial ...

Abstract:The kinetics of polymerization of methyl methacrylate initiated by Ce(IV)-Vanillin redox system was studied in aqueous solution of sulfuric acid at 40 °C. The rate of polymerization (Rp) and the reaction orders with respect to monomer, initiator and ligand have been determined and found to be 1.5, 0.5 and 0.5 respectively. The effect of concentration of sulfuric acid on the polymerization was also studied. The rate of polymerization was found to increase with increasing temperature 30-60 °C and decreases at higher temperature (>60 0 C). The overall activation energy (Ea) was found to be 36.7 kJ/mol. A suitable kinetic scheme has been proposed.

Aqueous polymerization of acrylonitrile initiated by Ce(IV)/p-hydroxy acetophenone (Ce(IV) – HAP) was studied in aqueous solution of sulfuric acid at 40°C. The rate of polymerization was investigated at various concentrations of monomer, initiator, activator, sulfuric acid and the effect of temperature of 30-70°C range was studied. The rate of polymerization is governed by the expression Rp = Kp [M]1.44[Ce(IV)]0.55[HAP]0.51. The activation energy of polymerization was found to be 17.9 kJ/mol. A probable mechanism consistent with the observed results is proposed and discussed.