Reactions in the System  O 2 ‐  NO  ‐  N 2 O  in a Conventional Furnace: II. Chemical Reactions Between  O 2 and NO

Abstract

There are several reactions occurring during the oxidation of samples in a conventional furnace. Many of these reactions can change the gas-phase composition during the experiments. 1,2 As long as the oxidizing gas is pure and fairly stable (for instance O 2 or NO) the main reactions that will occur are various exchange reactions. These reactions have been discussed in Part I of this paper. In gas mixtures there can also be a reaction between the different gas components to form new species. In gas mixtures of O 2 and NO (and N 2 ) various NO x species are formed, where NO x is a collective name for different oxidized nitrogen species, like NO, N 2 O, NO 2 , etc. The formation and the reaction of NO x are essential issues in many fields of science. The combustion of fossil fuel generates NO x , which is a severe environmental problem, and the main source of this pollutant is automobile emissions. There are many ways in which NO x has a negative effect on the environment, such as acting as a greenhouse gas and being responsible for the generation of ozone in photochemical smog. N 2 O is one of the species (though not the worst one) responsible for the ozone hole, etc. 3 Apart from many environmental problems with NO x , there are several technical applications where NO x is a vital gas component. In recent time the computer industry has shown an interest in the chemistry of NO x . We are now reaching the point when the dimensions of the data chips (and thereby their speed) are limited by the performance of the Si-SiO 2 interface. An annealing in NO x in the manufacturing process of data chips seems to give a better performance of the Si-SiO 2 interface, by the formation of a thin oxynitride layer at the Si-SiO 2 interface. 4 In order to understand the oxidation and oxynitration of silicon the reactions of O 2 and NO in the furnace, and especially on SiO 2 , have to be better understood. In the O 2 -NO furnace system there are several chemical reactions between O 2 and NO to N 2 O, NO 2 , and NO x . We have studied some of these reactions in a closed reaction chamber with the use of different isotopes and continuously probed the gas-phase composition with a mass spectrometer. We have especially focused on the formation of N 2 O and NO 2 , and have found that the reaction path is not as expected. 5 ExperimentalExchange reactions and chemical reactions of the O 2 -NO system have been studied by in situ probing of the gas-phase composition of a closed vacuum furnace system with a mass spectrometer. The amounts of the different gas components (chemical and isotopic components) can be calculated from the measured total pressure and composition. The reactions rates can thereby be evaluated from the time dependency of the amounts of reactants and reaction products. The vacuum furnace system used (see Fig. 1 of the preceding paper on p. 4566) consists of four main parts: an introduction chamber, a mass spectrometer, a gas-handling system, and a reaction chamber, The reaction chamber consists of a part where the walls are s...

Reactions in the System O 2 ‐ NO ‐ SiO2 in a Conventional Furnace: I. Oxygen Exchange Reactions

“…This number can be related to the calculated number of gas molecules colliding in the gas (gas-phase reactions) or colliding with the surface (reaction catalyzed by the surface). 26 The number of gasphase collisions can be calculated to 4и10 25 s Ϫ1 , from the gas-phase collision theory [4] where z is the collision frequency (s Ϫ1 ), p is the pressure (Pa), k is the Boltzmann constant, T is the temperature (K), is the collision cross section, and c the average speed of the NO molecules at 298 K [5] where Z is the collision density (m Ϫ3 s Ϫ1 ).…”

“…However, even when diffusion is rate limiting, an understanding of the chemical reactions active at the two interfaces (O 2 -oxide and oxide-substrate) is needed, since these reactions set the boundary conditions for diffusion. 3,4 The various oxygen exchange reactions, by using isotopic labeled oxygen, 3,[5][6][7] can be used to study the chemical reactions and the diffusion. There are three stable isotopes of oxygen which can be used, and the natural abundance of oxygen is 99.76% 16 O, 0.04% 17 O, and 0.2% 18 O.…”

“…The oxygen exchange reactions can thereby be used to evaluate the oxidation mechanisms. 3,4,7 The exchange O 2 o oxide has been more thoroughly studied during oxidation of silicon than metals. The reason for this is that far more studies have been made on oxidation of silicon, since it is a basic process in the manufacturing of computer chips.…”