The mechanism and kinetics of silicon etching with mixtures in low pressure conditions in a hot wall reactor have been analyzed. Experiments were conducted according to the variables of the system (temperature, total pressure, concentration, and total flow rate). It was observed that there are two zones of reaction according to the temperature, one controlled by gaseous diffusion and the other controlled by the reaction on the surface. The etch mechanism varies with the process conditions so that different thermodynamically stable species may be generated, depending on the adsorption of or . Both mechanisms compete, and a general kinetic equation has not yet been established.