Microelectronic devices are formed by first forming SiO₂ on a silicon wafer by chemical vapor deposition. This procedure is followed by coating the SiO₂ with a polymer called a photoresist. The pattern of the electronic circuit is then placed on the polymer and the sample is irradiated with ultraviolet light. If the polymer is a positive photoresist, the sections that were irradiated will dissolve in the appropriate solvent and those sections not irradiated will protect the SiO₂ from further treatment. The wafer is then exposed to strong acids, such as HF, which etch (i.e., dissolve) the exposed SiO₂. It is extremely important to know the kinetics of the reaction so that the proper depth of the channel can be achieved. The dissolution reaction is