Dislocation-Free Oxidation of Porous Silicon Formed Using Highly Phosphorus-Diffused Silicon and Its Application

Porous silicon was formed using highly phosphorous-diffused n-type silicon. Dislocation generation mechanisms due to the force caused by marked volume expansion at the early stage of porous silicon oxidation and strain generation caused by oxidation are investigated. The height of the step produced by oxidation and the relationship between the rate of increase in step height and stress are discussed. The experimental results concerning the step height versus the direct oxidation time are qualitatively explained based on the oxidation time dependence of the amount of SiO2 in oxidized porous silicon calculated using a simple model. Two dislocation-free oxidation methods are proposed. One is oxidation in wet oxygen through a SiO2 film deposited on the porous silicon by low-temperature chemical vapor deposition. The other is oxidation in dry and wet oxygen after annealing in nitrogen atmosphere. The porous silicon oxidized by the former dislocation-free oxidation method was applied to reduce the parasitic capacitance between the base electrode and the collector region in a high-speed bipolar transistor. This reduction resulted in an increase of the cut-off frequency and maximum frequency.