摘要
Formation of porous silicon by etching of silicon wafers with vanadium pentoxide (V2O5) dissolved in hydrofluoric acid (HF) has been studied with infrared spectroscopy and electron microscopy. V2O5 creates VO2+ in solution, which initiates the reaction by injecting holes into the silicon valence band. Much is known about the mechanism of etching that leads to flat Si surfaces; however, the transition to pore formation is not well understood. The rate of film growth depends linearly on the V2O5 concentration in aqueous solutions but has a nonlinear dependence on the formal HF concentration. Addition of ethanol greatly decreases the etch rate and changes the pore morphology from a mixture of {100} + {110} planes to predominantly {100} planes. A plot of thickness versus etch time evolves from a quadratic to a linear dependence, whereas the surface area depends linearly on the etch depth. These observations are consistent with a model in which pores with a uniform diameter nucleate randomly then lengthen linearly in time. The pore density increases at short times and then reaches a saturation value. The probability that the collision of a VO2+ ion with the surface leads to etching of a Si atom (reactive sticking coefficient) is similar to 3 x 10(-8).
- 出版日期2010