硅在HF溶液中的阳极溶解

The impedance response of n, p-, n', and p* silicon was studied during dissolutionropolishing inHE solutions. Characteristic capacitive and inductive impedances were seen as a function of potential and dopant concentration.For the n* and p* silicon, the electrode response was dominated by the potential drop across the Helmholtz layer and, athigher potentials, to the response of the oxide layer. Characteristic impedance responses were associated with Tafel dissolution and oxide formation. For the p" silicon close to the open-circuit potential, an additional contribution to the imped.ance response was seen from the space-charge layer. For the n silicon the impedance response was dominated by the potential drop across the space-charge layer.

The anodic dissolution of silicon in HF solutions has re-ceived considerable attention in the last few years due tothe observation that at low overpotentials, prior to theonset ofelectropolishing, silicon dissolves in such a way asto produce a porous layer (1). The main application for po-rous silicon layers is for dielectric isolation in integratedcircuits due to the chemically active nature of this material(2-4).

Turner (5) studied the anodic dissolution behavior ofp-type silicon (3.5 9 cm) in 5% HF solutions and observedthat on increasing the potential from the open-circuit potential in the positive direction, the current increased ex-ponentially with potential to a critical value above whichelectropolishing occurred.In the low-potential region, theformationof a film was reported that became delaminatedat potentials corresponding to electropolishing.The devel-opment of the flm was associated with a characteristicchange in interference colors.Theunissen (1) studied the dissolution of n-type siliconwith a range of dopant concentration in 5% HF solutionand concluded that the formation of porous layers was theresult of a partial dissolution process.Further,Theunissensuggested that the initiation process was due to the localbreakdown of the barrier in the depletion layer where thelocal feld exceeded some critical value.

Meek (6) studied the anodic dissolution of n- and p-typesilicon in 5% HF solution and over a wide range of dopantconcentrations. For the heavily doped n-type samples itwas noted that the current-potential curves were independent of the dopant (P, As, Sb). For n-type samples, thecritical current density was found to be dependent on dopant concentration and crystal orientation, although thiswas not true for the p-type material.Other studies have been carried out (7-9) in which themorphology of the porous layer has been studied as a function of crystal orientation, dopant concentration, potentialand hydrofluoric acid concentration.