Self-organized pore formation and open-loop-control in semiconductor etching

TL;DR

This paper presents a model for self-organized pore formation in semiconductor etching, showing how open-loop control can regulate pore morphology and suppress branching to produce regular, modulated pores.

Contribution

It introduces the Current-Burst-Model for understanding pore formation and demonstrates how open-loop control influences pore morphology in semiconductor etching.

Findings

The model explains inhomogeneous dissolution processes in etching.

Open-loop control can suppress side pore formation.

Regular, diameter-modulated pores can be achieved.

Abstract

Electrochemical etching of semiconductors, apart from many technical applications, provides an interesting experimental setup for self-organized structure formation capable e.g. of regular, diameter-modulated, and branching pores. The underlying dynamical processes governing current transfer and structure formation are described by the Current-Burst-Model: all dissolution processes are assumed to occur inhomogeneously in time and space as a Current Burst (CB); the properties and interactions between CB's are described by a number of material- and chemistry- dependent ingredients, like passivation and aging of surfaces in different crystallographic orientations, giving a qualitative understanding of resulting pore morphologies. These morphologies cannot be influenced only by the current, by chemical, material and other etching conditions, but also by an open-loop control, triggering the time scale given by the oxide dissolution time. With this method, under conditions where only branching pores occur, the additional signal hinders side pore formation resulting in regular pores with modulated diameter.