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Open Access Nano Express

'Wagon-wheel' mask as a tool to study anisotropy of porous silicon formation rate

Ekaterina V Astrova and Yuliya A Zharova*

Author Affiliations

Department of Solid State Electronics, Ioffe Physical Technical Institute Russian Academy of Sciences, Politekhnicheskaya 26, St. Petersburg, 194021, Russia

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Nanoscale Research Letters 2012, 7:421  doi:10.1186/1556-276X-7-421

Published: 27 July 2012

Abstract

Relationship between the rate of electrochemical formation of mesoporous Si and the crystallographic directions has been studied by local anodization of wafers through a mask having the form of narrow long wedges radiating from the center in all directions (‘wagon-wheel’ mask). The etching rates were found from the side etching under the thin transparent n-Si mask. On p+-substrates of various orientation diagrams characterizing the distribution of pore formation rates over different directions in the wafer plane were constructed for the first time. The wagon-wheel method was applied to study the current dependence of the anisotropy. It was found that the orientation-related difference between the pore formation rates is 5% to 25%, depending on the crystallographic direction and the etching current density. At a current density of approximately 9 mA/cm2, the etching rates are related as V100:V113:V110:V112:V111 = 1.000:0.900:0.836:0.824:0.750. A general tendency is observed toward weakening of the anisotropy with increasing current. The highest rate always corresponds to the <100 > direction, and the rate ratio between the other directions varies with increasing current, which leads to a change of their sequence.

Keywords:
Mesoporous Si; Anodization; Wagon-wheel mask; Anisotropy