1063-7397/01/3006- $25.00 © 2001 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 30, No. 6, 2001, pp. 381–393. Translated from Mikroelektronika, Vol. 30, No. 6, 2001, pp. 445–458.
Original Russian Text Copyright © 2001by Vorob’eva.
The quest for higher integration levels is arousing
the interest in submicrometer- and nanometer-scale ele-
ments. This area of research also deals with quantum-
effect devices, such as the single-electron transistor ,
arrays of ﬁeld-emission microcathodes [2–4], and tun-
nel-diode sensors . Another subject of investigation
is self-organized quantum dots . The problem is that
desired feature sizes cannot be obtained by existing
imaging techniques (e.g., optical or laser lithography).
This reason underlies the extensive research into the
fabrication of the arrays of nanometer-sized elements
(dots, wires, pillars, etc.); their charge-transfer and
optical properties; and potential applications for meso-
scopic functional electronics, sensorics, etc.
In view of the above, it appears worthwhile to
address the fabrication of pore arrays in metallic ﬁlms
by anodic oxidation, also known as anodizing. This
simple and inexpensive technique capitalizes on the
spontaneous pattern formation at the interface between
an electrolyte and a metal, namely, aluminum. After the
appropriate electrochemical processing (anodizing,
etching, deposition, polishing, etc.), we obtain an array
of pores with the desired dimensions. This array can
serve as a mask for creating arrays of pillars, dots, or
other mesoscopic objects.
Note that this approach exploits naturally occurring
patterns . Although the pore array is produced artiﬁ-
cially, its structure is governed by the properties of the
oxide itself [8, 9].
This paper deals with some important features of the
kinetics underlying the fabrication of microscopic pil-
lar arrays by the anodizing of an Al/Ta thin-ﬁlm struc-
ture. The arrays are examined by scanning electron
microscopy (SEM) and simultaneous current–voltage
The main aim of this study is to evaluate the range
over which pillar dimensions vary and to investigate the
kinetic parameters directly related to the regularity of
pillar arrays. A combined approach to the measure-
ments made it possible to develop optimal fabrication
processes. A good reproducibility of the physical and
morphological properties was thus achieved for large-
area pillar arrays.
The pattern of pores in
was transferred to Ta
by a technique of additive imaging similar to additive
etching . Speciﬁcally, the Al/Ta structure was pro-
cessed in three steps: (1) A porous
ﬁlm by the
anodizing of the Al ﬁlm was produced. (2) Using the
film as a mask,
pillars by the anodizing of
the Ta ﬁlm with another electrolyte were grown. (3) The
film was etched away. An array of
on the substrate was thus fabricated. Step 2 will be
referred to as forming.
The above process, as well as the deposition of the
Al and Ta ﬁlms, are detailed in . A careful account
of the anodizing of the Al/Ta structure is given in .
The starting structures were grown on standard glass
or glass–ceramic substrates of area
on Si(100) wafers 76 mm in diameter.
A Ta ﬁlm of 40–300 nm in thickness was deposited
before an Al ﬁlm 500–2000 nm in thickness.
Step 1 used three different electrolytes to obtain dif-
ferent pore diameters: (1) a 10% aqueous solution of
sulfuric acid, (2) a 3.6% aqueous solution of oxalic
Anodic-Oxidation Growth of Microscopic Pillar Arrays:
A. I. Vorob’eva
Belarussian State University of Information Science and Electronics, Belarus
Received October 11, 2000
—The three-step fabrication of microscopic pillar arrays by the anodic oxidation of Al/Ta thin-ﬁlm
structures on dielectric or silicon substrates is studied experimentally. The major features of pillar-growth kinet-
ics are described. The main properties of the arrays are evaluated by scanning electron microscopy and simul-
taneous current–voltage tracing. The ranges of variation for geometric array parameters are determined. The
pillars grown have a maximum height-to-diameter ratio of 17.0, a maximum height of 540 nm, and a minimum
radius of about 15 nm. The maximum density of pillars in an array is
. A good reproducibility
of physical and morphological properties is achieved for large-area pillar arrays. Potential applications of pillar
arrays are recited: light-emitting diodes, thin-ﬁlm controllers, solar batteries, spatial light modulators, polariz-
ers, etc. It is noted that an investigation into the fabrication of pillar arrays for ﬁeld-emitter displays is currently