ISSN 1063-7397, Russian Microelectronics, 2007, Vol. 36, No. 2, pp. 116–119. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © L.B. Jangidze, A.N. Tavkhelidze, M.O. Tetradze, T.N. Devidze, 2007, published in Mikroelektronika, 2007, Vol. 36, No. 2, pp. 136–140.
This study investigates the fabrication of Ag/Cu
electrodes by Cu electroplating of a reasonably ﬂat Ag
surface. This process is important for the creation of
high-current nanoelectronic devices.
A multilayered structure is ﬁrst formed on a silicon
wafer by magnetron sputtering deposition of a 0.1-
thick Ti ﬁlm and a 1.2-
m-thick Ag ﬁlm on which a Cu
ﬁlm is then grown by electroplating to a thickness of
0.45 to over 1 mm. The Si/Ti/Ag/Cu structure thus
obtained (Fig. 1) is characterized by weak adhesion
between the Ti and Ag layers, which allows us to fabri-
cate a Si/Ti and a Ag/Cu electrode by splitting the stack
along the Ti/Ag interface (Fig. 2) under heating or cool-
ing . In doing so, we must meet the essential require-
ment for the electrodes to be produced with conformal
METHODS AND RESULTS
In this study, we used n-Si(100) wafers 20, 40, or
50 mm in diameter and 1 or 2 mm thick. Surface ﬁnish
of Class 14 was imparted to both wafer sides with a
view to obtaining ﬁlms of desired structural quality.
Cu electroplating was performed in a mechanically
stirred sulfate electrolyte,
OH + H
, whose temperature was maintained
within the range 296.5–308 K; the current density was
. Being simple in composition, sulfate
electrolytes are stable and easy to adjust, allow compar-
atively high current densities, and offer a current yield
closer to a theoretically predicted value of 100%. The
ethanol inhibits formation of univalent copper ions and
thus makes for deposition of dense, ﬁne-grained copper
ﬁlms. Note that raising the electrolyte temperature
increases the allowable current densities, and stirring
the electrolyte accelerates copper deposition by encour-
aging growth in sulfate concentration near the cathode.
Electric current was drawn from the back side of the
wafer, which was insulated from the electrolyte.
The conditions of electroplating were adjusted to
form electrodes of desired diameter and shape. The
thickness uniformity of copper over the cathode surface
was improved by the following methods:
(i) Placing an insulator mask of suitable diameter
and thickness near the cathode surface,
(ii) Placing extra cathodes near the main one,
(iii) Rotating the cathode,
(iv) Changing to an anode of another shape,
(v) Passing an alternating current with a nonzero
direct-current (dc) component.
The surface conformality of the electrodes fabri-
cated was evaluated by optical measurement of Ag-sur-
face nonﬂatness using a Michelson interferometer .
The light source was a He–Ne laser emitting at the
= 632.8 nm. The specimen under exami-
nation served as one of the mirrors, and the interference
pattern was formed in the air gap between the other
Methods for Improving Surface Flatness
in Thick Cu Film Electrodeposition
L. B. Jangidze, A. N. Tavkhelidze, M. O. Tetradze, and T. N. Devidze
Tbilisi State University, Tbilisi, Georgia
Received March 29, 2006
—An experimental evaluation is reported of some methods for improving the surface ﬂatness of thick
Cu ﬁlms grown by electroplating. These are (1) placing an insulator mask of suitable diameter and thickness
near the cathode surface, (2) placing extra cathodes near the main one, (3) rotating the cathode, (4) changing to
an anode of another shape, and (5) passing an alternating current with a nonzero dc component. The surface
ﬂatness of Cu ﬁlms thus obtained is measured in absolute and relative terms.
PACS numbers: 81.15.-z
Original multilayered structure. The materials are
) Si, (
) Ti, (
) Ag, and (