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15th Edition: Measurement of Metal Film Thickness for Copper Interconnects |
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Feb 02, 2005 at 03:59 PM |
DANIELE CONTESTABLE-GILKES, SAILESH M. MERCHANT & MINSEOK OH, Agere Systems, Orlando, FL, USA
ABSTRACT
Increased device speed and improved electromigration are two main
drivers for the semiconductor industry's transition from aluminium to
copper for integrated circuit interconnects. A major disadvantage of
copper is its fast diffusion rate into underlying substrates.
Therefore, in order to benefit from the advantages of lower sheet
resistance and improved electromigration by using copper, a
high-quality, high-performance diffusion barrier is also necessary.
Various transition and refractory metals, their alloys, silicides and
nitrides, such as Ta and TaNx, prevent copper from diffusing into
adjacent dielectrics.
The deposition of the thin barrier layer, or
barrier bilayers, is followed by the PVD or CVD deposition of a copper
seed layer, which is a prerequisite for the subsequent bulk copper
deposition by electroplating. This introduces a new metal stack into an
already complicated integration scheme. Copper integration, along with
decreasing device sizes, and the transition to 300-mm size wafers,
provokes the need for accurate and reliable thickness measurements of
the constituent films to monitor and maintain strict process control.
Thus, the thickness of the barrier and seed layers, as well as the bulk
of the electroplated copper must be accurately monitored to ensure a
quality manufacturable process. This article describes a comparative
study of several techniques used to measure layer thickness.
 03 - Measurement of Metal Film Thickness for Copper...
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Wafer Processing 