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Disclosed is a process for controlling the crystalline phase of tantalum metal. Film thickness and substrate temperature are used to form the low resistivity alpha phase or the high resistivity beta phase.
English (United States)
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Method for Controlling the Crystalline Phase of Tantalum
Disclosed is a process for controlling the crystalline
phase of tantalum metal. Film thickness and substrate temperature
are used to form the low resistivity alpha phase or the high
resistivity beta phase.
Tantalum metal has two crystalline phases: The alpha (bcc)
phase has low resistivity (12-20 micro-ohm-cm.), and the beta
(tetragonal) phase has high resistivity (160-170 micro-ohm-cm.). For
electronic applications, the alpha phase is preferred, due to the
lower resistivity. However, the exact deposition conditions which
result in either alpha or beta phase films are unclear. It has been
reported that for evaporated films, substrate temperatures up to
100oC result in beta phase films; if the films are deposited at
temperatures greater than 240oC, the alpha phase is formed. On the
other hand, sputtered films require a deposition temperature greater
than 600oC to form the alpha phase.
The method described here is for controlling the phase by
changing the deposition conditions in a magnetron sputtering system.
The MRC 643 (Materials Research Corporation) magnetron sputtering
system has substrate heating during deposition, and variable scan
speed. Since the substrates are scanned past a stationary target,
the scan speed is one of the main parameters used to control film
thickness. It is disclosed that by lowering the scan speed (to
deposit a thicker film), the tantalum film is deposited in the alpha