The COntactless REsistivity
MApping measurement system COREMA-WT provides
nondestructive full wafer resistivity
characterization with utmost precision, resolution and measurement speed. It is
based on a contactless capacitance technique developed at the Fraunhofer
Institute for Applied Solid State Physics in Freiburg/Germany.
It is
most valuable for detailed, yet rapid, production compatible control of the
fabrication process steps that determine the lateral homogeneity of the wafer.
Exploratory process optimization is supported most effectively.
The capacitive metal electrodes above and below the wafer are positioned by fast
and precise xy translation. They are defining local sample and air capacitors at
the desired measurement spot. A charging voltage step is applied to the RC
circuit and the dynamic charge redistribution is recorded. The resistivity is
obtained
from
the initial and final charge values and the relaxation time. Since the
evaluation, based on first principles, is using relative units only and because
all geometric parameters cancel, the resistivity values are obtained in absolute
units without any instrumental calibration factors involved. A standard test
method documentation (DIN 50447) is available.
The individual measurement takes only a fraction of a second. Hence, full wafer
topography is obtained within very acceptable time. For instance, recording and
evaluating
100 mm diameter wafer topogram with a 1.4 mm step size between data points takes
approximately 20 minutes.
The system is typically used by vendors and customers for routine production
control and quality assessment of semi-insulating wafers. The standard system
with a resistivity measurement range 1E6 to 1E9 Ωcm range is preferentially used
for GaAs and InP. For SiC and GaN a system with extended range 1E5 to 1E12 Ωcm
is available.
The
complete measurement process, including data evaluation and professional
presentation is supported and controlled by user-friendly software based on
Microsoft Windows. The software interface includes setup of the desired
measurement routine, on-line supervision of the measurement process, display of
the topographic data and detailed statistical evaluation. Various topographic
displays including grey-scale,
color
coded as well as pseudo-3D representations are available, providing a
convincing, customer oriented product quality and assessment and specification
verification.
