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A
60 nm SiO 2 100 nm
film
SiO 2 film
Ag film
Ag film
Ag film
Silicon substrate Silicon substrate
Silicon substrate
B
Measured voltage (V)
A
Tip of M-AFM
C
C
20 nm SiO
Microwave oxide layer
image
Microwave
image
Oxide film thickness (nm)
Fig. 4. A: schematic diagram of the scanning process of
samples covered by oxide films with different thickness; B:
the relationship between the measured voltage and the
thickness of oxide film. Inset C and D are the microwave
images of Ag film and Ag film covered by a 60 nm oxide
layer measured by the M-AFM.
Ag film
Silicon substrate
B
Measured voltage (V)
Tip of M-AFM
1.342 V 1.349 V
20 nm SiO
oxide layer
D
D
11-13
May 2011, Aix-en-Provence, France
Fig. 5A depicts the schematic diagram of calibration
experiment. The M-AFM probe scanned the samples of Ag
film 20 times with different standoff distances ranging from
0 to 1000 nm. Fig. 5B shows the relationship between
measured voltage values and the standoff distances.
1.453 V 1.462 V
1000 nm
200 nm
Ag film
Ag film
Silicon substrate
Silicon substrate
Stand-off distance (nm)
C. Discussion
As shown in Fig. 4B, the measured voltage is monotone
increasing when the thickness of oxide layer is smaller than
60 nm. However, when the thickness of oxide layer covered
on the Ag film becomes larger than 60 nm, the measured
voltage almost keeps constant regardless of different
thickness of oxide layer. This result illustrates that the
electrical property of Ag film under the oxide layer would
affect the reflected microwave signals and thus can be
extracted from the measured voltage when the SiO 2 layer is
thinner than 60 nm. However, if the thickness of oxide layer
is larger than 60 nm, the microwave signals will spread to
other directions rather than penetrate the oxide layer to sense
the covered sample. Thereby, the electrical property of the
sample under a thick oxide layer can not be extracted from
the measured voltage. In the calibration experiment, the
similar phenomenon was observed. When the standoff
distance is larger than 200 nm, the change in the measured
voltage becomes very small. It means that the effective
detection range of the M-AFM probe tip in air is almost 3
times larger than that in the SiO 2 layer. The reason can be
explained as that microwave signals can propagate more
easily in the air than in the oxide layer due to the dielectric
attenuation.
The results suggest that the M-AFM can be used to
measure the electrical property of material under a thin oxide
layer, but the thickness and electromagnetic parameters of
the oxide layer should be considered in a quantitative
measurement.
IV. CONCLUSION
We carried out a group of experiment to verify the
M-AFM with the capacity of measuring the electrical
information of underlying materials. Some special samples
with different thickness of dielectric films (SiO 2 ) which
plays the role of oxide layer creating on the material surface
were fabricated. The thickness of oxide-layer is from 20 nm
to 100 nm with 20 nm increase in this work. As the results
shown, the M-AFM probe can sense the electrical
information of measured materials under the oxide layer with
a limited thickness of 60 nm.
ACKNOWLEDGMENT
This work was supported by the Japan Society for the
Promotion of Science under Grants-in-Aid for Scientific
Research (A) 20246028 and (S) 18106003.
Fig. 5. A: schematic diagram of the scanning process for Ag
film with different standoff distance; B: the relationship
between the measured voltage values and the standoff
distances.
REFERENCES
[1] J.J. Kopanski, J.F. Marchiando, and J.R. Loweny, Scanning capacitance
microscopy measurements and modeling: Progress towards dopant profiling
of silicon, Journal of Vacuum Science and Technology B: Microelectronics
337