Biomedical Engineering Reference
In-Depth Information
Fig. 6.6.
Left
: RCIB scan of the overlapping boxes.
Right
: Line cut of the image in
two consecutive measurements.
sensing surface. Standard photolithography and wet (BOE) etching were used
to pattern these features on the surface. Two overlapping rectangles, with
depths of 3 and 6 nm were etched resulting in four regions with different
oxide thickness; not etched, 3 nm deep, 6 nm deep, and 9 nm deep etched.
These values are consistent with the AFM measurements of the same sample.
System repeatability was tested by making consecutive measurements of the
same sample. Averaging boxes measuring 5 pixels by 5 pixels, or an area of
50
×
50
µ
m
2
, the RMS deviation in consecutive measurements was 0.01 nm
(Fig. 6.6).
6.2.4 Spectral Reflectivity Imaging Biosensor
The phase delay added by extra material can also be imaged using a sim-
pler approach. We propose a surface profilometry technique to be used as
a label-free microarray imaging device. Spectral reflectivity imaging biosen-
sor (SRIB) uses wavelength dependent reflectivity of a silicon substrate with
thick thermally grown SiO
2
(5-10
m), to accurately find the film thickness at
tens of thousands of different spots, and thus image the surface profile. This
technique, having a much lower finesse, is expected to be less sensitive than
RCIB, but should be more robust and offer higher throughput. A collimated
laser beam that can be tuned from 764 to 784 nm is reflected from a pellicle
beam splitter and is incident on the sample surface (Fig. 6.7). At any fixed
wavelength, reflection from the sample is imaged on a CCD camera (cam-
era pixel size is 13.7
µ
m and the magnification of the imaging system is 2.3).
Then the wavelength is stepped, and another image is taken. Repeating this
through the sweeping range of the laser, one can form a spectral reflectivity
curve for every 36
µ
m
2
area on the sample in the field of view. The separate
µ
