Imaging of an LCD Panel "Pixel"
This application note describes the automated stitching feature of the Nanosurf Nanite
AFM scripting interface in combination with the Nanosurf Report
Expert analysis software. AFM measurements on an LCD panel are used as an
example to demonstrate how stitching can thus be used to easily and efficiently
generate high-resolution topography maps of large surface areas.
High resolution imaging techniques like AFM are often limited in their
maximum scan range. When both the high lateral resolution of an AFM and a large
scan range are required, image stitching could be a solution. Image stitching is
commonly used when creating a single panoramic scene from multiple pictures. In
a more advanced implementation, this technique can also be used to combine
multiple AFM measurements to a single large image. Thus, AFM imaging of large
surface areas, e.g. 1 mm x 1 mm or 100 µm x 1 cm in size, can easily be
The Nanosurf Nanite AFM system is able to measure and stitch the
required images fully automatically. The user only has to specify the single AFM
image size and the size of the area to be measured. The AFM then takes care of
the rest. After measurement, the images are loaded into the Nanosurf Report
Expert post-processing software, and are stitched together to a single
image. This image still contains all metrological data and can therefore be
analyzed like any other AFM image with all available analysis functions,
including height and distance measurements, roughness calculation, grain and
particle analysis, cross section analysis, and of course 3D visualization.
Imaging of an LCD Panel "Pixel"
Modern flat screens manufacturing techniques (plasma, TFT-LCD, OLED) are
based on multi-layer processes that produce small and complex 3D surface
structures. Conventional optical microscopy generally falls short when it comes
to verifying the integrity and quality of such surface structures in three
dimensions. This is particularly true for failure analysis in the sub-micrometer
regime. AFM, on the other hand, is the ideal solution to measure 3D contour data
with sub-micrometer precision. With the stitching technique, this can now even
be accomplished on large surface areas, such as LCD panels.
Figure 1. Optical microscopy image of an LCD panel. The
image (660 µm x 660 µm; shown here at 120-fold magnification) was recorded using
a Nanosurf easyScope. A single LCD "pixel" is enclosed in the large red box. The
smaller white box corresponds to the area that can be typically covered by the
scan range of an AFM. The result of such a scan is shown in Figure 2.
Figure 1 shows an optical microscope image of an LCD panel at 120-fold
magnification. One pixel of the panel corresponds to the section enclosed in the
red box. This area, measuring 407 µm x 407 µm, is much larger than the area that
can normally be measured with an AFM, which would correspond to the smaller
white box in Figure 1. Figure 2 shows an actual AFM measurement in the area of
the white box. The advantages of AFM over optical microscopy - the much higher
resolution that is obtained, and the availability of 3D data - become clearly
Figure 2. AFM scan of a typical LCD panel area.
High-resolution topographic data is available for a limited scan area. The scan
here corresponds to 74 µm x 74 µm, and to the white box shown in Figure 1.
To image an entire LCD pixel would, however, require a scan size that is much
larger than those that can be obtained from a single AFM image. A way around
this obstacle, is the use of automated measurement of multiple sample areas,
followed by stitching of the resulting AFM images. The feasibility of this
process is demonstrated in the following example, which illustrates how a matrix
of 5x5 AFM images was acquired on an LCD panel and stitched together to a larger
image. The instrument used for this process was the Nanosurf Nanite
B AFM with an ATS-A100 automated translation stage.
After mounting the LCD sample on the translation stage, the AFM cantilever
tip was positioned over the region of interest, and the stitching script was
started (Figure 3). With the desired parameters set, the AFM system autonomously
acquired all images, saved all measurements to files, and transferred these to
Report Expert software, where the Stitching Module of this program stitched
all files together (see Figure 4). A 3D representation of the result is
presented in Figure 5, which shows how seamlessly the individual images are
merged into one.
Figure 3. Stitching script running in the Nanosurf
control software. The red box shows the Stitching dialog asking the user to
supply basic parameters for the stitching process.
Figure 4. The Stitching Module interface in the Nanosurf
Report Expert software. Simple yet powerful commands allow anyone to perform
stitching and to generate professional results.
Figure 5. 3D representation of a stitched AFM image. The
image (corresponding to the stitching result in Figure 4), shown here at
200-fold magnification, demonstrates how easily high-resolution 3-dimensional
data can be acquired using the Nanosurf Nanite B AFM and an automated
translation stage. It also demonstrates how seamless the result of the stitching
Using even more individual AFM images (10x10) for the stitching process
resulted in a high-resolution topographic map (Figure 6) of an even larger
surface area of the LCD panel (560 µm x 570 µm, after cutting off the rough
edges), almost similar in size to the optical image shown in Figure 1. More than
one complete LCD pixel can clearly be distinguished.
Figure 6. AFM stitching image of an LCD panel. The image
(560 µm x 570 µm; shown here at 160-fold magnification) is the result of 10x10
images recorded and stitched using the Nanosurf Nanite B and the stitching
features of the Nanosurf Control and Report software. The result is comparable
in size to the optical picture shown in Figure 1, but in this case offers much
more detail and 3D data.
The use of such large surface AFM data in quality control of LCD panel
production provides detailed information with regard to the individual
micro-fabrication process steps, and allows batch-wise approval or rejection of
production lots. In addition, the information provided by AFM measurements - in
particular AFM measurements spanning large surface areas, as is the case for
stitching - can even be used to adjust production parameters for future
This make the AFM not only a quality control instrument that provides the
highest possible resolution in industrial quality control processes, but also a
valuable optimization tool during product development and production. The
autonomous operation, the easy handling, and the excellent price/performance
ratio of the Nanosurf Nanite AFM make it the ideal tool for small and large
industries alike to move their quality control into the 21st century.
For more information on this source please visit Nanosurf