Supplemental Material A-1
This supplemental material contains a description of the image analysis method for determining
dewetted area from annealed films, and for particle detection of dewetted films etched in Kallings
Reagent no. 2.
Image analysis for determining dewetted area:
The substrate area exposed by a receded film after annealing at each temperature was determined by
analysis of three SEM images. Images examined were of a 11.6 x 9.3 μm area from the unetched half of
samples annealed at 300-700°C. Contrast between substrate and the film was sufficient to determine
exposed substrate area by digital image analysis. Digital image analysis was conducted by first applying a
1 pixel or 11.6 nm Gaussian blur. The blur reduces graininess in the image and evens out contrast
variations within the image while still retaining boundary information. Second, dewetted area was
designated using a threshold command that converted regions above the threshold value to white, and
those below to black. Threshold values were chosen for each image individually due to contrast and
brightness variations between each SEM image. Threshold values were determined by examining the
histogram of pixel grey values. The histograms usually consisted of two peaks in grey level values
generated due to the two most common grey level values belonging in general to the exposed substrate
area and the dewetted film. A value that approximately bisected the two peaks was chosen as the
threshold value. The exception was for the 300°C where a clear peak corresponding to exposed
substrate area was not visible. Threshold value was chosen for this temperature by finding a value close
to the peak generated from the alloy film that resulted in the desired delineation between dewetted
area and exposed substrate. The total number of black pixels for each image was divided by the total
number of pixels in the image to find the percent of the film area, as viewed from a top down
perspective, consisting of exposed substrate. An example image before and after image analysis is given
below in figure 1 of this supplemental material.
Image analysis for determining particle area:
The goal of the image analysis method for particle analysis was determining the prevalence and size of
the particles that had the characteristic appearance of copper and nickel silicides. The method relied on
the grey value contrast between silicide particles and the underlying substrate. Processing involved an
Adobe Photoshop default auto contrast, a 1 pixel (11.6nm for the resolution and magnification of
images examined) gaussian blur, and a threshold command that converted pixels with light intensity
below a certain value to pure black (indicative of substrate) and those above to pure white (indicative of
silicide particles). After processing “errors” were corrected by hand while toggling a transparent original.
These errors included groupings of white pixels that were converted to black and thus no longer
contributed to particle area or number while some black pixels clearly designating particle area were
converted to white. Corrected errors included portions of particles without enough contrast for
detection, removal of ambiguous pixels below a size threshold, and conversion of agglomerations of
small particles to substrate. The agglomerated particles detected by the processing method but
removed from silicide area measurement appear as clustered particles generally under 100nm in size
with an appearance of “beach sand” as seen in figure 1 (f) and (g) of the original document. Lone
particles detected to be smaller than 7 pixels (81.4 nm) did not contribute to particle area and number
Supplemental Material A-1
measurements and did not count towards particle area and number measurements. Other corrections
were conducted by hand including removal of particles detected to be smaller than 7 pix or 81.4 nm
across all samples. These particles were removed because their character could not be confirmed to be
characteristic of aligned silicides by EDX or alignment along the <001> silicon wafer’s [011] or [0-11]
directions. Numerous agglomerated particles generally under 100nm in size with an appearance of
“beach sand” prevalent for the 300°C annealing trial also did not contribute to particle number or area
size measurements. The end result of the human assisted image analysis method was a measurement of
the combined area as seen from a top down perspective of features or particles with a square or
rectangular shape, sufficient contrast against the substrate visible after etch, and a size greater than or
equal to approximately 81.4-100 nm. Three 11.6 x 9.3 μm SEM images of separate regions were
examined for each annealing temperature. The number of pixels corresponding to the area covered by
particles as seen from a top down perspective was converted to combined area measurement. Average
particle area was calculated by dividing the total surface coverage area by the number of particles for
each image. The number of particles was determined by counting, with particles lying on the edge of the
image counting as 1/2 and those in the corner counting as ¼, and particles that overlapped after image
processing counting as one. An example image of before and after image analysis is given below in
figure 2 of this supplemental material.
Figure 1. Dewetted area determined by digital processing.
Figure 2. Particle area and number determined by image analysis.