Three-Dimensional Surface Profiling Measurements
Dektak Stylus Profilers
Advanced Resolution Capabilities of
Dektak Stylus Profilers
Three-Dimensional Analysis Software
for Dektak Stylus Profilers
Characterization Beyond 2D Average Roughness
Three-Dimensional Interpretation of Surface Functionality
Flattening Filters and Terms Masking
for Setting up 3D Programs
Upgrade Capabilities of Stylus
Accurate Z-Height Interpretation of Dektak
Reliable Apex, Form and Slope Measurements
of Stylus Profilers
Bruker Nano Surfaces
Stylus-based surface profiling is a standard technique for accurate,
repeatable surface shape, topography and step height measurement in applications
ranging from semiconductor R&D to solar cell QC. In recent years, the
ability to map surfaces in 3D has greatly increased the capability of stylus
profilers; yet despite such recent advancements, it is not uncommon in
cutting-edge fabs, solar cell companies, industrial manufacturing facilities,
colleges, universities and various research institutes to see R&D, QC and
process monitoring operations performed still using technologies developed over
sixty years ago.
This application note describes the advantages of 3D measurement options
available through a combination of Bruker's Dektak®
Stylus Profiler and Vision® analysis software.
Capabilities of Three-Dimensional Surface Profiling Measurements
The advantages of 3D measurements are easy to see. Using a simple 2D profile,
as shown in figure 1, may not provide a complete picture of the sample surface.
With 3D capabilities, an entire area can be mapped, as shown in figure 2. This
enables visual inspection of defects and uniformity, as well as small surface
pits and spikes that may have otherwise been missed.
Figure 1. Traditional 2D stylus profilers may not provide
a complete picture of the sample surface. This profile from the same sample
shown in figure 2, can provide accurate height, width and roughness data, but
may miss defects or detailed surface features that can be measured by adding 3D
Figure 2. This image reveals how 3D measurements provide
a wealth of data for analyzing surface features such as area roughness, volume
and defect detection. (Image: 2 x 2mm scan of a nickel surface roughness scale
generated on the Dektak using Vision advanced analysis software.)
Benefits of Dektak Stylus Profilers
stylus profilers are designed to support both 2D and 3D surface profiling,
with precision stages, wafer alignment pins, color video imaging, advanced
parametric data analysis tools and other features for stable, and extremely
repeatable, surface shape measurements.
Advanced Resolution Capabilities of Dektak Styles Profilers
The advanced resolution capabilities allow users to visually interpret defect
roughness, symmetry and process resolution. The Dektak enables
1um Y axis stepping accuracy for higher overall 3D characterization and
resolution. This higher Y axis resolution, as shown in figure 2, reveals small
defects and tooling marks and accurately measures are roughness.
Three-Dimensional Analysis Software for Dektak Stylus Profilers
Analysis Software adds a range of analyses, filters, masking capabilities,
databasing, statistics and import/export functionality to Dektak
profilers. Chief among these features is the ability to automatically
combine multiple traces into an accurate 3D map of precision surfaces and
manipulate it using a very short, clear, user-friendly menu.
Three-Dimensional Surface Characterization Beyond 2D Average Roughness
In many applications, 2D average roughness (Ra) is the sole parameter
specified for monitoring surface texture. While Ra provides a quick gauge of
general roughness, it provides little insight into the functional
characteristics of the surface. Conversely, 3D metrology provides a clear
picture of surface characterization over an entire area. Significantly more data
is available than is possible with a single line profile. The risk of using 2D
Ra as the only gauge is that a part can be well within the specifi cation across
a single 2D profile (or even a sampling of 2D profiles), yet may still fail in
actual function because the single 2D profile missed a defect or other surface
features that would be readily evident in a 3D area map (see figure 3).
Figure 3. 3D image generated on the Dektak of 340nm
silica colloids on quartz. Note the small bumps on larger features with deep
crevasses. This sample shows the diffi culty characterizing complex surfaces
with 2D profi les as opposed to generating a 3D area map. (Sample provided by
Tomika Velarde of the Wirth Research Group.)
Three-Dimensional Interpretation of Surface Functionality
A much more comprehensive interpretation of surface functionality can be
derived using the 3D visualization, filtering and analysis options in Vision.
Specific 3D parameters, such as the S parameter set, can be used as much more
meaningful process control variables. As examples, 3D analysis can quantify the
ability of a bearing surface to retain oil, the visual brightness of a brushed
metal fi nish, or the tendency of a mating surface to chatter due to regularly
spaced machining marks. Customized parameters can also be generated to track
very specific functional aspects of surface texture.
Figures 4a and 4b show a profile of the same data shown in figure 3. The Vision
software provides a variety of data filters, including programmable low
pass, median, high pass and Fourier filters. Figure 4a shows a cross section of
the unfiltered figure 3 data with a measured Ra of 833 nanometers. Figure 4b
shows the same dataset after a high pass filter has been applied to filter out
the low frequency larger peaks and valleys, revealing the smaller bumps on the
surface. The data with the high pass filter applied exhibits much more accuracy,
reducing the Ra by more than a factor of ten to nominally about 70
Figure 4a. Vision software provides a range of filters
for manipulating data. Here, the unfi ltered data from figure 3 is shown. The
cross-section of data has a measured Ra of 833nm.
Figure 4b. A high pass fi lter on the dataset in figure
4a filters out the low frequency larger peaks and valleys to reveal the smaller
bumps on the surface and enable the roughness to be measured more accurately
(note: Ra = 70nm after the high pass filter has been applied).
Flattening Filters and Terms Masking
A secondary method of correctly interpreting the heights of each trace is to
use the Dektak "Flattening" features within the Vision software
package. The leftmost image in figure 5 shows raw data of a 3D map with
horizontal scan artifacts that can be caused by thermal drift or vibration. The
image on the right shows the same data after the flattening algorithm has been
Figure 5. The Dektak Vision software has a special
feature that can filter out scan artifacts caused by thermal drift or vibration
during a 3D map operation.
software also allows terms masks to be applied to remove features that may
be present across some traces but not in others. Terms masks can enable the
flattening algorithm to be applied to a selected area of data to remove scan
artifacts. Together, these two methods provide excellent interpretation of the
Z-heights for each trace, and thus enable excellent 3D mapping of the
In addition to data fi lters, the Vision software provides multiple color
palettes that enable various surface features to be enhanced and highlighted
(see figure 6). It even provides the ability to make the surface look "shiny" or
change the angle and intensity of the light shading of the image.
Figure 6. Vision software can be used to accentuate the
data by using different fi lters and color palettes to highlight and bring out
various features of the image.
Flexibility for Setting up 3D Programs
software includes a number of features that allow a user to optimize
scanning for best speed/best resolution. It can quickly and easily be used to
set up and run 3D maps with a variety of different parameters to accommodate
multiple applications. The Dektak generates 3D maps by combining several individual profi
le measurements or traces into a 3D image file. The user can visually determine
the area that needs to be mapped by using the color video microscope. The
operator simply uses the mouse to select the X and Y extent of the area of
interest, and the software automatically calculates the length and width of the
area to be measured, as well as the scan start location (see figure 7). Once the
operator selects the area to be mapped, the resolution of the map can be
determined by selecting how many individual traces are desired to map the area,
as well as the resolution of each individual trace. Up to 500 traces can be used
to create a map with a minimum spacing of 1 micron per trace.
Figure 7. This video image of the same sample in figures
3-6 shows how the programmable sample stage can be used to determine the X-Y
extent of a 3D map.
Upgrade Capabilities of Stylus Profilers
Stylus profilers are still largely used to obtain 2D profi le measurements
rather than to generate 3D images. The primary reason for this is that 2D
profilers are typically less expensive than 3D measurement tools. One major
advantage of the Dektak is that it provides a relatively low cost solution for 3D
imaging and analysis. Another advantage (that no other stylus profi ler offers)
is that the 2D model of the Dektak can be upgraded to a 3D metrology system by upgrading
from a manual sample stage to programmable sample positioning.
Accurate Z-Height Interpretation of Dektak Stylus Profilers
In a stylus profiler, a 3D map is built up from a series of 2D traces. To
accurately map the surface, it is necessary to correctly interpret the Z
(vertical) height of each trace relative to the others. Other profilers with 3D
capabilities make the assumption that each trace begins at the same Z height.
This technique would make it impossible to accurately image and measure samples
like the one in figure 3, where each scan begins at a different point in the Z
axis. The Dektak creates a 3D map by referencing all subsequent data
points to the very first data point taken in the very first trace. This results
in accurate measurements and 3D imaging of the surface in question.
Reliable Apex, Form and Slope Measurements of Stylus Profilers
A similar challenge is addressed when measuring the height of spherical or
aspherical surfaces, such as microlenses, lens molds, solder bumps, etc. With
simple 2D profile measurements, it is very difficult to determine the apex of a
spherical shape with a single scan. A variation of only a few hundred microns in
the scan start location can produce quite a difference in the apex measurements.
The deviation can be exponentially higher depending on the curvature of the
lens. Using 3D mapping always captures the true apex, resulting in highly
reliable height measurements.
During a scan, the stylus pivots and swings vertically in an arcing motion.
This arc motion can produce errors in slope measurements as the stylus rides up
one side of the slope and down the other. Figure 8 shows a pyramid configured
calibration standard, which is a 2D profile generated from a 3D image. The dark
line shows the affect of the arcing motion of the stylus to the data as the
slope on the left side of the pyramid is not as steep as the trailing slope on
the right side of the pyramid, giving the appearance that the standard is not
spherical. The Vision software includes a special MicroForm filter to correct
for the arcing motion of the stylus. Figure 8a in the gray exhibits the same
data with the MicroForm fi lter applied to correct the slope angles and provide
the true spherical shape of the lens. Figure 8b shows the 90 degree symmetrical
grating, which confi rms the gray corrected image of the scan.
Figure 8. Vision software contains a "MicroForm" fi lter
to provide more accurate slope and shape measurements by removing the shape of
the stylus arc. The shape of a calibration standard (line) leaning to the right
due to the motion of the stylus during the scan can be seen in 8a. The gray area
is the actual surface. The 90 degree symmetrical grating is evident in 8b.
Furthermore, Vision software includes a Multi-Region Analysis that lets a
user defi ne and compare multiple features within a dataset. Figure 9 shows a
raw scan and map of a solder bump array. Using the multi region analysis
function in Vision, the height of each bump, the diameter and the
coplanarity can be readily determined. The data can also be exported as a .csv
file, and stored in a customizable database for tracking and process
Figure 9. The Multi-region analysis feature of the Vision
software automatically provides height and diameter measurements of multiple
bumps within a 3D map.
Traditionally, stylus profilers have been confi ned to 2D analysis, however,
advances in hardware and software functionality have greatly expanded stylus
profiling capabilities. Now, 3D measurement is possible, providing comprehensive
visualization and quantification of precision surfaces for accurate assessment
of process parameters and part functionality. From gauging nanometer-scale etch
depth to measuring surface roughness on machined parts, the combination of Dektak Stylus Profilers and
software offers the most accurate and repeatable method of 3D
characterization available today.
About Bruker Nano Surfaces
Bruker Nano provides Atomic Force Microscope/Scanning Probe Microscope
(AFM/SPM) products that stand out from other commercially available systems for
their robust design and ease-of-use, whilst maintaining the highest resolution.
The NANOS measuring head, which is part of all our instruments, employs a unique
fiber-optic interferometer for measuring the cantilever deflection, which makes
the setup so compact that it is no larger than a standard research microscope
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