Getting the Small Picture
The latest microscopy innovations, some of which include new illumination techniques, automated instrumentation and digital cameras, hold promise for difficult industrial applications.
Anadigics Inc. of Warren, N.J., is a semiconductor company that helps provide the gift of
gab — and data, too. Its gallium-arsenide integrated circuits are used in
both wired and wireless telecommunications systems, and although its products operate
in the radio portion of the spectrum, they could benefit from improvements in light
Peter Tomic, a senior failure-analysis engineer
at the firm, said that he and his co-workers often place hair-thin probes on a device
to take electrical measurements of specific spots within a circuit. This involves
putting the probe on a metal trace, a thin strip with a width measured in tenths
of microns. He would like to have an automated setup consisting of a microscope,
probes and cameras to help with this delicate task and to overcome a microscope
limitation that hampers probe placement.
“The cameras would look at the
probes in a side view,” Tomic explained. “Generally speaking, metallurgical
microscopes with enough magnification to see the features and region of interest
don’t have enough depth of field.”
Demonstrating advances in noncontact surface profiling, a Zeiss laser
scanning microscope using specialized software enables the visualization of an array
of solder joints.
Although his ideal system doesn’t
exist, the latest microscopy innovations offer hope — and help — for
this and other industrial tasks. Products from companies such as Carl Zeiss MicroImaging
of Thornwood, N.Y., Leica Microsystems Inc. of Bannockburn, Ill., and Nikon Instruments
Inc. and Olympus America Inc., both of Melville, N.Y., are increasingly automated,
integrated with other systems and networks, and digital in nature. Optical improvements
also are being developed and deployed. The combination promises to improve performance
and drive down price, making it easier and less expensive to bring the very small
To illustrate the effects of various illumination techniques using a Nikon microscope, the left side of a
metallurgical sample of scratches was illuminated using differential interference contrast, and the right side, bright-field episcopic illumination.
The better to see you
Today’s optical microscopes are the product
of hundreds of years of scientific and engineering progress, but that doesn’t
mean that optical advances have stopped. The depth-of-field difficulty cited by
Tomic is one that bedevils more than semiconductor manufacturing. It affects any
process, such as machining or medical device assembly, where the distance from top
to bottom is significant. Another example of this depth challenge arises during
the inspection of the small gears and mechanical elements of microelectromechanical
systems, or MEMS.
Zeiss’ DeepView system uses hardware and software to combine
different planes into a single view with greater depth of focus.
To help overcome such issues, Zeiss
introduced DeepView, a combination of hardware and software that extends
of field. This process takes advantage of wavefront modulation and
The system can be used at various magnifications and with different
“This new technique effectively
increases the depth of field of that optic up to 20 times,” said Dan King,
assistant product manager for materials microscopy at Carl Zeiss MicroImaging.
Earlier last year, the company introduced
two other optical microscopy innovations: circular differential interference contrast
and a variation, total interference contrast. The former makes use of circularly
polarized light, which eliminates the contrast blackouts created by having light
polarized along an axis. The latter, an interferometric technique, allows step-height
measurements of films and coatings and provides other roughness parameters.
In an ink-jet sample on paper, the left side view was imaged using a bright-field lens, and the right, a dark-field lens.
A definite edge
Accurate step-height measurements using this approach
require a definite edge so that readings on either side of the step can be taken.
The technique also needs a fairly flat and uniform sample surface. According to
company literature, its measurement range is from 50 to 5000 nm. Unlike other height-profiling
and interferometry techniques, this approach can be used with any objective and
at any magnification.
Such improvements in cataloging the
third dimension aren’t confined to one company. Alwyn Eades is a professor
of materials science and engineering at Lehigh University in Bethlehem, Pa., and
president of the Microscopy Society of America, an organization that encompasses
both optical and electron microscopy. In his research, he employs electron microscopes
but is aware that optical instrument makers have significantly improved surface-height
The MM-60u microscope with Emax metrology software is seen in this typical Nikon measuring workstation.
“By integrating computers more
fully with such instruments, they have become much more automatic and a lot easier
to use,” he said. He added that, if you have the money to buy the instrument,
it’s going to be much easier to get surface profiles than it used to be. Before,
you needed a specialist.
The themes of greater computerization,
increased automation and easier use show up in other areas of microscopy. For example,
as in real estate, the key to surface inspection and other aspects of the industrial
use of microscopes is often location, location, location. This is not the location
of the microscope itself, but of the precise position of the area being inspected.
In fabricating and packaging a semiconductor
circuit or medical device, for example, both the design of the product and experience
may indicate that inspection and quality checks need to occur at specific spots.
The challenge in a manufacturing environment becomes one of quickly locating these
known problem areas and rapidly screening them. Ideally, this must be done without
resorting to specialists or highly trained individuals.
To help achieve this, microscope manufacturers
are revving their motors — literally. The stage and optics of microscopes
are increasingly being motorized and put under computer control. Michael Metzger,
department manager for Nikon Instruments, noted that the automation of microscopes
is increasing because motorized movement brings definite advantages. He said that
the company applies precision staging to determine where a defect is and to go back
and look for defects in the same area in future products.
With such an arrangement, the inspection
system can quickly move a unit into position and present an automatically focused
image to an inspector. The inspector can speedily classify a device as good or bad.
Such automation slashes inspection time and reduces the vagaries of human intervention.
Nikon’s precision movement technology
helps power its VMH 300 vision system, enabling the instrument to achieve 0.01-μm
positional resolution. This is greater than what can be done using the company’s
measuring microscopes, built to gauge microscopic dimensions. This exacting capability
has been used, according to Metzger, by various semiconductor and other companies
to achieve a competitive advantage. The companies, not surprisingly, do not want
their names revealed for fear of losing that edge.
The trend toward automation also is
affecting other microscope suppliers. Zeiss’ King noted that a quarter of
all microscope stands now sold are motorized, giving them the ability to automatically
adjust the distance to a specimen. What’s more, that percentage is growing.
Another aspect of the same trend is
the increasing use of digital cameras and interfaces. This enables the easy transmission
and manipulation of images and is part of the overall movement away from film and
toward digital image capture and storage.
Many microscope makers also produce
digital cameras. Nikon, for instance, is introducing a 12-megapixel camera this
month — a resolution greater than previously available. “We are able
to match or exceed the resolution of the human eye in our digital representations
now,” Metzger said.
For microscopes, this digital trend
has several implications. One is that they all must interface with a camera, which
sometimes means adding lenses and other elements to correct for distortions and
other optical problems. Another is that microscopes will more often sport some sort
of interface to hook up to the wider network. This will be necessary for both control
and data exchange.
There is, however, a third impact. The use of
software to run microscopes leads to crossover products, devices that are primarily
intended for other uses but that could be part of an industrial or surface inspection
arsenal. Olympus has produced a low-cost product that not only has some industrial
uses, but also is an educational and biomedical tool. The company’s MIC-D
system includes a built-in digital camera, an interface and software controls. It
is an inverted microscope with a light source that can be rotated through transmitted
light to reflected light. The system also can work with polarized light.
The Olympus MIC-D captured these chip images.
Because of its construction, the MIC-D
is not modular. The 640 x 480-pixel image sensor cannot be swapped out, and the
magnification of the microscope is limited to 2553. Achieving that requires a zoom
lens. Thus, the device does not offer the inspection power of a higher-end microscope.
However, the company’s scientific equipment group technical marketing specialist,
Peter Dimitruk, said the MIC-D does have some unique attributes. He said it hybridizes
characteristics of stereo, upright and inverted microscopes.
As an example of this melding of different
microscopes and technologies, Dimitruk said that the MIC-D easily can move from
20x to 255x magnification. The ratio of high to low magnification is greater than
12.8:1, a tough number to achieve with good image quality. Nonetheless, the system
can pull this off because of the design characteristics it shares with Olympus’
For many applications, the magnification
range and the illumination capabilities of the new device will be more than adequate.
For instance, manufacturers have used the microscope to look at plastic welds in
polarized light to determine the heat-penetration depth.
In another example of a crossover product,
Leica Microsystems recently introduced a fluorescent combination attachment, the
Fluor Combi, for its MZFL III fluorescence stereomicroscope. Primarily intended
for use in the life sciences, the device can be useful in product inspection. The
attachment enables users to switch from a stereo objective and stereo imaging to
a high-resolution compound objective, effectively bumping magnification up into
the 400x or 800x range. That power is needed for such tasks as examining cracks
and surface defects. The fluorescence can be useful in spotting unwanted intruders
in the manufacturing process.
The Leica MZFL III microscope captured this view of a polymer resin
grain under UV light.
“With the fluorescence, you can
look for trace residues of different photoresists or other contaminants that tend
to jump up at you under fluorescence imaging,” said Douglas Giszczynski, senior
marketing manager for stereomicroscopes at Leica. The company likens such inspection
to searching for a glowing needle in a haystack, he said.
He also noted that his company uses
some of the microscope technology in its macroscopes. These devices, such as the
M420, offer motorized focusing and a 6:1 maximum to minimum zoom ratio. Macroscopes
are intended for the somewhat coarse inspections of fairly large objects, but they
offer magnification ranges similar to those of stereomicroscopes.
The same Leica microscope and UV light enabled this image of carbon fiber.
Despite all of these advances in microscopes,
optical surface inspection does have its limits, and there may be no economical
way around them. Advanced Micro Devices Inc. of Sunnyvale, Calif., is another company
that makes integrated circuits, but they are of the mainstream CMOS variety. Bryan
Tracy, manager of the materials technology development department, said the company
builds its products on advanced CMOS technology. He pointed out that its semiconductor
manufacturing meets or exceeds the feature size and other requirements spelled out
in the International Technology Roadmap for Semiconductors prepared by International
Sematech, a research consortium based in Austin, Texas.
Tracy said that Advanced Micro has
been removing optical microscopes from its production line and replacing them with
electron microscopes. That’s because the latest manufacturing technology is
at the 0.13-μm node, with 0.2-μm lines separated by 0.2-μm spaces.
That puts the feature size well below the wavelength of light and makes the optical
inspection of surface features carved into conducting and insulating layers extremely
difficult and perhaps effectively impossible.
As Tracy explained, “That type
of a feature is really just too small for even ultraviolet. Even a deep-UV microscope
is pretty limited.
MORE FROM PHOTONICS MEDIA