Figure 6 - LaserTec’s Optelics offers six different wavelengths to selectively image components. a) Red filtration highlights the circuitry. b) Blue filtration highlights substrate. c) Overlay of the red and blue images illustrating context. Subject: circuit board. (Image courtesy of LaserTec and Nikon Metrology, Inc.)
LaserTec, one of the original pioneers in this field, now distributed through the Nikon Metrology group (Brighton, MI), has gone a step further with WIDE. Offered on the Optelics H1200W system, WIDE provides two distinctive contrast enhancement mechanisms that can operate simultaneously with its confocal mode. The “W” refers to wavelength. Integrated into the confocal light path is a high-intensity discharge lamp that generates six monochromatic wavelengths ranging from 405 nm (purple) to 630 nm (red) as well as white light. As shown in Figure 6, the wavelengths can be tuned to the subject under study to enhance or suppress contrast while taking confocal images. The “D” in “WIDE” refers to DIC (aka “Nomarski”), a well-known optical microscopy approach for enhancing edges in fine detail.
In addition to contrast enhancement, the H1200W has two mechanisms to extend the confocal’s surface metrology capabilities. The “I” in WIDE refers to a built-in interferometry system (both Mirau and Linnik interferometers are available), while the “E” stands for “Exceed,” and refers to a scanning probe option, realized through the addition of an objective-based AFM (only available outside the U.S.). With a combination of powerful optical microscopy, confocal, interferometry, and AFM on one stand, the Optelics sets a new level for hybrid instrumentation.
From traditional metals and polymers to exotic microfluidics
Traditional SWLIs have an edge when it comes to speed, large scan areas, and ultrafine Z resolution (1 nm or less). However, applications involving steep side walls (>~20°) and higher XY resolution are a better fit for confocals.
Figure 7 - Changes in metal surface during processing: a) prior to machining, RSa = 18.853 µm; b) after turning, RSa = 5.543 µm; and c) after final polish, RSa = 0.034 µm. (Images courtesy of Carl Zeiss, Inc.)
Figure 7 shows a routine surface roughness application that can be handled by either SWLI or industrial confocal. The average roughness, RSa, of an unmachined part (7a) changes dramatically after turning (7b) and after the final polish (7c).
Figure 8 - a) Measurement of roughness and cutting angle of a razor blade. (Image courtesy of Olympus Industrial.) b) Microfluidics channel intersection. (Courtesy of Bruker AXS and Hyphenated-Systems, Inc.)
Figure 8 clearly demonstrates the ability of industrial confocals to measure steep angles. The angles on the razor blade (8a) measured with the Olympus LEXT are 85°. Because they can measure deep channels as well, industrial confocals are finding a happy home in the new arena of microfluidics. Figure 8b characterizes the junction between multiple channels in a microfluidics cell, providing the side wall-angle measurement as well as channel depth and width.
Figure 9 - Measuring thickness of film on metal substrate. Upper left: Brightfield image of an inkjet printer nozzle. Upper right: 3-D confocal image revealing placement of film over metal substrate. Lower image: Surface profile of metal substrate with measurement bars depicting film thickness at unique points. (Images courtesy of Keyence.)
Because industrial confocals behave like microtomography devices, they can readily define the top and bottom of films on reflective substrates, providing an excellent method for measuring film thickness (Figure 9). In addition, they can image particles within the film, providing a unique tool for counting, size, and determining the distribution of inclusions such as bubbles or particles such as the metallic flakes in clear coat.
Figure 10 - Fluorescence + confocal: 3-D image of cracks in polymer laminate over metal (488 nm excitation, 3-D shadow projection, LD Epiplan® 50×/0.5 NA, 184.3 µm × 184.3 µm × 24.0 µm. Image size: 512 × 512 pixels. Sample: Dr. S. Rastogi, Dept. of Technical Engineering, TU, Eindhoven, The Netherlands. (Image courtesy of Carl Zeiss, Inc.)
Figure 10 demonstrates the advantages of adding fluorescence to confocal. In this particular example, the cracks were illuminated using a fluorescent dye. Twenty-one sections were collected and then reconstructed using a 3-D shadow projection. The resulting image clearly depicts the crack structure using the fluorescent component of the image and the underlying metal surface using the reflected light component.
Broader reach and a bright future
The new generation of industrial confocals is a practitioner’s dream. Easy to use, sleeker, faster, and more capable, they embody the current “lab to fab” movement, providing research-level capabilities for engineers and researchers as well as the ability to program simplified recipes for more routine analyses and use by less experienced operators. Finally, smaller players are moving into the mainstream, distributed by well-known microscope vendors with extensive reach. Hyphenated-Systems is now distributed by Bruker AXS, Sensofar by Leica, and LaserTec’s Optelics by Nikon Metrology. From paper to microfluidics, multilayered packaging materials to semiconductors, industrial confocals have a bright future.
- The Industrial Confocal and Scanning White Light Market. The Microscopy & Imaging Place, Inc., in press.
Ms. Foster is President and Chief Strategic Consultant,TheMicroscopy & Imaging Place, Inc., 7101 Royal Glen Trail, Ste. A, McKinney, TX 75070, U.S.A.; tel.: 972-924-5310; e-mail: firstname.lastname@example.org. The author welcomes questions and comments.