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  • Automated Metrology and Inspection

Photonics Spectra
Jan 2002
Michael Zecchino

Optical inspection and metrology will continue to enable component manufacturers to integrate metrology and yield-management strategies and reap the benefits of cost-efficient, scalable production.
The 2001 downturn in telecommunications has significantly affected component manufacturers and carriers alike. One result has been a substantial decrease in capital equipment spending as companies position themselves for a period of slow sales.

Nevertheless, these same manufacturers continue to invest in research and development, in yield management and in production efficiency. Many are focusing their energies on developing cost-effective, high-yield production systems to meet the needs of both current and next-generation networks. Their goal is to achieve scalable component production that will support an inevitable return to growth.

Automation for higher yields

Metrology and inspection technologies are receiving, and will continue to receive, much attention. Inefficient, manual techniques are being upgraded to faster and more repeatable automated process-control systems that can capture defects and provide early feedback for process improvement.

Despite the economic downturn, component manufacturers are investing in automated inspection and metrology solutions. Here, automated optical defect inspection identifies contamination on the surface of a laser diode.

Data from these automated systems integrate the manufacturing process, tying upstream processes to downstream results. In other industries, primarily data storage and semiconductor manufacturing, this move from low-yield, fragmented processing to tightly linked, automated process flows boosted yields four- to eightfold.

An example of this type of integration is the use of automated optical inspection in the production of the laser diode sources used in transmitter modules and as the pumps for erbium-doped fiber amplifier modules. Automated optical inspection is supplanting traditional manual inspection both for capturing surface defects and for measuring critical dimensions of the waveguide ridge. Rules-based image analysis provides objective, quantitative evaluation of device quality that can be used to adjust and improve prior processes.

With bar- and device-level serialization, these optical inspection data may be tracked by part throughout the process. Automated inspection stations, using the same software and protocols, may be employed at all inspection steps. Therefore, early part conditions may be correlated with the final performance to establish realistic, cost-appropriate process controls.

Next-generation metrology

Companies also are gearing up for the production of tomorrow’s network components. Updated metrology will control each new manufacturing concern.

For example, in the development of components for 40-GHz and higher networks, chromatic and polarization mode dispersion have an increasingly significant impact on the signal quality and bit error rate. Manufacturers are working with metrology companies to develop all-parameter testing that addresses both forms of dispersion as well as center wavelength, insertion loss, reflected power, polarization-dependent loss and other parameters.

All-parameter testing of a filter substrate for dense wavelength division multiplexing could account for dispersion, center wavelength, polarization-dependent and insertion losses.

At the component level, there is a move to integrate multiple components into single packages, thus reducing interconnect losses and simplifying manufacturing. Here we are seeing parallels to the semiconductor industry’s development of flip-chip and high-density interconnect packaging, with more devices being completed on a wafer. Wafer-scale probe testing, metrology and inspection will be employed more widely to capture defects and to measure the performance of a device before the next manufacturing step.

An example of this type of wafer-level processing is in the development of vertical-cavity surface-emitting lasers (VCSELs). Unlike some other types of lasers, the VCSELs’ laser cavities are completed on the wafer and, therefore, can be tested there. The ability to capture and eliminate problems at the wafer level helps drive down costs to meet the required price points in the cost-conscious metropolitan networking market.

Moreover, as networking technologies continue to develop and mature, so will the methods for measuring and controlling the quality of the components on which they are based. As they did for the semiconductor and data storage industries, standards and standards-generating bodies will emerge for optical component manufacturing, despite the disparity and sheer number of optical devices being rapidly developed. Metrology professionals have the skill and knowledge to help manufacturers establish these inspection standards and measurement protocols.

Meet the author

Michael Zecchino is marketing communications manager at Veeco Metrology Group in Tucson, Ariz. He holds degrees in industrial engineering from Pennsylvania State University in University Park and in English from the University of Louisville in Kentucky.

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