SAN JOSE, Calif.--Wafer metrology is in the midst of a major convergence, in which a new crop of optical CD tools are moving into the limelight and posing a threat to traditional CD-SEMs in the fab.
KLA-Tencor, Nanometrics, TEL, Therma-Wave, and others are pushing multi-function, optical CD pattern metrology tools, based on 3D scatterometry and related techniques for 130-nm designs and below. These tools are aimed to displace traditional 2D-enabled CD-SEMs for CD control applications in the fab. Applied Materials, KLA-Tencor, Hitachi, and many others sell CD-SEMs.
Scatterometry is a non-destructive optical technique that records and analyzes changes in the intensity of light reflected from a periodic scattering surface. Scatterometry makes use of zero-order optical scanning from grating targets.
Optical CD tools based on scatterometry and related technologies encompass several standalone metrology functions in the same unit: CD control, overlay, film thickness, among others. These "all-in-one" machines enable chip makers to procure one tool that supports several functions, thereby reducing costs.
The optical CD market is still in its infancy, but this technology is said to have some major advantages. First, CD-SEMs are running out of gas to inspect and measure next-generation designs, according to analysts. And the average selling price (ASP) for a CD-SEM tool is $2 million, which has become a problematic cost-of-ownership (COI) issue, they added.
"We're in the era of a metrology convergence," said Kevin Monahan, vice president of technology in the Patterning Solutions Group at KLA-Tencor Inc., a supplier of metrology and inspection equipment in San Jose. "The trend is moving towards a combination of tools and combination of technologies in one system."
KLA-Tencor also sells standalone CD-SEMs, which are not going away anytime soon, Monahan said. "CD-SEMs still have a place," he said in an interview with Silicon Strategies.
And CD-SEM technology is not standing still. At the recent SPIE event, for example, Japan's Hitachi High-Technologies Corp. claimed that it devised a 3D "stereo matching method" for CD-SEMs. The technology "has the same principal as the triangular surveying method for geometry to reconstruct 3D profile from 2-tilt images taken at different angles," according to a paper given at SPIE.
Still, CD-SEMs are mature, expensive products with limited functions, prompting the need for a new wave of machines. "To date, the front-running approach to integrated-pattern metrology have been variants of scatterometry," said Kit Ausschnit, a representative from IBM Corp., in a recent paper at SPIE. "Despite considerable progress throughout the industry, however, scatterometry implementation has been encumbered by several drawbacks," he said in the paper.
Slow throughput, laborious setup times, and the need for large targets to ensure incident illumination are among the problematic issues for the technology, he pointed out.
Still, vendors are shipping tools that promise to solve these issues for the 90-nm node and beyond. In February, for example, KLA-Tencor introduced the SpectraCD100--its next-generation inline optical CD metrology system for the 90- and 65-nm nodes. The tool performs thin film and CD metrology using spectroscopic ellipsometry technology. It can work in conjunction with the company's thin film measurement system--dubbed the ASET-F5x, which deploys spectroscopic scatterometry technology.
Spectroscopic CD technology is required for good reason: traditional CD measurements are not sufficient to predict yield and transistor performance. "Existing profile measurement technologies are destructive and do not offer the throughput required for production," according to KLA-Tencor. "Today, complete feature profile information is needed, including CD, sidewall angle, height and depth. Contact hole profile measurements are also critical, since contact hole sizes that are significantly reduced or closed at the bottom of the structure can result in significant yield loss."
Another semiconductor-equipment vendor--Therma-Wave Inc.--has a slightly different viewpoint: it believes that optical CD tools based on scatterometry will eventually dominate the metrology arena.
Scatterometry and CD-SEM tools will complement each other at the 90-nm node, but the landscape is expected to change at 65-nm and beyond, said Boris Lipkin, president and chief executive of Therma-Wave. The Fremont, Calif.-based company is a supplier of metrology equipment, including tools based on scatterometry.
"Everybody recognizes that a CD-SEM is running out of gas," Lipkin said. "I think people will extend the life of CD-SEMs at 90-nm. At 65-nm, I think (scatterometry-based machines) will displace CD-SEMs," Lipkin said in a recent interview with Silicon Strategies.
Therma-Wave believes that its integrated optical CD tool based on scatterometry is far superior than traditional CD-SEMs. It sells the 7431, a metrology tool that supports several metrology applications in the same box: CD control, thickness and profile.
Good and bad news
Not surprisingly, rival Nanometrics Inc. sees the market differently. CD-SEMs are not going away in the near term, but multi-function, optical CD tools have begun making inroads in the market, said Peter Gise, senior marketing manager for Nanometrics, a Freemont, Calif.-based supplier of metrology equipment.
"Optical CD is still in its infancy," Gise said. "Optical CD is still a small market, but it's becoming more important."
There is good and bad news for the newfangled multi-functional tools. Throughput has been an issue with scatterometry, but the integration of high-speed processors into current tools has accelerated the response times from hours to just seconds, he said.
On the other hand, the de-acceleration of the process-technology cycle from two to three years could push out the widespread adoption of new technologies and keep CD-SEMs in vogue for a long time.
Meanwhile, unlike many of its competitors, Nanometrics is pushing both standalone and integrated optical CD technologies. Last year, it rolled out the 9300 Advanced Metrology System, based on spectroscopic ellipsometry technology. The standalone tool can determine optical film properties then feed them directly to the optical CD metrology measurement recipes to optimize sensitivity for all linewidth and profile measurements.
It is also pushing integrated tools as well. Nanometrics' InTool Integrated Metrology solutions are designed for integration into wafer processing equipment. For example, it sell the NanoOCD/DUV 9010, an integrated metrology tool that combines spectroscopic ellipsometry and spectroscopic reflectometry.
"Integrated metrology is becoming more important, but it's a small market," Gise said. "Standalone will be around for many years to come."
Integrated metrology has made inroads for CVD, CMP, and etch. "I think the next frontier is lithography," he said.
Others are also entering the fray as well. Last year, Timbre Technologies Inc., a subsidiary of Japan's Tokyo Electron Ltd., announced a 3D scatterometry capability in its Optical Digital Profilometry (ODP) technology. This capability enables CD and 3D profile measurement along the x, y & z planes of hole and post grating structures for critical applications such as contact and via.
Special measurement considerations such as the amount of contact clearing, sidewall effects, and scumming are difficult for existing metrology approaches, whereas ODP, while still maturing, demonstrates good results, according to the company.