Modules Are In, But Supertools Endure
Alexander E. Braun, Senior Editor -- Semiconductor International, 11/1/1999
It is hardly news that new low-k dielectrics and gate materials (no longer just oxide) require new metrology capabilities. Although materials being proposed for this first new generation of low-k are tractable, there are unsolved questions about fully characterizing porosity or carbon- or fluorine-doped oxides. While current metrology can handle present developments, advanced capabilities are needed for second-generation and more advanced low-k.
Materials, smaller structures and thinner films affect metrology capabilities, while reduced process windows require additional performance. Before, a reflectometer could be used to measure etch to clear or CMP because of the simple materials involved. The wider process windows required for those simple stacks also tolerated some overpolish or overetch. With the combination of new materials and tighter process windows, additional capabilities are needed.
And, by the way, they should cost less.
Thus, the traditional metrology approach of a 'supertool' capable of doing everything, such as a box with a spectroscopic ellipsometer plus a reflectometer and infrared and other capabilities -- while not exactly passé -- is meeting resistance due to $700,000-plus price tags. The coming transition to 300 mm also is making cheaper tool sets more attractive.
 |
|
Fig 1 The
combination of optical techniques in one modular system, optimized for
specific applications, results in metrology systems that are not as
expensive while providing the desired results. (Source: Rudolph
Technologies) |
Probably, much of metrology's future will lie in 'Chinese menu'-like structures, whereby capabilities -- including custom software to provide easy-to-operate optimal solutions -- are selected for specific applications.
The recently introduced Rudolph S200 system, for example, uses a proprietary multi-angle laser ellipsometer for thin films. The ellipsometer also is very sensitive to etch-to-zero applications, and yet tolerant of refractive index changes in underlying materials. The ellipsometric measurements also can be combined with a spectroscopic reflectometer and provide a better capability to measure overetch and characterize polish rate across the entire process window at more than 100 wafers per hour (five sites per wafer).
Modular systems will be critical for gate characterization or their electrical equivalent, particularly in the case of l 20 Å gates. Rudolph has eliminated the primary cause of long-term difficulty in obtaining ellipsometer repeatability. If a microspot lens ellipsometer is used to measure on-product or a small spot, and high repeatability is attempted, stress birefringence in the lens -- slight temperature changes over time -- causes thickness measurements to vary by a few tenths of an Ångstrom. The new capability circumvents this, providing 0.01Å repeatability.
Supertools will not disappear. Pilot and research lines
can purchase all the capabilities, while production fabs can choose a mix of
metrologies for optimal price and performance.
Talkback
Related Content
Related Content
SPONSORED LINKS
