Optical film-thickness metrology enters the mix-and-match era
11/01/2006
Optical film measurement has evolved from manual offline analytical lab instruments to fully automated inline tools loaded with a wide array of measurement capabilities through adding and merging more optics and algorithms while retaining predecessors. These tools often have reflectometry, ellipsometry, visible and near IR broadband illumination, UV illumination options, normal incidence and variable angle capabilities, and, increasingly, even scatterometry for optical profile and CD measurement. Modern optical film measurement tools are more properly composite tool boxes, functioning as “metrology islands” and carrying price tags of ~$1 million.
The demands on optical film measurement tools are diverse. Thin film measurements must support process development, process diagnostics, and root cause analyses. Excursion control for ILD, ARC, and PMD deposition processes is also driving inexpensive film-thickness measurement for every-wafer sampling to eliminate scrap and to optimize equipment utilization. This set of demands is presently served by both stand-alone film-thickness tools and integrated metrology.
Recent thinking on metrology has largely focused on stand-alone vs. integrated. Clearly, the necessity for a very rapid time-to-result in metastable processes defined the initial integrated deployment. Integrated metrology has now gained adoption in applications where either a high sampling frequency is required or where there is a potential for only occasional excursions, but where any such undetected excursion would result in a disastrously high cost of scrap.
Industry dynamics are challenging film-thickness metrology beyond this simple stand-alone and integrated split. The dilemma is how to rationalize opposing and irreconcilable requirements within a single metrology product. One set of demands is for extremely high-resolution measurements on the most challenging materials, including profile, CDs, and micro-stress. Measurement capability is pushing the limits of present tools in these applications; throughput and price are secondary. This set of demands can be called the ultimate or bleeding edge film-thickness metrology.
At the other end of film-thickness metrology are high sampling frequencies for less challenging film-thickness measurements. For example, CMP feedback control, and ARC or PMD deposition monitoring for feed forward require every wafer sampling, which are fairly simple measurements. Speed (throughput) and cost are primary for these applications whereas capability need only be adequate for simple layers. The set of demands can be called bulk or commodity film-thickness metrology.
Industry demands have overstretched the prevailing monolithic metrology concept whereby metrology islands do it all. A single metrology tool cannot efficiently cover both capability and bulk sampling requirements without sacrificing speed or the necessary capability. Thus, the market has split into a high-end and a low-end segment, seen in both integrated and stand-alone arenas. Being led by integrated metrology, there is growing adoption of inexpensive and very fast sensor-based reflectometry products for the bulk/commodity low-end segment-typically for HDP-CVD, PECVD, CMP, and spin-on applications running at high throughputs. The high-end segment serves the most demanding applications, typically lithography and critical etch. The stand-alone arena is also splitting with the specialized highest capability composite tools serving the high-end segment and a growing adoption of single-purpose tools at roughly half the ASP that serve the bulk/commodity low-end market.
In the past, time-to-detection ushered in the integrated vs. stand-alone metrology. The emerging high-end vs. low-end bifurcation is being ushered in by fab economics. Mix-and-match is increasingly becoming a fab’s optical film-thickness metrology answer because it enables more sampling availability while preserving the necessary capability for the applications that truly demand it. It has become increasingly evident that dual segmentation into both high-end/low-end as well as stand-alone/integrated is the solution that measures up in today’s fabs.
Contact Peter Gillespie, VP of marketing and sales, at Tevet Process Control Technologies Inc., 5673 West Las Positas Blvd., Suite 213, Pleasanton, CA 94588, ph 925/734-6701, [email protected].
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Peter Gillespie,
Tevet Process Control Technologies, Pleasanton, California