Letter to the Editor

-- Semiconductor International, 1/1/1999

I would like to address a couple of errors found in 'Water Spots: The Scourge of Wafer Dryers' (August issue).

The article implies that the Marangoni drying principle requires an IPA/nitrogen atmosphere; in fact, the Marangoni principle involves only a surface tension gradient, regardless of how induced. As mentioned later in the article, STEAG is currently beta testing a solvent-free version of its Marangoni dryer in which the Marangoni effect is induced via thermal rather than chemical means.

The article incorrectly states that CFM's Direct Displace dryer employs the Marangoni effect. In testimony during the STEAG/CFM patent litigation, Christopher McConnell, chairman of CFM, stated that (a) the Marangoni principle was not used in the design of CFM's dryer, (b) he was not aware of the Marangoni principle prior to reading Philips publications, and (c) he has not observed the Marangoni effect as a factor in the operation of CFM's dryer. In addition, the patent litigation did not yield a jury verdict that 'Marangoni drying' is a type of Direct Displace drying. The verdict solely reflected the jury's view that STEAG's Marangoni dryer, using IPA/nitrogen, infringed CFM's patent; STEAG vigorously disagrees with that verdict and has filed an appeal.

Lastly, the article correctly mentions that the Marangoni effect is easily scaled to larger surfaces. However, this is only demonstrated by the two STEAG 300 mm Automated Wet Processors and TRIDENT 300 post-CMP cleaner currently installed at Semiconductor 300 in Dresden, Germany. A second TRIDENT 300 [was] scheduled to be installed December.

Kevin J. McLaughlin, Ph.D.
Technical Support Specialist,
Wet Process Division,
STEAG MicroTech Inc.