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Energy-Efficient and Reduced-Effluent Process for Ultraclean Surface Drying

Lawrence Livermore National Laboratory

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Technology Marketing Summary

Marangoni drying is used in semiconductor processing and  other industries to produce a dry, ultraclean surface on flat substrates.  In the conventional Marangoni drying step, e.g., for semiconductor wafer fab, an alcohol or other volatile organic compound (VOC) vapor is blown through a nozzle over the wet wafer surface or at the meniscus formed between the cleaning liquid and wafer as the wafer is lifted from an immersion bath.  The Marangoni effect causes a surface-tension gradient in the liquid allowing gravity to more easily pull the liquid completely off the wafer surface, effectively leaving a dry surface. 

Researchers at Lawrence Livermore National Laboratory (LLNL) have developed commercially important improvements to the Marangoni drying process for large, flat substrates. The method and apparatus developed at LLNL removes all water and contaminants using significantly less VOCs and water than conventional Marangoni drying and other drying techniques.

Description

LLNL’s improved processing step based on the Marangoni effect uses a moving-zone apparatus to combine surface processing (e.g., cleaning, developing or etching), rinsing and drying steps into one operation. 

A typical process and assembly for moving-zone Marangoni drying might include a processing solution  applicator followed by a rinsewater applicator and then a VOC reservoir, all just above the surface of the substrate to be processed and cleaned.  The applicator-reservoir assembly moves relative to the substrate to form a processing zone.  As it moves, both solution and rinsewater attach to the substrate surface, forming menisci.  A thin film of rinsewater is entrained on the substrate at the trailing edge of the assembly.  The VOC evaporates from the reservoir, is absorbed into the film of rinsewater, and lowers the surface tension of the film relative to the surface tension of the pure rinsewater.  This surface tension gradient is strong enough to pull the VOC/rinsewater film off the substrate surface, while particulates and dissolved impurities flow back into a rinsewater collection trough.  The film flow leaves the substrate completely dry within a few millimeters behind the assembly.

Benefits
  • The method and apparatus developed by LLNL can be integrated into conventional industrial processing tracks to allow processing, rinsing, and drying of substrates in one consolidated operation.
  • The operation can be carried out on a surface positioned horizontally (with geometry similar to meniscus coating) or vertically.
  • Moving-zone drying is an ambient temperature process.
  • The LLNL moving-zone process produces a cleaner surface than Marangoni drying with heat, forced air, or high-speed motion of the drying unit.
  • The LLNL process requires much smaller amounts of volatile organics and water compared to conventional Marangoni drying and other surface drying techniques.
Applications and Industries
  • The LLNL method and apparatus has application in processing of semiconductor wafers, flat panel displays, optics, and in other fabrication lines with aqueous processing tracks.
  • Marangoni drying is extremely efficient in producing ultraclean surfaces on both hydrophilic and hydrophobic substrates.
  • Aqueous processing lines in many industries can be made more cost- and process-efficient by implementing LLNL’s moving-zone Marangoni drying process.
More Information

Scientific papers have been published on this topic:

Michael C. Rushford, Jerald A. Britten, Shamasunder N. Dixit, Curly R. Hoaglan, Michael D. Aasen, and Leslie J. Summers, Wet-Etch Figuring for Precision Optical Contouring, Appl. Opt. 42, 5706-5713 (2003)

A Moving-Zone Marangoni Drying Process for Critical Cleaning and Wet Processing, Solid State Technology (1997) Volume: 40, Issue: 10, Publisher: PennWell, Pages: 143-148.

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 5,660,642
Patent
5,660,642
Moving zone Marangoni drying of wet objects using naturally evaporated solvent vapor
A surface tension gradient driven flow (a Marangoni flow) is used to remove the thin film of water remaining on the surface of an object following rinsing. The process passively introduces by natural evaporation and diffusion of minute amounts of alcohol (or other suitable material) vapor in the immediate vicinity of a continuously refreshed meniscus of deionized water or another aqueous-based, nonsurfactant rinsing agent. Used in conjunction with cleaning, developing or wet etching application, rinsing coupled with Marangoni drying provides a single-step process for 1) cleaning, developing or etching, 2) rinsing, and 3) drying objects such as flat substrates or coatings on flat substrates without necessarily using heat, forced air flow, contact wiping, centrifugation or large amounts of flammable solvents. This process is useful in one-step cleaning and drying of large flat optical substrates, one-step developing/rinsing and drying or etching/rinsing/drying of large flat patterned substrates and flat panel displays during lithographic processing, and room-temperature rinsing/drying of other large parts, sheets or continuous rolls of material.
Lawrence Livermore National Laboratory 08/26/1997
Issued
Technology Status
Development StageAvailabilityPublishedLast Updated
PrototypeAvailable01/06/201201/06/2012

Contact LLNL About This Technology

To: Catherine Elizondo<elizondo1@llnl.gov>