Standard home video equipment has been used to capture interference color changes that are observed when fluid is spinning on a wafer. Color rings are observed to spin radially outward with time. This indicates that the fluid surface profile is slightly concave at the center. This may relate to evaporation differences with radius or with restricted flow due to surface tension differences at the perimeter.

The following frames were collected for pure n-propanol spinning at 2000 RPM on a 2" silicon wafer. Data collection and analysis are being performed primarily by Carissa Hernandez with assistance from Dylan Haas.

The following 3-frame sequence is nice because you can track the colors as they gradually move radially outward from frame to frame. The top frame has a blue center with a green ring around it. The second frame has this blue then green ring pair shifted part way out. Finally the third image shows this blue/green ring pair shifted almost to the edge.
 

Time into Spinning Run	Fluid Thickness at Center	Video Frame Appearance at that Time
3.77 Seconds	About 0.86 microns
3.83 Seconds	About 0.63 microns
3.90 Seconds	About 0.53 microns

We have already analyzed a few of these video frames. For example frames 19 and 21 above are found to have these thickness profiles (19 is yellow and 21 is turquoise):

We expect to soon have thickness versus radius profiles at many other times throughout the spinning run, and to be able to relate these to the evaporation and flow physics that pertain to coating formation.

Dunbar P. Birnie, III
Professor
Department of Materials Science and Engineering
Rutgers, The State University of New Jersey   
607 Taylor Rd.
Piscataway, New Jersey, 08854-8065

Major revisions installed in December 2004

Based on earlier version from July 2000
Updated in February 2005.
Page started 1 May 1998
(c) 1998,1999,2000,2004,2005  D. P. Birnie, III