Checking wafer cleanliness by measuring static contact angle.
An optical tensiometer is the instrument of choice to measure the contact angle between a drop of water and a wafer. The wafer is placed on the sample stage and a drop is dispensed from the liquid dispenser onto the wafer. The sessile drop can be observed with a high quality camera. The optical tensiometer software analyzes the drop shape and measures the contact angles.
Typically, when assessing the cleanliness of a wafer, a contact angle of zero is desired: the liquid wets completely the surface. Impurities increase the contact angle which is detected by the optical tensiometer.
Studying surface coating properties by measuring dynamic contact angle
Once your wafer surface has been treated or coated, an optical tensiometer can tell you about Surface Free Energy (SFE), adhesion and heterogeneity to name a few. In that case, a dynamic contact angle is preferred even though a static contact angle can also be used. The production of drops with advanced and receded edges involves one of two strategies. Drops can be made to have advanced edges by addition of liquid. Receded edges may be produced by allowing sufficient evaporation or by withdrawing liquid from the drop. Alternately, both advanced and receded edges are produced when the stage on which the solid is held is tilted to the point of incipient motion. Using an instrument with high speed image capture capabilities shapes of drops in motion may be analyzed.
A video of such an experiment can be seen at http://www.attension.com/contact-angle.aspx together with an explanation of the measurement technique.
The two application examples presented above demonstrate how an optical tensiometer can be used by wafer manufacturer. Optical tensiometers are useful instruments for semiconductor process control, surface modification process development and quality control.
Attension
Attension provides precision tensiometers with outstanding simplicity of use for liquid and solid surface characterization in research and industrial processes. The offering consists of optical, force, bubble and volumetric tensiometers for all needs and budgets, ranging from versatile, fully automated instruments, to more compact, manual systems. We are present in www.attension.com
