(112g) A Way for Wafer Washing: Study of Rinsing Flow Dynamics on Rotating Silicon Wafers

During the manufacture of silicon circuits it is important that the surface of the wafer is extremely clean. It has been found that procedures for rinsing contaminants from the surface can be made faster and more effective when the wafer is rotating. However, when a jet of liquid is applied to a rotating surface, centrifugal forces can pull rivulets of liquid beyond the radially advancing wave-front. This is problematic because the rinsing flow is uneven and particles or other contaminants can build up along the edges of these rivulets, increasing product failure at these locations.
A better fundamental understanding of the flow in these systems is essential to improve the effectiveness of spin-rinsing processes while reducing yield losses due to rivulet formation. In the present work, we investigated the effects of wafer rotation rate, jet flow rate, and the presence of a thin liquid film on the wafer on the dynamics of the wave-front of the rinsing flow. It was found that reducing the rotation rate reduced rivulet formation but slowed the wave-front. Also, a higher jet flow rate reduced rivulet formation and increased wave-front speed, but this reduction of rivulet formation diminished at larger radial distances. Coating the wafer with a thin film of water also both reduced the extent of rivulet formation and increased wave-front speed when compared to a clean, dry wafer. Lastly, rivulet formation was studied on wafers coated with thin films of surfactant solutions to understand the effect of surface-tension gradients on the wave-front.