Modeling of Spin Coating Process to Control Submicron Film Thickness of Permeation Layer

Nanochips (R) cartridges (Fig 1) are disposable panels with 400 micro arrays (Fig 2) that can be independently used as test sites for various assays like genetic marker. Each site (Fig 3) is a permeation layer coated electrode with 80 mu diameter and 120 mu pitch. Permeation or "perm" layer is a thin film of a proprietary hydrogel material over the proprietary chip design. Perm layers were deposited on the electrodes using spin coating process with a proprietary solution. Performance of the cartridge depended on the quality and thickness of the permeation layer over these 400 electrodes. In this process one millimeter deep tear shaped well was constructed from the ceramic base to which 20x20 array of silicon chip were attached. These wells filled with 180 mu l proprietary solution and spun at fixed 1200 RPM for 20 seconds. Process was repeated three times at room temperature in a clean room. Post process treatment included 30 minutes in dry incubator, wash in Milli Q water, and finally, dry at room temperature. Quality of the 1,500 nm thick permeation layer was so demanding that more than half of the cartridges were rejected due to poor quality of the perm layer. Major causes of rejection were bubbles, high SD (Standard Deviation), and thickness (too thick or too thin) of the layer.