Water Washable Coatings for Plasma Dicing Processes

Abstract

As the dimensions of thin and tiny die trend smaller, they become candidates for laser assisted plasma singulation (LAPS), otherwise referred to as plasma dicing. The process involves creating a patterned mask whereby the plasma chemistry penetrates open areas and down into the substrate. When complete, the mask is cleaned leaving fully singulated die. Water washable coatings for mask creation are preferred. Ideally, they should exhibit high plasma resistance and be tuned for good laser interaction. Daetec's washable coatings exhibit thermal resistance over 300°C, making them the most unique materials on the market. [1] These are cast from water, processed, and removed by water. Simple spin coating achieves $< 5\mu \mathrm{m}$ coverage while conforming over high features is achieved by “nozzle-less” spraying with equipment designed by Ultrasonic Systems, Inc. (USI).[2] An ultrasonic head breaks the liquid into small drops to form a fine spray that deposits on faces and around corners. Once coated, substrates proceed to laser processing, tuned to delicately break through the washable layer with little or no effect to the substrate. Desired coating compositions use heat resistance, high melt viscosity, and sufficient type and amount of absorptivity for good laser engagement. These properties minimize snow-plow (“re-cast”) effects during laser patterning and further minimizing the need for substrate polishing (descum) preceeding the plasma process. Etching proceeds by the proven Bosch DRIE switched process for straight profiles using the Mosaic™ platform with Rapier™-S modules as produced by SPTS.[3] Plasma etch selectivity for silicon vs. erosion of Daetec's washable coatings as Si:mask, is observed to be 1,000:1, or greater.4 The process is finished with simple DIW rinsing, leaving the surface free of residue and ready for die pickup. This paper presents further details on plasma dicing using water washable coatings.