Washable Coating Properties for Plasma Dicing

As the dimensions of thin and tiny die trend smaller, they become candidates for laser assisted plasma dicing. Whether it's observed chipping or vibratory action of the saw causing pulling and pushing of small die from its adhesive carrier (film frame tape), yield loss for mechanical dicing rises as die become thinner & smaller. Since plasma etching is a non-mechanical process, there is little or no concern for chipping or cracking of the substrate. 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 due to their material and process safety. Ideally, they should be tuned for good laser interaction and high plasma resistance. Daetec's washable coatings exhibit thermal resistance over 300°C, making them one of the most unique materials on the market. These products contain heat resistant phenyl groups which are impermeable, dense, and inert, exhibiting properties similar to other phenyl-based moieties as polyimide (PI) and benzocyclobutene (BCB). But unlike the permanence of PI and BCB, water washable products are ideal for temporary applications. They are cast from liquid (spin or spray), processed, and removed by water. These inert and resistant properties help simplify each step in a plasma dicing line. Once coated, substrates proceed to laser processing whereby energies are tuned in accordance with the substrate. Desired coating compositions use high temperature resistant materials which have high melt viscosities combined with sufficient type and amount of absorptive compound to interact favorably with the ultraviolet laser. These properties minimize laser effects during grooving to help reduce irregularities before etching. Plasma dicing proceeds by the proven Bosch DRIE switched process for straight profiles. Plasma etch selectivity for silicon vs. erosion of Daetec's washable coating is often witnessed to be 1,000: 1, or greater. Upon process completion, simple washing by DIW is conducted to completely remove the washable coating, leaving the die surface free of residue and ready for pickup. In this paper, we discuss properties of washable coatings desirable to support plasma dicing process, as well as other demanding applications.