Particulate Contamination on Wafer Surfaces Resulting from Hexamethyldisilazane/Water Interactions

Abstract

A major step in the photolithographic processing of silicon wafers is the application of hexamethyldisilazane (HMDS) as a photoresist adhesion agent. At this time the preferred application technique is one known as vapor priming. In the vapor prime system, the silicon wafers are heated in a vacuum oven, where they are exposed to vapors of HMDS which are pulled from a container of the HMDS liquid. In vapor prime systems as they are presently configured, there is significant opportunity for contamination by atmospheric moisture. HMDS is known to be hygroscopic and to react with moisture to form ammonia and other reaction products. For the most part, the major result ascribed to this reaction has been a degradation of the adhesion promotion properties of the HMDS. In this investigation, however, we have looked at particulate contamination generated’by the HMDS/H₂O interaction. A model is proposed to describe the in-situ generation of particles from an HMDS/H2O reaction, and considerations for minimizing contamination in an HMDS vapor prime system are discussed.