Kenji Takahashi

Tailoring thermal property of ArF resists resins through monomer structure modification for sub-70-nm contact hole application by reflow process

Numerous resolution enhancement techniques have been introduced over the past few years as the design rule decreases rapidly. Among them are thermal reflow, SAFIER and RELACS just to name a few. Resist reflow is one of the simplest processes with a minimum process modification that only requires an additional baking step at or above its glass transition temperature after the contact holes have been developed. Since most of the methacrylic-based ArF resins have Tgs in vicinity of their thermal decomposition temperature, it is not desirable to expose the resins near Tg for a prolonged time. An approach to construct a resin that is physically or thermally viable, yet chemically stable is necessary and the easiest way of achieving this goal is to bring down Tg of the resin significantly so that there would be enough working space between thermal decomposition and glass transition. Out of several conceivable ways to lower the Tgs such as employing acrylic polymers, COMA type polymers etc., we have chosen to maintain the methacrylic platform because of its superior resolution capability. Our design strategy is to work on the pendent groups of methacrylic monomers to make polymer matrix more flexible. Thus, the incorporation of a more flexible unit, such as 2-methyl-2-adamantyloxycarbonylmethyl methacrylate, in our existing copolymer system reduced Tg almost by 30°C. In addition to its thermal property tuning ability, the resist sensitivity also has increased, presumably due to the out-stretched position of an acid labile protecting group for easy access of incoming acid molecules. Our newly developed resists based on the design concept showed a good C/H pattern profile and improved LER by reflow process at sub-70 nm node. We will discuss our newly designed materials in this paper in terms of material properties, resist characteristics and lithographic performances in relation to reflow processes.