High-contrast positive resists for e-beam mask making

The five major requirements for electron beam resists for chrome mask fabrication include high resolution, high speed, RIE etch resistance, thermal bake insensitivity, and long coated plate shelf life. High speed, high resolution and good RIE resistance are common attributes of chemically amplified resists (CAR) used primarily for Deep UV lithography. However, the environmental susceptibility to airborne amines, need for a long coated plate shelf life and the requirement for 140 Celsius postexpose bake (PEB) of some CAR or fundamental challenges of these families of resist for practical Cr lithography. We have been developing a series of fast amplified e beam resists which exhibit do not require PEB bake and are tolerant of airborne contaminants. The shelf life attributes of both negative and positive chemically amplified resists was examined and found to be susceptible to absorption of moisture. Some of the acid generators hydrolyzed in the dried films and led to changes in resist sensitivity or dark film loss. Long term film stability of CAR coated plates can be promoted by using hydrophobic solvents, stable acid generators, and most effectively by storage under anhydrous conditions.