Investigation of surface inhibition and its effects on the lithographic performance of polysulfone-novolac electron-beam resists

Current resist materials used for electron beam lithography applications, such as mask making, have relatively low contrasts as compared to modern optical resists. Recently, our group has been investigating two component, polsulfone-novolac (SNS) resists which offer high sensitivities and moderate contrasts for electron beam lithography. Surface inhibition, which can help to reduce top surface loss in unexposed and partially exposed regions of the resist, is a very desirable property in such resists in order increase resist contrast. The main phenomenon being investigated in this work is the effect of soft bake temperature on surface inhibition in SNS resists. It was found that surface inhibition decreases dramatically in this resist system as a function of increasing bake temperature above 90°C. Results from this study indicate that there is a segregation of the polar polysulfone inhibitor away from the resist-air interface at bake temperatures above 90°C. Results from studies using various techniques including X-ray photoelectron spectroscopy and contact angle measurements to investigate this phenomenon are reported. Methods to enhance surface inhibition, and hence improve resist contrast, such as using surfactant loaded developers were also investigated in this work.