Improved performance of Apex-E photoresist with the application of the electric-field-enhanced PEB

This paper describes a systematic and rigorously controlled set of experiments showing the effectiveness of the Electric Field Enhanced Post Exposure Bake (EFE-PEB) with 248nm KrF(ASML) exposures on Apex-E photoresist (IBM) where feature sizes ranged from 0.3 um to 0.5 um. Experimental results showed a significant improvement in process latitude and resist sensitivity for features with a k1 technology factor of 0.68 and below. The experiments were executed using a 248nm KrF stepper (ASML), NA 0.5, and Apex-E photoresist (IBM), which has a relatively high acid diffusivity. An improved experimental setup rigorously controls PEB time, PEB temperature, development time, focus drift, and other environmental variables. Cross sectional SEMs of five line arrays with L=S ranging from 337nm to 500 um show deeper trenches when the electric-field treatment was used. Exposures that were intentionally out of focus cleared 600nm deep in 1um thick photoresist in the control group, but did clear the full 1um with the application of the Electric Field during the PEB. A dose matrix experiment showed an 8% decrease in the dose to clear and two-fold increase in focus latitude. This comprehensive study demonstrated an increase in anisotropic acid diffusivity with the application of the electric field and confirmed that the EFE-PEB offers a relatively inexpensive and simple method for improving photoresist performance.