Stable e-beam metrology on ArF resist for advanced process control

We studied the effect of ArF resist shrinkage under electron bombardment during ebeam metrology and also the effect of resist shrink-age on the after-etch CD. The traditional approach is to reduce the electron energy and dose to minimize resist shrink-age, often at the cost of reduced precision and image quality. We found that resist trimming by high-density plasma etcher (ion density about 10(12)cm(-3)) can improve the stability of resist under ebeam. Exposed to beams of 600V and 300V accelerating voltage, fresh photoresist CD shrink-age was reduced by similar to70% and similar to50% after resist trimming in the etcher. The effect of resist trimming is similar to that of e-beam curing. More interestingly, after etch and clean of the wafer, no difference in average CD value was found between area exposed to ebeam measurement and area that were not measured. This suggests that the resist trimming step in the normal etching process may overwhelm resist shrink-age effect caused by ebeam metrology. The implication is that the key selection criteria for stable ebeam metrology on ArF resist is a beam that produces consistent shrinkage, not minimizing average shrink-age.