40-100nm contact-hole processes of ZEP520A e-beam resist on PCM prototyping applications

摘要

ZEP520A e-beam resist processes for 40 nm - 100 nm contact holes were studied for application of phase change memory (PCM) device prototyping. Post-application baking (PAB) temperature, post-development baking (PDB), e-beam currents, exposure doses, development time, and 3-types of development conditions on isolated and semi-dense (1:3) contact holes were investigated. Lowest PAB temperature for minimum exposure dose-to-size (E_(SIZE)) is 70 ℃. E_(SIZE) of 200 ℃ PAB is about 250 μC/cm~2 while that of 70 ℃ is 120 μC/cm~2 for 100 nm contact hole. E_(SIZE) of contact hole increases very quickly as the CD gets smaller than 60 nm. The CDs with beam currents of 100 pA and 200 pA are nearly the same while those with 2 nA differ very much. Sidewall profiles of contact holes exposed by 100 pA and 200 pA are near 90° while those exposed with 2 nA are tapered. It was found that ESIZE decreases with development time. The bottom of contact hole is broadened for prolonged development time. Contact hole CDs after PDB are generally kept as the original values. In general, there is little difference in CD between isolated and semi-dense patterns. The CD uniformity on the comer and center of contact-hole array (SEMBAR) are around 5% (3σ), showing a very weak proximity effect. Inter-layer mix-and-match processes were applied in the PCM manufacturing. TiW bottom electrode has the strongest signal waveform from the cross-shaped alignment marks than 250℃ PECVD oxide and TiN/Ti. The mix-and-match PCM device structure is, for the first time, ever demonstrated.