Yen Chuo

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

ZEP520A e-beam processes for 40-100nm contact holes were studied for application of phase change memory (PCM) device prototyping. Resist baking, e-beam and development process parameters were investigated on the isolated and semi-dense (1:3) contact holes. PAB temperature for minimum exposure dose-to-size (ESIZE) is 70°C. ESIZE of 200°C PAB is 250 μC/cm2 while that of 70°C is 120 μC/cm2 for 100nm contact hole. ESIZE of contact hole increases very quickly as the CD gets smaller than 60nm. CDs with beam currents of 100pA and 200pA are nearly the same while that with 2nA differs much. Sidewall profiles of contact holes exposed by 100pA and 200pA are near 90° while that exposed with 2nA is tapered. ESIZE decreases with development time. Bottom of contact hole is broadened for prolonged development time. CDs after PDB are not changed. There is little difference in CD between isolated and semi-dense patterns. CD uniformity on the corner and center of contact-hole array are around 5% (+/-3σ), showing a very weak proximity effect. Inter-layer mix-and-match processes were applied to PCM manufacturing. Cross-shaped alignment marks results in the strongest signal waveform on TiW bottom electrode than oxide and TiN/Ti. Mix-and-match PCM device structure was, for the first time, ever demonstrated.