26 May 1995 Application of alternating phase shift mask to device fabrication
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Abstract
In order to check the usefulness of an alternating Phase Shift Mask (PSM), we fabricated one and applied to 1.0 micrometers pitch gate-poly pattern of a mask-ROM device. Etched quartz type was used and multiphase shifter method was adopted using a g-line positive tone photoresist. Practically, defect-free PSM could be obtained through 4 times voting method. PSM was written with CORE-2564-PSM reticle writer which showed fast writing speed and simple second layer fabrication due to free of charge dissipation layer, making voting method easily possible. We used the g-line stepper having numerical aperture (NA) of 0.54 and coherence factor ((sigma) ) of 0.5. From this experiment we obtained depth of focus (DOF) of 1.0 micrometers which was the same as that of i-line case (Na 0.45, (sigma) 0.5) and was twice wider than that of conventional g-line case. And there was no loss of critical dimension uniformity for PSM. Conventional i-line reticle and g-line alternating PSM were applied to real device fabrication. Final electrical yield analysis revealed no difference between the two cases, indicating that application of alternating PSM to device fabrication is very promising. Device characteristics of two cases were almost same in speed and low Vcc margin, too.
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Sunggi Kim, Sang-Gyun Woo, Woo-Sung Han, Young-Bum Koh, Moon-Yong Lee, "Application of alternating phase shift mask to device fabrication", Proc. SPIE 2440, Optical/Laser Microlithography VIII, (26 May 1995); doi: 10.1117/12.209281; https://doi.org/10.1117/12.209281
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