Bitline contact (BLC), bitline (BL), and node contact (NC) fabrication are three interacting process loops during DRAM fabrication. BLC characteristics play an important role in subsequent BL and NC process loops. The complex structure of DRAM increases the difficulty of identifying the impact of BLC process variations on device shorts (BVC test failures) and device opens (DVC test failures). In this work, virtual DOEs using SEMulator3D® (Lam Research’s virtual fabrication platform) were carried out to better understand the effect of BLC characteristics on DVC and BVC failures, including BLC X and Y axis CD, etch sidewall angles, overlay (OVL) shift and roughness. From our studies, we have developed optimized process specification for X and Y axis CD, etch sidewall angles, OVL shift, and roughness during the bitline contact process loop. The results of this type of experiment can help developers identify key specifications and save resources during the early design phase of DRAM process development.
In this paper, we systematically explore potential Line edge roughness (LER) improvements that may be achieved on both line and via patterns by using the deposition/etch cycling process by virtual fabrication. The results show that deposition/etch cycling process is very effective in reducing high frequency noise and most of the LER and CD uniformity improvement occurs during the first deposition/etch cycle. These results can provide quantitative guidance on the optimal selection of deposition/etch amounts and the number of cycles needed to reduce LER.
In this paper, an active area cut approach using a self-aligned double patterning process for advanced DRAM was studied using virtual fabrication. The mandrel critical dimension, mandrel line edge roughness, mandrel overlays and spacer thicknesses were selected as input process variables in the virtual DOE to investigate their sensitivity to the final fin cut head to head (HTH) critical dimension (CD) and its uniformity (CDU). For the mean CD, the study illustrates that maximum mean CD can be obtained at a combination of mandrel CDs when the mandrel overlays approach a value of zero. The overlay of mandrel 1 in both the X and Y direction appears to have a stronger impact on the mean CD than the overlay of mandrel 2. We determined that the mean HTH CD decreased 0.44 and 0.93 nm, respectively, when the spacer 1 and spacer 2 thickness were increased by 1 nm. Our simulations also show that CDU is strongly impacted by the mandrel line edge roughness (LER), at a sensitivity of 1.16 nm / 1 nm. The lowest variation and maximum mean CD can be obtained using particular combinations of mandrel 1 CDs and spacer thicknesses. Overlays do not impact the final HTH CDU. From our study, we can provide clear guidance to developers about the relationship between process parameters and final HTH CD and CDU, showing that the integrated process should be centered at particular conditions to obtain an optimal process window.
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