By: M. David Levenson
WaferNews Technical Editor
In another step towards freeing chip architects from the tyranny of Manhattan geometries, The X Initiative and ASML have announced the first 0.25-micron diagonal features printed on wafers. An ASML PAS 5500/750 DUV step-and-scan tool equipped for annular illumination successfully patterned diagonally oriented interconnect structures characteristic of 0.18-micron node design rules.
These proof of concept results indicate that the X-architecture implemented by Simplex Solutions and fabricated on reticles by Dai Nippon Printing can be used to pattern interconnect layers. The wafer results also validated lithography simulations obtained with ASML MaskTool's LithoCruiser software. Risto Puhakka, of VLSI Research, observed that, "The results of ASML's experiments using current-generation equipment demonstrate that X-architecture designs are both production-worthy and manufacturable."
Jan Willis, the X Initiative steering group coordinator, pointed out that ASML's participation increased the number of participating companies to 33 and demonstrated solidifying supply-chain adoption. While the X Initiative has been portrayed as using diagonal lines at metal 4 and 5 (in orthogonal directions), obtaining the full benefit requires the "liquid routing" innovation, which allows a combination of x-y and diagonal orientations for every connection on metal layer 2 and above as required. Toshiba has shown that this freedom reduces both the wire length and the number of vias on a chip design. Until today, a question remained whether one could print and inspect the resulting irregular wafer patterns.
Adolph Hunter of ASML pointed out that the X-Wafers showed no difference in lithographic process window compared to Manhattan designs at the same dimension. Reticles patterned with both raster-scanned laser and vector-scanned e-beam technologies showed the same performance for printing dense and isolated features at 0.25-micron. Since the X-architecture has been shown compatible with existing reticle and exposure tool technology, future implementation steps should prove less challenging than past innovations, according to Kenneth Rygler of Rygler and Associates.