SAQP spacer merge and EUV self-aligned block decomposition at 28nm metal pitch on imec 7nm node

Abstract

Self-aligned quadruple patterning (SAQP) is not compatible with every design. It couldn’t pattern even number routing track, for examples 4 internal routing tracks with power rails side by side, due to the process footprint of conventional SAQP. On the other hand SAQP spacer merge technique is able to remove 1 internal metal line by merging 2 spacer into 1 spacer. It can offer additional track scaling and flexible design of track number, for example, 5.5 tracks together with 6.5 tracks to accomplish low and high performance device respectively. In this paper, SAQP spacer merge technique and self-aligned block (SAB) process are considered as one of potential patterning approaches for 1D style 28 nm metal pitch. SAQP spacer merge technique is indispensable for supporting 5.5T cell of 4 internal tracks with 28nm metal pitch. And 5.5T cell also requires the irregular metal color array for SAB and its biases which is litho-etch skew. SAB can be sized up double compared to conventional block process, it is biased over next metal line to takes advantage of material etch selectivity of SAQP structure inherently before metallization. To meets those requirement with automatic mask layout generation, we newly proposed forward decomposition algorithm and color-aware block resizing of SAB. The forward decomposition algorithm generates mandrel to spacer 1 to spacer 2 to mimics process order of SAQP spacer merge technique. And color-aware block resizing of SAB needs conditional bias depending on neighboring metal color. Additionally, edge placement error budget is analyzed with process variation band of source mask optimization (SMO) on top of overlay, line edge roughness (LER) and etch uniformity assumption. Simulation result seems to be fine to enable SAQP spacer merge and SAB integration. However, EUV stochastics reported that CD uniformity is not fit in Gaussian distribution. Considering beyond 3σ, restricted design rule may be needed. To see design availability, 3 representative standard library cells were verified in design rule restriction without area loss. This SAQP spacer merge decomposition algorithm is useful since it is possible to extend for Fin patterning application as well.