Native-Conflict-Aware Wire
Perturbation for Double Patterning
Szu-Yu Chen , Yao-Wen Chang
ICCAD 2010
Native conflict prediction
NC-Aware wire perturbation
Experimental result
• Foundries have been systematically reducing
the printed feature size (half pitch) for years.
• From Rayleigh criterion, the half pitch is
limited to 36 nm, which cannot satisfy the
desired sub-22nm technology nodes.
• The most popular solution for sub-22nm node
is double patterning technology (DPT).
• Two feature have to be assigned to different
masks if the distance of them is less than the
minimum double patterning spacing (DPspacing).
• Minimum pitch size = minimum width (Wmin)
+minimum spacing (Smin)
• DP-Spacing = 2Pmin - Wmin
• Not all the patterns can be directly
decomposed into two masks.
• Nevertheless, the stitch insertion might not be
powerful enough doe resolving all the conflicts.
• A conflict that cannot be resolved by inserting
stitches anywhere is called a native conflict (NC).
• In this paper, it deals with the NC issue by two
– (1) NC prediction.
– (2) NC removal
• NC conflict
• DPT-Compliant Redesign
– A native conflict can only be resolved by DPTcompliant redesign.
– DPT-compliant redesign should first predict the
occurrence and the locations of NCs, and then
further correct them.
Problem Formulation
• Given a post-routing layout, the minimum
spacing, and the double patterning spacing,
the problem finds a perturbed layout so that
the number of native conflicts is minimized,
subject to minimum-spacing rule and the
double-patterning constraint.
Native Conflict Prediction
• An odd cycle in the
conflict graph is not
necessarily a NC because
of the possible solution by
stitch insertion.
Native Conflict Prediction
• Pattern projection
Native Conflict Prediction
• Segmentation
Native Conflict Prediction
• Odd-Cycle Detection
– The existence of odd cycles can be determined by
a DFS algorithm.
– Finding all the odd cycles is time-consuming.
• Cycle basis
– A cycle basis is a basis if we treat every cycle as a
vector represented by series of edges, and the
linear combination of cycles is a ring sum
operation of cycles. Then the basis form a linearly
independent spanning set for all cycles.
Native Conflict Prediction
• Ring sum operation
– Let the edges in the cycles C1 and C2 be sets E1 and
E2, respectively. A ring sum operation on C1 and C2
is denoted as C1 ⊕ C2, which is a cycle with its
edge being a set, (E1’∩E2) ∪ (E1∩E2’).
Native Conflict Prediction
• Cycle basis of a graph can be found by
applying a modified DFS algorithm.
• For a connected graph G = (V,E), the result of
DFS traversal forms a spanning tree T on V.
Inserting any other edge e ϵ (E - T) causes a
• If there is no odd cycle in the cycle basis of a
graph, then the graph contains no odd cycle.
NC-Aware Wire Perturbation
NC-Aware Wire Perturbation
• Symbolic Layout Representation
– Every wire (via) is represented by two points.
– By the symbolic representation, it can perform the
compaction across layers simultaneously.
NC-Aware Wire Perturbation
• DPT-Compliance Checking
• Wire Perturbation
– Add DPT constraints to remove odd cycles.
– Perform a trial compaction to see whether the
level of DPT-compliance is improved.
NC-Aware Wire Perturbation
• Compaction
– The compaction problem is modeled as a longestpath problem on the constraint graph.
– (1) Wire Constraint Graph Construction
• An edge (u,v) → wire u is on the left or bottom of v.
• The transitive edges in the graph can be removed.
NC-Aware Wire Perturbation
• Compaction
– (2) Point Constraint Graph Construction
• An edge (u,v) with its weight w → point v should be on
the right of point u, and the distance between them
should be at least w.
• There are four constraints:
(1) Design-rule constraint
(2) Wire shape constraint
(3) Fixed-pin constraint
(4) Layout-boundary constraint
NC-Aware Wire Perturbation
NC-Aware Wire Perturbation
• DPT Constraint Generation
– (1) Separating Wire Pairs Generation
Experimental Result
Experimental Result
• It presents a NC-prediction method based on
geometry relation of features and a NC-aware
wire perturbation algorithm to minimize as
many NC’s in layout as possible.
• Perform an efficient method to find odd cycles.

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