TopographyAware OPC for Better DOF margin and CD

Topography-Aware OPC for Better DOF margin and CD control Puneet Gupta*, Andrew B. Kahng*†‡, Chul-Hong Park†, Kambiz Samadi†, and Xu Xu‡ * Blaze-DFM Inc. † ECE Dept. University of California, San Diego ‡ CSE Dept. University of California, San Diego

Motivation • The depth-of-focus variation corresponding to thickness variation severely affects the metal patterning of the subsequent upper layer • Standard OPC (SOPC) assigns zero defocus for each layer which will lead to CD variation of the metal feature that will be placed on that layer • Topography-aware OPC (TOPC) will compensate for thickness variation and will adjust the OPC and ORC accordingly

CD variation by topography (a) Side view showing thickness variation over regions with dense and sparse layout. (b) Top view showing CD variation when a line is patterned over a region with uneven wafer topography, i. e. , under conditions of varying defocus. New OPC technique that is aware of post-CMP topography variation is required

SOPC Simulation Results 0. 0 DOF -0. 3 DOF (a) OPC layer Original metal (b) Resist Image 0. 0 DOF -0. 3 DOF (c) (a) (b) (c) (d) Original layout and simulation result with zero DOF model Original layout and simulation result with -0. 3 um DOF model in the non-planar topography Standard OPC layout and simulation result with zero defocus model Standard OPC layout and simulation result with -0. 3 um DOF model in the non-planar topography SOPC cannot compensate CD variation induced by topography!!

Standard vs. Topography-Aware OPC and ORC • The following table shows four different combinations of OPC and ORC (STD, and T-A stands for Standard and Topographyaware methodologies, respectively) OPC ORC ∆CD Method (Drawn vs. Printed) STD � 0 STD T-A > 0 • T-A-OPC/STD-ORC combination does not make sense! T-A STD > 0 • T-A-OPC/T-A-ORC yields a small CD error and considers layers with uneven topography T-A � 0 • STD OPC/ORC will generate a small CD error, but the premise of this method is at fault • STD-OPC/T-A-ORC combination yields a large CD error and hence not desirable.

K-DML Assignment Problem • Always try to assign one feature to DML partition according to its height • However, assign two features within the distance of R to different DML Partition will result in Optical Error • Objective: Partition of all features into k DMLs to minimize the number of optical errors Distance < R Assignment according to height Modified Assignment

k-DML Assignment Algorithm • Compute the post-CMP topography and the height for each feature • Construct a network flow topology with vertex v for each feature and an edge between two close vertices • for (i = 1; i < k; i++) • Calculate edge capacitances • Solve the maximum S-T flow problem • All vertices on the S side of the cut are assigned to DML i S 1 10 T Max flow =1 Min cut =1

TOPC Flow Library & Technology Standard OPC Flow SOPC GDSII CMP Simulation DOF Marking Layer Input GDSII for TOPC SOPCed GDSII DOF Model Database TOPCed GDSII • A map of thickness variation from CMP simulation is converted to DML and then fed into GDSII for TOPC • TOPC applies different DOF models to metal lines according to DML

Experimental Setup • Sigma-C’s Solid-C – Check CD of metals on topography • Mentor’s OPCpro – TOPC, SOPC and ORC (Optical Rule Check) • Cadence SOC Encounter – Placement & Route • Synopsys Design Complier – Synthesis

DOF Enhancement Method SOPC Topography: thickness (µm) - directional DOF range (µm) + directional DOF range (µm) 0. 0 0. 25 0. 1 0. 35 0. 15 0. 2 0. 45 0. 05 0. 3 0. 48 0. 0 0. 25 0. 1 0. 38 0. 18 0. 2 0. 52 0. 12 0. 3 0. 49 0. 09 0. 9 Test pattern : 0. 14µm W/ 0. 9µm S • Evaluate DOF margin at a test pattern – TOPC enhances DOF margin as topography thickness has over 0. 2µm – Total DOF range of TOPC at 0. 2 um is increased by 0. 14 um compared to SOPC

EPE Reduction DOF (µm) DML TOPC (µm) TORC (µm) 2 0. 13 0. 26 1 0. 0 0. 13 -0. 26 0 CASE I -0. 13 DOF (µm) TOPC (µm) TORC (µm) DML 2 0. 0 1 0 CASE II 0. 0 0. 13 -0. 26 -0. 39 • EPE is evaluated by alu 128 testbed from Artisan TSMC 0. 09µm • CASE I: assume the stepper machine focuses on the average of the topography ( Focus on DML 1 ) • CASE II: assume the stepper machine focuses on DML 2

Conclusions and Ongoing works Testcase SOPC TOPC Improvement (%) Case I 4652 1510 67. 5 Case II 12855 3295 74. 4 • Conclusions – The novel methodology for wafer-topography aware OPC is proposed – For 90 nm foundry library, TOPC achieves up to 75% reduction of EPE at worst-case defocus • Ongoing works – Investigate the impact of a CD error reduction on RC parasitics of the circuit – Study new DML assignment to reduce the CD error at boundary of DMLs