1. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Top view of the studied mask and the splitting strategy for the investigated LELE process. (a) The test mask with line-end features. The pitch size is 360nm for both directions, and the line width (dLW) is 45nm. The mask consists of three pairs of line ends with different gap sizes. The distance between each pair of line ends is 45nm. The mask-splitting strategy is illustrated in (b) and (c). (b) The mask for the first patterning contains the line ends in dashed green color. (c) The mask for the second patterning consists of line-ends in solid red color. All feature sizes in this paper are specified in wafer scale. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

2. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Schematic setup of the simulated waferstack for the second lithography-etch step in a standard LELE process. The full diffraction spectrum resulting from the second mask through the imaging system is used as the illumination over the topographic waferstack. The waferstack consists of two BARC layers on top of a hardmask layer. The topography resulting from the first lithography-etch process (shown in Fig. ) is modeled by a patterned hardmask. The pitch size is 360nm. The spincoated BARC thickness (dBARC2) is 30nm, the patterned hardmask thickness (dHM) is 20nm, and the resist thickness (dresist) is 100nm. The setup is illustrated from the sideview in the y direction. Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

3. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Simulated waferstacks and field distributions for a full illumination of the waferstack. The scaling of the full field and the reflected field is different. The waferstack is illustrated in Fig., and the exposed mask for second patterning is shown in Fig.. The thickness of the upper BARC layer is 82nm. The full field and the reflected field are compared according to waferstacks (a) with planar topography and (b) with nonplanar topography. The most interested region of the photoresist is marked with a red rectangle. The impact of nonplanar wafer topography on the full-field distribution is hard to notice. However, the reflected field clearly demonstrates the varied intensity of reflected light caused by modified BARC efficiency. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

4. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. BARC thickness optimization for (a) unpatterned and (b) patterned waferstacks. Three approaches of the illumination on the waferstack are used, and the computed optimization curves are compared. The two-beam illumination (dotted line) predicts 82nm as the optimum for the unpatterned waferstack and 62nm for the patterned one. The rigorous model (solid green line) using the full- illumination approach predicts 92 and 18nm, respectively. The representative illumination (dashed red line) predicts almost the same optimum values of BARC thickness as the full illumination does. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

5. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Simulated resist profiles from the sideview: The y-parallel cut is taken at the center of the left line from the second mask (see Fig. ). A full illumination of the wafer according to the layout of the second mask is applied. (a, b) Profiles computed without considering the wafer topographies (unpatterned) from the first patterning. (c, d) Profiles computed when the topography is taken into account (patterning). Different BARC thickness values are used according to the optimization results shown in Fig.. Specifically, the 82-nm BARC thickness predicted by two-beam illumination over unpatterned waferstack, 92nm predicted by full illumination over unpatterned waferstack, and 18nm predicted by full illumination over patterned waferstack are taken. Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

6. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Printed resist profile from topview—footprint (solid red line). The original mask pattern is also displayed (dotted rectangle) in wafer scale. The simulated configurations are (a) unpatterned waferstack at 82-nm BARC thickness, (b) unpatterned waferstack at 92-nm BARC thickness, (c) patterned waferstack at 92nm BARC thickness, and (d) patterned waferstack at 92nm BARC thickness. A slight difference is observed in the printed shapes for different configurations. The most pronounced asymmetry can be observed for the topographic waferstack at the optimum BARC thickness of 18nm. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

7. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Compensation of resist asymmetry induced by wafer topography. Four serif features are added to compensate for the additional exposure due to scattered light from the center long line on the wafer. The resist footprint is displayed in the graph (half of the period is shown). The resist shape resulting from the mask without OPC is shown by the red solid line, and the one resulting from a mask with a simple OPC is shown by the green dashed line. A correction of symmetry can be observed. The serif is 15nm high and 12.5nm wide in wafer scale. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

8. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Top view of the studied geometries and the splitting strategy for the investigated resist freezing process. The process targets at the formation of (a) 1:1 contact holes and (b) 3:1 long contacts, respectively, by an appropriate exposure and processing of orthogonal L&S patterns. Three periods are shown in both the x and y directions. The first exposure of horizontal lines is displayed in dashed green color, and the second exposure of vertical lines is displayed in solid red, respectively. The line width is 45nm in both studied masks, while the horizontal lines are dense in (a) and semidense with 1:3 fill ratio in (b). All values are specified in wafer scale. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

9. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Schematic setup of the simulated waferstack for the second exposure in a resist freezing process. The rigorously simulated diffraction spectrum of the second mask and its transformation in the pupil plane of the projection lens is used as the illumination over the topographic waferstack. The optical properties of the frozen photoresist differ from that of the photoresist that is used in the second lithography step. As in Fig., the setup is shown from sideview in the x direction. The pitch size is 90nm, and the line width is 45nm. The BARC thickness (dBARC) is 34nm, and the resist thickness (dresist) is 100nm. The unfrozen resist has a refractive index of 1.71 and extinction of 0.028. Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

10. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. Sensitivity of CD vs difference between the extinction coefficients k of the frozen resist and unfrozen resist, respectively. Simulation result for the square contact pattern from Fig.. The simulated defocus is −55nm with a target CD of 45nm. (b) The table provides linear fitting coefficients Lk of corresponding curves at different positions inside the lithographic process window. Note the column is labeled as the target CD produced by the corresponding dose and defocus. Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

11. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. The printed resist pattern from the topview. Three pitches are shown. The ideal pattern of the first exposure is displayed by horizontal dashed lines. The vertical dashed lines present the simulated pattern for the second exposure. The simulated resist pattern is presented by red solid lines. Large refractive index and extinction differences between the frozen and unfrozen resist Δn and Δk are used: (a) Δn=0Δk=0.01, (b) Δn=0Δk=−0.01, (c) Δn=0.04Δk=0, (d) Δn=−0.04Δk=0. The results indicate that for the dense wafer topographies, only the resist CD is impacted. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723

12. Date of download: 9/20/2016 Copyright © 2016 SPIE. All rights reserved. The printed resist pattern from topview. Three pitches are shown. The ideal pattern of the first exposure is displayed by horizontal dashed lines. The vertical dashed lines present the simulated pattern for the second exposure. The simulated resist pattern is presented by red solid lines. Large refractive index and extinction differences between the frozen and unfrozen resist Δn and Δk are used: (a) Δn=0Δk=0.01, (b) Δn=0Δk=−0.01, (c) Δn=0.04Δk=0, (d) Δn=−0.04Δk=0. (Color online only.) Figure Legend: From: Efficient simulation and optimization of wafer topographies in double patterning J. Micro/Nanolith. MEMS MOEMS. 2009;8(4):043070-043070-10. doi:10.1117/1.3275723