Efficient Pattern Relocation for EUV Blank Defect Mitigation

Hongbo Zhang, Yuelin Du, Martin D.F. Wong, Yunfei Deng, Pawitter MangatSynopsys Inc., USADept. of ECE, Univ. of Illinois at Urbana-ChampaignGlobalFoundries Inc., USALayout Small-Angle Rotation and Shift for EUV Defect MitigationICCAD 2012OutlineIntroductionBackgroundProblem FormulationProblem SolutionsExperimental ResultsConclusionIntroductionEUV lithography has become a major solution to the next generation lithography process with finer resolution and reasonable throughput.ChallengesExotic light source setupResist tuning for line edge roughness and sensitivitydefect-free mask manufacturingIntroductionAt present, to make a defect-free EUV mask blank is still too costly and impractical.The buried defects in the multilayer (ML) reflective structure are the main source of blank defect.Defects could have significant impact when they are adjacent to the feature boundary, and severe printability issues, such as bridging or breaking of the printed lines

IntroductionMitigating the defectRemove the defect from the blank by using Ion-beam and electron beamThe defect location detection with 1030nm inaccuracyThroughput is still far from the requirementDamage on the ML structureOPC-like defect modeling and pattern modification methodRequires extremely precise defect location, height, width and process variation control

IntroductionAs the phase change is insignificant on the feature boundary, defects will have little impact on the printed wafer.

BackgroundEUV Mask PreparationBecause of the 13.5 nm wavelength, a multilayer (ML) structure is needed for the reflective optics.EUV mask is prepared through two stepsML structure is coated and blank defects will also be randomly generatedMask absorbers with designed patterns are placed on top of the mask blank with 4X reduction factorAs the layout to print is smaller than the blank, there is certain freedom to find the best layout location on the blank.

Rotation helps defect mitigation.

Mask preparation and fiducial generation flow

Problem FormulationDefinition of Solution SpaceDepending on the limits of the mask alignment tool and EUV scanner, the reticle may have a certain freedom in its small angle rotation and shift maximum shift upper bound F maxmaximum rotation upper bound maxThis small angle rotation does not contradict the possible 90, 180 or 270 rotation, which can happen simultaneously.

Problem FormulationDefinition of Solution SpaceThe shift amount in X-Y directions as (X, Y )rotation amount as the whole solution space is an Bounding Octahedron (BO)

Problem FormulationProhibited Relocation CubeDuring the layout relocation process, a defect might potentially impact different boundaries according to certain shift and rotation amountProhibited rectangle (PR) represent the defect relocation positions that a defect center should avoid.

Problem FormulationProhibited Relocation CubeIf we notate such prohibited relocation movement as (Xi,Yi, i), the prohibited movement should satisfy the following equations:

Problem FormulationProhibited Relocation CubeWhen i is small, a small angle approximation sini i and cosi 1 becomes valid.

To guarantee the validation of eq. 3 and eq. 4, the total error must be within the accuracy requirement EmaxTherefore, the maximum allowable rotation for linearity is less than a rotation bound linear , depending on the relocation accuracy and (Xd , Yd).

Problem FormulationProhibited Relocation CubeFor the scenario that, we can always slice the rotation range into small pieces

For each new piece, we only need to regenerate the new defect map (Xd,Yd) by calling rotation function once

Problem FormulationMitigation for Relocation InaccuracyThe real Xi, Yi and i could have offset.

Problem FormulationMinimum Cube Overlapping Problemeach pair of defect and feature boundary will generate a PRC through previous stepsIf we draw all the PRCs together in the BO, all the PRCs might overlap with each otherThe overlapping PRC number on one point represents the number of damaged boundaries once that relocation is adopted.

Problem SolutionsProblem ReductionThe outside defects have much larger movable regions than the inside ones. Only the prohibited rectangles covered by the cropped region need to be considered. The size of prohibited rectangle is exaggerated for better illustration.

Problem SolutionsSolutions for Min-CO Problemthe sweeping line algorithm is an efficient algorithm to solve the rectangle overlapping problemextend this sweeping line algorithm to solve the overlapping problem in 3D space, which is to sweep the (X,Y ) plane along the axis and then find the minimum overlapping region in each cross-section.

The overall flow

Experimental Results

Conclusionsa novel algorithm to mitigate defects by layout shift and rotation on blanks.transform the pattern relocation problem into a minimum cube relocation problem