A Technique to Measure Dose andFocus Based on CD-SEMKyoungmo Yang, Yutaka-Hojyo,Norio Hasegawa, Hideo Sakai,Lorena Ferry

Outline Motivations and objective Defocus・Dose measurement algorithm– MPPC Algorithm– Defocus・Dose measurement algorithm Experimental Conclusions and Acknowledgment More measurement solutions for Lithography2

Motivation Correct for systematic CD error due to processing tofurther improve CDU performanceDesignGaugeFEM waferCD-SEMLitho ParameterOptimizationCDU MasterFDZone3

MPPC Indices 9 indices form MPPC (Multiple Parameters ProfileCharacterization) method on CD-SEMLeft Top Rounding(LTR)Peak CD(PCD)Left Bottom Footing(LBF)Left White Band(LWB)Right Top Rounding(RTR)Right Bottom Footing(RBF)Top CD(TCD)Right White Band(RWB)Bottom CD(BCD)4

Focus and Dose Measurement aceIso-linefm1・f・ m9・・f1fm1fm4fm2fm3DoseFocusFEM waferAll chip measurement on FEM waferusing MPPC method to definepattern character. (f1 f9)Create FD model using each indicesDose and Focus measurementf1 modelIntersection pointf1f2fp1f4 modelf3 modelf2 modelf3fp2Dosefkfp3fpkCDU ocus and dose definition for each index using FD modelMeasure MPPC on CD-SEM5Dosef2FocusFD Modelf1f3f4Merge all index resultsand define focus and dose

Experimental 1 Target and process condition––––Nikon NSR-S620DTrack: Lithius ProViTarget: Line 50nm Pitch 250nmMetrology:CG4100 (HITACHI CD-SEM)– Wafer FEM wafer:Dose 11.1mJ/cm2 (0.5mJ/cm2 step)Focus 60nm (20nm step) CDU wafer:Dose split wafer 5wafers(Best, 0.5mJ/cm2, 0.25mJ/cm2)– Sampling 25 points per chip and full chip in waferincluding wafer edge area.6Reticle information

Experimental 1 Model generation and validation・90CD (nm)CD (nm)80CD-SEMMeasurement8040 30f1357030 2570 25 60202060 151050 5Computation50154010 Focus(nm)40FocusMeasuredFocus (nm)MeasuredFocus(nm)MeasuredDose (mJ/cm2)Measured Dose(mJ/cm2)1413R 2 0.99961211109140R 2 0.9969120100806040200-20910111213142D osesetpoint(mJ/cm2)Dose Setpoint (mJ/cm )-20 020 40 60 80 100 120 140F ocus setpoint(nm(nm))FocusSetpointModel Confirmation7DoseFD ModelingData FittingFEM waferFD Measurementfm1・9035f・ m9・・45LWB (nm)CD (nm)fm1・fm9・・

Experimental 1: Results11.01.53σA verage10.σA verage0. (nm)CD(nm)203σA .0690.0660.06971.6061.5069.2064.2066.6066.5066.50* Litho tool variation and offset are included on themeasurement results.0.00.04Measuremet resultsSetpoint3 Sigma (mJ/cm2)2.03 Sigma (µm)11.53 Sigma (nm)Defocus(µm)Focus (µm)Dose(mJ/cm2)Dose (mJ/cm2)Measurement Result (Average)Difference between Setpoint and MeasurementSlot1234567Without offset00DoseFocus- 0.13- 0.002- 0.21- 0.003- 0.180.001- 0.23- 0.001- 0.190.009- 0.180.006- 0.180.009With offset0.18- 0.003DoseFocus0.05- 0.005- 0.03- 0.0050.00- 0.002- 0.05- 0.004- 0.010.0060.000.0030.000.006* Difference between setpoint and measurementdata are less than 0.05mJ/cm2012345S lot num ber6Remark7Less than 1nm will be changed when doseis moving 0.1mJ/cm28

Experimental 1: Results Dose and focus fingerprint (Slot 01 Slot 04)Slot01Slot02Slot03Slot04-0.5mJ/cm2 0.5mJ/cm2-0.25mJ/cm2 0.25mJ/cm2DoseMapFocusMap9

Experimental 1: Results Dose and focus fingerprint (Slot 05 Slot 07)Slot05Slot06Slot07Slot05Dose BestDose BestDose BestDose BestDoseMapFocusMap10

Slot5Slot6Slot7Dose (mJ/cm2) Dose variation0.60.40.20-0.2-0.4-0.6494847464544Chip NoFocus (nm) Defocus 30-40-50-60494847464544Chip No434211414039Status 3 wafers were printed assame litho condition. Litho process variation andmeasurement uncertaintyare included.Analysis The variation of 3 wafers areless than 0.1mJ/cm2 of dosewhich included litho processvariation and measurementuncertainty. Dose measurementuncertainty 0.1mJ/cm2 –Litho process variation For the defocus result, lessthan 20nm (0.02um)variation between 3 wafers. Defocus measurementuncertainty 0.02um litho error.Scan DirectionExperimental 1: Analysis

Experimental 2 Target and process condition––––DoseNikon NSR 620Track: Lithius ProViTarget: Line 50nm Pitch 250nmMetrology: CG4100 (HITACHI CD-SEM) Rectangle scan (250kx * 35kx)– Wafer Reference wafer: Refer right side for dose and focus condition CDU wafer: after dose correction– Sampling 25 points per chip and full chip in wafer including wafer edge area12Focus

Experimental 2: Results Dose correctionDose MapCD MapCD Results3Sigma 2.572nm55535149CD (nm)Before correction474543413932% 5841757673589505421337253169185351009Leveling map37M P num ber3Sigma 1.954nm545250CD (nm)48After correction464442403836M P num 2584175767358950542133725316918534

Conclusions and Acknowledgements Conclusions– A technique for dose and focus measurement has been introduced– Estimated accuracy of dose and focus measurement are: Dose 0.1mJ/cm2 Focus 20nm (0.020µm)– 32% improvement of CDU after dose correction CDU Before/After correction: 2.572nm/1.954nm Future Steps– Dose and focus correction at the single pattern and contact.– Reference model correction will be necessary for more accuratemeasurement Acknowledgments–––A special thanks to Hitachi High Technologies; Shigeru-Yonekawa to arrange focus and dosemeasurement tool for this project.Also I’d like to thanks Maki-Tanaka, and Chie-Shishido for assistance and useful discussion for this work.Especially we’d also like to show our gratitude to the Nikon Corporation Development headquartersgroup for their support of this project. (Tomoharu-Fujiwara, Tsuyoshi-Toki, Toshio-Ohashi, DaishiTanaka, Takayuki-Morita, Yasuhiro-Iriuchijima, Kazuaki-Suzuki, Naruo-Sakasai, Keiko-Saotome)14

CG4100 (HITACHI CD-SEM) – Wafer FEM wafer: Dose 11.1mJ/cm2 (0.5mJ/cm2 step) Focus 60nm (20nm step) CDU wafer: Dose split wafer 5wafers (Best, 0.5mJ/cm 2, 0.25mJ/cm ) – Sampling 25 points per chip and full chi