Experimental Characterization of Topography Induced Immersion Bubble Defects

Transcription

1 Experimental Characterization of Topography Induced Immersion Bubble Defects Michael Kocsis a, Christian Wagner b, Sjoerd Donders b, Tony DiBiase c, Alex Wei d, Mohamed El-Morsi d, Greg Nellis d, Roxann Engelstad d, Peter De Bisschop e a: Intel Corp, b: ASML, c: KLA Tencor, d: University of Wisconsin, e: IMEC 1

2 Why Are We Concerned? Bubbles New immersion specific defect mechanism. Effect of Topography: May increase the probability of bubble formation Bubbles on surface are stationary May have a longer lifetime than those suspended in liquid Simulation Presented at Jan 2004 Workshop 2

3 Surface Bubbles on Flat Wafers Immersion tests have been done on flat wafers. Bubble defects were detected with a bright field inspection tool. Non-Topography related Act as micro-lenses Test using a KLA PCM Reticle, inspected on a KT2360 3

4 Bubble Magnification Effect: Principles total internal reflection diffracts the rays at the outer rim Bubble Dia >> λ refraction leads to defocusing of the image: magnified projected image is printed 4

5 Bubble Magnification Effect: Data Pattern magnified, and unsharp Light missing, due to reflection No Bubble Defect With Bubble Defect See ASML Paper: Bubble Investigation for Immersion Lithography Sjoerd Donders, Richard Moerman 5

6 Surface Conditions Play an Important Role Both simulations and experimental data: probability of bubble formation increases with contact angle. Bubble Defects vs Contact Angle on Flat Wafers Number of Bubble Defects 10X Increase Hydrophillic (67 Degrees) Contact Angle Hydrophobic (117 Degrees) 6

7 Topography Wafers Create wafers with extreme topography to get a first look at how serious a problem entrained bubbles may be. Etched Oxide Trenches (150nm, 250nm), MT1 Test Reticle, 0.13um Design Rules, Line/Space Arrays, Very Limited Random Logic Structures Top Coat (41nm) Contact Angle Resist (175nm) BARC (37nm) Oxide (150nm, 250nm) 0.125um-10.0um Silicon Worse case trench depth and contact angle. 7

8 Expose on 193nm Immersion Tool Immersion Prototype AT1150i Liquid containment Integrated Liquid Supply (temp, degassing, purity) Existing Lens modified for immersion Proven dry 3-D mapping of wafer surface 8

9 Experiment Run Plan Wafer Scanner Exposure 250nm Trench 193nm Immersion MT2 DF Reticle 150nm Trench 193nm Immersion MT2 DF Reticle 250nm Trench 193nm Immersion 1.5*E0 Open Frame 150nm Trench 193nm Immersion 1.5*E0 Open Frame Flat Test Wafer 193nm Immersion 1.5*E0 Open Frame 150nm Trench 193nm Dry 1.5*E0 Open Frame Open Frame: exposure of entire field area vs MT2 Dark Field reticle: ~30% exposure area. Flat wafers, and Dry exposures were used as comparisons to separate out non-topography related defects. 9

10 Topography Results Wafers were measured on a KT2360 Topography wafers exposed with open frame at 1.5xE0: high levels of residual resist remaining around the edges of the trenches; impossible to use for defect analysis. Topography wafers exposed with the MT2 reticle: high non-immersion related particle defect count non-optimum resist process, many defects could be filtered out of the data inspection sensitivity had to be detuned to prevent overload. 10

11 Topography Results The large bubble defects seen on the flat wafers were also seen on the topography wafer. Ref: No Defect Bubble Defect Late Breaking News: Some initial indication that these bubbles appear more frequently on certain areas within the field. 11

12 Topography Results The results have shown no evidence that any of the other defects found are caused by bubbles. Examples of typical defects, ~ 2000/wafer Smallest defects detected ~ 400nm (recipe had to be de-tuned to limit defect overload) 12

13 Does it match simulation results? Measured: Resist surface topography on the 250nm deep trench wafer with an (AFM). Dynamic contact angle of the top coat. Simulations: These conditions were then used by the UW Computational Mechanics Center to verify the results with CFD models that have been developed to predict when air will be entrained due to flow over topology. 13

14 400nm Line/250nm Space Array AFM Plot of Surface Topography 48nm Peak- Valley Simulation Results NO BUBBLES 14

15 3.0um Line/7.0um Space Array AFM Plot of Surface Topography 132nm Peak- Valley Simulation Results NO BUBBLES 15

16 10.0um Line/10.0um Space Array AFM Plot of Surface Topography 198nm Peak- Valley Simulation Results NO BUBBLES 16

17 UW Simulation Results Simulations agree with wafer inspection results in showing no topography bubble defects. All the simulations done with realistic contact angles and corner rounding show No topography bubble entrapment. Does this mean we are safe or are we just not looking at the right conditions? - Topography Type - Defect Mechanism - Other variable 17

18 Next Steps ISMT-IMEC joint project to more thoroughly test for topography related defects. Topography Reticle/Wafer: - Very wide range of topography (1D, 2D, H&V, BF&DF) - Trench depth, side wall angle, surface contact angle - Optimized for high contrast defect inspection Second level metrology reticle: - Dose sensitive structures covering the entire field. Optimize the resist process flow to achieve a low level of background defects, and do dry exposures for comparisons. 18

19 Next Step Topography Reticle 1um Label Ynm Xnm um Line Space XXXXXL YYYYYS 1 L/S V PADA LF PAD A DF L BAR Check PAD A DF PADA LF L/S H 29x29 Cell Array 100um Single Cell 10um 2 L BAR DRAM V L/S H Pad B BF DRAM V Pad A Small 45 L/S L BAR 1um Label 3 Check Pad B DF DRAM H Misc Pad B DF Misc Check Pad B BF 4 L/S V PADA LF PAD A DF L BAR Check PAD A DF PADA LF L/S H 5 L/S Small L BAR Small Check Pad B DF 45 L/S L/S V DRAM H L/S Small 110um XXX W YY D 6 Pad B BF Misc L BAR Misc Check L BAR L BAR Small Check 100um 1um 10um Label 7 L BAR Check 45 L/S Pad B BF Pad A Small Pad B DF 45 L/S L BAR 8 L/S V PADA LF PAD A DF L BAR Check PAD A DF PADA LF L/S H 9 110um XXX L YYY VP B 10 2nd L/S V 2nd LF 2nd DF 2nd LF 2nd DF 2n L/S H 100um 10um 1um Label Pad W 110um Space XXXXXW YYYYYS B 100um 10um 19

20 µ ~90 m Second Level Metrology Reticle H100 V100 H L BAR V100 V80 H100 V100 LABEL LABEL LABEL L BAR H100 V100 H80 H100 V100 H L BAR 3 V100 V80 V100 V80 V100 H100 V100 H100 4 H100 H100 H L BAR H100 V80 H100 V100 5 V L BAR V100 H100 V100 H100 V100 H100 Cr continues Cr continues 6 H100 H L BAR V100 H L BAR H100 V100 LABEL LABEL LABEL L BAR H100 V80 H100 V L BAR V L BAR 8 H100 V100 H80 ID 100 L BAR H100 V80 H100 V100 9 V100 H100 V100 H100 V100 H100 V100 V80 10 H80 V80 H100 V100 H100 V100 H80 V nm/100nm & 80nm/80nm H & V Line/Space Gratings First immersion exposures with this reticle set in Nov

21 Summary / Conclusions No evidence of topography caused bubble defects. - Limited set of line/space geometry - At defect detectability > 400nm The UW simulations concur with this finding and have shown no bubble formation on any realistic topography. Are we looking at the right conditions? - Topography type - Defect size - Other variable 21

22 Summary / Conclusions New Topography Reticle/Wafer Developed - Very wide range of topography - Optimized for defect inspection - First immersion exposures in Nov 04 It will be difficult to fully answer defect questions until an immersion tool is installed at a facility with a clean process, available defect metrology, and lots of exposure time (statistics). 22

23 Intel: Malcolm Delaney, John Urata Acknowledgments ISMT: Chris Van Peski, Rich Berger, Andrew Grenville, Greg Wells IMEC: Young-Chang Kim ASML: Wil Pijnenburg, Gerard Van Reijen KLA-Tencor: Verlyn Fischer, Gian Lorusso Infineon: Nickolay Stepanenko 23