CLEANING TECHNOLOGY OPTIONS FOR EUV MASK LIFETIME EXTENSION

Transcription

1 CLEANING TECHNOLOGY OPTIONS FOR EUV MASK LIFETIME EXTENSION Uwe Dietze Davide Dattilo SUSS MicroTec

2 OUTLINE Background EUVL Mask Life Time Concerns Potential Root Causes for Ru Damage Solutions & Mitigation Strategies Summary 2

3 BACKGROUND EUVL Mask Cleaning Needs Carbon Deposition Particle Deposition Ionic & Organic Contamination EUVL mask cleaning frequency higher than in 193i Lithography due to lack of pellicles Minimum of 100x clean is current target for cleaning technology development 3

4 BACKGROUND EUVL Mask Cleaning Requirements Absorber (TaBN) Ru capping layer ~ 40 pairs of Mo/Si multilayer stack Under EUV Exposure Particles Carbon Growth Handling / Storage / Use LTEM substrate Backside coating Not drawn to scale Particles Contamination Goal Restore Remove Preserve Ru degradation has the most dramatic impact on Mask Life Time 4

5 EUVL MASK LIFETIME CONCERNS Key Challenges for EUVL Mask Cleaning #1 Chemical Attack #2 Physical Damage #3 Backside Particle CD Shift, Reflectivity Change Ru Reflectivity Loss Ru Pitting Overlay Impact, Scanner Downtime Defect Detection CD-Control Litho Fidelity Litho Stability Mask Life Time TaBN Layer Ru Layer BS Contaminated BS Clean 5

6 Relative CD change [%] EUVL MASK LIFETIME CONCERNS Results obtained on early EUVL pattern masks As reported at the 2011 International Symposium on Extreme Ultraviolet Lithography # of Clean Dramatic CD shift on wafer prints and heave Ru peeling on masks observed after only 10x clean 6

7 EUVL MASK LIFETIME CONCERNS Results obtained on EUVL pattern masks made by DNP As reported at the 2011 International Symposium on Extreme Ultraviolet Lithography Reference Mask RMS 0.60nm Reference Mask RMS 0.18nm Some Nanometer Scale Bumps observed after 32x clean 7

8 EUVL MASK LIFETIME CONCERNS Results obtained on EUVL pattern masks made by DNP As reported at the 2012 SUSS Workshop Japan Reference Mask RMS 0.60nm ML roughness corner center Reference Mask RMS 0.18nm Severe Ru Pitting observed after 57x clean 8

9 EUVL MASK LIFETIME CONCERNS Results obtained on latest EUVL pattern masks As reported at the IEUVI Mask TWG, February 2013 EUV Reflectivity is increasing throughout 70 cleaning cycles. Average EUV Reflectivity increase is 0.04% per clean 9

10 EUVL MASK LIFETIME CONCERNS BS contamination added by Scanner Clamp As reported by IMEC at EMLC 2012 (1x clean) Before cleaning (ASML inspection results) AFTER cleaning (ASML inspection results) Cleanliness dramatically improved in single BS clean process Classification of remaining defects very time consuming if performed by operator Aggressive BS cleaning impacts also FS 10 IEUVI Mask TWG Toyama, Japan, 10 October 6, 2013

11 POTENTIAL ROOT CAUSES RU DAMAGE Impact of Absorber Etch Process on durability of Ru during cleaning As reported by SK Hynix at BACUS

12 POTENTIAL ROOT CAUSES RU LOSS Photo-Chemical Erosion Emission Spectrum of Medium Pressure Hg lamps As reported by SUSS at BACUS 2013 The following photolysis processes can be expected when using a low pressure Hg lamp, emitting down to 185nm: Oxygen: O 2 O. (1D) + O. (1D) O. (1D) + H 2 O HO. + HO. Water: H 2 O H. + HO. Suprasil Quartz used in current ISUV system, allowing 185 nm emission to interact with process media hn 254nm Ozone: O 3 O 2 + O (1D) O. (1D) + H 2 O HO. + HO. Hydroxyl radicals are usually responsible of Organic removal from the surface: OH. + RH R. + H 2 O R. + O 2 RO. 2 CO 2 + H 2 O Atomic Oxygen along with Hydroxyl Radicals could lead to Ru Oxidation and therefore damage: Ru(0) O. /OH. RuO 4 (volatile) Photochemical Processes for Water Treatment Chem. Rev. 1993, 93, Atomistic description of oxide formation on metal surfaces: the example of Ruthenium, Chem. Phys. Lett. 2002, 352,

13 POTENTIAL ROOT CAUSES RU PEELING Thermal Stress Extended emission spectra of Medium Pressure Hg lamps As reported by SUSS at BACUS 2013 Local heating of mask surface (Repeats 50 x per cleaning cicle!) Near IR emission is also observed due to Argon additives Functional Layers of EUVL Mask - Coefficient of Linear Thermal Expansion Mismatch Ru Peeling TaBN *10-6 *K -1 Ru *10-6 *K -1 Si *10-6 *K -1 Mo 5.2 *10-6 *K

14 POTENTIAL ROOT CAUSES RU PITTING Transient Cavitation Cavitation Bubble Growth As reported by SUSS at SPIE Lithography 2013 Pulsation Stable Cavitation Damage Free Collapse Transient Cavitation Violent Implosion = Damage Stable Cavitation Transient Cavitation Particle Pit created in Ru surface due to cavitation collapse Ru Surface 14

15 SOLUTIONS AND MITIGATION STRATEGIES Potential Root Cause 5ppm DIO3 Items Tested Results Presence of Oxidizing Species in process media 0.5% H2O2 5ppm + 0.5% H2O2 SC1 DICO2 Lower ISUV power No change to Ru Damage ISUV induced thermal stress Higher DI-Water Flow Lower DI-Water Temperature Higher ISUV Scan Speed Reduced Damage ISUV radiation < 200nm and > 700nm Low pressure Hg lamp Greatly reduced damage Results strongly suggest that IR induced thermal stress combined with formation of reactive species at radiation < 200nm is responsible for the damage 15

16 SOLUTIONS AND MITIGATION STRATEGIES Use of a low pressure Hg Lamp for ISUV process As reported by SUSS at BACUS Emission spectrum of Low Pressure Hg Lamp (as published by lamp vendor) shows distinct emission at 254nm + Negligible IR emission + Emission cut-off below 200nm + But can this lamp still remove organic material? 16

17 SOLUTIONS AND MITIGATION STRATEGIES Organic removal using low pressure Hg Lamp for ISUV process As reported by SUSS at BACUS The process usually starts with generation of excited Carbon (1) that reacts with Molecular Oxygen producing carbon-cationic radical and Oxygen radical (2): hn 254nm C C* (1) C* + O 2 C + + O 2 - (2) The Oxygen Radical can react with another organic species leading to Peroxyl radical (3) which in turn undergoes oxidative decomposition to CO 2 and water (4): R + O 2 - RO 2 - (3) RO 2 - CO 2 + H 2 O (4) Photochemical Processes for Water Treatment Chem. Rev. 1993, 93,

18 SOLUTIONS AND MITIGATION STRATEGIES Ru impact using low pressure Hg Lamp for ISUV process As reported by SUSS at BACUS 2013 EUV Blank exposed to Low Pressure Hg ISUV process for 12 hours + 12 hours treatment represents approx. 100x clean + No Ru Damage or Reflectivity Loss observed Measured Roughness: nm (Pre- and post measurement identically) 18

19 SOLUTIONS AND MITIGATION STRATEGIES Ru impact using low pressure Hg Lamp for ISUV process As reported by SUSS at BACUS 2013 EUV Pattern Mask exposed to low pressure and medium pressure Hg ISUV process for 6 hours + 6 hours treatment represents approx. 50x clean + Sever damage observed again where Ru was treated with Medium Pressure Hg lamp + Drastically reduced impact on Ru layer observed where surface was treated with the Low Pressure Hg lamp 19

20 SOLUTIONS AND MITIGATION STRATEGIES Promoting stable cavitation What s in the Cavity? As reported by SUSS at BACUS 2012 Gas Vapor or Depends on what s in the Cavity Added Gases (H2, CO2) Inherent gases Chemistry Decomposition, e.g. NH4OH, H2O2 Water Vapors Chemistry Vapors Media Properties are the key variables that define cavitation behavior and subsequent cleaning effect 20

21 SOLUTIONS AND MITIGATION STRATEGIES Promoting stable cavitation Ru Pitting comparing conventional and advanced media As reported by SUSS at BACUS 2013 PRE comparing conventional and advanced media Zero Pit for Chemical A + New media is greatly reducing risk of Ru pitting during Megasonic process + New Media also exhibits much higher PRE compared to conventional media 21

22 Cleanliness SOLUTIONS AND MITIGATION STRATEGIES Advanced EUVL Masks Cleaning Technology Carbon Carbon & Organic Removal Removal Surface Preparation Particle Removal Drying Residual Ion Removal Time in Time Process Surface Preservation 254nm ISUV SPM ISUV / + DIO DIW + 3 DIW Local AMC Control Hot DIW MegaSonic / Droplet Spray 254nm ISUV ISUV + DIW + DIW Low Temp Preservation SPM & DI03 Free New Media nm ISUV eliminates risk of inadvertent generation of Oxygen Radicals and excessive IR radiation + New media used in Megasonic eliminates risk of transient cavitation + Advanced EUVL mask cleaning 100% DIO3-, SPM- and NH4OH free 22

23 SUMMARY 100x clean is feasible today for in-fab mask maintenance The absorber etch process is a major factor for EUVL mask life time During mask cleaning, the following factors have been identified most critical for EUVL mask life time: IR radiation during ISUV process Ru Peeling Radiation <200nm during ISUV process Ru Loss Transient cavitation during Megasonic process Ru Pitting New media used during Megasonic process promoting stable cavitiaion have been introduced sucessfully to reduce risk of Ru pitting IR and <200nm radiation are eliminated when using a low pressure Hg lamp during ISUV process, therefore reducing risk of Ru Peeling and Ru Loss Total life time of masks will depend on frequency of maintenance cleans, which today are mostly affected by particles added to mask BS during clamping in scanner (improvements are urgently needed here). 23

24 SUSS MicroTec Photomask Equipment GmbH & Co. KG Ferdinand-von-Steinbeis Ring Sternenfels Germany 24