Mask Cleaning Processes and Challenges

Transcription

1 Mask Cleaning Processes and Challenges Brian J. Grenon Grenon Consulting, Inc. 92 Dunlop Way Colchester, VT Phone: Fax: Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 1

2 Mask Cleaning Processes verview What are we trying to clean? Mask Cleaning Processes Possible Contamination Sources Analysis of Mask Cleaning Processes What is Required? Summary and Conclusions Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 2

3 verview New mask cleaning processes are required to remove and eliminate particles on photomasks and to remove contaminants that can cause defect formation at 248, 193, 157nm and EUV lithography wavelengths. Current cleaning processes do not provide mask surfaces that are free from contamination. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 3

4 What are we trying to clean? Quartz Silica Gel Surface Chem ically Adsorbed W ater Physically A dsorbed W ater Si Si Si Si Si Si Si Chem ically adsorbed water - 4 to 6 / nm 2 Physically adsorbed water to 0.7 fractional monolayer Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 4

5 What are we trying to clean? Quartz Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 5

6 What are we trying to clean? Chromium The Mask Substrate - Cr The ESCA analyses indicate that the sputter process deposits chromium ions below the surface of the quartz. The non-conductive chromium presents a grounding challenge from an ESD perspective - particularly in a dry-environment. Contrary to common belief the chrome film is neither Conductive a bi-layer, it is an amorphous film containing Nitrogen, xygen, and Carbon The compositions change slightly from one blank manufacturer to another. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 6

7 What are we trying to clean? Chromium Chromium film 1200 angstroms Quartz Carbon contamination Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 7

8 What are we trying to clean? Chromium Chromium Dry Etched Images - 4 different mask suppliers Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 8

9 What are we trying to clean? MoSiN Chrome MoSiN Quartz ion species Depth profile of MoSiN Substrate Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 9

10 What are we trying to clean? MoSiN Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 10

11 What are we trying to clean? MoSiN Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 11

12 What are we trying to clean? MoSiN Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 12

13 Mask Cleaning Processes Mask Cleaning -The Reality All currently used mask cleaning processes leave residues. The contaminants are either sulfates, ammonium ions, organic compounds or digestive products of the cleaning tool. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 13

14 Mask Cleaning Processes Mask Cleaning Process verview There are essentially two fundamental mask cleaning processes in use: sulfuric acid/hydrogen peroxide (heated), usually followed by dilute ammonium hydroxide rinse Brush clean with detergents All reticles are exposed to sulfuric acid/hydrogen peroxide either as resist stripping process or final cleaning process. Whether ammonium hydroxide or detergents are used is often optional or arbitrary. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 14

15 Mask Cleaning Processes Mask Cleaning Process verview What happens during these processes? Rinsing with Ammonium ydroxide forms a surface layer of ammonium silicate - N Si - - N 4 +. can reduce transmission Quartz surface is modified Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 15

16 Mask Cleaning Processes Mask Cleaning Process verview What happens during these processes? Cleaning with detergents leaves a thin mono-molecular film of the detergent on the mask surfaces. (Langmuir-Blodgett Film) F F _ C 3 (C 2 ) x - - S 3 - Na + R _ C - C - C - S - K, Na, N 4 or Aliphatic sodium sulfonate F Fluorosulfonic acid salt Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 16

17 Mask Cleaning Processes Langmuir-Blodgett Films (detergents for contaminants on quartz or chromium surface) Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 17

18 Mask Cleaning Processes Langmuir-Blodgett Films (detergents for contaminants on quartz or chromium surface) Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 18

19 Possible Contamination Sources 1. Chemical reactions of cleaning chemicals with quartz and absorber surfaces (particularly chromium film). 2. Degradation products of cleaning tool materials, tank liners, tubing, filters. 3. ut-gassing from mask carriers and packaging materials. 4. Environmental contaminants. 5. Pellicle film and frame adhesives. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 19

20 Possible Contamination Sources Classical rgano-silylation of Resist Resist is Bulk Surface ydroxy-silicon compound Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 20

21 Possible Contamination Sources Classical rgano-silylation of Resist Resist is Bulk Surface ydroxy-silicon compound Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 21

22 Possible Contamination Sources In the case of optics contamination, the quartz becomes the bulk surface. Silylation occurs. Poly(methylmethacrylate methylmethacrylate) Bulk Surface Si - - Si - - Si - - Si - - Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 22

23 Analysis of Mask Cleaning Processes Plate #5, back, negative ions Plate #5, backside positive ions Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 23

24 Analysis of Mask Cleaning Processes Plate #5, chrome, negative ions Plate #5, chrome positive ions Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 24

25 Analysis of Mask Cleaning Processes Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 25

26 Analysis of Mask Cleaning Processes Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 26

27 Analysis of Mask Cleaning Processes 200 Backside Contamination # URSA Defects Energy kj 193nm Ret1 193nm Ret2 DUV Re t1 DUV Ret2 Line ar (DUV Ret2) Linear (DUV Ret1) Line ar (193nm Ret2) Line ar (193nm Ret1) Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 27

28 Analysis of Mask Cleaning Processes Quartz - Clean Process vs. Residue (Positive Ions) % concentration N_4 Na Si Ca K Si2C5h15 (PDMS) SiC39 (PDMS) C_6_5 C_4_9 C_5_11 C_2_5 112 B Al Mg Residue Quartz Akrion DI3+DI Quartz Akrion DI3+SC1 Quartz Akrion SPM+DI Quartz Akrion SC1+DI Quartz Akrion SPM+SC1 Quartz Chichibu Chichibu Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 28

29 Analysis of Mask Cleaning Processes 3.5 Quartz - Clean Process vs. Residue (Negative Ions) 3.0 % Concentration N S_3 S F Cl CN ^79Br Res idue C_2 C_2 Si2C393 (PDMS) 369 Quartz Akrion DI3+DI Quartz Akrion DI3+SC1 Quartz Akrion SPM+DI Quartz Akrion SC1+DI Quartz Akrion SPM+SC1 Quartz Chichibu Chichibu Si_2 Si 405 SiC32 (PDM S) Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 29

30 What is Required? Mask Cleaning Requirements All reticle surfaces must be free of environmentally-deposited contaminants therefore, mask cleaning processes must have the capability to REMVE: hydrocarbons detergents carbonized stains from repair processes surface deposits from out-gassed resist by-products possibly out-gassed organic compounds from packaging Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 30

31 What is Required? Mask Cleaning Requirements The cleaning processes must prevent the formation of surface modifying contaminants: Silicic acid Langmuir-Blodgett films from detergents Ammonium silicates Ammonium, Sodium or Potassium ions from detergents Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 31

32 Summary and Conclusions Current mask cleaning processes are inadequate at current and future lithography wavelengths. Detergents and wetting agents contaminate optical surfaces, sulfuric acid/peroxide chemistries react with current films. A clear understanding of the specific customers process, mask absorber and mask manufacturing conditions are required in order to meet customer needs. Mask cleanliness is a systemic challenge not just cleaning, but requires handling, storage, packaging and environmental considerations. The current chromium film is the biggest problem with mask cleaning, it is not stable to cleaning chemistries. Any new film should consider cleanability as a requirement. The current MoSiN film may present the same issues. Mask Supply Workshop - Grenon Consulting, Inc. 2/4/04 32