Lithography for Silicon-based and Flexible Electronics. Christopher K. Ober Materials Science & Engineering Cornell University

Transcription

1 Lithography for Silicon-based and Flexible Electronics Christopher K. Ober Materials Science & Engineering Cornell University

2 Smaller is Better Moore s Law after 40 Years Now few GHz Feature sizes of ~ 100 nm Microprocessors with thousands of transistors operating at a few MHz Feature sizes of ~ 0.5 µm 2

3 International Technology Roadmap for Semiconductors 3

4 Sowing the Seeds of Nanotechnology Richard Feynman, There is plenty of room at the bottom (1959) But. Gutenberg laid the foundation for microlithography when he invented the printing press (~1450) 4

5 Lithography: the printing press made small Resist Wafer Coat & Bake Typical exposure, bake and development times are in seconds! Mask Expose (193 nm or 157 nm) (seconds) Positive (PEB) Post-Exposure Bake (seconds) Negative Develop (seconds) Etch (Plasma) Strip 5

6 Making the Pattern Crosslinking Chain scission Polarity change h ν h ν h ν 6

7 The March to Smaller Dimensions 193 nm Immersion?

8 Photoresist Photosensitive material used for transferring pattern to substrate Has to Adhere to substrate Undergo radiation induced solubility change Possess etch resistance Be developable in aqueous base (or other solvent) Disappear when not wanted

9 Topics High resolution DUV lithography Without chemical amplification 193 nm immersion 157 nm lithography E-beam lithography Thick film lithography Future directions in lithography Imprint lithography Ink jet printing

10 Resists without Chemical Amplification Established technology Mostly used as electron-beam resists Was original basis of DUV resists High resolution (no acid diffusion problems) Sub 30 nm feature sizes possible Problem: Low sensitivity! How to improve? Currently low sensitivities are traded for high resolution 10

11 Electron Beam Lithography Characterized by expensive systems and long write times Typically used for mask making or MEMS devices e - 11

12 E-Beam Resists and Processing CORNELL NANOSCALE FACILTY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY Positive resists PMMA Toray EBR-9 PBS ZEP Photoresists as e-beam resists Negative resists COP Shipley SAL NEB-31 Multilayer systems Low/high molecular weight PMMA PMMA/copolymer Trilayer systems CNF NanoCourses

13 Poly(methyl methacrylate) (PMMA) CORNELL NANOSCALE FACILTY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY The most popular e-beam resist Extremely high-resolution Easy handling Excellent film characteristics Wide process latitude Usually dissolved in a solvent (e.g. anisole) Exposure causes scission of the polymer chains Solvent developer dissolves exposed (lighter molecular weight) resist CNF NanoCourses

14 PMMA E-Beam O E-beam Technology Group, Stanford Nanofabrication Facility Excellent resolution (<30 nm) + Contrast Low sensitivity (800µc/cm 100kV) How to improve sensitivity? -copolymerize with MAA for 4x increase in sensitivity 14 +

15 PMMA Characteristics CORNELL NANOSCALE FACILTY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY Positive acting Several viscosities available, allowing a wide range of resist thickness Not sensitive to white light Developer mixtures can be adjusted to control contrast and profile Appropriate processing results in undercut profile for liftoff Poor dry etch resistance No shelf life or film life issues CNF NanoCourses

16 P(MMA-MAA) Copolymer Resist CORNELL NANOSCALE FACILTY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY CORNELL NANOSCALE FACILITY Higher sensitivity than PMMA Can be exposed at a lower dose Faster Less contrast. Most useful in Bi-level resists with PMMA, to produce undercut profiles useful in liftoff processing Characteristics Positive acting Several viscosities available, allowing a wide range of resist thickness Not sensitive to white light Developer mixtures can be adjusted to control contrast and profile Poor dry etch resistance No shelf life or film life issues CNF NanoCourses

17 Styrene Monomers insensitive neg. tone resist insensitive pos. tone resist Sensitivity Highly sensitive Negative tone Introduction to Microlithography, p

18 E-beam Resists

19 Poly (1-Butene Sulphone) Very sensitive, but poor dry etch resistance! + R-SO 2 -R [RSO 2 R] + RSO R R + + SO 2 Again, favorable decomposition route. Note release of neutral species. 19

20 Key Concepts To Improve Sensitivity: (1) Build in bonds capable of cleavage (2) Ensure stability of intermediates (3) Release of neutral species, i.e. SO 2 20

21 UV Lithography Only optical lithography can provide the information output needed for high volume production Industry loves this and will keep pushing it as long as it can go 21

22 Azo resists 22

23 Azo Absorbance 23

24 Azo Patterning 24

25 UV Stepper Tool (248/193 nm) Canon FPA-5500iZ step-and-repeat i-line stepper for 300 mm is a mix-and-match companion for the company's 300 mm scanners, the FPA-5000ES3 (KrF) and the FPA-5000AS2 (ArF). The tool can be easily converted to or from 200 mm wafer size and can be used for patterning less-critical IC layers. The unit includes the same third-generation platform as the company's 300 mm scanners.

26 DNQ Resists Introduction to Microlithography, 2nd Ed., L. Thompson, C.G. Willons, M. J. Bowden, eds., ACS Books, Washington, 1994.

27 DNQ / Novolak Photoresists Interactions of Photoactive Molecule with Matrix Dissolution Rate ( /s) 10,000 + OH hν R p 10 + R 0 *Courtesy George Barclay (Shipley)

28 Limited Light Sources 248 nm 365 nm R = k 1 λ/na Changing Wavelengths 248 nm 193 nm 157 nm EUV (13 nm) X-ray

29 Resists with Chemical Amplification Resist Components Polymer Solvent Photoacid Generator (PAG) Additives (e.g. DI,plasticizer)

30 Positive Chemically Amplified Photoresist Chemistry hv H + PAG 0.40µm *Courtesy George Barclay (Shipley) 0.12µm

31 Photoacid Generator (PAG) Classes Non-Ionic PAGs Halogenated Compounds: Sulfonate Esters/Sulfones: Ionic PAGs Onium Salts: *Courtesy George Barclay (Shipley)

32 Positive Photoresist Technology Differential in Aqueous Base Solubility - Deprotection Chemistry 130 C + H + Dissolution Rate 40 A/sec 30,000 A/sec *Courtesy George Barclay (Shipley)

33 Photoresists for ArF (193 nm) Lithography The current state-of-the-art in the microelectronics industry. Capable of producing features as small as 65 nm. Nikon Precision, Inc. 33

34 Resist Transparency at 193 nm Aromatic groups are highly absorbing at 193 nm wavelength Phenolic groups used for 248 nm lithography cannot be used here Methacrylate groups are transparent Low plasma etch resistance Alicyclic groups are transparent Plasma etch resistance similar to aromatics Kunz RR, Allen RD, Hinsberg WD, Wallraff GM.. Proc. SPIE 1993; 1925: Takechi S, Kaimoto Y, Nozaki K, Abe N. J. Photopolym. Sci. Technol. 1992; 5:

35 First 193 nm Photoresist Poly(t-butyl methacrylate - methacrylic acid) Excellent transparency Excellent solubility Poor etch resistance Kunz RR, Allen RD, Hinsberg WD, Wallraff GM.. Proc. SPIE 1993; 1925:

36 Alicyclic Structures Improve Etch Resistance Cycloolefin-maleic anhydride (COMA) resist Norbornene group adds etch resistance Maleic anhydride group adds solubility Carboxylic acid leads to film swelling during development Allen RD, Wallraff GM, DiPietro RA, Kunz RR. J. Photopolym. Sci. Technol. 1994; 7: Allen RD, et al. J. Photopolym. Sci. Technol. 1995; 8:

37 Dry Film Photoresists polyester support sheet for the photosensitive material layer of photoactive monomer mixed with polymeric binder and other materials polyolefin cover sheet withich prevents photoresist from sticking or blocking when it is wound on a roll exposures can take several minutes 37

38 Dry Film Initiator Structure Cl Cl Cl N N 2 N N N light N Ia Ia + H 3 C H 2 C N R R Cl N + H 3 C H C N R R II N IIa 38

39 Dry Film Dye Formation R R R N R N Ia + CH N R R C N R R III R N R R N R R N R - electron C N R R R N R 39

40 Pattern Formation O O IIa + O CH 2 H 2 H 2 O C C C O O Polymer Network CH 2 IV CH 3 IIa + IV + * H C H 2 C H C H C * n O O Polymerized matrix OH OH V 40

41 Circuitization 41

42 Defined Systems System Cleaning/Wet Process Wet Stripper/Developer Large High Vacuum Coater* In-line Defect Inspection* Precision Lithography* Precision Wet Coat & Bake OLED Evaporation Source* Supplier Kraemer Koating Hollmuller Siegmund CHA ECD Azores Frontier Industrial KJL Small High Vacuum Coater* Manual Inspection Table *USDC supported TBD TBD 42

43 Cleaning/Wet Processing: Capability Unwind Rewind Scrub/ Rinse Kraemer Koating, to 14 width Poly Tank Poly Tank SS Tank Designed for cleaning and/or wet processing Recirculation w/cascading possible 0.2 to 10 FPM 0.5 PLI to 1.6 PLI Air Knife 43

44 Wet Stripper/Developer: Capability Hollmuller Siegmund (MacDermid) 1993 Up to 15 width Designed for Develop & Strip Heated tanks (three process and two rinse) Stripper: Stainless Steel (DuPont Riston II S-1100X) Developer: Polypropylene (DuPont Riston II D-2000) Air Knife Currently rebuilding web handling 44

45 Precision Lithography: Capability AzoresCorp, 2006 Based on proven FPD stepper 8 width, can handle up to 24 with new chucks g-line (436 nm) 4 µm L/S 230 to 760 mm/min 400 ppm distortion compensation Requires hole-punch pattern for pre- alignment: 45 Web handlers in test

46 Other Printing Methods A B Silicone pad C D Cliche Ink Substrate Transducer Ink reservoir E F Nozzle Substrate 46

47 Inkjet Methods Thermal Inkjet Printing Piezoelectric Inkjet Printing 47

48 Ink Jet Printing A Surface energy pattern Ink droplet B 500 nm C 48

49 Drop Spreading A B channel drain C gate source 100 µm 49

50 Wetting Control Surfactant molecules PEDOT A PEDOT/surfactant PEDOT B 50 µm C 50

51 Ink Jet Circuits A B B C 51

52 Printed Designs 52

53 Soft Lithography Umbrella term for unconventional lithography Includes molding, embossing and printing. Recent reviews: Gates, B.D. et al, Chem. Rev. 2005, 105, 1171 Gates, B.D. et al, Annu. Rev. Mater. Res. 2004, 34, 339 Resnick, D. J. et al, Materials Today, 2005, 8, 34 Included in ITRS roadmap (2010) 53

54 Comparison of Imprint Lithographies Christie R. K. Marrian and Donald M. Tennant, Nanofabrication, J. Vac. Sci. Technol. A 21(5) S

55 Step and Flash Process T. Bailey, B. J. Choi, M. Colburn, M. Meissl, S. Shaya, J. G. Ekerdt, S. V. Sreenivasan, and C. G. Willson, Step and flash imprint lithography: Template surface treatment and defect analysis, J. Vac. Sci. Technol. B

56 Sub-100 nm Features

57 Microcontact Printing (µcp) Uses a soft stamp to apply ink to a substrate Soft Stamp (i.e. PDMS) Wet with Ink i.e. thiol. Soft Stamp (i.e. PDMS) Transfer Ink Press Stamp Substrate, typically a metal Etch Ink binds by Chemisorption of Physisorbtion Forms self assembled monolayer (SAM) 57 at point of contact with substrate

58 Fabrication of Stamps for Soft Lithography Photoresist Hard Substrate Elastomeric pre-polymer Expose + Develop Cure/Heat Peel off Etch Elastomeric polymer Use as Hard Mold or. Use to make soft stamp Hard substrates include quartz, SiO 2, Cr. 58 Soft stamps made from PDMS, PFPE

59 Pros and Cons of µcp Can generate large patterns of SAM s (>cm 2 ) across curved surfaces. (Delamarche, E. et al. Langmuir 2003, 19, 8749) Good for fictionalization of surfaces for different applications, i.e. biomaterials (Brock, A. et al, Langmuir 2003, 19, 1611) Resolution depends on binding of ink to substrate. Can t be considered a universal method. 59

60 Nanoimprint lithography (NIL) Uses rigid mold (i.e. silicon) Ridged Mold Ridged Mold Ridged Mold Substrate Polymer Film Substrate Ridged Mold Substrate Heat > T g and Imprint Cool < T g Release Mold Etch, etc. High Temp., High Pressure High viscosity medium Can be difficult to fill all voids in the mold and obtain uniform patterns 60

61 Applications of NIL Extension of process used to make DVD s, holograms etc. SEM images of structures patterned by nanoimprint: (a) 10-nm diameter metal dots with a periodicity of 40 nm, and (b) Fresnel zone plates with a 125-nm minimum line width. (c) SEM image of features patterned by SAMIM. 61 Gates, B.D. et al, Annu. Rev. Mater. Res. 2004, 34, 339.

62 Problems with NIL Density of patterning layer Easiest Easy Very Difficult! (Slide Courtesy of G. Willson) Base layer Solution? Use a low viscosity patterning layer 62

63 Step-and-flash Imprint Lithography (SFIL) etch barrier Dispense Imprint Expose template release treatment UV Cure transfer layer Etch barrier: UV Curable monomer (low viscosity) Avoids density problems with NIL Residual layer (Slide Courtesy of G. Willson) Separate Breakthrough Etch Transfer Etch Halogen RI Etch 63 O 2 RI Etch

64 Composition of the Etch Barrier O 2 Etch Resistance X-Linker (Lowers Viscosity) UV Free- 64 Radical Initiator

65 Resolution of SFIL 30 nm 20 nm 20 nm Resolution theoretically limited by template Pattern fidelity not so good for small feature sizes-still some interaction between template and etch barrier (Slide Courtesy of G. Willson) 65

66 Step-and-Flash Imprint Lithography (SFIL) Low cost, potential for step-and-repeat process Formation of multilayer structures possible SEM images showing cross sections of multi-tiered structures on a template fabricated with alternating layers of ITO and PECVD oxide. Johnson et al., Microelectron. Eng (2003), 67,

67 Soft Lithography: Summary Low cost compared to Photolithography Potential for Step-and-repeat processes SFIL looks most promising technique Pattern fidelity issues must be overcome! Materials Chemistry Solution? 67