Advanced microfabrication 2017 Parallel patterning techniques sami franssilaaalto
Advanced microfabrication 2017 Parallel patterning techniques sami. franssila@aalto. fi
Timetable Week Date Topic 1 14. syys Intro: lithography 1 2 21. syys Intro: lithography 2 3 28. syys ALD launch 4 5. loka Student talks 1 5 12. loka Student talks 2 6 19. loka Student talks 3 interm week, no teaching 7 2. marras ALD midterm checkpoint 8 9. marras Bonding 9 16. marras C-SOI checkpoint 10 23. marras C-SOI final (Okmetic) 11 30. marras ALD final (Beneq)
Optical lithography with a mask a) film growth b) resist spin c) UV exposure d) development e) etching f) resist strip
Contact lithography Optical: gap= 0 µm d= 0. 1 µm gap λ = 193 nm èMinimum ~ 100 nm d = resist thickness
Image reversal • The image reversal capability is obtained by a special crosslinking agent in the resist formulation • It becomes active at temperatures above 110°C and - what is even more important - only in exposed areas of the resist. • The crosslinking agent together with exposed PAC leads to an almost insoluble (in developer) and no longer light sensitive substance. • The unexposed areas still behave like a normal unexposed positive photoresist. • After a flood exposure (no mask required) these areas are dissolved in standard developer for positive photoresist, the crosslinked areas remain. • The overall result is a negative image of the mask pattern.
Image reversal (AZ 5214)
Backside exposure Sensors and Actuators A 136 (2007) 412– 416
Backside non-collimated J. Micromech. Microeng. 18 (2008) 125015
Patterning inside microstructures A M Tentori and A E Herr 2011
Thick resists Do we assume resist absorption to be the same for unexposed and exposed resist ? How does exposure behave if absorption is constantly chaging ?
Profile shape In the calculation of resist wall profile, we assume that the resist thickness is much larger than the wavelength of exposure UV light and the horizontal diffraction distance is much smaller than the resist thickness. Microsystem Technologies 8 (2002) 308– 313
Thick SU-8 exposure J. Micromech. Microeng. 17 (2007) R 81–R 95
Optical projection lithography Sources of radiation (UV 365 nm-436 nm, DUV 193 nm-248 nm, EUV, X-rays, electrons, ions) Optical system I (lenses, mirrors) Mask (pattern) Optical system II (lenses, mirrors) Numerical aperture NA=sin Imaging medium (resist) Wafer (with patterns) Wafer stage (alignment mechanism)
Stepper lithography Resolution = k 1 /NA Depth of focus = k 2 /NA 2
Projection lithography scaling Resolution = k 1 /NA Depth of focus = k 2 /NA 2 Lin, MEMS 2010
Grey-scale lithography Ghodssi, JMEMS 2009
Double exposure grey scale Ghodssi, JMEMS 2009
(sub)resolution dimensions Ghodssi, JMEMS 2009
Moulding vs. imprinting Transport of material into mould vs. modification of existing material
Carbon black PDMS mask for UV
Replication: terminology jungle • • • Soft lithography Micro Contact Printing (µCP) Nanoimprint lithography (NIL) Hot embossing Lithography (HEL) Thermal nanoimprint (T-NIL) Step-and-stamp imprint lithography (SSIL) Step-and Flash Imprint Lithography (S-FIL) UV-embossing/ UV-NIL Injection molding (IM) Replication Moulding/molding
Imprinting/embossing • Press 3 D master into softened polymer • Remove after cooling below Tg Apply photofilm Press together Stamp release Residue clearing
Thermal NIL system force press soft compliance layer master polymer substrate heater vacuum pumping
Nanoimprint Lithography stamp Si, Si. O 2 thermoplast, Tg 60 -120 o. C PMMA, Tg ~ 100 o. C resist transferlayer Si, Si. O 2 substrate MIC – Department of Micro and Nanotechnology Anders Kristensen
Nanoimprint Lithography Temperature T 1 ~ Tg + 80 o. C P 1 ~ 100 – 1000 k. Pa T 2 ~ Tg - 20 o. C Pressure Release imprint pressure, when resist has hardened P 1 Tg T 2 20 o. C 0 0 timprint~ 1 – 10 minutes MIC – Department of Micro and Nanotechnology Anders Kristensen time
Nanoimprint Lithography Residual polymer layer hf ~ 10 – 100 nm MIC – Department of Micro and Nanotechnology Anders Kristensen
Nanoimprint Lithography Transfer resist pattern – e. g. etching MIC – Department of Micro and Nanotechnology Anders Kristensen
NIL results
Nanoimprinted Photonic Crystal Devices Silicon stamp: High lateral resolution Protrusion height ~ 100 nm Anders Kristensen
Requirements for replication -no undercut structures -smooth surfaces (with low surface energy) -no reaction between master and polymer -temperatures above Tflow -possibly intermediate release layers
Student talk topics 1 Positive resists 2 Negative resists 3 E-beam resists 4 DUV resists (Chemically Amplifdied Resists) 5 T-NIL resists 6 UV-NIL resists 7 Dry sheet resists 8 Spray-coated resists 9 Thick negative resists 10 Thick positive resists 11 Photopatterning OSTE 12 Hybrid and inorganic resists 13 Lift-off resists 14 Resist stripping 15 Resist flow 16 Block co-polymer patterning 17 Antireflection coatings with resists BARC/TARC
Half-time
- Slides: 32