3. Antireflex coatings Antireflex coating ARC @ INESC: 150, 400Å TiWN 2 Resist was exposed both to the light source and to reflected beams from resist/sample interfaces Impact of standing waves on the developed resist Problem solved after coating the film with an anti-reflex material (e.g. oxinitride) before exposure

4. Multilevel exposure

5. Wafer processing - V etching / lift-off process NEXT WEEK

6. Next generation lithography - Air environment - Complex mask fabrication ($4k-$12k) - Resists have low sensivity - High cost X-ray sources - vacuum environment - direct write systems (software masks) -slow writting over large areas - very high system cost

7. X-ray lithography Advantages: No vacuum environment required (no charged particles involved) Very small wavelength (< 14Å) - can produce 0.15 µm features High reproducibility (exposure independent of substrate type, surface reflections) Disadvantages: No optics involved – limited to 1:1 shadow printing (no image reduction is possible) Very expensive and complex mask fabrication (~10 days, cost is $4k-$12k) Low sensivity of the resists High cost of sufficiently bright X-ray sources (e.g. Synchrotron)

8. E-beam lithography Leica EBL-100, shown here with a 100 kV LaB6 electron source and a conventional SEM stage. The system is also available with a TFE source and laser-controlled stage. (Courtesy of Leica Lithography Systems Ltd.) COSTS ~$1M, for 2 inch areas maximum. Advantages: vacuum environment required (charged particles involved) Direct write system (software mask) the smaller the beam sizes, the better the resolution can produce down to 0.01  m features low defect densities At 30 keV, electrons travel >14  m deep into a resist layer Disadvantages: Very expensive system Slow writting 10-100 keV electron beam

9. E-beam lithography comercial systems

10. Ion Beam lithography Advantages: Computer-controlled beam No mask is needed Can produce sub-1 µm features Resists are more sensitive than electron beam resists Diffraction effects are minimized Less backscattering occurs Higher resolution Ion beam can detect surface features for very accurate registration Disadvantages: Reliable ion sources needed Swelling occurs when developing negative ion beam resists, limiting resolution Expensive as compared to light lithography systems Slower as compared to light lithography systems Tri-level processing required

11. Paul Scherrer Institute Electrom Beam Lithography System Co-axial Ion Source Multi-Cusp Ion Source http://lmn.web.psi.ch Ion Beam Source Ion Optics Vacuum Chamber Ion energies : 20 eV - 200 KeV Beam Current : up to 500 A/cm 2 Ion Specimens : H, He, Ar, Hf, Ga, Si, Au, Co, Pr, P+, BF2+, etc… ΔE ~ 6 eV (75KeV) ΔE ~ 0.5 eV (75KeV)

12. Focused Ion Beam Lithography (FIBS) Ion Beam Cannon Scanning Beam Exposure System  Feature size is limited by spot size  Can take up to 6 orders of magnitude longer than mask projection technology, depending on sample size ⇨ Not suitable for Industrial Purposes  Allows the exposure of very complex patterns in only one lithography step

13. Bibliography - VLSI Technology, S.M.Sze, McGraw-Hill International Editions - Nanoelectronics and information technology – Advanced Electronic Materials and Novel Devices, Rainer Waser (Ed.), Wiley-VCH (2003) - Microsystems: mechanical, chemical, optical, S.D.Sentura, M.A.Schmidt and J.Harrison, MIT press - Fundamentals of Microfabrication – The science of miniaturization, Marc J.Madou, CRC press (2002) - Spin Electronics - Chap.16, M.Ziese and M.J.Thornton (Ed.), Lecture Notes in Physics, Springer-Verlag http://www.cnf.cornell.edu/spiebook/toc.htm http://semiconductorglossary.com/default.asp?searchterm=lithography