Antireflex coatings

3. Antireflex coatings Impact of standing waves on the developed resist Resist was exposed both to the light source and to reflected beams from resist/sample interfaces Problem solved after coating the film with an anti-reflex material (e.g. oxinitride) before exposure Antireflex coating ARC @ INESC: 150, 400Å TiWN2

4. Multilevel exposure

5. Wafer processing - Vetching / lift-off process NEXT WEEK

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

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 10-100 keV electron beam • 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 0.01mm features • low defect densities • At 30 keV, electrons travel >14 mm deep into a resist layer • Disadvantages: • Very expensive system • Slow writting 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.

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. ΔE ~ 6 eV (75KeV) Paul Scherrer Institute Electrom Beam Lithography System Multi-Cusp Ion Source http://lmn.web.psi.ch Ion Beam Source Ion Optics ΔE ~ 0.5 eV (75KeV) Co-axial Ion Source Vacuum Chamber Ion energies : 20 eV - 200 KeV Beam Current : up to 500 A/cm2 Ion Specimens : H, He,Ar, Hf, Ga, Si, Au, Co, Pr, P+, BF2+, etc…

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

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