Antireflex coatings

Antireflex coating ARC @ INESC: 150, 400Å TiWN2

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

Multilevel exposure

Wafer processing - Vetching / lift-off process

NEXT WEEK

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

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)

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 0.01m 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

E-beam lithography comercial systems

Ion Beam lithographyAdvantages:

•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

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/cm2

Ion Specimens : H, He, Ar, Hf, Ga, Si, Au, Co, Pr, P+, BF2+, etc…

ΔE ~ 6 eV (75KeV)

ΔE ~ 0.5 eV (75KeV)

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

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