18 Printing 10

18 Printing 10 - Printing This lecture covers optics and...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
The development of exposure equipment has been a major driving force in technological advancements in the semiconductor industry Projection (far field) systems now dominate Are capable of astonishing CD definition using resolution enhancement techniques Alignment (overlay) is now in the tens of nm range! Printing This lecture covers optics and the exposure equipment used in lithography…
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Huygens Principle Each point on a wavefront acts as a source of waves Small features produce large diffractive effect Diffraction “Blurs” pattern Slit acts as optical low pass filter If slit is large, secondary wavefront has large radius of curvature If slit is small, (~ λ ) secondary wavefront has small radius of curvature I x
Background image of page 2
Real intensity profiles Mask transmission 2 - 98% Ideal energy transmission intensity Practical energy transmission intensity near diffraction limit MTF = I m /I o I o + I m I o - I m Modulation transfer function UV light, intensity I s I s
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Rayleigh criterion Energy transmitted x x 80 % Sum 2b At “Rayleigh Limit” where features are just resolved b Min pitch = 2b This is the operational region for IC lithography Light source Light source
Background image of page 4
Optical systems Near field – Fresnel diffraction e.g. contact or proximity printing Rarely used in advanced IC production - Mask and/ or wafer damage due to scratches - Registration errors due to differential expansion - 1:1 mask required Far field – Fraunhofer diffraction e.g. projection printing These systems dominate!
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Lens figure of merit: Numerical Aperture NA measure of a lens’ capability resolve images at plane of optimum focus α Parallel light 2 α is angle of acceptance Refractive index of surrounding medium , n (=1 for air) α sin n NA = Focal plane d f
Background image of page 6
Implications of Numerical Aperture Values range around 0.5 Rayleigh resolution limit is: So larger NA resolves smaller lines and spaces Better resolution at smaller λ (distortion correction easier at one wavelength) High NA comes at a price of a large lens aperture with consequent distortions 2 b k NA = * λ The “process factor” k ~ 0.6 for Rayleigh limit but recall that resist contrast can enhance ‘resolution’ so k values less than
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 34

18 Printing 10 - Printing This lecture covers optics and...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online