Download Lithography - Chemical Engineering IIT Madras

Index
 Focussed Ion Beam (more of a preparatory tool)
 Thickness measurements
 Ellipsometry, Interferometry, pulse technology
 SIMS
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FIB
 Similar to sputtering in some respects
 Generates beams with Liquid Metal Ion Source (LMIS)
 typically Gallium
 Steered using electric and magnetic fields
 Energy ~ 100 keV (flexible)
 Used for micro machining
 In Failure Analysis (FA)
 Use voltage contrast method in SEM to identify failing via in
a chain
 Use FIB to ‘cut’ the failing via
 Tilt the sample and obtain SEM
 Implant dopant in select areas with out mask (mainly for
modification)
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Thickness Measurement
 Optics: Amplitude, Phase, Polarity
 Linearly polarized light, circularly and elliptically polarized
 Phase difference = 90 degree, circle
 Phase difference = 0 degree, linear
 Polarizer / Analyzer, Quarter Wave Plate
 Fast axis, slow axis
 Combination of Polarizer + QW Plate can change linear
poliarized to elliptical polarized and vice versa

 Reflection in thin film:
 P and S components undergo different phase shifts
 polarization of reflected light depends on film thickness and
refractive index
 and wavelength of light
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Thickness Measurement
 Optics: Amplitude, Phase, Polarity
 Linearly polarized light, circularly and elliptically polarized
 Phase difference = 90 degree, circle
 Phase difference = 0 degree, linear
 Polarizer / Analyzer, Quarter Wave Plate
 Fast axis, slow axis
 Combination of Polarizer + QW Plate can change linear
poliarized to elliptical polarized and vice versa

 Reflection in thin film:
 P and S components undergo different phase shifts
 polarization of reflected light depends on film thickness and
refractive index
 and wavelength of light and angle of incidence
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Ellipsometer
Stokes’ Ellipsometer
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©Gaertner Scientific
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Ellipsometer
 Can measure thin metallic films (semi transparent)
 Non contact, non destructive technique
 Can also vary angle
 Angstrom level accuracy
 Newer techniques
 Stokes Ellipsometer
 Does not have moving parts (polarizer or analyzer)
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Interferometry
 Light from 200 to 800 nm
(Deuterium and W or Halogen lamps)
 Reflected light intensity vs
wavelength detected
 Film stack quality must be known
 Not as accurate as ellipsometery
 Also cannot be used (accurately) to
determine refractive index
 real and imaginary quantities
 Refractive index, exitinction
coefficient
Cheaper than ellipsometer
 (Another name; Spectral Reflectance )
© Nanometric
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Interferometry
 Wavelengths used from about 200nm to IR (1700 nm) in some
cases
 Plot of model vs experimental (to check for convergence)
 If film is very thin (less than one
cycle of oscillation), difficult to measure
 many stacks are also difficult to
measure
 May not give unique solution
 Remember n and k depend on
wavelength
 Even for reasonably thick film,
(single layer), approx thickness must be
known
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Pulse Technology
 Use a laser pulse to heat the surface
 Thermal expansion and contraction result in ultrasonic sound
generation
 Various interfaces reflect the pulse
 Pioneered by Rudolph Tech
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