E beam Flashcards
Achieving high-resolution
- High electron energy
- Low beam current
- Low-sensitivity resist
- Thin resist layer
- Optimized resist process
- Low pattern density
- Light and conductive substrate material
- Stable environment
Thermionic cathode
electrons have thermal
kinetic energy high enough to overcome
potential barrier (work function). Electrons
extracted by extraction electrode. Focused by
cathode lens to form the cross-over
Field-emission cathode
FE – sharp needle results in high field (≈10^8V/m), very small emission area, no need for cathode lens to focus emitted electrons
Focusing
Focusing depends on the
difference of voltage applied to
the lens elements and how rapid
is the change of potential
For stronger focusing power:
–Electrostatic lens: larger V different between electrodes or smaller gap, may lead to electrical breakdown
–Magnetic lens: higher coil current (dissipated by air/water colling) and smaller gap between poles
–Electrostatic lens generally have more aberrations (spherical, chromatic…), turning harder to focus small diameter beam
Space charge effect
– unique incharged particle optics, related with Coulomb repulsion, increases energy
spread and diameter of beam (higher
for higher current)
–Increased beam energy – reduction of space charge effect (without compromising beam current) and chromatic aberration
EBL systems – electron column
Electron gun
Electron gun alignment system –
Condenser lens
Beam blanking
Zoom lens
Stigmator
Apertures
Projection lens
Deflectors
Work stage
proximity effect
Scattering resulting from collisions of electrons with atoms in the sample lead to a larger area of energy deposition than the
original size of beam landing area
–Proximity effect is the main resolution limitation in EBL
Electron scattering and proximity effect
- Deposited energy from scattering electrons can extend to adjacent exposure areas if two patterns are too close to each other–distortion of exposed patterns.
- Even in same pattern, scattering can cause higher accumulated energy in the centre and lower energy near the edge.
- Proximity effect shows up in two aspects: intershape and intrashape.
- Smaller dose required for high density pattern
Correction of proximity effect
–dose correction (depending on pattern density)
–pattern size compensation:Most suitable for simple and highly repeated lines
Resolução e sensibilidade
For high-res, low sensitivity is prefered (but affects throughput) – low energy electrons, spreading from the center of
exposure area, only show their impact on resist pattern profile if sensitivity is very high
-E.g., SU8 is extremely sensitive to e-beam resist residues visible between patterns caused by BSE.
Residues would not occur for low sensitive resist.
Contrast
- Contrast quantified by the slope of development curves. Has critical
effect on resolution - High contrast facilitates pattern transfer by RIE and enables lithography of high-density patterns
–Even if low sensitivity resist is desirable for high-res, some high
sensitivity CA resists can be used due to their high contrast (allow
defining high aspect ratio profiles)
fotoresistes
- CA resists have higher sensitivity and improved RIE resistance over
PMMA - But CAR are very sensitive to processing conditions
