Positive Tone Electron Beam Resists:

ZEP520A generally needs about 20% less dose as PMMA and so write times are generally faster, although this depends a lot on exact develop conditions. Also, ZEP520A has generally about 2X the plasma etch resistance as PMMA, which can be helpful when etch selectivity is a concern. However, ZEP520A is expensive costing over 25X the cost of PMMA.

process conditions
spin speed curves
dose vs. depth curve for 20x40um feature
Comparison of Resist Thickness to Sensitivity
required dose for 50, 80, 100nm diameter circles
ZEP520A base dose on different substrates
ZEP520 process monitor (04/25/2012)
Alignment Characterization(04/03/2012)
Optimization Research on ZEP520
Comparison of ZEP520 to PMMA

PMMA is one of the oldest and most reliable electron beam resists in existence. It has excellent resolution. It is easier to remove than ZEP520A and so works better for liftoff processing. It is also relatively inexpensive.

process conditions
spin speed curves
Example of dose sensitivity curve (dose squares) and 100 nm line and space pattern.
dose vs. depth curve: 600nm PMMA on 1000A Si02
effect of resist thickness on base dose
Comparison of PMMA to ZEP520

Negative Tone Electron Beam Resists:

Being an inorganic material, HSQ has excellent plasma etch resistance and selectivity to silicon. It also has excellent resolution with some of the smallest features reported. However, HSQ needs high dose (~3X higher than PMMA), resulting in long write times and also can have some inconsistent and unusual behavior. It has higher line edge roughness than positive tone resists and can show field and subfield stitching errors more readily than positive tone resists.

HSQ resist process
HSQ Spin Curve

determining base dose for HSQ for thickness 15 to 100 nm
HSQ optimization study using 6% HSQ and 2 nA beam current

dose-depth curves for different post apply bake conditions

dose-depth curves for different develop conditions

Study 1 for hot plate bake and oven bake.
Study 2 HSQ contrast


minimum 6.5 nm isolated line using diluted HSQ and 100 pA beam current
10 nm dots on 40 nm pitch using "dots on the fly" technique

subfield stitching errors in curved structures
ring structure comparison with Argonne
ring structure before/after blank amp and with Ming Lu (BNL) conversion

HSQ dose vs. CD for 60nm squares
HSQ thickness uniformity on 200mm silicon wafers

pattern exposure order dependence in HSQ

journal publication list of HSQ and EBL
journal publication list of HSQ material and chemical properties
journal publication list of miscellaneous work on HSQ

ma-N is a polymer and is useful for liftoff processing on glass because ma-N can be removed with organic solvents whereas HSQ needst to be removed with BOE (HF) and this undesirably aslo attacks the glass substrate. ma-N is also exposable by DUV wavelengths. However, ma-N generally has lower resolution than HSQ and ma-N can also have adhesion problems.

process
maN-2403 dose sensitivity curve