Biomedical Engineering Reference
In-Depth Information
Electron source
CAD system
Pattern control
Condenser optics
Blanker
Optics control
Deflector
Projection optics
Substrate
X/Y stage
Vacuum chamber
Figure 12.2
(See companion CD for color igure.)
.Major.elements.of.an.EBL.system.
maintaining.pattern.idelity..The.maximum.delection.range.available.to.typical.Gaussian.
EBL. systems. is. approximately. 1.mm
2
. with. many. systems. operating. below. that.. Since.
substrates.are.usually.much.larger.than.the.delection.range,.the.last.major.component.
of.the.patterning.subsystem.is.the.X/Y.stage..Existing.commercial.systems.have.a.range.
of. motion. suficient. to. pattern. anywhere. on. 300.mm. wafers.. Other. commercial. entry-
level.systems.are.available.with.stages.sized.for.smaller.substrates..Most.systems.support.
some.sort.of.holder.for.irregular.shapes,.a.distinct.advantage.in.the.R&D.environment..
High-end.EBL.systems.use.laser.interferometry.to.gauge.the.position.of.the.stage.with.sub-
nanometer.accuracy..This.allows.patterns.larger.than.the.delection.ield.to.be.exposed.
by.stitching.together.ields.with.each.ield.containing.a.subset.of.the.larger.pattern..All.
of.this.equipment.must.operate.in.a.high.vacuum.which.brings.its.own.set.of.challenges.
to.equipment.designers.
12.3.1 resist
Without.a.surface.that.can.be.modiied.with.the.electron.beam.there.can.be.no.lithography..
For. conventional. EBL,. the. electron. beam. induces. solubility. changes. in. the. resist.. For.
positive. tone. resists,. the. e-beam. exposure. reduces. solubility.. For. negative. tone. resists,.
the. e-beam. exposure. increases. solubility.. Resist. sensitivity. is. commonly. measured. in.
