• Wafer processing controlled by energy and flux of bombarding ions
e.g. etch rate, etched feature quality• Ion energy measurement critical for process development• Wafer usually processed using RF excitation
typically, 2-60MHz• Difficult conditions in which to measure IED - electrical
filtering, high temperatures, sensor etched or coated during processing
• RFEA sensor for IED measurements developed, easily incorporated into existing reactors, compatible with majority of substrate bias conditions
Importance of ion energy distribution (IED) measurements
RFEA Schematic
-60V
0 to +V
-70V
-60V
+
Aperture
-
G1
G2
G3
C
G4
Insu
lato
r
Filter
Filter
Filter
Filter
Plasma
I
• Orifice diameter < Debye length λD
e.g. Te=3eV, Ne=1017m-3 …… λD~40µm
• Ion transit length < Ion mean free path λi
• RFEA depth 0.6mm ~ 100mTorr in Argon
Design considerations
Semion Electronics
Generator Match Plasma Reactor
Computer
Installation
• Located at any location inside a plasma reactor• Floating, RF bias, grounded• Connected through a vaccum port via ceramic beaded
cable
• Shape of IED determined by sheath potential, ion transit time and period of sheath potential waveform.
• For DC sheath, <E>~<Vs>, E~0
-60V
0 to +V
-70V
-60V
+
Aperture
-
G1
G2
G3
C
G4
Insu
lato
r
Filter
Filter
Filter
Filter
Plasma
I
IED
• For rf modulated sheath:• Ion transit time =
IED
-60V
0 to +V
-70V
-60V
+
Aperture
-
G1
G2
G3
C
G4
Insu
lato
r
Filter
Filter
Filter
Filter
Plasma
I