Semion SystemRetarding Field Ion Energy Analyzer“

• 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

Nickel Grid Structure

• Electron microscope image of a nickel grid

• Average ion energy• Ion flux

IV Curve and Calculated IED

• 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

Installation

• 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

IED Shape

Semion Electronics

Generator Match Plasma Reactor

Computer

Results DC Sheath - Pressure

Semion Electronics

Generator Match Plasma Reactor

Computer

Results RF Sheath - Bias

Semion Electronics

Generator Match Plasma Reactor

Computer

Results RF Sheath - Frequency

Spatial Uniformity

Spatial Uniformity

Spatial Uniformity

Spatial Uniformity