1. Chapter 5 Plasma and Ion Beam Processing of Thin Films
DC-, RF-, Magnetron-, Reactive- Sputtering
Target is a plate of the materials to be deposited.
DC sputtering(Diode or Cathodic sputtering)

2. - Film deposition rate depends on the sputtering pressure
and current variables
P  : sheath(cathode) is wide  Ions are far from target
(can be easily lost to the walls)
: Electron mean free path   ionization efficiency is low
 no plasma below 10 mTorr
P  : electron mean free path  and large ion current but
sputtered atoms undergo increased scattering
 not efficiently deposited

3. Disadvantages of DC sputtering:
Pd : discharge power density(W/cm2)
g : cathode-anode gap distance
ρ : atomic density
γe : Townsend secondary-electron emission coefficient
E : average sputtering energy
<Xth> : mean distance from the cathode sputtered atoms travel before they become thermalized
Disadvantages of DC sputtering:
After the thermalization, the depostion rate is decreased and there is no compaction or modification of deposited films.
Low deposition rate: increase the contamination level
Magnetron sputtering which operates in lower pressure is needed to overcome these disadvantages of DC sputtering. x

4. 5.2.4 AC(RF)-Sputtering (eq) For DC sputtering of SiO2
Target : Quartz disk with 0.1cm thick and  = 1016 cm
To draw a current density J=1mA/cm2, V=?
V=RI
For practical application, V=100 V and
 should be less than ~106 um
RF-sputtering is a suitable mean of depositing insulating thin films.
f > 50KHz : enough electrons to ionize gases(5~30MHz)
f < 50KHz : essentially DC sputtering at both electrodes
(ions follow the frequency changes)
Typically MHz is used : FCC (federal communications
commission) recommended

5. Target: powered electrode
Impedance-matching network(capacitor, inductor)
is needed to ensure the maximum power delivery x

6. Concept of target self-bias at RF electrodes
The disparity in electron & ion mobilities
 The positively charged electrode draws
more e- current than the negatively charged
electrode draws positive ion current
 no charge transfer through capacitor
 self – bias voltage (negative) at
target electrode (capacitively coupled
electrode)
Negative self-bias voltage to target is used in RF-sputtering or surface chemistry on the AC powered electrodes.

7. Electrode size effects
Both electrodes in RF sputtering system should sputter.
cause a contamination in the sputtered film.
The ratio of the voltage across the sheath at the small capacitively coupled electrode(Vc) to that across the large directly coupled electrode(Vd) including substrate and chamber walls, etc is given by
The fourth- power dependence means large Ad is very effective in raising the target sheath potential while minimizing ion bombardment of grounded fixtures.

8. Reactive sputtering
Simple inert-gas RF sputtering of insulating targets gives
low deposition rate and metal-rich films
Reactive sputtering eliminates disadvantages of
RF sputtering
- sputtering metallic target in the presence of a reactive gas
- eq). mixed with an inert gas (Ar)
oxides – Al2O3, SiO2, Ta2O5 (O2)
nitrides – TaN, TiN, Si3N4 (N2, NH3)
carbides – TiC, WC, SiC (CH4, C2H4, C3H8)

9. Hysteresis effects in reactive sputtering
A : doping, alloys
B : compounds
A : all N2 reacts with Ta film at low gas flow
 doped metal (Ta N0.01)
- atomic ratio of N to Ta
increases as N2 pressure increase
B : Compound formation on the metal
target : plasma impedance is effectively
lower in state B than in state A,
since ion-induced secondary electron
emission is much higher for
compounds than for metals. A B

10. 5.3 Magnetron Sputtering
Perpendicular Electric Magnetic Fields

11. In planar magnetrons, electrons are ideally trapped near the target,
enhancing the ionization efficiency.
- The most widely commercially practiced sputtering method
 high deposition rate ~ 1m/min for Al,
(10 times higher than conventional sputtering)
 reducing electron bombardment of substrate(reduce defects)
 extending the operating vacuum range(operate at lower pressure)

12. Substrate heating T t

13. : density
c : heat capacity
d : thickness
dT/dt : rate of temperature rise
p : incident power flux
Hc : heat of condensation
Ek : average kinetic energy of incident adatoms
Ep : plasma energy from electron, ion bombarding
L : heat loss
d• : deposition rate
: atomic volume
: Stephan-Boltzman
const.
 : emissivity

14. 5.5 Hybrid and Modified PVD Processes
5.5.1 Ion plating
- Relatively uniform coating of substrates with complex shapes
is achieved.
 coat steel and other metals with very hard films for use
in tools and wear-resistant applications.
Ti, Zr, Cr, Si in (N2, O2, CH4) + Ar plasma
 extremely good adhesion
 high “throwing power”  reduce shadowing effect
 near bulk density  suppress undesirable columnar growth
 RIP (reactive ion plating)
Nitrides, oxides, carbides

15. Activated reactive evaporation
Ion plating
Activated reactive evaporation
-2 ~ -5 KeV
ground, float, biased
inert gas
dc bias V e-

16. 5.5.2 Reactive evaporation process
- metal reacts with a gas to produce compound deposits
(oxides, carbides, nitrides)
- ARE (activated reactive evaporation) process
Plasma activation lowers the energy barrier for reaction
 compete with CVD
 no need for metal-containing compound gases

17. 5.5.4 Ion Beam Assisted Deposition(IBAD)
- Ion bombardment of films during sputter deposition is particularly
effective in modifying film properties.
Role of ion beams in IBAD
inert-gas ion beam to sputter atoms from a target to substrate
Inert ion (Ar+) or reactive ion (O2+) to modify film properties
during deposition by bombardment or chemical reaction.
- Use of broad-beam (Kaufman type) ion source x

18. x

19. Ion bombardment of films during evaporationx

20. Benefits from ion bombardment
Enhancement of adatom surface mobility
Stimulation of the early stages of film formation, e.g.,
nucleation, growth, and coalescence
Development of preferred crystal orientation
Lower substrate temperatures for the onset of epitaxy
Crystallization of amorphous films and amorphization of
crystalline films
Increased film/substrate adhesion
Modification of film adhesion
Stimulation of film-sorption effects and film surface reactivity
- Enhancement of density and refractive index of films x

21. 5.5.5 Ionized Cluster Beam (ICB) Deposition

22. - Ionized clusters affects film nucleation and growth
1. Increase the local temperature at impact
2. Surface diffusion of atoms is enhanced
3. Activated centers for nucleation are created
4. Coalescence of nuclei is fostered
5. Surface is sputter-cleaned
6. Chemical reactions between condensing atoms
and substrate are favored
- Strong adhesion, smooth surface, no columnar growth
low temperature growth, high quality single crystal growth
(epitaxial film), vacuum cleaness (10-7 torr)

23. 5.4 Plasma Etching
Plasma etching part 1
Plasma etching part 2