1. Why do we need “high-k” ? Why do we need ALD ? What is ALD ?
Lecture 4: High-k Dielectrics and Atomic Layer Deposition
Why do we need “high-k” ?
Why do we need ALD ?
What is ALD ?

3. Origin of the High k (or e0)
Since
High k must be generated from the ionic contribution
Lyddane-Sachs-Teller relation
Medium k requires large lattice polarizability (large splitting between
longitudinal and transversal optical phonon frequencies). HfO2, Y2O3, ...
Even higher k can be achieved through soft phonon (wTO 0) driven lattice
instability (near paraelectric to ferroelectric phase transition). SrTiO3, BaTiO3
-Ran Liu

4. Band Gap and Dielectric Constant of Potential Gate Dielectrics
- Ran Liu

5. Band Offsets of Dielectrics with Si
Source: John Robertson (Cambridge University), J. Vac. Sci. Technol. 18, 1785 (2000)
k=20-30
k very large
k=4

6. Schematic of the ALD process showing the division
of reaction into two self-limiting steps.
1st Reactant
2nd Reactant
Chemical Reaction A
Chemical Reaction B Self-limiting !
For example: HfCl4 + H2O on Si H-terminated Surface

7. Main Stream: HfO2 on Si (at the beginning)
HfSiON on Si (state-of-the-art)
Bright Field
BF image of HfO2 after 850C anneal
-from Glen Wilk/ASM

8. Effects of Annealing on crystal structure
poly-Si
HfO2
Si(100)
60 Å HfO2 annealed at 600ºC/30 sec in O2 – large grain poly-xtal

9. Hydroxylated GaAs Surface
ALD Growth of Al2O3 from Al(CH3)3 and H2O
N2, Al(CH3)3 Flow 
N2 Flow  Al
CH3 H
CH3 Al
CH3 Al
CH3 Al
CH3 Al
CH3 Al
CH3 Al
CH3 O O O OH OH OH O O O
GaAs Substrate
GaAs Substrate
GaAs Substrate
Hydroxylated GaAs Surface
Reaction with Al(CH3)3
Purge Al(CH3)3, CH4
-Ga-OH+Al(CH3)3
=> -Ga-O-Al(CH3)2+CH4
-Ga-O-Al(CH3)2+2H2O
=> -Ga-O-Al(OH)2+2CH4
N2, H2O Flow 
N2 Flow  H OH H
CH3 H
CH3 H OH H OH H OH H OH OH
CH3
CH3 OH OH OH OH OH Al OH Al OH Al Al Al Al O O O O O O
GaAa Substrate
GaAs Substrate
Reaction with H2O
Purge H2O, CH4

10. No native oxide visible
Native Oxide on GaAs
After ALD Al2O3 Growth
glue
Al2O3
Native Oxide
No native oxide visible
GaAs
GaAs
2 nm
2 nm
2 nm native oxide consumed/removed during ALD Al2O3 process
Native oxide not desorbed at 300C, reaction during ALD causes consumption
By D.A. Muller Bell Labs/Lucent Technologies

12. If you want to have ALD films, read JAP 97, 121301 (2005) and talk with me

17. 3 pages more….

18. ALD can be done at room temperature
using volatile procusors.
ALD as a universal dielectric deposition
technique can find wide applications in
varies of fields except for Si CMOS

19. ALD application in CNTFETs
Device Structure : oxide ( A Al2O3 or 200 A HfO2)
ALD Al2O3 or HfO2
Sungkok Kim by Prof. Mahammadi G
= 1.6uS (SiO2)
= 1.67 uS (ALD Al2O3)
gm becomes 10 times larger using ALD dielectrics