1. Thin film technology, intro lecture

2. This lecture Thin films vs. bulk Thickness dependent properties
Deposition processes in general
Growth modes and structure
Structural and interfacial stability
Interfaces and multilayer films
Film quality
Film characterization measurements

3. Thin films vs. bulk Properties different from bulk materials Density
Resistivity
Thermal conductivity
Refractive index
Dielectric constant …
Properties & structure thickness dependent

4. Thickness dependent resistivity

5. Thickness dependent dielectric constant
Atomic Layer Deposited SrTiO Vehkamäki

6. Thickness dependent structure
ALD deposited ZrO2: the 4 nm thick film is amorphous but the 12 nm thick film is polycrystalline, from ref. Kukli 2007.

7. 1D & 2D structures
Freund & Suresh

8. Generic deposition process

9. Starting surface Starting surface extremely important
Film structure depends on starting surface
Film adhesion depends on starting surface
Surface preparation before deposition
-baking (thermal)
-etching (chemical)
-bombarding (physical)
Cleaning either
-ex-situ (just prior to loading into reactor)
-in-situ (in the deposition reactor)

10. Starting surface (2) Chemical nature: passive or active surface groups
Physical nature: smooth, porous
Stability: thermal, chemical, UV
Softness/hardness: film growth on surface or penetration into substrate

11. PVD: Physical Vapor Deposition

12. PVD films
Poortmans: Thin film solar cells

13. CVD: Chemical Vapor Deposition
gas phase convection
diffusion through boundary layer
surface processes
(adsorption, film deposition, desorption)

14. CVD step coverage

15. ALD: Atomic Layer Deposition
Precursors introduced in pulses, with purging in-between

16. ALD: surface reactions

17. Plasma enhancement
CVD & ALD can be run at lower T in plasma enhanced mode
Activation of gas phase processes
Activation of surface processes
UV activation as a byproduct

18. Temperature ranges Liquid phase processes: LB, ECD, ... RT
PVD: RT but can be run at elevated T
ALD: oC
PECVD & PEALD: oC
CVD: oC

19. Film viewpoint amorphous nanocrystalline microcrystalline
polycrystalline
epitaxial
textured
Allen: MEMS

20. Epitaxial films No lattice match Polycrystalline film
Lattice match + other conditions  epitaxy possible but not guaranteed

21. More complex films non-stoichiometric: TiN vs. TiNx, x≈0.8
hydrogenated: a-Si vs. a-Si:H, 30 at% H
doped: USG vs. PSG, 5 wt% phosphorous
metals, oxides: 1-5% dopant
polysilicon: dopant
porous (on purpose !)
oriented crystals (piezoelectric, magnetic)

22. Doped oxides
SiOxCyFz
SiO2

23. Multilayer films Al
SiO2
SiNx W
Ti/TiN

24. Generic structure surface interface 2 interface 1 thin film 1
substrate
thin film 1
thin film 2
surface
interface 2
interface 1
thin film 1

25. Interfaces
Stability of interface in subsequent processing and during use ?
Barrier layers: extra films to stabilize interfaces

26. Annealing: chemical reactions
Surface reaction:
Titanium nitride formation
2Ti + N2  2 TiN
<Si> Ti N2
heat
Interface reaction:
Titanium silicide formation
Si + 2 Ti  TiSi2

27. Annealing: physical effects

28. Copper for IC metallization
General:
low variation
low particle generation
large process window
Barrier:
t < 10 nm thick
ρ < 500 µΩ-cm
Cl conc. < 2%
unif. < 2%
step coverage >90%
rate > 3 nm/min
Low-k:
CMP compatible
Tdepo < 400oC
adhesion on etch stopper
Copper seed
t > 2 nm
step coverage ~100%
rate > 10 nm/min
growth and adhesion on etch stopper
Etch stopper:
growth and adhesion
on dielectric
on barrier

29. Acoustic multilayers Al (300 nm) Mo (50 nm) ZnO (2300 nm) Au (200 nm)
Ni (50 nm)
SiO2 (1580 nm)
W (1350 nm)
TiW (30 nm)
TiW (30 nm)
glass wafer

30. Magnetic multilayers 1 nm CoFe 2.6 nm Cu 2.5 nm CoFe 0.8 nm Ru
substrate
5 nm Ta
15 nm PtMn
5 nm NiFe

31. Film quality (1) High density (non-porous) Defect-free
Low impurity content
Low stress (or tailored stress)
Stability
Smoothness ?
SiO2/Ti; Weileun Fang

32. Is smooth good ? Fluorine-doped zinc oxide (FZO)
(Poortmans)
Superstrate solar cell:
Repmann

33. Film quality (2) Uniformity: Homogeneity:
across-the-sample uniformity of thickness, resistivity, refractive index…
Usually given as U = (max-min):(2*ave), 1-10% typical
Homogeneity:
film has same structure and composition all over
e.g. grain size or dopant concentration is independent of position,
no stress gradient, no interfacial layer, …

34. Inhomogenous films
e.g. phosphorous-doped oxide with phosphorous gradient (and therefore refractive index gradient)
Grain size gradient
Messier 1986 JVST
GLAD/sculpted film: rotation and inclined deposition used to create inhomogenous film on purpose (evaporated MgF2; Messier book)

35. Structure variants SiH4 + nH2  Si + (n+2) H2
Percentage of silane increasing

36. Use quality
Is this material compatible with our environment (e.g. tissue) ?
Is this film erosion resistant in our application ?
Is this film free of pinholes ?
Does the film have spikes/protrusions ?
Are the impurities mobile ?
Getter films (consumed during use on purpose)

37. Productivity measures
Deposition rate
Thru-put (very different from rate !)
Yield of precursors (source gases/targets expensive)
Deposition on various substrates (e.g. porous)
Uniformity across the substrate
Uniformity across the batch
Repeatability run-to-run
Repeatability day-to-day

38. Film characterization needs
-spatial resolution (image spot size)
-depth resolution (surface vs. bulk properties)
-elemental detection (constituents, impurities)
-structural information (grain structure)
-dimensional characterization (thickness)
-mechanical properties (curvature, stress,…)
-surface properties (roughness, reflectivity,…)
-top view vs. cross sectional imaging
-defects (particles, pinholes,…)

39. Sputtered TiN characterization