20141103 thin film physics 2
TRANSCRIPT
-
8/10/2019 20141103 Thin Film Physics 2
1/29
1FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Epitaxy
-
8/10/2019 20141103 Thin Film Physics 2
2/29
2FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Epitaxial growth
Adatom movement is critical for epilayer growth At high temperature, low flux, epilayer is formed
Surface should be very clean: eg) with native oxide, poly Si will grow
? ?
-
8/10/2019 20141103 Thin Film Physics 2
3/29
3FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Heteroepitaxy
Commensurate : atomic spacing of overlayer is sameas that of substrate
Incommensurate : atomic spacing of overlayer is not same as that of substrate due to relaxed strain
Pseudomorphic(=coherent) : 1 to 1 correspondence between atomic rowsdue to strain
relaxed strained
Lattice constant ofsubstrate
Lattice constantof film
Lattice constant ofsubstrate
Lattice constantof film
=
(coherent)
-
8/10/2019 20141103 Thin Film Physics 2
4/29
4FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Condition for Heteroepitaxy: examples
-
8/10/2019 20141103 Thin Film Physics 2
5/29
5FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Terminology
Unit cell distortion according to Poissons ratio
//
//
//
//
as
af
as
substrate
Unstrained film
af
Strained film ?
?
?
?
-
8/10/2019 20141103 Thin Film Physics 2
6/29
FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Calculation of misfit and strain
Ex) substrateSrTiO3: as=3.905 filmLaAlO3: af=3.79Both STO and LAOcubic structure.
Misfit, f = l 3.905-3.79 l / 3.905 = 0.029
Pseudomorphic(coherent) growth af//= as: 3.905 af:3.57
// = (3.905-3.79)/3.79=0.03+3% (+) Tensile strain
= (3.57-3.79)/3.79=-0.058-5.8% (-) Compressive strain
=3.57-3.905/ 3.79 = 0.088 (8.8%)
as
af
as
SrTiO3
LaAlO3
af
?
?
(3.905-3.79)/3.?79=0.03+3%
(3.905-3.79)/3.?79=0.03+3%
(3.905-3.79)/3.?79=0.03
+3%
-
8/10/2019 20141103 Thin Film Physics 2
7/29
7FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Epitaxial relationship
-
8/10/2019 20141103 Thin Film Physics 2
8/29
8FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Heteroepitaxy growth mode
Growth modes : depending on surface/interface energy and strain caused by mismatch
(
)/
2. > and almost no misfit
3. > and misfit
1) 2)
1. < , regardless of misfit level
1. > , large misfit
-
8/10/2019 20141103 Thin Film Physics 2
9/29
9FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Relaxation
Strain relaxation by misfit dislocation formation.If ||=f, totally strained, and ||=0, totally relaxed
-
8/10/2019 20141103 Thin Film Physics 2
10/29
10FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Epitaxial relationship
hc
Gecomposition is highereasily relaxed
*GexSi1-xfilm / Si substrate*Critical thickness VS misfit
-
8/10/2019 20141103 Thin Film Physics 2
11/29
11FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Heteroepitaxy system between semiconductor
Epitaxybetween dissimilar materials:* band gap (Eg) engineeringtwo different SCs could be grown alternatelymodulated Eg* Strain engineeringstrain status could be engineered using lattice mismatch
?
?
-
8/10/2019 20141103 Thin Film Physics 2
12/29
12FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
2DEG (2 Dimensional Electron Gas)
Heteroepitaxy system between semiconductor
?
-
8/10/2019 20141103 Thin Film Physics 2
13/29
13FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Heterojunction (or hetero structure) devices
-
8/10/2019 20141103 Thin Film Physics 2
14/29
14FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Heteroepitaxy and superlattice
Superlattice: 1D periodic structure
of alternating ultrathin layers
Strained super lattice: superlatticefrom lattice mismatched layers
-
8/10/2019 20141103 Thin Film Physics 2
15/29
15FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Bufferlayer
Buffer layer also used for Heteroepitaxyof non-superlatticeapplications:eg) graded Si1-xGex layer
Use of buffer layer to reduce net strain accumulated
a) No buffer layer
b) With buffer layer
-
8/10/2019 20141103 Thin Film Physics 2
16/29
16FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Thin film deposition- Evaporation
1) thermal2) e beam
3) MBE- sputtering
-
8/10/2019 20141103 Thin Film Physics 2
17/29
17FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Physical vapor deposition
Deposition without chemical reaction Species to form films are physically dislodged from a source as a vapor: this vapor is
transported to substrate.
?
-
8/10/2019 20141103 Thin Film Physics 2
18/29
18FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Evaporation
simplest PVD thin films deposition technique using evaporation (or sublimation) of solid
source either bythermal or e-beamevaporation not the main dep. technique now for semiconductor industry (limited step coverage, less
reliability) any more, but still used for some specific purpose
?
-
8/10/2019 20141103 Thin Film Physics 2
19/29
19FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Source configuration for thermal evaporation
source charge
f
-
8/10/2019 20141103 Thin Film Physics 2
20/29
20FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Evaporation of sources
High temperature needed for some elements
E b
-
8/10/2019 20141103 Thin Film Physics 2
21/29
21FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
E-beam source
(Some materials which need high temperature to be evaporated)
E it i l th t h i MBE ( l l b it )
-
8/10/2019 20141103 Thin Film Physics 2
22/29
22FNNLFunctional Nanostructures & Nanoelectronics Lab
Semiconductor processing
Epitaxial growth technique: MBE (molecular beam epitaxy)
MBE is a ultra high vacuum form of evaporation to produce high quality, epitaxialfilms
M l l b it
-
8/10/2019 20141103 Thin Film Physics 2
23/29
23FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
Molecular beam epitaxy
E l S l tti b MBE
-
8/10/2019 20141103 Thin Film Physics 2
24/29
24FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
Example: Superlattice by MBE
PVD- Evaporation
1) thermal2) e beam3) MBE
- sputtering?
S tt i
-
8/10/2019 20141103 Thin Film Physics 2
25/29
25FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
Sputtering
Thin film deposition by energetic ion bombardment, which physically dislodge atoms from
target surface
substrate
target
S tt i
-
8/10/2019 20141103 Thin Film Physics 2
26/29
26FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
Sputtering
10KeV
DC diode Sp ttering
-
8/10/2019 20141103 Thin Film Physics 2
27/29
27FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
DC diode Sputtering
Magnetron Sputtering
-
8/10/2019 20141103 Thin Film Physics 2
28/29
28FNNLFunctional Nanostructures & Nanoelectronics Lab Semiconductor processing
Magnetron Sputtering
(Erosion ring)
(Erosion ring)
Magnetron Sputtering
-
8/10/2019 20141103 Thin Film Physics 2
29/29
29FNNL Semiconductor processing
Magnetron Sputtering
Target size larger than sample, distance optimization. Heart shaped magnetron to address erosion profile: Typical modern tools