micromechanical testing of thin films warrenoliver mts nano instruments oak ridge, tennessee
TRANSCRIPT
Micromechanical Testing of Thin Films
WarrenOliverMTS Nano Instruments
Oak Ridge, Tennessee
Nano Indenter® G200
Precise mechanical testing in the micro to “sub-nano” range of loads and displacements
Testing instrumentation: Nano Indenter ® XP
Coil/magnet assembly
Leaf spring
Capacitance gauge
Indenter
Sample
Nickel
0
5
10
15
20
25
30
0 100 200 300 400 500
Load
(m
N)
Displacement (nm)
0
5
10
15
20
25
30
0 500 1000 1500 2000
Lo
ad
(m
N)
Load-displacement behavior
Aluminum, typical of soft metallic behavior, shows very little displacement recovery upon unloading
Fused silica, typical of ceramic behavior, shows large elastic recovery upon unloading
Aluminum
Fused silica
Read Heads
The problem…
Indentation results for 1-m low-dielectric-constant (low-k) film on silicon
“skin” effect
substrate effect
All data are affected, to some extent, by either “skin” or substrate. So what is the modulus of this film? Problem is not too bad for 1-micron films, and hardness is less sensitive than modulus. But our microelectronics customers tell us they really want to test 200nm films!
The goal
The goal of this work is to develop an empirical model that:
• Is appropriate for a realistic range of low-k materials• Correctly models the influence of the silicon substrate• Requires no a-priori knowledge of film properties beyond
thickness• Can be incorporated into Testworks• Is relatively independent of diamond tip radius
Developing the model
There is much to be learned from the process of developing the model.
1. Survey experimental results. Select properties that bound the range of interest in terms of E and H.
2. Perform preliminary simulations to get y = f(E,H). Select
properties that bound the range of interest in terms of E and y.
3. Perform simulations for “boundary” samples.4. Calculate errors in modulus and hardness, relative to expected
properties for bulk materials. 5. Plot error as a function of parameters that are relevant, knowable,
and dimensionless. Derive model for error by curve fitting.6. Test model with more simulations (on materials inside boundaries)7. Test the model experimentally
Virtual IndenterTM Features
• Real area functions, spheres, flat punches• Bulk materials• Up to three stacked films• Particle/fiber/disk in a matrix• Range parameters easily• A variety of constitutive models• Automated Excel output
Uncorrected modulus from simulation
0
2
4
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18
20
0 100 200 300 400 500
Displacement Into Surface [nm]
E* O
P [
GP
a]
100nm film200nm film300nm film400nm film500nm film600nm film700nm film800nm film900nm film1000nm filmBulk
Uncorrected modulus vs. normalized contact radius
0
2
4
6
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0% 20% 40% 60% 80% 100% 120% 140% 160%
Displacement Into Surface/Film Thickness [%]
E* O
P [G
Pa]
100nm film200nm film300nm film400nm film500nm film600nm film700nm film800nm film900nm film1000nm filmBulk
Corrected modulus vs. normalized contact radius
0
2
4
6
8
10
12
14
16
18
20
0% 20% 40% 60% 80% 100% 120% 140% 160%
Displacement Into Surface/Film Thickness [%]
E* O
P [G
Pa]
100nm film200nm film300nm film400nm film500nm film600nm film700nm film800nm film900nm film1000nm filmBulk
Applying the model to experimental data
Wafers supplied by SEMATECH:
• 4 wafers of nominally the same film, different thicknesses• 250nm, 488nm, 747nm, 1156nm• k ~ 2.3• Technology targeted for use beyond 45nm node• Deposited using “porogen” and then UV cured to cause
residual pores. Cure times varied with thickness. UV cannot penetrate past 750nm.
Calculating modulus old way and new way
0
2
4
6
8
10
12
0 10 20 30 40 50 60
Contact Radius / Film Thickness [%]
EO
P [
GP
a]
250nm
488nm
747nm
1156nm
0
2
4
6
8
10
12
0 50 100 150 200 250 300
Displacement Into Surface [nm]
E* O
P [
GP
a]
250nm
488nm
747nm
1156nm
Old way: take minimum
New way: take data for 30% < a/t < 35%
Calculating modulus old way and new way
0
2
4
6
8
10
12
250 488 747 1156
Film Thickness [nm]
Mo
du
lus
[G
Pa]
Min of uncorrected data, E*_OP
Corrected E_OP over range 30% < a/t < 35%
10nm
- 20
nm
25nm
- 35
nm
40nm
- 50
nm
90nm
- 10
0nm
29nm
- 34
nm
63nm
- 74
nm
103n
m -
120n
m
168n
m -
195n
m
Moduli calculated by old way are too high by 30%, because data at minima are significantly affected by substrate.
Using new model also reduces uncertainty
0%
1%
2%
3%
4%
5%
6%
250 488 747 1156
Film Thickness [nm]
Rel
ativ
e u
nce
rtai
nty
[%
]
Min of uncorrected data, E*_OP
Corrected E_OP over range 30% < a/t < 35%
10nm
- 20
nm
25nm
- 35
nm 40nm
- 50
nm
90nm
- 10
0nm
29nm
- 34
nm
63nm
- 74
nm
103n
m -
120n
m
168n
m -
195n
m
Conclusions
A model has been developed to compensate for the influence of the substrate on the indentation properties of thin low-k films.
Model has been incorporated into a Testworks test method.
Model significantly reduces both error and uncertainty, especially for very thin films.
We continue to test the model on more low-k films.
Uniaxial Testing of Free Standing Films
Warren C. Oliver and Erik G. Herbert, MTS CorporationJohnathan Doan, Reflectivity
Nanovision Stage
Travel: 100 m x 100 mResolution/Noise: 2 nmFlatness of travel: 1-2 nmAccuracy: 0.01 %Settling Time: 2 ms-Capacitive feedback control
Automated Indent and Scan
Scan Procedure
Film
Step1) Scan substrate to determine slope of surface
Step 2) Find top of post
Step 3) Scan plane of predetermined slope just below top of post, but above film
Leveled Targeting Scan
8 μm Wide, Doubly Clamped Bridges
0
2
4
6
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14
0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-06
Displacement (m)
Lo
ad
on
Sa
mp
le (
μN
)
L = 34 μm L = 66 μm
L = 50 μm
L = 18 μm
Load Displacement Curves
9.95
10
10.05
4.95 5 5.05
Nominal ForceExcitation Force
Lo
ad
(m
N)
Time (seconds)
0
2
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6
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10
12
0 10 20 30 40 50 60 70 80
Nominal Force, P/P = Constant
Load (
mN
)
Time (seconds)
.
Continuous Stiffness Measurement Technique (CSM)
CSM - Elastic & Viscoelastic
Elastic Viscoelastic
-2
-1
0
1
2
-1
-0.5
0
0.5
1
0 10 20 30 40 50
Exc
itatio
n fo
rce
(µN
)
Response displacem
ent (nm)
Time (milliseconds)
-2
-1
0
1
2
-1
-0.5
0
0.5
1
0 10 20 30 40 50E
xcita
tion
forc
e (µ
N)
Response displacem
ent (nm)
Time (milliseconds)
= 0°
= 90°
8 μm Wide, Doubly Clamped Bridges
0
10
20
30
40
50
60
70
0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-06
Displacement (m)
Bri
dg
e S
tiff
nes
s (N
/m)
L = 34 μm
L = 66 μm
L = 50 μm
L = 18 μmHarmonic Displacement = 30 nm
Stiffness Displacement Curves
Describing Bridge Tensile Specimens
P
w L+(L-w)/2
h
L
PF
F
sin)(2sin2 rEAFP
For not quite so small angles!3
sin3
3tan
31
The Stiffness Displacement Relationship:
)()(2tansin2
)(
4 1 EwLhA
wL
AEhP r
3
2
)(
)(24
)(
4
wL
hEA
wL
A
dh
dP rr
Testworks: A Complete Solution
Now it gets Interesting
TestWorks and the Nano Indenter G200
Design of MEMS structural experiments was easily done with the flexibility and control offered by the TestWorks software
TestWorks provides a user interface that facilitates the design of new (i.e. MEMS) and novel experiments without the need to have knowledge of C++ programming
The Nano Indenter G200 system can provide this information quickly and reproducibly, offering manufacturers an attractive tool for product development
Thank you!