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1Metryx Copyright ©
Characterisation of Through Silicon Via (TSV) processes
utilising Mass Metrology
Liam Cunnane, Adrian Kiermasz PhD, Gary DitmerMetryx Ltd., Bristol UK
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Mass MetrologyPrinciplesMethodology
Through-Silicon Via (TSV) Process SequenceDeep Silicon Etch & Polymer cleanOxide LinerBarrier & Seed DepositionCopper ECP & CMP
Summary
Outline
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Normal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
Normal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
Normal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
Normal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
ALD
CMP
ETCHNormal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
PECVD PVD
Normal Distribution
x
dens
ity
43 45 47 49 51 53 55 57 59 61 630
0.1
0.2
0.3
0.4
ETCHΔ
Mas
s
Process Step
Principle of Mass Metrology
All Microelectronic devices are manufactured through a series ofprocess steps which add or remove material.
Accurate measurement of mass change allows production monitoring orsupports development in determining of a layer’s physical parameters.
Mass metrology provides the advantages of On-product measurement, an atomic-level sensitivity, and total flexibility in application.
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Mass ≠ WeightWeight Measurement
Unstable, irreproducible, not designed for semiconductor measurement use
Mass MeasurementLoad-cell utilising complex force measurement Real-time corrections for internal and external forces influencing measurementFully automatic wafer handling and host communication compliant
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Expressed as thickness on a 300mm wafer
Standard Mass error (80µg 1σ)
Detection capability:~1Å for a dense material such as Ta (TaN)<5Å for silicon, silicon oxide / nitride.
Advanced structures, with increased complexity, actually improves the sensitivity of mass metrology.
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Mass Metrology is a non-invasive method for In-line monitoring‘On-Product-Wafers’ Measurement, Backside Contact only
Mass change is a direct representation of process performance Mass excursions outside the normal distribution represent process problems
Pre-MeasurementM1
M2Post-Measurement
ΔM = | M1-M2 |
Simple Measurement
STI Oxide Fill deposition
110000
115000
120000
125000
130000
135000
140000
0 50 100 150 200 250 300
NumberM
ass
chan
ge (µ
g)
+ 5%
- 5%
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TSV - Process Steps
TSV Etch
TSV Cleaning
Oxide Liner
Barrier/Seed
Cu Plate
CMP
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Through Si Via (TSV) Study
Two Via types were studied. -TSV A: near straight walled
via with a AR of 5:1-TSV B: highly tapered via
with a AR of ~35:1
Mass change characteristics of each via type investigated
Exposed Area %
Asp
ect R
atio
0
0.5 1
1.5 2
2.5 3
0
10
20
30
40
Mass (mg)
0.0-30.0
30.0-60.0
60.0-90.0
90.0-120.0
120.0-150.0
150.0-180.0
180.0-210.0
210.0-240.0
240.0-270.0
TSV B
TSV A
RA
DA
TSV B
TSV A
Via Diameter ~ 5 um
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TSV By = -0.0024x2 + 1.1901x + 4.7453
R2 = 0.995
TSV Ay = -0.0022x2 + 1.2293x + 0.0903
R2 = 0.9992
0
50
100
150
0 50 100 150Etch Time % (Cycles)
Dep
th %
of P
OR
Depth TSV ADepth TSV B
Process requirements of each via type are unique.
Via etch process change and response is compared by normalizing to the related Process of Record (PoR).
Rate of change in etch rate is very similar, albeit slightly more pronounced on TSV B.
TSV B
TSV A
RA
DA
Etch Depth v Cycle time
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TSV By = -0.0038x2 + 1.3509x + 3.0548
R2 = 0.9893
TSV Ay = 0.9672x + 2.2678
R2 = 0.9999
0
50
100
150
0 50 100 150Etch Time % (cycles)
Mas
s Lo
ss %
of P
oR
Mass TSV AMass TSV B
Mass vs etch cycle time, more clearly shows the difference in behavior between TSV A & B.
TSV A exhibits a linear loss in mass vs cycle time suggesting the transport rate of species and by products in and out of the Via remains constant.
However, in the case of TSV B, the mass loss is rapidly slowing as the feature becomes deeper.
TSV B
TSV A
RA
DA
Mass Loss v Cycle time
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Production Monitoring of Si Etch
Chambers 1 & 2 are well matched
Reducing Si mass loss as the wafers are processed is due to polymer loading in the chamber
If a sudden shift of similar magnitude occurs in both chambers, it is known that this is related to incoming material
PhotolithographyHard-mask issue
-69000
-67000
-65000
-63000
-61000
-59000
1 26 51 76 101 126 151 176Measurement Number
Mas
s Lo
ss (u
g)
Chm 1 Chm 2 USL Target LSL
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Mas
s Lo
ss (u
g)Etch Chm
Stab
le
Uns
tabl
e
-2800
-2300
-1800
-1300
-800
-300Mass measurement of the polymer removed in the wet strip process, provides a clear quantitative measurement
Chamber B is exhibits a high level of variability in mass loss during the wet clean
Variability is related to the degree of polymer formed during the etch
Chamber A Chamber B
Data randomized across wet clean stations
Polymer Removal – Etch Chamber Sort
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Polymer Removal – Wet Station Sort
When post etch wafers are randomized between Wet Stations #1 & #2, the same mass should be removed
Mass removed in Station #1 is greater than Station #2, indicating a more aggressive chemistry
Mass offers a simple and direct method to monitor via wet cleaning and wet chemistry stability M
ass
Rem
oved
(ug)
System
Sys
tem
1
Sys
tem
2
-1400
-1200
-1000
-800
-600More Aggressive Less Aggressive
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0
5000
10000
15000
20000
25000
30000
1 2 3 4 5Aspect Ratio (AR)
Mas
s (u
g)
SidewallTop Surface
1:1 5:1 10:1 20:1 50:1
Mass of Oxide Liner over topography increases rapidly with exposed area and Aspect Ratio, as compared with the same nominal surface film thickness
40 nm TEOS Liner / 3 % Exposed Area
ITRS roadmap calls for AR values as high as 20:1 in the future.
Oxide Liner – (HAR, Surface Area & Mass)
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Liner / Barrier deposition, including sidewall coverage monitored non-destructively
Similar to the Oxide Liner, sidewall contribution of mass added increases on higher Aspect Ratio features
Line
r Mas
s (u
g)
Lot No.1 2 3 4 5 6 7 8
8500
9500
10500
11500
LinerBarrier
Liner / Barrier Sidewall Coverage
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Monitor Mass increase v. Top surface thickness
Selective bottom-up, void free fill, results in the mass increasing rapidly as compared to top surface thickness
If Voids are present then the mass will increase more slowly compared to increase in top surface thickness increase
Developing Effective Cu-Fill with Mass
Surface thickness ‘x’
Tota
l Mas
s (m
g)
Voiding
Fill Marginal
Fill Superior
Process C
Process A
Process B
Thickness ‘xa’
Thickness ‘xb’
Thickness ‘ya’
Thickness ‘yb’
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Mass removed during CMP reflects the mass of the Barrier & Cu Fill
This correlation of mass removed to mass deposited affirms the CMP process stability
-20.00
-15.00
-10.00
-5.00
0.00
5.00
10.00
15.00
20.00
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Data No
Mas
s D
evia
tion
(mg)
DEPCMP
Data is plotted in mg deviation from target
Metal Fill & CMP
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CMP Stability
Mass removed during CMP is well correlated to the mass added by Barrier + ECP
Therefore the CMP is observed to be well controlled. Where there is an undesirable CMP under- or over-polish, scatter will be seen in the data
This ‘compensation’ results in a mass stability of the wafers relative to post contact etch which is excellent
y = -1.0001x + 2E-13R 2 = 0.9997
-17.00
-12.00
-7.00
-2.00
3.00
8.00
-8.00 -3.00 2.00 7.00 12.00 17.00
DEP Mass (Barrier + ECP) Added
CM
P M
ass
(Bar
rier +
EC
P)
Rem
oved
Data is plotted in mg deviation from Target
LinerBarrier
Cu
LinerBarrier
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-15
-10
-5
0
5
10
15
TSV
Etch
Liner Barrier
Cu ECP CMP Final
Stability
Mass variation is shown relative to the mean for the group
Box-Whisker plots indicate the Mass stability relative to the previous step
The CMP process accommodates variance in the Fill process by adjusting the CMP polish
Final Mass Stability shown is relative to the post contact etch
Mas
s (m
g)
TSVLinerBarrier
Cu
LinerBarrier
Mass Stability
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Mass added Post TSV CMP
Mass measured post Etch and post CMP reflects the mass filling the TSV.
Process excursions related to Via Etch, Via Fill and CMP are all effectively monitored by the stability in this mass delta.
156000
157000
158000
159000
160000
161000
0 20 40 60 80 100Measurement Number
Mas
s A
dded
(ug)
TSVLinerBarrier
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Through-Silicon Via (TSV) Etch in Silicon Measure etched silicon volumeConfirms etch depth and profile meet process definition
Oxide LinerConfirm step coverage of liner
Barrier/SeedAccurate measurement of multi-stack layerDetermine effective sidewall coverage
Copper – ECD Fill and CMP Cleaning of Copper Oxide from Seed prior to ECPOptimization of Bottom Fill and Void preventionMonitor, affirm process stability
TSV Metrology – Summary
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