1. Lateral High Aspect Ratio (LHAR) Test
Structures for Thin Film Conformality
Measurements

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Why conformal thin films are important?
 Moore’s law – vertical scaling trend
 Core value proposition of ALD: conformal thin films
 New opportunities in manufacturing and material
science
MSW 13.-15.5.2018 Espoo, Finland
3D NAND
Source: Applied Materials post
3D NAND
FinFETs
Mayer et al. APL 82 (2003) 2883.

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Conformal film covers complex 3-D structures
uniformly with the same thickness and properties
Conformal film,
schematic example:
a. Optimized ALD
 Same film top (1), sidewall (2),
bottom (3), deep within (4)
Partly conformal & non-conformal films,
schematic examples
b. Partly conformal, typical for CVD
c. Noncormal with overhang,
from line-of-sight deposition
d. ”Superconformal”, i.e., preferential
filling inside the 3-D feature
(a)
(c) (d)(b)
(Side view)
1.
2.
3.4.

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Traditional way of measuring conformality:
Cross-sections of vertical trenches in silicon
• Measurement takes time & effort, accuracy operator-dependent
• Point-per-point analysis, wafer mapping quasi-impossible
Vertical HAR procedure:
Measure thickness
1. Top
2. Sidewall
3. Bottom
Calculate conformality:
• Bottom/top xx%
• Sidewall/top yy%
Aspect ratio
(height/width,
not in scale)
max ~50:1
1.
2.
3.
If thinner in trench
 conformality <100%

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Why chacterization of vertical microstructures is a
PROBLEM ?
Analysis needs cross-sectioning.
• Sample preparation (FIB) + special
analytical tools (HR-TEM) can take
weeks and cost 2000-3000 euros
for service
• Access to test structures is also a
headache.
• PillarHall enables to do all this
and much more without delay - in
a price point of a test chip

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Invention

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PillarHall® Innovative LHAR Test Structures:
Cross-section without cross-sectioning
1) Test chip as delivered – all silicon
2) Test chip after thin film deposition
PillarHall
+thin film (ALD,CVD)

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Schematic:
uncoated structure
Structure after coating with
ALD, CVD, …
Structure after peeling off the
top membrane
PillarHall® lateral
high-aspect-ratio
(LHAR) all-silicon
test chips

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LHAR3 PillarHall® Test Chip features:
9 different and 8 parallel LHARs in rectangular test
areas, AR from 2:1 to 10 000:1 (gap 500 nm)
Scale
100 µm
Vertical
trenches
Additional
directional
LHARs on edges Distance indicator markers
Cleavage
line
Chip size: 15x20 mm
31 HAR test structures in one chip
1 gap height (default 500 nm)
All silicon

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Two basic ways to characterize thin films
1 2

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PillarHall®: Remove top membrane to access
detailed, reproducible information of film on Si
Photo: Riikka Puurunen, VTT
Distance from LHAR opening (µm)
Reflectometry
Al2O3 ALD
For scientific publications, see: DOI
10.1116/1.4903941; DOI acs.langmuir.6b03007
More info to come: Puurunen et al., EuroCVD 2017,
accepted; ALD 2017, submitted

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Compatible surface analysis tools
COMPATIBLE SURFACE
ANALYSIS TOOLS e.g.
•Optical microscopy image
analysis
•Optical reflectometry
spectrometry (VIS to SWIR)
•Line scans and spectral
imaging
•Small spot Ellipsometry
•AFM and other SPMs
•SEM/EDS plan-view
•High resolution confocal
microscopy
•XPS, ToF-SIMS

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Saturation profile terminology for ALD
(as proposed by PillarHall)
Distance l (µm, mm, …)
Relative dimensionless distance (RDD) l / g [r.d.u.]
(RDD ~ aspect ratio AR)
Amount
grown
(nm,
# of atoms,
…)
(per cycle)
50%-thickness-
penetration-depth (PD50%)
Slope at PD50%
(  Lumped sticking coefficient)
GPC just
inside + initial slope
Knee
GPC just
outside
x1. 2.
3.
4.
5. 6.

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Predicting and modelling thermal ALD
Modeling growth kinetics of thin films made by atomic layer deposition
in lateral high-aspect-ratio structures M.Ylilammi, O. Ylivaara and R. L.
Puurunen, J.Appl.Phys. In press

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PillarHall®: Benefits
 Avoid the need for tedious cross-sections combined with
electron microscopy, needed for traditional vertical features
 Record-high aspect ratios >10000:1, exposing a parameter
space beyond access with traditional vertical structures
 Microscopic dimensions suitable for kinetic modelling
 Wafer mapping possibility, even nondestructively
 IC-compatible silicon test chips
 Accuracy in 3 dimensions
 Applicable at temperatures up to ~800°C

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PillarHall Test Chip Offering
 Test chips in VTT sales offering
 Analysis guide manual
 IC cleanliness proven certificate
 Accompanying service options
Chip size: 15 x 15 mm (LHAR4),
15x20 mm (LHAR3, in picture)
Gap height: 500 nm + options
Test Chips delivered in vacuum
release trays (Gel-Pak)

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Scientific publications using
PillarHall® test chips
1. Modeling growth kinetics of thin films made by atomic layer deposition in lateral high-aspect-
ratio structures, M. Ylilammi, O. M. E. Ylivaara, R. L. Puurunen, J. Appl. Phys. 123 (2018) art.
205301 (8 pages). https://doi.org/10.1063/1.5028178
2. Microscopic silicon-based lateral high-aspect-ratio structures for thin film conformality
analysis,
F. Gao, S. Arpiainen, R. L. Puurunen, J. Vac. Sci. Technol. A 33 (2015) 010601.
http://dx.doi.org/10.1116/1.4903941,
open access pdf.
3. Nucleation and Conformality of Iridium and Iridium Oxide Thin Films Grown by Atomic Layer
Deposition,
M. Mattinen, J. Hämäläinen, F. Gao, P. Jalkanen, K. Mizohata, J. Räisänen, R. L. Puurunen, M.
Ritala, M. Leskelä, Langmuir 32 (2016) 10559-10569. http://dx.doi.org/10.1021/acs.langmuir.6b03007
4. Influence of ALD temperature on thin film conformality: Investigation with microscopic lateral
high-aspect-ratio structures,
R. L. Puurunen, F. Gao, Proceedings of the International Baltic Conference on Atomic Layer
Deposition, 2-4 Oct 2016, St. Petersburg, Russia. Electronically published in IEEE Xplore,
http://ieeexplore.ieee.org/document/7886526/

18. CONTACT: Dr. Mikko Utriainen
Sales responsible of PillarHall @VTTFinland
Tel. +358 40 753 7415 mikko.utriainen@vtt.fi or pillarhall@vtt.fi