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Advanced Production Challenges for Automated Ultra-Thin Wafer Handling

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The handling of thin wafers in today’s production lines demands high standards of the automation as well as complex investigations with a closer look on the actual and future needs for an economic and competitive production of solar cells. This paper describes the analysis and evaluation methods developed by the authors for ultrathin wafers (<100 μm) which are created by a newly developed wafering technique. A short overview about the new handling experiments within the automation test platform at the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) is subsequently followed by detailed ultra-thin wafer handling experiments. Different approaches were tested for the automated handling of the ultra-thin silicon foils. The difference in handling of curled and flat substrates, caused by the newly developed wafering method, will be pointed out as well as the difficulties for transportation with high-speed parameter settings. While looking for a reliable gripping advanced production challenges are given due to the requirement of certain cleanliness.
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ADVANCED PRODUCTION CHALLENGES FOR AUTOMATED ULTRA-THIN WAFER HANDLING
Tim Giesen1, Roland Wertz1, Christian Fischmann1, Guido Kreck1,
Jonathan Govaerts², Jan Vaes², Maarten Debucquoy² and Alexander Verl1
1Fraunhofer Institute for Manufacturing Engineering and Automation IPA, Stuttgart, Germany
²Interuniversity Microelectronics Centre IMEC, Leuven, Belgium
tim.giesen@ipa.fraunhofer.de
ABSTRACT: The handling of thin wafers in today’s production lines demands high standards of the automation as
well as complex investigations with a closer look on the actual and future needs for an economic and competitive
production of solar cells. This paper describes the analysis and evaluation methods developed by the authors for ultra-
thin wafers (<100 µm) which are created by a newly developed wafering technique. A short overview about the new
handling experiments within the automation test platform at the Fraunhofer Institute for Manufacturing Engineering
and Automation (IPA) is subsequently followed by detailed ultra-thin wafer handling experiments. Different
approaches were tested for the automated handling of the ultra-thin silicon foils. The difference in handling of curled
and flat substrates, caused by the newly developed wafering method, will be pointed out as well as the difficulties for
transportation with high-speed parameter settings. While looking for a reliable gripping advanced production
challenges are given due to the requirement of certain cleanliness.
Keywords: Crystalline, Substrates, Manufacturing and Processing
1 INTRODUCTION
The test and demonstration of automated crystalline
wafer handling has been widely researched recently in
terms of the wafer integrity [1]. The results gave an
outlook on what to expect and what we’ll face in
photovoltaic mass manufacturing when the substrates are
getting thinner according to the international roadmaps
[2].
New technological approaches require for the
automation developers to look even beyond those aims of
the roadmap, as the wafering of ultra-thin substrates is
not utopistic and may be feasible for large-scale
manufacturing in the foreseeable future [3]. Therefore,
the scientific challenge of processing ultra-thin
photovoltaic wafers with less than 100 µm thickness is
paired with advanced requirements for the automation of
ultra-thin wafer handling. Only automated solutions for
new wafering techniques will be competitive in the future
wafer-based photovoltaic cell market. The gripping and
handling of ~50µm silicon foils needs to balance a high
throughput capability while taking care of a very
sensitive substrate and is therefore the key for an
extensive exploitation of new wafering techniques.
Crystalline photovoltaic wafers remain a very
sensitive object to be handled as such. The EU-funded
project SUGAR (Silicon Substrates from an Integrated
Automated Process) researches and develops a process
for wafering silicon ingots into ultra-thin foils. The
researchers focus not only on the integrity and capability
of the wafering process and cell processing, but also on
the feasibility and applicability of an automated handling.
Thus, the analysis and evaluation aims at the exploitation
of the new technology results and will assist on bringing
these project results into an industrial framework.
2 MATERIALS AND METHODS
The automated handling of ultra-thin wafers is tested,
demonstrated and evaluated with a newly developed
prototype handling cell (cf. Figure 1) which is connected
to different handling equipments within an industry-like
environment at the Fraunhofer IPA`s test and
demonstration centre.
Figure 1: Prototype handling cell with SCARA-robot for
integrated ultra-thin wafer assembly
In this in-line production handling platform different
opportunities of handling and automation solution are
tested with thin and ultra-thin silicon-based photovoltaic
substrates. For the development of new methods in
automated ultra-thin wafer handling new and prototypic
equipment was recently integrated. Thus several handling
issues for the special scope of ultra-thin wafer handling
can be investigated and demonstrated. Miniaturized
gripper test and evaluation, position accuracy
determination by digital image processing, a flexible
process flow for a mini-module assembly, ultra-thin
wafer carrier loading and conveyor transportation are
some of the applied automation tests which are dealing
with the challenges in the SUGAR project.
2.1 Ultra-thin wafer samples
The ultra-thin wafers for which the automated
handling is developed are produced in the laboratories of
the IMEC by using the “Stress induced Lift-off Method”
(SLiM-Cut). This method has been developed by the PV
researchers at the IMEC [3] and makes particularly
efficient use of bulk material by reducing kerf loss while
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producing wafers with a thickness of around 50 µm [4].
The different dimensioning of the investigated samples is
depicted in Figure 2. While the standard 6” wafers do
have edge lengths of around 156x156 mm the herein
handled ultra-thin SLiM-cut wafers are conditioned to a
size of 50x30 mm.
Figure 2: (1) 1-euro coin, (2) SLiM-Cut-wafer format, (3)
Standard 6” monocrystalline wafer
2.2 Handling Sequence
Today, a wafer thickness of 180 160 µm is
processed into solar cells at industrial production sites.
The handling issues, which were researched in the past
[5] do still remain. Due to the reduced size in thickness
while simultaneously demanding for increasing
throughput rates, the challenges for achieving a high
quality output in the production line need to be overcome
by new handling concepts.
Concerning the process flow of the SLiM-Cut
method the handling issues are well beyond of today’s
handling issues. As depicted in Figure 3 the process
sequence is different in comparison to the standard ingot
wafering. First, a stress inducing layer (A) is deposited on
a silicon substrate (e.g. metal). Certain temperatures
recipe activates the stress (B) and the crack propagation
(C) is subsequently carried out from a starting notch. The
lift-off of a silicon substrate attached to the stress induced
layer marks the start of the automated handling section. A
curled sample (D) needs to be cleaned in an etching bath
to become a flat silicon substrate. Finally, the flattened
wafer can be further processed into a photovoltaic cell
with (e.g.) IBC architecture.
Figure 3: Handling sequence in the SLiM-Cut process
flow (green arrows), [4].
The advanced handling sequences may be separated into
the following process sequences according to Figure 3:
C D: handling of coated and curled wafer samples
between lift-off and cleaning bath
D E: handling of flat ultra-thin silicon foils from a
liquid environment into a clean environment for cell
processing.
Thus, an automated handling method for curled and flat
wafer handling in liquid (wet) and air (dry) environment
has to be researched, developed and tested. The different
geometries of the handling objects as well as the different
opportunities for a gripper usage were considered first.
The experimental development of the handling solution
was then carried out on the handling test- and
demonstration platform at Fraunhofer IPA (see chapter 3
for the description of the handling experiments).
2.3 Specimen Diversification
According to the Slim-cut process flow the handling
object appears in different shapes and geometries. In a
first approach, thinned down 5” semi-squared wafers
with a thickness of ~50 µm were taken into account to
test and adapt the existing methods for automated
handling. The existing and validated [5] methods
consider a sample with 200 160 µm thickness and an
area of 156x156 mm.
A second sample size was given with a thinned down
5” wafer which was diced into 30x50 mm wafers. These
miniaturized wafer size was considered for handling test
because the format of 30x50 mm was expected to be
identical to one of the first wafers, which would be
gained by the Slim-cut processing. According to the
SLiM-cut mean substrate thickness of around 50 µm, the
miniaturized wafers were also thinned down.
For the general evaluation of the smaller sample size
also 30x50 mm wafers were taken for rough handling
investigations and first gripper parameter determination.
These samples were diced from a 700 µm thick
semiconductor wafer.
The curled lift-off samples from the SLiM-cut
process were also taken into consideration as a handling
sample. These curled substrates (cf. Figure 9) were the
most unknown handling objects in this row of
investigations. The coated and curled wafer samples may
appear in different shapes, depending on the bow strength
due to the induced stress.
3 HANDLING EXPERIMENTS AND RESULTS
To obtain a first overview on the feasibility of pick &
place applications with ultra-thin wafers the application
with the presented grippers was set up on a manipulating
device.
The Test procedure was performed as follows:
The cell/wafer is placed by hand symmetrically blow
the gripper on two conveyor ring belts.
The gripper is brought into a position right above the
cell but without touching the substrate.
The suction force generation will be started and the
cell is supposed to be gripped.
Vertical travelling of the gripper (z-axis) as well as a
horizontal stroke (x-axis) back and forth (z-stroke:
~40 mm, x-stroke: ~900 mm).
In summary the gripper travels a distance of ~80 mm
on the z-axis and ~1800 mm on the x-axis while the
wafer is attached.
The handling experiments were performed with a
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successive raise of the acceleration, deceleration and
velocity.
3.1 Handling Experiments with Bernoulli-gripper
There are three main gripping technologies present in
today`s industrial photovoltaic wafer production.
Bernoulli grippers can handle the ultra-thin flat wafers.
(cf. Figure 4). The pick-up process parameters in the
shown sequence are set to 0 mm pick-up height, 3 bar
operating pressure, 25 m/s² acceleration on 3 m/s top
speed. The wafer is gripped with a waiting time of
200 ms and then accelerated vertically. Due to the
absence of a wafer covering shield the wafer suffers
heavy uncontrolled vibrations. The bending is not only
caused by the air drag but also by the inertia forces of the
wafer.
Figure 4: Sequence of a thinned ~50 µm wafer pick-up
with a Bernoulli gripper
While Figure 4 shows the breakage-free vertical
movement of the gripper and wafer pair, the horizontal
transportation looks somewhat different. Figure 5 shows
the sequence of a high-speed video during the horizontal
transportation of an ultra-thin wafer. In detail, the
sequence shows the deceleration in x-direction
subsequently to a horizontal stroke of 800 mm. The
extreme transportation parameters (velocity v=3 m/s,
acceleration/deceleration a=25 m/s²) cause a heavy
irritation to the wafer while being gripped with 3 bar
Bernoulli operating pressure. The operating pressure of
3 bar was identified as being the optimal operating point
for this gripper and standard ~180 µm 6” wafers during
previous capability tests [5]. The ultra-thin wafer in
Figure 5 is on the edge of getting completely detached
from the gripper due to the fast movement. Furthermore,
the stiffness of the ultra-thin wafer is much lower than
compared to standard wafers. The brittle handling object
suffers a huge deformation due to the air drag in
horizontal direction. A breakage did not occur, unless the
handled wafers had already a visible crack. A wafer
handling with such a substrate deformation cannot be
regarded as a qualitative good and valid handling method.
It is still unknown, if micro structural defects in the wafer
may appear due to such extreme handling parameters.
Micro cracks <1 µm may be generated inside the wafer
and will painfully grow during subsequent handling or
thermal processes.
Figure 5: Horizontal transportation of ~50 µm wafer with
a standard Bernoulli gripper
Today, there is no quality inspection tool for such
wafer stresses and strains available. A reliably visual
quality inspection of the crystalline handling object, even
for standard wafers, requires still a sophisticated empiric
study and instrumentation of the inspection tool. The
implication of automated ultra-thin wafer handling needs
to be further evaluated by using different approaches
such as electrical performance characterization of the
wafer after the transportation test runs.
Nevertheless, it is feasible to handle the thinned ultra-
thin 5” wafers in a fully automated way with the
presented Bernoulli-grippers. In some cases the handling
of wafers with parameters for actual standard wafers
(180-160 µm thickness) could have been directly applied
to the ultra-thin wafer handling. But by taking a closer
look (Figure 4 captures 1-9) the handling research results
require additional efforts for wafer protection. Large area
support of the wafer during pick-up will be considered
with e.g. a vacuum area gripper.
3.2 Handling Experiment with Vacuum Gripper
The utilization of a vacuum gripper was also
evaluated for the ongoing handling tasks. First, a
perforation of the ultra-thin wafer surface was feared as a
result of the punctual vacuum gripping of the substrate.
Four vacuum suction cups were used for the gripping
device. But a breakage-free transfer of the ultra-thin
wafers was possible with the modified vacuum gripper.
Due to the punctual support of the wafer the substrate
suffers heavy uncontrolled vibrations (picture 3-7 in
Figure 6). But the plate-type shielding above the suction
cups avoid an even stronger vibration of the wafer. So
this handling method is feasible for the tested thinned
down ultra-thin wafers, but may not be the favorite one
due to the below listed disadvantages.
Figure 6: Sequence of a ~50 µm wafer pick-up and
placement vacuum suction cups.
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3.3 Handling Experiment with Area Vacuum Gripper
The third automated handling approach for the ultra-
thin wafers is the area vacuum gripper (Figure 7). The
pick-up process is the calmest one among the
investigated grippers (pictures 1-2 in Figure 7). But
repeatable position accuracy is not possible with a
smooth, thinned ultra-thin wafer: during the placement
procedure the wafer needs to be blown off. Several
observations showed an unsteady way of how the wafer
is released from the gripper’s surface. The placement
requires a much longer waiting time than the placement
with other grippers. In addition, the distance for the
placement was set at a certain altitude. Otherwise the
wafer would be heavily irritated and lifted when the
gripper travels away vertically after the placement is
completed due to a slipstream caused by the shape of the
gripper. While the covering gripper area supports the
wafer during the pick-up phase in a positive way the
irritation during placement could harm the wafer and
could cause chipping at the edges of the handled
substrate. E.g. the wafer may hit the conveyor belts in an
uncontrolled way. The placement takes extraordinary
long comparing the application with today`s standard
wafers. For the handling tests a waiting time for the
placement procedure of up to 600 ms was considered,
which has a huge effect on the overall cycle time for the
handling.
Figure 7: Sequence of a ~50 µm wafer pick-up and
placement with an area gripper
Nevertheless, the area gripper might be an
adequate solution for the handling of large area ultra
thin wafers in automated manufacturing lines.
3.4 Results of Handling Experiments
Summarizing, the breakage-free transfer of thinned
monocrystalline ultra-thin 5” wafers is generally possible
while some restrictions need to be considered.
Cup-based vacuum gripping of flat ultra-thin wafers
induces punctual loads and heavy vibrations on the
fragile crystalline substrate at the same time. It requires a
relatively high effort to find the suitable parameter
settings for a reliable pick-&-place application. The mass
application of the vacuum gripping for volume handling
would need to have a detailed look. Thus the cup based
vacuum wafer handling is not considered for the further
ultra-thin wafer handling method development.
Bernoulli-gripping of flat thin wafers causes heavy
vibrations during pick-up and placement of the handled
object but the harmfulness of heavy vibrations is
unknown as well as the limit of mechanical loads in
general. Previous investigations results were inconclusive
in terms of gripper dependant lowering of the mechanical
integrity of the wafer. Handling caused a reduced
mechanical strength. The question if micro-cracks do
occur during wafer vibration needs still to be answered.
The area gripping of flat thin wafers showed at first
good results in flat wafer handling. But considering the
SLiM-cut process flow with curled wafers the limitation
of the handling capability is reached when it comes to
manipulate handling objects with uneven or non-plate-
like surfaces. The slipping of the wafer has to be
considered when an evaluation in term of reliable
position accuracy is required. Long waiting times at
placement due to a stick-effect (up to 600 ms) prolonging
of cycle time essentially. An irritation of the ultra-thin
and therefore very light wafer after placement could
cause breakage, chipped edges or other losses of the
working pieces quality.
3.5 Grippers for Miniaturized Wafer Handling
The grippers for the accurate module assembly were
tested in comparison to the grippers for standard
156x156 mm wafers. The gripping principles remain the
same, such as Bernoulli-principle or conventional
vacuum applications. But in terms of the substrate sizes
the grippers were downsized and, if required, modified.
In comparison to the grippers presented [5], the handling
devices had to be reviewed and the downsizing was
necessary for an accurate wafer placement.
The selected grippers must not exceed the wafer`s
area of 30x50 mm for specific processing reasons.
Furthermore, there is no need for an implementation of a
slipstream shield because the handling of the ultra-thin
wafers is not performed with maximum parameter
settings. The application of the Bernoulli-gripper for the
substrate size had to be investigated as such. Bernoulli-
grippers do need to work with a certain substrate/object
size for a reliable and accurate handling. When the
handling substrate would be too small and therefore too
light, the air stream based suction principle of a
Bernoulli-gripper causes an irritation of the wafer before
the gripper would pick the wafer. Thus an accurate wafer
pick-and-place operation cannot be guaranteed for
smaller sizes. Figure 8 shows the grippers for the wafer
handling experiments with ultra-thin and miniaturized
substrates.
Figure 8: (1) Bernoulli, (2) composite gripper and (3)
vacuum cup for small area gripping
For the single grippers the optimal operating point had to
be identified. The single grippers are:
1. Bernoulli gripper with diameter of 20 mm
2. Composite gripper for limp textile handling
(d=30 mm) (miniaturized vacuum area gripper)
3. Vacuum suction cup I (d=7 mm)
For a breakage-free transfer the gripping process of the
downsized grippers was also observed with a high-speed
camera. According to the first results the gripper was
operated with 2 bar, 20 m/s² acceleration and 2 m/s top
speed on both axes. The gripper touches the wafer
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punctually during the gripping phase. The high-speed
records show no extreme deformation or other harmful
behavior of the wafer. The gripper-wafer system seems to
work properly. This procedure was validated by the
position accuracy test, were the Bernoulli grippers came
off well.
The gripping of the miniaturized ultra-thin wafers
with different vacuum suction cups was accompanied
with stronger vibrations of the handling object. Also, the
placement accuracy research of the vacuum grippers
ended up in less accurate placement of the wafers. One
reason may be the elastic behavior of the single contact
point, the suction cup. While the wafer is vibrating and
moving during the transportation, the suction cup may
not grip strong enough to avoid a slipping of the wafer. A
stronger gripping by applying a higher vacuum may harm
the wafers microstructure or would even break it.
Feasible vacuum operation parameters are -100 mbar and
200 mbar.
3.6 Curled/Bowed Wafers
Grippers for PV-wafer handling applications are
optimized for standard flat wafers. For providing a
reliable transport of the wafers within production
equipments the grippers aim at a minimum contact
between gripper and wafer but also on evenly distributed
contacts points in the contact area. For the new kind of
handling objects, the bowed wafers, the gripping
principles for standard flat wafers needed to be tested for
a suitable application with the curled wafers in a first
step.
Figure 9: Curled specimen from SLiM-cut process
Taking into consideration a prolonged transport distance
of 600 mm for upcoming specifications in a wet bench
environment, the handling parameters and used
components are further listed in Table 1. The grippers are
the same as for the miniaturized flat wafer handling test.
Additionally, also the Bernoulli grippers with a body
diameter of 30 and 40 mm were considered for a general
benchmarking and feasibility study of bowed substrate
handling.
The composite gripper was taken into consideration
as an area vacuum gripper for the ultra-thin wafer
handling. Curled wafers could not have been gripped
with this device. The gripper needs to approach the
handling object´s surface to a very close distance
(~0 mm) for a reliable pick-up. This cannot be realized
with the curled wafers. The maximum generated gripping
force is insufficient for a distance gripping of the curled
wafers.
The vacuum cup is able to pick the wafer on its metal
coated side with a very low vacuum pressure. But same
as for flat wafers the suction cup generates a strong
punctual force. This force generation is mainly
compensated by the metal layer which protects the thin
silicon layer in this case. But having in mind to use the
gripper in a liquid environment the gripper may suck a
fluid due to its vacuum function and could cause a
process error (e.g. destroyed vacuum, losing the attached
wafer). A gripping on the silicon side of the curled wafer
may be possible with a limited extend. It should be
avoided, that the wafer is compressed between vacuum
cup and ground for not breaking the silicon layer.
Therefore, a sophisticated metrology would need to
provide the information about position, height and shape
of the wafer to the handling device.
Table I: Tested handling parameters for curled wafers
with available gripping principles (* B20, B30 and B40
are Bernoulli grippers (AL), VCup: standard suction cup
(NBR), CGripper: Composite Gripper (POM).
Gripper*
Gripping
Area
[mm]
Handling
Pressure
[bar]
Speeds
[m/s;
m/s²]
B20
20
Yes
Min 0.1
2;20
B30
30
No
-
-
B40
40
No
-
-
VCup
7
Yes
Min.
-0.1
2;20
CGripper
40
No
-
-
Among the tested Bernoulli grippers the B20 was the
only one which was able to pick, transport and place a
SLliM-cut wafer. A complication was noticed when the
Bernoulli gripper`s area was increased (e.g. for the
components B30 & B40) and the curled wafers area
exceeded. No gripping was possible in this case. But even
for the more or less successful gripping with the
Bernoulli B20 a reliable handling could not be attested.
Gripping on the silicon (convex) side of the curled wafer
was not possible at all. The tests for gripping on the
metalized surface caused a further complication. Due to
the fact that the wafer is bowed towards the direction of
the gripper the Bernoulli cannot approach the wafer as
close as necessary.
Figure 10: Automated gripping of a curled slim-cut
specimen with a Bernoulli gripper
As a result, the curled wafer is gripped by the
Bernoulli-effect but the contact between wafer and
gripper is displaced. The usual contact points of small
Bernoulli grippers are in the gripper’s center or on the
edge of the gripper surface. But the bended corners touch
the gripper’s outer aluminum edge in a tangential way
and prevent the realization of the usual contact between
gripper and handling object (Figure 10). Thus, a gripping
is possible but yet a reliable handling of curled slim-cut
wafers. When the gripper is accelerated for
transportation, the attached substrate suffers heavy
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shaking and vibrations. Additionally the gripper tends to
lose the curled wafers, when the transportation
parameters were increased. A solution for automated
handling of different curled wafer bows was elaborated
and positively evaluated for future handling tasks.
4 ADVANCED AUTOMATED HANDLING ISSUES
The presence of ultra-thin wafers comes coherently
along with advanced manufacturing issues for the
automated production. When implementing new
technologies which make use of ultra-thin substrates and
sensitive layers, the production environment needs to be
reviewed in terms of a clean environment [6]. Most PV
manufacturing lines today are already set up in factories
with requirements for advanced cleanliness, e.g. for ISO
7/Class 10.000.
4.1 Contamination and Automated Handling
The automated transportation and gripping of parts
mostly causes contaminated surfaces of the handled
object unless special arrangements for cleanliness are
considered. The currently ongoing investigation in the
department of ultraclean technology and micro
manufacturing at the Fraunhofer IPA focuses besides
automated handling also on the particle contamination on
ultra-thin wafers due to handling by Bernoulli grippers.
The experiments are carried out in an ISO class 1
cleanroom. In a test set up different operating modes of
the grippers and measurements were carried out. In
simple initial experiments the gripping devices were
operated with clean air and the surfaces of handled
wafers were subsequently inspected with a KLA Tencor
surface scan.
First results showed an increase of the contamination
within a range from 0.6 µm 28 µm concerning the
particle size. Due to the circular outflow of the
compressed air for the Bernoulli-mechanism the
sedimentation of the contaminating particles on the
wafers surface was disturbed. A ring shaped area with
fewer particles could have been noticed. But
nevertheless, the surrounding area of the “particle-free”
circle was heavily contaminated as well as the ring
center. Upcoming researches will systematically
investigate the handling-caused contamination of ultra-
thin wafers. The cleaning of contaminated surfaces will
be evaluated in terms of applicability within an industrial
process flow. New handling concepts and methods may
be investigated for avoiding contamination by particles
due to automated handling.
7 SUMMARY
New technological approaches in PV request for the
automation developers to look even beyond the aims
of the roadmap, as the wafering of ultra-thin
substrates requires adapted automation concepts.
The proof of concept concerning automated ultra-thin
wafer handling was investigated and demonstrated
with thinned wafers.
Miniaturized ultra-thin wafers and appropriate
grippers were tested and evaluated for feasible
industrial-scaled transportation.
Automated gripping of curled or heavily bowed
substrates was demonstrated in the handling
laboratory.
Advanced challenges due to the decreased wafer
thickness and the substrate`s shape diversification
come along with an increased sensitivity for
particular contamination.
4 ACKNOLEDGEMENT
This work is co-funded by the European Commission
within the 7th Framework Program. Thanks to all partners
of the SUGAR-project consortium for the contributed
work and input.
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[2] SEMI PV Group Europe International Technology
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[3] Dross, F. et al: Slim-Cut: A Kerf-Loss-Free Method
for Wafering 50-µm-Thick Crystalline Si Wafers
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[4] Gordon, I.; et al.: Three novel ways of making thin-
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[5] Fischmann, C. et al..: Automated Handling and
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... According to the International Technology Roadmap for Semiconductors [3] reported in 2015, the recent developments of new photovoltaic concepts use ultra-thin silicon wafers. In the next 10 years, the silicon wafer thickness will decrease to about 120 µm or even less [4] in order to meet the demands of low cost, light weight and small size consumer electronics. The silicon wafer will become thinner and larger than usual and the ultra-thin wafers will be increasingly used in the semiconduct industry. ...
... They are typically used to handle rigid materials such as battery electrodes [7], silicon wafers [8]- [12], flat sheets [13] or rough surface workpieces [14]. Significantly, in [4], [5] and [15], the Bernoulli gripper is used for handling flexible thin silicon wafers (from 120 µm to 256 µm with an area of 156 × 156 mm) because of its "low force" capability. However, these devices are not mainly designed or used for handling the ultra-thin and fragile silicon wafers or workpieces. ...
... The initial ultrasonic wet etching greatly decrease etched surface roughness caused by ultrasonic cavitation effects, producing thin wafer of good uniformity in thickness. The temporary bonding was realized by employing photoresist as the bonding agent [22,23]. Unlike wax or adhesive tapes, bonding created with spin-coated photoresist not only secured adherence during CMP, but also led to a uniform ultra-thin agent with free stress. ...
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In this research proposed a state-of-the-art approach for safely manipulating delicate and thin flat sheets without direct physical contact. Instead of traditional suction systems, here and axial flow propellers are used to create a non-contact suction gripper system powered by electricity, granting precise control over the lifting process. This method incorporates a sophisticated program developed in Lab View, enabling seamless management of fan speed for optimal performance. This method delve into the complex dynamics of pressure distribution through advanced numerical analysis employing the k-epsilon model with scalable wall function algorithms. Through extensive computational fluid dynamics simulations, gain valuable insights into the intricate fluid mechanics involved, ensuring the effectiveness of proposed approach. Addressing potential challenges posed by vibrations, integrate constrained layer damping between the robot’s end effector and gripper, minimizing disruptive oscillations. The experimentation meticulously examines the interaction of factors like gap clearance, fan speed, and lifting force, elucidating crucial relationships essential for system optimization. Ultimately, this research demonstrates the successful non-contact handling of thin sheets ranging from 0.25 mm to 1 mm in thickness, showcasing the practicality and adaptability of our novel method for various industrial applications. A regression model was developed to identify the relationship between speed and discharge of rotors.
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Ensuring the necessary accuracy of positioning the objects of manipulation of Bernoulli's grippers in robotic cells is an urgent task and can be achieved by choosing rational parameters of the gripping process. The article conducts experimental studies of the process of handling by Bernoulli grippers of objects of manipulation at different operating parameters and their weight. For this purpose, an experimental setup was developed, which consists of an industrial robot IRB 4600, an IRC5 controller, a Raspberry Pi microcontroller and two clock-type micrometers. The method of determining the total positioning error of the "robot-gripper-object" system is presented, which takes into account the positioning errors of the industrial robot, the errors of the gripping device and the errors of basing the object of manipulation relative to the axis of symmetry of the gripping device. The ABB IRB 1600 industrial robot was programmed in the ABB RobotStudio environment to cyclically simulate the handling operation and to determine the deviation of the position of the manipulation object after its gripping from different distances. The first cycle of automatic mode was used to calibrate the micrometer indicators, while gripping the object was carried out from a distance of 0.02 mm. For better reliability of research results, 20 measurement cycles were performed for each of the variable parameters. As a result, it was found that the maximum base error of objects does not exceed 0.4 mm. When capturing objects from a distance of 0.5…1 mm, the mean value of the base error will be 0.08…0.15 mm, with a standard deviation of 0.025…0.035 mm. The paper studies the effect of the displacement Δ of the center of mass of the gripped object relative to the axis of the Bernoulli gripper on the accuracy of the base of the objects. It is established that when the center of mass of the gripped objects is shifted relative to the Bernoulli gripper axis up to 20 mm, the maximum base error of the objects increases 2.2 times.
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The swirl gripper is an electrically activated noncontact handling device that uses swirling airflow to generate a lifting force. This force can be used to pick up a workpiece placed underneath the swirl gripper without any contact. It is applicable, for example, on a semiconductor wafer production line, where contact must be avoided during the handling and moving of a workpiece to minimize damage. When a workpiece levitates underneath a swirl gripper, the gap height between them is critical for safe handling. Therefore, in this study, we develop a theoretical model of the swirl gripper, based on which a method to estimate the levitation gap height by detecting pressure at two points is proposed. Experiments indicate that the estimated gap height can track changes in actual gap height accurately in real time, when the gap height is relatively small and the inertia of airflow in the gap is negligible. In addition, the force between the gripper and workpiece can also be estimated using the detected pressure. As a result, a desired relationship between the force and gap height can be achieved by adjusting the rotating speed of the fan according to the real-time estimated force and gap height using a microcontroller. The control system was experimentally verified using a desired linear relationship. Because the stiffness of the force decreases with increasing gap height for a constant gripper fan rotating speed, the linear relationship between the force and gap height, which means a constant stiffness, is expected to enhance handling stability of workpieces.
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The handling of ultrathin wafers (<100 μm thickness) is a challenging task since these are among the thinnest and most fragile materials. This paper provides a soft-acting and noncontact gripping technology for ultrathin wafer based on the distributed Bernoulli principle, and also proposes an experimental measurement method for evaluating the performance. A distributed Bernoulli gripper for ultrathin wafers is designed, and the characteristics of the gripper are studied via theoretical analysis and experiments. Three performance indices for evaluating the properties of the soft gripping: deformation, vibration, and stress are presented. Through measurement experiments, the effects of the key operational parameters consisting of air flow rate and gap height on the performance indices are investigated. Based on the experimental data, the appropriate parameters settings are obtained. The comparison to present grippers reveals that the proposed gripping technology is superior in soft gripping thin and fragile materials. This paper provides guidance for implementing the distributed Bernoulli principle in practical applications of soft-acting and noncontact gripping for thin and fragile materials.
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Monolithic solar modules made from thin-film crystalline-silicon layers of high quality on glass substrates could lower the price of photovoltaic electricity substantially. This paper describes three different approaches that we are currently investigating to address the challenge to form high-quality crystalline-silicon layers on glass substrates. The SLiM-Cut approach is a wafering technique that results in 50-micron thick layers with a minimum of material loss. We show that crack initiation can be used as a means to better control the lift-off process. The epifree approach involves the lift-off of ultra-thin monocrystalline films formed by reorganization of cylindrical macropore arrays in silicon upon annealing. So far, films with a thickness of around 1 μm and very simple cells with an efficiency of up to 4.1% have been achieved. Finally, a seed layer approach is presented based on the epitaxial thickening by thermal CVD of monocrystalline silicon layers bonded on glass-ceramic substrates. Very promising cell efficiencies of 11% and Voc values of up to 610 mV have been achieved using a very simple and non-optimized cell structure.Graphical Abstract
Automated Handling and Transport of Crystalline Photovoltaic Wafers
  • C Fischmann
Fischmann, C. et al..: Automated Handling and Transport of Crystalline Photovoltaic Wafers. In: Proceedings of the 25th European Photovoltaic Solar Energy Conference and Exhibition, 6-10 September 2010, Valencia, Spain. Conference Proceedings Page 1677 -1681.
Detection and avoidance of contaminations on solar wafer and cells
  • F Bürger
  • R Wertz
  • A Verl
Bürger, F.; Wertz, R. and Verl, A. : Detection and avoidance of contaminations on solar wafer and cells. In: Proceedings of the 26th European Photovoltaic Solar Energy Conference, 5-8 September 2011, Hamburg, Germany. Page 2112-2113.
Europe International Technology Roadmap for Photovoltaic -Results
  • Semi Pv Group
SEMI PV Group Europe International Technology Roadmap for Photovoltaic -Results 2011 3rd Edition March 2012