Non-Silicon Thin-Film
PV Materials Progressand Challenges.
SolarCon, Republic of Korea.
David A Sanchez
Solar Materials/Applications Specialist

Materion - Advanced Chemicals

April 8, 2011

Materion Advanced Chemicals
PRIMARY MARKETSSERVED■ LED Lightinggg■ Alternative Energy■ Optical and Semiconductor
C tiCoatings■ Specialty Battery■ Specialty Inorganic
Chemical Applications■ Large Area Coatings■ Medical■ Research & Development

KEY PRODUCTS &SERVICES■ Phosphor Materials■ New Product Development
Partnering■ High Purity Chemicals■ Thin Film Deposition Materials■ Large Format Sputtering Targets■ Precious and Non-preciousMetals■ Precious Metal Refining &Recycling■ Materials for Research &Development2

Milwaukee Facility leads the Business Unit anddrives PV Material Development
First reported at AIMCAL in 2007 and SVC in 2009, thin film PV
target and powder production has grown each year.
Topics Covered
 Cadmium Sulfide (CdS)• Introduced in 2005 is mature for evaporation
pand somesputtering processes.
 Copper Indium Gallium (di) Selenide (CIGS)• CIGS targets and powders• Binary compounds and metal alloys.
 Challenges of the sputtering of Se containing targets.

3

CdS Sputtering Targets■ DDense customtmicrocrystalline
it lli CdS powderd isi consolidated
lid t dinto tiles at high volume for sputtering.
■ Indium bonding is the most efficient for reuse of the backingplates.
■ Use of a digital
multi-meter tests
nature of the tile.
■ CdS resistance isyp
y 1+ kilotypicallyohm.
■ For this range, RFis common but
some pulse DC
processes havebeen reported.
4

CdS Sputtering Targets■ Tiles with sizes up to 175mm x 200”
200 at densities exceeding
89% are produced for bonding or direct use.
■ Mosaic tile format is used for larger sputter tools.
■ Tiles are Indium bonded onto rigid or reinforced backing plates.
■ Target Performance considerations:•M
Managementt off re-deposition.
diti•

Sputtering power and arc sensitivity.

•Temperature of target and process.

S
Sequentially
i ll bondedb d d CdS tilesil ((on copper)) ffor a llarge width
id h sputtering
i process (M(Marchh 2011)2011).
5Effects of Power and Temperature on CdS■ Management of process conditions and surface/bulk temperatureof the target is critical to lifetime of the target.
• Re-deposition of alternate phases and sulfur loss are keyy concerns.

• Local regions of higher conductivity can alter plasma density.
Re deposition is lower density
Re-deposition
CdS. Aside from contamination - n,p or I type effects plasma.
SulfurS
lf lloss hhelps
l ratet bbutt alsolinfluences local conductivity.

Due tto hD
heatt or ddense plasma,llocal rate changes can shorten
target life or effect uniformity.

6

CIGS Sputtering Targets■ Standard single phase: Cu(InxGa1-x)Se2 powder is produced from a
range of Copper, Indium and Gallium levels.
■ Standard or Custom CIGS powders are manufactured and thenconsolidated into dense tiles for sputtering.
■ More than 50 different customer specified composition powders haveb
been
maded tto order.
d■ Standard Cu(In0.7Ga0.3)Se2 tiles exceeding 88% density are available up
to 125 mm x 125 mm or targets of 200mm in diameter.
■ The machined tiles/targets are fit for elastomer or indium bonding to rigid
backing plates.
■ Final film properties are influenced by initial composition and process.
■ Target Usability Contributors Include: •Sputtering approach.
•Low melting sub-phases•Free metals
7Sputtering of CIGS and the CIGS Film
■ Process conditions must be maintained
to keep –Se in the compound.
■ CIGS targets
gare fragile
g and sensitive
to thermal and mechanical stress.
■ With multi-meter readings in excess of1 kilo-ohm resistance, RF sputtering is
the most prevalent.
■Novel pulse DC and DC techniques
have been reported.

**all values are atomic %**target composition, as measured
by ICP**as deposited and post anneal
refer to film composition,d tdeterminedi dbby EDS***EDS values are different than
ICP bulk characterization valuesCuInGaSetarget
20 - 25
15 - 21
6-950

CIGS target after RF sputtering*

thin film
as deposited
post anneal
26.5 - 29.7
27.8 - 29.6
15.7 - 17.4
16.5 - 18.4
7.5 - 8.5
7.5 - 9.3
45.9 - 48.8
44.2 - 46.5

*CIGS films obtained by Mr. Wen-Tsai Yen and Dr. Yi-Cheng Lin On SLG at 1Kw at Taiwan
ROCNR.O.CNationaltil Ch
ChangHuaH UUniversityiit off EdEducationti DDepartment
tt off M
Mechatronics
h t i JJune 2008
2008.
8

CIGS Compound Sputtering Targets■ Backing plate stiffness and bonding
technique are important.
■

Backing plate bowing stress alongwith high temperatures can result inedge chipping. A.

■

In-plane chipped targets can sputter
but excessive chipping can increase
arcs and stabilitystability.

■ High target temperatures cantransform or embrittle targets.
■

Phase change,Phhmelting
lti or glassy
lappearance indicate hightemperature.

■Shear overload failures along
gstressed regions can delaminate
target from backing plate. B.

■Selenium loss can lead to melt-out
or increased archingarching.
9CIGS Binary Sputtering Targets■ Commercial and academic demand has grown for the binary compounds.
■ Issues with controlling important In / (In + Ga) and Ga / (In + Ga) ratios
in the CIGS layer led to requests for stable binary compounds.
■ Similar to the full CIGS target
target, -Se
Se retention and control remains a key
factor for the binary targets.
■ In2Se3 and Cu2Se targets seem to have an even more dramatic
conductivity vs temperature relationshiprelationship.
■ With less sub-phases possible the onset of melting and poisoning of
the target surface remain key hurdles for process development.
■ As with CIGS,CIGS the presence of Selenium in the compound limits target
conductivity and makes use of pulse DC or DC sputtering difficult.
■ Process approach and conditions are less advanced than CIGS.
■ Due to the complexities and limitations off sputtering –SeS compounds,
Industry has increased demand for conductive options.
■ Copper – Gallium and Copper-Indium-Gallium alloys have beendeveloped for sputteringsputtering.
10

Cu-Ga Alloy Sputtering Targets■ The CuGa Billet is cut/rolled into tiles or extruded for tubes.
■ Conductivity of the alloy allows DC and pDC to be used
■Limit of DC power is the stability of Gallium in the alloy.

■ UUp tto 25 at%t% Ga.
G theth alloyll iis stable
t bl andd machined
hi d iinto
t segmentst up tto
10mm thick.
■ Large single piece or mosaic assemblies can be conventionally bonded.

A Typical machined CuGa25billet

Typical CuGa25 targets for bondingbonding.
11

Cu-Ga Sputtering Targets for CIGS
■ With increasing Ga. Content, the CuGa alloy is too brittle and required thedevelopment of a proprietary powder/press process.
■ Typical CuGa25+ at% Ga round target is up to ~190mm in diameter
andd 1010mm thithick.
k■ Typical CuGa25+ at% Ga tiles are up to ~254mm long, 152mm wide
and 6mm thick.

Single CuGa25+ round targettarget.

3 CuGa25+ tiles ready for bonding.
bonding12

Cu-In-Ga Sputtering Targets■ Copper – Indium
Indi m – Gallium
Galli m targets require
req ire adadvanced
anced man
manufacturingfact ringtechniques due to large differences in constituent melting points.
■ Cu – ~1084 C

In – ~430 C

Ga – ~303 C■ With advanced manufacturing technology available, market trends show
minimum composition variance of +/- 2.5 at%.
■ Impact of Composition variances in a target:•Chance of sub-phases broadening the melting point range (of alloy) .

•Soft regions near higher melting regions make machining difficult.

•Inhomogeneous targets are likely to “melt-out”
melt out inin-situsitu.

■ Industry demands for higher composition control lead to a new process.
•New process reduces composition variance to +/-1at%.

•New process meets market demand for 500mm long,127mm wide and10mm thick targets.

13

CIGS powders for Printing■ Standard -200
200 meshCu(In0.7Ga0.3)Se2 powders are sized
in a custom process.
p
can complicatep■ Sub-phases
formulations.
■ Curing techniques may besensitive to different metallic
sub-phase impurities.
■ Energetic sizing benefits fromimmediate immersion in a protective
bi d /i k or suspension.
binder/inki■ Internal techniques offer a starting
composition and final D50 size < 5microns.
microns■ Materion continues to invest in
developing other methods to size,
protect and package finer powders.
powders

Example of sizing -200 mesh
CIGS tto < 5 um.
14

CIGS Nano Dispersions■ Standard Cu(In0.7
0 7Ga0.30 3)Se2 powders are further
reduced and dispersed in a custom process.
■ Dispersions provided in water or alcohol■ Available in 20 – 40wt% CIGS to liquid■ Particle sizes <100nm possible■ Additional compositions and dispersantspossible.
ibl15

MaterialTypePurity (%)

Cu-In-Ga-Se

target99.99

6 mm pcs. & less

99.99

-200 mesh

99.99

CuInSe2

6 mm pcs. & less99.999

Cu-In-Gatarget99.99■ Many materials for
CIGS efforts requiresignificant post
deposition processing
to achieve final film
properties.

Cu-In

powder
p

99.99

Cu-Ga

target99.99+

Cu2Se

target99.5

6 mm pcs. & less

99.5

CuSe

6 mm pcs.
pcs & less

99 5
99.5

In2Se3target99.9

6 mm pcs. & less99.999■ The environment ofeachh subsequentbt steptmust be weighed on
the following step.

Ga2Se36 mm pcs. & less99.999Cu

6 x 6 mm pellets

99.99*

3 x 3 mm pellets

99.99*

2-6 mm shot

99.99-99.999*-20, +50 mesh99.95*

target99.99, 99.999

3mm shot99.99 - 99.9999*

Ga

3 mm shot

99.99 - 99.9999

Se

3 mm shot

99.99, 99.999*■ Materion offers alarge selection ofmetal/alloy andcompound targets for
CIGS efforts.

■ Oxygen
Oxygen, moisture andtemperature control isimportant betweensteps.

In16Challenges for Sputtering Processes
Despite advances in producing and scaling of CdS, CIGS,CuGa, CIG and binary powders as targets, their delicate
nature puts pressure on the process.
 Any time, any amount of Selenium is part of the compound,the target conductivity quickly drops.
 Selenium
S l ianddG
Galliumllialso
l add
dd th
the riski k off –Se
S or –Ga
G vaporin the process.
• Aside from Arcs (pDC, DC) the free metal interactions withthe plasma (pDC, DC and RF) complicate sputtering.
 Selenium loss also reduces the integrity of the compound,gppoint reduction.
which results in melting
 Gallium loss in the alloys increases melt-out risk (CuGa) or

destabilizes the composition and integrity of the CIG targets.

17

Challenges for Sputtering Processes Overheated targets can sag or melt:• Melting point reduction due to alloy melt-out or sub-phases.
• High temperatures are associated with sputter process and cooling.

 For each compound to be maintained as a semiconductor, there

must be special care to limit the target temperature.
• Aggressive conditions or excessive arcs can liberate species.
— Metals can coalesce (due to sweat or redposition) to make arcs
unmanageable.
unmanageable— Metals can also create hot spots which can locally segregate or poolplasma.
— Sulfides and Selenides can also redeposit as a non-ideal
semiconducting or insulating phase which can “kill” or “poison” a target.

18Challenges for Sputtering Processes
Adapting classical semiconductor/FPD procedures for thinfilm PV assumption #1 - bonding.
 It was assumed that conventional bonding would serve the needsof the new market.
— Indium bonds are adequate for systems that are well cooled or have
durable, conductive targets in use.
— Most PV targets are semi-conducting at best and are made warm/hot by
aggressive technique deployment.
Elastomer and epoxy bonds can be required for sputter down or— Elastomer,sideways processes.
— Since cracking is also very common with the compound targets,elastomer bonding enables the target to be pushed even after many
cracks/arcs.
— Hybrid bonding systems have been needed for the thermally unstablecompounds or low melting point targets like CIG.

19

Challenges for Sputtering Processes
Overlooking plate deflection due to temperature or water pressure
destroys good targets.
Backing Plate Selection and Specification.

• It is important to note when the cooling water is in direct contact withthe backing plate/target assembly as deformation can flood thecchamber
a be witht water.
ate— Typical water pressures are 1.5 to 3.5 Bar (1 Bar = 1kPa).
— When there is a base plate, and no water contact, the thermal conductivity
and cost of the material are most important (Cu,(Cu MoMo, Ti)
Ti).
— Many compound targets or low melting point alloys provide very little or
fleeting reinforcement to the backing plate assembly.

• Oxygen Free – High Conductivity Copper has been standard but is
too soft to be a safe water barrier at 2.5 – 3.5 bar of typical
processes.

20Challenges for Sputtering Processes
 Specifying temper is very important.
important• Conventional OFHC C101000 annealed copper has a low yieldstrength (11 ksi “kilo-pound[-force] per square inch”).
• Work hardening C101000 increases the yield strength dramatically.
(30-45 ksi).
• Deformation of the backing plate can cause many issues
issues.
— Assembly of the tool may be impossible if bolt holes are deformed.
— Any deformation by the backing can crack Sulfide or Selenide targets.
— Excessive deformation, even without water breech, can make re-using thebacking plates difficult.

• Other,
Other more stiff materials (Molybdenum) or cheap (Stainless Steel)plates lack required thermal conductivity to minimize the risk to thethermally influenced –Se, –Ga or –In targets.
• The
Th Process
PEngineer
E ishould
h ld approve b
bestt choice
h i tto purchasing.
h i21

Challenges for Sputtering Processes ManyMEEngineersiuse clampedld platel t

calculations to calibrate their coolingstrategy.
 The dimensions (ro, Lx, and Ly), load

(Bar/Pascals) and modulus are known (ormeasured).
• To protect against deflection and to maintain thebest thermal conductivity Copper/Chrome
C18200 is excellent with a yield strength of 4060 ksi.
ksi

ClampedCld Ci
Circularl PlPlate,t
Uniform Load

 The Elastic Modulus is the material

property that describes stiffness.
• known for most materials it should be tested
from time to time as process conditions can“self anneal” the backing plate.

Clamped Rectangle Plate,
Uniform Load22Materion – Advanced Chemicals is your partner
for PV materials
Our latest realignment is just the next step in providing the broadest
experience and perspective to the quickly evolving PV thin filmmarket.
marketWe know we are an important part of both 1) this technology
development and 2) the effort to give the solar marketplace more
performance and value than before
before.
We will continue to produce and support the increasingly complex
demand of the PV solar market.
CdS for evaporation and sputtering continues to grow and CdTe
based approaches grow with utility scale supply projects
CIGS has met many challenges but tools are increasing in size andvolume with many technologies to address them.

23Challenges and Keys to Growth of Thin Film PV
Bonding and Backing plate specifications have to evolve to meetthe needs of the more fragile and thermally sensitive compounds.
Many materials for CIGS efforts require significant post deposition
processing to achieve final film properties.
The environment of each subsequentq
step
p must be weighed
gon thecurrent step to assure an effective manufacturing strategy.
Oxygen, moisture and temperature control is important at every step.
CIGS on the large scale, by any current approach, is still very far fromthe theoretical nameplate of the system in terms of performance, costand durability.
Many challenges remain in optimizing the right material and process forthe right application.

24Thank you for your attention!
Special Thanks to the Staff at Materion for the material calculations andproduct data/pictures used in this presentation.
Dr. Katharine Gardinier – PV compounds/targets - Milwaukee
Dr. Dejan Stojakovic – PV Alloys – Brewster
James Paloucek – Global Solar Materials Sales - MilwaukeeNNoraBiBiersackk – AdvancedAd
d Ch
Chemicalsi l SBU – Milwaukee
Milk
EJ Strother – Advanced Chemicals SBU Leader, Milwaukee
Mechanical Engineeringgg Information:
Robert Haag – Process Engineer Manager, Brewster
Michael Pasquariello – Continuous Improvement Specialist25