slide 1 derf june 2008 apcvd tio 2 vs pecvd sin x : the battle for antireflection supremacy...

DERFDERFJune 2008June 2008

APCVD TiOAPCVD TiO22 vs PECVD SiN vs PECVD SiNxx::

The Battle forThe Battle forAntireflection SupremacyAntireflection Supremacy

(Findings from a 3-yr ARC Linkage Project (Findings from a 3-yr ARC Linkage Project between ANU, SierraTherm & SunPower)between ANU, SierraTherm & SunPower)

06-June-200806-June-2008

Project details• Contributions over three years (AUD):

Contributor Cash In kind

Agreed Actual Agreed Actual

ARC $340,000 $385,000 – –

SierraTherm $120,000 $120,000 $492,000 $270,000

SunPower – – $339,000 $138,000

• Direct Personnel: Research Fellow: Keith/Bryce (2005-08)Research Fellow: Keith/Bryce (2005-08) MPhil student: Luke (2005-07)MPhil student: Luke (2005-07) Part-time contributions fromPart-time contributions from

- Mihail Ionescu (ANSTO)- Mihail Ionescu (ANSTO)- Jeff Simpson, Bob Spekkart (SierraTherm)- Jeff Simpson, Bob Spekkart (SierraTherm)- Dick Swanson (SunPower)- Dick Swanson (SunPower)

• Indirect Personnel: 2 x PhD students: Andy (2006-09), Bijaya (2006-09)2 x PhD students: Andy (2006-09), Bijaya (2006-09) 3 x honours students: Amarjit (2006), Simeon (2008), Lachlan (2008).3 x honours students: Amarjit (2006), Simeon (2008), Lachlan (2008). 3 x foreign students: Efthimios (2005), Joan (2007), Maria (2008)3 x foreign students: Efthimios (2005), Joan (2007), Maria (2008) 2 x summer students: Yunki (2006), Teng (2007-08) 2 x summer students: Yunki (2006), Teng (2007-08)

Comparison at beginningProperty APCVD TiO2 PECVD SiNx


1. Anti-reflection Good Fine



2. Cost Low ~3 x higher




3. Passivation ofbare Si

Terrible Good





Terrible Good

4. Passivation ofSiO2-Si

Good Excellent





Terrible Good


Good Excellent

5. Static charge Unknown ModeratePositive





Terrible Good


Good Excellent


6. Hydrogen content

Little, if any High





Terrible Good


Good Excellent


6. Hydrogen content

Little, if any High

7. Barrier towater vapour

No Yes





Terrible Good


Good Excellent


6. Hydrogen content

Little, if any High

7. Barrier towater vapour

No Yes

8. Reaction with EVA

Possibly No

Hope vs time

0

25,000

50,000

75,000

100,000

125,000

150,000

175,000

200,000

225,000

2005

2006

2007

2008

Ho

pe

(me)

Project goalAddress properties 4, 5, 6 & 7 to:

• Attain equivalent surface recombination (J0E)with TiO2/SiO2/Si compared to SiNx/SiO2/Sifor textured silicon after accelerated testing(damp-heat, UV).

TiO2 or SiNx

SiO2

n+ diffused silicon

n-type silicon

Mercury Maximum efficienty - 1D modeling with tauP=2e-3 s, J0e(Back) = 1e-13 A/cm2

20.0

20.5

21.0

21.5

22.0

22.5

0 20 40 60 80 100 120 140 160 180 200

FSF J0e [fA/cm2]

Max

imu

m E

ffic

ien

cy [

%]

Merc3.5

Merc3.7

Property 4: Passivation of SiO2-Si

Efficiency of rear-contact cells strongly affected by J0E

SiNx/SiO2

TiO2/SiO2

Causes for lower J0E (Andy)• Not contamination

Phew!Phew!

• Not moisture in reactants Good.Good.

• Loss of hydrogen during deposition at 400 oC Reversible with FGAReversible with FGA

Does not occur at lower 250 oCDoes not occur at lower 250 oC

• Stress on texture (?) HmmmHmmm

• No atomic H with APCVD, unlike PECVD Probably not a big deal – attain similar DProbably not a big deal – attain similar Ditit

• Static charge Need to add some!Need to add some!

Property 5: Static Charge

1E-15

1E-14

1E-13

1E-12

1E-11

1E-10

-1E+12 -5E+11 0 5E+11 1E+12

Insulator charge density (cm-2)

J0

Ee

ff (

A/c

m2

)

3.00E+12

1.00E+12

3.00E+11

1.00E+11

3.00E+10

1.00E+10

TiO2/SiO2 SiNx/SiO2

• 5 ohm-cm n-type

• All donor defects

• n = 1015

Add charge by corona? Adding charge by corona discharge has problems:

• our corona damages Si-SiO2 interface- will add gate (Tom/Klaus- will add gate (Tom/Klaus))

• charge is slowly removed by water vapour in atmosphere- add moisture barrier (Simeon/Maria),- add moisture barrier (Simeon/Maria),- anneal TiO- anneal TiO22 (Simeon/Maria) (Simeon/Maria)

Property 6: Hydrogen• Measurement

ERDA (Andy)ERDA (Andy)- Almost underway...- Almost underway...

SIMSSIMS RTA & PC (Teng)RTA & PC (Teng)

- increase/decrease in recomb as H evolves- increase/decrease in recomb as H evolves

• As deposited TiO2 is permeable to H2 and H+

HH22 lost during deposition at 400 oC lost during deposition at 400 oC post-deposition FGA replaces Hpost-deposition FGA replaces H22

FGA within N2 curtains replaces HFGA within N2 curtains replaces H22..

• Annealed TiO2 appears impermeable to H2 (Maria)

• H not bonded in significant concentration to TiO2 when FGA in N2 curtains. Will test FGA in separater NWill test FGA in separater N22 H known to alter crystal state but not necessarily bonded to Ti H known to alter crystal state but not necessarily bonded to Ti

and O.and O.

20 30 40 50 60 70 80 90 100 110 120 130 140 150

0

10

20

30

H Y

ield

[cou

nts]

Channel Number

2B 2C 2D 2B, 2C and 2D

Property 7: Moisture barrier

Occurs on* planar and texture (Thimios)* annealed, alnealed, RTA (Thimios)* n-type & p-type (Luke)* P & B diffusions (Joan)

Does it matter? Yes! Damp heat test degrade Si-SiO2.

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5

Damp-heat exposure (mins)

Eff

ec

tiv

e li

feti

me

(s

)

Planar,FGA

Planar,Alneal

Planar,RTA

Textured,FGA

Texutred,Alneal

Textured,RTA

0

Property 7: Moisture barrier

Does APCVD TiO2 prevent it degradation No! (Maria, Luke)

0.E+00

1.E-14

2.E-14

3.E-14

4.E-14

5.E-14

6.E-14

7.E-14

8.E-14

9.E-14

0 2000 4000 6000 8000 10000 12000 14000 16000

Time in damp heat (mins)

J0E

(A/c

m2

)

2a SiO2 control

2b SiO2

7a TiO2/SiO2 control

7b TiO2/SiO2

Mercury Maximum efficienty - 1D modeling with tauP=2e-3 s, J0e(Back) = 1e-13 A/cm2

20.0

20.5

21.0

21.5

22.0

22.5

0 20 40 60 80 100 120 140 160 180 200

FSF J0e [fA/cm2]

Max

imu

m E

ffic

ien

cy [

%]

Merc3.5

Merc3.7

Passivation of SiO2-Si after damp heat

Efficiency of rear-contact cells strongly affected by J0E

SiNx/SiO2

TiO2/SiO2

TiO2/SiO2

after damp-heat

DH degradation: cause / solution• Cause is not

removal or deposition of surface charge (Joan)removal or deposition of surface charge (Joan) removal of H at interfaceremoval of H at interface

• Increase in J0E corresponds to increase in Dit (Luke). Possibly due to wet oxidation at 85 oC wet oxidation at 85 oC silicic acid in SiOsilicic acid in SiO22 creating stress at Si-SiO2 interface creating stress at Si-SiO2 interface

• Solution requires moisture barrier HMDS: no success so farHMDS: no success so far Annealed TiOAnnealed TiO22: anneal removes H: anneal removes H Module encapsulationModule encapsulation (PECVD Si(PECVD SixxNNyy))

Conclusion – the best hope...

1E-15

1E-14

1E-13

1E-12

1E-11

1E-10

-1E+12 -5E+11 0 5E+11 1E+12

Insulator charge density (cm-2)

J0

Ee

ff (

A/c

m2

)

3.00E+12

1.00E+12

3.00E+11

1.00E+11

3.00E+10

1.00E+10

SixNy/SiO2TiO2/SiO2

2) Embed high Q without damage (gated corona?)

3) Engineer moisture barrier to prevent Q loss & DH deg.

1) Deposit hydrogenated TiO2

3a) Anneal TiO2

3b) Add barrier

3c) Vapour-tight module

What affects J0E• Charge in dielectrics, Q.

• Density of interface states, Dit(E), of donors and acceptors.

• Capture cross sections, p(E) & p(E).

• Surface doping Ns or bulk doping Nb

• Illumination n (at moderate and high injection)

QTiO2 QSiO2

CB

VB

FL

-

--

-

-

- +

+

+

+

n

p

slide 1 derf june 2008 apcvd tio 2 vs pecvd sin x : the battle for antireflection supremacy...

Documents

pecvd sin x slide

higher slide

anyhigh slide

si goodexcellent slide

antireflectiongoodfine

e sin x sio

vs pecvd sin x

passivation of sio