POLYSI CONTACTING WITH SECOND GENERATION FT PASTES … · ISE and ISFH Standard reliable TLM ISSUES: Multi-layer Multi-interface Thick layers Metal contacts penetrate (etch) polySi

POLYSI CONTACTING WITH SECOND GENERATION FT PASTES

AND ACCURATE CHARACTERIZATION OF CONTACT RESISTANCES

M.K. Stodolny1, B. Macco2, G.J.M. Janssen1, E. Kossen1, A.A. Mewe1,

N. Guillevin1, M. Koppes1, J. Melskens2, W.M.M. Kessels2, C.J.J. Tool1, J. Loffler1

METALLIZATION & INTERCONNECTION WORKSHOP 2019

2

1

OUTLINE

Industrial Fire-Through contacts to n+ and p+ polySi

J0,c with conventional pastes (GEN1)

J0,c with improved pastes (GEN2)

How to reliably measure contact resistance of local polySi contacts

TLM issues with polySi and possible solutions

Contact resistance measurements with a Cox&Strack method

Experimental efforts to realize Cox&Strack structures

Simulations to validate the approach

2

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)

B-tail depth below polySi (µm) (@1E18) (p+, i-, no- polySi)P-tail depth below polySi (µm) (@1E17) (n+polySi)

Series6

n-poly_model

INDUSTRIAL FIRE-THROUGH CONTACTS TO POLYSI

3

n+ polySi (Ag FT paste)

w/ P

-ta

il

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)

B-tail depth below polySi (µm) (p-, i-, no- polySi)P-tail depth below polySi (µm) (n-polySi)

n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

FT GEN1

n+ polySi

(modelling)

Stodolny et al, Metallization Workshop 2017

p+

polySi

oxide

tail

FT metal


4

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

Log. (p-poly_SiNx)

n+ polySi (Ag FT paste) p+ polySi (Ag-Al FT paste)

Shielding P- or B-tails below the polySi layers

reduce J0,c by at least an order of magnitude

Under FT paste, a local extensive etching of

polySi and metal penetrating the wafer

50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)

B-tail depth below p-polySi (µm)P-tail depth below polySi (µm)

n-poly_SiNx

n-poly_model

p-poly_SiNx

p-poly_SiNxGEN2n-poly_SiNxGEN2

w/ P

-ta

ilw

/ B

-ta

il

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

FT GEN1

p+ polySi

FT GEN1

n+ polySi

(modelling)

(guide to the eye)

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

Log. (p-poly_SiNx)

p+p+

polySi

oxide

tail

FT metal

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

Log. (p-poly_SiNx)


5


Under FT paste, a local extensive etching of

polySi and metal penetrating the wafer

50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx


w/ P

-ta

ilw

/ B

-ta

il

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

FT GEN1

p+ polySi

FT GEN1

n+ polySi

(modelling)

(guide to the eye)

Shielding P- or B-tails below the polySi layers

reduce J0,c by at least an order of magnitude

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

Log. (p-poly_SiNx)

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

gen 2 p-poly

Series1

p-poly_SiNx


WITH REDUCED RECOMBINATION

6

J0c,p+poly=200 fA/cm2J0c,n+poly=65 fA/cm2


50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx


w/ P

-ta

ilw

/ B

-ta

il

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

FT GEN1

p+ polySi

FT GEN1

n+ polySi

(modelling)

(guide to the eye)

p+ polySi

FT GEN2

50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx


n+ polySi

FT GEN2

n+ polySi (Ag FT paste GEN2) p+ polySi (Ag-Al FT paste GEN2)p+ polySi (Ag-Al FT GEN2)n+ polySi (Ag FT GEN2)

50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2 )


n-poly_SiNx

n-poly_model

p-poly_SiNx


GEN2 of Fire-Through pastes:

less aggressive and shallower etching into

the polySi layers allows lower J0,cStodolny et al, SiliconPV 2019

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

gen 2 p-poly

Series1

p-poly_SiNx

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

Log. (p-poly_SiNx)


WITH REDUCED RECOMBINATION

7

p+ polySi (Ag-Al FT paste GEN2)n+ polySi (Ag FT paste GEN2)

ESB mode

– sensitive to metal

PERC-p-poly

p-IBC Full poly IBC

PERPoly w/poly fingers

POLYSI PASSIVATING CONTACTS FOR VARIOUS SI

SOLAR CELLS – HOW ABOUT R_CONTACT?

Industrial polySi passivating contact cells

feature rather local contacts

than full area metallization

Contact resistance becomes important !

How to reliably measure ρc ?

8Stodolny et al, SiliconPV 2019

CONTACT RESISTANCE: TLM ISSUES WITH POLYSI

9

TLM on polySi:

Error ρc can increase

to 10-100 mΩcm2

TLM issues also reported by

ISE and ISFH

Standard reliable TLM ISSUES:Multi-layerMulti-interfaceThick layersMetal contacts penetrate(etch) polySi

ρmetal/poly/ρoxide ?

𝑹 = 𝟐𝑹𝒄 + 𝑹𝒔𝒉𝒆𝒆𝒕𝒅

𝒁

with 𝑅𝑠ℎ𝑒𝑒𝑡 =𝜌𝑏

ℎand assuming h <<d and h << W

𝑹𝒄 =𝑹𝒔𝒉𝒆𝒆𝒕𝑳𝑻

𝒁𝐜𝐨𝐭𝐡

𝑾

𝑳𝑻with 𝐿𝑇 = Τ𝝆𝒄 𝑅𝑠ℎ𝑒𝑒𝑡 so 𝑅𝑐 =

𝜌𝑐

𝑍𝐿𝑇coth

𝑊

𝐿𝑇

H. Berger, IEEE Int. Solid-State Circuits Conf., Dig. Tech. Papers,

vol. 12. Feb. 1969, pp. 160–161.

Gamze Kökbudak, FhISE, 33rd EUPVSEC

polySi

oxide

tail

FT metal

CONTACT RESISTANCE: TLM ISSUES WITH POLYSI

AND POSSIBLE SOLUTIONS

10

TLM: remove polySi and tail

➔ complicated bulk correction

➔ 3D simulations for every sample

TLM: on blocking substrate

tail provides lateral transport

➔ Etching of polySi by FT paste

results in overestimation of ρc

➔ Preserving tail difficult

Cox&Strack: remove polySi and tail

➔ Spreading resistance method to

obtain ρmetal/poly/ρoxide

Eidelloth & Brendel , IEEE Electron Device Letters,

Vol. 35, No. 1, January 2014

Rienäcker et al. IEEE Journal of Photovoltaics,

Vol. 7, No. 1, January 2017

Gamze Kökbudak, FhISE, 33rd EUPVSEC

R. H. Cox and H. Strack, Solid-State Electron.

10 (1967) 1213-1218.

CONTACT RESISTANCE WITH COX&STRACK METHOD

11

Width of contacts varied

Circular electrodes (Cox&Strack)

𝑹(𝒅) =𝝆𝒃𝒂𝒔𝒆𝒅𝝅

𝐚𝐫𝐜𝐭𝐚𝐧𝟒

Τ𝒅 𝒕+𝟒𝝆𝒄𝝅𝒅𝟐

+ 𝑹𝟎

p+ polySi

c-Si

diff.

polySi

tail

ρbase

Top view

12

COX&STRACK VALIDATION SIMULATIONS

Etching of conducting polySi and tail neccessary

p+ polySi

p c-Si

p+

p+ polySi

B-tail

blanket PVD Ag

PVD Ag

wet chemical patterning

of PVD-Ag/polySi/B-tail

p c-Si

p+

p+ polySi

B-tail

blanket PVD Ag

PVD Ag


of only PVD-Ag

Etc

he

d

COX&STRACK: INVESTIGATED STRUCTURES (I)

13


of polySi/B-tail

then FT paste


of PVD-Ag/polySi/B-tail

ρc (C&S) = ~2.6±1.9 mΩcm2poor C&S fitting

(misalignment issues*)

p+ polySi

p c-Si

p+

p+ polySi

B-tail

blanket PVD Ag

PVD Ag

p+ polySi

p c-Si

p+

B-tail

blanket FT Al

FT Ag-Al

SiNx p+ polySi*

Top view

14

COX&STRACK: INVESTIGATED STRUCTURES (II) &

VALIDATION SIMULATIONS

Laser isolation gives same results as etching

More sensitivity needed for such low ρc

p c-Si

p+

p+ polySi

B-tail

laser isolation

with PVD Ag

PVD Ag

blanket PVD Ag

ρc (C&S) ~2±2 mΩcm2

laser isolation

around FT paste

p c-Si

p+

B-tail

FT Ag-Al

blanket FT Al

ρc (C&S) ~<<5 mΩcm2

(not sensitive enough)

p+ polySi

Etc

he

d

IMPROVING THE ACCURACY

Effect ρwafer:

Very sensitive to base resistivity!

Lower resistivity wafers readily available

➔ experiment in progress…

15

0 50 100 150 2000

10

20

30

40

50

60

70

r wafe

r= 3

Wcm

Effect wafer resistivity

Resis

tance (

W)

1/diameter (cm-1)

r wafe

r= 2

Wcm

r waf

er=

1 W

cm

rwafer= 0.5 Wcm

rc= 0 mWcm2 , dwafer =165 mm

We would like to maximize

the contribution of ρc to the measured R

𝑹(𝒅) =𝝆𝒃𝒂𝒔𝒆𝒅𝝅

𝐚𝐫𝐜𝐭𝐚𝐧𝟒

Τ𝒅 𝒕+𝟒𝝆𝒄𝝅𝒅𝟐

+ 𝑹𝟎

CONCLUSIONS AND OUTLOOK

PolySi based contacts

Excellent passivation and selectivity

At the contact with FT (GEN2):

n+ J0,c = 65 fA/cm2

p+ J0,c = 200 fA/cm2

GEN3 coming soon

Reliable contact resistance measurements of local polySi contacts

TLM issues with polySi reviewed

Cox&Strack method implemented to polySi

Etching and laser isolation suitable for patterning

Simulations validated use of both method

Tunning ongoing to increase sensitivity for low ρc

16


polySi

oxide

tail

FT metal

p+ poly Si

c-Si

dif f .

poly Si

tail

p c-Si

p+

B-tail

FT Ag-Al

blanket FT Al

p+ poly Si

THANK YOU FOR YOUR

ATTENTION

TNO.NL/ECNPARTOFTNO

Acknowledgements• Projects executed with Topsector Energy subsidy of the Dutch Ministry of Economic Affairs

• ECN.TNO processing and characterization team for careful execution of the experiments

• TWENTE UNIVERSITY - MESA+ INSTITUTE FOR NANOTECHNOLOGY for HR SEM imaging

CONCLUSIONS AND OUTLOOK

PolySi based contacts

Excellent passivation and selectivity

At the contact with FT (GEN2):

n+ J0,c = 65 fA/cm2

p+ J0,c = 200 fA/cm2

GEN3 coming soon

Reliable contact resistance measurements of local polySi contacts

TLM issues with polySi reviewed

Cox&Strack method implemented to polySi

Etching and laser isolation suitable for patterning

Simulations validated use of both method

Tunning ongoing to increase sensitivity for low ρc

18


polySi

oxide

tail

FT metal

p+ poly Si

c-Si

dif f .

poly Si

tail

p c-Si

p+

B-tail

FT Ag-Al

blanket FT Al

p+ poly Si

SUPPORTING SLIDES

EXCELLENT SURFACE PASSIVATION OF

N+, P+ AND I-POLYSI ON TEXTURED SURFACES

n+ polySi ~ 1 fA/cm2

p+ polySi and i polySi < 10 fA/cm2Mewe et al, SiliconPV 2018

Stodolny et al, EUPVSEC 201820

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

SiNx AlOxSiNx

AlOxSiNxAlOx

after firing

before firing

11 fA/cm29 fA/cm2

15 fA/cm2

11 fA/cm2

21 fA/cm2

44 fA/cm2

polySi polySi polySi

10 fA/cm2

a b c

3 fA/cm2

4 fA/cm2

1 fA/cm2

2 fA/cm2

<1 fA/cm2

1 fA/cm2

~8 fA/cm2

n+ polySi

p+ polySi

i-polySi

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc(V

)n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc(V

)n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

texture

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc(V

)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

0,680

0,690

0,700

0,710

0,720

0,730

0,740

0,750

0,5 1 1,5 2 2,5 3 3,5

Imp

lie

d V

oc

(V)

n-poly BF

n-poly AF

p-poly BF

p-poly AF

i-poly BF

i-poly AF

Institute/Company

n+ polySi

p+ polySi

texture

ISFHISE

ISFHTrina

4 fA/cm2

2-4 fA/cm2

11 fA/cm2

27 fA/cm2

ISFHi-polySi78 fA/cm2

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

i-polySi

no-polySi (B-emt)

p+ polySi

n+ polySiw

/ P

-tai

lw

/ B

-tai

l

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

p+ polySi

i-polySi

no-polySi

n+ polySi(modelling)

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

(guide tothe eye)

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

GEN2

GEN2

50

500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


Series6

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx


(GEN1)

21


50

500

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx


w/ P

-ta

il

100

1000

0 0,1 0,2 0,3 0,4 0,5 0,6

Jo,c

on

tact

(fA

/cm

2)


n-poly_SiNx

n-poly_model

p-poly_SiNx

i-poly_SiNx

no-poly_SiNx

n+ polySi

FT GEN1

p+ polySi

FT GEN1

n+ polySi

(modelling)

(guide to the eye)

6

i-polySi (Ag-Al FT paste) no-polySi (B-emt Ag-Al FT)i-polySi (Ag-Al FT paste) no-polySi (B-emt Ag-Al FT)

Local i-polySi layer can reduce recombination

loss for screen-printed contacts on top of an

uniform shallow boron emitter See more @EUPVSEC2019

w/ B

-ta

il

Documents

POLYSI CONTACTING WITH SECOND GENERATION FT PASTES … · ISE and ISFH Standard reliable TLM ISSUES: Multi-layer Multi-interface Thick layers Metal contacts penetrate (etch) polySi