Combined PECVD Process Sensors in Thin Film Silicon …plasmetrex.com/dl/ref/applications/2013/S5-3_Gabriel-PVcomB.pdfCombined PECVD Process Sensors in Thin Film Silicon-Based Solar

Combined PECVD Process Sensors

in Thin Film Silicon-Based

Solar Cell Manufacturing

Onno Gabriel1, Lutz Eichhorn2, Bernd Stannowski1,

Michael Klick2, Rutger Schlatmann1

1 PVcomB, Helmholtz-Zentrum Berlin, Germany2 Plasmetrex GmbH, Berlin, Germany

13th European Advanced Process Control and Manufacturing Conference

Hilton Dresden Hotel, Germany - April 15-17, 2013

Competence Centre Thin-Film- and Nanotechnology

for Photovoltaics Berlin

Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20132

PV Market Growth

� > 5% PV contribution to electricity in Germany.

� c-Si technology „made in China“ @ 14-15 % module efficiency is

dominating.

� Competitiveness for large PV systems in southern Europe is reached.

30 GWp

= 215 Mio m2

(Source: EPIA)


PV Manufactoring Costs

� Manufactoring costs are driven towards 0.5 $/Wp

� Due to lower efficiency of thin film PV modules (10-14% vs. 14-

15%) even lower cost are required („BOS penalty)

Source: Ch. Breyer et al.

EUPVSEC 2011


Plasma Processes in Photovoltaic Industry

Material Functional Thin Films Deposition techniques

Front contact TCOs: ZnO, SnO2, ITO Sputtering, CVD

Absorber material a-Si:H, µc-Si:H,

p- und n-doped layers

low-pressure PECVD

Contact layers Al, Ag Sputtering, Evaporation

Interface layers TCOs, a-SiC:H, a-SiO:H low pressure PECVD

Passivation layers Si:N low pressure PECVD, ETP


Thin Film Silicon Solar Cells

Sputter Line A600 V7 Leybold Optics

PECVD clusterAKT1600 Applied Materials

glass

TCO

a-Si:H

(top cell)

µc-Si:H

bottom cell)

ZnO:Al

Al

encapsulation

foil

glass

3 m

m3

mm

3 µ

mSun light


Si BaselineSi Baseline

CIGS BaselineCIGS Baseline

Mo sputtering

back contact

P1 laser scribe

Cu/In /Ga

sputtering

Cleaning

Se evaporation

RTP

Chemical Bath

Deposition CdS/KCN

P3 scribing

ZnO: i-ZnO

sputtering front contact

Glass cleaning

P2 scribing

Cleaning

Etching

Encapsulation

TCO coated glass

PVcomB: Two Reference Lines for 30 x 30 cm2 Modules

Cleaning

P1 laser scribe

P2 laser scribing

P3 laser scribing

Glass substrates

ZnO/Ag sputtering

back contact

ZnO:Al sputtering

front contact

Silicon PECVD

Sputter Line A600 V7 Leybold Optics

PECVD clusterAKT1600 Applied Materials


PECVD Tool AKT1600A (Applied Materials)

AKT 1600A

cluster tool

ChA

ChBLoad

lock

ChD

� Three chamber PECVD cluster tool,

� Substrate size 30 x 30 cm²,

� fully automatic processing of up to 6

substrates per load.


Customized PECVD Chamber Window

Connector NEED Sensor View port OES

Outside

Side view

Inside


In situ Diagnostics at AKT Process Chambers

� Optical Emission Spectroscopy (OES)

� Non-linear Extended Electron Dynamics (NEED)

� Mass Spectrometer / Residual Gas Analyzer (RGA)


Optical Emission Spectroscopy (OES)

200 300 400 500 600 700 8000

100

200

300

400

500

600

700

800

µc-Si:H BCi deposition

a-Si:H BCn deposition

Si

Si

Si

SiH

Hβ

Inte

nsity (

a.u

.)

Wavelength (nm)

H2 fulcher

Hα

400 500 600 700 800 900 10000

500

1000

1500

2000

F

F

F

N2

N2

Process start

Process end

F

N2

N2

NF

N2

Inte

nsity (

a.u

.)

Wavelength (nm)

NF3 plasma clean

Species Transition Wavelength

Si 3s23p2 – s23p4s 288.3 nm

SiH X2Π – A2Δ 409 – 422 nm

Hα n=3 – n=2 656.3 nm

Hβ n=4 – n=2 486.1 nm

H2 2s3Σ+g – 3p3Π−

u 570 – 640 nm

F 2s22p4(3P)3s -

2s22p4(3P)3p

703.7 nm

F 2s22p4(3P)3s -

2s22p4(3P)3p

624.0 nm

Ar 3s23p4(3P)4s -

3s23p4(3P)4p

496.5 nm

Deposition

Chamber Clean� Relative densities of

electronically excited atoms and

small molecules (radicals).


Mass Spectrometry / Residual Gas Analysis (RGA)

µc-Si-i

a-Si-H BCn

SiHx

47SiF

Hx

67SiHF2?44CO244SiCH6?

48SiHF?49SiH2F?

16O

14N

19F

20HF

18H2O

21?

89?

Si2Hx

85SiF3

Si2Hx

SiF3

44CO2

48SiHF49SiH2F16O

14N

18H2O34PH3

19F20HF

47SiF

SiHx

Hx

89?

� Relative densities of stable

atoms and molecules after

ionization/dissociation in the

QMS.


Nonlinear Extended Electron Dynamics (NEED)

Source: Plasmetrex GmbH

RF discharge: Equivalent circuit

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0 36.87 73.74 110.61 147.48

Time (ns)

Current @ sensor (a.u.)

Voltage @ generator (a.u.)

NEED raw data

Pump

νeff - collision rate

ωgen - generator frequency

ωe - electron/plasma frequency

ne - electron density

Plasma resistivity = νeff ωgen

ωe (ne)2

(basically the collision rate

over electron density)

Resonance frequency of the total system depending on the bulk inductance Lp , the sheath capacitances

Cs and the inductance of the electrode system/chamber LC. (all directly depending on electron density, chamber design and

gap between electrode and substrate)

1

2


Data Management and Analysis

NEED

OES OES

spectra

Logfiles, Recipes

Mass

spectra

ChARGA

ChB

NEED

data

Sun

Workstation

Input

folder

PVcomB Data Server:

Scripts

MySQL

data base

Web

Server

Desktops,

Laptops

Desktops,

Laptops

LL

ChD

AMAT

cluster tool

Other Processes

+ Cell/Module

Analytics

AKT Process Data Base (03/2013):

� 101,000 AKT process steps

� 28 Mill. AKT parameters

� 2.5 Mill. OES spectra

� 1 Mill. mass spectra (RGA)

� 6 Mill. NEED data points

Desktops,

Laptops


�What process parameters

influence the quality of deposited

thin films and, thus, the solar cell

performance?

�Methods for PECVD process

monitoring?

Process parameters

Thin film growth process

Solar cell performance

Plasma properties

✓

✓

?

?


Substrate / Surface / Plasma

Temperatures


Glass substrate

Substrate / Surface / Plasma Temperatures

Electrode / Susceptor

(Temperature stabilized)

Heat

transfer

Plasma

1 µm

3 mm

4-5 cm

Higher plasma gas temperature result in a

higher surface temperature Tsur depending

on the thickness of glass substrates [1].

[1] S. Nunomura, M. Kondo and H. Akatsuka, Plasma Sources Science and Technology 15 (2006) 783-789

Thin film


Process Monitoring: µc-Si:H Absorber Layers

RF power (W)

H2 gas flow (sccm)

Tsub (°C)

controlled by PECVD recipe

automatic AKT control loop

(three different PECVD runs)


Impact of Process Parameters on OES Signals

OES: Hα line (a.u.)

� higher SiH4 conc.

→ higher ne density,

→ more excitaWon, more

emitted light.

� OES oscillations correlated

with Tsub → changes in gas

density due to temperature

oscillations.

� Ratio between emission lines

constant.

H2 gas flow (sccm)

Tsub (°C)

OES: Hα / Hβ (a.u.)


Impact of Process Parameters on NEED Signals

H2 gas flow (sccm)

Tsub (°C)

NEED: Plasma Resistivity (a.u.)

NEED: Resonance Frequ. (MHz

νeff ωgen

ωe2 ~

νeff

ne

� same trend: higher SiH4 conc.

→ higher ne density,

→ changes in gas density due

to temperature oscillations.


Impact of Substrate Temperature on NEED Data

� NEED data measured during the

deposition of 25 different a-Si:H i-layers.

� Substrate temperature Tsub varied

between 190 and 220°C

� The plasma resistivity follows the

expected trend, i.e. ~1/Tkin:

plasma resistivity ~

collision rate νeff ~ gas density n

gas density n ~ pV/(kBTkin)

→ plasma resisWvity ~ 1/Tkin

y = 3672.2x-1.081

10.0

10.5

11.0

11.5

12.0

12.5

13.0

13.5

170 180 190 200 210 220 230 240

NE

ED

: Pla

sma

Re

sist

ivit

y

Tsub (°C)

y = -0.0006x2 + 0.2684x - 24.167

4

5

6

7

170 180 190 200 210 220 230 240

NE

ED

: Re

son

an

ce F

req

ue

ncy

(M

Hz)

Tsub (°C)

νeff ωgen

ωe(ne)2

High pressure / low RF power


Chamber Cleaning & Conditioning


NF3/Ar Chamber Clean

NF3 gas flow (sccm)

Ar gas flow (sccm)

Pressure (Torr)

RF power (W)

AKT logfiles

Ar (470 nm)

Hα (656 nm)

F (703 nm)

Hβ (486nm)

Optical

Emission

Spectroscopy

H2 (m = 2)

SiH2 (m=30)

SiF3 (m=85)

HF (m =20)

F (m=19)

NF3 (m=71)

Mass

Spectrometry

Ar/NF3 plasma clean (500s) Ar purge

2 31


Ar/NF3 Chamber Clean

NEED: Resonance frequency (MHz)

NEED: Plasma resistivity (×10)

Pressure (Torr) Etch end points

(assumption):

- susceptor

- electrode

- entire chamber

2

3

1

Hα @ 656 nm (thick)

Hβ @ 486 nm (thin)

Ar @ 696 nm

F @ 703 nm

2 31


Reproducibility Over Many Processes

� Chamber clean (NF3/Ar plasma) after p-layer deposition, data of 9 runs:P

lasm

a r

esi

stiv

ity

Re

son

an

cefr

eq

ue

ncy

(MH

z)C

ha

mb

er

pre

ssu

re(T

orr

)

(Black curve: different chamber history, 1st run of the day)

Pressure (Torr)

NEED: Plasma Resistivity (a.u.)

NEED: Resonance Frequ. (MHz


Run-to-Run Stability


Example I: TCi Layer Deposition @ 190°C / 220°CT s

ub (°

C)°

NE

ED

: P

lasm

a

resi

stiv

ity

NE

ED

: R

eso

na

nce

fre

qu

en

cy (

MH

z)

Tsub = 190°C

Tsub = 220°C

pib i layer

νeff ωgen

ωe (ne)2

n~ 1/Tkin~

Reproducibility: i Layer Depositions

� NEED parameters during i-layer deposition of 10 single junctions

in one single day:

14.0

14.2

14.4

14.6

14.8

15.0

15.2

15.4

Pla

sma

resi

stiv

ity

Deposition start

Deposition end

4.5

4.6

4.7

4.8

4.9

5.0

5.1

Re

son

ance

fre

qu

en

cy (

MH

z)

Deposition start

Deposition end

� Clear trend over the day –

temperature effect?


Long Term Stability

NE

ED

: P

lasm

a

resi

stiv

ity

NE

ED

: R

eso

na

nce

fre

qu

en

cy (

MH

z)

Chamber A

Susceptor

Crash �

NEED data in Jan/Feb 2012 averaged during TCi layer deposition:


Long Term Stability

NE

ED

: P

lasm

a

resi

stiv

ity

NE

ED

: R

eso

na

nce

fre

qu

en

cy (

MH

z)Susceptor

defectA

KT:

Tsu

b(°

C)

Susceptor

exchange

new temperature control loop

new susceptor grounding Source: Plasmetrex GmbH


Summary

� PECVD Process monitoring established and evaluated at PVcomB in a reference

line for silicon-based thin film solar cell manufacturing.

� NEED, OES and MS result in complementary data giving insights into the

deposition process.

� NEED is proven to be a reliable in-line monitoring tool.

Thank you for your attention!

This work was supported by the Federal Ministry of Education (BMBF) and the state

government of Berlin (SENBWF) in the framework of the program “Spitzenforschung

und Innovation in den Neuen Ländern” (grant no. 03IS2151) and by the BMBF and the

Federal Ministry for Environment, Nature Conservation and Nuclear Safety (BMU) in

the framework of the program “Innovationsallianz Fotovoltaik” (grant no. 0325317C).

PVcomB Research Network

Documents

Combined PECVD Process Sensors in Thin Film Silicon …plasmetrex.com/dl/ref/applications/2013/S5-3_Gabriel-PVcomB.pdfCombined PECVD Process Sensors in Thin Film Silicon-Based Solar