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Information on the melt growth process through Lateral Photovoltage Scanning (LPS) measurements Anke Lüdge, H. Riemann, M. Renner Im Forschungsverbund Berlin e. V. Contents: 1. Introduction 2. The LPS method 3. Crystallization interface and striations 4. Measurement of the solid liquid interface in polycrystalline silicon 5. Summary and outlook

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Information on the melt growth process throughLateral Photovoltage Scanning (LPS) measurements

Anke Lüdge, H. Riemann, M. Renner

Im Forschungsverbund Berlin e. V.

Contents:

1. Introduction

2. The LPS method

3. Crystallization interface and striations

4. Measurement of the solid liquid interface in polycrystalline silicon

5. Summary and outlook

1. Introduction

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

The spatial distribution of electricallyactive impurities in semiconductor crystals is a compressed record of thecrystal growth.

The FZ Process : numerical model(calculated at EWH Hannover)

compared to LPS

The measurement of the doping striations can bemade by different methods:etching not quantitative, weak contrast,

only for highly doped samples4 point smaller resolution, but

quantitativeSR good resolution, slow,LPS good reproducibility, fast, half-

quantitatively, area scan

sample

Ohmiccontacts

x/y - table

yx

lens/collimatorFocus : 5 µm

modulatedlaser diode25 mW, 685 nm

optical fiber

modulation1 kHz

computer- signal processor board (lock-in)- Control of x/y tables

pre-amplifier

u = 0.5 ...10 µV

2. The LPS Method

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

d =91 mm

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

d =126 mm

f [1/min]

x x

f [1/min]

3. Crystallization interface and striations

measurement of the interface in FZ Si single crystals

-25

-20

-15

-10

-5

0

0 10 20 30 40 50 60 70 80 90

power spectrumpower spectrum

lower rotation rate : 10 U/min lower rotation rate : 4.8 U/min

contacts

2 0

18

16

14

12

10

- 8

- 6

- 4

- 2

00 2 0 4 0 60 8 0 100 12 0

X-ray topography

45 mm x 22 mm

50 mm x 50 mm with g = (111) and MoKaα radiation

3.4 at% Ge

5 at% Ge

<110>growthdirection

45 mm x 15 mm 45 mm x 15 mm

56 mm x 20 mm with g = (220) and MoKaα radiation

<100> growth direction

220

4.5 at% Ge

6.3 at% Ge

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

3. Crystallization interface and striations

germanium silicon crystals

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

LPS plot , contacts parallel to thegrowth direction

• contrasts at grain boundaries by space charge field and recombination

life time plotLPS plot 90 x 90 mm2 , contacts

across the growth direction

• determination of the phase boundary not possible until now• phase boundary visible clearly when contacts across the growth direction

4. Measurement of the phase boundary in poly silicon

Directionally solidified block silicon for PV applications

5. Summary and outlook

Acknowledgement:

The authors wish to thank H. Wawra from the IKZ for making the life timemeasurements.

• the LPS method allows to determine the solid-liquid interface of silicon,germanium and SiGe crystals, also for high dislocation densities and polycrystalline silicon

• the flow pattern of the crystal growth can be visualized• if the mean resistivity value is known, the specific resistivity can be calculated

by integrating the LPS curve - comparison to doping profiles• dislocations and grain boundaries generate changes of the LPS signal but do

not affect the determination of the phase boundary

The method can be carried out measuring the magnetic field of the current dipolewith SQUID sensors. This is investigated in a project with PTB Berlin and theUniversity Freiberg.

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements

Contactless and touchless measurement using SQUID sensors

I=10-2 mA

1.58*10-10 T

3.9*10-12 T

Anke Lüdge, H. Riemann, M. Renner : Information on the melt growth process through LPS measurements