lateral photovoltage scanning (lps) measurements information on the melt growth ... › pfd ›...
TRANSCRIPT
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