EpiCurve®TT Blue - Laytec

News from LayTec‘s Development Pipeline 

Dr. Kolja Haberland 

head of customer support

Outline 

For the Nitrides: 

• EpiCurve ® TT Blue 

• Pyro 400: Real GaN wafer temperature 

For PV applications: 

• EpiCurve ® SOLAR 

• Photovoltaic applications – ideal wavelengths 

• SolR – solution for in-line PV production 

7 June 2009 Product developments at LayTec 2009 

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Outline 









3

EpiCurve ® TT Blue 

Current Signal-to-noise ratio in Planetary ® 

GaN growth on single-sided polished sapphire wafer 

due to effects from aspheric bowing: resulting SNR: ±5km -1 

due to gas foil rotation 

±5km -1 


4


Signal-to-noise ratio: interference effect 

±20km -1 

GaN growth on double-sided polished sapphire wafer: ±20km -1 SNR (!) 

� laser interference with substrate back-side leads to increased noise 


5


Solution: 


• prototype of EpiCurve ® TT Blue 

• first measurements in AIX 

Planetary scheduled 

• Release: Q3 2009 


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Outline 









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Real surface temperature 

Pyrometry at 950nm - there are limits 

l< l gap 

absorbing substrates 

e.g. GaN on Si 

measured: wafer temperature 

= changed by wafer bow 

l> l gap 

transparent substrates 

e.g. GaN on sapphire 

measured: pocket temperature 

= unchanged by wafer bow 


8


Pyro 400 - pyrometry at 400nm 

GaN is transparent for l > 500 nm 

k 

0.00 

300 350 400 450 

l / nm 

500 550 600 

� usual IR pyrometers cannot measure GaN surface temperature 

0.40 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

measurement window 

of 400 nm pyrometer 


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Pyrometry at 400nm - ideal for GaN 

Idea: 

• select a wavelength 

where GaN is absorbing 

• measure emisson light 

directly from GaN buffer 

Challenges: 

• very low intensities 

due to Planck curve 

• high sensitivity to 

stray light 

Benefit: 

• real surface 

temperature of GaN 

400nm < l gap 

for GaN on sapphire or SiC 

measured: wafer temperature 

= changed by wafer bow 


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Temperature profile during the process 

At GaN growth temperature (1100°C): Temperature measured 

relatively to temperature profile of satellite 

satellite 

T / °C 

1130 

1125 

1120 

1115 

1110 

1105 

1100 

GaN/sapphire 

DT C < 0.5 K 

DT C = 8 K 

• small concave bowing 

• small DT (8 K) 

16 µm 

Temperature profile of satellite 

GaN/SiC 

DT C = 22 K 

DT C = 14 K 

64 µm 

1130 

1125 

1120 

1115 

1110 

1105 

• large convex bowing 

• aspherical bowing 

• very non-uniform T profile 


11 

1100


Temperature profile during the process 

At InGaN growth temperature (800°C) after GaN process optimization 

satellite 

T / °C 

815 

810 

805 

800 

795 

790 

785 

GaN/sapphire 

8 µm 

GaN/SiC 

• small convex bowing • small convex bowing 

• flat temperature profile across the wafers during InGaN-MQW 

growth 

• wafer curvature compensates for non-uniform pocket T 

26 µm 


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815 

810 

805 

800 

795 

790 

785

Outline 









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EpiCurve ® TT for PV applications 

Problem: Aspheric bowing 

EpiCurve TT: 

Curvature slope: 

envelope of small and 

large curvature axis 

because of 

aspheric bowing 

• Bigger problem for soft and thin substrates 

• substrate quality (initial aspheric bowing) has influence 

±5km -1 


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Solar cell application 

Example: growth on 

Germanium substrate: 

different substrate 

thickness 

Curvature [1/km] 

50 

0 

-50 

Ge01, 140-160 �m 

Ge01, 480-520 �m 

Ge02, 280-286 �m, low aspheric bow 

4000 6000 

time [a.u.] 

8000 10000 

05.06.2009, V:\Projekte\Compound\98-09-034 Curvature HighRes\Messungen\090310_Run_mit_Standard-Curve\2_EpiCurve_10_ISE_Messung_2009-03\EpiTT.opj 

±20km -1 

Standard EpiCurve TT: large aspheric bow and gas foil rotation effects 

superimpose desired information on strain effects in thin quaternary layers! 


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New EpiCurve design: EpiCurve TT SOLAR 

removing aspheric 

effects of curvature 

resolution 

improvement down to 

0.5 km -1 was achieved 

recently at ISE, 

Freiburg 

Curvature [a.u.] 

60 

40 

20 

0 

-20 

-40 

05.06.2009, V:\Projekte\Compound\98-09-034 Curvature HighRes\Messungen\090528 Run Fehlanpassung\ISE_Run_Fehlanpassung_EpiTT_v02_TZ.opj 

Ge02, 300µm, low aspheric bow 

Ge02, 140µm 

±3km -1 

±0.5km -1 

2000 3000 

Time [a.u.] 

4000 5000 

• big improvement for all applications, not only PV 

• can be combined with EpiCurve ® TT Blue 

• available: Q3 2009 


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Outline 




For solar cell applications: 





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PV applications – ideal wavelengths 

GaAs-based solar cells 

typical triple-junction solar cell: 

GaAs and InP based compounds 

on Germanium substrate 

What is the ideal reflectance 

wavelength for in-situ 

monitoring? 


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PV applications – ideal wavelengths 

Simulation of reflectance response of a solar 

cell for available EpiTT wavelengths 

best choice: 

950nm: 

• ideal for thickness 

measurements on thicker 

layers 

488nm: 

• for thin layer thickness 

measurements 

• for surface morphology 

investigation 

Reflection 

0.5 

0.4 

0.3 

0.5 

0.4 

0.3 

0.5 0 1000 2000 3000 4000 5000 6000 7000 8000 

0.4 

0.3 

0.5 

0.4 

0.3 

// 

0 1000 2000 3000 4000 5000 6000 7000 8000 

Growth time / s 


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// 

405nm 

488nm 

633nm 

950nm

Outline 









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SolR – solution for in-line PV production 

New brand: SolR TM 

layer thickness measurements and spectral analysis 

in-line and roll-to-roll for CIGS, CdTe and a-Si/µ-Si 

PV applications 


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Summary 

• EpiCurve TT capabilities are being further improved for 

measurements on double-side polished and aspheric 

wafers 

• LayTec extends its field of application to thin-film 

photovoltaics 


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Some gems 

need a little 

extra help to 

sparkle 

www.laytec.de

Outline 


• Temperature calibration – New method: Eutopticum 








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Outline 


• Temperature calibration – New method: Eutopticum 








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Summary 

• LayTec found innovative ways for absolute temperature 

calibration (reactor-to-reactor, ring-to-ring) 

• EpiCurve TT capabilities are being further improved for 

measurements on double-side polished and aspheric 

wafers 

• LayTec extends its field of application to thin-film 

photovoltaics 


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Temperature calibration 

Reflectance based temperature calibration 

• Eutopticum = specially 

designed layer 

structure 

• Reflectance changes 

with temperature 

• crossing point of 

633nm and 950nm 

reflectance is welldefined 

= calibration 

point 

Reflectance 

0,4 

0,3 

0,2 

0,1 

0,0 

3000nm 

GaN 

growth 

182nm 

AlGaN 

cap 

growth 

down-cooling 

1000 2000 3000 4000 5000 6000 7000 8000 9000 

time_sec 

R-Crossing 

always 

at 885°C 


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1200 

1100 

1000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

Wafer Temperature / °C



The individual temperature 

at the crossing point for 

each individual calibration 

wafer is already measured 

during production with 

black-body calibrated EpiTT 

or EpiCurve TT 

Wafer can be re-used for 

calibration many times! 

Reflectance 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

950nm 

633nm 

R 633nm / R 950nm =1.000 

is a highly stable Calibration point 

(better ±1K) 

0 100 200 300 400 500 600 700 800 900 1000 1100 

temperature in °C 

885°C 

slope: 

DR/DT= 0.05% / K 


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• Eutopics are a highly 

accurate, re-usable 

instrument for temperature 

calibration reactor to reactor 

and ring-to-ring 

• Method is part of LayTec‘s 

extensive temperature 

measurement and calibration 

program 

• patent pending 

non-calibrated TT at 

936°C at crossing point 

R950 

R633 

R crossing at 885°C 

adjust Delta and get accuracy better than ±1K 


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EpiCurve®TT Blue - Laytec

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