Curvature - Laytec

Analysis and Interpretation of EpiCurveTT 

Measurements in III-N Multiwafer MOVPE 

F. Brunner, T. Wernicke 

Ferdinand-Braun-Institut für 

Höchstfrequenztechnik (FBH) 

Gustav-Kirchhoff-Str. 4 

D-12489 Berlin 

www.fbh-berlin.de 

...translating ideas into innovation

Outline 

� MOVPE growth equipment 

� EpiCurveTT 

- What can be measured? 

� In-situ results & analysis 

- Example: 

sapphire/GaN/AlGaN/InGaN 

- Pocket temperature vs. 

process temperature 

- Reflectance @ 950 nm 

- Curvature 

& @ 405 nm

MOVPE growth equipment nitrides 

• AIX2400G3-HT planetary reactor with 11x2 / 8x3 inch configuration 

satellite 

• Water-cooled triple gas inlet (V-III-V), TaC-coated sandwich susceptor

In-situ analysis: temperature, reflectance, curvature 

LASER 

parallel 

laser beam 

� Pyrometric surface temperature measurement (+ emissivity correction) 

� Reflectance @ 405 nm + 950 nm (R 405 , R 950 ) 

substratewafer 

satellite 

CCD 

camera 

� Curvature measurement (resol.: ± 1 km -1 + wafer asphericity => ± 5 km -1 ) 

TT 

R 

Bow

Wafer asphericity (deviation from rotational symmetry) 

LiAlO 2 

bow: ~40 µm 

curvature || flat: 130 km -1 

curvature ⊥ flat: 2 km -1 

bow: ~30 µm 

curvature || flat: 50 km -1 

curvature ⊥ flat: 57km -1 

� Different curvature parallel and perpendicular to main flat 

GaN 

� Azimuthal position is unkown during in-situ curvature measurement 

due to satellite rotation

In-situ data 

� Example: 420 nm 

LD test structure 

GaN cap 

3x In 0.08GaN/ 

In 0.02GaN MQW 

GaN:Si 

wave guide 

(Al,Ga)N SL 

GaN buffer 

Sapphire 

R 405/950 nm 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

Desorption 

GaN 

Growth time (s) 

Process Temperature 

Pocket Temperature. 

Reflectance 

Curvature 

AlGaN/GaN 

InGaN 

T (°C) 

1200 

1000 

800 

600 

400 

200 

κ 

(km -1 ) 

300 

250 

200 

150 

100 

50 

0

Pocket temperature vs. process temperature 

desorption 

Pocket Temperature: 

# T gradient susceptor 

# T changes with process 

(e.g. reactor pressure) 

# Wafertemp ? 

GaN 

growth time 

AlGaN/GaN 


InGaN 

1200 

1000 

800 

600 

400 

T(°C) 

� ΔT - susceptor 

backside and 

frontside 

� Gas foil rotation 

causes ΔT 

� Reactor pressure 

change causes ΔT

Pocket Temperature (°C) 

Wafer-to-wafer & 

run-to-run analysis 

1100 

1080 

1060 

1040 

1020 

1000 

980 

Wafer 

#01 

E2621 

E2623 

E2624 

E2654 

E2655 

Wafer 

#03 

Wafer 

#05 

GaN Layer Temp 

Substrate Temp 

Wafer 

#07 

Wafer 

#09 

Wafer 

#11 

� Analysis of substrate 

and layer temperature 

� Pocket temperature 

variation mainly caused 

by satellite rotation (no 

individual rotation flow) 

� ΔT pock (W2W): ± 2K 

ΔT pock (R2R): ± 5K

Reflectance 



R 405/950 nm 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

Desorption 

GaN 




Reflectance 


AlGaN/GaN 

InGaN 

T (°C) 

1200 

1000 

800 

600 

400 

200 

κ 

(km -1 ) 

300 

250 

200 

150 

100 

50 

0

Reflectance measurement @ 950 nm or 633 nm 

GaN AlGaN 

� Whole structure 

transparent 

�� Fabry-Pérotoscillations 

� Growth rate 

fitting of FPO 

� Batch mode calc 

for multiwafer run

Wafer-to-wafer & 

run-to-run analysis 

rg (µm/h) 

2.15 

2.1 

2.05 

2 

1.95 

1.9 

1.85 

Growth rate (µm/h) 

center 

edge 

Wafer 

#01 

E2622 

E2623 

E2624 

Wafer 

#03 

Wafer 

#05 

Wafer 

#07 

600 mbar growth 

Wafer 

#09 

Wafer 

#11 

� Analysis of fit resultsfile 

using VBA-Scripts 

� r g ~2 µm/h 

Δr g (W2W): ± 20 nm/h 

Δr g (R2R): ± 10 nm/h 

� Variation mainly due to 

common sat rotation

Thickness uniformity tuning using R 950/ R 633 

� Definition of 

multiple centerto-edge 

wafer 

zones possible 

� Thickness 

homogeneity 

tuning in one 

growth run


� Batch-mode fitting during growth with marked regions 

� Adjust growth parameter according to fit result after step A, B, C, ... 

A 

Growth Rate (µm/h) 

2.2 

2.18 

2.16 

2.14 

2.12 

2.1 

2.08 

2.06 

2.04 

2.02 

2 

1.98 

1.96 

1.94 

1.92 

1.9 

1.88 

1.86 

1.84 

1.82 

1.8 

Variation MO1-Run Flow 

Δr G = 20 nm/h 

Pos #08-1 Pos #08-2 Pos #08-3 Pos #08-4 Pos #08-5 

Measurement Position Center -> Edge 

A




A 

B 


2.2 

2.18 

2.16 

2.14 

2.12 

2.1 

2.08 

2.06 

2.04 

2.02 

2 

1.98 

1.96 

1.94 

1.92 

1.9 

1.88 

1.86 

1.84 

1.82 

1.8 






B 

A




A 

B 

C 


2.2 

2.18 

2.16 

2.14 

2.12 

2.1 

2.08 

2.06 

2.04 

2.02 

2 

1.98 

1.96 

1.94 

1.92 

1.9 

1.88 

1.86 

1.84 

1.82 

1.8 




B 

A 

C




A B C D E 


2.2 

2.18 

2.16 

2.14 

2.12 

2.1 

2.08 

2.06 

2.04 

2.02 

2 

1.98 

1.96 

1.94 

1.92 

1.9 

1.88 

1.86 

1.84 

1.82 

1.8 






B 

A 

E 

D 

C

Reflectance 



R 405/950 nm 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

Desorption 

GaN 




Reflectance 


AlGaN/GaN 

InGaN 

T (°C) 

1200 

1000 

800 

600 

400 

200 

κ 

(km -1 ) 

300 

250 

200 

150 

100 

50 

0

Why 405 nm reflectance? 

2·n·r g ·t = m·λ 

λ �� ? 

� Good for low rate 

growth or material with 

larger bandgap 

(e.g. AlN ) 

� InGaN less 

transparent 

refractive index 

2.75 

2.50 

2.25 

4 3 2 1.5 E (eV) 

T=1060°C 

T=20°C 

GaN 

� Higher surface 

sensitivity 

2.00 

R405 R633 R950 (e.g. morphology) 300 400 500 600 700 800 900 1000 

wavelength (nm) 

AlN

Example R 405: AlN 

reflectance 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

405 nm 

633 nm 

950 nm 

~ 60 nm AlN 

2 4 6 

time (x1000 s) 

~ 2 µm GaN 

� Thickness information 

also for thin layers !

Example R 405 : InGaN MQW (const. T) 

Reflectance (405 nm) 

0.25 

0.24 

0.23 

0.22 

0.21 

0.20 

0.19 

0.18 

0.17 

R 405 

pocket temperature 

QW 

Barrier 

GaN InGaN-MQW 

growth time (s) 

cool down 

1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

-600 

-800 

� All quantum wells 

and barriers 

distinguishable 

� Temperature 

changes between 

barrier and well not 

visible in R 405

Simulation: InGaN composition vs. roughness 

reflectance @ 405 nm 

0.220 

0.215 

0.210 

0.205 

0.200 

0.195 

0.190 

In + 

In - 

In content 

6% 

12% 

18% 

24% 

30% 

In - 

In + 

3.5 4.0 4.5 5.0 

time (x1000 s) 

� InGaN content ↑ � R 405 amplitude ↑ 

� Roughness ↑ � Intensity ↓ 

reflectance @ 405 nm 

0.220 

0.215 

0.210 

0.205 

0.200 

0.195 

0.190 

roughness 

0 nm 

2 nm 

4 nm 

6 nm 

3.5 4.0 4.5 5.0 

time (x1000 s)




R 405/950 nm 

0.35 

0.30 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

Desorption 

GaN 




Reflectance 


AlGaN/GaN 

InGaN 

T (°C) 

1200 

1000 

800 

600 

400 

200 

κ 

(km -1 ) 

300 

250 

200 

150 

100 

50 

0

Wafer curvature 

Curvature (1/km) 

250 

200 

150 

100 

50 

0 

-50 

-100 

desorption 

GaN 




n-GaN (Al,Ga)N InGaN 

1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

cooling 

� Initial substrate 

curvature

Variation of initial substrate bow 

� Sapphire Spec: Bow < 10 µm (± 10 µm) 

� Curvature: ± 30 km -1 for 2 inch wafer 

Curvature: ± 15 km -1 for 3 inch wafer 

± 20 km -1 

± 5 km -1 

� as delivered � sorted by bow

Wafer Curvature 


250 

200 

150 

100 

50 

0 

-50 

-100 

desorption 

GaN 





1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

cooling 


curvature 

� Thermal induced 

substrate bow 

(concave)

Pure substrate bow 


50 

40 

30 

20 

T front 

T back 

T back -T front (K) 

0.5 1.0 1.5 2.0 

meas. (AIX2600G3-HT) 

calc. using 1/R c =α(T back -T front )/h 

R c 

"cool" gas 

hot susceptor 

600 700 800 900 1000 

d 

h 

T pock (°C) 

Al 2 O 3 (0001) 

h sapp =430 μm 

α sapp =8.0*10 -6 K -1 

f(H 2 )~ 20 slm 

p=150 mbar 

� Heating from 

below vs. cooling 

from above 

substrate 

� Depends on 

reactor and 

process 

� Adds to all other 

curve components



250 

200 

150 

100 

50 

0 

-50 

-100 

desorption 

GaN 





1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

cooling 


curvature 


substrate bow 

(concave) 

� Growth-related 

wafer bowing

GaN coalescence and bow 


225 

200 

175 

150 

125 

100 

75 

50 

25 

0 

GaN:nid @ 400 mbar @ 800 mbar 

r g =2.1 μm/h 

fast coalescence: 

|Δa GaN /a ES |~ -4*10 -4 

calc. 

Run time (s) 

r g =1.6 μm/h 

slow coalescence: 

|Δa GaN /a ES | < -5*10 -5 

concave 

convex 

7500 10000 

0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

-0.05 

-0.10 

-0.15 

-0.20 

-0.25 

Reflectance (@ 950 nm) 

� Coalescence after 

nucleation 

influences residual 

strain of GaN 

buffer



250 

200 

150 

100 

50 

0 

-50 

-100 

desorption 

GaN 





1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

cooling 


curvature 


substrate bow 

(concave) 

� Temperaturerelated 

curvature 

change

III-N: TEC mismatch 

Thermal expansion coeff. x10 -6 (K -1 ) 

8 

7 

6 

5 

4 

3 

2 

4H-SiC 

AlN 

(-30%) 

GaN 

(23%) 

InN 

Sapphire 

thermal expansion 

mismatch (ΔTEC) 

2.5 3.0 3.5 4.0 4.5 5.0 5.5 

Lattice constant a 0 (A) 

300 K 

Si 

� Thermal expansion 

coefficient mismatch in 

(Al,In,Ga)N material 

system



250 

200 

150 

100 

50 

0 

-50 

-100 

desorption 

GaN 





1200 

1000 

800 

600 

400 

T(°C) 

0 

-200 

-400 

cooling 


curvature 


substrate bow 

(concave) 

� Growth-related 

wafer bowing 

� Temperaturerelated 

curvature 

change 

� Lattice mismatch

Strain-induced curvature 


200 

150 

100 

50 

0 

-50 

r g (μm/h): 

meas. 

2.42 

Δa f /a ES : 

GaN GaN:Si 

0.49 

calc. 

-1.9*10 -3 

0.12 

0.25 0.50 0.75 0.04 

Thickness (μm) 

(Al,Ga)N 

5.5*10 -3 

InGaN 

-MQW 

0.25 

0.20 

0.15 

0.10 

0.00 

-0.05 

-0.10 

Reflectance (950 nm) 

� Lattice mismatch 

induced strain can 

be calculated 1 

� Material 

composition of 

pseudomorphically 

strained layers 

1 F. Brunner et al. JCG 310 (2008) 2432

Curvature changes wafer-temperature ! 


50 

0 

-50 

-100 

-150 

GaN 

InGaN- 

MQW 

growth time 

Cool 

down 

� InGaN growth sensitive 

to wafer temperature 

uniformity

Curvature changes wafer-temperature ! 


50 

0 

-50 

-100 

-150 

GaN 

InGaN- 

MQW 

growth time 

Cool 

down 

� InGaN growth sensitive 

to wafer temperature 

uniformity 

PL wavelength (RT) 

414 

413 

412 

411 

~ 1.5 nm 

~ 3.5 nm 

410 

0 5 10 15 20 25 

edge 

center 

PL meas. position (mm) 

bow 

�� In 

incorp 

center cooler than edge 

wafer 

satellite

Summary 

Temperature: 

� Shows response of pocket temperature to process changes 

Reflectance: 

� Immediate access to important growth parameters (e.g. growth rate) 

� Uniformity tuning using line scans across wafer diameter possible 

� Morphology check with highly surface-sensitive 405 nm reflectance 

Curvature measurement: 

� Indispensable for understanding different strain components 

� Quantitative analysis of material composition possible 

� Shows response of wafer temperature to process changes 

All: 

� Enabling fast wafer-to-wafer and run-to-run analysis

Thank you! 

Questions?

Curvature - Laytec

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