EpiTT / EpiCurve®TT LED-based for CCS reactor - Laytec

Recent product improvements 

Dr. Kolja Haberland 

senior manager 

customer support 

2 June 2008

Outline 


• EpiTT in CCS reactors 

- now available with LED light source 633nm/950nm 

- new wavelength: 405nm/950nm 

• EpiTT in AIXTRON reactors 

- new wavelength: 488nm 

• EpiTT and EpiCurve in horizontal HVPE systems 

- improved time resolution 

- ways towards an improved curvature performance 

• new EpiCurve option: "Curve only" 

2 June 2008 Recent product improvements 

2

EpiTT - experimental set-up 

EpiTT controller 

EpiTT 

optical head 

MOCVD or MBE systems 

T / °C 

emissivity corrected 

pyrometry (TT) 

• true temperature (TT) 

• wafer selective ± 1K 

• 450 - 1300°C 

control and analysis 

computer 

two measured parameters 

and 

double wavelength 

reflectance (R) 

R 

• � 1=950nm 

• � 2= user selectable 

• wafer selective 

• growth rate 


3


EpiTT - status until last month 

in AIXTRON G3/G4 planetary systems 

type of light source LED 

reflectance wavelength 405nm, 488nm, 633nm or 950nm 

pyrometry wavelength 950nm ± 5nm 

in AIXTRON Ltd. CCS systems 

type of light source halogen 

reflectance wavelength 633nm or 950nm 

pyrometry wavelength 950nm ± 35nm 


4



AIX G3/G4 

AIX Ltd. CCS 

LED 

(950±5)nm 

halogen 

(950±35)nm 


5

Principle of pyrometry 

How does Pyrometry work? 

incandescence intensity 

infra red visual ultra violet 

800°C 

700°C 

600°C 

500°C 

0.2 0.4 0.6 0.8 1.0 1.2 1.4 

photon energy / eV 

950nm 

Planck's equation: 

L = 

�. 

2 

h 4 c 3 

. 

(h�) 5 

eh��k T B -1 

intensity of emission or 

incandescence from heated 

black body is correlated to 

its temperature 

M. Planck, Verh. Dtsch. phys. Ges. Berlin, 2 (1900) 202 and 2 (1900) 237. 


6

Principle of pyrometry 

How does Pyrometry work? 

incandescence intensity 

infra red visual ultra violet 

800°C 

700°C 

600°C 

500°C 

0.2 0.4 0.6 0.8 1.0 1.2 1.4 

photon energy / eV 

950nm 

• temperature sensitivity 

increases with emission 

intensity 

• measured intensity scales 

with FWHM of filter 

• wide filter (± 35nm) was 

used in CCS reactors to 

compensate for very small 

viewport diameter (2 mm) 


7

Effect of spectroscopic bandwidth 

Simulation for a pyrometry filter: (950 ± 35) nm 

reflectance 

-50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 

time / s 

950nm 

920nm 

970nm 

average 

period of oscillations scale with wavelength (interference criteria) 

average intensity (= superposition) decreases over time 


8



stable envelope 

attenuation 

due to filter width 

LED 

(950±5)nm 

� no accurate growth rate fit possible 

halogen 

(950±35)nm 


9


Now available: EpiTT-LED for CCS 

advantages: 

• brighter light source and optimized detector amplification 

• now with narrow 950nm filter (FWHM ±5nm) - 

pyrometry reflectance becomes true second wavelength 

• free choice of wavelength: 405nm, 633nm, 950nm 

• same light source for all EpiTT systems 

• longer life-time, no bulb exchange anymore 

Upgrade easy possible - but detector must be exchanged as well 


10

EpTT on 6x2“ CCS reactor 

GaN / Sapphire template growth 

with LS-H 

(halogen) 

data courtesy of M. Kappers, C. McAleese, University of Cambridge 


11


GaN / Sapphire template growth 

with LS-LED 

(LED) 

• same SNR of 

633nm 

reflectance 

• same SNR of true 

temperature 

• 950nm signal now 

accurate for fit 



12


EpiTT- LED for CCS - 

also available as 

• EpiTwinTT 

• EpiCurve TT 

• EpiCurveTwin TT 

now available! 


13

Outline 












14


GaN / Sapphire MQW LED growth 

with new 

LS-LED 405nm 


2 June 2008 15 

Recent product improvements


GaN / Sapphire MQW LED growth 

with new 

LS-LED 405nm 

n-GaN MQW 

p-GaN 

Data: courtesy of M. Kappers, C. McAleese, University of Cambridge 


16

Outline 












17

EpiTT 488 

EpiTT 488nm 

• optimized for AlInGaP and AlGaN applications 

• shorter wavelength is good for 

- thin layers (faster oscillation) 

- morphology measurements 

- composition sensitivity 


18

Reflectance 


0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

• damping 

• high sensitivity 

for thin layers 

0.0 

100 200 300 400 500 600 700 800 900 

time / s 

Example: 

AlGaN/AlN/Si, 

T=1060°C 

(calculated) 

n 

3,0 

< � g 

roughness 

measurement 

2,5 

Reflectance 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

20% Al 

• small damping • no damping 

0.0 

100 200 300 400 500 600 700 800 900 

time / s 

> ~ � g 

composition 

sensitivity 

10% Al 

AlGaN 

T wafer = 1060°C 

>> � g 

best for growth rate 

20% Al 

10% Al 

2,0 

200 300 400 

Eg 500 600 700 

wavelength (nm) 

800 900 

0,0 

1000 

wavelength (nm) 

0.0 

100 200 300 400 500 600 700 800 900 


19 

Reflectance 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

1,0 

0,9 

0,8 

0,7 

0,6 

0,5 

0,4 

0,3 

0,2 

0,1 

k 

time / s


Example: AlInGaP 

� = 488nm 

� > 700nm � = 405nm 

only growth rate 

accessable 

growth rate and composition 

and morphology accessable 

only morphology 

accessable 


20


Example: AlInGaP 

optimum composition sensitivity 

around �=500nm 

EpiNet software inlcudes 

high temperature n,k database 

of AlGaInP for growth analysis 

M. Zorn et al. / Journal of Crystal Growth 287 (2006) 637–641 

M. Zorn et al. / Journal of Crystal Growth 298 (2007) 23–27 


21


Example: GaN/sapphire LED structure 

EpiTT 488nm ± 1nm 

AIX 2600G3 HT, 

24x2“ 

• high frequency of oscillation 

• higher signal for nucleation as 

for 633nm signal 

• no drastic absorption 

data courtesy of AIXTRON AG 


22


UV-LED structure: 

simulation of EpiTT reflectance data at 488nm ± 1nm 

5 � 

244nm or 248nm UV Pump 

50nm Al 0.55Ga 0.45N: Si- 

5nm Al0.49Ga0.51N: ud or Si- 

2.5nm Al0.36Ga0.64N: ud or Si- 

5nm Al0.49Ga0.51N: ud or Si- 

600nm Al 0.55Ga 0.45N: Si- 

500nm AlN:ud HTBL 

10nm AlN LTBL 

Single side polished c-plane Sapphire 

• relatively high frequency of oscillations 

• no observable absorption from Al 0.55GaN 

Al 0.55GaN 

488nm ± 1nm 

488nm: 

Optimal wavelength for 

UV-LED application! 

2 June 2008 23 


Outline 












24

EpiTT / EpiCurve ® in HVPE 

Challenges of horizontal HVPE reactors 

• high growth rate ( 10 ... 100 µm/h) 

• non-uniform growth 

• sample wobble 

• long distance viewport-sample 

• high curvature values 

• convection effects due to "chimney effect" 

• gas foil rotation / no rotation trigger 

• reproducibility of sample position (tilt) 

• bad quality of optical window / no optical window 


25


High time resolution mode for HVPE 

� higher data acquisition 

rate by using several 

points per revolution 

� time resolution 

increases with number 

of points 

� wobble will be 

compensated by wafer 

selective reflectance 

calibration 

� all data are displayed in 

one dataset for 

analysis 

example: 10 "virtual wafers" per revolution 


26


High time resolution mode for HVPE 

example: 

growth rate of 20 µm/h 

can be used for: 

• single wafer systems 

• with rotation trigger 

• for low wobble 

works up to a growth rate of 100 µm/h 


27


Effect of wavelength and GaN absorption 

~ 400nm = GaN is absorbing 

(Fabry Perot oscillations are 

attenuating) 

950/633nm = GaN is transparent 

(Fabry Perot oscillations are 

not attenuated) 

GaN bulk reflectance value is 

independent of thickness! 

no effects of non-uniformity anymore 


28

EpiCurve ® TT in HVPE 

Special EpiCurve ® set-up for HVPE 

special optics 

• reduces spot distance = bigger effective detector area 

• compensates for long distance to sample 

• accepts higher curvature values 

• symmetric measurement range (concave / convex) 

• better wobble compensation 

currently in lab test, 

will be tested at 

customer site soon 


29

EpiCurve ® TT in HVPE 

First lab test results 

concave: 1600 km -1 convex: -90 km -1 


30


Challenges of horizontal HVPE reactors 

• high growth rate � new measurement mode 

• non-uniform growth � 405nm measurement 

• sample wobble � big lens 

• long distance viewport-sample � special optics 

• high curvature values � special optics 

• convection effects � additional window 

• gas foil rotation / no rotation trigger 

• reproducibility of sample position (tilt) 

• bad quality of optical window / no optical window 

� reactor manufacturer 

2 June 2008 31 


Outline 












32

EpiCurve ® TT 

EpiCurve ® TT standard set-up for TSSEL 

EpiCurve 

optical head 

T / °C 

emissivity corrected 

pyrometry (TT) 

• wafer temperature 

• wafer selective ± 1K 

• 450 - 1400°C 

control and analysis 

computer 

three measured parameter 

double wavelength 

reflectance (R) 

R 

• �= 633nm and 950nm 


• growth rate 

• ternary composition 

1/r [km -1 ] 

• curvature 


wafer bowing 

curvature 

• temperature uniformity 

• quaternary composition (HR) 

• total strain fingerprint (HR) 


33

EpiCurve ® TT standard set-up for CCS 


optical 

heads 

EpiCurve ® TT 

Curve 

optical head 

PO5 

Requirement: 

two viewports on the 

same ring of wafer! 

Curve 

optical head 

PO4 

PO3 

PO2 

PO1 

ZONE A 

ZONE B 


optical head 

= special in-situ port 

(standard for new lids) 


34 

PO6

New EpiCurve ® option 

Curve only set-up for CCS 

Curve 

optical head 

Curve 

optical head 


35

New EpiCurve ® option 

Curve only (without EpiTT) 

• only curvature measurement 

• no temperature, no reflectance measurement 

• can be applied in CCS reactors that do not have the 

"second" in-situ viewport (e.g. old standard lid) 

• can be applied on others reactors with very limited 

optical access 

• can be upgraded later to EpiCurve TT ... 


36

Outline 

Summary 


- now available with LED light source 633/950nm 

- new wavelength: 405/950nm 








37

Some gems 

need a little 

extra help to 

sparkle 

www.laytec.de

EpiTT / EpiCurve®TT LED-based for CCS reactor - Laytec

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