In-situ Monitoring of AlGaN/GaN/AlN Growth Using LayTec EpiTT

In--situ In situ Monitoring Monitoring of of 

AlGaN/GaN/AlN Growth Growth Using Using 

LayTec LayTec EpiTT EpiTT 

Dongwon Yoo, Yoo, 

Jae-Hyun Jae Hyun Ryou, 

and Russell D. Dupuis 

School School of of Electrical Electrical and and Computer Computer Engineering 

Engineering 

Center Center for for Compound Compound Semiconductors 

Georgia Georgia Institute Institute of of Technology 

Technology 

Center Center Center Center for for for for Compound Compound Compound Compound Semiconductors Semiconductors Semiconductors 

Semiconductors / / Advanced Advanced Materials Materials and and Devices Devices Group 

Group

Thomas Thomas Swan Swan CCS CCS 7x2”” 7x2 MOCVD MOCVD Reactors: Reactors: 

Two Two III--Nitride III Nitride and and One One III--AsPSbN 

III AsPSbN System System 

�� MOCVD systems the in cleanroom of Georgia Tech CSS 

III--AsPSbN 

III AsPSbN MOCVD MOCVD System 

System 

III--Nitride III Nitride MOCVD MOCVD Systems Systems 



Group

Thomas Thomas Swan Swan MOCVD MOCVD Reactor Reactor and and 

EpiTT EpiTT Control/Monitor Systems Systems 

EpiTT control/monitor 

MOCVD control/monitor 

Swan Nitride MOCVD 

Reactor Control Systems 

LayTec EpiTT in--situ in situ 

growth monitoring 

systems 



Group

Thomas Thomas Swan Swan CCS CCS 7x2”” 7x2 Nitride Nitride MOCVD MOCVD 

System System Growth Growth Chamber Chamber 

Close-Coupled Showerhead (CCS) 

LayTec EpiTT 

Reflectance/Pyrometer 

Optical ports Pyrometer probes 

Flip-Lid: open for loading wafers Flip-Lid: closed for epitaxy 



Group

LayTec LayTec EpiTT EpiTT Optical Optical Reflectance Reflectance & & Emissivity-- 

Emissivity 

Corrected Corrected Pyrometer; Pyrometer; Three--Channel Three Channel Pyrometer 

Pyrometer 

Optical pyrometer 

for temperature 

uniformity 

measurements for 

heater zone 

balancing 

EpiTT in--situ in situ wafer 

measurement for 

six outer wafers 

(in sync with wafer 

rotation) 



Group

EpiTT EpiTT for for In--situ In situ and and Ex--situ Ex situ MOCVD MOCVD 

Growth Growth Monitoring 

Monitoring 

�� Emissivity-corrected Emissivity corrected temperature and optical reflectance 

�� Monitoring in sync with wafer rotation 

�� individual wafer monitoring on each pocket of susceptor 

�� Probing area adjustable (2” (2 sapphire and 10X10mm 2 GaN sub) 

�� In--situ In situ monitoring 

�� Surface “actual actual” temperature between pockets and susceptors for same type 

of substrates 

�� Surface morphology from reflectance 

��Morphology Morphology evolution, recovery, and degradation on a selected layer layer 

or 

an overall structure 

�� Wafer bending from reflectance oscillation (damping) 

�� Approximate growth rate and etch-back etch back rate from reflectance oscillation 

period 

�� Etching back effect monitoring 

�� Ex--situ Ex situ monitoring 

�� Growth rate calculation based on simulation/fitting 



Group

Example Example Application: Application: UV UV Photodetector 

Device Device Structure Structure 

250 µm dia mesa 

SiO 2 sidewall 

passivation 

n-metal (Ti/Al) 

25 nm GaN:Mg p-contact layer 

Grading 

p-metal (Ni/Au) 

SiO 2 

10 nm ~45% AlGaN:Mg 

150 nm ~45% AlGaN:ud absorption layer 

Grading 

100 nm ~60% AlGaN:Si+ n-contact layer 

700 nm ~60% AlGaN:Si- template layer 

AlN buffer/nucleation layer 

both side polished c-plane sapphire 

UV Illumination 



Group

MOCVD MOCVD Growth Growth Conditions 

Conditions 

�� Reactor: Thomas Swan 7x2” 7x2 

�� Precursors 

��Metalorganics 

Metalorganics: : TMGa, TMAl, TMIn, Cp 2Mg, Mg, 

��Hydrides: Hydrides: SiH 4, , and NH 3 

�� Carrier gas: UPH H 2 or N 2 

�� Pressure 

��50~600 50~600 Torr depending on the layer/structure grown 

�� Temperature 

��500~650 500~650 ° C for LT buffer growth 

��> > 1000 ° C for HT growth 

�� V/III ratio: low for AlGaN and high for InGaN 

�� Substrates: Sapphire, GaN, and SiC 



Group

In--situ In situ Growth Growth Monitoring Monitoring of of 

AlN AlN on on Sapphire Sapphire Substrates 

Substrates 

�� Surface morphology and EpiTT reflectance of AlN depending 

on growth condition 

�� Accurate in--situ in situ monitoring is critical for AlN growth 

0.25 

0.24 

0.23 

0.22 

0.21 

0.2 

0.19 

0.18 

0.17 

0.16 

0.15 

0.14 

0.13 

0.12 

0.11 

0.1 

0.09 

0.08 

0.07 

0.06 

LT AlN 

HT AlN 

0.05 

0 500 1000 1500 2000 

Time (sec) 

EpiTT reflectance change 

in relation to AFM 

surface morphology 

5x5 µm 2 

RMS rough = 12.6 nm 

5x5 µm 2 

RMS rough = 0.4 nm 

0.25 

0.24 

0.23 

0.22 

0.21 

HT AlN 

0.2 

0.19 

0.18 

0.17 

0.16 

0.15 

0.14 

0.13 

0.12 

0.11 

0.1 

0.09 

0.08 

0.07 

0.06 

0.05 

LT AlN 

0 500 1000 1500 2000 

Time (sec) 



Group 

Temperature

In--situ In situ Monitoring Monitoring of of Growth Growth Rate Rate and and 

Etching--Back Etching Back Rate Rate 

�� Growth vs. etch back depending on TMGa and NH 3 flow rate 

EpiTT temperature (C) 

1100 

1090 

1080 

1070 

1060 

1050 

1040 

1030 

1020 

1010 

TMGa 

60scc 

Rg= 

0.795nm/s 

TMGa 

45scc 

1-0415-1 GaN growth rate & desorption rate 100Torr 

TMGa 

30scc 

Growth 

Rg= Rg= 

0.55nm/s 0.367nm/s 

TMGa 

10sccm 

Rg=0.045nm/s 

NH3=5L 

etching back 

Dg= 

0.083nm/ 

s 

NH3=3L 

Dg= 

0.096nm/ 

s 

1000 

0 2000 4000 6000 

Time(S) 

8000 10000 12000 



Group 

NH3=1L 

Dg=0.15nm/s 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

Reflectance 

PyroTemp 

DetReflec 

Oscillation deflection


AlGaN/AlN AlGaN/AlN on on AlN/Sapphire Template Template 

�� Al 

Al0.5Ga 0.5Ga0.5 

1200 

1100 

1000 

900 

800 

700 

600 

500 

400 

0.5N/AlN N/AlN re-growth re growth on AlN template 

PyroTemp 

DetReflec 

AlN template 

during heat-up 

AlN AlGaN 

0 1000 2000 3000 4000 5000 6000 

0 

7000 

Time (sec) 



Group 

0.18 

0.16 

0.14 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02

In--situ In situ Growth Growth Monitoring Monitoring of of Al Al0.3 

0.3Ga Ga0.7 0.7N/GaN N/GaN on on 

Bulk Bulk GaN GaN Substrate Substrate and and GaN/Sapphire Template Template 

�� Reflectance comparison between substrates 

��Oscillation Oscillation behavior difference Single 

1200 

1100 

1000 

900 

800 

700 

600 

500 

AlGaN on Bulk GaN vs. AlGaN on GaN/Sapphire 

GaN AlGaN 

Temp on bulk GaN 

Temp on Sapphire 

Reflec on bulk GaN 

Reflec on Sapphire 

400 

0.05 

0 1000 2000 3000 4000 5000 6000 7000 

Time (sec) 

Substrate 

GaN on 

Sapphire 

50 mm dia. dia 



Group 

0.25 

0.2 

0.15 

0.1 

Single-side side polished 

GaN sub not supporting 

cavity mode for 

reflectance oscillation 

Substrate 

Bulk GaN 

15 x 15 mm 

EpiTT probing area adjusted 

for different substrate size 

GaN and AlGaN on sapphire substrate AlGaN on GaN/bulk GaN substrate 

GaN/bulk GaN substrate (no reflectance oscillation) 

oscillation (weak reflectance oscillation)


GaN GaN on on AlN/ AlN/6H 

6H--SiC SiC 

�� GaN on SiC substrate using conventional insulating AlN buffer 

��AlN AlN buffer layer thickness and GaN morphology evolution 

��Wafer Wafer bending effect for thick GaN growth 

GaN on AlN/6H-SiC substrate 

PyroTemp 

DetReflec 

AlN GaN 

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 

0 

13000 

Time (sec) 



Group 

0.16 

0.14 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02


GaN GaN on on n--AlGaN:Si/n 

n AlGaN:Si/n--6H 6H--SiC SiC 

�� GaN on SiC using conducting nn-AlGaN:Si AlGaN:Si (Al~0.1) buffer 

layer for vertical device geometry 

��AlGaN AlGaN and GaN morphology evolution: in--situ in situ monitoring 

helpful for growth condition optimization 

1100 

1000 

900 

800 

700 

600 

500 

PyroTemp 

GaN on AlGaN:Si/6H-SiC substrate 

AlGaN grading GaN 

DetReflec 

400 

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 1300 

Time (sec) 



Group

Summary Summary 

�� We have used the Laytec EpiTT to monitor the growth of a 

variety of III-N III N structures on SiC, GaN, AlN, and sapphire 

substrates 

�� Monitoring in real time permits a rapid evaluation of growth 

conditions 

�� Homoepitaxial growth on GaN and AlN substrates does not 

produce significant oscillations (as expected) 



Group

In-situ Monitoring of AlGaN/GaN/AlN Growth Using LayTec EpiTT

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