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Temperature calibration - Laytec

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<strong>Temperature</strong> <strong>calibration</strong><br />

Dr. Kolja Haberland<br />

Head of customer support<br />

18 October 2009


Outline<br />

• motivation<br />

• pyrometry<br />

• pre-<strong>calibration</strong><br />

• viewports<br />

• <strong>calibration</strong><br />

• solutions<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong> 2


Motivation<br />

Heteroepitaxy of III-Nitride semiconductors<br />

Wafer temperature has influence on:<br />

• material quality<br />

• composition of ternary compounds<br />

• evolving film stress<br />

substrate/wafer<br />

susceptor<br />

Bow<br />

Δz ~ ΔT<br />

Stress due to lattice mismatch results in wafer bowing which leads to:<br />

� Change in temperature uniformity across the wafer<br />

� Inhomogeneity of material properties<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

3


Motivation: temperature effects<br />

Vertical temperature profile of a III-N reactor<br />

2...20K<br />

20...50K<br />

>300K<br />

temperature<br />

vertical position in reactor<br />

reactor upper boundary<br />

gas<br />

wafer<br />

satellite susceptor<br />

main susceptor<br />

heater<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

4


Motivation: temperature effects<br />

<strong>Temperature</strong> access in III-N processes<br />

EpiCurve, Pyro400 (T wafer)<br />

EpiTT, EpiCurveTT (T pocket)<br />

thermo couple,<br />

light pipe<br />

reactor upper boundary<br />

wafer<br />

satellite susceptor<br />

main susceptor<br />

heater<br />

gas<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

5


Motivation<br />

<strong>Temperature</strong> <strong>calibration</strong><br />

• temperature is most important growth parameter<br />

• themocouple or light pipe temperature used to control<br />

reactor temperature in recipe have high offsets to pocket<br />

and wafer temperature<br />

• temperature measurement might be influenced by<br />

viewport geometry and window transparency<br />

� proper and accurate <strong>calibration</strong> of the EpiTT/EpiCurve<br />

pyrometer is essential<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

6


Outline<br />

• motivation<br />

• pyrometry<br />

• pre-<strong>calibration</strong><br />

• viewports<br />

• <strong>calibration</strong><br />

• solutions<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong> 7


Pyrometry<br />

Principle of pyrometry<br />

infra red visual ultra violet<br />

Planck's equation:<br />

intensity of emission or<br />

incandescence from heated<br />

black body is correlated to<br />

its temperature<br />

But emission of real body (wafer)<br />

is different from black body, so<br />

emissivity ε has to be determined<br />

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

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

8


Pyrometry<br />

Emissivity Corrected Pyrometry<br />

thermal emission and reflectance measured simultaneously at 950nm<br />

emissivity corrected temperature<br />

conservation of energy:<br />

α + r + t = 1<br />

opaque semiconductor:<br />

α + r = 1<br />

Kirchhoffs Law<br />

α (λ,T) = ε (λ,T)<br />

⇒ ε = 1 – r<br />

measure r and correct<br />

for changes of ε<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

9<br />

H. Grothe and F.G. Böbel, J. Cryst. Growth 127 (1993) 1010.


Outline<br />

• motivation<br />

• pyrometry<br />

• pre-<strong>calibration</strong><br />

• viewports<br />

• <strong>calibration</strong><br />

• solutions<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong> 10


Pre-<strong>calibration</strong><br />

Factory pre-<strong>calibration</strong> at LayTec<br />

Every pyrometer is pre-calibrated<br />

using a certified black body<br />

radiation source:<br />

• original viewport and window<br />

are used<br />

• <strong>calibration</strong> is accurate if<br />

viewports and windows on-site<br />

are identical (mind coated<br />

windows!)<br />

• <strong>calibration</strong> results in an<br />

accurate temperature<br />

measurement on black bodies<br />

• emissivity correction ensures<br />

accurate temperature during<br />

growth on all materials<br />

Important: keep reactor windows clean!<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

11


Pre-<strong>calibration</strong><br />

Black body <strong>calibration</strong><br />

• various temperature steps between<br />

400°C and 950°C are measured<br />

assuring linearity in the whole<br />

temperature range<br />

<strong>calibration</strong> report<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

12


Pre-<strong>calibration</strong><br />

Black body <strong>calibration</strong><br />

provides correct absolute<br />

temperature without any<br />

additional on-site <strong>calibration</strong> for<br />

the following MOVCD reactors:<br />

• AIXTRON planetary G3<br />

• AIXTRON planetary G4<br />

• AIXTRON 200 series<br />

example:<br />

measurement in AIX G3 with BB cal<br />

1060°C<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

13


Pre-<strong>calibration</strong><br />

Black body <strong>calibration</strong><br />

experience of major LED manufacturer:<br />

• "black body <strong>calibration</strong> of several EpiTT and<br />

EpiCurveTT systems minimized reactor-toreactor<br />

variations to less than 5K in AIXTRON<br />

G3/G4 systems"<br />

• residual temperature variations might even be real<br />

• important: keep windows clean<br />

• window cleaning is standard after any hardware<br />

equipment change (susceptor / ceiling)<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

14


Outline<br />

• motivation<br />

• pyrometry<br />

• pre-<strong>calibration</strong><br />

• viewports<br />

• <strong>calibration</strong><br />

• solutions<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong> 15


Pre-<strong>calibration</strong><br />

How is the situation for CCS/CRIUS systems?<br />

AIXTRON planetary G3/G4 AIXTRON CCS/CRIUS<br />

viewport is bigger than beam:<br />

- no clipping<br />

narrow tube<br />

in showerhead<br />

viewport is clipping beam:<br />

- intensity depends on specific viewport<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

16


Viewports<br />

CCS/CRIUS viewports<br />

"new" "old"<br />

• there are different<br />

viewport types in the<br />

field<br />

• different aperture<br />

positions and sizes<br />

• providing different<br />

intensities<br />

• during black body<br />

<strong>calibration</strong> type of<br />

viewport might be<br />

unknown<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

17


Viewports<br />

CCS/CRIUS viewports<br />

"new"<br />

additional effect:<br />

• nominal identical viewports have<br />

different aperture sizes<br />

• manufacturing tolerances of<br />

diameter is 2.2 mm ± 0.1 mm<br />

= 10% variation possible<br />

• this leeds to significant<br />

temperature variations<br />

� individual on-site <strong>calibration</strong><br />

needed!<br />

� re-<strong>calibration</strong> needed when<br />

changing showerhead<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

18


Viewports<br />

CCS/CRIUS viewports<br />

experiment:<br />

• using a black body<br />

calibrated EpiTT<br />

• measuring identical<br />

temperature ramps<br />

through 5 nominal<br />

identical viewports of<br />

"new type"<br />

• comparing to one "old<br />

type" viewport<br />

without in-situ<br />

<strong>calibration</strong> about 40K variation!<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

19


Outline<br />

• motivation<br />

• pyrometry<br />

• pre-<strong>calibration</strong><br />

• viewports<br />

• <strong>calibration</strong><br />

• solutions<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong> 20


Solutions<br />

LayTec's new solutions for T <strong>calibration</strong><br />

In-situ on-site <strong>calibration</strong> is necessary for certain reactor types<br />

� reference light source for in-situ viewport characterization<br />

• allows in-situ transmission measurement of each<br />

individual viewport<br />

• easy and quick solution to avoid ring-to-ring and<br />

reactor-to-reactor variations<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

21


Solutions<br />

patent pending<br />

Reference light source<br />

925°C hot susceptor surface is<br />

mimicked by this handheld<br />

"cool" reference light source<br />

• 950nm light source<br />

• uniform emitting area of 1 cm²<br />

• equals a temperature of<br />

925°C (black body calibrated)<br />

• put below showerhead<br />

• can measure viewport-toviewport<br />

variations on-site<br />

(ring-to-ring and reactor-toreactor)<br />

• takes just a few minutes<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

22


Solutions<br />

Reference light source in field test<br />

example: AIXTRON planetary reactor<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

23


Results of field test<br />

New method was used in Taiwan<br />

In 08/2009 all MOCVD systems in one fab were re-calibrated<br />

(all reactors running „same„ process, i.e. produced LEDs have same PL emission wavelength)<br />

Planetary MOCVD systems (preliminary results)<br />

• For most reactors the black body <strong>calibration</strong> was<br />

confirmed within ± 1 K<br />

• For other reactors (due to coated viewports or<br />

inappropriate vertical alignment) the <strong>calibration</strong> was<br />

corrected<br />

Result after <strong>calibration</strong>: true temperature variation<br />

between the reactors during MQW growth was 2K<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

24


Results of field test<br />

New method was used in Taiwan<br />

In 08/2009 all MOCVD systems in one fab were re-calibrated<br />

(all reactors running „same„ process, i.e. produced LEDs have same PL emission wavelength)<br />

Planetary MOCVD systems (preliminary results)<br />

• For most reactors the black body <strong>calibration</strong> was<br />

confirmed within ± 1 K<br />

• For other reactors (due to coated viewports or<br />

inappropriate vertical alignment) the <strong>calibration</strong> was<br />

corrected<br />

Result after <strong>calibration</strong>: true temperature variation<br />

between the reactors during MQW growth was 2K<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

25


Results of field test<br />

New method was used in Taiwan<br />

CCS MOCVD systems (preliminary results)<br />

• Reactor-to-reactor variation during MQW growth<br />

before <strong>calibration</strong>: 40K<br />

after <strong>calibration</strong>: 3K<br />

NB:<br />

• For EpiTT/EpiTwinTT/EpiCurveTT and EpiCurveTwinTT systems with halogen<br />

light source, an additional heating step to 1000°C is needed. Calibration time<br />

per reactor ~ 1.5 hours<br />

• For newer systems with LED light source the <strong>calibration</strong>can be done at room<br />

temperature. Calibration time per reactor ~ 0.5 hours<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

26


Results of field test<br />

New method was used in Taiwan<br />

Result of six EpiTT heads<br />

• residual variations might be<br />

real<br />

• reactors are optimized for<br />

uniform MQW temperature<br />

• growth is optimized for wafer<br />

temperature<br />

• EpiTT measures pocket<br />

temperature<br />

1200<br />

1180<br />

1160<br />

1140<br />

1120<br />

1100<br />

1080<br />

1060<br />

1040<br />

1020<br />

1000<br />

980<br />

960<br />

940<br />

920<br />

900<br />

880<br />

860<br />

840<br />

820<br />

800<br />

780<br />

760<br />

740<br />

720<br />

700<br />

680<br />

buffer<br />

barrier<br />

MQW<br />

1 2 3 4 5 6<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

27


<strong>Temperature</strong> <strong>calibration</strong><br />

New <strong>calibration</strong> recommendation<br />

• The reference lightsource will be recommended as<br />

standard <strong>calibration</strong> procedure as soon as additonal<br />

devices have been manufactured (work in progress) to<br />

equip field service<br />

• Eutectic run will be obsolete for all GaN systems<br />

from then on<br />

• EpiR DA systems (using 980nm light instead of<br />

950nm) will require a different version of light source<br />

• Not applicable for AIXTRON 200 series systems, as<br />

reactor cannot be opened<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

28


outline<br />

Summary<br />

• black body <strong>calibration</strong> is sufficient for some reactors<br />

(e.g. AIXTRON planetary G3/G4)<br />

• reason for variation of reactor-to-reactor and ring-to-ring<br />

T variations in CCS / CRIUS was found<br />

(viewport tolerances)<br />

• additional in-situ / on-site <strong>calibration</strong> needed for CCS /<br />

CRIUS<br />

• eutectic not precise enough<br />

• new reference light source will allow quick and realiable<br />

on-site <strong>calibration</strong> in almost any type of reactor<br />

18 October 2009 <strong>Temperature</strong> <strong>calibration</strong><br />

29


Some gems<br />

need a little<br />

extra help to<br />

sparkle<br />

www.laytec.de

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