l6 vapor phase epitaxy - linköping university · ⇛net doping ~low 1015cm-3 ... • since its...

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L6Vapor phase epitaxy

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Sublimation epitaxy-principle

Growth in a quasi-closed volume⇛ by sublimation of a solid SiCsource to a substrate ⇛ at lower temperature than the source⇛ the distance is small

Vacuum ambient & collision free transport ⇛ high growth rate

No chemical reactions ⇛ only intrinsic species: Si, Si2C, SiC2

No turbulence ⇛ uniform deposition

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Sublimation epitaxy - difference with bulk growth

• Lower T, shorter L, no effect of walls

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Process control

Characteristics to control:

⇛ growth rate ~50µm/hour

⇛ net doping ~low 1015cm-3

⇛ specular, smooth surface

Multi-parameter control

⇛ optimised growth

parameter window very small

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Growth rate

Temperature Temperature difference

10

100

4.4 4.45 4.5 4.55 4.6

Gro

wth

rat

e [µ

m/h

our]

104/T [K-1]

19502000Temperature [°C]

1900

128 kcal/mole

0

20

40

60

80

100

-10 -5 0 5 10

Gro

wth

rat

e [µ

m/h

r]

Relative coil position [mm]

2000oC

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Factors affecting purity

Potential contributors of impurity:

⇛ SiC source, graphite crucible

⇛ down to level of 1E15 cm-3 source is available

⇛ similar with graphite in respect to B and Al (IBIDEN-Japan)

What other factors?

⇛ System tightness, Si/C ratio, graphitization, uniformity of source sublimation

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Purity

Potential contributors of impurity ⇛system tightness, excess of C

Increase of base pressure 3 times With source graphitization increase of n-type doping 5 times switching n to p-type possible

1

10

100

10 20 30 40 50 60

n-ty

pe d

opin

g (c

m-3

) x10

15

base pressure (mbar) x10-7

1925oC

1

10

100

1000n-typep-type

Dop

ing

(cm

-3) x

1015

C/Si (degree of source graphitization)stronglow

step bunching

no graphitization

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L6 MBE - overview

• Molecular Beam Epitaxy (MBE) is an Ultra-High-Vacuum (UHV)-based technique forproducing high quality epitaxial structures with monolayer (ML) control.• Since its introduction in the 1970s as a tool for growing high-purity semiconductor films, MBE has evolved into one of the most widely used techniques for producing epitaxial layers of semiconductors, metals, insulators and superconductors as well, both at the research and the industrial production level. • The principle underlying MBE growth is relatively simple: it consists essentially ofatoms or clusters of atoms, which are produced by heating up a solid source. They thenmigrate in an UHV environment and impinge on a hot substrate surface, where they candiffuse and eventually incorporate into the growing film. • Despite the conceptual simplicity, a great technological effort is required to produce systems that yield the desired quality in terms of material purity, uniformity and interface control.•The choice of MBE and other growth techniques depends on the desired structure and needs:⇒ in the case of mass production, MBE suffers from a lower yield, compared to other techniques such as Liquid Phase Epitaxy (LPE) and Metalorganic Vapour Phase Deposition (MOCVD), due to a lower growth rate and wafer capability (currently, GaAs based MBE production systems are capable of up to 4X6” diameter wafers, compared to 5X10” of MOCVD). ⇒ MBE is the proper technique when some particular requirements are needed, such as abruptness and control of interfaces and doping profiles, thanks to the lower growth temperature and growth rate. ⇒ the control on the vacuum environment and on the quality of the source materials allows a much higher material purity, compared to non-UHV-based techniques, especially in Al-containing semiconductors for applications in high-mobility, high-speed devices. ⇒ the UHV environment allows the use of electron diffraction probes, which providefundamental information on the growth mechanisms.

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L6MBE equipment

• Main features: ultrahigh vacuum, molecular beams (ballistic fluxes), in-situ monitoring

► high purity, possibility to combine with measurement techniques.► growth of low dimensional layers and structures, growth control on a nano-scale level.► precise thickness and composition control.

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L6MBE main blocks

Possibility to grow III-V alloys and quantum heterostructures ( epilayermaterial is different from the substrate)

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L6MBE process characteristics

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L6Effusion cell

Effusion cell => the most critical part of MBE systems

Depending on the type of the sources:(i) MBE => solid source(ii) CBE or MO-MBE (chemical beam epitaxy) => metalorganiccompounds for group III source(iii) GS-MBE (gas source MBE) => hydrides as the group V source

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L6Effusion cell

Ballistic fluxes => no reactions in the gas phase

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L6MBE system

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L6

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L6CVD/MOCVD driving force

• In case metalorganic precursors are used => MOCVD

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L6CVD/MOCVD reactor design

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L6CVD/MOCVD

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L6

Growth species have to diffuse through the boundary layer to reach the substrate => diffusion limited mass transport

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L6

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L6

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L6Epitaxy on vicinal surfaces

/2kT

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L6Growth rate on vicinal surfaces

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L6Supersaturation on vicinal surfaces

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L6