advancing atomic layer deposition and atomic …...• ald-style gas dose delivery using “ald...

© Oxford Instruments 2018

Advancing Atomic Layer Deposition and

Atomic Layer Etching

Harm Knoops, Oxford Instruments Plasma Technology


• Structure:

• Miniaturization, more complex structures and more 3D

• Device:

• Lower damage, interface control

• Material:

• Wider range of tailored material solutions, lower thermal budget

Why are ALD and ALE gathering more interest?

GaN

buffer

AlGaN

Gate

substrate

source drain

Vorobyov et al., Opt. Mat. Exp. 7, 513 (2017)

GaN transistors Quantum devices Biosensing


Generalized ALE/ALD cycle

Faraz et al., J. Solid State Sci. Technol. 4, N5023 (2015)


Key features ALE vs. ALD

Faraz et al., J. Solid State Sci. Technol. 4, N5023 (2015)


• Conventional etching involves continuous amorphisation of several

atomic layers and chemical reactions in that amorphised layer

• ALD and ALE provide control and low damage options to allow

minimal influence on sensitive surfaces.

Low damage for minimal influence top layers

From O. Joubert, SEMATECH Workshop on Atomic-Layer-ETch (ALET) and - Clean (ALC) Technology, April 21, 2014

Conventional etching ALE

Increasing ion energies


• Why ALD and ALE?

• ALD

• Stress-control in oxides

• Low-resistivity nitrides

• Novel plasma gases

• ALE

• Processes

• Smoothening

• ALD and ALE

• Conclusion

Outline


• Cutting edge plasma ALD systems with

thermal ALD as standard

• Mixed mode operation within a single recipe

• No hardware changes required to switch

mode between plasma and thermal ALD

• e.g. start with thermal Al2O3 on sensitive

interface but continue with plasma ALD

for best material properties

Oxford Instruments ALD

FlexAL


• To limit etching of a polymer plasma

conditions can be set to reduce etching

• High pressure plasma allows growth on

polymers without etching them

• ALD deposit will also function as

protective layer, so generally etching is

minimal

Low damage for depositing on polymers

Rate of the resist removal during 50

plasma exposures of 5 s each


Applying substrate biasing to enhance the ion energy

The FlexAL ALD system can be equipped

with table bias for extended process

capabilities (e.g., higher conductivity,

higher crystallinity, stress control).

• Up to 550 °C temperature.

• Up to 100 W RF power.

• 13.56 MHz

• Up to 500 V resulting DC bias.

• Fully automated RF matching.


Material properties control by biasing

A wide range of properties can be tuned by substrate biasing in ALD

Faraz et al., ACS Appl. Mater. Interfaces 10, 13158 (2018)


Potential usage in devices

• Stress control on planar surfaces for MEMS devices.

• Anti-reflective TiO2 coating with low stress.

• Al2O3/HfO2 higher-k dielectric.

• Ta2O5 barrier layer with specific stress.

• Conductivity and superconductivity control of TiN and

NbN for quantum devices. Faster deposition of high-

quality material expected with biasing.

• Resistivity/work-function/stoichiometry control for gate

metals (e.g., TiN, HfN).

Vorobyov et al., Opt. Mat. Exp. 7, 513 (2017)

Superconductivity control

Stress control


Shestaeva

Shestaeva

Film stress in thermal and plasma ALD of Al2O3

• Stress decreases with deposition

temperature. Higher than

estimated from thermal stress.

growth related due to voids,

impurities or dislocations?

• Plasma similar material properties and

similar stress to thermal ALD. Ylivaara et al., Thin Solid Films 552, 124 (2014)

Shestaeva et al., Applied Optics 56, C47(2017)

Residual stress

Ohring, The Material Science of Thin Films, 1992


Beladiya et al., Proc. SPIE 106910E (2018)

Faraz et al., ACS Appl. Mater. Interfaces 10, 13158 (2018) 0 50 100 150 200 250 300-3000

-2000

-1000

0

1000

2000

Compressive

Al2O

3

TiO2

SiO2

Resid

ual S

tress (

MP

a)

Average bias voltage (V)

HfO2

Tensile

Film stress as a function of biasing for ALD oxides

• Generally tensile without biasing.

• Typically more compressive with

bias up to certain voltage.

• Bias trends very dependent on

material.


0 50 100 150 200 250 300-3000

-2000

-1000

0

1000

2000

Mixed

RutileAnatase

Monoclinic

Amorphous

Compressive

300 °C

TiO2

Resid

ual S

tress (

MP

a)

Average bias voltage (V)

150 °C

HfO2

Tensile

Relation of stress with crystallinity when biasing

• Crystallization can cause tensile

stress, further biasing generally

makes film compressive.

• Similar behaviour found for

Ta2O5, MoO3, and WO3.



Effect of bias duration for TiO2

0 100 200

-2250

-1500

-750

0

750

10 s bias

Average Bias Voltage (V)

Compressive

Re

sid

ua

l str

ess (

MP

a)

Tensile5 s bias

• ALD by TDMAT and 10 s O2 plasma at 300 °C.

• At 100 V near zero stress, for anti-reflective TiO2

coating with low stress.

Choosing bias duration can give additional control.

Precursor (A)

Purge

Co-reactant (B)

Source Plasma (RF-ICP)

Substrate Bias (RF-Bias)

Time

1 cycle 2 cycles



Effect of bias on plasma ALD TiN

• ALD by TDMAT and 10 s H2/Ar plasma at 200 °C.

• Tuning of crystallinity, resistivity, density, and

stress.



Effect of bias on plasma ALD NbN

• ALD by TBTDEN and 20 s

H2/Ar plasma at 250 °C.

• Similar trend as for other

conductive nitrides. Strong

correlation between film

resistivity and film stress.

• High superconducting

transition temperature of

12.9 K for ~45nm NbN film-4000

-3000

-2000

-1000

0

1000

2000

3000

0

100

200

300

400

500

0 15 30 45 60 75

Film

Str

es

s (

MP

a)

R.T

. R

esis

tivit

y (

µΩ

*cm

)

Bias RF power(W)

resistivity with 20s plasmaexposure

film stress on Si with 20s plasmaexposure

Tensile

Compressive

~40nm NbN films


• Robust ALD Process: Self-limiting ALD growth over wide temperature

window, high GPC (0.1 nm/cycle), Oxygen and carbon free (<2%)

• Digital layer thickness control from mono-layer to few layer material

• Tunable morphology: Control over basal plane or edge plane orientation

• Potential applications: Nano-electronics and catalysis

FlexAL2D: Plasma ALD of MoS2

www.oxinst.com/FlexAL2D

http://www.oxinst.com/FlexAL2D


• AlF3 ALD using TMA and SF6 plasma in FlexAL.

• Refractive index of 1.35 at 633 nm.

Aluminium fluoride (AlF3) ALD

Conformal

coating of GaP

nanowire

Wide temperature window

and no growth delayLow absorption over a wide range

Vos et al., Appl. Phys. Lett. 111, 113105 (2017)


• Why ALD and ALE?

• ALD

• Stress-control in oxides

• Low-resistivity nitrides

• Novel plasma gases

• ALE

• Processes

• Smoothening

• ALD and ALE

• Conclusion

Outline


ALE configuration

• ALD-style gas dose delivery using “ALD valves”

with 10 ms open-close response.

• Low bias power control 0.3 W to 300 W or 600 W.

• Ability to operate as a standard etch tool or in fast

low power ALE mode. Mode selection via

software recipe control.

• Wafer clamped mechanically using

helium backside cooling.

Oxford Instruments ALE tool

http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwix37Kbw4TOAhXBLcAKHfcPAnkQjRwIBw&url=http://www.swagelok.com/en/catalog/Product/Detail?part=6LVV-ALD3FR4-P-CV&psig=AFQjCNEq3bOJmb7BEf7GLnx0BtSUof4ZkA&ust=1469189390530629


Reliable gas delivery: OES analysis of CHF3 pulses

Repeatable

dosing using

ALE hardware

Dosing using

conventional

gas box

0

200

400

600

800

1000

1200

1400

1600

1800

2000

460 480 500 520 540

C2O

ES

in

ten

sit

y

Time (secs)

MKS1179 MFC

ALE hardware: 45 and 74msecs

Sensirion MFC: valved then not

Valve

closedValve open Valve closed

0

5000

10000

15000

20000

25000

30000

35000

40000

0.00E+00 1.00E+02 2.00E+02 3.00E+02 4.00E+02 5.00E+02 6.00E+02

0

1000

2000

3000

4000

5000

6000

2.10E+03 2.15E+03 2.20E+03 2.25E+03 2.30E+03 2.35E+03 2.40E+03 2.45E+03 2.50E+03 2.55E+03 2.60E+03

ALE hardware provides short

burst of gas to the chamber

with no residual gas


ALE Processing experience

Experience in processing materials

• Demonstrated results in a-Si, Si, SiO2, MoS2 ,

GaN, AlGaN layer etching.

• Collaboration with universities and institutes to

develop ALE recipes. ALEGRO project.

• Partnership with production manufactures to

develop solution for normally-off GaN HEMT.

Material Etched Dose Gas Etch Gas

Si or a-Si Cl2 Ar

MoS2 Cl2 Ar

SiO2 CHF3 or C4F8 Ar or O2

AlGaN/GaN Cl2, BCl3 Ar

AlGaN/GaN N2O BCl3


Si etching

• Etch rate 2 to 7Å/cycle (up to 70Å/min)

• Cl2 used in dose step, Ar used for etch

• Anisotropic profile

ALE processing results

25nm wide Si

trenches etched to

110nm depth by

ALE, HSQ mask

still in place

MoS2 etching and Raman results

• Small shift in peaks per 3 ALE cycle

• 40 ALE cycles removed all material

• Starting thickness 18 nm

• Cl2 used in dose step, Ar used for etch

• Low damage with no defect induced

peak at 227 cm-1

Raman spectra

after 17, 20 and

23 ALE cycles

200 225 250 350 400 450 5000

50

100

150

200

17 Cycles

20 Cycles

23 Cycles

Inte

nsity (

a.u

.)

Raman Shift (cm-1)


AlGaN/GaN ALE results: Ar/Cl2

• Etch rate 1.5-3 Å/cycle (up to 18 Å/min)

• Uniformity <±5% over 200mm

• Added roughness <<1nm. AFM data

indicates a smoothening effect

AFM data courtesy of Paolo Abrami in Collaboration with Bristol Uni

ALE smoothening

0

1

2

3

4

5

6

7

0 10 20 30 40

AlG

aN E

PC

(Å/c

ycle

)

DC bias (V)

with Cl2

No Cl2

AlGaN etching rate per cycle

(pm

)

AlGaN surface roughness decreases with ALE


Atomic Scale Processing Cluster


Conclusions

• ALD can be tuned to be low damage but ion energy can also be enhanced.

• Oxide film stress dependant on material (e.g. crystal phase) and plasma

conditions.

• Biasing allows low-resistivity nitrides and improved superconductive

properties. Novel plasma gases allows growth of fluorides and sulfides.

• Wide range of ALE processes available.

• ALE of silicon but also low damage etching of 2D materials such as MoS2.

• Smoothening of AlGaN observed. Could be important feature of ALE.

• Processes can be combined in cluster tool to allow atomic scale processing and

find synergy of alternating between processes and doing process flow in vacuum.

advancing atomic layer deposition and atomic …...• ald-style gas dose delivery using “ald...

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