Efrain Altamirano-Sanchez & Jean Francois de Marneffe

End-of-CMOS and beyond CMOS applications for Atomic Layer Etching

ETCH/UPM/IMEC

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DTCO

STCO

Logic Roadmap view

log 2

(#tr

ansi

sto

rs/$

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20152013201120092007

Happy scaling era# transistors per area

doubles every two yearfor same cost

14nm

20nm

28nm

40nm

65nm

90nm

Less happy scaling eraStill doubles but device

scaling provides diminishing returns

2017 2019 2021 2023 20252005

Heterogenous scaling2D Material for power gatingBack Side PDN MRAM….

20nm: First sign of troubleDouble patterning (cost !)Planar device runs out of steam

14nm: FinFETFinFET device saves the day

10nm7nm

5nm

7-5nm: At last ...EUV reduces cost

4-3nm:Nanowire/sheet FET to continue gate length scaling

3nm

2nm1.5nm

10-7nm: More troubleMulti-patterning cost escalates

Scaling boosters

Focus of process technology innovation is

Scale device and wire Scale basic logic cells Scale (sub-)system functions

Track height reduction

New ComputeMachine learningQuantum computingCryogenic electronics

2nm:High NA EUV?

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Basic principle of ALE and Quasi-ALE

Key features of ALE and q-ALE

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Control of REMOVAL to sub-nm scaleMain particularities: self-limiting / NOT uniformNOT layer-by-layer / may be damaging / FAST

Control of ADSORPTION to sub-nm scaleMain particularities: self limiting / uniformity / layer-by-layer / non-damaging / SLOW

Q-ALE = phases of process is partially

inter-mixed

ALE = phases are fully separated

Plasma etching

ALE

“reverse ALD”

Quasi - ALE

Thorsten Lill from Lam ResearchSEMICON West, July 10, 2014

FC Pulse Ion bombardment(A) (B)

Basic principle of q-ALE for SiO2 etching

Pulse of C4F8/CHF3 leading to ‘nanometer passivation’ at each cycle.

Short pulses allow to control thickness of deposition

Low energy Ar bombardment removes top layer; Ar time-bias drive FC accumulation-to-depleted regime.

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Gottlieb S. Oehrlein,ALE and Atomic Layer Clean TechnologyWorkshop San Francisco – April 21st, 2014

J. Vac. Sci. Technol. A 34(1), 01B102-7, 2016Time [s]

Quasi-ALE CMOS scaling

Quasi-ALE in N5 technology node

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DECDiamond EPI contact

WACWrapped Around contact

Fin patt. Gate patt. N& P WFM Metal gate SiN gate cap M0A contact etch

Contact metallization

N&P EPI

Series resistance: contact scheme, M0A material, contact resistivity

DECDiamond EPI contact

WACWrapped Around contact

1 FIN, HFIN 50 nm

Tungsten Cobalt Ruthenium

WAC

DEC

Results of TCAD simulation based on cell layouts

Local interconnect M0A plugs options: Single local interconnect Material – Liner thickness + barrier thickness

W-M0A: Tungsten, 3 nm + 2 nmCo-M0A: Cobalt, 3 nm + 2 nmRu-M0A: Ruthenium, 1.2 nm + 0.1 nm

Contact resistivity:Rho 0.5 and 1 [x 1e-9 Ohm.cm2 ]

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N5 self aligned contact (SAC): ILD0 SiOx etch selective to spacers & channel

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Minimize gate plug loss and low-k spacer recess during sac etch.

135 nm85 nm

EUV litho EUV litho TiN HM etch SAC etch SAC etch on channel SAC etch on field

Quasi-ALE for full self aligned Contact etch (N5)

• Dummy contact etch: Planar gate, no channel present.

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98nm contact etchGate cap recessSelectivity: 10:1 (SiO2: SiN)

ILD0 SiOx etch selective to Gate cap & spacers

Selectivity between SiO2 and SiNPulse of C4F8/CHF3 leading to ‘nanometer passivation’ at each cycle

Low energy Ar bombardment removes top layer; Ar time-bias drive FC accumulation-to-depleted regime.

Challenge of Q-ALE for SAC SiO2:Si3N4 etch: to build passivation much faster than in STD process.

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Fluorocarbon depleted condition

Fluorocarbon accumulation condition

Due to higher physical sputtering of SiN (lower bond strength), FC depleted conditions cannot provide selective etching of SiO2 over Si3N4

FC can accumulate on Si3N4

surface, protecting Si3N4 from chemical and physical etching.

J. Vac. Sci. Technol. A 34, 041307 (2016)

Quasi-ALE for N5 & N3 challenging dimensions

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N5 N3

Gate Pitch (nm) 42 32

Gate height over fin (nm) 85 ± 5 85 ± 5

Gate height over field (nm) 135 ± 5 135 ± 5

Contact CD (nm) 14 7

Contact AR 10 ~20N5

Challenge: Spacer removal for WAC

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WACWrapped Around contact

High selectivity to remove the spacers around the fins to enable WAC.

SAC etch

Confined EPI

ALE for 2D materials

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Benefits of 2D heterojunctions

• Vertical heterojunctions exhibit bipolar behavior with high field effect

ON/OFF ration >10^4

• Planar Heterojunctions exhibits High field effect ON/OFF ration (10^5)

and High electron mobility (m): 65 cm/Vs compared to that of isolated

multilayer.

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Heterojunction patterning

• The etching of one 2D material

towards another 2D materials is

challenging due to their chemical

similarity.

Potential solution:

Simplify the etch complexity by choosing an easier material to pattern with perfect selectivity to the underlaying 2D material

Roy et. al, ACS Nano 2015 9 (2), 2071-2079

2 nm2 nm2 nm2 nm2 nm

2.0 2.1 2.2

2.5 3.0

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WS2 and MoS2 300mm deposition

MoS2 (300 mm wafer processing)

WS2 (300 mm wafer processing)

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WS2 / MoS2 as heterojunction system

As model system, WS2 on MoS2 was used

1. Low temperature SiO2 hard mask was deposited and conventionally opened with CF4/H2

2. aSi patterning by ALE

3. Selective conversion of aSi into another 2D material, here: WS2 (WF6 as precursor).

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ALE Characteristics

• Cl-based ALE has intrinsic Si etch rates

of 6 Å / cycle

Experimental verification

In agreement with literature where

chemisorption depth of 6 Å is mentioned

• Low damage towards the substrate is

expected because of the separation of

dosing and activation0

50

100

150

200

250

0 6 12 18 24

Mea

sure

d t

hic

knes

s (A

)

# cycles

Etch rate determination on amorphous silicon

Before ALE

After ALE

Linear (After ALE)

Goodyear, A.; Cooke, M.; J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2017, 35 (1), 01A105.Patent EP 3139403, US 20170069469

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Surface topology

After ALE surface roughness reduced

Si on MoS2

RMS = 1.077 nm

MoS2 onlyRMS = 0.962 nm

ALE towards MoS2

RMS = 0.392 nm

Template wafer

MoS2 aSiMoS2 MoS2

Template wafer

Template wafer

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360 370 380 390 400 410 420 430 440 450 460 4700

10000

20000

30000

40000

50000

60000

70000 12 ALE cycles on the heterostructure

heterostructure

Inte

nsity (

arb

. un

its)

Raman shift (cm-1)

Raman Photoluminescence

No change in the Raman intensity = no etching of MoS2

Photoluminescence decreased to half

E12g

A1g

A exciton

B exciton

Heterostructure

12 ALEcycles

aSi

MoS2Template

wafer

MoS2Template

wafer

Silicon removal without damaging MoS2

RBS: The stoichiometric ratio of MoS2 was maintained within the measurement uncertainty.

ALE and the conversion of the structures towards WS2

• ALE etched structures were

immersed in 0.5% HF, H2O

rinsed and converted by

WF6 / H2S

• 200 s HF was necessary to

remove all oxide hardmask

and H-passivate the aSi

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No WS2 in the etched region

200 s HF (0.5%)

35 Å aSi

6 ALE cycles

ALE on Area Selective Deposition

AB

A

C

Substrate

Area selective deposition – Challenges

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Deposition time Interface• Line edge roughness

• Confinement of pattern

No-growth surface area• Undesired nucleation, contamination

Growth surface area• Deposition affected: pinholes,

blocking ...

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Figure 3

5.8 nm of TiN selectively deposited on 40 nm wide SiN spacesHigher particle density on patterned structures as compared to blankets, especially at aC corners.

Selective TiO2 and TiN deposition

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How ‘ALE’ can help

Surface treatment

ASD

ALE of nucleates

Surface treatment

ASD

ALE of nucleates

Etc...

A tool that combines: Surface functionalization /

ALD/ALE

Thank you

2D Materials in nanoelectronic systems

• Successor for gate-all-around structures on roadmap: 2D materials under investigation for application in logic

devices

2D-FET

TFET

• Properties:

No dangling bonds due to sulfur termination

Lower dielectric constant than Si

m is comparable to Si

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Short channel effects negligible for:

Radisavljevic, B. et. al, A. Nat. Nanotechnol. 2011, 6 (3), 147–150.

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Mo (1015 at/cm2) S (1015 at/cm2

) S/Mo

Reference No etch 6.8 12.6 1.9 ± 0.2

Sample 1MoS2 after 12

ALE cycles7.1 12.4 1.7 ± 0.2

Sample 2MoS2 after 12

ALE cycles7.0 12.6 1.8 ± 0.2

Sample 3MoS2 after 12

ALE cycles6.4 11.9 1.8 ± 0.2

The stoichiometric ratio of MoS2 was maintained within the measurement uncertainty.

RUTHERFORD BACKSCATTER SPECTROMETRY

Note on selectivity

Challenge of Q-ALE for SAC SiO2:Si3N4 etch: to build passivation much fasterthan in STD process

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