innovative plasma chemistry solutions to enable … plasma chemistry solutions to enable atomic...

© 2014 IBM Corporation

IBM Research

Innovative Plasma Chemistry Solutions to Enable Atomic Scale Precision

Eric A. Joseph, John Arnold* and Sebastian Engelmann

IBM T.J. Watson Research Center, Yorktown Heights, NY

* IBM Research at Albany Nanotech, Albany, NY


IBM Research | Silicon Science & Process Technology | ALET Workshop | April 2014

SEMATECH Atomic Layer Etch Workshop 2

Outline

Introduction and motivation for Atomic Scale Precision

History and Review of Atomic Layer Etch Approaches

Atomic Scale Precision with Alternative Etch Chemistries

Conclusions and Acknowledgements




Traditional Logic Scaling Challenges

Scaling of CMOS devices is reaching atomic scale limit

New materials and integration schemes are being evaluated and introduced to enable performance improvements

Poly/SiO2 gate stack

Metal/High K dielectric gate stack

John E. Kelly III – RPI Seminar, 2012

H. Iwai, Roadmap for 22 nm and beyond, J. Microelectronic Eng. March 2009




Motivation and Needs for Atomic Scale Precision

Deliver leading edge processing for 7nm node and beyond technology

• Aggressive feature sizes (< 20nm) & non-planar device geometries

Selectivity to atomically thin films and the introduction of new materials

C-Electronics Trigate Si Nanowire Device

Planar: PDSOI

Si

STISTI

BOX

n

+

nnFE

T

n

+

Si

STISTI

BOX

n

+

nnFE

T

n

+

SI InP

10 nmTiNn+-Ge n+-Ge

NiGe NiGe

Source DrainInGaAshigh-κ

InAlAs buffer

SiN

ZL

SI InP

10 nmTiNn+-Ge n+-Ge

NiGe NiGe

Source DrainInGaAshigh-κ

InAlAs buffer

SiN

ZL

III-V Device

PZT

M0-Pt

SiO2

M1Al

Al

PRM3

M4

PZT

M0-Pt

SiO2

M1Al

Al

PR

PZT

M0-Pt

SiO2

PZT

M0-Pt

SiO2

M1Al

Al

PRM3

M4

Piezo Device




Atomic Layer Deposition

Digital (nm/cycle) ; Surface Controlled

High accuracy ; Slow throughput

Key Attribute Conformality Picture: Cepheiden

M. Gutsche et al Future Fab Intl. Issue 14 (2/11/2003)




Requirements to Enable Atomic Layer Etch

Digital (nm/process)

Surface Controlled

High accuracy

Key Attribute Selectivity!

John E. Kelly III – RPI Seminar, 2012




History of ALE

Google Search ‘ALE Plasma’

Atmospheric Pressure

CxHyOz Chemistry!!

Multi-disciplinary (as expected)

IPA + SAKE




Atomic layer etch precision common for processing of III-V materials for

many years

Process based on inverse ALD using thermal desorption

No evaluation of selectivity for different III-V materials

History of ALE

Appl. Phys. Lett. 63, 3500 (1993);




Atomic Layer Etch by Anisotropic Wet Etch

Selective atomic scale

etch has been prevalent

for a considerable time

Etch capability defined by

crystallographic plane

orientation

Selectivity is chemistry

dependent! Prof. K. Sato, Dept. of Micro/Nano Systems Engineering, Nagoya University

(100) silicon wafer

(110) silicon wafer




Atomic Layer Etch by Pulsed Plasma

Tailored IEDF based ALET

Electron Temperature and ion energy drop

considerably during afterglow when

pulsing

Low energy ion etch with low sheath

voltages

S.-B. Wang and A. E. Wendt, Journal of Applied Physics 88, 643 (2000)

Economou and Donnelly, US 20110139748 A1, 2011




Pulsed plasma enables formation of ion-ion plasmas in electronegative gases

Negative ion etch can proceed with less damage

Due to the mass balance between predominant positive and negative ions Cl2+ vs Cl-

Chemistry differences between negative and positive CFx species CF3+ vs F-

Enables Novel Chemistry capability

Kanakasabapthy, Ph.D. Dissertation, University of Texas at Dallas, 2001

Negative Ion Extraction for Atomic Scale Precision Plasma On Plasma Off Plasma On Plasma Off

A. Agarwal, S. Rauf, and K. Collins, JOURNAL OF APPLIED PHYSICS 112, 033303 (2012)

Temporal dynamics of electrons, positive and negative ion flux to the bottom electrode in a CF4/Cl2 50/50 plasma The positive ion flux is the sum of the fluxes of Cl2+, Cl+, CF3+, and CF2+, while the negative ion flux is the sum of the fluxes of Cl- and F-.




Atomic Layer Etch by Self-Limiting Processes

Surface Limited

Inverse ALD

• Cyclical process

• Adsorption / Desorption

• Requires multiple purges

Reactant limited

CW Argon plasma with

pulsed fluorocarbon

• Pulsed bias power to

initiate etch reaction

• Etch depth controlled by

ion energy and

fluorocarbon thickness

KEREN J. KANARIK et. al., Moving atomic layer etch from lab to fab, Solid State Technology 2014

Metlzer et. al., JVST B, 2014

Time

(c) (b) (a) C 4 F 8

Ar

Flow Rate

No Bias

Etching Active

Time

Passivation

Active Time

Bias

(c) (b) (a) C 4 F 8

Ar

Flow Rate

No Bias

Etching Active

Time

Passivation

Active Time

Bias

(a) (a)

No Bias




Outline

Introduction and motivation for Atomic Scale Precision

History and Review of Atomic Layer Etch Approaches

Atomic Scale Precision with Alternative Etch Chemistries

Conclusions and Acknowledgements




Materials Innovations - Elements Employed in Silicon Technology

1980’s

2000’s

1990’s

New Materials Introduced each decade to enhance device capability

Etch chemistry still relies on the same set of halogen based chemistries to

enable device fabrication and integration




Mechanism and chemistry for SiO2:SiN Selectivity

(Zhang 1996)

Carbon-rich fluorocarbon gas and modest

H2 (C2F4/H2, C3F6/H2) gives good selectivity

Hydrogen-rich fluorocarbon with less C

(CHF3/H2) not useful for SiO2:Si3N4 selectivity

Structure!! - Importance of CF2 for selective deposition

• Radical generation variation with feed gas structure

(Samukawa 1999)

Industrial migration to C4F8 & C4F6 & C5F8

Zhang et al., “Fluorocarbon High Density Plasma. VII. Inv. of Sel. SiO2-to-Si3N4…,” J. Vac. Sci. Tech. A, 14(4), 2127 (1996)

S. Samukawa, “Differences in radical generation due to chemical bonding…”, J. Vac. Sci. Tech. A, 17(5), 2463 (1999)

M. Schaepkens, G. S. Oehrlein, et. al. J. Vac. Sci. Technol. A, Vol. 17, No. 1, Jan/Feb 1999

Gas F/C

CF4 4

C2F6 3

C3F6 2

C2F4 2

C4F8 2

C5F8 1.6

C4F6 1.5

Schaepkens, 1999

Etch Innovation: Chemistry




Mechanism and chemistry for SiO2:SiN Selectivity

(Zhang 1996)

Carbon-rich fluorocarbon gas and modest

H2 (C2F4/H2, C3F6/H2) gives good selectivity

Hydrogen-rich fluorocarbon with less C

(CHF3/H2) not useful for SiO2:Si3N4 selectivity

Structure!! - Importance of CF2 for selective deposition

• Radical generation variation with feed gas structure

(Samukawa 1999)

Industrial migration to C4F8 & C4F6 & C5F8

Zhang et al., “Fluorocarbon High Density Plasma. VII. Inv. of Sel. SiO2-to-Si3N4…,” J. Vac. Sci. Tech. A, 14(4), 2127 (1996)

S. Samukawa, “Differences in radical generation due to chemical bonding…”, J. Vac. Sci. Tech. A, 17(5), 2463 (1999)

M. Schaepkens, G. S. Oehrlein, et. al. J. Vac. Sci. Technol. A, Vol. 17, No. 1, Jan/Feb 1999

Gas F/C

CF4 4

C2F6 3

C3F6 2

C2F4 2

C4F8 2

C5F8 1.6

C4F6 1.5

Schaepkens, 1999

Etch Innovation: Chemistry

Inte

ns

ity (

a.u

.)

CF2

263 nm

C3

412 nmC2

516 nm




Spacer etch is the most critical low ion energy process for planar and non-planar devices

Selectivity to gate, fin, and substrate highly critical to maintain gate and fin profile and minimize substrate (BOX) recess

Non-Planar Device Profile and Selectivity Challenges

3D spacer formation

Gate

3D spacer

Fin Po

st

Gate

Etc

hP

ost

Sp

acer

Etc

h

~32nm

~20nm~20nm




Spacer Module & Atomic Precision

Spacer module considered most challenging, as all materials exposed to plasma remain on device

Module becomes even more challenging for novel device geometries (FinFET, Trigate, Nanowire)

Typical approach to enable processing has focused on alternating reactor configuration

First attempt to solve this issue from using a plasma chemistry approach

substrate

After spacer deposition

substrate

After spacer deposition

Traditional spacer process

substrate

Nitride thinning/

pull down

Si damage/

oxidation

After spacer etch

substrate

Nitride thinning/

pull down

Si damage/

oxidation

After spacer etch

Novel spacer process

substrate

Uniform

sidewall

coverageProtection by

FC deposit

After spacer etch

substrate

Uniform

sidewall


FC deposit

substrate

Uniform

sidewall


FC deposit

After spacer etch




Atomic Scale Precision with Novel ZEON Chemistry

0.0 0.5 1.0 1.5 2.0

0

10

20

30

40

50

60

Oxide

Nitride

Silicon

Etc

h r

ate

(n

m/m

in)

Fluorocarbon film thickness (nm)

Selective

nitride etching

Novel etch mechanism for selective nitride etch is achieved with ZEON gas

chemistry

Nitride etch rate favorably controlled by fluorocarbon reaction layer thickness

M. Schaepkens et al., J. Vac. Sci. Technol. A 17, 26 (1999)

0 1 2 3 4 5 6 7 8 0

100

200

300

400

500

Oxide

Nitride

Silicon

Etc

h R

ate

(nm

/min

)

Fluorocarbon Film Thickness (nm)

0 1 2 3 4 5 6 7 8 0

100

200

300

400

500

Oxide

Nitride

Silicon

Etc

h R

ate

(nm

/min

)

Fluorocarbon Film Thickness (nm)

Selective

oxide etching




ZEON SiN Spacer Process Performance

ZEON process has

better PDSOI Device

performance with

respect to HM and

spacer sidewall loss

Zeon gas process on

Trigate Devices shows

clean gate and desired

growth on Fin after

epitaxial growth

process

POR (CH3F/O2)

process shows

parasitic Si growth on

gate sidewall

POR

ZEON I

ZEON II

HM

PC

HKMG

Spacer

PDSOI Device

POR process Un-optimized Zeon gas process

Trigate Device

1.7

1.3

1.5

SOI loss

[nm]

ZEON II 0 0 4.5

ZEON I 2.5 0 4.3

POR process

4.4 0.2 6.8

Process SiN footing

[nm]

Spacer

loss [nm]

HM loss

[nm]

1.7

1.3

3.0

SOI loss

[nm]

ZEON II 0 0 4.5

ZEON I 2.5 0 4.3

POR process

4.4 0.2 6.8

Process SiN footing

[nm]

Spacer

loss [nm]

HM loss

[nm]




Post Spacer Deposition

Post Spacer Etch


Si loss is reduced considerably with the addition

of optimized wet cleans, tailored to remove

polymer from selective etch

No longer a wet process to remove oxidized silicon

Pseudo atomic scale precision achieved




Post Spacer Deposition

Post Spacer Etch


Pseudo atomic scale precision achieved




NVM Candidate Attributes

Phase Change Memory

Based upon the physical state of a chalcogenide material

Device performance determined by SET speed (crystallization) and RESET Current (melt-quench)

PCRAM Scalability Advantage

Scalability determined by current density across PCE – Device Reset Current

Spin-Momentum Transfer MRAM

Based on TMR and Spin polarized Current

Performance similar to DRAM with better density than SRAM

High speed switching possible (1 nsec)

Switching current scales with device size

Word

Line

I Bit Line

e-

Word

Line

II Bit Line

e-e-

SET

Bit Line

Word Lines

GroundSET

Bit Line

Word Lines

Ground




NVM Processing Challenges

Phase Change Memory

GeSbTe profile control critical given its

extremely high volatility in halogen etch

chemistries

Modification to the GST composition

can significantly alter material properties

Spin-Momentum Transfer MRAM

Difficult materials set with low volatility

requiring physical sputtering to pattern

Low temperature budget (< 300C)

Susceptible to damage/corrosion by etchant

Potentially damaging plasma processing

can effect underlying magnetics

PtMn

Co

CoFeB

CoFe

Al

Cu

CuN

Ta TaN

VPd

CoPdAl2O3

MgOIrMn

Bit line

W

GST

TiN

Bit line

W

GST

TiN

VLSI 2006

EELS and EDS data

show mostly Ta

some Ru is also possible –

visible in SEM

TaN

TaN

TaN/Ta

Ru

PtMn

AlOx

Possible TJ damage

and short

Likely post CMP

un-removed oxidation layer

TJ Stack Nominal Composition

Base layer AF Pinned layer Barrier Freelayer Cap and Hard Mask

50 TaN |20 Ta 175 38PtMn 5 CoFeB |14 70CF |7.5 Ru |24 CoFeB 7 Al / Ox POR 40 81NF 80TaN |100 Ru |700 TaN




Wafer 2, 7NGST

Wafer 9, 7NGST, etch step 1

Wafer 11, 7NGST, etch & clean

Wafer 12, 7NGST, etch & strip

Wafer 2, 7NGST

Wafer 9, 7NGST, etch step 1

Wafer 11, 7NGST, etch & clean

Wafer 12, 7NGST, etch & strip

Laser Reflectivity Data

Laser Reflectivity measurements used to determine (re)crystallization speed

Exposure to plasma chemistry significantly reduces speed by as much as three orders of magnitude

PCM: Effects of Processing on Crystallization Speed

As Deposited

Post Etch

Post Etch and Clean

Post Etch and Strip




Depth profiled XPS Analysis of partially etched GST reveals significant modification

Nitrogen, Antimony and Tellurium loss

Etch induced Modification ranges as much as 12nm in depth

X-ray absorption spectroscopy shows shifts in germanium absorption edge energy

Change in oxidation state: Ge-N replaced by Ge-O

Band Edge ShiftBand Edge Shift

0 2 4 6 8 10 12

0

5

10

15

20

25

Depth (nm)

Ato

mic

Fra

ction (

%)

Sb Metal

0 2 4 6 8 10 12

0

1

2

3

4

5

6

A

tom

ic F

ractio

n (

%) N

Depth (nm)

Characterization of Etch Induced PCM Material Modification




Effect of Cladding / Cap Layer

Data from literature demonstrates the effect of cap materials on the crystallization properties of GST films

Due to modification of the incubation time, changes in nucleation and potentially thermal conductivity effects

GST thickness also significantly effects crystallization time as well!

We can conclude that etch damage creates a thinner film (obvious) and leaves an oxide (GeO) atop the GST, behaving as a cladding layer.

Result is a significant increase in crystallization time and FCC HCP transition temperature

H-Y Cheng et al, NVMTS 2009 H-Y Cheng et al, NVMTS 2009




Repair / Removal of Modified Layer

Etch damage repair technique demonstrated on patterned structures

Technique is highly selective to undamaged N:GST

No Difference observed after 100% overetch

0s 30s 60s 120s

TiN

N:GST N:GST

TiN

Can original stoichiometry of the N:GST film be recovered after etch?

YES




Conclusions

Various methods to perform large scale ALE are currently under development

Key attribute for ALE is still selectivity and will rely heavily on plasma chemistry

to achieve atomic scale precision

A new ZEON etch chemistry has been developed for SiN etch applications

which exhibits Atomic Scale Precision based on a novel selective fluorocarbon

deposition mechanism

Use of the novel ZEON chemistry also demonstrates high selectivity to C-based materials

enabling use in SiN patterning applications with low LER/LWR

Plasma chemistry critical for complex Non-Volatile Memory materials as

selective volatilization and plasma induced material modification effect device

performance

Critical understanding needed to develop damage-free ALE




Acknowledgements

All results shown have been produced in the Microelectronics Research

Laboratory (MRL) at the T.J. Watson Research Center, Yorktown Heights

Authors would like to thank our etch colleagues in East Fishkill and Albany

Nanotech for helpful discussions and providing wafers.

Authors would also like to thank the MRL staff & MRL management for support

of this work

innovative plasma chemistry solutions to enable … plasma chemistry solutions to enable atomic...

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