materials and process challenges for advanced …...materials and process challenges for advanced...

© 2017 IBM Corporation

Materials and Process Challenges for Advanced Technology and the Role of Atomic Scale Precision

Eric A. JosephIBM T.J. Watson Research Center, Yorktown Heights, NY

© 2017 IBM CorporationCMC Conference 2017 – Richardson, Texas

AcknowledgementsCo-Authors Sebastian Engelmann, John Papalia, Nathan Marchack, Robert Bruce, Dominik Metzler and

Hiroyuki Miyazoe

Collaborators George Totir, Dave Rath, John Arnold, et al Prof. Gottlieb Oehrlein, Dominik Metzler* – University of Maryland David Boris, Scott Walton – Naval Research Lab

Funding and Resources: We gratefully acknowledge financial support of this work by the National Science Foundation

under award No. CBET-1134273 and US Department of Energy (DE-SC0001939). IBM Microelectronics Research Lab staff & management are also thanked for their support of this

work5/13/2017 E. A. Joseph et al2

* Dominik was both at UMD and at IBM as an intern during the course of this work


Outline Introduction and motivation for Atomic Scale Precision

Review of Atomic Layer Etch Approaches

Atomic Scale Precision with Plasma enhanced ALE (PE-ALE) Surface Chemistry Control Optimizing selectivity by atomic layer etch approaches Evaluation of PE-ALE processes during patterning Interaction of PE-ALE with patterning materials

ALE Implementation For Future Applications

Conclusions5/13/2017 E. A. Joseph et al3


Dennard Scaling and Moore’s Law have stagnated

Clock speed and chip performance relatively flat since 2007

Transistors / chip still increasing

April 20174

Moore’s Law and Scaling


Scaling vs. Innovation

5

Driving the innovation pipeline is critical as the benefits from traditional scaling decline

Prior to 90nm: performance improvement was from scaling … Now: innovation, materials and structures are key

New DeviceArchitecture

90nm and beyond:Strained Silicon

32nm and beyond:High K / Metal Gate

14nm and beyond:FinFET

Gain by Innovation

Traditional Gain

IBM Confidential


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 materials5/13/2017 E. A. Joseph et al6

F


Atomic Layer Removal processes to enable multi-color selectivity schemes– Expansion on existing patterning efforts– More than 2 materials involved – High aspect ratio features

Atomic Layer Removal (ALE / ALP) processes to enable advanced device technology– III-V and other candidate materials under evaluation– Composite material very prone to plasma damage

and/or chemical attack – Development of suitable dry etch / wet etch chemistries,

slurry / CMP processes as opportunity

B Turkot – ALE workshop 2014

B Turkot – ALE workshop 2014

Motivation and Needs for Atomic Scale Precision

5/13/2017 E. A. Joseph et al7


Atomic Layer Deposition

Digital (Angstrom/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 Etching

Digital (Angstrom/cycle) ; Surface Controlled

High accuracy

No damage to adjacent material

Key Attribute Selectivity!E. A. Joseph et al

John E. Kelly III – RPI Seminar, 2012

Si crystal

5/13/20179


Atomic Layer Etching

10E. A. Joseph et al

① Surface reaction ③ Energetic mechanism④ Etch Products Purge

Concept of ALE

Release mechanism

1 cycle

1. Surface Layer reaction 2. Purge excess reactant

3. Reaction mechanism release4. Byproduct Purge

Release mechanism

② Purge excess etchant

Purge

Huffman et al, 2015 VLSI-TSA TSS155/13/2017


Atomic Layer Etching 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 Etching by Self-Limiting Processes Surface Limited Inverse ALD

Wet-Chemistry Controlled Surface Reactions• Surface oxidation is performed

in H2O2 solution followed by native oxide removal in HCl.

Thermal-based Surface Reaction • Sequential exposure of thermally

activated chemical reactants tin(II) acetylacetonate (Sn(acac)2) and HF (HF-pyridine)

tin(II) acetylacetonate (Sn(acac)2) and HF (HF-pyridine)

Younghee Lee et al. ECS J. Solid State Sci. Technol. 2015;4:N5013-N5022

D. H. van Dorp, et al; ECS J. Solid State Sci. Technol. 2015, 4 (6) N5061-N5066



Plasma Enabled Atomic Layer Etch by Self-Limiting Process Surface Limited Energy controlled

surface reactions• Ion enhanced or noble gas

induced surface reactions• Requires multiple purges

Reactant limited Flux controlled

surface reactions• Pulsed bias power to initiate etch

reaction • Etch depth controlled by ion

energy and fluorocarbon thickness

KEREN J. KANARIK et. al., Predicting synery in ALE, JVST A 35(5), 05C302 (2017)

D. Metzler et al. JVST A 34(1), 01B102 (2016)



ALE Application Table

ALE Method will be chosen based on material/process requirements and structural considerations Optimization for process selectivity, anisotropy, throughput and ability to maintain ‘ALE

Window’ will be major focus

Wet process and Atomic Layer Cleans essential not only as ALE method, but also as post ALE optimization


ALE “window” driven by: Energy of desorption process Plasma chemistry and radical physi/chemisorption

PE-ALE Process space



Experimental Verification of Self-Limited SiO2 PE-ALE


Self-limited behavior observed for FC Reactant Limited SiO2 etch using C4F8

Metlzer et. al., JVST B, 2014


Metlzer et. al., JVST B, 2014

Self-limited behavior observed for FC Reactant Limited SiO2 etch using C4F85/13/2017 E. A. Joseph et al17

Experimental Verification of Self-Limited SiO2 PE-ALE


Verification of PE-ALE in Commercial Tooling

D. Metzler, et al., JVST A 32, 020603 (2014)


50C process10C process

60s

etch

ste

p75

s et

ch s

tep

90s

etch

ste

p

-20C process

OPL

SiO2

Si

Investigation of PE-ALE Process Space for Patterning

• Substrate temperature and etch step length are critical parameters

• General process capability verified

• TEM confirms limited atomic layer precision, but clear signs of selective etch behavior

100nm OPL/30nm SiO2/5nm SiN/50nm SiO2

SiN / SiO2interface



Optimized process of chemistry A for 200nm pitch pattern shows moderate selectivity to SiN, OPL, but not TiN

Running PE-ALE conditions in CW mode shows:

Significant selectivity loss

Significant uniformity increase

Easiest path for selectivity enhancement is through plasma parameter improvement

Complex interplay of optimizing energy control while maximizing chemistry control

SiN OPL TiN0

5

10

15

20

25

Sele

ctivi

ty (t

o O

xide)

Material

PE-ALE CW, lo Wb CW, Hi Wb

Oxide Etch

Application of PE-ALE to Silicon Oxide Etch



Application of PE-ALE to Silicon Oxide Etch

Small pitch patterning has very limited OPL budget

PE-ALE shows significant improvement of OPL budget, especially for lower substrate temperature

Difference in FC deposition species found, which may contribute to CD and roughness evolution

Sample CD LWR LERCW, CF4|CHF3, 50°C 17.4 7.5 5.1PE-ALE, Ar|C4F8, 50°C 15.9 7.7 4.6PE-ALE, Ar|C4F8, 10°C 14.9 7.2 3.8

CW 50°C PE-ALE 10°CPE-ALE 50°C



Application of PE-ALE to small pitch SiARC Open Same processes have been applied to 40nm pitch macros written

by e-beam

Even though a significant increase was found for PE-ALE on optical features, only minimal CD gain and LER/LWR increase were observed

Pattern fidelity is limited by substrate patterning step

VUV interactions of inert plasma during processing may play crucial role here

CW SiARC

PE-ALE SiARC



Atomic Scale Precision with Chemistry

0.0 0.5 1.0 1.5 2.00

10

20

30

40

50

60

OxideNitrideSilicon

Etch

rate

(nm/

min)

Fluorocarbon film thickness (nm)

Selective nitride etching

Novel etch mechanism for selective nitride etch is achieved with novel gas chemistry

Nitride etch rate favorably controlled by fluorocarbon reaction layer thickness

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

0 1 2 3 4 5 6 7 80

100

200

300

400

500

OxideNitrideSilicon

Etch

Rat

e (n

m/m

in)

Fluorocarbon Film Thickness (nm)0 1 2 3 4 5 6 7 8

0

100

200

300

400

500

OxideNitrideSilicon

Etch

Rat

e (n

m/m

in)

Fluorocarbon Film Thickness (nm)

Selective oxide etching

S. U. Engelmann et al. AVS Int’l Symp. 2012



Maximizing patterning performance through Chemistry:

Etch process conditions optimized for chemical etch

Careful optimization of gas molecule was done

No distinction of process gases by OES or electrical chamber readouts possible

Chemistry C chosen as most ideal precursor

A B C D0

10

20

30

40

50160170

Etch

Rat

e (n

m/m

in)

SiN SiO2

SOI OPL

Silicon Nitride



Post Spacer Deposition

Post Spacer Etch

Pseudo atomic scale precision achieved with Chemistry C for SiN Etch

Atomic Scale Precision with Chemistry

E. A. Joseph et. al. SMT ALE Workshop 20145/13/2017 E. A. Joseph et al25


Si loss is reduced considerably with the addition of optimized wet cleans, tailored to remove polymer from selective etch Wet / clean processes critical for maintaining atomic

scale precision post PE-ALE

Atomic Scale Precision with ChemistryPost Spacer Deposition

Post Spacer Etch

E. A. Joseph et. al. SMT ALE Workshop 20145/13/2017 E. A. Joseph et al26


Patterning DSA with High Selectivity Conditions - Nitride

Chemistry X based etch caused substantial pattern deformation

Successful etching of SiN hardmask using chemistry C at 21nm with extremely low LER & LWR (1.6 & 2.2nm) demonstrated.



Application of PE-ALE to SiARC open process

Different PE-ALE processes were tested as SiARC open processes

Precursor chemistry was substituted in, no further optimization was attempted Inert gases maintained throughout

process

Overall significant LER/LWR increase observed, regardless of precursor chemistry

VUV interactions of inert plasma during processing may play crucial role here CW, CF4 | CHF3

PE-ALE, Ar | C2H4

PE-ALE, He | Ar | C2H4

PE-ALE, He | HFC

PE-ALE, Ar | C4F8

110120130140150160170180

2468101214161820

Dashed lines = Post-lith measurements

CD (n

m)

CDCD, LWR, LER - Effect of SiARC process

LW

R an

d LE

R (n

m)

LWR LER



ALE window

ALE “window” driven by: Energy of desorption

process Plasma chemistry

and radical physi/chemisorption

Processing at the low energy limit maybe key for various material sets


Need for High Precision Ion Energy Control Ion Energy control is essential to enable atomic scale

precision Energy threshold chosen specifically to enable reactant

activation and removal of one material selective to all others

Novel plasma pulsing methods (waveforms) can be used to tailor ion energy distribution function


Large Area Plasma Processing System (LAPPS)*

Low Te plasma source developed at Naval Research Labs (NRL)

Plasma is generated by a high-energy electron beam

Low Te (< 0.5 eV) with high ne (1011 cm-3); large flux of low energy ions**

* Meger et al., US patent no. 5,874,807 (Feb. 1999)** S. G. Walton, et al., ECS Journal of Solid State Science and Technology 4(6), N5033 (2015)

*** D. R. Boris, et al., Plasma Sources Sci. Tech. 22, 065004-6 (2013) ;G. M. Petrov, et al., Plasma Sources Sci. Tech. 22, 065005-8 (2013)

0 0.03 0.06 0.09 0.120

0.2

0.4

0.6

0.8

1.0

kTe (

eV)

N2 Fraction by Flow 0 1 2 3 4

0

0.2

0.4

0.6

0.8

1.0 N2 flow (%) 0 1 3 5 10

Inte

nsity

(nor

mal

ize)

Energy/2 (eV)

Electron beam generated plasmas produced in Ar/N2 mixtures***


Graphene Damage Evaluation from Raman Shift

Negligible damage to graphene using LAPPS

Significantly higher process window observed for LAPPS

Significantly higher damage observed for ICP plasma


CNT Electrical Characteristics Comparison (LAPPS and ICP) In both LAPPS and ICP: Ar/CH4 gas chemistry used Modification of Ion, Ioff and Vt seen after

plasma exposure

For the Low Te LAPPS: Moderate modification in case of low Te plasma

Negligible damage to CNT properties

For ICP: Significant modification of Ion, Ioff and Vt seen

after plasma exposure Significant modification of semiconducting

property seen for ICP

Significant damage to CNT properties

Before Plasma After Plasma

LAPP

SIC

P


NVM Processing ChallengesPhase Change MemoryGeSbTe profile control critical given its extremely high

volatility in halogen etch chemistries

Modification to the GST composition can significantly alter material properties

Spin-Transfer Torque MRAMDifficult 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

Bit line

W

GST

TiN

Bit line

W

GST

TiN

VLSI 2006

EELS and EDS datashow mostly Ta some Ru is also possible –visible in SEM

TaN

TaN

TaN/Ta

Ru

PtMn

AlOxPossible TJ damage

and short

Likely post CMPun-removed oxidation layer

TJ Stack Nominal CompositionBase layer AF Pinned layer Barrier Freelayer Cap and Hard Mask50 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


PtMn

Co

CoFeB

CoFe

Al

Cu

CuN

Ta TaN

VPd

CoPdAl2O3

MgO

11nm


Metal ALE: PE-ALE Thermodynamics Approach

Calculations show favorable/non-favorable etch product formation in 2-step process

Favorable Thermodynamic reactions required for each magnetic material present in MTJ stack

Kim et al, J. Vac. Sci. Technol. A 33(2), Mar/Apr 2015


© 2017 IBM CorporationCMC Conference 2017 – Richardson, Texas36

Evaluating the impact of metals during ALE processes; TiN,TaNCoFeB, MgO and NiFe

Compared the impact of exposure during ion bombardment step

Thorough investigation ongoing Impact on pattern features Sidewall residue formation for each

layerResidues from layer by layer etch for

subsequent layers

PE-ALE: Metal Etch

| IBM Confidential

TaN

TiN


Conclusions Various methods to perform large scale ALE are currently under development Key attribute for ALE is selectivity

Most selective patterning solutions still depend on reaction chemistry and/or energy and under optimized conditions can achieve pseudo atomic scale precision

‘ALE Window’ will determine which method will be implemented and will rely heavily on surface chemistry & plasma physics (PE-ALE) to achieve atomic scale precision

Application of PE-ALE approaches is still challenging due to lack of understanding and in-situ process characterization Interaction of the OPL patterning material with inert plasma Vastly differing patterning results obtained based on feature pitch Significant difference in results for different sets of materials

Development of ALE methods for complex alloy materials will be both challenging and necessary for potential new memory and device structures



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materials and process challenges for advanced …...materials and process challenges for advanced...

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