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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
© 2017 IBM CorporationCMC Conference 2017 – Richardson, Texas
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
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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
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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
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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
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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
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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)
5/13/2017 E. A. Joseph et al8
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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
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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
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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
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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
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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)
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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
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ALE “window” driven by: Energy of desorption process Plasma chemistry and radical physi/chemisorption
PE-ALE Process space
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Experimental Verification of Self-Limited SiO2 PE-ALE
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Self-limited behavior observed for FC Reactant Limited SiO2 etch using C4F8
Metlzer et. al., JVST B, 2014
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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
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Verification of PE-ALE in Commercial Tooling
D. Metzler, et al., JVST A 32, 020603 (2014)
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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***
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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
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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
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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
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PtMn
Co
CoFeB
CoFe
Al
Cu
CuN
Ta TaN
VPd
CoPdAl2O3
MgO
11nm
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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
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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
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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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