0 Atomic Level Precision in Near-Zero Thickness Thin Film ...
Transcript of 0 Atomic Level Precision in Near-Zero Thickness Thin Film ...
Gelest Confidential - © 2019 by Gelest Inc. All rights reserved.
Atomic Level Precision in Near-Zero Thickness Thin Film
Deposition Through Chemistry and Process Innovation
Barry Arkles- Gelest Inc.
Jonathan Goff- Gelest Inc
Alain Kaloyeros- BFD Innovation
ALD symposium at 240th ECS Meeting
Atomic Layer Deposition Applications. Abstract #152628
Orlando, FL October 10-October 14, 2021
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Gelest Confidential - © 2019 by Gelest Inc. All rights reserved.
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Trends in Semiconductor Thin Film Technology1
Challenges in Material and Process Development
• The complexity and thermally and chemically sensitive nature of the device structures, where small
temperature fluctuations can induce undesirable reactions within substructures
The need for chemical sources that decompose cleanly and easily at the lowest temperature
possible is mandated by the drive toward more complex, smaller, and more “fragile”
semiconductor and hetero-device structures due to:
• The reduction in film thickness to “near-zero-thickness” (almost atomic dimensions), where thermally- and
chemically-induced migration, in addition to electromigration, can alter film properties and performance
• The desire to move towards more flexible substrates, such as plastic or polymer substrates, which
typically cannot withstand the same process temperatures as traditional substrates
• The introduction of new material technologies. Semiconductors in the 1990s utilized a maximum of ~ 12
elements; by 2022 ~50 elements are under consideration
• As a result, chemical-based vapor processes have emerged as the vehicles of choice in semiconductor
process development and deployment
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• Excellent thermal stability, exceptional chemical integrity, and strong resistance to breakdown
during storage, transport, and delivery, in order to maintain tight control over the manufacturing
process.
• High reactivity and ability to readily decompose using the lowest activation energy possible,
preferably at very low temperatures.
• Clean decomposition during deposition reaction with the formation of inert ligands and neutral
byproducts thus preventing their adsorption to substrates leading to film contamination.
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Trends in Semiconductor Vapor Phase Processes
Manufacturability requirements for source precursors
The strategy addresses primary show-stoppers for chemical sources by synthesizing and using
manufacturing-worthy precursors, including real-time, on-demand, without requiring storage:
• Highly pyrophoric and/or potentially explosive chemical sources.
• Chemicals too toxic to risk accumulation.
• Chemical sources with very short lifetime.
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Gelest Microelectronics Development Programs:Semiconductor & Heterodevice Focus Areas
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Engineering Chemistry
Integrated Synthesis
& Deposition
Transient Species
Deposition
Intermittent Pulsed
Deposition
TSD IPDISD
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Chemistry and Process Strategy
Process
Integrated Synthesis & Deposition (ISD)
• Gas on solid
• Gas with gas
• Vapor with liquid
Transient Species Deposition (TSD)
• Isotetrasilane
• Cobalt
Intermittent Pulse Deposition (RPD)
• Minimal number of process steps
• Higher throughput
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Allows use of known and desirable precursors in thin film fabrication overcoming
processes previous chemistry and process limitations.
• Not stable (short life-time)
• Accumulation and storage of highly toxic precursors is disallowed by safety standards
and/or regulatory limits
• Explosive compounds
Integrated Synthesis & Deposition (ISD)
Enables access to new classes of source chemicals.
Differentiation
• Not point of use
• Not in-situ formation
• No accumulation of precursors
Examples/Objectives
• SiN
• Co
• Graphene
• Ni, Ru films (325 ºC)
ISD is the real-time synthesis and use of precursors and chemicals
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Hydrazoic Acid (Hydrogen Azide) as a Nitrene Source
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-
HN3
Nitrene Transient Species insertion
into silicon –hydrogen bond
Chen et al, J. Phys. Chem. A 2007, 111, 6755-6759
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Vapor with Liquid ISD
Integrated Synthesis & Deposition (ISD) Examples
• Rate of precursor synthesis is
synchronized with the rate of
precursor consumption for
formation of the thin film
• End-point, real-time, in-situ
monitoring and detection of thin
film formation in the thin film
processing chamber
• Thin film formation feedback
transmitted to precursor
generation chamber
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What are the Benefits of Integrated Synthesis & Deposition?Illustrative Example: Silicon Nitride from Monosilylamine
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• Trisilylamine is the thermodynamic
product
• Monosilylamine is unstable, but deposits
silicon nitride at lower temperature
• Integrated generation & transport of
monosilylamine to deposition chamber
enables low temperature deposition
Si3N4 Si3N4
xs NH3 NH3 deficiency
< 550 ˚C > 650 ˚C
(unstable)
disproportionates
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Gas with Gas ISD
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Nickel Deposition for BEOL Interconnect
Current Commercial Nickel Process from Nickel Carbonyl
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Gas on Solid ISD
Integrated Synthesis & Deposition (ISD) Examples
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Transient Species Deposition (TSD) Examples
XRD patterns for strained CVD e-SiGe films grown at
550°C by co-deposition from isotetrasilane and germane:
Transient Species Deposition Overview
Examples:
1. Isotetrasilane: Si4H10 → :Si3H6 + SiH4
2. Cobalt: Co(CO)nYx → Co*(CO)n + Y
TS examples do not have protective ‘clothing’ of ligands
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Si Epitaxial Layers from Isotetrasilane
Precursor Temp. Pressure,
torr
Growth
Rate
nm/min
Gas Phase
Depletion
Silane 650° 80 11 No
Silane 750° 100 97 Yes
Disilane 650° 100 18 No
Disilane 700° 100 28 Yes
n-Tetrasilane 600° 100 <10 No
Isotetrasilane 550° 100 13 Yes
Isotetrasilane 550° 40 26 Yes
Isotetrasilane 550° 10 35 No
Isotetrasilane 525° 100 18 Yes
Isotetrasilane 500° 100 12 No
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CVD e-Si Results of IsotetrasilaneIsotetrasilane vs. Lower Order Perhydridosilanes
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The reductive elimination mechanism in the gas phase depletion-free process is
consistent with the formation of the bis(trihydridosilyl)silylene transient species
CVD Temperature
CVD from isotetrasilane at 500-550 oC yielded
high-quality e-Si films
(CVD from lower order perhydridosilanes
requires temperatures 600-750 oC)
Growth Rate Mechanisms
1. Faster growth rate process that displays gas-
source depletion at temperatures as low as
550 oC and working pressure of 100 torr
2. Gas phase depletion-free process with
slower growth rate values of 13 nm/min (550 oC) and 43 nm/min (600 oC)
This is supported by prior theoretical and experimental studies regarding gas phase reactions and
substrate surface adsorption and decomposition mechanisms of silanes
GC-MS analyses for isotetrasilane show that fragment bis(trihydridosilyl)silylene at m/z = 90 is stable
(intensity is 100%)
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What is a Transient Species?
A transient species (TS) is a reactive intermediate which has a limited lifetime
(ns - sec) in the condensed phase at or above room temperature
TS are formed in the vapor phase
• directly from a precursor in an inert gas stream
OR
• from a precursor co-reaction with an appropriate gas
Example
reductive elimination of silane from isotetrasilane to
form bis(trihydridosilyl)silylene TS
+
TS lifetime can be extended by controlling
concentration in the vapor phase
• by altering vacuum conditions
OR
• varying the inert gas carrier
TS species include
carbenes, nitrenes, silylenes, free radicals, coordination compounds with unsatisfied coordination spheres
ISD
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• Current thermal & plasma processes do not distinguish precursor decomposition from the transient species
required for deposition
• Typically activation of precursor requires higher energetic environments than required for deposition
• Separation of precursor activation (conversion to transient species) enables deposition at lower
temperature
• Transient species have high sticking coefficients resulting in process efficiency
• Research focus – identifying ideal/optimum decomposition temperature for formation of desired TS without
formation of broad spectrum of intermediates
Transient Species Deposition (TSD)
Separating formation of a transient (active) species material for deposition from the
deposition process
TS examples carbenesilylenes
cobalt complex with unsatisfied
coordination sphere
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• In IPD, the precursor (with or without carrier gas) is pulsed into the reaction zone. Upon
saturation of the substrate surface with the precursor, a monolayer is formed on the
substrate surface by adsorption.
• The adsorbed monolayer then undergoes complete conversion to a discrete atomic or
molecular layer of the desired composition within this single deposition cycle, without
any intervening pulse/exposure or reaction with other chemical species or co-reactants.
• The conversion could be aided or enabled by energy transfer provided from an energy
source, such as a heated substrate and/or remote or direct plasma.
• Oxidation and/or reduction may be used to initiate or facilitate conversion of the
adsorbed monolayer to the discrete atomic or molecular layer.
• The invention offers significant reduction in the time to generate thin films by eliminating
up to 75% of the steps required in ALD growth cycles, thus maximizing process
efficiency and leading to viable manufacturing COO and ROI.
Intermittent Pulsed Deposition (IPD)
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Substrate Substrate
(1) AB pulse (3) XY pulse
Substrate Substrate
(2) Inert gas purge (4) Inert gas purge
Substrate Substrate
(1) AB pulse (2) Inert gas purge
Reactant AB
Reactant XY
(1) Reactant ABON ON
ONON
ONON
ONON
One Cycle
(3) Reactant XY
(2) Inert gas purge
(4) Inert gas purge
Typical ALD
(1) Reactant ABON ON
ONON
One Cycle
(2) Inert gas purge
Reactant AB
Intermittent Pulsed Deposition
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Langmuir Adsorption Model
• Monolayer adsorption step is presumably in accordance with the Langmuir model
• Attraction strength between the surface and the first layer of adsorbed substance is much
greater than the strength between the first and second layers of adsorbed substances
• Langmuir adsorption model presumes that, at isothermal conditions, precursor partial
pressure Pp in the reaction zone is related to the precursor volume Vp adsorbed to the
substrate.
• The substrate can be reasonably considered as an ideal solid surface including an array
of distinct sites that can bind to the precursor
• an adsorbed precursor complex Aps between the precursor molecule (or a partial
precursor molecule) Mp and a substrate surface site S, with a corresponding equilibrium
constant Keq, as follows: Mp + S Aps
•
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Post-annealed Co from Cobalt Tricarbonyl Nitrosyl
at (%)
0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Ato
ms
%
Etch Level (2kev, 500s)
AN105
Cobalt
Oxygen
Carbon
Depth (nm)0
100
40
80
20
60
Parameter Value
Precursor T (oC) RT
Substrate T (oC) ~200
Pulse (sec) 0.1
N2 Carrier gas 100 sccm
Remote Plasma 2000W
The introduction of modified deposition processes ISD, TSD and IPD allows or expands the use of known precursor chemistry consistent with the demands of the complexity and thermally and chemically sensitive nature of the device structures.
Atomic Level Precision in Near-Zero Thickness Thin Film Deposition Through Chemistry and Process Innovation
Barry Arkles- Gelest Inc.
Jonathan Goff- Gelest Inc Alain Kaloyeros- BFD Innovation
ALD symposium at 240th ECS Meeting
Atomic Layer Deposition Applications. Abstract #152628 Orlando, FL October 10-October 14, 2021
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