0 atomic level precision in near-zero thickness thin film

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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

0



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



• 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.

2

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.



Gelest Microelectronics Development Programs:Semiconductor & Heterodevice Focus Areas

3

Engineering Chemistry

Integrated Synthesis

& Deposition

Transient Species

Deposition

Intermittent Pulsed

Deposition

TSD IPDISD



4

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



5

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



Hydrazoic Acid (Hydrogen Azide) as a Nitrene Source

6

-

HN3

Nitrene Transient Species insertion

into silicon –hydrogen bond

Chen et al, J. Phys. Chem. A 2007, 111, 6755-6759



8

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



What are the Benefits of Integrated Synthesis & Deposition?Illustrative Example: Silicon Nitride from Monosilylamine

9

• 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



10

Gas with Gas ISD



11

Nickel Deposition for BEOL Interconnect

Current Commercial Nickel Process from Nickel Carbonyl



12

Gas on Solid ISD

Integrated Synthesis & Deposition (ISD) Examples



13

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


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° 10 35 No


Isotetrasilane 500° 100 12 No


CVD e-Si Results of IsotetrasilaneIsotetrasilane vs. Lower Order Perhydridosilanes

15

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



• 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)


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



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

•

20

Co

L

LL

L


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

24

0 atomic level precision in near-zero thickness thin film

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