Fluid Flow Effects in ALD for

Semiconductor Manufacturing

Juan Pablo Trelles1 and Sandy Liao2

1 Design and Technology Solutions, Intel Corporation, Hillsboro, OR 97124, U. S. A.;

juan.p.trelles@intel.com2 Portland Technology Development, Intel Corporation, Hillsboro, OR 97124, U. S. A.;

szuya.s.liao@intel.com

11th International Conference on Atomic Layer Deposition (ALD 2011)

Cambridge, MA - June 28, 2011

1

ALD @ Intel

2

• Moore’s Law and the Semiconductor Research Roadmap

1. M. Bohr, Silicon Technology for 32 nm and Beyond System-on-Chip Products, IDF 2009

2. Intel Technology Journal, ISSN 1535-864X DOI 10.1535/itj.1202.01

• Since High-k Metal Gate ALD technology enabler

• ALD for High-Volume Manufacturing (HVM)o cost (precursors, equipment, throughput),

o control, reliability, yield, …

2

1st gen high-k metal gate

2nd gen high-k metal gate

1

3-D tri-gate transistors (22 nm)

)()()()()(

)()()( )()(

2

1

bAgCsBsAgB

bBgCsAsBgA

k

k

precursors surface termination bi-products film

ALD Chemistry

3

inject A insert B

inject B insert A

time

B(b) in A(b) inbi-prod out

bulk

AB film

bi-prod out

+ D(g), dilutant always present

• “Complementary Self-Limiting Surface Reactions”

• “Canonical” ideal ALD of A-B film

(g): gas, (s): surface, (b): bulk

Chemistry Process Film

4

(Input)

(Output)

Ideal Chemistry ≠ Ideal Process- stage duration = complete surface termination- no mixing, desorption, gas-phase reactions, etc

A(g)injection

B(g)injection

A(g)purge

B(g)purge

time

Q

gas flow

t1 t2 t3 t4

recipe

(4 stages)

Real

AxBy film

t1 t2 t3 t4time

deposition

rate

Ideal

y x

B(b).

A(b).

exhaust

Qin

wafer stack

Qout

ALD Reactor for HVM

• Multi-substrate batch reactor: 1 inlet (injector), 1 outlet (exhaust), 4 wafers

5

injector

Qin

Flow effects limit ideal ALD

dissimilar flow

resistance

non-uniform injection

recirculation

stagnation

Patterned Surfaces & ALD Chemistry

• ALD in semiconductor technology: (geometric) Multi-Scale

6

• Patterned topography increases substrate areao Process from “diffusion limited” to “reaction limited”

• Need to model effect of patterns in ALD process, e.g. Site Density ()

1. Intel Press Release, Intel First to Demonstrate Working 45nm Chips, 2006

blank

blank

pattern

patternblankpatternA

Af )(

ratio area

1

~ 10 cm

~ 1 cm ~ 1 um

wafer 1die pattern feature

~ 10 nm

Deposition ProcessConditions:

• Ideal A-B chemistry

• k1 = k2

• rB = 1.2 rA

• pattern = 5blank

• rQin const.

• 100% B(s) initial surf. term.

• D(g) pressure loading

• P ~ Torr (Kn << 1)

7

B(b) depositionB(s) consumptionA(g) transport +

A(g)

Qin

A(g) 1

2

3

4

5

6

7

Precursor Transport

8

A(g)

2 73 5 64

stagnant precursor residual deposition

non-uniform injection different deposition

Stagnation & Recirculation

9

Fluid Flow effects limit applicability of “estimates” in recipe formulation

1 2

recirculation inside injector:non-uniform injection, mixing

1A(g)

stagnant bi-products:reduce available Pv

1

2

C(g)

C(g)

dragging of stagnant gas: mixing, non-ALD growth

2B(g)

A(g)

Reactor Filling

10

reactor

inj. tube

• delay Pmax inj. line – reactor

• Pmin line Pmax reactor

Helmholtz resonator

delay• Pressure: line vs. reactor

• loading > 1 cycle

• by-product limits deposition

ideal = no bi-products

• Gas mass fraction:

loading bi-product

ALD Recipe

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CaseTime

Total Cycle

Time

Purge/Total

Growth

rate

Max

A(s)

I 50% T 1/2 59% 65%

II 50% T 2/3 63% 67%

III 75% T 2/3 93% 99%

IV 100% T 2/3 100% 100% complete

~ optimal

non-ALD

non-ALD

ALD

non-ALD

A(s) fractional coverage • inj. time growth rate• purge time ALD• purge time > 2/3 cycle• “optimal” recipe limited by flow effects

• optimal:+25% shorter cycle-7% growth rate

Summary

• ALD for HVM challenges: Fluid Flow Effects– Recirculation, Stagnation, Dissimilar Transport, etc.

– Increasing process throughput limits “ideal ALD”

• Patterned substrates affect process performance

– Increases effective area

• Bi-products detrimental

– Bi-product pressure <> precursor vapor pressure

• Steady-State driven by pressure oscillations (i.e., Helmholtz resonator)

• Most time spent in purges (i.e., no deposition, termination)

– 2/3 cycle time typical

– room for improvement? … <1/2 cycle possible?

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Thank You