ALD Tutorial

July 2011

Cambridge NanoTech ALD Tutorial

ALD Applications

Other applicationsRoll to rollInternal tube linersNano-glueBiocompatibleMagnetic

Semi / NanoelectronicsFlexible electronicsGate dielectricsGate electrodesMetal InterconnectsDiffusion barriersDRAMMultilayer-capacitorsRead heads

OpticalAntireflectionOptical filtersOLED layersPhotonic crystalsTransparent conductorsElectroluminescenceSolar cellsLasersIntegrated opticsUV blockingColored coatings

MEMSEtch resistanceHydrophobic / antistiction

Wear resistantBlade edgesMolds and diesSolid lubricantsAnti corrosion

NanostructuresInside poresNanotubesAround particlesAFM tips

ChemicalCatalysisFuel cells

Cambridge NanoTech Inc. Confidential

ALD Films

Oxides

Al2O3, HfO2, La2O3, SiO2, TiO2, ZnO, ZrO2, Ta2O5, In2O3, SnO2, ITO, FeOx, NiO2, MnOx, Nb2O5, MgO, NiO, Er2O3

Nitrides

WN, Hf3N4, Zr3N4, AIN, TiN, TaN, NbNx

Metals

Ru, Pt, W, Ni, Co

Sulphides

ZnS

0 200 400 600 800 1000 12000

200

400

600

800

1000

1200

1400

MgO

Nb2O5

Al2O3

Number of Cycles

Thic

knes

s in

Å

- ALD films deposited with digital control of thickness; “built layer-by layer”

- Each film has a characteristic growth rate for a particular temperatureALD Deposition Rates at 250°C

1.26 Å

1.08 Å

0.38 Å

Common ALD Materials


Benefits of ALD

• Perfect films– Digital control of film thickness– Excellent repeatability– 100% film density– Amorphous or crystalline films

• Conformal Coating– Excellent 3D conformality– Ultra high aspect ratio (>2,000:1)– Large area thickness uniformity– Atomically flat and smooth coating

• Challenging Substrates– Gentle deposition process for sensitive

substrates– Low temperature and low stress– Excellent adhesion– Coats challenging substrates – even teflon


ALD Reaction Sequence

Precursor A

Precursor B

Purge

Purge

Time

Single Cycle

ALD is based on the spatial separation of precursors

A single ALD cycle consists of the following steps:1) Exposure of the first precursor2) Purge or evacuation of the reaction chamber to remove the non-reacted precursors and the gaseous reaction by-products3) Exposure of the second precursor – or another treatment to activate the surface again for the reaction of the first precursor4) Purge or evacuation of the reaction chamber


In air H2O vapor is adsorbed on most surfaces, forming a hydroxyl group. With silicon this forms: Si-O-H (s)

After placing the substrate in the reactor, Trimethyl Aluminum (TMA) is pulsed into the reaction chamber.

Tri-methylaluminumAl(CH3)3(g)

CH

HH

H

Al

O

Methyl group(CH3)

Substrate surface (e.g. Si)

ALD Example Cycle for Al2O3

Deposition


Al(CH3)3 (g) + : Si-O-H (s) :Si-O-Al(CH3)2 (s) + CH4

Trimethylaluminum (TMA) reacts with the adsorbed hydroxyl groups,producing methane as the reaction product

C

H

H

H

H

Al

O

Reaction ofTMA with OH

Methane reactionproduct CH4

H

HH

HH C

C


ALD Cycle for Al2O3


C

HH

Al

O

Excess TMAMethane reactionproduct CH4

HH C

Trimethyl Aluminum (TMA) reacts with the adsorbed hydroxyl groups,until the surface is passivated. TMA does not react with itself, terminating the

reaction to one layer. This causes the perfect uniformity of ALD.The excess TMA is pumped away with the methane reaction product.


ALD Cycle for Al2O3


C

HH

Al

O

H2O

HH C

OHH

After the TMA and methane reaction product is pumped away, water vapor (H2O) is pulsed into the reaction chamber.

ALD Cycle for Al2O3


2 H2O (g) + :Si-O-Al(CH3)2 (s) :Si-O-Al(OH)2 (s) + 2 CH4

H

Al

O

O

H2O reacts with the dangling methyl groups on the new surface forming aluminum-oxygen (Al-O) bridges and hydroxyl surface groups, waiting for a new TMA pulse.

Again metane is the reaction product.

O

Al Al

New hydroxyl group

Oxygen bridges

Methane reaction product

Methane reaction product

ALD Cycle for Al2O3


H

Al

O

O

The reaction product methane is pumped away. Excess H2O vapor does not react with the hydroxyl surface groups, again causing perfect passivation to one atomic layer.

O O

Al Al

ALD Cycle for Al2O3


One TMA and one H2O vapor pulse form one cycle. Here three cycles are shown, with approximately 1 Angstrom per cycle.

O

H

Al Al Al

HH

OO

O OO OO

Al Al AlO O

O OO

Al Al AlO O

O OO

Al(CH3)3 (g) + :Al-O-H (s) :Al-O-Al(CH3)2 (s) + CH4

2 H2O (g) + :O-Al(CH3)2 (s) :Al-O-Al(OH)2 (s) + 2 CH4

Two reaction steps in each cycle:

ALD Cycle for Al2O3


ALD Deposition Characteristics

MgO Saturation Curve at 250°C

0.0 0.5 1.0 1.5 2.0 2.50.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Precursor Dose (seconds)

Gro

wth

Per

Cyc

le

0 200 400 600 800 1000 12000

200

400

600

800

1000

1200

1400

f(x) = 1.25895705521472 x − 1.02453987730064

Number of Cycles

Thic

knes

s (Å

)

Linear MgO Deposition

• ALD is insensitive to dose after saturation is achieved• Deposition rate remains unchanged with increasing dose


ALD “Window”

ALDWindow

Temperature

Desorption limited

Condensation limited

Activation energy limited

Decomposition limited

Growth Rate Å/cycle

Saturation Level

• Each ALD process has an ideal process “window” in which growth is saturated• Process parameters inside the ALD window allow for reliable and repeatable

results• The ALD window is defined by the precursor volatility / stability


ALD Reaction Temperatures

• ALD is a chemistry driven process• Based on precursor volatility/reactivity

150°CRoom T 150°C 200°C 250°C 300°C 350°C

Reactor Temp

High precursor volatility, lower thermal stability of precursors

Lower precursor volatility, Slow desorption of precursors

100°C

Most ALD Processes

>400°C


High Aspect Ratio Coatings

“Capillary tube”Cross Sectional SEMAAO template*

• ALD is uniquely suited to coat ultrahigh aspect ratio structures enabling precise control of the coatings thickness and composition.

• Cambridge NanoTech’s research systems offer deposition modes for ultra high aspect ratio (>2,000:1)

*Image courtesy of the University of MarylandCambridge NanoTech Inc. Confidential

Compositional Uniformity

Cross sectional EDX

Al2O3 Silica aerogel foam

2.102 2.104

2.1012.105

2.104

2.103 2.103

2.104

2.103 2.101

2.0992.101

2.104

2.101 2.103

Refractive Index – Ellipsometry

Ta2O5 - 500Å film


ALD Precursors

Good ALD precursors need to have the following characteristics:

Volatility Vapor pressure (> 0.1Torr at T < 200°C) without

decomposition Stability

No thermal decomposition in the reactor or on the substrate

Reactivity Able to quickly react with substrate in a self-limiting fashion (most precursors are air-sensitive)

Byproducts Should not etch growing film and/or compete for surface sites

Availability Precursor cylinders


Plasma Enhanced (PE)ALD

• Remote Plasma as a reactant

• Expands ALD window for materials by decreasing activation energy

• Lower temperature possible: avoids precursor decomposition

• Faster deposition cycle times

• Fewer contaminates in films

Fiji PE-ALD chamber

Precursor A

Plasma On

Purge

Plasma Purge

Time

Single Cycle


Plasma Enhanced (PE)ALD

Plasma ALD processes are used for a variety of oxides, nitrides, and metals, including titanium nitride, platinum, and other materials, allowing for low resistivity of titanium nitride, and significantly lower temperatures for depositing platinum.

Cambridge NanoTech Fiji Chamber Cambridge NanoTech Fiji Manifold


Variety of Material Types Possible

M1

A B C

Substrate Substrate Substrate

(A) Doped films: single “layers” of dopant film in between bulk- Doped films do not require “activation” by annealing

(B) Nanolaminate Films: stacks of alternating layers

(C) Graded films: composition slowly changes from material A to material B

ALD allows for the fabrication of different types of materials, all in the same deposition chamber, without the need for different hardware configurations.


Low Temperature ALD

• Some ALD processes can deposit films < 150°C: Al2O3, HfO2, SiO2, TiO2, ZnO, ZrO2, Ta2O5, SnO2, Nb2O5, MgO

• Ideal for merging organics with inorganics• Compatible with photoresist, plastics, biomaterials


Product Portfolio

Savannah Fiji Phoenix Tahiti

Compact, cost-effective system for research

Plasma system for research

Batch manufacturing system

Large area manufacturing system

Cambridge NanoTech ALD systems are engineered for a wide variety of applications from research to high-volume manufacturing. These systems deposit precise, conformal and ultra-thin films on multiple substrates. Their simplified system designs yield low startup and operating costs.

Research Production


Technology

ALD Tutorial