Cambridge NanoTech ALD Tutorial
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Transcript of Cambridge NanoTech ALD Tutorial
Cambridge NanoTech ALD Tutorial
July 2011
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
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
Substrate surface (e.g. Si)
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.
Substrate surface (e.g. Si)
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 Maryland
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