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Atomic Layer Deposition (ALD)

Atomic Layer Deposition (or ALD) is an advanced deposition technique that allows for ultra-thin films of a few nanometres to be deposited in a precisely controlled way. Not only does ALD provide excellent thickness control and uniformity but 3D structures can be covered with a conformal coating for high-aspect-ratio structures.

ALD relies on self-limiting surface reactions and therefore generally provides very low pin-hole and particle levels, which can benefit a wide range of applications. The level of film and interface control and high film quality provided are sought after for many applications. The usage of plasma allows for improved film properties, control thereof and a wide range of possible materials. The flexibility of unique surface pre-treatments allows for low damage processing.

Highlights

  • Self-limiting atomic layer-by-layer growth
  • Highly-conformal coating
  • Low pin-hole and particle levels
  • Low damage
  • Low-temperature process
  • Reduced nucleation delay
  • Wide range of materials and processes
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Atomic Layer Deposition Process

Atomic Layer Deposition typically involves a cycle of 4 steps that is repeated as many times as necessary to achieve the required deposited thickness. The example shows ALD of Al2O3 using Al(CH3), (TMA) and O2 plasma.

Step 1) Dosing of the substrate with a precursor vapour of TMA, which adsorbs on and reacts with the surface. With the correct choice of precursor and parameters, this reaction is self-limiting.

Step 2) Purging of all residual precursor and reaction products.

Step 3) Low damage remote plasma exposure to the surface with reactive oxygen radicals which oxidize the surface and remove surface ligands, this reaction is self-limiting due to the limited number of surface ligands.

Step 4) Reaction products are purged from the chamber.

Only step 3 varies between H2O for the thermal process or O2 plasma. As the ALD process deposits a (sub)angstrom thickness per cycle, control over the deposition process is obtained at the atomic scale.

 

ald-process-1st-stage-diagram

1st Half-Cycle

ald-process-2nd-stage-diagram

Purge

ald-process-3rd-stage-diagram

2nd Half-Cycle

ald-process-4th-stage-diagram

Purge

Thermal ALD

  • Conformal coating can be achieved even in high aspect ratio and complex structures
  • A wide variety of materials is possible with Atomic Layer Deposition, such as:
    • Oxides:
      Al2O3, HfO2, SiO2, TiO2, SrTiO3, Ta2O5, Gd2O3, ZrO2, Ga2O3, V2O5, Co3O4, ZnO, ZnO:Al, ZnO:B, In2O3:H, WO3, MoO3, Nb2O5, NiO, MgO, RuO2
    • Fluorides: MgF2, AlF3
    • Organic-hybrid materials: Alucone
    • Nitrides: TiN, TaN, Si3N4, AlN, GaN, WN, HfN, NbN, GdN, VN, ZrN
    • Metals: Pt, Ru, Pd, Ni, W
    • Sulfides: ZnS, MoS2

Remote Plasma Enhanced ALD (PEALD)

In addition to the benefits of thermal ALD, PEALD allows for a wider choice of precursor chemistry with enhanced film quality:

  • Plasma enables low-temperature ALD processes and the remote source maintains low plasma damage
  • Eliminates the need for water as a precursor, reducing purge times between ALD cycles - especially for low temperatures
  • Higher quality films through improved removal of impurities, leading to lower resistivity, higher density, etc
  • Effective metal chemistry through use of hydrogen plasma
  • Ability to control stoichiometry/phase
  • Reduced nucleation delay
  • Plasma surface treatment
  • Plasma cleaning of chamber is possible for some materials
Conformal coating of high aspect ratio (15:1) structure with high-rate plasma ALD SiO2

Conformal coating of high aspect ratio (15:1) structure with high-rate plasma ALD SiO2

Key Features of ALD

  • Guaranteed processes set up by our engineers
  • Plasma surface pre-treatments
  • Oxides
    • Low-temperature processing with high material quality
    • Doping and mixing
  • Nitrides (FlexAL)
    • Low resistivity
    • Low oxygen content, high refractive index
  • Metals
    • Low nucleation delay with plasma
    • Low-temperature deposition
  • Substrate biasing:
    • During plasma, ALD to control material properties
      • Stress, density, crystallinity (and others)
    • Before plasma ALD to pre-clean substrate surfaces
      • Etches Al2O3, HfO2, SiO2, Si3N4
    • After plasma, ALD to modify material and surface properties
  • Option to have substrate biasing for further process control and improved material properties.

 

ALD Plasma Process Diagram

Product Hardware

Our products offer the following capabilities.


OpAL
FlexAL
Loading Open load
Load lock or Cassette
Substrates Up to 200mm wafers & pieces directly on stage  Up to 200mm wafers handling and pieces on a carrier plate
Bubbled liquid & solid precursors Up to 4 plus water, ozone and gases Up to 8 plus water, ozone and gases
Max precursor source temperature 200ºC 200ºC
MFC controlled gas lines with rapid delivery system;  1) thermal gas precursors (e.g. NH<sub>3</sub>, O<sub>2</sub>) 2) plasma gases (e.g. O<sub>2</sub>, N<sub>2</sub>, H<sub>2</sub>) 2 internally. Up to 8 in externally mounted gas pod Up to 10 in externally mounted gas pod
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Wide Range of Materials

A wide variety of materials is possible with Atomic Layer Deposition and a wide range of processes can be guaranteed and set up by our process engineers. For novel processes, our extensive process knowledge and vast network allow us to provide starting point recipes that should be good starting blocks to go quickly towards a robust process.

Metals Fluorides Sulphides
Pt AlF<sub>3 MoS<sub>2
Ru MgF<sub>2

Often plasma-based processes are available utilizing our plasma knowledge and handling of MFC controlled gas mixtures including toxic gases.

2D Materials

FlexAL2D for ALD 2D Materials

2D materials growth can also be grown by ALD which is a new development with the aim to go toward high-quality MoS2 films. ALD chemistry control has the promise to be able to utilize 2D sulphides with their unique properties at CMOS compatible temperatures with precise digital thickness control over a large area (200mm wafers).

Find out more about FlexAL
Oxides Nitrides
Al<sub>2</sub>O<sub>3 AlN
Co<sub>3</sub>O<sub>4
Ga<sub>2</sub>O<sub>3 GaN
HfO<sub>2 HfN
In<sub>2</sub>O<sub>3
Li<sub>2</sub>CO<sub>3
MoO<sub>3
Nb<sub>2</sub>O<sub>5
NiO
SiO<sub>2 Si<sub>3</sub>N<sub>4
SnO<sub>2
Ta<sub>2</sub>O<sub>5 TaN
TiO<sub>2 TiN
WO<sub>3 WN
ZnO
ZrO2

Oxford Instruments Plasma Technology: ALD Equipment Advantages

Our Atomic Layer Deposition equipment is built on well over a decade of experience. Key features include of Oxford Instruments systems include:

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ALD Systems