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Atomic layer deposition (ALD)

An advanced deposition technique that allows for ultra-thin films of a few nanometres to be deposited in a precisely controlled way

Atomfab ALD

Atomfab PE-ALD system delivers fast, low damage, low CoO production plasma ALD processing for GaN power and RF devices

Atomic layer deposition (ALD)

  • High quality films grown with ultimate thickness accuracy, one atomic layer at a time
  • Up to 200 mm wafer with typical uniformity <±2%
  • Excellent step coverage even inside high aspect ratio structures
  • Highly-conformal coating
  • Low pin-hole and particle levels
  • Low damage & low-temperature process
  • Reduced nucleation delay
  • Wide range of materials and processes

ALD 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.

1st Half-Cycle

Purge

2nd Half-Cycle

Purge

ALD overview


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.

Benefits of ALD


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

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

Al2O3 deposited by FlexAL ALD - Courtesy by Eindhoven University of Technology

Plasma enhanced ALD (PE-ALD)

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 deposition of SiO2, TiO2 and Al2O3 by Plasma ALD, (CC BY 4.0 license), image library at www.AtomicLimits.com, 2021

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
    • 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.

Processes for ALD


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.

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

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).

Metals

Fluorides

Sulphides

Pt

AlF3

MoS2

Ru

MgF2

Featured DRIE products

PlasmaPro 100 Estrelas DRIE

The PlasmaPro 100 Estrelas platform is designed to give total flexibility for DRIE applications - serving a diverse set of process requirements across the MEMS, advanced packaging and nanotechnology markets. Developed for research and volume production, the PlasmaPro 100 Estrelas offers the ultimate flexibility with Bosch and cryogenic processes.

  • High etch rate and high selectivity with Bosch process
  • Smooth sidewall & high aspect ratio processes
  • Highly anisotropic (vertical) profile
  • Low rate, low power for nano-silicon etch and notch control (SOI)
  • Tapered via etches
  • Wide range of applications
  • Mechanical or electrostatic clamping (substrates’ compatibility)
  • Improved reproducibility
  • Increased mean time between cleans (MTBC)

Overview of PlasmaPro 100 Estrelas DRIE


DRIE or DSiE combines isotropic silicon etching and passivation steps repeatedly to obtain anisotropic profiles. Using high density plasma source and fast gas-switching capability, this technique enables you to achieve profile verticality, smooth sidewalls and high etching rates with high selectivity to masking materials.

From smooth sidewall processes to high rate cavity etches and high aspect ratio processes to tapered via etches, the PlasmaPro 100 Estrelas has been designed to ensure that the wide range of applications in MEMS, advanced packaging and nanotechnology can be realised without the need to change chamber hardware.

Nano and microstructures can be realised as the hardware has been designed with the ability to run Bosch™ and cryo etch technologies in the same chamber.

Features of PlasmaPro 100 Estrelas DRIE


  • Compatible with 50 mm to 200 mm substrates - ensures you have the ability to develop devices that can be taken to production using the same chamber hardware
  • Auto match - Process flexibility
  • Higher flow MFCs and associated generators - High radical densities
  • Reduced chamber volume and high throughput pumping - Ensures high gas conductance
  • Fast-acting close-coupled MFCs - Fast control (originally developed for ALD)

System requirements

  • High-density plasma (chemically-driven process)
  • Close-coupled gas pod
  • High flow and pumping
  • Fast and easy switching easy from liquid nitrogen (LN2) to the chiller and vice-versa
  • Advanced recipe editor
  • Heated liners and top plate
  • Efficient wafer cooling

Applications for PlasmaPro 100 Estrelas DRIE


Bosch applications

  • MEMS for smart devices, consumer & industrial electronics
  • Microfluids
  • Biomedical devices​
  • Through silicon via (TSV)
  • SiO2 and quartz etch
  • High Q capacitor arrays and high Q resonators for quantum devices

Cryo applications

Cryo-DSiE is typically used for smooth sidewalls and/or nano-etching and temperature sensitive materials, as it provides low temperature process (» -110 °C)

  • Nano applications
  • Photonics
  • Moulding

Specifications for PlasmaPro 100 Estrelas DRIE


Parameter

Bosch

Cryogenic

Mixed gas

Rate (μm/min)

High

Moderate

Low

Selectivity to PR

Very high

High

Low

Profile

Vertical

Vertical or sloped

Vertical or sloped

Aspect ratio

Very high

High

Low

Sidewalls

Scallops

Smooth

Smooth

ARDE control

Yes

Limited

Limited

Cleaning

Regular

Rare

Regular

Min. feature /nm

≈ 300

≈ 10

30

Global customer support

Oxford Instruments is committed to providing a comprehensive, flexible and reliable global customer support. We offer excellent quality service throughout the life of your system.

  • Remote diagnostics software provides quick and easy fault diagnosis and resolution.
  • Support contracts are available to suit the budget and situation.
  • Global spares in strategic locations for quick response.
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NEW: PTIQ software

PTIQ is the latest intelligent software solution for PlasmaPro and Ionfab processing equipment.

  • Exceptional level of responsive system control
  • Optimise system and process performance
  • Different levels of software to suit your requirements
  • Brand new intuitive layout and design
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Explore our comprehensive technical training courses

At Oxford Instruments Plasma Technology, we offer a wide range of technical training courses designed to suit all skill levels and needs.

  • Level 1 (Introductory): New system users for all platforms
  • Level 2 (Intermediate): Equipment and maintenance training for all platforms
  • Level 3 (Advanced): for plasma, ion beam and ALD systems
  • Specialist technical modules: process and handler technical training for all platforms
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