Reactive Sputtering

THE HEX SERIES

Simple Metals to Complex Compounds

Through RF and DC sputtering, many different films can be generated from simple metals to complex compounds. Often, when making a compound film, the stoichiometry of the film can appear different from the target used due to limitations brought in from plasma interactions. During the sputtering process, some parts of the compound can be broken up into its constituent elements and become gaseous (such as oxygen from oxides and nitrogen from nitride compounds), these gases may be pumped away from the chamber leaving the film with a lower proportion of oxygen / nitrogen than intended.

A key way to combat this issue is through reactive sputtering – this process involves introducing the gas that the resultant film is deficient in as a flow through the chamber during deposition. The gas will then either deposit directly onto the film alongside the sputtered material or interact with the flux directly and generate the required chemistry pre-deposition.

Reactive sputtering can also be used a way to reduce the cost of depositing a film. RF supplies can be more expensive and usually slower than their DC counterparts but with the added benefit of being able to deposit non-conducting samples. Reactive can offer a go-around by using a metallic target and introducing the gas needed to make the required compound in the flux, rather than the target itself.

PVD Reactive Sputtering – Annotated Schematic Layout

🧱 Vacuum Chamber

A sealed enclosure that maintains low pressure, enabling controlled sputtering.

Contains: target, substrate, plasma, and gas inlet/outlet.

🎯 Target (Cathode)

A metallic source material (e.g., Ti, Al).

Bombarded by energetic ions (usually Ar⁺) from the plasma.

Negative voltage applied (DC or RF, depending on conductivity).

⚡ Plasma Region

Created by RF or DC power.

Contains ionized argon (Ar) gas used to sputter the target.

Visualized as a glowing region near the target.

🌬️ Reactive Gases

Introduced alongside Ar (e.g., O₂ for oxides, N₂ for nitrides).

Mixes with sputtered atoms to form compounds before or during deposition.

🧪 Sputtered Metal Atoms

Ejected from the target surface due to ion collisions.

Move toward the substrate in a straight line in vacuum.

🔁 Gas-Metal Reaction Zone

Either in-flight or on the substrate.

Metal atoms react with O₂/N₂ to form compound films like TiO₂ or AlN.

🧱 Substrate (Anode or Grounded)

Collects the resultant compound film.

Film stoichiometry depends on gas flow, plasma energy, and reactivity.

Reactive Sputtering FAQs

Reactive sputtering is a variation of Physical Vapor Deposition (PVD) where a reactive gas (such as oxygen or nitrogen) is introduced into the vacuum chamber during the sputtering process. This gas reacts chemically with the sputtered metal atoms to form a compound thin film—typically an oxide, nitride, or carbide—on the substrate.

  • Sputtering Target: A pure metal (e.g., titanium, aluminum, or silicon) is bombarded with high-energy ions (usually from an argon plasma).

  • Reactive Gas: A gas like O₂, N₂, or CH₄ is added to the chamber.

  • Reaction: The metal atoms ejected from the target react with the reactive gas in-flight or on the substrate surface.

  • Deposition: The resulting compound (e.g., TiO₂, AlN, Si₃N₄) is deposited as a thin film.

  • Optical coatings (anti-reflective layers, interference filters)

  • Hard coatings (TiN or Al₂O₃ for cutting tools)

  • Semiconductor devices (SiNₓ for passivation or insulation)

  • Decorative coatings (colored TiN, ZrN for watches or hardware)

  • Enables deposition of compound films from metallic targets

  • Offers fine control over film composition by adjusting gas flow

  • Suitable for dense, high-quality coatings

  • Target poisoning: Excess reactive gas can form a compound layer on the target, reducing sputter efficiency.

  • Requires precise process control (gas flow, pressure, plasma power)

AspectStandard SputteringReactive Sputtering
Uses only inert gas✅❌
Forms pure metal films✅❌
Forms compound films❌✅
Needs precise gas control❌✅