Lift off

Stacked HEX to increase throw distance
THE HEX SERIES

Patterned thin films on surfaces

In the production of semiconductors and many other applications, there are cases that a thin film is needed to be deposited in a particular pattern. If this pattern and tolerance for that pattern are large, then a physical mask, usually steel or other cheap easily machined metal, can be placed over the sample and then deposited over. As the mask is removed, the deposition will be evident through the holes in said mask.

However, if the pattern is an intricate and requires lower tolerances and distances, then a physical mask can cause too much of a shadow on the sample and be unsuitable. In these cases, an alternative option known as a lift-off process can be utilised.

For lift-off, a pattern will be applied to the sample usually consisting of a photoresist and then a coating applied over the top. The deposition will occur across the entire sample (including the photoresist) and then subsequently washed away revealing the patterned deposition beneath.

In order to achieve this deposition, several features are required of the PVD system as whole. The deposition must ideally be done from a point source perpendicular to the sample (or as close to it as possible), so an extended throw-distance is essential; this is to minimize the deposition incident on the sidewalls of the photoresist and maintain the sharp edge of the mask as much as possible.

At Korvus Technology, we have developed a unique way to facilitate lift-off applications through the development of our stacked range of modular PVD systems. All the HEX series of PVD chambers can be stacked at any point in their lifetime to increase the distance between deposition source and sample table. This feature, tied in with our unique TAU mini-electron beam source and range of active and passive-cooled stages provide the perfect platform for high quality and simple lift-off deposition runs.

Frequently Asked Questions

Lift-off in PVD (Physical Vapor Deposition) is a patterning technique used to create precisely defined metal or thin film structures on a substrate. Instead of etching away unwanted material after deposition (like in subtractive processes), lift-off works by depositing material only where it’s needed, then removing the underlying resist to “lift off” the unwanted parts.

It’s especially useful for fine features, delicate substrates, and materials that are hard to etch—like gold or some oxides.

1. Resist Coating

A resist layer (usually photoresist or e-beam resist) is spin-coated onto the substrate.

2. Patterning

The resist is patterned using photolithography or electron beam lithography (EBL).

In lift-off, it’s common to use negative-tone resist or bi-layer resist to create undercut profiles, which help with clean lift-off.

3. PVD Deposition

The material (metal, oxide, etc.) is deposited using a PVD technique like:

Thermal evaporation, Electron beam evaporation, or Sputtering (can be trickier for lift-off due to directional scattering).

4. Lift-Off (Resist Removal)

The sample is soaked in a solvent (e.g., acetone or NMP) that dissolves the resist.

The material on top of the resist lifts off, leaving behind only the material that was deposited directly on the substrate.

  • Microelectronics: Creating contacts and metal traces on silicon

  • MEMS fabrication

  • Optoelectronics: Patterning thin film electrodes

  • Nano-fabrication: Producing nanostructures using e-beam lithography + lift-off

  • Sensors: Patterning functional thin films on chips

  • Use thermal or e-beam evaporation (they’re more directional = cleaner lift-off)

  • Use bi-layer resists to create an undercut for easy removal

  • Ensure the resist is fully developed and baked before deposition

  • Avoid thick films—lift-off is easier with thinner depositions (~<300 nm)

  • Use ultrasonic agitation or heated solvents (carefully) during resist removal to improve lift-off