Overview

Electron Beam Lithography (EBL) is a powerful technique for creating nanostructures that are too small to fabricate with conventional photolithography.

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Why use EBL? For two main reasons:

  • Scale: it's possible to create nanostructures with dimensions below 10nm.
  • Direct write: patterns are created directly from CAD designs without a physical mask, enabling frequent, cost-free changes - ideal for optimising, refining and prototyping designs.

State-of-the-art EBL systems can achieve resolutions of a few nanometres. The technique works by moving a highly focussed electron beam over a sample to write out a pattern designed with suitable CAD tools.

The pattern is recorded in an electron sensitive film (or resist) deposited on the sample before exposure by spin coating. The electron beam induces a change in the molecular structure and solubility of the resist film.

Following exposure to the electron beam, the resist is developed in a suitable solvent to selectively dissolve either the exposed or unexposed areas of the resist.

Pattern transfer

After exposing and developing, the resist layer on top of the sample can be used as a mask or template for transferring the pattern into a more useful medium.

There are two main pattern transfer techniques that can be applied: the first involves etching material away underneath the voids in the resist layer, the second involves depositing a layer of material - usually metal - all over the sample, then dissolving away the remaining resist to ‘lift off’ the deposited material on top, leaving the deposited material only in the areas where there was no resist present.


Specifications and capabilities

The Raith Voyager is a high-performance, turn-key electron beam lithography system ideally suited to R&D applications.

Specifications
  • 50kV beam acceleration, up to 40nA beam current
  • Wide range of sample handling from 5x5mm pieces to 6 inch semiconductor wafers
  • 150x150x20mm (XYZ) motorised stage travel
  • Laser interferometer monitoring and piezo actuators for ultra-fine stage control
  • Laser height sensing for on-the-fly focus correction during exposure
  • 500x500um writing field with real-time dynamic stigmation and distortion correction
  • 50MHz digital pattern generator
  • 20-bit single-stage electrostatic beam deflection (allows 0.5nm pixel size in 500um field)
  • Raith proprietary ‘traxx’ & ‘peridoxx’ writing technologies enabling continuous, stitch-free writing over very large areas
  • Window 7 based, Raith ‘Nanosuite’ control software with comprehensive GDSII editing and proximity correction tools for designing patterns
  • Multiple-user licence for ‘Nanosuite’ software allowing pattern preparation on any PC with access to the University network
Patterning capabilities
  • <10nm demonstrated patterning resolution
  • <25nm demonstrated overlay and stitching accuracy
  • <90 minute patterning time for 1cm2 area (50% coverage, grating pattern)

You can see a selection of images created by the EBL system in our image gallery.


Supporting facilities

Users of the EBL System can access a comprehensive range of supporting fabrication and characterisation systems based in the Nanoscience and Technology Centre cleanrooms on North Campus.

Many of these systems are part of the National Epitaxy Facility, dedicated to growing and fabricating III-V semiconductor materials and devices for customer across the UK. However, most of the fabrication and characterisation facilities are available to use on a wide range of other materials.

Fabrication:

  • Substrate preparation including, cleaving, solvent cleaning, ultrasonic bath and plasma asher
  • Resist deposition including spin coaters and hotplates
  • Resist developing and removal
  • Evaporators for depositing wide range of metals and other materials
  • Sputter coating of selected metals (Au, Ti, Ni, Zn)
  • Plasma enhanced chemical vapour deposition (PECVD) of SiO2 and Si3N4
  • Comprehensive range of chemical etching
  • Reactive Ion Etching
  • Inductively Coupled Plasma Etching
  • Bonding and device packaging

Characterisation:

  • High resolution scanning electron microscope (SEM) with EDX
  • Atomic force microscope (AFM)
  • Optical microscopes
  • Ellipsometer
  • Dektak surface profiler
  • Electrical and Optical test facilities

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