Fabrication via Electron Beam Lithography

Fabrication via Electron Beam Lithography at the Washington Nanofabrication Facility (WNF)

Fabrication via this PDK is available via the edX silicon photonics course, and via direct purchase.

• The fabrication is performed by Shane Patrick at the Washington Nanofabrication Facility at the University of Washington, Seattle.
• The EBeam tool was purchased by a grant obtained by Prof. Michael Hochberg.
• The process development was performed by Richard Bojko and Michael Hochberg’s group.
• Numerous fabrication runs (30+) were performed by L. Chrostowski’s group at UBC, Prof. D. Ratner’s group, and others, since 2011, to stabilize the fabrication process and develop devices.
• Fabrication coordination and PDK are provided by the SiEPIC program – www.siepic.ubc.ca. The fabrication flow has been used by many research groups, some examples which are provided in this document below, and online at the UW web page.
• Details on the Ebeam and UW – https://ebeam.mff.uw.edu/ebeamweb
• Typical cost for a single chip is 1,000-4,000.

##Fabrication

• Soitec UNIBOND. 6”. Prime grade. 220 nm silicon with a 6 sigma of 22.3 nm. Buried Oxide thickness of 3.017 µm with a 6 sigma of 6 nm.
• Negative resist, HSQ – https://ebeam.mff.uw.edu/ebeamweb/process/processmain.html
• Pattered using a JEOL JBX-6300FS e-beam, with mask data prep performed by software “Beamer”. Using the 4th Lens Mode and Normal writing.
• Single full-etch using ICP
• 82º sidewall angle
• Minimum isolated feature size of 60 nm.
• Shot Pitch – Default is 6 nm. This is a “snapping” of all layout features to a 6 nm grid. Periodic structures, e.g., Bragg gratings, should use integer multiples of the Shot Pitch to avoid quantization errors. Smaller shot pitches (more expensive) and Shot pitch fracturing are available.
• Write conditions – 4th Lens, 2-pass field shift writing, with default 6 nm shot pitch, 8 nA beam current.
• Oxide cladding deposition, 2-3 µm, PECVD.

GDS#	Name	Description
1	Si	Silicon 220 nm remaining.,Where drawn is 220 nm; elsewhere is 0 nm. Shot pitch = 6 nm.,Recommended for most silicon devices.
2	Text	Text labels for automated measurements.
3	SEM_ROI	SEM imaging requests (https://github.com/lukasc-ubc/SiEPIC_EBeam_PDK/wiki/Fabrication-via-Electron-Beam-Lithography#sem-images)
4	Si_p6nm	Fabricated at the same time as Layer “Si”, except with Shot Pitch Fracturing of 1 nm. Cost is similar to Layer “Si”. See description below. Recommended for Bragg gratings. Layer is perfectly aligned to Layer “Si”.
5	Si_p2nm	Fabricated at the same time as Layer “Si”, but not aligned to Layer “Si”. Shot Pitch = 2 nm. Cost is 8X higher than Layer “Si”.
6	Floorplan	Indicate the assigned area for your layout with a rectangle.

Layout Tools

There are numerous tools that can produce the GDS files required for fabrication. The following is a description of several tools used by SiEPIC researchers:

KLayout

• Free software.
• Tutorial for EBeam
• https://ebeam.mff.uw.edu/ebeamweb/training/cad_tut_main/cad_tutorial_main.html
• Download from http://www.klayout.de/
• Offers scripting capabilities, including PCells
• http://www.klayout.de/doc/about/about_pcells.html
• PDK for KLayout https://github.com/lukasc-ubc/SiEPIC_EBeam_PDK
• Design Rule Checking file provided “KLayout_EBeam_DRC.rtf”. Load the DRC file
• http://www.klayout.de/doc/manual/drc_basic.html#h2-172

Mentor Graphics

• Commercial EDA (Electronic Design Automation) tools.
• Mentor Graphics Pyxis – for mask layout
• Mentor Graphics Calibre – for verification
• PDKs available for EBeam, IME and imec fabrication.

MatlabGDSPhotonicsToolbox

• Free toolbox using commercial Matlab software
• http://www.mathworks.in/matlabcentral/fileexchange/46827-nicolasayotte-matlabgdsphotonicstoolbox
• Specifically designed for silicon photonics. Includes automated waveguide routing. Scripted components. PDKs for various processes including EBeam.

##SEM Images

• SEM images available upon request, at an additional cost (typically 5 incremental cost per image + setup time)

• Instrument: SEM JEOL JSM-7400; cold-field emission; operated at conditions near where the current of electrons emitted from the chip is not too different from the incident beam current which is typically 20-22 kV for the low beam currents used.

• SEM image requests are done by:

  1. https://ebeam.mff.uw.edu/ebeamweb/remote/remote/sem_inspection_sites.html
  2. Drawing a rectangle around the area of interest, on layer “SEM_ROI”. Choose the size based on available ones.
  3. Add a text label with a name, on layer “SEM_ROI”
  4. Add an arrow on layer “Si” to help locate the device.

• See example file “SEM/SEM.GDS”