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GDSII is the file format used for photomask submissions, direct-write laser lithography (DWL) exposures, and electron-beam lithography (EBL) exposures.  While not a recommended approach, this how-to provides details on how to prepare a design using AutoCAD such that it can be successfully converted into GDSII with a minimum of errors.

Converting from DXF saved from AutoCAD to GDSII often produces unintended results/defects in the design.  It is highly recommended to create your GDSII pattern using a native GDSII editor such as KLayout, or a script-based approach (Raith_GDSII, python-gdsii), rather than creating the design in AutoCAD and converting to GDSII.  Please see this page on GDSII design software options.

Step-by-step guide

  1. Make design as normal in AutoCAD; use mm for units.
  2. Make all features into polylines → select all elements → MPEDIT → Join.
  3. Select each element and use HATCH function → polygons should now appear shaded.
  4. Export the file as DXF.
  5. Open DXF file in KLayout.
    • N.B.  Before opening the file, check File > Reader Options, under the DXF tab and ensure that Database unit is 0.001 µm and DXF file unit is 1000 µm (assuming mm mode was used in AutoCAD).
  6. Ensure that all elements to be patterned are (shaded) polygons, and verify that the scaling is correct (GDSII assumes units of µm, not mm).
  7. Save as GDSII.

Troubleshooting

  1. Hatching large areas in AutoCAD can create issues in the conversion process
    1. Segmenting areas and hatching them separately can help prevent this from happening
    2. Particularly helpful with many small pillars or objects inside a larger area
  2. Discs in the DXF file may be rendered as path elements consisting of a single point, with path width equal to the disc diameter, and with rounded extension type (end caps).  Although this single-point path is rendered correctly by KLayout, it is not supported by Heidelberg lithography tools (e.g., MLA150 or DWL200 for photomask fabrication), instead raising an error that a path must have at least two points.  To rectify this, select "Eliminate zero-length paths (convert to BOUNDARY)" in the GDSII Writer Options section when saving as GDSII in KLayout: