Layout Design

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Layout Design Formats

When you want to create a pattern on a wafer with photolithography, you have to describe or digitize the pattern by geometric shapes, i.e. to distinguish the areas where UV light will expose the photoresist from the areas where it will not. This will be a required step for either the fabrication of a Cr blank mask (to use on a mask-aligner or a stepper), or for exposing the photoresist with a UV laser (direct laser writing).

To create a complete 2D layout, the patterns can be drawn using dedicated computer-assisted design (CAD) softwares, generated using mathematics softwares such as Matlab or Octave, or coded using python/ruby programmed scripts. There exist many layout file formats to describe such layouts. Some are proprietary, some public, some standard. While you can use your preferred CAD software to generate the layout, the design should be exported to formats that are compatible with the Heidelberg Instruments (HIMT) laser writing equipments used in CMi, such as (in order of recommendation):

  • gds, gdsii, gds2, GDSII (Graphic Database System for Information Interchange). The GDS file format is an industry standard and the recommended file format to flawlessly convert your design to the internal language of the HIMT direct laser writing equipment. General information about the GDS format are available here.
  • cif, CIF (Caltech Intermediate Format). The CIF file format is a concise and human readable text based description of the layout. In general, the CIF format is converted without issues but some proprietary text statements introduced in specific layout editors (such a Clewin) may not be interpretated correctly by the HIMT conversion tool. General information about the CIF format are available here.
  • dxf, DXF (Drawing Exchange Format). The DXF file format as been developped by Autodesk to enable data exchange between AutoCAD and related softwares. With many limitations and restrictions, DXF files may be accepted and converted correctly by the HIMT conversion tool. General information about the DXF format are available here.

Layout Editors: CAD software

The softwares and tools listed below (in order of preference) can export valid and standardized GDS format files for the HIMT laser writing equipment.

Software Description License/Installation
Klayout by Matthias Köfferlein, layout editor
  • Free software
  • Download links available on the Klayout website
  • Installed on CMi open office BM 1.132 computers
Tanner L-Edit IC by Mentor (Siemens), layout editor (part of Tanner Tools layout suite)
  • Distributed to EPFL through EUROPRACTICE membership
  • Utilization is strictly reserved to EPFL employees and students. No utilization of the tool can be done for commercial purpose. 
  • Network license pool
  • Contact the photolithography staff for installation files & licensing instructions.
LinkCAD by Bay Technology, layout file format conversion tool
  • License for CMi users
  • Contact the photolithography staff for installation files & licensing instructions.
  • Installed on CMi open office BM 1.132 computers
Clewin (v4)

by WieWeb software, layout editor

AutoCAD by AutoDESK, mechanical drawing software
Solidworks by Dassault Systems, mechanical drawing software

GDSII Toolbox

by Ulf Griesmann, Matlab/Octave GDS import/modify module
  • Free addon/fonctions for Matlab/Octave

Gdstk (GDSII Tool Kit)

by Lucas Heitzmann, C++ & Python GDS/OASIS import/modify module
  • Free addon/fonctions for Python & C++
LayoutEditor by Juspertor GmbH, layout editor
  • Packages: free (limited number of shapes/format), reduced (~EUR300), full (~EUR1100)
Glade by Peardrop Design Systems, layout editor
  • Packages: free (limited number of shapes/format), full (~EUR100/year)
Virtuoso Layout Suite by Cadence, professional layout suite
  • Payed software
Expert by Silvaco, professional layout suite
  • Payed software

CMi Layout Templates

You will find below basic CAD layout templates to use on CMi exposure equipment:

  1. LASER template
  2. MASK template
  3. RESOLUTION template

The LASER template is available for users that mainly operates the CMi direct laser writers (MLA 150, VPG 200) for the photolithography patterning steps. Description of the layers used in the template:

GDS #
Layer function
Notes
10
Wafer frame
This layer shows the last 3mm edge area from a 100mm SEMI wafer where it is not recommended to place devices. All critical cells/layers should be drawn in the white inner area. This layer is normally removed from the layout.
20
Alignment marks

This layer shows a set of 4 cross alignment marks that can be exposed during the first lithography step and used during the alignment sequence of the following exposed layers. Marks coordinates, in [um], are at (+/- 40000, 0) and (0,+/-40000).

An alternate set of square marks are located at (+/- 39000, 0) and (0,+/-39000).

For topside alignment (TSA), the marks can be moved, to adapt to the device, to any position on the wafer.

For backside alignment (BSA – MLA 150 only), the marks should stay along the x- or y-axis in the stage open window areas (see layer 60).

21
Vernier patterns
This layer shows an example of vernier patterns, matching with the alignment marks layout, that can be exposed at the second lithography step to measure the critical alignment with the first exposure.
40
Dicing marks
This matrix of crosses show an example guideline set for dicing the wafer into dies. The layer should be kept only if dicing will occur; the step size can be adjusted to adapt to the device dimensions.
60
MLA 150 BSA areas, vacuum lanes.
This layer shows the MLA 150 vacuum lanes and the position of the 4 open stage windows where BSA alignment marks should be located to be visible to the backside objectives.

The MASK template is available for users that operates the CMi mask-aligners (MA6 Gen3, MJB4) for the photolithography patterning steps. Description of the layers used in the template:

GDS #
Layer function
Notes
10
Wafer frame
This layer shows the last 3mm edge area from a 100mm SEMI wafer where it is not recommended to place devices. All critical cells/layers should be drawn in the white inner area. This layer is normally removed from the layout.
21
First MASK Alignment marks

This layer shows two sets of alignment marks (left and right) that should be included in the mask used for the first lithography step.

On each side, 3 marks are included for the exposure with 3 additional masks. Marks are located at (+/- 42000, 0) for mask N°2,  (+/-41600, 0) for mask N°3, and (+/-41200, 0) for mask N°4.

For topside alignment (TSA), the marks can be moved to any position on the x-axis.

For backside alignment (BSA – MLA 150 only), the marks should stay within the chuck open windows (see layer 61).

22 or 24

MASK N°2
Alignment marks

These layers (22 or 24) show the alignment marks layout that should be included on the mask N°2 and that will match with the first mask exposure at the (+/- 42000, 0) position.

Layer 22 is used if your mask if fabricated in CLEAR mode.

Layer 24 is used if your mask is fabricated in DARK mode.

An additional set of alignment marks is printed together for critical alignment between MASK N°2 and MASK N°3.

23 or 25
MASK N°3
Alignment marks

These layers (23 or 25) show the alignment marks layout that should be included on the mask N°3 and that will match with the first mask exposure at the (+/- 41600, 0) position.

Layer 23 is used if your mask if fabricated in CLEAR mode.

Layer 25 is used if your mask is fabricated in DARK mode.

An additional set of alignment marks is printed together for critical alignment between MASK N°3 and MASK N°4.

30
MASK frame
This layer shows the layout of the mask frame that can be exposed when fabricating a 5″ mask to be used with 100mm wafers. This layout includes the frame, the mask details and an open window for precise alignment of the wafer flat in first MASK exposure mode. This layer should be exposed in CLEAR mode.
41
Dicing marks
This matrix of crosses show an example guideline set for dicing the wafer into dies. The layer should be kept only if dicing will occur; the step size can be adjusted to adapt to the device dimensions.
61
MA6 Gen3 BSA areas
This layer shows the position of the two open  windows in the chuck of the MA6 Gen3 mask-aligner where BSA alignment marks should be located to be visible to the backside objectives.

The RESOLUTION template is available for users that want to include a small generic pattern in their layout for the evaluation of the photolithography resolution limits or to perform dose/focus optimizations using the built-in “series” option on the CMi laser writer (MLA 150, VPG 200).

GDS #
Layer function
Notes
50
Resolution Tests

This layer contains 4 test patterns which are adapted to the evaluation of resolution limits at different crititical dimensions (CD = 600nm, 1um, 2um, or 5um).

You should use only one of these patterns based on your combination of resist thickness and exposure equipment/configurations.

Please contact the photolithography staff for advice on how to properly use these layouts for dose/focus series optimizations.