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LEdit for Layouts

Tips and tricks on using LEdit for mask layouts.
  1. Standard Setup: For ease of use and consistency, try to use the standard setup. Select Setup->Design to get the Setup Design popup.

    • Select the "Technology" tab. The Technology Name should be "Generic 0.25um Technology". Technnology Units should be checked "Microns" and the Database Resolution should show 1 internal unit equals 1/1000 microns.

    • Select the "Grid" tab. Under the Mouse Grid, the Cursor Type should have the "Snapping" box checked. Your Mouse Snap Grid should be set the same as the address unit value you choose (usually 0.1 or 0.125 microns.)

    • If you are laying out 1X designs for 5X reticles, keep your internal unit at 1/1000 microns, but set your Mouse Snap Grid to 1/5 of your address unit size (usually, 0.02 or 0.025 microns) since this will scale to 5X. (It's not necessary and may lead to conversion problems if scale your internal units by 1/5.)

  2. Define Layers: Select Setup->Layers... to get the Setup Layers popup. On the left side will be a list of layers that you can choose to use for rendering your layout. Make sure that the layer(s) you choose to use has a GDSII number associated with it (under Import/Export.) If there is no associated GDSII number for a given layer, no data for that layer will be exported. The GDSII layer ID number is also what is used for specifying which structures will be written on a mask. For electronic devices, there is a naming convention which is part of the Technology setup(i.e., "Poly = 43"). For other applications, the naming convention doesn't need to be observed -- but each layer must have unique number between 0 and 64.

  3. Observe minimum feature spec: Make sure your minimum critical feature (line, space, or dot) size is no less than the critical dimension (CD) specified for the grade or type of mask you are ordering. You could get away with drawing things that are smaller that the specified CD, but they would not be guaranteed for dimensional control or appearance (for example, corners will be rounded.)

  4. Naming convention: Make sure to use simple naming conventions for your named structures (file names, cell names, subroutine names.) Stick to alphanumerics only (no characters like *&#%$) and do not use spaces (underscores, like "_" are OK.) The limit is 32 characters -- but if cells from different files are "instanced", LEdit appends the file name to the cell name to ensure unique reference pointers, so the final cell name may exceed this.

  5. Nifty files for reference:
    - ASML image field <1X Digitized Data Clear-GDSII> or <1X/5X Digitized Data Dark-GDSII> or <1X/5X DigitizedData Dark TannerDB>
    - Contact mask alignment marks <TannerDB> or <ZIP>

  6. Digitized Data Dark & Clear: It is possible to place images on the same mask with different polarities - in other words, one device with digitized-data-dark next to one that has digitized-data-clear. The simplest way to do this is to draw your layout so that there are only two distinct GDSII layers: one designated for digitized data dark, and the other, for digitized data clear.

    - The digitized data clear layer can be drawn just as you want it to appear.
    - In addition to the digitized data dark features you want, draw large boxes that cover and protect the digitized data clear structures.
    - Your data window should cover your entire write area. The maskwriter will write one layer and then the other right away.
    - For a sketch of this, refer to the Photomask Basics presentation.
    - If you have multiple layers that map to one clear (or dark) layer, just define the different layers (step 2) to export to your designated clear or dark GDSII layer number.
    - Here's an example in LEdit and in GDSII formats. The "TopStructure" cell defines a mask with six structures, three in dark and three in light. The "Dark" layer exports to GDSII layer number 4, which is arbitrarily chosen to be dark. The "Clear" layer exports to GDSII layer number 2.

  7. Multiple images on a single mask: Devices and device layers can be arrayed on a single mask; there is generally a data processing charge for this, depending on how complex the job is. Alternatively, you can array the images yourself which can save a little money and not all that much trouble once you've already gone through the task of mapping out where you want everything. This is one way to array one device that has multiple layers:
    - Starting with your layout, draw an "outline" layer around your device. This layer can be named anything (the default technology will have something called "drawn" or "outline"), but the layer should be defined WITHOUT a GDSII layer number. The purpose of the outline is to help make sure your device placement in the array is exact and consistent.
    - Copy your layout to other cells. Each cell that you copy to will be used to define one image in your array. Make sure you use "Copy" and not "Instance" since layers cannot be separated using Instance. If you do use Instance, make sure to flatten the cell (which removes all reference to the Instanced cell.)
    - In each of the copied cells, hide the layer you want for your image and hide the "outline". Delete all the remaining layers. Then "show" the layers you've just deleted. Now each of your cells should have only the outline and the layer you want to image.
    - In your top structure, array your cells.
    - In your layer definition (step 2 above), define your layers to output to a single GDSII layer number. If you have both digitized dark and digitized clear data on the same mask, then output to two layers and make sure you have dark boxes protecting your clear structures.
    - Here's an example in LEdit and GDSII formats. This is one of the layouts used in the EE410 class. The cells, TopStructure1 (digitized data clear), TopStructure2 (digitized data dark), and TopStructure3 (digitized data clear) define three different ASML reticle masks. Each of image is instanced from a cell with a single layer (plus the outline or "special" layer.) The various layers (Active, PWell, Poly, Metal1, NSelect, Contact) maps out to either GDSII layer number 2 (which has been chosen to indicate "digitized data clear" data) or number 4 (chosen for "dark" data.)

  8. Text: Select Draw -> Layout Generator -> Layout Text generator. A box pops up and you can enter this info:

    Layout Text String: TEXT YOU WANT TO APPEAR
    Layer name: select layer you want text on
    Cell name: layout text generator makes a new cell with your text in it
    Text Size: Height of text

  9. The critical check: Use LEdit to export your file to GDSII file format. Then, as a sanity check, re-import your GDSII file into LEdit. Make sure that your imported GDSII file looks like your original LEdit file. If it doesn't, there is a good chance there is a problem in one of the areas listed above. Be aware that unless you specify the technology when you import, the layer rendering may not be the same as when you exported from LEdit.

  10. Other tips and tricks: The User Guide (loaded on the PC) is the best place to start. Additionally, there are answer/questions posed by previous labmembers which appear as PDF files on the machines. If you have questions about how to do something in LEdit, feel free to contact Process Staff -- if we can't help you, we can forward your question to Tanner as we have a support agreement with them.

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