Mask Making using AutoCAD - Stanford University



Mask Making using AutoCAD

Open AutoCAD. Choose start from scratch, metric units. (no template)

Go into layer control by choosing Format, Layer in the top toolbar.

Add a new layer for each mask you desire to make. Ensure that the names are composed of three or less alphabetic characters.

Turn off the ‘0’ layer by clicking on the lightbulb in the layer window.

Before creating your mask ensure that you are on the correct layer (the default, even when turned off, is the base ‘0’ layer) as shown in the toolbar. NOTE: The base ‘0’ layer cannot be renamed and will NOT convert correctly.

Configure your mask such that 1 drawing unit = 10μm, and center the design (mask) at the coordinates 0,0. Prepare the mask using only open rectangles. Avoid using sequences of line segments as in some instances they will form unconnected shapes that will not successfully make it through the conversion processes. NOTE: Although different scales CAN be used, the use of 1 drawing unit to 10μm has the least problems in the conversion process.

Once the AutoCAD mask has been made, export the document to a .dxf file, which can be found under File, Export menu in the top toolbar.

Download a trial version of LinkCAD from the following website:



Open the program and select DXF as the import format and GDS-II as the export format. Then click next.

Next set the DXF import and GDS-II export settings as shown in the images below. If only one layer is used, be sure to flatten file structure in the GDS export settings.

Take note of your layer names and numbers, as they will be needed in the GDS-II conversion script.

Once you have successfully converted the DXF file to a GDS-II file, upload the file to your silicon account. It is useful to make a separate directory inside your home directory for each separate mask.

Next log onto gold, nickel, or gallium once you have already logged into your silicon account by simply typing in the name of that server.

Once logged in, change to the directory that your mask is located in, and type the following command as is shown in the following image.

gds2tap filename.gds

The conversion process begins and asks for the layer numbers as a list. Do NOT put the layer names in a list, rather the layer numbers. For example in my mask only ONE layer was used (actually two, the zero layer which was turned off and layer 1 which was used for the mask), so I typed a number 1. Suppose you had multiple masks on layers 1, 2, 3, and 4; you would type “1 2 3 4”. The conversion script then asks for the topmost layer which in my case would have been “L” or simply use the equal sign to have the program determine the topmost layer.

Last you need to determine which lithographic tool you are going to use your mask on, so that the conversion script creates a mask that is suited for that particular piece of equipment. Finally, specify the center of your mask. If you created the mask as instructed above, it will already be centered at 0,0.

Once you press enter after the center, the conversion script will initiate. It will first convert the GDS-II file to an intermediate format (.INT) which can be viewed with pgview to ensure the conversion is correct to this point.

If the mask looks fine, you can continue the conversion by exiting pgview and hitting enter. The final conversion portion of the script converts the mask to a set to two files named filename.tap and filename.tix and sorts and adds the number of flashes required on the pattern generator. WRITE THIS NUMBER DOWN, as it will be needed when you request the mask to be made.

The two files will be in your mask directory and must have their permissions changed to allow Marilyn to access them. To do this, type the following UNIX commands while still in your mask directory:

chmod o+r *.tap

chmod o+r *.tix

chmod o+rx .

NOTE: Please note the spaces and the "dot" in the last command.

The final thing you need to do now is to email Marilyn and tell her if you want an emulsion or a chrome mask made. The insides of the open rectangles will be clear (open) if you choose an emulsion mask, and they will be dark, chromed if you choose a chrome mask. NOTE: Positive Photoresist is attacked in the exposed regions and Negative Photoresist is attacked in the unexposed regions.

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