Mask design

Overview of Mask Design Process

Once we have a new sensor design from rigorous simulation and modeling, selected designs will be laid out for a photomask manufacturing.  A typical process is:

• 1. Design the fabrication flow of the sensor design (explanation elsewhere on wiki)

  2. Using AutoCAD, draw the sensor design (See AutoCAD Instructions for details)

  3. Lay down the sensor design on a wafer template (typically 4" wafer template)

  4. Save the AutoCAD file as DXF file (from DWG)

  5. Using K-Layout, open the DXF file, ensure highlighted regions are correct and/or use Boolean layer operations, and re-save as GDS2 file.

  6. Re-verify the converted GDS2 file (open and close it).

  7. Upload the GDS2 file with an ordering form to Photo Sciences, Inc. (forms are on their website, explanation below)

  8. Once the mask set is delivered, check under a microscope and have a fun time in fabrication!!!

AutoCAD Mask Design

This is a list of things to know if you are designing a mask in AutoCAD. Following the requirements from the beginning of the CAD process will allow for easy transition to the next step (the DXF and GDS2 files) and creating an error-free mask! 

Note: this is not intended to be a basic AutoCAD tutorial.

AutoCAD Requirements

    1. Use the "pline" command instead of "line" to draw shapes. 

        - Designs must be made of polyline shapes to be recognized by kLayout software.

        - There is a way to convert normal lines to polylines, but it is much easier to draw with pline to begin with!

        - TIP: If you like to work with reference lines, use the "line" command so none wind up in your final design accidentally.

    2. Immediately after you generate a closed polyline shape (i.e. a square), highlight it, right click, and select "pedit" > "close".

    COPYING AND PASTING between AutoCAD files may RE-OPEN polyline shapes.

    3. If you need to create any doughnut-like shape in a single mask step, create the inner and outer boundary with different AutoCAD layers (i.e. 3_Electrode_main and 3_Electrode_cut). 

        Why? KLayout will fill in the entirety of the outer shape (there's not a way to select the desired fill area unless they're separate layers).

    4. The software the mask company uses cannot recognize circles. If your design features a circle, you must put two half-circles next to each other for the mask to turn out right.

AutoCAD Tips

    0. MOST IMPORTANT TIME-SAVING TIP: When working with a large file (say, the tiled wafer) right-click the "Hardware Acceleration" icon  from the bottom toolbar (picture 

    above) and deselect "Smooth line display."

    1. Name your layers beginning with their mask number (i.e. 1_Cr_Electrode and 2_PR_Si_Etch_Mask)

    2. To save time on repetitive features, array shapes using either of the following methods:

            i) Copy command: 

• • 1. Highlight the shapes you want in an array. 

    2. Right click > type "Copy" 

• 1. Specify base point - click any point on your shape 

  2. Specify displacement - type "array" 

  3. Enter number of items to array - type "<# in row or col>" 

  4. Move your cursor in the direction you want the array (relative to the copy source).

     1. type "<Offset #>."  

                + Result gives each copied shape as independent pieces, closed if original was closed

                - Easy to edit individual elements of array, but cannot update all at once (must change and recopy the array)

                TIP: If you need to remove something (say, a logo from a previous revision) remove it and re-copy the array. 

            ii) Array command:

• • 1. Highlight desired array source 

    2. Type "Array" 

• 1. Size the array on top toolbar 

  2.  *WHEN READY* type "explode"

                + Prior to "explode," changes to the array source made by typing "arrayedit" > source can update every element in the array simultaneously (note: exit "arrayedit" mode with "arrayclose" command) 

                - Without explode, the arrayed shapes cannot be joined with other plines.

                - Explode may open things that were closed polylines in the source objects.

    3. Label die numerically so position on wafer is known

            i) Most common format: [ r r | c c ] rows and columns

            ii) Created by Samuel: [ q r c ] quadrant, row, and column 

    4. To create the text on a wafer:

            i) Use the text tool to create a line of text in a textbox. 

                Choose a font with thick lines! To change fonts: Double click your text. The following menu bar will appear:

                In this image, "Calibri" is the font, 100 is the text size.

            ii) Highlight the text > "txtexp" 

            iii) ...make sure the letters are closed polylines! Use the convertpoly command and choose the light option to convert 2D polylines to standard polylines--done!

                    Note: The txtexp and convertpoly commands are only available if the 'express tools' package is installed

            *) If something isn't working properly, make sure: 1) You're using Arial font (or similar) 2) You're in "standard" text style mode

    5. If you are creating a partial mask (half or quarter), create a single-die with all layers overlapping and rotate later. This strategy also helps for designing alignment marks! 

- Emma (Feb. 9, 2017)

 To install the express tools package (Windows only):

• 1. Go to control panel

  2. Go to Programs

  3. Go to Programs and Features

  4. Select AutoCAD

  5. Press Change

  6. When the install wizard starts, select 'Add or Remove Features'

  7. On the appropriate wizard screen, check the 'Express Tools' box, continue through the wizard, and press the finish button. 

- Michael

GDS2 File Prep

Note: Please make sure installing a 64-bit version of the GDS editor you choose (although there are several GDS editors, we've been using K-Layout for GDS file conversion).

Of course you need to have 64-bit operating system on your computer first to install 64-bit software.  The advantage of the 64-bit software gives you more flexibility in terms of file size.

In other words, the 64-bit software can handle a larger-size file better than 32-bit software, e.g., files larger than 1 GB - If you're curious about 64-bit vs. 32 bit, please check this out: Link <<< CLICK

1. Save the DWG file you've been working on AutoCAD to DXF file (it seems like any DXF file should work).

2. Open the DXF file using K-Layout and perform any necessary Boolean operation to merge or subtract drawings. (KLayout free download found here:  http://www.klayout.de)

    a)  If your KLayout toolbar does not contain the icons in the picture below, you are likely in the "KLayout (Viewer)" application. Close the window and 

    search your desktop for "KLayout (Editor)".

    b) To perform Boolean operations, find this menu option: 

4. Save the DXF file to GDS2 file (select “Layers shown in list.”--no other options need to be changed!)

5. Close and re-open the GDS2 file to check the integrity of the mask file.

    - Note:  After a GDS2 conversion process, layer names will be changed to numbers.  Use the GDS numbers on the order form for Photo Sciences.The layer order on GDS2 file will only be the same as in the DXF file if your layer names in the DXF file start with their order number.

6. Now you’re ready to start an order form!

- DK (May 28, 2015)

- Edits by Emma (Feb 16, 2017)

Mask Ordering Process:

Mask manufacturer: Photo Sciences, Inc. (http://dev.photo-sciences.com)

Point of contact:

     Kiomi Hamada - Account Manager (kiomih@photo-sciences.com) Tel: +1 (310) 634-1500 ext. 1524 DK: Kiomi is no longer working for PSI (confirmed from Cindy Munoz on Apr. 27, 2017)

     Cindy Munoz - Asst. Fast Track Product Manager (cindym@photo-sciences.com) Tel: +1 (310) 634-1570

1. Create an account on Photo Sciences, Inc website

2. Prepare an ordering form 

    - Which mask material type to order depends on your feature sizes--the Photo Sciences website has a list of  "Standard specs" and "Advanced specs" that list the capabilities of each mask option. 

    - For normal features: Option B / For backside features: Option D

    - 5” mask (with 0.90” thickness) is our typical choice - Soda lime for large features & quartz for small features (more details on their sheet).

    - Next to "Do you require plots for artwork approval" check "yes." Include "Please provide a proof for the order." in the Special Instructions / Comments section.

    -  If you are using the P-card, make sure to include "No taxes applied to the order" in the Special Instructions / Comments section.

         P-Card Billing address:

NEAL HALL

1616 Guadalupe

UTA Suite 3.302

Austin, TX 78701

The University of Texas at Austin 

Main Building, Room 132

110 Inner Campus Drive

Austin, TX 78712-1140

          Shipping address:

HALL GROUP (attn: Your Name)

PRC - The University of Texas at Austin

10100 Burnet Rd.

Bldg.160, Rm.1.108

Austin, TX 78758

3. Make a Zip file containing the converted GDS2 file and the order form. Upload it to your Photo Sciences, Inc. account.

4. Send an email to Kiomi Hamada or Cindy Munoz requesting a quote and proofs for the zip you uploaded. If you are using the P-card, stress that you are ordering from the University of Texas.

5. Review the proof file PSI to ensure your design was captured properly by their software. (Remember--their software does not recognize circles! See AutoCAD requirements/tips above)

        Note: Reversed text may produce an error in their software, but it will likely still come out alright in the actual masks if you are making a reverse mask

6. If using P-card: Once you have the quote and have reviewed the proof, check out the P-card from Christine. Place the order. If using company card: Ask Dr. Hall for the company card.

7. If using P-card: Once you receive an invoice from PSI, forward the invoice to Christine. If using company card: Forward the invoice to the current Si Audio admin.

Note: Critical dimension (CD) - Price break-down point: 5 µm, 3 µm, 1.5 µm and 1 µm

Pricing Estimates

CD 3 µm ± 0.5 µm - $380 CRSL

CD 2 µm ± 0.25 µm - $535 CRSL

CD 2 µm ± 0.15 µm - $880 CRSL - This is a new process they started offering recently (as of Apr. 2015)

CD 1.5 µm ± 0.15 µm - $920 CRQZ - This is possible with a quartz mask - a potential of inaccurate patterning when it uses with other mask materials (due to different thermal expansion coefficients in-between mask materials, i.e., soda lime vs. quartz.

- DK (May 28, 2015)

- Edits by Emma (Feb 16, 2017)

- DK (Apr. 4, 2017) - P-card billing address updated.

Alignment Marks on the Half-Mask Design

When you design a half-mask, a special attention is required to the alignment marks.

In this half-mask design, a mask will be used twice for two different patterns (i.e., the mask will be rotated 180 deg for two different patterns).

Therefore, the attention requires to maintain the alignment integrity through the fabrication process (so that you can align your subsequent mask to the patterned alignment mark on your substrate.

The following schematic shows an example how the alignment mark was designed: