Table of Contents:
Masks
Rob Ilic wrote a custom maskmaking supplement. It's an easy-to-use, open-source Java program. It offers many capabilities that L-Edit lacks, including the ability to:
• easily create numbered arrays
• build spirals and arbitrary function paths
• create unusual photonic crystal
• extend your control over text (and use any vector font!)
• easily transform greyscale or B&W images into printable shapes
There's also a more flexible Java package.
Resists
Priming
SOURCE: Staff AFS
Wafers should be clean before coating with photoresist. Cleaning a wafer before coating it may involve removal of the native oxide, or simply cleaning with solvents. A brand new wafer may only require an isopropyl or methanol rinse, or it may require SC1 or SC1/SC2. If there is grease on the wafer, methylene chloride may be required to remove it. If the wafer has been coated with resist before, this should be stripped before recoating.
The surfaces of many of the materials we want to put resist on oxidize very easily. The surface oxide forms long-range hydrogen bonds with water adsorbed from the air. When the resist is spun onto such a surface, it adheres to the water vapor rather than to the surface, and poor adhesion results. Priming is a standard process where the wafer surface is dehydrated, then coated with hexamethyldisilazane to improve adhesion.
The diagram below shows adhesion of resist to a surface silylated with HMDS.R. Dammel, Diazonaphthoquinone-based Resists, SPIE Press, 1993, p. 100.
HMDS may be applied in two ways. Liquid priming is the process of spinning HMDS, diluted in solvent, onto a dehydrated wafer. We use 20% HMDS in PGMEA, a common resist solvent. This is often effective, but is not as good as vapor priming. At CNF we have a YES LP-III Vacuum Oven in which the samples can be primed. During a 35-minute, pre-programmed cycle, the oven pumps down to dehydrate the samples, and then fills with pure HMDS vapor, resulting in a much more efficient prime than is possible otherwise.
User Processes:
PROCESS: Converting files for use on the pattern generator
SOURCE: Melina Blees (McEuen Group)
ADDED: 2/17/13
To print a mask on the PG3600, you must convert your original L-Edit file to a GDSII file, then to a pattern generator file.
1. In L-Edit, go to Export in the File menu, and export as a GDSII file. Fracture polygons to 8 vertices, and export Cell0 (or whatever your main file window is) and its hierarchy. Be sure to note what layer numbers correspond to what content on your mask.
2. Open the program WS_FTP. Set upload option to binary.
3. Log in with your CNF CAC account, and drag your GDSII file into the directory given.
4. Open the program Putty. Telnet to nnfvax.cnf.cornell.edu, and log in using your CNF account.
5. Type GDSPG. Press return to use the current directory. Give it the top-level cell (Cell0).
If you want to use image reversal, you will need to export the frame layer, and convert the layer to be image-reversed, using the frame layer simply to define its boundaries when asked (i.e. do not convert the frame layer as a layer of its own).
PROCESS: Converting files for use on the pattern generator
SOURCE: McEuen Group
ADDED: 2/17/13
* It is usually a good idea to start from an old mask as your template, since they contain the GDS alignment keys already.
* If you plan to wire bond to your sample, contact pads should never be smaller than 50x50um.
* Be sure to check the flash count on your completed file. The PG runs between 3,000 and 5,000 flashes per hour, so you can get an estimate of how long the mask will take to write. The Heidelberg writes by area, so a 5“ mask that uses the whole area (it doesn't matter if it's complex writing covering the area or just a border) will usually take just over two hours.
PROCESS: Gamma Tool Handling of Thin Wafers
SOURCE: Devin Wakefield (Baird Group)
ADDED: 1/8/15
A few steps allow the Genmark robotic arm to successfully recognize the thin wafer in the wafer carrier and safely transport the wafer between modules. First, a piece of scotch tape can be used to hold down the sensor that recognizes when a wafer carrier is present in the tool. (The sensor is the small white cylindrical button located where the wafer carrier H-bar sits.) A 'dummy' wafer of standard thickness is placed in the wafer carrier and the Genmark robotic arm can be used to scan/load this wafer as normal. The dummy wafer can then be exchanged for the thin wafer in the exact same slot. Finally, before running your process, place the tool in “Teach” mode to help the Genmark robotic arm carefully transport the wafer. (Click the Pause button on the computer, turn the key located on the keyboard to “Teach” mode, and click Auto.) You can now run your process. Remember to remove the scotch tape and return the keyboard key to its original position when finished. CNF staff (e.g. Dan or Garry) should be present when trying this for the first time as some troubleshooting may be required.