Photolithography
Photolithography is the process used to pattern samples. Contact lithography is the process used in MNMS Cleanroom.
Process
Typical process includes the following steps, but can also include other steps.
- Clean
- Adhesion promoter (if necessary)
- Expose
- Spin
- Develop
Other steps that might be necessary include:
- Dehydration bake
- Rest time
- Additional exposure steps, particularly for image reversal photoresist
- Edge bead removal
Equipment
Two spinners, three mask aligners and one flood exposure exist for photolithography:
- Flood Expose
- Glovebox Spinner
- Mask Aligner - EV420
- Mask Aligner - EV620
- Mask Aligner - Suss MJB3
- Maskless Aligner - Microlight 3D Smartprint UV
- Spinner
Clean
Cleaning can include many steps, depending on the cleanliness of your substrate and cleanliness required by following steps. Typical cleaning processes include but are not limited to:
- Plasma cleaning
- Oxygen Descum
- Argon/Oxygen Clean
- Argon Clean
- Chemical Cleaning
- Piranha
- RCA1
- RCA2
- Degrease
- Acetone, IPA, DI Water, IPA, Nitrogen Dry
- Many other variations possible
Adhesion Promoter
Many adhesion promotor's exist for various applications. Most commonly used at MNMS are:
- HMDS as deposited by MVD tool
- AP8000
- 1000mL spin coated using recipe 3
Expose
Using the equipment listed above, the sample can be exposed to UV light. The appropriate amount of expose time can be estimated using the formula (Exposure Time = Dose / Intensity). Dose can be found in the photoresist datasheet. Intensity can be measured using a UV intensity meter, or is already measured by staff and found on a intensity card listed at the tool. Ideally, this would be the best exposure time. However, the dose varies by application and practical experience. As you can see in the image below, various PR profiles are obtainable, and may be useful given the application. For example, the overcut profile may be desirable if the photoresist will be used as a mold, the vertical profile may be desirable for ICP DRIE etching, and the undercut profile may be desirable for thin film lift-off.
Spin
The spinner in the MNMS cleanroom allows for 3 spin speeds. Select the final spin speed that matches your desired photoresist thickness per recommendation in the photoresist manufacturer's technical data sheet. For more details on the spin process, check the Spinner equipment page.
Develop
There are many developers manufactured for photoresist development. A reasonable develop to use is the one recommended by the photoresist manufacturer, as developing times and suggestions are posted in the photoresist technical datasheet. However, other developers might work just as well. MNMS Cleanroom provides AZ400K, AZ917MIF, AZ300MIF, and SU-8 Developer. The typical development processes are listed below:
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AZ400K
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AZ917MIF
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