Process Guidelines rev. 1 (1063229)
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Basic Photoresist Processing Techniquesand Other Useful InformationPrepared By: Janice L. Eddington and Quinn LeonardThe University of Wisconsin-MadisonCenter for NanotechnologyKegonsa Research Campus3731 Schneider DriveStoughton, WI 53589Basic Photoresist Processing TechniquesTable of ContentsSectionPage1: Preparing Photoresist22: Preparing Samples for PR Coating43: Preparing Equipment for Coating and Baking84: Coating Samples175: Exposure Tools at CNTech256: Post Exposure Processes367: Laboratory Usage and Safety408: Commonly Used Abbreviations519: Frequently Asked Questions5210: Appendixa) Decanting Photoresistb) Spin Speed Curvesc) Diluting Photoresistd) Hotplate Calibration Curvese) Film Thickness Measurementf) E-sizingg) Design of Experimentsh) How Phase Shifting Worksi) MSDS5411: Contact Information1Basic Photoresist Processing TechniquesPart 1: Preparing PhotoresistGeneral Comments:You should pour some resist into a smaller bottle for your private use.
If you use the bulkbottle directly, you're likely to contaminate it. This costs money, screws up data for otherunsuspecting users, and slows everyone down waiting for a new bottle. Besides, it's likespitting into a well you may need to drink from later.Don't take more than you plan on using in the near future. Don't hoard resist; it goes bad,or gets forgotten and wasted. Do label your small bottle clearly: your name, kind of resist,date you put it in the small bottle, and expiration date from bulk bottle. Discard your ownresist if you know it to be contaminated.1.1 Cleanliness:-Keep or make everything as clean as possible before you pour your resist.-Prepare a small 2 oz. Qorpak bottle for your resista. Rinse your bottle with alcohol and blow dry. It is extremely important thatyour bottle is completely dry before it sees any resist.b.
Label your bottle with your name, kind of resist, date, and the expirationdate of the resist (located on the bulk bottle).c. If you are diluting resist, rinse and dry all glassware that will be used forvolume measurement.1.2 Decanting Photoresist from the Bulk Bottles:-Again, keep everything as clean as possible!-Open the bulk bottle only in the flow hood and only right before you are ready topour.-If the resist was refrigerated, you must wait for it to come to room temperaturebefore you open it (at least 3 hours for a quart bottle that’s more than 1/4 full).o Moisture in the cleanroom air can condense inside the cold bottle, spoilingthe resisto Plan accordingly!!-Open the bulk bottle carefully.
If the last person who used it didn’t wipe the rim,there may be a crust of dried resist that can fall into the bottle and contaminatethe whole bottle with particles.2Basic Photoresist Processing Techniques-If a crust exists, use a fresh cleanroom wipe with alcohol and carefully wipeaway the particles. Do not let the particles or alcohol contaminate the bulkresist.-Make a clean pour.o When you are ready to pour from the bulk bottle to your small bottle, do itin the flow hood.o Do not use a funnel. It allows an extra chance to contaminate your bottle.o Place a crystallization dish under your small Qorpak bottle to collect anyspilled resist.o Pour slowly and carefully.1.3 Cleanup and Storage:-If you get any resist on the rim of your small bottle, wipe with a fresh cleanroomwipe with alcohol to avoid crust formation.-Also, carefully clean the rim of the bulk bottle as stated above.
Blow somefiltered, dry nitrogen into the bottle to displace the more humid cleanroom air.Close the bottle securely and put it back where you found it (either in therefrigerator or above it). Bottles should be stored standing up, no lying on theirsides.-Clean any glassware that was used with alcohol to ensure removal of resist.Rinse with DI water, dry, and place back on the glassware rack.-Store your bottle of resist properly.
Everything that applies to the bulk bottleapplies to your small bottle. If you refrigerate your small bottle, let it warm upbefore you use it.-Do not pour resist directly from your bottle to the wafer. Plastic pipettes aresupplied for applying resist to wafers. Use the high pressure nitrogen gun toblow out any flashing within the pipette before use.3Basic Photoresist Processing TechniquesPart 2: Preparing Samples for PR CoatingGeneral Comments:Before applying photoresist, make sure your wafers are clean, free of particles andchemicals.
Never open any package of wafers you intend to coat, except in a cleanroomenvironment. Keep them sealed and in packaging until you are ready to use them. Propercleanliness procedures will ensure the best adhesion and film uniformity across the surfaceof your wafer. The remarks below apply equally to wafers and to other substrates, such asmembranes.2.1 Cleanliness:- Do not open wafer boxes outside the cleanroom.- Never handle wafers without gloves or tweezers.
Using gloved fingers does notmar PR surfaces, but can leave fingerprints. Tweezers will do some damage tothe PR, if an edge bead removal is not performed.- Wafers obtained from vendors in their original sealed packaging are consideredto be sufficiently clean and ready for direct use.- If there is concern about prior history of reclaimed wafers, give the wafers toQuinn Leonard. They will be sent out and re-polished.2.2 Spin-rinse and Drying:- There are two VERTEQ spin-rinse-dryers in the CNTech cleanroom.
One is for4” substrates; the other is for 5” substrates or masks on NIST rings.- Only use boats marked “A72-40MB” with the “H” bar facing towards you as youload your wafers into the dryer. See Figure 1 below.4Basic Photoresist Processing TechniquesFigure 1: Make sure the "H" Bar faces out towards you.- For the 5” spin-rinse-dryer in the back corner of the cleanroom (next to theHMDS oven), you will need to turn on the water and nitrogen supply on the backof the unit before you begin. Error codes will appear if either the nitrogen orwater supply is inadequate. Do not adjust spin speed or time on this unit. Thisunit is reserved for mask cleaning. See Anphong Ho or Janice Eddington if errorcodes appear.- For the spin-rinse-dryer in the front of the cleanroom (next to the fume hood),operation is simple.
Push START. Parameters are preprogrammed into thesystem. Do not change these parameters without checking with Quinn Leonardor Janice Eddington. Spinning too fast may break membranes.- If you need to clean wafers other than 4”, you can rinse and dry them manuallyand use Cycle 3 on the YES HMDS oven for a vacuum dehydration bake.5Basic Photoresist Processing Techniques2.3 YES HMDS Prime Oven:- Hexamethyldisilazane (HMDS) is widely used in the semiconductor industry toimprove photoresist adhesion to silicon and to oxides.
The HMDS reacts withthe oxide surface in a process known as silylation, forming a strong bond to thesurface. The methyls, meanwhile, will bond with the photoresist, enhancing thephotoresist adhesion.Figure 2: YES HMDS Prime Oven in Back Corner of Process Cleanroom1. Check the level of HMDS in the flask attached to the oven. HMDS is asuspected carcinogen and should be handled with care. Do not attempt to fill thevessel with HMDS yourself, contact Quinn Leonard or Janice Eddington if theHMDS level is low.2. Only quartz wafer boats may be used in the oven.
No Teflon is allowed. Quartzboats should be handled with the metal forks only, never with hands (gloved orungloved). Finger oils will destroy expensive boats.3. Load your wafers into a quartz boat and use a metal boat handler to transfer yourwafers into the oven (see Fig. 3). Close the door securely.6Basic Photoresist Processing TechniquesFigure 3: Loading Wafers into the HMDS Oven4. Several different cycles have been preprogrammed into the oven. Pleaseconsult the list on the oven door for the appropriate thumbwheel setting. Do notchange any of the preprogrammed cycles.5. Push START.
The system will begin an automatic pump/purge/prime sequence.The entire process takes approximately 25 min. Plan accordingly.6. Do not attempt to open the vacuum seal once the cycle has commenced. Youmust wait until the cycle has complete, the HMDS vapor has been evacuatedfrom the oven, and the oven has backfilled to atmosphere before the safetyinterlock will allow you to open the door.7. Once the sequence is complete, the COMPLETE light will flash and the systemwill audibly alarm (loudly!).
Press the red RESET button to silence the alarm.8. Using the metal boat handler, remove your wafers and close the door securely.9. Allow your wafers to cool before applying photoresist.7Basic Photoresist Processing TechniquesPart 3: Preparing Equipment for Coating and BakingGeneral Comments:Reserve any equipment you may need before starting your PR coating process.Remember to set the hotplate to your desired temperature and allow time for thetemperature to equilibrate before beginning. Do not do any photoresist coating untilyou understand how to keep the hotplates clean; i.e., ask for training. The resistedge bead must be removed from each wafer before it may be baked on anyhotplate.3.1 Reserving Equipment:- Equipment is reserved by simply placing a cleanroom Post-it Note in front of thetool or glassware you wish to work on.- Provide the following information on the Post-it Note:ooooNameTemperature (for hotplates)/Type of Chemical (for glassware)Approximate time neededDate- Please be considerate of others’ schedules.
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