LITHOGRAPHY TRAINING

Manual Coat Procedures

30 minute singe at 150C -

• Unless wafers just came out of a furnace or a deposition system (within one hour) they must get 30 minutes singe in the 150C Oven before resist coat. . This includes new material, wafers after furnace or deposition (after more than 1 hour), and wafers after resist strip.
• Resist lifting during develop or etch will result without this step
• Place the wafers in a Teflon cassette (ok up to 180C) and place the cassette in the Singe Oven.

HMDS (Hexamethyldisilazane) wafer prime must be done before resist coat.

• HMDS promotes adhesion of the resist to the oxide on the wafer surface (starting material, oxide films, nitride films because they have ~ 50A of oxide on top of the nitride, Aluminum films also because of oxide on the surface of the Aluminum, etc. all have improved adhesion with HMDS prime before coat.
• Use Personal Resist Bottles for the resist and the HMDS. Yellow labels can be obtained from Sharleen. Or use your own designated clean beakers (cover with foil when transferring from one hood to another). If you use a beaker you MUST fill out a Blue Hazardous Label (see below) and keep it with the beaker.
• For photo sensitive chemicals you should use brown glass bottles for storage. The ones with the droppers built right in are the best for dispensing HMDS and resist.
• Transfer all lithography chemicals with the stainless steel solvent cart. No chemicals may be carried in the lab.
• Most lithography chemicals (including personal resist bottles with the yellow labels) are stored in the two yellow cabinets behind the furnaces. Some (i.e. Polyimides) are stored in the refrigerator or freezer behind the ion implanter.
• Completely fill out the Blue Hazardous Labels (one for each beaker or container that does not have a yellow personal label on it - even water must have one) and keep it with the container. If you are working at the lithosolv or wbmiscres benches you may check that the MSDS sheet for the chemical you are using is there. If the MSDS sheet for the product is there, you may list the product name instead of the percentage of every chemical in the product. This option ONLY at these two benches because there is an MSDS book at the bench. Other benches in the lab require the complete list of all chemicals in the product.
• Make sure any open containers are at least 6 inches back from the front of the exhaust hood. Never bring an open container out from under the exhaust hood unless it is covered with foil. Also do not bring solvent or resist contaminated items out from under the exhaust hood, unless it is in a sealed plastic bag.

Manual Application of HMDS and Resist on the headway2 spinner

• Vacuum check the system without a chuck. If it spins, write it up as a problem on crystal and do not use it (your wafers may fly off the chuck during the spin step).
• Select the appropriate chuck. Make sure it is clean and has an o-ring on the inside. Choose the correct size chuck for your wafers.
• Vacuum check the system with the selected chuck. If it spins, choose a different chuck or clean the one you have selected with Acetone.
• Set up the appropriate spin speed and time (see spin speed charts for each resist in the lithography information book) using a dummy wafer. Step on the front of the pedal to start the spin, and after the speed is set, step on the back of the pedal if you want to stop it before the time is up.
• Place the first real wafer on the chuck and apply HMDS. Apply enough to cover about 50% of the wafer surface before the spin. HMDS spreads easily for a uniform coat.
• Place the protective plastic piece between you and the spinner
• Step on the front of the pedal to start the spin. When the time is up it will stop spinning. You will see color changes as the HMDS thickness changes.
• Apply photoresist to your wafer. Apply enough to cover about 50% of the wafer surface.
• Place the protective plastic piece between you and the spinner
• Step on the front of the pedal to start the spin. When the time is up it will stop spinning.
• Coating tips: If you notice some areas near the edge do not get covered with resist, it may be necessary to increase the time (typically 30 seconds) to 40 seconds and after applying the resist turn down the spin speed before you step on the pedal. Let the resist spread across the wafer and then increase the speed to the correct setting (just so the last 25 or 30 seconds is at the correct speed to get the desired thickness).
• Bake resist. You could use a hotplate bake or an oven bake. Check the webpages to see what bake temperature and time to use (you could just mimic the procedure used for the svgcoat system for coating and baking information). 3612 is baked for 1 minute at 90C on a hot plate. You could instead bake it at 90C in the oven for 25 minutes. When you coat both sides of the wafers you must use the oven for the second coat.
• NEVER put resist side down on a hotplate. If you need to coat both sides, bake in an oven for 25 minutes at the temp you need (90C or 110C) instead of 1 minute on the hotplate.

Clean up.

• You should find fresh foil when you come up to use the spinner and you should leave it that way. Do not leave your resist bottles or beakers etc. at the bench.
There should be a roll of foil above both spinners. Replacement rolls are on the top of the acid storage carts (along with gloves and wipes).
• Always dispose of solvent contaminated items properly. Never bring solvent contaminated items out from under an exhaust hood unless they are in a closed plastic bag (your glove can be used for small items). If you glove is contaminated (i.e. with photoresist) turn it inside out to prevent fumes during the transfer. Transfer the sealed bag under the hood of the lithosolv bench and place the black bucket under the hood. Open the black bucket under the hood and place the sealed bag in it. Replace the lid and clamp tightly then transfer the black bucket back under the solvent bench.
• When the black bucket is full, place it under the hood and seal its bag with a tie-wrap and transfer the sealed bag to the large white barrel (remove the clamp and the lid and place the sealed bag inside, replace the lid and secure the clamp).
• All of the lab air is 80% recirculated so any fumes released into the air will stay in the lab for a long time. Notify the staff immediately if you smell solvents. Evacuate the area and press the red button in the gowning room if the smell is strong (doing this supplies the office area with non-recirculated air, but the lab still remains 80% recirculated).