Specific Process Knowledge/Lithography/Coaters/Spin Coater: RCD8 processing: Difference between revisions

Resist dispense on the Spin Coater: RCD8 can only be done manually, as the motorized media arm was decommissioned in 2024. Manual dispense is done by administering the resist directly onto the substrate, after it has been loaded into the machine but before the recipe has been started. It can be done by pouring the resist directly from a bottle (for thin resists such as the AZ resists or SU-8 3005) or by pushing it out of a prefilled syringe (for thick resists like SU-8 3035 and XFT 75).  

Syringes should be filled the day before spin coating, and should be stored vertical in order to allow bubbles to settle at the top. A syringe consists of an end cap, the syringe barrel itself (30 ml or 55 ml, can be red or transparent), and a piston that seals of the syringe after filling. To fill a syringe, bring all parts to a fume hood along with the resist bottle. It is recommended to clean all parts with the nitrogen gun (these parts are normal labware, and thus not supplied particle free). Put the end cap on the syringe barrel and open the resist bottle. Hold the syringe at a slight angle and start pouring the resist from the bottle. Start gently and be patient; the flow of resist can quickly become too fast and too wide for the syringe. Let the resist flow down the side of the syringe to minimize bubble formation, but avoid the top couple of cm of the syringe. Stop pouring before it's too late; the viscous resist will continue to flow after you have lowered the bottle. Leave a couple of cm at the top to make sure there is room for the piston. When you have put down the resist bottle, insert the piston and push it all the way down to the surface of the resist in the syringe. Wipe any resist from the end of the syringe. If resist dripped on the outside of the bottle, wipe it off but avoid wiping the opening of the bottle (due to risk of contaminating the remaining resist). Finally, label your syringe and store it in the chemical cabinet (in E-4).

Start by removing the end cap from the syringe. For the first dispense, remove any air in the tip of the syringe by dispensing the first drop somewhere outside the substrate. Start the dispense in the center of the wafer, keeping the tip of the syringe as close to the substrate as possible (so the dispensed resist forms a continuous puddle, rather than strings that bunch up and trap air). Make sure the dispensed resist puddle is in the center of the substrate, otherwise all of the resist may flow to one side during spinning, causing the other side of the substrate to not be covered, even though enough resist was dispensed. During the dispense, the position of the puddle can be controlled by moving the tip of the syringe while continuing the dispense. Towards the end of the dispense, move the tip to the edge of the puddle. Stop the dispense but keep the tip at the last spot to allow the last resist to finish flowing. Now, lift the tip a couple of cm up, then down again and up again, in order to break the thin string of resist that forms between the tip and the puddle.