Timeline
Training:
- Photolithography- 3 hours
- Plasma Etcher- 3 hours
- Dektak and NMX- 1 hour
Wafer Preparation (3 hours): Three wafers will be prepared to etch. Two wafers are made of silicon and the third is silicon oxide.Preparing the wafers entails creating a pattern on the wafer using photoresist (resin). All the wafers will have photoresist 1813 on them. When etched, areas without photoresist will be engraved.
- Wash and Bake: All the wafers will be cleaned with isopropyl alcohol and blasted with nitrogen gas. This will remove any surface particles (dust) from the surface of the wafer. The wafers will then be loaded into a baker to bake for 20 minutes. The baker is an evaporator that will remove any water from the wafer which will help the photoresist stick to the wafer.
- Photolithography: A wafer is loaded into a coater and photoresist is placed onto the wafer using a pipet. The coater is closed and spins the wafer so that the photoresist spreads evenly across. The photoresist layer is less than a micron thick. This process is done for each wafer. The wafers are then placed on a hot plate so slightly harden the resist.
- Exposure: A mask and wafer are loaded into an aligner. A mask is a glass pane that has the negative image of a pattern. UV light passes through the clear areas of the mask and hits the photoresist underneath. The photoresist that is exposed to the light will change in chemistry. This change in chemistry will be different depending on the photoresist and will give different results in the next part.
- Lift Off: A chemical called MF 319 is placed in a glass dish. One at a time, a wafer is placed in the chemical. When removed, the wafer is placed under running water and then dried with nitrogen gas. Depending on the type of photoresist, the areas that was exposed to the light will either lift off (negative resist) or remain (positive resist).
- Microscope check: The wafers are placed under a microscope to make sure the liftoff was done completely.
Data Collection (3 hours):
- NMX: This machine will take the initial thickness of each wafer with photoresist.
- Plasma etch: A plasma ray of CF4 will be shot at each silicon wafer while CHF3 will be used for the silicon oxide wafer. This causes everything at the top to be removed at a certain rate. Areas of wafer that are under the photoresist are protected as the resist is removed first. Areas of exposed wafer will be etched before areas covers by photoresist. The etch lasts 5 minutes for each wafer.
- NMX: This machine will take the new thickness of each wafer with photoresist.
- Dektak: Will measure the depth of the etch.
- SEM: Cleave (break) wafer into smaller sample and place in electron microscope to see side view of wafer.