The MEMS Clean Room is located on the ground floor of the ETAS building. The main purpose of the Clean Room is to provide students and researchers a place to perform photolithography. There are two parts to the clean room. First there is an anti-chamber and second is the main clean room area. The anti-chamber is a class 10000 and is used for staging and for personnel to take an air shower to remove as much dust and particles as possible before you enter in the main clean room area. The main clean-room is a class 1000 and it houses all of the machines that you would perform your assignments or research on.
Photolithography (also called optical lithography) is a process used in microfabrication to selectively remove parts of a thin film (or the bulk of a substrate). It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical (photoresist, or simply “resist”) on the substrate. A series of chemical treatments then engraves the exposure pattern into the material underneath the photoresist. In a complex integrated circuit (for example, modern CMOS), a wafer will go through the photolithographic cycle up to 50 times.
Using the clean room’s machines, students can create objects, such as, antennas, sensors, and actuators .
Equipment: (In normal use order)
- Spin/Rinser/Dryer machine:
This is used to clean the surface of the wafer. There can be no contaminants on the surface or else there will be flaws in future fabrication steps. This machine uses deionized water to rinse the wafer, spins up to a few thousand rpms to dry the wafer, and uses hot air to finish the drying process.
- Thin Film Deposition Machine:
- Spin Coater:
- Mask aligner:
- Wet Bench:
- Dicing Saw:
- Probe Station:
This machine is used to deposit thin films of material onto a mounted surface inside a vacuum chamber. The thin film is created by positively charged ions (plasma) striking the surface of the material and individual molecules are sputtered off, similar to a pool ball striking a group of pool balls. You insert a small sample of almost any pure material (ie: aluminum, titanium, gold, silicon dioxide-¦). The vacuum chamber is pumped down to an extremely low pressure (press â‰ˆ 7.0 x 10^-7 mbar). Strong magnets are used to generate the plasma from inert Argon gas. The particles that are knocked off settle on the mounted wafer in the vacuum chamber. Thickness of the material is controlled by deposition time.
This machine has a micro needle on the tip of a cantilever beam. The needle is used to map the surface of the wafer. It can tell if the surface varies on a micro scale. This is important when the entire circuit is only a few microns long.
This is used to apply the photoresist onto the surface of the wafer. The photoresist is used to transfer a pattern onto the wafer. The photoresist reacts to ultraviolet light and the material properties are changed by this process.
This machine is what actually transfers the pattern onto the wafer. A mask is placed above the wafer. The mask has the desired pattern on it. A high intensity ultraviolet light is placed over the mask. The light only transmits through the openings in the pattern allowing the pattern is burned into the photoresist on the wafer.
This is used for all the chemical handling and etching of the materials. After the photoresist has been processed, then the pattern can be transferred into the thin film. This requires specific combinations of chemicals to etch specific materials. The photoresist shield specific parts of the wafer allowing the chemical to etch the exposed parts of the wafer. After the etching is complete the photoresist is stripped off.
Once the complete circuit has been completed using the steps mentioned above, it is ready to be cut into different parts. Normally the circuits are so small that many of the same circuit can be fabricated on the same wafer. The dicing saw is used to separate the individual circuits.
Once you have an individual circuit it is time to test it. This machine is set up to apply voltage using a power source to your circuit. It holds the wafer and has a microscope attached to a computer for visual inspection during testing.