- Slides: 6
SPUTTERING Micro/Nano Technology Center University of Louisville Summer Camp 2017
What is sputtering? Sputtering is a process that deposits a layer of metal or dielectric (non-conductor) to the surface of a wafer. Sputtering tools require two items: • • Silicon wafer Target materials (a source of very pure metal or dielectric) Sputtering is a method of taking atoms from the surface of the target and applying it to the surface of the wafer.
How does sputtering work? Wafers and the source materials will be loaded into the chamber of the sputtering tool where it will be pumped down to a determined vacuum level. Argon gas will be pumped into the chamber and a voltage bias or electric field will be applied between the wafer and source material resulting in a plasma glow.
Deposition Argon is a relatively heavy atom that is energized and will pick up speed from the electric field. When it meets the surface of the target it will hit with enough force to launch an atom of the source material or metal from the surface of the target. It will propel towards the wafer where it will adhere. Since this process is happening million of times per second we count on the law of averages to provide an even coating across the entire surface of the wafer.
Atomic Snowfall • You can picture this process the same way snow falls on your front yard. Your yard is the wafer and snow is the falling metal atoms. • The snow will coat your entire yard evenly and the depth will depend on the intensity of the snowfall and how long it snows. • The snow will not accumulate against tall vertical structures (the wall of your house) and or accumulate under overhangs (a patio table).
Metal Anneal After the snowfall the snow is not very tightly packed and the snowflakes have not yet settled into each other to minimize potential energy. Similarly, our metal layer has not fully settled after deposition. How do we make our atoms settle into a more dense structure? We make our surface dance again! If we heat up the wafer the metal atoms will move around slightly and nestle into each other creating a more organized surface that will have better electrical contact with our wafer. We perform this step by placing the wafer into the tube furnace for a time period at 350°C with either an inert (Nitrogen) or forming gas (2% Hydrogen + 98% Nitrogen).