Fabrication Process Flashcards
Oxide is used as….
A sacrificial layer
Polysilicon is used as….
A structural material
Silicon nitride is used as…
An electrical isolation between the polysilicon and the substrate
What type of silicon wafer is used as the base of MEMS devices?
150 mm n-type silicon,with 1-2 Ω-cm resistivity
What is done to reduce and prevent feedthrough to the substrate from electrostatic devices on the surface?
Phosphorous is used to dope the wafer through a diffusion furnace, using PSG/phosphosilicate glasss a sacrificial layer s the dopant source
What is PSG?
PSG/phosphosilicate glasss a sacrificial layer s the dopant source
WhAt is LPCVD? What is it used for?
Low pressure vapor chemical deposition - used to deposit a 600 nm silicon nitride onto the wafer after PSG is removed. The silicon nitride is an electrical isolation layer.
What is photolithography? Describe the process.
It is the process by which photoresist is used to etch patterns onto poly0. Approximately~ The wafer is first dehydrated, then Photoresist is spun onto the wafer, soft baked, aligned with mask , exposed to UV light, and then stripped of photoresist.
What and when is plasma etching used?
Plasma etching is used to remove the unwanted poly0 layer. It is after the photoresist has been patterned, and used before fthe photoresist is stripped, and after plasma etching, the photoresist is removed in a solvent bath.
What is anneal?
The process of heating metal or glass and allowing it to cool down slowly, in order to remove internal stresses and toughen it.
What happens after poly0 is plasma etched?
Photoresist is removed and another layer of PSG is depositted via LPVCD, after which it is annealed for 1hr in argon at 1050C. This sacrificial layer of phosphosilicate glass is removed layer to free the first mechanical yer of polysilicon, so it it often called FIRST OXIDE.
What happens after First Oxide is placed?
The sacrificial layer is patterned lithographically with theDIMPLES mask, with the dimples being transferred into the sacrificial layer via Reactive Ion Etching (RIE). The nominal dep of the dimples Re 750 nm.
What happens after RIE etching of the dimples on to FIrst Oxide?
The third mask layer, Anchor1,is used to pattern the wafer, and then again RIEd. This step provides whole anchors to be filled by poly1 layer.
How is polysilicon removed?
After the photoresist is removed by chemical dissolving, the polysilicon is still convert by the parts of the photoresist that stayed, and plasma etching removes the polysilicon then the remaining photoresist comes off in a solvent bath.
What is REI?
Reactive ion etching, used to remove unwanted oxide.
