Bullseye
Bullseye turns up in 2 fields: statistics, ceramics & glass. Here is what it means to the people in each one.
Bullseye in statistics
Wafer map pattern of concentric rings or a center spot, the signature of a radial process nonuniformity.
A bullseye is a wafer map where failures or parameter values form a center spot, a ring or a set of concentric bands. Many fab steps are radially symmetric, such as spin coating, single-wafer etch and deposition, CMP and wafer heating, so a bullseye usually points to one of them: center-fast etch, a chuck temperature gradient or a center-to-edge CMP profile. Its counterpart is the edge ring, with failures packed into the outer few millimeters.
"Bullseye on the Vt map, center die are 20 millivolts high. Smells like the anneal chuck again."
Bullseye in ceramics & glass
The thick central knob of a spun glass pane containing the punty scar.
A common term for the thick, circular center of a piece of crown glass, formed where the glass was attached to the punty during spinning. It features a prominent scar and distinct concentric ripples. Originally considered a low-quality byproduct of window glass manufacturing, these pieces are often used decoratively in doors and transoms.
"We need three more bullseye panes to finish the transom window above the main door."