What is Overlay?
How accurately a new pattern is placed relative to the patterns made in earlier steps. Misalignment causes defects such as missed contacts, so it is controlled at the nanometer level.
Field: Lithography
Overlay in the explanations
An LSI stacks dozens of patterned layers, so each must align precisely to the previous ones; overlay accuracy measures how small that misregistration is.
What is overlay accuracy in lithography?To measure overlay accuracy, dedicated marks (targets) combining patterns from the previous and current layers are made in places such as the scribe lines around chips.
What is placed on the wafer to measure overlay error?Self-aligned contacts remove the margin otherwise reserved for overlay error, tightening gate-to-contact spacing, and lead to techniques such as contact-over-active-gate (COAG) that further shrink cells.
Which technique covers the gate with insulator so that a sl…
Questions that mention Overlay (10)
- What is overlay accuracy in lithography?
- What is placed on the wafer to measure overlay error?
- Which technique covers the gate with insulator so that a slightly misaligned contact does not short to the gate?
- What causes "slip", a problem when large-diameter wafers are heat-treated at high temperature?
- What problem tends to occur when a deposited thin film has large internal stress?
- What is the technique called that transfers a pattern by pressing a mold with fine patterns into resist?
- In LELE (litho-etch-litho-etch) double patterning, what is especially strictly required?
- What is the measurement called that monitors a process by measuring product wafers partway through processing on the production line?
- Which correctly describes the general difference between "metrology" and "inspection" on a semiconductor production line?
- What is the main reason temperature is held extremely constant in cleanrooms, especially in exposure areas?
Related terms
Slip Yield Mobility Nanoimprint lithography 3D NAND SADP (self-aligned double patterning) ArF excimer laser Bottom anti-reflective coating (BARC) Chemically amplified resist Depth of focus (DOF)