In
silicon wafer
In electronics, a wafer (also called a slice or substrate) is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer ser ...
manufacturing overlay control is the control of pattern-to-pattern alignment necessary in the manufacture of
silicon wafer
In electronics, a wafer (also called a slice or substrate) is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer ser ...
s.
Silicon wafers are currently manufactured in a sequence of steps, each stage placing a pattern of material on the wafer; in this way
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
s, contacts, etc., all made of different materials, are laid down. In order for the final device to function correctly, these separate patterns must be aligned correctly – for example contacts, lines and transistors must all line up.
Overlay control has always played an important role in
semiconductor manufacturing
Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are ...
, helping to monitor layer-to-layer alignment on multi-layer device structures. Misalignment of any kind can cause short circuits and connection failures, which in turn impact
fab
Fab or FAB may refer to:
Commerce
* Fab (brand), a frozen confectionery
* Fab (website), an e-commerce design web site
* The FAB Awards, a food and beverage award
* FAB Link, a European electricity link
* Flavoured alcoholic beverage or alcop ...
yield and profit margins.
Overlay control has become even more critical now because the combination of increasing pattern density and innovative techniques such as
double patterning
Multiple patterning (or multi-patterning) is a class of technologies for manufacturing integrated circuits (ICs), developed for photolithography to enhance the feature density. It is expected to be necessary for the 10 nm and 7 nm node se ...
and 193 nm
immersion lithography
Immersion lithography is a photolithography resolution enhancement technique for manufacturing integrated circuits (ICs) that replaces the usual air gap between the final lens and the wafer surface with a liquid medium that has a refractive index ...
creates a novel set of pattern-based yield challenges at the 45 nm technology node and below. This combination causes error budgets to shrink below 30 percent of design rules, where existing overlay metrology solutions cannot meet total measurement uncertainty (TMU) requirements.
Overlay metrology solutions with both higher measurement accuracy/precision and process robustness are key factors when addressing increasingly tighter overlay budgets. Higher order overlay control and in-field metrology using smaller, micro-grating or other novel targets are becoming essential for successful production ramps and higher yields at 45 nm and beyond.
Examples of the widely adopted overlay measurement tools worldwide are KLA-Tencor's ARCHE
and the nanometric
CALIPER series, overlay metrology platforms.
Semiconductor device fabrication