semiconductor device fabrication 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 pres ...

, the inverse lithography technology (ILT) is an approach to

photomask A photomask is an opaque plate with holes or transparencies that allow light to shine through in a defined pattern. They are commonly used in photolithography and the production of integrated circuits (ICs or "chips") in particular. Masks are used ...

design. This is basically an approach to solve an inverse imaging problem: to calculate the shapes of the openings in a

("source") so that the passing light produces a good approximation of the desired pattern ("target") on the illuminated material, typically a

photoresist A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry. T ...

. As such, it is treated as a mathematical

optimization problem In mathematics, computer science and economics, an optimization problem is the problem of finding the ''best'' solution from all feasible solutions. Optimization problems can be divided into two categories, depending on whether the variables ...

of a special kind, because usually an analytical solution does not exist. In conventional approaches known as the

optical proximity correction Optical proximity correction (OPC) is a photolithography enhancement technique commonly used to compensate for image errors due to diffraction or process effects. The need for OPC is seen mainly in the making of semiconductor devices and is due to ...

(OPC) a "target" shape is augmented with carefully tuned rectangles to produce a "

Manhattan shape A taxicab geometry or a Manhattan geometry is a geometry whose usual distance function or metric of Euclidean geometry is replaced by a new metric in which the distance between two points is the sum of the absolute differences of their Cartesian ...

" for the "source", as shown in the illustration. The ILT approach generates curvilinear shapes for the "source", which deliver better approximations for the "target".Inverse Lithography Technology (ILT)
/ref> The ILT was proposed in 1980s, however at that time it was impractical due to the huge required computational power and complicated "source" shapes, which presented difficulties for verification (

design rule checking In electronic design automation, a design rule is a geometric constraint imposed on circuit board, semiconductor device, and integrated circuit (IC) designers to ensure their designs function properly, reliably, and can be produced with acceptabl ...

) and manufacturing. However in late 2000s developers started reconsidering ILT due to significant increases in computational power.

References

category:Lithography (microfabrication) Inverse problems {{Tech-stub