Inverse lithography

<p>In <a href="/facts/Semiconductor_device_fabrication/Jd23Mu1z">semiconductor device fabrication</a>, the inverse lithography technology (ILT) is an approach to <a href="/facts/Photomask/xCdRhIod">photomask</a> design. It is basically an approach to solve an <a href="/facts/Inverse_problem/Fe01pQ9E">inverse imaging problem</a>: to calculate the shapes of the openings in a <a href="/facts/Photomask/xCdRhIod">photomask</a> ("source") so that the passing light produces a good approximation of the desired pattern ("target") on the illuminated material, typically a <a href="/facts/Photoresist/XNnIkCjU">photoresist</a>. As such, it is treated as a mathematical <a href="/facts/Optimization_problem/QzwJfFEE">optimization problem</a> of a special kind, because usually an analytical solution does not exist. In conventional approaches known as the <a href="/facts/Optical_proximity_correction/lcmHTwdY">optical proximity correction</a> (OPC) a "target" shape is augmented with carefully tuned rectangles to produce a "<a href="/facts/Manhattan_shape/zU7gGUPv">Manhattan shape</a>" for the "source", as shown in the illustration. The ILT approach generates curvilinear shapes for the "source", which deliver better approximations for the "target".
</p><p>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 (<a href="/facts/Design_rule_checking/GW7N249M">design rule checking</a>) and manufacturing. However in late 2000s developers started reconsidering ILT due to significant increases in computational power.
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Inverse lithography open-in-new

Inverse lithography