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An illustration of OPC (Optical Proximity Correction). The blue Γ-like shape is what chip designers would like printed on a wafer, in green is the pattern on a mask after applying optical proximity correction, and the red contour is how the shape actually prints on the wafer (quite close to the desired blue target).
A photomask (also simply called a mask) is an opaque plate with transparent areas that allow light to shine through in a defined pattern. Photomasks are commonly used in photolithography for the production of integrated circuits (ICs or "chips") to produce a pattern on a thin wafer of material (usually silicon ).
With a proper optical imaging system between the mask and the wafer (or no imaging system if the mask is sufficiently closely positioned to the wafer such as in early lithography machines), the mask pattern is imaged on a thin layer of photoresist on the surface of the wafer and a light (UV or EUV)-exposed part of the photoresist experiences ...
By making the off-axis illumination (i.e., the light is illuminating the mask at an oblique angle), all the diffraction orders from the mask are tilted, which makes it more likely that the higher diffraction orders can make it through the projection lens and help form the image of the mask onto the wafer.
In both cases, the mask covers the entire wafer, and simultaneously patterns every die. Contact printing/lithography is liable to damage both the mask and the wafer, [38] and this was the primary reason it was abandoned for high volume production. Both contact and proximity lithography require the light intensity to be uniform across an entire ...
In semiconductor device fabrication, the inverse lithography technology (ILT) is an approach to photomask design. It is basically an approach to solve an inverse imaging problem : to calculate the shapes of the openings in a photomask ("source") so that the passing light produces a good approximation of the desired pattern ("target") on the ...
A benefit of using phase-shift masks in lithography is the reduced sensitivity to variations of feature sizes on the mask itself. This is most commonly used in alternating phase-shift masks, where the linewidth becomes less and less sensitive to the chrome width on the mask, as the chrome width decreases.
For example it is often used to mask off areas of a design when using a photoresist to produce printing plates for offset lithography or gravure. It is also frequently used during screen-printing. Ulano also produced a yellow-(amber-)coloured masking film called Amberlith that was light-safe only for blue-sensitive emulsions. They discontinued ...