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Planar NAND flash had several layers which use SADP below 80 nm pitch and SAQP below 40 nm pitch. 3D NAND flash used SADP for some layers. While it does not scale so aggressively laterally, the use of string stacking in 3D NAND would imply the use of multiple patterning (litho-etch style) to pattern the vertical channels.
In photolithography, several masks are used in turn, each one reproducing a layer of the completed design, and together known as a mask set. A curvilinear photomask has patterns with curves, which is a departure from conventional photomasks which only have patterns that are completely vertical or horizontal, known as manhattan geometry.
A standard logic process can be converted to a logic-plus-flash process through the addition of three more high voltage masks and three more core CTF masks, and none of these six masks is a critical layer (i.e. needs to use the most advanced part of the process).
An insulating layer of oxide is grown over the channel, then a conductive (silicon or aluminum) gate electrode is deposited, and a further thick layer of oxide is deposited over the gate electrode. The floating-gate electrode has no connections to other parts of the integrated circuit and is completely insulated by the surrounding layers of ...
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.
Like the first sale doctrine, a lawful owner of an authorized IC containing a mask work may freely import, distribute or use, but not reproduce the chip (or the mask). Mask work protection is characterized as a sui generis right, i.e., one created to protect specific rights where other (more general) laws were inadequate or inappropriate.
A refinement of MPW is multi-layer mask (MLM) arrangement, where a limited number of masks (e.g. 4) are changed during manufacturing at exposure phase. The rest of the masks are the same from the chip to chip on the whole wafer. [7] MLM approach is well suited for several specific cases:
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).