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The phrase depth of focus is sometimes erroneously used to refer to depth of field (DOF), which is the distance from the lens in acceptable focus, whereas the true meaning of depth of focus refers to the zone behind the lens wherein the film plane or sensor is placed to produce an in-focus image. Depth of field depends on the focus distance ...
Photolithography (also known as optical lithography) ... The depth of focus restricts the thickness of the photoresist and the depth of the topography on the wafer.
However, [clarification needed] the depth of focus, or tolerance in wafer topography flatness, is improved compared to the corresponding "dry" tool at the same resolution. [ 4 ] The idea for immersion lithography was patented in 1984 by Takanashi et al. [ 5 ] It was also proposed by Taiwanese engineer Burn J. Lin and realized in the 1980s. [ 6 ]
If the local slope is indicated by an angle α, the image is projected to be shifted in a 4× projection tool by 8α × (DOF/2) = 4α DOF, where DOF is the depth of focus. [87] For a depth of focus of 100 nm, a small local deviation from flatness of 2.5 mrad (0.14°) can lead to a pattern shift of 1 nm.
Good depth of focus requires diffracted light traveling at comparable angles with the optical axis, and this requires the appropriate illumination angle. [4] Assuming the correct illumination angle, OPC can direct more diffracted light along the right angles for a given pitch, but without the correct illumination angle, such angles will not ...
Sub resolution assist features that improves the depth of focus of isolated features. Phase-shift Mask: Etching quartz from certain areas of the mask (alt-PSM) or replacing Chrome with phase shifting Molybdenum Silicide layer (attenuated embedded PSM) to improve CD control and increase resolution Double or Multiple Patterning
Computational lithography came to the forefront of photolithography technologies in 2008 when the semiconductor industry faced challenges associated with the transition to a 22 nanometer CMOS microfabrication process and has become instrumental in further shrinking the design nodes and topology of semiconductor transistor manufacturing.
Moreover, STI has a higher degree of planarity making it essential in photolithographic applications, depth of focus budget by decreasing minimum line width. To planarize shallow trenches, a common method should be used such as the combination of resist etching-back (REB) and chemical mechanical polishing (CMP).