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Double patterning ?


Double patterning in VLSI:

        Multi patterning also called double patterning ,double patterning is introduced 32nm and lowers layers 10nm,7nm etc.

       Lithography pattern is a class of technologies for manufacturing IC's,developing for photolithography to enhance the feature of density and Optical microlithography (photolithography) is used for transferring the circuit patterns into silicon wafer.

     We are use illuminator uv light to shine light through this mask producing an image of the pattern  through the lens system ,which eventually projected down into a photo resist coated silicon wafer using a protection system.

     Double patterning is a technique that decomposes a single layout into two masks in order to increase pitch size and improve depth of focus.

    Their resolution capabilities have fallen further and further behind the target minimum feature size per each advanced nodes.

    their resolution capabilities have fallen further and further behind the target minimum feature size per each advanced node.

    As a result, optical lithography has finally become unable to print shapes on silicon with a single mask in a single pass starting at 20m.

    The solution to this problem is to use a technique that has existed for years in the photographic industry known as multi-patterning.

     Multi-patterning means more than one mask processes are used to manufacture each design layer.

     For each design layer, the layout geometry must be decomposed onto separate masks (or colors), typically based on proximity to the nearest shape.

    To represent a particular mask at the design level, a"color" is associated with each layout shape to indicate which mask is used to print the shape.

    In Double patterning the layout is divided in to two colors and are placed on two different masks.

     In Triple patterning the layout is divided in to three colors and are placed on original layout double pattering /triple patterning

     patterning, where a conventional lithography process is enhanced to produce double the expected number of features.

   The design is split over two lithography layers in a way that the minimum pitch is relaxed with respect to the target pitch.

  The increased pitch size enables higher resolution and better printability.

  In Double patterning technique the layout designers split all their routing in to two different masks called as Mask A and Mask B.

   The overall pitch between same metals will be increased by replacing single metal with single metal two masks.

   That is every metal is subdivided in to two masks.

    For example if two adjacent M1 metals should have 0.64 pitch, when two masks are divided M1 mask A and M1 mask B can have only 0.32 pitch.

     Due to which the routing space decreases and allows size of the chip to decrease.

DRC Colored Checks : 

    Design rule checks for colored metals are performed to know the accuracy for minimum spacing.

   The adjacent figure shows the minimum spacing for the same mask different metals.

   The DRC checks for :

1.Same Mask Same Metal Spacing

2.Same Mask Different Metal Spacing

3.Different Mask Same Metal



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