Explain scribe line and other structures related with CMOS.Ripunjay Tiwari
Ans. The scribe line is a specifically designed structure that surrounds the completed chip and is the point at which the chip is cut with a diamond saw. The construction of the scribe line varies from manufacturer to manufacturer, it is designed to prevent the ingress of ingress of contaminants from the side of the chip.
Several other structures are included on a mask including the alignment mark, critical dimension structures, vernier structures, and process check structures. The mask alignment mark is usually placed by the foundry to align one mask to the next. Critical dimension test structures can be measured after processing to check proper etching of narrow poly silicon or metal lines. Vernier structures are used to judge the alignment between layers. A vernier is a set of closely spaced parallel lines on two layers. Misalignment between the two layers can be judged by the alignment of the two verniers. Test structures such as chains of contacts and vias and test transistors ate used to evaluate contact resistance and transistor parameters. Often these structures can be placed along the scribe line so they do not consume useful wafer area.