Design and Fabrication of VLSI Devices
A chip consists of several layers of different materials on a silicon wafer. The shape, size and location of material in each layer must be accurately specified for proper fabrication. A mask is a specification of geometric shapes that need to be created on a certain layer. Several masks must be created, one for each layer. The actual fabrication process starts with the creation of a silicon wafer by crystal growth. The wafer is then processed for size and shape with proper tolerance. The wafer’s size is typically large enough to fabricate several dozen identical/different chips. Masks are used to create specific patterns of each material in a sequential manner and create a complex pattern of several layers. The order in which each layer is defined or `patterned’ is very important. Devices are formed by overlapping a material of certain shape in one layer by another material and shape in another layer. After patterning of all the layers, the wafer is cut into individual chips and packaged. Thus, the VLSI physical design is a process of creating all the necessary masks that define the sizes and location of the various devices and the interconnections between them.
KeywordsDesign Rule CMOS Process nMOS Transistor Gate Delay VLSI Circuit
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