TABLE OF CONTENTS This chapter shows how circuit design is converted into layout. The chapter describes the different layers of material that must be drawn to define transistors and wires, the typical design rules that must be followed, and some common pitfalls in creating layout.
Upon completion of this chapter the reader will be able to:
Visualize the three-dimensional structure to be manufactured from a piece of layout.
Describe the different layout layers used to draw a transistor.
Draw the layout for a CMOS gate.
Understand how design rules influence the size of layout.
Review layout for some of the most common mistakes.
Determine drawn, schematic, and layout transistor counts.
Understand three different methods of shielding wires.
Describe electromigration.
Layout is the task of drawing the physical dimensions and positions of all the layers of material that will ultimately need to be manufactured to produce an integrated circuit. Layout converts a circuit schematic to a form that is used to create the photolithography masks required to pattern each layer during the manufacturing process. As a result, layout specialists are often called mask designers. The area of the entire layout will determine the die area, which makes layout a critical step in determining the cost of manufacturing a given product.
Mask designers are often more artists than engineers. Layout is not something that can be analyzed easily with mathematical equations or numeric analysis. Mask designers must be able to look at two-dimensional drawings of layout and visualize the three-dimensional structures that...
