INTEGRATED CIRCUIT LAYOUT
DEFINITION:
FUNCTION
- To determine the number of connection layers and floor plans of the components on the wafer.
- To produce the patterns of the masks needed for integrated circuit fabrication process.
TYPES OF LAYOUT
- Stick Diagram
- A rough sketch of lines/sticks of different colours showing all the different layers of the design.
- The diagram is sketched without any rule and can be designed in a short period of time.
2. Actual Layout
- A true picture of how the composition and size of components to be produced in the IC.
- The exact composition of components according to the size specified by the design rules and take a long time to be designed.
STICK DIAGRAM
- A stick diagram is a cartoon of a layout.
- Does show all components/vias (except possibly tub ties), relative placement.
- Does not show exact placement, transistor sizes, wire lengths, wire widths, tub boundaries.
SIGNIFICANCE OF LAYOUT DESIGN
- IC layout is a way of communication between circuit designer and process engineer.
- It represents the tolerance that will guarantee successful IC fabrication and correct circuit operation.
- Circuit layout is required in generating masks for IC fabrication process.
DESIGN RULES
i) Lambda (λ ) unit
- can define design rules in terms of lambdas.
- can easily be scaled to different fabrication process as fabrication technology advances.
- 1λ = 1/2 minimum feature size,
- e.g, in 0. 6μm process, 1λ=0.3μm.
ii) Micron unit
- 1 micron = 1µm = 1x10-6 m
- Technology size @ feature size is mentioned in micron unit, e.g. feature size of 0.5 micron implies that the distance between the source and drain is 0.5µm
- A single strand of hair usually has a diameter of 20 to 180µm.
